Electrode sheets, electrode assemblies, battery cells, batteries and electrical devices

Abstract

This application discloses an electrode sheet, an electrode assembly, a battery cell, a battery, and an electrical device. The electrode sheet includes a current collector and an active material layer disposed on at least one side surface of the current collector. The active material layer includes a first active material layer and a second active material layer arranged sequentially in at least one direction from the center to the edge on the same side surface of the current collector. The first active material layer contains a first active material, and the second active material layer contains a second active material. The compaction density of the first active material is less than that of the second active material. The technical solution of this application improves the local pressure resistance of the electrode sheet by placing a first active material layer with strong pressure resistance at locations with high stress on the electrode sheet, and a second active material layer with slightly weaker pressure resistance at locations with low stress on the electrode sheet. This enhances the local pressure resistance of the electrode sheet, improves its anti-expansion properties, and extends the service life of the battery using this electrode sheet.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to an electrode sheet, electrode assembly, battery cell, battery, and electrical device. Background Technology

[0002] Lithium-ion batteries are widely used due to their long lifespan and high capacity. However, as they age, they tend to swell. Summary of the Invention

[0003] In view of the above problems, this application provides an electrode sheet, an electrode assembly, a battery cell, a battery, and an electrical device, aiming to solve the problem of battery swelling.

[0004] In a first aspect, embodiments of this application provide an electrode sheet, including a current collector and an active material layer disposed on at least one side surface of the current collector. The active material layer includes a first active material layer and a second active material layer located on the same side surface of the current collector and arranged sequentially in at least one direction from the center to the edge on the side surface. The first active material layer contains a first active material, and the second active material layer contains a second active material. The compaction density of the first active material is less than the compaction density of the second active material.

[0005] By configuring the active material layer to include a first active material layer and a second active material layer, where the elastic modulus of the first active material is greater than that of the second active material, and the first active material layer is closer to the center of the current collector surface (i.e., closer to the center of the electrode), and by placing a first active material layer with stronger pressure-bearing capacity at locations of higher stress on the electrode, while placing a second active material layer with slightly weaker pressure-bearing capacity at locations of lower stress on the electrode, the local pressure resistance of the electrode is improved. This makes it less likely that the pores between the active materials will be squeezed and destroyed during the aging process of the electrode, thereby improving the overall anti-expansion properties of the electrode and extending the service life of the battery using this electrode.

[0006] In some embodiments, the difference in compaction density between the first active substance and the second active substance is greater than 0.1 g / cc.

[0007] By setting the difference in compaction density between the first active material and the second active material to be greater than or equal to 0.1 g / cc, the pressure resistance of the first active material layer and the second active material layer can be better matched with the stress distribution on the electrode during battery aging, thereby improving the anti-expansion performance of the electrode.

[0008] In some embodiments, the electrode is a cathode electrode, and the first active material includes pressure-resistant graphite. Under a test condition of 8 MPa, the powder compaction density of the pressure-resistant graphite is 0.8 g / cc to 1.55 g / cc.

[0009] By selecting pressure-resistant graphite with a powder compaction density of 0.8 g / cc to 1.55 g / cc as the first active material, it is beneficial to ensure the pressure resistance of the first active material layer and extend the life of the electrode.

[0010] In some embodiments, the compaction density of the pressure-resistant graphite powder is 1.2 g / cc to 1.55 g / cc.

[0011] By selecting pressure-resistant graphite with a powder compaction density of 1.2 g / cc to 1.55 g / cc as the first active material, the pressure resistance of the electrode sheet is effectively improved.

[0012] In some embodiments, the area of ​​the first active material layer accounts for 20% to 60% of the total area of ​​the active material layer.

[0013] By setting the area ratio of the first active material layer in the active material layer to 20% to 60%, the voltage resistance boundary of the electrode can be improved while also taking into account the capacity of the battery.

[0014] In some embodiments, the same side surface of the current collector includes a central region connecting the center and an edge region connecting the edge, the central region being at least partially provided with the first active material layer, and the second active material layer being at least partially located in the edge region.

[0015] By setting a first active material layer in the middle region of the current collector surface and a second active material layer in the edge region of the current collector surface, that is, the first active material layer is located in the middle position of the electrode with higher stress and the second active material layer is located in the edge position of the electrode with lower stress, the pressure resistance of the middle position of the electrode is improved, thereby improving the overall anti-expansion property of the electrode.

[0016] In some embodiments, the center is a center point, the intermediate region is disposed around the center point, the edge region is disposed around the intermediate region, the first active material layer is located within the intermediate region, and the second active material layer is disposed around the outer periphery of the first active material layer.

[0017] By setting a first active material layer in the middle region of the current collector and setting a second active material layer around the outer periphery of the first active material layer, the stress distribution on the electrode is more closely aligned with that during battery aging, thereby better suppressing electrode expansion.

[0018] In some embodiments, the center is a midline, the midline is located within the intermediate region, the edge regions are distributed on both sides of the intermediate region, the intermediate region and the edge regions both extend from one end of the current collector to the other end, the first active material layer is located within the intermediate region, and the second active material layer is distributed outside the first active material layer.

[0019] By setting a first active material layer in the middle region of the current collector and a second active material layer on the outside of the first active material layer, the stress distribution on the electrode is more closely aligned with that during battery aging, thereby better suppressing electrode expansion.

[0020] In some embodiments, the first active material layer is in the form of a continuous strip, and the second active material layer is distributed on both sides of the first active material layer.

[0021] By setting the first active material layer as a continuous structure, it is convenient to prepare electrode sheets by coating and rolling.

[0022] In some embodiments, the electrode is used for winding, the current collector includes a plurality of flat sections and a plurality of bent sections, the electrode includes a plurality of first active material layers, the plurality of first active material layers are distributed one-to-one on the plurality of flat sections, and the second active material layers are disposed around the plurality of first active material layers.

[0023] By setting the electrode to include multiple first active material layers, and distributing the multiple first active material layers one-to-one on multiple flat sections of the current collector, when the multiple first active material layers are all set in the middle region, after the electrode is wound into a wound electrode assembly, the first active material layers are stacked and correspond to each other, and the first active material layers are located in the middle of the electrode assembly where the stress is relatively concentrated. By utilizing the first active material layers to bear the stress, the overall anti-expansion performance of the electrode assembly is improved.

[0024] In some embodiments, based on the area of ​​the surface of the current collector side where the active material layer is located, the area of ​​the middle region accounts for 20% to 50%, and the area of ​​the edge region accounts for 10% to 50%.

[0025] By optimizing the area ratio of the middle and edge regions, the voltage resistance boundary of the electrode can be improved while also taking into account the battery capacity.

[0026] In some embodiments, the active material layer further includes a third active material layer located between the first active material layer and the second active material layer, the third active material layer containing a third active material, the compaction density of the third active material being less than the compaction density of the second active material and greater than the compaction density of the first active material.

[0027] By setting a third active material layer between the first and second active material layers, the compaction density of the third active material layer is less than that of the second active material but greater than that of the first active material. This achieves the goal of gradually increasing the elastic modulus of the active material in the active material layer from the edge to the center. Consequently, the electrode's ability to withstand stress gradually increases from the edge to the center, which is closer to the stress distribution on the electrode during battery aging. This improves the local pressure resistance of the active material layer, enhances the anti-expansion performance of the electrode during aging, and extends the life of the battery using this electrode.

[0028] In some embodiments, the surface of the current collector is divided into adjacent coated areas and exposed areas, the active material layer is coated on the coated areas, and the exposed areas are connected to tabs.

[0029] By setting an exposed area on the surface of the current collector, the exposed area is used to connect the tabs as contact points for the battery during charging and discharging.

[0030] Secondly, embodiments of this application provide an electrode assembly, the electrode assembly comprising:

[0031] The electrode sheet provided in the first aspect of the embodiments of this application;

[0032] A separator covering at least one side of the electrode.

[0033] By using the electrode provided in the first aspect, the service life of the electrode assembly is improved.

[0034] Thirdly, embodiments of this application provide a battery cell, including a housing and an electrode assembly provided in the second aspect of this application, wherein the electrode assembly is disposed within the housing.

[0035] By employing the electrode assembly provided in the second aspect, the lifespan of the battery cell is improved.

[0036] Fourthly, embodiments of this application provide a battery, including the battery cell provided in the third aspect of this application.

[0037] By using battery cells provided by a third party, the battery lifespan is improved.

[0038] Fifthly, embodiments of this application provide an electrical device, comprising a battery cell provided in the third aspect of this application or a battery provided in the fourth aspect of this application.

[0039] By using the battery cells provided in the third aspect or the battery provided in the fourth aspect of this application, the stability of the operation of the electrical device is improved.

[0040] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0041] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0042] Figure 1 A cloud diagram of the expansion force at the end of the lifespan of a square battery.

[0043] Figure 2 This is a schematic diagram of the vehicle structure according to some embodiments of this application;

[0044] Figure 3 This is a schematic diagram of the exploded structure of a battery according to some embodiments of this application;

[0045] Figure 4 This is a schematic diagram of the exploded structure of a battery cell according to some embodiments of this application;

[0046] Figure 5 This is a schematic diagram of the structure of the electrode assembly in some embodiments of this application;

[0047] Figure 6 This is a schematic diagram of the front view structure of the electrode sheet in some embodiments of this application;

[0048] Figure 7 This is a side view structural diagram of the electrode sheet in some embodiments of this application;

[0049] Figure 8 for Figure 7 Enlarged structural diagram of section A in the middle;

[0050] Figure 9 for Figure 7 Enlarged structural diagram of section B in the middle;

[0051] Figure 10 This is a schematic diagram of the structure of a current collector in an electrode sheet according to some embodiments of this application;

[0052] Figure 11 This is a schematic diagram of the structure of another current collector in the electrode sheet of some embodiments of this application;

[0053] Figure 12 This is a schematic diagram of the front view structure of the electrode sheet in some other embodiments of this application;

[0054] Figure 13 This is a schematic diagram of the front view structure of the electrode sheet in some other embodiments of this application;

[0055] Figure 14 This is a schematic diagram of the front view structure of the electrode sheet in some other embodiments of this application;

[0056] Figure 15 This is a schematic diagram of the front view structure of the electrode sheet in some other embodiments of this application;

[0057] Figure 16 The figures show the compaction density curves of conventional graphite and pressure-resistant graphite. The compaction density test condition corresponding to the dashed line 1 in the figure is 8 MPa.

[0058] The reference numerals in the detailed embodiments are as follows:

[0059] 10-Electrode; 1-Current collector; 11-First surface; 111-Coated area; 112-Exposed area; 12-Second surface; 1101-Intermediate region; 1102-Edge region; 13-First end; 14-Second end; 2-Active material layer; 21-First active material layer; 22-Second active material layer; 23-Third active material layer; 101-Anode electrode; 102-Cathode electrode;

[0060] 20-Electrode assembly; 201-Anode tab; 202-Cathode tab; 203-Separator;

[0061] 30-Battery cell; 301-Casing; 302-End cap; 303-Anode adapter plate; 304-Cathode adapter plate; 305-Insulating component;

[0062] 40 - Battery; 401 - Box body; 4011 - Box body; 4012 - Box cover;

[0063] 50 - Electrical appliance; 501 - Controller; 502 - Motor. Detailed Implementation

[0064] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0065] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0066] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0067] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0068] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0069] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0070] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0071] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0072] Lithium-ion batteries are widely used due to their long lifespan and high capacity. However, as they age, they tend to swell.

[0073] The inventors, through research and analysis, discovered that the main causes of lithium-ion battery swelling include electrolyte oxidation and decomposition leading to gas production, and electrode expansion. Electrode expansion occurs because the electrode thickness increases during lithium-ion battery use. Typically, the expansion rate of the cathode electrode is about 4%, while the expansion rate of the anode electrode is over 20%, with graphite anodes exhibiting particularly severe expansion. This is because the change in lattice spacing after lithium ion insertion in the graphite anode leads to the formation of microscopic internal stress, resulting in irreversible expansion. Electrode expansion can cause the solid electrolyte interphase (SEI) film to rupture and continuously proliferate, thereby consuming active lithium and causing irreversible capacity loss in the lithium-ion battery, shortening its lifespan.

[0074] For a better understanding of battery swelling, please see [link / reference]. Figure 1 The inventors further studied and analyzed the distribution of expansion force during the aging process of lithium-ion batteries, discovering that the internal stress of the lithium-ion battery is mainly concentrated in the middle of the electrode during aging, gradually decreasing from the middle to the edge. The main reason for this phenomenon is that the temperature in the middle of the electrode is higher than that at the edge, making lithium ion insertion and extraction more active, and increasing the number of side reactions within the battery. This leads to greater expansion and increased stress in the middle of the electrode.

[0075] Based on the above findings, the inventors proposed an electrode that uses an active material with a lower compaction density under the same conditions in areas of relatively high stress, while using an active material with a higher compaction density under the same conditions in areas of relatively low stress. Since the active material with a lower compaction density has a higher elastic modulus under the same conditions, it can withstand greater stress, thereby improving the local pressure resistance of the electrode and extending the lifespan of batteries using this electrode.

[0076] The batteries disclosed in some embodiments of this application can be used, but are not limited to, in electrical devices such as vehicles, ships, or aircraft. A power system incorporating the batteries disclosed in this application can be used to construct such an electrical device.

[0077] Some embodiments of this application provide an electrical device that uses a battery as a power source. This electrical device can be, but is not limited to, vehicles, mobile phones, portable devices, laptops, ships, spacecraft, electric toys, and power tools. Vehicles can be, but are not limited to, gasoline-powered vehicles, natural gas-powered vehicles, or new energy vehicles. New energy vehicles can be, but are not limited to, pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles. Spacecraft include airplanes, rockets, space shuttles, and spacecraft. Electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys. Power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers.

[0078] For ease of explanation, the following embodiments will be described using a vehicle 50 as an example of an electrical device according to an embodiment of this application.

[0079] Please refer to Figure 2 , Figure 2 This is a schematic diagram of the structure of a vehicle 50 provided in some embodiments of this application. A battery 40 is disposed inside the vehicle 50, and the battery 40 may be located at the bottom, front, or rear of the vehicle 50. The battery 40 can be used to power the vehicle 50; for example, the battery 40 can serve as the operating power source for the vehicle 50. The vehicle 50 may also include a controller 501 and a motor 502. The controller 501 is used to control the battery 40 to supply power to the motor 502, for example, to meet the power needs of the vehicle 50 during starting, navigation, and driving.

[0080] In some embodiments of this application, the battery 40 can not only serve as the operating power source for the vehicle 50, but also as the driving power source for the vehicle 50, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 50.

[0081] Please refer to Figure 3 , Figure 3 This is an exploded view of a battery 40 provided in some embodiments of this application. The battery 40 includes a housing 401 and a battery cell 30, the battery cell 30 being housed within the housing 401. The housing 401 is a component that provides housing space for the battery cell 30, and the housing 401 can adopt various structures.

[0082] In some embodiments, the housing 401 may include a housing body 4011 and a housing cover 4012, which cover each other and together define a receiving space for accommodating the battery cell 30. Optionally, the housing body 4011 may be a hollow structure with one end open, and the housing cover 4012 may be a plate-like structure that covers the open side of the housing body 4011.

[0083] In battery 40, there can be multiple battery cells 30, which can be connected in series, parallel, or in a mixed configuration. A mixed configuration means that multiple battery cells 30 are connected in both series and parallel configurations. Multiple battery cells 30 can be directly connected in series, parallel, or in a mixed configuration, and then the entire assembly of the multiple battery cells 30 is housed within housing 401. Alternatively, battery 40 can also be composed of multiple battery cells 30 first connected in series, parallel, or in a mixed configuration to form a battery module, and then these battery modules are connected in series, parallel, or in a mixed configuration to form a whole, which is also housed within housing 401. Battery 40 may also include other structures, such as a busbar (not shown), for realizing the electrical connection between the multiple battery cells 30.

[0084] The battery cell 30 can be a secondary battery or a primary battery; it can also be a lithium-sulfur battery, a sodium-ion battery, or a magnesium-ion battery, but is not limited to these. The battery cell 30 can be cylindrical, flat, cuboid, or other shapes.

[0085] Please refer to Figure 4 , Figure 4 This is an exploded view of a battery cell 30 according to some embodiments of this application. A battery cell 30 refers to the smallest unit that makes up a battery. Figure 4 The battery cell 30 includes a housing 301, an end cap 302, an electrode assembly 20, and other functional components.

[0086] The housing 301 is a hollow structure with an opening at one end. The housing 301 is used in conjunction with the end cap 302 to form an internal environment that accommodates the electrode assembly 20, the electrolyte, and other functional components. The housing 301 can be of various shapes and sizes, such as cuboid, cylindrical, or hexagonal prism. Specifically, the shape of the housing 301 can be determined according to the specific shape and size of the electrode assembly 20. The material of the housing 301 can be, but is not limited to, copper, iron, aluminum, stainless steel, aluminum alloy, or plastic, etc., and is not limited thereto.

[0087] End cap 302 refers to a component that covers the opening of housing 301 to isolate the internal environment of battery cell 30 from the external environment. Optionally, the shape of end cap 302 can be adapted to the shape of housing 301 to fit the housing 301. Optionally, end cap 302 can be made of a material with a certain hardness and strength (such as aluminum alloy), so that end cap 302 is not easily deformed when subjected to compression and impact, so that battery cell 300 can have higher structural strength and improved safety performance. The material of end cap 302 can be, but is not limited to, copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and is not limited here.

[0088] The housing 301 may contain one or more electrode assemblies 20.

[0089] In some embodiments, the battery cell 30 further includes functional components such as an anode adapter 303 and a cathode adapter 304. The anode adapter 303 is used for electrical connection to the anode tab on the electrode assembly 20, and the cathode adapter 304 is used for electrical connection to the cathode tab on the electrode assembly 20, for outputting or inputting electrical energy into the battery cell 30. Understandably, the anode adapter 303 is made of a conductive material, and the material of the anode adapter 303 may be, but is not limited to, copper, iron, aluminum, etc. The cathode adapter 304 is made of a conductive material, and the material of the cathode adapter 304 may be, but is not limited to, copper, iron, aluminum, etc.

[0090] In some embodiments, the battery cell 30 further includes an insulating member 305 located inside the housing 301 to isolate the housing 301 from the electrode assembly 20, reducing the risk of short circuit. Exemplarily, the insulating member 305 may be made of plastic, rubber, or the like.

[0091] Please refer to Figure 5 , Figure 5 This is a schematic diagram of the structure of an electrode assembly 20 according to some embodiments of this application. The electrode assembly 20 is a component in the battery cell 30 where electrochemical reactions occur. The electrode assembly 20 is mainly formed by winding or stacking an electrode structure integrating an anode electrode 101 and a cathode electrode 102, and a separator 203 is usually provided between adjacent anode electrodes 101 and cathode electrodes 102.

[0092] The anode electrode 101 includes an anode current collector and an anode active material layer, the anode active material layer being coated on the surface of the anode current collector. Taking a lithium-ion battery as an example, the material of the anode current collector can be copper, and the anode active material layer includes an anode active material, which can be carbon or silicon, etc.

[0093] The cathode electrode 102 includes a cathode current collector and a cathode active material layer, with the cathode active material layer coated on the surface of the cathode current collector. Taking a lithium-ion battery as an example, the cathode current collector can be made of aluminum, and the cathode active material layer includes cathode active material, which can be lithium cobalt oxide, lithium iron phosphate, ternary lithium, or lithium manganese oxide, etc.

[0094] The separator 203 is a porous plastic film that allows lithium ions in the electrolyte to pass through freely, but isolates the anode electrode 101 and the cathode electrode 102, preventing electrons inside the battery from passing through freely. The separator 203 can be made of materials such as PP (polypropylene) or PE (polyethylene).

[0095] Both the anode and cathode current collectors have portions without an active material layer, and these portions without an active material layer are provided with connecting tabs. Specifically, the anode current collector is connected to an anode tab 201, and the cathode current collector is connected to a cathode tab 202. During the charging and discharging process of the battery, the positive and negative active material layers react with the electrolyte. Tab 201 connects to the anode adapter 303, and cathode tab 202 connects to the cathode adapter 304 to form a current loop. Of course, in some embodiments, the portions of the anode and cathode current collectors without an active material layer each constitute a tab.

[0096] According to some embodiments of this application, refer to Figures 6 to 10 , Figure 6 and Figure 7 This application shows schematic diagrams of the structure of the electrode 10 from different viewing angles in some embodiments. Figure 6 This shows a schematic diagram of the front view structure of the electrode 10. Figure 7 A side view of the electrode 10 is shown. Figure 8 and Figure 9 They are respectively Figure 7 Enlarged structural schematic diagram of two different parts of the electrode 10. This application provides an electrode 10, which includes a current collector 1 and an active material layer 2. The active material layer 2 is disposed on at least one surface of the current collector 1. The active material layer 2 includes a first active material layer 21 and a second active material layer 22 located on the same surface of the current collector 1 and arranged sequentially in at least one direction from the center to the edge of that surface. The first active material layer 21 contains a first active material, and the second active material layer 22 contains a second active material. The compaction density of the first active material is less than the compaction density of the second active material.

[0097] Current collector 1 refers to the component used to collect current. Depending on the application, current collector 1 can be either an anode current collector or a cathode current collector. When current collector 1 is an anode current collector, the corresponding active material layer 2 coated on the anode current collector is the anode active material layer, and the resulting electrode 10 is the anode electrode. When current collector 1 is a cathode current collector, the corresponding active material layer 2 coated on the cathode current collector is the cathode active material layer, and the resulting electrode 10 is the cathode electrode. Taking a lithium-ion battery as an example, optionally, the anode current collector is copper foil, and the cathode current collector is aluminum foil. Furthermore, current collector 1 can have various shapes, such as strips or squares, and is not limited here.

[0098] The active material layer 2 includes active material, conductive agent, and binder. Active material refers to the material that participates in the electrochemical oxidation / reduction reaction. Optionally, the active material is a powder. When active material layer 2 is the anode active material layer, the active material is the anode active material. When active material layer 2 is the cathode active material layer, the active material is the cathode active material. Taking a lithium-ion battery as an example, the anode active material can be, but is not limited to, soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxides, silicon carbide compounds, or lithium titanate, etc.; the cathode active material can be, but is not limited to, lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium iron manganese phosphate, lithium nickel cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium-rich manganese-based materials, etc. The conductive agent refers to the material that collects microcurrents between active materials and between the active material and current collector 1. The conductive agent can be, but is not limited to, conductive graphite, carbon nanotubes, acetylene black, etc. The binder is the material that binds the active materials together to enhance the electronic contact between the active material and the conductive agent, and between the active material and current collector 1. The binder may be, but is not limited to, styrene-butadiene rubber (SBR), acrylonitrile, acrylate, polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), etc.

[0099] The current collector 1 has a first surface 11 and a second surface 12 opposite to each other along the thickness direction of the current collector 1. At least one side surface of the current collector 1 refers to the first surface 11 and / or the second surface 12 of the current collector 1. It is understood that the active material layer 2 can be disposed on the first surface 11, or on the second surface 12, or the active material layer 2 can be disposed on both the first surface 11 and the second surface 12. Optionally, the active material layer 2 is disposed on the first surface 11, and a coating area 111 and an exposed area 112 are arranged adjacent to each other on the first surface 11, with the active material layer 2 disposed on the coating area 111.

[0100] The active material layer 2 includes a first active material layer 21 and a second active material layer 22 arranged sequentially in at least one direction from the center to the edge on the same side surface of the current collector 1. This statement contains at least four layers of meaning.

[0101] The first layer means that the active substance layer 2 includes a first active substance layer 21 and a second active substance layer 22. It can be understood that the active substance layer 2 may only include the first active substance layer 21 and the second active substance layer 22, or it may include other layers besides the first active substance layer 21 and the second active substance layer 22, which is not limited here.

[0102] The second meaning is that the first active material layer 21 and the second active material layer 22 are disposed on the surface of the current collector 1. It can be understood that the surface of the current collector 1 here refers to the side surface of the current collector 1 where the active material layer 2 is located. For example, if the active material layer 2 is located on the first surface 11, it refers to the first surface 11. If the active material layer 2 is located on the second surface 12, it refers to the second surface 12.

[0103] The third layer means that on the same side surface of the current collector 1, from the center to the edge, the first active material layer 21 and the second active material layer 22 are arranged sequentially. The center here can be the center point of one side surface of the current collector 1, or it can be the centerline of that side surface. The edge here refers to the boundary line of one side surface of the current collector 1. Understandably, the first active material layer 21 is closer to the center of the current collector 1 surface than the second active material layer 22, and the second active material layer 22 is closer to the edge of the current collector 1 surface than the first active material layer 21. It should be noted that it is not necessarily required that the first active material layer 21 is connected to the center of the current collector 1 surface; there can be a certain distance between them. Similarly, it is not necessarily required that the second active material layer 22 is connected to the edge of the current collector 1 surface; there can be a certain distance between them. Of course, it is not necessarily required that the first active material layer 21 and the second active material layer 22 are connected; they can be spaced apart. When the first active material layer 21 and the second active material layer 22 are spaced apart, the active material layer 2 may further include an intermediate active material layer located between the first active material layer 21 and the second active material layer 22. The elastic modulus of the active material contained in the intermediate active material layer may be greater than or less than the elastic modulus of the first active material.

[0104] The fourth layer means that the surface of the current collector 1 usually has multiple directions from the center to the edge. It is sufficient to arrange the first active material layer 21 and the second active material layer 22 in sequence in one or more directions. It is not necessary to arrange the first active material layer 21 and the second active material layer 22 in sequence in all directions from the center to the edge.

[0105] To better understand the fourth layer of meaning, please refer to... Figure 10In one embodiment, the current collector 1 is elongated. The center of one side surface of the current collector 1 refers to the centerline a extending along the direction of the current collector 1. The direction from the center to the edge of one side surface of the current collector 1 includes the OA direction and the OC direction shown in the figure. The first active material layer 21 and the second active material layer 22 in the active material layer 2 can be arranged sequentially in the OA direction, or sequentially in the OC direction, or sequentially in both the OA and OC directions.

[0106] Please refer to Figure 11 In another embodiment, the current collector 1 is square, and the center of one side surface of the current collector 1 refers to the center point O of the surface. The direction from the center to the edge of one side surface of the current collector 1 includes at least the OA direction, OB direction, OC direction, and OD direction shown in the figure. The first active material layer 21 and the second active material layer 22 in the active material layer 2 can be arranged sequentially in at least one of the OA direction, OB direction, OC direction, and OD direction.

[0107] The lower compaction density of the first active material compared to the second active material is a result of comparison under the same test conditions. It should be noted that the compaction density of the active material in active material layer 2 in this application refers to the compaction density of the active material itself, and not necessarily the compaction density of active material layer 2. That is, the compaction density of the first active material refers to the compaction density of the first active material itself, and not necessarily the compaction density of the first active material layer 21; the compaction density of the second active material refers to the compaction density of the second active material itself, and not necessarily the compaction density of the second active material layer 22.

[0108] The compaction density of an active material is generally related to its elastic modulus. Under the same test conditions, such as the same test pressure, a higher elastic modulus results in a lower compaction density, and vice versa. Understandably, the compaction density of the first active material is less than that of the second active material, meaning the elastic modulus of the first active material is greater than that of the second. It should be noted that the first and second active materials can be the same type of material or different types of materials. Taking the first and second active materials as anode active materials as an example, optionally, the first active material is a carbon material, such as graphite, and the second active material is a silicon material, such as a silicon carbide compound; optionally, the first active material is silicon, and the second active material is carbon; optionally, both the first and second active materials are carbon materials; optionally, both the first and second active materials are lithium titanate.

[0109] By configuring the active material layer 2 to include a first active material layer 21 and a second active material layer 22, the elastic modulus of the first active material is greater than that of the second active material, and the first active material layer 21 is closer to the center of the current collector 1 surface than the second active material layer 22, that is, closer to the center of the electrode 10. By setting the first active material layer 21 with strong pressure bearing capacity at the location of high stress on the electrode 10, and setting the second active material layer 22 with slightly weaker pressure bearing capacity at the location of low stress on the electrode 10, the local pressure resistance of the electrode 10 is improved, so that the pores between the active materials are not easily squeezed and destroyed during the aging process of the electrode 10, thereby improving the overall anti-expansion of the electrode 10 and extending the service life of the battery 40 using the electrode 10.

[0110] Please refer to some embodiments of this application. Figures 10 to 11 The same side surface of the current collector 1 includes a central region 1101 connecting the center and an edge region 1102 connecting the edge. The central region 1101 is at least partially provided with a first active material layer 21, and the second active material layer 22 is at least partially located in the edge region 1102.

[0111] The intermediate region 1101 and the edge region 1102 can be at least two regions on the first surface 11 of the current collector 1, or at least two regions on the second surface 12 of the current collector 1. Here, the intermediate region 1101 and the edge region 1102 can be arranged adjacently or spaced apart.

[0112] The intermediate region 1101 is at least partially provided with a first active substance layer 21. The intermediate region 1101 may be entirely provided with the first active substance layer 21, or a portion of the region may be provided with the first active substance layer 21.

[0113] The second active material layer 22 being located at least partly in the edge region 1102 means that the second active material layer 22 can be entirely disposed on the edge region 1102, or it can be partially disposed on the edge region 1102. For example, part of the second active material layer 22 is disposed on the edge region 1102, and the other part extends to the middle region 1101.

[0114] By setting a first active material layer 21 in the middle region 1101 of the current collector 1 surface and setting a second active material layer 22 in the edge region 1102 of the current collector 1 surface, that is, the first active material layer 21 is located in the middle position of the electrode 10 with higher stress and the second active material layer 22 is located in the edge position of the electrode 10 with lower stress, the pressure resistance of the middle position of the electrode 10 is improved, thereby improving the overall anti-expansion property of the electrode 10.

[0115] Please refer to the figures according to some embodiments of this application. Figure 11and Figure 12 The center of the surface of the current collector 1 is the center point O on the surface of the current collector 1. The intermediate region 1101 is set around the center point O, and the edge region 1102 is set around the intermediate region 1101. The first active material layer 21 is located in the intermediate region 1101, and the second active material layer 22 is set around the outer periphery of the first active material layer 21.

[0116] The fact that the intermediate region 1101 is set around the center point O does not necessarily mean that the center point O is also the center of the intermediate region 1101. That is to say, the intermediate region 1101 is not centrally symmetrically set around the center point O. For example, the boundary of the intermediate region 1101 can extend further away from the center point O in the OA direction, and closer to the center point O in the OC direction, without limitation. In addition, the shapes of the intermediate region 1101 and the edge region 1102 can be regular or irregular. Optionally, the intermediate region 1101 is square, the first active material layer 21 is also square, and multiple electrode sheets 10 are used to form a stacked electrode assembly 20 by being laid out in layers.

[0117] Optionally, the intermediate region 1101 and the edge region 112 are arranged adjacent to each other, the intermediate region 1101 is entirely provided with a first active material layer 21, and the edge region 112 is entirely provided with a second active material layer 22.

[0118] By setting a first active material layer 21 in the middle region 1101 of the current collector 1 and setting a second active material layer 22 around the outer periphery of the first active material layer 21, the stress distribution on the electrode 10 during battery aging is more closely aligned, thereby better suppressing the expansion of the electrode 10.

[0119] Please refer to the figures according to some embodiments of this application. Figure 6 , Figure 10 and Figure 14 The center of the surface of the current collector 1 is the centerline a of the surface of the current collector 1. The centerline a is located within the intermediate region 1101. The edge regions 1102 are distributed on both sides of the intermediate region 1101. Both the intermediate region 1101 and the edge regions 1102 extend from one end of the current collector 1 to the other end. The first active material layer 21 is located within the intermediate region 1101, and the second active material layer 22 is distributed outside the first active material layer 21.

[0120] The centerline 'a' refers to a line that is centrally located and bisects one side of the surface of the current collector 1. It does not necessarily mean that centerline 'a' is also the centerline of the intermediate region 1101; the intermediate region 1101 can be offset relative to centerline 'a'. The edge regions 1102 are distributed on both sides of the intermediate region 1101, specifically, the edge regions 1102 are located away from centerline 'a'.

[0121] Optionally, the current collector 1 is elongated and has two opposite ends along its length, namely a first end 13 and a second end 14. Both the middle region 1101 and the edge region 1102 extend from the first end 13 to the second end 14 of the current collector 1. Of course, in other embodiments, the current collector 1 is square, and the middle region 1101 and the edge region 1102 can extend from one end to the other along the length of the current collector 1, or they can extend from one end to the other along the width of the current collector 1.

[0122] Optionally, the surface of the current collector 1 is further provided with an exposed area 112, which is located within the edge region 1102 and extends from the first end 13 to the second end 14.

[0123] By setting a first active material layer 21 in the middle region 1101 of the current collector 1 and setting a second active material layer 22 on the outside of the first active material layer 21, the stress distribution on the electrode 10 during battery aging is more closely aligned, thereby better suppressing the expansion of the electrode 10.

[0124] Please refer to some embodiments of this application. Figure 6 and Figure 10 The first active material layer 21 is in the form of a continuous strip, and the second active material layer 22 is distributed on both sides of the first active material layer 21.

[0125] Understandably, from the first end 13 to the second end 14 of the current collector 1, the first active material layer 21 is a continuous layered structure.

[0126] Optionally, the surface of the current collector 1 includes a central region 1101 and two edge regions 1102. The two edge regions 1102 are respectively disposed on both sides of the central region 1101 and are adjacent to the central region 1101. The central region 1101 is entirely covered with a first active material layer 21, and the edge regions 1102 are entirely covered with a second active material layer 22. It can be understood that if there are two edge regions 1102 and the second active material layer 22 is disposed on the two edge regions 1102 respectively, then the number of second active material layers 22 is also two.

[0127] When preparing the electrode 10, the first active material layer 21 and the second active material layer 22 can be simultaneously covered on the middle region 1101 and the two edge regions 1102, respectively. Alternatively, the first active material layer 21 can be covered on the middle region 1101 first, and then the second active material layer 22 can be covered on the edge regions 1102, or the second active material layer 22 can be covered on the edge regions 1102 first, and then the first active material layer 21 can be covered on the middle region 1101.

[0128] By setting the first active material layer 21 as a continuous structure, it is convenient to prepare the electrode 10 by coating and rolling.

[0129] Please refer to some embodiments of this application. Figure 13 The electrode 10 is used for winding, and the current collector 1 includes multiple flat sections and multiple bent sections. The electrode 10 includes multiple first active material layers 21, which are distributed one-to-one on the multiple flat sections, and second active material layers 22 are arranged around the multiple first active material layers 21.

[0130] The electrode 10 is used for winding, so the resulting electrode assembly 20 is a wound electrode assembly. A wound electrode assembly can generally be divided into an unbent flat area and a bent arc area. The flat area on the current collector 1 is the straight part, and the arc area is the bent part.

[0131] "Multiple" refers to at least two, such as 2, 3, 10, 15, 20, 23, etc. Optionally, the number of the first active material layer 21 is 5 to 50.

[0132] Optionally, multiple first active material layers 21 are disposed on the middle region 1101 and distributed one-to-one on multiple flat sections, and second active material layers 22 are distributed on the edge region 1102 and on the bent section located in the middle region 1101, and the second active material layers 22 surround the outer periphery of the multiple first active material layers 21.

[0133] By setting the electrode 10 to include multiple first active material layers 21, and distributing the multiple first active material layers 21 one-to-one on multiple flat sections of the current collector 1, when the multiple first active material layers 21 are all set on the middle region 1101, after the electrode 10 is wound into a wound electrode assembly, each first active material layer 21 is stacked and corresponding, and the first active material layer 21 is located in the middle of the electrode assembly 20 where the stress is relatively concentrated. By utilizing the first active material layer 21 to bear the stress, the overall anti-expansion performance of the electrode assembly 20 is improved.

[0134] Please refer to some embodiments of this application. Figure 14 and Figure 15 The active material layer 2 further includes a third active material layer 23, which is located between the first active material layer 21 and the second active material layer 22. The third active material layer 23 contains a third active material, and under the same test conditions, the compaction density of the third active material is less than that of the second active material and greater than that of the first active material.

[0135] Understandably, the elastic modulus of the third active material is greater than that of the second active material, but less than that of the first active material. It should be noted that the third active material and the second active material can be of the same type or different types of materials. No limitation is made here.

[0136] Alternatively, please refer to Figure 15 The first active material layer 21 is disposed in the middle of the surface of the current collector 1, the third active material layer 23 is disposed around the outer periphery of the first active material layer 21, and the second active material layer 22 is disposed around the outer periphery of the third active material layer 23. The first active material layer 21, the second active material layer 22 and the third active material layer 23 are spliced ​​together to form the active material layer 2.

[0137] Alternatively, please refer to Figure 14 The first active material layer 21, the second active material layer 22 and the third active material layer 23 are all disposed on the surface of the current collector 1 and extend from the first end 13 to the second end 14. The third active material layer 23 is located between the first active material layer 21 and the second active material layer 22. The first active material layer 21, the second active material layer 22 and the third active material layer 23 are spliced ​​together to obtain the active material layer 2.

[0138] By providing a third active material layer 23 between the first active material layer 21 and the second active material layer 22, the compaction density of the third active material contained in the third active material layer 23 is less than that of the second active material and greater than that of the first active material. This achieves the goal of gradually increasing the elastic modulus of the active material in the active material layer 2 from the edge to the center. As a result, the electrode 10 gradually increases its ability to withstand stress from the edge to the center, which is closer to the stress distribution on the electrode 10 during battery aging. This improves the local pressure resistance of the active material layer 2, enhances the anti-expansion performance of the electrode 10 during aging, and extends the life of the battery 40 using the electrode 10.

[0139] According to some embodiments of this application, based on the area of ​​one side surface of the current collector 1 where the active material layer 2 is located, the area of ​​the middle region 1101 accounts for 20% to 60%, and the area of ​​the edge region 1102 accounts for 10% to 50%.

[0140] The shapes and area proportions of the intermediate region 1101 and the edge region 1102 on the current collector 1 can differ depending on the shape of the current collector. Optionally, the area proportion of the intermediate region 1101 can be 20%, 30%, 40%, 50%, or 60%. Optionally, the area proportion of the edge region 1102 can be 10%, 20%, 30%, 40%, or 50%.

[0141] When the first active material layer 21 is fully disposed on the middle region 1101 and the second active material layer 22 is fully disposed on the edge region 1102, the area size of the middle region 1101 and the area size of the edge region 1102 will affect the ratio of the first active material layer 21 and the second active material layer 22. Therefore, by optimizing the area ratio of the middle region 1101 and the edge region 1102, the voltage resistance boundary of the electrode 10 can be improved while also taking into account the capacity of the battery 40.

[0142] Please refer to some embodiments of this application. Figure 16 Electrode 10 is the cathode electrode, and the first active material includes pressure-resistant graphite. Under the test condition of 8 MPa, the powder compaction density of pressure-resistant graphite is 0.8 g / cc to 1.55 g / cc.

[0143] Optionally, the compaction density of the pressure-resistant graphite powder is 0.8 g / cc, 0.9 g / cc, 1 g / cc, 1.1 g / cc, 1.2 g / cc, 1.3 g / cc, 1.4 g / cc, 1.5 g / cc or 1.55 g / cc.

[0144] Optionally, the second active material includes conventional graphite. Under a test condition of 8 MPa, the powder compaction density of conventional graphite is greater than 1.55 g / cc.

[0145] By selecting pressure-resistant graphite with a powder compaction density of 0.8 g / cc to 1.55 g / cc as the first active material, it is beneficial to ensure the pressure resistance of the first active material layer 21 and extend the life of the electrode 10.

[0146] According to some embodiments of this application, in the active material layer 2, the area of ​​the first active material layer 21 accounts for 20% to 60%.

[0147] For an explanation of the area ratio of the first active material layer 21, please refer to [link / reference needed]. Figure 12 The area ratio of the first active material layer 21 refers to the ratio of the area of ​​the first active material layer 21 to the area of ​​the active material layer 2. When the active material layer 2 is obtained by splicing the first active material layer 21 and the second active material layer 22, the sum of the areas of the first active material layer 21 and the second active material layer 22 is the area of ​​the active material layer 2.

[0148] Optionally, the area percentage of the first active material layer 21 is 20%, 30%, 40%, 50%, or 60%.

[0149] By setting the area ratio of the first active material layer 21 in the active material layer 2 to 20% to 60%, the voltage resistance boundary of the electrode 10 can be improved while also taking into account the capacity of the battery 40.

[0150] According to some embodiments of this application, the difference in compaction density between the first active substance and the second active substance is greater than 0.1 g / cc.

[0151] Understandably, the greater the difference in compaction density between the first active material and the second active material, the greater the difference in pressure resistance between the first active material layer 21 and the second active material layer 22. If the difference in compaction density between the first active material and the second active material is too small, then the pressure resistance of the first active material layer 21 and the second active material layer 22 will be difficult to match the stress distribution on the electrode 10 during battery aging, and the anti-expansion performance of the electrode 10 during aging will be difficult to highlight. Ways to increase the difference in compaction density between the first active material and the second active material include selecting a first active material with a lower compaction density and / or selecting a second active material with a higher compaction density.

[0152] Optionally, the difference in compaction density between the first active substance and the second active substance is greater than or equal to 0.1 g / cc, 0.12 g / cc, 0.14 g / cc, 0.16 g / cc, or 0.18 g / cc.

[0153] By setting the difference in compaction density between the first active material and the second active material to be greater than or equal to 0.1 g / cc, the pressure resistance of the first active material layer 21 and the second active material layer 22 can be better matched with the stress distribution on the electrode 10 during battery aging, thereby improving the anti-expansion performance of the electrode 10.

[0154] Please refer to some embodiments of this application. Figure 6 , Figure 9 and Figure 10 The surface of the current collector 1 is divided into an adjacent coated area 111 and an exposed area 112. The active material layer 2 is coated on the coated area 111, and the exposed area 112 is connected to a tab (not shown).

[0155] The coating area 111 refers to the area on the surface of the current collector 1 used for coating the active material layer 2. The exposed area 112 refers to the area that avoids the active material layer 2 to keep the surface of the current collector 1 exposed.

[0156] By setting an exposed area 112 on the surface of the current collector 1, the exposed area 112 is used to connect the tabs as contact points for the battery during charging and discharging.

[0157] The following description is based on specific embodiments.

[0158] Examples 1 to 5

[0159] Please see Figure 10In this embodiment, conventional graphite films are deposited on regions A and C of the current collector 1, and a pressure-resistant graphite film is deposited on region B. The compaction densities P of the pressure-resistant graphite in the pressure-resistant graphite films at 8 MPa are 1.2 g / cc, 1.3 g / cc, 1.4 g / cc, 1.5 g / cc, and 1.55 g / cc, respectively, and the area ratio K of the pressure-resistant graphite films is 30%. The compaction densities P of the conventional graphite in the conventional graphite films at 8 MPa are all 1.65 g / cc. The obtained electrode samples were subjected to expansion force testing and cycle life testing under 25℃ and 1C / 1C charge / discharge conditions. The results are shown in Table 1.

[0160] Table 1. Effect of pressure-resistant graphite with different compaction densities P on battery life and expansion force.

[0161] P 1.2 1.3 1.4 1.5 1.55 Diving expansion force 63885 63372 62840 61811 60345 Number of diving cycles 8684 8581 8515 8407 8261

[0162] Examples 6 to 10

[0163] Please see Figure 10 In this embodiment, conventional graphite films are deposited on regions A and C of the current collector 1, and a pressure-resistant graphite film is deposited on region B. The pressure-resistant graphite film has a compaction density P of 1.4 g / cc at 8 MPa, and the area percentages K of the pressure-resistant graphite film are 20%, 30%, 40%, 50%, and 60%, respectively. The conventional graphite film has a compaction density P of 1.65 g / cc at 8 MPa. The obtained electrode samples were subjected to expansion force testing and cycle life testing under 25°C and 1C / 1C charge / discharge conditions. The results are shown in Table 2.

[0164] Table 2. Effect of different area percentages K of pressure-resistant graphite on lifespan and expansion force

[0165] K 20％ 30％ 40％ 50％ 60％ Diving expansion force 61710 62840 64530 65970 66640 Number of diving cycles 8354 8515 8662 8771 8856

[0166] Comparative Example

[0167] This comparative example uses... Figure 10 The partitioning method shown involves placing conventional graphite films in regions A, B, and C of the current collector 1. The compaction density P of conventional graphite at 8 MPa is 1.65 g / cc. The obtained electrode samples were subjected to expansion force testing and cycle life testing under 25°C and 1C / 1C charge / discharge conditions, with results of 56100 N and 7560 cycles, respectively.

[0168] In conclusion:

[0169] Compared with the comparative examples, the difference between Examples 1 to 5 is that a pressure-resistant graphite film layer is provided in region B of the current collector 1; the area ratio K of the pressure-resistant graphite film layer is 30%, and as the compaction density of the pressure-resistant graphite film decreases, the battery's water-induced expansion force increases from 56100N to 63885N, the battery's water-induced cycle life increases from 7560 cycles to 8684 cycles, the battery's water-induced expansion force threshold increases by 13.9%, and the cycle life improves by 14.9%.

[0170] Compared with the comparative examples, the difference between Examples 6 to 10 is that a pressure-resistant graphite film layer is provided in region B of the current collector 1; the compaction density P of the pressure-resistant graphite film layer is 1.4 g / cc. As the area ratio of the pressure-resistant graphite film increases, the battery's water pressure expansion force increases from 56100 N to 66640 N, the battery's water pressure cycle life increases from 7560 cycles to 8856 cycles, the battery's water pressure expansion threshold increases by 18.8%, and the cycle life improves by 17.1%.

[0171] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A pole piece, characterized in that, The electrode assembly comprises a current collector and an active material layer arranged on at least one side surface of the current collector, the active material layer comprises a first active material layer and a second active material layer arranged in sequence on the same side surface of the current collector and in at least one direction from the center to the edge of the side surface, the first active material layer comprises a first active material, the second active material layer comprises a second active material, the compaction density of the first active material is less than the compaction density of the second active material, and the active material layer further comprises a third active material layer arranged between the first active material layer and the second active material layer, the third active material layer comprises a third active material, the compaction density of the third active material is less than the compaction density of the second active material and greater than the compaction density of the first active material.

2. The pole piece of claim 1, wherein The difference between the compaction densities of the first active material and the second active material is greater than or equal to 0.1 g / cc.

3. The pole piece of claim 1, wherein The first active material comprises pressure-resistant graphite, and the powder compaction density of the pressure-resistant graphite is 0.8 g / cc to 1.55 g / cc under a test condition of 8 MPa.

4. The pole piece of claim 3, wherein The powder compaction density of the pressure-resistant graphite is 1.2 g / cc to 1.55 g / cc.

5. The pole piece of claim 1, wherein The area ratio of the first active material layer to the total area of the active material layer is 20% to 60%.

6. The pole piece according to any one of claims 1 to 5, characterized in that The same side surface of the current collector comprises a middle region connected to the center and an edge region connected to the edge, the middle region is at least partially provided with the first active material layer, and the second active material layer is at least partially arranged in the edge region.

7. The pole piece of claim 6, wherein The center is a center point, the middle region is arranged around the center point, the edge region is arranged around the middle region, the first active material layer is arranged in the middle region, and the second active material layer is arranged around the outer periphery of the first active material layer.

8. The pole piece of claim 6, wherein, The center is a center line, the center line is arranged in the middle region, the edge region is distributed on both sides of the middle region, the middle region and the edge region extend from one end of the current collector to the other end, the first active material layer is arranged in the middle region, and the second active material layer is distributed outside the first active material layer.

9. The pole piece of claim 8, wherein, The first active material layer is in a continuous strip shape, and the second active material layer is distributed on both sides of the first active material layer.

10. The pole piece of claim 8, wherein, The electrode assembly is arranged in a winding manner, the current collector comprises a plurality of flat segments and a plurality of bent segments, the electrode assembly comprises a plurality of first active material layers, the plurality of first active material layers are one-to-one correspondingly arranged on the plurality of flat segments, and the second active material layer is arranged around the plurality of first active material layers.

11. The pole piece of claim 6, wherein, The area ratio of the middle region to the area of the same side surface of the current collector on which the active material layer is arranged is 20% to 50%, and the area ratio of the edge region to the area of the same side surface of the current collector on which the active material layer is arranged is 10% to 50%.

12. The pole piece according to any one of claims 1 to 5, characterized in that The surface of the current collector is divided into adjacent coated regions and bare regions, the active material layer is coated on the coated regions, and the bare regions are connected with tabs.

13. An electrode assembly, characterized by The electrode assembly comprises: The pole piece according to any one of claims 1 to 12; An isolation film covering at least one side of the pole piece.

14. A battery cell, characterized by An electrode assembly according to claim 13, disposed within a housing.

15. A battery, characterized by A battery cell according to claim 14.

16. An electrical device, comprising: A battery according to claim 15.

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