Electrode assembly, battery cell, battery and electric device

Abstract

The embodiment of the invention provides an electrode assembly, a battery monomer, a battery and a power utilization device. The electrode assembly comprises a positive pole piece, a negative pole piece and an isolation assembly, wherein the isolation assembly is used for isolating the positive pole piece from the negative pole piece. And the positive pole piece, the isolation assembly and the negative pole piece are wound to form a bending area. The isolation assembly comprises a base body area and a reinforcing area connected to the base body area, and the thickness of the reinforcing area is larger than that of the base body area. The positive pole piece comprises a first bending part which is positioned in the bending area and is adjacent to the reinforcing area; the negative pole piece comprises a second bending part positioned in the bending area; the two sides of the first bent part are each provided with a reinforcing area and a second bent part. The total thickness of the reinforcing area located on the inner side of the first bending part is larger than or equal to the total thickness of the reinforcing area located on the outer side of the first bending part.

Description

[0001] This application is a divisional application of the invention titled "Electrode Assembly, Battery Cell, Battery and Electrical Device" with the application number 202280005439.6, the filing date of May 20, 2022, and the applicant Contemporary Amperex Technology Co., Limited. Technical Field

[0002] This application relates to the field of battery technologies, and more particularly, to an electrode assembly, a battery cell, a battery and an electrical device. Background Art

[0003] Battery cells are widely used in electronic devices, such as mobile phones, laptop computers, battery-powered vehicles, electric vehicles, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes and power tools, etc. Battery cells may include nickel-cadmium battery cells, nickel-metal hydride battery cells, lithium-ion battery cells and secondary alkaline zinc-manganese battery cells, etc.

[0004] In the development of battery technologies, how to improve the safety of battery cells is a research direction in battery technologies. Summary of the Invention

[0005] This application provides an electrode assembly, a battery cell, a battery and an electrical device, which can improve safety.

[0006] In a first aspect, an embodiment of this application provides an electrode assembly, including a positive electrode tab, a negative electrode tab and a separator assembly. The separator assembly is used to separate the positive electrode tab and the negative electrode tab. The separator assembly includes a matrix region and a reinforcing region connected to the matrix region. The thickness of the reinforcing region is greater than that of the matrix region. At least a part of the reinforcing region is located between adjacent positive electrode tab and negative electrode tab.

[0007] In the above technical solution, the reinforcing region can be used to correspond to the position of the negative electrode tab where lithium is likely to deposit. In this way, when lithium deposits on the negative electrode tab, the reinforcing region can effectively separate the positive electrode tab and the negative electrode tab, reducing the risk of lithium dendrites passing through the separator assembly, and improving the lifespan and safety. Compared with the reinforcing region, the matrix region may have a smaller thickness, which can reduce the amount of the separator assembly used, lower the cost and improve the energy density of the electrode assembly.

[0008] In some embodiments, the thickness of the reinforcing region is 2 μm - 100 μm.

[0009] The smaller the thickness of the strengthening region, the higher the energy density of the electrode assembly, but the higher the risk of lithium dendrites passing through the strengthening region. The larger the thickness of the strengthening region, the lower the energy density of the electrode assembly, but the lower the risk of lithium dendrites passing through the strengthening region, and the higher the safety of the electrode assembly. The above technical solution limits the thickness of the strengthening region to 2 μm - 100 μm to balance the energy density and safety of the electrode assembly.

[0010] In some embodiments, the positive electrode sheet, the separator assembly, and the negative electrode sheet are wound to form a bending region, and at least a part of the strengthening region is disposed in the bending region.

[0011] The above technical solution disposes at least a part of the strengthening region in the bending region where lithium precipitation is likely to occur. Even if lithium precipitation occurs in the bending region, the strengthening region can block lithium dendrites, reduce the probability of conduction between the positive electrode sheet and the negative electrode sheet, effectively reduce the short-circuit risk, and improve the service life and safety of the electrode assembly.

[0012] In some embodiments, the positive electrode sheet includes a first bending portion located in the bending region and adjacent to the strengthening region, and the negative electrode sheet includes a second bending portion adjacent to the first bending portion. The strengthening region includes a plurality of bending layers, and the plurality of bending layers are located in the bending region and stacked between the first bending portion and the second bending portion.

[0013] In the above technical solution, the plurality of bending layers can block lithium dendrites when lithium precipitation occurs in the second bending portion, reduce the risk of lithium dendrites contacting the first bending portion, and improve safety.

[0014] In some embodiments, the strengthening region and the second bending portion are provided at least on the inner side of the first bending portion.

[0015] The curvature of the second bending portion located on the inner side of the first bending portion is greater than that of the first bending portion. Therefore, the active material is more likely to fall off during the bending process of the second bending portion. That is to say, lithium precipitation is more likely to occur in the second bending portion on the inner side of the first bending portion. The strengthening region of the above technical solution can separate the first bending portion and the second bending portion located on the inner side of the first bending portion. Even if lithium precipitation occurs in the second bending portion, it can reduce the probability of lithium dendrites passing through the strengthening region, reduce the short-circuit risk, and improve safety.

[0016] In some embodiments, the first bent portion includes a first current collector and a first active material layer disposed on the surface of the first current collector, and the thickness of the first active material layer is h1. The second bent portion includes a second current collector and a second active material layer disposed on the surface of the second current collector, the thickness of the second active material layer is h2, the thickness of the bent layer is h3, and the thickness of the second current collector is h4. In the thickness direction of the first bent portion, the maximum distance between the first bent portion and the second bent portion is X. The number of layers of the bent layer between the first bent portion and the second bent portion is Y, and Y is a positive integer greater than 1. The active material capacity per unit area of the first active material layer is A1, and the active material capacity per unit area of the second active material layer is A2, and A2 / A1≥1. h1, h2, h3, h4, X, and Y satisfy:

[0017] The fewer the number of layers of the bent layer in the strengthening area, the higher the risk of lithium dendrites passing through the strengthening area; the more the number of layers of the bent layer in the strengthening area, the more complex the structure of the isolation component and the lower the energy density of the electrode component. The above technical solution can set the number of layers of the bent layer according to the above formula to balance the safety and energy density of the electrode component.

[0018] In some embodiments, the first bent portion includes a first current collector and a first active material layer disposed on the surface of the first current collector, and the thickness of the first active material layer is h1. The second bent portion includes a second current collector and a second active material layer disposed on the surface of the second current collector, the thickness of the second active material layer is h2, the thickness of the bent layer is h3, and the thickness of the second current collector is h4. In the thickness direction of the first bent portion, the maximum distance between the first bent portion and the second bent portion is X. The number of layers of the bent layer between the first bent portion and the second bent portion is Y, and Y is a positive integer greater than 1. The active material capacity per unit area of the first active material layer is A1, and the active material capacity per unit area of the second active material layer is A2, and A2 / A1<1. h1, h2, h3, h4, X, and Y satisfy:

[0019] In the above technical solution, the number of layers of the bent layer can be set according to the above formula to balance the safety and energy density of the electrode component.

[0020] In some embodiments, the value of h3 is 1 μm - 20 μm to balance the safety and energy density of the electrode component.

[0021] In some embodiments, the value of X is 10 μm - 5000 μm.

[0022] In some embodiments, the positive electrode tab includes a plurality of positive electrode bent portions arranged along the winding direction, and at least the positive electrode bent portion formed by the first bending of the positive electrode tab is set as the first bent portion.

[0023] The curvature of the positive electrode bending part formed by the first bending of the positive electrode tab is relatively large. During charging, lithium plating is more likely to occur on the negative electrode tab adjacent to the positive electrode bending part formed by the first bending of the positive electrode tab. In the above technical solution, the positive electrode bending part formed by the first bending of the positive electrode tab is set as the first bending part, so that the strengthening area can effectively isolate the positive electrode bending part formed by the first bending of the positive electrode tab from the lithium dendrites, reduce the short-circuit risk, and improve safety.

[0024] In some embodiments, the positive electrode bending part formed by the second bending of the positive electrode tab is also set as the first bending part.

[0025] In the above technical solution, the positive electrode bending part formed by the second bending of the positive electrode tab is set as the first bending part, so that the strengthening area can effectively isolate the positive electrode bending part formed by the second bending of the positive electrode tab from the lithium dendrites, reduce the short-circuit risk, and improve safety.

[0026] In some embodiments, the total thickness of the strengthening area located inside the positive electrode bending part formed by the first bending of the positive electrode tab is T1, and the total thickness of the strengthening area located inside the positive electrode bending part formed by the second bending of the positive electrode tab is T2, and T1≥T2.

[0027] The above technical solution makes T1≥T2 to reduce the risk of conduction between the positive electrode bending part formed by the first bending of the positive electrode tab and the lithium dendrites, and improve the safety of the battery cell.

[0028] In some embodiments, strengthening areas and second bending parts are arranged on both sides of the first bending part, and the total thickness of the strengthening area located inside the first bending part is greater than or equal to the total thickness of the strengthening area located outside the first bending part, so as to reduce the risk of conduction between the first bending part and the lithium dendrites and improve the safety of the battery cell.

[0029] In some embodiments, the positive electrode tab includes a plurality of positive electrode bending parts arranged along the winding direction, and at least the positive electrode bending part formed by the last bending of the positive electrode tab is set as the first bending part, so as to reduce the risk of conduction between the positive electrode bending part formed by the last bending of the positive electrode tab and the lithium dendrites and improve the safety of the battery cell.

[0030] In some embodiments, after the positive electrode tab, the separator assembly, and the negative electrode tab are wound, a flat area is also formed, and the flat area is connected to the bending area. At least part of the matrix area is arranged in the flat area.

[0031] The positive electrode plate and the negative electrode plate located in the flat region are both in a flat state. The active material in the flat region is not prone to falling off, and the negative electrode plate in the flat region is not prone to lithium deposition problems. Therefore, even if the above technical solution sets the substrate region to the flat region, the insulation between the positive and negative electrode plates can be improved, and the short-circuit risk can be reduced.

[0032] In some embodiments, both the strengthening region and the substrate region are provided in multiple numbers, and the multiple strengthening regions and the multiple substrate regions are alternately arranged along the winding direction.

[0033] In the above technical solution, the multiple strengthening regions can respectively correspond to the multiple positive bending portions of the positive electrode plate, so as to reduce the short-circuit risk of the multiple positive bending portions of the positive electrode plate and improve safety.

[0034] In some embodiments, along the winding direction, the thickness of the multiple strengthening regions gradually decreases from inside to outside.

[0035] Along the winding direction, the curvature of the positive bending portions of the positive electrode plate from inside to outside gradually decreases, and the risk of contact with lithium dendrites also gradually decreases. The above technical solution can increase the thickness of the strengthening region in the area with a high short-circuit risk and decrease the thickness of the strengthening region in the area with a low short-circuit risk, which can improve safety and save the usage amount of the isolation component.

[0036] In some embodiments, along the winding direction, the thickness difference between adjacent strengthening regions is 0.5 μm - 10 μm.

[0037] In some embodiments, the strengthening region is provided with a multi-layer structure, and the substrate region is provided with a single-layer structure.

[0038] In the above technical solution, on the premise of the same thickness, compared with the strengthening region with a single-layer structure, the strengthening region with a multi-layer structure can more effectively block lithium dendrites, reduce the short-circuit risk, and improve safety. On the premise of meeting the strength requirements, compared with the strengthening region with a single-layer structure, the strengthening region with a multi-layer structure can adopt a smaller thickness, which can reduce the usage amount of the isolation component and improve the energy density of the electrode assembly.

[0039] In some embodiments, the isolation component includes a first isolation layer and a second isolation layer. The first isolation layer is used to insulate and isolate the positive electrode plate and the negative electrode plate. At least a part of the second isolation layer is located between the positive electrode plate and the negative electrode plate and is stacked with the first isolation layer. The overlapping region of the first isolation layer with the second isolation layer and the second isolation layer form the strengthening region of the isolation component, and the non-overlapping region of the first isolation layer with the second isolation layer forms the substrate region.

[0040] In the above technical solution, an additional second isolation layer is added to the electrode assembly to form a strengthening region with a larger thickness on the isolation component, thereby reducing the short-circuit risk caused by lithium deposition and improving safety.

[0041] In some embodiments, the thickness of the second isolation layer is less than or equal to the thickness of the first isolation layer.

[0042] In the above technical solution, the first isolation layer and the second isolation layer can function as multi-layer protection. Therefore, the added second isolation layer can have a thickness not greater than that of the first isolation layer to reduce the amount of the second isolation layer used.

[0043] In some embodiments, at least a part of the second isolation layer is separated from the first isolation layer in the stacking direction of the first isolation layer and the second isolation layer.

[0044] When the first isolation layer is stretched under the extrusion of the lithium layer, the separated part of the second isolation layer from the first isolation layer is less affected by the first isolation layer, the degree of stretching of the second isolation layer is smaller, and the risk of generating defects is lower. The above technical solution can effectively reduce the risk of lithium dendrites passing through the first isolation layer and the second isolation layer and improve safety.

[0045] In some embodiments, the positive electrode sheet, the isolation component, and the negative electrode sheet are wound to form a bent region and a flat region, and the flat region is connected to the bent region. A part of the second isolation layer is located in the bent region, and another part of the second isolation layer is located in the flat region. In the bent region, the second isolation layer is separated from the first isolation layer. In the flat region, the second isolation layer is attached to the first isolation layer.

[0046] In the above technical solution, the risk of lithium precipitation in the bent region is relatively high. Separating the second isolation layer in the bent region from the first isolation layer can effectively reduce the risk of lithium dendrites passing through the first isolation layer and the second isolation layer and improve safety. In the flat region, the second isolation layer is attached to the first isolation layer, which can reduce the movement amplitude of the second isolation layer in the winding direction and reduce the risk of dislocation of the second isolation layer.

[0047] In some embodiments, the second isolation layer is formed by folding the end of the first isolation layer.

[0048] In the above technical solution, the second isolation layer directly extends from the end of the first isolation layer, eliminating the need to separately add and fix the second isolation layer, thereby making the winding process more convenient and improving the integrity of the electrode assembly.

[0049] In some embodiments, the positive electrode sheet, the isolation component, and the negative electrode sheet are wound, and the electrode assembly includes a starting section in the winding direction, and the end of the first isolation layer is located in the starting section.

[0050] In the above technical solution, the second isolation layer can extend from the starting section along the winding direction and pass through the positive electrode bending portion formed by the first bending of the positive electrode tab, which can reduce the risk of lithium dendrites passing through both the first isolation layer and the second isolation layer simultaneously and contacting the positive electrode bending portion of the positive electrode tab, improve safety, and can also reduce the length that the second isolation layer needs to extend, save the amount used, and reduce costs.

[0051] In some embodiments, the positive electrode tab, the isolation assembly, and the negative electrode tab are wound to form a bending region. The bending region includes a first bending portion close to the starting section along the winding direction. The first bending portion is provided with a first isolation layer and a second isolation layer, and the second isolation layer extends from the end of the first isolation layer and extends beyond the first bending portion.

[0052] In the above technical solution, at the first bending portion, the positive electrode tab and the negative electrode tab have the largest bending curvature, and during charging, the risk of lithium precipitation on the negative electrode tab is the highest. The second isolation layer extends and extends beyond the first bending portion. The first isolation layer and the second isolation layer can at least protect the first bending portion where lithium precipitation is most likely to occur, and at the same time can save the use of the second isolation layer, thereby improving the safety and service life of the electrode assembly while saving costs.

[0053] In some embodiments, the positive electrode tab, the isolation assembly, and the negative electrode tab are wound to form a bending region. The bending region includes a plurality of bending portions arranged along the winding direction. The electrode assembly includes a plurality of second isolation layers, and the first isolation layer and the plurality of second isolation layers are provided on at least one of the plurality of bending portions.

[0054] In the above technical solution, by providing the second isolation layer at some or all positions of the plurality of bending portions, the risk of short circuit at the bending portions can be effectively reduced, and safety can be improved.

[0055] In some embodiments, the plurality of second isolation layers are arranged at intervals along the winding direction.

[0056] The above technical solution can make the setting method of the second isolation layer more flexible, that is, the second isolation layer can be arbitrarily set to the position where the number of isolation layers needs to be increased, and at the same time, the waste caused by adding the second isolation layer at the position where the number of isolation layers does not need to be increased can be reduced, and the energy density can be improved.

[0057] In some embodiments, the electrode assembly includes a starting section along the winding direction. The plurality of bending portions include a first bending portion and a second bending portion. Along the winding direction, the first bending portion is closer to the starting section than the second bending portion. The thickness of the second isolation layer provided at the first bending portion is greater than the thickness of the second isolation layer provided at the second bending portion.

[0058] The above technical solution can strengthen the protection at the first bending part where short - circuit is more likely to occur, improve safety, and save the usage amount of the second isolation layer.

[0059] In some embodiments, the first isolation layer includes two surfaces along its thickness direction, and a plurality of second isolation layers are located on the same surface of the first isolation layer. When the first isolation layer is tensioned, the influence of the second isolation layer on the distance between the positive electrode plate and the negative electrode plate is reduced, the risk of lithium deposition is lowered, and safety is improved.

[0060] In some embodiments, a plurality of second isolation layers are bonded to the surface of the first isolation layer, which can reduce the risk of the second isolation layer shifting in position during the charge - discharge process of the electrode assembly and ensure the isolation effect of the second isolation layer.

[0061] In a second aspect, an embodiment of the present application provides a battery cell, including a housing and the electrode assembly of any one of the embodiments in the first aspect, and the electrode assembly is accommodated in the housing.

[0062] In a third aspect, an embodiment of the present application provides a battery, including a plurality of battery cells in the second aspect.

[0063] In a fourth aspect, an embodiment of the present application provides an electrical device, including the battery cell in the second aspect, and the battery cell is used to provide electrical energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required to be used in the embodiments of the present application. Obviously, the following described drawings are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the drawings.

[0065] Figure 1 It is a schematic structural diagram of a vehicle provided for some embodiments of the present application;

[0066] Figure 2 It is an explosion schematic diagram of a battery provided for some embodiments of the present application;

[0067] Figure 3 It is an explosion schematic diagram of a battery cell provided for some embodiments of the present application;

[0068] Figure 4 It is a schematic structural diagram of an electrode assembly provided for some embodiments of the present application;

[0069] Figure 5 For Figure 4 a partially enlarged schematic diagram of the electrode assembly shown;

[0070] Figure 6 For Figure 5Enlarged schematic view at box P;

[0071] Figure 7 is Figure 4 Schematic structural view of the electrode assembly shown before winding;

[0072] Figure 8 is Figure 7 Schematic structural view of the isolation assembly shown;

[0073] Figure 9 Schematic structural view of the isolation assembly of the electrode assembly provided by some other embodiments of the present application before winding;

[0074] Figure 10 Schematic structural view of the electrode assembly provided by some other embodiments of the present application;

[0075] Figure 11 is Figure 10 Enlarged partial schematic view of the electrode assembly shown;

[0076] Figure 12 is Figure 10 Schematic structural view of the electrode assembly shown before winding;

[0077] Figure 13 Schematic structural view of the electrode assembly provided by some other embodiments of the present application before winding;

[0078] Figure 14 Schematic structural view of the electrode assembly provided by some other embodiments of the present application.

[0079] Reference numerals in the specific embodiments are as follows:

[0080] 1, vehicle; 2, battery; 3, controller; 4, motor; 5, box; 5a, first box part; 5b, second box part; 5c, accommodation space; 6, battery cell; 10, electrode assembly; 100, starting section; 20, outer shell; 21, housing; 22, end cover; 30, electrode terminal; 11, positive electrode plate; 111, first bending part; 1111, first current collecting part; 1112, first active material layer; 11a, positive electrode bending part; 12, negative electrode plate; 121, second bending part; 1211, second current collecting part; 1212, second active material layer; 13, isolation assembly; 131, first isolation layer; 132, second isolation layer; 133, base film; 134, insulating layer; 13a, strengthening area; 13b, matrix area; 14, bending layer; A, straight area; B, bending area; B1, first bending position; B2, second bending position; W, winding direction. Specific embodiments

[0081] To make the objectives, technical solutions and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of this application. Apparently, the described embodiments are some, but not all, of the embodiments of this application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in this application without creative efforts shall fall within the scope of protection of this application.

[0082] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs; 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" and any variations thereof in the specification and claims of this application and the above drawings are intended to cover non-exclusive inclusion. The terms "first", "second", etc. in the specification and claims of this application or the above drawings are used to distinguish different objects and are not used to describe a specific order or primary-secondary relationship.

[0083] In the description of this application, it should be understood that the orientation or positional relationship indicated by the terms "center", "transverse", "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "axial", "radial", "circumferential", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to this application.

[0084] In the description of this application, it should be noted that unless otherwise clearly specified and limited, the terms "installed", "connected", "coupled", "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 directly connected, or indirectly connected through an intermediate medium, and it can be the internal communication of two elements. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0085] Referring to "embodiment" herein means that a specific feature, structure or characteristic described in connection with the embodiment can be included in at least one embodiment of this application. The phrase appearing in various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0086] As used herein, the term "and / or" merely describes an association relationship between associated objects, indicating that there can be three relationships. For example, A and / or B can represent three cases: A exists alone, A and B exist simultaneously, and B exists alone. Additionally, the character " / " in this text generally indicates that the associated objects before and after are in an "or" relationship.

[0087] As used in this application, "a plurality of" means two or more (including two). Similarly, "a plurality of groups" means two or more groups (including two groups), and "a plurality of sheets" means two or more sheets (including two sheets).

[0088] In this application, the battery cell may include a lithium-ion secondary battery cell, a lithium-ion primary battery cell, a lithium-sulfur battery cell, a sodium-lithium-ion battery cell, a sodium-ion battery cell, a magnesium-ion battery cell, etc., and the embodiments of this application do not limit this. The battery cell can be in a cylindrical shape, a flat shape, a cuboid shape, or other shapes, and the embodiments of this application do not limit this either. Generally, the battery cells are divided into three types according to the packaging method: cylindrical battery cells, square battery cells, and soft-pack battery cells, and the embodiments of this application do not limit this either.

[0089] The battery cell includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator. The battery cell mainly operates by the movement of metal ions between the positive electrode plate and the negative electrode plate. The positive electrode plate includes a positive current collector and a positive active material layer. The positive active material layer is coated on the surface of the positive current collector, and the current collector without the coated positive active material layer protrudes from the current collector with the coated positive active material layer. The current collector without the coated positive active material layer serves as the positive electrode tab. Taking a lithium-ion battery as an example, the material of the positive current collector can be aluminum, and the positive active material can be lithium cobaltate, lithium iron phosphate, ternary lithium, lithium manganate, etc. The negative electrode plate includes a negative current collector and a negative active material layer. The negative active material layer is coated on the surface of the negative current collector, and the current collector without the coated negative active material layer protrudes from the current collector with the coated negative active material layer. The current collector without the coated negative active material layer serves as the negative electrode tab. The material of the negative current collector can be copper, and the negative active material can be carbon, silicon, etc. To ensure that a large current can pass through without fusing, the number of positive electrode tabs is multiple and stacked together, and the number of negative electrode tabs is multiple and stacked together. The material of the separator can be PP (polypropylene), PE (polyethylene), etc. The electrode assembly can be a wound structure or a stacked structure, and the embodiments of this application are not limited thereto. The development of battery technology needs to consider multiple design factors simultaneously, such as performance parameters like energy density, cycle life, discharge capacity, charge-discharge rate, etc. Additionally, the safety of the battery also needs to be considered.

[0090] The battery mentioned in the embodiments of the present application refers to a single physical module including one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in the present application may include a battery module, a battery pack, etc. A battery generally includes a box for encapsulating one or more battery cells. The box can prevent liquids or other foreign objects from affecting the charging or discharging of the battery cells.

[0091] The separator has electrical insulation and is disposed between the positive electrode plate and the negative electrode plate. Its main function is to prevent the positive electrode plate and the negative electrode plate from coming into contact, thereby causing an internal short circuit in the electrode assembly. The separator has a large number of through micropores, which can ensure the free passage of electrolyte ions. In particular, the separator has good permeability to lithium ions. Exemplarily, the separator may include a separator base layer and a functional layer located on the surface of the separator base layer. The separator base layer may be at least one of polypropylene, polyethylene, ethylene-propylene copolymer, polybutylene terephthalate, etc., and the functional layer may be a mixture layer of ceramic oxide and binder.

[0092] The separator plays a very important role in the electrode assembly and can directly cause phenomena such as short circuit, performance degradation, and reduced lifespan of the electrode assembly.

[0093] When the battery cell is charging, metal ions are deintercalated from the positive electrode active material layer and intercalated into the negative electrode active material layer. However, some abnormal situations may occur, resulting in the precipitation of metal ions. Taking a lithium-ion battery cell as an example, due to reasons such as insufficient lithium intercalation space in the negative electrode active material layer, too much resistance for lithium ions to intercalate into the negative electrode active material layer, or too fast deintercalation of lithium ions from the positive electrode active material layer, the deintercalated lithium ions cannot be intercalated into the negative electrode active material layer of the negative electrode plate in an equal amount. The lithium ions that cannot be intercalated into the negative electrode plate can only gain electrons on the surface of the negative electrode plate, thereby forming metallic lithium, which is the phenomenon of lithium plating. Lithium plating not only degrades the performance of the battery cell and significantly shortens the cycle life, but also limits the fast charging capacity of the battery cell. In addition, when lithium plating occurs in the battery cell, the precipitated lithium metal is very reactive and can react with the electrolyte at a relatively low temperature, resulting in a decrease in the self-heating onset temperature (Tonset) and an increase in the self-heating rate of the battery cell, seriously endangering the safety of the battery cell. Moreover, when lithium plating is severe, the deintercalated lithium ions can form a lithium layer on the surface of the negative electrode plate. The lithium dendrites in the lithium layer may penetrate through the separator and cause a short circuit between the adjacent positive electrode plate and negative electrode plate, triggering a safety hazard.

[0094] The inventors have tried to increase the overall thickness of the separator to reduce the risk of lithium dendrites penetrating through the separator. However, increasing the thickness of the separator will reduce the energy density of the electrode assembly.

[0095] The inventors noticed that during the charge and discharge process, severe lithium plating only occurs in some areas of the negative electrode tab. In other words, in some areas of the negative electrode tab, lithium plating is not likely to occur or only occurs slightly, and the separator opposite to this part does not need to be thickened.

[0096] In view of this, the inventors of the present application proposed an electrode assembly, which includes a positive electrode tab, a negative electrode tab, and a separator assembly for separating the positive electrode tab and the negative electrode tab. The separator assembly includes a matrix area and a reinforcement area connected to the matrix area. The thickness of the reinforcement area is greater than that of the matrix area; at least part of the reinforcement area is located between the adjacent positive electrode tab and negative electrode tab. The reinforcement area can be used to correspond to the position where lithium plating is likely to occur on the negative electrode tab. In this way, when lithium plating occurs on the negative electrode tab, the reinforcement area can effectively separate the positive electrode tab and the negative electrode tab, reducing the risk of lithium dendrites passing through the separator assembly and improving the lifespan and safety. Compared with the reinforcement area, the matrix area can have a smaller thickness, which can reduce the amount of the separator assembly used, lower the cost, and improve the energy density of the electrode assembly.

[0097] For the convenience of description, the following embodiments are described by taking the electrical device as a vehicle as an example.

[0098] Figure 1 It is a schematic structural diagram of a vehicle provided by some embodiments of the present application. As Figure 1 shown, a battery 2 is arranged inside the vehicle 1, and the battery 2 can be arranged at the bottom, head, or tail of the vehicle 1. The battery 2 can be used for power supply of the vehicle 1. For example, the battery 2 can be used as the operating power source of the vehicle 1.

[0099] The vehicle 1 may further include a controller 3 and a motor 4. The controller 3 is used to control the battery 2 to supply power to the motor 4. For example, it is used for the working power requirements during the startup, navigation, and driving of the vehicle 1.

[0100] In some embodiments of the present application, the battery 2 can not only be used as the operating power source of the vehicle 1, but also as the driving power source of the vehicle 1, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1.

[0101] Figure 2 It is an explosion schematic diagram of a battery provided by some embodiments of the present application. As Figure 2 shown, the battery 2 includes a box body 5 and battery cells 6, and the battery cells 6 are accommodated in the box body 5.

[0102] The housing 5 is used to accommodate battery cells 6, and the housing 5 can have various structures. In some embodiments, the housing 5 can include a first housing part 5a and a second housing part 5b. The first housing part 5a and the second housing part 5b cover each other, and the first housing part 5a and the second housing part 5b jointly define an accommodation space 5c for accommodating the battery cells 6. The second housing part 5b can be a hollow structure with one end open, and the first housing part 5a is a plate-like structure. The first housing part 5a covers the open side of the second housing part 5b to form the housing 5 with the accommodation space 5c. Both the first housing part 5a and the second housing part 5b can also be hollow structures with one side open, and the open side of the first housing part 5a covers the open side of the second housing part 5b to form the housing 5 with the accommodation space 5c. Of course, the first housing part 5a and the second housing part 5b can have various shapes, such as a cylinder, a cuboid, etc.

[0103] To improve the sealing performance after the connection between the first housing part 5a and the second housing part 5b, a sealing member can also be provided between the first housing part 5a and the second housing part 5b, such as sealant, sealing ring, etc.

[0104] Assume that the first housing part 5a covers the top of the second housing part 5b. The first housing part 5a can also be called the upper cover, and the second housing part 5b can also be called the lower housing.

[0105] In the battery 2, there are multiple battery cells 6. The multiple battery cells 6 can be connected in series, in parallel, or in a mixed connection. A mixed connection means that there are both series and parallel connections among the multiple battery cells 6. The multiple battery cells 6 can be directly connected in series, in parallel, or in a mixed connection together, and then the whole formed by the multiple battery cells 6 is accommodated in the housing 5. Of course, it can also be that the multiple battery cells 6 are first connected in series, in parallel, or in a mixed connection to form battery modules, and then the multiple battery modules are connected in series, in parallel, or in a mixed connection to form a whole and are accommodated in the housing 5.

[0106] Figure 3 This is an explosion schematic diagram of the battery cell provided in some embodiments of the present application.

[0107] A battery cell 6 refers to the smallest unit that makes up the battery 2. As Figure 3 shown, the battery cell 6 includes a housing 20, an electrode assembly 10, and other functional components. The electrode assembly 10 is accommodated in the housing 20.

[0108] In some embodiments, the housing 20 includes an end cap 22 and a housing body 21.

[0109] The end cap 22 refers to a component that covers the opening of the housing 21 to isolate the internal environment of the battery cell 6 from the external environment. Without limitation, the shape of the end cap 22 can be adapted to the shape of the housing 21 to cooperate with the housing 21. Optionally, the end cap 22 can be made of a material with a certain hardness and strength (such as aluminum alloy). In this way, the end cap 22 is not easily deformed when subjected to extrusion and collision, enabling the battery cell 6 to have higher structural strength and improved safety performance. Functional components such as electrode terminals 30 can be provided on the end cap 22. The electrode terminals 30 can be used to electrically connect to the electrode assembly 10 for outputting or inputting the electrical energy of the battery cell 6.

[0110] In some embodiments, a pressure relief mechanism for releasing the internal pressure when the internal pressure or temperature of the battery cell 6 reaches a threshold value can also be provided on the end cap 22. The material of the end cap 22 can also be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc. The embodiments of the present application do not make special restrictions on this.

[0111] In some embodiments, an insulating member can also be provided on the inner side of the end cap 22. The insulating member can be used to isolate the electrical connection components in the housing 21 from the end cap 22 to reduce the risk of short circuit. Exemplarily, the insulating member can be plastic, rubber, etc.

[0112] The housing 21 is a component used to cooperate with the end cap 22 to form the internal environment of the battery cell 6. Among them, the formed internal environment can be used to accommodate the electrode assembly 10, electrolyte, and other components. The housing 21 and the end cap 22 can be independent components. An opening can be provided on the housing 21, and the end cap 22 is covered on the opening to form the internal environment of the battery cell 6. Without limitation, the end cap 22 and the housing 21 can also be integrated. Specifically, the end cap 22 and the housing 21 can first form a common connection surface before other components enter the housing, and when it is necessary to encapsulate the inside of the housing 21, the end cap 22 is then covered on the housing 21. The housing 21 can be of various shapes and sizes, such as cuboid, cylindrical, hexagonal prism, etc. Specifically, the shape of the housing 21 can be determined according to the specific shape and size of the electrode assembly 10. The material of the housing 21 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc. The embodiments of the present application do not make special restrictions on this.

[0113] The electrode assembly 10 is a component in the battery cell 6 that is immersed in the electrolyte to undergo an electrochemical reaction. One or more electrode assemblies 10 may be included within the housing 21. The electrode assembly 10 is mainly formed by winding a positive electrode plate and a negative electrode plate, and generally an insulating member is provided between the positive electrode plate and the negative electrode plate. The portions of the positive electrode plate and the negative electrode plate having the active material constitute the main body of the electrode assembly 10, and the portions of the positive electrode plate and the negative electrode plate without the active material respectively constitute the electrode tabs. The positive electrode tab and the negative electrode tab may be located together at one end of the main body or separately at both ends of the main body. During the charge and discharge process of the battery cell 6, the positive active material and the negative active material react with the electrolyte, and the electrode tabs are connected to the electrode terminals 30 to form a current loop.

[0114] Figure 4 Schematic structural diagram of the electrode assembly provided by some embodiments of the present application; Figure 5 is Figure 4 Partial enlarged schematic diagram of the electrode assembly shown; Figure 6 is Figure 5 Enlarged schematic diagram at the square P; Figure 7 is Figure 4 Schematic structural diagram of the electrode assembly shown before winding; Figure 8 is Figure 7 Schematic structural diagram of the insulating assembly shown.

[0115] As Figures 4 to 8 shown, the electrode assembly 10 of the embodiment of the present application includes a positive electrode plate 11, a negative electrode plate 12, and an insulating assembly 13. The insulating assembly 13 is used to insulate the positive electrode plate 11 and the negative electrode plate 12. The insulating assembly 13 includes a matrix region 13b and a strengthening region 13a connected to the matrix region 13b. The thickness of the strengthening region 13a is greater than the thickness of the matrix region 13b; at least a part of the strengthening region 13a is located between the adjacent positive electrode plate 11 and negative electrode plate 12.

[0116] The electrode assembly 10 can be of various shapes. For example, the electrode assembly 10 can be in the shape of a cylinder, a flat body, a prism (such as a triangular prism, a quadrangular prism, or a hexagonal prism), or other shapes.

[0117] The insulating assembly 13 can be one or more. Exemplarily, the insulating assembly 13 is provided as two. In the present application, one insulating assembly 13, the negative electrode plate 12, another insulating assembly 13, and the positive electrode plate 11 can be stacked in sequence first, and then wound two or more turns to form a wound structure. When the insulating assembly 13 is provided as multiple, only one insulating assembly 13 may be provided with the strengthening region 13a, or each insulating assembly 13 may be provided with the strengthening region 13a.

[0118] The isolation component 13 is a component including an insulating film for isolating the positive electrode plate 11 and the negative electrode plate 12. This insulating film has a large number of through micropores, which can ensure the free passage of metal ions; exemplarily, the insulating film has good permeability to lithium ions and can basically not block the passage of lithium ions.

[0119] Exemplarily, the isolation component 13 can be made of a single insulating film or multiple insulating films.

[0120] There can be one or more strengthening regions 13a. Exemplarily, there are multiple strengthening regions 13a, and adjacent strengthening regions 13a are connected by a matrix region 13b.

[0121] The strengthening region 13a can be entirely located between the positive electrode plate 11 and the negative electrode plate 12, or only partially located between the positive electrode plate 11 and the negative electrode plate 12.

[0122] The strengthening region 13a can be used to correspond to the position where lithium is likely to deposit on the negative electrode plate 12. In this way, when lithium deposits on the negative electrode plate 12, the strengthening region 13a can effectively separate the positive electrode plate 11 and the negative electrode plate 12, reduce the risk of lithium dendrites passing through the isolation component 13, and improve the lifespan and safety. Compared with the strengthening region 13a, the matrix region 13b can have a smaller thickness, which can reduce the amount of the isolation component 13 used, lower the cost, and increase the energy density of the electrode assembly 10.

[0123] In some embodiments, the thickness of the strengthening region 13a is 2μm - 100μm. Optionally, the thickness of the strengthening region 13a is 2μm, 5μm, 7μm, 10μm, 12μm, 20μm, 30μm, 50μm, 80μm or 100μm.

[0124] The smaller the thickness of the strengthening region 13a, the higher the energy density of the electrode assembly 10, but the higher the risk of the strengthening region 13a being penetrated by lithium dendrites. The larger the thickness of the strengthening region 13a, the lower the energy density of the electrode assembly 10, but the lower the risk of the strengthening region 13a being penetrated by lithium dendrites, and the higher the safety of the electrode assembly 10.

[0125] Through experiments and calculations, the inventors limit the thickness of the strengthening region 13a to 2μm - 100μm to balance the energy density and safety of the electrode assembly 10.

[0126] In some embodiments, the thickness of the strengthening region 13a is 5μm - 30μm.

[0127] In some embodiments, the strengthening region 13a is arranged as a multi-layer structure, and the matrix region 13b is arranged as a single-layer structure.

[0128] In the reinforcement region 13a, multiple separator layers are stacked together to form a multi-layer structure. The stacking direction of the multiple separator layers is parallel to the stacking direction of the positive electrode plate 11 and the negative electrode plate 12. In the reinforcement region 13a, two adjacent separator layers can be connected to each other or separated from each other.

[0129] For the reinforcement region 13a with a multi-layer structure, the thickness of the reinforcement region 13a refers to the sum of the thicknesses of the multiple separator layers.

[0130] The number of layers of the reinforcement region 13a is greater than or equal to 2. Exemplarily, the number of layers of the reinforcement region 13a can be 2 - 15.

[0131] In the matrix region 13b, the separator layer is single-layer. The matrix region 13b can be one or multiple. Exemplarily, both the matrix region 13b and the reinforcement region 13a are multiple, and the multiple matrix regions 13b and the multiple reinforcement regions 13a are alternately arranged along the winding direction W.

[0132] The matrix region 13b is used to correspond to the position of the negative electrode plate 12 where lithium is not easily deposited. The matrix region 13b has fewer layers, which can reduce the usage amount of the separator assembly 13 and improve the energy density of the battery cell.

[0133] When a lithium layer is deposited on the surface of the negative electrode plate 12, the lithium layer will squeeze the separator layer of the reinforcement region 13a close to the negative electrode plate 12, and the separator layer close to the negative electrode plate 12 will stretch under the extrusion of the lithium layer. When the pore diameter of the local micropores of the separator layer close to the negative electrode plate 12 becomes larger and a defect region is formed, smaller lithium dendrites in the lithium layer may pass through the defect region. The separator layer of the reinforcement region 13a far from the negative electrode plate 12 can insulate and isolate the lithium dendrites passing through the defect region from the positive electrode plate 11, thereby reducing the risk of contact between the lithium dendrites and the positive electrode plate 11 and providing safety.

[0134] The distance between the separator layer of the reinforcement region 13a far from the negative electrode plate 12 and the lithium layer is large, and the extrusion force it receives from the lithium layer is small, and the risk of its stretching under the extrusion force to generate a defect region is also small. The position where the defect region is generated during the stretching process of the separator layer is uncertain. Even if the separator layer far from the negative electrode plate 12 generates a defect region, the possibility that the defect region of the separator layer far from the negative electrode plate 12 exactly corresponds to the defect region of the separator layer close to the negative electrode plate 12 is very small, and it is difficult for lithium dendrites to pass through the reinforcement region 13a simultaneously. Therefore, by setting the reinforcement region 13a in the embodiment of the present application, the short-circuit risk can be effectively reduced and the safety can be improved.

[0135] On the premise of the same thickness, compared with the strengthening area 13a with a single-layer structure, the strengthening area 13a with a multi-layer structure can more effectively block lithium dendrites, reduce the risk of short circuit, and improve safety. Exemplarily, the protection effect of the strengthening area 13a composed of two 5-μm isolation layers is better than that of the strengthening area 13a composed of a single 10-μm isolation layer. In other words, on the premise of meeting the insulation requirements, compared with the strengthening area 13a with a single-layer structure, the strengthening area 13a with a multi-layer structure can adopt a smaller thickness, which can reduce the amount of the isolation component 13 used and improve the energy density of the electrode assembly 10.

[0136] In some embodiments, the positive electrode sheet 11, the isolation component 13, and the negative electrode sheet 12 are wound to form a bending area B, and at least a part of the strengthening area 13a is disposed in the bending area B.

[0137] The winding direction W is the circumferential winding direction of the positive electrode sheet 11, the negative electrode sheet 12, and the isolation component 13 from the inside to the outside. Exemplarily, in the figure, the winding direction W is the counterclockwise direction.

[0138] The bending area B is an area with a bending structure in the electrode assembly 10. In this bending area B, the positive electrode sheet 11, the negative electrode sheet 12, and the isolation component 13 are all bent. Exemplarily, the part of the positive electrode sheet 11 located in the bending area B is generally bent into an arc shape, and the part of the negative electrode sheet 12 located in the bending area B is generally bent into an arc shape.

[0139] The winding device winds the positive electrode sheet 11, the negative electrode sheet 12, and the isolation component 13 into several turns. Each turn can be constructed with several layers. One turn means starting from a certain point on the electrode assembly 10 as the starting end, and reaching another point as the ending end along the winding direction W for one week. The ending end, the starting end, and the center of this turn are on a straight line, and the starting end is between the ending end and the center of this turn.

[0140] The electrode assembly 10 can be entirely the bending area B, or only a part of the area can be the bending area B. Exemplarily, the electrolysis assembly includes a flat area A and a bending area B. The bending area B is connected to the flat area A, and the flat area A is an area with a flat structure of the electrode assembly 10.

[0141] The strengthening area 13a can be entirely disposed in the bending area B, or only a part can be disposed in the bending area B.

[0142] The positive electrode tab 11 and the negative electrode tab 12 located in the bending region B need to be bent, and the positive electrode active material layer and the negative electrode active material layer are prone to stress concentration during the bending process, resulting in the shedding of their respective active materials. Due to the shedding of the active materials, especially the shedding of the active materials on the negative electrode tab 12, the lithium intercalation sites in the negative electrode active material layer of the negative electrode tab 12 may be less than the number of lithium ions that can be provided by the positive electrode active material layer of its adjacent positive electrode tab 11, thereby triggering the phenomenon of lithium deposition. In the embodiments of the present application, at least a part of the strengthening region 13a is arranged in the bending region B. Even if lithium deposition occurs in the bending region B, the strengthening region 13a can block the lithium dendrites, reduce the probability of conduction between the positive electrode tab 11 and the negative electrode tab 12, effectively reduce the short-circuit risk, and improve the service life and safety of the electrode assembly 10.

[0143] In some embodiments, the positive electrode tab 11 includes a first bending portion 111 located in the bending region B and adjacent to the strengthening region 13a, and the negative electrode tab 12 includes a second bending portion 121 adjacent to the first bending portion 111. The strengthening region 13a includes a plurality of bending layers 14, and the plurality of bending layers 14 are located in the bending region B and stacked between the first bending portion 111 and the second bending portion 121.

[0144] The adjacent relationship between the first bending portion 111 and the second bending portion 121 means that there is no other layer of positive electrode tab or other layer of negative electrode tab between them. The adjacent relationship between the strengthening region 13a and the first bending portion 111 means that there is no other layer of positive electrode tab or other layer of negative electrode tab between them.

[0145] The positive electrode tab 11 includes a plurality of positive electrode bending portions 11a located in the bending region B, and the positive electrode bending portion 11a adjacent to the strengthening region 13a with a multi-layer structure is the first bending portion 111. In the positive electrode tab 11, some of the positive electrode bending portions 11a may be the first bending portion 111, or all of the positive electrode bending portions 11a may be the first bending portion 111.

[0146] The negative electrode tab 12 includes a plurality of negative electrode bending portions located in the bending region B. Exemplarily, the negative electrode bending portion adjacent to the first bending portion 111 and clamping the strengthening region 13a with the first bending portion 111 is the second bending portion 121.

[0147] In the electrode assembly 10, the strengthening region 13a and the second bending portion 121 may be provided only on the inner side of the first bending portion 111, or may be provided only on the outer side of the first bending portion 111, or may be provided on both sides of the first bending portion 111.

[0148] The plurality of bending layers 14 can block the lithium dendrites when lithium deposition occurs in the second bending portion 121, reduce the risk of contact between the lithium dendrites and the first bending portion 111, and improve the safety.

[0149] In some embodiments, at least the inner side of the first bending portion 111 is provided with a strengthening region 13a and a second bending portion 121.

[0150] The curvature of the second bending portion 121 located inside the first bending portion 111 is greater than that of the first bending portion 111. Therefore, the active material is more likely to fall off during the bending process of the second bending portion 121. That is to say, the second bending portion 121 inside the first bending portion 111 is more likely to have lithium plating. The strengthening region 13a can separate the first bending portion 111 and the second bending portion 121 located inside the first bending portion 111. Even if lithium plating occurs in the second bending portion 121, it can reduce the probability of lithium dendrites passing through the strengthening region 13a, reduce the short-circuit risk, and improve safety.

[0151] In some embodiments, the first bending portion 111 includes a first current collector portion 1111 and a first active material layer 1112 disposed on the surface of the first current collector portion 1111. The thickness of the first active material layer 1112 is h1. The second bending portion 121 includes a second current collector portion 1211 and a second active material layer 1212 disposed on the surface of the second current collector portion 1211. The thickness of the second active material layer 1212 is h2, the thickness of the bending layer 14 is h3, and the thickness of the second current collector portion 1211 is h4. In the thickness direction of the first bending portion 111, the maximum distance between the first bending portion 111 and the second bending portion 121 is X. The number of layers of the bending layer 14 located between the first bending portion 111 and the second bending portion 121 is Y, and Y is a positive integer greater than 1. The active material capacity per unit area of the first active material layer 1112 is A1, and the active material capacity per unit area of the second active material layer 1212 is A2.

[0152] The first current collector portion 1111 can be a part of the positive electrode current collector, and the first active material layer 1112 is a part of the positive electrode active material layer. The second current collector portion 1211 can be a part of the negative electrode current collector, and the second active material layer 1212 is a part of the negative electrode active material layer.

[0153] In the thickness direction of the first bending portion 111, the maximum distance between the surface of the first bending portion 111 facing the second bending portion 121 and the surface of the second bending portion 121 facing the first bending portion 111 is X. Exemplarily, the thickness direction of the first bending portion 111 can be the normal direction of the surface of the first bending portion 111 facing the second bending portion 121.

[0154] The active material capacity per unit area A1 of the first active material layer 1112 is defined as the ratio of the active material capacity of the first active material layer 1112 to the area of the surface of the first current collector 1111 coated with the first active material layer 1112. The active material capacity per unit area A2 of the second active material layer 1212 is defined as the ratio of the active material capacity of the second active material layer 1212 to the area of the surface of the second current collector 1211 coated with the second active material layer 1212.

[0155] Testing the average discharge capacity of the first active material layer 1112. Taking the positive electrode sheets 11 of the above-mentioned respective embodiments, small round pieces containing a single-sided first active material layer 1112 are obtained using a punching die. Using a lithium metal sheet as the counter electrode, a Ce lgard membrane as the separator, and a solution of LiPF 6 (1 mol / L) in EC + DMC + DEC (ethylene carbonate, dimethyl carbonate, and diethyl carbonate with a volume ratio of 1:1:1) as the electrolyte, 6 identical CR2430-type button cell monomers are assembled in a glove box under argon protection. ① After the cell monomers are assembled, they are left standing for 12 h. ② Constant current charging is carried out at a charging current of 0.1C until the voltage reaches the upper cut-off voltage x 1 V, and then the voltage x 1 V is maintained for constant voltage charging until the current is 50 μA. ③ Leave standing for 5 min. ④ Finally, constant current discharging is carried out at a discharging current of 0.1C until the voltage reaches the lower cut-off voltage y 1 V. ⑤ Leave standing for 5 min, and repeat steps ② - ⑤, recording the discharge capacity of the second cycle. The average value of the discharge capacities of the 6 button cells is the average discharge capacity of the single-sided first active material layer 1112, which can be used as the active material capacity per unit area A1 of the first active material layer 1112. For example, when the positive electrode active material is lithium iron phosphate, the upper cut-off voltage x 1 V = 3.75 V, and the lower cut-off voltage y 1 V = 2 V. When the positive electrode active material is lithium nickel cobalt manganese oxide (NCM), the upper cut-off voltage x 1 V = 4.25 V, and the lower cut-off voltage y 1 V = 2.8 V.

[0156] Testing the average discharge capacity of the second active material layer 1212. Taking the negative electrode sheets 12 of the above-mentioned respective embodiments, small round pieces having the same area as the above-mentioned positive electrode small round pieces and containing a single-sided second active material layer 1212 are obtained using a punching die. Using a lithium metal sheet as the counter electrode, a Ce lgard membrane as the separator, and a solution of LiPF 6A solution of EC + DMC + DEC (ethylene carbonate, dimethyl carbonate, and diethyl carbonate with a volume ratio of 1:1:1) at (1 mol / L) was used as the electrolyte, and six CR2430 coin cells were assembled in a glove box under argon protection. ① After the cells were assembled, they were left standing for 12 h. ② A constant current discharge was carried out at a discharge current of 0.05 C until the voltage reached the lower cut-off voltage y 2 mV. ③ Then, a constant current discharge was carried out again at a discharge current of 50 μA until the voltage reached the lower cut-off voltage y 2 mV. ④ After standing for 5 min, ⑤ a constant current discharge was carried out at a discharge current of 10 μA until the lower cut-off voltage y 2 mV was reached. ⑥ After standing for 5 minutes, ⑦ finally, a constant current charge was carried out at a charge current of 0.1 C until the final voltage reached the upper cut-off voltage x 2 V. ⑧ After standing for 5 minutes, steps ② - ⑧ were repeated, and the charge capacity of the second cycle was recorded. The average of the charge capacities of the six coin cells was the average charge capacity of the single-sided second active material layer 1212, which could be used as the active material capacity per unit area A2 of the second active material layer 1212. For example, when the negative electrode active material was graphite, the upper cut-off voltage x 2 V = 2 V, and the lower cut-off voltage y 2 V = 5 mV. When the negative electrode active material was silicon, the upper cut-off voltage x 2 V = 2 V, and the lower cut-off voltage y 2 V = 5 mV.

[0157] In some embodiments, A2 / A1 ≥ 1. h1, h2, h3, h4, X, and Y satisfy:

[0158] The fewer the number of layers of the bent layer 14 in the strengthening region 13a, the higher the risk of lithium dendrites passing through the strengthening region 13a; the more the number of layers of the bent layer 14 in the strengthening region 13a, the more complex the structure of the isolation component 13, and the lower the energy density of the electrode component 10. Through experiments and calculations, the inventor set the number of layers of the bent layer 14 according to the above formula to balance the safety and energy density of the electrode component 10.

[0159] In some embodiments, A2 / A1 < 1. h1, h2, h3, h4, X, and Y satisfy:

[0160] When A2 / A1 < 1, the lithium intercalation space of the second active material layer 1212 is insufficient. The lithium ions deintercalated from the first active material layer 1112 cannot be intercalated into the second active material layer 1212 in an equal amount. The lithium ions that cannot be intercalated into the second active material layer 1212 can only gain electrons on the surface of the second active material layer 1212, resulting in the phenomenon of lithium deposition. Compared with the electrode assembly 10 where A2 / A1 ≥ 1, the phenomenon of lithium deposition in the electrode assembly 10 with A2 / A1 < 1 is more serious, and the bending layer 14 of the strengthening region 13a requires more layers.

[0161] Through experiments and calculations, the inventor sets the number of layers of the bending layer 14 according to the above formula to balance the safety and energy density of the electrode assembly 10.

[0162] In some embodiments, the value of h1 is 5 μm - 80 μm. Optionally, the value of h1 is 5 μm, 10 μm, 20 μm, 30 μm, 50 μm, or 80 μm.

[0163] In some embodiments, the value of h2 is 10 μm - 100 μm. Optionally, the value of h2 is 10 μm, 20 μm, 30 μm, 50 μm, 80 μm, or 100 μm.

[0164] In some embodiments, the value of h3 is 1 μm - 20 μm. Optionally, the value of h3 is 1 μm, 3 μm, 5 μm, 10 μm, 15 μm, or 20 μm.

[0165] On the premise of meeting the isolation effect, the smaller the value of h3, the more layers the bending layer 14 of the strengthening region 13a has. If the value of h3 is too small, it will cause too many layers of the bending layer 14 of the strengthening region 13a, resulting in a complex structure of the isolation component 13 and being not easy to form. In view of this, the inventor sets the value of h3 to be greater than or equal to 1 μm.

[0166] The larger the value of h3, the greater the total thickness of the strengthening region 13a; if the value of h3 is too large, it will cause the energy density of the electrode assembly 10 to be low. In view of this, the inventor sets the value of h3 to be less than or equal to 20 μm to ensure the energy density of the electrode assembly 10.

[0167] In some embodiments, the value of h4 is 2 μm - 20 μm. Optionally, the value of h4 can be 2 μm, 3 μm, 5 μm, 10 μm, 15 μm, or 20 μm.

[0168] In some embodiments, the value of X is 10 μm - 5000 μm. Optionally, the value of X can be 10 μm, 20 μm, 50 μm, 100 μm, 500 μm, 1000 μm, 2000 μm, or 5000 μm.

[0169] In some embodiments, the positive electrode tab 11 includes a plurality of positive electrode bending portions 11a arranged along the winding direction W, and at least the positive electrode bending portion 11a formed by the first bending of the positive electrode tab 11 is set as the first bending portion 111. That is to say, the positive electrode bending portion 11a formed by the first bending of the positive electrode tab 11 is arranged adjacent to the strengthening region 13a.

[0170] The plurality of positive electrode bending portions 11a of the positive electrode tab 11 are all bent. Exemplarily, the positive electrode bending portion 11a is generally arc-shaped.

[0171] The positive electrode bending portion 11a formed by the first bending of the positive electrode tab 11 refers to the positive electrode bending portion 11a formed by the first bending of the positive electrode tab 11 during the winding process along the winding direction W.

[0172] The positive electrode bending portion 11a formed by the first bending of the positive electrode tab 11 has a relatively large curvature. During charging, the negative electrode tab 12 adjacent to the positive electrode bending portion 11a formed by the first bending of the positive electrode tab 11 is more likely to have a lithium plating problem. In this embodiment, the positive electrode bending portion 11a formed by the first bending of the positive electrode tab 11 is set as the first bending portion 111, so that the strengthening region 13a can effectively isolate the positive electrode bending portion 11a formed by the first bending of the positive electrode tab 11 from the lithium dendrites, reduce the short-circuit risk, and improve the safety.

[0173] In some embodiments, the positive electrode bending portion 11a formed by the second bending of the positive electrode tab 11 is also set as the first bending portion 111. That is to say, the positive electrode bending portion 11a formed by the second bending of the positive electrode tab 11 is also arranged adjacent to the strengthening region 13a.

[0174] The positive electrode bending portion 11a formed by the second bending of the positive electrode tab 11 refers to the positive electrode bending portion 11a formed by the second bending of the positive electrode tab 11 during the winding process along the winding direction W.

[0175] The strengthening region 13a adjacent to the positive electrode bending portion 11a formed by the first bending of the positive electrode tab 11 can be integrated with the strengthening region 13a adjacent to the positive electrode bending portion 11a formed by the second bending of the positive electrode tab 11, or can be arranged at intervals along the winding direction W.

[0176] The positive electrode bending portion 11a formed by the second bending of the positive electrode tab 11 has a relatively large curvature. During charging, the negative electrode tab 12 adjacent to the positive electrode bending portion 11a formed by the second bending of the positive electrode tab 11 is likely to have a lithium plating problem. In this embodiment, the positive electrode bending portion 11a formed by the second bending of the positive electrode tab 11 is set as the first bending portion 111, so that the strengthening region 13a can effectively isolate the positive electrode bending portion 11a formed by the second bending of the positive electrode tab 11 from the lithium dendrites, reduce the short-circuit risk, and improve the safety.

[0177] In some embodiments, the total thickness of the strengthening region 13a inside the positive electrode bending portion 11a formed by the first bending of the positive electrode sheet 11 is T1, and the total thickness of the strengthening region 13a inside the positive electrode bending portion 11a formed by the second bending of the positive electrode sheet 11 is T2, where T1 ≥ T2.

[0178] The curvature of the second bending portion 121 inside the positive electrode bending portion 11a formed by the first bending of the positive electrode sheet 11 is greater than the curvature of the second bending portion 121 inside the positive electrode bending portion 11a formed by the second bending of the positive electrode sheet 11. The second bending portion 121 inside the positive electrode bending portion 11a formed by the first bending of the positive electrode sheet 11 is more likely to form lithium deposition. In this embodiment, T1 ≥ T2 is used to reduce the risk of conduction between the positive electrode bending portion 11a formed by the first bending of the positive electrode sheet 11 and the lithium dendrites, thereby improving the safety of the battery cell.

[0179] In some embodiments, the number of layers of the isolation layer of the strengthening region 13a inside the positive electrode bending portion 11a formed by the first bending of the positive electrode sheet 11 is L1, and the number of layers of the isolation layer of the strengthening region 13a inside the positive electrode bending portion 11a formed by the second bending of the positive electrode sheet 11 is L2, where L1 ≥ L2.

[0180] In some embodiments, strengthening regions 13a and second bending portions 121 are provided on both sides of the first bending portion 111, and the total thickness of the strengthening region 13a inside the first bending portion 111 is greater than or equal to the total thickness of the strengthening region 13a outside the first bending portion 111.

[0181] The strengthening regions 13a on both sides of the first bending portion 111 may belong to the same isolation component 13 or may belong to two different isolation components 13 respectively.

[0182] The curvature of the second bending portion 121 inside the first bending portion 111 is greater than the curvature of the second bending portion 121 outside the first bending portion 111. The second bending portion 121 inside the first bending portion 111 is more likely to form lithium deposition. In this embodiment, the thickness of the strengthening region 13a inside the first bending portion 111 is not less than the thickness of the strengthening region 13a outside the first bending portion 111, so as to reduce the risk of conduction between the first bending portion 111 and the lithium dendrites and improve the safety of the battery cell.

[0183] In some embodiments, the number of layers of the isolation layer of the strengthening region 13a inside the first bending portion 111 is greater than or equal to the number of layers of the isolation layer of the strengthening region 13a outside the first bending portion 111.

[0184] In some embodiments, the positive electrode sheet 11, the separator assembly 13, and the negative electrode sheet 12 are wound to form a flat region A, and the flat region A is connected to the bent region B. At least a part of the base region 13b is disposed in the flat region A.

[0185] The flat region A is a region where the electrode assembly 10 has a flat structure, and the portions of the positive electrode sheet 11 and the negative electrode sheet 12 located in the flat region A are substantially flat. Exemplarily, the surfaces of each layer of the positive electrode sheet 11 and each layer of the negative electrode sheet 12 located in the flat region A are substantially flat.

[0186] The positive electrode sheet 11 and the negative electrode sheet 12 located in the flat region A are in a flat state, and the active material in the flat region A is not easily detached. The negative electrode sheet 12 located in the flat region A is not prone to lithium plating problems. Therefore, even if the base region 13b is disposed in the flat region A, the insulation between the positive and negative electrode sheets can be improved, and the short-circuit risk can be reduced.

[0187] In some embodiments, two bent regions B are provided, and the two bent regions B are respectively disposed at both ends of the flat region A.

[0188] In some embodiments, both ends of the reinforcing region 13a along the winding direction W are located in the flat region A, so that the reinforcing region 13a can pass through the bent region B as a whole, thereby reducing the short-circuit risk of the bent region B.

[0189] In some embodiments, in the winding direction W, the dimension by which the tail end of the reinforcing region 13a exceeds the bent region B is 3 mm - 500 mm. Optionally, the dimension by which the tail end of the reinforcing region 13a exceeds the bent region B is 10 mm - 100 mm.

[0190] In some embodiments, the separator assembly 13 includes a first separator layer 131 and a second separator layer 132. The first separator layer 131 is used to insulate and isolate the positive electrode sheet 11 and the negative electrode sheet 12, and at least a part of the second separator layer 132 is located between the positive electrode sheet 11 and the negative electrode sheet 12 and is laminated with the first separator layer 131. The region of the first separator layer 131 overlapping with the second separator layer 132 and the second separator layer 132 form the reinforcing region 13a of the separator assembly 13, and the region of the first separator layer 131 not overlapping with the second separator layer 132 forms the base region 13b.

[0191] Exemplarily, the first separator layer 131 can be understood as a separator layer between the positive electrode sheet 11 and the negative electrode sheet 12 in the related art, that is, the basic separator layer, and the second separator layer 132 can be understood as an additional separator layer, that is, the additional separator layer.

[0192] In the separator assembly 13, the second separator layer 132 can be one or multiple.

[0193] The first isolation layer 131 and the second isolation layer 132 can be two parts of an integral component, or two independent components provided separately.

[0194] The first isolation layer 131 and the second isolation layer 132 can be made of the same material or different materials.

[0195] In this embodiment, the thickness of the first isolation layer 131 and the thickness of the second isolation layer 132 are not limited. The thickness of the first isolation layer 131 can be greater than, equal to, or less than the thickness of the second isolation layer 132.

[0196] The first isolation layer 131 and the second isolation layer 132 are laminated between the positive electrode plate 11 and the negative electrode plate 12. The second isolation layer 132 can be independently disposed on the first isolation layer 131, that is, in the lamination direction of the first isolation layer 131 and the second isolation layer 132, there is no adhesion or other connection relationship between the surface of the second isolation layer 132 facing the first isolation layer 131 and the first isolation layer 131. Of course, the second isolation layer 132 can also be attached to the surface of the first isolation layer 131. Exemplarily, the second isolation layer 132 can be integrally attached to the first isolation layer 131, or only partially attached to the first isolation layer 131. Attachment refers to adhering connection.

[0197] In the embodiment of the present application, a second isolation layer 132 is additionally attached in the electrode assembly 10 to form a strengthened area 13a with a larger thickness on the isolation assembly 13, thereby reducing the short - circuit risk caused by lithium deposition and improving safety.

[0198] In some embodiments, in the strengthened area 13a, the number of layers of the second isolation layer 132 is 1 - 10. Exemplarily, in the strengthened area 13a, the number of layers of the second isolation layer 132 is 1, 2, 3, 5, or 10. When a strengthened area 13a is provided with a plurality of second isolation layers 132, the dimensions of the plurality of second isolation layers 132 along the winding direction W can be the same or different.

[0199] In some embodiments, there are a plurality of strengthened areas 13a in the isolation assembly 13, and the number of layers of the second isolation layer 132 in the plurality of strengthened areas 13a can be the same or different.

[0200] In some embodiments, the thickness of the second isolation layer 132 is less than or equal to the thickness of the first isolation layer 131.

[0201] The first isolation layer 131 and the second isolation layer 132 can function as multi - layer protection. Therefore, the added second isolation layer 132 can have a thickness not greater than that of the first isolation layer 131 to reduce the amount of the second isolation layer 132 used.

[0202] Optionally, the thickness of the second isolation layer 132 is less than that of the first isolation layer 131.

[0203] In some embodiments, the second isolation layer 132 is disposed on a side of the first isolation layer 131 facing the positive electrode tab 11.

[0204] In some embodiments, the thickness of the first isolation layer 131 is 2 μm - 30 μm. Optionally, the thickness of the first isolation layer 131 is 2 μm, 5 μm, 7 μm, 10 μm, 15 μm, 20 μm, or 30 μm.

[0205] In some embodiments, the thickness of the second isolation layer 132 is 1 μm - 25 μm. Optionally, the thickness of the second isolation layer 132 is 1 μm, 2 μm, 5 μm, 7 μm, 10 μm, 15 μm, 20 μm, or 25 μm.

[0206] In some embodiments, the porosity of the second isolation layer 132 is less than that of the first isolation layer 131. Since the second isolation layer 132 has a smaller porosity, when lithium dendrites pass through the first isolation layer 131, it is not easy for the lithium dendrites to pass through the micropores in the second isolation layer 132, thereby reducing the risk of the lithium dendrites conducting with the positive electrode tab 11 and improving safety.

[0207] In some embodiments, the second isolation layer 132 is a porous structure, and the pore diameter of the pores in the second isolation layer 132 is less than or equal to 1 μm.

[0208] The pore diameter of the pores in the second isolation layer 132 is small, and it is not easy for lithium dendrites to pass through, thereby reducing the risk of the lithium dendrites conducting with the positive electrode tab 11 and improving safety.

[0209] In some embodiments, the first isolation layer 131 includes a base film 133 and an insulating layer 134 coated on the surface of the base film 133. The base film 133 may be a porous thin film. Exemplarily, the base film 133 is made of a polymer material that is electrically insulating and has a liquid retention capacity, such as PP (polypropylene), PE (polyethylene), or PVDF (polyvinylidene fluoride).

[0210] The insulating layer 134 is a functional layer disposed on the surface of the base film 133. Exemplarily, the insulating layer 134 includes an inorganic material, a polymer binder, and a dispersant. The inorganic material may include at least one of boehmite and silica. The polymer binder may include at least one of PVDF and polystyrene - acrylate. The dispersant may include polyvinyl alcohol. The inorganic material can clamp the base film 133 and reduce the shrinkage of the base film 133. The polymer binder can adhere to the electrode tab and increase the overall stiffness of the electrode assembly 10.

[0211] The second isolation layer 132 may only include the base film 133, or may include both the base film 133 and the insulating layer 134 at the same time. Optionally, the base film 133 of the second isolation layer 132 is integrated with the base film 133 of the first isolation layer 131.

[0212] In the embodiments of the present application, the number of layers of the strengthening region 13a is determined by the number of layers of the base film 133. In other words, the number of layers of the strengthening region 13a refers to the number of layers of the base film 133 of the strengthening region 13a.

[0213] In some embodiments, the thickness of the insulating layer 134 is 0.5 μm - 10 μm. The particle size of the inorganic material is 0.1 μm - 10 μm. The content of the inorganic material in the insulating layer 134 is 70% - 98%; the content of the polymer binder is 1% - 20%; the content of the dispersant is 0.5% - 10%.

[0214] In some embodiments, in the stacking direction of the first isolation layer 131 and the second isolation layer 132, at least a part of the second isolation layer 132 is separated from the first isolation layer 131.

[0215] There is no adhesion or other connection relationship between at least a part of the second isolation layer 132 and the first isolation layer 131.

[0216] When the first isolation layer 131 (or the second isolation layer 132) is stretched under the extrusion of the lithium layer, the separated part of the second isolation layer 132 from the first isolation layer 131 is less affected by the first isolation layer 131, the stretching degree of the second isolation layer 132 is smaller, and the risk of generating defects is lower. Therefore, this embodiment can effectively reduce the risk of lithium dendrites passing through the first isolation layer 131 and the second isolation layer 132, and improve safety.

[0217] In some embodiments, the positive electrode sheet 11, the isolation assembly 13, and the negative electrode sheet 12 are wound to form a bent region B and a flat region A, and the flat region A is connected to the bent region B. A part of the second isolation layer 132 is located in the bent region B, and another part of the second isolation layer 132 is located in the flat region A. In the bent region B, the second isolation layer 132 is separated from the first isolation layer 131; in the flat region A, the second isolation layer 132 is attached to the first isolation layer 131.

[0218] The risk of lithium precipitation in the bent region B is relatively high. Separating the second isolation layer 132 in the bent region B from the first isolation layer 131 can effectively reduce the risk of lithium dendrites passing through the first isolation layer 131 and the second isolation layer 132, and improve safety. In the flat region A, the second isolation layer 132 is attached to the first isolation layer 131, which can reduce the moving amplitude of the second isolation layer 132 along the winding direction W and reduce the risk of misalignment of the second isolation layer 132.

[0219] In some embodiments, the second isolation layer 132 is formed by folding the end of the first isolation layer 131.

[0220] Exemplarily, the end of the first isolation layer 131 is folded to form the second isolation layer 132, and the folding position is the boundary between the first isolation layer 131 and the second isolation layer 132.

[0221] This embodiment enables the second isolation layer 132 to directly extend from the end of the first isolation layer 131 without separately adding and fixing the second isolation layer 132, thereby making the winding process more convenient and improving the integrity of the electrode assembly 10.

[0222] In some embodiments, the positive electrode sheet 11, the isolation assembly 13, and the negative electrode sheet 12 are wound, and the electrode assembly 10 includes a starting section 100 along the winding direction W, and the end of the first isolation layer 131 is located at the starting section 100.

[0223] The starting section 100 along the winding direction W refers to the end of the electrode assembly 10 located in the innermost circle.

[0224] The second isolation layer 132 can extend from the starting section 100 along the winding direction W and pass through the positive bending portion 11a formed by the first bending of the positive electrode sheet 11, which can reduce the risk of lithium dendrites passing through both the first isolation layer 131 and the second isolation layer 132 and contacting the positive bending portion 11a of the positive electrode sheet 11, improving safety. At the same time, this embodiment can also reduce the length that the second isolation layer 132 needs to extend, save usage, and reduce costs.

[0225] In some embodiments, the positive electrode sheet 11, the isolation assembly 13, and the negative electrode sheet 12 are wound to form a bending region B. The bending region B includes a first bending part B1 close to the starting section 100 along the winding direction W. The first bending part B1 is provided with the first isolation layer 131 and the second isolation layer 132, and the second isolation layer 132 extends from the end of the first isolation layer 131 and extends beyond the first bending part B1.

[0226] The first bending part B1 is the position where the electrode assembly 10 is first bent during the winding and forming process. Exemplarily, at the first bending part B1, the positive electrode sheet 11 is first bent, and the negative electrode sheet 12 is first bent.

[0227] At the first bending portion B1, the curvature of the positive electrode tab 11 and the negative electrode tab 12 is the largest, and during charging, the risk of lithium plating on the negative electrode tab 12 is the highest. The second isolation layer 132 extends beyond the first bending portion B1. The first isolation layer 131 and the second isolation layer 132 can at least protect the first bending portion B1 where lithium plating is most likely to occur, and at the same time, the use of the second isolation layer 132 can be saved, thereby improving the safety and service life of the electrode assembly 10 while saving costs.

[0228] Figure 9 Schematic diagram of the structure of the isolation assembly of the electrode assembly provided by some other embodiments of the present application before winding.

[0229] As Figure 9 shown, in some embodiments, the isolation assembly 13 is an overall single-layer structure. When the isolation assembly 13 is formed, a reinforced area 13a and a matrix area 13b with different thicknesses are directly formed.

[0230] Figure 10 Schematic diagram of the structure of the electrode assembly provided by some other embodiments of the present application; Figure 11 For Figure 10 shown, a partial enlarged schematic diagram of the electrode assembly; Figure 12 For Figure 10 shown, a schematic diagram of the structure of the electrode assembly before winding.

[0231] As Figures 10 to 12 described, in some embodiments, both the reinforced area 13a and the matrix area 13b are provided in multiple numbers, and the multiple reinforced areas 13a and the multiple matrix areas 13b are alternately arranged along the winding direction W.

[0232] The multiple reinforced areas 13a can respectively correspond to the multiple positive bending portions 11a of the positive electrode tab 11 to reduce the risk of short circuit at the multiple positive bending portions 11a of the positive electrode tab 11 and improve safety.

[0233] Each reinforced area 13a includes one or more second isolation layers 132. The number of layers of the multiple reinforced areas 13a can be the same or different.

[0234] In some embodiments, each reinforced area 13a can isolate a positive bending portion 11a of the positive electrode tab 11 and a negative bending portion of the negative electrode tab 12.

[0235] In some embodiments, the positive electrode tab 11, the isolation assembly 13, and the negative electrode tab 12 are wound to form a bending region B. The bending region B includes multiple bending portions arranged along the winding direction W. The electrode assembly 10 includes multiple second isolation layers 132, and the first isolation layer 131 and the multiple second isolation layers 132 are disposed on at least one of the multiple bending portions.

[0236] The bent portions are the positions where the electrode assembly 10 is bent during the winding process. Exemplarily, the plurality of bent portions include a first bent portion B1 and a second bent portion B2. At the first bent portion B1, both the positive electrode sheet 11 and the negative electrode sheet 12 are bent for the first time. At the second bent portion B2, both the positive electrode sheet 11 and the negative electrode sheet 12 are bent for the second time.

[0237] In this embodiment, by disposing the second isolation layer 132 at some or all of the positions among the plurality of bent portions, the risk of short circuit at the bent portions can be effectively reduced, and the safety can be improved.

[0238] It should be noted that one of the second isolation layers 132 can be set to extend through a plurality of bent portions, or each second isolation layer 132 can be set to extend through one bent portion.

[0239] In some embodiments, along the winding direction W, the plurality of second isolation layers 132 are arranged at intervals.

[0240] The plurality of second isolation layers 132 being arranged at intervals can be understood as that the plurality of second isolation layers 132 are not connected into a whole second isolation layer 132, but are split-type. This embodiment can make the setting method of the second isolation layer 132 more flexible, that is, the second isolation layer 132 can be arbitrarily set at the positions where the number of isolation layers needs to be increased, and at the same time, the waste caused by adding the second isolation layer 132 at the positions where the number of isolation layers does not need to be increased can be reduced, and the energy density can be improved.

[0241] In some embodiments, the electrode assembly 10 includes a starting section 100 along the winding direction W. The plurality of bent portions include a first bent portion B1 and a second bent portion B2. Along the winding direction W, the first bent portion B1 is closer to the starting section 100 than the second bent portion B2. The thickness of the second isolation layer 132 disposed at the first bent portion B1 is greater than the thickness of the second isolation layer 132 disposed at the second bent portion B2.

[0242] The risk of lithium deposition on the negative electrode sheet 12 at the first bent portion B1 is higher than the risk of lithium deposition on the negative electrode sheet 12 at the second bent portion B2. The risk of lithium dendrites passing through the second isolation layer 132 at the first bent portion B1 is higher than the risk of lithium dendrites passing through the second isolation layer 132 at the second bent portion B2. Therefore, in this embodiment, the thickness of the second isolation layer 132 disposed at the first bent portion B1 is greater than the thickness of the second isolation layer 132 disposed at the second bent portion B2, so as to strengthen the protection at the first bent portion B1 where short circuit is more likely to occur, improve the safety, and save the usage amount of the second isolation layer 132.

[0243] In some embodiments, a plurality of second isolation layers 132 are bonded to the surface of the first isolation layer 131, which can reduce the risk of the second isolation layer 132 shifting in position during the charge and discharge process of the electrode assembly 10 and ensure the isolation effect of the second isolation layer 132.

[0244] Optionally, both ends of the second isolation layer 132 in the winding direction W are bonded to the first isolation layer 131, and the middle part of the second isolation layer 132 in the winding direction W is separated from the first isolation layer 131.

[0245] In some embodiments, after the electrode assembly 10 is wound and formed, the electrode assembly 10 is hot-pressed from the outside to bond the second isolation layer 132 to the first isolation layer 131.

[0246] In some embodiments, the first isolation layer 131 includes two surfaces in its own thickness direction, and a plurality of second isolation layers 132 are located on the same surface of the first isolation layer 131.

[0247] A too large distance between the positive electrode plate 11 and the negative electrode plate 12 will affect the process of lithium intercalation and lead to an increase in the phenomenon of lithium deposition. By arranging a plurality of second isolation layers 132 on the same surface of the first isolation layer 131, when the first isolation layer 131 is tensioned, the influence of the second isolation layer 132 on the distance between the positive electrode plate 11 and the negative electrode plate 12 can be reduced, the risk of lithium deposition can be reduced, and the safety can be improved.

[0248] Figure 13 It is a schematic structural diagram of the electrode assembly provided by still some other embodiments of the present application before winding.

[0249] As Figure 13 shown, in some embodiments, along the winding direction W, the thickness of a plurality of strengthening regions 13a gradually decreases from the inside to the outside.

[0250] In this embodiment, along the winding direction W, the thickness of the innermost strengthening region 13a is greater than the thickness of the outermost strengthening region 13a. The thicknesses of two adjacent strengthening regions 13a may be the same or different.

[0251] Along the winding direction W, the curvature of the positive bending portion 11a of the positive electrode plate 11 from the inside to the outside gradually decreases, and the risk of contact with lithium dendrites also gradually decreases. In this embodiment, the thickness of the strengthening region 13a can be increased in the region with a high short-circuit risk and decreased in the region with a low short-circuit risk, which can improve the safety and save the amount of the isolation assembly 13.

[0252] In some embodiments, along the winding direction W, the thickness difference between two adjacent strengthening regions 13a is 0.5 μm - 10 μm. Optionally, the thickness difference between two adjacent strengthening regions 13a is 0.5 μm, 1 μm, 2 μm, 5 μm, 7 μm or 10 μm.

[0253] Figure 14 The structural schematic diagram of the electrode assembly provided for some other embodiments of the present application.

[0254] As Figure 14 shown, in some embodiments, the positive electrode tab 11 includes a plurality of positive electrode bending portions 11a arranged along the winding direction W, and at least the positive electrode bending portion 11a formed by the last bending of the positive electrode tab 11 is set as the first bending portion 111.

[0255] When the electrode assembly 10 expands and presses against the housing during charging, the housing will exert a reaction force on the electrode assembly 10. The region of the negative electrode tab 12 opposite to the positive electrode bending portion 11a formed by the last bending of the positive electrode tab 11 is prone to lithium deposition under the action of the reaction force. In this embodiment, at least a part of the strengthening region 13a is adjacent to the positive electrode bending portion 11a formed by the last bending of the positive electrode tab 11, so as to reduce the risk of conduction between the positive electrode bending portion 11a formed by the last bending of the positive electrode tab 11 and lithium dendrites, and improve the safety of the battery cell.

[0256] Exemplarily, the electrode assembly 10 is cylindrical. Each positive electrode bending portion 11a of the positive electrode tab 11 refers to one turn of the positive electrode tab.

[0257] According to some embodiments of the present application, the present application also provides a battery cell, which includes a housing and the electrode assembly of any one of the above embodiments, and the electrode assembly is accommodated in the housing.

[0258] According to some embodiments of the present application, the present application also provides a battery, which includes a plurality of battery cells of any one of the above embodiments.

[0259] According to some embodiments of the present application, the present application also provides an electrical device, which includes the battery cell of any one of the above embodiments, and the battery cell is used to provide electrical energy for the electrical device. The electrical device can be any of the above devices or systems that apply the battery cell.

[0260] According to some embodiments of the present application, with reference to Figures 4 to 8, this application provides an electrode assembly 10, which includes a positive electrode tab 11, a negative electrode tab 12, and a separator assembly 13. The separator assembly 13 is used to isolate the positive electrode tab 11 and the negative electrode tab 12. The separator assembly 13 includes a first separator layer 131 and a second separator layer 132. The first separator layer 131 is used to insulate and isolate the positive electrode tab 11 and the negative electrode tab 12. At least a part of the second separator layer 132 is located between the positive electrode tab 11 and the negative electrode tab 12 and is laminated with the first separator layer 131. The overlapping area of the first separator layer 131 with the second separator layer 132 and the second separator layer 132 form a strengthening area 13a of the separator assembly 13, and the non-overlapping area of the first separator layer 131 with the second separator layer 132 forms a matrix area 13b of the separator assembly 13. The thickness of the strengthening area 13a is greater than the thickness of the matrix area 13b. The second separator layer 132 is formed by folding the end of the first separator layer 131.

[0261] The positive electrode tab 11, the separator assembly 13, and the negative electrode tab 12 are wound to form a bent area B and a flat area A, and the flat area A is connected to the bent area B. At least a part of the strengthening area 13a is arranged in the bent area B, and at least a part of the matrix area 13b is arranged in the flat area A.

[0262] A part of the strengthening area 13a is arranged adjacent to the positive bending part 11a formed by the first bending of the positive electrode tab 11, and another part of the strengthening area 13a is arranged adjacent to the positive bending part 11a formed by the second bending of the positive electrode tab 11.

[0263] The following further illustrates this application with embodiments.

[0264] To make the invention purpose, technical solution, and beneficial technical effects of this application clearer, the following further describes this application in detail with embodiments. However, it should be understood that the embodiments of this application are only for explaining this application and not for limiting this application, and the embodiments of this application are not limited to the embodiments given in the specification. For the embodiments without specifying specific experimental conditions or operating conditions, they are made according to conventional conditions or according to the conditions recommended by the material suppliers.

[0265] Embodiment 1 can be prepared according to the following steps:

[0266] (i) Mix the positive active material LiNi 0.8 Co 0.1 Mn 0.1 O 2 , conductive agent acetylene black, and binder PVDF in a mass ratio of 96:2:2, add the solvent NMP, and stir under a vacuum mixer until the system is homogeneous to obtain a positive electrode paste; uniformly coat the positive electrode paste on the aluminum foil, dry it at room temperature and then transfer it to an oven for further drying, and then obtain the positive electrode tab through cold pressing, slitting, and blanking.

[0267] (ii) Mix the graphite as the negative electrode active material, acetylene black as the conductive agent, CMC as the thickening agent, and SBR as the binder in a mass ratio of 96.4:1:1.2:1.4, add deionized water as the solvent, and stir in a vacuum mixer until the system becomes homogeneous to obtain the negative electrode slurry; uniformly coat the negative electrode slurry on the copper foil, air-dry at room temperature and then transfer it to an oven for further drying, and then obtain the negative electrode plate through cold pressing, slitting, and cutting.

[0268] (iii) Mix ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1 to obtain an organic solvent, and then dissolve the fully dried lithium salt LiPF6 in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0269] (iv) Fold a 7-μm-thick polyethylene film to form a separator assembly. The separator assembly includes a first separator layer and a second separator layer, and the length of the second separator layer is 652.5 mm. The overlapping area of the first separator layer and the second separator layer and the second separator layer form the strengthening area of the separator assembly, and the non-overlapping area of the first separator layer and the second separator layer forms the matrix area of the separator assembly. The thickness of the strengthening area is 14 μm, and the thickness of the matrix area is 7 μm.

[0270] (v) Stack the positive electrode plate, the separator assembly, and the negative electrode plate together and wind them into multiple turns, and then flatten them into a flat shape after winding to prepare an electrode assembly.

[0271] (ⅵ) Install the electrode assembly into a square shell and weld the shell and the end cover; then go through processes such as liquid injection, standing, formation, and shaping to obtain a battery cell. Exemplarily, the capacity of the battery cell is 60 Ah.

[0272] In step (v), artificially make the gap between the innermost positive electrode plate and the innermost negative electrode plate 200 μm to accelerate the lithium deposition of the electrode assembly. In the wound electrode assembly, a first separator layer and a second separator layer are provided between the innermost positive electrode plate and the innermost negative electrode plate.

[0273] Example 2:

[0274] The preparation method of the battery cell in Example 2 refers to Example 1, and the difference is that: in step (ⅵ), artificially make the gap between the innermost two positive electrode plates and the innermost two negative electrode plates 200 μm, the length of the second separator layer is 873.6 mm, and a first separator layer and a second separator layer are also provided between the second positive electrode plate and the second negative electrode plate.

[0275] Comparative Example 1:

[0276] The preparation method of the battery cell of Comparative Example 1 refers to Example 1, with the difference that: the isolation component of Comparative Example 1 is not folded and the isolation component is a single-layer structure.

[0277] Comparative Example 2:

[0278] The preparation method of the battery cell of Comparative Example 2 refers to Example 2, with the difference that: the isolation component of Comparative Example 2 is not folded and the isolation component is a single-layer structure.

[0279] 80 battery cells were prepared for each of Example 1, Example 2, Comparative Example 1, and Comparative Example 2, and each battery cell was tested.

[0280] Specifically, in a normal temperature environment, the battery cells were charged at a rate of 1C and discharged at a rate of 1C, and cyclic charge and discharge were performed in a high SOC (e.g., 0.9 - 1) range.

[0281] 40 battery cells of Example 1 were fully charged after 500 cycles, then left standing for 24 hours, the amplitude of the voltage drop of the battery cells was detected, and the self-discharge rate of each battery cell was calculated, and then the average value was obtained. The self-discharge rate is the voltage drop / time. The remaining 40 battery cells of Example 1 were subjected to 2000 cycles, and the number of battery cell failures was recorded during the cycles, and the failure rate was calculated.

[0282] Example 2, Comparative Example 1, and Comparative Example 2 were also tested according to the above steps.

[0283] The evaluation results of Examples 1 - 2 and Comparative Examples 1 - 2 are shown in Table 1.

[0284] Table 1 Self-discharge rate Failure rate Example 1 0.027 mV / h 0％ Example 2 0.053 mV / h 2.5％ Comparative Example 1 0.71 mV / h 92.5％ Comparative Example 2 0.89 mV / h 95％

[0285] Referring to Examples 1 - 2 and Comparative Examples 1 - 2, by providing a strengthening region between the positive electrode plate and the negative electrode plate, the risk of short circuit can be reduced when lithium metal is deposited on the negative electrode plate, and the service life of the battery cell can be extended.

[0286] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments may be combined with each other.

[0287] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features, but these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. An electrode assembly, characterized in that, it includes a positive electrode tab, a negative electrode tab and a separator assembly, and the separator assembly is used to separate the positive electrode tab and the negative electrode tab; the positive electrode tab, the separator assembly and the negative electrode tab are wound to form a bent area; the separator assembly includes a matrix area and a reinforcing area connected to the matrix area, and the thickness of the reinforcing area is greater than the thickness of the matrix area; the positive electrode tab includes a first bent portion located in the bent area and adjacent to the reinforcing area; the negative electrode tab includes a second bent portion located in the bent area; both sides of the first bent portion are provided with the reinforcing area and the second bent portion; the total thickness of the reinforcing area located inside the first bent portion is greater than or equal to the total thickness of the reinforcing area located outside the first bent portion.

2. The electrode assembly according to claim 1, characterized in that, the thickness of the reinforcing area is 2μm - 100μm.

3. The electrode assembly according to claim 1, characterized in that, the reinforcing area includes a plurality of bent layers, and the plurality of bent layers are located in the bent area and laminated between the first bent portion and the second bent portion.

4. The electrode assembly according to claim 3, characterized in that, the reinforcing area located inside the first bent portion includes at least two of the bent layers; the reinforcing area located outside the first bent portion includes at least two of the bent layers.

5. The electrode assembly according to claim 3, characterized in that, the first bent portion includes a first current collector and a first active material layer provided on the surface of the first current collector, and the thickness of the first active material layer is h1; the second bent portion includes a second current collector and a second active material layer provided on the surface of the second current collector, the thickness of the second active material layer is h2, the thickness of the bent layer is h3, and the thickness of the second current collector is h4; in the thickness direction of the first bent portion, the maximum distance between the first bent portion and the second bent portion is X; the number of the bent layers located between the first bent portion and the second bent portion is Y, and Y is a positive integer greater than 1; the active material capacity per unit area of the first active material layer is A1, and the active material capacity per unit area of the second active material layer is A2, and A2 / A1≥1; h1, h2, h3, h4, X and Y satisfy:

6. The electrode assembly according to claim 3, characterized in that, the first bent portion includes a first current collector and a first active material layer provided on the surface of the first current collector, and the thickness of the first active material layer is h1; the second bent portion includes a second current collector and a second active material layer provided on the surface of the second current collector, the thickness of the second active material layer is h2, the thickness of the bent layer is h3, and the thickness of the second current collector is h4; in the thickness direction of the first bent portion, the maximum distance between the first bent portion and the second bent portion is X; The number of the bending layers between the first bending portion and the second bending portion is Y, and Y is a positive integer greater than 1; The active material capacity per unit area of the first active material layer is A1, and the active material capacity per unit area of the second active material layer is A2, and A2 / A1 < 1; h1, h2, h3, h4, X, and Y satisfy:

7. The electrode assembly according to claim 5 or 6, characterized in that the value of h3 is 1 μm - 20 μm.

8. The electrode assembly according to claim 5 or 6, characterized in that the value of X is 10 μm - 5000 μm.

9. The electrode assembly according to claim 1, characterized in that the positive electrode tab includes a plurality of positive electrode bending portions arranged along the winding direction, and at least the positive electrode bending portion formed by the first bending of the positive electrode tab is set as the first bending portion.

10. The electrode assembly according to claim 9, characterized in that the positive electrode bending portion formed by the second bending of the positive electrode tab is also set as the first bending portion.

11. The electrode assembly according to claim 10, characterized in that the total thickness of the strengthening region inside the positive electrode bending portion formed by the first bending of the positive electrode tab is T1, and the total thickness of the strengthening region inside the positive electrode bending portion formed by the second bending of the positive electrode tab is T2, and T1 ≥ T2.

12. The electrode assembly according to claim 1, characterized in that the positive electrode tab includes a plurality of positive electrode bending portions arranged along the winding direction, and at least the positive electrode bending portion formed by the last bending of the positive electrode tab is set as the first bending portion.

13. The electrode assembly according to claim 1, characterized in that the positive electrode tab, the isolation assembly, and the negative electrode tab are wound to form a flat region, and the flat region is connected to the bending region; At least a part of the base region is arranged in the flat region.

14. The electrode assembly according to claim 13, characterized in that both the strengthening region and the base region are provided in plurality, and the plurality of strengthening regions and the plurality of base regions are alternately arranged along the winding direction.

15. The electrode assembly according to claim 14, characterized in that along the winding direction, the thicknesses of the plurality of strengthening regions gradually decrease from inside to outside.

16. The electrode assembly according to claim 15, characterized in that along the winding direction, the thickness difference between adjacent strengthening regions is 0.5 μm - 10 μm.

17. The electrode assembly according to claim 1, characterized in that the strengthening region is provided with a multi-layer structure, and the base region is provided with a single-layer structure.

18. The electrode assembly according to claim 1, characterized in that the isolation assembly includes a first isolation layer and a second isolation layer, the first isolation layer is used for insulating and isolating the positive electrode tab and the negative electrode tab, and at least a part of the second isolation layer is located between the positive electrode tab and the negative electrode tab and is stacked with the first isolation layer; The region of the first isolation layer overlapping with the second isolation layer and the second isolation layer form the strengthening region of the isolation component, and the region of the first isolation layer not overlapping with the second isolation layer forms the matrix region.

19. The electrode assembly according to claim 18, wherein, the thickness of the second isolation layer is less than or equal to the thickness of the first isolation layer.

20. The electrode assembly according to claim 18, wherein, in the stacking direction of the first isolation layer and the second isolation layer, at least a part of the second isolation layer is separated from the first isolation layer.

21. The electrode assembly according to claim 20, wherein, the positive electrode sheet, the isolation component and the negative electrode sheet are wound to form a flat region, and the flat region is connected to the bent region; a part of the second isolation layer is located in the bent region, and another part of the second isolation layer is located in the flat region; in the bent region, the second isolation layer is separated from the first isolation layer; in the flat region, the second isolation layer is attached to the first isolation layer.

22. The electrode assembly according to claim 18, wherein, the second isolation layer is formed by folding the end of the first isolation layer.

23. The electrode assembly according to claim 22, wherein, the positive electrode sheet, the isolation component and the negative electrode sheet are wound, and the electrode assembly includes a starting section along the winding direction, and the end of the first isolation layer is located in the starting section.

24. The electrode assembly according to claim 23, wherein, the bent region includes a first bent part close to the starting section along the winding direction, and the first isolation layer and the second isolation layer are arranged at the first bent part, and the second isolation layer extends from the end of the first isolation layer and extends beyond the first bent part.

25. The electrode assembly according to claim 18, wherein, the bent region includes a plurality of bent parts arranged along the winding direction, the electrode assembly includes a plurality of the second isolation layers, and the first isolation layer and the plurality of the second isolation layers are arranged at at least one of the plurality of bent parts.

26. The electrode assembly according to claim 25, wherein, along the winding direction, the plurality of the second isolation layers are arranged at intervals.

27. The electrode assembly according to claim 25, wherein, the electrode assembly includes a starting section along the winding direction; the plurality of bent parts include a first bent part and a second bent part, and along the winding direction, the first bent part is closer to the starting section than the second bent part; the thickness of the second isolation layer arranged at the first bent part is greater than the thickness of the second isolation layer arranged at the second bent part.

28. The electrode assembly according to claim 25, wherein, the first isolation layer includes two surfaces along its thickness direction, and the plurality of the second isolation layers are located on the same surface of the first isolation layer.

29. The electrode assembly according to claim 25, It is characterized in that a plurality of the second isolation layers are bonded to the surface of the first isolation layer.

30. The electrode assembly according to claim 1, It is characterized in that the second bent portion is adjacent to the strengthening region.

31. A battery cell, It is characterized in that it includes a housing and the electrode assembly according to any one of claims 1-30, and the electrode assembly is accommodated in the housing.

32. A battery, It is characterized in that it includes a plurality of the battery cells according to claim 31.

33. An electrical device, It is characterized in that it includes the battery cell according to claim 32, and the battery cell is used to provide electrical energy.

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