WO2023193768A1 - 负极片及锂离子电池 - Google Patents

负极片及锂离子电池 Download PDF

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Publication number
WO2023193768A1
WO2023193768A1 PCT/CN2023/086614 CN2023086614W WO2023193768A1 WO 2023193768 A1 WO2023193768 A1 WO 2023193768A1 CN 2023086614 W CN2023086614 W CN 2023086614W WO 2023193768 A1 WO2023193768 A1 WO 2023193768A1
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Prior art keywords
negative electrode
film layer
graphite particles
electrode film
lithium
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PCT/CN2023/086614
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English (en)
French (fr)
Inventor
张保海
彭冲
李俊义
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珠海冠宇电池股份有限公司
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Publication of WO2023193768A1 publication Critical patent/WO2023193768A1/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
    • H01M4/134—Electrodes based on metals, Si or alloys
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1395—Processes of manufacture of electrodes based on metals, Si or alloys
    • 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
    • H01M4/362—Composites
    • H01M4/364—Composites as mixtures
    • 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
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • 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
    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • 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 present disclosure relates to the field of battery technology, and in particular, to a negative electrode sheet and a lithium-ion battery.
  • a lithium battery includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte.
  • the negative electrode sheet includes a metal sheet and a functional layer covering the metal sheet.
  • the functional layer is formed by a mixture of graphite particles and silicon particles.
  • Embodiments of the present disclosure provide a negative electrode sheet and a lithium-ion battery to solve the problem in related technologies that the functional layer where graphite particles and silicon particles are mixed is prone to lithium precipitation, thereby affecting the battery life and life of the lithium-ion battery.
  • a negative electrode sheet including:
  • a first negative electrode film layer is attached to the surface of the negative electrode current collector; and the active material of the first negative electrode film layer includes silicon particles and first graphite particles;
  • the active material of the film layer includes second graphite particles, and the particle size of the second graphite particles is larger than the particle size of the first graphite particles.
  • the beneficial effects of the embodiments of the present disclosure are: by sequentially disposing the first negative electrode film layer and the second negative electrode film layer on the surface of the negative electrode current collector, that is, the first negative electrode film layer is attached to the surface of the negative electrode current collector, and the second negative electrode film
  • the layer is attached to the surface of the first negative electrode film layer, and the active material of the first negative electrode film layer includes silicon particles and first graphite particles, and the active material of the second negative electrode film layer includes second graphite particles, that is, the negative electrode film layer is divided into Two layers, in which the active material of the negative electrode film layer close to the negative electrode current collector includes a mixture of silicon particles and graphite particles, and the active material of the other negative electrode film layer far away from the negative electrode current collector includes graphite particles, so that when lithium ions move to the negative electrode sheet When at The concentration of lithium ions at the film layer decreases and the speed slows down, allowing sufficient time for lithium ions to be embedded in the silicon particles and the first graphite particles, thereby reducing
  • the particle size of the first graphite particles is smaller than the particle size of the second graphite particles, that is, the particle size of the first graphite particles is smaller, by using the first graphite particles with a small particle size, the outer periphery of the silicon particles can be covered with more of the first graphite particles, thereby more effectively improving the dynamic performance of the silicon particles.
  • larger second graphite particles are selected. On the one hand, large particles can improve compaction; on the other hand, large second graphite particles have more gaps between them. Compared with small particles of graphite particles, the compaction can be improved.
  • the embodiments of the present disclosure can also make the following improvements.
  • the particle size of the first graphite particles is smaller than the particle size of the silicon particles.
  • the first graphite particles and the second graphite particles are obtained from similar graphite through screening.
  • the D50 particle size of the silicon particles in the first negative electrode film layer is 6 ⁇ m-10 ⁇ m, and the D90 particle size is 18 ⁇ m-22 ⁇ m; the D50 particle size of the first graphite particles is The particle size of D90 is 2 ⁇ m-4.5 ⁇ m and 4.7 ⁇ m-6 ⁇ m.
  • the D50 particle diameter of the second graphite particles in the second negative electrode film layer is 11 ⁇ m-14 ⁇ m, and the D90 particle diameter is 22 ⁇ m-29 ⁇ m.
  • the particle size of the second graphite particles is greater than 7 ⁇ m.
  • the ratio of the thickness of the first negative electrode film layer to the thickness of the second negative electrode film layer is 1:9-9:1.
  • the negative electrode sheet is the negative electrode sheet described in any one of the above.
  • a method for preparing a negative electrode sheet including:
  • the negative electrode current collector coated with the first negative electrode film layer slurry and the second negative electrode film layer slurry is dried.
  • obtaining first graphite particles, silicon particles and second graphite particles, and mixing the first graphite particles and the silicon particles to form a mixed material includes:
  • a certain amount of similar graphite particles is obtained, the graphite particles are screened, and the graphite particles with a particle size smaller than a preset range are used as the first graphite particles, and the remaining graphite particles are used as the second graphite particles.
  • Figure 1 is a schematic diagram of the first negative electrode film layer and the second negative electrode film layer in the negative electrode sheet provided by an embodiment of the present disclosure
  • Figure 2 is a schematic structural diagram of first graphite particles, silicon particles, mixed materials and second graphite particles provided by an embodiment of the present disclosure
  • FIG. 3 is a flow chart of a method for preparing a negative electrode sheet according to an embodiment of the present disclosure.
  • Negative current collector 100.
  • First negative electrode film layer 210.
  • First graphite particles 220.
  • Silicon particles 230, mixed material
  • 300 second negative electrode film layer
  • 310 second graphite particles.
  • lithium-ion batteries have become the power source for various devices. People's performance requirements for lithium-ion batteries have also been further improved. The requirement for lithium-ion batteries to have a longer life is an important indicator of lithium-ion batteries.
  • a lithium battery includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; the negative electrode sheet includes a metal sheet and a functional layer covering the metal sheet.
  • this functional layer is made of a mixture of graphite and silicon. Because the lithium storage capacity of silicon is much greater than that of graphite, it can increase the energy density of lithium-ion batteries, thereby improving the battery life and life of lithium-ion batteries.
  • the volume of silicon particles is easy to expand during the charge and discharge process, the structure of the electrode material is easy to collapse and the particles are differentiated during the cycle, resulting in the loss of electronic conductivity between active materials and between active materials and current collectors, and due to silicon The particles themselves have poor electrical conductivity, resulting in irreversible capacity loss, which in turn affects the battery life and cycle life of lithium-ion batteries.
  • a negative electrode sheet which includes a negative electrode current collector, and a first negative electrode film layer and a second negative electrode film layer are sequentially provided on the surface of the negative electrode current collector, that is, the first negative electrode film layer is attached to On the surface of the negative electrode current collector, the second negative electrode film layer is attached to the surface of the first negative electrode film layer, and the active material of the first negative electrode film layer includes silicon particles and first graphite particles, and the active material of the second negative electrode film layer Including second graphite particles, that is, the negative electrode film layer is divided into two layers, in which the active material of the negative electrode film layer close to the negative electrode current collector includes a mixture of silicon particles and first graphite particles, and the active material of the other negative electrode film layer far away from the negative electrode current collector
  • the substance includes second graphite particles, so that when lithium ions move to the negative electrode sheet, part of the lithium ions are first embedded in the second graphite particles in the second negative electrode film layer, and the remaining lithium ions
  • Part of the lithium ions are first embedded in the second negative electrode film layer, so that the concentration of lithium ions moving to the first negative electrode film layer is reduced and the speed becomes slow, so that the lithium ions have enough time to be embedded in the silicon particles and the first graphite particles, and then The aggregation density of lithium ions at the silicon particles and the first graphite particles nearby is reduced, and the phenomenon of uneven distribution of lithium ion concentration is reduced, that is, the precipitation of lithium is reduced.
  • the diameter is smaller than the particle diameter of the second graphite particles, that is, the particle diameter of the first graphite particles is smaller.
  • first graphite particles By using the first graphite particles with a small diameter, more first graphite particles can be coated on the periphery of the silicon particles, so that the silicon particles can be more Effectively improve the dynamic properties of silicon particles.
  • larger second graphite particles are selected. On the one hand, the larger particles can improve compaction; on the other hand, the larger second graphite particles can have more gaps between them, so that they are incompatible with the small graphite particles.
  • the ratio can increase the porosity of the negative electrode sheet, thereby increasing the liquid retention capacity of the battery core, reducing the surface polarization of the negative electrode sheet, and improving the dynamic performance of the negative electrode sheet. Therefore, the battery life and life of the lithium-ion battery can be effectively improved by adopting the above structure.
  • embodiments of the present disclosure provide a negative electrode sheet, including a negative current collector 100, a first negative electrode film layer 200 attached to the surface of the negative current collector 100; and an active material of the first negative electrode film layer 200 It includes silicon particles 220 and first graphite particles 210; the second negative electrode film layer 300 is attached to the surface of the first negative electrode film layer 200; and the active material of the second negative electrode film layer 300 includes the second graphite particles 310.
  • the negative current collector 100 can be a copper foil, which mainly plays a conductive role and serves as a carrier of the negative electrode film layer, and the thickness of the copper foil can be 4-15 ⁇ m, for example, the thickness of the copper foil can be 4 ⁇ m, 7 ⁇ m, 11 ⁇ m or 15 ⁇ m.
  • the copper foil may be one of a homogeneous copper foil, a porous copper foil or a copper foil with a carbon coating layer.
  • the first negative electrode film layer 200 may be a film layer obtained by coating the first negative electrode film layer 200 slurry on the surface of the negative electrode current collector 100 and drying it.
  • the slurry of the first negative electrode film layer 200 may include deionized water, that is, the silicon particles 220 and the first graphite particles 210 are uniformly mixed with the deionized water to form a slurry, and the slurry is applied on the copper foil to form
  • the first negative electrode film layer 200 has an active material mixed with silicon particles 220 and first graphite particles 210 .
  • the second negative electrode film layer 300 may be a film layer obtained by coating the second negative electrode film layer 300 slurry on the surface of the first negative electrode film layer 200 and drying it.
  • the slurry of the first negative electrode film layer 200 may include deionized water, that is, the second graphite particles 310 are mixed with deionized water. The mixture is mixed into a slurry, and the slurry is applied on the copper foil to form a second negative electrode film layer 300 having an active material of second graphite particles 310 .
  • both the first graphite particles 210 and the second graphite particles 310 may include one or more of artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon, hard carbon, organic polymer compound carbon; silicon
  • the particles 220 may include one or more of silicon oxide materials, silicon carbide materials, and nano-silicon materials.
  • the negative electrode sheet provided in this embodiment is divided into two layers by dividing the negative electrode film layer.
  • the active material of the negative electrode film layer close to the negative current collector 100 includes a mixture of silicon particles 220 and graphite particles, and the other layer is far away from the negative current collector 100 .
  • the active material of the negative electrode film layer includes graphite particles, so that when lithium ions move to the negative electrode sheet, some lithium ions are first embedded in the graphite particles in the second negative electrode film layer 300 , and the remaining lithium ions are embedded in the first negative electrode film layer 200 , because some lithium ions are first embedded in the second negative electrode film layer 300, the concentration of lithium ions moving to the first negative electrode film layer 200 is reduced and the speed becomes slow, so that the lithium ions have enough time to be embedded in the silicon particles and the first negative electrode film layer 200.
  • the particle size of the first graphite particles 210 is smaller than the particle size of the silicon particles 220 .
  • the outer periphery of the silicon particle 220 may be completely covered by the first graphite particle 210 , that is, the first graphite particle 210 surrounds the silicon particle 220 and is attached to the outer periphery of the silicon particle 220 .
  • the ratio of D90 of the first graphite particles 210 to the D90 of the silicon particles 220 may be 0.2-0.5.
  • the ratio of the D90 of the first graphite particles 210 to the D90 of the silicon particles 220 may be 0.2, 0.3 or 0.5, so that the particle size of the first graphite particles 210 can be much smaller than the silicon particles 220 .
  • the D50 particle diameter of the silicon particle 220 is 6 ⁇ m-10 ⁇ m, and the D90 particle diameter is 18 ⁇ m-22 ⁇ m; for example, the D50 of the silicon particle 220 may be 6 ⁇ m, 8 ⁇ m, or 10 ⁇ m; the D90 of the silicon particle 220 may be 18 ⁇ m, 20 ⁇ m or 22 ⁇ m.
  • the D50 particle size of the first graphite particles 210 is 2 ⁇ m-4.5 ⁇ m, and the D90 particle size is 4.7 ⁇ m-6 ⁇ m.
  • the D50 particle size of the first graphite particles 210 may be 2 ⁇ m, 3 ⁇ m, or 4.5 ⁇ m; the first graphite The D90 of the particles 210 may be 4.7 ⁇ m, 5.5 ⁇ m, or 6 ⁇ m.
  • D50 refers to the particle diameter at which the cumulative distribution of particles is 50%, also called the median diameter or median particle diameter. This is a typical value indicating the particle size. This value accurately divides the whole into two equal parts, that is It means that 50% of the particles exceed this value and 50% of the particles are below this value. If the D50 of a sample is 6 ⁇ m, it means that among the particles of all particle sizes that make up the sample, particles larger than 6 ⁇ m account for 50%, and particles smaller than 6 ⁇ m also account for 50%.
  • D90 refers to the particle size at which the cumulative distribution of particles is 90%, that is, the volume content of particles smaller than this size accounts for 90% of all particles.
  • the main function of using large-diameter silicon particles 220 in combination with small-diameter graphite particles is to further improve the dynamic performance of the negative electrode sheet.
  • the silicon particles 220 have poor dynamic properties, especially the D90 silicon particles 220, which have larger particle sizes and poor dynamic properties. Therefore, using the first graphite particles 210 to coat the D90 silicon particles 220 can effectively improve the dynamic performance of the silicon particles 220 and improve the lithium deposition around the silicon particles 220, thereby effectively increasing the charging speed of the lithium-ion battery.
  • the first graphite particles 210 with a small particle size can make the outer periphery of the silicon particles 220 coated with more first graphite particles 210 , thereby more effectively improving the dynamic performance of the silicon particles 220 .
  • the dynamic performance of the first graphite particles 210 is significantly better than that of the silicon particles 220 , the lithium ions around the silicon particles 220 can be quickly embedded into the first graphite particles 210 , thus effectively improving the precipitation around the silicon particles 220 .
  • the content of silicon particles 220 in the first negative electrode film layer 200 may be 0.1%-30%.
  • the content of silicon particles 220 can be 0.1%, 5%, 10%, 20% or 30%, and the specific content can be set according to actual conditions.
  • the first negative electrode film layer 200 may also include a first conductive agent, a first binder and a first thickener, and the mixed material 230, the first conductive agent, the first binder and the first thickener mass
  • the ratios are respectively 75wt%-99wt%: 0.1wt%-5wt%: 0.1wt%-5wt%: 0.5wt%-5wt%.
  • the mass ratio of the mixed material 230, the first conductive agent, the first binder and the first thickener may be, 75wt%: 0.1wt%: 0.1wt%: 0.5wt%, 85wt%: 2wt% : 3wt%: 2.5wt%, 96.9wt%: 0.5wt%: 1.3wt%: 1.3wt% or 99wt%: 5wt%: 5wt%: 5wt%: 5wt%.
  • the first conductive agent may be one or more of conductive carbon black, carbon fiber, Ketjen black, acetylene black, carbon nanotubes and graphene.
  • the first thickener may be sodium carboxymethylcellulose or lithium carboxymethylcellulose.
  • the first binder can be a water-based binder, for example, it can be styrene-butadiene rubber, nitrile rubber, butadiene rubber, modified styrene-butadiene rubber, sodium polyacrylate, water-based polyacrylonitrile copolymer or polypropylene One or several mixtures of acid esters.
  • the first graphite particles 210 and the second graphite particles 310 are obtained by sieving the same kind of graphite, and the particle size of the first graphite particles 210 may be smaller than the particle size of the second graphite particles 310 .
  • the D50 particle diameter of the second graphite particles 310 in the second negative electrode film layer 300 may be 11 ⁇ m-14 ⁇ m, and the D90 particle diameter may be 22 ⁇ m-29 ⁇ m.
  • first graphite particles 210 and the second graphite particles 310 are of the same type of graphite.
  • the D10 particles in the graphite particles are screened out. This part of the graphite particles is used as the first graphite particles 210, and the remaining graphite particles are used as the second graphite particles.
  • the particle diameter of the second graphite particles 310 is greater than 7 ⁇ m, that is, after the D10 particles are screened out from the graphite particles, the remaining graphite particles with a particle size smaller than 7 ⁇ m are removed and used as the second graphite particles. 310.
  • the large particles can improve compaction; on the other hand, the large second graphite particles 310 can have more gaps between them, so that they can be compared with the small particles of graphite.
  • the particles can increase the porosity of the negative electrode sheet, thereby increasing the liquid retention capacity of the battery core, reducing the surface polarization of the negative electrode sheet, and improving the dynamic performance of the negative electrode sheet, thus further improving the battery life and life of the lithium battery.
  • the reason why the first graphite particles 210 and the second graphite particles 310 are made of the same type of graphite is that the materials are similar, their physical and chemical parameters are the same, and the transmission resistance of lithium ions in the material is the same; at the same time, the same type of graphite is selected to make them roll-pressed.
  • the material's compaction parameters are similar, the two layers of graphite particles are in closer contact, thereby avoiding delamination.
  • the second negative electrode film layer 300 also includes a second conductive agent, a second binder and a second thickener, and the second graphite particles 310, the second conductive agent, the second binder and the second thickener
  • the mass ratios are respectively 75wt%-99wt%: 0.1wt%-5wt%: 0.1wt%-5wt%: 0.5wt%-5wt%.
  • the mass ratio of the second graphite particles 310, the second conductive agent, the second binder and the second thickener may be, 75wt%: 0.1wt%: 0.1wt%: 0.5wt%, 85wt%: 2wt%: 3wt%: 2.52wt%, 96.9wt%: 0.5wt%: 1.3wt%: 1.3wt% or 99wt%: 5wt%: 5wt%: 5wt%: 5wt%.
  • the second conductive agent may be one or more of conductive carbon black, carbon fiber, Ketjen black, acetylene black, carbon nanotubes and graphene.
  • the second thickener may be sodium carboxymethylcellulose or lithium carboxymethylcellulose.
  • the second binder can be a water-based binder, for example, it can be styrene-butadiene rubber, nitrile rubber, butadiene rubber, modified styrene-butadiene rubber, sodium polyacrylate, water-based polyacrylonitrile copolymer or polypropylene One or several mixtures of acid esters.
  • the ratio of the thickness d1 of the first negative electrode film layer 200 to the thickness d2 of the second negative electrode film layer 300 may be 1:9-9:1.
  • the ratio of the thickness d1 of the first negative electrode film layer 200 to the thickness d2 of the second negative electrode film layer 300 may be 1:9, 5:5 or 9:1, and the thickness d1 of the first negative electrode film layer 200 may be 44 ⁇ m, and the thickness d2 of the second negative electrode film layer 300 may be 56 ⁇ m.
  • An embodiment of the present disclosure also provides a lithium ion battery, which includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, and the negative electrode sheet is the negative electrode sheet in the above embodiment.
  • the first negative electrode film layer 200 and the second negative electrode film layer 300 are sequentially arranged on the surface of the negative electrode current collector 100, that is, the first negative electrode film layer 200 is attached to the surface of the negative electrode current collector 100.
  • the second negative electrode film layer 300 is attached to the surface of the first negative electrode film layer 200, and the active material of the first negative electrode film layer 200 includes silicon particles 220 and first graphite particles 210.
  • the active material of the second negative electrode film layer 300 Including second graphite particles 310, that is, the negative electrode film layer is divided into two layers, in which the active material of the negative electrode film layer close to the negative electrode current collector includes a mixture of silicon particles 220 and first graphite particles 210, and the other negative electrode far away from the negative electrode current collector 100
  • the active material of the film layer includes second graphite particles 310, so that when lithium ions move to the negative electrode sheet, some lithium ions are first embedded in the second graphite particles 310 in the second negative electrode film layer, and the remaining lithium ions are embedded in the first graphite particles 310.
  • the concentration of lithium ions moving to the first negative electrode film layer 100 is reduced, thereby reducing the concentration of lithium ions at the silicon particles and the first graphite near them.
  • the aggregation of particles 210 further reduces the uneven distribution of lithium ion concentration, that is, reduces the precipitation of lithium, thereby improving the battery life and life of the lithium ion battery.
  • an embodiment of the present disclosure also provides a method for preparing a negative electrode sheet, including:
  • obtaining first graphite particles, silicon particles and second graphite particles, and mixing the first graphite particles and silicon particles to form a mixed material includes:
  • a certain amount of similar graphite particles is obtained, the graphite particles are screened, and the graphite particles with a particle size smaller than a preset range are used as the first graphite particles, and the remaining graphite particles are used as the second graphite particles.
  • First graphite particles 210, silicon particles 220 and second graphite particles 310 are obtained, and the first graphite particles 210 and silicon particles 220 are mixed to form a mixed material.
  • obtaining the first graphite particles 210, silicon particles 220 and second graphite particles 310, and mixing the first graphite particles 210 and the silicon particles 220 to form a mixed material includes:
  • Graphite particles are obtained, the graphite particles are screened, and graphite particles with a particle size smaller than a preset range are used as first graphite particles 210 , and the remaining graphite particles are used as second graphite particles 310 .
  • a certain amount of graphite particles and silicon particles 220 are obtained: wherein the D10 particle size of the graphite particles is 5 ⁇ m, the D50 particle size is 13 ⁇ m, and the D90 particle size is 25 ⁇ m; the D10 graphite particles are screened out as For the first graphite particles 210, the remaining graphite particles with a particle size less than 7 ⁇ m are removed as the second graphite particles 310, that is, the particle size range of the first graphite particles 210 can be 1-5 ⁇ m; the particle size of the second graphite particles 310 can be 8 -27 ⁇ m.
  • the D50 particle diameter of the silicon particles 220 is 8 ⁇ m, and the D90 particle diameter is 20 ⁇ m.
  • the first graphite particles 210 and the silicon particles 220 are taken according to a mass ratio of 95:5, and the two are mixed to obtain a mixed material 230 .
  • the first negative electrode film layer 200 slurry To prepare the first negative electrode film layer 200 slurry, mix the mixture material 230, the first conductive agent, the first binder, and the first thickener evenly to obtain the first negative electrode film layer 200 slurry.
  • the mixed material 230, the first conductive agent, the first binder, and the first thickener are added to the mixing tank at a mass ratio of 96.9wt%: 0.5wt%: 1.3wt%: 1.3wt%, And use deionized water to prepare the first negative electrode film layer 200 slurry, the above ratio is the dry material mass ratio, and the slurry Solid content is 42%.
  • the first conductive agent in this embodiment can be conductive carbon black
  • the first thickener can be sodium carboxymethylcellulose
  • the first binder can be water-emulsified styrene-butadiene rubber
  • the first graphite particles 210 It can be artificial graphite.
  • the second graphite particles 310, the second conductive agent, the second binder, and the second thickener are evenly mixed to obtain the second negative electrode film layer 300 slurry.
  • the second graphite particles 310, the second conductive agent, the second thickener, and the second binder into the stirring tank at a mass ratio of 96.9wt%: 0.5wt%: 1.3wt%: 1.3wt%, and use Deionized water is used to prepare the slurry for the second negative electrode film layer 300.
  • the above ratio is the dry material mass ratio, and the solid content in this slurry is 42%.
  • the second conductive agent in this embodiment can be conductive carbon black
  • the second thickener can be sodium carboxymethylcellulose
  • the second binder can be water-emulsified styrene-butadiene rubber
  • the first graphite particles 210 It can be artificial graphite.
  • a coating machine is used to coat the first negative electrode film layer 200 slurry containing silicon on the surface of the negative current collector 100 , and the second negative electrode film layer 300 of pure graphite particles without silicon is coated on the surface of the negative current collector 100 .
  • a negative electrode film layer 200 is formed on the surface of the slurry. Then it is dried in a five-stage oven. The temperatures of each oven section are 60°C, 80°C, 110°C, 110°C, and 100°C respectively. After drying, the thickness of the second negative electrode film layer 300 can be 55um, and the thickness of the first negative electrode film can be 55um.
  • the thickness of the layer 200 may be 55um, so that the ratio of the thickness of the first negative electrode film layer 200 to the thickness of the second negative electrode film layer 300 is 5:5.
  • the compacted density of the sheet can be 1.75g/cm 2 , thereby completing the preparation of the negative electrode sheet.
  • lithium cobalt oxide as the positive active material, add the positive active material, conductive agent and thickener into the stirring tank at a mass ratio of 97.2:1.5:1.3, and add NMP (N-methylpyrrolidone) solvent for thorough mixing. Stir and pass the mixed slurry through a screen to finally prepare the positive electrode slurry.
  • the solid content of the positive electrode slurry is 70% to 75%, and then a coater is used to coat the slurry on the positive electrode current collector.
  • the positive electrode current collector can be aluminum foil, and it is dried at 120°C to obtain the positive electrode sheet. .
  • the negative electrode sheet prepared above, the positive electrode sheet, and the separator are rolled together to form a core, packaged with aluminum plastic film, baked to remove moisture, and then injected with electrolyte.
  • the battery core can be obtained by using a hot-pressing process.
  • the difference between this embodiment and Embodiment 1 is that the ratio of the thickness of the first negative electrode film layer 200 to the thickness of the second negative electrode film layer 300 is 3:7.
  • the difference between this embodiment and Embodiment 1 is that the ratio of the thickness of the first negative electrode film layer 200 to the thickness of the second negative electrode film layer 300 is 7:3.
  • Embodiment 1 The difference between this embodiment and Embodiment 1 is that the mass ratio of the first graphite particles 210 to the silicon particles 220 is 90:10.
  • Embodiment 1 The difference between this embodiment and Embodiment 1 is that the D50 particle size of the silicon particles 220 in the first negative electrode film layer 200 is 9 ⁇ m, and the D90 particle size is 22 ⁇ m.
  • the particle size of D10 in the graphite particles is 3 ⁇ m
  • the particle size of D50 is 11 ⁇ m
  • the particle size of D90 is 22 ⁇ m. That is, the D10 particles of the graphite particles are screened out as the first graphite particles. 210.
  • the particle size of the first graphite particles 210 is not larger than 3 ⁇ m, and the remaining graphite particles are removed from the particles smaller than 7 ⁇ m as the second graphite particles 310.
  • the difference between this embodiment and Example 1 is that the particle size of D10 in the graphite particles is 3 ⁇ m, the particle size of D50 is 14 ⁇ m, and the particle size of D90 is 28 ⁇ m. That is, the D10 particles of the graphite particles are screened out as the first graphite particles. 210.
  • the particle size of the first graphite particles 210 is not larger than 3 ⁇ m, and the remaining graphite particles are removed from the particles smaller than 7 ⁇ m as the second graphite particles 310.
  • the negative electrode film layer has a one-layer structure, that is, the active material includes silicon particles 220 and graphite particles, which are mixed and then coated on the negative current collector 100 to form a negative electrode with one layer of negative electrode film layer. piece.
  • the difference between this embodiment and Example 1 is that the graphite particles are not screened, that is, some of the graphite particles are directly The graphite particles are used as first graphite particles 210 , and the remaining graphite particles are used as second graphite particles 310 .
  • the graphite particles with small particle sizes are not screened out as the first graphite particles 210 in the first negative electrode film layer 200 , and the graphite particles with large particle sizes are used as the second graphite particles in the second negative electrode film layer 300 310.
  • the D10 particle size of the graphite particles is 5 ⁇ m
  • the D50 particle size is 13 ⁇ m
  • the D90 particle size is 25 ⁇ m.
  • the D50 particle size of the silicon particles 220 is 8 ⁇ m
  • the D90 particle size is 20 ⁇ m.
  • Each battery cell prepared above was subjected to 1.2C step charging/0.7C discharge at 25°C, and the battery was disassembled at different cycles to confirm the lithium deposition on the negative electrode surface of the battery.
  • the disassembly results and energy density are as follows:
  • Table 1 shows the main relevant parameters of Examples 1-7 and Comparative Examples 1-2.
  • the degree of lithium precipitation on the surface of the negative electrode sheet is represented by 0, 1, 2, 3, 4, and 5.
  • 0 no lithium precipitation
  • 5 represents severe lithium precipitation
  • 1, 2, 3, and 4 represent different lithium precipitation. The larger the number, the more serious the degree of lithium precipitation.
  • Examples 1 to 3 are the effects of the different thicknesses between the first negative electrode film layer 200 and the second negative electrode film layer 300 on the lithium evolution of the negative electrode sheet. That is, when the first negative electrode film layer 200 When the thickness between the first negative electrode film layer 300 and the second negative electrode film layer 300 is 5:5 and 3:7, when the lithium ion battery undergoes 500T (cycle) charge and discharge, no lithium is precipitated on the surface of the negative electrode sheet; when the first negative electrode film When the ratio of the thickness of the layer 200 to the thickness of the second negative electrode film layer 300 reaches 7:3, when the lithium ion battery undergoes 500T (cycle) charge and discharge, the surface lithium precipitation degree of the negative electrode sheet is 1.
  • the thickness between the first negative electrode film layer 200 and the second negative electrode film layer 300 The ratio has a certain impact on the battery capacity retention rate and expansion rate.
  • the thickness between the first negative electrode film layer 200 and the second negative electrode film layer 300 is 5:5, 3:7 and 7:3, when the lithium ion battery undergoes 700T (cycle) charge and discharge, the The capacity retention rates are 82.57%, 86.09%, and 81.7% respectively; when the lithium-ion battery undergoes 700T (cycle) charge and discharge, the expansion rates of the lithium-ion battery are 9.58%, 9.29%, and 10.21% respectively. And their energy densities are 817wh/L, 815wh/L, and 819wh/L respectively.
  • the negative electrode film layer by dividing the negative electrode film layer into two layers, and disposing the second negative electrode film layer 300 whose active material is a layer of pure graphite particles on the outer layer, and the first negative electrode film layer whose active material is a mixture of graphite particles and silicon particles 220
  • the layer 200 is disposed in the inner layer, so that when lithium ions move to the negative electrode sheet, some lithium ions are first embedded in the graphite particles in the second negative electrode film layer 300, and the remaining lithium ions are embedded in the first negative electrode film layer 200.
  • Part of the lithium ions are first embedded in the second negative electrode film layer 300, so that the concentration of lithium ions moving to the first negative electrode film layer 200 is reduced and the speed becomes slow, so that the lithium ions have enough time to be embedded in the silicon particles and the first graphite particles. , thereby reducing the aggregation density of lithium ions at the silicon particles 220 and the nearby first graphite particles 210, thereby reducing the uneven distribution of lithium ion concentration, that is, reducing the precipitation of lithium, thereby improving the performance of the lithium-ion battery. battery life and lifespan. As the thickness of the first negative electrode film layer 200 increases, the energy density of the lithium-ion battery does not change much.
  • the content of lithium ions embedded in the second negative electrode film layer 300 decreases, resulting in more lithium ions embedded in the first negative electrode film. layer 200, thereby increasing the density of lithium ions accumulated in and around the silicon particles 220, thereby causing the precipitation of lithium ions.
  • the capacity retention rate of the lithium-ion battery can be gradually increased; at the same time, as the thickness of the first negative electrode film layer 200 increases, That is, as the content of silicon particles 220 in the negative electrode sheet increases, the expansion rate of the lithium-ion battery will also increase. Therefore, when selecting the thickness of the first negative electrode film layer 200 and the thickness of the second negative electrode film layer 300 , comprehensive considerations need to be made to obtain a lithium-ion battery with excellent overall performance.
  • Example 1 and Example 4 it can be seen from Example 1 and Example 4 that when the ratio of the silicon particles 220 to the first graphite particles 210 in the first negative electrode film layer 200 reaches 10:90, the lithium ion battery undergoes 500T (cycle) charge and discharge. When , the degree of lithium precipitation on the surface of the negative electrode sheet is 1. When the lithium-ion battery undergoes 700T (cycle) charge and discharge, the capacity retention rate of the lithium-ion battery is 79.52%; when the lithium-ion battery undergoes 700T (cycle) charge and discharge, the expansion rate of the lithium-ion battery is 10.09% respectively; energy Density is 821wh/L.
  • Embodiment 1 and Embodiment 5 when the particle size of the silicon particles 220 in the first negative electrode film layer 200 is larger, that is, when the particle size D50 of the silicon particle 220 reaches 9 ⁇ m and the particle size D90 reaches 22 ⁇ m,
  • the degree of lithium precipitation on the surface of the negative electrode sheet is 0.
  • the capacity retention rate of the lithium-ion battery is 80.03%; when the lithium-ion battery undergoes 700T (cycle) charge and discharge, the expansion rate of the lithium-ion battery is 10.62% respectively.
  • Embodiment 1 and Embodiment 6 that when the particle size of the graphite particles in the first negative electrode film layer 200 is smaller, that is, the particle size of the graphite particles D10 reaches 3 ⁇ m, the particle size of D50 reaches 11 ⁇ m, and the particle size of D90 When it reaches 22 ⁇ m, that is, when the particle size of the first graphite particle 210 and the particle size of the second graphite particle 310 both decrease accordingly, but the particle size of the second graphite particle 310 is still much larger than the particle size of the first graphite particle 210, the lithium When an ion battery undergoes 500T (cycle) charge and discharge, the degree of lithium precipitation on the surface of the negative electrode sheet is 0.
  • the capacity retention rate of the lithium-ion battery is 84.77%; when the lithium-ion battery undergoes 700T (cycle) charge and discharge, the expansion rate of the lithium-ion battery is 9.56% respectively; and
  • the energy density is 816wh/L.
  • Example 1 and Example 7 when the particle size of the graphite particles in the second negative electrode film layer 300 is larger, that is, when the particle size D50 of the graphite particles reaches 14 ⁇ m and the particle size D90 reaches 28 ⁇ m, lithium ions When the battery undergoes 500T (cycle) charge and discharge, the degree of lithium precipitation on the surface of the negative electrode sheet is 0. When the lithium-ion battery undergoes 700T (cycle) charge and discharge, the capacity retention rate of the lithium-ion battery is 77.27%; when the lithium-ion battery undergoes 700T (cycle) charge and discharge, the expansion rate of the lithium-ion battery is 11.77% respectively; and The energy density is 823wh/L.
  • the second graphite particles 310 in the second negative electrode film layer 300 have a larger particle size, they can increase the porosity of the negative electrode sheet compared with small particles, thereby increasing the liquid retention capacity of the battery core and reducing the surface polarization of the negative electrode sheet. Improve the dynamic performance of the negative electrode sheet, thereby further improving the battery life and life of the lithium battery.
  • the number of graphite particles in the second negative electrode film layer 300 will be significantly reduced, which will in turn lead to a significant reduction in the amount of lithium ions embedded in the second negative electrode film layer 300, resulting in more graphite particles.
  • Lithium ions accumulate near the silicon particles 220, thereby affecting the capacity retention rate and expansion rate of the lithium-ion battery.
  • Comparative Example 1 when the slurry mixed with silicon particles 220 and graphite particles is applied to the negative electrode current collector to form a negative electrode film layer, the lithium ion battery undergoes 500T (cycle) charge and discharge.
  • the surface lithium precipitation degree of the negative electrode sheet is 5; when the lithium ion battery undergoes 700T (cycle) charge and discharge, the capacity retention rate of the lithium ion battery is 65.32%; when the lithium ion battery undergoes 700T (cycle) charge and discharge, the lithium ion
  • the expansion rate of the battery is 17.65% respectively; the energy density is 820wh/L.
  • Comparative Example 2 when the graphite particles are not screened, that is, part of the graphite particles are directly used as the first graphite particles 210 and the remaining graphite particles are used as the second graphite particles 310, the lithium-ion battery passes through the battery after 500T (Cycle) of charge and discharge, the surface lithium precipitation degree of the negative electrode sheet is 4; when the lithium-ion battery passes through 700T (cycle) of charge and discharge, the capacity retention rate of the lithium-ion battery is 69.32%; the lithium-ion battery passes through 700T (cycle) ), the expansion rate of the lithium-ion battery is 15.31% respectively; the energy density is 815wh/L.
  • Comparative Example 2 Compared Comparative Example 2 with Comparative Example 1, although the overall performance of the lithium-ion battery can be improved to a certain extent by dividing the negative electrode film layer into two layers, the lithium deposition situation is still serious, and the capacity of the lithium-ion battery is still relatively serious. The retention rate is still low, and the expansion rate of lithium-ion batteries is large.
  • first and second are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of indicated technical features. Therefore, features defined as “first”, “second” and “third” may explicitly or implicitly include at least one of these features.
  • “plurality” means at least two, such as two, three, etc., unless otherwise explicitly and specifically limited.
  • connection In the embodiments of the present disclosure, unless otherwise explicitly stated and limited, the terms “installation”, “connection”, “connection”, “fixing” and other terms should be understood in a broad sense. For example, it can be a fixed connection or a removable connection. Detachable connection, or integration; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediary; it can be an internal connection between two elements or an interaction between two elements, unless otherwise There are clear limits. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present disclosure can be understood according to specific circumstances.
  • the first feature "on” or “below” the second feature may be that the first and second features are in direct contact, or the first and second features are in intermediate contact. Indirect media contact.
  • the terms “above”, “above” and “above” the first feature is above the second feature may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is higher in level than the second feature.
  • "Below”, “below” and “beneath” the first feature to the second feature may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature has a smaller horizontal height than the second feature.
  • references to the terms “one embodiment,” “some embodiments,” “an example,” “specific examples,” or “some examples” or the like means that specific features are described in connection with the embodiment or example.
  • structures, materials or features are included in at least one embodiment or example of embodiments of the present disclosure.
  • the schematic expressions of the above terms are not necessarily directed to the same embodiment or example.
  • the specific features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
  • those skilled in the art may combine and combine different embodiments or examples and features of different embodiments or examples described in this specification unless they are inconsistent with each other.

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Abstract

本公开实施例涉及电池技术领域，具体涉及一种负极片及锂离子电池，用以解决石墨颗粒和硅颗粒混合的功能层易出现析锂现象，从而影响锂离子电池的续航和寿命的技术问题，该负极片包括负极集流体，第一负极膜层贴于负极集流体的表面上；且第一负极膜层的活性物质包括硅颗粒和第一石墨颗粒；第二负极膜层贴于第一负极膜层的表面上，第二负极膜层的活性物质包括第二石墨颗粒；即将负极膜层分成了两层，从而使得当锂离子移动至负极片处时，部分锂离子先嵌入第二负极膜层中，剩余的锂离子嵌入第一负极膜层中，从而降低了锂离子在硅颗粒处及其附近石墨颗粒处的聚集，进而降低了锂的析出，由此提高了锂离子电池的续航和寿命。

Description

负极片及锂离子电池
本申请要求于2022年4月7日提交中国专利局、申请号为202210360401.2、申请名称为“负极片、锂离子电池及负极片的制备方法”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本公开涉及电池技术领域，尤其涉及一种负极片及锂离子电池。
背景技术
近年来，随着便携式电子产品销量呈现爆发式增长，锂离子电池已经成为各种设备的电源。相关技术中，锂电池包括正极片、负极片、隔膜和电解液，负极片包括金属片以及覆盖在金属片上的功能层，功能层由石墨颗粒和硅颗粒混合形成。
然而，在锂离子电池充放电的过程中，由于硅颗粒和石墨颗粒导电性及储锂量存在差异，从而导致充电时两种材料的电位及极化程度存在差异，进而导致石墨颗粒和硅颗粒混合的功能层析锂现象的产生，由此影响了锂离子电池的续航和寿命。
申请内容
本公开实施例提供一种负极片及锂离子电池，用以解决相关技术中石墨颗粒和硅颗粒混合的功能层易出现析锂现象，从而影响锂离子电池的续航和寿命。
本公开实施例解决上述技术问题的方案如下：
一种负极片，包括，
负极集流体；
第一负极膜层，其贴于所述负极集流体的表面上；且所述第一负极膜层的活性物质包括硅颗粒和第一石墨颗粒；
第二负极膜层，其贴于所述第一负极膜层的表面上；且所述第二负极 膜层的活性物质包括第二石墨颗粒，所述第二石墨颗粒的粒径大于所述第一石墨颗粒的粒径。
本公开实施例的有益效果是：通过在负极集流体的表面上依次设置第一负极膜层和第二负极膜层，即第一负极膜层贴于负极集流体的表面上，第二负极膜层贴于第一负极膜层的表面上，且第一负极膜层的活性物质包括硅颗粒和第一石墨颗粒，第二负极膜层的活性物质包括第二石墨颗粒，即将负极膜层分成了两层，其中靠近负极集流体的负极膜层的活性物质包括硅颗粒和石墨颗粒的混合物，另一远离负极集流体的负极膜层的活性物质包括石墨颗粒，从而使得当锂离子移动至负极片处时，部分锂离子先嵌入第二负极膜层中的石墨颗粒内，剩余的锂离子嵌入第一负极膜层中，由于部分锂离子先嵌入第二负极膜层中，使得移动至第一负极膜层处的锂离子浓度降低且速度变缓慢，从而使得锂离子具有足够的时间嵌入硅颗粒和第一石墨颗粒中，进而降低了锂离子在硅颗粒处及其附近第一石墨颗粒处的聚集，减轻了锂离子浓度分布不均的现象，即降低了锂的析出。同时，由于第一石墨颗粒的粒径小于第二石墨颗粒的粒径，即第一石墨颗粒的粒径较小，通过采用小粒径的第一石墨颗粒能够使得硅颗粒的外周包覆较多的第一石墨颗粒，从而能够更加有效的提高硅颗粒动力学性能。另外，选用较大颗粒的第二石墨颗粒，其一方面大颗粒可以提高压实；另一方面，大颗粒的第二石墨颗粒之间具有较多的缝隙，与小颗粒的石墨颗粒相比可以能够提高负极片的孔隙率，进而能够提高电芯保液量，降低负极片表面极化，提高负极片动力学性能。由此，通过采用以上结构能够有效的提高锂离子电池的续航和寿命。
在上述技术方案的基础上，本公开实施例还可以做如下改进。
在一种可能的实现方式中，所述第一石墨颗粒的粒径小于所述硅颗粒的粒径。
在一种可能的实现方式中，所述第一石墨颗粒和所述第二石墨颗粒是由同类石墨通过筛分得到。
在一种可能的实现方式中，所述第一负极膜层中的硅颗粒的D50的粒径为6μm-10μm、D90的粒径为18μm-22μm；所述第一石墨颗粒的D50的粒径为2μm-4.5μm、D90的粒径为4.7μm-6μm。
在一种可能的实现方式中，所述第二负极膜层中的第二石墨颗粒的D50的粒径为11μm-14μm、D90的粒径为22μm-29μm。
在一种可能的实现方式中，所述第二石墨颗粒的粒径均大于7μm。
在一种可能的实现方式中，所述第一负极膜层的厚度与所述第二负极膜层的厚度之比为1:9-9:1。
在一种可能的实现方式中，其包括正极片、负极片、隔膜和电解液，所述负极片为以上任一项所述的负极片。
一种负极片的制备方法，包括，
获取第一石墨颗粒、硅颗粒和第二石墨颗粒，并将所述第一石墨颗粒与所述硅颗粒进行混合组成混合物料；
将所述混合物料、第一导电剂、第一粘结剂、第一增稠剂混合均匀，以得到第一负极膜层浆料；
将第二石墨颗粒、第二导电剂、第二粘结剂、第二增稠剂混合均匀，以得到第二负极膜层浆料；
将所述第一负极膜层浆料涂敷在负极集流体的表面上，将所述第二负极膜层浆料涂敷在所述第一负极膜层浆料表面上；
对涂有所述第一负极膜层浆料和所述第二负极膜层浆料的所述负极集流体进行烘干。
在一种可能的实现方式中，获取第一石墨颗粒、硅颗粒和第二石墨颗粒，并将所述第一石墨颗粒与所述硅颗粒进行混合组成混合物料包括：
获取一定量的同类石墨颗粒，筛选所述石墨颗粒，将粒径小于预设范围的所述石墨颗粒作为所述第一石墨颗粒，其余所述石墨颗粒作为所述第二石墨颗粒。
附图说明
图1为本公开实施例提供的负极片中的第一负极膜层和第二负极膜层的示意图；
图2为本公开实施例提供的第一石墨颗粒、硅颗粒、混合物料及第二石墨颗粒的结构示意图；
图3为本公开实施例提供的负极片的制备方法的流程图。
附图标记说明：
100、负极集流体；200、第一负极膜层；210、第一石墨颗粒；220、
硅颗粒；230、混合物料；300、第二负极膜层；310、第二石墨颗粒。
具体实施方式
近年来，随着便携式电子产品销量呈现爆发式增长，锂离子电池已经成为各种设备的电源。人们对锂离子电池的性能要求也进一步提高，要求锂离子电池具备较长的寿命是作为锂离子电池的一项重要指标。
相关技术中，锂电池包括正极片、负极片、隔膜和电解液；其中负极片包括金属片以及覆盖在金属片上的功能层。为了提高锂电池的能量密度，此功能层由石墨和硅混合而成，因为硅的储锂量远大于石墨，从而能够提升锂离子电池的能量密度，进而能够提高锂离子电池的续航和寿命。
然而，在锂离子电池充放电的过程中，由于硅及氧化硅材料和石墨材料导电性及储锂量差异，导致充电时两种材料的电位及极化程度存在差异，使得硅颗粒的电位高，硅颗粒附近的石墨颗粒电位最低，导致负极片中锂离子浓度分布不均，从而出现析锂现象。同时，由于硅颗粒在充放电过程中体积易膨胀，使得电极材料在循环过程中结构易崩塌且颗粒分化，从而导致活性物质之间及活性物质与集流体之间丧失电子导电能力，并且由于硅颗粒本身导电性差，从而导致不可逆容量损失，进而影响了锂离子电池的续航和循环寿命。
有鉴于此，本公开实施例提供了一种负极片，其包括负极集流体，且在负极集流体的表面上依次设置第一负极膜层和第二负极膜层，即第一负极膜层贴于负极集流体的表面上，第二负极膜层贴于第一负极膜层的表面上，且第一负极膜层的活性物质包括硅颗粒和第一石墨颗粒，第二负极膜层的活性物质包括第二石墨颗粒，即将负极膜层分成了两层，其中靠近负极集流体的负极膜层的活性物质包括硅颗粒和第一石墨颗粒的混合物，另一远离负极集流体的负极膜层的活性物质包括第二石墨颗粒，从而使得当锂离子移动至负极片处时，部分锂离子先嵌入第二负极膜层中的第二石墨颗粒内，剩余的锂离子嵌入第一负极膜层中，由于部分锂离子先嵌入第二负极膜层中，使得移动至第一负极膜层处的锂离子浓度降低且速度变缓慢，从而使得锂离子具有足够的时间嵌入硅颗粒和第一石墨颗粒中，进而降低了锂离子在硅颗粒处及其附近第一石墨颗粒处的聚集密度，减轻了锂离子浓度分布不均的现象，即降低了锂的析出。同时，由于第一石墨颗粒的粒 径小于第二石墨颗粒的粒径，即第一石墨颗粒的粒径较小，通过采用小粒径的第一石墨颗粒能够使得硅颗粒的外周包覆较多的第一石墨颗粒，从而能够更加有效的提高硅颗粒动力学性能。另外，选用较大颗粒的第二石墨颗粒，其一方面大颗粒可以提高压实；另一方面，大颗粒的第二石墨颗粒之间可以具有较多的缝隙，从而与小颗粒的石墨颗粒相比能够提高负极片的孔隙率，进而能够提高电芯保液量，降低负极片表面极化，提高负极片动力学性能。由此，通过采用以上结构能够有效的提高了锂离子电池的续航和寿命。
为了使本申请实施例的上述目的、特征和优点能够更加明显易懂，下面将结合本申请实施例中的附图，对本申请实施例中的技术方案进行清楚、完整地描述。显然，所描述的实施例仅仅是本申请的一部分实施例，而不是全部的实施例。基于本申请中的实施例，本领域普通技术人员在没有作出创造性劳动的前提下所获得的所有其它实施例，均属于本申请保护的范围。
参考图1和图2，本公开实施例提供了一种负极片，包括负集流体100，第一负极膜层200贴于负集流体100的表面上；且第一负极膜层200的活性物质包括硅颗粒220和第一石墨颗粒210；第二负极膜层300贴于第一负极膜层200的表面上；且第二负极膜层300的活性物质包括第二石墨颗粒310。
其中，负集流体100可以为铜箔，其主要是起导电作用，同时作为负极膜层的载体，且铜箔的厚度可以为4-15μm，例如铜箔的厚度可以为4μm、7μm、11μm或15μm。其中，铜箔可以为均质铜箔、多孔铜箔或带涂炭层的铜箔中的一种。
示例性地，第一负极膜层200可以是通过第一负极膜层200浆料涂于负极集流体100的表面上，且通过烘干后得到的膜层。其中，第一负极膜层200浆料可以包括去离子水，即通过去离子水将硅颗粒220和第一石墨颗粒210混合均匀形成浆料，并将此浆料涂于铜箔上，从而形成具有硅颗粒220和第一石墨颗粒210混合的活性物质的第一负极膜层200。
示例性地，第二负极膜层300可以是通过第二负极膜层300浆料涂于第一负极膜层200的表面上，且可以通过烘干后得到的膜层。其中，第一负极膜层200浆料可以包括去离子水，即通过去离子水将第二石墨颗粒310 和成浆料，并将此浆料涂于铜箔上，从而形成具有第二石墨颗粒310的活性物质的第二负极膜层300。
示例性地，第一石墨颗粒210和第二石墨颗粒310均可以包括人造石墨、天然石墨、中间相碳微球、软碳、硬碳、有机聚合物化合物碳中的一种或多种；硅颗粒220可以包括氧化亚硅材料、碳化硅材料、纳米硅材料中的一种或多种。
本实施例中提供的负极片，通过将负极膜层分成了两层，其中靠近负集流体100的负极膜层的活性物质包括硅颗粒220和石墨颗粒的混合物，另一远离负集流体100的负极膜层的活性物质包括石墨颗粒，从而使得当锂离子移动至负极片处时，部分锂离子先嵌入第二负极膜层300中的石墨颗粒内，剩余的锂离子嵌入第一负极膜层200中，由于部分锂离子先嵌入第二负极膜层300中，使得移动至第一负极膜层200处的锂离子浓度降低且速度变缓慢，从而使得锂离子具有足够的时间嵌入硅颗粒和第一石墨颗粒中，从而降低了锂离子在硅颗粒220处及其附近石墨颗粒处的聚集密度，进而减轻了锂离子浓度分布不均的现象，即降低了锂的析出，由此提高了锂离子电池的续航能力和寿命。
继续参照图1和图2，第一石墨颗粒210的粒径小于硅颗粒220的粒径。
示例性地，硅颗粒220的外周可以被第一石墨颗粒210完全包覆，即第一石墨颗粒210围绕硅颗粒220一周，且贴附于硅颗粒220的外周。例如，第一石墨颗粒210的D90与硅颗粒220的D90之比可以为0.2-0.5。其中，第一石墨颗粒210的D90与硅颗粒220的D90之比可以为0.2、0.3或0.5，从而使得第一石墨颗粒210的粒径能够远小于硅颗粒220。
示例性地，硅颗粒220的D50的粒径为6μm-10μm、D90的粒径为18μm-22μm；例如，硅颗粒220的D50可以为6μm、8μm或10μm；硅颗粒220的D90可以为18μm、20μm或22μm。第一石墨颗粒210的D50的粒径为2μm-4.5μm、D90的粒径为4.7μm-6μm，例如，第一石墨颗粒210的D50的粒径可以为2μm、3μm或4.5μm；第一石墨颗粒210的D90可以为4.7μm、5.5μm或6μm。
其中，D50是指颗粒累积分布为50％的粒径，也叫中位径或中值粒径，这是一个表示粒度大小的典型值，该值准确地将总体划分为二等份，也就 是说有50％的颗粒超过此值，有50％的颗粒低于此值。如果一个样品的D50＝6μm，说明在组成该样品的所有粒径的颗粒中，大于6μm的颗粒占50％，小于6μm的颗粒也占50％。
D90是指颗粒累积分布为90％的粒径，即小于此粒径的颗粒体积含量占全部颗粒的90％
本实施例中采用大粒径的硅颗粒220和小粒径的石墨颗粒相配合的主要作用是进一步提高负极片的动力学性能。因为，硅颗粒220动力学性能差，尤其是D90的硅颗粒220，其粒径较大且动力学性能较差。由此，使用第一石墨颗粒210包覆在D90硅颗粒220周围可以有效提高硅颗粒220动力学性能，改善硅颗粒220周围析锂的情况，从而能够有效的提高锂离子电池的充电速度。同时，采用小粒径的第一石墨颗粒210能够使得硅颗粒220的外周包覆较多的第一石墨颗粒210，从而能够更加有效的提高硅颗粒220动力学性能。换言之，由于第一石墨颗粒210的动力学性能明显优于硅颗粒220，从而使得硅颗粒220外周的锂离子能够快速的嵌入第一石墨颗粒210内，因此能够有效的改善了硅颗粒220周围析锂的情况，即有效的提高了负极片的动力学性能，从而能够有效的提高锂离子电池的续航和寿命。
在一些实施例中，第一负极膜层200中的硅颗粒220含量可以为0.1％-30％。示例性地，硅颗粒220含量可以为0.1％、5％、10％、20％或30％，其具体的含量可以根据实际情况进行设定。
另外，第一负极膜层200还可以包括第一导电剂、第一粘结剂和第一增稠剂，且混合物料230、第一导电剂、第一粘结剂和第一增稠剂质量比分别为75wt％-99wt％：0.1wt％-5wt％：0.1wt％-5wt％：0.5wt％-5wt％。示例性地，混合物料230、第一导电剂、第一粘结剂和第一增稠剂的质量比可以为，75wt％：0.1wt％：0.1wt％：0.5wt％，85wt％：2wt％：3wt％：2.5wt％，96.9wt％：0.5wt％：1.3wt％：1.3wt％或者99wt％：5wt％：5wt％：5wt％。
示例性地，第一导电剂可以为导电碳黑、碳纤维、科琴黑、乙炔黑、碳纳米管和石墨烯中的一种或多种。
第一增稠剂可以为羧甲基纤维素钠或羧甲基纤维素锂。
第一粘结剂可以为水性粘结剂，例如，可以为丁苯橡胶、丁腈橡胶、丁二烯橡胶、改性丁苯橡胶、聚丙烯酸钠、水性聚丙烯腈共聚物或聚丙烯 酸酯中的一种或者几种混合物。
在一些实施例中，第一石墨颗粒210和所述第二石墨颗310粒是由同类石墨通过筛分得到，第一石墨颗粒210的粒径可以小于第二石墨颗粒310的粒径。
示例性地，第二负极膜层300中的第二石墨颗粒310的D50的粒径可以为11μm-14μm、D90的粒径可以为22μm-29μm。
可以理解为，第一石墨颗粒210和第二石墨颗粒310为同一类石墨，将该石墨颗粒中D10颗粒筛分出，此部分石墨颗粒作为第一石墨颗粒210，剩下的石墨颗粒作为第二石墨颗粒310。且在一些实施例中，第二石墨颗粒310的粒径均大于7μm，即将石墨颗粒中D10颗粒筛分出后，将剩余的石墨颗粒中粒径小于7μm的石墨颗粒去除后作为第二石墨颗粒310。通过将第二石墨颗粒310选为较大颗粒，其一方面大颗粒可以提高压实；另一方面，大颗粒的第二石墨颗粒310之间可以具有较多的缝隙，从而与小颗粒的石墨颗粒相比能够提高负极片的孔隙率，进而能够提高电芯保液量，降低负极片表面极化，提高负极片动力学性能，由此进一步提高了锂电池的电池的续航和寿命。同时，通过将第一石墨颗粒210和第二石墨颗粒310选用同一类石墨的原因在于材质相近，其物化参数相同，锂离子在材料中的传输阻力相同；同时，选用同类石墨使其且辊压时材料的压实参数相近，从而使得两层石墨颗粒接触更加紧密，进而避免出现分层。
另外，第二负极膜层300还包括第二导电剂、第二粘结剂和第二增稠剂，且第二石墨颗粒310、第二导电剂、第二粘结剂和第二增稠剂质量比分别为75wt％-99wt％：0.1wt％-5wt％：0.1wt％-5wt％：0.5wt％-5wt％。示例性地，第二石墨颗粒310、第二导电剂、第二粘结剂和第二增稠剂的质量比可以为，75wt％：0.1wt％：0.1wt％：0.5wt％，85wt％：2wt％：3wt％：2.52wt％，96.9wt％：0.5wt％：1.3wt％：1.3wt％或者99wt％：5wt％：5wt％：5wt％。
示例性地，第二导电剂可以为导电碳黑、碳纤维、科琴黑、乙炔黑、碳纳米管和石墨烯中的一种或多种。
第二增稠剂可以为羧甲基纤维素钠或羧甲基纤维素锂。
第二粘结剂可以为水性粘结剂，例如，可以为丁苯橡胶、丁腈橡胶、丁二烯橡胶、改性丁苯橡胶、聚丙烯酸钠、水性聚丙烯腈共聚物或聚丙烯 酸酯中的一种或者几种混合物。
在一些实施例中，第一负极膜层200的厚度d1与第二负极膜层300的厚度d2之比可以为1：9-9：1。示例性地，第一负极膜层200的厚度d1与第二负极膜层300的厚度d2之比可以为1：9、5：5或9：1，第一负极膜层200的厚度d1可以为44μm，第二负极膜层300的厚度d2可以为56μm。
本公开实施例还提供了一种锂离子电池，其包括正极片、负极片、隔膜和电解液，且负极片为上述实施例中的负极片。
本实施例中提供的锂离子电池，通过在负极集流体100的表面上依次设置第一负极膜层200和第二负极膜层300，即第一负极膜层200贴于负极集流体100的表面上，第二负极膜层300贴于第一负极膜层200的表面上，且第一负极膜层200的活性物质包括硅颗粒220和第一石墨颗粒210，第二负极膜层300的活性物质包括第二石墨颗粒310，即将负极膜层分成了两层，其中靠近负极集流体的负极膜层的活性物质包括硅颗粒220和第一石墨颗粒210的混合物，另一远离负极集流体100的负极膜层的活性物质包括第二石墨颗粒310，从而使得当锂离子移动至负极片处时，部分锂离子先嵌入第二负极膜层中的第二石墨颗粒310内，剩余的锂离子嵌入第一负极膜层中，由于部分锂离子先嵌入第二负极膜层300中，使得移动至第一负极膜层100处的锂离子浓度降低，从而降低了锂离子在硅颗粒处及其附近第一石墨颗粒210处的聚集，进而减轻了锂离子浓度分布不均的现象，即降低了锂的析出，由此提高了锂离子电池的续航和寿命。
如图3所示，本公开实施例还提供了一种负极片的制备方法，包括，
S1：获取第一石墨颗粒、硅颗粒和第二石墨颗粒，并将第一石墨颗粒与硅颗粒进行混合组成混合物料；
S2：将混合物料、第一导电剂、第一粘结剂、第一增稠剂混合均匀，以得到第一负极膜层浆料；
S3：将第二石墨颗粒、第二导电剂、第二粘结剂、第二增稠剂混合均匀，以得到第二负极膜层浆料；
S4：将第一负极膜层浆料涂敷在负极集流体的表面上，将第二负极膜层浆料涂敷在第一负极膜层浆料表面上；
S5：对涂有第一负极膜层浆料和第二负极膜层浆料的负极集流体进行烘干。
需要说明的是，以上制备方法可以按照以上顺序进行，也可以按照实际需要进行调换。
示例性地，获取第一石墨颗粒、硅颗粒和第二石墨颗粒，并将第一石墨颗粒与硅颗粒进行混合组成混合物料包括：
获取一定量的同类石墨颗粒，筛选石墨颗粒，将粒径小于预设范围的石墨颗粒作为第一石墨颗粒，其余石墨颗粒作为第二石墨颗粒。
为了能够更好的说明一种负极片、锂离子电池及负极片的制备方法，下面将结合对比例和实施例进行详细说明。
实施例1
(一)负极片的制备
(1)物料准备：
获取第一石墨颗粒210、硅颗粒220和第二石墨颗粒310，并将第一石墨颗粒210与硅颗粒220进行混合组成混合物料。其中，获取第一石墨颗粒210、硅颗粒220和第二石墨颗粒310，并将第一石墨颗粒210与所述硅颗粒220进行混合组成混合物料包括：
获取石墨颗粒，筛选所述石墨颗粒，将粒径小于预设范围的石墨颗粒作为第一石墨颗粒210，其余石墨颗粒作为第二石墨颗粒310。
示例性地，获取一定量的石墨颗粒和硅颗粒220：其中，石墨颗粒的D10的粒径为5μm、D50的粒径为13μm、D90的粒径为25μm；将D10的石墨颗粒筛分出作为第一石墨颗粒210，剩余的除去粒径小于7μm的石墨颗粒作为第二石墨颗粒310，即第一石墨颗粒210的粒径范围可以为1-5μm；第二石墨颗粒310的粒径可以为8-27μm。其中，硅颗粒220的D50的粒径为8μm、D90的粒径为20μm。
将第一石墨颗粒210与硅颗粒220按照质量比为95:5取料，并将两者进行混合后得到混合物料230。
(2)浆料制备：
第一负极膜层200浆料的制备，将混合物料230、第一导电剂、第一粘结剂、第一增稠剂混合均匀，以得到第一负极膜层200浆料。
示例性地，将混合物料230、第一导电剂、第一粘结剂、第一增稠剂按96.9wt％：0.5wt％：1.3wt％：1.3wt％的质量比加入到搅拌罐中，且用去离子水配成第一负极膜层200浆料，以上比例为干料质量比，且此浆料中 固含量为42％。同时，本实施例中的第一导电剂可以为导电炭黑，第一增稠剂可以为羧甲基纤维素钠，第一粘结剂可以为水乳型丁苯橡胶，第一石墨颗粒210可以为人造石墨。
第二负极膜层300浆料的制备，将第二石墨颗粒310、第二导电剂、第二粘结剂、第二增稠剂混合均匀，以得到第二负极膜层300浆料。
将第二石墨颗粒310、第二导电剂、第二增稠剂、第二粘结剂按96.9wt％：0.5wt％：1.3wt％：1.3wt％的质量比加入到搅拌罐中，且用去离子水配成第二负极膜层300浆料，以上比例为干料质量比，且此浆料中固含量为42％。同时，本实施例中的第二导电剂可以为导电炭黑，第二增稠剂可以为羧甲基纤维素钠，第二粘结剂可以为水乳型丁苯橡胶，第一石墨颗粒210可以为人造石墨。
(3)负极片的制备：
将第一负极膜层200浆料涂敷在负集流体100的表面上，将第二负极膜层300浆料涂敷在第一负极膜层200浆料的表面上；对涂有第一负极膜层200浆料和第二负极膜层300浆料的负集流体100进行烘干。
示例性地，利用涂布机将含硅的第一负极膜层200浆料涂敷于负集流体100的的表面上，不含硅的纯石墨颗粒的第二负极膜层300涂敷于第一负极膜层200浆料的表面上。然后将其以5段烘箱进行干燥，每段烤箱的温度分别为60℃、80℃、110℃、110℃、100℃，干燥后第二负极膜层300的厚度可以为55um，第一负极膜层200的厚度可以为55um，使得第一负极膜层200的层厚与第二负极膜层300的厚度之比为5：5。重复涂布完成负集流体100的另一侧的双层膜层，从而使得负集流体100的两侧的表面上均涂有两层负极膜层；利用辊压机进行加压处理，使得负极片的压实密度可以为1.75g/cm2，从而完成负极片的制备。
(二)正极极片的制备
以钴酸锂为正极活性材料，将正极活性材料、导电剂及增稠剂按照质量比为97.2：1.5：1.3的质量比加入到搅拌罐中，加入NMP(N-甲基吡咯烷酮)溶剂进行充分搅拌，并将此混合后的浆料过筛网，最终配成正极浆料。其中，正极浆料固含量为70％～75％，再利用涂布机将浆料涂覆到正极集流体上，正极集流体可以为铝箔，在120℃温度下烘干，即得到正极极片。
(三)组装电芯
将上述制备的负极片和正极片、隔膜一起卷绕形成卷芯，用铝塑膜包装，烘烤去除水分后注入电解液，采用热压化成工艺化成即可得到电芯。
实施例2
本实施例与实施例1不同的地方在于：第一负极膜层200的厚度与第二负极膜层300的厚度之比为3：7。
实施例3
本实施例与实施例1不同的地方在于：第一负极膜层200的厚度与第二负极膜层300的厚度之比为7：3。
实施例4
本实施例与实施例1不同的地方在于：第一石墨颗粒210与硅颗粒220的质量比为90：10。
实施例5
本实施例与实施例1不同的地方在于：第一负极膜层200中硅颗粒220的D50的粒径为9μm，D90的粒径为22μm。
实施例6
本实施例与实施例1不同的地方在于：石墨颗粒中D10的粒径为3μm，D50的粒径为11μm，D90的粒径为22μm，即将石墨颗粒的D10的颗粒筛选出作为第一石墨颗粒210，第一石墨颗粒210中的粒径不大于3μm，剩余的石墨颗粒除去小于7μm的颗粒作为第二石墨颗粒310。
实施例7
本实施例与实施例1不同的地方在于：石墨颗粒中D10的粒径为3μm，D50的粒径为14μm，D90的粒径为28μm，即将石墨颗粒的D10的颗粒筛选出作为第一石墨颗粒210，第一石墨颗粒210中的粒径不大于3μm，剩余的石墨颗粒除去小于7μm的颗粒作为第二石墨颗粒310。
对比例1
本实施例与实施例1不同的地方在于：负极膜层为一层结构，即活性物质包括硅颗粒220和石墨颗粒，其混合后涂于负集流体100上形成具有一层负极膜层的负极片。
对比例2
本实施例与实施例1不同的地方在于：未筛选石墨颗粒，即直接将部分 石墨颗粒作为第一石墨颗粒210，将剩余的石墨颗粒作为第二石墨颗粒310。换言之，本实施例中的并未筛选出小粒径的石墨颗粒作为第一负极膜层200中的第一石墨颗粒210，将大粒径的作为第二负极膜层300中的第二石墨颗粒310。其中，石墨颗粒的石墨颗粒中D10的粒径为5μm，D50的粒径为13μm，D90的粒径为25μm，硅颗粒220的D50的粒径为8μm，D90的粒径为20μm。
对上述制备的每种电芯在25℃条件下进行1.2C阶梯充电/0.7C放电，并在不同循环次数下拆解电池确认电池负极表面析锂情况，拆解结果和能量密度如下：
表1给出实施例1-7和对比例1-2主要相关参数表
在表1中，负极片表面析锂程度用0、1、2、3、4、5来表示，0代表不析锂，5代表严重析锂，1、2、3、4代表不同的析锂程度，数字越大代表析锂程度越严重。
由表1可以看出，实施例1至实施例3是第一负极膜层200和第二负极膜层300之间厚度不同而对负极片析锂作用的影响，即当第一负极膜层200和第二负极膜层300之间的厚度为5：5和3:7时，在锂离子电池经过500T(周期)的充放电时，负极片的表面均未有锂析出；当第一负极膜层200的厚度与第二负极膜层300的厚度之比达到7：3时，在在锂离子电池经过500T(周期)的充放电时，负极片的表面锂析出程度为1。
同时，还可以看出第一负极膜层200和第二负极膜层300之间的厚度之 比对电池容量的保持率和膨胀率具有一定的影响。当第一负极膜层200和第二负极膜层300之间的厚度为5：5、3:7和7:3时，在锂离子电池经过700T(周期)的充放电时，锂离子电池的容量保持率分别为82.57％、86.09％、81.7％；锂离子电池经过700T(周期)的充放电时，锂离子电池的膨胀率分别为9.58％、9.29％、10.21％。且其能量密度分别为817wh/L、815wh/L、819wh/L。
由上可知，通过将负极膜层分成两层，且将活性物质为纯石墨颗粒层的第二负极膜层300设置于外层，将活性物质为石墨颗粒与硅颗粒220混合的第一负极膜层200设置于内层，从而使得当锂离子移动至负极片处时，部分锂离子先嵌入第二负极膜层300中的石墨颗粒内，剩余的锂离子嵌入第一负极膜层200中，由于部分锂离子先嵌入第二负极膜层300中，使得移动至第一负极膜层200处的锂离子浓度降低且速度变缓慢，从而使得锂离子具有足够的时间嵌入硅颗粒和第一石墨颗粒中，进而降低了锂离子在硅颗粒220处及其附近第一石墨颗粒210处的聚集密度，进而减轻了锂离子浓度分布不均的现象，即降低了锂的析出，由此提高了锂离子电池的续航能力和寿命。随着第一负极膜层200厚度的增大，锂离子电池的能量密度变化不大。但是，当第一负极膜层200较厚时，即第二负极膜层300较薄时，嵌入第二负极膜层300中的锂离子含量降低，从而导致较多的锂离子嵌入第一负极膜层200，进而增大锂离子再硅颗粒220及其附近聚集的密度，由此导致锂离子的析出。同时，随着第一负极膜层200厚度的增加，即负极片中硅颗粒220含量的增多使得锂离子电池的容量保持率能够逐渐增加；同时，随着第一负极膜层200厚度的增加，即负极片中硅颗粒220含量的增多使得锂离子电池的膨胀率也会增大。由此，在选择第一负极膜层200厚度和第二负极膜层300厚度的厚度时，需要综合考虑以得到综合性能较优异的锂离子电池。
由实施例1和实施4可以看出，当第一负极膜层200中硅颗粒220与第一石墨颗粒210含量之比达到10：90时，锂离子电池经过电池经过500T(周期)的充放电时，负极片的表面锂析出程度为1。在锂离子电池经过700T(周期)的充放电时，锂离子电池的容量保持率为79.52％；锂离子电池经过700T(周期)的充放电时，锂离子电池的膨胀率分别为10.09％；能量密度为821wh/L。
由此可知，当硅颗粒220含量较多时，能量密度虽然基本保持不变，但是会增大负极片表面析锂的程度，同时还能够降低锂离子电池的容量保持率， 并能够增大锂离子电池的膨胀率。因此，选择加入适量的硅颗粒220才能够有效提高锂离子电池的综合性能。
由实施例1和实施例5可以看出，当第一负极膜层200中的硅颗粒220的粒径较大时，即硅颗粒220的粒径D50达到9μm、D90的粒径达到22μm时，锂离子电池经过电池经过500T(周期)的充放电时，负极片的表面锂析出程度为0。在锂离子电池经过700T(周期)的充放电时，锂离子电池的容量保持率为80.03％；锂离子电池经过700T(周期)的充放电时，锂离子电池的膨胀率分别为10.62％。
由此可知，当硅颗粒220颗粒较大时，会降低锂离子电池的容量保持率，并能够增大锂离子电池的膨胀率。因为，硅颗粒220的粒径越大其动力学性能就越差，且体积越易膨胀。因此，选择加入合理粒径的硅颗粒220才能够有效提高锂离子电池的综合性能。
由实施例1和实施例6可以看出，当第一负极膜层200中的石墨颗粒的粒径较小时，即石墨颗粒的粒径D10达到3μm、D50的粒径达到11μm、D90的粒径达到22μm时，即第一石墨颗粒210的粒径和第二石墨颗粒310的粒径均相应减小，但是第二石墨颗粒310的粒径仍远大于第一石墨颗粒210的粒径时，锂离子电池经过电池经过500T(周期)的充放电时，负极片的表面锂析出程度为0。在锂离子电池经过700T(周期)的充放电时，锂离子电池的容量保持率为84.77％；锂离子电池经过700T(周期)的充放电时，锂离子电池的膨胀率分别为9.56％；且能量密度为816wh/L。
由此可知，第一石墨颗粒210的粒径和第二石墨颗粒310的粒径均适当减小时，锂离子电池的能量密度、析锂情况及体积膨胀率均未有明显变化，但是锂离子电池的容量保持率有一定的提升。因此，可以通过适当的减小石墨颗粒的粒径，能够使得锂离子电池在保持能量密度、析锂情况及体积膨胀率基本不变的前提下，使其容量保持率提高。
由实施例1和实施例7可以看出，当第二负极膜层300中的石墨颗粒的粒径较大时，即石墨颗粒的粒径D50达到14μm、D90的粒径达到28μm时，锂离子电池经过电池经过500T(周期)的充放电时，负极片的表面锂析出程度为0。在锂离子电池经过700T(周期)的充放电时，锂离子电池的容量保持率为77.27％；锂离子电池经过700T(周期)的充放电时，锂离子电池的膨胀率分别为11.77％；且能量密度为823wh/L。
由此可知，当第二负极膜层300中石墨颗粒的粒径较大时，虽然锂离子电池的能量密度增大，但是锂离子电池的容量保持率呈较明显的下降趋势，同时体积膨胀率也呈交明显的增大趋势。因此，第二负极膜层300中的第二石墨颗粒310虽然粒径较大，相比与小颗粒能够提高负极片的孔隙率，进而能够提高电芯保液量，降低负极片表面极化，提高负极片动力学性能，由此进一步提高了锂电池的电池的续航和寿命。但是，当其粒径过大时，会导致第二负极膜层300中的石墨颗粒数量明显的减少，进而导致第二负极膜层300中嵌入的锂离子量明显降低，由此导致较多的锂离子聚集在硅颗粒220附近，从而影响了锂离子电池的容量保持率和膨胀率。
由对比例1可以看出，当将硅颗粒220和石墨颗粒混合的浆料涂于负极集流体上形成一层负极膜层时，其锂离子电池经过电池经过500T(周期)的充放电时，负极片的表面锂析出程度为5；在锂离子电池经过700T(周期)的充放电时，锂离子电池的容量保持率为65.32％；锂离子电池经过700T(周期)的充放电时，锂离子电池的膨胀率分别为17.65％；能量密度为820wh/L。
由此，通过实施例1至实施例7与对比例1相比较可知，通过采用本公开实施例的结构能够有效的降低锂离子的析出程度，并能够明显的提高锂离子电池的容量保持率，降低锂离子电池的膨胀率。
由对比例2可以看出，当未将石墨颗粒进行筛分，即直接将部分石墨颗粒作为第一石墨颗粒210，将剩余的石墨颗粒作为第二石墨颗粒310时，锂离子电池经过电池经过500T(周期)的充放电时，负极片的表面锂析出程度为4；在锂离子电池经过700T(周期)的充放电时，锂离子电池的容量保持率为69.32％；锂离子电池经过700T(周期)的充放电时，锂离子电池的膨胀率分别为15.31％；能量密度为815wh/L。
由此，由对比例2与对比例1相比较，虽然通过将负极膜层分成两层能够使得锂离子电池的综合性能有一定的改善，但是析锂情况仍然比较严重，同时锂离子电池的容量保持率仍较低，且锂离子电池的膨胀率较大。
进一步，通过实施例1至实施例7与对比例2相比较可知，通过采用本公开实施例的结构能够有效的降低锂离子的析出程度，并能够明显的提高锂离子电池的容量保持率，降低锂离子电池的膨胀率。即，通过将第一负极膜层200中的石墨颗粒选用较小的粒径，使其能够将硅颗粒220的外周完全包覆，从而能够有效的提高的锂离子电池整体的动力学性能，降低锂离子的析 出程度，并能够明显的提高锂离子电池的容量保持率，降低锂离子电池的膨胀率。
进一步，通过实施例1至实施例7与对比例2相比较可知，通过采用本公开实施例的结构能够有效的降低锂离子的析出程度，并能够明显的提高锂离子电池的容量保持率，降低锂离子电池的膨胀率。即，通过将第一负极膜层中的石墨颗粒选用较小的粒径，使其能够将硅颗粒的外周完全包覆，从而能够有效的提高的锂离子电池整体的动力学性能，降低锂离子的析出程度，并能够明显的提高锂离子电池的容量保持率，降低锂离子电池的膨胀率。
在本公开实施例的描述中，需要理解的是，术语“中心”、“纵向”、“横向”、“长度”、“宽度”、“厚度”、“上”、“下”等指示的方位或位置关系为基于附图所示的方位或位置关系，仅是为了便于描述本公开实施例和简化描述，而不是指示或暗示所指的装置或元件必须具有特定的方位、以特定的方位构造和操作，因此不能理解为对本公开实施例的限制。
此外，术语“第一”、“第二”仅用于描述目的，而不能理解为指示或暗示相对重要性或者隐含指明所指示的技术特征的数量。由此，限定有“第一”、“第二”“第三”的特征可以明示或者隐含地包括至少一个该特征。在本公开实施例的描述中，“多个”的含义是至少两个，例如两个，三个等，除非另有明确具体的限定。
在本公开实施例中，除非另有明确的规定和限定，术语“安装”、“相连”、“连接”、“固定”等术语应做广义理解，例如，可以是固定连接，也可以是可拆卸连接，或成一体；可以是机械连接，也可以是电连接；可以是直接相连，也可以通过中间媒介间接相连，可以是两个元件内部的连通或两个元件的相互作用关系，除非另有明确的限定。对于本领域的普通技术人员而言，可以根据具体情况理解上述术语在本公开实施例中的具体含义。
在本公开实施例中，除非另有明确的规定和限定，第一特征在第二特征“上”或“下”可以是第一和第二特征直接接触，或第一和第二特征通过中间媒介间接接触。而且，第一特征在第二特征“之上”、“上方”和“上面”可是第一特征在第二特征正上方或斜上方，或仅仅表示第一特征水平高度高于第二特征。第一特征在第二特征“之下”、“下方”和“下面”可以是第一特征在第二特征正下方或斜下方，或仅仅表示第一特征水平高度小于第二特征。
在本说明书的描述中，参考术语“一个实施例”、“一些实施例”、“示例”、“具体示例”、或“一些示例”等的描述意指结合该实施例或示例描述的具体特征、结构、材料或者特点包含于本公开实施例的至少一个实施例或示例中。在本说明书中，对上述术语的示意性表述不必须针对的是相同的实施例或示例。而且，描述的具体特征、结构、材料或者特点可以在任一个或多个实施例或示例中以合适的方式结合。此外，在不相互矛盾的情况下，本领域的技术人员可以将本说明书中描述的不同实施例或示例以及不同实施例或示例的特征进行结合和组合。
尽管上面已经示出和描述了本公开实施例的实施例，可以理解的是，上述实施例是示例性地，不能理解为对本公开实施例的限制，本领域的普通技术人员在本公开实施例的范围内可以对上述实施例进行变化、修改、替换和变型。

Claims (15)

  1. 一种负极片，其特征在于，包括：
    负极集流体；
    第一负极膜层，其贴于所述负极集流体的表面上；且所述第一负极膜层的活性物质包括硅颗粒和第一石墨颗粒；
    第二负极膜层，其贴于所述第一负极膜层的表面上；且所述第二负极膜层的活性物质包括第二石墨颗粒，所述第二石墨颗粒的粒径大于所述第一石墨颗粒的粒径。
  2. 根据权利要求1所述的负极片，其特征在于，所述第一石墨颗粒的粒径小于所述硅颗粒的粒径。
  3. 根据权利要求1所述的负极片，其特征在于，所述硅颗粒的外壁被所述第一石墨颗粒包覆。
  4. 根据权利要求1所述的负极片，其特征在于，所述第一石墨颗粒的D90的粒径与所述硅颗粒的D90的粒径的比值为0.2-0.5。
  5. 根据权利要求1所述的负极片，其特征在于，所述第一石墨颗粒和所述第二石墨颗粒为同一类石墨。
  6. 根据权利要求1-5任一项所述的负极片，其特征在于，所述第一负极膜层中的硅颗粒的D50的粒径为6μm-10μm、D90的粒径为18μm-22μm；所述第一石墨颗粒的D50的粒径为2μm-4.5μm、D90的粒径为4.7μm-6μm。
  7. 根据权利要求1-5任一项所述的负极片，其特征在于，所述第二负极膜层中的第二石墨颗粒的D50的粒径为11μm-14μm、D90的粒径为22μm-29μm。
  8. 根据权利要求7所述的负极片，其特征在于，所述第二石墨颗粒的粒径均大于7μm。
  9. 根据权利要求1-5任一项所述的负极片，其特征在于，所述第一负极膜层中的硅颗粒的含量为0.1％-30％。
  10. 根据权利要求1-5任一项所述的负极片，其特征在于，所述第一负极膜层还包括第一导电剂、第一粘结剂和第一增稠剂，所述第一负极膜层中，所述硅颗粒和所述第一石墨颗粒的混合物料的质量比为75wt％-99wt％。
  11. 根据权利要求10所述的负极片，其特征在于，所述第一导电剂的质 量比为0.1wt％-5wt％，所述第一粘结剂的质量比为0.1wt％-5wt％，所述第一增稠剂的质量比为0.5wt％-5wt％。
  12. 根据权利要求1-5任一项所述的负极片，其特征在于，所述第二负极膜层还包括第二导电剂、第二粘结剂和第二增稠剂，所述第二负极膜层中，所述第二石墨颗粒的质量比为75wt％-99wt％。
  13. 根据权利要求12所述的负极片，其特征在于，所述第二导电剂的质量比为0.1wt％-5wt％，所述第二粘结剂的质量比为0.1wt％-5wt％，所述第二增稠剂的质量比为0.5wt％-5wt％。
  14. 根据权利要求1-5任一项所述的负极片，其特征在于，所述第一负极膜层的厚度与所述第二负极膜层的厚度之比为1:9-9:1。
  15. 一种锂离子电池，其特征在于，其包括正极片、负极片、隔膜和电解液，所述负极片为以上权利要求1-14任一项所述的负极片。
PCT/CN2023/086614 2022-04-07 2023-04-06 负极片及锂离子电池 WO2023193768A1 (zh)

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