Battery cells, battery packs and electrical devices

Abstract

A battery cell, a battery device, and a power-consuming device are provided. The battery cell includes an electrode assembly, which includes a positive electrode sheet. The positive electrode sheet includes a current collector, a first active material layer, and a second active material layer. The first active material layer is disposed on the surface of the current collector. The first active material layer includes a first main region and a first thinned region arranged along the width direction of the positive electrode sheet, and the thickness of the first main region is greater than the thickness of the first thinned region. A second active material layer is disposed on the side of the first main region facing away from the current collector. The second active material layer includes a second main region and a second thinned region arranged along the width direction, and the thickness of the second main region is greater than the thickness of the second thinned region. A step surface is formed in the area of ​​the first main region facing away from the current collector that is not covered by the second active material layer. The step surface connects the outer surfaces of the first and second thinned regions. The presence of the step surface reduces the active material at the edge of the positive electrode sheet, resulting in a lower risk of lithium plating.

Description

Technical Field

[0001] This application relates to the field of batteries, and more specifically, to a battery cell, a battery device, and an electrical device. Background Technology

[0002] Batteries are widely used in the new energy field, such as in electric vehicles and new energy vehicles, which have become a new trend in the automotive industry. The development of battery technology must consider multiple design factors simultaneously, such as energy density, discharge capacity, and charge / discharge rate. Furthermore, battery reliability also needs to be considered. However, current battery reliability is relatively poor. Summary of the Invention

[0003] The purpose of this application is to provide a battery cell, a battery device, and an electrical device, which aims to improve the problem of poor battery reliability in related technologies.

[0004] In a first aspect, embodiments of this application provide a battery cell, the battery cell including an electrode assembly, the electrode assembly including a positive electrode sheet, the positive electrode sheet including a current collector and a first active material layer, the first active material layer being disposed on at least one surface of the current collector along the thickness direction of the current collector, the first active material layer including a first main region and a first thinned region arranged along the width direction of the positive electrode sheet, the thickness of the first main region being greater than the thickness of the first thinned region, and at least one end of the first main region being connected to the first thinned region along the width direction; wherein, the positive electrode sheet further includes a second active material layer, the second active material layer being disposed on the side of the first main region away from the current collector, the second active material layer including a second main region and a second thinned region arranged along the width direction of the positive electrode sheet, the thickness of the second main region being greater than the thickness of the second thinned region, and at least one end of the second main region being connected to the second thinned region along the width direction, a step surface being formed in the area of ​​the first main region away from the current collector that is not covered by the second active material layer, the step surface connecting the outer surface of the first thinned region and the outer surface of the second thinned region.

[0005] In the above technical solution, by setting a stepped surface, the dimension of the second active material layer along the width direction is smaller than that of the first active material layer along the width direction. Compared with the prior art, the presence of the stepped surface reduces the content of active material at the edge of the positive electrode sheet, which is beneficial to improving the CB value at the edge of the positive electrode sheet, reducing the risk of lithium plating at the edge of the positive electrode sheet, and improving the reliability of the battery cell. During coating, a double-layer coating die can be used to coat the first and second active material layers. The distance between the double-layer coating die and the current collector is determined by the thickness of the first active material layer. The double-layer coating die can be closer to the current collector. The pressure of the double-layer coating die when spraying the active material slurry is lower, which is beneficial to controlling the output amount, improving the coating uniformity, controlling the morphology of the first and second thinning areas, reducing the risk of edge bulging, thereby reducing the risk of lithium plating and improving the reliability of the battery cell.

[0006] As an optional technical solution in this application embodiment, the thickness of the first main body region is H1, and the thickness of the second main body region is H2, satisfying: 100μm≤H1+H2≤200μm.

[0007] In the above technical solution, when H1+H2≥100μm, the thickness of the first main body region and the sum of the thicknesses of the second main body region are relatively large. This is more suitable for using a dual-layer coating die to coat the first and second active material layers, which helps control the morphology of the first and second thinning areas, reduces the risk of edge bulging, and thus helps reduce the risk of lithium plating and improve the reliability of the battery cell. Furthermore, a larger sum of the thicknesses of the first and second main body regions makes it easier to maintain the morphology of the first and second active material layers after coating, and even if the active material slurry flows, the step surface is less likely to disappear. When H1+H2≤200μm, the thickness of the first and second main body regions is not too large, ensuring that the thicknesses of both the first and second main body regions are not excessive. This prevents excessive pressure from the dual-layer coating die when spraying the active material slurry, which helps control the output, improves coating uniformity, helps control the morphology of the first and second thinning areas, reduces the risk of edge bulging, and thus helps reduce the risk of lithium plating and improve the reliability of the battery cell.

[0008] As an optional technical solution in this application embodiment, the thickness of the first main body area is H1, and the thickness of the second main body area is H2, satisfying: 1≤H1 / H2≤2.

[0009] In the above technical solution, when H1 / H2≥1, the thickness of the first main body region is relatively large, and the thickness of the second main body region is relatively small. This prevents the reduction of active material at the edge of the positive electrode from being too large, which is beneficial to improving the energy density of the battery cell. Furthermore, when using a dual-layer coating die to coat the first and second active material layers, the dual-layer coating die can be placed further away from the current collector, reducing the risk of the dual-layer coating die scratching the current collector. When H1 / H2≤2, the thickness of the first main body region is not too large, and the thickness of the second main body region is not too small. This is beneficial to improving the CB value at the edge of the positive electrode, reducing the risk of lithium plating at the edge of the positive electrode, and improving the reliability of the battery cell. Furthermore, when using a double-layer coating die to coat the first and second active material layers, the thickness of the first main body area is not too large, so that the pressure of the double-layer coating die when spraying the active material slurry is not too large, which is beneficial to control the output and improve the uniformity of coating. The thickness of the second main body area is not too small, which is beneficial to make the active material particles evenly distributed and reduce the risk of scratches caused by uneven distribution of active material particles in the second main body area.

[0010] As an optional technical solution in this application embodiment, the thickness of the first main body region is H1, which satisfies: 50μm≤H1≤150μm.

[0011] In the above technical solution, when H1 ≥ 50 μm, the thickness of the first main body region is relatively large. When using a dual-layer coating die to coat the first and second active material layers, the dual-layer coating die can be located further away from the current collector, reducing the risk of the dual-layer coating die scratching the current collector. When H1 ≤ 150 μm, the thickness of the first main body region is not too large, so that the pressure of the dual-layer coating die when spraying the active material slurry is not too high. This is beneficial for controlling the output, improving the uniformity of coating, controlling the morphology of the first thinned region, reducing the risk of edge bulging, thereby reducing the risk of lithium plating and improving the reliability of the battery cell.

[0012] As an optional technical solution in this application embodiment, the thickness of the second main body region is H2, which satisfies: 50μm≤H2≤100μm.

[0013] In the above technical solution, when H2 ≥ 50 μm, the thickness of the second main body region is relatively large, which is beneficial to reducing the content of active material at the edge of the positive electrode, improving the CB value at the edge of the positive electrode, reducing the risk of lithium plating at the edge of the positive electrode, and improving the reliability of the battery cell. When H2 ≤ 100 μm, the thickness of the second main body region is not too large, so that the reduction of active material at the edge of the positive electrode is not too large, which is beneficial to improving the energy density of the battery cell.

[0014] As an optional technical solution in this application embodiment, the dimension of the step surface along the width direction is L, which satisfies: 0.5mm≤L≤10mm.

[0015] In the above technical solution, when L ≥ 0.5 mm, the step surface has a relatively large dimension along its width, which is beneficial for reducing the content of active material at the edge of the positive electrode, improving the CB value at the edge of the positive electrode, reducing the risk of lithium plating at the edge of the positive electrode, and improving the reliability of the battery cell. When L ≤ 10 mm, the step surface is not too large along its width, ensuring that the reduction in active material at the edge of the positive electrode is not excessive, which is beneficial for improving the energy density of the battery cell. Therefore, when 0.5 mm ≤ L ≤ 10 mm, both the energy density and reliability of the battery cell can be balanced.

[0016] As an optional technical solution in this application embodiment, 2mm≤L≤7mm.

[0017] In the above technical solutions, when L ≥ 2 mm, the step surface has a larger dimension along the width direction, which is more conducive to reducing the content of active material at the edge of the positive electrode, improving the CB value at the edge of the positive electrode, reducing the risk of lithium plating at the edge of the positive electrode, and improving the reliability of the battery cell. When L ≤ 7 mm, the step surface is not too large along the width direction, so the reduction of active material at the edge of the positive electrode is not too large, which is conducive to improving the energy density of the battery cell. Therefore, when 0.5 mm ≤ L ≤ 10 mm, it is possible to better balance the energy density and reliability of the battery cell.

[0018] As an optional technical solution in this application embodiment, the material of the first active material layer and the material of the second active material layer are the same.

[0019] In the above technical solution, when the materials of the first active material layer and the second active material layer are the same, the risk of cross-contamination caused by switching of active material slurry can be reduced, and the rheological stability problem can be improved. Furthermore, micro-interface channels can be formed between the first and second active material layers, thereby facilitating electrolyte wetting.

[0020] As an optional technical solution in this application embodiment, the materials of the first active material layer and the second active material layer are different.

[0021] In the above technical solution, when the materials of the first active material layer and the second active material layer are different, the advantages of the materials of the first active material layer and the second active material layer can be brought into play respectively, thereby improving the energy density, reliability and cycle life of the battery cell and reducing the cost of the battery cell.

[0022] As an optional technical solution in this application embodiment, one of the first active material layer and the second active material layer is made of lithium phosphate, and the other of the first active material layer and the second active material layer is made of lithium transition metal oxide.

[0023] In the above technical solutions, lithium phosphates exhibit high thermal stability, low oxygen production, and a low risk of thermal runaway. Lithium transition metal oxides have high energy density. When one of the first and second active material layers comprises lithium phosphates, and the other comprises lithium transition metal oxides, the advantages of lithium phosphates and lithium transition metal oxides can be leveraged respectively, improving the energy density, reliability, and cycle life of the battery cell while reducing its cost.

[0024] As an optional technical solution in this application embodiment, the electrode assembly includes a positive electrode tab disposed at one end of the current collector along the width direction; the positive electrode further includes an insulating layer disposed on the surface of the current collector, and the insulating layer covers a portion of the positive electrode tab.

[0025] In the above technical solution, by setting an insulating layer on the surface of the current collector and covering a portion of the positive electrode tab, the risk of short circuits caused by burrs from die-cutting the positive electrode tab piercing the separator and contacting the negative electrode sheet is reduced, thus improving the reliability of the battery cell. Furthermore, during coating, the first active material layer, the second active material layer, and the insulating layer can be coated simultaneously. The distance between the coating die and the current collector is determined by the thickness of the first active material layer. When the thickness of the first active material layer is smaller, the thickness of the insulating layer can also be reduced. This smaller insulating layer thickness, on the one hand, reduces the external force required to fold the electrode tab, lowering the risk of tab breakage. On the other hand, it helps to compress the space for folding the electrode tab, increasing the energy density of the battery cell. Finally, it facilitates the cutting of the electrode tab, improving the ease of cutting.

[0026] As an optional technical solution in this application embodiment, the insulating layer covers at least a portion of the outer surface of the first thinned area.

[0027] In the above technical solution, by covering at least a portion of the outer surface of the first thinned region with an insulating layer, the electron transport path can be blocked, making the portion of the first thinned region covered by the insulating layer less likely to participate in the electrochemical reaction, thereby reducing the risk of lithium plating.

[0028] As an optional technical solution in this application embodiment, the maximum thickness of the insulating layer is H3, which satisfies: 3μm≤H3≤30μm.

[0029] In the above technical solutions, when H3 ≥ 3 μm, the maximum thickness of the insulating layer is relatively large, which helps reduce the risk of short circuits caused by burrs from die-cutting the positive electrode tab piercing the separator and contacting the negative electrode sheet, thus improving the reliability of the battery cell. When H3 ≤ 30 μm, the maximum thickness of the insulating layer is not too large. On the one hand, this helps reduce the external force required to fold the electrode tab, reducing the risk of tab breakage. On the other hand, it helps to compress the space for folding the electrode tab, increasing the energy density of the battery cell. Furthermore, it facilitates the cutting of the electrode tab, improving the ease of cutting the electrode tab.

[0030] As an optional technical solution in this application embodiment, 5μm≤H3≤20μm.

[0031] In the above technical solutions, when H3 ≥ 5 μm, the maximum thickness of the insulating layer is greater, which is more conducive to reducing the risk of short circuits caused by burrs from die-cutting the positive electrode tab piercing the separator and contacting the negative electrode sheet, thus improving the reliability of the battery cell. When H3 ≤ 20 μm, the maximum thickness of the insulating layer is not too large. On the one hand, it helps to reduce the external force required for folding the electrode tab, reducing the risk of electrode tab breakage. On the other hand, it helps to compress the space for folding the electrode tab, increasing the energy density of the battery cell. Furthermore, it facilitates the cutting of the electrode tab, improving the convenience of cutting the electrode tab.

[0032] As an optional technical solution in this application embodiment, along the thickness direction of the current collector, the first active material layer is provided on both opposite surfaces of the current collector, and the second active material layer is provided on the side of the first main area of ​​each first active material layer away from the current collector.

[0033] In the above technical solution, by providing a first active material layer on both surfaces of the current collector that are arranged opposite to each other, and providing a second active material layer on the side of the first main area of ​​each first active material layer away from the current collector, it is beneficial to improve the CB value at the edge of the positive electrode, reduce the risk of lithium plating at the edge of the positive electrode, and improve the reliability of the battery cell.

[0034] Secondly, embodiments of this application also provide a battery device, which includes the aforementioned battery cell.

[0035] Thirdly, embodiments of this application also provide an electrical device, which includes the aforementioned battery cell, and the battery cell is used to provide electrical energy to the electrical device. Attached Figure Description

[0036] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This application provides structural schematic diagrams of vehicles for some embodiments;

[0038] Figure 2 Exploded views of battery devices provided in some embodiments of this application;

[0039] Figure 3 This is a schematic diagram of the structure of a battery cell provided in some embodiments of this application;

[0040] Figure 4 Exploded views of a single battery cell provided in some embodiments of this application;

[0041] Figure 5 This is a schematic diagram of the structure of an electrode assembly provided in some embodiments of this application;

[0042] Figure 6 Cross-sectional views of the positive electrode sheet provided in some embodiments of this application;

[0043] Figure 7 Cross-sectional views of the positive electrode sheet provided in other embodiments of this application;

[0044] Figure 8 A cross-sectional view of the positive electrode sheet provided in some embodiments of this application.

[0045] Icons: 10-Box body; 11-First box body; 12-Second box body; 20-Battery cell; 21-Outer shell; 211-Shell; 212-End cap; 22-Electrode assembly; 221-Main body; 222-Taper; 223-Negative electrode; 224-Positive electrode; 2241-Current collector; 22411-Positive electrode; 2242-First active material layer; 22421-First main body area; 22422-First thinned area; 2 24221 - Outer surface of the first thinned area; 2243 - Second active material layer; 22431 - Second main body area; 22432 - Second thinned area; 224321 - Outer surface of the second thinned area; 2244 - Step surface; 2245 - Insulating layer; 2246 - First arc surface; 225 - Separator; 25 - Electrode terminal; 27 - Insulating component; 100 - Battery device; 200 - Controller; 300 - Motor; 1000 - Vehicle. Detailed Implementation

[0046] 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 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.

[0047] 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 description 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 description, claims, and accompanying drawings of this application are intended to cover non-exclusive inclusion. The terms "first," "second," etc., in the description, claims, or accompanying drawings of this application are used to distinguish different objects, not to describe a specific order or hierarchy.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] In this application, "multiple" means two or more (including two).

[0053] In this embodiment of the application, the battery cell can be a secondary battery, which refers to a battery cell that can be recharged to activate the active materials and continue to be used after the battery cell has been discharged.

[0054] Battery cells include, but are not limited to, lithium-ion batteries, sodium-ion batteries, sodium-lithium-ion batteries, lithium metal batteries, sodium metal batteries, lithium-sulfur batteries, magnesium-ion batteries, nickel-metal hydride batteries, nickel-cadmium batteries, lead-acid batteries, etc.

[0055] A single battery cell typically includes an electrode assembly. The electrode assembly includes a positive electrode, a negative electrode, and a separator. 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. The separator, positioned between the positive and negative electrodes, reduces the risk of short circuits while allowing active ions to pass through.

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

[0057] 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.

[0058] As an example, the positive electrode current collector can be a foil or a composite current collector. For example, as a foil, it can be aluminum with a silver-plated surface, stainless steel with a silver-plated surface, stainless steel, copper, aluminum, nickel, carbon electrode, carbon, or titanium, etc. Composite current collectors can include a polymer material base layer and a metal layer. Composite current collectors can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0059] 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 positive electrode active materials in battery cells 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 / 3Mn 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 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds.

[0060] In some embodiments, the positive electrode can be a foamed metal. The foamed metal can be foamed nickel, foamed copper, foamed aluminum, foamed alloys, 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, lithium source material, potassium metal, or sodium metal can also be filled and / or deposited within the foamed metal, where the lithium source material is lithium metal and / or a lithium-rich material.

[0061] In some embodiments, the negative electrode can be a negative electrode sheet, and the negative electrode sheet can include a negative current collector.

[0062] As an example, the negative electrode current collector can be a foil, a foamed metal, or a composite current collector. For example, as a foil, it can be aluminum with a silver-plated surface, stainless steel with a silver-plated surface, stainless steel, copper, aluminum, nickel, carbon electrodes, carbon, or titanium, etc. The foamed metal can be nickel foam, copper foam, aluminum foam, foam alloy, etc. The composite current collector can include a polymer material base layer and a metal layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0063] As an example, the negative electrode sheet may include a negative current collector and a negative active material disposed on at least one surface of the negative current collector.

[0064] 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.

[0065] 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 in battery cells may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0066] In some embodiments, the positive current collector can be made of aluminum, and the negative current collector can be made of copper.

[0067] In some embodiments, the separator is a separator membrane. The separator membrane can be any known porous structure separator membrane with good chemical and mechanical stability.

[0068] As an example, the material of the separator may include at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different. The separator may be a separate component located between the positive and negative electrodes, or it may be attached to the surfaces of the positive and negative electrodes.

[0069] 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.

[0070] In some embodiments, the battery cell also includes an electrolyte, which acts as a conductor of ions between the positive and negative electrodes. The electrolyte can be liquid, gel-like, or solid. Liquid electrolytes include electrolyte salts and solvents.

[0071] In some embodiments, the electrolyte salt may include 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.

[0072] In some embodiments, the solvent may include at least one selected from 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 selected from 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.

[0073] Among them, the gel electrolyte includes a polymer as the electrolyte backbone network, combined with an ionic liquid - lithium salt.

[0074] Solid electrolytes include polymer solid electrolytes, inorganic solid electrolytes, and composite solid electrolytes.

[0075] As an example, polymer solid electrolytes can be polyethers (polyoxyethylene), polysiloxanes, polycarbonates, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, monoionic polymers, polyionic liquids-lithium salts, cellulose, etc.

[0076] As an example, inorganic solid electrolytes may include 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 phosphate sulfide, silver sulfide germanium ore), amorphous sulfides), halide solid electrolytes, nitride solid electrolytes, and hydride solid electrolytes.

[0077] As an example, composite solid electrolytes are formed by adding inorganic solid electrolyte fillers to polymer solid electrolytes.

[0078] In some embodiments, the electrode assembly is a wound structure. The positive electrode and the negative electrode are wound into a wound structure.

[0079] In some implementations, the electrode assembly is a stacked structure.

[0080] As an example, multiple positive and negative electrode plates can be set, and multiple positive and multiple negative electrode plates can be stacked alternately.

[0081] As an example, multiple positive electrode sheets can be set, and negative electrode sheets are folded to form multiple stacked folded segments, with a positive electrode sheet sandwiched between adjacent folded segments.

[0082] As an example, both the positive and negative electrode sheets are folded to form multiple stacked folded segments.

[0083] As an example, multiple separators can be provided, each positioned between any adjacent positive or negative electrode plates.

[0084] As an example, the separator can be continuously arranged between any adjacent positive or negative electrode plates by folding or rolling.

[0085] In some embodiments, the electrode assembly can be cylindrical, flat, or polygonal, etc.

[0086] In some embodiments, the electrode assembly has tabs that allow current to be drawn from the electrode assembly. The tabs include a positive tab and a negative tab.

[0087] In some embodiments, the battery cell may include a housing. The housing is used to encapsulate components such as electrode assemblies and electrolytes. The housing may be made of steel, aluminum, or a composite metal (such as a copper-aluminum composite housing).

[0088] In some embodiments, the housing can be a sealed structure or a non-sealed structure. As an example, when the housing is a sealed structure, it can protect the electrode assembly and prevent, to some extent, electrolyte leakage. When the housing is a non-sealed structure, it can still protect the electrode assembly, and a sealing bag may be included between the housing and the electrode assembly to encapsulate the electrode assembly and electrolyte. Specifically, the sealing bag can be a bag-shaped insulating component or an aluminum-plastic film.

[0089] 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 battery cells, such as hexagonal prismatic battery cells.

[0090] The battery device 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, which are connected in series, parallel, or mixed connections via a busbar.

[0091] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells; as an example, a battery cell assembly can be a battery module, which is formed by arranging multiple battery cells and fixing them together to form an independent module.

[0092] As an example, a battery module can be formed by bundling multiple battery cells together with cable ties.

[0093] In some embodiments, the battery device may be a battery pack, which may include a housing and one or more individual battery cell assemblies housed within the housing.

[0094] 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.

[0095] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple battery cells to the housing.

[0096] As an example, the enclosure may include a first enclosure and a second enclosure. The first enclosure and the second enclosure are fastened together to form a closed space inside the enclosure to house the individual battery cells. Here, "closed" refers to covering or closing, and can be either sealed or unsealed. The first enclosure may be a top cover or a bottom plate.

[0097] 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.

[0098] As an example, the housing can be part of the vehicle's chassis structure. For instance, the housing's roof can be at least part of the vehicle's floor, or the housing's frame can be at least part of the vehicle's crossbeams and longitudinal beams.

[0099] In some embodiments, the battery device refers to an energy storage device, which includes a housing with a door on at least one side. Energy storage devices include energy storage containers, energy storage cabinets, etc.

[0100] Currently, judging from market trends, battery applications are becoming increasingly widespread. Batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of battery applications, market demand is also constantly increasing.

[0101] The development of battery technology must consider multiple design factors simultaneously, such as energy density, discharge capacity, and charge / discharge rate. Additionally, battery reliability must also be considered. However, current battery reliability is relatively poor.

[0102] Electrode assemblies are the components in a battery cell where electrochemical reactions occur. They include positive and negative electrodes. During the charging and discharging process of a battery cell, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes. To reduce the risk of lithium plating, the lithium insertion capacity of the negative electrode is typically greater than the lithium extraction capacity of the positive electrode. However, during the coating process of the positive electrode, the coating weight of the active material slurry fluctuates, and surface shrinkage during the drying process causes the active material slurry to migrate, resulting in bulging at the edges of the active material layer. This increases the extraction capacity at the edges of the positive electrode and decreases the CB value (the ratio of the lithium insertion capacity of the negative electrode to the lithium extraction capacity of the positive electrode) at the edges, leading to an increased risk of lithium plating. Lithium dendrites are easily formed on the surface of the negative electrode, and these dendrites can easily pierce the separator and contact the positive electrode, causing a short circuit and resulting in poor battery reliability.

[0103] Therefore, this application provides a battery cell, which includes an electrode assembly, and the electrode assembly includes a positive electrode sheet. The positive electrode sheet includes a current collector and a first active material layer. Along the thickness direction of the current collector, at least one surface of the current collector is provided with the first active material layer. The first active material layer includes a first main region and a first thinned region arranged along the width direction of the positive electrode sheet. The thickness of the first main region is greater than the thickness of the first thinned region. Along the width direction, at least one end of the first main region is connected to the first thinned region. The positive electrode sheet also includes a second active material layer, with the second active material layer disposed on the side of the first main region facing away from the current collector. The second active material layer includes a second main region and a second thinned region arranged along the width direction of the positive electrode sheet. The thickness of the second main region is greater than the thickness of the second thinned region. Along the width direction, at least one end of the second main region is connected to the second thinned region. A portion of the surface of the first main region facing away from the current collector that is not covered by the second active material layer forms a stepped surface, which connects the outer surfaces of the first and second thinned regions.

[0104] By setting a stepped surface, the dimension of the second active material layer along the width direction is smaller than that of the first active material layer. Compared with the prior art, the presence of the stepped surface reduces the content of active material at the edge of the positive electrode sheet, which is beneficial to improving the CB value at the edge of the positive electrode sheet, reducing the risk of lithium plating at the edge of the positive electrode sheet, and improving the reliability of the battery cell. During coating, a double-layer coating die can be used to coat the first and second active material layers. The distance between the double-layer coating die and the current collector is determined by the thickness of the first active material layer. The double-layer coating die can be closer to the current collector. The pressure of the double-layer coating die when spraying the active material slurry is lower, which is beneficial to control the output, improve the coating uniformity, control the morphology of the first and second thinning areas, reduce the risk of edge bulging, thereby reducing the risk of lithium plating and improving the reliability of the battery cell.

[0105] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use battery cells and battery devices, such as mobile phones, portable devices, laptops, electric vehicles, electric toys, power tools, vehicles, ships and spacecraft, etc. For example, spacecraft include airplanes, rockets, space shuttles and spacecraft.

[0106] For ease of explanation, the following embodiments will use a vehicle as an example of an electrical device.

[0107] Please refer to Figure 1 , Figure 1 This is a schematic diagram of the structure of a vehicle 1000 provided in some embodiments of this application. A battery device 100 is disposed inside the vehicle 1000, and the battery device 100 may be located at the bottom, front, or rear of the vehicle 1000. The battery device 100 can be used to power the vehicle 1000; for example, the battery device 100 can serve as the operating power source for the vehicle 1000.

[0108] The vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 is used to control the battery device 100 to supply power to the motor 300, for example, for the power needs of the vehicle 1000 during startup, navigation and driving.

[0109] In some embodiments of this application, the battery device 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0110] Please refer to Figure 2 , Figure 2 This is an exploded view of a battery device 100 provided in some embodiments of this application. The battery device 100 may include a housing 10 and battery cells 20, the housing 10 being used to house the battery cells 20.

[0111] The housing 10 has an enclosed space inside for accommodating the battery cells 20. The housing 10 can have various structures. In some embodiments, the housing 10 may include a first housing body 11 and a second housing body 12, which are interlocked. The first housing body 11 and the second housing body 12 can have various shapes, such as cuboids or cylinders. The first housing body 11 can be a hollow structure open on one side, and the second housing body 12 can also be a hollow structure open on one side. The open side of the second housing body 12 interlocks with the open side of the first housing body 11, thus forming a housing 10 with an enclosed space. Alternatively, the first housing body 11 can be a hollow structure open on one side, and the second housing body 12 can be a plate-like structure, with the second housing body 12 interlocked with the open side of the first housing body 11, thus forming a housing 10 with an accommodating chamber.

[0112] In the battery device 100, there can be one or more battery cells 20. If there are multiple battery cells 20, they can be connected in series, parallel, or in a mixed configuration. A mixed configuration means that multiple battery cells 20 are connected in both series and parallel. Alternatively, multiple battery cells 20 can be first connected in series, parallel, or in a mixed configuration to form a battery module, and then multiple battery modules can be connected in series, parallel, or in a mixed configuration to form a whole, which is then housed within the housing 10. Another option is that all battery cells 20 can be directly connected in series, parallel, or in a mixed configuration, and then the whole consisting of all battery cells 20 is housed within the housing 10.

[0113] In some embodiments, the battery device 100 may further include a busbar component, through which multiple battery cells 20 can be electrically connected to each other to achieve series, parallel, or mixed connection of the multiple battery cells 20. The busbar component may be a metallic conductor, such as copper, iron, aluminum, stainless steel, aluminum alloy, etc.

[0114] Please refer to Figure 3 , Figure 4 , Figure 5 and Figure 6 , Figure 3 This is a schematic diagram of the structure of a battery cell 20 provided in some embodiments of this application. Figure 4 An exploded view of a battery cell 20 provided in some embodiments of this application. Figure 5 This is a schematic diagram of the structure of the electrode assembly 22 provided in some embodiments of this application. Figure 6This is a cross-sectional view of the positive electrode 224 provided in some embodiments of this application. Embodiments of this application provide a battery cell 20, which includes an electrode assembly 22. The electrode assembly 22 includes a positive electrode 224, which includes a current collector 2241 and a first active material layer 2242. Along the thickness direction of the current collector 2241, at least one surface of the current collector 2241 is provided with the first active material layer 2242. The first active material layer 2242 includes a first main region 22421 and a first thinned region 22422 arranged along the width direction of the positive electrode 224. The thickness of the first main region 22421 is greater than the thickness of the first thinned region 22422. Along the width direction, at least one end of the first main region 22421 is connected to the first thinned region 22422. The positive electrode 224 also includes a second active material layer 2243, which is disposed on the side of the first main region 22421 opposite to the current collector 2241. The second active material layer 2243 includes a second main body region 22431 and a second thinned region 22432 arranged along the width direction of the positive electrode sheet 224. The thickness of the second main body region 22431 is greater than the thickness of the second thinned region 22432. Along the width direction, at least one end of the second main body region 22431 is connected to the second thinned region 22432. The area of ​​the first main body region 22421 that is not covered by the second active material layer 2243 on the surface away from the current collector 2241 forms a stepped surface 2244. The stepped surface 2244 connects the outer surface 224221 of the first thinned region and the outer surface 224321 of the second thinned region.

[0115] Battery cell 20 refers to the smallest unit that makes up battery device 100.

[0116] The housing 21 includes a housing 211 and an end cap 212. The housing 211 has a receiving space with an opening at one end for accommodating the electrode assembly 22. The end cap 212 is connected to the housing 211 and closes the opening.

[0117] End cap 212 refers to a component that covers the opening of housing 211 to isolate the internal environment of battery cell 20 from the external environment. The shape of end cap 212 can be adapted to the shape of housing 211 to fit it. Optionally, end cap 212 can be made of a material with certain hardness and strength (such as aluminum alloy), so that end cap 212 is not easily deformed under pressure and impact, giving battery cell 20 higher structural strength and improved reliability. The material of end cap 212 can include, but is not limited to, copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc. Battery cell 20 also includes an insulating member 27, which is disposed inside end cap 212. The insulating member 27 can be used to isolate the electrical connection components inside housing 211 from end cap 212 to reduce the risk of short circuit. For example, insulating member 27 can be plastic, rubber, etc.

[0118] The housing 211 is a component used to cooperate with the end cap 212 to form the internal environment of the battery cell 20. This internal environment can accommodate the electrode assembly 22, electrolyte, and other components. The housing 211 and the end cap 212 can be independent components. An opening can be provided on the housing 211, and the end cap 212 can be used to close the opening to form the internal environment of the battery cell 20. Alternatively, the end cap 212 and the housing 211 can be integrated. Specifically, the end cap 212 and the housing 211 can form a common mating surface before other components are inserted into the housing. When it is necessary to encapsulate the interior of the housing 211, the end cap 212 closes the housing 211. The housing 211 can have various shapes and sizes, such as cuboid, cylindrical, hexagonal prism, etc. Specifically, the shape of the housing 211 can be determined according to the specific shape and size of the electrode assembly 22. The material of the housing 211 can include, but is not limited to, copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc.

[0119] In some embodiments, the housing 211 may have an opening at only one end, with one end cap 212 correspondingly provided. In other embodiments, the housing 211 may have openings at both ends, with two end caps 212 correspondingly provided, the two end caps 212 respectively closing the two opposite openings of the housing 211. Figure 3 and Figure 4 In the embodiment shown, the housing 211 has an opening at only one end, and an end cap 212 is provided accordingly.

[0120] Electrode terminals 25 may also be provided on the end cap 212 or the housing 211. These terminals are used for electrical connection to the tabs 222 of the electrode assembly 22 to input or output electrical energy from the battery cell 20. The electrode terminals 25 and tabs 222 can be directly connected, for example, by direct welding. Alternatively, they can be indirectly connected, for example, through a current collector. The current collector can be a metallic conductor, such as copper, iron, aluminum, steel, or aluminum alloy.

[0121] Electrode assembly 22 is the component in the battery cell 20 where electrochemical reactions occur. The housing 211 may contain one or more electrode assemblies 22. The electrode assembly 22 is mainly formed by winding or stacking positive electrode 224 and negative electrode 223, and typically a separator 225 is provided between the positive electrode 224 and the negative electrode 223. The portions of the positive electrode 224 and the negative electrode 223 containing active material constitute the main body 221 of the electrode assembly 22, while the portions of the positive electrode 224 and the negative electrode 223 without active material each constitute a tab 222. The positive and negative tabs may be located together at one end of the main body 221 or separately at both ends of the main body 221. During the charging and discharging process of the battery cell 20, the positive and negative active materials react with the electrolyte.

[0122] The electrode assembly 22 includes a positive electrode 224, a separator 225, and a negative electrode 223, which are wound or stacked. In other words, the electrode assembly 22 can be a wound electrode assembly or a stacked electrode assembly.

[0123] The positive electrode 224 includes a current collector 2241, a first active material layer 2242, and a second active material layer 2243. Please refer to... Figure 6 The thickness direction of the current collector 2241 is the X direction shown in the figure. In some embodiments, the first active material layer 2242 is disposed on only one surface of the current collector 2241 along the thickness direction of the current collector 2241, and the second active material layer 2243 is disposed on the side of the first active material layer 2242 facing away from the current collector 2241. In other embodiments, the first active material layer 2242 is disposed on two surfaces of the current collector 2241 opposite to each other along the thickness direction of the current collector 2241, and the second active material layer 2243 is disposed on the side of each first active material layer 2242 facing away from the current collector 2241.

[0124] The current collector 2241 can be a foil or a composite current collector. For example, as a foil, it can be aluminum with a silver-plated surface, stainless steel with a silver-plated surface, stainless steel, copper, aluminum, nickel, carbon electrode, carbon, or titanium, etc. The composite current collector can include a polymer material base layer and a metal layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0125] Both the first active material layer 2242 and the second active material layer 2243 include a positive electrode active material, which 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 positive electrode active materials for battery cells 20 may also be used. These positive electrode active materials may be used alone or in combination of two or more.

[0126] Please refer to Figure 6 The width direction of the positive electrode 224 is the Y direction shown in the figure.

[0127] The first active material layer 2242 includes a first main body region 22421 and a first thinned region 22422, which are arranged along the width direction of the positive electrode 224. The first main body region 22421 is the main part of the first active material layer 2242, and it performs the main function of the first active material layer 2242. The first thinned region 22422 is the thinned portion of the first active material layer 2242 located at one end of the first main body region 22421 along the width direction of the positive electrode 224. "The thickness of the first main body region 22421 is greater than the thickness of the first thinned region 22422" means that the minimum thickness of the first main body region 22421 is greater than the maximum thickness of the first thinned region 22422, or in other words, the thickness of the first main body region 22421 at any position is greater than the thickness of the first thinned region 22422 at any position. In some embodiments, the first main body region 22421 is connected to the first thinning region 22422 at only one end along the width direction, that is, the first thinning region 22422 is only disposed at one end of the first main body region 22421 along the width direction. In other embodiments, the first thinning region 22422 is connected to both ends of the first main body region 22421 along the width direction, that is, the first thinning region 22422 is disposed at both ends of the first main body region 22421 along the width direction.

[0128] The second active material layer 2243 includes a second main region 22431 and a second thinned region 22432, which are arranged along the width direction of the positive electrode 224. The second main region 22431 is the main part of the second active material layer 2243, and it realizes the main function of the second active material layer 2243. The second thinned region 22432 is the thinned portion of the second active material layer 2243 located at one end of the second main region 22431 along the width direction of the positive electrode 224. "The thickness of the second main region 22431 is greater than the thickness of the second thinned region 22432" means that the minimum thickness of the second main region 22431 is greater than the maximum thickness of the second thinned region 22432, or in other words, the thickness of the second main region 22431 at any position is greater than the thickness of the second thinned region 22432 at any position. In some embodiments, the second body region 22431 is connected to the second thinning region 22432 at only one end along the width direction, that is, the second thinning region 22432 is only disposed at one end of the second body region 22431 along the width direction. In other embodiments, the second thinning region 22432 is connected to both ends of the second body region 22431 along the width direction, that is, the second thinning region 22432 is disposed at both ends of the second body region 22431 along the width direction.

[0129] The second active material layer 2243 is disposed on the side of the first main body region 22421 away from the current collector 2241, that is, the second main body region 22431 and the second thinning region 22432 are both disposed on the side of the first main body region 22421 away from the current collector 2241.

[0130] The surface of the first main body region 22421 facing away from the current collector 2241 includes a stepped surface 2244, which is a region of the first main body region 22421 facing away from the current collector 2241 that is not covered by the second active material layer 2243. The outer surface 224221 of the first thinned region connects the surface of the current collector 2241 facing the first active material layer 2242 and the surface of the first main body region 22421 facing away from the current collector 2241. The outer surface 224321 of the second thinned region connects the surfaces of the first main body region 22421 and the second main body region 22431 facing away from the current collector 2241. The stepped surface 2244 connects the outer surfaces 224221 of the first thinned region and the outer surfaces 224321 of the second thinned region.

[0131] By setting the stepped surface 2244, the dimension of the second active material layer 2243 along the width direction is smaller than that of the first active material layer 2242 along the width direction. Compared with the prior art, the presence of the stepped surface 2244 reduces the content of active material at the edge of the positive electrode 224, which is beneficial to improving the CB value at the edge of the positive electrode 224, reducing the risk of lithium plating at the edge of the positive electrode 224, and improving the reliability of the battery cell 20. During coating, a double-layer coating die can be used to coat the first active material layer 2242 and the second active material layer 2243. The distance between the double-layer coating die and the current collector 2241 is determined by the thickness of the first active material layer 2242. The double-layer coating die can be closer to the current collector 2241. The pressure of the double-layer coating die when spraying the active material slurry is smaller, which is beneficial to controlling the output amount, improving the uniformity of coating, controlling the morphology of the first thinning area 22422 and the second thinning area 22432, reducing the risk of edge bulging, thereby reducing the risk of lithium plating and improving the reliability of the battery cell 20.

[0132] Please refer to Figure 3 , Figure 4 , Figure 5 and Figure 6 In some embodiments, the thickness of the first main body region 22421 is H1, and the thickness of the second main body region 22431 is H2, satisfying: 100μm≤H1+H2≤200μm.

[0133] H1 represents the thickness of the first main body region 22421. During measurement, it can be obtained through tomographic scanning and then measured by software. During measurement, the thickness of the first main body region 22421 at multiple different locations can be measured, and the average value is taken as H1.

[0134] H2 represents the thickness of the second main body region 22431. During measurement, it can be obtained through tomographic scanning and then measured by software. During measurement, the thickness of the second main body region 22431 at multiple different locations can be measured, and the average value is taken as H2.

[0135] H1+H2 represents the sum of the thickness of the first main body region 22421 and the thickness of the second main body region 22431. H1+H2 can take values ​​such as 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 180μm, 190μm, 200μm, etc.

[0136] When H1+H2≥100μm, the thickness of the first main body region 22421 and the sum of the thicknesses of the second main body region 22431 are relatively large. This makes it more suitable for coating the first active material layer 2242 and the second active material layer 2243 using a dual-layer coating die. This helps control the morphology of the first thinned region 22422 and the second thinned region 22432, reduces the risk of edge bulging, and thus helps reduce the risk of lithium plating, thereby improving the reliability of the battery cell 20. Furthermore, the relatively large thickness of the first main body region 22421 and the sum of the thicknesses of the second main body region 22431 makes it easier to maintain the morphology of the first active material layer 2242 and the second active material layer 2243 after coating. Even if the active material slurry flows, the step surface 2244 is less likely to disappear. When H1+H2≤200μm, the sum of the thickness of the first main body region 22421 and the thickness of the second main body region 22431 will not be too large. This ensures that the thickness of the first main body region 22421 and the thickness of the second main body region 22431 will not be too large, and the pressure of the double-layer coating die head when spraying the active material slurry will not be too large. This is beneficial for controlling the output, improving the uniformity of coating, controlling the morphology of the first thinning region 22422 and the second thinning region 22432, reducing the risk of edge bulging, thereby reducing the risk of lithium plating and improving the reliability of the battery cell 20.

[0137] Please refer to Figure 3 , Figure 4 , Figure 5 and Figure 6 In some embodiments, the thickness of the first main body region 22421 is H1, and the thickness of the second main body region 22431 is H2, satisfying: 1≤H1 / H2≤2.

[0138] H1 / H2 represents the ratio of the thickness of the first main body region 22421 to the thickness of the second main body region 22431.

[0139] H1 / H2 can take the following values: 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, etc.

[0140] When H1 / H2≥1, the thickness of the first main body region 22421 is relatively large, while the thickness of the second main body region 22431 is relatively small. This prevents excessive reduction in the amount of active material at the edge of the positive electrode 224, which is beneficial for improving the energy density of the battery cell 20. Furthermore, when using a dual-layer coating die to coat the first active material layer 2242 and the second active material layer 2243, the dual-layer coating die can be positioned further away from the current collector 2241, reducing the risk of the dual-layer coating die scratching the current collector 2241. When H1 / H2≤2, the thickness of the first main body region 22421 is not excessively large, and the thickness of the second main body region 22431 is not excessively small. This is beneficial for improving the CB value at the edge of the positive electrode 224, reducing the risk of lithium plating at the edge of the positive electrode 224, and improving the reliability of the battery cell 20. Furthermore, when using a double-layer coating die to coat the first active material layer 2242 and the second active material layer 2243, the thickness of the first main body area 22421 is not too large, so that the pressure of the double-layer coating die when spraying the active material slurry is not too large, which is beneficial to control the output and improve the uniformity of coating. The thickness of the second main body area 22431 is not too small, which is beneficial to make the active material particles evenly distributed and reduce the risk of scratches caused by uneven distribution of active material particles in the second main body area 22431.

[0141] Please refer to Figure 3 , Figure 4 , Figure 5 and Figure 6 In some embodiments, the thickness of the first main body region 22421 is H1, which satisfies: 50μm≤H1≤150μm.

[0142] H1 can be 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, etc.

[0143] When H1 ≥ 50 μm, the thickness of the first main body region 22421 is relatively large. When using a dual-layer coating die to coat the first active material layer 2242 and the second active material layer 2243, the dual-layer coating die can be positioned further away from the current collector 2241, reducing the risk of the dual-layer coating die scratching the current collector 2241. When H1 ≤ 150 μm, the thickness of the first main body region 22421 is not too large, ensuring that the pressure of the dual-layer coating die when spraying the active material slurry is not too high. This is beneficial for controlling the output, improving the uniformity of coating, controlling the morphology of the first thinned region 22422, reducing the risk of edge bulging, thereby reducing the risk of lithium plating and improving the reliability of the battery cell 20.

[0144] Please refer to Figure 3 , Figure 4 , Figure 5and Figure 6 In some embodiments, the thickness of the second main body region 22431 is H2, which satisfies: 50μm≤H2≤100μm.

[0145] H2 can be in the following sizes: 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm, etc.

[0146] When H2 ≥ 50 μm, the thickness of the second main body region 22431 is relatively large, which is beneficial for reducing the content of active material at the edge of the positive electrode 224, improving the CB value at the edge of the positive electrode 224, reducing the risk of lithium plating at the edge of the positive electrode 224, and improving the reliability of the battery cell 20. When H2 ≤ 100 μm, the thickness of the second main body region 22431 is not too large, so that the reduction of active material at the edge of the positive electrode 224 is not too large, which is beneficial for improving the energy density of the battery cell 20.

[0147] Please refer to Figure 3 , Figure 4 , Figure 5 and Figure 6 In some embodiments, the dimension of the step surface 2244 along the width direction is L, which satisfies: 0.5mm≤L≤10mm.

[0148] L represents the dimension of the step surface 2244 along the width direction. During measurement, it can be obtained through tomographic scanning and then measured using software. The dimension along the width direction at multiple different locations on the step surface 2244 can be measured, and the average value is taken as L.

[0149] L can take: 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm, 6.5mm, 7mm, 7.5mm, 8mm, 8.5mm, 9mm, 9.5mm, 10mm, etc.

[0150] When L ≥ 0.5 mm, the step surface 2244 has a larger dimension along its width, which is beneficial for reducing the content of active material at the edge of the positive electrode 224, increasing the CB value at the edge of the positive electrode 224, reducing the risk of lithium plating at the edge of the positive electrode 224, and improving the reliability of the battery cell 20. When L ≤ 10 mm, the dimension of the step surface 2244 is not too large along its width, so that the reduction in active material at the edge of the positive electrode 224 is not too large, which is beneficial for improving the energy density of the battery cell 20. Therefore, when 0.5 mm ≤ L ≤ 10 mm, both the energy density and reliability of the battery cell 20 can be balanced.

[0151] Optionally, 2mm ≤ L ≤ 7mm.

[0152] The thickness L can be: 2mm, 2.2mm, 2.5mm, 2.8mm, 3mm, 3.2mm, 3.5mm, 3.8mm, 4mm, 4.2mm, 4.5mm, 4.8mm, 5mm, 5.2mm, 5.5mm, 5.8mm, 6mm, 6.2mm, 6.5mm, 6.8mm, 7mm, etc.

[0153] When L ≥ 2 mm, the step surface 2244 has a larger dimension along its width, which is more conducive to reducing the content of active material at the edge of the positive electrode 224, improving the CB value at the edge of the positive electrode 224, reducing the risk of lithium plating at the edge of the positive electrode 224, and improving the reliability of the battery cell 20. When L ≤ 7 mm, the dimension of the step surface 2244 along its width is not too large, so that the reduction of active material at the edge of the positive electrode 224 is not too large, which is conducive to improving the energy density of the battery cell 20. Therefore, when 0.5 mm ≤ L ≤ 10 mm, it is possible to better balance the energy density and reliability of the battery cell 20.

[0154] In some embodiments, the materials of the first active material layer 2242 and the second active material layer 2243 are the same.

[0155] "The materials of the first active material layer 2242 and the second active material layer 2243 are the same" means that the main components of the first active material layer 2242 and the second active material layer 2243 are the same. Specifically, the main component of the first active material layer 2242 is the component with the highest content in its composition, and similarly, the main component of the second active material layer 2243 is the component with the highest content in its composition. For example, if the most abundant component in both the first and second active material layers is lithium iron phosphate, then the materials of the first and second active material layers 2242 and 2243 can be considered the same. Similarly, if the most abundant component in both the first and second active material layers 2242 and 2243 is lithium cobalt oxide, then the materials of the first and second active material layers 2242 and 2243 can also be considered the same.

[0156] When the materials of the first active material layer 2242 and the second active material layer 2243 are the same, the risk of cross-contamination caused by switching of active material slurry can be reduced, and the rheological stability problem can be improved. Furthermore, micro-interface channels can be formed between the first active material layer 2242 and the second active material layer 2243, thereby facilitating electrolyte wetting.

[0157] In other embodiments, the materials of the first active material layer 2242 and the second active material layer 2243 are different.

[0158] "The materials of the first active material layer 2242 and the second active material layer 2243 are different" means that the main components of the first active material layer 2242 and the second active material layer 2243 are different. The main component of the first active material layer 2242 is the component with the highest content in its composition, and similarly, the main component of the second active material layer 2243 is the component with the highest content in its composition. For example, if the most abundant component of the first active material layer 2242 is lithium iron phosphate, and the most abundant component of the second active material layer 2243 is lithium cobalt oxide, then the materials of the first active material layer 2242 and the second active material layer 2243 are considered to be different. Similarly, if the most abundant component of the first active material layer 2242 is lithium manganese iron phosphate, and the most abundant component of the second active material layer 2243 is lithium nickel cobalt manganese oxide, then the materials of the first active material layer 2242 and the second active material layer 2243 are considered to be different.

[0159] When the materials of the first active material layer 2242 and the second active material layer 2243 are different, the advantages of the materials of the first active material layer 2242 and the second active material layer 2243 can be brought into play respectively, thereby improving the energy density, reliability and cycle life of the battery cell 20 and reducing the cost of the battery cell 20.

[0160] In some embodiments, one of the first active material layer 2242 and the second active material layer 2243 is made of lithium phosphate, and the other of the first active material layer 2242 and the second active material layer 2243 is made of lithium transition metal oxide.

[0161] Examples of lithium phosphates may include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also known as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0162] Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (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 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 O2 and its modified compounds, etc.

[0163] Optionally, the material of the first active material layer 2242 includes lithium phosphate, and the material of the second active material layer 2243 includes lithium transition metal oxide.

[0164] Lithium-containing phosphates exhibit high thermal stability and low oxygen production, resulting in a lower risk of thermal runaway. Lithium transition metal oxides offer higher energy density. When one of the first active material layer 2242 and the second active material layer 2243 comprises a lithium-containing phosphate, and the other comprises a lithium transition metal oxide, the advantages of both lithium-containing phosphates and lithium transition metal oxides can be leveraged to improve the energy density, reliability, and cycle life of the battery cell 20, while reducing the cost of the battery cell 20.

[0165] Please refer to Figure 7 , Figure 7This is a cross-sectional view of the positive electrode 224 provided for other embodiments of this application. In some embodiments, the electrode assembly 22 includes a positive tab 22411 disposed at one end of the current collector 2241 along its width direction. The positive electrode 224 also includes an insulating layer 2245 disposed on the surface of the current collector 2241, and the insulating layer 2245 covers a portion of the positive tab 22411.

[0166] Please refer to Figure 7 The electrode assembly 22 includes a positive electrode tab 22411. The portion of the current collector 2241 not covered by the first active material layer 2242 constitutes the positive electrode tab 22411, which is located at one end of the current collector 2241 along its width direction. A first thinning region 22422 is located at one end of the first main body region 22421 along its width direction near the positive electrode tab 22411, and a second thinning region 22432 is located at one end of the second main body region 22431 along its width direction near the positive electrode tab 22411.

[0167] The insulating layer 2245 is a coating applied to the surface of the current collector 2241. The insulating layer 2245 is provided on at least one surface of the current collector 2241 along its thickness direction. The insulating layer 2245 can be made of a polymer or a ceramic material.

[0168] By providing an insulating layer 2245 on the surface of the current collector 2241 and covering a portion of the positive electrode tab 22411, the risk of short circuits caused by burrs generated during die-cutting of the positive electrode tab 22411 piercing the separator 225 and contacting the negative electrode sheet is reduced, thus improving the reliability of the battery cell 20. Furthermore, during coating, the first active material layer 2242, the second active material layer 2243, and the insulating layer 2245 can be coated simultaneously. The distance between the coating die and the current collector 2241 is determined by the thickness of the first active material layer 2242. When the thickness of the first active material layer 2242 is smaller, the thickness of the insulating layer 2245 can also be reduced. This smaller thickness of the insulating layer 2245, on the one hand, reduces the external force required to fold the electrode tab 222, lowering the risk of tab breakage. On the other hand, it helps to compress the space of the folded electrode tab 222, increasing the energy density of the battery cell 20. Finally, it facilitates cutting the electrode tab 222, improving the ease of cutting.

[0169] Please refer to Figure 7 In some embodiments, the insulating layer 2245 covers at least a portion of the outer surface 224221 of the first thinned region.

[0170] The insulating layer 2245 may cover only a portion of the outer surface 224221 of the first thinned area, or the insulating layer 2245 may completely cover the outer surface 224221 of the first thinned area.

[0171] The outer surface 224221 of the first thinned region includes a first arcuate surface 2246 that faces away from the first main body region 22421 along its width direction. The first arcuate surface 2246 connects the surface of the current collector 2241 facing the first active material layer 2242 and the stepped surface 2244. An insulating layer 2245 covers at least a portion of the first arcuate surface 2246. Please refer to... Figure 7 ,exist Figure 7 In the embodiment shown, the insulating layer 2245 covers a portion of the first arcuate surface 2246.

[0172] By covering at least a portion of the outer surface 224221 of the first thinned region with insulating layer 2245, the electron transport path can be blocked, making the portion of the first thinned region 22422 covered by insulating layer 2245 less likely to participate in electrochemical reactions, thereby reducing the risk of lithium plating.

[0173] Please refer to Figure 7 In some embodiments, the maximum thickness of the insulating layer 2245 is H3, satisfying: 3μm≤H3≤30μm.

[0174] H3 indicates the maximum thickness of the 2245 insulation layer. It can be measured via tomographic scanning followed by software measurement.

[0175] H3 can be in the following sizes: 3μm, 5μm, 8μm, 10μm, 12μm, 15μm, 18μm, 20μm, 22μm, 25μm, 28μm, 30μm, etc.

[0176] When H3 ≥ 3 μm, the maximum thickness of the insulating layer 2245 is relatively large, which helps reduce the risk of short circuits caused by burrs generated during the die-cutting of the positive electrode tab 22411 piercing the separator 225 and contacting the negative electrode sheet, thus improving the reliability of the battery cell 20. When H3 ≤ 30 μm, the maximum thickness of the insulating layer 2245 is not too large. On the one hand, this helps reduce the external force required for folding the electrode tab 222, reducing the risk of the electrode tab 222 breaking. On the other hand, it helps compress the space of the folded electrode tab 222, increasing the energy density of the battery cell 20. Furthermore, it facilitates the cutting of the electrode tab 222, improving the ease of cutting the electrode tab 222.

[0177] Optionally, 5μm≤H3≤20μm.

[0178] H3 can be: 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, etc.

[0179] When H3 ≥ 5 μm, the maximum thickness of the insulating layer 2245 is greater, which is more conducive to reducing the risk of short circuits caused by burrs generated during the die-cutting of the positive electrode tab 22411 piercing the separator 225 and contacting the negative electrode sheet, thus improving the reliability of the battery cell 20. When H3 ≤ 20 μm, the maximum thickness of the insulating layer 2245 is not too large. On the one hand, this helps to reduce the external force required for folding the electrode tab 222, reducing the risk of electrode tab 222 breakage. On the other hand, it helps to compress the space of the folded electrode tab 222, increasing the energy density of the battery cell 20. Furthermore, it facilitates the cutting of the electrode tab 222, improving the ease of cutting the electrode tab 222.

[0180] Please refer to Figure 8 , Figure 8 This is a cross-sectional view of the positive electrode 224 provided in some embodiments of this application. In some embodiments, along the thickness direction of the current collector 2241, a first active material layer 2242 is provided on both opposite surfaces of the current collector 2241, and a second active material layer 2243 is provided on the side of the first main body region 22421 of each first active material layer 2242 away from the current collector 2241.

[0181] The positive electrode 224 includes two first active material layers 2242, which are respectively disposed on two surfaces of the current collector 2241 that are disposed opposite to each other along the thickness direction of the current collector 2241. A second active material layer 2243 is disposed in a one-to-one correspondence with the first active material layers 2242. Each second active material layer 2243 is disposed on the side of the first main body region 22421 of a first active material layer 2242 that faces away from the current collector 2241. The surface of the first main body region 22421 of each first active material layer 2242 that faces away from the current collector 2241 includes a stepped surface 2244.

[0182] By providing a first active material layer 2242 on both opposite surfaces of the current collector 2241, and providing a second active material layer 2243 on the side of the first main body region 22421 of each first active material layer 2242 away from the current collector 2241, it is beneficial to improve the CB value at the edge of the positive electrode 224, reduce the risk of lithium plating at the edge of the positive electrode 224, and improve the reliability of the battery cell 20.

[0183] To make the technical problems, technical solutions, and beneficial effects solved by the embodiments of this application clearer, the following will provide a more detailed description in conjunction with Comparative Examples 1-3 and Embodiments 1-21. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. 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.

[0184] Example 1

[0185] I. Preparation of battery cell 20

[0186] 1) Preparation of positive electrode 224

[0187] LiNi, the positive electrode active material 0.8 Co 0.1 Mn 0.1 A positive electrode slurry is prepared in N-methylpyrrolidone (NMP) using O2, conductive agent Super P, and binder polyvinylidene fluoride (PVDF). The solid content of the positive electrode slurry is 65 wt%, and the solid component is LiNi. 0.8 Co 0.1 Mn 0.1The mass ratio of O2, Super P, and PVDF is 8.5:1:0.5. The positive electrode slurry is coated on the upper and lower surfaces of the current collector 2241 aluminum foil using a double-layer coating die. After drying at 85°C, it is cold-pressed, then trimmed, cut, and slit. Finally, it is dried under vacuum at 85°C for 4 hours to form the positive electrode sheet 224. The positive electrode sheet 224 includes the current collector 2241, the first active material layer 2242, and the second active material layer 2243. Along the thickness direction of the current collector 2241, the first active material layer 2242 is provided on both opposite surfaces of the current collector 2241. The second active material layer 2243 corresponds one-to-one with the first active material layer 2242. The first active material layer 2242 includes a first main body region 22421 and a first thinned region 22422 arranged along the width direction of the positive electrode 224. The thickness of the first main body region 22421 is greater than the thickness of the first thinned region 22422. Along the width direction, one end of the first main body region 22421 is connected to the first thinned region 22422. The second active material layer 2243 is disposed on the side of the first main body region 22421 away from the current collector 2241. The second active material layer 2243 includes a second main body region 22431 and a second thinned region 22432 arranged along the width direction of the positive electrode 224. The thickness of the second main body region 22431 is greater than the thickness of the second thinned region 22432. Along the width direction, one end of the second main body region 22431 is connected to the second thinning region 22432. The area of ​​the first main body region 22421 that is not covered by the second active material layer 2243 on the surface away from the current collector 2241 forms a step surface 2244. The step surface 2244 connects the outer surface 224221 of the first thinning region and the outer surface 224321 of the second thinning region.

[0188] 2) Preparation of negative electrode 223

[0189] Graphite, conductive agent Super P, thickener carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) are mixed evenly in deionized water to prepare a negative electrode slurry. The solid content of the negative electrode slurry is 30 wt%, and the mass ratio of graphite, silicon suboxide, Super P, CMC, and binder styrene-butadiene rubber (SBR) in the solid components is 88:7:3:2. The negative electrode slurry is coated on the upper and lower surfaces of the current collector 2241 copper foil and dried at 85°C. Then, it is cold-pressed, trimmed, cut into sheets, and slit. Finally, it is dried under vacuum at 120°C for 12 hours to prepare the negative electrode sheet 223.

[0190] 3) Preparation of electrolytes

[0191] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), the thoroughly dried electrolyte salt LiPF6 was dissolved in a mixed solvent (the mixed solvent included ethylene carbonate (EC) and diethyl carbonate (DEC), and ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a mass ratio of 50:50) and mixed evenly to obtain a liquid electrolyte with a concentration of 1 mol / L.

[0192] 4) Preparation of the spacer 225

[0193] A 16μm polyethylene film is used as the separator 225.

[0194] 5) Preparation of battery cell 20

[0195] The positive electrode 224, the separator 225, and the negative electrode 223 are stacked in sequence, with the separator 225 positioned between the positive electrode 224 and the negative electrode 223 to isolate them. The electrode assembly 22 is then wound up and placed inside an aluminum shell 21. The electrolyte prepared above is injected into the dried shell 21. The process includes encapsulation, settling, formation, shaping, and capacity testing to complete the preparation of the battery cell 20.

[0196] The thickness of the first main body region 22421 is H1, the thickness of the second main body region 22431 is H2, and the dimension of the step surface 2244 along the width direction is L. H1, H2 and L are all obtained by tomographic scanning and then measured by software.

[0197] In the preparation steps of the positive electrode 224 in Comparative Examples 1 to 3, the positive electrode slurry is coated on the upper and lower surfaces of the aluminum foil of the current collector 2241. Each side of the current collector 2241 has only a single layer of active material. The thickness of the single layer of active material is represented by H4, which is obtained by tomographic scanning and then measured by software.

[0198] The preparation method of the battery cell 20 in Examples 2-21 is the same as that in Example 1, except that H1, H2 and L are different, as shown in Table 1.

[0199] II. Performance Parameter Testing

[0200] 1) Methods for testing volumetric energy density

[0201] At 25℃, battery cell 20 is charged at a constant current of 0.33C to a cutoff voltage of 4.15V, and then charged at a constant voltage of 4.15V to a current of 0.05C. At this point, battery cell 20 is fully charged. After the fully charged secondary battery is allowed to rest for 5 minutes, it is discharged at a constant current of 0.33C to a cutoff voltage of 2.8V. The discharge capacity at this point is the actual capacity of battery cell 20 at 0.33C, denoted as C0. Then, battery cell 20 is charged at a constant current of 0.33C0 to a cutoff voltage of 4.3V, and then charged at a constant voltage to a current of 0.05C. At this point, battery cell 20 is fully charged. After the fully charged battery cell 20 is allowed to rest for 5 minutes, it is discharged at a constant current of 0.33C0 to a cutoff voltage of 2.8V. The discharge energy Q of the secondary battery is obtained. Based on the outer envelope dimensions of battery cell 20, the volume of battery cell 20 is calculated to be V. The volumetric energy density of battery cell 20 is Q / V.

[0202] 2) Methods for testing the degree of lithium plating

[0203] The battery cell 20 was placed in an environment of 25°C and charged at a constant current of 0.5C to the upper limit voltage. Then, it was charged at a constant voltage of the upper limit voltage to the cutoff current of 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 0.5C to the lower limit voltage, allowed to stand for 5 minutes. This constitutes one charge-discharge cycle. Then, the same steps were repeated for 1000 charge-discharge cycles. Next, the battery cell 20 was charged at a constant current of 0.5C to the upper limit voltage, then charged at a constant voltage of the upper limit voltage to the cutoff current of 0.05C, allowed to stand for 5 minutes, and then disassembled to observe the lithium plating on the negative electrode 223.

[0204] If no white lithium metal is deposited, it is recorded as "no lithium deposition"; if white lithium metal is deposited and the lithium deposition area percentage is greater than 0 and less than 5%, it is recorded as "slight lithium deposition"; if white lithium metal is deposited and the lithium deposition area percentage is greater than or equal to 5% and less than or equal to 10%, it is recorded as "moderate lithium deposition"; if white lithium metal is deposited and the lithium deposition area percentage is greater than 10%, it is recorded as "heavy lithium deposition". The lithium deposition area percentage is the percentage of the lithium deposition area relative to the surface area of ​​the negative electrode 223 opposite to the separator 225.

[0205] 3) Method for confirming whether current collector 2241 is damaged

[0206] The positive electrode 224 is disassembled from the battery cell 20. The first active material layer 2242 and the second active material layer 2243 of the positive electrode 224 are removed. The surface morphology of the current collector 2241 is observed using SEM, and high-resolution images are captured. The surface of the current collector 2241 is examined for scratches in the SEM images. If scratches are found, the current collector 2241 is confirmed to be damaged.

[0207] 4) Method for confirming whether there are scratches on the surface of the second active material layer 2243

[0208] The positive electrode 224 was removed from the battery cell 20, and the surface morphology of the second active material layer 2243 was observed using SEM, and high-resolution images were captured. The SEM images were then used to examine the surface of the second active material layer 2243 for scratches.

[0209] III. Test Results

[0210] The experimental results of Comparative Examples 1-3 and Examples 1-21 are shown in Table 1 below:

[0211] Table 1

[0212]

[0213] Please refer to Table 1. As shown in Comparative Examples 1 to 3, when a single-layer coating is used to form the active material layer, although the volumetric energy density of the battery cell 20 is high, the degree of lithium plating is large. Lithium dendrites are prone to pierce the separator 225 and contact the positive electrode 224, thus causing a short circuit and poor battery reliability.

[0214] Please refer to Table 1. As shown in Examples 1 to 21, by setting the stepped surface 2244, the degree of lithium plating is reduced, while the volumetric energy density is still relatively large, so that the battery cell 20 has high reliability while maintaining a large volumetric energy density.

[0215] Please refer to Table 1, as shown in Examples 2-7 and 10-13. When 100μm≤H1+H2≤200μm, the volumetric energy density of the battery cell 20 is relatively large and the degree of lithium plating is relatively low, so that the battery cell 20 has high reliability while maintaining a large volumetric energy density.

[0216] Please refer to Table 1. As shown in Examples 2 to 5, when 1≤H1 / H2≤2, the volumetric energy density of the battery cell 20 is relatively large and the degree of lithium plating is relatively low, so that the battery cell 20 has high reliability while maintaining a large volumetric energy density.

[0217] Please refer to Table 1. As shown in Examples 2 to 7, when 50μm≤H1≤150μm, it is not easy to damage the current collector 2241, and the battery cell 20 has a high volumetric energy density and a low degree of lithium plating.

[0218] Please refer to Table 1. As shown in Examples 10-12, when 50μm≤H2≤100μm, it is not easy to generate scratches on the surface of the active material layer, and the degree of lithium plating is low, and the volumetric energy density of the battery cell 20 is large.

[0219] Please refer to Table 1. As shown in Examples 15-20, when 0.5mm≤L≤10mm, the volumetric energy density of the battery cell 20 is high and the risk of lithium plating is low, which can balance the volumetric energy density and reliability of the battery cell 20.

[0220] Please refer to Table 1, as shown in Examples 2, 17, and 18. When 2mm≤L≤7mm, the volumetric energy density of the battery cell 20 is high and the risk of lithium plating is low, which can balance the volumetric energy density and reliability of the battery cell 20.

[0221] This application embodiment also provides a battery device 100, which includes the aforementioned battery cell 20.

[0222] This application embodiment also provides an electrical device, which includes the aforementioned battery cell 20, and the battery cell 20 is used to provide electrical energy to the electrical device.

[0223] This application provides a battery cell 20, which includes an electrode assembly 22, and the electrode assembly 22 includes a positive electrode 224. The positive electrode 224 includes a current collector 2241 and a first active material layer 2242. The first active material layer 2242 is disposed on at least one surface of the current collector 2241 along the thickness direction. The first active material layer 2242 includes a first main region 22421 and a first thinned region 22422 arranged along the width direction of the positive electrode 224. The thickness of the first main region 22421 is greater than the thickness of the first thinned region 22422. At least one end of the first main region 22421 is connected to the first thinned region 22422 along the width direction. The positive electrode 224 also includes a second active material layer 2243, which is disposed on the side of the first main region 22421 opposite to the current collector 2241. The second active material layer 2243 includes a second main body region 22431 and a second thinned region 22432 arranged along the width direction of the positive electrode sheet 224. The thickness of the second main body region 22431 is greater than the thickness of the second thinned region 22432. Along the width direction, at least one end of the second main body region 22431 is connected to the second thinned region 22432. The area of ​​the first main body region 22421 that is not covered by the second active material layer 2243 on the surface away from the current collector 2241 forms a stepped surface 2244. The stepped surface 2244 connects the outer surface 224221 of the first thinned region and the outer surface 224321 of the second thinned region. By setting the stepped surface 2244, the dimension of the second active material layer 2243 along the width direction is smaller than that of the first active material layer 2242 along the width direction. Compared with the prior art, the presence of the stepped surface 2244 reduces the content of active material at the edge of the positive electrode 224, which is beneficial to improving the CB value at the edge of the positive electrode 224, reducing the risk of lithium plating at the edge of the positive electrode 224, and improving the reliability of the battery cell 20. During coating, a double-layer coating die can be used to coat the first active material layer 2242 and the second active material layer 2243. The distance between the double-layer coating die and the current collector 2241 is determined by the thickness of the first active material layer 2242. The double-layer coating die can be closer to the current collector 2241. The pressure of the double-layer coating die when spraying the active material slurry is smaller, which is beneficial to controlling the output amount, improving the uniformity of coating, controlling the morphology of the first thinning area 22422 and the second thinning area 22432, reducing the risk of edge bulging, thereby reducing the risk of lithium plating and improving the reliability of the battery cell 20.

[0224] The thickness of the first main body region 22421 is H1, and the thickness of the second main body region 22431 is H2, satisfying: 50μm≤H1+H2≤200μm. When H1+H2≥50μm, the sum of the thicknesses of the first main body region 22421 and the second main body region 22431 is relatively large, which is more suitable for coating the first active material layer 2242 and the second active material layer 2243 using a double-layer coating die. This is beneficial for controlling the morphology of the first thinned region 22422 and the second thinned region 22432, reducing the risk of edge bulging, thereby reducing the risk of lithium plating and improving the reliability of the battery cell 20. Furthermore, the relatively large sum of the thicknesses of the first main body region 22421 and the second main body region 22431 makes it easier to maintain the morphology of the first active material layer 2242 and the second active material layer 2243 after coating. Even if the active material slurry flows, the step surface 2244 is less likely to disappear. When H1+H2≤200μm, the sum of the thickness of the first main body region 22421 and the thickness of the second main body region 22431 will not be too large. This ensures that the thickness of the first main body region 22421 and the thickness of the second main body region 22431 will not be too large, and the pressure of the double-layer coating die head when spraying the active material slurry will not be too large. This is beneficial for controlling the output, improving the uniformity of coating, controlling the morphology of the first thinning region 22422 and the second thinning region 22432, reducing the risk of edge bulging, thereby reducing the risk of lithium plating and improving the reliability of the battery cell 20.

[0225] The thickness of the first main body region 22421 is H1, satisfying: 50μm≤H1≤150μm. When H1≥50μm, the thickness of the first main body region 22421 is relatively large. When using a dual-layer coating die to coat the first active material layer 2242 and the second active material layer 2243, the dual-layer coating die can be farther away from the current collector 2241, reducing the risk of the dual-layer coating die scratching the current collector 2241. When H1≤150μm, the thickness of the first main body region 22421 is not too large, so that the pressure of the dual-layer coating die when spraying the active material slurry is not too high. This is beneficial for controlling the output, improving the uniformity of coating, controlling the morphology of the first thinned region 22422, reducing the risk of edge bulging, thereby reducing the risk of lithium plating and improving the reliability of the battery cell 20.

[0226] The thickness of the second main body region 22431 is H2, satisfying: 50μm≤H2≤100μm. When H2≥50μm, the thickness of the second main body region 22431 is relatively large, which is beneficial to reducing the content of active material at the edge of the positive electrode 224, improving the CB value at the edge of the positive electrode 224, reducing the risk of lithium plating at the edge of the positive electrode 224, and improving the reliability of the battery cell 20. When H2≤100μm, the thickness of the second main body region 22431 is not too large, so that the reduction of active material at the edge of the positive electrode 224 is not too large, which is beneficial to improving the energy density of the battery cell 20.

[0227] Along the width direction, the dimension of the step surface 2244 is L, satisfying: 0.5mm ≤ L ≤ 10mm. When L ≥ 0.5mm, the dimension of the step surface 2244 along the width direction is relatively large, which is beneficial for reducing the content of active material at the edge of the positive electrode 224, improving the CB value at the edge of the positive electrode 224, reducing the risk of lithium plating at the edge of the positive electrode 224, and improving the reliability of the battery cell 20. When L ≤ 10mm, the dimension of the step surface 2244 along the width direction is not too large, so that the reduction of active material at the edge of the positive electrode 224 is not too large, which is beneficial for improving the energy density of the battery cell 20. Therefore, when 0.5mm ≤ L ≤ 10mm, both the energy density and reliability of the battery cell 20 can be balanced.

[0228] The electrode assembly 22 includes a positive tab 22411, which is disposed at one end of the current collector 2241 along its width. The positive electrode sheet 224 also includes an insulating layer 2245, which is disposed on the surface of the current collector 2241 and covers a portion of the positive tab 22411. By providing the insulating layer 2245 on the surface of the current collector 2241 and covering a portion of the positive tab 22411, the risk of short circuits caused by burrs generated during the die-cutting of the positive tab 22411 piercing the separator 225 and coming into contact with the negative electrode sheet is reduced, thereby improving the reliability of the battery cell 20. Furthermore, during coating, the first active material layer 2242, the second active material layer 2243, and the insulating layer 2245 can be coated simultaneously. The distance between the coating die and the current collector 2241 is determined by the thickness of the first active material layer 2242. When the thickness of the first active material layer 2242 is smaller, the thickness of the insulating layer 2245 can also be reduced. Thus, a smaller insulating layer 2245 thickness has several advantages. First, it reduces the external force required to fold the tab 222, lowering the risk of tab breakage. Second, it helps compress the space of the tab 222, increasing the energy density of the battery cell 20. Third, it facilitates cutting the tab 222, improving the ease of cutting the tab 222.

[0229] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A battery cell, characterized in that, include: An electrode assembly includes a positive electrode sheet, the positive electrode sheet including a current collector and a first active material layer, the first active material layer being disposed on at least one surface of the current collector along the thickness direction of the current collector, the first active material layer including a first main body region and a first thinned region arranged along the width direction of the positive electrode sheet, the thickness of the first main body region being greater than the thickness of the first thinned region, and at least one end of the first main body region being connected to the first thinned region along the width direction; The positive electrode sheet further includes a second active material layer. The second active material layer is disposed on the side of the first main body region away from the current collector. The second active material layer includes a second main body region and a second thinned region arranged along the width direction of the positive electrode sheet. The thickness of the second main body region is greater than the thickness of the second thinned region. Along the width direction, at least one end of the second main body region is connected to the second thinned region. The area of ​​the first main body region away from the current collector that is not covered by the second active material layer forms a stepped surface. The stepped surface connects the outer surface of the first thinned region and the outer surface of the second thinned region. Along the width direction, the dimension of the stepped surface is L, where 2mm≤L≤7mm.

2. The battery cell according to claim 1, characterized in that, The thickness of the first main body region is H1, and the thickness of the second main body region is H2, satisfying: 100μm≤H1+H2≤200μm.

3. The battery cell according to claim 1, characterized in that, The thickness of the first main body region is H1, and the thickness of the second main body region is H2, satisfying: 1≤H1 / H2≤2.

4. The battery cell according to claim 1, characterized in that, The thickness of the first main body region is H1, which satisfies: 50μm≤H1≤150μm.

5. The battery cell according to claim 1, characterized in that, The thickness of the second main body region is H2, which satisfies: 50μm≤H2≤100μm.

6. The battery cell according to any one of claims 1-5, characterized in that, The material of the first active material layer is the same as the material of the second active material layer.

7. The battery cell according to any one of claims 1-5, characterized in that, The materials of the first active material layer and the second active material layer are different.

8. The battery cell according to claim 7, characterized in that, The material of one of the first active material layer and the second active material layer includes lithium phosphate, and the material of the other of the first active material layer and the second active material layer includes lithium transition metal oxide.

9. The battery cell according to any one of claims 1-5, characterized in that, The electrode assembly includes a positive electrode tab, which is disposed at one end of the current collector along the width direction; The positive electrode sheet further includes an insulating layer disposed on the surface of the current collector and covering a portion of the positive electrode tab.

10. The battery cell according to claim 9, characterized in that, The insulating layer covers at least a portion of the outer surface of the first thinned area.

11. The battery cell according to claim 9, characterized in that, The maximum thickness of the insulating layer is H3, which satisfies the following condition: 3μm≤H3≤30μm.

12. The battery cell according to claim 11, characterized in that, 5μm≤H3≤20μm.

13. The battery cell according to any one of claims 1-5, characterized in that, Along the thickness direction of the current collector, the first active material layer is provided on both opposite surfaces of the current collector, and the second active material layer is provided on the side of the first main body region of each first active material layer away from the current collector.

14. A battery device, characterized in that, Includes the battery cell according to any one of claims 1-13.

15. An electrical appliance, characterized in that, Includes a battery cell according to any one of claims 1-13, the battery cell being used to provide electrical energy to the electrical device.

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