Self-supporting dry-method thick electrode, preparation method thereof and lithium ion battery

Abstract

The invention provides a self-supporting dry method thick electrode and a preparation method thereof. The self-supporting dry-method thick electrode comprises a current collector and an active layer stacked on the surface of the current collector, the active layer is obtained by coating the current collector with electrode slurry, the electrode slurry comprises an active substance, a binder and a conductive agent, the conductive agent comprises conductive carbon black and pore-forming modified vapor-phase growth carbon fibers, and the conductive carbon black and the pore-forming modified vapor-phase growth carbon fibers are uniformly distributed on the surface of the active layer. The porosity of the pore-forming modified vapor growth carbon fiber is 40%-70%. The high porosity of the pore-forming modified vapor phase growth carbon fiber and the nano-particle characteristics of the conductive carbon black are complementary to form a multi-stage conductive network. Through the combination, the interface resistance between the pore-forming modified vapor growth carbon fiber and the conductive carbon black is reduced, and the overall conductivity is enhanced, so that a thick electrode is difficult to consider high energy density, high rate performance and high dynamic performance of a lithium ion battery at the same time.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a self-supporting dry-process thick electrode and a preparation method thereof, and a lithium-ion battery. Background Art

[0002] Lithium-ion batteries, the primary power source for new energy vehicles and consumer electronics, are widely used due to their high energy density, high safety, long cycle life, and environmental friendliness. The energy density of a lithium-ion battery is primarily determined by the current collector, separator, positive and negative electrode materials, binder, conductive agent, and electrolyte. The positive and negative electrode materials and conductive agent have the greatest impact on lithium-ion battery performance. The electrochemical properties of the electrode materials are the determining factor in lithium-ion battery performance.

[0003] Currently, thick electrodes are one of the effective methods for increasing the energy density of lithium-ion batteries. Traditional methods mainly use wet processes, such as slurry coating. Although slurry coating can produce thick electrodes with high loading capacity, the thickness of wet thick electrodes increases, the binder floats during baking, and the electrode is prone to cracking. The upper limit of coating is low. Increasing electrode thickness leads to longer electron / ion transmission paths and increased electrode impedance. Thick electrodes have poor kinetic performance and generally poor rate performance. Summary of the Invention

[0004] The main purpose of the present invention is to provide a self-supporting dry thick electrode and its preparation method, and a lithium ion battery, so as to solve the problem in the prior art that thick electrodes are difficult to achieve high energy density, high rate performance and high dynamic performance of lithium ion batteries.

[0005] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, a self-supporting dry-process thick electrode is provided, comprising a current collector and an active layer superimposed on the surface of the current collector, wherein the active layer is obtained by coating an electrode slurry on the current collector, the electrode slurry comprising an active material, a binder and a conductive agent, the conductive agent comprising conductive carbon black and pore-forming modified vapor-grown carbon fiber, the porosity of the pore-forming modified vapor-grown carbon fiber being 40% to 70%.

[0006] Furthermore, the porosity of the pore-forming modified vapor-grown carbon fiber is 50% to 60%, and / or the average pore size of the pore-forming modified vapor-grown carbon fiber is 5 to 10 nm, and / or the specific surface area of ​​the pore-forming modified vapor-grown carbon fiber is 20 m 2 / g~30m 2 / g.

[0007] Furthermore, the mass ratio of the conductive carbon black to the pore-forming modified vapor-grown carbon fiber is (1-2):1; and / or the particle size of the conductive carbon black is 35-45 nm, and the specific surface area of ​​the conductive carbon black is 50-70 m 2 / g.

[0008] Furthermore, the mass ratio of the above-mentioned active material, binder and conductive agent is (0.92~0.97): (0.02~0.05): (0.01~0.03); and / or the active material is selected from any one or more of graphite, hard carbon, mesophase carbon microbeads, lithium iron phosphate and lithium nickel cobalt manganese oxide; and / or the binder is selected from any one or more of polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber and carboxymethyl cellulose; and / or, the above-mentioned current collector is a carbon-coated current collector foil, and the surface roughness Ra of the carbon-coated current collector foil is 0.5~2μm.

[0009] According to one aspect of the present invention, a method for preparing the above-mentioned self-supporting dry-process thick electrode is provided, which comprises: mixing raw materials including an active material, a binder and a conductive agent, and then sequentially performing fiberization treatment, banburying treatment, screening granulation, roller passing and continuous rolling to form an active layer; compounding the active layer with a current collector to obtain a self-supporting dry-process thick electrode; the conductive agent comprises conductive carbon black and pore-forming modified vapor-grown carbon fiber.

[0010] Furthermore, the above-mentioned preparation method includes a preparation process of pore-modified vapor-grown carbon fiber, and the preparation process includes: mixing the vapor-grown carbon fiber with an oxidant and then performing an oxidation reaction to obtain oxidatively etched vapor-grown carbon fiber; performing a reduction reaction on the oxidatively etched vapor-grown carbon fiber with a reducing agent to obtain pore-modified vapor-grown carbon fiber; wherein the temperature of the oxidation reaction is 0 to 5°C, and the time of the oxidation reaction is 3 to 5 hours; and / or the temperature of the reduction reaction is 80 to 100°C, and the time of the reduction reaction is 3 to 5 hours; and / or the reducing agent is selected from any one or more of formaldehyde, sodium hydroxide and ascorbic acid; the oxidant is selected from any one or more of potassium permanganate, nitric acid, concentrated sulfuric acid and hydrogen peroxide.

[0011] Furthermore, the fiberization treatment is performed by high-speed shearing, the linear speed of the high-speed shearing is 50 to 120 m / s, and the time of the high-speed shearing is 0.5 to 10 min.

[0012] Furthermore, the temperature of the banburying treatment is 20-80° C., and the time of the banburying treatment is 5-10 minutes.

[0013] Furthermore, the above mixing is carried out under stirring conditions, the stirring speed is 600 to 2400 rpm / min, and the stirring time is 15 to 30 minutes; and / or the mesh number of the sieving granulation is 10 to 15 meshes; and / or the temperature of the continuous rolling is 20 to 200°C; and / or the compounding method is flat-plate hot pressing compounding or hot roller pressing compounding, and the temperature of the flat-plate hot pressing compounding and hot roller pressing compounding is independently 100 to 180°C.

[0014] According to another aspect of the present invention, a lithium ion battery is provided, comprising a positive electrode and a negative electrode, wherein the positive electrode is the above-mentioned self-supporting dry-process thick electrode.

[0015] By applying the technical solution of the present invention, the high porosity structure of the pore-forming modified vapor-grown carbon fiber directly affects the electrolyte infiltration and lithium ion diffusion efficiency. Its rich pore structure provides storage space for the electrolyte and can be used as an "ion buffer pool", which is conducive to the absorption and storage of the electrolyte. The conductive agent is around the main material. When the battery is charged and discharged, the main material can quickly obtain Li from the conductive agent. + , which shortens Li + On the other hand, the electrolyte is stored to reduce the local lithium ion concentration gradient, which is conducive to the rapid diffusion of lithium ions inside the electrode. 2 / g of conductive carbon black can fill the tiny gaps between active materials, forming dense point contacts and reducing the contact resistance between particles. In addition, conductive carbon black can accelerate surface ion exchange, reduce ohmic polarization by shortening the electron transmission distance, alleviate polarization, and improve capacity output at high rates. Controlling the porosity of the pore-forming modified vapor-grown carbon fiber to 40% to 70% provides more anchor points for the conductive carbon black nanoparticles. The conductive carbon black can be embedded in the pores of the pore-forming modified vapor-grown carbon fiber or attached to its surface to form a closer physical contact. The high porosity of the pore-forming modified vapor-grown carbon fiber is complemented by the nanoparticle characteristics of the conductive carbon black to construct a multi-level conductive network. This combination reduces the interface resistance between the pore-forming modified vapor-grown carbon fiber and the conductive carbon black, enhancing the overall conductivity. At the same time, the fiber reinforcement effect of the pore-forming modified vapor-grown carbon fiber is used to improve mechanical stability. DETAILED DESCRIPTION

[0016] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0017] As analyzed in the background technology of this application, there is a problem in the existing technology that thick electrodes are difficult to take into account the high energy density, high rate performance and high dynamic performance of lithium-ion batteries. This application provides a self-supporting dry thick electrode and its preparation method, and a lithium-ion battery.

[0018] In a typical embodiment of the present application, a self-supporting dry-process thick electrode is provided, comprising a current collector and an active layer superimposed on the surface of the current collector, wherein the active layer is obtained by coating an electrode slurry on the current collector, the electrode slurry comprising an active substance, a binder and a conductive agent, the conductive agent comprising conductive carbon black and pore-forming modified vapor-grown carbon fiber, the porosity of the pore-forming modified vapor-grown carbon fiber being 40% to 70%.

[0019] The high porosity of the pore-forming modified vapor-grown carbon fiber directly affects the electrolyte infiltration and lithium ion diffusion efficiency. Its rich pore structure provides storage space for the electrolyte and can be used as an "ion buffer pool", which is conducive to the absorption and storage of electrolyte. The conductive agent is around the main material. When the battery is charged and discharged, the main material can quickly obtain Li from the conductive agent. + , which shortens Li + On the other hand, the electrolyte is stored to reduce the local lithium ion concentration gradient, which is conducive to the rapid diffusion of lithium ions inside the electrode. 2 / g of conductive carbon black can fill the tiny gaps between active materials, forming dense point contacts and reducing the contact resistance between particles. In addition, conductive carbon black can accelerate surface ion exchange, reduce ohmic polarization by shortening the electron transmission distance, alleviate polarization, and improve capacity output at high rates. Controlling the porosity of the pore-forming modified vapor-grown carbon fiber to 40% to 70% provides more anchor points for the conductive carbon black nanoparticles. The conductive carbon black can be embedded in the pores of the pore-forming modified vapor-grown carbon fiber or attached to its surface to form a closer physical contact. The high porosity of the pore-forming modified vapor-grown carbon fiber is complemented by the nanoparticle characteristics of the conductive carbon black to construct a multi-level conductive network. This combination reduces the interface resistance between the pore-forming modified vapor-grown carbon fiber and the conductive carbon black, enhancing the overall conductivity. At the same time, the fiber reinforcement effect of the pore-forming modified vapor-grown carbon fiber is used to improve mechanical stability.

[0020] In addition, the porosity of the pore-forming modified vapor-grown carbon fiber can be 40%, 45%, 50%, 55%, 60%, 65% or 70%. Of course, the porosity of the pore-forming modified vapor-grown carbon fiber can be any point value within the range of 40% to 70%, which will not be repeated here.

[0021] In one embodiment of the present application, the porosity of the pore-forming modified vapor-grown carbon fiber is 50% to 60%, and / or the average pore size of the pore-forming modified vapor-grown carbon fiber is 5 to 10 nm, and / or the specific surface area of ​​the pore-forming modified vapor-grown carbon fiber is 20 m 2 / g~30m 2 / g.

[0022] Further optimization of the porosity, specific surface area, and average pore size of the pore-modified vapor-grown carbon fibers provides a more appropriate number of anchoring points for the conductive carbon black, allowing it to embed into the pores of the pore-modified vapor-grown carbon fibers or adhere to their surface, forming a closer physical contact. This combination reduces the interfacial resistance between the pore-modified vapor-grown carbon fibers and the conductive carbon black, enhancing overall conductivity.

[0023] In addition, the porosity of the pore-forming modified vapor-grown carbon fiber can be 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59% or 60%. Of course, the porosity of the pore-forming modified vapor-grown carbon fiber can be any point value within the range of 50% to 60%, which will not be repeated here.

[0024] The average pore size of the pore-forming modified vapor-grown carbon fiber can be 5 nm, 6 nm, 7 nm, 8 nm, 9 nm or 10 nm. Of course, the average pore size of the pore-forming modified vapor-grown carbon fiber can be any point value within the range of 5 to 10 nm, which will not be repeated here.

[0025] The specific surface area of ​​the pore-forming modified vapor-grown carbon fiber can be 20m 2 / g, 21m 2 / g、22m 2 / g, 23m 2 / g、24m 2 / g, 25m 2 / g, 26m 2 / g、27m 2 / g、28m 2 / g、29m 2 / g or 30m 2 / g, of course, the specific surface area of ​​the pore-forming modified vapor-grown carbon fiber can be 20m 2 / g~30m 2 The arbitrary point values ​​within / g are not described here.

[0026] In one embodiment of the present application, the mass ratio of the conductive carbon black to the pore-forming modified vapor-grown carbon fiber is (1-2):1; and / or the particle size of the conductive carbon black is 35-45 nm, and the specific surface area of ​​the conductive carbon black is 50-70 m 2 / g.

[0027] Controlling the mass ratio of conductive carbon black to pore-forming modified vapor-grown carbon fibers, and the particle size and specific surface area of ​​the conductive carbon black within the above ranges helps to achieve better coordination between the macroscopic skeleton structure formed by the pore-forming modified vapor-grown carbon fibers and the microscopic pores filled by the conductive carbon black in the skeleton gaps, thereby obtaining a multi-level conductive network of "macropores-mesopores-micropores". This structure is particularly important in thick electrodes. The combination of conductive agents at this ratio can not only ensure the conductivity of the electrode, enhance the mechanical strength of the electrode, reduce the expansion and contraction of the electrode during the cycle, improve the cycle stability of the battery, but also reduce the risk of increased polarization due to excessively long electron transmission paths.

[0028] In addition, the mass ratio of the above-mentioned conductive carbon black to the pore-forming modified vapor-grown carbon fiber can be 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1 or 2:1. Of course, the mass ratio of the above-mentioned conductive carbon black to the pore-forming modified vapor-grown carbon fiber can be any point value within (1 to 2):1, which will not be repeated here.

[0029] The particle size of the conductive carbon black can be 35nm, 36nm, 37nm, 38nm, 39nm, 40nm, 41nm, 42nm, 43nm, 44nm or 45nm. Of course, the particle size of the conductive carbon black can be any point value within 35 to 45nm, which will not be repeated here.

[0030] The specific surface area of ​​conductive carbon black can be 50m 2 / g、52m 2 / g、54m 2 / g、55m 2 / g、57m 2 / g, 60m 2 / g、62m 2 / g、64m 2 / g、65m 2 / g、67m 2 / g or 70m 2 / g, of course, the specific surface area of ​​conductive carbon black can be 50 to 70 m 2 / g, any point value is not repeated here. In one embodiment of the present application, the mass ratio of the above-mentioned active material, binder and conductive agent is (0.92-0.97): (0.02-0.05): (0.01-0.03); and / or the active material is selected from any one or more of graphite, hard carbon, mesophase carbon microbeads, lithium iron phosphate and lithium nickel cobalt manganese oxide; and / or the binder is selected from any one or more of polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber and carboxymethyl cellulose.

[0031] Selecting the above mass ratios of active material, binder and conductive agent helps to bring out the synergy between the components, so that the electrode has high energy density while having excellent mechanical properties and coatability of the corresponding slurry.

[0032] In addition, the mass ratio of the above-mentioned active material, binder and conductive agent can be 0.92:0.05:0.03, 0.93:0.04:0.03, 0.94:0.05:0.01, 0.95:0.02:0.03, 0.96:0.01:0.02 or 0.97:0.02:0.01. Of course, the mass ratio of the above-mentioned active material, binder and conductive agent can be any point value within (0.92~0.97):(0.02~0.05):(0.01~0.03), which will not be repeated here.

[0033] In one embodiment of the present application, the current collector is a carbon-coated current collector foil, and the surface roughness Ra of the carbon-coated current collector foil is 0.5-2 μm.

[0034] The current collector with a surface roughness within the above range helps to improve the firmness of its bonding with the electrode and reduce the shedding of the electrode during the charge and discharge process, thereby being more conducive to obtaining a thick electrode with better mechanical strength, electrical conductivity and stability, thereby helping to improve the dynamics of the thick electrode, and is suitable for battery applications requiring high stability and long life. Furthermore, the current collector is selected from a carbon-coated current collector, and the foil includes one or more of copper foil, aluminum foil, stainless steel foil and nickel foil, wherein the conductive agent in the carbon coating layer is composed of one or more of carbon black, conductive graphite, graphene, carbon nanotubes and polyimide carbonized compounds, which is conducive to improving the interfacial bonding force and conductivity during the composite process. In addition, a foil having the above surface roughness is obtained by one or more physical treatment methods selected from etching, sandblasting, wire drawing and polishing.

[0035] In addition, the surface roughness Ra of the above-mentioned carbon-coated current collector foil can be 0.5μm, 0.6μm, 0.8μm, 1.0μm, 1.2μm, 1.5μm, 1.8μm, 1.9μm or 2μm. Of course, the surface roughness Ra of the above-mentioned carbon-coated current collector foil can be any point value within 0.5~2μm, which will not be repeated here.

[0036] The preparation process of the carbon-coated current collector foil includes:

[0037] The metal foil is cleaned and pretreated to clean the oil stains, oxide layer and other impurities on the surface, and the etched metal foil is prepared by high-energy physical impact method. The roughness of the etched metal foil is Ra 0.2-0.4 μm, so that the etched metal foil and the carbon coating layer are more firmly bonded.

[0038] The dry (pure dry solvent-free) electrode preparation process is to glue the current collector and the prepared membrane together to prepare the electrode. Therefore, the adhesive with the above softening point has a certain fluidity after melting at high temperature, thereby filling the pores of the membrane and firmly bonding the membrane and the current collector together.

[0039] The softening point of the binder in the coating of the carbon-coated current collector foil is 90-120° C., and the thickness of the coating of the carbon-coated current collector foil is 1-5 μm.

[0040] In addition, the softening point of the binder in the coating of the carbon-coated current collector foil is 90°C, 95°C, 100°C, 105°C, 110°C, 115°C or 120°C. Of course, the softening point of the binder in the coating of the above-mentioned carbon-coated current collector foil can be any point value within the range of 90 to 120°C, which will not be repeated here.

[0041] The coating thickness of the carbon-coated current collector foil can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 or 5 μm. Of course, the coating thickness of the above-mentioned carbon-coated current collector foil can be any point value within 1 to 5 μm, which will not be repeated here.

[0042] In another typical embodiment of the present application, a method for preparing the above-mentioned self-supporting dry-process thick electrode is provided, which comprises: mixing raw materials including active materials, binders and conductive agents, and then successively performing fiberization treatment, banburying treatment, screening granulation, roller and continuous rolling to form an active layer; compounding the active layer with the current collector to obtain a self-supporting dry-process thick electrode; the conductive agent comprises conductive carbon black and pore-forming modified vapor-grown carbon fiber.

[0043] Through a series of meticulous processing steps, the above preparation method can produce thick electrodes with a more uniform structure that can achieve the high energy density, high rate performance, and high dynamic performance of lithium-ion batteries. It is suitable for automated production lines and improves production efficiency and product quality. However, because the powder after fiberization and mixing is very sticky, if the powder is directly fed into the roller, bridging will occur, resulting in holes in the prepared membrane or direct breakage. Sieving and granulation can avoid these problems.

[0044] In one embodiment of the present application, the above-mentioned preparation method includes a preparation process of pore-modified vapor-grown carbon fiber, and the preparation process includes: mixing the vapor-grown carbon fiber with an oxidant and then performing an oxidation reaction to obtain oxidatively etched vapor-grown carbon fiber; performing a reduction reaction on the oxidatively etched vapor-grown carbon fiber with a reducing agent to obtain pore-modified vapor-grown carbon fiber; wherein the temperature of the oxidation reaction is 0 to 5°C, and the time of the oxidation reaction is 3 to 5 hours; and / or the temperature of the reduction reaction is 80 to 100°C, and the time of the reduction reaction is 3 to 5 hours; and / or the reducing agent is selected from any one or more of formaldehyde, sodium hydroxide and ascorbic acid; the oxidant is selected from any one or more of potassium permanganate, nitric acid, concentrated sulfuric acid and hydrogen peroxide.

[0045] By selecting and controlling the above redox reaction conditions, the pore structure of the carbon fiber can be effectively controlled, the risk of excessive oxidation damaging the vapor-grown carbon fiber structure can be reduced, and ultimately a pore-modified vapor-grown carbon fiber with excellent mechanical strength and pore structure can be obtained.

[0046] In addition, the temperature of the oxidation reaction can be 0°C, 1°C, 2°C, 3°C, 4°C or 5°C. Of course, the temperature of the above oxidation reaction can be any point value within the range of 0-5°C, which will not be repeated here.

[0047] The oxidation reaction time can be 3 h, 3.5 h, 4 h, 4.5 h or 5 h. Of course, the oxidation reaction time can be any point value within 3 to 5 h, which will not be repeated here.

[0048] The temperature of the reduction reaction can be 80°C, 85°C, 90°C, 95°C or 100°C. Of course, the temperature of the reduction reaction can be any point value within the range of 80-100°C, which will not be repeated here.

[0049] The reduction reaction time can be 3 h, 3.5 h, 4 h, 4.5 h or 5 h. Of course, the reduction reaction time can be any value within 3 to 5 h, which will not be repeated here.

[0050] In one embodiment of the present application, the fiberization treatment is performed by high-speed shearing, the linear speed of the high-speed shearing is 50 to 120 m / s, and the time of the high-speed shearing is 0.5 to 10 min.

[0051] High-speed shearing can, on the one hand, initially form a fibrous interwoven structure among the active material, binder, and conductive agent, tightening the bonds between the components and thus enhancing the overall structural stability of the active layer, making it less susceptible to cracking and shedding during subsequent use. Furthermore, high-speed shearing increases the material's specific surface area, increasing the contact area between the active material and the electrolyte, which in turn improves the battery's charge and discharge efficiency and the adequacy of the chemical reaction.

[0052] In addition, the linear velocity of the above-mentioned high-speed shearing can be 50m / s, 55m / s, 60m / s, 65m / s, 70m / s, 75m / s, 80m / s, 85m / s, 90m / s, 95m / s, 100m / s, 105m / s, 110m / s, 115m / s or 120m / s. Of course, the linear velocity of the above-mentioned high-speed shearing can be any point value within the range of 50 to 120m / s, which will not be repeated here.

[0053] The time of the high-speed shearing can be 0.5 min, 1 min, 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min or 10 min. Of course, the time of the high-speed shearing can be any point value within 0.5 to 10 min, which will not be repeated here.

[0054] In one embodiment of the present application, the temperature of the banburying treatment is 20-80° C., and the time of the banburying treatment is 5-10 minutes.

[0055] The banburying treatment allows the active material, binder and conductive agent to be mixed together more fully and evenly. The uniform distribution of each component can ensure the consistency of the performance of the active layer, avoid the situation where local performance differences are too large, and improve the overall quality and stability of the product. Specifically, the banburying treatment can make the binder play a better role. It can fully wrap the active material and conductive agent particles, enhance the bonding force between the particles, and improve the cohesion of the active layer, so that it is not easy for particles to fall off or the active layer structure to be damaged when subjected to external forces or during the charge and discharge cycle, thereby extending the service life of the product. In addition, the banburying treatment allows the conductive agent to be more evenly dispersed in the active material, forming a more complete conductive network, thereby reducing the resistance of the active layer, improving the electron transmission efficiency, and helping to improve the charge and discharge performance and power characteristics of the battery. Selecting the above specific banburying treatment temperature and time can help further improve the uniformity and electrical properties of the active layer.

[0056] In addition, the temperature of the above-mentioned banburying treatment can be 20°C, 30°C, 40°C, 50°C, 60°C, 70°C or 80°C. Of course, the temperature of the above-mentioned banburying treatment can be any point value within the range of 20 to 80°C, which will not be repeated here.

[0057] The time of the above-mentioned banburying treatment can be 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes or 10 minutes. Of course, the time of the above-mentioned banburying treatment can be any point value within 5 to 10 minutes, which will not be repeated here.

[0058] In one embodiment of the present application, the above-mentioned mixing is carried out under stirring conditions, the stirring speed is 600-2400 rpm / min, and the stirring time is 15-30 min; and / or the mesh number of the sieving granulation is 10-15 mesh; and / or the temperature of the continuous rolling is 20-200°C; and / or the compounding method is flat-plate hot pressing compounding or hot roller pressing compounding, and the temperature of the flat-plate hot pressing compounding and the hot roller pressing compounding is independently 100-180°C.

[0059] The stirring speed helps improve mixing uniformity, and the mixing equipment is selected from one or more of a planetary mixer, a high-speed shear mixer, a ball mill, and an airflow mixer. The mesh size of the sieving granulation is within the above range, which helps reduce the risk of holes or direct breakage in the prepared membrane.

[0060] In addition, the stirring speed can be 600rpm / min, 700rpm / min, 800rpm / min, 900rpm / min, 1000rpm / min, 1100rpm / min, 1200rpm / min, 1300rpm / min, 1400rpm / min, 1500rpm / min, 1600rpm / min, 1700rpm / min, 1800rpm / min, 1900rpm / min, 2000rpm / min, 2100rpm / min, 2200rpm / min, 2300rpm / min or 2400rpm / min. Of course, the above stirring speed can be any point value within the range of 600 to 2400rpm / min, which is not repeated here.

[0061] The stirring time can be 15min, 16min, 17min, 18min, 19min, 20min, 21min, 22min, 23min, 24min, 25min, 26min, 27min, 28min, 29min or 30min. Of course, the above stirring time can be any point value within 15 to 30min, which is not repeated here.

[0062] The mesh number of the sieve granulation can be 10 mesh, 11 mesh, 12 mesh, 13 mesh, 14 mesh or 15 mesh. Of course, the mesh number of the sieve granulation can be any point value within 10 to 15 mesh, which will not be repeated here.

[0063] The temperature of continuous rolling can be 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C or 200°C. Of course, the temperature of the above-mentioned continuous rolling can be any point value within the range of 20 to 200°C, which will not be repeated here.

[0064] The temperatures of the flat-plate hot pressing composite and the hot roller pressing composite can be independently 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C or 180°C. Of course, the temperatures of the above-mentioned flat-plate hot pressing composite and the hot roller pressing composite can be independently any point value within the range of 100-180°C, which will not be repeated here.

[0065] On the one hand, continuous rolling can make the structure and performance of the active layer more uniform along the length direction, reducing the risk of local uneven thickness or large density differences. This helps to improve the performance consistency of the battery at different locations, reduce problems such as uneven battery aging caused by local performance differences, and extend the overall service life of the battery. On the other hand, the continuous rolling process is suitable for large-scale continuous production, enabling rapid preparation and molding of the active layer, improving production efficiency, and reducing production costs. The continuous rolling equipment is selected from one or more of a single-roller rolling machine, a double-roller rolling machine, and a four-roller continuous rolling machine.

[0066] The selected compounding method and conditions help to improve the strength and effect of the compounding of the active layer and the current collector, and improve the conductivity. The compounding equipment is selected from one or more of a hot press compounding machine, a cold press compounding machine and an ultrasonic compounding machine.

[0067] In addition, the present application provides a method for preparing vapor-grown carbon fiber, which is as follows:

[0068] A gas containing a carbon source (such as methane, acetylene, ethylene, etc.) and a gas carrying a catalyst (metal nanoparticles) are introduced into a high-temperature reactor. The reaction temperature is generally between 1000 and 1300°C, and the pressure in the reactor is between 50 and 300 Pa. The gas flow rate is 30 mL / min to 200 mL / min.

[0069] In addition, the above reaction temperature can generally be 1000°C, 1050°C, 1100°C, 1150°C, 1200°C, 1250°C or 1300°C. Of course, the above reaction temperature can generally be any point value within the range of 1000-1300°C, which will not be repeated here.

[0070] The pressure inside the reactor can be 50Pa, 70Pa, 90Pa, 100Pa, 120Pa, 150Pa, 170Pa, 190Pa, 210Pa, 230Pa, 250Pa, 280Pa or 300Pa. Of course, the pressure inside the reactor can be any value within the range of 50 to 300Pa, which will not be repeated here.

[0071] The gas flow rate can be 30mL / min, 50mL / min, 70mL / min, 90mL / min, 110mL / min, 130mL / min, 150mL / min, 180mL / min or 200mL / min. Of course, the above gas flow rate can be any point value within 30mL / min to 200mL / min, which will not be repeated here.

[0072] Purification treatment: In air or oxygen atmosphere, heat the vapor-grown carbon fiber to 500-700°C to remove the carbon component in the impurities by reacting with oxygen to produce carbon dioxide. Soak the vapor-grown carbon fiber sample in a 1-5 mol / L acid solution for 6-48 hours, stirring continuously at a stirring speed of 100-300 rpm to remove catalyst impurities.

[0073] In addition, the vapor-grown carbon fiber can be heated to 500°C, 550°C, 600°C, 650°C or 700°C. Of course, the vapor-grown carbon fiber can be heated to any point value within the range of 500 to 700°C, which will not be repeated here.

[0074] The vapor-grown carbon fiber sample can be immersed in an acid solution of 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L or 5 mol / L. Of course, the vapor-grown carbon fiber sample can be immersed in any point value within the acid solution of 1 to 5 mol / L, which will not be repeated here.

[0075] The immersion time of the vapor-grown carbon fiber sample can be 6h, 8h, 10h, 12h, 15h, 18h, 20h, 25h, 30h, 35h, 40h, 45h or 48h. Of course, the immersion time of the vapor-grown carbon fiber sample can be any point value within 6 to 48h, which will not be repeated here.

[0076] Stirring is carried out continuously during the soaking period. The stirring speed can be 100rpm, 120rpm, 140rpm, 150rpm, 170rpm, 190rpm, 200rpm, 220rpm, 240rpm, 250rpm, 270rpm, 290rpm or 300rpm. Of course, the stirring speed can be any point value within the range of 100 to 300rpm, which is not repeated here.

[0077] In another typical embodiment of the present application, a lithium-ion battery is provided, comprising a positive electrode and a negative electrode, wherein the positive electrode is the above-mentioned self-supporting dry-process thick electrode.

[0078] The lithium-ion battery including the above-mentioned self-supporting dry thick electrode has high energy density, high rate performance and high kinetic performance.

[0079] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0080] Example 1

[0081] Preparation of vapor-grown carbon fiber:

[0082] A gas containing acetylene and Co-carrying metal nanoparticles is introduced into a high-temperature reactor. The reaction temperature is generally 1300°C and the pressure in the reactor is 200 Pa. The gas flow rate is 100 mL / min.

[0083] Purification: Heat the vapor-grown carbon fiber to 700°C in an air or oxygen atmosphere to remove the carbon impurities by reacting with oxygen to produce carbon dioxide. Immerse the vapor-grown carbon fiber sample in a 5 mol / L acid solution for 20 hours, stirring continuously at 300 rpm, to remove catalyst impurities.

[0084] Preparation of pore-modified vapor-grown carbon fibers:

[0085] The vapor-grown carbon fibers were dispersed in concentrated sulfuric acid, and potassium permanganate was slowly added. The reaction was carried out at a low temperature of 5°C. During the reaction, part of the carbon structure of the vapor-grown carbon fibers was oxidized to form gases such as carbon dioxide, which escaped, thus forming a porous structure. The reaction time was 5 hours.

[0086] The vapor-grown carbon fibers that had undergone oxidation etching were dispersed in a hydrazine hydrate solution and reacted at 100°C for 3 hours to reduce the oxygen-containing functional groups in the vapor-grown carbon fibers, thereby restoring their conductive properties while retaining the pore-forming structure. The pore-forming modified vapor-grown carbon fibers had a porosity of 60%, an average pore diameter of 8 nm, and a specific surface area of ​​25 m 2 / g.

[0087] The active material NCM613 (LiNi 0.6 Co 0.1 Mn 0.3 O2), binder polytetrafluoroethylene and conductive agent are mixed in a mass ratio of 0.92:0.05:0.03, and then subjected to fiberization treatment, banburying treatment, screening granulation, roller and continuous rolling to form an active layer. Among them, the conductive agent is conductive carbon black and pore-forming modified vapor-grown carbon fiber, the mass ratio of the two is 2:1, the particle size of the conductive carbon black is 35-45nm, and the specific surface area of ​​the conductive carbon black is 50-70m 2 / g. Mixing was carried out under stirring conditions at a speed of 1400 rpm / min for 30 minutes. Fiberization was performed using high-speed shearing at a linear speed of 120 m / s for 10 minutes. The banburying temperature was 80°C for 10 minutes. The mesh size of the sieving granulation was 15 mesh, and the continuous rolling temperature was 100°C.

[0088] The active layer and the carbon-coated aluminum foil were compounded at 180° C. by hot roller pressing to obtain a positive electrode. The thickness of the positive electrode sheet was 180 μm.

[0089] Example 2

[0090] The difference from Example 1 is that the vapor-grown carbon fiber is dispersed in concentrated sulfuric acid, and then potassium permanganate is slowly added. The reaction is carried out at a low temperature of 5°C for 4 hours. During the reaction, part of the carbon structure of the vapor-grown carbon fiber is oxidized into gases such as carbon dioxide and escapes, thereby forming a porous structure.

[0091] The vapor-grown carbon fibers that have undergone oxidation etching are dispersed in a hydrazine hydrate solution and reacted at 80°C for 4 hours to reduce the oxygen-containing functional groups in the vapor-grown carbon fibers, restoring their conductive properties while retaining the pore-forming structure. The porosity of the pore-modified vapor-grown carbon fibers is 50%, and a positive electrode is finally obtained.

[0092] Example 3

[0093] The difference from Example 1 is that the vapor-grown carbon fiber is dispersed in concentrated sulfuric acid, and then potassium permanganate is slowly added. The reaction is carried out at a low temperature of 5°C for 3 hours. During the reaction, part of the carbon structure of the vapor-grown carbon fiber is oxidized into gases such as carbon dioxide and escapes, thereby forming a porous structure.

[0094] The vapor-grown carbon fibers that have undergone oxidation etching are dispersed in a hydrazine hydrate solution and reacted at 80°C for 4 hours to reduce the oxygen-containing functional groups in the vapor-grown carbon fibers, restoring their conductive properties while retaining the pore-forming structure. The porosity of the pore-modified vapor-grown carbon fibers is 40%, and a positive electrode is finally obtained.

[0095] Example 4

[0096] The difference from Example 1 is that the vapor-grown carbon fibers are dispersed in concentrated sulfuric acid, and then potassium permanganate is slowly added. The reaction is carried out at a low temperature of 0°C. During the reaction, part of the carbon structure of the vapor-grown carbon fibers is oxidized to form gases such as carbon dioxide, which escape, thereby forming a porous structure. The reaction time is 5 hours.

[0097] The vapor-grown carbon fibers that had undergone oxidation etching were dispersed in a hydrazine hydrate solution and reacted at 100°C for 5 hours to reduce the oxygen-containing functional groups in the vapor-grown carbon fibers, restoring their conductive properties while retaining the pore-forming structure. The porosity of the pore-modified vapor-grown carbon fibers was 70%, and a positive electrode was finally obtained.

[0098] Example 5

[0099] The difference from Example 1 is that the mass ratio of the conductive carbon black to the pore-forming modified vapor-grown carbon fiber is 1:1, and a positive electrode is finally obtained.

[0100] Example 6

[0101] The difference from Example 1 is that the mass ratio of the conductive carbon black to the pore-forming modified vapor-grown carbon fiber is 1:2, and a positive electrode is finally obtained.

[0102] Example 7

[0103] The difference from Example 1 is that the active material ternary NCM, the binder polytetrafluoroethylene and the conductive agent are in a mass ratio of 0.97:0.02:0.01, and finally a positive electrode is obtained.

[0104] Example 8

[0105] The difference from Example 1 is that the active material ternary NCM, the binder polytetrafluoroethylene and the conductive agent are in a mass ratio of 0.91:0.06:0.03, and finally a positive electrode is obtained.

[0106] Example 9

[0107] The difference from Example 1 is that the mixing was carried out under stirring conditions, the stirring speed was 2000 rpm / min, and the stirring time was 30 minutes. The fiberization treatment was carried out by high-speed shearing, the high-speed shearing line speed was 80 m / s, and the high-speed shearing time was 10 minutes. The above-mentioned banburying treatment temperature was 80°C, and the banburying treatment time was 10 minutes. The mesh size of the sieving granulation was 10 mesh; the continuous rolling temperature was 120°C, and finally the positive electrode was obtained.

[0108] Comparative Example 1

[0109] The difference from Example 1 is that vapor-grown carbon fibers are directly used, that is, the conductive agent is a combination of conductive carbon black and vapor-grown carbon fibers, and finally a positive electrode is obtained.

[0110] Comparative Example 2

[0111] The difference from Example 1 is that the vapor-grown carbon fibers are dispersed in concentrated sulfuric acid, and then potassium permanganate is slowly added. The reaction is carried out at a low temperature of 0°C. During the reaction, part of the carbon structure of the vapor-grown carbon fibers is oxidized to form gases such as carbon dioxide, which escape, thereby forming a porous structure. The reaction time is 1 hour.

[0112] The vapor-grown carbon fibers that have undergone oxidation etching are dispersed in a hydrazine hydrate solution and reacted at 80°C for 2 hours to reduce the oxygen-containing functional groups in the vapor-grown carbon fibers, restoring their conductive properties while retaining the pore-forming structure. The porosity of the pore-modified vapor-grown carbon fibers is 30%, and a positive electrode is finally obtained.

[0113] Comparative Example 3

[0114] The difference from Example 1 is that the vapor-grown carbon fibers are dispersed in concentrated sulfuric acid, and then potassium permanganate is slowly added. The reaction is carried out at a low temperature of 0°C. During the reaction, part of the carbon structure of the vapor-grown carbon fibers is oxidized to form gases such as carbon dioxide, which escape, thereby forming a porous structure. The reaction time is 10 hours.

[0115] The vapor-grown carbon fibers that have undergone oxidation etching are dispersed in a hydrazine hydrate solution and reacted at 100°C for 5 hours to reduce the oxygen-containing functional groups in the vapor-grown carbon fibers, restoring their conductive properties while retaining the pore-forming structure. The porosity of the pore-formed vapor-grown carbon fibers is 80%, and a positive electrode is finally obtained.

[0116] Performance testing:

[0117] Preparation of a dry-process graphite anode: Graphite (active material), polytetrafluoroethylene (PTFE) (binder), and SP (conductive agent) (SP) were mixed in a mass ratio of 0.97:0.02:0.01. The mixture was then subjected to fiberization, sieve granulation, roller processing, and continuous rolling to form the active layer. Mixing was performed with stirring at a speed of 1400 rpm / min for 30 minutes. Fiberization was performed using high-speed shearing at a line speed of 80 m / s for 10 minutes. The sieve granulation had a mesh size of 10, and the continuous rolling temperature was 100°C. The active layer was then laminated with carbon-coated copper foil at 150°C using hot roller pressing to produce a dry-process graphite anode sheet with a thickness of 150 μm.

[0118] The positive electrodes, separators, and dry-process graphite negative electrodes of Examples 1 to 9 and Comparative Examples 1 to 3 were stacked in order and then superimposed; the tabs were welded and placed in an outer packaging aluminum-plastic film. After vacuum packaging, liquid injection, standing at room temperature for 48 hours, formation, shaping, and capacity testing, a soft-pack laminated lithium-ion battery was obtained.

[0119] The obtained lithium-ion battery was subjected to initial efficiency and cycle tests on a charge and discharge device. The cycle test steps are as follows: 1C constant current and constant voltage charging, cut-off voltage 4.3V, cut-off current 0.05C, and then 1C constant current discharge, cut-off voltage 2.75V.

[0120] The data of the first efficiency, cycle performance (capacity retention rate after 1000 cycles), and 1C constant current charging ratio of the above lithium-ion batteries are listed in Table 1.

[0121] Table 1

[0122]

[0123]

[0124] Among them, Examples 1 to 5, Example 7 and Example 9 changed some conditions, and the first efficiency, cycle performance (capacity retention rate after 1000 cycles), and 1C constant current charging ratio of the corresponding lithium-ion batteries were all better.

[0125] Compared with Examples 1 and 5, the mass ratio of the conductive carbon black to the pore-forming modified vapor-grown carbon fiber (1:2) in Example 6 is outside the preferred range of (1 to 2):1, which slightly weakens the synergistic effect between the macro-skeleton structure formed by the pore-forming modified vapor-grown carbon fiber and the micro-pores filled with conductive carbon black in the skeleton gaps. Therefore, the first efficiency, cycle performance (capacity retention rate after 1000 cycles), and 1C constant current charging ratio of the lithium-ion battery in Example 6 are all reduced.

[0126] Since the amount of the active material ternary NCM is reduced in Example 8, its energy density is reduced compared with Example 7.

[0127] In Comparative Example 1, the vapor-grown carbon fiber was not subjected to pore-forming modification, and the porosity of the pore-formed vapor-grown carbon fiber in Comparative Example 2 and Comparative Example 3 was outside the range of 40% to 70%, thereby weakening the interaction between the pore structure of the pore-formed vapor-grown carbon fiber and the conductive carbon black nanoparticles, which is not conducive to reducing the interface resistance between the pore-formed vapor-grown carbon fiber and the conductive carbon black. As a result, Comparative Examples 1 to 3 are significantly worse than the first efficiency, cycle performance (capacity retention rate after 1000 cycles), and 1C constant current charging ratio of the corresponding lithium-ion batteries in the embodiments of the present application.

[0128] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0129] The high porosity of the pore-forming modified vapor-grown carbon fiber directly affects the electrolyte infiltration and lithium ion diffusion efficiency. Its rich pore structure provides storage space for the electrolyte and can be used as an "ion buffer pool", which is conducive to the absorption and storage of electrolyte. The conductive agent is around the main material. When the battery is charged and discharged, the main material can quickly obtain Li from the conductive agent. + , which shortens Li + On the other hand, the electrolyte is stored to reduce the local lithium ion concentration gradient, which is conducive to the rapid diffusion of lithium ions inside the electrode. 2 / g of conductive carbon black can fill the tiny gaps between active materials, forming dense point contacts and reducing the contact resistance between particles. In addition, conductive carbon black can accelerate surface ion exchange, reduce ohmic polarization by shortening the electron transmission distance, alleviate polarization, and improve capacity output at high rates. Controlling the porosity of the pore-forming modified vapor-grown carbon fiber to 40% to 70% provides more anchor points for the conductive carbon black nanoparticles. The conductive carbon black can be embedded in the pores of the pore-forming modified vapor-grown carbon fiber or attached to its surface to form a closer physical contact. The high porosity of the pore-forming modified vapor-grown carbon fiber is complemented by the nanoparticle characteristics of the conductive carbon black to construct a multi-level conductive network. This combination reduces the interface resistance between the pore-forming modified vapor-grown carbon fiber and the conductive carbon black, enhancing the overall conductivity. At the same time, the fiber reinforcement effect of the pore-forming modified vapor-grown carbon fiber is used to improve mechanical stability.

[0130] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A self-supporting dry thick electrode, characterized in that: The self-supporting dry-process thick electrode includes a current collector and an active layer superimposed on the surface of the current collector. The active layer is obtained by coating the current collector with an electrode slurry. The electrode slurry includes an active material, a binder and a conductive agent. The conductive agent includes conductive carbon black and pore-forming modified vapor-grown carbon fibers. The porosity of the pore-forming modified vapor-grown carbon fibers is 40% to 70%.

2. The self-supporting dry thick electrode according to claim 1, characterized in that: The porosity of the pore-forming modified vapor-grown carbon fiber is 50% to 60%, and / or the average pore diameter of the pore-forming modified vapor-grown carbon fiber is 5 to 10 nm, and / or the specific surface area of ​​the pore-forming modified vapor-grown carbon fiber is 20 m 2 / g~30m 2 / g.

3. The self-supporting dry thick electrode according to claim 1 or 2, characterized in that: The mass ratio of the conductive carbon black to the pore-forming modified vapor-grown carbon fiber is (1-2):1; and / or the particle size of the conductive carbon black is 35-45 nm, and the specific surface area of ​​the conductive carbon black is 50-70 m 2 / g.

4. The self-supporting dry thick electrode according to any one of claims 1 to 3, characterized in that: The mass ratio of the active material, the binder and the conductive agent is (0.92-0.97): (0.02-0.05): (0.01-0.03); and / or the active material is selected from any one or more of graphite, hard carbon, mesocarbon microbeads, lithium iron phosphate and lithium nickel cobalt manganese oxide; and / or the binder is selected from any one or more of polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber and carboxymethyl cellulose; And / or, the current collector is a carbon-coated current collector foil, and the surface roughness Ra of the carbon-coated current collector foil is 0.5 to 2 μm.

5. A method for preparing a self-supporting dry thick electrode according to any one of claims 1 to 4, characterized in that: The preparation method comprises: The raw materials including active material, binder and conductive agent are mixed and then subjected to fiberization treatment, banburying treatment, sieving granulation, roller and continuous rolling in sequence to form an active layer; Compounding the active layer with the current collector to obtain the self-supporting dry-process thick electrode; The conductive agent comprises conductive carbon black and pore-forming modified vapor-grown carbon fibers.

6. The preparation method according to claim 5, characterized in that The preparation method includes a preparation process of the pore-forming modified vapor-grown carbon fiber, and the preparation process includes: The vapor-grown carbon fiber is mixed with an oxidant and subjected to an oxidation reaction to obtain an oxidatively etched vapor-grown carbon fiber; performing a reduction reaction on the oxidatively etched vapor-grown carbon fiber and a reducing agent to obtain the pore-modified vapor-grown carbon fiber; Wherein, the temperature of the oxidation reaction is 0-5°C, and the time of the oxidation reaction is 3-5h; and / or the temperature of the reduction reaction is 80-100° C., and the time of the reduction reaction is 3-5 hours; and / or the reducing agent is selected from any one or more of formaldehyde, sodium hydroxide and ascorbic acid; The oxidant is selected from any one or more of potassium permanganate, nitric acid, concentrated sulfuric acid and hydrogen peroxide.

7. The preparation method according to claim 5 or 6, characterized in that: The fiberization treatment is carried out in a high-speed shearing manner, the linear speed of the high-speed shearing is 50 to 120 m / s, and the time of the high-speed shearing is 0.5 to 10 minutes.

8. The preparation method according to any one of claims 5 to 7, characterized in that The temperature of the banburying treatment is 20-80° C., and the time of the banburying treatment is 5-10 minutes.

9. The preparation method according to any one of claims 5 to 8, characterized in that The mixing is carried out under stirring conditions, the stirring speed is 600 to 2400 rpm / min, and the stirring time is 15 to 30 minutes; and / or the mesh number of the sieving granulation is 10 to 15 meshes; and / or the temperature of the continuous rolling is 20 to 200°C; and / or the compounding method is flat-plate hot pressing compounding or hot roller pressing compounding, and the temperatures of the flat-plate hot pressing compounding and the hot roller pressing compounding are each independently 100 to 180°C.

10. A lithium ion battery comprising a positive electrode and a negative electrode, characterized in that: The positive electrode is a self-supporting dry-process thick electrode according to any one of claims 1 to 4.

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