Battery cell and electric device comprising same

Abstract

The application discloses an electric core and an electric device comprising the same. The electric core comprises an electrode assembly. The electrode assembly is formed by winding a positive electrode tab, a negative electrode tab and a separator arranged between the positive electrode tab and the negative electrode tab. The negative electrode tab comprises a negative electrode current collector, a first active material layer and a second active material layer, the negative electrode current collector is located between the first active material layer and the second active material layer, the first active material layer faces the winding center of the electrode assembly, and the second active material layer faces away from the winding center of the electrode assembly. The first active material layer and the second active material layer both comprise a first active substance and a binder, the first active substance comprises a silicon-based material, the binder of the first active material layer comprises butadiene styrene rubber and sodium carboxymethyl cellulose, and the binder of the second active material layer comprises polyacrylic acid and sodium carboxymethyl cellulose.

Description

Technical Field

[0001] This application relates to the field of energy storage devices, and in particular to a battery cell and an electrical device including the battery cell. Background Technology

[0002] With the widespread application of electrochemical devices (such as lithium-ion batteries) in various electronic products, users are placing increasingly higher demands on the energy density of these devices. For this reason, silicon is typically used as the negative electrode active material because it boasts a specific capacity as high as 4200 mAh / g. However, as a negative electrode active material, silicon experiences significant volume changes during lithium-ion insertion and extraction, leading to overall expansion and deformation of the battery cell. Furthermore, silicon has poor electronic and ionic conductivity, resulting in deteriorated kinetic performance of the battery cell and a higher susceptibility to lithium plating. Summary of the Invention

[0003] One object of this application is to provide a battery cell that can balance dynamic performance and cyclic expansion performance, and an electrical device including the battery cell.

[0004] This application provides a battery cell including an electrode assembly. The electrode assembly is formed by winding a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrode. The negative electrode includes a negative current collector, a first active material layer, and a second active material layer, with the negative current collector located between the first and second active material layers. The first active material layer faces the winding center of the electrode assembly, and the second active material layer faces away from the winding center of the electrode assembly. Both the first and second active material layers include a first active material and a binder. The first active material includes a silicon-based material, and the binder for the first active material layer includes styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC). The binder for the second active material layer includes polyacrylic acid (PAA) and sodium carboxymethyl cellulose (CMC).

[0005] The battery cell provided in this application provides a first active material layer containing SBR and CMC on the surface of the negative electrode current collector facing the winding center, and a second active material layer containing PAA and CMC on the surface of the negative electrode current collector away from the winding center. Since the second active material layer has high adhesion, it can ensure the overall strength of the negative electrode sheet. The first active material layer has good toughness and elongation, which can adapt to the expansion of silicon. Furthermore, the second active material layer consumes less electrolyte, reducing the problems of lithium plating at corners and the generation of purple spots. Therefore, the battery cell can simultaneously achieve excellent dynamic performance and cycle expansion performance.

[0006] According to some embodiments of this application, the content of silicon-based material in the first active material layer and the content of silicon-based material in the second active material layer are equal, so that the battery cell can have both excellent cycle expansion performance and dynamic performance.

[0007] According to some embodiments of this application, the CMC content of the first active material layer is greater than the CMC content of the second active material layer. Since PAA has stronger adhesion than SBR, the CMC content in the second active material layer can be reduced and the active material content can be increased accordingly, thereby further improving the energy density of the battery cell.

[0008] According to some embodiments of this application, the difference between the CMC content of the first active material layer and the CMC content of the second active material layer ranges from 0.1wt% to 3wt%, which allows the battery cell to have both superior cycle expansion performance and dynamic performance.

[0009] According to some embodiments of this application, the CMC content of the first active material layer and the CMC content of the second active material layer are both 0.1wt%-10wt%, which can further improve cycle stability and improve kinetic performance.

[0010] According to some embodiments of this application, both the first active material layer and the second active material layer further include a conductive agent, which includes at least one of conductive carbon black, Ketjen black, graphene, carbon nanotubes or carbon fibers.

[0011] According to some embodiments of this application, both the first active material layer and the second active material layer further include a second active substance, which is at least one of artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon, or hard carbon.

[0012] According to some embodiments of this application, the content of the second active substance in the first active material layer and the content of the second active substance in the second active material layer are equal, so that the battery cell can have both excellent cycle expansion performance and dynamic performance.

[0013] According to some embodiments of this application, the CB value of the second active material layer is greater than that of the first active material layer, which can improve the dynamic performance of the surface of the negative electrode sheet away from the winding center and increase the energy density.

[0014] According to some embodiments of this application, the difference between the CB value of the second active material layer and the CB value of the first active material layer is 0.01-0.05, which enables the battery cell to have both excellent cyclic expansion performance and dynamic performance.

[0015] A second aspect of this application also provides an electrical device including the aforementioned battery cell. Attached Figure Description

[0016] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0017] Figure 1 This is a schematic diagram of the structure of a battery cell provided in an embodiment of this application.

[0018] Figure 2 for Figure 1 A schematic diagram of the interface of the electrode assembly of the battery cell shown.

[0019] Explanation of main component symbols

[0020] 100 cells

[0021] Electrode assembly 20

[0022] Casing 10

[0023] Positive conductive plate 30

[0024] Negative conductive plate 40

[0025] Positive electrode plate 21

[0026] Positive current collector 211

[0027] Positive electrode active material layer 212

[0028] Positive electrode 213

[0029] Diaphragm 23

[0030] Negative electrode plate 22

[0031] Negative current collector 221

[0032] First active material layer 222

[0033] Second active material layer 223

[0034] Negative electrode tab 224 Detailed Implementation

[0035] The technical solutions in the embodiments of this application are described clearly and in detail below. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the specification of this application is for the purpose of describing particular embodiments only and is not intended to limit this application.

[0036] The embodiments of this application will be described in detail below. However, this application may be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Rather, these exemplary embodiments are provided to provide a thorough and detailed understanding of this application to those skilled in the art.

[0037] Additionally, for brevity and clarity, the dimensions or thicknesses of various components and layers may be enlarged in the accompanying drawings. Throughout the text, the same numerical values ​​refer to the same elements. As used herein, the terms "and / or" and "and / or" include any and all combinations of one or more of the associated enumerated items. Furthermore, it should be understood that when element A is referred to as "connecting" element B, element A may be directly connected to element B, or there may be an intermediate element C and element A and element B may be indirectly connected to each other.

[0038] Furthermore, when describing the implementation of this application, the word "may" refers to "one or more implementations of this application".

[0039] The technical terms used herein are for the purpose of describing particular embodiments and are not intended to limit this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. It should be further understood that the term "comprising," as used in this specification, means the presence of the described features, values, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, values, steps, operations, elements, components, and / or combinations thereof.

[0040] Spatial terms, such as "above," may be used herein for convenience in describing the relationship between one element or feature and another element (or feature) or feature (or feature) illustrated in the figures. It should be understood that, in addition to the directions depicted in the figures, spatial terms are intended to include different orientations of the device or apparatus during use or operation. For example, if the device in the figure is flipped, an element described as "above" or "on" other elements or features would be oriented "below" or "under" other elements or features. Therefore, the exemplary term "above" can include both above and below orientations. It should be understood that although the terms first, second, third, etc., may be used herein to describe various elements, components, regions, layers, and / or portions, these elements, components, regions, layers, and / or portions should not be limited by these terms. These terms are used to distinguish one element, component, region, layer, or portion from another element, component, region, layer, or portion. Therefore, a first element, component, region, layer, or portion discussed below may be referred to as a second element, component, region, layer, or portion without departing from the teachings of the exemplary embodiments.

[0041] Please see Figure 1This application provides a battery cell 100, including a housing 10, an electrode assembly 20, a positive conductive plate 30, and a negative conductive plate 40. The electrode assembly 20 is housed within the housing 10. Both the positive conductive plate 30 and the negative conductive plate 40 are connected to the electrode assembly 20 and extend from one side of the housing 10 to connect to external components. The positive conductive plate 30 and the negative conductive plate 40 may also extend from different sides of the housing 10; this application does not impose limitations. In this embodiment, the housing 10 is a packaging bag obtained by encapsulating with a sealing film, such as aluminum-plastic film or steel-plastic film. In other embodiments, the housing 10 may also be a metal housing or a rigid plastic housing, such as a steel housing or an aluminum housing.

[0042] Please see Figure 2 The electrode assembly 20 includes a positive electrode 21, a negative electrode 22, and a separator 23 disposed between the positive electrode 21 and the negative electrode 22. The electrode assembly 20 is formed by stacking and winding the positive electrode 21, the separator 23, and the negative electrode 22.

[0043] The positive electrode 21 includes a positive current collector 211, a positive active material layer 212, and a positive electrode tab 213. The positive electrode tab 213 is disposed on one side of the positive current collector 211 and connects the positive current collector 211 and the positive conductive plate 30. The positive active material layer 212 is disposed on the surface of the positive current collector 211. The positive active material layer 212 may be disposed on one surface or two opposite surfaces of the positive current collector 211, which is not limited in this application. In some embodiments, the positive active material layer 212 includes at least one of lithium cobalt oxide, lithium iron phosphate, lithium manganese iron phosphate, sodium iron phosphate, lithium vanadium phosphate, sodium vanadium phosphate, lithium vanadium oxide phosphate, sodium vanadium oxide phosphate, lithium vanadium oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium-rich manganese-based materials, or lithium nickel cobalt aluminum oxide. In some embodiments, the positive electrode active material layer 212 may further include a conductive agent and a binder. The conductive agent in the positive electrode active material layer 212 may include at least one of conductive carbon black, Ketjen black, graphene, carbon nanotubes, or carbon fibers. The binder in the positive electrode active material layer 212 may include at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyvinylpyrrolidone, polyaniline, polyimide, polyamide-imide, polysiloxane, styrene-butadiene rubber, epoxy resin, polyester resin, or polyurethane resin. It should be understood that the above description is merely an example, and the positive electrode active material layer 212 may be made of any other suitable material.

[0044] The separator 23 is used to prevent direct contact between the positive electrode 21 and the negative electrode 22, thereby reducing the risk of short circuits between them. The substrate of the separator 23 may include at least one of polypropylene, polyethylene, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate, or polyethylene glycol. An inorganic coating and / or an organic coating may be provided on the surface of the substrate of the separator 23. The separator may be of a type commonly used in the prior art.

[0045] In some embodiments, the cell 100 may further include an electrolyte. The electrolyte may be one or more of a gel electrolyte, a solid electrolyte, and an electrolyte solution, wherein the electrolyte solution includes a lithium salt and a non-aqueous solvent. The lithium salt is selected from one or more of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, or lithium difluoroborate. For example, LiPF6 is chosen as the lithium salt because it has high ionic conductivity and can improve cycle characteristics.

[0046] The negative electrode 22 includes a negative current collector 221, a first active material layer 222, a second active material layer 223, and a negative electrode tab 224. The negative electrode tab 224 is disposed on one side of the negative current collector 221 and connects the negative current collector 221 and the negative conductive plate 40. The negative current collector 221 is located between the first active material layer 222 and the second active material layer 223, with the first active material layer 222 facing the winding center 20a of the electrode assembly 20 and the second active material layer 223 facing away from the winding center 20a of the electrode assembly 20. In some embodiments, the first active material layer 222 is coated on the surface of the negative current collector 221 facing the winding center 20a, and the second active material layer 223 is coated on the surface of the negative current collector 221 facing away from the winding center 20a. The negative current collector 221 has the function of current collection, and its material may include at least one of Ni, Ti, Cu, Ag, Au, Pt, Fe, Al, and combinations thereof.

[0047] Both the first active material layer 222 and the second active material layer 223 include a first active substance and a binder. The first active substance includes a silicon-based material, which has high specific capacity, thus improving the energy density of the battery cell. In some embodiments, the silicon-based material includes at least one of silicon, silicon alloy, silicon oxide, or silicon-carbon composite.

[0048] The binders for the first active material layer 222 include styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC). The binders for the second active material layer 223 include polyacrylic acid (PAA) and sodium carboxymethyl cellulose (CMC). Polyacrylic acid (PAA) has low swelling and high elastic modulus, and a high carboxyl content, forming strong hydrogen bonds with silicon, providing high adhesion. However, PAA has high rigidity and poor flexibility, which can lead to material loss during electrode processing, resulting in electrode breakage in the later stages of cycling. Furthermore, PAA has poor kinetic properties, causing temperature rise during high-rate charging and discharging. Sodium carboxymethyl cellulose (CMC) has self-healing hydrogen bonds, effectively adapting to volume expansion during cycling. However, CMC has generally poor adhesion, high brittleness, and poor flexibility, making the electrode prone to cracking during charging and discharging. Styrene-butadiene rubber (SBR) has good toughness, high elongation, and good kinetic properties; however, SBR has weak adhesion and is prone to deformation. This application balances the dynamic performance and cycle expansion performance of the cell 100 by disposing a first active material layer 222 containing SBR and CMC on the surface of the negative electrode current collector 221 facing the winding center 20a, and disposing a second active material layer 223 containing PAA and CMC on the surface of the negative electrode current collector 221 away from the winding center 20a.

[0049] like Figure 2 As shown, the electrode assembly 20, formed by winding the positive electrode 21, the negative electrode 22, and the separator 23 disposed between the positive and negative electrode 21, has four corners. These corners are the points where the electrode assembly 20 (positive electrode 21, negative electrode 22) bends. Research has revealed that wound cells are prone to lithium plating at the corner interfaces in the later stages of cycling due to insufficient cell balance (CB) and insufficient electrolyte caused by compression at the corners. CB refers to the margin by which the negative electrode capacity exceeds the positive electrode capacity within the same stage and under the same conditions. This application provides a first active material layer 222 containing SBR and CMC on the side of the negative electrode 22 facing the winding center 20a, and a second active material layer 223 containing PAA and CMC on the side of the negative electrode 22 away from the winding center 20a. The poor electrolyte resistance of SBR causes the first active material layer 222 to consume electrolyte quickly, while the good electrolyte resistance of the second active material layer 223 reduces electrolyte consumption. As a result, the opposite sides of the negative electrode 22 will not experience lithium plating and purple spots at the corners due to insufficient CB or insufficient electrolyte caused by compression at the corners in the later stages of cycling.

[0050] The types and contents of silicon-based materials in the first active material layer 222 and the second active material layer 223 can be the same or different. Because SBR itself has poor adhesion, when the contents of silicon-based materials in the first active material layer 222 and the second active material layer 223 are the same, more CMC needs to be added to the first active material layer 222 to ensure the adhesion between the first active material layer 222 and the negative electrode current collector 221; moreover, the PAA of the second active material layer 223 has stronger adhesion, allowing for a reduction in the amount of CMC used in the second active material layer 223. Therefore, when the contents of silicon-based materials are the same, the CMC content in the first active material layer 222 is greater than the CMC content in the second active material layer 223. In some embodiments, the difference in CMC content between the first active material layer 222 and the second active material layer 223 ranges from 0.1wt% to 3wt%, thus enabling the cell 100 to simultaneously possess excellent cycle expansion performance and kinetic performance. Preferably, the difference between the CMC content of the first active material layer 222 and the CMC content of the second active material layer 223 is in the range of 0.1wt%-0.5wt%, which can further improve cycle stability and improve kinetic performance.

[0051] In some embodiments, the CMC content of the first active material layer 222 and the CMC content of the second active material layer 223 are both 0.1wt%-10wt%, which allows the cell 100 to simultaneously possess excellent cycle expansion performance and kinetic performance. Preferably, the CMC content of the first active material layer 222 is 0.1wt%-5wt%, and the CMC content of the second active material layer 223 is 0.1wt%-10wt%, which can further improve cycle stability and enhance kinetic performance.

[0052] The SBR content of the first active material layer 222 and the PAA content of the second active material layer 223 can be the same or different. In some embodiments, the SBR content of the first active material layer 222 and the PAA content of the second active material layer 223 are both 1wt%-20wt%, which allows the cell 100 to simultaneously possess excellent cycle expansion performance and kinetic performance. Preferably, the SBR content of the first active material layer 222 is 1wt%-10wt%, and the PAA content of the second active material layer 223 is 1wt%-20wt%, which can further improve cycle stability and enhance kinetic performance.

[0053] In some embodiments, both the first active material layer 222 and the second active material layer 223 may further include a second active substance. The second active substance may be at least one of artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon, or hard carbon. The type and content of the second active substance in the first active material layer 222 and the second active material layer 223 may be the same or different, and this application does not impose any restrictions.

[0054] In some embodiments, in the first active material layer 222, the mass of the silicon-based material is 3%-100% of the total mass of the first and second active materials, and the mass of the second active material is 0%-97% of the total mass of the first and second active materials; in the second active material layer 223, the mass of the silicon-based material is 3%-100% of the total mass of the first and second active materials, and the mass of the second active material is 0%-97% of the total mass of the first and second active materials, thus enabling the cell 100 to simultaneously possess excellent cycle expansion performance and kinetic performance. Preferably, in the first active material layer 222, the mass of the silicon-based material is 3%-50% of the total mass of the first and second active materials, and the mass of the second active material is 50%-97% of the total mass of the first and second active materials; in the second active material layer 223, the mass of the silicon-based material is 10%-80% of the total mass of the first and second active materials, and the mass of the second active material is 20%-90% of the total mass of the first and second active materials, thus further improving cycle stability and kinetic performance.

[0055] In some embodiments, both the first active material layer 222 and the second active material layer 223 may further include a conductive agent. The conductive agent may include at least one of conductive carbon black, Ketjen black, graphene, carbon nanotubes, or carbon fibers. The type and content of the conductive agent in the first active material layer 222 and the second active material layer 223 may be the same or different, and this application does not impose any restrictions.

[0056] In some embodiments, the conductive agent content in both the first active material layer 222 and the second active material layer 223 is 0.1 wt%-10 wt%, which allows the battery cell to simultaneously possess excellent cycle expansion performance and kinetic performance. Preferably, the conductive agent content in the first active material layer 222 is 0.1 wt%-5 wt%, and the conductive agent content in the second active material layer 223 is 0.1 wt%-10 wt%, which further enhances cycle stability and improves kinetic performance.

[0057] In some embodiments, the coating weight of the second active material layer 223 is greater than the coating weight of the first active material layer 222, that is, the CB value of the second active material layer 223 is greater than the CB value of the first active material layer 222. CB value = (specific capacity of negative electrode active material × areal density of negative electrode sheet × content ratio of negative electrode active material) / (specific capacity of positive electrode active material × areal density of positive electrode sheet × content ratio of positive electrode active material). The second active material layer 223 located on the side of the negative electrode 22 away from the winding center 20a adopts a large CB design, which can improve the dynamic performance of the surface of the negative electrode 22 away from the winding center 20a. The first active material layer 222 located on the side of the negative electrode 22 facing the winding center 20a has a small expansion, and its small CB design can improve the energy density. At the same time, the CB value of the second active material layer 223 is greater than that of the first active material layer 222, which can ensure that the second active material layer 223 and the first active material layer 222 have the same expansion rate, avoiding the deformation problem caused by the different expansion amounts of the two sides of the negative electrode 22.

[0058] In some embodiments, the difference between the CB value of the second active material layer 223 containing PAA and CMC and the CB value of the first active material layer 222 containing SBR and CMC is 0.01-0.05, thus balancing the energy density, kinetic performance, and cycle expansion performance of the cell 100. Preferably, the difference between the CB value of the second active material layer 223 and the CB value of the first active material layer 222 is 0.01-0.03, thus further balancing the energy density, kinetic performance, and cycle expansion performance of the cell 100.

[0059] One embodiment of this application also provides an electrical device, including a battery cell 100. The electrical device specifically refers to mobile phones, portable devices, laptops, electric vehicles, electric cars, ships, spacecraft, electric toys, and power tools, etc. It is understood that the electrical device is not limited to these, and can be any electrical device using the battery cell 100.

[0060] The following are some specific embodiments and comparative examples to better illustrate this application, wherein a lithium-ion battery is used as an example.

[0061] Example 1

[0062] Preparation of the positive electrode sheet: Lithium cobalt oxide, carbon nanotubes, conductive carbon black, and polyvinylidene fluoride (PVDF) were dissolved in an N-methylpyrrolidone (NMP) solution at a weight ratio of 96.2:0.5:0.3:3 to form a positive electrode slurry. A 12 μm thick aluminum foil was used as the positive electrode current collector. The positive electrode slurry was coated onto the current collector to obtain the positive electrode active material layer. After drying, cold pressing, and cutting, the positive electrode sheet was obtained. The coating weight of the positive electrode active material layer was 13 mg / cm³.2 The compacted density is 3.5 g / cm³. 3 .

[0063] Preparation of the negative electrode: The first and second negative electrode active materials are dissolved in deionized water to form a first active material layer slurry and a second active material layer slurry. The first negative electrode active material comprises 15 wt% silicon oxide, 81 wt% graphite, 0.5 wt% conductive carbon black, 2.8 wt% SBR, and 0.7 wt% CMC. In the first negative electrode active material, silicon oxide accounts for 16% of the total mass of silicon oxide and graphite, and graphite accounts for 84% of the total mass of silicon oxide and graphite, i.e., silicon accounts for 16% and graphite accounts for 84%. The second negative electrode active material comprises 15 wt% silicon oxide, 81 wt% graphite, 0.5 wt% conductive carbon black, 3 wt% PAA, and 0.5 wt% CMC. In the second negative electrode active material, silicon oxide accounts for 16% of the total mass of silicon oxide and graphite, and graphite accounts for 84% of the total mass of silicon oxide and graphite, i.e., silicon oxide accounts for 16% and graphite accounts for 84%. The difference in CMC content between the first and second negative electrode active materials is 0.2 wt%. A 10 μm thick copper foil is used as the negative electrode current collector. The first active material layer slurry is coated onto one surface of the current collector to obtain the first active material layer. Then, the second active material layer slurry is coated onto the other surface of the current collector to obtain the second active material layer. After drying, cold pressing, and cutting, the negative electrode sheet is obtained. The coating weight of the first active material layer is 5.0 mg / cm³. 2 The coating weight of the second active material layer is 5.15 mg / cm³. 2 The compacted density is 1.6 g / cm³. 3 The CB value of the first active material layer is 1.06, the CB value of the second active material layer is 1.09, and the difference between the CB value of the first active material layer and the CB value of the second active material layer is 0.03.

[0064] Preparation of the diaphragm: A 6μm polyethylene membrane was selected as the diaphragm.

[0065] Preparation of electrolyte: Ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed in a weight ratio of 20:30:40:10 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0066] Lithium-ion battery fabrication: Positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to provide insulation. The electrodes are then wound to form the electrode assembly. A first active material layer containing SBR and CMC is located on the surface of the negative electrode facing the winding center, while a second active material layer containing PAA and CMC is located on the surface of the negative electrode away from the winding center. The electrode assembly is placed in an outer aluminum-plastic film packaging, dehydrated at 80°C, injected with the aforementioned electrolyte, and encapsulated. After formation, degassing, encapsulation, and edge trimming processes, the lithium-ion battery is obtained.

[0067] Example 2-11

[0068] Except for the components of the first and second negative electrode active materials and CB, the rest are the same as in Example 1. The parameters of Examples 1-11 are shown in Table 1.

[0069] Table 1

[0070]

[0071] In this context, " / " represents nothing.

[0072] Comparative Example 1

[0073] The lithium-ion battery was prepared in a manner largely similar to that in Example 1, except that the negative electrode film consisted only of a first active material layer containing SBR and CMC. Two first active material layers were formed on the two opposing surfaces of the negative electrode current collector, located on the two surfaces of the negative electrode facing and away from the winding center, respectively. The coating weight of both first active material layers was 5 mg / cm². 2 .

[0074] Comparative Example 2

[0075] The lithium-ion battery was prepared in a manner largely similar to that in Example 1, except that the negative electrode film only included a second active material layer containing PAA and CMC. Two second active material layers were formed on two opposing surfaces of the negative electrode current collector, located on the surfaces of the negative electrode facing and away from the winding center, respectively. The coating weight of both second active material layers was 5 mg / cm². 2 .

[0076] The lithium-ion batteries prepared in Examples 1-11 and Comparative Examples 1 and 2 were subjected to the following tests, and the test results are shown in Table 1.

[0077] Discharge temperature rise test:

[0078] At 25℃, the lithium-ion battery was charged to 4.30V with a constant current of 1.0C, then charged to 0.05C with a constant voltage of 4.30V, and left to stand for 10 minutes; then discharged to 2.0V with a constant current of 4.0C, and left to stand for 15 minutes. Temperature rise of the battery cell was measured by attaching temperature sensing wires to the middle of the diagonal of the cell.

[0079] Cyclic performance test:

[0080] At 25℃, the lithium-ion battery was charged to 4.30V at a constant current of 1.0C, then charged to 0.05C at a constant voltage of 4.30V, and allowed to stand for 10 minutes. Then, the battery was discharged to 2.0V at a constant current of 4.0C, and allowed to stand for 15 minutes. This constitutes one cycle. This cycle was repeated 500 times, and the initial capacity Q0 was recorded. The discharge capacity of the 500th cycle was taken as the battery capacity Q2, and the capacity retention rate was calculated. The capacity retention rate (%) was calculated as Q2 / Q0 × 100%.

[0081] Cyclic expansion rate test:

[0082] The lithium-ion battery is placed in an environment of 25°C, and the battery voltage is adjusted to 3.60V, i.e., the initial thickness of the battery in a half-charge state is measured and denoted as T0. The half-charge state is not limited to 50% state of charge; it satisfies 30% < state of charge < 50%. When 500 cycles are completed, the PPG (Panel Pressure Gap) thickness of the battery in a fully charged state (100% state of charge) is measured and denoted as T2. Cyclic expansion rate (%) = T2 / T0 × 100%.

[0083] Looping interface test:

[0084] At 25°C, the lithium-ion battery was charged to 4.30V at a constant current of 2C on the 501st cycle. The battery was then disassembled while fully charged to obtain the negative electrode. Lithium plating was observed at the corners of the negative electrode. If any point at the corner of the negative electrode is found to be greater than or equal to 1mm... 2 and less than 2mm 2 If lithium deposition is found in a specific area, it is considered to be slight lithium deposition at the corner of the negative electrode. If any area at the corner of the negative electrode is found to have a lithium deposition greater than or equal to 2mm, it is considered to be a minor lithium deposition. 2 and less than 5mm 2 If lithium deposition is found in a region, it is considered moderate lithium deposition at the corner of the negative electrode. If any point at the corner of the negative electrode is found to be greater than or equal to 5mm... 2 The presence of lithium plating in certain areas indicates severe lithium plating at the corners of the negative electrode.

[0085] Table 2

[0086]

[0087] As can be seen from Table 2, the lithium-ion batteries prepared in Examples 1-11 have good discharge temperature rise (discharge temperature rise of 40℃-43℃), capacity retention performance (cycle retention rate of 78%-80%), and expansion performance (cycle expansion rate of 10%-12%). At the same time, the interface is well maintained after cycling (there may be no lithium plating at the corners, reducing the risk of lithium plating at the corners), thus achieving both excellent kinetic performance and cycle expansion performance.

[0088] As illustrated by the comparison of Examples 1-11 and Comparative Examples 1-2, by disposing a first active material layer containing SBR and CMC on the surface of the negative electrode sheet facing the winding center, and disposing a second active material layer containing PAA and CMC on the surface of the negative electrode current collector away from the winding center, the risk of lithium plating at the battery corner can be reduced, the cycle retention rate can be improved, and the cycle expansion rate and discharge temperature rise can be reduced.

[0089] The comparison of Examples 1-7 shows that when the silicon content and CB difference are the same, as the CMC difference increases, the corner lithium plating becomes more severe, the cycle retention rate increases, and the cycle expansion rate decreases. Specifically, when the CMC difference is 0-0.1wt%, the discharge temperature rise remains at 40℃, there is no lithium plating at the corner, the cycle retention rate increases with the increase of the CMC difference, and the cycle expansion rate decreases with the increase of the CMC difference; when the CMC difference is 0.1-0.5wt%, the discharge temperature rise increases with the increase of the CMC difference when the CMC difference reaches 0.2wt%, lithium plating occurs at the corner when the CMC difference reaches 0.2wt%, the cycle retention rate reaches its maximum at the CMC difference reaches 0.2wt% and then remains unchanged, and the cycle expansion rate decreases to its minimum at the CMC difference reaches 0.2wt% and then remains unchanged; when the CMC difference is greater than 0.5wt%, the discharge temperature rise increases with the increase of the CMC difference, the lithium plating at the corner is more severe, the cycle retention rate remains at 80%, and the cycle expansion rate remains at 10%; and when the CMC difference is equal to 3wt%, the discharge temperature rise reaches 42℃.

[0090] A comparison of Examples 2 and 7 with Examples 1 and 3-6 shows that when the CMC difference is too small (Example 2), its cycle expansion rate is greater than that of other examples; when the CMC difference is too large (Example 7), its discharge temperature rise and lithium plating are greater than those of other examples.

[0091] A comparison of Examples 10 and 11 with Examples 1, 8, and 9 shows that when the CB difference is less than 0.01 (Example 10), its discharge temperature rise, cycle interface after 500 cycles, and cycle expansion rate are greater than those of the other examples; when the CB difference is greater than 0.05 (Example 11), its cycle performance and expansion performance are worse than those of the other examples.

[0092] As illustrated by the comparisons in Examples 1 and 8-11, when the silicon content and CMC difference are the same, as the CB difference increases, the discharge temperature rise decreases, the corner lithium plating becomes less severe, the cycle retention rate increases, and the cycle expansion rate decreases. Specifically, when the CB difference is greater than or equal to 0.03, there is no lithium plating at the corner, the cycle retention rate remains at 80%, and the cycle expansion rate remains at 10%; when the CB difference is 0.05, the discharge temperature rise reaches 41°C.

[0093] The above-disclosed embodiments are merely preferred embodiments of this application and should not be construed as limiting the scope of this application. Therefore, any equivalent variations made in accordance with this application are still within the scope of this application.

Claims

1. A battery cell comprising an electrode assembly, the electrode assembly being formed by winding a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, characterized in that, The negative electrode sheet includes a negative current collector, a first active material layer, and a second active material layer. The negative current collector is located between the first active material layer and the second active material layer. The first active material layer faces the winding center of the electrode assembly, and the second active material layer is away from the winding center of the electrode assembly. Both the first active material layer and the second active material layer include a first active substance and a binder. The first active substance includes a silicon-based material. The binder of the first active material layer includes styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC). The binder of the second active material layer includes polyacrylic acid (PAA) and sodium carboxymethyl cellulose (CMC). The CMC content of the first active material layer is greater than the CMC content of the second active material layer.

2. The battery cell as described in claim 1, characterized in that, The content of silicon-based material in the first active material layer is equal to the content of silicon-based material in the second active material layer.

3. The battery cell as described in claim 1 or 2, characterized in that, The difference between the CMC content of the first active material layer and the CMC content of the second active material layer ranges from 0.1wt% to 3wt%.

4. The battery cell as described in claim 3, characterized in that, The CMC content of the first active material layer and the CMC content of the second active material layer are both 0.1wt%-10wt%.

5. The battery cell as described in claim 1, characterized in that, The silicon-based material includes at least one of silicon, silicon alloys, silicon oxides, or silicon-carbon composites.

6. The battery cell as described in claim 1, characterized in that, Both the first active material layer and the second active material layer further include a conductive agent, which includes at least one of conductive carbon black, Ketjen black, graphene, carbon nanotubes or carbon fibers.

7. The battery cell as described in claim 1, characterized in that, Both the first active material layer and the second active material layer further include a second active substance, which is at least one of artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon, or hard carbon.

8. The battery cell as described in claim 7, characterized in that, The content of the second active substance in the first active material layer is equal to the content of the second active substance in the second active material layer.

9. The battery cell as described in claim 1, characterized in that, The CB value of the second active material layer is greater than that of the first active material layer.

10. The battery cell as described in claim 9, characterized in that, The difference between the CB value of the second active material layer and the CB value of the first active material layer is 0.01-0.

05.

11. An electrical appliance, characterized in that, Includes the battery cell as described in any one of claims 1 to 10.

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