Negative electrode sheet, secondary battery, and electric device

Abstract

A first aspect of the present application provides a negative electrode sheet, comprising a negative electrode current collector, and a first material layer and a second material layer provided on at least one surface of the negative electrode current collector, wherein in a thickness direction of the negative electrode sheet, the second material layer is provided between the negative electrode current collector and the first material layer; the first material layer comprises a first active material, and the first active material comprises a first carbon material and a first silicon material; the second material layer comprises a second active material, and the second active material comprises a second carbon material; and a graphitization degree of the first carbon material is G1, and a graphitization degree of the second carbon material is G2, wherein G1 > G2. Using a first material layer in combination with a second material layer achieves a balance between energy density, kinetic performance, and volume expansion rate in secondary batteries.

Description

An anode sheet, a secondary battery, and an electric device TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemistry, and in particular to an anode sheet, a secondary battery, and an electric device. BACKGROUND

[0002] Secondary batteries, such as lithium ion batteries, have the advantages of high energy storage density, high open-circuit voltage, low self-discharge rate, long cycle life, good safety, and the like, and have been widely used as power sources in products such as mobile phones, unmanned aerial vehicles, two-wheeled vehicles, power tools, and energy storage systems.

[0003] With the increasing demand for energy density of lithium ion batteries, silicon anodes have gradually become an important direction for the development of lithium ion batteries. While silicon material as the negative active material of lithium ion batteries improves the energy density, the poor electronic conductivity and ion transport of silicon material itself leads to the problem of insufficient kinetics of lithium ion batteries. On the other hand, during the process of deintercalating lithium ions, silicon material will cause a large volume change, resulting in a large volume expansion of lithium ion batteries. Therefore, it is difficult to balance the energy density, kinetic performance, and volume expansion rate of lithium ion batteries.

[0004] SUMMARY

[0005] The purpose of the present application is to provide an anode sheet, a secondary battery, and an electric device to balance the energy density, kinetic performance, and volume expansion rate of the secondary battery. The specific technical solutions are as follows:

[0006] It should be noted that the present application uses lithium ion batteries as an example to explain the present application in the summary of the present application, but the secondary battery of the present application is not limited to lithium ion batteries. The specific technical solutions are as follows:

[0007] The first aspect of the present application provides an anode sheet, comprising a negative current collector and a first substance layer and a second substance layer arranged on at least one surface of the negative current collector, along the thickness direction of the anode sheet, the second substance layer is arranged between the negative current collector and the first substance layer; the first substance layer comprises a first active material, the first active material comprises a first carbon material and a first silicon material; the second substance layer comprises a second active material, the second active material comprises a second carbon material; the graphitization degree of the first carbon material is G1, the graphitization degree of the second carbon material is G2; G1>G2. The first substance layer and the second substance layer are used in combination, which is beneficial to balance the energy density, kinetic performance, and volume expansion rate of the anode sheet as a whole, and further beneficial to balance the energy density, kinetic performance, and volume expansion rate of the secondary battery.

[0008] In some embodiments of the present application, 95%≤G1≤98%; and / or, 90%≤G2≤94%. By regulating G1 and / or G2 within the above range, the first substance layer has high energy density and kinetic performance, and the expansion rate of the second substance layer is low, so that the first substance layer and the second substance layer used in combination are conducive to giving consideration to the energy density, kinetic performance and volume expansion rate of the secondary battery.

[0009] In some embodiments of the present application, 3%≤G1-G2≤6%. By regulating G1-G2 within the above range, the first substance layer has high energy density and kinetic performance, and the expansion rate of the second substance layer is low, so that the first substance layer and the second substance layer used in combination are conducive to better giving consideration to the energy density, kinetic performance and volume expansion rate of the secondary battery.

[0010] In some embodiments of the present application, the OI value of the first substance layer is 3 to 6, and the OI value of the second substance layer is 2 to 4. By regulating the OI value of the first substance layer and the OI value of the second substance layer within the above range, the first substance layer has high energy density and kinetic performance, and the expansion rate of the second substance layer is low, so that the first substance layer and the second substance layer used in combination are conducive to better giving consideration to the energy density, kinetic performance and volume expansion rate of the secondary battery.

[0011] In some embodiments of the present application, the second active material comprises a second silicon material; the mass percentage content of the first silicon material based on the mass of the first substance layer is W1, and the mass percentage content of the second silicon material based on the mass of the second substance layer is W2; W1>W2. The first substance layer and the second substance layer used in combination are conducive to better giving consideration to the energy density, kinetic performance and volume expansion rate of the secondary battery.

[0012] In some embodiments of the present application, 30%≤W1≤70%, and 0%<W2≤10%. By regulating W1 and W2 within the above range, the energy density of the first substance layer and the second substance layer is higher, so that the first substance layer and the second substance layer used in combination are conducive to better giving consideration to the energy density, kinetic performance and volume expansion rate of the secondary battery.

[0013] In some embodiments of the present application, the second substance layer does not contain a silicon material. The first substance layer and the second substance layer used in combination are conducive to better giving consideration to the energy density, kinetic performance and volume expansion rate of the secondary battery.

[0014] In some embodiments of the present application, the first carbon material has a charge capacity of 2C to 6C; the second carbon material has a charge capacity of 1.5C to 2C, and the charge capacity of the first carbon material is stronger than that of the second carbon material. The charge capacity of the first carbon material and the charge capacity of the second carbon material are within the above range, which is conducive to improving the charge rate of the secondary battery.

[0015] In some embodiments of the present application, the first carbon material has a gram capacity of C1, and the second carbon material has a gram capacity of C2, C2>C1. The second material layer close to the negative current collector contains the second carbon material with higher gram capacity, which on the one hand helps to improve the capacity of the secondary battery, and on the other hand the second carbon material has good cycle stability, which is conducive to improving the adhesion between the second material layer and the negative current collector, and further improving the structural stability of the overall negative electrode sheet. Therefore, the first material layer and the second material layer are used in combination, which is conducive to better balancing the energy density, kinetic performance and volume expansion rate of the secondary battery.

[0016] In some embodiments of the present application, 340mAh / g≤C1≤365mAh / g; 366mAh / g≤C2≤380mAh / g. By adjusting C1 and C2 within the above range, the first material layer and the second material layer have high capacity, and the overall structural stability of the negative electrode sheet is high, so that the first material layer and the second material layer are used in combination, which is conducive to better balancing the energy density, kinetic performance and volume expansion rate of the secondary battery.

[0017] In some embodiments of the present application, the first carbon material has a Dv50 of D1, and the second carbon material has a Dv50 of D2, D2>D1. The Dv50 of the first carbon material in the first material layer closer to the surface layer of the negative electrode sheet is smaller, that is, the first carbon material has a larger specific surface area than the second carbon material, which can expose more ion binding sites, further improve the kinetic performance, and also reduce the risk of lithium precipitation. Therefore, the kinetic performance of the secondary battery is further improved and the risk of lithium precipitation is reduced, and it is also conducive to balancing the energy density and the volume expansion rate.

[0018] In some embodiments of the present application, 8μm≤D1≤10μm, 11μm≤D2≤15μm. By adjusting D1 and D2 within the above range, the kinetic performance of the first material layer is further improved and the risk of lithium precipitation is reduced, so that the kinetic performance of the secondary battery is further improved and the risk of lithium precipitation is reduced, and it is also conducive to balancing the energy density and the volume expansion rate.

[0019] In some embodiments of the present application, the first carbon material comprises natural graphite, and the second carbon material comprises at least one of artificial graphite or modified graphite. By selecting the first and second carbon materials as described above, it is beneficial to meet G1>G2, so as to balance the energy density, kinetic performance and volume expansion rate of the secondary battery.

[0020] In some embodiments of the present application, the first carbon material comprises first natural graphite, and the mass percentage of the first natural graphite in the first substance layer is A1, 3%≤A1≤30%; the second carbon material comprises second artificial graphite, and the mass percentage of the second artificial graphite in the second substance layer is A2, 90%≤A2≤98%. By regulating A1 and A2 within the above range, the content of the first natural graphite in the first substance layer is relatively small, and the content of the first silicon material is relatively large, so that the first substance layer has high energy density and good kinetic performance. The second substance layer mainly comprises the second artificial graphite, which has good cycle stability and low thickness expansion rate, so that the overall structural stability of the negative electrode sheet is improved. Therefore, the first substance layer and the second substance layer are used in combination, which is beneficial to balance the energy density, kinetic performance and volume expansion rate of the secondary battery.

[0021] In some embodiments of the present application, the first carbon material further comprises first artificial graphite, and the mass percentage of the first artificial graphite in the first substance layer is B1, 10%≤B1≤50%. By regulating B1 within the above range, the first substance layer has high energy density, good kinetic performance and low expansion rate, so that the first substance layer and the second substance layer are used in combination, which is beneficial to better balance the energy density, kinetic performance and volume expansion rate of the secondary battery.

[0022] In some embodiments of the present application, the first carbon material further comprises at least one of hard carbon or soft carbon. The kinetic performance of the first substance layer is further improved, so that the first substance layer and the second substance layer are used in combination, which is beneficial to better balance the energy density, kinetic performance and volume expansion rate of the secondary battery.

[0023] In some embodiments of the present application, the first substance layer further comprises a first binder, and the mass percentage of the first binder in the first substance layer is W N1 ; the second substance layer further comprises a second binder, and the mass percentage of the second binder in the second substance layer is W N2 ; W N1 ≥W N2 . The first substance layer and the second substance layer obtained in combination are used, and the energy density, kinetic performance and volume expansion rate of the secondary battery are further balanced.

[0024] In some embodiments of the present application, 2.5%≤W N1 ≤5%; and / or, 1.5%≤W N2 ≤2.5%. By regulating W N1 and / or W N2 within the above ranges, it is beneficial to better balance the energy density, kinetic performance, and volume expansion rate of the secondary battery.

[0025] In some embodiments of the present application, the first adhesive comprises one or more of sodium alginate, styrene butadiene rubber, polyvinyl alcohol, or polyethylene glycol; and / or, the second adhesive comprises one or more of polyacrylic acid, polymethyl methacrylate, or polyacrylonitrile. By selecting the above first and / or second adhesives, it is beneficial to better balance the energy density, kinetic performance, and volume expansion rate of the secondary battery.

[0026] In some embodiments of the present application, the first substance layer further comprises a first conductive agent, the mass percentage content of the first conductive agent based on the mass of the first substance layer being W D1 ; the second substance layer further comprises a second conductive agent, the mass percentage content of the second conductive agent based on the mass of the second substance layer being W D2 ; 0.45%≤W D1 ≤0.5%; and / or, 0.35%≤W D2 ≤1%. By regulating W D1 and / or W D2 within the above ranges, it is beneficial to better balance the energy density, kinetic performance, and volume expansion rate of the secondary battery.

[0027] In some embodiments of the present application, W D1 ≥W D2 . It is beneficial to make the first substance layer and the second substance layer have good conductive performance, so that the secondary battery has good charge and discharge performance, and it is beneficial to better balance the energy density, kinetic performance, and volume expansion rate of the secondary battery.

[0028] In some embodiments of the present application, the first conductive agent and the second conductive agent each independently comprises one or more of carbon black, ketjen black, acetylene black, carbon nanotube, graphene, or carbon fiber. By selecting the above first and second conductive agents, it is beneficial to better balance the energy density, kinetic performance, and volume expansion rate of the secondary battery.

[0029] In some embodiments of the present application, the first silicon material comprises one or more of pure silicon, a silicon alloy material, a silicon-carbon composite material, or a silicon oxide. By selecting the above first silicon material, the first substance layer has a high energy density, and thus, the first substance layer and the second substance layer used in combination facilitate better balancing of the energy density, kinetic performance, and volume expansion rate of the secondary battery.

[0030] In some embodiments of the present application, the second silicon material comprises one or more of pure silicon, a silicon alloy material, a silicon-carbon composite material, or a silicon oxide. By selecting the above second silicon material, the second substance layer has a high energy density, and thus, the first substance layer and the second substance layer used in combination facilitate better balancing of the energy density, kinetic performance, and volume expansion rate of the secondary battery.

[0031] In some embodiments of the present application, the thickness of the first substance layer is H1, the thickness of the second substance layer is H2, 0.1≤H1 / H2≤1, and 20μm≤H1≤150μm.

[0032] A second aspect of the present application provides a secondary battery comprising the negative electrode tab in any of the foregoing embodiments.

[0033] A third aspect of the present application provides an electric device comprising the secondary battery in any of the foregoing embodiments.

[0034] Advantages of the present application:

[0035] A first aspect of the present application provides a negative electrode tab comprising a negative electrode current collector and a first substance layer and a second substance layer disposed on at least one surface of the negative electrode current collector, the second substance layer being disposed between the negative electrode current collector and the first substance layer along the thickness direction of the negative electrode tab; the first substance layer comprises a first active material, the first active material comprising a first carbon material and a first silicon material; the second substance layer comprises a second active material, the second active material comprising a second carbon material; the graphitization degree of the first carbon material is G1, the graphitization degree of the second carbon material is G2; G1>G2. The first substance layer and the second substance layer used in combination facilitate better balancing of the energy density, kinetic performance, and volume expansion rate of the secondary battery. BRIEF DESCRIPTION OF DRAWINGS

[0036] The accompanying drawings, which are included to provide a further understanding of the present application and are incorporated in and constitute a part of this application, illustrate embodiments of the present application and serve to explain the present application. Features of the present application, both as to organization and method of operation, together with an understanding of the same, can be best understood by reference to the following detailed description, when considered in connection with the accompanying drawings, wherein:

[0037] FIG. 1 is a structural schematic diagram of a negative electrode tab in some embodiments of the present application. DETAILED DESCRIPTION

[0038] For purposes of the present application, the following terms have the following meanings. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Numerous specific details are described herein in order to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that the present application can be practiced without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to unnecessarily obscure aspects of the present application.

[0039] It should be noted that the specific embodiments of the present application are explained by taking lithium ion batteries as examples of secondary batteries, but the secondary batteries of the present application are not limited to lithium ion batteries. The specific technical solutions are as follows:

[0040] The first aspect of the present application provides a negative electrode tab, comprising a negative electrode current collector, and a first substance layer and a second substance layer arranged on at least one surface of the negative electrode current collector, the second substance layer is arranged between the negative electrode current collector and the first substance layer along the thickness direction of the negative electrode tab; the first substance layer comprises a first active material, the first active material comprises a first carbon material and a first silicon material; the second substance layer comprises a second active material, the second active material comprises a second carbon material; the graphitization degree of the first carbon material is G1, the graphitization degree of the second carbon material is G2; G1>G2. The first substance layer is closer to the surface of the negative electrode tab than the second substance layer, the first substance layer also contains the first carbon material with a higher graphitization degree, the first carbon material has a small interlayer spacing of crystal face, good electrical conductivity, small ion diffusion impedance, fast lithium ion diffusion rate, and the first substance layer has better kinetic performance; and the first substance layer contains the first silicon material, and the first substance layer also has a higher energy density. The second substance layer contains the second carbon material with a low graphitization degree, and has a low expansion rate. Therefore, the first substance layer and the second substance layer are used in combination, which is beneficial to taking into account the energy density, kinetic performance and volume expansion rate of the negative electrode tab as a whole, and thus is beneficial to taking into account the energy density, kinetic performance and volume expansion rate of the secondary battery.

[0041] In some embodiments of the present application, 95%≤G1≤98%. For example, G1 can be 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98% or a range between any two of them. By adjusting G1 within the above range, the first carbon material has good kinetic performance, which is beneficial to obtaining a first substance layer with good kinetics, and thus the first substance layer and the second substance layer are used in combination, which is beneficial to better taking into account the kinetic performance, energy density and volume expansion rate of the secondary battery.

[0042] In some embodiments of the present application, 90%≤G2≤94%. For example, G2 can be 90%, 90.5%, 91%, 91.5%, 92%, 92.5%, 93%, 93.5%, 94%, or a range between any two of them. By regulating G2 within the above range, the second carbon material has small cyclic expansion and good cyclic stability, so that the first material layer and the second material layer used in combination can better balance the volume expansion rate and the cyclic performance of the secondary battery.

[0043] In some embodiments of the present application, 95%≤G1≤98% and 90%≤G2≤94%. By regulating G1 and G2 within the above range, the first material layer has high energy density and kinetic performance, and the second material layer has low expansion rate, so that the first material layer and the second material layer used in combination can better balance the energy density, kinetic performance and volume expansion rate of the secondary battery.

[0044] In some embodiments of the present application, 3%≤G1-G2≤6%. For example, G1-G2 can be 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, or a range between any two of them. By regulating G1-G2 within the above range, the first material layer has high energy density and kinetic performance, and the second material layer has low expansion rate, so that the first material layer and the second material layer used in combination can better balance the energy density, kinetic performance and volume expansion rate of the secondary battery.

[0045] In the present application, when the first carbon material comprises multiple substances, G1 is the graphitization degree measured after mixing the multiple substances. When the second carbon material comprises multiple substances, G2 is the graphitization degree measured after mixing the multiple substances.

[0046] In some embodiments of the present application, the OI value of the first material layer is 3 to 6, and the OI value of the second material layer is 2 to 4. For example, the OI value of the first material layer can be 3, 3.5, 4, 4.5, 5, 5.5, 6, or a range between any two of them. For example, the OI value of the second material layer can be 2, 2.5, 3, 3.5, 4, or a range between any two of them. By regulating the OI value of the first material layer and the OI value of the second material layer within the above range, the first material layer has high energy density and kinetic performance, and the second material layer has low expansion rate, so that the first material layer and the second material layer used in combination can better balance the energy density, kinetic performance and volume expansion rate of the secondary battery. In the present application, the OI value of the first material layer is used to represent the orientation index of the first material layer, i.e. the anisotropy degree of the grain arrangement in the first material layer. The OI value of the second material layer is used to represent the orientation index of the second material layer, i.e. the anisotropy degree of the grain arrangement in the second material layer.

[0047] In some embodiments of the present application, as shown in FIG. 1, the negative electrode tab includes a negative current collector 10 and a first substance layer 30 and a second substance layer 20 arranged on both surfaces of the negative current collector 10, along the thickness direction of the negative electrode tab, the second substance layer 20 is arranged between the negative current collector 10 and the first substance layer 30, the first substance layer 30 includes a first active material 31 and a first silicon material 32, and the second substance layer 20 includes a second carbon material 21 and a second silicon material 22. The mass percentage content of the first silicon material in the first substance layer is W1 based on the mass of the first substance layer, and the mass percentage content of the second silicon material in the second substance layer is W2 based on the mass of the second substance layer; W1>W2. That is, the silicon content in the first substance layer is greater than that in the second substance layer, the first substance layer is a high-graphitization first carbon material matched with a high content of silicon, and since the first substance layer is closer to the surface layer of the negative electrode tab, it is beneficial to shorten the active ion (such as lithium ion) transmission path involving Si, alleviate the kinetic problem caused by the poor conductivity of the silicon material, and thus better balance the energy density and kinetic performance of the first substance layer. The second substance layer is a low-graphitization second carbon material matched with a low content of silicon, and has a low volume expansion rate, and the second substance layer is closer to the negative current collector, and the low expansion rate is beneficial to reduce the risk of demolding of the second substance layer and improve the overall structural stability of the negative electrode tab. Therefore, the above-mentioned first substance layer and second substance layer are used in combination, which is beneficial to better balance the energy density, kinetic performance and volume expansion rate of the secondary battery.

[0048] In some embodiments of the present application, 30%≤W1≤70%, 0%<W2≤10%. For example, W1 can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or a range between any two of them. For example, W2 can be 0.01%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range between any two of them. The first substance layer includes a first silicon material, and the second substance layer includes a second silicon material, while W1 and W2 are regulated in the above range, the energy density of the first substance layer and the second substance layer is higher, and thus the first substance layer and the second substance layer are used in combination, which is beneficial to better balance the energy density, kinetic performance and volume expansion rate of the secondary battery.

[0049] In some embodiments of the present application, W2 = 0%, i.e., the second substance layer does not include silicon material. In some embodiments of the present application, 30%≤ W1≤ 70%, W2 = 0%, i.e., the first substance layer includes the first silicon material, and the second substance layer does not include silicon material. The second substance layer does not include silicon material, and the expansion rate of the second substance layer is further reduced. At the same time, the first substance layer contains the first carbon material and the first silicon material, which is conducive to balancing the energy density and kinetic performance of the secondary battery. Therefore, the first substance layer and the second substance layer are used in combination, and the energy density, kinetic performance and volume expansion rate of the secondary battery are balanced.

[0050] In some embodiments of the present application, the charge capacity of the first carbon material is 2C to 6C, and the charge capacity of the second carbon material is 1.5C to 2C. The charge capacity of the first carbon material is stronger than that of the second carbon material. For example, the charge capacity of the first carbon material can be 2C, 2.5C, 3C, 3.5C, 4C, 4.5C, 5C, 5.5C, 6C or a range between any two of them. For example, the charge capacity of the second carbon material can be 1.5C, 1.6C, 1.7C, 1.8C, 1.9C, 2C or a range between any two of them. The charge capacity of the first carbon material and the charge capacity of the second carbon material are within the above range, which is conducive to improving the charge rate of the secondary battery.

[0051] In some embodiments of the present application, the gram capacity of the first carbon material is C1, and the gram capacity of the second carbon material is C2, C2 > C1. The second substance layer close to the negative electrode current collector contains the second carbon material with higher gram capacity, which is conducive to improving the capacity of the secondary battery on the one hand, and the second carbon material has good cycle stability, which is conducive to improving the adhesion between the second substance layer and the negative electrode current collector, and further improving the structural stability of the whole negative electrode sheet. Therefore, the first substance layer and the second substance layer are used in combination, which is conducive to better balancing the energy density, kinetic performance and volume expansion rate of the secondary battery.

[0052] In some embodiments of the present application, 340 mAh / g≤C1≤365 mAh / g; 366 mAh / g≤C2≤380 mAh / g. For example, C1may be 340 mAh / g, 341 mAh / g, 342 mAh / g, 343 mAh / g, 344 mAh / g, 345 mAh / g, 346 mAh / g, 347 mAh / g, 348 mAh / g, 349 mAh / g, 350 mAh / g, 351 mAh / g, 352 mAh / g, 353 mAh / g, 354 mAh / g, 355 mAh / g, 356 mAh / g, 357 mAh / g, 358 mAh / g, 359 mAh / g, 360 mAh / g, 361 mAh / g, 362 mAh / g, 363 mAh / g, 364 mAh / g, 365 mAh / g, or a range between any two of them. For example, C2may be 366 mAh / g, 367 mAh / g, 368 mAh / g, 369 mAh / g, 370 mAh / g, 371 mAh / g, 372 mAh / g, 373 mAh / g, 374 mAh / g, 375 mAh / g, 376 mAh / g, 377 mAh / g, 378 mAh / g, 379 mAh / g, 380 mAh / g, or a range between any two of them. By adjusting C1and C2within the above ranges, the first substance layer and the second substance layer have high capacity, and the overall structure stability of the negative electrode sheet is high, so that the first substance layer and the second substance layer are used in combination, which is conducive to better balancing the energy density, kinetic performance and volume expansion rate of the secondary battery.

[0053] In the present application, when the first carbon material contains multiple substances, C1is the gram capacity measured after mixing the multiple substances. When the second carbon material contains multiple substances, C2is the gram capacity measured after mixing the multiple substances.

[0054] In some embodiments of the present application, the Dv50 of the first carbon material is D1, the Dv50 of the second carbon material is D2, and D2>D1. The Dv50 of the first carbon material in the first substance layer closer to the surface layer of the negative electrode sheet is smaller, that is, the specific surface area of the first carbon material is larger than that of the second carbon material, which can expose more ion binding sites, further improve the kinetic performance, and also reduce the risk of lithium precipitation. Thus, the kinetic performance of the secondary battery is further improved and the risk of lithium precipitation is reduced, while it is also conducive to balancing the energy density and the volume expansion rate.

[0055] In some embodiments of the present application, 8 μm≤D1≤10 μm, 11 μm≤D2≤15 μm. For example, D1 can be 8 μm, 8.1 μm, 8.2 μm, 8.3 μm, 8.4 μm, 8.5 μm, 8.6 μm, 8.7 μm, 8.8 μm, 8.9 μm, 9 μm, 9.1 μm, 9.2 μm, 9.3 μm, 9.4 μm, 9.5 μm, 9.6 μm, 9.7 μm, 9.8 μm, 9.9 μm, 10 μm, or a range between any two of the above values. For example, D2 can be 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, or a range between any two of the above values. By adjusting D1 and D2 within the above ranges, the kinetic performance of the first substance layer is further improved and the risk of lithium precipitation is reduced, thereby further improving the kinetic performance of the secondary battery and reducing the risk of lithium precipitation, while also being conducive to balancing the energy density and volume expansion rate.

[0056] In the present application, when the first carbon material comprises multiple substances, D1 is the Dv50 measured after mixing the multiple substances. When the second carbon material comprises multiple substances, D2 is the Dv50 measured after mixing the multiple substances.

[0057] In some embodiments of the present application, the first carbon material comprises natural graphite, and the second carbon material comprises at least one of artificial graphite or modified graphite. By selecting the above first carbon material and second carbon material, it is conducive to meeting G1>G2, thereby being conducive to balancing the energy density, kinetic performance, and volume expansion rate of the secondary battery.

[0058] In the present application, natural graphite refers to a naturally occurring layered graphite material. Artificial graphite refers to a graphite material obtained by organic carbonization followed by high-temperature graphitization treatment, and modified graphite refers to a graphite material obtained by coating, surface treatment, doping, structural modification, or the like. The present application does not limit the treatment method of the above artificial graphite and modified graphite, as long as it meets the requirements of the first carbon material and the second carbon material of the present application.

[0059] In some embodiments of the present application, the first active material includes a first carbon material and a first silicon material, the first carbon material includes a first natural graphite, a mass percentage of the first natural graphite is A1 based on a mass of the first substance layer, 3%≤A1≤30%, a mass percentage of the first silicon material is W1, 30%≤W1≤70%. For example, A1 can be 3%, 5%, 7%, 9%, 10%, 12%, 14%, 15%, 17%, 19%, 20%, 22%, 24%, 25%, 27%, 29%, 30%, or a range between any two of the numbers. The second active material includes a second carbon material and a second silicon material, the second carbon material includes a second artificial graphite, a mass percentage of the second artificial graphite is A2 based on a mass of the second substance layer, 90%≤A2≤98%, a mass percentage of the second silicon material is W2, 0%≤W2≤10%. For example, A2 can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or a range between any two of the numbers. By adjusting A1 and A2 within the above range, the content of the first natural graphite in the first substance layer is relatively small, and the content of the first silicon material is relatively large, so that the first substance layer has high energy density and good kinetic performance. The second artificial graphite is mainly in the second substance layer, which has good cycle stability and low thickness expansion rate, so that the overall structural stability of the negative electrode plate is improved. Therefore, the first substance layer and the second substance layer are used in combination, which is conducive to balancing the energy density, kinetic performance and volume expansion rate of the secondary battery.

[0060] In some embodiments of the present application, the first active material includes a first carbon material and a first silicon material, the first carbon material includes a first natural graphite and a first artificial graphite; a mass percentage of the first natural graphite is A1 based on a mass of the first substance layer, 3%≤A1≤30%, a mass percentage of the first artificial graphite is B1, 10%≤B1≤50%, a mass percentage of the first silicon material is W1, 30%≤W1≤70%. For example, B1 can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or a range between any two of the numbers. The first substance layer includes the first natural graphite, the first artificial graphite and the first silicon material, and B1 is adjusted within the above range, so that the first substance layer has high energy density, good kinetic performance and low expansion rate at the same time. Therefore, the first substance layer and the second substance layer are used in combination, which is conducive to better balancing the energy density, kinetic performance and volume expansion rate of the secondary battery.

[0061] In some embodiments of the present application, the first active material comprises a first carbon material and a first silicon material, and the first carbon material comprises a first natural graphite, a first artificial graphite and a hard carbon. In some embodiments of the present application, the mass percentage content of the first natural graphite is A1, the mass percentage content of the first artificial graphite is B1, the mass percentage content of the hard carbon is E1, and the mass percentage content of the first silicon material is W1, based on the mass of the first substance layer, 3%≤A1≤30%, 10%≤B1≤50%, 1%≤E1≤15%, and 30%≤W1≤70%. The hard carbon material has good kinetic performance, which can further improve the kinetic performance of the first substance layer. Therefore, the first substance layer and the second substance layer are used in combination, which is conducive to better balancing the energy density, kinetic performance and volume expansion rate of the secondary battery.

[0062] In some embodiments of the present application, the first active material comprises a first carbon material and a first silicon material, and the first carbon material comprises a first natural graphite, a first artificial graphite and a soft carbon. In some embodiments of the present application, the mass percentage content of the first natural graphite is A1, the mass percentage content of the first artificial graphite is B1, the mass percentage content of the soft carbon is E2, and the mass percentage content of the first silicon material is W1, based on the mass of the first substance layer, 3%≤A1≤30%, 10%≤B1≤50%, 1%≤E2≤15%, and 30%≤W1≤70%. The soft carbon material has good kinetic performance, which can further improve the kinetic performance of the first substance layer. Therefore, the first substance layer and the second substance layer are used in combination, which is conducive to better balancing the energy density, kinetic performance and volume expansion rate of the secondary battery.

[0063] In some embodiments of the present application, the first active material comprises a first carbon material and a first silicon material, and the first carbon material comprises a first natural graphite, a first artificial graphite, a hard carbon and a soft carbon. In some embodiments of the present application, the mass percentage content of the first natural graphite is A1, the mass percentage content of the first artificial graphite is B1, the mass percentage content of the hard carbon is E1, the mass percentage content of the soft carbon is E2, and the mass percentage content of the first silicon material is W1, based on the mass of the first substance layer, 3%≤A1≤30%, 10%≤B1≤50%, 1%≤E1≤10%, 1%≤E2≤10%, and 30%≤W1≤70%. The kinetic performance of the first substance layer is further improved. Therefore, the first substance layer and the second substance layer are used in combination, which is conducive to better balancing the energy density, kinetic performance and volume expansion rate of the secondary battery.

[0064] In the present application, the hard carbon refers to a carbon material which is difficult to graphitize even at a high temperature above 2500℃, and the soft carbon refers to an amorphous carbon material which can be graphitized at a high temperature above 2500℃.

[0065] In the present application, the first carbon material with different graphitization degrees, gram capacities, Dv50, and charge capacities can be purchased and selected according to the test methods of the graphitization degrees, gram capacities, Dv50, and charge capacities provided in the present application. Similarly, the second carbon material can also be obtained by the similar method.

[0066] In some embodiments of the present application, the first substance layer further comprises a first binder, and the mass percentage of the first binder based on the mass of the first substance layer is W N1 ; the second substance layer further comprises a second binder, and the mass percentage of the second binder based on the mass of the second substance layer is W N2 ; W N1 ≥ W N2 . In some embodiments of the present application, W N1 = W N2 , and the first substance layer and the second substance layer both have good kinetic performance. In some embodiments of the present application, W N1 > W N2 . When the silicon content in the first substance layer is high, the content of the matching first binder is relatively high, which is beneficial to improve the flexibility of the first substance layer, relieve the stress in the expansion process of the first silicon material, reduce the probability of brittle fracture of the negative electrode sheet, improve the structural stability of the negative electrode sheet, and further improve the cycle expansion rate of the secondary battery. When the silicon content in the second substance layer is low, the content of the matching second binder is relatively low, which is beneficial to better balance the kinetic performance. Therefore, the first substance layer and the second substance layer are used in combination, and the energy density, kinetic performance, and volume expansion rate of the secondary battery are further balanced.

[0067] In some embodiments of the present application, 2.5% ≤ W N1 ≤ 5%. For example, W N1 may be 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5%, or a range between any two of the above values. By adjusting W N1 within the above range, the flexibility of the first substance layer is improved, the stress in the expansion process of the first silicon material is relieved, the probability of brittle fracture of the negative electrode sheet is reduced, the structural stability of the negative electrode sheet is improved, and the cycle expansion rate of the secondary battery is further improved. Therefore, the first substance layer and the second substance layer are used in combination, which is beneficial to better balance the energy density, kinetic performance, and volume expansion rate of the secondary battery.

[0068] In some embodiments of the present application, 1.5%≤W N2 ≤2.5%. For example, W N2 may be 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, or a range between any two of them. By adjusting W N2 Within the above range, the second substance layer is conducive to better balancing the energy density, so that the first substance layer and the second substance layer are used in combination, which is conducive to further balancing the energy density, kinetic performance, and volume expansion rate of the secondary battery.

[0069] In some embodiments of the present application, 2.5%≤W N1 ≤5%, 1.5%≤W N2 ≤2.5%. By adjusting W N1 and W N2 Within the above range, it is conducive to further balancing the energy density, kinetic performance, and volume expansion rate of the secondary battery.

[0070] In some embodiments of the present application, the first adhesive includes one or more of sodium alginate, styrene butadiene rubber, polyvinyl alcohol, or polyethylene glycol. The above first adhesive has good flexibility, and by selecting the above first adhesive, it is conducive to further improving the flexibility of the first substance layer, reducing the probability of brittle fracture of the negative electrode sheet, improving the structural stability of the negative electrode sheet, and improving the cycle expansion rate of the secondary battery. Thus, the first substance layer and the second substance layer are used in combination, which is conducive to better balancing the energy density, kinetic performance, and volume expansion rate of the secondary battery.

[0071] In some embodiments of the present application, the second adhesive includes one or more of polyacrylic acid, polymethyl methacrylate, or polyacrylonitrile. The above second adhesive has good adhesion, which is conducive to improving the adhesion between the second substance layer and the negative current collector, reducing the risk of demolding of the second substance layer, and improving the overall structural stability of the negative electrode sheet. Thus, the first substance layer and the second substance layer are used in combination, which is conducive to better balancing the energy density, kinetic performance, and volume expansion rate of the secondary battery.

[0072] In some embodiments of the present application, the first adhesive includes one or more of sodium alginate, styrene butadiene rubber, polyvinyl alcohol, or polyethylene glycol; and the second adhesive includes one or more of polyacrylic acid, polymethyl methacrylate, or polyacrylonitrile. By selecting the above first adhesive and the second adhesive, it is conducive to better balancing the energy density, kinetic performance, and volume expansion rate of the secondary battery.

[0073] In some embodiments of the present application, the first substance layer further comprises a first conductive agent, and the mass percentage content of the first conductive agent is W D1 ; the second substance layer further comprises a second conductive agent, and the mass percentage content of the second conductive agent is W D2 .

[0074] In some embodiments of the present application, 0.45%≤W D1 ≤0.5%. For example, W D1 may be 0.45%, 0.46%, 0.47%, 0.48%, 0.49%, 0.5%, or a range between any two of them. By adjusting W D1 within the above range, it is beneficial to make the first substance layer have good conductive performance, so that the secondary battery has good charge-discharge performance, and it is beneficial to better balance the energy density, kinetic performance and volume expansion rate of the secondary battery.

[0075] In some embodiments of the present application, 0.35%≤W D2 ≤1%. For example, W D2 may be 0.35%, 0.36%, 0.37%, 0.38%, 0.39%, 0.4%, 0.41%, 0.42%, 0.43%, 0.44%, 0.45%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or a range between any two of them. By adjusting W D2 within the above range, it is beneficial to make the second substance layer have good conductive performance, so that the secondary battery has good charge-discharge performance, and it is beneficial to better balance the energy density, kinetic performance and volume expansion rate of the secondary battery.

[0076] In some embodiments of the present application, 0.45%≤W D1 ≤0.5%, and 0.35%≤W D2 ≤1%. By adjusting W D1 and W D2 within the above range, it is beneficial to better balance the energy density, kinetic performance and volume expansion rate of the secondary battery.

[0077] In some embodiments of the present application, W D1 ≥ W D2 . In some embodiments of the present application, W D1 = W D2 . In some embodiments of the present application, the content of the first silicon material is greater than the content of the second silicon material, W D1 > W D2The first material layer and the second material layer have good conductivity, and thus the secondary battery has good charge-discharge performance, and the energy density, kinetic performance and volume expansion rate of the secondary battery can be better balanced.

[0078] In some embodiments of the present application, the first conductive agent and the second conductive agent each independently include one or more of carbon black, ketjen black, acetylene black, carbon nanotube, graphene or carbon fiber. By selecting the above-mentioned first conductive agent and the second conductive agent, the energy density, kinetic performance and volume expansion rate of the secondary battery can be better balanced.

[0079] In some embodiments of the present application, the first silicon material includes one or more of pure silicon, a silicon alloy material, a silicon-carbon composite material or silicon oxide. The silicon alloy material can include, but is not limited to, at least one of Si-Ag alloy, Si-Zn alloy, Si-Al alloy or Si-Fe alloy. By selecting the above-mentioned first silicon material, the first material layer has high energy density, and thus the first material layer and the second material layer used in combination can better balance the energy density, kinetic performance and volume expansion rate of the secondary battery.

[0080] In some embodiments of the present application, the second silicon material includes one or more of pure silicon, a silicon alloy material, a silicon-carbon composite material or silicon oxide. The silicon alloy material can include, but is not limited to, at least one of Si-Ag alloy, Si-Zn alloy, Si-Al alloy or Si-Fe alloy. By selecting the above-mentioned second silicon material, the second material layer has high energy density, and thus the first material layer and the second material layer used in combination can better balance the energy density, kinetic performance and volume expansion rate of the secondary battery.

[0081] In some embodiments of the present application, the thickness of the first material layer is H1, the thickness of the second material layer is H2, 0.1≤H1 / H2≤1, and 20μm≤H1≤150μm. For example, H1 / H2 can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or a range between any two of them. For example, H1 can be 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm or a range between any two of them. In some embodiments of the present application, H1=H2. In some embodiments of the present application, 0.1≤H1 / H2<1, that is, the thickness of the first material layer is less than the thickness of the second material layer, which is more conducive to balancing the kinetic performance and volume expansion rate of the secondary battery.

[0082] In some embodiments of the present application, 40 pm ≤ H2≤ 200 pm. For example, H2may be 40 pm, 50 pm, 60 pm, 70 pm, 80 pm, 90 pm, 100 pm, 110 pm, 120 pm, 130 pm, 140 pm, 150 pm, 160 pm, 170 pm, 180 pm, 190 pm, 200 pm, or a range between any two of these values.

[0083] The negative current collector of the present application is not particularly limited as long as the object of the present application can be achieved, and for example, can include a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, or a composite current collector (for example, a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, or the like).

[0084] The thickness of the negative current collector of the present application is not particularly limited as long as the object of the present application can be achieved, and for example, the thickness of the negative current collector is 4 pm to 15 pm. The thickness of the negative electrode sheet of the present application is not particularly limited as long as the object of the present application can be achieved, and for example, the thickness of the negative electrode sheet is 30 pm to 330 pm.

[0085] The second aspect of the present application provides a secondary battery including the negative electrode sheet of any one of the foregoing embodiments.

[0086] In the present application, the secondary battery further includes a positive electrode sheet including a positive current collector and a positive electrode material layer provided on at least one surface of the positive current collector. The above-mentioned "positive electrode material layer provided on at least one surface of the positive current collector" means that the positive electrode material layer can be provided on one surface of the positive current collector in the thickness direction thereof, or can be provided on both surfaces of the positive current collector in the thickness direction thereof. Note that the "surface" herein can be the entire area of the surface of the positive current collector, or can be a partial area of the surface of the positive current collector, and the present application is not particularly limited as long as the object of the present application can be achieved.

[0087] The positive current collector of the present application is not particularly limited as long as the object of the present application can be achieved, and for example, can include an aluminum foil, an aluminum alloy foil, or a composite current collector (for example, an aluminum-carbon composite current collector), or the like.

[0088] The positive electrode material layer includes a positive electrode active material, and the positive electrode active material of the present application is not particularly limited as long as the object of the present application can be achieved, and for example, can include at least one of lithium nickel cobalt manganese oxide (for example, NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based material, lithium cobaltate (LiCoO2), lithium manganate, lithium manganese iron phosphate, or lithium titanate, but is not limited thereto.

[0089] The positive electrode material layer can further include a conductive agent and a binder, and the kind of the conductive agent and the binder is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the conductive agent can be at least one of the first conductive agent and / or the second conductive agent described above, and the binder can be at least one of the first binder and / or the second binder described above. The mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode material layer is not particularly limited in the present application, and can be selected by a person skilled in the art according to actual needs as long as the purpose of the present application can be achieved.

[0090] The thickness of the positive electrode current collector and the positive electrode material layer is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, and the thickness of the positive electrode material layer is 30 μm to 250 μm.

[0091] Optionally, the positive electrode sheet can further include a conductive layer, and the conductive layer is located between the positive electrode current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited and can be a commonly used conductive layer in the art. The conductive layer includes a conductive agent and a binder. The conductive agent and the binder in the conductive layer are not particularly limited in the present application, and for example, can be at least one of the conductive agent and the binder described above.

[0092] In the present application, the secondary battery further includes a separator film for separating the positive electrode sheet and the negative electrode sheet, preventing internal short circuit of the secondary battery, allowing electrolyte ions to pass freely, and not affecting the electrochemical charging and discharging process. The separator film is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the material of the separator film can include, but is not limited to, at least one of polyethylene (PE), polyolefin (PO) based on polypropylene (PP), polyester (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of the separator film can include at least one of a woven film, a non-woven film, a microporous film, a composite film, a calendered film, or a spunlaid film.

[0093] In some embodiments of the present application, the separator film can include a substrate layer and a surface treatment layer. The substrate layer can be a non-woven fabric, a film, or a composite film having a porous structure, and the material of the substrate layer can include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganics.

[0094] For example, the inorganic layer includes inorganic particles and a binder, the inorganic particles are not particularly limited, and for example, can include at least one of alumina, silica, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder is not particularly limited, and for example, can be at least one of the above-described binders. The polymer layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0095] In the present application, the secondary battery further includes an electrolyte including a lithium salt and other non-aqueous solvent.

[0096] The lithium salt is not particularly limited in the present application as long as the object of the present application can be achieved. For example, the lithium salt can include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. The concentration of the lithium salt in the electrolyte is not particularly limited in the present application as long as the object of the present application can be achieved.

[0097] The non-aqueous solvent according to the present application is not particularly limited as long as the object of the present application can be achieved, and for example, at least one of a carbonate compound, a carboxylic acid ester compound, an ether compound, or other organic solvents can be included. The carbonate compound can include, but is not limited to, at least one of a chain carbonate compound, a cyclic carbonate compound, or a fluoro-carbonate compound. The chain carbonate compound can include, but is not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The cyclic carbonate can include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinyl ethylene carbonate (VEC). The fluoro-carbonate compound can include, but is not limited to, at least one of fluoro-ethylene carbonate (FEC), 1,2-difluoro-ethylene carbonate, 1,1-difluoro-ethylene carbonate, 1,1,2-trifluoro-ethylene carbonate, 1,1,2,2-tetrafluoro-ethylene carbonate, 1-fluoro-2-methyl-ethylene carbonate, 1-fluoro-1-methyl-ethylene carbonate, 1,2-difluoro-1-methyl-ethylene carbonate, 1,1,2-trifluoro-2-methyl-ethylene carbonate, or trifluoromethyl-ethylene carbonate. The carboxylic acid ester compound can include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valerolactone, or caprolactone. The ether compound can include, but is not limited to, at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The other organic solvent can include, but is not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidinone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. The content of the non-aqueous solvent in the electrolyte is not particularly limited as long as the object of the present application can be achieved.

[0098] The secondary battery further includes a case for accommodating the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte, and other components known in the art of secondary batteries, and the present application does not limit the other components. The case is not particularly limited as long as it can achieve the object of the present application, and can be a case known in the art. For example, the case can be a hard case or a flexible case. The material of the hard case can be a metal, and the type of the metal is not particularly limited, and a metal hard case known in the art can be used as long as the object of the present application can be achieved. The flexible case can be a metal plastic film, for example, an aluminum plastic film, a steel plastic film, or the like.

[0099] The preparation process of the secondary battery of the present application is well known to those skilled in the art, and the present application is not particularly limited, for example, the preparation process of the secondary battery can include but is not limited to the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and winding, folding, etc. as needed to obtain an electrode assembly of a wound structure, placing the electrode assembly into the case, injecting the electrolyte into the case and sealing to obtain the secondary battery. Alternatively, the positive electrode sheet, the separator and the negative electrode sheet are stacked in order, and then the four corners of the entire stack structure are fixed with adhesive tape to obtain an electrode assembly of a stack structure, the electrode assembly is placed into the case, the electrolyte is injected into the case and sealed to obtain the secondary battery. In addition, the overcurrent prevention element, the guide plate, etc. can also be placed in the case as needed, thereby preventing the pressure inside the secondary battery from rising, overcharging and discharging.

[0100] In some embodiments of the present application, the secondary battery of the present application can include but is not limited to: a lithium metal secondary battery, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery or a lithium ion polymer secondary battery, etc. In some embodiments of the present application, the secondary battery includes a lithium ion battery.

[0101] The third aspect of the present application provides an electrical device including the secondary battery of any one of the preceding embodiments. Thus, the electrical device provided by the present application has good use performance.

[0102] The present application does not particularly limit the type of the electrical device, which can be any electrical device known in the art. In some embodiments of the present application, the electrical device can include but is not limited to a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, an electric tool, a flash, a camera, a household large storage battery and a lithium ion capacitor, etc.

[0103] Embodiments

[0104] Hereinafter, embodiments and comparative examples are given to more specifically explain the embodiments of the present application. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are on a mass basis.

[0105] Test methods and apparatus:

[0106] Cycling test:

[0107] (1) Charge the lithium ion battery at 25℃ to 4V at a constant current of 2.3C, then charge to 4V at a constant voltage until the current reaches 1C, continue to charge the lithium ion battery to 4.3V at a constant current of 1C, then charge to 4.3V at a constant voltage until the current reaches 0.05C, stand for 15min, then discharge to 2.5V at a rate of 3C, stand for 15min, take this as a cycle, repeat the above process for 400 cycles.

[0108] Record the initial capacity of the lithium ion battery C0, the discharge capacity after 400 cycles C', calculate the cycle capacity retention rate of the lithium ion battery, cycle capacity retention rate = C' / C0x100%.

[0109] (2) Place the lithium ion battery in a 25℃ environment, charge the lithium ion battery to 3.6V at a constant current of 1C, then charge to 3.6V at a constant voltage until the current reaches 0.05C, that is, test the initial thickness of the lithium ion battery at half charge, denoted as T0; after 400 cycles according to step (1), charge to 4V at a constant current of 2.3C, then charge to 4V at a constant voltage until the current reaches 1C, charge to 4.3V at a constant current of 1C, then charge to 4.3V at a constant voltage until the current reaches 0.05C, reach full charge state, test the thickness of the lithium ion battery after cycling at full charge, denoted as T2;

[0110] Wherein the formula for calculating the cycle expansion rate is: cycle expansion rate (%) = T2 / T0x100%.

[0111] Low-temperature lithium precipitation level test:

[0112] Charge the lithium ion battery to 4.3V at a constant current of X (X = 1C, 1.2C, 1.3C, 1.4C, 1.5C, 1.6C, 1.7C, 1.8C, 1.9C, 2C……) at 5℃, then charge to 4.3V at a constant voltage until the current reaches 0.05C, stand for 15min, then discharge to 2.5V at a rate of 0.5C, stand for 30min. Take this as a cycle, repeat the above process for 10 cycles, charge to 4.3V at a constant current of X, then charge to 4.3V at a constant voltage until the current reaches 0.05C, reach full charge state, disassemble the lithium ion battery after full charge, observe whether lithium precipitation occurs on the negative electrode plate, if there is no lithium precipitation area on the negative electrode plate, continue to increase the value of X, if it is found that there is a region with lithium precipitation on the negative electrode plate with a size greater than or equal to 2mm 2 , then determine that the negative electrode plate has lithium precipitation, record the maximum value of X when there is no lithium precipitation as the lithium precipitation level test result.

[0113] 4C discharge temperature rise test:

[0114] Charging the lithium ion battery at 1C constant current to 4.3V at 25℃, then charging at 4.3V constant voltage to current reaches 0.05C, static 15min; then discharging at 4C rate constant current to 2.5V, static 15min, using temperature wire to get the body temperature rise of the lithium ion battery in the middle of the diagonal line of the lithium ion battery body, the difference between the highest temperature in the temperature rise process and 25℃ is recorded as the discharge temperature rise. Among them, the lithium ion battery body refers to the largest surface among the surfaces of the lithium ion battery.

[0115] Weight energy density test:

[0116] Charging the lithium ion battery at 0.5C constant current to 4.3V at 25℃, then charging at 4.3V constant voltage to current reaches 0.05C, static 15min, then discharging at 0.5C rate to 2.5V, record the discharge energy; weigh the mass of the lithium ion battery. The weight energy density of the lithium ion battery = discharge energy / mass of the lithium ion battery.

[0117] OI value test:

[0118] The OI value of the negative electrode active material layer is used to characterize the orientation index of the active material in the negative electrode active material layer. The OI value of the negative electrode active material layer can be calculated by using the X-ray diffraction spectrum measured by the X-ray powder diffractometer.

[0119] OI value = C004 / C110, wherein C004 is the peak area of the 004 characteristic diffraction peak of the negative electrode active material layer, and C110 is the peak area of the 110 characteristic diffraction peak of the negative electrode active material layer.

[0120] Specific test method: control the environmental temperature to be 25℃, the environmental humidity <2%, take the negative electrode sheet sample, the size is 30mm*30mm, use double-sided tape to paste the sheet on one end of a clean glass slide, place it in the Bruker D8Discover X-ray powder diffractometer, set the scanning angle range to be 50°-80°, step length 0.01°, each step time 0.9S, start the equipment to obtain the X-ray diffraction spectrum of the first material layer, use the software DIFFRAC.EVAV4.2.2 to obtain the peak area of the 004 crystal face diffraction peak and the peak area of the 110 crystal face diffraction peak of the first material layer, so as to obtain the OI value of the first material layer by the formula OI = C004 / C110. Scrape off the first material layer on the surface of the negative electrode sheet, and test the OI value of the second material layer in the same way as above.

[0121] Graphitization degree test:

[0122] The average interlayer spacing d002 of the C(002) crystal plane in the crystal structure of the first carbon material is tested using an X-ray diffractometer (such as a Bruker D8 Discover), and the testing method refers to the standard JB / T 4220-2011 “Determination method of lattice parameters of artificial graphite”. Then the graphitization degree G1 of the first carbon material is calculated according to the formula G1 = (0.344-d002) / (0.344-0.3354) x 100%. In the above formula, d002 is the average interlayer spacing of the C(002) crystal plane in the crystal structure of the material, expressed in nanometers (nm). Replace the first carbon material with the second carbon material, and the graphitization degree G2 of the second carbon material can be obtained.

[0123] When the first carbon material contains multiple substances, G1 is the graphitization degree measured after the multiple substances are mixed according to the proportions in the corresponding example or comparative example. When the second carbon material contains multiple substances, G2 is the graphitization degree measured after the multiple substances are mixed according to the proportions in the corresponding example or comparative example.

[0124] Gram capacity test:

[0125] The first carbon material, the binder, and the conductive agent conductive carbon black (Super P) are mixed in a mass ratio of 96:0.5:3.5, deionized water is added as a solvent, and a slurry with a solid content of 45wt% is prepared, which is then coated on one surface of a copper foil and dried; the above steps are repeated on the other surface of the copper foil to obtain a test electrode. The test electrode and a lithium sheet are assembled into a button cell, wherein the binder is butadiene rubber (SBR) and polyacrylic acid (PAA) in a mass ratio of 1:1, the electrolyte is the electrolyte in Example 1-1, and the separator is the separator in Example 1-1.

[0126] The button cell is discharged at 0.05C constant current to 0.005V at 25°C, then continues to discharge at 50μA constant current to 0.005V, stands for 1h, continues to discharge at 10μA to 0.005V, and then charges at 0.05C constant current to 2V, and the charge capacity is recorded. The gram capacity C1 of the first carbon material = charge capacity / mass of the first carbon material in the button cell.

[0127] Replace the first carbon material with the second carbon material, and the gram capacity C2 of the second carbon material can be measured.

[0128] When the first carbon material contains multiple substances, C1 is the gram capacity measured after the multiple substances are mixed according to the proportions in the corresponding example or comparative example. When the second carbon material contains multiple substances, C2 is the gram capacity measured after the multiple substances are mixed according to the proportions in the corresponding example or comparative example.

[0129] Charging capacity test:

[0130] The first carbon material, the binder, and the conductive agent Super P were mixed in a mass ratio of 96:0.5:3.5, deionized water was added as a solvent, and a slurry with a solid content of 45 wt% was prepared, which was then coated on one surface of a copper foil and dried. The above step was repeated on the other surface of the copper foil to obtain a test electrode. The test electrode and the positive electrode in Example 1-1 were assembled into a single-layer stacked battery, wherein the binder was SBR and PAA in a mass ratio of 1:1, the electrolyte was the electrolyte in Example 1-1, and the separator was the separator in Example 1-1.

[0131] The lithium ion battery was charged at a constant current of X (X = 1C, 1.2C, 1.3C, 1.4C, 1.5C, 1.6C, 1.7C, 1.8C, 1.9C, 2C, and so on) to 4.3V at 25°C, and then held at 4.3V until the current reached 0.05C, and then rested for 15 min. Subsequently, the battery was discharged at a rate of 0.5C to 2.5V, and then rested for 30 min. This was taken as one cycle, and the above process was repeated for 10 cycles. The capacity retention rate after 10 cycles was calculated as the discharge capacity in the 10th cycle / the discharge capacity in the first cycle. When the capacity retention rate after 10 cycles was ≥99%, it was considered that the first carbon material could meet the charging capacity. During the test, the value of X was continuously increased, and the maximum value of X at which the capacity retention rate after 10 cycles was ≥99% was recorded as the charging capacity test result of the first carbon material. The capacity retention rate after 10 cycles refers to the capacity retention rate of each lithium ion battery during the first 1 to 10 cycles.

[0132] When the first carbon material is replaced by the second carbon material, the charging capacity of the second carbon material can be measured.

[0133] When the first carbon material comprises multiple substances, the charging capacity of the first carbon material is the charging capacity measured after the multiple substances are mixed according to the proportions in the corresponding example or comparative example. When the second carbon material comprises multiple substances, the charging capacity of the second carbon material is the charging capacity measured after the multiple substances are mixed according to the proportions in the corresponding example or comparative example.

[0134] Dv50 test:

[0135] The Dv50 of the first carbon material and the second carbon material was measured by using a Mastersizer 3000 particle size tester produced by Malvern. Dv50 refers to the particle size reaching 50% of the volume accumulation from the small particle size in the particle size distribution of the material on the volume basis.

[0136] Example 1-1

[0137] Preparation of a positive electrode

[0138] The positive electrode active material LiNi 0.8 Co 0.1 Mn0.1 O2(NCM811), conductive agent conductive carbon black (Super P), binder polyvinylidene fluoride were mixed in a mass ratio of 97.9:0.9:1.2, N-methyl pyrrolidone (NMP) was added as a solvent, and a slurry with a solid content of 75wt% was prepared. After uniform stirring in a vacuum, a positive electrode slurry was obtained. The positive electrode slurry was uniformly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10μm, dried at 120℃, and a positive electrode tab with a single coated positive electrode material layer was obtained. The coated weight of the positive electrode material layer was 13mg / cm 2 Then the above steps were repeated on the other surface of the aluminum foil, and a positive electrode tab with a double coated positive electrode material layer was obtained. After drying at 120℃ and cold pressing, the positive electrode tab with a size of 74mm×867mm was obtained by cutting and welding the tabs. The compaction density of the single positive electrode material layer was 3.45g / cm 3 .

[0139] <Preparation of a negative electrode tab>

[0140] The first carbon material, the first silicon material, the first binder, and the conductive agent Super P were mixed in a mass ratio of 66:30:0.5:3.5, and deionized water was added as a solvent to prepare a slurry with a solid content of 45wt%. After uniform stirring in a vacuum mixer, a first material layer slurry was obtained. The first carbon material was a first natural graphite, G1=96%, C1=350, D1=9, and the charge capacity was 5C. The first silicon material was SiC. The first binder was SBR and PAA in a mass ratio of 1:1.

[0141] The second carbon material, the second binder, and the conductive agent Super P were mixed in a mass ratio of 97.6:0.4:2, and deionized water was added as a solvent to prepare a slurry with a solid content of 45wt%. After uniform stirring in a vacuum mixer, a second material layer slurry was obtained. The second carbon material was a second artificial graphite. G2=92%, C2=373, D2=13, and the charge capacity was 1.8C. The second binder was SBR and PAA in a mass ratio of 1:1.

[0142] The first material layer slurry was uniformly coated on one surface of a negative electrode current collector copper foil with a thickness of 6μm, dried at 120℃, and a negative electrode tab with a single coated first material layer was obtained. Then the second material layer slurry was coated on the surface of the first material layer, dried at 120℃, and a negative electrode tab with a single coated first material layer and a second material layer was obtained. The coated weight of the first material layer was 6mg / cm 2 , and the coated weight of the second material layer was 6mg / cm 2Then the above steps are repeated on the other surface of the copper foil, i.e. a negative electrode sheet with double-side coated negative electrode material layers is obtained. After drying at 120℃, cold pressing, cutting, and welding of the tabs, a negative electrode sheet with a size of 78mm×875mm is obtained for use. The thickness of the first material layer on one side H1 is 50μm, and the tap density is 1.6g / cm 3 The thickness of the second material layer on one side H2 is 70μm, and the tap density is 1.6g / cm 3 .

[0143] <Preparation of electrolyte>

[0144] Vinyl carbonate, propylene carbonate, diethyl carbonate, and methyl ethyl carbonate are mixed in a mass ratio of 2:3:4:1 to obtain an organic solvent, and then electrolyte salt LiPF6 is added to the organic solvent and mixed uniformly to obtain an electrolyte. The concentration of the electrolyte salt is 1mol / L based on the mass of the electrolyte, and the rest is the organic solvent.

[0145] <Separator>

[0146] A porous polyethylene film (provided by Celgard) with a thickness of 7μm is used as the separator.

[0147] <Preparation of lithium ion battery>

[0148] The positive electrode sheet, the separator, and the negative electrode sheet prepared above are stacked in order with the separator between the positive electrode sheet and the negative electrode sheet to play a role of isolation, and then wound to obtain an electrode assembly. The electrode assembly is placed in an aluminum plastic film packaging bag, and water is removed at 80℃. The electrolyte prepared above is injected, and then vacuum packaging, standing, formation, degassing, and edge cutting are performed to obtain a lithium ion battery. The upper limit voltage of formation is 4.15V, the formation temperature is 70℃, and the standing time of formation is 2h.

[0149] Examples 1-2 to 1-14

[0150] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0151] Examples 2-1 to 2-18

[0152] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as Example 1-1. Among them, Examples 2-11, 2-13 to 2-15 also add a second silicon material SiC according to Table 2 when preparing the second material layer slurry.

[0153] Examples 3-1 to 3-14

[0154] The rest is the same as Example 1-1 except that the relevant preparation parameters are adjusted according to Table 3.

[0155] Comparative Example 1

[0156] The rest is the same as Example 1-1 except that the relevant preparation parameters are adjusted according to Table 1.

[0157] The preparation parameters and performance tests of each example and comparative example are shown in Tables 1 to 3.

[0158] Referring to Table 1, it can be seen from Example 1-1 to Example 1-14 and Comparative Example 1 that in the examples, the first material layer comprises a first carbon material and a first silicon material, the second material layer comprises a second carbon material, and the graphitization degree G1 of the first carbon material is greater than the graphitization degree G2 of the second carbon material, and the obtained lithium ion battery has high energy density, cycle capacity retention rate and lithium precipitation level, and low cycle expansion rate and 4C discharge temperature rise; while in Comparative Example 1, the graphitization degree G1 of the first carbon material is less than the graphitization degree G2 of the second carbon material, the obtained lithium ion battery has low lithium precipitation level, high cycle expansion rate and 4C discharge temperature rise, and energy density is equivalent or lower than that of the examples. Thus, it is shown that the lithium ion battery in the examples of the present application can better balance the energy density, kinetic performance and volume expansion rate compared with the lithium ion battery in the comparative examples.

[0159] The graphitization degree G1, charge capacity, gram capacity C1 and particle size D1 of the first carbon material are related to each other, and the graphitization degree G2, charge capacity, gram capacity C2 and particle size D2 of the second carbon material are related to each other. The above parameters will generally affect the OI value and G1-G2 value of the first material layer and the second material layer, and also affect the energy density, kinetic performance and volume expansion rate of the lithium ion battery. By adjusting the above parameters within the scope of the present application, the obtained lithium ion battery has high energy density, cycle capacity retention rate and lithium precipitation level, and low cycle expansion rate and 4C discharge temperature rise, that is, the lithium ion battery can balance the energy density, kinetic performance and volume expansion rate.

[0160] Referring to Table 2, it can be seen from Example 1-1, Example 2-1 to Example 2-18 that the type and content of the first carbon material, the type and content of the second carbon material generally affect the energy density, kinetic performance and volume expansion rate of the lithium ion battery. By adjusting the mass percentage content A1 of the first natural graphite, the mass percentage content B1 of the first artificial graphite, and the mass percentage content A2 of the second artificial graphite within the range of the present application, the obtained lithium ion battery has high energy density, cycle capacity retention rate and lithium precipitation level, and low cycle expansion rate and 4C discharge temperature rise, that is, the lithium ion battery can balance the energy density, kinetic performance and volume expansion rate.

[0161] It can be seen from Example 2-1 to Example 2-7, Example 2-11, Example 2-13 to Example 2-15 that the content of the first silicon material in the first substance layer and the content of the second silicon material in the second substance layer generally affect the energy density, kinetic performance and volume expansion rate of the lithium ion battery. By adjusting the mass percentage content W1 of the first silicon material and the mass percentage content W2 of the second silicon material within the range of the present application and W1 > W2, the obtained lithium ion battery has high energy density, cycle capacity retention rate and lithium precipitation level, and low cycle expansion rate and 4C discharge temperature rise, that is, the lithium ion battery can balance the energy density, kinetic performance and volume expansion rate.

[0162] Table 3

[0163] It can be seen from Example 1-1, Example 3-1 to Example 3-14 that by adjusting the mass percentage content W N1 of the first binder, the mass percentage content W N2 of the second binder, the mass percentage content W D1 of the first conductive agent, the mass percentage content W D2 of the second conductive agent within the above range, and W N1 ≥ W N2 , W D1 ≥ W D2 , the obtained lithium ion battery has high energy density, cycle capacity retention rate and lithium precipitation level, and low cycle expansion rate and 4C discharge temperature rise, that is, the lithium ion battery can balance the energy density, kinetic performance and volume expansion rate.

[0164] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting; it is not intended to exclude myriad other embodiments of the present application that other inventors can develop based on the description herein. It must be noted that, as used in the specification and the appended claims, the singular forms "a," "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a component" or "the component" can include a plurality of such components unless the context clearly dictates otherwise. It is further noted that the conjunction "or" as used herein is intended to encompass both the exclusive or and the inclusive or unless the context clearly dictates otherwise. It is to be understood that the terms "comprising," "including," "containing," or "having" and variations thereof, are intended to be broad and encompass the occurrence of zero instances of a stated element as well as any positive integer number of instances of the stated element. It is to be further understood that the terms "substantially," "approximately," and "about" are used herein to represent a value, amount, or other characteristic that reasonably can vary, depending on the variables involved. Unless otherwise defined, all terms of art used herein have their ordinary and customary meanings.

[0165] The use of the terms "one or more of," "any one of," or "one of" with respect to a list of elements should be understood as meaning that any one element from among the listed elements can be used, and that no more than one of the listed elements can be used. The use of the terms "at least one of," "at least one," or "one or more of," with respect to a list of elements should be understood as meaning that any one or any combination of the listed elements can be used. For example, "at least one of A or B" means A alone, B alone, or A and B together.

[0166] The above description is intended to be illustrative and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the application should, therefore, be determined not with reference to the above description, but instead with reference to the appended claims, along with their full scope of equivalents.

Claims

A negative electrode sheet includes a negative electrode current collector and a first substance layer and a second substance layer provided on at least one surface of the negative electrode current collector, the second substance layer being provided between the negative electrode current collector and the first substance layer in a thickness direction of the negative electrode sheet; The first substance layer includes a first active material including a first carbon material and a first silicon material; The second substance layer includes a second active material including a second carbon material; A graphitization degree of the first carbon material is G1, and a graphitization degree of the second carbon material is G2; G1>G2. The negative electrode sheet according to claim 1, wherein 95%≤G1≤98%; and / or, 90%≤G2≤94%. The negative electrode sheet according to claim 1 or 2, wherein 3%≤G1-G2≤6%. The negative electrode sheet according to any one of claims 1 to 3, wherein An OI value of the first substance layer is 3 to 6, and an OI value of the second substance layer is 2 to 4. The negative electrode sheet according to any one of claims 1 to 4, wherein The second active material includes a second silicon material; a mass percentage content of the first silicon material is W1 based on a mass of the first substance layer, and a mass percentage content of the second silicon material is W2 based on a mass of the second substance layer; W1>W2. The negative electrode sheet according to claim 5, wherein 30%≤W1≤70%, and 0%<W2≤10%. The negative electrode sheet according to any one of claims 1 to 4, wherein The second substance layer does not include a silicon material. The negative electrode sheet according to any one of claims 1 to 7, wherein A charge capacity of the first carbon material is 2C to 6C; a charge capacity of the second carbon material is 1.5C to 2C, and the charge capacity of the first carbon material is stronger than the charge capacity of the second carbon material. The negative electrode sheet according to any one of claims 1 to 8, wherein A gram capacity of the first carbon material is C1, and a gram capacity of the second carbon material is C2, C2>C1. The negative electrode sheet according to claim 9, wherein 340mAh / g≤C1≤365mAh / g; and 366mAh / g≤C2≤380mAh / g. The negative electrode sheet according to any one of claims 1 to 10, wherein A Dv50 of the first carbon material is D1, and a Dv50 of the second carbon material is D2, D2>D1. The negative electrode sheet according to claim 11, wherein 8μm≤D1≤10μm, and 11μm≤D2≤15μm. The negative electrode sheet according to any one of claims 1 to 12, wherein The first carbon material includes natural graphite, and the second carbon material includes at least one of artificial graphite or modified graphite. The negative electrode sheet according to claim 13, wherein The first carbon material includes a first natural graphite, and a mass percentage content of the first natural graphite is A1 based on a mass of the first substance layer, 3%≤A1≤30%; The second carbon material includes a second artificial graphite, and a mass percentage content of the second artificial graphite is A2 based on a mass of the second substance layer, 90%≤A2≤98%. The negative electrode sheet according to claim 14, wherein The first carbon material further includes a first artificial graphite, and a mass percentage content of the first artificial graphite is B1 based on a mass of the first substance layer, 10%≤B1≤50%. The negative electrode sheet according to claim 15, wherein The first carbon material further includes at least one of hard carbon or soft carbon. The negative electrode sheet according to any one of claims 1 to 16, wherein The first substance layer further comprises a first adhesive, and a mass percentage content of the first adhesive based on a mass of the first substance layer is W N1 ; the second substance layer further comprises a second adhesive, and a mass percentage content of the second adhesive based on a mass of the second substance layer is W N2 ; W N1 ≥ W N2 . The negative electrode sheet according to claim 17, wherein 2.5% < W N1 ≤ 5%; and / or, 1.5% < W N2 ≤ 2.5%. The negative electrode sheet according to claim 17 or 18, wherein The first binder includes one or more of sodium alginate, styrene butadiene rubber, polyvinyl alcohol, or polyethylene glycol; and / or, The second binder includes one or more of polyacrylic acid, polymethyl methacrylate, or polyacrylonitrile. The negative electrode sheet according to any one of claims 1 to 19, wherein The first substance layer further includes a first conductive agent, and a mass percentage content of the first conductive agent is W based on a mass of the first substance layer D1 ; the second substance layer further includes a second conductive agent, and a mass percentage content of the second conductive agent is W based on a mass of the second substance layer D2 ; 0.45% ≤ W D1 ≤ 0.5%; and / or, 0.35% ≤ W D2 ≤ 1%. The negative electrode sheet according to claim 20, wherein W D1 ≥W D2 . The negative electrode sheet according to claim 20 or 21, wherein The first conductive agent and the second conductive agent each independently include one or more of carbon black, ketjen black, acetylene black, carbon nanotube, graphene, or carbon fiber. The negative electrode sheet according to any one of claims 1 to 22, wherein The first silicon material includes one or more of pure silicon, silicon alloy material, silicon-carbon composite material, or silicon oxide. The negative electrode sheet according to claim 5, wherein The second silicon material includes one or more of pure silicon, a silicon alloy material, a silicon-carbon composite material, or a silicon oxide. The negative electrode sheet according to any one of claims 1 to 24, wherein The first substance layer has a thickness of H1, and the second substance layer has a thickness of H2, 0.1≤H1 / H2≤1, and 20 μm≤H1≤150 μm. A secondary battery including the negative electrode sheet of any one of claims 1 to 25. An electric device including the secondary battery of claim 26.

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