WO2024011482A1 - 负极极片、二次电池、电池模块、电池包和用电装置 - Google Patents

负极极片、二次电池、电池模块、电池包和用电装置 Download PDF

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WO2024011482A1
WO2024011482A1 PCT/CN2022/105621 CN2022105621W WO2024011482A1 WO 2024011482 A1 WO2024011482 A1 WO 2024011482A1 CN 2022105621 W CN2022105621 W CN 2022105621W WO 2024011482 A1 WO2024011482 A1 WO 2024011482A1
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negative electrode
active material
material particles
negative
film layer
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PCT/CN2022/105621
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English (en)
French (fr)
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吴启凡
张明
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宁德时代新能源科技股份有限公司
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Priority to CN202280062028.0A priority Critical patent/CN118077072A/zh
Priority to PCT/CN2022/105621 priority patent/WO2024011482A1/zh
Publication of WO2024011482A1 publication Critical patent/WO2024011482A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the field of battery technology, and in particular to a negative electrode plate, a secondary battery, a battery module, a battery pack and an electrical device.
  • Lithium-ion batteries have been widely used as an important new energy storage device in recent years due to their high energy density and good cycle performance.
  • battery costs due to the scarcity of active material resources related to lithium-ion batteries, battery costs have always remained high, and at the same time, they are facing serious problems such as depletion of related resources. Therefore, it is necessary to develop other low-cost metal ion secondary battery systems.
  • Sodium-ion batteries have become a popular research direction in recent years due to their low cost, abundant resources, and similar manufacturing processes to lithium-ion batteries.
  • This application was made in view of the above-mentioned issues, and its purpose is to provide a negative electrode sheet, a secondary battery, a battery module, a battery pack and a power device that can effectively improve the energy density and rate performance of sodium-ion batteries.
  • a first aspect of the present application provides a negative electrode sheet, including: a negative electrode current collector; and a negative electrode film layer located on at least one surface of the negative electrode current collector, the negative electrode film layer including first negative electrode active material particles and The second negative active material particles, the first negative active material particles include a plurality of adsorption pores, the tap density of the first negative active material particles is 0.4g/cm 3 ⁇ 1.4g/cm 3 , optionally 0.6g/cm 3 ⁇ 1.0g/cm 3 ; the second negative electrode active material particles have a layered structure, and the tap density of the second negative electrode active material particles is 0.05g/cm 3 ⁇ 1.5g/cm 3 , wherein, based on the first negative electrode active material particles and the total mass of the second negative active material particles.
  • the mass percentage of the first negative active material particles is 70% to 95%, optionally 80% to 95%; the mass percentage of the second negative active material particles is 5% ⁇ 30%, optionally 5% ⁇ 10%, the compacted density PD of the negative electrode diaphragm meets: 0.8g/cm 3 ⁇ PD ⁇ 1.3g/cm 3 , optionally, 1.0g/cm 3 ⁇ PD ⁇ 1.2g/cm 3 .
  • the first negative active material particles include a plurality of adsorption pores, and the tap density is within the above-mentioned appropriate range. After cold pressing, the first negative active material particles can still have a sufficient number of adsorption pores inside. As a result, Na + can be smoothly adsorbed and deintercalated by the first negative active material particles during the charge and discharge process. Furthermore, the second negative active material particles have a layered structure. During the cold pressing process, the second negative active material particles can fill the gaps between the plurality of first active material particles or on the surface of the first negative active material particles.
  • the negative active material particles in the negative electrode film layer are in close contact, which can improve the transmission performance of electrons and sodium ions in the negative electrode sheet, thereby improving the rate performance of the sodium ion battery.
  • the second negative electrode active material particles have a layered structure. Compared with the first negative electrode active material particles, the second negative electrode active material particles have limited ability to adsorb and embed sodium ions. The content of the first negative electrode active material particles and the second negative electrode active material particles is within the above-mentioned appropriate range, which can further ensure that the sodium ion battery has high energy density.
  • the median particle diameter D50 of the first negative active material particles is 1 ⁇ m to 50 ⁇ m, optionally 5 ⁇ m to 10 ⁇ m.
  • the median particle size of the first negative electrode active material particles is within the above-mentioned appropriate range. On the one hand, it can increase the production capacity of the negative electrode sheet; on the other hand, it can provide an appropriate amount of active sites on the surface of the first negative electrode active material particles, thereby increasing sodium ions. Coulombic efficiency of the battery.
  • the first negative electrode active material particles have a suitable median particle diameter, which not only enables the first negative electrode active material particles to have good electron and sodium ion transport properties inside the particles, but also enables the first negative electrode active material particles to have lower The particle interface resistance. Therefore, the negative electrode sheet of the present application is applied to sodium-ion batteries, which can allow sodium-ion batteries to have high energy density, high Coulombic efficiency, good rate performance and cycle performance.
  • the elongation rate E of the negative electrode current collector satisfies: 0.1% ⁇ E ⁇ 0.2%, optionally, 0.1% ⁇ E ⁇ 0.15%.
  • the first negative electrode active material particles and the second negative electrode active material particles are compounded, and the second negative electrode active material particles are used to have a sliding function, so that the negative electrode active material particles can be in close contact during the cold pressing process, thereby making the negative electrode active.
  • the material particles have high powder compaction density. Therefore, compared with negative electrode active material particles with lower compaction density, under the same cold pressing parameters, the negative electrode current collector of the present application can have a lower elongation rate, thereby maintaining good electrical conductivity and mechanical strength.
  • the single-sided coating weight of the negative electrode film layer is within a suitable range, it not only allows electrons and sodium ions to have a suitable migration path in the negative electrode sheet, but also enables the negative electrode sheet to have a suitable capacity. Therefore, when the negative electrode sheet of the present application is used in a sodium-ion battery, it can allow the sodium-ion battery to have good rate performance and high energy density.
  • the increase in compaction density of the negative electrode film layer is mainly achieved through the sliding effect of the second negative electrode active material particles during the cold pressing process, and has no significant effect on the porosity of the negative electrode film layer. Influence. This not only increases the compaction density of the negative electrode film layer, but also maintains the electrolyte wettability of the negative electrode film layer, thereby ensuring that the negative secondary battery has high energy density and good rate performance.
  • the first negative active material particles are selected from one or more of hard carbon, soft carbon, and mesocarbon microspheres; the second negative active material particles are selected from artificial graphite, natural graphite, and graphene. one or more types.
  • the above-mentioned first negative electrode active material particles and second negative electrode active material particles can enable the negative electrode film layer to have high compaction density and excellent electronic conductivity. When used in sodium-ion batteries, it can allow sodium-ion batteries to have high compaction density and excellent electronic conductivity. cycle performance.
  • the first negative active material particles include one or more of irregular-shaped first negative active material particles, spherical first negative active material particles, or quasi-spherical first negative active material particles.
  • the process flexibility of the negative electrode sheet can be improved and the sodium-ion battery can have high energy density.
  • the first negative active material particles include one or more of irregular-shaped hard carbon particles, spherical hard carbon particles, or quasi-spherical hard carbon particles.
  • the negative active material particles can have low cost and high theoretical gram capacity, thereby improving the energy density, rate performance and cycle stability of the sodium ion battery.
  • the increase in compaction density of the negative electrode film layer is mainly achieved through the sliding function of the second negative electrode active material particles during the cold pressing process. Therefore, for hard carbon particles, they can achieve high compaction density of the negative electrode film without deformation or slippage. As a result, hard carbon materials can be used in sodium-ion batteries, making sodium-ion batteries have broad application prospects.
  • the negative electrode film layer further includes a flexible binder, and the flexible binder includes styrene-acrylic emulsion, a copolymer of divinylidene fluoride and tetrafluoroethylene, a copolymer of divinylidene fluoride and hexafluoropropylene, One or more of the copolymers of fluorodiethylene and acrylic esters, polytetrafluoroethylene, nitrile rubber, and hydrogenated nitrile rubber.
  • the negative electrode film layer includes the above-mentioned flexible binder and can have good flexibility.
  • the negative electrode film layer can have smaller stress during the cold pressing process, the negative electrode active material particles can accumulate more easily, and the negative electrode current collector can have a lower elongation rate. As a result, the compaction density of the negative electrode film layer can be further increased, thereby increasing the energy density of the sodium-ion battery.
  • the negative electrode film layer includes: 80wt% to 97wt% of negative electrode active material particles, 0wt% to 5wt% of conductive agent, 2wt% to 10wt% of binder, and 0.5 wt% to 5wt% dispersant, wherein the negative active material particles include the first negative active material particles and the second negative active material particles.
  • the negative electrode film layer includes the above-mentioned components, and the content of each component is within the above-mentioned appropriate range, which can ensure that the negative electrode film layer has a high compaction density and good electron and sodium ion transmission performance. Therefore, the negative electrode sheet of the present application is applied to sodium-ion batteries, which can allow sodium-ion batteries to have high energy density and good cycle performance.
  • a second aspect of the present application provides a secondary battery, including the negative electrode plate of the first aspect of the present application.
  • the secondary battery of the present application includes the negative electrode sheet of the first aspect of the present application, thereby being able to have high energy density and good rate performance.
  • a third aspect of the present application provides a battery module including the secondary battery of the second aspect of the present application.
  • a fourth aspect of the application provides a battery pack, including the battery module of the third aspect of the application.
  • a fifth aspect of the present application provides an electrical device, including at least one selected from the secondary battery of the second aspect of the present application, the battery module of the third aspect of the present application, or the battery pack of the fourth aspect of the present application. kind.
  • the battery module, battery pack, and electrical device of the present application include the secondary battery of the present application, and therefore have at least the same advantages as the secondary battery.
  • Figure 1 is a schematic diagram of the elongation test of the negative electrode current collector according to an embodiment of the present application.
  • FIG. 2 is a schematic diagram of a secondary battery according to an embodiment of the present application.
  • FIG. 3 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 2 .
  • Figure 4 is a schematic diagram of a battery module according to an embodiment of the present application.
  • Figure 5 is a schematic diagram of a battery pack according to an embodiment of the present application.
  • FIG. 6 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG. 5 .
  • FIG. 7 is a schematic diagram of a power consumption device using a secondary battery as a power source according to an embodiment of the present application.
  • Figure 8 is a scanning electron microscope image (SEM image) of the negative electrode plate in Example 1 of the present application.
  • Ranges disclosed herein are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit that define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive of the endpoints, and may be arbitrarily combined, that is, any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, understand that ranges of 60-110 and 80-120 are also expected. Furthermore, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2- 3, 2-4 and 2-5.
  • the numerical range “a-b” represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers.
  • the numerical range “0-5" means that all real numbers between "0-5" have been listed in this article, and "0-5" is just an abbreviation of these numerical combinations.
  • a certain parameter is an integer ⁇ 2
  • the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially.
  • step (c) means that step (c) may be added to the method in any order.
  • the method may include steps (a), (b) and (c). , may also include steps (a), (c) and (b), may also include steps (c), (a) and (b), etc.
  • condition "A or B” is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists) ; Or both A and B are true (or exist).
  • the inventor found that during the charging process, Na + is embedded or adsorbed on the hard carbon negative electrode of the sodium-ion battery. Therefore, negative active material particles with multiple adsorption pores are selected as the negative electrode of the sodium-ion battery.
  • the insertion or adsorption of Na + occurs in the battery, thereby realizing the capacity of the battery.
  • the compaction density of the negative electrode film layer is reduced, which will not only affect the energy density of the sodium-ion battery, but also lead to the loss of electrons and sodium ions in the negative electrode sheet.
  • the transmission path increases, thereby reducing the transmission performance of electrons and sodium ions in the negative electrode plate, thereby worsening the rate performance of the sodium-ion battery.
  • the inventor proposed a negative electrode plate, a secondary battery, a battery module, a battery pack and an electrical device after in-depth thinking and extensive experiments.
  • a first aspect of the present application provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode film layer.
  • the negative electrode film layer is located on at least one surface of the negative electrode current collector.
  • the negative electrode film layer includes first negative electrode active material particles and second negative electrode active material particles.
  • the first negative electrode active material particles include a plurality of adsorption pores.
  • the first negative electrode active material particles The tap density is 0.4g/cm 3 ⁇ 1.4g/cm 3 .
  • the second negative electrode active material particles have a layered structure, and the tap density of the second negative electrode active material particles is 0.05g/cm 3 to 1.5g/cm 3 .
  • the mass percentage of the first negative active material particles is 70% to 95%, and the mass percentage of the second negative active material particles is 5% ⁇ 30%.
  • the compacted density PD of the negative electrode film layer satisfies: 0.8g/cm 3 ⁇ PD ⁇ 1.3g/cm 3 , 0.8g/cm 3 ⁇ PD ⁇ 1.2g/cm 3 , 0.8g/cm 3 ⁇ PD ⁇ 1.1g/cm 3 , 0.8g/cm 3 ⁇ PD ⁇ 1.0g/cm 3 , 1.0g/cm 3 ⁇ PD ⁇ 1.3g/cm 3 , 1.0g/cm 3 ⁇ PD ⁇ 1.2g/cm 3 or 1.0g/cm 3 ⁇ PD ⁇ 1.1g/cm 3 .
  • the tap density of the first negative active material is 0.6g/cm 3 to 1.0g/cm 3 .
  • the mass percentage of the first negative active material particles is 80% to 95%, and the mass percentage of the second negative active material particles is 80% to 95%.
  • the content is 5% to 20%. More optionally, based on the total mass of the first negative active material particles and the second negative active material particles, the mass percentage of the first negative active material particles is 90% to 95%, and the mass percentage of the second negative active material particles is 90% to 95%.
  • the content is 5% to 10%
  • the inventor of the present application unexpectedly discovered that the negative electrode film layer of the present application includes first negative electrode active material particles and second negative electrode active material particles that meet the above conditions, and the two negative electrode active material particles are compounded It can make the negative electrode film layer have high compaction density. Therefore, the negative electrode sheet of the present application is applied to a sodium-ion battery, which can enable the sodium-ion battery to have high energy density and good rate performance.
  • the first negative active material particles include a plurality of adsorption pores, and the tap density is within the above-mentioned appropriate range. After cold pressing, the first negative active material particles have There can still be a sufficient number of adsorption pores inside. As a result, Na + can be smoothly adsorbed and deintercalated by the first negative active material particles during the charge and discharge process. Furthermore, the second negative active material particles have a layered structure. During the cold pressing process, the second negative active material particles can fill the gaps between the plurality of first active material particles or on the surface of the first negative active material particles.
  • the negative active material particles in the negative electrode film layer are in close contact, which can improve the transmission performance of electrons and sodium ions in the negative electrode sheet, thereby improving the rate performance of the sodium ion battery.
  • the second negative electrode active material particles have a layered structure. Compared with the first negative electrode active material particles, the second negative electrode active material particles have limited ability to adsorb and embed sodium ions. The content of the first negative electrode active material particles and the second negative electrode active material particles is within the above-mentioned appropriate range, which can further ensure that the sodium ion battery has high energy density.
  • the median particle diameter D50 of the first negative active material particles may be 1 ⁇ m ⁇ 50 ⁇ m, optionally 5 ⁇ m ⁇ 10 ⁇ m.
  • D50 can be 1 ⁇ m, 3 ⁇ m, 5 ⁇ m, 8 ⁇ m, 10 ⁇ m, 15 ⁇ m, 20 ⁇ m, 25 ⁇ m, 35 ⁇ m, 45 ⁇ m, 50 ⁇ m or within the range of any of the above values.
  • the median particle size of the first negative electrode active material particles is within the above-mentioned suitable range. On the one hand, it can reduce the difficulty of preparing the first negative electrode active material particles, thereby increasing the production capacity of the negative electrode sheet. On the other hand, it can have a suitable specific surface area, so that the surface of the first negative active material particles has an appropriate amount of active sites, thereby improving the Coulombic efficiency of the sodium ion battery.
  • the first negative electrode active material particles have a suitable median particle diameter, which not only enables the first negative electrode active material particles to have good electron and sodium ion transport properties inside the particles, but also enables the first negative electrode active material particles to have lower The particle interface resistance. Therefore, the negative electrode sheet of the present application is applied to sodium-ion batteries, which can allow sodium-ion batteries to have high energy density, high Coulombic efficiency, good rate performance and cycle performance.
  • the elongation rate E of the negative electrode current collector may satisfy: 0.1% ⁇ E ⁇ 0.2%, optionally, 0.1% ⁇ E ⁇ 0.15%.
  • E can be 0.1%, 0.12%, 0.15%, 0.18%, 0.2% or within the range of any of the above values.
  • the first negative electrode active material particles and the second negative electrode active material particles are compounded, and the second negative electrode active material particles are used to have a sliding function, so that the negative electrode active material particles can be cooled when cold. are in close contact during the pressing process, so that the negative active material particles have a high powder compaction density. Therefore, compared with negative electrode active material particles with lower compaction density, under the same cold pressing parameters, the negative electrode current collector of the present application can have a lower elongation rate, thereby maintaining good electrical conductivity and mechanical strength.
  • the single-sided coating weight CW of the negative electrode film layer can be 2 mg/cm 2 to 13 mg/cm 2 , optionally 5 mg/cm 2 to 12 mg/cm 2 .
  • CW can be 2 mg/cm 2 , 5 mg/cm 2 , 8 mg/cm 2 , 10 mg/cm 2 , 12 mg/cm 2 , 13 mg/cm 2 or within the range of any of the above values.
  • the single-sided coating weight of the above-mentioned negative electrode film layer can represent the solid component content in the negative electrode slurry coated by the single-sided negative electrode film layer per unit area, which can be numerically equal to the surface density of the single-sided negative electrode film layer. .
  • the single-sided coating weight of the negative electrode film layer is within the above-mentioned appropriate range, which is beneficial to controlling the thickness of the negative electrode film layer within an appropriate range. This not only allows electrons and sodium ions to have appropriate migration paths in the negative electrode piece, but also allows the negative electrode piece to have appropriate capacity. Therefore, when the negative electrode sheet of the present application is used in a sodium-ion battery, it can allow the sodium-ion battery to have good rate performance and high energy density.
  • the negative electrode film layer can satisfy: 30% ⁇ P ⁇ 60%. Alternatively, 45% ⁇ P ⁇ 55%.
  • CW represents the single-sided coating weight of the negative electrode film layer
  • PA represents the true coating weight of the single-sided negative electrode film layer.
  • the inventor unexpectedly discovered that when the parameter P of the negative electrode film layer satisfies the above conditions, it can be considered that the increase in compaction density of the negative electrode film layer is mainly due to the second negative electrode active material in the cold pressing process. It is realized by the sliding effect of particles and has no significant impact on the porosity of the negative electrode film layer. This not only increases the compaction density of the negative electrode film layer, but also maintains the electrolyte wettability of the negative electrode film layer, thereby ensuring that the negative secondary battery has high energy density and good rate performance.
  • the first negative active material particles can be selected from one or more of hard carbon, soft carbon, and mesocarbon microspheres (MCMB); the second negative active material particles can be selected from artificial graphite, natural stone One or more of ink and graphene.
  • MCMB mesocarbon microspheres
  • the production process of particles selected from the above types of materials is mature, which facilitates processing to obtain first negative electrode active material particles and second negative electrode active material particles that meet the conditions of the present application.
  • the second negative electrode active material particles can not only fill the gaps of the plurality of first negative electrode active material particles or exert a sliding effect on the surface of the first negative electrode active material particles.
  • the negative electrode sheet of the present application can have high compaction density and excellent electron conductivity.
  • sodium-ion batteries it can allow sodium-ion batteries to have high compaction density and good cycle performance.
  • the first negative active material particles may include one or more of irregular-shaped first negative active material particles, spherical first negative active material particles, or quasi-spherical first negative active material particles.
  • the first negative electrode active material particles and the second negative electrode active material particles are compounded, and the contents of the first negative electrode active material particles and the second negative electrode active material particles are within the scope of the present application, regardless of the first negative electrode active material particles.
  • the negative electrode film layer can have a high compaction density. This can improve the process flexibility of the negative electrode and allow sodium-ion batteries to have high energy density.
  • the first negative active material particles may be hard carbon particles.
  • hard carbon materials have abundant sources and simple preparation processes.
  • the hard carbon particles themselves have large lattice spacing and are porous, making them an ideal choice for the first negative electrode active material particles in this application.
  • conventional hard carbon materials have high hardness and almost no deformation or slippage during the cold pressing process and are used in negative electrode film layers, the compaction density of the negative electrode film layer is usually low.
  • the second negative electrode active material particles with a layered structure can fill in the gaps of the first negative electrode active material particles or exert a sliding effect on the surface of the first negative electrode active material particles. Therefore, the first negative electrode active material particles do not need to be deformed.
  • the negative electrode sheet of the present application is used in a sodium-ion battery, which can reduce the cost of the sodium-ion battery and improve the energy density, rate performance and cycle stability of the sodium-ion battery.
  • the first negative active material particles may include one or more of irregular-shaped hard carbon particles, spherical hard carbon particles, or quasi-spherical hard carbon particles.
  • the negative active material particles when the first negative active material particles are selected from the hard carbon particles with the above morphology, the negative active material particles can have low cost and high theoretical gram capacity, thereby increasing the energy of the sodium ion battery. Density, rate capability and cycling stability.
  • the first negative active material particles include one or more of irregular-shaped hard carbon particles, spherical hard carbon particles, or quasi-spherical hard carbon particles.
  • PA represents the single-sided negative electrode
  • the parameter P of the negative electrode film layer meets the above conditions, it can be considered that the increase in compaction density of the negative electrode film layer is mainly achieved through the sliding function of the second negative electrode active material particles during the cold pressing process. of. Therefore, for hard carbon particles, they can achieve high compaction density of the negative electrode film without deformation or slippage. As a result, hard carbon materials can be used in sodium-ion batteries, making sodium-ion batteries have broad application prospects.
  • the negative electrode film layer may also include a flexible binder.
  • the flexible binder includes styrene-acrylic emulsion, a copolymer of divinylidene fluoride and tetrafluoroethylene, a copolymer of divinylidene fluoride and hexafluoropropylene, One or more types of copolymers of divinylidene fluoride and acrylic esters, polytetrafluoroethylene, nitrile rubber, and hydrogenated nitrile rubber.
  • the negative electrode film layer includes the above-mentioned flexible binder and can have good flexibility.
  • the negative electrode film layer can have smaller stress during the cold pressing process, the negative electrode active material particles can accumulate more easily, and the negative electrode current collector can have a lower elongation rate.
  • the compaction density of the negative electrode film layer can be further increased, thereby increasing the energy density of the sodium-ion battery.
  • the negative electrode film layer may include: 80wt% to 97wt% of negative active material particles, 0wt% to 5wt% of conductive agent, 2wt% to 10wt% of binder, and 0.5wt% to 5wt% dispersant, wherein the negative active material particles include first negative active material particles and second negative active material particles.
  • the negative electrode film layer includes the above-mentioned components, and the content of each component is within the above-mentioned appropriate range, which can ensure that the negative electrode film layer has a higher compaction density and good electron and Sodium ion transport properties. Therefore, the negative electrode sheet of the present application is applied to sodium-ion batteries, which can allow sodium-ion batteries to have high energy density and good cycle performance.
  • each negative electrode film layer given in this application refers to the parameter range of the negative electrode film layer on one side.
  • the negative electrode film layers are disposed on both surfaces of the negative electrode current collector, if the parameters of the negative electrode film layers on either side meet the requirements of this application, it is deemed to fall within the protection scope of this application.
  • the first negative active material particles in this application can be obtained in a variety of ways, which are not limited here.
  • the first negative active material particles can be obtained commercially or homemade.
  • acetylene gas can be introduced to coat the ball-milled particles with vapor deposition carbon, thereby preparing first negative electrode active material particles with irregular shapes.
  • the first negative active material particles may be spherical hard carbon particles or quasi-spherical hard carbon particles.
  • the first negative active material particles can be prepared by the following steps: dehydration and carbonization of starch and/or lignin below 200°C to obtain pre-carbonized particles with a fixed preliminary morphology (for example, papermaking lignin, potato starch, corn starch, rice starch).
  • the Dv50 of the obtained pre-carbonized particles are 50 ⁇ m, 25 ⁇ m, 10 ⁇ m, and 6 ⁇ m respectively, and the morphology is spherical or quasi-spherical).
  • salts containing N, P, S, and halogen can be added to the starch and/or lignin.
  • polymer dehydrating agents such as ammonium salts, phosphates, sulfates, sulfites, persulfates, halides or polymers of the above salts; heat-treat the pre-carbonized particles at 400 to 800°C to obtain an easy-to-use dehydrating agent.
  • Carbonized particles pulverized by ball mill or airflow mill; pulverized by ball mill or airflow mill to pulverize the above-mentioned carbonized particles to further obtain particles of other particle sizes close to spherical or cullet morphology for example, potato starch carbon particles with a particle size of 25 ⁇ m are ground to 20 ⁇ m by a first-stage ball mill, The morphology is still close to spherical, and after being ground by a three-stage ball mill to 5 ⁇ m, the morphology is close to that of cullet; the rice starch with a particle size of 6 ⁇ m is still close to spherical after being ground by a first-stage ball mill to 5 ⁇ m, and after being ground by a third-stage ball mill, it is ground to 1.5
  • the morphology of ⁇ m particles is in the shape of cullet; the corn starch carbon particles with a particle size of 10 ⁇ m can be obtained by airflow crushing to obtain 1 ⁇ m cullet shape carbon
  • tap density has a meaning known in the art and can be measured using methods known in the art. For example, you can refer to the standards GB/T 5162-2006 and GB/T 24533-2009 and use a powder tap density tester (such as Dandong Baite BT-310) to test.
  • a powder tap density tester such as Dandong Baite BT-310
  • the median particle size has a meaning well known in the art, which can represent the particle size corresponding to when the cumulative particle size distribution percentage of the particles reaches 50%.
  • Median particle size can be determined using methods and instruments known in the art. For example, you can refer to the GB/T 19077-2016 particle size distribution laser diffraction method and use a laser particle size analyzer (such as the British Malvern Mastersizer 2000E) to measure it.
  • the elongation rate E of the negative electrode current collector has a meaning known in the art, which can represent the length change rate of the negative electrode current collector in the negative electrode piece in the mechanical direction before and after cold pressing.
  • the elongation E can be measured using methods and instruments known in the art.
  • the single-sided coating weight of the negative electrode film layer has a meaning known in the art and can be measured using methods known in the art. For example, after the negative electrode piece is cold-pressed, a punching machine is used to punch out a number of discs with an area S 2 that are completely coated with slurry and discs that are not coated with slurry, and are weighed separately to obtain the average mass M 2.
  • n 1.
  • the thickness d 0 of the single-sided negative electrode film layer can be measured with a multimeter.
  • the thickness d 1 of the negative electrode piece can be measured with a multimeter.
  • a second aspect of the present application provides a secondary battery.
  • a secondary battery In some embodiments, it may be a sodium-ion battery.
  • a secondary battery typically includes a positive electrode plate, a negative electrode plate, an electrolyte and a separator.
  • active ions are inserted and detached back and forth between the positive and negative electrodes.
  • the electrolyte plays a role in conducting ions between the positive and negative electrodes.
  • the isolation film is placed between the positive electrode piece and the negative electrode piece. It mainly prevents the positive and negative electrodes from short-circuiting and allows ions to pass through.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector.
  • the positive electrode film layer includes the positive electrode active material of the first aspect of the present application.
  • the positive electrode current collector has two surfaces facing each other in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • the metal foil aluminum foil can be used.
  • the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer.
  • the composite current collector can be formed by forming metal materials (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) on polymer material substrates (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the cathode active material when the secondary battery is a sodium-ion battery, may be a cathode active material known in the art for sodium-ion batteries.
  • the cathode active material may be a cathode active material known in the art for sodium-ion batteries.
  • only one type of positive electrode active material may be used alone, or two or more types may be combined.
  • the positive active material can be selected from sodium iron composite oxide (NaFeO 2 ), sodium cobalt composite oxide (NaCoO 2 ), sodium chromium composite oxide (NaCrO 2 ), sodium manganese composite oxide (NaMnO 2 ), sodium nickel Composite oxide (NaNiO 2 ), sodium nickel titanium composite oxide (NaNi 1/2 Ti 1/2 O 2 ), sodium nickel manganese composite oxide (NaNi 1/2 Mn 1/2 O 2 ), sodium iron manganese composite Oxide (Na 2/3 Fe 1/3 Mn 2/3 O 2 ), sodium nickel cobalt manganese composite oxide (NaNi 1/3 Co 1/3 Mn 1/3 O 2 ), sodium iron phosphate compound (NaFePO 4 ), sodium manganese phosphate compound (NaMn P O 4 ), sodium cobalt phosphate compound (NaCoPO 4 ), Prussian blue materials, polyanionic materials (phosphates, fluorophosphates, pyrophosphates, sulfates), etc.,
  • the positive electrode film layer optionally further includes a binder.
  • the binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene At least one of ethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.
  • the positive electrode film layer optionally further includes a conductive agent.
  • the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components in a solvent (such as N -methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode piece can be obtained.
  • a solvent such as N -methylpyrrolidone
  • the negative electrode plate includes the negative electrode plate of the first aspect of the application.
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, where the negative electrode film layer includes a negative electrode active material.
  • the negative electrode current collector has two opposite surfaces in its own thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.
  • the negative electrode current collector may be a metal foil or a composite current collector.
  • the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base material.
  • the composite current collector can be formed by forming metal materials (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the negative electrode film layer optionally further includes a conductive agent.
  • the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the negative electrode film layer optionally includes other auxiliaries, such as thickeners (such as sodium carboxymethylcellulose (CMC-Na)) and the like.
  • thickeners such as sodium carboxymethylcellulose (CMC-Na)
  • the negative electrode sheet can be prepared in the following manner: using the above-mentioned components for preparing the negative electrode sheet, such as first negative active material particles, second negative active material particles, and optional slip increment groups.
  • the components, conductive agent, binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes , you can get the negative electrode piece.
  • a solvent such as deionized water
  • the electrolyte plays a role in conducting ions between the positive and negative electrodes.
  • the type of electrolyte in this application can be selected according to needs.
  • the electrolyte can be liquid, gel, or completely solid.
  • the electrolyte is an electrolyte solution.
  • the electrolyte solution includes electrolyte salts and solvents.
  • the electrolyte salt can be selected from one or more of NaPF 6 , NaClO 4 , NaBCl 4 , NaSO 3 CF 3 and Na(CH 3 )C 6 H 4 SO 3 .
  • the solvent may be selected from the group consisting of ethylene carbonate, propylene carbonate, methylethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, Butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate At least one of ester, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.
  • the electrolyte optionally further includes additives.
  • additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.
  • the secondary battery further includes a separator film.
  • a separator film There is no particular restriction on the type of isolation membrane in this application. Any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be used.
  • the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the isolation film can be a single-layer film or a multi-layer composite film, with no special restrictions. When the isolation film is a multi-layer composite film, the materials of each layer can be the same or different, and there is no particular limitation.
  • the positive electrode piece, the negative electrode piece and the separator film can be made into an electrode assembly through a winding process or a lamination process.
  • the secondary battery may include an outer packaging.
  • the outer packaging can be used to package the above-mentioned electrode assembly and electrolyte.
  • the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.
  • the outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag.
  • the material of the soft bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.
  • FIG. 2 shows a square-structured secondary battery 5 as an example.
  • the outer package may include a housing 51 and a cover 53 .
  • the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity.
  • the housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 can cover the opening to close the accommodation cavity.
  • the positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is packaged in the containing cavity.
  • the electrolyte soaks into the electrode assembly 52 .
  • the number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.
  • secondary batteries can be assembled into battery modules, and the number of secondary batteries contained in the battery module can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery module.
  • FIG. 4 is a battery module 4 as an example.
  • a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 .
  • the plurality of secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may further include a housing having a receiving space in which a plurality of secondary batteries 5 are received.
  • the above-mentioned battery modules can also be assembled into a battery pack.
  • the number of battery modules contained in the battery pack can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery pack.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box.
  • the battery box includes an upper box 2 and a lower box 3 .
  • the upper box 2 can be covered with the lower box 3 and form a closed space for accommodating the battery module 4 .
  • Multiple battery modules 4 can be arranged in the battery box in any manner.
  • the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided by the present application.
  • the secondary battery, battery module, or battery pack may be used as a power source for the electrical device, or may be used as an energy storage unit for the electrical device.
  • the electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, and electric golf carts). , electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.
  • a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.
  • Fig. 7 is an electrical device as an example.
  • the electric device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc.
  • a battery pack or battery module can be used.
  • the device may be a mobile phone, a tablet, a laptop, etc.
  • the device is usually required to be thin and light, and a secondary battery can be used as a power source.
  • the positive electrode active material sodium nickel manganese composite oxide (NaNi 1/2 Mn 1/2 O 2 ), conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) in an appropriate amount in a weight ratio of 92:5:3.
  • NMP N-methylpyrrolidone
  • the positive electrode slurry was coated on the positive electrode current collector aluminum foil with a thickness of 13 ⁇ m, dried at 100°C, and pressed to obtain the positive electrode. Extreme piece.
  • the negative active material particles include first negative active material particles and second negative active material particles.
  • the first negative active material particles are irregular-shaped hard carbon particles
  • the second negative active material particles are artificial graphite particles
  • the first negative active material particles are irregularly shaped hard carbon particles.
  • the median particle size D50 of the material particles is 5 ⁇ m. Based on the total mass of the negative active material particles, the mass percentage Q1 of the first negative active material particles is 70%, and the mass percentage Q2 of the second negative active material particles is 30%.
  • the single-sided coating weight CW of the negative electrode piece is 9 mg/cm 2 .
  • Example 2 Based on the preparation method of Example 1, the median particle diameter D50 of the first negative electrode active material particles as well as Q 1 and Q 2 were adjusted to prepare the sodium ion batteries of Examples 7 to 14.
  • Example 2 Based on the preparation method of Example 1, the morphology of the first negative active material particles and Q 1 and Q 2 were adjusted to prepare the sodium ion battery of Examples 15 to 16.
  • the type of the second negative electrode active material and Q 1 and Q 2 were adjusted to prepare the sodium ion batteries of Examples 17 to 19.
  • the second negative active material used in Example 17 is natural graphite
  • the second negative active material used in Example 18 is graphene
  • the second negative active material used in Example 19 is natural graphite and graphene at a ratio of 1:1. The mass ratio of the mixed materials.
  • Example 1 Based on the preparation method of Example 1, the single-sided coating weight of the negative electrode film layer and Q 1 and Q 2 were adjusted to prepare the sodium ion batteries of Examples 20 to 23.
  • Example 1 Based on the preparation method of Example 1, the tap density of the first negative active material and Q 1 and Q 2 were adjusted to prepare the sodium ion batteries of Examples 24 to 27.
  • Example 1 Based on the preparation method of Example 1, the tap density of the second negative electrode active material and Q 1 and Q 2 were adjusted to prepare the sodium ion batteries of Examples 28 to 29.
  • the types of binders used in Q 1 , Q 2 and the negative electrode sheet were adjusted to prepare the sodium ion batteries of Examples 30 to 34.
  • the binder used in the negative electrode sheet of Example 30 is styrene-butadiene rubber SBR
  • the binder used in the negative electrode sheet of Example 31 is hydrogenated nitrile rubber
  • the binder used in the negative electrode sheet of Example 32 is SBR. It is a copolymer of divinylidene fluoride and hexafluoropropylene.
  • the binder used in the negative electrode sheet of Example 33 is a copolymer of divinylidene fluoride and acrylic esters.
  • the binder used in the negative electrode sheet of Example 34 is polytetrafluoroethylene.
  • the composition of the negative active material particles was adjusted to prepare sodium ion batteries of Comparative Examples 1 to 3.
  • the relevant preparation parameters of the negative electrode plates of the above-mentioned Examples 1 to 34 and Comparative Examples 1 to 5 are as shown in Table 1 below.
  • Q 1 represents the mass proportion of the first negative active material particles based on the total mass of the negative active material particles
  • Q 2 represents the mass proportion of the second negative active material particles based on the total mass of the negative active material particles
  • the first The tap density ⁇ 1 and D50 of the negative active material particles and the tap density ⁇ 2 of the second negative active material particles can be tested according to the method described above in this specification, and PA can be calculated according to the method described above in this specification.
  • Example 1 0.85 70 5 1.15 30 2.07
  • Example 2 0.85 75 5 1.15 25 2.07
  • Example 3 0.85 80 5 1.15 20 2.07
  • Example 4 0.85 85 5 1.15 15 2.07
  • Example 5 0.85 90 5 1.15 10 2.07
  • Example 6 0.85 95 5 1.15 5 2.07
  • Example 7 0.85 90 1 1.15 10 2.07
  • Example 8 0.85 90 3 1.15 10 2.07
  • Example 9 0.85 90 8 1.15 10 2.07
  • Example 11 0.85 90 20 1.15 10 2.07
  • Example 12 0.85 90 30 1.15 10 2.07
  • Example 13 0.85 90 50 1.15 10 2.07
  • Example 14 0.85 90 60 1.15 10 2.07
  • Example 15 0.85 90 5 1.15 10 2.07
  • Example 16 0.85 90 5 1.15 10 2.07
  • Example 17 0.85 90 5 1.15 10 2.07
  • Example 18 0.85 90 5 0.4 10 2.07
  • Example 19 0.85
  • Example 1 9 85.7 0.12 1.05 48.8%
  • Example 2 9 86.5 0.12 1.04 49.3%
  • Example 3 9 87.4 0.12 1.03 49.8%
  • Example 4 9 88.2 0.12 1.02 50.2%
  • Example 5 9 89.1 0.12 1.01 50.7%
  • Example 6 90.0 0.12 1.00 51.2%
  • Example 7 9 91.8 0.12 0.98 52.2%
  • Example 8 9 90.9 0.12 0.99 51.7%
  • Example 10 9 88.2 0.12 1.02 50.2%
  • Example 11 9 86.5 0.12 1.04 49.3%
  • Example 12 9 84.1 0.12 1.07 47.8%
  • Example 13 9 82.6 0.12 1.09 46.8%
  • Example 14 9 85.7 0.12 1.05 48.8%
  • Example 15 9 78.3 0.12 1.15 43.9%
  • Example 16 9 78.3 0.12 1.15 43.9%
  • Example 17 9 89.1 0.12 1.
  • the negative electrode film layer includes first negative electrode active material particles and second negative electrode active material particles, and when the first negative electrode active material particles and the second negative electrode active material particles meet the conditions of the present application, it can be achieved
  • the negative electrode film layer has high compaction density and suitable parameter P, which enables the sodium-ion battery to have both high energy density and long cycle life.
  • the second negative electrode active material particles can be filled into the gaps between the first negative electrode active material particles or on the surface of the first negative electrode active material particles, and exert a sliding function during the cold pressing process.
  • the negative electrode film layer can have a high compaction density
  • Examples 15 to 16 use spherical hard carbon particles or quasi-spherical hard carbon particles as the first negative electrode active material particles. Although the negative electrode film layer has Higher compaction density, but the corresponding sodium-ion battery cycle life is shorter. This may be because the electrolyte wetting performance of the negative electrode film layers of Examples 15 to 16 is lower than that of the negative electrode film layer of Example 5.
  • the second negative electrode active material particles with a layered structure can all exert a sliding function, thereby increasing the compaction density of the negative electrode film layer.
  • the tap density of the second negative active material particles is within a suitable range, the negative electrode film layer can have a high compaction density, and the sodium ion battery can have a high compaction density. and longer cycle life.
  • the flexible binder can increase the compaction density of the negative electrode film layer, improve the long-term cycle performance of the sodium-ion battery, and increase the energy of the sodium-ion battery. density and cycle life.
  • Comparative Examples 1 to 3 only used hard carbon particles with a median particle size of 5 ⁇ m and different morphologies as negative electrode active material particles, and the compaction density of the negative electrode film layer was low. As a result, the negative electrode plate not only has a lower energy density, but also has a longer transmission path for electrons and sodium ions. Therefore, the energy density and cycle life of the sodium-ion battery are lower.
  • Comparative Examples 4 and 5 the first negative electrode active material particles and the second negative electrode active material particles with a layered structure are used for compounding, in Comparative Example 4, the content of the first negative electrode active material particles is lower than that of the present application.
  • the energy density of the sodium-ion battery is significantly reduced; in Comparative Example 5, the content of the first negative active material particles is higher than the range limited by this application, and the second negative active material particles increase the compaction density of the negative electrode film layer. The effect is limited. Therefore, the energy density and cycle life of the sodium-ion battery of Comparative Example 5 are also not ideal.

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Abstract

本申请提供了一种负极极片、二次电池、电池模块、电池包和用电装置。该负极极片包括负极集流体和负极膜层，负极膜层位于负极集流体的至少一个表面上，负极膜层包括第一负极活性材料颗粒和第二负极活性材料颗粒，第一负极活性材料颗粒包括多个吸附孔，其振实密度为0.4g/cm 3～1.4g/cm 3；第二负极活性材料颗粒具有层状结构，其振实密度为0.05g/cm 3～1.5g/cm 3，其中，基于第一负极活性材料颗粒和第二负极活性材料颗粒的总质量，第一负极活性材料颗粒的质量百分含量为70％～95％；第二负极活性材料颗粒的质量百分含量为5％～30％，负极膜片的压实密度PD满足：0.8g/cm 3≤PD≤1.3g/cm 3。

Description

负极极片、二次电池、电池模块、电池包和用电装置 技术领域
本申请涉及电池技术领域，尤其涉及一种负极极片、二次电池、电池模块、电池包和用电装置。
背景技术
随着能源与环境问题的日益凸显，新能源产业得到了越来越多的重视。锂离子电池因其能量密度高、循环性能好等特点，近年来作为一种重要的新型储能装置被广泛应用。然而，由于锂离子电池相关活性物质资源稀缺，电池成本始终居高不下，而且同时面临相关资源枯竭等严峻问题，因此需要开发其他低成本金属离子二次电池体系。
钠离子电池由于其成本低、资源丰富、与锂离子电池制造工艺相仿等优势，成为近年来的热门研究方向。
但是，受限于目前钠离子电池正负极材料较低的克容量与电压平台，钠离子电池能量密度与锂离子电池相比始终存在较大差距，无法真正实现商业化应用。此外，钠离子电池的首次库伦效率和倍率性能也有待提高。
发明内容
本申请是鉴于上述课题而进行的，其目的在于，提供一种负极极片、二次电池、电池模块、电池包和用电装置，能够有效提升钠离子电池的能量密度和倍率性能。
本申请的第一方面提供了一种负极极片，包括：负极集流体；以及负极膜层，该负极膜层位于负极集流体的至少一个表面上，负极膜层包括第一负极活性材料颗粒和第二负极活性材料颗粒，第一负极活性材料颗粒包括多个吸附孔，第一负极活性材料颗粒的振实密度为0.4g/cm 3～1.4g/cm 3，可选为0.6g/cm 3～1.0g/cm 3；第二负极活性材料颗 粒具有层状结构，第二负极活性材料颗粒的振实密度为0.05g/cm 3～1.5g/cm 3，其中，基于第一负极活性材料颗粒和第二负极活性材料颗粒的总质量，第一负极活性材料颗粒的质量百分含量为70％～95％，可选为80％～95％；第二负极活性材料颗粒的质量百分含量为5％～30％，可选为5％～10％，负极膜片的压实密度PD满足：0.8g/cm 3≤PD≤1.3g/cm 3，可选地，1.0g/cm 3≤PD≤1.2g/cm 3。
第一负极活性材料颗粒中包括多个吸附孔，且振实密度在上述合适的范围内，经冷压后，第一负极活性材料颗粒的内部仍然能够具有足够数量的吸附孔。由此，Na +能够在充放电过程中顺利地被第一负极活性材料颗粒吸附、脱嵌。进一步地，第二负极活性材料颗粒具有层状结构，在冷压过程中，第二负极活性材料颗粒一方面能够填充至多个第一活性材料颗粒之间的空隙或在第一负极活性材料颗粒表面，通过层状结构发挥滑移作用，从而使得负极活性材料颗粒在冷压过程中紧密地接触，提升负极活性材料颗粒的粉末压实密度，进而使得经冷压后的负极膜层具备合适的压实密度。由此，负极膜层中的负极活性材料颗粒接触紧密，从而能够提升负极极片中电子及钠离子的传输性能，进而提升钠离子电池的倍率性能。此外，第二负极活性材料颗粒为层状结构，相较于第一负极活性材料颗粒，第二负极活性材料颗粒吸附和嵌入钠离子的能力有限。第一负极活性材料颗粒与第二负极活性材料颗粒的含量在上述合适的范围内，能够进一步保证钠离子电池具备高能量密度。
在任意实施方式中，第一负极活性材料颗粒的中位粒径D50为1μm～50μm，可选为5μm～10μm。
第一负极活性材料颗粒的中位粒径在上述合适的范围，一方面能够提升负极极片的产能；另一方面能够使得第一负极活性材料颗粒表面具有适量的活性位点，进而提升钠离子电池的库伦效率。此外，第一负极活性材料颗粒具有合适的中位粒径，不仅能够使得第一负极活性材料颗粒的颗粒内部具有良好的电子及钠离子传输性能，还能够使得第一负极活性材料颗粒具有较低的颗粒界面电阻。由此，本申请的负极极片应用于钠离子电池，能够允许钠离子电池具备高能量密度、 高库伦效率、良好的倍率性能和循环性能。
在任意实施方式中，负极集流体的延展率E满足：0.1％≤E≤0.2％，可选地，0.1％≤E≤0.15％。本申请通过第一负极活性材料颗粒和第二负极活性材料颗粒复配，利用第二负极活性材料颗粒具备滑移功能，能够使得负极活性材料颗粒在冷压过程中紧密地接触，从而使得负极活性材料颗粒具备高粉末压实密度。因此，相较于压实密度较低的负极活性材料颗粒，在相同的冷压参数下，本申请的负极集流体能够具备更低的延展率，从而能够保持良好的导电性能和机械强度。
在任意实施方式中，根据权利要求1-3中任一项的负极极片，其中，负极膜层的单面涂布重量CW为2mg/cm 2～13mg/cm 2。负极膜层的单面涂布重量在合适的范围内，不仅能够使得电子及钠离子在负极极片中具有合适的迁移路径，还能够使得负极极片具有合适的容量。因此，本申请的负极极片应用于钠离子电池，能够允许钠离子电池具备良好的倍率性能和高能量密度。
在任意实施方式中，负极膜层满足：30％≤P≤60％，可选地，45％≤P≤55％，其中，P＝[1-(CW)/(d*PA)]*100％，d＝d 0/(1+E)，CW表示负极膜层的单面涂布重量，PA表示单面负极膜层的真密度，E表示负极集流体的延展率，d 0表示单面负极膜层的厚度。负极膜层的参数P满足上述条件时，可认为负极膜层压实密度的提升主要是通过冷压过程中第二负极活性材料颗粒的滑移作用实现的，对负极膜层的孔隙率无显著影响。由此，不仅提升了负极膜层的压实密度，还能够保持负极膜层的电解液浸润性，从而保证负二次电池具备高能量密度和良好的倍率性能。
在任意实施方式中，第一负极活性材料颗粒选自硬碳、软碳、中间相碳微球中的一种或几种；第二负极活性材料颗粒选自人造石墨、天然石墨、石墨烯中的一种或几种。上述第一负极活性材料颗粒和第二负极活性材料颗粒能够使得负极膜层具备高压实密度和优异的电子传导能力，应用于钠离子电池中，能够允许钠离子电池具备高压实密度和良好的循环性能。
在任意实施方式中，第一负极活性材料颗粒包括不规则形状第一 负极活性材料颗粒、球形第一负极活性材料颗粒或类球形第一负极活性材料颗粒中的一种或几种。第一负极活性材料颗粒具有上述形貌时，能够提升负极极片的工艺灵活性，并允许钠离子电池具备高能量密度。
在任意实施方式中，第一负极活性材料颗粒包括不规则形状硬碳颗粒、球形硬碳颗粒或类球形硬碳颗粒中的一种或几种。第一负极活性材料颗粒选自上述形貌的硬碳颗粒时，能够使得负极活性材料颗粒具备低成本和高理论克容量，从而提升钠离子电池的能量密度、倍率性能和循环稳定性。
在任意实施方式中，单面负极膜层的压实密度PD满足：1.0g/cm 3≤PD≤1.2g/cm 3；负极膜层满足：30％≤P≤60％，可选地，45％≤P≤55％，其中，P＝[1-(CW)/(d*PA)]*100％，d＝d 0/(1+E)，CW表示负极膜层的单面涂布重量，PA表示单面负极膜层的真密度，E表示负极集流体的延展率，d 0表示单面负极膜层的厚度。负极膜层的参数P满足上述条件时，可认为负极膜层压实密度的提升主要是通过冷压过程中第二负极活性材料颗粒的滑移功能实现的。因此，对于硬碳颗粒来说，其无需发生形变或滑移，也能够使得负极膜层具备高压实密度。由此，能够将硬碳材料应用于钠离子电池中，使得钠离子电池具备广阔的应用前景。
在任意实施方式中，负极膜层还包括柔性粘结剂，柔性粘结剂包括苯丙乳液、偏氟二乙烯与四氟乙烯的共聚物、偏氟二乙烯与六氟丙烯的共聚物、偏氟二乙烯与丙烯酸酯类的共聚物、聚四氟乙烯、丁腈橡胶、氢化丁腈橡胶的一种或几种。负极膜层包括上述柔性粘结剂，能够具有良好的柔韧性。由此，负极膜层在冷压过程中，能够具有更小的应力，负极活性材料颗粒更易堆积，且负极集流体能够具备更低的延展率。由此，能够进一步提升负极膜层的压实密度，从而提升钠离子电池的能量密度。
在任意实施方式中，基于负极膜层的总质量，负极膜层包括：80wt％～97wt％的负极活性材料颗粒、0wt％～5wt％的导电剂、2wt％～10wt％的粘结剂以及0.5wt％～5wt％的分散剂，其中，所述负极活性材料颗粒包括所述第一负极活性材料颗粒和所述第二负极活性 材料颗粒。负极膜层中包括上述组份，且各组份的含量在上述合适的范围内，能够保证负极膜层具有较高的压实密度以及良好的电子及钠离子的传输性能。由此，本申请的负极极片应用于钠离子电池，能够允许钠离子电池具备高能量密度和良好的循环性能。
本申请的第二方面提供一种二次电池，包括本申请第一方面的负极极片。
本申请的二次电池包括本申请第一方面的负极极片，由此能够具备高能量密度和良好的倍率性能。
本申请的第三方面提供一种电池模块，包括本申请的第二方面的二次电池。
本申请的第四方面提供一种电池包，包括本申请的第三方面的电池模块。
本申请的第五方面提供一种用电装置，包括选自本申请的第二方面的二次电池、本申请的第三方面的电池模块或本申请的第四方面的电池包中的至少一种。
本申请的电池模块、电池包、用电装置包括本申请的二次电池，因而至少具有与二次电池相同的优势。
附图说明
图1为本申请一实施方式的负极集流体的延展率测试示意图。
图2是本申请一实施方式的二次电池的示意图。
图3是图2所示的本申请一实施方式的二次电池的分解图。
图4是本申请一实施方式的电池模块的示意图。
图5是本申请一实施方式的电池包的示意图。
图6是图5所示的本申请一实施方式的电池包的分解图。
图7是本申请一实施方式的二次电池用作电源的用电装置的示意图。
图8是本申请实施例1的负极极片的扫描电镜图(SEM图)。
附图标记说明：
1电池包；2上箱体；3下箱体；4电池模块；5二次电池；51壳 体；52电极组件；53盖板
具体实施方式
以下，适当地参照附图详细说明具体公开了本申请的负极极片、二次电池、电池模块、电池包和用电装置的实施方式。但是会有省略不必要的详细说明的情况。例如，有省略对已众所周知的事项的详细说明、实际相同结构的重复说明的情况。这是为了避免以下的说明不必要地变得冗长，便于本领域技术人员的理解。此外，附图及以下说明是为了本领域技术人员充分理解本申请而提供的，并不旨在限定权利要求书所记载的主题。
本申请所公开的“范围”以下限和上限的形式来限定，给定范围是通过选定一个下限和一个上限进行限定的，选定的下限和上限限定了特别范围的边界。这种方式进行限定的范围可以是包括端值或不包括端值的，并且可以进行任意地组合，即任何下限可以与任何上限组合形成一个范围。例如，如果针对特定参数列出了60-120和80-110的范围，理解为60-110和80-120的范围也是预料到的。此外，如果列出的最小范围值1和2，和如果列出了最大范围值3，4和5，则下面的范围可全部预料到：1-3、1-4、1-5、2-3、2-4和2-5。在本申请中，除非有其他说明，数值范围“a-b”表示a到b之间的任意实数组合的缩略表示，其中a和b都是实数。例如数值范围“0-5”表示本文中已经全部列出了“0-5”之间的全部实数，“0-5”只是这些数值组合的缩略表示。另外，当表述某个参数为≥2的整数，则相当于公开了该参数为例如整数2、3、4、5、6、7、8、9、10、11、12等。
如果没有特别的说明，本申请的所有实施方式以及可选实施方式可以相互组合形成新的技术方案。
如果没有特别的说明，本申请的所有技术特征以及可选技术特征可以相互组合形成新的技术方案。
如果没有特别的说明，本申请的所有步骤可以顺序进行，也可以随机进行，优选是顺序进行的。例如，所述方法包括步骤(a)和(b)，表示所述方法可包括顺序进行的步骤(a)和(b)，也可以包括顺序进行的 步骤(b)和(a)。例如，所述提到所述方法还可包括步骤(c)，表示步骤(c)可以任意顺序加入到所述方法，例如，所述方法可以包括步骤(a)、(b)和(c)，也可包括步骤(a)、(c)和(b)，也可以包括步骤(c)、(a)和(b)等。
如果没有特别的说明，本申请所提到的“包括”和“包含”表示开放式，也可以是封闭式。例如，所述“包括”和“包含”可以表示还可以包括或包含没有列出的其他组分，也可以仅包括或包含列出的组分。
如果没有特别的说明，在本申请中，术语“或”是包括性的。举例来说，短语“A或B”表示“A，B，或A和B两者”。更具体地，以下任一条件均满足条件“A或B”：A为真(或存在)并且B为假(或不存在)；A为假(或不存在)而B为真(或存在)；或A和B都为真(或存在)。
为了改善提升钠离子电池的能量密度和倍率性能，对钠离子电池的负极活性材料进行选取十分重要。
发明人经深入研究，发现：在充电过程中，钠离子电池的在硬碳负极发生Na +的嵌入或者吸附，选取具有多个吸附孔的负极活性材料颗粒作为钠离子电池的负极，在充电过程中发生Na +的嵌入或者吸附，从而实现电池的容量发挥。然而，具有多个吸附孔的负极活性材料颗粒制备成负极膜层之后，负极膜层的压实密度降低，不仅会影响钠离子电池的能量密度、还会导致负极极片中电子和钠离子的传输路径增长，从而降低负极极片中电子及钠离子的传输性能，进而恶化钠离子电池的倍率性能。
基于此，发明人经深入思考与大量实验，提出了一种负极极片、二次电池、电池模块、电池包和用电装置。
负极极片
本申请第一方面提供一种负极极片，其包括负极集流体以及负极膜层。该负极膜层位于负极集流体的至少一个表面上，负极膜层包括第一负极活性材料颗粒和第二负极活性材料颗粒，第一负极活性材料颗粒包括多个吸附孔，第一负极活性材料颗粒的振实密度为0.4g/cm 3～1.4g/cm 3。第二负极活性材料颗粒具有层状结构，第二负极活性材料颗粒的振实密度为0.05g/cm 3～1.5g/cm 3。其中，基于第一负 极活性材料颗粒和第二负极活性材料颗粒的总质量，第一负极活性材料颗粒的质量百分含量为70％～95％，第二负极活性材料颗粒的质量百分含量为5％～30％。负极膜层的压实密度PD满足：0.8g/cm 3≤PD≤1.3g/cm 3，0.8g/cm 3≤PD≤1.2g/cm 3，0.8g/cm 3≤PD≤1.1g/cm 3，0.8g/cm 3≤PD≤1.0g/cm 3，1.0g/cm 3≤PD≤1.3g/cm 3，1.0g/cm 3≤PD≤1.2g/cm 3或1.0g/cm 3≤PD≤1.1g/cm 3。可选地，第一负极活性材料的振实密度为0.6g/cm 3～1.0g/cm 3。可选地，基于第一负极活性材料颗粒和第二负极活性材料颗粒的总质量，第一负极活性材料颗粒的质量百分含量为80％～95％，第二负极活性材料颗粒的质量百分含量为5％～20％。更可选地，基于第一负极活性材料颗粒和第二负极活性材料颗粒的总质量，第一负极活性材料颗粒的质量百分含量为90％～95％，第二负极活性材料颗粒的质量百分含量为5％～10％
虽然机理尚不明确，但本申请的发明人意外地发现：本申请的负极膜层中包括满足上述条件的第一负极活性材料颗粒和第二负极活性材料颗粒，两种负极活性材料颗粒复配能够在使得负极膜层具备高压实密度的。由此，本申请的负极极片应用于钠离子电池，能够使得钠离子电池具备高能量密度和良好的倍率性能。
具体地，并非意在受限于任何理论或解释，第一负极活性材料颗粒中包括多个吸附孔，且振实密度在上述合适的范围内，经冷压后，第一负极活性材料颗粒的内部仍然能够具有足够数量的吸附孔。由此，Na +能够在充放电过程中顺利地被第一负极活性材料颗粒吸附、脱嵌。进一步地，第二负极活性材料颗粒具有层状结构，在冷压过程中，第二负极活性材料颗粒一方面能够填充至多个第一活性材料颗粒之间的空隙或在第一负极活性材料颗粒表面，通过层状结构发挥滑移作用，从而使得负极活性材料颗粒在冷压过程中紧密地接触，提升负极活性材料颗粒的粉末压实密度，进而使得经冷压后的负极膜层具备合适的压实密度。由此，负极膜层中的负极活性材料颗粒接触紧密，从而能够提升负极极片中电子及钠离子的传输性能，进而提升钠离子电池的倍率性能。此外，第二负极活性材料颗粒为层状结构，相较于第一负极活性材料颗粒，第二负极活性材料颗粒吸附和嵌入钠离子的能力有 限。第一负极活性材料颗粒与第二负极活性材料颗粒的含量在上述合适的范围内，能够进一步保证钠离子电池具备高能量密度。
在一些实施方式中，第一负极活性材料颗粒的中位粒径D50可为1μm～50μm，可选为5μm～10μm。例如，D50可以为1μm，3μm，5μm，8μm，10μm，15μm，20μm，25μm，35μm，45μm，50μm或处于以上任何数值所组成的范围内。
并非意在受限于任何理论或解释，第一负极活性材料颗粒的中位粒径在上述合适的范围，一方面能够降低第一负极活性材料颗粒的制备难度，从而能够提升负极极片的产能；另一方面能够具有合适的比表面积，从而使得第一负极活性材料颗粒表面具有适量的活性位点，进而提升钠离子电池的库伦效率。此外，第一负极活性材料颗粒具有合适的中位粒径，不仅能够使得第一负极活性材料颗粒的颗粒内部具有良好的电子及钠离子传输性能，还能够使得第一负极活性材料颗粒具有较低的颗粒界面电阻。由此，本申请的负极极片应用于钠离子电池，能够允许钠离子电池具备高能量密度、高库伦效率、良好的倍率性能和循环性能。
在一些实施方式中，负极集流体的延展率E可满足：0.1％≤E≤0.2％，可选地，0.1％≤E≤0.15％。例如，E可以为0.1％，0.12％，0.15％，0.18％，0.2％或处于以上任何数值所组成的范围内。
并非意在受限于任何理论或解释，本申请通过第一负极活性材料颗粒和第二负极活性材料颗粒复配，利用第二负极活性材料颗粒具备滑移功能，能够使得负极活性材料颗粒在冷压过程中紧密地接触，从而使得负极活性材料颗粒具备高粉末压实密度。因此，相较于压实密度较低的负极活性材料颗粒，在相同的冷压参数下，本申请的负极集流体能够具备更低的延展率，从而能够保持良好的导电性能和机械强度。
在一些实施方式中，负极膜层的单面涂布重量CW可以为2mg/cm 2～13mg/cm 2，可选为5mg/cm 2～12mg/cm 2。例如，CW可以为2mg/cm 2，5mg/cm 2，8mg/cm 2，10mg/cm 2，12mg/cm 2，13mg/cm 2或处于以上任何数值所组成的范围内。
上述负极膜层的单面涂布重量，可以表示单位面积内，单面负极膜层所涂布的负极浆料中的固体组份含量，其在数值上可以等于单面负极膜层的面密度。
并非意在受限于任何理论或解释，负极膜层的单面涂布重量在上述合适的范围内，有利于控制负极膜层的厚度在合适的范围内。由此，不仅能够使得电子及钠离子在负极极片中具有合适的迁移路径，还能够使得负极极片具有合适的容量。因此，本申请的负极极片应用于钠离子电池，能够允许钠离子电池具备良好的倍率性能和高能量密度。
在一些实施方式中，负极膜层可满足：30％≤P≤60％。可选地，45％≤P≤55％。
其中，P＝[1-CW/(d*PA)]*100％，d＝d 0(1+E)；CW表示负极膜层的单面涂布重量；PA表示单面负极膜层的真密度，可以通过下式计算得到：PA＝1/(∑x i/ρ i)，其中，x i表示组成负极膜层的第i种组份在负极膜层中的质量占比，ρi表示第i种组份的密度；E表示负极集流体的延展率；d 0表示单面负极膜层的厚度。
并非意在受限于任何理论或解释，发明人意外地发现，负极膜层的参数P满足上述条件时，可认为负极膜层压实密度的提升主要是通过冷压过程中第二负极活性材料颗粒的滑移作用实现的，对负极膜层的孔隙率无显著影响。由此，不仅提升了负极膜层的压实密度，还能够保持负极膜层的电解液浸润性，从而保证负二次电池具备高能量密度和良好的倍率性能。
本申请对第一负极活性材料颗粒和第二负极活性材料颗粒的材质不作限制。在一些实施方式中，第一负极活性材料颗粒可选自硬碳、软碳、中间相碳微球(MCMB)中的一种或几种；第二负极活性材料颗粒可选自人造石墨、天然石墨、石墨烯中的一种或几种。
选自上述种类材料的颗粒生产工艺成熟，便于加工得到满足本申请的条件的第一负极活性材料颗粒和第二负极活性材料颗粒。此外，当第二负极活性材料颗粒选自上述种类的材料时，第二负极活性材料不仅能够填充至多个第一负极活性材料颗粒的空隙中或在第一负极活性材料颗粒表面、发挥滑移作用，以提升负极活性材料的压实密度， 而且能够具备优异的电子传导能力。由此，本申请的负极极片能够具备高压实密度和优异的电子传导能力，应用于钠离子电池中，能够允许钠离子电池具备高压实密度和良好的循环性能。
本申请对第一负极活性材料颗粒的形貌不作限制。在一些实施方式中，第一负极活性材料颗粒可包括不规则形状第一负极活性材料颗粒、球形第一负极活性材料颗粒或类球形第一负极活性材料颗粒中的一种或几种。
本申请的负极极片中，第一负极活性材料颗粒与第二负极活性材料颗粒复配，且第一负极活性材料颗粒与第二负极活性材料颗粒的含量在本申请的范围内，无论第一负极活性材料颗粒具有何种形貌，负极膜层均可以具备高压实密度。由此，能够提升负极极片的工艺灵活性，并允许钠离子电池具备高能量密度。
在一些实施方式中，第一负极活性材料颗粒可以为硬碳颗粒。
发明人经研究发现，硬碳材料具有较低的储能电压、较高的容量和良好的循环稳定性。此外，硬碳材料来源丰富、制备工艺简单。更重要的是，硬碳颗粒本身的晶格间距大、多孔，是本申请的第一负极活性材料颗粒的理想选择。虽然常规的硬碳材料自身硬度大、冷压过程中几乎不发生形变和滑移，应用于负极膜层中，负极膜层的压实密度通常较低，但是，本申请的负极膜层中，具有层状结构的第二负极活性材料颗粒能够填入第一负极活性材料颗粒的空隙中或在第一负极活性材料颗粒表面并发挥滑移作用，由此，第一负极活性材料颗粒无需发生形变，也能够使得负极膜层具备高压实密度。因此，第一负极活性材料颗粒为硬碳颗粒时，本申请的负极极片应用于钠离子电池，能够降低钠离子电池的成本，提升钠离子电池的能量密度、倍率性能和循环稳定性。
在一些实施方式中，第一负极活性材料颗粒可包括不规则形状硬碳颗粒、球形硬碳颗粒或类球形硬碳颗粒中的一种或几种。
并非意在受限于任何理论或解释，第一负极活性材料颗粒选自上述形貌的硬碳颗粒时，能够使得负极活性材料颗粒具备低成本和高理论克容量，从而提升钠离子电池的能量密度、倍率性能和循环稳定性。
在一些实施方式中，第一负极活性材料颗粒包括不规则形状硬碳颗粒、球形硬碳颗粒或类球形硬碳颗粒中的一种或几种。单面负极膜层的压实密度PD满足：1.0g/cm 3≤PD≤1.2g/cm 3；负极膜层满足：30％≤P≤60％，可选地，45％≤P≤55％，其中，P＝[1-(CW)/(d*PA)]*100％，d＝d 0/(1+E)，CW表示负极膜层的单面涂布重量，PA表示单面负极膜层的真密度，可以通过下式计算得到：PA＝1/(∑x i/ρ i)，其中，x i表示组成负极膜层的第i种组份在负极膜层中的质量占比，ρi表示第i种组份的密度；E表示负极集流体的延展率，d 0表示单面负极膜层的厚度。
并非意在受限于任何理论或解释，负极膜层的参数P满足上述条件时，可认为负极膜层压实密度的提升主要是通过冷压过程中第二负极活性材料颗粒的滑移功能实现的。因此，对于硬碳颗粒来说，其无需发生形变或滑移，也能够使得负极膜层具备高压实密度。由此，能够将硬碳材料应用于钠离子电池中，使得钠离子电池具备广阔的应用前景。
在一些实施方式中，负极膜层还可包括柔性粘结剂，柔性粘结剂包括苯丙乳液、偏氟二乙烯与四氟乙烯的共聚物、偏氟二乙烯与六氟丙烯的共聚物、偏氟二乙烯与丙烯酸酯类的共聚物、聚四氟乙烯、丁腈橡胶、氢化丁腈橡胶的一种或多种。
并非意在受限于任何理论或解释，负极膜层包括上述柔性粘结剂，能够具有良好的柔韧性。由此，负极膜层在冷压过程中，能够具有更小的应力，负极活性材料颗粒更易堆积，且负极集流体能够具备更低的延展率。由此，能够进一步提升负极膜层的压实密度，从而提升钠离子电池的能量密度。
在一些实施方式中，基于负极膜层的总质量，负极膜层可包括：80wt％～97wt％的负极活性材料颗粒、0wt％～5wt％的导电剂、2wt％～10wt％的粘结剂以及0.5wt％～5wt％的分散剂，其中，负极活性材料颗粒包括第一负极活性材料颗粒和第二负极活性材料颗粒。
并非意在受限于任何理论或解释，负极膜层中包括上述组份，且各组份的含量在上述合适的范围内，能够保证负极膜层具有较高的压 实密度以及良好的电子及钠离子的传输性能。由此，本申请的负极极片应用于钠离子电池，能够允许钠离子电池具备高能量密度和良好的循环性能。
需要说明的是，本申请所给的各负极膜层参数均指单侧负极膜层的参数范围。当负极膜层设置在负极集流体的两个表面上时，其中任意一侧的负极膜层参数满足本申请，即认为落入本申请的保护范围内。
本申请中的第一负极活性材料颗粒可通过多种方式获得，在此不作限定，例如，第一负极活性材料颗粒可通过商购或自制获得。
作为一个示例，第一负极活性材料颗粒可以为具有不规则形状的硬碳颗粒，第一负极活性材料颗粒可通过如下步骤制备：将椰壳置于300℃下，以对椰壳进行预炭化处理；用对辊机将预碳化处理后的椰壳粉碎为直径2mm左右的颗粒，经筛分除去杂质；在400℃～800℃下对颗粒进行热处理，可选的通入卤素或卤化氢气体以除去灰分，得到易于球磨加工的颗粒；对颗粒进行以及球磨，Dv50＝50μm/40μm/25μm/20μm/9μm/5μm/3μm/1μm的碳颗粒；将球磨后的颗粒置于惰性气氛中，保持温度为1150℃，以使球磨后的颗粒炭化，可选的，可通入乙炔气体，以对球磨后的颗粒进行气相沉积碳包覆，从而制备得到具有不规则形状的第一负极活性材料颗粒。
作为另一个示例，第一负极活性材料颗粒可以为球形硬碳颗粒或类球形硬碳颗粒。第一负极活性材料颗粒可通过如下步骤制备：将淀粉和/或木质素经200℃以下脱水碳化，获得初步形貌固定的预炭化颗粒(例如，造纸木质素、马铃薯淀粉、玉米淀粉、大米淀粉获得的预炭化颗粒Dv50分别为50μm、25μm、10μm、6μm，形貌为球形或类球形)，可选地，淀粉和/或木质素中还可以加入含N、P、S、卤素的盐类或聚合物类脱水剂，例如铵盐、磷酸盐、硫酸盐、亚硫酸盐、过硫酸盐、卤化物或者上述盐类的聚合物；在400～800℃下对预炭化颗粒进行热处理，得到易于球磨或者气流磨粉碎的炭化颗粒；球磨或者气流磨粉碎上述炭化颗粒，进一步获得接近球形或者碎玻璃形貌的其他粒度颗粒(例如，粒径为25μm马铃薯淀粉碳颗粒一级球磨磨粉至20μm，形貌仍接近球形，通过三级球磨磨粉至5μm形貌接近碎玻璃 形貌；粒径为6μm大米淀粉经过一级球磨磨粉至5μm形貌仍接近球形，经过3级球磨磨粉至1.5μm颗粒形貌为碎玻璃形；粒径为10μm玉米淀粉碳颗粒经过气流粉碎可获得1μm碎玻璃形貌碳颗粒)；将上述颗粒置于惰性气氛中，保持温度为1150℃，以使球磨后的颗粒炭化，可选的，可通入乙炔气体，以对球磨后的颗粒进行气相沉积碳包覆，从而制备得到球形第一负极活性材料颗粒或类球形第一负极活性材料颗粒。
在本申请中，振实密度具有本领域公知的含义，可以用本领域已知的方法测定。例如可参照标准GB/T 5162-2006和GB/T 24533-2009，使用粉体振实密度测试仪(如丹东百特BT-310)测试。
在本申请中，中位粒径具有本领域公知的含义，其可以表示颗粒的累计粒度分布百分数达到50％时所对应的粒径。中位粒径可采用本领域已知的方法和仪器测定。例如，可以参照GB/T 19077-2016粒度分布激光衍射法，采用激光粒度分析仪(例如英国马尔文Mastersizer 2000E)测定。
在本申请中，负极膜层的压实密度具有本领域公知的含义，可以用本领域已知的方法测定。例如，负极极片冷压后，用冲片机分别冲出面积为S 1的完全涂布有浆料的圆片和未涂布有浆料的圆片若干，分别进行称重得到平均质量W 2、W 1，分别测量厚度得到平均厚度T 2、T 1，负极膜层的压实密度PD＝(W 2-W 1)/(T 2-T 1)/S 1。
在本申请中，负极集流体的延展率E具有本领域公知的含义，其可以表示负极极片中的负极集流体在冷压前后机械方向的长度变化率。延展率E可采用本领域已知的方法和仪器测定。作为一个示例，如图1所示，可以取长度为2m的经涂布、干燥后的负极极片，选取两个标记点A 1、A 2，A 1、A 2的连线与负极极片的长度方向平行；用尺子准确量取标记点A 1、A 2之间的距离，记为L 1；对负极极片以一定的压力进行冷压后，在此量取A 1、A 2之间的距离，记为L 2，则E＝(L 2-L 1)/L 1。
在本申请中，负极膜层的单面涂布重量具有本领域公知的含义，可以用本领域已知的方法测定。例如，负极极片冷压后，用冲片机分 别冲出面积为S 2的完全涂布有浆料的圆片和未涂布有浆料的圆片若干，分别进行称重得到平均质量M 2、M 1，负极极片的单面涂布重量CW＝(M 2-M 1)/nS 2，其中，n表示负极膜层的数量，当负极极片为单面涂布时，n＝1，当负极极片为双面涂布时，n＝2。
在本申请中，单面负极膜层的厚度d 0可通过万分尺测量得到。例如，负极极片冷压后，可用万分尺测量负极极片的厚度d 1，将负极极片表面的负极膜层刮除、用溶剂洗净后，再用万分尺测量负极集流体的厚度d 2，d 0＝(d 1-d 2)/n，其中，n表示负极膜层的数量，当负极极片为单面涂布时，n＝1，当负极极片为双面涂布时，n＝2。
另外，以下适当参照附图对本申请的二次电池、电池模块、电池包和用电装置进行说明。
二次电池
本申请的第二方面提供一种二次电池。在一些实施方式中，其可以为钠离子电池。
通常情况下，二次电池包括正极极片、负极极片、电解质和隔离膜。在电池充放电过程中，活性离子在正极极片和负极极片之间往返嵌入和脱出。电解质在正极极片和负极极片之间起到传导离子的作用。隔离膜设置在正极极片和负极极片之间，主要起到防止正负极短路的作用，同时可以使离子通过。
[正极极片]
正极极片包括正极集流体以及设置在正极集流体至少一个表面上的正极膜层，所述正极膜层包括本申请第一方面的正极活性材料。
作为示例，正极集流体具有在其自身厚度方向相对的两个表面，正极膜层设置在正极集流体相对的两个表面的其中任意一者或两者上。
在一些实施方式中，所述正极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可采用铝箔。复合集流体可包括高分子材料基层和形成于高分子材料基层至少一个表面上的金属层。复合集流体可通过将金属材料(铝、铝合金、镍、镍合金、钛、钛合金、银及 银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
在一些实施方式中，当二次电池为钠离子电池时，正极活性材料可采用本领域公知的用于钠离子电池的正极活性材料。作为示例，正极活性材料可以仅单独使用一种，也可以将两种以上组合。其中，正极活性物质可选自钠铁复合氧化物(NaFeO 2)、钠钴复合氧化物(NaCoO 2)、钠铬复合氧化物(NaCrO 2)、钠锰复合氧化物(NaMnO 2)、钠镍复合氧化物(NaNiO 2)、钠镍钛复合氧化物(NaNi 1/2Ti 1/2O 2)、钠镍锰复合氧化物(NaNi 1/2Mn 1/2O 2)、钠铁锰复合氧化物(Na 2/3Fe 1/3Mn 2/3O 2)、钠镍钴锰复合氧化物(NaNi 1/3Co 1/3Mn 1/3O 2)、钠铁磷酸化合物(NaFePO 4)、钠锰磷酸化合物(NaMn PO 4)、钠钴磷酸化合物(NaCoPO 4)、普鲁士蓝类材料、聚阴离子材料(磷酸盐、氟磷酸盐、焦磷酸盐、硫酸盐)等，但本申请并不限定于这些材料，本申请还可以使用其他可被用作钠离子电池正极活性物质的传统公知的材料。
在一些实施方式中，正极膜层还可选地包括粘结剂。作为示例，所述粘结剂可以包括聚偏氟乙烯(PVDF)、聚四氟乙烯(PTFE)、偏氟乙烯-四氟乙烯-丙烯三元共聚物、偏氟乙烯-六氟丙烯-四氟乙烯三元共聚物、四氟乙烯-六氟丙烯共聚物及含氟丙烯酸酯树脂中的至少一种。
在一些实施方式中，正极膜层还可选地包括导电剂。作为示例，所述导电剂可以包括超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的至少一种。
在一些实施方式中，可以通过以下方式制备正极极片：将上述用于制备正极极片的组分，例如正极活性材料、导电剂、粘结剂和任意其他的组分分散于溶剂(例如N-甲基吡咯烷酮)中，形成正极浆料；将正极浆料涂覆在正极集流体上，经烘干、冷压等工序后，即可得到正极极片。
[负极极片]
本申请的二次电池中，负极极片包括本申请第一方面的负极极片。
负极极片包括负极集流体以及设置在负极集流体至少一个表面上的负极膜层，所述负极膜层包括负极活性材料。
作为示例，负极集流体具有在其自身厚度方向相对的两个表面，负极膜层设置在负极集流体相对的两个表面中的任意一者或两者上。
在一些实施方式中，所述负极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可以采用铜箔或铝箔。复合集流体可包括高分子材料基层和形成于高分子材料基材至少一个表面上的金属层。复合集流体可通过将金属材料(铜、铜合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
在一些实施方式中，负极膜层还可选地包括导电剂。导电剂可选自超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的至少一种。
在一些实施方式中，负极膜层还可选地包括其他助剂，例如增稠剂(如羧甲基纤维素钠(CMC-Na))等。
在一些实施方式中，可以通过以下方式制备负极极片：将上述用于制备负极极片的组分，例如第一负极活性材料颗粒、第二负极活性材料颗粒、可选的滑移增量组份、导电剂、粘结剂和任意其他组分分散于溶剂(例如去离子水)中，形成负极浆料；将负极浆料涂覆在负极集流体上，经烘干、冷压等工序后，即可得到负极极片。
[电解质]
电解质在正极极片和负极极片之间起到传导离子的作用。本申请对电解质的种类没有具体的限制，可根据需求进行选择。例如，电解质可以是液态的、凝胶态的或全固态的。
在一些实施方式中，所述电解质采用电解液。所述电解液包括电解质盐和溶剂。
在一些实施方式中，电解质盐可选自NaPF 6、NaClO 4、NaBCl 4、NaSO 3CF 3及Na(CH 3)C 6H 4SO 3中的一种或几种。
在一些实施方式中，溶剂可选自碳酸亚乙酯、碳酸亚丙酯、碳酸 甲乙酯、碳酸二乙酯、碳酸二甲酯、碳酸二丙酯、碳酸甲丙酯、碳酸乙丙酯、碳酸亚丁酯、氟代碳酸亚乙酯、甲酸甲酯、乙酸甲酯、乙酸乙酯、乙酸丙酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、丁酸甲酯、丁酸乙酯、1,4-丁内酯、环丁砜、二甲砜、甲乙砜及二乙砜中的至少一种。
在一些实施方式中，所述电解液还可选地包括添加剂。例如添加剂可以包括负极成膜添加剂、正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温或低温性能的添加剂等。
[隔离膜]
在一些实施方式中，二次电池中还包括隔离膜。本申请对隔离膜的种类没有特别的限制，可以选用任意公知的具有良好的化学稳定性和机械稳定性的多孔结构隔离膜。
在一些实施方式中，隔离膜的材质可选自玻璃纤维、无纺布、聚乙烯、聚丙烯及聚偏二氟乙烯中的至少一种。隔离膜可以是单层薄膜，也可以是多层复合薄膜，没有特别限制。在隔离膜为多层复合薄膜时，各层的材料可以相同或不同，没有特别限制。
在一些实施方式中，正极极片、负极极片和隔离膜可通过卷绕工艺或叠片工艺制成电极组件。
在一些实施方式中，二次电池可包括外包装。该外包装可用于封装上述电极组件及电解质。
在一些实施方式中，二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。二次电池的外包装也可以是软包，例如袋式软包。软包的材质可以是塑料，作为塑料，可列举出聚丙烯、聚对苯二甲酸丁二醇酯以及聚丁二酸丁二醇酯等。
本申请对二次电池的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。例如，图2是作为一个示例的方形结构的二次电池5。
在一些实施方式中，参照图3，外包装可包括壳体51和盖板53。其中，壳体51可包括底板和连接于底板上的侧板，底板和侧板围合形成容纳腔。壳体51具有与容纳腔连通的开口，盖板53能够盖设于 所述开口，以封闭所述容纳腔。正极极片、负极极片和隔离膜可经卷绕工艺或叠片工艺形成电极组件52。电极组件52封装于所述容纳腔内。电解液浸润于电极组件52中。二次电池5所含电极组件52的数量可以为一个或多个，本领域技术人员可根据具体实际需求进行选择。
电池模块和电池包
在一些实施方式中，二次电池可以组装成电池模块，电池模块所含二次电池的数量可以为一个或多个，具体数量本领域技术人员可根据电池模块的应用和容量进行选择。
图4是作为一个示例的电池模块4。参照图4，在电池模块4中，多个二次电池5可以是沿电池模块4的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个二次电池5进行固定。
可选地，电池模块4还可以包括具有容纳空间的外壳，多个二次电池5容纳于该容纳空间。
在一些实施方式中，上述电池模块还可以组装成电池包，电池包所含电池模块的数量可以为一个或多个，具体数量本领域技术人员可根据电池包的应用和容量进行选择。
图5和图6是作为一个示例的电池包1。参照图5和图6，在电池包1中可以包括电池箱和设置于电池箱中的多个电池模块4。电池箱包括上箱体2和下箱体3，上箱体2能够盖设于下箱体3，并形成用于容纳电池模块4的封闭空间。多个电池模块4可以按照任意的方式排布于电池箱中。
用电装置
另外，本申请还提供一种用电装置，所述用电装置包括本申请提供的二次电池、电池模块、或电池包中的至少一种。所述二次电池、电池模块、或电池包可以用作所述用电装置的电源，也可以用作所述用电装置的能量存储单元。所述用电装置可以包括移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能系统等，但不限于此。
作为所述用电装置，可以根据其使用需求来选择二次电池、电池模块或电池包。
图7是作为一个示例的用电装置。该用电装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该用电装置对二次电池的高功率和高能量密度的需求，可以采用电池包或电池模块。
作为另一个示例的装置可以是手机、平板电脑、笔记本电脑等。该装置通常要求轻薄化，可以采用二次电池作为电源。
实施例
以下，说明本申请的实施例。下面描述的实施例是示例性的，仅用于解释本申请，而不能理解为对本申请的限制。实施例中未注明具体技术或条件的，按照本领域内的文献所描述的技术或条件或者按照产品说明书进行。所用试剂或仪器未注明生产厂商者，均为可以通过市购获得的常规产品。
实施例1
1)正极极片的制备
将正极活性材料钠镍锰复合氧化物(NaNi 1/2Mn 1/2O 2)、导电剂乙炔黑、粘结剂聚偏二氟乙烯(PVDF)按92:5:3重量比在适量的N-甲基吡咯烷酮(NMP)中充分搅拌混合，使其形成均匀的正极浆料；将正极浆料涂覆于厚度为13μm的正极集流体铝箔上，在100℃下干燥后、经压制得到正极极片。
2)负极极片的制备
将负极活性材料颗粒、导电剂乙炔黑、粘结剂苯丙乳液、增稠剂羟甲基纤维素钠(CMC-Na)按94:1:4:1重量比在适量的去离子水中充分搅拌混合，使其形成均匀的负极浆料；将负极浆料涂覆于厚度为8μm的负极集流体铜箔的两个表面上，在100℃下干燥后、经压制得到负极极片。
其中，负极活性材料颗粒包括第一负极活性材料颗粒和第二负极活性材料颗粒，第一负极活性材料颗粒为不规则形状硬碳颗粒，第二负极活性材料颗粒为人造石墨颗粒，第一负极活性材料颗粒的中位粒径D50为5μm。基于负极活性材料颗粒的总质量，第一负极活性材 料颗粒的质量百分含量Q 1为70％，第二负极活性材料颗粒的质量百分含量Q 2为30％。负极极片的单面涂布重量CW为9mg/cm 2。
3)隔离膜
采用聚乙烯PE隔离膜(celgard)
4)电解液的制备
将等体积的碳酸乙烯酯(EC)及碳酸丙烯酯(PC)混合均匀，得到有机溶剂，然后将NaPF 6均匀溶解在上述有机溶剂中，得到电解液，其中NaPF 6的浓度为1mol/L。
5)电池的制备
将上述正极极片、隔离膜、负极极片按顺序叠好，加入上述电解液并封口，得到钠离子电池。
实施例2至6
基于实施例1的制备方法，调整Q 1、Q 2，制备实施例2至6的钠离子电池。
实施例7至14
基于实施例1的制备方法，调整第一负极活性材料颗粒的中位粒径D50以及Q 1、Q 2，制备实施例7至14的钠离子电池。
实施例15至16
基于实施例1的制备方法，调整第一负极活性材料颗粒的形貌以及Q 1、Q 2，制备实施例15至16的钠离子电池。
实施例17至19
基于实施例1的制备方法，调整第二负极活性材料的种类以及Q 1、Q 2，制备实施例17至19的钠离子电池。其中，实施例17所用的第二负极活性材料为天然石墨，实施例18所用的第二负极活性材料为石墨烯，实施例19所用的第二负极活性材料为天然石墨和石墨烯以1:1的质量比混合而成的材料。
实施例20至23
基于实施例1的制备方法，调整负极膜层的单面涂布重量以及Q 1、Q 2，制备实施例20至23的钠离子电池。
实施例24至27
基于实施例1的制备方法，调整第一负极活性材料的振实密度以及Q 1、Q 2，制备实施例24至27的钠离子电池。
实施例28至29
基于实施例1的制备方法，调整第二负极活性材料的振实密度以及Q 1、Q 2，制备实施例28至29的钠离子电池。
实施例30至34
基于实施例1的制备方法，调整Q 1、Q 2以及负极极片所用的粘结剂的种类，制备实施例30至34的钠离子电池。其中，实施例30的负极极片所用的粘结剂为丁苯橡胶SBR，实施例31的负极极片所用的粘结剂为氢化丁腈橡胶，实施例32的负极极片所用的粘结剂为偏氟二乙烯与六氟丙烯的共聚物，实施例33的负极极片所用的粘结剂为偏氟二乙烯与丙烯酸酯类的共聚物，实施例34的负极极片所用的粘结剂为聚四氟乙烯。
对比例1至3
基于实施例1的制备方法，调整负极活性材料颗粒的组成，制备对比例1至3的钠离子电池。其中，对比例1的负极活性材料颗粒由D50＝5μm的不规则形状硬碳颗粒组成，对比例2的负极活性材料颗粒由D50＝5μm的球形硬碳颗粒组成，对比例3的负极活性材料颗粒由D50＝5μm的类球形硬碳颗粒组成。
对比例4至5
基于实施例1的制备方法，调整Q 1、Q 2，制备对比例4至5的钠离子电池。
上述实施例1～34、对比例1～5的负极极片的相关制备参数如下述表1所示。其中，Q 1表示基于负极活性材料颗粒的总质量，第一负极活性材料颗粒的质量占比；Q 2表示基于负极活性材料颗粒的总质量，第二负极活性材料颗粒的质量占比；第一负极活性材料颗粒的振实密度ρ 1、D50、第二负极活性材料颗粒的振实密度ρ 2可按照本说明书上述记载的方法进行测试，PA可按照本说明书上述记载的方法进行计算。
上述实施例1～34、对比例1～5的负极极片的相关测试参数如下 表2所示。其中，CW、d 0、E、PD可按照本说明书上述记载的方法进行测试，P可按照本说明书上述记载的方法进行计算。
对实施例1的负极极片进行SEM测试，所得的SEM图如图8所示。
表1：实施例1～34与对比例1～5的负极极片的制备参数
序号 ρ 1/(g/cm 3) Q 1/％ D50/μm ρ 2/(g/cm 3) Q 2/％ PA/(g/cm 3)
实施例1 0.85 70 5 1.15 30 2.07
实施例2 0.85 75 5 1.15 25 2.07
实施例3 0.85 80 5 1.15 20 2.07
实施例4 0.85 85 5 1.15 15 2.07
实施例5 0.85 90 5 1.15 10 2.07
实施例6 0.85 95 5 1.15 5 2.07
实施例7 0.85 90 1 1.15 10 2.07
实施例8 0.85 90 3 1.15 10 2.07
实施例9 0.85 90 8 1.15 10 2.07
实施例10 0.85 90 10 1.15 10 2.07
实施例11 0.85 90 20 1.15 10 2.07
实施例12 0.85 90 30 1.15 10 2.07
实施例13 0.85 90 50 1.15 10 2.07
实施例14 0.85 90 60 1.15 10 2.07
实施例15 0.85 90 5 1.15 10 2.07
实施例16 0.85 90 5 1.15 10 2.07
实施例17 0.85 90 5 1.15 10 2.07
实施例18 0.85 90 5 0.4 10 2.07
实施例19 0.85 90 5 1.15 10 2.07
实施例20 0.85 90 5 1.15 10 2.07
实施例21 0.85 90 5 1.15 10 2.07
实施例22 0.85 90 5 1.15 10 2.07
实施例23 0.85 90 5 1.15 10 2.07
实施例24 0.4 90 5 1.15 10 2.07
实施例25 0.6 90 5 1.15 10 2.07
实施例26 1.0 90 5 1.15 10 2.07
实施例27 1.4 90 5 1.15 10 2.07
实施例28 0.85 85 5 0.7 15 2.07
实施例29 0.85 85 5 1.3 15 2.07
实施例30 0.85 85 5 1.15 15 2.07
实施例31 0.85 85 5 1.15 15 2.07
实施例32 0.85 85 5 1.15 15 2.07
实施例33 0.85 85 5 1.15 15 2.07
实施例34 0.85 85 5 1.15 15 2.07
对比例1 0.85 100 5 1.15 0 2.07
对比例2 0.85 100 5 1.15 0 2.07
对比例3 0.85 100 5 1.15 0 2.07
对比例4 0.85 50 5 1.15 50 2.07
对比例5 0.85 98 5 1.15 2 2.07
表2：实施例1～34与对比例1～5的负极极片的测试参数
序号 CW/(mg/cm 2) d 0/μm E/％ PD/(g/cm 3) P/％
实施例1 9 85.7 0.12 1.05 48.8％
实施例2 9 86.5 0.12 1.04 49.3％
实施例3 9 87.4 0.12 1.03 49.8％
实施例4 9 88.2 0.12 1.02 50.2％
实施例5 9 89.1 0.12 1.01 50.7％
实施例6 9 90.0 0.12 1.00 51.2％
实施例7 9 91.8 0.12 0.98 52.2％
实施例8 9 90.9 0.12 0.99 51.7％
实施例9 9 89.1 0.12 1.01 50.7％
实施例10 9 88.2 0.12 1.02 50.2％
实施例11 9 86.5 0.12 1.04 49.3％
实施例12 9 84.1 0.12 1.07 47.8％
实施例13 9 82.6 0.12 1.09 46.8％
实施例14 9 85.7 0.12 1.05 48.8％
实施例15 9 78.3 0.12 1.15 43.9％
实施例16 9 78.3 0.12 1.15 43.9％
实施例17 9 89.1 0.12 1.01 50.7％
实施例18 9 89.1 0.12 1.01 50.7％
实施例19 9 89.1 0.12 1.01 50.7％
实施例20 3 28.6 0.12 1.05 48.8％
实施例21 5 48.5 0.12 1.03 49.8％
实施例22 7 68.6 0.12 1.02 50.2％
实施例23 13 132.7 0.12 0.98 52.2％
实施例24 9 91.8 0.12 0.98 52.2％
实施例25 9 90.0 0.12 1.00 51.2％
实施例26 9 89.1 0.12 1.01 50.7％
实施例27 9 88.2 0.12 1.02 50.2％
实施例28 9 89.1 0.12 1.01 50.7％
实施例29 9 89.1 0.12 1.01 50.7％
实施例30 9 95.7 0.9 0.94 54.1％
实施例31 9 89.1 0.12 1.01 50.4％
实施例32 9 89.1 0.12 1.01 50.8％
实施例33 9 89.1 0.12 1.01 50.8％
实施例34 9 89.1 0.12 1.01 50.8％
对比例1 9 105.9 1.6 0.85 58.6％
对比例2 9 90.0 0.3 1.00 51.2％
对比例3 9 91.8 0.3 0.98 51.2％
对比例4 9 81.8 0.12 1.10 46.4％
对比例5 9 103.4 1.5 0.87 57.6％
另外，将上述实施例1～34和对比例1～5中得到的钠离子电池进行性能测试。测试结果如下表3所示。
(1)能量密度测试
在25℃下，以0.33C倍率恒流充电至电压为4.2V，之后以4.2V恒压充电至电流为0.05C，此时二次电池达到满充状态，之后静置5min，以0.33C倍率恒流放电至电压为2.5V，再静置5min，记录二次电池0.5C倍率恒流放电时的容量和电压平台，最后测量二次电池的质量。
二次电池的能量密度(Wh/kg)＝(二次电池0.33C倍率恒流放电时的容量×二次电池0.33C倍率恒流放电时的电压平台)/二次电池的质量。
(2)循环寿命测试
25℃下，将二次电池以1/3C恒流充电至4.2V，再以4.2V恒定电压充电至电流为0.05C，搁置5min，再以1/3C放电至2.8V，所得容量记为初始容量C 0。对上述同一个电池重复以上步骤，并同时记录循环第n次后电池的放电容量C n，则每次循环后电池容量保持率P n＝C n/C 0*100％，以P n≤80％时对应的最小n值作为二次电池的循环寿命。
表3：实施例1～34与对比例1～5的性能测试结果
序号 能量密度/(Wh/kg) 循环寿命/cycles
实施例1 112 1902
实施例2 112 1911
实施例3 113 1912
实施例4 113 1900
实施例5 114 1984
实施例6 114 1978
实施例7 113.5 1650
实施例8 113.5 1866
实施例9 114 1900
实施例10 114 1901
实施例11 114.5 1904
实施例12 114.5 1811
实施例13 115 1764
实施例14 115 1065
实施例15 117 1795
实施例16 117 1790
实施例17 114 1997
实施例18 114 1980
实施例19 114 1998
实施例20 40 1993
实施例21 60 1996
实施例22 95 1992
实施例23 140 1805
实施例24 113.5 1945
实施例25 114 1954
实施例26 114 1930
实施例27 114.5 1923
实施例28 114 1941
实施例29 114 1925
实施例30 114 1911
实施例31 114 1797
实施例32 114 1691
实施例33 114 1696
实施例34 114 1593
对比例1 84 1021
对比例2 113 1322
对比例3 113 1209
对比例4 30 589
对比例5 84 1330
综合实施例1至34可知，负极膜层中包括第一负极活性材料颗粒和第二负极活性材料颗粒，且第一负极活性材料颗粒和第二负极活性材料颗粒满足本申请的条件时，能够使得负极膜层具备高压实密度和合适的参数P，并使得钠离子电池兼具高能量密度和长循环寿命。如图8所示，第二负极活性材料颗粒能够填充至第一负极活性材料颗粒之间的空隙中或在第一负极活性材料颗粒表面，并在冷压过程中发挥滑移功能。由此，负极膜层能够具备高压实密度
具体地，综合实施例1至6可知，其他条件相同时，第一负极活性材料颗粒的含量越高，第二负极活性材料颗粒的含量越低，钠离子电池的能量密度越高；第一负极活性材料颗粒的含量越低，第二负极活性材料颗粒的含量越高，负极膜层的压实密度越高。压实密度过高，可能影响负极膜层的电解液浸润性能；压实密度过低，可能影响负极膜层的电子及钠离子的传输性能。因此，需要将第一负极活性材料颗粒的含量和第二负极活性材料颗粒的含量控制在合适的范围内。
综合实施例5、7至14可知，其他条件相同时，随着第一负极活性材料颗粒的中位粒径D50的增大，钠离子电池的循环寿命呈先增大后减小的趋势。这可能与第一负极活性材料颗粒表面的活性位点数量和比表面积有关。
综合实施例5、15至16可知，其他条件相同时，相对于实施例5，实施例15至16以球形硬碳颗粒或类球形硬碳颗粒作为第一负极活性材料颗粒，虽然负极膜层具备更高的压实密度，但是对应的钠离子电池的循环寿命较短。这可能是因为实施例15至16的负极膜层的电解液浸润性能相对于实施例5的负极膜层有所下降。
综合实施例5、17至19可知，具有层状结构的第二负极活性材料颗粒均能够发挥滑移功能，从而提升负极膜层的压实密度。
综合实施例5、20至23可知，其他条件相同时，负极膜层的单面涂布重量越高，负极膜层的压实密度越低。这可能是因为负极膜层较厚时，在冷压过程中，第二负极活性材料在压力的作用下发 挥的滑移功能有限。
综合实施例5、24至27可知，其他条件相同时，随着第一负极活性材料颗粒的振实密度的提高，负极膜层的压实密度也随之增大，钠离子电池的循环寿命随之缩短。这可能是因为：随着第一负极活性材料颗粒振实密度的提升，第一负极活性材料颗粒内部的吸附孔数量减少，从而允许负极膜层具备更高的压实密度。相应地，随着第一负极活性材料颗粒内部的吸附孔数量减少，第一负极活性材料颗粒内部的储钠空间也减少，因此钠离子电池的循环寿命随之缩短。
综合实施例5、28至29可知，第二负极活性材料颗粒的振实密度在合适的范围内，均能够使得负极膜层具备高压实密度，并使得钠离子电池具备较高的压实密度和较长的循环寿命。
综合实施例5、30至34可知，相较于常规的负极粘结剂SBR，柔性粘结剂能够提升负极膜层的压实密度，改善钠离子电池的长期循环性能，提升钠离子电池的能量密度和循环寿命。
而相对于此，对比例1至3仅使用了中位粒径为5μm的、不同形貌的硬碳颗粒作为负极活性材料颗粒，负极膜层的压实密度较低。由此，负极极片不仅具有较低的能量密度，而且还具有较长的电子和钠离子传输路径，因此，钠离子电池的能量密度和循环寿命较低。对比例4和5中虽然利用了第一负极活性材料颗粒和具有层状结构的第二负极活性材料颗粒进行复配，但是，对比例4中，第一负极活性材料颗粒的含量低于本申请限定的范围，钠离子电池的能量密度显著降低；对比例5中，第一负极活性材料颗粒的含量高于本申请限定的范围，第二负极活性材料颗粒对负极膜层的压实密度的提升作用有限，因此，对比例5的钠离子电池的能量密度和循环寿命也不理想。
需要说明的是，本申请不限定于上述实施方式。上述实施方式仅为示例，在本申请的技术方案范围内具有与技术思想实质相同的构成、发挥相同作用效果的实施方式均包含在本申请的技术范围内。此外，在不脱离本申请主旨的范围内，对实施方式施加本领 域技术人员能够想到的各种变形、将实施方式中的一部分构成要素加以组合而构筑的其它方式也包含在本申请的范围内。

Claims (15)

  1. 一种负极极片，包括：
    负极集流体；以及
    负极膜层，所述负极膜层位于所述负极集流体的至少一个表面上，所述负极膜层包括第一负极活性材料颗粒和第二负极活性材料颗粒，所述第一负极活性材料颗粒包括多个吸附孔，所述第一负极活性材料颗粒的振实密度为0.4g/cm 3～1.4g/cm 3，可选为0.6g/cm 3～1.0g/cm 3；所述第二负极活性材料颗粒具有层状结构，所述第二负极活性材料颗粒的振实密度为0.05g/cm 3～1.5g/cm 3。
    其中，基于所述第一负极活性材料颗粒和第二负极活性材料颗粒的总质量，所述第一负极活性材料颗粒的质量百分含量为70％～95％，可选为80％～95％；所述第二负极活性材料颗粒的质量百分含量为5％～30％，可选为5％～10％，
    所述负极膜片的压实密度PD满足：0.8g/cm 3≤PD≤1.3g/cm 3，可选地，1.0g/cm 3≤PD≤1.2g/cm 3。
  2. 根据权利要求1所述的负极极片，其中，所述第一负极活性材料颗粒的中位粒径D50为1μm～50μm，可选为5μm～10μm。
  3. 根据权利要求1或2所述的负极极片，其中，所述负极集流体的延展率E满足：0.1％≤E≤0.2％，可选地，0.1％≤E≤0.15％。
  4. 根据权利要求1-3中任一项所述的负极极片，其中，所述负极膜层的单面涂布重量CW为2mg/cm 2～13mg/cm 2。
  5. 根据权利要求1-4中任一项所述的负极极片，其中，所述负极膜层满足：30％≤P≤60％，可选地，45％≤P≤55％，
    其中，P＝[1-(CW)/(d*PA)]*100％，d＝d 0/(1+E)，CW表示所述负极膜层的单面涂布重量，PA表示单面所述负极膜层的真密度，E表示所述负极集流体的延展率，d 0表示单面所述负极膜层的厚度。
  6. 根据权利要求1-5中任一项所述的负极极片，其中，所述第一负极活性材料颗粒选自硬碳、软碳、中间相碳微球中的一种或几种； 所述第二负极活性材料颗粒选自人造石墨、天然石墨、石墨烯中的一种或几种。
  7. 根据权利要求1-6中任一项所述的负极极片，其中，所述第一负极活性材料颗粒包括不规则形状第一负极活性材料颗粒、球形第一负极活性材料颗粒或类球形第一负极活性材料颗粒中的一种或几种。
  8. 根据权利要求1-7中任一项所述的负极极片，其中，所述第一负极活性材料颗粒包括不规则形状硬碳颗粒、球形硬碳颗粒或类球形硬碳颗粒中的一种或几种。
  9. 根据权利要求8所述的负极极片，其中，单面所述负极膜层的压实密度PD满足：1.0g/cm 3≤PD≤1.2g/cm 3；
    所述负极膜层满足：30％≤P≤60％，可选地，45％≤P≤55％，其中，P＝[1-(CW)/(d*PA)]*100％，d＝d 0/(1+E)，CW表示所述负极膜层的单面涂布重量，PA表示单面所述负极膜层的真密度，E表示所述负极集流体的延展率，d 0表示单面所述负极膜层的厚度。
  10. 根据权利要求1-9中任一项所述的负极极片，其中，所述负极膜层还包括柔性粘结剂，所述柔性粘结剂包括苯丙乳液、偏氟二乙烯与四氟乙烯的共聚物、偏氟二乙烯与六氟丙烯的共聚物、偏氟二乙烯与丙烯酸酯类的共聚物、聚四氟乙烯、丁腈橡胶、氢化丁腈橡胶的一种或几种。
  11. 根据权利要求1-10中任一项所述的负极极片，其中，基于所述负极膜层的总质量，所述负极膜层包括：80wt％～97wt％的负极活性材料颗粒、0wt％～5wt％的导电剂、2wt％～10wt％的粘结剂以及0.5wt％～5wt％的分散剂，其中，所述负极活性材料颗粒包括所述第一负极活性材料颗粒和所述第二负极活性材料颗粒。
  12. 一种二次电池，包括根据权利要求1-11中任一项所述的负极极片。
  13. 一种电池模块，包括权利要求12所述的二次电池。
  14. 一种电池包，包括权利要求13所述的电池模块。
  15. 一种用电装置，包括选自权利要求12所述的二次电池、权利要求13所述的电池模块或权利要求14所述的电池包中的至少一种。
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