WO2024020927A1 - 二次电池及其制备方法、用电装置 - Google Patents

二次电池及其制备方法、用电装置 Download PDF

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WO2024020927A1
WO2024020927A1 PCT/CN2022/108554 CN2022108554W WO2024020927A1 WO 2024020927 A1 WO2024020927 A1 WO 2024020927A1 CN 2022108554 W CN2022108554 W CN 2022108554W WO 2024020927 A1 WO2024020927 A1 WO 2024020927A1
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active material
material layer
optionally
negative electrode
porous
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PCT/CN2022/108554
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English (en)
French (fr)
Inventor
刘良彬
王家政
严青伟
董晓斌
李圆
吕子建
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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/CN2022/108554 priority Critical patent/WO2024020927A1/zh
Priority to CN202280068374.XA priority patent/CN118104005A/zh
Publication of WO2024020927A1 publication Critical patent/WO2024020927A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • 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 secondary batteries, and specifically relates to a secondary battery, a preparation method thereof, and an electrical device.
  • Secondary batteries such as lithium-ion batteries are widely used due to their advantages such as high energy density and good cycle performance.
  • the market has put forward higher requirements for the capacity and cycle performance of secondary batteries.
  • it is usually difficult for secondary batteries with traditional technology to ensure good cycle performance and low impedance at higher capacities.
  • this application provides a secondary battery and a preparation method thereof.
  • the secondary battery can have high capacity, good cycle performance and low impedance.
  • This application also provides an electrical device containing the secondary battery.
  • a secondary battery including a negative electrode piece, and the negative electrode piece includes:
  • a first negative active material layer is disposed on at least one surface of the negative current collector, the first negative active material layer includes a silicon-based material and a porous material;
  • a second negative electrode active material layer is disposed on a surface of the first negative electrode active material layer away from the negative electrode current collector.
  • the negative electrode sheet includes a negative electrode current collector, a first negative electrode active material layer and a second negative electrode active material layer.
  • the first negative active material layer close to the negative current collector includes silicon-based materials and porous materials.
  • the silicon-containing negative electrode sheet has a low cyclic expansion rate, and the secondary battery has both high capacity and Better cycle performance and lower impedance.
  • the porous material includes at least one of porous carbon, porous metal, and porous ceramic;
  • the porous carbon includes at least one of porous graphite, porous resin carbon, porous biomass carbon, activated carbon, porous carbon fiber and expanded graphite;
  • the porous metal includes at least one of porous nickel, porous copper, porous titanium, porous gold, porous stainless steel and porous metal alloy materials;
  • the porous ceramic includes at least one of porous Si 3 N 4 , porous Al 2 O 3 and porous SiC.
  • the above-mentioned porous materials used in the negative electrode sheet can improve the impedance and cycle performance of the secondary battery without causing deterioration in the electrochemical performance of the negative electrode sheet.
  • the pore diameter of the porous material is 10 nm to 1000 nm; optionally, the pore diameter of the porous material is 30 nm to 300 nm.
  • the pore size of the porous material is within the above range, which is beneficial to the lithium ion transmission and cycle expansion rate of the negative electrode plate, and further improves the impedance and cycle performance of the secondary battery.
  • the porous material has a porosity P ⁇ 30%; optionally, the porous material has a porosity 40% ⁇ P ⁇ 80%.
  • the porosity of the porous material is within the above range, which can improve the lithium ion transmission performance and cycle expansion rate of the negative electrode sheet.
  • the secondary battery has lower impedance and better cycle performance.
  • the mass percentage of the porous material is less than or equal to 10%, and may optionally be 2% to 8%.
  • the content of the porous material in the first negative active material layer is controlled within the above range.
  • the secondary battery has higher capacity and energy density, lower impedance and better cycle performance.
  • the mass percentage of the silicon-based material is greater than or equal to 30%, and may optionally be 40% to 60%.
  • the silicon-based material has a higher theoretical capacity, and the content of the silicon-based material in the first negative active material layer is within the above range, and the secondary battery has a higher capacity.
  • the thickness of the first negative active material layer is denoted as D1
  • the volume particle size distribution Dv50 of the porous material is denoted as D0
  • the negative electrode piece satisfies 0.5 ⁇ D0/D1 ⁇ 0.8; optionally Optionally, the negative electrode piece satisfies 0.6 ⁇ D0/D1 ⁇ 0.7.
  • the ratio of the Dv50 of the porous material to the thickness of the first negative active material layer is within the above range, which is beneficial to forming connected pores in the first negative active material layer and further improving the impedance of the secondary battery.
  • the thickness of the first negative active material layer is marked as D1
  • the thickness of the second negative active material layer is marked as D2
  • the negative electrode piece satisfies: 3 ⁇ D2/D1 ⁇ 9;
  • the negative electrode piece satisfies: 4 ⁇ D2/D1 ⁇ 7.
  • the thickness of the first negative active material layer is less than or equal to 15 ⁇ m; optionally, the thickness of the first negative active material layer is 5 ⁇ m to 13 ⁇ m.
  • the first negative active material layer includes a first conductive agent.
  • the first conductive agent includes at least one of graphite, superconducting carbon, acetylene black, Ketjen black, conductive carbon black, graphene, carbon dots, carbon nanotubes, carbon nanofibers and graphite.
  • the mass percentage of the first conductive agent is greater than or equal to 25%, and more optionally is 25% to 40%.
  • the first conductive agent includes graphite; the graphite satisfies at least one of the following conditions (I)-(V):
  • the volume particle size distribution Dv50 of the graphite is 3 ⁇ m to 8 ⁇ m, optionally 4 ⁇ m to 7 ⁇ m;
  • the volume particle size distribution Dv99 of the graphite is 9 ⁇ m ⁇ 15 ⁇ m, optionally 10 ⁇ m ⁇ 13 ⁇ m;
  • the mass percentage of graphite is less than 40%, optionally 25% to 35%;
  • the first Coulombic efficiency of the graphite is 85% to 93%, optionally 87% to 92%.
  • the first conductive agent includes carbon nanotubes.
  • the mass percentage of the carbon nanotubes is less than or equal to 5.0%.
  • the carbon nanotube has a diameter of 0.4 nm to 20 nm.
  • the carbon nanotubes include at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes, and more optionally include single-walled carbon nanotubes.
  • the first conductive agent includes carbon nanotubes
  • the thickness of the first negative active material layer is denoted as D1
  • the axial length of the carbon nanotubes is denoted as L1
  • the negative electrode piece satisfies L1/D1>1; optionally, the negative electrode piece satisfies 1.5 ⁇ L1/D1 ⁇ 5.0.
  • the first negative active material layer includes a first binder.
  • the glass transition temperature of the first binder is ⁇ 25°C.
  • the first adhesive includes at least one of styrene-butadiene rubber, modified styrene-butadiene rubber, methyl acrylate, ethyl acrylate, butyl acrylate, lauryl acrylate, and butadiene.
  • the mass percentage of the first binder is greater than or equal to 15%, and more optionally is 15% to 25%.
  • the second negative active material includes graphite, and the graphite satisfies at least one of the following conditions (1)-(4):
  • the mass percentage of graphite is greater than or equal to 80%, optionally 90% to 96.5%;
  • the Dv50 of the graphite is 10 ⁇ m ⁇ 20 ⁇ m, optionally 12 ⁇ m ⁇ 18 ⁇ m;
  • the Dv99 of the graphite is ⁇ 45 ⁇ m; it can be selected from 30 ⁇ m to 42 ⁇ m;
  • the morphology of the graphite is secondary particles.
  • the second negative active material layer includes both graphite and silicon-based material; optionally, in the second negative active material layer, the mass percentage of the silicon-based material is less than or equal to 5%.
  • the second negative active material layer satisfies at least one of the following conditions (i)-(iii):
  • the second negative active material layer includes a second binder, and optionally, in the second negative active material layer, the mass percentage of the second binder is less than or equal to 4%;
  • the second negative active material layer includes a second conductive agent, and optionally, in the second negative active material layer, the mass percentage of the second conductive agent is less than or equal to 1.5%;
  • the second negative active material layer includes a second conductive agent, and the second conductive agent includes carbon nanotubes.
  • the carbon nanotubes The mass percentage is less than or equal to 0.15%.
  • this application also provides a method for preparing a secondary battery, including the following steps of preparing a negative electrode plate:
  • the first negative electrode slurry includes silicon-based material and porous material
  • a second negative electrode slurry is coated on a surface of the first negative electrode active material layer away from the negative electrode current collector to prepare a second negative electrode active material layer.
  • the solid content of the first negative electrode slurry is less than or equal to 30%, optionally 15% to 25%.
  • controlling the solid content of the first negative electrode slurry within the above range can ensure better dispersion and appropriate viscosity of the slurry, which is beneficial to the quality of the negative electrode sheet. preparation.
  • the present application also provides an electrical device, including a secondary battery selected from the above or a secondary battery prepared according to the above preparation method.
  • Figure 1 is a scanning electron microscope (SEM) image of a cross-section of a negative electrode plate according to an embodiment of the present application
  • Figure 2 is a partial enlarged view of the scanning electron microscope (SEM) of Figure 1;
  • Figure 3 is a schematic diagram of a secondary battery according to an embodiment of the present application.
  • Figure 4 is an exploded view of the secondary battery according to an embodiment of the present application shown in Figure 3;
  • FIG. 5 is a schematic diagram of a battery module according to an embodiment of the present application.
  • Figure 6 is a schematic diagram of a battery pack according to an embodiment of the present application.
  • FIG 7 is an exploded view of the battery pack according to an embodiment of the present application shown in Figure 6;
  • Figure 8 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present application.
  • the present application provides a secondary battery, a battery module, a battery pack and an electrical device using the secondary battery.
  • This kind of secondary battery is suitable for various electrical devices that use batteries, such as mobile phones, portable devices, laptops, battery cars, electric toys, power tools, electric cars, ships and spacecraft.
  • spacecraft include aircraft, rockets , space shuttles and spacecrafts, etc.
  • a first aspect of the present application provides a secondary battery including a negative electrode plate described below.
  • Secondary batteries also known as rechargeable batteries or storage batteries, refer to batteries that can be charged to activate active materials and continue to be used after the battery is discharged.
  • a secondary battery normally includes a positive electrode plate, a negative electrode plate, a separator and an electrolyte.
  • active ions such as lithium ions
  • the isolation film is placed between the positive electrode piece and the negative electrode piece. It mainly prevents the positive and negative electrodes from short-circuiting and allows active ions to pass through.
  • the electrolyte is between the positive electrode piece and the negative electrode piece and mainly plays the role of conducting active ions.
  • the negative electrode sheet includes: a negative electrode current collector, a first negative electrode active material layer and a second negative electrode active material layer.
  • a first negative active material layer is disposed on at least one surface of the negative current collector, and the first negative active material layer includes a silicon-based material and a porous material.
  • the second negative electrode active material layer is disposed on a surface of the first negative electrode active material layer away from the negative electrode current collector.
  • the silicon-containing negative electrode sheet of the present application has a lower cyclic expansion rate during the charge and discharge process, so that the secondary battery has both high High capacity, better cycle performance and lower impedance.
  • the negative electrode current collector may be a metal foil or a composite current collector.
  • the metal foil copper foil can be used.
  • the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base material.
  • the composite current collector can be formed by forming metal materials such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy on a polymer material substrate.
  • Polymer material substrates include polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE) ) and other base materials.
  • the porous material includes at least one of porous carbon, porous metal, and porous ceramics.
  • the porous carbon includes at least one of porous graphite, porous resin carbon, porous biomass carbon, activated carbon, porous carbon fiber and expanded graphite.
  • the porous metal includes at least one of porous nickel, porous copper, porous titanium, porous gold, porous stainless steel, and porous metal alloy materials (such as Al-Mg-Si alloy materials).
  • the porous ceramic includes at least one of porous Si 3 N 4 , porous Al 2 O 3 and porous SiC.
  • the above-mentioned porous materials used in the negative electrode sheet can improve the impedance and cycle performance of the secondary battery without causing deterioration in the electrochemical performance of the negative electrode sheet.
  • the pore diameter of the porous material ranges from 10 nm to 1000 nm, optionally from 30 nm to 300 nm.
  • the pore diameter of the porous material may be in the range of any of the following values: 10 nm, 20 nm, 50 nm, 100 nm, 200 nm, 500 nm, 800 nm or 1000 nm.
  • the pore size of the porous material is within the above range, which is beneficial to the lithium ion transmission and cycle expansion rate of the negative electrode plate, and further improves the impedance and cycle performance of the secondary battery.
  • the porous material has a porosity P ⁇ 30%. Alternatively, 40% ⁇ P ⁇ 80%.
  • the porosity of the porous material is within the above range, which can improve the lithium ion transmission performance and cycle expansion rate of the negative electrode sheet.
  • the secondary battery has lower impedance and better cycle performance.
  • the pore diameter of a porous material refers to the average pore diameter of the porous material, which is a well-known meaning in the art, and can be tested using methods known in the art.
  • the average pore diameter evaluation method refers to GB/T 19587-2017 and GB/T 21650.2-2008, and is tested using the TriStar 3020 pore size distribution meter.
  • the adsorbed gas is adsorbed on the test site under a series of gradually increasing pressures.
  • the pore size distribution of porous materials can be characterized by plotting the volume of pores at each level and the corresponding partial pressure; at the same time, the average pore size can be calculated.
  • GB/T 21650.2-2008 mercury intrusion method and gas adsorption method can be used to determine the porosity of solid materials.
  • the porosity testing method is to obtain the true density of the material through AccuPyc 1340 true density meter testing. The specific operation is to weigh a sample of a certain mass, place it in a true density tester, seal the test system, and pass in helium gas according to the procedure.
  • Material porosity P 1- ⁇ 0/ ⁇ r ⁇ 100%. The porosity in this article was measured using the same method.
  • the mass percentage of the porous material is less than or equal to 10%, optionally 2% to 8%.
  • the mass percentage of the porous material can be in the range of any of the following values: 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% Or 10%.
  • the content of the porous material in the first negative active material layer is controlled within the above range.
  • the secondary battery has higher capacity and energy density, lower impedance and better cycle performance.
  • the silicon-based material may be selected from one or more of elemental silicon, silicon oxide compounds (such as silicon oxide), silicon carbon composites, silicon nitrogen composites, silicon alloys and prelithiated silicon oxide compounds. species; it can be selected from at least one of silicon-carbon composite, silicon-oxygen compound and pre-lithiated silicon-oxygen compound.
  • the mass percentage of the silicon-based material is greater than or equal to 30%, and may optionally be 40% to 60%.
  • the silicon-based material has a higher theoretical capacity.
  • the content of the silicon-based material in the first negative electrode active material layer is within the above range.
  • the secondary battery has a higher capacity and at the same time can ensure a low cyclic expansion rate of the negative electrode plate and improve Cycle performance.
  • the thickness of the first negative active material layer is denoted as D1
  • the volume particle size distribution Dv50 of the porous material is denoted as D0
  • the negative electrode piece satisfies 0.5 ⁇ D0/D1 ⁇ 0.8.
  • the ratio of the Dv50 of the porous material to the thickness of the first negative active material layer is within the above range, which is beneficial to forming connected pores in the first negative active material layer and further improving the impedance of the secondary battery.
  • Dv50 refers to the particle size corresponding to when the cumulative particle size distribution number of particles reaches 50% in the volume cumulative distribution curve. Its physical meaning is that 50% of the particles have a particle size smaller (or larger) than it.
  • Dv50 can be easily measured using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer of Malvern Instruments Co., Ltd. in the UK, referring to the GB/T19077-2016 particle size distribution laser diffraction method.
  • the thickness of the negative active material layer can be tested by methods known in the art, for example, it can be tested by a step test method.
  • the stylus of the step meter gently scratches the surface of the sample with very small force.
  • the micron or even nanometer-level fluctuations on the surface of the sample are amplified by millions of times through the sensor connected to the stylus, and then converted into electronic signals and input into In computer software, it is finally displayed in the form of numerical and graphical data.
  • the thickness of the first negative active material layer is denoted as D1
  • the thickness of the second negative active material layer is denoted as D2
  • the negative electrode piece satisfies: 3 ⁇ D2/D1 ⁇ 9.
  • 4 ⁇ D2/D1 ⁇ 7 the negative electrode sheet has a higher capacity and at the same time can suppress the volume expansion of the silicon-based material during charging and discharging, so that the capacity of the secondary battery can be better exerted.
  • the thickness of the first negative active material layer is less than or equal to 15 ⁇ m, and may be 5 ⁇ m to 13 ⁇ m.
  • the first negative active material layer includes a first conductive agent.
  • the first conductive agent can improve the electronic conductive performance of the first negative active material layer.
  • the first conductive agent includes at least one of graphite, superconducting carbon, acetylene black, Ketjen black, conductive carbon black, graphene, carbon dots, carbon nanotubes, carbon nanofibers, and graphite.
  • the first conductive agent includes at least one of graphite, carbon nanotubes and conductive carbon black.
  • the mass percentage of the first conductive agent is greater than or equal to 25%, and more preferably 25% to 40%.
  • Silicon-based materials have poor electrical conductivity. The inventor found through research that if the content of the first conductive agent in the first negative active material layer is within the above range, it can effectively improve the cyclic expansion of the silicon-based material while forming a good conductive network. , thereby improving the capacity and cycle performance of secondary batteries.
  • the first conductive agent includes graphite.
  • the volume particle size distribution Dv50 of graphite is 3 ⁇ m to 8 ⁇ m, optionally 4 ⁇ m to 7 ⁇ m. Selecting small particles of graphite with Dv50 within the above range will help form a conductive network on the surface of the silicon-based material and buffer the expansion of the silicon-based material.
  • the volume particle size distribution Dv99 of graphite is 9 ⁇ m to 15 ⁇ m, optionally 10 ⁇ m to 13 ⁇ m. By selecting graphite with Dv99 not exceeding 15 ⁇ m and further controlling the particle size of the graphite, the cycle performance of the secondary battery is better.
  • the mass percentage of the graphite is less than 40%, optionally 25% to 35%.
  • the particle morphology of graphite is primary particles.
  • the first Coulombic efficiency of graphite is 85% to 93%, optionally 87% to 92%.
  • the first conductive agent includes carbon nanotubes.
  • the mass percentage of carbon nanotubes is less than or equal to 5.0%, optionally 0.5% to 2%.
  • the carbon nanotube content within the above range can further improve the capacity and cycle performance of the secondary battery.
  • the diameter of the carbon nanotubes ranges from 0.4 nm to 20 nm.
  • the diameter of the carbon nanotube can be in the range of any of the following values: 0.4nm, 0.8nm, 1nm, 2nm, 4nm, 5nm, 8nm, 10nm, 12nm, 15nm, 18nm or 20nm.
  • Carbon nanotubes with diameters within the above range have better mechanical properties and better electrical conductivity, and can further improve the cycle performance of secondary batteries.
  • the carbon nanotubes include at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes, optionally including single-walled carbon nanotubes.
  • the first conductive agent includes carbon nanotubes
  • the thickness of the first negative active material layer is denoted as D1
  • the axial length of the carbon nanotubes is denoted as L1
  • the negative electrode plate satisfies L1/D1>1; optional Ground, the negative pole piece satisfies 1.5 ⁇ L1/D1 ⁇ 5.0.
  • the first negative active material layer includes a first binder.
  • the first binder is a binder with a glass transition temperature ⁇ 25°C.
  • the first binder may include, but is not limited to, at least one of styrene-butadiene rubber, modified styrene-butadiene rubber, methyl acrylate, ethyl acrylate, butyl acrylate, lauryl acrylate, and butadiene.
  • Choose a binder with a lower glass transition temperature which can be in a highly elastic state in a relatively wide temperature range, have a high elastic limit and a large elongation at break, and match silicon-based materials with large volume changes. It can effectively control the volume expansion of the negative electrode piece.
  • the mass percentage of the first binder is greater than or equal to 15%, and more preferably 15% to 25%. Controlling the content of the first binder within the above range can effectively suppress the expansion of the silicon-based material and improve the cycle performance of the secondary battery.
  • the first negative active material layer optionally includes other auxiliaries, such as dispersants (such as carboxymethyl cellulose or its sodium salt (CMC-Na)) and the like.
  • auxiliaries such as dispersants (such as carboxymethyl cellulose or its sodium salt (CMC-Na)) and the like.
  • each component such as silicon-based material, porous material, first conductive agent, first binder and optional other auxiliaries
  • the second negative active material layer includes a second negative active material.
  • the second negative active material may be a negative active material for batteries known in the art.
  • the second negative active material may include at least one of the following materials: graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, and the like.
  • the silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon carbon composites, silicon nitrogen composites and silicon alloys.
  • the tin-based material may be selected from at least one of elemental tin, tin oxide compounds and tin alloys.
  • the present application is not limited to these materials, and other traditional materials that can be used as battery negative electrode active materials can also be used. Only one type of these negative electrode active materials may be used alone, or two or more types may be used in combination.
  • the second negative active material layer includes graphite.
  • the graphite includes at least one of artificial graphite and natural graphite.
  • the mass percentage of the graphite is greater than or equal to 80%; optionally, it is 90 to 96.5%.
  • the volume distribution particle size Dv50 of the graphite is 10 to 20 ⁇ m; optionally, it is 12 ⁇ m to 18 ⁇ m.
  • the volume distribution particle size of the graphite is Dv99 ⁇ 45 ⁇ m; optionally, it is 30 ⁇ m to 42 ⁇ m.
  • the graphite is in the form of secondary particles.
  • the second negative active material layer includes both graphite and silicon-based materials; optionally, in the second negative active material layer, the mass percentage of the silicon-based material is less than or equal to 5%.
  • the content of the silicon-based material in the second negative electrode active material layer is within the above range, which can reduce the deterioration of the contact between the silicon-based material and the electrolyte. At the same time, it can control the lower silicon content in the second active material layer located away from the negative electrode current collector, which can further Reduce the cyclic expansion rate of the negative electrode piece, avoid the deterioration of the negative electrode piece, and improve the cycle performance of the secondary battery while ensuring a higher capacity.
  • the second negative active material layer includes a second binder.
  • the second binder may include styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polyacrylonitrile (PAN), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA) ), at least one of sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).
  • SBR styrene-butadiene rubber
  • PAA polyacrylic acid
  • PAN polyacrylonitrile
  • PAAS sodium polyacrylate
  • PAM polyacrylamide
  • PVA polyvinyl alcohol
  • SA sodium alginate
  • PMAA polymethacrylic acid
  • CMCS carboxymethyl chitosan
  • the mass percentage of the second binder is less than or equal to 4%, optionally 1.5% to 3%.
  • the second negative active material layer includes a second conductive agent.
  • the second conductive agent includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the mass percentage of the second conductive agent is less than or equal to 1.5%, such as 0.5% to 1.0%.
  • the second conductive agent includes carbon nanotubes; optionally, in the second negative electrode active material layer, the mass percentage of carbon nanotubes is less than or equal to 0.15%.
  • the second negative active material layer optionally also includes other auxiliaries, such as thickeners (such as sodium carboxymethyl cellulose (CMC-Na)) and the like.
  • auxiliaries such as thickeners (such as sodium carboxymethyl cellulose (CMC-Na)) and the like.
  • FIG 1 is a scanning electron microscope (SEM) image of a cross-section of the negative electrode sheet according to an embodiment of the present application. It can be clearly seen from the figure that the negative electrode current collector of the negative electrode sheet has a first negative electrode active material layer and a third negative electrode active material layer in sequence. Two negative electrode active material layers, the thickness of the first negative electrode active material layer is smaller than the second negative electrode active material layer, and the thickness ratio is 3 ⁇ D2/D1 ⁇ 9.
  • Figure 2 which is a partially enlarged view of the scanning electron microscope (SEM) of Figure 1. It can be seen from the figure that the first negative active material layer has a rich porous structure.
  • the sampling can be carried out as follows:
  • step (2) Bake the negative electrode sheet dried in step (1) at a certain temperature and time (for example, 200-500°C, 1h ⁇ 3h). Select any area in the baked negative electrode sheet, and first Sampling the second negative active material layer (you can choose to use a blade scraper to sample), the scraping depth does not exceed the boundary area between the first negative active material layer and the second negative active material layer; then use the same method to sample the first negative active material layer sampling.
  • a certain temperature and time for example, 200-500°C, 1h ⁇ 3h.
  • the interfusion layer can be scraped off first, and then the first negative active material layer can be scraped and sampled.
  • step (3) Sieve the negative active material collected in step (2) (for example, through a 100-300 mesh mesh), and finally obtain the above-mentioned material parameters (such as particle size, particle size, etc.) that can be used to test the present application. Specific surface area, etc.) negative active material sample.
  • material parameters such as particle size, particle size, etc.
  • an optical microscope or a scanning electron microscope can be used to assist in determining the position of the boundary area between the first negative active material layer and the second negative active material layer.
  • the mass proportion of the silicon-based material in the negative active material layer can be measured using instruments and methods known in the art. For example, when the test sample is taken from a prepared secondary battery, obtain the silicon-based material through the above steps, digest the silicon-based material with reference to EPA-3052-1996 "Microwave Acid Digestion Method for Silicates", and then digest it according to EPA6010D-2014 "Inductively Coupled Plasma Atomic Emission Spectrometry” uses the ICAP-7000 inductively coupled plasma optical emission spectrometer (ICP-OES) of the American Thermo Fisher Scientific company to measure the content of silicon element.
  • ICP-OES inductively coupled plasma optical emission spectrometer
  • the specific test method is as follows: use 10 mL of nitric acid with a mass fraction of 65% and 10 mL of hydrofluoric acid with a mass fraction of 40% to conduct microwave digestion of 0.5 g of silicon-based material samples. After digestion, add it to a 50 mL volumetric flask to constant volume, and then use ICAP- The 7000 type ICP-OES measures the content of silicon element and calculates the mass ratio of silicon-based materials based on the content of silicon element.
  • the mass proportions of the binder and the dispersant in the negative active material layer can be measured simultaneously using instruments and methods known in the art.
  • the powder material is obtained through the above steps and the mass ratio of the binder and dispersant is measured by thermogravimetric method (the test equipment can use a thermogravimetric analyzer), that is, Can.
  • the parameters of the first negative active material layer and the second negative active material layer given in this application refer to the parameter range of one side of the negative electrode sheet.
  • the parameters of the first negative electrode active material layer or the second negative electrode active material layer on any one of the surfaces satisfy this requirement.
  • the ranges such as the thickness of the negative active material layer mentioned in this application refer to the parameters of the film layer that is compacted by cold pressing and used to assemble the battery.
  • the negative electrode piece can be prepared through the following steps S110 to S130:
  • Step S110 Prepare a first negative electrode slurry and a second negative electrode slurry respectively.
  • the first negative electrode slurry includes silicon-based material and porous material.
  • Step S120 Coat the first negative electrode slurry on at least one surface of the negative electrode current collector to prepare a first negative electrode active material layer;
  • Step S130 Coat the second negative electrode slurry on the surface of the first negative electrode active material layer away from the negative electrode current collector to prepare a second negative electrode active material layer.
  • the solid content of the first negative electrode slurry is less than or equal to 30%, and may optionally be 20% to 25%.
  • controlling the solid content of the first negative electrode slurry within the above range can ensure better dispersion and appropriate viscosity of the slurry, which is beneficial to the quality of the negative electrode sheet. preparation.
  • the first negative electrode slurry and the second negative electrode slurry can be coated simultaneously through a dual-chamber coating equipment, or the coating equipment can be used to first coat the first negative electrode slurry and then coat the second negative electrode. slurry.
  • the first negative electrode slurry is coated on the surface of the negative electrode current collector to form a first negative electrode active material layer, and the second negative electrode slurry is applied on the first negative electrode active material layer to form a second negative electrode active material layer; finally, it is dried and cold pressed. and other steps to obtain the negative electrode piece.
  • One embodiment of the present application also provides a method for preparing a secondary battery, including the above steps of preparing a negative electrode piece.
  • the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector.
  • the positive active material layer includes a positive active material.
  • the positive electrode current collector has two surfaces opposite in its own thickness direction, and the positive electrode active material layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • the metal foil aluminum foil can be used.
  • the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer.
  • the composite current collector can be formed by forming metal materials such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy on a polymer material substrate.
  • Polymer material substrates include polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE) ) and other base materials.
  • the cathode active material may be a cathode active material known in the art for batteries.
  • the cathode active material may include at least one of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds.
  • the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials of batteries can also be used. Only one type of these positive electrode active materials may be used alone, or two or more types may be used in combination.
  • lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO 2 ), lithium nickel oxides (such as LiNiO 2 ), lithium manganese oxides (such as LiMnO 2 , LiMn 2 O 4 ), lithium Nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1/3 Co 1/3 Mn 1/3 O 2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (can also be abbreviated to NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O 2 (can also be abbreviated to NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (can also be abbreviated to NCM 622 ), LiNi At least one of 0.8 Co 0.1 Mn 0.1 O 2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as Li Li
  • the olivine structure contains Examples of lithium phosphates may include, but are not limited to, lithium iron phosphate (such as LiFePO 4 (also referred to as LFP)), composites of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), lithium manganese phosphate and carbon. At least one of composite materials, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon.
  • lithium iron phosphate such as LiFePO 4 (also referred to as LFP)
  • composites of lithium iron phosphate and carbon such as LiMnPO 4
  • LiMnPO 4 lithium manganese phosphate and carbon.
  • At least one of composite materials, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon At least one of composite materials, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon.
  • the positive active material layer optionally further includes a binder.
  • the binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene tripolymer. At least one of a meta-copolymer, a tetrafluoroethylene-hexafluoropropylene copolymer and a fluorine-containing acrylate resin.
  • the positive active material layer optionally further includes a conductive agent.
  • the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components in a solvent (such as N -methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode piece can be obtained.
  • a solvent such as N -methylpyrrolidone
  • the electrolyte plays a role in conducting ions between the positive and negative electrodes.
  • the type of electrolyte in this application can be selected according to needs.
  • the electrolyte can be liquid, gel, or completely solid.
  • the electrolyte is an electrolyte solution.
  • the electrolyte solution includes electrolyte salts and solvents.
  • the electrolyte salt may be selected from the group consisting of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonimide, lithium bistrifluoromethanesulfonimide, trifluoromethane At least one of lithium sulfonate, lithium difluorophosphate, lithium difluoroborate, lithium dioxaloborate, lithium difluorodioxalate phosphate and lithium tetrafluoroxalate phosphate.
  • the solvent may be selected from the group consisting of ethylene carbonate, propylene carbonate, methylethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, Butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate At least one of ester, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.
  • the electrolyte optionally also includes additives.
  • additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.
  • a separator film is further included in the secondary battery.
  • isolation membrane There is no particular restriction on the type of isolation membrane in this application. Any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be used.
  • the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the isolation film can be a single-layer film or a multi-layer composite film, with no special restrictions. When the isolation film is a multi-layer composite film, the materials of each layer can be the same or different, and there is no particular limitation.
  • the positive electrode piece, the negative electrode piece, and the separator film can be made into an electrode assembly through a winding process or a lamination process.
  • the secondary battery may include an outer packaging.
  • the outer packaging can be used to package the above-mentioned electrode assembly and electrolyte.
  • the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.
  • the outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag.
  • the material of the soft bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.
  • FIG. 3 shows a square-structured secondary battery 5 as an example.
  • the outer package may include a housing 51 and a cover 53 .
  • the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity.
  • the housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 can cover the opening to close the accommodation cavity.
  • the positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is packaged in the containing cavity.
  • the electrolyte soaks into the electrode assembly 52 .
  • the number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.
  • secondary batteries can be assembled into battery modules, and the number of secondary batteries contained in the battery module can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery module.
  • FIG. 5 is a battery module 4 as an example.
  • a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 .
  • the plurality of secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may further include a housing having a receiving space in which a plurality of secondary batteries 5 are received.
  • the above-mentioned battery modules can also be assembled into a battery pack.
  • the number of battery modules contained in the battery pack can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.
  • 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 2 and a lower box 3 .
  • the upper box 2 can be covered with the lower box 3 and form a closed space for accommodating the battery module 4 .
  • Multiple battery modules 4 can be arranged in the battery box in any manner.
  • the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided by the present application.
  • the secondary battery, battery module, or battery pack can be used as a power source for the power-consuming device, or as an energy storage unit of the power-consuming device.
  • Electrical devices may include mobile equipment, electric vehicles, electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.
  • mobile devices can be, for example, mobile phones, laptops, etc.; electric vehicles can be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc. , but not limited to this.
  • secondary batteries, battery modules or battery packs can be selected according to its usage requirements.
  • FIG. 8 shows an electrical device 6 as an example.
  • the electric device 6 is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or the like.
  • a battery pack or battery module can be used.
  • the device may be a mobile phone, a tablet, a laptop, etc.
  • the device is usually required to be thin and light, and a secondary battery can be used as a power source.
  • First negative electrode slurry fully stir and mix silicone oxide, first binder, dispersant (CMC-Na), first conductive agent and porous material in deionized water to prepare first negative electrode slurry.
  • the Dv50 of silicon oxide is 6.8 ⁇ m
  • the Dv50 of graphite in the first conductive agent is 3.5 ⁇ m
  • the diameter of the carbon nanotube (CNT) is 2 nm
  • the axial length is 15 ⁇ m.
  • Second negative electrode slurry artificial graphite, binder (SBR), dispersant (CMC-Na), conductive carbon black (Super-P, SP) according to the mass ratio of 96.2%: 1.8%: 1.2%: 0.8% Stir and mix thoroughly in deionized water to prepare a second negative electrode slurry, in which the Dv50 of artificial graphite is 14.3 ⁇ m.
  • the first negative electrode slurry is evenly applied on a current collector copper foil with a thickness of 8 ⁇ m and dried to form a first negative electrode active material layer.
  • the second negative electrode slurry is evenly applied on the first negative electrode active material layer and dried to form a first negative electrode active material layer.
  • the second negative active material layer is cold pressed and cut to obtain the negative electrode piece.
  • the thickness of the first negative active material layer is 12 ⁇ m
  • the thickness of the second negative active material layer is 39 ⁇ m
  • the compacted density of the negative electrode sheet is 1.65g/cm 3
  • the coating weight is 8.2 mg/cm 2 , among which the oxidation
  • the mass percentage of silicone in the first negative electrode active material layer is 40%.
  • Preparation of the positive electrode sheet Dissolve the positive active material LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM 811 ), the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black in a mass ratio of 97%:1.5%:1.5%. In the solvent N-methylpyrrolidone (NMP), stir thoroughly and mix evenly to prepare a positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, and then dried, cold pressed, and cut to obtain the positive electrode. Extreme piece.
  • NMP N-methylpyrrolidone
  • Isolation film Polypropylene film is used.
  • Electrolyte preparation Mix ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1, and then uniformly dissolve LiPF 6 in the above solution to obtain Electrolyte.
  • the concentration of LiPF 6 is 1 mol/L.
  • Preparation of secondary battery stack and wind the positive electrode sheet, separator film, and negative electrode sheet in order to obtain the electrode assembly; put the electrode assembly into the outer packaging, add the electrolyte prepared above, package, let stand, and form , aging and other processes, a secondary battery is obtained.
  • Example 1 The difference between Examples 2 to 18, Comparative Examples 1 to 2 and Example 1 is that the composition of the first negative active material layer of the negative electrode sheet is different.
  • the composition of the first negative active material layer of the negative electrode sheets of Examples 1 to 18 and Comparative Examples 1 to 2 can be seen in Table 1.
  • the secondary batteries prepared in the above examples and comparative examples were charged at a constant temperature of 45°C at a constant current rate of 1C until the voltage was 4.25V, and then charged at a constant voltage of 4.25V until the current was less than or equal to 0.05mA. Let it stand for 5 minutes, then discharge it at a constant current rate of 1C until the voltage is 2.5V, and let it stand for 5 minutes. This is a cycle charge and discharge process. The discharge capacity this time is recorded as the discharge capacity of the first cycle of the secondary battery.
  • the secondary battery was subjected to 300 cycle charge and discharge tests according to the above method, and the discharge capacity of the 300th cycle was recorded.
  • Capacity retention rate CR45°C (%) of the secondary battery after 300 cycles at 45°C discharge capacity of the 300th cycle/discharge capacity of the first cycle ⁇ 100%.
  • the thickness of the negative electrode plate of the secondary battery when the cold pressing process is completed is recorded as h0.
  • the secondary battery is cycled for 300cls and charged at a constant current rate of 1C to The voltage is 4.25V, and then charged at a constant voltage of 4.25V until the current is less than or equal to 0.05mA, and then left to stand for 5 minutes.
  • the capacity retention rate of the secondary batteries of Examples 1 to 18 after 300 cycles at 45°C is 92.9% to 96.9%
  • the cycle expansion rate ⁇ h300 is 41.3% to 49.2%
  • the DC impedance DCR It is 356m ⁇ 672m ⁇ .
  • the secondary battery has good cycle stability and small DC impedance, and has good cycle performance and dynamic performance.
  • the secondary batteries of Comparative Examples 1 to 2 did not contain porous materials. After 300 cycles at 45°C, the capacity retention rates were 85.3% and 89.1%, the cycle expansion rates ⁇ h300 were 56.5% and 58.4%, and the DC impedance DCR was 797m ⁇ and 831m ⁇ . , the cycle performance and kinetic performance are not as good as those in Examples 1 to 18. It can be seen that by adding porous materials in the first active material layer, the secondary battery can have both better cycle performance and lower impedance.

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Abstract

本申请提供了一种二次电池，包括负极极片，负极极片包括：负极集流体、第一负极活性材料层及第二负极活性材料层。第一负极活性材料层设置在负极集流体的至少一个表面上，第一负极活性材料层包括硅基材料和多孔材料；第二负极活性材料层设置在第一负极活性材料层的远离负极集流体的表面上。

Description

二次电池及其制备方法、用电装置 技术领域
本申请涉及二次电池领域，具体涉及一种二次电池及其制备方法、用电装置。
背景技术
锂离子电池等二次电池由于具有能量密度高、循环性能好等优点而受到广泛的应用。随着电动汽车、航天、储能等领域的发展，市面上对于二次电池的容量及循环性能提出了更高的要求。然而传统技术的二次电池通常难以在较高容量的情况下，保证较好的循环性能及较低的阻抗。
发明内容
基于上述问题，本申请提供一种二次电池及其制备方法，二次电池能够兼具较高的容量、较好的循环性能及较低的阻抗。
本申请还提供了含有该二次电池的用电装置。
本申请的一个方面，提供了一种二次电池，包括负极极片，所述负极极片包括：
负极集流体；
第一负极活性材料层，设置在所述负极集流体的至少一个表面上，所述第一负极活性材料层包括硅基材料和多孔材料；及
第二负极活性材料层，设置在所述第一负极活性材料层的远离所述负极集流体的表面上。
本申请的二次电池中，负极极片包括负极集流体、第一负极活性材料层及第二负极活性材料层。靠近负极集流体的第一负极活性材料层中包括硅基材料和多孔材料，在充放电过程中，含硅的负极极片具有较低的循环膨胀率，二次电池兼具较高的容量、较好的循环性能及较低的阻抗。
在任意实施方式中，所述多孔材料包括多孔碳、多孔金属及多孔陶瓷中的至少一种；
可选地，所述多孔碳包括多孔石墨、多孔树脂碳、多孔生物质碳、活性碳、多孔碳纤维及膨胀石墨中的至少一种；
可选地，所述多孔金属包括多孔镍、多孔铜、多孔钛、多孔金、多孔不锈钢及多孔金属 合金材料中的至少一种；
可选地，所述多孔陶瓷包括多孔Si 3N 4、多孔Al 2O 3及多孔SiC中的至少一种。
上述多孔材料应用于负极极片中，能够改善二次电池的阻抗及循环性能，且不会造成负极极片电化学性能恶化。
在任意实施方式中，所述多孔材料的孔径为10nm～1000nm；可选地，所述多孔材料的孔径为30nm～300nm。多孔材料的孔径在上述范围内，有利于负极极片的锂离子传输及循环膨胀率，进一步改善二次电池的阻抗及循环性能。
在任意实施方式中，所述多孔材料的孔隙率P≥30％；可选地，所述多孔材料的孔隙率为40％≤P≤80％。多孔材料的孔隙率在上述范围内，能够改善负极极片的锂离子传输性能及循环膨胀率，二次电池具有较低的阻抗及较好循环性能。
在任意实施方式中，在所述第一负极活性材料层中，所述多孔材料的质量百分比小于等于10％，可选为2％～8％。第一负极活性材料层中多孔材料的含量控制在上述范围内，二次电池在具有较高容量、能量密度的同时，具有较低的阻抗及较好的循环性能。
在任意实施方式中，在所述第一负极活性材料层中，所述硅基材料的质量百分比大于等于30％，可选为40％～60％。硅基材料具有较高的理论容量，第一负极活性材料层中硅基材料的含量在上述范围内，二次电池具有更高的容量。
在任意实施方式中，所述第一负极活性材料层的厚度记为D1，所述多孔材料的体积粒径分布Dv50记为D0，则所述负极极片满足0.5≤D0/D1≤0.8；可选地，所述负极极片满足0.6≤D0/D1≤0.7。多孔材料的Dv50与第一负极活性材料层的厚度比值在上述范围内，有利于在第一负极活性材料层中形成连通的孔隙，进一步改善二次电池的阻抗。
在任意实施方式中，所述第一负极活性材料层的厚度记为D1，所述第二负极活性材料层的厚度记为D2，则所述负极极片满足：3≤D2/D1≤9；可选地，所述负极极片满足：4≤D2/D1≤7。
在任意实施方式中，所述第一负极活性材料层的厚度小于等于15μm；可选地，所述第一负极活性材料层的厚度为5μm～13μm。
在任意实施方式中，所述第一负极活性材料层包括第一导电剂。
可选地，所述第一导电剂包括石墨、超导碳、乙炔黑、柯琴黑、导电炭黑、石墨烯、碳点、碳纳米管、碳纳米纤维及石墨中的至少一种。
可选地，在所述第一负极活性材料层中，所述第一导电剂的质量百分比大于等于25％， 更可选为25％～40％。
在任意实施方式中，所述第一导电剂包括石墨；所述石墨满足下述(Ⅰ)-(Ⅴ)中的至少一个条件：
(Ⅰ)所述石墨的体积粒径分布Dv50为3μm～8μm，可选为4μm～7μm；
(Ⅱ)所述石墨的体积粒径分布Dv99为9μm～15μm，可选为10μm～13μm；
(Ⅲ)在所述第一负极活性材料层中，所述石墨的质量百分比为小于40％，可选为25％～35％；
(Ⅳ)所述石墨的颗粒形貌为一次颗粒；
(Ⅴ)所述石墨的首次库伦效率为85％～93％，可选为87％～92％。
在任意实施方式中，所述第一导电剂包括碳纳米管。
可选地，在所述第一负极活性材料层中，所述碳纳米管的质量百分比小于等于5.0％。
可选地，所述碳纳米管的管径为0.4nm～20nm。
可选地，所述碳纳米管包括单壁碳纳米管及多壁碳纳米管中的至少一种，更可选为包括单壁碳纳米管。
在任意实施方式中，所述第一导电剂包括碳纳米管，所述第一负极活性材料层的厚度记为D1，所述碳纳米管的轴向长度记为L1，所述负极极片满足L1/D1＞1；可选地，所述负极极片满足1.5≤L1/D1≤5.0。
在任意实施方式中，所述第一负极活性材料层包括第一粘结剂。
可选地，所述第一粘结剂的玻璃化温度≤25℃。
可选地，所述第一粘结剂包括丁苯橡胶、改性丁苯橡胶、丙烯酸甲酯、丙烯酸乙酯、丙烯酸丁酯及丙烯酸月桂酯及丁二烯中的至少一种。
可选地，在所述第一负极活性材料层中，所述第一粘结剂的质量百分比大于等于15％，更可选为15％～25％。
选用具有较低玻璃化温度的柔性粘结剂，其可以在相对较宽的温度区间处于高弹态，具有较高的弹性极限及较大的断裂伸长率，配合体积变化较大的硅基材料能够有效地控制负极极片的体积膨胀。
在任意实施方式中，所述第二负极活性材料包括石墨，所述石墨满足下述(1)-(4)中的至少一个条件：
(1)所述石墨的质量百分比大于等于80％，可选为90％～96.5％；
(2)所述石墨的Dv50为10μm～20μm，可选为12μm～18μm；
(3)所述石墨的Dv99≤45μm；可选为30μm～42μm；
(4)所述石墨的形貌为二次颗粒。
在任意实施方式中，所述第二负极活性材料层同时包括石墨和硅基材料；可选地，在所述第二负极活性材料层中，所述硅基材料的质量百分比小于等于5％。
在任意实施方式中，所述第二负极活性材料层满足下述(i)-(iii)中的至少一个条件：
(i)所述第二负极活性材料层包括第二粘结剂，可选地，在所述第二负极活性材料层中，所述第二粘结剂的质量百分比小于等于4％；
(ii)所述第二负极活性材料层包括第二导电剂，可选地，在所述第二负极活性材料层中，所述第二导电剂的质量百分比小于等于1.5％；
(iii)所述第二负极活性材料层包括第二导电剂，且所述第二导电剂包括碳纳米管，可选地，在所述第二负极活性材料层中，所述碳纳米管的质量百分比小于等于0.15％。
第二方面，本申请还提供了一种二次电池的制备方法，包括以下制备负极极片的步骤：
制备第一负极浆料：所述第一负极浆料包括硅基材料和多孔材料；
制备第二负极浆料；
将所述第一负极浆料涂覆在负极集流体的至少一个表面上制备第一负极活性材料层；
将第二负极浆料涂覆在所述第一负极活性材料层的远离所述负极集流体的表面上制备第二负极活性材料层。
在一些实施例中，所述第一负极浆料的固含量小于等于30％，可选为15％～25％。在碳纳米管及粘结剂含量较高的情况下，控制第一负极浆料的固含量在上述范围内，能够确保浆料较好的分散性及较合适的粘度，有利于负极极片的制备。
第三方面，本申请还提供了一种用电装置，包括选自上述的二次电池或者包括根据上述的制备方法制备的二次电池。
本申请的一个或多个实施例的细节在下面的附图和描述中提出，本申请的其它特征、目的和优点将从说明书、附图及权利要求书变得明显。
附图说明
图1为本申请一实施方式的负极极片的截面的扫描电子显微镜图(SEM)；
图2为图1的扫描电子显微镜图(SEM)的局部放大图；
图3为本申请一实施方式的二次电池的示意图；
图4为图3所示的本申请一实施方式的二次电池的分解图；
图5为本申请一实施方式的电池模块的示意图；
图6为本申请一实施方式的电池包的示意图；
图7为图6所示的本申请一实施方式的电池包的分解图；
图8为本申请一实施方式的二次电池用作电源的用电装置的示意图；
附图标记说明：
1电池包；2上箱体；3下箱体；4电池模块；5二次电池；51壳体；52电极组件；53盖板；6用电装置。
为了更好地描述和说明这里公开的那些发明的实施例和/或示例，可以参考一副或多副附图。用于描述附图的附加细节或示例不应当被认为是对所公开的发明、目前描述的实施例和/或示例以及目前理解的这些发明的最佳模式中的任何一者的范围的限制。
具体实施方式
为了便于理解本申请，下面将参照相关附图对本申请进行更全面的描述。附图中给出了本申请的较佳实施例。但是，本申请可以以许多不同的形式来实现，并不限于本文所描述的实施例。相反地，提供这些实施例的目的是使对本申请的公开内容的理解更加透彻全面。
除非另有定义，本文所使用的所有的技术和科学术语与属于本申请的技术领域的技术人员通常理解的含义相同。本文中在本申请的说明书中所使用的术语只是为了描述具体的实施例的目的，不是旨在于限制本申请。本文所使用的术语“和/或”包括一个或多个相关的所列项目的任意的和所有的组合。
本申请提供了一种二次电池、和使用该二次电池的电池模块、电池包及用电装置。这种二次电池适用于各种使用电池的用电装置，例如手机、便携式设备、笔记本电脑、电瓶车、电动玩具、电动工具、电动汽车、船舶和航天器等，例如，航天器包括飞机、火箭、航天飞机和宇宙飞船等。
以下适当参照附图对本申请的二次电池、电池模块、电池包和用电装置进行说明。
二次电池
本申请的第一方面提供一种二次电池，其包括下文所述的负极极片。
二次电池又称为充电电池或蓄电池，是指在电池放电后可通过充电的方式使活性材料激 活而继续使用的电池。
通常情况下，二次电池包括正极极片、负极极片、隔离膜及电解液。在电池充放电过程中，活性离子(例如锂离子)在正极极片和负极极片之间往返嵌入和脱出。隔离膜设置在正极极片和负极极片之间，主要起到防止正负极短路的作用，同时可以使活性离子通过。电解液在正极极片和负极极片之间，主要起到传导活性离子的作用。
负极极片
在本申请实施方式中，负极极片包括：负极集流体、第一负极活性材料层及第二负极活性材料层。第一负极活性材料层设置在负极集流体的至少一个表面上，第一负极活性材料层包括硅基材料和多孔材料。第二负极活性材料层设置在第一负极活性材料层的远离负极集流体的表面上。
本申请的二次电池中，通过在第一负极活性材料层中加入多孔材料，在充放电过程中，本申请含硅的负极极片具有较低的循环膨胀率，从而二次电池兼具较高的容量、较好的循环性能及较低的阻抗。
在一些实施例中，负极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可以采用铜箔。复合集流体可包括高分子材料基层和形成于高分子材料基材至少一个表面上的金属层。复合集流体可通过将铜、铜合金、镍、镍合金、钛、钛合金、银及银合金等金属材料形成在高分子材料基材上而形成。高分子材料基材包括如聚丙烯(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)、聚乙烯(PE)等的基材。
在一些实施例中，多孔材料包括多孔碳、多孔金属及多孔陶瓷中的至少一种。
可选地，多孔碳包括多孔石墨、多孔树脂碳、多孔生物质碳、活性碳、多孔碳纤维及膨胀石墨中的至少一种。
可选地，多孔金属包括多孔镍、多孔铜、多孔钛、多孔金、多孔不锈钢及多孔金属合金材料(例如Al-Mg-Si合金材料)中的至少一种。
可选地，多孔陶瓷包括多孔Si 3N 4、多孔Al 2O 3及多孔SiC中的至少一种。
上述多孔材料应用于负极极片中，能够改善二次电池的阻抗及循环性能，且不会造成负极极片电化学性能恶化。
在一些实施例中，多孔材料的孔径为10nm～1000nm，可选为30nm～300nm。可选地，多孔材料的孔径可为以下任意数值构成的范围：10nm、20nm、50nm、100nm、200nm、500nm、800nm或1000nm。多孔材料的孔径在上述范围内，有利于负极极片的锂离子传输及循 环膨胀率，进一步改善二次电池的阻抗及循环性能。
在一些实施例中，多孔材料的孔隙率P≥30％。可选地，40％≤P≤80％。多孔材料的孔隙率在上述范围内，能够改善负极极片的锂离子传输性能及循环膨胀率，二次电池具有较低的阻抗及较好循环性能。
多孔材料的孔径是指多孔材料的平均孔隙孔径，为本领域公知的含义，可以采用本领域已知的方法测试。平均孔隙孔径评估方法参照GB/T 19587-2017和GB/T 21650.2-2008，采用TriStar 3020型孔径分布仪测试，通过在恒定温度下，吸附气在一系列逐步升高的压力下吸附在待测材料上，通过各级孔径的体积与对应的分压下的曲线图，可以表征多孔材料的孔径分布；同时可以计算得到平均孔径。
孔隙率由以下等式定义：孔隙率＝(1-(多孔材料的质量[g]/多孔材料的体积[cm 3]/材料真密度))×100[％]。可采用GB/T 21650.2-2008压汞法和气体吸附法测定固体材料的孔隙率。本申请中，孔隙率测试方法：通过AccuPyc 1340型真密度仪测试得到材料的真密度。具体操作为，称取一定质量的样品，置于真密度测试仪中，密闭测试系统，按程序通入氦气。通过检测样品室和膨胀室中的气体压力，再根据波尔定律(PV＝nRT)可计算真实体积Vr，则真实密度ρr＝m/Vr。材料表观密度可通过将一定质量粉体装入内径为10mm的圆柱模具中，施加200MPa的压力得到对应粉体的表观体积V0，则材料的表观密度为ρ0＝m/V0。材料孔隙率P＝1-ρ0/ρr×100％。本文中的孔隙率均采用相同方法测试得到。
在一些实施例中，在第一负极活性材料层中，多孔材料的质量百分比小于等于10％，可选为2％～8％。可选地，在第一负极活性材料层中，多孔材料的质量百分比可以为以下任意数值构成的范围：2％、3％、4％、5％、6％、7％、8％、9％或者10％。第一负极活性材料层中多孔材料的含量控制在上述范围内，二次电池在具有较高容量、能量密度的同时，具有较低的阻抗及较好的循环性能。
在一些实施例中，硅基材料可选自单质硅、硅氧化合物(例如氧化亚硅)、硅碳复合物、硅氮复合物、硅合金和预锂化硅氧化合物中的一种或几种；可选为硅碳复合物、硅氧化合物和预锂化硅氧化合物中的至少一种。
在一些实施例中，在第一负极活性材料层中，硅基材料的质量百分比大于等于30％，可选为40％～60％。硅基材料具有较高的理论容量，第一负极活性材料层中硅基材料的含量在上述范围内，二次电池具有更高的容量，同时能够保证负极极片较低的循环膨胀率，改善循环性能。
在一些实施例中，第一负极活性材料层的厚度记为D1，多孔材料的体积粒径分布Dv50记为D0，则负极极片满足0.5≤D0/D1≤0.8。可选地，0.6≤D0/D1≤0.7。多孔材料的Dv50与第一负极活性材料层的厚度比值在上述范围内，有利于在第一负极活性材料层中形成连通的孔隙，进一步改善二次电池的阻抗。
本申请中，Dv50指在体积累积分布曲线中，颗粒的累计粒度分布数达到50％时所对应的粒径，它的物理意义是粒径小于(或大于)它的颗粒占50％。作为示例，Dv50可以参照GB/T19077-2016粒度分布激光衍射法，采用激光粒度分析仪方便地测定，如英国马尔文仪器有限公司的Mastersizer 2000E型激光粒度分析仪。
本申请中，负极活性材料层的厚度可以选用本领域已知的方法进行测试，例如，可以通过台阶仪测试方法进行测试。台阶仪的测针以十分微小的力轻轻划过样品表面，样品表面微米甚至纳米级别的高低起伏通过与测针连接的传感器得到千百万倍的放大，然后被转换成电子信号，输入到电脑软件中，最终以数字和图形的数据形式展现出来。
在一些实施例中，第一负极活性材料层的厚度记为D1，第二负极活性材料层的厚度记为D2，则负极极片满足：3≤D2/D1≤9。可选地，4≤D2/D1≤7。通过上述厚度的设定，负极极片在具有较高容量的同时，能够抑制充放电过程中硅基材料的体积膨胀，二次电池的容量发挥更佳。
在一些实施例中，第一负极活性材料层的厚度小于等于15μm，可选为5μm～13μm。
在一些实施例中，第一负极活性材料层包括第一导电剂。第一导电剂能够改善第一负极活性材料层的电子导电性能。
在一些实施例中，第一导电剂包括石墨、超导碳、乙炔黑、柯琴黑、导电炭黑、石墨烯、碳点、碳纳米管、碳纳米纤维及石墨中的至少一种。可选地，第一导电剂包括石墨、碳纳米管及导电炭黑中的至少一种。
在一些实施例中，在第一负极活性材料层中，第一导电剂的质量百分比大于等于25％，更可选为25％～40％。硅基材料的导电性能较差，发明人研究发现，第一负极活性材料层中，第一导电剂含量在上述范围内，能够在形成良好导电网络的同时，有效地改善硅基材料的循环膨胀，从而改善二次电池的容量发挥及循环性能。
在一些实施例中，第一导电剂包括石墨。
在一些实施例中，石墨的体积粒径分布Dv50为3μm～8μm，可选为4μm～7μm。选用Dv50在上述范围内的小颗粒石墨，有助于在硅基材料表面形成导电网络，同时缓冲硅基材料的膨 胀。
在一些实施例中，石墨的体积粒径分布Dv99为9μm～15μm，可选为10μm～13μm。通过选用Dv99不超过15μm的石墨，进一步控制石墨的颗粒尺寸，二次电池的循环性能更佳。
在一些实施例中，在第一负极活性材料层中，上述石墨的质量百分比小于40％，可选为25％～35％。
在一些实施例中，石墨的颗粒形貌为一次颗粒。
在一些实施例中，石墨的首次库伦效率为85％～93％，可选为87％～92％。
在一些实施例中，第一导电剂包括碳纳米管。
在一些实施例中，在第一负极活性材料层中，碳纳米管的质量百分比小于等于5.0％，可选为0.5％～2％。碳纳米管含量在上述范围内，能够进一步改善二次电池的容量发挥及循环性能。
在一些实施例中，碳纳米管的管径为0.4nm～20nm。可选地，碳纳米管的管径可以为以下任意数值构成的范围：0.4nm、0.8nm、1nm、2nm、4nm、5nm、8nm、10nm、12nm、15nm、18nm或20nm。管径在上述范围内的碳纳米管具有较好的机械性及较佳的导电性，能够进一步改善二次电池的循环性能。
在一些实施例中，碳纳米管包括单壁碳纳米管及多壁碳纳米管中的至少一种，可选为包括单壁碳纳米管。
在一些实施例中，第一导电剂包括碳纳米管，第一负极活性材料层的厚度记为D1，碳纳米管的轴向长度记为L1，负极极片满足L1/D1＞1；可选地，负极极片满足1.5≤L1/D1≤5.0。
在一些实施例中，第一负极活性材料层包括第一粘结剂。
在一些实施例中，第一粘结剂为玻璃化温度≤25℃的粘结剂。第一粘结剂可包括但不限于丁苯橡胶、改性丁苯橡胶、丙烯酸甲酯、丙烯酸乙酯、丙烯酸丁酯、丙烯酸月桂酯及丁二烯中的至少一种。选用具有较低玻璃化温度的粘结剂，其可以在相对较宽的温度区间处于高弹态，具有较高的弹性极限及较大的断裂伸长率，配合体积变化较大的硅基材料能够有效地控制负极极片的体积膨胀。
在一些实施例中，在第一负极活性材料层中，第一粘结剂的质量百分比大于等于15％，更可选为15％～25％。控制第一粘结剂含量在上述范围内，能够有效地抑制硅基材料膨胀，改善二次电池的循环性能。
在一些实施例中，第一负极活性材料层可选地包括其他助剂，例如分散剂(如羧甲基纤 维素或其钠盐(CMC-Na))等。
在本申请中，应理解的是，第一负极活性材料层中的各组分(如硅基材料、多孔材料、第一导电剂、第一粘结剂以及任选的其他助剂)之和为100质量％。
在一些实施例中，第二负极活性材料层包括第二负极活性材料。第二负极活性材料可采用本领域公知的用于电池的负极活性材料。作为示例，第二负极活性材料可包括以下材料中的至少一种：石墨、软炭、硬炭、硅基材料、锡基材料和钛酸锂等。硅基材料可选自单质硅、硅氧化合物、硅碳复合物、硅氮复合物以及硅合金中的至少一种。锡基材料可选自单质锡、锡氧化合物以及锡合金中的至少一种。但本申请并不限定于这些材料，还可以使用其他可被用作电池负极活性材料的传统材料。这些负极活性材料可以仅单独使用一种，也可以将两种以上组合使用。
在一些实施例中，第二负极活性材料层包括石墨。
可选地，所述石墨包括人造石墨和天然石墨中的至少一种。
在一些实施例中，在第二负极活性材料层中，所述石墨的质量百分比大于等于80％；可选为90～96.5％。
在一些实施例中，所述石墨的体积分布粒径Dv50为10～20μm；可选为12μm～18μm。
在一些实施例中，所述石墨的体积分布粒径Dv99≤45μm；可选为30μm～42μm。
在一些实施例中，所述石墨的形貌为二次颗粒。
在一些实施例中，第二负极活性材料层同时包括石墨和硅基材料；可选地，在第二负极活性材料层中，硅基材料的质量百分比小于等于5％。第二负极活性材料层中硅基材料含量在上述范围内，能够减少硅基材料与电解液接触恶化，同时控制远离负极集流体设置的第二活性材料层中较低的含硅量，能够进一步降低负极极片的循环膨胀率，避免负极极片恶化，在保证较高容量的情况下，改善二次电池的循环性能。
在一些实施例中，所述第二负极活性材料层中包括第二粘结剂。可选地，第二粘结剂可包括丁苯橡胶(SBR),聚丙烯酸(PAA)、聚丙烯腈(PAN)、聚丙烯酸钠(PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)、聚甲基丙烯酸(PMAA)及羧甲基壳聚糖(CMCS)中的至少一种。
可选地，在第二负极活性材料层中，第二粘结剂的质量百分比小于等于4％，可选为1.5％～3％。
在一些实施例中，第二负极活性材料层包括第二导电剂。可选地，第二导电剂包括超导 碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的至少一种。
可选地，在第二负极活性材料层中，第二导电剂的质量百分比小于等于1.5％，例如0.5％～1.0％。
在一些实施例中，第二导电剂包括碳纳米管；可选地，在第二负极活性材料层中，碳纳米管的质量百分比小于等于0.15％。
在一些实施例中，第二负极活性材料层还可选地包括其他助剂，例如增稠剂(如羧甲基纤维素钠(CMC-Na))等。
参阅图1，是本申请一实施例的负极极片的截面的扫描电子显微镜图(SEM)，由图可明显看出，负极极片的负极集流体上依次有第一负极活性材料层及第二负极活性材料层，第一负极活性材料层的厚度小于第二负极活性材料层，厚度比为3≤D2/D1≤9。参阅图2，是图1的扫描电子显微镜图(SEM)的局部放大图，从图上可以看出，第一负极活性材料层具有丰富的多孔结构。
需要说明的是，上述各种参数测试，可以在二次电池制备过程中取样测试，也可以从制备好的二次电池中取样测试。
当上述测试样品是从制备好的二次电池中取样时，作为示例，可以按如下步骤进行取样：
(1)将二次电池做放电处理(为了安全起见，一般使电池处于满放状态)；将电池拆卸后取出负极极片，使用碳酸二甲酯(DMC)将负极极片浸泡一定时间(例如2-10小时)；然后将负极极片取出并在一定温度和时间下干燥处理(例如40℃-70℃，2h-5h)，干燥后取出负极极片。此时即可以在干燥后的负极极片中取样测试本申请上述的负极活性材料层相关的各参数(例如负极活性材料层的面密度、压实密度、厚度等)。
(2)将步骤(1)干燥后的负极极片在一定温度及时间下烘烤(例如200-500℃，1h～3h)，在烘烤后的负极极片中任选一区域，先对第二负极活性材料层取样(可以选用刀片刮粉取样)，刮粉深度不超过第一负极活性材料层与第二负极活性材料层的分界区；然后用同样的方式对第一负极活性材料层取样。因在负极活性材料层制备过程中，第一负极活性材料层和第二负极活性材料层之间的分界区可能存在互融层(即互融层中同时存在两种负极活性材料)，为了测试的准确性，在对第一负极活性材料层取样时，可以先将互融层刮掉，然后再对第一负极活性材料层刮粉取样。
(3)将步骤(2)收集到的负极活性材料做过筛处理(例如用100目-300目的筛网过筛)，最终得到可以用于测试本申请具有上述各材料参数(例如粒径、比表面积等)的负极活性材 料样品。
在上述取样过程中，可以用光学显微镜或扫描电子显微镜辅助判断第一负极活性材料层与第二负极活性材料层之间的分界区位置。
在本申请中，硅基材料在负极活性材料层中的质量占比可以用本领域公知的仪器及方法进行测定。例如，当测试样品是从制备好的二次电池中取样时，通过上述步骤获取硅基材料，参考EPA-3052-1996《硅酸盐的微波酸式消解法》将硅基材料消解，然后依据EPA6010D-2014《电感耦合等离子体原子发射光谱法》，采用美国赛默飞世尔科技(Thermo Fisher Scientific)公司的ICAP-7000型电感耦合等离子发射光谱仪(ICP-OES)测定硅元素的含量。具体测试方法如下：采用10mL质量分数为65％的硝酸和10mL质量分数为40％的氢氟酸将0.5g硅基材料样品进行微波消解，消解后加入50mL容量瓶中定容，之后采用ICAP-7000型ICP-OES测定硅元素的含量，根据硅元素的含量计算出硅基材料的质量比。
在本申请中，粘结剂和分散剂在负极活性材料层中的质量占比可以用本领域公知的仪器及方法同时进行测定。例如，当测试样品是从制备好的二次电池中取样时，通过上述步骤获取粉体材料通过热重法(测试设备可采用热重分析仪)测试出粘结剂以及分散剂的质量比即可。
在本申请中，导电剂在负极活性材料层中的质量占比可以用本领域公知的仪器及方法进行测定。例如，当测试样品是从制备好的二次电池中取样时，通过上述步骤获取粉体材料，通过上述所给方法测试出硅基材料、粘结剂和分散剂的质量比；则导电剂的质量比＝第一负极膜层的质量比-硅基材料的质量比-粘结剂的质量比-分散剂的质量比。
另外需要说明的是，本申请所给的第一负极活性材料层及第二负极活性材料层的各参数，例如第一负极活性材料层的厚度，均指负极极片单面的参数范围。当负极集流体的两个表面上均设置有第一负极活性材料层和第二负极活性材料层时，其中任意一个表面上的第一负极活性材料层或第二负极活性材料层的参数满足本申请，即认为落入本申请的保护范围内。且本申请所述的负极活性材料层厚度等范围均是指经冷压压实后并用于组装电池的膜层参数。
在一些实施例中，可以通过以下步骤S110～S130制备负极极片：
步骤S110：分别制备第一负极浆料及第二负极浆料，第一负极浆料包括硅基材料和多孔材料。
步骤S120：将第一负极浆料涂覆在负极集流体的至少一个表面上制备第一负极活性材料层；
步骤S130：将第二负极浆料涂覆在所述第一负极活性材料层的远离所述负极集流体的表面上制备第二负极活性材料层。
在一些实施例中，第一负极浆料的固含量小于等于30％，可选为20％～25％。在碳纳米管及粘结剂含量较高的情况下，控制第一负极浆料的固含量在上述范围内，能够确保浆料较好的分散性及较合适的粘度，有利于负极极片的制备。
在一些实施例中，第一负极浆料及第二负极浆料可通过双腔涂布设备同时进行涂布，也可以用涂布设备先涂布第一负极浆料，再涂布第二负极浆料。
其中，第一负极浆料涂覆在负极集流体表面形成第一负极活性材料层，第二负极浆料在第一负极活性材料层上形成第二负极活性材料层；最后经烘干、冷压等工序，即可得到负极极片。
本申请一实施方式，还提供一种二次电池的制备方法，包括上述步骤制备负极极片。
正极极片
正极极片包括正极集流体以及设置在正极集流体至少一个表面的正极活性材料层，正极活性材料层包括正极活性材料。
作为示例，正极集流体具有在其自身厚度方向相对的两个表面，正极活性材料层设置在正极集流体相对的两个表面的其中任意一者或两者上。
在一些实施例中，正极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可采用铝箔。复合集流体可包括高分子材料基层和形成于高分子材料基层至少一个表面上的金属层。复合集流体可通过将铝、铝合金、镍、镍合金、钛、钛合金、银及银合金等金属材料形成在高分子材料基材上而形成。高分子材料基材包括如聚丙烯(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)、聚乙烯(PE)等的基材。
在一些实施例中，正极活性材料可采用本领域公知的用于电池的正极活性材料。作为示例，正极活性材料可包括以下材料中的至少一种：橄榄石结构的含锂磷酸盐、锂过渡金属氧化物及其各自的改性化合物。但本申请并不限定于这些材料，还可以使用其他可被用作电池正极活性材料的传统材料。这些正极活性材料可以仅单独使用一种，也可以将两种以上组合使用。其中，锂过渡金属氧化物的示例可包括但不限于锂钴氧化物(如LiCoO 2)、锂镍氧化物(如LiNiO 2)、锂锰氧化物(如LiMnO 2、LiMn 2O 4)、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(如LiNi 1/3Co 1/3Mn 1/3O 2(也可以简称为NCM 333)、LiNi 0.5Co 0.2Mn 0.3O 2(也可以简称为NCM 523)、LiNi 0.5Co 0.25Mn 0.25O 2(也可以简称为NCM 211)、LiNi 0.6Co 0.2Mn 0.2O 2 (也可以简称为NCM 622)、LiNi 0.8Co 0.1Mn 0.1O 2(也可以简称为NCM 811)、锂镍钴铝氧化物(如LiNi 0.85Co 0.15Al 0.05O 2)及其改性化合物等中的至少一种。橄榄石结构的含锂磷酸盐的示例可包括但不限于磷酸铁锂(如LiFePO 4(也可以简称为LFP))、磷酸铁锂与碳的复合材料、磷酸锰锂(如LiMnPO 4)、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中的至少一种。
在一些实施例中，正极活性材料层还可选地包括粘结剂。作为示例，粘结剂可以包括聚偏氟乙烯(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-六氟丙烯共聚物及含氟丙烯酸酯树脂中的至少一种。
在一些实施例中，正极活性材料层还可选地包括导电剂。作为示例，导电剂可以包括超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的至少一种。
在一些实施例中，可以通过以下方式制备正极极片：将上述用于制备正极极片的组分，例如正极活性材料、导电剂、粘结剂和任意其他的组分分散于溶剂(例如N-甲基吡咯烷酮)中，形成正极浆料；将正极浆料涂覆在正极集流体上，经烘干、冷压等工序后，即可得到正极极片。
电解质
电解质在正极极片和负极极片之间起到传导离子的作用。本申请对电解质的种类没有具体的限制，可根据需求进行选择。例如，电解质可以是液态的、凝胶态的或全固态的。
在一些实施例中，电解质采用电解液。电解液包括电解质盐和溶剂。
在一些实施例中，电解质盐可选自六氟磷酸锂、四氟硼酸锂、高氯酸锂、六氟砷酸锂、双氟磺酰亚胺锂、双三氟甲磺酰亚胺锂、三氟甲磺酸锂、二氟磷酸锂、二氟草酸硼酸锂、二草酸硼酸锂、二氟二草酸磷酸锂及四氟草酸磷酸锂中的至少一种。
在一些实施例中，溶剂可选自碳酸亚乙酯、碳酸亚丙酯、碳酸甲乙酯、碳酸二乙酯、碳酸二甲酯、碳酸二丙酯、碳酸甲丙酯、碳酸乙丙酯、碳酸亚丁酯、氟代碳酸亚乙酯、甲酸甲酯、乙酸甲酯、乙酸乙酯、乙酸丙酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、丁酸甲酯、丁酸乙酯、1,4-丁内酯、环丁砜、二甲砜、甲乙砜及二乙砜中的至少一种。
在一些实施例中，电解液还可选地包括添加剂。例如添加剂可以包括负极成膜添加剂、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、改善电池高温或低温性能的添加剂等。
隔离膜
在一些实施例中，二次电池中还包括隔离膜。本申请对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，隔离膜的材质可选自玻璃纤维、无纺布、聚乙烯、聚丙烯及聚偏二氟乙烯中的至少一种。隔离膜可以是单层薄膜，也可以是多层复合薄膜，没有特别限制。在隔离膜为多层复合薄膜时，各层的材料可以相同或不同，没有特别限制。
在一些实施例中，正极极片、负极极片和隔离膜可通过卷绕工艺或叠片工艺制成电极组件。
在一些实施例中，二次电池可包括外包装。该外包装可用于封装上述电极组件及电解质。
在一些实施例中，二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。二次电池的外包装也可以是软包，例如袋式软包。软包的材质可以是塑料，作为塑料，可列举出聚丙烯、聚对苯二甲酸丁二醇酯以及聚丁二酸丁二醇酯等。
本申请对二次电池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。例如，图3是作为一个示例的方形结构的二次电池5。
在一些实施例中，参照图4，外包装可包括壳体51和盖板53。其中，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能够盖设于开口，以封闭容纳腔。正极极片、负极极片和隔离膜可经卷绕工艺或叠片工艺形成电极组件52。电极组件52封装于容纳腔内。电解液浸润于电极组件52中。二次电池5所含电极组件52的数量可以为一个或多个，本领域技术人员可根据具体实际需求进行选择。
在一些实施例中，二次电池可以组装成电池模块，电池模块所含二次电池的数量可以为一个或多个，具体数量本领域技术人员可根据电池模块的应用和容量进行选择。
图5是作为一个示例的电池模块4。参照图5，在电池模块4中，多个二次电池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二次电池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，多个二次电池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为一个或多个，具体数量本领域技术人员可根据电池包的应用和容量进行选择。
图6和图7是作为一个示例的电池包1。参照图6和图7，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能够盖设于下箱体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。
另外，本申请还提供一种用电装置，用电装置包括本申请提供的二次电池、电池模块、或电池包中的至少一种。二次电池、电池模块、或电池包可以用作用电装置的电源，也可以用作用电装置的能量存储单元。用电装置可以包括移动设备、电动车辆、电气列车、船舶及卫星、储能系统等，但不限于此。其中，移动设备例如可以是手机、笔记本电脑等；电动车辆例如可以是纯电动车、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，但不限于此。
作为用电装置，可以根据其使用需求来选择二次电池、电池模块或电池包。
图8是作为一个示例的用电装置6。该用电装置6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二次电池的高功率和高能量密度的需求，可以采用电池包或电池模块。
作为另一个示例的装置可以是手机、平板电脑、笔记本电脑等。该装置通常要求轻薄化，可以采用二次电池作为电源。
实施例
以下，说明本申请的实施例。下面描述的实施例是示例性的，仅用于解释本申请，而不能理解为对本申请的限制。实施例中未注明具体技术或条件的，按照本领域内的文献所描述的技术或条件或者按照产品说明书进行。所用试剂或仪器未注明生产厂商者，均为可以通过市购获得的常规产品。
实施例1：
负极极片制备：
第一负极浆料：将氧化亚硅、第一粘结剂、分散剂(CMC-Na)、第一导电剂及多孔材料在去离子水中充分搅拌混合，制备成第一负极浆料。其中氧化亚硅的Dv50为6.8μm，第一导电剂中石墨的Dv50为3.5μm，碳纳米管(CNT)的管径为2nm，轴向长度为15μm。
第二负极浆料：将人造石墨、粘结剂(SBR)、分散剂(CMC-Na)、导电炭黑(Super-P，SP)按照96.2％：1.8％：1.2％：0.8％的质量比在去离子水中充分搅拌混合，制备成第二负极浆料，其中人造石墨的Dv50为14.3μm。
将第一负极浆料均匀涂敷在厚度为8μm的集流体铜箔上烘干形成第一负极活性材料层，将第二负极浆料均匀涂敷在第一负极活性材料层之上烘干形成第二负极活性材料层，经冷压、分切后得到负极极片。其中，第一负极活性材料层的厚度为12μm，第二负极活性材料层的厚度为39μm，负极极片的压实密度为1.65g/cm 3、涂布重量为8.2mg/cm 2，其中氧化亚硅在第一负极活性材料层中的质量百分比为40％。
正极极片制备：将正极活性材料LiNi 0.8Co 0.1Mn 0.1O 2(NCM 811)、粘结剂聚偏氟乙烯(PVDF)、导电剂乙炔黑按照质量比为97％:1.5％:1.5％溶于溶剂N-甲基吡咯烷酮(NMP)中，充分搅拌混合均匀后制备成正极浆料；将正极浆料均匀涂覆在正极集流体铝箔上，之后经过烘干、冷压、分切，得到正极极片。
隔离膜：采用聚丙烯膜。
电解液制备：将碳酸亚乙酯(EC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)按体积比1:1:1混合，然后将LiPF 6均匀溶解在上述溶液中，得到电解液。该电解液中，LiPF 6的浓度为1mol/L。
二次电池制备：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；将电极组件放入外包装中，加入上述制备的电解液，经封装、静置、化成、老化等工序后，得到二次电池。
实施例2～18、对比例1～2：
实施例2～18、对比例1～2与实施例1的区别在于，负极极片的第一负极活性材料层组成不同。实施例1～18、对比例1～2的负极极片的第一负极活性材料层组成可参见表1。
表1实施例1～13及对比例1的负极极片第一负极活性材料层组成。
Figure PCTCN2022108554-appb-000001
Figure PCTCN2022108554-appb-000002
Figure PCTCN2022108554-appb-000003
注：表1中的质量百分比均为物质在第一负极活性材料层中的质量百分比。
测试部分：
二次电池在45℃下的循环性能测试
将上述各实施例和对比例制备的二次电池在45℃的恒温环境下，以1C倍率恒流充电至电压为4.25V，再在4.25V电压下恒压充电至电流小于等于0.05mA，之后静置5min，然后以1C倍率恒流放电至电压为2.5V，静置5min，此为一个循环充放电过程，此次的放电容量记为二次电池第1次循环的放电容量。将二次电池按照上述方法进行300次循环充放电测试，记录第300次循环的放电容量。
二次电池45℃循环300次后的容量保持率CR45℃(％)＝第300次循环的放电容量/第1次循环的放电容量×100％。
二次电池在45℃下的极片循环膨胀性能测试
将二次电池的负极极片完成冷压工序时的极片厚度记为h0，按上述二次电池在45℃下的循环性能测试方法，将二次电池循环300cls，以1C倍率恒流充电至电压为4.25V，再在4.25V电压下恒压充电至电流小于等于0.05mA，之后静置5min。在干燥房中拆解循环后的电芯，将300cls循环后的负极极片厚度记为h300，二次电池在45℃下的极片300cls循环膨胀率Δh300(％)＝(h300-h0)/h0*100％。
直流阻抗DCR测试
将上述各实施例和对比例制备的二次电池在25℃的恒温环境下，以0.33C倍率恒流充电至电压为4.25V，再在4.25V电压下恒压充电至电流小于等于0.05mA，之后静置5min，然后以1C倍率恒流放电30min，调节电芯至50％SOC，即电芯保留50％电量，静置60min。然后以3C放电30S，记录放电前电压V1，放后电压V2，放电电流I1，则DCR＝(V1-V2)/I1。
实施例1～18、对比例1～2的二次电池的电化学测试结果记录在表2中。
表2实施例1～18、对比例1～2的二次电池的电化学性能
Figure PCTCN2022108554-appb-000004
Figure PCTCN2022108554-appb-000005
从表2相关数据可以看出，实施例1～18的二次电池在45℃循环300圈后的容量保持率为92.9％～96.9％，循环膨胀率Δh300为41.3％～49.2％，直流阻抗DCR为356mΩ～672mΩ，二次电池具有较好的循环稳定性及较小的直流阻抗，循环性能及动力学性能较好。对比例1～2的二次电池中不含有多孔材料，45℃循环300圈后的容量保持率为85.3％和89.1％，循环膨胀率Δh300为56.5％和58.4％，直流阻抗DCR为797mΩ和831mΩ，循环性能及动力学性能均不及实施例1～18，可见通过在第一活性材料层中添加多孔材料，二次电池能够兼具较好的循环性能及较低的阻抗。
以上所述实施例的各技术特征可以进行任意的组合，为使描述简洁，未对上述实施例中的各个技术特征所有可能的组合都进行描述，然而，只要这些技术特征的组合不存在矛盾，都应当认为是本说明书记载的范围。
以上所述实施例仅表达了本申请的几种实施方式，其描述较为具体和详细，但并不能因此而理解为对发明专利范围的限制。应当指出的是，对于本领域的普通技术人员来说，在不脱离本申请构思的前提下，还可以做出若干变形和改进，这些都属于本申请的保护范围。因此，本申请专利的保护范围应以所附权利要求为准。

Claims (20)

  1. 一种二次电池，包括负极极片，所述负极极片包括：
    负极集流体；
    第一负极活性材料层，设置在所述负极集流体的至少一个表面上，所述第一负极活性材料层包括硅基材料和多孔材料；及
    第二负极活性材料层，设置在所述第一负极活性材料层的远离所述负极集流体的表面上。
  2. 根据权利要求1所述的二次电池，其中，所述多孔材料包括多孔碳、多孔金属及多孔陶瓷中的至少一种；
    可选地，所述多孔碳包括多孔石墨、多孔树脂碳、多孔生物质碳、活性碳、多孔碳纤维及膨胀石墨中的至少一种；
    可选地，所述多孔金属包括多孔镍、多孔铜、多孔钛、多孔金、多孔不锈钢及多孔金属合金材料中的至少一种；
    可选地，所述多孔陶瓷包括多孔Si 3N 4、多孔Al 2O 3及多孔SiC中的至少一种。
  3. 根据权利要求1或2所述的二次电池，其中，所述多孔材料的孔径为10nm～1000nm；可选地，所述多孔材料的孔径为30nm～300nm。
  4. 根据权利要求1～3任一项所述的二次电池，其中，所述多孔材料的孔隙率P≥30％；可选地，所述多孔材料的孔隙率为40％≤P≤80％。
  5. 根据权利要求1～4任一项所述的二次电池，其中，在所述第一负极活性材料层中，所述多孔材料的质量百分比小于等于10％，可选为2％～8％。
  6. 根据权利要求1～5任一项所述的二次电池，其中，在所述第一负极活性材料层中，所述硅基材料的质量百分比大于等于30％，可选为40％～60％。
  7. 根据权利要求1～6任一项所述的二次电池，其中，所述第一负极活性材料层的厚度记为D1，所述多孔材料的体积粒径分布Dv50记为D0，则所述负极极片满足0.5≤D0/D1≤0.8；可选地，所述负极极片满足0.6≤D0/D1≤0.7。
  8. 根据权利要求1～7任一项所述的二次电池，其中，所述第一负极活性材料层的厚度记为D1，所述第二负极活性材料层的厚度记为D2，则所述负极极片满足：3≤D2/D1≤9；可选地，所述负极极片满足：4≤D2/D1≤7。
  9. 根据权利要求1～8任一项所述的二次电池，其中，所述第一负极活性材料层的厚度小于等于15μm；可选地，所述第一负极活性材料层的厚度为5μm～13μm。
  10. 根据权利要求1～9任一项所述的二次电池，其中，所述第一负极活性材料层包括第一导电剂；
    可选地，所述第一导电剂包括石墨、超导碳、乙炔黑、柯琴黑、导电炭黑、石墨烯、碳点、碳纳米管、碳纳米纤维及石墨中的至少一种；
    可选地，在所述第一负极活性材料层中，所述第一导电剂的质量百分比大于等于25％，更可选为25％～40％。
  11. 根据权利要求1～10任一项所述的二次电池，其中，所述第一导电剂包括石墨；所述石墨满足下述(Ⅰ)-(Ⅴ)中的至少一个条件：
    (Ⅰ)所述石墨的体积粒径分布Dv50为3μm～8μm，可选为4μm～7μm；
    (Ⅱ)所述石墨的体积粒径分布Dv99为9μm～15μm，可选为10μm～13μm；
    (Ⅲ)在所述第一负极活性材料层中，所述石墨的质量百分比小于40％，可选为25％～35％；
    (Ⅳ)所述石墨的颗粒形貌为一次颗粒；
    (Ⅴ)所述石墨的首次库伦效率为85％～93％，可选为87％～92％。
  12. 根据权利要求10～11任一项所述的二次电池，其中，所述第一导电剂包括碳纳米管；
    可选地，在所述第一负极活性材料层中，所述碳纳米管的质量百分比小于等于5.0％；
    可选地，所述碳纳米管的管径为0.4nm～20nm；
    可选地，所述碳纳米管包括单壁碳纳米管及多壁碳纳米管中的至少一种，更可选为包括单壁碳纳米管。
  13. 根据权利要求10～12任一项所述的二次电池，其中，所述第一导电剂包括碳纳米管，所述第一负极活性材料层的厚度记为D1，所述碳纳米管的轴向长度记为L1，所述负极极片满足L1/D1＞1；可选地，所述负极极片满足1.5≤L1/D1≤5.0。
  14. 根据权利要求1～13任一项所述的二次电池，其中，所述第一负极活性材料层包括第一粘结剂；
    可选地，所述第一粘结剂的玻璃化温度≤25℃；
    可选地，所述第一粘结剂包括丁苯橡胶、改性丁苯橡胶、丙烯酸甲酯、丙烯酸乙酯、丙烯酸丁酯及丙烯酸月桂酯及丁二烯中的至少一种；
    可选地，在所述第一负极活性材料层中，所述第一粘结剂的质量百分比大于等于15％，更可选为15％～25％。
  15. 根据权利要求1～14任一项所述的二次电池，其中，所述第二负极活性材料包括石墨，所述石墨满足下述(1)-(4)中的至少一个条件：
    (1)所述石墨的质量百分比大于等于80％，可选为90％～96.5％；
    (2)所述石墨的Dv50为10μm～20μm，可选为12μm～18μm；
    (3)所述石墨的Dv99≤45μm，可选为30μm～42μm；
    (4)所述石墨的形貌为二次颗粒。
  16. 根据权利要求1～15任一项所述的二次电池，其中，所述第二负极活性材料层同时包括石墨和硅基材料；可选地，在所述第二负极活性材料层中，所述硅基材料的质量百分比小于等于5％。
  17. 根据权利要求1～16任一项所述的二次电池，其中，所述第二负极活性材料层满足下述(i)-(iii)中的至少一个条件：
    (i)所述第二负极活性材料层包括第二粘结剂，可选地，在所述第二负极活性材料层中，所述第二粘结剂的质量百分比小于等于4％；
    (ii)所述第二负极活性材料层包括第二导电剂，可选地，在所述第二负极活性材料层中，所述第二导电剂的质量百分比小于等于1.5％；
    (iii)所述第二负极活性材料层包括第二导电剂，且所述第二导电剂包括碳纳米管，可选地，在所述第二负极活性材料层中，所述碳纳米管的质量百分比小于等于0.15％。
  18. 权利要求1～17任一项所述的二次电池的制备方法，包括采用以下步骤制备负极极片：
    制备第一负极浆料：所述第一负极浆料包括硅基材料和多孔材料；
    制备第二负极浆料；
    将所述第一负极浆料涂覆在负极集流体的至少一个表面上制备第一负极活性材料层；
    将第二负极浆料涂覆在所述第一负极活性材料层的远离所述负极集流体的表面上制备第二负极活性材料层。
  19. 根据权利要求18所述的二次电池的制备方法，其中，所述第一负极浆料的固含量小于等于30％，可选为15％～25％。
  20. 一种用电装置，包括选自权利要求1～17任一项所述的二次电池或者包括根据权利要求18～19任一项所述的制备方法制备的二次电池。
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