WO2023201871A1 - 一种负极极片及其制备方法和用途 - Google Patents

一种负极极片及其制备方法和用途 Download PDF

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WO2023201871A1
WO2023201871A1 PCT/CN2022/100402 CN2022100402W WO2023201871A1 WO 2023201871 A1 WO2023201871 A1 WO 2023201871A1 CN 2022100402 W CN2022100402 W CN 2022100402W WO 2023201871 A1 WO2023201871 A1 WO 2023201871A1
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Prior art keywords
negative electrode
electrode layer
binder
current collector
graphite
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PCT/CN2022/100402
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English (en)
French (fr)
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李峥
冯玉川
沈志鹏
陈凯
何泓材
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苏州清陶新能源科技有限公司
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Publication of WO2023201871A1 publication Critical patent/WO2023201871A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1393—Processes of manufacture of electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the embodiments of the present application relate to the technical field of lithium-ion batteries, such as a negative electrode plate and its preparation method and use.
  • CN101087021A discloses a preparation method of artificial graphite negative electrode material for lithium-ion batteries.
  • the preparation method is as follows: pulverizing coal-based or petroleum-based needle coke, preheating, adding modifiers and catalysts, drying and granulating at 800 Heat treatment in the temperature range of °C to 3000 °C for 1 to 48 hours, however, the prepared graphite material has a specific capacity of only 350mAh/g, which is far smaller than the theoretical specific capacity of graphite of 370mAh/g.
  • CN105118974A discloses a silicon-based negative electrode material and its preparation method. Due to the introduction of electrospinning equipment to integrate the silicon material into the carbon nanofibers, the problems of volume expansion of the silicon-carbon material and breakage of the silicon-carbon particles are effectively solved. At the same time, it is effective It reduces the late regeneration phenomenon of the SEI membrane and uses the nanofiber structure to effectively improve the mechanical strength of the negative electrode material. However, the low efficiency and poor consistency of electrospinning equipment make it difficult to industrialize silicon-based negative electrode materials produced by nanofibers. mass production. This patent specifically proposes a production process that is simple to prepare and easy to convert into mass production, and artificial graphite and SiO-based silicon-carbon composite anode materials have high capacity, high rate, and high conductivity.
  • Embodiments of the present application provide a negative electrode piece and its preparation method and use.
  • Embodiments of the present application provide a first negative electrode layer on the side of the negative electrode sheet close to the current collector, and the first negative electrode layer includes graphite and silicon, thereby increasing the energy density of the overall negative electrode and increasing the capacity of the negative electrode while being far away from the current collector.
  • the presence of the second graphite negative electrode layer on one side further inhibits the expansion of the silicon material, making the negative electrode sheet suitable for existing commercial and large-scale lithium-ion battery systems.
  • inventions of the present application provide a negative electrode sheet.
  • the negative electrode sheet includes a current collector, a first negative electrode layer and a second negative electrode layer.
  • the first negative electrode layer is located between the current collector and the second negative electrode layer. ;
  • the negative active material in the first negative electrode layer includes graphite and silicon materials, and the negative active material in the second negative electrode layer includes graphite; the graphite in the first negative electrode layer is carbon-coated graphite;
  • the first negative electrode layer includes a first binder and a first conductive agent; the first binder is a polyacrylonitrile binder.
  • the embodiments of this application do not specifically limit the type of silicon negative active material.
  • any known silicon negative active material can be used in this application; this is only a schematic example.
  • the silicon anode active material includes elemental silicon, silicon oxide compounds, coated silicon-based materials, etc.
  • the embodiments of this application have no special limitations on the method and type of carbon coating.
  • any known carbon coating method that can improve electronic conductivity can be used in this application; after The electronic conductivity of carbon-coated graphite has been significantly improved, overcoming the problem of low electronic conductivity of the first negative electrode layer that affects the overall internal resistance of the negative electrode layer.
  • polyacrylonitrile binder refers to a type of polymer obtained through the free polymerization reaction of monomer acrylonitrile that can be used as a binder.
  • it can be LA132 and/or LA133 binder. .
  • the embodiment of the present application uses a high-tensile negative electrode current collector, combined with a polyacrylonitrile-based binder, to ensure that the current collector can adapt to the volume change of the silicon-oxygen material.
  • the graphite provided in the embodiments of the present application is selected from one of natural graphite and artificial graphite.
  • the artificial graphite is selected from one of single particle artificial graphite, secondary particle artificial graphite, and a composite of single particle artificial graphite and secondary particle artificial graphite.
  • the second negative electrode layer is not provided in the negative electrode sheet, there will be a technical problem that the interface between the silicon-oxygen material and the electrolyte is unstable.
  • the second negative electrode layer includes a second binder and a second conductive agent.
  • the second adhesive is a water-based adhesive.
  • the bonding force between the first binder and the current collector is greater than the bonding force between the second binder and the current collector.
  • the binder in the first negative electrode layer is selected to have a stronger binding force with the current collector to further overcome the expansion caused by the introduction of silicon in the first negative electrode layer.
  • the second negative electrode layer can continue to use conventional binders.
  • the second negative electrode layer can use conventional water-based binders that are easily known to those skilled in the art, including but not Limited to polyvinyl alcohol, polyacrylic acid, polyethylene glycol, polyacrylamide, styrene-butadiene rubber or hydroxymethylcellulose, etc.
  • the mass proportion of the binder in the second negative electrode layer is greater than the mass proportion of the binder in the first negative electrode layer.
  • the mass proportion of the binder in the first negative electrode layer is 3 to 5 wt%, such as 3 wt%, 4 wt% or 5 wt%.
  • the mass proportion of the binder in the second negative electrode layer is 4 to 8 wt%, such as 4 wt%, 5 wt%, 6 wt%, 7 wt% or 8 wt%.
  • the current collector of the first negative electrode layer is made of a high tensile material.
  • the current collector matches the high expansion performance of the first negative electrode layer and can further resist the expansion of the first negative electrode layer caused by the introduction of silicon. .
  • the tensile strength of the current collector is greater than or equal to 350N/cm 2 , such as 360N/cm 2 , 380N/cm 2 , 400N/cm 2 , 450N/cm 2 , 480N/cm 2 or 500N/cm 2 , etc.
  • the embodiment of this application uses a high-tensile negative electrode current collector, combined with a polyacrylonitrile-based binder, to ensure that the current collector can adapt to the volume change of the silicon-oxygen material.
  • the mass of silicon material in the first negative electrode layer is 3% to 5% of the negative electrode active material in the first negative electrode layer.
  • the graphite in the first negative electrode layer is carbon-coated graphite, which can improve the conductivity of the first negative electrode layer.
  • the silicon material includes silicon-oxygen material.
  • the mass proportion of the first conductive agent in the first negative electrode layer is greater than the mass proportion of the second conductive agent in the second negative electrode layer.
  • the first conductive agent includes any one or a combination of at least two of CNT, VGCF, super P, carbon black, acetylene black, or graphene.
  • the mass proportion of the CNT and/or VGCF in the first conductive agent is 15 to 25 wt%.
  • the selection of the second conductive agent includes but is not limited to carbon-based materials, powdered nickel or other metal particles or conductive polymers.
  • the carbon-based materials may include carbon black, graphite, superP, acetylene black (such as, KETCHENTM black or DENKATM black), carbon fibers and nanotubes, graphene, etc.
  • conductive polymers include polyaniline, polythiophene, polyacetylene, polypyrrole, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate wait.
  • the mass proportion of the first conductive agent in the first negative electrode layer is larger than the conventional mass proportion. This can better realize the transmission of electrons during the charging and discharging process and prevent the addition of silicon-oxygen material from causing The conductive performance of the negative electrode layer decreases. On the other hand, the expansion of the silicon-oxygen material will cause the electron transmission path to be destroyed, thus affecting the electron transmission.
  • the thickness of the first negative electrode layer is 5% to 40% of the thickness of the second negative electrode layer, such as 5%, 8%, 10%, 13%, 15%, 18%, 20%, 23%. , 25%, 28%, 30%, 33%, 35%, 38% or 40%, preferably 16 to 25%.
  • the thickness of the first negative electrode layer is in the range of 16% to 25% of the thickness of the second negative electrode layer, which can better achieve the technical effect of improving the battery energy density and cycle retention rate, and if the first negative electrode layer If the thickness of the negative electrode layer is too thick, the expansion coefficients of the two sides of the first negative electrode layer close to the current collector and those far away from the current collector will be different, which can easily cause the electrode piece to fall off and peel between the first negative electrode layer and the second negative electrode layer. If the first negative electrode layer is too thick, the expansion coefficient will be different. If the thickness of the negative electrode layer is too small, the effect of increasing energy density will not be obvious.
  • the thickness of the first negative electrode layer is 16 to 55 ⁇ m, such as 16 ⁇ m, 18 ⁇ m, 20 ⁇ m, 23 ⁇ m, 25 ⁇ m, 28 ⁇ m, 30 ⁇ m, 33 ⁇ m, 35 ⁇ m, 38 ⁇ m, 40 ⁇ m, 43 ⁇ m, 45 ⁇ m, 48 ⁇ m, 50 ⁇ m, 53 ⁇ m or 55 ⁇ m. wait.
  • the thickness of the second negative electrode layer is 170-210 ⁇ m, such as 170 ⁇ m, 175 ⁇ m, 180 ⁇ m, 185 ⁇ m, 190 ⁇ m, 195 ⁇ m, 200 ⁇ m, 205 ⁇ m or 210 ⁇ m, etc.
  • the coating area density of the first negative electrode layer is 30-50g/m 2 , such as 30g/m 2 , 33g/m 2 , 35g/m 2 , 38g/m 2 , 40g/m 2 , 43g/m 2 , 45g/m 2 , 48g/m 2 or 50g/m 2 , etc.
  • the area density of the second negative electrode layer is 150-170g/m 2 , such as 150g/m 2 , 155g/m 2 , 160g/m 2 , 165g/m 2 or 170g/m 2 etc.
  • embodiments of the present application provide a method for preparing the negative electrode sheet as described in the first aspect, the preparation method comprising:
  • the slurry of the first negative electrode layer is applied to the surface of the current collector to obtain the first negative electrode layer, and the slurry of the second negative electrode layer is applied to the surface of the first negative electrode layer to obtain the negative electrode piece.
  • the preparation of the slurry of the first negative electrode layer and the slurry of the second negative electrode layer are conventional technical means.
  • the preparation method of the negative electrode layer slurry includes: mixing the negative electrode active material, the binder, the solvent and the conductive agent to obtain the negative electrode layer slurry.
  • embodiments of the present application further provide a lithium-ion battery, which includes the negative electrode plate as described in the first aspect.
  • the lithium-ion battery provided in the embodiment of the present application can be a liquid battery or a solid-state battery, and is not particularly limited.
  • the negative electrode piece When it is a liquid lithium ion battery, it includes the negative electrode piece, the positive electrode piece, the separator and the electrolyte as described in the first aspect.
  • the positive electrode plate, separator and electrolyte in a liquid lithium-ion battery are all easily known and available to those skilled in the art, that is, the corresponding materials and preparation methods that can be assembled to obtain a complete lithium-ion battery are applicable.
  • the negative electrode sheet When it is a solid-state lithium-ion battery, it includes the negative electrode sheet, the positive electrode sheet and the solid electrolyte layer as described in the first aspect.
  • the positive electrode sheet and solid electrolyte layer in solid-state lithium-ion batteries are easily known and available to those skilled in the art, that is, the corresponding materials and preparation methods that can be assembled to obtain a complete lithium-ion battery are applicable.
  • the negative electrode sheet provided in the embodiment of the present application has a first negative electrode layer on the side close to the current collector, and the first negative electrode layer includes both graphite and silicon, which increases the energy density of the overall negative electrode, increases the capacity of the negative electrode, and is far away from the current collector.
  • the existence of the second graphite negative electrode layer on the side of the current collector further inhibits the expansion of the silicon material.
  • the first-cycle expansion rate improves the energy density of traditional graphite-based negative electrode lithium batteries and increases the cycle life of the battery, making it suitable for existing commercial and large-scale lithium-ion battery systems.
  • the preparation method is simple and does not require Complex preparation steps.
  • the battery provided by this application has a negative electrode gram capacity of more than 375mAh/g at 0.33C, an expansion rate of the negative electrode in the first cycle of less than 38%, and a capacity retention rate of more than 85.8% after 500 cycles.
  • the capacity of the negative electrode layer can be further adjusted. After considering the thickness, the proportion of silicon material and the adhesiveness of the first binder, the gram capacity of the negative electrode at 0.33C can reach more than 375mAh/g, the expansion rate of the negative electrode in the first cycle is less than 30%, and the capacity remains after 500 cycles. The rate can reach over 93.4%.
  • the negative electrode for lithium batteries of the present application includes a current collector and a first negative electrode layer and a second negative electrode layer on it.
  • the first negative electrode layer includes 95 to 97 wt% of carbon-coated graphite material and 3 to 5 wt% of silicon oxide compound.
  • the second negative electrode layer uses 100% graphite as an active material material and includes a second binder and a second conductive agent.
  • the above percentages are the proportion of the negative electrode active material rather than the proportion of the negative electrode layer.
  • 95 to 97 wt% means that the carbon-coated graphite material accounts for 95 to 97 wt of the negative electrode active material in the first negative electrode layer. %.
  • the polyacrylonitrile binders mentioned in this application include but are not limited to copolymers of the monomer acrylonitrile and simple deformations of the copolymers, such as simple functional group substitutions, changes in functional group positions, changes in the number of functional groups and the number of monomers.
  • the resulting polymer has unchanged bonding properties.
  • the first negative electrode layer includes: a negative active material composed of 95 to 97 wt% graphite material and 3 to 5 wt% silicon oxide compound, accounting for 90 to 97 wt% of the first negative electrode layer.
  • the layer contains 3 to 5 wt% polyacrylonitrile binder and 1 to 5 wt% of the first conductive agent. More specifically, the first conductive agent also includes 15 to 20 wt% of CNT and/or VGCF.
  • the silicon oxygen compound in the first negative electrode layer active material When the silicon oxygen compound in the first negative electrode layer active material When the weight ratio is greater than 5wt%, it is difficult to suppress the expansion of the silicon-oxygen compound during the charge and discharge process, causing the performance of the battery to deteriorate. When the weight ratio of the silicon-oxygen compound in the active material of the first negative electrode layer is less than 3wt%, the performance of the lithium battery will deteriorate. The energy density increase is not obvious.
  • the first conductive agent includes at least one or both of CNT or VGCF.
  • the fibrous structure of CNT and VGCF has a certain aspect ratio, which is conducive to the formation of linear conductive channels in the first negative electrode layer when the silicon oxide compound expands, improving the transmission efficiency of lithium ions and electrons. Ensure that the battery's capacity performance and cycle performance do not deteriorate.
  • the aspect ratio of CNT and VGCF is >1000; preferably, the aspect ratio of CNT and VGCF is >2000.
  • the second negative electrode layer includes: a second negative electrode active material, 4 to 8 wt% of a binder, and 1 to 5 wt% of a second conductive agent.
  • the second negative electrode layer includes: : Graphite as the only active material material, 4-8wt% binder, and 1-3wt% second conductive agent.
  • the second negative electrode active material may be a mixture of one or more negative electrode active materials, but its expansion performance should be smaller than that of the first negative electrode layer; therefore, as a preferred embodiment, the second negative electrode active material
  • the negative active material is entirely composed of graphite negative active material.
  • the bonding force of the first binder to the current collector is greater than that of the second binder, and the content of the binder in the second negative electrode layer is greater than the content of the binder in the first negative electrode layer;
  • This application uses a negative electrode system with high binder content.
  • the first negative electrode layer has a stronger interaction with the current collector to avoid the problem of pole piece falling off caused by silicon expansion.
  • the content of the second binder in this application is greater than the content of the first binder based on the selection of the second negative electrode layer being far away from the current collector.
  • the projected area of the second negative electrode layer on the current collector is greater than or equal to the projected area of the first negative electrode on the current collector.
  • the graphite material may be selected from natural graphite and artificial graphite.
  • the artificial graphite is selected from one of the group consisting of single particle artificial graphite, secondary particle artificial graphite, and a composite of single particle artificial graphite and secondary particle artificial graphite.
  • the graphite in the first negative electrode layer is carbon-coated graphite.
  • carbon-coated graphite can help compensate for the decrease in conductivity of the entire negative electrode layer caused by the addition of silicon-oxygen compounds.
  • silicon-oxygen compounds when silicon-oxygen compounds are added, When the compound expands, the conductive agent can form a conductive network, effectively avoiding the destruction of the conductive path caused by the expansion of silicon.
  • Carbon coating of graphite is known in the art, such as coating the surface of graphite with a carbonaceous coating layer. This application has no special requirements on the actual carbon coating method. On the basis of not violating the concept of this application, any known carbon coating method or structure can be used in this application.
  • This application improves the energy density of the overall negative electrode and increases the capacity of the negative electrode by arranging a first negative electrode layer on the side of the negative electrode sheet close to the current collector, and the first negative electrode layer includes graphite and silicon, while also increasing the capacity of the negative electrode.
  • the use of a graphite negative electrode with small expansion further suppresses the expansion of the first negative electrode layer, making the negative electrode sheet suitable for the existing commercial lithium-ion battery system used on a large scale.
  • this application chooses to add silicon material close to the current collector. in the first negative electrode layer. The expansion caused by the addition of silicon is avoided through the interaction between the negative electrode layer and the current collector.
  • the negative electrode current collector is selected from a current collector with high tensile properties.
  • it can be a copper foil; preferably, the tensile strength of the negative electrode current collector is greater than or equal to 350 N/cm. 2 .
  • the first negative electrode layer includes a first binder and a first conductive agent
  • the first negative electrode layer includes a first binder and a first conductive agent
  • the first adhesive is a polyacrylonitrile adhesive
  • the first conductive agent includes one or more combinations of carbon black, super-P, CNT, VGCF, acetylene black, graphene.
  • the first conductive agent contains at least 15 wt% to 25 wt% CNT and/or VGCF.
  • the second negative electrode layer includes a second binder and a second conductive agent
  • the binder in the first negative electrode layer is selected to have a stronger binding force with the current collector to further overcome the expansion caused by the introduction of silicon in the first negative electrode layer.
  • the second negative electrode layer can continue to use conventional binders.
  • the second negative electrode layer can use conventional water-based binders that are easily known to those skilled in the art, including but not Limited to polyvinyl alcohol, polyacrylic acid, polyethylene glycol, polyacrylamide, styrene-butadiene rubber or hydroxymethylcellulose, etc.
  • the selection of the second conductive agent includes but is not limited to carbon-based materials, powdered nickel or other metal particles or conductive polymers.
  • the carbon-based materials may include carbon black, graphite, superP, acetylene black (such as KETCHENTM black or DENKATM black), carbon fiber and nanotubes, graphene, etc. particles;
  • conductive polymers include polyaniline, polythiophene, polyacetylene, polypyrrole, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, etc.
  • the thickness of the first negative electrode layer is 5% to 40% of the thickness of the second negative electrode layer, such as 5%, 8%, 10%, 13%, 15%, 18%, 20%, 23%. , 25%, 28%, 30%, 33%, 35%, 38% or 40%, preferably 16% to 25%.
  • the thickness of the first negative electrode layer is in the range of 16% to 25% of the thickness of the second negative electrode layer, which can better achieve the technical effect of improving the battery energy density and cycle retention rate, and if the first negative electrode layer If the thickness of the layer is too thick, the expansion coefficients of the two sides of the first negative electrode layer close to the current collector and those far away from the current collector will be different, which may easily cause the electrode piece to fall off and the first negative electrode layer and the second negative electrode layer to peel off. If the thickness of the layer is too small, the effect of increasing energy density will not be obvious.
  • the thickness of the first negative electrode layer is 16 to 55 ⁇ m, such as 16 ⁇ m, 18 ⁇ m, 20 ⁇ m, 23 ⁇ m, 25 ⁇ m, 28 ⁇ m, 30 ⁇ m, 33 ⁇ m, 35 ⁇ m, 38 ⁇ m, 40 ⁇ m, 43 ⁇ m, 45 ⁇ m, 48 ⁇ m, 50 ⁇ m, 53 ⁇ m or 55 ⁇ m. wait.
  • the thickness of the second negative electrode layer is 170-210 ⁇ m, such as 170 ⁇ m, 175 ⁇ m, 180 ⁇ m, 185 ⁇ m, 190 ⁇ m, 195 ⁇ m, 200 ⁇ m, 205 ⁇ m or 210 ⁇ m, etc.
  • the present application provides a method for preparing the negative electrode sheet as described in the first aspect, the preparation method comprising:
  • the slurry of the first negative electrode layer is applied to the surface of the current collector to obtain the first negative electrode layer, and the slurry of the second negative electrode layer is applied to the surface of the first negative electrode layer to obtain the negative electrode piece.
  • the area density of the first negative electrode layer is 30-50g/m 2 , such as 30g/m 2 , 35g/m 2 , 40g/m 2 , 45g/m 2 or 50g/m 2 , etc.
  • the areal density of the second negative electrode layer is 150-170g/m 2 , such as 150g/m 2 , 155g/m 2 , 160g/m 2 , 165g/m 2 or 170g/m 2 , etc.;
  • This application provides a lithium battery including the above-mentioned negative electrode.
  • the lithium battery includes a positive electrode, a negative electrode, an electrolyte, and a battery casing including the above structure.
  • the positive electrode includes a current collector and a positive active material layer formed on the current collector;
  • the positive electrode current collector is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery. Specifically, copper, stainless steel, aluminum, nickel, titanium, or a metal current collector whose surface is treated with carbon or other substances can be used.
  • the positive electrode current collector may generally have a thickness of 3 ⁇ m to 500 ⁇ m.
  • the positive electrode current collector may have fine unevenness formed on its surface to improve adhesion of the positive electrode active material.
  • various shapes of positive electrode current collectors such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabric bodies can be used.
  • the positive active material layer may include a positive active material.
  • the positive electrode active material is a compound capable of reversibly intercalating and deintercalating lithium. Specifically, it may include a lithium transition metal composite oxide containing lithium and at least other elements selected from the group consisting of nickel, cobalt, manganese and aluminum. A transition metal; preferably, it may include transition metals such as lithium and nickel, cobalt or manganese.
  • the lithium transition metal composite oxide may be a lithium manganese-based oxide (such as LiMnO 2 , LiMn 2 O 4 , etc.), a lithium cobalt-based oxide (such as LiCoO 2 , etc.), a lithium nickel-based oxide (such as LiNiO 2, etc.), lithium nickel manganese oxides (such as LiNi 1-y Mn y O 2 (where 0 ⁇ y ⁇ 1), LiMn 2-z Ni z O 4 (where 0 ⁇ z ⁇ 2), etc.), lithium Nickel-cobalt oxides (such as LiNi 1-y1 Co y1 O 2 (where 0 ⁇ y 1 ⁇ 1), etc.), lithium manganese-cobalt oxides (such as LiCo 1-y2 Mn y2 O 2 (where 0 ⁇ y 2 ⁇ 1), LiMn 2-z1 Co z1 O 4 (where 0 ⁇ z 1 ⁇ 2), etc.), lithium nickel manganese cobalt oxides (such as Li(Ni p Co q Mn
  • the lithium transition metal composite oxide can be LiCoO 2 , LiMnO 2 , LiNiO 2 , lithium nickel manganese cobalt oxide (such as Li(Ni 0.6 Mn 0.2 Co 0.2 )O 2 , Li(Ni 0.5 Mn 0.3 Co 0.2 )O 2 , Li(Ni 0.7 Mn 0.15 Co 0.15 )O 2 or LiNi 0.8 Mn 0.1 Co 0.1 )O 2, etc., or lithium nickel cobalt aluminum oxide materials (such as Li(Ni 0.8 Co 0.15 Al 0.05 )O 2 , etc.).
  • lithium nickel manganese cobalt oxide such as Li(Ni 0.6 Mn 0.2 Co 0.2 )O 2 , Li(Ni 0.5 Mn 0.3 Co 0.2 )O 2 , Li(Ni 0.7 Mn 0.15 Co 0.15 )O 2 or LiNi 0.8 Mn 0.1 Co 0.1 )O 2, etc.
  • lithium nickel cobalt aluminum oxide materials such as Li(Ni 0.8 Co
  • the lithium The transition metal composite oxide may be Li(Ni 0.6 Mn 0.2 Co 0.2 )O 2 , Li(Ni 0.5 Mn 0.3 Co 0.2 )O 2 , Li(Ni 0.7 Mn 0.15 Co 0.15 )O 2 or Li(Ni 0.8 Mn 0.1 Co 0.1 ) O2, etc., and any one thereof or a mixture of two or more thereof may be used.
  • the amount of the positive active material included in the positive active material layer may be 80 wt% to 99 wt%, preferably 92 wt% to 98.5 wt%.
  • the positive electrode active material layer may also include a positive electrode binder and/or a positive electrode conductive material.
  • the positive electrode binder is used to bind active materials, conductive materials, current collectors and other components together.
  • it can include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC) selected from the group consisting of At least one of the group consisting of , starch, hydroxypropyl cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, styrene-butadiene rubber and fluorine rubber One, preferably polyvinylidene fluoride.
  • CMC carboxymethylcellulose
  • the amount of the cathode binder contained in the cathode active material layer may be 1 to 20 wt%, preferably 1.2 to 10 wt%.
  • the conductive material is mainly used to assist and improve conductivity in secondary batteries, and is not particularly limited as long as it has conductivity without causing chemical changes.
  • the conductive material may include graphite, such as natural graphite or artificial graphite; carbon materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black and thermal black; Conductive fibers, such as carbon fibers and metal fibers; conductive tubes, such as carbon nanotubes; metal powders, such as fluorocarbon powders, aluminum powders and nickel powders; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and polyphenylene derivatives, and carbon black may be preferably included from the perspective of improving conductivity.
  • the specific surface area of the positive conductive material may be 80 m 2 /g to 200 m 2 /g, preferably 100 m 2 /g to 150 m 2 /g.
  • the amount of the positive conductive material included in the positive active material layer may be 1 to 20 wt%, preferably 1.2 to 10 wt%.
  • the thickness of the cathode active material layer may be 30 ⁇ m to 400 ⁇ m, preferably 50 ⁇ m to 110 ⁇ m.
  • the positive electrode can be manufactured by coating a positive electrode slurry containing a positive electrode active material and a selective positive electrode binder, a positive electrode conductive material, and a solvent for forming the positive electrode slurry on a positive electrode current collector, and then drying and rolling.
  • the solvent for forming the positive electrode slurry may include an organic solvent, such as N-methyl-2-pyrrolidone (NMP), and the amount may be such that the positive electrode active material is included and optionally includes a positive electrode binder, a positive electrode conductive material, etc. to obtain optimal viscosity.
  • NMP N-methyl-2-pyrrolidone
  • the amount of the positive electrode slurry-forming solvent included in the positive electrode slurry may be such that the concentration of solids including the positive electrode active material and optionally the positive electrode binder and the positive electrode conductive material is 50 wt% to 95 wt%, Preferably 70wt% to 90wt%.
  • the electrolyte may be a liquid electrolyte, a solid electrolyte, or a mixture of a solid electrolyte and a liquid electrolyte.
  • a separator should also be installed in the battery system.
  • the main function of the separator is to separate the negative electrode from the positive electrode and provide a path for the movement of lithium ions.
  • Any separator can be used without particular limitation as long as it is a separator commonly used in secondary batteries.
  • a separator having excellent electrolyte wettability and low resistance to ion movement in the electrolyte is preferred.
  • porous polymer films may be used, for example, polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene/butene copolymers, ethylene/hexene copolymers and ethylene/methacrylate copolymers
  • a typical porous nonwoven fabric for example, a nonwoven fabric formed of glass fiber, polyethylene terephthalate fiber, etc. having a high melting point can be used.
  • a coated separator containing a ceramic component or polymer material can be used to ensure heat resistance or mechanical strength, and can be selectively used in a single-layer or multi-layer structure.
  • the electrolyte used in the present application may be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc. that can be used in the production of secondary batteries, but it is not Limited to this.
  • the electrolyte may include an organic solvent and a lithium salt.
  • organic solvent may be used without particular limitation as long as it can serve as a medium through which ions participating in the electrochemical reaction of the battery can move.
  • organic solvent ester solvents such as methyl acetate, ethyl acetate, ⁇ -butyrolactone and ⁇ -caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents can be used.
  • cyclohexanone such as cyclohexanone
  • aromatic hydrocarbon solvents such as benzene and fluorobenzene
  • carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl carbonate Methyl ester (EMC), ethylene carbonate (EC) and propylene carbonate (PC); alcoholic solvents such as ethanol and isopropanol; nitriles such as R-CN (where R is linear, branched or cyclic C2-C20 hydrocarbon group, and may contain a double bond aromatic ring or ether bond); amide, such as dimethylformamide; dioxolane, such as 1,3-dioxolane; or sulfolane.
  • DMC dimethyl carbonate
  • DEC diethyl carbonate
  • MEC methyl ethyl carbonate
  • EMC ethyl carbonate Methyl ester
  • carbonate-based solvents are preferred, and cyclic carbonates (such as ethylene carbonate or propylene carbonate) with high ion conductivity and high dielectric constant that can increase the charge/discharge performance of the battery Mixtures with low viscosity linear carbonate compounds such as ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate are more preferred.
  • cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte may be excellent.
  • any compound can be used as the lithium salt without particular limitation as long as it can provide lithium ions used in lithium secondary batteries.
  • LiPF 6 , LiClO 4 , LiAsF 6 , LiBF 4 , LiSbF6, LiAlO 4 , LiAlCl 4 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiN(C 2 F 5 SO 3 ) 2 , LiN(C 2 F5SO2 ) 2 , LiN ( CF3SO2 ) 2 , LiCl, LiI, LiB( C2O4 ) 2 , etc. can be used as the lithium salt.
  • the lithium salt can be used in a concentration range of 0.1-2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, thereby exhibiting excellent performance, and lithium ions can move efficiently.
  • the electrolyte may be a solid electrolyte
  • the solid electrolyte particles may include one or more polymer components, oxide solid electrolytes, sulfide solid electrolytes, halide solid electrolytes, borate solid electrolytes, nitrogen chemical solid electrolyte or hydride solid electrolyte.
  • lithium salts should be used for review.
  • the polymer-based component may comprise one or more polymeric materials selected from the group consisting of: polyethylene glycol, polyethylene oxide (PEO), poly(p-phenylene) ether) (PPO), poly(methyl methacrylate) (PMMA), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polyvinylidene fluoride co-hexafluoropropylene (PVDF-HFP), poly Vinyl chloride (PVC) and their combinations.
  • PEO polyethylene oxide
  • PPO poly(p-phenylene) ether)
  • PMMA poly(methyl methacrylate)
  • PAN polyacrylonitrile
  • PVDF polyvinylidene fluoride
  • PVDF-HFP polyvinylidene fluoride co-hexafluoropropylene
  • PVC poly Vinyl chloride
  • the oxide particles may include one or more of garnet ceramics, LISICON-type oxides, NASICON-type oxides, and perovskite-type ceramics.
  • the garnet ceramic may be selected from the group consisting of: Li 6.5 La 3 Zr 1.75 Te 0.25 O 12 , Li 7 La 3 Zr 2 O 12 , Li 6.2 Ga 0.3 La 2.95 Rb 0.05 Zr 2 O 12. Li 6.85 La 2.9 Ca 0.1 Zr 1.75 Nb 0.25 O 12 , Li 6.25 Al 0.25 La 3 Zr 2 O 12 , Li 6.75 La 3 Zr 1.75 Nb 0.25 O 12 , Li 6.75 La 3 Zr 1.75 Nb 0.25 O 12 and their combination.
  • the LISICON type oxide may be selected from the group consisting of Li 14 Zn(GeO 4 ) 4 , Li 3+x (P 1-x Si x )O4 (where 0 ⁇ x ⁇ 1), Li 3+x Ge x V 1-x O 4 (where 0 ⁇ x ⁇ 1) and their combinations.
  • NASICON-type oxides can be defined by LiMM'( PO4 ) 3 , where M and M' are independently selected from Al, Ge, Ti, Sn, Hf, Zr and La.
  • the NASICON type oxide may be selected from the group comprising Li 1+x Al x Ge 2-x (PO 4 ) 3 (LAGP) (where 0 ⁇ x ⁇ 2), Li 1+x Al x Ti 2-x (PO 4 ) 3 (LATP) (where 0 ⁇ x ⁇ 2), Li 1+x Y x Zr 2-x ( PO 4 ) 3 (LYZP) (where 0 ⁇ x ⁇ 2), Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 , LiTi 2 (PO 4 ) 3 , LiGeTi(PO 4 ) 3 , LiGe 2 (PO 4 ) 3 , LiHf 2 (PO 4 ) 3 and their combinations.
  • the one or more perovskite-type ceramics may be selected from the group consisting of Li 3.3 La 0.53 TiO 3 , LiSr 1.65 Zr 1.3 Ta 1.7 O 9 , Li 2x-y Sr 1-x Ta y Zr 1-y O 3 (where _ _ _ _ _ ⁇ x ⁇ 0.25) and their combinations.
  • the one or more oxide-based materials may have an ionic conductivity of greater than or equal to about 10 ⁇ 5 S/cm to less than or equal to about 10 ⁇ 1 S/cm.
  • the sulfide solid-state electrolyte is one or more sulfide-based materials selected from the group consisting of Li 2 SP 2 S 5 , Li 2 SP 2 S 5 -MSx (where M is Si, Ge and Sn and 0 ⁇ x ⁇ 2), Li 3.4 Si 0.4 P 0.6 S 4 , Li 10 GeP 2 S 11.7 O 0.3 , Li 9.6 P 3 S 12 , Li 7 P 3 S 11 , Li 9 P 3 S 9 O 3 , Li 10.35 Si 1.35 P 1.65 S 12 , Li 9.81 Sn 0.81 P 2.19 S 12 , Li 10 (Si 0.5 Ge 0.5 )P 2 S 12 , Li(Ge 0.5 Sn 0.5 )P 2 S 12 , Li(Si 0.5 Sn 0.5 )PsS 12 , Li 10 GeP 2 S 12 ( LGPS ) , Li 6 PS 5 _ 4 , Li 10 SnP 2 S 12 , Li 10 SiP 2 S 12 , Li 9.54 Si 1.74 P 1.44
  • the halide solid-state electrolyte may include one or more halide-based materials selected from the group consisting of Li 2 CdCl 4 , Li 2 MgCl 4 , Li 2 CdI 4 , Li 2 ZnI 4 , Li 3 OCl, LiI, Li 5 ZnI 4 , Li 3 OCl 1-x Brx (where 0 ⁇ x ⁇ 1) and combinations thereof.
  • the borate solid electrolyte is one or more borate-based materials selected from the group consisting of: Li 2 B 4 O 7 , Li 2 O-(B 2 O 3 )-(P 2 O 5) and their combinations.
  • the nitride solid-state electrolyte may be selected from one or more nitride-based materials from the group including Li 3 N, Li 7 PN 4 , LiSi 2 N 3 , LiPON, and combinations thereof.
  • the hydride solid-state electrolyte may be one or more hydride-based materials selected from the group consisting of Li 3 AlH 6 , LiBH 4 , LiBH 4 -LiX (where X is one of Cl, Br and I ), LiNH 2 , Li 2 NH, LiBH 4 -LiNH 2 and combinations thereof.
  • the solid electrolyte may be a quasi-solid electrolyte comprising a mixture of the non-aqueous liquid electrolyte solution and solid electrolyte system detailed above, for example, including one or more ionic liquids and one or more Various metal oxide particles such as aluminum oxide (Al 2 O 3 ) and/or silicon dioxide (SiO 2 ).
  • This embodiment provides a negative electrode piece, based on the negative electrode piece provided in the above specific embodiment:
  • the thickness of the first negative electrode layer is 40 ⁇ m, and the thickness of the second negative electrode layer is 200 ⁇ m.
  • the first negative electrode layer is located between the current collector and the second negative electrode layer.
  • the thickness of the first negative electrode layer is 20% of the thickness of the second negative electrode layer.
  • the first negative electrode layer is SiO, carbon-coated artificial graphite, polyacrylonitrile and carbon nanotubes (the mass ratio of SiO to carbon-coated artificial graphite is 4:96), and the second negative electrode layer is artificial graphite, conductive carbon black and polyacrylic acid;
  • the preparation method of the negative electrode piece is as follows:
  • This embodiment provides a negative electrode piece, based on the negative electrode piece provided in the above specific embodiment:
  • the thickness of the first negative electrode layer is 30 ⁇ m, the thickness of the second negative electrode layer is 180 ⁇ m, the first negative electrode layer is located between the current collector and the second negative electrode layer, the thickness of the first negative electrode layer is 16.7 and the thickness of the second negative electrode layer is 16.7;
  • the first negative electrode layer is SiO, carbon-coated artificial graphite, polyacrylonitrile and carbon fiber (the mass ratio of SiO to carbon-coated artificial graphite is 3:97), and the second negative electrode layer is artificial graphite and conductive carbon black. , styrene-butadiene rubber and sodium carboxymethyl cellulose;
  • the preparation method of the negative electrode piece is as follows:
  • This embodiment provides a negative electrode piece, based on the negative electrode piece provided in the above specific embodiment:
  • the first negative electrode thickness is 52 ⁇ m, the thickness of the second negative electrode layer is 208 ⁇ m
  • the first negative electrode layer is located between the current collector and the second negative electrode layer, the thickness of the first negative electrode layer is 1/1 of the thickness of the second negative electrode layer 4;
  • the first negative electrode layer is SiO, carbon-coated artificial graphite, polyacrylonitrile and carbon nanotubes (the mass ratio of SiO to carbon-coated artificial graphite is 5:95), and the second negative electrode layer is artificial graphite, conductive Carbon black and polyacrylic acid.
  • the thickness of the first negative electrode layer is 100 ⁇ m, and the thickness of the first negative electrode layer is 50% of the thickness of the second negative electrode layer.
  • Example 1 The difference between this embodiment and Example 1 is that in this embodiment, the mass ratio of SiO to carbon-coated artificial graphite is 8:92.
  • the binder of the first negative electrode layer in this embodiment is CMC+SBR.
  • Example 1 The difference between this comparative example and Example 1 is that the negative electrode layer in this comparative example is only one layer, and the negative electrode active material is pure artificial graphite.
  • Example 1 The difference between this comparative example and Example 1 is that the negative electrode layer in this comparative example is only one layer, and the composition of the negative electrode active material is the same as that of the first negative electrode layer in Example 1.
  • Positive electrode sheet Weigh NCM811, polyvinylidene fluoride, and conductive carbon black in a mass ratio of 90:5:5, disperse them in NMP, prepare positive electrode slurry, apply it on the surface of the aluminum foil, dry and roll The positive electrode piece is formed and die-cut into the corresponding shape.
  • the negative electrode sheet provided in Examples 1-6 and Comparative Examples 1-2 is used as the negative electrode, the prepared positive electrode sheet is used as the positive electrode, a polyolefin separator is used, ethylene carbonate is used as the electrolyte, and LiCF 3 SO is added to the electrolyte. 3. Get the battery.
  • the electrochemical performance test was performed on the batteries provided in Examples 1-6 and Comparative Examples 1-2.
  • the test conditions were as follows: 25°C and a constant current of 0.33C for charge and discharge tests. The results are shown in Table 1.
  • Example 1 and Example 5 It can be seen from the data results of Example 1 and Example 5 that the mass proportion of silicon material in the first negative electrode layer is too large. Although it can effectively increase the energy density of the battery, it will also affect the first-cycle expansion rate of the negative electrode, resulting in battery The cycle retention rate decreases.
  • Example 1 From the data results of Example 1 and Comparative Example 1, it can be seen that compared with the pure graphite negative electrode, the capacity of the negative electrode provided by the present application has been significantly improved while maintaining a lower expansion rate and better cycle stability. .
  • Example 1 From the data results of Example 1 and Comparative Example 2, it can be seen that compared with the single-layer negative electrode structure, the negative electrode provided by the present application has a higher capacity, a significantly lower expansion rate, and better cycle stability.
  • the negative electrode sheet provided by the embodiment of the present application has a first negative electrode layer on the side close to the current collector, and the first negative electrode layer includes both graphite and silicon, which improves the energy density of the overall negative electrode and improves the efficiency of the negative electrode. capacity, and the existence of the second graphite negative electrode layer on the side away from the current collector further inhibits the expansion of the silicon material, making it suitable for existing commercial and large-scale lithium-ion battery systems, and the preparation method is simple , without complicated preparation steps.
  • the battery provided by this application has a negative electrode gram capacity of more than 375mAh/g at 0.33C, an expansion rate of the negative electrode in the first cycle of less than 38%, and a capacity retention rate of more than 85.8% after 500 cycles.
  • the capacity of the negative electrode layer can be further adjusted. After considering the thickness, the proportion of silicon material and the adhesiveness of the first binder, the gram capacity of the negative electrode at 0.33C can reach more than 375mAh/g, the expansion rate of the negative electrode in the first cycle is less than 30%, and the capacity remains after 500 cycles. The rate can reach over 93.4%.

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Abstract

一种负极极片及其制备方法和用途。负极极片包括集流体、第一负极层和第二负极层，第一负极层位于集流体和第二负极层之间；其中，第一负极层中的负极活性物质包括石墨和硅材料，第二负极层中的负极活性物质包括石墨。通过在负极极片的靠近集流体一侧设置第一负极层，且第一负极层中包括石墨和硅，提高了整体负极的能量密度，提升了负极的容量，同时远离集流体一侧的第二负极层的存在，进一步地抑制了硅材料的膨胀，使得负极极片适配于现有的商业化大规模使用的锂离子电池体系。

Description

一种负极极片及其制备方法和用途 技术领域
本申请实施例涉及锂离子电池技术领域，例如一种负极极片及其制备方法和用途。
背景技术
随着锂离子电池的大范围商业化使用，锂离子电池的容量、循环性能、安全性能收到广泛关注，其中石墨作为一种较早使用到锂离子电池负极的材料，因其导电性好，结晶度高，具有良好的层状结构，适合Li +的脱出/嵌入。目前，投入汽车等较大型设备使用的电池多以石墨为负极材料，存在容量较低的问题，为提高电池的容量性能，有技术人员提出使用硅碳材料代替石墨作为锂离子电池的负极，但硅基材料存在易膨胀的问题，循环寿命差，多次循环后发生负极材料坍塌和从集流体上脱落的现象。而且现在硅碳负极的相关研究大多还处于实验室阶段，
CN101087021A公开了一种锂离子电池用人造石墨负极材料的制备方法，其制备方法为：将煤系或石油系针状焦粉碎，预热处理，添加改性剂和催化剂，干燥制粒，在800℃～3000℃温度范围内热处理1～48小时，然而制备得到的石墨材料，其比容量也只有350mAh/g，远小于石墨的理论比容量370mAh/g。
CN105118974A公开了一种硅基负极材料及其制备方法，由于引入静电纺丝设备把硅材料融入碳纳米纤维中，从而有效解决了硅碳材料的体积膨胀和硅碳颗粒破碎的问题，同时有效的降低了SEI膜的后期重生现象，利用纳米纤维结构有效提高了负极材料的机械强度，可静电纺丝设备效率低，一致性差的问题使得纳米纤维这种方式生产的硅基负极材料很难实现工业化量产。此专利针对性的提出制备工艺简单，量产转化容易的生产工艺且人造石墨、SiO基硅碳复合负极材料具备高容量，高倍率，高导电率的负极材料。
因此，如何提升石墨负极的容量，又能降低负极活性材料的膨胀，且适配于现有的商业化大规模使用的锂离子电池体系，是亟待解决的技术问题。
发明内容
本申请实施例提供一种负极极片及其制备方法和用途。本申请实施例通过 在负极极片的靠近集流体一侧设置第一负极层，且第一负极层中包括石墨和硅，提高了整体负极的能量密度，提升了负极的容量，同时远离集流体一侧的第二石墨负极层的存在，进一步地抑制了硅材料的膨胀，使得负极极片适配于现有的商业化大规模使用的锂离子电池体系。
第一方面，本申请实施例提供一种负极极片，所述负极极片包括集流体、第一负极层和第二负极层，第一负极层位于所述集流体和第二负极层之间；
其中，第一负极层中的负极活性物质包括石墨和硅材料，第二负极层中的负极活性物质包括石墨；所述第一负极层中的石墨为碳包覆后的石墨；
所述第一负极层中包括第一粘结剂和第一导电剂；所述第一粘结剂为聚丙烯腈粘结剂。
本申请实施例对硅负极活性物质的种类没有特别限定，在不违背本申请申请构思的基础上，任何已知的硅负极活性物质材料均能用于本申请中；仅仅作为示意性的举例，而非对保护范围任何限定，硅负极活性物质材料包括单质硅、硅氧化合物、经过包覆处理的硅基材料等等。
本申请实施例对碳包覆的方法和种类没有特别的限定，在不违背本申请申请构思的基础上，任何已知的能够提高电子电导的碳包覆方法均能用于本申请中；经过碳包覆的石墨电子电导率有了明显提升，克服了第一负极层电子电导偏低而影响负极层整体内阻的问题。
可以理解的是，聚丙烯腈粘结剂是指经由单体丙烯腈经自由聚合反应而得到的一类可作为粘结剂的聚合物，示例性的，可以为LA132和/或LA133粘结剂。
在实际生产过程中，即使在锂离子电池的石墨负极中加入少量的硅氧化合物也会存在硅氧化合物在充放电过程中发生膨胀，从而引发整个负极层从集流体上发生脱落。令人意外的，采用聚丙烯腈类粘结剂可有效地抑制硅氧化合物的膨胀，且相较于其他的粘结剂，聚丙烯腈类粘结剂与集流体的粘结作用更强，可有效防止负极层的脱落，提高电池的循环寿命。
与此同时，本申请实施例选用高抗拉的负极集流体，配合聚丙烯腈类粘结剂，能够保证集流体可以适应硅氧材料的体积变化。
本申请实施例中提供的石墨，选自天然石墨和人造石墨中的一种。进一步地，人造石墨选自单颗粒人造石墨、二次颗粒人造石墨及单颗粒人造石墨和二 次颗粒人造石墨的复合中的一种。
对于多层负极体系而言，由于靠近集流体的负极活性物质层受到集流体对其的粘结作用力，因此其膨胀率通常小于远离集流体的一侧的负极活性物质层，因此本申请选择将硅材料加入靠近集流体的第一负极层中。通过负极层与集流体的相互作用来避免由于加入硅而导致的膨胀。
本申请实施例中，如果负极极片中不设置第二负极层，则会出现硅氧材料与电解液界面不稳定的技术问题。
优选地，所述第二负极层中包括第二粘结剂和第二导电剂。
优选地，所述第二粘结剂为水性粘结剂。
优选地，所述第一粘结剂与集流体的粘结力大于所述第二粘结剂与集流体的粘结力。
本申请实施例中，第一负极层中的粘结剂选择与集流体粘结力更强的类型，以进一步克服第一负极层中，因为引入硅而引起的膨胀。相比之下，由于纯石墨负极膨胀小，第二负极层可以继续使用常规的粘结剂，例如第二负极层中可以为本领域技术人员易知的常规的水性粘结剂，包括但不限于聚乙烯醇、聚丙烯酸、聚乙二醇、聚丙烯酰胺、丁苯橡胶或羟甲基纤维素等。
在实际生产过程中，即使在锂离子电池的石墨负极中加入少量的硅氧化合物也会存在硅氧化合物在充放电过程中发生膨胀，从而引发整个负极层从集流体上发生脱落。令人意外的，采用聚丙烯腈类粘结剂可有效地抑制硅氧化合物的膨胀，且相较于其他的粘结剂，聚丙烯腈类粘结剂与集流体的粘结作用更强，可有效防止负极层的脱落，提高电池的循环寿命。
进一步优选地，所述第二负极层中粘结剂的质量占比大于第一负极层中粘结剂的质量占比。
优选地，所述第一负极层中的粘结剂的质量占比为3～5wt％，例如3wt％、4wt％或5wt％等。
优选地，所述第二负极层中的粘结剂的质量占比为4～8wt％，例如4wt％、5wt％、6wt％、7wt％或8wt％等。
优选地，所述第一负极层的集流体为高抗拉的材质，该集流体与第一负极层的高膨胀性能相匹配，可以进一步抵抗第一负极层由于引入了硅以后所引起的膨胀。
所述集流体的拉伸强度大于等于350N/cm 2，例如360N/cm 2、380N/cm 2、400N/cm 2、450N/cm 2、480N/cm 2或500N/cm 2等。
本申请实施例选用高抗拉的负极集流体，配合聚丙烯腈类粘结剂，能够保证集流体可以适应硅氧材料的体积变化。
优选地，所述第一负极层中的硅材料的质量为所述第一负极层中的负极活性物质的3～5％。
本申请实施例中，硅氧材料的加入如果过多，会导致负极材料在充放电过程中膨胀率过高，导致锂电池的充放电性能下降，循环保持率大幅下降，而如果加入量过少，又不能起到增加电池容量的作用。
本申请实施例中，第一负极层中的石墨为经过碳包覆的石墨，可提高第一负极层的导电性。
优选地，所述硅材料包括硅氧材料。
优选地，所述第一导电剂在第一负极层中的质量占比大于所述第二导电剂在第二负极层中的质量占比。
优选地，第一导电剂包括CNT、VGCF、super P、炭黑、乙炔黑、或石墨烯中的任意一种或至少两种的组合。
优选地，所述CNT和/或VGCF在第一导电剂中的质量占比为15～25wt％。
本申请实施例中，第二导电剂的选择包括但不限于碳基材料、粉末镍或其他金属颗粒或导电聚合物，例如碳基材料可包括碳黑、石墨、superP、乙炔黑(诸如，KETCHENTM黑或DENKATM黑)、碳纤维和纳米管、石墨烯等等的颗粒；导电聚合物包括聚苯胺、聚噻吩、聚乙炔、聚吡咯、聚(3,4-乙撑二氧噻吩)聚磺苯乙烯等。
本申请实施例中，第一负极层中的第一导电剂质量占比比常规的质量占比更多，这样可以较好地实现充放电过程中电子的传输，防止因硅氧材料的加入，导致的负极层的导电性能的下降，另一方面，硅氧材料发生膨胀会导致电子传输路径被破坏，从而影响电子的传输。
优选地，所述第一负极层的厚度为所述第二负极层的厚度的5～40％，例如5％、8％、10％、13％、15％、18％、20％、23％、25％、28％、30％、33％、35％、38％或40等％，优选为16～25％。
本申请实施例中，第一负极层的厚度为所述第二负极层的厚度的16～25％范 围内，可以更好地实现提高电池能量密度及循环保持率的技术效果，而如果第一负极层的厚度过厚，则第一负极层靠近集流体和远离集流体的两侧膨胀系数不同，容易引起极片脱落和第一负极层、第二负极层之间的剥离，如过第一负极层的厚度过小，则提升能量密度的效果不明显。
优选地，所述第一负极层的厚度为16～55μm，例如16μm、18μm、20μm、23μm、25μm、28μm、30μm、33μm、35μm、38μm、40μm、43μm、45μm、48μm、50μm、53μm或55μm等。
优选地，所述第二负极层的厚度为170～210μm，例如170μm、175μm、180μm、185μm、190μm、195μm、200μm、205μm或210μm等。
优选地，所述第一负极层的涂覆面密度为30～50g/m 2，例如30g/m 2、33g/m 2、35g/m 2、38g/m 2、40g/m 2、43g/m 2、45g/m 2、48g/m 2或50g/m 2等。
优选地，所述第二负极层的面密度为150～170g/m 2，例如150g/m 2、155g/m 2、160g/m 2、165g/m 2或170g/m 2等
第二方面，本申请实施例提供一种如第一方面所述的负极极片的制备方法，所述制备方法包括：
将第一负极层的浆料涂覆于集流体的表面，得到第一负极层，将第二负极层的浆料涂覆于第一负极层的表面，得到所述负极极片。
其中，第一负极层的浆料和第二负极层中的浆料的制备均为常规技术手段。
示例性地，负极层浆料的制备方法包括：将负极活性物质、粘结剂、溶剂和导电剂混合，得到负极层浆料。
第三方面，本申请实施例还提供一种锂离子电池，所述锂离子电池包括如第一方面所述的负极极片。
本申请实施例提供的锂离子电池，可为液态电池或固态电池，不作特别限定。
当其为液态锂离子电池时，其包括如第一方面所述的负极极片、正极极片、隔膜和电解液。
液态锂离子电池中的正极极片、隔膜以及电解液均为本领域技术人员易知且易得的，即可以组装得到完整的锂离子电池的相应的物质以及制备方法均适用。
当其为固态锂离子电池时，其包括如第一方面所述的负极极片、正极极片 和固态电解质层。
固态锂离子电池中的正极极片和固态电解质层均为本领域技术人员易知且易得的，即可以组装得到完整的锂离子电池的相应的物质以及制备方法均适用。
与相关技术相比，本申请实施例具有以下有益效果：
本申请实施例提供的负极极片，在靠近集流体一侧设置第一负极层，且第一负极层中同时包括石墨和硅，提高了整体负极的能量密度，提升了负极的容量，且远离集流体一侧的第二石墨负极层的存在，进一步地抑制了硅材料的膨胀通过集流体、粘结剂的种类和用量、面密度和厚度的相互配合，协同作用，既降低了负极材料的首圈膨胀率，提升了传统石墨基负极锂电池的能量密度，又提升了电池的循环寿命，使其适配于现有的商业化大规模使用的锂离子电池体系，且制备方法简单，无需复杂的制备步骤。本申请提供的电池，0.33C下的负极克容量可达375mAh/g以上，负极首圈膨胀率在38％以下，循环500圈后的容量保持率可达85.8％以上，进一步地调整负极层的厚度，硅材料的占比以及第一粘结剂的粘结性后，0.33C下的负极克容量可达375mAh/g以上，负极首圈膨胀率在30％以下，循环500圈后的容量保持率可达93.4％以上。
在阅读并理解了详细描述后，可以明白其他方面。
具体实施方式
下面通过具体实施例来进一步说明本申请的技术方案。本领域技术人员应该明了，所述实施例仅仅是帮助理解本申请，不应视为对本申请的具体限制。
本申请的锂电池用负极包括集流体及其上的第一负极层和第二负极层，第一负极层包括95～97wt％的经碳包覆的石墨材料和3～5wt％的硅氧化合物作为活性材料并包括聚丙烯腈类粘结剂作为第一粘结剂，第二负极层采用100％石墨作为活性物质材料，并包括第二粘结剂和第二导电剂。
可以理解的是，上述百分含量均为占负极活性物质的比例而非负极层的比例，如95～97wt％表示经碳包覆的石墨材料占第一负极层中负极活性物质的95～97wt％。
已知的是，硅具有较高的容量，但由于较大的膨胀性能而被限制使用；本申请中，借助于集流体对第一负极层的粘结力，有效抑制了第一负极层的膨胀性能，如此，即使在第一负极层中加入高膨胀性能的硅负极活性材料，也不会 引起负极层整体发生不可预期的体积膨胀。通过多层负极的设置解决了目前膨胀性能和能量密度矛盾的问题。
本申请所提及的聚丙烯腈粘结剂包括但不限于单体丙烯腈的共聚物及其共聚物的简单变形，如发生简单的官能团取代、官能团位置的变化，官能团数量变化及单体数量变化得到的粘结性能未发生改变的聚合物。
在本申请的一个实施例中，第一负极层包括：占第一负极层90～97wt％的由95～97wt％的石墨材料和3～5wt％硅氧化合物组成的负极活性材料，第一负极层中3～5wt％的聚丙烯腈粘结剂，及1～5wt％的第一导电剂，更具体地，第一导电剂中还包括15～20wt％的CNT和/或VGCF。当各组分配比满足上述范围时，可以有效提高石墨系负极锂电池的能量密度，同时使得锂电池原有的优异的循环保持率不发生下降，当第一负极层活性物质中的硅氧化合物的重量比大于5wt％时，硅氧化合物在充放电过程中的膨胀难以抑制，使得电池的性能发生劣化，当第一负极层活性物质中的硅氧化合物的重量比小于3wt％时，锂电池的能量密度提升不明显。
优选地，所述第一导电剂至少包括CNT或VGCF中的一种或两种。相比于其他导电剂，CNT和VGCF的纤维状结构具有一定的长径比，有利于硅氧化合物在膨胀时在第一负极层中形成线状导电通道，提升锂离子和电子的传输效率，保证电池的容量性能和循环性能不发生劣化。
本申请对CNT和VGCF的具体种类没有特别限定，在不违背本申请申请构思的基础上，任何已知的具有相当长泾比的CNT、VGCF产品均能用于本申请中，作为一种示意性的举例，CNT和VGCF的长径比>1000；优选地，CNT和VGCF的长径比>2000。
在本申请的一个实施例中，第二负极层包括：第二负极活性物质材料，4～8wt％的粘结剂，及1～5wt％的第二导电剂，具体地，第二负极层包括：石墨作为唯一的活性物质材料，4～8wt％的粘结剂，及1-3wt％的第二导电剂。
可以理解的是，第二负极活性物质材料可以是一种或多种负极活性物质组成的混合物，但其膨胀性能应小于第一负极层；因此，作为一种优选的实施方式，所述第二负极活性物质全部由石墨负极活性物质组成。
作为一种优选的实施方式，第一粘结剂对集流体的粘结力大于第二粘结剂，第二负极层中粘结剂的含量大于第一负极层中粘结剂的含量；
本申请采用高粘结剂含量的负极体系，通过粘结剂含量和种类的调整，使得第一负极层与集流体具有更强的相互作用，以避免硅膨胀所带来的极片脱落问题。本申请中第二粘结剂的含量大于第一粘结剂的含量是基于第二负极层远离集流体的选择。通过加大第二负极层中粘结剂的含量，与集流体共同对第一负极层形成“夹持”作用，进一步抑制第一负极层的膨胀和结构变化。
在本申请的一个实施例中，第二负极层在集流体上的投影面积大于等于第一负极在集流体上的投影面积。
本申请对第一负极活性材料和第二负极活性材料中的石墨材料没有特别限定，在不违背本申请申请构思的基础上，任何已知的可以作为负极活性物质的石墨材料均能用于本申请中，仅仅作为示意性的举例而非对保护范围的任何限定，石墨材料可以选自天然石墨和人造石墨中的一种。进一步地，人造石墨选自单颗粒人造石墨、二次颗粒人造石墨及单颗粒人造石墨和二次颗粒人造石墨的复合中的一种。
本申请中第一负极层中的石墨为碳包覆后的石墨，采用碳包覆的石墨即可有利于弥补由于硅氧化合物的加入带来的整个负极层导电性能的下降，同时当硅氧化合物发生膨胀时可以导电剂形成导电网络，有效避免因硅膨胀带来的导电路径被破坏的现象。
对石墨进行碳包覆是本领域已知的，比如在石墨表面包覆一层碳质包覆层。本申请对实际碳包覆的方法没有特别要求，在不违背本申请申请构思的基础上，任何已知的碳包覆方式或结构均能用于本申请中。
本申请通过在负极极片的靠近集流体一侧设置第一负极层，且第一负极层中包括石墨和硅，提高了整体负极的能量密度，提升了负极的容量，同时远离集流体一侧采用膨胀较小的石墨负极，进一步地抑制了第一负极层的膨胀，使得负极极片适配于现有的商业化大规模使用的锂离子电池体系。
本申请中，负极层与集流体之间存在的粘结力，因此负极活性物质层靠近集流体一侧的膨胀率通常小于远离集流体的一侧，因此本申请选择将硅材料加入靠近集流体的第一负极层中。通过负极层与集流体的相互作用来避免由于加入硅而导致的膨胀。
作为一种优选地实施方式，所述负极用集流体选用具有高抗拉性能的集流体，在一些实施例中，可以为铜箔；优选地，负极集流体的拉伸强度大于等于 350N/cm 2。例如350N/cm 2、400N/cm 2、450N/cm 2等。
所述第一负极层包括第一粘结剂和第一导电剂；
所述第一负极层包括第一粘结剂和第一导电剂；
所述第一粘结剂为聚丙烯腈类粘结剂；
所述第一导电剂包括炭黑、super-P、CNT、VGCF、乙炔黑，石墨烯中的一种或几种组合。
在一些实施例中，所述第一导电剂中至少包含15wt％～25wt％的CNT和/或VGCF。
所述第二负极层包括第二粘结剂和第二导电剂；
本申请中，第一负极层中的粘结剂选择与集流体粘结力更强的类型，以进一步克服第一负极层中，因为引入硅而引起的膨胀。相比之下，由于纯石墨负极膨胀小，第二负极层可以继续使用常规的粘结剂，例如第二负极层中可以为本领域技术人员易知的常规的水性粘结剂，包括但不限于聚乙烯醇、聚丙烯酸、聚乙二醇、聚丙烯酰胺、丁苯橡胶或羟甲基纤维素等。
本申请中，第二导电剂的选择包括但不限于碳基材料、粉末镍或其他金属颗粒或导电聚合物，例如碳基材料可包括碳黑、石墨、superP、乙炔黑(诸如，KETCHENTM黑或DENKATM黑)、碳纤维和纳米管、石墨烯等等的颗粒；导电聚合物包括聚苯胺、聚噻吩、聚乙炔、聚吡咯、聚(3,4-乙撑二氧噻吩)聚磺苯乙烯等。
优选地，所述第一负极层的厚度为所述第二负极层的厚度的5～40％，例如5％、8％、10％、13％、15％、18％、20％、23％、25％、28％、30％、33％、35％、38％或40等％，优选为16％～25％。
本申请中，第一负极层的厚度为所述第二负极层的厚度的16％～25％范围内，可以更好地实现提高电池能量密度及循环保持率的技术效果，而如果第一负极层的厚度过厚，则第一负极层靠近集流体和远离集流体的两侧膨胀系数不同，容易引起极片脱落和第一负极层、第二负极层之间的剥离，如过第一负极层的厚度过小，则提升能量密度的效果不明显。
优选地，所述第一负极层的厚度为16～55μm，例如16μm、18μm、20μm、23μm、25μm、28μm、30μm、33μm、35μm、38μm、40μm、43μm、45μm、48μm、50μm、53μm或55μm等。
优选地，所述第二负极层的厚度为170～210μm，例如170μm、175μm、180μm、185μm、190μm、195μm、200μm、205μm或210μm等。
第二方面，本申请提供一种如第一方面所述的负极极片的制备方法，所述制备方法包括：
将第一负极层的浆料涂覆于集流体的表面，得到第一负极层，将第二负极层的浆料涂覆于第一负极层的表面，得到所述负极极片。
优选地，所述第一负极层的面密度为30～50g/m 2，例如30g/m 2、35g/m 2、40g/m 2、45g/m 2或50g/m 2等。
优选地，所述第二负极层的面密度为150～170g/m 2，例如150g/m 2、155g/m 2、160g/m 2、165g/m 2或170g/m 2等；
本申请提供一种包括上述负极的锂电池。
该锂电池包括正极、负极、电解质，以及包含上述结构的电池外壳。
所述正极包括集流体和在集流体上形成的正极活性物质层；
所述正极集流体没有特别限制，只要其具有导电性而不在电池中引起化学变化即可。具体地，可以使用铜，不锈钢，铝，镍，钛，或用表面经过碳或其他物质处理的金属集流体。
所述正极集流体通常可以具有3μm至500μm的厚度。
所述正极集流体可以具有在其表面上形成的微细凹凸，以改善正极活性材料的粘附性。例如，可以使用诸如膜、片、箔、网、多孔体、泡沫和无纺布体等各种形状的正极集流体。
所述正极活性材料层可以包含正极活性材料。
所述正极活性材料是能够使锂可逆地嵌入和脱嵌的化合物，具体地，可以包含锂过渡金属复合氧化物，其含有锂和其他选自由镍、钴、锰和铝组成的组中的至少一种过渡金属；优选地，可以为包含锂及镍、钴或锰等过渡金属。
更具体地，所述锂过渡金属复合氧化物可以是锂锰类氧化物(例如LiMnO 2、LiMn 2O 4等)、锂钴类氧化物(例如LiCoO 2等)、锂镍类氧化物(例如LiNiO 2等)、锂镍锰类氧化物(例如LiNi 1-yMn yO 2(其中0<y<1)、LiMn 2-zNi zO 4(其中0<z<2)等)、锂镍钴类氧化物(例如LiNi 1-y1Co y1O 2(其中0<y 1<1)等)、锂锰钴类氧化物(例如LiCo 1-y2Mn y2O 2(其中0<y 2<1)、LiMn 2-z1Co z1O 4(其中0<z 1<2)等)、锂镍锰钴类氧化物(例如Li(Ni pCo qMn r1)O 2(其中0<p<1，0<q<1，0<r1<1，p+q+r1＝1)、或锂镍钴 过渡金属(M)氧化物(例如Li(Ni p2Co q2Mn r3A S2)O 2(其中M选自由Al、Fe、V、Cr、Ti、Ta、Mg和Mo组成的组，p 2、q 2、r 3和s 2各自是独立元素的原子分数，并且0<p 2<1、0<q 2<1、0<r 3<1、0<s 2<1、p 2+q 2+r 3+s 2＝1)等)等，并且可以包含其任一种或其两种以上的化合物。这些当中，从能够增加电池的容量和稳定性的方面而言，所述锂过渡金属复合氧化物可以是LiCoO 2、LiMnO 2、LiNiO 2、锂镍锰钴氧化物(例如Li(Ni 0.6Mn 0.2Co 0.2)O 2、Li(Ni 0.5Mn 0.3Co 0.2)O 2、Li(Ni 0.7Mn 0.15Co 0.15)O 2或LiNi 0.8Mn 0.1Co 0.1)O 2等、或锂镍钴铝氧化物(例如Li(Ni 0.8Co 0.15Al 0.05)O 2等)等。当考虑根据对形成锂过渡金属复合氧化物的构成元素的类型和含量比进行控制而得到的显著改善效果时，所述锂过渡金属复合氧化物可以是Li(Ni 0.6Mn 0.2Co 0.2)O 2、Li(Ni 0.5Mn 0.3Co 0.2)O 2、Li(Ni 0.7Mn 0.15Co 0.15)O 2或Li(Ni 0.8Mn 0.1Co 0.1)O 2等，并且可以使用其任一种或其两种以上的混合物。
正极活性材料层中包含的所述正极活性材料的量可以为80wt％至99wt％，优选92wt％至98.5wt％。
除了含有上述正极活性材料之外，所述正极活性材料层还可以包含正极粘结剂和/或正极导电材料。
所述正极粘结剂是用来活性材料、导电材料以及集流体等组分粘结在一起，具体地，可以包含选自由聚偏二氟乙烯、聚乙烯醇、羧甲基纤维素(CMC)、淀粉、羟丙基纤维素、聚乙烯基吡咯烷酮、聚四氟乙烯、聚乙烯、聚丙烯、乙烯-丙烯-二烯单体、苯乙烯-丁二烯橡胶和氟橡胶组成的组中的至少一种，优选聚偏二氟乙烯。
所述正极活性材料层中包含的正极粘结剂的量可以为1wt％至20wt％，优选1.2wt％至10wt％。
所述导电材料主要用于辅助和改善二次电池中的导电性，并且没有特别限制，只要其具有导电性而不引起化学变化即可。具体地，所述导电材料可以包含石墨，例如天然石墨或人造石墨；碳类材料，例如炭黑、乙炔黑、科琴黑、槽法炭黑、炉黑、灯黑和热裂法炭黑；导电纤维，例如碳纤维和金属纤维；导电管，例如碳纳米管；金属粉末，例如碳氟化合物粉末、铝粉末和镍粉末；导电晶须，例如氧化锌和钛酸钾；导电金属氧化物，例如钛氧化物；以及聚亚苯基衍生物，并且从改善导电性的方面而言，可优选包含炭黑。
所述正极导电材料的比表面积可以为80m 2/g至200m 2/g，优选100m 2/g至 150m 2/g。
所述正极活性材料层中包含的正极导电材料的量可以为1wt％至20wt％，优选1.2wt％至10wt％。
所述正极活性材料层的厚度可以为30μm至400μm，优选50μm至110μm。
所述正极可通过在正极集流体上涂覆包含正极活性材料和选择性的正极粘结剂、正极导电材料以及正极浆料形成用溶剂的正极浆料，然后进行干燥和辊压来制造。
所述正极浆料形成用溶剂可以包含有机溶剂，例如N-甲基-2-吡咯烷酮(NMP)，并且用量可以为使得当包含正极活性材料并选择性地包含正极粘合剂、正极导电材料等时获得优选的粘度。例如，正极浆料中包含的所述正极浆料形成用溶剂的量可以为使得包含正极活性材料、并选择性地包含正极粘合剂和正极导电材料的固体的浓度为50wt％至95wt％，优选70wt％％至90wt％。
本申请对电解质的种类没有特别限定，在不违背本申请申请构思的基础上，任何已知的电解质材料均能用于本申请中。作为示意性的举例，电解质可以是液态电解液、固态电解质或固态电解质与液态电解液的混合形式。
当电解质采用液态电解液时，电池体系中还应设置隔膜。
隔膜的主要作用是将负极和正极隔开并提供锂离子的移动路径。可以使用任何隔膜而没有特别限制，只要它是二次电池中常用的隔膜即可。特别地，优选具有优异的电解液润湿性并且对电解质中的离子移动阻力低的隔膜。具体地，可以使用多孔聚合物膜，例如，使用聚烯烃类聚合物例如乙烯均聚物、丙烯均聚物、乙烯/丁烯共聚物、乙烯/己烯共聚物和乙烯/甲基丙烯酸酯共聚物制造的多孔聚合物膜，或具有其两层以上的层压结构。并且，可以使用典型的多孔无纺布，例如，由具有高熔点的玻璃纤维、聚对苯二甲酸乙二醇酯纤维等形成的无纺布。此外，可以使用包含陶瓷组分或聚合物材料的涂覆隔膜来确保耐热性或机械强度，并且可以选择性地以单层或多层结构使用。
另外，本申请中使用的电解质可以是可用于二次电池的制造的有机液体电解质、无机液体电解质、固体聚合物电解质、凝胶型聚合物电解质、固体无机电解质、熔融型无机电解质等，但是不限于此。
具体地，所述电解质可以包含有机溶剂和锂盐。
可以使用任何有机溶剂而没有特别的限制，只要它可以充当参与电池的电 化学反应的离子可移动穿过的介质即可。具体地，作为所述有机溶剂，可以使用酯类溶剂，例如乙酸甲酯、乙酸乙酯、γ-丁内酯和ε-己内酯；醚类溶剂，例如二丁醚或四氢呋喃；酮类溶剂，例如环己酮；芳族烃类溶剂，例如苯和氟苯；碳酸酯类溶剂，例如碳酸二甲酯(DMC)、碳酸二乙酯(DEC)、碳酸甲乙酯(MEC)、碳酸乙甲酯(EMC)、碳酸亚乙酯(EC)和碳酸亚丙酯(PC)；醇类溶剂，例如乙醇和异丙醇；腈例如R-CN(其中R是直链、支链或环状的C2-C20烃基团，并可包含双键芳族环或醚键)；酰胺，例如二甲基甲酰胺；二氧戊环，例如1,3-二氧戊环；或环丁砜。在上述溶剂当中，碳酸酯类溶剂是优选的，并且可以增加电池的充电/放电性能的具有高离子传导性和高介电常数的环状碳酸酯(例如碳酸亚乙酯或碳酸亚丙酯)和低粘度线性碳酸酯类化合物(例如碳酸乙甲酯、碳酸二甲酯或碳酸二乙酯)的混合物是更优选的。在这种情况下，当所述环状碳酸酯和所述链状碳酸酯以约1:1至约1:9的体积比混合时，电解质的性能可能是优异的。
任何化合物均可以用作所述锂盐而没有特别限制，只要它可以提供锂二次电池中所用的锂离子即可。具体地，LiPF 6、LiClO 4、LiAsF 6、LiBF 4、LiSbF6、LiAlO 4、LiAlCl 4、LiCF 3SO 3、LiC 4F 9SO 3、LiN(C 2F 5SO 3) 2、LiN(C 2F 5SO 2) 2、LiN(CF 3SO 2) 2、LiCl、LiI、LiB(C 2O 4) 2等可用作所述锂盐。所述锂盐的使用浓度范围可以为0.1-2.0M。当所述锂盐的浓度在上述范围内时，所述电解质具有合适的导电性和粘度，从而表现出优异的性能，并且锂离子可以有效地移动。
作为一种实施方式，电解质可以是固态电解质，固态电解质颗粒可包含一种或多种聚合物的组分、氧化物固态电解质、硫化物固态电解质、卤化物固态电解质、硼酸盐固态电解质、氮化物固态电解质或氢化物固态电解质。当使用聚合物颗粒时，应采用锂盐进行复核。作为一种实施方式，基于聚合物的组分可包含选自包括以下各者的组的一种或多种聚合物材料：聚乙二醇、聚环氧乙烷(PEO)、聚(对苯醚)(PPO)、聚(甲基丙烯酸甲酯)(PMMA)、聚丙烯腈(PAN)、聚偏二氟乙烯(PVDF)、聚偏二氟乙烯共六氟丙烯(PVDF-HFP)、聚氯乙烯(PVC)以及它们的组合。可以理解的是，聚合物材料高的离子电导率对整体固态电解质材料的性能是有利的，优选地，聚合物材料应具有大于或等于10-4S/cm的离子电导率。
作为一种实施方式，氧化物颗粒可包含一种或多种石榴石陶瓷、LISICON型氧化物、NASICON型氧化物和钙钛矿型陶瓷。作为示意性的举例，石榴石陶 瓷可选自包括以下各者的组：Li 6.5La 3Zr 1.75Te 0.25O 12、Li 7La 3Zr 2O 12、Li 6.2Ga 0.3La 2.95Rb 0.05Zr 2O 12、Li 6.85La 2.9Ca 0.1Zr 1.75Nb 0.25O 12、Li 6.25Al 0.25La 3Zr 2O 12、Li 6.75La 3Zr 1.75Nb 0.25O 12、Li 6.75La 3Zr 1.75Nb 0.25O 12以及它们的组合。LISICON型氧化物可选自包括以下各者的组：Li 14Zn(GeO 4) 4、Li 3+x(P 1-xSi x)O4(其中0<x<1)、Li 3+xGe xV 1-xO 4(其中0<x<1)以及它们的组合。NASICON型氧化物可由LiMM′(PO 4) 3定义，其中M和M′独立地选自Al、Ge、Ti、Sn、Hf、Zr和La。优选地，NASICON型氧化物可选自包括以下各者的组：Li 1+xAl xGe 2-x(PO 4) 3(LAGP)(其中0≤x≤2)、Li 1+xAl xTi 2-x(PO 4) 3(LATP)(其中0≤x≤2)、Li 1+xY xZr 2-x(PO 4) 3(LYZP)(其中0≤x≤2)、Li 1.3Al 0.3Ti 1.7(PO 4) 3、LiTi 2(PO 4) 3、LiGeTi(PO 4) 3、LiGe 2(PO 4) 3、LiHf 2(PO 4) 3以及它们的组合。一种或多种钙钛矿型陶瓷可选自包括以下各者的组：Li 3.3La 0.53TiO 3、LiSr 1.65Zr 1.3Ta 1.7O 9、Li 2x-ySr 1-xTa yZr 1-yO 3(其中x＝0.75y且0.60<y<0.75)、Li 3/8Sr 7/16Nb 3/4Zr 1/4O 3、Li 3xLa (2/3-x)TiO 3(其中0<x<0.25)以及它们的组合。优选地，一种或多种基于氧化物的材料可具有大于或等于约10 -5S/cm至小于或等于约10 -1S/cm的离子电导率。
硫化物固态电解质选自包括以下各者的组的一种或多种基于硫化物的材料：Li 2S-P 2S 5、Li 2S-P 2S 5-MSx(其中M是Si、Ge和Sn且0≤x≤2)、Li 3.4Si 0.4P 0.6S 4、Li 10GeP 2S 11.7O 0.3、Li 9.6P 3S 12、Li 7P 3S 11、Li 9P 3S 9O 3、Li 10.35Si 1.35P 1.65S 12、Li 9.81Sn 0.81P 2.19S 12、Li 10(Si 0.5Ge 0.5)P 2S 12、Li(Ge 0.5Sn 0.5)P 2S 12、Li(Si 0.5Sn 0.5)PsS 12、Li 10GeP 2S 12(LGPS)、Li 6PS 5X(其中X是Cl、Br或I)、Li 7P 2S 8I、Li 10.35Ge 1.35P 1.65S 12、Li 3.25Ge 0.25P 0.75S 4、Li 10SnP 2S 12、Li 10SiP 2S 12、Li 9.54Si 1.74P 1.44S 11.7Cl 0.3、(1-x)P 2S 5-xLi 2S(其中0.5≤x≤0.7)以及它们的组合。
卤化物固态电解质可包括选自包括以下各者的组的一种或多种基于卤化物的材料：Li 2CdCl 4、Li 2MgCl 4、Li 2CdI 4、Li 2ZnI 4、Li 3OCl、LiI、Li 5ZnI 4、Li 3OCl 1-xBrx(其中0<x<1)以及它们的组合。
硼酸盐固态电解质选自包括以下各者的组的一种或多种基于硼酸盐的材料：Li 2B 4O 7、Li 2O-(B 2O 3)-(P 2O 5)以及它们的组合。
氮化物固态电解质可选自包括以下各者的组的一种或多种基于氮化物的材料：Li 3N、Li 7PN 4、LiSi 2N 3、LiPON以及它们的组合。
氢化物固态电解质可选自包括以下各者的组的一种或多种基于氢化物的材 料：Li 3AlH 6、LiBH 4、LiBH 4-LiX(其中X是Cl、Br和I中的一者)、LiNH 2、Li 2NH、LiBH 4-LiNH 2以及它们的组合。
作为一种特别的实施方式，固态电解质可以是准固体电解质，其包含上文详述的非水液体电解质溶液和固态电解质系统的混合体，例如，包括一种或多种离子液体以及一种或多种金属氧化物颗粒(诸如，氧化铝(Al 2O 3)和/或二氧化硅(SiO 2))。
实施例1
本实施例提供一种负极极片，基于上述具体实施方式提供的负极极片：
其中，第一负极层厚度为40μm，第二负极层厚度为200μm，第一负极层位于所述集流体和第二负极层之间，第一负极层的厚度为第二负极层厚度为20％；
第一负极层中为SiO、碳包覆的人造石墨、聚丙烯腈和碳纳米管(SiO与碳包覆的人造石墨的质量比为4:96)，第二负极层中为人造石墨、导电炭黑和聚丙烯酸；
所述负极极片的制备方法如下：
(1)按照4:96的质量比称取硅氧化合物(SiO)和带有碳包覆层的石墨，混合均匀，得到第一混合负极活性物质，将第一混合负极活性物质、碳纳米管和聚丙烯腈以90:6:4的质量比与去离子分散混合，得到第一负极层浆料，将第一负极层浆料单面涂布于铜箔(拉伸强度为350N/cm 2)表面，干燥辊压后得到第一负极层；
(2)将人造石墨、导电炭黑和聚丙烯酸以92:2:6的质量比分散于去离子水中，得到第二负极层浆料，将第二负极层浆料涂布于第一负极层表面，干燥辊压后得到所述负极极片。
实施例2
本实施例提供一种负极极片，基于上述具体实施方式提供的负极极片：
第一负极层厚度为30μm，第二负极层厚度为180μm，第一负极层位于所述集流体和第二负极层之间，第一负极层的厚度为第二负极层厚度为16.7；
第一负极层中为SiO、碳包覆的人造石墨、聚丙烯腈和碳纤维(SiO与碳包覆的人造石墨的质量比为3:97)，第二负极层中为人造石墨、导电炭黑、丁苯橡胶和羧甲基纤维素钠；
所述负极极片的制备方法如下：
(1)按照3:97的质量比称取硅氧化合物(SiO)和带有碳包覆层的石墨，混合均匀，得到第一混合负极活性物质，将第一混合负极活性物质、碳纳米管和聚丙烯腈以92:3:5的质量比与去离子分散混合，得到第一负极层浆料，将第一负极层浆料单面涂布于铜箔(拉伸强度为350N/cm 2)表面，干燥辊压后得到第一负极层；
(2)将人造石墨、导电炭黑、丁苯橡胶和羧甲基纤维素钠以92:2:3:3的质量比分散于去离子水中，得到第二负极层浆料，将第二负极层浆料涂布于第一负极层表面，干燥辊压后得到所述负极极片。
实施例3
本实施例提供一种负极极片，基于上述具体实施方式提供的负极极片：
其中，第一负极(厚度为52μm，第二负极层厚度为208μm，第一负极层位于所述集流体和第二负极层之间，第一负极层的厚度为第二负极层厚度为1/4；
第一负极层中为SiO、碳包覆的人造石墨、聚丙烯腈和碳纳米管(SiO与碳包覆的人造石墨的质量比为5:95)，第二负极层中为人造石墨、导电炭黑和聚丙烯酸。
其余制备方法与参数实施例1保持一致。
实施例4
本实施例与实施例1的区别为，本实施例中第一负极层的厚度为100μm，第一负极层的厚度为第二负极层厚度为50％。
其余制备方法与参数实施例1保持一致。
实施例5
本实施例与实施例1的区别为，本实施例中SiO与碳包覆的人造石墨的质量比为8:92。
其余制备方法与参数与实施例1保持一致。
实施例6
本实施例与实施例1的区别为，本实施例中第一负极层的粘结剂为CMC+SBR。
其余制备方法与参数与实施例1保持一致。
对比例1
本对比例与实施例1的区别为，本对比例中负极层仅为一层，且负极活性 物质为纯人造石墨。
制备方法与参数与实施例1中的步骤(2)保持一致。
对比例2
本对比例与实施例1的区别为，本对比例中负极层仅为一层，且负极活性物质组成与实施例1中第一负极层组成相同。
制备方法与参数与实施例1中的步骤(2)保持一致。
电池制备：
正极极片：按质量比90:5:5称取NCM811、聚偏氟乙烯、导电炭黑，分散于NMP中，制备正极浆料浆料，涂布于铝箔表面上，经烘干、辊压形成正极极片，模切形成相应的形状。
以实施例1-6与对比例1-2提供的负极极片为负极，制备得到的正极极片为正极，采用聚烯烃隔膜，碳酸亚乙酯为电解液，在电解液中添加LiCF 3SO 3，得到电池。
对实施例1-6与对比例1-2提供的电池进行电化学性能测试，测试条件如下：25℃，以0.33C的恒流电流进行充放电测试，其结果如表1所示。
表1
Figure PCTCN2022100402-appb-000001
从实施例1与实施例4的数据结果可知，第一负极层的厚度过厚，会影响负极的首圈膨胀率，导致负极的首圈膨胀率上升，电池在持续的充放电过程中，容量有所下降，循环保持率下降。
从实施例1与实施例5的数据结果可知，第一负极层中硅材料的质量占比 过大，虽可有效提升电池的能量密度，但是也会影响负极的首圈膨胀率，从而导致电池的循环保持率发生下降。
从实施例1与实施例6的数据结果可知，第一负极层中的粘结剂的粘结力与第二负极层中一致时，首圈膨胀率上升，电池的循环性能劣化的情况。
从实施例1与对比例1的数据结果可知，与纯石墨负极相比，本申请提供的负极，在保持较低的膨胀率以及较好的循环稳定性的基础上，其容量得到了明显提升。
从实施例1与对比例2的数据结果可知，采用单层的负极结构相比，本申请提供的负极，容量较高，且膨胀率明显降低，循环稳定性较好。
综上所述，本申请实施例提供的负极极片，在靠近集流体一侧设置第一负极层，且第一负极层中同时包括石墨和硅，提高了整体负极的能量密度，提升了负极的容量，且远离集流体一侧的第二石墨负极层的存在，进一步地抑制了硅材料的膨胀，使其适配于现有的商业化大规模使用的锂离子电池体系，且制备方法简单，无需复杂的制备步骤。本申请提供的电池，0.33C下的负极克容量可达375mAh/g以上，负极首圈膨胀率在38％以下，循环500圈后的容量保持率可达85.8％以上，进一步地调整负极层的厚度，硅材料的占比以及第一粘结剂的粘结性后，0.33C下的负极克容量可达375mAh/g以上，负极首圈膨胀率在30％以下，循环500圈后的容量保持率可达93.4％以上。
以上所述的具体实施例，对本申请的目的、技术方案和有益效果进行了进一步详细说明，所应理解的是，以上所述仅为本申请的具体实施例而已，并不用于限制本申请，凡在本申请的精神和原则之内，所做的任何修改、等同替换、改进等，均应包含在本申请的保护范围之内。

Claims (15)

  1. 一种负极极片，其中，所述负极极片包括集流体、第一负极层和第二负极层，第一负极层位于所述集流体和第二负极层之间；
    其中，第一负极层中的负极活性物质包括石墨和硅材料，第二负极层中的负极活性物质包括石墨；所述第一负极层中的石墨为碳包覆后的石墨；
    所述第一负极层中包括第一粘结剂和第一导电剂；所述第一粘结剂为聚丙烯腈粘结剂。
  2. 根据权利要求1所述的负极极片，其中，所述第二负极层中包括第二粘结剂和第二导电剂。
  3. 根据权利要求2所述的负极极片，其中，所述第二粘结剂为水性粘结剂。
  4. 根据权利要求2或3所述的负极极片，其中，所述第一粘结剂与集流体的粘结力大于所述第二粘结剂与集流体的粘结力。
  5. 根据权利要求2-4任一项所述的负极极片，其中，所述第一导电剂在第一负极层中的质量占比大于所述第二导电剂在第二负极层中的质量占比。
  6. 根据权利要求1-5任一项所述的负极极片，其中，第一导电剂包括CNT、VGCF、super P、炭黑、乙炔黑、或石墨烯中的任意一种或至少两种的组合。
  7. 根据权利要求6所述的负极极片，其中，所述CNT和/或VGCF在第一导电剂中的质量占比为15～25wt％。
  8. 根据权利要求2-7任一项所述的负极极片，其中，所述第二负极层中粘结剂的质量占比大于第一负极层中粘结剂的质量占比。
  9. 根据权利要求8所述的负极极片，其中，所述第一负极层中的粘结剂的质量占比为3～5wt％；
    优选地，所述第二负极层中的粘结剂的质量占比为4～8wt％。
  10. 根据权利要求1所述的负极极片，其中，所述集流体的拉伸强度大于等于350N/cm 2。
  11. 根据权利要求10所述的负极极片，其中，所述第一负极层中的硅材料的质量为所述第一负极层中的负极活性物质的3～5％；
    优选地，所述硅材料包括硅氧材料。
  12. 根据权利要求11所述的负极极片，其中，所述第一负极层的厚度为所述第二负极层的厚度的5～40％，优选为16～25％；
    优选地，所述第一负极层的厚度为16～55μm；
    优选地，所述第二负极层的厚度为170～210μm。
  13. 一种如权利要求1-12任一项所述的负极极片，其中，所述第一负极层的涂覆面密度为30～50g/m 2。
  14. 一种如权利要求1-13任一项所述的负极极片的制备方法，其中，所述制备方法包括：
    将第一负极层的浆料涂覆于集流体的表面，得到第一负极层，将第二负极层的浆料涂覆于第一负极层的表面，得到所述负极极片。
  15. 一种锂离子电池，其中，所述锂离子电池包括如权利要求1-13任一项所述的负极极片。
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