Electrode assembly, battery cell, battery and electrical device

Abstract

The embodiments of the present application provide an electrode assembly, a battery cell, a battery, and an electrical device. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and an isolation assembly, and the isolation assembly is used to isolate the positive electrode sheet and the negative electrode sheet. The isolation assembly includes a substrate area and a reinforcement area connected to the substrate area, and the thickness of the reinforcement area is greater than the thickness of the substrate area. At least part of the reinforcement area is located between adjacent positive and negative electrode sheets. The reinforcement area can be used to correspond to the position of the negative electrode sheet that is easy to precipitate lithium, so that when the negative electrode sheet precipitates lithium, the reinforcement area can effectively separate the positive electrode sheet and the negative electrode sheet, reduce the risk of lithium dendrites passing through the isolation assembly, and improve the life and safety. Relative to the reinforcement area, the substrate area can have a smaller thickness, which can reduce the amount of isolation assembly used, reduce costs, and improve the energy density of the electrode assembly.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202111062600.7, filed on September 10, 2021, entitled “Electrode assembly and related battery cells, batteries, devices and manufacturing methods”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to the field of battery technology, and more specifically, to an electrode assembly, a battery cell, a battery, and an electrical device. Background Art

[0004] Battery cells are widely used in electronic devices, such as mobile phones, laptop computers, electric vehicles, electric cars, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes, and electric tools, etc. Battery cells can include nickel-cadmium battery cells, nickel-hydrogen battery cells, lithium-ion battery cells, and secondary alkaline zinc-manganese battery cells, etc.

[0005] In the development of battery technology, how to improve the safety of battery cells is a research direction in battery technology. Summary of the invention

[0006] The present application provides an electrode assembly, a battery cell, a battery, and an electrical device, which can improve safety.

[0007] In a first aspect, an embodiment of the present application provides an electrode assembly, including a positive electrode sheet, a negative electrode sheet, and a separation assembly, wherein the separation assembly is used to separate the positive electrode sheet from the negative electrode sheet. The separation assembly includes a substrate region and a reinforcement region connected to the substrate region, wherein the thickness of the reinforcement region is greater than the thickness of the substrate region. At least a portion of the reinforcement region is located between adjacent positive electrode sheets and negative electrode sheets.

[0008] In the above technical solution, the reinforcement area can be used to correspond to the position of the negative electrode sheet that is easy to precipitate lithium. In this way, when the negative electrode sheet precipitates lithium, the reinforcement area can effectively separate the positive electrode sheet and the negative electrode sheet, reduce the risk of lithium dendrites passing through the isolation component, and improve the life and safety. Compared with the reinforcement area, the base area can have a smaller thickness, which can reduce the amount of isolation components, reduce costs, and improve the energy density of the electrode assembly.

[0009] In some embodiments, the thickness of the reinforcement region is 2 μm-100 μm.

[0010] The smaller the thickness of the reinforcement area, the higher the energy density of the electrode assembly, but the risk of lithium dendrites penetrating the reinforcement area is higher. The larger the thickness of the reinforcement area, the lower the energy density of the electrode assembly, but the lower the risk of lithium dendrites penetrating the reinforcement area, and the higher the safety of the electrode assembly. The above technical solution limits the thickness of the reinforcement area to 2μm-100μm to balance the energy density and safety of the electrode assembly.

[0011] In some embodiments, the positive electrode sheet, the isolation assembly, and the negative electrode sheet are wound to form a bending region, and at least a portion of the reinforcement region is disposed in the bending region.

[0012] The above technical solution sets at least part of the reinforced area in the bending area where lithium is easily deposited. Even if lithium deposition occurs in the bending area, the reinforced area can block lithium dendrites, reduce the probability of conduction between the positive electrode sheet and the negative electrode sheet, effectively reduce the risk of short circuit, and improve the service life and safety of the electrode assembly.

[0013] In some embodiments, the positive electrode sheet includes a first bending portion located in the bending area and adjacent to the reinforcement area, and the negative electrode sheet includes a second bending portion adjacent to the first bending portion. The reinforcement area includes a plurality of bending layers, and the plurality of bending layers are located in the bending area and stacked between the first bending portion and the second bending portion.

[0014] In the above technical solution, the multiple bending layers can block lithium dendrites when lithium is deposited in the second bending portion, reduce the risk of lithium dendrites contacting the first bending portion, and improve safety.

[0015] In some embodiments, at least the inner side of the first bending portion is provided with a reinforcement area and a second bending portion.

[0016] The curvature of the second bend located inside the first bend is greater than that of the first bend, so the second bend is more likely to have active material fall off during the bending process, that is, the second bend inside the first bend is more likely to have lithium deposition. The reinforcement area of ​​the above technical solution can separate the first bend from the second bend located inside the first bend, and even if lithium is deposited in the second bend, the probability of lithium dendrites passing through the reinforcement area can be reduced, thereby reducing the risk of short circuit and improving safety.

[0017] In some embodiments, the first bend portion includes a first current collecting portion and a first active material layer disposed on the surface of the first current collecting portion, and the thickness of the first active material layer is h1. The second bend portion includes a second current collecting portion and a second active material layer disposed on the surface of the second current collecting portion, the thickness of the second active material layer is h2, the thickness of the bend layer is h3, and the thickness of the second current collecting portion is h4. In the thickness direction of the first bend portion, the maximum spacing between the first bend portion and the second bend portion is X. The number of bend layers between the first bend portion and the second bend 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:

[0018]

[0019] The fewer the number of bending layers in the reinforcement area, the higher the risk of lithium dendrites passing through the reinforcement area; the more the number of bending layers in the reinforcement area, the more complex the structure of the isolation assembly, and the lower the energy density of the electrode assembly. The above technical solution can set the number of bending layers according to the above formula to balance the safety and energy density of the electrode assembly.

[0020] In some embodiments, the first bend portion includes a first current collecting portion and a first active material layer disposed on the surface of the first current collecting portion, and the thickness of the first active material layer is h1. The second bend portion includes a second current collecting portion and a second active material layer disposed on the surface of the second current collecting portion, the thickness of the second active material layer is h2, the thickness of the bend layer is h3, and the thickness of the second current collecting portion is h4. In the thickness direction of the first bend portion, the maximum spacing between the first bend portion and the second bend portion is X. The number of bend layers between the first bend portion and the second bend 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:

[0021]

[0022] In the above technical solution, the number of bending layers can be set according to the above formula to balance the safety and energy density of the electrode assembly.

[0023] In some embodiments, the value of h3 is 1 μm-20 μm to balance the safety and energy density of the electrode assembly.

[0024] In some embodiments, the value of X is 10 μm-5000 μm.

[0025] In some embodiments, the positive electrode sheet includes a plurality of positive bending portions arranged along a winding direction, and at least the positive bending portion formed by the first bending of the positive electrode sheet is set as the first bending portion.

[0026] The curvature of the positive electrode bent portion formed by the first bending of the positive electrode sheet is relatively large. During charging, the negative electrode sheet adjacent to the positive electrode bent portion formed by the first bending of the positive electrode sheet is more likely to have lithium deposition problems. The above technical solution sets the positive electrode bent portion formed by the first bending of the positive electrode sheet as the first bending portion, so that the reinforcement area can effectively isolate the positive electrode bent portion formed by the first bending of the positive electrode sheet from lithium dendrites, reduce the risk of short circuit, and improve safety.

[0027] In some embodiments, the positive electrode bending portion formed by the second bending of the positive electrode sheet is also configured as the first bending portion.

[0028] The above technical solution sets the positive electrode bending portion formed by the second bending of the positive electrode plate as the first bending portion, so that the reinforcement area can effectively isolate the positive electrode bending portion formed by the second bending of the positive electrode plate from the lithium dendrites, reduce the short circuit risk, and improve safety.

[0029] In some embodiments, the total thickness of the reinforced area inside the positive bending portion formed by the first bending of the positive electrode sheet is T1, and the total thickness of the reinforced area inside the positive bending portion formed by the second bending of the positive electrode sheet is T2, and T1≥T2.

[0030] The above technical solution makes T1≥T2, so as to reduce the risk of the positive electrode bent portion formed by the first bending of the positive electrode plate being connected to the lithium dendrites, thereby improving the safety of the battery cell.

[0031] In some embodiments, a reinforcement area and a second bending portion are provided on both sides of the first bending portion, and the total thickness of the reinforcement area located on the inner side of the first bending portion is greater than or equal to the total thickness of the reinforcement area located on the outer side of the first bending portion, so as to reduce the risk of conduction between the first bending portion and the lithium dendrites and improve the safety of the battery cell.

[0032] In some embodiments, the positive electrode plate includes multiple positive electrode bends arranged along the winding direction, and at least the positive electrode bend formed by the last bend of the positive electrode plate is set as the first bend, so as to reduce the risk of conduction between the positive electrode bend formed by the last bend of the positive electrode plate and lithium dendrites, thereby improving the safety of the battery cell.

[0033] In some embodiments, the positive electrode sheet, the isolation assembly and the negative electrode sheet are wound to form a straight region, and the straight region is connected to the bent region. At least part of the base region is disposed in the straight region.

[0034] The positive electrode sheets and the negative electrode sheets located in the straight area are both in a straight state, the active materials in the straight area are not easy to fall off, and the negative electrode sheets located in the straight area are not prone to lithium deposition problems. Therefore, even if the above technical solution sets the substrate area to the flat area, it can improve the insulation between the positive and negative electrode sheets and reduce the risk of short circuit.

[0035] In some embodiments, the reinforcement region and the base region are both provided in plurality, and the plurality of reinforcement regions and the plurality of base regions are alternately arranged along the winding direction.

[0036] In the above technical solution, the multiple reinforcement areas can respectively correspond to the multiple positive bending portions of the positive electrode sheet, so as to reduce the risk of short circuit in the multiple positive bending portions of the positive electrode sheet and improve safety.

[0037] In some embodiments, along the winding direction, the thickness of the plurality of reinforced regions gradually decreases from the inside to the outside.

[0038] Along the winding direction, the curvature of the positive electrode bending portion of the positive electrode sheet from the inside to the outside gradually decreases, and the risk of contact with lithium dendrites gradually decreases. The above technical solution can increase the thickness of the reinforcement area in the area with high short circuit risk and reduce the thickness of the reinforcement area in the area with low short circuit risk, which can improve safety and save the amount of isolation components.

[0039] In some embodiments, along the winding direction, the thickness difference between adjacent reinforcement regions is 0.5 μm-10 μm.

[0040] In some embodiments, the reinforcement region is configured as a multi-layer structure, and the base region is configured as a single-layer structure.

[0041] In the above technical solution, under the premise of the same thickness, compared with the reinforcement area with a single-layer structure, the reinforcement area with a multi-layer structure can more effectively block lithium dendrites, reduce the risk of short circuit, and improve safety. Under the premise of meeting the strength requirements, compared with the reinforcement area with a single-layer structure, the reinforcement area with a multi-layer structure can adopt a smaller thickness, which can reduce the amount of isolation components and improve the energy density of the electrode assembly.

[0042] In some embodiments, the isolation assembly includes a first isolation layer and a second isolation layer, the first isolation layer is used to insulate and isolate the positive electrode sheet and the negative electrode sheet, and at least a portion of the second isolation layer is located between the positive electrode sheet and the negative electrode sheet and is stacked with the first isolation layer. The area of ​​the first isolation layer overlapping with the second isolation layer and the second isolation layer form a reinforcement area of ​​the isolation assembly, and the area of ​​the first isolation layer that does not overlap with the second isolation layer forms a substrate area.

[0043] In the above technical solution, a second isolation layer is additionally added to the electrode assembly to form a reinforcement area with a larger thickness on the isolation assembly, thereby reducing the risk of short circuit caused by lithium plating and improving safety.

[0044] In some embodiments, the thickness of the second isolation layer is less than or equal to the thickness of the first isolation layer.

[0045] In the above technical solution, the first isolation layer and the second isolation layer can play the role of multi-layer protection, so the added second isolation layer can have a thickness no greater than that of the first isolation layer to reduce the amount of the second isolation layer.

[0046] In some embodiments, in a stacking direction of the first isolation layer and the second isolation layer, at least a portion of the second isolation layer is disposed separately from the first isolation layer.

[0047] When the first isolation layer is stretched under the pressure of the lithium layer, the portion of the second isolation layer separated from the first isolation layer is less affected by the first isolation layer, the second isolation layer is stretched to a lesser extent, and the risk of 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.

[0048] In some embodiments, the positive electrode sheet, the isolation assembly, and the negative electrode sheet are wound to form a bent region and a straight region, and the straight region is connected to the bent region. A portion of the second isolation layer is located in the bent region, and another portion of the second isolation layer is located in the straight region. In the bent region, the second isolation layer is separated from the first isolation layer. In the straight region, the second isolation layer is attached to the first isolation layer.

[0049] In the above technical solution, the risk of lithium deposition in the bending area is higher. Separating the second isolation layer from the first isolation layer in the bending area can effectively reduce the risk of lithium dendrites passing through the first isolation layer and the second isolation layer, thereby improving safety. In the straight area, the second isolation layer is attached to the first isolation layer, which can reduce the movement of the second isolation layer along the winding direction and reduce the risk of dislocation of the second isolation layer.

[0050] In some embodiments, the second isolation layer is formed by folding an end portion of the first isolation layer.

[0051] In the above technical solution, the second isolation layer is extended directly from the end of the first isolation layer, and there is no 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.

[0052] In some embodiments, the positive electrode sheet, the isolation assembly and the negative electrode sheet are wound, 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.

[0053] 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 plate, which can reduce the risk of lithium dendrites passing through the first isolation layer and the second isolation layer at the same time and contacting the positive electrode bending portion of the positive electrode plate, thereby improving safety and reducing the length of the second isolation layer that needs to be extended, saving usage and reducing costs.

[0054] In some embodiments, the positive electrode sheet, the isolation assembly and the negative electrode sheet are wound to form a bending area, and the bending area includes a first bending portion close to the starting section along the winding direction, and 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 exceeds the first bending portion.

[0055] In the above technical solution, at the first bending part, the curvature of the positive electrode sheet and the negative electrode sheet is the largest, and during charging, the negative electrode sheet has the highest risk of lithium deposition. The second isolation layer extends beyond the first bending part, and the first isolation layer and the second isolation layer can at least protect the first bending part, which is most prone to lithium deposition, and can also save the use of the second isolation layer, thereby saving costs and improving the safety and service life of the electrode assembly.

[0056] In some embodiments, the positive electrode sheet, the isolation assembly and the negative electrode sheet are wound to form a bending region. The bending region includes a plurality of bending locations 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 arranged at least one of the plurality of bending locations.

[0057] In the above technical solution, a second isolation layer is provided at part or all of the multiple bending parts, which can effectively reduce the risk of short circuit at the bending parts and improve safety.

[0058] In some embodiments, a plurality of second isolation layers are spaced apart along the winding direction.

[0059] The above technical solution can make the setting 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. At the same time, it can also reduce the waste caused by adding the second isolation layer at the position where the number of isolation layers does not need to be increased, thereby improving the energy density.

[0060] In some embodiments, the electrode assembly includes a starting section along a winding direction. The plurality of bending locations include a first bending location and a second bending location, and along the winding direction, the first bending location is closer to the starting section than the second bending location. The thickness of the second isolation layer disposed at the first bending location is greater than the thickness of the second isolation layer disposed at the second bending location.

[0061] The above technical solution can strengthen the protection at the first bending part which is more prone to short circuit, improve the safety, and save the amount of the second isolation layer.

[0062] In some embodiments, the first isolation layer includes two surfaces along its own thickness direction, and multiple second isolation layers are located on the same surface of the first isolation layer, so as to reduce the influence of the second isolation layer on the distance between the positive electrode plate and the negative electrode plate when the first isolation layer is tensioned, reduce the risk of lithium plating, and improve safety.

[0063] In some embodiments, multiple second isolation layers are bonded to the surface of the first isolation layer, which can reduce the risk of positional displacement of the second isolation layer during the charge and discharge process of the electrode assembly and ensure the isolation effect of the second isolation layer.

[0064] In a second aspect, an embodiment of the present application provides a battery cell, comprising a housing and an electrode assembly according to any one of the embodiments of the first aspect, wherein the electrode assembly is accommodated in the housing.

[0065] In a third aspect, an embodiment of the present application provides a battery comprising a plurality of battery cells according to the second aspect.

[0066] In a fourth aspect, an embodiment of the present application provides an electrical device, comprising the battery cell of the second aspect, wherein the battery cell is used to provide electrical energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without paying creative work.

[0068] Figure 1 A schematic diagram of the structure of a vehicle provided in some embodiments of the present application;

[0069] Figure 2 An exploded schematic diagram of a battery provided in some embodiments of the present application;

[0070] Figure 3 An exploded schematic diagram of a battery cell provided in some embodiments of the present application;

[0071] Figure 4 A schematic diagram of the structure of an electrode assembly provided in some embodiments of the present application;

[0072] Figure 5 for Figure 4 A partial enlarged schematic diagram of the electrode assembly shown;

[0073] Figure 6 for Figure 5An enlarged schematic diagram at box P;

[0074] Figure 7 for Figure 4 The schematic diagram of the structure of the electrode assembly before winding is shown;

[0075] Figure 8 for Figure 7 A schematic diagram of the structure of the isolation assembly shown;

[0076] Fig. 9 A schematic diagram of the structure of an isolation assembly of an electrode assembly provided in some other embodiments of the present application before winding;

[0077] Fig.10 A schematic diagram of the structure of an electrode assembly provided in some other embodiments of the present application;

[0078] Fig.11 for Fig.10 A partial enlarged schematic diagram of the electrode assembly shown;

[0079] Fig.12 for Fig.10 The schematic diagram of the structure of the electrode assembly before winding is shown;

[0080] Fig.13 A schematic diagram of the structure of an electrode assembly before winding provided in some other embodiments of the present application;

[0081] Fig.14 A schematic diagram of the structure of an electrode assembly provided in some further embodiments of the present application.

[0082] The reference numerals of the specific embodiments are as follows:

[0083] 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. Shell; 21. Shell; 22. End cover; 30. Electrode terminal; 11. Positive electrode sheet; 111. First bending part; 1111. First current collecting part; 1112. First active material layer; 11a. Positive bending part part; 12, negative electrode plate; 121, second bending portion; 1211, second current collecting portion; 1212, second active material layer; 13, isolation component; 131, first isolation layer; 132, second isolation layer; 133, base film; 134, insulating layer; 13a, reinforcement area; 13b, substrate area; 14, bending layer; A, straight area; B, bending area; B1, first bending part; B2, second bending part; W, winding direction. DETAILED DESCRIPTION

[0084] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0085] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by technicians in the technical field of the present application; the terms used in the specification of the application herein are only for the purpose of describing specific embodiments and are not intended to limit the present application; the terms "including" and "having" and any variations thereof in the specification and claims of the present application and the above-mentioned drawings are intended to cover non-exclusive inclusions. The terms "first", "second", etc. in the specification and claims of the present application or the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order or a primary and secondary relationship.

[0086] In the description of the present application, it should be understood that the terms "center", "lateral", "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0087] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", and "attached" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0088] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0089] The term "and / or" in this article is only a description of the association relationship of the associated objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0090] The term "multiple" as used in this application refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple sheets" refers to more than two sheets (including two sheets).

[0091] In the present application, battery cells may include lithium-ion secondary battery cells, lithium-ion primary battery cells, lithium-sulfur battery cells, sodium-lithium-ion battery cells, sodium-ion battery cells or magnesium-ion battery cells, etc., and the embodiments of the present application do not limit this. Battery cells may be cylindrical, flat, rectangular or other shapes, etc., and the embodiments of the present application do not limit this. Battery cells are generally divided into three types according to the packaging method: cylindrical battery cells, square battery cells and soft-pack battery cells, and the embodiments of the present application do not limit this.

[0092] The battery cell includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator. The battery cell mainly relies on the movement of metal ions between the positive electrode sheet and the negative electrode sheet to work. The positive electrode sheet includes a positive electrode collector and a positive electrode active material layer. The positive electrode active material layer is coated on the surface of the positive electrode collector. The current collector not coated with the positive electrode active material layer protrudes from the current collector coated with the positive electrode active material layer. The current collector not coated with the positive electrode active material layer serves as the positive electrode tab. Taking lithium-ion batteries as an example, the material of the positive electrode collector can be aluminum, and the positive electrode active material can be lithium cobalt oxide, lithium iron phosphate, ternary lithium or lithium manganese oxide, etc. The negative electrode sheet includes a negative electrode collector and a negative electrode active material layer. The negative electrode active material layer is coated on the surface of the negative electrode collector. The current collector not coated with the negative electrode active material layer protrudes from the current collector coated with the negative electrode active material layer. The current collector not coated with the negative electrode active material layer serves as the negative electrode tab. The material of the negative electrode collector can be copper, and the negative electrode active material can be carbon or silicon, etc. In order to ensure that a large current can pass without melting, the number of positive pole ears is multiple and stacked together, and the number of negative pole ears is multiple and stacked together. The material of the separator can be PP (polypropylene) or PE (polyethylene), etc. The electrode assembly can be a winding structure or a laminated structure, and the embodiments of the present application are not limited to this. The development of battery technology must simultaneously consider multiple design factors, such as performance parameters such as energy density, cycle life, discharge capacity, and charge and discharge rate. In addition, the safety of the battery must also be considered.

[0093] 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 or a battery pack. The battery generally includes a box for encapsulating one or more battery cells. The box can prevent liquid or other foreign matter from affecting the charging or discharging of the battery cells.

[0094] The separator has electronic insulation properties and is disposed between the positive electrode sheet and the negative electrode sheet. Its main function is to prevent the positive electrode sheet and the negative electrode sheet from contacting each other, thereby causing an internal short circuit in the electrode assembly. The separator has a large number of through-holes, which can ensure the free passage of electrolyte ions. In particular, the separator has good permeability to lithium ions. Exemplarily, the separator may include an isolation base layer and a functional layer located on the surface of the isolation base layer. The isolation 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.

[0095] Isolators play a very important role in electrode assemblies and can directly cause short circuits, reduced performance and lifespan of electrode assemblies.

[0096] When the battery cell is charging, metal ions are released from the positive electrode active material layer and embedded in the negative electrode active material layer, but some abnormal situations may occur, resulting in the precipitation of metal ions. Taking lithium-ion battery cells as an example, due to insufficient lithium embedding space in the negative electrode active material layer, too much resistance for lithium ions to embed in the negative electrode active material layer, or too fast lithium ions escaping from the positive electrode active material layer, the released lithium ions cannot be embedded in the negative electrode active material layer of the negative electrode plate in equal amounts. The lithium ions that cannot be embedded in the negative electrode plate can only obtain electrons on the surface of the negative electrode plate, thereby forming metallic lithium. This is the lithium precipitation phenomenon. Lithium precipitation not only reduces the performance of the battery cell and greatly shortens the cycle life, but also limits the fast charging capacity of the battery cell. In addition, when lithium precipitation occurs in the battery cell, the precipitated lithium metal is very active and can react with the electrolyte at a lower temperature, causing the battery cell self-heating starting temperature (Tonset) to decrease and the self-heating rate to increase, seriously endangering the safety of the battery cell. Furthermore, when lithium precipitation is severe, the released lithium ions can form a lithium layer on the surface of the negative electrode. The lithium dendrites of the lithium layer may pass through the isolation piece and cause a short circuit between the adjacent positive and negative electrodes, posing a safety hazard.

[0097] The inventors have attempted to increase the thickness of the separator as a whole to reduce the risk of lithium dendrites penetrating the separator. However, increasing the thickness of the separator will reduce the energy density of the electrode assembly.

[0098] The inventors noticed that during the charge and discharge process, only a part of the negative electrode plate is prone to severe lithium deposition. In other words, a part of the negative electrode plate is not prone to lithium deposition or only slightly deposits lithium, and the isolation piece corresponding to this part does not need to be thickened.

[0099] In view of this, the inventor of the present application has proposed an electrode assembly, which includes a positive electrode sheet, a negative electrode sheet and an isolation assembly, and the isolation assembly is used to isolate the positive electrode sheet and the negative electrode sheet. The isolation assembly includes a substrate area and a reinforcement area connected to the substrate area, and the thickness of the reinforcement area is greater than the thickness of the substrate area; at least part of the reinforcement area is located between adjacent positive and negative electrode sheets. The reinforcement area can be used to correspond to the position of the negative electrode sheet that is easy to precipitate lithium, so that when the negative electrode sheet precipitates lithium, the reinforcement area can effectively separate the positive electrode sheet and the negative electrode sheet, reduce the risk of lithium dendrites passing through the isolation assembly, and improve the life and safety. Relative to the reinforcement area, the substrate area can have a smaller thickness, which can reduce the amount of isolation assembly used, reduce costs, and improve the energy density of the electrode assembly.

[0100] For the convenience of description, the following embodiments are described by taking the electric device as a vehicle as an example.

[0101] Figure 1 This is a schematic diagram of the structure of a vehicle provided in some embodiments of the present application. Figure 1 As shown, a battery 2 is disposed inside the vehicle 1, and the battery 2 may be disposed at the bottom, head, or tail of the vehicle 1. The battery 2 may be used to power the vehicle 1, for example, the battery 2 may be used as an operating power source for the vehicle 1.

[0102] The vehicle 1 may further include a controller 3 and a motor 4 , wherein the controller 3 is used to control the battery 2 to supply power to the motor 4 , for example, to meet the power requirements of starting, navigating, and driving the vehicle 1 .

[0103] In some embodiments of the present application, the battery 2 can not only serve as an operating power source for the vehicle 1, but also serve as a driving power source for the vehicle 1, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1.

[0104] Figure 2 Schematic diagram of an explosion of a battery provided in some embodiments of the present application. Figure 2 As shown, the battery 2 includes a box body 5 and a battery cell 6 , and the battery cell 6 is accommodated in the box body 5 .

[0105] The box 5 is used to accommodate the battery cell 6, and the box 5 can be of various structures. In some embodiments, the box 5 can include a first box portion 5a and a second box portion 5b, the first box portion 5a and the second box portion 5b cover each other, and the first box portion 5a and the second box portion 5b jointly define a storage space 5c for accommodating the battery cell 6. The second box portion 5b can be a hollow structure with one end open, the first box portion 5a is a plate-like structure, and the first box portion 5a covers the open side of the second box portion 5b to form a box 5 with a storage space 5c; the first box portion 5a and the second box portion 5b can also be hollow structures with one side open, and the open side of the first box portion 5a covers the open side of the second box portion 5b to form a box 5 with a storage space 5c. Of course, the first box portion 5a and the second box portion 5b can be of various shapes, such as a cylinder, a cuboid, etc.

[0106] In order to improve the sealing performance after the first box body part 5a and the second box body part 5b are connected, a sealing member, such as a sealant, a sealing ring, etc., may also be provided between the first box body part 5a and the second box body part 5b.

[0107] Assuming that the first box body portion 5a covers the top of the second box body portion 5b, the first box body portion 5a can also be called an upper box cover, and the second box body portion 5b can also be called a lower box.

[0108] In the battery 2, there are multiple battery cells 6. Multiple battery cells 6 can be connected in series, in parallel, or in mixed connection. Mixed connection means that multiple battery cells 6 are both connected in series and in parallel. Multiple battery cells 6 can be directly connected in series, in parallel, or in mixed connection, and then the whole formed by multiple battery cells 6 is accommodated in the box 5; of course, multiple battery cells 6 can also be connected in series, in parallel, or in mixed connection to form a battery module, and multiple battery modules are then connected in series, in parallel, or in mixed connection to form a whole, and accommodated in the box 5.

[0109] Figure 3 An exploded schematic diagram of a battery cell provided in some embodiments of the present application.

[0110] The battery cell 6 refers to the smallest unit that constitutes the battery 2. Figure 3 As shown, the battery cell 6 includes a housing 20 , an electrode assembly 10 and other functional components, and the electrode assembly 10 is accommodated in the housing 20 .

[0111] In some embodiments, the housing 20 includes an end cap 22 and a shell 21 .

[0112] The end cap 22 refers to a component that covers the opening of the shell 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 shell 21 to match the shell 21. Optionally, the end cap 22 can be made of a material with a certain hardness and strength (such as aluminum alloy), so that the end cap 22 is not easily deformed when squeezed and collided, so that the battery cell 6 can have a higher structural strength and the safety performance can also be improved. Functional components such as electrode terminals 30 can be provided on the end cap 22. The electrode terminal 30 can be used to be electrically connected to the electrode assembly 10 for outputting or inputting electrical energy of the battery cell 6.

[0113] 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 may also be provided on the end cap 22. The material of the end cap 22 may also be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., which is not particularly limited in the embodiments of the present application.

[0114] In some embodiments, an insulating member may be provided inside the end cap 22, and the insulating member may be used to isolate the electrical connection components in the housing 21 from the end cap 22 to reduce the risk of short circuit. For example, the insulating member may be plastic, rubber, or the like.

[0115] The shell 21 is a component used to cooperate with the end cap 22 to form the internal environment of the battery cell 6, wherein the formed internal environment can be used to accommodate the electrode assembly 10, the electrolyte and other components. The shell 21 and the end cap 22 can be independent components, and an opening can be set on the shell 21, and the internal environment of the battery cell 6 is formed by covering the opening with the end cap 22 at the opening. Without limitation, the end cap 22 and the shell 21 can also be integrated. Specifically, the end cap 22 and the shell 21 can form a common connection surface before other components are put into the shell, and when the interior of the shell 21 needs to be encapsulated, the end cap 22 covers the shell 21. The shell 21 can be of various shapes and sizes, such as a rectangular parallelepiped, a cylindrical shape, a hexagonal prism, etc. Specifically, the shape of the shell 21 can be determined according to the specific shape and size of the electrode assembly 10. The material of the shell 21 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiment of the present application does not impose any special restrictions on this.

[0116] The electrode assembly 10 is a component of the battery cell 6 that is immersed in the electrolyte to produce an electrochemical reaction. One or more electrode assemblies 10 may be included in the shell 21. The electrode assembly 10 is mainly formed by winding a positive electrode sheet and a negative electrode sheet, and an isolation member is usually provided between the positive electrode sheet and the negative electrode sheet. The parts of the positive electrode sheet and the negative electrode sheet with active materials constitute the main body of the electrode assembly 10, and the parts of the positive electrode sheet and the negative electrode sheet without active materials each constitute a lug. The positive electrode lug and the negative electrode lug may be located together at one end of the main body or respectively at both ends of the main body. During the charge and discharge process of the battery cell 6, the positive electrode active material and the negative electrode active material react with the electrolyte, and the lugs connect the electrode terminals 30 to form a current loop.

[0117] Figure 4 A schematic diagram of the structure of an electrode assembly provided in some embodiments of the present application; Figure 5 for Figure 4 A partial enlarged schematic diagram of the electrode assembly shown; Figure 6 for Figure 5 An enlarged schematic diagram at box P; Figure 7 for Figure 4 The schematic diagram of the structure of the electrode assembly before winding is shown; Figure 8 for Figure 7 Schematic diagram of the structure of the isolation component shown.

[0118] like Figures 4 to 8 As shown, the electrode assembly 10 of the embodiment of the present application includes a positive electrode sheet 11, a negative electrode sheet 12 and an isolation assembly 13, and the isolation assembly 13 is used to isolate the positive electrode sheet 11 from the negative electrode sheet 12. The isolation assembly 13 includes a base region 13b and a reinforcement region 13a connected to the base region 13b, and the thickness of the reinforcement region 13a is greater than the thickness of the base region 13b; at least a portion of the reinforcement region 13a is located between the adjacent positive electrode sheet 11 and the negative electrode sheet 12.

[0119] The electrode assembly 10 may be in various shapes. For example, the electrode assembly 10 may be cylindrical, flat, prism (eg, triangular prism, quadrangular prism or hexagonal prism) or other shapes.

[0120] The isolation component 13 may be one or more. Exemplarily, the isolation component 13 is set to two, and the present application may first stack one isolation component 13, the negative electrode sheet 12, another isolation component 13 and the positive electrode sheet 11 in sequence, and then wind them more than two times to form a winding structure. When the isolation component 13 is set to multiple, only one isolation component 13 may be provided with a reinforcement area 13a, or each isolation component 13 may be provided with a reinforcement area 13a.

[0121] The isolation component 13 is a component including an insulating film, which is used to isolate the positive electrode plate 11 and the negative electrode plate 12. The insulating film has a large number of through micropores, which can ensure the free passage of metal ions; illustratively, the insulating film has good permeability to lithium ions and basically cannot block the passage of lithium ions.

[0122] Exemplarily, the isolation component 13 may be made of one insulating film or may be made of multiple insulating films.

[0123] The reinforcement area 13a may be one or more. Exemplarily, there are more than one reinforcement area 13a, and adjacent reinforcement areas 13a are connected through the base area 13b.

[0124] The reinforcing area 13 a may be entirely located between the positive electrode sheet 11 and the negative electrode sheet 12 , or may be only partially located between the positive electrode sheet 11 and the negative electrode sheet 12 .

[0125] The reinforcement area 13a can be used to correspond to the position of the negative electrode plate 12 that is easy to precipitate lithium. In this way, when the negative electrode plate 12 precipitates lithium, the reinforcement area 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 life and safety. Compared with the reinforcement area 13a, the base area 13b can have a smaller thickness, which can reduce the amount of isolation component 13, reduce costs, and improve the energy density of the electrode assembly 10.

[0126] In some embodiments, the thickness of the reinforcement region 13a is 2 μm-100 μm. Optionally, the thickness of the reinforcement region 13a is 2 μm, 5 μm, 7 μm, 10 μm, 12 μm, 20 μm, 30 μm, 50 μm, 80 μm or 100 μm.

[0127] The smaller the thickness of the reinforcement region 13a, the higher the energy density of the electrode assembly 10, but the higher the risk of the reinforcement region 13a being penetrated by lithium dendrites. The larger the thickness of the reinforcement region 13a, the lower the energy density of the electrode assembly 10, but the lower the risk of the reinforcement region 13a being penetrated by lithium dendrites, and the higher the safety of the electrode assembly 10.

[0128] After experiments and calculations, the inventors limit the thickness of the reinforcement region 13 a to 2 μm-100 μm to balance the energy density and safety of the electrode assembly 10 .

[0129] In some embodiments, the thickness of the reinforcement region 13 a is 5 μm-30 μm.

[0130] In some embodiments, the reinforcement region 13a is configured as a multi-layer structure, and the base region 13b is configured as a single-layer structure.

[0131] In the reinforcement area 13a, multiple isolation layers are stacked together to form a multilayer structure. The stacking direction of the multiple isolation layers is parallel to the stacking direction of the positive electrode sheet 11 and the negative electrode sheet 12. In the reinforcement area 13a, two adjacent isolation layers can be connected to each other or separated from each other.

[0132] For the reinforcement region 13a having a multi-layer structure, the thickness of the reinforcement region 13a refers to the sum of the thicknesses of the plurality of isolation layers.

[0133] 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 may be 2-15.

[0134] In the base region 13b, the isolation layer is a single layer. The base region 13b can be one or more. Exemplarily, the base region 13b and the reinforcement region 13a are both multiple, and the multiple base regions 13b and the multiple reinforcement regions 13a are alternately arranged along the winding direction W.

[0135] The substrate area 13b is used to correspond to the position of the negative electrode plate 12 that is not easy to deposit lithium. The substrate area 13b has a smaller number of layers, which can reduce the amount of the isolation component 13 and improve the energy density of the battery cell.

[0136] When a lithium layer is deposited on the surface of the negative electrode sheet 12, the lithium layer will squeeze the isolation layer near the negative electrode sheet 12 in the reinforcement area 13a, and the isolation layer near the negative electrode sheet 12 will stretch under the pressure of the lithium layer. When the pore size of the local micropores in the isolation layer near the negative electrode sheet 12 becomes larger and forms a defective area, smaller lithium dendrites in the lithium layer may pass through the defective area. The isolation layer of the reinforcement area 13a away from the negative electrode sheet 12 can insulate and isolate the lithium dendrites passing through the defective area from the positive electrode sheet 11, thereby reducing the risk of contact between the lithium dendrites and the positive electrode sheet 11 and providing safety.

[0137] The distance between the isolation layer far away from the negative electrode sheet 12 and the lithium layer in the reinforcement area 13a is relatively large, and the extrusion pressure from the lithium layer is relatively small. The risk of stretching and generating defective areas under the extrusion pressure is also relatively small. The position of the defective area generated in the isolation layer during the stretching process is uncertain. Even if the isolation layer far away from the negative electrode sheet 12 generates a defective area, the possibility that the defective area of ​​the isolation layer far away from the negative electrode sheet 12 is exactly opposite to the defective area of ​​the isolation layer close to the negative electrode sheet 12 is very small, and it is difficult for lithium dendrites to pass through the reinforcement area 13a at the same time. Therefore, by setting the reinforcement area 13a, the embodiment of the present application can effectively reduce the risk of short circuit and improve safety.

[0138] Under the premise of the same thickness, compared with the reinforcement area 13a with a single-layer structure, the reinforcement area 13a with a multi-layer structure can more effectively block lithium dendrites, reduce the risk of short circuit, and improve safety. Exemplarily, the protective effect of the reinforcement area 13a composed of two layers of 5μm isolation layers is better than the protective effect of the reinforcement area 13a composed of a single-layer isolation layer of 10μm. In other words, under the premise of meeting the insulation requirements, compared with the reinforcement area 13a with a single-layer structure, the reinforcement area 13a with a multi-layer structure can adopt a smaller thickness, which can reduce the amount of isolation assembly 13 and improve the energy density of the electrode assembly 10.

[0139] 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, and at least a portion of the reinforcement region 13 a is disposed in the bending region B.

[0140] The winding direction W is the direction in which the positive electrode sheet 11, the negative electrode sheet 12 and the isolation assembly 13 are wound from the inside to the outside. For example, in the figure, the winding direction W is counterclockwise.

[0141] The bending region B is a region with a bending structure in the electrode assembly 10, and the positive electrode sheet 11, the negative electrode sheet 12 and the isolation assembly 13 are all bent in the bending region B. Exemplarily, the portion of the positive electrode sheet 11 located in the bending region B is generally bent into an arc shape, and the portion of the negative electrode sheet 12 located in the bending region B is generally bent into an arc shape.

[0142] The winding equipment winds the positive electrode sheet 11, the negative electrode sheet 12 and the isolation assembly 13 into several circles, each circle can be constructed with several layers, and one circle refers to a point on the electrode assembly 10 as the starting end, and the end end is located at another point along the winding direction W. The end end is in a straight line with the starting end and the center of this circle, and the starting end is between the end end and the center of this circle.

[0143] The electrode assembly 10 may be entirely a bending region B, or only a portion of the region may be a bending region B. Exemplarily, the electrolytic assembly includes a straight region A and a bending region B, the bending region B is connected to the straight region A, and the straight region A is a region of the electrode assembly 10 having a straight structure.

[0144] The reinforcement area 13a may be entirely disposed in the bending region B, or only partially disposed in the bending region B.

[0145] The positive electrode sheet 11 and the negative electrode sheet 12 located in the bending area 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 and cause the respective active materials to fall off. Due to the falling off of active materials, especially the falling off of active materials on the negative electrode sheet 12, the number of lithium ions that can be provided by the negative electrode active material layer of the negative electrode sheet 12 may be less than that of the positive electrode active material layer of the adjacent positive electrode sheet 11, thereby causing lithium precipitation. In the embodiment of the present application, at least part of the reinforcement area 13a is arranged in the bending area B. Even if lithium precipitation occurs in the bending area B, the reinforcement area 13a can block lithium dendrites, reduce the probability of conduction between the positive electrode sheet 11 and the negative electrode sheet 12, effectively reduce the risk of short circuit, and improve the service life and safety of the electrode assembly 10.

[0146] In some embodiments, the positive electrode sheet 11 includes a first bending portion 111 located in the bending region B and adjacent to the reinforcement region 13a, and the negative electrode sheet 12 includes a second bending portion 121 adjacent to the first bending portion 111. The reinforcement 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.

[0147] The first bending portion 111 and the second bending portion 121 are adjacent to each other, which means that there is no other positive electrode sheet or another negative electrode sheet between them. The reinforcing area 13a and the first bending portion 111 are adjacent to each other, which means that there is no other positive electrode sheet or another negative electrode sheet between them.

[0148] The positive electrode sheet 11 includes a plurality of positive bending portions 11a located in the bending region B, and the positive bending portion 11a adjacent to the reinforcing region 13a having a multi-layer structure is a first bending portion 111. In the positive electrode sheet 11, some of the positive bending portions 11a may be the first bending portion 111, or all of the positive bending portions 11a may be the first bending portion 111.

[0149] The negative electrode sheet 12 includes a plurality of negative bending portions located in the bending area B. Exemplarily, the negative bending portion adjacent to the first bending portion 111 and sandwiching the reinforcement area 13 a with the first bending portion 111 is the second bending portion 121 .

[0150] In the electrode assembly 10, the reinforcement area 13a and the second bending portion 121 may be provided only on the inner side of the first bending portion 111, or only on the outer side of the first bending portion 111, or on both sides of the first bending portion 111.

[0151] The multiple bending layers 14 can block lithium dendrites when lithium is deposited in the second bending portion 121, thereby reducing the risk of lithium dendrites contacting the first bending portion 111 and improving safety.

[0152] In some embodiments, at least the inner side of the first bending portion 111 is provided with a reinforcement area 13 a and a second bending portion 121 .

[0153] 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, so the active material is more likely to fall off during the bending process of the second bending portion 121, that is, the second bending portion 121 inside the first bending portion 111 is more likely to precipitate lithium. The reinforcement area 13a can separate the first bending portion 111 from the second bending portion 121 located inside the first bending portion 111, and even if lithium is precipitated in the second bending portion 121, the probability of lithium dendrites passing through the reinforcement area 13a can be reduced, thereby reducing the risk of short circuit and improving safety.

[0154] In some embodiments, the first bend portion 111 includes a first current collecting portion 1111 and a first active material layer 1112 disposed on the surface of the first current collecting portion 1111, and the thickness of the first active material layer 1112 is h1. The second bend portion 121 includes a second current collecting portion 1211 and a second active material layer 1212 disposed on the surface of the second current collecting portion 1211, the thickness of the second active material layer 1212 is h2, the thickness of the bend layer 14 is h3, and the thickness of the second current collecting portion 1211 is h4. In the thickness direction of the first bend portion 111, the maximum spacing between the first bend portion 111 and the second bend portion 121 is X. The number of layers of the bend layer 14 located between the first bend portion 111 and the second bend 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.

[0155] The first current collector 1111 may be a part of the positive electrode current collector, and the first active material layer 1112 may be a part of the positive electrode active material layer. The second current collector 1211 may be a part of the negative electrode current collector, and the second active material layer 1212 may be a part of the negative electrode active material layer.

[0156] 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 may be the normal direction of the surface of the first bending portion 111 facing the second bending portion 121.

[0157] The active material capacity per unit area A1 of the first active material layer 1112 is the ratio of the active material capacity of the first active material layer 1112 to the area of ​​the surface of the first current collecting section 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 the ratio of the active material capacity of the second active material layer 1212 to the area of ​​the surface of the second current collecting section 1211 coated with the second active material layer 1212.

[0158] The average discharge capacity test of the first active material layer 1112. Take the positive electrode sheet 11 of each of the above embodiments, and use a punching die to obtain a small disc containing a single-sided first active material layer 1112. Use a metal lithium sheet as the counter electrode, a Celgard film as the isolation membrane, and a solution of EC+DMC+DEC (ethylene carbonate, dimethyl carbonate, diethyl carbonate in a volume ratio of 1:1:1) dissolved with LiPF6 (1 mol / L) as the electrolyte, and assemble 6 identical CR2430 button battery cells in an argon-protected glove box. ① After the battery cell is assembled, let it stand for 12 hours, ② perform constant current charging at a charging current of 0.1C until the voltage reaches the upper cut-off voltage x1V, then maintain the voltage x1V for constant voltage charging until the current is 50μA, ③ let it stand for 5 minutes, ④ finally perform constant current discharge at a discharge current of 0.1C until the voltage reaches the lower cut-off voltage y1V, ⑤ let it stand for 5 minutes, repeat steps ②-⑤, and record the discharge capacity of the second cycle. The average value of the discharge capacity of the 6 button batteries 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 active material is lithium iron phosphate, the upper cut-off voltage x1V = 3.75V, and the lower cut-off voltage y1V = 2V. When the positive active material is lithium nickel cobalt manganese oxide (NCM), the upper cut-off voltage x1V = 4.25V, and the lower cut-off voltage y1V = 2.8V.

[0159] The average discharge capacity test of the second active material layer 1212. Take the negative electrode plates 12 of the above-mentioned embodiments, and use a punching die to obtain a small disc with the same area as the above-mentioned positive electrode disc and containing a single-sided second active material layer 1212. Use a metal lithium sheet as the counter electrode, a Celgard film as the isolation membrane, and a solution of EC+DMC+DEC (ethylene carbonate, dimethyl carbonate, diethyl carbonate in a volume ratio of 1:1:1) dissolved with LiPF6 (1 mol / L) as the electrolyte, and assemble 6 CR2430 button batteries in an argon-protected glove box. ① After the battery is assembled, let it stand for 12 hours, ② discharge it at a constant current of 0.05C until the voltage reaches the lower cut-off voltage y2mV, ③ then discharge it at a constant current of 50μA until the voltage reaches the lower cut-off voltage y2mV, ④ let it stand for 5 minutes, ⑤ then discharge it at a constant current of 10μA until the lower cut-off voltage y2mV is reached, ⑥ let it stand for 5 minutes, ⑦ finally charge it at a constant current of 0.1C until the final voltage reaches the upper cut-off voltage x2V, ⑧ let it stand for 5 minutes, repeat steps ②-⑧, and record the charging capacity of the second cycle. The average value of the charging capacity of the 6 button batteries is the average charging capacity of the single-sided second active material layer 1212, which can be used as the active material capacity per unit area A2 of the second active material layer 1212. For example, when the negative active material is graphite, the upper cut-off voltage x2V=2V, and the lower cut-off voltage y2V=5mV. When the negative electrode active material is silicon, the upper cut-off voltage x2V=2V, and the lower cut-off voltage y2V=5mV.

[0160] In some embodiments, A2 / A1≥1. h1, h2, h3, h4, X, and Y satisfy:

[0161]

[0162] The fewer the number of bending layers 14 in the reinforcement area 13a, the higher the risk of lithium dendrites passing through the reinforcement area 13a; the more the number of bending layers 14 in the reinforcement area 13a, the more complex the structure of the isolation assembly 13, and the lower the energy density of the electrode assembly 10. After experiments and calculations, the inventors set the number of bending layers 14 according to the above formula to balance the safety and energy density of the electrode assembly 10.

[0163] In some embodiments, A2 / A1<1. h1, h2, h3, h4, X, and Y satisfy:

[0164]

[0165] When A2 / A1<1, the second active material layer 1212 has insufficient lithium insertion space, and the lithium ions released from the first active material layer 1112 cannot be inserted into the second active material layer 1212 in equal amounts. The lithium ions that cannot be inserted into the second active material layer 1212 can only obtain electrons on the surface of the second active material layer 1212, thereby causing lithium precipitation. Compared with the electrode assembly 10 with A2 / A1≥1, the electrode assembly 10 with A2 / A1<1 has a more serious lithium precipitation phenomenon, and the bending layer 14 of the reinforcement area 13a requires more layers.

[0166] After experiments and calculations, the inventors set the number of bending layers 14 according to the above formula to balance the safety and energy density of the electrode assembly 10.

[0167] In some embodiments, the value of h1 is 5 μm-80 μm. Alternatively, the value of h1 is 5 μm, 10 μm, 20 μm, 30 μm, 50 μm or 80 μm.

[0168] In some embodiments, the value of h2 is 10 μm-100 μm. Alternatively, the value of h2 is 10 μm, 20 μm, 30 μm, 50 μm, 80 μm or 100 μm.

[0169] In some embodiments, the value of h3 is 1 μm-20 μm. Alternatively, the value of h3 is 1 μm, 3 μm, 5 μm, 10 μm, 15 μm or 20 μm.

[0170] On the premise of satisfying the isolation effect, the smaller the value of h3 is, the more layers of the bending layer 14 of the reinforcement area 13a are. If the value of h3 is too small, the number of layers of the bending layer 14 of the reinforcement area 13a will be too many, resulting in a complex structure of the isolation component 13 and difficulty in forming. In view of this, the inventor sets the value of h3 to be greater than or equal to 1μm.

[0171] The larger the value of h3 is, the greater the total thickness of the reinforcement area 13a is; if the value of h3 is too large, the energy density of the electrode assembly 10 will 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.

[0172] In some embodiments, the value of h4 is 2 μm-20 μm. Alternatively, the value of h4 may be 2 μm, 3 μm, 5 μm, 10 μm, 15 μm or 20 μm.

[0173] In some embodiments, the value of X is 10 μm-5000 μm. Alternatively, the value of X may be 10 μm, 20 μm, 50 μm, 100 μm, 500 μm, 1000 μm, 2000 μm or 5000 μm.

[0174] In some embodiments, the positive electrode sheet 11 includes a plurality of positive bending portions 11a arranged along the winding direction W, and at least the positive bending portion 11a formed by the first bending of the positive electrode sheet 11 is arranged as the first bending portion 111. That is, the positive bending portion 11a formed by the first bending of the positive electrode sheet 11 is arranged adjacent to the reinforcement area 13a.

[0175] The plurality of positive electrode bending portions 11a of the positive electrode sheet 11 are all bent. Exemplarily, the positive electrode bending portion 11a is substantially in an arc shape.

[0176] The positive electrode bent portion 11 a formed by the first bending of the positive electrode sheet 11 refers to the positive electrode bent portion 11 a formed by the first bending of the positive electrode sheet 11 during the winding process along the winding direction W.

[0177] The curvature of the positive bent portion 11a formed by the first bending of the positive electrode sheet 11 is relatively large. During charging, the negative electrode sheet 12 adjacent to the positive bent portion 11a formed by the first bending of the positive electrode sheet 11 is more likely to have lithium deposition problems. In this embodiment, the positive bent portion 11a formed by the first bending of the positive electrode sheet 11 is set as the first bent portion 111, so that the reinforcement area 13a can effectively isolate the positive bent portion 11a formed by the first bending of the positive electrode sheet 11 from lithium dendrites, reduce the risk of short circuit, and improve safety.

[0178] In some embodiments, the positive bent portion 11a formed by the second bending of the positive electrode sheet 11 is also provided as the first bent portion 111. In other words, the positive bent portion 11a formed by the second bending of the positive electrode sheet 11 is also provided adjacent to the reinforcement area 13a.

[0179] The positive electrode bent portion 11 a formed by the second bending of the positive electrode sheet 11 refers to the positive electrode bent portion 11 a formed by the second bending of the positive electrode sheet 11 during the winding process along the winding direction W.

[0180] The reinforcing area 13a adjacent to the positive bent portion 11a formed by the first bending of the positive electrode sheet 11 may be connected as one with the reinforcing area 13a adjacent to the positive bent portion 11a formed by the second bending of the positive electrode sheet 11, or may be arranged at intervals along the winding direction W.

[0181] The curvature of the positive bent portion 11a formed by the second bending of the positive electrode sheet 11 is relatively large. During charging, the negative electrode sheet 12 adjacent to the positive bent portion 11a formed by the second bending of the positive electrode sheet 11 is prone to lithium deposition. In this embodiment, the positive bent portion 11a formed by the second bending of the positive electrode sheet 11 is set as the first bent portion 111, so that the reinforcement area 13a can effectively isolate the positive bent portion 11a formed by the second bending of the positive electrode sheet 11 from lithium dendrites, reduce the risk of short circuit, and improve safety.

[0182] In some embodiments, the total thickness of the reinforced area 13a located inside the positive bending portion 11a formed by the first bending of the positive electrode sheet 11 is T1, and the total thickness of the reinforced area 13a located inside the positive bending portion 11a formed by the second bending of the positive electrode sheet 11 is T2, and T1≥T2.

[0183] The curvature of the second bent portion 121 located inside the positive bent portion 11a formed by the first bending of the positive electrode sheet 11 is greater than the curvature of the second bent portion 121 located inside the positive bent portion 11a formed by the second bending of the positive electrode sheet 11, and the second bent portion 121 located inside the positive bent portion 11a formed by the first bending of the positive electrode sheet 11 is more prone to lithium deposition. In this embodiment, T1≥T2 is set to reduce the risk of the positive bent portion 11a formed by the first bending of the positive electrode sheet 11 being connected to the lithium dendrite, thereby improving the safety of the battery cell.

[0184] In some embodiments, the number of isolation layers of the reinforcement area 13a located inside the positive bending portion 11a formed by the first bending of the positive electrode sheet 11 is L1, and the number of isolation layers of the reinforcement area 13a located inside the positive bending portion 11a formed by the second bending of the positive electrode sheet 11 is L2, and L1≥L2.

[0185] In some embodiments, a reinforcement area 13a and a second bending portion 121 are provided on both sides of the first bending portion 111, and the total thickness of the reinforcement area 13a located on the inner side of the first bending portion 111 is greater than or equal to the total thickness of the reinforcement area 13a located on the outer side of the first bending portion 111.

[0186] The reinforcement areas 13 a on both sides of the first bending portion 111 may belong to the same isolation component 13 , or may respectively belong to two different isolation components 13 .

[0187] The curvature of the second bent portion 121 located inside the first bent portion 111 is greater than the curvature of the second bent portion 121 located outside the first bent portion 111, and lithium deposition is more likely to occur in the second bent portion 121 located inside the first bent portion 111. In this embodiment, the thickness of the reinforcement area 13a located inside the first bent portion 111 is not less than the thickness of the reinforcement area 13a located outside the first bent portion 111, so as to reduce the risk of the first bent portion 111 being connected to the lithium dendrites and improve the safety of the battery cell.

[0188] In some embodiments, the number of isolation layers of the reinforcement region 13 a located inside the first bending portion 111 is greater than or equal to the number of isolation layers of the reinforcement region 13 a located outside the first bending portion 111 .

[0189] In some embodiments, the positive electrode sheet 11 , the isolation assembly 13 and the negative electrode sheet 12 are wound to form a straight region A, and the straight region A is connected to the bent region B. At least a portion of the base region 13 b is disposed in the straight region A.

[0190] The straight region A is a region where the electrode assembly 10 has a straight structure, and the positive electrode sheet 11 and the negative electrode sheet 12 are substantially straightly arranged in the straight region A. Exemplarily, the surface of each layer of the positive electrode sheet 11 and the surface of each layer of the negative electrode sheet 12 in the straight region A are substantially flat.

[0191] The positive electrode sheet 11 and the negative electrode sheet 12 located in the straight area A are both in a straight state, the active material in the straight area A is not easy to fall off, and the negative electrode sheet 12 located in the straight area A is not easy to have lithium deposition problems. Therefore, even if the substrate area 13b is set to the straight area A, the insulation between the positive and negative electrode sheets can be improved and the risk of short circuit can be reduced.

[0192] In some embodiments, two bending regions B are provided, and the two bending regions B are provided at two ends of the straight region A respectively.

[0193] In some embodiments, both ends of the reinforcement region 13a along the winding direction W are located in the straight region A, so that the reinforcement region 13a can pass through the bending region B as a whole, thereby reducing the risk of short circuit in the bending region B.

[0194] In some embodiments, in the winding direction W, the tail end of the reinforcement region 13a exceeds the bending region B by 3mm-500mm. Optionally, the tail end of the reinforcement region 13a exceeds the bending region B by 10mm-100mm.

[0195] In some embodiments, the isolation assembly 13 includes a first isolation layer 131 and a second isolation layer 132, the first isolation layer 131 is used to insulate and isolate the positive electrode sheet 11 and the negative electrode sheet 12, and at least a portion of the second isolation layer 132 is located between the positive electrode sheet 11 and the negative electrode sheet 12 and is stacked with the first isolation layer 131. The area of ​​the first isolation layer 131 that overlaps with the second isolation layer 132 and the second isolation layer 132 form a reinforcement area 13a of the isolation assembly 13, and the area of ​​the first isolation layer 131 that does not overlap with the second isolation layer 132 forms a base area 13b.

[0196] Exemplarily, the first isolation layer 131 can be understood as an isolation layer between the positive electrode plate 11 and the negative electrode plate 12 in the related art, that is, a basic isolation layer, and the second isolation layer 132 can be understood as an additional isolation layer, that is, an additional isolation layer.

[0197] In the isolation component 13 , the number of the second isolation layer 132 may be one or more.

[0198] The first isolation layer 131 and the second isolation layer 132 may be two parts of an integrated component, or may be two independent components provided separately.

[0199] The first isolation layer 131 and the second isolation layer 132 may be made of the same material or different materials.

[0200] This embodiment does not limit the thickness of the first isolation layer 131 and the thickness of the second isolation layer 132 . The thickness of the first isolation layer 131 may be greater than, equal to, or less than the thickness of the second isolation layer 132 .

[0201] The first isolation layer 131 and the second isolation layer 132 are stacked between the positive electrode sheet 11 and the negative electrode sheet 12. The second isolation layer 132 can be independently arranged on the first isolation layer 131, that is, in the stacking 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. For example, the second isolation layer 132 can be attached to the first isolation layer 131 as a whole or only partially. Attachment refers to an adhesive connection.

[0202] In the embodiment of the present application, a second isolation layer 132 is additionally added to the electrode assembly 10 to form a reinforcement area 13 a with a relatively large thickness on the isolation assembly 13 , thereby reducing the risk of short circuit caused by lithium deposition and improving safety.

[0203] In some embodiments, in the reinforcement area 13a, the number of layers of the second isolation layer 132 is 1 to 10. Exemplarily, in the reinforcement area 13a, the number of layers of the second isolation layer 132 is 1, 2, 3, 5 or 10. When a plurality of second isolation layers 132 are provided in one reinforcement area 13a, the sizes of the plurality of second isolation layers 132 along the winding direction W may be the same or different.

[0204] In some embodiments, the isolation component 13 has multiple reinforcement regions 13 a , and the number of layers of the second isolation layer 132 in the multiple reinforcement regions 13 a may be the same or different.

[0205] 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 .

[0206] The first isolation layer 131 and the second isolation layer 132 can play the role of multi-layer protection, so the added second isolation layer 132 can have a thickness no greater than that of the first isolation layer 131 to reduce the amount of the second isolation layer 132 used.

[0207] Optionally, the thickness of the second isolation layer 132 is smaller than the thickness of the first isolation layer 131 .

[0208] In some embodiments, the second isolation layer 132 is disposed on a side of the first isolation layer 131 facing the positive electrode sheet 11 .

[0209] 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.

[0210] 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.

[0211] In some embodiments, the porosity of the second isolation layer 132 is less than the porosity 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 lithium dendrites being connected to the positive electrode plate 11 and improving safety.

[0212] In some embodiments, the second isolation layer 132 is a porous structure, and the pore size of the pores in the second isolation layer 132 is less than or equal to 1 μm.

[0213] The pores in the second isolation layer 132 have a small pore size, and lithium dendrites are not easy to pass through, thereby reducing the risk of lithium dendrites being connected to the positive electrode plate 11 and improving safety.

[0214] 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 film. Exemplarily, the base film 133 is made of a polymer material that is electrically insulating and has liquid retention capacity, such as PP (polypropylene), PE (polyethylene) or PVDF (polyvinylidene fluoride).

[0215] 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, and the dispersant may include polyvinyl alcohol. The inorganic material can clamp the base film 133 to reduce the shrinkage of the base film 133. The polymer binder can be bonded to the pole piece to increase the overall stiffness of the electrode assembly 10.

[0216] The second isolation layer 132 may include only the base film 133, or may include both the base film 133 and the insulating layer 134. Optionally, the base film 133 of the second isolation layer 132 is connected to the base film 133 of the first isolation layer 131 as a whole.

[0217] In the embodiment of the present application, the number of layers of the reinforcement area 13a is determined by the number of layers of the base film 133. In other words, the number of layers of the reinforcement area 13a refers to the number of layers of the base film 133 of the reinforcement area 13a.

[0218] 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%, and the content of the dispersant is 0.5%-10%.

[0219] In some embodiments, in a stacking direction of the first isolation layer 131 and the second isolation layer 132 , at least a portion of the second isolation layer 132 is disposed separately from the first isolation layer 131 .

[0220] At least a portion of the second isolation layer 132 has no connection relationship such as adhesion with the first isolation layer 131 .

[0221] When the first isolation layer 131 (or the second isolation layer 132) is stretched under the pressure of the lithium layer, the portion of the second isolation layer 132 separated from the first isolation layer 131 is less affected by the first isolation layer 131, the second isolation layer 132 is less stretched, and the risk of 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, thereby improving safety.

[0222] 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 and a straight region A, and the straight region A is connected to the bending region B. A portion of the second isolation layer 132 is located in the bending region B, and another portion of the second isolation layer 132 is located in the straight region A. In the bending region B, the second isolation layer 132 is separated from the first isolation layer 131; in the straight region A, the second isolation layer 132 is attached to the first isolation layer 131.

[0223] The risk of lithium deposition in the bending region B is relatively high. Separating the second isolation layer 132 from the first isolation layer 131 in the bending region B can effectively reduce the risk of lithium dendrites passing through the first isolation layer 131 and the second isolation layer 132, thereby improving safety. In the straight region A, the second isolation layer 132 is attached to the first isolation layer 131, which can reduce the movement amplitude of the second isolation layer 132 along the winding direction W and reduce the risk of the second isolation layer 132 being misplaced.

[0224] In some embodiments, the second isolation layer 132 is formed by folding an end portion of the first isolation layer 131 .

[0225] Exemplarily, the end of the first isolation layer 131 is folded to form the second isolation layer 132 , and the folded portion is the boundary between the first isolation layer 131 and the second isolation layer 132 .

[0226] In this embodiment, the second isolation layer 132 extends directly from the end of the first isolation layer 131 , and there is no need to separately add and fix the second isolation layer 132 , thereby making the winding process more convenient and improving the integrity of the electrode assembly 10 .

[0227] 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 a winding direction W, and an end of the first isolation layer 131 is located at the starting section 100 .

[0228] The starting section 100 along the winding direction W refers to the end portion of the electrode assembly 10 located at the innermost circle.

[0229] The second isolation layer 132 can extend from the starting section 100 along the winding direction W and pass through the positive electrode bending portion 11a formed by the first bending of the positive electrode plate 11, which can reduce the risk of lithium dendrites passing through the first isolation layer 131 and the second isolation layer 132 at the same time and contacting the positive electrode bending portion 11a of the positive electrode plate 11, thereby improving safety. At the same time, this embodiment can also reduce the length of the second isolation layer 132 that needs to be extended, save usage, and reduce costs.

[0230] In some embodiments, the positive electrode sheet 11, the isolation assembly 13 and the negative electrode sheet 12 are wound to form a bending area B, and the bending area B includes a first bending portion B1 close to the starting section 100 along the winding direction W, and the first bending portion B1 is provided with a first isolation layer 131 and a second isolation layer 132, and the second isolation layer 132 extends from the end of the first isolation layer 131 and exceeds the first bending portion B1.

[0231] The first bending position B1 is the position where the electrode assembly 10 is bent for the first time during the winding process. Exemplarily, at the first bending position B1, the positive electrode sheet 11 is bent for the first time, and the negative electrode sheet 12 is bent for the first time.

[0232] At the first bending portion B1, the curvature of the positive electrode sheet 11 and the negative electrode sheet 12 is the largest, and during charging, the risk of lithium deposition in the negative electrode sheet 12 is the highest. The second isolation layer 132 extends beyond the first bending portion B1, and the first isolation layer 131 and the second isolation layer 132 can at least protect the first bending portion B1, which is most prone to lithium deposition, and can also save the use of the second isolation layer 132, thereby saving costs and improving the safety and service life of the electrode assembly 10.

[0233] Fig. 9 A schematic diagram of the structure of the isolation assembly of the electrode assembly before winding provided in other embodiments of the present application.

[0234] like Fig. 9 As shown, in some embodiments, the isolation component 13 is a single-layer structure as a whole. When the isolation component 13 is formed, a reinforcement area 13a and a base area 13b with different thicknesses are directly formed.

[0235] Fig.10 A schematic diagram of the structure of an electrode assembly provided in some other embodiments of the present application; Fig.11 for Fig.10 A partial enlarged schematic diagram of the electrode assembly shown; Fig.12 for Fig.10 The schematic diagram of the structure of the electrode assembly before winding is shown.

[0236] like Figures 10 to 12 As mentioned above, in some embodiments, the reinforcement area 13a and the base area 13b are both provided in plurality, and the plurality of reinforcement areas 13a and the plurality of base areas 13b are alternately provided along the winding direction W.

[0237] The multiple reinforcement areas 13 a may respectively correspond to the multiple positive bending portions 11 a of the positive electrode sheet 11 , so as to reduce the risk of short circuit of the multiple positive bending portions 11 a of the positive electrode sheet 11 and improve safety.

[0238] Each reinforcement region 13a includes one or more second isolation layers 132. The number of layers of the plurality of reinforcement regions 13a may be the same or different.

[0239] In some embodiments, each reinforcement region 13 a can isolate a positive electrode bending portion 11 a from a negative electrode bending portion of the negative electrode tab 12 .

[0240] 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 plurality of bending locations arranged along the winding direction W, the electrode assembly 10 includes a plurality of second isolation layers 132, and the first isolation layer 131 and the plurality of second isolation layers 132 are arranged at least one of the plurality of bending locations.

[0241] The bending part is the position where the electrode assembly 10 is bent during the winding process. Exemplarily, the multiple bending parts include a first bending part B1 and a second bending part B2, at the first bending part B1, the positive electrode sheet 11 and the negative electrode sheet 12 are both bent for the first time, and at the second bending part B2, the positive electrode sheet 11 and the negative electrode sheet 12 are both bent for the second time.

[0242] In this embodiment, the second isolation layer 132 is provided at part or all of the multiple bending parts, which can effectively reduce the risk of short circuit at the bending parts and improve safety.

[0243] It should be noted that one of the second isolation layers 132 may be arranged to extend through a plurality of bending portions, or each of the second isolation layers 132 may be arranged to extend through one bending portion.

[0244] In some embodiments, along the winding direction W, a plurality of second isolation layers 132 are arranged at intervals.

[0245] The plurality of second isolation layers 132 are arranged at intervals, which can be understood as the plurality of second isolation layers 132 are not connected to form a whole second isolation layer 132, but are separated. This embodiment can make the arrangement of the second isolation layer 132 more flexible, that is, the second isolation layer 132 can be arbitrarily arranged at a 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 132 at a position where the number of isolation layers does not need to be increased can be reduced, thereby improving the energy density.

[0246] In some embodiments, the electrode assembly 10 includes a starting section 100 along a winding direction W. The plurality of bending locations include a first bending location B1 and a second bending location B2, and along the winding direction W, the first bending location B1 is closer to the starting section 100 than the second bending location B2. The thickness of the second isolation layer 132 disposed at the first bending location B1 is greater than the thickness of the second isolation layer 132 disposed at the second bending location B2.

[0247] The risk of lithium deposition of the negative electrode sheet 12 at the first bending portion B1 is higher than the risk of lithium deposition of the negative electrode sheet 12 at the second bending portion B2, and the risk of lithium dendrites passing through the second isolation layer 132 at the first bending portion B1 is higher than the risk of lithium dendrites passing through the second isolation layer 132 at the second bending portion B2. Therefore, in this embodiment, the thickness of the second isolation layer 132 arranged at the first bending portion B1 is greater than the thickness of the second isolation layer 132 arranged at the second bending portion B2, so as to strengthen protection at the first bending portion B1 which is more prone to short circuit, improve safety, and save the amount of the second isolation layer 132.

[0248] In some embodiments, multiple second isolation layers 132 are bonded to the surface of the first isolation layer 131 , which can reduce the risk of positional displacement of the second isolation layer 132 during the charge and discharge process of the electrode assembly 10 and ensure the isolation effect of the second isolation layer 132 .

[0249] Optionally, two ends of the second isolation layer 132 along the winding direction W are bonded to the first isolation layer 131 , and a middle portion of the second isolation layer 132 along the winding direction W is separated from the first isolation layer 131 .

[0250] In some embodiments, after the electrode assembly 10 is wound, the electrode assembly 10 is heat-pressed from the outside so that the second isolation layer 132 is bonded to the first isolation layer 131 .

[0251] In some embodiments, the first isolation layer 131 includes two surfaces along its thickness direction, and the plurality of second isolation layers 132 are located on the same surface of the first isolation layer 131 .

[0252] Too large a distance between the positive electrode sheet 11 and the negative electrode sheet 12 will affect the lithium insertion process, resulting in aggravated lithium plating. By setting multiple 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 sheet 11 and the negative electrode sheet 12 can be reduced, thereby reducing the risk of lithium plating and improving safety.

[0253] Fig.13 A schematic diagram of the structure of an electrode assembly before winding provided in some other embodiments of the present application.

[0254] like Fig.13 As shown, in some embodiments, along the winding direction W, the thickness of the plurality of reinforcement regions 13 a gradually decreases from the inside to the outside.

[0255] In this embodiment, the thickness of the innermost reinforcement area 13a is greater than the thickness of the outermost reinforcement area 13a along the winding direction W. The thicknesses of two adjacent reinforcement areas 13a may be the same or different.

[0256] Along the winding direction W, the curvature of the positive electrode bending portion 11a of the positive electrode sheet 11 from the inside to the outside gradually decreases, and the risk of contact with lithium dendrites gradually decreases. In this embodiment, the thickness of the reinforcement area 13a can be increased in the area with high short circuit risk, and the thickness of the reinforcement area 13a can be reduced in the area with low short circuit risk, which can improve safety and save the amount of isolation component 13.

[0257] In some embodiments, the thickness difference between adjacent reinforcement regions 13 a is 0.5 μm-10 μm along the winding direction W. Optionally, the thickness difference between adjacent reinforcement regions 13 a is 0.5 μm, 1 μm, 2 μm, 5 μm, 7 μm or 10 μm.

[0258] Fig.14 A schematic diagram of the structure of an electrode assembly provided in some further embodiments of the present application.

[0259] like Fig.14 As shown, in some embodiments, the positive electrode sheet 11 includes a plurality of positive bending portions 11 a arranged along the winding direction W, and at least the positive bending portion 11 a formed by the last bending of the positive electrode sheet 11 is set as the first bending portion 111 .

[0260] The electrode assembly 10 expands and squeezes the shell during charging, and the shell exerts a reaction force on the electrode assembly 10. The area of ​​the negative electrode sheet 12 opposite to the positive electrode bending portion 11a formed by the last bend of the positive electrode sheet 11 is prone to lithium deposition under the action of the reaction force. In this embodiment, at least part of the reinforcement area 13a is adjacent to the positive electrode bending portion 11a formed by the last bend of the positive electrode sheet 11, so as to reduce the risk of the positive electrode bending portion 11a formed by the last bend of the positive electrode sheet 11 being connected to the lithium dendrites, thereby improving the safety of the battery cell.

[0261] Exemplarily, the electrode assembly 10 is cylindrical. Each positive electrode bending portion 11a of the positive electrode sheet 11 refers to a circle of the positive electrode sheet.

[0262] According to some embodiments of the present application, the present application further provides a battery cell, which includes a housing and an electrode assembly according to any of the above embodiments, wherein the electrode assembly is accommodated in the housing.

[0263] According to some embodiments of the present application, the present application also provides a battery, comprising a plurality of battery cells according to any one of the above embodiments.

[0264] According to some embodiments of the present application, the present application further provides an electric device, comprising a battery cell of any of the above embodiments, the battery cell is used to provide electric energy for the electric device. The electric device can be any of the above equipment or systems using the battery cell.

[0265] According to some embodiments of the present application, referring to Figures 4 to 8The present application provides an electrode assembly 10, which includes a positive electrode sheet 11, a negative electrode sheet 12 and an isolation assembly 13, wherein the isolation assembly 13 is used to isolate the positive electrode sheet 11 from the negative electrode sheet 12. The isolation assembly 13 includes a first isolation layer 131 and a second isolation layer 132, wherein the first isolation layer 131 is used to insulate and isolate the positive electrode sheet 11 from the negative electrode sheet 12, and at least a portion of the second isolation layer 132 is located between the positive electrode sheet 11 and the negative electrode sheet 12 and is stacked with the first isolation layer 131. The area of ​​the first isolation layer 131 that overlaps with the second isolation layer 132 and the second isolation layer 132 form a reinforcement area 13a of the isolation assembly 13, and the area of ​​the first isolation layer 131 that does not overlap with the second isolation layer 132 forms a base area 13b of the isolation assembly 13, and the thickness of the reinforcement area 13a is greater than the thickness of the base area 13b. The second isolation layer 132 is formed by folding the end of the first isolation layer 131.

[0266] The positive electrode sheet 11 , the isolation assembly 13 and the negative electrode sheet 12 are wound to form a bending area B and a straight area A, and the straight area A is connected to the bending area B. At least part of the reinforcement area 13a is disposed in the bending area B, and at least part of the base area 13b is disposed in the straight area A.

[0267] A portion of the reinforcement area 13 a is disposed adjacent to the positive electrode bending portion 11 a formed by the first bending of the positive electrode sheet 11 , and another portion of the reinforcement area 13 a is disposed adjacent to the positive electrode bending portion 11 a formed by the second bending of the positive electrode sheet 11 .

[0268] The present application is further described below with reference to embodiments.

[0269] In order to make the invention purpose, technical scheme and beneficial technical effect of the present application clearer, the present application is further described in detail below in conjunction with the examples. However, it should be understood that the examples of the present application are only for explaining the present application, not for limiting the present application, and the examples of the present application are not limited to the examples given in the specification. The specific experimental conditions or operating conditions not specified in the examples are made under conventional conditions, or are made under the conditions recommended by the material supplier.

[0270] Example 1 can be prepared according to the following steps:

[0271] (i) The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2, conductive agent acetylene black, and binder PVDF are mixed in a mass ratio of 96:2:2, solvent NMP is added, and stirred under the action of a vacuum mixer until the system is uniform to obtain positive electrode slurry; the positive electrode slurry is evenly coated on aluminum foil, dried at room temperature, and then transferred to an oven for further drying, and then cold pressed, slit, and cut into pieces to obtain positive electrode sheets.

[0272] (ii) Mixing negative electrode active material graphite, conductive agent acetylene black, thickener CMC, and binder SBR in a mass ratio of 96.4:1:1.2:1.4, adding solvent deionized water, and stirring under the action of a vacuum stirrer until the system becomes uniform to obtain a negative electrode slurry; coating the negative electrode slurry evenly on a copper foil, drying it at room temperature, and then transferring it to an oven for further drying, and then cold pressing, slitting, and cutting to obtain a negative electrode sheet.

[0273] (iii) Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0274] (iv) A polyethylene film of 7 μm thick is folded to form an isolation assembly, the isolation assembly comprising a first isolation layer and a second isolation layer, the length of the second isolation layer being 652.5 mm. The area of ​​the first isolation layer overlapping with the second isolation layer and the second isolation layer forming a reinforcement area of ​​the isolation assembly, the area of ​​the first isolation layer not overlapping with the second isolation layer forming a base area of ​​the isolation assembly, the thickness of the reinforcement area being 14 μm, and the thickness of the base area being 7 μm.

[0275] (v) The positive electrode sheet, the separator assembly and the negative electrode sheet are stacked together and wound into multiple turns, and then flattened into a flat shape after winding to prepare an electrode assembly.

[0276] (vi) The electrode assembly is installed in a square housing, and the housing and the end cap are welded; then, a battery cell is obtained through processes such as liquid injection, static placement, chemical formation, and shaping. For example, the capacity of the battery cell is 60 Ah.

[0277] In step (v), the gap between the innermost positive electrode sheet and the innermost negative electrode sheet is artificially increased to 200 μm to accelerate the lithium deposition of the electrode assembly. In the wound electrode assembly, a first isolation layer and a second isolation layer are provided between the innermost positive electrode sheet and the innermost negative electrode sheet.

[0278] Embodiment 2:

[0279] The preparation method of the battery cell of Example 2 refers to Example 1, except that: in step (vi), the gap between the two innermost circles of positive electrode sheets and the two innermost circles of negative electrode sheets is artificially made to 200 μm, the length of the second isolation layer is 873.6 mm, and the first isolation layer and the second isolation layer are also provided between the second circle of positive electrode sheets and the second circle of negative electrode sheets.

[0280] Comparative Example 1:

[0281] The preparation method of the battery cell of Comparative Example 1 refers to that of Example 1, except that: the isolation component of Comparative Example 1 is not folded, and the isolation component is a single-layer structure.

[0282] Comparative Example 2:

[0283] The preparation method of the battery cell of Comparative Example 2 refers to that of Example 2, except that: the isolation component of Comparative Example 2 is not folded, and the isolation component is a single-layer structure.

[0284] 80 battery cells were prepared in each of Example 1, Example 2, Comparative Example 1 and Comparative Example 2, and each battery cell was tested.

[0285] Specifically, under normal temperature, the battery cells are charged at a 1C rate and discharged at a 1C rate, and cyclic charge and discharge are performed in a high SOC range (eg, 0.9-1).

[0286] The 40 battery cells of Example 1 were fully charged after 500 cycles, and then left to stand for 24 hours. 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 calculated. The self-discharge rate is voltage drop / time. The remaining 40 battery cells of Example 1 were cycled for 2000 times, and the number of battery cell failures was recorded during the cycle process, and the failure rate was calculated.

[0287] Example 2, Comparative Example 1 and Comparative Example 2 were also tested according to the above steps.

[0288] The evaluation results of Examples 1-2 and Comparative Examples 1-2 are shown in Table 1.

[0289] Table 1

[0290] Self-discharge rate Failure rate Example 1 0.027mV / h 0％ Example 2 0.053mV / h 2.5％ Comparative Example 1 0.71mV / h 92.5％ Comparative Example 2 0.89mV / h 95％

[0291] With reference to Example 1-2 and Comparative Example 1-2, a reinforcement area is provided between the positive electrode sheet and the negative electrode sheet, which can reduce the risk of short circuit when lithium is deposited on the negative electrode sheet and increase the service life of the battery cell.

[0292] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application may be combined with each other.

[0293] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein, but these modifications or replacements do not cause the essence of the corresponding technical solutions to 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 sheet, a negative electrode sheet and an isolation component, wherein the isolation component is used to isolate the positive electrode sheet from the negative electrode sheet; The isolation assembly comprises a first isolation layer and a second isolation layer, the first isolation layer is used to insulate and isolate the positive electrode sheet from the negative electrode sheet, and at least a portion of the second isolation layer is located between the positive electrode sheet and the negative electrode sheet and is stacked on the first isolation layer; The thickness of the second isolation layer is less than or equal to the thickness of the first isolation layer; The area of ​​the first isolation layer overlapping with the second isolation layer and the second isolation layer form a reinforcement area of ​​the isolation assembly, and the area of ​​the first isolation layer not overlapping with the second isolation layer forms a base area of ​​the isolation assembly; The base region is connected to the reinforcement region, and the thickness of the reinforcement region is greater than the thickness of the base region; at least a portion of the reinforcement region is located between the adjacent positive electrode sheet and the negative electrode sheet.

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

3. The electrode assembly according to claim 1, characterized in that: The positive electrode sheet, the isolation assembly and the negative electrode sheet are wound to form a bending area, and at least a portion of the reinforcement area is arranged in the bending area.

4. The electrode assembly according to claim 3, characterized in that: The positive electrode sheet includes a first bending portion located in the bending area and adjacent to the reinforcement area, and the negative electrode sheet includes a second bending portion adjacent to the first bending portion; The reinforcement area 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.

5. The electrode assembly according to claim 4, characterized in that: The reinforcement area and the second bending portion are provided at least on the inner side of the first bending portion.

6. The electrode assembly according to claim 4, characterized in that: The first bending portion includes a first current collecting portion and a first active material layer disposed on a surface of the first current collecting portion, and the thickness of the first active material layer is h1; The second bending portion includes a second current collecting portion and a second active material layer disposed on a surface of the second current collecting portion, the second active material layer has a thickness of h2, the bending layer has a thickness of h3, and the second current collecting portion has a thickness of h4; In the thickness direction of the first bending portion, the maximum distance between the first bending portion and the second bending portion is X; The number of layers of the bending layer between the first bending portion and the second bending portion is Y, where Y is a positive integer greater than 1; The active material capacity per unit area of ​​the first active material layer is A1, 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 4, characterized in that: The first bending portion includes a first current collecting portion and a first active material layer disposed on a surface of the first current collecting portion, and the thickness of the first active material layer is h1; The second bending portion includes a second current collecting portion and a second active material layer disposed on a surface of the second current collecting portion, the second active material layer has a thickness of h2, the bending layer has a thickness of h3, and the second current collecting portion has a thickness of h4; In the thickness direction of the first bending portion, the maximum distance between the first bending portion and the second bending portion is X; The number of layers of the bending layer between the first bending portion and the second bending portion is Y, where Y is a positive integer greater than 1; The active material capacity per unit area of ​​the first active material layer is A1, 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:

8. The electrode assembly according to claim 6, characterized in that: The value of h3 is 1 μm-20 μm.

9. The electrode assembly according to claim 6, characterized in that: The value of X is 10 μm to 5000 μm.

10. The electrode assembly according to claim 4, characterized in that: The positive electrode sheet includes a plurality of positive bending portions arranged along a winding direction, and at least the positive bending portion formed by the first bending of the positive electrode sheet is set as the first bending portion.

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

12. The electrode assembly according to claim 11, characterized in that: The total thickness of the reinforcement area located inside the positive bending portion formed by the first bending of the positive electrode sheet is T1, and the total thickness of the reinforcement area located inside the positive bending portion formed by the second bending of the positive electrode sheet is T2, and T1≥T2.

13. The electrode assembly according to claim 4, characterized in that: The reinforcement area and the second bending portion are provided on both sides of the first bending portion, and the total thickness of the reinforcement area located on the inner side of the first bending portion is greater than or equal to the total thickness of the reinforcement area located on the outer side of the first bending portion.

14. The electrode assembly according to claim 4, characterized in that: The positive electrode sheet includes a plurality of positive bending portions arranged along a winding direction, and at least the positive bending portion formed by the last bending of the positive electrode sheet is set as the first bending portion.

15. The electrode assembly according to claim 3, characterized in that: The positive electrode sheet, the isolation assembly and the negative electrode sheet are wound to form a straight region, and the straight region is connected to the bent region; At least a portion of the base region is disposed in the flat area.

16. The electrode assembly according to claim 15, characterized in that The reinforcement area and the base area are both provided in plurality, and the plurality of reinforcement areas and the plurality of base areas are alternately arranged along the winding direction.

17. The electrode assembly according to claim 16, characterized in that: Along the winding direction, the thickness of the plurality of reinforced regions gradually decreases from the inside to the outside.

18. The electrode assembly according to claim 17, characterized in that Along the winding direction, the thickness difference between adjacent reinforcement areas is 0.5 μm-10 μm.

19. The electrode assembly according to claim 1, characterized in that: The reinforcement area is configured as a multi-layer structure, and the base area is configured as a single-layer structure.

20. The electrode assembly according to claim 1, characterized in that In a stacking direction of the first isolation layer and the second isolation layer, at least a portion of the second isolation layer is disposed separately from the first isolation layer.

21. The electrode assembly according to claim 20, characterized in that The positive electrode sheet, the isolation assembly and the negative electrode sheet are wound to form a bending area and a straight area, and the straight area is connected to the bending area; A portion of the second isolation layer is located in the bending area, and another portion of the second isolation layer is located in the straight area; In the bending area, the second isolation layer is separated from the first isolation layer; in the straight area, the second isolation layer is attached to the first isolation layer.

22. The electrode assembly according to claim 1, characterized in that The second isolation layer is formed by folding the end portion of the first isolation layer.

23. The electrode assembly according to claim 22, characterized in that The positive electrode sheet, the isolation assembly and the negative electrode sheet are wound together, 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, characterized in that The positive electrode sheet, the isolation assembly and the negative electrode sheet are wound to form a bending area, and the bending area includes a first bending portion close to the starting section along the winding direction, and the first isolation layer and the second isolation layer are provided at the first bending portion, and the second isolation layer extends from the end of the first isolation layer and exceeds the first bending portion.

25. The electrode assembly according to claim 1, characterized in that The positive electrode sheet, the isolation assembly and the negative electrode sheet are wound to form a bending area; The bending region includes a plurality of bending locations arranged along a 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 least one of the plurality of bending locations.

26. The electrode assembly according to claim 25, characterized in that Along the winding direction, the plurality of second isolation layers are arranged at intervals.

27. The electrode assembly according to claim 25, characterized in that The electrode assembly includes a starting section along a winding direction; the plurality of bending portions include a first bending portion and a second bending portion, and 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 disposed at the first bending portion is greater than the thickness of the second isolation layer disposed at the second bending portion.

28. The electrode assembly according to claim 25, characterized in that The first isolation layer includes two surfaces along its thickness direction, and a 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, characterized in that A plurality of the second isolation layers are bonded to the surface of the first isolation layer.

30. A battery cell, characterized in that: It comprises a housing and an electrode assembly according to any one of claims 1 to 29, wherein the electrode assembly is accommodated in the housing.

31. A battery, characterized in that: Comprising a plurality of battery cells according to claim 30.

32. An electrical device, characterized in that: The battery cell according to claim 30 is included, and is used to provide electrical energy.

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