Battery cell and electric device comprising same

Abstract

The application discloses an electric core and a power consumption device comprising the same. The electric core comprises a negative electrode sheet. The negative electrode sheet comprises a current collector, a first active material layer and a second active material layer. The first active material layer is arranged on at least one surface of the current collector. The second active material layer is arranged on the surface of the first active material layer away from the current collector. 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 polyacrylic acid (PAA) and sodium carboxymethyl cellulose (CMC), and the binder of the second active material layer comprises styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC).

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 a negative electrode sheet. The negative 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 at least one surface of the current collector. The second active material layer is disposed on the surface of the first active material layer away from the current collector. 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. The binder for the first active material layer includes polyacrylic acid (PAA) and sodium carboxymethyl cellulose (CMC), and the binder for the second active material layer includes styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC).

[0005] The negative electrode of the battery cell provided in this application has a double-layer structure, which includes a first active material layer containing PAA and CMC. PAA has a high carboxyl content and can form strong hydrogen bonds with silicon-based materials. Therefore, the first active material layer has high adhesion and can ensure the overall strength of the negative electrode. In addition, the negative electrode also includes a second active material layer containing SBR and CMC. The second active material layer has good toughness and elongation, can adapt to the expansion of silicon, and is not prone to lithium plating. Thus, the battery cell can simultaneously achieve excellent dynamic performance and cycle expansion performance.

[0006] According to some embodiments of this application, the silicon-based material content of the first active material layer and the silicon-based material content of the second active material layer are equal. When the silicon-based material content is equal, the second active material layer has good kinetic performance and will not experience the problem of outer layer lithium plating. At the same time, the first active material layer has good adhesion performance and can be firmly bonded to the current collector. Furthermore, its expansion performance is better than that of the second active material layer, and it will not experience the problem of electrode demolding.

[0007] According to some embodiments of this application, the CMC content of the first active material layer is less than the CMC content of the second active material layer. Since PAA has stronger adhesion than SBR, the CMC content in the first active material layer can be reduced and the active material content 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 enables the battery cell to have both excellent 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% to 10wt%, which can further improve cycle stability and improve kinetic performance.

[0010] According to some embodiments of this application, the silicon-based material content of the first active material layer is greater than that of the second active material layer. The first active material layer, located at the bottom, has stronger adhesion; combined with a high-silicon design, it can suppress its own expansion to prevent excessive expansion and improve energy density. The second active material layer, located at the top, has weaker adhesion; combined with a low-silicon design, it can suppress its own expansion to prevent excessive expansion and also suppress the expansion of the first active material layer.

[0011] According to some embodiments of this application, the silicon-based material includes at least one of silicon, silicon alloy, silicon oxide, or silicon-carbon composite.

[0012] 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.

[0013] 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.

[0014] A second aspect of this application also provides an electrical device including the aforementioned battery cell. Attached Figure Description

[0015] 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:

[0016] Figure 1This is a schematic diagram of the structure of a battery cell provided in an embodiment of this application.

[0017] Figure 2 This is a cross-sectional schematic diagram of a negative electrode sheet provided in an embodiment of this application.

[0018] Explanation of main component symbols

[0019] 100 cells

[0020] Electrode assembly 20

[0021] Casing 10

[0022] Earl 30

[0023] Negative electrode plate 21

[0024] Current collector 211

[0025] First active material layer 212

[0026] Second active material layer 213 Detailed Implementation

[0027] 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.

[0028] 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 thereby convey this application thoroughly and in detail to those skilled in the art.

[0029] 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.

[0030] Furthermore, when describing the implementation of this application, the word "may" refers to "one or more implementations of this application".

[0031] 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.

[0032] 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.

[0033] Please see Figure 1 This application provides a battery cell 100, including a housing 10, an electrode assembly 20, and tabs 30. The electrode assembly 20 is housed within the housing 10. The tabs 30 are connected to the electrode assembly 20 and extend from one side of the housing 10 to connect to external components. There are two tabs 30, one being a positive tab and the other a negative tab. In this embodiment, the housing 10 is a packaging bag obtained by encapsulating with a 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.

[0034] The electrode assembly 20 includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The electrode assembly 20 may be formed by stacking and winding the positive electrode, the separator, and the negative electrode, or the electrode assembly 20 may be formed by alternately stacking the positive electrode, the separator, and the negative electrode; this application does not impose any limitations.

[0035] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on the positive current collector. In some embodiments, the positive active material layer 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 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 active material layer may further include a conductive agent and a binder. The conductive agent in the positive active material layer may include at least one of conductive carbon black, Ketjen black, graphene, carbon nanotubes, or carbon fibers. The binder in the positive active material layer 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 active material layer may be made of any other suitable material.

[0036] The separator is used to prevent direct contact between the positive and negative electrode plates, thereby reducing the risk of short circuits caused by contact between them. The substrate of the separator 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 applied to the surface of the separator substrate.

[0037] 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.

[0038] Please see Figure 2The negative electrode 21 includes a current collector 211, a first active material layer 212, and a second active material layer 213. The first active material layer 212 is disposed on the surface of the current collector 211, and the second active material layer 213 is disposed on the surface of the first active material layer 212 facing away from the current collector 211. The current collector 211 has the function of collecting current, and its material may include at least one of Ni, Ti, Cu, Ag, Au, Pt, Fe, Al, and combinations thereof. In this embodiment, the first active material layer 212 is disposed on two opposite surfaces of the current collector 211, and the second active material layer 213 is disposed on each surface of the first active material layer 212 facing away from the current collector 211. In other embodiments, the first active material layer 212 may be disposed on only one surface of the current collector 211.

[0039] Both the first active material layer 212 and the second active material layer 213 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.

[0040] The binder for the first active material layer 212 includes polyacrylic acid (PAA) and sodium carboxymethyl cellulose (CMC). The binder for the second active material layer 213 includes styrene-butadiene rubber (SBR) 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 to provide high adhesion. The hydrogen bonds of sodium carboxymethyl cellulose (CMC) have self-healing properties, effectively accommodating volume expansion during cycling. Styrene-butadiene rubber (SBR) has good toughness, high elongation, and good kinetic properties. The configuration of the binders for the first active material layer 212 and the second active material layer 213 balances the kinetic performance and cycle expansion performance of the cell 100.

[0041] The silicon-based material content in the first active material layer 212 and the second active material layer 213 can be the same or different. When the silicon-based material content is the same, the second active material layer 213, including SBR and CMC, has good kinetic performance and will not cause lithium plating. The first active material layer 212, including PAA and CMC, has good adhesion, firmly adhering to the current collector 211, and its expansion performance is better than that of the second active material layer 213, preventing electrode demolding. Because SBR itself has poor adhesion, when the silicon-based material content is the same, more CMC needs to be added to the second active material layer 213 to ensure the adhesion between the second active material layer 213 and the first active material layer 212. Moreover, the PAA in the first active material layer 212 has good adhesion, allowing for a reduction in the amount of CMC used in the first active material layer 212. Therefore, when the silicon-based material content is the same, the CMC content in the second active material layer 213 is greater than the CMC content in the first active material layer 212. In some embodiments, the difference between the CMC content of the first active material layer 212 and the CMC content of the second active material layer 213 ranges from 0.1 wt% to 3 wt%, which allows the cell to simultaneously possess excellent cycle expansion performance and kinetic performance. Preferably, the difference between the CMC content of the first active material layer 212 and the CMC content of the second active material layer 213 ranges from 0.1 wt% to 0.5 wt%, which further enhances cycle stability and improves kinetic performance.

[0042] In some embodiments, the CMC content of the first active material layer 212 and the CMC content of the second active material layer 213 are both 0.1 wt% to 10 wt%, which allows the cell to simultaneously possess excellent cycle expansion performance and kinetic performance. Preferably, the CMC content of the first active material layer 212 is 0.1 wt% to 10 wt%, and the CMC content of the second active material layer 213 is 0.1 wt% to 5 wt%, which can further improve cycle stability and enhance kinetic performance.

[0043] In some embodiments, the PAA content of the first active material layer 212 and the SBR content of the second active material layer 213 are both 1wt% to 20wt%, which allows the cell to simultaneously possess excellent cycle expansion performance and kinetic performance. Preferably, the PAA content of the first active material layer 212 is 1wt%-20wt%, and the SBR content of the second active material layer 213 is 1wt%-10wt%, which can further improve cycle stability and enhance kinetic performance.

[0044] In some embodiments, the silicon-based material content in the first active material layer 212 is greater than that in the second active material layer 213. The second active material layer 213 has weaker adhesion, and this, combined with a lower silicon-based material content, ensures that the expansion of the second active material layer 213 is not excessive, while simultaneously suppressing the expansion of the first active material layer 212. The first active material layer 212 has stronger adhesion, and this, combined with a higher silicon-based material content, minimizes expansion while simultaneously increasing energy density. Thus, a relatively balanced adhesion and expansion force between the first and second active material layers 212 and 213 can be ensured, guaranteeing the overall deformation of the battery cell and resulting in better dynamic performance.

[0045] In some embodiments, both the first active material layer 212 and the second active material layer 213 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.

[0046] In some embodiments, in the first active material layer 212, 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 213, 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 battery cell to simultaneously possess excellent cycle expansion performance and dynamic performance. Preferably, when the content of silicon-based material in the first active material layer 212 is greater than the content of silicon-based material in the second active material layer 213, the mass of silicon-based material in the second active material layer 213 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 first active material layer 212, the mass of 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, which can further improve cycle stability and improve kinetic performance.

[0047] In some embodiments, both the first active material layer 212 and the second active material layer 213 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.

[0048] In some embodiments, the conductive agent content in both the first active material layer 212 and the second active material layer 213 is 0.1 wt% to 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 212 is 0.1 wt% to 10 wt%, and the conductive agent content in the second active material layer 213 is 0.1 wt% to 5 wt%, which further enhances cycle stability and improves kinetic performance.

[0049] 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.

[0050] The following are some specific embodiments and comparative examples to better illustrate this application, wherein a lithium-ion battery is used as an example.

[0051] Example 1

[0052] 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 .

[0053] 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, 81 wt% graphite, 0.5 wt% conductive carbon black, 3 wt% PAA, and 0.5 wt% CMC. In the first negative electrode active material, silicon accounts for 16% of the total mass of silicon and graphite, and graphite accounts for 84% of the total mass of silicon and graphite, i.e., silicon accounts for 16% and graphite accounts for 84%. The second negative electrode active material comprises 15 wt% silicon, 81 wt% graphite, 0.5 wt% conductive carbon black, 2.8 wt% SBR, and 0.7 wt% CMC. In the second negative electrode active material, silicon accounts for 16% of the total mass of silicon and graphite, and graphite accounts for 84% of the total mass of silicon and graphite, i.e., silicon accounts for 16% and graphite accounts for 84%. The difference in CMC content between the first and second negative electrode active materials is 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 the current collector to obtain the first active material layer. Then, the second active material layer slurry is coated onto the first active material layer to obtain the second active material layer. After drying, cold pressing, and cutting, the negative electrode sheet is obtained. The coating weight of both the first and second active material layers is 5 mg / cm³. 2 The compacted density is 1.6 g / cm³. 3 .

[0054] Preparation of the separator membrane: Polyethylene film was selected as the separator membrane.

[0055] 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.

[0056] Lithium-ion battery fabrication: The positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to provide insulation. The electrode assembly is then wound to obtain the electrode assembly. The electrode assembly is placed in an outer aluminum-plastic film package, and after dehydration at 80°C, the electrolyte is injected and the battery is sealed. Following formation, degassing, sealing, and trimming processes, the lithium-ion battery is obtained.

[0057] Examples 2-8

[0058] Except for the different compositions of the first and second negative electrode active materials, the rest are the same as in Example 1. The parameters of Examples 1-8 are shown in Table 1.

[0059] Comparative Example 1

[0060] The lithium-ion battery was prepared in a manner largely similar to that in Example 1, except that the negative electrode film layer consisted only of a second active material layer containing SBR and CMC, and the coating weight of the second active material layer was 10 mg / cm³. 2 That is, the coating thickness of the second active material layer is equal to the sum of the coating thickness of the first active material layer and the coating thickness of the second active material layer in Example 1.

[0061] Comparative Example 2

[0062] 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 PAA and CMC, and the coating weight of the first active material layer was 10 mg / cm³. 2 That is, the coating thickness of the first active material layer is equal to the sum of the coating thickness of the first active material layer and the coating thickness of the second active material layer in Example 1.

[0063] The relevant parameters for Examples 1-9 are shown in Table 1.

[0064] Table 1

[0065]

[0066] In this context, " / " represents nothing.

[0067] The lithium-ion batteries prepared in Examples 1-9 and Comparative Examples 1 and 2 were subjected to the following tests, and the test results are shown in Table 2.

[0068] Discharge temperature rise test:

[0069] 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 left to stand for 10 minutes; then the battery was discharged to 2.0V at 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.

[0070] Cyclic performance test:

[0071] At 25℃, the lithium-ion battery is 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 is discharged to 2.0V at a constant current of 4.0C, and allowed to stand for 15 minutes. This constitutes one cycle. This cycle is repeated 500 times, and the initial capacity Q0 is recorded. The capacity of the 500th discharge cycle is taken as the battery capacity Q2. The capacity retention rate is calculated as follows: Capacity retention rate (%) = Q2 / Q0 × 100%.

[0072] Cyclic expansion rate test:

[0073] The lithium-ion battery is placed in an environment of 25°C, and the battery voltage is adjusted to 3.60V, i.e., in a half-charge state. The initial thickness of the battery is measured and denoted as T0. The half-charge state is not limited to 50% state of charge; it only needs to satisfy 30% < state of charge < 50%. After 500 cycles, the PPG (Panel Pressure Gap) thickness of the battery is measured in a fully charged state (100% state of charge) and denoted as T2. Cyclic expansion rate (%) = T2 / T0 × 100%.

[0074] Lithium deposition test on negative electrode:

[0075] At 25℃, the lithium-ion battery was charged to 4.30V with a constant current of X (X=1,2,3)C, then charged to 0.05C with a constant voltage of 4.30V, and left to stand for 5 minutes; then discharged to 2.0V with a constant current of 1C, and left to stand for 5 minutes. This constitutes one cycle, and the cycle was repeated 10 times. After that, the battery was disassembled in a fully charged state to obtain the negative electrode. If any part of the negative electrode is found to be greater than or equal to 2mm... 2 The lithium deposition in the region is determined to be lithium deposition on the negative electrode, and the unit is C.

[0076] Table 2

[0077] Discharge temperature rise / ℃ Lithium plating level Cycle retention rate Cyclic expansion rate Example 1 40 3C 80％ 10％ Example 2 40 3C 78％ 11.5％ Example 3 40 3C 79％ 11％ Example 4 40.2 3.3C 80％ 10％ Example 5 40.5 3.5C 80％ 10％ Example 6 42 4C 80％ 10％ Example 7 42.5 4.5C 80％ 10％ Example 8 41 3C 78％ 13％ Example 9 40 3C 79％ 14％ Comparative Example 1 40 2C 77％ 13％ Comparative Example 2 43 1.5C 75％ 12％

[0078] As shown in Table 2, the lithium-ion batteries prepared in Examples 1-9 exhibit good discharge temperature rise (discharge temperature rise of 40℃~43℃), lithium plating performance (lithium plating level of 3C~5C), and capacity retention performance (cycle retention rate of 78%~80%). Furthermore, they effectively suppress negative electrode expansion (cycle expansion rate of 10%~14%), thus simultaneously achieving excellent kinetic performance and cycle expansion performance. A higher lithium plating level indicates a lower degree of lithium plating at the same charging rate; for example, Example 4 exhibits the lowest degree of lithium plating, while Comparative Example 2 shows the highest degree.

[0079] As shown in Table 2, by comparing Examples 1-9 with Comparative Examples 1-2, it can be seen that configuring the negative electrode sheet into a bilayer structure consisting of a first active material layer containing PAA and CMC and a second active material layer containing SBR and CMC can improve the lithium plating level of the battery, improve the cycle retention rate, reduce the cycle expansion rate, and also reduce the discharge temperature rise (compared to Comparative Example 2).

[0080] As can be seen from the comparison of Examples 8 and 9 with Comparative Examples 1-2, when the silicon content in the negative electrode is relatively high, the scheme of the embodiments of this application can also improve the lithium plating level and cycle retention rate of the battery.

[0081] As illustrated by the comparison in Examples 1-7, when the silicon content is the same, as the CMC difference increases, the discharge temperature rise increases, the lithium plating level increases, the cycle retention rate increases, and the cycle expansion rate decreases. Specifically, when the CMC difference is 0-0.1 wt%, the discharge temperature rise is maintained at 40°C, the lithium plating level is maintained at 3°C, 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 0.1-0.5 wt%, as the CMC difference increases, the discharge temperature rise increases, the lithium plating level increases, the cycle retention rate increases to a maximum at a CMC difference of 0.2 and then remains constant, and the cycle expansion rate decreases to a minimum at a CMC difference of 0.2 and then remains constant. When the CMC difference is greater than 0.5 wt%, as the CMC difference increases, the discharge temperature rise increases, the lithium plating level increases, the cycle retention rate remains at 80%, and the cycle expansion rate remains at 10%. Furthermore, when the CMC difference is equal to 3 wt%, the discharge temperature rise reaches 42°C.

[0082] 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 is greater than that of other examples, but its lithium plating level is better.

[0083] The comparison of Examples 1, 8, and 9 shows that when the silicon content of the first active material layer and the silicon content of the second active material layer are the same, the obtained kinetic performance and cyclic expansion performance are superior.

[0084] 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 a negative electrode sheet, characterized in that, The negative electrode sheet includes: current collector; A first active material layer is disposed on at least one surface of the current collector; and A second active material layer is disposed on the surface of the first active material layer away from the current collector. Both the first and second active material layers include a first active substance and a binder. The first active substance includes a silicon-based material, and the binder of the first active material layer includes polyacrylic acid (PAA) and sodium carboxymethyl cellulose (CMC). The binder of the second active material layer includes styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC). The content of silicon-based material in the first and second active material layers is equal, and the content of CMC in the first and second active material layers is less than the content of CMC in the second active material layer. The difference between the content of CMC in the first and second active material layers ranges from 0.1 wt% to 3 wt%.

2. The battery cell as described in claim 1, 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%.

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

4. 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.

5. 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.

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 second active substance, which is at least one of artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon, or hard carbon.

7. An electrical appliance, characterized in that, Includes the battery cell as described in any one of claims 1 to 6.

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