WO2023246795A1 - 负极片、二次电池和用电设备 - Google Patents

负极片、二次电池和用电设备 Download PDF

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WO2023246795A1
WO2023246795A1 PCT/CN2023/101453 CN2023101453W WO2023246795A1 WO 2023246795 A1 WO2023246795 A1 WO 2023246795A1 CN 2023101453 W CN2023101453 W CN 2023101453W WO 2023246795 A1 WO2023246795 A1 WO 2023246795A1
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negative electrode
electrode layer
electrode sheet
silicon
active material
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PCT/CN2023/101453
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English (en)
French (fr)
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韩晓燕
马永军
郭姿珠
高天骥
孙华军
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比亚迪股份有限公司
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Publication of WO2023246795A1 publication Critical patent/WO2023246795A1/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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • 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
    • 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
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • 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
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • 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
    • 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
    • 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
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • 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
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/483—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides for non-aqueous cells
    • 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
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • 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
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • 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 belongs to the field of batteries, and specifically relates to a negative electrode sheet, a secondary battery and electrical equipment.
  • lithium-ion battery anode materials mostly use graphite, but the specific capacity of graphite is only 350mAh/g.
  • silicon material as the anode material can greatly improve the energy density of lithium-ion batteries.
  • silicon anode batteries due to the large volume expansion of the silicon anode during the process of deintercalating lithium, and the cycle performance needs to be improved, silicon anode batteries have not been commercialized on a large scale.
  • one purpose of the present disclosure is to propose a negative electrode sheet, a secondary battery and an electrical device, which not only have a lower cost, but also can reduce the volume of a single cycle of the battery during charging and discharging. rate of change, thus improving its battery energy density while improving its cycle stability.
  • the present disclosure provides a negative electrode sheet.
  • the negative electrode sheet includes:
  • a first negative electrode layer is provided on the surface of the negative electrode current collector, the first negative electrode layer includes a silicon-based active material and a piezoelastic additive;
  • the second negative electrode layer is disposed on a surface of the first negative electrode layer away from the negative electrode current collector, the second negative electrode layer includes graphite;
  • the rebound rate of the negative electrode sheet is 2%-40%, and the compression rate of the negative electrode sheet is 2%-40%; the pressure X meets 0.3MPa ⁇ X ⁇ 5Mpa.
  • a first negative electrode layer including a silicon-based active material and a piezoelastic additive is formed on the negative electrode current collector, and then a second negative electrode layer including graphite is formed on the first negative electrode layer, wherein the first The piezoelastic additive in the negative electrode layer has resilience and compressibility, so that the first negative electrode layer exhibits piezoelastic properties.
  • the volume of the negative electrode sheet gradually expands.
  • the volume of the graphite negative electrode increases when lithium is inserted. The expansion can reach 10%, while the volume expansion of silicon-based active materials is greater when lithium is embedded.
  • the volume expansion of silicon can reach 300% after lithium is embedded, and the volume expansion of SiOx can be up to 120% after lithium is embedded.
  • the battery core will bear pressure from the outside (such as the package body and the case) due to expansion.
  • the pressure elastic additive in the first negative electrode layer The volume shrinks under pressure, releasing part of the space for the silicon-based active material, thereby buffering the larger volume expansion of the silicon-based active material during the lithium insertion process, and slowing down the larger expansion of the first negative electrode layer during the lithium insertion process. Volume expansion rate.
  • the active material of the negative electrode sheet gradually shrinks in volume.
  • the external pressure on the battery core gradually decreases or even disappears.
  • the pressure elastic additive in the first negative electrode layer rebounds, and the volume Gradually recovers, occupying the space released by the volume shrinkage of the active material, thereby delaying the volume shrinkage of the first negative electrode layer caused by the delithiation of the active material. Therefore, the first negative electrode layer with piezoelastic properties can buffer the larger volume of the negative electrode sheet during the charge and discharge process. Variety.
  • the piezoelastic additive in the first negative electrode layer has conductive properties, so its volume rebounds during the discharge process.
  • the piezoelastic additive can reduce the volume change rate of the first negative electrode layer during the charge and discharge process, it can reduce the volume expansion rate of the first negative electrode layer and the second negative electrode layer during the charge and discharge process.
  • the difference can avoid the problem of gradual crack separation of the first negative electrode layer and the second negative electrode layer due to the large difference in volume expansion rate of the double layers during long-term cycling.
  • a second negative electrode layer containing graphite is formed on the surface of the negative electrode sheet.
  • the negative electrode sheet of the present application can not only have a lower cost, but also reduce the volume change rate of a single cycle of the battery during the charge and discharge process, thereby increasing the energy density of the battery and improving its cycle stability.
  • the negative electrode sheet according to the above embodiments of the present disclosure may also have the following additional technical features:
  • the thickness of one side of the first negative electrode layer is 5 ⁇ m-50 ⁇ m. As a result, the battery energy density can be increased while its cycle stability can be improved.
  • the mass ratio of the silicon-based active material to the pressure elastic additive is 100:3-30.
  • the battery energy density can be increased while its cycle stability can be improved.
  • the silicon-based active material accounts for 3% to 100% of the total active material mass. As a result, the battery energy density can be increased while its cycle stability can be improved.
  • the first negative electrode layer further includes graphite, and the mass ratio of the total mass of the silicon-based active material and the graphite to the pressure elastic additive is 100:3-30.
  • the silicon-based active material includes at least one of SiO x , Si, silicon carbon material Si/C and silicon-based alloy, where x takes a value of 0 ⁇ x ⁇ 2, and
  • silicon-based alloys also include at least one of Al, Mg, B, Ni, Fe, Cu and Co.
  • the first negative electrode layer further includes a first conductive agent, the first conductive agent includes at least one of single-walled carbon nanotubes and carbon black.
  • the first negative electrode layer further includes a first binder including at least one of polyacrylic acid, sodium alginate, and polyimide.
  • the piezoelastic additive is three-dimensional graphene. This can improve the cycle stability of the battery.
  • the three-dimensional graphene satisfies at least one of the following conditions (1)-(5):
  • the particle size of the three-dimensional graphene is 500nm-20 ⁇ m;
  • the pore volume of the three-dimensional graphene is 1cm 3 /g-10cm 3 /g;
  • the three-dimensional graphene includes overlapping graphene sheets, and the breaking strength between the graphene sheets is 20N/m-50N/m;
  • the three-dimensional graphene includes overlapping graphene sheets, and the lateral size of the graphene sheets is 10nm-100nm;
  • the average pore diameter of the three-dimensional graphene is not greater than 250 nm.
  • the graphene sheets have a lateral size of 10 nm-20 nm.
  • the second negative electrode layer has a single-side thickness of 5 ⁇ m-80 ⁇ m.
  • the silicon-based negative electrode material in the negative electrode sheet accounts for 3% to 90% of the total active material mass of the negative electrode. As a result, the energy density of the battery is increased while its cost is reduced.
  • the present disclosure proposes a secondary battery.
  • the secondary battery includes the above-mentioned negative electrode sheet. Therefore, the secondary battery has high energy density and high cycle stability.
  • the present disclosure provides an electrical device.
  • the electrical device has the above-mentioned secondary battery.
  • Figure 1 is a schematic structural diagram of a negative electrode sheet according to an embodiment of the present disclosure
  • Figure 2 is a schematic flow chart of a method for preparing a negative electrode sheet according to an embodiment of the present disclosure
  • Figure 3 is a cycle spectrum chart of the battery corresponding to Example 1 and Comparative Example 1.
  • the technical solution of this application is based on the following findings:
  • One way in the prior art is to use a mixture of silicon and graphite to prepare negative electrode sheets, that is, the graphite negative active material is mixed with Si/C silicon carbon material or SiO x as the negative electrode.
  • Materials used to increase battery energy density are significantly lower than that of graphite; at the same time, the volume of silicon-based materials expands greatly during the process of deintercalating lithium. For example, the volume expansion of silicon can reach 300% after lithium intercalation, and SiO Volume expansion can reach 120%.
  • Another way is to double-coat the negative electrode sheet, with the bottom layer using a silicon-rich layer and the surface layer using a graphite layer.
  • the silicon-rich layer can use high-cost binders and conductive agents, while the graphite layer still uses a conventional combination of binders and conductive agents, which can effectively reduce costs.
  • the present disclosure provides a negative electrode sheet.
  • the negative electrode sheet includes a negative electrode current collector 100 , a first negative electrode layer 200 and a second negative electrode layer 300 .
  • a first negative electrode layer 200 is provided on the surface of the negative electrode current collector 100 , and the first negative electrode layer 200 includes a silicon-based active material and a piezoelastic additive.
  • the second negative electrode layer 300 is disposed on the surface of the first negative electrode layer 200 away from the negative electrode current collector 100 , and the second negative electrode layer 300 includes graphite.
  • the rebound rate of the negative electrode sheet is 2%-40% and the compression rate is 2%-40%; the pressure
  • the rebound rate of the negative electrode sheet is 5%, 8%, 10%, 12%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, etc.
  • the compression rate of the negative plate is 5%, 8%, 10%, 12%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 32% , 35%, 38%, 40%, etc.; the pressure
  • the elastic additive has resilience and compressibility, so that the first negative electrode layer 200 exhibits piezoelastic properties.
  • the volume of the negative electrode sheet gradually expands.
  • the volume of silicon after lithium insertion The expansion can reach 300%, and the volume expansion of SiO x after lithium insertion can reach 120%.
  • the battery core Under the condition that the volume of the battery pack or battery case is fixed, the battery core will bear pressure from the outside (such as the package body and the case) due to expansion. At this time, under the action of pressure, the pressure spring in the first negative electrode layer 200 The additive shrinks in volume under pressure, releasing part of the space for the silicon-based active material, thereby buffering the larger volume expansion of the silicon-based active material during the lithium insertion process, and slowing down the larger expansion of the first negative electrode layer 200 during the lithium insertion process. Large volume expansion rate. During the discharge process, as lithium ions escape, the active material in the negative electrode sheet gradually shrinks in volume.
  • the first negative electrode layer 200 with piezoelastic properties can buffer the negative electrode sheet during the charge and discharge process.
  • the first negative electrode layer 200 with piezoelastic properties can buffer the large volume change of the negative electrode sheet during charging and discharging.
  • the piezoelastic additive in the first negative electrode layer 200 rebounds in volume during the discharge process.
  • it can help good physical contact between the silicon-based active material particles in the first negative electrode layer 200 and ensure a good electronic conductive network.
  • the piezoelastic additive can reduce the volume change rate of the first negative electrode layer 200 during the charge and discharge process, it can reduce the difference in the volume expansion rate of the first negative electrode layer 200 and the second negative electrode layer 300 during the charge and discharge process, thereby avoiding During long-term cycling, the double layers of the first negative electrode layer 200 and the second negative electrode layer 300 have a large difference in volume expansion rate, causing the double layers to gradually crack and separate.
  • the thickness of one side of the first negative electrode layer 200 is 5 ⁇ m-50 ⁇ m, such as 5 ⁇ m, 10 ⁇ m, 15 ⁇ m, 20 ⁇ m, 25 ⁇ m, 30 ⁇ m, 35 ⁇ m, 40 ⁇ m, 45 ⁇ m, 50 ⁇ m.
  • One-sided thickness refers to the thickness of the first negative electrode layer 200 or the second negative electrode layer 300 on the coating surface; when the negative electrode layer is coated on both sides of the current collector, the "unilateral thickness” in this disclosure refers to both sides The thickness of the first negative electrode layer 200 or the second negative electrode layer 300 in either side of the negative electrode layer.
  • the mass ratio of the silicon-based active material to the pressure elastic additive is 100:3-30, such as 100:3-25, 100:5-22, 100:8-20, 100 :10-18, 100:12-16, 100:13-15, etc. If the addition amount of the compression elastic additive is too low, the compression rebound performance of the pole piece cannot be achieved. Therefore, adding the above-mentioned ratio of the piezoelastic additive to the first negative electrode layer 200 can reduce the cost while improving the battery energy density and cycle stability.
  • the silicon-based active material accounts for 3%-100% of the total active material mass fraction in the first negative electrode layer 200, such as 5%-95%, 10%-90%, 15%-85% , 20%-80%, 25%-75%, 30%-70%, 40%-60%, 45%-50%, etc.
  • the silicon-based active material accounts for 10%-60% of the total active material mass fraction in the first negative electrode layer 200 .
  • the first negative electrode layer 200 further includes graphite, and the mass ratio of the total mass of the silicon-based active material and the graphite to the pressure elastic additive is 100:3-30, for example, 100:3-25 , 100:5-22, 100:8-20, 100:10-18, 100:12-16, 100:13-15, etc.
  • the silicon-based active materials include at least one of SiO x , Si, Si/C and silicon-based alloys, where x The value is 0 ⁇ x ⁇ 2, and the silicon-based alloy includes at least one of Al, Mg, B, Ni, Fe, Cu and Co in addition to Si.
  • the first negative electrode layer further includes a first conductive agent
  • the first conductive agent includes but is not limited to at least one of single-walled carbon nanotubes and carbon black; in some embodiments of the present disclosure, the first conductive agent A conductive agent includes single-walled carbon nanotubes.
  • the above-mentioned first negative electrode layer 200 further includes a first binder, and the first binder includes but is not limited to at least one of polyacrylic acid, sodium alginate, and polyimide; in this disclosure In some embodiments, the first binder includes polyacrylic acid.
  • the mass ratio of the silicon-based active material or the composite material of the silicon-based active material and graphite, the first conductive agent, the first binder and the pressure elastic additive is 100:0.1-2.5:0.1-30 : 3-30, for example 100: 0.5-2.5: 0.1-30: 3-30, 100: 1-2.3: 0.1-30: 3-30, 100: 1.2-2: 0.1-30: 3-30, 100: 1.5-2: 0.1-30: 3-30, 100: 0.1-2.5: 0.5-30: 3-30, 100: 0.1-2.5: 1-30: 3-30, 100: 0.1-2.5: 5-25: 3-30, 100: 0.1-2.5: 10-20: 3-30, 100: 0.1-2.5: 15-20: 3-30, 100: 0.1-2.5: 0.1-30: 5-25, 100: 0.1- 2.5: 0.1-30: 10-20, 100: 0.1-2.5: 0.1-30: 15-20.
  • the added amount of the first conductive agent is too high, the cost will be increased on the one hand, and the energy density of the cell will be reduced on the other hand. If the added amount of the first conductive agent is too low, the conductive performance of the cell will be reduced; if the first binder is added If the amount of the first binder is too high, in addition to increasing the cost and reducing the energy density of the battery core, it will also increase the polarization of the battery and increase the internal resistance of the battery.
  • the silicon base will During the repeated expansion and contraction of the active material, the pole pieces are pulverized, resulting in a sharp decline in cycle performance; if the amount of pressure elastic additive added is too high, it will not only increase the cost, but also reduce the energy density of the battery.
  • the pressure elastic additive is three-dimensional graphene.
  • the three-dimensional graphene satisfies at least one of the following conditions (1)-(5):
  • the particle size of the three-dimensional graphene is 500nm-20 ⁇ m, such as 1 ⁇ m-20 ⁇ m, 3 ⁇ m-18 ⁇ m, 5 ⁇ m-15 ⁇ m, 7 ⁇ m-13 ⁇ m, 10 ⁇ m-12 ⁇ m, etc.;
  • the pore volume of the three-dimensional graphene is 1cm 3 /g-10cm 3 /g, such as 3cm 3 /g-8cm 3 /g, 5cm 3 /g-7cm 3 /g, etc.;
  • the three-dimensional graphene includes overlapping graphene sheets, and the breaking strength between the graphene sheets is 20N/m-50N/m, such as 25N/m-45N/m, 30N/m-45N/m. m, 35N/m-45N/m, 40N/m-45N/m, etc.;
  • the three-dimensional graphene includes overlapping graphene sheets, and the lateral size of the graphene sheets is 10nm-100nm, such as 10nm-20nm, 20nm-100nm, 30nm-90nm, 40nm-80nm, 50nm-70nm ,;
  • the average pore diameter of the three-dimensional graphene does not exceed 250nm, such as 10nm, 30nm, 50nm, 80nm, 100nm, 120nm, 150nm, 170nm, 200nm, 220nm, 250nm, etc.
  • the pore volume of the above three-dimensional graphene can be measured by using the nitrogen adsorption method on the three-dimensional graphene.
  • the fracture strength of the above-mentioned graphene sheets can be obtained by using an atomic force microscope (AFM) to conduct nanoindentation testing on the overlap of three-dimensional graphene: fix the three-dimensional graphene on a silicon wafer with small holes on the surface. Use a probe to apply pressure to the graphene sheet on the small hole. The position of the pressure should be near the overlap of two adjacent graphene sheets. Record the critical point that can cause the overlap of the two graphene sheets to break. Pressure, that is, the fracture strength of the overlap between graphene sheets is obtained.
  • the above-mentioned lateral dimensions refer to the length or width of the graphene sheet, etc., and can be known from electron micrographs of three-dimensional graphene.
  • the above three-dimensional graphene can be grown using plasma chemical vapor deposition (PECVD).
  • PECVD plasma chemical vapor deposition
  • An exemplary preparation method includes the following steps: passing a mixed gas of carbon source (such as C 2 H 2 ) and H 2 into a deposition chamber heated to a certain temperature in the plasma deposition equipment, and turning on the plasma generator to deposit the The three-dimensional graphene material is deposited and grown by the PECVD method on the substrate (such as Cu) placed in the chamber.
  • the auxiliary gas such as Ar, He, etc.
  • the auxiliary gas such as Ar, He, etc.
  • the resulting sample is then taken out of the deposition chamber, and the three-dimensional graphene material is peeled off from the substrate and broken into the desired particle size.
  • three-dimensional graphene can be obtained that meets the following conditions: particle size 500nm-20 ⁇ m, pore volume 1cm 3 /g-10cm 3 /g, formed by overlapping graphene sheets with lateral dimensions 10nm-100nm. , the average pore diameter does not exceed 250nm, and the fracture strength between graphene sheets is 20N/m-50N/m.
  • An exemplary preparation method includes the following steps: passing a mixed gas of carbon source (such as C 2 H 2 ) and H 2 into a deposition chamber heated to a certain temperature in the plasma deposition equipment, and turning on the plasma generator to deposit the The three-dimensional graphene material is deposited and grown by the PECVD method on the substrate (such as Cu) placed in the chamber. After the growth of the three-dimensional graphene is completed, the auxiliary gas (such as Ar, He, etc.) is introduced to cool the deposition chamber to At room temperature, the resulting sample is then taken out of the deposition chamber, and the three-dimensional graphene material is peeled off from the substrate and broken into the desired particle size.
  • the PECVD process can generate high energy density and large volume plasma, which can decompose the carbon source C 2 H 2 into more carbon-containing reaction free radicals, thereby achieving the growth of three-dimensional graphene.
  • the inflow flow of C 2 H 2 is 20mL/min
  • the inflow flow of H 2 is 250mL/min
  • the temperature of deposition growth can be 950°C
  • the inflow flow of auxiliary gas Ar is 200mL/min
  • the plasma generator The operating power is 300W.
  • a sufficient pore volume can ensure that three-dimensional graphene has excellent compression properties, and an appropriate pore size and fracture strength between graphene sheets can ensure that three-dimensional graphene has good resilience after compression and will not The structure collapses due to pressure and loses its resilience. As a result, the compression-rebound properties of the battery are stably maintained during the battery cycle.
  • Three-dimensional graphene with the above characteristics has excellent compression-resilience properties, so that the prepared first negative electrode layer 200 exhibits high piezoelastic properties, thereby buffering the large volume expansion of the negative electrode sheet during charging.
  • the second negative electrode layer 300 is provided on a surface of the first negative electrode layer 200 away from the negative electrode current collector 100 , and the second negative electrode layer 300 includes graphite.
  • the inventor found that since silicon and graphite have different delithiation platforms (silicon delithiation platform is 0.4V-0.5V), while graphite's delithiation platform is around 0.1V, in the early stage of full battery discharge, graphite needs to bear most of the discharge. current, thus causing a large discharge polarization of the graphite material. In order to reduce the discharge polarization of the graphite negative electrode, the lithium ions migrated out of the graphite negative electrode quickly migrate to the positive electrode.
  • the second negative electrode layer 300 containing graphite is formed into the first negative electrode.
  • the second negative electrode layer 300 containing graphite is formed on the layer 200 on the surface of the negative electrode sheet. Because the fast charging performance of graphite is better than that of the silicon-containing negative electrode, it is beneficial to improve the instantaneous charging and high-rate instantaneous discharge performance of the battery.
  • the single-sided thickness of the second negative electrode layer 300 is 5 ⁇ m-80 ⁇ m, such as 5 ⁇ m, 10 ⁇ m, 15 ⁇ m, 20 ⁇ m, 25 ⁇ m, 30 ⁇ m, 35 ⁇ m, 40 ⁇ m, 45 ⁇ m, 50 ⁇ m, 55 ⁇ m, 60 ⁇ m, 65 ⁇ m. , 70 ⁇ m, 75 ⁇ m, 80 ⁇ m.
  • the second negative electrode layer 300 further includes a second conductive agent.
  • the second conductive agent includes but is not limited to acetylene black, conductive carbon black, and the like.
  • the second negative electrode layer 300 further includes a second binder.
  • the second binder includes but is not limited to sodium carboxymethylcellulose, styrene-butadiene rubber, and the like.
  • the mixing ratio of the graphite, the second conductive agent and the second binder used to form the second negative electrode layer 300 in this application can be a conventional setting for forming graphite negative electrodes in the art.
  • this application by forming a second negative electrode layer 300 containing graphite on the first negative electrode layer 200 containing silicon, and by differentiating the conductive agent and binder of the first negative electrode layer 200 and the second negative electrode layer 300, it can be ensured respectively.
  • the respective capacities and cycle stability of the graphite in the second negative electrode layer 300 and the silicon-based active material in the first negative electrode layer 200 significantly reduce the cost of the negative electrode sheet.
  • the negative electrode sheet of the present application has a lower volume change rate during the charging and discharging process, thereby improving the energy density of the battery and improving its cycle stability.
  • the negative electrode sheet proposed in this application is close to the negative electrode current collector 100 Because of its relatively high discharge platform, the SiO The repeated volume expansion of SiO x during cycling helps improve the battery cycle performance.
  • this application limits the silicon-based negative electrode material in the negative electrode sheet to account for 3%-90% of the total active material mass of the negative electrode, where the total active material refers to all active materials in the negative electrode sheet that can deintercalate lithium, For example, 5%-90%, 10%-90%, 15%-85%, 20%-80%, 25%-75%, 30%-70%, 40%-60%, 45%-50%.
  • the negative electrode sheet is prepared by compounding the silicon-based active material and graphite in the above ratio. On the one hand, it can solve the problem of interlayer separation during double-layer coating. On the other hand, the difficulty and cost of process implementation are low. , which can reduce costs while maintaining the full performance of the silicon-based active materials and graphite in the negative electrode sheet, and improving the energy density of the battery.
  • the negative electrode sheet of the present application can not only have a lower cost, but also reduce the volume expansion rate of the battery during a single cycle during charging, thereby improving the energy density of the battery while improving its cycle stability.
  • the method for preparing the above negative electrode sheet is described below. According to an embodiment of the present disclosure, referring to Figure 2, the method includes:
  • a first slurry including a silicon-based active material and a piezoelastic additive is applied on the negative electrode current collector 100 to form the first negative electrode layer 200 on the negative electrode current collector 100 .
  • the piezoelastic additive has resilience and compressibility, so that the first negative electrode layer 200 exhibits piezoelastic properties.
  • the volume of the negative electrode sheet gradually expands, and the graphite anode lithium-embedded
  • the volume expansion can reach 10%, while the volume expansion of silicon-based active materials is even greater when lithium is embedded.
  • the volume expansion of silicon can reach 300% after lithium is embedded, and the volume expansion of SiOx can reach 120% after lithium is embedded.
  • the battery core Under the working condition of fixed battery pack volume (such as cylindrical battery), the battery core will bear the pressure from the external package due to expansion. At this time, under the action of pressure, the pressure elastic additive in the first negative electrode layer 200 will expand under the action of pressure. The volume shrinks and releases part of the space for the silicon-based active material, thereby buffering the large volume expansion of the silicon-based active material during the lithium intercalation process, and slowing down the large volume expansion rate of the first negative electrode layer 200 during the lithium intercalation process. . During the discharge process, as lithium ions escape, the active material in the negative electrode sheet gradually shrinks in volume. At this time, the external pressure on the battery core gradually decreases or even disappears, and the pressure elastic additive in the first negative electrode layer 200 rebounds.
  • the volume gradually recovers, occupying the space released by the volume shrinkage of the active material, thereby delaying the volume shrinkage of the first negative electrode layer 200 caused by the delithiation of the active material. Therefore, the first negative electrode layer 200 with piezoelastic properties can buffer the negative electrode sheet during the charge and discharge process.
  • the first negative electrode layer 200 with piezoelastic properties can buffer the large volume change of the negative electrode sheet during charging and discharging.
  • the piezoelastic additive in the first negative electrode layer 200 rebounds in volume during the discharge process. On the one hand, it can help good physical contact between the silicon-based active material particles in the first negative electrode layer 200 and ensure a good electronic conductive network.
  • the piezoelastic additive can reduce the volume shrinkage rate of the first negative electrode layer 200 during the discharge process, it can reduce the difference in the volume change rate of the first negative electrode layer 200 and the second negative electrode layer 300 during the charge and discharge process, and avoid During long-term cycling, the double layers of the first negative electrode layer 200 and the second negative electrode layer 300 have a large difference in volume expansion rate, causing the double layers to gradually crack and separate.
  • a second slurry including graphite is applied on the first negative electrode layer 200 to form the second negative electrode layer 300 on the first negative electrode layer 200 to obtain a negative electrode sheet.
  • silicon and graphite have different delithiation platforms (silicon delithiation platform is 0.4V-0.5V), while graphite's delithiation platform is around 0.1V, in the early stage of full battery discharge, graphite needs to bear most of the discharge. current, thus causing a large discharge polarization of the graphite material.
  • the lithium ions migrated out of the graphite negative electrode quickly migrate to the positive electrode.
  • the second negative electrode layer 300 containing graphite is formed into the first negative electrode.
  • a second negative electrode layer 300 containing graphite is formed on the surface of the negative electrode sheet. Because the fast charging performance of graphite is better than that of the silicon-containing negative electrode, the instantaneous charging and high-rate instantaneous discharge performance of the battery are improved.
  • the second slurry may further include a second conductive agent and a second binder.
  • a second negative electrode layer 300 containing graphite is formed on the first negative electrode layer 200 containing silicon, and by differentiating the conductive agent and binder of the first negative electrode layer 200 and the second negative electrode layer 300, the graphite can be ensured respectively.
  • the respective capacity and cycle stability of silicon-based active materials significantly reduce the cost of the negative electrode sheet.
  • the above-mentioned first slurry may further include a first binder and/or a first conductive agent.
  • this method can be used to prepare the above-mentioned battery with lower cost and smaller volume expansion rate in a single cycle, thereby increasing the battery energy density and improving the cycle stability.
  • the characteristics and advantages described above for the negative electrode sheet are also applicable to the method of preparing the negative electrode sheet.
  • the solid content of the first slurry and the second slurry are conventional parameters for preparing negative electrode sheets in this field. No further details will be given here.
  • the present disclosure proposes a secondary battery.
  • the secondary battery includes the above-mentioned negative electrode sheet. Therefore, by using the above-mentioned negative electrode sheet with high energy density and high cycle stability, the secondary battery exhibits higher energy density and higher cycle stability. It should be noted that the features and advantages described above for the negative electrode sheet and its preparation method are also applicable to the secondary battery, and will not be described again here.
  • the present disclosure provides an electrical device.
  • the electrical equipment can be vehicles such as cars and boats, or laptop computers, mobile terminals, etc.
  • the electrical device has the above-mentioned secondary battery. Therefore, by loading the electrical equipment with the above-mentioned secondary battery with higher energy density and higher cycle stability, the electrical equipment has excellent cruising range and safety performance. It should be noted that the features and advantages described above for the secondary battery are also applicable to the electrical equipment and will not be described again here.
  • Methods for preparing negative electrode sheets include:
  • first negative electrode layer
  • the three-dimensional graphene used in Example 1 includes overlapping graphene sheets and the three-dimensional graphene has a porous structure.
  • the three-dimensional graphene has an average particle size of 0.6 ⁇ m and a pore volume of 2.5 cm 3 /g.
  • the average pore diameter of the porous structure is 100nm; through AFM nanoindentation testing, the fracture strength of the joints of overlapping graphene sheets in three-dimensional graphene was measured to be 30N/m.
  • the lateral dimensions of the sheets range from 10nm to 100nm.
  • Methods for preparing negative electrode sheets include:
  • the three-dimensional graphene used in Example 2 includes overlapping graphene sheets and the three-dimensional graphene has a porous structure.
  • the three-dimensional graphene has an average particle size of 0.6 ⁇ m and a pore volume of 2.5 cm 3 /g.
  • the average pore diameter of the porous structure is 100nm; through AFM nanoindentation testing, the fracture strength of the joints of overlapping graphene sheets in three-dimensional graphene was measured to be 30N/m.
  • the lateral dimensions of the sheets range from 10nm to 100nm.
  • Example 3 The difference between Example 3 and Example 1 is that a silicon carbon material with a gram specific capacity of 1250 mAh / g is used to replace SiO A second negative electrode layer with a thickness of 29 ⁇ m on one side was formed on the first negative electrode layer on both sides of the foil to obtain a negative electrode sheet.
  • Example 4 The difference between Example 4 and Example 1 is that the average particle size of the three-dimensional graphene used is 1.5 ⁇ m, the pore volume is 4 cm 3 /g, and the average pore size of the porous structure in the three-dimensional graphene is 150 nm; nanoindentation is performed by AFM After testing, the fracture strength of the joints of overlapping graphene sheets in three-dimensional graphene was measured to be 45N/m.
  • Prepare the first slurry The first slurry is coated on both sides of the copper foil (the coating surface density on both sides is the same, and the density on one side is 19.6g/m 2 ), and then cured and rolled to form a single-side thickness of 12 on the copper foil.
  • micron first negative electrode layer maintaining the same first coating layer capacity as in Example 2).
  • Example 6 The difference between Example 6 and Example 2 is that the average particle size of the three-dimensional graphene used in Example 6 is 10 ⁇ m, the pore volume is 8 cm 3 /g, and the average pore size of the porous structure in the three-dimensional graphene is 150 nm; nanometer analysis was carried out by AFM.
  • the fracture strength of the joints of overlapping graphene sheets in three-dimensional graphene was measured to be 20N/m, and the lateral size of the overlapping graphene sheets was 10nm-100nm.
  • Methods for preparing negative electrode sheets include:
  • the areal density is 42g/m 2
  • the thickness of one side of the formed first negative electrode layer is 26 ⁇ m.
  • the density of one side of the second negative electrode layer is 41g/m 2 , and the thickness of one side of the second negative electrode layer is 26 ⁇ m.
  • Preparation of battery for specific capacity test Assemble the negative electrode sheet, PE separator and 100 micron thick lithium foil prepared in each example and comparative example.
  • the electrolyte uses 1 mol/L LiPF6.
  • the EC and EMC volume ratio is 1:1.
  • Preparation of test cells for recycling Mix NCM811 with PVDF and conductive agent Sup-P according to the mass ratio of 100:1.6:1.2 to make a slurry. Coat the surface of the aluminum foil on both sides with a density of 200g/ m2 on one side. into a positive electrode piece. Then, the prepared positive electrode sheet was assembled into a battery with the negative electrode sheet and PE separator obtained in Examples 1-6 and Comparative Examples 1-3 respectively. The electrolyte was 1 mol/L LiPF 6 and the volume ratio of EC to EMC was 1:1. Test the cycle performance of the corresponding battery.
  • the first charge-discharge specific capacity test of the negative electrode After the battery is discharged to 0.005V at a constant current of 0.1C, then discharged to 0.005V at a constant current of 0.05C, and then charged to 1.5V at a constant current of 0.1C.
  • the total mass of the negative electrode layer the mass of the first negative electrode layer + the mass of the second negative electrode layer.
  • the test results are shown in Table 1 and Figure 3.
  • Test method for the negative electrode sheet's resilience Apply a pressure of X 1 Mpa to the negative electrode sheet, measure the thickness H 1 of the negative electrode sheet under the pressure of 2 , then the rebound rate of the pole piece is:
  • Pole piece rebound rate r (H 2 -H 1 )/H 1
  • Test method for the compression performance of the negative electrode sheet Apply a pressure of
  • Pole piece compression rate P (H 3 -H 4 )/H 3

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Abstract

本申请公开了一种负极片、二次电池和用电设备，其中负极片包括：负极集流体、第一负极层和第二负极层，所述第一负极层设在所述负极集流体的表面上，所述第一负极层包括硅基活性材料和弹性添加剂；所述第二负极层设在所述第一负极层上远离所述负极集流体的表面上，所述第二负极层包括石墨，在沿所述负极片厚度方向被施加压力X后，所述负极片的回弹率为2％-40％，所述负极片的压缩率为2％-40％；所述压力X满足0.3MPa≤X≤5Mpa。

Description

负极片、二次电池和用电设备
优先权信息
本公开请求于2022年06月21日向中国国家知识产权局提交的、专利申请号为202210706153.2、公开名称为“负极片及其应用”的中国专利公开的优先权，并且其全部内容通过引用结合在本公开中。
技术领域
本公开属于电池领域，具体涉及一种负极片、二次电池和用电设备。
背景技术
随着电动汽车的发展及市场对电动汽车续航里程需求的不断提升，提高锂离子电池能量密度已经成为了各个电池厂商以及研究机构不断追逐的方向。目前商用的锂离子电池负极材料，多采用石墨，但石墨的比容量只有350mAh/g，采用硅材料作为负极材料，可以极大提高锂离子电池的能量密度。但是由于硅负极在脱嵌锂过程中存在很大的体积膨胀，同时循环性能还有待提升，因此导致硅负极电池未大规模商业化。
公开内容
本公开旨在至少在一定程度上解决相关技术中的技术问题之一。为此，本公开的一个目的在于提出一种负极片、二次电池和用电设备，该负极片不仅可以具有较低的成本，而且可以减小电池在充放电过程中单次循环产生的体积变化率，从而在提高其电池能量密度的同时提高其循环稳定性。
在本公开的一个方面，本公开提出了一种负极片。根据本公开对实施例，所述负极片包括：
负极集流体；
第一负极层，所述第一负极层设在所述负极集流体的表面上，所述第一负极层包括硅基活性材料和压弹添加剂；
第二负极层，所述第二负极层设在所述第一负极层上远离所述负极集流体的表面上，所述第二负极层包括石墨；
在沿所述负极片厚度方向被施加压力X后，所述负极片的回弹率为2％-40％，所述负极片的压缩率为2％-40％；所述压力X满足0.3MPa＜X≤5Mpa。
根据本公开实施例的负极片，通过在负极集流体上形成包括硅基活性材料和压弹添加剂的第一负极层，然后在第一负极层上形成包括石墨的第二负极层，其中第一负极层中的压弹添加剂具有回弹性和压缩性，从而使得第一负极层表现出压弹特性，在电池充电时，随着负极嵌锂，负极片体积逐渐膨胀，石墨负极在嵌锂时体积膨胀可达10％，而硅基活性材料，在嵌锂时体积膨胀更大，例如硅在嵌锂后体积膨胀可达300％，SiOx嵌锂后体积膨胀可达120％。在固定电池包或电池壳体体积的工况下，电芯因膨胀则会承受来自外部(如包体、壳体)的压力，此时在压力作用下，第一负极层中的压弹添加剂在压力作用下体积收缩，释放一部分空间给硅基活性材料，从而缓冲了硅基活性材料在嵌锂过程中产生的较大的体积膨胀，减缓了第一负极层在嵌锂时的较大的体积膨胀率。而在放电的过程中，随着锂离子的脱出，负极片活性材料逐渐体积收缩，此时电芯承受的外压力逐渐减小甚至消除，第一负极层中的压弹添加剂发生回弹，体积逐渐恢复，占据活性材料体积收缩释放的空间，进而延缓第一负极层因活性材料脱锂导致的体积收缩，因此具有压弹特性的第一负极层可以缓冲负极片在充放电过程中较大体积变化。同时第一负极层中的压弹添加剂因为兼具导电性能，因此其在放电过程中体积回弹，一方面可以帮助第一负极层中的硅基活性材料颗粒间良好的物理接触，保证良好的电子导电网络，再一方面，因为压弹添加剂可以减小第一负极层在充放电过程中的体积变化率，因此可以缩小第一负极层与第二负极层在充放电过程中体积膨胀率的差异，避免在长期循环过程中第一负极层与第二负极层双层因体积膨胀率较大差异而导致双层逐渐出现裂纹分离的问题。同时将含石墨的第二负极层形成在负极片的表层，因为石墨的快充性能优于含硅负极，因此有利于提高电池的瞬时充电以及大倍率瞬时放电性能。由此，本申请的负极片不仅可以具有较低的成本，而且可以减小电池在充放电过程中单次循环产生的体积变化率，从而在提高其电池能量密度的同时提高其循环稳定性。
另外，根据本公开上述实施例的负极片还可以具有如下附加的技术特征：
在本公开的一些实施例中，所述第一负极层的单侧厚度为5μm-50μm。由此，可以在提高其电池能量密度的同时提高其循环稳定性。
在本公开的一些实施例中，所述硅基活性材料与压弹添加剂的质量比为100：3-30。由此，可以在提高其电池能量密度的同时提高其循环稳定性。
在本公开的一些实施例中，在所述第一负极层中，所述硅基活性材料占总活性材料质量的3％-100％。由此，可以在提高其电池能量密度的同时提高其循环稳定性。
在本公开的一些实施例中，所述第一负极层还包括石墨，所述硅基活性材料和所述石墨的总质量与压弹添加剂的质量比为100：3-30。
在本公开的一些实施例中，所述硅基活性材料包括SiOx、Si、硅碳材料Si/C和硅基合金中的至少之一，其中x取值为0<x<2，所述硅基合金除含Si外，还包括Al、Mg、B、Ni、Fe、Cu和Co中的至少一种。
在本公开的一些实施例中，所述第一负极层还包括第一导电剂，所述第一导电剂包括单壁碳纳米管和炭黑中的至少之一。
在本公开的一些实施例中，所述第一负极层还包括第一粘结剂，所述第一粘结剂包括聚丙烯酸、海藻酸钠和聚酰亚胺中的至少之一。
在本公开的一些实施例中，所述压弹添加剂为三维石墨烯。由此可以提高电池的循环稳定性。
在本公开的一些实施例中，所述三维石墨烯满足下列(1)-(5)至少之一条件：
(1)所述三维石墨烯的粒径为500nm-20μm；
(2)所述三维石墨烯的孔体积为1cm3/g-10cm3/g；
(3)所述三维石墨烯包括相互搭接的石墨烯片，所述石墨烯片间的断裂强度为20N/m-50N/m；
(4)所述三维石墨烯包括相互搭接的石墨烯片，所述石墨烯片的横向尺寸为10nm-100nm；
(5)所述三维石墨烯的平均孔径不大于250nm。
在本公开的一些实施例中，所述石墨烯片的横向尺寸为10nm-20nm。
在本公开的一些实施例中，所述第二负极层的单侧厚度为5μm-80μm。
在本公开的一些实施例中，所述负极片中硅基负极材料占负极总活性材料质量的3％-90％。由此，在提高电池能量密度的同时降低其成本。
在本公开的第二个方面，本公开提出了一种二次电池。根据本公开的实施例，所述二次电池包括上述的负极片。由此，该二次电池在具有较高能量密度的同时具有较高的循环稳定性。
在本公开的第三个方面，本公开提出了一种用电设备。根据本公开的实施例，所述用电设备具有上述的二次电池。
本公开实施例的优点将会在下面的说明书中部分阐明，一部分根据说明书是显而易见的，或者可以通过本公开实施例的实施而获知。
附图说明
附图是用来提供对本公开的进一步理解，并且构成说明书的一部分，与下面的具体实施方式一起用于解释本公开，但并不构成对本公开的限制。在附图中：
图1是根据本公开一个实施例的负极片的结构示意图；
图2是根据本公开一个实施例的制备负极片的方法流程示意图；
图3是实施例1以及对比例1对应电池的循环谱图。
具体实施方式
下面详细描述本公开的实施例，所述实施例的示例在附图中示出，其中自始至终相同或类似的标号表示相同或类似的元件或具有相同或类似功能的元件。下面通过参考附图描述的实施例是示例性的，旨在用于解释本公开，而不能理解为对本公开的限制。
本申请的技术方案是基于下列发现完成的：现有技术中一种方式是采用硅与石墨混用的方式制备负极片，即石墨负极活性材料中掺入Si/C硅碳材料或者SiOx作为负极材料，用于提高电池能量密度。然而石墨负极中掺入硅后，电池的循环性能较石墨显著下降；同时硅基材料脱嵌锂过程中体积膨胀很大，例如硅在嵌锂后体积膨胀可达300％，SiOx嵌锂后体积膨胀可达120％。常规的粘结剂对于硅基材料来说粘结力不足，需要采用粘结力更强的粘结剂，如聚丙烯酸等。而且，常规的炭黑等导电剂已不能满足SiOx的导电需要，需要加入碳纳米管，甚至需要加入成本高昂的单壁碳纳米管以保证其容量的正常发挥。然而石墨并不需要这种成本高的聚丙烯酸粘结剂和单壁碳纳米管导电剂，但采用硅基材料与石墨混用的方式，则使得整个负极片活性层中采用了这两种成本高的粘结剂和导电剂，造成了电池成本的急剧增加。另一种方式是将负极片进行双层涂布，底层采用富硅层，表层采用石墨层。采用富硅层与石墨层双层涂布的方式，这样富硅层可以采用成本高的粘结剂和导电剂，石墨层则依旧采用常规的粘结剂和导电剂组合，可以有效降低成本。但是在实验中发现，因为富硅层与石墨层在充放电过程中悬殊的体积膨胀率，导致在循环过程中，存在双层逐渐剥离的问题，导致电池循环性能悬崖式下跌。
鉴于此，在本公开的一个方面，本公开提出了一种负极片。根据本公开的实施例，参考图1，该负极片包括负极集流体100、第一负极层200和第二负极层300。
需要说明的是，本领域技术人员可以根据实际需要对负极集流体100的材质进行选择，例如采用铜箔。
根据本公开的实施例，参考图1，第一负极层200设在负极集流体100的表面上，并且第一负极层200包括硅基活性材料和压弹添加剂。第二负极层300设在第一负极层200远离负极集流体100的表面上，第二负极层300包括石墨。在沿该负极片厚度方向被施加压力X后，该负极片的回弹率为2％-40％，压缩率为2％-40％；压力X满足0.3MPa≤X≤5Mpa。例如，所述负极片的回弹率为5％，8％，10％，12％，15％，18％，20％，23％，25％，28％，30％，32％，35％，38％，40％等；所述负极片的压缩率为5％，8％，10％，12％，15％，18％，20％，23％，25％，28％，30％，32％，35％，38％，40％等；所述压力X满足0.3Mpa，0.5Mpa，0.8Mpa，1Mpa，1.5Mpa，2Mpa，2.5Mpa，3Mpa，3.5Mpa，4Mpa，4.5Mpa，5Mpa等。
发明人发现，弹性添加剂具有回弹性和压缩性，从而使得第一负极层200表现出压弹特性，在电池充电时，随着负极嵌锂，负极片体积逐渐膨胀，例如硅在嵌锂后体积膨胀可达300％，SiOx嵌锂后体积膨胀可达120％。
在固定电池包或电池壳体体积的工况下，电芯因膨胀则会承受来自外部(如包体、壳体)的压力，此时在压力作用下，第一负极层200中的压弹添加剂在压力作用下体积收缩，释放一部分空间给硅基活性材料，从而缓冲了硅基活性材料在嵌锂过程中产生的较大的体积膨胀，减缓了第一负极层200在嵌锂时的较大的体积膨胀率。而在放电的过程中，随着锂离子的脱出，负极片中活性材料逐渐体积收缩，此时电芯承受的外压力逐渐减小甚至消除，第一负极层200中的压弹添加剂发生回弹，体积逐渐恢复，占据活性材料体积收缩释放的空间，进而延缓第一负极层200因活性材料脱锂导致的体积收缩，因此具有压弹特性的第一负极层200可以缓冲负极片在充放电过程中较大体积变化。即具有压弹特性的第一负极层200可以缓冲负极片在充放电过程中较大体积变化。
同时第一负极层200中的压弹添加剂在放电过程中体积回弹，一方面可以帮助第一负极层200中的硅基活性材料颗粒间良好的物理接触，保证良好的电子导电网络，再一方面，因为压弹添加剂可以减小第一负极层200在充放电过程中的体积变化率，因此可以缩小第一负极层200与第二负极层300在充放电过程中体积膨胀率的差异，避免在长期循环过程中第一负极层200与第二负极层300双层因体积膨胀率较大差异而导致双层逐渐出现裂纹分离的问题。
本公开中，负极片的回弹性能和压缩性能的测试方法如下：沿负极片的厚度方向对负极片施加一个值为X1Mpa的压力，测定负极片在X1Mpa压力下的厚度为H1；然后撤掉该压力，待负极片的厚度稳定后，再测定负极片的厚度，记作H2，则该负极片的厚度回弹率r1＝(H2-H1)/H1。沿负极片的厚度方向对初始厚度为H3的负极片施加一个值为X2Mpa的压力，测定负极片在X2Mpa压力下的厚度，记作H4，则该负极片的厚度压缩率p＝(H3-H4)/H3。因此，上述“在沿该负极片厚度方向被施加第一压力X后，该负极片的回弹率为2％-40％，压缩率为2％-40％；第一压力X满足0.3MPa≤X≤5Mpa”可以理解为：沿负极片的厚度方向对负极片施加0.3MPa≤X1≤5Mpa的压力X1，测定负极片在该压力X1下的厚度为H1；然后撤掉该压力，待负极片的厚度稳定后，再测定负极片的厚度，记作H2，则负极片100的厚度回弹率r1＝(H2-H1)/H1，r1在2％-40％的范围内；沿负极片的厚度方向对初始厚度为H3的负极片施加0.3MPa≤X2≤5Mpa的压力X2，测定负极片在该压力X2下的厚度，记作H4，则该负极片的厚度压缩率p＝(H3-H4)/H3，p在2％-40％的范围内。r1和p可以相同也可以不同，X1和X2可以相同也可以不同。
在本公开一些实施方式中，上述第一负极层200的单侧厚度为5μm-50μm，例如5μm、10μm、15μm、20μm、25μm、30μm、35μm、40μm、45μm、50μm。
由于负极片中的负极层可以是涂覆在集流体中的单面，也可以是涂覆在集流体的两面，因此，当负极层涂覆在集流体中的单面时，本公开中的“单侧厚度”是指涂覆面的第一负极层200或第二负极层300的厚度；当负极层涂覆在集流体中的两面时，本公开中的“单侧厚度”是指两侧中任意一侧负极层中的第一负极层200或第二负极层300的厚度。
在本公开一些实施方式中，所述硅基活性材料与所述压弹添加剂的质量比为100：3-30，例如100:3-25、100:5-22、100:8-20、100:10-18、100:12-16、100:13-15等。若压弹添加剂添加量过低，则无法实现极片的压缩回弹性能。由此，在第一负极层200中加入上述比例的压弹添加剂，可以在降低成本的同时提高电池能量密度和循环稳定性。
在本公开一些实施方式中，在第一负极层200中硅基活性材料占总活性材料质量分数为3％-100％，例如5％-95％，10％-90％，15％-85％，20％-80％，25％-75％，30％-70％，40％-60％，45％-50％等。发明人发现，第一负极层200中活性材料可以是纯硅基活性材料，若硅基活性材料过少，虽然可以起到改善电池能量密度的效果，但从工艺成本以及收益来看，收益不显著。在本公开另一些实施方式中，在第一负极层200中硅基活性材料占总活性材料质量分数为10％-60％。
在本公开一些实施方式中，第一负极层200还包括石墨，硅基活性材料和所述石墨的总质量与所述压弹添加剂的质量比为100：3-30，例如100:3-25、100:5-22、100:8-20、100:10-18、100:12-16、100:13-15等。
本领域技术人员可以根据实际需要对上述硅基活性材料和压弹添加剂的具体类型进行选择，例如硅基活性材料包括SiOx、Si、Si/C和硅基合金中的至少之一，其中x取值为0<x<2，并且硅基合金除含Si外，还包括Al、Mg、B、Ni、Fe、Cu和Co等元素中的至少一种。
在本公开一些实施方式中，第一负极层还包括第一导电剂，第一导电剂包括但不限于单壁碳纳米管和炭黑中的至少之一；在本公开一些实施方式中，第一导电剂包括单壁碳纳米管。
在本公开一些实施方式中，上述第一负极层200还包括第一粘结剂，第一粘结剂包括但不限于聚丙烯酸、海藻酸钠和聚酰亚胺中的至少之一；在本公开一些实施方式中，第一粘结剂包括聚丙烯酸。
在本公开一些实施方式中，硅基活性材料或硅基活性材料与石墨的复合材料、第一导电剂、第一粘结剂和压弹添加剂的质量比为100：0.1-2.5：0.1-30：3-30，例如100：0.5-2.5：0.1-30：3-30，100：1-2.3：0.1-30：3-30，100：1.2-2：0.1-30：3-30，100：1.5-2：0.1-30：3-30，100：0.1-2.5：0.5-30：3-30，100：0.1-2.5：1-30：3-30，100：0.1-2.5：5-25：3-30，100：0.1-2.5：10-20：3-30，100：0.1-2.5：15-20：3-30，100：0.1-2.5：0.1-30：5-25，100：0.1-2.5：0.1-30：10-20，100：0.1-2.5：0.1-30：15-20。若第一导电剂添加量过高，则一方面增加成本，另一方面降低电芯能量密度，若第一导电剂添加量过低，则会降低电芯导电性能；若第一粘结剂添加量过高，则除了增加成本，降低电芯能量密度外，还会增大电池极化，增大电池内阻，若第一粘结剂添加量过低，则在电池循环过程中，硅基活性材料在反复膨胀收缩过程中，极片粉化，导致循环性能急剧下降；若压弹添加剂添加量过高，则增加成本外，会降低电池能量密度。
本公开一些实施方式中，压弹添加剂为三维石墨烯。本公开一些实施方式中，，该三维石墨烯满足下列(1)-(5)至少之一条件：
(1)所述三维石墨烯的粒径为500nm-20μm，例如1μm-20μm，3μm-18μm，5μm-15μm，7μm-13μm，10μm-12μm等；
(2)所述三维石墨烯的孔体积为1cm3/g-10cm3/g，例如3cm3/g-8cm3/g，5cm3/g-7cm3/g等；
(3)所述三维石墨烯包括相互搭接的石墨烯片，所述石墨烯片间的断裂强度为20N/m-50N/m，例如25N/m-45N/m，30N/m-45N/m，35N/m-45N/m，40N/m-45N/m等；
(4)所述三维石墨烯包括相互搭接的石墨烯片，所述石墨烯片的横向尺寸为10nm-100nm，例如10nm-20nm，20nm-100nm，30nm-90nm，40nm-80nm，50nm-70nm，；
(5)所述三维石墨烯的平均孔径不超过250nm，例如10nm，30nm，50nm，80nm，100nm，120nm，150nm，170nm，200nm，220nm，250nm等。
上述三维石墨烯的孔体积可以通过对三维石墨烯采用氮吸附法测得。上述石墨烯片的断裂强度可通过对三维石墨烯采用原子力显微镜(Atomic Force Microscope，AFM)对搭接处进行纳米压痕测试得到：将三维石墨烯固定在表面开设有小孔的硅片上，用探针对小孔上的石墨烯片施加一个压力，施加压力的位置应在相邻两石墨烯片材的搭接位置附近，记录能使两个石墨烯片材的搭接处断裂的临界压力，即获得石墨烯片间搭接处的断裂强度。上述横向尺寸是指石墨烯片材的长度或宽度等，可通过三维石墨烯的电子显微镜照片获知。
本申请一些实施方式中，上述三维石墨烯可以采用等离子体化学气相沉积法(PECVD)生长得到。示例性的制备方法包括以下步骤：将碳源(如C2H2)和H2的混合气体通入到等离子沉积设备中加热至一定温度的沉积室中，开启等离子体发生器，以在沉积室中放置的基底(如Cu)上通过PECVD法沉积生长三维石墨烯材料，待三维石墨烯的生长结束后，通入辅助气体(如Ar、He等)以在惰性气氛下使沉积室冷却至室温，之后将所得样品从沉积室取出，并从基底上将三维石墨烯材料剥离下来，并将其破碎至所需的粒径。通过调整生长条件，可以获得满足以下条件的三维石墨烯：粒径500nm-20μm、孔体积为1cm3/g-10cm3/g、由横向尺寸为10nm-100nm的石墨烯片相互搭接生长形成、平均孔径不超过250nm，石墨烯片间的断裂强度为20N/m-50N/m。
示例性的制备方法包括以下步骤：将碳源(如C2H2)和H2的混合气体通入到等离子沉积设备中加热至一定温度的沉积室中，开启等离子体发生器，以在沉积室中放置的基底(如Cu)上通过PECVD法沉积生长三维石墨烯材料，待三维石墨烯的生长结束后，通入辅助气体(如Ar、He等)以在惰性气氛下使沉积室冷却至室温，之后将所得样品从沉积室取出，并从基底上将三维石墨烯材料剥离下来，并将其破碎至所需的粒径。PECVD过程中可产生高能量密度和较大体积的等离子体，可将碳源C2H2分解成较多的含碳反应自由基，进而实现三维石墨烯的生长。其中，C2H2的通入流量为20mL/min，H2的通入流量为250mL/min，沉积生长的温度可以是950℃，辅助气体Ar的通入流量为200mL/min，等离子发生器的工作功率为300W。
具体的，足量的孔体积，可以保证三维石墨烯具有优良的压缩性能，适宜的孔径大小以及石墨烯片间的断裂强度，则保证三维石墨烯在压缩后具有良好的回弹性能，不会因压力导致结构坍塌，失去回弹性能。由此在电池循环过程中，稳定保持其压缩-回弹性能。具备以上特性的三维石墨烯，具有优异的压缩-回弹性能，从而使得制备得到的第一负极层200表现出较高的压弹特性，进而以缓冲负极片在充电过程中较大体积膨胀。
根据本公开的实施例，参考图1，第二负极层300设在第一负极层200上远离负极集流体100的表面上，并且第二负极层300包括石墨。发明人发现，由于硅与石墨具有不同的脱锂平台(硅脱锂平台0.4V-0.5V)，而石墨的脱锂平台在0.1V左右，在全电池放电初期，石墨需要承担大部分的放电电流，因此导致石墨材料放电极化大，为了减小石墨负极放电极化，使得石墨负极迁出的锂离子快速迁移至正极，由此本申请将含石墨的第二负极层300形成第一负极层200上，即将含石墨的第二负极层300形成在负极片表层，因为石墨的快充性能优于含硅负极，因此有利于提高电池的瞬时充电以及大倍率瞬时放电性能。
在本公开的一些实施方式中，上述第二负极层300的单侧厚度为5μm-80μm，例如5μm、10μm、15μm、20μm、25μm、30μm、35μm、40μm、45μm、50μm、55μm、60μm、65μm、70μm、75μm、80μm。
在本公开的一些实施方式中，第二负极层300还包括第二导电剂，例如第二导电剂包括但不限于乙炔黑、导电炭黑等。
在本公开的一些实施方式中，第二负极层300还包括第二粘结剂，例如第二粘结剂包括但不限于羧甲基纤维素钠和丁苯橡胶等。
需要说明的是，本申请中形成第二负极层300的石墨、第二导电剂和第二粘结剂的混合比例可以是本领域形成石墨负极的常规设置。同时本申请中通过在含硅的第一负极层200上形成含石墨的第二负极层300，通过差异化第一负极层200与第二负极层300的导电剂以及粘结剂，可以分别保证第二负极层300中石墨与第一负极层200中硅基活性材料各自容量以及循环稳定性的发挥，显著降低了负极片的成本。
本公开中，在沿所述负极片厚度方向被施加压力X后，所述负极片的回弹率为2％-40％，所述负极片的压缩率为2％-40％；所述压力X满足0.3≤X≤5Mpa。由此，本申请的负极片在充放电过程中具有较低的体积变化率，从而在提高其电池能量密度的同时提高其循环稳定性。
另外，在实际应用中，用户在使用电池的过程中，通常不会将电池完全放电后才进行充电，属于浅放电的使用场景，这时，对于本申请提出的负极片，靠近负极集流体100的第一负极层200内的SiOx因其较高的放电平台，就不会放电或者仅放出少量的电量，也就是说SiOx在实际的使用过程中会经常处于浅放状态，这样减少了SiOx在循环过程中反复的体积膨胀，有助于电池循环性能的提升。
在本公开的一些实施方式中，本申请限定负极片中硅基负极材料占负极总活性材料质量的3％-90％，其中总活性材料指负极片中可进行脱嵌锂的所有活性材料，例如5％-90％，10％-90％，15％-85％，20％-80％，25％-75％，30％-70％，40％-60％，45％-50％。具体的，本申请中通过采用上述比例将硅基活性材料与石墨复配制备负极片，一方面可以解决双层涂布时层间分离的问题，另一方面，工艺实施难度和成本均较低，从而可以在降低成本的同时保持负极片中硅基活性材料和石墨性能的充分发挥，提高电池的能量密度。
由此，本申请的负极片不仅可以具有较低的成本，而且可以减小电池在充电过程中单次循环产生的体积膨胀率，从而在提高其电池能量密度的同时提高其循环稳定性。
为了方便理解，下面对制备上述负极片的方法进行描述。根据本公开的实施例，参考图2，该方法包括：
S100：在负极集流体上施加包括硅基活性材料和压弹添加剂的第一浆料
该步骤中，在负极集流体100上施加包括硅基活性材料和压弹添加剂的第一浆料，以便在负极集流体100上形成第一负极层200。发明人发现，压弹添加剂具有回弹性和压缩性，从而使得第一负极层200表现出压弹特性，在电池充电时，随着负极嵌锂，负极片体积逐渐膨胀，石墨负极在嵌锂时体积膨胀可达10％，而硅基活性材料，在嵌锂时体积膨胀更大，例如硅在嵌锂后体积膨胀可达300％，SiOx嵌锂后体积膨胀可达120％。在固定电池包体积的工况下(如圆柱电池)，电芯因膨胀则会承受来自外部包体的压力，此时在压力作用下，第一负极层200中的压弹添加剂在压力作用下体积收缩，释放一部分空间给硅基活性材料，从而缓冲了硅基活性材料在嵌锂过程中产生的较大的体积膨胀，减缓了第一负极层200在嵌锂时的较大的体积膨胀率。而在放电的过程中，随着锂离子的脱出，负极片中活性材料逐渐体积收缩，此时电芯承受的外压力逐渐减小甚至消除，第一负极层200中的压弹添加剂发生回弹，体积逐渐恢复，占据活性材料体积收缩释放的空间，进而延缓第一负极层200因活性材料脱锂导致的体积收缩，因此具有压弹特性的第一负极层200可以缓冲负极片在充放电过程中较大体积变化。即具有压弹特性的第一负极层200可以缓冲负极片在充放电过程中较大体积变化。同时第一负极层200中的压弹添加剂在放电过程中体积回弹，一方面可以帮助第一负极层200中的硅基活性材料颗粒间良好的物理接触，保证良好的电子导电网络，再一方面，因为压弹添加剂可以减小第一负极层200在放电过程中的体积收缩率，因此可以缩小第一负极层200与第二负极层300在充放电过程中体积变化率的差异，避免在长期循环过程中第一负极层200与第二负极层300双层因体积膨胀率较大差异而导致双层逐渐出现裂纹分离的问题。
S200：在第一负极层上施加包括石墨的第二浆料
该步骤中，在上述第一负极层200上施加包括石墨的第二浆料，以便在第一负极层200上形成第二负极层300，得到负极片。发明人发现，由于硅与石墨具有不同的脱锂平台(硅脱锂平台0.4V-0.5V)，而石墨的脱锂平台在0.1V左右，在全电池放电初期，石墨需要承担大部分的放电电流，因此导致石墨材料放电极化大，为了减小石墨负极放电极化，使得石墨负极迁出的锂离子快速迁移至正极，由此本申请将含石墨的第二负极层300形成第一负极层200上，即将含石墨的第二负极层300形成在负极片表层，因为石墨的快充性能优于含硅负极，因此提高电池的瞬时充电以及大倍率瞬时放电性能。
在本公开的一些实施方式中，该第二浆料可以进一步包括第二导电剂和第二粘结剂。本申请中通过在含硅的第一负极层200上形成含石墨的第二负极层300，通过差异化第一负极层200与第二负极层300的导电剂以及粘结剂，可以分别保证石墨与硅基活性材料各自容量以及循环稳定性的发挥，显著降低了负极片的成本。
在本公开的一些实施方式中，上述第一浆料中可以进一步包括第一粘结剂和/或第一导电剂。
由此，采用该方法可以制备得到上述具有较低的成本和较小单次循环产生的体积膨胀率，从而在提高其电池能量密度的同时提高其循环稳定性。需要说明的是，上述针对负极片所描述的特征和优点同样适用于该制备负极片的方法，同时第一浆料和第二浆料的固含量等均为本领域制备负极片的常规参数，此处不再赘述。
在本公开的第三个方面，本公开提出了一种二次电池。根据本公开的实施例，该二次电池包括上述的负极片。由此，该二次电池通过采用上述具有高能量密度和高循环稳定性的负极片，使得该二次电池表现出较高能量密度和较高的循环稳定性。需要说明的是，上述针对负极片及其制备方法所描述的特征和优点同样适用于该二次电池，此处不再赘述。
在本公开的第四个方面，本公开提出了一种用电设备。该用电设备可以是车、船等交通工具，也可以是笔记本电脑、移动终端等。根据本公开的实施例，该用电设备具有上述的二次电池。由此，该用电设备通过装载上述具有较高能量密度和较高循环稳定性的二次电池，使得用电设备具有优异的续航里程和安全性能。需要说明的是，上述针对二次电池所描述的特征和优点同样适用于该用电设备，此处不再赘述。
下面参考具体实施例，对本公开进行描述，需要说明的是，这些实施例仅仅是描述性的，而不以任何方式限制本公开。
实施例1
制备负极片的方法包括：
(1)将SiOx(x＝1.02)、石墨、单壁碳纳米管、聚丙烯酸和三维石墨烯质量比为30：70：0.2：5：5混合制备第一浆料，然后将第一浆料双面涂布在铜箔表面上(两面涂布面密度相同，单侧面密度为43g/m2)，然后经固化后辊压，以便在铜箔两侧上分别形成单侧厚度为27μm的第一负极层；
(2)将石墨与羧甲基纤维素钠、丁苯橡胶和炭黑按照质量比为100：1.5：1.5：1混合制备第二浆料，然后将第二浆料涂布在铜箔两侧的第一负极层表面上(单侧面密度为43g/m2)，然后经固化后辊压，以便在铜箔两侧的第一负极层上分别形成单侧厚度为27μm的第二负极层，得到负极片。
实施例1所用三维石墨烯包括相互搭接的石墨烯片材且三维石墨烯具有多孔结构，该三维石墨烯的平均粒径为0.6μm，孔体积为2.5cm3/g，该三维石墨烯中多孔结构的平均孔径为100nm；经AFM进行纳米压痕测试，测得三维石墨烯中相互搭接在一起的石墨烯片材连接处的断裂强度为30N/m，相互搭接在一起的石墨烯片材的横向尺寸为10nm-100nm。
实施例2
制备负极片的方法包括：
(1)将SiOx(x＝1.02)、单壁碳纳米管、聚丙烯酸和三维石墨烯质量比为100：0.5：10：15混合制备第一浆料，然后将第一浆料双面涂布在铜箔表面上(两面涂布面密度相同，单侧面密度为17.5g/m2)，然后经固化后辊压，以便在铜箔两侧上分别形成单侧厚度为11μm的第一负极层；
(2)将石墨与羧甲基纤维素钠、丁苯橡胶和炭黑按照质量比为100：1.5：1.5：1混合制备第二浆料，然后将第二浆料涂布在铜箔两面的第一负极层表面上(单侧面密度为62g/m2)，然后经固化后辊压，以便在铜箔两面的第一负极层上分别形成单侧厚度为39μm的第二负极层，得到负极片。
实施例2所用三维石墨烯包括相互搭接的石墨烯片材且三维石墨烯具有多孔结构，该三维石墨烯的平均粒径为0.6μm，孔体积为2.5cm3/g，该三维石墨烯中多孔结构的平均孔径为100nm；经AFM进行纳米压痕测试，测得三维石墨烯中相互搭接在一起的石墨烯片材连接处的断裂强度为30N/m，相互搭接在一起的石墨烯片材的横向尺寸为10nm-100nm。
实施例3
实施例3与实施例1的区别在于，采用克比容量1250mAh/g的硅碳材料替换实施例1中的SiOx，第二负极层的单侧面涂覆面密度为46g/m2，以便在铜箔两面的第一负极层上分别形成单侧厚度为29μm的第二负极层，得到负极片。
实施例4
实施例4与实施例1的区别在于，采用的三维石墨烯平均粒径为1.5μm，孔体积为4cm3/g，该三维石墨烯中多孔结构的平均孔径为150nm；经AFM进行纳米压痕测试，测得三维石墨烯中相互搭接在一起的石墨烯片材连接处的断裂强度为45N/m。
实施例5
实施例5与实施例2的区别在于，步骤(1)替换为，将SiOx(x＝1.02)、单壁碳纳米管、聚丙烯酸和三维石墨烯质量比为100：0.5：10：30混合制备第一浆料。第一浆料双面涂布在铜箔表面上(两面涂布面密度相同，单侧面密度为19.6g/m2)，然后经固化后辊压，以便在铜箔上形成单侧厚度为12微米的第一负极层，保持与实施例2相同的第一涂布层面容量)。
实施例6
实施例6与实施例2的区别在于，实施例6所用三维石墨烯的平均粒径为10μm，孔体积为8cm3/g，该三维石墨烯中多孔结构的平均孔径为150nm；经AFM进行纳米压痕测试，测得三维石墨烯中相互搭接在一起的石墨烯片材连接处的断裂强度为20N/m，相互搭接在一起的石墨烯片材的横向尺寸为10nm-100nm。
对比例1
制备负极片的方法包括：
将SiOx(x＝1.02)、石墨、单壁碳纳米管与聚丙烯酸质量比为15：85：0.1：3混合制备浆料，然后将浆料双面涂布在铜箔表面上(两面涂布面密度相同，单侧面密度为82.5g/m2)，然后经固化后辊压，以便在铜箔两侧分别上形成单侧厚度为51.5μm的负极层，得到负极片。
对比例2
对比例2与实施例1的区别是：
(1)第一浆料的配比为SiOx(x＝1.02)、石墨、单壁碳纳米管、聚丙烯酸和三维石墨烯质量比为30：70：0.2：5：0.5；涂覆单面面密度为42g/m2，形成的第一负极层的单侧厚度为26μm。
(2)第二负极层的单侧面密度为41g/m2，所得第二负极层的单侧厚度为26μm。
对比例3
对比例3与实施例1的区别是：步骤(1)中，第一浆料的配比为SiOx(x＝1.02)、石墨、单壁碳纳米管、聚丙烯酸和三维石墨烯质量比为30：70：0.2：5：2，第一浆料在铜箔两侧中的每一侧涂覆面密度41.8g/m2，形成的第一负极层的单侧厚度为26微米。
比容量测试用电池制备：将各实施例和对比例制备的负极片、PE隔膜与100微米厚的锂箔，电解液采用1mol/L的LiPF6，EC与EMC体积比为1:1，组装为电池，将电池在0.005V-1.5V之间充放电。
循环用测试电池制备：将NCM811与PVDF和导电剂Sup-P按照100:1.6:1.2质量比混合制浆，按照在铝箔表面按照单面面密度为200g/m2的进行双面涂布，制成正极片。然后将制备的正极片分别与实施例1-6和对比例1-3所得负极片、PE隔膜，电解液采用1mol/L的LiPF6，EC与EMC体积比为1:1，组装为电池。测试对应电池的循环性能。
负极首次充放电比容量测试：将电池在0.1C恒流放电至0.005V后，再以0.05C恒流放电至0.005V，然后以0.1C充电至1.5V。负极首次放电比容量＝放电容量/负极层总质量；负极首次充电比容量＝充电容量/负极层总质量。其中，负极层总质量＝第一负极层质量+第二负极层质量。
容量保持率测试：在0.5C下首先恒定电流充电至4.25V，然后在4.25V下恒定电压充电至截止电流为0.1C，然后1C放电至2.5V，如此循环300次，记录首次放电容量和循环300次后的放电容量，容量保持率＝循环300次后的放电容量/首次放电容量。测试结果如表1和图3所示。
表1

由图3可以看出，采用实施例1负极片的电池循环稳定性明显优于对比例1，并且由表1可知，采用实施例2-6所得电池也具有优异的循环稳定性能，表明采用本申请的负极片不仅可以降低电池成本，同时可以显著改善电池循环性能。
将上述经过首次充放电比容量测试后的全电池拆解，取各实施例或对比例对应的全电池拆解获得的正极极片分别进行极片回弹性能和压缩性能的测试，结果汇总在下表2-3中。
对实施例1-6以及对比例1-3所得负极片的回弹性能和压缩性能进行评价，对应结果如表2-3所示。
负极片回弹性能测试方法：对负极片施加X1Mpa的压力，测定在X1Mpa压力下负极片厚度H1，然后撤掉压力，待负极片厚度稳定后，再测定负极片的厚度H2，则极片的回弹率为：
极片回弹率r＝(H2-H1)/H1
负极片压缩性能测试方法：对初始厚度为H3的极片施加一个压力X2Mpa，记录X2Mpa压力下极片的厚度H4，则负极片的压缩率为：
极片压缩率P＝(H3-H4)/H3
表2负极片回弹性能和压缩性能数据(X1＝0.5Mpa，X2＝0.3Mpa)
表3负极片回弹性能和压缩性能数据(X1＝5Mpa，X2＝5Mpa)
结合表1-表3可以看出，实施例1-6的负极片，具有较高的回弹性能和压缩性能，同时通过实施例1与对比例2的数据可以看出，按照常规导电剂的加入量加入三维石墨烯时，因三维石墨烯加入量少，对比例2的极片不具有压缩回弹性能，与常规极片性能一样，其组装的电池循环300次后容量保持率明显低于实施例1-6。通过对比例3可知，虽然加入一定量的三维石墨烯然而极片回弹率和压缩率不在2％-40％范围内时，其循环性能相比于实施例也会一定程度上降低。
以上所述实施例仅表达了本公开的几种实施方式，其描述较为具体和详细，但并不能因此而理解为对本公开专利范围的限制。应当指出的是，对于本领域的普通技术人员来说，在不脱离本公开构思的前提下，还可以做出若干变形和改进，这些都属于本公开的保护范围。因此，本公开专利的保护范围应以所附权利要求为准。

Claims (13)

  1. 一种负极片，其中，包括：
    负极集流体；
    第一负极层，所述第一负极层设在所述负极集流体的表面上，所述第一负极层包括硅基活性材料和压弹添加剂；
    第二负极层，所述第二负极层设在所述第一负极层上远离所述负极集流体的表面上，所述第二负极层包括石墨；
    在沿所述负极片厚度方向被施加压力X后，所述负极片的回弹率为2％-40％，所述负极片的压缩率为2％-40％；所述压力X满足0.3MPa≤X≤5Mpa。
  2. 根据权利要求1所述的负极片，其中，所述第一负极层的单侧厚度为5μm-50μm。
  3. 根据权利要求1或2所述的负极片，其中，所述硅基活性材料与所述压弹添加剂的质量比为100：3-30。
  4. 根据权利要求1-3中任意一项所述的负极片，其中，所述第一负极层还包括石墨，所述硅基活性材料和所述石墨的总质量与所述压弹添加剂的质量比为100：3-30。
  5. 根据权利要求1-4中任意一项所述的负极片，其中，所述硅基活性材料包括SiOx、Si、硅碳材料和硅基合金中的至少之一，其中x取值为0<x<2，所述硅基合金除含Si外，还包括Al、Mg、B、Ni、Fe、Cu和Co中的至少一种。
  6. 根据权利要求1-5中任意一项所述的负极片，其中，所述第一负极层还包括：
    第一导电剂，所述第一导电剂包括单壁碳纳米管和炭黑中的至少之一；
    第一粘结剂，所述第一粘结剂包括聚丙烯酸、海藻酸钠和聚酰亚胺中的至少之一。
  7. 根据权利要求1-6中任意一项所述的负极片，其中，所述压弹添加剂为三维石墨烯。
  8. 根据权利要求7所述的负极片，其中，所述三维石墨烯满足下列(1)-(5)至少之一条件：
    (1)所述三维石墨烯的粒径为500nm-20μm；
    (2)所述三维石墨烯的孔体积为1cm3/g-10cm3/g；
    (3)所述三维石墨烯包括相互搭接的石墨烯片，所述石墨烯片间的断裂强度为20N/m-50N/m；
    (4)所述三维石墨烯包括相互搭接的石墨烯片，所述石墨烯片的横向尺寸为10nm-100nm；
    (5)所述三维石墨烯的平均孔径不超过250nm。
  9. 根据权利要求8所述的负极片，其中，所述石墨烯片的横向尺寸为10nm-20nm。
  10. 根据权利要求1-9中任意一项所述的负极片，其中，所述第二负极层的单侧厚度为5μm-80μm。
  11. 根据权利要求1-10中任意一项所述的负极片，其中，所述负极片中硅基活性材料占负极总活性材料质量的3％-90％。
  12. 一种二次电池，其中，所述二次电池包括权利要求1-11中任意一项所述的负极片。
  13. 一种用电设备，其中，所述用电设备具有权利要求12所述的二次电池。
PCT/CN2023/101453 2022-06-21 2023-06-20 负极片、二次电池和用电设备 WO2023246795A1 (zh)

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