WO2025246770A1 - 一种二次电池及电子装置 - Google Patents

一种二次电池及电子装置

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Publication number
WO2025246770A1
WO2025246770A1 PCT/CN2025/091642 CN2025091642W WO2025246770A1 WO 2025246770 A1 WO2025246770 A1 WO 2025246770A1 CN 2025091642 W CN2025091642 W CN 2025091642W WO 2025246770 A1 WO2025246770 A1 WO 2025246770A1
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Prior art keywords
negative electrode
lithium
electrolyte
material layer
secondary battery
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Application number
PCT/CN2025/091642
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English (en)
French (fr)
Inventor
许靖磊
李军飞
刘建禹
刘漫漫
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Ningde Amperex Technology Ltd
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Ningde Amperex Technology Ltd
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Publication of WO2025246770A1 publication Critical patent/WO2025246770A1/zh
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Anticipated expiration legal-status Critical

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Classifications

    • 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
    • H01M10/54—Reclaiming serviceable parts of waste accumulators
    • 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
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0568—Liquid materials characterised by the solutes
    • 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
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0569—Liquid materials characterised by the solvents
    • 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
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • 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
    • 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
    • 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
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M2010/4292—Aspects relating to capacity ratio of electrodes/electrolyte or anode/cathode
    • 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

  • This application relates to the field of electrochemical technology, and in particular to a secondary battery and electronic device.
  • Secondary batteries such as lithium-ion batteries
  • smartphones wearable devices, consumer drones, and electric vehicles due to their advantages such as high energy density, long cycle life, and no memory effect.
  • the market demands increasingly higher levels of performance in terms of kinetics and high-temperature float charging.
  • lithium-ion batteries have many side reactions between the positive electrode and the electrolyte, and between the negative electrode and the electrolyte during cycling, resulting in a large initial impedance and a significant increase in impedance during cycling, which affects the kinetic performance and high-temperature float charging performance of lithium-ion batteries.
  • the purpose of this application is to provide a secondary battery and electronic device to improve the kinetic performance and high-temperature float charging performance of the secondary battery.
  • the specific technical solution is as follows:
  • the first aspect of this application provides a secondary battery comprising a negative electrode sheet and an electrolyte.
  • the negative electrode sheet includes a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector.
  • the negative electrode material layer includes a first negative electrode material layer and a second negative electrode material layer stacked thereon, with the second negative electrode material layer located between the first negative electrode material layer and the negative current collector.
  • the thickness of the first negative electrode material layer is H 1 ⁇ m
  • the thickness of the second negative electrode material layer is H 2 ⁇ m, where 20 ⁇ H 1 ⁇ 40 and 60 ⁇ H 2 ⁇ 90.
  • the first negative electrode material layer includes a first negative electrode active material
  • the second negative electrode material layer includes a second negative electrode active material.
  • the Dv50 of the first negative electrode active material is greater than that of the second negative electrode active material.
  • the electrolyte comprises lithium difluorophosphate and a propionate ester compound, where the propionate ester compound includes propyl propionate. Based on the mass of the electrolyte, the mass percentage of lithium difluorophosphate is W 1 %, and the mass percentage of propyl propionate is W 2 %, where 0.1 ⁇ W 1 ⁇ 1 and 10 ⁇ W 2 %. ⁇ 60, 4 ⁇ W1 ⁇ H1 ⁇ 35 .
  • This application designs the negative electrode structure and electrolyte composition, and controls the values of H1 , H2 , W1 , W2 , and W1 ⁇ H1 within the above ranges, and ensures that the Dv50 of the first and second negative electrode active materials satisfies the above relationships.
  • This improves the wettability of the electrolyte on the negative electrode, reduces side reactions between the positive electrode and the electrolyte, and between the negative electrode and the electrolyte during cycling, increases the solubility of lithium salt in the electrolyte and the conductivity of the electrolyte, and facilitates the transport of lithium ions in the negative electrode and the electrolyte. This reduces the initial impedance of the secondary battery and the impedance growth during cycling, thereby improving the kinetic performance and high-temperature float charge performance of the secondary battery.
  • 2 ⁇ H 2 / H 1 ⁇ 4.5 By adjusting the value of H 2 / H 1 within the above range, the wettability of the electrolyte to the negative electrode can be further improved, and the side reactions between the negative electrode and the electrolyte during cycling can be reduced. This is beneficial to reducing the initial impedance of the secondary battery and the impedance growth during cycling, thereby improving the kinetic performance and high-temperature float charge performance of the secondary battery.
  • 0.005 ⁇ W1 / H1 ⁇ 0.05 By adjusting the value of W1 / H1 within the above range, it is beneficial to leverage the synergistic effect between the negative electrode and the electrolyte, further improving the dynamic performance of the first negative electrode material layer. This, in turn, helps to further reduce the initial impedance of the secondary battery and the impedance growth during cycling, thereby further improving the dynamic performance and high-temperature float charge performance of the secondary battery.
  • 250 ⁇ W2 ⁇ H1 ⁇ 2400 250 ⁇ W2 ⁇ H1 ⁇ 2400.
  • the electrolyte includes a polynitrile compound, and the mass percentage of the polynitrile compound is W 3 % based on the mass of the electrolyte, where 0.1 ⁇ W 3 ⁇ 5.
  • the polynitrile compound includes at least one selected from succinic anhydride, glutaronitrile, adiponitrile, heptanonitrile, octanoic anhydride, methylglutaronitrile, 1,3,5-pentanetricarbonyl, 1,2,3-propanetricarbonyl, 1,3,6-hexanetrionitrile, or 1,2,3-tris(2-cyanoethoxy)propane.
  • the stability of both the positive and negative electrode plates can be simultaneously improved, as well as the electrochemical and thermal stability of the electrolyte. This reduces the initial impedance and impedance growth during cycling of the secondary battery, improves the kinetic performance of the secondary battery, and also enhances the high-temperature float charge performance of the secondary battery.
  • the mass percentage of the propionate compound is W 4 %, 10 ⁇ W 4 ⁇ 65, and 0.154 ⁇ W 2 / W 4 ⁇ 1.
  • the propionate compound further includes at least one of methyl propionate, ethyl propionate, butyl acrylate, or butyl propionate.
  • the inclusion of the aforementioned propionate compound in the electrolyte further reduces the initial impedance of the secondary battery and the impedance increase during cycling, thereby further improving the kinetic performance and high-temperature float charge performance of the secondary battery.
  • the Dv50 of the first negative electrode active material is 12 ⁇ m to 14.9 ⁇ m
  • the Dv90 of the first negative electrode active material is 20.5 ⁇ m to 25.9 ⁇ m.
  • the Dv50 of the second negative electrode active material is 10 ⁇ m to 11.5 ⁇ m
  • the Dv90 of the second negative electrode active material is 19.4 ⁇ m to 24.8 ⁇ m.
  • the first negative electrode active material and the second negative electrode active material each independently include at least one of natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microspheres, silicon carbide, silicon oxide, or lithium titanate.
  • the negative electrode sheet includes a first negative electrode material layer and a second negative electrode material layer, and the values of H1 and H2 are controlled within the scope of this application, and the relationship between the Dv50 of the first and second negative electrode active materials is controlled within the scope of this application, and the electrolyte includes lithium difluorophosphate and propyl propionate, and the values of W1 , W2 , and W1 ⁇ H1 are controlled within the scope of this application, the selection of the above-mentioned first and second negative electrode active materials can enable the secondary battery to have good kinetic performance and high-temperature float charging performance.
  • the second aspect of this application provides an electronic device that includes the secondary battery provided in the first aspect of this application.
  • the secondary battery provided in this application has good kinetic performance and high-temperature float charging performance, thereby giving the electronic device a long service life and good performance.
  • the secondary battery includes a negative electrode sheet and an electrolyte.
  • the negative electrode sheet includes a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector.
  • the negative electrode material layer includes a first negative electrode material layer and a second negative electrode material layer stacked together, with the second negative electrode material layer located between the first negative electrode material layer and the negative current collector.
  • the thickness of the first negative electrode material layer is H 1 ⁇ m
  • the thickness of the second negative electrode material layer is H 2 ⁇ m, where 20 ⁇ H 1 ⁇ 40 and 60 ⁇ H 2 ⁇ 90.
  • the first negative electrode material layer includes a first negative electrode active material
  • the second negative electrode material layer includes a second negative electrode active material.
  • the Dv50 of the first negative electrode active material is greater than that of the second negative electrode active material.
  • the electrolyte includes lithium difluorophosphate and a propionate ester compound, where the propionate ester compound includes propyl propionate. Based on the mass of the electrolyte, the mass percentage of lithium difluorophosphate is W 1 %, and the mass percentage of propyl propionate is W 2 %, where 0.1 ⁇ W 1 ⁇ 1 and 10 ⁇ W 2. ⁇ 60, 4 ⁇ W1 ⁇ H1 ⁇ 35 .
  • This application designs the negative electrode structure and electrolyte composition, and controls the values of H1 , H2 , W1 , W2 , and W1 ⁇ H1 within the above ranges, and ensures that the Dv50 of the first and second negative electrode active materials satisfies the above relationships.
  • This improves the wettability of the electrolyte on the negative electrode, reduces side reactions between the positive electrode and the electrolyte, and between the negative electrode and the electrolyte during cycling, increases the solubility of lithium salt in the electrolyte and the conductivity of the electrolyte, and facilitates the transport of lithium ions in the negative electrode and the electrolyte. This reduces the initial impedance of the secondary battery and the impedance growth during cycling, thereby improving the kinetic performance and high-temperature float charge performance of the secondary battery.
  • Figure 1 is a schematic diagram of the negative electrode sheet along its own thickness direction according to one embodiment of this application;
  • Figure 2 shows the impedance of the lithium-ion batteries of Examples 1-1 and Comparative Example 1 of this application as a function of the number of cycles.
  • Figure 3 shows the change rate of thickness of the lithium-ion batteries in Examples 1-1 and Comparative Example 1 of this application as a function of charging time.
  • negative electrode 10 negative current collector 11
  • first negative electrode material layer 12 second negative electrode material layer 13.
  • lithium-ion batteries are used as an example of secondary batteries to illustrate this application; however, the secondary batteries in this application are not limited to lithium-ion batteries.
  • the specific technical solution is as follows:
  • the first aspect of this application provides a secondary battery, comprising a negative electrode sheet and an electrolyte.
  • the negative electrode sheet includes a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector.
  • the negative electrode material layer includes a first negative electrode material layer and a second negative electrode material layer stacked thereon, with the second negative electrode material layer located between the first negative electrode material layer and the negative current collector.
  • the thickness of the first negative electrode material layer is H 1 ⁇ m
  • the thickness of the second negative electrode material layer is H 2 ⁇ m, where 20 ⁇ H 1 ⁇ 40 and 60 ⁇ H 2 ⁇ 90.
  • the value of H 1 can be 20, 23, 25, 28, 30, 32, 36, 38, 40, or a range of any two of these values
  • the value of H 2 can be 60, 63, 65, 68, 70, 72, 76, 78, 80, 83, 85, 87, 90, or a range of any two of these values.
  • the first negative electrode material layer includes a first negative electrode active material
  • the second negative electrode material layer includes a second negative electrode active material.
  • the Dv50 of the first negative electrode active material is greater than that of the second negative electrode active material.
  • the electrolyte includes lithium difluorophosphate ( LiPO2F2 ) and a propionate compound, which includes propyl propionate.
  • the mass percentage of lithium difluorophosphate is W 1 %
  • the mass percentage of propyl propionate is W 2 %, where 0.1 ⁇ W 1 ⁇ 1, 10 ⁇ W 2 ⁇ 60, and 4 ⁇ W 1 ⁇ H 1 ⁇ 35.
  • the value of W1 can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or a range of any two values
  • the value of W2 can be 10, 15, 20, 24, 30, 35, 40, 46, 50, 54, 60, or a range of any two values
  • the value of W1 ⁇ H1 can be 4, 8, 10, 12, 15, 17, 20, 23, 25, 28, 30, 35, or a range of any two values.
  • the negative electrode sheet includes a first negative electrode material layer and a second negative electrode material layer.
  • electrolyte consumption can be reduced, and the electrolyte can have good wettability to the first and second negative electrode material layers. This improves the wettability of the electrolyte to the negative electrode sheet, which is beneficial for the transport of lithium ions in the negative electrode sheet. It can also reduce the side reactions between the negative electrode sheet and the electrolyte during cycling, thereby reducing the initial impedance of the secondary battery and the impedance growth during cycling, and thus improving the kinetic performance and high-temperature float charge performance of the secondary battery.
  • the first negative electrode material layer includes a first negative electrode active material
  • the second negative electrode material layer includes a second negative electrode active material.
  • the Dv50 of the first negative electrode active material is greater than that of the second negative electrode active material.
  • the first negative electrode active material has a smaller specific surface area, which can reduce side reactions between the negative electrode sheet and the electrolyte and reduce the initial impedance of the secondary battery.
  • the second negative electrode active material has a smaller particle size, which can improve the wettability of the electrolyte to the negative electrode sheet, increase the diffusion path of lithium ions, and reduce the impedance growth during the cycling process of the secondary battery, thereby improving the kinetic performance and high-temperature float charge performance of the secondary battery.
  • the electrolyte comprises lithium difluorophosphate and propyl propionate, and the values of W1 and W2 are controlled within the aforementioned range.
  • Lithium difluorophosphate can participate in the film formation process at both the positive and negative electrode interfaces, forming a denser and more stable positive electrode solid electrolyte interphase (CEI) film and negative electrode solid electrolyte interphase (SEI) film, reducing side reactions between the positive electrode and the electrolyte, and between the negative electrode and the electrolyte.
  • CEI positive electrode solid electrolyte interphase
  • SEI solid electrolyte interphase
  • Propyl propionate has a high dielectric constant and better solvent kinetics, which can improve the solubility of lithium salt in the electrolyte and the conductivity of the electrolyte, which is beneficial to the transport of lithium ions in the electrolyte. This can reduce the initial impedance of the secondary battery and the impedance growth during cycling, thereby improving the kinetic performance and high-temperature float charge performance of the secondary battery.
  • W1 ⁇ H1 within the aforementioned range, it is beneficial to leverage the synergistic effect between the negative electrode and the electrolyte, forming a denser and more stable SEI film at the negative electrode interface.
  • H1 When the value of H1 is too small, for example, less than 20, it is difficult to improve the impedance growth of the secondary battery during cycling, thus affecting the kinetic performance and high-temperature float charging performance of the secondary battery.
  • the value of H1 When the value of H1 is too large, for example, greater than 40, the kinetic performance of the first negative electrode material layer is too poor, and the wettability of the electrolyte to the second negative electrode material layer is too poor, resulting in a slow lithium-ion transport speed on the negative electrode sheet. This leads to excessive initial impedance and impedance growth during cycling, thus affecting the kinetic performance and high-temperature float charging performance of the secondary battery.
  • H2 When the value of H2 is too small, for example, less than 60, it is difficult to improve the initial impedance of the secondary battery, thus affecting the kinetic performance and high-temperature float charging performance of the secondary battery.
  • the value of H2 When the value of H2 is too large, for example, greater than 90, the wettability of the electrolyte to the second negative electrode material layer is too poor, and the side reactions between the negative electrode sheet and the electrolyte increase during cycling, leading to excessive initial impedance and impedance growth during cycling, thus affecting the kinetic performance and high-temperature float charging performance of the secondary battery.
  • the wettability of the electrolyte to the negative electrode sheet is too poor, the transport speed of lithium ions on the negative electrode sheet is too slow, and there are too many side reactions between the negative electrode sheet and the electrolyte, resulting in excessive growth of the initial impedance and the impedance during cycling of the secondary battery, thereby affecting the kinetic performance and high-temperature float charging performance of the secondary battery.
  • W1 When the value of W1 is too small, for example, less than 0.1, the mass percentage of lithium difluorophosphate is too low, making it difficult to form dense and stable CEI and SEI films at the positive and negative electrode interfaces. This leads to excessive side reactions between the positive electrode and the electrolyte, and between the negative electrode and the electrolyte, resulting in excessive initial impedance and impedance growth during cycling, thus affecting the kinetic performance and high-temperature float charge performance of the secondary battery.
  • W1 When the value of W1 is too large, for example, greater than 1, the mass percentage of lithium difluorophosphate is too high, resulting in poor solubility in the electrolyte, making it difficult to dissolve completely and causing electrolyte turbidity, making it unsuitable for use in secondary batteries.
  • W2 When the value of W2 is too small, for example, less than 10, the mass percentage of propyl propionate is too low, resulting in low solubility of the lithium salt in the electrolyte, affecting the electrolyte conductivity and hindering lithium ion transport. This leads to excessive initial impedance and impedance growth during cycling, thus affecting the kinetic performance and high-temperature float charge performance of the secondary battery.
  • W1 ⁇ H1 When the value of W1 ⁇ H1 is too small, for example, less than 4, it is not conducive to the synergistic effect between the negative electrode and the electrolyte. A dense and stable SEI film is difficult to form at the negative electrode interface, and there are too many side reactions between the negative electrode and the electrolyte. This leads to excessive initial impedance and impedance growth during cycling of the secondary battery, thus affecting the kinetic performance and high-temperature float charge performance of the secondary battery. When the value of W1 ⁇ H1 is too large, for example, greater than 35, it is not conducive to the synergistic effect between the negative electrode and the electrolyte.
  • the kinetic performance of the first negative electrode material layer is too poor, and the wettability of the electrolyte to the second negative electrode material layer is also too poor.
  • the transport speed of lithium ions on the negative electrode is too slow, and the solubility of lithium difluorophosphate in the electrolyte is too poor. This leads to excessive initial impedance and impedance growth during cycling of the secondary battery, thus affecting the kinetic performance and high-temperature float charge performance of the secondary battery.
  • the negative electrode sheet includes a first negative electrode material layer and a second negative electrode material layer, and by adjusting the values of H1 and H2 within the above-mentioned range, the Dv50 of the first negative electrode active material and the second negative electrode active material satisfies the above-mentioned relationship, and the electrolyte includes lithium difluorophosphate and propyl propionate, and by adjusting the values of W1 , W2 , and W1 ⁇ H1 within the above-mentioned range, the initial impedance of the secondary battery and the impedance growth during the cycling process can be reduced, thereby improving the dynamic performance and high-temperature float charging performance of the secondary battery.
  • the length direction of the negative electrode sheet is defined as Y, and its thickness direction as Z.
  • the negative electrode sheet typically has a long side and a short side, and the aforementioned length direction refers to the extension direction of the long side of the negative electrode sheet. It should be understood that the above definition of direction is for the convenience of describing the purpose of this application.
  • the negative electrode sheet 10 includes a negative current collector 11 and a second negative electrode material layer 13 and a first negative electrode material layer 12 sequentially disposed on one surface of the negative current collector 11.
  • H1 is the thickness of the first negative electrode material layer
  • H2 is the thickness of the second negative electrode material layer.
  • the negative electrode material layers can be disposed on one surface of the negative current collector along its thickness direction, or on two surfaces of the negative current collector along its thickness direction. It should be noted that the "surface” here can be the entire surface area of the negative current collector, or only a portion of the surface area of the negative current collector; this application has no particular limitation, as long as the purpose of this application is achieved.
  • the value of H2 / H1 can be 2, 2.3, 2.5, 2.8, 3, 3.2, 3.6, 3.8, 4, 4.2, 4.5, or a range consisting of any two of these values.
  • the electrolyte can achieve good wettability to the first and second negative electrode material layers, improving the wettability of the electrolyte to the negative electrode sheet, which is beneficial for the transport of lithium ions in the negative electrode sheet.
  • W ⁇ sub> 1 ⁇ /sub> /H ⁇ sub>1 ⁇ /sub> ⁇ 0.05 the value of W ⁇ sub>1 ⁇ /sub> /H ⁇ sub>1 ⁇ /sub> can be 0.005, 0.01, 0.015, 0.02, 0.024, 0.03, 0.036, 0.04, 0.045, 0.05, or a range of any two of these values.
  • 250 ⁇ W2 ⁇ H1 ⁇ 2400 250 ⁇ W2 ⁇ H1 ⁇ 2400.
  • the value of W2 ⁇ H1 can be 250, 500, 800, 1000, 1200, 1500, 1800, 2000, 2400, or a range of any two of these values.
  • the electrolyte includes a polynitrile compound, and the mass percentage of the polynitrile compound is W 3 % based on the mass of the electrolyte, where 0.1 ⁇ W 3 ⁇ 5.
  • the polynitrile compound includes at least one selected from succinic anionyl nitrile, glutaronitrile, adiponitrile, heptanonitrile, octanoic anionyl nitrile, methylglutaronitrile, 1,3,5-pentanetricarbonyl nitrile, 1,2,3-propanetricarbonyl nitrile, 1,3,6-hexanetrionitrile, or 1,2,3-tris(2-cyanoethoxy)propane.
  • the value of W 3 can be 0.1, 0.6, 1, 1.5, 2, 2.4, 3, 3.6, 4, 4.5, 5, or a range consisting of any two of these values.
  • the aforementioned polynitrile compound is further introduced, and its mass percentage W is controlled within the aforementioned range (W 3 %).
  • the strong coordination ability of the polynitrile compound allows it to complex with high-valence metal ions (e.g., cobalt ions) at the positive electrode interface, reducing the phase transition reaction of the positive electrode active material caused by metal ion dissolution and forming a more stable CEI film.
  • the negative electrode interface At the negative electrode interface, it can undergo a reduction reaction to form a stable SEI film, simultaneously improving the stability of both the positive and negative electrode plates. Furthermore, the high carbon-nitrogen triple bond energy in the polynitrile compound makes it less susceptible to oxidation, reducing oxidative decomposition and gas production in the electrolyte, and improving the electrochemical and thermal stability of the electrolyte. This reduces the initial impedance and impedance growth during cycling of the secondary battery, improving its kinetic performance and high-temperature float charge performance.
  • high temperature refers to a temperature greater than or equal to 40°C.
  • the value of W ⁇ sub>3 ⁇ /sub> ⁇ H ⁇ sub>1 ⁇ /sub> can be 50, 80, 100, 120, 150, 180, 200, or a range of any two of these values.
  • the mass percentage of the propionate ester compound is W 4 % based on the mass of the electrolyte, where 10 ⁇ W 4 ⁇ 65 and 0.154 ⁇ W 2 / W 4 ⁇ 1.
  • the value of W 4 can be 10, 15, 20, 24, 30, 35, 40, 46, 50, 54, 60, 65, or a range of any two of these values
  • the value of W 2 / W 4 can be 0.154, 0.3, 0.35, 0.4, 0.5, 0.62, 0.7, 0.85, 0.9, 1, or a range of any two of these values.
  • adjusting the mass percentage content W4 % and the W2 / W4 value of the propionate compound within the aforementioned range can improve the solubility of lithium salts in the electrolyte and the conductivity of the electrolyte, which is beneficial for the transport of lithium ions in the electrolyte. This helps to reduce the initial impedance of the secondary battery and the impedance growth during cycling, thereby improving the kinetic performance and high-temperature float charging performance of the secondary battery.
  • the propionate compound further includes at least one of methyl propionate, ethyl propionate, butyl acrylate, or butyl propionate.
  • the inclusion of the aforementioned propionate compound can improve the solubility of lithium salts in the electrolyte and the conductivity of the electrolyte, which is beneficial for lithium ion transport in the electrolyte. This further reduces the initial impedance of the secondary battery and the impedance increase during cycling, thereby further improving the kinetic performance and high-temperature float charge performance of the secondary battery.
  • the electrolyte also includes other organic solvents.
  • This application does not particularly limit the types of other organic solvents, as long as they achieve the purpose of this application.
  • other organic solvents may include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents.
  • the aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds.
  • the aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC).
  • the aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC).
  • the aforementioned fluorocarbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate.
  • FEC fluoroethylene carbonate
  • the aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, ⁇ -butyrolactone, decanolactone, valproic acid lactone, or caprolactone.
  • the aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran.
  • the aforementioned other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.
  • the mass percentage of other organic solvents is from 14% to 81%.
  • the mass percentage of other organic solvents may be 14%, 19%, 24%, 30%, 40%, 50%, 62%, 70%, 78%, 81%, or a range consisting of any two of these values.
  • the electrolyte also includes lithium salts.
  • the lithium salt may include, but is not limited to , at least one of LiPF6 , LiBF4 , LiAsF6 , LiClO4 , LiB (C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3 , Li2SiF6 , lithium bis ( oxalato ) borate ( LiBOB ) , or lithium difluoroborate. Based on the mass of the electrolyte, the mass percentage of lithium salt is 8% to 15%.
  • the electrolyte may include lithium salts, lithium difluorophosphate, propyl propionate, and other organic solvents.
  • the mass percentages of lithium salts, lithium difluorophosphate, and propyl propionate are as described above, and the mass percentages of other organic solvents range from 24% to 81%.
  • Secondary batteries comprising the above-described electrolytes exhibit good kinetic performance and high-temperature float charging performance.
  • the electrolyte may include lithium salts, lithium difluorophosphate, propyl propionate, polynitrile compounds, and other organic solvents.
  • the mass percentages of lithium salts, lithium difluorophosphate, propyl propionate, and polynitrile compounds are as described above, while the mass percentages of other organic solvents range from 19% to 81%.
  • Secondary batteries comprising the above-described electrolytes exhibit good kinetic performance and high-temperature float-charge performance.
  • the electrolyte may include lithium salts, lithium difluorophosphate, propionate compounds, and other organic solvents.
  • the propionate compounds include propyl propionate and at least one of methyl propionate, ethyl propionate, butyl acrylate, or butyl propionate.
  • the mass percentages of lithium salts, lithium difluorophosphate, and propionate compounds are as described above, and the mass percentages of other organic solvents are 19% to 81%. Secondary batteries comprising the above electrolytes exhibit good kinetic performance and high-temperature float-charge performance.
  • the electrolyte may include lithium salts, lithium difluorophosphate, propionate compounds, polynitrile compounds, and other organic solvents.
  • the propionate compounds include propyl propionate and at least one of methyl propionate, ethyl propionate, butyl acrylate, or butyl propionate.
  • the mass percentages of lithium salts, lithium difluorophosphate, propionate compounds, and polynitrile compounds are as described above, and the mass percentages of other organic solvents are 14% to 81%. Secondary batteries comprising the above electrolytes exhibit better kinetic performance and high-temperature float-charge performance.
  • the Dv50 of the first negative electrode active material is from 12 ⁇ m to 14.9 ⁇ m
  • the Dv90 of the first negative electrode active material is from 20.5 ⁇ m to 25.9 ⁇ m.
  • the Dv50 of the first negative electrode active material can be 12 ⁇ m, 12.3 ⁇ m, 12.7 ⁇ m, 13 ⁇ m, 13.4 ⁇ m, 13.7 ⁇ m, 14 ⁇ m, 14.5 ⁇ m, 14.9 ⁇ m, or a range of any two of these values
  • the Dv90 of the first negative electrode active material can be 20.5 ⁇ m, 21 ⁇ m, 21.6 ⁇ m, 22 ⁇ m, 22.4 ⁇ m, 23 ⁇ m, 23.5 ⁇ m, 24 ⁇ m, 24.6 ⁇ m, 25 ⁇ m, 25.9 ⁇ m, or a range of any two of these values.
  • the consumption of electrolyte by the negative electrode sheet can be reduced, the wettability of the electrolyte on the negative electrode sheet can be improved, which is beneficial for the transport of lithium ions in the negative electrode sheet. It can also reduce the side reactions between the negative electrode sheet and the electrolyte during cycling, and improve the stability of the negative electrode sheet. This is beneficial for reducing the initial impedance of the secondary battery and the impedance growth during cycling, thereby improving the kinetic performance of the secondary battery and the high-temperature float charge performance of the secondary battery.
  • the Dv50 of the second negative electrode active material is from 10 ⁇ m to 11.5 ⁇ m
  • the Dv90 of the second negative electrode active material is from 19.4 ⁇ m to 24.8 ⁇ m.
  • the Dv50 of the second negative electrode active material can be 10 ⁇ m, 10.3 ⁇ m, 10.5 ⁇ m, 10.7 ⁇ m, 11 ⁇ m, 11.2 ⁇ m, 11.5 ⁇ m, or a range consisting of any two of these values
  • the Dv90 of the second negative electrode active material can be 19.4 ⁇ m, 20 ⁇ m, 20.5 ⁇ m, 21 ⁇ m, 21.6 ⁇ m, 22 ⁇ m, 22.4 ⁇ m, 23 ⁇ m, 23.5 ⁇ m, 24 ⁇ m, 24.8 ⁇ m, or a range consisting of any two of these values.
  • the wettability of the electrolyte to the negative electrode sheet can be improved, and the side reactions between the negative electrode sheet and the electrolyte during cycling can be reduced. This is beneficial to reducing the initial impedance of the secondary battery and the impedance growth during cycling, which in turn is beneficial to improving the dynamic performance of the secondary battery and also beneficial to improving the high-temperature float charging performance of the secondary battery.
  • Dv50 refers to the particle size that, in the volumetric particle size distribution of the material, reaches 50% of the cumulative volume from the smallest particle size.
  • Dv90 refers to the particle size that, in the volumetric particle size distribution of the material, reaches 90% of the cumulative volume from the smallest particle size.
  • the Dv90 of the first negative electrode active material is smaller than the thickness H1 of the first negative electrode material layer.
  • first and second anode active materials with different Dv50 and Dv90 values can be obtained through mechanical crushing (e.g., ball milling).
  • the Dv50 and Dv90 values of both the first and second anode active materials can be controlled by adjusting the ball milling time.
  • extending the ball milling time decreases the Dv50 of the first anode active material, while shortening it increases it.
  • extending the ball milling time decreases the Dv90 of the first anode active material, while shortening it increases it.
  • extending the ball milling time decreases the Dv50 of the second anode active material, while shortening it increases it.
  • the first and second negative electrode active materials each independently include at least one of natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microspheres, silicon carbide (SiC), silicon oxide (SiO2) ( 0 ⁇ x ⁇ 2), or lithium titanate.
  • the selection of the aforementioned first and second negative electrode active materials can enable the secondary battery to possess good kinetic performance and high-temperature float charge performance.
  • the types of the first and second negative electrode active materials can be the same or different.
  • the first negative electrode material layer includes a first negative electrode active material, and may also include a first negative electrode binder and a first negative electrode conductive agent; alternatively, the first negative electrode material layer may also include a first negative electrode binder, a first negative electrode conductive agent, or a first thickener.
  • the mass percentage content of the first negative electrode active material may be 86% to 99%
  • the mass percentage content of the first negative electrode binder may be 0.5% to 5%
  • the mass percentage content of the first negative electrode conductive agent may be 0.5% to 5%
  • the mass percentage content of the first thickener may be 0% to 4%.
  • the second negative electrode material layer includes a second negative electrode active material, and may also include a second negative electrode binder and a second negative electrode conductive agent.
  • the second negative electrode material layer may also include a second negative electrode binder, a second negative electrode conductive agent, or a second thickener.
  • the mass percentage content of the second negative electrode active material may be 86% to 99%
  • the mass percentage content of the second negative electrode binder may be 0.5% to 5%
  • the mass percentage content of the second negative electrode conductive agent may be 0.5% to 5%
  • the mass percentage content of the second thickener may be 0% to 4%.
  • the first negative electrode binder and the second negative electrode binder may each independently include, but are not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, polyamide-imide, styrene-butadiene rubber, or polyvinylidene fluoride.
  • the first negative electrode conductive agent and the second negative electrode conductive agent may each independently include, but are not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metallic materials, or conductive polymers.
  • Conductive carbon black may include, but is not limited to, at least one of acetylene black or Ketjen black.
  • the aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and/or multi-walled carbon nanotubes.
  • the aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and/or carbon nanofibers.
  • the aforementioned metallic materials may include, but are not limited to, metal powders and/or metal fibers.
  • the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver.
  • the aforementioned conductive polymer may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole.
  • This application does not impose any particular limitation on the types of the first and second thickeners, as long as they achieve the purpose of this application.
  • the first and second thickeners may each independently include, but are not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose.
  • the negative electrode current collector may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector.
  • the composite current collector may be a lithium copper composite current collector, a carbon copper composite current collector, a nickel copper composite current collector, a titanium copper composite current collector, etc.
  • the thickness of the negative electrode current collector may be from 4 ⁇ m to 15 ⁇ m.
  • the negative electrode material layer may further include a conductive layer located between the negative electrode current collector and the second negative electrode material layer.
  • a conductive layer located between the negative electrode current collector and the second negative electrode material layer.
  • the composition of the conductive layer which can be a conductive layer commonly used in the art.
  • the conductive layer may include a conductive agent and a binder.
  • the conductive agent and binder in the conductive layer which may be at least one of the aforementioned first negative electrode conductive agent and first negative electrode binder.
  • the preparation method of the negative electrode sheet may include, but is not limited to, the following steps: (1) preparing a first negative electrode slurry and a second negative electrode slurry; (2) coating the second negative electrode slurry onto one surface of the negative electrode current collector, drying it, and forming a second negative electrode material layer on one surface of the negative electrode current collector; then coating the first negative electrode slurry onto the surface of the second negative electrode material layer, drying it, and forming the second negative electrode material layer and the first negative electrode material layer sequentially on one surface of the negative electrode current collector; (3) repeating the above steps on the other surface of the negative electrode current collector, forming the first negative electrode material layer and the second negative electrode material layer on both surfaces of the negative electrode current collector; (4) obtaining the negative electrode sheet by cold pressing, cutting, and welding the negative electrode tabs.
  • the thickness H1 of the first negative electrode material layer can be controlled by adjusting the coating surface density of the first negative electrode material layer. For example, when other conditions remain unchanged, increasing the coating surface density of the first negative electrode material layer increases H1 ; decreasing the coating surface density of the first negative electrode material layer decreases H1 .
  • the thickness H2 of the second negative electrode material layer can be controlled by adjusting the coating surface density of the second negative electrode material layer. For example, when other conditions remain unchanged, increasing the coating surface density of the second negative electrode material layer increases H2 ; decreasing the coating surface density of the second negative electrode material layer decreases H2 .
  • the secondary battery further includes a positive electrode sheet, which includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector.
  • a positive electrode sheet which includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector.
  • positive electrode material layer disposed on at least one surface of the positive current collector means that the positive electrode material layer can be disposed on one surface of the positive current collector along its thickness direction, or on two surfaces of the positive current collector along its thickness direction.
  • surface here can refer to the entire surface area of the positive current collector, or only a portion thereof; this application does not impose any particular limitation, as long as the purpose of this application is achieved.
  • the positive electrode current collector may contain aluminum foil, aluminum alloy foil, or composite current collectors (such as aluminum-carbon composite current collectors).
  • This application also does not impose any particular limitation on the thickness of the positive electrode current collector, as long as it achieves the purpose of this application.
  • the thickness of the positive electrode current collector may be from 5 ⁇ m to 20 ⁇ m.
  • the positive electrode material layer includes a positive electrode active material.
  • the positive electrode active material may include, but is not limited to, lithium nickel cobalt manganese oxide (e.g., NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide ( LiCoO2 ), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate.
  • the positive electrode material layer may further include a positive electrode conductive agent and a positive electrode binder.
  • a positive electrode conductive agent and a positive electrode binder may be at least one of the aforementioned first negative electrode conductive agent and first negative electrode binder.
  • This application does not impose any particular limitation on the mass ratio of the positive electrode active material, positive electrode conductive agent, and positive electrode binder in the positive electrode material layer. Those skilled in the art can select them according to actual needs, as long as the purpose of this application is achieved.
  • the thickness of the cathode material layer can be from 30 ⁇ m to 120 ⁇ m.
  • the compaction density of the cathode material layer can be from 3 g/ cm3 to 5 g/ cm3 .
  • the positive electrode may further include a conductive layer located between the positive current collector and the positive electrode material layer.
  • the composition of the conductive layer is not particularly limited and can be any conductive layer commonly used in the art.
  • the conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer; for example, it can be at least one of the aforementioned first negative electrode conductive agent and first negative electrode binder.
  • the secondary battery also includes a separator.
  • the material of the separator may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) primarily composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid.
  • the type of separator may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.
  • the separator may include a substrate layer and a surface treatment layer.
  • the substrate layer may be a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide.
  • a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used.
  • a surface treatment layer is provided on at least one surface of the substrate layer.
  • the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic substances.
  • the inorganic layer comprises inorganic particles and a binder.
  • the inorganic particles may include at least one selected from alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate.
  • the binder in the inorganic layer may be at least one of the aforementioned first negative electrode binders.
  • the polymer layer comprises a polymer, the polymer material of which includes at least one selected from polyamide, polyacrylonitrile, acrylate polymers, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).
  • the thickness of the separator there is no particular limitation on the thickness of the separator, as long as it can achieve the purpose of this application.
  • the thickness of the separator can be from 3 ⁇ m to 30 ⁇ m.
  • the secondary battery also includes a casing for housing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the field of secondary batteries.
  • a casing for housing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the field of secondary batteries.
  • This application does not limit the scope of these other components.
  • This application does not impose any particular limitation on the casing; it can be a casing known in the art, as long as it achieves the purpose of this application.
  • the casing can be a rigid casing or a flexible casing.
  • the material of the rigid casing can be metal; this application does not limit the type of metal and can use known metal rigid casings, as long as they achieve the purpose of this application.
  • the flexible casing can be a metal plastic film, such as aluminum-plastic film, steel-plastic film, etc.
  • the fabrication process of the secondary battery described in this application is well known to those skilled in the art, and this application does not impose any particular limitations.
  • the fabrication process of the secondary battery may include, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the secondary battery.
  • overcurrent protection elements, conductive plates, etc. may be placed in the housing as needed to prevent pressure rise and overcharging/discharging inside the secondary battery.
  • the second aspect of this application provides an electronic device that includes the secondary battery provided in the first aspect of this application.
  • the secondary battery provided in this application has good kinetic performance and high-temperature float charging performance, thereby giving the electronic device a long service life and good performance.
  • electronic devices may include, but are not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.
  • the negative electrode sheets were disassembled.
  • the negative electrode sheets were cleaned with dimethyl carbonate (DMC), dried at 60°C, and the cross-section along the thickness direction of the negative electrode sheets was polished with argon ions. Then, the cross-section of the negative electrode sheets was observed using a scanning electron microscope (SEM), and the thicknesses H1 of the first negative electrode material layer, H2 of the second negative electrode material layer, and the ratio H2 / H1 were measured.
  • DMC dimethyl carbonate
  • SEM scanning electron microscope
  • the lithium-ion battery was discharged to 3V at a constant current of 0.2C and then disassembled.
  • the electrolyte was collected by centrifugation, squeezing or other methods. Then, gas chromatography-mass spectrometry (GC-MS, Agilent 8890 instrument) and ion chromatography (IC, AQUION ion chromatograph) were used to test the individual components in the electrolyte and determine their content.
  • GC-MS gas chromatography-mass spectrometry
  • IC ion chromatography
  • the lithium-ion battery was placed in a 25°C constant temperature chamber and left to stand for 4 hours. Then, it was charged at a constant current of 0.7C to the rated voltage (4.48V in this embodiment), charged at a constant voltage of 4.48V to a current of 0.05C, left to stand for 2 hours, and then discharged at a constant current of 0.2C to a voltage of 3.0V.
  • the capacity of the lithium-ion battery measured at this time is recorded as the reference capacity C1 , that is, the capacity at 100% SOC (State of Charge).
  • the lithium-ion battery was charged at a constant current of 0.7C to a voltage of 4.48V, then charged at a constant voltage of 4.48V to a current of 0.05C.
  • the voltage and current of the lithium-ion battery were measured at each of these three different SOCs.
  • the voltage-to-current ratio was calculated to obtain the impedance at 70% SOC (denoted as R1) , 20% SOC (denoted as R2) , and 10% SOC (denoted as R3 ) .
  • the initial impedance of the lithium-ion battery was evaluated by the values of R1 , R2 , and R3 . The smaller the values of R1 , R2 , and R3 , the smaller the initial impedance; the larger the values of R1 , R2 , and R3 , the larger the initial impedance.
  • the lithium-ion battery was placed in a 25°C constant temperature chamber and allowed to stand for 4 hours. Then, it was sequentially discharged at a constant current of 0.02C to 0.3C (70% SOC), 0.8C (20% SOC), and 0.9C (10% SOC).
  • the voltage at 70% SOC is denoted as U'70 % , and the current as I'70 % .
  • the voltage is denoted as U'20 %
  • the current as I'20 %
  • the voltage is denoted as U'10%
  • the current I'10 % .
  • the lithium-ion battery was then charged at a constant current of 0.7C to a voltage of 4.48V, then charged at a constant voltage of 4.48V to a current of 0.05C. After standing for 2 hours, it was discharged at a constant current of 0.5C to a voltage of 3.0V. This constitutes one charge-discharge cycle.
  • the lithium-ion battery was charged and discharged according to the above method. A discharge capacity recovery test was performed every 50 charge-discharge cycles. The lithium-ion battery was charged at a constant current of 0.7C to a voltage of 4.48V, then charged at a constant voltage of 4.48V to a current of 0.05C, and allowed to stand for 2 hours.
  • the average value of R70% , R20% , and R10% is calculated as the impedance value of the lithium-ion battery at the corresponding number of cycles. The charging and discharging method described above is followed until 1000 cycles are completed.
  • the impedance of a lithium-ion battery at the 300th cycle is denoted as R300
  • the impedance at the 1000th cycle is denoted as R1000
  • the lithium-ion battery was placed in a 25°C constant temperature chamber and left to stand for 4 hours. Then, it was charged at a constant current of 0.7C to 4.48V, and then charged at a constant voltage of 4.48V to a current of 0.05C. After standing for 2 hours, it was discharged at a constant current of 0.2C to a voltage of 3.0V. The lithium-ion battery was then charged again at a constant current of 0.7C to 4.48V, and then charged at a constant voltage of 4.48V to a current of 0.05C. The thickness of the lithium-ion battery at this point was measured and recorded as the initial thickness T ⁇ sub>0 ⁇ /sub>.
  • the lithium-ion battery was then placed in a 55°C constant temperature chamber and left to stand for 1.5 hours. Finally, the lithium-ion battery was charged at a constant current of 0.4C to 4.48V, and then charged at a constant voltage of 4.48V to a current of 60mA. The lithium-ion battery was continuously charged at a constant current (100mA) and constant voltage (4.48V). The thickness of the lithium-ion battery was measured every 96 hours and recorded as Ti . The thickness change rate was recorded as Ti / T0 . When Ti / T0 reached 108.5%, the charging time at this point was recorded. Three lithium-ion batteries were tested for each example and comparative example. The average charging time of the three batteries was calculated and recorded as D. The high-temperature float charging performance was evaluated using the value of D. A larger D value indicates better high-temperature float charging performance, and a smaller D value indicates worse high-temperature float charging performance.
  • the first thickener sodium carboxymethyl cellulose
  • Super P conductive carbon black
  • SBR styrene-butadiene rubber
  • Super P sodium carboxymethyl cellulose
  • a second negative electrode slurry was uniformly coated onto one surface of a 10 ⁇ m thick copper foil used as a negative electrode current collector, with a coating density of 5.81 mg/ cm2 . The coating was then dried at 85°C to obtain a negative electrode sheet with a single-sided coating of the second negative electrode material layer.
  • a first negative electrode slurry was uniformly coated onto the surface of the second negative electrode material layer away from the negative electrode current collector, with a coating density of 2.33 mg/ cm2 . This was dried at 85°C to obtain a negative electrode sheet with both a single-sided coating of the second and first negative electrode material layers.
  • lithium salts lithium hexafluorophosphate ( LiPF6 ), lithium difluorophosphate, and propyl propionate were added to the base solvent and mixed thoroughly to obtain the electrolyte. Based on the mass of the electrolyte, the mass percentages of lithium salt LiPF6 , lithium difluorophosphate ( W1 %), and propyl propionate ( W2 %) are shown in Table 1, with the remainder being the base solvent.
  • Lithium cobalt oxide positive electrode active material
  • conductive carbon black Super P
  • carbon nanotubes CNTs
  • PVDF, Mw 7 ⁇ 106
  • positive electrode binder Lithium cobalt oxide
  • Super P conductive carbon black
  • CNTs carbon nanotubes
  • PVDF, Mw 7 ⁇ 106
  • positive electrode binder Lithium cobalt oxide
  • Super P conductive carbon black
  • CNTs carbon nanotubes
  • PVDF, Mw 7 ⁇ 106
  • positive electrode binder positive electrode binder
  • the above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode material. After drying at 120°C, the sheet was cold-pressed, cut, and welded with positive electrode tabs to obtain a positive electrode sheet with dimensions of 74 mm ⁇ 851 mm for later use.
  • the thickness of the positive electrode material layer is 92 ⁇ m, and the compaction density of the positive electrode material layer is 4.15 g/ cm3 .
  • a porous polyethylene film (provided by Celgard) with a thickness of 7 ⁇ m was used as the substrate layer.
  • NMP N-methylpyrrolidone
  • the mixture was stirred evenly under vacuum to obtain an inorganic slurry with a solid content of 30 wt%.
  • This inorganic slurry was then uniformly coated onto one surface of the substrate layer to form an inorganic layer with a thickness of 2 ⁇ m.
  • This polymer layer slurry was then uniformly coated onto the surfaces of one inorganic layer and the other substrate layer, with a coating density of 2.5 mg/ cm2 , forming a polymer layer. This resulted in a separator membrane with one side containing both an inorganic layer and a polymer layer, and the other side containing only a polymer layer.
  • the positive electrode, separator, and negative electrode prepared above are stacked and wound sequentially to obtain a wound electrode assembly.
  • the side of the separator containing the inorganic layer and the polymer layer faces the positive electrode, and the side containing only the polymer layer faces the negative electrode.
  • the electrode assembly is placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. After vacuum sealing, standing, formation (0.3C constant current charging to 3.5V, then 1C constant current charging to 3.9V), capacity testing, degassing, and edge trimming, a lithium-ion battery is obtained.
  • H1 is controlled by adjusting the coating surface density of the first negative electrode material layer
  • H2 is controlled by adjusting the coating surface density of the second negative electrode material layer.
  • the rest is the same as in Examples 1-1. Specifically, the Dv50 and Dv90 of the first negative electrode active material and the second negative electrode active material are adjusted by controlling the ball milling time.
  • the negative electrode slurry was uniformly coated onto one surface of a 10 ⁇ m thick copper foil current collector, with a coating density of 8.14 mg/ cm2 .
  • the foil was then dried at 85°C to obtain a negative electrode sheet with a single-sided negative electrode material layer.
  • the above steps were then repeated on the other surface of the same copper foil to obtain a negative electrode sheet with a double-sided negative electrode material layer.
  • a negative electrode sheet with dimensions of 76 mm ⁇ 867 mm was obtained for later use.
  • the thickness of the negative electrode material layer is 105 ⁇ m, and the Dv50 and Dv90 of the negative electrode active material are 11 ⁇ m and 22 ⁇ m, respectively.
  • H1 is controlled by adjusting the coating surface density of the first negative electrode material layer
  • H2 is controlled by adjusting the coating surface density of the second negative electrode material layer.
  • Example 1-1 Except for adjusting the relevant preparation parameters according to Table 1 in the ⁇ Preparation of Electrolyte> section, the rest is the same as in Example 1-1. Specifically, when the mass percentage of lithium difluorophosphate W1 % changes, the mass percentage of the base solvent changes accordingly, while the mass ratio of each component in the base solvent and the mass percentages of lithium salt and propyl propionate remain unchanged.
  • Example 1-1 Except for adjusting the relevant preparation parameters according to Table 1 in the ⁇ Preparation of Electrolyte> section, the rest is the same as in Example 1-1. Specifically, when the mass percentage of propyl propionate W changes by 2 %, the mass percentage of the base solvent changes accordingly, while the mass ratio of each component in the base solvent and the mass percentages of lithium salt and lithium difluorophosphate remain unchanged.
  • this application designs the negative electrode structure and electrolyte composition, and controls the values of H1 , H2 , W1 , W2 , and W1 ⁇ H1 within the range of this application, and controls the Dv50 of the first negative electrode active material to be greater than the Dv50 of the second negative electrode active material.
  • the R1 , R2 , R3 , and K of the lithium-ion battery are smaller, that is, the initial impedance and the impedance growth during the cycling process are smaller, and D is larger, indicating that the lithium-ion battery has good kinetic performance and high-temperature float charging performance.
  • the lithium-ion battery in Comparative Example 1 does not include a first negative electrode material layer and a second negative electrode material layer in its negative electrode sheet; the lithium-ion batteries in Comparative Examples 2 to 3 have H1 values that are not within the scope of this application; the lithium-ion batteries in Comparative Examples 4 to 5 have H2 values that are not within the scope of this application; the lithium-ion battery in Comparative Example 6 does not include lithium difluorophosphate in its electrolyte and the value of W1 ⁇ H1 is not within the scope of this application; the lithium-ion batteries in Comparative Examples 7 to 8 have W1 and W1 ⁇ H1 values that are not within the scope of this application; the lithium-ion battery in Comparative Example 9 does not include propyl propionate in its electrolyte; the lithium-ion batteries in Comparative Examples 10 to 11 have W2 values that are not within the scope of this application; the lithium-ion battery in Comparative Example 12 does not include lithium difluorophosphate and propyl propionate in its electro
  • H1 typically affects the kinetic performance and high-temperature float charging performance of lithium-ion batteries. As can be seen from Examples 1-1 to 1-3 and Comparative Examples 2 to 3, when the value of H1 is too small, such as in Comparative Example 2, the lithium-ion battery exhibits larger values for R1 , R2 , R3 , and K, meaning a larger initial impedance and greater impedance increase during cycling, while D is smaller.
  • the lithium-ion battery exhibits larger values for R1 , R2 , R3 , and K, meaning a larger initial impedance and greater impedance increase during cycling, while D is smaller, indicating poor kinetic performance and high-temperature float charging performance.
  • the lithium-ion battery exhibits smaller values for R1 , R2 , R3 , and K, meaning a smaller initial impedance and less impedance increase during cycling, while D is larger, indicating good kinetic performance and high-temperature float charging performance.
  • H2 typically affects the kinetic performance and high-temperature float charging performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-4 to 1-5, and Comparative Examples 4 to 5, when the value of H2 is too small, such as in Comparative Example 4, the lithium-ion battery exhibits larger values for R1 , R2 , R3 , and K, meaning a greater initial impedance and a larger impedance increase during cycling, while D is smaller.
  • the lithium-ion battery exhibits larger values for R1 , R2 , R3 , and K, meaning a greater initial impedance and a larger impedance increase during cycling, while D is smaller, indicating poor kinetic performance and high-temperature float charging performance.
  • the lithium-ion battery exhibits smaller values for R1 , R2 , R3 , and K, meaning a smaller initial impedance and a smaller impedance increase during cycling, while D is larger, indicating good kinetic performance and high-temperature float charging performance.
  • the relationship between the Dv50 values of the first and second negative electrode active materials typically affects the kinetic performance and high-temperature float charging performance of lithium-ion batteries.
  • the lithium-ion battery exhibits larger R1 , R2 , R3 , and K values, meaning a greater initial impedance and greater impedance growth during cycling, while D is smaller, indicating poor kinetic performance and high-temperature float charging performance.
  • the lithium-ion battery exhibits smaller R1 , R2 , R3 , and K values, meaning a smaller initial impedance and less impedance growth during cycling, while D is larger, indicating good kinetic performance and high-temperature float charging performance.
  • the value of W1 typically affects the kinetic performance and high-temperature float charging performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-7 to 1-10, and Comparative Examples 6 to 8, when the value of W1 is too small, such as in Comparative Examples 6 and 7, the lithium-ion battery exhibits larger values for R1 , R2 , R3 , and K, meaning a larger initial impedance and greater impedance increase during cycling, while D is smaller.
  • the lithium-ion battery exhibits larger values for R1 , R2 , R3 , and K, meaning a larger initial impedance and greater impedance increase during cycling, while D is smaller, indicating poor kinetic performance and high-temperature float charging performance.
  • the lithium-ion battery exhibits smaller values for R1 , R2 , R3 , and K, meaning a smaller initial impedance and less impedance increase during cycling, while D is larger, indicating good kinetic performance and high-temperature float charging performance.
  • W2 typically affects the kinetic performance and high-temperature float charging performance of lithium-ion batteries. From Examples 1-1 and 1-13 to...
  • Examples 1-14 and Comparative Examples 9 to 11 show that when the value of W2 is too small, such as in Comparative Examples 9 and 10, the R1 , R2 , R3 , and K of the lithium-ion battery are larger, meaning the initial impedance and the impedance increase during cycling are greater, while D is smaller.
  • the value of W2 is too large, such as in Comparative Example 11, the R1 , R2 , R3 , and K of the lithium-ion battery are larger, meaning the initial impedance and the impedance increase during cycling are greater, while D is smaller, indicating poor kinetic performance and high-temperature float charging performance of the lithium-ion battery.
  • the R1 , R2 , R3 , and K of the lithium-ion battery are smaller, meaning the initial impedance and the impedance increase during cycling are smaller, while D is larger, indicating that the lithium-ion battery has good kinetic performance and high-temperature float charging performance.
  • the value of W1 ⁇ H1 typically affects the kinetic performance and high-temperature float charging performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-7 to 1-10, and Comparative Examples 6 to 8, when the value of W1 ⁇ H1 is too small, such as in Comparative Examples 6 and 7, the lithium-ion battery exhibits larger values for R1 , R2 , R3 , and K, meaning a larger initial impedance and greater impedance growth during cycling, while D is smaller.
  • the lithium-ion battery exhibits larger values for R1 , R2 , R3 , and K, meaning a larger initial impedance and greater impedance growth during cycling, while D is smaller, indicating poor kinetic performance and high-temperature float charging performance.
  • the lithium-ion battery exhibits smaller values for R1 , R2 , R3 , and K, meaning a smaller initial impedance and less impedance growth during cycling, while D is larger, indicating good kinetic performance and high-temperature float charging performance.
  • H2 / H1 typically affects the kinetic performance and high-temperature float charging performance of lithium-ion batteries.
  • the lithium-ion battery exhibits smaller R1 , R2 , R3 , and K values, meaning smaller initial impedance and smaller impedance growth during cycling.
  • D is larger, indicating that the lithium-ion battery possesses good kinetic performance and high-temperature float charging performance.
  • the value of W1 / H1 typically affects the kinetic performance and high-temperature float charging performance of lithium-ion batteries. As can be seen from Examples 1-1 to 1-12, when the value of W1 / H1 is within the range specified in this application, the lithium-ion battery exhibits smaller R1 , R2 , R3 , and K values, meaning smaller initial impedance and smaller impedance growth during cycling. Simultaneously, D is larger, indicating that the lithium-ion battery possesses good kinetic performance and high-temperature float charging performance.
  • the value of W2 ⁇ H1 typically affects the kinetic performance and high-temperature float charging performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-13 to 1-16, when the value of W2 ⁇ H1 is within the range of this application, the lithium-ion battery exhibits smaller R1 , R2 , R3 , and K values, meaning smaller initial impedance and smaller impedance growth during cycling, while D is larger, indicating that the lithium-ion battery possesses good kinetic performance and high-temperature float charging performance.
  • the lithium-ion battery of Example 1-1 has an impedance of 46.1 m ⁇ after 300 cycles and an impedance of 50.4 m ⁇ after 1000 cycles, with a K value of 6.14 ⁇ 10 ⁇ 3 m ⁇ /cycle.
  • the lithium-ion battery of Comparative Example 1 has an impedance of 59.0 m ⁇ after 300 cycles and an impedance of 66.2 m ⁇ after 1000 cycles, with a K value of 10.29 ⁇ 10 ⁇ 3 m ⁇ /cycle.
  • the smaller K value of Example 1-1 compared to Comparative Example 1 indicates that the lithium-ion battery of Example 1-1 exhibits less impedance growth during cycling and better kinetic performance.
  • the lithium-ion battery of Example 1-1 has a smaller thickness change rate.
  • the D value of Example 1-1 is 1248h, while the D value of Comparative Example 1 is 932h.
  • the larger D value of Example 1-1 compared to Comparative Example 1 indicates that the lithium-ion battery of Example 1-1 has better high-temperature float charging performance.
  • the electrolyte includes polynitrile compounds and the mass percentage W of these compounds is controlled within the scope of this application, the lithium-ion battery exhibits smaller R1 , R2 , R3 , and K values, meaning smaller initial impedance and smaller impedance growth during cycling.
  • D is larger, indicating that the lithium-ion battery possesses good kinetic performance and high-temperature float-charge performance.
  • the value of W3 ⁇ H1 typically affects the kinetic performance and high-temperature float charging performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-1 to 2-7, and 2-11, when the value of W3 ⁇ H1 is within the range of this application, the lithium-ion battery exhibits smaller R1 , R2 , R3 , and K values, meaning smaller initial impedance and impedance growth during cycling, while D is larger, indicating that the lithium-ion battery possesses good kinetic performance and high-temperature float charging performance.
  • the lithium-ion battery exhibits smaller R1 , R2 , R3 , and K values, meaning smaller initial impedance and smaller impedance growth during cycling, while a larger D value, indicating that the lithium-ion battery possesses good kinetic performance and high-temperature float charge performance.
  • the value of W2 / W4 typically affects the kinetic performance and high-temperature float charging performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-8 to 2-10, when the value of W2 / W4 is within the range of this application, the lithium-ion battery exhibits smaller R1 , R2 , R3 , and K values, meaning smaller initial impedance and smaller impedance growth during cycling, while D is larger, indicating that the lithium-ion battery possesses good kinetic performance and high-temperature float charging performance.
  • the Dv50 and Dv90 of the first negative electrode active material typically affect the kinetic performance and high-temperature float charge performance of lithium-ion batteries. From...
  • the Dv50 and Dv90 of the second negative electrode active material typically affect the kinetic performance and high-temperature float charge performance of lithium-ion batteries. From...
  • the R1 , R2 , R3 , and K of the lithium-ion battery are relatively small, that is, the initial impedance and the impedance growth during the cycling process are relatively small, while D is relatively large, indicating that the lithium-ion battery has good kinetic performance and high-temperature float charging performance.
  • first negative electrode active material typically affects the kinetic performance and high-temperature float charge performance of lithium-ion batteries.
  • the lithium-ion battery has smaller R1 , R2 , R3 , and K, meaning smaller initial impedance and smaller impedance growth during cycling, while D is larger, indicating that the lithium-ion battery has good kinetic performance and high-temperature float charge performance.
  • the type of second negative electrode active material typically affects the kinetic performance and high-temperature float charge performance of lithium-ion batteries.
  • the lithium-ion battery has smaller R1 , R2 , R3 , and K, meaning smaller initial impedance and smaller impedance growth during cycling, while D is larger, indicating that the lithium-ion battery has good kinetic performance and high-temperature float charge performance.

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Abstract

本申请提供了一种二次电池及电子装置。二次电池的负极材料层包括层叠设置的第一负极材料层和第二负极材料层，第二负极材料层位于第一负极材料层和负极集流体之间，第一负极材料层的厚度为H1μm，第二负极材料层的厚度为H2μm，20≤H1≤40，60≤H2≤90；第一负极材料层中第一负极活性材料的Dv50大于第二负极材料层中第二负极活性材料的Dv50，电解液包括二氟磷酸锂和丙酸酯化合物，丙酸酯化合物包括丙酸丙酯；基于电解液的质量，二氟磷酸锂的质量百分含量为W1％，丙酸丙酯的质量百分含量为W2％，0.1≤W1≤1，10≤W2≤60，4≤W1×H1≤35。本申请二次电池的动力学性能和高温浮充性能良好。

Description

一种二次电池及电子装置
本申请要求于2024年5月31日提交中国国家知识产权局专利局、申请号为202410707511.0、发明名称为“一种二次电池及电子装置”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请涉及电化学技术领域，特别是涉及一种二次电池及电子装置。
背景技术
二次电池，例如锂离子电池，因其高能量密度、长循环寿命及无记忆效应等优点，被广泛应用于智能手机、穿戴设备、消费级无人机以及电动汽车等领域。随着锂离子电池在上述领域中的广泛应用，市场对锂离子电池动力学性能和高温浮充性能的要求越来越高。
然而，现有的锂离子电池在循环过程中正极极片与电解液、负极极片与电解液之间的副反应较多，初始阻抗较大，在锂离子电池的循环过程中阻抗增长也较大，从而影响锂离子电池的动力学性能和高温浮充性能。
发明内容
本申请的目的在于提供一种二次电池及电子装置，以提高二次电池的动力学性能和高温浮充性能。具体技术方案如下：
本申请的第一方面提供了一种二次电池，其包括负极极片和电解液，负极极片包括负极集流体和设置于负极集流体至少一个表面的负极材料层，负极材料层包括层叠设置的第一负极材料层和第二负极材料层，第二负极材料层位于第一负极材料层和负极集流体之间，第一负极材料层的厚度为H1μm，第二负极材料层的厚度为H2μm，20≤H1≤40，60≤H2≤90；第一负极材料层包括第一负极活性材料，第二负极材料层包括第二负极活性材料，第一负极活性材料的Dv50大于第二负极活性材料的Dv50；电解液包括二氟磷酸锂和丙酸酯化合物，丙酸酯化合物包括丙酸丙酯；基于电解液的质量，二氟磷酸锂的质量百分含量为W1％，丙酸丙酯的质量百分含量为W2％，0.1≤W1≤1，10≤W2≤60，4≤W1×H1≤35。本申请通过对负极极片结构和电解液成分进行设计，并且调控H1、H2、W1、W2、W1×H1的值在上述范围内，以及第一负极活性材料和第二负极活性材料的Dv50满足上述关系，能够改善电解液对负极极片的浸润性，减少循环过程中正极极片与电解液、负极极片与电解液之间的副反应，提高锂盐在电解液中的溶解度以及电解液的电导率，有利于锂离子在负极极片和电解液中的传输，从而能够减小二次电池的初始阻抗以及循环过程中的阻抗增长，进而提高二次电池的动力学性能和高温浮充性能。
在本申请的一些实施方案中，2≤H2/H1≤4.5。通过调控H2/H1的值在上述范围内，能够进一步改善电解液对负极极片的浸润性，同时还能够减少循环过程中负极极片与电解液之间的副反应，从而有利于减小二次电池的初始阻抗以及循环过程中的阻抗增长，进而有利于提高二次电池的动力学性能和高温浮充性能。
在本申请的一些实施方案中，0.005≤W1/H1≤0.05。通过调控W1/H1的值在上述范围内，有利于发挥负极极片与电解液之间的协同作用，进一步提高第一负极材料层的动力学性能，从而有利于进一步减小二次电池的初始阻抗以及循环过程中的阻抗增长，进而有利于进一步提高二次电池的动力学性能和高温浮充性能。
在本申请的一些实施方案中，250≤W2×H1≤2400。通过调控W2×H1的值在上述范围内，有利于发挥负极极片与电解液之间的协同作用，提高第一负极材料层的动力学性能，从而有利于进一步减小二次电池的初始阻抗以及循环过程中的阻抗增长，进而有利于进一步提高二次电池的动力学性能和高温浮充性能。
在本申请的一些实施方案中，电解液包括多腈化合物，基于电解液的质量，多腈化合物的质量百分含量为W3％，0.1≤W3≤5，多腈化合物包括丁二腈、戊二腈、己二腈、庚二腈、辛二腈、甲基戊二腈、1,3,5-戊三甲腈、1,2,3-丙三甲腈、1,3,6-己烷三腈或1,2,3-三(2-氰基乙氧基)丙烷中的至少一种。在电解液包括二氟磷酸锂和丙酸丙酯的基础上，进一步引入上述多腈化合物并且调控其质量百分含量W3％在上述范围内，能够同时提高正极极片和负极极片的稳定性，提高电解液的电化学稳定性和热稳定性，从而在减小二次电池的初始阻抗以及循环过程中的阻抗增长，提高二次电池的动力学性能的同时，还能够提高二次电池的高温浮充性能。
在本申请的一些实施方案中，50≤W3×H1≤200。通过调控W3×H1的值在上述范围内，能够在减小二次电池的初始阻抗以及循环过程中的阻抗增长，提高二次电池的动力学性能的同时，进一步提高二次电池的高温浮充性能。
在本申请的一些实施方案中，基于电解液的质量，丙酸酯化合物的质量百分含量为W4％，10≤W4≤65，0.154≤W2/W4≤1。在电解液包括二氟磷酸锂和丙酸丙酯的基础上，调控丙酸酯化合物的质量百分含量W4％和W2/W4的值在上述范围内，有利于进一步减小二次电池的初始阻抗以及循环过程中的阻抗增长，从而有利于提高二次电池的动力学性能和高温浮充性能。
在本申请的一些实施方案中，丙酸酯化合物还包括丙酸甲酯、丙酸乙酯、丙烯酸丁酯或丙酸丁酯中的至少一种。在电解液包括二氟磷酸锂和丙酸丙酯的基础上，电解液还包括上述丙酸酯化合物，有利于进一步减小二次电池的初始阻抗以及循环过程中的阻抗增长，从而有利于进一步提高二次电池的动力学性能和高温浮充性能。
在本申请的一些实施方案中，第一负极活性材料的Dv50为12μm至14.9μm，第一负极活性材料的Dv90为20.5μm至25.9μm。通过调控第一负极活性材料的Dv50和Dv90在上述范围内，能够改善电解液对负极极片的浸润性，减少循环过程中负极极片与电解液之间的副反应，提高负极极片的稳定性，从而有利于进一步减小二次电池的初始阻抗以及循环过程中的阻抗增长，进而有利于提高二次电池的动力学性能，还有利于提高二次电池的高温浮充性能。
在本申请的一些实施方案中，第二负极活性材料的Dv50为10μm至11.5μm，第二负极活性材料的Dv90为19.4μm至24.8μm。通过调控第二负极活性材料的Dv50和Dv90在上述范围内，能够进一步改善电解液对负极极片的浸润性，减少循环过程中负极极片与电解液之间的副反应，从而有利于减小二次电池的初始阻抗以及循环过程中的阻抗增长，进而有利于提高二次电池的动力学性能，还有利于提高二次电池的高温浮充性能。
在本申请的一些实施方案中，第一负极活性材料和第二负极活性材料各自独立地包括天然石墨、人造石墨、软碳、硬碳、中间相碳微球、硅碳化合物、硅氧化合物或钛酸锂中的至少一种。在负极极片包括第一负极材料层和第二负极材料层，并且调控H1和H2的值、第一负极活性材料和第二负极活性材料的Dv50的关系在本申请范围内，以及电解液包括二氟磷酸锂和丙酸丙酯，并且调控W1、W2、W1×H1的值在本申请范围内的基础上，选用上述第一负极活性材料和第二负极活性材料，可以使得二次电池具有良好的动力学性能和高温浮充性能。
本申请的第二方面提供了一种电子装置，其包括本申请第一方面提供的二次电池。本申请提供的二次电池具有良好的动力学性能和高温浮充性能，从而本申请提供的电子装置具有较长的使用寿命和良好的性能。
本申请的有益效果：
本申请提供了一种二次电池及电子装置。该二次电池包括负极极片和电解液，负极极片包括负极集流体和设置于负极集流体至少一个表面的负极材料层，负极材料层包括层叠设置的第一负极材料层和第二负极材料层，第二负极材料层位于第一负极材料层和负极集流体之间，第一负极材料层的厚度为H1μm，第二负极材料层的厚度为H2μm，20≤H1≤40，60≤H2≤90；第一负极材料层包括第一负极活性材料，第二负极材料层包括第二负极活性材料，第一负极活性材料的Dv50大于第二负极活性材料的Dv50；电解液包括二氟磷酸锂和丙酸酯化合物，丙酸酯化合物包括丙酸丙酯；基于电解液的质量，二氟磷酸锂的质量百分含量为W1％，丙酸丙酯的质量百分含量为W2％，0.1≤W1≤1，10≤W2≤60，4≤W1×H1≤35。本申请通过对负极极片结构和电解液成分进行设计，并且调控H1、H2、W1、W2、W1×H1的值在上述范围内，以及第一负极活性材料和第二负极活性材料的Dv50满足上述关系，能够改善电解液对负极极片的浸润性，减少循环过程中正极极片与电解液、负极极片与电解液之间的副反应，提高锂盐在电解液中的溶解度以及电解液的电导率，有利于锂离子在负极极片和电解液中的传输，从而能够减小二次电池的初始阻抗以及循环过程中的阻抗增长，进而提高二次电池的动力学性能和高温浮充性能。
当然，实施本申请的任一产品或方法并不一定需要同时达到以上所述的所有优点。
附图说明
为了更清楚地说明本申请实施例或现有技术中的技术方案，下面将对实施例或现有技术描述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，对于本领域普通技术人员来讲，还可以根据这些附图获得其他的实施例。
图1为本申请一种实施方案的负极极片沿自身厚度方向的结构示意图；
图2为本申请实施例1-1和对比例1的锂离子电池的阻抗随循环圈数的变化图；
图3为本申请实施例1-1和对比例1的锂离子电池的厚度变化率随充电时间的变化图。
附图标记：负极极片10，负极集流体11，第一负极材料层12，第二负极材料层13。
具体实施方式
下面将结合本申请实施例中的附图，对本申请实施例中的技术方案进行清楚、完整地描述，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。本领域技术人员基于本申请所获得的所有其他实施例，都属于本申请保护的范围。
需要说明的是，在以下内容中，以锂离子电池作为二次电池的例子来解释本申请，但是本申请的二次电池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二次电池，其包括负极极片和电解液，负极极片包括负极集流体和设置于负极集流体至少一个表面的负极材料层，负极材料层包括层叠设置的第一负极材料层和第二负极材料层，第二负极材料层位于第一负极材料层和负极集流体之间，第一负极材料层的厚度为H1μm，第二负极材料层的厚度为H2μm，20≤H1≤40，60≤H2≤90。例如，H1的值可以为20、23、25、28、30、32、36、38、40或为其中任意两个数值组成的范围，H2的值可以为60、63、65、68、70、72、76、78、80、83、85、87、90或为其中任意两个数值组成的范围。第一负极材料层包括第一负极活性材料，第二负极材料层包括第二负极活性材料，第一负极活性材料的Dv50大于第二负极活性材料的Dv50。电解液包括二氟磷酸锂(LiPO2F2)和丙酸酯化合物，丙酸酯化合物包括丙酸丙酯；基于电解液的质量，二氟磷酸锂的质量百分含量为W1％，丙酸丙酯的质量百分含量为W2％，0.1≤W1≤1，10≤W2≤60，4≤W1×H1≤35。例如，W1的值可以为0.1、0.2、0.3、0.4、0.5、0.6、0.7、0.8、0.9、1或为其中任意两个数值组成的范围，W2的值可以为10、15、20、24、30、35、40、46、50、54、60或为其中任意两个数值组成的范围，W1×H1的值可以为4、8、10、12、15、17、20、23、25、28、30、35或为其中任意两个数值组成的范围。
负极极片包括第一负极材料层和第二负极材料层，并且调控H1、H2的值在上述范围内，能够减少电解液的消耗，使电解液对第一负极材料层和第二负极材料层具有良好的浸润性，改善电解液对负极极片的浸润性，有利于锂离子在负极极片中的传输，还能够减少循环过程中负极极片与电解液之间的副反应，从而能够减小二次电池的初始阻抗以及循环过程中的阻抗增长，进而提高二次电池的动力学性能和高温浮充性能。第一负极材料层包括第一负极活性材料，第二负极材料层包括第二负极活性材料，第一负极活性材料的Dv50大于第二负极活性材料的Dv50，第一负极活性材料的比表面积较小，能够减少负极极片与电解液之间的副反应，减小二次电池的初始阻抗，而第二负极活性材料的粒径较小，能够改善电解液对负极极片的浸润性，增加锂离子的扩散路径，减小二次电池循环过程中的阻抗增长，从而提高二次电池的动力学性能和高温浮充性能。电解液包括二氟磷酸锂和丙酸丙酯，并且调控W1、W2的值在上述范围内，二氟磷酸锂能够同时参与正极界面和负极界面的成膜过程，形成更为致密和稳定的正极固体电解质界面(CEI)膜和负极固体电解质界面(SEI)膜，减少正极极片与电解液、负极极片与电解液之间的副反应，而丙酸丙酯的介电常数大，溶剂动力学性能更好，能够提高锂盐在电解液中的溶解度以及电解液的电导率，有利于锂离子在电解液中的传输，从而能够减小二次电池的初始阻抗以及循环过程中的阻抗增长，进而提高二次电池的动力学性能和高温浮充性能。通过调控W1×H1的值在上述范围内，有利于发挥负极极片与电解液之间的协同作用，在负极界面形成更为致密和稳定的SEI膜，进一步减小负极极片与电解液之间的副反应，还能够改善电解液对负极极片的浸润性，有利于锂离子在负极极片中的传输，提高第一负极材料层的动力学性能，从而能够进一步减小二次电池的初始阻抗以及循环过程中的阻抗增长，进而进一步提高二次电池的动力学性能和高温浮充性能。
当H1的值过小时，例如小于20，难以改善二次电池在循环过程中的阻抗增长，从而影响二次电池的动力学性能和高温浮充性能。当H1的值过大时，例如大于40，第一负极材料层的动力学性能过差，同时电解液对第二负极材料层的浸润性过差，锂离子在负极极片的传输速度过慢，导致二次电池的初始阻抗以及循环过程中的阻抗增长过大，从而影响二次电池的动力学性能和高温浮充性能。当H2的值过小时，例如小于60，难以改善二次电池的初始阻抗，从而影响二次电池的动力学性能和高温浮充性能。当H2的值过大时，例如大于90，电解液对第二负极材料层的浸润性过差，在循环过程中负极极片与电解液之间的副反应增多，导致二次电池的初始阻抗以及循环过程中的阻抗增长过大，从而影响二次电池的动力学性能和高温浮充性能。
当第一负极活性材料的Dv50小于第二负极活性材料的Dv50时，电解液对负极极片的浸润性过差，锂离子在负极极片的传输速度过慢，同时负极极片与电解液之间的副反应过多，导致二次电池的初始阻抗以及循环过程中的阻抗增长过大，从而影响二次电池的动力学性能和高温浮充性能。
当W1的值过小时，例如小于0.1，二氟磷酸锂的质量百分含量过低，难以在正极界面和负极界面形成致密和稳定的CEI膜和SEI膜，正极极片与电解液、负极极片与电解液之间的副反应过多，导致二次电池的初始阻抗以及循环过程中的阻抗增长过大，从而影响二次电池的动力学性能和高温浮充性能。当W1的值过大时，例如大于1，二氟磷酸锂的质量百分含量过高，其在电解液中的溶解性过差，难以溶解完全，电解液出现浑浊现象，难以应用于二次电池。当W2的值过小时，例如小于10，丙酸丙酯的质量百分含量过低，锂盐在电解液中的溶解度过低，影响电解液的电导率，不利于锂离子在电解液中的传输，导致二次电池的初始阻抗以及循环过程中的阻抗增长过大，从而影响二次电池的动力学性能和高温浮充性能。当W2的值过大时，例如大于60，丙酸丙酯的质量百分含量过高，不利于锂离子的溶解，影响锂离子在电解液中的传输，从而影响二次电池的动力学性能和高温浮充性能。
当W1×H1的值过小时，例如小于4，不利于发挥负极极片和电解液之间的协同作用，在负极界面难以形成致密和稳定的SEI膜，负极极片与电解液之间的副反应过多，导致二次电池的初始阻抗以及循环过程中的阻抗增长过大，从而影响二次电池的动力学性能和高温浮充性能。当W1×H1的值过大时，例如大于35，不利于负极极片和电解液发挥协同作用，第一负极材料层的动力学性能过差，电解液对第二负极材料层的浸润性也过差，锂离子在负极极片的传输速度过慢，同时二氟磷酸锂在电解液中的溶解性过差，导致二次电池的初始阻抗以及循环过程中的阻抗增长过大，从而影响二次电池的动力学性能和高温浮充性能。
因此，负极极片包括第一负极材料层和第二负极材料层，并且调控H1和H2的值在上述范围内、第一负极活性材料和第二负极活性材料的Dv50满足上述关系，以及电解液包括二氟磷酸锂和丙酸丙酯，并且调控W1、W2、W1×H1的值在上述范围内，能够减小二次电池的初始阻抗以及循环过程中的阻抗增长，提高二次电池的动力学性能和高温浮充性能。
为方便理解，在本申请中，定义负极极片自身长度方向为Y，自身厚度方向为Z。负极极片通常具有长边和短边，上述长度方向为负极极片长边的延伸方向。应理解，以上对于方向的定义是为了方便描述本申请的目的。如图1所示，负极极片10包括负极集流体11以及依次设置于负极集流体11的一个表面的第二负极材料层13、第一负极材料层12。H1为第一负极材料层的厚度，H2为第二负极材料层的厚度。在本申请中，负极材料层可以设置于负极集流体沿自身厚度方向上的一个表面，也可以设置于负极集流体沿自身厚度方向上的两个表面。需要说明，这里的“表面”可以是负极集流体表面的全部区域，也可以是负极集流体表面的部分区域，本申请没有特别限制，只要能实现本申请目的即可。
在本申请的一些实施方案中，2≤H2/H1≤4.5。例如，H2/H1的值可以为2、2.3、2.5、2.8、3、3.2、3.6、3.8、4、4.2、4.5或为其中任意两个数值组成的范围。通过调控H2/H1的值在上述范围内，能够使电解液对第一负极材料层和第二负极材料层具有良好的浸润性，改善电解液对负极极片的浸润性，有利于锂离子在负极极片中的传输，同时还能够减少循环过程中负极极片与电解液之间的副反应，从而有利于减小二次电池的初始阻抗以及循环过程中的阻抗增长，进而有利于提高二次电池的动力学性能和高温浮充性能。
在本申请的一些实施方案中，0.005≤W1/H1≤0.05。例如，W1/H1的值可以为0.005、0.01、0.015、0.02、0.024、0.03、0.036、0.04、0.045、0.05或为其中任意两个数值组成的范围。通过调控W1/H1的值在上述范围内，有利于发挥负极极片与电解液之间的协同作用，在负极界面形成更为致密和稳定的SEI膜，更进一步减小负极界面与电解液之间的副反应，还能够进一步改善电解液对负极极片的浸润性，有利于锂离子在负极极片中的传输，进一步提高第一负极材料层的动力学性能，从而有利于进一步减小二次电池的初始阻抗以及循环过程中的阻抗增长，进而有利于进一步提高二次电池的动力学性能和高温浮充性能。
在本申请的一些实施方案中，250≤W2×H1≤2400。例如，W2×H1的值可以为250、500、800、1000、1200、1500、1800、2000、2400或为其中任意两个数值组成的范围。通过调控W2×H1的值在上述范围内，有利于发挥负极极片与电解液之间的协同作用，提高锂盐在电解液中的溶解度以及电解液的电导率，还能够改善电解液对负极极片的浸润性，有利于锂离子在电解液和负极极片中的传输，提高第一负极材料层的动力学性能，从而有利于进一步减小二次电池的初始阻抗以及循环过程中的阻抗增长，进而有利于进一步提高二次电池的动力学性能和高温浮充性能。
在本申请的一些实施方案中，电解液包括多腈化合物，基于电解液的质量，多腈化合物的质量百分含量为W3％，0.1≤W3≤5。多腈化合物包括丁二腈、戊二腈、己二腈、庚二腈、辛二腈、甲基戊二腈、1,3,5-戊三甲腈、1,2,3-丙三甲腈、1,3,6-己烷三腈或1,2,3-三(2-氰基乙氧基)丙烷中的至少一种。例如，W3的值可以为0.1、0.6、1、1.5、2、2.4、3、3.6、4、4.5、5或为其中任意两个数值组成的范围。在电解液包括二氟磷酸锂和丙酸丙酯的基础上，进一步引入上述多腈化合物并且调控其质量百分含量W3％在上述范围内，多腈化合物较强的配位能力能够与正极界面的高价金属离子(例如钴离子)络合，减小金属离子溶出所导致的正极活性材料的相变反应，形成更为稳定的CEI膜，在负极界面则能够发生还原反应形成稳定的SEI膜，同时提高正极极片和负极极片的稳定性，并且，多腈化合物中的碳氮三键键能较高，不易被氧化，能够减少电解液的氧化分解产气，提高电解液的电化学稳定性和热稳定性，从而在减小二次电池的初始阻抗以及循环过程中的阻抗增长，提高二次电池的动力学性能的同时，还能够提高二次电池的高温浮充性能。在本申请中，高温是指温度大于或等于40℃。
在本申请的一些实施方案中，50≤W3×H1≤200。例如，W3×H1的值可以为50、80、100、120、150、180、200或为其中任意两个数值组成的范围。通过调控W3×H1的值在上述范围内，有利于发挥负极极片与电解液之间的协同作用，在负极界面发生还原反应形成稳定的SEI膜，提高负极极片的稳定性，还能够改善电解液对负极极片的浸润性，有利于锂离子在负极极片中的传输，提高第一负极材料层的动力学性能，减少电解液的氧化分解产气，提高电解液的电化学稳定性和热稳定性，从而在减小二次电池的初始阻抗以及循环过程中的阻抗增长，提高二次电池的动力学性能的同时，还能够进一步提高二次电池的高温浮充性能。
在本申请的一些实施方案中，基于电解液的质量，丙酸酯化合物的质量百分含量为W4％，10≤W4≤65，0.154≤W2/W4≤1。例如，W4的值可以为10、15、20、24、30、35、40、46、50、54、60、65或为其中任意两个数值组成的范围，W2/W4的值可以为0.154、0.3、0.35、0.4、0.5、0.62、0.7、0.85、0.9、1或为其中任意两个数值组成的范围。在电解液包括二氟磷酸锂和丙酸丙酯的基础上，调控丙酸酯化合物的质量百分含量W4％和W2/W4的值在上述范围内，能够提高锂盐在电解液中的溶解度以及电解液的电导率，有利于锂离子在电解液中的传输，从而有利于减小二次电池的初始阻抗以及循环过程中的阻抗增长，进而有利于提高二次电池的动力学性能和高温浮充性能。
在本申请的一些实施方案中，丙酸酯化合物还包括丙酸甲酯、丙酸乙酯、丙烯酸丁酯或丙酸丁酯中的至少一种。在电解液包括二氟磷酸锂和丙酸丙酯的基础上，电解液还包括上述丙酸酯化合物，能够提高锂盐在电解液中的溶解度以及电解液的电导率，有利于锂离子在电解液中的传输，有利于进一步减小二次电池的初始阻抗以及循环过程中的阻抗增长，从而有利于进一步提高二次电池的动力学性能和高温浮充性能。
在本申请中，电解液还包括其它有机溶剂。本申请对其它有机溶剂的种类没有特别限制，只要能实现本申请的目的即可。例如，其它有机溶剂可以包括但不限于碳酸酯化合物、羧酸酯化合物、醚化合物或其它有机溶剂中的至少一种。上述碳酸酯化合物可以包括但不限于链状碳酸酯化合物、环状碳酸酯化合物或氟代碳酸酯化合物中的至少一种。上述链状碳酸酯化合物可以包括但不限于碳酸二甲酯(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)或碳酸甲乙酯(MEC)中的至少一种。上述环状碳酸酯可以包括但不限于碳酸乙烯酯(EC)、碳酸亚丙酯(PC)、碳酸亚丁酯(BC)或碳酸乙烯基亚乙酯(VEC)中的至少一种。上述氟代碳酸酯化合物可以包括但不限于氟代碳酸乙烯酯(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-甲基亚乙酯或碳酸三氟甲基亚乙酯中的至少一种。上述羧酸酯化合物可以包括但不限于甲酸甲酯、乙酸甲酯、乙酸乙酯、乙酸正丙酯、乙酸叔丁酯、γ-丁内酯、癸内酯、戊内酯或己内酯中的至少一种。上述醚化合物可以包括但不限于二丁醚、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、1-乙氧基-1-甲氧基乙烷、2-甲基四氢呋喃或四氢呋喃中的至少一种。上述其它有机溶剂可以包括但不限于二甲亚砜、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、二甲基甲酰胺、磷酸三甲酯、磷酸三乙酯或磷酸三辛酯中的至少一种。基于电解液的质量，其它有机溶剂的质量百分含量为14％至81％。例如，其它有机溶剂的质量百分含量可以为14％、19％、24％、30％、40％、50％、62％、70％、78％、81％或为其中任意两个数值组成的范围。
在本申请中，电解液还包括锂盐。本申请对锂盐没有特别限制，只要能实现本申请的目的即可。例如，锂盐可以包括但不限于LiPF6、LiBF4、LiAsF6、LiClO4、LiB(C6H5)4、LiCH3SO3、LiCF3SO3、LiN(SO2CF3)2、LiC(SO2CF3)3、Li2SiF6、双草酸硼酸锂(LiBOB)或二氟硼酸锂中的至少一种。基于电解液的质量，锂盐的质量百分含量为8％至15％。
在一些实施方案中，电解液可以包括锂盐、二氟磷酸锂、丙酸丙酯和其它有机溶剂。锂盐、二氟磷酸锂和丙酸丙酯的质量百分含量如上文所述，其它有机溶剂的质量百分含量为24％至81％。包括上述电解液的二次电池具有良好的动力学性能和高温浮充性能。
在一些实施方案中，电解液可以包括锂盐、二氟磷酸锂、丙酸丙酯、多腈化合物和其它有机溶剂。锂盐、二氟磷酸锂、丙酸丙酯、多腈化合物的质量百分含量如上文所述，其它有机溶剂的质量百分含量为19％至81％。包括上述电解液的二次电池具有良好的动力学性能和高温浮充性能。
在一些实施方案中，电解液可以包括锂盐、二氟磷酸锂、丙酸酯化合物和其它有机溶剂。上述丙酸酯化合物包括丙酸丙酯以及丙酸甲酯、丙酸乙酯、丙烯酸丁酯或丙酸丁酯中的至少一种。锂盐、二氟磷酸锂、丙酸酯化合物的质量百分含量如上文所述，其它有机溶剂的质量百分含量为19％至81％。包括上述电解液的二次电池具有良好的动力学性能和高温浮充性能。
在一些实施方案中，电解液可以包括锂盐、二氟磷酸锂、丙酸酯化合物、多腈化合物和其它有机溶剂。上述丙酸酯化合物包括丙酸丙酯以及丙酸甲酯、丙酸乙酯、丙烯酸丁酯或丙酸丁酯中的至少一种。锂盐、二氟磷酸锂、丙酸酯化合物、多腈化合物的质量百分含量如上文所述，其它有机溶剂的质量百分含量为14％至81％。包括上述电解液的二次电池具有更好的动力学性能和高温浮充性能。
在本申请的一些实施方案中，第一负极活性材料的Dv50为12μm至14.9μm，第一负极活性材料的Dv90为20.5μm至25.9μm。例如，第一负极活性材料的Dv50可以为12μm、12.3μm、12.7μm、13μm、13.4μm、13.7μm、14μm、14.5μm、14.9μm或为其中任意两个数值组成的范围，第一负极活性材料的Dv90可以为20.5μm、21μm、21.6μm、22μm、22.4μm、23μm、23.5μm、24μm、24.6μm、25μm、25.9μm或为其中任意两个数值组成的范围。通过调控第一负极活性材料的Dv50和Dv90在上述范围内，能够减小负极极片对电解液的消耗，改善电解液对负极极片的浸润性，有利于锂离子在负极极片中的传输，还能够减少循环过程中负极极片与电解液之间的副反应，提高负极极片的稳定性，从而有利于减小二次电池的初始阻抗以及循环过程中的阻抗增长，进而有利于提高二次电池的动力学性能，还有利于提高二次电池的高温浮充性能。
在本申请的一些实施方案中，第二负极活性材料的Dv50为10μm至11.5μm，第二负极活性材料的Dv90为19.4μm至24.8μm。例如，第二负极活性材料的Dv50可以为10μm、10.3μm、10.5μm、10.7μm、11μm、11.2μm、11.5μm或为其中任意两个数值组成的范围，第二负极活性材料的Dv90可以为19.4μm、20μm、20.5μm、21μm、21.6μm、22μm、22.4μm、23μm、23.5μm、24μm、24.8μm或为其中任意两个数值组成的范围。通过调控第二负极活性材料的Dv50和Dv90在上述范围内，能够改善电解液对负极极片的浸润性，减少循环过程中负极极片与电解液之间的副反应，从而有利于减小二次电池的初始阻抗以及循环过程中的阻抗增长，进而有利于提高二次电池的动力学性能，还有利于提高二次电池的高温浮充性能。
本申请中，Dv50是指在材料的体积基准的粒度分布中，从小粒径测起、达到体积累积50％的粒径。Dv90是指在材料的体积基准的粒度分布中，从小粒径测起、达到体积累积90％的粒径。在一些实施方案中，第一负极活性材料的Dv90小于第一负极材料层的厚度H1。
通常情况下，不同Dv50、Dv90的第一负极活性材料和第二负极活性材料可以通过机械破碎(例如球磨)得到。例如，可以通过调控球磨时间来调控第一负极活性材料的Dv50、Dv90以及第二负极活性材料的Dv50、Dv90。当其它条件不变时，球磨时间延长，第一负极活性材料的Dv50减小；球磨时间缩短，第一负极活性材料的Dv50增大。当其它条件不变时，球磨时间延长，第一负极活性材料的Dv90减小；球磨时间缩短，第一负极活性材料的Dv90增大。当其它条件不变时，球磨时间延长，第二负极活性材料的Dv50减小；球磨时间缩短，第二负极活性材料的Dv50增大。当其它条件不变时，球磨时间延长，第二负极活性材料的Dv90减小；球磨时间缩短，第二负极活性材料的Dv90增大。
在本申请的一些实施方案中，第一负极活性材料和第二负极活性材料各自独立地包括天然石墨、人造石墨、软碳、硬碳、中间相碳微球、硅碳化合物SiC、硅氧化合物SiOx(0＜x≤2)或钛酸锂中的至少一种。在负极极片包括第一负极材料层和第二负极材料层，并且调控H1和H2的值、第一负极活性材料和第二负极活性材料的Dv50的关系在本申请范围内，以及电解液包括二氟磷酸锂和丙酸丙酯，并且调控W1、W2、W1×H1的值在本申请范围内的基础上，选用上述第一负极活性材料和第二负极活性材料，可以使得二次电池具有良好的动力学性能和高温浮充性能。在本申请中，第一负极活性材料和第二负极活性材料的种类可以相同，也可以不同。
在本申请中，第一负极材料层包括第一负极活性材料，还可以包括第一负极粘结剂和第一负极导电剂，或者，第一负极材料层还可以包括第一负极粘结剂、第一负极导电剂或第一增稠剂。基于第一负极材料层的质量，第一负极活性材料的质量百分含量可以为86％至99％，第一负极粘结剂的质量百分含量可以为0.5％至5％，第一负极导电剂的质量百分含量可以为0.5％至5％，第一增稠剂的质量百分含量可以为0％至4％。
在本申请中，第二负极材料层包括第二负极活性材料，还可以包括第二负极粘结剂和第二负极导电剂，或者，第二负极材料层还可以包括第二负极粘结剂、第二负极导电剂或第二增稠剂。基于第二负极材料层的质量，第二负极活性材料的质量百分含量可以为86％至99％，第二负极粘结剂的质量百分含量可以为0.5％至5％，第二负极导电剂的质量百分含量可以为0.5％至5％，第二增稠剂的质量百分含量可以为0％至4％。
本申请对第一负极粘结剂、第二负极粘结剂、第一负极导电剂和第二负极导电剂的种类没有特别限制，只要能够实现本申请目的即可。例如，第一负极粘结剂和第二负极粘结剂各自独立地可以包括但不限于聚丙烯酸、聚丙烯酸钠、聚丙烯酸钾、聚丙烯酸锂、聚酰亚胺、聚乙烯醇、聚酰胺酰亚胺、丁苯橡胶或聚偏氟乙烯中的至少一种。例如，第一负极导电剂和第二负极导电剂各自独立地可以包括但不限于导电炭黑(Super P)、碳纳米管(CNTs)、碳纤维、鳞片石墨、石墨烯、金属材料或导电聚合物中的至少一种，导电炭黑可以包括但不限于乙炔黑或科琴黑中的至少一种。上述碳纳米管可以包括但不限于单壁碳纳米管和/或多壁碳纳米管。上述碳纤维可以包括但不限于气相生长碳纤维(VGCF)和/或纳米碳纤维。上述金属材料可以包括但不限于金属粉和/或金属纤维，具体地，金属可以包括但不限于铜、镍、铝或银中的至少一种。上述导电聚合物可以包括但不限于聚亚苯基衍生物、聚苯胺、聚噻吩、聚乙炔或聚吡咯中的至少一种。本申请对第一增稠剂和第二增稠剂的种类没有特别限制，只要能够实现本申请目的即可。例如，第一增稠剂和第二增稠剂各自独立地可以包括但不限于羧甲基纤维素钠或羧甲基纤维素锂中的至少一种。
本申请对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，负极集流体可以包含铜箔、铜合金箔、镍箔、不锈钢箔、钛箔、泡沫镍、泡沫铜或复合集流体，示例性地，复合集流体可以为锂铜复合集流体、碳铜复合集流体、镍铜复合集流体、钛铜复合集流体等。本申请对负极集流体的厚度没有特别限制，只要能够实现本申请目的即可，例如，负极集流体的厚度可以为4μm至15μm。
任选地，负极材料层还可以包含导电层，导电层位于负极集流体和第二负极材料层之间。本申请对导电层的组成没有特别限制，可以是本领域常用的导电层。例如，导电层包括导电剂和粘结剂。本申请对导电层中的导电剂和粘结剂没有特别限制，例如可以是上述第一负极导电剂和上述第一负极粘结剂中的至少一种。
本申请对负极极片的制备方法没有特别限制，只要能够实现本申请目的即可。例如，负极极片的制备方法可以包括但不限于以下步骤：(1)配制第一负极浆料和第二负极浆料；(2)将第二负极浆料涂覆在负极集流体的一个表面上，烘干后，在负极集流体的一个表面上形成第二负极材料层；然后将第一负极浆料涂覆在第二负极材料层的表面上，烘干后，在负极集流体的一个表面上依次形成第二负极材料层和第一负极材料层；(3)在负极集流体的另一个表面上重复以上步骤，在负极集流体的两个表面上均形成第一负极材料层和第二负极材料层；(4)经冷压、裁片、焊接负极极耳，得到负极极片。
通常情况下，可以通过调控第一负极材料层的涂布面密度来调控第一负极材料层的厚度H1。例如，当其它条件不变时，第一负极材料层的涂布面密度增大，H1增大；第一负极材料层的涂布面密度减小，H1减小。
通常情况下，可以通过调控第二负极材料层的涂布面密度来调控第二负极材料层的厚度H2。例如，当其它条件不变时，第二负极材料层的涂布面密度增大，H2增大；第二负极材料层的涂布面密度减小，H2减小。
在本申请中，二次电池还包括正极极片，正极极片包括正极集流体以及设置于正极集流体至少一个表面的正极材料层。上述“设置于正极集流体至少一个表面的正极材料层”是指，正极材料层可以设置于正极集流体沿自身厚度方向上的一个表面，也可以设置于正极集流体沿自身厚度方向上的两个表面。需要说明，这里的“表面”可以是正极集流体表面的全部区域，也可以是正极集流体表面的部分区域，本申请没有特别限制，只要能实现本申请目的即可。
本申请对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，正极集流体可以包含铝箔、铝合金箔或复合集流体(例如铝碳复合集流体)等。本申请对正极集流体的厚度没有特别限制，只要能够实现本申请目的即可。例如，正极集流体的厚度可以为5μm至20μm。
正极材料层包括正极活性材料，本申请对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，正极活性材料可以包含但不限于镍钴锰酸锂(例如NCM811、NCM622、NCM523、NCM111)、镍钴铝酸锂、磷酸铁锂、富锂锰基材料、钴酸锂(LiCoO2)、锰酸锂、磷酸锰铁锂或钛酸锂中的至少一种。
正极材料层还可以包括正极导电剂和正极粘结剂，本申请对正极导电剂和正极粘结剂的种类没有特别限制，只要能够实现本申请目的即可，例如，可以是上述第一负极导电剂和上述第一负极粘结剂中的至少一种。本申请对正极材料层中正极活性材料、正极导电剂、正极粘结剂的质量比没有特别限制，本领域技术人员可以根据实际需要选择，只要能够实现本申请目的即可。
本申请对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，正极材料层的厚度可以为30μm至120μm。本申请对正极材料层的压实密度没有特别限制，只要能够实现本申请目的即可。例如，正极材料层的压实密度可以为3g/cm3至5g/cm3。
任选地，正极极片还可以包含导电层，导电层位于正极集流体和正极材料层之间。导电层的组成没有特别限制，可以是本领域常用的导电层。导电层包括导电剂和粘结剂。本申请对导电层中的导电剂和粘结剂没有特别限制，例如，可以是上述第一负极导电剂和上述第一负极粘结剂中的至少一种。
在本申请中，二次电池还包括隔离膜。本申请对隔离膜没有特别限制，只要能够实现本申请目的即可。例如，隔离膜的材料可以包括但不限于聚乙烯(PE)、聚丙烯(PP)为主的聚烯烃(PO)类、聚酯(例如，聚对苯二甲酸二乙酯(PET)膜)、纤维素、聚酰亚胺(PI)、聚酰胺(PA)、氨纶或芳纶中的至少一种。隔离膜的类型可以包括织造膜、非织造膜、微孔膜、复合膜、碾压膜或纺丝膜中的至少一种。
在一些实施方案中，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或聚酰亚胺中的至少一种。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。
在一些实施方案中，无机物层包括无机颗粒和粘结剂。本申请对无机颗粒没有特别限制，例如无机颗粒可以包括氧化铝、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、氢氧化钙或硫酸钡中的至少一种。本申请对无机物层中的粘结剂没有特别限制，例如无机物层中的粘结剂可以是上述第一负极粘结剂中的至少一种。在一些实施方案中，聚合物层包括聚合物，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、聚乙烯吡咯烷酮、聚乙烯醚、聚偏氟乙烯或聚(偏氟乙烯-六氟丙烯)中的至少一种。
在本申请中，隔离膜的厚度没有特别限制，只要能实现本申请的目的即可，例如隔离膜的厚度可以为3μm至30μm。
在本申请中，二次电池还包括壳体，用于容纳正极极片、隔离膜、负极极片和电解液，以及二次电池领域中已知的其它部件，本申请对上述其它部件不做限定。本申请对壳体没有特别限制，可以为本领域公知的壳体，只要能够实现本申请目的即可。例如，壳体可以为硬壳壳体或柔性壳体。硬壳壳体的材料可以为金属，本申请对金属的种类不做限定，可以采用本领域已知的金属硬壳壳体，只要能实现本申请的目的即可。柔性壳体可以为金属塑膜，例如铝塑膜、钢塑膜等。
本申请的二次电池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，二次电池的制备过程可以包括但不限于以下步骤：将正极极片、隔离膜和负极极片按顺序堆叠，并根据需要将其卷绕、折叠等操作得到卷绕结构的电极组件，将电极组件放入壳体内，将电解液注入壳体并封口，得到二次电池。或者，将正极极片、隔离膜和负极极片按顺序堆叠，然后用胶带将整个叠片结构的四个角固定好得到叠片结构的电极组件，将电极组件置入壳体内，将电解液注入壳体并封口，得到二次电池。此外，也可以根据需要将防过电流元件、导板等置于壳体中，从而防止二次电池内部的压力上升、过充放电。
本申请的第二方面提供了一种电子装置，其包括本申请第一方面提供的二次电池。本申请提供的二次电池具有良好的动力学性能和高温浮充性能，从而本申请提供的电子装置具有较长的使用寿命和良好的性能。
本申请对电子装置的种类没有特别限定，其可以是用于现有技术中已知的任何电子装置。例如，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。
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：
厚度的测试
将各实施例和对比例的锂离子电池以0.2C放电至3V后，拆解得到负极极片，用碳酸二甲酯(DMC)将负极极片清洗干净后，60℃烘干，用氩离子抛光负极极片沿厚度方向的截面。然后使用扫描电子显微镜(SEM)观察负极极片的上述截面并测试第一负极材料层的厚度H1、第二负极材料层的厚度H2以及H2/H1。
第一负极活性材料和第二负极活性材料的Dv50、Dv90的测试
按照国家标准《粒度分布激光衍射法》(GB/T19077-2016)，使用激光粒度仪(型号为MS3000)测试第一负极活性材料和第二负极活性材料的Dv50、Dv90。
电解液组分的测试：
将锂离子电池以0.2C恒定电流放电至3V后拆解，采用离心、挤压或者其他方式收集电解液，然后采用气相色谱-质谱联用仪(GC-MS，仪器型号为Agilent 8890)和离子色谱(IC，仪器型号为AQUION离子色谱)进行测试，得到电解液中的各个组分并测试其含量。
初始阻抗的测试
将锂离子电池置于25℃恒温箱中，静置4h后，以0.7C恒流充电至额定电压(本申请实施例为4.48V)，以4.48V恒压充电至电流为0.05C，静置2h，然后以0.2C恒流放电至电压为3.0V，此时测得的锂离子电池的容量记为参考容量C1，即100％SOC(State of Charge，荷电状态)下的容量。将锂离子电池以0.7C恒流充电至电压为4.48V，以4.48V恒压充电至电流为0.05C，静置10min，然后以0.1C依次恒流放电至0.3C1(70％SOC)，0.8C1(20％SOC)，0.9C1(10％SOC)，并分别测试上述三种不同的SOC下锂离子电池的电压和电流，计算电压与电流的比值得到70％SOC的阻抗记为R1、20％SOC的阻抗记为R2、10％SOC阻抗记为R3。通过锂离子电池的R1、R2、R3的值来评价其初始阻抗大小。锂离子电池的R1、R2、R3的值越小，初始阻抗越小，R1、R2、R3的值越大，初始阻抗越大。
阻抗增长的测试
将锂离子电池置于25℃恒温箱中，静置4h后，以0.02C依次恒流放电至0.3C1(70％SOC)，0.8C1(20％SOC)，0.9C1(10％SOC)。在70％SOC下锂离子电池的电压记为U'70％，电流记为I'70％；在20％SOC下锂离子电池的电压记为U'20％，电流记为I'20％；在10％SOC下锂离子电池的电压记为U'10％，电流记为I'10％。将锂离子电池以0.7C恒流充电至电压为4.48V，以4.48V恒压充电至电流为0.05C，静置2h，然后以0.5C恒流放电至电压为3.0V，此为一圈充放电循环。将锂离子电池按照上述方法进行充放电循环，每50圈充放电循环进行一次放电容量恢复测试，将锂离子电池以0.7C恒流充电至电压为4.48V，以4.48V恒压充电至电流为0.05C，静置2h，然后以0.2C依次恒流放电至0.3C1(70％SOC)，0.8C1(20％SOC)，0.9C1(10％SOC)。在70％SOC下锂离子电池的电压记为U70％，电流记为I70％；在20％SOC下锂离子电池的电压记为U20％，电流记为I20％；在10％SOC下锂离子电池的电压记为U10％，电流记为I10％。通过以下公式计算得到R70％、R20％、R10％：R70％＝(U70％-U'70％)/(I70％-I'70％)；R20％＝(U20％-U'20％)/(I20％-I'20％)；R10％＝(U10％-U'10％)/(I10％-I'10％)。计算R70％、R20％、R10％的平均值作为锂离子电池在对应循环圈数下的阻抗值。按照上述充放电方式直至循环1000圈。每个实施例和对比例取3个锂离子电池进行测试，计算3个锂离子电池阻抗的平均值作为锂离子电池的阻抗。锂离子电池在循环第300圈时的阻抗记为R300，循环第1000圈时的阻抗记为R1000。通过以下公式计算得到的K来评价锂离子电池的阻抗增长：K＝(R1000-R300)/(1000-300)。K的值越小，阻抗增长越小，K的值越大，阻抗增长越大。
高温浮充性能的测试
将锂离子电池置于25℃恒温箱中，静置4h后，以0.7C恒流充电至4.48V，以4.48V恒压充电至电流为0.05C，静置2h，然后以0.2C恒流放电至电压为3.0V，再将锂离子电池以0.7C恒流充电至4.48V，以4.48V恒压充电至电流为0.05C，测量此时锂离子电池的厚度记为初始厚度T0。将锂离子电池置于55℃恒温箱中，静置1.5h。将锂离子电池以0.4C恒流充电至4.48V，以4.48V恒压充电至电流为60mA。持续以恒流(100mA)恒压(4.48V)进行充电，其中每96h测量锂离子电池的厚度记为Ti，记锂离子电池的厚度变化率为Ti/T0，当Ti/T0的值达到108.5％时，记录此时锂离子电池以恒流(100mA)恒压(4.48V)充电的充电时间。每个实施例和对比例取3个锂离子电池进行测试，计算3个锂离子电池上述充电时间的平均值，记为D。通过D的值来评价其高温浮充性能。锂离子电池的D的值越大，高温浮充性能越好，D的值越小，高温浮充性能越差。
实施例1-1
<负极极片的制备>
将第一负极活性材料人造石墨、第一负极粘结剂丁苯橡胶(SBR，重均分子量Mw＝5×106)、第一增稠剂羧甲基纤维素钠(CMC-Na，Mw＝7×105)、第一负极导电剂导电炭黑(Super P)按照质量比96:1.5:1.5:1进行混合，然后加入去离子水作为溶剂，调配成固含量为50wt％的浆料，真空搅拌均匀后得到第一负极浆料。
将第二负极活性材料人造石墨、第二负极粘结剂丁苯橡胶(SBR，Mw＝5×106)、第二增稠剂羧甲基纤维素钠(CMC-Na，Mw＝7×105)、第二负极导电剂导电炭黑(Super P)按照质量比96:1.5:1.5:1进行混合，然后加入去离子水作为溶剂，调配成固含量为50wt％的浆料，真空搅拌均匀后得到第二负极浆料。
将第二负极浆料均匀涂覆在厚度为10μm的负极集流体铜箔的一个表面上，涂布面密度为5.81mg/cm2，85℃条件下烘干，得到单面涂布第二负极材料层的负极极片。然后，将第一负极浆料均匀涂覆在第二负极材料层远离负极集流体的表面上，涂布面密度为2.33mg/cm2，85℃条件下烘干，得到单面涂布第二负极材料层和第一负极材料层的负极极片。之后，在该铜箔的另一个表面上重复以上步骤，得到双面涂布第二负极材料层和第一负极材料层的负极极片。再经冷压、裁片、焊接负极极耳镍极耳，得到规格为76mm×867mm的负极极片待用。其中，第一负极材料层的厚度H1、第二负极材料层的厚度H2如表1所示，第一负极活性材料和第二负极活性材料的Dv50、Dv90如表3所示。
<电解液的制备>
在含水量小于10ppm的氩气气氛手套箱中，将其它有机溶剂碳酸乙烯酯(EC)、碳酸丙烯酯(PC)、碳酸二乙酯(DEC)以质量比1:1:1混合均匀作为基础溶剂，然后向基础溶剂中加入锂盐六氟磷酸锂(LiPF6)、二氟磷酸锂和丙酸丙酯，混合均匀后，得到电解液。其中，基于电解液的质量，锂盐LiPF6的质量百分含量为12.5％，二氟磷酸锂的质量百分含量W1％和丙酸丙酯的质量百分含量W2％如表1所示，其余为基础溶剂。
<正极极片的制备>
将正极活性材料钴酸锂、正极导电剂导电炭黑(Super P)、正极导电剂碳纳米管(CNT)、正极粘结剂聚偏氟乙烯(PVDF，Mw＝7×106)按照质量比97:0.8:0.7:1.5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70wt％的浆料，真空搅拌均匀后得到正极浆料。将正极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，120℃条件下烘干，得到单面涂布正极材料层的正极极片。然后在铝箔的另一个表面上重复以上步骤，即得到双面涂布正极材料层的正极极片。120℃条件下烘干后冷压，再经裁片、焊接正极极耳铝极耳，得到规格为74mm×851mm的正极极片待用。其中，正极材料层的厚度为92μm，正极材料层的压实密度为4.15g/cm3。
<隔离膜的制备>
采用厚度为7μm的多孔聚乙烯薄膜(Celgard公司提供)作为基材层。将无机颗粒氧化铝和无机物层粘结剂聚偏氟乙烯(Mw＝7×106)按质量比4:1进行混合，加入N-甲基吡咯烷酮(NMP)，在真空搅拌机作用下搅拌均匀，得到固含量为30wt％的无机物浆料，再将无机物浆料均匀涂覆在基材层的一个表面，形成厚度为2μm的无机物层。然后，将聚合物聚偏氟乙烯(Mw＝7×106)溶解在去离子水中，得到固含量为25wt％的聚合物层浆料，再将聚合物层浆料均匀涂覆在一侧无机物层和另一侧基材层的表面，涂布面密度为2.5mg/cm2，形成聚合物层，得到一侧含有无机物层和聚合物层，另一侧只含有聚合物层的隔离膜。
<锂离子电池的制备>
将上述制备得到的正极极片、隔离膜以及负极极片按顺序堆叠卷绕得到卷绕结构的电极组件，其中隔离膜含有无机物层和聚合物层的一侧面向正极极片，只含有聚合物层的一侧面向负极极片。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(0.3C恒流充电至3.5V，再以1C恒流充电至3.9V)、容量、脱气、切边等工序得到锂离子电池。
实施例1-2至实施例1-16
除了在<负极极片的制备>、<电解液的制备>中按照表1调控相关制备参数以外，其余与实施例1-1相同。其中，通过调控第一负极材料层的涂布面密度来调控H1，通过调控第二负极材料层的涂布面密度来调控H2。当二氟磷酸锂的质量百分含量W1％或丙酸丙酯的质量百分含量W2％变化时，基础溶剂的质量百分含量随之改变，基础溶剂中各组分的质量比、锂盐的质量百分含量不变。
实施例2-1至实施例2-7
除了在<负极极片的制备>中通过调控第一负极材料层的涂布面密度使H1的值如表2所示，在<电解液的制备>中按照表2所示还加入多腈化合物1,2,3-三(2-氰基乙氧基)丙烷以外，其余与实施例1-1相同。其中，当多腈化合物的质量百分含量W3％变化时，基础溶剂的质量百分含量随之改变，基础溶剂中各组分的质量比、锂盐、二氟磷酸锂和丙酸丙酯的质量百分含量不变。
实施例2-8至实施例2-10
除了在<电解液的制备>中按照表2所示还加入丙酸酯化合物丙酸甲酯以外，其余与实施例1-1相同。其中，当丙酸丙酯的质量百分含量W2％和丙酸酯化合物的质量百分含量W4％变化时，基础溶剂的质量百分含量随之改变，基础溶剂中各组分的质量比、锂盐和二氟磷酸锂的质量百分含量不变。
实施例2-11
除了在<电解液的制备>中按照表2所示还加入多腈化合物1,2,3-三(2-氰基乙氧基)丙烷和丙酸酯化合物丙酸甲酯，基础溶剂的质量百分含量随之改变，基础溶剂中各组分的质量比、锂盐和二氟磷酸锂的质量百分含量不变以外，其余与实施例1-1相同。
实施例3-1至实施例3-8
除了在<负极极片的制备>中按照表3调控相关制备参数以外，其余与实施例1-1相同。其中，通过调控球磨时间来调控第一负极活性材料的Dv50、Dv90和第二负极活性材料的Dv50、Dv90。
对比例1
除了<负极极片的制备>采用以下制备方法以外，其余与实施例1-1相同。
<负极极片的制备>
将负极活性材料人造石墨、负极粘结剂丁苯橡胶(SBR，Mw＝5×106)、增稠剂羧甲基纤维素钠(CMC-Na，Mw＝7×105)、负极导电剂导电炭黑(Super P)按照质量比96:1.5:1.5:1进行混合，然后加入去离子水作为溶剂，调配成固含量为50wt％的浆料，真空搅拌均匀后得到负极浆料。将负极浆料均匀涂覆在厚度为10μm的负极集流体铜箔的一个表面上，涂布面密度为8.14mg/cm2，85℃条件下烘干，得到单面涂布负极材料层的负极极片。之后，在该铜箔的另一个表面上重复以上步骤，得到双面涂布负极材料层的负极极片。再经冷压、裁片、焊接负极极耳镍极耳，得到规格为76mm×867mm的负极极片待用。其中，负极材料层的厚度为105μm，负极活性材料的Dv50为11μm、Dv90为22μm。
对比例2至对比例5
除了在<负极极片的制备>中按照表1调控相关制备参数以外，其余与实施例1-1相同。其中，通过调控第一负极材料层的涂布面密度来调控H1，通过调控第二负极材料层的涂布面密度来调控H2。
对比例6
除了在<电解液的制备>中不加入二氟磷酸锂，基础溶剂的质量百分含量随之改变，基础溶剂中各组分的质量比、锂盐和丙酸丙酯的质量百分含量不变以外，其余与实施例1-1相同。
对比例7至对比例8
除了在<电解液的制备>中按照表1调控相关制备参数以外，其余与实施例1-1相同。其中，当二氟磷酸锂的质量百分含量W1％变化时，基础溶剂的质量百分含量随之改变，基础溶剂中各组分的质量比、锂盐和丙酸丙酯的质量百分含量不变。
对比例9
除了在<电解液的制备>中不加入丙酸丙酯，基础溶剂的质量百分含量随之改变，基础溶剂中各组分的质量比、锂盐和二氟磷酸锂的质量百分含量不变以外，其余与实施例1-1相同。
对比例10至对比例11
除了在<电解液的制备>中按照表1调控相关制备参数以外，其余与实施例1-1相同。其中，当丙酸丙酯的质量百分含量W2％变化时，基础溶剂的质量百分含量随之改变，基础溶剂中各组分的质量比、锂盐和二氟磷酸锂的质量百分含量不变。
对比例12
除了在<电解液的制备>中不加入二氟磷酸锂和丙酸丙酯，基础溶剂的质量百分含量随之改变，基础溶剂中各组分的质量比和锂盐的质量百分含量不变以外，其余与实施例1-1相同。
对比例13
除了在<负极极片的制备>中按照表1调控相关制备参数，第一负极活性材料的Dv50为11μm、Dv90为22μm，第二负极活性材料的Dv50为13μm、Dv90为23μm以外，其余与实施例1-1相同。
各实施例和对比例的制备参数和性能参数如表1至表3所示。
表1

注：表1中的“/”表示无对应参数。
从实施例1-1至实施例1-16、对比例1至对比例13可以看出，本申请通过对负极极片结构和电解液成分进行设计，并且调控H1、H2、W1、W2、W1×H1的值在本申请范围内，以及调控第一负极活性材料的Dv50大于第二负极活性材料的Dv50，锂离子电池的R1、R2、R3、K更小，即初始阻抗以及循环过程中的阻抗增长更小，同时D更大，表明锂离子电池具有良好的动力学性能和高温浮充性能。而对比例1的锂离子电池，其负极极片不包括第一负极材料层和第二负极材料层；对比例2至对比例3的锂离子电池，其H1的值不在本申请范围内；对比例4至对比例5的锂离子电池，其H2的值不在本申请范围内；对比例6的锂离子电池，其电解液中不包括二氟磷酸锂且W1×H1的值不在本申请范围内；对比例7至对比例8的锂离子电池，其W1和W1×H1的值不在本申请范围内；对比例9的锂离子电池，其电解液中不包括丙酸丙酯；对比例10至对比例11的锂离子电池，其W2的值不在本申请范围内；对比例12的锂离子电池，其电解液中不包括二氟磷酸锂和丙酸丙酯，对比例13的锂离子电池，其第一负极活性材料的Dv50小于第二负极活性材料的Dv50，对比例1至对比例13的锂离子电池，R1、R2、R3、K更大，即初始阻抗以及循环过程中的阻抗增长更大，同时D更小，表明锂离子电池的动力学性能和高温浮充性能差。
H1的值通常会影响锂离子电池的动力学性能和高温浮充性能。从实施例1-1至实施例1-3、对比例2至对比例3可以看出，当H1的值过小时，例如对比例2，锂离子电池的R1、R2、R3、K更大，即初始阻抗以及循环过程中的阻抗增长更大，同时D更小；当H1的值过大时，例如对比例3，锂离子电池的R1、R2、R3、K更大，即初始阻抗以及循环过程中的阻抗增长更大，同时D更小，表明锂离子电池的动力学性能和高温浮充性能差。当H1的值在本申请范围内时，锂离子电池的R1、R2、R3、K更小，即初始阻抗以及循环过程中的阻抗增长更小，同时D更大，表明锂离子电池具有良好的动力学性能和高温浮充性能。
H2的值通常会影响锂离子电池的动力学性能和高温浮充性能。从实施例1-1、实施例1-4至实施例1-5、对比例4至对比例5可以看出，当H2的值过小时，例如对比例4，锂离子电池的R1、R2、R3、K更大，即初始阻抗以及循环过程中的阻抗增长更大，同时D更小；当H2的值过大时，例如对比例5，锂离子电池的R1、R2、R3、K更大，即初始阻抗以及循环过程中的阻抗增长更大，同时D更小，表明锂离子电池的动力学性能和高温浮充性能差。当H2的值在本申请范围内时，锂离子电池的R1、R2、R3、K更小，即初始阻抗以及循环过程中的阻抗增长更小，同时D更大，表明锂离子电池具有良好的动力学性能和高温浮充性能。
第一负极活性材料和第二负极活性材料的Dv50的大小关系通常会影响锂离子电池的动力学性能和高温浮充性能。从实施例1-1、对比例13可以看出，当第一负极活性材料的Dv50小于第二负极活性材料的Dv50时，例如对比例13，锂离子电池的R1、R2、R3、K更大，即初始阻抗以及循环过程中的阻抗增长更大，同时D更小，表明锂离子电池的动力学性能和高温浮充性能差。当第一负极活性材料的Dv50大于第二负极活性材料的Dv50时，锂离子电池的R1、R2、R3、K更小，即初始阻抗以及循环过程中的阻抗增长更小，同时D更大，表明锂离子电池具有良好的动力学性能和高温浮充性能。
W1的值通常会影响锂离子电池的动力学性能和高温浮充性能。从实施例1-1、实施例1-7至实施例1-10、对比例6至对比例8可以看出，当W1的值过小时，例如对比例6和对比例7，锂离子电池的R1、R2、R3、K更大，即初始阻抗以及循环过程中的阻抗增长更大，同时D更小；当W1的值过大时，例如对比例8，锂离子电池的R1、R2、R3、K更大，即初始阻抗以及循环过程中的阻抗增长更大，同时D更小，表明锂离子电池的动力学性能和高温浮充性能差。当W1的值在本申请范围内时，锂离子电池的R1、R2、R3、K更小，即初始阻抗以及循环过程中的阻抗增长更小，同时D更大，表明锂离子电池具有良好的动力学性能和高温浮充性能。
W2的值通常会影响锂离子电池的动力学性能和高温浮充性能。从实施例1-1、实施例1-13至
实施例1-14、对比例9至对比例11可以看出，当W2的值过小时，例如对比例9和对比例10，锂离子电池的R1、R2、R3、K更大，即初始阻抗以及循环过程中的阻抗增长更大，同时D更小；当W2的值过大时，例如对比例11，锂离子电池的R1、R2、R3、K更大，即初始阻抗以及循环过程中的阻抗增长更大，同时D更小，表明锂离子电池的动力学性能和高温浮充性能差。当W2的值在本申请范围内时，锂离子电池的R1、R2、R3、K更小，即初始阻抗以及循环过程中的阻抗增长更小，同时D更大，表明锂离子电池具有良好的动力学性能和高温浮充性能。
W1×H1的值通常会影响锂离子电池的动力学性能和高温浮充性能。从实施例1-1、实施例1-7至实施例1-10、对比例6至对比例8可以看出，当W1×H1的值过小时，例如对比例6和对比例7，锂离子电池的R1、R2、R3、K更大，即初始阻抗以及循环过程中的阻抗增长更大，同时D更小；当W1×H1的值过大时，例如对比例8，锂离子电池的R1、R2、R3、K更大，即初始阻抗以及循环过程中的阻抗增长更大，同时D更小，表明锂离子电池的动力学性能和高温浮充性能差。当W1×H1的值在本申请范围内时，锂离子电池的R1、R2、R3、K更小，即初始阻抗以及循环过程中的阻抗增长更小，同时D更大，表明锂离子电池具有良好的动力学性能和高温浮充性能。
H2/H1的值通常会影响锂离子电池的动力学性能和高温浮充性能。从实施例1-1至实施例1-6可以看出，当H2/H1的值在本申请范围内时，锂离子电池的R1、R2、R3、K较小，即初始阻抗以及循环过程中的阻抗增长较小，同时D较大，表明锂离子电池具有良好的动力学性能和高温浮充性能。
W1/H1的值通常会影响锂离子电池的动力学性能和高温浮充性能。从实施例1-1至实施例1-12可以看出，当W1/H1的值在本申请范围内时，锂离子电池的R1、R2、R3、K较小，即初始阻抗以及循环过程中的阻抗增长较小，同时D较大，表明锂离子电池具有良好的动力学性能和高温浮充性能。
W2×H1的值通常会影响锂离子电池的动力学性能和高温浮充性能。从实施例1-1、实施例1-13至实施例1-16可以看出，当W2×H1的值在本申请范围内时，锂离子电池的R1、R2、R3、K较小，即初始阻抗以及循环过程中的阻抗增长较小，同时D较大，表明锂离子电池具有良好的动力学性能和高温浮充性能。
从图2可以看出，实施例1-1的锂离子电池在循环第300圈时的阻抗为46.1mΩ，在循环第1000圈时的阻抗为50.4mΩ，K值为6.14×10-3mΩ/圈。而对比例1的锂离子电池在循环第300圈时的阻抗为59.0mΩ，在循环第1000圈时的阻抗为66.2mΩ，K值为10.29×10-3mΩ/圈。实施例1-1的K值相较于对比例1更小，表明实施例1-1的锂离子电池在循环过程中的阻抗增长更小，动力学性能更好。
从图3可以看出，相同的充电时间下，实施例1-1的锂离子电池的厚度变化率更小，当锂离子电池的厚度变化率达到108.5％时，实施例1-1的D为1248h，而对比例1的D为932h。实施例1-1的D值相较于对比例1更大，表明实施例1-1的锂离子电池的高温浮充性能更好。
表2

注：表2中的“/”表示无对应参数。
电解液包括多腈化合物以及多腈化合物的质量百分含量W3％通常会影响锂离子电池的动力学性能和高温浮充性能。从实施例1-1、实施例2-1至实施例2-7、实施例2-11可以看出，当电解液包括多腈化合物以及调控多腈化合物的质量百分含量W3％在本申请范围内时，锂离子电池的R1、R2、R3、K较小，即初始阻抗以及循环过程中的阻抗增长较小，同时D较大，表明锂离子电池具有良好的动力学性能和高温浮充性能。
W3×H1的值通常会影响锂离子电池的动力学性能和高温浮充性能。从实施例1-1、实施例2-1至实施例2-7、实施例2-11可以看出，当W3×H1的值在本申请范围内时，锂离子电池的R1、R2、R3、K较小，即初始阻抗以及循环过程中的阻抗增长较小，同时D较大，表明锂离子电池具有良好的动力学性能和高温浮充性能。
电解液包括丙酸酯化合物以及丙酸酯化合物的质量百分含量W4％通常会影响锂离子电池的动力学性能和高温浮充性能。从实施例1-1、实施例2-8至实施例2-10可以看出，当电解液包括丙酸酯化合物并且调控丙酸酯化合物的质量百分含量W4％在本申请范围内时，锂离子电池的R1、R2、R3、K较小，即初始阻抗以及循环过程中的阻抗增长较小，同时D较大，表明锂离子电池具有良好的动力学性能和高温浮充性能。
W2/W4的值通常会影响锂离子电池的动力学性能和高温浮充性能。从实施例1-1、实施例2-8至实施例2-10可以看出，当W2/W4的值在本申请范围内时，锂离子电池的R1、R2、R3、K较小，即初始阻抗以及循环过程中的阻抗增长较小，同时D较大，表明锂离子电池具有良好的动力学性能和高温浮充性能。
表3
第一负极活性材料的Dv50和Dv90通常会影响锂离子电池的动力学性能和高温浮充性能。从
实施例1-1、实施例3-1至实施例3-4可以看出，当第一负极活性材料的Dv50和Dv90在本申请范围内时，锂离子电池的R1、R2、R3、K较小，即初始阻抗以及循环过程中的阻抗增长较小，同时D较大，表明锂离子电池具有良好的动力学性能和高温浮充性能。
第二负极活性材料的Dv50和Dv90通常会影响锂离子电池的动力学性能和高温浮充性能。从
实施例1-1、实施例3-5至实施例3-7可以看出，当第二负极活性材料的Dv50和Dv90在本申请范围内时，锂离子电池的R1、R2、R3、K较小，即初始阻抗以及循环过程中的阻抗增长较小，同时D较大，表明锂离子电池具有良好的动力学性能和高温浮充性能。
第一负极活性材料的种类通常会影响锂离子电池的动力学性能和高温浮充性能。从实施例1-1、实施例3-8可以看出，选用本申请范围内的第一负极活性材料，锂离子电池的R1、R2、R3、K较小，即初始阻抗以及循环过程中的阻抗增长较小，同时D较大，表明锂离子电池具有良好的动力学性能和高温浮充性能。
第二负极活性材料的种类通常会影响锂离子电池的动力学性能和高温浮充性能。从实施例1-1、实施例3-8可以看出，选用本申请范围内的第二负极活性材料，锂离子电池的R1、R2、R3、K较小，即初始阻抗以及循环过程中的阻抗增长较小，同时D较大，表明锂离子电池具有良好的动力学性能和高温浮充性能。
需要说明的是，在本文中，诸如第一和第二等之类的关系术语仅仅用来将一个实体或者操作与另一个实体或操作区分开来，而不一定要求或者暗示这些实体或操作之间存在任何这种实际的关系或者顺序。而且，术语“包括”、“包含”或者其任何其他变体意在涵盖非排他性的包含，从而使得包括一系列要素的过程、方法、物品或者设备不仅包括那些要素，而且还包括没有明确列出的其他要素，或者是还包括为这种过程、方法、物品或者设备所固有的要素。
本说明书中的各个实施例均采用相关的方式描述，各个实施例之间相同相似的部分互相参见即可，每个实施例重点说明的都是与其他实施例的不同之处。
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 (12)

  1. 一种二次电池，其包括负极极片和电解液，所述负极极片包括负极集流体和设置于所述负极集流体至少一个表面的负极材料层，所述负极材料层包括层叠设置的第一负极材料层和第二负极材料层，所述第二负极材料层位于所述第一负极材料层和所述负极集流体之间，所述第一负极材料层的厚度为H1μm，所述第二负极材料层的厚度为H2μm，20≤H1≤40，60≤H2≤90；
    所述第一负极材料层包括第一负极活性材料，所述第二负极材料层包括第二负极活性材料，所述第一负极活性材料的Dv50大于所述第二负极活性材料的Dv50；
    所述电解液包括二氟磷酸锂和丙酸酯化合物，所述丙酸酯化合物包括丙酸丙酯；基于所述电解液的质量，所述二氟磷酸锂的质量百分含量为W1％，所述丙酸丙酯的质量百分含量为W2％，0.1≤W1≤1，10≤W2≤60，4≤W1×H1≤35。
  2. 根据权利要求1所述的二次电池，其中，2≤H2/H1≤4.5。
  3. 根据权利要求1所述的二次电池，其中，0.005≤W1/H1≤0.05。
  4. 根据权利要求1所述的二次电池，其中，250≤W2×H1≤2400。
  5. 根据权利要求1至4中任一项所述的二次电池，其中，所述电解液包括多腈化合物，基于所述电解液的质量，所述多腈化合物的质量百分含量为W3％，0.1≤W3≤5；
    所述多腈化合物包括丁二腈、戊二腈、己二腈、庚二腈、辛二腈、甲基戊二腈、1,3,5-戊三甲腈、1,2,3-丙三甲腈、1,3,6-己烷三腈或1,2,3-三(2-氰基乙氧基)丙烷中的至少一种。
  6. 根据权利要求5所述的二次电池，其中，50≤W3×H1≤200。
  7. 根据权利要求1至4中任一项所述的二次电池，其中，基于所述电解液的质量，所述丙酸酯化合物的质量百分含量为W4％，10≤W4≤65，0.154≤W2/W4≤1。
  8. 根据权利要求7所述的二次电池，其中，所述丙酸酯化合物还包括丙酸甲酯、丙酸乙酯、丙烯酸丁酯或丙酸丁酯中的至少一种。
  9. 根据权利要求1至4中任一项所述的二次电池，其中，所述第一负极活性材料的Dv50为12μm至14.9μm，所述第一负极活性材料的Dv90为20.5μm至25.9μm。
  10. 根据权利要求1至4中任一项所述的二次电池，其中，所述第二负极活性材料的Dv50为10μm至11.5μm，所述第二负极活性材料的Dv90为19.4μm至24.8μm。
  11. 根据权利要求1至4中任一项所述的二次电池，其中，所述第一负极活性材料和所述第二负极活性材料各自独立地包括天然石墨、人造石墨、软碳、硬碳、中间相碳微球、硅碳化合物、硅氧化合物或钛酸锂中的至少一种。
  12. 一种电子装置，其包括权利要求1至11中任一项所述的二次电池。
PCT/CN2025/091642 2024-05-31 2025-04-28 一种二次电池及电子装置 Pending WO2025246770A1 (zh)

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