Battery cell, negative electrode sheet, battery device, and electric device

Abstract

This application provides a battery cell, a negative electrode sheet, a battery device, and an electrical device. The battery cell includes a wound electrode assembly, which includes a negative electrode sheet. The negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one side of the negative current collector. The negative active layer includes a first negative active layer and a second negative active layer disposed sequentially away from the negative current collector. The first negative active layer includes a first graphite material and optionally a first silicon-based material. The second negative active layer includes a second silicon-based material and a second graphite material. The mass content of silicon in the first negative active layer is denoted as A, and the mass content of silicon in the second negative active layer is denoted as B, where 2.5% ≤ B ≤ 68%, and B > A. When the battery cell is in a 0% SOC state within 50 cycles of charge and discharge, the tensile strength of the negative current collector is ≥ 40 kgf / mm². 2 Elongation at break ≥ 5.0%.

Description

Technical Field

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

[0002] With increasing global emphasis on environmental pollution, the demand for clean energy is growing stronger, leading to a surge in demand for lithium-ion batteries in clean energy storage, electric vehicles, and power tools. Improving the energy density of lithium-ion batteries and developing high-energy-density lithium-ion batteries has become an inevitable trend in their development. Currently, increasing the theoretical specific capacity of the negative electrode active material in lithium-ion batteries is one of the most effective ways to improve energy density. Silicon materials have a theoretical specific capacity as high as 4200 mAh / g, more than 11 times that of graphite-based negative electrodes in current commercial lithium-ion batteries, and are considered the most promising negative electrode material for commercial application to improve the energy density of lithium-ion batteries in the short term.

[0003] However, when pure silicon or high silicon materials are used for the negative electrode in the wound electrode assembly, the expansion of silicon near the current collector layer causes the negative electrode to extend. When the tensile strength and elongation at break of the negative current collector are low, cracks or breaks are likely to occur at the outer corner of the electrode assembly, which may puncture the separator and cause battery safety issues. Moreover, the low elongation at break of the negative current collector also makes it easy for cracks or breaks to occur due to the large corner angle of the inner circle. Summary of the Invention

[0004] This application provides a battery cell, a negative electrode sheet, a battery device, and an electrical device to solve the problem that the negative electrode sheet in a silicon-containing wound electrode assembly is prone to cracking or breakage.

[0005] The first aspect of this application provides a battery cell, including a wound electrode assembly. The electrode assembly includes a negative electrode sheet, which includes a negative current collector and a negative active layer disposed on at least one side of the negative current collector. The negative active layer includes a first negative active layer and a second negative active layer. The first negative active layer is disposed on at least one side of the negative current collector, and the second negative active layer is disposed on the side of the first negative active layer away from the first negative active layer. The first negative active layer includes a first graphite material and optionally a first silicon-based material, and the second negative active layer includes a second silicon-based material and a second graphite material. The mass content of silicon in the first negative active layer is denoted as A, and the mass content of silicon in the second negative active layer is denoted as B, where 2.5% ≤ B ≤ 68%, and B > A. When the battery cell is in a 0% SOC state within 50 cycles of charge and discharge, the tensile strength of the negative current collector is ≥ 40 kgf / mm². 2 Elongation at break ≥ 5.0%.

[0006] This application avoids the expansion of the negative electrode current collector caused by silicon expansion when the second negative electrode active layer with more silicon is in direct contact with the negative electrode current collector. This reduces the expansion loss of the negative electrode current collector due to silicon expansion, thus allowing the negative electrode current collector to maintain more ductility to meet the elongation requirements of the outer negative electrode sheet (corresponding to the outermost two turns of the winding structure), thereby controlling the occurrence of cracks or fissures in the outer negative electrode sheet. Simultaneously, a negative electrode current collector with suitable strength and elongation at break is used, providing sufficient ductility and strength for the expansion of the outer negative electrode sheet, while also providing sufficient ductility for the large-angle bending of the inner negative electrode sheet (corresponding to the innermost two turns of the winding structure). Furthermore, this application controls the mass content of silicon in the second negative electrode active layer, thereby controlling the expansion caused by silicon while utilizing silicon to improve the energy density of the battery cell. Therefore, by combining the silicon content, the aforementioned layered coating method, and the tensile strength and elongation at break of the negative electrode current collector, this application effectively controls the risk of cracking or splitting of the negative electrode sheet caused by silicon expansion in the wound electrode assembly.

[0007] In any embodiment of the first aspect, 5.5% ≤ B ≤ 48%. Further control of the silicon content in the second negative electrode active layer achieves a balanced control of energy density and expansion degree.

[0008] In any embodiment of the first aspect, 2.5% ≤ BA ≤ 68%; optionally 5.5% ≤ BA ≤ 48%, and further optionally 10% ≤ BA ≤ 40%. By controlling the silicon content in the first and second negative electrode active layers within the above range, the volume expansion of the active layer near the current collector can be better controlled, reducing damage caused by the material's expansion of the current collector during charging.

[0009] In any embodiment of the first aspect, 0% ≤ A ≤ 40%, and optionally 0 ≤ A ≤ 20%.

[0010] In any embodiment of the first aspect, the mass content of silicon in the first silicon-based material and the second silicon-based material is independently 30%-70%, optionally 35%-65%. This utilizes the combination of silicon and carbon materials to improve the structural stability of the silicon-based material.

[0011] In any embodiment of the first aspect, the first silicon-based material and the second silicon-based material are each independently selected from one or more of elemental silicon, silicon-oxygen complexes, and silicon-carbon complexes.

[0012] In any embodiment of the first aspect, at least one of the first silicon-based material and the second silicon-based material comprises the silicon-carbon composite.

[0013] In any embodiment of the first aspect, the first silicon-based material and the second silicon-based material each independently comprise the silicon-carbon composite.

[0014] In any embodiment of the first aspect, the first silicon-based material and the second silicon-based material each independently comprise a silicon-carbon composite satisfying one or more of the following characteristics: 1) The silicon-carbon composite includes porous carbon and silicon-containing material located in the pores and on the surface of the porous carbon. Optionally, the porous carbon is hard carbon, and the silicon-containing material may include crystalline silicon. 2) The silicon-carbon composite also includes a carbon-containing coating layer located on the surface of the porous carbon and / or silicon material; 3) The average particle size of the silicon-carbon composite is 2μm-15μm, and can be selected as 7μm-11μm; 4) The powder resistivity of silicon-carbon composite at 8 MPa is 4 Ω·cm - 17 Ω·cm; 5) The BET specific surface area of ​​the silicon-carbon composite is 1.0 m². 2 / g-6.7m 2 / g.

[0015] In any embodiment of the first aspect, when the battery cell is in a 100% SOC state within 50 charge-discharge cycles, the elongation at break of the negative electrode current collector is ≥3.5%.

[0016] In any embodiment of the first aspect, when the battery cell is in a 100% SOC state within 50 cycles of charge and discharge, the elongation at break of the negative electrode sheet is ≥1.5%.

[0017] In any embodiment of the first aspect, the thickness of the negative electrode current collector is 5 μm-10 μm, optionally 6 μm-8 μm.

[0018] In any embodiment of the first aspect, the thickness of the second negative electrode active layer accounts for 10%-90% of the total thickness of the negative electrode active layer, optionally 12%-80%, and further optionally 15%-70%. By distributing the thickness of the two negative electrode active layers, the influence of the silicon-based material on the overall expansion of the negative electrode active layer is further controlled, thereby reducing the risk of elongation loss and cracking of the negative electrode sheet.

[0019] In any embodiment of the first aspect, the first negative electrode active layer further includes a first binder, and the second negative electrode active layer further includes a second binder, wherein the first binder and the second binder each independently include any one or more of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan.

[0020] In any embodiment of the first aspect, the mass content of the first binder in the first negative electrode active layer is less than the mass content of the second binder in the second negative electrode active layer.

[0021] In any embodiment of the first aspect, the mass content of the first binder in the first negative electrode active layer is 0.5%-5%, and more preferably 1.5%-3.5%.

[0022] In any embodiment of the first aspect, the mass content of the second binder in the second negative electrode active layer is 1%-5%, and more preferably 1.5%-4.5%.

[0023] In any embodiment of the first aspect, the first negative electrode active layer further includes a first conductive agent, and the second negative electrode active layer further includes a second conductive agent. The first conductive agent and the second conductive agent each independently include one or more of carbon black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers, or a mixture thereof.

[0024] In any embodiment of the first aspect, the mass content of the first conductive agent in the first negative electrode active layer is 0.05%-1%, and the mass content of the second conductive agent in the second negative electrode active layer is 0.05%-2%.

[0025] In any embodiment of the first aspect, the second conductive agent comprises carbon black and carbon nanotubes, wherein the mass ratio of carbon black to carbon nanotubes is 6:4-9:1, and more preferably 8:2-8.5:1.5. Carbon nanotubes have better conductivity than carbon black, thus the problem of poor intrinsic conductivity of silicon materials can be improved by using carbon nanotubes. Moreover, the linearity of carbon nanotubes can also have a certain restraining effect on the expansion of silicon-based materials, and can also play a role in controlling the elongation of the negative electrode sheet.

[0026] In any embodiment of the first aspect, the negative electrode sheet further includes a base coating layer disposed between the negative current collector and the first negative electrode active layer, the base coating layer including a base conductive agent and a base binder.

[0027] In any embodiment of the first aspect, the base coating has one or more of the following features: Conductive agents used in primer coatings include carbon black; The primer adhesive includes polyvinylidene fluoride; The adhesive content in the primer layer is 70%-90% by mass.

[0028] In any embodiment of the first aspect, the thickness of the base coating is 0.2 μm to 2 μm.

[0029] In any embodiment of the first aspect, the first graphite material and the second graphite material each independently comprise artificial graphite and / or natural graphite; optionally, the average particle size of the artificial graphite is 3μm-20μm, preferably 4μm-18μm; optionally, the average particle size of the natural graphite is 3μm-20μm, preferably 4μm-18μm.

[0030] In any embodiment of the first aspect, the electrode assembly further includes a positive electrode sheet, which includes a positive current collector. The tensile strength of the positive current collector is 30 kgf / mm² when the battery cell is in a 100% SOC state within 50 charge-discharge cycles. 2 -50Kgf / mm 2 Elongation at break ≥1.5%.

[0031] A second aspect of this application provides a negative electrode sheet, comprising a negative current collector and a negative active layer disposed on at least one side of the negative current collector. The negative active layer comprises a first negative active layer and a second negative active layer. The first negative active layer is disposed on at least one side of the negative current collector, and the second negative active layer is disposed on the side of the first negative active layer away from the first negative active layer. The first negative active layer comprises a first graphite material and optionally a first silicon-based material, and the second negative active layer comprises a second silicon-based material and a second graphite material. The mass content of silicon in the first negative active layer is denoted as A, and the mass content of silicon in the second negative active layer is denoted as B, wherein 2.5% ≤ B ≤ 68%, and B > A; the tensile strength of the negative current collector is ≥ 40 kgf / mm². 2 Elongation at break ≥ 5.0%.

[0032] In any implementation of the second aspect, 5.5% ≤ B ≤ 48%.

[0033] In any embodiment of the second aspect, 2.5% ≤ BA ≤ 68%; optionally 5.5% ≤ BA ≤ 48%, and further optionally 10% ≤ BA ≤ 40%.

[0034] In any implementation of the second aspect, 0% ≤ A ≤ 40%, and optionally 0 ≤ A ≤ 20%.

[0035] In any embodiment of the second aspect, the mass content of silicon element in the first silicon-based material and the second silicon-based material is independently 30%-70%, and optionally 35%-65%.

[0036] In any embodiment of the second aspect, the first silicon-based material and the second silicon-based material are each independently selected from one or more of elemental silicon, silicon-oxygen composites, and silicon-carbon composites.

[0037] In any embodiment of the second aspect, at least one of the first silicon-based material and the second silicon-based material comprises a silicon-carbon composite.

[0038] In any embodiment of the second aspect, the first silicon-based material and the second silicon-based material each independently comprise a silicon-carbon composite.

[0039] In any embodiment of the second aspect, the first silicon-based material and the second silicon-based material each independently comprise a silicon-carbon composite satisfying one or more of the following characteristics: 1) The silicon-carbon composite includes porous carbon and silicon-containing material located in the pores and on the surface of the porous carbon. Optionally, the porous carbon is hard carbon, and the silicon-containing material may include crystalline silicon. 2) The silicon-carbon composite also includes a carbon-containing coating layer located on the surface of the porous carbon and / or silicon material; 3) The average particle size of the silicon-carbon composite is 2μm-15μm, and can be selected as 7μm-11μm; 4) The powder resistivity of silicon-carbon composite at 8 MPa is 4 Ω·cm - 17 Ω·cm; 5) The BET specific surface area of ​​the silicon-carbon composite is 1.0 m². 2 / g-6.7m 2 / g.

[0040] In any embodiment of the second aspect, the thickness of the negative electrode current collector is 5μm-10μm, and optionally 6μm-8μm.

[0041] In any embodiment of the second aspect, the thickness of the second negative electrode active layer accounts for 10%-90% of the total thickness of the negative electrode active layer, optionally 12%-80%, and more preferably 15%-70%.

[0042] In any embodiment of the second aspect, the first negative electrode active layer further includes a first binder, and the second negative electrode active layer further includes a second binder. The first binder and the second binder each independently include any one or more of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan.

[0043] In any embodiment of the second aspect, the mass content of the first binder in the first negative electrode active layer is less than the mass content of the second binder in the second negative electrode active layer.

[0044] In any embodiment of the second aspect, the mass content of the first binder in the first negative electrode active layer is 0.5%-5%, and more preferably 1.5%-3.5%.

[0045] In any embodiment of the second aspect, the mass content of the second binder in the second negative electrode active layer is 1%-5%, and more preferably 1.5%-4.5%.

[0046] In any embodiment of the second aspect, the first negative electrode active layer further includes a first conductive agent, and the second negative electrode active layer further includes a second conductive agent. The first conductive agent and the second conductive agent each independently include one or more of carbon black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers, or a mixture thereof.

[0047] In any embodiment of the second aspect, the mass content of the first conductive agent in the first negative electrode active layer is 0.05%-1%, and the mass content of the second conductive agent in the second negative electrode active layer is 0.05%-2%.

[0048] In any embodiment of the second aspect, the second conductive agent comprises carbon black and carbon nanotubes, wherein the mass ratio of carbon black to carbon nanotubes is 6:4-9:1, and more preferably 8:2-8.5:1.5.

[0049] In any embodiment of the second aspect, the negative electrode sheet further includes a base coating layer disposed between the negative current collector and the first negative electrode active layer, the base coating layer including a base conductive agent and a base binder.

[0050] In any embodiment of the second aspect, the base coating has one or more of the following features: Conductive agents used in primer coatings include carbon black; The primer adhesive includes polyvinylidene fluoride; The adhesive content in the primer layer is 70%-90% by mass.

[0051] A third aspect of this application provides a battery device comprising a plurality of battery cells, the battery cells including any of the battery cells provided in the first aspect above.

[0052] The fourth aspect of this application provides an electrical device, including a battery cell or a battery device, wherein the battery cell includes any of the battery cells provided in the first aspect above, and the battery device includes any of the battery devices provided in the third aspect above. Attached Figure Description

[0053] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0054] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application.

[0055] Figure 2 yes Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0056] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0057] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0058] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0059] Figure 6 This is a schematic diagram of an electrical device in which a single battery cell is used as a power source according to one embodiment of this application.

[0060] The accompanying drawings are not drawn to scale.

[0061] Explanation of reference numerals in the attached figures:

[0062] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Casing; 52 Electrode assembly; 53 End cap. Detailed Implementation

[0063] The embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to illustrate the principles of this application by way of example, but should not be used to limit the scope of this application, that is, this application is not limited to the described embodiments.

[0064] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the battery cell, negative electrode, battery assembly, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0065] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0066] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0067] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0068] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0069] Unless otherwise specified, the terms "comprising" and "including" as used in this application are open-ended. For example, "comprising" and "including" may mean that other components not listed may also be included or contained.

[0070] Unless otherwise specified, the term "or" is inclusive in this application. For example, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0071] [Negative electrode plate]

[0072] As mentioned earlier, when pure silicon or high-silicon materials are used in the negative electrode sheet of a wound electrode assembly, the negative electrode sheet is prone to cracking or breakage. To solve this problem, some technologies have modified the formulation of the negative electrode slurry, increasing the binder content to constrain the expansion of active material particles and reduce electrode stretching caused by the rebound of the active material film in the near-negative electrode current collector region. However, increasing the binder will reduce the battery energy density, and different active materials require different amounts of binder due to their varying content. Excessive binder addition can also affect the conductivity (increased internal resistance), kinetic performance, and stable SEI formation of the negative electrode sheet, leading to uncontrollable performance of the negative electrode sheet.

[0073] To address the problem of cracking or breakage of the negative electrode sheet in a silicon-containing wound electrode assembly, this application provides a negative electrode sheet in a first embodiment. The negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one side of the negative current collector. The negative active layer includes a first negative active layer and a second negative active layer. The first negative active layer is disposed on at least one side of the negative current collector, and the second negative active layer is disposed on the side of the first negative active layer away from it. The first negative active layer includes a first graphite material and optionally a first silicon-based material. The second negative active layer includes a second silicon-based material and a second graphite material. The mass content of silicon in the first negative active layer is denoted as A, and the mass content of silicon in the second negative active layer is denoted as B, where 2.5% ≤ B ≤ 68%, and B > A. When the battery cell is at 0% SOC, the tensile strength of the negative current collector is ≥ 40 kgf / mm². 2 Elongation at break ≥ 5.0%.

[0074] This application avoids the expansion of the negative electrode current collector caused by silicon expansion when the second negative electrode active layer with more silicon is in direct contact with the negative electrode current collector. This reduces the expansion loss of the negative electrode current collector due to silicon expansion, thus allowing the negative electrode current collector to maintain more ductility to meet the elongation requirements of the outer negative electrode sheet (corresponding to the outermost two turns of the winding structure), thereby controlling the occurrence of cracks or fissures in the outer negative electrode sheet. Simultaneously, a negative electrode current collector with suitable strength and elongation at break is used, providing sufficient ductility and strength for the expansion of the outer negative electrode sheet, while also providing sufficient ductility for the large-angle bending of the inner negative electrode sheet (corresponding to the innermost two turns of the winding structure). Furthermore, this application controls the mass content of silicon in the second negative electrode active layer, thereby controlling the expansion caused by silicon while utilizing silicon to improve the energy density of the battery cell. Therefore, by combining the silicon content, the aforementioned layered coating method, and the tensile strength and elongation at break of the negative electrode current collector, this application effectively controls the risk of cracking or splitting of the negative electrode sheet caused by silicon expansion in the wound electrode assembly.

[0075] The silicon content in the first negative electrode active layer and the silicon content in the second negative electrode film layer can be tested using the following method:

[0076] The negative electrode material of the first negative electrode film layer or the negative electrode material of the second negative electrode film layer is collected by scraping powder, and the negative electrode material is tested by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0077] The tensile strength and elongation at break of the negative electrode current collector were obtained by testing using the following method:

[0078] The negative electrode current collector to be tested is cut into uniform size (e.g., 150mm*15mm) to obtain the test sample. The test sample is loaded onto a tensile testing machine, and the tensile testing machine is started (the tensile testing machine runs at a speed of 2mm / min). The tensile stress and displacement data are recorded at a frequency of 100ms. After processing, the elongation at break and tensile strength data of the negative electrode current collector are obtained.

[0079] The tensile strength and elongation at break of the aforementioned negative electrode current collector are characteristic of the negative electrode current collector. When this negative electrode sheet is applied to a battery cell, although there is elongation loss during charge-discharge cycles, the loss is low. Therefore, when the battery cell is in the 0% SOC state within 50 charge-discharge cycles, the tensile strength and elongation at break of the negative electrode current collector are also within the aforementioned range.

[0080] The method for adjusting the state of charge (SOC) of a single battery cell to 0% can be performed using test methods known in the art. As an example, the following method can be used for testing: 1) Determine the rated capacity of the battery cell: This can be the ampere-hour capacity specified by the manufacturer; or it can be that the battery cell is charged at a constant current and constant voltage of 0.33C to the upper voltage limit within the specified usable voltage range of the battery cell, and then discharged at 0.33C to the lower voltage limit, at which point the battery cell is at 0% SOC.

[0081] The negative electrode current collector with the above-mentioned tensile strength and elongation at break can be selected from conventional negative electrode current collectors, and this application does not impose any special restrictions on its source.

[0082] In some embodiments, 2.85% ≤ B ≤ 66.5%, optionally 5.5% ≤ B ≤ 48%, and further optionally 5.7% ≤ B ≤ 46.55%, thereby further controlling the silicon content in the second negative electrode active layer and achieving a balanced control of energy density and expansion degree.

[0083] In some embodiments, 2.5% ≤ BA ≤ 68%, optionally 2.85% ≤ BA ≤ 66.5%; further optionally 5.5% ≤ BA ≤ 48%, further optionally 10% ≤ BA ≤ 40%. By controlling the silicon content in the first and second negative electrode active layers within the above range, the volume expansion of the active layer near the current collector can be better controlled, reducing damage caused by the material's expansion on the current collector during charging.

[0084] In some embodiments, 0% ≤ A ≤ 40%, and optionally 0 ≤ A ≤ 20%. When A is 0%, it means that no first silicon-based material is provided in the first negative electrode active layer. The higher the silicon content in the first negative electrode active layer, the greater the energy density of the corresponding battery cell, but the expansion during charging is also relatively greater. By controlling the value of A within the above range, a balance between energy density and expansion control is achieved.

[0085] In silicon-based materials, carbon materials can alleviate the stress compression caused by silicon expansion to a certain extent. In some embodiments, the mass content of silicon in the first silicon-based material and the second silicon-based material is independently 30%-70%, and can be selected as 35%-65%. Thus, the combination of silicon and carbon materials improves the structural stability of silicon-based materials.

[0086] In this application, the first silicon-based material and the second silicon-based material are each independently selected from one or more of elemental silicon, silicon-oxygen complexes, and silicon-carbon complexes.

[0087] In some embodiments, at least one of the first silicon-based material and the second silicon-based material comprises a silicon-carbon composite.

[0088] In some embodiments, the first silicon-based material and the second silicon-based material each independently comprise a silicon-carbon composite, hereinafter referred to as the first silicon-carbon composite material and the second silicon-carbon composite material.

[0089] The first silicon-carbon composite material and the second silicon-carbon composite material of this application can be prepared using conventional silicon-carbon composites or conventional preparation methods, such as depositing nano-silicon materials on porous carbon by chemical vapor deposition, and further carbon coating, such as using amorphous carbon coating.

[0090] In some embodiments, the first silicon-carbon composite material and the second silicon-carbon composite material are each independently selected from silicon-carbon composites that satisfy one or more of the following characteristics: 1) The silicon-carbon composite includes porous carbon and silicon-containing material located in the pores and on the surface of the porous carbon. Optionally, the porous carbon is hard carbon, and the silicon-containing material may include crystalline silicon. 2) The silicon-carbon composite also includes a carbon-containing coating layer located on the surface of the porous carbon and / or silicon material; 3) The average particle size of the silicon-carbon composite is 2μm-15μm, and can be selected as 7μm-11μm; 4) The powder resistivity of silicon-carbon composite at 8 MPa is 4 Ω·cm - 17 Ω·cm; 5) The BET specific surface area of ​​the silicon-carbon composite is 1.0 m². 2 / g-6.7m 2 / g.

[0091] In some embodiments, the silicon-carbon composite comprises porous carbon and silicon-containing material located in the pores and on the surface of the porous carbon. The porous carbon, acting as a carrier for the silicon-containing material, provides support for the material while simultaneously offering expansion space for the expansion of the nano-silicon particles, effectively mitigating the stress compression caused by expansion during charging. Especially when the silicon-containing material has a nanometer-scale particle size, it exhibits higher specific capacity and is better dispersed within the pores of the porous carbon. Furthermore, it allows for more efficient utilization of the pores' buffering effect on expansion. When this silicon-carbon composite is applied in a wound electrode assembly, it can significantly alleviate the stretching of the outer negative electrode sheet caused by silicon expansion.

[0092] In some embodiments, the porous carbon may optionally be hard carbon. When the porous carbon is hard carbon, it has stronger support, a more stable pore structure, and is harder, thus providing better porosity for the negative electrode active layer, providing a smoother path for active ion transport, and improving the charging capability of the battery cell.

[0093] In some embodiments, the silicon-containing material includes at least one of elemental silicon, silicon oxides, silicon nitrides, and silicon alloys. In some embodiments, the silicon-containing material includes crystalline silicon, thereby further improving the structural stability of the silicon-containing material and the energy density of the battery cell.

[0094] In some embodiments, the silicon-carbon composite further includes a carbon-containing coating layer located on the surface of the porous carbon and / or silicon material. This can improve the conductivity of the silicon-carbon composite, reduce the internal impedance of the battery cell, and effectively reduce the probability of direct contact between the silicon-containing material in the porous carbon channels and the external environment, thereby improving the chemical stability of the silicon-carbon composite.

[0095] In some embodiments, the silicon content in the silicon-carbon composite is 30%-70% by mass. This approach, while maximizing the specific capacity of the negative electrode active material by utilizing silicon, also facilitates the full dispersion of silicon in the carbon-containing porous material and helps control the expansion of silicon during charging.

[0096] In this application, the method for testing the silicon content in the silicon-carbon composite can be a method known in the art. As an example, the following method can be used for testing: a certain amount of silicon-carbon composite is taken, and the mass of silicon element in the silicon-carbon composite is obtained by inductively coupled plasma optical emission spectrometry (ICP-OES). The mass percentage of silicon element in the silicon-carbon composite can be calculated.

[0097] In addition to providing structural support and buffering for the expansion of silicon-containing materials, the pores in the silicon-carbon composite also form between the particles. To further improve the flow of lithium ions through the intraparticle and interparticle pores, in some embodiments, the average particle size of the silicon-carbon composite is 2μm-15μm. Optionally, the average particle size of the silicon-carbon composite is 7μm-11μm. This average particle size distribution between the silicon-carbon composite and the graphite material facilitates the use of interparticle gaps to increase the compaction of the negative electrode active layer, thereby further improving the energy density of the battery cell.

[0098] The average particle size of the aforementioned silicon-carbon composite can be tested using equipment and methods known in the art. For example, a scanning electron microscope (SEM) can be used (e.g., ZEISS Sigma 300), referring to JY / T010-1996, to obtain SEM images of the negative electrode sheet. As an example, the test can be performed as follows: Randomly select a test sample of length × width = 50 mm × 100 mm on the negative electrode sheet. Randomly select multiple test areas (e.g., 5 areas) within the test sample, and at a certain magnification (e.g., 1000x when measuring silicon-carbon composites), read the particle size of each silicon-carbon composite particle in each test area (i.e., take the distance between the two farthest points on the silicon-carbon composite particle as the particle size). Count the number and particle size values ​​of silicon-carbon composite particles in each test area, and take the arithmetic mean of the silicon-carbon composite particles in each test area, which is the number-average particle size of the silicon-carbon composite particles in the test sample. To ensure the accuracy of the test results, multiple test samples (e.g., 10) can be taken and the above test can be repeated. The average value of each test sample can be taken as the final test result.

[0099] In some embodiments, the powder resistivity of the silicon-carbon composite at 8 MPa is 4 Ω·cm-17 Ω·cm. This control of powder resistivity improves the conductivity of the silicon-carbon composite, thereby increasing the charging rate of the battery cell.

[0100] In this application, the powder resistivity of silicon-carbon composites can be determined using methods known in the art. As an example, a four-probe method can be used, where two probes apply voltage and the other two probes measure current. The powder resistivity can be calculated by measuring the resistance value. Models of four-probe semiconductor powder resistivity testers include the ST-2722.

[0101] In some embodiments, the BET specific surface area of ​​the silicon-carbon composite is 1.0 m². 2 / g-6.7m 2 / g.

[0102] In this application, the method for testing the BET specific surface area of ​​the silicon-carbon composite can be a method known in the art. As an example, referring to GB / T 19587-2017, the nitrogen adsorption specific surface area analysis method can be used. The sample tube containing the first graphite material sample is immersed in liquid nitrogen at -196℃, and the amount of nitrogen adsorbed on the surface of the solid sample at different pressures of 0.05-0.30 MPa is measured. Based on the BET multilayer adsorption theory and calculation formula, the monolayer adsorption amount of the sample is obtained, and thus the BET specific surface area is obtained. This test can be performed using a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0103] The silicon-carbon composite used in this application is derived from conventional silicon-carbon composites in the art, which, in addition to silicon and carbon, may also contain oxygen, nitrogen, and other elements. In some embodiments, the carbon content, by mass, is greater than 70% of the total amount of elements other than silicon in the second negative electrode active layer. By controlling the carbon content in the total amount of elements other than silicon, the silicon-carbon composite is made predominantly composed of silicon and carbon, thus better leveraging the structural and electrical performance advantages of these two elements.

[0104] The tensile strength and elongation at break of the negative electrode current collector in this application can be adjusted by the microstructure such as the grain size of the negative electrode current collector itself, or by the thickness of the current collector. For example, under the premise of the same composition, the larger the thickness of the negative electrode current collector, the higher the tensile strength. However, increasing the thickness of the negative electrode current collector will lead to a decrease in the energy density of the battery cell. Conversely, the smaller the thickness of the negative electrode current collector, the lower the tensile strength. Although the energy density of the battery cell can be increased by reducing the thickness of the negative electrode current collector, the smaller the thickness, the more likely the negative electrode sheet will be to curl during processing.

[0105] In some implementations, while satisfying the above-mentioned tensile strength and elongation at break, in order to improve the volumetric energy density of the battery cell by reducing the thickness of the negative electrode current collector as much as possible while reducing the risk of edge curling of the negative electrode sheet, the thickness of the negative electrode current collector is 5μm-10μm, and can be selected as 6μm-8μm.

[0106] In some embodiments, the thickness of the second negative electrode active layer accounts for 10%-90% of the total thickness of the negative electrode active layer, optionally 12%-80%, and further optionally 15%-70%. By distributing the thickness of the two negative electrode active layers, the influence of the silicon-carbon composite material on the overall expansion of the negative electrode active layer is further controlled, thereby reducing the risk of elongation loss and cracking of the negative electrode sheet.

[0107] The thicknesses of the aforementioned negative electrode current collector, negative electrode active layer, and second negative electrode active layer can be measured using the CP-SEM method. Different corresponding thicknesses can be measured from the microscopic images, and the proportions can be calculated.

[0108] As an example, the negative electrode current collector can be a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, pure metals, alloys, or surface-treated metals can be used, including but not limited to stainless steel, copper, aluminum, nickel, titanium, or silver. The composite current collector may include a polymer material substrate and a metal layer. The composite current collector can be formed by forming a metal material (copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0109] In some embodiments, the first negative electrode active layer further includes a first binder, and the second negative electrode active layer further includes a second binder. The first binder and the second binder each independently include any one or more of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan.

[0110] To further enhance the restraint of the second negative electrode active layer on the expansion of the silicon-carbon composite material, in some embodiments, the mass content of the first binder in the first negative electrode active layer is less than the mass content of the second binder in the second negative electrode active layer.

[0111] In some embodiments, the mass content of the first binder in the first negative electrode active layer is 0.5%-5%, more preferably 1.5%-3.5%; and / or the mass content of the second binder in the second negative electrode active layer is 1%-5%, more preferably 1.5%-4.5%. By providing the first or second binder within the above-mentioned mass content range, the influence of the binder on the energy density is minimized while ensuring sufficient bonding effect.

[0112] In some embodiments, the first negative electrode active layer further includes a first conductive agent, and the second negative electrode active layer further includes a second conductive agent. The first and second conductive agents each independently comprise one or more of carbon black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers, or a mixture thereof. The aforementioned carbon black includes, but is not limited to, superconducting carbon, acetylene black, and Ketjen black.

[0113] Since silicon has weaker conductivity than carbon materials, in order to fully reduce the resistivity of the first negative electrode active layer and the second negative electrode active layer and improve the charging rate of the battery cell, in some embodiments, the mass content of the first conductive agent in the first negative electrode active layer is 0.05%-1%, and the mass content of the second conductive agent in the second negative electrode active layer is 0.05%-2%.

[0114] In some embodiments, the second conductive agent comprises carbon black and carbon nanotubes, with a mass ratio of carbon black to carbon nanotubes of 6:4-9:1, and more preferably 8:2-8.5:1.5. Carbon nanotubes have better conductivity than carbon black, thus they can be used to improve the poor intrinsic conductivity of silicon materials. Furthermore, the linearity of carbon nanotubes can also restrain the expansion of silicon-carbon composite materials and play a role in controlling the elongation of the negative electrode sheet.

[0115] During repeated charge-discharge cycles, the adhesion between the negative electrode active layer and the negative electrode current collector is affected by repeated stress compression. This can lead to powder shedding or even peeling after long cycles. In some embodiments, the negative electrode sheet also includes a base coating layer, which is disposed between the negative electrode current collector and the first negative electrode active layer. The base coating layer includes a base conductive agent and a base adhesive. Utilizing this base coating layer increases the adhesion between the negative electrode active layer and the negative electrode current collector, further extending the cycle life of the battery cell.

[0116] In some embodiments, the primer coating has one or more of the following characteristics:

[0117] The primer conductive agent includes carbon black, which reduces the cost of conductivity;

[0118] The primer adhesive includes polyvinylidene fluoride, which increases the adhesion between the primer layer and the negative electrode current collector;

[0119] The binder content in the primer layer is 40%-60% by mass, which reduces the influence of the binder on the conductivity between the negative electrode current collector and the negative electrode active layer while achieving better adhesion.

[0120] The thickness of the base coating is 0.2μm-2μm, and the impact of the base coating on the energy density of the battery cells is controlled as much as possible.

[0121] In some embodiments, the first graphite material and the second graphite material each independently comprise artificial graphite and / or natural graphite; optionally, the average particle size of the artificial graphite is 3μm-20μm, or optionally 4μm-18μm; optionally, the average particle size of the natural graphite is 3μm-20μm, or optionally 4μm-18μm. Furthermore, graphite materials with appropriate properties can be selected according to the performance requirements of the battery cell. For example, to improve the fast-charging performance of the battery cell, fast-charging graphite can be used as the second graphite material; for example, to improve the energy density of the battery cell, high-density graphite can be used as the first graphite material. The above is an illustrative description and is not intended to limit the selection of graphite materials.

[0122] [Battery cell]

[0123] In this embodiment of the application, the battery cell can be a secondary battery, which refers to a battery cell that can be recharged to activate the active materials and continue to be used after the battery cell has been discharged.

[0124] The battery cell can be a lithium-ion battery, sodium-ion battery, sodium-lithium-ion battery, lithium metal battery, lithium-sulfur battery, magnesium-ion battery, nickel-metal hydride battery, nickel-cadmium battery, lead-acid battery, etc., and the embodiments of this application are not limited to this.

[0125] A second aspect of this application provides a battery cell including a wound electrode assembly. The electrode assembly includes a negative electrode sheet, which includes any of the negative electrode sheets provided in the first embodiment described above. The negative electrode sheet of this application effectively controls the risk of cracking or splitting of the negative electrode sheet due to silicon expansion by combining the silicon content, the aforementioned layered coating method, and the tensile strength and elongation at break of the negative electrode current collector.

[0126] In some implementations, to further reduce the risk of cracking or splitting of the negative electrode sheet, the elongation at break of the negative electrode current collector is ≥3.5% when the battery cell is in a 100% SOC state within 50 charge-discharge cycles.

[0127] In some implementations, by selecting the elongation at break of the negative electrode current collector and controlling the composition of the negative electrode active layer, the elongation at break of the negative electrode sheet is made ≥1.5% when the battery cell is in a 100% SOC state within 50 charge-discharge cycles. This further reduces the risk of cracking and splitting of the negative electrode sheet.

[0128] When testing the elongation at break of the negative current collector and the negative electrode sheet, it is first necessary to disassemble the corresponding negative current collector and negative electrode sheet. The specific disassembly process is as follows:

[0129] A battery cell at 100% SOC (State of Charge) within 50 charge-discharge cycles is disassembled to obtain the negative electrode sheet. The negative electrode sheet is then soaked in dimethyl carbonate (DMC) for a specific time (e.g., 2-10 hours). Next, the negative electrode sheet is removed and dried at a specific temperature and time (e.g., 40℃-70℃, 2h-5h). After drying, the negative electrode sheet is removed and becomes the negative electrode sheet to be tested. Scraping off the film layer on the negative electrode sheet yields the negative current collector to be tested. This process for obtaining the negative electrode sheet is also applicable to other tests requiring the negative electrode sheet in a battery cell.

[0130] The test method for the elongation at break of the negative electrode current collector or negative electrode sheet when the battery cell is in a 100% SOC state within 50 charge-discharge cycles is as follows:

[0131] Cut the negative electrode current collector or negative electrode sheet to be tested into uniform size (e.g., 150mm*15mm), load the sample onto the tensile testing machine, start the tensile testing machine (tensile testing machine running speed 2mm / min), and record tensile stress and displacement data at a frequency of 100ms. After processing, obtain the electrode sheet breaking elongation and tensile strength data.

[0132] [Positive electrode plate]

[0133] Because the expansion of the negative electrode active layer also causes the positive electrode sheet to stretch, in some embodiments, to prevent the positive electrode sheet from cracking or splitting, the electrode assembly further includes a positive electrode sheet, which includes a positive current collector. When the battery cell is in a 100% SOC state within 50 charge-discharge cycles, the tensile strength of the positive current collector is 30 kgf / mm². 2 -50 Kgf / mm 2 .

[0134] The test method for the tensile strength of the positive current collector when the battery cell is in a 100% SOC state within 50 charge-discharge cycles can refer to the test method for the tensile strength of the negative current collector when the battery cell is in a 100% SOC state within 50 charge-discharge cycles, and will not be repeated here.

[0135] The positive electrode sheet typically also includes a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer comprising a positive electrode active material.

[0136] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0137] As an example, the positive current collector can be a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, pure metals, alloys, or surface-treated metals can be used, including but not limited to stainless steel, copper, aluminum, nickel, titanium, or silver. The composite current collector may include a polymer material base layer and a metal layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0138] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0139] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0140] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0141] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0142] In some embodiments, the positive current collector can be made of aluminum, and the negative current collector can be made of copper.

[0143] [Electrolytes]

[0144] In some embodiments, the battery cell also includes an electrolyte, which acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. The electrolyte can be liquid, gel, or solid.

[0145] Liquid electrolytes include electrolyte salts and solvents.

[0146] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0147] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone. The solvent may also be an ether solvent. Ether solvents may include one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyl tetrahydrofuran, diphenyl ether, and crown ethers.

[0148] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain properties of the battery cell, such as additives that improve the overcharge / fast charge performance of the battery cell, additives that improve the high-temperature performance of the battery cell, and additives that improve the low-temperature performance of the battery cell.

[0149] The gel electrolyte includes a polymer as a backbone network and can be used in conjunction with an ionic liquid-lithium salt.

[0150] Solid electrolytes include polymer solid electrolytes, inorganic solid electrolytes, and composite solid electrolytes.

[0151] As an example, the polymers of polymeric solid electrolytes may include polyethers (polyoxyethylene), polysiloxanes, polycarbonates, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, monoionic polymers, polyionic liquids, cellulose, etc.

[0152] As an example, inorganic solid electrolytes can be one or more of the following: oxide solid electrolytes (crystalline perovskite, sodium superconducting ion conductor, garnet, amorphous LiPON thin film), sulfide solid electrolytes (crystalline lithium superconducting ion conductor (lithium-germanium-phosphorus-sulfur, sulfosilium-germanium), amorphous sulfides), halide solid electrolytes, nitride solid electrolytes, and hydride solid electrolytes.

[0153] As an example, composite solid electrolytes are formed by adding inorganic solid electrolyte fillers to polymer solid electrolytes.

[0154] [Isolation Component]

[0155] In some embodiments, the electrode assembly further includes an isolator disposed between the positive and negative electrodes.

[0156] In some embodiments, the separator is a separator membrane. This application does not impose any particular limitation on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0157] As an example, the main material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramic. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation. The separator can be a single component located between the positive and negative electrodes, or it can be attached to the surfaces of the positive and negative electrodes. An inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating can also be applied to the surface of the separator.

[0158] In some embodiments, the separator is a solid electrolyte. The solid electrolyte is disposed between the positive and negative electrodes, serving both to transport ions and to isolate the positive and negative electrodes.

[0159] [Electrode Assembly]

[0160] In some embodiments, the electrode assembly can be cylindrical, flat, or polygonal, etc.

[0161] In some embodiments, the electrode assembly is provided with tabs that allow current to be drawn from the electrode assembly. The tabs include a positive tab and a negative tab.

[0162] shell

[0163] In some embodiments, the battery cell may include a casing. The casing may be a steel casing, an aluminum casing, a plastic casing (such as a polypropylene casing), a composite metal casing (such as a copper-aluminum composite casing), or an aluminum-plastic film, etc. In some embodiments, the casing may be a sealed structure or a non-sealed structure. As an example, when the casing is a non-sealed structure, the casing serves to protect the electrode assembly, and a sealing bag is included between the casing and the electrode assembly to encapsulate the electrode assembly and electrolyte. Specifically, the sealing bag may be a bag-shaped insulating component or an aluminum-plastic film. When the casing is a sealed structure, it is used to encapsulate components such as the electrode assembly and electrolyte.

[0164] As an example, the battery cell can be a cylindrical battery cell, a prismatic battery cell, a pouch battery cell, or a battery cell of other shapes. Prismatic battery cells include prismatic battery cells, blade-shaped battery cells, and multi-prismatic batteries, such as hexagonal prismatic batteries. This application does not have any particular limitations.

[0165] In some embodiments, the housing includes an end cap and a housing, the housing having an opening, and the end cap covering the opening. The housing may have one or more openings. The end cap may also have one or more.

[0166] Figure 1 The example shown is a square-structured battery cell 5.

[0167] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and an end cap 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the end cap 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0168] Electrode terminals

[0169] In some embodiments, at least one electrode terminal is provided on the housing, and the electrode terminal is electrically connected to the tab. The electrode terminal can be directly connected to the tab, or it can be indirectly connected to the tab through a current collector. The electrode terminal can be provided on the end cap or on the housing.

[0170] Pressure relief mechanism

[0171] In some embodiments, a pressure relief mechanism is provided on the casing. The pressure relief mechanism is used to release the internal gas of the battery cell.

[0172] As an example, the internal pressure or temperature of a battery cell is actuated to release the internal pressure or temperature when it reaches a predetermined threshold. When the internal pressure or temperature of the battery cell reaches the predetermined threshold, the pressure relief mechanism is activated or a weak structure in the pressure relief mechanism is broken, thereby forming an opening or channel for the internal pressure or temperature to be released. The threshold design varies depending on the design requirements. The threshold may depend on the materials of one or more of the positive electrode, negative electrode, electrolyte, and separator in the battery cell.

[0173] As an example, the pressure relief mechanism can be integrally molded with the housing.

[0174] As an example, the pressure relief mechanism can also be separately installed and connected to the housing.

[0175] The term "actuation" as used in this application refers to the activation or actuation of the pressure relief mechanism to a certain state, thereby releasing the internal pressure and temperature of the battery cell. The actions of the pressure relief mechanism may include, but are not limited to: movement of components within the mechanism to form an exhaust channel, rupture, breakage, tearing, or opening of at least a portion of the mechanism, etc. When the pressure relief mechanism is activated, the high-temperature, high-pressure substances inside the battery cell are discharged as waste from the activated portion. This method allows for pressure and temperature relief of the battery cell under controllable pressure or temperature, thereby preventing potentially more serious accidents.

[0176] In some embodiments, when the housing is a non-sealed structure, the pressure relief mechanism can be configured as a through hole for venting gas inside the battery cell.

[0177] The emissions from battery cells mentioned in this application include, but are not limited to: electrolyte, dissolved or split positive and negative electrode plates, fragments of separators, high-temperature and high-pressure gases generated by the reaction, flames, etc.

[0178] The battery apparatus mentioned in the embodiments of this application may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple battery cells connected in series, parallel, or mixed connections via a busbar.

[0179] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells.

[0180] As an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple battery cells together to form an independent module. As another example, a battery module can be formed by bundling multiple battery cells together with cable ties.

[0181] Figure 3 This is battery module 4 as an example. (See reference...) Figure 3 In the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other way. Furthermore, these multiple secondary battery cells 5 can be fixed in place using fasteners.

[0182] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0183] In some embodiments, the battery device may be a battery pack, which includes a housing and one or more individual battery cells housed within the housing.

[0184] As an example, the battery cell assembly can be a battery module, which can be housed in a housing by fixing the battery module in the housing.

[0185] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple battery cells to the housing.

[0186] As an example, the enclosure may include a first enclosure and a second enclosure. The first enclosure and the second enclosure are fastened together to form a closed space inside the enclosure to house the individual battery cells. Here, "closed" refers to covering or closing, and can be either sealed or unsealed. The first enclosure may be a top cover or a bottom plate.

[0187] As an example, the enclosure may include a top cover, a frame, and a bottom plate. The top cover and bottom plate are connected to the frame, creating an enclosed space inside the enclosure to house the individual battery cells.

[0188] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0189] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0190] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use individual battery cells, such as mobile phones, portable devices, laptops, electric vehicles, electric toys, power tools, vehicles, ships, and spacecraft. For example, spacecraft include airplanes, rockets, space shuttles, and spacecraft.

[0191] As the electrical device, a single secondary battery cell, a battery module, or a battery pack can be selected according to its usage requirements.

[0192] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0193] [Example]

[0194] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0195] Example 1

[0196] Preparation of negative electrode sheet:

[0197] Preparation of the first negative electrode slurry: The first graphite material (artificial graphite with a Dv50 particle size of 15μm), the first conductive agent acetylene black, the first binder SBR, and the dispersant sodium carboxymethyl cellulose were mixed in a mass ratio of 96.5:0.5:2:1 to prepare the first negative electrode slurry.

[0198] Preparation of the second negative electrode slurry: The second active material, the second conductive agent, the second binder SBR, and the second dispersant sodium carboxymethyl cellulose were mixed in a mass ratio of 95:1:3:1 to prepare the second negative electrode slurry. The second negative electrode active material is a mixture of the second silicon-carbon composite material and the second graphite material in a mass ratio of 4:6. The second graphite material is artificial graphite with a Dv50 particle size of 15 μm. The second silicon-carbon composite material includes porous hard carbon and silicon-containing materials located in the pores and on the surface of the porous carbon. Part of the silicon-containing material is crystalline silicon with a Dv50 particle size of 9 μm and a BET specific surface area of ​​approximately 2 m². 2 / g, silicon content and powder resistivity are recorded in Table 1; the second conductive agent consists of carbon black and carbon nanotubes in a mass ratio of 8:2.

[0199] Preparation of primer slurry: The primer conductive agent SP conductive carbon black and the primer binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 8:2 to prepare the primer slurry.

[0200] Preparation of negative electrode sheet: A base coating slurry is coated on a negative electrode current collector copper foil with a thickness of 7 μm, and dried to form a base coating layer with a thickness of 0.5 μm; using a dual-cavity coating device, the first negative electrode slurry and the second negative electrode slurry are simultaneously coated on the surface of the current collector copper foil with the base coating layer, and after drying-cold pressing-slitting, the negative electrode sheet of Example 1 is obtained. The first negative electrode slurry forms the first negative electrode active layer, and the second negative electrode slurry forms the second negative electrode active layer, with a thickness ratio of 5:5.

[0201] Preparation of the positive electrode: The positive electrode active material LiNi... 0.9 Co 0.05 Mn 0.05 O2, polyvinylidene fluoride (PVDF) binder, and acetylene black conductive agent were dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 97:1.5:1.5 and thoroughly mixed to prepare a positive electrode slurry. The positive electrode slurry was then uniformly coated onto a positive electrode current collector aluminum foil (tensile strength 35 kgf / mm²). 2 The material is processed by drying, cold pressing, and slitting to obtain the positive electrode sheet (with an elongation at break of 2.5%).

[0202] Separator membrane: Polypropylene membrane.

[0203] Electrolyte: The solvent is a mixture of ethylene carbonate EC, methyl ethyl carbonate DEC and diethyl carbonate EMC in a volume ratio of 1:1:1. LiPF6 is an active lithium salt with a concentration of 1 mol / L.

[0204] Assembly: The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly; the electrode assembly is placed in an outer packaging, the electrolyte prepared above is added, and after processes such as encapsulation, standing, formation, and aging, a battery cell is obtained.

[0205] test:

[0206] Charge and discharge process: The fresh battery cells obtained above are charged to 4.25V at 25℃ and 0.33C constant current, and then discharged to 2.5V at 0.33C. At this time, the battery cells are at 0% SOC. Then they are charged to 4.25V at 0.33C constant current, at which time the battery cells are at 100% SOC.

[0207] Tensile strength and elongation at break tests of negative electrode sheet and negative electrode current collector:

[0208] For each of the above embodiments and comparative examples, at least three parallel samples were prepared. For each parallel sample, two battery cells were randomly selected and adjusted to 0% SOC and 100% SOC states respectively using the above charge-discharge method. The battery cells at 0% SOC and 100% SOC states were disassembled, and the negative electrode sheet was obtained. The negative electrode sheet was then soaked in dimethyl carbonate (DMC) for 5 hours. The negative electrode sheet was then removed and dried at 50°C for 5 hours. After drying, the negative electrode sheet was removed, which is the negative electrode sheet to be tested. The film layer on the negative electrode sheet was scraped off to obtain the negative current collector to be tested.

[0209] The negative electrode sheet and negative current collector to be tested are cut into uniform sizes (e.g., 150mm*15mm) to obtain the test sample. The test sample is loaded onto a tensile testing machine, and the tensile testing machine is started to perform the test (the tensile testing machine runs at a speed of 2mm / min). The tensile stress and displacement data are recorded at a frequency of 100ms. After processing, the elongation at break and tensile strength data of the negative electrode sheet and negative current collector under 0% SOC and 100% SOC conditions are obtained.

[0210] The elongation loss of the negative electrode current collector is equal to the difference between the elongation at break of the negative electrode current collector in the 0% state and the elongation at break of the negative electrode current collector in the 100% state.

[0211] Crack condition test of negative electrode sheet:

[0212] Cycle the battery according to the above charging and discharging process. When the number of cycles reaches 1000 (if the battery capacity retention rate drops to 80% before reaching 1000 cycles, stop the cycle charging and discharging when the cycle capacity retention rate reaches 80%), and finally bring the battery cell to 100% SOC, disassemble and observe the cracking of the outermost two negative electrode plates (i.e., the outer ring in Table 1) and the innermost two negative electrode plates (i.e., the inner ring in Table 1) of the winding structure. If no cracks are observed in the negative electrode current collector, mark it as OK; if cracks are observed in the negative electrode current collector, mark it as NG.

[0213] Example 2

[0214] Based on Example 1, copper foil with different tensile strengths is used as the negative electrode current collector, and the rest is the same as in Example 1.

[0215] Examples 3 to 6

[0216] Based on Example 2, the mass content of silicon in the second negative electrode active layer is adjusted by adjusting the mass content of silicon in the second silicon-carbon composite material (i.e., using the same hard carbon as porous carbon and adjusting the loading of silicon-containing materials) or by adjusting the ratio of the second silicon-carbon composite material to the second graphite material. The rest is the same as in Example 2.

[0217] Comparative Example 1

[0218] Based on Example 1, copper foil with different tensile strengths is used as the negative electrode current collector, and the rest is the same as in Example 1.

[0219] Comparative Example 2

[0220] Based on Example 1, copper foil with different elongation at break is used as the negative electrode current collector, and the rest is the same as in Example 1.

[0221] Comparative Example 3

[0222] Based on Example 2, the mass content of silicon in the second negative electrode active layer was adjusted by adjusting the second silicon-carbon composite material and the ratio of the second silicon-carbon composite material to the second graphite material, and the rest was the same as in Example 2.

[0223] The key parameters and test results of the above embodiments and comparative examples are recorded in Table 1. The average particle size of the second silicon-carbon composite material obtained by testing the average particle size in the negative electrode using the method described above is basically equivalent to the Dv50 particle size of the second silicon-carbon composite material, and is presented in Table 1 as the average particle size.

[0224] In Table 1, the mass ratio is the mass ratio of the second silicon-carbon composite material and the second graphite material, and the silicon element mass content B is the silicon element mass content in the second negative electrode active layer.

[0225] Table 1

[0226] Based on the above data, it can be seen that when the silicon content (B) in the second negative electrode active layer is controlled between 2.5% and 68% and the tensile strength of the negative electrode current collector is controlled to be ≥40 kgf / mm, 2 When the elongation at break is ≥5.0%, no cracks are generated in either the inner or outer ring of the negative electrode sheet. Reducing the silicon content, under the premise of using the same negative electrode current collector, helps to reduce the elongation loss of the negative electrode current collector, thereby avoiding the risk of cracking and delamination of the negative electrode sheet under long-term cycling.

[0227] The following examines the effects of different compositions of the second silicon-carbon composite material on the negative electrode sheet.

[0228] The differences between Examples 7 to 10 and Example 1 are that the silicon content and powder resistivity in the second silicon-carbon composite material are different (i.e., the same hard carbon is used as porous carbon, and the loading of silicon-containing materials is adjusted), and the silicon content B in the second negative electrode active layer is different. All other materials used are the same as in Example 1. The specific different parameters and test results are recorded in Table 2.

[0229] Table 2

[0230] As can be seen from the data in Table 2, with the increase of silicon content, the fracture elongation of both the negative electrode current collector and the negative electrode sheet decreases at 100% SOC, the elongation loss of the negative electrode sheet increases, and the tensile strength of the positive electrode current collector also decreases. This indicates that the expansion of silicon material during charging causes stress compression on both the negative electrode current collector and the positive electrode current collector, and this effect increases with the increase of silicon content.

[0231] The following examines the effect of the particle size of the second silicon-carbon composite material on the negative electrode sheet.

[0232] Examples 11 to 15 are based on Example 1, mainly adjusting the particle size of the second silicon-carbon composite material (i.e., selecting hard carbon with a corresponding particle size and loading it with the same mass content of silicon-containing material, so the mass content of silicon element in the obtained second silicon-carbon composite material is basically the same as that in Example 1, and the resistivity is basically the same as that in Example 1). The main relevant parameters and test results of the second silicon-carbon composite material are shown in Table 3.

[0233] The test method for the compaction density of the negative electrode active layer is as follows:

[0234] Ten circular negative electrode sheets with a diameter of 14 mm are cut. The area of ​​the negative electrode sheet is calculated as S = π × 0.7. 2 Weigh each negative electrode sheet and calculate the average mass as m1 (g); measure the thickness of each negative electrode sheet and take the average value L1 (cm); wash away the negative electrode active layer to obtain the negative electrode current collector, weigh each negative electrode current collector and calculate the average mass as m0 (g); measure the thickness of each negative electrode current collector and take the average value L0 (cm); compaction density = (m1-m0) / [(L1-L0)×S].

[0235] 2C Capacity Retention Rate:

[0236] The battery cell was placed in a constant temperature environment of 25°C and charged at a constant current of 0.33C to 4.25V, at which point the battery cell was at 100% SOC. Then, it was discharged at a constant current of 0.33C to 2.5V, at which point the battery cell was at 0% SOC. The capacity C was recorded. 0.33 Then, it was charged at a constant current rate of 2.0C to 4.25V to 100% SOC, and discharged at a constant current rate of 0.33C to 2.5V to 0% SOC. The discharge capacity C2 and C2 / C were recorded. 0.33 Capacity retention at 2C rate.

[0237] Table 3

[0238] As can be seen from the data in Table 3, although the compaction density of the negative electrode active layer can be improved with the increase of the average particle size of the second silicon-carbon composite material, it can be found that the fracture elongation of the negative electrode current collector and the negative electrode sheet gradually decreases when the battery cell is in a 100% SOC state. This indicates that if the particle size of the silicon-carbon composite material is controlled within an appropriate range, the elongation loss of the negative electrode current collector can be kept within a small range.

[0239] As the average particle size of the second silicon-carbon composite material decreases, the 2C capacity retention rate of the battery cell improves, indicating that the smaller the average particle size, the better the lithium-ion diffusion kinetics and the better the fast charging capability of the battery cell.

[0240] The following examines the effect of the thickness of the negative electrode current collector on the negative electrode sheet.

[0241] The difference between Examples 16 to 19 and Example 1 lies in the selection of different negative electrode current collector copper foils, which are specifically recorded in Table 4.

[0242] Table 4

[0243] The data comparison in Table 4 shows that when the tensile strength and thickness of the negative electrode current collector are the same, the elongation loss of the negative electrode sheet decreases to a certain extent as the thickness of the negative electrode current collector increases, indicating that increasing the thickness of the negative electrode current collector is beneficial to resisting expansion. Moreover, when the thickness of the negative electrode current collector is further increased, although the tensile strength of the negative electrode current collector increases, the elongation loss also increases significantly, indicating that simply increasing the thickness of the negative electrode current collector has limited effect on resisting expansion.

[0244] The following examines the effect of the thickness ratio of the second negative electrode active layer in the negative electrode active layer on the extension of the negative electrode current collector.

[0245] Examples 20 to 25 are based on Example 1, but the thickness ratio of the second negative electrode active layer is adjusted while the total thickness of the negative electrode active layer remains unchanged. The test results are shown in Table 5.

[0246] Table 5

[0247] According to the data comparison in Table 5, it can be found that as the thickness ratio of the second negative electrode active layer increases, the content of silicon in the negative electrode active layer increases, the expansion force is greater at 100% SOC, the fracture elongation of both the negative electrode current collector and the negative electrode sheet gradually decreases, and the elongation loss of the negative electrode sheet increases. However, the negative electrode current collector of this application can still prevent cracks from appearing in the inner and outer rings of the negative electrode sheet.

[0248] The following examines the effect of binder content on the negative electrode sheet.

[0249] Examples 26 to 29 are based on Example 1, with adjustments made to the amounts of the first graphite material and the first binder in the first negative electrode slurry, but the total proportion of the two in the first negative electrode slurry remains unchanged; similarly, the amounts of the second active material and the second binder in the second negative electrode slurry are adjusted, but the composition of the second active material remains unchanged, and the total proportion of the second negative electrode active material and the second binder in the second negative electrode slurry remains unchanged. Table 6 records the proportion of the binder and the test results.

[0250] Table 6

[0251] As can be seen from the data in Table 6, when the content of the first binder increases from 1.5% and the content of the second binder increases from 2%, the elongation at break of the negative current collector and the negative electrode sheet both increase to a certain extent under 100% SOC conditions, indicating that the binder plays a certain role in restraining the expansion of silicon.

[0252] The following examines the effect of the composition of the second conductive agent on the negative electrode sheet.

[0253] Examples 30 to 33 are based on Example 1, except that the mass ratio of carbon black to carbon nanotubes in the second conductive agent is adjusted. The rest are the same as in Example 1. The specific mass ratio and test results are recorded in Table 7.

[0254] Table 7

[0255] As can be seen from the data in Table 7, with the increase of carbon nanotube content in the second conductive agent, the elongation at break of both the negative electrode current collector and the negative electrode sheet increases. This indicates that the carbon nanotubes play a certain role in restraining the expansion of the silicon-carbon composite material, thereby buffering the squeezing effect on the negative electrode current collector and maintaining a high elongation at break of both the negative electrode current collector and the negative electrode sheet in the 100% SOC state.

[0256] The following examines the impact of the undercoating layer on the cycle performance of the negative electrode and the battery cell.

[0257] Example 33 does not have a base coating layer, and is otherwise the same as Example 1.

[0258] Examples 34 and 35 adjust the thickness of the base coating, as detailed in Table 8, and the rest are the same as in Example 1.

[0259] The capacity retention rates of Examples 1, 33 to 35, after 1000 cycles at a 0.33C rate are recorded in Table 8.

[0260] The test results are recorded in Table 8.

[0261] Table 8

[0262] As can be seen from the data in Table 8, when a base coating is set, since the lower negative electrode active material is graphite and the base coating thickness is very small, the difference in base coating thickness has little impact on the negative electrode current collector. The fracture elongation rate in Table 8 only reflects the deviation of the test parameters. However, without a base coating, the negative electrode current collector is more susceptible to corrosion and oxidation. Combined with the expansion of the second negative electrode active layer, this will reduce the elongation rate of the negative electrode current collector.

[0263] The following examines the impact of different types of silicon-based materials on the cycle performance of the negative electrode and the battery cell.

[0264] In Example 36, the second silicon-carbon composite was replaced with a silicon-oxygen composite. The particle size and powder resistivity of the silicon-oxygen composite were also basically the same as those of the second silicon-carbon composite. The rest were the same as in Example 1.

[0265] In Example 37, the second silicon-carbon composite was replaced with a silicon-oxygen composite. The particle size and powder resistivity of the silicon-oxygen composite were also basically the same as those of the second silicon-carbon composite. The rest was the same as in Example 3.

[0266] In Example 38, the second silicon-carbon composite was replaced with a silicon-oxygen composite. The particle size and powder resistivity of the silicon-oxygen composite were also basically the same as those of the second silicon-carbon composite. The rest was the same as in Example 4.

[0267] In Example 39, the second silicon-carbon composite was replaced with a silicon-oxygen composite. The particle size and powder resistivity of the silicon-oxygen composite were also basically the same as those of the second silicon-carbon composite. The rest was the same as in Example 5.

[0268] The main parameters and test results of Examples 36 to 39 are recorded in Table 9.

[0269] Table 9

[0270] As can be seen from the data in Table 9, when silicon-carbon composite is selected as the silicon-based material for the second negative electrode active layer in the negative electrode film, compared with silicon-oxygen composite of the same content, silicon-carbon composite has stronger structural stability and lower volume expansion rate during cycling, thus reducing the elongation of the negative electrode current collector.

[0271] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A battery cell, comprising a wound electrode assembly, the electrode assembly including a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative active layer disposed on at least one side of the negative current collector. The negative electrode active layer includes a first negative electrode active layer and a second negative electrode active layer. The first negative electrode active layer is disposed on at least one side of the negative electrode current collector, and the second negative electrode active layer is disposed on the side of the first negative electrode active layer away from the first negative electrode active layer. The first negative electrode active layer includes a first graphite material and an optional first silicon-based material, and the second negative electrode active layer includes a second silicon-based material and a second graphite material. The mass content of silicon element in the first negative electrode active layer is denoted as A, and the mass content of silicon element in the second negative electrode active layer is denoted as B, where 2.5% ≤ B ≤ 68%, and B > A. When the battery cell is in a 0% SOC state within 50 charge-discharge cycles, the tensile strength of the negative electrode current collector is ≥40 kgf / mm². 2 Elongation at break ≥ 5.0%.

2. The battery cell according to claim 1, wherein, 5.5％≤B≤48％。 3. The battery cell according to claim 1 or 2, wherein, 2.5% ≤ BA ≤ 68%; optionally 5.5% ≤ BA ≤ 48%, further optionally 10% ≤ BA ≤ 40%.

4. The battery cell according to any one of claims 1 to 3, wherein, 0% ≤ A ≤ 40%, optionally 0 ≤ A ≤ 20%.

5. The battery cell according to any one of claims 1 to 4, wherein, The mass content of silicon in the first silicon-based material and the second silicon-based material is independently 30%-70%, and optionally 35%-65%.

6. The battery cell according to any one of claims 1 to 5, wherein, The first silicon-based material and the second silicon-based material are each independently selected from one or more of elemental silicon, silicon-oxygen compounds, and silicon-carbon compounds; Optionally, at least one of the first silicon-based material and the second silicon-based material includes the silicon-carbon composite; Further optionally, the first silicon-based material and the second silicon-based material each independently comprise the silicon-carbon composite; Alternatively, the first silicon-based material and the second silicon-based material each independently comprise a silicon-carbon composite that satisfies one or more of the following characteristics: 1) The silicon-carbon composite comprises porous carbon and silicon-containing material located in the pores and on the surface of the porous carbon. Optionally, the porous carbon is hard carbon, and the silicon-containing material may include crystalline silicon. 2) The silicon-carbon composite further includes a carbon-containing coating layer, which is located on the surface of the porous carbon and / or silicon material; 3) The average particle size of the silicon-carbon composite is 2μm-15μm, and can be selected as 7μm-11μm; 4) The powder resistivity of the silicon-carbon composite at 8 MPa is 4 Ω·cm-17 Ω·cm; 5) The BET specific surface area of ​​the silicon-carbon composite is 1.0 m². 2 / g-6.7m 2 / g.

7. The battery cell according to any one of claims 1 to 6, wherein, When the battery cell is in a 100% SOC state within 50 charge-discharge cycles, the elongation at break of the negative electrode current collector is ≥3.5%.

8. The battery cell according to any one of claims 1 to 7, wherein, When the battery cell is in a 100% SOC state within 50 charge-discharge cycles, the elongation at break of the negative electrode sheet is ≥1.5%.

9. The battery cell according to any one of claims 1 to 8, wherein, The thickness of the negative electrode current collector is 5μm-10μm, and can be selected as 6μm-8μm.

10. The battery cell according to any one of claims 1 to 9, wherein, The thickness of the second negative electrode active layer accounts for 10%-90% of the total thickness of the negative electrode active layer, optionally 12%-80%, and further optionally 15%-70%.

11. The battery cell according to any one of claims 1 to 10, wherein, The first negative electrode active layer further includes a first binder, and the second negative electrode active layer further includes a second binder. The first binder and the second binder each independently include any one or more of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan. Optionally, the mass content of the first binder in the first negative electrode active layer is less than the mass content of the second binder in the second negative electrode active layer.

12. The battery cell according to claim 11, wherein, The first binder has a mass content of 0.5%-5% in the first negative electrode active layer, and is further optionally 1.5%-3.5%; and / or The second binder has a mass content of 1%-5% in the second negative electrode active layer, and is further optionally 1.5%-4.5%.

13. The battery cell according to any one of claims 1 to 12, wherein, The first negative electrode active layer further includes a first conductive agent, and the second negative electrode active layer further includes a second conductive agent. The first conductive agent and the second conductive agent each independently comprise one or more of carbon black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers, or a mixture thereof.

14. The battery cell according to claim 13, wherein, The mass content of the first conductive agent in the first negative electrode active layer is 0.05%-1%, and the mass content of the second conductive agent in the second negative electrode active layer is 0.05%-2%.

15. The battery cell according to claim 13 or 14, wherein, The second conductive agent comprises carbon black and carbon nanotubes, wherein the mass ratio of carbon black to carbon nanotubes is 6:4-9:1, and more preferably 8:2-8.5:1.

5.

16. The battery cell according to any one of claims 1 to 15, wherein, The negative electrode sheet further includes a base coating layer, which is disposed between the negative current collector and the first negative active layer. The base coating layer includes a base conductive agent and a base binder.

17. The battery cell according to claim 16, wherein, The base coating has one or more of the following characteristics: The conductive agent in the primer includes carbon black; The primer adhesive includes polyvinylidene fluoride; The adhesive comprises 70%-90% by mass in the base coating.

18. The battery cell according to claim 16 or 17, wherein, The thickness of the base coating is 0.2μm-2μm.

19. The battery cell according to any one of claims 1 to 18, wherein, The first graphite material and the second graphite material each independently include artificial graphite and / or natural graphite; optionally, the average particle size of the artificial graphite is 3μm-20μm, preferably 4μm-18μm; optionally, the average particle size of the natural graphite is 3μm-20μm, preferably 4μm-18μm.

20. The battery cell according to any one of claims 1 to 19, wherein, The electrode assembly further includes a positive electrode sheet, which includes a positive current collector. When the battery cell is in a 100% SOC state within 50 charge-discharge cycles, the tensile strength of the positive current collector is 30 kgf / mm². 2 -50Kgf / mm 2 Elongation at break ≥1.5%.

21. A negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active layer disposed on at least one side of the negative electrode current collector, The negative electrode active layer includes a first negative electrode active layer and a second negative electrode active layer. The first negative electrode active layer is disposed on at least one side of the negative electrode current collector, and the second negative electrode active layer is disposed on the side of the first negative electrode active layer away from the first negative electrode active layer. The first negative electrode active layer includes a first graphite material and an optional first silicon-based material, and the second negative electrode active layer includes a second silicon-based material and a second graphite material. The mass content of silicon element in the first negative electrode active layer is denoted as A, and the mass content of silicon element in the second negative electrode active layer is denoted as B, where 2.5% ≤ B ≤ 68%, and B > A. The tensile strength of the negative electrode current collector is ≥40 kgf / mm². 2 Elongation at break ≥ 5.0%.

22. The negative electrode sheet according to claim 21, wherein, 5.5％≤B≤48％。 23. The negative electrode sheet according to claim 21 or 22, wherein, 2.5% ≤ BA ≤ 68%; optionally 5.5% ≤ BA ≤ 48%, further optionally 10% ≤ BA ≤ 40%.

24. The negative electrode sheet according to any one of claims 21 to 23, wherein, 0% ≤ A ≤ 40%, optionally 0 ≤ A ≤ 20%.

25. The negative electrode sheet according to any one of claims 21 to 24, wherein, The mass content of silicon in the first silicon-based material and the second silicon-based material is independently 30%-70%, and optionally 35%-65%.

26. The negative electrode sheet according to any one of claims 21 to 25, wherein, The first silicon-based material and the second silicon-based material are each independently selected from one or more of elemental silicon, silicon-oxygen compounds, and silicon-carbon compounds; Optionally, at least one of the first silicon-based material and the second silicon-based material includes the silicon-carbon composite; Further optionally, the first silicon-based material and the second silicon-based material each independently comprise the silicon-carbon composite; Alternatively, the first silicon-based material and the second silicon-based material each independently comprise a silicon-carbon composite that satisfies one or more of the following characteristics: 1) The silicon-carbon composite comprises porous carbon and silicon-containing material located in the pores and on the surface of the porous carbon. Optionally, the porous carbon is hard carbon, and the silicon-containing material may include crystalline silicon. 2) The silicon-carbon composite further includes a carbon-containing coating layer, which is located on the surface of the porous carbon and / or silicon material; 3) The average particle size of the silicon-carbon composite is 2μm-15μm, and can be selected as 7μm-11μm; 4) The powder resistivity of the silicon-carbon composite at 8 MPa is 4 Ω·cm-17 Ω·cm; 5) The BET specific surface area of ​​the silicon-carbon composite is 1.0 m². 2 / g-6.7m 2 / g.

27. The negative electrode sheet according to any one of claims 21 to 26, wherein, The thickness of the negative electrode current collector is 5μm-10μm, and can be selected as 6μm-8μm.

28. The negative electrode sheet according to any one of claims 21 to 27, wherein, The thickness of the second negative electrode active layer accounts for 10%-90% of the total thickness of the negative electrode active layer, preferably 12%-80%, and more preferably 15%-70%.

29. The negative electrode sheet according to any one of claims 21 to 28, wherein, The first negative electrode active layer further includes a first binder, and the second negative electrode active layer further includes a second binder. The first binder and the second binder each independently include any one or more of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan. Optionally, the mass content of the first binder in the first negative electrode active layer is less than the mass content of the second binder in the second negative electrode active layer.

30. The negative electrode sheet according to claim 29, wherein, The first binder has a mass content of 0.5%-5% in the first negative electrode active layer, and is further optionally 1.5%-3.5%; and / or The second binder has a mass content of 1%-5% in the second negative electrode active layer, and is further optionally 1.5%-4.5%.

31. The negative electrode sheet according to any one of claims 21 to 30, wherein, The first negative electrode active layer further includes a first conductive agent, and the second negative electrode active layer further includes a second conductive agent. The first conductive agent and the second conductive agent each independently comprise one or more of carbon black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers, or a mixture thereof.

32. The negative electrode sheet according to claim 31, wherein, The mass content of the first conductive agent in the first negative electrode active layer is 0.05%-1%, and the mass content of the second conductive agent in the second negative electrode active layer is 0.05%-2%.

33. The negative electrode sheet according to claim 31 or 32, wherein, The second conductive agent comprises carbon black and carbon nanotubes, wherein the mass ratio of carbon black to carbon nanotubes is 6:4-9:1, and more preferably 8:2-8.5:1.

5.

34. The negative electrode sheet according to any one of claims 21 to 33, wherein, The negative electrode sheet further includes a base coating layer, which is disposed between the negative current collector and the first negative active layer. The base coating layer includes a base conductive agent and a base binder.

35. The negative electrode sheet according to claim 34, wherein, The base coating has one or more of the following characteristics: The conductive agent in the primer includes carbon black; The primer adhesive includes polyvinylidene fluoride; The adhesive comprises 70%-90% by mass in the base coating.

36. A battery device comprising a plurality of battery cells, wherein, The battery cell includes any one of claims 1 to 20.

37. An electrical device comprising a single battery cell or a battery assembly, wherein, The battery cell includes any one of claims 1 to 20, and the battery device includes the battery device of claim 36.

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