JP2013026142A - Lithium semi-redox flow battery renewable both by electrical charge and by chemical oxidation using oxidant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a battery using lithium as a negative electrode active material, capable of being scaled up and having high capacity, and also quickly renewable after discharge.SOLUTION: A lithium semi-redox flow battery includes: a battery body comprising a lithium negative electrode (1), a negative electrode side electrolyte chamber (2) storing an organic electrolyte, a solid electrolyte separation membrane (3), a positive electrode side electrolyte chamber (4) storing a water-soluble electrolyte including an ionic active material ((M/M), and a positive electrode collector (5); a storage tank (6) storing the water-soluble electrolyte; and a circulation passage (7) connecting the positive electrode side electrolyte chamber of the battery body and the storage tank via a freely opened/closed valve.

Description

  The present invention relates to a lithium semi-redox flow battery that combines a negative electrode of a lithium battery and a positive electrode of a redox flow battery and can be regenerated by both electrical charging and chemical oxidation by adding an oxidizing agent to the positive electrode active material.

The detrimental consequences of global warming caused by the depletion of non-renewable energy sources and the CO ₂ generated by the burning of fossil fuels have led to worldwide attention attracting alternative energy sources that are harmless to the environment. It is turning rapidly to development.
Li-ion batteries have inherently higher capacity and weight energy density compared to acid-lead, Ni-Cd or Ni-MH type batteries, so they can be used in small portable devices to large electric vehicles such as hybrid electric vehicles. It is considered a power source option for a wide range of applications across the system (Non-Patent Documents 1-3). However, in order for lithium-ion batteries to be scaled up to meet future application needs for automobiles, there is a problem that the input / output of lithium ions during charging / discharging is restricted by the structure of the positive electrode material. (Non-Patent Documents 2 to 5).
Against this background, in order to achieve further developments in lithium battery technology, the development of new lithium battery concepts including alternative chemistry, combinations of various electrode pairs, new electrolytes, etc. Various researches such as the design of a new battery prototype to be used have been made.
Recently, a prominent search for high capacity has been directed to lithium-air batteries that have an open battery structure and use oxygen from the air as the positive electrode active material (Non-Patent Documents 1 and 3). The introduction of a protective glass ceramic layer for lithium metal by PolyplusCo. (LISICON, LiM ₂ (PO ₄ ) ₃ ) (Patent Document 1) opened another way to build a new type of lithium battery. While the LISICON layer is stable in water and in aprotic electrolytes, it selectively conducts Li ⁺ , thus creating the possibility of combining two seemingly impossible-to-combine electrolytes. Focusing on this possibility, we clarified the prototype of a group of batteries such as Li-metal, Li-air, Li-NiOOH, Li-AgO, including the concept of a hybrid electrolyte system using LISICON as a separator. (Non-Patent Documents 6 to 11).
On the other hand, a redox flow battery is mentioned as one of the forms of a high capacity battery. The redox flow battery is mainly used for storing surplus power in a power plant by utilizing its high capacity. However, the redox flow battery uses only a water-soluble electrolyte as the electrolyte, and has the disadvantage that the battery voltage is low, and regeneration after discharge is performed only by relatively time-consuming charging, At present, it is not suitable for a wide range of future applications such as electric vehicles.

US Pat. No. 7,282,295 (2007)

J. Phys. Chem. Lett., 2010, 1, 2193-2203 J. Power Sources 2010, 195, 2419-2430 Adv. Energy Mater., 2011, 1, 34-50 Solid State Ionics 2008, 179, 752-760 Chem. Soc. Rev., 2009, 38, 2565-2575 Chem. Sus. Chem., 2010, 3, 1009-1019 Electrochem. Commun., 2009, 11, 1834-1837 J. Power Sources 2010, 195, 358-361 Electrochem. Commun., 2010, 12, 1686-1689 J. Am. Chem. Soc., 2009, 131, 15098-15099 Chem. Commun., 2010, 46, 2055-2057

  An object of the present invention is to obtain a large capacity battery capable of being scaled up in a battery using lithium as a negative electrode active material, and to obtain a battery that can be quickly regenerated after discharging.

In the battery using lithium as a negative electrode active material, instead of using a solid positive electrode and a liquid electrolyte as in a conventional battery, the present inventors have used a redox couple of M ^{n +} / M ^{(n-1) +} . The above-mentioned problems have been solved by providing a new type of battery that uses an aqueous solution containing as both a positive electrode active material and an electrolyte.

Hereinafter, a typical example of the lithium redox flow battery according to the present invention will be described with reference to FIG. As shown in FIG. 2, the lithium redox flow battery according to the present invention comprises a lithium negative electrode (1) / a negative electrode side electrolyte chamber (2) containing an organic electrolyte, a solid electrolyte separation membrane (3), and an ionic active material. A battery body composed of a positive electrode side electrolyte chamber (4) / positive electrode current collector (5) containing a water soluble electrolyte containing (M ^{n +} / M ^{(n-1) +} ), and the water soluble electrolyte And a circulation path (7) for connecting the positive electrode side electrolyte chamber of the battery body and the storage tank via an openable / closable valve.

As the negative electrode active material of the lithium negative electrode used in the battery of the present invention, for example, a negative electrode active material that can be used for the negative electrode of a lithium ion battery, such as metallic lithium, can be used.
As said organic electrolyte solution used for the battery of this invention, the organic electrolyte solution which can be used for the negative electrode side electrolyte solution of a lithium ion battery can be used.
As the solid electrolyte separation membrane used in the battery of the present invention, a membrane made of a solid electrolyte that selectively conducts lithium ions, such as LISICON, is used.
Examples of the ionic active material (M ^{n +} / M ^{(n-1) +} ) used in the battery of the present invention include Cr ³⁺ / Cr ²⁺ , Fe ³⁺ / Fe ²⁺ , V ³⁺ / V ^Examples thereof include ion pairs such as ²⁺ and VO ₂ ⁺ / VO ^2+, and complex ion pairs such as Fe (CN) ₆ ³⁻ / Fe (CN) ₆ ⁴⁻ . FIG. 2 shows an example in which Fe ³⁺ / Fe ²⁺ is used as (M ^{n +} / M ^{(n−1) +} ).

In the battery, during discharge, the elution reaction of Li ⁺ of Li → Li ⁺ + e ⁻ is performed on the negative electrode side, and the ionicity of M ^{n +} → M ^{(n−1) +} + e ⁻ is performed on the positive electrode side. The reduction reaction of the active material proceeds.
After discharging, if the positive electrode side electrolyte chamber and the circulation path valve are opened to circulate the positive side electrolyte solution between the positive electrode side electrolyte chamber and the storage tank, the positive electrode side in the storage tank The ionic active material (M ^{n +} ) in the electrolyte is reduced to M ^{(n−1) +} .

In ^order to return M ^{(n-1) +} generated at the time of discharge to M ^{n +} , the battery is electrically charged, the reaction of Li ⁺ + e ⁻ → Li proceeds at the negative electrode, and M ^{(n−1) at the} positive electrode. ^{) ++} e- → M ^{n +} However, this charging method takes time in the charging process.

In order to solve this problem, the present inventors have developed a simpler and faster regeneration method using an oxidizing agent. In this method, an oxidizing agent is added to a water-soluble electrolyte containing M ^{(n-1) +} generated during discharge, and M ^{(n-1) +} is chemically oxidized in a short time and regenerated to ^{Mn +} . To do.
As the oxidizing agent, for example, solid powder (NH ₄ ) ₂ S ₂ O ₈ or liquid H ₂ O ₂ can be used. (NH ₄ ) ₂ S ₂ O ₈ is an inexpensive and powerful oxidant and is extremely fast (within 10 seconds) through the chemical reaction of 2Fe ²⁺ + S ₂ O ₈ ²⁻ → 2Fe ³⁺ + 2SO ₄ ^2- , Fe ²⁺ can be oxidized back to Fe ³⁺ .
The regeneration of M ^{n +} by electrical charging needs to be performed after stopping the discharge of the battery, but the regeneration of M ^{n +} by chemical oxidation can be performed concurrently with the discharge of the battery. Therefore, when this method is used, the battery of the present invention can be continuously discharged as long as the metallic lithium of the negative electrode remains.

The present application provides the following inventions.
<1> Lithium negative electrode / negative electrode side electrolyte chamber containing organic electrolyte / solid electrolyte separation membrane / positive electrode side containing water-soluble electrolyte containing ionic active material (M ^{n +} / M ^{(n-1) +} ) A battery body composed of an electrolyte chamber / positive electrode current collector, a storage tank for storing the water-soluble electrolyte, and a positive electrode side electrolyte chamber of the battery body and the storage tank are connected via an openable / closable valve. A lithium semi-redox flow battery comprising a circulation path.
<2> The lithium semi-redox flow battery according to <1>, wherein a valve for adding an oxidizing agent is provided in a tank that stores the water-soluble electrolyte.
<3> The lithium semi-redox flow battery according to <1> or <2>, wherein a negative electrode active material that can be used for a negative electrode of a lithium ion battery is used as the active material of the lithium negative electrode.
<4> The lithium semi-redox flow battery according to <3>, wherein the negative electrode active material usable for the negative electrode of the lithium ion battery is metallic lithium.
<5> Cr ³⁺ / Cr ²⁺ , Fe ³⁺ / Fe ²⁺ , V ³⁺ / V ²⁺ , VO ₂ ⁺ / VO as ionic active materials (M ^{n +} / M ^{(n-1) +} ) The lithium semi-redox flow battery according to <1> to <4>, wherein one kind of ion pair of ²⁺ or a complex ion pair thereof is used.
<6> Charging the battery of Li ⁺ + e ⁻ → Li, M ^{(n−1) +} + e ⁻ → M ^{n + with} the ionic active material reduced to M ^{(n−1) +} during discharge The lithium semi-redox flow battery according to <1> to <5>, wherein the battery is regenerated to M ^{n +} using a process.
<7> An ionic active material that has been reduced to M ^{(n-1) +} during discharge is regenerated to M ^{n +} by adding an oxidizing agent to a water-soluble electrolyte and oxidizing it. The lithium semi-redox flow battery according to <1> to <5>.
<8> The ionic active material that has been reduced to M ^{(n-1) +} during discharge is charged to the battery as Li ⁺ + e ⁻ → Li, M ^{(n−1) +} + e− → M ^{n +} using process, added with an electrical charging method for reproducing the M ^{n +,} the oxidizing agent in a water-soluble electrolyte, by oxidation, a combination of chemical oxidation method of reproducing the M ^{n +,} to play M ^{n +} The lithium semi-redox flow battery according to <1> to <5>.
<9> The lithium semi-redox flow according to <7> or <8>, wherein (NH ₄ ) ₂ S ₂ O ₈ or liquid H ₂ O ₂ is used as the oxidizing agent. battery.

The lithium semi-redox flow battery of the present invention can avoid a slow diffusion process at the time of intercalation of Li ions into an electrode in a conventional lithium ion battery by using a redox couple aqueous solution as a positive electrode active material. Further, by providing a storage tank for storing the redox couple aqueous solution and circulatingly supplying the aqueous solution from here to the positive electrode electrolyte chamber of the battery body, the battery capacity can be increased.
The liquid positive electrode comprising the redox couple aqueous solution of the present invention can be regenerated not only by electrical charging which takes a relatively long time after discharge but also by rapid chemical oxidation.
In the battery of the present invention, these electrical charging and chemical oxidation are combined, and a relatively small amount of discharge or intermittent discharge is caused by charging, and a large amount of discharge or continuous discharge is chemically oxidized. Thus, the liquid positive electrode can be regenerated.
In addition, the lithium semi-redox flow battery of the present invention not only functions in a stationary mode like any other closed battery by closing a circuit valve depending on the intended use, but also a conventional redox flow battery. It can be easily switched to function in the flow mode as well as the battery.

FIG. 6 is a structural diagram of a conventional redox flow battery. From the negative electrode / organic electrolyte / solid electrolyte separation membrane / aqueous electrolyte containing the ionic active material (M ^{n +} / M ^{(n-1) +} ) and its external storage tank / current collector (electrode) Explanatory drawing of the lithium semi redox flow battery comprised. The conceptual diagram at the time of discharge of the lithium semi redox flow battery of this invention. Example 1 A discharge profile at a current density of 0.5 mA / cm ² in a stationary mode of a lithium semi-redox flow battery of the present invention. The conceptual diagram at the time of charge (electric charge) of the lithium semi redox flow battery of this invention. The charge / discharge cycle characteristics of the lithium semi-redox flow battery of the present invention in the flow mode in discharge and charge current density of 0.2 mA / cm ² , 2 hours of charge / 2 hours of discharge (Example 2). The conceptual diagram at the time of discharging continuously the lithium semi-redox flow battery of this invention, adding an oxidizing agent to a positive electrode solution at appropriate time (chemical charge) in flow mode. In the discharge at a current density of 0.5 mA / cm ² in the flow mode of the lithium semi-redox flow battery of the present invention, when the Fe ³⁺ in the positive electrode solution is almost reduced to Fe ²⁺ , the oxidizing agent (NH ₄ ) ₂ Discharge profile when performing continuous discharge by adding S ₂ O ₈ (Example 3).

The invention is illustrated in more detail by the following examples.
FIG. 3 shows the configuration of the battery of the present invention used in the experiment. The negative electrode chamber (2) and the positive electrode chamber (4) are separated by a LISICON plate (3) having a thickness of 0.15 mm that selectively allows the movement of Li ⁺ . The negative electrode chamber is filled with an aprotic electrolyte (1M LiClO ₄ in ethylene carbonate / dimethyl carbonate), and Li metal is attached as the negative electrode (1). The positive electrode chamber contains an aqueous solution of FeCl ₃ serving as both an electrolyte and a positive electrode active material, and a Ti mesh is inserted as a current collector (5). A storage tank (6) is attached to the positive electrode chamber via valves 1 and 2 and a pump, and an aqueous solution of FeCl ₃ can be circulated between the positive electrode chamber and the storage tank by the pump. .
This battery becomes a closed battery when it is operated in the stationary mode with the valves 1 and 2 closed, and becomes an open battery when it is operated in the flow mode with the valves 1 and 2 opened and operated.
In the following experiment, both stationary mode and flow mode were performed. Operation was possible in any mode. In flow mode, the flow rate used was ¹ mL min ⁻¹ .
The Fe ³⁺ aqueous solution was prepared by dissolving FeCl ₃ .6H ₂ O in distilled water.

Example 1
In the apparatus shown in FIG. 3, 7 ml of a 0.1 M FeCl ₃ aqueous solution was accommodated in the positive electrode chamber as an electrolyte for the positive electrode, and a discharge test was performed at a current density of 0.5 mAcm ⁻² in the static mode.
During discharge, the Li negative electrode elutes as Li ⁺ and diffuses from the aprotic electrolyte through the LISCON plate into the aqueous electrolyte in the positive electrode chamber, during which Fe ³⁺ is reduced to Fe ²⁺ . The chemical reaction involved in the discharge process is simple and is described as follows.
(1) Positive electrode reaction: Fe ³⁺ ＋ e- → Fe ²⁺
(2) Negative electrode reaction: Li → Li ⁺ + e-
(3) Overall battery: Fe ³⁺ + Li → Fe ²⁺ + Li ⁺
FIG. 4 shows the obtained discharge curve. A gradual decrease in battery voltage was observed during the long discharge period.

Example 2
In the apparatus shown in FIG. 3, 12 mL of 0.1 M FeCl ₃ aqueous solution is circulated between the positive electrode chamber and the storage tank at a flow rate of ¹ mL min ⁻¹ as the electrolyte for the positive electrode, and the charge / discharge test is performed in the flow mode. It was.
At the time of charging, as shown in FIG. 5, Fe ²⁺ is oxidized and returned to Fe ³⁺ , and Li ⁺ is re-deposited on the negative electrode surface as Li metal. This can be expressed by the reverse reaction of the discharge reactions (1)-(3) described above.
FIG. 6 shows discharge-charge curves in the first, third, fifth, tenth and twentieth cycles when an FeCl ₃ aqueous solution (0.1 M, 12 mL) is operated in the flow mode. Both the discharging and charging processes were performed for 2 hours per cycle at a current density of 0.2 mAcm ⁻² respectively. The discharge-charge curve shows an almost flat voltage in the range of 3.31 to 3.4V on discharge and 3.93 to 4.18V on charge, indicating that the system has relatively stable cycling characteristics. .

Example 3
In the apparatus shown in FIG. 3, 20 mL of 0.1 M FeCl ₃ aqueous solution is circulated between the positive electrode chamber and the storage tank at a flow rate of ¹ mL min ⁻¹ as the electrolyte for the positive electrode, and discharged in the flow mode. A test was conducted to regenerate FeCl _{3 with} an oxidizing agent.
When complete discharge occurs in the above flow mode and Fe ³⁺ almost becomes Fe ²⁺ , as shown in FIG. 7, by adding powder of oxidizing agent (NH ₄ ) ₂ S ₂ O ₈ to the storage tank, Fe Can fully oxidize ²⁺ back to Fe ³⁺ (if 20 mL of 0.1M FeCl ₃ add 228.2 mg (NH ₄ ) ₂ S ₂ O ₈ to fully oxidize after complete discharge Is necessary). Thereafter, it is possible to regenerate Fe ^{3+ in} almost the same state as in the initial stage by repeating the addition of the oxidant (NH ₄ ) ₂ S ₂ O ₈ powder every time of complete discharge.
FIG. 8 shows a discharge curve when an FeCl ₃ aqueous solution (0.1 M, 20 mL) is operated in the flow mode. During the discharge, the positive electrode solution circulated through the system via a peristaltic pump and its acidity was adjusted to pH 1.7 by adding the HCl solution dropwise to the stock solution. The oxidant was introduced into the system by batch feeding (NH ₄ ) ₂ S ₂ O ₈ to the storage tank when Fe ³⁺ was fully converted to Fe ²⁺ .
The discharge cycle shown in FIG. 8 batches (NH ₄ ) 2 S ₂ O ₈ powder into the storage tank when Fe ³⁺ is almost completely converted to Fe ²⁺ and the discharge voltage starts to drop rapidly. It was obtained by supplying.
If the battery is discharged at a constant current density of 0.5 mAcm ⁻² , if the hydrolysis of Fe ^{3+ in} the cathode solution is completely suppressed by the addition of HCL, Fe ³⁺ in the cathode solution is It will be completely converted to Fe ²⁺ in 107.2 hours. Also, 228.2 mg of (NH ₄ ) ₂ S ₂ O ₈ powder will be required to fully oxidize the reduced Fe ²⁺ from an aqueous FeCl ₃ solution (0.1 M, 20 mL). In FIG. 8, the discharge voltage starts to drop sharply, and from the discharge time when the oxidizing agent is added, Fe ³⁺ in the positive electrode solution is completely converted to Fe ²⁺ in each cycle, and the discharge cycle is determined by stoichiometry. It can be seen that by proceeding batch feeding of an amount of (NH ₄ ) ₂ S ₂ O ₈ , it is possible to continue to proceed in an almost constant state. Note that small protrusions on the discharge curve are due to temperature fluctuations.
It should be noted that in this form of redox flow battery, (NH ₄ ) ₂ S ₂ O ₈ is actually consumed as fuel at the positive electrode rather than FeCl ₃ .

Claims (9)

Lithium negative electrode / negative electrode side electrolyte chamber containing organic electrolyte / solid electrolyte separation membrane / positive electrode side electrolyte chamber containing water-soluble electrolyte containing ionic active material (M ^{n +} / M ^{(n-1) +} ) / Battery body composed of a positive electrode current collector, a storage tank for storing the water-soluble electrolyte, and a circulation path for connecting the positive electrode side electrolyte chamber of the battery body and the storage tank via an openable / closable valve A lithium semi-redox flow battery characterized by comprising:   The lithium semi-redox flow battery according to claim 1, wherein a valve for adding an oxidizing agent is provided in a tank for storing a water-soluble electrolyte.   The lithium semi-redox flow battery according to claim 1, wherein a negative electrode active material that can be used for a negative electrode of a lithium ion battery is used as an active material of the lithium negative electrode.   The lithium semi-redox flow battery according to claim 3, wherein the negative electrode active material that can be used for the negative electrode of the lithium ion battery is metallic lithium. As the ionic active material ^{(M n + / M (n} -1) +), Cr 3+ / Cr 2+, Fe 3+ / Fe 2+, V 3+ / V 2+, the VO ₂ ⁺ / VO ²⁺ The lithium semi-redox flow battery according to any one of claims 1 to 3, wherein one kind of ion pair or complex ion pair thereof is used. The ionic active material that is reduced during discharge to M ^{(n-1) +} is used as the battery charging process Li ⁺ + e ⁻ → Li, M ^{(n−1) +} + e− → M ^{n +} The lithium semi-redox flow battery according to claim 1, wherein the lithium semi-redox flow battery is regenerated to M ^{n +} . The ionic active material reduced to M ^{(n-1) +} during discharge is regenerated to ^{Mn +} by adding an oxidizing agent to the aqueous electrolyte and oxidizing it. Item 6. The lithium semi-redox flow battery according to any one of Items 1 to 5. The ionic active material that is reduced during discharge to M ^{(n-1) +} is used as the battery charging process Li ⁺ + e ⁻ → Li, M ^{(n−1) +} + e− → M ^{n +} characterized Te, electrical charging method for reproducing the M ^{n +,} adding an oxidizing agent to the aqueous electrolytic solution, by oxidation, a combination of chemical oxidation method of reproducing the M ^{n +,} to play the M ^{n +} The lithium semi-redox flow battery according to any one of claims 1 to 5. The lithium semi-redox flow battery according to claim 7 or 8, characterized in that solid powdery (NH ₄ ) ₂ S ₂ O ₈ or liquid H ₂ O ₂ is used as an oxidant.

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