WO2020177760A1 - 负极、二次电池和包含二次电池的装置 - Google Patents

负极、二次电池和包含二次电池的装置 Download PDF

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WO2020177760A1
WO2020177760A1 PCT/CN2020/078166 CN2020078166W WO2020177760A1 WO 2020177760 A1 WO2020177760 A1 WO 2020177760A1 CN 2020078166 W CN2020078166 W CN 2020078166W WO 2020177760 A1 WO2020177760 A1 WO 2020177760A1
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active material
negative electrode
material layer
secondary battery
battery
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PCT/CN2020/078166
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English (en)
French (fr)
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郭明奎
王天生
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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 EP22168100.0A priority Critical patent/EP4047681B1/en
Priority to EP20766175.2A priority patent/EP3800706B1/en
Publication of WO2020177760A1 publication Critical patent/WO2020177760A1/zh
Priority to US17/150,096 priority patent/US11600816B2/en
Priority to US18/103,531 priority patent/US20230170474A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1393—Processes of manufacture of electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • 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
    • 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
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • 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 belongs to the technical field of energy storage devices, and specifically relates to a negative electrode, a secondary battery, and a device containing the secondary battery.
  • the secondary battery represented by the lithium ion secondary battery completes the charging and discharging process through the reciprocating insertion and extraction of active ions between the positive and negative active materials, and has become an important energy source.
  • the market demand for power-type secondary batteries will show explosive growth. While this brings opportunities for the development of the secondary battery industry, it also poses a severe challenge to the cycle life of the secondary battery. In order to enhance the market competitiveness of secondary batteries, it is indeed necessary to increase their cycle life.
  • the design of the negative electrode will directly affect the performance of the secondary battery.
  • the current negative electrode usually has a uniform negative electrode film on one or both sides of the current collector.
  • the inventor’s research has found that the negative electrode swells during the battery cycle, resulting in insufficient electrolyte infiltration, which causes the battery’s capacity to rapidly decay.
  • the inventors further found that by reducing the tightness of the active material particles in the negative electrode to improve the liquid absorption capacity of the negative electrode, the cycle life of the secondary battery can be improved. However, this will result in an increase in the thickness of the negative electrode, which will disadvantageously reduce the energy density of the secondary battery. In addition, there may also be a problem of poor contact between the active material particles, which affects the electron conduction of the negative electrode, thereby reducing the dynamic performance of the secondary battery.
  • the electrode can maintain a sufficient electrolyte content during the cycle, so that although the cycle life of the secondary battery can be improved to a certain extent, a higher content is added
  • the electrolyte will increase the internal pressure of the battery, which will cause the problem of battery cycle expansion and affect the safety performance of the battery.
  • using more electrolyte also increases battery cost.
  • the inventor has conducted a lot of research to improve the traditional negative electrode, so that the negative electrode can increase its own liquid absorption and storage capacity while having good accumulation performance of active material particles, so as to obtain a high A secondary battery with energy density and cycle life.
  • a negative electrode which includes:
  • the first active material and the second active material are each independently oval-like particles with through holes and/or blind holes, and the average pore diameter of the first active material is larger than the average of the second active material Aperture.
  • a second aspect of the present application provides a secondary battery including the negative electrode according to the first aspect of the present application.
  • a third aspect of the present application provides a device including the secondary battery according to the second aspect of the present application.
  • the negative electrode of the present application adopts a composite layer structure of the negative electrode film, wherein the first active material in the first active material layer and the second active material in the second active material layer have through holes and/or Oval-shaped particles with blind holes, and the average pore diameter of the first active material is larger than the average pore diameter of the second active material, which enables the negative electrode to have a good accumulation of active material particles while greatly increasing its own liquid absorption Liquid storage capacity. Therefore, the negative electrode of the present application enables the secondary battery using it to increase the cycle life on the premise of higher energy density.
  • the device of the present application includes the secondary battery provided by the present application, and therefore has at least the same advantages as the secondary battery.
  • FIG. 1 is a schematic diagram of a negative electrode structure provided by some embodiments of the application.
  • Fig. 2 is a schematic diagram of an embodiment of a secondary battery.
  • Fig. 3 is an exploded view of Fig. 2.
  • Fig. 4 is a schematic diagram of an embodiment of a battery module.
  • Fig. 5 is a schematic diagram of an embodiment of a battery pack.
  • Fig. 6 is an exploded view of Fig. 5.
  • Fig. 7 is a schematic diagram of an embodiment of a device in which a secondary battery is used as a power source.
  • any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and any upper limit may be combined with any other upper limit to form an unspecified range.
  • every point or single value between the end points of the range is included in the range. Therefore, each point or single numerical value can be used as its own lower limit or upper limit in combination with any other point or single numerical value or in combination with other lower or upper limits to form an unspecified range.
  • the negative electrode includes: a negative electrode current collector; a first active material layer close to the negative electrode current collector, the first active material layer containing a first active material; and a first active material layer disposed on the first active material layer away from the negative electrode current collector
  • the second active material layer on the surface of the second active material layer contains a second active material; the first active material and the second active material are each independently oval-like with through holes and/or blind holes Shaped particles, and the average pore diameter of the first active material is larger than the average pore diameter of the second active material.
  • Fig. 1 is a schematic diagram of the structure of a negative electrode as an example.
  • the negative electrode includes a negative electrode current collector 521, a first active material layer 522 formed on the negative electrode current collector 521, and a second active material layer 523 formed on the surface of the first active material layer 522 away from the negative electrode current collector 521.
  • the composite layer structure negative electrode membrane including the first active material layer and the second active material layer can be formed on one side surface of the negative electrode current collector, or can be formed on two opposite sides of the negative electrode current collector in the thickness direction of the negative electrode current collector. surface.
  • through hole refers to a hole that penetrates the active material particles.
  • blind hole refers to a hole that extends inward to a predetermined depth from the surface of the active material particle, but does not penetrate the active material particle.
  • the first active material and the second active material are each independently oval-like particles with through holes and/or blind holes, in other words, the first active material is an oval-like particle, and it has The porous structure includes one or more of through holes and blind holes; the second active material is an oval-like particle, and it has a porous structure including one or more of through holes and blind holes.
  • the selection of the morphology and pore structure of the first active material and the selection of the morphology and pore structure of the second active material are independent of each other.
  • Exemplary test methods for the average pore diameter of active materials can refer to the standard GB/T19587-2017 "Gas adsorption BET method to determine the specific surface area of solid materials", GB/T21650.2-2008 mercury intrusion method and gas adsorption method to determine the pore size distribution of solid materials and Porosity-Part 2: Gas adsorption analysis of mesopores and macropores.
  • the American Micromeritics TriStar II 3020 instrument can be used to test the average pore size of the active material particles.
  • the inventor found that the negative electrode adopts a composite layer structure of the negative electrode film, and the first active material in the first active material layer and the second active material in the second active material layer use elliptical particles, thus It can improve the accumulation performance between particles, make good contact between particles, and at the same time form pores suitable for electrolyte infiltration.
  • the first active material and the second active material also have a porous structure including one or more of through holes and blind holes, and the second active material layer far from the negative electrode current collector adopts a second active material with a smaller average pore diameter
  • the first active material layer close to the negative electrode current collector adopts the first active material with a larger average pore size. This combined structural feature can greatly increase the liquid absorption and liquid storage capacity of the negative electrode itself.
  • the negative electrode of the present application can significantly alleviate the cycle deterioration caused by insufficient electrolyte infiltration on the premise that the secondary battery adopting it has a higher energy density, and improve the cycle life of the battery. More preferably, the negative electrode of the present application not only maintains high electronic conductivity, but also improves its active ion transport performance, so that the battery can also have excellent dynamic performance.
  • the inventor also found that when the negative electrode adopts a composite layer structure of the negative electrode membrane, the problem of cracking of the active material layer can also be effectively improved.
  • the reason is that two or more active material layers are coated layer by layer, which reduces the internal stress of the active material layer during the drying process of the negative electrode, thereby solving the problem of cracking caused by the increase in coating weight.
  • a continuous conductive network is formed in the negative electrode membrane, which can further improve the cycle life and dynamic performance of the battery.
  • the porosity of the first active material is greater than the porosity of the second active material.
  • the inventor found that the first active material used in the first active material layer of the inner layer has a larger average pore size and a higher porosity, so that the first active material layer has stronger liquid absorption and retention for the electrolyte. .
  • the second active material used in the second active material layer is more dense, with a smaller average pore size and lower porosity, which can ensure that the negative electrode has a higher energy density, and at the same time further improve the negative electrode's liquid storage capacity.
  • the negative electrode can maintain a relatively high electrolyte retention when its volume expands during the cycle. Therefore, the use of the negative electrode can further improve the cycle performance of the battery under the premise of a higher energy density. More preferably, the dynamic performance of the battery can also be improved.
  • the average particle size D v 50 is the particle size corresponding to the cumulative volume distribution percentage of particles reaching 50%.
  • the particles with a larger average particle size D v 50 are more loosely arranged, which can increase the liquid storage rate of the pole piece, but will affect the electronic conductivity between the particles.
  • the average particle size D v 50 of the first active material is preferably 8 ⁇ m-18 ⁇ m, more preferably 10 ⁇ m-16 ⁇ m.
  • the D v 50 of the first active material is in an appropriate range, which can improve the negative electrode’s ability to absorb and store liquid, and at the same time make the negative electrode have higher active ion and electron transport performance, so that the battery has a higher cycle life and power Learn performance.
  • the first active material has an appropriate D v 50, which can also increase the proportion of the active material in the first active material layer per unit volume, thereby helping to increase the energy density of the battery.
  • the average particle size D v 50 of the second active material is preferably 5 ⁇ m-15 ⁇ m, more preferably 6 ⁇ m-12 ⁇ m.
  • the second active material layer adopts a second active material with an appropriate D v 50, which can improve the liquid retention capacity of the negative electrode and at the same time increase the energy density of the negative electrode.
  • the smaller the D v 50 of the second active material is the more fully the contact with the electrolyte is, the more favorable the charge exchange between the active ions and the electrons, and the faster the battery is charged.
  • the D v 50 of the second active material is within an appropriate range, which is also conducive to preparing an active material layer with higher consistency, thereby improving the cycle life of the battery.
  • the negative electrode simultaneously satisfies that the average particle size D v 50 of the first active material is 8 ⁇ m-18 ⁇ m, and the average particle size D v 50 of the second active material is 5 ⁇ m-15 ⁇ m.
  • the size of the active material particles of the first active material layer and the second active material layer have a reasonable combination, which can maintain the stability of the particle accumulation structure during the circulation process, thereby not only preventing the particles between adjacent active material layers from mixing It can also maintain the proper pore structure between the active material particles, thereby effectively exerting the effect of the composite layer structure of the negative electrode membrane on the negative electrode liquid absorption and storage capacity and active ion transport performance. Therefore, the battery adopting the negative electrode can have higher cycle performance and dynamic performance.
  • the electrolyte is also easy to fully contact with the active material with large pore size, which facilitates the deintercalation of active ions and improves the dynamic performance.
  • the use of an active material with a smaller average pore size is beneficial to increase the proportion of the active material per unit volume of the active material layer, thereby increasing the energy density of the negative electrode.
  • the average pore size of the first active material may be 60nm-150nm, preferably 70nm-140nm, more preferably 80nm-120nm.
  • the average pore diameter of the first active material is within an appropriate range, which can better improve the liquid absorption capacity and dynamic performance of the negative electrode.
  • the average pore size of the second active material may be 5nm-35nm, preferably 10nm-30nm, more preferably 15nm-25nm. Within an appropriate range of the average pore diameter of the second active material, the negative electrode can have a higher liquid holding capacity while increasing the energy density.
  • the average pore size of the first active material may be 60nm-150nm, preferably 70nm-140nm, more preferably 80nm-120nm; and the average pore size of the second active material may be 5nm-35nm, preferably 10nm-30nm, more preferably 15nm-25nm.
  • the first active material layer close to the negative electrode current collector selects the first active material with a larger average pore size, which is beneficial to use the capillary action to make the electrolyte quickly infiltrate the negative electrode, improve the liquid absorption rate of the negative electrode piece, and at the same time, keep away from the negative electrode current collector.
  • the second active material layer selects a second active material with a smaller average pore size, and the smaller porosity of the second active material layer helps improve the liquid storage capacity of the negative electrode.
  • the elliptical particles are also spherical particles, and the outer edge surface of the particles is roughly a three-dimensional curved surface.
  • the ratio of the length of the short diameter to the length of the long diameter of the oval-shaped active material particles is ⁇ 1. The closer the value is to 1, the more round the particle shape is, and the greater the shear force between particles. The smaller the ratio of the length of the short diameter to the length of the long diameter, the more the shape of the pellets tends to be elliptical, and the easier it is for the particles to fit into each other.
  • the ratio of the length of the short diameter to the length of the long diameter of the first active material may be 0.4-1, preferably 0.5-1, more preferably 0.6-0.9.
  • the ratio of the length of the short diameter to the length of the long diameter of the first active material is within an appropriate range, which can make good contact between the particles, ensure the higher electronic conductivity of the negative electrode, and increase the porosity of the first active material layer, thereby increasing The amount of electrolyte infiltration of the negative electrode.
  • the ratio of the length of the short diameter to the length of the long diameter of the second active material is 0.3-1, preferably 0.4-0.8.
  • the ratio of the length of the short diameter to the length of the long diameter of the first active material is within an appropriate range, which enables the formation of pores between the particles suitable for electrolyte infiltration, and increases the compactness of the particles, thereby improving the electrolyte retention and energy of the negative electrode density.
  • the negative electrode simultaneously satisfies: the ratio of the short diameter to the long diameter of the first active material is 0.5-1, preferably 0.6-0.9; and the ratio of the short diameter to the long diameter of the second active material is 0.3 -1, preferably 0.4-0.8. Selecting an active material with a larger ratio of short diameter to long diameter to be placed on the negative current collector, and selecting an active material with a small ratio of short diameter to long diameter to be placed on the first active material layer is beneficial Further improve the liquid absorption and storage capacity of the negative electrode.
  • the specific surface area of the active material particles the stronger the adsorption capacity of the electrolyte.
  • the specific surface area of the first active material is greater than the specific surface area of the second active material. This helps to improve the battery's liquid absorption capacity and liquid storage capacity.
  • the specific surface area of the first active material is preferably 6.9m 2 /g-9.6m 2 /g, more preferably 7.5m 2 /g-9.1m 2 /g, especially preferably 8.0m 2 /g- 8.7m 2 /g.
  • the second active substance is preferably a specific surface area of 1.3m 2 /g-3.1m 2 / g, more preferably 2.0m 2 /g-2.5m 2 / g.
  • the apparent density value is the ratio of the mass of the material to the volume of water discharged by the material. The smaller the apparent density value, the larger the volume of open pores contained in the material, and the stronger the liquid absorption and storage capacity.
  • the apparent density value is in the proper range, which is also conducive to making the battery obtain a higher energy density.
  • the apparent density of the first active material is preferably 0.5 g/cm 3 -1.2 g/cm 3 , more preferably 0.6 g/cm 3 -1.0 g/cm 3 .
  • the apparent density of the second active material is preferably 1.5 g/cm 3 -2.0 g/cm 3 , more preferably 1.6 g/cm 3 -1.9 g/cm 3 .
  • the area density of each active material layer is within an appropriate range, which can further improve the energy density and cycle life of the battery. In addition, it also helps to improve the uniformity of the negative electrode.
  • the area density of each active material layer is equal to the mass of the active material layer divided by its area.
  • the surface density of the first active material layer is preferably 20g / m 2 -100g / m 2 , more preferably 30g / m 2 -90g / m 2 .
  • the surface density of the second active material layer is preferably 20g / m 2 -100g / m 2 , more preferably 30g / m 2 -90g / m 2 .
  • the inventor further researched and found that when the ratio of the areal density of the first active material layer to the areal density of the second active material layer is 0.3-3, the energy density and cycle performance of the battery can be further improved. More preferably, the ratio of the areal density of the first active material layer to the areal density of the second active material layer is 0.5-2.
  • the porosity of the negative electrode membrane of the composite layer structure can be 40.1%-67.9%, for example, 44.5%, 45.4%, 50%, 55%, 59.9%, 60.5%, 62.5%, 64.5%, 65.2 %, 66.5%, 67.9%, etc.
  • the negative electrode membrane of the composite layer structure can have an appropriate porosity.
  • the secondary battery using the negative electrode can simultaneously take into account higher energy density and cycle performance.
  • the second active material and the first active material are each independently selected from materials capable of receiving and extracting lithium ions.
  • Materials that can receive and extract lithium ions can include one or more of soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon-oxygen compounds, silicon-carbon composites, lithium titanate, and metals that can form alloys with lithium. kind.
  • the second active material and the first active material are both artificial graphite.
  • An exemplary preparation method of artificial graphite as the second active material includes: uniformly mixing artificial graphite particles with an intercalating agent that can decompose and release gas, and the mass ratio of the intercalating agent in the resulting mixture is greater than 0% and less than or equal to 5 %; Carry out the intercalation reaction at about 100°C for 1h ⁇ 3h, such as 2h; make the intercalation agent be embedded between the graphite particles; then transfer the reaction product to the sintering furnace, and sinter at 800°C-1000°C in a protective atmosphere for 8h- 10h, you can get the active material particles.
  • the intercalating agent can be selected from, but not limited to, one or more of lithium carbonate, sodium carbonate, potassium carbonate, ammonium nitrate, lithium chlorate, ammonium oxalate, and acetic acid.
  • a similar method can be used to prepare artificial graphite as the first active material, wherein the first active material can obtain a larger average pore size by increasing the amount of intercalation agent that can decompose and release gas. Furthermore, the first active material can also obtain a higher porosity. For example, in a mixture of artificial graphite particles and an intercalating agent that can decompose and release gas, the mass ratio of the intercalating agent may be 15%-35%.
  • the negative electrode current collector can be made of metal foil, carbon-coated metal foil or porous metal plate, and preferably copper foil.
  • the first active material layer and the second active material layer may each independently include a conductive agent.
  • the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the first active material layer and the second active material layer may each independently include a binder.
  • This application does not specifically limit the type of binder, and can be selected according to actual needs.
  • the binder may be one or more of styrene-butadiene rubber (SBR), styrene-butadiene rubber (SBCs), and water-based acrylic resin.
  • the first active material layer and the second active material layer may each independently include a thickening agent, such as sodium carboxymethyl cellulose (CMC-Na).
  • a thickening agent such as sodium carboxymethyl cellulose (CMC-Na).
  • CMC-Na sodium carboxymethyl cellulose
  • this application is not limited to this, and this application can also use other materials that can be used as a thickener for the negative electrode.
  • the average particle size D v 50 of the active material can be conveniently measured with a laser particle size analyzer, such as the Mastersizer 3000 laser particle size analyzer of Malvern Instruments Co., Ltd., UK.
  • a laser particle size analyzer such as the Mastersizer 3000 laser particle size analyzer of Malvern Instruments Co., Ltd., UK.
  • the specific surface area of the active material is a well-known meaning in the art, and it can be measured by instruments and methods known in the art. For example, it can be measured by the nitrogen adsorption specific surface area analysis test method and calculated by the BET (Brunauer Emmett Teller) method, where nitrogen
  • the adsorption specific surface area analysis test can be performed by the TriStar II specific surface and pore analyzer of Micromeritics, USA. The test can refer to GB/T 19587-2004.
  • the apparent density of the active material can be measured using instruments and methods known in the art. For details, please refer to the national standard GB/T24586-2009 for determination of apparent density, true density and porosity of iron ore.
  • true volume particle weight/true density
  • the true density can be measured by a true density tester (such as AccuPyc II 1340).
  • the ratio of the length of the short axis to the length of the long axis of the active material can be determined by using instruments and methods known in the art.
  • a second aspect of the present application provides a secondary battery, which includes a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the negative electrode is the negative electrode according to the first aspect of the present application.
  • the positive electrode includes a positive electrode current collector, a positive electrode membrane provided on at least one surface of the positive electrode current collector and including a positive electrode active material.
  • the specific type and composition of the positive pole piece are not specifically limited, and can be selected according to actual needs.
  • the positive electrode active material is selected from, but not limited to, layered lithium transition metal oxides with the chemical formula Li a M 1-x M'x O 2 and the chemical formula LiFe y Mn 1-yz M" z PO 4 / One or a mixture of C b lithium iron phosphate materials, where 0.9 ⁇ a ⁇ 1.1, 0 ⁇ x ⁇ 0.1, 0.1 ⁇ y ⁇ 0.9, 0 ⁇ z ⁇ 0.9, b ⁇ 0, M is Co, At least one of Mn and Ni, M'is one of Al, Mg, B, Zr, Si, Ti, Cr, Fe, V, Cu, Ca, Zn, Nb, Mo, Sr, Sb, W, and Bi Or several, M" is one or several of Cr, Mg, Ti, Al, Zn, W, Nb, Zr.
  • the positive electrode membrane may optionally include a conductive agent.
  • a conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the positive electrode membrane may optionally include a binder.
  • a binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), and polyvinyl alcohol (PVA).
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • EVA ethylene-vinyl acetate copolymer
  • PVA polyvinyl alcohol
  • the positive electrode current collector can be a metal foil, a carbon-coated metal foil or a porous metal plate, preferably an aluminum foil.
  • the electrolyte includes a solvent and a solute.
  • the specific type and composition of the solvent and the solute are not specifically limited, and can be selected according to actual needs.
  • the solvent can be selected from one or more of organic carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, etc., which are electrically insulating but can conduct ions .
  • the solute can be selected from one or more lithium salts of LiPF 6 , LiBF 4 , LiBOB, LiAsF 6 , Li(CF 3 SO 2 ) 2 N, LiCF 3 SO 3 , and LiClO 4 .
  • the separator is interposed between the positive pole piece and the negative pole piece for isolation.
  • the type of the separator is not specifically limited, and it can be any separator material used in existing batteries.
  • Fig. 2 shows a secondary battery 5 with a square structure as an example.
  • the secondary battery may include an outer package for packaging the positive pole piece, the negative pole piece, the separator and the electrolyte.
  • the outer packaging of the secondary battery may be a soft bag, such as a pouch type soft bag.
  • the material of the soft bag can be plastic, for example, it can include one or more of polypropylene PP, polybutylene terephthalate PBT, polybutylene succinate PBS, and the like.
  • the outer packaging of the secondary battery may also be a hard shell, such as a hard plastic shell, aluminum shell, steel shell, and the like.
  • the outer package may include a housing 51 and a cover 53.
  • the housing 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity.
  • the housing 51 has an opening communicating with the containing cavity, and a cover plate 53 can cover the opening to close the containing cavity.
  • the positive pole piece, the negative pole piece and the separator may be laminated or wound to form a laminated structure electrode assembly or a wound structure electrode assembly 52.
  • the electrode assembly 52 is packaged in the receiving cavity.
  • the electrolyte is infiltrated in the electrode assembly 52.
  • the number of electrode assemblies 52 included in the secondary battery 5 can be one or several, which can be adjusted according to requirements.
  • the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.
  • Fig. 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. Of course, it can also be arranged in any other manner. Furthermore, the plurality of secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may further include a housing having an accommodation space, and a plurality of secondary batteries 5 are accommodated in the accommodation space.
  • the above-mentioned battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.
  • FIGS 5 and 6 show the battery pack 1 as an example.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box.
  • the battery box includes an upper box body 2 and a lower box body 3.
  • the upper box body 2 can be covered on the lower box body 3 and forms a closed space for accommodating the battery module 4.
  • Multiple battery modules 4 can be arranged in the battery box in any manner.
  • a device in a third aspect of the present application, includes the secondary battery of the second aspect of the present application.
  • the secondary battery can be used as a power source of the device, and can also be used as an energy storage unit of the device.
  • the device can be, but is not limited to, mobile devices (such as mobile phones, laptop computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf Vehicles, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
  • the device can select a secondary battery, battery module, or battery pack according to its usage requirements.
  • Fig. 7 is a device as an example.
  • the device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.
  • a battery pack or battery module can be used.
  • the device may be a mobile phone, a tablet computer, a notebook computer, etc.
  • the device is generally required to be thin and light, and a secondary battery can be used as a power source.
  • the batteries of Examples 1-19 and Comparative Examples 1 and 2 were prepared according to the following methods.
  • the linear speed of stirring is controlled at 4-10m/min, and the stirring and mixing time is 60-150min, until the system is uniform, and the cathode slurry is obtained;
  • the positive pole pieces are obtained by drying, cold pressing, slitting and cutting.
  • the negative electrode active material, conductive carbon black Super-P, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) shown in Table 1 in Comparative Examples 1 and 2 are in a weight ratio 96:1:2:1 for mixing. After fully stirring and mixing in a deionized water solvent system, a negative electrode slurry is obtained; the negative electrode slurry is evenly coated on both surfaces of the negative electrode current collector Cu foil, refer to The areal densities shown in Comparative Examples 1 and 2 in Table 1 were coated, dried at room temperature and then transferred to an oven to continue drying, and then cold-pressed and slit to obtain negative pole pieces.
  • SBR binder styrene butadiene rubber
  • CMC-Na thickener sodium carboxymethyl cellulose
  • SBR binder styrene butadiene rubber
  • CMC-Na thickener sodium carboxymethyl cellulose
  • the slurry A was uniformly coated on the two surfaces of the negative current collector Cu foil, and the coating was carried out with reference to the areal density shown in Examples 1-19 in Table 1. After drying at room temperature, it was transferred to an oven to continue drying. Obtain the pole piece A coated with the first active material layer; then coat the slurry B on both surfaces of the pole piece A, refer to the areal density shown in Examples 1-19 in Table 1, for coating, and bake Dry, then cold press and slit to obtain a negative electrode with two active material layers.
  • the graphite in Table 1 is all artificial graphite.
  • the lithium ion secondary battery made by the negative electrode obtained in Examples 1-19 and Comparative Examples 1 and 2 was subjected to a current of 0.5C (that is, the current value of completely discharging the theoretical capacity within 2h).
  • the charging is constant current and constant voltage charging
  • the charge termination voltage is 4.2V
  • the cut-off current is 0.05C
  • the discharge termination voltage is 3.0V
  • the BOL (Before of life) of the battery is the discharge capacity C b at the first cycle.
  • the test condition is 1C/1C cycle under normal temperature conditions, the voltage range is 3.0V-4.2V, the middle is left for 5min, and the discharge capacity C e is recorded during each cycle.
  • the ratio of C e to C b , C e /C b is the capacity retention rate during this cycle. Test the capacity retention rate of the battery after 2000 cycles.
  • Example 1-19 and Comparative Examples 1 and 2 The related parameters of the negative electrodes provided in Examples 1-19 and Comparative Examples 1 and 2 are shown in Table 1, and the negative electrode test results provided in Examples 1-19 and Comparative Examples 1 and 2 are shown in Table 2, and Examples 1-19 and Comparative Example 1 , 2 The test results of the secondary battery prepared with the negative electrode provided are shown in Table 3.
  • Examples 1-18 of the present application adopt a composite layer structure of the negative electrode film, wherein the first active material layer and the second active material layer in the first active material layer
  • the second active material is elliptical particles with through holes and/or blind holes, and the average pore diameter of the first active material is larger than the average pore diameter of the second active material, thereby enabling the negative electrode to have good active material particles While stacking performance, it greatly increases its own liquid absorption and storage capacity, so that the secondary battery adopting it has a higher energy density and improves the cycle life.
  • Examples 1-7 show that by changing the average pore size of the first active material, its apparent density and specific surface area will change accordingly, especially affecting the pole piece liquid absorption and liquid retention performance and circulation capacity. It can also be seen that the average pore size is preferably controlled at 70nm-140nm, more preferably 80nm-120nm, which can further improve the liquid absorption and liquid retention capacity of the negative electrode, thereby further improving the cycle performance of the battery.
  • the average pore size of the second active material is preferably controlled in the range of 10nm-30nm, more preferably 15nm-25nm, which can further improve the liquid absorption and retention capacity of the negative electrode and further improve the cycle performance of the battery.

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Abstract

本申请公开一种负极、二次电池和包含二次电池的装置，负极包括：集流体；靠近集流体的第一活性物质层，所述第一活性物质层包含第一活性物质；和设置在所述第一活性物质层远离所述集流体的表面的第二活性物质层，所述第二活性物质层包含第二活性物质；所述第一活性物质和所述第二活性物质各自独立地为具有通孔和/或盲孔的类椭圆形颗粒，且所述第一活性物质的平均孔径大于所述第二活性物质的平均孔径。

Description

负极、二次电池和包含二次电池的装置
相关申请的交叉引用
本申请要求享有于2019年03月06日提交的名称为“一种负极及其锂离子二次电池”的中国专利申请201910169334.4的优先权，该申请的全部内容通过引用并入本文中。
技术领域
本申请属于储能装置技术领域，具体涉及一种负极、二次电池和包含二次电池的装置。
背景技术
以锂离子二次电池为代表的二次电池是通过活性离子在正、负极活性物质之间往复嵌入和脱出来完成充电和放电过程，已经成为重要的能源。例如，随着新能源汽车的迅速普及，市场对动力型二次电池的需求量将呈现爆发式增长。这为二次电池行业的发展带来机遇的同时，也对二次电池的循环寿命提出了严峻的挑战。为了增强二次电池的市场竞争力，确有必要提高其循环寿命。
发明内容
负极的设计将直接影响二次电池的性能。现有的负极通常是在集流体的一侧或两侧表面具有均一的负极膜片。然而经本发明人的研究发现，负极在电池循环过程中因发生膨胀而导致其电解液浸润量不足，由此造成了电池的容量快速衰减。
本发明人进一步发现，通过降低负极中活性物质颗粒的堆积紧密程度来提高负极的吸液能力，可以改善二次电池的循环寿命。但是，这样将导致负极厚度增加，从而会不利地降低二次电池的能量密度。另外，活性物 质颗粒之间还可能发生接触变差的问题，影响负极的电子传导，由此会使二次电池的动力学性能降低。或者，通过在二次电池中添加更多的电解液，来使电极在循环过程中能保持足够的电解液含量，这样虽然可以在一定程度上改善二次电池的循环寿命，但是加入更高含量的电解液会增加电池内压，由此会导致电池循环膨胀问题，影响电池的安全性能。另外，使用更多的电解液也增加了电池成本。
本发明人进行了大量的研究，旨在改善传统的负极，以使负极在具有良好的活性物质颗粒堆积性能的同时，能增加其自身的吸液储液能力，从而获得能同时兼顾较高的能量密度和循环寿命的二次电池。
因此，本申请的第一方面提供一种负极，其包括：
负极集流体；
靠近负极集流体的第一活性物质层，所述第一活性物质层包含第一活性物质；和设置在所述第一活性物质层远离所述负极集流体的表面的第二活性物质层，所述第二活性物质层包含第二活性物质；
所述第一活性物质和所述第二活性物质各自独立地为具有通孔和/或盲孔的类椭圆形颗粒，且所述第一活性物质的平均孔径大于所述第二活性物质的平均孔径。
本申请的第二方面提供一种二次电池，其包括根据本申请第一方面所述的负极。
本申请的第三方面提供一种装置，其包括根据本申请第二方面所述的二次电池。
相比于现有技术，本申请至少包括如下所述的有益效果：
令人惊奇地发现，本申请的负极采用复合层结构的负极膜片，其中第一活性物质层中的第一活性物质和第二活性物质层中的第二活性物质为具有通孔和/或盲孔的类椭圆形颗粒，且第一活性物质的平均孔径大于第二活性物质的平均孔径，由此能使负极在具有良好的活性物质颗粒堆积性能的同时，大幅度增加其自身的吸液储液能力。因此，本申请的负极使得采用其的二次电池在具有较高能量密度的前提下，提高循环寿命。本申请的装置包括本申请提供的二次电池，因而至少具有与所述二次电池相同的优 势。
附图说明
为了更清楚地说明本申请实施例的技术方案，下面将对本申请实施例中所需要使用的附图作简单地介绍，显而易见地，下面所描述的附图仅仅是本申请的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据附图获得其他的附图。
图1为本申请一些实施例提供的负极结构示意图。
图2是二次电池的一实施方式的示意图。
图3是图2的分解图。
图4是电池模块的一实施方式的示意图。
图5是电池包的一实施方式的示意图。
图6是图5的分解图。
图7是二次电池用作电源的装置的一实施方式的示意图。
具体实施方式
为了使本申请的发明目的、技术方案和有益技术效果更加清晰，以下结合具体实施例对本申请进行详细说明。应当理解的是，本说明书中描述的实施例仅仅是为了解释本申请，并非为了限定本申请。
为了简便，本文仅明确地公开了一些数值范围。然而，任意下限可以与任何上限组合形成未明确记载的范围；以及任意下限可以与其它下限组合形成未明确记载的范围，同样任意上限可以与任意其它上限组合形成未明确记载的范围。此外，尽管未明确记载，但是范围端点间的每个点或单个数值都包含在该范围内。因而，每个点或单个数值可以作为自身的下限或上限与任意其它点或单个数值组合或与其它下限或上限组合形成未明确记载的范围。
在本文的描述中，需要说明的是，除非另有说明，“以上”、“以下”为包含本数，“一种或几种”中“几种”的含义是两种或两种以上。
本申请的上述发明内容并不意欲描述本申请中的每个公开的实施方式 或每种实现方式。如下描述更具体地举例说明示例性实施方式。在整篇申请中的多处，通过一系列实施例提供了指导，这些实施例可以以各种组合形式使用。在各个实例中，列举仅作为代表性组，不应解释为穷举。
负极
首先，说明本申请的第一方面提供的负极。所述负极包括：负极集流体；靠近该负极集流体的第一活性物质层，所述第一活性物质层包含第一活性物质；和设置在所述第一活性物质层远离所述负极集流体的表面的第二活性物质层，所述第二活性物质层包含第二活性物质；所述第一活性物质和所述第二活性物质各自独立地为具有通孔和/或盲孔的类椭圆形颗粒，且所述第一活性物质的平均孔径大于所述第二活性物质的平均孔径。
图1是作为一个示例的负极的结构示意图。负极包括负极集流体521、形成于负极集流体521上的第一活性物质层522和形成于第一活性物质层522远离负极集流体521的表面上的第二活性物质层523。可以理解的是，包含第一活性物质层和第二活性物质层的复合层结构负极膜片可以形成于负极集流体的一侧表面，也可以形成于负极集流体在自身厚度方向相对的两个表面。
术语“通孔”即为贯穿活性物质颗粒的孔。
术语“盲孔”即为由活性物质颗粒的表面向内延伸预定深度，但未贯穿活性物质颗粒的孔。
所述第一活性物质和所述第二活性物质各自独立地为具有通孔和/或盲孔的类椭圆形颗粒，换句话说，所述第一活性物质为类椭圆形颗粒，且其具有包括通孔和盲孔中的一种或几种的多孔结构；所述第二活性物质为类椭圆形颗粒，且其具有包括通孔和盲孔中的一种或几种的多孔结构。第一活性物质的形貌、孔结构的选择与第二活性物质的形貌、孔结构的选择是彼此独立的。
活性物质的平均孔径的示例性测试方法可参考标准GB/T19587-2017《气体吸附BET法测定固态物质比表面积》、GB/T21650.2-2008压汞法和气体吸附法测定固体材料孔径分布和孔隙度-第2部分：气体吸附法分析介 孔和大孔。例如可采用美国麦克micromeritics TriStar II 3020仪器，测试活性物质颗粒的平均孔径。
发明人经过大量研究发现，负极采用复合层结构的负极膜片，且其中第一活性物质层中的第一活性物质和第二活性物质层中的第二活性物质采用类椭圆形颗粒，由此能改善颗粒之间的堆积性能，使颗粒之间形成良好接触的同时，还形成适于电解液浸润的孔隙。第一活性物质和第二活性物质还具有包括通孔和盲孔中的一种或几种的多孔结构，并且，远离负极集流体的第二活性物质层采用平均孔径较小的第二活性物质，靠近负极集流体的第一活性物质层采用平均孔径较大的第一活性物质，此种组合结构特点能大幅度增加负极自身的吸液和储液能力。因此，本申请的负极能使得采用其的二次电池在具有较高能量密度的前提下，显著缓解电解液浸润量不足导致的循环恶化，提高电池的循环寿命。更优选地，本申请的负极不仅保持了较高的电子传导性能，其活性离子传输性能也得到提升，因此还能使电池兼具优异的动力学性能。
发明人还发现，当负极采用复合层结构的负极膜片时，还可以有效改善活性物质层开裂问题。其原因为：逐层涂布两个以上活性物质层，降低了负极烘干过程中活性物质层的内应力，由此解决了因涂布重量增加导致的开裂问题。负极膜片内形成连续的导电网络，能进一步提升电池的循环寿命及动力学性能。
在一些优选的实施例中，第一活性物质的孔隙率大于第二活性物质的孔隙率。发明人发现，内层的第一活性物质层采用的第一活性物质具有更大的平均孔径和更高的孔隙率，使得第一活性物质层对电解液具有更强的吸液力和滞留力。同时，第二活性物质层采用的第二活性物质更加密实，其平均孔径较小且孔隙率较低，能保证负极具有较高的能量密度，同时进一步提高负极的储液能力。尤其是，负极在循环过程中体积膨胀时仍能保持较高的电解液保持量。因此，采用该负极能使电池在具有较高的能量密度的前提下，进一步提升循环性能。更优选地，电池的动力学性能也能得到提升。
平均粒径D v50是颗粒累计体积分布百分数达到50％时所对应的粒径。平均粒径D v50大的颗粒之间排列更为疏松，能提升极片的储液率，但是会影响颗粒之间的电子传导能力。在一些实施例中，第一活性物质的平均粒径D v50优选为8μm-18μm，更优选为10μm-16μm。第一活性物质的D v50在适当范围内，能在提升负极的吸液储液能力的同时，使负极具有较高的活性离子和电子传输性能，从而使电池具有较高的循环寿命和动力学性能。第一活性物质具有适当的D v50，还能提高单位体积第一活性物质层内活性物质的占比，从而有利于提高电池的能量密度。
在一些实施例中，第二活性物质的平均粒径D v50优选为5μm-15μm，更优选为6μm-12μm。第二活性物质层采用具有适当D v50的第二活性物质，能提升负极的保液能力，同时还提升负极的能量密度。此外，第二活性物质的D v50越小，其与电解液的接触越充分，越有利于活性离子与电子的电荷交换，从而更有利于电池的快速充电。而第二活性物质的D v50在适当范围内，还有利于制备一致性较高的活性物质层，从而提升电池的循环寿命。
在一些优选的实施例中，负极同时满足第一活性物质的平均粒径D v50为8μm-18μm，第二活性物质的平均粒径D v50为5μm-15μm。第一活性物质层和第二活性物质层的活性物质颗粒大小具有合理的搭配，能在循环过程中保持颗粒堆积结构的稳定性，由此不仅能抑制相邻活性物质层之间的颗粒发生混排，还能保持活性物质颗粒之间适当的孔隙结构，从而有效发挥复合层结构的负极膜片对负极吸液储液能力以及活性离子传输性能的提升作用。因此，采用该负极的电池能具有较高的循环性能和动力学性能。
活性物质的平均孔径越大，电解液易于在颗粒中扩散，提高吸液能力。电解液还容易与大孔径的活性物质充分接触，这有利于活性离子的脱嵌，提高动力学性能。而采用平均孔径较小的活性物质，有利于提高活性物质层单位体积内的活性物质占比，从而提升负极的能量密度。
在一些实施例中，第一活性物质的平均孔径可以为60nm-150nm，优选为70nm-140nm，更优选为80nm-120nm。第一活性物质的平均孔径在适当范围内，能较好地提高负极的吸液能力和动力学性能。
在一些实施例中，第二活性物质的平均孔径可以为5nm-35nm，优选为10nm-30nm，更优选为15nm-25nm。第二活性物质的平均孔径的适当范围内，能使负极具有较高的保液能力的同时，提高能量密度。
在一些优选的实施例中，第一活性物质的平均孔径可以为60nm-150nm，优选为70nm-140nm，更优选为80nm-120nm；且第二活性物质的平均孔径可以为5nm-35nm，优选为10nm-30nm，更优选为15nm-25nm。靠近负极集流体的第一活性物质层选择平均孔径较大的第一活性物质，有利于利用毛细作用使得电解液快速浸润负极，提高负极极片的吸液速率，同时，远离负极集流体的的第二活性物质层选择平均孔径较小的第二活性物质，第二活性物质层较小的孔隙率有助于提高负极的储液能力。
类椭圆形颗粒也即类球形颗粒，颗粒的外边缘面大致为三维曲面。类椭圆形活性物质颗粒的短径长度与长径长度比值≤1。该值越接近1，则该颗粒形状就越趋向圆形，颗粒之间的剪切力越大。短径长度与长径长度比值越小，表明该颗粒料形状就越趋向椭圆形，颗粒之间越容易相互嵌合。
在一些实施例中，第一活性物质短径长度与长径长度比值可以为0.4-1，优选为0.5-1，更优选为0.6-0.9。第一活性物质的短径长度与长径长度比值在适当范围内，能使颗粒之间形成良好接触，保证负极较高的电子传导性能的同时，提高第一活性物质层的孔隙率，从而提高负极的电解液浸润量。
在一些实施例中，第二活性物质短径长度与长径长度比值为0.3-1，优选为0.4-0.8。第一活性物质的短径长度与长径长度比值在适当范围内，能使颗粒之间形成适于电解液浸润的孔隙的同时，提高颗粒堆积密实程度，从而提高负极的电解液保持能力和能量密度。
在一些优选的实施例中，负极同时满足：第一活性物质短径长度与长径长度比值为0.5-1，优选为0.6-0.9；且第二活性物质短径长度与长径长度比值为0.3-1，优选为0.4-0.8。选择短径长度与长径长度比值较大的活性物质设置在所述负极集流体上，选择短径长度与长径长度比值较小的活性物质设置在所述第一活性物质层上，有利于进一步提高所述负极的吸液和储液能力。
比表面积越大的活性物质颗粒，对电解液的吸附能力越强。在一些实施例中，第一活性物质的比表面积大于第二活性物质的比表面积。这样有助于提高电池的吸液能力和储液能力。
在一些实施例中，第一活性物质比表面积优选为6.9m 2/g–9.6m 2/g，更优选为7.5m 2/g–9.1m 2/g，尤其优选为8.0m 2/g–8.7m 2/g。
在一些实施例中，第二活性物质比表面积优选为1.3m 2/g–3.1m 2/g，更优选为2.0m 2/g-2.5m 2/g。
表观密度值是材料的质量与材料排开水的体积之比。表观密度值越小，表明该材料中含有的开孔孔隙体积越大，吸液和储液能力越强。表观密度值在适当范围内，还有利于使电池获得较高的能量密度。
在一些实施例中，第一活性物质的表观密度优选为0.5g/cm 3-1.2g/cm 3，更优选为0.6g/cm 3-1.0g/cm 3。
在一些实施例中，第二活性物质的表观密度优选为1.5g/cm 3-2.0g/cm 3，更优选为1.6g/cm 3-1.9g/cm 3。
复合层结构的负极膜片中，各活性物质层的面密度在适当范围内，能使进一步提高电池的能量密度和循环寿命。此外，还有利于提高负极的一致性。各活性物质层的面密度等于该活性物质层的质量除以其面积。
在一些实施例中，第一活性物质层的面密度优选为20g/m 2-100g/m 2，更优选为30g/m 2-90g/m 2。
在一些实施例中，第二活性物质层的面密度优选为20g/m 2-100g/m 2，更优选为30g/m 2-90g/m 2。
发明人进一步研究发现，当第一活性物质层的面密度与第二活性物质层的面密度的比值为0.3-3时，可进一步提升电池的能量密度和循环性能。更优选地，第一活性物质层的面密度与第二活性物质层的面密度的比值为0.5-2。
在一些实施例中，复合层结构的负极膜片的孔隙率可以为40.1％-67.9％，例如44.5％、45.4％、50％、55％、59.9％、60.5％、62.5％、64.5％、65.2％、66.5％、67.9％等。通过第一活性物质层和第二活性物质层的合理 搭配，能使复合层结构的负极膜片具有适当的孔隙率。采用该负极的二次电池能同时兼顾较高的能量密度和循环性能。
在一些可选的实施例中，第二活性物质和第一活性物质各自独立地选自能接收和脱出锂离子的材料。能接收和脱出锂离子的材料可包括软碳、硬碳、人造石墨、天然石墨、硅、硅氧化合物、硅碳复合物、钛酸锂和能与锂形成合金的金属中的一种或几种。
在一些优选的实施例中，第二活性物质和第一活性物质均为人造石墨。
具有前文所述多孔结构的人造石墨可商购获得，或者采用本领域已知的方法制备得到。作为第二活性物质的人造石墨的示例性制备方法包括：将人造石墨颗粒与可分解释放出气体的插层剂混合均匀，所得混合料中插层剂的质量占比为大于0％小于等于5％；在100℃左右进行插层反应1h～3h，如2h；使得插层剂嵌入石墨颗粒层间；然后将反应产物转移至烧结炉中，在800℃-1000℃、保护气氛中烧结8h-10h，即可得到活性物质颗粒。插层剂可选自但不限于碳酸锂、碳酸钠、碳酸钾、硝酸铵、氯酸锂、草酸铵、醋酸中的一种或几种。
可采用类似的方法制备作为第一活性物质的人造石墨，其中可通过增加可分解释放出气体的插层剂的添加量，来使第一活性物质获得较大的平均孔径。进一步地，还使第一活性物质获得较高的孔隙率。例如，人造石墨颗粒与可分解释放出气体的插层剂的混合料中，插层剂的质量占比可以为15％-35％。
在一些实施例中，负极集流体可以采用金属箔材、涂炭金属箔材或多孔金属板等材料，优选采用铜箔。
可以理解的是，负极中任意一个负极膜片为上述包含第一活性物质层和第二活性物质层的复合层结构时，即落入本申请的保护范围内。
在一些可选的实施例中，第一活性物质层和第二活性物质层还可各自独立地包括导电剂。本申请对导电剂的种类不做具体限定，可以根据实际需求进行选择。作为示例，导电剂可包括超导碳、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一种或几种。
在一些可选的实施例中，第一活性物质层和第二活性物质层还可各自 独立地包括粘结剂。本申请对粘结剂的种类不做具体限定，可以根据实际需求进行选择。作为示例，粘结剂可以是丁苯橡胶(SBR)、苯乙烯-丁二烯橡胶(SBCs)和水性丙烯酸树脂中的一种或几种。
在一些可选的实施例中，第一活性物质层和第二活性物质层还可各自独立地包括增稠剂，如羧甲基纤维素钠(CMC-Na)。但本申请并不限于此，本申请还可以使用其它可被用作负极的增稠剂的材料。
在本文中，活性物质的平均粒径D v50可以用激光粒度分析仪方便地测定，如英国马尔文仪器有限公司的Mastersizer 3000型激光粒度分析仪。
活性物质的比表面积为本领域公知的含义，可以用本领域公知的仪器及方法进行测定，例如可以用氮气吸附比表面积分析测试方法测试，并用BET(Brunauer Emmett Teller)法计算得出，其中氮气吸附比表面积分析测试可以是通过美国Micromeritics公司的Tri StarⅡ型比表面与孔隙分析仪进行，测试可以参照GB/T 19587-2004。
活性物质的表观密度可采用本领域公知的仪器及方法进行测定。具体可参考国家标准GB/T24586-2009铁矿石表观密度、真密度和孔隙率的测定。示例性测试方法如下：取一定质量活性物质颗粒置于比重瓶中，用适量煤油浸泡一定时间后，倒出多余煤油，测量出颗粒吸收煤油体积，即为开孔孔隙体积，颗粒表观密度＝颗粒重量/(真体积+孔隙体积)。其中真体积＝颗粒重量/真密度，真密度可采用真密度测试仪(如AccuPyc II 1340)测试得到。
活性物质的短径长度与长径长度比值可采用本领域公知的仪器及方法进行测定。示例性测试方法如下：将活性物质单层铺设并粘于导电胶上(活性物质可以是制备负极膜片的原料或从成型的负极膜片中取样)，且相邻颗粒之间彼此相互接触，制成长×宽＝5cm×5cm的待测样品。使用扫描电镜(如ZEISS Sigma300)对待测样品中颗粒进行测试。测试可参考JY/T010-1996。为了确保测试结果的准确性，可以在待测样品中随机选取至少50个不同颗粒进行扫描测试，计算各颗粒的短径长度与长径长度比，再计算该至少50个短径长度与长径长度比的平均值，即为活性物质的短径长度与长径长度比值。
负极膜片的孔隙率为本领域公知的含义，可以用本领域公知的仪器及方法进行测定。具体可参考国家标准GB/T24586-2009铁矿石表观密度、真密度和孔隙率的测定。孔隙率P＝(V 1-V 2)/V 1×100％，V 1表示表观体积，V 2表示真实体积。
二次电池
本申请第二方面提供一种二次电池，其包括正极、负极、电解液及隔离膜，其中，所述负极为根据本申请第一方面所述的负极。
在一些实施例中，正极包括正极集流体、设置在正极集流体的至少一个表面上且包括正极活性材料的正极膜片。正极极片的具体种类及组成均不受具体限制，可根据实际需求进行选择。
在一些实施例中，正极活性材料选自但不限于化学式为Li aM 1-xM’ xO 2的层状锂过渡金属氧化物及化学式为LiFe yMn 1-y-zM” zPO 4/C b的磷酸铁锂材料中的一种或者几种的混合物，其中0.9≤a≤1.1，0≤x≤0.1，0.1≤y≤0.9，0≤z≤0.9，b≥0，M为Co、Mn、Ni的至少一种，M’为Al、Mg、B、Zr、Si、Ti、Cr、Fe、V、Cu、Ca、Zn、Nb、Mo、Sr、Sb、W及Bi中的一种或几种，M”为Cr、Mg、Ti、Al、Zn、W、Nb、Zr中的一种或几种。
在一些实施例中，正极膜片还可选的包括导电剂。本申请对导电剂的种类不做具体限定，可以根据实际需求进行选择。作为示例，导电剂可包括超导碳、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一种或几种。
在一些实施例中，正极膜片还可选的包括粘结剂。本申请对粘结剂的种类不做具体限定，可以根据实际需求进行选择。作为示例，粘结剂可包括聚偏二氟乙烯(PVDF)、聚四氟乙烯(PTFE)、乙烯-醋酸乙烯酯共聚物(EVA)及聚乙烯醇(PVA)中的一种或几种。
在一些实施例中，正极集流体可采用金属箔材、涂炭金属箔材或多孔金属板，优选采用铝箔。
在一些实施例中，所述电解液包含溶剂和溶质，溶剂和溶质的具体种类及组成均不受具体限制，可根据实际需求进行选择。例如所述溶剂可选 自对电子绝缘但可传导离子的含碳酸亚乙酯、碳酸亚丙酯、碳酸二甲酯、碳酸二乙酯、碳酸甲乙酯等碳酸有机酯类一种或几种。所述溶质可选自LiPF 6、LiBF 4、LiBOB、LiAsF 6、Li(CF 3SO 2) 2N、LiCF 3SO 3、LiClO 4中的一种或几种锂盐。
在本申请第二方面的二次电池中，隔离膜是介于正极极片和负极极片之间起隔离的作用。所述隔离膜的种类并不受具体限制，可以是现有电池中使用的任何隔离膜材料。例如聚乙烯、聚丙烯、聚偏氟乙烯、无纺布、聚纤维材质的薄膜以及它们的多层复合膜。
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。如图2是作为一个示例的方形结构的二次电池5。
在一些实施例中，二次电池可包括外包装，用于封装正极极片、负极极片、隔离膜和电解液。
在一些实施例中，二次电池的外包装可以是软包，例如袋式软包。软包的材质可以是塑料，如可包括聚丙烯PP、聚对苯二甲酸丁二醇酯PBT、聚丁二酸丁二醇酯PBS等中的一种或几种。二次电池的外包装也可以是硬壳，例如硬塑料壳、铝壳、钢壳等。
在一些实施例中，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叠片或卷绕形成叠片结构电极组件或卷绕结构电极组件52。电极组件52封装于所述容纳腔。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几个，可根据需求来调节。
在一些实施例中，二次电池可以组装成电池模块，电池模块所含二次电池的数量可以为多个，具体数量可根据电池模块的应用和容量来调节。
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。
在一些实施例中，上述电池模块还可以组装成电池包，电池包所含电池模块的数量可以根据电池包的应用和容量进行调节。
图5和图6是作为一个示例的电池包1。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。
装置
在本申请的第三方面提供一种装置，所述装置包括本申请第二方面的二次电池。所述二次电池可以用作所述装置的电源，也可以作为所述装置的能量存储单元。所述装置可以但不限于是移动设备(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。
所述装置可根据其使用需求来选择二次电池、电池模块或电池包。
图7是作为一个示例的装置。该装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该装置对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
为详细说明技术方案的技术内容、构造特征、所实现目的及效果，以下结合具体实施例详予说明。应理解，这些实施例仅用于说明本申请而不用于限制本申请的范围。除非另有声明，以下实施例中所报道的所有份、 百分比、和比值都是基于重量计，而且实施例中使用的所有试剂都可商购获得或是按照常规方法进行合成获得，并且可直接使用而无需进一步处理，以及实施例中使用的仪器均可商购获得。
实施例1-19和对比例1、2的电池均按照下述方法进行制备。
(1)正极极片的制备
将正极活性材料-镍钴锰三元活性物质LiNi 1/3Co 1/3Mn 1/3O 2、导电炭黑Super-P、粘结剂PVDF按重量比94:3:3在N-甲基吡咯烷酮溶剂体系中在真空搅拌机进行充分搅拌，搅拌线速度控制为4-10m/min，搅拌混合时间60-150min，至体系呈均一状，获得正极浆料；将所述正极浆料涂覆于Al箔基材的两个表面上，通过烘干、冷压、分条、裁切，得到正极极片。
(2)负极极片的制备
i、单层活性物质层负极的制备(对比例1、2按照该方法制备)
将表1中对比例1、2所示的负极活性材料、导电炭黑Super-P、粘结剂丁苯橡胶(SBR)、增稠剂羧甲基纤维素钠(CMC-Na)按照重量比96:1:2:1进行混合，在去离子水溶剂体系中充分搅拌混合均匀后，得到负极浆料；将所述负极浆料均匀涂覆在负极集流体Cu箔的两个表面上，参照表1中对比例1、2所示的面密度进行涂布，室温晾干后转移至烘箱继续干燥，然后经过冷压、分切得到负极极片。
ii、双层活性物质层负极的制备(实施例1-19负极按照该方法制备)
将表1中实施例1-19所示的第一活性物质、导电炭黑Super-P、粘结剂丁苯橡胶(SBR)、增稠剂羧甲基纤维素钠(CMC-Na)按照重量比96:1:2:1进行混合，在去离子水溶剂体系中充分搅拌混合均匀后，得到浆料A；
将表1中实施例1-19所示的第二活性物质、导电炭黑Super-P、粘结剂丁苯橡胶(SBR)、增稠剂羧甲基纤维素钠(CMC-Na)按照重量比96:1:2:1进行混合，在去离子水溶剂体系中充分搅拌混合均匀后，得到浆料B；
先将所述浆料A均匀涂覆在负极集流体Cu箔的两个表面上，参照表1中实施例1-19所示的面密度进行涂布，室温晾干后转移至烘箱继续干燥，得到涂覆了第一活性物质层的极片A；接着在极片A的两个表面涂覆所述 浆料B，参照表1中实施例1-19所示的面密度进行涂布，烘干，然后经过冷压、分切，得到具有两个活性物质层的负极。
表1中石墨均为人造石墨。
(3)电解液的制备
将碳酸亚乙酯(EC)、碳酸甲乙酯(EMC)按照体积比3:7进行混合，得到有机溶剂；将充分干燥的LiPF 6溶解于混合后的有机溶剂中，配制成浓度1mol/L的电解液。
(4)隔离膜的制备
选PE/PP/PE三层多孔聚合薄膜作为隔离膜。
(5)锂离子二次电池的制备
将上述正极极片、隔离膜、负极极片按顺序叠好，使隔离膜处于正、负极极片之间起到隔离的作用，然后卷绕得到裸电芯；将合格裸电芯通过极耳焊接在顶盖上，置于外包装壳中，干燥后注入电解液，经过真空封装、静置、化成、整形等工序，获得锂离子二次电池。
测试部分
(1)吸液能力的测试采用以下方法：
采用电解液浸泡法测试极片吸液能力。负极极片在冷压后，将实施例1-19和对比例1、2得到的负极各取3个，在同样条件下，将负极极片放入同等重量的电解液中，常温(25℃)浸泡12h后取出，称量浸泡前后极片重量；极片吸液能力＝(浸泡后极片重量-浸泡前极片重量)/浸泡前极片重量。
(2)保液能力的测试采用以下方法：
测试100N压紧力下负极极片中电解液残留量来表征极片保液能力。极片在冷压后，将实施例1-19和对比例1、2得到的负极各取9个，在同样条件下，将负极极片放入同等重量电解液中，常温(25℃)浸泡12h后取出，称量浸泡前后极片重量，极片初始保液量＝(浸泡后极片重量-浸泡前极片重量)/浸泡前极片重量。
然后将实施例1-19和对比例1、2得到的负极各取6个吸有电解液的负极极片放在两片钢板之间，类似三明治结构，采用夹具将钢板-负极极片-钢板结构夹紧，然后采用冲压设备对夹具施加100N的力；实施例1-19和 对比例1、2的负极各取3个保持30min、另各取3个保持60min停止施力；将夹具取出，拆开取出负极极片，测量该负极极片重量，得到100N压紧力下极片保液能力。极片保液能力＝(压紧力施力后极片重量-浸泡前极片重量)/浸泡前极片重量。
(3)循环性能的测试采用以下方法：
常温(25℃)下，将实施例1-19和对比例1、2方法得到的负极所制作锂离子二次电池以0.5C(即2h内完全放掉理论容量的电流值)的电流进行第一次充电和放电，充电为恒流恒压充电，充电终止电压为4.2V，截至电流为0.05C，放电终止电压为3.0V，然后电池搁置24h。之后在同样的条件下，先进行充放电测试，以1C电流进行恒流恒压充电，充电终止电压为4.2V，截至电流为0.05C，以1C电流进行放电，放电终止电压为3.0V，记录电池的BOL(Before of life)，即首次循环时放电容量C b。然后进行循环寿命检测，测试条件为常温条件下，进行1C/1C循环，电压范围为3.0V-4.2V，中间搁置5min，每次循环过程记录放电容量C e。C e与C b的比值C e/C b即为此次循环过程中的容量保持率。测试电池循环2000圈后的容量保持率。
实施例1-19和对比例1、2提供的负极的相关参数见表1，实施例1-19和对比例1、2提供的负极测试结果见表2，实施例1-19和对比例1、2提供的负极所制备的二次电池的测试结果见表3。
表1实施例1-19和对比例1、2提供的负极的相关参数
Figure PCTCN2020078166-appb-000001
表2实施例1-19和对比例1、2提供的负极测试结果
Figure PCTCN2020078166-appb-000002
表3实施例1-19和对比例1、2提供的负极所制备的锂离子二次电池的测试结果
Figure PCTCN2020078166-appb-000003
从测试数据来看，相较于对比例1、2，本申请实施例1-18通过采用复合层结构的负极膜片，其中第一活性物质层中的第一活性物质和第二活性物质层中的第二活性物质为具有通孔和/或盲孔的类椭圆形颗粒，且第一活性物质的平均孔径大于第二活性物质的平均孔径，由此能使负极在具有良好的活性物质颗粒堆积性能的同时，大幅度增加其自身的吸液和储液能力，从而使采用其的二次电池在具有较高能量密度的前提下，提高循环寿命。
实施例1-7表明改变第一活性物质的平均孔径，其表观密度及比表面积将随之变化，尤其是影响极片吸液保液性能及循环能力。还可以看到其平均孔径尺寸优选控制在70nm-140nm，更优选为80nm-120nm，能进一步提高负极的吸液和保液能力，从而使电池的循环性能进一步提高。
实施例8-13保持第一活性物质层颗粒孔径尺寸不变，变化第二活物质层颗粒平均孔径尺寸，其表观密度及比表面积将随之变化，尤其是影响极片吸液保液性能及循环能力。还可以看到第二活性物质的平均孔径尺寸优选控制在10nm-30nm范围内，更优选15nm-25nm，这样能进一步提高负极的吸液保液能力，并进一步提高电池的循环性能。
实施例14-18保持两层活性物质颗粒平均孔径不变，改变第一层和第二层活性物质颗粒的粒径D v50及其短径/长径比值，其表观密度及比表面积将随之变化，可以看到，当优化第一活性物质和第二活性物质之间的搭配时，能进一步提高负极的吸液保液能力，并进一步提高电池的循环性能。
需要说明的是，尽管在本文中已经对上述各实施例进行了描述，但并非因此限制本申请的专利保护范围。因此，基于本申请的创新理念，对本文所述实施例进行的变更和修改，或利用本申请说明书及附图内容所作的等效结构或等效流程变换，直接或间接地将以上技术方案运用在其他相关的技术领域，均包括在本申请的专利保护范围之内。

Claims (14)

  1. 一种负极，包括：
    负极集流体；
    靠近负极集流体的第一活性物质层，所述第一活性物质层包含第一活性物质；和设置在所述第一活性物质层远离所述负极集流体的表面的第二活性物质层，所述第二活性物质层包含第二活性物质；
    所述第一活性物质和所述第二活性物质各自独立地为具有通孔和/或盲孔的类椭圆形颗粒，且所述第一活性物质的平均孔径大于所述第二活性物质的平均孔径。
  2. 根据权利要求1所述的负极，其中，所述第一活性物质的孔隙率大于所述第二活性物质的孔隙率。
  3. 根据权利要求1或2所述的负极，其中，所述第一活性物质的粒径D v50为8μm-18μm，优选为10μm-16μm；和/或
    所述第二活性物质的粒径D v50为5μm-15μm，优选为6μm-12μm。
  4. 根据权利要求1-3任一项所述的负极，其中，所述第一活性物质的平均孔径为70nm-140nm，优选为80nm-120nm；和/或
    所述第二活性物质的平均孔径为10nm-30nm，优选为15nm-25nm。
  5. 根据权利要求1-4任一项所述的负极，其中，所述第一活性物质的短径长度与长径长度比值为0.5-1，优选为0.6-0.9；和/或
    所述第二活性物质的短径长度与长径长度比值为0.3-1，优选为0.4-0.8。
  6. 根据权利要求1-5任一项所述的负极，其中，所述第一活性物质的比表面积为6.9m 2/g–9.6m 2/g，优选为8m 2/g–8.7m 2/g；和/或
    所述第二活性物质的比表面积为1.3m 2/g–3.1m 2/g，优选为2m 2/g-2.5m 2/g。
  7. 根据权利要求1-6任一项所述的负极，其中，所述第一活性物质的表观密度为0.5g/cm 3-1.2g/cm 3，优选为0.6g/cm 3-1.0g/cm 3；和/或
    所述第二活性物质的表观密度为1.5g/cm 3-2.0g/cm 3，优选为1.6g/cm 3-1.9g/cm 3。
  8. 根据权利要求1-7任一项所述的负极，其中，所述第一活性物质层的面密度为20g/m 2-100g/m 2，优选为30g/m 2-90g/m 2；和/或，
    所述第二活性物质层的面密度为20g/m 2-100g/m 2，优选为30g/m 2-90g/m 2。
  9. 根据权利要求1-8任一项所述的负极，其中，所述第一活性物质层的面密度与所述第二活性物质层的面密度的比值为0.3-3，优选为0.5-2。
  10. 根据权利要求1-9任一项所述的负极，其中，所述第二活性物质和第一活性物质各自独立地包括软碳、硬碳、人造石墨、天然石墨、硅、硅氧化合物、硅碳复合物、钛酸锂和能与锂形成合金的金属中的一种或几种。
  11. 根据权利要求10所述的负极，其中，所述第二活性物质和第一活性物质均为人造石墨。
  12. 一种二次电池，包括如权利要求1-11任一项所述的负极。
  13. 根据权利要求12所述的二次电池，其中，所述二次电池包括锂离子二次电池。
  14. 一种装置，包括如权利要求12或13所述的二次电池。
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