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

Abstract

This application provides a battery cell, a negative electrode sheet, a battery device, and a power consumption device. The battery cell includes a stacked electrode assembly, which includes a negative electrode sheet. The negative electrode sheet 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 includes a first negative electrode film layer and a second negative electrode film layer, with the first negative electrode film layer disposed between the negative current collector and the second negative electrode film layer. The first negative electrode film layer includes a first negative electrode active material, which includes a first graphite material and optionally a first silicon-based material. The second negative electrode film layer includes a second negative electrode active material, which includes the first silicon-based material and the second graphite material. The silicon content in the second negative electrode film layer, denoted as A, is 2.5% ≤ A ≤ 65% by mass, and the silicon content in the first negative electrode film layer, denoted as B, is 0% < A - B ≤ 57%. The tensile strength of the negative current collector is ≥ 38 kgf / mm². 2 .

Description

Technical Field

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

[0002] A lithium-ion secondary battery has a structure in which a lithium-salt-containing electrolyte is injected into an electrode assembly, the electrode assembly comprising: a positive electrode and a negative electrode formed by coating each electrode active material onto an electrode current collector; and a porous separator disposed between the two electrodes. Here, each electrode is obtained by coating a slurry containing active materials, a binder, and a conductive material onto the electrode current collector, followed by drying and pressing. In recent years, high-energy-density lithium-ion batteries have been widely used in the electric vehicle industry. Silicon, with its high specific capacity, has become a widely used high-capacity negative electrode material. Summary of the Invention

[0003] This application provides a battery cell, a negative electrode, a battery device, and an electrical device to improve the cycle life of a battery under fast charging conditions.

[0004] The first aspect of this application provides a battery cell, including a stacked electrode assembly. The electrode assembly includes a negative electrode sheet, which 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 includes a first negative electrode film layer and a second negative electrode film layer, with the first negative electrode film layer disposed between the negative current collector and the second negative electrode film layer. The first negative electrode film layer includes a first negative electrode active material, which includes a first graphite material and optionally a first silicon-based material. The second negative electrode film layer includes a second negative electrode active material, which includes the first silicon-based material and the second graphite material. The silicon content in the second negative electrode film layer, denoted as A, is 2.5% ≤ A ≤ 65% by mass, optionally 4.5% ≤ A ≤ 57%. The silicon content in the first negative electrode film layer, denoted as B, is 0% < A B ≤ 57% by mass. The tensile strength of the negative current collector is ≥ 38 kgf / mm². 2 .

[0005] This application incorporates a first silicon-based material in the upper second negative electrode film layer, with the silicon-based material primarily disposed in the second negative electrode film layer. This allows the upper layer to utilize the first silicon-based material to form a high porosity, enabling rapid lithium-ion insertion. Simultaneously, a high-strength negative electrode current collector with the aforementioned tensile strength is used to further constrain the expansion of the silicon material during charging and resist the elongation and deformation of the negative electrode current collector, thereby improving the battery cycle life.

[0006] In any embodiment of the first aspect of this application, the elongation at break of the negative electrode current collector is ≥3.0%.

[0007] In any embodiment of the first aspect of this application, the thickness of the negative electrode current collector is 3μm-8μm, and optionally 4μm-6μm.

[0008] In any embodiment of the first aspect of this application, the first silicon-based material and the second silicon-based material each independently include one or more of elemental silicon, silicon-oxygen composites, and silicon-carbon composites;

[0009] Optionally, at least one of the first silicon-based material and the second silicon-based material includes a silicon-carbon composite.

[0010] Further optionally, at least one of the first silicon-based material and the second silicon-based material comprises a silicon-carbon composite that satisfies one or more of the following characteristics:

[0011] 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;

[0012] 2) The silicon-carbon composite also includes a carbon-containing coating layer located on the surface of the porous carbon and / or silicon material;

[0013] 3) The silicon content in the silicon-carbon composite is 30%-70% by mass, and can be further selected as 35%-65%;

[0014] 4) The average particle size of the silicon-carbon composite is 2μm-15μm, and can be further selected as 7μm-11μm;

[0015] 5) The powder resistivity of silicon-carbon composite at 8 MPa is 4 Ω·cm - 17 Ω·cm;

[0016] 6) The BET specific surface area of ​​the silicon-carbon composite is 1.0 m². 2 / g-6.7m 2 / g.

[0017] In any embodiment of the first aspect of this application, 0% ≤ B ≤ 40%, and optionally 0% ≤ B ≤ 20%.

[0018] In any embodiment of the first aspect of this application, 12% ≤ AB ≤ 40%, and optionally 17% ≤ AB ≤ 27%.

[0019] In any embodiment of the first aspect of this application, the first negative electrode film layer further includes a first binder, and the second negative electrode film layer further includes a second binder, wherein the mass content of the first binder in the first negative electrode film layer is less than the mass content of the second binder in the second negative electrode film layer. Optionally, the mass content of the first binder is 1%-4%, and / or the mass content of the second binder is 2%-5%.

[0020] In any embodiment of the first aspect of this application, the ratio of the thickness H1 of the first film layer to the thickness H2 of the second negative electrode film layer is 1:9 to 9:1.

[0021] In any embodiment of the first aspect of this application, the total single-sided coating weight of the negative electrode film is 60 mg / 1540.25 mm. 2 -200 mg / 1540.25 mm 2 Optionally, 70mg / 1540.25mm 2 -160 mg / 1540.25 mm 2 .

[0022] In any embodiment of the first aspect of this application, the electrode assembly further includes a positive electrode sheet, the positive electrode sheet including a positive current collector, the elongation at break of the positive current collector being ≥0.8%, and optionally the thickness of the positive current collector being 8μm-15μm, more preferably 10μm-14μm.

[0023] The second aspect of this application provides a negative electrode sheet, comprising 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 comprises a first negative electrode film layer and a second negative electrode film layer, the first negative electrode film layer being disposed between the negative current collector and the second negative electrode film layer. The first negative electrode film layer comprises a first negative electrode active material, which includes a first graphite material and optionally a first silicon-based material. The second negative electrode film layer comprises a second negative electrode active material, which includes the first silicon-based material and the second graphite material. The silicon content in the second negative electrode film layer, denoted as A, is 2.5% ≤ A ≤ 65% by mass, optionally 4.5% ≤ A ≤ 57%. The silicon content in the first negative electrode film layer, denoted as B, is 0% < A ≤ 57% by mass. The tensile strength of the negative current collector is ≥ 38 kgf / mm². 2 .

[0024] This application incorporates a first silicon-based material in the upper second negative electrode film layer, with the silicon-based material primarily disposed in the second negative electrode film layer. This allows the upper layer to utilize the first silicon-based material to form a high porosity, enabling rapid lithium-ion insertion. Simultaneously, a high-strength negative electrode current collector with the aforementioned tensile strength is used to further constrain the expansion of the silicon material during charging and resist the elongation and deformation of the negative electrode current collector, thereby improving the battery cycle life.

[0025] In any embodiment of the second aspect of this application, the elongation at break of the negative electrode current collector is ≥3.0%.

[0026] In any embodiment of the second aspect of this application, the thickness of the negative electrode current collector is 3μm-8μm, and optionally 4μm-6μm.

[0027] In any embodiment of the second aspect of this application, the first silicon-based material and the second silicon-based material each independently include one or more of elemental silicon, silicon-oxygen complex, and silicon-carbon complex;

[0028] Optionally, at least one of the first silicon-based material and the second silicon-based material includes a silicon-carbon composite.

[0029] Further optionally, at least one of the first silicon-based material and the second silicon-based material comprises a silicon-carbon composite that satisfies one or more of the following characteristics:

[0030] 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;

[0031] 2) The silicon-carbon composite also includes a carbon-containing coating layer located on the surface of the porous carbon and / or silicon material;

[0032] 3) The silicon content in the silicon-carbon composite is 30%-70% by mass, and can be further selected as 35%-65%;

[0033] 4) The average particle size of the silicon-carbon composite is 2μm-15μm, and can be further selected as 7μm-11μm;

[0034] 5) The powder resistivity of silicon-carbon composite at 8 MPa is 4 Ω·cm - 17 Ω·cm;

[0035] 6) The BET specific surface area of ​​the silicon-carbon composite is 1.0 m². 2 / g-6.7m 2 / g.

[0036] In any embodiment of the second aspect of this application, 0% ≤ B ≤ 40%, and optionally 0% ≤ B ≤ 20%.

[0037] In any embodiment of the second aspect of this application, 12% ≤ AB ≤ 40%, or optionally 17% ≤ AB ≤ 27%.

[0038] In any embodiment of the second aspect of this application, the first negative electrode film layer further includes a first binder, and the second negative electrode film layer further includes a second binder, wherein the mass content of the first binder in the first negative electrode film layer is less than the mass content of the second binder in the second negative electrode film layer. Optionally, the mass content of the first binder is 1%-4%, and / or the mass content of the second binder is 2%-5%.

[0039] In any embodiment of the second aspect of this application, the ratio of the thickness H1 of the first film layer to the thickness H2 of the second negative electrode film layer is 1:9 to 9:1.

[0040] In any embodiment of the second aspect of this application, the total single-sided coating weight of the negative electrode film is 60 mg / 1540.25 mm. 2 -200 mg / 1540.25 mm 2 Optionally, 70mg / 1540.25mm 2 -160 mg / 1540.25 mm 2 .

[0041] A third aspect of this application provides a battery device comprising one or more battery cells according to any embodiment of the first aspect of this application.

[0042] The fourth aspect of this application provides an electrical device, including a battery cell of any embodiment of the first aspect of this application, or a battery device of the third aspect of this application. Attached Figure Description

[0043] 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.

[0044] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application.

[0045] Figure 2 yes Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0046] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0047] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0048] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0049] Figure 6 This is a schematic diagram of an electrical device in which a single battery cell is used as a power source according to one embodiment of this application.

[0050] The accompanying drawings are not drawn to scale.

[0051] Explanation of reference numerals in the attached figures:

[0052] 1 Battery pack; 2 Upper casing; 3 Lower casing; 4 Battery module; 20 Battery cell; 21 Outer casing; 211 Housing; 2111 Opening; 212 End cap; 22 Stacked electrode assembly; 23 Positive electrode terminal; 24 Negative electrode terminal; 25 Pressure relief mechanism. Detailed Implementation

[0053] 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.

[0054] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the negative electrode, battery cell, battery assembly, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0055] 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.

[0056] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0057] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0058] 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.

[0059] 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.

[0060] 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).

[0061] [Negative electrode plate]

[0062] 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 comprising a negative electrode active material.

[0063] 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.

[0064] To improve the cycle performance of a battery under fast charging conditions, a first embodiment of this application provides a negative electrode sheet, including 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 includes a first negative electrode film layer and a second negative electrode film layer, with the first negative electrode film layer disposed between the negative current collector and the second negative electrode film layer. The first negative electrode film layer includes a first negative electrode active material, which includes a first graphite material and optionally a first silicon-based material. The second negative electrode film layer includes a second negative electrode active material, which includes a first silicon-based material and a second graphite material. The silicon content in the second negative electrode film layer, denoted as A, is 2.5% ≤ A ≤ 65% by mass, optionally 4.5% ≤ A ≤ 57%. The silicon content in the first negative electrode film layer, denoted as B, is 0% < A ≤ 57% by mass. The tensile strength of the negative current collector is ≥ 38 kgf / mm². 2 .

[0065] This application incorporates a first silicon-based material in the upper second negative electrode film layer, with the silicon-based material primarily disposed in the second negative electrode film layer. This allows the upper layer to utilize the first silicon-based material to form a high porosity, enabling rapid lithium-ion insertion. Simultaneously, a high-strength negative electrode current collector with the aforementioned tensile strength is used to further constrain the expansion of the silicon material during charging and resist the elongation and deformation of the negative electrode current collector, thereby improving the battery cycle life.

[0066] The silicon content in the first and second anode films described above can be tested using the following method:

[0067] The negative electrode sheet was thoroughly cleaned with DMC (dimethyl carbonate), and after drying, the negative electrode material in the second negative electrode film layer was collected. The negative electrode material was then tested using inductively coupled plasma atomic emission spectrometry (ICP-OES).

[0068] The greater the strength of the negative electrode current collector, the worse its ductility. In order to improve the processability of the negative electrode current collector and adapt to the extension of the negative electrode film caused by silicon expansion in the silicon-carbon composite, and reduce the risk of breakage of the negative electrode sheet, in some embodiments, the breakage elongation of the negative electrode current collector is ≥3.0%.

[0069] It should be noted that the tensile strength and elongation at break of the negative electrode current collector described in this application are parameters measured when the battery cell is in a 0% SOC state within 50 charge-discharge cycles.

[0070] The tensile strength of the negative electrode current collector has a meaning known in the art and can be tested using methods and instruments well-known in the art, for example, by the following method:

[0071] Take a negative electrode current collector sample with a length of 100 mm and a width of 15 mm, accurate to 0.05 mm. Clamp the sample symmetrically in the upper and lower clamps of the measuring instrument, with a 50 mm gap between the clamps. Start the measuring instrument and maintain a loading speed of (5 ± 1) mm / min at a stable speed. Record the maximum load at which the sample fails in shear. Then calculate the tensile strength σt of the sample according to the following formula: σt=P / (b×d) Where P is the maximum load (N), b is the width of the sample (mm), and d is the thickness of the sample.

[0072] The elongation at break of the negative electrode current collector has a meaning known in the art and can be tested using methods and instruments well-known in the art, for example, by the following method: Take a rectangular negative electrode current collector sample with a length of 100 mm and a width of 15 mm, and denote the initial length of the sample as L0. Perform a tensile test using a tensile machine at a tensile speed of 2 mm / min, accurate to 0.05 mm. The test ends when the rectangular negative electrode current collector sample breaks. Denote the length of the sample at the point of breakage as L1. Denote the tensile strength at the point of breakage as the breaking strength. The elongation at break is calculated as (L1 / L0)-1.

[0073] The tensile strength of the negative electrode current collector in this application can be adjusted by the microstructure of the negative electrode current collector itself, such as the grain size, or by adjusting the thickness of the current collector. For example, under the same composition, a larger thickness of the negative electrode current collector results in higher tensile strength, but increasing the thickness of the negative electrode current collector leads to a decrease in the energy density of the battery cell. Conversely, a smaller thickness of the negative electrode current collector results in lower tensile strength. Although the energy density of the battery cell can be increased by reducing the thickness of the negative electrode current collector, a smaller thickness of the negative electrode current collector increases the risk of edge curling during the processing of the negative electrode sheet. In some embodiments, while satisfying the above-mentioned tensile strength, in order to increase the volumetric energy density of the battery cell as much as possible by reducing the thickness of the negative electrode current collector while reducing the risk of edge curling of the negative electrode sheet, the thickness of the negative electrode current collector is 3μm-8μm, and can be selected as 4μm-6μm.

[0074] The thickness of the aforementioned negative electrode current collector can be observed under a scanning electron microscope.

[0075] As an example, the negative electrode current collector can be a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, pure metals, alloys, or surface-treated metals can be used, including but not limited to stainless steel, copper, aluminum, nickel, titanium, or silver. The composite current collector may include a polymer material substrate and a metal layer. The composite current collector can be formed by forming a metal material (copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0076] When a battery is fast-charged, a large number of lithium ions rapidly flood into the silicon-based anode. However, due to the structural characteristics of silicon and the limitations of lithium ion migration rate, these lithium ions cannot be uniformly distributed throughout the anode material, resulting in the so-called "lithium ion concentration polarization" phenomenon. This accumulation is not only because the upper region is in direct contact with the electrolyte, resulting in a shorter lithium ion migration path, but also because during fast charging, the influx rate of lithium ions exceeds the adaptation rate of the internal structure of the silicon-based material, causing the accumulation rate of lithium ions in the upper layer to be much greater than their diffusion rate within the silicon material.

[0077] The uneven distribution of lithium-ion concentration, known as "lithium-ion concentration polarization," can lead to a series of problems. First, it may increase localized structural stress in the silicon-based anode, accelerating material degradation and affecting battery cycle stability and lifespan. Second, excessive accumulation of upper-layer lithium ions can trigger lithium plating, forming lithium metal dendrites. These dendrites not only reduce the battery's coulombic efficiency but may also penetrate the separator, causing internal short circuits and safety issues. Furthermore, the uneven distribution of lithium-ion concentration also affects the battery's overall energy density and power density, limiting its performance in high-power applications.

[0078] In some embodiments, the first silicon-based material and the second silicon-based material each independently include one or more of elemental silicon, silicon-oxygen complex, and first silicon-carbon complex.

[0079] 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.

[0080] In some embodiments, at least one of the first silicon-based material and the second silicon-based material may optionally include a silicon-carbon composite.

[0081] By incorporating a silicon-carbon composite in the upper second negative electrode layer and controlling the silicon content, the silicon-containing material can be fully dispersed within the pores of the silicon-carbon composite. The carbon-containing porous material forms a support structure and pores to alleviate the expansion of the silicon material caused by lithium intercalation during charging. Simultaneously, a high-strength negative electrode current collector with the aforementioned tensile strength is used to further restrain the expansion of the silicon material during charging and resist the extension and deformation of the negative electrode current collector. Furthermore, the supporting effect of the carbon-containing porous material forms pores between the silicon-carbon composite, allowing the large influx of lithium ions during charging to be injected into the entire second negative electrode layer and smoothly enter the first negative electrode layer. This enables the silicon material and porous carbon material located throughout the thickness of the second negative electrode layer to fully and rapidly intercalate lithium, while the second negative electrode layer also quickly enters the lithium intercalation state. Therefore, while achieving fast charging, the concentration polarization of lithium ions in the upper layer is alleviated, thereby suppressing the risk of shortened cycle life and reduced safety of battery cells caused by lithium ion concentration polarization.

[0082] 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.

[0083] In some embodiments, optionally at least one of the first silicon-based material and the second silicon-based material comprises a silicon-carbon composite that satisfies one or more of the following characteristics:

[0084] 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;

[0085] 2) The silicon-carbon composite also includes a carbon-containing coating layer located on the surface of the porous carbon and / or silicon material;

[0086] 3) The silicon content in the silicon-carbon composite is 30%-70% by mass;

[0087] 4) The average particle size of the silicon-carbon composite is 2μm-15μm, optionally 7μm-11μm;

[0088] 5) The powder resistivity of silicon-carbon composite at 8 MPa is 4 Ω·cm - 17 Ω·cm;

[0089] 6) The BET specific surface area of ​​the silicon-carbon composite is 1.0 m². 2 / g-6.7m 2 / g.

[0090] In some embodiments, the silicon-carbon composite comprises porous carbon and silicon-containing material dispersed in the pores of the porous carbon. The porous carbon, acting as a carrier for the silicon-containing material, provides support for the material while simultaneously offering expansion space within the pores, 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, allowing for more efficient utilization of the carbon's pore-buffering effect on expansion.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] In some embodiments, the silicon content in the silicon-carbon composite is 30%-70% by mass, optionally 35%-65%. 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] In some embodiments, the BET specific surface area of ​​the silicon-carbon composite is 1.0 m². 2 / g-6.7m 2 / g.

[0101] 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.

[0102] The first 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.

[0103] In some embodiments, 0% ≤ B ≤ 40%, and optionally 0% ≤ B ≤ 20%, the silicon element exists in at least one of elemental silicon, silicon-oxygen complex, and second silicon-carbon complex. That is, the first negative electrode film layer may also contain silicon element.

[0104] In some implementations, 12% ≤ AB ≤ 40%. By controlling the difference in silicon content between the second and first negative electrode layers as described above, better ion transport matching between the upper and lower layers is achieved, thereby synergistically improving battery cycle performance. In some embodiments, the first negative electrode film layer further includes a first binder, and the second negative electrode film layer further includes a second binder. The mass content of the first binder in the first negative electrode film layer is less than the mass content of the second binder in the second negative electrode film layer. Optionally, the mass content of the first binder is 1%-4%, and / or the mass content of the second binder is 2%-5%. As an example, the first binder and the second binder may each independently include at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0105] In some embodiments, the ratio of the thickness H1 of the first negative electrode film to the thickness H2 of the second negative electrode film is 1:9 to 9:1. Controlling the thickness ratio of the second negative electrode film in the negative electrode film allows the second negative electrode film to have sufficient room to exert its advantages while avoiding the difficulty in controlling the cycle life of the battery cell due to the second negative electrode film having too large a proportion.

[0106] In some embodiments, the total single-sided coating weight of the negative electrode film is 60 mg / 1540.25 mm. 2 -200 mg / 1540.25 mm 2 Optionally, 70mg / 1540.25mm 2 -160mg / 1540.25mm 2 .

[0107] In some embodiments, the first graphite material and the second graphite material may be the same or different, and may be graphite commonly used in negative electrode active materials in the battery field, such as artificial graphite and natural graphite.

[0108] In some embodiments, the negative electrode film may optionally include a conductive agent. As an example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0109] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0110] [Battery cell]

[0111] A single battery cell can be a rechargeable battery. A rechargeable battery is a battery cell that can be recharged after it has been discharged, allowing the active materials to be activated and the cell to continue to be used.

[0112] The battery cell can be a lithium-ion battery, sodium-ion battery, sodium-lithium-ion battery, lithium metal battery, lithium-sulfur battery, magnesium-ion battery, nickel-metal hydride battery, nickel-cadmium battery, lead-acid battery, etc., and the embodiments of this application are not limited to this.

[0113] 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.

[0114] The second embodiment of this application provides a battery cell, which includes a stacked electrode assembly, the electrode assembly including a negative electrode sheet, and the negative electrode sheet including any of the negative electrode sheets provided in the first embodiment above.

[0115] In the negative electrode sheet of this application, a first silicon-based material is disposed in the upper second negative electrode film layer, and the silicon-based material is mainly disposed in the second negative electrode film layer, so that the upper layer uses the first silicon-based material to form a high porosity, thereby realizing the rapid insertion of lithium ions; at the same time, a high-strength negative electrode current collector with the above-mentioned tensile strength is used to further restrain the expansion of silicon material during charging and resist the extension and deformation of the negative electrode current collector, thereby improving the battery cycle life.

[0116] In some embodiments, the electrode assembly further includes a positive electrode sheet, which typically includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector, the positive electrode film layer including a positive active material.

[0117] 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.

[0118] Since the extension of the negative electrode will cause the extension of the positive electrode, in order to improve the structural stability of the positive electrode, in some embodiments, the elongation at break of the positive current collector is ≥0.8%, and the thickness of the positive current collector is 8μm-15μm, optionally 10μm-14μm.

[0119] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0120] 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 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] [Electrolytes]

[0125] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0126] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0127] 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.

[0128] 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.

[0129] In some embodiments, the electrolyte may optionally include additives. As examples, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0130] In some embodiments, the gel electrolyte comprises a polymer as a backbone network and can be used in conjunction with an ionic liquid-lithium salt.

[0131] In some embodiments, the solid electrolyte includes polymer solid electrolyte, inorganic solid electrolyte, and composite solid electrolyte.

[0132] 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.

[0133] 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.

[0134] As an example, composite solid electrolytes are formed by adding inorganic solid electrolyte fillers to polymer solid electrolytes.

[0135] [Isolation Component]

[0136] 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.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] [Electrode Assembly]

[0141] The electrode assembly can be a wound structure, a stacked structure, or a hybrid structure of wound and stacked.

[0142] In some embodiments, the electrode assembly is a wound structure. The positive electrode and the negative electrode are wound into a wound structure.

[0143] In some implementations, the electrode assembly is a stacked structure.

[0144] As an example, multiple positive and negative electrode plates can be set, and multiple positive and multiple negative electrode plates can be stacked alternately.

[0145] 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.

[0146] As an example, both the positive and negative electrode sheets are folded to form multiple stacked folded segments.

[0147] As an example, multiple separators can be provided, each positioned between any adjacent positive or negative electrode plates.

[0148] As an example, the separator can be continuously arranged between any adjacent positive or negative electrode plates by folding or rolling.

[0149] In some embodiments, the electrode assembly can be cylindrical, flat, or polygonal, etc.

[0150] 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.

[0151] [shell]

[0152] 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.

[0153] 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.

[0154] In some embodiments, the housing includes an end cap and a housing, the housing having an opening, and the end cap covering the opening. The housing may have one or more openings. The end cap may also have one or more.

[0155] For example, Figure 1 This is an example of a square-structured battery cell 5. In some implementations, please refer to... Figure 2 , Figure 2 The image shows an exploded view of the structure of a battery cell 20 provided in some embodiments of this application. The battery cell 20 includes a housing 21 and a stacked electrode assembly 22, the housing 21 being used to house the stacked electrode assembly 22.

[0156] The outer casing 21 can also be used to contain electrolytes, such as electrolyte solutions. The outer casing 21 can have various structural forms.

[0157] In some embodiments, the housing 21 may include a housing 211 and an end cap 212. The housing 211 is a hollow structure with an opening 2111 on one side, and the end cap 212 covers the opening 2111 of the housing 211 and forms a sealed connection to form a sealed space for accommodating the stacked electrode assembly 22 and the electrolyte.

[0158] When assembling the battery cell 20, the stacked electrode assembly 22 can be placed into the housing 211 first, and the electrolyte can be filled into the housing 211. Then, the end cap 212 can be closed onto the opening 2111 of the housing 211.

[0159] The housing 211 can have various shapes, such as a cylinder or a cuboid. The shape of the housing 211 can be determined based on the specific shape of the stacked electrode assembly 22. For example, if the stacked electrode assembly 22 has a cylindrical structure, a cylindrical housing can be used; if the stacked electrode assembly 22 has a cuboid structure, a cuboid housing can be used. Of course, the end cap 212 can also have various structures, such as a plate-like structure or a hollow structure with an opening 2111 at one end. For example, in... Figure 2 In the case, the shell 211 has a cuboid structure, and the end cap 212 has a plate-like structure, which is closed at the opening 2111 of the shell 211.

[0160] In some embodiments, such as Figure 2As shown, the battery cell 20 may further include a positive electrode terminal 23, a negative electrode terminal 24, and a pressure relief mechanism 25. The positive electrode terminal 23 and the pressure relief mechanism 25 may both be mounted on the end cap 212, while the negative electrode terminal 24 is mounted on the end of the housing 211 opposite to the end cap 212. In other embodiments, the positive electrode terminal 23, the pressure relief mechanism 25, and the negative electrode terminal 24 are all mounted on one end of the end cap 212. Both the positive electrode terminal 23 and the negative electrode terminal 24 are used for electrical connection with the stacked electrode assembly 22 to realize the input and output of electrical energy of the battery cell 20. The pressure relief mechanism 25 is used to release the internal pressure of the battery cell 20 when the internal pressure or temperature reaches a predetermined value.

[0161] For example, the pressure relief mechanism 25 may be a component such as an explosion-proof valve, an explosion-proof disc, a gas valve, a pressure relief valve, or a safety valve.

[0162] Understandably, the outer casing 21 is not limited to the structure described above; it can also be other structures. For example, the outer casing 21 may include a housing 211 and two end caps 212. The housing 211 is a hollow structure with openings 2111 on opposite sides. One end cap 212 is fitted onto one opening 2111 of the housing 211 to form a sealed connection, thereby creating a sealed space for accommodating the stacked electrode assembly 22 and the electrolyte. The positive electrode terminal 23 and the negative electrode terminal 24 are respectively mounted on their respective end caps 212. In this structure, a pressure relief mechanism 25 may be mounted on one end cap 212, or a pressure relief mechanism 25 may be mounted on both end caps 212.

[0163] It should be noted that, in this embodiment of the application, the stacked electrode assembly 22 housed within the housing 21 can be one or more. For example, in... Figure 2 In this configuration, there is one stacked electrode assembly 22. The stacked electrode assembly 22 is the component within the battery cell 20 where the electrochemical reaction occurs.

[0164] [Battery Device]

[0165] 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.

[0166] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells.

[0167] 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.

[0168] 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.

[0169] 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.

[0170] Figure 3 This is battery module 4 as an example. (See reference...) Figure 3 In the battery module 4, multiple secondary 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.

[0171] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0172] 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.

[0173] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper 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.

[0174] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple battery cells to the housing.

[0175] 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.

[0176] 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.

[0177] 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.

[0178] 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.

[0179] 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.

[0180] As the electrical device, a single secondary battery cell, a battery module, or a battery pack can be selected according to its usage requirements.

[0181] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0182] [Example]

[0183] 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.

[0184] Example 1

[0185] The manufacturing process of negative electrode sheets

[0186] Artificial graphite, conductive agent acetylene black, thickener (CMC), and binder (SBR) are dispersed in deionized water at a mass ratio of 96:2:1:1 and stirred to form a first negative electrode film slurry. The obtained first negative electrode film slurry is then coated on the negative electrode current collector copper foil and dried. The thickness of the first negative electrode film is 42 μm.

[0187] The silicon-carbon composite (with a silicon content of 65% by mass, an average particle size of 7.6 μm, a powder resistivity of 12.1 Ω·cm at 8 MPa, and a BET of 2.6 m) was used. 2 The following ingredients (g), artificial graphite, conductive agent acetylene black, thickener (CMC), and binder (SBR) are dispersed in deionized water at a mass ratio of 38:57:1:1:3 and stirred to form a homogenized slurry for the second negative electrode film layer. This second negative electrode film layer slurry is then coated onto the copper foil of the negative electrode current collector, which has already been coated with the first negative electrode film layer. The thickness of the second negative electrode film layer is 42 μm, and the total single-sided coating weight of the negative electrode film layer is 146 mg / 1540.25 mm. 2 After drying and cold pressing, the negative electrode sheet is obtained.

[0188] Positive electrode sheet

[0189] A positive electrode slurry was prepared by uniformly mixing the ternary active material nickel-cobalt-manganese (NCM811), the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black in an N-methylpyrrolidone (NMP) solvent at a mass ratio of 97:1:2. The positive electrode slurry was then uniformly coated on the surface of aluminum foil and dried, followed by cold pressing to obtain the positive electrode sheet.

[0190] Separating membrane

[0191] Polyethylene film (PE diaphragm) is used as the separation membrane.

[0192] electrolyte

[0193] Ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate were mixed in a volume ratio of 1:1:1 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.

[0194] Assembly:

[0195] The positive electrode, separator, and negative electrode are stacked in sequence to obtain an electrode assembly. The electrode assembly is placed in a packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion secondary battery is obtained.

[0196] The method for testing the silicon content was as follows: The silicon content in the first and second negative electrode films was tested using alkaline fusion-inductively coupled plasma atomic emission spectrometry (ICP-OES). The negative electrode sheets were collected by scraping powder from the first and second negative electrode films, then ground, mixed with KOH crystals, subjected to high-temperature melting, dissolved in hot water, diluted, and finally analyzed using ICP-OES equipment. The silicon content of the first negative electrode film was found to be 57%, and the silicon content of the second negative electrode film was found to be 40%.

[0197] The tensile strength of the negative electrode current collector was obtained by testing it using the following method: Take a negative electrode current collector sample with a length of 100 mm and a width of 15 mm, accurate to 0.05 mm. Clamp the sample symmetrically in the upper and lower clamps of the measuring instrument, with a 50 mm gap between the clamps. Start the measuring instrument and maintain a loading speed of (5±1) mm / min at a stable rate. Record the maximum load at which the sample fails under shear. Then calculate the tensile strength σt of the sample according to the following formula: σt=P / (b×d) Where P is the maximum load (N), b is the width of the sample (mm), and d is the thickness of the sample. The tensile strength of the negative electrode current collector in Example 1 is 38 kgf / mm². 2 .

[0198] The elongation at break of the positive and negative current collectors was obtained by testing using the following method: A negative electrode current collector sample with a length of 100 mm and a width of 15 mm was taken, and the initial length of the sample was recorded as L0. A tensile test was conducted using a tensile machine at a tensile speed of 2 mm / min, accurate to 0.05 mm. The test ended when the rectangular sample broke, and the length of the sample at the point of breakage was recorded as L1. The tensile strength at the point of breakage was recorded as the breaking strength, and the elongation at break was calculated as (L1 / L0)-1. The elongation at break of the positive and negative electrode current collectors in Example 1 were 1.8% and 3%, respectively.

[0199] Scanning electron microscopy revealed that the thicknesses of the current collectors for the positive and negative electrodes were 12 μm and 4 μm, respectively.

[0200] The average particle size of the aforementioned silicon-carbon composite can be tested as follows: Randomly select a test sample with dimensions of 50mm x 100mm on the negative electrode sheet. Randomly select multiple test areas (e.g., 5 areas) within the test sample. At a certain magnification (e.g., 1000x when measuring the first silicon-carbon composite), read the particle size of each first silicon-carbon composite particle in each test area (i.e., take the distance between the two farthest points on the first silicon-carbon composite particle as its particle size). Count the number and particle size values ​​of the first silicon-carbon composite particles in each test area. Take the arithmetic mean of the first silicon-carbon composite particles in each test area; this is the average particle size of the first silicon-carbon composite particles in the test sample. To ensure the accuracy of the test results, the above test can be repeated with multiple test samples (e.g., 10 samples), and the average value of each test sample can be taken as the final test result.

[0201] The silicon content in the silicon-carbon composite particles can be measured using inductively coupled plasma atomic emission spectrometry (ICP-OES). The silicon content in both the first and second silicon-carbon composite particles of Example 1 was measured to be 65%.

[0202] The thicknesses of the first and second negative electrode films were measured using the CP-SEM method, with the corresponding thicknesses measured in the microscopic images. The results for both films were 42 μm.

[0203] Cyclic performance test: At 25°C, the secondary batteries prepared in each embodiment and comparative example were charged at a constant current rate of 0.33C to the charging cutoff voltage of 4.25V, then charged at a constant voltage rate to a current of 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current rate of 0.5C to the discharge cutoff voltage of 2.5V, allowed to stand for 5 minutes. This constitutes one charge-discharge cycle. The capacity of the first discharge process is recorded as C1. Cyclic charge-discharge tests were then conducted on the batteries using this method, with a charging rate equivalent to 2C, until the capacity of the nth discharge process reached 0.8C1. The cycle was then terminated, and the number of cycles at this point was recorded as the cycle life of the battery at 25°C.

[0204] The test results are recorded in Table 1.

[0205] Example

[0206] Examples 2-3 and Comparative Example 1

[0207] The difference between Examples 2-3 and Comparative Example 1 and Example 1 is that they use negative electrode current collectors with different tensile strengths or elongations at break, as detailed in Table 1.

[0208] Table 1

[0209] As can be seen from the data in Table 1, when the tensile strength of the negative electrode current collector is lower than the lower limit of strength specified in this application, the substrate is damaged after cycling, thus posing a safety hazard. Furthermore, as the elongation at break of the negative electrode current collector increases, the retention rate of the fast-charging life of the battery cell improves.

[0210] Examples 4-7 and Comparative Example 2

[0211] The difference between Examples 4-7 and Comparative Example 2 and Example 1 is that the silicon content in the first negative electrode film is changed by adjusting the raw material ratio, so that the difference between the silicon content A in the second negative electrode film and the silicon content B in the first negative electrode film is different, as shown in Table 2.

[0212] Table 2

[0213] As can be seen from the data in Table 2, when the difference in silicon content between the first and second negative electrode films exceeds the required protection range, the substrate is damaged after cycling, thus posing a safety hazard.

[0214] Examples 8-13 and Comparative Examples 3-4

[0215] The difference between Examples 8-13 and Comparative Examples 3-4 and Example 1 is that the silicon content in the first and second negative electrode films is changed by adjusting the raw material ratio, as detailed in Table 3.

[0216] Table 3

[0217] As can be seen from the data in Table 3, when the silicon content in the second negative electrode film is too high, the substrate is damaged after cycling, thus posing a safety hazard. Conversely, when the silicon content in the second negative electrode film is too high, the specific capacity of the negative electrode is too low.

[0218] Examples 14-16

[0219] The difference between Examples 14-16 and Example 8 is that the thickness of the negative electrode current collector is different, as detailed in Table 4.

[0220] Table 4

[0221] As can be seen from the data in Table 4, with the increase of the thickness of the negative electrode current collector, the cycle life of the battery cell is improved to a certain extent, whether under normal cycling or fast charging.

[0222] Examples 17-20

[0223] The difference between Example 17 and Example 8 is that a first silicon-carbon composite with a different average particle size was used in the preparation of the negative electrode sheet, as detailed in Table 5.

[0224] Table 5

[0225] As can be seen from the data in Table 5, when the average particle size of the first silicon-carbon composite is small, the lifespan of normal cycling and fast charging is slightly shorter, but the fast charging lifespan retention rate is slightly higher; when the average particle size of the first silicon-carbon composite is relatively high, the lifespan of normal cycling and fast charging is slightly longer, but the fast charging lifespan retention rate is slightly lower.

[0226] Examples 21-22

[0227] The difference between Examples 21-22 and Example 8 is that the thicknesses of the first and second negative electrode films were changed, and the silicon content in the second negative electrode film was adjusted to 45%, as detailed in Table 6.

[0228] Table 6

[0229] Examples 23-25

[0230] The difference between Examples 23-25 ​​and Example 8 is that positive current collectors with different thicknesses and elongations at break are used, as detailed in Table 7.

[0231] Table 7

[0232] Example 26 and Comparative Examples 5-6

[0233] The difference between Comparative Example 5 and Example 8 is that the silicon content in the first and second films of Comparative Example 5 is the same, while the difference between Example 26 and Comparative Example 8, as well as between Comparative Example 6 and Comparative Example 5, is that a silicon-oxygen composite is used instead of a silicon-carbon composite, as detailed in Table 8.

[0234] Table 8

[0235] Comparing Example 8 with Comparative Example 5 and Example 26 with Comparative Example 6, it is evident that when the same silicon content is evenly distributed across the two film layers, the fast-charging lifespan retention rate is relatively poor. Furthermore, the cycle life of battery cells using silicon-oxygen composites is relatively worse than that of battery cells using silicon-carbon composites.

[0236] Example 27-

[0237] The difference between Example 27 and Example 8 is that a first silicon-carbon composite with different silicon content is used to prepare a second negative electrode film with different thickness and silicon content, and the thickness of the first negative electrode film is also adjusted accordingly, as detailed in Table 9.

[0238] Table 9

[0239] As can be seen from the data in Table 9, when using a first silicon-carbon composite with different silicon contents, the battery cell can achieve excellent cycle life, fast charge life retention rate, and safety performance.

[0240] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A battery cell, comprising a stacked electrode assembly, the electrode assembly including a negative electrode sheet, the negative electrode sheet including 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 first negative electrode film layer and a second negative electrode film layer, the first negative electrode film layer being disposed between the negative current collector and the second negative electrode film layer. The first negative electrode film layer includes a first negative electrode active material, which includes a first graphite material and optionally a first silicon-based material; The second negative electrode film layer includes a second negative electrode active material, which includes a first silicon-based material and a second graphite material. The silicon content in the second negative electrode film layer, denoted as A, is 2.5% ≤ A ≤ 65% by mass, and can be optionally 4.5% ≤ A ≤ 57%. By mass, the silicon content in the first negative electrode film layer is denoted as B, and 0% < AB ≤ 57%; The tensile strength of the negative electrode current collector is ≥38Kgf / mm². 2 .

2. The battery cell according to claim 1, wherein, The elongation at break of the negative electrode current collector is ≥3.0%.

3. The battery cell according to claim 1 or 2, wherein, The thickness of the negative electrode current collector is 3μm-8μm, and can be selected as 4μm-6μm.

4. The battery cell according to claims 1 to 3, wherein, The first silicon-based material and the second silicon-based material each independently include one or more of elemental silicon, silicon-oxygen complexes, and silicon-carbon complexes; Optionally, at least one of the first silicon-based material and the second silicon-based material includes the silicon-carbon composite; Further optionally, at least one of the first silicon-based material and the second silicon-based material comprises a silicon-carbon composite that satisfies one or more of the following characteristics: 1) The silicon-carbon composite comprises porous carbon and silicon-containing material 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 content in the silicon-carbon composite is 30%-70% by mass, and may be further selected as 35%-65%; 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.

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

6. The battery cell according to any one of claims 1 to 5, wherein, 12% ≤ AB ≤ 40%, or 17% ≤ AB ≤ 27%.

7. The battery cell according to any one of claims 1 to 6, wherein, The first negative electrode film layer further includes a first binder, and the second negative electrode film layer further includes a second binder. The mass content of the first binder in the first negative electrode film layer is less than the mass content of the second binder in the second negative electrode film layer.

8. The battery cell according to claim 7, wherein, The first adhesive has a mass content of 1%-4%, and / or the second adhesive has a mass content of 2%-5%.

9. The battery cell according to any one of claims 1 to 8, wherein, The ratio of the thickness H1 of the first film layer to the thickness H2 of the second negative electrode film layer is 1:9 to 9:

1.

10. The battery cell according to any one of claims 1 to 9, wherein, The total weight of the single-sided coating of the negative electrode film is 60 mg / 1540.25 mm. 2 -200 mg / 1540.25 mm 2 Optionally, 70mg / 1540.25mm 2 -160 mg / 1540.25 mm 2 .

11. The battery cell according to any one of claims 1 to 10, wherein, The electrode assembly further includes a positive electrode sheet, which includes a positive current collector. The elongation at break of the positive current collector is ≥0.8%, and optionally the thickness of the positive current collector is 8μm-15μm, and more preferably 10μm-14μm.

12. A negative electrode sheet, comprising 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 comprising a first negative electrode film layer and a second negative electrode film layer, the first negative electrode film layer being disposed between the negative current collector and the second negative electrode film layer. The first negative electrode film layer includes a first negative electrode active material, which includes a first graphite material and optionally a first silicon-based material; The second negative electrode film layer includes a second negative electrode active material, which includes a first silicon-based material and a second graphite material. The silicon content in the second negative electrode film layer, denoted as A, is 2.5% ≤ A ≤ 65% by mass, and can be optionally 4.5% ≤ A ≤ 57%. By mass, the silicon content in the first negative electrode film layer is denoted as B, and 0% < AB ≤ 57%; The tensile strength of the negative electrode current collector is ≥38Kgf / mm². 2 .

13. The negative electrode sheet according to claim 12, wherein, The elongation at break of the negative electrode current collector is ≥3.0%.

14. The negative electrode sheet according to claim 12 or 13, wherein, The thickness of the negative electrode current collector is 3μm-8μm, and can be selected as 4μm-6μm.

15. The negative electrode sheet according to any one of claims 12 to 14, wherein, The first silicon-based material and the second silicon-based material each independently include one or more of elemental silicon, silicon-oxygen complexes, and silicon-carbon complexes; Optionally, at least one of the first silicon-based material and the second silicon-based material includes the silicon-carbon composite; Further optionally, at least one of the first silicon-based material and the second silicon-based material comprises a silicon-carbon composite that satisfies one or more of the following characteristics: 1) The silicon-carbon composite comprises porous carbon and silicon-containing material 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 content in the silicon-carbon composite is 30%-70% by mass, and may be further selected as 35%-65%; 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.

16. The battery cell according to any one of claims 12 to 15, wherein, 0% ≤ B ≤ 40%, optionally 0% ≤ B ≤ 20%.

17. The negative electrode sheet according to any one of claims 12 to 16, wherein, 12% ≤ AB ≤ 40%.

18. The negative electrode sheet according to any one of claims 12 to 17, wherein, The first negative electrode film layer further includes a first binder, and the second negative electrode film layer further includes a second binder. The mass content of the first binder in the first negative electrode film layer is less than the mass content of the second binder in the second negative electrode film layer.

19. The negative electrode sheet according to claim 18, wherein, The first adhesive has a mass content of 1%-4%, and / or the second adhesive has a mass content of 2%-5%.

20. A battery device comprising one or more battery cells according to any one of claims 1 to 11.

21. An electrical device comprising a battery cell according to any one of claims 1 to 11, or a battery device according to claim 20.

Images