WO2024092569A1 - 负极活性材料及其制备方法、以及包含其的二次电池及用电装置 - Google Patents

负极活性材料及其制备方法、以及包含其的二次电池及用电装置 Download PDF

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WO2024092569A1
WO2024092569A1 PCT/CN2022/129326 CN2022129326W WO2024092569A1 WO 2024092569 A1 WO2024092569 A1 WO 2024092569A1 CN 2022129326 W CN2022129326 W CN 2022129326W WO 2024092569 A1 WO2024092569 A1 WO 2024092569A1
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negative electrode
silicon
electrode active
active material
based material
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PCT/CN2022/129326
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English (en)
French (fr)
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吴凯
吕子建
王家政
刘良彬
邓静娴
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宁德时代新能源科技股份有限公司
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Priority to PCT/CN2022/129326 priority Critical patent/WO2024092569A1/zh
Priority to CN202280005823.6A priority patent/CN116724415A/zh
Priority to US18/424,914 priority patent/US20240170653A1/en
Publication of WO2024092569A1 publication Critical patent/WO2024092569A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/02—Silicon
    • C01B33/021—Preparation
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/80—Particles consisting of a mixture of two or more inorganic phases
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/12—Surface area
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/14—Pore volume
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/40—Electric properties
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application belongs to the field of battery technology, and specifically relates to a negative electrode active material and a preparation method thereof, as well as a secondary battery and an electrical device containing the same.
  • the purpose of the present application is to provide a negative electrode active material and a preparation method thereof, as well as a secondary battery and an electrical device containing the same, wherein the negative electrode active material has high capacity, high first coulombic efficiency and low volume expansion, and enables the secondary battery to have high energy density, high first coulombic efficiency, long cycle life and long storage life.
  • the present application provides a negative electrode active material, which includes a matrix material and a silicon-based material, wherein the matrix material includes a plurality of pore structures, at least a portion of the silicon-based material is located in the pore structure of the matrix material, and the silicon-based material includes a crystalline silicon-based material.
  • the area formed by a distance extending from the outer surface of a particle of the negative electrode active material toward the inside of the particle by 0.5 times the length between any point on the outer surface of the particle and the core of the particle is recorded as an outer area, and the area inside the outer area is recorded as an inner area.
  • the total cross-sectional area of the crystalline silicon-based material in the outer area is smaller than the total cross-sectional area of the crystalline silicon-based material in the inner area.
  • the negative electrode active material provided in the present application includes a matrix material having multiple pore structures and a silicon-based material at least part of which is located in the pore structure of the matrix material, wherein the silicon-based material includes a crystalline silicon-based material, and in the cross-sectional image of the negative electrode active material, the total cross-sectional area of the crystalline silicon-based material in the outer region is smaller than the total cross-sectional area of the crystalline silicon-based material in the inner region, thereby the crystalline silicon-based material is mainly located in the inner region of the negative electrode active material, and thus the negative electrode active material provided in the present application can have high capacity, high first coulombic efficiency and low volume expansion, and can enable the secondary battery to have high energy density, high first coulombic efficiency, long cycle life and long storage life.
  • the cross-sectional image of the negative electrode active material includes a cross-sectional image passing through a particle core of the negative electrode active material.
  • the ratio ⁇ 1 of the total cross-sectional area of the crystalline silicon-based material in the outer region to the total cross-sectional area of the crystalline silicon-based material in the inner region is (0-50): 100, and can be optionally (0-10): 100.
  • the silicon-based material further comprises an amorphous silicon-based material, and optionally, in the cross-sectional image of the negative electrode active material, the total cross-sectional area of the amorphous silicon-based material in the outer region is greater than the total cross-sectional area of the amorphous silicon-based material in the inner region.
  • the ratio ⁇ 2 of the total cross-sectional area of the amorphous silicon-based material in the inner region to the total cross-sectional area of the amorphous silicon-based material in the outer region is (0-30): 100, and can be optionally (0-10): 100.
  • the outer region of the negative electrode active material mainly contains amorphous silicon-based materials, and contains no or a small amount of crystalline silicon-based materials, thereby fully exerting the effect of the crystalline silicon-based materials on the improvement of the first coulomb efficiency, and fully exerting the effect of the amorphous silicon-based materials on the improvement of the cycle performance and the reduction of the volume expansion.
  • the ratio ⁇ 1 of the total cross-sectional area of the crystalline silicon-based material to the total cross-sectional area of the amorphous silicon-based material is (0-25):100, optionally (0-5):100, and more optionally, the total cross-sectional area of the crystalline silicon-based material is 0.
  • the outer region of the negative electrode active material mainly contains amorphous silicon-based material, and contains no or a small amount of crystalline silicon-based material, thereby fully exerting the effect of the crystalline silicon-based material on the improvement of the first coulomb efficiency, and fully exerting the effect of the amorphous silicon-based material on the improvement of the cycle performance and the reduction of the volume expansion.
  • the ratio ⁇ 2 of the total cross-sectional area of the crystalline silicon-based material to the total cross-sectional area of the amorphous silicon-based material is 100:(0-250), and can be optionally 100:(0-100).
  • the internal area of the negative electrode active material may contain only crystalline silicon-based materials, or may contain a mixture of crystalline silicon-based materials and amorphous silicon-based materials at the same time, and by further adjusting the total cross-sectional area of the crystalline silicon-based material and the total cross-sectional area of the amorphous silicon-based material within a suitable range, the crystalline silicon-based material can better play a role in improving the first coulomb efficiency.
  • the ratio ⁇ 1 of the total cross-sectional area of the crystalline silicon-based material to the total cross-sectional area of the negative electrode active material is greater than 0 and less than or equal to 25%, and can be optionally 5%-20%.
  • the crystalline silicon-based material can fully exert its effect of improving the first coulomb efficiency, and can avoid its significant adverse effect on the cycle performance and storage performance of the secondary battery.
  • the ratio ⁇ 2 of the total cross-sectional area of the amorphous silicon-based material to the total cross-sectional area of the negative electrode active material is greater than or equal to 35% and less than 100%, and can be optionally 40%-60%.
  • the amorphous silicon-based material can fully exert its effect of improving the cycle performance and reducing the volume expansion, and can avoid its greater adverse effect on the first coulomb efficiency of the secondary battery.
  • the mass percentage of the crystalline silicon-based material in the silicon-based material is greater than 0 and less than or equal to 40wt%, and can be optionally 10wt%-30wt%.
  • the content of the crystalline silicon-based material is within the above range, the crystalline silicon-based material can fully exert its effect of improving the first coulombic efficiency, while avoiding its greater adverse effects on the cycle performance and storage performance of the secondary battery.
  • At least a portion of the silicon-based material is located in the pore structure of the base material, and there is a gap between the silicon-based material and the base material.
  • the part of the pores can be used as a space to accommodate the volume expansion of the silicon-based material, and buffer the stress generated during the expansion of the silicon-based material.
  • the grain size of the crystalline silicon-based material is greater than 0 and less than or equal to 10nm, and can be optionally 2nm-8nm.
  • the crystalline silicon-based material has a suitable grain size, it can improve the first coulombic efficiency of the secondary battery while avoiding a significant adverse effect on the cycle performance and storage performance of the secondary battery.
  • the crystalline silicon-based material includes one or more of crystalline elemental silicon, silicon oxide, silicon-carbon material, silicon-nitrogen complex and silicon alloy material.
  • the crystalline silicon-based material includes crystalline elemental silicon.
  • the amorphous silicon-based material includes one or more of amorphous elemental silicon, silicon oxide, silicon-carbon material, silicon-nitrogen complex and silicon alloy material.
  • the amorphous silicon-based material includes amorphous elemental silicon.
  • the silicon-based material includes a vapor-deposited silicon-based material, and optionally includes vapor-deposited elemental silicon.
  • the porosity of the matrix material is 30%-60%, and can be 40%-50%.
  • the porosity of the matrix material is within the above range, it is conducive to accommodating sufficient silicon-based materials, thereby facilitating the improvement of the energy density of the secondary battery.
  • the matrix material includes one or more of a carbon material, a graphite material, and a transition metal oxide material.
  • the matrix material includes a carbon material
  • the carbon material includes one or more of activated carbon, biomass carbon, pyrolytic carbon and resin carbon.
  • the carbon material includes one or more of activated carbon, biomass carbon, pyrolytic carbon and resin carbon.
  • it can also promote the transmission of active ions and increase the specific capacity of negative electrode active materials.
  • the porous structure of carbon materials is more uniform, which is also conducive to the dispersion of silicon-based materials.
  • the negative electrode active material further includes a coating layer, and the coating layer is located on at least a portion of the surface of the base material.
  • the coating layer is located on the outside of the negative electrode active material, thereby further preventing the silicon-based material from directly contacting the electrolyte and reducing the reactivity of the silicon-based material after contacting the air, thereby reducing the electrolyte side reaction, reducing the consumption of active ions, and improving the cycle performance of the secondary battery.
  • the coating layer includes one or more of a carbon material, a conductive polymer, a metal oxide, and a metal sulfide.
  • the coating layer includes a carbon material, and optionally, the carbon material includes one or more of hard carbon, soft carbon, graphene, carbon fiber and carbon nanotube.
  • the coating layer includes a carbon material, it helps to improve the conductivity of the silicon-based material.
  • the coating layer has a thickness of 0 nm-200 nm, and can be optionally 10 nm-150 nm.
  • the coating layer has a thickness within the above range, it is beneficial for the negative electrode active material to have a high specific capacity and low volume expansion.
  • the negative electrode active material includes carbon and silicon.
  • the mass percentage of carbon element in the negative electrode active material is 40wt%-60wt%, and can be optionally 45wt%-50wt%.
  • the mass percentage of silicon element in the negative electrode active material is 38wt%-58wt%, and can be optionally 40wt%-55wt%.
  • the negative electrode active material When the content of carbon element and/or silicon element in the negative electrode active material is within the above range, it is beneficial for the negative electrode active material to have both high specific capacity and high conductivity.
  • the negative electrode active material further includes other elements, and the other elements include one or more of oxygen, metal and nitrogen.
  • the sum of the mass percentages of other elements in the negative electrode active material is 0wt%-20wt%, and can be optionally 0wt%-10wt%.
  • the pore volume of the negative electrode active material is 0.001 cm 3 /g-0.02 cm 3 /g, and can be 0.01 cm 3 /g-0.02 cm 3 /g.
  • the internal voids of the negative electrode active material are within a suitable range, which can improve the specific capacity and first coulombic efficiency of the negative electrode active material on the one hand, and buffer the stress generated during the expansion of the silicon-based material on the other hand.
  • the average particle size Dv50 of the negative electrode active material is 4 ⁇ m-12 ⁇ m.
  • the average particle size Dv50 of the negative electrode active material helps to reduce surface activity, reduce interface side reactions, reduce SEI film formation consumption, and is also beneficial to improve active ion and electron transport performance, thereby further improving the cycle performance of the secondary battery.
  • the BET specific surface area of the negative electrode active material is 1m2 /g- 15m2 /g.
  • the BET specific surface area of the negative electrode active material is within the above range, it is helpful to reduce surface activity, reduce interface side reactions, reduce SEI film formation consumption, and improve the first coulombic efficiency and cycle performance of the secondary battery.
  • the second aspect of the present application provides a method for preparing a negative electrode active material, comprising the following steps: providing a matrix material including multiple pore structures; dispersing a silicon-based material into the pore structure of the matrix material to obtain a negative electrode active material, wherein the negative electrode active material comprises a matrix material and a silicon-based material, the matrix material comprises multiple pore structures, at least a portion of the silicon-based material is located in the pore structure of the matrix material, the silicon-based material comprises a crystalline silicon-based material, and the area formed by the outer surface of the particle of the negative electrode active material extending toward the inside of the particle by a distance of 0.5 times the length between any point on the outer surface of the particle and the core of the particle is recorded as an outer area, and the area inside the outer area is recorded as an inner area.
  • the total cross-sectional area of the crystalline silicon-based material in the outer area is smaller than the total cross-sectional area of the crystalline silicon-based material
  • the porosity of the matrix material is 30%-60%, and can be 40%-50%.
  • the porosity of the matrix material is within the above range, it is beneficial for the deposition process to proceed smoothly, and it is also beneficial for the negative electrode active material to have a suitable silicon content, a suitable specific surface area and/or a suitable pore volume.
  • the matrix material includes one or more of a carbon material, a graphite material, and a transition metal oxide material.
  • the matrix material includes a carbon material
  • the carbon material includes one or more of activated carbon, biomass carbon, pyrolytic carbon and resin carbon.
  • the average particle size Dv50 of the matrix material is 4 ⁇ m-12 ⁇ m.
  • the average particle size Dv50 of the matrix material is within the above range, it is beneficial for the deposition process to proceed smoothly, and it is also beneficial for the negative electrode active material to have a suitable silicon content, a suitable specific surface area and/or a suitable pore volume.
  • the step of dispersing the silicon-based material into the pore structure of the base material comprises the following steps: placing the base material including a plurality of pore structures as a substrate in a reaction furnace, introducing a first mixed gas containing a silicon source gas, and depositing at a first temperature T1 for a first time t1 , and stopping the introduction of the first mixed gas after the reaction; after the temperature in the furnace drops to a second temperature T2 , introducing a second mixed gas containing a silicon source gas, and depositing at a second temperature T2 for a second time t2 , and obtaining a negative electrode active material after the reaction, wherein the silicon-based material comprises a crystalline silicon-based material and an amorphous silicon-based material, and in a cross-sectional image of the negative electrode active material, the total cross-sectional area of the crystalline silicon-based material in the outer region is smaller than the total cross-sectional area of the crystalline silicon-based material in the inner region, and the
  • the method before the first mixed gas containing the silicon source gas is introduced, the method further includes the following steps: placing a base material including a plurality of pore structures as a substrate in a reaction furnace, and performing a purging treatment and a pre-heating treatment using a protective gas, wherein the pre-heating temperature is optionally 200° C.-300° C. This is conducive to removing the remaining moisture in the base material, and further facilitates the subsequent smooth deposition and formation of a crystalline silicon-based material.
  • the volume proportion V1 of the silicon source gas in the first mixed gas is greater than the volume proportion V2 of the silicon source gas in the second mixed gas.
  • This is conducive to adjusting the distribution area of crystalline silicon-based materials and amorphous silicon-based materials, so that the crystalline silicon-based materials are mainly located in the inner area of the negative electrode active material, and the amorphous silicon-based materials are mainly located in the outer area of the negative electrode active material, so that the crystalline silicon-based materials can fully exert the effect of improving the first coulomb efficiency, and the amorphous silicon-based materials can fully exert the effect of improving the cycle performance and reducing the volume expansion.
  • T 1 >T 2 .
  • the first temperature during deposition it is helpful to adjust the distribution area of the crystalline silicon-based material and the amorphous silicon-based material, so that the crystalline silicon-based material is mainly located in the inner area of the negative electrode active material, and the amorphous silicon-based material is mainly located in the outer area of the negative electrode active material, so that the crystalline silicon-based material can give full play to the effect of improving the first coulomb efficiency, and the amorphous silicon-based material can give full play to the effect of improving the cycle performance and reducing the volume expansion.
  • t 1 ⁇ t 2 t 1 ⁇ t 2 .
  • the first mixed gas includes a silicon source gas and a protective gas.
  • a volume proportion V1 of the silicon source gas in the first mixed gas is 10%-50%.
  • the total gas flow rate of the first mixed gas is 0.5 L/min-20 L/min.
  • the first temperature T1 is 500°C-700°C.
  • the first time t1 is 0.5h-8h, and can be optionally 0.5h-4h.
  • the composition ratio of the first mixed gas By adjusting at least one of the composition ratio of the first mixed gas, the total gas flow rate of the first mixed gas, the first temperature and the first time within the above-mentioned range, it is beneficial to form a crystalline silicon-based material, and is also beneficial to adjust the distribution area, grain size, deposition amount and other parameters of the crystalline silicon-based material.
  • the second mixed gas includes a silicon source gas and a protective gas.
  • a volume proportion V2 of the silicon source gas in the second mixed gas is 5%-20%.
  • the second mixed gas includes silicon source gas, carbon source gas and protective gas.
  • the volume proportion V2 of the silicon source gas in the second mixed gas is 5%-20%, and the volume proportion of the carbon source gas is 5%-10%.
  • the total gas flow rate of the second mixed gas is 0.5 L/min-20 L/min.
  • the second temperature T2 is 400°C-500°C.
  • the second time t2 is 2h-16h, and can be optionally 4h-16h.
  • the composition ratio of the second mixed gas By adjusting at least one of the composition ratio of the second mixed gas, the total gas flow rate of the second mixed gas, the second temperature and the second time within the above-mentioned range, it is beneficial to form amorphous silicon-based materials, and is also beneficial to adjust parameters such as the distribution area and deposition amount of the amorphous silicon-based materials.
  • the total gas flow rate of the second mixed gas is the same as the total gas flow rate of the first mixed gas.
  • the method further comprises the step of forming a coating layer on at least the surface of the obtained negative electrode active material, wherein the coating layer comprises one or more of a carbon material, a conductive polymer, a metal oxide and a metal sulfide.
  • the step of forming the coating layer includes the following steps: placing the obtained negative electrode active material in a reaction furnace, introducing a third mixed gas containing a carbon source gas, and depositing the negative electrode active material at a third temperature T 3 for a third time t 3 to obtain a carbon-coated negative electrode active material. This is conducive to forming a uniform carbon layer.
  • the third mixed gas includes a carbon source gas and a protective gas.
  • a volume proportion V3 of the carbon source gas in the third mixed gas is 10%-50%.
  • the total gas flow rate of the third mixed gas is 0.5 L/min-20 L/min.
  • the third temperature T3 is 600°C-700°C.
  • the third time t3 is 0.5h-2h.
  • the composition ratio of the third mixed gas By adjusting at least one of the composition ratio of the third mixed gas, the total gas flow rate of the third mixed gas, the third temperature and the third time within the above range, it is beneficial to form a coating layer of appropriate thickness, thereby avoiding the coating layer being too thick to reduce the first coulombic efficiency and/or specific capacity of the negative electrode active material.
  • a third aspect of the present application provides a secondary battery, comprising a negative electrode plate, wherein the negative electrode plate comprises the negative electrode active material described in the first aspect of the present application or the negative electrode active material prepared by the method described in the second aspect of the present application.
  • a fourth aspect of the present application provides an electrical device, which includes the secondary battery of the third aspect of the present application.
  • the negative electrode active material provided by the present application can have high capacity, high first coulombic efficiency and low volume expansion, and can also enable the secondary battery to have high energy density, high first coulombic efficiency, long cycle life and long storage life.
  • the electric device of the present application includes the secondary battery provided by the present application, and thus has at least the same advantages as the secondary battery.
  • FIG. 1 is a schematic diagram of a cross-sectional image of a negative electrode active material of the present application.
  • FIG. 2 is a schematic diagram of a battery cell according to an embodiment of the present application.
  • FIG. 3 is an exploded schematic diagram of an embodiment of a battery cell of the present application.
  • FIG. 4 is a schematic diagram of an embodiment of a battery module of the present application.
  • FIG. 5 is a schematic diagram of an embodiment of a battery pack of the present application.
  • FIG. 6 is an exploded schematic diagram of the embodiment of the battery pack shown in FIG. 5 .
  • FIG. 7 is a schematic diagram of an embodiment of an electric device including the secondary battery of the present application as a power source.
  • range disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range.
  • the range defined in this way can be inclusive or exclusive of end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60-120 and 80-110 is listed for a specific parameter, it is understood that the range of 60-110 and 80-120 is also expected.
  • the numerical range "a-b" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers.
  • the numerical range "0-5" represents that all real numbers between "0-5" have been fully listed herein, and "0-5" is just the abbreviation of these numerical combinations.
  • a parameter is expressed as an integer ⁇ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.
  • the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially.
  • the method may further include step (c), which means that step (c) may be added to the method in any order.
  • the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.
  • the “include” and “comprising” mentioned in this application represent open-ended or closed-ended expressions.
  • the “include” and “comprising” may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.
  • the term "or” is inclusive.
  • the phrase “A or B” means “A, B, or both A and B”. More specifically, any of the following conditions satisfies the condition "A or B”: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).
  • a specific area such as an internal area or an external area
  • the corresponding material such as a crystalline silicon-based material or an amorphous silicon-based material
  • the corresponding material such as a crystalline silicon-based material or an amorphous silicon-based material
  • the values of the parameters mentioned in the present application can be measured by various test methods commonly used in the art, for example, they can be measured according to the test methods given in the examples of the present application.
  • Silicon has a theoretical specific capacity of up to 4200mAh/g, which can significantly improve the energy density of secondary batteries. Silicon also has a voltage platform slightly higher than that of graphite, so it is not easy to form dendrites at the negative electrode, which can improve the safety performance of secondary batteries. Silicon is widely distributed in the earth's crust, has abundant resources, and is cheap, which can reduce the production cost of secondary batteries. Therefore, materials containing silicon (hereinafter referred to as silicon-based materials) have become highly potential negative electrode active materials.
  • silicon-based materials also have some disadvantages. Unlike carbon-based materials such as graphite, silicon-based materials react with metals (such as lithium, sodium, etc.) through alloying reactions during the charge and discharge process, which results in a huge volume effect, which can easily cause particle breakage and pulverization, and then lead to pulverization of the negative electrode film layer, which is easy to lose electrical contact with the current collector.
  • metals such as lithium, sodium, etc.
  • SEI solid electrolyte interface
  • silicon is a semiconductor material with low intrinsic conductivity. When used as a negative electrode active material, it will affect the capacity volatilization of the secondary battery, or require an additional amount of conductive agent when used, thereby reducing the actual coating weight of the negative electrode active material and affecting the energy density of the secondary battery.
  • the main modification methods for the above problems include the following aspects.
  • the inventors of the present application have proposed a new type of negative electrode active material through extensive research, which has high capacity, high first coulombic efficiency and low volume expansion, and can enable secondary batteries to have high energy density, high first coulombic efficiency, long cycle life and long storage life.
  • the first aspect of the embodiment of the present application provides a negative electrode active material.
  • the negative electrode active material includes a matrix material and a silicon-based material, the matrix material includes a plurality of pore structures, at least a portion of the silicon-based material is located in the pore structure of the matrix material, the silicon-based material includes a crystalline silicon-based material, the region formed by the outer surface of the particle of the negative electrode active material extending toward the inside of the particle from 0.5 times the length between any point on the outer surface of the particle and the core of the particle is recorded as the outer region, the region inside the outer region is recorded as the inner region, and in the cross-sectional image of the negative electrode active material, the total cross-sectional area of the crystalline silicon-based material in the outer region is smaller than the total cross-sectional area of the crystalline silicon-based material in the inner region.
  • a dual beam focused ion beam microscope can be used to prepare a cross section of the negative electrode active material particles, the cross section passes through the central area of the negative electrode active material, and can be selected to pass through the particle core of the negative electrode active material, and then the cross-sectional image characteristics of the negative electrode active material can be observed by a transmission electron microscope (TEM) or a high resolution transmission electron microscope (HRTEM).
  • TEM transmission electron microscope
  • HRTEM high resolution transmission electron microscope
  • the cross-sectional image of the negative electrode active material includes a cross-sectional image passing through a particle core of the negative electrode active material.
  • particle core refers to the intersection of the longest diameter (or longest diagonal line) and the shortest diameter (or shortest diagonal line) of the negative electrode active material particle.
  • FIG1 is a schematic diagram of a cross-sectional image of a negative electrode active material 100 of the present application, and the cross-sectional image passes through the particle core O of the negative electrode active material 100.
  • the negative electrode active material 100 includes an outer region 101 and an inner region 102 located inside the outer region 101, the intersection of the longest diameter (or the longest diagonal line) and the shortest diameter (or the shortest diagonal line) of the negative electrode active material particle is the particle core O, the length between any point P on the outer surface of the particle and the particle core O is recorded as Rn , and the area formed by the outer surface of the particle of the negative electrode active material extending to the inside of the particle from 0.5 times the length Rn between any point P on the outer surface of the particle and the particle core O is recorded as the outer region 101.
  • the length R n is expressed as a variable value, that is, the length from different positions on the outer surface of the particle to the core of the particle is a constantly changing value, and thus the distance from different positions on the outer surface of the particle to the inside of the particle is also a constantly changing value. Therefore, the area enclosed by all points on the outer surface of the negative electrode active material particle and the outer surface of the particle after extending the corresponding distance (i.e., 0.5R n ) to the inside of the particle is the external area.
  • the total cross-sectional area of the crystalline silicon-based material in the external region is smaller than the total cross-sectional area of the crystalline silicon-based material in the internal region
  • the external region does not contain crystalline silicon-based material and the total cross-sectional area of the crystalline silicon-based material in the external region is 0, it is also considered to satisfy the condition “the total cross-sectional area of the crystalline silicon-based material in the external region is smaller than the total cross-sectional area of the crystalline silicon-based material in the internal region”.
  • the negative electrode active material provided in the present application includes a matrix material having multiple pore structures and a silicon-based material at least part of which is located in the pore structure of the matrix material, wherein the silicon-based material includes a crystalline silicon-based material, and in the cross-sectional image of the negative electrode active material, the total cross-sectional area of the crystalline silicon-based material in the outer region is smaller than the total cross-sectional area of the crystalline silicon-based material in the inner region, thereby the crystalline silicon-based material is mainly located in the inner region of the negative electrode active material, and thus the negative electrode active material provided in the present application can have high capacity, high first coulombic efficiency and low volume expansion, and can enable the secondary battery to have high energy density, high first coulombic efficiency, long cycle life and long storage life.
  • the crystalline silicon-based material helps to improve the first coulombic efficiency of the secondary battery, but the crystalline silicon-based material has a large volume expansion and poor structural stability, which is not conducive to improving the cycle performance of the secondary battery and reducing the volume expansion of the secondary battery.
  • the negative electrode active material provided in the present application can have high capacity, high first coulombic efficiency and low volume expansion, and can also enable the secondary battery to take into account high energy density, high first coulombic efficiency, long cycle life and long storage life.
  • the silicon-based material further comprises an amorphous silicon-based material.
  • the silicon-based material includes a crystalline silicon-based material and an amorphous silicon-based material.
  • the total cross-sectional area of the crystalline silicon-based material in the outer region is smaller than the total cross-sectional area of the crystalline silicon-based material in the inner region, and the total cross-sectional area of the amorphous silicon-based material in the outer region is larger than the total cross-sectional area of the amorphous silicon-based material in the inner region.
  • the total cross-sectional area of the amorphous silicon-based material in the outer region is greater than the total cross-sectional area of the amorphous silicon-based material in the inner region is not limited to the inner region must contain amorphous silicon-based material, when the inner region does not contain amorphous silicon-based material, and the total cross-sectional area of the amorphous silicon-based material in the inner region is 0, it is also considered to satisfy “the total cross-sectional area of the amorphous silicon-based material in the outer region is greater than the total cross-sectional area of the amorphous silicon-based material in the inner region”.
  • the silicon-based materials of the present application include both crystalline silicon-based materials and amorphous silicon-based materials, and the crystalline silicon-based materials are mainly located in the internal area of the negative electrode active material, while the amorphous silicon-based materials are mainly located in the external area of the negative electrode active material. Therefore, the negative electrode active material provided by the present application can have high capacity, high first coulombic efficiency and low volume expansion, and can enable the secondary battery to have high energy density, high first coulombic efficiency, long cycle life and long storage life.
  • the crystalline silicon-based material helps to improve the first coulomb efficiency of the secondary battery, but the crystalline silicon-based material has a large volume expansion and poor structural stability, which is not conducive to improving the cycle performance of the secondary battery and reducing the volume expansion of the secondary battery; the amorphous silicon-based material has a small volume expansion, which is conducive to improving the cycle performance of the secondary battery and reducing the volume expansion of the secondary battery, but the amorphous silicon-based material has a low first coulomb efficiency, resulting in a large loss of actual capacity of the secondary battery.
  • the negative electrode active material By making the crystalline silicon-based material mainly located in the inner area of the negative electrode active material, and the amorphous silicon-based material mainly located in the outer area of the negative electrode active material, it can give full play to the effect of the crystalline silicon-based material on the improvement of the first coulomb efficiency, and can give full play to the effect of the amorphous silicon-based material on the improvement of the cycle performance and the reduction of the volume expansion. Therefore, the negative electrode active material provided in the present application can have high capacity, high first coulomb efficiency and low volume expansion, and can also make the secondary battery take into account high energy density, high first coulomb efficiency, long cycle life and long storage life.
  • the ratio ⁇ 1 of the total cross-sectional area of the crystalline silicon-based material in the outer region to the total cross-sectional area of the crystalline silicon-based material in the inner region is (0-50):100, and can be optionally (0-40):100, (0-30):100, (0-20):100, (0-15):100, (0-10):100, (0-5):100.
  • the ratio ⁇ 1 of the total cross-sectional area of the crystalline silicon-based material in the outer region to the total cross-sectional area of the crystalline silicon-based material in the inner region may be 0, that is, the above-mentioned outer region of the negative electrode active material does not contain crystalline silicon-based material.
  • the crystalline silicon-based material By locating the crystalline silicon-based material mainly in the internal area of the negative electrode active material, the crystalline silicon-based material can fully exert its effect on improving the first coulombic efficiency while avoiding its significant adverse effects on the cycle performance and storage performance of the secondary battery.
  • the ratio ⁇ 2 of the total cross-sectional area of the amorphous silicon-based material in the inner region to the total cross-sectional area of the amorphous silicon-based material in the outer region is (0-30): 100, and can be optionally (0-25): 100, (0-20): 100, (0-15): 100, (0-10): 100, (0-5): 100.
  • the ratio ⁇ 2 of the total cross-sectional area of the amorphous silicon-based material in the inner region to the total cross-sectional area of the amorphous silicon-based material in the outer region may be 0, that is, the above-mentioned inner region of the negative electrode active material does not contain amorphous silicon-based material.
  • the effect of the amorphous silicon-based material on improving the cycle performance and reducing the volume expansion can be fully exerted.
  • the ratio ⁇ 1 of the total cross-sectional area of the crystalline silicon-based material to the total cross-sectional area of the amorphous silicon-based material is (0-25):100, optionally (0-20):100, (0-15):100, (0-10):100, (0-5):100, and more optionally, the total cross-sectional area of the crystalline silicon-based material is 0, that is, the above-mentioned outer region of the negative electrode active material does not contain crystalline silicon-based material.
  • the outer region of the negative electrode active material mainly contains amorphous silicon-based material, and does not contain or contains a small amount of crystalline silicon-based material, thereby fully exerting the effect of the crystalline silicon-based material on the improvement of the first coulomb efficiency, and fully exerting the effect of the amorphous silicon-based material on the improvement of the cycle performance and the reduction of the volume expansion.
  • the ratio ⁇ 2 of the total cross-sectional area of the crystalline silicon-based material to the total cross-sectional area of the amorphous silicon-based material is 100:(0-250), and can be optionally 100:(0-100), 100:(0-80), 100:(0-60), 100:(0-40), 100:(0-30), 100:(0-20), 100:(0-10), 100:(0-5).
  • the internal area of the negative electrode active material may contain only crystalline silicon-based material, or may contain a mixture of crystalline silicon-based material and amorphous silicon-based material at the same time, and by further adjusting the total cross-sectional area of the crystalline silicon-based material and the total cross-sectional area of the amorphous silicon-based material within a suitable range, the crystalline silicon-based material can better play the role of improving the first coulomb efficiency.
  • the ratio ⁇ 1 of the total cross-sectional area of the crystalline silicon-based material to the total cross-sectional area of the negative electrode active material is greater than 0 and less than or equal to 25%, for example, it can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25% or any range of the above values.
  • the ratio ⁇ 1 of the total cross-sectional area of the crystalline silicon-based material to the total cross-sectional area of the negative electrode active material is 5%-20%, 8%-20%, 10%-20%, 12%-20%, 12%-18%.
  • the crystalline silicon-based material can fully exert its effect on improving the first coulombic efficiency, while avoiding its significant adverse effects on the cycle performance and storage performance of the secondary battery.
  • the ratio ⁇ 2 of the total cross-sectional area of the amorphous silicon-based material to the total cross-sectional area of the negative electrode active material is greater than or equal to 35% and less than 100%, and can be optionally 40%-65%, 40%-60%, 40%-55%, or 40%-50%.
  • the amorphous silicon-based material can fully exert its effect of improving cycle performance and reducing volume expansion, while avoiding a significant adverse effect on the first coulombic efficiency of the secondary battery.
  • the mass percentage of the crystalline silicon-based material in the silicon-based material is greater than 0 and less than or equal to 40wt%, for example, it can be 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt% or any range consisting of the above values.
  • the mass percentage of the crystalline silicon-based material in the silicon-based material is 5wt%-40wt%, 5wt%-35wt%, 10wt%-35wt%, 10wt%-30wt%.
  • the crystalline silicon-based material can fully exert its effect on improving the first coulombic efficiency, while avoiding its significant adverse effects on the cycle performance and storage performance of the secondary battery.
  • At least a portion of the silicon-based material is located in the pore structure of the base material, and there is a gap between the silicon-based material and the base material.
  • the pores can be used as space to accommodate the volume expansion of the silicon-based material and buffer the stress generated during the expansion of the silicon-based material.
  • the grain size of the crystalline silicon-based material is greater than 0 and less than or equal to 10 nm, for example, it can be 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm or any range thereof.
  • the grain size of the crystalline silicon-based material is 2 nm-10 nm, 2 nm-8 nm.
  • the grain size of the crystalline silicon-based material When the grain size of the crystalline silicon-based material is large, it is beneficial to improve the first coulombic efficiency of the secondary battery, but it is not conducive to the cycle performance and storage performance of the secondary battery. Therefore, when the crystalline silicon-based material has a suitable grain size, it can not only improve the first coulombic efficiency of the secondary battery, but also avoid a significant adverse effect on the cycle performance and storage performance of the secondary battery.
  • the grain size of the crystalline silicon-based material is well known in the art and can be measured using instruments and methods well known in the art, such as a high-resolution transmission electron microscope.
  • the crystalline silicon-based material includes one or more of crystalline elemental silicon, silicon oxide, silicon-carbon material, silicon-nitrogen complex and silicon alloy material.
  • the crystalline silicon-based material includes crystalline elemental silicon (also called crystalline silicon).
  • the amorphous silicon-based material includes one or more of amorphous elemental silicon, silicon oxide, silicon-carbon material, silicon-nitrogen complex and silicon alloy material.
  • the amorphous silicon-based material includes amorphous elemental silicon (also known as amorphous silicon or amorphous silicon).
  • the silicon-based material includes a vapor-deposited silicon-based material, and optionally includes vapor-deposited elemental silicon, wherein the vapor-deposited elemental silicon includes vapor-deposited crystalline silicon and vapor-deposited amorphous silicon.
  • the matrix material includes a plurality of pore structures, and at least a portion of the silicon-based material is located in the pore structure of the matrix material, so that the matrix material can effectively alleviate the volume expansion of the silicon-based material and avoid the crushing and pulverization of the silicon-based material or the negative electrode active material.
  • the porosity of the matrix material is 30%-60%, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60% or any range thereof.
  • the porosity of the matrix material is 40%-50%.
  • the porosity of the matrix material is within the above range, it is conducive to accommodating sufficient silicon-based materials, thereby facilitating improving the energy density of the secondary battery.
  • the matrix material includes one or more of a carbon material, a graphite material, and a transition metal oxide material. These matrix materials all include a plurality of pore structures, thereby relieving the volume expansion of the silicon-based material and improving the conductivity of the silicon-based material.
  • the matrix material includes a transition metal oxide material.
  • the pore structure of the transition metal oxide material is controllable and adjustable, and the pore size is more uniform, which is conducive to the uniform dispersion of the silicon-based material.
  • the molecular formula of the transition metal oxide is M x O y , 0 ⁇ x ⁇ 2, 0 ⁇ y ⁇ 3, and M includes one or more elements selected from Ni, Co, Mn, Ti and Cu.
  • the transition metal oxide includes one or more selected from NiO, Ni 2 O 3 , CoO, Co 2 O 3 , MnO, Mn 2 O 3 , TiO, TiO 2 , Ti 2 O 3 , Cu, Cu 2 O and CuO.
  • the matrix material includes a graphite material, such as natural graphite, which can not only alleviate the volume expansion of the silicon-based material and improve the conductivity of the silicon-based material, but also promote the transmission of active ions and improve the specific capacity of the negative electrode active material.
  • a graphite material such as natural graphite
  • the matrix material includes a carbon material
  • the carbon material includes one or more of activated carbon, biomass carbon, pyrolytic carbon, and resin carbon.
  • the carbon material includes one or more of activated carbon, biomass carbon, pyrolytic carbon, and resin carbon.
  • the negative electrode active material further includes a coating layer, and the coating layer is located on at least a portion of the surface of the base material.
  • the coating layer is located on the outside of the negative electrode active material, thereby further preventing the silicon-based material from directly contacting the electrolyte and reducing the reactivity of the silicon-based material after contact with air, thereby reducing electrolyte side reactions, reducing active ion consumption, and improving the cycle performance of the secondary battery.
  • the coating layer can also buffer the volume expansion of the silicon-based material, which is also conducive to improving the storage performance of the secondary battery.
  • the coating layer includes one or more of a carbon material, a conductive polymer, a metal oxide, and a metal sulfide.
  • the carbon material includes one or more of hard carbon, soft carbon, graphene, carbon fiber, and carbon nanotubes.
  • the conductive polymer includes one or more of polyaniline, polypyrrole, and polythiophene.
  • the metal oxide includes one or more of iron oxide, zinc oxide, tin oxide, copper oxide, and titanium oxide.
  • the metal sulfide includes one or more of tin sulfide, molybdenum sulfide, titanium sulfide, iron sulfide, and copper sulfide.
  • the coating layer includes a carbon material, and optionally, the carbon material includes one or more of hard carbon, soft carbon, graphene, carbon fiber, and carbon nanotubes.
  • the coating layer can also contribute part of the capacity and increase the specific capacity of the negative electrode active material.
  • the coating layer includes a carbon material, it also helps to improve the conductivity of the silicon-based material.
  • the coating layer has a thickness of 0 nm to 200 nm, optionally 10 nm to 200 nm, 10 nm to 180 nm, or 10 nm to 150 nm.
  • the coating layer has a thickness within the above range, it is beneficial for the negative electrode active material to have a high specific capacity and low volume expansion.
  • the coating layer has a thickness of 0 nm, it means that the negative electrode active material does not have a coating layer.
  • the negative electrode active material includes carbon and silicon.
  • the mass percentage of carbon in the negative electrode active material is 40wt%-60wt%, for example, it can be 40wt%, 42wt%, 44wt%, 46wt%, 48wt%, 50wt%, 52wt%, 54wt%, 56wt%, 58wt%, 60wt% or any range of the above values.
  • the mass percentage of carbon in the negative electrode active material is 45wt%-50wt%.
  • the mass percentage of silicon in the negative electrode active material is 38wt%-58wt%, for example, it can be 40wt%, 42wt%, 44wt%, 46wt%, 48wt%, 50wt%, 52wt%, 54wt%, 56wt%, 58wt% or any range of the above values.
  • the mass percentage of silicon in the negative electrode active material is 40wt%-55wt%.
  • the negative electrode active material When the content of carbon element and/or silicon element in the negative electrode active material is within the above range, it is beneficial for the negative electrode active material to have both high specific capacity and high conductivity.
  • the carbon content in the negative electrode active material can be tested with reference to GB/T 20123-2006/ISO 15350:2000, and the testing instrument can be HCS-140 infrared carbon-sulfur analyzer.
  • the silicon content in the negative electrode active material can be tested with reference to GB/T20975.5-2020.
  • the negative electrode active material includes other elements in addition to carbon and silicon, and the other elements include one or more of oxygen, metal and nitrogen.
  • the distribution area of the other elements is not specifically limited, for example, the other elements may be located in at least one of the coating layer, the silicon-based material and the matrix material.
  • the sum of the mass percentages of other elements in the negative electrode active material is 0wt%-20wt%, optionally 0wt%-10wt%, 0wt%-5wt%.
  • the sum of the mass percentages of other elements in the negative electrode active material is 0wt%, it means that the negative electrode active material does not include elements other than carbon and silicon.
  • the pore volume of the negative electrode active material is 0.001 cm 3 /g-0.02 cm 3 /g, and can be 0.01 cm 3 /g-0.02 cm 3 /g.
  • the internal voids of the negative electrode active material are within a suitable range, which can improve the specific capacity and first coulombic efficiency of the negative electrode active material on the one hand, and buffer the stress generated during the expansion of the silicon-based material on the other hand.
  • the pore volume of the negative electrode active material has a well-known meaning in the art and can be measured by instruments and methods well-known in the art. For example, it can be tested with reference to GB/T 21650.2-2008.
  • the testing instrument can be the TRISTAR II 3020 Specific Surface Area and Porosity Analyzer of Micromeritics, USA.
  • the average particle size Dv50 of the negative electrode active material is 4 ⁇ m-12 ⁇ m.
  • the average particle size Dv50 of the negative electrode active material helps to reduce surface activity, reduce interface side reactions, reduce SEI film formation consumption, and is also beneficial to improve active ion and electron transport performance, thereby further improving the cycle performance of the secondary battery.
  • the average particle size Dv50 of the negative electrode active material has a well-known meaning in the art, which indicates the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 50%, and can be measured by instruments and methods known in the art. For example, it can be conveniently measured by a laser particle size analyzer with reference to GB/T 19077-2016.
  • the test instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.
  • the BET specific surface area of the negative electrode active material is 1m 2 /g-15m 2 /g.
  • the BET specific surface area of the negative electrode active material is within the above range, it helps to reduce surface activity, reduce interface side reactions, reduce SEI film formation consumption, and improve the first coulombic efficiency and cycle performance of the secondary battery.
  • the BET specific surface area of the negative electrode active material has a well-known meaning in the art and can be measured by instruments and methods well-known in the art. For example, it can be tested by nitrogen adsorption specific surface area analysis test method with reference to GB/T 19587-2017 and calculated by BET (Brunauer Emmett Teller) method.
  • the nitrogen adsorption specific surface area analysis test can be performed by TRISTAR II 3020 specific surface area and porosity analyzer of Micromeritics, USA.
  • a second aspect of the embodiments of the present application provides a method for preparing a negative electrode active material, which can prepare the negative electrode active material of the first aspect of the embodiments of the present application.
  • the method comprises the following steps: providing a matrix material comprising a plurality of pore structures; dispersing a silicon-based material into the pore structures of the matrix material, so as to obtain a negative electrode active material, wherein the negative electrode active material comprises a matrix material and a silicon-based material, the matrix material comprises a plurality of pore structures, at least a portion of the silicon-based material is located in the pore structures of the matrix material, the silicon-based material comprises a crystalline silicon-based material, an area formed by a distance extending from the outer surface of a particle of the negative electrode active material toward the inside of the particle by 0.5 times the length between any point on the outer surface of the particle and the core of the particle is recorded as an outer area, an area inside the outer area is recorded as an inner area, and in a cross-sectional image of the negative electrode active material, a total cross-sectional area of the crystalline silicon-based material in the outer area is smaller than a total cross-sectional area of the crystalline silicon-based material in the inner area
  • the porosity of the matrix material is 30%-60%, and can be optionally 40%-50%.
  • the porosity of the matrix material is within the above range, it is conducive to the smooth progress of the deposition process, and it is also conducive to the negative electrode active material having a suitable silicon content, a suitable specific surface area and/or a suitable pore volume.
  • the porosity of the matrix material When the porosity of the matrix material is too small, part of the silicon-based material is easily deposited on the surface of the matrix material, affecting the first coulombic efficiency of the negative electrode active material; when the porosity of the matrix material is too large, it is easy to have insufficient silicon-based material deposition and cause the negative electrode active material to have a large specific surface area, thereby increasing the interface side reaction, increasing the irreversible consumption of active ions, and reducing the first coulombic efficiency of the negative electrode active material.
  • the average particle size Dv50 of the matrix material is 4 ⁇ m-12 ⁇ m.
  • the average particle size Dv50 of the matrix material is within the above range, it is conducive to the smooth progress of the deposition process, and it is also conducive to the negative electrode active material having a suitable silicon content, a suitable specific surface area and/or a suitable pore volume.
  • the average particle size Dv50 of the matrix material When the average particle size Dv50 of the matrix material is too small, the deposition effect of the silicon-based material is poor, which is not conducive to the subsequent two-stage deposition; when the average particle size Dv50 of the matrix material is too large, it is easy to have insufficient silicon-based material deposition and cause the negative electrode active material to have a large specific surface area, thereby increasing the interface side reaction, increasing the irreversible consumption of active ions, and reducing the first coulomb efficiency of the negative electrode active material.
  • the matrix material includes one or more of a carbon material, a graphite material, and a transition metal oxide material.
  • the matrix material includes a carbon material
  • the carbon material includes one or more of activated carbon, biomass carbon, pyrolytic carbon, and resin carbon.
  • the matrix material can be obtained by commercial purchase or prepared according to methods known in the art, for example, by high temperature pyrolysis of an organic carbon source or by chemical activation treatment.
  • the organic carbon source may include one or more of a biomass material and a polymer material.
  • the chemical activation treatment may be obtained by using a pore-forming agent (e.g., an alkaline solution) to form pores in the matrix material (e.g., a carbon material).
  • a pore-forming agent e.g., an alkaline solution
  • the step of dispersing the silicon-based material into the pore structure of the base material comprises the following steps: placing the base material including a plurality of pore structures as a substrate in a reaction furnace, introducing a first mixed gas containing a silicon source gas, and depositing the material at a first temperature T 1 for a first time t 1 , and then stopping the introduction of the first mixed gas; after the temperature in the furnace drops to a second temperature T 2 , introducing a second mixed gas containing a silicon source gas, and depositing the material at a second temperature T 2 for a second time t 2 , and then obtaining a negative electrode active material, wherein the silicon-based material comprises a crystalline silicon-based material and an amorphous silicon-based material, and in a cross-sectional image of the negative electrode active material, the total cross-sectional area of the crystalline silicon-based material in the outer region is smaller than the total cross-sectional area of the crystalline silicon-based material in the inner region, and the total cross-
  • the process of dispersing the silicon-based material into the pore structure of the matrix material is a vapor deposition process, which includes a chemical vapor deposition process and a physical vapor deposition process, and can be optionally a chemical vapor deposition process, for example, any one of a thermal chemical vapor deposition process, a plasma enhanced chemical vapor deposition process, and a microwave plasma assisted chemical vapor deposition process.
  • the reaction furnace includes but is not limited to any one of a deposition furnace, a rotary furnace, a tubular furnace, and a fluidized bed.
  • the present application adopts a two-stage vapor deposition process to deposit crystalline silicon-based materials and amorphous silicon-based materials in the pore structure of the base material in batches.
  • the vapor deposition process is conducive to better deposition and uniform dispersion of silicon-based materials in the pore structure of the base material, and can avoid the problem of silicon-based materials agglomerating and/or being deposited in large quantities on the surface of the base material.
  • the method before the first mixed gas containing the silicon source gas is introduced, the method further comprises the step of placing a base material including a plurality of pore structures as a substrate in a reaction furnace, and performing a purging treatment and a pre-heating treatment using a protective gas, wherein the pre-heating temperature is optionally 200° C.-300° C. This is conducive to removing the remaining moisture in the base material, and further facilitates the subsequent smooth deposition and formation of a crystalline silicon-based material.
  • the volume proportion V1 of the silicon source gas in the first mixed gas is greater than the volume proportion V2 of the silicon source gas in the second mixed gas.
  • T 1 >T 2 .
  • t 1 ⁇ t 2 in the step of dispersing the silicon-based material into the pore structure of the matrix material, t 1 ⁇ t 2 .
  • the first temperature during deposition to be greater than the second temperature
  • the pressure in the furnace can be adjusted to a slightly positive pressure, for example, 200Pa-600Pa higher than the atmospheric pressure, thereby facilitating a smooth deposition process.
  • the first mixed gas includes a silicon source gas and a protective gas.
  • the volume proportion V1 of the silicon source gas in the first mixed gas is 10%-50%, for example, it can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or any range consisting of the above values.
  • the total gas flow rate of the first mixed gas is 0.5 L/min-20 L/min.
  • it can be 1 L/min, 2 L/min, 3 L/min, 4 L/min, 5 L/min, 6 L/min, 7 L/min, 8 L/min, 9 L/min, 10 L/min, 12 L/min, 14 L/min, 16 L/min, 18 L/min, 20 L/min or any range thereof.
  • the first temperature T1 is 500°C-700°C, for example, it can be 520°C, 540°C, 560°C, 580°C, 600°C, 620°C, 640°C, 660°C, 680°C, 700°C or any range thereof.
  • the first time t1 is 0.5h-8h, for example, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h or any range thereof.
  • the first time t1 is 0.5h-4h.
  • the composition ratio of the first mixed gas By adjusting at least one of the composition ratio of the first mixed gas, the total gas flow rate of the first mixed gas, the first temperature and the first time within the above-mentioned range, it is beneficial to form a crystalline silicon-based material, and is also beneficial to adjust the distribution area, grain size, deposition amount and other parameters of the crystalline silicon-based material.
  • the deposition amount of the crystalline silicon-based material may be insufficient, which is not conducive to the improvement of the first coulombic efficiency of the secondary battery;
  • the first temperature is too low, it is not conducive to the formation of crystalline silicon-based materials;
  • the first temperature is too high, the grain size of the silicon-based material increases, which is not conducive to the improvement of the cycle performance and storage performance of the secondary battery;
  • the deposition amount of the crystalline silicon-based material may be insufficient, which is not conducive to the improvement of the first coulombic efficiency of the secondary battery; when the first temperature is too low, it is not conducive to the formation of crystalline silicon-based materials; when the first temperature is too high, the grain size of the silicon-based material increases, which is not conducive to the improvement of the cycle performance and storage performance of the secondary battery; when the first time is too short, the deposition amount of the crystalline silicon-based material may be insufficient, which is not conducive to the improvement of the first coulombic efficiency of the secondary battery; when the
  • the pressure in the furnace can be adjusted to a slightly positive pressure, for example, 200Pa-600Pa higher than the atmospheric pressure, thereby facilitating a smooth deposition process.
  • the second mixed gas may include a silicon source gas and a protective gas.
  • the volume proportion V2 of the silicon source gas in the second mixed gas is 5%-20%, for example, it can be 5%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20% or any range consisting of the above values.
  • the second mixed gas may include a silicon source gas, a carbon source gas and a protective gas.
  • the volume proportion V2 of the silicon source gas in the second mixed gas is 5%-20%, and the volume proportion of the carbon source gas is 5%-10%.
  • the total gas flow rate of the second mixed gas is 0.5 L/min-20 L/min.
  • it can be 1 L/min, 2 L/min, 3 L/min, 4 L/min, 5 L/min, 6 L/min, 7 L/min, 8 L/min, 9 L/min, 10 L/min, 12 L/min, 14 L/min, 16 L/min, 18 L/min, 20 L/min or any range thereof.
  • the second temperature T2 is 400°C-500°C, for example, 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C or any range thereof.
  • the second time t2 is 2h-16h, for example, it can be 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h or any range thereof.
  • the second time t2 is 4h-16h.
  • the composition ratio of the second mixed gas By adjusting at least one of the composition ratio of the second mixed gas, the total gas flow rate of the second mixed gas, the second temperature and the second time within the above-mentioned range, it is beneficial to form amorphous silicon-based materials, and is also beneficial to adjust parameters such as the distribution area and deposition amount of the amorphous silicon-based materials.
  • the amorphous silicon-based material may be deposited on the surface of the base material, which may increase the difficulty of preparing the negative electrode slurry, and may also increase the interface side reactions and the irreversible consumption of active ions;
  • the deposition amount of the amorphous silicon-based material may be insufficient, resulting in a larger specific surface area of the negative electrode active material, increased interface side reactions, increased irreversible consumption of active ions, and reduced first coulombic efficiency; when the second temperature is too low, the surface area of the negative electrode active material may be larger, the interface side reactions may increase, the irreversible consumption of active ions may increase, and the first coulombic efficiency may decrease.
  • the deposition effect of silicon-based materials is poor, and effective deposition cannot be carried out; when the second temperature is too high, crystalline silicon-based materials are easily formed, which is not conducive to the improvement of the cycle performance and storage performance of the secondary battery; when the second time is too short, the deposition amount of amorphous silicon-based materials may be insufficient, resulting in a larger specific surface area of the negative electrode active material, increased interface side reactions, increased irreversible consumption of active ions, and reduced first coulombic efficiency; when the second time is too long, amorphous silicon-based materials may be deposited on the surface of the matrix material, which may increase the difficulty of preparing the negative electrode slurry, and may also increase interface side reactions and irreversible consumption of active ions.
  • the total gas flow rate of the second mixed gas may be the same as the total gas flow rate of the first mixed gas.
  • the method further comprises the step of forming a coating layer on at least a surface of the obtained negative electrode active material, wherein the coating layer comprises one or more of a carbon material, a conductive polymer, a metal oxide and a metal sulfide.
  • the method of forming the coating layer on at least the surface of the obtained negative electrode active material is not particularly limited and can be selected according to the composition of the coating layer.
  • any of solid phase coating, liquid phase coating or gas phase coating can be used.
  • the step of forming the coating layer comprises the following steps: mixing the obtained negative electrode active material with the coating material and subjecting the mixture to carbonization treatment.
  • the coating material comprises one or more of asphalt (such as coal tar, petroleum asphalt, etc.) and polymer materials.
  • the temperature of the carbonization treatment is 500°C-1000°C.
  • the step of forming the coating layer includes the following steps: placing the obtained negative electrode active material in a reaction furnace, introducing a third mixed gas containing a carbon source gas, and depositing the negative electrode active material at a third temperature T 3 for a third time t 3 to obtain a carbon-coated negative electrode active material, thereby facilitating the formation of a uniform carbon layer.
  • the third mixed gas includes a carbon source gas and a protective gas.
  • the volume proportion V3 of the carbon source gas in the third mixed gas is 10%-50%, for example, it can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or any range consisting of the above values.
  • the total gas flow rate of the third mixed gas is 0.5 L/min-20 L/min.
  • it can be 1 L/min, 2 L/min, 3 L/min, 4 L/min, 5 L/min, 6 L/min, 7 L/min, 8 L/min, 9 L/min, 10 L/min, 12 L/min, 14 L/min, 16 L/min, 18 L/min, 20 L/min or any range thereof.
  • the third temperature T3 is 600°C-700°C, for example, it can be 600°C, 610°C, 620°C, 630°C, 640°C, 650°C, 660°C, 670°C, 680°C, 690°C, 700°C or any range thereof.
  • the third time t3 is 0.5h-2h, for example, it can be 0.5h, 0.6h, 0.8h, 1h, 1.2h, 1.4h, 1.6h, 1.8h, 2h or any range thereof.
  • the composition ratio of the third mixed gas By adjusting at least one of the composition ratio of the third mixed gas, the total gas flow rate of the third mixed gas, the third temperature and the third time within the above range, it is beneficial to form a coating layer of appropriate thickness, thereby avoiding the coating layer being too thick to reduce the first coulombic efficiency and/or specific capacity of the negative electrode active material.
  • the term "protective gas” includes nitrogen and rare gases, and the rare gas may include one or more of argon, helium, and the like.
  • the term "silicon source gas” refers to a gas that can form the silicon-based material of the present application.
  • the silicon source gas includes but is not limited to monosilane (H 4 Si), disilane (H 6 Si 2 ), trisilane (H 8 Si 3 ), silicon tetrachloride (Cl 4 Si), trichlorosilane (Cl 3 HSi), dichlorosilane (Cl 2 H 2 Si), chlorosilane (ClH 3 Si), silicon tetrafluoride (F 4 Si), trifluorosilane (F 3 HSi), difluorosilane (F 2 H 2 Si), fluorosilane (FH 3 Si), hexachlorodisilane (Cl 6 Si 2 ), pentachlorodisilane (Cl 5 HSi 2 ), tetrachlorodisilane (Cl 4 H 2 Si 2 , including 1,1,2,2 -tetrachlorodisi
  • carbon source gas refers to a gas that can form a carbon material.
  • the carbon source gas includes but is not limited to one or more of methane, ethane, propane, isopropane, butane, isobutane, ethylene, propylene, butene, acetylene, ethyl chloride, ethyl fluoride, difluoroethane, methyl chloride, methyl fluoride, difluoromethane, trifluoromethane, vinyl chloride, vinyl fluoride, difluoroethylene, methylamine, formaldehyde, benzene, toluene, xylene, styrene and phenol.
  • a third aspect of the embodiments of the present application provides a secondary battery.
  • the secondary battery mentioned in the embodiments or implementations of the present application refers to a single physical module including one or more battery cells to provide higher voltage and capacity.
  • the secondary battery mentioned in the present application may include a battery cell, a battery module or a battery pack, etc.
  • a battery cell is the smallest unit that makes up a secondary battery, which can realize the function of charging and discharging alone.
  • the present application has no particular restrictions on the shape of the battery cell, which can be cylindrical, square or any other shape.
  • Figure 2 is a battery cell 5 of a square structure as an example.
  • the battery cell includes an electrode assembly and an electrolyte
  • the single cell may further include an outer package.
  • the electrode assembly may be made of a positive electrode sheet, a negative electrode sheet, and a separator by a winding process and/or a lamination process, and the outer package may be used to encapsulate the above-mentioned electrode assembly.
  • the outer package may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.
  • the outer package may also be a soft package, such as a bag-type soft package.
  • the material of the soft package may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT) and polybutylene succinate (PBS).
  • the outer package may include a shell 51 and a cover plate 53.
  • the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate are enclosed to form a receiving cavity.
  • the shell 51 has an opening connected to the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity.
  • the electrode assembly 52 is encapsulated in the receiving cavity.
  • the number of electrode assemblies 52 contained in the battery cell 5 can be one or more, which can be adjusted according to needs.
  • battery cells can be assembled into a battery module, and the number of battery cells contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.
  • FIG. 3 is a schematic diagram of a battery module 4 as an example. As shown in FIG. 4, in the battery module 4, multiple battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other manner. The multiple battery cells 5 can be further fixed by fasteners.
  • the battery module 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.
  • the battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.
  • Figures 5 and 6 are schematic diagrams of a battery pack 1 as an example.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box.
  • the battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 is used to cover the lower box body 3 and form a closed space for accommodating the battery modules 4.
  • Multiple battery modules 4 can be arranged in the battery box in any manner.
  • secondary batteries may include but are not limited to lithium-ion batteries, sodium-ion batteries, and the like.
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector and including a negative electrode active material.
  • the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.
  • the negative electrode film layer includes the negative electrode active material of the first aspect of the embodiment of the present application or the negative electrode active material prepared by the method described in the second aspect of the embodiment of the present application. This enables the secondary battery to have high energy density, high first coulombic efficiency, long cycle life and long storage life.
  • the negative electrode film layer may further include other negative electrode active materials in addition to the above-mentioned negative electrode active materials.
  • the other negative electrode active materials include but are not limited to natural graphite, artificial graphite, soft carbon, hard carbon, elemental silicon, silicon oxide, silicon nitrogen compound, silicon alloy material, elemental tin, tin oxide, tin alloy material, and one or more of lithium titanate. The present application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials for secondary batteries may also be used.
  • the negative electrode film layer may further include a negative electrode conductive agent.
  • a negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the negative electrode film layer may further include a negative electrode binder.
  • the negative electrode binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).
  • SBR styrene-butadiene rubber
  • SR-1B water-soluble unsaturated resin
  • PAM polyacrylamide
  • PVA polyvinyl alcohol
  • SA sodium alginate
  • CMCS carboxymethyl chitosan
  • the negative electrode film layer may also optionally include other additives.
  • other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.
  • the negative electrode current collector may be a metal foil or a composite current collector.
  • the metal foil copper foil may be used.
  • the composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer.
  • the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy.
  • the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).
  • the negative electrode film layer is usually formed by coating the negative electrode slurry on the negative electrode current collector, drying and cold pressing.
  • the negative electrode slurry is usually formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional auxiliary agents in a solvent and stirring them uniformly.
  • the solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.
  • the negative electrode plate does not exclude other additional functional layers in addition to the negative electrode film layer.
  • the negative electrode plate described in the present application may also include a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode plate described in the present application may also include a protective layer covering the surface of the negative electrode film layer.
  • a conductive primer layer e.g., composed of a conductive agent and a binder
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector and including a positive electrode active material.
  • the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.
  • the positive electrode film layer includes a positive electrode active material, and the positive electrode active material can be a positive electrode active material for a secondary battery known in the art.
  • the positive electrode active material may include one or more of a lithium transition metal oxide, a lithium phosphate containing an olivine structure, and their respective modified compounds.
  • lithium transition metal oxides may include one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds.
  • lithium phosphate containing an olivine structure may include one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, and their respective modified compounds.
  • the present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for secondary batteries may also be used.
  • the positive electrode active material for the lithium ion battery may include one or more of a lithium transition metal oxide and a modified compound thereof of the general formula Li a Ni b Co c M d O e A f . 0.8 ⁇ a ⁇ 1.2, 0.5 ⁇ b ⁇ 1, 0 ⁇ c ⁇ 1, 0 ⁇ d ⁇ 1, 1 ⁇ e ⁇ 2, 0 ⁇ f ⁇ 1, M includes one or more selected from Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A includes one or more selected from N, F, S and Cl.
  • a positive electrode active material for a lithium ion battery may include one or more of LiCoO2 , LiNiO2 , LiMnO2 , LiMn2O4 , LiNi1/3Co1/ 3Mn1 / 3O2 ( NCM333 ) , LiNi0.5Co0.2Mn0.3O2 ( NCM523 ) , LiNi0.6Co0.2Mn0.2O2 ( NCM622 ) , LiNi0.8Co0.1Mn0.1O2 ( NCM811), LiNi0.85Co0.15Al0.05O2 , LiFePO4 , and LiMnPO4 .
  • the positive electrode active material may include but is not limited to one or more of sodium-containing transition metal oxides, polyanion materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian blue materials.
  • the positive active material for a sodium ion battery may include one or more of NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, NaNi1/2Ti1/2O2, NaNi1/2Mn1/2O2, Na2/3Fe1/3Mn2/3O2 , NaNi1 / 3Co1 / 3Mn1 / 3O2 , NaFePO4 , NaMnPO4 , NaCoPO4 , Prussian blue - based materials, and materials of the general formula XpM'q ( PO4 ) rOxY3 -x .
  • X includes one or more selected from H + , Li + , Na + , K + and NH4 + , M ' is a transition metal cation, which may be selected from one or more selected from V, Ti, Mn, Fe, Co, Ni, Cu and Zn, and Y is a halogen anion, which may be selected from one or more selected from F, Cl and Br.
  • the modified compound of each positive electrode active material mentioned above may be a compound obtained by doping and/or surface coating the positive electrode active material.
  • the positive electrode film layer may further include a positive electrode conductive agent.
  • a positive electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the positive electrode film layer may further include a positive electrode binder.
  • the positive electrode binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin.
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • PTFE polytetrafluoroethylene
  • vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • the metal foil aluminum foil may be used.
  • the composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer.
  • the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy.
  • the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).
  • the positive electrode film layer is usually formed by coating the positive electrode slurry on the positive electrode current collector, drying and cold pressing.
  • the positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder and any other components in a solvent and stirring them uniformly.
  • the solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.
  • the electrolyte plays a role in conducting active ions between the positive electrode plate and the negative electrode plate.
  • the present application has no specific restrictions on the type of the electrolyte, which can be selected according to needs.
  • the electrolyte can include one or more selected from solid electrolytes and liquid electrolytes (i.e., electrolytes).
  • the electrolyte is an electrolyte solution
  • the electrolyte solution includes an electrolyte salt and a solvent.
  • the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium bisoxalatoborate (LiBOB), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).
  • LiPF 6 lithium hexafluorophosphate
  • LiBF 4 lithium perchlorate
  • the electrolyte salt may include one or more of sodium hexafluorophosphate (NaPF 6 ), sodium tetrafluoroborate (NaBF 4 ), sodium perchlorate (NaClO 4 ), sodium hexafluoroarsenate (NaAsF 6 ), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalatoborate (NaDFOB), sodium dioxalatoborate (NaBOB), sodium difluorophosphate (NaPO 2 F 2 ), sodium difluorobis(oxalatophosphate) (NaDFOP) and sodium tetrafluorooxalato
  • the solvent may include ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sul
  • the electrolyte may further include additives, for example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high temperature performance, additives that improve battery low temperature power performance, etc.
  • the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high temperature performance, additives that improve battery low temperature power performance, etc.
  • Secondary batteries using electrolytes and some secondary batteries using solid electrolytes also include a separator.
  • the separator is arranged between the positive electrode plate and the negative electrode plate, and mainly plays the role of preventing the positive and negative electrodes from short-circuiting, while allowing active ions to pass through.
  • the present application has no particular restrictions on the type of separator, and any known porous structure separator with good chemical stability and mechanical stability can be selected.
  • the material of the isolation membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the isolation membrane may be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer are the same or different.
  • the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte can be assembled to form a secondary battery.
  • the positive electrode sheet, the separator, and the negative electrode sheet can be formed into an electrode assembly through a winding process and/or a lamination process, and the electrode assembly is placed in an outer package, and the electrolyte is injected after drying. After vacuum packaging, standing, formation, shaping and other processes, a battery cell is obtained.
  • Multiple battery cells can also be further connected in series, in parallel or in mixed connection to form a battery module.
  • Multiple battery modules can also be connected in series, in parallel or in mixed connection to form a battery pack. In some embodiments, multiple battery cells can also directly form a battery pack.
  • the present application also provides an electrical device, which includes the secondary battery of the present application.
  • the secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device.
  • the electrical device can be, but is not limited to, a mobile device (such as a mobile phone, a tablet computer, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc.
  • the electrical device may select a specific type of secondary battery, such as a battery cell, a battery module or a battery pack, according to its usage requirements.
  • Fig. 7 is a schematic diagram of an electric device as an example.
  • the electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.
  • a battery pack or a battery module can be used as a power source.
  • the electric device may be a mobile phone, a tablet computer, a notebook computer, etc.
  • the electric device is usually required to be light and thin, and a battery cell may be used as a power source.
  • Pause the introduction of the first mixed gas wait for the furnace temperature to drop to 450°C, introduce the second mixed gas according to 15% monosilane + 85% argon (volume ratio), the total gas flow rate is 2L/min, and continue to deposit for 8h. Turn off the second mixed gas, heat it to 650°C again, and introduce the third mixed gas according to 20% acetylene + 80% argon (volume ratio), the total gas flow rate is 2L/min, the deposition time is 0.5h, and after the end, cool, discharge, and pass through a 325 mesh sieve to obtain a negative electrode active material.
  • the negative electrode active material prepared above is mixed evenly with the conductive agent conductive carbon black and carbon nanotubes, and the binder polyacrylic acid in a mass ratio of 95:1.9:0.1:3, added to the solvent deionized water, and stirred under the action of a fast mixer until the system is uniform to obtain a negative electrode slurry with a solid content of 45%; the negative electrode slurry is evenly coated on the negative electrode collector copper foil and dried at 85°C and cold pressed to obtain a negative electrode sheet.
  • the positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), the conductive agent carbon black (Super P), and the binder polyvinylidene fluoride (PVDF) are fully stirred and mixed in a proper amount of solvent NMP at a mass ratio of 97:1:2 to form a uniform positive electrode slurry; the positive electrode slurry is evenly coated on the surface of the positive electrode current collector aluminum foil, and after drying and cold pressing, the positive electrode sheet is obtained.
  • Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed evenly in a volume ratio of 20:20:60 as an organic solvent, then LiPF6 is dissolved in the above organic solvent, and fluoroethylene carbonate (FEC) is added.
  • the concentration of LiPF6 in the electrolyte is 1 mol/L, and the mass percentage of FEC is 5wt%.
  • Preparation of secondary batteries stack and wind the positive electrode sheet, separator, and negative electrode sheet in order to obtain an electrode assembly; place the electrode assembly in an outer package, inject electrolyte after drying, and obtain a secondary battery through vacuum packaging, standing, formation, shaping and other processes.
  • the negative electrode active material prepared above was mixed with the conductive agent conductive carbon black and the binder polyacrylic acid in a mass ratio of 8:1:1, added to the solvent deionized water, and stirred under the action of a rapid mixer until the system was uniform to obtain a negative electrode slurry with a solid content of 45%; the negative electrode slurry was evenly coated on the negative electrode current collector copper foil and dried and cold pressed at 85°C to obtain an electrode sheet.
  • a metal lithium sheet was used as the counter electrode, a Celgard 2400 isolation membrane was used, and the same electrolyte as in the preparation of the secondary battery was injected to assemble a button battery.
  • the preparation method of the secondary battery and button battery is similar to that of Example 1, except that the preparation process parameters of the negative electrode active material are adjusted, as shown in Table 1 for details.
  • the preparation methods of the secondary battery and button battery are similar to those of Example 1, except that the preparation process parameters of the negative electrode active material are adjusted.
  • Amorphous carbon-coated crystalline silicon is used as the negative electrode active material, and the coating layer thickness is 300nm.
  • the preparation methods of the secondary battery and button battery are similar to those of Example 1, except that the preparation process parameters of the negative electrode active material are adjusted.
  • 1kg of commercially available porous biomass carbon with a porosity of 45% was selected as the substrate, placed in a vapor deposition furnace, the furnace body rotation rate was maintained at 0.5rpm, argon was used for purging, and preheated to 200°C.
  • the furnace body rotation rate was maintained at 0.5rpm
  • argon was used for purging, and preheated to 200°C.
  • the total gas flow rate is 2L/min
  • the pressure in the furnace is a slightly positive pressure of 400Pa higher than the atmospheric pressure
  • the deposition time is 12h.
  • the preparation method of the secondary battery and button battery is similar to that of Example 1, except that the preparation process parameters of the negative electrode active material are adjusted.
  • the preparation method of the secondary battery and button battery is similar to that of Example 1, except that the preparation process parameters of the negative electrode active material are adjusted.
  • 1kg of commercially available porous biomass carbon with a porosity of 45% was selected as the substrate, placed in a vapor deposition furnace, the furnace body rotation rate was maintained at 0.5rpm, argon was used for purging, and the temperature was pre-heated to 200°C. The temperature was continued to rise to 450°C, and the first mixed gas was introduced according to 15% monosilane + 85% argon (volume ratio), the total gas flow rate was 2L/min, the pressure in the furnace was a slight positive pressure of 400Pa higher than the atmospheric pressure, and the deposition time was 8h.
  • the introduction of the first mixed gas was suspended, the temperature in the furnace was increased to 600°C, and the second mixed gas was introduced according to 30% monosilane + 70% argon (volume ratio), the total gas flow rate was 2L/min, and the deposition time was 4h.
  • the second mixed gas was turned off, the temperature was raised to 650°C again, and the third mixed gas was introduced according to 20% acetylene + 80% argon (volume ratio), the total gas flow rate was 2L/min, and the deposition time was 0.5h.
  • the material was cooled, discharged, and sieved through a 325-mesh sieve to obtain the negative electrode active material.
  • a double-beam focused ion beam microscope is used to cut a sample from the core of the negative electrode active material particle to obtain a cross-sectional image of the negative electrode active material particle, and then a high-resolution transmission electron microscope is used to observe and calculate the grain size of the crystalline silicon-based material.
  • the area with lattice fringe characteristics is taken as a grain, and the diameter of the area is taken as the grain size, and the average value of at least 50 grain sizes is taken as the test result.
  • the test instrument can be the Helios 5 CX focused ion beam/scanning electron microscope dual-beam system of Thermo Fisher Scientific and the Spectra S/TEM scanning transmission electron microscope of Thermo Fisher Scientific.
  • the grain area is calculated based on the grain shape being spherical, and the spherical diameter is calculated using the grain size.
  • the region extending from the outer surface of the negative electrode active material particle to the inside of the particle by 0.5 times the length between any point on the outer surface of the particle and the particle core is recorded as the outer region, and the region inside the outer region is recorded as the inner region.
  • the ratio of the total cross-sectional area of the crystalline silicon-based material in the outer region to the total cross-sectional area of the crystalline silicon-based material in the inner region is recorded as ⁇ 1
  • the ratio of the total cross-sectional area of the crystalline silicon-based material in the outer region of the above-mentioned cross-sectional image to the total cross-sectional area of the amorphous silicon-based material is recorded as ⁇ 1
  • the ratio of the total cross-sectional area of the crystalline silicon-based material in the inner region of the above-mentioned cross-sectional image to the total cross-sectional area of the amorphous silicon-based material is recorded as ⁇ 2
  • the ratio of the total cross-sectional area of the crystalline silicon-based material in the above-mentioned cross-sectional image to the total cross-sectional area of the negative electrode active material is recorded as ⁇ 1
  • the testing instrument can be HCS-140 infrared carbon-sulfur analyzer.
  • the volume particle size distribution curve of the negative electrode active material is obtained, and the particle size corresponding to the cumulative volume distribution percentage reaching 50% is taken as the average particle size Dv50.
  • the test instrument can be the Mastersizer 3000 laser particle size analyzer of Malvern Instruments Ltd., UK.
  • the nitrogen adsorption specific surface area analysis test method is used for testing, and the specific surface area of the negative electrode active material is calculated by the BET (Brunauer Emmett Teller) method.
  • the test instrument can be the TRISTAR II 3020 specific surface area and porosity analyzer of Micromeritics, USA.
  • the pore volume of the negative electrode active material is tested with reference to GB/T 21650.2-2008.
  • the testing instrument may be the TRISTAR II 3020 surface area and porosity analyzer from Micromeritics, USA.
  • the button battery prepared above was allowed to stand for 60 minutes, it was discharged at a constant current of 0.05C to 5mV, and then discharged at 50 ⁇ A to 5mV.
  • the total discharge capacity of the button battery was recorded as the initial lithium insertion capacity.
  • the button battery was charged at a constant current of 0.1C to 0.8V, and the charging capacity of the button battery was recorded as the initial lithium desorption capacity.
  • the first coulombic efficiency of the negative electrode active material initial lithium removal capacity/initial lithium insertion capacity.
  • the secondary battery prepared above is fully charged at 0.5C and then fully discharged at 1C. This is a cycle charge and discharge process.
  • the discharge capacity at this time is recorded as the initial discharge capacity.
  • the secondary battery is subjected to a cycle charge and discharge test according to the above method, and the discharge capacity after each cycle is recorded until the discharge capacity of the secondary battery decays to 80% of the initial discharge capacity.
  • the number of cycles at this time is used to characterize the cycle performance of the secondary battery. The higher the number of cycles of the secondary battery, the better the cycle performance.
  • the secondary battery prepared above was fully charged at 0.33C, then disassembled in a drying room to obtain the negative electrode sheet, and the thickness H1 of the negative electrode sheet in the fully charged state was recorded.
  • the volume expansion rate of the negative electrode sheet ( H1 - H0 )/ H0 , H0 represents the initial thickness of the negative electrode sheet after cold pressing.
  • the negative electrode active material provided by the present application can have high capacity, high first coulomb efficiency and low volume expansion, and can also make the secondary battery take into account high energy density, high first coulomb efficiency, long cycle life and long storage life.
  • the negative electrode active materials prepared in the above embodiments of the present application all meet the requirement that the total cross-sectional area of the crystalline silicon-based material in the outer region of the cross-sectional image is less than the total cross-sectional area of the crystalline silicon-based material in the inner region. It can be seen from the test results of Tables 2 and 3 that when the total cross-sectional area of the crystalline silicon-based material in the outer region of the cross-sectional image of the negative electrode active material is greater than the total cross-sectional area of the crystalline silicon-based material in the inner region, the cycle performance of the secondary battery is poor and the volume expansion is high, and the secondary battery cannot take into account high energy density, high first coulomb efficiency, long cycle life and long storage life.
  • the secondary battery using the negative electrode active material can better take into account high energy density, high first coulomb efficiency, long cycle life and long storage life.
  • Comparative Example 1 uses carbon-coated crystalline silicon as the negative electrode active material. Crystalline silicon has a huge volume effect, but the carbon layer on the surface has limited protective effect on the crystalline silicon. Moreover, the carbon layer will break after multiple charge and discharge cycles, which will lead to repeated destruction and reconstruction of the SEI film, increasing the irreversible consumption of active ions. Moreover, as the number of charge and discharge cycles increases, the thickness of the SEI film also increases, and the impedance of the secondary battery also increases. Therefore, the cycle performance of the secondary battery prepared in Comparative Example 1 is very poor.
  • the silicon-based material only includes crystalline silicon-based material, but does not include amorphous silicon-based material. Since the crystalline silicon-based material has a large volume expansion and poor structural stability, the secondary battery has poor cycle performance and high volume expansion, and the secondary battery cannot have high energy density, high first coulomb efficiency, long cycle life and long storage life.
  • the silicon-based material only includes amorphous silicon-based material, but does not include crystalline silicon-based material. Since the first coulomb efficiency of the amorphous silicon-based material is low, the actual capacity loss of the secondary battery is large, and thus the secondary battery cannot have high energy density, high first coulomb efficiency, long cycle life and long storage life.
  • the crystalline silicon-based material is located in the outer region of the negative electrode active material, while the amorphous silicon-based material is located in the inner region of the negative electrode active material, which results in poor cycle performance and high volume expansion of the secondary battery, and cannot enable the secondary battery to have high energy density, high first coulombic efficiency, long cycle life and long storage life.

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Abstract

本申请提供一种负极活性材料及其制备方法、以及包含其的二次电池及用电装置，所述负极活性材料包括基体材料以及硅基材料，所述基体材料包括多个孔结构，所述硅基材料的至少一部分位于所述基体材料的孔结构中，所述硅基材料包括晶态的硅基材料，由所述负极活性材料的颗粒外表面向颗粒内部延伸自所述颗粒外表面任一点与所述颗粒核心之间的长度的0.5倍的距离所构成的区域记为外部区域，所述外部区域内侧的区域记为内部区域，在所述负极活性材料的截面图像中，所述外部区域中的所述晶态的硅基材料的总截面积小于所述内部区域中的所述晶态的硅基材料的总截面积。本申请提供的二次电池能兼顾高能量密度、高首次库伦效率、长循环寿命和长存储寿命。

Description

负极活性材料及其制备方法、以及包含其的二次电池及用电装置 技术领域
本申请属于电池技术领域，具体涉及一种负极活性材料及其制备方法、以及包含其的二次电池及用电装置。
背景技术
近年来，二次电池被广泛应用于水力、火力、风力和太阳能电站等储能电源***，以及电动工具、电动自行车、电动摩托车、电动汽车、军事装备、航空航天等多个领域。在二次电池高速发展过程中对能量密度提出了更高的要求，石墨是二次电池最常用的负极活性材料，但是石墨的容量发挥已接近其理论比容量372mAh/g，硅由于具有高达4200mAh/g的理论比容量以及较低的成本而引起人们广泛关注，但是，硅在充放电过程中存在巨大的体积效应，易造成颗粒破碎、粉化，进而导致二次电池的首次库伦效率、循环性能和存储性能均较差。
发明内容
本申请的目的在于提供一种负极活性材料及其制备方法、以及包含其的二次电池及用电装置，所述负极活性材料具有高容量、高首次库伦效率和低体积膨胀，并且能使二次电池兼顾高能量密度、高首次库伦效率、长循环寿命和长存储寿命。
本申请第一方面提供一种负极活性材料，所述负极活性材料包括基体材料以及硅基材料，所述基体材料包括多个孔结构，所述硅基材料的至少一部分位于所述基体材料的孔结构中，所述硅基材料包括晶态的硅基材料，由所述负极活性材料的颗粒外表面向颗粒内部延伸自所述颗粒外表面任一点与所述颗粒核心之间的长度的0.5倍的距离所构成的区域记为外部区域，所述外部区域内侧的区域记为内部区域，在所述负极活性材料的截面图像中，所述外部区域中的所述晶态的硅基材料的总截面积小于所述内部区域中的所述晶态的硅基材料的总截面积。
本申请提供的负极活性材料包括具有多个孔结构的基体材料以及至少一部分位于基体材料的孔结构中的硅基材料，所述硅基材料包括晶态的硅基材料，并且在所述负极活性材料的截面图像中，所述外部区域中的所述晶态的硅基材料的总截面积小于所述内部区域中的所述晶态的硅基材料的总截面积，由此所述晶态的硅基材料主要位于所述负极活性材料的内部区域，进而本申请提供的负极活性材料能具有高容量、高首次库伦效率和低体积膨胀，并且能使二次电池兼顾高能量密度、高首次库伦效率、长循环寿命和长存储寿命。
在本申请的任意实施方式中，所述负极活性材料的截面图像包括经过所述负极活性材料的颗粒核心的截面图像。
在本申请的任意实施方式中，在所述负极活性材料的截面图像中，所述外部区域中的所述晶态的硅基材料的总截面积与所述内部区域中的所述晶态的硅基材料的总截面积之比α1为(0-50):100，可选为(0-10):100。通过使晶态的硅基材料主要位于负极活性材料的内部区域，既能够充分发挥晶态的硅基材料对首次库伦效率的提升作用，又能避免其对二次电池的循环性能和存储性能产生较大不利影响。
在本申请的任意实施方式中，所述硅基材料还包括非晶态的硅基材料，可选地，在所述负极活性材料的截面图像中，所述外部区域中的所述非晶态的硅基材料的总截面积大于所述内部区域中的所述非晶态的硅基材料的总截面积。通过使非晶态的硅基材料主要位于负极活性材料的外部区域，能充分发挥非晶态的硅基材料对循环性能的提升作用和对体积膨胀的降低作用。
在本申请的任意实施方式中，所述内部区域中的所述非晶态的硅基材料的总截面积与所述外部区域中的所述非晶态的硅基材料的总截面积之比α2为(0-30):100，可选为(0-10):100。负极活性材料的外部区域主要含有非晶态的硅基材料，不含或者含有少量晶态的硅基材料，由此既能够充分发挥晶态的硅基材料对首次库伦效率的提升作用，又能充分发挥非晶态的硅基材料对循环性能的提升作用和对体积膨胀的降低作用。
在本申请的任意实施方式中，在所述负极活性材料的截面图像的外部区域中，所述晶态的硅基材料的总截面积与所述非晶态的硅基材料的总截面积之比β1为(0-25):100，可选为(0-5):100，更可选地，所述晶态的硅基材料的总截面积为0。负极活性材料的外部区域主要含有非晶态的硅基材料，不含或者含有少量晶态的硅基材料，由此既能够充分发挥晶态的硅基材料对首次库伦效率的提升作用，又能充分发挥非晶态的硅基材料对循环性能的提升作用和对体积膨胀的降低作用。
在本申请的任意实施方式中，在所述负极活性材料的截面图像的内部区域中，所述晶态的硅基材料的总截面积与所述非晶态的硅基材料的总截面积之比β2为100:(0-250)，可选为100:(0-100)。负极活性材料的内部区域可以仅包含晶态的硅基材料，又可以同时包含晶态的硅基材料和非晶态的硅基材料的混合物，并且通过进一步调节晶态的硅基材料的总截面积与非晶态的硅基材料的总截面积在合适的范围内，能够更好地发挥晶态的硅基材料对首次库伦效率的提升作用。
在本申请的任意实施方式中，在所述负极活性材料的截面图像中，所述晶态的硅基材料的总截面积与所述负极活性材料的总截面积的比值γ1为大于0且小于等于25％，可选为5％-20％。当晶态的硅基材料的总截面积在上述范围内时，既能够充分发挥晶态的硅基材料对首次库伦效率的提升作用，又能够避免其对二次电池的循环性能和存储性能产生较大不利影响。
在本申请的任意实施方式中，在所述负极活性材料的截面图像中，所述非晶态的硅基材料的总截面积与所述负极活性材料的总截面积的比值γ2为大于等于35％且小于100％，可选为40％-60％。当非晶态的硅基材料的总截面积在上述范围内时，既能够充分发挥非晶态的硅基材料对循环性能的提升作用和对体积膨胀的降低作用，又能够避免其对二次电池的首次库伦效率产生较大不利影响。
在本申请的任意实施方式中，所述硅基材料中的所述晶态的硅基材料的质量百分含量为大于0且小于等于40wt％，可选为10wt％-30wt％。当晶态的硅基材料的含量在上述 范围内时，既能够充分发挥晶态的硅基材料对首次库伦效率的提升作用，又能避免其对二次电池的循环性能和存储性能产生较大不利影响。
在本申请的任意实施方式中，所述硅基材料的至少一部分位于所述基体材料的孔结构中，并且所述硅基材料与所述基体材料之间具有空隙。当硅基材料与基体材料之间具有空隙时，该部分孔隙可以作为容纳硅基材料体积膨胀的空间，缓冲硅基材料膨胀过程中产生的应力。
在本申请的任意实施方式中，所述晶态的硅基材料的晶粒尺寸为大于0且小于等于10nm，可选为2nm-8nm。当晶态的硅基材料具有合适的晶粒尺寸时，既能提升二次电池的首次库伦效率，同时又能避免对二次电池的循环性能和存储性能产生较大不利影响。
在本申请的任意实施方式中，所述晶态的硅基材料包括晶态的单质硅、硅氧化物、硅碳材料、硅氮复合物和硅合金材料中的一种或多种，可选地，所述晶态的硅基材料包括晶态的单质硅。
在本申请的任意实施方式中，所述非晶态的硅基材料包括非晶态的单质硅、硅氧化物、硅碳材料、硅氮复合物和硅合金材料中的一种或多种，可选地，所述非晶态的硅基材料包括非晶态的单质硅。
在本申请的任意实施方式中，所述硅基材料包括气相沉积硅基材料，可选地包括气相沉积单质硅。
在本申请的任意实施方式中，所述基体材料的孔隙率为30％-60％，可选为40％-50％。当基体材料的孔隙率在上述范围内时，有利于容纳足够的硅基材料，进而有利于提升二次电池的能量密度。
在本申请的任意实施方式中，所述基体材料包括碳材料、石墨材料和过渡金属氧化物材料中的一种或多种。
在本申请的任意实施方式中，所述基体材料包括碳材料，所述碳材料包括活性碳、生物质碳、热解碳和树脂碳中的一种或多种。由此除了可以起到缓解硅基材料的体积膨胀、提高硅基材料的导电性之外，还可以促进活性离子的传输，提高负极活性材料的比容量。并且与石墨材料相比，碳材料的多孔结构更均匀，由此还有利于硅基材料的分散。
在本申请的任意实施方式中，所述负极活性材料还包括包覆层，所述包覆层位于所述基体材料的至少部分表面。包覆层位于所述负极活性材料的外侧，由此可以进一步阻止硅基材料与电解液直接接触，降低硅基材料与空气接触后的反应活性，从而能够减少电解液副反应、降低活性离子消耗，提高二次电池的循环性能。
在本申请的任意实施方式中，所述包覆层包括碳材料、导电聚合物、金属氧化物和金属硫化物中的一种或多种。
在本申请的任意实施方式中，所述包覆层包括碳材料，可选地，所述碳材料包括硬碳、软碳、石墨烯、碳纤维和碳纳米管中的一种或多种。包覆层包括碳材料时，有助于提升硅基材料的导电性。
在本申请的任意实施方式中，所述包覆层的厚度为0nm-200nm，可选为10nm-150nm。包覆层的厚度在上述范围内时，有利于负极活性材料具有高比容量和低体积膨胀。
在本申请的任意实施方式中，所述负极活性材料包括碳元素和硅元素。
在本申请的任意实施方式中，所述负极活性材料中碳元素的质量百分含量为40wt％-60wt％，可选为45wt％-50wt％。
在本申请的任意实施方式中，所述负极活性材料中硅元素的质量百分含量为38wt％-58wt％，可选为40wt％-55wt％。
当负极活性材料中碳元素和/或硅元素的含量在上述范围内时，有利于负极活性材料兼顾高比容量和高导电性。
在本申请的任意实施方式中，所述负极活性材料还包括其他元素，所述其他元素包括氧元素、金属元素和氮元素中的一种或多种。
在本申请的任意实施方式中，所述负极活性材料中其他元素的质量百分含量之和为0wt％-20wt％，可选为0wt％-10wt％。
在本申请的任意实施方式中，所述负极活性材料的孔容为0.001cm 3/g-0.02cm 3/g，可选为0.01cm 3/g-0.02cm 3/g。负极活性材料的孔容在上述范围内时，负极活性材料内部空隙在合适的范围内，一方面能够提升负极活性材料的比容量和首次库伦效率，另一方面还可以缓冲硅基材料膨胀过程中产生的应力。
在本申请的任意实施方式中，所述负极活性材料的平均粒径Dv50为4μm-12μm。负极活性材料的平均粒径Dv50在上述范围内时，有助于降低表面活性，减少界面副反应、降低SEI膜成膜消耗，还有利于提升活性离子和电子传输性能，从而能够进一步提升二次电池的循环性能。
在本申请的任意实施方式中，所述负极活性材料的BET比表面积为1m 2/g-15m 2/g。负极活性材料的BET比表面积在上述范围内时，有助于降低表面活性，减少界面副反应、降低SEI膜成膜消耗，提升二次电池的首次库伦效率和循环性能。
本申请第二方面提供一种负极活性材料的制备方法，包括如下步骤：提供包括多个孔结构的基体材料；将硅基材料分散至所述基体材料的孔结构中，即得到负极活性材料，其中，所述负极活性材料包括基体材料以及硅基材料，所述基体材料包括多个孔结构，所述硅基材料的至少一部分位于所述基体材料的孔结构中，所述硅基材料包括晶态的硅基材料，由所述负极活性材料的颗粒外表面向颗粒内部延伸自所述颗粒外表面任一点与所述颗粒核心之间的长度的0.5倍的距离所构成的区域记为外部区域，所述外部区域内侧的区域记为内部区域，在所述负极活性材料的截面图像中，所述外部区域中的所述晶态的硅基材料的总截面积小于所述内部区域中的所述晶态的硅基材料的总截面积。
在本申请的任意实施方式中，所述基体材料的孔隙率为30％-60％，可选为40％-50％。基体材料的孔隙率在上述范围内时，有利于沉积工艺顺利进行，还有利于负极活性材料具有合适的硅元素含量、合适的比表面积和/或合适的孔容。
在本申请的任意实施方式中，所述基体材料包括碳材料、石墨材料和过渡金属氧化物材料中的一种或多种。
在本申请的任意实施方式中，所述基体材料包括碳材料，所述碳材料包括活性碳、生物质碳、热解碳和树脂碳中的一种或多种。
在本申请的任意实施方式中，所述基体材料的平均粒径Dv50为4μm-12μm。当基体材料的平均粒径Dv50在上述范围内时，有利于沉积工艺顺利进行，还有利于负极活性材 料具有合适的硅元素含量、合适的比表面积和/或合适的孔容。
在本申请的任意实施方式中，将硅基材料分散至所述基体材料的孔结构中的步骤包括如下步骤：将包括多个孔结构的基体材料作为基底置于反应炉内，通入含有硅源气体的第一混合气并在第一温度T 1下沉积第一时间t 1，结束后停止通入第一混合气；待炉内温度降至第二温度T 2后，通入含有硅源气体的第二混合气，并在第二温度T 2下沉积第二时间t 2，结束后即得到负极活性材料，其中，所述硅基材料包括晶态的硅基材料以及非晶态的硅基材料，在所述负极活性材料的截面图像中，所述外部区域中的所述晶态的硅基材料的总截面积小于所述内部区域中的所述晶态的硅基材料的总截面积，所述外部区域中的所述非晶态的硅基材料的总截面积大于所述内部区域中的所述非晶态的硅基材料的总截面积。
在本申请的任意实施方式中，在通入含有硅源气体的第一混合气之前，还包括步骤：将包括多个孔结构的基体材料作为基底置于反应炉内，使用保护气体进行吹扫处理和预升温处理，可选地，所述预升温的温度为200℃-300℃。由此有利于除去基体材料中残存的水分，进而有利于后续顺利沉积并形成晶态的硅基材料。
在本申请的任意实施方式中，所述第一混合气中的所述硅源气体的体积占比V 1大于所述第二混合气中的所述硅源气体的体积占比V 2。由此有利于调节晶态的硅基材料和非晶态的硅基材料的分布区域，使晶态的硅基材料主要位于负极活性材料的内部区域，而非晶态的硅基材料主要位于负极活性材料的外部区域，从而既能够充分发挥晶态的硅基材料对首次库伦效率的提升作用，又能充分发挥非晶态的硅基材料对循环性能的提升作用和对体积膨胀的降低作用。
在本申请的任意实施方式中，T 1>T 2。通过调节沉积时的第一温度大于第二温度，有利于调节晶态的硅基材料和非晶态的硅基材料的分布区域，使晶态的硅基材料主要位于负极活性材料的内部区域，而非晶态的硅基材料主要位于负极活性材料的外部区域，从而既能够充分发挥晶态的硅基材料对首次库伦效率的提升作用，又能充分发挥非晶态的硅基材料对循环性能的提升作用和对体积膨胀的降低作用。
在本申请的任意实施方式中，t 1<t 2。通过调节沉积时的第一时间小于第二时间，有利于调节晶态的硅基材料的含量及其分布区域。
在本申请的任意实施方式中，所述第一混合气包括硅源气体和保护气体，可选地，所述第一混合气中的所述硅源气体的体积占比V 1为10％-50％。
在本申请的任意实施方式中，所述第一混合气的总气体流量为0.5L/min-20L/min。
在本申请的任意实施方式中，第一温度T 1为500℃-700℃。
在本申请的任意实施方式中，第一时间t 1为0.5h-8h，可选为0.5h-4h。
通过调节第一混合气的组成比例、第一混合气的总气体流量、第一温度和第一时间等中的至少一者在上述范围内，有利于形成晶态的硅基材料，还有利于调节晶态的硅基材料的分布区域、晶粒尺寸、沉积量等参数。
在本申请的任意实施方式中，所述第二混合气包括硅源气体和保护气体，可选地，所述第二混合气中的所述硅源气体的体积占比V 2为5％-20％。
在本申请的任意实施方式中，所述第二混合气包括硅源气体、碳源气体和保护气体，可选地，所述第二混合气中的所述硅源气体的体积占比V 2为5％-20％，所述碳源气体 的体积占比为5％-10％。
在本申请的任意实施方式中，所述第二混合气的总气体流量为0.5L/min-20L/min。
在本申请的任意实施方式中，第二温度T 2为400℃-500℃。
在本申请的任意实施方式中，第二时间t 2为2h-16h，可选为4h-16h。
通过调节第二混合气的组成比例、第二混合气的总气体流量、第二温度和第二时间等中的至少一者在上述范围内，有利于形成非晶态的硅基材料，还有利于调节非晶态的硅基材料的分布区域、沉积量等参数。
在本申请的任意实施方式中，所述第二混合气的总气体流量与所述第一混合气的总气体流量相同。
在本申请的任意实施方式中，所述方法还包括如下步骤：在所获得的负极活性材料的至少表面形成包覆层，所述包覆层包括碳材料、导电聚合物、金属氧化物和金属硫化物中的一种或多种。
在本申请的任意实施方式中，所述形成包覆层的步骤包括以下步骤：将所获得的负极活性材料置于反应炉内，通入含有碳源气体的第三混合气，并在第三温度T 3下沉积第三时间t 3，得到碳包覆的负极活性材料。由此有利于形成均匀的碳层。
在本申请的任意实施方式中，所述第三混合气包括碳源气体和保护气体，可选地，所述第三混合气中的所述碳源气体的体积占比V 3为10％-50％。
在本申请的任意实施方式中，所述第三混合气的总气体流量为0.5L/min-20L/min。
在本申请的任意实施方式中，第三温度T 3为600℃-700℃。
在本申请的任意实施方式中，第三时间t 3为0.5h-2h。
通过调节第三混合气的组成比例、第三混合气的总气体流量、第三温度和第三时间等中的至少一者在上述范围内，有利于形成合适厚度的包覆层，避免包覆层过厚降低负极活性材料的首次库伦效率和/或比容量。
本申请第三方面提供一种二次电池，包括负极极片，所述负极极片包括本申请第一方面所述的负极活性材料或通过本申请第二方面所述的方法制备得到的负极活性材料。
本申请第四方面提供一种用电装置，其包括本申请第三方面的二次电池。
本申请提供的负极活性材料能具有高容量、高首次库伦效率和低体积膨胀，并且还能使二次电池兼顾高能量密度、高首次库伦效率、长循环寿命和长存储寿命。本申请的用电装置包括本申请提供的二次电池，因而至少具有与所述二次电池相同的优势。
附图说明
为了更清楚地说明本申请实施例的技术方案，下面将对本申请实施例中所需要使用的附图作简单地介绍。显而易见地，下面所描述的附图仅仅是本申请的一些实施方式，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据附图获得其他的附图。
图1是本申请的负极活性材料的一截面图像的示意图。
图2是本申请的电池单体的一实施方式的示意图。
图3是本申请的电池单体的一实施方式的分解示意图。
图4是本申请的电池模块的一实施方式的示意图。
图5是本申请的电池包的一实施方式的示意图。
图6是图5所示的电池包的实施方式的分解示意图。
图7是包含本申请的二次电池作为电源的用电装置的一实施方式的示意图。
在附图中，附图未必按照实际的比例绘制。附图标记说明如下：1电池包，2上箱体，3下箱体，4电池模块，5电池单体，51壳体，52电极组件，53盖板，100负极活性材料，101外部区域，102内部区域，O颗粒核心。
具体实施方式
以下，适当地参照附图详细说明具体公开了本申请的负极活性材料及其制备方法、以及包含其的二次电池及用电装置的实施方式。但是会有省略不必要的详细说明的情况。例如，有省略对已众所周知的事项的详细说明、实际相同结构的重复说明的情况。这是为了避免以下的说明不必要地变得冗长，便于本领域技术人员的理解。此外，附图及以下说明是为了本领域技术人员充分理解本申请而提供的，并不旨在限定权利要求书所记载的主题。
本申请所公开的“范围”以下限和上限的形式来限定，给定范围是通过选定一个下限和一个上限进行限定的，选定的下限和上限限定了特别范围的边界。这种方式进行限定的范围可以是包括端值或不包括端值的，并且可以进行任意地组合，即任何下限可以与任何上限组合形成一个范围。例如，如果针对特定参数列出了60-120和80-110的范围，理解为60-110和80-120的范围也是预料到的。此外，如果列出的最小范围值1和2，和如果列出了最大范围值3，4和5，则下面的范围可全部预料到：1-3、1-4、1-5、2-3、2-4和2-5。在本申请中，除非有其他说明，数值范围“a-b”表示a到b之间的任意实数组合的缩略表示，其中a和b都是实数。例如数值范围“0-5”表示本文中已经全部列出了“0-5”之间的全部实数，“0-5”只是这些数值组合的缩略表示。另外，当表述某个参数为≥2的整数，则相当于公开了该参数为例如整数2、3、4、5、6、7、8、9、10、11、12等。
如果没有特别的说明，本申请的所有实施方式以及可选实施方式可以相互组合形成新的技术方案，并且这样的技术方案应被认为包含在本申请的公开内容中。
如果没有特别的说明，本申请的所有技术特征以及可选技术特征可以相互组合形成新的技术方案，并且这样的技术方案应被认为包含在本申请的公开内容中。
如果没有特别的说明，本申请的所有步骤可以顺序进行，也可以随机进行，优选是顺序进行的。例如，所述方法包括步骤(a)和(b)，表示所述方法可包括顺序进行的步骤(a)和(b)，也可以包括顺序进行的步骤(b)和(a)。例如，所述提到所述方法还可包括步骤(c)，表示步骤(c)可以任意顺序加入到所述方法，例如，所述方法可以包括步骤(a)、(b)和(c)，也可包括步骤(a)、(c)和(b)，也可以包括步骤(c)、(a)和(b)等。
如果没有特别的说明，本申请所提到的“包括”和“包含”表示开放式，也可以是封闭式。例如，所述“包括”和“包含”可以表示还可以包括或包含没有列出的其他组分，也可以仅包括或包含列出的组分。
如果没有特别的说明，在本申请中，术语“或”是包括性的。举例来说，短语“A或B”表示“A，B，或A和B两者”。更具体地，以下任一条件均满足条件“A或B”：A 为真(或存在)并且B为假(或不存在)；A为假(或不存在)而B为真(或存在)；或A和B都为真(或存在)。
如果没有特别的说明，在本申请中，术语“第一”、“第二”等是用于区别不同对象，而不是用于描述特定顺序或主次关系。
在本申请中，术语“多个”、“多种”是指两个或两种以上。
在本申请中，“主要位于”某一特定区域(例如内部区域或外部区域)是指对应的材料(例如可为晶态的硅基材料或非晶态的硅基材料)的至少一半位于该特定区域中，并且还包括了对应的材料(例如可为晶态的硅基材料或非晶态的硅基材料)全部位于该特定区域(例如内部区域或外部区域)中的情形。
除非另有说明，本申请中使用的术语具有本领域技术人员通常所理解的公知含义。
除非另有说明，本申请中提到的各参数的数值可以用本领域常用的各种测试方法进行测定，例如，可以按照本申请的实施例中给出的测试方法进行测定。
硅具有高达4200mAh/g的理论比容量，可以显著提高二次电池的能量密度；硅还具有略高于石墨的电压平台，由此负极不易形成枝晶，可以提高二次电池的安全性能；硅在地壳中分布较广、资源丰富、价格低廉，从而可以降低二次电池的生产成本。因此，含有硅元素的材料(下文称为硅基材料)成为极具潜力的负极活性材料。
但是，硅基材料也存在一些缺点。与石墨等碳基材料不同，硅基材料在充放电过程中是通过合金化反应与金属(例如锂、钠等)反应，由此存在巨大的体积效应，易造成颗粒破碎、粉化，进而导致负极膜层出现粉化问题，易与集流体失去电接触。此外，由于硅基材料的体积效应还会导致其颗粒表面的固态电解质界面(SEI)膜反复破坏与重建，进一步增加了活性离子的不可逆消耗，最终影响二次电池的容量。因此，硅基材料作为负极活性材料使用时通常存在不可逆容量高、首次库伦效率低、体积膨胀大的缺陷，由此导致二次电池的实际容量损失大且循环寿命差。
此外，硅是一种半导体材料，其本征电导率较低，作为负极活性材料使用时会影响二次电池的容量挥发，或者需要在使用时额外增加导电剂用量，由此会降低了负极活性材料的实际涂布重量，影响二次电池的能量密度。
目前，针对上述问题的主要的改性方法包括以下几个方面。
(1)减小硅基材料的尺寸至纳米级，缓解其体积效应。但是，本申请的发明人研究发现，纳米硅基材料的高比表面积会进一步加剧界面副反应，增加活性离子不可逆消耗，并降低首次库伦效率。
(2)制备多孔的硅基材料，利用其自身的形变缓解体积效应。但是，本申请的发明人研究发现，采用多孔硅基材料时，其体积效应并不能得到有效缓解，对于首次库伦效率的改善也有限。
(3)在硅基材料表面包覆导电碳层，增加硅基材料的导电性，并缓解体积效应。但是，本申请的发明人研究发现，导电碳层太薄时，包覆不完全，由此导致二次电池的容量衰减快且循环寿命短；导电碳层太厚时，其刚性较强，二次电池充放电过程中更易出现破碎、粉化问题，进而对于首次库伦效率的改善也有限。
因此，上述改性方法均不能使二次电池兼顾高能量密度、高首次库伦效率、低体积膨胀和长循环寿命。
鉴于此，本申请的发明人通过大量研究提出一种新型的负极活性材料，其具有高容量、高首次库伦效率和低体积膨胀，并且能使二次电池兼顾高能量密度、高首次库伦效率、长循环寿命和长存储寿命。
负极活性材料
本申请实施方式第一方面提供一种负极活性材料。所述负极活性材料包括基体材料以及硅基材料，所述基体材料包括多个孔结构，所述硅基材料的至少一部分位于所述基体材料的孔结构中，所述硅基材料包括晶态的硅基材料，由所述负极活性材料的颗粒外表面向颗粒内部延伸自所述颗粒外表面任一点与所述颗粒核心之间的长度的0.5倍的距离所构成的区域记为外部区域，所述外部区域内侧的区域记为内部区域，在所述负极活性材料的截面图像中，所述外部区域中的所述晶态的硅基材料的总截面积小于所述内部区域中的所述晶态的硅基材料的总截面积。
在本申请中，可以采用双束聚焦离子束显微镜(Dual Beam FIB-SEM)制备负极活性材料颗粒的截面，该截面经过负极活性材料的中心区域，可选为经过负极活性材料的颗粒核心，然后可以通过透射电子显微镜(Transmission Electron Microscope，简称TEM)或高分辨透射电子显微镜(High Resolution Transmission Electron Microscope，简称HRTEM)观察负极活性材料的截面图像特征。在观察负极活性材料的截面图像时，晶态的硅基材料会产生晶格条纹，由此能够容易地区分晶态的硅基材料和非晶态的硅基材料。
在本申请中，所述负极活性材料的截面图像包括经过所述负极活性材料的颗粒核心的截面图像。
在本申请中，“颗粒核心”是指负极活性材料颗粒的最长直径(或最长对角线)与最短直径(或最短对角线)的交点。
图1是本申请的负极活性材料100的一截面图像的示意图，且该截面图像经过负极活性材料100的颗粒核心O。如图1所示，负极活性材料100包括外部区域101和位于外部区域101内侧的内部区域102，负极活性材料颗粒的最长直径(或最长对角线)与最短直径(或最短对角线)的交点为颗粒核心O，颗粒外表面任一点P与颗粒核心O之间的长度记为R n，由负极活性材料的颗粒外表面向颗粒内部延伸自颗粒外表面任一点P与颗粒核心O之间的长度R n的0.5倍的距离所构成的区域记为外部区域101。
需要说明的是，这里的“长度R n”是指颗粒外表面任一点距离颗粒核心的长度，当负极活性材料具有非理想球状以外的规则或不规则形貌时，长度R n表示为变动值，即颗粒外表面不同位置距离颗粒核心的长度为不断变化的数值，由此颗粒外表面不同位置向颗粒内部延伸的距离也为不断变化的数值。因此，负极活性材料颗粒外表面所有点向颗粒内部延伸相应的距离(即0.5R n)后获得的所有点与颗粒外表面共同围成的区域，即为外部区域。
在本申请中，如下描述“所述外部区域中的所述晶态的硅基材料的总截面积小于所述内部区域中的所述晶态的硅基材料的总截面积”并非限制为外部区域中必须包含晶态的硅基材料，当外部区域中不包含晶态的硅基材料，对应所述外部区域中的所述晶态的硅基材料的总截面积为0时，也认为满足“所述外部区域中的所述晶态的硅基材料的总截面积小于所述内部区域中的所述晶态的硅基材料的总截面积”。
本申请提供的负极活性材料包括具有多个孔结构的基体材料以及至少一部分位于基体材料的孔结构中的硅基材料，所述硅基材料包括晶态的硅基材料，并且在所述负极活性材料的截面图像中，所述外部区域中的所述晶态的硅基材料的总截面积小于所述内部区域中的所述晶态的硅基材料的总截面积，由此所述晶态的硅基材料主要位于所述负极活性材料的内部区域，进而本申请提供的负极活性材料能具有高容量、高首次库伦效率和低体积膨胀，并且能使二次电池兼顾高能量密度、高首次库伦效率、长循环寿命和长存储寿命。
这是由于晶态的硅基材料有助于提高二次电池的首次库伦效率，但是，晶态的硅基材料体积膨胀大、结构稳定性差，不利于提升二次电池的循环性能和降低二次电池的体积膨胀。通过使晶态的硅基材料主要位于负极活性材料的内部区域，既能够充分发挥晶态的硅基材料对首次库伦效率的提升作用，又能避免其对二次电池的循环性能和存储性能产生较大不利影响。因此，本申请提供的负极活性材料能具有高容量、高首次库伦效率和低体积膨胀，并且还能使二次电池兼顾高能量密度、高首次库伦效率、长循环寿命和长存储寿命。
在一些实施例中，所述硅基材料还包括非晶态的硅基材料。
在一些实施例中，所述硅基材料包括晶态的硅基材料和非晶态的硅基材料，在所述负极活性材料的截面图像中，所述外部区域中的所述晶态的硅基材料的总截面积小于所述内部区域中的所述晶态的硅基材料的总截面积，所述外部区域中的所述非晶态的硅基材料的总截面积大于所述内部区域中的所述非晶态的硅基材料的总截面积。
在本申请中，如下描述“所述外部区域中的所述非晶态的硅基材料的总截面积大于所述内部区域中的所述非晶态的硅基材料的总截面积”并非限制为内部区域中必须包含非晶态的硅基材料，当内部区域中不包含非晶态的硅基材料，对应所述内部区域中的所述非晶态的硅基材料的总截面积为0时，也认为满足“所述外部区域中的所述非晶态的硅基材料的总截面积大于所述内部区域中的所述非晶态的硅基材料的总截面积”。
本申请的硅基材料同时包括晶态的硅基材料以及非晶态的硅基材料，并且晶态的硅基材料主要位于负极活性材料的内部区域，而非晶态的硅基材料主要位于负极活性材料的外部区域，由此本申请提供的负极活性材料能具有高容量、高首次库伦效率和低体积膨胀，并且能使二次电池兼顾高能量密度、高首次库伦效率、长循环寿命和长存储寿命。
这是由于晶态的硅基材料有助于提高二次电池的首次库伦效率，但是，晶态的硅基材料体积膨胀大、结构稳定性差，不利于提升二次电池的循环性能和降低二次电池的体积膨胀；非晶态的硅基材料的体积膨胀小，有利于提升二次电池的循环性能和降低二次电池的体积膨胀，但是非晶态的硅基材料的首次库伦效率较低，导致二次电池实际容量损失大。通过使晶态的硅基材料主要位于负极活性材料的内部区域，而非晶态的硅基材料主要位于负极活性材料的外部区域，既能够充分发挥晶态的硅基材料对首次库伦效率的提升作用，又能充分发挥非晶态的硅基材料对循环性能的提升作用和对体积膨胀的降低作用。因此，本申请提供的负极活性材料能具有高容量、高首次库伦效率和低体积膨胀，并且还能使二次电池兼顾高能量密度、高首次库伦效率、长循环寿命和长存储寿命。
在一些实施例中，在所述负极活性材料的截面图像中，所述外部区域中的所述晶态的硅基材料的总截面积与所述内部区域中的所述晶态的硅基材料的总截面积之比α1为(0- 50):100，可选为(0-40):100，(0-30):100，(0-20):100，(0-15):100，(0-10):100，(0-5):100。在一些实施例中，在所述负极活性材料的截面图像中，所述外部区域中的所述晶态的硅基材料的总截面积与所述内部区域中的所述晶态的硅基材料的总截面积之比α1可为0，即负极活性材料的上述外部区域中不含晶态的硅基材料。
通过使晶态的硅基材料主要位于负极活性材料的内部区域，既能够充分发挥晶态的硅基材料对首次库伦效率的提升作用，又能避免其对二次电池的循环性能和存储性能产生较大不利影响。
在一些实施例中，在所述负极活性材料的截面图像中，所述内部区域中的所述非晶态的硅基材料的总截面积与所述外部区域中的所述非晶态的硅基材料的总截面积之比α2为(0-30):100，可选为(0-25):100，(0-20):100，(0-15):100，(0-10):100，(0-5):100。在一些实施例中，在所述负极活性材料的截面图像中，所述内部区域中的所述非晶态的硅基材料的总截面积与所述外部区域中的所述非晶态的硅基材料的总截面积之比α2可为0，即负极活性材料的上述内部区域中不含非晶态的硅基材料。
通过使非晶态的硅基材料主要位于负极活性材料的外部区域，能充分发挥非晶态的硅基材料对循环性能的提升作用和对体积膨胀的降低作用。
在一些实施例中，在所述负极活性材料的截面图像的外部区域中，所述晶态的硅基材料的总截面积与所述非晶态的硅基材料的总截面积之比β1为(0-25):100，可选为(0-20):100，(0-15):100，(0-10):100，(0-5):100，更可选地，所述晶态的硅基材料的总截面积为0，即负极活性材料的上述外部区域中不含晶态的硅基材料。负极活性材料的外部区域主要含有非晶态的硅基材料，不含或者含有少量晶态的硅基材料，由此既能够充分发挥晶态的硅基材料对首次库伦效率的提升作用，又能充分发挥非晶态的硅基材料对循环性能的提升作用和对体积膨胀的降低作用。
在一些实施例中，在所述负极活性材料的截面图像的内部区域中，所述晶态的硅基材料的总截面积与所述非晶态的硅基材料的总截面积之比β2为100:(0-250)，可选为100:(0-100)，100:(0-80)，100:(0-60)，100:(0-40)，100:(0-30)，100:(0-20)，100:(0-10)，100:(0-5)。负极活性材料的内部区域可以仅包含晶态的硅基材料，又可以同时包含晶态的硅基材料和非晶态的硅基材料的混合物，并且通过进一步调节晶态的硅基材料的总截面积与非晶态的硅基材料的总截面积在合适的范围内，能够更好地发挥晶态的硅基材料对首次库伦效率的提升作用。
在一些实施例中，在所述负极活性材料的截面图像中，所述晶态的硅基材料的总截面积与所述负极活性材料的总截面积的比值γ1为大于0且小于等于25％，例如可以为5％，6％，7％，8％，9％，10％，11％，12％，13％，14％，15％，16％，17％，18％，19％，20％，21％，22％，23％，24％，25％或以上任何数值组成的范围。可选地，所述晶态的硅基材料的总截面积与所述负极活性材料的总截面积的比值γ1为5％-20％，8％-20％，10％-20％，12％-20％，12％-18％。
当晶态的硅基材料的总截面积在上述范围内时，既能够充分发挥晶态的硅基材料对首次库伦效率的提升作用，又能够避免其对二次电池的循环性能和存储性能产生较大不利影响。
在一些实施例中，在所述负极活性材料的截面图像中，所述非晶态的硅基材料的总 截面积与所述负极活性材料的总截面积的比值γ2为大于等于35％且小于100％，可选为40％-65％，40％-60％，40％-55％，40％-50％。
当非晶态的硅基材料的总截面积在上述范围内时，既能够充分发挥非晶态的硅基材料对循环性能的提升作用和对体积膨胀的降低作用，又能够避免其对二次电池的首次库伦效率产生较大不利影响。
在一些实施例中，所述硅基材料中的所述晶态的硅基材料的质量百分含量为大于0且小于等于40wt％，例如可以为5wt％，10wt％，15wt％，20wt％，25wt％，30wt％，35wt％，40wt％或以上任何数值组成的范围。可选地，所述硅基材料中的所述晶态的硅基材料的质量百分含量为5wt％-40wt％，5wt％-35wt％，10wt％-35wt％，10wt％-30wt％。
当晶态的硅基材料的含量在上述范围内时，既能够充分发挥晶态的硅基材料对首次库伦效率的提升作用，又能避免其对二次电池的循环性能和存储性能产生较大不利影响。
在一些实施例中，所述硅基材料的至少一部分位于所述基体材料的孔结构中，并且所述硅基材料与所述基体材料之间具有空隙。当硅基材料与基体材料之间具有空隙时，该部分孔隙可以作为容纳硅基材料体积膨胀的空间，缓冲硅基材料膨胀过程中产生的应力。
在一些实施例中，所述晶态的硅基材料的晶粒尺寸为大于0且小于等于10nm，例如可以为2nm，3nm，4nm，5nm，6nm，7nm，8nm，9nm，10nm或以上任何数值组成的范围。可选地，所述晶态的硅基材料的晶粒尺寸为2nm-10nm，2nm-8nm。
晶态的硅基材料的晶粒尺寸较大时，有利于提升二次电池的首次库伦效率但是对于二次电池的循环性能和存储性能不利。因此，当晶态的硅基材料具有合适的晶粒尺寸时，既能提升二次电池的首次库伦效率，同时又能避免对二次电池的循环性能和存储性能产生较大不利影响。
晶态的硅基材料的晶粒尺寸为本领域公知的含义，可以用本领域公知的仪器及方法进行测定。例如可以采用高分辨透射电子显微镜测试。
在一些实施例中，所述晶态的硅基材料包括晶态的单质硅、硅氧化物、硅碳材料、硅氮复合物和硅合金材料中的一种或多种，可选地，所述晶态的硅基材料包括晶态的单质硅(又称晶体硅)。
在一些实施例中，所述非晶态的硅基材料包括非晶态的单质硅、硅氧化物、硅碳材料、硅氮复合物和硅合金材料中的一种或多种，可选地，所述非晶态的硅基材料包括非晶态的单质硅(又称非晶硅或者无定形硅)。
在一些实施例中，所述硅基材料包括气相沉积硅基材料，可选地包括气相沉积单质硅，所述气相沉积单质硅包括气相沉积晶体硅和气相沉积非晶硅。
基体材料包括多个孔结构，并且硅基材料的至少一部分位于基体材料的孔结构中，由此基体材料可以有效地缓解硅基材料的体积膨胀，避免硅基材料或负极活性材料破碎、粉化。
在一些实施例中，所述基体材料的孔隙率为30％-60％，例如可以为30％，35％，40％，45％，50％，55％，60％或以上任何数值组成的范围。可选地，所述基体材料的孔隙率为40％-50％。
当基体材料的孔隙率在上述范围内时，有利于容纳足够的硅基材料，进而有利于提升二次电池的能量密度。
在一些实施例中，所述基体材料包括碳材料、石墨材料和过渡金属氧化物材料中的一种或多种。这些基体材料均包括多个孔结构，由此可以起到缓解硅基材料的体积膨胀的作用，此外，还可以提高硅基材料的导电性。
在一些实施例中，所述基体材料包括过渡金属氧化物材料。过渡金属氧化物材料的孔结构可控可调，且孔尺寸更均一，由此有利于硅基材料分散均匀。可选地，所述过渡金属氧化物的分子式为M xO y，0＜x≤2，0＜y≤3，M包括选自Ni、Co、Mn、Ti和Cu中的一种或多种元素。例如，所述过渡金属氧化物包括选自NiO、Ni 2O 3、CoO、Co 2O 3、MnO、Mn 2O 3、TiO、TiO 2、Ti 2O 3、Cu、Cu 2O和CuO中的一种或多种。
在一些实施例中，所述基体材料包括石墨材料，例如天然石墨。由此除了可以起到缓解硅基材料的体积膨胀、提高硅基材料的导电性之外，还可以促进活性离子的传输，提高负极活性材料的比容量。
在一些实施例中，所述基体材料包括碳材料，所述碳材料包括活性碳、生物质碳、热解碳和树脂碳中的一种或多种。由此除了可以起到缓解硅基材料的体积膨胀、提高硅基材料的导电性之外，还可以促进活性离子的传输，提高负极活性材料的比容量。并且与石墨材料相比，碳材料的多孔结构更均匀，由此还有利于硅基材料的分散。
在一些实施例中，所述负极活性材料还包括包覆层，所述包覆层位于所述基体材料的至少部分表面。包覆层位于所述负极活性材料的外侧，由此可以进一步阻止硅基材料与电解液直接接触，降低硅基材料与空气接触后的反应活性，从而能够减少电解液副反应、降低活性离子消耗，提高二次电池的循环性能。此外，包覆层还可以起到缓冲硅基材料体积膨胀的作用，由此还有利于改善二次电池的存储性能。
在一些实施例中，所述包覆层包括碳材料、导电聚合物、金属氧化物和金属硫化物中的一种或多种。
在一些实施例中，所述碳材料包括硬碳、软碳、石墨烯、碳纤维和碳纳米管中的一种或多种。
在一些实施例中，所述导电聚合物包括聚苯胺、聚吡咯和聚噻吩中的一种或多种。
在一些实施例中，所述金属氧化物包括氧化铁、氧化锌、氧化锡、氧化铜和氧化钛中的一种或多种。
在一些实施例中，所述金属硫化物包括硫化锡、硫化钼、硫化钛、硫化铁和硫化铜中的一种或多种。
在一些实施例中，所述包覆层包括碳材料，可选地，所述碳材料包括硬碳、软碳、石墨烯、碳纤维和碳纳米管中的一种或多种。由此，包覆层除了可以阻止硅基材料与电解液直接接触、缓冲硅基材料体积膨胀之外，还可以贡献部分容量，提高负极活性材料的比容量。此外，包覆层包括碳材料时，还有助于提升硅基材料的导电性。
在一些实施例中，所述包覆层的厚度为0nm-200nm，可选为10nm-200nm，10nm-180nm，10nm-150nm。包覆层的厚度在上述范围内时，有利于负极活性材料具有高比容量和低体积膨胀。在本申请中，当包覆层的厚度为0nm时，表示负极活性材料不具有包覆层。
在一些实施例中，所述负极活性材料包括碳元素和硅元素。
在一些实施例中，所述负极活性材料中碳元素的质量百分含量为40wt％-60wt％，例如可以为40wt％，42wt％，44wt％，46wt％，48wt％，50wt％，52wt％，54wt％，56wt％，58wt％，60wt％或以上任何数值组成的范围。可选地，所述负极活性材料中碳元素的质量百分含量为45wt％-50wt％。
在一些实施例中，所述负极活性材料中硅元素的质量百分含量为38wt％-58wt％，例如可以为40wt％，42wt％，44wt％，46wt％，48wt％，50wt％，52wt％，54wt％，56wt％，58wt％或以上任何数值组成的范围。可选地，所述负极活性材料中硅元素的质量百分含量为40wt％-55wt％。
当负极活性材料中碳元素和/或硅元素的含量在上述范围内时，有利于负极活性材料兼顾高比容量和高导电性。
负极活性材料中碳元素含量可以参照GB/T 20123-2006/ISO 15350:2000进行测试，测试仪器可以为HCS-140型红外碳硫分析仪。负极活性材料中硅元素含量可以参照GB/T20975.5-2020进行测试。
在一些实施例中，所述负极活性材料除包括碳元素和硅元素之外，还包括其他元素，所述其他元素包括氧元素、金属元素和氮元素中的一种或多种。所述其他元素的分布区域不受具体限制，例如可以位于所述包覆层、所述硅基材料和所述基体材料中的至少一者中。
在一些实施例中，所述负极活性材料中其他元素的质量百分含量之和为0wt％-20wt％，可选为0wt％-10wt％，0wt％-5wt％。在本申请中，当负极活性材料中其他元素的质量百分含量之和为0wt％时，表示负极活性材料不包括碳元素和硅元素之外的其他元素。
在一些实施例中，所述负极活性材料的孔容为0.001cm 3/g-0.02cm 3/g，可选为0.01cm 3/g-0.02cm 3/g。负极活性材料的孔容在上述范围内时，负极活性材料内部空隙在合适的范围内，一方面能够提升负极活性材料的比容量和首次库伦效率，另一方面还可以缓冲硅基材料膨胀过程中产生的应力。
在本申请中，负极活性材料的孔容为本领域公知的含义，可以用本领域公知的仪器及方法进行测定。例如可以参照GB/T 21650.2-2008进行测试。测试仪器可以为美国Micromeritics公司的TRISTAR II 3020型比表面积与孔隙度分析仪。
在一些实施例中，所述负极活性材料的平均粒径Dv50为4μm-12μm。负极活性材料的平均粒径Dv50在上述范围内时，有助于降低表面活性，减少界面副反应、降低SEI膜成膜消耗，还有利于提升活性离子和电子传输性能，从而能够进一步提升二次电池的循环性能。
在本申请中，负极活性材料的平均粒径Dv50为本领域公知的含义，其表示材料累计体积分布百分数达到50％时所对应的粒径，可以用本领域已知的仪器及方法进行测定。例如可以参照GB/T 19077-2016，采用激光粒度分析仪方便地测定。测试仪器可以为英国马尔文仪器有限公司的Mastersizer 3000型激光粒度分析仪。
在一些实施例中，所述负极活性材料的BET比表面积为1m 2/g-15m 2/g。负极活性材料的BET比表面积在上述范围内时，有助于降低表面活性，减少界面副反应、降低SEI膜 成膜消耗，提升二次电池的首次库伦效率和循环性能。
在本申请中，负极活性材料的BET比表面积为本领域公知的含义，可以用本领域公知的仪器及方法进行测定。例如可以参照GB/T 19587-2017，采用氮气吸附比表面积分析测试方法测试，并用BET(Brunauer Emmett Teller)法计算得出，氮气吸附比表面积分析测试可以通过美国Micromeritics公司的TRISTAR II 3020型比表面积与孔隙度分析仪进行。
制备方法
本申请实施方式第二方面提供一种负极活性材料的制备方法，其能制备本申请实施方式第一方面的负极活性材料。
所述方法包括如下步骤：提供包括多个孔结构的基体材料；将硅基材料分散至所述基体材料的孔结构中，即得到负极活性材料，其中，所述负极活性材料包括基体材料以及硅基材料，所述基体材料包括多个孔结构，所述硅基材料的至少一部分位于所述基体材料的孔结构中，所述硅基材料包括晶态的硅基材料，由所述负极活性材料的颗粒外表面向颗粒内部延伸自所述颗粒外表面任一点与所述颗粒核心之间的长度的0.5倍的距离所构成的区域记为外部区域，所述外部区域内侧的区域记为内部区域，在所述负极活性材料的截面图像中，所述外部区域中的所述晶态的硅基材料的总截面积小于所述内部区域中的所述晶态的硅基材料的总截面积。
在一些实施例中，所述基体材料的孔隙率为30％-60％，可选为40％-50％。基体材料的孔隙率在上述范围内时，有利于沉积工艺顺利进行，还有利于负极活性材料具有合适的硅元素含量、合适的比表面积和/或合适的孔容。基体材料的孔隙率过小时，部分硅基材料容易沉积在基体材料表面，影响负极活性材料的首次库伦效率；基体材料的孔隙率过大时，容易存在硅基材料沉积量不足而导致负极活性材料比表面积过大的问题，由此会增加界面副反应、增加活性离子不可逆消耗、降低负极活性材料的首次库伦效率。
在一些实施例中，所述基体材料的平均粒径Dv50为4μm-12μm。当基体材料的平均粒径Dv50在上述范围内时，有利于沉积工艺顺利进行，还有利于负极活性材料具有合适的硅元素含量、合适的比表面积和/或合适的孔容。当基体材料的平均粒径Dv50过小时，硅基材料的沉积效果较差，不利于后续进行两段式沉积；当基体材料的平均粒径Dv50过大时，容易存在硅基材料沉积量不足而导致负极活性材料比表面积过大的问题，由此会增加界面副反应、增加活性离子不可逆消耗、降低负极活性材料的首次库伦效率。
在一些实施例中，所述基体材料包括碳材料、石墨材料和过渡金属氧化物材料中的一种或多种。
在一些实施例中，所述基体材料包括碳材料，所述碳材料包括活性碳、生物质碳、热解碳和树脂碳中的一种或多种。
在本申请中，基体材料可以通过市购获得，或者根据本领域已知的方法制备获得，例如可以通过高温热解有机碳源得到或者通过化学活化处理得到。所述有机碳源可包括生物质材料和高分子材料中的一种或多种。所述化学活化处理可采用造孔剂(例如碱性溶液)对基体材料(例如碳材料)进行造孔获得。
在一些实施例中，将硅基材料分散至所述基体材料的孔结构中的步骤包括如下步骤：将包括多个孔结构的基体材料作为基底置于反应炉内，通入含有硅源气体的第一混合气并在第一温度T 1下沉积第一时间t 1，结束后停止通入第一混合气；待炉内温度降至第 二温度T 2后，通入含有硅源气体的第二混合气，并在第二温度T 2下沉积第二时间t 2，结束后即得到负极活性材料，其中，所述硅基材料包括晶态的硅基材料以及非晶态的硅基材料，在所述负极活性材料的截面图像中，所述外部区域中的所述晶态的硅基材料的总截面积小于所述内部区域中的所述晶态的硅基材料的总截面积，所述外部区域中的所述非晶态的硅基材料的总截面积大于所述内部区域中的所述非晶态的硅基材料的总截面积。
在一些实施例中，将硅基材料分散至所述基体材料的孔结构中的工艺为气相沉积工艺，所述气相沉积工艺包括化学气相沉积工艺和物理气相沉积工艺，可选为化学气相沉积工艺，例如可以为热化学气相沉积工艺、等离子体增强化学气相沉积工艺、微波等离子体辅助化学气相沉积工艺中的任一种。
在一些实施例中，所述反应炉包括但不限于沉积炉、回转炉、管式炉和流化床中的任一种。
本申请采用两段式气相沉积工艺在基体材料的孔结构中分次沉积晶态的硅基材料和非晶态的硅基材料，与常规的液相沉积工艺相比，通过气相沉积工艺有利于硅基材料更好地沉积并均匀分散在基体材料的孔结构中，并可以避免硅基材料出现团聚问题和/或大量沉积在基体材料表面的问题。
在一些实施例中，在通入含有硅源气体的第一混合气之前，所述方法还包括步骤：将包括多个孔结构的基体材料作为基底置于反应炉内，使用保护气体进行吹扫处理和预升温处理，可选地，所述预升温的温度为200℃-300℃。由此有利于除去基体材料中残存的水分，进而有利于后续顺利沉积并形成晶态的硅基材料。
在一些实施例中，在将硅基材料分散至所述基体材料的孔结构中的步骤中，所述第一混合气中的所述硅源气体的体积占比V 1大于所述第二混合气中的所述硅源气体的体积占比V 2。由此有利于调节晶态的硅基材料和非晶态的硅基材料的分布区域，使晶态的硅基材料主要位于负极活性材料的内部区域，而非晶态的硅基材料主要位于负极活性材料的外部区域，从而既能够充分发挥晶态的硅基材料对首次库伦效率的提升作用，又能充分发挥非晶态的硅基材料对循环性能的提升作用和对体积膨胀的降低作用。
在一些实施例中，在将硅基材料分散至所述基体材料的孔结构中的步骤中，T 1>T 2。
在一些实施例中，在将硅基材料分散至所述基体材料的孔结构中的步骤中，t 1<t 2。
在一些实施例中，在将硅基材料分散至所述基体材料的孔结构中的步骤中，T 1>T 2并且t 1<t 2。
在将硅基材料分散至所述基体材料的孔结构中的步骤中，通过调节沉积时的第一温度大于第二温度，有利于调节晶态的硅基材料和非晶态的硅基材料的分布区域，使晶态的硅基材料主要位于负极活性材料的内部区域，而非晶态的硅基材料主要位于负极活性材料的外部区域，从而既能够充分发挥晶态的硅基材料对首次库伦效率的提升作用，又能充分发挥非晶态的硅基材料对循环性能的提升作用和对体积膨胀的降低作用。
通过调节沉积时的第一时间小于第二时间，有利于调节晶态的硅基材料的含量及其分布区域。
在一些实施例中，通入含有硅源气体的第一混合气后可调节所述炉内压力为微正压，例如可为高于大气压200Pa-600Pa，由此有利于沉积工艺顺利进行。
在一些实施例中，所述第一混合气包括硅源气体和保护气体，可选地，所述第一混合气中的所述硅源气体的体积占比V 1为10％-50％，例如可以为10％，15％，20％，25％，30％，35％，40％，45％，50％或以上任何数值组成的范围。
在一些实施例中，所述第一混合气的总气体流量为0.5L/min-20L/min。例如可以为1L/min，2L/min，3L/min，4L/min，5L/min，6L/min，7L/min，8L/min，9L/min，10L/min，12L/min，14L/min，16L/min，18L/min，20L/min或以上任何数值组成的范围。
在一些实施例中，第一温度T 1为500℃-700℃，例如可以为520℃，540℃，560℃，580℃，600℃，620℃，640℃，660℃，680℃，700℃或以上任何数值组成的范围。
在一些实施例中，第一时间t 1为0.5h-8h，例如可以为1h，2h，3h，4h，5h，6h，7h，8h或以上任何数值组成的范围。可选地，第一时间t 1为0.5h-4h。
通过调节第一混合气的组成比例、第一混合气的总气体流量、第一温度和第一时间等中的至少一者在上述范围内，有利于形成晶态的硅基材料，还有利于调节晶态的硅基材料的分布区域、晶粒尺寸、沉积量等参数。
第一混合气中硅源气体的体积占比过高和/或第一混合气的总气体流量过大时，晶态的硅基材料的含量增加、分布面积增加，由此对于二次电池的循环性能和存储性能的改善不利；第一混合气中硅源气体的体积占比过低和/或第一混合气的总气体流量过小时，晶态的硅基材料的沉积量可能不足，对于二次电池首次库伦效率的改善不利；第一温度过低时，不利于形成晶态的硅基材料；第一温度过高时，硅基材料的晶粒尺寸增加，对于二次电池的循环性能和存储性能的改善不利；第一时间过短时，晶态的硅基材料的沉积量可能不足，对于二次电池首次库伦效率的改善不利；第一时间过长时，晶态的硅基材料的含量增加、分布面积增加，由此对于二次电池的循环性能和存储性能的改善不利。
在一些实施例中，通入含有硅源气体的第二混合气后可调节所述炉内压力为微正压，例如可为高于大气压200Pa-600Pa，由此有利于沉积工艺顺利进行。
在一些实施例中，所述第二混合气可包括硅源气体和保护气体，可选地，所述第二混合气中的所述硅源气体的体积占比V 2为5％-20％，例如可以为5％，6％，8％，10％，12％，14％，16％，18％，20％或以上任何数值组成的范围。
在一些实施例中，所述第二混合气可包括硅源气体、碳源气体和保护气体，可选地，所述第二混合气中的所述硅源气体的体积占比V 2为5％-20％，所述碳源气体的体积占比为5％-10％。由此有利于调节晶态的硅基材料和非晶态的硅基材料的分布区域，使晶态的硅基材料主要位于负极活性材料的内部区域，而非晶态的硅基材料主要位于负极活性材料的外部区域，从而既能够充分发挥晶态的硅基材料对首次库伦效率的提升作用，又能充分发挥非晶态的硅基材料对循环性能的提升作用和对体积膨胀的降低作用。
在一些实施例中，所述第二混合气的总气体流量为0.5L/min-20L/min。例如可以为1L/min，2L/min，3L/min，4L/min，5L/min，6L/min，7L/min，8L/min，9L/min，10L/min，12L/min，14L/min，16L/min，18L/min，20L/min或以上任何数值组成的范围。
在一些实施例中，第二温度T 2为400℃-500℃，例如可以为400℃，410℃，420℃，430℃，440℃，450℃，460℃，470℃，480℃，490℃或以上任何数值组成的范围。
在一些实施例中，第二时间t 2为2h-16h，例如可以为2h，3h，4h，5h，6h，7h，8h， 9h，10h，11h，12h，13h，14h，15h，16h或以上任何数值组成的范围。可选地，第二时间t 2为4h-16h。
通过调节第二混合气的组成比例、第二混合气的总气体流量、第二温度和第二时间等中的至少一者在上述范围内，有利于形成非晶态的硅基材料，还有利于调节非晶态的硅基材料的分布区域、沉积量等参数。
第二混合气中硅源气体的体积占比过高和/或第二混合气的总气体流量过大时，非晶态的硅基材料可能沉积在基体材料表面，由此可能增加负极浆料的制备难度，同时还可能增加界面副反应和活性离子不可逆消耗；第二混合气中硅源气体的体积占比过低和/或第二混合气的总气体流量过小时，非晶态的硅基材料的沉积量可能不足，由此导致负极活性材料的比表面积较大、界面副反应增加、活性离子不可逆消耗增加、首次库伦效率降低；第二温度过低时，硅基材料的沉积效果差，且无法进行有效沉积；第二温度过高时，易形成晶态的硅基材料，对于二次电池循环性能和存储性能的改善不利；第二时间过短时，非晶态的硅基材料的沉积量可能不足，由此导致负极活性材料的比表面积较大、界面副反应增加、活性离子不可逆消耗增加、首次库伦效率降低；第二时间过长时，非晶态的硅基材料可能沉积在基体材料表面，由此可能增加负极浆料的制备难度，同时还可能增加界面副反应和活性离子不可逆消耗。
在一些实施例中，所述第二混合气的总气体流量与所述第一混合气的总气体流量可以相同。
在一些实施例中，所述方法还包括如下步骤：在所获得的负极活性材料的至少表面形成包覆层，所述包覆层包括碳材料、导电聚合物、金属氧化物和金属硫化物中的一种或多种。
在所获得的负极活性材料的至少表面形成包覆层的方法不受具体的限制，可以根据包覆层的组成进行选择，例如可以采用固相包覆、液相包覆或气相包覆中的任一种。
在一些实施例中，所述形成包覆层的步骤包括以下步骤：将所获得的负极活性材料与包覆材料混合后经碳化处理得到。可选地，所述包覆材料包括沥青(例如煤沥青、石油沥青等)和高分子材料中的一种或多种。可选地，所述碳化处理的温度为500℃-1000℃。
在一些实施例中，所述形成包覆层的步骤包括以下步骤：将所获得的负极活性材料置于反应炉内，通入含有碳源气体的第三混合气，并在第三温度T 3下沉积第三时间t 3，得到碳包覆的负极活性材料。由此有利于形成均匀的碳层。
在一些实施例中，所述第三混合气包括碳源气体和保护气体，可选地，所述第三混合气中的所述碳源气体的体积占比V 3为10％-50％，例如可以为10％，15％，20％，25％，30％，35％，40％，45％，50％或以上任何数值组成的范围。
在一些实施例中，所述第三混合气的总气体流量为0.5L/min-20L/min。例如可以为1L/min，2L/min，3L/min，4L/min，5L/min，6L/min，7L/min，8L/min，9L/min，10L/min，12L/min，14L/min，16L/min，18L/min，20L/min或以上任何数值组成的范围。
在一些实施例中，第三温度T 3为600℃-700℃，例如可以为600℃，610℃，620℃，630℃，640℃，650℃，660℃，670℃，680℃，690℃，700℃或以上任何数值组成的范围。
在一些实施例中，第三时间t 3为0.5h-2h，例如可以为0.5h，0.6h，0.8h，1h，1.2h，1.4h，1.6h，1.8h，2h或以上任何数值组成的范围。
通过调节第三混合气的组成比例、第三混合气的总气体流量、第三温度和第三时间等中的至少一者在上述范围内，有利于形成合适厚度的包覆层，避免包覆层过厚降低负极活性材料的首次库伦效率和/或比容量。
在本申请中，术语“保护气体”包括氮气和稀有气体，所述稀有气体可包括氩气、氦气等中的一种或多种。
在本申请中，术语“硅源气体”是指能够形成本申请的硅基材料的气体，可选地，所述硅源气体包括但不限于甲硅烷(H 4Si)、乙硅烷(H 6Si 2)、丙硅烷(H 8Si 3)、四氯化硅(Cl 4Si)、三氯硅烷(Cl 3HSi)、二氯硅烷(Cl 2H 2Si)、氯硅烷(ClH 3Si)、四氟化硅(F 4Si)、三氟硅烷(F 3HSi)、二氟硅烷(F 2H 2Si)、氟硅烷(FH 3Si)、六氯二硅烷(Cl 6Si 2)、五氯二硅烷(Cl 5HSi 2)、四氯二硅烷(Cl 4H 2Si 2，包括1,1,2,2-四氯二硅烷、1,1,1,2-四氯二硅烷)、三氯二硅烷(Cl 3H 3Si 2，包括1,1,2-三氯二硅烷、1,1,1-三氯二硅烷)、二氯二硅烷(Cl 2H 4Si 2，包括1,1-二氯二硅烷、1,2-二氯二硅烷)、一氯二硅烷(ClH 5Si 2)、六氟二硅烷(F 6Si 2)、五氟二硅烷(F 5HSi 2)、1,1,2,2-四氟二硅烷(F 4H 2Si 2)、1,1,1-三氟二硅烷(F 3H 3Si 2)、二氟二硅烷(F 2H 4Si 2，包括1,1-二氟二硅烷、1,2-二氟二硅烷)、一氟二硅烷(FH 5Si 2)、甲基硅烷、乙基硅烷、二甲基硅烷、三甲基硅烷、四甲基硅烷、甲基二硅烷、二甲基二硅烷、三甲基二硅烷、四甲基二硅烷、六甲基硅烷、甲基三氯硅烷、甲基氯硅烷、氯乙基硅烷、二氯二甲基硅烷和二氯二乙基硅烷中的一种或多种。
在本申请中，“碳源气体”是指能够形成碳材料的气体，可选地，所述碳源气体包括但不限于甲烷、乙烷、丙烷、异丙烷、丁烷、异丁烷、乙烯、丙烯、丁烯、乙炔、氯乙烷、氟乙烷、二氟乙烷、氯甲烷、氟甲烷、二氟甲烷、三氟甲烷、氯乙烯、氟乙烯、二氟乙烯、甲胺、甲醛、苯、甲苯、二甲苯、苯乙烯和苯酚中的一种或多种。
如果没有特别的说明，在本申请的制备方法中所使用的各原料及其仪器等均可以通过市购获得。
二次电池
本申请实施方式第三方面提供一种二次电池。
本申请的实施例或实施方式中所提到的二次电池是指包括一个或多个电池单体以提供更高的电压和容量的单一的物理模块。例如，本申请中所提到的二次电池可以包括电池单体、电池模块或电池包等。电池单体是组成二次电池的最小单元，其独自能够实现充放电的功能。本申请对电池单体的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。如图2是作为一个示例的方形结构的电池单体5。
在一些实施例中，电池单体包括电极组件以及电解质，单体电池还可包括外包装。电极组件可通过卷绕工艺和/或叠片工艺由正极极片、负极极片以及隔离膜等制成，外包装可用于封装上述电极组件。外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。外包装也可以是软包，例如袋式软包。所述软包的材质可以是塑料，如聚丙烯(PP)、聚对苯二甲酸丁二醇酯(PBT)和聚丁二酸丁二醇酯(PBS)中的一种或多种。
在一些实施例中，如图3所示，外包装可包括壳体51和盖板53。壳体51可包括底板 和连接于底板上的侧板，底板和侧板围合形成容纳腔。壳体51具有与容纳腔连通的开口，盖板53用于盖设所述开口，以封闭所述容纳腔。电极组件52封装于所述容纳腔。电池单体5所含电极组件52的数量可以为一个或多个，可根据需求来调节。
在本申请的一些实施例中，电池单体可以组装成电池模块，电池模块所含电池单体的数量可以为多个，具体数量可根据电池模块的应用和容量来调节。图3是作为一个示例的电池模块4的示意图。如图4所示，在电池模块4中，多个电池单体5可以是沿电池模块4的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个电池单体5进行固定。
可选地，电池模块4还可以包括具有容纳空间的外壳，多个电池单体5容纳于该容纳空间。
在一些实施例中，上述电池模块还可以组装成电池包，电池包所含电池模块的数量可以根据电池包的应用和容量进行调节。图5和图6是作为一个示例的电池包1的示意图。如图5和图6所示，在电池包1中可以包括电池箱和设置于电池箱中的多个电池模块4。电池箱包括上箱体2和下箱体3，上箱体2用于盖设下箱体3，并形成用于容纳电池模块4的封闭空间。多个电池模块4可以按照任意的方式排布于电池箱中。
本申请对二次电池种类没有特别的限制，例如，二次电池可以包括但不限于锂离子电池、钠离子电池等。
[负极极片]
在一些实施例中，所述负极极片包括负极集流体以及设置在所述负极集流体至少一个表面且包括负极活性材料的负极膜层。例如，所述负极集流体具有在自身厚度方向相对的两个表面，所述负极膜层设置在所述负极集流体的两个相对表面中的任意一者或两者上。
在一些实施例中，所述负极膜层包括本申请实施方式第一方面的负极活性材料或通过本申请实施方式第二方面所述的方法制备得到的负极活性材料。由此能使二次电池兼顾高能量密度、高首次库伦效率、长循环寿命和长存储寿命。
在一些实施例中，所述负极膜层还可以进一步包括除了上述负极活性材料以外的其他负极活性材料。在一些实施例中，所述其他负极活性材料包括但不限于天然石墨、人造石墨、软碳、硬碳、单质硅、硅氧化物、硅氮复合物、硅合金材料、单质锡、锡氧化物、锡合金材料、和钛酸锂中的一种或多种。本申请并不限定于这些材料，还可以使用其他可被用作二次电池负极活性材料的传统公知的材料。
在一些实施例中，所述负极膜层还可选地包括负极导电剂。本申请对所述负极导电剂的种类没有特别的限制，作为示例，所述负极导电剂可包括超导碳、导电石墨、乙炔黑、碳黑、科琴黑、碳点、碳纳米管、石墨烯和碳纳米纤维中的一种或多种。
在一些实施例中，所述负极膜层还可选地包括负极粘结剂。本申请对所述负极粘结剂的种类没有特别的限制，作为示例，所述负极粘结剂可包括丁苯橡胶(SBR)、水溶性不饱和树脂SR-1B、水性丙烯酸类树脂(例如，聚丙烯酸PAA、聚甲基丙烯酸PMAA、聚丙烯酸钠PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)和羧甲基壳聚糖(CMCS)中的一种或多种。
在一些实施例中，所述负极膜层还可选地包括其他助剂。作为示例，其他助剂可包 括增稠剂，例如，羧甲基纤维素钠(CMC)、PTC热敏电阻材料等。
在一些实施例中，所述负极集流体可采用金属箔片或复合集流体。作为所述金属箔片的示例，可采用铜箔。所述复合集流体可包括高分子材料基层以及形成于所述高分子材料基层至少一个表面上的金属材料层。作为示例，所述金属材料可包括铜、铜合金、镍、镍合金、钛、钛合金、银和银合金中的一种或多种。作为示例，所述高分子材料基层可包括聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)和聚乙烯(PE)中的一种或多种。
所述负极膜层通常是将负极浆料涂布在负极集流体上，经干燥、冷压而成的。所述负极浆料通常是将负极活性材料、可选的导电剂、可选地粘结剂、其他可选的助剂分散于溶剂中并搅拌均匀而形成的。溶剂可以是N-甲基吡咯烷酮(NMP)或去离子水，但不限于此。
所述负极极片并不排除除了所述负极膜层之外的其他附加功能层。例如，在一些实施例中，本申请所述的负极极片还可以包括夹在所述负极集流体和所述负极膜层之间、设置于所述负极集流体表面的导电底涂层(例如由导电剂和粘结剂组成)；在一些实施例中，本申请所述的负极极片还可以包括覆盖在所述负极膜层表面的保护层。
[正极极片]
在一些实施例中，所述正极极片包括正极集流体以及设置在所述正极集流体至少一个表面且包括正极活性材料的正极膜层。例如，所述正极集流体具有在自身厚度方向相对的两个表面，所述正极膜层设置于所述正极集流体的两个相对表面中的任意一者或两者上。
所述正极膜层包括正极活性材料，所述正极活性材料可采用本领域公知的用于二次电池的正极活性材料。
当本申请的二次电池为锂离子电池时，所述正极活性材料可包括锂过渡金属氧化物、橄榄石结构的含锂磷酸盐及其各自的改性化合物中的一种或多种。锂过渡金属氧化物的示例可包括锂钴氧化物、锂镍氧化物、锂锰氧化物、锂镍钴氧化物、锂锰钴氧化物、锂镍锰氧化物、锂镍钴锰氧化物、锂镍钴铝氧化物及其各自的改性化合物中的一种或多种。橄榄石结构的含锂磷酸盐的示例可包括磷酸铁锂、磷酸铁锂与碳的复合材料、磷酸锰锂、磷酸锰锂与碳的复合材料、磷酸锰铁锂、磷酸锰铁锂与碳的复合材料及其各自的改性化合物中的一种或多种。本申请并不限定于这些材料，还可以使用其他可被用作二次电池正极活性材料的传统公知的材料。
在一些实施例中，为了进一步提高二次电池的能量密度，用于锂离子电池的正极活性材料可以包括通式为Li aNi bCo cM dO eA f的锂过渡金属氧化物及其改性化合物中的一种或多种。0.8≤a≤1.2，0.5≤b＜1，0＜c＜1，0＜d＜1，1≤e≤2，0≤f≤1，M包括选自Mn、Al、Zr、Zn、Cu、Cr、Mg、Fe、V、Ti和B中的一种或多种，A包括选自N、F、S和Cl中的一种或多种。
作为示例，用于锂离子电池的正极活性材料可包括LiCoO 2、LiNiO 2、LiMnO 2、LiMn 2O 4、LiNi 1/3Co 1/3Mn 1/3O 2(NCM333)、LiNi 0.5Co 0.2Mn 0.3O 2(NCM523)、LiNi 0.6Co 0.2Mn 0.2O 2(NCM622)、LiNi 0.8Co 0.1Mn 0.1O 2(NCM811)、LiNi 0.85Co 0.15Al 0.05O 2、LiFePO 4和LiMnPO 4中的一种或多种。
当本申请的二次电池为钠离子电池时，所述正极活性材料可包括但不限于含钠过渡金属氧化物、聚阴离子材料(如磷酸盐、氟磷酸盐、焦磷酸盐、硫酸盐等)、普鲁士蓝类材料中的一种或多种。
作为示例，用于钠离子电池的正极活性材料可包括NaFeO 2、NaCoO 2、NaCrO 2、NaMnO 2、NaNiO 2、NaNi 1/2Ti 1/2O 2、NaNi 1/2Mn 1/2O 2、Na 2/3Fe 1/3Mn 2/3O 2、NaNi 1/3Co 1/3Mn 1/3O 2、NaFePO 4、NaMnPO 4、NaCoPO 4、普鲁士蓝类材料和通式为X pM’ q(PO 4) rO xY 3-x的材料中的一种或多种。在通式X pM’ q(PO 4) rO xY 3-x中，0＜p≤4，0＜q≤2，1≤r≤3，0≤x≤2，X包括选自H +、Li +、Na +、K +和NH 4 +中的一种或多种，M’为过渡金属阳离子，可选为包括选自V、Ti、Mn、Fe、Co、Ni、Cu和Zn中的一种或多种，Y为卤素阴离子，可选为包括选自F、Cl和Br中的一种或多种。
在本申请中，上述各正极活性材料的改性化合物可以是对所述正极活性材料进行掺杂改性和/或表面包覆改性。
在一些实施例中，所述正极膜层还可选地包括正极导电剂。本申请对所述正极导电剂的种类没有特别的限制，作为示例，所述正极导电剂包括超导碳、导电石墨、乙炔黑、碳黑、科琴黑、碳点、碳纳米管、石墨烯和碳纳米纤维中的一种或多种。
在一些实施例中，所述正极膜层还可选地包括正极粘结剂。本申请对所述正极粘结剂的种类没有特别的限制，作为示例，所述正极粘结剂可包括聚偏氟乙烯(PVDF)、聚四氟乙烯(PTFE)、偏氟乙烯-四氟乙烯-丙烯三元共聚物、偏氟乙烯-六氟丙烯-四氟乙烯三元共聚物、四氟乙烯-六氟丙烯共聚物和含氟丙烯酸酯类树脂中的一种或多种。
在一些实施例中，所述正极集流体可采用金属箔片或复合集流体。作为所述金属箔片的示例，可采用铝箔。所述复合集流体可包括高分子材料基层以及形成于所述高分子材料基层至少一个表面上的金属材料层。作为示例，所述金属材料可包括铝、铝合金、镍、镍合金、钛、钛合金、银和银合金中的一种或多种。作为示例，所述高分子材料基层可包括聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)和聚乙烯(PE)中的一种或多种。
所述正极膜层通常是将正极浆料涂布在正极集流体上，经干燥、冷压而成的。所述正极浆料通常是将正极活性材料、可选的导电剂、可选的粘结剂以及任意的其他组分分散于溶剂中并搅拌均匀而形成的。溶剂可以是N-甲基吡咯烷酮(NMP)，但不限于此。
[电解质]
电解质在正极极片和负极极片之间起到传导活性离子的作用。本申请对所述电解质的种类没有具体的限制，可根据需求进行选择。例如，所述电解质可以包括选自固态电解质及液态电解质(即电解液)中的一种或多种。
在一些实施例中，所述电解质采用电解液，所述电解液包括电解质盐和溶剂。
当本申请的二次电池为锂离子电池时，作为示例，所述电解质盐可包括六氟磷酸锂(LiPF 6)、四氟硼酸锂(LiBF 4)、高氯酸锂(LiClO 4)、六氟砷酸锂(LiAsF 6)、双氟磺酰亚胺锂(LiFSI)、双三氟甲磺酰亚胺锂(LiTFSI)、三氟甲磺酸锂(LiTFS)、二氟草酸硼酸锂(LiDFOB)、二草酸硼酸锂(LiBOB)、二氟磷酸锂(LiPO 2F 2)、二氟二草酸磷酸锂(LiDFOP)和四氟草酸磷酸锂(LiTFOP)中的一种或多种。
当本申请的二次电池为钠离子电池，特别地，为钠离子二次电池时，所述电解质盐 可包括六氟磷酸钠(NaPF 6)、四氟硼酸钠(NaBF 4)、高氯酸钠(NaClO 4)、六氟砷酸钠(NaAsF 6)、双氟磺酰亚胺钠(NaFSI)、双三氟甲磺酰亚胺钠(NaTFSI)、三氟甲磺酸钠(NaTFS)、二氟草酸硼酸钠(NaDFOB)、二草酸硼酸钠(NaBOB)、二氟磷酸钠(NaPO 2F 2)、二氟二草酸磷酸钠(NaDFOP)和四氟草酸磷酸钠(NaTFOP)中的一种或多种。
所述溶剂的种类不受具体的限制，可根据实际需求进行选择。在一些实施例中，作为示例，所述溶剂可包括碳酸乙烯酯(EC)、碳酸亚丙酯(PC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸亚丁酯(BC)、氟代碳酸亚乙酯(FEC)、甲酸甲酯(MF)、乙酸甲酯(MA)、乙酸乙酯(EA)、乙酸丙酯(PA)、丙酸甲酯(MP)、丙酸乙酯(EP)、丙酸丙酯(PP)、丁酸甲酯(MB)、丁酸乙酯(EB)、1,4-丁内酯(GBL)、环丁砜(SF)、二甲砜(MSM)、甲乙砜(EMS)和二乙砜(ESE)中的一种或多种。
在一些实施例中，所述电解液中还可选地包括添加剂。例如，所述添加剂可以包括负极成膜添加剂，也可以包括正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温性能的添加剂、改善电池低温功率性能的添加剂等。
[隔离膜]
采用电解液的二次电池、以及一些采用固态电解质的二次电池中，还包括隔离膜。所述隔离膜设置在所述正极极片和所述负极极片之间，主要起到防止正极和负极短路的作用，同时可以使活性离子通过。本申请对所述隔离膜的种类没有特别的限制，可以选用任意公知的具有良好的化学稳定性和机械稳定性的多孔结构隔离膜。
在一些实施例中，所述隔离膜的材质可以包括玻璃纤维、无纺布、聚乙烯、聚丙烯和聚偏二氟乙烯中的一种或多种。所述隔离膜可以是单层薄膜，也可以是多层复合薄膜。所述隔离膜为多层复合薄膜时，各层的材料相同或不同。
[制备方法]
本申请的二次电池的制备方法是公知的。在一些实施例中，可将正极极片、隔离膜、负极极片和电解液组装形成二次电池。作为示例，可将正极极片、隔离膜、负极极片经卷绕工艺和/或叠片工艺形成电极组件，将电极组件置于外包装中，烘干后注入电解液，经过真空封装、静置、化成、整形等工序，得到电池单体。多个电池单体还可以进一步经由串联或并联或混联组成电池模块。多个电池模块还可以经由串联或并联或混联形成电池包。在一些实施例中，多个电池单体还可以直接组成电池包。
用电装置
本申请实施方式还提供一种用电装置，所述用电装置包括本申请的二次电池。所述二次电池可以用作所述用电装置的电源，也可以用作所述用电装置的能量存储单元。所述用电装置可以但不限于是移动设备(例如手机、平板电脑、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能***等。
所述用电装置可以根据其使用需求来选择二次电池的具体类型，例如电池单体、电 池模块或电池包。
图7是作为一个示例的用电装置的示意图。该用电装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该用电装置对高功率和高能量密度的需求，可以采用电池包或电池模块作为电源。
作为另一个示例的用电装置可以是手机、平板电脑、笔记本电脑等。该用电装置通常要求轻薄化，可以采用电池单体作为电源。
实施例
下述实施例更具体地描述了本申请公开的内容，这些实施例仅仅用于阐述性说明，因为在本申请公开内容的范围内进行各种修改和变化对本领域技术人员来说是明显的。除非另有声明，以下实施例中所报道的所有份、百分比、和比值都是基于质量计，而且实施例中使用的所有试剂都可商购获得或是按照常规方法进行合成获得，并且可直接使用而无需进一步处理，以及实施例中使用的仪器均可商购获得。
实施例1
(1)负极活性材料的制备
选取1kg孔隙率为45％的市售多孔生物质碳作为基底，置于气相沉积炉内，保持炉体转动速率为0.5rpm，使用氩气进行吹扫处理，并预升温至200℃。继续升温至600℃，并按照30％甲硅烷+70％氩气(体积比)通入第一混合气，总气体流量为2L/min，炉内压力为高于大气压400Pa的微正压，沉积时间为4h。暂停通入第一混合气，待炉内温度降至450℃，按照15％甲硅烷+85％氩气(体积比)通入第二混合气，总气体流量为2L/min，继续沉积8h。关闭第二混合气，再次升温至650℃，并按照20％乙炔+80％氩气(体积比)通入第三混合气，总气体流量为2L/min，沉积时间为0.5h，结束后冷却、出料、过325目筛，得到负极活性材料。
(2)二次电池(全电池)的制备
负极极片的制备：将上述制备的负极活性材料与导电剂导电碳黑和碳纳米管、粘结剂聚丙烯酸按照质量比95:1.9:0.1:3混合均匀后，加入至溶剂去离子水中，在快速搅拌机作用下搅拌至体系呈均一状，获得固含量为45％的负极浆料；将负极浆料均匀涂覆在负极集流体铜箔上并在85℃下烘干、冷压后得到负极极片。
正极极片的制备：将正极活性材料LiNi 0.8Co 0.1Mn 0.1O 2(NCM811)、导电剂碳黑(Super P)、粘结剂聚偏氟乙烯(PVDF)按质量比97:1:2在适量的溶剂NMP中充分搅拌混合，形成均匀的正极浆料；将正极浆料均匀涂覆于正极集流体铝箔的表面上，经干燥、冷压后，得到正极极片。
电解液的制备：将碳酸乙烯酯(EC)、碳酸甲乙酯(EMC)和碳酸二乙酯(DEC)按照体积比20:20:60混合均匀作为有机溶剂，然后将LiPF 6溶解在上述有机溶剂中，并加入氟代碳酸乙烯酯(FEC)，电解液中LiPF 6的浓度为1mol/L，FEC的质量百分含量为5wt％。
隔离膜的制备：采用Celgard 2400隔离膜。
二次电池的制备：将正极极片、隔离膜、负极极片按顺序堆叠并卷绕，得到电极组件；将电极组件置于外包装中，干燥后注入电解液，经过真空封装、静置、化成、整形等工序，得到二次电池。
(3)扣式电池(半电池)的制备
将上述制备的负极活性材料与导电剂导电碳黑、粘结剂聚丙烯酸按照质量比8:1:1混合均匀后，加入至溶剂去离子水中，在快速搅拌机作用下搅拌至体系呈均一状，获得固含量为45％的负极浆料；将负极浆料均匀涂覆在负极集流体铜箔上并在85℃下烘干、冷压后得到电极极片。以金属锂片作为对电极，采用Celgard 2400隔离膜，并注入与上述制备二次电池时相同的电解液，组装得到扣式电池。
实施例2-19和对比例5
二次电池和扣式电池的制备方法与实施例1类似，不同之处在于调整了负极活性材料的制备工艺参数，具体详见表1。
对比例1
二次电池和扣式电池的制备方法与实施例1类似，不同之处在于调整了负极活性材料的制备工艺参数。
采用无定形碳包覆的晶体硅作为负极活性材料，包覆层厚度为300nm。
对比例2
二次电池和扣式电池的制备方法与实施例1类似，不同之处在于调整了负极活性材料的制备工艺参数。
选取1kg孔隙率为45％的市售多孔生物质碳作为基底，置于气相沉积炉内，保持炉体转动速率为0.5rpm，使用氩气进行吹扫处理，并预升温至200℃。继续升温至600℃，并按照30％甲硅烷+70％氩气(体积比)通入第一混合气，总气体流量为2L/min，炉内压力为高于大气压400Pa的微正压，沉积时间为12h。关闭第一混合气，再次升温至650℃，并按照20％乙炔+80％氩气(体积比)通入第二混合气，总气体流量为2L/min，沉积时间为0.5h，结束后冷却、出料、过325目筛，得到负极活性材料。
对比例3
二次电池和扣式电池的制备方法与实施例1类似，不同之处在于调整了负极活性材料的制备工艺参数。
选取1kg孔隙率为45％的市售多孔生物质碳作为基底，置于气相沉积炉内，保持炉体转动速率为0.5rpm，使用氩气进行吹扫处理，并预升温至200℃。继续升温至450℃，并按照15％甲硅烷+85％氩气(体积比)通入第一混合气，总气体流量为2L/min，炉内压力为高于大气压400Pa的微正压，沉积时间为16h。关闭第一混合气，再次升温至650℃，并按照20％乙炔+80％氩气(体积比)通入第二混合气，总气体流量为2L/min，沉积时间为0.5h，结束后冷却、出料、过325目筛，得到负极活性材料。
对比例4
二次电池和扣式电池的制备方法与实施例1类似，不同之处在于调整了负极活性材料的制备工艺参数。
选取1kg孔隙率为45％的市售多孔生物质碳作为基底，置于气相沉积炉内，保持炉体转动速率为0.5rpm，使用氩气进行吹扫处理，并预升温至200℃。继续升温至450℃，并按照15％甲硅烷+85％氩气(体积比)通入第一混合气，总气体流量为2L/min，炉内压力为高于大气压400Pa的微正压，沉积时间为8h。暂停通入第一混合气，提高炉内温度至600℃，并按照30％甲硅烷+70％氩气(体积比)通入第二混合气，总气体流量为2L/min， 沉积时间为4h。关闭第二混合气，再次升温至650℃，并按照20％乙炔+80％氩气(体积比)通入第三混合气，总气体流量为2L/min，沉积时间为0.5h，结束后冷却、出料、过325目筛，得到负极活性材料。
表1
Figure PCTCN2022129326-appb-000001
测试部分
(1)晶态的硅基材料的晶粒尺寸以及面积测试
采用双束聚焦离子束显微镜从负极活性材料的颗粒核心截取样品，获得负极活性材料颗粒的截面图像，然后通过高分辨透射电子显微镜观察并计算晶态的硅基材料的晶粒尺寸，在所获取的截面图像中，以具备晶格条纹特征的区域为一个晶粒，该区域的直径作为晶粒尺寸，并取至少50个晶粒尺寸的平均值作为测试结果。测试仪器可以采用赛默飞世尔公司的Helios 5 CX聚焦离子束/扫描电镜双束***和赛默飞世尔公司的Spectra S/TEM扫描透射电子显微镜。
晶粒面积以晶粒形状为球形计算获得，并且球形直径采用晶粒尺寸进行计算。
由负极活性材料的颗粒外表面向颗粒内部延伸自颗粒外表面任一点与颗粒核心之间的长度的0.5倍的距离所构成的区域记为外部区域，外部区域内侧的区域记为内部区域。
上述截面图像中，外部区域中的晶态的硅基材料的总截面积与内部区域中的晶态的硅基材料的总截面积之比记为α1，上述截面图像的外部区域中晶态的硅基材料的总截面积与非晶态的硅基材料的总截面积之比记为β1，上述截面图像的内部区域中的晶态的硅基材料的总截面积与非晶态的硅基材料的总截面积之比记为β2，上述截面图像中的晶态的硅基材料的总截面积与负极活性材料的总截面积的比值记为γ1，上述截面图像中的非晶态的硅基材料的总截面积与负极活性材料的总截面积的比值记为γ2。
(2)负极活性材料的元素含量测试
参照GB/T 20123-2006/ISO 15350:2000测试负极活性材料中碳元素含量，测试仪器可以为HCS-140型红外碳硫分析仪。
参照GB/T 20975.5-2020测试负极活性材料中硅元素含量。
(3)负极活性材料的平均粒径Dv50测试
参照GB/T 19077-2016，得到负极活性材料的体积粒度分布曲线，取累计体积分布百分数达到50％时所对应的粒径作为平均粒径Dv50。测试仪器可以为英国马尔文仪器有限公司的Mastersizer 3000型激光粒度分析仪。
(4)负极活性材料的比表面积测试
参照GB/T 19587-2004，采用氮气吸附比表面积分析测试方法测试，并用BET(Brunauer Emmett Teller)法计算得出负极活性材料的比表面积。测试仪器可为美国Micromeritics公司的TRISTAR II 3020型比表面积与孔隙度分析仪。
(5)负极活性材料的孔容测试
参照GB/T 21650.2-2008测试负极活性材料的孔容。测试仪器可以为美国Micromeritics公司的TRISTAR II 3020型比表面积与孔隙度分析仪。
(6)首次库伦效率测试
将上述制备的扣式电池静置60min后，以0.05C恒流放电至5mV，然后以50μA放电至5mV，记录扣式电池的总放电容量即为初始嵌锂容量；静置10min后，将扣式电池以0.1C恒流充电至0.8V，记录扣式电池的充电容量即为初始脱锂容量。
负极活性材料的首次库伦效率＝初始脱锂容量/初始嵌锂容量。
(7)二次电池的循环性能测试
在25℃下，将上述制备的二次电池以0.5C满充后再以1C满放，此为一个循环充放电 过程，记录此时的放电容量，即为初始放电容量。将二次电池按照上述方法进行循环充放电测试，记录每圈循环后的放电容量，直至二次电池的放电容量衰减为初始放电容量的80％，用此时的循环圈数表征二次电池的循环性能。二次电池的循环圈数越高，循环性能越好。
(8)负极极片的体积膨胀测试
在25℃下，将上述制备的二次电池以0.33C满充后，在干燥房拆解获取负极极片，记录满充状态下的负极极片的厚度H 1。负极极片的体积膨胀率＝(H 1-H 0)/H 0，H 0表示负极极片冷压后的初始厚度。
表2
Figure PCTCN2022129326-appb-000002
Figure PCTCN2022129326-appb-000003
表3
序号 γ1 γ2 α1 β1 β2
实施例1 15％ 48％ 3.1:100 0.9:100 100:10
实施例2 20％ 43％ 10:100 5:100 100:2
实施例3 25％ 38％ 40:100 20:100 100:0
实施例4 10％ 53％ 0:100 0:100 100:60
实施例5 5％ 58％ 0:100 0:100 100:240
对比例5 40％ 25％ 120:100 80:100 100:0
综合表2测试结果可知，通过使硅基材料的至少一部分位于基体材料的孔结构中，使硅基材料包括晶态的硅基材料和非晶态的硅基材料，并使晶态的硅基材料主要位于负极活性材料的内部区域，而非晶态的硅基材料主要位于负极活性材料的外部区域，既能够充分发挥晶态的硅基材料对首次库伦效率的提升作用，又能充分发挥非晶态的硅基材料对循环性能的提升作用和对体积膨胀的降低作用。由此，本申请提供的负极活性材料能具有高容量、高首次库伦效率和低体积膨胀，并且还能使二次电池兼顾高能量密度、高首次库伦效率、长循环寿命和长存储寿命。
本申请的上述实施例制备的负极活性材料均满足，截面图像中的外部区域中的晶态的硅基材料的总截面积小于内部区域中的所述晶态的硅基材料的总截面积。综合表2和表3的测试结果可知，当负极活性材料的截面图像中的外部区域中的晶态的硅基材料的总截面积大于内部区域中的所述晶态的硅基材料的总截面积时，二次电池的循环性能差且体积膨胀高，不能使二次电池兼顾高能量密度、高首次库伦效率、长循环寿命和长存储寿命。综合表2和表3的测试结果还可知，当负极活性材料进一步满足，截面图像中的外部区域中的晶态的硅基材料的总截面积与内部区域中的晶态的硅基材料的总截面积之比α1为(0-50):100，可选为(0-10):100时，采用所述负极活性材料的二次电池能更好地兼顾高能量密度、高首次库伦效率、长循环寿命和长存储寿命。
对比例1采用碳包覆的晶体硅作为负极活性材料，晶体硅具有巨大的体积效应，而表面的碳层对晶体硅保护作用有限，并且在多次充放电后碳层即会出现破裂，进而导致SEI膜反复破坏与重建，增加了活性离子的不可逆消耗；并且随着充放电次数增加，SEI膜厚度也不断增加，进而二次电池的阻抗也会不断增加。因此，对比例1制备的二次电池的循环性能很差。
对比例2制备的负极活性材料中，硅基材料仅包括晶态的硅基材料，而不包括非晶态的硅基材料，由于晶态的硅基材料体积膨胀大、结构稳定性差，进而导致二次电池的循环性能差且体积膨胀高，不能使二次电池兼顾高能量密度、高首次库伦效率、长循环寿命和长存储寿命。
对比例3制备的负极活性材料中，硅基材料仅包括非晶态的硅基材料，而不包括晶态的硅基材料，由于非晶态的硅基材料的首次库伦效率较低，导致二次电池实际容量损失大，由此也不能使二次电池兼顾高能量密度、高首次库伦效率、长循环寿命和长存储寿命。
对比例4制备的负极活性材料中，晶态的硅基材料位于负极活性材料的外部区域，而非晶态的硅基材料位于负极活性材料的内部区域，由此导致二次电池的循环性能差且体积膨胀高，不能使二次电池兼顾高能量密度、高首次库伦效率、长循环寿命和长存储寿命。
需要说明的是，本申请不限定于上述实施方式。上述实施方式仅为示例，在本申请的技术方案范围内具有与技术思想实质相同的构成、发挥相同作用效果的实施方式均包含在本申请的技术范围内。此外，在不脱离本申请主旨的范围内，对实施方式施加本领域技术人员能够想到的各种变形、将实施方式中的一部分构成要素加以组合而构筑的其它方式也包含在本申请的范围内。

Claims (28)

  1. 一种负极活性材料，其中，所述负极活性材料包括基体材料以及硅基材料，所述基体材料包括多个孔结构，所述硅基材料的至少一部分位于所述基体材料的孔结构中，所述硅基材料包括晶态的硅基材料，由所述负极活性材料的颗粒外表面向颗粒内部延伸自所述颗粒外表面任一点与所述颗粒核心之间的长度的0.5倍的距离所构成的区域记为外部区域，所述外部区域内侧的区域记为内部区域，在所述负极活性材料的截面图像中，所述外部区域中的所述晶态的硅基材料的总截面积小于所述内部区域中的所述晶态的硅基材料的总截面积。
  2. 根据权利要求1所述的负极活性材料，其中，所述负极活性材料的截面图像包括经过所述负极活性材料的颗粒核心的截面图像。
  3. 根据权利要求1或2所述的负极活性材料，其中，在所述负极活性材料的截面图像中，所述外部区域中的所述晶态的硅基材料的总截面积与所述内部区域中的所述晶态的硅基材料的总截面积之比α1为(0-50):100，可选为(0-10):100。
  4. 根据权利要求1-3任一项所述的负极活性材料，其中，所述硅基材料还包括非晶态的硅基材料，可选地，在所述负极活性材料的截面图像中，所述外部区域中的所述非晶态的硅基材料的总截面积大于所述内部区域中的所述非晶态的硅基材料的总截面积。
  5. 根据权利要求4所述的负极活性材料，其中，所述内部区域中的所述非晶态的硅基材料的总截面积与所述外部区域中的所述非晶态的硅基材料的总截面积之比α2为(0-30):100，可选为(0-10):100。
  6. 根据权利要求1-5任一项所述的负极活性材料，其中，
    在所述负极活性材料的截面图像的外部区域中，所述晶态的硅基材料的总截面积与所述非晶态的硅基材料的总截面积之比β1为(0-25):100，可选为(0-5):100，更可选地，所述晶态的硅基材料的总截面积为0；和/或，
    在所述负极活性材料的截面图像的内部区域中，所述晶态的硅基材料的总截面积与所述非晶态的硅基材料的总截面积之比β2为100:(0-250)，可选为100:(0-100)。
  7. 根据权利要求1-6任一项所述的负极活性材料，其中，
    在所述负极活性材料的截面图像中，所述晶态的硅基材料的总截面积与所述负极活性材料的总截面积的比值γ1为大于0且小于等于25％，可选为5％-20％；和/或，
    在所述负极活性材料的截面图像中，所述非晶态的硅基材料的总截面积与所述负极活性材料的总截面积的比值γ2为大于等于35％且小于100％，可选为40％-60％。
  8. 根据权利要求1-7任一项所述的负极活性材料，其中，所述硅基材料中的所述晶态的硅基材料的质量百分含量为大于0且小于等于40wt％，可选为10wt％-30wt％。
  9. 根据权利要求1-8任一项所述的负极活性材料，其中，所述硅基材料的至少一部分位于所述基体材料的孔结构中，并且所述硅基材料与所述基体材料之间具有空隙。
  10. 根据权利要求1-9任一项所述的负极活性材料，其中，所述晶态的硅基材料的晶粒尺寸为大于0且小于等于10nm，可选为2nm-8nm。
  11. 根据权利要求1-10任一项所述的负极活性材料，其中，
    所述晶态的硅基材料包括晶态的单质硅、硅氧化物、硅碳材料、硅氮复合物和硅合 金材料中的一种或多种，可选地，所述晶态的硅基材料包括晶态的单质硅；和/或，
    所述非晶态的硅基材料包括非晶态的单质硅、硅氧化物、硅碳材料、硅氮复合物和硅合金材料中的一种或多种，可选地，所述非晶态的硅基材料包括非晶态的单质硅；和/或，
    所述硅基材料包括气相沉积硅基材料，可选地包括气相沉积单质硅。
  12. 根据权利要求1-11任一项所述的负极活性材料，其中，所述基体材料满足如下条件(1)至(3)中的至少一者：
    (1)所述基体材料的孔隙率为30％-60％，可选为40％-50％；
    (2)所述基体材料包括碳材料、石墨材料和过渡金属氧化物材料中的一种或多种；
    (3)所述基体材料包括碳材料，所述碳材料包括活性碳、生物质碳、热解碳和树脂碳中的一种或多种。
  13. 根据权利要求1-12任一项所述的负极活性材料，其中，所述负极活性材料还包括包覆层，所述包覆层位于所述基体材料的至少部分表面，所述包覆层满足如下条件(1)至(3)中的至少一者：
    (1)所述包覆层包括碳材料、导电聚合物、金属氧化物和金属硫化物中的一种或多种；
    (2)所述包覆层包括碳材料，可选地，所述碳材料包括硬碳、软碳、石墨烯、碳纤维和碳纳米管中的一种或多种；
    (3)所述包覆层的厚度为0nm-200nm，可选为10nm-150nm。
  14. 根据权利要求1-13任一项所述的负极活性材料，其中，所述负极活性材料包括碳元素和硅元素，
    可选地，所述负极活性材料中碳元素的质量百分含量为40wt％-60wt％，更可选为45wt％-50wt％；
    可选地，所述负极活性材料中硅元素的质量百分含量为38wt％-58wt％，更可选为40wt％-55wt％。
  15. 根据权利要求14所述的负极活性材料，其中，所述负极活性材料还包括其他元素，所述其他元素包括氧元素、金属元素和氮元素中的一种或多种，
    可选地，所述负极活性材料中其他元素的质量百分含量之和为0wt％-20wt％，更可选为0wt％-10wt％。
  16. 根据权利要求1-15任一项所述的负极活性材料，其中，
    所述负极活性材料的孔容为0.001cm 3/g-0.02cm 3/g，可选为0.01cm 3/g-0.02cm 3/g；和/或，
    所述负极活性材料的平均粒径Dv50为4μm-12μm；和/或，
    所述负极活性材料的BET比表面积为1m 2/g-15m 2/g。
  17. 一种负极活性材料的制备方法，包括如下步骤：提供包括多个孔结构的基体材料；将硅基材料分散至所述基体材料的孔结构中，即得到负极活性材料，其中，所述负极活性材料包括基体材料以及硅基材料，所述基体材料包括多个孔结构，所述硅基材料的至少一部分位于所述基体材料的孔结构中，所述硅基材料包括晶态的硅基材料，由所述负极活性材料的颗粒外表面向颗粒内部延伸自所述颗粒外表面任一点与所述颗粒核心 之间的长度的0.5倍的距离所构成的区域记为外部区域，所述外部区域内侧的区域记为内部区域，在所述负极活性材料的截面图像中，所述外部区域中的所述晶态的硅基材料的总截面积小于所述内部区域中的所述晶态的硅基材料的总截面积。
  18. 根据权利要求17所述的方法，其中，所述基体材料满足如下条件(1)至(4)中的至少一者：
    (1)所述基体材料的孔隙率为30％-60％，可选为40％-50％；
    (2)所述基体材料包括碳材料、石墨材料和过渡金属氧化物材料中的一种或多种；
    (3)所述基体材料包括碳材料，所述碳材料包括活性碳、生物质碳、热解碳和树脂碳中的一种或多种；
    (4)所述基体材料的平均粒径Dv50为4μm-12μm。
  19. 根据权利要求17或18所述的方法，其中，将硅基材料分散至所述基体材料的孔结构中的步骤包括如下步骤：将包括多个孔结构的基体材料作为基底置于反应炉内，通入含有硅源气体的第一混合气并在第一温度T 1下沉积第一时间t 1，结束后停止通入第一混合气；待炉内温度降至第二温度T 2后，通入含有硅源气体的第二混合气，并在第二温度T 2下沉积第二时间t 2，结束后即得到负极活性材料，其中，所述硅基材料包括晶态的硅基材料以及非晶态的硅基材料，在所述负极活性材料的截面图像中，所述外部区域中的所述晶态的硅基材料的总截面积小于所述内部区域中的所述晶态的硅基材料的总截面积，所述外部区域中的所述非晶态的硅基材料的总截面积大于所述内部区域中的所述非晶态的硅基材料的总截面积。
  20. 根据权利要求19所述的方法，其中，在通入含有硅源气体的第一混合气之前，还包括步骤：将包括多个孔结构的基体材料作为基底置于反应炉内，使用保护气体进行吹扫处理和预升温处理，可选地，所述预升温的温度为200℃-300℃。
  21. 根据权利要求19或20所述的方法，其中，
    所述第一混合气中的所述硅源气体的体积占比V 1大于所述第二混合气中的所述硅源气体的体积占比V 2；和/或，
    T 1>T 2；和/或，
    t 1<t 2。
  22. 根据权利要求19-21任一项所述的方法，其中，
    所述第一混合气包括硅源气体和保护气体，可选地，所述第一混合气中的所述硅源气体的体积占比V 1为10％-50％；和/或，
    所述第一混合气的总气体流量为0.5L/min-20L/min；和/或，
    第一温度T 1为500℃-700℃；和/或，
    第一时间t 1为0.5h-8h，可选为0.5h-4h。
  23. 根据权利要求19-22任一项所述的方法，其中，
    所述第二混合气包括硅源气体和保护气体，可选地，所述第二混合气中的所述硅源气体的体积占比V 2为5％-20％；和/或，
    所述第二混合气包括硅源气体、碳源气体和保护气体，可选地，所述第二混合气中的所述硅源气体的体积占比V 2为5％-20％，所述碳源气体的体积占比为5％-10％；和/或，
    所述第二混合气的总气体流量为0.5L/min-20L/min；和/或，
    第二温度T 2为400℃-500℃；和/或，
    第二时间t 2为2h-16h，可选为4h-16h；和/或，
    所述第二混合气的总气体流量与所述第一混合气的总气体流量相同。
  24. 根据权利要求17-23任一项所述的方法，还包括如下步骤：在所获得的负极活性材料的至少表面形成包覆层，所述包覆层包括碳材料、导电聚合物、金属氧化物和金属硫化物中的一种或多种。
  25. 根据权利要求24所述的方法，其中，所述形成包覆层的步骤包括以下步骤：将所获得的负极活性材料置于反应炉内，通入含有碳源气体的第三混合气，并在第三温度T 3下沉积第三时间t 3，得到碳包覆的负极活性材料。
  26. 根据权利要求25所述的方法，其中，
    所述第三混合气包括碳源气体和保护气体，可选地，所述第三混合气中的所述碳源气体的体积占比V 3为10％-50％；和/或，
    所述第三混合气的总气体流量为0.5L/min-20L/min；和/或
    第三温度T 3为600℃-700℃；和/或，
    第三时间t 3为0.5h-2h。
  27. 一种二次电池，包括负极极片，所述负极极片包括权利要求1-16任一项所述的负极活性材料或通过权利要求17-26任一项所述的方法制备得到的负极活性材料。
  28. 一种用电装置，包括权利要求27所述的二次电池。
PCT/CN2022/129326 2022-11-02 2022-11-02 负极活性材料及其制备方法、以及包含其的二次电池及用电装置 WO2024092569A1 (zh)

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