Secondary battery and electric device

Abstract

This application provides a secondary battery, including a negative electrode sheet, which includes a negative current collector and a negative electrode film layer located on at least one side of the negative current collector. The negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer, with the second negative electrode film layer disposed between the negative current collector and the first negative electrode film layer. The first negative electrode film layer includes a first silicon-based material and a first graphite material, and the second negative electrode film layer includes a second graphite material. The graphitization degree of the first graphite material is less than that of the second graphite material, and the average particle size of the first graphite material is less than that of the second graphite material. The secondary battery of this application has improved power performance.

Description

Technical Field

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

[0002] In recent years, with the increasingly wide range of applications, rechargeable batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, aerospace, and many other fields. With the rapid development of rechargeable batteries, higher requirements have been placed on their power performance.

[0003] Therefore, improving the power performance of secondary batteries has become an urgent technical problem to be solved. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide a secondary battery and an electrical device, wherein the secondary battery of this application has improved power performance.

[0005] To achieve the above objectives, a first aspect of this application provides a secondary battery, including a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative electrode film layer located on at least one side of the negative current collector; the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer, the second negative electrode film layer being disposed between the negative current collector and the first negative electrode film layer; the first negative electrode film layer includes a first silicon-based material and a first graphite material, the second negative electrode film layer includes a second graphite material; the graphitization degree of the first graphite material is less than that of the second graphite material, and the average particle size of the first graphite material is less than that of the second graphite material.

[0006] In this application, the negative electrode film layer includes a first negative electrode film layer located on the outer layer and a second negative electrode film layer located on the inner layer. Since the graphitization degree and average particle size of the first graphite material in the first negative electrode film layer are smaller than those of the second graphite material in the second negative electrode film layer, and the first negative electrode film layer is doped with a first silicon-based material, the first graphite material has more ion transport channels and more lithium intercalation active sites. Placing the first graphite material and the first silicon-based material in the first negative electrode film layer, which has easier contact with the electrolyte, facilitates lithium-ion intercalation, reduces the charge transfer impedance of the secondary battery, and improves the power performance of the secondary battery. Furthermore, since the density of the first silicon-based material is lower than that of the graphite material, and the average particle size of the first graphite material is smaller than that of the second graphite material, the porosity of the first negative electrode film layer is greater than that of the second negative electrode active material layer after cold pressing, which is more conducive to liquid-phase mass transfer and further improves the power performance of the secondary battery.

[0007] In some embodiments, the graphitization degree of the first graphite material is 91.0% to 93.0%. This increases the number of lithium intercalation active sites on the surface of the first graphite material, thereby improving the lithium intercalation capability of the first active material layer and benefiting the power performance of the secondary battery.

[0008] In some embodiments, the graphitization degree of the second graphite material is 93.0% to 96.0%. This ensures that the lithium intercalation active sites on the surface of the second graphite material are within a suitable range, thereby benefiting the power performance of the secondary battery.

[0009] In some embodiments, the average particle size of the first graphite material is 3 μm to 20 μm. Therefore, the porosity of the first negative electrode film is relatively large after cold pressing, which is beneficial for liquid-phase mass transfer and thus improves the power performance of the secondary battery.

[0010] In some embodiments, the average particle size of the second graphite material is 6 μm to 25 μm. Therefore, after cold pressing, the porosity of the second negative electrode film is within a suitable range, which is beneficial for liquid-phase mass transfer, thereby improving the power performance of the secondary battery.

[0011] In some embodiments, the OI value of the first graphite material is greater than that of the second graphite material. This increases the number of lithium-ion insertion / extraction sites and shortens the diffusion distance of lithium ions in the negative electrode active material, reducing lithium-ion transport time and thus improving overall ion transport performance, thereby enhancing the power performance of the secondary battery.

[0012] In some embodiments, the OI value of the first graphite material is 2 to 9, and / or the OI value of the second graphite material is 2 to 9. This is beneficial to the power performance of the secondary battery.

[0013] In some embodiments, the OI value of the first graphite material is 3.7 to 7.5, and / or the OI value of the second graphite material is 2 to 3.7. This is beneficial to the power performance of the secondary battery.

[0014] In some embodiments, the specific surface area of ​​the first graphite material is greater than that of the second graphite material. This improves the charging capability of the first negative electrode film layer with the first silicon-based material, thereby enhancing the power performance of the secondary battery.

[0015] In some embodiments, the specific surface area of ​​the first graphite material is 1.0 m². 2 / g~3.4m 2 / g. This results in a large number of lithium intercalation active sites in the first graphite material, which is beneficial for improving the fast charging capability of the first negative electrode film.

[0016] In some embodiments, the specific surface area of ​​the second graphite material is 1.0 m². 2 / g~3.0m 2 / g. This ensures that the number of lithium intercalation active sites in the second graphite material is within a suitable range, which is beneficial for improving the fast charging capability of the second negative electrode film.

[0017] In some embodiments, the first silicon-based material includes one or more of elemental silicon, silicon-carbon composites, silicon-oxygen materials, and silicon alloys.

[0018] In some embodiments, the first silicon-based material comprises the silicon-carbon composite, the silicon-carbon composite satisfying one or more of the following characteristics:

[0019] (1) The silicon-carbon composite comprises porous carbon and silicon-containing material dispersed in the pores of the porous carbon;

[0020] (2) The silicon-carbon composite further includes a carbon-containing coating layer, which is located on the surface of the porous carbon and / or the silicon-containing material;

[0021] (3) The silicon content in the silicon-carbon composite is 30% to 70% by mass;

[0022] (4) The average particle size of the silicon-carbon composite is 2 μm to 15 μm;

[0023] (5) The powder resistivity of the silicon-carbon composite at 8 MPa is 4 Ω·cm to 17 Ω·cm;

[0024] (6) The BET specific surface area of ​​the silicon-carbon composite is 1.0 m². 2 / g~6.7m 2 / g.

[0025] In some embodiments, the second negative electrode film layer includes a second silicon-based material, which includes one or more of elemental silicon, silicon-carbon composites, silicon-oxygen materials, and silicon alloys.

[0026] In some embodiments, the mass percentage N1 of the first silicon-based material in the total mass of the first silicon-based material and the first graphite material, and the mass percentage N2 of the second silicon-based material in the total mass of the second silicon-based material and the second graphite material, satisfy the condition: N1 > N2. This facilitates lithium-ion intercalation, reduces the charge transfer impedance of the secondary battery, and improves the power performance of the secondary battery.

[0027] In some embodiments, N1 is 10% to 100%; and / or, N2 is 0% to 30%. This further improves the power performance of the secondary battery.

[0028] In some embodiments, the mass percentage M1 of silicon in the first negative electrode film and the mass percentage M2 of silicon in the second negative electrode film satisfy the condition: 3 ≤ M1 - M2 ≤ 70%. This is beneficial for balancing the cycle life and power performance of the secondary battery.

[0029] In some implementations, 3% ≤ M1-M2 ≤ 42%. This is more conducive to balancing the cycle life and power performance of the secondary battery.

[0030] In some embodiments, the mass percentage (M1) of silicon in the first negative electrode film is 3% to 70%. This is more beneficial to the power performance of the secondary battery.

[0031] In some embodiments, the mass percentage (M2) of silicon in the second negative electrode film is 0% to 21%. This is beneficial for balancing the cycle life and power performance of the secondary battery.

[0032] In some embodiments, the first negative electrode film layer includes a first conductive agent; the first conductive agent includes carbon nanotubes. This improves the conductivity of the first negative electrode film layer, thereby enhancing the power performance of the secondary battery.

[0033] In some embodiments, the first conductive agent accounts for 0.05% to 0.5% of the mass of the first negative electrode film. This allows for a balance between the power performance and energy density of the secondary battery.

[0034] In some embodiments, the porosity of the first negative electrode film is greater than that of the second negative electrode film. Therefore, the first negative electrode film, which is in contact with the electrolyte, is more conducive to liquid-phase mass transfer, further improving the power performance of the secondary battery.

[0035] In some embodiments, the porosity of the first negative electrode film is 20% to 40%. This is more conducive to liquid-phase mass transfer and further improves the power performance of the secondary battery.

[0036] In some embodiments, the porosity of the second negative electrode film is 10% to 30%. This is more conducive to improving the power performance of the secondary battery.

[0037] In some embodiments, the coating mass ratio of the first negative electrode film layer to the second negative electrode film layer is 1:9 to 9:1. This is more conducive to improving the power performance of the secondary battery.

[0038] In some embodiments, the coating mass of the first negative electrode film layer is 20 mg / 1540.25 mm. 2 ~100mg / 1540.25mm 2 .

[0039] In some embodiments, the coating mass of the second negative electrode film layer is 20 mg / 1540.25 mm. 2 ~120mg / 1540.25mm 2 .

[0040] In some embodiments, a positive electrode sheet is included, the positive electrode sheet including a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector, the positive electrode film layer including a positive active material and a lithium supplement agent.

[0041] In some embodiments, the lithium replenishing agent accounts for 0.5% to 5% of the mass of the positive electrode film.

[0042] In some embodiments, the lithium replenishing agent accounts for 1% to 3% of the mass of the positive electrode film.

[0043] In some embodiments, the lithium replenishing agent includes sacrificial lithium replenishing agents and / or non-sacrificial lithium replenishing agents.

[0044] In some embodiments, the sacrificial lithium replenisher includes one or more of Li2O2, Li2O, LiN3, Li2C2O4, and Li2C4O4.

[0045] In some embodiments, the non-sacrificial lithium supplement comprises Li a MnO y The material is given by the following conditions: 2≤a≤8, 2≤y≤4.

[0046] In some embodiments, the non-sacrificial lithium replenisher includes one or more of Li2AO2, Li2BO3, Li3DO4, Li5EO4, and Li6FO4; wherein A includes one or more of Ni, Co, Fe, Mn, Zn, Mg, Ca, Cu, Mo, and Nb; B includes one or more of Ni, Co, Fe, Mn, Sn, Mo, Ru, and Cr; C includes one or more of Ni, Co, Fe, Mn, Sn, V, Nb, Cr, and Mo; D includes one or more of Ni, Co, Fe, Mn, Sn, Cr, V, and Mo; E includes one or more of Ni, Co, Mn, Sn, Cr, and Mo; and F includes one or more of Ni, Mn, Sn, Cr, and Mo.

[0047] In some embodiments, the non-sacrificial lithium replenishing agent includes one or more of Li2NiO2, Li2CuO2, Li2MnO3, Li3VO4, Li3NbO4, Li5FeO4, Li6CoO4, and their doped compounds or coating modifiers.

[0048] A second aspect of this application provides an electrical device including the secondary battery provided in the first aspect. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the negative electrode sheet according to one embodiment of this application.

[0050] Figure 2 This is a schematic diagram of a battery cell according to one embodiment of this application.

[0051] Figure 3 yes Figure 2 An exploded view of a battery cell according to one embodiment of this application is shown.

[0052] Figure 4 This is a schematic diagram of a battery module according to one embodiment of this application.

[0053] Figure 5 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0054] Figure 6 yes Figure 5 An exploded view of a battery pack according to one embodiment of this application is shown.

[0055] Figure 7 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0056] Explanation of reference numerals in the attached figures:

[0057] 10 Negative electrode; 101 Negative electrode current collector; 102 First negative electrode film layer; 103 Second negative electrode film layer; 1 Battery pack; 2 Upper casing; 3 Lower casing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0058] The embodiments of the secondary battery and power-consuming device of this application are hereby disclosed in detail with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0059] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0060] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0061] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0062] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0063] Unless otherwise specified, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0064] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in this application.

[0065] High-nickel and silicon-carbon rechargeable batteries have become one of the most commonly used high-energy-density lithium-ion batteries on the market. However, the power performance of high-nickel and silicon-carbon systems has limited their application in the field of power batteries. Therefore, it is necessary to further improve the power performance of rechargeable batteries.

[0066] In related technologies, the power performance of secondary batteries can be improved by increasing the conductivity of the electrolyte or increasing the specific surface area of ​​the negative electrode active material. However, increasing the conductivity of the electrolyte will increase gas production, and increasing the specific surface area of ​​the negative electrode active material will increase lithium consumption and deteriorate the cycle performance of the secondary battery. Therefore, the improvement methods in related technologies will bring new challenges.

[0067] Based on this, this application provides a secondary battery and an electrical device, wherein the secondary battery prepared in this application has improved energy-power performance. The following provides a more detailed description of this application and its optional embodiments.

[0068] Secondary batteries

[0069] The first aspect of this application provides a secondary battery, wherein the negative electrode includes a negative current collector and a negative electrode film layer located on at least one side of the negative current collector; the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer, the second negative electrode film layer being disposed between the negative current collector and the first negative electrode film layer; the first negative electrode film layer includes a first silicon-based material and a first graphite material, and the second negative electrode film layer includes a second graphite material; the graphitization degree of the first graphite material is less than that of the second graphite material, and the average particle size of the first graphite material is less than that of the second graphite material.

[0070] In this application, the negative electrode film layer includes a first negative electrode film layer located on the outer layer and a second negative electrode film layer located on the inner layer. Since the graphitization degree and average particle size of the first graphite material in the first negative electrode film layer are smaller than those of the second graphite material in the second negative electrode film layer, and the first negative electrode film layer is doped with a first silicon-based material, the first graphite material has more ion transport channels and more lithium intercalation active sites. Placing the first graphite material and the first silicon-based material in the first negative electrode film layer, which has easier contact with the electrolyte, facilitates lithium-ion intercalation, reduces the charge transfer impedance of the secondary battery, and improves the power performance of the secondary battery. Furthermore, since the density of the first silicon-based material is lower than that of the graphite material, and the average particle size of the first graphite material is smaller than that of the second graphite material, the porosity of the first negative electrode film layer is greater than that of the second negative electrode active material layer after cold pressing, which is more conducive to liquid-phase mass transfer and further improves the power performance of the secondary battery.

[0071] In some implementations, such as Figure 1As shown, the negative electrode 10 includes a negative current collector 101 and a negative electrode film layer located on one side surface of the negative current collector. The negative electrode film layer includes a first negative electrode film layer 103 and a second negative electrode film layer 102. The second negative electrode film layer 102 is located between the negative current collector 101 and the first negative electrode film layer 103. The first negative electrode film layer 103 includes a first silicon-based material and a first graphite material, and the second negative electrode film layer 102 includes a second graphite material.

[0072] Graphitization degree is an indicator of the extent to which carbon atoms in graphite form a close-packed hexagonal graphite crystal structure. The closer the lattice size of graphite is to the lattice constant of ideal graphite, the higher its graphitization degree. In this application, the graphitization degree can be measured using an X-ray diffractometer (e.g., Bruker D8 Discover), and specific testing methods can be found in JIS K 0131-1996, JB / T4220-2011, and GB / T 24533-2019. Specifically, powder samples from the first and second negative electrode layers are scraped and subjected to XRD testing. The d002 value is first measured, and then the graphitization degree is calculated using the formula G = (0.344 - d002) / (0.344 - 0.3354) × 100%, where d002 is the interlayer spacing in the graphite crystal structure expressed in nanometers (nm). In X-ray diffraction analysis, a copper target can be used as the anode target, with CuKα rays as the radiation source, and the ray wavelength... The scanning 2θ angle range is 20°-80°, and the scanning rate can be 4° / min.

[0073] In this application, the average particle size is the arithmetic mean of the particle sizes, which can be tested using equipment and methods known in the art. For example, a scanning electron microscope (e.g., ZEISS Sigma 300) can be used, referring to JY / T010-1996, to obtain a scanning electron microscope (SEM) image of the negative electrode sheet. As an example, the test can be performed as follows: Randomly select a test sample with a length × width of 50 mm × 100 mm on the first and second negative electrode film layers. Randomly select multiple test areas (e.g., 5) in the test sample, and at a certain magnification (e.g., 1000x), read the particle size of each graphite particle in each test area (i.e., take the distance between the two farthest points on the graphite particle as the particle size). Count the number and particle size values ​​of graphite particles in each test area, and take the arithmetic mean of the graphite particles in each test area, which is the average particle size of the graphite particles in the test sample. To ensure the accuracy of the test results, multiple test samples (e.g., 10) can be taken and the above test can be repeated. The average value of each test sample can be taken as the final test result.

[0074] In some embodiments, the degree of graphitization of the first graphite material is 91.0% to 93.0%. A degree of graphitization within this range increases the number of lithium-intercalation active sites on the surface of the first graphite material, thereby improving the lithium-intercalation capability of the first active material layer and benefiting the power performance of the secondary battery. Exemplarily, the degree of graphitization of the first graphite material is a value within a range of 91.0%, 91.5%, 92%, 92.5%, 93.0%, or any combination thereof.

[0075] In some embodiments, the degree of graphitization of the second graphite material is 93.0% to 96.0%. A degree of graphitization within this range ensures that the lithium intercalation active sites on the surface of the second graphite material are within a suitable range, thereby benefiting the power performance of the secondary battery. Exemplarily, the degree of graphitization of the second graphite material is a value within a range of 93.0%, 93.5%, 94.0%, 94.5%, 95.0%, 95.5%, 96.0%, or any combination thereof.

[0076] In some embodiments, the average particle size of the first graphite material is 3 μm to 20 μm, optionally 4 μm to 13 μm. When the average particle size of the first graphite material is within the above range, the porosity of the first negative electrode film layer is relatively large after cold pressing, which is beneficial for liquid-phase mass transfer and thus improves the power performance of the secondary battery. Exemplarily, the average particle size of the first graphite material is a value within a range of 3 μm, 4 μm, 5 μm, 8 μm, 10 μm, 13 μm, 15 μm, 18 μm, 20 μm, or any combination thereof.

[0077] In some embodiments, the average particle size of the second graphite material is 6 μm to 25 μm, optionally 9 μm to 19 μm. When the average particle size of the second graphite material is within the above range, the porosity of the second negative electrode film layer is within a suitable range after cold pressing, which is beneficial for liquid-phase mass transfer, thereby improving the power performance of the secondary battery. Exemplarily, the average particle size of the second graphite material is a value within a range of 6 μm, 9 μm, 10 μm, 12 μm, 15 μm, 18 μm, 19 μm, 20 μm, 23 μm, 25 μm, or any combination thereof.

[0078] In some embodiments, the OI value of the first graphite material is greater than that of the second graphite material. By setting the OI value of the first graphite material to be greater than that of the second graphite material, it is possible to increase the lithium-ion insertion / extraction sites and shorten the diffusion distance of lithium ions in the negative electrode active material, thereby reducing the lithium-ion transport time and improving the overall ion transport performance, which in turn improves the power performance of the secondary battery.

[0079] In this application, the OI value has a meaning known in the art. The OI value refers to the ratio of the intensity of the 004 crystal plane diffraction peak to the intensity of the 110 crystal plane diffraction peak in graphite material, which can reflect the degree of anisotropy of graphite. The 004 crystal plane corresponds to the graphite layer structure parallel to the negative electrode sheet, and the 110 crystal plane corresponds to the graphite layer structure perpendicular to the negative electrode sheet. In some embodiments, powders of the first and second negative electrode film layers are scraped off and subjected to XRD tests to obtain the intensities of the 004 crystal plane diffraction peak and the 110 crystal plane diffraction peak. According to the general rules of X-ray diffraction analysis and the methods for determining the lattice parameters of graphite JIS K 0131-1996 and JB / T4220-2011, X-ray diffraction patterns are obtained. Then, the ratio I of the intensity of the 004 crystal plane diffraction peak to the intensity of the 110 crystal plane diffraction peak is calculated. 004 / I 110 Obtain the OI value of graphite.

[0080] In some embodiments, the OI value of the first graphite material is 2 to 9, optionally 3.7 to 7.5. An OI value within this range allows the first graphite material to have more lithium intercalation active sites, enabling more lithium ions to intercalate and deintercalate on its surface. This improves the charging capability of the first active layer and consequently enhances the power performance of the secondary battery. Exemplarily, the OI value of the first graphite material is a value within the range of 2, 2.5, 3, 3.7, 4, 4.5, 5, 6, 7, 7.5, 8, 8.5, 9, or any combination thereof.

[0081] In some embodiments, the OI value of the second graphite material is 2 to 9, optionally 2 to 3.7. An OI value within this range ensures that the second graphite material has a suitable number of lithium intercalation active sites, thereby improving the charging capability of the second negative electrode film and consequently improving the power performance of the secondary battery. Exemplarily, the OI value of the second graphite material is a value within the range of 2, 2.5, 3, 3.7, 4, 4.5, 5, 6, 7, 8, 9, or any combination thereof.

[0082] In some embodiments, the specific surface area of ​​the first graphite material is greater than that of the second graphite material. By setting the specific surface area of ​​the first graphite material to be greater than that of the second graphite material, the lithium-ion insertion channels in the first graphite material are more numerous than those in the second graphite material. Therefore, the kinetic performance of the first negative electrode film containing the first graphite material is better than that of the second negative electrode film containing the second graphite material. This can improve the charging capability of the first negative electrode film containing the first silicon-based material, thereby improving the power performance of the secondary battery.

[0083] In this application, specific surface area has a meaning known in the art, and it can be measured using instruments or methods known in the art. Specifically, powder samples of the first and second negative electrode film layers are scraped off as test samples, and the specific surface area of ​​the test samples is measured using the gas adsorption method, specifically according to the standard test of GB / T19587-2017, and calculated using the BET (Brunauer Emmett Teller) method. The testing instrument can be the Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0084] In some embodiments, the specific surface area of ​​the first graphite material is 1.0 m². 2 / g~3.4m 2 / g, optionally 1.6m 2 / g~3.0m 2 / g. The specific surface area of ​​the first graphite material is within the above range, resulting in a large number of lithium intercalation active sites in the first graphite material, which is beneficial to improving the fast charging capability of the first negative electrode film. For example, the specific surface area of ​​the first graphite material is 1.0 m². 2 / g, 1.2m 2 / g, 1.5m 2 / g, 1.6m 2 / g, 1.8m 2 / g, 2.0m 2 / g, 2.2m 2 / g, 2.5m 2 / g, 2.8m 2 / g, 3.0m 2 / g, 3.2m 2 / g, 3.4m 2 / g or a range between the values ​​of either / g or any two of them.

[0085] In some embodiments, the specific surface area of ​​the second graphite material is 1.0 m². 2 / g~3.0m 2 / g, optionally 1.2m 2 / g~2.3m 2 / g. The specific surface area of ​​the second graphite material is within the above-mentioned range, ensuring that the number of lithium-intercalation active sites in the second graphite material is within a suitable range. This is beneficial for improving the fast-charging capability of the second anode film. For example, the specific surface area of ​​the second graphite material is 1.0 m². 2 / g, 1.2m 2 / g, 1.5m 2 / g, 1.8m 2 / g, 2.0m 2 / g, 2.3m 2 / g, 2.5m 2 / g, 2.8m 2 / g, 3.0m 2 / g or a range between the values ​​of either / g or any two of them.

[0086] In some embodiments, the first silicon-based material includes one or more of elemental silicon, silicon-carbon composites, silicon-oxygen materials, and silicon alloys.

[0087] In some embodiments, the first silicon-based material includes a silicon-carbon composite. The silicon-carbon composite can be prepared using conventional silicon-carbon composites or conventional preparation methods, such as depositing nano-silicon materials on porous carbon by chemical vapor deposition, and can be further coated with carbon, such as amorphous carbon coating.

[0088] In some embodiments, the silicon-carbon composite satisfies one or more of the following characteristics:

[0089] (1) The silicon-carbon composite includes porous carbon and silicon-containing materials dispersed in the pores of the porous carbon; optionally, the porous carbon is hard carbon;

[0090] (2) The silicon-carbon composite also includes a carbon-containing coating layer located on the surface of porous carbon and / or silicon-containing materials;

[0091] (3) The silicon content in the silicon-carbon composite is 30% to 70% by mass;

[0092] (4) The average particle size of the silicon-carbon composite is 2 μm to 15 μm, and optionally 7 μm to 11 μm;

[0093] (5) The powder resistivity of silicon-carbon composite at 8 MPa is 4 Ω·cm to 17 Ω·cm;

[0094] (6) The BET specific surface area of ​​the silicon-carbon composite is 1.0 m². 2 / g~6.7m 2 / g.

[0095] In some embodiments, the silicon-carbon composite includes a core comprising porous carbon and silicon-containing material dispersed in the pores of the porous carbon. The porous carbon, acting as a carrier for the silicon-containing material, provides support for the nanoscale silicon-containing material and, simultaneously, provides expansion space for the expansion of the silicon nanoparticles, effectively mitigating the stress compression caused by expansion during charging. Especially when the silicon-containing particles are in the nanometer range, the specific capacity is higher and dispersion in the pores of the porous carbon is facilitated. Furthermore, the buffering effect of the porous carbon's pores on expansion can be more fully utilized. When this silicon-carbon composite is applied in a wound electrode assembly, it can significantly alleviate the stretching of the outer negative electrode sheet caused by silicon expansion.

[0096] In some embodiments, the porous carbon may optionally be hard carbon. When the porous carbon is hard carbon, it has stronger support, a more stable pore structure, and is harder, thus providing better porosity for the negative electrode active layer, providing a smoother path for active ion transport, and improving the charging capability of the battery cell.

[0097] In some embodiments, the silicon-containing material includes at least one of elemental silicon, silicon oxides, silicon nitrides, and silicon alloys. In some embodiments, the silicon-containing material includes crystalline silicon, thereby further improving the structural stability of the silicon-containing material and the energy density of the battery cell.

[0098] In some embodiments, the silicon-carbon composite further includes a carbon-containing coating layer that coats the surface of the core. This can improve the conductivity of the silicon-carbon composite and reduce the internal impedance of the battery cell, while also effectively reducing the probability of direct contact between the silicon-containing material in the porous carbon channels and the external environment, thereby improving the chemical stability of the silicon-carbon composite.

[0099] In some embodiments, the silicon content in the silicon-carbon composite is 30% to 70% by mass. This approach, while maximizing the specific capacity of the negative electrode active material by utilizing silicon, also facilitates the full dispersion of silicon in the carbon-containing porous material and helps control the expansion of silicon during charging.

[0100] In this application, the method for testing the silicon content in the silicon-carbon composite can be a method known in the art. As an example, the following method can be used for testing: a certain amount of silicon-carbon composite is taken, and the mass of silicon element in the silicon-carbon composite is obtained by inductively coupled plasma optical emission spectrometry (ICP-OES). The mass percentage of silicon element in the silicon-carbon composite can be calculated.

[0101] In addition to providing structural support and buffering for the expansion of silicon materials, the pores in the silicon-carbon composite also form between the particles. To further improve the flow of lithium ions through the intraparticle and interparticle pores, in some embodiments, the average particle size of the silicon-carbon composite is 2 μm to 15 μm. Optionally, the average particle size of the silicon-carbon composite is 7 μm to 11 μm, or 5 μm to 10 μm. This creates a particle size distribution between the average particle size of the silicon-carbon composite and the average particle size of the graphite material, which is more conducive to increasing the compaction of the negative electrode active layer by utilizing the interparticle gaps, thereby further improving the energy density of the battery cell.

[0102] The average particle size of the aforementioned silicon-carbon composite can be tested using equipment and methods known in the art. For example, a scanning electron microscope (SEM) (e.g., ZEISS Sigma 300) can be used, referring to JY / T010-1996, to obtain SEM images of the negative electrode sheet. As an example, the test can be performed as follows: Randomly select a test sample of length × width = 50 mm × 100 mm on the negative electrode sheet. Randomly select multiple test areas (e.g., 5 areas) within the test sample, and at a certain magnification (e.g., 1000x when measuring silicon-carbon composites), read the particle size of each silicon-carbon composite particle in each test area (i.e., take the distance between the two farthest points on the silicon-carbon composite particle as the particle size). Count the number and particle size values ​​of silicon-carbon composite particles in each test area, and take the arithmetic mean of the silicon-carbon composite particles in each test area, which is the average particle size of the silicon-carbon composite particles in the test sample. To ensure the accuracy of the test results, multiple test samples (e.g., 10) can be taken and the above test can be repeated. The average value of each test sample can be taken as the final test result.

[0103] In some embodiments, the silicon-carbon composite powder resistivity at 8 MPa is 4 Ω·cm to 17 Ω·cm. Controlling the powder resistivity improves the conductivity of the silicon-carbon composite, thereby increasing the charging rate of the battery cell. Exemplarily, the silicon-carbon composite powder resistivity at 8 MPa is a value within the range of 4 Ω·cm, 5 Ω·cm, 7 Ω·cm, 10 Ω·cm, 13 Ω·cm, 15 Ω·cm, 17 Ω·cm, or any combination thereof.

[0104] In this application, the powder resistivity of silicon-carbon composites can be determined using methods known in the art. As an example, a four-probe method can be used, where two probes apply voltage and the other two probes measure current. The powder resistivity can be calculated by measuring the resistance value. Models of four-probe semiconductor powder resistivity testers include the ST-2722.

[0105] In some embodiments, the BET specific surface area of ​​the silicon-carbon composite is 1.0 m². 2 / g~6.7m 2 / g. For example, the specific surface area of ​​the silicon-carbon composite is 1.0 m². 2 / g, 2.0m 2 / g, 3.0m 2 / g, 4.0m 2 / g, 5.0m 2 / g, 6.0m 2 / g, 6.7m 2 / g or a range between the values ​​of either / g or any two of them.

[0106] In this application, the method for testing the BET specific surface area of ​​the silicon-carbon composite can be a method known in the art. As an example, referring to GB / T 19587-2017, a nitrogen adsorption specific surface area analysis method can be used. The sample tube containing the first graphite material sample is immersed in liquid nitrogen at -196℃, and the amount of nitrogen adsorbed on the surface of the solid sample at different pressures of 0.05 to 0.30 is measured. Based on the BET multilayer adsorption theory and calculation formula, the amount of monolayer adsorption of the sample is obtained, and thus the BET specific surface area is obtained. This test can be performed using a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0107] In some embodiments, the silicon-oxygen material includes at least one of unpre-lithium silicon-oxygen compounds, pre-lithium silicon-oxygen compounds, unpre-magnesium silicon-oxygen compounds, and pre-magnesium silicon-oxygen compounds. Specifically, the silicon-oxygen material includes materials with the chemical formula SiO. x The material is given by , where 0 < x < 2. Optionally, 0.5 ≤ x ≤ 1.5.

[0108] In some embodiments, the second negative electrode film layer includes a second silicon-based material, which includes one or more of elemental silicon, silicon-carbon composites, silicon-oxygen materials, and silicon alloys.

[0109] In some embodiments, the mass percentage N1 of the first silicon-based material in the total mass of the first silicon-based material and the first graphite material, and the mass percentage N2 of the second silicon-based material in the total mass of the second silicon-based material and the second graphite material, satisfy the condition: N1 > N2. In this application, by setting N1 greater than N2, the silicon material can be mainly distributed in the first negative electrode film layer, which is more easily in contact with the electrolyte. This is beneficial for lithium-ion intercalation and can reduce the charge transfer impedance of the secondary battery, thereby improving the power performance of the secondary battery.

[0110] In some embodiments, the mass percentage N1 of the first silicon-based material in the total mass of the first silicon-based material and the first graphite material is 10% to 100%, optionally, N1 is 10% to 60%. A mass percentage of the first silicon-based material within this range results in greater porosity of the first negative electrode film, which is more beneficial to the power performance of the secondary battery. Exemplarily, N1 is a value within a range of 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, or any combination thereof.

[0111] In some embodiments, the mass percentage (N2) of the second silicon-based material in the total mass of the second silicon-based material and the second graphite material is 0% to 30%, optionally 0% to 20%. When the mass percentage of the second silicon-based material is within the above range, it is possible to improve the lifespan of the secondary battery without excessively affecting its power performance, thus achieving a balance between cycle life and power performance. For example, the mass percentage of the second silicon-based material is a value within a range of 0%, 5%, 10%, 15%, 20%, 25%, 30%, or any combination thereof.

[0112] In some embodiments, the mass percentage M1 of silicon in the first negative electrode film and the mass percentage M2 of silicon in the second negative electrode film satisfy the following condition: 3% ≤ M1 - M2 ≤ 70%, optionally, 3% ≤ M1 - M2 ≤ 42%. In this application, by setting the difference between the mass percentage of silicon in the first negative electrode film and the mass percentage of silicon in the second negative electrode film within the above range, it is possible to achieve a balance between cycle life and power performance of the secondary battery. For example, the values ​​of M1-M2 are values ​​within a range of 3%, 10%, 20%, 30%, 42%, 50%, 60%, 70%, or any combination thereof.

[0113] In some embodiments, the mass percentage M1 of silicon in the first negative electrode film layer is 3% to 70%, optionally 3% to 42%. M1 within this range results in greater porosity of the first negative electrode film layer, which is more beneficial to the power performance of the secondary battery. Exemplarily, the value of M1 is a value within a range of 3%, 10%, 20%, 30%, 42%, 50%, 60%, 70%, or any combination thereof.

[0114] In some embodiments, the mass percentage M2 of silicon in the second negative electrode film is 0% to 21%, optionally 0% to 14%. Within this range, M2 can improve the lifespan of the secondary battery without excessively affecting its power performance, thus achieving a balance between cycle life and power performance. For example, the value of M2 is a value within a range of 0%, 3%, 5%, 10%, 14%, 20%, 21%, or any combination thereof.

[0115] In this application, the mass percentage of silicon can be determined by inductively coupled plasma optical emission spectrometry (ICP). Specifically, powders from the first and second negative electrode layers are scraped off, and 0.2 g of each scraped powder is weighed into a 100 mL beaker. 10 mL of 10% w / w nitric acid solution is added, and the mixture is heated and digested at 120 °C for 0.5 hours. The solution is then diluted to volume with a 100 mL volumetric flask, and 1 mL is transferred to the flask and diluted again to obtain the test solution. The mass fraction of silicon in the test solution is determined using inductively coupled plasma optical emission spectrometry (ICP-OES).

[0116] In some embodiments, the first negative electrode film layer includes a first conductive agent, which includes carbon nanotubes. The addition of a first silicon-based material to the first negative electrode film layer can degrade the conductivity of the first active layer, resulting in poor charging capability of the first negative electrode film layer. In this application, by introducing a highly conductive first conductive agent into the first negative electrode film layer, it is beneficial to improve the conductivity of the first negative electrode film layer, thereby improving the power performance of the secondary battery.

[0117] In some embodiments, the mass percentage of carbon nanotubes in the first negative electrode film is 0.05% to 2%, optionally 0.05% to 0.5%. A carbon nanotube content within this range can improve the conductivity of the first negative electrode film without affecting the loading of the negative electrode active material, thus not affecting the energy density of the battery. This achieves a balance between the power performance and energy density of the secondary battery. Exemplarily, the mass percentage of carbon nanotubes in the first negative electrode film is a value within the range of 0.05%, 0.1%, 0.2%, 0.25%, 0.3%, 0.4%, 0.5%, or any combination thereof.

[0118] In some embodiments, the first negative electrode film layer includes a second conductive agent, which includes conductive carbon black. The combination of carbon nanotubes and carbon black can provide good conductivity, further improving the power performance of the first negative electrode film layer.

[0119] In some embodiments, the first negative electrode film layer includes a first binder, which includes one or more of the following: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylic acid, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc. The first binder can improve the bonding effect between the components in the first negative electrode film layer, making the structure of the first negative electrode film layer more stable.

[0120] In some embodiments, the first negative electrode film layer further includes a first thickener, which optionally includes sodium carboxymethyl cellulose.

[0121] In some embodiments, the second negative electrode film layer includes a third conductive agent, which may include conductive carbon black or a combination of conductive carbon black and carbon nanotubes. Adding a third conductive agent to the second negative electrode film layer can promote lithium-ion transport within the second negative electrode film layer and improve the power performance of the secondary battery.

[0122] In some embodiments, the second negative electrode film layer includes a second binder, which includes one or more of the following: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyacrylic acid, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, and nylon. The second binder can improve the bonding effect between the components in the second negative electrode film layer, making the structure of the second negative electrode film layer more stable.

[0123] In some embodiments, the second negative electrode film layer further comprises a second thickener, optionally including sodium carboxymethyl cellulose.

[0124] In some embodiments, the porosity of the first negative electrode film is greater than that of the second negative electrode film. By setting the porosity of the first negative electrode film to be greater than that of the second negative electrode film, the first negative electrode film in contact with the electrolyte is more conducive to liquid-phase mass transfer, which further improves the power performance of the secondary battery.

[0125] In this application, the term "porosity" refers to the number of pores per unit area in the channel from the surface of the negative electrode film to the substrate. The porosity of the first negative electrode film and the second negative electrode film can be measured by any suitable method known in the art. Exemplarily, the test can be performed as follows: Randomly select a test sample with a length × width of 50 mm × 100 mm on either the first or second negative electrode film. Randomly select multiple test areas (e.g., 5) within the test sample, and observe and count the percentage of the area of ​​pores between particles in the first and / or second negative electrode film to the total area at a certain magnification (e.g., 1000x). This yields the porosity of the first and / or second negative electrode film. To ensure the accuracy of the test results, the above test can be repeated on multiple test samples (e.g., 10), and the average value of each test sample can be taken as the final test result.

[0126] In some embodiments, the porosity of the first negative electrode film is 20% to 40%, optionally 30% to 40%. A porosity within this range is more conducive to liquid-phase mass transfer, further improving the power performance of the secondary battery. Exemplarily, the porosity of the first negative electrode film is a value within a range of 20%, 25%, 30%, 35%, 40%, or any combination thereof.

[0127] In some embodiments, the porosity of the second negative electrode film is 10% to 30%, optionally 15% to 25%. Controlling the porosity of the second negative electrode film within the above range is beneficial for improving its liquid-phase mass transfer capability, thereby improving the power performance of the secondary battery. Exemplarily, the porosity of the second negative electrode film is a value within a range of 10%, 15%, 20%, 25%, 30%, or any combination thereof.

[0128] In some embodiments, the coating mass ratio of the first negative electrode film layer and the second negative electrode film layer is 1:9 to 9:1, optionally 1:7 to 1:1. When the coating mass ratio of the first negative electrode film layer and the second negative electrode film layer satisfies the above relationship, the porosity of the first negative electrode film layer is relatively high, which is beneficial to liquid phase mass transfer and further improves the power performance of the secondary battery. For example, the coating mass ratio of the first negative electrode film layer and the second negative electrode film layer is a value within a range of 1:9, 1:8, 1:7, 1:6, 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, or any combination thereof.

[0129] In some embodiments, the coating mass of the first negative electrode film layer is 20 mg / 1540.25 mm. 2 ~100mg / 1540.25mm 2 The coating quality of the first negative electrode film layer is within the aforementioned range, ensuring that the porosity of the first negative electrode film layer is within a suitable range, which is beneficial to the power performance of the secondary battery. For example, the coating quality of the first negative electrode film layer is 20 mg / 1540.25 mm. 2 40mg / 1540.25mm 2 50mg / 1540.25mm 2 80mg / 1540.25mm 2 100mg / 1540.25mm 2 Or the value between any two of them within a range.

[0130] In some embodiments, the coating mass of the second negative electrode film is 20 mg / 1540.25 mm. 2 ~120mg / 1540.25mm 2The coating quality of the second negative electrode film layer within the aforementioned range is beneficial for improving the lifespan of the secondary battery. For example, the coating quality of the second negative electrode film layer is 20 mg / 1540.25 mm. 2 50mg / 1540.25mm 2 80mg / 1540.25mm 2 100mg / 1540.25mm 2 120mg / 1540.25mm 2 Or the value between any two of them within a range.

[0131] In some embodiments, the secondary battery includes a positive electrode sheet, which includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes a positive active material and a lithium replenishing agent. In this application, adding a lithium replenishing agent to the positive electrode film layer can replenish the lithium ions consumed by the first negative electrode film layer, thus improving the cycle life of the secondary battery.

[0132] In some embodiments, the lithium replenishing agent constitutes 0.5% to 5% of the positive electrode film by mass, optionally 1% to 3%. Within this range, the lithium replenishing agent is advantageous in providing an appropriate amount of active lithium, thereby achieving a better lithium replenishment effect and further improving the cycle life of the secondary battery. Exemplarily, the lithium replenishing agent constitutes 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any combination thereof by mass within this range.

[0133] In some implementations, the lithium replenishing agent includes sacrificial lithium replenishing agents and / or non-sacrificial lithium replenishing agents.

[0134] In some embodiments, the sacrificial lithium replenishing agent includes one or more of Li2O2, Li2O, LiN3, Li2C2O4, and Li2C4O4.

[0135] In some embodiments, non-sacrificial lithium replenishers include those with the chemical formula Li. a MnO yThe material, wherein 2≤a≤8, 2≤y≤4; optionally, the non-sacrificial lithium replenisher includes one or more of Li2AO2, Li2BO3, Li3DO4, Li5EO4, and Li6FO4, wherein A includes one or more of Ni, Co, Fe, Mn, Zn, Mg, Ca, Cu, Mo, and Nb; B includes one or more of Ni, Co, Fe, Mn, Sn, Mo, Ru, and Cr; and C includes one or more of Ni, Co, Fe, Mn, Sn, V, Nb, Cr, and Mo. One or more of the following: D includes one or more of Ni, Co, Fe, Mn, Sn, Cr, V, and Mo; E includes one or more of Ni, Co, Mn, Sn, Cr, and Mo; F includes one or more of Ni, Mn, Sn, Cr, and Mo; further optionally, the non-sacrificial lithium replenishing agent includes one or more of Li2NiO2, Li2CuO2, Li2MnO3, Li3VO4, Li3NbO4, Li5FeO4, Li6CoO4, and their doped compounds or coating modifiers. Using the above-mentioned lithium replenishing agents is beneficial for improving the cycle life of secondary batteries.

[0136] In some embodiments of this application, the delithiation products of the lithium replenishing agent include Li 5-x FeO 4-y Li 5-x CoO 4-y Li 2-z MnO2, Li 1.2-r Ni 0.13 Fe 0.13 Mn 0.54 O2 or Li 1-t At least one of FePO4, wherein 4≤x≤5, 2≤y≤3, 1.6≤z≤2, 1≤r≤1.2, and 0.8≤t≤1.

[0137] The term "secondary battery" used in this article refers to a single battery cell, a battery module, or a battery pack. These will be explained separately below.

[0138] Typically, a single secondary battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0139] Negative electrode sheet

[0140] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0141] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0142] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0143] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0144] Positive electrode sheet

[0145] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0146] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the opposite surfaces of the positive current collector. In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0147] In some embodiments, when the battery cell is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0148] During the charging and discharging process of a battery, Li undergoes insertion / extraction and consumption, resulting in varying molar Li content at different discharge states. In the examples of positive electrode active materials in this application, the molar Li content refers to the initial state of the material, i.e., before feeding. When the positive electrode active material is applied to the battery system, the molar Li content changes after charge-discharge cycles.

[0149] In the examples of positive electrode active materials in this application, the molar content of oxygen is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of oxygen will fluctuate.

[0150] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0151] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0152] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0153] electrolytes

[0154] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0155] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0156] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0157] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0158] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0159] Separating membrane

[0160] In some embodiments, the battery cell also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0161] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0162] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0163] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0164] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0165] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 The example shown is a square-structured battery cell 5.

[0166] In some implementations, refer to Figure 3 The outer packaging may include a housing 51 and a top cover assembly 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can cover the opening to close the receiving cavity. A positive electrode sheet, a negative electrode sheet, and a separator can be formed into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0167] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0168] Figure 4 This is battery module 4, used as an example. (See reference...) Figure 4 In battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0169] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0170] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0171] Figure 5 and Figure 6 This is battery pack 1 as an example. (See reference...) Figure 5 and Figure 6 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0172] Electrical appliances

[0173] The second aspect of this application provides an electrical device that includes the secondary battery provided in the first aspect of this application.

[0174] Secondary batteries can be used as a power source for electrical devices or as an energy storage unit for electrical devices. Electrical devices can include, but are not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0175] As an electrical device, you can choose individual battery cells, battery modules, or battery packs according to your usage requirements.

[0176] Figure 7This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0177] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0178] Example

[0179] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0180] Example 1

[0181] Preparation of secondary batteries:

[0182] S1, Preparing the negative electrode sheet, specifically including the following steps:

[0183] a. Preparation of the first negative electrode slurry: Active material formed by mixing the first graphite material and the first silicon-based silicon-carbon composite, conductive carbon, carbon nanotubes, sodium carboxymethyl cellulose, and styrene-butadiene rubber at a mass ratio of 97:1:0.5:0.5:1 are mixed evenly, and an appropriate amount of deionized water is added to form the first negative electrode slurry. The first graphite material has an average particle size of 9 μm, a graphitization degree of 92.5%, and a specific surface area of ​​2.5 m². 2 / g, OI value 6, the mass percentage of silicon element in the first silicon-based material silicon-carbon composite is 50%;

[0184] b. Preparation of the second negative electrode slurry: The second graphite material, conductive carbon, sodium carboxymethyl cellulose, and styrene-butadiene rubber are thoroughly mixed in an appropriate amount of deionized water at a mass ratio of 97:1:1:1 to form the second negative electrode slurry. The second graphite material has an average particle size of 15 μm, a graphitization degree of 95%, and a specific surface area of ​​1.9 m². 2 / g, OI value is 4;

[0185] c. The second negative electrode slurry is coated onto one side of the copper foil of the negative electrode current collector. After drying, the first negative electrode slurry is coated onto the dried second negative electrode slurry. After drying and cold pressing, a second negative electrode film layer and a first negative electrode film layer are formed respectively. The first negative electrode film layer and the second negative electrode film layer constitute the negative electrode film layer, thus obtaining the negative electrode sheet; wherein, the coating mass of the first negative electrode film layer is 30mg / 1540.25mm.2 The coating mass of the second negative electrode film is 120 mg / 1540.25 mm. 2 The coating mass ratio of the first negative electrode slurry to the second negative electrode slurry is 1:4; the cold-pressed thickness of the first negative electrode film is 35μm, and the cold-pressed thickness of the second negative electrode film is 67μm; the mass percentage M1 of silicon in the first negative electrode film is 42%.

[0186] S2, Preparing a secondary battery, specifically includes the following steps:

[0187] d. Preparation of the positive electrode: The nickel-cobalt-manganese ternary positive electrode material (LiNi) is prepared... 0.9 Co 0.05 Mn 0.05 O2), conductive carbon black, and polyvinylidene fluoride are mixed evenly in a mass ratio of 97:2:1, then added to the solvent N-methylpyrrolidone and stirred until homogeneous to form a positive electrode slurry. The positive electrode slurry is then coated onto a positive electrode current collector aluminum foil, dried, and cold-pressed to form a positive electrode film. The coating mass of the positive electrode film is 260 mg / 1540.25 mm. 2 ,

[0188] e. Preparation of electrolyte: Ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 1:2:1 to form an organic solvent. LiPF6 is dissolved in the organic solvent to obtain an electrolyte with a LiPF6 concentration of 1 mol / L.

[0189] f. Separating membrane: Polyethylene microporous film is used as the separating membrane substrate. Inorganic alumina powder, polyvinylpyrrolidone and acetone are mixed evenly in a weight ratio of 3:1.5:5.5 to form a slurry and coated on one side of the separating membrane substrate. After drying, the separating membrane is obtained with a thickness of 10μm.

[0190] g. Stack the above-mentioned positive electrode sheet, separator, and negative electrode sheet in sequence and wind them. After processes such as encapsulation, liquid injection, formation, and degassing, a lithium-ion secondary battery is obtained.

[0191] Negative electrode film parameter testing:

[0192] (1) Element content test

[0193] After discharging the secondary battery to 3V with a constant current of 1C, disassemble it, remove the negative electrode, and scrape off the first and second negative electrode films respectively. Weigh 0.2g of the first negative electrode film into a 100mL beaker, add 10mL of 10% w / w nitric acid solution, heat and digest at 120℃ for 0.5 hours, then dilute to volume with a 100mL volumetric flask, and then use a pipette to transfer 1mL to a 100mL volumetric flask and dilute to volume to obtain the solution to be tested.

[0194] The solution to be tested was analyzed by inductively coupled plasma atomic emission spectrometry (ICP) using an EXPEC 6000 instrument.

[0195] In Example 1, the mass percentage of silicon in the first negative electrode film layer is 42%.

[0196] (2) Porosity test

[0197] A test sample measuring 50mm x 100mm is randomly selected from the first and second negative electrode films. A cross-section of the sample is obtained using a cross-section cutting device. Multiple test areas (e.g., 5) are randomly selected from the cross-section using SEM. At a certain magnification, the proportion of the area of ​​pores between particles in the first and second negative electrode films to the total area is observed and statistically analyzed. This yields the porosity of the first and second negative electrode films. To ensure the accuracy of the test results, the above test can be repeated with 10 test samples, and the average value of each sample is taken as the final test result.

[0198] The porosity of the first negative electrode film layer in Example 1, measured by the above method, is 26%, and the porosity of the second negative electrode film layer is 20%.

[0199] Performance testing of secondary batteries:

[0200] (1) Internal resistance test

[0201] At 25°C, the secondary battery in Example 1 was charged to 4.25V at a constant current of 0.5C, then charged to 0.05C at a constant voltage, and then discharged to 50% SOC at a constant current of 0.5C. The voltage U1 at this time was recorded. Then, it was discharged at a constant current of 3C for 10 seconds, and the voltage U2 after discharge was recorded.

[0202] The DCR of 3C at 50% SOC is (U1-U2) / 3C. The test results are recorded in Table 2 below.

[0203] (2) 4C charge and discharge capacity retention test

[0204] At 25°C, the secondary battery in Example 1 was subjected to charge-discharge tests according to the following steps:

[0205] ① Let stand for 5 minutes;

[0206] ② Charge at a constant current of 1C to 4.25V, then continue charging at a constant voltage to 0.05C;

[0207] ③ Let stand for 5 minutes;

[0208] ④ Discharge at a constant current of 1C to 2.5V and record the discharge capacity C1;

[0209] ⑤ Let stand for 5 minutes;

[0210] ⑥ Charge at a constant current of 4C to 4.25V, then continue charging at a constant voltage to 0.05C;

[0211] ⑦ Let stand for 5 minutes;

[0212] ⑧ Discharge at a constant current of 4C to 2.5V and record the discharge capacity C2;

[0213] 4C charge / discharge capacity retention rate (%) = (C1 / C2) × 100%, and the test results are recorded in Table 2 below.

[0214] Examples 2 and 3

[0215] The secondary battery was prepared using the same method as in Example 1, except that the degree of graphitization of the first graphite material in the first negative electrode film layer and the degree of graphitization of the second graphite material in the second negative electrode film layer were adjusted according to Table 1 below.

[0216] Examples 4 to 7

[0217] The secondary battery was prepared using the same method as in Example 1, except that the average particle size of the first graphite material in the first negative electrode film layer and the average particle size of the second graphite material in the second negative electrode film layer were adjusted according to Table 1 below.

[0218] Comparative Example 1

[0219] The secondary battery was prepared using the same method as in Example 1, except that the degree of graphitization of the first graphite material in the first negative electrode film layer was greater than that of the second graphite material in the second negative electrode film layer, and the average particle size of the first graphite material was smaller than that of the second graphite material.

[0220] Comparative Example 2

[0221] The secondary battery was prepared using the same method as in Example 1, except that the degree of graphitization of the first graphite material in the first negative electrode film layer was less than that of the second graphite material in the second negative electrode film layer, and the average particle size of the first graphite material was greater than that of the second graphite material.

[0222] Comparative Example 3

[0223] The secondary battery was prepared using the same method as in Example 1, except that the degree of graphitization of the first graphite material in the first negative electrode film layer was greater than that of the second graphite material in the second negative electrode film layer, and the average particle size of the first graphite material was greater than that of the second graphite material.

[0224] The performance of the secondary batteries prepared in Examples 2 to 7 and Comparative Examples 1 to 3 were tested using the same test method as in Example 1.

[0225] Table 1 below shows the relevant parameters of the negative electrode films prepared in Examples 1 to 7 and Comparative Examples 1 to 3. Table 2 below shows the performance test results of the secondary batteries prepared in Examples 1 to 7 and Comparative Examples 1 to 3.

[0226] Table 1

[0227]

[0228]

[0229] Table 2

[0230]

[0231] As can be seen from Tables 1 and 2, compared with Comparative Example 1 (the degree of graphitization of the first graphite material is greater than that of the second graphite material), Comparative Example 2 (the average particle size of the first graphite material is greater than that of the second graphite material), and Comparative Example 3 (the degree of graphitization of the first graphite material is greater than that of the second graphite material, and the average particle size of the first graphite material is greater than that of the second graphite material), in Examples 1 to 7, by controlling the degree of graphitization of the first graphite material to be less than that of the second graphite material, and the average particle size of the first graphite material to be less than that of the second graphite material, the internal resistance of the secondary battery can be significantly reduced, and its capacity retention rate at high rates can be improved, which is beneficial to the power performance of the secondary battery.

[0232] Example 8

[0233] The secondary battery was prepared using the same method as in Example 1, except that the preparation process of the second negative electrode slurry was as follows: the second graphite material, the second silicon-carbon material, conductive carbon, sodium carboxymethyl cellulose, and styrene-butadiene rubber were thoroughly mixed in an appropriate amount of deionized water at a mass ratio of 97:1:0.5:0.5:1 to form the second negative electrode slurry, and the mass percentage M2 of silicon element in the second negative electrode film layer was 14%.

[0234] Examples 9 to 12

[0235] The secondary battery was prepared using the same method as in Example 8, except that the mass percentage of silicon in the first negative electrode film M1, the mass percentage of silicon in the second negative electrode film M2, and the difference M1-M2 were different. The specific parameters were adjusted according to Table 3 below.

[0236] The negative electrode films prepared in Examples 8 to 12 were subjected to parameter tests using the same test method as in Example 1, and the secondary batteries prepared in Examples 8 to 12 were subjected to performance tests using the same test method as in Example 1.

[0237] Table 3 below shows the relevant parameters of the negative electrode film prepared in Examples 8 to 12 and the performance test results of the secondary batteries prepared in Examples 8 to 12.

[0238] Table 3

[0239]

[0240] As can be seen from Table 3, by setting the mass percentage of silicon in the first negative electrode film layer M1 to 3% to 70%, the mass percentage of silicon in the second negative electrode film layer M2 to 0% to 21%, and setting 3≤M1-M2≤70%, the internal resistance of the secondary battery can be significantly reduced and its capacity retention rate at high rates can be improved, which is beneficial to the power performance of the secondary battery.

[0241] Example 13

[0242] The secondary battery was prepared using the same method as in Example 1, except that the preparation process of the positive electrode was as follows: A nickel-cobalt-manganese ternary positive electrode material (LiNi) was prepared... 0.9 Co 0.05 Mn 0.05 O2), lithium supplementer Li5FeO4, conductive carbon black, and polyvinylidene fluoride are mixed evenly in a mass ratio of 95:2:2:1, and then added to the solvent N-methylpyrrolidone. The mixture is stirred until homogeneous to form a positive electrode slurry. This slurry is then coated onto a positive electrode current collector aluminum foil, dried, and cold-pressed to form a positive electrode film. The coating mass of the positive electrode film is 260 mg / 1540.25 mm. 2 .

[0243] Examples 14 to 20

[0244] The secondary battery was prepared using the same method as in Example 13, except that the mass percentage M1 of silicon in the first negative electrode film, the type of lithium replenisher, and the amount of lithium replenisher were adjusted according to Table 4 below.

[0245] The performance of the secondary batteries prepared in Examples 13 to 20 was tested using the same test method as in Example 1.

[0246] In addition, the secondary batteries of Examples 1 and 13 to 20 were subjected to cycle performance tests at 25°C according to the following test procedures:

[0247] ① Let stand for 5 minutes;

[0248] ② Charge at a constant current of 0.5C to 4.25V, then continue charging at a constant voltage to 0.05C;

[0249] ③ Let stand for 5 minutes;

[0250] ④ Discharge at a constant current of 0.5C to 2.5V and record the discharge capacity D1 of the first cycle;

[0251] ⑤ Let stand for 5 minutes;

[0252] ⑥ Repeat steps ② to ⑤ above until the capacity retention rate is less than D1*70%, record the corresponding number of cycles, and record the test results in Table 4 below.

[0253] Table 4 below shows the lithium replenishing agents used in Examples 13 to 20 and the performance test results of the secondary batteries prepared in Examples 13 to 20. Additionally, for ease of comparison, relevant test data from Example 1 are also shown here.

[0254] Table 4

[0255]

[0256] As can be seen from Table 4, by setting a lithium replenishing agent in the positive electrode film layer, and setting different amounts of lithium replenishing agent corresponding to different silicon element contents of the anode, the cycle performance of the secondary battery can be significantly improved.

[0257] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A secondary battery, characterized in that, The device includes a negative electrode sheet, which includes a negative current collector and a negative electrode film layer located on at least one side of the negative current collector; the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer, wherein the second negative electrode film layer is disposed between the negative current collector and the first negative electrode film layer. The first negative electrode film layer includes a first silicon-based material and a first graphite material, and the second negative electrode film layer includes a second graphite material; The degree of graphitization of the first graphite material is less than that of the second graphite material, and the average particle size of the first graphite material is less than that of the second graphite material.

2. The secondary battery according to claim 1, characterized in that, The graphitization degree of the first graphite material is 91.0% to 93.0%.

3. The secondary battery according to claim 1 or 2, characterized in that, The degree of graphitization of the second graphite material is 93.0% to 96.0%.

4. The secondary battery according to any one of claims 1 to 3, characterized in that, The average particle size of the first graphite material is 3μm to 20μm.

5. The secondary battery according to any one of claims 1 to 4, characterized in that, The average particle size of the second graphite material is 6 μm to 25 μm.

6. The secondary battery according to any one of claims 1 to 5, characterized in that, The OI value of the first graphite material is greater than the OI value of the second graphite material.

7. The secondary battery according to any one of claims 1 to 6, characterized in that, The OI value of the first graphite material is 2 to 9, and / or the OI value of the second graphite material is 2 to 9.

8. The secondary battery according to any one of claims 1 to 7, characterized in that, The OI value of the first graphite material is 3.7 to 7.5, and / or the OI value of the second graphite material is 2 to 3.

7.

9. The secondary battery according to any one of claims 1 to 8, characterized in that, The specific surface area of ​​the first graphite material is greater than that of the second graphite material.

10. The secondary battery according to any one of claims 1 to 9, characterized in that, The specific surface area of ​​the first graphite material is 1.0 m². 2 / g~3.4m 2 / g.

11. The secondary battery according to any one of claims 1 to 10, characterized in that, The specific surface area of ​​the second graphite material is 1.0 m². 2 / g~3.0m 2 / g.

12. The secondary battery according to any one of claims 1 to 11, characterized in that, The first silicon-based material includes one or more of elemental silicon, silicon-carbon composites, silicon-oxygen materials, and silicon alloys.

13. The secondary battery according to claim 12, characterized in that, The first silicon-based material includes the silicon-carbon composite, which satisfies one or more of the following characteristics: (1) The silicon-carbon composite comprises porous carbon and silicon-containing material dispersed in the pores of the porous carbon; (2) The silicon-carbon composite further includes a carbon-containing coating layer, which is located on the surface of the porous carbon and / or the silicon-containing material; (3) The silicon content in the silicon-carbon composite is 30% to 70% by mass; (4) The average particle size of the silicon-carbon composite is 2 μm to 15 μm; (5) The powder resistivity of the silicon-carbon composite at 8 MPa is 4 Ω·cm to 17 Ω·cm; (6) The BET specific surface area of ​​the silicon-carbon composite is 1.0 m². 2 / g~6.7m 2 / g.

14. The secondary battery according to any one of claims 1 to 13, characterized in that, The second negative electrode film layer includes a second silicon-based material, which includes one or more of elemental silicon, silicon-carbon composite, silicon-oxygen material, and silicon alloy.

15. The secondary battery according to claim 14, characterized in that, The mass percentage N1 of the first silicon-based material in the total mass of the first silicon-based material and the first graphite material, and the mass percentage N2 of the second silicon-based material in the total mass of the second silicon-based material and the second graphite material, satisfy: N1 > N2.

16. The secondary battery according to claim 15, characterized in that, N1 is 10%–100%; and / or, N2 is 0%–30%.

17. The secondary battery according to any one of claims 14 to 16, characterized in that, The mass percentage of silicon in the first negative electrode film layer, M1, and the mass percentage of silicon in the second negative electrode film layer, M2, satisfy the following condition: 3 ≤ M1 - M2 ≤ 70%.

18. The secondary battery according to claim 17, characterized in that, 3% ≤ M1 - M2 ≤ 42%.

19. The secondary battery according to claim 17 or 18, characterized in that, The mass percentage (M1) of silicon in the first negative electrode film layer is 3% to 70%.

20. The secondary battery according to any one of claims 17 to 19, characterized in that, The mass percentage (M2) of silicon in the second negative electrode film layer is 0% to 21%.

21. The secondary battery according to any one of claims 1 to 20, characterized in that, The first negative electrode film layer includes a first conductive agent; the first conductive agent includes carbon nanotubes.

22. The secondary battery according to claim 21, characterized in that, The first conductive agent accounts for 0.05% to 0.5% of the mass of the first negative electrode film.

23. The secondary battery according to any one of claims 1 to 22, characterized in that, The porosity of the first negative electrode film is greater than that of the second negative electrode film.

24. The secondary battery according to any one of claims 1 to 23, characterized in that, The porosity of the first negative electrode film layer is 20% to 40%.

25. The secondary battery according to any one of claims 1 to 24, characterized in that, The porosity of the second negative electrode film is 10% to 30%.

26. The secondary battery according to any one of claims 1 to 25, characterized in that, The coating mass ratio of the first negative electrode film layer to the second negative electrode film layer is 1:9 to 9:

1.

27. The secondary battery according to any one of claims 1 to 26, characterized in that, The coating mass of the first negative electrode film layer is 20 mg / 1540.25 mm. 2 ~100mg / 1540.25mm 2 .

28. The secondary battery according to any one of claims 1 to 27, characterized in that, The coating mass of the second negative electrode film is 20 mg / 1540.25 mm. 2 ~120mg / 1540.25mm 2 .

29. The secondary battery according to any one of claims 1 to 28, characterized in that, The device includes a positive electrode sheet, which includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes a positive active material and a lithium supplement agent.

30. The secondary battery according to claim 29, characterized in that, The lithium supplement agent accounts for 0.5% to 5% of the mass of the positive electrode film.

31. The secondary battery according to claim 29 or 30, characterized in that, The lithium replenishing agent accounts for 1% to 3% of the mass of the positive electrode film.

32. The secondary battery according to any one of claims 29 to 31, characterized in that, The lithium replenishing agent includes sacrificial lithium replenishing agents and / or non-sacrificial lithium replenishing agents.

33. The secondary battery according to claim 32, characterized in that, The sacrificial lithium supplement includes one or more of Li2O2, Li2O, LiN3, Li2C2O4, and Li2C4O4.

34. The secondary battery according to claim 32 or 33, characterized in that, The non-sacrificial lithium supplement includes the chemical formula Li. a MnO y The material is given by the following conditions: 2≤a≤8, 2≤y≤4.

35. The secondary battery according to any one of claims 32 to 34, characterized in that, The non-sacrificial lithium replenishing agent includes one or more of Li2AO2, Li2BO3, Li3DO4, Li5EO4, and Li6FO4; Wherein, A includes one or more of Ni, Co, Fe, Mn, Zn, Mg, Ca, Cu, Mo, and Nb; B includes one or more of Ni, Co, Fe, Mn, Sn, Mo, Ru, and Cr; C includes one or more of Ni, Co, Fe, Mn, Sn, V, Nb, Cr, and Mo; D includes one or more of Ni, Co, Fe, Mn, Sn, Cr, V, and Mo; E includes one or more of Ni, Co, Mn, Sn, Cr, and Mo; and F includes one or more of Ni, Mn, Sn, Cr, and Mo.

36. The secondary battery according to any one of claims 32 to 35, characterized in that, The non-sacrificial lithium replenishing agent includes one or more of Li2NiO2, Li2CuO2, Li2MnO3, Li3VO4, Li3NbO4, Li5FeO4, Li6CoO4 and their doped compounds or coating modifiers.

37. An electrical device, characterized in that, The electrical device includes the secondary battery as described in any one of claims 1 to 36.

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