WO2021189338A1 - 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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WO2021189338A1
WO2021189338A1 PCT/CN2020/081305 CN2020081305W WO2021189338A1 WO 2021189338 A1 WO2021189338 A1 WO 2021189338A1 CN 2020081305 W CN2020081305 W CN 2020081305W WO 2021189338 A1 WO2021189338 A1 WO 2021189338A1
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silicon
negative electrode
carbon
particles
based material
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PCT/CN2020/081305
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English (en)
French (fr)
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廖群超
崔航
谢远森
王超
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宁德新能源科技有限公司
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Priority to JP2021539889A priority Critical patent/JP2022530297A/ja
Priority to EP20927208.7A priority patent/EP3965189A4/en
Priority to PCT/CN2020/081305 priority patent/WO2021189338A1/zh
Priority to CN202080006619.7A priority patent/CN113196524B/zh
Publication of WO2021189338A1 publication Critical patent/WO2021189338A1/zh
Priority to US17/690,252 priority patent/US20220199996A1/en

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    • H—ELECTRICITY
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    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
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    • 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
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    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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    • 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
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    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1393—Processes of manufacture of electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
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    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
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    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
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    • 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
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    • 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
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    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/661—Metal or alloys, e.g. alloy coatings
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    • H01M4/667—Composites in the form of layers, e.g. coatings
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    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
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    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present disclosure relates to the field of electronic technology, and in particular to a negative electrode material, a negative pole piece, an electrochemical device and an electronic device.
  • Silicon-based materials have a theoretical specific capacity as high as 4200 mAh/g, which is a promising negative electrode material for next-generation electrochemical devices (for example, lithium ion batteries).
  • silicon-based materials have a volume expansion of about 300% during charging and discharging, and have poor electrical conductivity. For this reason, the industry usually uses silicon-based materials and graphite materials to be mixed in a certain proportion, but despite this, it is still difficult to meet people's increasing demand for capacity density and dynamics.
  • the present disclosure significantly improves the rate performance of the electrochemical device by defining the relationship between the surface characteristics, particle distribution and morphology of the silicon-based material and the carbon material, while improving the cycle performance and Deformation rate.
  • the present disclosure provides a negative electrode material, comprising: a silicon-based material and a carbon material, wherein the Raman spectrum of the carbon material displacement range of 1255 ⁇ 1355cm -1 and a peak 1575 ⁇ 1600cm -1, respectively D and G peaks
  • the peaks in the Raman spectrum of the silicon-based material with shifts ranging from 1255 to 1355 cm -1 and 1575 to 1600 cm -1 are D peak and G peak, respectively, and the scattering peak intensity ratio D/G of the carbon material is A
  • the scattering peak intensity ratio D/G of the silicon-based material is B, where 0.15 ⁇ A ⁇ 0.9, 0.8 ⁇ B ⁇ 2.0, and 0.2 ⁇ BA ⁇ 1.8.
  • the value of Dn50/Dv50 of the carbon material is E
  • the value of Dn50/Dv50 of the silicon-based material is F
  • F>E the value of Dn50/Dv50 of the silicon-based material
  • the value E of Dn50/Dv50 of the carbon material is 0.1 to 0.65; and/or the value F of Dn50/Dv50 of the silicon-based material is 0.3 to 0.85.
  • the average sphericity of the carbon material is H
  • the average sphericity of the silicon-based material is I
  • the silicon-based material includes SiO x C y M z , where 0 ⁇ x ⁇ 2, 0 ⁇ y ⁇ 1, 0 ⁇ z ⁇ 0.5, and M represents lithium, magnesium, titanium or aluminum.
  • the carbon material includes graphite.
  • 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; Pole piece.
  • the present disclosure also provides an electronic device, including the electrochemical device described above.
  • the present disclosure significantly improves the cycle performance, deformation rate, and rate performance of the electrochemical device by selecting the silicon-based material and the carbon material in the negative electrode material with appropriate Raman spectrum intensity.
  • Fig. 1 is a schematic diagram of a negative pole piece of the present disclosure.
  • FIG. 2 is a schematic diagram of the electrode assembly of the electrochemical device of the present disclosure.
  • FIG. 3 is a Raman spectrum diagram of the silicon-based material SiO x in Example 3 of the present disclosure.
  • FIG. 4 is a Raman spectrum diagram of carbon material graphite in Example 3 of the present disclosure.
  • FIG. 5 is a discharge rate diagram of Example 3 and Comparative Example 1 of the present disclosure.
  • Silicon-based materials for example, silicon-oxygen materials
  • the silicon-based materials can significantly increase the energy density of the electrode assembly, but the silicon-based materials have poor electrical conductivity and have a larger volume during the process of deintercalating lithium Expansion and contraction, compared with pure graphite negative electrode, need to add more poorly conductive binder to maintain the structure of the negative pole piece.
  • silicon-based materials are usually mixed with a certain proportion of carbon materials (for example, graphite) as negative electrode materials.
  • the mixed negative electrode material still has the problems of poor conductivity and large volume expansion, which hinders the further large-scale application of silicon-based materials.
  • the performance of the mixed negative electrode material is determined by the silicon-based material and the carbon material. Simply improving the silicon-based material cannot maximize the electrical performance of the negative electrode. However, at present, the kinetics and cycle performance of the negative electrode are mainly improved by improving the interface stability and conductivity of the silicon-based material, and the reasonable combination of surface coating, morphology and particle size between the silicon-based material and the carbon material is ignored.
  • the present disclosure starts from a reasonable match between silicon-based materials and carbon materials (for example, graphite), defines the relationship between the surface structure characteristics, particle distribution, and morphology of silicon-based material particles and carbon material particles, and significantly improves the cycle of electrochemical devices Performance, deformation rate and rate performance.
  • silicon-based materials and carbon materials for example, graphite
  • anode material which includes a silicon-based material and a carbon material.
  • the silicon-based material is a silica particulate material.
  • the silicon-based material includes SiO x C y M z , where 0 ⁇ x ⁇ 2, 0 ⁇ y ⁇ 1, 0 ⁇ z ⁇ 0.5, and M represents at least one of lithium, magnesium, titanium, or aluminum .
  • the silicon-based material includes at least one of silicon, silicon oxide (SiO x , 0.5 ⁇ x ⁇ 1.6), silicon carbon, and silicon alloy.
  • the carbon material in the negative electrode material includes graphite and/or graphene.
  • the peaks in the Raman spectrum of the carbon material with shifts ranging from 1255 to 1355 cm -1 and 1575 to 1600 cm -1 are D peak and G peak, respectively, and the scattering peak intensity ratio D/G of the carbon material is A
  • the peaks with a shift range of 1255 to 1355 cm -1 and 1575 to 1600 cm -1 are the D peak and the G peak, respectively, and the scattering peak intensity ratio D/G of the silicon-based material is B.
  • the Raman scattering peak intensity ratio of the carbon material and the silicon-based material satisfies 0.2 ⁇ BA ⁇ 1.8, and 0.15 ⁇ A ⁇ 0.9, 0.8 ⁇ B ⁇ 2.0.
  • the cycle performance and kinetics of the negative electrode material reach the best level.
  • the Raman scattering peak intensity difference between silicon-based material particles and carbon material particles is less than 0.2, the Raman scattering peak intensity ratio D/G of the silicon-based material is too low or the Raman scattering peak intensity ratio D/G of the carbon material is too low The problem is too high.
  • the proportion of SP2 hybrid structure in the coating layer on the surface of the silicon-based particles increases, which hinders the diffusion of lithium ions, increases the polarization, causes the precipitation of metallic lithium, and creates safety hazards.
  • the graphite particles are wettable with the electrolyte.
  • the negative electrode material formed by the composite of such graphite and silicon-based materials has poor dynamics, the polarization of the electrode assembly increases during the cycle, and the cycle performance also deteriorates.
  • the Raman scattering peak intensity difference between silicon-based materials and carbon materials is greater than 1.8, the Raman scattering peak intensity ratio of silicon-based materials is too high or the Raman scattering peak intensity ratio of carbon materials is too low D/G.
  • the disorder of the carbon coating layer on the surface of the silicon-based particles increases, reducing its electronic conductivity; while the surface of the carbon material is covered with an amorphous carbon coating layer that is too thick and contains a lot of defects, resulting in The specific capacity of the negative electrode material is reduced, which affects the energy density and first-time efficiency of the electrochemical device.
  • the negative electrode material composed of such graphite and silicon-based materials has poor kinetic and cycle performance, and the energy density will also be reduced.
  • the surface of the particles of the silicon-based material contains a carbon-containing coating layer, and the intensity ratio of the Raman scattering peak of the carbon-containing coating layer I1330/I1580 is 0.8-2.0.
  • the thickness of the carbon-containing coating layer is 0.5 nm to 50 nm.
  • the mass of the carbon-containing coating layer of the silicon-based material accounts for 0.1% to 10% of the total mass of the silicon-based material and the carbon-containing coating layer.
  • the average particle size of the silicon-based particles is 0.1 ⁇ m to 30 ⁇ m. If the average particle size of the silicon-based material is too small, the silicon-based material is prone to agglomeration and consumes more electrolyte to form the SEI film due to the large specific surface area. If the average particle size of the silicon-based material is too large, it is not conducive to suppressing the volume expansion of the silicon-based material, and it is also easy to cause the deterioration of the conductivity of the active material layer. In addition, if the average particle size of the silicon-based material is too large, the strength of the negative pole piece will decrease. In some embodiments, the specific surface area of the silicon-based material particles is 1.0 m 2 /g to 15 m 2 /g.
  • the thickness of the amorphous carbon coating layer is 5 nm to 500 nm.
  • the intensity ratio I1330/I1580 of the Raman scattering peak of the carbon material (for example, graphite) particles is 0.2 ⁇ 0.9.
  • the particle size of the carbon material (for example, graphite) particles ranges from 0.01 ⁇ m to 80 ⁇ m, and the specific surface area is less than 30 m 2 /g.
  • the carbon material (eg, graphite) particles may be secondary particles or a mixture of secondary particles and primary particles, where the secondary particles account for more than 70%.
  • the OI value of the carbon material (for example, graphite) particles is the ratio of the (004) peak to the (110) peak intensity in the XRD diffraction peak of the carbon material, and the OI value is 1-30.
  • the value of Dn50/Dv50 of the carbon material is E
  • the value of Dn50/Dv50 of the silicon-based material is F
  • F>E where Dn50 is the particle number reference distribution obtained by the laser scattering particle size analyzer. Cumulative 50% of the particle diameter, Dv50 is the cumulative 50% particle diameter of the volume reference distribution obtained by the laser scattering particle size analyzer. Dn50/Dv50 characterizes the degree of concentration of particle distribution. The closer the value of Dn50/Dv50 is to 1, the more concentrated the particle size distribution.
  • the cycle performance and rate performance of the electrochemical device are better. This is because the lithium-intercalation expansion of silicon-based materials is much larger than that of carbon materials (for example, graphite). In order to reduce the stress generated during expansion, the average particle size of silicon-based materials is smaller than that of carbon material particles.
  • the active material of the negative electrode includes In the case of silicon-based materials and carbon materials, the distribution of silicon-based material particles is more concentrated than that of carbon material particles, which is beneficial to disperse in the gaps where the carbon material particles are stacked, and minimizes the impact of the expansion of the silicon-based material on the overall expansion of the negative electrode.
  • the value F of Dn50/Dv50 of the silicon-based material is 0.3-0.85.
  • SEI solid electrolyte interface membranes
  • the excessively large particles of silicon-based materials not only increase the stress generated during the expansion process of lithium insertion, but also cause the particles of silicon-based materials to rupture, expose fresh interfaces and react with the electrolyte, consume reversible lithium, and deteriorate the cycle performance of electrochemical devices;
  • the particles increase the diffusion path of lithium ions, increase the concentration polarization, and affect the rate performance of the electrochemical device.
  • the value E of Dn50/Dv50 of the carbon material is 0.1 to 0.65.
  • the value of Dn50/Dv50 of the carbon material is less than 0.1, there are too many fine particles and large particles in the carbon material; when there are too many fine particles, the specific surface area of the carbon material is too large, which reduces the first efficiency of the electrochemical device; when the large particles are too large For a long time, the transmission distance of lithium ions is increased, which deteriorates the expansion and rate performance of the electrochemical device.
  • the average sphericity of the carbon material is H
  • the average sphericity of the silicon-based material is I
  • 0.1 ⁇ I-H ⁇ 0.3 The ratio of the shortest diameter to the longest diameter of the particles is the sphericity, and the sphericity of the particles can be tested with an automatic static image analyzer.
  • the sphericity of the sphere is 1.
  • the average sphericity I of the silicon-based material is 0.8 to 1.0. As the sphericity of the silicon-based material decreases, the capacity retention rate of the electrochemical device decreases and the deformation rate increases. This is due to the huge volume expansion of silicon-based materials in the process of lithium insertion.
  • the stress caused by the expansion causes the surface of the silicon-based material particles to crack, exposing fresh interfaces and contact with the electrolyte, generating more SEI and accelerating the electrolyte. Corrosion to silicon-based materials. Silicon-based materials with higher sphericity can effectively and evenly disperse the stress generated by expansion, alleviate surface cracks, and reduce the rate of corrosion of the surface of silicon-based materials.
  • the average sphericity H of the carbon material is 0.6 to 0.8.
  • the sphericity of carbon materials (for example, graphite) that is too high or too low will affect the electrochemical performance of the electrochemical device.
  • the sphericity of the carbon material is too high to fix the silicon-based material particles in the gaps of the carbon material particles, increasing the particle displacement caused by the silicon-based material in the process of expansion and contraction, thereby increasing the deformation of the electrochemical device and causing the capacity attenuation
  • the low sphericity of the carbon material increases the anisotropy, slows down the insertion rate of lithium ions, and affects the kinetics of the electrochemical device.
  • 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. 1, 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 carbon-based current collector.
  • the active material layer 2 includes any one of the above-mentioned negative electrode materials.
  • the mass percentage of the silicon-based material in the active material layer is 5%-30%.
  • the active material layer further includes a binder and a conductive agent.
  • 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 conductive agent includes at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, vapor-grown carbon fibers, nano-carbon fibers, conductive carbon black, acetylene black, Ketjen black, conductive graphite, or graphene.
  • the mass percentage of the conductive agent in the active material layer is 0.5% to 5%.
  • the thickness of the active material layer is 50 ⁇ m to 200 ⁇ m
  • the single-sided compaction density of the active material layer is 1.4 g/cm 3 to 1.9 g/cm 3
  • the porosity of the active material layer is 15% to 35% .
  • 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.
  • the positive electrode piece 10 may include a positive electrode current collector and a positive electrode active material layer coated on the positive electrode 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 this field 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 electrode active material includes 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 material may include a positive electrode active material that has been 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 of high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene.
  • 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 include alumina (Al 2 O 3 ), oxide Silicon (SiO 2 ), magnesium oxide (MgO), titanium oxide (TiO 2 ), hafnium dioxide (HfO 2 ), tin oxide (SnO 2 ), ceria (CeO 2 ), nickel oxide (NiO), zinc oxide (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 barium sulfate At least one of them.
  • the pores of the isolation membrane have a diameter in the range of about 0.01 ⁇ m to 1 ⁇ m.
  • Binders include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyethylene pyrrolidine At least one of ketone, 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 further include an electrolyte.
  • the electrolyte includes dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), ethylene carbonate (EC), propylene carbonate (PC), propylene propionate At least two of esters (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 electrode assembly or an electronic device including the above-mentioned electrochemical device.
  • the electronic device may include any electronic device that uses a rechargeable battery, such as a mobile phone, a tablet computer, and a charging device.
  • the current collector adopts copper foil with a thickness of 10 ⁇ m; the active material adopts SiO x (0.5 ⁇ x ⁇ 1.6) and graphite.
  • the D/G values of SiO x and graphite are shown in Table 1, where SiO x accounts for The mass ratio of the active material is 10%; the binder adopts polyacrylic acid; the active material, conductive carbon black, and binder are mixed in a mass ratio of 95:1.2:3.8 and then dispersed in water to form a slurry, which is stirred and coated on The copper foil is dried, cold pressed, and slit to obtain a negative pole piece.
  • Preparation of positive pole piece After taking positive active material LiCoO 2 , conductive carbon black, and binder polyvinylidene fluoride (PVDF) at a mass ratio of 96.7:1.7:1.6 in an N-methylpyrrolidone solvent system, stir and mix well. Coating on the aluminum foil, and then drying and cold pressing to obtain a positive pole piece.
  • positive active material LiCoO 2 LiCoO 2 , conductive carbon black, and binder polyvinylidene fluoride (PVDF) at a mass ratio of 96.7:1.7:1.6 in an N-methylpyrrolidone solvent system
  • Battery preparation Polyethylene porous polymer film is used as the separator, and the positive pole piece, separator film, and negative pole piece are stacked in sequence, so that the separator is in the middle of the positive and negative pole pieces for isolation, and rolled Wind the electrode assembly.
  • the electrode assembly is placed in the outer packaging aluminum plastic film, the electrolyte containing ethylene carbonate (EC) and propylene carbonate (PC) is injected and packaged, and the lithium ion battery is obtained through the process flow of chemical formation, degassing, and trimming.
  • EC ethylene carbonate
  • PC propylene carbonate
  • Example 2-17 and Comparative Examples 1-10 in addition to the differences in the surface structure, particle distribution and morphology of SiO x particles and graphite particles, the preparation of positive pole pieces, negative pole pieces, and lithium ion batteries were all carried out.
  • Example 1 is the same, and the parameter differences are shown in the corresponding table.
  • Malvern automatic image particle size analyzer uses image-directed Raman spectroscopy (MDRS) to accurately analyze the microstructure and morphology of the particles, and get the best results of all particles.
  • MDRS image-directed Raman spectroscopy
  • the longest diameter and the shortest diameter are calculated, and the ratio of the shortest diameter/the longest diameter is calculated to obtain the sphericity of the particles.
  • the adsorption amount of the sample monolayer is calculated based on the Brownauer-Ett-Taylor adsorption theory and its formula, and the specific surface area of the solid is calculated .
  • W the mass of gas adsorbed by the solid sample under relative pressure
  • test voltage is set to 40kV
  • the current is 30mA
  • the scan angle range is 10 to 85°
  • the scan step is 0.0167°
  • the time set for each step is 0.24s.
  • the OI value of graphite is obtained by calculating the ratio of (004) peak and (110) peak intensity in the XRD diffraction peaks of graphite.
  • the negative electrode material, conductive carbon black and binder polyacrylic acid (PAA) are mixed with deionized water according to the mass ratio of 80:10:10 to form a slurry, and a 100um thick coating is coated with a doctor blade. After 12 hours of vacuum at 85°C After drying in the drying box, in a dry environment, a punch is used to cut into discs with a diameter of 1 cm. In the glove box, a metal lithium sheet is used as a counter electrode, a ceglard composite film is selected as the isolation film, and an electrolyte is added to assemble the button cell. Use LAND series battery test test to charge and discharge the battery to test its charge and discharge performance.
  • PAA conductive carbon black and binder polyacrylic acid
  • using the first lithium removal capacity compared to the previous first lithium insertion capacity is the first efficiency of the material.
  • the test temperature is 25°C/45°C. It is charged to 4.4V at a constant current of 0.7C, then charged to 0.025C at a constant voltage, and discharged to 3.0V at 0.5C after standing for 5 minutes.
  • the capacity obtained in this step is the initial capacity, and the 0.7C charge/0.5C discharge is carried out for a cycle test, and the capacity at each step is used as the ratio of the initial capacity to obtain the capacity attenuation curve.
  • the number of turns from 25°C cycling to 90% of the capacity retention rate is recorded as the room temperature cycle performance of the electrode assembly, and the number of turns from 45°C cycling to 80% is recorded as the high temperature cycling performance of the electrode assembly.
  • Table 1 shows the comparison when the SiO x of Examples 1 to 3 and Comparative Examples 1 to 2 have different Raman scattering intensities D/G, and Table 2 shows the performance comparison of the corresponding full batteries.
  • the specific capacity here is the capacity obtained when the delithiation cut-off voltage is 2.0V (the same below).
  • Examples 1 to 3 and Comparative Examples 1 to 2 use SiO x with different D/G strengths to match the same graphite. From Table 1, it can be seen that the increase in D/G strength of SiO x has a slight effect on the contrast surface area, and other parameters are basically controlled. At the same level.
  • FIG. 3 shows the Raman spectrum of the silicon-based material SiO x in Example 3 of the present disclosure.
  • FIG. 4 shows the Raman spectrum of the carbon material graphite in Example 3 of the present disclosure.
  • Table 3 shows the comparison when the graphites of Examples 4 to 6 and Comparative Examples 3 to 4 have different Raman scattering intensities D/G, and Table 4 shows the performance comparison of the corresponding full batteries.
  • Examples 4 to 6 and Comparative Examples 3 to 4 used graphite with different Raman scattering intensities D/G, and other conditions were basically the same.
  • Table 5 shows the comparison when the SiO x of Examples 7-9 and Comparative Example 5 have different Dn50/Dv50, and Table 6 shows the performance comparison of the corresponding full batteries.
  • Dn50/Dv50 characterizes the concentration of particle distribution, while Dv50 indicates the particle size when the volume reaches 50%. Only the Dn50/Dv50 values of SiO x in Examples 7-9 and Comparative Example 5 are different, and there is no significant difference in other parameters.
  • Dn50/Dv50 characterizes the degree of concentration of particle distribution. The closer its value is to 1, the more concentrated the particle size distribution. It can be seen from the electrical performance results of Examples 7-9 and Comparative Example 5 that when the Dn50/Dv50 value of SiO x is greater than the Dn50/Dv50 value of graphite, the performance of the electrochemical device is better. This is because the lithium-intercalation expansion of silicon-based materials is much greater than that of graphite. In order to reduce the stress generated when silicon-based materials expand, the average particle size of silicon-based materials is smaller than that of graphite.
  • the active material on the negative electrode is made of silicon-based
  • the material particles and graphite particles are compositely composed
  • the silicon-based material particles are more concentrated than the graphite particles, it is beneficial to be dispersed in the gaps of the graphite particles, so that the expansion of the silicon-based material has the least influence on the overall expansion of the negative electrode.
  • the larger the Dn50/Dv50 value of SiO x is the better the cycle performance and expansion performance of the electrochemical device is when it matches the same graphite. This is due to the poor distribution and concentration of silicon-based material particles. Particles, too small particles will increase the contact area with the electrolyte, produce more SEI, consume the electrolyte and the limited reversible lithium in the electrode assembly.
  • Too large particles not only increase the stress generated during the expansion process of lithium insertion, cause the particles to rupture, expose fresh interfaces to react with the electrolyte, consume reversible lithium, and deteriorate cycle performance; at the same time, large silicon-based material particles increase the diffusion path of lithium ions and increase Concentration polarization affects the rate performance of electrochemical devices.
  • Table 7 shows the comparison when the graphites of Examples 10-12 and Comparative Examples 6-7 have different Dn50/Dv50, and Table 8 shows the performance comparison of the corresponding full batteries.
  • Table 9 shows the comparison when the SiO x of Examples 13-15 and Comparative Example 8 have different sphericities, and Table 10 shows the performance comparison of the corresponding full batteries.
  • Table 11 shows the comparison when the graphites of Examples 13, 16-17 and Comparative Examples 9-10 have different sphericities
  • Table 12 shows the performance comparison of the corresponding full batteries.
  • the sphericity of graphite is too high or too low will affect the electrochemical performance of the electrochemical device.
  • the sphericity of graphite is too high to fix the silicon-based material particles in the gaps of the graphite particles, and increase the displacement of the silicon-based material particles caused by the expansion and contraction of the silicon-based material, thereby increasing the deformation of the electrochemical device and causing Capacity decay; on the other hand, the excessively low sphericity of graphite increases anisotropy, slows down the insertion rate of lithium ions, and affects the kinetics of electrochemical devices.

Abstract

一种负极材料、负极极片、电化学装置和电子装置。负极材料包括硅基材料和碳材料，其中，碳材料的拉曼光谱中位移范围为1255～1355cm -1与1575～1600cm -1的峰分别为D峰和G峰，硅基材料的拉曼光谱中位移范围为1255～1355cm -1与1575～1600cm -1的峰分别为D峰和G峰，碳材料的散射峰强度比D/G为A，硅基材料的散射峰强度比D/G为B，其中，0.15≤A≤0.9，0.8≤B≤2.0，0.2＜B-A＜1.8。通过选择合适的拉曼光谱强度的负极材料中的硅基材料和碳材料，显著改善了电化学装置的循环性能、变形率以及倍率性能。

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
硅基材料具有高达4200mAh/g的理论比容量，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，硅基材料在充放电过程中具有约300％的体积膨胀，并且导电性较差。为此，工业界通常采用硅基材料和石墨材料按一定的比例混合应用，但尽管如此，仍然难以满足人们对能力密度和动力学日益增长的需求。
目前，研究人员主要通过改善硅基材料的界面稳定性和导电性来提高负极动力学，降低电极组件的循环中的膨胀。然而，目前的改善效果难以令人满意。
发明内容
鉴于以上所述现有技术的缺点，本公开通过限定硅基材料与碳材料的表面特征、颗粒分布以及形貌的关系，显著改善电化学装置的倍率性能，同时改善电化学装置的循环性能和变形率。
本公开提供一种负极材料，包括：硅基材料和碳材料，其中，所述碳材料的拉曼光谱中位移范围为1255～1355cm -1与1575～1600cm -1的峰分别为D峰和G峰，所述硅基材料的拉曼光谱中位移范围为1255～1355cm -1与1575～1600cm -1的峰分别为D峰和G峰，所述碳材料的散射峰强度比D/G为A，所述硅基材料的散射峰强度比D/G为B，其中，0.15≤A≤0.9，0.8≤B≤2.0，0.2<B-A<1.8。
在上述负极材料中，其中，所述碳材料的Dn50/Dv50的值为E，所述硅基材料的Dn50/Dv50的值为F，并且F>E。
在上述负极材料中，其中，所述碳材料的Dn50/Dv50的值E为0.1～0.65；和/或所述硅基材料的Dn50/Dv50的值F为0.3～0.85。
在上述负极材料中，其中，所述碳材料的平均球形度为H，所述硅基材料的平均球形度为I，并且0.1＜I-H≤0.3。
在上述负极材料中，其中，所述碳材料的平均球形度H为0.6～0.8。
在上述负极材料中，其中，所述硅基材料的平均球形度I为0.8～1.0。
在上述负极材料中，其中，所述硅基材料包括SiO xC yM z，其中0≤x≤2，0≤y≤1，0≤z≤0.5，M表示锂、镁、钛或铝中的至少一种；所述碳材料包括石墨。
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。
本公开通过选择合适的拉曼光谱强度的负极材料中的硅基材料和碳材料，显著改善了电化学装置的循环性能、变形率以及倍率性能。
附图说明
图1是本公开的负极极片的示意图。
图2是本公开的电化学装置的电极组件的示意图。
图3是本公开的实施例3中的硅基材料SiO x的拉曼光谱图。
图4是本公开的实施例3中的碳材料石墨的拉曼光谱图。
图5是本公开的实施例3和对比例1的放电倍率图。
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(例如，硅氧材料)作为下一代高比容量负极材料，可以显著提升电极组件的能量密度，但是硅基材料的导电性较差，并且在脱嵌锂 过程中存在较大的体积膨胀和收缩，相对于纯石墨负极，需要加入更多的导电性差的粘结剂来维持负极极片的结构稳定。在实际应用中，通常将硅基材料与一定比例的碳材料(例如，石墨)混合作为负极材料。然而，混合的负极材料依然存在导电性差、体积膨胀大的的问题，这阻碍了硅基材料的进一步规模化应用。此外，混合的负极材料的性能是硅基材料和碳材料共同决定的，单纯的改善硅基材料并不能将负极的电性能发挥到极致。然而，当前主要通过改善硅基材料的界面稳定性和导电性来提高负极动力学和循环性能，忽略了硅基材料与碳材料之间表面包覆、形貌和粒径的合理搭配。
本公开从硅基材料和碳材料(例如，石墨)之间的合理匹配出发，限定硅基材料颗粒与碳材料颗粒的表面结构特征、颗粒分布以及形貌的关系，显著改善电化学装置的循环性能、变形率以及倍率性能。
本公开的一些实施例提供了一种负极材料，负极材料包括硅基材料和碳材料。在一些实施例中，硅基材料为硅氧颗粒材料。在一些实施例中，硅基材料包括SiO xC yM z，其中0≤x≤2，0≤y≤1，0≤z≤0.5，M表示锂、镁、钛或铝中的至少一种。在一些实施例中，硅基材料包括硅、硅氧(SiO x，0.5≤x≤1.6)、硅碳、硅合金中的至少一种。在一些实施例中，负极材料中的碳材料包括石墨和/或石墨烯等。
在一些实施例中，碳材料的拉曼光谱中位移范围为1255～1355cm -1与1575～1600cm -1的峰分别为D峰和G峰，碳材料的散射峰强度比D/G为A，硅基材料的拉曼光谱中位移范围为1255～1355cm -1与1575～1600cm -1的峰分别为D峰和G峰，硅基材料的散射峰强度比D/G为B。碳材料与硅基材料的拉曼散射峰强度比满足0.2<B-A<1.8，且0.15≤A≤0.9，0.8≤B≤2.0。当碳材料与硅基材料的拉曼散射峰强度比满足0.2<B-A<1.8时，负极材料的循环性能以及动力学达到最佳水平。当硅基材料颗粒与碳材料颗粒的拉曼散射峰强度差值小于0.2时，存在硅基材料的拉曼散射峰强度比D/G过低或者碳材料的拉曼散射峰强度比D/G过高的问题。此时，硅基颗粒表面的包覆层中的SP2杂化结构比例增大，阻碍锂离子的扩散，增大极化，造成金属锂的析出，产生安全隐患，而石墨颗粒与电解液浸润性较差，影响锂离子从溶剂中脱出 并且迁移至碳材料表面的速率。这样的石墨和硅基材料复合而成的负极材料动力学差，电极组件在循环过程中的极化增加，循环性能也恶化。当硅基材料与碳材料的拉曼散射峰强度差值大于1.8时，存在硅基材料的拉曼散射峰强度比D/G过高或者碳材料的拉曼散射峰强度比D/G过低的问题，此时，硅基颗粒表面碳包覆层的无序度增加，降低其的电子导电率；而碳材料的表面覆盖一层过厚且含有大量缺陷的无定形碳包覆层，导致负极材料的比容量降低，影响电化学装置的能量密度和首次效率，这样的石墨和硅基材料复合而成的负极材料动力学和循环性能差，能量密度也会降低。
在一些实施例中，硅基材料的颗粒表面含有含碳包覆层，含碳包覆层的拉曼散射峰的强度比I1330/I1580为0.8～2.0。在一些实施例中，含碳包覆层的厚度为0.5nm～50nm。在一些实施例中，硅基材料的含碳包覆层的质量占硅基材料和含碳包覆层的总质量的0.1％～10％。
在一些实施例中，硅基颗粒的平均粒径为0.1μm～30μm。如果硅基材料的平均粒径过小，硅基材料容易发生团聚，并且由于比表面积大而消耗更多的电解液来形成SEI膜。如果硅基材料的平均粒径过大，不利于抑制硅基材料的体积膨胀，也容易引起活性物质层的导电性能的恶化。另外，如果硅基材料的平均粒径太大，则会使得负极极片的强度降低。在一些实施例中，硅基材料颗粒的比表面积为1.0m 2/g～15m 2/g。
在一些实施例中，碳材料(例如，石墨)颗粒的表面存在无定形碳包覆层，无定形碳包覆层的厚度为5nm～500nm。在一些实施例中，碳材料(例如，石墨)颗粒的拉曼散射峰的强度比I1330/I1580为0.2～0.9。在一些实施例中，碳材料(例如，石墨)颗粒的粒径范围为0.01μm～80μm，比表面积小于30m 2/g。在一些实施例中，碳材料(例如，石墨)颗粒可以是二次颗粒或者二次颗粒与一次颗粒的混合，其中二次颗粒占70％以上。在一些实施例中，碳材料(例如，石墨)颗粒的OI值是碳材料的XRD衍射峰中(004)峰和(110)峰峰强的比值，OI值为1～30。
在一些实施例中，碳材料的Dn50/Dv50的值为E，硅基材料的Dn50/Dv50的值为F，并且F>E，其中，Dn50是采用激光散射粒度仪测试得到的颗粒数基准分布累计50％的颗粒直径，Dv50是采用激光散射粒度仪测试得到的体积 基准分布累计50％的颗粒直径。Dn50/Dv50表征颗粒分布的集中程度，Dn50/Dv50的值越趋近于1，颗粒粒度分布越集中。在一些实施例中，硅基材料的Dn50/Dv50的值大于碳材料的Dn50/Dv50的值时，电化学装置的循环性能和倍率性能更好。这是由于硅基材料的嵌锂膨胀远大于碳材料(例如，石墨)，为了减小膨胀时产生的应力，硅基材料的平均粒径小于碳材料的颗粒，当负极极片的活性物质包括硅基材料和碳材料时，硅基材料颗粒比碳材料颗粒分布更为集中，有利于分散在碳材料颗粒堆积的缝隙中，使硅基材料的膨胀对负极极片的整体膨胀影响最小。
在一些实施例中，硅基材料的Dn50/Dv50的值F为0.3～0.85。硅基材料的Dn50/Dv50值越大，匹配同样的碳材料，膨胀性能更好，这是由于硅基材料颗粒分布集中度差时，存在大量过大或者过小的颗粒，颗粒过多会导致与电解液接触面积增大，产生更多的固体电解质界面膜(SEI，solid electrolyte interface)，消耗电解液以及电极组件中有限的可逆锂。硅基材料的颗粒过大不仅增加嵌锂膨胀过程中产生的应力，导致硅基材料的颗粒破裂，裸露出新鲜界面与电解液反应，消耗可逆锂，恶化电化学装置的循环性能；同时大的颗粒增加锂离子的扩散路径，增加浓差极化，影响电化学装置的倍率性能。
在一些实施例中，碳材料的Dn50/Dv50的值E为0.1～0.65。碳材料的Dn50/Dv50的值小于0.1时，碳材料中存在细小颗粒和大颗粒过多；当细小颗粒过多时导致碳材料的比表面积过大，降低电化学装置的首次效率；当大颗粒过多时，增加锂离子的传输距离，恶化电化学装置的膨胀和倍率性能。当碳材料的Dn50/Dv50的值大于0.65时，碳材料的粒径分布过于集中，不利于碳材料在负极极片中的堆积，导致电化学装置的膨胀增大，电接触恶化，循环性能也随之恶化，并且加工成本显著增加。
在一些实施例中，碳材料的平均球形度为H，硅基材料的平均球形度为I，并且0.1＜I-H≤0.3。颗粒的最短直径与最长直径的比值为球形度，可以利用自动静态图像分析仪测试颗粒的球形度，球体的球形度为1。在一些实施例中，硅基材料的平均球形度I为0.8～1.0。随着硅基材料的球形度降低，电化学装置的容量保持率下降，变形率提高。这是由于硅基材料在嵌锂的过程中会产生巨大的体积膨胀，膨胀产生的应力使硅基材料颗粒表面破裂，暴露 出新鲜界面与电解液接触，产生更多的SEI，并加速电解液对硅基材料的腐蚀。球形度较高的硅基材料能有效均匀分散膨胀所产生的应力，缓解表面裂纹产生，减小硅基材料表面被腐蚀的速率。
在一些实施例中，碳材料的平均球形度H为0.6～0.8。碳材料(例如，石墨)的球形度过高或者过低都会影响电化学装置的电化学性能。碳材料的球形度过高无法将硅基材料颗粒固定在碳材料颗粒的间隙中，增大硅基材料在膨胀收缩的过程中造成的颗粒位移，从而增大电化学装置的变形，引起容量衰减；另一方面，碳材料的球形度过低使各项异性增加，减缓锂离子的嵌入速度，影响电化学装置的动力学。
如图1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1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、镍箔或碳基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，活性物质层中的硅基材料的质量百分比为5％～30％。
在一些实施例中，活性物质层还包括粘结剂和导电剂。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，导电剂包括单壁碳纳米管、多壁碳纳米管、气相生长碳纤维、纳米碳纤维、导电炭黑、乙炔黑、科琴黑、导电石墨或石墨烯中的至少一种。在一些实施例中，活性物质层中的导电剂的质量百分比为0.5％～5％。在一些实施例中，活性物质层的厚度为50μm～200μm，活性物质层的单面压实密度为1.4g/cm 3～1.9g/cm 3，活性物质层的孔隙率为15％～35％。
如图2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包括经过掺杂或包覆处理的正极活性物质。
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，无机颗粒包括氧化铝(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。粘结剂包括聚偏氟乙烯、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极组件的电子装置或包括上述电化学装置的电子装置。在一些实施例中，电子装置可以包括手机、平板电脑、充电等使用充电电池的任何电子装置。
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
负极极片的制备：集流体采用铜箔，厚度为10μm；活性材料采用SiO x(0.5≤x≤1.6)和石墨，SiO x和石墨的D/G值如表1所示，其中SiO x占活性材料的质量比为10％；粘结剂采用聚丙烯酸；将活性材料、导电炭黑、粘结剂按质量比95：1.2：3.8混合后分散于水中形成浆料，经搅拌、涂布于铜箔上干燥、冷压、分条后得到负极极片。
正极极片制备：取正极活性物质LiCoO 2、导电炭黑、粘结剂聚偏二氟乙烯(PVDF)按质量比96.7：1.7：1.6在N-甲基吡咯烷酮溶剂体系中充分搅拌混合均匀后，涂覆于铝箔上，再经烘干、冷压，得到正极极片。
电池制备：以聚乙烯多孔聚合薄膜作为隔离膜，将正极极片、隔离膜、负极极片按顺序依次叠好，使隔离膜处于正积极片和负极极片中间起到隔离的作用，并卷绕得到电极组件。将电极组件置于外包装铝塑膜中，注入含有碳酸乙烯酯(EC)和碳酸丙烯酯(PC)的电解液并封装，经过化成，脱气，切边等工艺流程得到锂离子电池。
在实施例2～17与对比例1～10中，除了SiO x颗粒和石墨颗粒的表面结构、颗粒分布和形貌的差异之外，正极极片、负极极片、锂离子电池制备均与实施例1相同，参数的差异示出于相应的表格中。
实施例和对比例的各项参数的测定方法如下。
球形度测试：
利用马尔文自动图像粒度分析仪对一定数量(大于5000)分散的颗粒进行图像捕捉以及处理，然后通过图像导向拉曼光谱技术(MDRS)，准确分析颗粒的微观结构和形态，得到所有颗粒的最长直径以及最短直径，计算最短直径/最长直径的比值计算得到颗粒的球形度。
比表面积测试：
在恒温低温下，测定不同相对压力时的气体在固体表面的吸附量后，基于布朗诺尔-埃特-泰勒吸附理论及其公式求得试样单分子层吸附量，从而计算出固体的比表面积。
BET公式：
Figure PCTCN2020081305-appb-000001
其中：W—相对压力下固体样品所吸附的气体的质量
Wm---铺满一单分子层的气体饱和吸附量
斜率：(c-1)/(WmC)，截距：1/WmC，总比表面积：(Wm*N*Acs/M)
比表面积：S＝St/m，其中m为样品质量，Acs：每个N2分子的所占据的平均面积16.2A 2。
称取1.5～3.5g粉末样品装入TriStar II 3020的测试测试样品管中，200℃脱气120min后进行测试。
粒度测试：
50ml洁净烧杯中加入约0.02g粉末样品，加入约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，通过激光散射粒度仪测试得到的体积基准分布中累计50％直径Dv50与数量基准分布中的累计50％直径Dn50，计算Dn50/Dv50的比值。
X射线衍射(XRD)测试：
称取样品1.0～2.0g倒入玻璃样品架的凹槽内，并用玻璃片将其压实和磨平，采用X射线衍射仪(布鲁克，D8)按照JJS K 0131-1996《X射线衍射分析法通则》进行测试，测试电压设置40kV，电流为30mA，扫描角度范围为10～85°，扫描步长为0.0167°，每个步长所设置的时间为0.24s。通过计算石墨的XRD衍射峰中(004)峰和(110)峰峰强的比值，得到石墨的OI值。
首次效率测试：
将负极材料、导电炭黑与粘结剂聚丙烯酸(PAA)按照质量比80：10：10加去离子水经过搅成浆料，利用刮刀涂层100um厚度的涂层，85℃经过12小时真空干燥箱烘干后，在干燥环境中用冲压机切成直径为1cm的圆片，在手套箱中以金属锂片作为对电极，隔离膜选择ceglard复合膜，加入电解液组装成扣式电池。运用蓝电(LAND)系列电池测试测试对电池进行充放电测试，测试其充放电性能。
首先采用0.05C放电至0.005V，静止5分钟后，用50μA放电至0.005V，再静止5分钟后，用10μA放电至0.005V，得到材料的首次嵌锂容量；然后用0.1C充电至2V，得到首次脱锂容量。最终，用首次脱锂容量比上首次嵌锂容量即为材料的首次效率。
电池循环性能测试：
测试温度为25℃/45℃，以0.7C恒流充电到4.4V，再恒压充电到0.025C，静置5分钟后以0.5C放电到3.0V。以此步得到的容量为初始容量，进行0.7C充电/0.5C放电进行循环测试，以每一步的容量与初始容量做比值，得到容量衰减曲线。以25℃循环截至到容量保持率为90％的圈数记为电极组件的室温 循环性能，以45℃循环截至到80％的圈数记为电极组件的高温循环性能，通过比较上述两种情况下的循环圈数而得到材料的循环性能。
倍率性能测试：
在25℃下，以0.2C放电到3.0V，静置5min，以0.5C充电到4.45V，恒压充电到0.05C后静置5分钟，调整放电倍率，分别以0.2C、0.5C、1C、1.5C、2.0C进行放电测试，分别得到放电容量，以每个倍率下得到的容量与0.2C得到的容量对比，通过比较2C与0.2C下的比值得到倍率性能。
变形率测试：
用螺旋千分尺测试半充时新鲜电极组件的厚度，在25℃下循环至400cls或在45℃下循环至200cls时，电极组件处于满充状态下，再用螺旋千分尺测试此时电极组件的厚度，与初始半充时新鲜电极组件的厚度对比，即可得此时变形率。
下面描述各个实施例和对比例的参数设置和性能结果。表1示出了实施例1～3和对比例1～2的SiO x具有不同拉曼散射强度D/G时的对比，表2示出了相应的全电池的性能比较。
表1
Figure PCTCN2020081305-appb-000002
*此处的比容量为脱锂截至电压为2.0V所获得的容量(下同)。
实施例1～3与对比例1～2采用不同D/G强度的SiO x匹配同一款石墨，从表1可以看出SiO x的D/G强度的提高对比表面积有轻微影响，其他参数基本控制在相同水平。图3示出了本公开的实施例3中的硅基材料SiO x的拉曼光谱图。图4示出了本公开的实施例3中的碳材料石墨的拉曼光谱图。
表2
Figure PCTCN2020081305-appb-000003
Figure PCTCN2020081305-appb-000004
从实施例1～3和对比例1、2的电性能结果可以看出，当石墨颗粒与硅基材料颗粒的拉曼散射峰强度差值(B-A)不满足0.2～1.8的范围时，显著恶化电化学装置的电化学性能。当硅基材料颗粒的拉曼散射峰强度比D/G的值大于2.0时，包覆硅基材料的碳材料的无序程度增加，导致硅基材料颗粒的电子导电性降低，影响电化学装置的动力学性能。当硅基材料颗粒的拉曼散射峰强度比D/G的值过小时，碳材料包覆层中的SP2杂化结构比例增多，阻碍锂离子的扩散，增大极化，造成金属锂在硅基材料颗粒表面析出，产生安全隐患。对比例2的变形率低是由于容量衰减快，负极材料嵌入的锂少导致的。图5示出了实施例3和对比例1的放电倍率图，实施例3中的电化学装置的倍率性能明显更优于对比例1中的电化学装置的倍率性能。
表3示出了实施例4～6和对比例3～4的石墨具有不同拉曼散射强度D/G时的对比，表4示出了相应的全电池的性能比较。
表3
Figure PCTCN2020081305-appb-000005
实施例4～6和对比例3～4采用不同拉曼散射强度D/G的石墨，其余条件基本相同。
表4
Figure PCTCN2020081305-appb-000006
Figure PCTCN2020081305-appb-000007
从实施例4～6和对比例3～4的电性能结果可以看出，即使石墨颗粒与硅基材料颗粒的拉曼散射峰强度差值(B-A)满足0.2<B-A<1.8，当石墨颗粒的拉曼散射峰的强度比D/G过小(小于0.15)时，石墨颗粒表面没有无定形包覆，与电解液的浸润性差，恶化电化学装置的动力学性能；当石墨颗粒的拉曼散射峰的强度比D/G大于0.9时，石墨颗粒表面覆盖一层过厚且含有大量缺陷的无定形碳包覆层，导致负极材料的首次效率和比容量降低；此外过厚的无定形碳会消耗部分锂离子，导致电化学装置的容量衰减加速。
表5示出了实施例7～9和对比例5的SiO x具有不同Dn50/Dv50时的对比，表6示出了相应的全电池的性能比较。
表5
Figure PCTCN2020081305-appb-000008
Dn50/Dv50和Dv50没有直接的关系，Dn50/Dv50表征颗粒分布的集中程度，而Dv50表明的是体积到达50％时的颗粒粒径。实施例7～9和对比例5仅SiO x的Dn50/Dv50值有差异，其他参数无明显差异。
表6
Figure PCTCN2020081305-appb-000009
Dn50/Dv50表征颗粒分布的集中程度，其数值越趋近于1，颗粒粒度分布越集中。从实施例7～9和对比例5的电性能结果可以看出，SiO x的 Dn50/Dv50值大于石墨的Dn50/Dv50值时，电化学装置的性能较好。这是由于硅基材料的嵌锂膨胀远大于石墨，为了减小硅基材料膨胀时产生的应力，硅基材料的平均粒径小于石墨的平均粒径，当负极极片上的活性物质由硅基材料颗粒和石墨颗粒复合组成时，硅基材料颗粒比石墨颗粒分布更为集中时，有利于分散在石墨颗粒的缝隙中，使硅基材料的膨胀对负极极片的整体膨胀影响最小。此外，SiO x的Dn50/Dv50值越大，匹配同样的石墨，电化学装置的循环性能、膨胀性能更优，这是由于硅基材料颗粒分布集中度差时，存在大量过大或者过小的颗粒，颗粒过小会导致与电解液接触面积增大，产生更多的SEI，消耗电解液以及电极组件中有限的可逆锂。颗粒过大不仅增加嵌锂膨胀过程中产生的应力，导致颗粒破裂，裸露出新鲜界面与电解液反应，消耗可逆锂，恶化循环性能；同时大的硅基材料颗粒增加锂离子的扩散路径，增加浓差极化，影响电化学装置的倍率性能。
表7示出了实施例10～12和对比例6～7的石墨具有不同Dn50/Dv50时的对比，表8示出了相应的全电池的性能比较。
表7
Figure PCTCN2020081305-appb-000010
实施例10～12和对比例6～7中仅石墨的Dn50/Dv50值有差异，其他参数无明显差异。
表8
Figure PCTCN2020081305-appb-000011
从实施例10～12和对比例6～7的电性能结果可以看出，SiO x的Dn50/Dv50值大于石墨的Dn50/Dv50值时，电化学装置的性能较好。另外，当石墨颗粒的Dn50/Dv50的值小于0.1时，石墨颗粒中存在细小颗粒和大颗粒过多；小颗粒过多导致比表面积过大，降低电化学装置的首次效率；当大颗粒过多时，增加锂离子的传输距离，恶化电化学装置的膨胀和倍率性能。当石墨颗粒的Dn50/Dv50的值大于0.65时，石墨的粒径分布过于集中，不利于石墨在负极极片中的堆积，导致电化学装置的膨胀增大，电接触恶化，循环性能也随之恶化，并且加工成本显著增加。
表9示出了实施例13～15和对比例8的SiO x具有不同球形度时的对比，表10示出了相应的全电池的性能比较。
表9
Figure PCTCN2020081305-appb-000012
实施例13～15与对比例8中仅SiO x的球形度不同，所匹配的为同款石墨，其他参数无太大差异。
表10
Figure PCTCN2020081305-appb-000013
通过实施例13～15和对比例8的对比可以看出，随着SiO x的球形度降低，电化学装置的容量保持率下降，变形率提高。这是由于SiO x在嵌锂的过程中会产生巨大的体积膨胀，膨胀产生的应力使硅基材料颗粒表面破裂，暴露出新鲜界面与电解液接触，产生更多的SEI，从而加速电解液对SiO x的腐蚀。 球形度较高的SiO x能有效均匀分散嵌锂膨胀所产生的应力，缓解表面裂纹的产生，减少表面SEI堆积以及负极材料的腐蚀速率。
表11示出了实施例13、16～17和对比例9～10的石墨具有不同球形度时的对比，表12示出了相应的全电池的性能比较。
表11
Figure PCTCN2020081305-appb-000014
实施例13、16、17与对比例9、10所采用的石墨仅球形度不同，匹配同款SiO x，并且其他参数无太大差异。
表12
Figure PCTCN2020081305-appb-000015
从实施例13、16、17和对比例9、10的对比可以看出，石墨的球形度过高或者过低都会影响电化学装置的电化学性能。石墨的球形度过高无法将硅基材料颗粒固定在石墨颗粒的间隙中，增大硅基材料在膨胀与收缩的过程中造成的硅基材料颗粒位移，从而增大电化学装置的变形，引起容量衰减；另一方面，石墨的球形度过低使各项异性增加，减缓锂离子的嵌入速度，影响电化学装置的动力学。
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：
    硅基材料和碳材料，
    其中，所述碳材料的拉曼光谱中位移范围为1255～1355cm -1与1575～1600cm -1的峰分别为D峰和G峰，所述硅基材料的拉曼光谱中位移范围为1255～1355cm -1与1575～1600cm -1的峰分别为D峰和G峰，所述碳材料的散射峰强度比D/G为A，所述硅基材料的散射峰强度比D/G为B，其中，0.15≤A≤0.9，0.8≤B≤2.0，0.2<B-A<1.8。
  2. 根据权利要求1所述的负极材料，其中，所述碳材料的Dn50/Dv50的值为E，所述硅基材料的Dn50/Dv50的值为F，并且F>E。
  3. 根据权利要求1所述的负极材料，其中，所述碳材料的Dn50/Dv50的值E为0.1～0.65；和/或所述硅基材料的Dn50/Dv50的值F为0.3～0.85。
  4. 根据权利要求1所述的负极材料，其中，所述碳材料的平均球形度为H，所述硅基材料的平均球形度为I，并且0.1＜I-H≤0.3。
  5. 根据权利要求1所述的负极材料，其中，所述碳材料的平均球形度H为0.6～0.8。
  6. 根据权利要求1所述的负极材料，其中，所述硅基材料的平均球形度I为0.8～1.0。
  7. 根据权利要求1所述的负极材料，其中，所述硅基材料包括SiO xC yM z，其中0≤x≤2，0≤y≤1，0≤z≤0.5，M表示锂、镁、钛或铝中的至少一种；所述碳材料包括石墨。
  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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