WO2023202289A1 - 负极极片及其制备方法、二次电池、电池模块、电池包和用电装置 - Google Patents

负极极片及其制备方法、二次电池、电池模块、电池包和用电装置 Download PDF

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WO2023202289A1
WO2023202289A1 PCT/CN2023/082058 CN2023082058W WO2023202289A1 WO 2023202289 A1 WO2023202289 A1 WO 2023202289A1 CN 2023082058 W CN2023082058 W CN 2023082058W WO 2023202289 A1 WO2023202289 A1 WO 2023202289A1
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Prior art keywords
layer
negative electrode
graphite
lithium
battery
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PCT/CN2023/082058
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English (en)
French (fr)
Inventor
陈祥斌
瞿登宏
高凯
来佑磊
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宁德时代新能源科技股份有限公司
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Publication of WO2023202289A1 publication Critical patent/WO2023202289A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—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
    • H01M4/133—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
    • H01M4/1391—Processes of manufacture of 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
    • H01M4/139—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
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/20—Mountings; Secondary casings or frames; Racks, modules or packs; Suspension devices; Shock absorbers; Transport or carrying devices; Holders
    • H01M50/258—Modular batteries; Casings provided with means for assembling
    • 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 technical field of secondary batteries, and in particular to a negative electrode plate for secondary batteries, a preparation method of the negative electrode plate, and secondary batteries, battery modules, battery packs and electrical devices including the negative electrode plate. .
  • lithium-ion batteries are widely used in energy storage power systems such as hydraulic, thermal, wind and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, Military equipment, aerospace and other fields. Due to the great development of lithium-ion batteries, higher requirements have been put forward for their energy density, cycle performance and safety performance.
  • graphite is usually used as an active material for negative electrode plates of lithium ion secondary batteries.
  • the rebound rate of the negative electrode plate is too high, causing the expansion force of the lithium-ion battery to be too large, causing the separator to be squeezed, resulting in poor electrolyte infiltration and further polarization. increase.
  • the capacity fading of lithium-ion batteries is accelerated and the service life is shortened.
  • an excessive rebound rate of the negative electrode piece can also cause the corners of the electrode piece to break, increasing the safety risks of lithium-ion batteries.
  • the purpose of this application is to provide a low rebound rate negative electrode sheet, thereby improving the service life and safety performance of lithium-ion batteries using the negative electrode sheet, while ensuring the rate performance of the battery, and reducing the Battery capacity fades.
  • the present application provides the following embodiments.
  • a negative electrode sheet which includes a current collector and an active material layer disposed on at least one surface of the current collector.
  • the active material Layers include:
  • the first graphite layer is disposed on at least one surface of the current collector, the lithium titanate layer is disposed on the surface of the first graphite layer, and the second graphite layer is disposed on the surface of the lithium titanate layer.
  • the OI value of the first graphite layer is greater than or equal to 20.0, and can be selected from 30.0 to 40.0.
  • the OI value of the second graphite layer is less than or equal to 15.0, and can be selected from 8.0 to 12.0.
  • the lithium titanate layer in the active material layer By arranging the lithium titanate layer in the active material layer, the rebound caused by the volume change of the negative electrode piece during the manufacturing process and the battery charging and discharging process is effectively reduced, thereby greatly improving the service life and safety of the lithium-ion battery. performance.
  • a first graphite layer with a higher OI value between the lithium titanate layer and the current collector layer By arranging a second graphite layer with a lower OI value on the surface of the lithium titanate layer, the densification degree of the SEI film on the surface of the active material layer is improved, the consumption of active lithium ions is delayed, and the capacity fading of the battery is reduced.
  • the thickness of the first graphite layer is 100 ⁇ m or less.
  • the first graphite layer has an OI value within the above-mentioned specific range, and at the same time, the adverse effects of graphite volume changes on the rebound characteristics of the negative electrode sheet due to volume changes during the manufacturing and use of lithium-ion batteries are minimized.
  • the thickness of the lithium titanate layer is 25-50 ⁇ m.
  • the lithium titanate layer can fully play the role of reducing the rebound of the negative electrode piece, while maintaining the rate performance of the lithium-ion battery.
  • the thickness of the second graphite layer is 100 ⁇ m or less.
  • the second graphite layer has an OI value within the above-mentioned specific range, and at the same time, the adverse effects of graphite volume changes on the rebound characteristics of the negative electrode sheet due to volume changes during the manufacturing and use of lithium-ion batteries are minimized.
  • the thickness of the active material layer is 50-150 ⁇ m.
  • the negative electrode piece has good wetting ability on the premise of ensuring the energy density of the negative electrode piece.
  • the compacted density of the negative electrode piece is 0.9-1.8 g/cm 3 .
  • the energy density of the lithium-ion battery can be ensured, and at the same time, the rebound rate of the negative electrode piece can be further reduced, thereby ensuring the safety performance, rate performance and cycle performance of the battery.
  • this application provides a method for preparing a negative electrode sheet, including:
  • first graphite layer including first graphite on at least one surface of the current collector
  • lithium titanate layer including lithium titanate on the surface of the first graphite layer
  • a second graphite layer including second graphite is formed on the surface of the lithium titanate layer to obtain a laminate having an active material layer on at least one surface of the current collector.
  • the active material layer includes a first graphite layer, a lithium titanate layer and second graphite layer;
  • the laminate is cold-pressed to obtain a negative electrode piece
  • the OI value of the first graphite is greater than 2.0 and less than or equal to 6.0, and can be selected from 3.0 to 5.0.
  • the OI value of the second graphite is greater than or equal to 0.5 and less than 2.0, and can be selected from 1.0 to 1.5.
  • the first graphite layer and the second graphite layer respectively have OI values within the above-mentioned specific range.
  • the cold pressing pressure is 15-70T.
  • the energy density of the negative electrode sheet can be controlled, and at the same time, potential safety hazards caused by the particles in the active material layer being fragmented during the pressing process are avoided.
  • the OI value of the first graphite layer formed is greater than or equal to 20.0, optionally 30.0-40.0, and the OI value of the second graphite layer formed is less than or equal to 15.0, optionally: 8.0 ⁇ 12.0.
  • the rate performance of the lithium-ion battery using the negative electrode plate can be fully guaranteed, and at the same time, the rate performance of the lithium-ion battery can be reduced. capacity attenuation.
  • the negative electrode piece formed has a compacted density of 0.9 to 1.8 g/cm 3 .
  • the capacity of the lithium-ion battery using the negative electrode sheet can be fully guaranteed, while ensuring that the negative electrode sheet has a compacted density within the above range.
  • the present application provides a secondary battery, which includes:
  • the negative electrode sheet of the first aspect of the application or the negative electrode sheet prepared according to the preparation method of the second aspect of the application;
  • the service life and safety performance of the secondary battery of the present application are improved, while the rate performance is fully guaranteed, and the capacity fading is reduced.
  • the present application provides a battery module, which includes the secondary battery of the third aspect of the present application.
  • the present application provides a battery pack, which includes the battery module of the fourth aspect of the present application.
  • the present application provides an electrical device, which includes the secondary battery of the third aspect of the present application, the battery module of the fourth aspect of the present application, or the battery pack of the fifth aspect of the present application.
  • the negative electrode sheet of the present application by providing an active material layer including a first graphite layer with a specific OI value, a lithium titanate layer and a second graphite layer with a specific OI value on the current collector, the negative electrode can be effectively reduced.
  • the rebound caused by the volume change of the chip during the manufacturing process and the battery charging and discharging process can improve the service life and safety performance of the lithium-ion battery, while fully ensuring the battery's rate performance and reducing the battery's capacity attenuation.
  • FIG. 1 is an exemplary schematic diagram of a negative electrode plate having an active material layer on one surface of a current collector according to an embodiment of the present application.
  • FIG. 2 is a graph showing a change trend in rebound rate of the negative electrode sheet in Example 1, Comparative Examples 1 and 2, and Comparative Examples 1 and 2.
  • Figure 3a is a graph showing the expansion force of the lithium-ion batteries in Example 1, Comparative Examples 1-2 and Comparative Examples 1-2 as a function of the number of cycles.
  • Figure 3b is a graph showing the change in capacity retention rate of the lithium-ion batteries in Example 1, Comparative Examples 1-2 and Comparative Examples 1-2 as a function of the number of cycles.
  • Figure 4a is a graph showing the change in capacity retention rate of the lithium-ion battery in Example 2 and Comparative Examples 3 to 4 as a function of the number of cycles.
  • Figure 4b is a bar graph of the rate capacity retention rate of the lithium ion batteries in Example 2 and Comparative Examples 3 to 4.
  • FIG. 5 is a schematic diagram of a secondary battery according to an embodiment of the present application.
  • FIG. 6 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 5 .
  • FIG. 7 is a schematic diagram of a battery module according to an embodiment of the present application.
  • Figure 8 is a schematic diagram of a battery pack according to an embodiment of the present application.
  • FIG. 9 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG. 8 .
  • FIG. 10 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment 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. Additionally, 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 to 3, 1 to 4, 1 to 5, 2 to 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).
  • Lithium-ion batteries in the related art usually use graphite as the negative active material.
  • negative electrode sheets using graphite as the negative active material are prone to rebound due to volume changes during the manufacturing process and during battery charging and discharging.
  • the rebound of the negative electrode plate causes the cell expansion force to be too large, squeezing the diaphragm, resulting in poor electrolyte infiltration, and then increasing polarization, causing accelerated capacity attenuation of the cell and shortening its service life.
  • excessive rebound of the negative electrode piece will also cause the corners of the electrode piece to break, increasing the safety risk of the battery core. Therefore, in order to improve the service life and safety performance of lithium-ion batteries, it is urgent to reduce the rebound caused by volume changes in the negative electrode plate during the manufacturing process and during the battery charging and discharging process.
  • lithium titanate Li 4 Ti 5 O 12
  • graphite it has been proposed to mix lithium titanate (Li 4 Ti 5 O 12 ) and graphite and apply it to the active material layer of the negative electrode sheet to utilize the "zero strain" of lithium titanate to reduce the rebound of the negative electrode sheet.
  • the electronic conductivity of lithium titanate is only 10 -13 s/cm, which greatly limits the electron transmission between the current collector and the active material layer in the negative electrode piece, resulting in the degradation of the rate performance of lithium-ion batteries.
  • the lithium potential of lithium titanate is 1.5 V, and it cannot form a solid electrolyte interface film (SEI film). Therefore, the active material layer mixed with lithium titanate is difficult to form a dense SEI film, resulting in repeated destruction and regeneration of the SEI film, exacerbating the consumption of active lithium, and thus causing the capacity fading of lithium-ion batteries.
  • the related art negative electrode plates still need to be improved in terms of reducing the rebound rate of the electrode plates, while ensuring the rate performance of the battery and reducing the capacity fading of the battery.
  • the present application proposes a negative electrode sheet, which includes a current collector and an active material layer disposed on at least one surface of the current collector.
  • the active material layer includes:
  • a first graphite layer is disposed on at least one surface of the current collector, a lithium titanate layer is disposed on the surface of the first graphite layer, a second graphite layer is disposed on the surface of the lithium titanate layer, and
  • the OI value of the first graphite layer is greater than or equal to 20.0, and can be selected from 30.0 to 40.0.
  • the OI value of the second graphite layer is less than or equal to 15.0, and can be selected from 8.0 to 12.0.
  • the application provides a lithium titanate layer (63) in the active material layer (60), which can reduce the manufacturing process of the negative electrode sheet (6). Neutralize the rebound caused by volume changes during battery charging and discharging, thereby improving the service life and safety performance of lithium-ion batteries.
  • the lattice constant and volume change of lithium titanate crystals is less than 1% when inserting or extracting lithium ions. This characteristic of lithium titanate can be called "zero strain”. Therefore, providing the lithium titanate layer (63) in the active material layer (60) can reduce the rebound of the negative electrode piece due to volume changes during charging and discharging.
  • providing the lithium titanate layer (63) can also relieve and/or disperse the stress accumulated in the first and second graphite layers (62, 64) of the negative electrode plate during the manufacturing process, such as cold pressing, thereby reducing subsequent use.
  • the pole piece rebounds due to the slow release of stress during the process.
  • the cycle performance and service life of the battery can be improved, the specific capacity attenuation caused by cycling can be reduced, and the battery can have very good resistance to overcharge and over-discharge.
  • by reducing the rebound of the negative electrode piece it can also prevent the electrode piece from breaking at the corners and improve the safety performance of the battery.
  • the lithium titanate layer may include lithium titanate, a conductive agent, a binder, and optionally a thickener.
  • the lithium titanate may be polycrystalline spherical particles.
  • the particle size D50 of the lithium titanate particles may be 4 to 15 ⁇ m.
  • the types of conductive agents, binders and optional thickeners are not specifically limited, and those skilled in the art can select them according to actual needs.
  • the contents of lithium titanate, conductive agent, binder and optional thickener in the lithium titanate layer are not specifically limited, and those skilled in the art can select according to actual needs.
  • the amount of lithium titanate may be 85-96% by weight; the amount of conductive agent may be 0.5-10.0% by weight; and the amount of binder may be 0.3-2.0% by weight %; the amount of optional thickener may be 0.1 to 1.0% by weight.
  • the problem caused by the low electronic conductivity of lithium titanate is solved.
  • the problem of rate performance degradation is greater than or equal to 20.0, and can be selected from 30.0 to 40.0.
  • the first graphite layer has a higher OI value within the above range, which means that a higher proportion of (004) crystal planes parallel to the graphite sheet structure are exposed in the first graphite layer.
  • This structure is very conducive to the flow of electrons on the surface of graphite, and the electron flow
  • the transmission of the current collector greatly increases the electronic conductivity of the negative electrode piece.
  • this structure can also enhance the bonding between the first graphite layer and the current collector. Therefore, disposing the first graphite layer with a higher OI value within the above range on the surface of the current collector can fully ensure the rate performance of the lithium-ion battery by improving the electronic conductivity.
  • the first graphite layer may include first graphite, a conductive agent, a binder, and optionally a thickener.
  • the first graphite may be a commercially available product with certain OI value specifications.
  • the first graphite may be graphite with an OI value greater than 2.0 and less than or equal to 6.0, optionally 3.0 to 5.0.
  • the types of conductive agents, binders and optional thickeners are not specifically limited, and those skilled in the art can select them according to actual needs.
  • the contents of the first graphite, conductive agent, binder and optional thickener in the first graphite layer are not specifically limited, and those skilled in the art can select according to actual needs.
  • the amount of the first graphite may be 90.0-98.0% by weight; the amount of the conductive agent may be 0.3-4.0% by weight; and the amount of the binder may be 0.3-2.0% by weight. ; The amount of optional thickener may be 0.1 to 1.0% by weight.
  • the OI value of the first graphite layer can be adjusted by changing the OI value of the first graphite, the manufacturing process parameters of the negative electrode sheet, such as cold pressing pressure and/or the thickness of the first graphite layer, etc., so that it is greater than or equal to 20.0, optional It is in the range of 30.0 ⁇ 40.0.
  • the conduction rate of lithium ions can be increased, the rate performance of the lithium ion battery can be improved, and the SEI film on the surface of the active material layer can be improved.
  • the degree of densification delays the consumption of active lithium ions, thereby reducing the capacity fading of the battery.
  • the OI value of the second graphite layer can be less than or equal to 15.0, and can be selected from 8.0 to 12.0.
  • the second graphite layer has a lower OI value within the above range, which means that the second graphite layer has a higher proportion of exposed (110) crystal planes perpendicular to the graphite sheet structure.
  • This structure is very conducive to the insertion and extraction of lithium ions in graphite, thereby increasing the conduction rate of lithium ions.
  • the (110) crystal plane of graphite comes into contact with the electrolyte, an SEI film can be formed on it, while the SEI film is not easily formed on the (004) crystal plane. Therefore, the (110) crystal plane with a higher exposure ratio can also increase the density of the SEI film formed on the surface of the negative active material layer, thereby delaying the consumption of active lithium ions during battery charging and discharging and reducing battery capacity fading. Therefore, disposing a second graphite layer with a lower OI value within the above range on the surface of the lithium titanate layer can fully ensure the rate performance of the lithium-ion battery while reducing the capacity fading of the lithium-ion battery.
  • the second graphite layer may include second graphite, a conductive agent, a binder, and optionally a thickener.
  • the second graphite may be a commercially available product with certain OI value specifications.
  • the second graphite may be graphite with an OI value greater than or equal to 0.5 and less than 2.0, optionally ranging from 1.0 to 1.5.
  • the types of conductive agents, binders and optional thickeners are not specifically limited, and those skilled in the art can select them according to actual needs.
  • the contents of the second graphite, conductive agent, binder and optional thickener in the second graphite layer are not specifically limited, and those skilled in the art can select according to actual needs.
  • the amount of the second graphite may be 90.0-98.0% by weight; the amount of the conductive agent may be 0.3-4.0% by weight; and the amount of the binder may be 0.3-2.0% by weight. ; The amount of optional thickener may be 0.1 to 1.0% by weight.
  • the OI value of the second graphite layer can be adjusted by changing the OI value of the second graphite, the manufacturing process parameters of the negative electrode sheet, such as cold pressing pressure and/or the thickness of the second graphite layer, etc., to make it less than or equal to 15.0, optionally Within the range of 8.0 ⁇ 12.0.
  • the thickness of the first graphite layer may be less than or equal to 100 ⁇ m.
  • an OI value of the first graphite layer of greater than or equal to 20.0, optionally 30.0 to 40.0 can be achieved; at the same time, the graphite is affected by volume changes during the manufacturing and use of lithium-ion batteries. The adverse effects caused by the rebound characteristics of the negative electrode piece are minimized, and the productivity of the negative electrode piece can be improved.
  • the thickness of the lithium titanate layer may be 25-50 ⁇ m.
  • the thickness of the lithium titanate layer is greater than or equal to 25 ⁇ m, the lithium titanate layer can fully play the role of reducing the rebound of the negative electrode piece.
  • the thickness of the lithium titanate layer is less than or equal to 50 ⁇ m, the adverse impact of the low electronic conductivity of lithium titanate on the electron transport characteristics of the negative electrode plate is minimized, thereby further ensuring the rate performance of the lithium-ion battery.
  • the thickness of the second graphite layer is less than or equal to 100 ⁇ m.
  • an OI value of the second graphite layer less than or equal to 15.0 and optionally 8.0 to 12.0 can be achieved; at the same time, the graphite is affected by volume changes during the manufacturing and use of lithium-ion batteries. The adverse effects caused by the rebound characteristics of the negative electrode piece are minimized, and the productivity of the negative electrode piece can be improved.
  • the thickness of the active material layer is 50-150 ⁇ m.
  • the thickness of the active material layer is greater than or equal to 50 ⁇ m, the energy density of the negative electrode sheet can be ensured, thereby ensuring the capacity of the battery.
  • the thickness of the active material layer is less than or equal to 150 ⁇ m, the wettability of the pole piece during the preparation process can be ensured and production efficiency can be improved.
  • the compacted density of the negative electrode piece is 0.9-1.8g/cm 3 .
  • Negative pole The compacted density of the sheet is mainly affected by the cold pressing pressure, but also by factors such as the properties of the active material in the active material layer, such as the grain size of lithium titanate.
  • the compacted density of the negative electrode sheet is greater than or equal to 0.9g/ cm3 , the energy density of the lithium-ion battery can be fully ensured, thereby ensuring the battery capacity, reducing the manufacturing cost of the battery, and ensuring the rate performance and cycle performance of the battery. .
  • the compacted density of the negative electrode piece is less than or equal to 1.8g/ cm3 , the wettability of the electrode piece during the preparation process can be ensured, the production efficiency of the electrode piece can be improved, and the rebound of the negative electrode piece can be further reduced, thereby further Slow down the capacity fading caused by excessive battery expansion force, further reduce the safety risks caused by the negative electrode plate rebound, and further improve the battery's rate performance and cycle performance.
  • This application also provides a method for preparing a negative electrode piece, including:
  • first graphite layer including first graphite on at least one surface of the current collector
  • lithium titanate layer including lithium titanate on the surface of the first graphite layer
  • a second graphite layer including a second graphite is formed on the surface of the lithium titanate layer to obtain a laminate having an active material layer on at least one surface of the current collector.
  • the active material layer includes a first graphite layer and a lithium titanate layer. and a second graphite layer;
  • the laminated body is cold-pressed to obtain a negative electrode piece
  • the OI value of the first graphite is greater than 2.0 and less than or equal to 6.0, and can be selected from 3.0 to 5.0.
  • the OI value of the second graphite is greater than or equal to 0.5 and less than 2.0, and can be selected from 1.0 to 1.5. Both the first graphite and the second graphite may be commercially available products with corresponding OI values.
  • the preparation method of the present application can effectively prepare the negative electrode sheet of the first aspect of the present application.
  • the laminate may be formed by coating the first graphite layer, the lithium titanate layer, and the second graphite layer layer by layer in a conventional coating manner. Coating may be performed using a slurry formed by mixing the first graphite, lithium titanate, or the second graphite serving as the negative electrode active material, a conductive agent, a binder, an optional thickener, and deionized water serving as a solvent.
  • the mass ratio of the active material to the solvent deionized water in the slurry can be 1:0.5 ⁇ 2, or optionally 1:0.8 ⁇ 1.5.
  • the shipping viscosity of the slurry can be 5,000 to 25,000 mPa ⁇ s.
  • the slurry will be too thick, the viscosity of the slurry will be too high, and it is difficult to coat, and the uniformity of the coating layer will be poor; if the amount of deionized water added is too high, the slurry will be too thin. To achieve a fixed coating thickness, it is necessary to increase the time of the coating process and reduce the production efficiency of the pole piece.
  • the laminate is The thickness of the first graphite layer formed on at least one surface may be less than or equal to 200 ⁇ m; the thickness of the lithium titanate layer formed on the surface of the first graphite layer may be less than or equal to 100 ⁇ m; the second graphite layer formed on the surface of the lithium titanate layer The thickness may be less than or equal to 200 ⁇ m; the thickness of the active material layer including the first graphite layer, the lithium titanate layer and the second graphite layer may be 100-300 ⁇ m.
  • the cold pressing pressure may range from 15 to 70T.
  • the cold pressing pressure can be determined according to demand, so that combined with the OI value of the graphite raw material, layer thickness and other factors, the OI values of the first graphite layer and the second graphite layer respectively fall into the specific ranges mentioned above.
  • choosing the cold pressing pressure within the above range can also advantageously control the active material of the negative electrode sheet to achieve a reasonable compaction density. When the pressure is greater than or equal to 15T, the compaction density of the negative electrode sheet can be guaranteed, thereby ensuring the energy of the battery. density.
  • the cold pressing pressure is less than or equal to 70T, it can avoid the density of the pole piece being too high, which will lead to a decrease in the wettability of the electrolyte, thereby ensuring the production efficiency of the battery. It can also avoid the particles in the active material layer from being broken during the pressing process, thereby affecting Battery safety.
  • the OI value of the first graphite layer formed can be greater than or equal to 20.0, optionally 30.0 to 40.0, and the OI value of the second graphite layer formed can be less than or equal to 15.0. It can be selected from 8.0 to 12.0.
  • the use of the negative electrode sheet can be fully guaranteed. improve the rate performance of lithium-ion batteries while reducing the capacity fading of lithium-ion batteries.
  • the compacted density of the formed negative electrode piece may be 0.9-1.8 g/cm 3 .
  • the compaction density of the obtained negative electrode sheet is adjusted to the above range, the capacity of the lithium-ion battery using the negative electrode sheet can be fully guaranteed, and the electrode sheet can be ensured at the same time. wettability during the preparation process and the production efficiency of the pole pieces.
  • the thickness of the first graphite layer may be less than or equal to 100 ⁇ m; the thickness of the lithium titanate layer may be 25-50 ⁇ m; and the thickness of the second graphite layer may be less than or equal to 100 ⁇ m.
  • the thickness of the active material layer formed may be 50 to 150 ⁇ m.
  • This application also provides a secondary battery, which includes:
  • the present application also provides a battery module, which includes the secondary battery of the present application as described above.
  • the present application also provides a battery pack, which includes the battery module of the present application as described above.
  • the present application also provides an electrical device, which includes the secondary battery of the present application as described above, the battery module of the present application as described above, or the battery pack of the present application as described above.
  • the negative electrode sheet of the present application by providing an active material layer including a first graphite layer with a specific higher OI value, a lithium titanate layer, and a second graphite layer with a specific lower OI value on the current collector, It can effectively reduce the rebound caused by the volume change of the negative electrode plate during the manufacturing process and the battery charging and discharging process, thereby improving the service life and safety performance of the lithium-ion battery, while fully ensuring the battery's rate performance and reducing the battery's capacity attenuation. .
  • a secondary battery is provided.
  • 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 separator 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 may include a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector.
  • the positive electrode current collector has two surfaces opposite in its own thickness direction, and the positive electrode active material layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.
  • the above-mentioned positive electrode current collector can 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.
  • Composite current collectors can be Metal materials (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) are formed on polymer material substrates (such as polypropylene (PP), polyethylene terephthalate (PET) ), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PET polyethylene terephthalate
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the positive active material layer includes a positive active material.
  • Cathode active materials include, but are not limited to, lithium cobalt oxide, lithium nickel manganese cobalt oxide, lithium nickel manganese aluminate, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium iron silicate, lithium vanadium silicate, Lithium cobalt silicate, lithium manganese silicate, spinel type lithium manganate, spinel type lithium nickel manganate, lithium titanate, etc. One or more of these may be used as the positive electrode active material.
  • the positive active material layer optionally further includes a binder.
  • the binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene tripolymer.
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • PTFE polytetrafluoroethylene
  • vinylidene fluoride-tetrafluoroethylene-propylene terpolymer vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene tripolymer.
  • the positive active material layer optionally further includes a conductive agent.
  • a conductive agent used for the positive active material layer may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the preparation of the positive electrode sheet can be carried out according to methods known in the art.
  • the positive electrode active material, conductive agent and binder can be dispersed in a solvent (such as N-methylpyrrolidone (NMP)) to form a uniform positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, After drying, cold pressing and other processes, the positive electrode piece is obtained.
  • NMP N-methylpyrrolidone
  • the negative electrode sheet in the secondary battery of the present application uses the negative electrode sheet for secondary batteries as described above, which includes a current collector and an active material layer disposed on at least one surface of the current collector.
  • the active material layer includes a third a graphite layer, a lithium titanate layer and a second graphite layer.
  • the first graphite layer is disposed on at least one surface of the current collector
  • the lithium titanate layer is disposed on the surface of the first graphite layer
  • the second graphite layer is disposed on the surface of the lithium titanate layer
  • the OI value of the first graphite layer The OI value of the second graphite layer is less than or equal to 15.0 and can be selected from 8.0 to 12.0.
  • the negative electrode plate In the case where the active material layer is formed on only one surface of the current collector, the negative electrode plate The current collector and the active material layer may have a structure as exemplarily shown in FIG. 1 . In the case where active material layers are formed on both surfaces of the current collector, the two active material layers of the negative electrode plate may have a symmetrical structure.
  • the negative electrode current collector can use metal foil or composite current collector.
  • the metal foil copper foil can be used.
  • the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base material.
  • the composite current collector can be formed by forming metal materials (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyterephthalate Ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • the first graphite layer, lithium titanate layer, and second graphite layer in the negative active material layer may each include other auxiliary agents such as a binder, a conductive agent, and optionally a thickener.
  • the conductive agents used in the first graphite layer, the lithium titanate layer and the second graphite layer can be the same as or different from each other, and those skilled in the art can select according to needs.
  • the conductive agent may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the binders used in the first graphite layer, the lithium titanate layer and the second graphite layer can be the same as or different from each other, and those skilled in the art can select according to needs.
  • the binder may be selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), One or more of polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).
  • the auxiliary agent optionally includes a thickening agent, such as sodium carboxymethyl cellulose (CMC-Na) and the like.
  • a first graphite layer including first graphite can be formed on at least one surface of the current collector, and a lithium titanate layer including lithium titanate can be formed on the surface of the first graphite layer.
  • a second graphite layer including second graphite is formed on the surface of the layer, thereby obtaining an active material layer including a first graphite layer, a lithium titanate layer and a second graphite layer, and then the obtained active material layer has on at least one surface of the current collector
  • the laminate of active material layers is cold-pressed, and after drying, cold-pressing and other processes, a negative electrode piece is obtained.
  • the OI value of the first graphite is greater than 2.0 and less than or equal to 6.0, and can be selected from 3.0 to 5.0.
  • the OI value of the second graphite is greater than or equal to 0.5 and less than 2.0, and can be selected from 1.0 to 1.5.
  • the above-mentioned first graphite, conductive agent, binder and optional other auxiliaries can be dispersed in a solvent (such as deionized water) to form a uniform slurry, and the slurry can be applied through a conventional coating process. Coating on at least one surface of the negative electrode current collector, and then drying to obtain a first graphite layer. Lithium titanate, conductive agent, binder and optional other auxiliaries are dispersed in a solvent (such as deionized water) to form a uniform slurry, and the slurry is coated on the first layer through a conventional coating process. on the surface of the graphite layer, and then dried to obtain a lithium titanate layer.
  • a solvent such as deionized water
  • the above-mentioned second graphite, conductive agent, binder and optional other auxiliaries are dispersed in a solvent (such as deionized water) to form a uniform slurry, and the slurry is coated on the titanium surface through a conventional coating process. on the surface of the lithium acid layer, and then dried to obtain a second graphite layer.
  • a solvent such as deionized water
  • the obtained laminate including the current collector, the first graphite layer, the lithium titanate layer and the second graphite layer is cold-pressed under a pressure of 15 to 70 T to obtain a negative electrode piece.
  • the electrolyte plays a role in conducting ions between the positive and negative electrodes.
  • the type of electrolyte in this application can be selected according to needs.
  • the electrolyte can be liquid, gel, or completely solid.
  • the electrolyte is an electrolyte solution.
  • the electrolyte solution includes electrolyte salts and solvents.
  • the electrolyte salt may be selected from lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium bisfluorosulfonyl imide ( LiFSI), lithium bistrifluoromethanesulfonimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoromethanesulfonate borate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO 2 F 2 ), one or more of lithium difluorodioxalate phosphate (LiDFOP) and lithium tetrafluorooxalate phosphate (LiTFOP).
  • LiFSI lithium bisfluorosulfonyl imide
  • LiTFSI lithium bis
  • the solvent may be selected from fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), carbonic acid Dimethyl ester (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA) ), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), butyric acid
  • FEC fluoroethylene carbonate
  • EC ethylene carbonate
  • PC propylene carbonate
  • EMC diethyl carbonate
  • DMC dipropyl carbonate
  • MPC methyl propyl carbonate
  • EPC ethyl propy
  • additives are optionally included in the electrolyte.
  • the electrolyte may include negative electrode film-forming additives, positive electrode film-forming additives, additives to improve battery overcharge performance, additives to improve battery high-temperature performance, additives to improve battery low-temperature performance, etc.
  • the separator separates the positive and negative electrodes, preventing short circuits within the battery and allowing active ions to move between the positive and negative electrodes through the separator.
  • the type of separator is not particularly limited, and any well-known porous structure separator with good chemical stability and mechanical stability can be used.
  • the material of the separator can be selected from fiberglass films, non-woven films, polyethylene (PE) films, polypropylene (PP) films, polyvinylidene fluoride films, and films containing one of them or One or more of two or more multi-layer composite films.
  • the separator can be a single-layer separator or a multi-layer composite separator, with no particular limitation.
  • 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 can be made into an electrode assembly through a winding process or a lamination process.
  • the second graphite layer on the negative electrode sheet faces the separator.
  • the secondary battery may include an outer packaging.
  • the outer packaging can be used to package the electrode assembly and electrolyte as described above.
  • 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. Examples of plastics include polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).
  • FIG. 5 shows a square-structured secondary battery 5 as an example.
  • the outer package may include a housing 51 and a top cover assembly 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 top cover assembly 53 can cover the opening to close the accommodation cavity.
  • the positive electrode piece, the negative electrode piece and the separator 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. electrolyte Wet 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. 7 shows the 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 selected by those skilled in the art according to the application and capacity of the battery pack.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box.
  • the battery box includes an upper box 2 and a lower box 3 .
  • the upper box 2 can be covered with the lower box 3 and form a closed space for accommodating the battery module 4 .
  • Multiple battery modules 4 can be arranged in the battery box in any manner.
  • the present application also provides an electrical device, which includes the secondary battery, battery module, or battery pack provided by the present application.
  • the secondary battery, battery module, or battery pack can be used as a power source for the power-consuming device, or as an energy storage unit of the power-consuming device.
  • Electrical devices may include, but are not limited to, 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, electric golf golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
  • secondary batteries, battery modules or battery packs can be selected according to its usage requirements.
  • Figure 10 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 power-consuming device may be a mobile phone, a tablet computer, a laptop computer, etc.
  • the electrical device is usually required to be light and thin, and secondary batteries can be used as power sources.
  • lithium titanate (Jiawei New Energy Co., Ltd., model T200), conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium hydroxymethylcellulose (CMC) according to 97.2: Add the mass ratio of 0.8:0.8:1.2 to deionized water and stir thoroughly. After mixing evenly, prepare a slurry (solid content 50%) for forming a lithium titanate layer. Through conventional processes, the above slurry is evenly coated on the first graphite layer formed above, and then dried at a temperature of 80 to 150° C., thereby forming a lithium titanate layer on the first graphite layer.
  • SBR binder styrene-butadiene rubber
  • CMC thickener sodium hydroxymethylcellulose
  • the second graphite with an OI value greater than or equal to 0.5 and less than 2.0, the conductive agent carbon black, the binder styrene-butadiene rubber (SBR), and the thickener sodium hydroxymethylcellulose (CMC) according to 97.2:0.8:0.8 : 1.2 was added to deionized water and stirred thoroughly. After mixing evenly, a slurry (solid content 50%) for forming the second graphite sheet layer was prepared. Through conventional processes, the above slurry is evenly coated on the lithium titanate layer formed above, and then dried at a temperature of 80 to 150° C., thereby forming a second graphite layer on the lithium titanate layer.
  • the current collector formed as described above is coated with a first graphite layer, a lithium titanate layer and a third
  • the pole piece of the active material layer of the digraphite layer is cold-pressed under a pressure of 15 to 70T, and then slit to obtain the negative electrode piece.
  • the following method is used to prepare the battery core.
  • the cathode active material LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM 811) (Ningbo Rongbai New Energy Technology Co., Ltd., model S85E), conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) (Japan Kureha Co., Ltd., model W9200) was mixed according to the mass ratio of 97:1.5:1.5 and the solvent N-methylpyrrolidone (NMP) was added, and then stirred thoroughly and mixed evenly to prepare a cathode slurry (solid content 70%).
  • NCM 811 Noningbo Rongbai New Energy Technology Co., Ltd., model S85E
  • PVDF binder polyvinylidene fluoride
  • the positive electrode slurry is evenly coated on a current collector aluminum foil with a thickness of 13 ⁇ m at a coating amount of 0.2 mg/ mm2 , then dried at a temperature of 100 to 130°C, and cooled under a pressure of 40T. Press and then cut to obtain the positive electrode piece.
  • the positive electrode sheet obtained in the above steps, the polypropylene film as the separator (Yunnan Enjie New Materials Co., Ltd., model ND7) and the negative electrode sheet were stacked in the above order, so that the second graphite layer on the negative electrode sheet faced the separator.
  • the bare cells are obtained by winding. Weld the tabs on the bare battery core and install the bare battery core into the aluminum case.
  • the assembled battery core is baked at 100°C to remove water, and then the electrolyte is injected to obtain an uncharged battery. After the uncharged battery is left standing, hot and cold pressed, formed, shaped, and tested for capacity, the lithium-ion battery is obtained.
  • the OI values of the first and second graphite layers were determined by X-ray diffraction method on a polycrystalline X-ray diffractometer (Bruker, D8Discover). Place the sample to be tested horizontally on the sample stage On the graph, continuous mode scanning (scanning interval 10-80°, scanning speed 2°/min) was used to obtain the corresponding diffraction spectrum. According to the diffraction spectrum, it is determined that the diffraction peak intensity of the (004) crystal plane is I(004), and the diffraction peak intensity of the (110) crystal plane is I(110).
  • the OI value calculation formula is as follows:
  • the samples of the first graphite layer and the second graphite layer to be tested are obtained by the following method:
  • the thickness values of the first graphite layer, lithium titanate layer and second graphite layer of the negative electrode piece are d1, d2 and d3 respectively.
  • the thickness of graphite that should be scraped off is determined by a micrometer. Cut a small piece of 2 cm ⁇ 2 cm from the negative electrode sheet obtained above by scraping off the predetermined thickness layer to obtain a sample for measuring the OI value of the second graphite layer.
  • the thickness values of the first graphite layer, lithium titanate layer and second graphite layer of the negative electrode piece are d1, d2 and d3 respectively.
  • Use a scraper to evenly scrape off the surface (d3+d2 +d1/2) thickness of graphite, the thickness to be scraped off is determined by a micrometer. Cut a small piece of 2 cm ⁇ 2 cm from the negative electrode sheet obtained above by scraping off the prescribed thickness layer to obtain a sample for measuring the OI value of the first graphite layer.
  • the thickness of the negative electrode piece after cold pressing is recorded as R.
  • the positive electrode sheet, separator and negative electrode sheet are laminated, and then after sufficient rebound, before being rolled into a bare cell, the thickness of the negative electrode sheet is measured and recorded as S.
  • T After being fully charged, measure the thickness of the negative electrode piece and record it as T.
  • the thickness of the negative electrode piece was measured and recorded as U.
  • a clamp consisting of three aluminum plates was used to hold the battery and pressure sensor before charging and discharging the battery. Specifically, place the pressure sensor in the upper space between the first aluminum plate and the second aluminum plate, place the battery in the lower space between the second aluminum plate and the third aluminum plate, and then apply a preload force of 200kgf. F 0 secure the clamp with bolts.
  • the battery was cycled at a temperature of 45°C under cycle conditions of a charge rate of 0.5C and a discharge rate of 1C.
  • the reading of the pressure sensor in the clamp when the battery cell is fully charged is recorded as the battery expansion force F n of the lithium ion corresponding to the number of cycles.
  • the expansion force growth rate E n of the battery per cycle is calculated according to the following formula:
  • the rate capacity retention rate Q 2 of the battery is measured. Specifically, at 25°C, Charge the battery to 4V at a constant current of 1/3C, then charge at a constant voltage of 4V until the current is 0.05C, leave it aside for 5 minutes, and then discharge it to 2.5V at 0.1C. The average capacity obtained after 5 cycles is recorded as the initial capacity D 0 . Then, the battery was charged under the same conditions as above, discharged at 2C, and the average capacity obtained after 5 cycles was recorded as the initial capacity D 2 .
  • the rate capacity retention rate Q2 of the battery is calculated according to the following formula:
  • the first graphite with an OI value of 5.0 (Betteri New Materials Group Co., Ltd., model BFC-18) to prepare the slurry for forming the first graphite layer
  • the slurry is coated on both surfaces of the current collector at a coating amount of 0.04 mg/mm, and then dried at 100°C to form a first graphite layer with a thickness of 60 ⁇ m; it will be used to form lithium titanate
  • the slurry of the layer is coated on the first graphite layer at a coating amount of 0.12 mg/ mm2 , and then dried at 100°C to form a lithium titanate layer with a thickness of 80 ⁇ m
  • use the second graphite with an OI value of 1.0 (Betteri New Materials Group Co., Ltd., model GSN) prepares a slurry for forming the second graphite layer, coats the slurry on the lithium titanate layer at a coating amount of 0.04mg/ mm2 , and then
  • the active material layer including the first graphite layer, the lithium titanate layer and the second graphite layer is coated on both surfaces of the current collector.
  • the electrode piece coated with the above active material layer on the current collector was cold pressed under a pressure of 40T, and then cut into pieces to obtain the negative electrode piece of Example 1.
  • the thicknesses of the first graphite layer, lithium titanate layer and second graphite layer in the obtained negative electrode sheet were 30 ⁇ m, 40 ⁇ m and 30 ⁇ m respectively.
  • the thickness R of the negative electrode piece obtained by cold pressing is 206 ⁇ m, and the compacted density is 1.6 g/cm 3 .
  • the negative electrode sheet of Example 1 was used to prepare a lithium ion battery.
  • the rebound rate of the negative electrode piece of Example 1 before winding was measured by the method described above.
  • the rebound rate of the negative electrode sheet after full charge, the rebound rate of the negative electrode sheet after 100 cycles, and the rebound rate of the negative electrode sheet after 200 cycles of the lithium-ion battery prepared using the negative electrode sheet of Example 1 were measured by the method described above.
  • the measurement results of the rebound rate of the negative electrode piece of Example 1 at different stages are shown in Table 1.
  • Example 1 negative The change trend of the rebound rate of the pole piece is shown in Figure 2.
  • the cyclic expansion force of the lithium ion battery prepared in Example 1 was measured by the test method described above.
  • the results of the cyclic expansion force and the corresponding expansion force growth rate of the lithium-ion battery prepared in Example 1 after 200 cycles are also shown in Table 1.
  • the graph of the expansion force of the lithium-ion battery prepared in Example 1 as a function of the number of cycles is shown in Figure 3a.
  • the cycle capacity retention rate of the lithium ion battery prepared in Example 1 was measured by the test method described above.
  • the results of the cycle capacity retention rate P 200 of the lithium-ion battery prepared in Example 1 after 200 cycles are also shown in Table 1.
  • the graph of the cycle capacity retention rate of the lithium-ion battery prepared in Example 1 as a function of the number of cycles is shown in Figure 3b.
  • a negative electrode plate including only an active material layer of the second graphite layer was formed on a current collector copper foil with a thickness of 6 ⁇ m.
  • the formation method of the second graphite layer is basically the same as the corresponding method in Example 1, but the thickness of the active material layer including the second graphite layer after the coating and drying processes is 200 ⁇ m.
  • the electrode piece coated with the above active material layer on the current collector was cold pressed under a pressure of 40T, and then cut into pieces to obtain the negative electrode piece of Comparative Example 1.
  • the thickness of the active material layer after cold pressing was 100 ⁇ m.
  • the thickness R of the negative electrode piece obtained by cold pressing is 206 ⁇ m, and the compacted density is 1.6 g/cm 3 .
  • the OI value of the second graphite layer in the negative electrode sheet of Comparative Example 1 was measured by the test method described above, and the results are also shown in Table 1.
  • the cyclic expansion force of the lithium ion battery prepared in Comparative Example 1 was measured by the test method described above.
  • the results of the cyclic expansion force and the corresponding expansion force growth rate after 200 cycles using the lithium-ion battery prepared in Comparative Example 1 are also shown in Table 1.
  • the graph of the expansion force of the lithium-ion battery prepared in Comparative Example 1 as a function of the number of cycles is shown in Figure 3a.
  • a negative electrode piece including only an active material layer of the first graphite layer was formed on a current collector copper foil with a thickness of 6 ⁇ m.
  • the formation method of the first graphite layer is basically the same as the corresponding method in Example 1, and the only difference lies in the thickness of the active material layer including only the first graphite layer after the coating and drying processes. is 200 ⁇ m.
  • the electrode piece coated with the above active material layer on the current collector was cold pressed under a pressure of 40T, and then cut into pieces to obtain the negative electrode piece of Comparative Example 2.
  • the thickness of the active material layer after cold pressing was 100 ⁇ m.
  • the thickness R of the negative electrode piece obtained by cold pressing is 206 ⁇ m, and the compacted density is 1.6 g/cm 3 .
  • the OI value of the first graphite layer in the negative electrode sheet of Comparative Example 2 was measured by the test method described above, and the results are also shown in Table 1.
  • the cyclic expansion force of the lithium ion battery prepared in Comparative Example 2 was measured by the test method described above.
  • the results of the cyclic expansion force and the corresponding expansion force growth rate after 200 cycles using the lithium-ion battery prepared in Comparative Example 2 are also shown in Table 1.
  • the graph of the expansion force of the lithium-ion battery prepared in Comparative Example 2 as a function of the number of cycles is shown in Figure 3a.
  • the cycle capacity retention rate of the lithium ion battery prepared in Comparative Example 2 was measured by the test method described above.
  • the results of the cycle capacity retention rate P 200 of the lithium-ion battery prepared in Comparative Example 2 after 200 cycles are also shown in Table 1.
  • the graph of the cycle capacity retention rate of the lithium-ion battery prepared in Comparative Example 2 as a function of the number of cycles is shown in Figure 3b.
  • a negative electrode sheet including only an active material layer of a lithium titanate layer and a second graphite layer was formed on a current collector copper foil with a thickness of 6 ⁇ m.
  • the formation method of the lithium titanate layer and the second graphite layer is basically the same as the corresponding method in Example 1.
  • the thicknesses of the lithium titanate layer and the second graphite layer formed after the coating and drying processes were 100 ⁇ m and 100 ⁇ m respectively.
  • the electrode piece coated with the above-mentioned active material layer on the current collector was cold-pressed under a pressure of 40 T, and then cut into pieces to obtain the negative electrode piece of Comparative Example 1.
  • the thickness of the active material layer after cold pressing was 100 ⁇ m.
  • the thickness R of the negative electrode piece obtained by cold pressing is 206 ⁇ m, and the compacted density is 1.6 g/cm 3 .
  • the OI value of the second graphite layer in the negative electrode piece of Comparative Example 1 was measured by the test method described above, and the results are also shown in Table 1.
  • the cyclic expansion force of the lithium ion battery prepared in Comparative Example 1 was measured by the test method described above.
  • the results of the cyclic expansion force and the corresponding expansion force growth rate after 200 cycles using the lithium-ion battery prepared in Comparative Example 1 are also shown in Table 1.
  • the graph of the expansion force of the lithium-ion battery prepared in Comparative Example 1 as a function of the number of cycles is shown in Figure 3a.
  • the cycle capacity retention rate of the lithium ion battery prepared in Comparative Example 1 was measured by the test method described above.
  • the results of the cycle capacity retention rate P 200 of the lithium-ion battery prepared in Comparative Example 1 after 200 cycles are also shown in Table 1.
  • the graph of the cycle capacity retention rate of the lithium-ion battery prepared in Comparative Example 1 as a function of the number of cycles is shown in Figure 3b.
  • a negative electrode sheet including only an active material layer of a first graphite layer and a lithium titanate layer was formed on a current collector copper foil with a thickness of 6 ⁇ m.
  • the formation method of the first graphite layer and the lithium titanate layer is basically the same as the corresponding method in Example 1.
  • the thicknesses of the first graphite layer and the lithium titanate layer formed after the coating and drying processes were 100 ⁇ m and 100 ⁇ m respectively. ⁇ m.
  • the electrode piece coated with the above active material layer on the current collector was cold-pressed under a pressure of 40 T, and then cut into pieces to obtain the negative electrode piece of Comparative Example 2.
  • the thickness of the active material layer after cold pressing was 100 ⁇ m.
  • the thickness R of the obtained negative electrode piece was 206 ⁇ m, and the compacted density was 1.6 g/cm 3 .
  • the OI value of the first graphite layer in the negative electrode sheet of Comparative Example 2 was measured by the test method described above, and the results are also shown in Table 1.
  • the negative electrode sheet of Comparative Example 2 was used to prepare a lithium ion battery by the method described above.
  • the rebound rate of the negative electrode piece of Comparative Example 2 at different stages was measured by the method described above, and the results are also shown in Table 1.
  • the change trend of the rebound rate of the negative electrode piece of Comparative Example 2 is shown in Figure 2.
  • the cyclic expansion force of the lithium ion battery prepared in Comparative Example 2 was measured by the test method described above.
  • the results of the cyclic expansion force and the corresponding expansion force growth rate of the lithium-ion battery prepared in Comparative Example 2 after 200 cycles are also shown in Table 1.
  • the graph of the expansion force of the lithium-ion battery prepared in Comparative Example 2 as a function of the number of cycles is shown in Figure 3a.
  • the cycle capacity retention rate of the lithium ion battery prepared in Comparative Example 2 was measured by the test method described above.
  • the results of the cycle capacity retention rate P 200 of the lithium-ion battery prepared in Comparative Example 2 after 200 cycles are also shown in Table 1.
  • the graph of the cycle capacity retention rate of the lithium-ion battery prepared in Comparative Example 2 as a function of the number of cycles is shown in Figure 3b.
  • the active material layer of the negative electrode sheet includes a first graphite layer with a relatively high OI value, a lithium titanate layer, and a second graphite layer with a relatively low OI value.
  • the rebound of the negative electrode plate during the manufacturing process and battery charge and discharge cycles is suppressed.
  • the rate performance of the lithium-ion battery is fully guaranteed, and the lithium-ion battery during the cycle process The capacity fading is significantly reduced.
  • the negative electrode sheet does not include lithium titanate, so the rebound of the negative electrode sheet during the manufacturing process and cycling process of the lithium-ion battery cannot be suppressed.
  • the rebound rate of the negative electrode sheet was obviously too high; as shown in Figure 3a, in the lithium-ion battery manufacturing process During the charge and discharge cycle of ion batteries, the expansion force of the battery is also obviously too high.
  • the cycle performance of the battery is poor, and the battery capacity significantly decays as the number of charge and discharge cycles increases.
  • Comparative Example 1 the rebound of the negative electrode sheet was reduced, but because the active material layer did not include the first graphite layer and the lithium titanate layer was directly formed on the surface of the current collector, the electron conductivity of the negative electrode sheet was poor. Compared with Example 1, the lithium-ion battery of Comparative Example 1 has poor rate performance, and both rate capacity retention rates Q1 and Q2 are significantly reduced.
  • the negative electrode plates and lithium ion batteries of Examples 2 to 8 and Comparative Examples 3 to 4 were prepared by substantially the same method as in Example 1, except that the only difference lies in the OI value of the first graphite and/or the second graphite used. They are shown in Table 2 respectively.
  • the OI values of the first graphite layer and the second graphite layer in the negative electrode sheets of Examples 2 to 8 and Comparative Examples 3 to 4 measured according to the method described above are also shown in Table 2.
  • the lithium titanate layer included in the active material layer can effectively suppress the rebound of the negative electrode piece.
  • the OI values of the first graphite layer disposed on the surface of the current collector are all greater than or equal to 20.0, this means that the first graphite layer has a relatively high proportion of (004) crystal planes parallel to the graphite sheet structure exposed. It is beneficial to the flow of electrons on the graphite surface and the transmission of electrons through the current collector. The electron conductivity of the negative electrode plate is greatly increased, thereby fully ensuring the rate performance of the lithium-ion battery.
  • the OI values of the second graphite layer are all less than 15.0, this means that a relatively large proportion of the second graphite layer is exposed
  • the higher (110) crystal plane perpendicular to the graphite sheet structure is conducive to the insertion and extraction of lithium ions in graphite, and the lithium ion conduction rate of the negative electrode sheet is greatly increased.
  • the second graphite layer has a higher proportion of (110) crystal faces exposed, which can form a denser and more stable SEI film on the interface when in contact with the electrolyte, thereby delaying the formation of active lithium ions during the battery charge and discharge process. consumption, significantly reducing battery capacity fading.
  • the cycle capacity retention rate P 200 of the lithium ion battery after 200 cycles reaches more than 88.6%
  • the rate capacity retention rates Q 1 and Q 2 reach more than 84.0% and 76.0% respectively.
  • the negative electrode sheets and lithium ion batteries of Examples 9-10 were prepared by substantially the same method as in Example 1, except that the OI values of the first graphite and/or the second graphite used are as shown in Table 3 respectively. .
  • the OI values of the first graphite layer and the second graphite layer in the negative electrode sheets of Examples 9 to 10 measured according to the method described above are also shown in Table 3.
  • the OI value of the second graphite layer is within the optional range of 8 to 12 in this application. It can be seen from the results in Table 2 and Table 3 that compared with Examples 3 to 5, when the OI value of the second graphite layer is within the above optional range, the cycle performance and rate of the lithium-ion battery can be better balanced. Performance improvements.
  • the negative electrode sheets and lithium ion batteries of Examples 11 to 12 were prepared by substantially the same method as in Example 1, except that during the preparation process of the negative electrode sheets, the coating amount of the slurry was adjusted so that The thicknesses of the first graphite layer, the lithium titanate layer and the second graphite layer in the negative electrode sheets of Examples 11 to 12 after the cold pressing process are as shown in Table 4.
  • the thickness of the lithium titanate layer is within the optional range of 25 to 50 ⁇ m in this application, and can maintain lithium ions. While improving the cycle performance and rate performance of the battery, it ensures that the lithium titanate layer can fully exert its effect of inhibiting the rebound of the negative electrode piece.
  • the negative electrode sheets and lithium ion batteries of Examples 13 to 14 were prepared by substantially the same method as in Example 1, except that during the preparation process of the negative electrode sheets, the coating amount of the slurry was adjusted so that The compacted densities of the negative electrode sheets of Examples 13 to 14 are shown in Table 4.
  • the compacted density of the negative electrode piece is within the optional range of 0.9 to 1.8 g/cm 3 in this application. It can be seen from the results in Table 1 and Table 4 that compared with Example 14, the electrolyte infiltration ability of the negative electrode plate is fully guaranteed, thereby further ensuring the rate performance of the battery. In addition, the compacted density of the negative electrode piece is within the above-mentioned limited range of the present application, which can further reduce the rebound of the negative electrode piece during the manufacturing process of the lithium-ion battery and the charge and discharge cycle.

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Abstract

本申请提供了一种二次电池用负极极片及其制备方法，以及包括该负极极片的二次电池、电池模块、电池包和用电装置。本申请的负极极片包括集流体和设置在集流体的至少一个表面上的活性材料层，活性材料层包括第一石墨层、钛酸锂层和第二石墨层，第一石墨层设置在所述集流体的至少一个表面上，钛酸锂层设置在所述第一石墨层的表面上，第二石墨层设置在所述钛酸锂层的表面上，并且第一石墨层的OI值大于等于20.0，第二石墨层的OI值小于等于15.0。

Description

负极极片及其制备方法、二次电池、电池模块、电池包和用电装置
相关申请的交叉引用
本申请要求享有于2022年04月20日提交的名称为“负极极片及其制备方法、二次电池、电池模块、电池包和用电装置”的中国专利申请202210414297.0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
本申请涉及二次电池技术领域，尤其是涉及一种二次电池用负极极片，该负极极片的制备方法，以及包括该负极极片的二次电池、电池模块、电池包和用电装置。
背景技术
近年来，随着锂离子电池的应用范围越来越广泛，锂离子电池广泛应用于水力、火力、风力和太阳能电站等储能电源系统，以及电动工具、电动自行车、电动摩托车、电动汽车、军事装备、航空航天等多个领域。由于锂离子电池取得了极大的发展，因此对其能量密度、循环性能和安全性能等也提出了更高的要求。
相关技术中通常使用石墨作为锂离子二次电池负极极片的活性材料。然而，在相关技术的锂离子二次电池的制造和使用过程中，负极极片的反弹率过高，使得锂离子电池的膨胀力过大，隔膜受到挤压，电解液浸润不良，进而极化增大。导致锂离子电池的容量衰减加速，使用寿命缩短。另一方面，负极极片的反弹率过大还会导致极片拐角发生断裂，加大锂离子电池的安全风险。
因此，相关技术中亟需反弹率降低、从而提升锂离子电池的使用寿命和安全性能的负极极片。
发明内容
鉴于相关技术中存在的问题，本申请的目的在于提供一种低反弹率负极极片，从而提升使用该负极极片的锂离子电池的使用寿命和安全性能，同时保证电池的倍率性能，并且减少电池的容量衰减。
为了解决上述技术问题，本申请提供了如下的实施例，在一方面，本申请提供一种负极极片，其包括集流体和设置在集流体的至少一个表面上的活性材料层，该活性材料层包括：
第一石墨层；
钛酸锂层；和
第二石墨层，
第一石墨层设置在集流体的至少一个表面上，钛酸锂层设置在第一石墨层的表面上，第二石墨层设置在钛酸锂层的表面上。
第一石墨层的OI值大于等于20.0，可选为30.0～40.0，第二石墨层的OI值小于等于15.0，可选为8.0～12.0。
由此，通过在活性材料层中设置钛酸锂层，有效地减少了负极极片在制造工艺中以及电池充放电过程中由于体积变化造成的反弹，从而大大提升锂离子电池的使用寿命和安全性能。通过在钛酸锂层和集流体层之间设置具有较高OI值的第一石墨层，解决了钛酸锂电子电导率过低造成倍率性能劣化的问题。通过在钛酸锂层的表面上设置具有较低OI值的第二石墨层，提升了活性材料层表面SEI膜的致密化程度，延缓了活性锂离子的消耗，从而减少了电池的容量衰减。
在任意实施方式中，第一石墨层的厚度小于等于100μm。
由此，可以保证第一石墨层具有上述特定范围内的OI值，同时，使得石墨在锂离子电池制造和使用过程中因体积变化对负极极片的反弹特性造成的不利影响得以最小化。
在任意实施方式中，钛酸锂层的厚度为25～50μm。
由此，可以充分发挥钛酸锂层减少负极极片反弹的作用，同时，保持锂离子电池的倍率性能。
在任意实施方式中，第二石墨层的厚度小于等于100μm。
由此，可以保证第二石墨层具有上述特定范围内的OI值，同时，使得石墨在锂离子电池制造和使用过程中因体积变化对负极极片的反弹特性造成的不利影响得以最小化。
在任意实施方式中，活性材料层的厚度为50～150μm。
由此，可以在保证负极极片能量密度的前提下，保证负极极片具有良好的浸润能力。
在任意实施方式中，负极极片的压实密度为0.9～1.8g/cm3。
由此，可以确保锂离子电池的能量密度，同时，进一步减少负极极片的反弹率，从而确保电池的安全性能、倍率性能和循环性能。
在第二方面，本申请提供一种负极极片的制备方法，包括：
提供集流体；
在集流体的至少一个表面上形成包括第一石墨的第一石墨层；
在第一石墨层的表面上形成包括钛酸锂的钛酸锂层；
在钛酸锂层的表面上形成包括第二石墨的第二石墨层，得到在集流体的至少一个表面上具有活性材料层的层叠体，活性材料层包括第一石墨层、钛酸锂层和第二石墨层；
对层叠体进行冷压，得到负极极片；
其中，第一石墨的OI值大于2.0且小于等于6.0，可选为3.0～5.0，第二石墨的OI值大于等于0.5且小于2.0，可选为1.0～1.5。
由此，可以保证负极极片经冷压后，第一石墨层和第二石墨层分别具有上述特定范围内的OI值。
在任意实施方式中，冷压压力为15～70T。
由此，可以控制负极极片的能量密度，同时，避免了活性材料层中的颗粒在压制过程中碎裂而产生的安全性隐患。
在任意实施方式中，对层叠体进行冷压后，形成的第一石墨层的OI值大于等于20.0，可选为30.0～40.0，形成的第二石墨层的OI值小于等于15.0，可选为8.0～12.0。
由此，如上文所述，通过保证第一石墨层和第二石墨层分别具有上述特定范围内的OI值，能够充分保证应用该负极极片的锂离子电池的倍率性能，同时减少锂离子电池的容量衰减。
在任意实施方式中，对叠体进行冷压后，形成的负极极片的压实密度为0.9～1.8g/cm3。
由此，如上文所述，通过保证负极极片具有以上范围内的压实密度，能够充分保证应用该负极极片的锂离子电池的容量，同时确保极 片在制备过程中的浸润性以及极片的生产效率。
在第三方面，本申请提供一种二次电池，其包括：
正极极片；
本申请第一方面的负极极片、或根据本申请第二方面的制备方法制备的负极极片；
电解质；和
隔膜。
如上所述，本申请的二次电池的使用寿命和安全性能得到提升，同时倍率性能得以充分保证，并且容量衰减得以减少。
在第四方面，本申请提供一种电池模块，其包括本申请第三方面的二次电池。
在第五方面，本申请提供一种电池包，其包括本申请第四方面的电池模块。
在第六方面，本申请提供一种用电装置，其包括本申请第三方面的二次电池、本申请第四方面的电池模块、或本申请第五方面的电池包。
在本申请的负极极片中，通过在集流体上提供包括具有特定OI值第一石墨层、钛酸锂层和具有特定OI值的第二石墨层的活性材料层，能够有效地减少负极极片在制造工艺中以及电池充放电过程中由于体积变化造成的反弹，从而提升锂离子电池的使用寿命和安全性能，同时充分保证电池的倍率性能，同时减少电池的容量衰减。
附图说明
图1是本申请一实施方式的在集流体的一个表面上具有活性材料层的负极极片的示例性示意图。
图2是实施例1、对照例1～2和比较例1～2中的负极极片的反弹率变化趋势图。
图3a是实施例1、对照例1～2和比较例1～2中的锂离子电池的膨胀力随循环次数变化的曲线图。
图3b是实施例1、对照例1～2和比较例1～2中的锂离子电池的容量保持率随循环次数变化的曲线图。
图4a是实施例2和比较例3～4中的锂离子电池的容量保持率随循环次数变化的曲线图。
图4b是实施例2和比较例3～4中的锂离子电池的倍率容量保持率的柱状图。
图5是本申请一实施方式的二次电池的示意图。
图6是图5所示的本申请一实施方式的二次电池的分解图。
图7是本申请一实施方式的电池模块的示意图。
图8是本申请一实施方式的电池包的示意图。
图9是图8所示的本申请一实施方式的电池包的分解图。
图10是以本申请一实施方式的二次电池用作电源的用电装置的示意图。
附图标记说明：
1 电池包
2 上箱体
3 下箱体
4 电池模块
5 二次电池
51 壳体
52 电极组件
53 顶盖组件
6 负极极片
61 集流体
60 活性材料层
62 第一石墨层
63 钛酸锂层
64 第二石墨层
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二次电池用负极极片及其制备方法、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，可选是顺序进行的。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)。
相关技术中的锂离子电池通常使用石墨作为负极活性材料，但以石墨为负极活性材料的负极极片容易在制造工艺中以及在电池充放电过程中由于体积变化而造成反弹。一方面，负极极片反弹导致电芯膨胀力过大，挤压隔膜导致电解液浸润不良，进而极化增大，引发电芯容量衰减加速，使用寿命缩短。另一方面，负极极片反弹过大还会导致极片拐角发生断裂，加大电芯的安全风险。因此，为了提升锂离子电池的使用寿命和安全性能，亟需减少负极极片在制造工艺中以及电池充放电过程中由于体积变化造成的反弹。
相关技术中已提出将钛酸锂(Li4Ti5O12)与石墨混合应用于负极极片的活性材料层，以利用钛酸锂的“零应变性”来减少负极极片的反弹。然而，钛酸锂的电子电导率只有10-13s/cm，极大地限制了负极极片中集流体与活性材料层之间的电子传输，导致锂离子电池的倍率性能劣化。而且，钛酸锂的对锂电位是1.5V，无法形成固体电解质界面膜(SEI膜)。因此，混有钛酸锂的活性材料层难以形成致密的SEI膜，导致SEI膜反复破坏和再生，加剧活性锂的消耗，从而导致锂离子电池的容量衰减。
因此，相关技术的负极极片在降低极片反弹率、同时保证电池的倍率性能并且减少电池的容量衰减方面仍有待改进。
本申请的一个实施方式中，本申请提出了一种负极极片，其包括集流体和设置在集流体的至少一个表面上的活性材料层，该活性材料层包括：
第一石墨层；
钛酸锂层；和
第二石墨层，
第一石墨层设置在集流体的至少一个表面上，钛酸锂层设置在第一石墨层的表面上，第二石墨层设置在钛酸锂层的表面上，并且
第一石墨层的OI值大于等于20.0，可选为30.0～40.0，第二石墨层的OI值小于等于15.0，可选为8.0～12.0。
虽然机理尚不明确，但本申请人意外地发现：如图1所示，本申请在活性材料层(60)中设置钛酸锂层(63)，能够减少负极极片(6)在制造工艺中以及电池充放电过程中由于体积变化造成的反弹，从而提升锂离子电池的使用寿命和安全性能。钛酸锂晶体在嵌入或脱出锂离子时晶格常数和体积变化小于1％。钛酸锂的这一特性可以称作“零应变性”。因此，在活性材料层(60)中设置钛酸锂层(63)能够减少负极极片在充放电过程中由于体积变化造成的反弹。而且，设置钛酸锂层(63)还能够缓解和/或分散负极极片在制造过程中例如冷压时在第一和第二石墨层(62、64)中积累的应力，从而减少后续使用过程中应力缓慢释放造成的极片反弹。通过减少负极极片的反弹，可以提升电池的循环性能和使用寿命，减少循环带来的比容量衰减，使电池具有非常好的耐过充、过放特征。另外，通过减少负极极片的反弹，还可以避免极片在拐角处发生断裂，提升电池的安全性能。
钛酸锂层可以包括钛酸锂、导电剂、粘结剂和任选的增稠剂。在本申请中，钛酸锂只要能够起到上文所述的减少负极极片反弹的作用即可，对钛酸锂的种类不做具体限制。可选地，钛酸锂可以是多晶球状颗粒。可选地，钛酸锂颗粒的粒径D50可以为4～15μm。导电剂、粘结剂和任选的增稠剂的种类不做具体限制，本领域技术人员可以根据实际需求进行选择。钛酸锂层中钛酸锂、导电剂、粘结剂和任选的增稠剂的含量不做具体限制，本领域技术人员可以根据实际需求进行选择。可选地，相对于钛酸锂层的总重量，钛酸锂的量可以是85～96重量％；导电剂的量可以是0.5～10.0重量％；粘结剂的量可以是0.3～2.0重量％；任选的增稠剂的量可以是0.1～1.0重量％。
在本申请中，通过在集流体的至少一个表面上，即在钛酸锂层和集流体层之间设置具有较高OI值的第一石墨层，解决了钛酸锂电子电导率过低造成倍率性能劣化的问题。具体来说，第一石墨层的OI值大于等于20.0，可选为30.0～40.0。第一石墨层具有上述范围内的较高的OI值，意味着第一石墨层中暴露有比例更高的平行于石墨片层结构的(004)晶面。这种结构非常有利于电子在石墨表面的流动，以及电子通 过集流体的传输，使得负极极片的电子传导率大大增加。而且，这种结构还能够增强第一石墨层与集流体之间的粘接。因此，在集流体表面上设置具有上述范围内的较高的OI值的第一石墨层能够通过提升电子传导率来充分保证锂离子电池的倍率性能。
第一石墨层可以包括第一石墨、导电剂、粘结剂和任选的增稠剂。第一石墨可以是具有一定OI值规格的市售产品。可选地，第一石墨可以是OI值大于2.0且小于等于6.0、可选为3.0～5.0的石墨。导电剂、粘结剂和任选的增稠剂的种类不做具体限制，本领域技术人员可以根据实际需求进行选择。第一石墨层中第一石墨、导电剂、粘结剂和任选的增稠剂的含量不做具体限制，本领域技术人员可以根据实际需求进行选择。可选地，相对于第一石墨层总重量，第一石墨的量可以是90.0～98.0重量％；导电剂的量可以是0.3～4.0重量％；粘结剂的量可以是0.3～2.0重量％；任选的增稠剂的量可以是0.1～1.0重量％。
第一石墨层的OI值可以通过改变第一石墨的OI值、负极极片的制造工艺参数例如冷压压力和/或第一石墨层的厚度等加以调节，使之处于大于等于20.0、可选为30.0～40.0的范围内。
在本申请中，通过在钛酸锂层的表面上设置具有较低OI值的第二石墨层，能够提高锂离子的传导速率，提升锂离子电池的倍率性能，同时提高活性材料层表面SEI膜的致密化程度，延缓活性锂离子的消耗，从而减少电池的容量衰减。具体来说，第二石墨层的OI值可以小于等于15.0，可选为8.0～12.0。第二石墨层具有上述范围内的较低的OI值，意味着第二石墨层中暴露有比例更高的垂直于石墨片层结构的(110)晶面。这种结构非常有利于锂离子在石墨中的嵌入和脱出，从而提高锂离子的传导速率。而且，当石墨的(110)晶面与电解液接触时，能够在其上形成SEI膜，而(004)晶面上则不易形成SEI膜。因此，暴露比例更高的(110)晶面还可以提高负极活性材料层表面上形成的SEI膜的致密度，从而延缓电池充放电过程中活性锂离子的消耗，减少电池的容量衰减。因此，在钛酸锂层表面上设置具有上述范围内的较低的OI值的第二石墨层能够充分保证锂离子电池的倍率性能，同时减少锂离子电池的容量衰减。
第二石墨层可以包括第二石墨、导电剂、粘结剂和任选的增稠剂。 第二石墨可以是具有一定OI值规格的市售产品。可选地，第二石墨可以是OI值大于等于0.5且小于2.0、可选为1.0～1.5的石墨。导电剂、粘结剂和任选的增稠剂的种类不做具体限制，本领域技术人员可以根据实际需求进行选择。第二石墨层中第二石墨、导电剂、粘结剂和任选的增稠剂的含量不做具体限制，本领域技术人员可以根据实际需求进行选择。可选地，相对于第二石墨层总重量，第二石墨的量可以是90.0～98.0重量％；导电剂的量可以是0.3～4.0重量％；粘结剂的量可以是0.3～2.0重量％；任选的增稠剂的量可以是0.1～1.0重量％。
第二石墨层的OI值可以通过改变第二石墨的OI值、负极极片的制造工艺参数例如冷压压力和/或第二石墨层的厚度等加以调节，使之小于等于15.0、可选为8.0～12.0的范围内。
在一些实施方式中，第一石墨层的厚度可以小于等于100μm。当第一石墨层的厚度小于等于100μm时，可以实现大于等于20.0、可选为30.0～40.0的第一石墨层的OI值；同时，使得石墨在锂离子电池制造和使用过程中因体积变化对负极极片的反弹特性造成的不利影响得以最小化，并且可以提高负极极片的生产率。
在一些实施方式中，钛酸锂层的厚度可以为25～50μm。当钛酸锂层的厚度大于等于25μm时，可以充分地发挥钛酸锂层减少负极极片反弹的作用。当钛酸锂层的厚度小于等于50μm时，钛酸锂的低电子电导率对负极极片的电子传输特性造成的不利影响得以最小化，从而进一步确保锂离子电池的倍率性能。
在一些实施方式中，第二石墨层的厚度小于等于100μm。当第二石墨层的厚度小于等于100μm时，可以实现小于等于15.0、可选为8.0～12.0的第二石墨层的OI值；同时，使得石墨在锂离子电池制造和使用过程中因体积变化对负极极片的反弹特性造成的不利影响得以最小化，并且可以提高负极极片的生产率。
在一些实施方式中，活性材料层的厚度为50～150μm。当活性材料层的厚度大于等于50μm时，可以确保负极极片的能量密度，从而确保电池的容量。当活性材料层的厚度小于等于150μm时，可以确保极片在制备过程中的浸润能力，并提高生产效率。
在一些实施方式中，负极极片的压实密度为0.9～1.8g/cm3。负极极 片的压实密度主要受到冷压压力的影响，同时也受到活性材料层中的活性材料特性例如钛酸锂的晶粒大小等因素的影响。当负极极片的压实密度大于等于0.9g/cm3时，可以充分确保锂离子电池的能量密度，从而确保电池的容量，还可以降低电池的制造成本，并且确保电池的倍率性能和循环性能。当负极极片的压实密度小于等于1.8g/cm3时，可以确保极片在制备过程中的浸润性，并提高极片的生产效率，并且还可以进一步减少负极极片的反弹，从而进一步减缓电池膨胀力过大引起的容量衰减，并进一步减少负极极片反弹带来的安全风险，并且进一步提升电池的倍率性能和循环性能。
本申请还提供一种负极极片的制备方法，包括：
提供集流体；
在集流体的至少一个表面上形成包括第一石墨的第一石墨层；
在第一石墨层的表面上形成包括钛酸锂的钛酸锂层；
在钛酸锂层的表面上形成包括第二石墨的第二石墨层，得到在集流体的至少一个表面上具有活性材料层的层叠体，上述活性材料层包括第一石墨层、钛酸锂层和第二石墨层；
对层叠体进行冷压，得到负极极片；
其中，第一石墨的OI值大于2.0且小于等于6.0，可选为3.0～5.0，第二石墨的OI值大于等于0.5且小于2.0，可选为1.0～1.5。第一石墨和第二石墨都可以是具有对应OI值的市售产品。
本申请的制备方法可以有效地制备本申请的第一方面的负极极片。
在一些实施方式中，层叠体可以通过以常规涂覆方式逐层涂覆第一石墨层、钛酸锂层和第二石墨层形成。可以使用将充当负极活性材料的第一石墨、钛酸锂或第二石墨以及导电剂、粘结剂、任选的增稠剂与充当溶剂的去离子水混合形成的浆料进行涂覆。可选地，浆料中活性材料与溶剂去离子水的质量比可以为1:0.5～2，可选为1:0.8～1.5。可选地，浆料的出货粘度可以为5000～25000mPa·s。去离子水添加量过低，会导致浆料过浓，浆料粘度过大，不易涂覆，且涂覆层均匀度较差；去离子水添加量过高，会导致浆料过稀，为了达到固定的涂层厚度，需要增加涂覆的工艺的时间，降低极片生产效率。
可选地，在制备负极极片的过程中，冷压工序之前，层叠体的至 少一个表面上形成的第一石墨层的厚度可以小于等于200μm；第一石墨层的表面上形成的钛酸锂层的厚度可以小于等于100μm；钛酸锂层的表面上形成的第二石墨层的厚度可以小于等于200μm；包括第一石墨层、钛酸锂层和第二石墨层的活性材料层的厚度可以为100～300μm。
在一些实施方式中，冷压压力可以为15～70T。可选地，冷压压力可以根据需求确定，以便与石墨原料的OI值、层厚度等因素结合，使第一石墨层和第二石墨层的OI值分别落入上文所述的特定范围。而且，冷压压力在上述范围内选择还可以有利地控制负极极片的活性材料达到合理的压实密度，当压力大于等于15T时，可以保证负极极片的压实密度，从而保证电池的能量密度。当冷压压力小于等于70T时，可以避免极片的密度过高导致电解液浸润性降低，从而保证电池的生产效率，同时还可以避免活性材料层中的颗粒在压制过程中碎裂，进而影响电池的安全性。
在一些实施方式中，在对层叠体进行冷压后，形成的第一石墨层的OI值可以大于等于20.0，可选为30.0～40.0，形成的第二石墨层的OI值可以小于等于15.0，可选为8.0～12.0。如上文所述，对层叠体进行冷压后，当得到的负极极片的第一石墨层和第二石墨层的OI值分别被调控至上述范围内时，能够充分保证应用该负极极片的锂离子电池的倍率性能，同时减少锂离子电池的容量衰减。
在一些实施方式中，对层叠体进行冷压后，形成的负极极片的压实密度可以为0.9～1.8g/cm3。如上文所述，对层叠体进行冷压后，当得到的负极极片的压实密度被调控至上述范围内时，能够充分保证应用该负极极片的锂离子电池的容量，同时确保极片在制备过程中的浸润性以及极片的生产效率。
可选地，在对层叠体进行冷压后，第一石墨层的厚度可以小于等于100μm；钛酸锂层的厚度可以为25～50μm；第二石墨层的厚度可以小于等于100μm。
可选地，对层叠体进行冷压后，形成的活性材料层的厚度可以为50～150μm。
本申请还提供一种二次电池，其包括：
正极极片；
如上所述的本申请的负极极片、或根据如上所述的本申请的制备方法制备的负极极片；
电解质；和
隔膜。
本申请还提供一种电池模块，其包括如上所述的本申请的二次电池。
本申请还提供一种电池包，其包括如上所述的本申请的电池模块。
本申请还提供一种用电装置，其包括如上所述的本申请的二次电池、如上所述的本申请的电池模块、或如上所述的本申请的电池包。
在本申请的负极极片中，通过在集流体上提供包括具有特定的较高OI值第一石墨层、钛酸锂层和具有特定的较低OI值的第二石墨层的活性材料层，能够有效地减少负极极片在制造工艺中以及电池充放电过程中由于体积变化造成的反弹，从而提升锂离子电池的使用寿命和安全性能，同时充分保证电池的倍率性能，同时减少电池的容量衰减。
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。
本申请的一个实施方式中，提供一种二次电池。
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]
正极极片可以包括正极集流体以及设置在正极集流体至少一个表面的正极活性材料层。作为示例，正极集流体具有在其自身厚度方向相对的两个表面，正极活性材料层设置在正极集流体相对的两个表面的其中任意一者或两者上。
上述正极集流体可以采用金属箔片或复合集流体。例如，作为金属箔片，可以采用铝箔。复合集流体可以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。复合集流体可以通过将 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)上而形成。
正极活性材料层包括正极活性材料。正极活性材料包括，但不限于钴酸锂、镍锰钴酸锂、镍锰铝酸锂、磷酸铁锂、磷酸钒锂、磷酸钴锂、磷酸锰锂、硅酸铁锂、硅酸钒锂、硅酸钴锂、硅酸锰锂、尖晶石型锰酸锂、尖晶石型镍锰酸锂、钛酸锂等。正极活性材料可以使用这些中的一种或几种。
正极活性物质层还可选地包括粘结剂。但对粘结剂的种类不做具体限制，本领域技术人员可以根据实际需求进行选择。作为示例，粘结剂可以包括聚偏氟乙烯(PVDF)、聚四氟乙烯(PTFE)、偏氟乙烯-四氟乙烯-丙烯三元共聚物、偏氟乙烯-六氟丙烯-四氟乙烯三元共聚物、四氟乙烯-六氟丙烯共聚物及含氟丙烯酸酯树脂中的一种或几种。
正极活性物质层还可选地包括导电剂。但对导电剂的种类不做具体限制，本领域技术人员可以根据实际需求进行选择。作为示例，用于正极活性物质层的导电剂可以选自超导碳、乙炔黑、碳黑、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。
正极极片的制备可以根据本领域已知的方法来进行。作为示例，可以将正极活性材料、导电剂和粘结剂分散于溶剂(例如N-甲基吡咯烷酮(NMP))中，形成均匀的正极浆料；将正极浆料涂覆在正极集流体上，经烘干、冷压等工序后，得到正极极片。
[负极极片]
本申请的二次电池中的负极极片使用如上文所述的二次电池用负极极片，其包括集流体和设置在集流体的至少一个表面上的活性材料层，该活性材料层包括第一石墨层、钛酸锂层和第二石墨层。第一石墨层设置在集流体的至少一个表面上，钛酸锂层设置在第一石墨层的表面上，第二石墨层设置在钛酸锂层的表面上，并且第一石墨层的OI值大于等于20.0，可选为30.0～40.0，第二石墨层的OI值小于等于15.0，可选为8.0～12.0。
在集流体的仅一个表面上形成活性材料层的情形中，负极极片的 集流体和活性材料层可以具有如图1所示例性示出的结构。在集流体的两个表面上均形成活性材料层的情形中，负极极片的两个活性材料层可以具有对称的结构。
负极集流体可以采用金属箔片或复合集流体。例如，作为金属箔片，可以采用铜箔。复合集流体可以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。复合集流体可以通过将金属材料(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)上而形成。负极活性材料层中的第一石墨层、钛酸锂层和第二石墨层均可以包括粘结剂、导电剂和任选的增稠剂等其他助剂。
第一石墨层、钛酸锂层和第二石墨层中分别使用的导电剂可以彼此相同或不同，本领域技术人员可以根据需求进行选择。作为示例，导电剂可选自超导碳、乙炔黑、碳黑、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。
第一石墨层、钛酸锂层和第二石墨层中分别使用的粘结剂可以彼此相同或不同，本领域技术人员可以根据需求进行选择。作为示例，粘结剂可选自丁苯橡胶(SBR)、聚丙烯酸(PAA)、聚丙烯酸钠(PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)、聚甲基丙烯酸(PMAA)及羧甲基壳聚糖(CMCS)中的一种或几种。
第一石墨层、钛酸锂层和第二石墨层中分别使用的其他助剂可以彼此相同或不同，本领域技术人员可以根据需求进行选择。作为示例，助剂可选地包括增稠剂，例如羧甲基纤维素钠(CMC-Na)等。
可以通过本申请的制备方法，在集流体的至少一个表面上形成包括第一石墨的第一石墨层，在第一石墨层的表面上形成包括钛酸锂的钛酸锂层，在钛酸锂层的表面上形成包括第二石墨的第二石墨层，从而得到包括第一石墨层、钛酸锂层和第二石墨层的活性材料层，然后对得到的在集流体的至少一个表面上具有活性材料层的层叠体进行冷压，经烘干、冷压等工序后，得到负极极片。第一石墨的OI值大于2.0且小于等于6.0，可选为3.0～5.0。第二石墨的OI值大于等于0.5且小于2.0，可选为1.0～1.5。
作为示例，可以将上述第一石墨、导电剂、粘结剂和任选的其他助剂分散于溶剂(例如去离子水)中，形成均匀的浆料，通过常规的涂覆工艺将该浆料涂覆在负极集流体的至少一个表面上，然后进行烘干，得到第一石墨层。将钛酸锂、导电剂、粘结剂和任选的其他助剂分散于溶剂(例如去离子水)中，形成均匀的浆料，通过常规的涂覆工艺将该浆料涂覆在第一石墨层的表面上，然后进行烘干，得到钛酸锂层。将上述第二石墨、导电剂、粘结剂和任选的其他助剂分散于溶剂(例如去离子水)中，形成均匀的浆料，通过常规的涂覆工艺将该浆料涂覆在钛酸锂层的表面上，然后进行烘干，得到第二石墨层。接下来，在15～70T的压力下对得到的包括集流体、第一石墨层、钛酸锂层和第二石墨层的层叠体进行冷压，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，上述电解质采用电解液。电解液包括电解质盐和溶剂。
作为示例，电解质盐可选自六氟磷酸锂(LiPF6)、四氟硼酸锂(LiBF4)、高氯酸锂(LiClO4)、六氟砷酸锂(LiAsF6)、双氟磺酰亚胺锂(LiFSI)、双三氟甲磺酰亚胺锂(LiTFSI)、三氟甲磺酸锂(LiTFS)、二氟草酸硼酸锂(LiDFOB)、二草酸硼酸锂(LiBOB)、二氟磷酸锂(LiPO2F2)、二氟二草酸磷酸锂(LiDFOP)及四氟草酸磷酸锂(LiTFOP)中的一种或几种。
作为示例，溶剂可选自氟代碳酸乙烯酯(FEC)、碳酸亚乙酯(EC)、碳酸亚丙基酯(PC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸亚丁酯(BC)、甲酸甲酯(MF)、乙酸甲酯(MA)、乙酸乙酯(EA)、乙酸丙酯(PA)、丙酸甲酯(MP)、丙酸乙酯(EP)、丙酸丙酯(PP)、丁酸甲酯(MB)、丁酸乙酯(EB)、1,4-丁内酯(GBL)、环丁砜(SF)、二甲砜(MSM)、甲乙砜(EMS)及二乙砜(ESE)中的一种或几种。
在一些实施方式中，电解质中还可选地包括添加剂。例如，电解质中可以包括负极成膜添加剂、正极成膜添加剂、改善电池过充性能的添加剂、改善电池高温性能的添加剂、改善电池低温性能的添加剂等。
[隔膜]
隔膜将正极极片与负极极片隔开，防止电池内部发生短路，同时使得活性离子能够穿过隔膜在正负极之间移动。在本申请的二次电池中，隔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膜。
在一些实施方式中，隔膜的材质可以选自玻璃纤维薄膜、无纺布薄膜、聚乙烯(PE)薄膜、聚丙烯(PP)薄膜、聚偏二氟乙烯薄膜、以及包含它们中的一种或两种以上的多层复合薄膜中的一种或几种。隔膜可以是单层隔膜，也可以是多层复合隔膜，没有特别限制。在隔膜为多层复合隔膜时，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、负极极片和隔膜可以通过卷绕工艺或叠片工艺制成电极组件。在本申请中，组装电极组件时，将负极极片上的第二石墨层面向隔膜。
在一些实施方式中，二次电池可以包括外包装。该外包装可以用于封装如上所述的电极组件及电解液。
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(PP)、聚对苯二甲酸丁二醇酯(PBT)以及聚丁二酸丁二醇酯(PBS)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5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6，外包装可包括壳体51和顶盖组件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，顶盖组件53能够盖设于开口，以封闭容纳腔。正极极片、负极极片和隔膜可经卷绕工艺或叠片工艺形成电极组件52。电极组件52封装于容纳腔内。电解液 浸润于电极组件52中。二次电池5所含电极组件52的数量可以为一个或多个，本领域技术人员可根据具体实际需求进行选择。
在一些实施方式中，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7是作为一个示例的电池模块4。参照图7，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本领域技术人员可以根据电池包的应用和容量进行选择。
图8和图9是作为一个示例的电池包1。参照图8和图9，在电池包1中可以包括电池箱和设置于电池箱中的多个电池模块4。电池箱包括上箱体2和下箱体3，上箱体2能够盖设于下箱体3，并形成用于容纳电池模块4的封闭空间。多个电池模块4可以按照任意的方式排布于电池箱中。
另外，本申请还提供一种用电装置，该装置包括本申请提供的二次电池、电池模块、或电池包。二次电池、电池模块、或电池包可以用作用电装置的电源，也可以用作用电装置的能量存储单元。用电装置可以包括，但不限于移动设备(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。
作为用电装置，可以根据其使用需求来选择二次电池、电池模块或电池包。
图10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。
作为另一个示例的用电装置可以是手机、平板电脑、笔记本电脑等。该用电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。
负极极片的制备
将OI值大于2.0且小于等于6.0的第一石墨、导电剂碳黑(贝特瑞新材料集团股份有限公司，型号BSC)、粘结剂丁苯橡胶(SBR)(中国石油吉林石化公司，型号1520)、增稠剂羟甲基纤维素钠(CMC)(日本大赛璐株式会社，型号200)按照97.2：0.8：0.8：1.2的质量比加入到去离子水中并充分搅拌，混合均匀后制备成用于形成第一石墨层的浆料(固含量为50％)。通过常规工艺，将上述浆料均匀地涂布在厚度为6μm的集流体铜箔上，然后在80～150℃的温度下烘干，从而在集流体铝箔上形成第一石墨层。
接下来，将钛酸锂(珈伟新能源股份有限公司，型号T200)、导电剂碳黑、粘结剂丁苯橡胶(SBR)、增稠剂羟甲基纤维素钠(CMC)按照97.2：0.8：0.8：1.2的质量比加入到去离子水中并充分搅拌，混合均匀后制备成用于形成钛酸锂层的浆料(固含量50％)。通过常规工艺，将上述浆料均匀地涂布在上述形成的第一石墨层上，然后在80～150℃的温度下烘干，从而在第一石墨层上形成钛酸锂层。
接下来，将OI值大于等于0.5且小于2.0的第二石墨、导电剂碳黑、粘结剂丁苯橡胶(SBR)、增稠剂羟甲基纤维素钠(CMC)按照97.2：0.8：0.8：1.2的重量比加入到去离子水中并充分搅拌，混合均匀后制备成用于形成第二石墨片层的浆料(固含量50％)。通过常规工艺，将上述浆料均匀地涂布在上述形成的钛酸锂层上，然后在80～150℃的温度下烘干，从而在钛酸锂层上形成第二石墨层。
将上述形成的在集流体上涂布有包括第一石墨层、钛酸锂层和第 二石墨层的活性材料层的极片在15～70T的压力下冷压，然后进行分切，得到负极极片。
电池的制备
在本申请的实施例中，电芯的制备采用以下方法。
(1)正极极片的制备
将正极活性材料LiNi0.8Co0.1Mn0.1O2(NCM 811)(宁波容百新能源科技股份有限公司，型号S85E)、导电剂碳黑、和粘结剂聚偏二氟乙烯(PVDF)(日本吴羽株式会社，型号W9200)按照97：1.5：1.5的质量比混合并加入溶剂N-甲基吡咯烷酮(NMP)，然后充分搅拌，混合均匀后制备成正极浆料(固含量70％)。通过常规工艺，将正极浆料以0.2mg/mm2的涂覆量均匀地涂布在厚度为13μm的集流体铝箔上，然后在100～130℃的温度下烘干，在40T的压力下冷压，然后进行分切，得到正极极片。
(2)电解液的制备
在氩气气氛手套箱中(H2O<0.1ppm，O2<0.1ppm)，将有机溶剂碳酸乙烯酯(EC)/碳酸甲乙酯(EMC)按照体积比3/7混合均匀，加入12.5％LiPF6锂盐溶解于有机溶剂中(摩尔浓度1.2mol/L)，搅拌均匀，得到用于锂离子电池的电解液。
(3)电池的制备
将以上步骤中得到的正极极片、作为隔膜的聚丙烯膜(云南恩捷新材料股份有限公司，型号ND7)和负极极片以上述顺序层叠，使负极极片上的第二石墨层面向隔膜。然后卷绕得到裸电芯。在裸电芯上焊接极耳，并将裸电芯装入铝壳中。将装配的电芯在100℃下烘烤除水，然后注入电解液，得到不带电的电池。不带电的电池依次经静置、热冷压、化成、整形、容量测试后，得到锂离子电池。
性能测试
(1)第一和第二石墨层的OI值
第一和第二石墨层的OI值的测定通过X射线衍方法在多晶X射线衍射仪(Bruker，D8Discover)上进行。将待测样品水平放在样品台 上，采用连续模式扫描(扫描区间10～80°，扫描速度2°/min)，得到相应的衍射谱图。根据衍射谱图确定(004)晶面的衍射峰强度为I(004)，(110)晶面的衍射峰强度为I(110)，OI值计算公式如下：
OI＝I(004)/I(110)
在上述测量中，第一石墨层和第二石墨层的待测样品通过以下方法获得：
取一块10cm×10cm的负极极片，该负极极片的第一石墨层、钛酸锂层和第二石墨层厚度值分别为d1、d2和d3，用刮刀均匀地刮去表面d3/2厚度的石墨，该刮去的厚度通过万分尺确定。从如上所述得到的刮去规定厚度层的负极极片上裁取2cm×2cm的小片，得到用于测量第二石墨层OI值的样品。
取一块10cm×10cm的负极极片，该负极极片的第一石墨层、钛酸锂层和第二石墨层厚度值分别为d1、d2和d3，用刮刀均匀地刮去表面(d3+d2+d1/2)厚度的石墨，该刮去的厚度通过万分尺确定。上如上所述得到的刮去规定厚度层的负极极片上裁取2cm×2cm的小片，得到用于测量第一石墨层OI值的样品。
(2)负极极片反弹率
使用万分尺测量负极极片的厚度。冷压后负极极片的厚度记为R。在电池的制备中，将正极极片、隔膜和负极极片层叠，然后经历充分的反弹之后，在卷绕成裸电芯之前，测量负极极片的厚度，并记为S。经化成满充后，测量负极极片的厚度，并记为T。将制备的锂离子电池在45℃的温度下在预紧力200kgf、充电倍率0.5C且放电倍率1C的循环条件下循环100圈后，测量负极极片的厚度，并记为U。在上述循环条件下循环200圈后，测量负极极片的厚度，并记为V。根据以下公式计算不同阶段的负极极片的反弹率：
反弹率(卷绕)＝(S/R-1)×100％
反弹率(化成满充)＝(T/R-1)×100％
反弹率(循环100圈)＝(U/R-1)×100％
反弹率(循环200圈)＝(V/R-1)×100％
以不同阶段的反弹率为纵坐标进行作图，可以得到负极极片的反弹率变化趋势图。
(3)电池膨胀力
在对电池进行充放电循环之前，使用由三片铝板构成的夹具对电池和压力传感器进行夹持。具体而言，将压力传感器放置于第一片铝板与第二片铝板之间的上层空间，将电池放置于第二片铝板与第三片铝板之间的下层空间，然后施加200kgf的预紧力F0将夹具使用螺栓固定。
接下来，将电池在45℃的温度下在充电倍率0.5C且放电倍率1C的循环条件下循环。每次循环过程中电芯满充状态时夹具中压力传感器的读数记为对应循环圈数的锂离子的电池膨胀力Fn。以循环圈数为横坐标，以对应循环圈数的锂离子电池的膨胀力为纵坐标，可以得到膨胀力随循环次数变化的曲线图。
每次循环的电池的膨胀力增长率En根据以下公式计算：
En＝[(Fn–200)/200)]×100％
(4)循环容量保持率
在45℃下，将电池以1/3C恒流充电至4V，再以4V恒定电压充电至电流为0.05C，搁置5min，再以1/3C放电至2.5V，所得容量记为初始容量C0。然后，将电池在上述相同条件下循环，并记录循环第n次后电池的放电容量Cn。每次循环后电池的循环容量保持率Pn根据以下公式计算：
Pn＝(Cn/C0)×100％
以循环圈数为横坐标，以对应循环圈数后锂离子电池的循环容量保持率为纵坐标，可以得到电池的循环容量保持率随循环次数变化的曲线图。
(5)倍率容量保持率
在25℃下，将电池以1/3C恒流充电至4V，再以4V恒定电压充电至电流为0.05C，搁置5min，再以0.1C放电至2.5V，循环5次所得容量平均值记为初始容量D0。然后，将电池在上述相同条件下充电，以1C放电，循环5次所得容量平均值记为初始容量D1。电池的倍率容量保持率Q1根据以下公式计算：
Q1＝(D1/D0)×100％
类似地，测量电池的倍率容量保持率Q2。具体而言，在25℃下， 将电池以1/3C恒流充电至4V，再以4V恒定电压充电至电流为0.05C，搁置5min，再以0.1C放电至2.5V，循环5次所得容量平均值记为初始容量D0。然后，将电池在上述相同条件下充电，以2C放电，循环5次所得容量平均值记为初始容量D2。电池的倍率容量保持率Q2根据以下公式计算：
Q2＝(D2/D0)×100％
实施例1
根据上文所述的负极极片的制造方法，使用OI值为5.0的第一石墨(贝特瑞新材料集团股份有限公司，型号BFC-18)制备用于形成第一石墨层的浆料，将该浆料以0.04mg/mm2的涂覆量在集流体的两个表面上涂布，然后在100℃下烘干，形成厚度为60μm的第一石墨层；将用于形成钛酸锂层的浆料以0.12mg/mm2的涂覆量在第一石墨层上涂布，然后在100℃下烘干，形成厚度为80μm的钛酸锂层；使用OI值为1.0的第二石墨(贝特瑞新材料集团股份有限公司，型号GSN)制备用于形成第二石墨层的浆料，将该浆料以0.04mg/mm2的涂覆量在钛酸锂层上涂布，然后在100℃下烘干，形成厚度为60μm的第二石墨层。由此，在集流体的两个表面上均涂布有包括第一石墨层、钛酸锂层和第二石墨层的活性材料层。接下来，将在集流体上涂布有上述活性材料层的极片在40T的压力下冷压，然后进行分切，得到实施例1的负极极片。在实施例1中，经冷压后，所得到的负极极片中第一石墨层、钛酸锂层和第二石墨层的厚度分别是30μm、40μm和30μm。冷压得到的负极极片的厚度R为206μm，压实密度为1.6g/cm3。
通过上文所述的测试方法，分别测量实施例1的负极极片中的第一石墨层和第二石墨层的OI值，结果示于表1中。
通过上文所述的方法，使用实施例1的负极极片制备锂离子电池。在制备过程中，通过上文所述的方法测量实施例1的负极极片在卷绕之前的反弹率。另外，通过上文所述的方法测量使用实施例1的负极极片制备的锂离子电池在化成满充后负极极片的反弹率、循环100圈后负极极片的反弹率和循环200圈后负极极片的反弹率。实施例1的负极极片在不同阶段的反弹率的测量结果示于表1中。实施例1的负 极极片的反弹率变化趋势图如图2所示。
通过上文所述的测试方法，测量实施例1中制备的锂离子电池的循环膨胀力。实施例1中制备的锂离子电池在循环200圈后的循环膨胀力和对应的膨胀力增长率的结果也示于表1中。实施例1中制备的锂离子电池的膨胀力随循环次数变化的曲线图如图3a所示。
通过上文所述的测试方法，测量实施例1中制备的锂离子电池的循环容量保持率。实施例1中制备的锂离子电池在循环200圈后的循环容量保持率P200的结果也示于表1中。实施例1中制备的锂离子电池的循环容量保持率随循环次数变化的曲线图如图3b所示。
通过上文所述的测试方法，测量实施例1中制备的锂离子电池的倍率容量保持率Q1和Q2，测量结果也示于表1中。
对照例1
在厚度为6μm的集流体铜箔上形成仅包括第二石墨层的活性材料层的负极极片。在对照例1中，第二石墨层的形成方法与实施例1中的对应方法基本相同，但包括第二石墨层的活性材料层在涂布和烘干工序后的厚度为200μm。接下来，将在集流体上涂布有上述活性材料层的极片在40T的压力下冷压，然后进行分切，得到对照例1的负极极片。在对照例1中，经冷压后，活性材料层的厚度为100μm。冷压得到得到的负极极片的厚度R为206μm，压实密度为1.6g/cm3。
通过上文所述的测试方法，测量对照例1的负极极片中的第二石墨层OI值，结果也示于表1中。
通过上文所述的方法，使用对照例1的负极极片制备锂离子电池。通过上文所述的方法测量对照例1的负极极片在不同阶段的反弹率，结果也示于表1中。对照例1的负极极片的反弹率变化趋势图如图2所示。
通过上文所述的测试方法，测量使用对照例1中制备的锂离子电池的循环膨胀力。使用对照例1中制备的锂离子电池在循环200圈后的循环膨胀力和对应的膨胀力增长率的结果也示于表1中。对照例1中制备的锂离子电池的膨胀力随循环次数变化的曲线图如图3a所示。
通过上文所述的测试方法，测量对照例1中制备的锂离子电池的 循环容量保持率。对照例1中制备的锂离子电池在循环200圈后的循环容量保持率P200的结果也示于表1中。对照例1中制备的锂离子电池的循环容量保持率随循环次数变化的曲线图如图3b所示。
通过上文所述的测试方法，测量对照例1中制备的锂离子电池的倍率容量保持率Q1和Q2，测量结果也示于表1中。
对照例2
在厚度为6μm的集流体铜箔上形成仅包括第一石墨层的活性材料层的负极极片。在对照例2中，第一石墨层的形成方法与实施例1中的对应方法基本相同，不同之处仅在于，仅包括第一石墨层的活性材料层在涂布和烘干工序后的厚度为200μm。接下来，将在集流体上涂布有上述活性材料层的极片在40T的压力下冷压，然后进行分切，得到对照例2的负极极片。在对照例2中，经冷压后，活性材料层的厚度为100μm。冷压得到的负极极片的厚度R为206μm，压实密度为1.6g/cm3。
通过上文所述的测试方法，测量对照例2的负极极片中的第一石墨层OI值，结果也示于表1中。
通过上文所述的方法，使用对照例2的负极极片制备锂离子电池。通过上文所述的方法测量对照例2的负极极片在不同阶段的反弹率，结果也示于表1中。对照例2的负极极片的反弹率变化趋势图如图2所示。
通过上文所述的测试方法，测量使用对照例2中制备的锂离子电池的循环膨胀力。使用对照例2中制备的锂离子电池在循环200圈后的循环膨胀力和对应的膨胀力增长率的结果也示于表1中。对照例2中制备的锂离子电池的膨胀力随循环次数变化的曲线图如图3a所示。
通过上文所述的测试方法，测量对照例2中制备的锂离子电池的循环容量保持率。对照例2中制备的锂离子电池在循环200圈后的循环容量保持率P200的结果也示于表1中。对照例2中制备的锂离子电池的循环容量保持率随循环次数变化的曲线图如图3b所示。
通过上文所述的测试方法，测量对照例2中制备的锂离子电池的倍率容量保持率Q1和Q2，测量结果也示于表1中。
比较例1
在厚度为6μm的集流体铜箔上形成仅包括钛酸锂层和第二石墨层的活性材料层的负极极片。在比较例1中，钛酸锂层和第二石墨层的形成方法与实施例1中的对应方法基本相同。比较例1中在涂布和烘干工序后形成的钛酸锂层和第二石墨层的厚度分别为100μm和100μm。接下来，将在集流体上涂布有上述活性材料层的极片在40T的压力下冷压，然后进行分切，得到比较例1的负极极片。在比较例1中，经冷压后，活性材料层的厚度为100μm。冷压得到的负极极片的厚度R为206μm，压实密度为1.6g/cm3。通过上文所述的测试方法，测量比较例1的负极极片中的第二石墨层OI值，结果也示于表1中。
通过上文所述的方法，使用比较例1的负极极片制备锂离子电池。通过上文所述的方法测量比较例1的负极极片在不同阶段的反弹率，结果也示于表1中。比较例1的负极极片的反弹率变化趋势图如图2所示。
通过上文所述的测试方法，测量使用比较例1中制备的锂离子电池的循环膨胀力。使用比较例1中制备的锂离子电池在循环200圈后的循环膨胀力和对应的膨胀力增长率的结果也示于表1中。比较例1中制备的锂离子电池的膨胀力随循环次数变化的曲线图如图3a所示。
通过上文所述的测试方法，测量比较例1中制备的锂离子电池的循环容量保持率。比较例1中制备的锂离子电池在循环200圈后的循环容量保持率P200的结果也示于表1中。比较例1中制备的锂离子电池的循环容量保持率随循环次数变化的曲线图如图3b所示。
通过上文所述的测试方法，测量比较例1中制备的锂离子电池的倍率容量保持率Q1和Q2，测量结果也示于表1中。
比较例2
在厚度为6μm的集流体铜箔上形成仅包括第一石墨层和钛酸锂层的活性材料层的负极极片。在比较例2中，第一石墨层和钛酸锂层的形成方法与实施例1中的对应方法基本相同。比较例2中在涂布和烘干工序后形成的第一石墨层和钛酸锂层的厚度分别为100μm和100 μm。接下来，将在集流体上涂布有上述活性材料层的极片在40T的压力下冷压，然后进行分切，得到比较例2的负极极片。在比较例2中，经冷压后，活性材料层的厚度为100μm。所得到的负极极片的厚度R为206μm，压实密度为1.6g/cm3。
通过上文所述的测试方法，测量比较例2的负极极片中的第一石墨层OI值，结果也示于表1中。
通过上文所述的方法，使用比较例2的负极极片制备锂离子电池。通过上文所述的方法测量比较例2的负极极片在不同阶段的反弹率，结果也示于表1中。比较例2的负极极片的反弹率变化趋势图如图2所示。
通过上文所述的测试方法，测量使用比较例2中制备的锂离子电池的循环膨胀力。比较例2中制备的锂离子电池在循环200圈后的循环膨胀力和对应的膨胀力增长率的结果也示于表1中。比较例2中制备的锂离子电池的膨胀力随循环次数变化的曲线图如图3a所示。
通过上文所述的测试方法，测量比较例2中制备的锂离子电池的循环容量保持率。比较例2中制备的锂离子电池在循环200圈后的循环容量保持率P200的结果也示于表1中。比较例2中制备的锂离子电池的循环容量保持率随循环次数变化的曲线图如图3b所示。
通过上文所述的测试方法，测量比较例2中制备的锂离子电池的倍率容量保持率Q1和Q2，测量结果也示于表1中。
表1

从表1的结果可以看出，在实施例1中，负极极片的活性材料层包括OI值相对较高的第一石墨层、钛酸锂层和OI值相对较低的第二石墨层。在活性材料层中上述各层的共同作用下，负极极片在制造过程中和电池充放电循环中的反弹均受到抑制，同时锂离子电池的倍率性能得以充分保证，并且循环过程中锂离子电池的容量衰减显著降低。
在对照例1和对照例2中，负极极片均不包括钛酸锂，从而无法抑制锂离子电池在制造过程中和循环过程中负极极片的反弹。与实施例1相比，在对照例1和对照例2中，如图2所示，在锂离子电池的制造过程中，负极极片的反弹率明显过高；如图3a所示，在锂离子电池的充放电循环过程中，电池的膨胀力也明显过高。结果，如图3b所示，电池的循环性能不佳，随着充放电循环次数的增加，电池容量显著衰减。
在比较例1中，负极极片的反弹得以降低，但由于活性材料层不包括第一石墨层，钛酸锂层直接形成在集流体的表面，负极极片的电子传导性能较差。与实施例1相比，比较例1的锂离子电池的倍率性能不佳，倍率容量保持率Q1和Q2均显著降低。
在比较例2中，负极极片的反弹也得以降低，但由于活性材料层不包括第二石墨层，活性材料层表面无法形成稳定、致密的SEI膜，充放电过程中锂离子不断消耗，锂离子电池的容量容易衰减。如图3b所示，与实施例1相比，比较例2的锂离子电池在经历充放电循环后，电池的容量衰减得更多，循环200圈后的循环容量保持率P200偏低。
实施例2～8和比较例3～4
通过与实施例1中基本上相同的方法制备实施例2～8和比较例3～4的负极极片和锂离子电池，不同之处仅在于，所用第一石墨和或第二石墨的OI值分别如表2所示。根据上文所述的方法测得的实施例2～8和比较例3～4的负极极片中的第一石墨层和第二石墨层的OI值也示于表2中。
通过上文所述的测试方法，分别测量实施例2～8和比较例3～4中 的负极极片在不同阶段的反弹率、实施例2～8和比较例3～4中的锂离子电池在循环200圈后的循环膨胀力和对应的膨胀力增长率、循环容量保持率P200以及倍率容量保持率Q1和Q2，结果一并示于表2中。
对于实施例2和比较例3～4中制备的锂离子电池，循环容量保持率随循环次数变化的曲线图如图4a所示。另外，显示实施例2和比较例3～4的锂离子电池的倍率容量保持率的柱状图如图4b所示。
表2
从表1和表2的结果可以看出，在实施例1～8中，活性材料层中包括的钛酸锂层能够有效地抑制负极极片反弹。同时，由于设置在集流体表面上的第一石墨层的OI值均大于等于20.0，这就意味着第一石墨层中暴露有比例较高的平行于石墨片层结构的(004)晶面，有利于电子在石墨表面的流动以及电子通过集流体的传输，负极极片的电子传导率大大增加，从而充分保证锂离子电池的倍率性能。此外，由于第二石墨层的OI值均小于15.0，这就意味着第二石墨层中暴露有较比例 较高的垂直于石墨片层结构的(110)晶面，有利于锂离子在石墨中的嵌入和脱出，负极极片的锂离子传导速率大大增加。不仅如此，第二石墨层中暴露有比例较高的(110)晶面，在与电解液接触时，能够在界面上形成更加致密、稳定的SEI膜，从而延缓电池充放电过程中活性锂离子的消耗，显著减少电池的容量衰减。在实施例1～8中，锂离子电池循环200圈后的循环容量保持率P200达到88.6％以上，并且倍率容量保持率Q1和Q2分别达到84.0％以上和76.0％以上。
在比较例3和比较例4中，第二石墨层的OI值较大，超出了本申请的范围，意味着第二石墨层中暴露的(110)晶面比例降低，而(004)晶面比例增加，不利于锂离子的嵌入和脱出，并且与电解质接触时形成的SEI膜致密程度降低。结果，如图4a所示，与实施例2相比，比较例3和比较例4的锂离子电池在经历充放电循环后，电池的容量衰减得更多，循环200圈后的循环容量保持率P200显著更低。另外，如图4b所示，与实施例2相比，比较例3和比较例4的锂离子电池在1C和2C条件下的倍率容量保持率Q1和Q2均显著降低。
实施例9～10
通过与实施例1中基本上相同的方法制备实施例9～10的负极极片和锂离子电池，不同之处仅在于，所用第一石墨和或第二石墨的OI值分别如表3所示。根据上文所述的方法测得的实施例9～10的负极极片中的第一石墨层和第二石墨层的OI值也示于表3中。
表3

通过上文所述的测试方法，分别测量实施例9～10中的负极极片在不同阶段的反弹率、实施例9～10中的锂离子电池在循环200圈后的膨胀力增长率、循环容量保持率P200以及倍率容量保持率Q1和Q2，结果一并示于表3中。
在实施例9～10中，第二石墨层的OI值在本申请的可选范围8～12内。从表2和表3的结果可以看出，与实施例3～5相比，当第二石墨层的OI值处于上述可选范围内时，可以更好地平衡锂离子电池的循环性能和倍率性能的提升。
实施例11～12
通过与实施例1中基本上相同的方法制备实施例11～12的负极极片和锂离子电池，不同之处仅在于，在负极极片的制备过程中，调整浆料的涂覆量，使得实施例11～12的负极极片中的第一石墨层、钛酸锂层和第二石墨层在冷压工序后的厚度如表4中所示。
表4
通过上文所述的测试方法，分别测量实施例11～12中的负极极片在不同阶段的反弹率、实施例11～12中的锂离子电池在循环200圈后的膨胀力增长率、循环容量保持率P200以及倍率容量保持率Q1和Q2，结果一并示于表4中。
从表1和表4的结果可以看出，与实施例11和12相比，在实施例1中，钛酸锂层的厚度在本申请的可选范围25～50μm内，可以在保持锂离子电池的循环性能和倍率性能的同时，以保证钛酸锂层充分发挥抑制负极极片反弹的效果。
实施例13～14
通过与实施例1中基本上相同的方法制备实施例13～14的负极极片和锂离子电池，不同之处仅在于，在负极极片的制备过程中，调整浆料的涂覆量，使得实施例13～14的负极极片的压实密度如表4中所示。
通过上文所述的测试方法，分别测量实施例13～14中的负极极片在不同阶段的反弹率、实施例13～14中的锂离子电池在循环200圈后的膨胀力增长率、循环容量保持率P200以及倍率容量保持率Q1和Q2，结果一并示于表4中。
在实施例1和13中，负极极片的压实密度在本申请的可选范围0.9～1.8g/cm3内。从表1和表4的结果可以看出，与实施例14相比，负极极片的电解液浸润能力得以充分保证，从而进一步保证电池的倍率性能。另外，负极极片的压实密度处于本申请的上述有限范围内，还可以进一步降低负极极片在锂离子电池的制造过程中和充放电循环过程中的反弹。
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 (14)

  1. 一种负极极片，包括集流体和设置在所述集流体的至少一个表面上的活性材料层，其特征在于，
    所述活性材料层包括：
    第一石墨层；
    钛酸锂层；和
    第二石墨层，
    所述第一石墨层设置在所述集流体的至少一个表面上，所述钛酸锂层设置在所述第一石墨层的表面上，所述第二石墨层设置在所述钛酸锂层的表面上，并且
    所述第一石墨层的OI值大于等于20.0，可选为30.0～40.0，所述第二石墨层的OI值小于等于15.0，可选为8.0～12.0。
  2. 根据权利要求1所述的负极极片，其中，所述第一石墨层的厚度小于等于100μm。
  3. 根据权利要求1或2所述的负极极片，其中，所述钛酸锂层的厚度为25～50μm。
  4. 根据权利要求1～3中任一项所述的负极极片，其中，所述第二石墨层的厚度小于等于100μm。
  5. 根据权利要求1～4中任一项所述的负极极片，其中，所述活性材料层的厚度为50～150μm。
  6. 根据权利要求1～5中任一项所述的负极极片，其中，所述负极极片的压密为0.9～1.8g/cm3。
  7. 一种负极极片的制备方法，其中，包括：
    提供集流体；
    在所述集流体的至少一个表面上形成包括第一石墨的第一石墨层；
    在所述第一石墨层的表面上形成包括钛酸锂的钛酸锂层；
    在所述钛酸锂层的表面上形成包括第二石墨的第二石墨层，得到在所述集流体的至少一个表面上具有活性材料层的层叠体，所述活性材料层包括所述第一石墨层、所述钛酸锂层和所述第二石墨层；和
    对所述层叠体进行冷压，得到所述负极极片；
    其中，所述第一石墨的OI值大于2.0且小于等于6.0，可选为3.0～5.0，所述第二石墨的OI值大于等于0.5且小于2.0，可选为1.0～1.5。
  8. 根据权利要求7所述的制备方法，其中，所述冷压压力为15～70T。
  9. 根据权利要求7或8所述的制备方法，其中，对所述层叠体进行冷压后，形成的所述第一石墨层的OI值大于等于20.0，可选为30.0～40.0，形成的所述第二石墨层的OI值小于等于15.0，可选为8.0～12.0。
  10. 根据权利要求7～9中任一项所述的制备方法，其中，对所述层叠体进行冷压后，形成的所述负极极片的压实密度为0.9～1.8g/cm3。
  11. 一种二次电池，其中，包括：
    正极极片；
    根据权利要求1～6中任一项所述的负极极片、或根据权利要求7～10中任一项所述的制备方法制备的负极极片；
    电解质；和
    隔膜。
  12. 一种电池模块，其中，包括权利要求11所述的二次电池。
  13. 一种电池包，其中，包括权利要求12所述的电池模块。
  14. 一种用电装置，其中，包括权利11所述的二次电池、权利要求12所述的电池模块、或权利要求13所述的电池包。
PCT/CN2023/082058 2022-04-20 2023-03-17 负极极片及其制备方法、二次电池、电池模块、电池包和用电装置 WO2023202289A1 (zh)

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