US20200176998A1

US20200176998A1 - Methods for heating and charging energy storage devices at very low temperatures

Info

Publication number: US20200176998A1
Application number: US16/254,415
Authority: US
Inventors: Jahangir S Rastegar; Philip C Kwok
Original assignee: Omnitek Partners LLC
Current assignee: Omnitek Partners LLC
Priority date: 2018-12-03
Filing date: 2019-01-22
Publication date: 2020-06-04
Also published as: US20200176999A1; US20230207914A1; US11211809B2; US11594908B2; US20200389033A1; US20200176835A1; US11211810B2

Abstract

A method for heating an energy storage device having a core with an electrolyte, the method including: providing the energy storage device having inputs and characteristics of a capacitance across the electrolyte and the core and internal surface capacitance between the inputs which can store electric field energy between internal electrodes of the energy storage device that are coupled to the inputs; switching between an input voltage and a grounding input provided to one of the inputs at a frequency sufficient to effectively short the internal surface capacitance of the energy storage device to generate heat and raise a temperature of the electrolyte; and discontinuing the switching when the temperature of the electrolyte is above a predetermined temperature that is considered sufficient to increase a charging efficiency of the energy storage device.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of earlier U.S. Provisional Application No. 62/774,823, filed on Dec. 3, 2018, the entire contents thereof being incorporated herein by reference.

BACKGROUND

1. Field

The present invention relates generally to energy storage devices, such as supercapacitors and lithium ion batteries, for fast charging and operation at high rate at very low temperatures, more particularly to methods and apparatus for fast charging of energy storage devices, such as supercapacitors and lithium ion batteries and to supercapacitors and lithium ion batteries that are designed to be charged at high rates as well as for high discharge rate operation at very low temperatures. Herein, by very low temperature it is meant the temperatures at which an electrolyte in an interior of such energy storage devices at least hinders charging, such as at temperatures where the electrolyte becomes nearly solid in super-capacitors, usually around −45 degrees C., but as low as −54 degrees C. or below.

2. Prior Art

A supercapacitor (SC), sometimes referred to as an ultra-capacitor, and formerly referred to as an electric double-layer capacitor (EDLC) is a high-capacity electrochemical capacitor with capacitance values up to 10,000 Farads at 1.2 volt that bridge the gap between electrolytic capacitors and rechargeable batteries (each of which are collectively referred to herein as a “supercapacitor”). Such supercapacitors typically store 10 to 100 times more energy per unit volume or mass than electrolytic capacitors, can accept and deliver charge much faster than batteries, and tolerate many more charge and discharge cycles than rechargeable batteries. They are however around 10 times larger than conventional batteries for a given charge. The construction and properties of many different types of supercapacitors are well known in the art.
In certain applications, such as in munitions, supercapacitors may be required to be charged as well as discharge at very low temperatures, sometimes as low as −40 to −65 degrees F. or even lower. Similar very low charging and operating temperatures may also be faced in many commercial applications, such is in supercapacitors used in vehicles for direct powering or for regeneration circuits used during braking. At such very low temperatures, the supercapacitor electrolyte becomes solid, thereby hampering or preventing ion transportation within the electrolyte. As a result, the supercapacitor rate of charge and discharge is greatly diminished. As a result, the user may be unable to charge or when the temperature levels are not very low and the supercapacitor is not provided with enough thermal insulation protection, must wait a relatively long time to charge the supercapacitor. It is appreciated by those skilled in the art that this is the case for all currently available supercapacitors.
Similarly, charging methods and devices for currently available rechargeable batteries, such as lithium ion batteries, cannot be used for charging these batteries at low temperatures. Although applicable to any rechargeable battery having an electrolyte interior, reference below will be made to lithium ion batteries by way of example. However, such low temperatures with regard to lithium ion batteries can be much higher than that discussed above with regard to supercapacitors, such as close to zero degrees C., and still hinder charging, damage the battery and even cause fire hazard because the components of a lithium ion battery are highly sensitive to temperature. At low temperature, the “viscous” resistance of the electrolyte to the movement of lithium ions increases. This increase in resistance causes higher losses during charging and discharging of the lithium ion battery. Low temperature charging passes (relatively high) currents through the components representing the battery electrical-chemical reactions, and is well known to result in so-called lithium plating, which is essentially irreversible, prevents battery charging, and permanently damages the battery.

SUMMARY

It is therefore highly desirable to have methods and apparatus for rapid charging of energy storage devices, such as supercapacitors and lithium ion batteries available for storing electrical energy in military products such as munitions and in commercial products such as in electric and hybrid vehicles, in vehicle regeneration circuitry and power tools, in which the charging rate is critical for achieving the required system performance.
It is also highly desirable to have energy storage devices, such as supercapacitors and lithium ion batteries, with the capability of being charged and discharged at significantly faster rates at the aforementioned very low temperatures.
It is also highly desirable that the energy storage devices, such as supercapacitors and lithium ion batteries, could be readily implemented in almost any of the currently available designs to minimize the amount of changes and modifications that have to be done to current manufacturing processes for their production.
A need therefore exists for the development of methods and apparatus for rapid charging and discharging of energy storage devices, such as supercapacitors and lithium ion batteries, of different types and designs at very low temperatures of sometimes −65 to −45 degrees F. or sometimes even lower.
There is also a need for methods to design and construct energy storage devices, such as supercapacitors and lithium ion batteries, which can be charged and discharged significantly faster than is currently possible at very low temperatures.
Such methods and apparatus for rapid charging and discharging of currently available energy storage devices, such as supercapacitors and lithium ion batteries, of different types and designs at very low temperatures of sometimes −65 to −45 degrees F. or sometimes even lower will allow munitions and vehicles or other devices to be charged and/or discharged significantly faster and readied for operation. In commercial applications, such as vehicles in which supercapacitors and/or lithium ion batteries are used, such methods and apparatus for rapid charging the same at very low temperatures of sometimes −65 to −45 degrees F. or sometimes even lower will allow the operation of the vehicles and the like at such very low temperatures.
Such methods to design and construct energy storage devices, such as supercapacitors and lithium ion batteries, that can be charged and discharged significantly faster than is possible will allow munitions and/or vehicles using the same to be charged significantly faster and readied for operation at very low temperatures of sometimes −65 to −45 degrees F. or sometimes even lower.
Herein are described novel methods and apparatus for rapid charging and discharging of currently available energy storage devices, such as supercapacitors and lithium ion batteries, of various types and designs at very low temperatures of sometimes −65 to −45 degrees F. or sometimes even lower.
Herein are also described novel methods and apparatus for the design and construction of energy storage devices, such as supercapacitors and lithium ion batteries, that are designed with the capability of being charged and discharged very rapidly at very low temperatures of sometimes −65 to −45 degrees F. or sometimes even lower.
In addition, herein are also described methods and apparatus for rapid charging and/or discharging of the energy storage devices, such as supercapacitors and lithium ion batteries, that are designed with the capability of being charged and discharged very rapidly at very low temperatures of sometimes −65 to −45 degrees F. or sometimes even lower.
Although the novel methods and apparatus are described with regard to very low temperatures as low as −65, such methods and apparatus are applicable in all low temperature environments, including slightly below 0 degrees C., to provide increased charging and discharging performance.
Accordingly, a method is provided for heating an energy storage device having a core with an electrolyte. The method comprising: providing the energy storage device having inputs and characteristics of a capacitance across the electrolyte and the core and internal surface capacitance between the inputs which can store electric field energy between internal electrodes of the energy storage device that are coupled to the inputs; switching between an input voltage and a grounding input provided to one of the inputs at a frequency sufficient to effectively short the internal surface capacitance of the energy storage device to generate heat and raise a temperature of the electrolyte; and discontinuing the switching when the temperature of the electrolyte is above a predetermined temperature that is considered sufficient to increase a charging efficiency of the energy storage device.
The method can comprise providing the input voltage through a first switch and providing the grounding input through a second switch, wherein the switching comprises simultaneously coupling the input voltage to the one input through operation of the first switch and decoupling the grounding input from the one input through operation of the second switch during a first time interval and thereafter, simultaneously decoupling the input voltage from the one input through operation of the first switch and coupling the grounding input to the one input during a second time interval through operation of the second switch, wherein the first interval and the second interval are subsequently repeated at the frequency sufficient to effectively short the internal surface capacitance of the energy storage device. The first switch can be a normally closed switch that couples the input voltage to the one input when a first switching voltage is below a first predetermined voltage and/or the second switch can be a normally open switch that decouples the grounding voltage from the one input when a second switching voltage is below a second predetermined voltage. The providing of the grounding input can comprise coupling the one input to a circuit ground through the second switch and a sink resistor. The method can comprise selecting the input voltage and a resistance of the sink resistor such that nearly the same charge of the energy storage device occurs during the first time interval as discharge from the energy storage device occurs during the second time interval.
The predetermined temperature can be a first predetermined temperature, where the method can comprise initiating the switching when the temperature of the electrolyte is below a second predetermined temperature that is considered to at least reduce the charging efficiency of the energy storage device, wherein the second predetermined temperature is a lower temperature than the first predetermined temperature.
The method can comprise obtaining at least one of a measurement and an approximation of the temperature of the electrolyte. The obtaining can comprise directly measuring the temperature of the electrolyte with a temperature sensor positioned at one or more of the electrolyte and a surface of the energy storage device. The obtaining can comprise: applying an initial charging input to the energy storage device, measuring a rate of charging using the initial charging input, and determining a charging rate at the initial charging input, wherein if a rate of charging is determined to be less than a predetermined charging rate, the electrolyte temperature is approximated as being less than the predetermined temperature.
The method can comprise providing a controller for controlling the switching and the discontinuing. The method can comprise obtaining by the controller at least one of a measurement and an approximation of the temperature of the electrolyte. The obtaining can comprise directly measuring the temperature of the electrolyte with a temperature sensor coupled to the controller and positioned at one or more of the electrolyte and a surface of the energy storage device. The obtaining can be performed periodically.
The method can comprise producing the input voltage from an AC source provided through an AC to DC converter.
The method can comprise: obtaining an energy storage type for the energy storage device; and retrieving from a look-up table the predetermined temperature that corresponds to the obtained energy storage type, wherein the look-up table correlates different energy storage types with corresponding predetermined temperatures.
The method can comprise coupling the input voltage to the one input to charge the energy storage device while the temperature of the electrolyte is above the predetermined temperature.
The energy storage device can be a lithium ion battery or a supercapacitor.
Also provided is a method for charging an energy storage device having a core with an electrolyte. The method comprising: providing the energy storage device having inputs and characteristics of a capacitance across the electrolyte and the core and internal surface capacitance between the inputs which can store electric field energy between internal electrodes of the energy storage device that are coupled to the inputs; switching between an input voltage and a grounding input provided to one of the inputs at a frequency sufficient to effectively short the internal surface capacitance of the energy storage device to generate heat and raise a temperature of the electrolyte; periodically obtaining a measurement that correlates to the temperature of the electrolyte, wherein the switching is initiated when the measurement indicates that the temperature of the electrolyte is below a low temperature threshold that is considered to at least reduce the charging efficiency of the energy storage device, wherein the switching is discontinued when the measurement indicates that the temperature of the electrolyte is above a high temperature threshold that is considered sufficient to increase a charging efficiency of the energy storage device, and wherein the low temperature threshold is a lower temperature than the high temperature threshold; and providing the input voltage to the one input to charge the energy storage device while the measurement indicates that the temperature of the electrolyte is above the high temperature threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the apparatus of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where:

FIG. 1 is a schematic of a simplified supercapacitor shown with a lumped core with its equivalent lumped internal resistance and inductance elements.

FIG. 2 illustrates a schematic of an embodiment of a supercapacitor rapid charging system for charging at very low temperatures and super capacitor to be charged at very low temperatures.

FIGS. 3-7 illustrate embodiments of flow charts of methods for charging supercapacitors at very low temperatures.

FIG. 8 illustrates an embodiment of a supercapacitor to be charged at very low temperatures.

FIG. 9 illustrates a schematic of a supercapacitor charging unit.

FIG. 10 illustrates a circuit diagram of a 2-30 MHz RF Power Amplifier.

FIG. 11 illustrates an equivalent circuitry of a lithium ion battery.

FIG. 12 illustrates a block diagram of a structure of a method of charging/discharging a lithium ion battery at low temperatures.

FIG. 13 illustrates a block diagram of main components of an embodiment of a processor controlled lithium ion battery charging and discharging unit at low temperatures.

FIG. 14 illustrates a block diagram of an alternative embodiment of a processor controlled lithium ion battery charging and discharging unit for low temperature of FIG. 13 for use only as a lithium ion battery charging unit for all temperatures including at low temperatures.

FIG. 15 illustrates a block diagram of an alternative embodiment of a processor controlled lithium ion battery charging and discharging unit for low temperature of FIG. 13 and for maintaining the battery core temperature during charging and discharging processes.

FIG. 16 illustrates a block diagram of an alternative embodiment of a processor controlled lithium ion battery charging and discharging unit for low temperature of FIG. 15 for use only as a Lithium ion battery charging unit for all temperatures including at low temperatures.

FIG. 17 illustrates a block diagram of another alternative embodiment of a processor controlled lithium ion battery charging and discharging unit for low temperature of FIG. 15 for use to keep the core temperature of a Lithium ion battery above a prescribed temperature for efficient discharging at all temperatures including at low temperatures.

FIG. 18 illustrates a block diagram of an alternative embodiment of a processor controlled lithium ion battery charging and discharging unit for low temperature of FIG. 17 for use to keep the core temperature of a Lithium ion battery above a prescribed temperature for efficient discharging at all temperatures including at low temperatures.

FIG. 19 illustrates a block diagram of an alternative embodiment of a processor controlled lithium ion battery charging and discharging unit for low temperature of FIG. 18 for use to keep the core temperature of a Lithium ion battery above a prescribed temperature for efficient discharging at all temperatures including at low temperatures.

FIG. 20 illustrates a flow chart diagram for charging a lithium ion battery for low temperature by keeping the core temperature of the Lithium ion battery above a prescribed temperature for efficient charging at all temperatures including at low temperatures.

FIG. 21 illustrates a flow chart diagram of discharging a lithium ion battery for low temperature by keeping the core temperature of the Lithium ion battery above a prescribed temperature for efficient discharging at all temperatures including at low temperatures.

FIG. 22 illustrates a circuit diagram of an embodiment of a heating circuit for a battery or energy storage device.

FIG. 23 is a schematic model of a supercapacitor having additional detail as compared to the model of FIG. 1.

FIG. 24 illustrates a circuit diagram implementation of the embodiment of the battery heating circuit of FIG. 22.

FIG. 25 illustrates a circuit diagram of the embodiment of the battery heating circuit of FIG. 22 with a battery temperature sensor and controller that activates the battery heating circuit when a prescribed low temperature threshold is detected.

FIG. 26 illustrates an alternative circuit diagram of the embodiment of the battery heating circuit of FIG. 25.

FIG. 27 illustrates the circuit diagram of another embodiment of the battery heating circuit.

FIG. 28 illustrates a circuit diagram of the embodiment of the battery heating circuit of FIG. 27 with a battery temperature sensor and controller that activates a battery heating circuit when a prescribed low temperature threshold is detected.

FIG. 29 illustrates a circuit diagram of another embodiment of a battery heating circuit.

FIG. 30 illustrates a circuit diagram of the embodiment of the battery heating circuit of FIG. 29 with a battery temperature sensor and controller that activates a battery heating circuit when a prescribed low temperature threshold is detected.

FIG. 31 illustrates a plot of a Li-ion battery heating as a function of time from a temperature of −30 deg. C to 20 deg. C using the heating circuit of embodiment of 27.

FIG. 32 illustrates a plot of an internal resistance of a standard 18650 cell Li-ion battery (battery part number is LGABB418650) in a temperature range of −55° C. to 45° C.

FIG. 33 illustrates a plot of the internal inductance of a standard 18650 cell Li-ion battery (battery part number is LGABB418650) in a temperature range of −55° C. to 45° C.

FIG. 34 illustrates a circuit diagram of another embodiment of a battery heating circuit.

FIG. 35 illustrates the circuit diagram of the embodiment of FIG. 34 as modified to provide a sinusoidal high frequency heating AC voltage.

FIG. 36 illustrates a circuit diagram of another embodiment of a battery heating circuit.

FIG. 37 illustrates a circuit diagram of the embodiment of FIG. 36 as modified to provide a sinusoidal high frequency heating AC voltage.

FIG. 38 illustrates an alternative modified circuit diagram of the embodiment of FIG. 37.

FIG. 39 illustrates a plot of the available battery current at the rated voltage as a function of temperature for several battery types.

FIG. 40 illustrates a circuit diagram of another embodiment of a battery heating circuit.

FIG. 41 illustrates a modified circuit diagram of the embodiment of the battery heating circuit FIG. 40.

FIG. 42 illustrates a circuit diagram of another embodiment of a battery heating circuit.

FIG. 43 illustrates a modified circuit diagram of the embodiment of the battery heating circuit FIG. 42.

DETAILED DESCRIPTION

All currently available supercapacitor types and designs exhibit internal resistance and inductance, which can be modeled as being in series. Both internal resistance and inductance of supercapacitors are relatively low. The inductance of supercapacitors is significantly higher for wound supercapacitors as compared to those that are flat and stacked in construction. The leakage current may be represented by a separate resistor in parallel with the capacitor. In general, the supercapacitor resistance may be ignored in short term operations. The supercapacitor inductance can also be ignored for low frequency operations.
In the schematic of FIG. 1, a simplified model of a supercapacitor 20 is shown with a lumped capacitor core 21 within which the aforementioned equivalent internal resistance and inductance are shown as two pairs of in-series resistors and inductors, which are connected to the supercapacitor capacitance C. In FIG. 1, the in-series resistor and inductor pairs are indicated by the resistances R1 and R2 and inductances L1 and L2. In most supercapacitors, the resistances of the resistors R1 and R2 are very low. In the present model, the pairs of lumped in-series resistors and inductors are connected on one end to the supercapacitor capacitance C and on the other end to the supercapacitor terminals 22. In FIG. 1, the internal resistance of the supercapacitor, which is the cause of leakage is modeled as a lumped resistor R3. In FIG. 1 and for the sake of simplicity and since the simplification does not affect the methods and apparatus for charging and discharging supercapacitors to be described, the electrical model of the supercapacitor is considered to be as shown in FIG. 1.
In the first embodiment shown schematically in FIGS. 2, 3 and 5, a supercapacitor charger unit 11 having an internal processor 11 a would first obtain the internal temperature of the supercapacitor core at step S1 a or S1 b. Such processor comprises a hardware, component such as a PLC or CPU and can include software and a memory storing such software and also storing data such as predetermined values used in the methods described below. In applications, such as munitions in which the munitions has been stored at the ambient temperature, the supercapacitor core temperature may be obtained by measuring the ambient temperature at step S1 a and approximating the internal temperature of the supercapacitor core using some function of the ambient temperature, such as equating the ambient temperature to the supercapacitor core temperature. Alternatively, the supercapacitor core temperature can be directly measured by an internal sensor 12 (such as a thermocouple based sensor or other temperature measurement sensors known in the art), with the measured temperature signal being provided to the processor 11 a via wiring 13 connected to the sensor capacitor terminals 14. The sensor 12 is used by the processor 11 a to determine if the supercapacitor can be charged at its regular rate or if the core temperature is so low that the supercapacitor electrolyte has become solid or very close to it, thereby hampering or preventing ion transportation within the electrolyte and preventing the supercapacitor from being rapidly charged at its regular (liquid electrolyte state) rate. As yet another alternative, the temperature sensor can be positioned on an exterior surface of the supercapacitor and the obtained temperature used to approximate the internal temperature of the supercapacitor core using some function of the exterior surface temperature, such as equating the exterior surface temperature to the supercapacitor core temperature.
Alternatively, as shown in FIG. 5, the supercapacitor core temperature may be obtained based on an assumption, such as by applying the regular charging voltage (or any appropriate initial voltage level) to the super capacitor via the charging unit 11 at step S1 b and if the processor 11 a determines that the supercapacitor does not charge at its regular rate at step S2 b, i.e., for example, the measured charging current is significantly lower than a known regular charging current rate, then the processor 11 a can assume that the supercapacitor core temperature is very low and below that where the same can be charged at its regular (liquid electrolyte state) rate.
Hereinafter, as discussed above, very low temperature is used to indicate temperature levels at which the supercapacitor electrolyte is rendered solid or effectively incapable of allowing relatively free transport of its ions.
It will be appreciated by those skilled in the art that for safety reasons, the processor 11 a of the charger unit 11 can also determine the charge level of the supercapacitor prior to the start of the charging cycle. In addition, the temperature sensor 12 can be employed to ensure that a low charging rate is in fact due to low supercapacitor core electrolyte temperature level as was earlier described.
In the schematic of FIG. 2, the charger unit 11 is shown to be powered internally, such as by a battery. In many applications, however, the charger unit 11 can be powered by an external source (not shown). The charging unit 11 functions similarly irrespective of the source of charger unit 11 power.
Then, once the processor 11 a has determined that the supercapacitor core temperature is very low and that due to the very low temperature level the supercapacitor (which can also be determined not to be fully charged) cannot be rapidly charged at either step S2 a or S2 b, the charger unit 11 can begin to charge the supercapacitor at step S5 a. In the schematic of FIG. 2 the charger unit 11 is shown to be connected to the supercapacitor 20 via wires 15 connecting the terminals 22 of the supercapacitor 20 to the corresponding terminals 16 of the charger unit 11.
However, if the processor 11 a determines the core temperature of the super capacitor is not less than a predetermined temperature (e.g., the core is at a temperature above which normal charging can be conducted) at step S2 a or S2 b (the determination at step S2 a or S2 b is NO), the charger unit would charge the supercapacitor conventionally at step S3, and continue to do so until the super capacitor is determined to be fully charged at step S4 or charging is otherwise terminated.
On the other hand, if the determination at step S2 a or S2 b is YES, the charger unit 11 can input one or more of a predetermined voltage and current to the terminals 22 of the supercapacitor which will cause internal components of the energy storage device to generate heat. As a first exemplary input, the charger unit 11 can apply a relative high frequency voltage to the supercapacitor at step S5 a. The high frequency voltage can be at a peak voltage of around the maximum allowable charging supercapacitor voltage or even significantly higher. Here, high frequency means a frequency at which the supercapacitor capacitor effectively shorts and inductances L1 and L2 and resistances R1 and R2 are caused to generate heat. The processor 11 a can then periodically continue to obtain the supercapacitor core temperature by any of the methods discussed above, such as at some predetermined intervals (shown by line S6 in FIGS. 3 and 5). The periodic obtainment of the supercapacitor core temperature can be by direct measurement or assumption as discussed above, such as by measuring the internal temperature with the temperature sensor 12 at step S1 a or by attempting to charge the capacitor at the regular charging voltage at step S1 b and measuring the charging rate from the charging current. Alternatively, more than one method can be used, such as both methods (S1 a and S1 b) for measuring the core temperature until either the core (the supercapacitor electrolyte) temperature has reached a desired level for proper charging of the supercapacitor or until the supercapacitor nominal charging rate has been reached. At which time the applied high frequency voltage signal is terminated at step S2 a and/or S2 b and the processor 11 a instructs the charging unit 11 to conventionally charge the supercapacitor to the desired level at steps S3 and S4. The temperature level and/or charging rate measurements may be repeated as needed, such as at regular intervals, particularly at very low ambient temperature conditions to ensure that the process of charging is not interrupted by “re-freezing” of the supercapacitor electrolyte.
An alternative embodiment is now described using the schematic of FIG. 2 and the flow diagrams of FIGS. 4 and 6 in which similar steps are numbered similarly to those illustrated in FIGS. 3 and 5, respectively. In the alternative embodiment, once the core 12 of the (not fully charged) supercapacitor 20 is determined to be at very low temperature at step S2 a or S2 b using any one or combinations of aforementioned techniques, the processor 11 a instructs the charging unit 11 to heat the core 12 at step S5 b by passing a constant current through the equivalent internal resistance R3 through the supercapacitor terminals 22 and the aforementioned two pairs of serially connected resistors and inductors. The current is generated by the charging unit 11 through the wiring 15. In general, and depending on the type and design of the supercapacitor 20 and its charging state and the electrolyte temperature, the current may be applied at voltages that are significantly higher than the voltage rating of the supercapacitor. This is usually possible since frozen electrolytes of a capacitor with low level of charge can withstand significantly higher voltages. When using the heating voltages that are above the rated voltage of the supercapacitor, the processor 11 a can regularly monitor the core temperature and the charging state of the supercapacitor at S6 and properly lower the heating voltage as the supercapacitor begins to be charged at or close to its nominal rate.
In general, due to the very high internal resistance level R3 of most supercapacitors, the methods illustrated in FIGS. 3 and 5 of providing heat to the supercapacitor core via the equivalent inductances L1 and L2 of the supercapacitor may be more effective. Such methods illustrated in FIGS. 3 and 5 may also be safer since the high frequency current may be applied at or even above the rated voltage of the supercapacitor. However, it will be appreciated by those skilled in the art that since the inductor core in this case is in effect the conductive supercapacitor electrolyte, the amount of heat that may be generated in many supercapacitors could be relatively low.
In the lump model shown in FIG. 1, the aforementioned heat generated per second (P) by the application of a constant voltage to the supercapacitor terminals is given by
$\begin{matrix} P = \frac{V^{2}}{R_{1} + R_{2} + R_{3}} & (1) \end{matrix}$
As can be seen from the above equation, since the leakage resistance R3 is very large, the amount of heat that can be generated per second for a relatively low voltage that can be applied to a supercapacitor (with, for example, a rate voltage of 2.7 Volts) is very small. For example, for a typical 100 F supercapacitor with a rated voltage of 2.7 V and with a serial resistance R1+R2=50 mΩ and leaking resistance R3=10 kΩ will, according to equation (1) above only generate heat at a rate of:
$P = \frac{{(2.7 V)}^{2}}{(10 k Ω + 50 m Ω)} = 0.73 mW$
In another alternative embodiment, the following method can be used instead of the previously described application of a constant voltage to significantly increase the above rate of heat generation within the core 21 of a typical supercapacitor 20, such as the one shown schematically in FIG. 1. In this method, shown in FIG. 7, once the charger unit 11 has determined that the battery is not charged completely and that the battery core is at a very low temperature at steps S1 c and S2 c, as was previously described, then the charger unit 11 would apply an alternating current (AC) with a peak voltage of V_pat a high frequency f to the terminals at step S5 c. The behavior of the lumped circuitry (consisting of the resistors R1, R2 and R3 and inductors L1 and L2 as shown in FIGS. 1 and 2) will now be very different than that indicated by the above equation (1). At a high frequency f, the capacitor C provides very low impedance, effectively shorting the leakage resistor R3 which is in parallel with it. As a result, the total resistance to the applied current becomes very small since the resistances R1 and R2 are very small. As a result, the total heat generated per second becomes very large and therefore the very cold supercapacitor core electrolyte can be heated very rapidly to the temperature at which it can be charged at or close to its nominal charging rate. It is noted that at such very high frequencies, the inductors L1 and L2 also provide high impedance but would usually contribute significantly less heat in a supercapacitor environment than those generated by low resistances R1 and R2. The heat generated per second (power P) is given approximately by the equation (2) below.
$\begin{matrix} P = \frac{1}{2} \frac{V_{p}^{2}}{R_{1} + R_{2} + 2 π f (L_{1} + L_{2}) + \frac{R_{3}}{1 + 2 π {fCR}_{3}}} & (2) \end{matrix}$
For the aforementioned 100 F supercapacitor with a typical total inductance of L1+L2=0.06 μH and R1+R2=50 mΩ and leaking resistance R3=10Ω, with an applied AC voltage of V_p=1 V at frequency f=1,000 Hz, the heat generated per second can reach 9.3 W. It is noted the above calculations are approximate and does not consider change in the supercapacitor capacitance at very low temperatures and with the applied high frequency voltage.
It will be appreciated by those skilled in the art that the charger unit 11 would require not only the processor 11 a but any electronics and logic circuitry for the core temperature measurement and for providing the indicated currents and voltage inputs for the described supercapacitor heating process as well as safe charging of the supercapacitor. These technologies are widely used in practice and are considered to be well known in the art.
In the above embodiments, the inductance or the internal resistance of the supercapacitors is used by the described charging unit to heat up the supercapacitor core (mainly its electrolyte) to a temperature at which electrolyte ions are provided with enough mobility to allow rapid charging of the supercapacitor. It consists of a series resistance and an inductance, and the leakage current is represented by a resistor in parallel with the capacitor, FIG. 1. The series resistance (R1 and R2 in FIG. 1) ranges from a few milliohms to several tens milliohms. The inductance (L1 and L2 in FIG. 1) depends on the construction and can be ignored for low frequency operation. The leakage resistance can also be ignored for short-term operation. The electrolyte in supercapacitors forms a conductive connection between the two electrodes which distinguishes them from electrolytic capacitors where the electrolyte is the second electrode (the cathode). Supercapacitor electrodes are generally thin coatings applied and electrically connected to a conductive, metallic current collector. Electrodes must have good conductivity, high temperature stability, long-term chemical stability, high corrosion resistance and high surface areas per unit volume and mass. Other requirements include environmental friendliness and low cost.
Referring now to FIG. 8, no matter the type and design of the super-conductor and its electrodes, another embodiment relates to additional resistive and/or inductive elements added to the supercapacitor electrode surface or otherwise distributing such resistive and/or inductive elements throughout the supercapacitor core. Similarly, such additional resistive and/or inductive elements can also be added to a rechargeable battery, such as a lithium ion battery. These added resistive and/or inductive elements can be electrically insulated by dielectric materials to prevent them from interfering with the operation of the energy storage device. The added resistive R4 and/or inductive elements L3 can be distributed throughout the core and as close as possible to its electrolyte material. Then when the core temperature is determined to be low as was previously described, passing current through the added resistances generates heat to increase the temperature of the electrolyte and thereby allowing charging at its nominal rate once the core temperature rises above some predetermined temperature or charging ability. When an inductive element is added, an alternating current of high enough frequency can be used for the heating of the electrolyte thereby facilitating the process of rapid charging at very low temperatures. With such a supercapacitor 20 a, additional terminals 14 a can be provided for inputting the required electrical input for heating the core though independent wiring 13 a from the charger unit of electronic logic can be provided to use only one set of terminals 22 to both charge the supercapacitor 20 a and input the additional inductor(s) L3 and resistor(s) R4 for heating the core.
A block diagram of a supercapacitor testing unit 100 is shown in FIG. 9. A function generator 102 is provided, such as a 25 MHz arbitrary waveform generator. A power amplifier 104 is also provided and can be constructed by modifying an available 2-30 MHz RF power amplifier by matching the supercapacitor impedance and the required power range as described below. The DC power source 106 is provided by a regulated source with output voltage and current limit setting. The test load or user device 108 can be a high power resistor, which is used to measure the available energy stored in the supercapacitor.
The function generator frequency and the power amplifier voltage amplitude can be manually set. A host computer 110 equipped with a DAQ and DSP board can provide the means of controlling the process and for data collection and online analysis and feedback. A DSP board clock can be used to provide for fast input/output operations and sampling time. The provided system can allow continuous measurement of the voltage and current across the load and the consumed power, thereby the load impedance. The DC power source 106 can also be controllable by the DSP based controller 110 to achieve a desired charging profile. The test load can be used to measure an amount of energy the charged supercapacitor can provide following charging. A switch 112, controlled by the DSP controller 110, can be used to connect the supercapacitor 114 to the desired circuitries. A set of voltage and current sensors 116, 118 report their values to the DSP A/D converter via the DAQ. The controller 110 can communicate with a host computer to exchange the command and status of each device. The DSP controller 110 can also generate charging pulses.
The supercapacitor testing unit can be designed to apply a high frequency sinusoidal AC voltage signal with and without DC bias to the supercapacitor load. The voltage and frequency of the AC signal can be manually or automatically controlled. The voltage across the load and the current passing through the supercapacitor load and their phase are measured. The power applied to the load and the impedance of the load can then be calculated.
The high frequency 25 MHz function generator 102 can be used as an input to the power amplifier 104. The power amplifier 104 can be constructed by the modification of the input and output impedance of an existing RF power amplifier. A circuit diagram of an existing 2-30 MHz RF power amplifier design is shown in FIG. 10. The nominal power output of this device can be 30 Watt, which is appropriate for superconductor charging.
An existing host computer will be provided with a DAQ and a DSP board for this purpose. The required software for running the system with proper data communication, sensor data acquisition and processing and generating the required control signals can be stored in a memory (not shown) accessible by the controller 110.
The charging unit 100 can measure the impedance of the supercapacitor 114 at different AC frequency, temperature and voltage. The function generator 102 can be used to generate sinusoid with adjustable voltage signal, for example up to 25 MHz. The power amplifier 104 will then produce and apply an AC voltage at a predetermined (preset) voltage level to the supercapacitor. The switch 112 controlled by the pulse generator will be used to apply the AC voltage to the supercapacitor 114 for a predetermined time period, such as an adjustable short duration of 10 to 100 microseconds depending on the AC voltage frequency. The short duration of the input power ensures that the total input energy is negligible. The input voltage and current waveform is then measured and used to calculate the supercapacitor impedance.
Tests of the superconductor charging can be conducted at various temperatures, such as at −20° C., −25° C., −35° C., −45° C., −48° C., −54° C., and −65° C. The tests can also use various AC voltage amplitudes, such as 2.7 V, 3.2 V, 4.5 V, 6 V, 8 V and 10 V. The AC voltage frequency range can be 2 MHz to 25 MHz, and testing can be performed in 0.5 MHz steps.
As was previously described, the application of high frequency AC voltage to the supercapacitor is for the purpose of heating the supercapacitor core at low temperatures, in particular its electrolyte, before charging it with an applied DC voltage.
An objective of the testing device is to determine at what point the AC voltage must cease and the DC charging should begin so as to build a database for use in the methods described above. At very low temperatures of below around −45° C. to 48° C., the electrolyte is nearly frozen solid and the impedance of the supercapacitor is very high. But as the electrolyte becomes active (melt), the rapid increase in the effective capacitance of the supercapacitor causes the impedance to rapidly drop, thereby causing the passing current level to increase accordingly. In the tests, the AC current level is measured and after it has increased by a factor of 10, 25, 50, 75 and 100 then the AC voltage can be switched off and the DC charging voltage applied to the supercapacitor. In the test, for example, the supercapacitor can be charged at 3.2 V until the charging current drops to 20 mA, at which point the supercapacitor will be considered to be fully charged. The available stored energy is then measured by discharging the stored energy in the supercapacitor through the test load 108.
The AC current and voltage profiles and the DC charging time are recorded. The tests can be performed while the supercapacitor is inside a temperature chamber 120. The tests can be performed with the capacitor wrapped in a typical thermal insulation jacket and without thermal insulation to mimic a supercapacitor installed within a housing that provides certain level of thermal insulation against heat loss and outside of any housing, respectively.
During the tests, the supercapacitor 114 will be considered damaged if the stored energy is less than 95% of the expected available stored energy.
Such testing can be used to optimize the above described methods for charging supercapacitors at low temperature to achieve full charge in minimum amount of time and used to formulate a general time optimal strategy for charging supercapacitors at low temperatures. A range of AC voltage and frequency for preheating of the supercapacitor and its follow up DC charging and the expected optimal AC to DC switching point can be determined for different low temperature levels which can be tested and fine-tuned to obtain the desired time-optimal strategy for implementation.
Thus, the above testing device and methods can be used to obtain statistical information regarding the time needed to charge various size and configuration supercapacitors to full charge at various low temperatures. The statistical information generated can include the mean time required to charge a capacitor at a given temperature and its standard deviation at a certain confidence level, such as 95%.
It will be appreciated by those skilled in the art that the disclosed testing device and method for charging supercapacitors at low temperatures can be applied to the other methods described above (such as at FIGS. 3-6) and/or for different types of commonly known supercapacitors, ultracapacitors and so-called hybrid capacitors and the like as well as to rechargeable batteries, such as lithium ion batteries.
The above method and devices for rapid charging of supercapacitors at low temperatures can also be used to similarly enable and/or significantly increase the charging rate of lithium-ion and other similar rechargeable batteries at low temperatures. As discussed above, low temperature charging is in general even more an issue for lithium-ion and other similar rechargeable batteries since their rate of charging is low at even higher temperatures than supercapacitors, usually even a few degrees below zero C.
In the case of lithium-ion and other similar rechargeable batteries, similar to the previously described method for supercapacitors, the charging process includes similar steps. After determining that the lithium ion battery requires charging and that its core is at a low temperature that prohibits/minimizes charging, the battery electrolyte and electrodes are heated by similar methods as described above with regard to FIGS. 3-7, by inputting one or more of a predetermined voltage and current input to terminals of the battery causing internal components thereof to generate heat, such as with the application of an AC high frequency voltage, usually in the order of 1-10 MHz and sometimes higher depending on the battery size and construction. Then once the battery core, particularly its electrolyte, has reached a desired predetermined temperature or charging ability, which may be detected directly with a temperature sensor as described above or assumed, such as by detecting the charging rates with AC and/or DC voltages, as also described above, the battery can be charged conventionally using DC voltages following well known electronic and logic circuitry and procedures to ensure safe and rapid charging.
It will be appreciated by those in the art that in many cases n lithium-ion and other similar rechargeable battery charging (including supercapacitor charging), the optimal charging time can be achieved by overlapping AC voltage and DC voltage charging during a portion of the time, usually before switching from the AC to DC voltages.
A basic operation of Lithium ion batteries may be approximately modeled with the equivalent (lumped) circuitry shown in FIG. 11. In this model, the resistor R_eis considered to be the electrical resistance against electrons from freely moving in conductive materials with which the electrodes and wiring are fabricated. The equivalent resistor R_Irepresents the (“essentially viscous”) resistance to free movement of lithium ions by the battery electrolyte. The equivalent inductor L_Irepresents the (“essentially inertial”) resistance to change in its state of motion, which is insignificant until the frequency of the required motion becomes extremely high. The capacitor C_sis the surface capacitance, which can store electric field energy between electrodes, acting similar to parallel plates of capacitors. The resistor R_cand capacitor C_crepresent the electrical-chemical mechanism of the battery in which C_cis intended to indicate the electrical energy that is stored as chemical energy during the battery charging and that can be discharged back as electrical energy during the battery discharging, and R_cindicates the equivalent resistor in which part of the discharging electrical energy is consumed (lost) and essentially converted to heat. The terminals A and B are intended to indicate the terminals of the lithium ion battery and C and D are other internal points in the circuitry.
It will be appreciated by those skilled in the art that many different Lithium ion types and designs and different chemical compositions are currently available. It is also appreciated by those skilled in the art that other models of the Lithium ion batteries have also been developed. The model presented in the schematic of FIG. 11 does however represent the basic components of Lithium ion batteries as far as the disclosed method and apparatus for charging such batteries at low temperatures are concerned. Therefore the methods and apparatus described herein applies to all different types and designs of Lithium ion batteries with all different design structures and chemistries and not just those having the configuration represented by FIG. 11. The reasons that currently available Lithium ion battery charging methods and devices cannot be used for charging these batteries at low temperatures of even close to zero degrees C. are briefly described above and well described in the published literature and have been shown to damage the battery and even cause a fire hazard if used.
In the approximated equivalent (lumped) circuitry model of Lithium ion batteries shown in FIG. 11, three components of the battery, namely R_I, R_cand C_c, are highly sensitive to temperature. At low temperature, the resistance of the resistor R_Iincreases due to the increase in the “viscous” resistance of the electrolyte to the movement of lithium ions. This increase in resistance causes higher losses during charging and discharging of the lithium ion battery. Low temperature charging passes (relatively high) currents through the indicated components R_cand C_crepresenting the battery electrical-chemical reactions, and is well known that results in so-called lithium plating, which is essentially irreversible, prevents battery charging, and permanently damages the battery.
An embodiment of a method for charging lithium ion batteries at low temperatures can be described as follows. Consider the circuit model of FIG. 11. If an AC current with high enough frequency is applied to the battery, due to the low impedance of the capacitor C_s, there will be no significant voltage drop across the capacitor, i.e., between the junctions C and D, and the circuit effectively behaves as if the capacitor C_swere shorted. As a result, the applied high frequency AC current is essentially passed through the resistors R_eand R_Iand not through the R_cand C_cbranch to damage the electrical-chemical components of the battery. Any residual current passing through the R_cand C_cbranch would also not damage the battery due to a high frequency and zero DC component of the applied current. The high frequency AC current passing through the resistors R_eand R_Iwill then heat the battery core, thereby increasing its temperature. If the high frequency AC current is applied for a long enough period of time, the battery core temperature will rise enough to make it safe to charge using commonly used DC charging methods.
Furthermore, when the demanded frequency of AC current becomes high, the inductance L_Iindicates high AC voltage potential requirement from the charging device. In other words, while there is an AC voltage limitation on the charging device, the inductance L_Iwould become dominate when the frequency is high enough so that all voltage potential drop falls across it. Even though there is still part of the energy being transferred into heat from this inductor, it is far less than from R_I. Therefore, the high frequency AC current can be chosen with the inductance L_Itaken into consideration.
In the device designed to provide the aforementioned high frequency AC current to raise the battery core temperature to a safe charging temperature, provision can be made to periodically assess the temperature status of the battery core and determine if a safe charging temperature level has been reached.
Although temperature sensors can be used, similarly to that discussed above with regard to the supercapacitor of FIG. 12, in the method and apparatus for charging Lithium ion batteries at low temperatures, two basic methods may be used to assess the battery core temperature without the need for temperature sensors (thus, not requiring a special configuration of the lithium ion battery for use in such methods or with such apparatus). In one method, as the aforementioned high frequency AC current is applied to the battery, the battery impedance is regularly measured. Since the resistance of the resistor R_Iis high at low temperatures, the level of battery impedance indicates if the battery core temperature is low or around a safe temperature for charging. When using this method, the impedance of the battery can be measured a priori for the charger to use to determine when the battery core safe charging temperature has been reached.
A second method for determining if the battery core temperature has reached a safe charging temperature level while applying the aforementioned high frequency AC current is as follows. In this method, the high frequency AC current is periodically turned off and current is discharged from the battery through a resistive load for a very short duration. If the battery core is still cold, then the voltage across the load will be low.
It will be appreciated by those skilled in the art that both methods described above can be readily incorporated in the battery charging unit. In fact, the electrical and electronic circuitry required to apply the aforementioned high frequency AC current as well the above one and/or both methods of assessing the Lithium ion battery core temperature for safe charging may be readily incorporated in one single charging unit. Such a unit can also use commonly used methods to charge the battery once the battery core temperature has been raised to a safe charging level.
Furthermore, once DC charging has begun, the charging unit may be programmed to periodically assess the battery core temperature and if detects that the temperature is approaching an unsafe (low) temperature, then the high frequency AC current would be turned on and the DC charging current is turned off. Alternatively, a high frequency AC current may be superimposed on the charging DC current.
The Lithium ion battery may also be provided with a temperature sensor to measure its temperature such as those used in some currently available Lithium ion batteries. The temperature sensor input, which can be in addition to one or both aforementioned methods, may then be used to determine the safe charging temperature of the battery.
The aforementioned high frequency AC current may also be used to increase Lithium ion battery core temperature at low temperatures to achieve higher discharge rates. As such, the present method provides the means of charging Lithium ion batteries at low temperatures as well as providing the means of increasing the performance of Lithium ion batteries, i.e., increasing their discharge rate, at low temperatures.
The block diagram of the apparatus using the present novel method for charging and/or discharging Lithium ion batteries 206 having an electrolyte battery core 208 at low temperature is shown in FIG. 12. The charging/discharging unit 200 (collectively referred to herein as a “charging unit”) is provided with electrical and electronic circuitry to provide the aforementioned high frequency AC current and the charging DC current, both with voltage controls, and can include a processor 202, such as a microprocessor or CPU for controlling the process of measuring the battery core temperature as previously described and increasing the core temperature if below the battery safe charging temperature and charging when the battery core temperature above the said safe charging temperature. The charging unit 200 having wiring to connect to the terminals 210 of the battery 206. The process steps for carrying out such methods can be stored as software on a memory device accessible by the processor 202. The charging unit 200 would periodically check the temperature by using one or both aforementioned methods based on the battery impedance and/or alternatively from an external or internal battery temperature sensor source 204 to properly direct the charging process.
Alternatively, the charging unit of FIG. 12 may function as a charging and discharging control unit and increase the battery core temperature when it is below the aforementioned safe charging temperature for charging by applying an appropriate high frequency AC current to the battery to be followed by a DC charging current. And if the battery temperature is low enough to significantly degrade its performance, i.e., its desired discharge rate, the charging unit 200 would also apply the high frequency AC current to the battery 206 to increase its core temperature to increase its discharge rate.
An embodiment 300 of the Lithium ion charging and discharging unit is shown in the block diagram of FIG. 13. Although the unit 300 can be used to solely charge lithium ion batteries at low temperatures, the unit 300 is intended for use as a charging and discharging unit for Lithium ion batteries at all temperatures including at low temperatures.
It is appreciated here that for Lithium battery charging low temperature is intended to indicate those battery core temperatures at which DC currents (continuous or pulsed or other variations known in the art or the like) causes damage to the battery or that the battery cannot effectively be charged. In the Lithium ion battery discharging process, low temperature is intended to indicate temperatures at which the Lithium ion battery discharge rate is significantly lower than its normal rate. In Lithium ion batteries the latter temperatures are generally lower than those for safe charging of the battery.
The unit 300 is powered by an external power source as shown schematically by arrow 302, which might for example be an outlet provided outdoors for charging the Lithium ion batteries of an electric car. A microprocessor-based controller 304 (alternatively referred to herein and in FIG. 13 as a “control unit”) is used for determining the status of the battery 301 which may or may not have an internal or external temperature sensor 303 as was previously discussed while being charged and which when its battery core is determined to be below a safe charging temperature would instruct the AC and DC current generator 306 to output high frequency AC current, shown schematically by arrow AC 307) and when it is safe to charge, would instruct the AC and DC current generator 306 to output DC current, shown schematically by arrow DC 308 using the indicated switching element 310. The control unit 304 may be programmed (the instructions of which may be stored in a memory provided in the unit 300 and accessible by the control unit 304) to increase the internal temperature of the battery 301 a safe amount to allow the battery 301 to be charged at faster rates. The high frequency AC and DC currents are generated by the indicated AC and DC current generator 306, which is powered from the unit input power 302, and which is in direct communication with the control unit 306 as indicated by the arrow 312. The control unit 304 is also in constant communication with the AC and DC current switching element 310 and can determine if one or the other of the AC or DC current needs to be turned on or off In this embodiment only one of the AC or DC current can be turned on simultaneously.
In the embodiment 300 of FIG. 13, when either the AC or the DC current is turned on, the current is passed through a charging voltage, current and impedance measurement and charging and discharging regulation unit 314 as indicated by arrow 316 a, which is used to determine the aforementioned current, voltage and impedance measurements needed for the control unit 304 to control the charging process as was previously described. The charging voltage, current and impedance measurement and charging and discharging regulation unit 314 also regulates the charging current during the charging cycles and the discharging current during the discharging cycles as directed by the control unit 304 to ensure proper and safe operation of the battery 301 and the charging and discharging unit 300. The charging and discharging connections between the above charging voltage, current and impedance measurement and charging and discharging regulation unit 314 and the Lithium ion battery 301 are indicated schematically by arrow 316 b. The battery discharge is routed through the AC and DC current switching element 310 as shown schematically by arrow 318. The control unit 304 is also in communication with all the system units as shown in FIG. 13 as well as the battery temperature sensor 303 if such a sensor is provided. Although shown separately, the charging voltage, current and impedance measurement and charging and discharging regulation unit 314 can be integrated into the control unit 304.
Once the battery core temperature has reached a safe charging level, the battery can then be charged using a DC current or any other currently available technique for example with or without charging pulses, etc., that are well known in the art and are used for efficient and safe charging of Lithium ion batteries. Any one of the well-known methods for safeguarding the discharging process may also be employed. Similarly, different hardware designs are also well known in the art and may be used in the design of the charging and discharging circuitry of this and the following embodiments after the aforementioned safe core temperature levels (measured directly or via the aforementioned impedance related techniques) have been reached for charging the battery and when the desired core temperature (measured directly or via the aforementioned impedance related techniques) has been reached for efficient discharge (usually in terms of fast discharge rates and lower internal losses which are higher at low temperatures).
A block diagram of an alternative embodiment of a microprocessor controlled lithium ion battery charging and discharging unit 320 for low temperatures is shown in FIG. 14. The embodiment 320 is intended for use as the means for just charging Lithium ion batteries at all temperatures including at low temperatures when the battery core temperature is below its safe charging temperature level. All components of the embodiment 320 are the same as those of the embodiment 300 of FIG. 13 except that in the embodiment 320, the charging voltage, current and impedance measurement and charging and discharging regulation unit 314 a is modified to eliminate its discharging regulation function. The Lithium ion charging unit 320 functions as previously described to charge the battery using a DC current (continuous or pulsed or other variations known in the art or the like) while the battery core temperature is above its safe charging temperature as measured using one or more of the previously described methods. If the battery core temperature is determined to be below or approaching the battery safe charging temperature, then the charging DC current is disconnected and the high frequency AC current is applied as was previously described for the embodiment of FIG. 13 to raise the battery core temperature above its safe charging temperature. The core temperature measurement can be made either continuously or at short enough intervals of time to ensure that the battery core temperature does not drop below its safe charging temperature during its charging.
A block diagram of another alternative embodiment of the microprocessor controlled lithium ion battery charging and discharging unit 340 for low temperatures is shown in FIG. 15. All components of the embodiment 340 are the same as those of the embodiment 300 of FIG. 13 except that in the embodiment 340, the AC and DC current switching element 310 of FIG. 13 is replaced by an AC and DC current mixing element 342. Depending on the detail design of the charging voltage, current and impedance measurement and charging and discharging regulation unit 314 b, some routine modifications may be made to its design to accommodate the mixed AC and DC current signals.
The operation of the microprocessor controlled lithium ion battery charging and discharging unit 340 of FIG. 5 is similar to that of the embodiment 300 of FIG. 13 except for the following. In the embodiment 300 of FIG. 13 and during a battery charging cycle, the unit 300 can either apply a high frequency AC current or a DC current to the battery. During low temperature charging, the unit 300 applied the high frequency AC current until a safe battery core temperature is reached. The charging DC current (continuous or pulsed or other variations known in the art or the like) is then applied to charge the battery 301. In the embodiment 340 of FIG. 15, when the battery core temperature is below its safe charging temperature, the unit will similarly apply a high frequency voltage to the battery to raise its core temperature to a safe charging level. However, the provision of the AC and DC current mixing element allows the embodiment 340 maintain the battery core temperature at a safe charging temperature level when it is detected to be dropping close to the safe charging temperature. Whenever such a condition is detected, by adding the high frequency AC current to the charging DC current, the core temperature is raised above its safe charging temperature. By continuous or frequent measurement of the battery core temperature, the temperature can be maintained above the battery safe charging temperature and be continuously charged. This situation is regularly encountered when the Lithium ion battery is exposed to a very cold environment and particularly if the battery is relatively small and has a geometrical shape in which the ratio of its surface area to volume is relatively high such as in batteries that are relatively thin with large surface areas.
The high frequency AC current may also be applied to the battery 301 during the discharging cycles when the battery core temperature is below or is dropping to levels close to a predetermined optimal level for efficient discharge (usually determined in terms of achievable discharge rates and lower internal losses, which are higher at low temperatures). In this embodiment, the battery core temperature can be measured at least periodically via temperature sensor(s) if provided and/or using the aforementioned impedance related measuring techniques.
A block diagram of an alternative embodiment of the microprocessor controlled lithium ion battery charging and discharging unit 360 for low temperatures is shown in FIG. 16. The embodiment 360 is intended for use as the means for just charging Lithium ion batteries at all temperatures including at low temperatures when the battery core temperature is below its safe charging temperature level. All components of the embodiment 360 are the same as those of the embodiment 340 of FIG. 15 except that in the embodiment 360, the charging voltage, current and impedance measurement and charging and discharging regulation unit 314 c is modified to eliminate its discharging regulation function. The Lithium ion charging unit 360 functions as described for the embodiment 340 of FIG. 15 to raise the battery core temperature to a safe charging temperature level, to be followed by charging using a DC current (continuous or pulsed or other variations known in the art or the like) while the battery core temperature is above its safe charging temperature as measured using one or more of the previously described methods. Then whenever the battery core temperature is detected to have dropped to close to its safe charging temperature, the control unit 304 instructs the AC and DC current generator to add a high frequency AC current to the charging DC current, thereby raising the battery core temperature above the safe charging temperature. By continuous or frequent measurement of the battery core temperature, the core temperature can be maintained above the battery safe charging temperature while continuously charging the battery.
A block diagram of another alternative embodiment of the novel microprocessor controlled lithium ion battery charging and discharging unit 380 for low temperatures is shown in FIG. 17. The embodiment 380 is intended for use as the means for keeping the core temperature of a Lithium ion battery above a prescribed level for efficient discharging at all temperatures including at low temperatures. All components of the embodiment 380 are the same as those of the embodiment 360 of FIG. 15 except that in the embodiment 380, the charging voltage, current and impedance measurement and charging and discharging regulation unit 314 d is modified to only provide discharge regulation and voltage, current and battery impedance measurements functionality. While the battery 301 is being used to power certain load, i.e., while electrical energy is being discharged from the battery, the high frequency AC current may also be applied to the battery whenever the battery core temperature is measured to be below or if it is dropping close to levels predetermined to be optimal for efficient battery discharge (usually determined in terms of achievable discharge rates and low internal losses, which are higher at low temperatures). In this embodiment, the battery core temperature can be measured at least periodically via temperature sensor(s) 303 if provided or using the aforementioned impedance related measuring techniques.
In the embodiment 380 of FIG. 17, the high frequency AC current producing generator element 306 a is powered from an external source 302. External powering of the AC current generator 306 a may be necessary in certain situations, for example when the charged battery core is at such a low temperature that cannot provide enough power to the AC current generator 306 a or that it cannot provide enough power to raise the core temperature to the required operating temperature in short enough period of time. If such situations are not expected to be encountered, the AC current generator 306 a may be powered directly by the Lithium ion battery 301 itself or after an initial external powering period. The embodiment of FIG. 18 illustrates such a discharging control unit 400 in which the AC current generator 306 a of the discharging control unit is powered by the battery 301 itself.
The embodiment 400 shown in FIG. 18 is similar in functionality and design to the embodiment 380 of FIG. 17 except for the source of AC current generator powering. In the embodiment 400, the AC current generator 306 a is powered from the device discharge power and AC generator powering control unit 402 as shown by the arrow 404. The AC current generator 306 a is in direct communication with the system control unit 304 as shown in FIG. 18. The discharge power and AC generator powering control unit 402 gets its power from the battery via the voltage, current and impedance measurement and discharging regulation unit 314 a as indicated by arrow 406. The input and output currents to the battery 301 are via the connection indicated by the two-way arrow 316 a. The battery discharge is through the discharge power and AC generator powering control unit 402 as shown by the discharging power arrow 318. The generated AC current is provided to the voltage, current and impedance measurement and discharging regulation unit 314 a, which is in communication with the system control unit 304, for increasing the battery core temperature when it is or about to fall below a prescribed temperature level.
The embodiment 400 of FIG. 18 may also be provided with an external source of powering for its high frequency AC current generator similar to the embodiment 380 of Figure 17. The device will then have the capability of using the external power source, particularly as an initial source of power to bring the battery core temperature to a prescribed level before switching to an internal mode of powering as shown in the embodiment of FIG. 18. Such a configuration is shown in the embodiment 420 shown in FIG. 19, which is similar in functionality and design to the embodiment 400 of FIG. 18 except for the source powering the AC current generator 306 a. In the embodiment 400 of FIG. 18, the AC current generator 306 a is only powered by the arrow 404. However, in the embodiment 420 of FIG. 19, the AC current generator 306 a also can take energy from the external input power 302, and depending on the situation, select one or both of the power sources to heat the battery 301.
FIGS. 20 and 21 show flow charts for charging and discharging a lithium ion battery at any temperature. As discussed above, if it is determined that a battery needs to be charged, a measurement is obtained of the internal temperature of the lithium ion battery at step S10. A determination is then made at step S12 as to whether the obtained temperature is lower than some predetermined threshold temperature at which the battery cannot be charged or cannot be efficiently charged. If such determination at step S12 is no, the method proceeds to steps S14 and S16 to conventionally charge the battery. However, if the determination at step S12 is yes, the method proceeds to step S18 where high frequency AC voltage current is input to the lithium ion battery to heat the interior thereof. Such process can loop back to step S10 along route S20, periodically or at some regular interval until the determination of step S12 is no, at which time the battery is charged conventionally at steps S14 and S16 until fully charged or the process is otherwise terminated. Thus, In FIG. 20, while the battery's core temperature is detected to be lower than a predetermined temperature, to avoid damage the battery, the heating procedure is executed until the core temperature rises high enough.
In FIG. 21, a measurement is made at step S10 to obtain a measurement of the battery internal temperature. Similarly to FIG. 20, if the core temperature is determined to be less than a predetermined temperature at step S12, the battery is input with a high-frequency, AC voltage current at step S18 to heat the interior of the battery. Such process loops back to step S10 via S20 as discussed above with regard to FIG. 20 until the core temperature is determined to be above such predetermined threshold temperature at step S12, at which time the process continues to step S22 to discharge the lithium ion battery conventionally to a load. Thus, as can be seen at loop S24, while the battery's core temperature is low so that the discharging efficiency is dropping, the heating procedure is also executed until the core temperature rises above the predetermined temperature. Thus, the discharging at step S22 is not be interrupted during the heating procedure at step S18.
In both FIGS. 20 and 21, the alternative steps discussed above for determining whether the battery core has too low a temperature (without the use of a temperature sensor) and cannot be charged conventionally can also be used, in which case step S12 determines whether the core temperature is too cold based on such determinations and not on a direct temperature measurement. Of course, both determinations can be used and the method can include logic for making the determination in step S12 based on multiple inputs (e.g., the temperature measurement, the battery impedance as described above with regard to the first method and/or the voltage across a small load with regard to the second method discussed above).
It is appreciated by those skilled in the art that numerous variations of the described designs shown by the block diagrams of FIGS. 13-19 are also possible for performing the indicated functions. The disclosure of the indicated embodiments by no means is intended to limit their implementation only in the described manner, rather to demonstrate the various combinations of functionalities that can be incorporated in a given design and their general purpose.
It is also appreciated that the means of controlling the operation of the disclosed embodiments can be with the use of a microprocessor based control unit. However, it is also appreciated that that the general functions performed by the microprocessor may also be performed by appropriate electronics and logic circuitry. Similar circuitry designs have been developed for the control of various processes in the industry and commercially and may be designed for the control of the disclosed Lithium ion battery charging and discharging devices for all temperature operation including low temperature operation.
Lastly, any of the above methods can be practiced without the initial determination of the core temperature of the energy storage device. That is, a conventional charging input can be used regardless of the temperature of the energy storage device's core and such determination can be made while the charging input is being applied. In this case, the core temperature determination can be made periodically and if the temperature of the core is obtained (directly measured or assumed) is below the predetermined threshold that would hinder further charging or approaching within some limit of the predetermined threshold, the alternative inputs discussed above for heating the internal components of the energy storage device can be superimposed over the charging input or the charging input can be stopped and the alternative input applied until the charging input can be resumed, such as when the predetermined threshold is reached. The same can also be for the discharging methods discussed above.
FIG. 22 illustrates the diagram of one embodiment of a heating circuit for a battery or energy storage device 450, such as a Lithium-ion battery or nickel metal hydride battery or lead-acid battery or other rechargeable or non-rechargeable battery, and for super-capacitors of various types. In the diagram of FIG. 22, the device 450 is shown as a single battery, however, it may also be a super-capacitor or more than one serially or in parallel connected batteries or super-capacitors.
As can be seen in FIG. 22, an external power source is used to apply a positive current flow (indicated by the positive voltage V+) into the battery 450 through the switch “SW1”. A resistor “R SINK” is used to draw current from the battery through the switch “SW2”. The signal for opening and closing the switches SW1 and SW2 are provided by the controller.
In this embodiment, the previously described high frequency AC voltage that is applied to the battery 450 to heat its electrolyte is provided by the proper on/off switching of the switches SW1 and SW2 as follows. The process consists of applying a current into and drawing current out of the battery at the desired (high enough) frequency, to effectively short the equivalent capacitor C_s(FIG. 11) in the case of the Lithium-ion batteries as described by the model of FIG. 11, and the equivalent capacitance between the electrodes of other types of batteries and for the super-capacitors. For the super-capacitors, the model of FIG. 1 may be made more detailed by separating the overall capacitance C of FIG. 1 into a capacitor C, which essentially describes the electrical energy that is stored as chemical energy, and a parallel capacitor C_s, which essentially indicates the capacitance between the device electrodes.
In the above process of passing a high frequency AC current through the battery 450, FIG. 21, when the switch SW1 is closed, the switch SW2 is opened and vice versa. The switching signals to enable or disable the SW1 and SW2 are sent by the controller. The controller can be a circuit based on a microcontroller, a combinational logic circuit, a FPGA or the like. The current flow into the battery during the positive cycle is controlled by varying the voltage level of the voltage source “V+”. By increasing the level of voltage “V+” would increase the current flow into the battery 450. The amount of voltage drops and current flow from the battery is controlled by changing the resistance value of “R SINK”, i.e., by reducing the resistance of the resistor “R SINK”, the current flow out of the battery 450 is increased. It is therefore appreciated by those skilled in the art that the resulting effective high frequency AC voltage becomes close to a square wave. In general, the voltage level “V+” needs to be balanced to get a nearly the same charge and discharge from the battery during each cycle of the AC voltage application. In addition, and as described later in this disclosure, since the battery characteristics changes with temperature, the provided controller is desired to vary the characteristics of the said AC voltage application for optimal rate of heating of the battery.
FIG. 24 illustrates a circuit diagram implementation of the embodiment of the battery heating circuit of FIG. 22. In the circuit of FIG. 22, the switch SW1 is implemented by a P-Channel MOSFET “M1” and the switch SW2 is implemented by a N-Channel MOSFET “M2”. The resistors R1 and R2 are pull-up and pull-down resistors required to properly bias the gate input of the MOSFETs. The MOSFET M1 acts as a closed switch while M2 acts as an open switch when the voltage level of the control signal VG1 and VG2 are both at 0 V. The MOSFET M1 acts an open switch while M2 acts as a closed switch when the voltage level of the control signal VG1 is above the gate-source threshold voltage of M1 and VG2 is above the gate-source threshold voltage of M2. To disable both switches when the heating circuit is not used, VG1 is set to above the gate-source threshold voltage of M1 and VGS is set to be 0 V. Alternatively, disconnecting the circuit from the voltage source V+ can also disable the switches.
It is appreciated by those skilled in the art that the implementation of the circuit diagram of FIG. 22 as shown in FIG. 24 is not unique and that many other circuits that with the same functionality may be designed and that the circuit example of FIG. 24 is not intended to exclude any other circuits that can provide the same functionality.
FIG. 25 illustrates a circuit diagram of the embodiment of FIG. 24 with a provided controller that uses a temperature sensor input to activate the battery heating circuitry when a prescribed low temperature threshold is detected. The device is shown to be provided with a temperature sensor, which is used to detect the battery temperature. The controller consists of a microcontroller. The outputs voltage level of the temperature sensor is usually designed to be proportional to the battery temperature being measured. The microcontroller monitors the output voltage of the temperature sensor using one of the internal ADC channels “A1”, FIG. 25. When the temperature voltage output is below a certain preset threshold value, the microcontroller applies the driving signals to M1 and M2 as was previously described for the embodiment of FIG. 24, therefore initiating the battery heating process. The driving signals are sent to the gate terminals of M1 and M2 though two digital output pins D1 and D2 respectively. The microcontroller by be programmed to change the switching frequency of M1 and M2, i.e., the frequency of the heating current), depending on the measured battery temperatures as described later in this disclosure.
The temperature sensor can be a low-voltage temperature sensor IC such as the TMP35, a thermocouple module, a Resistance Temperature Detector (RTD) or a thermistor. The battery temperature is generally measured at the battery surface, in which case during the described heating process, the battery core temperature is generally higher than the measured surface temperature. For relatively small batteries, e.g., those with a diameter of up to 1 inch, the difference may not introduce any issue since the difference may be only a few degrees C., and the temperature threshold for low temperature may be set a few degrees lower than the desired threshold to account for this difference. Alternatively, particularly for larger batteries and super-capacitors, a thermal model of the battery may be used together with the time history of the heating energy input into the battery to estimate average (or peak high or low) internal temperature of the battery core and use that for setting the said controller low temperature threshold for switching the heating circuit on and off. Thermal modeling of batteries and super-capacitors are well known in the art and for the present embodiments only a very simplified model would generally suffice. A modeling technique that is specifically tailored for use in Lithium-ion and other similar batteries and in super-capacitors is described later in this disclosure.
It is appreciated by those skilled in the art that the usual practice for temperature threshold setting would be to set a range of temperature, below which heating process is turned on and above which it is turned off.
When an outside AC power source is used to power the circuit of FIG. 24 or 25, an AC to DC converter and voltage regulator shown in the dashed line box in FIG. 25 may be used to supply the voltage V+ to the circuit of FIG. 24 and as well as for powering the microcontroller and temperature sensor for the circuit of FIG. 25. The AC to DC converter and the voltage regulator may be integrated into the same circuit board with the rest of the components of the circuits or may be designed as an external component.
FIG. 26 illustrates the circuit diagram shown in FIG. 25 with the temperature sensor implemented by using a thermistor or an RTD. The thermistor can be either an NTC or a PTC type thermistor. The thermistor and the RTD resistance are proportional to the temperature. Therefore, the resistor R3 in series with either a thermistor or an RTD forms a voltage divider. The voltage measured by the microcontroller ADC channel A1 is therefore proportional to the temperature measured. The resistance value of R3 can be adjusted for different sensitivity.
FIG. 27 illustrates another embodiment of a battery heating circuit utilizing dual polarity power supplies V+ and V− to apply both positive and negative current flow into the battery. When the P-Channel MOSFET M1 is enabled while the N-Channel MOSFET M2 is disabled, the positive voltage source V+ is connected to the positive terminal of the battery and the current flows from the source into the battery. The voltage level of V+ must be larger than the voltage across the battery. When M2 is enabled while M1 is disabled, the negative voltage source V− is connected to the positive terminal of the battery and the current flows from the battery into the source. The voltage level of V− is preferably lower than the voltage across the battery to balance the current flow. Resistors R1 and R4 are used to ensure the M1 and M2 are both disabled when the control signal voltage is 0 V. Resistors R2 and R3 can be used to adjust the output DC offset voltage value. The control signal from the controller is AC coupled through a capacitor C1. When the control signal voltage is positive, M2 is enabled and M1 is disabled. When the control signal voltage is negative, M1 is enabled and M2 is disabled.
FIG. 28 illustrates a circuit diagram of the controller with the circuit diagram shown in FIG. 27. The controller consists of a temperature sensor and a microcontroller. The temperature sensor is used to monitor the temperature of the battery 450, which to be heated if below a prescribed temperature threshold. The outputs voltage level of the temperature sensor is proportional to the battery temperature. The temperature sensor can be a low-voltage temperature sensor IC such as the TMP35, a thermocouple module, a Resistance Temperature Detector (RTD) or a thermistor. The microcontroller monitors the output voltage of the temperature sensor using one of the internal ADC channels “A1”. When the temperature voltage output is below a certain preset threshold value, the microcontroller applies the control signals to M1 and M2, therefore, initiating the heating process as was previously described. The control signals are sent to the gate terminals of M1 and M2 though digital output pin D1. The AC coupled through the capacitor C1 allows control signal voltage level at the gate terminal of M1 and M2 to be both positive and negative while the digital pin D1 outputs a voltage value between 0 V and a positive preset value. The microcontroller can change the switching frequency of M1 and M2 at different battery temperatures if as is described later, particularly when the battery is intended to operate at very low temperatures, e.g., below −40 degrees C. The AC to DC converters 1 and 2 are used to supply the positive and negative voltage source for the heating process, as well as for powering the microcontroller and temperature sensor though a voltage regulator. The AC to DC converters and the voltage regulator can be integrated into the same circuit board with the rest of the components or they can be external components.
FIG. 29 illustrates the block diagram of another embodiment of the battery 450 heating circuit utilizing a single power supply to apply both positive and negative current flow into the battery 450. Four switches SW1A, SW1B, SW2A and SW2B are used for this purpose. The switches can be implemented by relays, semiconductor switch ICs or MOSFETs. When SW1A and SW1B are closed while SW2A and SW2B are open, the positive voltage source V+ is connected to the positive terminal of the battery 450 while the circuit ground is connected to the negative terminal of the said battery. The current then flows from the source into the battery 450. When SW2A and SW2B are closed while SW1A and SW1B are open, the positive voltage source V+ is connected to the negative terminal of the battery 450, while the circuit ground is connected to the positive terminal of the said battery. Then the current flows from the battery 450 into the source. The voltage level V+ is preferably larger than the voltage across the battery 450. A controller is used to drive all four switches at the proper sequence and frequency.
FIG. 30 illustrates a circuit diagram of the battery heating controller with the circuit of the embodiment of FIG. 29. The switches are implemented by MOSFETs M1A, M1B, M2A and M2B representing SW1A, SW1B, SW2A and SW2B, respectively. The controller is a microcontroller and is provided with a temperature sensor. The temperature sensor is used to monitor the temperature of the battery 450. The outputs voltage level of the temperature sensor is proportional to the battery temperature. The temperature sensor can be a low-voltage temperature sensor IC such as the TMP35, a thermocouple module, a Resistance Temperature Detector (RTD) or a thermistor. The microcontroller monitors the output voltage of the temperature sensor using one of the internal ADC channels “A1”. When the temperature voltage output is below the prescribed threshold value, the microcontroller initiates the battery heating process by applying the control signals from digital pins D1 and D2 to the MOSFETs through a driver circuit consists of Resistor R1 to R4, MOSFET M3 and M4. The driver circuit ensures the M1A, M1B, M2A and M2B can be completely driven into cut-off mode (open) or saturation mode (closed) regardless of the difference voltage level between the control signals voltage and the source voltage of V+. When digital pin D1 is at logic high while D2 is at logic low, M1A and M1B act as closed switches while M2A and M2B act as open switches. Therefore, current flows from the source into the battery 450. When digital pin D1 is at logic low while D2 is at logic high, M1A and M1B act as open switches while M2A and M2B act as closed switches. Therefore, current flows from the battery 450 into the source. The frequency of the switching, i.e., the frequency of the applied current (AC heating current) is therefore set and controlled by the controller and may be varying as a function of the battery temperature as is described later in the disclosure. An AC to DC converter is used to supply the voltage source for the heating process, as well as for powering the microcontroller and temperature sensor though a voltage regulator. The AC to DC converter and the voltage regulator can be integrated into the same circuit board with the rest of the components or they can be external components.
FIG. 31 shows an example of increasing the temperature of a standard model 18650 cell Li-ion battery, as measured on the outside surface of the battery, while it was heated from −30° C. to 20° C. using a circuit based on the design shown in FIG. 27. The battery part number is LGABB418650.
As was previously described in this disclosure, the internal resistance and inductance of Li-ion based batteries and in fact all rechargeable and primary batteries and super-capacitors vary by temperature, with the changes becoming very significant at lower temperatures. As an example, FIGS. 32 and 33 are the plots of measured internal resistance and internal inductance of a standard 18650 cell Li-ion battery (battery part number is LGABB418650), respectively, in the temperature range of −55° C. to 45° C.
It is appreciated that as it is shown in the plots of FIGS. 32 and 32, since the internal resistance and inductance of the batteries and super-capacitors to be heated by the application of the described high frequency voltage (current) vary significantly as a function of temperature, particularly at very low temperatures at which achieving higher heating rates is highly desirable. Therefore, the amplitude and frequency of the applied high frequency voltage (current) must be adjusted for optimal heating rate as the temperature varies. In the various embodiments of the present invention this is readily accomplished by providing stored data, for example in the form of a table, in the controller and microcontroller of the embodiments of FIGS. 22 and 24-30. It is appreciated by those skilled in the art that an examination of the typical plots of FIGS. 32 and 33 shows that such look-up tables require only a very limited size due to the simple shapes of the plotted curves. In a more universal device, such look-up table data may also be stored in the controller and microcontroller memory for a wide range of batteries and super-capacitors that are commonly used. Alternatively, the user may be provided with the option of entering the related look-up table data from using a number of data communication means known in the art.
FIG. 34 illustrates another embodiment of a battery heating circuit utilizing a Push-Pull amplifier comprised of a PNP type Bipolar Junction Transistor Q1 and a PNP type Bipolar Junction Transistor Q2. The base terminals of both transistors are driven by the same control signal voltage. When the signal voltage is positive, Q1 is activated while Q2 is in cut-off mode and acts as an open switch. Current flows from the positive voltage source V+ into the battery. When the signal voltage is negative, Q2 is activated while Q1 is in cut-off mode and acts as an open switch. Current flows from the battery into the negative voltage source V−. The control signal is sent from a controller which is similar to the control circuit shown in FIG. 28. The controller outputs digital pulses through AC coupling capacitor C1. The AC coupled control signal is then amplified by a device such as an Operational Amplifier U1. The ratio of resistors R1 and R2 is used to configure the voltage level of the output signal of U1. The AC coupled and amplified control signal is then send to drive the transistors Q1 and Q2.
It is appreciated by those skilled in the art that the switching circuits of the embodiments of FIGS. 22 and 24-30 produce a nearly square wave shaped voltage input for battery and super-capacitor heating. Such square wave shaped high frequency voltages are effective for heating the various indicated batteries, including Li-ion and lead-acid batteries and super-capacitors if they are produced at high enough frequencies as was previously indicated. IN certain applications, particularly when the battery or super-capacitor to be heated has high inductance, it may be desired to employ heating AC voltages that are closer to being purely sinusoidal. For this purpose, as an example, the heating circuit of the embodiment of FIG. 34 may be modified as illustrated in FIG. 35. In this circuit, the resistor R3, and capacitors C3 and C1 together forms a filter, which turns the square wave controller generated signal into an essentially sinusoidal signal.
FIG. 36 illustrates another embodiment of a battery heating circuit utilizing a Power Operational Amplifier Integrated Circuit U1. The Power Operational Amplifier Integrated Circuit U1 can be configured as inverting or non-inverting amplifier. FIG. 36 illustrates an example of U1 as configured as an inverting amplifier. In this embodiment, the control signal is sent from a controller, which may be similar to the control circuit shown in the embodiment of FIG. 28. The control signal is sent to the input of U1 via an AC coupling capacitor C1. The ratio of resistors R1 and R2 is used to configure the voltage level of the output of U1. The output power of U1 is then used to apply heating for the battery via an AC coupling capacitor C2. The capacitor C2 is required to prevent damage to the output terminal of U1.
FIG. 37 illustrates a modified alternative of the battery heating circuit embodiment of FIG. 36. In this circuit, the resistor R3, and capacitors C3 and C1 together forms a filter, which turns the square wave controller generated signal into an essentially sinusoidal signal.
FIG. 38 illustrates a modified alternative of the battery heating circuit of the embodiment of FIG. 37. In this circuit, a transformer T1 is used to provide impedance matching between the battery and the output of the Power Operational Amplifier Integrated Circuit U1. The transformer T1 is necessary when the battery impedance is much smaller than the output impedance of the Power Operational Amplifier Integrated Circuit U1. The coil resistance of N1 inside T1 should be high enough to maintain output efficiency of U1, as well as to reduce power dissipation within U1. Ac coupling capacitor C2 is also required to prevent the coil resistance of N2 from loading the battery.
It is appreciated that the battery heating circuit embodiments of FIGS. 22, 24-30 and 34-38 use external power supply for their operation. In certain applications, it is desirable for the battery heating circuit to operate using power provided by the battery itself. For battery types such as Li-ion, NiMH and Lead Acid, the maximum output current that is available at the rated voltage is lower at lower battery temperatures. FIG. 39 is a typical plot showing the maximum output current levels of a Li-ion, a NiMH and a VRLA (Valve-Regulated Lead-Acid) batteries as a function temperature. As can be see in FIG. 39, the available current drops significantly at lower temperatures. For this reason, the following battery heating circuit embodiments of the present invention are divided into those for applications in which the battery can still provide enough current to directly power the heating circuit and those in which the available current level is not high enough and require intermediate storage. The two circuit types are desired to work together for optimal performance, i.e. once the battery is heated enough so that it can provide the required current levels, then the heating circuit is switched to direct powering mode.
FIG. 40 illustrates another embodiment of a battery 450 heating circuit, which uses power from the said battery that is being heated directly, therefore the embodiment does not require an external power supply. The circuit embodiment of FIG. 40 is a modification of the basic heating circuit of the embodiment of FIG. 22. In the circuit of FIG. 40, the voltage source V+ is provided by a step-up voltage regulator which acquires the input voltage from the battery 450 terminals via a LC filter comprised of an inductor L1 and a capacitor C1. The step-up voltage regulator outputs a voltage level which is an increased voltage level of the input voltage. The LC filter allows the input voltage level of the voltage regulator remains stable during the heating process when the current is flowing into and out of the battery alternatively. The voltage regulator requires a minimum amount of input current to maintain the output voltage level and to provide enough current for the heating process. The available current at rated voltage for a typical Li-ion, NiMH and Lead Acid battery is shown in FIG. 39. The circuit of FIG. 40 is ideal for operating at a battery temperature above a certain value which allows enough current for the heating process while maintaining the voltage level of V+. For example, a Li-ion 28V battery pack is used with the circuit in FIG. 40 and the minimum required current for the circuit in FIG. 40 to operate properly is around 5 A. Therefore, the minimum operating temperature for this example is −20° C. as shown in FIG. 39.
It is appreciated that the heating circuit embodiment of FIG. 40, which is powered by the battery 450 itself, may also be provided with an external powering. As a result, the user will be able to use external power for heating the battery 450 when such an external power source is available, thereby saving the battery charges and accelerating the battery heating process. In this case, the optional terminals of V+ and Circuit Ground can be wired to an external power supply. It is appreciated that once the battery temperature has increased up to an appropriate value, the external power supply can be disconnected, and the subsequence heating process can be powered by the battery itself. In many such applications, the external power source is used to bring the battery temperature to or close to room temperature or a temperature that the battery performance is near optimal or at the desired level, and then the external powering is terminated, and the battery power is used to maintain the battery temperature at the desired level.
Examples of such applications are vehicles or power tool batteries, where the vehicle or the power tool is stored in unheated garage or storage where external power is available. Then the user would first heat the battery in cold temperature and when it is at the desired temperature level, the external power is disconnected, and the battery temperature is maintained at the desired level using the battery power. The user can then use the vehicle and power toll in very cold weather without losing battery performance. It is appreciated by those skilled in the art that such applications are plentiful and includes most devices and systems that are used at one time or another in low temperature environments.
FIG. 41 illustrates the battery heating circuit embodiment of FIG. 40 as modified to allow for operation at very low temperatures at which the battery cannot provide high enough current for operation of the circuit directly from the battery itself. The battery heating circuit embodiment of FIG. 41 operates without external power. The voltage source V+ is provided by a step-up voltage regulator which acquires the input voltage from the capacitor C2 via a LC filter comprised of an inductor L1 and a capacitor C1. The capacitor C2 is charged when the switch SW3 is switched to position A. Once the capacitor is fully charged, the controller switches SW3 to position B and the voltage regulator draws energy from C2 to provide energy for the heating process. Once the voltage across C2 drops to a certain level and no longer able to maintain the operation of the voltage regulator, SW3 is switched to position A and to be fully charged once again. This process repeats until the controller senses that the battery temperature is above the prescribed threshold for direct self-powering. The battery can then be used to directly power the heating circuit as was previously described for the embodiment of FIG. 40.
FIG. 42 illustrates another embodiment of a battery 450 heating circuit, which uses power from the said battery that being heated directly, therefore the embodiment does not require an external power supply. The circuit embodiment of FIG. 42 is a modification of the basic heating circuit of the embodiment of FIG. 29. The voltage source V+ is provided by a step-up voltage regulator which acquires the input voltage from the battery 450 terminals via a LC filter comprised of an inductor L1 and a capacitor C1. The step-up voltage regulator outputs a voltage level, which is higher than the input voltage level. The LC filter allows the input voltage level of the voltage regulator to remain stable during the heating process when the current is alternatively flowing into and out of the battery 450. The voltage regulator requires a minimum amount of input current to maintain the output voltage level and to provide enough current for the heating process. The available current at rated voltage for a typical Li-ion, NiMH and Lead Acid battery is shown in FIG. 39. The circuit in FIG. 42 is ideal for operating at a battery 450 temperature that is above the level at which the battery can provide enough current for the heating process while maintaining the required voltage level of V+. For example, a Li-ion 28V battery pack is used with the circuit in FIG. 42 and the minimum required current for the circuit in FIG. 42 to operate properly is around 5 A. Therefore, the minimum operating temperature for this example is −20° C. as shown in FIG. 39.
It is appreciated that the heating circuit embodiment of FIG. 42, which is powered by the battery 450 itself, may also be provided with an external powering. As a result, the user will be able to use external power for heating the battery 450 when such an external power source is available, thereby saving the battery charges and accelerating the battery heating process. In this case, the optional terminals of V+ and Circuit Ground can be wired to an external power supply. It is appreciated that once the battery temperature has increased up to an appropriate value, the external power supply can be disconnected, and the subsequence heating process can be powered by the battery itself. In many such applications, the external power source is used to bring the battery temperature to or close to room temperature or a temperature that the battery performance is near optimal or at the desired level, and then the external powering is terminated, and the battery power is used to maintain the battery temperature at the desired level. Examples of such applications as vehicles or power tool batteries and other similar applications were previously discussed.
FIG. 43 illustrates the battery heating circuit embodiment of FIG. 42 as modified to allow for operation at very low temperatures at which the battery cannot provide high enough current for operation of the circuit directly from the battery itself. The battery heating circuit embodiment of FIG. 43 operates without external power. The voltage source V+ is provided by a step-up voltage regulator which acquires the input voltage from the capacitor C2 via a LC filter comprised of an inductor L1 and a capacitor C1. The capacitor C2 is being charged when the switch SW3 is switched to position A. Once the capacitor is fully charged, the controller switches SW3 to position B and the voltage regulator draws energy from C2 to provide energy for the heating process. Once the voltage across C2 drops to a certain level and no longer able to maintain the operation of the voltage regulator, SW3 is switched to position A and to be fully charged once again. This process repeats until the controller senses that the battery temperature is above a certain value. This process repeats until the controller senses that the battery temperature is above the prescribed threshold for direct self-powering. The battery can then be used to directly power the heating circuit as was previously described for the embodiment of FIG. 42.
It is appreciated by those skilled in the art that in most applications, batteries and super-capacitors are housed in a closed environment, such as a battery pack. In some applications, such as in the case of lead-acid batteries, the battery may not be positioned in a relatively closed housing. In all these applications, when the battery or super-capacitor is being heated using one of the above embodiments of the present invention, the temperature measured by a sensor that is attached to the outside surface of the battery or super-capacitor would generally be lower than that of the battery and super-capacitor core. In all these applications, a thermal model of the battery or super-capacitor core, its housing (including insulation layer and/or paint), and other covering layers can be used to predict the core temperature by measuring the temperature of the battery and super-capacitor outside surface. In these models, the amount of input heating energy and the measured outside surface temperature as a function of time together with the initial temperature of the battery (usually the same as the temperature measured on the battery surface) are used to predict the battery or super-capacitor core temperature. It is also appreciated by those skilled in the art that such a model can be readily programmed into the processor of the controllers of the various embodiments of the present invention.
While there has been shown and described what is considered to be preferred embodiments of the invention, it will, of course, be understood that various modifications and changes in form or detail could readily be made without departing from the spirit of the invention. It is therefore intended that the invention be not limited to the exact forms described and illustrated, but should be constructed to cover all modifications that may fall within the scope of the appended claims.

Claims

What is claimed is:

1. A method for heating an energy storage device having a core with an electrolyte, the method comprising:

providing the energy storage device having inputs and characteristics of a capacitance across the electrolyte and the core and internal surface capacitance between the inputs which can store electric field energy between internal electrodes of the energy storage device that are coupled to the inputs;

switching between an input voltage and a grounding input provided to one of the inputs at a frequency sufficient to effectively short the internal surface capacitance of the energy storage device to generate heat and raise a temperature of the electrolyte; and

discontinuing the switching when the temperature of the electrolyte is above a predetermined temperature that is considered sufficient to increase a charging efficiency of the energy storage device.

2. The method of claim 1, comprising providing the input voltage through a first switch and providing the grounding input through a second switch, wherein the switching comprises simultaneously coupling the input voltage to the one input through operation of the first switch and decoupling the grounding input from the one input through operation of the second switch during a first time interval and thereafter, simultaneously decoupling the input voltage from the one input through operation of the first switch and coupling the grounding input to the one input during a second time interval through operation of the second switch, wherein the first interval and the second interval are subsequently repeated at the frequency sufficient to effectively short the internal surface capacitance of the energy storage device.

3. The method of claim 2, wherein the first switch is a normally closed switch that couples the input voltage to the one input when a first switching voltage is below a first predetermined voltage.

4. The method of claim 3, wherein the second switch is a normally open switch that decouples the grounding voltage from the one input when a second switching voltage is below a second predetermined voltage.

5. The method of claim 2, wherein the providing the grounding input comprises coupling the one input to a circuit ground through the second switch and a sink resistor.

6. The method of claim 5, comprising selecting the input voltage and a resistance of the sink resistor such that nearly the same charge of the energy storage device occurs during the first time interval as discharge from the energy storage device occurs during the second time interval.

7. The method of claim 1, wherein the predetermined temperature is a first predetermined temperature, the method comprising initiating the switching when the temperature of the electrolyte is below a second predetermined temperature that is considered to at least reduce the charging efficiency of the energy storage device, wherein the second predetermined temperature is a lower temperature than the first predetermined temperature.

8. The method of claim 1, comprising obtaining at least one of a measurement and an approximation of the temperature of the electrolyte.

9. The method of claim 8, wherein the obtaining comprises directly measuring the temperature of the electrolyte with a temperature sensor positioned at one or more of the electrolyte and a surface of the energy storage device.

10. The method of claim 8, wherein the obtaining comprises: applying an initial charging input to the energy storage device, measuring a rate of charging using the initial charging input, and determining a charging rate at the initial charging input, wherein if a rate of charging is determined to be less than a predetermined charging rate, the electrolyte temperature is approximated as being less than the predetermined temperature.

11. The method of claim 1, comprising providing a controller for controlling the switching and the discontinuing.

12. The method of claim 11, comprising obtaining by the controller at least one of a measurement and an approximation of the temperature of the electrolyte.

13. The method of claim 12, wherein the obtaining comprises directly measuring the temperature of the electrolyte with a temperature sensor coupled to the controller and positioned at one or more of the electrolyte and a surface of the energy storage device.

14. The method of claim 12, wherein the obtaining is performed periodically.

15. The method of claim 1, comprising producing the input voltage from an AC source provided through an AC to DC converter.

16. The method of claim 1, comprising:

obtaining an energy storage type for the energy storage device; and

retrieving from a look-up table the predetermined temperature that corresponds to the obtained energy storage type, wherein the look-up table correlates different energy storage types with corresponding predetermined temperatures.

17. The method of claim 1, comprising coupling the input voltage to the one input to charge the energy storage device while the temperature of the electrolyte is above the predetermined temperature.

18. The method of claim 1, wherein the energy storage device is a lithium ion battery or a supercapacitor.

19. A method for charging an energy storage device having a core with an electrolyte, the method comprising:

switching between an input voltage and a grounding input provided to one of the inputs at a frequency sufficient to effectively short the internal surface capacitance of the energy storage device to generate heat and raise a temperature of the electrolyte;

periodically obtaining a measurement that correlates to the temperature of the electrolyte,

wherein the switching is initiated when the measurement indicates that the temperature of the electrolyte is below a low temperature threshold that is considered to at least reduce the charging efficiency of the energy storage device, wherein the switching is discontinued when the measurement indicates that the temperature of the electrolyte is above a high temperature threshold that is considered sufficient to increase a charging efficiency of the energy storage device, and wherein the low temperature threshold is a lower temperature than the high temperature threshold; and

providing the input voltage to the one input to charge the energy storage device while the measurement indicates that the temperature of the electrolyte is above the high temperature threshold.