Battery cell and electric device comprising same

Abstract

This application discloses a battery cell and an electrical device including the battery cell. The battery cell includes an electrode assembly. The electrode assembly includes multiple layers of negative electrode sheets, multiple layers of positive electrode sheets, and multiple layers of separator films. The multiple layers of negative electrode sheets include a first portion and a second portion, wherein the first portion is closer to the center of the electrode assembly than the second portion in the thickness direction of the battery cell. The negative electrode sheet of the first portion includes a first current collector and a first active material layer disposed on at least one surface of the first current collector, and the negative electrode sheet of the second portion includes a second current collector and a second active material layer disposed on at least one surface of the second 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 of the first active material layer includes styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC), and the binder of the second active material layer includes polyacrylic acid (PAA) 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 undergoes significant volume changes during lithium-ion insertion and extraction, leading to overall expansion and deformation of the battery cell. Furthermore, lithium-ion batteries generate considerable heat during high-rate charge and discharge, and the inconsistent heat dissipation conditions inside and outside the cell result in a large temperature difference between the two surfaces. Summary of the Invention

[0003] One object of this application is to provide a battery cell that can balance expansion deformation and internal and external temperature differences, and an electrical device including the battery cell.

[0004] This application provides a battery cell including an electrode assembly. The electrode assembly includes multiple layers of negative electrode sheets, multiple layers of positive electrode sheets, and multiple layers of separator films, with separator films disposed between adjacent negative and positive electrode sheets. The multiple layers of negative electrode sheets include a first portion and a second portion, wherein the first portion is closer to the center of the electrode assembly than the second portion in the thickness direction of the battery cell. The negative electrode sheet of the first portion includes a first current collector and a first active material layer disposed on at least one surface of the first current collector, and the negative electrode sheet of the second portion includes a second current collector and a second active material layer disposed on at least one surface of the second 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 of the first active material layer includes styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC), and the binder of the second active material layer includes polyacrylic acid (PAA) and sodium carboxymethyl cellulose (CMC).

[0005] The battery cell provided in this application has an inner negative electrode sheet comprising a first active material layer containing SBR and CMC, and an outer negative electrode sheet comprising a second active material layer containing PAA and CMC. Since PAA contains a high carboxyl content, it can form strong hydrogen bonds with silicon-based materials, meaning the outer layer has high adhesion, which strengthens the binding force on the inner layer of the battery cell and improves the expansion and deformation of the inner negative electrode sheet. Furthermore, the inner negative electrode sheet has better kinetic performance and generates less heat, thus improving the poor heat dissipation inside the battery cell and balancing the expansion and deformation of the battery cell and the temperature difference between the inside and outside.

[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 the same, the first active material layer located on the inner side / inner ring has better kinetic performance and generates less heat, which can reduce the problem of excessive temperature rise caused by poor internal heat dissipation; the second active material layer located on the outer side / outer ring has poorer kinetic performance and generates more heat, but the heat dissipation of the outer side / outer ring is better. At the same time, the second active material layer located on the outer side / outer ring has stronger adhesive force and its expansion performance is better than that of the first active material layer located on the inner side / inner ring, thereby achieving a strong binding force on the outer layer.

[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 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 can further improve the expansion deformation and internal and external temperature difference of the battery cell.

[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 the expansion deformation and internal and external temperature difference of the battery cell.

[0010] According to some embodiments of this application, the content of silicon-based material in the first active material layer is less than the content of silicon-based active material in the second active material layer. The first active material layer has weaker adhesion, coupled with a lower silicon-based material content; while the second active material layer has stronger adhesion, coupled with a higher silicon-based material content. This ensures a more balanced adhesion and expansion force between the inside and outside of the cell, ensuring the overall deformation of the cell. At the same time, the design dynamics of the lower silicon content on the inner side / inner ring will also be better.

[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, the electrode assembly is a wound structure, with a first part located in the inner ring of the electrode assembly and a second part located in the outer ring of the electrode assembly along the winding direction of the electrode assembly; or, the electrode assembly is a stacked structure, with a first part located in the inner side of the electrode assembly and a second part located in the outer side of the electrode assembly in the thickness direction of the electrode assembly.

[0013] According to some embodiments of this application, the number of layers of the negative electrode sheet in the first part is N1, and the number of layers of the negative electrode sheet in the second part is N2, where 1 / 5 ≤ N1 / N2 ≤ 1, N1 ≥ 1, and N2 ≥ 1. The number of layers of the negative electrode sheet located on the inner side / inner ring, including the first active material layer, is less than or equal to the number of layers of the negative electrode sheet located on the outer side / outer ring, including the second active material layer. This results in a stronger binding force between the negative electrode sheet located on the outer side / outer ring and the negative electrode sheet located on the inner side / inner ring, and a more significant improvement in the expansion and deformation of the negative electrode sheet located on the inner side / inner ring, including the first active material layer.

[0014] According to some embodiments of this application, 1 / 2≤N1 / N2≤1, so that the number of negative electrode layers including the first active material layer on the inner side / inner ring is not too low, thereby ensuring that the cell has low expansion deformation while also ensuring that the cell generates less heat inside.

[0015] 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.

[0016] 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.

[0017] A second aspect of this application also provides an electrical device including the aforementioned battery cell. Attached Figure Description

[0018] 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:

[0019] Figure 1 This is a schematic diagram of the structure of a battery cell provided in an embodiment of this application.

[0020] Figure 2 This is a cross-sectional schematic diagram of an electrode assembly provided in an embodiment of this application.

[0021] Figure 3 This is a top view of a negative electrode sheet provided in an embodiment of this application.

[0022] Figure 4 for Figure 3 The diagram shows a cross-sectional view of the negative electrode sheet.

[0023] Explanation of main component symbols

[0024] 100 cells

[0025] Electrode assembly 20

[0026] Casing 10

[0027] Earl 30

[0028] Positive electrode plate 21

[0029] Negative electrode plate 23

[0030] Separator 22

[0031] Positive current collector 211

[0032] Positive electrode active material layer 212

[0033] Part 1, 23a

[0034] Part 23b

[0035] First current collector 231

[0036] First active material layer 232

[0037] Second collector fluid 233

[0038] Second active material layer 234 Detailed Implementation

[0039] 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.

[0040] 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.

[0041] 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.

[0042] Furthermore, when describing the implementation of this application, the word "may" refers to "one or more implementations of this application".

[0043] 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.

[0044] 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.

[0045] 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.

[0046] Please see Figure 2 The electrode assembly 20 includes a positive electrode 21, a negative electrode 23, and a separator 22 disposed between the positive electrode 21 and the negative electrode 23. The electrode assembly 20 has a stacked structure, formed by alternating layers of positive electrode 21, separator 22, and negative electrode 23. Specifically, along the thickness direction H of the electrode assembly 20, the electrode assembly 20 includes multiple layers of positive electrode 21, multiple layers of negative electrode 23, and multiple layers of separator 22. A separator 22 is disposed between adjacent positive electrode 21 and negative electrode 23.

[0047] The positive electrode 21 includes a positive current collector 211 and a positive active material layer 212 disposed on the surface of the positive current collector 211. The positive current collector 211 may include at least one of Ni, Ti, Cu, Ag, Au, Pt, Fe, Al, and combinations thereof. The positive active material layer 212 may include 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.

[0048] The separator 22 is used to prevent direct contact between the positive electrode 21 and the negative electrode 23, thereby reducing the risk of short circuits between them. The substrate of the separator 22 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 substrate of the separator 22. The separator may be of a type commonly used in the prior art.

[0049] 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.

[0050] Please see Figure 2 In the thickness direction H of the electrode assembly 20, the multilayer negative electrode sheet 23 includes a first portion 23a and a second portion 23b, with the first portion 23a being closer to the center of the electrode assembly 20 than the second portion 23b. Specifically, in the thickness direction H of the electrode assembly 20, the first portion 23a is located on the inner side of the electrode assembly 20, and the second portion 23b is located on the outer side of the electrode assembly 20. When the electrode assembly 20 has a stacked structure, the negative electrode sheet 23 of the first portion 23a and the negative electrode sheet 23 of the second portion 23b are separated from each other and are not connected.

[0051] In some embodiments, the electrode assembly 20 is a wound structure, formed by stacking and winding a positive electrode 21, a separator 22, and a negative electrode 23. Along the winding direction of the electrode assembly 20, a first portion 23a is located in the inner ring of the electrode assembly 20, and a second portion 23b is located in the outer ring of the electrode assembly 20. See also... Figure 3 and Figure 4 The negative electrode plate 23 of the first part 23a and the negative electrode plate 23 of the second part 23b are connected as one unit.

[0052] Please see Figure 2 and Figure 4 The negative electrode 23 of the first portion 23a includes a first current collector 231 and a first active material layer 232 disposed on the surface of the first current collector 231. In this embodiment, the first active material layer 232 is disposed on two opposite surfaces of the first current collector 231. In other embodiments, the first active material layer 232 may be disposed on only one surface of the first current collector 231. The first current collector 231 may include at least one of Ni, Ti, Cu, Ag, Au, Pt, Fe, Al, and combinations thereof.

[0053] The negative electrode 23 of the second part 23b includes a second current collector 233 and a second active material layer 234 disposed on the surface of the second current collector 233. In this embodiment, the second active material layer 234 is disposed on two opposite surfaces of the second current collector 233. In other embodiments, the second active material layer 234 may be disposed on only one surface of the second current collector 233. The second current collector 233 may include at least one of Ni, Ti, Cu, Ag, Au, Pt, Fe, Al, and combinations thereof.

[0054] Both the first active material layer 232 and the second active material layer 234 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.

[0055] The binders for the first active material layer 232 include styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC). The binders for the second active material layer 234 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. The hydrogen bonds of sodium carboxymethyl cellulose (CMC) have a self-healing function, effectively adapting to volume expansion during cycling. SBR has good toughness, high elongation, and good kinetic properties. By configuring the first active material layer 232 located in the inner layer and the second active material layer 234 located in the outer layer, the expansion deformation and internal and external temperature difference of the cell 100 can be balanced.

[0056] The silicon-based material content in the first active material layer 232 and the second active material layer 234 can be the same or different. When the silicon-based material content is the same, the first active material layer 232 located on the inner side / inner ring has better kinetic performance and generates less heat, which can reduce the problem of excessive temperature rise caused by poor internal heat dissipation; the second active material layer 234 located on the outer side / outer ring has poorer kinetic performance and generates more heat, but the heat dissipation of the outer side / outer ring is better. At the same time, the second active material layer 234 located on the outer side / outer ring has stronger adhesive force and its expansion performance is better than that of the first active material layer 232 located on the inner side / inner ring, thereby achieving a strong binding force on the outer layer.

[0057] When the silicon-based material content is the same, because the SBR itself has poor adhesion, more CMC needs to be added to the first active material layer 232 to ensure the adhesion between the first active material layer 232 and the first current collector 231; moreover, the PAA of the second active material layer 234 has better adhesion, allowing for a reduction in the amount of CMC used in the second active material layer 234. Therefore, when the silicon-based material content is the same, the CMC content in the first active material layer 232 is greater than the CMC content in the second active material layer 234. In some embodiments, the difference between the CMC content of the first active material layer 232 and the CMC content of the second active material layer 234 ranges from 0.1wt% to 3wt%, which can improve the expansion deformation and internal and external temperature difference of the battery cell. Preferably, the difference between the CMC content of the first active material layer 232 and the CMC content of the second active material layer 234 ranges from 0.1wt% to 0.5wt%, which can further improve the expansion deformation and internal and external temperature difference of the battery cell.

[0058] In some embodiments, the CMC content of the first active material layer 232 and the CMC content of the second active material layer 234 are both 0.1wt% to 10wt%, which can improve the expansion deformation and internal and external temperature difference of the battery cell. Preferably, the CMC content of the first active material layer 232 is 0.1wt% to 5wt%, and the CMC content of the second active material layer 234 is 0.1wt% to 10wt%, which can further improve the expansion deformation and internal and external temperature difference of the battery cell.

[0059] In some embodiments, the SBR content of the first active material layer 232 and the PAA content of the second active material layer 234 are both 1wt% to 20wt%, which can improve the expansion deformation and internal and external temperature difference of the battery cell. Preferably, the SBR content of the first active material layer 232 is 1wt% to 10wt%, and the PAA content of the second active material layer 234 is 1wt% to 20wt%.

[0060] In some embodiments, the content of silicon-based material in the first active material layer 232 is less than the content of silicon-based material in the second active material layer 234. The first active material layer 232 has weaker adhesive force, coupled with a lower content of silicon-based material; while the second active material layer 234 has stronger adhesive force, coupled with a higher content of silicon-based material. This ensures a relatively balanced adhesive force and expansion force inside and outside the cell 100, ensuring the overall deformation of the cell 100. At the same time, the design dynamics of the low silicon content on the inner side / inner ring are also better.

[0061] In some embodiments, both the first active material layer 232 and the second active material layer 234 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.

[0062] In some embodiments, in the first active material layer 232, 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 234, 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 improving the expansion and deformation of the battery cell and the internal and external temperature difference. Preferably, in the first active material layer 232, 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 234, 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 improving the expansion and deformation of the battery cell and the internal and external temperature difference.

[0063] In some embodiments, both the first active material layer 232 and the second active material layer 234 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. In some embodiments, the content of the conductive agent in both the first active material layer 232 and the second active material layer 234 is 0.1 wt% to 10 wt%, which can improve the expansion deformation and internal / external temperature difference of the battery cell. Preferably, the content of the conductive agent in the first active material layer 232 is 0.1 wt% to 5 wt%, and the content of the conductive agent in the second active material layer 234 is 0.1 wt% to 10 wt%, which can further improve the expansion deformation and internal / external temperature difference of the battery cell.

[0064] In some embodiments, the number of layers of the negative electrode 23 in the first part 23a is N1, and the number of layers of the negative electrode 23 in the second part 23b is N2. Wherein, 1 / 5 ≤ N1 / N2 ≤ 1, N1 ≥ 1, and N2 ≥ 1. The number of layers of the negative electrode 23 located on the inner side / inner ring, including the first active material layer 232, is less than or equal to the number of layers of the negative electrode 23 located on the outer side / outer ring, including the second active material layer 234. This results in a stronger binding force of the negative electrode 23 located on the outer side / outer ring on the negative electrode 23 located on the inner side / inner ring, and a more significant improvement in the expansion and deformation of the negative electrode 23 located on the inner side / inner ring, including the first active material layer 232.

[0065] In some embodiments, 1 / 2≤N1 / N2≤1, so that the number of layers of the negative electrode 23 including the first active material layer 232 on the inner side / inner ring is not too low, thereby ensuring that the cell 100 has low expansion deformation while also ensuring that the cell 100 generates less heat inside.

[0066] 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.

[0067] The following are some specific embodiments and comparative examples to better illustrate this application, wherein a lithium-ion battery is used as an example.

[0068] Example 1

[0069] 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 .

[0070] 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, 2.8 wt% SBR, and 0.7 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, 3 wt% PAA, and 0.5 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 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 the negative electrode current collector to obtain the first active material layer. Simultaneously, the second active material layer slurry is coated onto another negative electrode current collector to obtain the second active material layer. After drying, cold pressing, and cutting, negative electrode sheets including the first and second active material layers are obtained. The coating weight of both the first and second active material layers is 10 mg / cm³. 2 The compacted density is 1.6 g / cm³. 3 .

[0071] Preparation of the separator membrane: Polyethylene film was selected as the separator membrane.

[0072] 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.

[0073] Lithium-ion battery fabrication: A positive electrode sheet, a separator, a negative electrode sheet including a first active material layer, and a negative electrode sheet including a second active material layer are stacked sequentially to obtain an electrode assembly with a stacked structure. The electrode assembly is placed in an outer packaging aluminum-plastic film, and after dehydration at 80°C, the electrolyte is injected and the assembly is sealed. The lithium-ion battery is obtained through processes such as formation, degassing, sealing, and edge trimming. The negative electrode sheet has a total of 16 layers, with 8 layers comprising the first portion of the first active material layer and 8 layers comprising the second portion of the second active material layer.

[0074] Examples 2-9

[0075] 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 1-9 are shown in Table 1.

[0076] Table 1

[0077]

[0078] In this context, " / " represents nothing.

[0079] Examples 10-15

[0080] Except for the number of layers of the negative electrode sheet in the first part and the number of layers of the negative electrode sheet in the second part, the rest are the same as in Example 1. The relevant parameters of Examples 1 and 10-15 are shown in Table 2.

[0081] Table 2

[0082]

[0083] Comparative Example 1

[0084] The lithium-ion battery was prepared in a manner similar to that in Example 1, except that the active material layers of the 16-layer negative electrode were all first active material layers containing SBR and CMC, but did not include second active material layers containing PAA and CMC, i.e., there was only one type of active material layer.

[0085] Comparative Example 2

[0086] The lithium-ion battery was prepared in a manner similar to that in Example 1, except that the active material layers of the 16-layer negative electrode were all second active material layers containing PAA and CMC, and did not include the first active material layer containing SBR and CMC, i.e., there was only one type of active material layer.

[0087] The lithium-ion batteries prepared in Examples 1-15 and Comparative Examples 1 and 2 were subjected to the following tests, and the test results are shown in Table 3.

[0088] Discharge temperature rise and temperature difference test of lithium-ion batteries:

[0089] During the stacking process, the temperature sensing wire is placed between the innermost and outermost diagonal lines of the electrode assembly to facilitate subsequent measurement of the internal and external temperature rise of the battery.

[0090] 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 4.3V, and left to stand for 10 minutes; then discharged to 2.0V at a constant current of 4.0C, and left to stand for 15 minutes. A temperature sensor was connected to a temperature testing instrument to record the temperature rise of the battery during the charging and discharging process.

[0091] Cyclic performance test:

[0092] 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 4.3V, and allowed to stand for 10 minutes. Next, 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 discharge capacity of the 500th cycle is taken as the battery capacity Q2. The capacity retention rate is calculated as follows: Capacity retention rate (%) = Q2 / Q0 × 100%.

[0093] Cyclic expansion rate test:

[0094] The lithium-ion battery is placed in an environment of 25℃, and the battery voltage is adjusted to 3.60V, i.e., in a half-charge state. The initial thickness of the cell is measured and denoted as T0. The half-charge state is not limited to 50% state of charge; it only needs to meet the condition 30% < state of charge < 50%. After 500 cycles, the PPG (Panel Pressure Gap) thickness of the fully charged cell is measured and denoted as T2. Cyclic expansion rate (%) = T2 / T0 × 100%.

[0095] Table 3

[0096] External temperature rise during discharge / °C Discharge temperature difference / ℃ Cycle retention rate Cyclic expansion rate Example 1 40 3 80％ 10％ Example 2 40 3 78％ 11.5％ Example 3 40 3 79％ 11％ Example 4 40.2 3.3 80％ 10％ Example 5 40.5 3.5 80％ 10％ Example 6 42 4 80％ 10％ Example 7 42.5 4.5 80％ 10％ Example 8 41 3 78％ 13％ Example 9 42 4 72％ 15％ Example 10 41 4 80％ 10％ Example 11 40.5 3.5 80％ 10％ Example 12 42 4.5 80％ 10％ Example 13 40 3 79％ 11％ Example 14 40.3 3.2 80％ 10％ Example 15 40.7 3.7 80％ 10％ Comparative Example 1 40 5 77％ 13％ Comparative Example 2 43 5 75％ 12％

[0097] As can be seen from Table 3, the lithium-ion batteries prepared in Examples 1-15 have good discharge temperature rise (discharge temperature rise of 40℃~43℃), discharge temperature difference (discharge temperature difference of 3℃~5℃) and capacity retention performance (cycle retention rate of 72%~80%), and can effectively suppress the expansion of the negative electrode (cycle expansion rate of 10%~15%).

[0098] As shown in Table 3, by comparing Examples 1-7, Examples 10-15 and Comparative Examples 1-2, it can be seen that placing a negative electrode sheet containing a first active material layer of SBR and CMC in the inner layer of the electrode assembly and placing a negative electrode sheet containing a second active material layer of PAA and CMC in the outer layer of the electrode assembly can reduce the discharge temperature difference of the battery, improve its cycle retention rate and reduce its cycle expansion rate.

[0099] 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 solution of the present application can also reduce the discharge temperature difference of the battery.

[0100] The comparison of Examples 1-7 shows that when the silicon content is the same, as the CMC difference increases, the discharge temperature rise increases, the discharge temperature difference 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 discharge temperature difference 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%, the discharge temperature rise and the discharge temperature difference both increase with the increase of the CMC difference, the cycle retention rate reaches its maximum when the CMC difference reaches 0.5 wt% and then remains unchanged, and the cycle expansion rate reaches its minimum when the CMC difference reaches 0.5 wt% and then remains unchanged; when the CMC difference is greater than 0.5 wt%, the discharge temperature rise and the discharge temperature difference both increase with the increase of the CMC difference, the cycle retention rate is maintained at 80%, and the cycle expansion rate is maintained at 10%; and when the CMC difference is equal to 3 wt%, the discharge temperature rise reaches 42°C.

[0101] 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 cyclic expansion rate is greater than that of other examples; when the CMC difference is too large (Example 7), its discharge temperature rise and discharge temperature difference are greater than those of other examples.

[0102] As illustrated by the comparisons in Examples 1 and 10-15, as the ratio N1 / N2 of the number of layers in the first negative electrode sheet and the second negative electrode sheet increases, the discharge temperature rise and discharge temperature difference decrease. When 1 / 5 ≤ N1 / N2 ≤ 1, the cycle retention rate remains at 80%, the cycle expansion rate remains at 10%, and there are good discharge temperature rise and discharge temperature difference. When 1 / 2 ≤ N1 / N2 ≤ 1, the discharge temperature rise is approximately maintained at 40°C, and the discharge temperature difference is approximately maintained at 3°C. When 0 < N1 / N2 < 1 / 5, the discharge temperature rise is 41°C to 42°C, and the discharge temperature difference is 4°C to 5°C. When N1 / N2 > 1, the cycle retention rate and cycle expansion rate increase slightly with the increase of N1 / N2.

[0103] 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. An electric chip comprising an electrode assembly including a plurality of negative electrode sheets, a plurality of positive electrode sheets, and a plurality of separator films provided between adjacent ones of the negative electrode sheets and the positive electrode sheets, characterized by, The multi-layer negative electrode sheet comprises a first part and a second part, the first part is closer to the center of the electrode assembly than the second part in the thickness direction of the battery cell; The negative electrode sheet of the first part comprises a first current collector and a first active material layer arranged on at least one surface of the first current collector, and the negative electrode sheet of the second part comprises a second current collector and a second active material layer arranged on at least one surface of the second 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 styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC), the binder of the second active material layer comprises polyacrylic acid (PAA) and sodium carboxymethyl cellulose (CMC), the content of CMC in the first active material layer is greater than the content of CMC in the second active material layer, and the difference between the content of CMC in the first active material layer and the content of CMC in the second active material layer ranges from 0.1wt% to 3wt%.

2. The cell of claim 1, wherein, The content of the silicon-based material in the first active material layer is equal to the content of the silicon-based material in the second active material layer.

3. The cell of claim 1 or 2, wherein The content of CMC in the first active material layer and the content of CMC in the second active material layer both range from 0.1wt% to 10wt%.

4. The cell of claim 1, wherein, The content of the silicon-based material in the first active material layer is less than the content of the silicon-based material in the second active material layer.

5. The cell of claim 1 wherein, The silicon-based material comprises at least one of silicon, a silicon alloy, an oxide of silicon, or a silicon-carbon composite.

6. The cell of claim 1 wherein, The electrode assembly is in a wound structure, and along the winding direction of the electrode assembly, the first part is located at the inner circle of the electrode assembly, and the second part is located at the outer circle of the electrode assembly; or The electrode assembly is in a stacked structure, and in the thickness direction of the electrode assembly, the first part is located at the inner side of the electrode assembly, and the second part is located at the outer side of the electrode assembly.

7. The cell of claim 1 wherein, The number of layers of the negative electrode sheet of the first part is N1, and the number of layers of the negative electrode sheet of the second part is N2, wherein 1 / 5≤N1 / N2≤1, N1≥1, and N2≥1.

8. The cell of claim 7, wherein, 1 / 2≤N1 / N2≤1.

9. The cell of claim 1 wherein, The first active material layer and the second active material layer both further comprise a conductive agent, and the conductive agent comprises at least one of conductive carbon black, Ketjen black, graphene, carbon nanotubes, or carbon fibers.

10. The cell of claim 1 wherein, The first active material layer and the second active material layer both further comprise a second active substance, and the second active substance is at least one of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, or hard carbon.

11. An electrical device, characterized by The battery cell as claimed in any one of claims 1 to 10.

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