WO2024092726A1 - 电极组件、电池单体、电池和用电装置 - Google Patents

电极组件、电池单体、电池和用电装置 Download PDF

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Publication number
WO2024092726A1
WO2024092726A1 PCT/CN2022/129904 CN2022129904W WO2024092726A1 WO 2024092726 A1 WO2024092726 A1 WO 2024092726A1 CN 2022129904 W CN2022129904 W CN 2022129904W WO 2024092726 A1 WO2024092726 A1 WO 2024092726A1
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Prior art keywords
region
pole piece
electrode assembly
active material
electrode sheet
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PCT/CN2022/129904
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English (en)
French (fr)
Inventor
魏楷宁
牛从酥
陈文伟
李晓伟
王巧阁
冯念云
Original Assignee
宁德时代新能源科技股份有限公司
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Priority to PCT/CN2022/129904 priority Critical patent/WO2024092726A1/zh
Publication of WO2024092726A1 publication Critical patent/WO2024092726A1/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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H01M10/0587—Construction or manufacture of accumulators having only wound construction elements, i.e. wound positive electrodes, wound negative electrodes and wound separators
    • 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

Definitions

  • the present application relates to the field of battery technology, and in particular to an electrode assembly, a battery cell, a battery and an electrical device.
  • the overall production process of batteries is long and complex, including a series of processes such as coating, sheeting, winding, assembly, laser welding, and injection.
  • the processing of the electrode assembly inside the battery cell is particularly important and will directly affect the performance of the battery cell. Therefore, how to improve the performance of the electrode assembly is still a technical problem that needs to be solved.
  • the present application provides an electrode assembly, a battery cell, a battery and an electrical device, which can reduce the possibility of fracture of the bent portion of the electrode sheet, while also ensuring the energy density of the battery cell.
  • an electrode assembly comprising: a first pole piece, a second pole piece and a separation membrane, wherein the first pole piece, the second pole piece and the separation membrane are wound to form the electrode assembly, the separation membrane is used to separate the first pole piece from the second pole piece, and the polarities of the first pole piece and the second pole piece are opposite; wherein the first pole piece comprises a first region and a second region, the first region and the second region are alternately arranged and connected in sequence along the winding direction, and after the electrode assembly is wound, the second region is at least partially located at the bending portion of the first pole piece, the first region is coated with a first active material, the second region is coated with a second active material, and the expansion rate of the second active material is less than the expansion rate of the first active material.
  • the forces acting on the curved portion and the flat portion of the first pole piece are also different.
  • the possibility of fracture of the curved portion of the pole piece can be reduced, and the safety performance of the electrode assembly during use can be ensured.
  • there is no blank area on the pole piece provided in the embodiment of the present application which can also ensure the energy density of the battery cell.
  • the second pole sheet includes a third region and a fourth region, the third region and the fourth region are alternately arranged and connected in sequence along the winding direction, after the electrode assembly is wound, the fourth region is at least partially located at the bending portion of the second pole sheet, the third region is coated with a third active material, the fourth region is coated with a fourth active material, and the expansion rate of the third active material is greater than the expansion rate of the fourth active material.
  • the expansion forces on the flat and curved portions of the electrode assembly can be differentiated to a greater extent, further reducing the possibility of fracture of the curved portion of the pole piece, thereby ensuring the safety of the electrode assembly during use.
  • active materials of different properties can be coated as needed, making the design of the battery cell more flexible, thereby meeting more diverse needs.
  • a difference between the expansion rate of the first active material and the expansion rate of the second active material is (0%, 4%).
  • the appropriate difference range can not only reduce the possibility of fracture of the bent portion of the pole piece, but also help to ensure the normal use of the electrode assembly in the battery cell.
  • the powder OI value of the second active material is less than the powder OI value of the first active material.
  • suitable active material powder to prepare the electrode assembly it is beneficial to ensure that the expansion rate of the second active material is smaller than the expansion rate of the first active material. At the same time, it can also improve the dynamic performance of the electrode assembly, reduce the possibility of lithium plating in the electrode sheet, and reduce the increase in electrode sheet thickness caused by lithium plating.
  • the compacted density of the second active material is less than the compacted density of the first active material.
  • Selecting active materials with appropriate compaction density is beneficial to ensuring that the thickness of the second active material increased during the charge and discharge process is less than the thickness of the first active material increased, reducing the possibility of fracture of the pole piece in the second region, and ensuring the charge and discharge performance of the electrode assembly and the safety performance of the electrode assembly during use.
  • the second active material is fast-charging graphite.
  • the expansion force on the bent portion of the first pole piece can be reduced while taking into account the energy density of the electrode assembly, thereby ensuring the charge and discharge performance and safety performance of the battery cell.
  • the second region has a first curvature
  • the first curvature is the curvature corresponding to the portion of the second region located at the bent portion of the electrode assembly.
  • the range of the second region can be set more reasonably according to needs, thereby specifically reducing the possibility of fracture of the bent portion of the pole piece.
  • the first pole piece is an anode pole piece
  • the second pole piece is a cathode pole piece
  • the first pole piece covers the second pole piece
  • the first first region of the anode electrode sheet covers the first third region of the cathode electrode sheet, and the last second region of the anode electrode sheet covers the last fourth region of the cathode electrode sheet.
  • the anode electrode sheet fully covers the cathode electrode sheet, avoid lithium deposition in the electrode assembly, and improve the safety performance of the battery cell.
  • the second region has a first curvature
  • the fourth region has a second curvature
  • the first curvature is the curvature corresponding to the portion of the second region located at the curved portion of the anode electrode sheet
  • the second curvature is the curvature corresponding to the portion of the fourth region located at the curved portion of the cathode electrode sheet, and along the winding direction, the difference between the first curvature of the last second region of the anode electrode sheet and the second curvature of the last fourth region of the cathode electrode sheet belongs to (0, ⁇ ).
  • Setting a suitable curvature range at the winding end positions of the anode electrode sheet and the cathode electrode sheet can reduce the risk of lithium plating of the electrode assembly 120 and is beneficial to improving the energy density of the battery cell.
  • the difference in arc length corresponding to the last second region of the anode pole piece and the last fourth region of the cathode pole piece is (5 mm, 3 ⁇ /4*R mm), where R is the radius corresponding to the last second region of the anode pole piece.
  • the difference in length between the first first region of the anode electrode sheet and the first third region of the cathode electrode sheet is [20 mm, 60 mm].
  • a battery cell comprising the electrode assembly described in any of the above embodiments.
  • a battery comprising the battery cell described in any of the above embodiments.
  • an electrical device comprising: a battery as described in any of the above embodiments, wherein the battery is used to provide electrical energy to the electrical device.
  • FIG1 is a schematic structural diagram of a vehicle provided in an embodiment of the present application.
  • FIG. 2 is a schematic diagram of the exploded structure of a battery cell provided in an embodiment of the present application.
  • FIG. 3 is a schematic diagram of a processing device for an electrode assembly provided in an embodiment of the present application.
  • FIG. 4 is a schematic diagram of the exploded structure of an electrode assembly provided in an embodiment of the present application.
  • FIG5 is a cross-sectional schematic diagram of an electrode assembly provided in an embodiment of the present application.
  • FIG6 is a cross-sectional schematic diagram of a first pole piece provided in an embodiment of the present application.
  • FIG. 7 is a cross-sectional schematic diagram of another first pole piece provided in an embodiment of the present application.
  • FIG. 8 is a schematic diagram of the electrode assembly shown in FIG. 5 with the separator omitted.
  • FIG. 9 is a schematic diagram of the expansion of a first pole piece and a second pole piece provided in an embodiment of the present application.
  • FIG. 10 is an enlarged schematic diagram of portion H in FIG. 5 .
  • a and/or B can represent: A exists, A and B exist, and B exists.
  • the character "/" in this application generally indicates that the associated objects before and after are in an "or" relationship.
  • multiple refers to more than two (including two).
  • multiple groups refers to more than two groups (including two groups)
  • multiple sheets refers to more than two sheets (including two sheets).
  • the battery cell may include a lithium-ion secondary battery, a lithium-ion primary battery, a lithium-sulfur battery, a sodium-lithium-ion battery, a sodium-ion battery, a lithium metal battery or a magnesium-ion battery, etc., and the embodiments of the present application do not limit this.
  • the battery cell may be cylindrical, flat, rectangular or other shapes, etc., and the embodiments of the present application do not limit this. Battery cells are generally divided into three types according to the packaging method: cylindrical battery cells, square battery cells and soft-pack battery cells, and the embodiments of the present application do not limit this.
  • the battery mentioned in the embodiments of the present application refers to a single physical module including one or more battery cells to provide higher voltage and capacity.
  • the battery mentioned in the present application may include a battery module or a battery pack.
  • the battery generally includes a box for encapsulating one or more battery cells. The box can prevent liquid or other foreign matter from affecting the charging or discharging of the battery cells.
  • the battery cell includes an electrode assembly and an electrolyte.
  • the electrode assembly is composed of a cathode electrode sheet, an anode electrode sheet and a separator.
  • the battery cell mainly relies on the movement of metal ions between the cathode electrode sheet and the anode electrode sheet to work.
  • the cathode electrode sheet includes a cathode current collector and a cathode active material layer.
  • the cathode active material layer is coated on the surface of the cathode current collector.
  • the cathode current collector not coated with the cathode active material layer protrudes from the cathode current collector coated with the cathode active material layer.
  • the cathode current collector not coated with the cathode active material layer serves as a cathode tab.
  • the material of the cathode current collector may be aluminum, and the cathode active material may be lithium cobalt oxide, lithium iron phosphate, ternary lithium or lithium manganese oxide, etc.
  • the anode electrode sheet includes an anode current collector and an anode active material layer.
  • the anode active material layer is coated on the surface of the anode current collector.
  • the anode current collector not coated with the anode active material layer protrudes from the anode current collector coated with the anode active material layer.
  • the anode current collector not coated with the anode active material layer serves as an anode tab.
  • the material of the anode current collector may be copper, and the anode active material may be carbon, silicon, lithium metal or lithium alloy, etc.
  • the cathode tabs are multiple and stacked together, and the anode tabs are multiple and stacked together.
  • the material of the isolation film can be polypropylene (PP) or polyethylene (PE).
  • the battery may include multiple battery cells, wherein the multiple battery cells may be connected in series, in parallel, or in a hybrid connection, wherein the hybrid connection refers to a mixture of series and parallel connections.
  • multiple battery cells may be connected in series, in parallel, or in a hybrid connection to form a battery module, and multiple battery modules may be connected in series, in parallel, or in a hybrid connection to form a battery.
  • multiple battery cells may be directly formed into a battery, or may be first formed into a battery module, and the battery module may then be formed into a battery.
  • the battery is further disposed in an electrical device to provide electrical energy to the electrical device.
  • the battery cells in the battery often convert chemical energy into electrical energy through the chemical reaction inside it, and then conduct the electrical energy through the pole ears of the electrode assembly to supply power to external electrical equipment.
  • the electrode assembly in the battery cell is prone to expansion, which causes a certain expansion force between the pole piece and the isolation membrane, affecting the normal chemical reaction between the anode pole piece and the cathode pole piece. In severe cases, it may cause the pole piece to break, affecting the safety performance of the battery cell.
  • the electrode assembly may include two approximately parallel large surface parts and a corner part connecting the large surface parts.
  • the expansion force on the corner part When the expansion force is generated inside the electrode assembly, the expansion force on the corner part will be greater than the expansion force on the large surface part, and it is more likely to be affected by the expansion force and break.
  • a larger polarization interval will be formed at the corner parts on both sides of the electrode assembly, which will increase the conduction distance of lithium ions, resulting in an increase in the polarization effect of the battery cell, making the battery cell more prone to lithium precipitation, which will affect the performance and safety of the battery cell in severe cases.
  • the present application provides an electrode assembly, in which the corner portion and the large surface portion of the electrode assembly are coated with active materials with different expansion rates, and the expansion rate of the active material coated on the corner portion is less than the expansion rate of the active material coated on the large surface portion.
  • the expansion degree of the active material coated on the corner portion is smaller, which can reduce the possibility of the pole piece at the corner fracture, and ensure the performance of the electrode assembly and the safety performance of the electrode assembly during use.
  • the smaller expansion degree can also reduce the occurrence of lithium precipitation in the corner portion of the electrode assembly.
  • the electrode assembly provided in the embodiment of the present application can still fully coat the active material on the pole piece, thereby improving the energy density of the battery cell.
  • Electrical equipment may be vehicles, mobile phones, portable devices, laptops, ships, spacecraft, electric toys, and electric tools, etc.
  • Vehicles may be fuel vehicles, gas vehicles, or new energy vehicles, and new energy vehicles may be pure electric vehicles, hybrid vehicles, or extended-range vehicles, etc.
  • spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc.
  • electric toys include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc.
  • electric tools include metal cutting electric tools, grinding electric tools, assembly electric tools, and railway electric tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc.
  • the embodiments of the present application do not impose any special restrictions on the above-mentioned electrical equipment.
  • FIG1 it is a structural schematic diagram of a vehicle 1 of an embodiment of the present application.
  • the vehicle 1 can be a fuel vehicle, a gas vehicle or a new energy vehicle.
  • the new energy vehicle can be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc.
  • a motor 40, a controller 30 and a battery 10 can be arranged inside the vehicle 1, and the controller 30 is used to control the battery 10 to power the motor 40.
  • a battery 10 can be arranged at the bottom or the front or rear of the vehicle 1.
  • the battery 10 can be used to power the vehicle 1.
  • the battery 10 can be used as an operating power supply for the vehicle 1, for the circuit system of the vehicle 1, for example, for the working power demand during the start, navigation and operation of the vehicle 1.
  • the battery 10 can not only be used as an operating power supply for the vehicle 1, but also as a driving power supply for the vehicle 1, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1.
  • the battery 10 may include a box body, the interior of the box body is a hollow structure, and the hollow structure can be used to accommodate multiple battery cells. According to different power requirements, the number of battery cells in the battery 10 can be set to any value. Multiple battery cells can be connected in series, parallel or mixed to achieve a larger capacity or power. Since the number of battery cells included in each battery 10 may be large, in order to facilitate installation, the battery cells can be grouped, and each group of battery cells constitutes a battery module. The number of battery cells included in the battery module is not limited, and blocks can be set according to requirements. These battery modules can be connected in series, parallel or mixed.
  • FIG. 2 shows a decomposed structure of a battery cell 100, which may include an outer shell 110 and an inner electrode assembly 120.
  • the shell 110 may be a hollow structure for accommodating the electrode assembly 120.
  • the battery cell 100 may be provided with one or more electrode assemblies 120 according to practical applications.
  • the electrode assembly 120 is a component in the battery cell 100 where an electrochemical reaction occurs.
  • the electrode assembly 120 may be a cylinder or a cuboid, etc., and the shape of the outer shell of the battery cell 100 may be provided correspondingly according to the shape of the electrode assembly 120.
  • Each electrode assembly 120 may have a first pole tab 120a and a second pole tab 120b. The polarities of the first pole tab 120a and the second pole tab 120b are opposite.
  • the second pole tab 120b is an anode pole tab.
  • the cathode pole tab may be formed by stacking a portion of the cathode pole sheet that is not coated with a cathode active material layer
  • the anode pole tab may be formed by stacking a portion of the anode pole sheet that is not coated with an anode active material layer.
  • the battery cell 100 is also provided with an electrode terminal 130, which is used to be electrically connected to the electrode assembly 120 to output the electrical energy of the battery cell 100.
  • the electrode terminal 130 may include a cathode electrode terminal and an anode electrode terminal, the cathode electrode terminal is used to be electrically connected to the cathode tab, and the anode electrode terminal is used to be electrically connected to the anode tab.
  • the cathode electrode terminal may be directly connected to the cathode tab or indirectly connected, and the anode electrode terminal may be directly connected to the anode tab or indirectly connected.
  • the cathode electrode terminal is electrically connected to the cathode tab via a connecting member 140
  • the anode electrode terminal is electrically connected to the anode tab via a connecting member 140.
  • the electrode assembly can be prepared by winding.
  • FIG. 3 shows a schematic diagram of the structure of an apparatus for processing an electrode assembly 120
  • FIG. 4 is a schematic diagram of the exploded structure of the electrode assembly 120.
  • the electrode assembly 120 may include a first pole piece 121, a second pole piece 122, and a separation film 123.
  • the separation film 123 is used to separate the first pole piece 121 from the second pole piece 122.
  • the first pole piece 121 is connected to the first pole ear 1211
  • the second pole piece 122 is connected to the second pole ear 1221.
  • FIG. 4 shows a schematic diagram of an example in which the first pole ear 1211 and the second pole ear 1221 are respectively arranged at both ends of the electrode assembly 120, but the present embodiment is not limited thereto.
  • the first pole piece assembly and the second pole piece assembly are first cut to obtain the first pole piece 121 and the second pole piece 122 of a preset length, wherein the cut first pole piece 121 and the second pole piece 122 and the isolation film 123 can be respectively arranged on a plurality of roller assemblies 101 for the subsequent winding process.
  • a plurality of isolation films 123 can be arranged in the electrode assembly to ensure the insulation between the first pole piece 121 and the second pole piece 122.
  • the winding needle 102 clamps the winding starting end of the isolation film 123.
  • the winding needle clamps a plurality of isolation films 123
  • the winding starting ends of the plurality of isolation films 123 are basically aligned.
  • the first pole piece 121 and the second pole piece 122 of the preset length cut are respectively brought into the winding by the friction force of the isolation film 123, and the electrode assembly 120 is obtained after winding.
  • FIG5 shows a schematic cross-sectional view of an electrode assembly 120 provided in an embodiment of the present application on a plane formed by a first direction W and a second direction T, wherein the second direction T is perpendicular to the thickness direction of the battery cell, the third direction Z is perpendicular to the second direction T and parallel to the pole piece of the electrode assembly 120, and the first direction W is perpendicular to the plane formed by the second direction T and the third direction Z.
  • FIG6 shows a schematic cross-sectional view of a first pole piece 121 in the electrode assembly 120 on the same plane. As shown in Figures 4 to 6, the electrode assembly 120 includes a first electrode sheet 121, a second electrode sheet 122 and an isolation film 123.
  • the first electrode sheet 121, the second electrode sheet 122 and the isolation film 123 are wound to form the electrode assembly 120.
  • the isolation film 123 is used to isolate the first electrode sheet 121 and the second electrode sheet 122.
  • the polarities of the first electrode sheet 121 and the second electrode sheet 122 are opposite; wherein the first electrode sheet 121 includes a first region 1211 and a second region 1212, and the first region 1211 and the second region 1212 are alternately arranged and connected in sequence along the winding direction.
  • the second region 1212 is at least partially located at the bending portion of the first electrode sheet 121, the first region 1211 is coated with a first active material, and the second region 1212 is coated with a second active material, and the expansion rate of the second active material is less than the expansion rate of the first active material.
  • the first electrode sheet 121, the second electrode sheet 122 and the isolation film 123 are wound into an electrode assembly 120 with a circular cross section under the drive of the winding needle 102, and then the wound electrode assembly 120 is pressed down to avoid the phenomenon of fluffy opening of the inner circle of the wound electrode assembly 120.
  • the shape of the electrode assembly 120 can also be adapted to the shape of the shell. Therefore, in the embodiment of the present application, the cross section of the electrode assembly 120 can be as shown in Figure 5.
  • the first pole piece 121 after winding may include multiple plane parts and multiple curved parts
  • the plane part refers to the surface approximately parallel on the cross section of the electrode assembly shown in FIG5
  • the curved part refers to the part approximately arc on the cross section of the electrode assembly shown in FIG5.
  • the second region 1212 is at least partially located on the curved part of the first pole piece 121
  • the first region 1211 is at least partially located on the plane part of the first pole piece 121 and connected to the second region 1212.
  • the first region 1211 and the second region 1212 are alternately arranged in sequence along the winding direction as shown in FIG5, starting from the winding starting position A1 of the first pole piece 121, a first first region 1211 is arranged, and along the winding direction, a first second region 1212 is arranged, and the first second region 1212 is connected to the first first region 1211; continuing along the winding direction, a second first region 1211 is arranged, and the second first region 1211 is connected to the first second region 1212.
  • the first regions 1211 and the second regions 1212 are alternately arranged and connected in the winding direction, and starting from the second first region 1211, each first region 1211 is connected to two adjacent second regions 1212.
  • the first pole piece 121 may be terminated by the second region 1212, and at the winding termination position A2 of the first pole piece 121, the second region 1212 may be located at a part of the bent portion.
  • the second region 1212 may be entirely located in the curved portion. As shown in FIG5 , the second region 1212 may be located in the entire curved portion of the first pole piece 121, and the first region 1211 may be located in the entire planar portion of the first pole piece 121. As shown in FIG6 , the second region 1212 may be located in a portion of the curved portion of the first pole piece 121, such as a portion of the curved portion of the first pole piece 121 that is located within a certain angle range, and the first region 1211 is the portion of the first pole piece 121 other than the second region 1212, that is, the first region 1211 includes a portion of the planar portion and the curved portion of the first pole piece 121.
  • the first first region 1211 may include a planar portion and a portion of the next curved portion
  • the second first region 1211 may include a portion of the previous curved portion, a planar portion, and a portion of the next curved portion.
  • the first region 1211 and the second region 1212 are alternately arranged and connected in sequence along the winding direction.
  • the second region 1212 includes a portion of the planar portion and the bend of the first pole piece 121, and the first region 1211 may be located at a portion of the planar portion of the first pole piece 121.
  • the first first region 1211 may include a portion of the planar portion
  • the first second region 1212 may include a portion of the previous planar portion, the bend, and a portion of the next planar portion.
  • the first region 1211 and the second region 1212 are alternately arranged and connected in sequence along the winding direction.
  • Different active materials may be coated on the first region 1211 and the second region 1212, for example, active materials with different expansion rates.
  • the first region 1211 may be coated with a first active material
  • the second region 1212 may be coated with a second active material
  • the expansion rate of the first active material is different from the expansion rate of the second active material.
  • the expansion rate refers to the ratio of the increase in the thickness of the pole piece as the number of charge and discharge times increases during the use of the electrode assembly.
  • the expansion rate of the first active substance refers to the ratio of the increase in the thickness of the portion of the first pole piece where the first active substance is located as the number of charge and discharge times increases.
  • the expansion rate can be calculated based on the pole piece thickness of a new battery cell and the pole piece thickness of an aged battery cell. Specifically, the first pole piece of a new battery cell in a fully charged state is disassembled, and the thickness of the first region of the new battery cell is measured as M 1 and the thickness of the second region is measured as M 2 ; the first pole piece of an aged battery cell in a fully charged state is disassembled, and the thickness of the first region of the aged battery cell is measured as N 1 and the thickness of the second region is N 2 , respectively. Then, the expansion rate of the first active material coated on the first region is M 1 /N 1 - 1, and the expansion rate of the second active material coated on the second region is M 2 /N 2 -1. In the embodiment of the present application, the expansion rate of the second active material M 2 /N 2 -1 is less than the expansion rate of the first active material M 1 /N 1 -1.
  • the increase in the thickness of the pole piece is mainly due to factors such as the lattice expansion of the active material itself on the current collector, the aging of the pole piece, the accumulation of byproducts, and lithium precipitation.
  • the curved portion of the electrode assembly 120 is more likely to break than the flat portion.
  • a second active material with a smaller expansion rate can be coated on the second region 1212, so that during the charge and discharge process of the battery cell, the second active material expands less on the second region 1212, which can reduce the expansion force on the first pole piece 121 in the second region 1212.
  • an active material with a smaller expansion rate can be coated to reduce the expansion force on the area.
  • the expansion forces on the curved portion and the flat portion of the first pole piece 121 are also different.
  • the possibility of fracture of the curved portion of the pole piece can be reduced, and the safety performance of the electrode assembly 120 during use can be ensured.
  • there is no blank area on the pole piece provided in the embodiment of the present application which can also ensure the energy density of the battery cell.
  • the second pole piece 122 includes a third region 1221 and a fourth region 1222, and the third region 1221 and the fourth region 1222 are alternately arranged and connected in sequence along the winding direction.
  • the fourth region 1222 is at least partially located at the bending portion of the second pole piece 122, the third region 1221 is coated with a third active material, and the fourth region 1222 is coated with a fourth active material, and the expansion rate of the fourth active material is less than the expansion rate of the third active material.
  • the second pole piece 122 may also be provided with different regions, and different active materials may be coated on different regions.
  • the fourth region 1222 may be entirely located in the curved portion, for example, located in the entire curved portion of the second pole piece 122, or located in a portion within a certain angle range in the curved portion of the second pole piece 122; or, only a portion of the fourth region 1222 may be located in the curved portion, for example, the fourth region 1222 may include a portion of the planar portion and the curved portion of the second pole piece 122.
  • the third region 1221 is connected to the fourth region 1222, and they are alternately arranged in sequence along the winding direction.
  • Figure 5 shows the situation where the fourth region 1222 is located in the entire curved portion of the second pole piece 122.
  • a first third region 1221 is provided, and the first third region 1221 includes a planar portion of the second pole piece 122 starting from the winding starting position B1.
  • a first fourth region 1222 is provided, and the first fourth region 1222 includes a curved portion connected to the first third region 1221.
  • a second third region 1221 is provided.
  • a plurality of third regions 1221 and fourth regions 1222 may be provided on the second pole piece 122.
  • the second pole piece 122 may be terminated by the fourth region 1222, and at the winding termination position B2 of the second pole piece 122, the fourth region 1222 may include only a portion of the curved portion.
  • the third region 1221 of the second pole piece 122 may also be coated with a third active material, and the fourth region 1222 may be coated with a fourth active material, wherein the expansion rate of the fourth active material may be less than the expansion rate of the third active material.
  • the expansion degree of the fourth active material on the fourth region is less than the expansion degree of the third active material on the third region, which can reduce the expansion force on the second pole piece 122 in the fourth region.
  • the second pole piece 122 is fully coated with active materials, which can also ensure the energy density of the second pole piece 122.
  • the expansion forces on the planar portion and the curved portion of the electrode assembly 120 can be differentiated to a greater extent, further reducing the possibility of fracture of the curved portion of the pole piece, thereby ensuring the safety performance of the electrode assembly 120 during use.
  • different regions are provided on the first pole piece 121 and the second pole piece 122, and active materials of different properties can be coated as needed, making the design of the battery cell more flexible, thereby meeting more diverse needs.
  • the difference between the expansion rate of the first active material and the expansion rate of the second active material belongs to (0%, 4%).
  • the difference between the expansion rate of the first active material and the expansion rate of the second active material is too large, there may be a difference in the thickness growth of the first electrode sheet where the first region and the second region are located.
  • the active materials coated on the first region and the second region may have a significant step structure, so that the second region of the first electrode sheet is separated from the isolation film, affecting the normal electrochemical reaction of the electrode assembly. Therefore, a suitable difference range can reduce the possibility of fracture of the bent portion of the electrode sheet, and is also conducive to ensuring the normal use of the electrode assembly in the battery cell.
  • the powder OI value of the second active material is smaller than the powder OI value of the first active material.
  • the OI value of the powder of the active material is related to the expansion degree of the active material during the charge and discharge process. Under the same charge and discharge conditions, the greater the OI value of the powder of the active material, the greater the increase in the thickness of the pole piece where the active material is located. Therefore, when selecting the second active material, an active material with a smaller powder OI value can be selected, which is conducive to reducing the expansion rate of the second active material. Specifically, the OI value of the powder of the second active material can be 0.5-7.
  • the powder OI value G OI of the active material and the particle size D50 ( ⁇ m) of the powder can satisfy 2.8 ⁇ 100/(D50+2.8 ⁇ G OI ) ⁇ 12.
  • the active material can have good kinetic properties.
  • the powder OI value G OI of the second active material and the particle size D50 ( ⁇ m) of the powder can satisfy 4 ⁇ 100/(D50+2.8 ⁇ G OI ) ⁇ 8.5, thereby further improving the kinetic properties of the electrode assembly in the second region, reducing the possibility of lithium deposition in the second region, and reducing the increase in the thickness of the electrode sheet due to lithium deposition in the second region.
  • the compaction density P3k (g/cm 3 ) of the active material powder and the average particle size Dv50 ( ⁇ m) of the active material can satisfy 0.15 ⁇ 1/Dv50+0.2/P3k ⁇ 1, so that the active material has good dynamic performance, where G is the acceleration of gravity.
  • the compaction density P3k (g/cm 3 ) of the second active material powder and the average particle size Dv50 ( ⁇ m) of the second active material can satisfy 0.15 ⁇ 1/Dv50+0.2/P3k ⁇ 0.5, thereby further improving the dynamic performance of the electrode assembly in the second region, reducing the possibility of lithium precipitation in the second region, and reducing the increase in the thickness of the electrode sheet in the second region due to lithium precipitation.
  • suitable active material powder to prepare the electrode assembly it is beneficial to ensure that the expansion rate of the second active material is smaller than the expansion rate of the first active material. At the same time, it can also improve the dynamic performance of the electrode assembly, reduce the possibility of lithium plating in the electrode sheet, and reduce the increase in electrode sheet thickness caused by lithium plating.
  • the compaction density of the second active material is less than the compaction density of the first active material.
  • the compaction density of the active material is closely related to the capacity, internal resistance, and cycle performance of the battery cell.
  • the OI value of the active material after rolling can be changed by adjusting the compaction density of the active material during the rolling process of preparing the electrode assembly. The larger the OI value of the active material after rolling, the brittler and harder the pole piece where the active material is located is, and the easier it is to break.
  • the compaction density of the second active material is less than the compaction density of the first active material, which is conducive to achieving an OI value of the second active material after rolling that is less than the OI value of the first active material after rolling, so that during the charge and discharge process, the increased thickness of the pole piece where the second active material is located is less than the increased thickness of the pole piece where the first active material is located.
  • the relationship between the OI value V OI of the active material on the first pole piece after rolling and the compaction density PD of the active material on the first pole piece can satisfy 0.7 ⁇ (80/V OI +43/PD) ⁇ PD/V OI ⁇ 21.5, so as to ensure the cycle life of the battery cell under high-rate rapid charging.
  • the OI value V OI and the compaction density PD of the second active material after rolling can satisfy 1.8 ⁇ (80/V OI +43/PD) ⁇ PD/V OI ⁇ 16, further improving the charging speed and cycle life of the second region.
  • Selecting active materials with appropriate compaction density is beneficial to ensuring that the thickness of the second active material increased during the charge and discharge process is less than the thickness of the first active material increased, reducing the possibility of fracture of the pole piece in the second region, and ensuring the charge and discharge performance of the electrode assembly and the safety performance of the electrode assembly during use.
  • the second region 1212 has a first curvature, and the first curvature is the curvature corresponding to the portion of the second region 1212 located at the curved portion of the electrode assembly 120 .
  • the curved portion of the first pole piece 121 is located at both ends of the electrode assembly 120 along the first direction W.
  • the curved portion of the first pole piece 121 is approximated as a semicircular arc, and the first arc refers to the arc corresponding to the portion of the second area 1212 of the first pole piece 121 occupied on the semicircular arc.
  • the second region 1212 may include a curved portion within the range of (0, ⁇ ] radians. Similarly, at the other end of the electrode assembly 120 along the first direction W, the second region 1212 may also include a curved portion within the range of (0, ⁇ ] radians.
  • the radian corresponding to the portion of the second region 1212 located at the curved portion of the electrode assembly 120 is ⁇ , that is, the first radian is ⁇ .
  • a portion of the second region 1212 is located at the planar portion of the electrode assembly 120, and another portion is located at the curved portion of the electrode assembly 120. It can be seen from FIG7 that the radian corresponding to the portion of the second region 1212 located at the curved portion of the electrode assembly 120 is also ⁇ , that is, the first radian is also ⁇ .
  • the arc corresponding to the portion of the second region 1212 located at the curved portion of the electrode assembly 120 may also be any angle. As shown in FIG6 , at one end of the electrode assembly 120 along the first direction W, the first arc corresponding to the curved portion of the second region 1212 is ⁇ 1; at the other end of the electrode assembly 120 along the first direction W, the first arc corresponding to the curved portion of the second region 1212 is ⁇ 2. Both ⁇ 1 and ⁇ 2 are less than ⁇ radians, and ⁇ 1 and ⁇ 2 may be the same arc, or different values may be designed according to requirements.
  • the range of the second region 1212 can be set more reasonably according to needs, thereby specifically reducing the possibility of fracture of the bent portion of the pole piece.
  • the first arc corresponding to the last second region 1212 of the wound first pole piece 121 may belong to [ ⁇ /2, ⁇ ].
  • the winding end position A2 of the first pole piece 121 and the winding end position B2 of the second pole piece 122 are both located on the curved portion of the first pole piece 121.
  • the winding end portion of the first pole piece 121 is away from the winding end portion of the second pole piece 122 along the winding direction.
  • the first pole piece 121 is an anode pole piece and the second pole piece 122 is a cathode pole piece, in order to reduce the lithium deposition of the electrode assembly 120, it is necessary to ensure that the first pole piece 121 covers the second pole piece 122.
  • the first radian is less than ⁇ /2 radians, the position of the last second region 1212 of the second pole piece 122 is small, and it is easy to form unqualified products due to production errors; if the first radian is greater than ⁇ radians, the winding end position of the first pole piece 121 will be located on the plane portion of the first pole piece 121, affecting the flatness of the plane portion of the electrode assembly, and easily generating the risk of stress concentration, which is not conducive to ensuring the safety performance of the battery cell.
  • the first arc corresponding to the last second region 1212 of the wound first pole piece 121 may further belong to [ ⁇ /2, 3 ⁇ /4].
  • the first pole piece 121 is an anode pole piece
  • the second pole piece 122 is a cathode pole piece
  • the first pole piece 121 covers the second pole piece 122 .
  • the anode pole piece is often coated with active materials such as graphite or a mixture of graphite and other active materials in different mass ratios. These active materials can have fast charging performance.
  • Fast charging performance refers to the equivalent rate greater than or equal to 2.2C when charging a battery with a SOC of 3%-80% at 25°C. Specifically, after fully charging at an equivalent rate greater than or equal to 2.2C and fully discharging at 1C for 10 times, the battery is fully charged at an equivalent rate greater than or equal to 2.2C, the anode pole piece is disassembled and the lithium deposition on the surface is observed. If there is no lithium deposition area on the surface of the anode pole piece, it is considered that the active material has fast charging performance.
  • the first region and the second region can be set only on the anode plate, and the expansion rate of the active material coated in the first region 1211 of the anode plate is greater than the expansion rate of the active material coated in the second region 1212, which can at least reduce the possibility of the bending portion of the anode plate breaking.
  • the third region and the fourth region can also be set on the cathode plate at the same time, and the expansion rate of the active material coated in the third region 1221 of the cathode plate can also be greater than the expansion rate of the active material coated in the fourth region 1222, so as to reduce the possibility of the bending portion of the plate breaking to a greater extent.
  • different regions can also be set only on the cathode plate, and active materials with different expansion rates can be coated in different regions to reduce the possibility of the bending portion of the cathode plate breaking.
  • the anode electrode sheet can cover the cathode electrode sheet.
  • the total length of the anode electrode sheet can be greater than the total length of the cathode electrode sheet.
  • the anode electrode sheet can enter the winding before the cathode electrode sheet and end the winding later than the cathode electrode sheet.
  • the anode electrode sheet is wrapped around the outer layer of the cathode electrode sheet.
  • the first first region 1211 of the anode electrode sheet covers the first third region 1221 of the cathode electrode sheet, and the last second region 1212 of the anode electrode sheet covers the last fourth region 1222 of the cathode electrode sheet.
  • the anode electrode sheet fully covers the cathode electrode sheet, thereby avoiding lithium deposition in the electrode assembly 120 and improving the safety performance of the battery cell.
  • the second region 1212 has a first curvature and the fourth region 1222 has a second curvature
  • the first curvature is the curvature corresponding to the portion of the second region 1212 located at the curved portion of the anode pole piece
  • the second curvature is the curvature corresponding to the portion of the fourth region 1222 located at the curved portion of the cathode pole piece, and along the winding direction, the difference between the first curvature of the last second region 1212 of the anode pole piece and the second curvature of the last fourth region 1222 of the cathode pole piece belongs to (0, ⁇ ).
  • FIG8 is a schematic diagram of the electrode assembly 120 in FIG5 omitting the separator 123.
  • the last second region 1212 of the anode electrode sheet is the C portion in FIG8, and the last fourth region 1222 of the cathode electrode sheet is the D portion in FIG8, then the difference between the first arc corresponding to the C portion and the second arc corresponding to the D portion is the length of the C portion longer than the D portion.
  • the difference between the first arc corresponding to the C portion and the second arc corresponding to the D portion is 0, then during the production process, a slight error may cause the anode electrode sheet to fail to completely cover the cathode electrode sheet, bringing the risk of lithium deposition; if the difference between the first arc corresponding to the C portion and the second arc corresponding to the D portion is ⁇ , then at least one of the winding end position of the anode electrode sheet and the winding end position of the cathode electrode sheet will fall on the plane portion of the electrode assembly 120, affecting the flatness of the plane portion, easily generating the risk of stress concentration, and affecting the safety performance of the battery cell.
  • the difference in the corresponding radians of ⁇ between the two will result in the last second region 1212 of the anode electrode being unable to undergo an electrochemical reaction to provide electrical energy, resulting in a waste of active materials and being unfavorable for improving the energy density of the battery cell.
  • Setting a suitable curvature range at the winding end positions of the anode electrode sheet and the cathode electrode sheet can reduce the risk of lithium plating of the electrode assembly 120 and is beneficial to improving the energy density of the battery cell.
  • the length Ln -1 of the n-1th second region of the anode electrode sheet is greater than the length Kn -1 of the n-1th fourth region of the cathode electrode sheet
  • the length Ln -2 of the n-2th second region of the anode electrode sheet is greater than the length Kn -2 of the n-2th fourth region of the cathode electrode sheet
  • the length L1 of the first second region of the anode electrode sheet is greater than the length K1 of the first fourth region of the cathode electrode sheet.
  • the length of the latter second region is greater than the length of the previous second region.
  • the length Ln -1 of the n-1 second region is greater than the length Ln -2 of the n-2 second region
  • the length Ln -2 of the n-2 second region is greater than the length Ln -3 of the n-3 second region
  • the length L2 of the second second region is greater than the length L1 of the first second region.
  • the transition point between the first region and the second region may be located at the curved portion of the first pole piece. Since the expansion rates of the first active material and the second active material are different, the thickness increased when the expansion occurs at the transition point between the first region and the second region also has a certain difference. Therefore, the transition point is set at the curved portion of the first pole piece, which can reserve space for the expansion difference at the transition point, avoid the shell of the battery cell squeezing the transition point and causing stress concentration on the first pole piece, which is conducive to ensuring the safety performance of the electrode assembly.
  • the difference between the n-1th second region and the n-3th second region can be greater than 0.9*(2*S+Duu+Da*2+Dll+Dc*2)* ⁇ 2, and less than 1.1*(2*S+Duu+Da*2+Dll+Dc*2)* ⁇ 2, wherein, as shown in FIG10, S is the thickness of the isolation film, Duu is the thickness of the current collector of the first pole piece, Dll is the thickness of the current collector of the second pole piece, Da is the thickness of the first active material coated on one side of the current collector of the first pole piece, Dc is the thickness of the second active material coated on one side of the current collector of the second pole piece, and ⁇ 2 is the angle corresponding to the parts of the n-1th second region and the n-3th second region on the bent portion of the first pole piece.
  • the difference between the n-2th second region and the n-4th second region can be greater than 0.9*(2*S+Duu+Da*2+Dll+Dc*2)* ⁇ 1 and less than 1.1*(2*S+Duu+Da*2+Dll+Dc*2)* ⁇ 1, where ⁇ 1 is the angle corresponding to the parts of the n-2th second region and the n-4th second region on the bent portion of the first pole piece.
  • the difference in arc length corresponding to the last second region 1212 of the anode pole piece and the last fourth region 1222 of the cathode pole piece is (5 mm, 3 ⁇ /4*R mm), where R is the radius corresponding to the last second region 1212 of the anode pole piece.
  • the anode electrode sheet and the cathode electrode sheet are both electrodes of a preset length, and the difference in arc length corresponding to the last second region 1212 of the anode electrode sheet and the last second region 1212 of the wound cathode electrode sheet is the difference in length between the C and D parts in FIG8 after they are unfolded into a plane.
  • the second region 1212 and the fourth region 1222 can be approximated as circular arcs for calculation.
  • the schematic diagram of the unfolded C and D parts in FIG8 can be shown in FIG9.
  • part C and part D are too small, for example, less than or equal to 5 mm, the requirement that the anode electrode sheet is wrapped around the cathode electrode sheet may not be met after being wound into the electrode assembly 120; if the difference between part C and part D is too large, the length of the remaining electrode sheet in part C is large, resulting in a waste of active materials coated on part C, which is not conducive to improving the energy density of the battery cell.
  • the length relationship between the anode electrode sheet and the cathode electrode sheet is within a suitable range, which can ensure that the wound anode electrode sheet is wrapped around the outside of the cathode electrode sheet to avoid lithium plating and can maximize the energy density of the battery cell.
  • the difference in arc length corresponding to the last second region 1212 of the anode electrode sheet and the last second region 1212 of the cathode electrode sheet may be (10 mm, ⁇ /2*R mm).
  • the wound anode electrode sheet can be further ensured to be wrapped around the outside of the cathode electrode sheet, thereby preventing lithium deposition in the electrode assembly 120 and increasing the energy density of the battery cell as much as possible.
  • the difference in length between the first first region 1211 of the anode electrode sheet and the first third region 1221 of the cathode electrode sheet is [20 mm, 60 mm].
  • the first region 1211 of the wound anode electrode sheet is part E in Figure 8
  • the first third region 1221 of the wound cathode electrode sheet is part F in Figure 8.
  • the difference in length between the two is that part E is longer than part F.
  • the cathode electrode's winding starting position B1 may exceed the anode electrode's winding starting position A1, bringing about the risk of lithium plating; if the difference between the two lengths is too large, for example greater than 60 mm, then more areas in the first region 1211 of the anode electrode will not be able to undergo electrochemical reactions with the active material on the cathode electrode to provide electrical energy, resulting in a waste of active materials and not being conducive to improving the energy density of the battery cell.
  • Setting a suitable size range at the winding starting position of the anode electrode sheet and the cathode electrode sheet can reduce the risk of lithium plating of the electrode assembly 120 and is beneficial to improving the energy density of the battery cell.
  • the difference in length between the first first region 1211 of the anode electrode sheet and the first first region 1211 of the cathode electrode sheet may be [20, 40] mm.
  • the present application also provides a battery cell, comprising the electrode assembly 120 described in any one of the above embodiments.
  • the present application also provides a battery, comprising the battery cell described in any of the above embodiments.
  • the present application also provides an electrical device, comprising the battery described in any of the above embodiments, wherein the battery is used to provide electrical energy to the electrical device.

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Abstract

本申请实施例提供了一种电极组件、电池单体、电池和用电装置。该电极组件包括：第一极片、第二极片和隔离膜，第一极片、第二极片和隔离膜卷绕形成电极组件，隔离膜用于隔离第一极片和第二极片，第一极片和第二极片的极性相反；其中，第一极片包括第一区域和第二区域，第一区域和第二区域沿卷绕方向依次交替设置并连接，电极组件卷绕后，第二区域至少部分位于第一极片的弯曲部，第一区域涂覆有第一活性材料，第二区域涂覆有第二活性材料，第二活性材料的膨胀率小于第一活性材料的膨胀率。本申请实施例提供电极组件可以减少极片的弯曲部断裂的可能性，同时也能够保证电池单体的能量密度。

Description

电极组件、电池单体、电池和用电装置 技术领域
本申请涉及电池技术领域，特别是涉及一种电极组件、电池单体、电池和用电装置。
背景技术
节能减排是汽车产业可持续发展的关键。在这种情况下，电动车辆由于其节能环保的优势成为汽车产业可持续发展的重要组成部分。而对于电动车辆而言，电池技术又是关乎其发展的一项重要因素。
电池的整体制作流程长，且工艺复杂，包括涂布、制片、卷绕、组装、激光焊、注液等一系列工序。其中，电池单体内部电极组件的加工过程尤为重要，会直接影响电池单体的性能。因此，如何提高电极组件的性能仍然是一个需要解决的技术问题。
发明内容
本申请提供了一种电极组件、电池单体、电池和用电装置，可以减少极片的弯曲部断裂的可能性，同时也能够保证电池单体的能量密度。
第一方面，提供了一种电极组件，包括：第一极片、第二极片和隔离膜，所述第一极片、所述第二极片和所述隔离膜卷绕形成所述电极组件，所述隔离膜用于隔离所述第一极片和所述第二极片，所述第一极片和所述第二极片的极性相反；其中，所述第一极片包括第一区域和第二区域，所述第一区域和所述第二区域沿卷绕方向依次交替设置并连接，所述电极组件卷绕后，所述第二区域至少部分位于所述第一极片的弯曲部，所述第一区域涂覆有第一活性材料，所述第二区域涂覆有第二活性材料，所述第二活性材料的膨胀率小于所述第一活性材料的膨胀率。
通过在第一极片的第一区域和第二区域涂覆膨胀率不同的活性物质，在电池单体的充放电过程中，由于不同的活性材料的性能不同，第一极片上弯曲部与平面部受到的作用力也不同，通过合理的设计，能够减少极片的弯曲部断裂的可能性，保证电极组件在使用过程中的安全性能。同时，本申请实施例提供的极片上不存在留白区域，也能够保证电池单体的能量密度。
在一些实施例中，所述第二极片包括第三区域和第四区域，所述第三区域和所述第四区域沿卷绕方向依次交替设置并连接，所述电极组件卷绕后，所述第四区 域至少部分位于所述第二极片的弯曲部，所述第三区域涂覆有第三活性材料，所述第四区域涂覆有第四活性材料，所述第三活性材料的膨胀率大于所述第四活性材料的膨胀率。
通过在第二极片的第三区域和第四区域涂覆膨胀率不同的活性物质，能够更大程度地区别电极组件的平面部与弯曲部受到的膨胀力，进一步减少极片的弯曲部断裂的可能性，保证电极组件在使用过程中的安全性能。同时在第一极片和第二极片上设置不同区域，还可以根据需要涂覆不同性质的活性物质，使得电池单体的设计更加灵活，从而满足更多样的需求。
在一些实施例中，所述第一活性材料的膨胀率与所述第二活性材料的膨胀率的差值属于(0％,4％)。
合适的差值范围既可以减少极片的弯曲部断裂的可能性，也有利于保证电极组件在电池单体中的正常使用。
在一些实施例中，所述第二活性材料的粉料OI值小于所述第一活性材料的粉料OI值。
通过选择合适的活性物质粉料来制备电极组件，有利于保证第二活性材料的膨胀率小于第一活性材料的膨胀率，同时也可以提高电极组件的的动力学性能，降低极片析锂的可能性，减少由于析锂导致的极片厚度增加。
在一些实施例中，所述第二活性材料的压实密度小于所述第一活性材料的压实密度。
选择压实密度合适的活性材料，有利于保证充放电过程中第二活性材料增加的厚度小于第一活性材料增加的厚度，减少第二区域所在的极片断裂的可能性，保证电极组件的充放电性能以及电极组件在使用过程中的安全性能。
在一些实施例中，所述第二活性材料为快充石墨。
这样可以在降低第一极片的弯曲部受到的膨胀力的同时，兼顾电极组件的能量密度，保证电池单体的充放电性能与安全性能。
在一些实施例中，所述电极组件卷绕后，所述第二区域具有第一弧度，所述第一弧度为所述第二区域位于所述电极组件的弯曲部的部分对应的弧度。
这样可以根据需求更合理地设置第二区域的范围，从而有针对性地减少极片的弯曲部断裂的可能性。
在一些实施例中，所述第一极片为阳极极片，所述第二极片为阴极极片，所述第一极片覆盖所述第二极片。
这样可以减少电极组件析锂的可能，保证电池单体的电极组件在使用过程中的充放电性能和安全性能。
在一些实施例中，沿所述卷绕方向，所述阳极极片的第一个第一区域覆盖所述阴极极片的第一个第三区域，所述阳极极片的最后一个第二区域覆盖所述阴极极片的最后一个第四区域。
这样可以保证在卷绕后的电极组件中，阳极极片充分覆盖阴极极片，避免电极组件的析锂，提高电池单体的安全性能。
在一些实施例中，所述第二区域具有第一弧度，所述第四区域具有第二弧度，所述第一弧度为所述第二区域位于所述阳极极片的弯曲部的部分对应的弧度，所述第二弧度为所述第四区域位于所述阴极极片的弯曲部的部分对应的弧度，沿所述卷绕方向，所述阳极极片的最后一个所述第二区域的所述第一弧度与所述阴极极片的最后一个所述第四区域的所述第二弧度的差值属于(0,π)。
在阳极极片和阴极极片的卷绕收尾位置设置合适的弧度范围可以降低电极组件120的析锂风险，同时有利于提高电池单体的能量密度。
在一些实施例中，沿卷绕方向，所述阳极极片的最后一个第二区域与所述阴极极片的最后一个第四区域对应的弧长的差值属于(5mm,3π/4*R mm)，其中R为阳极极片最后一个第二区域对应的半径。
这样可以进一步地在保证卷绕后的阳极极片包裹在阴极极片的外侧，从而能够在避免电极组件发生析锂的同时，也能够尽可能地提高电池单体的能量密度。
在一些实施例中，沿所述卷绕方向，所述阳极极片的第一个第一区域与所述阴极极片的第一个第三区域的长度之差属于[20mm,60mm]。
这样可以进一步地保证卷绕后的阳极极片包裹在阴极极片的外侧，从而能够在避免电极组件发生析锂的同时，也能够尽可能地提高电池单体的能量密度。
第二方面，提供了一种电池单体，包括上述任一实施例所述的电极组件。
第三方面，提供了一种电池，包括上述任一实施例所述的电池单体。
第四方面，提供了一种用电装置，包括：上述任一实施例所述的电池，所述电池用于为用电装置提供电能。
附图说明
为了更清楚地说明本申请实施例的技术方案，下面将对本申请实施例中所需要使用的附图作简单地介绍，显而易见地，下面所描述的附图仅仅是本申请的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据附图获得其他的附图。
图1是本申请实施例提供的一种车辆的结构示意图。
图2是本申请实施例提供的一种电池单体的分解结构示意图。
图3是本申请实施例提供的一种电极组件的加工装置的示意图。
图4是本申请实施例提供的一种电极组件的分解结构示意图。
图5是本申请实施例提供的一种电极组件的截面示意图。
图6是本申请实施例提供的一种第一极片的截面示意图。
图7是本申请实施例提供的另一种第一极片的截面示意图。
图8是图5示出的电极组件省略了隔离膜的示意图。
图9是本申请实施例提供的一种第一极片和第二极片的展开示意图。
图10是图5中的H部分的放大示意图。
在附图中，附图并未按照实际的比例绘制。
具体实施方式
下面结合附图和实施例对本申请的实施方式作进一步详细描述。以下实施例的详细描述和附图用于示例性地说明本申请的原理，但不能用来限制本申请的范围，即本申请不限于所描述的实施例。
在本申请的描述中，需要说明的是，除非另有说明，“多个”的含义是两个以上；术语“上”、“下”、“左”、“右”、“内”、“外”等指示的方位或位置关系仅是为了便于描述本申请和简化描述，而不是指示或暗示所指的装置或元件必须具有特定的方位、以特定的方位构造和操作，因此不能理解为对本申请的限制。此外，术语“第一”、“第二”、“第三”等仅用于描述目的，而不能理解为指示或暗示相对重要性。“垂直”并不是严格意义上的垂直，而是在误差允许范围之内。“平行”并不是严格意义上的平行，而是在误差允许范围之内。本申请所使用的所有的技术和科学术语与属于本申请的技术领域的技术人员通常理解的含义相同；本申请中在申请的说明书中所使用的术语只是为了描述具体的实施例的目的，不是旨在于限制本申请；本申请的说明书和权利要求书及上述附图说明中的术语“包括”和“具有”以及它们的任何变形，意图在于覆盖不排他的包含。
下述描述中出现的方位词均为图中示出的方向，并不是对本申请的具体结构进行限定。在本申请的描述中，还需要说明的是，除非另有明确的规定和限定，术语“安装”、“相连”、“连接”应做广义理解，例如，可以是固定连接，也可以是可拆卸连接，或一体地连接；可以是直接相连，也可以通过中间媒介间接相连。对于本领域的普通技术人员而言，可视具体情况理解上述术语在本申请中的具体含义。
在本申请中提及“实施例”意味着，结合实施例描述的特定特征、结构或特性可以包含在本申请的至少一个实施例中。在说明书中的各个位置出现该短语并不一定均是指相同的实施例，也不是与其它实施例互斥的独立的或备选的实施例。本领域技术人员显式地和隐式地理解的是，本申请所描述的实施例可以与其它实施例相结合。
本申请中术语“和/或”，仅仅是一种描述关联对象的关联关系，表示可以存在三种关系，例如，A和/或B，可以表示：存在A，存在A和B，存在B这三种情况。另外，本申请中字符“/”，一般表示前后关联对象是一种“或”的关系。
本申请中出现的“多个”指的是两个以上(包括两个)，同理，“多组”指的是两组以上(包括两组)，“多片”指的是两片以上(包括两片)。
在本申请的实施例中，相同的附图标记表示相同的部件，并且为了简洁，在不同实施例中，省略对相同部件的详细说明。应理解，附图示出的本申请实施例中的各种部件的厚度、长宽等尺寸，以及集成装置的整体厚度、长宽等尺寸仅为示例性说明，而不应对本申请构成任何限定。
本申请中，电池单体可以包括锂离子二次电池、锂离子一次电池、锂硫电池、钠锂离子电池、钠离子电池、锂金属电池或镁离子电池等，本申请实施例对此并不限定。电池单体可呈圆柱体、扁平体、长方体或其它形状等，本申请实施例对此也 不限定。电池单体一般按封装的方式分成三种：柱形电池单体、方形电池单体和软包电池单体，本申请实施例对此也不限定。
本申请的实施例所提到的电池是指包括一个或多个电池单体以提供更高的电压和容量的单一的物理模块。例如，本申请中所提到的电池可以包括电池模块或电池包等。电池一般包括用于封装一个或多个电池单体的箱体。箱体可以避免液体或其他异物影响电池单体的充电或放电。
电池单体包括电极组件和电解液，电极组件由阴极极片、阳极极片和隔离膜组成。电池单体主要依靠金属离子在阴极极片和阳极极片之间移动来工作。阴极极片包括阴极集流体和阴极活性物质层，阴极活性物质层涂覆于阴极集流体的表面，未涂覆阴极活性物质层的阴极集流体凸出于已涂覆阴极活性物质层的阴极集流体，未涂覆阴极活性物质层的阴极集流体作为阴极极耳。以锂离子电池为例，阴极集流体的材料可以为铝，阴极活性物质可以为钴酸锂、磷酸铁锂、三元锂或锰酸锂等。阳极极片包括阳极集流体和阳极活性物质层，阳极活性物质层涂覆于阳极集流体的表面，未涂覆阳极活性物质层的阳极集流体凸出于已涂覆阳极活性物质层的阳极集流体，未涂覆阳极活性物质层的阳极集流体作为阳极极耳。阳极集流体的材料可以为铜，阳极活性物质可以为碳、硅、锂金属或锂合金等。为了保证通过大电流而不发生熔断，阴极极耳的数量为多个且层叠在一起，阳极极耳的数量为多个且层叠在一起。隔离膜的材质可以为聚丙烯(polypropylene，PP)或聚乙烯(polyethylene，PE)等。
为了满足不同的电力需求，电池可以包括多个电池单体，其中，多个电池单体之间可以串联或并联或混联，混联是指串联和并联的混合。可选地，多个电池单体可以先串联或并联或混联组成电池模块，多个电池模块再串联或并联或混联组成电池。也就是说，多个电池单体可以直接组成电池，也可以先组成电池模块，电池模块再组成电池。电池再进一步设置于用电设备中，为用电设备提供电能。
电池中的电池单体往往是通过其内部的化学反应将化学能转化为电能，通过电极组件的极耳将电能导出，从而向外部用电设备供电的。在充放电的过程中，电池单体中的电极组件容易产生膨胀，使得极片与隔离膜之间产生一定的膨胀力，影响阳极极片和阴极极片之间的正常化学反应，严重时可能会导致极片的断裂，影响电池单体的安全性能。在一些电极组件中，例如，方形电池的电极组件，电极组件可以包括近似平行的两个大面部分和连接大面部分的拐角部分，在电极组件内部产生了膨胀力的情况下，拐角部分受到的膨胀力会比大面部分受到的膨胀力更大，更容易受到膨胀力的作用而发生断裂。另一方面，在电极组件的两边的拐角部分会形成较大的极化区间，增加锂离子的传导距离，导致电池单体的极化作用增大，使得电池单体更容易析锂，严重时会影响电池单体的性能与安全。
鉴于此，本申请提供了一种电极组件，电极组件的拐角部分和大面部分涂覆有膨胀率不同的活性材料，且涂覆在拐角部分的活性材料的膨胀率小于涂覆在大面部分的活性材料的膨胀率，则在电池单体的充放电过程中，涂覆在拐角部分的活性材料的膨胀程度较小，能够减少拐角处的极片断裂的可能性，保证电极组件的性能以及电极 组件在使用过程中的安全性能。同时，较小的膨胀程度也可以减少电极组件在拐角部分的析锂现象的发生。另外，相较于在电极组件上留有空白区域的方案，本申请实施例提供的电极组件仍然能够在极片上充分涂覆活性物质，从而提高电池单体的能量密度。
本申请实施例描述的技术方案均适用于各种使用电池的用电设备。用电设备可以是车辆、手机、便携式设备、笔记本电脑、轮船、航天器、电动玩具和电动工具等等。车辆可以是燃油汽车、燃气汽车或新能源汽车，新能源汽车可以是纯电动汽车、混合动力汽车或增程式汽车等；航天器包括飞机、火箭、航天飞机和宇宙飞船等等；电动玩具包括固定式或移动式的电动玩具，例如，游戏机、电动汽车玩具、电动轮船玩具和电动飞机玩具等等；电动工具包括金属切削电动工具、研磨电动工具、装配电动工具和铁道用电动工具，例如，电钻、电动砂轮机、电动扳手、电动螺丝刀、电锤、冲击电钻、混凝土振动器和电刨等等。本申请实施例对上述用电设备不做特殊限制。
以下实施例为了方便说明，以用电设备为车辆为例进行说明。例如，如图1所示，为本申请一个实施例的一种车辆1的结构示意图，车辆1可以为燃油汽车、燃气汽车或新能源汽车，新能源汽车可以是纯电动汽车、混合动力汽车或增程式汽车等。车辆1的内部可以设置马达40，控制器30以及电池10，控制器30用来控制电池10为马达40的供电。例如，在车辆1的底部或车头或车尾可以设置电池10。电池10可以用于车辆1的供电，例如，电池10可以作为车辆1的操作电源，用于车辆1的电路系统，例如，用于车辆1的启动、导航和运行时的工作用电需求。在本申请的另一实施例中，电池10不仅仅可以作为车辆1的操作电源，还可以作为车辆1的驱动电源，替代或部分地替代燃油或天然气为车辆1提供驱动动力。
电池10可以包括箱体，箱体内部为中空结构，该中空结构可以用于容纳多个电池单体。根据不同的电力需求，电池10中的电池单体的数量可以设置为任意数值。多个电池单体可通过串联、并联或混联的方式连接以实现较大的容量或功率。由于每个电池10中包括的电池单体的数量可能较多，为了便于安装，可以将电池单体分组设置，每组电池单体组成电池模块。电池模块中包括的电池单体的数量不限，可以根据需求设置块，这些电池模块可通过串联、并联或混联的方式进行连接。
例如，图2示出了一种电池单体100的分解结构，可以包括外部的外壳110和内部的电极组件120。外壳110可以为中空结构，该中空结构用于容纳电极组件120。电池单体100可以根据实际应用设置一个或者多个电极组件120。电极组件120是电池单体100中发生电化学反应的部件。电极组件120可以是圆柱体或者长方体等，并且，可以根据电极组件120的形状，对应设置电池单体100的外壳的形状。每个电极组件120可以具有第一极耳120a和第二极耳120b。第一极耳120a和第二极耳120b的极性相反。例如，当第一极耳120a为阴极极耳时，第二极耳120b为阳极极耳。阴极极耳可以由阴极极片上未涂覆阴极活性物质层的部分层叠形成，阳极极耳可以由阳极极片上未涂覆阳极活性物质层的部分层叠形成。
电池单体100上还设置有电极端子130，电极端子130用于与电极组件120电连接，以输出电池单体100的电能。电极端子130可以包括阴极电极端子和阳极电极端子，阴极电极端子用于与阴极极耳电连接，阳极电极端子用于与阳极极耳电连接。阴极电极端子与阴极极耳可以直接连接，也可以间接连接，阳极电极端子与阳极极耳可以直接连接，也可以间接连接。示例性的，阴极电极端子通过一个连接构件140与阴极极耳电连接，阳极电极端子通过一个连接构件140与阳极极耳电连接。
在本申请实施例中，电极组件可以通过卷绕的方式制备，例如，图3示出了加工电极组件120的装置的结构示意图，图4为电极组件120的分解结构示意图。如图3和图4所示，电极组件120可以包括第一极片121、第二极片122和隔离膜123，隔离膜123用于隔离第一极片121和第二极片122。第一极片121连接第一极耳1211，第二极片122连接第二极耳1221，图4示出的是第一极耳1211和第二极耳1221分别设置于电极组件120的两端为例的示意图，但本实施例并不限于此。
具体地，如图3和图4所示，在加工该电极组件120时，在进行卷绕之前，先将第一极片组件和第二极片组件切断，以获得预设长度的第一极片121和第二极片122，其中，该切断后的第一极片121和第二极片122、隔离膜123可以分别设置于多个过辊组件101上，以用于后续卷绕过程。从图3可以看出，电极组件中可以设置多层隔离膜123，以保证第一极片121和第二极片122之间的绝缘。在进行卷绕时，卷针102夹持隔离膜123的卷绕起始端，若卷针夹持多个隔离膜123，则多个隔离膜123的卷绕起始端基本对齐，卷针106起卷后，再将切断的预设长度的第一极片121和第二极片122由隔离膜123的摩擦力分别带入进行卷绕，卷绕后获得电极组件120。
图5示出了本申请实施例提供的一种电极组件120在第一方向W和第二方向T形成的平面上的截面示意图，其中，第二方向T垂直于电池单体的厚度方向，第三方向Z垂直于第二方向T且平行于电极组件120的极片，第一方向W垂直于第二方向T和第三方向Z形成的平面。图6示出的是电极组件120中的第一极片121在相同平面上的截面示意图。如图4至图6所示，电极组件120包括第一极片121、第二极片122和隔离膜123，第一极片121、第二极片122和隔离膜123卷绕形成电极组件120，隔离膜123用于隔离第一极片121和第二极片122，第一极片121和第二极片122的极性相反；其中，第一极片121包括第一区域1211和第二区域1212，第一区域1211和第二区域1212沿卷绕方向依次交替设置并连接，所述电极组件120卷绕后，所述第二区域1212至少部分位于所述第一极片121的弯曲部，所述第一区域1211涂覆有第一活性材料，所述第二区域1212涂覆有第二活性材料，所述第二活性材料的膨胀率小于所述第一活性材料的膨胀率。
在电极组件120的生产过程中，第一极片121、第二极片122和隔离膜123在卷针102的带动下卷绕为截面为圆形的电极组件120，再对卷绕后的电极组件120进行下压，以避免卷绕形成的电极组件120出现内圈蓬松开口的现象，同时在一些非圆柱体形状的电池单体的生产过程中，例如方形电池单体，也能够使得电极组件120的形状适应壳体的形状。因此，在本申请实施例中，电极组件120的截面可以如图5所示。
以电极组件120中的第一极片121为例，卷绕后的第一极片121可以包括多个平面部和多个弯曲部，平面部指的是图5所示的电极组件的截面上近似平行的表面，弯曲部指的是图5所示的电极组件的截面上近似圆弧的部分。第二区域1212至少部分位于所述第一极片121的弯曲部，第一区域1211至少部分位于第一极片121的平面部上，并与第二区域1212连接。第一区域1211和第二区域1212沿卷绕方向依次交替设置可以如图5所示，从第一极片121的卷绕起始位置A1开始，设置有第一个第一区域1211，沿卷绕方向，设置有第一个第二区域1212，该第一个第二区域1212与第一个第一区域1211连接；继续沿卷绕方向，设置有第二个第一区域1211，该第二个第一区域1211与第一个第二区域1212连接。以此类推，第一区域1211与第二区域1212沿卷绕方向依次交替设置并连接，从第二个第一区域1211开始，每个第一区域1211连接两个相邻的第二区域1212。第一极片121可以由第二区域1212收尾，在第一极片121的卷绕收尾位置A2，第二区域1212可以位于弯曲部的一部分。
在一种可能的实施方式中，第二区域1212可以全部位于弯曲部。如图5所示，第二区域1212可以位于第一极片121的整个弯曲部，则第一区域1211可以位于第一极片121的整个平面部。如图6所示，第二区域1212可以位于第一极片121的弯曲部的一部分，例如第一极片121的弯曲部中位于一定角度范围内的部分，则第一区域1211为第一极片121中除第二区域1212之外的部分，也就是说，第一区域1211包括第一极片121上平面部和弯曲部的一部分。参考图6，沿卷绕方向，第一个第一区域1211可以包括一个平面部分和下一个弯曲部的一部分，第二个第一区域1211可以包括上一个弯曲部的一部分、平面部分和下一个弯曲部的一部分。以此类推，第一区域1211与第二区域1212沿卷绕方向依次交替设置并连接。
在另一种可能的实施方式中，第二区域1212可以只有一部分位于弯曲部，如图7所示，第二区域1212包括第一极片121的平面部的一部分和弯曲部，则第一区域1211可以位于第一极片121的平面部的一部分。参考图7，沿卷绕方向，第一个第一区域1211可以包括平面部的一部分，第一个第二区域1212可以包括上一个平面部的一部分、弯曲部和下一个平面部的一部分。以此类推，第一区域1211与第二区域1212沿卷绕方向依次交替设置并连接。
第一区域1211和第二区域1212上可以涂覆不同的活性材料，例如膨胀率不同的活性材料。具体地，第一区域1211可以涂覆有第一活性材料，第二区域1212可以涂覆有第二活性材料，第一活性材料的膨胀率与于第二活性材料的膨胀率不同。膨胀率指的是在电极组件的使用过程中，极片的厚度随着充放电次数的增加而增加的比例，例如，第一活性物质的膨胀率指的是第一活性物质位于的第一极片的部分的厚度随着充放电次数的增加而增加的比例。膨胀率可以根据新电池单体的极片厚度和老化电池单体的极片厚度来计算。具体地，将处于满充状态的新电池单体的第一极片拆解出来，分别测量出新电池单体的第一区域的厚度为M 1、第二区域的厚度为M 2；再将处于满充状态的老化电池单体的第一极片拆解出来，分别测量出老化电池单体的第一区域的厚度为N 1、第二区域的厚度为N 2，则第一区域上涂覆的第一活性物质的膨胀率为M 1/N 1- 1，第二区域上涂覆的第二活性物质的膨胀率为M 2/N 2-1。在本申请实施例中，第二活性物质的膨胀率M 2/N 2-1小于第一活性物质的膨胀率M 1/N 1-1。
极片厚度的增加主要是由于集流体上活性物质本身的晶格膨胀、极片的老化、副产物堆积、析锂等因素。在其他条件都相同的情况下，极片的膨胀率越大，极片的厚度增加就越大，产生的膨胀力也就越大，而膨胀力往往是造成极片断裂的主要原因。尤其是在卷绕式的电极组件120中，电极组件120受到膨胀力后，电极组件120的弯曲部相较于平面部更容易发生断裂。因此，可以在第二区域1212涂覆膨胀率更小的第二活性材料，这样在电池单体的充放电过程中，第二活性材料在第二区域1212上膨胀的程度较小，能够减少第一极片121在第二区域1212受到的膨胀力。同时，也可以针对传统电极组件120中受到膨胀力较大的区域，涂覆膨胀率较小的活性物质，减少该区域受到的膨胀力。
通过在第一极片121的第一区域和第二区域涂覆膨胀率不同的活性物质，在电池单体的充放电过程中，由于不同的活性材料的性能不同，第一极片121上弯曲部与平面部受到的膨胀力也不同，通过合理的设计，能够减少极片的弯曲部断裂的可能性，保证电极组件120在使用过程中的安全性能。同时，本申请实施例提供的极片上不存在留白区域，也能够保证电池单体的能量密度。
根据本申请的一些实施例，可选地，第二极片122包括第三区域1221和第四区域1222，第三区域1221和第四区域1222沿卷绕方向依次交替设置并连接，电极组件120卷绕后，第四区域1222至少部分位于第二极片122的弯曲部，第三区域1221涂覆有第三活性材料，第四区域1222涂覆有第四活性材料，第四活性材料的膨胀率小于第三活性材料的膨胀率。
与第一极片121类似，第二极片122也可以设置有不同的区域，并且在不同区域上涂覆不同的活性材料。在第二极片122中，第四区域1222可以全部位于弯曲部，例如位于第二极片122的整个弯曲部，或者位于第二极片122的弯曲部中的一定角度范围内的部分；或者，第四区域1222可以只有一部分位于弯曲部，例如第四区域1222可以包括第二极片122的平面部的一部分和弯曲部。第三区域1221与第四区域1222连接，且沿卷绕方向依次交替设置。以图5为例，图5示出的是第四区域1222位于第二极片122的整个弯曲部的情况。从第二极片122的卷绕起始位置B1开始，设置有第一个第三区域1221，该第一个第三区域1221包括第二极片122上从卷绕起始位置B1开始的平面部，沿卷绕方向，设置有第一个第四区域1222，该第一个第四区域1222包括与第一个第三区域1221连接的弯曲部，继续沿卷绕方向，设置有第二个第三区域1221。以此类推，第二极片122上可以设置多个第三区域1221和第四区域1222。第二极片122可以由第四区域1222收尾，在第二极片122的卷绕收尾位置B2，第四区域1222可以只包括弯曲部的一部分。
第二极片122的第三区域1221也可以涂覆有第三活性材料，第四区域1222涂覆有第四活性材料，其中，第四活性材料的膨胀率可以小于第三活性材料的膨胀率。则在电池单体的充放电过程中，第四活性材料在第四区域上膨胀的程度小于第三活性 材料在第三区域上膨胀的程度，能够降低第二极片122在第四区域受到的膨胀力。同时，第二极片122上充分涂覆活性物质，也能够保证第二极片122上的能量密度。
通过在第二极片122的第三区域和第四区域涂覆膨胀率不同的活性物质，能够更大程度地区别电极组件120的平面部与弯曲部受到的膨胀力，进一步减少极片的弯曲部断裂的可能性，保证电极组件120在使用过程中的安全性能。同时在第一极片121和第二极片122上设置不同区域，还可以根据需要涂覆不同性质的活性物质，使得电池单体的设计更加灵活，从而满足更多样的需求。
根据本申请的一些实施例，可选地，第一活性材料的膨胀率与第二活性材料的膨胀率的差值属于(0％,4％)。
在电池单体的充放电过程中，如果第一活性材料的膨胀率与第二活性材料的膨胀率的差值过大，有可能会使得第一区域和第二区域所在的第一极片的部分的厚度增长出现差异，严重时可能导致第一区域和第二区域上涂覆的活性材料出现明显的台阶结构，使得第一极片的第二区域与隔离膜分离，影响电极组件正常的电化学反应。因此，合适的差值范围既可以减少极片的弯曲部断裂的可能性，也有利于保证电极组件在电池单体中的正常使用。
根据本申请的一些实施例，可选地，第二活性材料的粉料OI值小于第一活性材料的粉料OI值。
活性材料的粉料OI值与活性材料在充放电过程中的膨胀程度有关，在相同的充放电条件下，活性材料的粉料OI值越大，活性物质所在的极片厚度增加得越大。因此，在选择第二活性材料时，可以选择粉料OI值较小的活性材料，有利于降低第二活性材料的膨胀率。具体地，第二活性材料的粉料OI值可以为0.5-7。
可选地，活性材料的粉料OI值G OI与粉料的粒径D50(μm)可以满足2.8≤100/(D50+2.8×G OI)≤12，当一种活性材料可以满足上述不等式，则该活性材料可以具有较好的动力学性能。在本申请实施例中，第二活性材料的粉料OI值G OI与粉料的粒径D50(μm)可以满足4≤100/(D50+2.8×G OI)≤8.5，从而进一步提高电极组件在第二区域的动力学性能，降低第二区域析锂的可能性，减少第二区域由于析锂导致的极片厚度增加。
可选地，活性材料的粉料在3000kg×G的压力下，粉料的压实密度P3k(g/cm 3)与活性材料的平均粒径Dv50(μm)可以满足0.15≤1/Dv50+0.2/P3k≤1，以使得活性材料具有较好的动力学性能，其中，G为重力加速度。在本申请实施例中，第二活性材料的粉料压实密度P3k(g/cm 3)与第二活性材料的平均粒径Dv50(μm)可以满足0.15≤1/Dv50+0.2/P3k≤0.5，从而进一步提高电极组件在第二区域的动力学性能，降低第二区域析锂的可能性，减少第二区域由于析锂导致的极片厚度增加。
通过选择合适的活性物质粉料来制备电极组件，有利于保证第二活性材料的膨胀率小于第一活性材料的膨胀率，同时也可以提高电极组件的的动力学性能，降低极片析锂的可能性，减少由于析锂导致的极片厚度增加。
根据本申请的一些实施例，可选地，第二活性材料的压实密度小于第一活 性材料的压实密度。
活性材料的压实密度与电池单体的容量、内阻、循环性能等密切相关，可以在制备电极组件的辊压工序中，通过调节活性材料的压实密度来改变活性材料辊压后的OI值。活性材料辊压后的OI值越大，活性材料所在的极片越脆越硬，也就越容易发生断裂。因此，第二活性材料的压实密度小于第一活性材料的压实密度，有利于实现第二活性材料辊压后的OI值小于第一活性材料辊压后的OI值，从而在充放电过程中，使得第二活性材料所在的极片增加的厚度小于第一活性材料所在的极片增加的厚度。
为了保证新制备的电极组件的第一区域和第二区域的厚度一致，当第一活性材料和第二活性材料采取压实密度不同的两种材料时，第一极片上涂覆的第一活性材料和第二活性材料的质量也有所差异。具体地，在第一区域涂覆质量为m 1的第一活性物质，该第一活性物质的压实密度为PD 1；在第二区域涂覆质量为m 2的第二活性物质，该第二活性物质的压实密度为PD 2。则m 1和m 2之间可以满足m 1＝PD 1/PD 2*m 2。
可选地，第一极片上的活性材料辊压后的OI值V OI与第一极片上的活性材料的压实密度PD之间的关系可以满足0.7≤(80/V OI+43/PD)×PD/V OI≤21.5，以保证电池单体在大倍率快速充电下的循环寿命。在本申请实施例中，第二活性材料的辊压后的OI值V OI和压实密度PD可以满足1.8≤(80/V OI+43/PD)×PD/V OI≤16，进一步提高第二区域的充电速度和循环寿命。
选择压实密度合适的活性材料，有利于保证充放电过程中第二活性材料增加的厚度小于第一活性材料增加的厚度，减少第二区域所在的极片断裂的可能性，保证电极组件的充放电性能以及电极组件在使用过程中的安全性能。
根据本申请的一些实施例，可选地，电极组件120卷绕后，第二区域1212具有第一弧度，第一弧度为第二区域1212位于电极组件120的弯曲部的部分对应的弧度。
在图5示出的截面中，第一极片121的弯曲部位于电极组件120沿第一方向W的两端。将第一极片121的弯曲部近似为半圆弧，则第一弧度指的是第一极片121的第二区域1212在半圆弧上占据的部分对应的弧度。
在电极组件120沿第一方向W的一端，第二区域1212可以包括在(0,π]弧度范围内的弯曲部。类似地，在电极组件120沿第一方向W的另一端，第二区域1212也可以包括在(0,π]弧度范围内的弯曲部。在图5中，第二区域1212位于电极组件120的弯曲部的部分对应的弧度为π，即第一弧度为π。在另一种可能的实施方式中，例如图7所示的第一极片中，第二区域1212的一部分位于电极组件120的平面部，另一部分位于电极组件120的弯曲部，则可以从图7中看出，第二区域1212位于电极组件120的弯曲部的部分对应的弧度也是π，即第一弧度也为π。
可选地，第二区域1212位于电极组件120的弯曲部的部分对应的弧度也可以为任意角度。如图6所示，在电极组件120沿第一方向W的一端，第二区域1212在弯曲部对应的第一弧度为θ1；在电极组件120沿第一方向W的另一端，第二区域1212 在弯曲部对应的第一弧度为θ2。θ1和θ2均小于π弧度，θ1和θ2可以为相同的弧度，也可以根据需求设计不同的值。
这样可以根据需求更合理地设置第二区域1212的范围，从而有针对性地减少极片的弯曲部断裂的可能性。
可选地，卷绕后的第一极片121的最后一个的第二区域1212对应的第一弧度可以属于[π/2,π]。
如图5所示，第一极片121的卷绕收尾位置A2和第二极片122的卷绕收尾位置B2均位于第一极片121的弯曲部上，在一种可能的实施方式中，第一极片121的卷绕收尾部分沿卷绕方向远离第二极片122的卷绕收尾部分。尤其是在第一极片121为阳极极片，第二极片122为阴极极片的情况下，为了减少电极组件120的析锂，需要保证第一极片121覆盖第二极片122。若第一弧度小于π/2弧度，则留给第二极片122的最后一个第二区域1212的位置较小，容易因为生产误差而形成不合格的产品；若第一弧度大于π弧度，则第一极片121的卷绕收尾位置会位于第一极片121的平面部，影响电极组件的平面部的平整度，容易产生应力集中的风险，不利于保证电池单体的安全性能。
可选地，卷绕后的第一极片121的最后一个的第二区域1212对应的第一弧度可以进一步属于[π/2,3π/4]。
根据本申请的一些实施例，可选地，第一极片121为阳极极片，第二极片122为阴极极片，第一极片121覆盖第二极片122。
阳极极片上涂覆的往往是石墨、或石墨与其它活性物质按不同质量比得到的混合物等活性材料，这些活性材料可以具有快充性能，快充性能指的是在25℃下，对3％-80％SOC的电池进行充电时的等效倍率大于或等于2.2C。具体地，以等效倍率大于或等于2.2C满充、以1C满放重复10次后，再将电池以等效倍率大于或等于2.2C的充电流程进行满充，拆解出阳极极片并观察表面析锂情况，若阳极极片表面无析锂区域，则认为该活性材料具有快充性能。
活性材料在充放电过程中的膨胀往往在阳极极片上体现得较为明显，因此可以仅在阳极极片上设置第一区域和第二区域，且在阳极极片上的第一区域1211涂覆的活性材料的膨胀率大于第二区域1212涂覆的活性材料的膨胀率，至少能够减少阳极极片的弯曲部断裂的可能性。可选地，也可以同时在阴极极片上设置第三区域和第四区域，且在阴极极片的第三区域1221涂覆的活性材料的膨胀率也可以大于在第四区域1222涂覆的活性材料的膨胀率，从而能够在更大程度上减少极片的弯曲部断裂的可能性。另外，也可以仅在阴极极片上设置不同区域，且在不同区域涂覆膨胀率不同的活性材料，来减少阴极极片的弯曲部断裂的可能性。
为了避免析锂现象的发生，阳极极片可以覆盖阴极极片。阳极极片的总长度可以大于阴极极片的总长度，在卷绕过程中，阳极极片可以先于阴极极片进入卷绕，且晚于阴极极片结束卷绕。在阳极极片、阴极极片和隔离膜123卷绕形成的电极组件120中，阳极极片包裹在阴极极片的外层。
这样可以减少电极组件120析锂的可能，保证电池单体的电极组件120在使用过程中的充放电性能和安全性能。
根据本申请的一些实施例，可选地，沿卷绕方向，阳极极片的第一个第一区域1211覆盖阴极极片的第一个第三区域1221，阳极极片的最后一个第二区域1212覆盖所述阴极极片的最后一个第四区域1222。
如图5所示，在阳极极片和阴极极片的卷绕起始部分，在第一个第一区域1211和第一个第三区域1221的结束位置基本对齐的情况下，第一个第一区域1211的长度大于第一个第三区域1221的长度；在阳极极片和阴极极片的卷绕收尾部分，在最后一个第二区域1212和最后一个第四区域1222的起始位置基本对齐的情况下，最后一个第二区域1212位于弯曲部的部分对应的弧度大于最后一个第四区域1222位于弯曲部的部分对应的弧度。
这样可以保证在卷绕后的电极组件中，阳极极片充分覆盖阴极极片，避免电极组件120的析锂，提高电池单体的安全性能。
根据本申请的一些实施例，可选地，第二区域1212具有第一弧度，第四区域1222具有第二弧度，第一弧度为第二区域1212位于阳极极片的弯曲部的部分对应的弧度，第二弧度为第四区域1222位于阴极极片的弯曲部的部分对应的弧度，沿卷绕方向，阳极极片的最后一个第二区域1212的第一弧度与阴极极片的最后一个第四区域1222的第二弧度的差值属于(0,π)。
以图8为例，图8为图5中的电极组件120省略了隔离膜123的示意图。沿卷绕方向，阳极极片的最后一个第二区域1212为图8中的C部分，阴极极片的最后一个第四区域1222为图8中的D部分，则C部分对应的第一弧度和D部分对应的第二弧度的差值即为C部分长于D部分的长度。若C部分对应的第一弧度和D部分对应的第二弧度的差值为0，则在生产过程中，稍有误差就有可能导致阳极极片不能完全覆盖阴极极片，带来析锂风险；若C部分对应的第一弧度和D部分对应的第二弧度的差值为π，则阳极极片的卷绕收尾位置和阴极极片的卷绕收尾位置这两者中至少有一者会落在电极组件120的平面部，影响平面部的平整度，容易产生应力集中的风险，影响电池单体的安全性能。同时，两者对应的弧度的差为π会导致阳极极片的最后一个第二区域1212不能发生电化学反应以提供电能，导致活性材料的浪费，也不利于提高电池单体的能量密度。
在阳极极片和阴极极片的卷绕收尾位置设置合适的弧度范围可以降低电极组件120的析锂风险，同时有利于提高电池单体的能量密度。
在本申请实施例中，如图8和图9所示，以C部分为阳极极片沿卷绕方向的第n个第二区域、D部分为阴极极片沿卷绕方向的第n个第四区域为例，阳极极片第n-1个第二区域的长度L n-1大于阴极极片第n-1个第四区域的长度K n-1，阳极极片第n-2个第二区域的长度L n-2大于阴极极片第n-2个第四区域的长度K n-2，以此类推，阳极极片第1个第二区域的长度L 1大于阴极极片第1个第四区域的长度K 1。这样有利于保证阳极极片和阴极极片上的过渡点对齐，避免随着卷绕半径的增大而导致第二区域与第四 区域错位，保证第二区域与第四区域的至少部分位于相应极片的弯曲部。
在同一极片中，沿卷绕方向，除了最后一个第二区域之外，后一个第二区域的长度大于前一个第二区域的长度。如图8和图9所示，以第一极片为例，第n-1个第二区域的长度L n-1大于第n-2个第二区域的长度L n-2，第n-2个第二区域的长度L n-2大于第n-3个第二区域的长度L n-3，以此类推，第二个第二区域的长度L 2大于第一个第二区域的长度L 1。这样可以保证第一极片上的过渡点对齐，避免随着卷绕半径的增大而导致第一极片上的第二区域错位，保证第二区域的至少部分位于第一极片的弯曲部。
在一种可能的实施方式中，第一区域和第二区域的过渡点可以位于第一极片的弯曲部。由于第一活性材料和第二活性材料的膨胀率不同，在第一区域和第二区域的过渡点处产生膨胀时增加的厚度也具有一定的差异。因此过渡点设置于第一极片的弯曲部，可以为过渡点处的膨胀差异预留空间，避免电池单体的外壳对过渡点产生挤压而造成第一极片上的应力集中，有利于保证电极组件的安全性能。
为了尽可能地对齐第一区域和第二区域的过渡点，沿卷绕方向，第n-1个第二区域和第n-3个第二区域的差可以大于0.9*(2*S+Duu+Da*2+Dll+Dc*2)*θ2，且小于1.1*(2*S+Duu+Da*2+Dll+Dc*2)*θ2，其中，如图10所示，S为隔离膜的厚度，Duu为第一极片的集流体的厚度，Dll为第二极片的集流体的厚度，Da为第一极片的集流体的一侧涂覆的第一活性材料的厚度，Dc为第二极片的集流体的一侧涂覆的第二活性材料的厚度，θ2为第n-1个第二区域和第n-3个第二区域在第一极片的弯曲部上的部分对应的角度。
类似地，第n-2个第二区域和第n-4个第二区域的差可以大于0.9*(2*S+Duu+Da*2+Dll+Dc*2)*θ1，且小于1.1*(2*S+Duu+Da*2+Dll+Dc*2)*θ1，其中，θ1为第n-2个第二区域和第n-4个第二区域在第一极片的弯曲部上的部分对应的角度。
根据本申请的一些实施例，可选地，沿卷绕方向，阳极极片的最后一个第二区域1212与阴极极片的最后一个第四区域1222对应的弧长的差值属于(5mm,3π/4*R mm)，其中R为阳极极片最后一个第二区域1212对应的半径。
在阳极极片和阴极极片卷绕为电极组件120之前，阳极极片和阴极极片均为预设长度的极片，则阳极极片的最后一个第二区域1212与卷绕后的阴极极片的最后一个第二区域1212对应的弧长的差，即为图8中的C部分和D部分展开为平面后两者的长度的差。其中，可以将第二区域1212和第四区域1222近似为圆弧进行计算。图8中的C部分和D部分展开后的示意图可以如图9所示。
C部分和D部分的长度的差过小，例如小于或等于5mm，在卷绕为电极组件120后可能会无法满足阳极极片包裹在阴极极片外面的要求；C部分和D部分的差过大，C部分空余的极片长度较大，导致C部分涂覆的活性材料的浪费，不利于提高电池单体的能量密度。
阳极极片和阴极极片之间的长度关系具有合适的范围，可以保证卷绕后的阳极极片包裹在阴极极片的外侧，避免发生析锂，并且能够尽可能地提高电池单体的 能量密度。
可选地，沿卷绕方向，阳极极片的最后一个第二区域1212与阴极极片的最后一个第二区域1212对应的弧长的差值可以属于(10mm,π/2*R mm)。
这样可以进一步地在保证卷绕后的阳极极片包裹在阴极极片的外侧，从而能够在避免电极组件120发生析锂的同时，也能够尽可能地提高电池单体的能量密度。
根据本申请的一些实施例，可选地，沿卷绕方向，阳极极片的第一个第一区域1211与阴极极片的第一个第三区域1221的长度之差属于[20mm,60mm]。
以图8为例，卷绕后的阳极极片的第一个第一区域1211为图8中的E部分，卷绕后的阴极极片的第一个第三区域1221为图8中的F部分，两者的长度之差即为E部分大于F部分的长度。
两者的长度之差如果为0，则在生产过程中，稍有误差就有可能使得阴极极片的卷绕起始位置B1超出阳极极片的卷绕起始位置A1，带来析锂风险；两者的长度之差如果过大，例如大于60mm，则会导致阳极极片的第一个第一区域1211中存在较多区域不能与阴极极片上的活性物质发生电化学反应来提供电能，导致活性材料的浪费，也不利于提高电池单体的能量密度。
在阳极极片和阴极极片的卷绕起始位置设置合适的尺寸范围可以降低电极组件120的析锂风险，同时有利于提高电池单体的能量密度。
可选地，沿卷绕方向，阳极极片的第一个第一区域1211与阴极极片的第一个第一区域1211的长度之差可以属于[20,40]mm。
这样可以进一步地保证卷绕后的阳极极片包裹在阴极极片的外侧，从而能够在避免电极组件120发生析锂的同时，也能够尽可能地提高电池单体的能量密度。
本申请还提供了一种电池单体，包括上述实施例中任一实施例所述的电极组件120。
本申请还提供了一种电池，包括上述实施例中任一实施例所述的电池单体。
本申请还提供了一种用电装置，包括上述实施例中任一实施例所述的电池，该电池用于为用电装置提供电能。
虽然已经参考优选实施例对本申请进行了描述，但在不脱离本申请的范围的情况下，可以对其进行各种改进并且可以用等效物替换其中的部件。尤其是，只要不存在结构冲突，各个实施例中所提到的各项技术特征均可以任意方式组合起来。本申请并不局限于文中公开的特定实施例，而是包括落入权利要求的范围内的所有技术方案。

Claims (14)

  1. 一种电极组件，其特征在于，包括：
    第一极片、第二极片和隔离膜，所述第一极片、所述第二极片和所述隔离膜卷绕形成所述电极组件，所述隔离膜用于隔离所述第一极片和所述第二极片，所述第一极片和所述第二极片的极性相反；
    其中，所述第一极片包括第一区域和第二区域，所述第一区域和所述第二区域沿卷绕方向依次交替设置并连接，所述电极组件卷绕后，所述第二区域至少部分位于所述第一极片的弯曲部，所述第一区域涂覆有第一活性材料，所述第二区域涂覆有第二活性材料，所述第二活性材料的膨胀率小于所述第一活性材料的膨胀率。
  2. 根据权利要求1所述的电极组件，其特征在于，
    所述第二极片包括第三区域和第四区域，所述第三区域和所述第四区域沿卷绕方向依次交替设置并连接，所述电极组件卷绕后，所述第四区域至少部分位于所述第二极片的弯曲部，所述第三区域涂覆有第三活性材料，所述第四区域涂覆有第四活性材料，所述第四活性材料的膨胀率小于所述第三活性材料的膨胀率。
  3. 根据权利要求1或2所述的电极组件，其特征在于，
    所述第一活性材料的膨胀率与所述第二活性材料的膨胀率的差值属于(0％,4％)。
  4. 根据权利要求1至3中任一项所述的电极组件，其特征在于，
    所述第二活性材料的粉料OI值小于所述第一活性材料的粉料OI值。
  5. 根据权利要求1至4中任一项所述的电极组件，其特征在于，
    所述第二活性材料的压实密度小于所述第一活性材料的压实密度。
  6. 根据权利要求1至5中任一项所述的电极组件，其特征在于，
    所述电极组件卷绕后，所述第二区域具有第一弧度，所述第一弧度为所述第二区域位于所述电极组件的弯曲部的部分对应的弧度。
  7. 根据权利要求1至6中任一项所述的电极组件，其特征在于，
    所述第一极片为阳极极片，所述第二极片为阴极极片，所述第一极片覆盖所述第二极片。
  8. 根据权利要求7所述的电极组件，其特征在于，
    沿所述卷绕方向，所述阳极极片的第一个第一区域覆盖所述阴极极片的第一个第三区域，所述阳极极片的最后一个第二区域覆盖所述阴极极片的最后一个第四区域。
  9. 根据权利要求8所述的电极组件，其特征在于，
    所述第二区域具有第一弧度，所述第四区域具有第二弧度，所述第一弧度为所述第二区域位于所述阳极极片的弯曲部的部分对应的弧度，所述第二弧度为所述第四区域位于所述阴极极片的弯曲部的部分对应的弧度，沿所述卷绕方向，所述阳极极片的最后一个所述第二区域的所述第一弧度与所述阴极极片的最后一个所述第四区域的所述第二弧度的差值属于(0,π)。
  10. 根据权利要求8或9所述的电极组件，其特征在于，
    沿卷绕方向，所述阳极极片的最后一个第二区域与所述阴极极片的最后一个第四区域对应的弧长的差值属于(5mm,3π/4*R mm)，其中R为阳极极片最后一个第二区域对应的半径。
  11. 根据权利要求8至10中任一项所述的电极组件，其特征在于，沿所述卷绕方向，所述阳极极片的第一个第一区域与所述阴极极片的第一个第三区域的长度之差属于[20mm,60mm]。
  12. 一种电池单体，其特征在于，包括：
    根据权利要求1至11中任一项所述的电极组件。
  13. 一种电池，其特征在于，包括：根据权利要求12所述的电池单体。
  14. 一种用电装置，其特征在于，包括：权利要求13所述的电池，所述电池用于为所述用电装置提供电能。
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