A positive electrode sheet and a supercapacitor

Abstract

This invention provides a positive electrode and a supercapacitor. The positive electrode includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector. The positive active material layer includes a first positive active material and a second positive active material, both of which comprise carbon materials. The carbon material in the second positive active material is modified with Lewis acid. This invention improves the technical problems of gas generation, capacity reduction, and increased resistance in supercapacitors during long-term charge-discharge cycles by using Lewis acid-modified carbon materials combined with large-particle-size carbon materials as positive active materials in the positive electrode. It also broadens the operating voltage window of the supercapacitor, increases its energy density, and improves its high-voltage cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of supercapacitor technology and relates to a positive electrode and a supercapacitor. Background Technology

[0002] Supercapacitors, also known as electric double-layer capacitors, electrochemical capacitors, gold capacitors, or farad capacitors, are a new type of energy storage device that falls between traditional capacitors and batteries. A supercapacitor can be viewed as two non-reactive electrode plates suspended in an electrolyte. When a voltage is applied to the plates, the positive plate attracts negative ions from the electrolyte, and the negative plate attracts positive ions, effectively forming two capacitive storage layers. The separated positive ions are near the negative plate, and the negative ions are near the positive plate. Therefore, supercapacitors are a novel energy storage material, standing out due to their long cycle life, high power density, and wide operating temperature range. The performance of a supercapacitor depends heavily on the composition of the electrode materials and the design of the electrode structure.

[0003] Supercapacitors generally consist of three main components: electrodes, electrolyte, and separator. Among these, electrodes are a crucial component that affects the performance of the capacitor.

[0004] CN103854879A discloses a supercapacitor positive electrode sheet and a supercapacitor, relating to the field of capacitors. The supercapacitor positive electrode sheet includes an aluminum foil layer, a lithium manganese oxide layer, and a conductive adhesive layer. The conductive adhesive layer is coated on both the front and back sides of the aluminum foil layer, and the lithium manganese oxide layer is coated on the conductive adhesive layer.

[0005] CN216389084U discloses a positive electrode for a supercapacitor, relating to the field of supercapacitor technology. It includes a foamed nickel current collector, with an adhesive layer at the top of the foamed nickel current collector, a conductive graphene layer at the top of the adhesive layer, a plurality of conductive activated carbon layers at the top of the conductive graphene layer, and an extended structure at the top of the conductive activated carbon layer.

[0006] Supercapacitor electrode structures are typically symmetrically designed. In this structure, the positive electrode is at a positive potential and the negative electrode is at a negative potential during charging. Therefore, when the voltage window is increased or after long-term charging and discharging, the positive electrode potential is higher and may reach the decomposition potential of the electrolyte. This can lead to some side reactions. These side reactions can produce gases that damage the capacitor, and some of the byproducts of the side reactions may affect the pore structure of the active material, thereby reducing the capacitor's capacitance, increasing its resistance, and causing the capacitor to fail. Summary of the Invention

[0007] The purpose of this invention is to provide a positive electrode and a supercapacitor. This invention improves the technical problems of gas generation, capacity reduction and resistance increase in supercapacitors during long-term charge and discharge by using Lewis acid surface-modified carbon materials combined with large-particle-size carbon materials as positive electrode active materials in the positive electrode. It also broadens the operating voltage window of the supercapacitor, improves its energy density and high-voltage cycle performance.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, the positive active material layer comprising a first positive active material and a second positive active material, both the first positive active material and the second positive active material comprising carbon material, wherein the carbon material in the second positive active material is modified with Lewis acid.

[0010] This invention uses carbon materials as the active material of the positive electrode. Lewis acid surface modification is performed on the surface or bulk phase of some carbon materials to enhance the adsorption of ions. Furthermore, by mixing two materials with different structures as positive electrode materials, the operating voltage window of the supercapacitor is broadened, its energy density is increased, and its high-voltage cycle performance is improved.

[0011] The Lewis acid modification method of the present invention includes the following three methods: (1) depositing a metal precursor (or boride) onto a pre-prepared nitrogen-doped carbon material (or oxygen-doped carbon material or sulfur-doped carbon material), that is, preparing a nitrogen (oxygen or sulfur) doped carbon material by post-processing or in-situ generation, and then loading the metal onto the nitrogen-doped carbon material by impregnation, precipitation deposition, hydrothermal synthesis or sol-gel method to obtain a Lewis acid modified carbon material;

[0012] (2) Simultaneously introduce metal species (or borides) and nitrogen (or oxygen or sulfur) species onto carbon materials. That is, coordinate metal precursors with different types of nitrogen (or oxygen or sulfur) ligands in a certain volume of solution to obtain metal (or boron) complexes. Then add carbon materials as carriers to this solution, stir for a certain time, remove the solution, and after drying and grinding, place the obtained solid material in a high-temperature tube furnace under the protection of inert gas for calcination. After the obtained solid material is treated with or without acid, washed and dried, Lewis acid modified carbon materials are obtained.

[0013] (3) The in-situ generated metal (or) or metal oxide (or boron oxide) is loaded onto nitrogen (or oxygen or sulfur) doped carbon material, that is, the metal precursor, nitrogen (or oxygen or sulfur) precursor and carbon support are mixed together, and then calcined at high temperature to obtain Lewis acid modified carbon material.

[0014] Preferably, the carbon materials in the first and second positive electrode active materials independently include any one or a combination of at least two of activated carbon, activated carbon fiber, capacitive carbon, graphene, carbon nanotubes or graphite.

[0015] Preferably, the Lewis acid-modified carbon material contains a Lewis acid structure.

[0016] Preferably, the Lewis acid structure exists on the surface and / or in the bulk phase of the carbon material.

[0017] Preferably, the Lewis acid structure includes any one or a combination of at least two of MNC, MSC, or MOC, wherein N is nitrogen, C is carbon, O is oxygen, S is sulfur, and M includes any one or a combination of at least two of Fe, Al, Ti, Zn, Sn, or B.

[0018] The Lewis acid-modified carbon material described in this invention is mainly formed by high-temperature sintering of a mixture of carbon source, nitrogen source, oxygen source, or sulfur source and metal source.

[0019] Preferably, the median particle size D50 of the first positive electrode active material is 6 to 10 μm, for example: 6 μm, 7 μm, 8 μm, 9 μm or 10 μm.

[0020] Preferably, the median particle size D50 of the second positive electrode active material is 1 to 4 μm, for example: 1 μm, 1.5 μm, 2 μm, 3 μm or 4 μm, etc.

[0021] This invention uses two active materials with different particle sizes and surface structures. The second positive electrode active material has a smaller particle size and contains more Lewis acid components on its surface. The presence of Lewis acid components can significantly enhance the adsorption of ions by the positive electrode material during charging. The combination of the two materials with different particle sizes can significantly improve the energy density of the electrode, thus giving the supercapacitor a high voltage window, energy density and high voltage aging life.

[0022] Preferably, the mass ratio of the first positive electrode active material and the second positive electrode active material in the positive electrode active material layer is (50-90):(10-50), for example: 50:50, 60:40, 70:30, 80:20 or 90:10, etc.

[0023] Preferably, the positive electrode active material layer further includes a conductive agent and a binder.

[0024] Preferably, the conductive agent includes any one or a combination of at least two of conductive carbon black, graphene, carbon nanotubes, VGCF, or conductive graphite.

[0025] Preferably, the adhesive comprises any one or a combination of at least two of polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, sodium carboxymethyl cellulose, sodium alginate, or polyacrylic acid.

[0026] Preferably, the total mass ratio of the first positive electrode active material and the second positive electrode active material in the positive electrode active material layer to the mass ratio of the conductive agent and the binder is (70-95):(2-15):(3-15), for example: 70:15:15, 75:10:15, 80:1:10, 85:8:7 or 95:2:3, etc.

[0027] In a second aspect, the present invention provides a method for preparing a positive electrode sheet as described in the first aspect, the method comprising the following steps:

[0028] A slurry is obtained by mixing a first active substance, a second active substance, a conductive agent, and a binder with a solvent.

[0029] The slurry is coated on at least one side of the positive current collector, and then rolled to obtain the positive electrode sheet.

[0030] Thirdly, the present invention provides a supercapacitor comprising a positive electrode as described in the first aspect.

[0031] Preferably, the supercapacitor further includes a negative electrode, a separator, and an electrolyte.

[0032] Preferably, the negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side of the negative current collector.

[0033] Preferably, the negative electrode active material layer includes a negative electrode active material, a conductive agent, and a binder.

[0034] Preferably, the negative electrode active material includes any one or a combination of at least two of activated carbon, activated carbon fiber, capacitive carbon, graphene, carbon nanotubes, or graphite.

[0035] Preferably, the conductive agent includes any one or a combination of at least two of conductive carbon black, graphene, carbon nanotubes, VGCF, or conductive graphite.

[0036] Preferably, the adhesive comprises any one or a combination of at least two of polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, sodium carboxymethyl cellulose, sodium alginate, or polyacrylic acid.

[0037] Preferably, the mass ratio of negative electrode active material, conductive agent and binder in the negative electrode active material layer is (70-95):(2-15):(3-15), for example: 70:15:15, 75:10:15, 80:1:10, 85:8:7 or 95:2:3, etc.

[0038] Preferably, the positive electrode and the negative electrode are disposed on both sides of the separator.

[0039] Preferably, the positive electrode active material layer of the positive electrode sheet is close to the separator.

[0040] Preferably, the negative electrode active material layer of the negative electrode sheet is close to the separator.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] (1) This invention improves the technical problems of gas generation, capacity reduction and resistance increase in supercapacitors during long-term charging and discharging by using Lewis acid surface-modified carbon materials in combination with large-particle-size carbon materials as positive electrode active materials, thereby broadening the working voltage window of supercapacitors, increasing their energy density and improving their high-voltage cycle performance.

[0043] (2) The positive electrode sheet described in this invention can be used in supercapacitors with a capacity of more than 130F, an energy density of more than 7.1Wh / kg, no gas generation during 500h float charging at 65℃, and a capacity retention rate of more than 84%. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the structure of a supercapacitor made from the positive electrode sheet of the present invention, wherein 10 is the positive electrode sheet, 11 is the positive current collector, 12 is the positive active material layer, 13 is the positive active material layer, 20 is the negative electrode sheet, 21 is the negative current collector, 22 is the negative active material layer, 23 is the negative active material layer, and 30 is the separator. Detailed Implementation

[0045] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0046] Example 1

[0047] This embodiment provides a positive electrode sheet, which is prepared by the following method:

[0048] S1: Activated carbon with a particle size of 6 μm, activated carbon with a particle size of 3 μm containing BNC structure, conductive carbon black, and PTFE are mixed in a mass ratio of 72:8:10:10 to prepare a slurry. The activated carbon containing BNC structure is prepared by the following method: nitrogen-doped activated carbon is impregnated in a boric acid solution with a concentration of 1 mol / L for 1 h, and the impregnated product is calcined at 600 °C for 1 h.

[0049] S2: Coat the above slurry onto a carbon-coated aluminum foil with a thickness of 25 μm using a double-sided coating method, with a single-sided surface density of 10 mg / cm³. 2 The surface density of both sides is 20 mg / cm³. 2 ;

[0050] S3: Roll the electrode sheet;

[0051] S4: The rolled electrode sheet is slitting and cutting to obtain the positive electrode sheet.

[0052] Example 2

[0053] This embodiment provides a positive electrode sheet, which is prepared by the following method:

[0054] S1: A slurry is prepared by mixing 10 μm capacitive carbon, 4 μm capacitive carbon containing Al-NC doped structure, carbon nanotubes, and styrene-butadiene rubber in a mass ratio of 64:16:12:8. The capacitive carbon containing Al-NC doped structure is prepared by the following method: nitrogen-doped capacitive carbon is activated and then acid-washed with a 0.5 mol / L hydrochloric acid solution. The acid-washed product is washed with water until neutral and then impregnated in a 1 mol / L AlCl3 solution for 1 h. The impregnated product is then calcined at 600 °C for 1 h.

[0055] S2: Coat the above slurry onto a carbon-coated aluminum foil with a thickness of 25 μm using a double-sided coating method, with a single-sided surface density of 10 mg / cm³. 2 The surface density of both sides is 20 mg / cm³. 2 ;

[0056] S3: Roll the electrode sheet;

[0057] S4: The rolled electrode sheet is slitting and cutting to obtain the positive electrode sheet.

[0058] Example 3

[0059] This embodiment provides a positive electrode sheet, which is prepared by the following method:

[0060] S1: Activated carbon fibers with a particle size of 8 μm, activated carbon fibers with a particle size of 3 μm containing Fe-SC structure modification, graphene, and polytetrafluoroethylene are mixed in a mass ratio of 40:40:12:8 to prepare a slurry. The activated carbon fibers containing Fe-SC structure modification are prepared by the following method: 0.202 g of ferric nitrate and 0.250 g of thiourea are dissolved and dispersed in water, then 0.500 g of activated carbon fibers are added and stirred evenly. Finally, the mixture is dried for 12 h and ground evenly to obtain a solid powder. Under a nitrogen atmosphere, the temperature of the solid powder is raised to 900 °C at a heating rate of 5 °C / min. Then, it is calcined at 900 °C for 2 h under a nitrogen atmosphere and at a temperature of 900 °C. Finally, it is cooled to room temperature to obtain the Fe-SC structure modified activated carbon fibers.

[0061] S2: Coat the above slurry onto a carbon-coated aluminum foil with a thickness of 25 μm using a double-sided coating method, with a single-sided surface density of 10 mg / cm³. 2 The surface density of both sides is 20 mg / cm³. 2 ;

[0062] S3: Roll the electrode sheet;

[0063] S4: The rolled electrode sheet is slitting and cutting to obtain the positive electrode sheet.

[0064] Comparative Example 1

[0065] The only difference between this comparative example and Example 1 is that only the first positive electrode active material is used; all other conditions and parameters are exactly the same as in Example 1.

[0066] Comparative Example 2

[0067] The only difference between this comparative example and Example 1 is that only the second positive electrode active material is used; all other conditions and parameters are exactly the same as in Example 1.

[0068] Comparative Example 3

[0069] The only difference between this comparative example and Example 1 is that the second positive electrode active material is replaced with a carbon material of the same particle size and without Lewis acid on the surface. All other conditions and parameters are exactly the same as in Example 1.

[0070] Performance testing:

[0071] A negative electrode slurry is prepared by mixing activated carbon, conductive carbon black, and PTFE in a mass ratio of 80:10:10.

[0072] The negative electrode slurry was coated onto a copper foil with a thickness of 25 μm using a double-sided coating method, with a single-sided areal density of 10 mg / cm³. 2 The surface density of both sides is 20 mg / cm³. 2After rolling, the material is slitted and cut into sheets to obtain the negative electrode sheet. The negative electrode sheet and the positive electrode sheet prepared in the examples and comparative examples are then used to make a supercapacitor. The structural schematic diagram of the supercapacitor is shown in the figure. Figure 1 As shown, it includes a positive electrode 10 and a negative electrode 20, as well as a separator 30 disposed between the positive electrode 10 and the negative electrode 20.

[0073] The positive electrode 10 includes a positive current collector 11 and positive active material layers 12 and 13 bonded to the surface of the positive current collector 11. The active materials in the positive active material layers 12 and 13 are composed of a first positive active material and a second positive active material. Alternatively, the positive electrode 10 may contain only the positive active material layer 12, which is located near the separator 30.

[0074] Similarly, the negative electrode sheet 20 includes a negative electrode current collector 21 and a negative electrode active material layer 22 and a negative electrode active material layer 23 bonded to the surface of the negative electrode current collector 21, wherein the negative electrode active material layer is composed of negative electrode active material, such as... Figure 1 As shown. The negative electrode 20 may also contain only the negative electrode active material layer 22, which is close to the separator 30.

[0075] Then, the cells were taken separately for capacity, energy density, and 3.0V 65℃ 500h float charge performance tests to determine their performance. The separator was a cellulose separator, the electrolyte solvent was acetonitrile, and the solute was spirocyclic quaternary ammonium salt. The test results are shown in Table 1.

[0076] Table 1

[0077]

[0078] As can be seen from Table 1, and from Examples 1-3, the positive electrode sheet of the present invention can achieve a capacity of over 130F and an energy density of over 7.1Wh / kg in a supercapacitor. It can also achieve no gas generation during 500 hours of float charging at 65℃ and a capacity retention rate of over 84%.

[0079] As can be seen from the comparison between Example 1 and Comparative Examples 1-3, the present invention uses two active materials with different particle sizes and surface structures. The second positive electrode active material has a smaller particle size and contains more Lewis acid components on its surface. The presence of Lewis acid components can significantly enhance the adsorption of ions by the positive electrode material during charging. The combination of the two particle size materials can significantly improve the energy density of the electrode, thus giving the supercapacitor a high voltage window, energy density and high voltage aging life.

[0080] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A positive electrode sheet, characterized by, The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector. The positive active material layer includes a first positive active material and a second positive active material, both of which comprise carbon materials. The carbon material in the second positive electrode active material contains a Lewis acid structure; The Lewis acid structure includes any one or at least two of MNC, MSC or MOC, wherein N is nitrogen, C is carbon, O is oxygen, S is sulfur, and M includes any one or at least two of Fe, Al, Ti, Sn or B. The median particle size D50 of the first positive electrode active material is 6~10μm; The median particle size D50 of the second positive electrode active material is 1~4 μm; The mass ratio of the first positive electrode active material and the second positive electrode active material in the positive electrode active material layer is (50~90):(10~50).

2. The cathode sheet of claim 1, wherein, The carbon materials in the first and second positive electrode active materials independently include any one or a combination of at least two of activated carbon, graphene, carbon nanotubes, or graphite.

3. The cathode sheet of claim 1, wherein The Lewis acid structure exists on the surface and / or in the bulk phase of the carbon material.

4. The cathode sheet of claim 1, wherein The positive electrode active material layer also includes a conductive agent and a binder.

5. The cathode sheet of claim 4, wherein The conductive agent includes any one or a combination of at least two of conductive carbon black, graphene, carbon nanotubes, VGCF, or conductive graphite.

6. The positive electrode sheet as described in claim 4, characterized in that, The adhesive includes any one or a combination of at least two of polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, sodium carboxymethyl cellulose, sodium alginate, or polyacrylic acid.

7. The positive electrode sheet as described in claim 4, characterized in that, The total mass ratio of the first positive electrode active material and the second positive electrode active material in the positive electrode active material layer to the mass ratio of the conductive agent and the binder is (70~95): (2~15): (3~15).

8. A method for preparing a positive electrode sheet as described in any one of claims 1-7, characterized in that, The preparation method includes the following steps: A slurry is obtained by mixing a first active substance, a second active substance, a conductive agent, and a binder with a solvent. The slurry is coated on at least one side of the positive current collector, and then rolled to obtain the positive electrode sheet.

9. A supercapacitor, characterized in that, The supercapacitor comprises a positive electrode as described in any one of claims 1-7.

10. The supercapacitor as described in claim 9, characterized in that, The supercapacitor also includes a negative electrode, a separator, and an electrolyte.

11. The supercapacitor as described in claim 10, characterized in that, The negative electrode sheet includes a negative current collector and a layer of negative active material disposed on at least one side of the negative current collector.

12. The supercapacitor as described in claim 11, characterized in that, The negative electrode active material layer includes a negative electrode active material, a conductive agent, and a binder.

13. The supercapacitor as described in claim 12, characterized in that, The negative electrode active material includes any one or a combination of at least two of activated carbon, graphene, carbon nanotubes, or graphite.

14. The supercapacitor as described in claim 12, characterized in that, The conductive agent includes any one or a combination of at least two of conductive carbon black, graphene, carbon nanotubes, VGCF, or conductive graphite.

15. The supercapacitor as described in claim 12, characterized in that, The adhesive includes any one or a combination of at least two of polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, sodium carboxymethyl cellulose, sodium alginate, or polyacrylic acid.

16. The supercapacitor as described in claim 12, characterized in that, The mass ratio of negative electrode active material, conductive agent and binder in the negative electrode active material layer is (70~95): (2~15): (3~15).

17. The supercapacitor as described in claim 10, characterized in that, The positive electrode and the negative electrode are disposed on both sides of the diaphragm.

18. The supercapacitor as described in claim 10, characterized in that, The positive electrode active material layer of the positive electrode sheet is close to the separator.

19. The supercapacitor as described in claim 10, characterized in that, The negative electrode active material layer of the negative electrode sheet is close to the separator.

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