Electrode assembly, battery monomer, battery and electric equipment

Abstract

The embodiment of the invention discloses an electrode assembly, a battery monomer, a battery and electric equipment. The electrode assembly comprises a first pole piece and a second pole piece which are opposite in polarity, the first pole piece and the second pole piece are wound to form the electrode assembly, the first pole piece comprises a first current collector and a first active material layer laid on the surface of the first current collector, and the second pole piece comprises a second active material layer laid on the surface of the second current collector. An average compaction density of a portion of the first active material layer laid on a first inner region of the first current collector is smaller than an average compaction density of a portion laid on a first outer region of the first current collector, the first inner region being located on a side of the first outer region close to a winding axis of the electrode assembly. According to the electrode assembly, the battery monomer, the battery and the electric equipment provided by the embodiment of the invention, the performance of the electrode assembly can be improved.

Description

Technical Field

[0001] The present application relates to the field of batteries, and more specifically, to an electrode assembly, a battery cell, a battery and an electrical device. Background Art

[0002] Energy conservation and emission reduction are the key to the sustainable development of the automobile industry. In this case, electric vehicles have become an important part of the sustainable development of the automobile industry due to their advantages of energy conservation and environmental protection. For electric vehicles, battery technology is an important factor in their development.

[0003] The overall production process of batteries is long and complex, including a series of processes such as coating, sheet making, assembly, laser welding, and liquid injection. Among them, the processing process of the electrode assembly inside the battery cell is particularly important, which will directly affect the processing efficiency and performance of the battery cell. Therefore, how to improve the processing efficiency and performance of the electrode assembly is a technical problem that needs to be solved urgently. Summary of the invention

[0004] The embodiments of the present application provide an electrode assembly, a battery cell, a battery, and an electrical device, which can improve the performance of the electrode assembly.

[0005] In a first aspect, an electrode assembly is provided, comprising: a first pole sheet and a second pole sheet with opposite polarities, the first pole sheet and the second pole sheet being wound to form the electrode assembly, the first pole sheet comprising a first current collector and a first active material layer laid on the surface of the first current collector, the average compaction density of a portion of the first active material layer laid on a first internal region of the first current collector being less than the average compaction density of a portion laid on a first external region of the first current collector, and the first internal region is located on a side of the first external region close to the winding axis of the electrode assembly.

[0006] Therefore, in the electrode assembly of the embodiment of the present application, the average compaction density of the portion of the first active material layer located in the inner circle area of ​​the electrode assembly is set to be smaller than the average compaction density of the portion located in the outer circle area, so that the porosity of the portion of the first active material layer located in the inner circle area is greater than the porosity of the portion located in the outer circle area. In this way, the inner circle area with a larger porosity can accommodate more electrolyte, which can effectively solve the problem of lithium deposition caused by the easy extrusion of the electrolyte in the inner circle area, that is, it can effectively reduce the lithium deposition phenomenon of the electrode assembly, thereby improving the performance and cycle life of the battery cell.

[0007] In some embodiments, the average thickness of the portion of the first active material layer laid in the first inner region is greater than the average thickness of the portion laid in the first outer region. By setting the average thickness of the inner portion of the first active material layer to be larger and the average thickness of the outer portion to be smaller, it is easy to achieve the effect that the average compaction density of the portion of the first active material layer laid in the first inner region of the first current collector is smaller and the average compaction density of the portion laid in the first outer region is larger, which is convenient for processing.

[0008] In some embodiments, the average thickness of the first inner region is less than the average thickness of the first outer region, so that the average compaction density of the portion of the first active material layer laid in the first inner region is smaller, while the average compaction density of the portion laid in the first outer region is larger.

[0009] In some embodiments, the average thickness of the first outer region is in the range of [5 μm, 10 μm]. The average thickness of the first outer region should not be too large, so that the thickness of the first pole piece will not be too large, so as to improve the energy density of the battery cell assembled with the first pole piece. On the contrary, the average thickness of the first outer region should not be too small, so that the thickness of the first pole piece will not be too small, so as to improve the structural strength and structural stability of the first pole piece, thereby improving the performance of the electrode assembly.

[0010] In some embodiments, the average thickness of the first inner region is in the range of [2 μm, 6 μm]. The average thickness of the first inner region should not be too large, so that the thickness of the first pole piece will not be too large, so as to improve the energy density of the battery cell assembled with the first pole piece. On the contrary, the average thickness of the first inner region should not be too small, so as to improve the structural strength and structural stability of the first pole piece, thereby improving the performance of the electrode assembly.

[0011] In some embodiments, the first pole piece further includes: a first primer layer disposed at least partially between the first current collector and the first active material layer. The first primer layer can be used to connect and fix the first current collector and the first active material layer, and can also be used to increase the conductivity of the first pole piece.

[0012] In some embodiments, the first inner region is in direct contact with the active material layer, and the first primer layer is disposed between the first outer region and the active material layer. In this way, regardless of whether different regions of the first current collector have thickness differences, since the first outer region of the first current collector has one more first primer layer than the first inner region, it is convenient to achieve that the average thickness of the inner part of the first active material layer is larger than the average thickness of its outer part, and thus it is convenient to achieve that the average compaction density of the inner part of the first active material layer is smaller than the average compaction density of its outer part.

[0013] In some embodiments, the first primer layer is disposed in the entire region between the first current collector and the first active material layer. In this way, the first primer layer can more effectively connect and fix the first current collector and the first active material layer, increase the conductivity of the first pole piece, improve the structural strength and structural stability of the first pole piece, and improve the performance of the first pole piece.

[0014] In some embodiments, the average thickness of the portion of the first primer layer laid in the first inner region is less than the average thickness of the portion laid in the first outer region. In this way, regardless of whether there is a thickness difference between the first inner region and the first outer region of the first current collector, the thickness difference of the first primer layer can be used to achieve that the average thickness H of the inner portion of the first active material layer is greater than the average thickness H of its outer portion, which has a simple structure and is easy to implement.

[0015] In some embodiments, along the winding direction of the electrode assembly, the ratio of the total length of the first outer region to the total length of the first pole piece is in the range of [1 / 3, 2 / 3]. The length ratio should not be too large, otherwise the length of the portion of the first active material layer laid in the first outer region of the first current collector will be too large, increasing the processing cost and difficulty of the first pole piece. On the contrary, the length ratio should not be too small, and the total length of the first outer region will not be too small, so that the length of the portion of the first active material layer laid in the first outer region meets the design requirements, effectively reducing the problem of lithium deposition in the inner circle of the electrode assembly, thereby improving the performance of the battery cell.

[0016] In some embodiments, along the winding direction of the electrode assembly, the ratio of the total length of the first inner region to the total length of the first pole piece is in the range of [1 / 3, 1 / 2]. The length ratio should not be too large, otherwise the length of the thinned first inner region will be too large to reduce the structural strength and stability of the first pole piece, thereby reducing the performance of the battery cell. On the contrary, the length ratio should not be too small, then the length of the first inner region will not be too small, so that the length of the portion of the first active material layer laid in the first inner region can meet the design requirements, effectively reduce the problem of lithium deposition in the inner circle of the electrode assembly, and thereby improve the performance of the battery cell.

[0017] In some embodiments, the difference between the average thickness of the portion of the first active material layer laid in the first internal area and the average thickness of the portion laid in the first external area is H, where H is in μm, and the average compaction density of the portion of the first active material layer laid in the first internal area is Y, where Y is in g / cm3, and H and Y satisfy Y=KH, where the value range of K is [0.1, 0.4].

[0018] Taking into account that the average compaction density Y of the portion of the first active material layer laid in the first internal area has a certain range of values, therefore, if the proportional coefficient K is too large, the difference H will be too large. In this case, on the one hand, the average thickness of the portion of the first active material layer laid in the first internal area of ​​the first current collector may be too large, which will make the thickness of the first pole sheet too large, thereby affecting the energy density of the battery cell formed by the first pole sheet. On the other hand, the average thickness of the portion of the first active material layer laid in the first external area of ​​the first current collector may be too small, which will cause lithium deposition and may also cause the structural strength of the first pole sheet to be weak, affecting the performance of the first pole sheet.

[0019] On the contrary, if the proportional coefficient K is too small, the difference H will be too small. For example, the difference H may approach zero, which will make the thickness of the portion of the first active material layer laid in the first internal area approximately equal to the thickness of the portion of the first active material layer laid in the first external area. Correspondingly, the difference between the average compaction density of the portion of the first active material layer laid in the first internal area and the average compaction density of the portion of the first active material layer laid in the first external area will also be too small, which may affect the performance of the first electrode and fail to solve the lithium plating problem well.

[0020] In some embodiments, the average compaction density of the portion of the first active material layer laid on the first internal region is Y, and the unit of Y is g / cm3. The total coating mass of the material laid on the surface of the first current collector facing the first active material layer is M, and the unit of M is g / 1540.25mm2. Y and M satisfy Y=NM, where the value range of N is [0.8, 8].

[0021] When the total coating mass M of the material laid on the surface of the first current collector facing the first active material layer is constant, if the proportional coefficient N is too large, the average compaction density Y of the portion of the first active material layer laid in the first internal area will be too large and the porosity will be too small. Correspondingly, the average compaction density of the portion of the first active material layer laid in the first external area will be larger and the porosity will be smaller, which will increase the lithium precipitation phenomenon, increase the processing difficulty of the first pole piece, and increase the processing cost of the first pole piece. On the contrary, if the proportional coefficient N is too small, the average compaction density Y of the portion of the first active material layer laid in the first internal area will be too small, which may fail to meet the design requirements of the first pole piece, reduce the performance of the first pole piece, and further reduce the performance of the electrode assembly formed by the first pole piece.

[0022] In some embodiments, the average thickness of the portion of the first pole piece corresponding to the first internal region is substantially equal to the average thickness of the portion corresponding to the first external region, so that the two outer surfaces of the first pole piece are relatively flat, which facilitates subsequent processing into an electrode assembly, and makes the spacing between different pole piece layers in the electrode assembly relatively uniform, thereby reducing the problem of lithium plating caused by large spacing differences, which can not only improve the space utilization and energy density of the battery cell, but also reduce lithium plating during the long-term charge and discharge cycle of the battery cell, thereby improving the cycle life and safety of the battery cell.

[0023] In some embodiments, the first pole piece includes two first active material layers, and the first current collector is located between the two first active material layers to simultaneously reduce lithium plating on both sides of the first pole piece and further improve the performance of the electrode assembly and the battery cell.

[0024] In some embodiments, the second electrode sheet includes a second current collector and a second active material layer laid on the surface of the second current collector, the average compaction density of the portion of the second active material layer laid on the second internal region of the second current collector is less than the average compaction density of the portion laid on the second external region of the second current collector, and the second internal region is located on the side of the second external region close to the winding axis of the electrode assembly.

[0025] The average compaction density of the part of the second active material layer of the second electrode sheet of the embodiment of the present application located in the inner circle area of ​​the electrode assembly is less than the average compaction density of the part located in the outer circle area, and the porosity of the part of the second active material layer located in the inner circle area is also greater than the porosity of the part located in the outer circle area. In this way, the inner circle area with a larger porosity can accommodate more electrolyte, which can effectively solve the problem of lithium deposition caused by the easy extrusion of electrolyte in the inner circle area, that is, it can effectively reduce the lithium deposition phenomenon of the electrode assembly, thereby improving the performance and cycle life of the battery cell.

[0026] In some embodiments, the second pole piece includes two second active material layers, and the second current collector is located between the two second active material layers to simultaneously reduce the lithium deposition phenomenon on both sides of the second pole piece and further improve the performance of the electrode assembly and the battery cell.

[0027] In some embodiments, the first pole piece is a negative pole piece, and the second pole piece is a positive pole piece, so as to reduce lithium plating.

[0028] In some embodiments, the electrode assembly is a cylinder.

[0029] In a second aspect, a battery cell is provided, comprising: the electrode assembly in the first aspect or any one embodiment of the first aspect.

[0030] In a third aspect, a battery is provided, comprising a plurality of battery cells, wherein the battery cells comprise the electrode assembly according to the first aspect or any one of the embodiments of the first aspect.

[0031] In a fourth aspect, an electrical device is provided, comprising: the battery cell in the second aspect or any one of the embodiments of the second aspect and / or the battery in the third aspect or any one of the embodiments of the third aspect, wherein the battery cell and the battery are used to provide electrical energy to the electrical device.

[0032] In some embodiments, the electrical equipment is a vehicle, a ship or a spacecraft. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic diagram of the structure of a vehicle according to an embodiment of the present application;

[0034] Figure 2 This is a schematic diagram of the exploded structure of a battery according to an embodiment of the present application;

[0035] Figure 3 This is a schematic diagram of the exploded structure of a battery cell according to an embodiment of the present application;

[0036] Figure 4 A schematic cross-sectional structure diagram of an electrode assembly according to an embodiment of the present application;

[0037] Figure 5 This is a schematic diagram of the unfolded structure of a first pole piece according to an embodiment of the present application;

[0038] Figures 6 to 16 They are schematic cross-sectional structures of at least part of the first pole piece in different embodiments of the present application. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present application will be described below in conjunction with the accompanying drawings.

[0040] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0041] Unless otherwise defined, all technical and scientific terms used in this application have the same meanings as those commonly understood by technicians in the technical field of this application; the terms used in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned drawings and any variations thereof are intended to cover non-exclusive inclusions. The terms "first", "second", etc. in the specification and claims of this application or the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order or a primary and secondary relationship.

[0042] Reference to "embodiments" in this application means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in this application may be combined with other embodiments.

[0043] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", and "attached" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0044] The term "and / or" in this application is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this application generally indicates that the associated objects before and after are in an "or" relationship.

[0045] In the embodiments of the present application, the same reference numerals represent the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments. It should be understood that the thickness, length, width and other dimensions of various components in the embodiments of the present application shown in the drawings, as well as the overall thickness, length, width and other dimensions of the integrated device are only exemplary descriptions and should not constitute any limitation to the present application.

[0046] The term "multiple" as used in this application refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple sheets" refers to more than two sheets (including two sheets).

[0047] In the present application, battery cells may include lithium-ion secondary batteries, lithium-ion primary batteries, lithium-sulfur batteries, sodium-lithium-ion batteries, sodium-ion batteries or magnesium-ion batteries, etc., and the embodiments of the present application do not limit this. Battery cells 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.

[0048] In the embodiment of the present application, the battery cell may be a secondary battery. A secondary battery refers to a battery cell that can be continuously used by activating active materials by charging after the battery cell is discharged.

[0049] The battery cell can be a lithium ion battery, a sodium ion battery, a sodium lithium ion battery, a lithium metal battery, a sodium metal battery, a lithium sulfur battery, a magnesium ion battery, a nickel hydrogen battery, a nickel cadmium battery, a lead storage battery, etc., which is not limited in the embodiments of the present application.

[0050] In some implementations, the battery cell in the embodiments of the present application may be a metal battery. Specifically, the metal battery may include a lithium metal secondary battery, a sodium metal battery, or a magnesium metal battery, etc., which is not limited in the embodiments of the present application.

[0051] A battery cell generally includes an electrode assembly. The electrode assembly includes a positive electrode, a negative electrode, and a separator. During the charge and discharge process of the battery cell, active ions (such as lithium ions) are embedded and removed between the positive electrode and the negative electrode. The separator is set between the positive electrode and the negative electrode to prevent the positive and negative electrodes from short-circuiting, while allowing active ions to pass through.

[0052] In some embodiments, the positive electrode may be a positive electrode sheet, and the positive electrode sheet may include a positive electrode current collector and a positive electrode active material disposed on at least one surface of the positive electrode current collector.

[0053] As an example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material is disposed on either or both of the two facing surfaces of the positive electrode current collector.

[0054] As an example, the positive electrode current collector may be a metal foil, a foam metal or a composite current collector. For example, as a metal foil, aluminum or stainless steel, stainless steel, copper, aluminum, nickel, carbon electrode, carbon, nickel or titanium with a silver surface treatment may be used. The foam metal may be a nickel foam, a copper foam, an aluminum foam, an alloy foam, or carbon foam. The composite current collector may include a polymer material base and a metal layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0055] As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0056] In some embodiments, the negative electrode may be a negative electrode sheet, and the negative electrode sheet may include a negative electrode current collector and a negative electrode active material disposed on at least one surface of the negative electrode current collector.

[0057] As an example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material is disposed on either or both of the two facing surfaces of the negative electrode current collector.

[0058] As an example, the negative electrode current collector can be a metal foil, a foamed metal or a composite current collector. For example, as a metal foil, aluminum or stainless steel treated with silver, stainless steel, copper, aluminum, nickel, carbon electrode, carbon, nickel or titanium, etc. can be used. The composite current collector may include a polymer material base and a metal layer. The foamed metal may be a nickel foam, a copper foam, an aluminum foam, an alloy foam, or carbon foam, etc. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0059] As an example, the negative electrode active material may adopt the negative electrode active material for battery cells known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc.

[0060] In some embodiments, the electrode assembly further includes a separator disposed between the positive electrode and the negative electrode.

[0061] In some embodiments, the separator is a separator. The present application has no particular limitation on the type of separator, and any known separator with a porous structure having good chemical stability and mechanical stability can be selected.

[0062] As an example, the main material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramics.

[0063] In some embodiments, the separator is a solid electrolyte, which is disposed between the positive electrode and the negative electrode and serves to transmit ions and isolate the positive and negative electrodes.

[0064] In some embodiments, the battery cell further includes an electrolyte, which acts as a conductor of ions between the positive and negative electrodes. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. The electrolyte can be liquid, gel or solid.

[0065] In some embodiments, the electrode assembly is a wound structure, wherein the positive electrode sheet and the negative electrode sheet are wound into the wound structure.

[0066] In some embodiments, the electrode assembly is a laminate structure.

[0067] As an example, a plurality of positive electrode sheets and a plurality of negative electrode sheets may be provided respectively, and the plurality of positive electrode sheets and the plurality of negative electrode sheets may be alternately stacked.

[0068] As an example, a plurality of positive electrode sheets may be provided, and the negative electrode sheet may be folded to form a plurality of stacked folded segments, with a positive electrode sheet being sandwiched between adjacent folded segments.

[0069] As an example, both the positive electrode sheet and the negative electrode sheet are folded to form a plurality of folded sections that are stacked.

[0070] As an example, a plurality of separators may be provided, each of which is provided between any adjacent positive electrode sheets or negative electrode sheets.

[0071] As an example, the separator may be disposed continuously, and may be disposed between any adjacent positive electrode sheets or negative electrode sheets by folding or winding.

[0072] In some embodiments, the shape of the electrode assembly can be cylindrical, flat, or polygonal.

[0073] In some embodiments, the electrode assembly is provided with tabs, which can lead current out of the electrode assembly. The tabs include a positive tab and a negative tab.

[0074] In some embodiments, the battery cell may include a housing. The housing is used to encapsulate components such as electrode assemblies and electrolytes. The housing may be a steel housing, an aluminum housing, a plastic housing (such as polypropylene), a composite metal housing (such as a copper-aluminum composite housing), or an aluminum-plastic film. The housing includes a shell and a cover plate.

[0075] As an example, the battery cell can be a cylindrical battery cell, a prismatic battery cell, a soft-pack battery cell or a battery cell of other shapes. The prismatic battery cell includes a square shell battery cell, a blade-shaped battery cell, a polygonal battery, such as a hexagonal battery, etc. There is no special limitation in this application.

[0076] The battery mentioned in the embodiments of the present application may include one or more battery cells to provide a single physical module with higher voltage and capacity. When there are multiple battery cells, the multiple battery cells are connected in series, in parallel or in mixed connection through a busbar component.

[0077] In some embodiments, the battery may be a battery module. When there are multiple battery cells, the multiple battery cells are arranged and fixed to form a battery module.

[0078] In some embodiments, the battery may be a battery pack, which includes a case and battery cells, wherein the battery cells or battery modules are accommodated in the case.

[0079] In some embodiments, the box body can be used as a part of the chassis structure of the vehicle. For example, part of the box body can become at least a part of the floor of the vehicle, or part of the box body can become at least a part of the cross beam and longitudinal beam of the vehicle.

[0080] The battery cell in the embodiment of the present application is provided with an electrode assembly inside, and an electrolyte is injected inside the battery cell. During the use of the battery cell, after multiple cycles of charge and discharge, expansion is likely to occur between the pole pieces, especially for the wound electrode assembly, where the expansion force is greater between the pole pieces in the central area close to the central winding axis, causing the electrolyte in this area to be more easily squeezed out, thereby increasing the movement resistance of ions in this area, and easily causing lithium deposition in the central area of ​​the pole piece, thereby affecting the performance and service life of the battery cell.

[0081] Therefore, the embodiment of the present application provides an electrode assembly, a battery cell, a battery and an electrical device, which can solve the above problems. The electrode assembly of the embodiment of the present application includes a first pole piece and a second pole piece with opposite polarities, and the first pole piece and the second pole piece are wound together to form an electrode assembly. The first pole piece includes a first current collector and a first active material layer arranged on the surface of the first current collector, and the average compaction density of the portion of the first active material layer laid in the first inner region of the first current collector is less than the average compaction density of the portion laid in the first outer region of the first current collector, wherein the first inner region is located on the side of the first outer region close to the winding axis of the electrode assembly. In other words, the average compaction density of the portion of the first active material layer located in the inner ring region of the electrode assembly is less than the average compaction density of the portion located in the outer ring region, and the porosity of the portion of the first active material layer located in the inner ring region is also greater than the porosity of the portion located in the outer ring region. In this way, the inner ring region with a larger porosity can accommodate more electrolyte, which can effectively solve the problem of lithium precipitation caused by the easy extrusion of the electrolyte in the inner ring region, that is, it can effectively reduce the lithium precipitation phenomenon of the electrode assembly, thereby improving the performance and cycle life of the battery cell.

[0082] The technical solutions described in the embodiments of the present application are applicable to various electrical devices using batteries.

[0083] Electrical equipment may be vehicles, mobile phones, portable devices, laptops, ships, spacecraft, electric toys, electric tools, and the like. 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, and the like; spacecraft include airplanes, rockets, space shuttles, and spacecraft, and the like; electric toys include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, and the like; 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, and the like. The embodiments of the present application do not impose any special restrictions on the above-mentioned electrical equipment.

[0084] For the convenience of description, the following embodiments are described by taking the electric device as a vehicle as an example.

[0085] For example, Figure 1As shown, it is a structural schematic diagram of a vehicle 1 according to an embodiment of the present application. The vehicle 1 may be a fuel vehicle, a gas vehicle or a new energy vehicle. The new energy vehicle may be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A motor 40, a controller 30 and a battery 10 may be arranged inside the vehicle 1. The controller 30 is used to control the battery 10 to supply power to the motor 40. For example, a battery 10 may be arranged at the bottom, front or rear of the vehicle 1. The battery 10 may be used to supply power to the vehicle 1. For example, the battery 10 may be used as an operating power source for the vehicle 1, for the circuit system of the vehicle 1, for example, for the working power requirements during the start-up, navigation and operation of the vehicle 1. In another embodiment of the present application, the battery 10 may not only be used as an operating power source for the vehicle 1, but also as a driving power source for the vehicle 1, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1.

[0086] In order to meet different power requirements, 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. The battery may also be referred to as a battery pack. Optionally, 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. In other words, multiple battery cells may be directly connected to form a battery, or may be first connected to form a battery module, and then the battery module may be connected to form a battery.

[0087] For example, Figure 2 FIG. 1 is a schematic diagram showing the structure of a battery 10 according to an embodiment of the present application. The battery 10 may include a plurality of battery cells 20. Figure 2 As shown, the battery 10 may further include a box body 11 , the interior of the box body 11 is a hollow structure, and a plurality of battery cells 20 are accommodated in the box body 11 . Figure 2 A possible implementation of the box 11 of the embodiment of the present application is shown, such as Figure 2 As shown, the box body 11 may include two parts, which are respectively referred to as a first part 111 and a second part 112, and the first part 111 and the second part 112 are buckled together. The shapes of the first part 111 and the second part 112 may be determined according to the shapes of the plurality of battery cells 20 inside, and at least one of the first part 111 and the second part 112 has an opening. For example, Figure 2 As shown, the first part 111 and the second part 112 can both be hollow rectangular parallelepipeds and each has only one open face, the opening of the first part 111 and the opening of the second part 112 are arranged opposite to each other, and the first part 111 and the second part 112 are interlocked to form a box body 11 with a closed chamber.

[0088] For example, different from Figure 2As shown, only one of the first part 111 and the second part 112 may be a hollow cuboid with an opening, while the other may be in the shape of a plate to cover the opening. For example, here, the second part 112 is a hollow cuboid with only one face as an opening face, and the first part 111 is in the shape of a plate. Then, the first part 111 covers the opening of the second part 112 to form a box 11 with a closed chamber, which can be used to accommodate multiple battery cells 20. Multiple battery cells 20 are connected in parallel, in series, or in a mixed combination and placed in the box 11 formed by the first part 111 and the second part 112 being buckled together.

[0089] Optionally, the battery 10 may also include other structures, which are not described one by one here. For example, the battery 10 may also include a busbar, which is used to realize the electrical connection between multiple battery cells 20, such as parallel connection, series connection or mixed connection. Specifically, the busbar can realize the electrical connection between the battery cells 20 by connecting the electrode terminals 214 of the battery cells 20. Further, the busbar can be fixed to the electrode terminals 214 of the battery cells 20 by welding. The electrical energy of multiple battery cells 20 can be further led out through the box 11 through the conductive mechanism.

[0090] The number of battery cells 20 in the battery 10 can be set to any value according to different power requirements. Multiple battery cells 20 can be connected in series, in parallel or in a mixed manner to achieve a larger capacity or power. Since the number of battery cells 20 included in each battery 10 may be large, in order to facilitate installation, the battery cells 20 can also be arranged in groups, and each group of battery cells 20 constitutes a battery module. The number of battery cells 20 included in the battery module is not limited and can be set according to demand.

[0091] Figure 3 This is a schematic diagram of a partial exploded structure of a battery cell 20 according to an embodiment of the present application, for example, Figure 3 The battery cell 20 shown may be Figure 2 Any battery cell 20. Figure 3 As shown, the battery cell 20 of the embodiment of the present application may include: a housing 21. Specifically, the housing 21 may include: a shell 211, which is a hollow structure with at least one opening 2111; a cover plate 212, which is used to cover the opening 2111 of the shell 211; and an electrode assembly 22, which is accommodated in the housing 21.

[0092] It should be understood that the housing 211 of the present embodiment is a component for accommodating the electrode assembly 22, and the housing 211 may be a hollow structure with an opening 2111 formed at one end or at multiple ends. For example, if the housing 211 is a hollow structure with an opening 2111 formed at one end, the corresponding cover plate 212 may be provided as one; for another example, Figure 3As shown, if the shell 211 is a hollow structure with openings 2111 formed at two opposite ends, two cover plates 212 can be provided, and the two cover plates 212 cover the openings 2111 at the two ends of the shell 211 respectively.

[0093] The housing 211 may be in various shapes, such as a cylinder, a cuboid, or other polyhedrons. Figure 3 As shown, in the embodiment of the present application, the shell 211 is mainly described as a cylindrical structure as an example.

[0094] It should be understood that the cover plate 212 of the embodiment of the present application is used to cover the opening 2111 of the housing 211 to isolate the internal environment of the battery cell 20 from the external environment. The shape of the cover plate 212 can be adapted to the shape of the housing 211, such as Figure 3 As shown, the shell 211 is a cylindrical structure, and the cover plate 212 is a circular plate structure matched with the shell 211 .

[0095] In the embodiment of the present application, the shell 211 can be made of various materials, such as copper, iron, aluminum, steel, aluminum alloy, etc. The cover plate 212 can also be made of various materials, such as copper, iron, aluminum, steel, aluminum alloy, etc. Optionally, the material of the cover plate 212 can be the same as or different from that of the shell 211.

[0096] It should be understood that the battery cell 20 also includes an electrode terminal 214. The electrode terminal 214 of the embodiment of the present application is used to electrically connect to the electrode assembly 22 inside the battery cell 20 to output the electrical energy of the battery cell 20. Specifically, the battery cell 20 may include at least two electrode terminals 214, and the at least two electrode terminals 214 may include at least one positive electrode terminal and at least one negative electrode terminal, the positive electrode terminal is used to electrically connect to the positive electrode tab of the electrode assembly 22, and the negative electrode terminal is used to electrically connect to the negative electrode tab of the electrode assembly 22. The positive electrode terminal may be directly connected to the positive electrode tab or indirectly connected, and the negative electrode terminal may be directly connected to the negative electrode tab or indirectly connected. Exemplarily, the positive electrode terminal may be electrically connected to the positive electrode tab through a connecting member, and the negative electrode terminal may be electrically connected to the negative electrode tab through a connecting member.

[0097] In some embodiments, at least two electrode terminals 214 included in the battery cell 20 may be located on different walls, or may also be located on different walls. Figure 3 As shown, in the cylindrical battery cell 20 of the embodiment of the present application, the two electrode terminals 214 can be respectively located on two oppositely arranged cover plates 212, so that each electrode terminal 214 is electrically connected to the corresponding pole lug 221 located at both ends of the electrode assembly 22.

[0098] In the battery cell 20, the electrode assembly 22 is a component in the battery cell 20 where an electrochemical reaction occurs. According to actual use requirements, the electrode assembly 22 in the housing 211 can be set to one or more. Figure 3 As shown, an electrode assembly 22 is disposed in the battery cell 20. The type and shape of the electrode assembly 22 can also be set according to actual use needs. For example, the electrode assembly 22 can be a cylinder, a cuboid, etc. Figure 3 As shown, if the shell 211 is a cylindrical structure, the corresponding electrode assembly 22 may also be a cylindrical structure to improve the internal space utilization of the battery cell 20 and the energy density of the battery cell 20; for example, if the shell 211 is a rectangular structure, the electrode assembly 22 may be a rectangular structure or a cylindrical structure, but the embodiments of the present application are not limited to this.

[0099] It should be understood that Figure 3 As shown, the electrode assembly 22 includes a pole ear 221 and an electrode body 222, wherein the pole ear 221 of the electrode assembly 22 may include a positive pole ear and a negative pole ear, the positive pole ear may be formed by stacking a portion of the positive electrode sheet that is not coated with the positive electrode active material layer, and the negative pole ear may be formed by stacking a portion of the negative electrode sheet that is not coated with the negative electrode active material layer; the electrode body 222 may be formed by stacking or winding the positive electrode sheet and the negative electrode sheet.

[0100] The electrode assembly according to the embodiment of the present application will be described below in conjunction with the accompanying drawings. Figure 4 The cross-sectional schematic diagram of the electrode assembly 22 of the embodiment of the present application is shown. Figure 4 Can be Figure 3 The cross-sectional schematic diagram of the electrode assembly 22 included in the battery cell 20 shown, the cross-section is perpendicular to the height direction of the electrode assembly 22, or the cross-section is parallel to the end surface where the electrode ear 221 of the electrode assembly 22 is located; Figure 5 The schematic diagram of the structure of the first pole piece 3 of the electrode assembly 22 of the embodiment of the present application is shown. Figure 5 The first pole piece 3 is shown in an unfolded state. Figure 5 The first pole piece 3 shown can be Figure 4 The first pole piece 3 of the electrode assembly 22 is shown.

[0101] like Figure 4 and Figure 5As shown, the electrode assembly 22 of the embodiment of the present application includes: a first pole piece 3 and a second pole piece 4 with opposite polarities, the first pole piece 3 and the second pole piece 4 are wound to form the electrode assembly 22, the first pole piece 3 includes a first current collector 31 and a first active material layer 32 laid on the surface of the first current collector 31, the average compaction density of the portion 321 of the first active material layer 32 laid on the first internal region 311 of the first current collector 31 is less than the average compaction density of the portion 322 laid on the first external region 312 of the first current collector 31, and the first internal region 311 is located on the side of the first external region 312 close to the winding axis of the electrode assembly 22.

[0102] It should be understood that the embodiment of the present application mainly takes the electrode assembly 22 as a wound electrode assembly 22 as an example, and the shape of the electrode assembly 22 can be flexibly set according to actual applications. For example, the electrode assembly 22 can be as follows Figure 4 The cylindrical shape shown; for example, different from Figure 4 The electrode assembly 22 may also be in the shape of a square column, but the embodiments of the present application are not limited thereto.

[0103] In the embodiment of the present application, the electrode assembly 22 includes a first electrode sheet 3 and a second electrode sheet 4 with opposite polarities. For example, the first electrode sheet 3 can be a positive electrode sheet, and the second electrode sheet 4 can be a negative electrode sheet; or Figure 4 As shown, the first pole piece 3 may also be a negative pole piece, and the second pole piece 4 may be a positive pole piece. Further, the electrode assembly 22 may also include a separator 5, which may be used to separate the first pole piece 3 from the second pole piece 4. For example, the separator 5 may be located between the first pole piece 3 and the second pole piece 4.

[0104] It should be understood that the first pole piece 3 of the embodiment of the present application may include a pole ear portion 301 and a main body portion 302, wherein the pole ear portion 301 is used to form the pole ear 221 of the electrode assembly 22, and the main body portion 302 is used to form the electrode main body portion 222 of the electrode assembly 22. Specifically, the pole ear portion 301 of the first pole piece 3 can be formed by stacking the portion of the first pole piece 3 that is not coated with the first active material layer 32. For example, for a positive pole piece, the pole ear portion 301 can be formed by stacking the portion of the positive pole piece that is not coated with the positive active material layer; for a negative pole piece, the pole ear portion 301 can be formed by stacking the portion of the negative pole piece that is not coated with the negative active material layer. The main body portion 302 of the first pole piece 3 is used to wind to form the electrode main body portion 222 of the electrode assembly 22.

[0105] For the convenience of description, the first current collector 31 included in the first pole piece 3 of the embodiment of the present application mainly refers to the first current collector 31 of the main body 302 of the first pole piece 3; correspondingly, the first active material layer 32 of the first pole piece 3 mainly refers to the first active material layer 32 of the main body 302 of the first pole piece 3, and this part of the first active material layer 32 is laid on the corresponding surface of the first current collector 31.

[0106] For the convenience of description, the embodiment of the present application defines a length direction X and a width direction Y for the first pole piece 3. Specifically, the length direction X of the first pole piece 3 is the extension direction of the first pole piece 3, and Figure 5 The length direction X of the first pole piece 3 shown corresponds to Figure 4 the width direction Y of the first pole piece 3 is the arrangement direction of the ear portion 301 and the main body portion 302 of the first pole piece 3, and the length direction X and the width direction Y are perpendicular to each other.

[0107] It should be understood that the first active material layer 32 is laid on the surface of the first current collector 31 of the embodiment of the present application means that: along the thickness direction of the first pole piece 3, the first current collector 31 includes two surfaces arranged opposite to each other, and the first active material layer 32 is laid on any one of the two surfaces. Among them, the thickness direction of the first pole piece 3 is perpendicular to the length direction X and the width direction Y of the first pole piece 3, that is, the length direction X, the width direction Y and the thickness direction of the first pole piece 3 are perpendicular to each other.

[0108] The first inner region 311 of the first current collector 31 of the embodiment of the present application corresponds to the inner region 303 of the first pole piece 3, that is, located in the inner circle region of the first pole piece 3. In contrast, the first outer region 312 of the first current collector 31 corresponds to the outer region 304 of the first pole piece 3, that is, located in the outer circle region of the first pole piece 3. Figure 4 and Figure 5 As shown, the inner region 303 of the first pole piece 3 is closer to the central winding axis of the first pole piece 3 than the outer region 304 .

[0109] Therefore, in the electrode assembly 22 of the embodiment of the present application, the average compaction density of the portion 321 of the first active material layer 32 located in the inner ring area of ​​the electrode assembly 22 is less than the average compaction density of the portion 322 located in the outer ring area, and the porosity of the portion 321 of the first active material layer 32 located in the inner ring area is also greater than the porosity of the portion 322 located in the outer ring area. In this way, the inner ring area with a larger porosity can accommodate more electrolyte, which can effectively solve the problem of lithium deposition caused by the easy extrusion of the electrolyte in the inner ring area, that is, it can effectively reduce the lithium deposition phenomenon of the electrode assembly 22, thereby improving the performance and cycle life of the battery cell 20.

[0110] It should be understood that in the embodiment of the present application, the average compaction density of the portion 321 of the first active material layer 32 laid in the first inner region 311 is less than the average compaction density of the portion 322 laid in the first outer region 312, which can be achieved in a variety of ways. For example, it can be achieved by adjusting the cold pressing process; for another example, it can also be achieved by setting different thicknesses in different regions of the first pole piece 3.

[0111] Figure 6 and Figure 7 Partial cross-sectional schematic diagrams of the first pole piece 3 of different embodiments of the present application are respectively shown, for example, Figure 6 and Figure 7 Can be Figure 5 The schematic diagram of a possible partial cross section of the first pole piece 3 shown in FIG. 1 is perpendicular to the width direction Y of the first pole piece 3. Figures 5 to 7 As shown, different compaction densities can be achieved by setting different thicknesses in different regions of the first active material layer 32 .

[0112] In the embodiment of the present application, the average thickness H1 of the portion 321 of the first active material layer 32 laid in the first inner region 311 is greater than the average thickness H1 of the portion 322 laid in the first outer region 312. Before the compaction treatment, that is, when the first active material layer 32 is laid on the surface of the first current collector 31, the coating thickness of different regions can be set to be the same or different. However, after the compaction treatment, by setting the average thickness H1 of the inner portion 321 of the first active material layer 32 to be larger and the average thickness H2 of the outer portion 322 to be smaller, it is easy to achieve the effect that the average compaction density of the portion 321 of the first active material layer 32 laid in the first inner region 311 of the first current collector 31 is smaller, while the average compaction density of the portion 322 laid in the first outer region 312 is larger, which is convenient for processing.

[0113] It should be understood that the average thickness H1 of the portion 321 of the first active material layer 32 laid in the first inner region 311 may refer to: the average value of the thickness of the portion 321 of the first active material layer 32 laid in the first inner region 311 of the first current collector 31 along the thickness direction Z of the first pole piece 3. For example, the drawings of the embodiments of the present application all take the case where the thickness of the portion 321 of the first active material layer 32 laid in the first inner region 311 of the first current collector 31 is uniform and equal.

[0114] Similarly, the average thickness H2 of the portion 322 of the first active material layer 32 laid in the first outer region 312 of the first current collector 31 may refer to: along the thickness direction Z of the first pole piece 3, the average value of the thickness dimension of the portion 322 of the first active material layer 32 laid in the first outer region 312. For example, the drawings of the embodiments of the present application all take the thickness of the portion 322 of the first active material layer 32 laid in the first outer region 312 as an example. Among them, the thickness direction Z of the first pole piece 3 of the embodiment of the present application is perpendicular to the length direction X and the width direction Y of the first pole piece 3.

[0115] It should be understood that the average thickness H1 of the portion 321 of the first active material layer 32 of the embodiment of the present application laid in the first inner region 311 can be flexibly set according to the actual application; similarly, the average thickness H2 of the portion 322 of the first active material layer 32 laid in the first outer region 312 of the first current collector 31 can also be flexibly set according to the actual application. For example, if the first electrode sheet 3 is a positive electrode sheet, the value range of the average thickness H1 of the portion 321 of the first active material layer 32 laid in the first inner region 311 can be set to [70μm, 300μm]; the value range of the average thickness H2 of the portion 322 of the first active material layer 32 laid in the first outer region 312 of the first current collector 31 can be set to [70μm, 220μm]. For another example, if the first electrode sheet 3 is a negative electrode sheet, the average thickness H1 of the portion 321 of the first active material layer 32 laid in the first internal area 311 can be set to a value range of [40μm, 220μm]; the average thickness H2 of the portion 322 of the first active material layer 32 laid in the first external area 312 of the first current collector 31 can be set to a value range of [40μm, 200μm].

[0116] It should be understood that the different thicknesses of different regions of the first active material layer 32 in the embodiment of the present application can be achieved in a variety of ways. Figure 6For example, the surface of the first active material layer 32 away from the first current collector 31 can be uneven to achieve the thickness requirements of different regions. Specifically, before the compaction treatment, that is, when the first active material layer 32 is laid on the surface of the first current collector 31, the coating thickness of different regions can be set to be the same or different. For example, the average thickness H1 of the inner part 321 of the first active material layer 32 can be set to be equal to or unequal to the average thickness H2 of the outer part 322, but after a special compaction treatment, the average thickness H1 of the inner part 321 of the first active material layer 32 can be larger, while the average thickness H2 of the outer part 322 is smaller, thereby achieving a smaller average compaction density of the portion 321 of the first active material layer 32 laid in the first inner region 311, and a larger average compaction density of the portion 322 laid in the first outer region 312.

[0117] For example, Figure 6 Differently, the surface of the first active material layer 32 away from the first current collector 31 can also be substantially flush, and this can be achieved by different configurations. Figure 7 As shown, the first current collector 31 can be partially thickened or partially thinned so that different regions of the first current collector 31 have thickness differences, thereby achieving a thickness difference of the first active material layer 32. For example, the average thickness H3 of the first internal region 311 is less than the average thickness H4 of the first external region 312, so as to achieve a smaller average compaction density of the portion 321 of the first active material layer 32 laid in the first internal region 311, while the average compaction density of the portion 322 laid in the first external region 312 is larger. Among them, the above-mentioned thickness difference of the first current collector 31 can be achieved by increasing the thickness of the first internal region 311 of the first current collector 31, or by thinning the thickness of the first external region 312 of the first current collector 31, and here, the other side surface of the first current collector 31 is taken as an example as being flush, but the embodiments of the present application are not limited thereto.

[0118] Specifically, in the process of laying the first active material layer 32 on the surface of the first current collector 31, the surface of the first active material layer 32 away from the first current collector 31 can be set to be basically flush. Since different regions of the first current collector 31 have different thicknesses, the average thickness H1 of the portion 321 of the first active material layer 32 laid in the first inner region 311 is larger, while the average thickness H2 of the portion 322 laid in the first outer region 312 is smaller. In addition, during the compaction process, since the surface of the first active material layer 32 away from the first current collector 31 is basically flush, it is not necessary to perform special compaction treatment on different regions; after the compaction treatment, the surface of the first active material layer 32 away from the first current collector 31 can still be kept basically flush, which is convenient for the subsequent processing of the first pole piece 3 and assembly into the electrode assembly 22.

[0119] It should be understood that the thickness of different regions of the first current collector 31 in the embodiment of the present application can be flexibly set according to actual applications. For example, the thickness of different regions can be set in different implementations, but the embodiment of the present application is not limited thereto.

[0120] In the embodiment of the present application, the lengths of different regions of the first current collector 31 can also be flexibly set according to actual applications. For example, the lengths of different regions can be set in different implementations, but the embodiment of the present application is not limited thereto.

[0121] In some embodiments, along the winding direction of the electrode assembly 22, the ratio of the total length L2 of the first external region 312 to the total length L0 of the first pole piece 3 is in the range of [1 / 3, 2 / 3]. For example, if the thickness difference of different regions of the first current collector 31 is achieved by increasing the thickness of the first external region 312, the length ratio should not be too large, for example, it usually does not exceed 2 / 3, otherwise the length of the portion 322 of the first active material layer 32 laid in the first external region 312 of the first current collector 31 will be too large, increasing the processing cost and difficulty of the first pole piece 3. On the contrary, the length ratio should not be too small, for example, it usually does not fall below 1 / 3, and the total length L2 of the first external region 312 will not be too small, so that the length of the portion 322 of the first active material layer 32 laid in the first external region 312 meets the design requirements, effectively reducing the problem of lithium deposition in the inner circle of the electrode assembly 22, and thus improving the performance of the battery cell 20.

[0122] In some embodiments, along the winding direction of the electrode assembly 22, the ratio of the total length L1 of the first inner region 311 to the total length L0 of the first pole piece 3 is in the range of [1 / 3, 1 / 2]. For example, if the thickness difference of different regions of the first current collector 31 is achieved by thinning the first inner region 311 of the first current collector 31, the length ratio should not be too large, for example, it usually does not exceed 1 / 2, otherwise the length L1 of the thinned first inner region 311 is too large, which will reduce the structural strength and stability of the first pole piece 3, thereby reducing the performance of the battery cell 20. On the contrary, the length ratio should not be too small, for example, it usually does not fall below 1 / 3, then the length L1 of the first inner region 311 will not be too small, so that the length of the portion 321 of the first active material layer 32 laid in the first inner region 311 can meet the design requirements, effectively reduce the problem of lithium deposition in the inner circle of the electrode assembly 22, and thereby improve the performance of the battery cell 20.

[0123] It should be understood that the winding direction of the electrode assembly 22 of the embodiment of the present application may include a clockwise direction or a counterclockwise direction, for example, Figure 4 Take the clockwise direction as an example. In addition, the length of each region of the first pole piece 3 of the embodiment of the present application along the winding direction of the electrode assembly 22 is consistent with the length of the corresponding region along the length direction of the first pole piece 3. For example, along the winding direction of the electrode assembly 22, the total length L0 of the first current collector 31, the total length L1 of the first inner region 311, and the total length L2 of the first outer region 312 correspond to: along the length direction X of the first pole piece 3, the length L0 of the first current collector 31, the total length L1 of the first inner region 311, and the total length L2 of the first outer region 312.

[0124] It should be understood that, when the surface of the first active material layer 32 away from the first current collector 31 is substantially flush, the thickness difference of different regions of the first active material layer 32 can also be achieved by other means.

[0125] In some embodiments, the first pole piece 3 further includes: a first primer layer 33 disposed in at least a portion of the area between the first current collector 31 and the first active material layer 32. The first primer layer 33 can be used to connect and fix the first current collector 31 and the first active material layer 32, and can also be used to increase the conductivity of the first pole piece 3. For example, the material of the first primer layer 33 may include a bonding material and / or a conductive material. For another example, the first primer layer 33 may include a conductive material. Taking lithium batteries as an example, commonly used lithium battery conductive materials may include traditional conductive agents, such as conductive carbon black (SP), conductive graphite, carbon fiber, etc.; or, may also include new conductive agents, such as carbon nanotubes, graphene and mixed conductive slurries thereof. For another example, the first primer layer 33 may include a bonding material. Still taking lithium batteries as an example, commonly used bonding materials mainly include at least one of the following: polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR) emulsion, carboxymethyl cellulose (CMC), polyacrylic acid (PAA) and polyacrylonitrile (PAN) and polyacrylate.

[0126] It should be understood that different thicknesses of different regions of the first active material layer 32 can be achieved by different arrangements of the first primer layer 33 and the first current collector 31 .

[0127] In some embodiments, the first primer layer 33 may be disposed in a partial region between the first current collector 31 and the first active material layer 32 to achieve different thicknesses in different regions of the first active material layer 32. Figure 8 and Fig. 9 Partial cross-sectional schematic diagrams of the first pole piece 3 of different embodiments of the present application are respectively shown, for example, Figure 8 and Fig. 9 Can be Figures 3 to 5 The schematic diagram of a possible partial cross-section of the first pole piece 3 of the electrode assembly 22 shown is perpendicular to the width direction Y of the first pole piece 3 .

[0128] like Figure 8 and Fig. 9As shown, the first inner region 311 is in direct contact with the first active material layer 32, and the first primer layer 33 is disposed between the first outer region 312 and the first active material layer 32. That is, the first primer layer 33 is not disposed between the first inner region 311 of the first current collector 31 and the corresponding inner portion 321 of the first active material layer 32, so that the first current collector 31 of this portion is in direct contact with the first active material layer 32; and the first primer layer 33 is disposed between the first outer region 312 of the first current collector 31 and the corresponding outer portion 322 of the first active material layer 32, so that the first current collector 31 of this portion is indirectly connected with the first active material layer 32 through the first primer layer 33. In this way, regardless of whether different areas of the first current collector 31 have thickness differences, since the first external area 312 of the first current collector 31 is provided with an additional first primer layer 33 compared to the first internal area 311, it is convenient to achieve that the average thickness H1 of the internal part 321 of the first active material layer 32 is larger than the average thickness H2 of its external part 322, and thus it is convenient to achieve that the average compaction density of the internal part 321 of the first active material layer 32 is smaller than the average compaction density of the external part 322.

[0129] For example, Figure 8 As shown, it can be Figure 7 On the basis of the first pole piece 3 shown, a first primer layer 33 is further partially provided to achieve different thicknesses in different regions of the first active material layer 32. Specifically, on the basis that the first inner region 311 and the first outer region 312 of the first current collector 31 have a thickness difference, the first primer layer 33 may not be provided in the first inner region 311 of the first current collector 31, and the first primer layer 33 may be provided in the first outer region 312 of the first current collector 31. In this way, when the surface of the first active material layer 32 away from the first current collector 31 is substantially flush, the difference between the average thickness H1 of the portion 321 of the first active material layer 32 laid in the first inner region 311 and the average thickness H2 of the portion 322 of the first active material layer 32 laid in the first outer region 312 is equal to: the sum of the thickness difference between the first inner region 311 and the first outer region 312 of the first current collector 31 and the thickness of the first primer layer 33 located in the first outer region 312 of the first current collector 31. Therefore, by adjusting the thickness difference between the first internal region 311 and the first external region 312 of the first current collector 31 and the thickness of the first primer layer 33 located in the first external region 312 of the first current collector 31, the difference between the average thickness H1 and the average thickness H2 can be adjusted, and then the difference between the average compaction density of the portion 321 of the first active material layer 32 laid in the first internal region 311 and the average compaction density of the portion 322 of the first active material layer 32 laid in the first external region 312 can also be adjusted.

[0130] For example, Fig. 9 As shown, different thicknesses of different regions of the first active material layer 32 can be achieved by providing a first primer layer 33 and not providing the first primer layer 33 on the basis that there is no thickness difference between the first inner region 311 and the first outer region 312 of the first current collector 31. Specifically, when the surface of the first active material layer 32 away from the first current collector 31 is substantially flush, the difference between the average thickness H1 of the portion 321 of the first active material layer 32 laid in the first inner region 311 and the average thickness H2 of the portion 322 of the first active material layer 32 laid in the first outer region 312 is equal to the thickness of the first primer layer 33 located in the first outer region 312 of the first current collector 31. Therefore, the difference between the average thickness H1 and the average thickness H2 can be directly adjusted by adjusting the coating thickness of the first primer layer 33, and the difference between the average compaction density of the portion 321 of the first active material layer 32 laid in the first internal area 311 and the average compaction density of the portion 322 of the first active material layer 32 laid in the first external area 312 can also be adjusted. The structure is simple and easy to implement.

[0131] In some embodiments, the first primer layer 33 may also be disposed in the entire region between the first current collector 31 and the first active material layer 32, and different thicknesses in different regions of the first active material layer 32 may also be achieved. Fig.10 and Fig.11 Partial cross-sectional schematic diagrams of the first pole piece 3 of different embodiments of the present application are respectively shown, for example, Fig.10 and Fig.11 Can be Figures 3 to 5 The schematic diagram of a possible partial cross-section of the first pole piece 3 of the electrode assembly 22 shown is perpendicular to the width direction Y of the first pole piece 3 .

[0132] like Fig.10 and Fig.11 As shown, the first primer layer 33 is disposed in the entire region between the first current collector 31 and the first active material layer 32. In this way, the first primer layer 33 can more effectively connect and fix the first current collector 31 and the first active material layer 32, and can also increase the conductivity of the first pole piece 3, improve the structural strength and structural stability of the first pole piece 3, and can also improve the performance of the first pole piece 3.

[0133] In some embodiments, along the thickness direction Z of the first pole piece 3, a portion 331 of the first primer layer 33 corresponding to the first inner region 311 sinks relative to a portion 332 corresponding to the first outer region 312. In this way, regardless of whether there is a thickness difference between the first inner region 311 and the first outer region 312 of the first current collector 31, the height difference between the portion 331 of the first primer layer 33 corresponding to the first inner region 311 and the portion 332 corresponding to the first outer region 312 can achieve that the average thickness H1 of the inner portion 321 of the first active material layer 32 is greater than the average thickness H2 of its outer portion 322, and further, the average compaction density of the portion 321 of the first active material layer 32 laid in the first inner region 311 is less than the average compaction density of the portion 322 of the first active material layer 32 laid in the first outer region 312.

[0134] like Fig.10 As shown, along the thickness direction Z of the first pole piece 3, the relationship between the average thickness H5 of the portion 331 of the first primer layer 33 corresponding to the first inner region 311 and the average thickness H6 of the portion 332 corresponding to the first outer region 312 can be flexibly set according to practical applications. For example, if there is a thickness difference between the first inner region 311 and the first outer region 312 of the first current collector 31, the average thickness H5 may be greater than, equal to, or less than the average thickness H6, and the average thickness H1 of the inner portion 321 of the first active material layer 32 may be greater than the average thickness H2 of the outer portion 322 thereof, and the structure of the first primer layer 33 is more flexible.

[0135] In some embodiments, the average thickness H5 of the portion 331 of the first primer layer 33 laid in the first inner region 311 is less than the average thickness H6 of the portion 332 laid in the first outer region 312. In this way, regardless of whether there is a thickness difference between the first inner region 311 and the first outer region 312 of the first current collector 31, the average thickness H1 of the inner portion 321 of the first active material layer 32 can be greater than the average thickness H2 of the outer portion 322 thereof through the thickness difference of the first primer layer 33, and the structure is simple and easy to implement.

[0136] It should be understood that for the various embodiments described above, the average thickness H1 of the portion 321 of the first active material layer 32 laid in the first inner region 311 and the average thickness H2 of the portion 322 of the first active material layer 32 laid in the first outer region 312 in the embodiment of the present application may be related to various factors. For example, it may be related to the compaction density of the first active material layer 32, or it may be related to the mass of the material on the surface of the first current collector 31, but the embodiment of the present application is not limited thereto.

[0137] In some embodiments, the difference between the average thickness H1 of the portion 321 of the first active material layer 32 laid in the first internal region 311 and the average thickness H2 of the portion 322 laid in the first external region 312 is H, that is, H=H1-H2, the unit of H is μm, the average compaction density of the portion 321 of the first active material layer 32 laid in the first internal region 311 is Y, the unit of Y is g / cm3, H and Y satisfy Y=KH, where the value range of K is [0.1, 0.4].

[0138] Taking into account that the average compaction density Y of the portion 321 of the first active material layer 32 laid in the first internal area 311 has a certain range of values, therefore, if the proportional coefficient K is too large, the difference H will be too large. In this case, on the one hand, the average thickness H1 of the portion 321 of the first active material layer 32 laid in the first internal area 311 of the first current collector 31 may be too large, which will make the thickness of the first pole piece 3 too large, thereby affecting the energy density of the battery cell 20 formed by the processing of the first pole piece 3; on the other hand, the average thickness H2 of the portion 322 of the first active material layer 32 laid in the first external area 312 of the first current collector 31 may be too small, which will cause lithium precipitation and may also cause the structural strength of the first pole piece 3 to be weak, affecting the performance of the first pole piece 3.

[0139] On the contrary, if the proportional coefficient K is too small, the difference H will be too small. For example, the difference H may approach zero, which will make the thickness H1 of the portion 321 of the first active material layer 32 laid in the first internal area 311 and the thickness H2 of the portion 322 of the first active material layer 32 laid in the first external area 312 approximately equal. Correspondingly, the difference between the average compaction density of the portion 321 of the first active material layer 32 laid in the first internal area 311 and the average compaction density of the portion 322 of the first active material layer 32 laid in the first external area 312 will also be too small, which may affect the performance of the first electrode 3 and fail to solve the lithium plating problem well.

[0140] Therefore, the proportionality coefficient K of the embodiment of the present application should not be too small or too small. For example, the proportionality coefficient K can be specifically set to 0.1, 0.15, 0.2, 0.25, 0.3, 0.35 or 0.4 to improve the performance of the first electrode 3 and effectively solve the problem of lithium deposition.

[0141] In some embodiments, the average compaction density of the portion 321 of the first active material layer 32 laid on the first internal region 311 is Y, and the unit of Y is g / cm3. The total coating mass of the material laid on the surface of the first current collector 31 facing the first active material layer 32 is M, and the unit of M is g / 1540.25mm2. Y and M satisfy Y=NM, where the value range of N is [0.8, 8].

[0142] The material laid on the surface of the first current collector 31 facing the first active material layer 32 includes the first active material layer 32 and the first primer layer 33 laid on one side of the first current collector 31, and the mass of the first primer layer 33 may be zero. That is, if the first primer layer 33 is not provided between the first current collector 31 and the first active material layer 32, the total coating mass of the material laid on the surface of the first current collector 31 facing the first active material layer 32 includes the total mass of all the first active material layers 32 coated on one side of the first current collector 31; if the first primer layer 33 is provided between the first current collector 31 and the first active material layer 32, the total coating mass of the material laid on the surface of the first current collector 31 facing the first active material layer 32 includes the sum of the total mass of the first active material layer 32 coated on one side of the first current collector 31 and the total mass of the first primer layer 33 coated between the first current collector 31 and the first active material layer 32.

[0143] It should be understood that, when the total coating mass M of the material laid on the surface of the first current collector 31 facing the first active material layer 32 is constant, if the proportional coefficient N is too large, the average compaction density Y of the portion 321 of the first active material layer 32 laid in the first internal region 311 will be too large and the porosity will be too small. Correspondingly, the average compaction density of the portion 322 of the first active material layer 32 laid in the first external region 312 will be larger and the porosity will be smaller, which will increase the lithium precipitation phenomenon, increase the difficulty of processing the first pole piece 3, and increase the processing cost of the first pole piece 3. On the contrary, if the proportional coefficient N is too small, the average compaction density Y of the portion 321 of the first active material layer 32 laid in the first internal region 311 will be too small, which may fail to meet the design requirements of the first pole piece 3, reduce the performance of the first pole piece 3, and further reduce the performance of the electrode assembly 22 formed by the first pole piece 3.

[0144] Therefore, the value of the proportionality coefficient N should not be too large or too small. For example, the proportionality coefficient N can be specifically set to 0.8, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5 or 8 to improve the performance of the first pole piece 3.

[0145] In the embodiment of the present application, the above figures mainly take the case where the thickness of the portion 321 of the first active material layer 32 laid in the first inner region 311 of the first current collector 31 is substantially the same as an example, or differently therefrom, the thickness of the inner portion 321 can also be set to a step type. Similarly, the thickness of the portion 322 of the first active material layer 32 laid in the first outer region 312 of the first current collector 31 in the above figures is substantially the same, or differently therefrom, the thickness of the outer portion 322 can also be set to a step type.

[0146] Specifically, Fig.12 A partial cross-sectional schematic diagram of the first pole piece 3 of another embodiment of the present application is shown, for example, Fig.12 Can be Figures 3 to 5 A schematic diagram of a possible partial cross-section of the first pole piece 3 of the electrode assembly 22 , wherein the cross-section is perpendicular to the width direction Y of the first pole piece 3 .

[0147] like Fig.12 As shown, the thickness of the first active material layer 32 at different positions of the portion 321 of the first inner region 311 of the first current collector 31 may not be equal. For example, the thickness of the inner portion 321 of the first active material layer 32 may be gradually reduced from the direction away from the outer portion 322 to the direction close to the outer portion 322, so that the corresponding compaction density gradually increases to reduce lithium precipitation and improve the performance and service life of the electrode assembly 22 and the battery cell 22. Specifically, the thickness difference of the first active material layer 32 can be achieved by the thickness difference of the first current collector 31 and the thickness difference of the first primer layer 33. For example, a thickness difference can be set in the first inner region 311 of the first current collector 31, and the first primer layer 33 is not set in the first inner region 311; in addition, the first primer layer 33 is set in the first outer region 312 of the first current collector 31 to achieve that the average thickness H2 of the portion 322 of the first active material layer 32 laid in the first outer region 312 is minimized, while the average thickness of the portion 321 of the first active material layer 32 laid in the first inner region 311 of the first current collector 31 is larger, and in the portion 321 of the first active material layer 32 laid in the first inner region 311 of the first current collector 31: the average thickness H1' of the area away from the first outer region 312 is greater than the average thickness H1 of the area close to the first outer region 312, that is, H1>H1'>H2.

[0148] It should be understood that the above Figures 6 to 12 In each embodiment shown, the first active material layer 32 on any one side of the first current collector 31 is used as an example for description. The first active material layer 32 on the other side of the first current collector 31 can be flexibly arranged according to actual application.

[0149] Fig.13 A cross-sectional schematic diagram of a first pole piece 3 of another embodiment of the present application is shown, for example, Fig.13 Can be Figures 3 to 5 The schematic diagram of a possible cross section of the first pole piece 3 of the electrode assembly 22 shown in FIG. 2 is perpendicular to the width direction Y of the first pole piece 3. Fig.13 As shown, a first active material layer 32 with inconsistent compaction density according to an embodiment of the present application is disposed on one side of the first current collector 31 , for example, Fig.13 To set Figure 7 The first active material layer 32 shown in FIG. Figures 6 to 12 However, the other side of the first current collector 31 is provided with a first active material layer 32' with a uniform compaction density, for example, the other side of the first current collector 31 can be provided with a first active material layer 32' with a uniform thickness to simplify the structure and facilitate processing.

[0150] For example, unlike Fig.13 In the arrangement shown, the first active material layers 32 with inconsistent compaction densities of the embodiment of the present application can be respectively arranged on both sides of the first current collector 31. Specifically, the first pole piece 3 includes two first active material layers 32, and the first current collector 31 is located between the two first active material layers 32. The two first active material layers 32 can be any first active material layers 32 with inconsistent compaction densities described above, so as to simultaneously reduce the phenomenon of lithium deposition on both sides of the first pole piece 3, and further improve the performance of the electrode assembly 22 and the battery cell 20.

[0151] Fig.14 and Fig.15 Two possible cross-sectional schematic diagrams of the first electrode sheet 3 including two first active material layers 32 of the embodiment of the present application are shown, for example, Fig.14 and Fig.15 Can be respectively as Figures 3 to 5 A schematic diagram of a possible cross-section of the first pole piece 3 of the middle electrode assembly 22 , wherein the cross-section is perpendicular to the width direction Y of the first pole piece 3 .

[0152] In some embodiments, the first active material layer 32 may be disposed on both sides of the first current collector 31, and the arrangement is the same, so that the first electrode sheet 3 is a symmetrical structure relative to the plane perpendicular to the thickness direction Z, so as to facilitate processing and improve processing efficiency. Fig.14 and Fig.15 For example, Fig.14 By adopting Figure 7 Taking the arrangement of the first current collector 31 and two first active material layers 32 as an example, Fig.15 By adopting Fig. 9 The manner shown is to arrange the first current collector 31 , the two first primer layers 33 , and the two first active material layers 32 as an example, but the embodiments of the present application are not limited thereto.

[0153] Fig.16 Another possible cross-sectional schematic diagram of the first electrode sheet 3 including two first active material layers 32 of the embodiment of the present application is shown, for example, Fig.16 Can be Figures 3 to 5 A schematic diagram of a possible cross-section of the first pole piece 3 of the middle electrode assembly 22 , wherein the cross-section is perpendicular to the width direction Y of the first pole piece 3 .

[0154] In some embodiments, the first active material layer 32 is disposed on both sides of the first current collector 31, but the arrangement method and / or the size of the arrangement may be different, so that the first electrode sheet 3 is an asymmetric structure relative to the plane perpendicular to the thickness direction Z, which is more flexible and has more applications. Fig.16 As shown, Fig.16 By using Figure 8 and Fig. 9 The first current collector 31, two first undercoat layers 33 and two first active material layers 32 are arranged in the manner shown in the embodiment shown in the figure. For another example, the arrangement shown in any two other embodiments in the present application can also be adopted. For another example, the arrangement of the same embodiment can also be adopted, but the thickness of the corresponding areas of the two first active material layers 32 are arranged to be different, and the embodiments of the present application are not limited thereto.

[0155] In some embodiments, the average thickness of the portion 303 of the first pole piece 3 corresponding to the first inner region 311 is substantially equal to the average thickness 304 of the portion corresponding to the first outer region 312. Figures 14 to 16 As shown, the portion 303 of the first pole piece 3 corresponding to the first internal region 311 of the first current collector 31 can be called the internal region 303 of the first pole piece 3, and the portion 304 of the first pole piece 3 corresponding to the first external region 312 of the first current collector 31 can be called the external region 304 of the first pole piece 3. The average thickness of the internal region 303 of the first pole piece 3 and the average thickness of the external region 304 of the first pole piece 3 are both equal to H0, so that the two outer surfaces of the first pole piece 3 are relatively flat, which is convenient for subsequent processing into the electrode assembly 22, so that the spacing between different pole piece layers in the electrode assembly 22 is relatively uniform, reducing the lithium plating problem caused by the large difference in spacing, which can not only improve the space utilization and energy density of the battery cell 20, but also reduce lithium plating during the long-term charge and discharge cycle of the battery cell 20, thereby improving the cycle life and safety of the battery cell 20.

[0156] In the embodiments of the present application, Figures 13 to 16As shown, the average thickness H4 of the first outer region 312 of the first current collector 31 can be greater than the average thickness H3 of the first inner region 311. For example, the thickness difference of different regions of the first current collector 31 can be achieved by increasing the thickness of the first outer region 312, or the thickness difference of different regions of the first current collector 31 can be achieved by thinning the first inner region 311 of the first current collector 31; or, the thickness of different regions of the first current collector 31 can be set equal, that is, the average thickness H4 of the first outer region 312 can be equal to the average thickness H3 of the first inner region 311, and the embodiments of the present application are not limited thereto. Among them, for the first current collector 31 in different embodiments, the values ​​of the thickness of different regions of the first current collector 31 can be flexibly set according to actual applications.

[0157] In some embodiments, if the first pole piece 3 is a positive pole piece, correspondingly, the value range of the thickness of each partial region of the first current collector 31 is generally set to [5μm, 20μm], for example, the value range of the average thickness H4 of the first outer region 312 and / or the value range of the average thickness H3 of the first inner region 311 can be generally set to [5μm, 20μm]. If the first pole piece 3 is a negative pole piece, correspondingly, the value range of the thickness of each partial region of the first current collector 31 is generally set to [5μm, 10μm], for example, the value range of the average thickness H4 of the first outer region 312 and / or the value range of the average thickness H3 of the first inner region 311 can be generally set to [5μm, 10μm].

[0158] If the thickness of the first current collector 31 is too large, the thickness of the first pole piece 3 will be too large accordingly, which may reduce the space occupied by the electrode assembly 22 formed by the first pole piece 3 in the battery cell 20, thereby reducing the energy density of the battery cell 20. Therefore, even if one side or two opposite sides of the first outer region 312 of the first current collector 31 are thickened, the average thickness H4 of the first outer region 312 is usually not too large.

[0159] On the contrary, if the thickness of the first current collector 31 is too small, the thickness of the first pole piece 3 will be too small, which will reduce the structural strength and stability of the first pole piece 3, and further reduce the structural strength and stability of the electrode assembly 22 formed by the first pole piece 3. Therefore, even if one side or two opposite sides of the first inner region 311 of the first current collector 31 are thinned, the average thickness H3 of the first inner region 311 is usually not too large, for example, usually not less than 5 μm.

[0160] It should be understood that in the above, the first pole piece 3 included in the electrode assembly 22 of the embodiment of the present application is mainly used as an example for description. The second pole piece 4 of the embodiment of the present application can be arranged in a different manner from the first pole piece 3. For example, the second pole piece 4 can be arranged in a manner in which the compaction density is evenly distributed, or the second pole piece 4 of the embodiment of the present application can also be arranged in a manner similar to the first pole piece 3. Specifically, the second pole piece 4 includes a second current collector and a second active material layer laid on the surface of the second current collector, the average compaction density of the portion of the second active material layer laid on the second inner region of the second current collector is less than the average compaction density of the portion laid on the second outer region of the second current collector, and the second inner region is located on the side of the second outer region close to the winding axis of the electrode assembly 22.

[0161] It should be understood that the above description of the first pole piece 3 in the embodiment of the present application is also applicable to the second pole piece 4. Figures 5 to 16 The embodiments shown can be applicable to the second pole piece 4, wherein the first current collector 31 corresponds to the second current collector, the first active material layer 32 corresponds to the second active material layer, and the first base coating layer 33 corresponds to the second base coating layer included in the second pole piece 4. For the sake of brevity, they are not described one by one here.

[0162] For example, the second pole piece 4 includes two second active material layers, and the second current collector is located between the two second active material layers, that is, the second pole piece 4 may correspond to Figures 14 to 16 The first pole piece 4 shown is used to improve the performance of the electrode assembly 22 and the battery cell 20 formed by winding the first pole piece 3 and the second pole piece 4.

[0163] Therefore, the average compaction density of the part of the second active material layer of the second pole piece 4 of the embodiment of the present application located in the inner circle area of ​​the electrode assembly 22 is less than the average compaction density of the part located in the outer circle area, and the porosity of the part of the second active material layer located in the inner circle area is also greater than the porosity of the part located in the outer circle area. In this way, the inner circle area with a larger porosity can accommodate more electrolyte, which can effectively solve the problem of lithium deposition caused by the easy extrusion of the electrolyte in the inner circle area, that is, it can effectively reduce the lithium deposition phenomenon of the electrode assembly, thereby improving the performance and cycle life of the battery cell.

[0164] In addition, in order to further reduce the lithium plating phenomenon, if the first pole piece 3 is a negative pole piece and the second pole piece 4 is a positive pole piece, then when the compaction density of the first active material layer 32 of the first pole piece 3 is set to be unevenly distributed, the second pole piece 4 can adopt a similar method, and also set the compaction density distribution of the second active material layer to be uneven, or the compaction density distribution of the second active material layer can also be set to be uniform, and the embodiments of the present application are not limited to this. However, if the first pole piece 3 is a positive pole piece and the second pole piece 4 is a negative pole piece, then when the compaction density of the first active material layer 32 of the first pole piece 3 is set to be unevenly distributed, the corresponding second pole piece 4 usually also needs to adopt a similar method, and also set the compaction density distribution of the second active material layer to be uneven, so as to reduce lithium plating.

[0165] For example, the following uses the comparison between multiple embodiments as an example to describe the differences between different embodiments.

[0166] In the first embodiment, the first pole piece 3 is set as the positive pole piece, the second pole piece 4 is set as the negative pole piece, and both pole pieces are made of Fig.15 Specifically, for the positive electrode sheet, the activated carbon material SP, calcium hydroxide and polyacrylate are stirred and mixed in a ratio of 40%, 6% and 54% respectively to obtain a slurry of the first primer layer 33; the slurry of the first primer layer 33 is sized according to the length of the positive electrode sheet of the cylindrical electrode assembly 22, such as Fig.15 As shown, it is coated on the aluminum foil of the first outer region 312, wherein the length L2 of the first outer region 312 is equal to the length L1 of the first inner region 311, and each occupies 1 / 2 of the total length L0 of the positive electrode sheet. The positive electrode active material lithium iron phosphate, the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) are dissolved in the solvent N-methylpyrrolidone (NMP) at a mass ratio of 97:0.8:2.2, and the slurry of the positive electrode active material layer is obtained after sufficient stirring and mixing. The slurry of the positive electrode active material layer is coated on the slurry of the first primer layer and the first inner region 311 to obtain as shown. Fig.15 The positive electrode is shown.

[0167] Similarly, for the negative electrode, the same Fig.15 In the embodiment shown, SP, CMC and SBR are mixed in a ratio of 60%, 10% and 30% respectively to obtain a slurry of the second primer layer, and the slurry of the second primer layer is sized according to the length of the positive electrode sheet of the cylindrical electrode assembly 22, such as Fig.15As shown, the aluminum foil is coated on the second outer region, wherein the length of the second outer region is also equal to the length of the second inner region, and each occupies 1 / 2 of the total length of the negative electrode sheet. The artificial graphite of the negative electrode active material layer, the conductive agent acetylene black, the binder styrene butadiene rubber (SBR) and the thickener sodium carboxymethyl cellulose (CMC) are dissolved in the solvent deionized water according to the mass ratio of 96.5:0.7:1.8:1, and the slurry of the negative electrode active material layer is obtained after mixing evenly. The slurry of the negative electrode active material layer is coated on the second primer layer to obtain the negative electrode sheet.

[0168] The positive electrode sheet, the isolation film 5, and the negative electrode sheet are stacked in order, so that the isolation film 5 is located between the positive electrode sheet and the negative electrode sheet and can isolate the positive electrode sheet from the negative electrode sheet; then the stacked components are wound to obtain the electrode assembly 22; the electrode assembly 22 is set in a shell, and after drying, a LiPF6 electrolyte with a mass fraction of 11% is injected; after processes such as formation and standing, a battery cell 20 is obtained.

[0169] In the second embodiment, different from the above-mentioned first embodiment, the ratio of the length L1 of the first internal area 311 in the positive electrode plate to the length L2 of the first external area 312 is set to 1:2, and the ratio of the length of the second internal area in the negative electrode plate to the length of the second external area is also set to 1:2, and the rest is exactly the same as the first embodiment.

[0170] In the third embodiment, the arrangement of the positive electrode plate is consistent with that of the first embodiment, but the negative electrode plate is not partially coated with a primer layer, but the primer layer is provided in the entire area, that is, the compaction density of the active material layer of the negative electrode plate is evenly distributed, and the other arrangements are consistent with the first embodiment.

[0171] In the fourth embodiment, contrary to the arrangement of the third embodiment, the arrangement of the negative electrode plate is consistent with that of the first embodiment, but the positive electrode plate does not adopt the method of locally coating the primer layer, but the primer layer is provided in the entire area, that is, the compaction density of the active material layer of the positive electrode plate is evenly distributed, and the other arrangements are consistent with the first embodiment.

[0172] In the fifth embodiment, neither the positive electrode plate nor the negative electrode plate adopts the method of locally coating the primer layer, but the primer layer is provided in the entire area, that is, the compaction density of the active material layer of the positive electrode plate and the negative electrode plate is evenly distributed, and the other settings are consistent with the first embodiment.

[0173] The experimental results of each embodiment are shown in Table 1. As shown in Table 1, when the power battery health state (State of Health, SOH) is 80% and 70% respectively, the inner ring lithium deposition phenomenon of the electrode assembly 22 of the fifth embodiment is the most serious, followed by the third embodiment; while the inner ring lithium deposition phenomenon of the electrode assembly 22 of the first embodiment and the second embodiment is more ideal.

[0174] Table 1

[0175]

[0176] Therefore, in the embodiment of the present application, for the wound electrode assembly 22, at least one of the two pole pieces included therein can be set to have an uneven compaction density distribution. Taking the first pole piece 3 as an example, the average compaction density of the portion 321 of the first active material layer 32 located in the inner circle area of ​​the electrode assembly 22 is less than the average compaction density of the portion 322 located in the outer circle area, and the porosity of the portion 321 of the first active material layer 32 located in the inner circle area is also greater than the porosity of the portion 322 located in the outer circle area. In this way, the inner circle area with a larger porosity can accommodate more electrolyte, which can effectively solve the problem of lithium deposition caused by the easy extrusion of the electrolyte in the inner circle area, that is, it can effectively reduce the lithium deposition phenomenon of the electrode assembly 22, thereby improving the performance and cycle life of the battery cell 20.

[0177] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and parts thereof may be replaced with equivalents without departing from the scope of the present application. In particular, the various technical features mentioned in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. An electrode assembly, characterized in that: include: A first pole piece (3) and a second pole piece (4) with opposite polarities, wherein the first pole piece (3) and the second pole piece (4) are wound to form the electrode assembly, The first pole piece (3) comprises a first current collector (31) and a first active material layer (32) laid on the surface of the first current collector (31). The average compaction density of a portion (321) of the first active material layer (32) laid on the first inner region (311) of the first current collector (31) is less than the average compaction density of a portion (322) laid on the first outer region (312) of the first current collector (31), and the first inner region (311) is located on a side of the first outer region (312) close to the winding axis of the electrode assembly.

2. The electrode assembly according to claim 1, wherein The average thickness of the portion (321) of the first active material layer (32) laid in the first inner region (311) is greater than the average thickness of the portion (322) laid in the first outer region (312).

3. The electrode assembly according to claim 1 or 2, characterized in that: The average thickness of the first inner region (311) is smaller than the average thickness of the first outer region (312).

4. The electrode assembly according to claim 3, characterized in that The average thickness of the first outer region (312) is in the range of [5 μm, 10 μm].

5. The electrode assembly according to claim 3 or 4, characterized in that: The average thickness of the first inner region (311) is in the range of [2 μm, 6 μm].

6. The electrode assembly according to any one of claims 1 to 5, characterized in that: The first pole piece (3) further comprises: A first undercoat layer (33) is provided in at least a portion of the region between the first current collector (31) and the first active material layer (32).

7. The electrode assembly according to claim 6, characterized in that The first inner region (311) is in direct contact with the active material layer (32), and the first primer layer (33) is provided between the first outer region (312) and the active material layer (32).

8. The electrode assembly according to claim 6, wherein: The first primer layer (33) is provided in the entire region between the first current collector (31) and the first active material layer (32).

9. The electrode assembly according to claim 8, characterized in that The average thickness of the portion (331) of the first primer layer (33) laid in the first inner region (311) is smaller than the average thickness of the portion (332) laid in the first outer region (312).

10. The electrode assembly according to any one of claims 1 to 9, characterized in that: Along the winding direction of the electrode assembly, the ratio of the total length of the first outer region (312) to the total length of the first pole piece (3) is in the range of [1 / 3, 2 / 3].

11. The electrode assembly according to any one of claims 1 to 10, characterized in that: Along the winding direction of the electrode assembly, the ratio of the total length of the first inner region (311) to the total length of the first pole piece (3) is in the range of [1 / 3, 1 / 2].

12. The electrode assembly according to any one of claims 1 to 11, characterized in that: The difference between the average thickness of the portion (321) of the first active material layer (32) laid in the first inner region (311) and the average thickness of the portion (322) laid in the first outer region (312) is H, where H is expressed in μm, and the average compacted density of the portion (321) of the first active material layer (32) laid in the first inner region (311) is Y, where Y is expressed in g / cm 3 , H and Y satisfy Y=KH, where the value range of K is [0.1, 0.4].

13. The electrode assembly according to any one of claims 1 to 12, characterized in that: The average compaction density of the portion (321) of the first active material layer (32) laid in the first inner region (311) is Y, where the unit of Y is g / cm 3 The total coating mass of the material laid on the surface of the first current collector (31) facing the first active material layer (32) is M, and the unit of M is g / 1540.25mm 2 , Y and M satisfy Y=NM, where the value range of N is [0.8, 8].

14. The electrode assembly according to any one of claims 1 to 13, characterized in that: The average thickness of the portion (303) of the first pole piece (3) corresponding to the first inner region (311) is substantially equal to the average thickness (304) of the portion corresponding to the first outer region (312).

15. The electrode assembly according to any one of claims 1 to 14, characterized in that: The first pole piece (3) comprises two first active material layers (32), and the first current collector (31) is located between the two first active material layers (32).

16. The electrode assembly according to any one of claims 1 to 15, characterized in that The second pole piece (4) comprises a second current collector and a second active material layer laid on the surface of the second current collector. The average compaction density of the portion of the second active material layer laid in the second inner region of the second current collector is less than the average compaction density of the portion laid in the second outer region of the second current collector, and the second inner region is located on the side of the second outer region close to the winding axis of the electrode assembly.

17. The electrode assembly according to claim 16, wherein: The second pole piece (4) comprises two second active material layers, and the second current collector is located between the two second active material layers.

18. The electrode assembly according to any one of claims 1 to 17, characterized in that The first pole piece (3) is a negative pole piece, and the second pole piece (4) is a positive pole piece.

19. The electrode assembly according to any one of claims 1 to 18, characterized in that The electrode assembly is cylindrical.

20. A battery cell, characterized in that: include: The electrode assembly according to any one of claims 1 to 19.

21. A battery, characterized in that: include: A plurality of battery cells, each comprising the electrode assembly according to any one of claims 1 to 19.

22. An electrical device, characterized in that: include: The battery cell according to claim 20 and / or the battery according to claim 21, wherein the battery cell and the battery are used to provide electrical energy.

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