TWI387987B - Super capacitor and method for making the same - Google Patents

Description

Supercapacitor and preparation method thereof

The invention relates to a supercapacitor and a preparation method thereof, in particular to a carbon nanotube-based supercapacitor and a preparation method thereof.

Super Capacitor, also known as electrochemical capacitors, electric double layer capacitors. Supercapacitors have high specific power and long cycle life with a wide operating temperature range. It has extremely important and broad application prospects in mobile communication, information technology, electric vehicles, aerospace and defense technology.

The supercapacitor includes an electrode, a separator, and an electrolyte solution, both of which are disposed in the electrolyte solution. The electrode includes a current collector and an electrode material disposed on the current collector. In the prior art, the preparation method of the supercapacitor is generally after the electrode material is sufficiently ground, a certain amount of the binder is added thereto and stirred uniformly, and then pressed in the foamed nickel by a compression method such as a compression method, a cold isostatic pressing method or a hot isostatic pressing method. On the current collectors such as graphite sheets, nickel sheets, aluminum sheets or copper sheets, electrodes of a certain shape can be formed; and then the electrodes are placed in an electrolyte solution containing a separator to form a supercapacitor. This preparation method is complicated.

The determinant of the influence of its capacity in supercapacitors is the electrode material. The ideal electrode material requires high crystallinity, good electrical conductivity, large specific surface area, and micropores are concentrated in a certain range (required micropores greater than 2 nm). Previous supercapacitor materials mainly include: activated carbon series and transition metal oxide series. The material of the activated carbon series is poor in electrical conductivity, and the resulting capacitor has a large equivalent series resistance. Moreover, the actual utilization ratio of the specific surface area of the activated carbon series is not exceeded. Over 30%, electrolyte ions are difficult to enter, and thus are not suitable as electrode materials for supercapacitors. The use of a transition metal oxide as an electrode material has a good effect in increasing the capacity of a supercapacitor. However, its cost is too high to be promoted.

The emergence of carbon nanotubes (CNTs) provides new opportunities for the development of supercapacitors. The carbon nanotube is a nano-scale seamless tubular graphite structure carbon material with a diameter ranging from several nanometers to several tens of nanometers and a tube length of several micrometers to several tens of micrometers. The carbon nanotube has a large specific surface area, high crystallinity and good electrical conductivity. The inner and outer diameters of the tube can be controlled by a synthetic process, and the specific surface utilization rate can be 100%. Therefore, it can be an ideal supercapacitor material.

The use of carbon nanotubes as supercapacitor materials was first reported in Chunming Niu et al. (see High power electrochemical capacitors based on carbon nanotube electrodes, Applied Physics Letter, Chunming Niu et al., vol 70, p1480-1482 (1997). )). They purchased pure multi-walled carbon nanotube powder, chemically modified it with nitric acid, placed in water for repeated filtration and washing, and dried to form a thin film electrode. The two thin film electrodes were placed in a H ₂ SO ₄ electrolyte solution having a mass fraction of 38%, and a super capacitor was fabricated by encapsulation. In the preparation method of the thin film electrode, since the raw material of the carbon nanotube used is powdery, agglomeration is extremely likely to occur, and the carbon nanotubes in the prepared thin film electrode are unevenly distributed, so it is necessary to chemically modify the carbon nanotubes. Sex. However, even if the chemically modified carbon nanotubes still have agglomeration, the resulting film electrode has poor toughness and is easily broken, which affects the performance of the supercapacitor.

In view of this, it is necessary to provide a supercapacitor having a high capacitance and a large power density and a method of manufacturing the same.

A supercapacitor comprising: a first electrode, the first electrode comprising a first carbon nanotube film; a first current collector, the first carbon nanotube film being disposed in the first current collector a second electrode, the second electrode comprises a second carbon nanotube film; a second current collector, the second carbon nanotube film is disposed on the second current collector; a diaphragm, The diaphragm is disposed between the first electrode and the second electrode, and is respectively disposed apart from the first electrode and the second electrode; an electrolyte solution, the first electrode, the second electrode, and the first set An electric body, a second current collector and a separator are disposed in the electrolyte solution; an outer casing, the first electrode, the second electrode, the first current collector, the second current collector, the separator and the electrolyte solution are both Set in the housing. The carbon nanotubes in the first carbon nanotube film and the second carbon nanotube film are uniformly distributed and parallel to the surface of the carbon nanotube film.

A method for preparing a supercapacitor, comprising the steps of: providing a carbon nanotube array formed on a substrate; providing a pressing device, extruding the carbon nanotube array to obtain a nanotube film; providing a separator, The two identical carbon nanotube films are separated by the separator and placed in a casing; an electrolyte solution is supplied, and the electrolyte solution is injected into the outer casing to form a supercapacitor.

The method for preparing a carbon nanotube film further comprises cutting the carbon nanotube film into a predetermined size and shape.

Compared with the prior art, the supercapacitor and the preparation method thereof have the following advantages: First, the carbon nanotube has good electrical conductivity and has a large specific surface area, and the obtained supercapacitor has a higher specific capacitance. And conductivity; second, the carbon nanotubes in the carbon nanotube film are evenly distributed, so it is not necessary to chemically modify the carbon nanotube film with good toughness. It is used to make supercapacitor electrodes of various shapes; thirdly, the carbon nanotube film is obtained by extruding a carbon nanotube array by a pressing device, the preparation method is simple, and the nanometer can be controlled according to different pressure modes. The carbon nanotubes in the carbon tube film are isotropic or oriented in a fixed direction or in different directions.

The supercapacitor of the present technical solution and a method of manufacturing the same will be described in detail below with reference to the accompanying drawings

Referring to FIG. 1 , an embodiment of the present technical solution provides a supercapacitor 10 having a flat type structure, including: a first electrode 101, the first electrode 101 includes a first carbon nanotube film; a current collector 103, the first electrode 101 is disposed on the first current collector 103; a second electrode 102, the second electrode 102 includes a second carbon nanotube film; and a second current collector 104, the second electrode 102 is disposed on the second current collector 104; a diaphragm 105 disposed between the first electrode 101 and the second electrode 102 and respectively associated with the first electrode 101 and the second electrode 102 are spaced apart; an electrolyte solution 106, the first electrode 101, the second electrode 102, the first current collector 103, the second current collector 104, and the separator 105 are disposed in the electrolyte a solution 106; a housing 107, the first electrode 101, the second electrode 102, the first set The electric body 103, the second current collector 104, the diaphragm 105, and the electrolyte solution 106 are all disposed in the outer casing 107. In the first carbon nanotube film and the second carbon nanotube film, the carbon nanotubes are uniformly distributed and parallel to the surface of the carbon nanotube film.

Further, the first carbon nanotube film and the second carbon nanotube film comprise a plurality of carbon nanotubes, the plurality of carbon nanotubes being isotropic or oriented in a fixed direction or oriented in different directions arrangement. The first carbon nanotube film and the second carbon nanotube film are mutually attracted by the van der Waals force, and are closely combined to form a self-supporting structure, so that the first carbon nanotube film and The second carbon nanotube film has good toughness and can be bent. Therefore, the first carbon nanotube film and the second carbon nanotube film in the embodiment of the technical solution may be a planar structure or a curved structure. The length and width of the first carbon nanotube film and the second carbon nanotube film are not limited, and a carbon nanotube film having any length and width can be formed according to actual needs. The first carbon nanotube film and the second carbon nanotube film have a thickness of 1 micrometer to 1 millimeter.

The separator 20 is a glass fiber or polymer film that allows electrolyte ions in the electrolyte solution 22 to pass therethrough to prevent the first electrode 12 and the second electrode 14 from contacting.

The electrolytic solution 22 is a sodium hydroxide aqueous solution, a potassium hydroxide aqueous solution, a sulfuric acid aqueous solution, a nitric acid aqueous solution, a lithium chlorate propylene carbonate solution, a tetraethylammonium tetrafluoroborate propylene carbonate solution, or any of the above. Combined mixture.

The outer casing 107 is a glass outer casing or a stainless steel outer casing.

The material of the current collector may be graphite, nickel, aluminum or copper, etc., and the current collector may be a metal substrate, preferably a copper sheet. The shape and size of the current collector are not limited, and can be changed according to actual needs. The carbon nanotube film itself has strong viscosity, so the carbon nanotube film can be directly adhered to the surface of the current collector 12, or the carbon nanotube film is adhered thereto by an adhesive. On the surface of the collector.

The current collector in the supercapacitor 10 is an optional structure, because the carbon nanotube film has good electrical conductivity and certain self-supporting property and stability, and can be directly used in the carbon nanotube in practical application. The surface of the film is coated with a layer of conductive paste without the need for the current collector described above.

It can be understood that the structure type of the supercapacitor is not limited, and it is also possible to be a coin type or a winding type.

Referring to FIG. 2, an embodiment of the present technical solution provides a method for preparing the above supercapacitor 10, which specifically includes the following steps:

Step 1: providing a carbon nanotube array formed on a substrate, preferably the array is an array of aligned carbon nanotubes.

The carbon nanotube array provided by the embodiments of the present technical solution is one of a single-walled carbon nanotube array, a double-walled carbon nanotube array, and a multi-walled carbon nanotube array. The method for preparing the carbon nanotube array adopts a chemical vapor deposition method, and the specific steps thereof include: (a) providing a flat substrate, the substrate may be selected from a P-type or N-type germanium substrate, or a germanium substrate having an oxide layer formed thereon. The embodiment of the technical solution preferably adopts a 4-inch germanium substrate; (b) uniformly forms a catalyst layer on the surface of the substrate, and the catalyst layer material may be selected from iron (Fe), cobalt (Co), nickel (Ni) or any One of the combined alloys; (c The substrate formed with the catalyst layer is annealed in air at 700 ° C to 900 ° C for about 30 minutes to 90 minutes; (d) the treated substrate is placed in a reaction furnace and heated to 500 ° C in a protective gas atmosphere~ At 740 ° C, the carbon source gas is then introduced for about 5 minutes to 30 minutes to grow to obtain a carbon nanotube array. The carbon nanotube array is an array of pure carbon nanotubes formed by a plurality of carbon nanotubes that are parallel to each other and perpendicular to the substrate. The carbon nanotube array has a height greater than 100 microns and is substantially the same as the substrate area described above, wherein a portion of the carbon nanotubes are intertwined with each other. The aligned carbon nanotube array contains substantially no impurities, such as amorphous carbon or residual catalyst metal particles, etc., by controlling the growth conditions described above.

In the embodiment of the technical solution, the carbon source gas may be a chemically active hydrocarbon such as acetylene, ethylene or methane. The preferred carbon source gas in the embodiment of the technical solution is acetylene; the shielding gas is nitrogen or an inert gas, and the technical solution is The preferred shielding gas for the examples is argon.

It can be understood that the carbon nanotube array provided by the embodiments of the present technical solution is not limited to the above preparation method, and may be a graphite electrode constant current arc discharge deposition method, a laser evaporation deposition method or the like.

Step 2: providing a pressure applying device, extruding the carbon nanotube array to obtain a carbon nanotube film.

The pressure applying device applies a certain pressure to the carbon nanotube array. During the pressing process, the carbon nanotube array is separated from the grown substrate by pressure to form a carbon nanotube film having a self-supporting structure composed of a plurality of carbon nanotubes, and the The plurality of carbon nanotubes are substantially parallel to the surface of the carbon nanotube film. In the embodiment of the technical solution, The pressing device is an indenter, the surface of the indenter is smooth, and the shape and extrusion direction of the indenter determine the arrangement of the carbon nanotubes in the prepared carbon nanotube film. Specifically, when the planar indenter is extruded in a direction perpendicular to the substrate grown by the carbon nanotube array, a carbon nanotube film is obtained which is isotropically arranged (see FIG. 3); When the roller-shaped indenter is pressed in a certain fixed direction, a carbon nanotube film in which the carbon nanotubes are aligned in the fixed direction can be obtained (refer to FIG. 4); when the roller-shaped indenter is used When the direction is rolled, a carbon nanotube film in which the carbon nanotubes are aligned in different directions can be obtained.

It can be understood that when the above-mentioned carbon nanotube array is extruded by the above different methods, the carbon nanotubes are poured under the action of pressure, and are attracted and connected with adjacent carbon nanotubes through the van der Waals force. A carbon nanotube film having a self-supporting structure composed of a plurality of carbon nanotubes. The plurality of carbon nanotubes are substantially parallel to the surface of the carbon nanotube film and are isotropic or oriented in a fixed direction or in different directions. In addition, under the action of pressure, the carbon nanotube array is separated from the grown substrate, so that the carbon nanotube film is easily detached from the substrate.

Those skilled in the art will appreciate that the degree of tilt (inclination) of the above-described carbon nanotube array is related to the magnitude of the pressure, and the greater the pressure, the greater the angle of inclination. The thickness of the prepared carbon nanotube film depends on the height and pressure of the carbon nanotube array. The higher the height of the carbon nanotube array and the lower the applied pressure, the greater the thickness of the prepared carbon nanotube film; conversely, the smaller the height of the carbon nanotube array and the higher the applied pressure, the prepared The smaller the thickness of the carbon nanotube film.

In addition, the carbon nanotube film prepared in the second step can be further made Treat with an organic solvent. Specifically, the organic solvent may be dropped on the surface of the carbon nanotube film by a test tube to infiltrate the entire carbon nanotube film. The organic solvent is a volatile organic solvent such as ethanol, methanol, acetone, dichloroethane or chloroform, and ethanol is preferably used in the embodiment of the present invention. After the carbon nanotube film is infiltrated by an organic solvent, the parallel carbon nanotube segments in the carbon nanotube film partially aggregate into the carbon nanotube bundle under the surface tension of the volatile organic solvent. The carbon nanotube film has a small surface volume ratio, low viscosity, good mechanical strength and toughness, and the carbon nanotube film treated with an organic solvent can be conveniently applied to a macroscopic field.

In the embodiment of the technical solution, the width of the carbon nanotube film is related to the size of the substrate on which the carbon nanotube array is grown, and the length of the carbon nanotube film is not limited and can be prepared according to actual needs. In the embodiment of the technical solution, a 4-inch substrate growth aligned carbon nanotube array is used.

It can be understood that the carbon nanotube film in the embodiment of the technical solution can be cut into a predetermined shape and size according to practical applications to expand the application range thereof.

Step 3: A diaphragm 105 is provided, and the two carbon nanotube films are disposed at intervals on both sides of the diaphragm 105 and are housed in a casing 107.

The above-mentioned carbon nanotube film is cut into two first electrodes 101 and second electrodes 102 having a certain shape and area. The first electrode 101 and the second electrode 102 are placed in a vacuum oven to be dried until the first electrode 101 and the second electrode 102 are at constant weight. The first electrode 101 and the second electrode 102 are spaced apart, and the separator 105 is spaced apart from the first electrode 101 and Between the second electrodes 102. The embodiment of the technical solution uses a nonwoven fabric as the separator 105.

The first electrode 101 and the second electrode 102 may further be disposed on a first current collector 103 and a second current collector 104, respectively. The material of the first collector 103 and the second collector 104 may be graphite, nickel, aluminum or copper or the like. The first current collector 103 and the second current collector 104 may be a metal substrate, preferably a copper plate. The shape and size of the first current collector 103 and the second current collector 104 are not limited, and may be changed according to actual needs. Since the carbon nanotubes in the aligned carbon nanotube array provided in the first step of the embodiment of the technical solution are very pure, and since the specific surface area of the carbon nanotube itself is very large, the carbon nanotube film itself has Strong stickiness. In the third step of the embodiment of the present technical solution, the carbon nanotube film can be directly adhered to the surfaces of the first current collector 103 and the second current collector 104 by its own viscosity. Alternatively, the carbon nanotube film is adhered to the surfaces of the first collector 103 and the second collector 104 by a binder.

The current collector in the supercapacitor electrode 10 is an optional structure because the carbon nanotube film has good electrical conductivity and a certain self-supporting property and stability, and can be directly used in the nano carbon in practical applications. The surface of the tube film is coated with a layer of conductive paste without the need for the first current collector 103 and the second current collector 104 described above.

In step four, an electrolyte solution 106 is provided, and the electrolyte solution 106 is injected into the outer casing 107 to form a supercapacitor 10.

The electrolyte solution 106 is injected into the outer casing 107, the first electrode 101, the second electrode 102, the first current collector 103, the second current collector 104, and The separators 105 are each disposed in the electrolyte solution 106. The packaging process of the entire supercapacitor 10 is carried out in a glove drying oven filled with an inert gas.

Please refer to FIG. 5 , which is a graph of charge and discharge cycles of the supercapacitor of the embodiment of the present invention at a current of 3 mA. It can be seen from the figure that the charge-discharge curve has a distinct approximation of the triangular symmetry. Under the condition of constant current charge and discharge, the voltage has a significant linear relationship with time. This indicates that the reluctance of the supercapacitor electrode reaction is very good. The constant current discharge test shows that the specific capacitance of the supercapacitor is greater than 100 law / gram at the current intensity.

The supercapacitor 10 employs the above-described carbon nanotube film as an electrode. The carbon nanotubes in the carbon nanotube film are uniformly distributed and oriented in an isotropic manner or in a fixed orientation or in different directions. The carbon nanotube film has a high specific surface area utilization when used as an electrode of a supercapacitor. Moreover, in the carbon nanotube film, the carbon nanotubes are uniformly distributed. The carbon nanotube film has good toughness and can be bent into an electrode having an arbitrary shape for preparing supercapacitors of various structures.

In summary, the present invention has indeed met the requirements of the invention patent, and has filed a patent application according to law. However, the above description is only a preferred embodiment of the present invention, and it is not possible to limit the scope of the patent application of the present invention. Equivalent modifications or variations made by persons skilled in the art in light of the spirit of the invention are intended to be included within the scope of the following claims.

10‧‧‧Supercapacitors

101‧‧‧First carbon nanotube film

102‧‧‧Second carbon nanotube film

103‧‧‧First current collector

104‧‧‧Second current collector

105‧‧‧Separator

106‧‧‧ electrolyte

107‧‧‧Shell

FIG. 1 is a schematic structural view of a super capacitor according to an embodiment of the present technical solution.

2 is a flow chart of a method for preparing a supercapacitor according to an embodiment of the present technical solution schematic diagram.

3 is a scanning electron micrograph of an isotropic carbon nanotube film obtained in an embodiment of the present technical solution.

4 is a scanning electron micrograph of a preferred orientation carbon nanotube film obtained in an embodiment of the present technical solution.

FIG. 5 is a constant current charge and discharge curve of the super capacitor of the embodiment of the present technical solution.

10‧‧‧Supercapacitors

101‧‧‧First carbon nanotube film

102‧‧‧Second carbon nanotube film

103‧‧‧First current collector

104‧‧‧Second current collector

105‧‧‧Separator

106‧‧‧ electrolyte

107‧‧‧Shell

Claims (17)

A supercapacitor comprising: two electrodes; a diaphragm disposed between the two electrodes and spaced apart from the two electrodes; an electrolyte solution, the two electrodes and a diaphragm Provided in the electrolyte solution, the improvement is that the electrode comprises a carbon nanotube film, wherein the carbon nanotube film is evenly distributed and parallel to the surface of the carbon nanotube film Isotropically arranged. The supercapacitor according to claim 1, wherein the supercapacitor has a flat type structure. The supercapacitor of claim 1, wherein the supercapacitor comprises two current collectors, and the two electrodes are respectively disposed on the two current collectors, the electrode arrangement Between the current collector and the diaphragm. The supercapacitor of claim 1, wherein the supercapacitor comprises a casing, and the two current collectors, the separator and the electrolyte are disposed in the casing. The supercapacitor according to claim 1, wherein the carbon nanotubes in the carbon nanotube film are attracted to each other by van der Waals force, and are closely combined to form a plurality of carbon nanotubes. Self-supporting structure. The supercapacitor of claim 1, wherein the carbon nanotube film has a thickness of from 1 micrometer to 1 millimeter. A supercapacitor comprising: two electrodes; a diaphragm disposed between the two electrodes and spaced apart from the two electrodes; an electrolyte solution, the two electrodes and a diaphragm Provided in the electrolyte solution, the improvement is that the electrode comprises a carbon nanotube film, The carbon nanotubes in the carbon nanotube film are uniformly distributed and aligned in different directions parallel to the surface of the carbon nanotube film. A method for preparing a supercapacitor, comprising the steps of: providing a carbon nanotube array formed on a substrate; providing a pressing device, extruding the carbon nanotube array to obtain a carbon nanotube film; providing a separator, The two identical carbon nanotube films are disposed on both sides of the separator at intervals and are loaded into a casing; and an electrolyte solution is supplied, and the electrolyte solution is injected into the outer casing to form a super package. Capacitor. The method for preparing a supercapacitor according to claim 8, wherein the method for preparing the carbon nanotube array comprises the steps of: providing a flat substrate, wherein the substrate is selected from a P-type germanium substrate and an N-type germanium. a substrate or a germanium substrate formed with an oxide layer; a catalyst layer uniformly formed on the surface of the substrate, the catalyst layer material being selected from one of iron (Fe), cobalt (Co), nickel (Ni) or any combination thereof; The substrate formed with the catalyst layer is annealed in air at 700 ° C to 900 ° C for about 30 minutes to 90 minutes; the treated substrate is placed in a reaction furnace, heated to 500 ° C to 740 ° C in a protective gas atmosphere, and then passed through The carbon source gas is reacted for about 5 minutes to 30 minutes, and an array of carbon nanotubes is grown, and a part of the carbon nanotubes in the array of carbon nanotubes are intertwined with each other. The method for preparing a supercapacitor according to claim 8, wherein the pressing device is a planar indenter. a method for preparing a supercapacitor according to claim 8 of the patent application, The pressure applying device is a roller-shaped indenter. The method for preparing a supercapacitor according to claim 10, wherein the process of extruding the carbon nanotube array is performed by using a planar indenter in a direction perpendicular to a substrate grown by the carbon nanotube array. Pressure. The method for preparing a supercapacitor according to claim 11, wherein the process of extruding the carbon nanotube array is performed by using a roller-shaped indenter in a certain fixed direction. The method for preparing a supercapacitor according to claim 11, wherein the process of extruding the carbon nanotube array is rolling in different directions by using a roller-shaped indenter. The method for preparing a supercapacitor according to claim 8, wherein the method for preparing the carbon nanotube film further comprises the steps of: providing two current collectors, the two nanocarbons Tube films are respectively disposed on the two current collectors. The method for preparing a supercapacitor according to claim 15, wherein the carbon nanotube film is directly adhered to the surface of the current collector or the carbon nanotube film is adhered by a binder. The collector surface. The method for producing a supercapacitor according to claim 8, wherein the method further comprises cutting the carbon nanotube film into a predetermined size and shape.