WO2022140975A1 - 一种负极极片、包含该负极极片的电化学装置及电子装置 - Google Patents

一种负极极片、包含该负极极片的电化学装置及电子装置 Download PDF

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WO2022140975A1
WO2022140975A1 PCT/CN2020/140366 CN2020140366W WO2022140975A1 WO 2022140975 A1 WO2022140975 A1 WO 2022140975A1 CN 2020140366 W CN2020140366 W CN 2020140366W WO 2022140975 A1 WO2022140975 A1 WO 2022140975A1
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silicon
negative electrode
pole piece
based particles
porosity
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PCT/CN2020/140366
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English (en)
French (fr)
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廖群超
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宁德新能源科技有限公司
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Priority to EP20967326.8A priority Critical patent/EP4270532A4/en
Priority to CN202080097358.4A priority patent/CN115136348A/zh
Priority to KR1020237025218A priority patent/KR20230117625A/ko
Priority to PCT/CN2020/140366 priority patent/WO2022140975A1/zh
Publication of WO2022140975A1 publication Critical patent/WO2022140975A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1395—Processes of manufacture of electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/364—Composites as mixtures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the field of electrochemistry, and in particular, to a negative electrode piece, an electrochemical device including the negative electrode piece, and an electronic device.
  • Lithium-ion secondary batteries have the advantages of high energy storage density, high open-circuit voltage, low self-discharge rate, long cycle life, and good safety. They are widely used in various fields such as electrical energy storage, mobile electronic equipment, electric vehicles, and aerospace equipment. With the rapid development of mobile electronic devices and electric vehicles, the market has put forward higher and higher requirements for the energy density, safety, cycle performance and service life of lithium-ion secondary batteries.
  • silicon-based materials Since the theoretical capacity of silicon-based materials reaches 4200mAh/g, which is currently known as the negative electrode material with the highest theoretical capacity, and at the same time, silicon is abundant in reserves and low in price, silicon-based materials are often used as negative electrode pieces in lithium-ion secondary batteries at present. as the next generation high gram capacity anode material.
  • the volume change rate of silicon-based materials is as high as 300% in the process of lithium deintercalation, which will generate a large amount of solid electrolyte interphase (SEI), which consumes the limited lithium ions and electrolytes in lithium ion secondary batteries.
  • SEI solid electrolyte interphase
  • the impedance of the lithium-ion secondary battery is increased, which seriously hinders its industrialized and large-scale application.
  • the main solution to the current problem is to nanoscale and compound silicon-based materials, but the nanoscale preparation process is complex, high energy consumption, and the ultra-high specific surface area makes it easy to agglomerate, so it is impossible to completely solve the problem of silicon-based materials.
  • the purpose of the present application is to provide a negative pole piece, an electrochemical device and an electronic device including the negative pole piece, so as to improve the cycle performance and the problems of expansion and deformation of the electrochemical device.
  • the present application is explained by taking a lithium ion battery as an example of an electrochemical device, but the electrochemical device of the present application is not limited to a lithium ion battery.
  • a first aspect of the present application provides a negative electrode pole piece, which includes a negative electrode material layer, the negative electrode material layer includes silicon-based particles and graphite particles, the silicon content B in the silicon-based particles is 20wt% to 60wt%, and the pores of the silicon-based particles The rate ⁇ 1 is 15% to 60%, and the negative pole piece porosity ⁇ 2 is 15% to 41%.
  • the porosity ⁇ 1 of the silicon-based particle refers to the percentage of the volume of pores in the silicon-based particle to the total volume of the silicon-based particle.
  • negative electrode pole piece porosity ⁇ 2 refers to the percentage of the volume of various inter-particle pores in the negative electrode pole piece to the total volume of the negative electrode pole piece.
  • the silicon content B in the silicon-based particles is 20wt% to 60wt%, for example, the lower limit of the silicon content B may be included in the following values: 20wt%, 30wt% or 36wt%; silicon content The upper limit of B may be included in the following values: 40 wt %, 50 wt % or 60 wt %.
  • the silicon content B When the silicon content B is less than 20wt%, the gram capacity of the negative electrode material layer is small; when the silicon content B is greater than 60wt%, the volume change rate of the silicon-based particles in the process of lithium deintercalation is accelerated, which will generate more SEI and accelerate the consumption of lithium ions The lithium ion and electrolyte in the battery significantly increase the impedance of the lithium ion battery.
  • the porosity ⁇ 1 of the silicon-based particles is 15% to 60%, for example, the lower limit of the porosity ⁇ 1 of the silicon-based particles may include the following values: 15%, 16%, 18%, 25% , 30% or 33%; the upper limit of the porosity ⁇ 1 of the silicon-based particles may be included in the following values: 38%, 45%, 47%, 56% or 60%.
  • the porosity ⁇ 1 of the silicon-based particles When the porosity ⁇ 1 of the silicon-based particles is less than 15%, the reserved space is difficult to buffer the volume expansion of lithium intercalation of nano-silicon, and the mechanical strength of the carbonaceous material is difficult to withstand the huge expansion stress, which will lead to the rupture of the silicon-based particle structure and deteriorate its Electrochemical performance; when the porosity ⁇ 1 of the silicon-based particles is greater than 60%, the pores are too large and the compressive strength of the carbonaceous material is reduced, which causes the silicon-based particles to be easily broken during processing and deteriorates their electrochemical performance.
  • the porosity ⁇ 2 of the negative electrode is 15% to 41%.
  • the lower limit of the porosity ⁇ 2 of the negative electrode may include the following values: 15%, 19% or 28%; the porosity of the negative electrode
  • the upper limit value of the rate ⁇ 2 may be included in the following values: 35% or 41%.
  • the porosity of the negative pole piece is less than 15%, it is difficult for the electrolyte to fully infiltrate, which will increase the transmission distance of lithium ions and deteriorate the kinetics of the lithium ion battery; when the porosity of the negative pole piece is greater than 41%, the lithium ion The battery is prone to contact failure between silicon-based particles and graphite particles during cycling, resulting in deterioration of cycle performance and lower energy density of lithium-ion batteries.
  • the pores in the silicon-based particles and the negative electrode plate each independently comprise micropores with a pore diameter of less than 2 nm, mesopores with a pore diameter of 2 nm to 50 nm, or macropores with a pore diameter of more than 50 nm.
  • the number of the above-mentioned micropores, mesopores and macropores is not particularly limited, as long as the purpose of the present application can be achieved.
  • the negative electrode pole piece provided by the present application comprises a negative electrode material layer
  • the negative electrode material layer comprises silicon-based particles and graphite particles
  • pores are made in the silicon-based particles and in the negative electrode pole piece
  • the porosity of the silicon-based particles ⁇ 1 The silicon content B in the silicon-based particles, and the porosity ⁇ 2 of the negative electrode pole piece are controlled within the above range, so as to jointly relieve the lithium insertion expansion of the negative electrode pole piece.
  • the negative pole piece can not only have a certain space for lithium insertion and expansion, but also take into account the stability of its structure and processability, which can fundamentally solve the problem of lithium ion battery failure due to volume expansion and deformation of negative electrode active materials. Effectively improve the cycle performance and expansion deformation problems of lithium-ion batteries.
  • the sum ⁇ of the porosity ⁇ 1 of the silicon-based particles and the porosity ⁇ 2 of the negative electrode pole piece satisfies: 45% ⁇ 90%.
  • the lower limit of the sum ⁇ of the porosity ⁇ 1 of the silicon-based particles and the porosity ⁇ 2 of the negative electrode pole piece may be included in the following values: 45%, 46%, 49%, 53%, 58%, 61% or 62% %;
  • the upper limit of the sum ⁇ of the porosity ⁇ 1 of the silicon-based particles and the porosity ⁇ 2 of the negative pole piece can be included in the following values: 65%, 71%, 73%, 88% or 90%.
  • the lower limit of the P value can be included in the following values: 0.2, 0.4, 0.5 or 0.8; the upper limit value of the P value can be included in the following values: 1.1, 1.5 or 1.6.
  • the reserved pores in the silicon-based particles are difficult to buffer the volume expansion of lithium intercalation of nano-silicon.
  • the content of the silicon-based particles in the negative electrode material layer is 3 wt % to 80 wt %.
  • the lower limit of the content of the silicon-based particles in the negative electrode material layer may include the following values: 3 wt %, 10 wt %, 20 wt %, 25 wt %, 30 wt %, 35 wt % or 40 wt %;
  • the upper limit value of the content may include the following values: 45 wt %, 55 wt %, 60 wt %, 70 wt % or 80 wt %.
  • the content of graphite particles in the negative electrode material layer is not particularly limited in the present application, as long as the purpose of the present application can be achieved.
  • the content of graphite particles in the negative electrode material layer may be 20wt% to 97wt%, and the lower limit of the content of graphite particles in the negative electrode material layer may include the following values: 20wt%, 25wt%, 30wt% or 40wt%, the negative electrode material
  • the upper limit of the content of graphite particles in the layer may be included in the following values: 50 wt %, 60 wt %, 70 wt %, 80 wt % or 90 wt %.
  • the silicon-based particles may contain silicon elements, carbon elements, and oxygen elements, and the silicon-based particles may further contain nitrogen elements, phosphorus elements, sulfur elements, and the like.
  • the type of silicon-based particles is not particularly limited in the present application, as long as the purpose of the present application can be achieved.
  • the peak intensity ratio of the D peak to the G peak of the silicon-based particle measured by Raman is 0.2 to 2; wherein, the D peak is the displacement range of the Raman spectrum of the silicon-based particle is 1255 cm ⁇ The peaks from 1 to 1355 cm- 1 , and the G peaks are peaks with shifts ranging from 1575 cm- 1 to 1600 cm -1 in the Raman spectrum of silicon-based particles.
  • the peak intensity ratio of the D peak to the G peak of the silicon-based particles is controlled within the above range by the Raman test, the carbonaceous material of the silicon-based particles has sufficient pore defects, which is beneficial to restrain its expansion and deformation during the cycle. Thereby, the anti-expansion performance and cycle performance of the negative pole piece are improved.
  • the present application there is a carbon material on the surface of the silicon-based particles.
  • the present application does not specifically limit the type of the carbon material, as long as the purpose of the present application can be achieved.
  • the carbon material may include amorphous carbon, carbon nanomaterials At least one of tubes, carbon nanoparticles, vapor-deposited carbon fibers, or graphene, and the like.
  • the carbon nanotubes may comprise at least one of single-walled carbon nanotubes or multi-walled carbon nanotubes.
  • the present application does not specifically limit the preparation method of the carbon material present on the surface of the silicon-based particles, as long as the purpose of the present application can be achieved.
  • the content of the carbon material is not particularly limited, as long as the purpose of the present application can be achieved, for example, it can be 0.01wt% to 1wt% of the silicon-based particles, for example, 0.01wt%, 0.1wt%, 0.5wt% % or 1wt%.
  • the presence of carbon material on the surface of the silicon-based particles is beneficial to improve the interface stability of the surface of the silicon-based particles, so as to restrain the offset of the silicon-based particles, and can also effectively alleviate the structural damage caused by the volume expansion and contraction of the silicon-based particles, and avoid the generation of fresh interfaces. , thereby improving the cycle performance and expansion deformation of the negative pole piece.
  • the polymer material there is a polymer material on the surface of the silicon-based particle.
  • the application does not have any special restrictions on the type of the polymer material, as long as the purpose of the present application can be achieved.
  • the polymer material may contain polyvinylidene fluoride. At least one of ethylene (PVDF), carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose (CMC-Na), polyvinyl pyrrolidone (PVP), polyacrylic acid, polystyrene butadiene rubber and its derivatives, etc. kind.
  • the polymer material may include sodium carboxymethylcellulose, polyvinylpyrrolidone, polyvinylidene fluoride, and sodium polyacrylate (PAANa).
  • PAANa sodium polyacrylate
  • the present application does not specifically limit the preparation method of the polymer material present on the surface of the silicon-based particle, as long as the purpose of the present application can be achieved.
  • the content of the polymer material is not particularly limited, as long as the purpose of the present application can be achieved, it can be 0wt% to 0.4wt% of the silicon-based particles, for example, 0wt%, 0.025wt%, 0.15wt% or 0.4 wt%.
  • the silicon-based particles have an average particle size Dv50 of less than 20 ⁇ m.
  • the average particle size Dv50 of the silicon-based particles is greater than 20 ⁇ m, problems such as scratches are prone to occur during the processing of the negative pole piece, and the mutual contact points between the particles are reduced, thereby affecting the cycle performance of the negative pole piece.
  • the average particle diameter Dv50 of the silicon-based particles of the present application is controlled to be within the above range, the cycle performance of the negative electrode sheet can be improved.
  • the particle size of the graphite particles is not particularly limited as long as the purpose of the present application can be achieved.
  • the silicon-based particles have a specific surface area of less than 50 m 2 /g.
  • the specific surface area of the silicon-based particles is greater than 50m 2 /g, the specific surface area of the silicon-based particles is too large, and side reactions will affect the performance of the lithium-ion battery, and at the same time, a higher proportion of the binder needs to be consumed. As a result, the bonding force between the negative electrode material layer and the negative electrode current collector is reduced, and the internal resistance growth rate is high.
  • the size of the specific surface area of the graphite particles is not particularly limited, as long as the purpose of the present application can be achieved.
  • the compacted density of the negative electrode sheet of the present application is 1.0 g/cm 3 to 1.9 g/cm 3 , which enables the lithium ion battery to have high energy density.
  • the negative electrode current collector contained in the negative electrode sheet is not particularly limited, as long as the purpose of the present application can be achieved, for example, it may contain copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam , foam copper or composite current collectors, etc.
  • the thickness of the negative electrode current collector and the negative electrode material layer is not particularly limited, as long as the purpose of the present application can be achieved, for example, the thickness of the negative electrode current collector is 6 ⁇ m to 10 ⁇ m, and the thickness of the negative electrode material layer is 30 ⁇ m to 120 ⁇ m.
  • the thickness of the negative electrode sheet is not particularly limited, as long as the purpose of the present application can be achieved, for example, the thickness of the negative electrode sheet is 50 ⁇ m to 150 ⁇ m.
  • the negative electrode sheet may further comprise a conductive layer, and the conductive layer is located between the negative electrode current collector and the negative electrode material layer.
  • the composition of the conductive layer is not particularly limited, and may be a conductive layer commonly used in the art.
  • the conductive layer includes a conductive agent and a binder.
  • the positive electrode sheet in the present application is not particularly limited, as long as the purpose of the present application can be achieved.
  • a positive electrode sheet typically includes a positive current collector and a layer of positive material.
  • the positive electrode current collector is not particularly limited, as long as the purpose of the present application can be achieved, for example, it may include aluminum foil, aluminum alloy foil, or composite current collector.
  • the positive electrode material layer includes a positive electrode active material, and the positive electrode active material is not particularly limited, as long as the purpose of the application can be achieved. At least one of lithium iron, lithium-rich manganese-based material, lithium cobaltate, lithium manganate, lithium iron manganese phosphate, or lithium titanate.
  • the thicknesses of the positive electrode current collector and the positive electrode material layer are not particularly limited as long as the purpose of the present application can be achieved.
  • the thickness of the positive electrode current collector is 8 ⁇ m to 12 ⁇ m
  • the thickness of the positive electrode material layer is 30 ⁇ m to 120 ⁇ m.
  • the positive electrode sheet may further comprise a conductive layer, and the conductive layer is located between the positive electrode current collector and the positive electrode material layer.
  • the composition of the conductive layer is not particularly limited, and may be a conductive layer commonly used in the art.
  • the conductive layer includes a conductive agent and a binder.
  • the conductive agent described above is not particularly limited as long as the purpose of the present application can be achieved.
  • the conductive agent may include at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fiber, flake graphite, Ketjen black, or graphene, and the like.
  • the above-mentioned binder is not particularly limited, and any binder known in the art can be used as long as the purpose of the present application can be achieved.
  • the binder may include polyacryl alcohol, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyimide, polyamideimide, styrene butadiene rubber (SBR), polyvinyl alcohol ( At least one of PVA), polyvinylidene fluoride, polytetrafluoroethylene (PTFE), carboxymethyl cellulose or sodium carboxymethyl cellulose (CMC-Na) and the like.
  • SBR styrene-butadiene rubber
  • SBR styrene-butadiene rubber
  • the separator in the present application is not particularly limited as long as the purpose of the present application can be achieved.
  • polyethylene (PE), polypropylene (PP)-based polyolefin (PO) separators polyester films (such as polyethylene terephthalate (PET) films), cellulose films, polyimide Amine film (PI), polyamide film (PA), spandex or aramid film, woven film, non-woven film (non-woven fabric), microporous film, composite film, diaphragm paper, rolled film, spinning film, etc. at least one of.
  • the release film may include a substrate layer and a surface treatment layer.
  • the substrate layer can be a non-woven fabric, film or composite film with a porous structure, and the material of the substrate layer can include at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide, etc. kind.
  • polypropylene porous membranes, polyethylene porous membranes, polypropylene non-woven fabrics, polyethylene non-woven fabrics, or polypropylene-polyethylene-polypropylene porous composite membranes may be used.
  • at least one surface of the substrate layer is provided with a surface treatment layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.
  • the inorganic layer includes inorganic particles and a binder
  • the inorganic particles are not particularly limited, and can be selected from aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, ceria, nickel oxide, for example , at least one of zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate.
  • the binder is not particularly limited, for example, it can be selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyethylene One or a combination of rolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.
  • the polymer layer contains a polymer, and the material of the polymer includes polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly( At least one of vinylidene fluoride-hexafluoropropylene) and the like.
  • the lithium ion battery of the present application further includes an electrolyte, and the electrolyte may be one or more of a gel electrolyte, a solid electrolyte, and an electrolyte, and the electrolyte includes a lithium salt and a non-aqueous solvent.
  • the lithium salt may include LiPF 6 , LiBF 4 , LiAsF 6 , LiClO 4 , LiB(C 6 H 5 ) 4 , LiCH 3 SO 3 , LiCF 3 SO 3 , LiN(SO 2 CF 3 ) 2. At least one of LiC(SO 2 CF 3 ) 3 , LiSiF 6 , LiBOB or lithium difluoroborate.
  • LiPF 6 may be chosen as the lithium salt because it gives high ionic conductivity and improves cycling characteristics.
  • the non-aqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvents, or a combination thereof.
  • the above-mentioned carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluorocarbonate compound, or a combination thereof.
  • Examples of the above-mentioned chain carbonate compound are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), carbonic acid Methyl ethyl ester (MEC) and combinations thereof.
  • Examples of cyclic carbonate compounds are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylethylene carbonate (VEC), and combinations thereof.
  • Examples of fluorocarbonate compounds are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate Ethyl carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-dicarbonate Fluoro-1-methylethylene, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, and combinations thereof.
  • carboxylate compounds are methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, ⁇ -butyrolactone , caprolactone, valerolactone, mevalonolactone, caprolactone, and combinations thereof.
  • ether compounds examples include dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethyl ether Oxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.
  • Examples of the above-mentioned other organic solvents are dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, Formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters and combinations thereof.
  • the present application also provides an electrochemical device, comprising a negative pole piece, the negative pole piece is the negative pole piece mentioned in any of the above embodiments, and the electrochemical device has good cycle performance, anti-expansion performance, and rate performance. and volumetric energy density.
  • the electrochemical device of the present application is not particularly limited, and it may include any device in which an electrochemical reaction occurs.
  • the electrochemical device may include, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery, and the like.
  • the present application also provides an electronic device comprising the electrochemical device described in the embodiments of the present application, and the electronic device has good cycle performance, anti-expansion performance, rate performance and volumetric energy density.
  • electronic devices may include, but are not limited to, notebook computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, headsets, VCRs, LCD TVs, portable cleaners, portable CD players, mini discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, assisted bicycles, bicycles, Lighting equipment, toys, game consoles, clocks, power tools, flashlights, cameras, large-scale household storage batteries and lithium-ion capacitors, etc.
  • an electrochemical device can be manufactured by the following process: overlapping the positive electrode and the negative electrode through a separator, wrapping them, folding them, etc., and putting them into the casing as needed, injecting the electrolyte into the casing and sealing it, wherein
  • the separator used is the aforementioned separator provided in this application.
  • an overcurrent preventing element, a guide plate, etc. may be placed in the case to prevent pressure rise and overcharge and discharge inside the electrochemical device.
  • a negative electrode pole piece an electrochemical device and an electronic device comprising the negative electrode pole piece provided by the present application
  • the negative electrode material layer of the negative electrode pole piece contains silicon-based particles and graphite particles
  • the silicon content B in the silicon-based particles is 20wt% to 60wt%
  • the porosity ⁇ 1 of the silicon-based particles is 15% to 60%
  • the porosity ⁇ 2 of the negative pole piece is 15% to 41%
  • Fig. 2 is the SEM image of Fig. 1 magnification
  • Fig. 3 is the cycle decay curve of Example 3 of the application and Comparative Example 1;
  • FIG. 4 is the expansion curve of the lithium ion battery of Example 3 and Comparative Example 1.
  • FIG. 4 is the expansion curve of the lithium ion battery of Example 3 and Comparative Example 1.
  • Reference numerals 10. Pores in silicon-based particles; 20. Pores in negative pole pieces.
  • the present application is explained by taking a lithium ion battery as an example of an electrochemical device, but the electrochemical device of the present application is not limited to a lithium ion battery.
  • FIG. 1 shows a SEM image of a cross-section of a negative pole piece in an embodiment of the present application
  • FIG. 2 is a magnified SEM image of FIG. 1.
  • the pores 10 in the silicon-based particles are the pores in the silicon-based particles.
  • the pores 20 of the negative pole piece refer to the pores between various particles in the negative electrode material layer.
  • the interface of the silicon-based particles was photographed using scanning electron microscope transmission mode (STEM), and the obtained STEM image was used to determine the porosity. Specifically: use Image J software to binarize the image threshold (threshold), calibrate the size according to the scale, and use Analyze Particles to count the area of the pores to obtain the area ratio, which is the silicon-based particle the porosity ⁇ 1 ; take any 20 or more silicon-based particles in the pole piece to carry out the same test, and take the average value.
  • STEM scanning electron microscope transmission mode
  • the silicon-based particles were sliced, and the elemental mass percentage mean was measured using EDS (energy dispersive X-ray spectroscopy) linear scan.
  • a button cell was used to test the gram capacity of the negative electrode material layer. Put the assembled button battery at 25°C constant temperature for 5min, discharge it to 0.005V at 0.05C, let it stand for 5min, use 20 ⁇ A to discharge to 0.005V, the sum of the two-step discharge capacity is D0, after standing for 5min, According to 0.1C charging to 2.0V, the charging capacity at this time is C0, and the first charging efficiency is C0/D0 ⁇ 100%.
  • Dv50 is the cumulative 50% diameter of the particles in the volume reference distribution obtained by the laser scattering particle size analyzer.
  • the test temperature is 25/45°C, charge to 4.4V with 0.7C constant current, charge to 0.025C with constant voltage, and discharge to 3.0V with 0.5C after standing for 5 minutes.
  • the capacity obtained in this step was taken as the initial capacity, and 0.7C charge/0.5C discharge was carried out for cycle test, and the capacity decay curve was obtained by taking the ratio of the capacity in each step to the initial capacity.
  • the room temperature cycle performance of the lithium-ion battery was recorded as the number of cycles from 25°C to 90% of the capacity retention rate, and the high-temperature cycle performance of the lithium-ion battery was recorded as the number of cycles from 45°C to 80%.
  • the cycle performance of the material is obtained by the number of cycles in this case.
  • discharge at 0.2C to 3.0V let stand for 5 minutes, charge at 0.5C to 4.45V, charge at constant voltage to 0.05C, and then let stand for 5 minutes, adjust the discharge rate, respectively, at 0.2C, 0.5C, 1C , 1.5C, 2.0C for discharge test, respectively, to obtain the discharge capacity, compare the capacity obtained at each rate with the capacity obtained at 0.2C, and compare the rate performance by comparing the ratio of 2C and 0.2C.
  • the porous carbon material with a porosity of 41% was placed in a closed gas reactor containing silicon, heated to 500 ° C and kept for 4 h, and after cooling, sieved and demagnetized to obtain the porosity of the silicon-based particles ⁇ 1 It is 30% of silicon-based particles, wherein the carbon content of the silicon-based particles is 64 wt%, and the silicon content B in the silicon-based particles is 36 wt%.
  • the negative electrode active material, graphite particles and nano-conductive carbon black prepared above are mixed according to the mass ratio of 30:66.5:3.5 to obtain the first mixture; the first mixture and the binder PAA are added to the deionized water according to the mass ratio of 95:5 , prepare a slurry with a solid content of 45%, and stir evenly to obtain the first mixed slurry; evenly coat the first mixed slurry on one surface of the negative current collector copper foil with a thickness of 8 ⁇ m, and the air drying After drying at 120 °C for 2 min, a negative electrode sheet with a coating weight of 7.5 mg/cm 2 was obtained with a single-sided coating of negative active material.
  • the single-sided coating of the negative pole piece has been completed; then, the above steps are repeated on the other surface of the negative pole piece to obtain a negative pole piece coated with negative active material on both sides, and the cold pressing is completed. After that, a negative electrode pole piece with a negative pole piece porosity ⁇ 2 of 15% was obtained, and the pole piece was cut into a size of 41 mm ⁇ 61 mm for use.
  • the positive active material lithium cobalt oxide (LiCoO 2 ), nano-conductive carbon black, and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97.5:1.0:1.5, and N-methylpyrrolidone (NMP) is added as a solvent.
  • NMP N-methylpyrrolidone
  • the single-side coating of the positive electrode sheet is completed.
  • the above steps are repeated on the other surface of the positive electrode sheet to obtain a positive electrode sheet coated with positive active material on both sides.
  • the pole piece is cut into a size of 38mm ⁇ 58mm for use.
  • Lithium salt lithium hexafluorophosphate is added to dissolve and evenly mix to obtain an electrolyte solution with a lithium salt concentration of 1.15 mol/L.
  • Alumina and polyvinylidene fluoride were mixed in a mass ratio of 90:10 and dissolved in deionized water to form a ceramic slurry with a solids content of 50%. Then, the ceramic slurry was uniformly coated on one side of the porous substrate (polyethylene, thickness 7 ⁇ m, average pore size 0.073 ⁇ m, porosity 26%) by gravure coating, and dried to obtain a ceramic coating
  • the bilayer structure with the porous substrate, the thickness of the ceramic coating is 50 ⁇ m.
  • PVDF Polyvinylidene fluoride
  • polyacrylate was mixed in a mass ratio of 96:4 and dissolved in deionized water to form a polymer slurry with a solids content of 50%. Then, the polymer slurry is uniformly coated on both surfaces of the above-mentioned double-layer structure of the ceramic coating layer and the porous substrate by the gravure coating method, and is subjected to drying treatment to obtain a separator, wherein the single layer formed by the polymer slurry is The coating thickness is 2 ⁇ m.
  • the above-prepared positive pole piece, separator and negative pole piece are stacked in sequence, so that the separator is placed between the positive pole and the negative pole to play a role of isolation, and the electrode assembly is obtained by winding.
  • the electrode assembly is placed in an aluminum-plastic film packaging bag, dried and then injected into the electrolyte, and the lithium-ion battery is obtained through the processes of vacuum packaging, standing, chemical formation, degassing, and trimming.
  • Example 2 Example 3, Example 4, Example 5, Example 6, Example 7, Example 8, Example 9, Example 10, Example 11, Example 12, Example 13, Example 14.
  • Example 15 Example 16 and Example 17, ⁇ preparation of negative electrode active material>, ⁇ preparation of negative pole piece>, ⁇ preparation of positive pole piece>, ⁇ preparation of electrolyte>, ⁇ preparation of separator
  • the preparation steps of Preparation> and ⁇ Preparation of Li-ion Battery> are the same as those in Example 1, and the changes of relevant preparation parameters are shown in Table 1:
  • ⁇ 1 is 30% of silicon-based particles, wherein the carbon content of the silicon-based particles is 64 wt%, and the silicon content B in the silicon-based particles is 36 wt%.
  • Example 19 Example 20, Example 21, Example 22, Example 23, Example 24, Example 25, Example 26, Example 27, Example 28, Example 29, Example 30, Example 31.
  • Example 32 and Example 33 ⁇ preparation of negative electrode active material>, ⁇ preparation of negative pole piece>, ⁇ preparation of positive pole piece>, ⁇ preparation of electrolyte>, ⁇ preparation of separator> and ⁇ Preparation of lithium ion battery>
  • the preparation steps are the same as in Example 18, and the changes in relevant preparation parameters are shown in Table 2:
  • Comparative Example 1 Comparative Example 2, Comparative Example 3, Comparative Example 4, Comparative Example 5 and Comparative Example 6, ⁇ preparation of negative electrode active material>, ⁇ preparation of negative electrode pole piece>, ⁇ preparation of positive electrode pole piece>, ⁇ The preparation steps of Electrolyte Preparation>, ⁇ Preparation of Separator> and ⁇ Preparation of Lithium Ion Battery> are the same as in Example 1, and the changes of relevant preparation parameters are shown in Table 3:
  • Example 1 Example 2, Example 3, Example 4, Example 5, Example 6, Example 7, Example 8, Example 9, Example 10, Comparative Example 1, Comparative Example 2, Comparative Example 3.
  • the preparation parameters of Comparative Example 4 are shown in Table 4:
  • Example 1 Example 2, Example 3, Example 4, Example 5, Example 6, Example 7, Example 8, Example 9, Example 10, Comparative Example 1, Comparative Example 2, Comparative Example 3.
  • Table 5 The test results of Comparative Example 4 are shown in Table 5:
  • Example 11 The preparation parameters of Example 11, Example 12, Example 13, Example 14, Example 15, Example 16, Example 17, Comparative Example 5, and Comparative Example 6 are shown in Table 6:
  • Example 11 The test results of Example 11, Example 12, Example 13, Example 14, Example 15, Example 16, Example 17, Comparative Example 5, and Comparative Example 6 are shown in Table 7:
  • Example 3 Example 18, Example 19, Example 20, Example 21, Example 22, Example 23, Example 24, Example 25, Example 26, Example 27, Example 28, Example 29.
  • the preparation parameters of Example 30, Example 31, Example 32, and Example 33 are shown in Table 8:
  • Example 3 Example 18, Example 19, Example 20, Example 21, Example 22, Example 23, Example 24, Example 25, Example 26, Example 27, Example 28, Example 29.
  • the test results of Example 30, Example 31, Example 32, and Example 33 are shown in Table 9:
  • Example 1 Example 2, Example 3, Example 4, Example 5 and Comparative Example 1 and Comparative Example 2 that when the porosity of the silicon-based particles is constant, the porosity of the negative pole piece is too low.
  • the cycle performance and expansion performance of lithium-ion batteries deteriorated significantly. This is because the pores inside the silicon-based particles cannot completely relieve the volume expansion of silicon during lithium intercalation. The swelling makes it difficult for the electrolyte to fully infiltrate, which increases the transport distance of lithium ions and deteriorates the kinetics of lithium ion batteries.
  • FIG. 3 shows the cyclic decay curves of Example 3 and Comparative Example 1;
  • FIG. 4 shows the expansion curves of Example 3 and Comparative Example 1.
  • Example 6 Example 7, Example 8, Example 9, Example 10 and Comparative Example 3 and Comparative Example 4
  • the porosity of the negative pole piece is constant, the porosity of the silicon-based particles is too low, The cycle performance and expansion performance of lithium-ion batteries have deteriorated significantly. This is because the space reserved inside the silicon-based particles is difficult to buffer the volume expansion of lithium intercalation of nano-silicon. At this time, the mechanical strength of carbonaceous materials cannot withstand huge expansion stress. Causes the silicon-based particle structure to disintegrate during cycling.
  • the porosity of the silicon-based particles is too high, the compressive strength of the carbonaceous material decreases, which causes the silicon-based particles to be easily broken during processing and deteriorates the electrical properties. The energy density also decreases.
  • Example 10 From Example 1, Example 2, Example 3, Example 4, Example 5, Example 6, Example 7, Example 8, Example 9, Example 10, it can be seen that the negative electrode in the lithium ion battery
  • the reasonable combination of sheet porosity and porosity of silicon-based particles can more effectively improve the cycle performance and anti-expansion performance of lithium-ion batteries, and increase their volumetric energy density.
  • Example 11 Example 12, Example 13, Example 14, Example 15 and Comparative Example 5 and Comparative Example 6, it can be seen that when the silicon content B is constant, there is no significant difference in the gram capacity of the negative electrode material layer. As the porosity of the silicon-based particles increases, the specific surface area of the silicon-based particles gradually increases.
  • Example 13 From Example 13, Example 16, and Example 17, it can be seen that the change of the silicon content B in the silicon-based particles leads to the change of the P value, which will affect the gram capacity of the negative electrode material layer and the specific surface of the silicon-based particles.
  • Example 11 Example 12, Example 13, Example 14, Example 15, Example 16, Example 17, Comparative Example 5, Comparative Example 6, it can be found that when the P value is too small, the internal The remaining pores are difficult to buffer the volume expansion of lithium intercalation of nano-silicon.
  • the mechanical strength of the carbonaceous material cannot withstand the huge expansion stress, which leads to the fragmentation of the silicon-based particle structure and deteriorates the electrochemical performance of the lithium-ion battery;
  • the pores reserved inside the silicon-based particles are too large, which not only deteriorates the mechanical compressive strength of carbonaceous materials, but also easily breaks during processing, exposing a large number of fresh interfaces, deteriorating the first efficiency and cycle performance of lithium-ion batteries, and Reduce the overall energy density of Li-ion batteries.
  • the cycle performance, anti-expansion performance and volumetric energy density of the lithium-ion battery can be effectively improved.
  • the silicon-based particles can not only have a certain space for silicon to intercalate lithium and expand, but also can Take into account the stability of its structure and processability.
  • Example 18 Example 19, Example 20, Example 21, Example 22, Example 23, Example 24, Example 25, Example 26, Example 27, Example 28, Example 29, Example Compared with Example 3, Example 30, Example 31, Example 32, Example 33 and Example 3, adding 0.1wt% of SCNT on the surface of silicon-based particles can significantly improve the cycle performance, and adding 0.1wt% of MCNT has a slight effect on the cycle performance.
  • the addition of 0.05wt% SCNT and 0.05wt% MCNT can improve the cycle performance to a certain extent.
  • Example 18, Example 21, Example 22, Example 23, Example 24 changed the addition amount of SCNT.
  • Example 18 Example 25, Example 26, and Example 27 compare different dispersants, without adding dispersants, SCNT cannot be dispersed, and the cycle performance and deformation of lithium-ion batteries deteriorate; PVP and PVDF are used as dispersants, compared with CMC. The cycle performance of -Na and PAANa is slightly deteriorated.
  • Example 29 and Example 30 the amount of dispersant added was changed.
  • the dispersant amount was 0.4 wt%, the dispersion effect was improved, but too much dispersant would deteriorate the rate performance; when the dispersant amount was 0.025 wt%, the dispersion effect was poor, and the cycle Performance and rate performance deteriorate relative to the dispersant at 0.15 wt%.
  • Example 28, Example 31, Example 32, and Example 33 compared the coating of different carbon materials. From the results, the coating effect of CNT and graphene was the best. This is because after coating CNT and graphene, not only increased The electronic conductivity of the material can also increase the contact sites between the materials and reduce the cycle decay caused by contact failure.
  • the negative pole piece provided by the present application by controlling the porosity ⁇ 1 of the silicon-based particles, the silicon content B in the silicon-based particles, and the porosity of the negative pole piece ⁇ 2 within a reasonable range, the negative pole piece is jointly alleviated.
  • the lithium intercalation and expansion of the device fundamentally solves the problem of failure of the electrochemical device due to the volume expansion and deformation of the negative electrode active material, and effectively improves the cycle performance and expansion and deformation of the electrochemical device.

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Abstract

本申请提供了一种负极极片、包含该负极极片的电化学装置和电子装置，其中负极极片包含负极材料层，所述负极材料层包含硅基颗粒和石墨颗粒，所述硅基颗粒中硅含量B为20wt％至60wt％，所述硅基颗粒的孔隙率α 1为15％至60％，所述负极极片孔隙率α 2为15％至41％，通过以上设计，使负极极片既能有一定的空间供嵌锂膨胀，又能兼顾其结构的稳定性和加工性，从而有效改善电化学装置的循环性能和膨胀变形的问题。

Description

一种负极极片、包含该负极极片的电化学装置及电子装置 技术领域
本申请涉及电化学领域，具体涉及一种负极极片、包含该负极极片的电化学装置及电子装置。
背景技术
锂离子二次电池具有储能密度大、开路电压高、自放电率低、循环寿命长、安全性好等优点，广泛应用于电能储存、移动电子设备、电动汽车和航天航空设备等各个领域。随着移动电子设备和电动汽车进入高速发展阶段，市场对锂离子二次电池的能量密度、安全性、循环性能和使用寿命等都提出了越来越高的要求。
由于硅基材料的理论容量达到4200mAh/g，是目前已知具有最高理论容量的负极材料，同时硅储量丰富，价格低廉，因此，目前锂离子二次电池中的负极极片往往使用硅基材料作为下一代高克容量负极材料。但硅基材料在脱嵌锂过程中体积变化率高达300％以上，会产生大量的固体电解质界面膜(Solid Electrolyte Interphase，SEI)，消耗锂离子二次电池中有限的锂离子和电解液，显著增加了锂离子二次电池的阻抗，严重阻碍其工业化大规模应用。
当前问题的主要解决途径是对硅基材料纳米化和复合化，但对其纳米化的制备工艺复杂、能耗高，且超高的比表面积使其容易产生团聚，从而无法彻底解决硅基材料循环稳定性差的问题；而硅基材料与碳质材料的复合化，由于碳质材料不能承受硅基材料嵌锂时高达300％的体积膨胀，锂离子二次电池的结构在循环过程中被破坏，因此也不能完全解决硅基材料的问题。
发明内容
本申请的目的在于提供一种负极极片、包含该负极极片的电化学装置及电子装置，以改善电化学装置的循环性能和膨胀变形的问题。
需要说明的是，在以下内容中，以锂离子电池作为电化学装置的例子来解释本申请，但是本申请的电化学装置并不仅限于锂离子电池。
具体技术方案如下：
本申请的第一方面提供了一种负极极片，其包含负极材料层，负极材料层包含硅基颗粒和 石墨颗粒，硅基颗粒中硅含量B为20wt％至60wt％，硅基颗粒的孔隙率α 1为15％至60％，负极极片孔隙率α 2为15％至41％。
在本申请中，“硅基颗粒的孔隙率α 1”是指，硅基颗粒中孔隙的体积与硅基颗粒总体积的百分比。在本申请中，“负极极片孔隙率α 2”是指，负极极片中各种颗粒间孔隙的体积与负极极片总体积的百分比。
在本申请的一种实施方案中，硅基颗粒中硅含量B为20wt％至60wt％，例如，硅含量B的下限值可以包含以下数值中：20wt％、30wt％或36wt％；硅含量B的上限值可以包含以下数值中：40wt％、50wt％或60wt％。当硅含量B小于20wt％时，负极材料层的克容量小；当硅含量B大于60wt％时，硅基颗粒在脱嵌锂过程中体积变化率加快，会产生更多SEI，加速消耗锂离子电池中的锂离子和电解液，显著增加锂离子电池的阻抗。
本申请中，硅基颗粒的孔隙率α 1为15％至60％，例如，硅基颗粒的孔隙率α 1的下限值可以包括以下数值中：15％、16％、18％、25％、30％或33％；硅基颗粒的孔隙率α 1的上限值可以包括以下数值中：38％、45％、47％、56％或60％。当硅基颗粒的孔隙率α 1小于15％时，预留的空间难以缓冲纳米硅的嵌锂体积膨胀，碳质材料的机械强度难以承受巨大膨胀应力，将导致硅基颗粒结构破裂，恶化其电化学性能；当硅基颗粒的孔隙率α 1大于60％时，孔隙过大，碳质材料的抗压强度降低，导致硅基颗粒在加工时容易破裂，恶化其电化学性能。
本申请中，负极极片孔隙率α 2为15％至41％，例如，负极极片孔隙率α 2的下限值可以包括以下数值中：15％、19％或28％；负极极片孔隙率α 2的上限值可以包括以下数值中：35％或41％。当负极极片孔隙率α 2小于15％时，电解液难以充分浸润，会增加锂离子的传输距离，恶化锂离子电池的动力学；当负极极片孔隙率α 2大于41％时，锂离子电池在循环中容易出现硅基颗粒和石墨颗粒间接触失效，导致循环性能恶化、降低锂离子电池的能量密度。
在本申请中，硅基颗粒内和负极极片的孔隙各自独立地包含孔径小于2nm的微孔、孔径为2nm至50nm的介孔或大于50nm的大孔。在本申请中，对上述微孔、介孔和大孔的数量没有特别限定，只要能够实现本申请目的即可。
整体而言，本申请提供的负极极片包含负极材料层，该负极材料层包含硅基颗粒和石墨颗粒，在硅基颗粒内和负极极片中制造孔隙，将硅基颗粒的孔隙率α 1、硅基颗粒中硅含量B、负极极片孔隙率α 2控制在上述范围内，共同缓解负极极片的嵌锂膨胀。通过以上设计，负极极片既能有一定的空间供嵌锂膨胀，又能兼顾其结构的稳定性和加工性，能够从根本上解决由于 负极活性材料体积膨胀变形导致锂离子电池失效的问题，有效改善锂离子电池的循环性能和膨胀变形的问题。
在本申请的一种实施方案中，硅基颗粒的孔隙率α 1与负极极片孔隙率α 2之和α满足：45％＜α＜90％。例如，硅基颗粒的孔隙率α 1与负极极片孔隙率α 2之和α的下限值可以包括以下数值中：45％、46％、49％、53％、58％、61％或62％；硅基颗粒的孔隙率α 1与负极极片孔隙率α 2之和α的上限值可以包括以下数值中：65％、71％、73％、88％或90％。当负极极片孔隙率α 2和硅基颗粒的孔隙率α 1之和α控制在上述范围时，锂离子电池的循环性能和抗膨胀性能得到显著提升。
在本申请的一种实施方案中，硅基颗粒的孔隙率α 1与硅含量B满足：P＝0.5α 1/(B-α 1B)，0.2≤P≤1.6。例如，P值的下限值可以包括以下数值中：0.2、0.4、0.5或0.8；P值的上限值可以包括以下数值中：1.1、1.5或1.6。
当P值小于0.2时，硅基颗粒中预留的孔隙难以缓冲纳米硅的嵌锂体积膨胀，碳质材料的机械强度难以承受巨大的膨胀应力，将导致硅基颗粒结构碎裂，恶化其电化学性能；当P值大于1.6时，硅基颗粒中预留的孔隙过大，将恶化碳质材料的机械抗压强度，导致硅基颗粒在加工时容易破裂，暴露出大量的新鲜界面，恶化其首次效率和循环性能，降低锂离子电池的能量密度。因此，将P值控制在上述范围内，能够有效改善锂离子电池的能量密度、循环性能和抗膨胀性能。
在本申请的一种实施方案中，负极材料层中硅基颗粒的含量为3wt％至80wt％。例如，负极材料层中硅基颗粒的含量的下限值可以包括以下数值中：3wt％、10wt％、20wt％、25wt％、30wt％、35wt％或40wt％；负极材料层中硅基颗粒的含量的上限值可以包括以下数值：45wt％、55wt％、60wt％、70wt％或80wt％。通过将负极材料层中硅基颗粒的含量控制在上述范围内，使负极材料层保持高克容量，从而提升锂离子电池的能量密度。
本申请对负极材料层中石墨颗粒的含量没有特别限定，只要能够实现本申请目的即可。例如，负极材料层中石墨颗粒的含量可以为20wt％至97wt％，负极材料层中石墨颗粒的含量的下限值可以包括以下数值中：20wt％、25wt％、30wt％或40wt％，负极材料层中石墨颗粒的含量的上限值可以包括以下数值中：50wt％、60wt％、70wt％、80wt％或90wt％。通过将负极材料层中石墨颗粒的含量控制在上述范围内，使负极材料层增强导电性，减少其与电解液的接触，减少SEI的产生。
在本申请的一种实施方案中，硅基颗粒可以包含硅元素、碳元素、氧元素，硅基颗粒还可以包含氮元素、磷元素、硫元素等。本申请对硅基颗粒的种类没有特别限定，只要能够实现本申请目的即可，例如，可以包括纳米硅、硅纳米硅、硅碳、纳米氧化硅或硅-金属合金等中的至少一种。
在本申请的一种实施方案中，硅基颗粒采用拉曼测试的D峰与G峰的峰强比值为0.2至2；其中，D峰为硅基颗粒的拉曼光谱中位移范围为1255cm -1至1355cm- 1的峰，G峰为硅基颗粒的拉曼光谱中位移范围为1575cm -1至1600cm -1的峰。当硅基颗粒采用拉曼测试的D峰与G峰的峰强比值控制在上述范围内时，硅基颗粒的碳质材料有足够的孔隙缺陷，有利于抑制其在循环过程中的膨胀变形，从而提高负极极片的抗膨胀性能和循环性能。
在本申请的一种实施方案中，硅基颗粒表面存在碳材料，本申请对碳材料的种类没有特别限制，只要能够实现本申请目的即可，例如，碳材料可以包含无定形碳、碳纳米管、碳纳米粒子、气相沉积碳纤维或石墨烯等中的至少一种。在本申请的一些实施例中，碳纳米管可以包含单壁碳纳米管或多壁碳纳米管中的至少一种。本申请对硅基颗粒表面存在碳材料的制备方法没有特别限制，只要能够实现本申请目的即可。在本申请中，对碳材料的含量没有特别限制，只要能够实现本申请目的即可，例如，可以为硅基颗粒的0.01wt％至1wt％，例如，0.01wt％、0.1wt％、0.5wt％或1wt％。通过使硅基颗粒表面存在碳材料，有利于提升硅基颗粒表面的界面稳定性，以束缚硅基颗粒的偏移，也可以有效缓解硅基颗粒体积膨胀收缩引起的结构破坏，避免产生新鲜界面，从而改善负极极片的循环性能和膨胀变形。
在本申请的一种实施方案中，硅基颗粒表面存在高分子材料，本申请对高分子材料的种类没有特别限制，只要能够实现本申请目的即可，例如，高分子材料可以包含聚偏氟乙烯(PVDF)、羧甲基纤维素(CMC)、羧甲基纤维素钠(CMC-Na)、聚乙烯基吡咯烷酮(PVP)、聚丙烯酸、聚丁苯橡胶及其衍生物等中的至少一种。在本申请的一些实施例中，高分子材料可以包含羧甲基纤维素钠、聚乙烯基吡咯烷酮、聚偏氟乙烯和聚丙烯酸钠(PAANa)。本申请对硅基颗粒表面存在高分子材料的制备方法没有特别限制，只要能够实现本申请目的即可。在本申请中，对高分子材料的含量没有特别限制，只要能够实现本申请目的即可，可以为硅基颗粒的0wt％至0.4wt％，例如，0wt％、0.025wt％、0.15wt％或0.4wt％。
在本申请的一种实施方案中，硅基颗粒的平均粒径Dv50小于20μm。不限于任何理论，当硅基颗粒的平均粒径Dv50大于20μm时，在负极极片加工过程中容易出现划痕等问题，同时减少颗粒间的相互接触位点，从而影响负极极片的循环性能。通过控制本申请硅基颗粒的平 均粒径Dv50在上述范围内，能够改善负极极片的循环性能。在本申请中，对石墨颗粒的粒径没有特别限定，只要能够实现本申请目的即可。
在本申请的一种实施方案中，硅基颗粒的比表面积小于50m 2/g。不限于任何理论，当硅基颗粒的比表面积大于50m 2/g时，硅基颗粒的比表面积过大，副反应会影响锂离子电池的性能，同时需要消耗更高比例的粘结剂，会造成负极材料层与负极集流体之间粘结力的降低，内阻增长率较高。在本申请中，对石墨颗粒比表面积的大小没有特别限定，只要能够实现本申请目的即可。
本申请的负极极片的压实密度为1.0g/cm 3至1.9g/cm 3，能够使锂离子电池具有高能量密度。
在本申请中，对负极极片中包含的负极集流体没有特别限制，只要能够实现本申请目的即可，例如，可以包含铜箔、铜合金箔、镍箔、不锈钢箔、钛箔、泡沫镍、泡沫铜或复合集流体等。在本申请中，对负极集流体和负极材料层的厚度没有特别限制，只要能够实现本申请目的即可，例如，负极集流体的厚度为6μm至10μm，负极材料层的厚度为30μm至120μm。本申请中，负极极片的厚度没有特别限制，只要能够实现本申请目的即可，例如，负极极片的厚度为50μm至150μm。
任选地，所述负极极片还可以包含导电层，所述导电层位于负极集流体和负极材料层之间。所述导电层的组成没有特别限制，可以是本领域常用的导电层。所述导电层包括导电剂和粘结剂。
本申请中的正极极片没有特别限制，只要能够实现本申请目的即可。例如，正极极片通常包含正极集流体和正极材料层。其中，正极集流体没有特别限制，只要能够实现本申请目的即可，例如，可以包含铝箔、铝合金箔或复合集流体等。正极材料层包括正极活性材料，正极活性材料没有特别限制，只要能够实现本申请目的即可，例如，可以包含镍钴锰酸锂(811、622、523、111)、镍钴铝酸锂、磷酸铁锂、富锂锰基材料、钴酸锂、锰酸锂、磷酸锰铁锂或钛酸锂中的至少一种。在本申请中，正极集流体和正极材料层的厚度没有特别限制，只要能够实现本申请目的即可。例如，正极集流体的厚度为8μm至12μm，正极材料层的厚度为30μm至120μm。
任选地，所述正极极片还可以包含导电层，所述导电层位于正极集流体和正极材料层之间。所述导电层的组成没有特别限制，可以是本领域常用的导电层。所述导电层包括导电剂和粘结剂。
上述所述导电剂没有特别限制，只要能够实现本申请目的即可。例如，导电剂可以包括导 电炭黑(Super P)、碳纳米管(CNTs)、碳纤维、鳞片石墨、科琴黑或石墨烯等中的至少一种。上述所述粘结剂没有特别限制，可以使用本领域公知的任何粘结剂，只要能够实现本申请目的即可。例如，粘结剂可以包括聚丙烯醇、聚丙烯酸钠、聚丙烯酸钾、聚丙烯酸锂、聚酰亚胺、聚酰亚胺、聚酰胺酰亚胺、丁苯橡胶(SBR)、聚乙烯醇(PVA)、聚偏氟乙烯、聚四氟乙烯(PTFE)、羧甲基纤维素或羧甲基纤维素钠(CMC-Na)等中的至少一种。例如，粘结剂可选用丁苯橡胶(SBR)。
在本申请中的隔离膜没有特别限制，只要能够实现本申请目的即可。例如，聚乙烯(PE)、聚丙烯(PP)为主的聚烯烃(PO)类隔膜，聚酯膜(例如聚对苯二甲酸二乙酯(PET)膜)、纤维素膜、聚酰亚胺膜(PI)、聚酰胺膜(PA)，氨纶或芳纶膜、织造膜、非织造膜(无纺布)、微孔膜、复合膜、隔膜纸、碾压膜、纺丝膜等中的至少一种。
例如，隔离膜可以包括基材层和表面处理层。基材层可以为具有多孔结构的无纺布、膜或复合膜，基材层的材料可以包括聚乙烯、聚丙烯、聚对苯二甲酸乙二醇酯和聚酰亚胺等中的至少一种。任选地，可以使用聚丙烯多孔膜、聚乙烯多孔膜、聚丙烯无纺布、聚乙烯无纺布或聚丙烯-聚乙烯-聚丙烯多孔复合膜。任选地，基材层的至少一个表面上设置有表面处理层，表面处理层可以是聚合物层或无机物层，也可以是混合聚合物与无机物所形成的层。
例如，无机物层包括无机颗粒和粘结剂，所述无机颗粒没有特别限制，例如可以选自氧化铝、氧化硅、氧化镁、氧化钛、二氧化铪、氧化锡、二氧化铈、氧化镍、氧化锌、氧化钙、氧化锆、氧化钇、碳化硅、勃姆石、氢氧化铝、氢氧化镁、氢氧化钙和硫酸钡等中的至少一种。所述粘结剂没有特别限制，例如可以选自聚偏氟乙烯、偏氟乙烯-六氟丙烯的共聚物、聚酰胺、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯酸盐、聚乙烯呲咯烷酮、聚乙烯醚、聚甲基丙烯酸甲酯、聚四氟乙烯和聚六氟丙烯中的一种或几种的组合。聚合物层中包含聚合物，聚合物的材料包括聚酰胺、聚丙烯腈、丙烯酸酯聚合物、聚丙烯酸、聚丙烯酸盐、聚乙烯呲咯烷酮、聚乙烯醚、聚偏氟乙烯或聚(偏氟乙烯-六氟丙烯)等中的至少一种。本申请的锂离子电池还包括电解质，电解质可以是凝胶电解质、固态电解质和电解液中的一种或多种，电解液包括锂盐和非水溶剂。
在本申请一些实施方案中，锂盐可以包括LiPF 6、LiBF 4、LiAsF 6、LiClO 4、LiB(C 6H 5) 4、LiCH 3SO 3、LiCF 3SO 3、LiN(SO 2CF 3) 2、LiC(SO 2CF 3) 3、LiSiF 6、LiBOB或二氟硼酸锂中的至少一种。举例来说，锂盐可以选用LiPF 6，因为它可以给出高的离子导电率并改善循环特性。
非水溶剂可为碳酸酯化合物、羧酸酯化合物、醚化合物、其它有机溶剂或它们的组合。上述碳酸酯化合物可为链状碳酸酯化合物、环状碳酸酯化合物、氟代碳酸酯化合物或其组合。上述链状碳酸酯化合物的实例为碳酸二甲酯(DMC)、碳酸二乙酯(DEC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸甲乙酯(MEC)及其组合。环状碳酸酯化合物的实例为碳酸亚乙酯(EC)、碳酸亚丙酯(PC)、碳酸亚丁酯(BC)、碳酸乙烯基亚乙酯(VEC)及其组合。氟代碳酸酯化合物的实例为碳酸氟代亚乙酯(FEC)、碳酸1,2-二氟亚乙酯、碳酸1,1-二氟亚乙酯、碳酸1,1,2-三氟亚乙酯、碳酸1,1,2,2-四氟亚乙酯、碳酸1-氟-2-甲基亚乙酯、碳酸1-氟-1-甲基亚乙酯、碳酸1,2-二氟-1-甲基亚乙酯、碳酸1,1,2-三氟-2-甲基亚乙酯、碳酸三氟甲基亚乙酯及其组合。上述羧酸酯化合物的实例为甲酸甲酯、乙酸甲酯、乙酸乙酯、乙酸正丙酯、乙酸叔丁酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、γ-丁内酯、癸内酯、戊内酯、甲瓦龙酸内酯、己内酯及其组合。上述醚化合物的实例为二丁醚、四甘醇二甲醚、二甘醇二甲醚、1,2-二甲氧基乙烷、1,2-二乙氧基乙烷、乙氧基甲氧基乙烷、2-甲基四氢呋喃、四氢呋喃及其组合。上述其它有机溶剂的实例为二甲亚砜、1,2-二氧戊环、环丁砜、甲基环丁砜、1,3-二甲基-2-咪唑烷酮、N-甲基-2-吡咯烷酮、甲酰胺、二甲基甲酰胺、乙腈、磷酸三甲酯、磷酸三乙酯、磷酸三辛酯和磷酸酯及其组合。
本申请还提供了一种电化学装置，包括负极极片，所述负极极片为上述任一实施方案所说的负极极片，该电化学装置具有良好的循环性能、抗膨胀性能、倍率性能和体积能量密度。
本申请的电化学装置没有特别限定，其可以包括发生电化学反应的任何装置。在一些实施例中，电化学装置可以包括，但不限于：锂金属二次电池、锂离子二次电池(锂离子电池)、锂聚合物二次电池或锂离子聚合物二次电池等。
本申请还提供了一种电子装置，包含本申请实施方案中所述的电化学装置，该电子装置具有良好的循环性能、抗膨胀性能、倍率性能和体积能量密度。
本申请的电子装置没有特别限定，其可以是用于现有技术中已知的任何电子装置。在一些实施例中，电子装置可以包括，但不限于，笔记本电脑、笔输入型计算机、移动电脑、电子书播放器、便携式电话、便携式传真机、便携式复印机、便携式打印机、头戴式立体声耳机、录像机、液晶电视、手提式清洁器、便携CD机、迷你光盘、收发机、电子记事本、计算器、存储卡、便携式录音机、收音机、备用电源、电机、汽车、摩托车、助力自行车、自行车、照明器具、玩具、游戏机、钟表、电动工具、闪光灯、照相机、家庭用大型蓄电池和锂离子电容器等。
电化学装置的制备过程为本领域技术人员所熟知的，本申请没有特别的限制。例如电化学装置可以通过以下过程制造：将正极极片和负极极片经由隔离膜重叠，并根据需要将其卷绕、折叠等操作后放入壳体内，将电解液注入壳体并封口，其中所用的隔离膜为本申请提供的上述隔离膜。此外，也可以根据需要将防过电流元件、导板等置于壳体中，从而防止电化学装置内部的压力上升、过充放电。
本申请提供的一种负极极片、包含该负极极片的电化学装置和电子装置，由于该负极极片的负极材料层中包含硅基颗粒和石墨颗粒，该硅基颗粒中硅含量B为20wt％至60wt％，硅基颗粒的孔隙率α 1为15％至60％，负极极片孔隙率α 2为15％至41％，使得该负极极片既能有一定的空间供嵌锂膨胀，又能兼顾其结构的稳定性和加工性，能够从根本上解决由于负极活性材料膨胀变形导致电化学装置失效的问题，有效改善电化学装置的循环性能和膨胀变形的问题。
附图说明
为了更清楚地说明本申请和现有技术的技术方案，下面对实施例和现有技术中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本申请的一些实施例。
图1为本申请一种实施方案的负极极片断面SEM图；
图2为图1放大倍数的SEM图；
图3为本申请实施例3和对比例1的循环衰减曲线；
图4为实施例3和对比例1的锂离子电池膨胀曲线。
附图标记：10.硅基颗粒内的孔隙；20.负极极片的孔隙。
具体实施方式
为使本申请的目的、技术方案、及优点更加清楚明白，以下参照附图和实施例，对本申请进一步详细说明。显然，所描述的实施例仅仅是本申请一部分实施例，而不是全部的实施例。基于本申请中的实施例，本领域普通技术人员所获得的所有其他技术方案，都属于本申请保护的范围。
需要说明的是，本申请的具体实施方式中，以锂离子电池作为电化学装置的例子来解释本申请，但是本申请的电化学装置并不仅限于锂离子电池。
图1示出了本申请一种实施方案中的负极极片断面SEM图，图2为图1放大倍数的SEM图，参见图2，硅基颗粒内的孔隙10为硅基颗粒内部的孔隙，负极极片的孔隙20是指负极材料层中各种颗粒间的孔隙。
实施例
以下，举出实施例及对比例来对本申请的实施方式进行更具体地说明。各种的试验及评价按照下述的方法进行。另外，只要无特别说明，“份”、“％”为质量基准。
测试方法和设备：
负极极片孔隙率测试：
采用同一模具冲切50片半径为d的负极极片，使用万分尺分别测量每片极片的厚度h，并装入AccuPyc 1340仪器的样品仓中，在密闭的样品仓中采用氦气(He)对极片进行填充，由此利用波尔定律PV＝nRT测得极片的真体积V。测试完成后清点小圆片的数量，计算出样品的表观体积πd 2×50×h。最后通过如下公式获得负极极片的孔隙率α 2：α 2＝1-V/πd 2×50×h。
硅基颗粒的孔隙率测试：
采用扫描电镜透射模式(STEM)拍摄硅基颗粒的界面，并使用所得到的STEM像来测定孔隙率。具体的：将STEM图片采用Image J软件对图片阈值(threshold)做二值化处理，根据比例尺标定尺寸后，利用分析粒子(Analyze Particles)统计孔隙的面积，获得面积占比，即为硅基颗粒的孔隙率α 1；在极片中取任意20个以上的硅基颗粒进行相同的测试，取平均值。
硅基颗粒中硅含量的测试：
将硅基颗粒切片，使用EDS(X射线能谱分析)线性扫描测试元素质量百分比均值。
比表面积测试：
在恒温低温(-199℃至-193℃)下，测定不同相对压力时的气体在固体表面的吸附量后，基于布朗诺尔-埃特-泰勒吸附理论及其公式(BET公式)求得试样单分子层吸附量，从而计算出固体的比表面积。
BET公式：
Figure PCTCN2020140366-appb-000001
其中：W---相对压力(P/P0)下固体样品所吸附的气体的质量，单位cm 3/g；
Wm---铺满一单分子层的气体饱和吸附量，单位cm 3/g；
C---与第一层吸附热和凝聚热有关的常数；
斜率：(c-1)/(WmC)，截距：1/WmC，总比表面积：(Wm×N×Acs/M)；
比表面积：S＝St/m，其中m为样品质量，Acs：每个N2分子的所占据的平均面积16.2A 2。
称取1.5g至3.5g粉末样品装入TriStar II 3020的测试测试样品管中，200℃脱气120min后进行测试。
负极材料层克容量测试方法：
采用扣式电池测试负极材料层克容量。将组装的扣式电池在25℃恒温环境下，静置5min，按照0.05C放电至0.005V，静置5min，采用20μA放电至0.005V，两步放电容量之和为D0，静置5min后，按照0.1C充电至2.0V，此时的充电容量即为C0，首次充电效率即为C0/D0×100％。
负极极片压实密度测试：
利用冲片机在负极极片上冲切面积为S的小圆片，称量其质量为M 1，用万分尺测量其厚度为H 1；采用同样的冲片机冲切相同面积S的集流体，并称量其质量M 2，用万分尺测量其厚度为H 2；其负极压实密度为：(M 1-M 2)/(H 1-H 2)/S。
粒度测试：
50ml洁净烧杯中加入约0.02g粉末样品，加入约20ml去离子水，再滴加几滴1％的表面活性剂，使粉末完全分散于水中，120W超声清洗机中超声5分钟，利用激光散射粒度仪MasterSizer 2000测试粒度分布。
Dv50为颗粒采用激光散射粒度仪测试得到的体积基准分布中累计50％的直径。
循环性能测试：
测试温度为25/45℃，以0.7C恒流充电到4.4V，恒压充电到0.025C，静置5分钟后以0.5C放电到3.0V。以此步得到的容量为初始容量，进行0.7C充电/0.5C放电进行循环测试，以每一步的容量与初始容量做比值，得到容量衰减曲线。以25℃循环截至到容量保持率为90％的圈数记为锂离子电池的室温循环性能，以45℃循环截至到80％的圈数记为锂离子电池的高温循环性能，通过比较上述两种情况下的循环圈数而得到材料的循环性能。
放电倍率测试：
在25℃下，以0.2C放电到3.0V，静置5min，以0.5C充电到4.45V，恒压充电到0.05C后静置5分钟，调整放电倍率，分别以0.2C、0.5C、1C、1.5C、2.0C进行放电测试，分别得到放电容量，以每个倍率下得到的容量与0.2C得到的容量对比，通过比较2C与0.2C下的比值比较倍率性能。
锂离子电池满充膨胀率测试：
用螺旋千分尺测试半充时新鲜锂离子电池的厚度，循环至400圈(cls)时，锂离子电池处于满充状态下，再用螺旋千分尺测试此时锂离子电池的厚度，与初始半充时新鲜锂离子电池的厚度对比，即可得此时满充锂离子电池膨胀率。
能量密度计算：
将锂离子电池在25℃下充电至4.45V后，用激光测厚仪测试锂离子电池的长、宽、高，得到锂离子电池的体积(V)，再采用0.2C放电至3V，得到锂离子电池放电容量(C)和平均电压平台(U)，其体积能量密度(ED)可通过如下公式计算得到：ED＝C×U/V。
实施例1
<负极活性材料的制备>
将孔隙率为41％的多孔碳材料放置到密闭的含有含硅的气体反应器中，加热到500℃并保温4h，冷却后经过筛分、除磁即可得到硅基颗粒的孔隙率α 1为30％的硅基颗粒，其中，硅基颗粒的含碳量为64wt％，硅基颗粒中硅含量B为36wt％。
<负极极片的制备>
将上述制备得到的负极活性材料、石墨颗粒和纳米导电炭黑按照质量比30:66.5:3.5混合，得到第一混合物；将第一混合物与粘结剂PAA按照质量比95:5加入去离子水中，调配成为固含量为45％的浆料，并搅拌均匀得到第一混合浆料；将第一混合浆料均匀涂覆在厚度为8μm的负极集流体铜箔的一个表面上，在空气干燥性中120℃条件下经过2min烘干，得到涂层重量为7.5mg/cm 2的单面涂布负极活性材料的负极极片。以上步骤完成后，即已完成负极极片的单面涂布；然后，在该负极极片的另一个表面上重复以上步骤，即得到双面涂布负极活性材料的负极极片，冷压完成后，即得到负极极片孔隙率α 2为15％的负极极片，将极片裁切成 41mm×61mm的规格待用。
<正极极片的制备>
将正极活性材料钴酸锂(LiCoO 2)、纳米导电炭黑、聚偏二氟乙烯(PVDF)按照重量比97.5:1.0:1.5进行混合，加入N-甲基吡咯烷酮(NMP)作为溶剂，调配成为固含量为75％的浆料，并搅拌均匀。将浆料均匀涂覆在厚度为10μm的正极集流体铝箔的一个表面上，90℃条件下烘干，得到涂层厚度为110μm的正极极片。以上步骤完成后，即完成正极极片的单面涂布。之后，在该正极极片的另一个表面上重复以上步骤，即得到双面涂布正极活性材料的正极极片。涂布完成后，将极片裁切成38mm×58mm的规格待用。
<电解液的制备>
在干燥氩气气氛中，将有机溶剂碳酸乙烯酯(EO)、碳酸甲乙酯和碳酸二乙酯以质量比EC︰EMC︰DEC＝30︰50︰20混合得到有机溶液，然后向有机溶剂中加入锂盐六氟磷酸锂溶解并混合均匀，得到锂盐的浓度为1.15Mol/L的电解液。
<隔离膜的制备>
将氧化铝与聚偏氟乙烯依照质量比90:10混合并将其溶入到去离子水中以形成固含量为50％的陶瓷浆料。随后采用微凹涂布法将陶瓷浆料均匀涂布到多孔基材(聚乙烯，厚度7μm，平均孔径为0.073μm，孔隙率为26％)的其中一面上，经过干燥处理以获得陶瓷涂层与多孔基材的双层结构，陶瓷涂层的厚度为50μm。
将聚偏二氟乙烯(PVDF)与聚丙烯酸酯依照质量比96:4混合并将其溶入到去离子水中以形成固含量为50％的聚合物浆料。随后采用微凹涂布法将聚合物浆料均匀涂布到上述陶瓷涂层与多孔基材双层结构的两个表面上，经过干燥处理以获得隔离膜，其中聚合物浆料形成的单层涂层厚度为2μm。
<锂离子电池的制备>
将上述制备得到的正极极片、隔离膜、负极极片按顺序叠好，使隔离膜处于正极和负极中间已起到隔离的作用，卷绕得到电极组件。将电极组件置于铝塑膜包装袋中，干燥后注入电解液，经过真空封装、静置、化成、脱气、切边等工序得到锂离子电池。
实施例2、实施例3、实施例4、实施例5、实施例6、实施例7、实施例8、实施例9、 实施例10、实施例11、实施例12、实施例13、实施例14、实施例15、实施例16和实施例17中，<负极活性材料的制备>、<负极极片的制备>、<正极极片的制备>、<电解液的制备>、<隔离膜的制备>及<锂离子电池的制备>的制备步骤均与实施例1相同，相关制备参数的变化如表1中所示：
表1
Figure PCTCN2020140366-appb-000002
实施例18
<负极活性材料的制备>
1)将孔隙率为41％的多孔碳材料放置到密闭的含有含硅的气体反应器中，加热到500℃并保温4h，冷却后经过筛分、除磁即可得到硅基颗粒的孔隙率α 1为30％的硅基颗粒，其中，硅基颗粒的含碳量为64wt％，硅基颗粒中硅含量B为36wt％。
2)将1)中得到的硅基颗粒加入到含有羧甲基纤维素钠(CMC-Na)分散剂的单壁碳纳米 管(SCNT)中分散2小时，直至形成均匀的混合溶液，喷雾干燥得到粉末，破碎，400目过筛得到负极材料，其中，硅基颗粒：SCNT：羧甲基纤维素钠的质量比为99.75:0.1:0.15。
<负极极片的制备>、<正极极片的制备>、<电解液的制备>、<隔离膜的制备>、<锂离子电池的制备>，与实施例3相同。
实施例19、实施例20、实施例21、实施例22、实施例23、实施例24、实施例25、实施例26、实施例27、实施例28、实施例29、实施例30、实施例31、实施例32和实施例33中，<负极活性材料的制备>、<负极极片的制备>、<正极极片的制备>、<电解液的制备>、<隔离膜的制备>及<锂离子电池的制备>的制备步骤均与实施例18相同，相关制备参数的变化如表2中所示：
表2
Figure PCTCN2020140366-appb-000003
Figure PCTCN2020140366-appb-000004
注：表2中的“/”表示不存在该对应制备参数。
对比例1、对比例2、对比例3、对比例4、对比例5和对比例6中，<负极活性材料的制备>、<负极极片的制备>、<正极极片的制备>、<电解液的制备>、<隔离膜的制备>及<锂离子电池的制备>的制备步骤均与实施例1相同，相关制备参数的变化如表3中所示：
表3
Figure PCTCN2020140366-appb-000005
实施例1、实施例2、实施例3、实施例4、实施例5、实施例6、实施例7、实施例8、实施例9、实施例10、对比例1、对比例2、对比例3、对比例4的制备参数如表4所示：
表4
Figure PCTCN2020140366-appb-000006
Figure PCTCN2020140366-appb-000007
实施例1、实施例2、实施例3、实施例4、实施例5、实施例6、实施例7、实施例8、实施例9、实施例10、对比例1、对比例2、对比例3、对比例4的测试结果如表5所示：
表5
Figure PCTCN2020140366-appb-000008
实施例11、实施例12、实施例13、实施例14、实施例15、实施例16、实施例17、对比例5、对比例6的制备参数如表6所示：
表6
Figure PCTCN2020140366-appb-000009
实施例11、实施例12、实施例13、实施例14、实施例15、实施例16、实施例17、对比例5、对比例6的测试结果如表7所示：
表7
Figure PCTCN2020140366-appb-000010
实施例3、实施例18、实施例19、实施例20、实施例21、实施例22、实施例23、实施例24、实施例25、实施例26、实施例27、实施例28、实施例29、实施例30、实施例31、实施例32、实施例33的制备参数如表8所示：
表8
Figure PCTCN2020140366-appb-000011
注：表8中的“/”表示不存在该对应制备参数。
实施例3、实施例18、实施例19、实施例20、实施例21、实施例22、实施例23、实施例24、实施例25、实施例26、实施例27、实施例28、实施例29、实施例30、实施例31、实施例32、实施例33的测试结果如表9所示：
表9
Figure PCTCN2020140366-appb-000012
Figure PCTCN2020140366-appb-000013
从实施例1、实施例2、实施例3、实施例4、实施例5和对比例1、对比例2可以看出，当硅基颗粒的孔隙率一定时，负极极片孔隙率过低，锂离子电池的循环性能和膨胀性能显著恶化，这是由于硅基颗粒内部的孔隙不能完全缓解硅嵌锂时的体积膨胀，需要依靠负极极片孔隙率进一步缓解硅的嵌锂膨胀；此外，体积膨胀使电解液难以充分浸润，会增加锂离子的传输距离，恶化锂离子电池的动力学。当负极极片孔隙率过高时，负极材料层的颗粒间缝隙过大，颗粒间接触面积降低，会减少锂离子的嵌入点，且锂离子电池在循环中容易出现脱模的情况，造成锂离子电池循环性能、抗膨胀性能以及动力学的显著恶化，此外，负极极片的压实密度降低，锂离子电池的体积能量密度也显著降低。图3示出了实施例3和对比例1的循环衰减曲线；图4示出了实施例3和对比例1的膨胀曲线。
从实施例6、实施例7、实施例8、实施例9、实施例10和对比例3、对比例4可以看出，当负极极片孔隙率一定时，硅基颗粒的孔隙率过低，锂离子电池的循环性能和膨胀性能出现显著的恶化，这是由于硅基颗粒内部预留的空间难以缓冲纳米硅的嵌锂体积膨胀，此时碳质材料的机械强度难以承受巨大膨胀应力，容易导致硅基颗粒结构在循环过程中碎裂。当硅基颗粒的孔隙率过高时，碳质材料的抗压强度降低，导致硅基颗粒在加工时容易碎裂，恶化电性能，且随着极片压密的降低，锂离子电池的体积能量密度也随之降低。
通过实施例1、实施例2、实施例3、实施例4、实施例5、实施例6、实施例7、实施例8、实施例9、实施例10可以看出，锂离子电池中负极极片孔隙率和硅基颗粒的孔隙率的合理搭 配，能够更加有效地改善锂离子电池的循环性能和抗膨胀性能、提高其体积能量密度。
从实施例11、实施例12、实施例13、实施例14、实施例15和对比例5、对比例6可以看出，硅含量B一定的情况下，负极材料层的克容量没有显著差异，随着硅基颗粒的孔隙率的增加，硅基颗粒的比表面积逐渐增大。
从实施例13、实施例16、实施例17可以看出，硅基颗粒中硅含量B的变化，导致P值的变化，会影响负极材料层的克容量和硅基颗粒的比表面。
通过实施例11、实施例12、实施例13、实施例14、实施例15、实施例16、实施例17和对比例5、对比例6可以发现，当P值过小时，硅基颗粒内部预留的孔隙难以缓冲纳米硅的嵌锂体积膨胀，此时碳质材料的机械强度难以承受巨大膨胀应力，导致硅基颗粒结构碎裂，恶化锂离子电池的电化学性能；当P值过大时，硅基颗粒内部预留的孔隙过大，不仅恶化碳质材料的机械抗压强度，硅基颗粒在加工时容易碎裂，暴露出大量新鲜界面，恶化锂离子电池首次效率和循环性能，而且降低锂离子电池的整体能量密度。当P值在在本申请限定范围内时，能够有效提升锂离子电池的循环性能、抗膨胀性能以及体积能量密度，此时的硅基颗粒既能有一定的空间供硅嵌锂膨胀，又能兼顾其结构的稳定和加工性。
从实施例18、实施例19、实施例20、实施例21、实施例22、实施例23、实施例24、实施例25、实施例26、实施例27、实施例28、实施例29、实施例30、实施例31、实施例32、实施例33与实施例3对比，在硅基颗粒表面添加含量为0.1wt％的SCNT可显著提升循环性能，添加0.1wt％的MCNT对循环性能有轻微提升，添加0.05wt％的SCNT和0.05wt％的MCNT对循环性能有一定提升。实施例18、实施例21、实施例22、实施例23、实施例24改变了SCNT的添加量，控制SCNT添加量≤0.5％可有效提升循环性能，但SCNT添加量达到0.5wt％时，循环性能相对于0.1wt％添加量提升不明显，反而对首次效率有恶化；SCNT添加量达到1wt％时，过多的SCNT导致浆料无法加工。实施例18、实施例25、实施例26、实施例27对比不同分散剂，不添加分散剂，SCNT无法分散效果差，循环性能和锂离子电池变形恶化；PVP和PVDF作为分散剂，相对于CMC-Na和PAANa的循环性能有轻微恶化。实施例18、实施例28、
实施例29、实施例30改变了分散剂的添加量，分散剂量为0.4wt％时，分散效果提升，但分散剂过多会恶化倍率性能；分散剂量为0.025wt％时，分散效果差，循环性能和倍率性能相对于含量为0.15wt％的分散剂会有恶化。实施例28、实施例31、实施例32、实施例33对比不同碳材料包覆，从结果上看CNT和石墨烯包覆效果最好，这是由于包覆CNT和石墨烯后，不仅增加了材料的电子导电率，同时可以增加材料间的接触位点，减少因为接触失效导致的循环衰减。
综合上述分析可知，本申请提供的负极极片，通过将硅基颗粒的孔隙率α 1、硅基颗粒中硅含量B、负极极片孔隙率α 2控制在合理范围内，共同缓解负极极片的嵌锂膨胀，从根本上解决了由于负极活性材料体积膨胀变形导致电化学装置失效的问题，有效改善了电化学装置的循环性能和膨胀变形的问题。
以上所述仅为本申请的较佳实施例，并不用以限制本申请，凡在本申请的精神和原则之内，所做的任何修改、等同替换、改进等，均应包含在本申请保护的范围之内。

Claims (11)

  1. 一种负极极片，其包含负极材料层，所述负极材料层包含硅基颗粒和石墨颗粒，所述硅基颗粒中硅含量B为20wt％至60wt％，所述硅基颗粒的孔隙率α 1为15％至60％，所述负极极片孔隙率α 2为15％至41％。
  2. 根据权利要求1所述的负极极片，其中，所述硅基颗粒的孔隙率α 1与所述负极极片孔隙率α 2之和α满足：45％＜α＜90％。
  3. 根据权利要求1所述的负极极片，其中，所述硅基颗粒的孔隙率α 1与所述硅含量B满足：P＝0.5α 1/(B-α 1B)，0.2≤P≤1.6。
  4. 根据权利要求1所述的负极极片，所述负极材料层中硅基颗粒的含量为3wt％至80wt％。
  5. 根据权利要求1所述的负极极片，其中，所述硅基颗粒包含硅元素、碳元素和氧元素。
  6. 根据权利要求1所述的负极极片，其中，所述硅基颗粒采用拉曼测试的D峰与G峰的峰强比值为0.2至2；
    所述D峰为硅基颗粒的拉曼光谱中位移范围为1255cm -1至1355cm -1的峰，所述G峰为硅基颗粒的拉曼光谱中位移范围为1575cm -1至1600cm -1的峰。
  7. 根据权利要求1所述的负极极片，其中，所述硅基颗粒表面存在碳材料，所述碳材料包含无定形碳、碳纳米管、碳纳米粒子、气相沉积碳纤维或石墨烯中的至少一种。
  8. 根据权利要求1所述的负极极片，其中，所述硅基颗粒的平均粒径Dv50小于20μm。
  9. 根据权利要求1所述的负极极片，其中，所述硅基颗粒的比表面积小于50m 2/g。
  10. 一种电化学装置，其包含权利要求1至9中任一权利要求所述的负极极片。
  11. 一种电子装置，其包含权利要求10中所述的电化学装置。
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