High-energy-density lithium ion capacitor based on porous carbon electrode and preparation method of high-energy-density lithium ion capacitor

Abstract

The invention provides a high-energy-density lithium ion capacitor based on a porous carbon electrode and a preparation method of the high-energy-density lithium ion capacitor, and relates to the technical field of lithium ion capacitors. The high-energy-density lithium ion capacitor based on the porous carbon electrode comprises a positive electrode, a negative electrode, an electrolyte and a diaphragm, the positive electrode is composed of a specific porous carbon material, the porous carbon material has a hierarchical porous structure, the micropore diameter is 0.3-1 nm, the mesopore diameter is 2-20 nm, the macropore diameter is 50-500 nm, micropores, mesopores and macropores are communicated with one another, and the specific surface area is 1500-3000 m / g. Through the graded porous carbon material of the positive electrode, rich storage space is provided for lithium ions by virtue of a unique micropore, mesopore and macropore intercommunication structure of the graded porous carbon material. The micro pores can efficiently adsorb lithium ions, the mesopores and the macropores construct a rapid transmission channel, and the energy density of the capacitor is not lower than 300 Wh / kg at the 0.1 C charge-discharge rate under the cooperation of the negative electrode silicon-based composite material.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion capacitors, and specifically to a high-energy-density lithium-ion capacitor based on a porous carbon electrode and a preparation method thereof. Background Art

[0002] With the rapid development of modern electronic devices, electric vehicles and other fields, higher requirements are put forward for the performance of energy storage devices such as energy density, power density and cycle life. As a new type of energy storage device, the lithium-ion capacitor combines the advantages of lithium-ion batteries and supercapacitors, has high energy density and power density, and shows broad application prospects in many fields. However, at present, the traditional lithium-ion capacitors are still difficult to meet the growing demand in terms of energy density.

[0003] There are many deficiencies in the existing electrode materials and preparation processes. For example, the porous structure of the positive electrode material is not ideal enough to fully provide channels for the storage and transmission of lithium ions; the capacity of the negative electrode material is limited, and volume expansion is likely to occur during charge and discharge, resulting in the destruction of the electrode structure and affecting the cycle performance of the capacitor; the composition and formula of the electrolyte are not optimized enough to effectively improve ionic conductivity and stability; the performance of the separator also needs to be improved, and it is difficult to effectively prevent short circuits between the positive and negative electrodes while ensuring the transmission of lithium ions. In addition, the imperfect preparation process makes it difficult for the overall performance of the capacitor to reach the best state, restricting its further development and application. Therefore, it is of great practical significance to develop a lithium-ion capacitor with high energy density, good cycle performance and high power density and its preparation method. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides a high-energy-density lithium-ion capacitor based on a porous carbon electrode and a preparation method thereof, which solves the problems that the traditional lithium-ion capacitors are still difficult to meet the growing demand in terms of energy density and so on.

[0005] To achieve the above object, the present invention is realized through the following technical solutions: A high-energy-density lithium-ion capacitor based on a porous carbon electrode and a preparation method thereof, including:

[0006] Composition of Lithium-Ion Capacitor: The lithium-ion capacitor of the present invention includes a positive electrode, a negative electrode, an electrolyte, and a separator. The positive electrode is composed of a specific porous carbon material, which has a hierarchical porous structure with micropores having a pore diameter of 0.3 - 1 nm, mesopores having a pore diameter of 2 - 20 nm, and macropores having a pore diameter of 50 - 500 nm, and the micropores, mesopores, and macropores are interconnected, with a specific surface area between 1500 - 3000 m² / g. This unique hierarchical porous structure provides abundant storage and transmission channels for lithium ions, which is beneficial to improving the energy density and charge-discharge performance of the capacitor. The negative electrode is selected as a silicon-based composite material, in which the mass proportion of silicon is 20% - 50%, and the rest is carbon material (one or more of amorphous carbon, graphite, or graphene). Silicon has a high theoretical specific capacity, and the composite with carbon material can alleviate the volume expansion problem of silicon during charge and discharge, improving the stability and cycling performance of the negative electrode. The electrolyte is composed of a lithium salt, an organic solvent, and an additive. The lithium salt is one of lithium bis(fluorosulfonyl)imide (LiFSI), lithium hexafluorophosphate (LiPF 6 6), or a mixture of the two in a molar ratio of 1:(0.5 - 1.5), with a concentration of 1.0 - 1.5 mol / L; the organic solvent is a mixture of ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate in a volume ratio of (1 - 3):(1 - 3):(1 - 3); the additive is fluoroethylene carbonate (FEC), and its volume fraction in the electrolyte is 2% - 5%. This electrolyte formulation can effectively improve the ionic conductivity, enhance the interfacial stability between the electrode and the electrolyte, and improve the overall performance of the capacitor. The separator uses a polyolefin porous membrane with a porosity of 40% - 60%, an average pore diameter of 0.05 - 0.2 μm, and a tensile strength of not less than 10 MPa. This separator can effectively isolate the positive and negative electrodes, while ensuring the smooth transmission of lithium ions and preventing the occurrence of short-circuit phenomena.

[0007] Preparation Method of Porous Carbon Material: Using phenolic resin and nano-silica as raw materials, mixing them in a mass ratio of (2 - 5):(1 - 3), adding an appropriate amount of catalyst and solvent, and stirring and reacting at 40 - 80°C for 2 - 6 hours to form a uniform precursor solution. The catalyst is one of hydrochloric acid, sulfuric acid, or p-toluenesulfonic acid, and the dosage is 0.5% - 2% of the mass of phenolic resin; the solvent is one of ethanol, methanol, or acetone. Spray-dry the precursor solution to obtain microsphere precursors, with an inlet air temperature of 120 - 180°C and an outlet air temperature of 60 - 100°C for spray drying. Perform carbonization and etching treatments on the microsphere precursors in sequence. The carbonization temperature is 700 - 1000°C, and the carbonization time is 2 - 5 hours, carried out under the protection of an inert gas; the etching treatment uses a hydrofluoric acid solution with a mass fraction of 5% - 15%, and the etching time is 1 - 3 hours. After etching, wash with water and dry to obtain the required porous carbon material. The porous carbon material prepared by this method has an ideal hierarchical porous structure and a high specific surface area.

[0008] Preparation method of silicon-based composite material: Mechanically ball-mill and mix silicon powder and carbon source in a ball mill for 5 - 10 hours with a ball-to-material ratio of (10 - 20):1, and the carbon source is one of sucrose, glucose or starch. Then carry out carbonization treatment at 600 - 900 °C for 2 - 4 hours under the protection of inert gas. The silicon-based composite material prepared by this method can effectively improve the volume expansion problem of silicon and enhance the performance of the anode material.

[0009] Preparation method of lithium-ion capacitor: Prepare the positive electrode sheet by mixing porous carbon material, conductive agent and binder in a mass ratio of (80 - 90):(5 - 10):(5 - 10), adding an appropriate amount of N-methylpyrrolidone (NMP) to make a slurry. The conductive agent is a mixture of acetylene black, carbon nanotubes and graphene in a mass ratio of (1 - 3):(1 - 3):(1 - 3), and the binder is polyvinylidene fluoride (PVDF). Uniformly coat the slurry on the aluminum foil (positive electrode current collector) with a roughened surface (the surface roughness Ra after roughening is 0.5 - 2 μm), with a coating thickness of 50 - 100 μm, dry at 80 - 120 °C for 12 - 24 hours, and then compact under a pressure of 10 - 20 MPa. Prepare the negative electrode sheet by mixing the silicon-based composite material, conductive agent and binder in a mass ratio of (70 - 80):(10 - 15):(10 - 15), adding an appropriate amount of deionized water to make a slurry. The conductive agent is conductive carbon black, and the binder is a mixture of sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) in a mass ratio of (1 - 2):(1 - 2). Uniformly coat the slurry on the copper-plated stainless steel foil (negative electrode current collector, with a copper layer thickness of 5 - 15 μm), with a coating thickness of 80 - 120 μm, dry at 60 - 90 °C for 8 - 16 hours, and then compact under a pressure of 8 - 15 MPa. Assemble the lithium-ion capacitor. In a glove box filled with argon, stack the positive electrode sheet, the above-mentioned separator, and the negative electrode sheet in sequence, and make the separator closely adhere to the positive electrode sheet and the negative electrode sheet on both sides respectively. Then inject the above-mentioned electrolyte with an injection amount of 0.5 - 1.5 mL per gram of electrode material. Finally, encapsulate with an aluminum-plastic film at an encapsulation temperature of 100 - 150 °C and an encapsulation pressure of 0.5 - 1 MPa. When preparing the positive electrode sheet, perform plasma treatment on the surface of the positive electrode current collector before coating the slurry, with a treatment time of 5 - 15 minutes and a treatment power of 100 - 300 W to enhance the adhesion between the slurry and the current collector. When preparing the negative electrode sheet, perform annealing treatment on the negative electrode sheet after drying, with an annealing temperature of 300 - 500 °C and an annealing time of 1 - 3 hours under the protection of inert gas to improve the structure and performance of the negative electrode sheet.

[0010] The present invention provides a high-energy density lithium-ion capacitor based on a porous carbon electrode and its preparation method. It has the following beneficial effects:

[0011] 1. In the present invention, the hierarchically porous carbon material of the positive electrode, with its unique interconnected structure of micropores, mesopores, and macropores, provides abundant storage space for lithium ions. The micropores can efficiently adsorb lithium ions, while the mesopores and macropores construct fast transmission channels. Coupled with the synergy of the silicon-based composite material of the negative electrode, the energy density of the capacitor is not less than 300 Wh / kg at a charge-discharge rate of 0.1C. In Example 1, it reaches 320 Wh / kg, and in Example 2, it is 310 Wh / kg, far exceeding 200 Wh / kg of the comparative example. It can effectively extend the battery life of electronic devices or reduce the charging frequency of electric vehicles, meeting the application scenarios with high energy requirements.

[0012] 2. The porous carbon material prepared from phenolic resin and nano-silica as raw materials by a specific process in the present invention has a hierarchically porous structure with precise control and a high specific surface area. This material greatly improves the electrode reaction kinetics performance and accelerates the ion diffusion rate, laying a foundation for the high-performance performance of the capacitor.

[0013] 3. When preparing the positive electrode plate in the present invention, the positive electrode current collector is treated by plasma, which enhances the adhesion between the slurry and the current collector, and improves the conductivity and stability of the electrode. When preparing the negative electrode plate, the dried negative electrode plate is annealed to improve its structure and performance, further enhancing the overall performance of the capacitor. Although these additional treatment steps are simple, the effect on performance improvement is significant.

[0014] 4. The preparation method of the present invention uses common industrial materials and equipment, with easy operation control and relatively low cost. Whether it is the acquisition of raw materials or the implementation of the production process, it has the feasibility of large-scale production, providing a strong guarantee for the commercial promotion and wide application of the product, and is expected to meet the large demand of the market for high-energy-density lithium-ion capacitors. Detailed implementation manners

[0015] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0016] Example 1:

[0017] The embodiment of the present invention provides a high-energy-density lithium-ion capacitor based on a porous carbon electrode and its preparation method, including:

[0018] Preparation of porous carbon material: Weigh 2 g of phenolic resin and 1 g of nano-silica, add 0.01 g of hydrochloric acid (catalyst) and 5 mL of ethanol (solvent), and stir and react at 40 °C for 6 hours to form a precursor solution. Spray-dry the precursor solution with an inlet air temperature of 120 °C and an outlet air temperature of 60 °C to obtain a microsphere precursor. Carbonize the microsphere precursor at 700 °C for 2 hours (under inert gas protection), then etch it with a 5% hydrofluoric acid solution for 3 hours, wash it with water and dry it after etching to obtain the porous carbon material.

[0019] Preparation of silicon-based composite material: Ball-mill and mix 2 g of silicon powder and 1 g of sucrose (carbon source) in a ball mill for 5 hours with a ball-to-material ratio of 10:1. Then carbonize it at 600 °C for 2 hours (under inert gas protection) to obtain the silicon-based composite material.

[0020] Preparation of lithium-ion capacitor: Prepare the positive electrode sheet. Mix the porous carbon material with a conductive agent (acetylene black, carbon nanotubes, and graphene mixed in a mass ratio of 1:1:1) and a binder (PVDF) in a mass ratio of 80:10:10, and add an appropriate amount of NMP to make a slurry. Coat the slurry on an aluminum foil with a surface roughness Ra of 0.5 μm, with a coating thickness of 50 μm, dry it at 80 °C for 24 hours, and then compact it under a pressure of 10 MPa. Prepare the negative electrode sheet. Mix the silicon-based composite material with conductive carbon black and a binder (CMC and SBR mixed in a mass ratio of 1:1) in a mass ratio of 70:15:15, and add an appropriate amount of deionized water to make a slurry. Coat the slurry on a copper-plated stainless steel foil with a copper layer thickness of 5 μm, with a coating thickness of 80 μm, dry it at 60 °C for 16 hours, and then compact it under a pressure of 8 MPa. Assemble the lithium-ion capacitor in a glove box filled with argon, stack the positive electrode sheet, polyolefin porous membrane (porosity of 40%, average pore diameter of 0.05 μm), and negative electrode sheet in sequence, inject the electrolyte (lithium salt is LiFSI, concentration is 1.0 mol / L, organic solvents are ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate mixed in a volume ratio of 1:1:1, and the volume fraction of FEC is 2%), and the electrolyte injection amount is 0.5 mL per gram of electrode material. Finally, encapsulate it with an aluminum-plastic film at an encapsulation temperature of 100 °C and an encapsulation pressure of 0.5 MPa. Before preparing the positive electrode sheet, perform plasma treatment on the aluminum foil surface for 5 minutes at 100 W; after drying the negative electrode sheet, anneal it at 300 °C for 1 hour (under inert gas protection).

[0021] Example 2:

[0022] An embodiment of the present invention provides a high-energy-density lithium-ion capacitor based on a porous carbon electrode and its preparation method, including:

[0023] Preparation of porous carbon material: Weigh 5 g of phenolic resin and 3 g of nano-silica, add 0.05 g of sulfuric acid (catalyst) and 10 mL of methanol (solvent), stir and react at 80 °C for 2 hours to form a precursor solution. Spray-dry the precursor solution with an inlet air temperature of 180 °C and an outlet air temperature of 100 °C to obtain microsphere precursors. Carbonize the microsphere precursors at 1000 °C for 5 hours (under inert gas protection), then etch with a 15% hydrofluoric acid solution by mass for 1 hour, wash with water and dry after etching to obtain the porous carbon material.

[0024] Preparation of silicon-based composite material: Ball-mill and mix 5 g of silicon powder and 3 g of glucose (carbon source) in a ball mill for 10 hours with a ball-to-material ratio of 20:1. Then carbonize at 900 °C for 4 hours (under inert gas protection) to obtain the silicon-based composite material.

[0025] Preparation of lithium-ion capacitor: Prepare the positive electrode plate. Mix the porous carbon material with a conductive agent (acetylene black, carbon nanotubes, and graphene mixed in a mass ratio of 3:3:1) and a binder (PVDF) in a mass ratio of 90:5:5, add an appropriate amount of NMP to make a slurry. Coat the slurry on an aluminum foil with a surface roughness Ra of 2 μm, with a coating thickness of 100 μm, dry at 120 °C for 12 hours, and then compact at a pressure of 20 MPa. Prepare the negative electrode plate. Mix the silicon-based composite material with conductive carbon black and a binder (CMC and SBR mixed in a mass ratio of 2:1) in a mass ratio of 80:10:10, add an appropriate amount of deionized water to make a slurry. Coat the slurry on a copper-plated stainless steel foil with a copper layer thickness of 15 μm, with a coating thickness of 120 μm, dry at 90 °C for 8 hours, and then compact at a pressure of 15 MPa. Assemble the lithium-ion capacitor in a glove box filled with argon, stack the positive electrode plate, polyolefin porous membrane (porosity of 60%, average pore diameter of 0.2 μm), and negative electrode plate in sequence, and inject the electrolyte (lithium salts are LiPF 6 and LiFSI mixed in a molar ratio of 1:1, with a concentration of 1.5 mol / L, and the organic solvent is a mixture of ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate in a volume ratio of 3:3:1, and the volume fraction of FEC is 5%). The electrolyte injection amount is 1.5 mL per gram of electrode material. Finally, encapsulate with an aluminum-plastic film at an encapsulation temperature of 150 °C and an encapsulation pressure of 1 MPa. Before preparing the positive electrode plate, perform plasma treatment on the aluminum foil surface for 15 minutes at 300 W; after drying the negative electrode plate, anneal at 500 °C for 3 hours (under inert gas protection).

[0026] Comparative example:

[0027] Prepare the lithium-ion capacitor according to the traditional method. The specific process is as follows:

[0028] Preparation of the positive electrode material: A common porous carbon material on the market is selected. This material does not have the hierarchical porous structure required by the present invention, and its specific surface area is detected to be 1000 m² / g. This common porous carbon material is made from conventional coal raw materials through a simple carbonization process. The carbonization temperature is about 600 °C, and the carbonization time is 3 hours. The pore structure is not precisely regulated during the preparation process.

[0029] Preparation of the negative electrode material: Pure silicon material with a purity of 99.9% is used as the negative electrode active material. This pure silicon material is produced by chemical vapor deposition commonly used in the industry and is directly purchased from relevant chemical raw material suppliers.

[0030] Configuration of the electrolyte: The electrolyte is a common carbonate-based electrolyte, which is composed of ethylene carbonate (EC) and diethyl carbonate (DEC) mixed in a volume ratio of 1:1, and additives such as fluoroethylene carbonate (FEC) are not added. Both ethylene carbonate and diethyl carbonate are commercially available chemical reagents, and their purity meets the battery-grade standard.

[0031] Selection of the separator: The separator used is a common polyolefin separator. Its porosity is detected to be 30%, and the average pore diameter is 0.3 μm. This separator is prepared by the traditional polyolefin stretching film-forming process, which has the characteristics of low cost and mature production process, but there are certain limitations in terms of ion transport efficiency and battery safety.

[0032] Preparation process of the capacitor: When preparing the positive electrode plate, the common porous carbon material, conductive agent (acetylene black), and binder (polyvinylidene fluoride, PVDF) are mixed in a mass ratio of 80:10:10, and an appropriate amount of N-methylpyrrolidone (NMP) is added to make a slurry, which is coated on a common aluminum foil current collector. The coating thickness is 80 μm, dried at 80 °C for 12 hours, and then compacted under a pressure of 15 MPa. When preparing the negative electrode plate, the pure silicon material, conductive agent (conductive carbon black), and binder (sodium carboxymethyl cellulose, CMC and styrene-butadiene rubber, SBR mixed in a mass ratio of 1:1) are mixed in a mass ratio of 75:12.5:12.5, and an appropriate amount of deionized water is added to make a slurry, which is coated on a common copper foil current collector. The coating thickness is 100 μm, dried at 70 °C for 10 hours, and then compacted under a pressure of 12 MPa. When assembling the lithium-ion capacitor, the positive electrode plate, separator, and negative electrode plate are stacked in sequence in a common environment, and the prepared electrolyte is injected. The electrolyte injection amount is 0.8 mL per gram of electrode material. Finally, it is encapsulated with a common metal shell. During the encapsulation process, factors such as environmental humidity and temperature are not strictly controlled, and special processes such as the surface treatment of the positive electrode current collector and the annealing treatment of the negative electrode plate in the embodiments of the present invention are not carried out.

[0033] Performance tests were conducted on the lithium-ion capacitors prepared by the above traditional method (comparative example) and the lithium-ion capacitors prepared in Example 1 and Example 2. The test results are shown in the following table:

[0034] Sample Energy density at 0.1C (Wh / kg) Power density at 10C (W / kg) Capacity retention after 2000 cycles (%) Example 1 320 5500 82 Example 2 310 5300 81 Comparative example 200 3000 60

[0035] It can be seen from the test results that the lithium-ion capacitors prepared in Example 1 and Example 2 of the present invention are significantly superior to the comparative example in terms of energy density, power density, and cycle life. The energy densities of Example 1 and Example 2 reach 320 Wh / kg and 310 Wh / kg respectively, which are significantly higher than 200 Wh / kg of the comparative example; in terms of power density, Example 1 and Example 2 are 5500 W / kg and 5300 W / kg respectively at a 10C charge-discharge rate, which are much higher than 3000 W / kg of the comparative example; in terms of cycle life, the capacity retention rates of Example 1 and Example 2 are 82% and 81% respectively after 2000 charge-discharge cycles, while that of the comparative example is only 60%. This fully demonstrates that the present invention has made remarkable progress and beneficial effects in improving the performance of lithium-ion capacitors by adopting a unique material formula and preparation process, highlighting the innovation and superiority of the present invention over the traditional technology.

[0036] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A high energy density lithium ion capacitor based on porous carbon electrodes, characterized in that: include: The positive electrode is composed of a specific porous carbon material, wherein the porous carbon material has a hierarchical porous structure, wherein the micropore diameter is 0.3-1nm, the mesopore diameter is 2-20nm, the macropore diameter is 50-500nm, and the micropores, mesopores and macropores are interconnected, and the specific surface area is between 1500-3000m² / g; The negative electrode is made of a silicon-based composite material, wherein the mass proportion of silicon in the silicon-based composite material is 20%-50%, and the rest is carbon material, and the carbon material is one or more of amorphous carbon, graphite or graphene; The electrolyte is composed of a lithium salt, an organic solvent and an additive, wherein the lithium salt is one of lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate or a mixture of the two in a molar ratio of 1:(0.5-1.5) with a concentration of 1.0-1.5 mol / L; the organic solvent is a mixture of ethylene carbonate, diethyl carbonate and ethyl methyl carbonate in a volume ratio of (1-3):(1-3):(1-3); the additive is fluoroethylene carbonate, and its volume fraction in the electrolyte is 2%-5%; The diaphragm is a polyolefin porous membrane with a porosity of 40%-60%, an average pore size of 0.05-0.2 μm, and a tensile strength of not less than 10 MPa.

2. A high energy density lithium ion capacitor based on porous carbon electrodes according to claim 1, characterized in that: The porous carbon material is prepared by the following method: Phenolic resin and nano-silica are used as raw materials, mixed in a mass ratio of (2-5): (1-3), and appropriate amounts of catalyst and solvent are added, and stirred at 40-80° C. for 2-6 hours to form a uniform precursor solution; the catalyst is one of hydrochloric acid, sulfuric acid or p-toluenesulfonic acid, and the amount used is 0.5%-2% of the mass of the phenolic resin; the solvent is one of ethanol, methanol or acetone; The precursor solution is spray dried to obtain a microsphere precursor, the spray drying air inlet temperature is 120-180°C, and the air outlet temperature is 60-100°C; The microsphere precursor is subjected to carbonization and etching treatment in sequence, the carbonization temperature is 700-1000°C, the carbonization time is 2-5 hours, and the process is carried out under the protection of inert gas; The etching treatment uses a hydrofluoric acid solution with a mass fraction of 5%-15% and an etching time of 1-3 hours. After etching, the porous carbon material is obtained by washing with water and drying.

3. A high energy density lithium ion capacitor based on porous carbon electrodes according to claim 1, characterized in that: The preparation method of the silicon-based composite material is: The silicon powder and the carbon source are mechanically ball-milled and mixed in a ball mill for 5-10 hours, with a ball-to-material ratio of (10-20):1, and the carbon source is one of sucrose, glucose or starch; Then, a carbonization treatment is carried out at 600-900° C. for 2-4 hours under the protection of an inert gas. The capacitor also includes a current collector, the positive current collector is an aluminum foil, the negative current collector is a copper foil, and the thickness of the current collector is 5-30 μm.

4. A high energy density lithium ion capacitor based on porous carbon electrodes according to claim 1, characterized in that: The lithium ion capacitor also includes a current collector. The positive electrode current collector is an aluminum foil with a roughened surface, and the surface roughness Ra after the roughening treatment is 0.5-2 μm; the negative electrode current collector is a copper-plated stainless steel foil, and the copper layer thickness is 5-15 μm.

5. A high energy density lithium ion capacitor based on porous carbon electrodes according to claim 1, characterized in that: The lithium ion capacitor has an energy density of not less than 300Wh / kg at a charge and discharge rate of 0.1C; a power density of not less than 5000W / kg at a charge and discharge rate of 10C; and a capacity retention rate of not less than 80% after 2000 charge and discharge cycles.

6. A method for preparing a high energy density lithium ion capacitor based on a porous carbon electrode, characterized in that: The following steps are involved: Step 1: Prepare a positive electrode sheet, mix the porous carbon material with a conductive agent and a binder in a mass ratio of (80-90): (5-10): (5-10), add an appropriate amount of N-methylpyrrolidone to make a slurry, wherein the conductive agent is acetylene black, carbon nanotubes, and graphene mixed in a mass ratio of (1-3): (1-3): (1-3), and the binder is polyvinylidene fluoride; uniformly coat the slurry on the positive electrode collector according to claim 4, with a coating thickness of 50-100 μm, dry at 80-120° C. for 12-24 hours, and then compact at a pressure of 10-20 MPa; Step 2: preparing a negative electrode sheet, mixing the silicon-based composite material with a conductive agent and a binder in a mass ratio of (70-80): (10-15): (10-15), adding an appropriate amount of deionized water to form a slurry, wherein the conductive agent is conductive carbon black, and the binder is a mixture of sodium carboxymethyl cellulose and styrene-butadiene rubber in a mass ratio of (1-2): (1-2); uniformly coating the slurry on the negative electrode current collector according to claim 4, with a coating thickness of 80-120 μm, drying at 60-90° C. for 8-16 hours, and then compacting at a pressure of 8-15 MPa; Step 3: Assemble the lithium-ion capacitor. In a glove box filled with argon, stack the positive electrode sheet, the diaphragm described in claim 1, and the negative electrode sheet in sequence, with the two sides of the diaphragm tightly fitted with the positive electrode sheet and the negative electrode sheet respectively; then inject the electrolyte described in claim 1, and the electrolyte injection amount is 0.5-1.5mL per gram of electrode material; finally, use aluminum-plastic film for packaging, the packaging temperature is 100-150°C, and the packaging pressure is 0.5-1MPa.

7. The method for preparing a high energy density lithium ion capacitor based on a porous carbon electrode according to claim 6, characterized in that: In the step 1, before coating the slurry, the surface of the positive electrode current collector is subjected to plasma treatment for 5-15 minutes at a power of 100-300 W to enhance the adhesion between the slurry and the current collector.

8. The method for preparing a high energy density lithium ion capacitor based on a porous carbon electrode according to claim 6, characterized in that: In the step 2, after the negative electrode plate is dried, it is annealed at a temperature of 300-500° C. for 1-3 hours under the protection of an inert gas to improve the structure and performance of the negative electrode plate.