Battery cell, method for manufacturing battery cell, battery device, and electric device

Abstract

The invention provides a battery monomer, a manufacturing method of the battery monomer, a battery device and a power utilization device. The battery monomer comprises a shell and an electrode assembly, the electrode assembly is accommodated in the shell, the electrode assembly comprises a positive pole piece and a negative pole piece, and the positive pole piece and the negative pole piece are arranged in a winding manner. The electrode assembly comprises a bending area and a straight area connected to the bending area. The positive pole piece comprises a positive current collector and a first active material layer, the first active material layer is arranged on the inner side of the positive current collector and comprises a first part and a second part which are arranged in the winding direction, the compaction density of the first part is larger than that of the second part, and at least part of the first part is arranged in the bending area. At least part of the second part is arranged in the straight area. According to the invention, the reliability of the battery monomer can be effectively improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a battery cell, a method for manufacturing the battery cell, a battery device, and an electrical device. Background Technology

[0002] With the development of new energy technologies, batteries are being used more and more widely, for example in mobile phones, laptops, electric vehicles, electric cars, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes, and power tools.

[0003] In the development of battery technology, the reliability of individual battery cells directly affects the reliability, cost of use, and user experience of end products. Therefore, how to effectively improve the reliability of individual battery cells is a continuous technical challenge in battery technology. Summary of the Invention

[0004] In view of the above problems, this application provides a battery cell, a method for manufacturing a battery cell, a battery device, and an electrical device, which can effectively improve the reliability of the battery cell.

[0005] In a first aspect, embodiments of this application provide a battery cell, which includes a casing and an electrode assembly. The electrode assembly is housed within the casing and includes a positive electrode and a negative electrode, which are wound together. The electrode assembly includes a bending region and a straight region connected to the bending region. The positive electrode includes a positive current collector and a first active material layer, which is disposed inside the positive current collector. The first active material layer includes a first portion and a second portion disposed along the winding direction. The compaction density of the first portion is greater than that of the second portion. At least a portion of the first portion is disposed in the bending region, and at least a portion of the second portion is disposed in the straight region.

[0006] The first part has a higher compaction density, resulting in greater contact between active material particles. This makes it difficult for the electrolyte to penetrate the interior of the first part, lengthening the path for lithium ion extraction and thus weakening its conductivity. Therefore, by placing at least a portion of the first part in the bending region, the lithium ion extraction capability of the first active material layer of the positive electrode sheet located in the bending region is reduced, thereby decreasing the risk of lithium plating in the bending region of the electrode assembly and improving the reliability of the battery cell. Furthermore, adjusting the compaction density has minimal impact on the participation of the active materials in the first and second parts during charge and discharge operations, resulting in a relatively high utilization rate of the active materials in the battery cell and helping to reduce capacity loss.

[0007] In some embodiments of the first aspect, the thickness of the first portion is less than the thickness of the second portion.

[0008] The above technical solution can not only improve the structural stability of the electrode assembly, but also further reduce the risk of lithium plating in the bending area of ​​the electrode assembly, thereby further improving the reliability of the battery cell.

[0009] In some embodiments of the first aspect, the first active material layer further includes a first transition portion connected between the first portion and the second portion, the thickness of the first transition portion gradually increasing along the direction from the first portion to the second portion.

[0010] The thickness of the first transition portion gradually increases along the direction from the first portion to the second portion, so that the first active material layer smoothly transitions from the smaller thickness of the first portion to the larger thickness of the second portion. This can reduce the local stress concentration caused by the abrupt change in thickness, thereby reducing the risk of damage and peeling of the active material.

[0011] In some embodiments of the first aspect, the active material capacity per unit area of ​​the first portion is less than or equal to the active material capacity per unit area of ​​the second portion.

[0012] The electrode assembly of the above-mentioned technical solution features a more rational arrangement of active materials on the electrode plates, resulting in better economic efficiency and a reduced risk of lithium plating. Furthermore, it can, to a certain extent, reduce the risk of ion deposition while minimizing the impact on the electrical performance of the electrode assembly.

[0013] In some embodiments of the first aspect, the first portion is entirely located in the bending region.

[0014] The above technical solution only sets the first part for the bending area, so that the size of the first part along the winding direction is relatively short, thereby improving the preparation efficiency of the positive electrode sheet and reducing the cost.

[0015] In some embodiments of the first aspect, one end of the first portion along the winding direction is located in the bending region, and the other end of the first portion along the winding direction is located in the straight region.

[0016] The above technical solution sets one part of the first part in the bending area and the other part extends to the straight area. In other words, the first part passes through the junction of the straight area and the bending area, so that the positive electrode sheet has good structural consistency at the junction of the straight area and the bending area, thereby reducing the risk of the positive electrode sheet breaking at the junction of the straight area and the bending area during the winding process.

[0017] In some embodiments of the first aspect, the first portion passes through a bending region, and both ends of the first portion along the winding direction are located in a straight region.

[0018] The above technical solution can further increase the size of the first part along the winding direction, so that the first part can pass through the entire bending area, thereby further reducing the lithium ion extraction capability in the first active material layer of the positive electrode sheet located in the bending area, and thus further reducing the risk of lithium plating in the bending area of ​​the electrode assembly.

[0019] In some embodiments of the first aspect, there are multiple first portions and multiple second portions, and the multiple first portions and multiple second portions are alternately arranged along the winding direction.

[0020] The above technical solution sets the number of first parts and second parts to be multiple, which can improve the design flexibility of the entire positive electrode sheet by flexibly combining multiple first parts and multiple second parts.

[0021] In some embodiments of the first aspect, the positive electrode sheet includes a plurality of positive electrode bent portions located in a bending region and a plurality of positive electrode straight portions located in a straight region, the plurality of positive electrode bent portions and the plurality of positive electrode straight portions being alternately connected along the winding direction. Among the plurality of positive electrode bent portions, at least the two innermost positive electrode bent portions of the electrode assembly are provided with a first portion.

[0022] The above technical solution can further reduce the risk of ion deposition in the bending area of ​​the electrode assembly by specifically setting the first part at least on the two positive electrode bending parts located at the innermost part of the electrode assembly.

[0023] In some embodiments of the first aspect, a first portion is provided in each of the multiple positive electrode bends. This can further reduce the risk of ion deposition in the bend region of the electrode assembly.

[0024] In some embodiments of the first aspect, the compaction density a1 of the first portion and the compaction density a2 of the second portion satisfy the relationship: 0.02 g / cc ≤ a1 - a2 ≤ 3 g / cc.

[0025] The above technical solution, by setting the compaction density a1 of the first part and the compaction density a2 of the second part to satisfy the above relationship, can improve the structural stability of the positive electrode sheet while reducing the risk of ion precipitation in the bending area of ​​the electrode assembly, thereby reducing the risk of strip breakage of the positive electrode sheet.

[0026] In some embodiments of the first aspect, the compaction density a1 of the first portion and the compaction density a2 of the second portion satisfy the relationship: 0.05 g / cc ≤ a1 - a2 ≤ 1 g / cc.

[0027] It can further improve the balance between reducing the risk of ion deposition in the bending area of ​​the electrode assembly and the risk of breakage of the positive electrode sheet.

[0028] In some embodiments of the first aspect, the dimension b1 of the first portion along the winding direction and the length b2 of the straight region satisfy the relationship: 2mm≤b1≤2*b2.

[0029] The above technical solution provides tolerance space for the manufacturing process of the electrode assembly by setting the dimension b1 of the first part along the winding direction to satisfy the above relationship, thereby improving the success rate of setting the first part in the bending area.

[0030] In some embodiments of the first aspect, the dimension b1 of the first portion along the winding direction and the length b2 of the straight region satisfy the relationship: 5mm ≤ b1 ≤ b2.

[0031] This not only improves the manufacturing process tolerance of the electrode assembly, but also increases the setup space of the second part, thereby reducing the setup difficulty within the second part.

[0032] In some embodiments of the first aspect, the positive electrode further includes a second active material layer disposed outside the positive current collector. The second active material layer includes a third portion and a fourth portion disposed along the winding direction. The compaction density of the third portion is greater than that of the fourth portion. At least a portion of the third portion is disposed in the bending region, and at least a portion of the fourth portion is disposed in the straight region. The projection of the third portion along the thickness direction of the positive electrode at least partially overlaps with the projection of the first portion along the thickness direction.

[0033] The above technical solution can help reduce the difficulty of preparing the first part and improve the preparation efficiency and product yield by setting rollers on opposite sides of the positive electrode sheet along its own thickness direction and rolling the two rollers synchronously.

[0034] Secondly, embodiments of this application provide a method for manufacturing a single battery cell, the method comprising:

[0035] A positive electrode sheet is provided, wherein the positive electrode sheet includes a positive current collector and a first active material layer, the first active material layer being disposed on one side surface of the positive current collector along its own thickness direction;

[0036] The first active material layer is processed to form a first part and a second part along the length direction of the positive electrode sheet, wherein the compaction density of the first part is greater than that of the second part.

[0037] A negative electrode sheet is provided, and a positive electrode sheet and a negative electrode sheet are wound to form an electrode assembly, with a first active material layer located inside the positive current collector. The electrode assembly includes a bending region and a straight region connected to the bending region, at least a portion of the first part is disposed in the bending region, and at least a portion of the second part is disposed in the straight region.

[0038] Provide a housing to house the electrode assembly.

[0039] The first part of the aforementioned technical solution has a high compaction density, resulting in greater contact between active material particles and making it difficult for the electrolyte to penetrate into the interior of the first part. This lengthens the path for lithium ions to escape from the first part, thereby weakening the lithium ion conductivity in the first part. Therefore, by placing at least a portion of the first part in the bending region, the lithium ion extraction capability in the first active material layer of the positive electrode sheet located in the bending region is reduced, thereby decreasing the risk of lithium plating in the bending region of the electrode assembly and improving the reliability of the battery cell. Furthermore, adjusting the compaction density has minimal impact on the participation of the active materials in the first and second parts during charge and discharge operations, resulting in a relatively high utilization rate of the active materials in the battery cell and helping to reduce capacity loss in the battery cell.

[0040] In some embodiments of the second aspect, the positive electrode sheet further includes a second active material layer, wherein the second active material layer and the first active material layer are respectively disposed on opposite sides of the positive current collector along the thickness direction.

[0041] The steps for treating the first active material layer include:

[0042] The first and second active material layers are subjected to a first rolling process.

[0043] A portion of the first active material layer and a portion of the second active material layer after the first rolling are subjected to a second rolling, so that the first active material layer forms a first part and the second active material layer forms a third part corresponding to the first part;

[0044] The second part is the portion of the first active material layer that has not been rolled a second time, and the fourth part is the portion of the second active material layer that has not been rolled a second time. The compaction density of the third part is greater than that of the fourth part, and the pressure of the second roll is greater than that of the first roll.

[0045] The above-described technical solution enables the simultaneous formation of the first and third parts by simultaneously rolling two rollers on opposite sides of the positive electrode sheet along its thickness direction. This reduces the difficulty of preparing the first part and improves manufacturing efficiency and product yield. Furthermore, the positive electrode sheet provided in this application allows for the differentiation of compaction density between the first and second parts directly through rolling during the cold pressing process in battery cell manufacturing, which helps improve battery cell production efficiency and reduce production costs.

[0046] Thirdly, this application provides a battery device that includes a battery cell provided in any of the embodiments of the first aspect.

[0047] Fourthly, this application provides an electrical device that includes a battery cell provided in any embodiment of the first aspect or a battery device provided in any embodiment of the second aspect, wherein the battery cell or battery device is used to store or provide electrical energy.

[0048] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0049] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0050] Figure 1 These are schematic diagrams of the vehicle structure provided in some embodiments of this application;

[0051] Figure 2 This is an exploded structural diagram of a battery device provided in some embodiments of this application;

[0052] Figure 3 This is a schematic diagram of the structure of a battery module provided in some embodiments of this application;

[0053] Figure 4 This is a schematic diagram of the exploded structure of a single battery cell provided in some embodiments of this application;

[0054] Figure 5 This is a front view of the electrode assembly of a battery cell provided in some embodiments of this application;

[0055] Figure 6 for Figure 5 Schematic diagram of the cross-sectional structure along AA;

[0056] Figure 7 for Figure 6 A magnified schematic diagram of the local structure at point H;

[0057] Figure 8 This is a process flow diagram of a method for manufacturing a single battery cell provided in some embodiments of this application.

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

[0059] 1. Vehicle; 2. Battery unit; 3. Controller; 4. Motor; 5. Housing; 5a. First housing section; 5b. Second housing section; 5c. Housing space; 6. Battery module; 7. Battery cell;

[0060] 10. Outer shell; 20. Electrode assembly; 21. Bending area; 22. Straight area;

[0061] 30. Positive electrode sheet; 30a. Positive electrode bend; 30b. Positive electrode straight section; 31. Positive electrode current collector; 32. First active material layer; 321. First part; 322. Second part; 323. First transition part; 33. Second active material layer; 331. Third part; 332. Fourth part; 333. Second transition part;

[0062] 40. Negative electrode sheet; K. Winding direction. Detailed Implementation

[0063] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0064] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in the specification of this application is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms "comprising" and "having," and any variations thereof, in the specification, claims, and foregoing drawings of this application are intended to cover non-exclusive inclusion. The terms "first," "second," etc., in the specification, claims, or foregoing drawings of this application are used to distinguish different objects, rather than to describe a specific order or hierarchy.

[0065] In this application, the reference to "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.

[0066] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "attachment" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0067] In this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, in this application, the character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0068] In the embodiments of this application, the same reference numerals denote the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments. It should be understood that the thickness, length, width, and other dimensions of various components in the embodiments of this application shown in the accompanying drawings, as well as the overall thickness, length, width, and other dimensions of the integrated device, are merely illustrative and should not constitute any limitation on this application.

[0069] In this application, "multiple" means two or more (including two).

[0070] In this application, the term "parallel" includes not only the case of absolute parallelism, but also the case of approximate parallelism as commonly understood in engineering; similarly, "perpendicular" includes not only the case of absolute perpendicularity, but also the case of approximate perpendicularity as commonly understood in engineering.

[0071] In this embodiment of the application, the battery cell can be a secondary battery cell, which refers to a battery cell that can be used again after being discharged by recharging to activate the active materials.

[0072] The battery cell can be a lithium-ion battery cell, a sodium-ion battery cell, a sodium-lithium-ion battery cell, a lithium metal battery cell, a sodium metal battery cell, a lithium-sulfur battery cell, a magnesium-ion battery cell, a nickel-metal hydride battery cell, a nickel-cadmium battery cell, a lead-acid battery cell, etc., but the embodiments of this application are not limited to this.

[0073] A single battery cell typically includes an electrode assembly. The electrode assembly consists of a positive electrode and a negative electrode. During the charging and discharging process of a single battery cell, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes.

[0074] In some embodiments, the positive electrode may be a positive electrode sheet, which may include a positive electrode current collector and a positive electrode active material disposed on at least one surface of the positive electrode current collector.

[0075] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material is disposed on either or both of the two opposite surfaces of the positive current collector.

[0076] As an example, the positive current collector can be a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, pure metals, alloys, or surface-treated metals can be used, including but not limited to stainless steel, copper, aluminum, nickel, titanium, or silver. The composite current collector may include a polymer material base layer and a metal layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0077] As an example, the positive electrode active material may include at least one of the following materials: lithium phosphate, lithium transition metal oxide, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium phosphate may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites. Examples of lithium transition metal oxide may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.8 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Modified compounds refer to substances obtained by modification methods such as doping or coating based on the above-mentioned substances.

[0078] In some embodiments, the positive electrode can be a foamed metal. The foamed metal can be foamed nickel, foamed copper, foamed aluminum, foamed alloy, or foamed carbon, etc. When foamed metal is used as the positive electrode, the surface of the foamed metal may or may not contain a positive electrode active material. As an example, a positive electrode active material is filled and / or deposited within the foamed metal.

[0079] In some embodiments, the negative electrode may be a negative electrode sheet, and the negative electrode sheet may include a negative electrode current collector.

[0080] As an example, the negative electrode current collector can be a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, pure metals, alloys, or surface-treated metals can be used, including but not limited to stainless steel, copper, aluminum, nickel, titanium, or silver. The composite current collector may include a polymer material substrate and a metal layer. The composite current collector can be formed by forming a metal material (copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0081] As an example, the negative electrode sheet may include a negative electrode current collector and a negative electrode active material disposed on at least one surface of the negative electrode current collector.

[0082] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0083] As an example, the negative electrode active material may be a negative electrode active material known in the art for use in battery cells. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for battery cells may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0084] In some embodiments, the negative electrode can be a foamed metal. The foamed metal can be foamed nickel, foamed copper, foamed aluminum, foamed alloy, or foamed carbon, etc. When foamed metal is used as the negative electrode sheet, the surface of the foamed metal may or may not have a negative electrode active material.

[0085] As an example, negative electrode active materials can be filled or / and deposited within the negative electrode current collector.

[0086] In some embodiments, the positive current collector can be made of aluminum, and the negative current collector can be made of copper.

[0087] In some embodiments, the electrode assembly further includes an isolator disposed between the positive and negative electrodes.

[0088] In some embodiments, the separator is a separator membrane. This application does not impose any particular limitation on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0089] As an example, the main material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramic. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation. The separator can be a single component located between the positive and negative electrodes, or it can be attached to the surfaces of the positive and negative electrodes. An inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating can also be applied to the surface of the separator.

[0090] In some embodiments, the separator is a solid electrolyte. The solid electrolyte is disposed between the positive and negative electrodes, serving both to transport ions and to isolate the positive and negative electrodes.

[0091] In some embodiments, the battery cell also includes an electrolyte, which acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. The electrolyte can be liquid, gel, or solid.

[0092] Liquid electrolytes include electrolyte salts and solvents.

[0093] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0094] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone. The solvent may also be an ether solvent. Ether solvents may include one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyl tetrahydrofuran, diphenyl ether, and crown ethers.

[0095] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain properties of the battery cell, such as additives that improve the overcharge / fast charge performance of the battery cell, additives that improve the high-temperature performance of the battery cell, and additives that improve the low-temperature performance of the battery cell.

[0096] The gel electrolyte includes a polymer as a backbone network and can be used in conjunction with an ionic liquid-lithium salt.

[0097] Solid electrolytes include polymer solid electrolytes, inorganic solid electrolytes, and composite solid electrolytes.

[0098] As an example, the polymers of polymeric solid electrolytes may include polyethers (polyoxyethylene), polysiloxanes, polycarbonates, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, monoionic polymers, polyionic liquids, cellulose, etc.

[0099] As an example, inorganic solid electrolytes can be one or more of the following: oxide solid electrolytes (crystalline perovskite, sodium superconducting ion conductor, garnet, amorphous LiPON thin film), sulfide solid electrolytes (crystalline lithium superconducting ion conductor (lithium germanium phosphorus sulfide, silver sulfide germanium ore), amorphous sulfides), halide solid electrolytes, nitride solid electrolytes, and hydride solid electrolytes.

[0100] As an example, composite solid electrolytes are formed by adding inorganic solid electrolyte fillers to polymer solid electrolytes.

[0101] The electrode assembly can be a wound structure, a stacked structure, or a hybrid structure of wound and stacked.

[0102] In some implementations, the electrode assembly is a wound structure. The positive and negative electrode sheets are wound into a wound structure.

[0103] In some implementations, the electrode assembly is a stacked structure.

[0104] As an example, multiple positive and negative electrodes can be set, and multiple positive and multiple negative electrodes can be stacked alternately.

[0105] As an example, multiple positive electrode plates can be provided, and negative electrode plates can be folded to form multiple stacked folded segments, with a positive electrode plate sandwiched between adjacent folded segments.

[0106] As an example, both the positive and negative electrode plates are folded to form multiple stacked folded segments.

[0107] As an example, multiple separators can be provided, each positioned between any adjacent positive or negative electrode plates.

[0108] As an example, the separators can be continuously arranged, either by folding or rolling between any adjacent positive or negative electrode plates.

[0109] In some embodiments, the electrode assembly can be cylindrical, flat, or polygonal, etc.

[0110] In some embodiments, the electrode assembly is provided with tabs that allow current to be drawn from the electrode assembly. The tabs include a positive tab and a negative tab.

[0111] In some embodiments, the battery cell may include a casing. The casing may be a steel casing, an aluminum casing, a plastic casing (such as a polypropylene casing), a composite metal casing (such as a copper-aluminum composite casing), or an aluminum-plastic film, etc. In some embodiments, the casing may be a sealed structure or a non-sealed structure. As an example, when the casing is a non-sealed structure, the casing serves to protect the electrode assembly, and a sealing bag is included between the casing and the electrode assembly to encapsulate the electrode assembly and electrolyte. Specifically, the sealing bag may be a bag-shaped insulating component or an aluminum-plastic film. When the casing is a sealed structure, it is used to encapsulate components such as the electrode assembly and electrolyte.

[0112] As an example, a battery cell can be a cylindrical battery cell, a prismatic battery cell, a pouch battery cell, or a battery cell of other shapes. Prismatic battery cells include prismatic battery cells, blade-shaped battery cells, and multi-prismatic batteries, such as hexagonal prismatic batteries.

[0113] In some embodiments, the housing includes an end cap and a housing, the housing having an opening, and the end cap covering the opening. The housing may have one or more openings. The end cap may also have one or more.

[0114] In some embodiments, at least one electrode terminal is provided on the housing, and the electrode terminal is electrically connected to the tab. The electrode terminal can be directly connected to the tab, or it can be indirectly connected to the tab through a current collector. The electrode terminal can be provided on the end cap or on the housing.

[0115] The battery apparatus mentioned in the embodiments of this application may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple battery cells connected in series, parallel, or mixed connections via a busbar.

[0116] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells.

[0117] As an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple battery cells together to form an independent module. As another example, a battery module can be formed by bundling multiple battery cells together with cable ties.

[0118] In some embodiments, the battery device may be a battery pack, which includes a housing and one or more individual battery cells housed within the housing.

[0119] As an example, the battery cell assembly can be a battery module, which can be housed in a housing by fixing the battery module in the housing.

[0120] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple battery cells to the housing.

[0121] As an example, the enclosure may include a top cover, a frame, and a bottom plate. The top cover and bottom plate are connected to the frame, creating an enclosed space inside the enclosure to house the individual battery cells.

[0122] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0123] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use individual battery cells, such as mobile phones, portable devices, laptops, electric vehicles, electric toys, power tools, vehicles, ships, and spacecraft. For example, spacecraft include airplanes, rockets, space shuttles, and spacecraft.

[0124] With the development of new energy technologies, batteries are being used more and more widely, for example in mobile phones, laptops, electric vehicles, electric cars, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes, and power tools.

[0125] In the development of battery technology, the reliability of individual battery cells directly affects the reliability, cost of use, and user experience of end products. For typical battery cells, improper arrangement of active materials in the electrode plates of the electrode assembly can easily lead to lithium plating risk, seriously affecting the reliability of the battery cell.

[0126] The wound electrode assembly includes a flat region and a bent region. The thickness of the active material layer on the inner side of the flat region of the positive electrode is equal to the thickness of the active material layer on the inner side of the bent region of the positive electrode, and both the inner and outer active material layers of the flat and bent regions of the positive electrode are made of the same material. The thickness of the active material layer on the outer side of the flat region of the negative electrode is equal to the thickness of the active material layer on the outer side of the bent region of the negative electrode, and both the outer and outer active material layers of the flat and bent regions of the negative electrode are made of the same material.

[0127] In the bending region, the radius of the inner active material layer of the positive electrode is larger than the radius of the outer active material layer of the negative electrode located inside the positive electrode; that is, the radius of the outer active material layer of the negative electrode is smaller than the radius of the inner active material layer of the positive electrode located outside the negative electrode. In the straight region, the inner active material layer of the positive electrode is positioned correspondingly to the outer active material layer of the negative electrode.

[0128] When the capacity design of the inner active material layer in the flat region of the positive electrode meets the requirements, an excessive amount of active material in the inner bending region of the positive electrode makes the negative electrode, located inside the positive electrode, prone to lithium plating. Conversely, when the capacity design of the outer active material layer in the flat region of the negative electrode meets the requirements, an insufficient amount of active material in the outer bending region of the negative electrode is prone to causing lithium plating. Therefore, this type of electrode assembly, with its unreasonable arrangement of active materials in the electrodes, is prone to lithium plating risks, seriously affecting the reliability of the battery cell.

[0129] Based on the above considerations, this application provides a battery cell, which includes a casing and an electrode assembly. The electrode assembly is housed in the casing and includes a positive electrode and a negative electrode, which are wound together. The electrode assembly includes a bending region and a straight region connected to the bending region. The positive electrode includes a positive current collector and a first active material layer. The first active material layer is disposed inside the positive current collector and includes a first portion and a second portion disposed along the winding direction. The compaction density of the first portion is greater than that of the second portion. At least a portion of the first portion is disposed in the bending region, and at least a portion of the second portion is disposed in the straight region.

[0130] The first part has a higher compaction density and a greater degree of contact between active material particles, making it difficult for the electrolyte to penetrate into the interior of the first part. This results in a longer path for lithium ions to escape from the first part, thereby weakening the lithium ion conductivity in the first part. Therefore, by placing at least a portion of the first part in the bending region, the lithium ion extraction capability in the first active material layer of the positive electrode sheet located in the bending region is reduced, thereby decreasing the risk of ion deposition in the bending region of the electrode assembly and improving the reliability of the battery cell.

[0131] Furthermore, the positive electrode sheet provided in this application embodiment can directly achieve differentiated compaction densities of the first and second parts through rolling during the cold pressing process of battery cell manufacturing, which helps to improve the production efficiency of battery cells and reduce production costs. The adjustment of compaction density has minimal impact on the participation of the active materials in the first and second parts during charge and discharge operations, resulting in a relatively high utilization rate of the active materials in the battery cell and helping to reduce capacity loss in the battery cell.

[0132] The battery cell provided in the embodiments of this application is described below with reference to the accompanying drawings.

[0133] Figure 1 The diagram shows the structural features of a vehicle provided in some embodiments of this application.

[0134] Continue to refer to Figure 1 The vehicle 1 is equipped with a battery device 2, which may be located at the bottom, front, or rear of the vehicle 1. The battery device 2 can be used to power the vehicle 1; for example, the battery device 2 can serve as the operating power source for the vehicle 1.

[0135] The vehicle 1 may also include a controller 3 and a motor 4. The controller 3 is used to control the battery device 2 to supply power to the motor 4, for example, for the power needs of the vehicle 1 during starting, navigation and driving.

[0136] In some embodiments of this application, the battery device 2 can not only serve as the operating power source for the vehicle 1, but also as the driving power source for the vehicle 1, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1.

[0137] Figure 2 An exploded schematic diagram of a battery device provided in some embodiments of this application.

[0138] Continue to refer to Figure 2 The battery device 2 includes a housing 5 and individual battery cells, with the individual battery cells housed within the housing 5.

[0139] The housing 5 is used to house individual battery cells, and the housing 5 can have various structures. In some embodiments, the housing 5 may include a first housing portion 5a and a second housing portion 5b, which overlap each other, and together define a housing space 5c for housing the individual battery cells. The second housing portion 5b may be a hollow structure with one end open, and the first housing portion 5a may be a plate-like structure, with the first housing portion 5a covering the open side of the second housing portion 5b to form a housing 5 with the housing space 5c; alternatively, both the first housing portion 5a and the second housing portion 5b may be hollow structures with one side open, with the open side of the first housing portion 5a covering the open side of the second housing portion 5b to form a housing 5 with the housing space 5c. Of course, the first housing portion 5a and the second housing portion 5b can have various shapes, such as cylinders, cuboids, etc.

[0140] To improve the sealing performance after the first housing part 5a and the second housing part 5b are connected, a sealing element, such as sealant or sealing ring, can also be provided between the first housing part 5a and the second housing part 5b.

[0141] Assuming that the first box section 5a covers the top of the second box section 5b, the first box section 5a can also be called the upper box cover, and the second box section 5b can also be called the lower box.

[0142] In battery device 2, there can be one or more battery cells. If there are multiple battery cells, they can be connected in series, parallel, or in a mixed manner. A mixed connection means that multiple battery cells are connected in both series and parallel. Multiple battery cells can be directly connected in series, parallel, or in a mixed manner, and then the whole assembly of multiple battery cells is housed in housing 5. Alternatively, multiple battery cells can first be connected in series, parallel, or in a mixed manner to form battery module 6, and then multiple battery modules 6 can be connected in series, parallel, or in a mixed manner to form a whole assembly, which is then housed in housing 5.

[0143] Figure 3 for Figure 2 The diagram shows the structure of the battery module.

[0144] In some embodiments, continue to refer to Figure 3 The battery cells 7 are multiple, and these cells are first connected in series, parallel, or in a mixed manner to form a battery module 6. The multiple battery modules 6 are then connected in series, parallel, or in a mixed manner to form a whole, which is housed in the casing.

[0145] Multiple battery cells 7 in battery module 6 can be electrically connected through a busbar component to achieve parallel, series, or mixed connection of multiple battery cells 7 in battery module 6.

[0146] Figure 4 This is a schematic diagram of the exploded structure of a single battery cell provided in some embodiments of this application. Figure 5 This is a front view schematic diagram of the electrode assembly of a battery cell provided in some embodiments of this application. Figure 6 for Figure 5 A schematic diagram of the cross-sectional structure along AA. Figure 7 for Figure 6 A magnified schematic diagram of the structure at point H.

[0147] Continue to refer to Figures 4 to 7 This application provides a battery cell 7, which includes a housing 10 and an electrode assembly 20. The electrode assembly 20 is housed in the housing 10 and includes a positive electrode 30 and a negative electrode 40, which are wound together. The electrode assembly 20 includes a bending region 21 and a straight region 22 connected to the bending region 21. The positive electrode 30 includes a positive current collector 31 and a first active material layer 32. The first active material layer 32 is disposed inside the positive current collector 31 and includes a first portion 321 and a second portion 322 disposed along the winding direction K. The compaction density of the first portion 321 is greater than that of the second portion 322. At least a portion of the first portion 321 is disposed in the bending region 21, and at least a portion of the second portion 322 is disposed in the straight region 22.

[0148] Exemplarily, the housing 10 is a component used to form the internal environment of the battery cell 7. The formed internal environment can accommodate the electrode assembly 20, electrolyte, and other components. Optionally, the housing 10 can be, but is not limited to, made of metallic or non-metallic materials. For example, metallic materials can be copper, aluminum, or stainless steel; non-metallic materials can be polyethylene, polypropylene, or polyvinyl chloride.

[0149] Electrode assembly 20 is the component in the battery cell 7 where electrochemical reactions occur. Electrode assembly 20 is mainly formed by winding or stacking positive and negative electrode sheets, and a separator is usually provided between the positive and negative electrode sheets. The portions of the positive and negative electrode sheets containing active material constitute the main body of electrode assembly 20, while the portions of the positive and negative electrode sheets without active material each constitute a tab. The positive and negative tabs can be located together at one end of the main body or separately at both ends of the main body. During the charging and discharging process of the battery, the positive and negative active materials react with the electrolyte, and the tabs connect to the electrode terminals to form a current loop.

[0150] The battery cell 7 in this application embodiment can be, but is not limited to, a lithium-ion battery cell or a sodium-ion battery cell, etc.

[0151] In this embodiment, the winding direction K is the direction in which the positive electrode 30 and the negative electrode 40 are wound circumferentially from the inside out. Figure 6 In this configuration, the winding direction K is counterclockwise. It can be understood that, to a certain extent, the winding direction K is parallel to the length direction of the positive electrode 30, and the winding direction K is parallel to the length direction of the negative electrode 40.

[0152] The greater the compaction density of the first active material layer 32 of the positive electrode 30, the greater the contact between the active material particles, making it more difficult for the electrolyte to penetrate into the interior of the first active material layer 32. This results in a longer path for lithium ions to escape from the first active material layer 32, thereby weakening the conductivity of lithium ions in the first active material layer 32.

[0153] For example, compaction density refers to the weight of the active material per unit volume. The compaction density P can be measured by first cutting a standard small circle with an area of ​​S from the electrode to be tested, then weighing the standard small circle W1, then measuring the thickness D1 of the standard small circle, and then measuring the weight W2 and the thickness D2 of the current collector in the standard small circle. The compaction density P can then be obtained by the formula: P = (W1 - W2) / (S(D1 - D2)).

[0154] Thus, the first part 321 has a higher compaction density and a greater degree of contact between active material particles, making it difficult for the electrolyte to penetrate into the interior of the first part 321. This results in a longer path for lithium ions to escape from the first part 321, thereby weakening the conductivity of lithium ions in the first part 321. Therefore, by placing at least a portion of the first part 321 in the bending region 21, the lithium ion extraction capability in the first active material layer 32 of the positive electrode 30 located in the bending region 21 is reduced, thereby reducing the risk of ion deposition in the bending region 21 of the electrode assembly 20 and improving the reliability of the battery cell 7.

[0155] Furthermore, the positive electrode sheet 30 provided in this embodiment can directly achieve the differentiated compaction density setting of the first part 321 and the second part 322 through rolling during the cold pressing process of battery cell 7 manufacturing, which helps to improve the production efficiency of battery cell 7 and reduce production costs. The adjustment of compaction density has little impact on the participation of active materials in the first part 321 and the second part 322 in charge and discharge operations, resulting in a relatively high utilization rate of active materials in battery cell 7, which helps to reduce the capacity loss of battery cell 7.

[0156] It should be noted that the number of turns of the electrode assembly 20 can be one or more. The electrode assembly 20 includes two bending regions 21, and a straight region 22 is connected between the two bending regions 21. When the number of turns of the electrode assembly 20 is N, the positive electrode 30 includes N layers of positive electrode bending portions 30a in each bending region 21, and the positive electrode 30 includes 2N layers of positive electrode straight portions 30b in the straight region 22, where N is an integer.

[0157] The fact that at least a portion of the first part 321 is disposed in the bending region 21 means that at least a portion of the first part 321 is disposed on at least one layer of positive electrode bending portion 30a. The fact that at least a portion of the second part 322 is disposed in the straight region 22 means that at least a portion of the second part 322 is disposed on at least one layer of positive electrode straight portion 30b.

[0158] For example, when there is only one first part 321 and one second part 322, at least a portion of the first part 321 is disposed on a positive electrode bending portion 30a, and at least a portion of the second part 322 is disposed on a positive electrode straight portion 30b.

[0159] When there are multiple first portions 321 and multiple second portions 322, the number of first portions 321 may correspond to the number of positive electrode bending portions 30a, and the number of second portions 322 may correspond to the number of positive electrode straight portions 30b. Multiple first portions 321 are arranged in a one-to-one correspondence with multiple positive electrode bending portions 30a, and multiple second portions 322 are arranged in a one-to-one correspondence with multiple positive electrode straight portions 30b. At least a portion of each first portion 321 is disposed on each layer of positive electrode bending portions 30a, and at least a portion of each second portion 322 is disposed on each layer of positive electrode bending portions 30a.

[0160] When there are multiple first portions 321 and multiple second portions 322, the number of first portions 321 may be less than the number of positive electrode bending portions 30a, and the number of second portions 322 may be less than the number of positive electrode straight portions 30b. At least a portion of a first portion 321 is disposed on a layer of positive electrode bending portions 30a, and at least a portion of a second portion 322 is disposed on a layer of positive electrode bending portions 30a.

[0161] Alternatively, the number of turns of the electrode assembly 20 may not be an integer. The number of turns of the electrode assembly 20 may be N+M, where N is an integer and M is a non-integer. For example, N can be, but is not limited to, 4, 8, 10, or 12, and M can be, but is not limited to, 1 / 3, 1 / 2, 2 / 3, or 3 / 4. It is understood that when the number of turns of the electrode assembly 20 is not an integer, for example, when the number of turns of the electrode assembly 20 is N+M, the number of layers in the positive electrode bending portion 30a in the two bending regions 21 of the electrode assembly 20 may be the same or different; the number of layers in the positive electrode straight portion 30b in the straight region 22 of the electrode assembly 20 may be 2N, 3N, or 4N, etc.

[0162] In some embodiments, the thickness of the first portion 321 is less than the thickness of the second portion 322.

[0163] In this embodiment, the first part 321 and the second part 322 of the first active material layer 32 of the positive electrode sheet 30 differ not only in compaction density but also in thickness.

[0164] On the one hand, the thickness of the first part 321 is less than that of the second part 322. Since the first part 321 is located in the bending area 21, its smaller thickness can better adapt to the deformation caused by bending during the winding process, which helps to reduce the risk of local stress concentration and material fatigue caused by bending itself.

[0165] On the other hand, if all parameters of the active material in the first part 321 are the same as those in the second part 322, except for thickness, such as the type, weight ratio, and specific capacity of the active material, then the type refers to the variety of active material; the weight ratio refers to the ratio of the weight of the active material in the first part 321 to the total weight of the first part 321 and the ratio of the weight of the active material in the second part 322 to the total weight of the second part 322; and the specific capacity refers to the ratio of the capacitance released by the active material to the mass of the active material. The thickness of the first part 321 is less than the thickness of the second part 322, which allows the active material capacity per unit area of ​​the first part 321 to be less than that of the second part 322, thereby further reducing the risk of lithium plating in the bending region 21 of the electrode assembly 20.

[0166] Optionally, the thickness of the second part 322 is 0.5%-20% greater than the thickness of the first part 321.

[0167] The above technical solution can not only improve the structural stability of the electrode assembly 20, but also further reduce the risk of lithium plating in the bending region 21 of the electrode assembly 20, so as to further improve the reliability of the battery cell 7.

[0168] In some embodiments, the first active material layer 32 further includes a first transition portion 323, which is connected between the first portion 321 and the second portion 322, and the thickness of the first transition portion 323 gradually increases along the direction from the first portion 321 to the second portion 322.

[0169] For example, the gradual change in thickness of the first transition portion 323 can be achieved through various processes. For instance, a step-by-step coating process can be used, where active materials of different thicknesses are coated in different areas, gradually increasing the thickness to achieve the gradual change in thickness of the first transition portion 323. Alternatively, an automated coating device can be used, adjusting the coating speed or the concentration of the coating material to achieve the gradual change in thickness of the first transition portion 323. A rolling process can also be employed, gradually increasing the pressure during the rolling process to achieve the gradual change in thickness of the first transition portion 323.

[0170] It is understandable that when the first part 321 is rolled using a rolling process to make the compaction density of the first part 321 greater than that of the second part 322, a first transition part 323 with gradually varying thickness can be naturally formed on both sides of the first part 321 along the length direction of the positive electrode sheet 30. This simplifies the manufacturing process and helps to reduce the overall manufacturing cost of the battery cell 7.

[0171] The thickness of the first transition portion 323 gradually increases along the direction from the first portion 321 to the second portion 322, so that the first active material layer 32 smoothly transitions from the smaller thickness of the first portion 321 to the larger thickness of the second portion 322. This can reduce the local stress concentration caused by the sudden change in thickness, thereby reducing the risk of damage and peeling of the active material.

[0172] In some embodiments, the active material capacity per unit area of ​​the first portion 321 is less than or equal to the active material capacity per unit area of ​​the second portion 322.

[0173] If the active material capacity per unit area of ​​the first part 321 is less than that of the second part 322, it is less likely that there will be an excess of active material in the first part 321, making the arrangement of the active material in the positive electrode 30 more reasonable and reducing the risk of ion deposition. This structure of electrode assembly 20 results in a more reasonable arrangement of the active material in the electrode, better economic efficiency, and a reduced risk of lithium plating.

[0174] When the active material capacity per unit area of ​​the second part 322 meets the design requirements, that is, when the active material capacity per unit area of ​​the second part 322 reaches the first preset value, since the active material capacity per unit area of ​​the first part 321 is smaller than that of the active material capacity per unit area of ​​the second part 322, relative to the first preset value, it is equivalent to reducing the active material capacity per unit area of ​​the first part 321, making it less likely for lithium plating to occur in the bending area 21 of the electrode assembly 20.

[0175] For example, the active material capacity per unit area of ​​the first part 321 can be made smaller than that per unit area of ​​the second part 322 in a variety of ways.

[0176] In some examples, the thickness of the first portion 321 is less than the thickness of the second portion 322, so that the active material capacity per unit area of ​​the first portion 321 is less than that of the second portion 322. This can be achieved by having all parameters of the active material in the first portion 321 identical to those in the second portion 322, except for the thickness. Alternatively, the parameters of the active material in the first portion 321 can also differ from those in the second portion 322, as long as the active material capacity per unit area of ​​the first portion 321 is less than that of the second portion 322. It should be noted that these other parameters can be, but are not limited to, the type of active material, weight ratio, and specific gravity.

[0177] In some examples, the specific capacity of the active material in the first part 321 is less than that of the active material in the second part 322, so that the active material capacity per unit area of ​​the first part 321 is less than that of the active material per unit area of ​​the second part 322. This can be achieved by having all parameters of the active material in the first part 321 identical to those in the second part 322, except for the specific capacity. Alternatively, the parameters of the active material in the first part 321 can also differ from those in the second part 322, as long as the active material capacity per unit area of ​​the first part 321 is less than that of the second part 322. It should be noted that other parameters of the active material can be, but are not limited to, the type, weight ratio, and thickness of the active material.

[0178] In some examples, the weight ratio of the active material in the first part 321 to the total weight of the first part 321 is less than the weight ratio of the active material in the second part 322 to the total weight of the second part 322, so that the active material capacity per unit area of ​​the first part 321 is less than that of the second part 322. This can be achieved by having all parameters of the active material in the first part 321 identical to those in the second part 322, except for the weight ratio. Alternatively, the parameters of the active material in the first part 321 can also be different from those in the second part 322, as long as the active material capacity per unit area of ​​the first part 321 is less than that of the second part 322. It should be noted that other parameters of the active material can be, but are not limited to, the type of active material, its specific gravity, and its thickness.

[0179] If the active material capacity per unit area of ​​the first portion 321 is equal to that of the second portion 322, the lithium ion extraction capability in the first portion 321 is reduced due to the higher compaction density of the first portion 321 compared to the second portion 322, thus lowering the risk of lithium plating. Furthermore, the active material capacity per unit area of ​​the first portion 321 is not reduced, thereby minimizing the impact on the electrical performance of the electrode assembly 20 while reducing the risk of ion plating.

[0180] The electrode assembly 20 of the above-mentioned technical solution features a more rational arrangement of active materials on the electrode plates, resulting in better economic efficiency and a reduced risk of lithium plating. Furthermore, it can also, to a certain extent, reduce the impact on the electrical performance of the electrode assembly 20 while mitigating the risk of ion deposition.

[0181] In some embodiments, the first portion 321 is entirely located in the bending region 21.

[0182] As described above, the electrode assembly 20 can have one or more turns. The electrode assembly 20 includes two bending regions 21, and a straight region 22 is connected between the two bending regions 21. When the electrode assembly 20 has N turns, the positive electrode 30 includes N layers of positive electrode bending portions 30a in each bending region 21, and the positive electrode 30 includes 2N positive electrode straight portions 30b in the straight region 22, where N is an integer.

[0183] The fact that at least a portion of the first part 321 is disposed in the bending region 21 means that at least a portion of the first part 321 is disposed on at least one layer of positive electrode bending portion 30a. The fact that at least a portion of the second part 322 is disposed in the straight region 22 means that at least a portion of the second part 322 is disposed on at least one layer of positive electrode straight portion 30b.

[0184] For example, when both the first part 321 and the second part 322 are one, the first part 321 may be located entirely in a part of a positive electrode bending section 30a, that is, both ends of the first part 321 along the winding direction K do not extend beyond the two ends of the positive electrode bending section 30a along the winding direction K; or the first part 321 may be located entirely in the entire area of ​​a positive electrode bending section 30a, that is, both ends of the first part 321 along the winding direction K coincide with the two ends of the positive electrode bending section 30a along the winding direction K.

[0185] When there are multiple first parts 321 and multiple second parts 322, the number of first parts 321 may correspond to the number of positive electrode bending portions 30a, and the number of second parts 322 may correspond to the number of positive electrode straight portions 30b. Multiple first parts 321 are arranged in a one-to-one correspondence with multiple positive electrode bending portions 30a, and multiple second parts 322 are arranged in a one-to-one correspondence with multiple positive electrode straight portions 30b. Each first part 321 may be entirely located in a portion of each layer of positive electrode bending portions 30a, meaning that both ends of each first part 321 along the winding direction K do not extend beyond the two ends of the positive electrode bending portion 30a in the same layer along the winding direction K; alternatively, each first part 321 may be entirely located in the entire area of ​​each layer of positive electrode bending portions 30a, meaning that both ends of each first part 321 along the winding direction K coincide with the two ends of the positive electrode bending portion 30a in the same layer along the winding direction K.

[0186] When there are multiple first portions 321 and multiple second portions 322, the number of first portions 321 may be less than the number of positive electrode bending portions 30a, and the number of second portions 322 may be less than the number of positive electrode straight portions 30b. One of the multiple first portions 321 may be entirely located within a portion of one of the multiple bending portions, meaning that both ends of this first portion 321 along the winding direction K do not extend beyond the two ends of the positive electrode bending portion 30a in the same layer along the winding direction K; alternatively, one of the multiple first portions 321 may be entirely located within the entire area of ​​one of the multiple positive electrode bending portions, meaning that both ends of this first portion 321 along the winding direction K coincide with the two ends of the positive electrode bending portion 30a in the same layer along the winding direction K.

[0187] The above technical solution only sets the first part 321 for the bending region 21, so that the first part 321 is relatively short in size along the winding direction K, thereby improving the preparation efficiency of the positive electrode sheet 30 and reducing the cost.

[0188] In some embodiments, one end of the first portion 321 along the winding direction K is located in the bending region 21, and the other end of the first portion 321 along the winding direction K is located in the straight region 22.

[0189] For example, when there is only one first part 321 and one second part 322, a part of the first part 321 may be located in a portion of a positive electrode bending portion 30a, and another part of the first part 321 may be located in a portion of a positive electrode straight portion 30b connected to this positive electrode bending portion 30a; or a part of the first part 321 may be located in the entire area of ​​a positive electrode bending portion 30a, and another part of the first part 321 may be located in a portion of a positive electrode straight portion 30b connected to this positive electrode bending portion 30a.

[0190] It is understandable that when there are multiple parts 321 and 322, the setting method is roughly the same as when there is only one part 321 and 322, and will not be repeated here.

[0191] Due to the winding of the electrode assembly 20, the stress at the junction of the straight region 22 and the bent region 21 in the electrode assembly 20 is relatively large. Therefore, the above technical solution, by placing a portion of the first part 321 in the bent region 21 and extending another portion into the straight region 22, that is, by having the first part 321 pass through the junction of the straight region 22 and the bent region 21, ensures that the positive electrode sheet 30 has better structural consistency at the junction of the straight region 22 and the bent region 21. This reduces the risk of the positive electrode sheet 30 breaking due to uneven stress distribution at the junction of the straight region 22 and the bent region 21 during the winding process.

[0192] In some embodiments, the first portion 321 passes through the bending region 21, and both ends of the first portion 321 along the winding direction K are located in the straight region 22.

[0193] For example, when there is only one first part 321 and one second part 322, a portion of the first part 321 is located in the entire area of ​​the positive electrode bending portion 30a, and another portion of the first part 321 is located in the local area of ​​the two positive electrode straight portions 30b connected to this positive electrode bending portion 30a.

[0194] It is understandable that when there are multiple parts 321 and 322, the setting method is roughly the same as when there is only one part 321 and 322, and will not be repeated here.

[0195] The above technical solution can further increase the size of the first part 321 along the winding direction K, so that the first part 321 can pass through the entire bending region 21, thereby further reducing the lithium ion extraction capability in the first active material layer 32 of the positive electrode 30 located in the bending region 21, thereby further reducing the risk of lithium plating in the bending region 21 of the electrode assembly 20.

[0196] In some embodiments, there are multiple first portions 321 and multiple second portions 322, and the multiple first portions 321 and multiple second portions 322 are alternately arranged along the winding direction K.

[0197] In some examples, the electrode assembly 20 includes two bending regions 21, and a straight region 22 is connected between the two bending regions 21. Each bending region 21 includes multiple positive electrode bending portions 30a, and the straight region 22 includes multiple positive electrode straight portions 30b. At least one of the multiple positive electrode bending portions 30a is provided with a plurality of first portions 321 and a plurality of second portions 322, and at least one of the multiple positive electrode straight portions 30b is provided with a plurality of first portions 321 and a plurality of second portions 322.

[0198] In some examples, the electrode assembly 20 includes two bending regions 21, and a straight region 22 is connected between the two bending regions 21. Each bending region 21 includes multiple layers of positive electrode bending portions 30a, and the straight region 22 includes multiple layers of positive electrode straight portions 30b. Each layer of positive electrode bending portion 30a is provided with a first portion 321, and each layer of positive electrode straight portion 30b is provided with a second portion 322.

[0199] The above technical solution sets the number of first part 321 fitted with second part 322 to be multiple, which can improve the design flexibility of the entire positive electrode 30 through the flexible combination of multiple first parts 321 and multiple second parts 322.

[0200] In some embodiments, the positive electrode 30 includes a plurality of positive electrode bent portions 30a located in the bending region 21 and a plurality of positive electrode straight portions 30b located in the straight region 22, the plurality of positive electrode bent portions 30a and the plurality of positive electrode straight portions 30b being alternately connected along the winding direction K. Among the plurality of positive electrode bent portions 30a, at least the two innermost positive electrode bent portions 30a located in the electrode assembly 20 are provided with a first portion 321.

[0201] For example, the two innermost positive electrode bends 30a of the electrode assembly 20 refer to the two positive electrode bends 30a closest to the starting end of the winding from the positive electrode sheet 30 along the winding direction K of the electrode assembly 20. That is, the two positive electrode bends 30a closest to the winding axis.

[0202] It is understandable that the negative electrode 40 includes multiple negative electrode bending portions located in the bending region 21 and multiple negative electrode straight portions located in the straight region 22. In the bending region 21, the bending stress of the negative electrode bending portion closer to the inside of the electrode assembly 20 is greater, and the risk of the active material layer on the outside of the negative electrode bending portion is also relatively greater. This makes the lithium intercalation capability of the active material layer on the outside of the negative electrode bending portion closer to the inside of the electrode assembly 20 worse. Therefore, in the bending region 21, the risk of ion deposition is more likely to occur between the first active material layer 32 of the positive electrode bending portion 30a closer to the inside of the electrode assembly 20 and the active material layer on the outside of the negative electrode bending portion.

[0203] Thus, by specifically placing the first part 321 on at least the two innermost positive electrode bends 30a of the electrode assembly 20, the above technical solution can further reduce the risk of ion deposition in the bend region 21 of the electrode assembly 20.

[0204] In some embodiments, the positive electrode 30 includes a plurality of positive electrode bent portions 30a located in the bending region 21 and a plurality of positive electrode straight portions 30b located in the straight region 22, the plurality of positive electrode bent portions 30a and the plurality of positive electrode straight portions 30b being alternately connected along the winding direction K. Among the plurality of positive electrode bent portions 30a, the two innermost positive electrode bent portions 30a located in the electrode assembly 20 are provided with first portions 321. This reduces the risk of ion deposition in the bending region 21 of the electrode assembly 20 while reducing the number of first portions 321, which is beneficial for cost reduction.

[0205] In some embodiments, each of the plurality of positive electrode bends 30a is provided with a first portion 321. This can further reduce the risk of ion deposition in the bend region 21 of the electrode assembly 20.

[0206] In some embodiments, the compaction density a1 of the first part 321 and the compaction density a2 of the second part 322 satisfy the relationship: 0.02g / cc≤a1-a2≤3g / cc.

[0207] As an example, a1-a2 can be, but is not limited to, 0.02g / cc, 0.1g / cc, 0.5g / cc, 0.8g / cc, 1g / cc, 1.2g / cc, 1.5g / cc, 2g / cc, 2.5g / cc, 3g / cc, etc.

[0208] Understandably, the smaller the difference between the compaction density a1 of the first part 321 and the compaction density a2 of the second part 322, the smaller the difference in lithium-ion insertion / extraction capability between the first part 321 and the second part 322, and the worse the effect of reducing the risk of ion deposition in the bending region 21 of the electrode assembly 20. At the same time, the smaller the stress difference between the first part 321 and the second part 322 during the winding process of the positive electrode 30, the better the overall structural stability of the positive electrode 30.

[0209] The greater the difference between the compaction density a1 of the first part 321 and the compaction density a2 of the second part 322, the greater the difference in lithium-ion insertion / extraction capability between the first part 321 and the second part 322, and the better the effect of reducing the risk of ion deposition in the bending region 21 of the electrode assembly 20. At the same time, the greater the stress difference between the first part 321 and the second part 322 during the winding process of the positive electrode sheet 30, the lower the overall structural stability of the positive electrode sheet 30.

[0210] Thus, by setting the compaction density a1 of the first part 321 and the compaction density a2 of the second part 322 to satisfy the above relationship, the above technical solution can improve the structural stability of the positive electrode 30 while reducing the risk of ion deposition in the bending region 21 of the electrode assembly 20, thereby reducing the risk of strip breakage of the positive electrode 30.

[0211] In some embodiments, the compaction density a1 of the first portion 321 and the compaction density a2 of the second portion 322 satisfy the relationship: 0.05 g / cc ≤ a1 - a2 ≤ 1 g / cc. This can further improve the balance between reducing the risk of ion deposition in the bending region 21 of the electrode assembly 20 and the risk of strip breakage in the positive electrode sheet 30.

[0212] As an example, a1-a2 can be, but is not limited to, 0.05g / cc, 0.06g / cc, 0.07g / cc, 0.08g / cc, 0.09g / cc, 0.1g / cc, 0.2g / cc, 0.3g / cc, 0.4g / cc, 0.5g / cc, 0.6g / cc, 0.7g / cc, 0.8g / cc, 0.9g / cc, 1g / cc, etc.

[0213] In some embodiments, the dimension b1 of the first portion 321 along the winding direction K and the length b2 of the straight region 22 satisfy the relationship: 2mm≤b1≤2*b2.

[0214] For example, the dimension b1 of the first portion 321 along the winding direction K can be understood as the dimension of the first portion 321 along the length direction of the positive electrode 30, that is, the length of the first portion 321. The length of the flat region 22 can be understood as the dimension of the flat region 22 along the length direction of the electrode assembly 20.

[0215] As an example, the dimension b1 of the first part 321 along the winding direction K can be, but is not limited to, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 15mm, 20mm, etc.

[0216] Understandably, the larger the dimension b1 of the first part 321 along the winding direction K, the easier it will be to position the first part 321 in the bending region 21 during the winding of the positive electrode sheet 30. However, the dimension b1 of the first part 321 along the winding direction K cannot exceed twice the length b2 of the straight region 22, in order to provide space for the second part 322.

[0217] The above technical solution provides tolerance space for the manufacturing process of electrode assembly 20 by setting the dimension b1 of the first part 321 along the winding direction K to satisfy the above relationship, thereby improving the success rate of setting the first part 321 in the bending area 21.

[0218] In some embodiments, the dimension b1 of the first portion 321 along the winding direction K and the length b2 of the straight region 22 satisfy the relationship: 5mm≤b1≤b2. This can further improve the manufacturing process tolerance of the electrode assembly 20, while also increasing the installation space of the second portion 322, thereby reducing the installation difficulty within the second portion 322.

[0219] As an example, the dimension b1 of the first part 321 along the winding direction K can be, but is not limited to, 5mm, 10mm, 11mm, 12mm, 13mm, 14mm, 15mm, 16mm, 17mm, 18mm, 19mm, 20mm, 25mm, 30mm, etc.

[0220] In some embodiments, the positive electrode 30 further includes a second active material layer 33 disposed on the outside of the positive current collector 31. The second active material layer 33 includes a third portion 331 and a fourth portion 332 disposed along the winding direction K. The compaction density of the third portion 331 is greater than that of the fourth portion 332. At least a portion of the third portion 331 is disposed in the bending region 21, and at least a portion of the fourth portion 332 is disposed in the straight region 22. The projection of the third portion 331 along the thickness direction of the positive electrode 30 and the projection of the first portion 321 along the thickness direction at least partially overlap.

[0221] For example, the projection of the third part 331 along the thickness direction of the positive electrode 30 overlaps with the projection of the first part 321 along the thickness direction, or the projection of the third part 331 along the thickness direction of the positive electrode 30 overlaps with the projection of the first part 321 along the thickness direction.

[0222] The above technical solution can help reduce the difficulty of preparing the first part 321 and the third part 331 by setting rollers on opposite sides of the positive electrode sheet 30 along its own thickness direction, and rolling the two rollers synchronously to form the first part 321 and the third part 331 at the same time. This helps to reduce the difficulty of preparing the first part 321 and improve the preparation efficiency and product yield.

[0223] In some embodiments, the thickness of the third portion 331 is less than the thickness of the fourth portion 332.

[0224] In this embodiment, the third part 331 and the fourth part 332 of the second active material layer 33 of the positive electrode 30 differ not only in compaction density but also in thickness.

[0225] On the one hand, the thickness of the third part 331 is less than that of the fourth part 332. Since the third part 331 is located in the bending area 21, its smaller thickness can better adapt to the deformation caused by bending during the winding process, which helps to reduce the risk of local stress concentration and material fatigue caused by bending itself.

[0226] On the other hand, if all parameters of the active material in the third part 331 are the same as those in the fourth part 332, except for thickness, such as the type, weight ratio, and specific capacity of the active material, then the type refers to the variety of active material; the weight ratio refers to the ratio of the weight of the active material in the third part 331 to the total weight of the third part 331, and the ratio of the weight of the active material in the fourth part 332 to the total weight of the fourth part 332; and the specific capacity refers to the ratio of the capacitance released by the active material to the mass of the active material. The thickness of the third part 331 is less than the thickness of the fourth part 332, which allows the active material capacity per unit area of ​​the third part 331 to be less than that of the fourth part 332, thereby further reducing the risk of lithium plating in the bending region 21 of the electrode assembly 20.

[0227] Optionally, the thickness of the fourth part 332 is 0.5%-20% greater than the thickness of the third part 331.

[0228] In some embodiments, the second active material layer 33 further includes a second transition portion 333, which is connected between the third portion 331 and the fourth portion 332, and the thickness of the second transition portion 333 gradually increases along the direction from the third portion 331 to the fourth portion 332.

[0229] For example, the gradual change in thickness of the second transition portion 333 can be achieved through various processes. For instance, a step-by-step coating process can be used, where active materials of different thicknesses are coated in different areas, gradually increasing the thickness to achieve the gradual change in thickness of the second transition portion 333. Alternatively, an automated coating device can be used, adjusting the coating speed or the concentration of the coating material to achieve the gradual change in thickness of the second transition portion 333. A rolling process can also be employed, gradually increasing the pressure during the rolling process to achieve the gradual change in thickness of the second transition portion 333.

[0230] It is understandable that when the third part 331 is rolled using a rolling process to make the compaction density of the third part 331 greater than that of the fourth part 332, a second transition part 333 with gradually varying thickness can be naturally formed on both sides of the third part 331 along the length of the positive electrode sheet 30. This simplifies the manufacturing process and helps to reduce the overall manufacturing cost of the battery cell 7.

[0231] The thickness of the second transition portion 333 gradually increases along the direction from the third portion 331 to the fourth portion 332, so that the second active material layer 33 smoothly transitions from the smaller thickness of the third portion 331 to the larger thickness of the fourth portion 332. This can reduce the local stress concentration caused by the abrupt change in thickness, thereby reducing the risk of damage and peeling of the active material.

[0232] In some embodiments, the active material capacity per unit area of ​​the third portion 331 is less than or equal to the active material capacity per unit area of ​​the fourth portion 332.

[0233] In some embodiments, the third portion 331 is entirely located in the bending region 21.

[0234] In some embodiments, one end of the third portion 331 along the winding direction K is located in the bending region 21, and the other end of the third portion 331 along the winding direction K is located in the straight region 22.

[0235] In some embodiments, the third portion 331 passes through the bending region 21, and both ends of the third portion 331 along the winding direction K are located in the straight region 22.

[0236] In some embodiments, there are multiple third portions 331 and multiple fourth portions 332, and the multiple third portions 331 and multiple fourth portions 332 are alternately arranged along the winding direction K.

[0237] Based on the battery cell 7 provided in the embodiments of this application, the embodiments of this application also provide a method for manufacturing the battery cell 7. Figure 8 This is a process flow diagram illustrating a method for manufacturing a battery cell 7 according to some embodiments of this application. Continuing with... Figure 8 As shown, the manufacturing method of the battery cell 7 may include steps 01, 02, 03 and 04.

[0238] Step 01, provide a positive electrode 30, wherein the positive electrode 30 includes a positive current collector 31 and a first active material layer 32, the first active material layer 32 being disposed on one side surface of the positive current collector 31 along its own thickness direction;

[0239] Step 02: The first active material layer 32 is processed to form a first part 321 and a second part 322 arranged along the length direction of the positive electrode 30, wherein the compaction density of the first part 321 is greater than that of the second part 322.

[0240] Step 03: Provide a negative electrode sheet 40, wind the positive electrode sheet 30 and the negative electrode sheet 40 to form an electrode assembly 20, and place the first active material layer 32 inside the positive current collector 31. The electrode assembly 20 includes a bending region 21 and a straight region 22 connected to the bending region 21. At least a portion of the first part 321 is disposed in the bending region 21, and at least a portion of the second part 322 is disposed in the straight region 22.

[0241] Step 04: Provide housing 10 and install electrode assembly 20 inside housing 10.

[0242] In relation to step 02 above, the first active material layer 32 can be processed by various processes to form the first part 321 and the second part 322.

[0243] In some examples, the first active material layer 32 can be processed by segmented control of the pressure roller. Specifically, during the compaction process, by applying segmented pressure to the pressure roller, the compaction density of different regions of the first active material layer 32 of the positive electrode 30 can be effectively adjusted. For example, a controllable pressure device can be provided on the pressure roller to apply greater pressure to a portion of the first active material layer 32 to form a first portion 321 with a greater compaction density, and to apply less pressure to a portion of the first active material layer 32 to form a second portion 322 with a smaller compaction density.

[0244] In some examples, the first active material layer 32 can also be processed by multiple rolling processes. Specifically, multiple rolling processes refer to rolling a portion of the first active material layer 32 multiple times to gradually densify the active material particles in that portion, forming the first portion 321. The other portion of the first active material layer 32 is rolled only once or a few times to form the second portion 322.

[0245] In some examples, the first active material layer 32 can also be treated by a localized heat treatment process. Specifically, localized heat treatment is a method of controlling compaction density by heating the active material layer to change its particle structure. The active material particles can be further densified by heating a portion of the first active material layer 32, thereby increasing its compaction density to form the first portion 321. The other portion of the unheated first active material layer 32 forms the second portion 322.

[0246] The first part 321 of the above-mentioned technical solution has a high compaction density, resulting in greater contact between active material particles. This makes it difficult for the electrolyte to penetrate the interior of the first part 321, lengthening the path for lithium ion extraction and thus weakening the lithium ion conductivity in the first part 321. Therefore, by placing at least a portion of the first part 321 in the bending region 21, the lithium ion extraction capability in the first active material layer 32 of the positive electrode 30 located in the bending region 21 is reduced, thereby decreasing the risk of lithium plating in the bending region 21 of the electrode assembly 20 and improving the reliability of the battery cell 7. Furthermore, the adjustment of the compaction density has minimal impact on the participation of the active materials in the first part 321 and the second part 322 in charge-discharge operation, resulting in a relatively high utilization rate of the active materials in the battery cell 7, which helps to reduce the capacity loss of the battery cell 7.

[0247] In some embodiments, the positive electrode 30 further includes a second active material layer 33, and the second active material layer 33 and the first active material layer 32 are respectively disposed on opposite sides of the positive current collector 31 along the thickness direction.

[0248] The steps for treating the first active material layer 32 include:

[0249] The first active material layer 32 and the second active material layer 33 are subjected to a first rolling process.

[0250] A portion of the first active material layer 32 and a portion of the second active material layer 33 after the first rolling are subjected to a second rolling, so that the first active material layer 32 forms a first part 321 and the second active material layer 33 forms a third part 331 corresponding to the first part 321.

[0251] Among them, the other part of the first active material layer 32 that has not been rolled for the second time is the second part 322, the other part of the second active material layer 33 that has not been rolled for the second time is the fourth part 332 corresponding to the second part 322, the compaction density of the third part 331 is greater than the compaction density of the fourth part 332, and the pressure of the second roll is greater than the pressure of the first roll.

[0252] After the positive electrode 30 and the negative electrode 40 are wound to form the electrode assembly 20, the second active material layer 33 is located outside the positive current collector 31, at least a portion of the third part 331 is disposed in the bending region 21, and at least a portion of the fourth part 332 is disposed in the straight region 22.

[0253] The correspondence between the first part 321 and the third part 331 means that the positions and structural dimensions of the first part 321 and the third part 331 are matched. It can be understood that the projection of the third part 331 along the thickness direction of the positive electrode 30 overlaps with the projection of the first part 321 along the thickness direction.

[0254] The second part 322 corresponds to the fourth part 332, meaning that the positions and structural dimensions of the second part 322 and the fourth part 332 are matched. It can be understood that the projection of the fourth part 332 along the thickness direction of the positive electrode 30 overlaps with the projection of the second part 322 along the thickness direction.

[0255] The first roll pressing can be a continuous cold pressing, while the second roll pressing can be an intermittent cold pressing.

[0256] For example, a first roller group is set up to perform a first roll pressing on the first active material layer 32 and the second active material layer 33. The first roller group includes two first rollers, which are respectively disposed on opposite sides of the positive electrode sheet 30 along its own thickness direction. One of the two first rollers is used to roll the first active material layer 32, and the other of the two first rollers is used to roll the second active material layer 33. The positive electrode sheet 30 passes between the two first rollers.

[0257] A second roller group is set up to perform a second rolling process on the first active material layer 32 and the second active material layer 33. The second roller group is located downstream of the first roller group and includes two second rollers. The two second rollers are respectively located on opposite sides of the positive electrode sheet 30 along its own thickness direction. One of the two second rollers is used to roll the first active material layer 32, and the other of the two second rollers is used to roll the second active material layer 33. The positive electrode sheet 30 passes between the two second rollers.

[0258] The two second rollers can move closer to or further away from each other along the thickness direction of the positive electrode sheet 30. When the two second rollers move closer to each other, they can perform a second rolling press on the first active material layer 32 and the second active material layer 33. When the two second rollers move further away from each other, they can disengage from the first active material layer 32 and the second active material layer 33 respectively, so as to release the pressure applied to the first active material layer 32 and the second active material layer 33.

[0259] The length of the first portion 321 can be controlled by adjusting the duration of the rolling pressure of the second roller group and the belt speed of the positive electrode sheet 30. The length of the second portion 322, i.e., the distance between two adjacent first portions 321 along the length of the positive electrode sheet 30, can be controlled by controlling the rolling interval of the second roller group. The compaction density of the first portion 321 can be controlled by adjusting the rolling pressure of the second roller group. The number of first portions 321 prepared can be controlled by adjusting the number of rolling cycles of the second roller group. The operating parameters of the second roller group can be adjusted and selected according to actual preparation requirements.

[0260] The above-described technical solution enables the simultaneous formation of the first part 321 and the third part 331 by simultaneously rolling two rollers on opposite sides of the positive electrode sheet 30 along its thickness direction. This helps reduce the difficulty of preparing the first part 321 and improves the preparation efficiency and product yield. Furthermore, the positive electrode sheet 30 provided in this embodiment can directly achieve differentiated compaction densities of the first part 321 and the second part 322 through rolling during the cold pressing process in the manufacturing of the battery cell 7, which helps improve the production efficiency of the battery cell 7 and reduce production costs.

[0261] It is understood that the manufacturing method of the battery cell 7 in the embodiments of this application can be used to implement the battery cell 7 provided in any of the embodiments of this application. The technical features and specific details of the battery cell 7 provided in any of the embodiments of this application can be mapped to the manufacturing method of the battery cell 7 in the embodiments of this application. The specific details of the battery cell 7 implemented by each step of the manufacturing method of the battery cell 7 can be found in the description of the corresponding part of the battery cell 7 provided in the embodiments of this application. For the sake of brevity, they will not be repeated here.

[0262] According to some embodiments of this application, this application also provides a battery device 2, including a battery cell 7 of any of the above schemes.

[0263] According to some embodiments of this application, this application also provides an electrical device, including a battery cell 7 or a battery device 2 of any of the above schemes, wherein the battery cell 7 or the battery device 2 is used to store or provide electrical energy.

[0264] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions. All technical features and optional technical features of this application can be combined to form new technical solutions.

[0265] To better understand the battery cell 7 provided in the embodiments of this application, based on the same inventive concept, embodiments of the battery cell 7 in practical applications are provided here for illustration.

[0266] This application provides a battery cell 7, which includes a housing 10 and an electrode assembly 20. The electrode assembly 20 is housed within the housing 10 and includes a positive electrode 30 and a negative electrode 40, which are wound together. The electrode assembly 20 includes a bending region 21 and a straight region 22 connected to the bending region 21. The positive electrode 30 includes a positive current collector 31 and a first active material layer 32, which is disposed inside the positive current collector 31. The first active material layer 32 includes a first portion 321 and a second portion 322 disposed along the winding direction K. The compaction density of the first portion 321 is greater than that of the second portion 322, and the thickness of the first portion 321 is less than that of the second portion 322. At least a portion of the first portion 321 is disposed in the bending region 21, and at least a portion of the second portion 322 is disposed in the straight region 22.

[0267] The positive electrode 30 includes a plurality of positive electrode bent portions 30a located in the bending region 21 and a plurality of positive electrode straight portions 30b located in the straight region 22. The plurality of positive electrode bent portions 30a and the plurality of positive electrode straight portions 30b are alternately connected along the winding direction K. Among the plurality of positive electrode bent portions 30a, at least the two innermost positive electrode bent portions 30a located in the electrode assembly 20 are provided with a first portion 321.

[0268] The first part 321 has a higher compaction density and a greater degree of contact between active material particles, making it difficult for the electrolyte to penetrate into the interior of the first part 321. This results in a longer path for lithium ions to escape from the first part 321, thereby weakening the lithium ion conductivity in the first part 321. Therefore, by placing at least a portion of the first part 321 in the bending region 21, the lithium ion extraction capability in the first active material layer 32 of the positive electrode 30 located in the bending region 21 is reduced, thereby reducing the risk of lithium plating in the bending region 21 of the electrode assembly 20 and improving the reliability of the battery cell 7.

[0269] Furthermore, the positive electrode sheet 30 provided in this embodiment can directly achieve the differentiated compaction density setting of the first part 321 and the second part 322 through rolling during the cold pressing process of battery cell 7 manufacturing, which helps to improve the production efficiency of battery cell 7 and reduce production costs. The adjustment of compaction density has little impact on the participation of active materials in the first part 321 and the second part 322 in charge and discharge operations, resulting in a relatively high utilization rate of active materials in battery cell 7, which helps to reduce the capacity loss of battery cell 7.

[0270] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A battery cell, characterized by, The application relates to a battery, comprising: a housing; an electrode assembly accommodated in the housing, the electrode assembly comprising a positive electrode tab and a negative electrode tab, the positive electrode tab and the negative electrode tab being wound together; the electrode assembly comprising a bending region and a flat region connected to the bending region; the positive electrode tab comprising a positive electrode current collector and a first active material layer, the first active material layer being arranged on the inner side of the positive electrode current collector, the first active material layer comprising a first portion and a second portion arranged in a winding direction, the first portion having a higher compaction density than the second portion, at least part of the first portion being arranged in the bending region, and at least part of the second portion being arranged in the flat region.

2. The battery cell of claim 1, wherein, The thickness of the first portion is smaller than the thickness of the second portion.

3. The battery cell of claim 2, wherein, The first active material layer further comprises a first transition portion connected between the first portion and the second portion, the thickness of the first transition portion gradually increasing in the direction from the first portion to the second portion.

4. The battery cell of claim 1, wherein, The unit area active material capacity of the first portion is less than or equal to the unit area active material capacity of the second portion.

5. The battery cell of claim 1, wherein, The first portion is entirely located in the bending region.

6. The battery cell of claim 1, wherein, One end of the first portion in the winding direction is located in the bending region, and the other end of the first portion in the winding direction is located in the flat region.

7. The battery cell of claim 1, wherein, The first portion passes through the bending region, and both ends of the first portion in the winding direction are located in the flat region.

8. The battery cell of claim 1, wherein, Both the first portion and the second portion are multiple, and the multiple first portions and the multiple second portions are arranged alternately in the winding direction.

9. The battery cell of claim 1, wherein, The positive electrode tab comprises multiple positive electrode bending portions located in the bending region and multiple positive electrode flat portions located in the flat region, and the multiple positive electrode bending portions and the multiple positive electrode flat portions are alternately connected in the winding direction. Among the multiple positive electrode bending portions, at least two positive electrode bending portions located at the innermost part of the electrode assembly are provided with the first portion.

10. The battery cell of claim 9, wherein, Both the multiple positive electrode bending portions are provided with the first portion.

11. The battery cell of claim 1, wherein, The compaction density a1 of the first portion and the compaction density a2 of the second portion satisfy the relationship: 0.02g / cc<=a1-a2<=3g / cc.

12. The battery cell of claim 11, wherein, The compaction density a1 of the first portion and the compaction density a2 of the second portion satisfy the relationship: 0.05g / cc<=a1-a2<=1g / cc.

13. The battery cell of claim 1, wherein, The size b1 of the first portion in the winding direction and the length b2 of the flat region satisfy the relationship: 2mm<=b1<=2*b2.

14. The battery cell of claim 13, wherein, The size b1 of the first portion in the winding direction and the length b2 of the flat region satisfy the relationship: 5mm<=b1<=b2.

15. The battery cell of any one of claims 1-14, wherein, The positive electrode tab further comprises a second active material layer, the second active material layer being arranged on the outer side of the positive electrode current collector, the second active material layer comprising a third portion and a fourth portion arranged in the winding direction, the third portion having a higher compaction density than the fourth portion, at least part of the third portion being arranged in the bending region, and at least part of the fourth portion being arranged in the flat region; A projection of the third portion along a thickness direction of the positive electrode tab and a projection of the first portion along the thickness direction at least partially overlap.

16. A method of manufacturing a battery cell, characterized by, Comprising: Providing a positive electrode tab, wherein the positive electrode tab comprises a positive electrode current collector and a first active material layer, the first active material layer being disposed on one side surface of the positive electrode current collector along a thickness direction of the positive electrode current collector; Processing the first active material layer to form the first active material layer into a first portion and a second portion along a length direction of the positive electrode tab, wherein a compaction density of the first portion is greater than a compaction density of the second portion; Providing a negative electrode tab, winding the positive electrode tab and the negative electrode tab to form an electrode assembly, and disposing the first active material layer on an inner side of the positive electrode current collector, wherein the electrode assembly comprises a bent region and a flat region connected to the bent region, at least a portion of the first portion is disposed in the bent region, and at least a portion of the second portion is disposed in the flat region; Providing a housing, and installing the electrode assembly in the housing.

17. The method of manufacturing a battery cell according to claim 16, wherein The positive electrode tab further comprises a second active material layer, the second active material layer and the first active material layer being disposed on opposite side surfaces of the positive electrode current collector along the thickness direction, respectively; The processing the first active material layer comprises: Firstly rolling the first active material layer and the second active material layer; Secondly rolling a portion of the first active material layer and a portion of the second active material layer after the first rolling to form the first portion of the first active material layer and a third portion of the second active material layer corresponding to the first portion; wherein another portion of the first active material layer not subjected to the second rolling is the second portion, another portion of the second active material layer not subjected to the second rolling is a fourth portion corresponding to the second portion, a compaction density of the third portion is greater than a compaction density of the fourth portion, and a pressure of the second rolling is greater than a pressure of the first rolling.

18. A battery device characterized by comprising: A plurality of battery cells as claimed in any one of claims 1-15.

19. An electrical device, comprising: A battery cell as claimed in any one of claims 1-15 or a battery device as claimed in claim 18, for storing or providing electrical energy.

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