WO2021226841A1 - 负极材料、负极极片、电化学装置和电子装置 - Google Patents

负极材料、负极极片、电化学装置和电子装置 Download PDF

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WO2021226841A1
WO2021226841A1 PCT/CN2020/089841 CN2020089841W WO2021226841A1 WO 2021226841 A1 WO2021226841 A1 WO 2021226841A1 CN 2020089841 W CN2020089841 W CN 2020089841W WO 2021226841 A1 WO2021226841 A1 WO 2021226841A1
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silicon
negative electrode
electrode material
sheet
flake
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PCT/CN2020/089841
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English (en)
French (fr)
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张成波
谢远森
鲁宇浩
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宁德新能源科技有限公司
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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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • 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

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  • the present disclosure relates to the field of electronic technology, and in particular to a negative electrode material, a negative pole piece, an electrochemical device and an electronic device.
  • the compacted density of the negative pole piece made by directly using silicon-based material as the negative electrode material is only 1.2g/cm 3 , which is far lower than the compact density of graphite-based negative pole piece of 1.8g/cm 3 , and far lower than that of silicon.
  • the theoretical true density of the base material is 2.3g/cm 3 , and the compact density is too low will cause more gaps between the anode materials, affect the volume energy density of the anode material, and cause the reduction and circulation of the volume energy density of the electrochemical device Deterioration of performance.
  • the present disclosure greatly improves the compaction density of the negative electrode material and improves the negative electrode material by adding a sheet-shaped carbon fluoride with a specific diameter to thickness ratio to the negative electrode material including the silicon-based material.
  • the present disclosure provides a negative electrode material, including: a silicon-based material and a sheet-shaped carbon fluoride; wherein the diameter-to-thickness ratio of the sheet-shaped carbon fluoride is greater than 2.
  • the sheet-shaped carbon fluoride includes at least one of fluorinated graphite, fluorinated hard carbon, fluorinated soft carbon, or fluorinated graphene.
  • the silicon-based material includes at least one of silicon oxide, silicon, silicon-carbon composite material, or silicon alloy.
  • the silicon-based material satisfies at least one of the following: the surface of the silicon oxide has the flaky carbon fluoride; the particle size range of the silicon oxide satisfies 1 ⁇ m ⁇ Dv50 ⁇ 10 ⁇ m The specific surface area of the silicon oxide is less than 10m 2 /g; the general formula of the silicon oxide is SiO x , where 0 ⁇ x ⁇ 2; the silicon includes silicon microparticles, silicon nanoparticles, and silicon nanowires Or at least one of silicon nano-film; the silicon alloy includes at least one of silicon-iron alloy, silicon-aluminum alloy, silicon-nickel alloy, or silicon-iron-aluminum alloy.
  • the particle size range of the sheet-shaped carbon fluoride satisfies Dv50 ⁇ 10 ⁇ m, and the mass of the fluorine element in the sheet-shaped carbon fluoride accounts for 0.05% to 15% of the total mass of the negative electrode material %.
  • the present disclosure also provides a negative electrode piece, which includes: a current collector; an active material layer located on the current collector; wherein the active material layer includes any of the above-mentioned negative electrode materials.
  • the present disclosure also provides an electrochemical device, including: a positive pole piece; a negative pole piece; a separator, arranged between the positive pole piece and the negative pole piece; wherein the negative pole piece is the above-mentioned negative Pole piece.
  • the present disclosure also provides an electronic device, including the electrochemical device described above.
  • the anode material includes a silicon-based material and a flaky carbon fluoride, and the aspect ratio of the flaky carbon fluoride is greater than 2, thereby increasing the compaction density and density of the anode material containing the silicon-based material. Volume energy density density, and improved cycle performance.
  • Fig. 1 is a scanning electron microscope image of a flake fluorinated graphite according to an embodiment of the present disclosure.
  • Fig. 2 is a cross-sectional scanning electron microscope image of a flake fluorinated graphite in an embodiment of the present disclosure.
  • Fig. 3 is an exemplary image of a negative pole piece of the present disclosure.
  • Fig. 4 is a schematic diagram of an electrode assembly of an electrochemical device of the present disclosure.
  • Fig. 5 is the discharge capacity retention rate of the battery in Comparative Example 1 and Example 2 of the present disclosure under different cycle cycles.
  • Fig. 6 is a schematic diagram of the volume energy density under different flake fluorinated graphite contents in the embodiments of the present disclosure.
  • Silicon-based materials have high theoretical capacity and are widely regarded as the preferred anode materials for next-generation lithium-ion batteries. Using silicon-based materials as anode materials can increase the energy density of lithium-ion batteries. However, silicon-based materials are directly used as anode materials.
  • the prepared negative pole piece has a low compaction density and poor cycle performance, and the low compaction density results in a low volume energy density of the negative electrode material.
  • the negative electrode materials in some embodiments of the present disclosure include silicon-based materials and fluorocarbons with a diameter-to-thickness ratio greater than 2, which can greatly increase the volumetric energy density and improve the cycle performance compared to when silicon-based materials are used directly as the negative electrode materials. .
  • the negative electrode material includes: a silicon-based material and a sheet-shaped fluorocarbon; wherein the diameter-to-thickness ratio of the sheet-shaped fluorocarbon is greater than 2.
  • the flake carbon fluoride may be fluorinated graphite flake as shown in FIGS. 1 and 2.
  • the diameter-to-thickness ratio of the sheet-shaped carbon fluoride refers to the ratio L/H of the diameter L of the circumscribed circle of the sheet-shaped carbon fluoride projection and the thickness H of the sheet-shaped carbon fluoride.
  • the cross-sectional view of the flake carbon fluoride is taken by electron microscopy to measure and calculate the diameter-to-thickness ratio of the flake carbon fluoride.
  • the negative electrode material includes flake graphite fluoride with a diameter-to-thickness ratio greater than 2, the flake graphite fluoride material easily slips in the direction of the sheet, and the flake carbon fluoride easily acts as a lubrication.
  • the gaps between the silicon-based materials are fully filled, and the compaction density and volumetric energy density are improved.
  • the flake fluorocarbon will generate carbon and lithium fluoride after the first charge. Carbon can increase the conductivity of the negative electrode material, and lithium fluoride can reduce the side reaction between the silicon-based material and the electrolyte, thereby improving the negative electrode.
  • the cycle performance of the material since the negative electrode material includes flake graphite fluoride with a diameter-to-thickness ratio greater than 2, the flake graphite fluoride material easily slips in the direction of
  • flake carbon fluoride is lower than that of silicon-based material. Adding flake carbon fluoride to the anode material containing silicon-based material will cause the specific capacity of the anode material to decrease, which is not conducive to the anode material.
  • adding flake carbon fluoride can increase the compaction density of the negative electrode material.
  • the increase of the compaction density is beneficial to increase the volume energy density of the negative electrode material. Therefore, to increase the volume energy density of the negative electrode material, the compaction must be made. The increase in the solid density can offset the adverse effect of the decrease in the specific capacity on the volumetric energy density.
  • the increase in the compaction density of the negative electrode material can offset the adverse effect of the decrease in the specific capacity on the volume energy density, thereby increasing the volume energy density of the negative electrode material.
  • the diameter-to-thickness ratio of the flake fluoride in the negative electrode material is not greater than 2
  • the flake carbon fluoride is not easy to play a lubricating effect and cannot effectively fill the gap between the silicon-based materials, so the pressure of the negative electrode material cannot be greatly increased.
  • Solid density that is, the increase in the compaction density of the negative electrode material after adding silicon fluoride with a diameter-to-thickness ratio of not more than 2 cannot offset the adverse effect of the decrease in specific capacity on the volume energy density. Therefore, when the diameter-to-thickness ratio is not more than 2 In the case of fluorocarbons, the volumetric energy density of the negative electrode material cannot be increased. Based on this, in some embodiments of the present disclosure, the diameter-to-thickness ratio of the flaky fluorocarbons is defined to be greater than 2 to ensure that the flaky fluorocarbons can improve the cycle Improve the volume energy density of the negative electrode material at the same time.
  • the powder compaction density of the negative electrode material under a pressure of 150 MPa is above 1.4 g/cm 3. If the compaction density is too low, the silicon-based materials cannot be in effective electrical contact with each other, which is not conducive to the cycle performance of the negative electrode material.
  • the ratio of the Dv50 of the sheet-shaped fluorocarbon to the Dv50 of the silicon-based material is greater than 1
  • the size of the sheet-shaped fluorocarbon is too large compared to the gap of the silicon-based material, and the sheet-shaped fluorocarbon cannot effectively fill the silicon-based material
  • the gap between them is not conducive to increasing the compaction density, and also not conducive to increasing the volume energy density, and will cause the electrical contact between the silicon-based materials to deteriorate, which is not conducive to the improvement of the cycle performance. Therefore, in some of the disclosures
  • the ratio of the Dv50 of the sheet-shaped fluorocarbon to the Dv50 of the silicon-based material is controlled to be less than 1.
  • the mass of the flaky carbon fluoride accounts for 0.1% to 20% of the total mass of the silicon-based material and the flaky carbon fluoride. In some embodiments, when the ratio of the mass of the flake carbon fluoride to the total mass of the silicon-based material and the total mass of the flake carbon fluoride is less than 0.1%, the negative electrode material contains too little flake carbon fluoride. The carbon fluoride can't obviously play its role, and its effect on improving the compaction density, conductivity and cycle performance of the negative electrode material is not obvious.
  • the negative electrode material contains a large amount of flake carbon fluoride.
  • the volume energy density of the negative electrode material is affected by both the compaction density and the specific capacity.
  • the addition of flake carbon fluoride to the negative electrode material containing silicon-based materials can increase the compaction density but reduce the specific capacity of the negative electrode material.
  • the mass of fluorocarbons accounts for more than 20% of the total mass of silicon-based materials and flake fluorocarbons, the increase in compaction density of flake fluorocarbons is not enough to offset the disadvantages of reduced specific capacity on volumetric energy density. Influence, will cause the volumetric energy density of the negative electrode material to decrease.
  • the sheet-shaped fluorocarbon includes at least one of fluorinated graphite, fluorinated hard carbon, fluorinated soft carbon, or fluorinated graphene.
  • the silicon-based material includes at least one of silicon oxide, silicon, silicon-carbon composite material, or silicon alloy.
  • the silicon-based material at least satisfies one of the following (a) to (f):
  • the silicon oxide has flaky carbon fluoride on the surface.
  • the conductivity of silicon oxide is poor, so when (a) is satisfied, the conductivity of silicon oxide can be increased to improve cycle performance.
  • the particle size range of silicon oxide satisfies 1 ⁇ m ⁇ Dv50 ⁇ 10 ⁇ m. If the particle size of silicon oxide is too small, it will increase the consumption of electrolyte and is not conducive to the cycle performance; if the particle size of silicon oxide is too large, it will cause degradation of rate performance. Therefore, in some embodiments, it is set to satisfy (b) to control The particle size range of the silicon oxide compound.
  • the specific surface area of silicon oxide is less than 10 m 2 /g. In some embodiments, when the specific surface area of silicon oxide is not less than 10m 2 /g, more electrolyte will be consumed to form an SEI (solid electrolyte interface) film, resulting in excessive loss of first charge capacity and increased adhesion. Therefore, the specific surface area of silicon oxide is set to be less than 10 m 2 /g.
  • the general formula of silicon oxide is SiO x , where 0 ⁇ x ⁇ 2.
  • certain point defects such as holes, are introduced into silicon oxide. By introducing point defects, the conductivity of silicon oxide can be improved, thereby improving cycle performance. .
  • Silicon includes at least one of silicon microparticles, silicon nanoparticles, silicon nanowires, or silicon nanofilms.
  • the silicon alloy includes at least one of silicon-iron alloy, silicon-aluminum alloy, silicon-nickel alloy, or silicon-iron-aluminum alloy.
  • the particle size range of the flake carbon fluoride satisfies Dv50 ⁇ 10 ⁇ m, and the mass of the fluorine element in the flake carbon fluoride accounts for 0.05% to 15% of the total mass of the negative electrode material.
  • Flake carbon fluoride will generate carbon and lithium fluoride after the first charge. Carbon can increase conductivity.
  • Lithium fluoride can be used as an SEI film to reduce the reaction between silicon-based materials and electrolyte. However, when the content of fluorine is Too much, it will accelerate the consumption of lithium ions, reduce the capacity and conductivity, so the content of fluorine is limited.
  • the silicon-based material in the negative electrode material and the flaky carbon fluoride are compounded by at least one of physical mixing and mechanical spheroidal ink.
  • the flaky carbon fluoride when preparing the negative electrode material, can be mixed with the silicon-based material at a certain mass percentage, and the mixing can be performed by using a planetary ball mill, a V-shaped mixer, a three-dimensional mixer, At least one of the airflow mixer or the horizontal mixer is mixed, and then the mixed silicon-based material and the flake fluorocarbon can be further subjected to a ball milling mechanical reaction, so that at least a part of the outer surface of the silicon-based material is covered with the flake fluorocarbon Compound adhesion coating.
  • the silicon-based material may be at least one of silicon oxide, pure silicon, silicon carbon, or silicon alloy.
  • pure silicon may be microparticles, nanoparticles, nanowires, nanofilms, or nanospheres. At least one.
  • the negative pole piece includes a current collector 1 and an active material layer 2.
  • the active material layer 2 is located on the current collector 1. It should be understood that although the active material layer 2 is shown as being located on one side of the current collector 1 in FIG. 2, this is only exemplary, and the active material layer 2 may be located on both sides of the current collector 1.
  • the current collector of the negative pole piece may include at least one of copper foil, aluminum foil, nickel foil, or fluorocarbon current collector.
  • the active material layer 2 includes any one of the above-mentioned negative electrode materials.
  • the active material layer further includes a silicon-based material conductive agent and/or a binder.
  • the binder may include carboxymethyl cellulose (CMC), polyacrylic acid, polyvinylpyrrolidone, polyaniline, polyimide, polyamideimide, polysiloxane, polystyrene-butadiene At least one of rubber, epoxy resin, polyester resin, polyurethane resin, or polyfluorene.
  • the mass percentage of the binder in the active material layer is 0.5%-10%.
  • the thickness of the active material layer is 50 ⁇ m to 200 ⁇ m, and the compacted density of the negative electrode material in the active material layer under a pressure of 5 t is 0.8 g/cm 3 to 5 g/cm 3 .
  • the mass content of the carbon element in the active material layer is 0-80%.
  • the specific surface area of the negative electrode material in the active material layer ranges from 1 m 2 /g to 50 m 2 /g.
  • the conductive agent may include at least one of conductive carbon black, Ketjen black, acetylene black, carbon nanotubes, VGCF (Vapor Grown Carbon Fiber), or graphene.
  • the electrochemical device includes a positive pole piece 10, a negative pole piece 12, and a separator disposed between the positive pole piece 10 and the negative pole piece 12. 11.
  • the positive pole piece 10 may include a positive current collector and a positive active material layer coated on the positive current collector. In some embodiments, the positive active material layer may only be coated on a partial area of the positive current collector.
  • the positive active material layer may include a positive active material, a conductive agent, and a binder. Al foil can be used as the positive electrode current collector, and similarly, other positive electrode current collectors commonly used in the art can also be used.
  • the conductive agent of the positive pole piece may include at least one of conductive carbon black, sheet graphite, graphene, or carbon nanotubes.
  • the binder in the positive pole piece may include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, styrene-acrylate copolymer, styrene-butadiene copolymer, polyamide, polyacrylonitrile, Polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene At least one of them.
  • the positive active material includes, but is not limited to, at least one of lithium cobaltate, lithium nickelate, lithium manganate, lithium nickel manganate, lithium nickel cobaltate, lithium iron phosphate, lithium nickel cobalt aluminate or lithium nickel cobalt manganate,
  • the above positive active material can be doped or coated.
  • the isolation film 11 includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid.
  • polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene.
  • polyethylene and polypropylene they have a good effect on preventing short circuits, and can improve the stability of the battery through the shutdown effect.
  • the thickness of the isolation film is in the range of about 5 ⁇ m to 500 ⁇ m.
  • the surface of the isolation membrane may further include a porous layer, the porous layer is disposed on at least one surface of the isolation membrane, the porous layer includes inorganic particles and a binder, and the inorganic particles are selected from alumina (Al 2 O 3 ), Silicon oxide (SiO 2 ), magnesium oxide (MgO), titanium oxide (TiO 2 ), hafnium dioxide (HfO 2 ), tin oxide (SnO 2 ), ceria (CeO 2 ), nickel oxide (NiO), oxide Zinc (ZnO), calcium oxide (CaO), zirconium oxide (ZrO 2 ), yttrium oxide (Y 2 O 3 ), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or sulfuric acid At least one of barium.
  • alumina Al 2 O 3
  • Silicon oxide SiO 2
  • magnesium oxide MgO
  • titanium oxide TiO 2
  • hafnium dioxide HfO 2
  • the pores of the isolation membrane have a diameter in the range of about 0.01 ⁇ m to 1 ⁇ m.
  • the binder is selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyethylene pyrrole At least one of alkanone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene.
  • the porous layer on the surface of the isolation membrane can improve the heat resistance, oxidation resistance and electrolyte infiltration performance of the isolation membrane, and enhance the adhesion between the isolation membrane and the pole piece.
  • the negative pole piece 12 may be the negative pole piece as described above.
  • the electrode assembly of the electrochemical device is a wound electrode assembly or a stacked electrode assembly.
  • the electrochemical device includes a lithium ion battery, but the present disclosure is not limited thereto.
  • the electrochemical device may also include an electrolyte.
  • the electrolyte includes, but is not limited to, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), ethylene carbonate (EC), propylene carbonate (PC), At least two of propyl propionate (PP).
  • the electrolyte may additionally include at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), or dinitrile compound as an additive to the electrolyte.
  • the electrolyte further includes a lithium salt.
  • the positive pole piece, the separator film, and the negative pole piece are sequentially wound or stacked to form an electrode piece, and then packed into, for example, an aluminum plastic film for packaging, and injection electrolysis Lithium-ion battery is made by liquid, formed and packaged. Then, perform performance test and cycle test on the prepared lithium-ion battery.
  • the embodiments of the present disclosure also provide an electronic device including the above-mentioned electrochemical device.
  • the electronic device of the present application is not particularly limited, and it can be used in any electronic device known in the prior art.
  • electronic devices may include, but are not limited to, notebook computers, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, headsets, Video recorders, LCD TVs, portable cleaners, portable CD players, mini discs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, assisted bicycles, bicycles, Lighting equipment, toys, game consoles, clocks, power tools, flashlights, cameras, large household storage batteries and lithium-ion capacitors, etc.
  • Anode material preparation SiO x (0 ⁇ x ⁇ 2, Dv50: 6 ⁇ m, specific surface area: 2m 2 /g) and flake graphite fluoride (diameter-thickness ratio: 5, Dv50: 4.5 ⁇ m) according to the mass of 95:5 After mixing, it is placed in a planetary ball mill for further surface adhesion treatment, and the particle size ratio of flake graphite to SiO x is 0.75 (that is, the ratio of Dv50 of flake graphite fluoride to Dv50 of SiO x is 0.75). The sample after the ball milling treatment was used as the negative electrode material.
  • Negative pole piece preparation The negative electrode material, conductive agent conductive acetylene black, and binder polyacrylic resin (PAA) are fully stirred and mixed in deionized water at a weight ratio of 80:10:10 to make a negative electrode slurry, and then the negative electrode The slurry is evenly coated on the front and back sides of the negative electrode current collector copper foil, and then dried at 85°C to form the negative electrode active material layer, and then cold press, slitting, cutting, and welding the negative electrode tabs to obtain the negative electrode. piece.
  • PAA binder polyacrylic resin
  • positive electrode material lithium cobalt oxide (molecular formula is LiCoO 2 ), conductive agent (acetylene black), binder (polyvinylidene fluoride, PVDF) in N-form at a mass ratio of 96:2:2 Stir and mix the base pyrrolidone thoroughly to make a positive electrode slurry, and then evenly coat the obtained positive electrode slurry on the positive and negative sides of the positive electrode current collector aluminum foil, and then dry at 85°C and undergo cold pressing, slitting, and cutting. , Weld the positive pole lug to obtain the positive pole piece.
  • LiCoO 2 LiCoO 2
  • conductive agent acetylene black
  • binder polyvinylidene fluoride, PVDF
  • the solution prepared by mass ratio 8:92 is used as the electrolyte of the lithium ion battery.
  • the isolation membrane adopts a ceramic-coated polyethylene (PE) material isolation membrane.
  • PE polyethylene
  • the positive pole piece, the isolation film, and the negative pole piece are stacked in order to obtain an electrode assembly, and the isolation film is placed between the positive and negative electrodes to play a role of isolation.
  • the electrode assembly is placed in a packaging case, electrolyte is injected and packaged, and the final lithium-ion battery is formed after chemical formation.
  • Examples 2-7 and Comparative Examples 1-2 the methods for preparing the negative pole piece, the positive pole piece and the battery are the same as those of Example 1, and the methods of Examples 2-7 and Comparative Examples 1-2 are the same as those of Example 1. The only difference lies in the preparation of the negative electrode material.
  • Example 2 The difference between Example 2 and Example 1 is that the mass of the flake fluorinated graphite in Example 2 accounts for 10% of the total mass of SiO x and the flake fluorinated graphite.
  • Example 3 The difference between Example 3 and Example 1 lies in that the mass of flake fluorinated graphite in Example 3 accounts for 15% of the total mass of SiO x and flake fluorinated graphite.
  • Example 4 The difference between Example 4 and Example 1 is that the mass of flake fluorinated graphite in Example 4 accounts for 20% of the total mass of SiO x and flake fluorinated graphite.
  • Example 5 The difference between Example 5 and Example 1 is that the mass of flake fluorinated graphite in Example 5 accounts for 10% of the total mass of SiO x and flake fluorinated graphite, and the diameter of the flake fluorinated graphite in Example 5 The thickness ratio is 2.
  • Example 6 The difference between Example 6 and Example 1 is that the mass of flake fluorinated graphite in Example 6 accounts for 10% of the total mass of SiO x and flake fluorinated graphite, and the Dv50 of flake fluorinated graphite in Example 6 is The ratio of Dv50 of SiO x is 1.
  • Example 7 The difference between Example 7 and Example 1 is that the mass of flake fluorinated graphite in Example 7 accounts for 10% of the total mass of SiO x and flake fluorinated graphite, and the Dv50 of flake fluorinated graphite in Example 7 is The ratio of Dv50 of SiO x is 2.
  • Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that in Comparative Example 1, SiO x (0 ⁇ x ⁇ 2, Dv50: 6 ⁇ m, specific surface area: 2 m 2 /g) is directly used as a negative electrode material without any treatment.
  • Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that: in Comparative Example 2, non-flaky fluorinated graphite with a diameter-to-thickness ratio of 1 is used, and in Comparative Example 2, the mass of non-flaky fluorinated graphite accounts for SiO x and non-flaky fluorine. 10% of the total mass of graphite.
  • the powder compaction density meter is used to put a specific weight of powder in the standard module, and the compression height of the powder in the standard module is measured under different pressures of MPa, so that the compression height and the cross-sectional area of the standard module can be calculated The volume of the powder under different pressures is then combined with the weight of the powder to calculate the compacted density of the powder.
  • the content of flake fluorinated graphite in Table 1 is the ratio of the mass of flake fluorinated graphite in the negative electrode material to the total mass of flake fluorinated graphite and SiO x , and the diameter-to-thickness ratio is the diameter and thickness of the flake fluorinated graphite in the negative electrode material.
  • Ratio, the Dv50 ratio is the ratio of the Dv50 of the flake fluorinated graphite to the Dv50 of SiO x
  • the volume energy density the compact density of the negative electrode material x the specific capacity of the negative electrode material.
  • Comparative Example 1 Comparative Example 1, when only silicon-based materials are used as the negative electrode material without adding flake graphite fluoride, the compacted density of the negative electrode material is only 1.35g/cc and the 200-week cycle capacity retention rate is only 88.6%.
  • the 200-week cycle capacity retention rate in Examples 1-7 and Comparative Example 2 where graphite fluoride is added is higher than that in Comparative Example 1.
  • Retention rate that is, adding carbon fluoride to the negative electrode material containing silicon-based material can significantly increase the compaction density of the negative electrode material and the 200-week cycle capacity retention rate.
  • the discharge capacity retention rates of the batteries in Comparative Example 1 and Example 2 under different cycles of cycles were counted, and the results are shown in Figure 5. It can be seen that the discharge capacity retention rate of Example 2 under any cycle cycles Both are higher than Comparative Example 1, that is, adding flake carbon fluoride to the negative electrode material containing silicon-based material can improve the cycle performance of the negative electrode material. Therefore, in some embodiments of the present disclosure, the negative electrode material includes flake carbon fluoride. .
  • the volume energy density of Comparative Example 2 is somewhat different than that of Comparative Example 1. Based on this, in some embodiments of the present disclosure, the diameter-to-thickness ratio of the sheet-shaped carbon fluoride is greater than 2, to ensure that the volumetric energy density and cycle performance of the negative electrode material are simultaneously improved.
  • the volume energy density of Examples 1 to 4 first increases and then decreases as the content of flake fluorinated graphite increases. This is because the volume energy density is the product of the specific capacity and the compaction density.
  • the specific capacity of the negative electrode material decreases with the increase of the flake fluorinated graphite content, and the compact density of the negative electrode material increases with the increase of the flake fluorinated graphite content. Therefore, the volume energy density first increases and then decreases with the increase of the content of flake fluorinated graphite (refer to FIG. 6), and the volume energy density reaches the maximum value near 10% of the flake fluorinated graphite content.
  • the mass of the flaky carbon fluoride is controlled to account for 0.1% to 20% of the total mass of the silicon-based material and the flaky carbon fluoride, so as to ensure that the volumetric energy density and the volume energy density of the negative electrode material are simultaneously increased. Cycle performance.

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Abstract

一种负极材料、负极极片、电化学装置和电子装置，该负极材料包括硅基材料和片状碳氟化物；其中，所述片状碳氟化物的径厚比大于2。通过在含有硅基材料的负极材料中加入径厚比大于2的碳氟化物，提高了含有硅基材料的负极材料的压实密度和体积能量密度，并且改善了循环性能。

Description

负极材料、负极极片、电化学装置和电子装置 技术领域
本公开涉及电子技术领域，尤其涉及一种负极材料、负极极片、电化学装置和电子装置。
背景技术
硅基材料的理论比容量达到4200mAh/g，远高于碳材料的理论比容量(372mAh/g)，是具有应用前景的下一代电化学装置(例如，锂离子电池)的负极材料。
然而，直接采用硅基材料作为负极材料制作的负极极片的压实密度仅为1.2g/cm 3，远低于石墨类负极极片的压实密度1.8g/cm 3，也远低于硅基材料的理论真密度2.3g/cm 3，压实密度过低将导致负极材料之间存在较多的间隙，影响负极材料的体积能量密度，并造成电化学装置的体积能量密度的降低和循环性能的劣化。
发明内容
鉴于以上所述现有技术的缺点，本公开通过对包括有硅基材料的负极材料中添加特定径厚比的片状碳氟化物，从而极大地提高了负极材料的压实密度，提升了负极材料的体积能量密度，并改善了循环性能。
本公开提供一种负极材料，包括：硅基材料和片状碳氟化物；其中，所述片状碳氟化物的径厚比大于2。
在上述负极材料中，其中，所述片状碳氟化物的Dv50＝A，所述硅基材料的Dv50＝B，A/B<1。
在上述负极材料中，其中，所述片状碳氟化物的质量占所述硅基材料和所述片状碳氟化物的总质量的0.1％～20％。
在上述负极材料中，其中，所述片状碳氟化物包括氟化石墨、氟化硬碳、氟化软碳或氟化石墨烯中的至少一种。
在上述负极材料中，其中，所述硅基材料包括硅氧化物、硅、硅碳复合材料或硅合金中的至少一种。
在上述负极材料中，其中，所述硅基材料至少满足如下之一：所述硅氧化物的表面具有所述片状碳氟化物；所述硅氧化物的粒径范围满足1μm＜Dv50＜10μm；所述硅氧化物的比表面积小于10m 2/g；所述硅氧化物的通式为SiO x，其中，0＜x＜2；所述硅包括硅微米颗粒、硅纳米颗粒、硅纳米线或硅纳米薄膜中的至少一种；所述硅合金包括硅铁合金、硅铝合金、硅镍合金或硅铁铝合金中的至少一种。
在上述负极材料中，其中，所述片状碳氟化物的粒径范围满足Dv50＜10μm，所述片状碳氟化物中的氟元素的质量占所述负极材料的总质量的0.05％～15％。
本公开还提供了一种负极极片，包括：集流体；活性物质层，位于所述集流体上；其中，所述活性物质层包括上述任一负极材料。
本公开还提供了一种电化学装置，包括：正极极片；负极极片；隔离膜，设置于所述正极极片和所述负极极片之间；其中，所述负极极片为上述负极极片。
本公开还提供了一种电子装置，包括上述电化学装置。
在本公开的一些实施例中，负极材料包括硅基材料和片状碳氟化物，并且片状碳氟化物的径厚比大于2，从而提高了含有硅基材料的负极材料的压实密度和体积能量密度密度，并且改善了循环性能。
附图说明
图1是本公开实施例的一种片状氟化石墨的扫描电子显微镜图。
图2是本公开实施例中一种片状氟化石墨的剖面扫描电子显微镜图。
图3是本公开的一种负极极片的示例性图像。
图4是本公开的一种电化学装置的电极组件的示意图。
图5是本公开对比例1和实施例2中电池在不同循环周数下的放电容量保持率。
图6是本公开实施例中不同片状氟化石墨含量下的体积能量密度的示意图。
具体实施方式
下面的实施例可以使本领域技术人员更全面地理解本申请，但不以任何方式限制本申请。
硅基材料具有较高的理论容量，被广泛认为是下一代锂离子电池优选的负极材料，使用硅基材料作为负极材料可以提高锂离子电池的能量密度，但是，直接采用硅基材料作为负极材料制备的负极极片的压实密度较低且循环性能较差，较低的压实密度又导致负极材料的体积能量密度较低。
本公开一些实施例中的负极材料中包括：硅基材料和径厚比大于2的碳氟化物，相比于直接使用硅基材料作为负极材料时，能够大幅度提高体积能量密度并改善循环性能。
本公开的一些实施例中提出了一种负极材料，负极材料包括：硅基材料和片状碳氟化物；其中，片状碳氟化物的径厚比大于2。在一些实施例中，片状碳氟化物可以是如图1和图2所示的片状氟化石墨。本公开的一些实施例中，片状碳氟化物的径厚比是指片状碳氟化物投影的外接圆的直径L和片状碳氟化物的厚度H的比值L/H，可以使用扫面电子显微拍摄片状碳氟化物的剖面图来测量和计算片状碳氟化物的径厚比。在一些实施例中，由于负极材料中包括径厚比大于2的片状氟化石墨，片状氟化石墨材料容易沿片层方向滑移，此时片状碳氟化物容易起到润滑作用，从而充分填充硅基材料间的间隙，提高压实密度和体积能量密度。同时，片状碳氟化物在首次充电后会生成碳和氟化锂，碳可以增加负极材料的导电性，氟化锂可以减小硅基材料与电解液之间的副反应，从而可以改善负极材料的循环性能。
需要注意的是，片状碳氟化物的理论容量低于硅基材料的理论容量，含有硅基材料的负极材料中加入片状碳氟化物会造成负极材料的比容量降低，这不利于负极材料的体积能量密度，但加入片状碳氟化物可以提高负极材料的压实密度，压实密度的增加有利于提高负极材料的体积能量密度，因此，要提高负极材料的体积能量密度，必须使得压实密度的增加量能够抵消比容量降低量对体积能量密度的不利影响。当负极材料中的片状碳氟化物的径厚比大于2时，负极材料的压实密度的增加量能够抵消比容量降低量对体积能 量密度的不利影响，从而提高负极材料的体积能量密度，而当负极材料中片状氟化物的径厚比不大于2时，片状碳氟化物不易起到润滑的作用，无法有效填充硅基材料之间的间隙，因此不能大幅度提高负极材料的压实密度，即加入径厚比不大于2的硅氟化物后负极材料的压实密度的增加量不能抵消比容量降低量对体积能量密度的不利影响，因此当加入径厚比不大于2的片状碳氟化物时，负极材料的体积能量密度无法提高，基于此，在本公开的一些实施例中限定了片状碳氟化物的径厚比大于2以保证片状碳氟化物能够在改善循环性能的同时提高负极材料的体积能量密度。
在一些实施例中，负极材料在150Mpa压力下的粉体压实密度在1.4g/cm 3以上。如果压实密度过低，会导致硅基材料彼此之间无法有效电接触，不利于负极材料的循环性能。
在本公开的一些实施例中，片状碳氟化物的Dv50＝A，硅基材料的Dv50＝B，A/B<1。当片状碳氟化物的Dv50与硅基材料的Dv50的比率大于1时，片状碳氟化物的尺寸相比于硅基材料的间隙过大，片状碳氟化物无法有效地填充硅基材料之间的间隙，不利于提高压实密度，也就不利于提高体积能量密度，并且会造成硅基材料之间的电接触变差，从而不利于循环性能的改善，因此，在本公开的一些实施例中，控制片状碳氟化物的Dv50与硅基材料的Dv50的比率小于1。
在本公开的一些实施例中，片状碳氟化物的质量占硅基材料和片状碳氟化物的总质量的0.1％～20％。在一些实施例中，当片状碳氟化物的质量占硅基材料和片状碳氟化物总质量的比值小于0.1％时，负极材料中所包含的片状碳氟化物过少，此时片状碳氟化物无法明显发挥其作用，其对提高负极材料的压实密度、导电性和循环性能方面的作用不明显。当负极材料中的片状碳氟化物的质量占硅基材料和片状碳氟化物的总质量的比值大于20％时，负极材料中含有大量的片状碳氟化物。负极材料的体积能量密度同时受压实密度和比容量影响，含有硅基材料的负极材料中加入片状碳氟化物能够提高压实密度但会降低负极材料的比容量，当负极材料中的片状碳氟化物的质量占硅基材料和片状碳氟化物的总质量的比值大于20％时，片状碳氟化物对压实密度的提高量不足以抵消比容量降低对体积能量密度的不利影响，将造成负极材料的体积能量密度降低。
在本公开的一些实施例中，片状碳氟化物包括氟化石墨、氟化硬碳、氟化软碳或氟化石墨烯中的至少一种。
在本公开的一些实施例中，硅基材料包括硅氧化物、硅、硅碳复合材料或硅合金中的至少一种。
在本公开的一些实施例中，硅基材料至少满足如下(a)～(f)之一：
(a)硅氧化物的表面具有片状碳氟化物。在一些实施例中，硅氧化物的导电性较差，因此当满足(a)时能够提高硅氧化物的导电性以改善循环性能。
(b)硅氧化物的粒径范围满足1μm＜Dv50＜10μm。硅氧化物的粒径过小会增加电解液的消耗，也不利于循环性能；硅氧化物的粒径过大时会导致倍率性能劣化，因此在一些实施例中设置为满足(b)以控制硅氧化合物的粒径范围。
(c)硅氧化物的比表面积小于10m 2/g。在一些实施例中，硅氧化物的比表面积不小于10m 2/g时会消耗较多的电解液形成SEI(solid electrolyte interface,固体电解质界面)膜，造成首充容量损失过多，增加粘结剂的消耗，因此硅氧化物的比表面积设置为小于10m 2/g。
(d)硅氧化物的通式为SiO x，其中，0＜x＜2。在一些实施例中，由于硅氧化物中0＜x＜2，因此硅氧化物中引入了一定的点缺陷，例如空穴，通过引入点缺陷可以提高硅氧化物的导电性，从而改善循环性能。
(e)硅包括硅微米颗粒、硅纳米颗粒、硅纳米线或硅纳米薄膜中的至少一种。
(f)硅合金包括硅铁合金、硅铝合金、硅镍合金或硅铁铝合金中的至少一种。
在本公开的一些实施例中，其中，片状碳氟化物的粒径范围满足Dv50＜10μm，片状碳氟化物中的氟元素的质量占负极材料的总质量的0.05％～15％。片状碳氟化物在首次充电后会生成碳和氟化锂，其中碳可以增加导电性，氟化锂可以作为SEI膜减小硅基材料与电解液之间的反应，但当氟元素的含量过多时，会加速消耗锂离子，降低容量和导电性，因此限制氟元素的含量。
在本公开的一些实施例中，负极材料中的硅基材料与片状碳氟化物通过物理混合、机械球墨中的至少一种进行复合。在一些实施例中，在制备负极 材料时，可以将片状碳氟化物按一定的质量百分比与硅基材料进行混合，混合时可以是使用行星球磨机、V型混料机、三维混料机、气流混料机或卧式搅拌机中至少一种进行混合，然后可以进一步将混合后的硅基材料和片状碳氟化物进行球磨机械反应，使硅基材料的外表面至少一部分被片状碳氟化物附着包覆。其中硅基材料可以是硅氧化物、纯硅、硅碳或硅合金中的至少一种，在一些实施例中，纯硅可以是微米颗粒、纳米颗粒、纳米线、纳米薄膜或纳米球中的至少一种。
如图3所示，本公开的一些实施例提供了一种负极极片，负极极片包括集流体1和活性物质层2。活性物质层2位于集流体1上。应该理解，虽然图2中将活性物质层2示出为位于集流体1的一侧上，但是这仅是示例性的，活性物质层2可以位于集流体1的两侧上。在一些实施例中，负极极片的集流体可以包括铜箔、铝箔、镍箔或碳氟集流体中的至少一种。在一些实施例中，活性物质层2包括上述任一种负极材料。
在一些实施例中，活性物质层还包括硅基材料导电剂和/或粘结剂。在一些实施例中，粘结剂可以包括羧甲基纤维素(CMC)、聚丙烯酸、聚乙烯基吡咯烷酮、聚苯胺、聚酰亚胺、聚酰胺酰亚胺、聚硅氧烷、聚丁苯橡胶、环氧树脂、聚酯树脂、聚氨酯树脂或聚芴中的至少一种。在一些实施例中，活性物质层中的粘结剂的质量百分比为0.5％～10％。在一些实施例中，活性物质层的厚度为50μm～200μm，活性物质层中的负极材料在5t的压力下的压实密度为0.8g/cm 3～5g/cm 3。在一些实施例中，活性物质层中的碳元素的质量含量为0～80％。在一些实施例中，活性物质层中的负极材料的比表面积为1m 2/g～50m 2/g。在一些实施例中，导电剂可以包括导电炭黑、科琴黑、乙炔黑、碳纳米管、VGCF(Vapor Grown Carbon Fiber，气相成长碳纤维)或石墨烯中的至少一种。
如图4所示，本公开的一些实施例提供了一种电化学装置，电化学装置包括正极极片10、负极极片12以及设置于正极极片10和负极极片12之间的隔离膜11。正极极片10可以包括正极集流体和涂覆在正极集流体上的正极活性物质层。在一些实施例中，正极活性物质层可以仅涂覆在正极集流体的部分区域上。正极活性物质层可以包括正极活性物质、导电剂和粘结剂。正极集流体可以采用Al箔，同样，也可以采用本领域常用的其他 正极集流体。正极极片的导电剂可以包括导电炭黑、片层石墨、石墨烯或碳纳米管中的至少一种。正极极片中的粘结剂可以包括聚偏氟乙烯、偏氟乙烯-六氟丙烯的共聚物、苯乙烯-丙烯酸酯共聚物、苯乙烯-丁二烯共聚物、聚酰胺、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯酸盐、羧甲基纤维素纳、聚醋酸乙烯酯、聚乙烯呲咯烷酮、聚乙烯醚、聚甲基丙烯酸甲酯、聚四氟乙烯或聚六氟丙烯中的至少一种。正极活性物质包括但不限于钴酸锂、镍酸锂、锰酸锂、镍锰酸锂、镍钴酸锂、磷酸铁锂、镍钴铝酸锂或镍钴锰酸锂中的至少一种，以上正极活性物质可以经过掺杂或包覆处理。
在一些实施例中，隔离膜11包括聚乙烯、聚丙烯、聚偏氟乙烯、聚对苯二甲酸乙二醇酯、聚酰亚胺或芳纶中的至少一种。例如，聚乙烯包括选自高密度聚乙烯、低密度聚乙烯或超高分子量聚乙烯中的至少一种。尤其是聚乙烯和聚丙烯，它们对防止短路具有良好的作用，并可以通过关断效应改善电池的稳定性。在一些实施例中，隔离膜的厚度在约5μm～500μm的范围内。
在一些实施例中，隔离膜表面还可包括多孔层，多孔层设置在隔离膜的至少一个表面上，多孔层包括无机颗粒和粘结剂，无机颗粒选自氧化铝(Al 2O 3)、氧化硅(SiO 2)、氧化镁(MgO)、氧化钛(TiO 2)、二氧化铪(HfO 2)、氧化锡(SnO 2)、二氧化铈(CeO 2)、氧化镍(NiO)、氧化锌(ZnO)、氧化钙(CaO)、氧化锆(ZrO 2)、氧化钇(Y 2O 3)、碳化硅(SiC)、勃姆石、氢氧化铝、氢氧化镁、氢氧化钙或硫酸钡中的至少一种。在一些实施例中，隔离膜的孔具有在约0.01μm～1μm的范围的直径。粘结剂选自聚偏氟乙烯、偏氟乙烯-六氟丙烯的共聚物、聚酰胺、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯酸盐、羧甲基纤维素纳、聚乙烯呲咯烷酮、聚乙烯醚、聚甲基丙烯酸甲酯、聚四氟乙烯或聚六氟丙烯中的至少一种。隔离膜表面的多孔层可以提升隔离膜的耐热性能、抗氧化性能和电解质浸润性能，增强隔离膜与极片之间的粘接性。
在一些实施例中，负极极片12可以为如上所述的负极极片。
在本公开的一些实施例中，电化学装置的电极组件为卷绕式电极组件或堆叠式电极组件。
在一些实施例中，电化学装置包括锂离子电池，但是本公开不限于此。在一些实施例中，电化学装置还可以包括电解液。在一些实施例中，电解液包括但不限于碳酸二甲酯(DMC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸乙烯酯(EC)、碳酸丙烯酯(PC)、丙酸丙酯(PP)中的至少两种。此外，电解液还可以额外地包括作为电解液添加剂的碳酸亚乙烯酯(VC)、氟代碳酸乙烯酯(FEC)或二腈化合物中的至少一种。在一些实施例中，电解液还包括锂盐。
在本公开的一些实施例中，以锂离子电池为例，将正极极片、隔离膜、负极极片按顺序卷绕或堆叠成电极件，之后装入例如铝塑膜中进行封装，注入电解液，化成、封装，即制成锂离子电池。然后，对制备的锂离子电池进行性能测试及循环测试。
本领域的技术人员将理解，以上描述的电化学装置(例如，锂离子电池)的制备方法仅是实施例。在不背离本申请公开的内容的基础上，可以采用本领域常用的其他方法。
本公开的实施例还提供了包括上述电化学装置的电子装置。本申请的电子装置没有特别限定，其可以是用于现有技术中已知的任何电子装置。在一些实施例中，电子装置可以包括，但不限于，笔记本电脑、笔输入型计算机、移动电脑、电子书播放器、便携式电话、便携式传真机、便携式复印机、便携式打印机、头戴式立体声耳机、录像机、液晶电视、手提式清洁器、便携CD机、迷你光盘、收发机、电子记事本、计算器、存储卡、便携式录音机、收音机、备用电源、电机、汽车、摩托车、助力自行车、自行车、照明器具、玩具、游戏机、钟表、电动工具、闪光灯、照相机、家庭用大型蓄电池和锂离子电容器等。
下面列举了一些具体实施例和对比例以更好地对本公开进行说明，其中，采用锂离子电池作为示例。
实施例1
负极材料制备：将SiO x(0<x<2,Dv50:6μm,比表面积:2m 2/g)与片状氟化石墨(径厚比:5，Dv50:4.5μm)按95:5的质量比混合后置于行星式球磨机中进一步进行表面附着处理，片状石墨与SiO x的粒径比为0.75(即片状氟化石 墨的Dv50与SiO x的Dv50比率为0.75)。将上述球磨处理后的样品作为负极材料。
负极极片制备：将负极材料、导电剂导乙炔黑、粘结剂聚丙烯酸类树脂(PAA)按照重量比80：10：10在去离子水中充分搅拌混合均匀制成负极浆料，之后将负极浆料均匀涂覆在负极集流体铜箔的正反两面上，然后在85℃下烘干，形成负极活性材料层，然后进行冷压、分条、裁片、焊接负极极耳，得到负极极片。
正极极片制备：将正极材料钴酸锂(分子式为LiCoO 2)、导电剂(导乙炔黑)、粘结剂(聚偏二氟乙烯，PVDF)按质量比96：2：2在N-甲基吡咯烷酮中充分搅拌混合均匀制成正极浆料，然后将所得正极浆料均匀涂布在正极集流体铝箔的正反两面上，然后在85℃下烘干并经过冷压、分条、裁片、焊接正极极耳，得到正极极片。
电池制备：将锂盐LiPF 6与非水有机溶剂(碳酸乙烯酯(EC)：碳酸二乙酯(DEC)：碳酸亚丙酯(PC)：丙酸丙酯(PP)：碳酸亚乙烯酯(VC)的质量比＝20:30:20:28:2)按质量比8：92配制而成的溶液作为锂离子电池的电解液。隔离膜采用陶瓷涂覆的聚乙烯(PE)材料隔离膜。将正极极片、隔离膜、负极极片按顺序叠好得到电极组件，使隔离膜处于正负极中间起到隔离的作用。将电极组件置于包装壳中，注入电解液并封装，进行化成之后制成最终的锂离子电池。
在实施例2～7以及对比例1～2中，负极极片制备、正极极片制备和电池制备的方法与实施例1相同，实施例2～7以及对比例1～2与实施例1的区别仅在于负极材料的制备不同。
实施例2与实施例1的区别在于：实施例2中片状氟化石墨的质量占SiO x和片状氟化石墨的总质量的10％。
实施例3与实施例1的区别在于：实施例3中片状氟化石墨的质量占SiO x和片状氟化石墨的总质量的15％。
实施例4与实施例1的区别在于：实施例4中片状氟化石墨的质量占SiO x和片状氟化石墨的总质量的20％。
实施例5与实施例1的区别在于：实施例5中片状氟化石墨的质量占SiO x和片状氟化石墨的总质量的10％，且实施例5中片状氟化石墨的径厚比为2。
实施例6与实施例1的区别在于：实施例6中片状氟化石墨的质量占SiO x和片状氟化石墨的总质量的10％，实施例6中片状氟化石墨的Dv50与SiO x的Dv50的比率为1。
实施例7与实施例1的区别在于：实施例7中片状氟化石墨的质量占SiO x和片状氟化石墨的总质量的10％，实施例7中片状氟化石墨的Dv50与SiO x的Dv50的比率为2。
对比例1与实施例1的区别在于：对比例1中将SiO x(0<x<2,Dv50:6μm,比表面积:2m 2/g)不做任何处理，直接作为负极材料。
对比例2与实施例1的区别在于：对比例2中采用径厚比为1的非片状氟化石墨，且对比例2中非片状氟化石墨的质量占SiO x和非片状氟化石墨的总质量的10％。
实施例和对比例的各项性能参数的测定方法如下。
循环性能测试方法：
以0.5C倍率充电至4.45V，改为4.45V恒压充电直至电流降到0.025C，静置5分钟后，用0.5C倍率放电至3.0V，即完成一周循环，记录放电容量，作为锂离子电池的容量。重复200周循环，记录放电容量，作为锂离子电池的剩余容量。容量保持率＝剩余容量/初始容量*100％。
粉体压实密度测试：
采用粉体压实密度仪，将特定重量的粉体至于标准模块中，在不同兆帕的压力下测得标准模块内粉体的压缩高度，从而由压缩高度以及标准模块的截面积可以计算得不同压力下的粉体体积，进而结合粉体的重量计算得粉体的压实密度。
粒度测试：
50ml洁净烧杯中加入0.02g粉末样品，加入20ml去离子水，再滴加几滴1％的表面活性剂，使粉末完全分散于水中，120W超声清洗机中超声5分钟，利用MasterSizer 2000测试粒度分布。
比容量测试方法：
以0.05C的倍率恒流放电至5mV，静止5分钟后，改为50uA的电流继续放电至5mV，再静止5分钟后，改用10uA的电流继续放电至5mV；再以0.05C的倍率恒流充电至2V，静止30分钟后即完成充放电比容量测试。
对实施例1～7以及对比例1～2的测试结果进行数据统计，统计结果见表1。
表1
Figure PCTCN2020089841-appb-000001
表1中的片状氟化石墨含量为负极材料中片状氟化石墨的质量占片状氟化石墨和SiO x总质量的比率，径厚比为负极材料中片状氟化石墨的径厚比，Dv50比率为片状氟化石墨的Dv50与SiO x的Dv50的比值，体积能量密度＝负极材料的压实密度×负极材料的比容量。
对比实施例1～7和对比例1～2的测试结果可以看出，对比例1中只采用硅基材料作为负极材料，而不加入片状氟化石墨时，负极材料的压实密度仅为1.35g/cc且200周循环容量保持率仅为88.6％，加入片状氟化石墨的实施例1～7和对比例2中的200周循环容量保持率均高于对比例1中的循环容量 保持率，即在含有硅基材料的负极材料中加入碳氟化物可以明显提高负极材料的压实密度以及200周循环容量保持率。将对比例1和实施例2中的电池在不同循环周数下的放电容量保持率进行统计，结果如图5所示，可以看出，在任何循环周数下实施例2的放电容量保持率均高于对比例1，即在含有硅基材料的负极材料中加入片状碳氟化物能够提高负极材料的循环性能，因此在本公开的一些实施例中，负极材料中包括片状碳氟化物。
对比实施例2、5和对比例2的测试结果可以看出，负极材料的压实密度、体积能量密度和200周循环容量保持率随片状氟化石墨的径厚比增加而增加，降低片状氟化石墨的径厚比会导致负极材料的压实密度的降低，从而导致体积能量密度的降低。这是因为当片状氟化石墨的径厚比增加时，片状氟化石墨片层间较弱的范德华力促使片状氟化石墨更容易沿着片层方向进行滑移，即片状氟化石墨宏观的片层结构形貌更容易起到润滑的作用，从而充分填充硅基材料之间的间隙，提升了负极材料的压实密度，增加了硅基材料之间的电接触，从而提高了体积能量密度和循环性能。而当片状氟化石墨的径厚比减小时，片状氟化石墨难以充分填充硅基材料之间的间隙，导致压实密度的增加量减小，硅基材料之间难以实现电接触，造成负极材料的导电网络变差，进而导致循环性能劣化。
需要注意的是，对比例2中的体积能量密度甚至已经低于对比例1中的体积能量密度，这是片状氟化石墨的比容量小于SiO x的比容量，向SiO x中加入片状氟化石墨会将降低负极材料的比容量，这不利于提高体积能量密度，当片状氟化石墨的径厚比小于2时(以对比例2为例)，加入片状碳氟化物后负极材料的压实密度的增加量较小，负极材料压实密度的增加量不足以抵消比容量降低对体积能量密度的不利影响，因此对比例2的体积能量密度相比于对比例1反而有所降低，基于此，在本公开的一些实施例中，片状碳氟化物的径厚比大于2，以保证同时提高负极材料的体积能量密度密度和循环性能。
对比实施例1～4的负极材料的比容量测试结果可以看出，负极材料的比容量随着片状氟化石墨含量的增加而降低，这是因为片状氟化石墨的比容量小于硅基材料的比容量，随着负极材料中片状氟化石墨的含量的增加，负极 材料整体的比容量将会降低。对比实施例1～4的压实密度的测试结果可以看出，负极材料的压实密度随着片状氟化石墨含量的增加而增加，这是因为负极材料中片状氟化石墨含量增加后更加充分的填充了硅基材料之间的间隙。对比实施例1～4的体积能量密度的测试结果可以看出，实施例1～4中体积能量密度随片状氟化石墨含量的增加先增加后降低。这是因为体积能量密度为比容量和压实密度的乘积，负极材料的比容量随片状氟化石墨含量的增加而降低，负极材料的压实密度随片状氟化石墨含量的增加而升高，所以体积能量密度随片状氟化石墨的含量的增加先增加后降低(参考附图6)，体积能量密度在片状氟化石墨含量为10％的附近达到最大值。
对比实施例1～4的200周循环容量保持率的测试结果可以看出，实施例1～4中200周循环容量保持率相比于对比例1明显改善，这是由于只有硅基材料的负极材料的导电性较差且压实密度较低，硅基材料之间的接触不佳造成导电性的进一步恶化，片状氟化石墨的引入增加了负极材料的压实密度，从而增加了硅基材料之间的电接触，并且片状氟化石墨在首次充电后转化为碳和氟化锂，其中碳可以进一步增加导电性，氟化锂作为SEI膜可以减少硅基材料与电解液之间副反应的发生，片状氟化石墨的引入极大的改善了硅基负极的循环性能。
基于此，在本公开的一些实施例中控制片状碳氟化物的质量占硅基材料和片状碳氟化物的总质量的0.1％～20％，从而保证同时提高负极材料的体积能量密度和循环性能。
对比实施例2、6和7的测试结果可以看出，当增加片状氟化石墨与SiO x的Dv50比值时会导致压实密度的降低，从而导致体积能量密度的降低。这是由于当片状氟化石墨的粒径大于SiO x时，片状氟化石墨只能起到滑移的作用，硅基材料间较小的空隙就不能得到有效的填充，从而降低了负极材料的压实密度，劣化了体积能量密度，负极材料的导电性也会受到影响，从而不利于循环性能，因此在本公开的一些实施例中，片状碳氟化物的Dv50与硅基材料的Dv50的比率小于1。
以上描述仅为本公开的较佳实施例以及对所运用技术原理的说明。本领域技术人员应当理解，本公开中所涉及的公开范围，并不限于上述技术 特征的特定组合而成的技术方案，同时也应涵盖在不脱离上述公开构思的情况下，由上述技术特征或其等同特征进行任意组合而形成的其它技术方案。例如上述特征与本公开中公开的具有类似功能的技术特征进行互相替换而形成的技术方案。

Claims (10)

  1. 一种负极材料，包括：
    硅基材料和片状碳氟化物；
    其中，所述片状碳氟化物的径厚比大于2。
  2. 根据权利要求1所述的负极材料，其中，所述片状碳氟化物的Dv50＝A，所述硅基材料的Dv50＝B，A/B<1。
  3. 根据权利要求1所述的负极材料，其中，所述片状碳氟化物的质量占所述硅基材料和所述片状碳氟化物的总质量的0.1％～20％。
  4. 根据权利要求1所述的负极材料，其中，所述片状碳氟化物包括氟化石墨、氟化硬碳、氟化软碳或氟化石墨烯中的至少一种。
  5. 根据权利要求1所述的负极材料，其中，所述硅基材料包括硅氧化物、硅、硅碳复合材料或硅合金中的至少一种。
  6. 根据权利要求5所述的负极材料，其中，所述硅基材料至少满足如下之一：
    所述硅氧化物的表面具有所述片状碳氟化物；
    所述硅氧化物的粒径范围满足1μm＜Dv50＜10μm；
    所述硅氧化物的比表面积小于10m 2/g；
    所述硅氧化物的通式为SiO x，其中，0＜x＜2；
    所述硅包括硅微米颗粒、硅纳米颗粒、硅纳米线或硅纳米薄膜中的至少一种；
    所述硅合金包括硅铁合金、硅铝合金、硅镍合金或硅铁铝合金中的至少一种。
  7. 根据权利要求1所述的负极材料，其中，所述片状碳氟化物的粒径范围满足Dv50＜10μm，所述片状碳氟化物中的氟元素的质量占所述负极材料的总质量的0.05％～15％。
  8. 一种负极极片，包括：
    集流体；
    活性物质层，位于所述集流体上；
    其中，所述活性物质层包括根据权利要求1至7中任一项所述的负极材料。
  9. 一种电化学装置，包括：
    正极极片；
    负极极片；
    隔离膜，设置于所述正极极片和所述负极极片之间；
    其中，所述负极极片为根据权利要求8所述的负极极片。
  10. 一种电子装置，包括根据权利要求9所述的电化学装置。
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