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

Abstract

Provided in the present application are a battery cell, a negative electrode sheet, a battery device and an electric device. The battery cell comprises an electrode assembly, the electrode assembly comprises a negative electrode sheet, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer arranged on at least one side of the negative electrode current collector, and the negative electrode active layer comprises a first negative electrode active layer and a second negative electrode active layer, wherein the first negative electrode active layer is arranged on at least one side of the negative electrode current collector, and the second negative electrode active layer is arranged on the side of the first negative electrode active layer away from the negative electrode current collector; and the first negative electrode active layer comprises a first graphite material and a silicon-based material, the second negative electrode active layer comprises a second graphite material, and the degree of graphitization of the second graphite material is greater than or equal to 90% and less than the degree of graphitization of the first graphite material, which is less than or equal to 96%.

Description

Battery cells, negative electrode plates, battery devices and electrical devices Cross-references to related applications

[0001] This application claims priority to Chinese patent application 202411754916.6, filed December 2, 2024, entitled “Battery cell, negative electrode, battery device and power consumption device”, and Chinese patent application 202510092082.5, filed January 21, 2025, entitled “Battery cell, negative electrode, battery device and power consumption device”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery technology, and in particular to a battery cell, a negative electrode, a battery device, and an electrical device. Background Technology

[0003] With the development of the battery industry, the demand for high-energy-density batteries is increasing. Currently, mainstream graphite anodes are no longer sufficient to meet these demands, making silicon anodes a popular option. During charging, silicon undergoes significant volume expansion, leading to high stress within the electrode assembly. This high stress not only affects the electrolyte reabsorption rate but also the structural stability of the positive and negative electrode active materials, resulting in high lithium consumption rates or excessive loss of these active materials, ultimately shortening the lifespan of individual battery cells. Therefore, reducing the expansion force of silicon-containing systems is crucial.

[0004] As the demand for electric vehicle range increases, so too does the demand for charging speed. Especially given the limited number of charging stations on highways, reducing charging time can greatly improve the comfort of car owners. Therefore, improving the charging speed of silicon-based systems is a top priority. Summary of the Invention

[0005] This application provides a battery cell, a negative electrode, a battery device, and an electrical device, so that the battery cell can take into account the characteristics of high energy density, long cycle life, and fast charging.

[0006] A first aspect of this application provides a battery cell including an electrode assembly. The electrode assembly includes a negative electrode sheet, which includes a negative current collector and a negative active layer disposed on at least one side of the negative current collector. The negative active layer includes a first negative active layer and a second negative active layer. The first negative active layer is disposed on at least one side of the negative current collector, and the second negative active layer is disposed on the side of the first negative active layer away from the negative current collector. The first negative active layer includes a first graphite material and a silicon-based material, and the second negative active layer includes a second graphite material, wherein 90% ≤ the graphitization degree of the second graphite material < the graphitization degree of the first graphite material ≤ 96%.

[0007] This application places the silicon-based material in the lower first negative electrode active layer. During charging, it is constrained by the upper second negative electrode active layer, reducing the thickness increase of the first negative electrode active layer. This reduces the internal stress caused by expansion in the electrode assembly, not only providing sufficient space for electrolyte reflux but also reducing the loss of active sites on the positive and negative electrode plates, thereby extending the cycle life of the battery cell. Furthermore, this application's research found that within a graphitization range of 90%-96%, the graphitization of the second graphite material can provide a high electron transport rate, while an appropriate degree of disorder can shorten the Li... + The migration distance is relatively short, so when a second graphite material with a low degree of graphitization is placed on the upper layer, its lithium-ion transport rate is faster, thereby improving the charging capacity of the battery cell. The first graphite material has a higher degree of graphitization, resulting in a higher specific capacity and more stable cycle life. Placing the first graphite material with a high degree of graphitization on the lower layer allows the high specific capacity advantage to be more easily realized under the compressive stress of the upper layer. At the same time, the better lubricity of graphite with a high degree of graphitization makes the sliding of graphite particles during cold pressing more conducive to fully utilizing the interparticle gaps when mixing with silicon-based materials, thereby better improving the compaction density of the lower first negative electrode active layer and thus improving the energy density of the battery cell. Therefore, the combination of the two materials balances energy density and improves charging capacity.

[0008] In any embodiment of the first aspect, the graphitization degree of the first graphite material is between 94% and 96%. By controlling the graphitization degree as described above, the charging rate of the underlying first negative electrode active layer is maximized while improving the energy density of the battery cell.

[0009] In any embodiment of the first aspect, the average particle size of the first graphite material is 6 μm to 25 μm. When the average particle size of the first graphite material in the lower layer is within the above range, the exposed lithium-intercalation surface of the first graphite material is controlled, which helps to reduce lithium consumption and thereby improve the cycle life of the battery.

[0010] In any embodiment of the first aspect, the specific capacity of the first graphite material is higher than that of the second graphite material, and the specific capacity of the first negative electrode active layer is 422 mAh / g-1482 mAh / g. This utilizes the first active material to increase the energy density of the battery cell.

[0011] In any embodiment of the first aspect, the BET specific surface area of ​​the first graphite material is 1.5 m² / g - 3.0 m² / g. 2 / g. The aforementioned BET specific surface area helps reduce lithium consumption, thereby improving the cycle life of individual battery cells.

[0012] In any embodiment of the first aspect, the degree of graphitization of the second graphite material is between 91% and 93%. By controlling the degree of graphitization as described above, the influence of the second graphite material on the energy density is minimized as much as possible, and the degree of disorder of the second graphite material is utilized as much as possible to improve the charging rate of the battery cell.

[0013] In any embodiment of the first aspect, the average particle size of the second graphite material is 3 μm-20 μm. By controlling the average particle size of the second graphite material, the contact area between the second graphite material and the electrolyte is increased, thereby improving the charging capacity; at the same time, the problem of increased lithium consumption due to increased exposed surface area of ​​the second graphite material caused by excessively small particle size is controlled.

[0014] In any embodiment of the first aspect, the BET specific surface area of ​​the second graphite material is 0.6 m². 2 / g-3.4m 2 / g. By utilizing the aforementioned control of BET specific surface area, the contact area between the second graphite material and the electrolyte is also increased, thereby improving the charging capacity; at the same time, the problem of increased lithium consumption due to the increased exposed surface of the second graphite material caused by excessively small particle size is controlled.

[0015] In any embodiment of the first aspect, the mass content of silicon in the first negative electrode active layer is 2.5%-68%, optionally 5.5%-48%. Controlling the silicon content within the above range can, on the one hand, control excessive expansion caused by a high silicon content, and on the other hand, utilize silicon to achieve the purpose of increasing the energy density of the battery cell.

[0016] In any embodiment of the first aspect, when the battery cell is in a 0% SOC state within 50 charge-discharge cycles, the thickness of the first negative electrode active layer is 6 μm-40 μm. This thickness of the first negative electrode active layer is beneficial for reducing the Li in the first negative electrode active layer. + This increases the transmission distance, reduces the concentration polarization of lithium ions in the upper and lower layers, and improves the overall charging capacity of the battery cell.

[0017] In any embodiment of the first aspect, when the battery cell is in a 0% SOC state within 50 charge-discharge cycles, the thickness of the second negative electrode active layer is 10 μm-70 μm, optionally 12 μm-68 μm. The thickness of the second negative electrode active layer within the above range provides sufficient lithium-ion diffusion space for lithium-ion injection during fast charging of the battery cell, which helps reduce concentration polarization of lithium ions in the negative electrode sheet and further improves the charging rate of the battery cell.

[0018] In any embodiment of the first aspect, the silicon-carbon composite-based material includes one or more of elemental silicon, silicon-oxygen composites, and silicon-carbon composites; optionally, the silicon-based material includes the silicon-carbon composite.

[0019] In any embodiment of the first aspect, the silicon-carbon composite satisfies one or more of the following characteristics:

[0020] 1) The silicon-carbon composite includes porous carbon and silicon-containing materials dispersed in the pores of the porous carbon, wherein the porous carbon is optionally hard carbon;

[0021] 2) The silicon-carbon composite also includes a carbon-containing coating layer, which is located on the surface of porous carbon and / or silicon-containing materials;

[0022] 3) The silicon content in the silicon-carbon composite is 30%-70% by mass;

[0023] 4) The average particle size of the silicon-carbon composite is 2μm-15μm, optionally 7μm-11μm;

[0024] 5) The powder resistivity of silicon-carbon composite at 8 MPa is 4 Ω·cm - 17 Ω·cm;

[0025] 6) The BET specific surface area of ​​the silicon-carbon composite is 1.0 m². 2 / g-6.7m2 / g.

[0026] In any embodiment of the first aspect, the first negative electrode active layer further includes a first conductive agent, which includes carbon nanotubes. Optionally, the mass content of carbon nanotubes in the first negative electrode active layer is 0.05%-0.5%. The carbon nanotubes placed in the first negative electrode active layer enhance the electronic conductivity of the silicon material and, on the other hand, utilize the linear structure of the carbon nanotubes to improve the binding of silicon particles and reduce expansion.

[0027] In any embodiment of the first aspect, the second negative electrode active layer comprises a second conductive agent, which comprises carbon nanotubes. Optionally, the carbon nanotube content in the first negative electrode active layer is higher than the carbon nanotube content in the second negative electrode active layer. Carbon nanotubes are used to improve the conductivity of the second negative electrode active layer. When the carbon nanotube content in the first negative electrode active layer is higher than the carbon nanotube content in the second negative electrode active layer, it is beneficial to reduce the cost of the second negative electrode active layer.

[0028] In any embodiment of the first aspect, the first negative electrode active layer further includes a first adhesive, and the second negative electrode active layer further includes a second adhesive, wherein the first adhesive and the second adhesive each independently include any one or more of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, and polyvinyl alcohol.

[0029] In any embodiment of the first aspect, the mass content of the first binder in the first negative electrode active layer is higher than the mass content of the second binder in the second negative electrode active layer, so as to further improve the restraint of the first negative electrode active layer on the expansion of the silicon-carbon composite material.

[0030] In any embodiment of the first aspect, optionally, the first binder has a mass content of 1%-5% in the first negative electrode active layer, more preferably 1.5%-4.5%; optionally, the second binder has a mass content of 0.5%-5% in the second negative electrode active layer, more preferably 1.5%-3.5%. Providing the first or second binder within the above-mentioned mass content range ensures sufficient bonding while minimizing the influence of the binder on the energy density.

[0031] In any embodiment of the first aspect, the negative electrode sheet further includes a base coating layer disposed between the negative electrode current collector and the first negative electrode active layer. The base coating layer includes a conductive agent and a third binder. Optionally, the thickness of the base coating layer is 0.3 μm-1.5 μm. Optionally, the mass content of the third binder in the base coating layer is 50%-80%. Due to the large expansion of the silicon system and the relatively smooth surface of the negative electrode current collector, there is a risk of powder shedding during long-term cycling. Adding a base coating layer can increase the adhesion between the negative electrode active layer and the negative electrode current collector, further extending the cycle life of the battery cell.

[0032] A second aspect of this application provides a negative electrode sheet, including a negative current collector and a negative active layer disposed on at least one side of the negative current collector. The negative active layer includes a first negative active layer and a second negative active layer. The first negative active layer is disposed on at least one side of the negative current collector, and the second negative active layer is disposed on the side of the first negative active layer away from the negative current collector. The first negative active layer includes a first graphite material and a silicon-based material; the second negative active layer includes a second graphite material, where 90% ≤ the graphitization degree of the second graphite material < the graphitization degree of the first graphite material ≤ 96%.

[0033] In any embodiment of the second aspect, the graphitization degree of the first graphite material is between 90% and 96%, and / or the average particle size of the first graphite material is between 6 μm and 25 μm.

[0034] In any embodiment of the second aspect, the specific capacity of the first graphite material is higher than that of the second graphite material, the specific capacity of the first negative electrode active layer is 422 mAh / g-1482 mAh / g, and / or the BET specific surface area of ​​the first graphite material is 1.5 m². 2 / g-3.0m 2 / g.

[0035] In any embodiment of the second aspect, the degree of graphitization of the second graphite material is between 91% and 93%.

[0036] In any embodiment of the second aspect, the average particle size of the second graphite material is 3 μm-20 μm, and / or the BET specific surface area of ​​the second graphite material is 0.6 m². 2 / g-3.4m2 / g.

[0037] In any embodiment of the second aspect, the mass content of silicon in the first negative electrode active layer is 2.5%-68%, and optionally 5.5%-48%.

[0038] In any embodiment of the second aspect, the thickness of the first negative electrode active layer is 6μm-40μm, and / or the thickness of the second negative electrode active layer is 10μm-70μm, optionally 12μm-68μm.

[0039] In any embodiment of the second aspect, the silicon-based material includes one or more of elemental silicon, silicon-oxygen composites, and silicon-carbon composites; optionally, the silicon-based material includes the silicon-carbon composite.

[0040] In any embodiment of the second aspect, the silicon-carbon composite 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, optionally the porous carbon being hard carbon; 2) The silicon-carbon composite further comprises a carbon-containing coating layer located on the surface of the porous carbon and / or the silicon material; 3) The silicon content in the silicon-carbon composite is 30%-70% by mass; 4) The average particle size of the silicon-carbon composite is 2μm-15μm, further optionally 7μm-11μm; 5) The powder resistivity of the silicon-carbon composite at 8MPa is 4Ω·cm-17Ω·cm; 6) The BET specific surface area of ​​the silicon-carbon composite is 1.0m². 2 / g-6.7m 2 / g.

[0041] In any embodiment of the second aspect, the first negative electrode active layer further includes a conductive agent, which includes carbon nanotubes, optionally with a mass content of 0.05%-0.5% in the first negative electrode active layer.

[0042] In any embodiment of the second aspect, the negative electrode sheet further includes a base coating layer disposed between the negative electrode current collector and the first negative electrode active layer. The base coating layer includes a third conductive agent and a third binder. Optionally, the thickness of the base coating layer is 0.2 μm-2 μm. Optionally, the mass content of the third binder in the base coating layer is 70%-90%.

[0043] A third aspect of this application provides a battery device comprising a plurality of battery cells, wherein the battery cells include any embodiment of the battery cells of the second aspect of this application.

[0044] A fourth aspect of this application provides an electrical device, including a battery cell or a battery device, wherein the battery cell includes any embodiment of the battery cell of the second aspect of this application, and the battery device includes any embodiment of the battery device of the third aspect of this application. Attached Figure Description

[0045] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0046] Figure 1 is a schematic diagram of a battery cell according to one embodiment of this application.

[0047] Figure 2 is an exploded view of a battery cell according to an embodiment of this application shown in Figure 1.

[0048] Figure 3 is a schematic diagram of a battery module according to one embodiment of this application.

[0049] Figure 4 is a schematic diagram of a battery pack according to one embodiment of this application.

[0050] Figure 5 is an exploded view of the battery pack of one embodiment of this application shown in Figure 4.

[0051] Figure 6 is a schematic diagram of an electrical device in which a single battery cell is used as a power source according to an embodiment of this application.

[0052] The accompanying drawings are not drawn to scale.

[0053] Explanation of reference numerals in the attached figures:

[0054] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Casing; 52 Electrode assembly; 53 End cap. Detailed Implementation

[0055] The embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to illustrate the principles of this application by way of example, but should not be used to limit the scope of this application, that is, this application is not limited to the described embodiments.

[0056] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the negative electrode sheet, battery cell, battery device, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0057] 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.

[0058] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0059] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0060] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0061] Unless otherwise specified, the terms "comprising" and "including" as used in this application are open-ended. For example, "comprising" and "including" may mean that other components not listed may also be included or contained.

[0062] Unless otherwise specified, the term "or" is inclusive in this application. For example, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0063] [Negative electrode plate]

[0064] A negative electrode typically includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0065] 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.

[0066] To improve the cycle life and charging rate of high-energy-density battery cells, a first embodiment of this application provides a negative electrode sheet, including a negative electrode current collector and a negative electrode active layer disposed on at least one side of the negative electrode current collector. The negative electrode active layer includes a first negative electrode active layer and a second negative electrode active layer. The first negative electrode active layer is disposed on at least one side of the negative electrode current collector, and the second negative electrode active layer is disposed on the side of the first negative electrode active layer away from the negative electrode current collector. The first negative electrode active layer includes a first graphite material and a silicon-based material, and the second negative electrode active layer includes a second graphite material, and 90% ≤ the graphitization degree of the second graphite material < the graphitization degree of the first graphite material ≤ 96%.

[0067] By placing the silicon-based material within the lower first negative electrode active layer, it is constrained by the upper second negative electrode active layer during charging. This reduces the thickness increase of the first negative electrode active layer, thereby lowering the internal stress caused by expansion in the electrode assembly. This not only provides sufficient space for electrolyte reflux but also reduces the loss of active sites on the positive and negative electrode plates, thus extending the cycle life of the battery cell. Furthermore, this research found that within a graphitization range of 90%-96%, the graphitization of the second graphite material can provide a high electron transport rate, while an appropriate degree of disorder can shorten the Li... +The migration distance is relatively short, so when a second graphite material with a low degree of graphitization is placed on the upper layer, its lithium-ion transport rate is faster, thereby improving the charging capacity of the battery cell. The first graphite material has a higher degree of graphitization, resulting in a higher specific capacity and more stable cycle life. Placing the first graphite material with a high degree of graphitization on the lower layer allows the high specific capacity advantage to be more easily realized under the compressive stress of the upper layer. At the same time, the better lubricity of graphite with a high degree of graphitization makes the sliding of graphite particles during cold pressing more conducive to fully utilizing the interparticle gaps when mixing with silicon-based materials, thereby better improving the compaction density of the lower first negative electrode active layer and thus improving the energy density of the battery cell. Therefore, the combination of the two materials balances energy density and improves charging capacity.

[0068] The degree of graphitization is an indicator of the extent to which carbon atoms form a close-packed hexagonal graphite crystal structure. The closer the lattice size is to the lattice constant of ideal graphite, the higher the degree of graphitization. The degree of graphitization of the first and second graphite materials mentioned above can be determined using instruments and methods known in the art. For example, Appendix E of the national standard GB / T24533-2019 "Graphite Anode Materials for Lithium-ion Batteries" can be referred to. Artificial graphite is also applicable to the Chinese machinery industry standard JB / T4220-2011 "Methods for Determining Lattice Parameters of Artificial Graphite". The specific determination steps include: first, scraping the powder from the upper part of the negative electrode sheet, which is the second negative electrode active layer powder; then scraping the powder near the negative electrode current collector; if SEM-EDS confirms that the powder contains silicon, it can be confirmed as the first negative electrode active layer powder. Then, X-ray diffractometer (such as Bruker D8 Discover) is used for testing. First, the size of d002 was measured. Then, the degree of graphitization was calculated using the formula G = (0.344 - d002) / (0.344 - 0.3354) × 100%, where d002 is the interlayer spacing in the graphite crystal structure in nm. In the X-ray diffraction analysis, Cu Kα rays were used as the radiation source, the ray wavelength scan ranged from 20° to 80° at a 2θ angle, and the scan rate was 4° / min.

[0069] Higher graphitization results in higher specific capacity, but also higher cost. Furthermore, denser graphite stacking increases electron transport resistance in the electrode. In some embodiments, the graphitization degree of the first graphite material is between 94% and 96%. By controlling the graphitization degree, the charging rate of the underlying first negative electrode active layer can be maximized while improving the energy density of the individual battery cells.

[0070] In some embodiments, the average particle size of the first graphite material is 6 μm-25 μm. When the average particle size of the first graphite material in the lower layer is within the above range, the exposed lithium intercalation surface of the first graphite material is controlled, which helps to reduce lithium consumption and thus improve the cycle life of the battery.

[0071] The average particle size of the first graphite material can be tested using equipment and methods known in the art. For example, a scanning electron microscope (SEM) can be used (e.g., ZEISS Sigma 300), referring to JY / T010-1996, to obtain an SEM image 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) within the test sample, and at a certain magnification (e.g., 1000x when measuring the first graphite material), read the particle size of each complete first graphite material particle in each test area (i.e., take the distance between the two farthest points on the first graphite material particle as the particle size). Count the number and particle size values ​​of complete first graphite material particles in each test area, and take the arithmetic mean of the first graphite material particles in each test area, which is the average particle size of the first graphite material 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.

[0072] The above test methods can also be applied to the testing of the average particle size of the second graphite material and silicon-based material.

[0073] In some embodiments, the specific capacity of the first graphite material is higher than that of the second graphite material, and the specific capacity of the first negative electrode active layer is 422 mAh / g-1482 mAh / g. This allows the first active material to be used to increase the energy density of the battery cell.

[0074] The specific capacity of the first negative electrode active layer can be tested using the following method: ① The negative electrode sheet is scraped to obtain the first negative electrode active layer material near the negative electrode current collector; ② The first negative electrode active layer material is soaked in pure solvent DMC and cut into small discs with a diameter of 7 mm; ③ The small discs are assembled with lithium metal sheets to form a coin cell. The electrolyte solvent is EC-DMC (volume ratio 5:5), and the lithium salt is LiPF6 with a concentration of 1 mol / L; ④ The test voltage range is 5 mV-2 V, and the rate is 0.1 C / 0.1 C; the charge and discharge process is as follows: charge at a constant current of 0.1 C to 2 V, let stand for 10 min, discharge at a constant current of 0.1 C to 5 mV, let stand for 10 min, and repeat this process twice. ⑤ Instrument: Shanghai Chenhua Electrochemical Workstation CHI700E.

[0075] In some embodiments, the BET specific surface area of ​​the first graphite material is 1.5 m². 2 / g-3.0m 2 / g. The aforementioned BET specific surface area helps reduce lithium consumption, thereby improving the cycle life of individual battery cells.

[0076] The BET specific surface area test method for the aforementioned first graphite material can refer to GB / T 19587-2017. The nitrogen adsorption specific surface area analysis method is used, in which the sample tube containing the first graphite material sample is immersed in liquid nitrogen at -196℃. The amount of nitrogen adsorbed on the surface of the solid sample at different pressures of 0.05-0.30 MPa is measured. Based on the BET multilayer adsorption theory and calculation formula, the monolayer adsorption amount of the sample is obtained, and thus the BET specific surface area is calculated. This test can be performed using a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0077] In order to improve the charging rate of the battery cell by making the most of the disorder of the second graphite material while minimizing its impact on energy density, in some embodiments, the graphitization degree of the second graphite material is between 91% and 93%.

[0078] In some embodiments, the average particle size of the second graphite material is 3μm-20μm. By controlling the average particle size of the second graphite material, the contact area between the second graphite material and the electrolyte is increased, thereby improving the charging capacity; at the same time, the problem of increased lithium consumption due to increased exposed surface area of ​​the second graphite material caused by excessively small particle size is controlled.

[0079] In some embodiments, the BET specific surface area of ​​the second graphite material is 0.6 m². 2 / g-3.4m 2 / g. By utilizing the aforementioned control of BET specific surface area, the contact area between the second graphite material and the electrolyte is also increased, thereby improving charging capacity; at the same time, the problem of increased lithium consumption due to increased exposed surface area of ​​the second graphite material caused by excessively small particle size is controlled. The BET testing method for the second graphite material is the same as that for the first graphite material.

[0080] In some embodiments, the silicon content in the first negative electrode active layer is 2.5%-68% by mass, and optionally 5.5%-48%. Controlling the silicon content within the above range can, on the one hand, control excessive expansion caused by a high silicon content, and on the other hand, utilize silicon to achieve the goal of increasing the energy density of the battery cell.

[0081] The silicon content in the first negative electrode active layer can be tested using the following method:

[0082] The negative electrode material of the first negative electrode active layer was collected by scraping powder, and the negative electrode material was tested by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0083] In some embodiments, when the battery cell is at 0% SOC, the thickness of the first negative electrode active layer is 6 μm-40 μm. This thickness of the first negative electrode active layer is beneficial for reducing the Li- content of the first negative electrode active layer. + The transmission distance is increased, reducing the concentration polarization of lithium ions between the upper and lower layers and improving the overall charging capacity of the battery cell. The method for adjusting the state of charge (SOC) of the battery cell to 0% can be tested using methods known in the art. As an example, the following method can be used: 1) Determine the rated capacity of the battery cell: This can be the ampere-hour capacity specified by the manufacturer; or, within the specified usable voltage range of the battery cell, charge it at 25°C and 0.33C at a constant current and constant voltage to the upper voltage limit, then discharge it at 0.33C to the lower voltage limit, at which point the battery cell is at 0% SOC.

[0084] In some embodiments, when the battery cell is at 0% SOC, the thickness of the second negative electrode active layer is 10μm-70μm, optionally 12μm-68μm. A thickness within this range provides sufficient lithium-ion diffusion space for lithium-ion injection during fast charging of the battery cell, which helps reduce concentration polarization of lithium ions in the negative electrode and further improves the charging rate of the battery cell.

[0085] The thicknesses of the first and second negative electrode active layers can be measured using the CP-SEM method, where the corresponding thicknesses are measured in the microscopic images.

[0086] The silicon-carbon composite of this application can be prepared using conventional silicon-carbon composites or conventional preparation methods, such as depositing nano-silicon materials on porous carbon by chemical vapor deposition, and further carbon coating, such as using amorphous carbon coating.

[0087] In some embodiments, the silicon-based material includes one or more of elemental silicon, silicon-oxygen composites, and silicon-carbon composites.

[0088] In some embodiments, the silicon-oxygen complex includes at least one of unpre-lithium silicon-oxygen compound, pre-lithium silicon-oxygen compound, unpre-magnesium silicon-oxygen compound, and pre-magnesium silicon-oxygen compound.

[0089] In some embodiments, the silicon-based material may be the silicon-carbon composite.

[0090] In some embodiments, the silicon-carbon composite may optionally satisfy one or more of the following characteristics:

[0091] 1) The silicon-carbon composite includes porous carbon and silicon-containing material dispersed in the pores of the porous carbon, wherein the porous carbon is optionally hard carbon;

[0092] 2) The silicon-carbon composite also includes a carbon-containing coating layer located on the surface of the porous carbon and / or silicon material;

[0093] 3) The silicon content in the silicon-carbon composite is 30%-70% by mass;

[0094] 4) The average particle size of the silicon-carbon composite is 2μm-15μm, optionally 7μm-11μm;

[0095] 5) The powder resistivity of silicon-carbon composite at 8 MPa is 4 Ω·cm - 17 Ω·cm;

[0096] 6) The BET specific surface area of ​​the silicon-carbon composite is 1.0 m². 2 / g-6.7m 2 / g.

[0097] In some embodiments, the silicon-carbon composite includes 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 while its pores offer expansion space, effectively mitigating stress caused by expansion during charging. Especially when the silicon-containing material has a nanometer-scale particle size, it exhibits higher specific capacity and is better dispersed within the pores of the porous carbon. Furthermore, it allows for more efficient utilization of the porous carbon's buffering effect on expansion. When this silicon-carbon composite is used in wound electrode assemblies, it can significantly alleviate the stretching of the outer negative electrode sheet caused by silicon expansion.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] In some embodiments, the silicon content in the silicon-carbon composite is 30%-70% by mass. This approach, while maximizing the specific capacity of the negative electrode active material by utilizing silicon, also facilitates the full dispersion of silicon in the carbon-containing porous material and helps control the expansion of silicon during charging.

[0102] 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.

[0103] In addition to providing structural support and buffering for the expansion of silicon-containing materials, the pores in the silicon-carbon composite also form between the particles. To further improve the flow of lithium ions through the intraparticle and interparticle pores, in some embodiments, the average particle size of the silicon-carbon composite is 2μm-15μm. Optionally, the average particle size of the silicon-carbon composite is 7μm-11μm, or 5μm-10μm. 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, thus facilitating the use of interparticle gaps to increase the compaction of the negative electrode active layer, thereby further improving the energy density of the battery cell.

[0104] 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.

[0105] In some embodiments, the powder resistivity of the silicon-carbon composite at 8 MPa is 4 Ω·cm-17 Ω·cm. This control of powder resistivity improves the conductivity of the silicon-carbon composite, thereby increasing the charging rate of the battery cell.

[0106] 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. At 8 MPa, the powder resistivity can be calculated by measuring the resistance value. Models of four-probe semiconductor powder resistivity testers include the ST-2722.

[0107] In some embodiments, the BET specific surface area of ​​the silicon-carbon composite is 1.0 m². 2 / g-6.7m 2 / g.

[0108] In this application, the method for testing the BET specific surface area of ​​the silicon-carbon composite can be a method known in the art. As an example, referring to GB / T 19587-2017, the nitrogen adsorption specific surface area analysis method can be used. The sample tube containing the first graphite material sample is immersed in liquid nitrogen at -196℃, and the amount of nitrogen adsorbed on the surface of the solid sample at different pressures of 0.05-0.30 MPa is measured. Based on the BET multilayer adsorption theory and calculation formula, the monolayer adsorption amount of the sample is obtained, and thus the BET specific surface area is obtained. This test can be performed using a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0109] The silicon-carbon composite used in this application is derived from conventional silicon-carbon composites in the art, which, in addition to silicon and carbon, may also contain oxygen, nitrogen, and other elements. In some embodiments, the carbon content, by mass, is greater than 70% of the total amount of elements other than silicon in the first negative electrode active layer. By controlling the carbon content in the total amount of elements other than silicon, the silicon-carbon composite is made predominantly composed of silicon and carbon, thus better leveraging the structural and electrical performance advantages of these two elements.

[0110] In some embodiments, the first negative electrode active layer further includes a first conductive agent, which includes carbon nanotubes. Optionally, the mass content of carbon nanotubes in the first negative electrode active layer is 0.05%-0.5%. The carbon nanotubes placed in the first negative electrode active layer enhance the electronic conductivity of the silicon material on the one hand, and improve the binding of silicon particles and reduce expansion on the other hand, thanks to the linear structure of the carbon nanotubes.

[0111] In some embodiments, the second negative electrode active layer comprises a second conductive agent, which includes carbon nanotubes. Optionally, the carbon nanotube content in the first negative electrode active layer is higher than that in the second negative electrode active layer. Carbon nanotubes are used to improve the conductivity of the second negative electrode active layer. When the carbon nanotube content in the first negative electrode active layer is higher than that in the second negative electrode active layer, it is beneficial to reduce the cost of the second negative electrode active layer.

[0112] In some embodiments, the first negative electrode active layer further includes a first adhesive, and the second negative electrode active layer further includes a second adhesive. The first adhesive and the second adhesive each independently include any one or more of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, and polyvinyl alcohol.

[0113] To further enhance the restraint of the first negative electrode active layer on the expansion of the silicon-carbon composite material, in some embodiments, the mass content of the first binder in the first negative electrode active layer is optionally higher than the mass content of the second binder in the second negative electrode active layer.

[0114] In some embodiments, optionally, the first binder has a mass content of 1%-5% in the first negative electrode active layer, and more preferably 1.5%-4.5%; optionally, the second binder has a mass content of 0.5%-5% in the second negative electrode active layer, and more preferably 1.5%-3.5%. By providing the first or second binder within the above-mentioned mass content range, the influence of the binder on the energy density is minimized while ensuring sufficient bonding effect.

[0115] In some embodiments, the negative electrode sheet further includes a base coating layer disposed between the negative electrode current collector and the first negative electrode active layer. The base coating layer includes a conductive agent and a third binder. Optionally, the thickness of the base coating layer is 0.2 μm-2 μm; optionally, the mass content of the third binder in the base coating layer is 70%-90%. Due to the large expansion of the silicon system and the relatively smooth surface of the negative electrode current collector, there is a risk of powder shedding during long-term cycling. Adding a base coating layer can increase the adhesion between the negative electrode active layer and the negative electrode current collector, further extending the cycle life of the battery cell.

[0116] The third adhesive can be the same as the first and second adhesives. In some embodiments, the third adhesive includes any one or more of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and styrene-butadiene rubber.

[0117] 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 material substrate and a metal layer formed on at least one surface of the polymer material 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0118] In some embodiments, the second negative electrode active layer may optionally include a conductive agent. As an example, the conductive agent may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0119] In some embodiments, the conductive agent in the first negative electrode active layer may also include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, graphene, and carbon nanofibers.

[0120] In some embodiments, the negative electrode active layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0121] [Battery cell]

[0122] In this embodiment of the application, the battery cell can be a secondary battery, which refers to a battery cell that can be recharged to activate the active materials and continue to be used after the battery cell has been discharged.

[0123] The battery cell can be a lithium-ion battery, sodium-ion battery, sodium-lithium-ion battery, lithium-sulfur battery, magnesium-ion battery, nickel-metal hydride battery, nickel-cadmium battery, lead-acid battery, etc., and the embodiments of this application are not limited to this.

[0124] A single battery cell typically includes an electrode assembly. The electrode assembly includes a positive electrode, a negative electrode, and a separator, with the separator positioned between the positive and negative electrodes. During the charging and discharging process of a single battery cell, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, prevents short circuits between the positive and negative electrodes while allowing active ions to pass through.

[0125] In order to improve the fast charging capability and cycle performance of the battery, one embodiment of this application provides a battery cell including an electrode assembly, the electrode assembly including a negative electrode sheet according to any of the foregoing embodiments.

[0126] [Positive electrode plate]

[0127] A positive electrode typically 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 active material.

[0128] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0129] As an example, the positive current collector can be a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, pure metals, alloys, or surface-treated metals can be used, including but not limited to stainless steel, copper, aluminum, nickel, titanium, or silver. The composite current collector may include a polymer material base layer and a metal layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0130] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 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 0.1O2 (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.

[0131] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0132] 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.

[0133] 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.

[0134] [Electrolytes]

[0135] In some embodiments, the battery cell also includes an electrolyte, which acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. The electrolyte can be liquid, gel, or solid.

[0136] Liquid electrolytes include electrolyte salts and solvents.

[0137] 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.

[0138] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone. The solvent may also be an ether solvent. Ether solvents may include one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyl tetrahydrofuran, diphenyl ether, and crown ethers.

[0139] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain properties of the battery cell, such as additives that improve the overcharge / fast charge performance of the battery cell, additives that improve the high-temperature performance of the battery cell, and additives that improve the low-temperature performance of the battery cell.

[0140] The gel electrolyte includes a polymer as a backbone network and can be used in conjunction with an ionic liquid-lithium salt.

[0141] Solid electrolytes include polymer solid electrolytes, inorganic solid electrolytes, and composite solid electrolytes.

[0142] As an example, the polymers of polymeric solid electrolytes may include polyethers (polyoxyethylene), polysiloxanes, polycarbonates, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, monoionic polymers, polyionic liquids, cellulose, etc.

[0143] As an example, inorganic solid electrolytes can be one or more of the following: oxide solid electrolytes (crystalline perovskite, sodium superconducting ion conductor, garnet, amorphous LiPON thin film), sulfide solid electrolytes (crystalline lithium superconducting ion conductor (lithium-germanium-phosphorus-sulfur, sulfosilium-germanium), amorphous sulfides), halide solid electrolytes, nitride solid electrolytes, and hydride solid electrolytes.

[0144] As an example, composite solid electrolytes are formed by adding inorganic solid electrolyte fillers to polymer solid electrolytes.

[0145] [Isolation Component]

[0146] In some embodiments, the secondary battery 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.

[0147] In some embodiments, the separator is a separator membrane. This application does not impose any particular limitation on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0148] As an example, the main material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramic. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation. The separator can be a single component located between the positive and negative electrodes, or it can be attached to the surfaces of the positive and negative electrodes. An inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating can also be applied to the surface of the separator.

[0149] In some embodiments, the separator is a solid electrolyte. The solid electrolyte is disposed between the positive and negative electrodes, serving both to transport ions and isolate the positive and negative electrodes. In some embodiments, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0150] [Electrode Assembly]

[0151] The electrode assembly can be a wound structure, a stacked structure, or a hybrid structure of wound and stacked.

[0152] In some embodiments, the electrode assembly is a wound structure. The positive electrode and the negative electrode are wound into a wound structure.

[0153] In some implementations, the electrode assembly is a stacked structure.

[0154] As an example, multiple positive and negative electrode plates can be set, and multiple positive and multiple negative electrode plates can be stacked alternately.

[0155] As an example, multiple positive electrode sheets can be set, and negative electrode sheets are folded to form multiple stacked folded segments, with a positive electrode sheet sandwiched between adjacent folded segments.

[0156] As an example, both the positive and negative electrode sheets are folded to form multiple stacked folded segments.

[0157] As an example, multiple separators can be provided, each positioned between any adjacent positive or negative electrode plates.

[0158] As an example, the separator can be continuously arranged between any adjacent positive or negative electrode plates by folding or rolling.

[0159] In some embodiments, the electrode assembly can be cylindrical, flat, or polygonal, etc.

[0160] In some embodiments, the electrode assembly is provided with tabs that allow current to be drawn from the electrode assembly. The tabs include a positive tab and a negative tab.

[0161] shell

[0162] In some embodiments, the battery cell may include a casing. The casing may be a steel casing, an aluminum casing, a plastic casing (such as a polypropylene casing), a composite metal casing (such as a copper-aluminum composite casing), or an aluminum-plastic film, etc. In some embodiments, the casing may be a sealed structure or a non-sealed structure. As an example, when the casing is a non-sealed structure, the casing serves to protect the electrode assembly, and a sealing bag is included between the casing and the electrode assembly to encapsulate the electrode assembly and electrolyte. Specifically, the sealing bag may be a bag-shaped insulating component or an aluminum-plastic film. When the casing is a sealed structure, it is used to encapsulate components such as the electrode assembly and electrolyte.

[0163] As an example, the battery cell can be a cylindrical battery cell, a prismatic battery cell, a pouch battery cell, or a battery cell of other shapes. Prismatic battery cells include prismatic battery cells, blade-shaped battery cells, and multi-prismatic batteries, such as hexagonal prismatic batteries. This application does not have any particular limitations.

[0164] In some embodiments, the housing includes an end cap and a housing, the housing having an opening, and the end cap covering the opening. The housing may have one or more openings. The end cap may also be provided one or more.

[0165] Figure 1 shows a square-structured battery cell 5 as an example.

[0166] In some embodiments, referring to FIG2, the outer packaging may include a housing 51 and an end cap 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the end cap 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0167] In some embodiments, at least one electrode terminal is provided on the housing, and the electrode terminal is electrically connected to the tab. The electrode terminal can be directly connected to the tab, or it can be indirectly connected to the tab through a current collector. The electrode terminal can be provided on the end cap or on the housing.

[0168] In some embodiments, a pressure relief mechanism is provided on the casing. The pressure relief mechanism is used to release the internal gas of the battery cell.

[0169] As an example, the internal pressure or temperature of a battery cell is actuated to release the internal pressure or temperature when it reaches a predetermined threshold. When the internal pressure or temperature of the battery cell reaches the predetermined threshold, the pressure relief mechanism is activated or a weak structure in the pressure relief mechanism is broken, thereby forming an opening or channel for the internal pressure or temperature to be released. The threshold design varies depending on the design requirements. The threshold may depend on the materials of one or more of the positive electrode, negative electrode, electrolyte, and separator in the battery cell.

[0170] As an example, the pressure relief mechanism can be integrally molded with the housing.

[0171] As an example, the pressure relief mechanism can also be separately installed and connected to the housing.

[0172] The term "actuation" as used in this application refers to the activation or actuation of the pressure relief mechanism to a certain state, thereby releasing the internal pressure and temperature of the battery cell. The actions of the pressure relief mechanism may include, but are not limited to: movement of components within the mechanism to form an exhaust channel, rupture, breakage, tearing, or opening of at least a portion of the mechanism, etc. When the pressure relief mechanism is activated, the high-temperature, high-pressure substances inside the battery cell are discharged as waste from the activated portion. This method allows for pressure and temperature relief of the battery cell under controllable pressure or temperature, thereby preventing potentially more serious accidents.

[0173] In some embodiments, when the housing is a non-sealed structure, the pressure relief mechanism can be configured as a through hole for venting gas inside the battery cell.

[0174] The emissions from battery cells mentioned in this application include, but are not limited to: electrolyte, dissolved or split positive and negative electrode plates, fragments of separators, high-temperature and high-pressure gases generated by the reaction, flames, etc.

[0175] Battery device

[0176] The battery apparatus mentioned in the embodiments of this application may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple battery cells connected in series, parallel, or mixed connections via a busbar.

[0177] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells.

[0178] As an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple battery cells together to form an independent module. As another example, a battery module can be formed by bundling multiple battery cells together with cable ties.

[0179] In some embodiments, the battery device may be a battery pack, which includes a housing and one or more individual battery cells housed within the housing.

[0180] As an example, the battery cell assembly can be a battery module, which can be housed in a housing by fixing the battery module in the housing.

[0181] Figure 3 shows a battery module 4 as an example. Referring to Figure 3, in the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary battery cells 5 can be fixed in place using fasteners.

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

[0183] In some embodiments, the battery 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.

[0184] Figures 4 and 5 show a battery pack 1 as an example. Referring to Figures 4 and 5, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 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.

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

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

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

[0188] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0189] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use individual battery cells, such as mobile phones, portable devices, laptops, electric vehicles, electric toys, power tools, vehicles, ships, and spacecraft. For example, spacecraft include airplanes, rockets, space shuttles, and spacecraft.

[0190] In addition, this application also provides an electrical device, which includes the secondary battery provided in this application. The secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., 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.

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

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

[0193] [Example]

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

[0195] Example 1

[0196] The manufacturing process of negative electrode sheets

[0197] A primer conductive agent SP conductive carbon black and a primer binder polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 8:2 to prepare a primer slurry. The primer slurry was then coated onto a negative electrode current collector copper foil with a thickness of 7 μm and dried to form a primer layer with a thickness of 0.5 μm.

[0198] The first graphite material, silicon-carbon composite (with a silicon content of 50% by mass and a powder resistivity of 10 Ω·cm), binder (SBR), conductive carbon black, conductive carbon nanotubes, and thickener (CMC) were dispersed in deionized water at a mass ratio of 56.6:38:3:1:0.3:1.1 and stirred to form a first negative electrode slurry.

[0199] The second graphite material, binder (SBR), conductive carbon black and thickener (CMC) are dispersed in deionized water at a mass ratio of 96.5:2:0.4:1.1 and stirred to form a homogenized slurry to form the second negative electrode slurry.

[0200] Using a dual-cavity coating equipment, the first negative electrode slurry and the second negative electrode slurry are simultaneously coated on the surface of the current collector copper foil with a base coating. After drying, cold pressing and slitting, the negative electrode sheet of Example 1 is obtained. The first negative electrode slurry forms the first negative electrode active layer, and the second negative electrode slurry forms the second negative electrode active layer. The thickness of the first negative electrode active layer is 11 μm, and the thickness of the second negative electrode active layer is 48 μm.

[0201] Positive electrode sheet

[0202] The positive electrode active material is a ternary material, nickel-cobalt-manganese (LiNi). 0.8 Co 0.1 Mn 0.1 O2, conductive carbon black (a conductive agent), and polyvinylidene fluoride (PVDF) (a binder) are mixed uniformly in N-methylpyrrolidone (NMP) solvent at a mass ratio of 97:2:1 to prepare a positive electrode slurry. The positive electrode slurry is then uniformly coated on the surface of aluminum foil and dried, followed by cold pressing to obtain the positive electrode sheet.

[0203] Separating membrane

[0204] Polyethylene film (PE diaphragm) is used as the separation membrane.

[0205] electrolyte

[0206] Ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed in a volume ratio of 1:2:1 to obtain an organic solvent. The fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0207] Assembly:

[0208] The positive electrode, separator, and negative electrode are stacked in sequence to obtain an electrode assembly. The electrode assembly is placed in a housing (237.5mm×115.2mm×32.6mm in size), dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion secondary battery is obtained.

[0209] Cyclic life test procedure:

[0210] Test temperature: 25℃; Charge / discharge voltage range: 2.5V-4.25V; Protection voltage range: 2.45-4.3V;

[0211] Capacity calibration was performed by performing two charge-discharge cycles at 0.33C / 0.33C.

[0212] Based on the calibrated capacity test constant rate (0.5C / 0.5C) charge-discharge cycles, capacity and voltage calibration are performed every 100 cycles, and the cell capacity retention rate is calculated after 1500 cycles. The longer the lifespan, the higher the cell capacity retention rate after 1500 cycles.

[0213] Charging capability testing procedure:

[0214] Test temperature: 25℃; Charge / discharge voltage range: 2.5V-4.25V; Protection voltage range: 2.45-4.3V;

[0215] Test process:

[0216] Capacity calibration was performed by performing two charge-discharge cycles at 0.33C / 0.33C.

[0217] Based on the calibrated capacity test charging curves at different rates, with a charging cutoff voltage of 4.25V, and monitoring using the anode potential (charging can be stopped early when the anode potential is below -10mV), the charging rates are 0.33C, 0.5C, 1C, 1.5C, 2C, 2.5C, and 3C. The maximum charging rate curves of the battery at different SOCs are obtained. Based on these curves, the time T required for charging in the 10% to 80% SOC range (assuming no lithium plating in the battery cells) is calculated using the following formula, in minutes. This is used to evaluate the charging capability of each battery cell.

[0218] T=(0.1 / C10%SOC+0.1 / C20%SOC+0.1 / C30%SOC+0.1 / C40%SOC+0.1 / C50%SOC+0.1 / C60%SOC+0.1 / C70%SOC+0.1 / C80%SOC)×60.

[0219] The shorter the charging time, the stronger the charging capacity.

[0220] Methods for testing volumetric energy density:

[0221] The prepared battery cells were placed in a 25°C constant temperature chamber and left to stand for 30 minutes to allow them to reach a constant temperature. The battery cells were then charged at a constant current of 0.5C to a voltage of 4.25V, then charged at a constant voltage of 4.25V to a current of 0.05C, and discharged at 0.5C to a voltage of 2.5V. The discharge energy was recorded.

[0222] Volumetric energy density = Discharge energy / (Length × Width × Thickness of battery cell).

[0223] The testing method for the graphitization degree of the first and second graphite materials is as follows: First, scrape off the powder from the upper part of the negative electrode sheet, which is the powder of the second negative electrode active layer. Then, scrape off the powder near the negative electrode current collector. If SEM-EDS confirms that the powder contains silicon, it can be confirmed as the powder of the first negative electrode active layer. Then, X-ray diffractometer (such as Bruker D8 Discover) is used for testing. First, the size of d002 is measured, and then the graphitization degree is calculated according to the formula G = (0.344 - d002) / (0.344 - 0.3354) × 100%, where d002 is the interlayer spacing in the graphite crystal structure in nm. In the X-ray diffraction analysis test, Cu Kα rays are used as the radiation source, the ray wavelength scanning 2θ angle range is 20° to 80°, and the scanning rate is 4° / min. Thus, the graphitization degree values ​​G of the first and second graphite materials are 95% and 92%, respectively.

[0224] The average particle sizes of the first graphite material and the second graphite material were measured to be 16.6 μm and 12.4 μm, respectively, according to the method described above.

[0225] Test method for specific capacity of the first negative electrode active layer: 1. Remove the second negative electrode active layer from the negative electrode sheet by scraping off powder, obtaining the negative electrode current collector and the first negative electrode active layer disposed on its surface; 2. Cut the above-mentioned powder-removed negative electrode sheet into small circular pieces with a diameter of 7mm; 3. Assemble the small circular pieces with a lithium metal sheet into a coin cell. The electrolyte solvent is a mixture of EC and DMC (volume ratio of 5:5), wherein the lithium salt is LiPF6 and the lithium salt concentration is 1mol / L; 4. The test voltage range is 5mV-2V, the rate is 0.1C / 0.1C, and the charge / discharge process is as follows: charge at a constant current of 0.1C to 2V, let stand for 10min, discharge at a constant current of 0.1C to 5mV, let stand for 10min, and repeat this process twice; Instrument: Shanghai Chenhua Electrochemical Workstation CHI700E. The test result is 1027mAh / g.

[0226] The BET specific surface area of ​​the first and second graphite materials and the silicon-carbon composite was determined according to GB / T 19587-2017, using the nitrogen adsorption specific surface area analysis method. Sample tubes containing the first and second graphite materials and the silicon-carbon composite were immersed in liquid nitrogen at -196℃. The amount of nitrogen adsorbed on the solid sample surface at different pressures (0.05-0.30 MPa) was measured. Based on the BET multilayer adsorption theory and calculation formula, the monolayer adsorption amount was calculated, and thus the BET specific surface area was obtained. This test can be performed using a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA. Finally, the measured specific surface area integrals of the first graphite material, the second graphite material, and the silicon-carbon composite were 2.2 m². 2 / g, 1.9m 2 / g and 2.3m 2 / g.

[0227] The thicknesses of the first and second anode active layers were measured using CP-SEM, and their corresponding thicknesses in the microscopic images were 11 μm and 48 μm, respectively.

[0228] Test method for silicon content in the first negative electrode active layer: The first negative electrode active layer material was collected by scraping powder, and the silicon mass percentage was found to be 19% by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0229] Test method for silicon content in silicon-carbon composites: Take a certain amount of silicon-carbon composite and obtain the mass percentage of silicon in the silicon-carbon composite by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0230] Methods for testing the average particle size of silicon-carbon composites:

[0231] The average particle size of the silicon-carbon composite can be tested using equipment and methods known in the art. For example, a scanning electron microscope (SEM) can be used (e.g., ZEISS Sigma 300), referring to JY / T010-1996, to obtain SEM images of the negative electrode sheet. As an example, the test can be performed as follows: Randomly select a test sample of length × width = 50 mm × 100 mm on the negative electrode sheet. Randomly select multiple test areas (e.g., 5 areas) within the test sample, and at a certain magnification (e.g., 1000x when measuring the silicon-carbon composite), read the particle size of each complete 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 complete 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 used to repeat the above test, and the average value of each test sample can be taken as the final test result. The average particle size of the silicon-carbon composite measured in Example 1 was 9 μm.

[0232] The average particle size of each material obtained by testing the average particle size in the negative electrode using the method described above is basically equivalent to its Dv50 particle size, and is presented in Table 1 as average particle size.

[0233] The method for testing the resistivity of silicon-carbon composite powders involves a four-probe method, where two probes apply voltage and the other two measure current. The powder resistivity can be calculated by measuring the resistance at 8 MPa. Models of four-probe semiconductor powder resistivity testers include the ST-2722.

[0234] Method for determining the mass content of carbon nanotubes in the first anode active layer: Take the upper and lower layer powders, observe the carbon nanotubes using TEM, and compare the carbon nanotube content in the upper and lower layers by the area ratio of the carbon nanotubes. TEM instrument model: JEM-F200.

[0235] Test methods for the mass content of the first binder in the first negative electrode active layer and the second binder in the second negative electrode active layer: The mass percentage of the binder is determined by TG+DSC. The detailed test method is as follows: ① Manually or automatically scrape the powder of the first and second negative electrode active layers. First, scrape the powder from the upper part of the negative electrode sheet, which is the powder of the second negative electrode active layer. Then scrape the powder near the negative electrode current collector. If SEM-EDS confirms that the powder contains silicon, it can be confirmed that the powder is the powder of the first negative electrode active layer. The automatic powder scraper is from Shenzhen Haoneng; ② A high-temperature slide rail furnace capable of passing N2 is used to simulate the TG program heating process (model: SK-G10123K-610-HS), and the temperature is set in stages according to the thermal properties of the binder; ③ An electronic balance with an accuracy of 1 / 100,000 is used to evaluate the difference in the mass of the scraped powder before and after heating to determine the binder content (model: BSA224S). The N2 atmosphere binder pyrolysis temperature is set to 220℃-400℃ and 400℃-600℃ to obtain the percentage content of the binder.

[0236] Examples 2-4 and Comparative Examples 1-2

[0237] The differences between Examples 2-4 and Comparative Examples 1-2 and the Examples are: the degree of graphitization of the first graphite material and the second graphite material is different (the degree of graphitization is adjusted by adjusting the sintering temperature), and the average particle size and specific surface area of ​​the first graphite material and the second graphite material are also slightly different, as detailed in Table 1.

[0238] Table 1

[0239] As shown in Table 1, within a graphitization range of 90%-96%, the lower graphitization of the second graphite material in the upper layer and the higher graphitization of the first graphite material in the lower layer achieve excellent energy density, cycle life, and charging rate for the battery cell. Specifically, a comparison of Example 1 with Comparative Examples 1 and 2 reveals that when the graphitization of the second graphite material is not less than that of the first graphite material, the second graphite material cannot provide a sufficiently high electron transport rate, resulting in poor charging capability of the battery cell. Furthermore, the first graphite material cannot provide the advantage of cycle stability, leading to poor capacity retention of the battery cell.

[0240] Examples 5-8

[0241] The difference between Examples 5-8 and Example 1 is that the average particle size of the first graphite material or the second graphite material is different, and the specific surface area of ​​the first graphite material and the second graphite material is also different, as detailed in Table 2.

[0242] Table 2

[0243] As shown in Table 2, when the average particle size of the first graphite material in the lower layer is in the range of 6-16.6 μm, the exposed lithium-intercalation surface of the first graphite material decreases with the increase of the average particle size, which helps to reduce lithium consumption and thus improve the capacity retention rate of the battery cells while maintaining a relatively high charging rate. However, as the particle size continues to increase, the transport of lithium ions within the graphite material is affected, resulting in a slight decrease in capacity retention. Furthermore, when the average particle size of the second graphite material in the upper layer is in the range of 3-20 μm, it increases the contact area between the second graphite material and the electrolyte, thereby improving charging capability. However, when the average particle size of the second graphite material is smaller than a certain threshold, lithium consumption increases, leading to a decrease in the capacity retention rate of the battery cells.

[0244] Examples 9-11

[0245] The difference between Examples 9-13 and Example 1 is that the mass ratio of the first graphite material and the silicon-carbon composite is adjusted to make the silicon content in the first negative electrode active layer different and the specific capacity of the first negative electrode active layer different, as detailed in Table 3.

[0246] Example 12

[0247] The difference between Example 12 and Example 1 is that a silicon-carbon composite with a silicon element content of 70% by mass is mixed with the first graphite material as the active material of the first negative electrode active layer, and the mass ratio of the first graphite material and the silicon-carbon composite is adjusted, as shown in Table 3. The test results are shown in Table 3.

[0248] Example 13

[0249] The difference between Example 13 and Example 1 is that a mixture of first graphite material and elemental silicon in a mass ratio of 26.6:68 is used as the active material of the first negative electrode active layer, as shown in Table 3. The test results are shown in Table 3.

[0250] Comparative Example 3

[0251] The difference between Comparative Example 3 and Comparative Example 1 is that Comparative Example 3 uses a mixture of first graphite material and elemental silicon at a mass ratio of 26.6:68 as the active material of the first negative electrode active layer, as shown in Table 3. The test results are shown in Table 3.

[0252] Table 3

[0253] As can be seen from the data in Table 3, controlling the silicon content in the first negative electrode active layer within the range of 2.5-68 wt% increases the expansion during charging, leading to a decrease in the capacity retention rate of the battery cells. However, the energy density of the battery cells can still be improved by utilizing silicon. When the silicon content is high, such as exceeding 48%, the lack of porous carbon buffering when using elemental silicon as the silicon-based material results in a more significant decrease in the capacity retention rate of the battery cells. However, Example 13 still performs better than Comparative Example 3, indicating that the control of the graphitization degree of the two graphite materials in this application can play a role when matched with any silicon content.

[0254] Examples 14-19 and Comparative Example 4

[0255] The difference between Examples 14-19 and Example 1 is that the thickness of the first or second negative electrode active layer is different when the battery cell is in the 0% SOC state of the first charge-discharge cycle; the difference between Comparative Example 4 and Comparative Example 1 is that the thickness of the first negative electrode active layer is different when the battery cell is in the 0% SOC state of the first charge-discharge cycle, as detailed in Table 4.

[0256] Table 4

[0257] As shown in Table 4, with the increase in the thickness of the first negative electrode active layer, the charging time of the battery cell increases. Simultaneously, the silicon content in the negative electrode active layer increases, thus increasing the energy density of the battery cell. However, the expansion caused by silicon intensifies, leading to a decrease in the capacity retention rate of the battery cell. With the increase in the thickness of the second negative electrode active layer, the active material increases, thus increasing the energy density of the battery cell. When the thickness of the second negative electrode active layer increases from 10 μm to 48 μm, the content of the second graphite material increases, resulting in a decrease in charging time. Furthermore, the increased binding of the underlying silicon layer also increases the capacity retention rate. However, when the thickness of the second negative electrode active layer continues to increase, the corresponding absolute lithium intercalation amount increases, leading to an increase in charging time. This also prevents the high cycle stability advantage of the underlying first graphite material from being fully realized, resulting in a decrease in capacity retention rate. In addition, a comparison of the data from Example 5 and Comparative Example 4 shows the optimizing effect of controlling the first and second graphite materials in this application on capacity retention rate and charging capability.

[0258] Examples 20-25

[0259] The difference between Examples 20-25 and Example 1 is that different silicon-carbon composites are used, but the mass content of silicon in the first negative electrode active layer remains unchanged, as detailed in Table 5.

[0260] Table 5

[0261] As can be seen from the data in Table 5, with the same silicon content, the powder resistivity increases with the increase of silicon-carbon composite particle size, leading to a longer charging time for the battery cells. Furthermore, the specific surface area decreases with the increase of silicon-carbon composite particle size, thus reducing lithium consumption and increasing the capacity retention of the battery cells. Meanwhile, a comparison of the data from Examples 1, 25, and 12 shows that the increased silicon content in the silicon-carbon composite leads to an increase in powder resistivity, resulting in a longer charging time for the battery cells.

[0262] Examples 26-28

[0263] The difference between Examples 26-28 and Example 1 is that the carbon nanotube content in the first negative electrode active layer is different. Correspondingly, the conductive carbon black content is adjusted so that the total proportion of conductive carbon black and carbon nanotubes remains unchanged. See Table 6 for details.

[0264] Table 6

[0265] As can be seen from the data in Table 6, placing carbon nanotubes in the first negative electrode active layer can enhance the electronic conductivity of silicon materials by utilizing carbon nanotubes, and can also improve the binding of silicon particles and reduce expansion by utilizing the linear structure of carbon nanotubes, thereby optimizing the capacity retention and charging capability of the single cell.

[0266] Examples 29-35

[0267] The difference between Examples 29-35 and Example 1 is that the binder content in the first or second negative electrode active layer is different, and the content of graphite material is adjusted accordingly, as detailed in Table 7.

[0268] Table 7

[0269] As can be seen from the data in Table 7, setting the first or second adhesive within a certain range can improve the capacity retention rate to a certain extent while ensuring sufficient bonding effect and minimizing the influence of the adhesive on the energy density.

[0270] Examples 36-38

[0271] The difference between Examples 36-38 and Example 1 lies in the base coating, as detailed in Table 8.

[0272] Comparative Example 6

[0273] The difference from Comparative Example 1 is that no base coat is applied.

[0274] Table 8

[0275] As can be seen from the data in Table 9, adding a base coating can increase the adhesion between the negative electrode active layer and the negative electrode current collector, thereby further extending the cycle life of the battery cell.

[0276] Although preferred embodiments have been described in this application, various modifications can be made and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A battery cell, comprising an electrode assembly, the electrode assembly including a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative active layer disposed on at least one side of the negative current collector, the negative active layer including a first negative active layer and a second negative active layer, the first negative active layer being disposed on at least one side of the negative current collector, and the second negative active layer being disposed on the side of the first negative active layer away from the negative current collector. The first negative electrode active layer comprises a first graphite material and a silicon-based material; The second negative electrode active layer comprises a second graphite material, wherein 90% ≤ the graphitization degree of the second graphite material < the graphitization degree of the first graphite material ≤ 96%.

2. The battery cell according to claim 1, wherein, The graphitization degree of the first graphite material is between 94% and 96%.

3. The battery cell according to claim 1 or 2, wherein, The average particle size of the first graphite material is 6μm-25μm.

4. The battery cell according to any one of claims 1 to 3, wherein, The specific capacity of the first graphite material is higher than that of the second graphite material, the specific capacity of the first negative electrode active layer is 422 mAh / g-1482 mAh / g, and / or the BET specific surface area of ​​the first graphite material is 1.5 m². 2 / g-3.0m 2 / g.

5. The battery cell according to any one of claims 1 to 4, wherein, The graphitization degree of the second graphite material is between 91% and 93%.

6. The battery cell according to any one of claims 1 to 5, wherein, The average particle size of the second graphite material is 3μm-20μm.

7. The battery cell according to any one of claims 1 to 6, wherein, The BET specific surface area of ​​the second graphite material is 0.6 m². 2 / g-3.4m 2 / g.

8. The battery cell according to any one of claims 1 to 7, wherein, The silicon content in the first negative electrode active layer is 2.5%-68% by mass, and can be selected as 5.5%-48%.

9. The battery cell according to any one of claims 1 to 8, wherein, When the battery cell is in a 0% SOC state within 50 charge-discharge cycles, the thickness of the first negative electrode active layer is 6μm-40μm.

10. The battery cell according to any one of claims 1 to 9, wherein, When the battery cell is in a 0% SOC state within 50 charge-discharge cycles, the thickness of the second negative electrode active layer is 10μm-70μm, and can be selected as 12μm-68μm.

11. The battery cell according to any one of claims 1 to 9, wherein, The silicon-based material includes one or more of elemental silicon, silicon-oxygen compounds, and silicon-carbon compounds; Optionally, the silicon-based material includes the silicon-carbon composite; Further, optionally, the silicon-carbon composite includes 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, wherein the porous carbon is optionally hard 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 silicon material; 3) The silicon-carbon composite contains 30%-70% silicon by mass; 4) The average particle size of the silicon-carbon composite is 2μm-15μm, and may be further selected as 7μm-11μm; 5) The powder resistivity of the silicon-carbon composite at 8 MPa is 4 Ω·cm - 17 Ω·cm; 6) The BET specific surface area of ​​the silicon-carbon composite is 1.0 m². 2 / g-6.7m 2 / g.

12. The battery cell according to any one of claims 1 to 11, wherein, The first negative electrode active layer further includes a first conductive agent, which includes carbon nanotubes. Optionally, the mass content of the carbon nanotubes in the first negative electrode active layer is 0.05%-0.5%.

13. The battery cell according to claim 12, wherein, The second negative electrode active layer includes a second conductive agent, which includes carbon nanotubes. Optionally, the carbon nanotube content in the first negative electrode active layer is higher than the carbon nanotube content in the second negative electrode active layer.

14. The battery cell according to any one of claims 1 to 13, wherein, The first negative electrode active layer further includes a first adhesive, and the second negative electrode active layer further includes a second adhesive. The first adhesive and the second adhesive each independently include any one or more of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, and polyvinyl alcohol. Optionally, the mass content of the first binder in the first negative electrode active layer is higher than the mass content of the second binder in the second negative electrode active layer; Optionally, the mass content of the first binder in the first negative electrode active layer is 1%-5%, and more preferably 1.5%-4.5%; Optionally, the mass content of the second binder in the second negative electrode active layer is 0.5%-5%, and more preferably 1.5%-3.5%.

15. The battery cell according to any one of claims 1 to 14, wherein, The negative electrode sheet further includes a base coating layer disposed between the negative current collector and the first negative electrode active layer. The base coating layer includes a third conductive agent and a third binder. Optionally, the thickness of the base coating layer is 0.2 μm-2 μm. Optionally, the mass content of the third binder in the base coating layer is 70%-90%.

16. A negative electrode sheet, comprising a negative current collector and a negative active layer disposed on at least one side of the negative current collector, the negative active layer comprising a first negative active layer and a second negative active layer, the first negative active layer being disposed on at least one side of the negative current collector, and the second negative active layer being disposed on the side of the negative current collector away from the first negative active layer. The first negative electrode active layer comprises a first graphite material and a silicon-based material; The second negative electrode active layer comprises a second graphite material, wherein 90% ≤ the graphitization degree of the second graphite material < the graphitization degree of the first graphite material ≤ 96%.

17. The negative electrode sheet according to claim 16, wherein, The graphitization degree of the first graphite material is between 90% and 96%, and / or the average particle size of the first graphite material is between 6 μm and 25 μm.

18. The negative electrode sheet according to claim 16 or 17, wherein, The specific capacity of the first graphite material is higher than that of the second graphite material, the specific capacity of the first negative electrode active layer is 422 mAh / g-1482 mAh / g, and / or the BET specific surface area of ​​the first graphite material is 1.5 m². 2 / g-3.0m 2 / g.

19. The negative electrode sheet according to any one of claims 16 to 18, wherein, The graphitization degree of the second graphite material is between 91% and 93%.

20. The negative electrode sheet according to any one of claims 16 to 19, wherein, The average particle size of the second graphite material is 3μm-20μm, and / or the BET specific surface area of ​​the second graphite material is 0.6m². 2 / g-3.4m 2 / g.

21. The negative electrode sheet according to any one of claims 16 to 20, wherein, The silicon content in the first negative electrode active layer is 2.5%-68% by mass, and can be selected as 5.5%-48%.

22. The negative electrode sheet according to any one of claims 16 to 21, wherein, The thickness of the first negative electrode active layer is 6μm-40μm, and / or the thickness of the second negative electrode active layer is 10μm-70μm, optionally 12μm-68μm.

23. The negative electrode sheet according to any one of claims 16 to 22, wherein, The silicon-based material includes one or more of elemental silicon, silicon-oxygen compounds, and silicon-carbon compounds; Optionally, the silicon-based material includes the silicon-carbon composite; Further optionally, the silicon-based material comprises a silicon-carbon composite satisfying 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, wherein the porous carbon is optionally hard 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 silicon material; 3) The silicon-carbon composite contains 30%-70% silicon by mass; 4) The average particle size of the silicon-carbon composite is 2μm-15μm, and may be further selected as 7μm-11μm; 5) The powder resistivity of the silicon-carbon composite at 8 MPa is 4 Ω·cm-17 Ω·cm; 6) The BET specific surface area of ​​the silicon-carbon composite is 1.0 m². 2 / g-6.7m 2 / g.

24. The negative electrode sheet according to any one of claims 16 to 23, wherein, The first negative electrode active layer further includes a conductive agent, which includes carbon nanotubes. Optionally, the mass content of the carbon nanotubes in the first negative electrode active layer is 0.05%-0.5%.

25. The negative electrode sheet according to any one of claims 16 to 24, wherein, The negative electrode sheet further includes a base coating layer disposed between the negative current collector and the first negative electrode active layer. The base coating layer includes a third conductive agent and a third binder. Optionally, the thickness of the base coating layer is 0.2 μm-2 μm. Optionally, the mass content of the third binder in the base coating layer is 70%-90%.

26. A battery device comprising a plurality of battery cells, wherein, The battery cell comprises any one of claims 1 to 15.

27. An electrical device comprising a single battery cell or a battery assembly, wherein, The battery cell comprises any one of claims 1 to 15, and the battery device comprises the battery device of claim 26.

Images