Battery cell and manufacturing method therefor, battery, and electric device

Abstract

A battery cell and a manufacturing method therefor, a battery, and an electric device, relating to the technical field of lithium batteries. The battery cell comprises a negative electrode sheet, wherein a negative electrode film layer of the negative electrode sheet comprises a silicon-carbon composite material and graphite, and the silicon-carbon composite material comprises a porous carbon matrix and a silicon-containing substance distributed in the porous carbon matrix. The negative electrode film layer comprises a first negative electrode film layer and a second negative electrode film layer, the second negative electrode film layer is arranged between the first negative electrode film layer and a negative electrode current collector, and the mass proportion of the silicon-carbon composite material in the first negative electrode film layer is higher than the mass proportion of the silicon-carbon composite material in the second negative electrode film layer. The silicon-carbon composite material is selected as at least part of a silicon-containing material and is added to the negative electrode film layer, the silicon-carbon composite material has a structure in which the silicon-containing substance is distributed in the porous carbon matrix, and the porous carbon matrix can provide space for volume expansion of silicon, reducing mechanical stress, thereby exhibiting relatively low volume expansion during charging and discharging, and mitigating the degradation of the cycle performance of the battery cell caused by the volume expansion of silicon.

Description

A battery cell and its preparation method, a battery and an electrical device thereof

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese Patent Application No. 202510365598.2, filed on March 26, 2025, entitled “A battery cell and its preparation method, battery and power device”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of lithium battery technology, and in particular to a battery cell and its preparation method, a battery and an electrical device. Background Technology

[0004] In recent years, with the increasingly widespread application of lithium-ion batteries, they have been widely used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. Due to the significant advancements in lithium-ion battery technology, higher requirements have been placed on their energy density, cycle performance, and safety performance. Furthermore, due to the increasingly limited selection of positive electrode active materials, lithium phosphate-containing positive electrode materials are considered the best choice for meeting safety requirements.

[0005] However, the relatively low energy density of lithium phosphate cathode materials limits their application in some high-performance scenarios. Silicon has a high theoretical specific capacity, which can effectively increase the energy density of batteries. Combining silicon with lithium phosphate cathode materials can significantly improve the energy density of individual battery cells; however, silicon expands in volume by up to 300% during charge and discharge, which leads to a decrease in the cycle performance of individual battery cells. Summary of the Invention

[0006] This application is made in view of the above-mentioned problems, and its purpose is to provide a battery cell and a method for preparing the same, as well as a battery and an electrical device, which can improve the cycle performance of the battery cell.

[0007] To achieve the above objectives, a first aspect of this application provides a battery cell comprising: a positive electrode and a negative electrode. The positive electrode includes a positive active material comprising lithium phosphate. The negative electrode includes a negative electrode film and a negative electrode current collector. The negative electrode film comprises a silicon-carbon composite material and graphite. The silicon-carbon composite material comprises a porous carbon matrix and silicon-containing materials distributed within the porous carbon matrix. The Dv50 particle size of the silicon-carbon composite material is 3 μm to 8.5 μm. The negative electrode film includes a first negative electrode film and a second negative electrode film. The second negative electrode film is disposed between the first negative electrode film and the negative electrode current collector. The mass percentage of the silicon-carbon composite material in the first negative electrode film is W1, and the mass percentage of the silicon-carbon composite material in the second negative electrode film is W2, where W1 > W2.

[0008] Therefore, this application includes lithium phosphate-containing battery cells where the Dv50 particle size of the silicon-containing material in the negative electrode film is within the aforementioned range, and at least half of the silicon-containing material is disposed in the region of the negative electrode film close to the positive electrode. However, conventional silicon-carbon negative electrodes expand significantly, repeatedly expanding and contracting during cycling, with fresh interfaces repeatedly forming and continuously consuming lithium ions, thus deteriorating the cycle life of the single cell. The silicon-carbon negative electrode material used in this application comprises a porous carbon matrix and silicon-containing material distributed within the porous carbon matrix. The residual pores in the porous carbon matrix provide space for the volume expansion of silicon, reducing mechanical stress, thereby exhibiting lower volume expansion during charge and discharge, compensating for the aforementioned cycle disadvantages of the battery cell. Furthermore, the poor thermodynamic and kinetic properties of silicon-carbon negative electrode materials worsen the DC internal resistance of the battery. Therefore, this application uses silicon-carbon particles with smaller Dv50 and places at least half of the silicon-carbon negative electrode in the first film layer, shortening the lithium-ion transport distance of the silicon-carbon negative electrode material, improving the polarization of the battery, and reducing the DC internal resistance of the battery.

[0009] In any embodiment, the Dv50 particle size of the silicon-carbon composite material is 3 μm to 7.5 μm. By further ensuring that the Dv50 particle size of the silicon-carbon composite material is within the above range, this application facilitates a shorter lithium-ion diffusion distance and a reduced polarization degree of the silicon-carbon composite material, thereby improving the DC resistance degradation of the battery cell after discharge to 10% SOC.

[0010] In any embodiment, the pitch of the silicon-carbon composite material is ≤1.1. By ensuring that the pitch of the silicon-carbon composite material is within the above range, this application uses a porous carbon substrate with a smaller pitch, resulting in more uniform pore volume and fluidization state between particles. This makes the distribution of silicon-containing materials in the silicon-carbon composite material more uniform, which is beneficial for improving the cycle performance of the battery cell.

[0011] In any embodiment, the Dv10 particle size of the silicon-carbon composite material is ≥2μm, and the Dv90 particle size is ≤18μm. By ensuring that the Dv10 and Dv90 particle sizes of the silicon-carbon composite material are within the above-mentioned ranges, this application not only facilitates ensuring that the particle size distribution of the silicon-carbon composite material is within the above-mentioned ranges, but also improves the cycle performance of the battery cell.

[0012] In any embodiment, W1 > 2W2. By ensuring that the mass percentage of silicon-carbon composite material in the first negative electrode film layer and the mass percentage of silicon-carbon composite material in the second negative electrode film layer meet the above conditions, this application can achieve a greater amount of silicon-carbon composite material disposed in the region of the negative electrode film layer away from the negative electrode current collector, even when the thickness of the first negative electrode film layer is greater than that of the second negative electrode film layer. This shortens the lithium-ion transport distance, reduces the polarization degree of the negative electrode sheet, and thus improves the DC resistance degradation of the battery cell after discharge to 10% SOC.

[0013] In any embodiment, at least two-thirds of the silicon-carbon composite material in the negative electrode film is located in the first negative electrode film layer. By placing more silicon-carbon composite material in the first negative electrode film layer, this application achieves a greater concentration of silicon-carbon composite material in the region of the negative electrode film layer away from the negative electrode current collector, even when the thickness of the first negative electrode film layer is smaller than that of the second negative electrode film layer. This shortens the lithium-ion transport distance, reduces the polarization of the negative electrode sheet, and thus improves the DC resistance degradation of the battery cell after discharge to 10% SOC.

[0014] In any embodiment, in the scanning electron microscope (SEM) image of the cross-section of the negative electrode sheet, the number of silicon-carbon particles in the first negative electrode film layer is ≥10, and the number of silicon-carbon particles in the second negative electrode film layer is <10. The test method for the number of silicon-carbon particles in the first negative electrode film layer and the number of silicon-carbon particles in the second negative electrode film layer is as follows: The negative electrode sheet is prepared using a Japanese electronic ion polisher. The preparation voltage is 7.5kV, the argon flow rate is 5.5L / min, and the time is 80min. The prepared cross-section electrode sheet is characterized using a Thermo Fisher Scientific Apreo 2s to obtain a scanning electron microscope image. The scanning electron microscope image is magnified 500 times. In backscatter mode, silicon-carbon particles are bright white, and graphite particles are dark gray. The number of bright white particles in the first negative electrode film layer and the second negative electrode film layer are counted respectively. This application, by ensuring that the number of silicon-carbon particles in the first and second negative electrode films in the scanning electron microscope images of the negative electrode cross-section are within the aforementioned range, facilitates the placement of more silicon-carbon composite materials in the first negative electrode film, shortens the lithium-ion transport distance, reduces the polarization degree of the negative electrode, and thereby improves the deterioration of DC resistance of the battery cell after discharge to 10% SOC.

[0015] In any embodiment, the mass percentage of silicon in the negative electrode film is greater than 0 and less than or equal to 9 wt%. By ensuring that the mass percentage of silicon in the negative electrode film is within the above range, this application is advantageous in increasing the energy density of lithium phosphate battery cells without significantly reducing cycle performance.

[0016] In any embodiment, the mass percentage of silicon in the first negative electrode film is 2wt% to 3wt%, and the mass percentage of silicon in the second negative electrode film is 0% to 1wt%. This application, by ensuring that the mass percentages of silicon in the first and second negative electrode films are within the aforementioned ranges, facilitates the placement of more silicon-carbon composite material in the first negative electrode film, shortening the lithium-ion transport distance, reducing the polarization of the negative electrode sheet, and thereby improving the DC resistance degradation of the battery cell after discharge to 10% SOC.

[0017] In any implementation, the capacity of the negative electrode is greater than 370 mAh / g and less than or equal to 700 mAh / g.

[0018] In any embodiment, the capacity of the first negative electrode film is 435 mAh / g to 470 mAh / g, and the capacity of the second negative electrode film is 370 mAh / g to 400 mAh / g. This application, by ensuring that the capacities of the first and second negative electrode films are within the aforementioned ranges, facilitates the placement of more silicon-carbon composite material in the first negative electrode film, shortening the lithium-ion transport distance, reducing the polarization of the negative electrode sheet, and thereby improving the DC resistance degradation of the battery cell after discharge to 10% SOC.

[0019] The second aspect of this application provides a method for preparing a battery cell, comprising: preparing a positive electrode sheet and a negative electrode sheet respectively; the positive electrode sheet includes a positive active material, the positive active material including a lithium phosphate; the negative electrode sheet includes a negative electrode film and a negative electrode current collector; the negative electrode film includes a silicon-carbon composite material and graphite; the silicon-carbon composite material includes a porous carbon matrix and silicon-containing materials distributed in the porous carbon matrix; the Dv50 particle size of the silicon-carbon composite material is 3μm~8.5μm; the silicon-carbon composite material is prepared by chemical vapor deposition; the negative electrode film includes a first negative electrode film and a second negative electrode film, the second negative electrode film being disposed between the first negative electrode film and the negative electrode current collector; the mass percentage of the silicon-carbon composite material in the first negative electrode film is higher than the mass percentage of the silicon-carbon composite material in the second negative electrode film.

[0020] Therefore, this application includes lithium phosphate-containing battery cells where the Dv50 particle size of the silicon-containing material in the negative electrode film is within the aforementioned range, and at least half of the silicon-containing material is disposed in the region of the negative electrode film close to the positive electrode. However, conventional silicon-carbon negative electrodes expand significantly, repeatedly expanding and contracting during cycling, with fresh interfaces repeatedly forming and continuously consuming lithium ions, thus deteriorating the cycle life of the single cell. The silicon-carbon negative electrode material used in this application comprises a porous carbon matrix and silicon-containing material distributed within the porous carbon matrix. The residual pores in the porous carbon matrix provide space for the volume expansion of silicon, reducing mechanical stress, thereby exhibiting lower volume expansion during charge and discharge, compensating for the aforementioned cycle disadvantages of the battery cell. Furthermore, the poor thermodynamic and kinetic properties of silicon-carbon negative electrode materials worsen the DC internal resistance of the battery. Therefore, this application uses silicon-carbon particles with smaller Dv50 and places at least half of the silicon-carbon negative electrode in the first film layer, shortening the lithium-ion transport distance of the silicon-carbon negative electrode material, improving the polarization of the battery, and reducing the DC internal resistance of the battery.

[0021] In any embodiment, carbon coating is performed using chemical vapor deposition (CVD) when preparing lithium-containing phosphates. This application improves the uniformity of carbon coating on lithium-containing phosphates by employing CVD, thereby improving the conductivity and kinetic performance of the lithium-containing phosphates, and ultimately mitigating the deterioration of DC resistance in battery cells after discharge to 10% SOC.

[0022] In any embodiment, preparing the positive electrode sheet includes coating the surface of the positive electrode current collector with a positive electrode active slurry, wherein the coating amount of the positive electrode active slurry is 16 mg / cm² to 32.5 mg / cm². By keeping the coating amount of the positive electrode active slurry within the above range, this application reduces the diffusion distance of lithium ions from the surface to the interior, lowers the diffusion resistance, and makes it easier for lithium ions to be inserted into the negative electrode active material. This is beneficial for the battery cell to maintain both energy density and improve the DC resistance degradation of the battery cell after discharge to 10% SOC.

[0023] A third aspect of this application provides a battery comprising the battery cell described in the above embodiments or a battery cell prepared according to the preparation method of the battery cell described in the above embodiments.

[0024] The fourth aspect of this application provides an electrical device that includes the battery described in the above embodiments, the battery being used to provide electrical energy. Attached Figure Description

[0025] Figure 1 is a schematic diagram of one embodiment of the negative electrode sheet in the battery cell of this application.

[0026] Figure 2 is a schematic diagram of another embodiment of the negative electrode sheet in the battery cell of this application.

[0027] Figure 3 is a schematic diagram of a battery cell according to one embodiment of this application.

[0028] Figure 4 is an exploded view of a battery cell according to an embodiment of this application, as shown in Figure 3.

[0029] Figure 5 is a schematic diagram of a battery module according to one embodiment of this application.

[0030] Figure 6 is a schematic diagram of a battery pack according to one embodiment of this application.

[0031] Figure 7 is an exploded view of the battery pack of one embodiment of this application shown in Figure 6.

[0032] Figure 8 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.

[0033] Figure 9 is a scanning electron microscope image of the cross-section of the negative electrode sheet in Embodiment 12 of this application.

[0034] Explanation of reference numerals in the attached figures:

[0035] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly; 510 Negative electrode sheet; 511 Negative current collector; 512 First negative electrode film layer; 513 Second negative electrode film layer. Embodiments of the present invention

[0036] The following detailed description, with appropriate reference to the accompanying drawings, discloses a battery cell, its preparation method, the battery, and an electrical device according to this application. However, unnecessary details may be omitted. For example, detailed descriptions of well-known facts and repetitive descriptions of 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 to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0037] 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.

[0038] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0039] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0040] 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.

[0041] To improve the energy density of lithium phosphate battery cells, silicon-containing materials are introduced into the negative electrode as the negative electrode active material. However, due to the inherently poor thermodynamics and kinetics of silicon-containing materials compared to graphite, the DC resistance of lithium phosphate battery cells deteriorates after discharge to 10% SOC.

[0042] To further improve the DC resistance degradation of lithium phosphate battery cells, including those containing silicon materials, smaller particle sizes of silicon materials can be selected to shorten the lithium-ion diffusion distance. Additionally, placing more than half of the silicon material in the negative electrode layer near the positive electrode further shortens the lithium-ion transport distance and improves the battery cell's DC resistance. However, smaller particle sizes of silicon materials exhibit worse cycle performance compared to larger particles. Furthermore, the silicon material positioned in the negative electrode layer near the positive electrode experiences a higher frequency and number of lithium-ion insertions and extractions, consuming more lithium ions and contributing to poor cycle performance.

[0043] Based on this, this application proposes a battery cell and its preparation method, a battery and an electrical device. The following provides a more detailed description of this application and optional embodiments.

[0044] This application provides a battery cell comprising: a positive electrode and a negative electrode. The positive electrode includes a positive active material comprising lithium phosphate. The negative electrode includes a negative electrode film and a negative electrode current collector. The negative electrode film comprises a silicon-carbon composite material and graphite. The silicon-carbon composite material comprises a porous carbon matrix and silicon-containing materials distributed within the porous carbon matrix. The Dv50 particle size of the silicon-carbon composite material is 3 μm to 8.5 μm. The negative electrode film includes a first negative electrode film and a second negative electrode film, the second negative electrode film being disposed between the first negative electrode film and the negative electrode current collector. The mass percentage of the silicon-carbon composite material in the first negative electrode film is W1, and the mass percentage of the silicon-carbon composite material in the second negative electrode film is W2, where W1 > W2.

[0045] Lithium-containing phosphates refer to a class of phosphates containing lithium ions (Li). + ) and phosphate ions (PO4³ - Lithium phosphates are compounds widely used as cathode materials in lithium-ion batteries. Common lithium-containing phosphates include lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), lithium cobalt phosphate (LiCoPO4), and lithium nickel phosphate (LiNiPO4). Lithium-containing phosphates offer advantages such as high safety, long cycle life, and environmental friendliness as cathode materials, but they also suffer from low energy density.

[0046] Silicon-carbon composite material refers to a new type of composite material that combines silicon (Si) and carbon (C) materials. The carbon material forms a porous structure, and silicon-containing materials are distributed in the porous structure. The porous structure can provide space for the volume expansion of silicon, reduce mechanical stress, and at the same time, the porous structure can increase the contact area between the electrode and the electrolyte, thereby improving the lithium-ion diffusion rate.

[0047] It should be noted that silicon-carbon composite materials can be obtained through chemical vapor deposition. Chemical vapor deposition deposits silane gas into the pores of porous carbon to form silicon-carbon composite materials. After formation and recycling, the pores of the porous carbon may contain a variety of different silicon-containing substances, such as silicon particles.

[0048] DV50 particle size refers to the range of 50% of particle diameter, which can reflect the average particle size of the particle system. DV50 particle size can be measured by the following method: using a laser particle size analyzer of model Mastersizer3000 to obtain a volumetric particle size distribution map, the DV50 particle size of silicon-containing materials can be obtained from the peaks in the volumetric particle size distribution map.

[0049] As an example, the Dv50 particle size of the silicon-carbon composite material can be 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm or 8.5μm.

[0050] The first negative electrode film layer is a layered structure that is far from the negative electrode current collector and contains negative electrode active material. The second negative electrode film layer is a layered structure that is close to the negative electrode current collector and contains negative electrode active material. The first negative electrode film layer is bonded to the second negative electrode film layer, and the second negative electrode film layer is bonded to the negative electrode current collector.

[0051] It should be noted that the mass of the first negative electrode film layer and the second negative electrode film layer can be the same or different. For example, the mass ratio of the first negative electrode film layer and the second negative electrode film layer can be 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2 or 9:1.

[0052] Optionally, the first negative electrode film layer and the second negative electrode film layer have the same mass, that is, the mass ratio of the first negative electrode film layer and the second negative electrode film layer is 5:5.

[0053] The mass percentage of silicon-carbon composite material in the first negative electrode film layer refers to the percentage of the mass of silicon-carbon composite material in the first negative electrode film layer relative to the total mass of the first negative electrode film layer. The mass percentage of silicon-carbon composite material in the second negative electrode film layer refers to the percentage of the mass of silicon-carbon composite material in the second negative electrode film layer relative to the total mass of the second negative electrode film layer.

[0054] Figure 1 is a schematic diagram of one embodiment of the negative electrode sheet in the battery cell of this application. The negative electrode sheet 510 includes a negative current collector 511, a second negative electrode film layer 513 respectively disposed on two surfaces of the negative current collector 511, and a first negative electrode film layer 512 respectively disposed on the surfaces of the two second negative electrode film layers 513.

[0055] Figure 2 is a schematic diagram of another embodiment of the negative electrode sheet in the battery cell of this application. The negative electrode sheet 510 includes a negative current collector 511, a second negative electrode film layer 513 respectively disposed on one of the surfaces of the negative current collector 511, and a first negative electrode film layer 512 respectively disposed on the surface of the second negative electrode film layer 513.

[0056] This application includes lithium phosphate-containing battery cells where the Dv50 particle size of the silicon-containing material in the negative electrode film is within the aforementioned range, and where at least half of the silicon-containing material is disposed in the region of the negative electrode film close to the positive electrode. However, small-particle silicon-containing materials with the aforementioned Dv50 particle size range have a larger specific surface area, increasing the contact area with the electrolyte, leading to more side reactions and the formation of a thicker SEI film. Repeated rupture and regeneration of the SEI film consumes electrolyte and lithium ions, reducing the cycle performance of the battery cell. Furthermore, the silicon-containing material disposed in the region of the negative electrode film close to the positive electrode experiences a higher number and frequency of lithium ion insertion / extraction, consuming more lithium ions, which also leads to a decrease in the cycle performance of the battery cell.

[0057] This application selects silicon-carbon composite material as at least part of the silicon-containing material to add to the negative electrode film layer. The silicon-carbon composite material has a structure in which silicon-containing materials are distributed in a porous carbon matrix. It combines the high capacity of silicon and the stability of carbon materials. The silicon-carbon composite material can effectively alleviate the problems of silicon volume expansion, pulverization and low conductivity through the buffering effect of the porous carbon matrix, the improvement of conductivity and the stabilization of the SEI film. As a result, it has a lower volume expansion during charging and discharging, which makes up for the cycle disadvantage of the battery cell caused by the above.

[0058] In some embodiments, the Dv50 particle size of the silicon-carbon composite material is 3 μm to 7.5 μm.

[0059] Optionally, the Dv50 particle size of the silicon-carbon composite material is 6μm~7.5μm.

[0060] This application further reduces the Dv50 particle size of the silicon-carbon composite material within the aforementioned range, which helps to shorten the diffusion distance of lithium ions, reduce the polarization degree of the silicon-carbon composite material, and thus improve the deterioration of DC resistance of the battery cell after discharge to 10% SOC.

[0061] In some embodiments, the diameter of the silicon-carbon composite material is ≤1.1.

[0062] Spacing is a parameter used to describe the uniformity of particle distribution in a material, and usually refers to the average distance between particles.

[0063] The radial distance can be calculated using the following formula:

[0064] Span = (DV90 - DV10) / DV50;

[0065] Wherein, Span refers to the particle size of the silicon-carbon composite material, DV90 refers to the DV90 particle size of the silicon-carbon composite material, DV10 refers to the DV10 particle size of the silicon-carbon composite material, and DV50 refers to the DV50 particle size of the silicon-carbon composite material.

[0066] As an example, the pitch of silicon-carbon composite materials can be 0.1, 0.2, 0.5, 0.8, 1 or 1.1.

[0067] This application achieves a more uniform distribution of silicon-containing materials in the silicon-carbon composite material by using a porous carbon substrate with a smaller diameter and more similar pore volume and fluidization state between particles, which is beneficial for improving the cycle performance of battery cells.

[0068] In some embodiments, the silicon-carbon composite material has a Dv10 particle size ≥ 2 μm and a Dv90 particle size ≤ 18 μm.

[0069] DV10 particle size refers to the range of 10% of particle diameter, which is used to describe the fine particulate portion of a particulate system.

[0070] DV90 particle size refers to the range of 90% of particle diameter, which is used to describe the coarse particle portion of a particulate system.

[0071] The DV10 and DV90 particle sizes can be measured using the following method: A laser particle size analyzer (model Mastersizer3000) is used to obtain a cumulative particle size distribution map. The DV10 and DV90 particle sizes of the silicon-containing material can be obtained from the peaks in the cumulative particle size distribution map.

[0072] Silicon-carbon composite materials with a small DV10 particle size often have excessively high silicon content due to processing issues, leading to poor cycle performance of the battery cells. Silicon-carbon composite materials with a large DV90 particle size are difficult to process and also exhibit poor kinetics. This application addresses this issue by ensuring that the Dv10 and Dv90 particle sizes of the silicon-carbon composite material are within the aforementioned ranges. This not only facilitates ensuring the particle size distribution of the silicon-carbon composite material is within these ranges but also improves the cycle performance of the battery cells.

[0073] In some implementations, W1 > 2W2.

[0074] This application achieves the above-mentioned conditions by ensuring that the mass ratio of silicon-carbon composite material in the first negative electrode film layer and the mass ratio of silicon-carbon composite material in the second negative electrode film layer meet the above-mentioned conditions. This allows for the presence of more silicon-carbon composite material in the region of the negative electrode film layer that is far from the negative electrode current collector, even when the thickness of the first negative electrode film layer is greater than that of the second negative electrode film layer. This shortens the lithium-ion transport distance, reduces the polarization of the negative electrode sheet, and thus improves the DC resistance degradation of the battery cell after discharge to 10% SOC.

[0075] In some embodiments, at least two-thirds of the silicon-carbon composite material in the negative electrode film is located in the first negative electrode film layer.

[0076] This application, by placing more silicon-carbon composite material in the first negative electrode film layer, enables more silicon-carbon composite material to be disposed in the region of the negative electrode film layer away from the negative electrode current collector, even when the thickness of the first negative electrode film layer is smaller than that of the second negative electrode film layer. This shortens the lithium-ion transport distance, reduces the polarization degree of the negative electrode sheet, and thus improves the deterioration of DC resistance of the battery cell after discharge to 10% SOC.

[0077] In some embodiments, in the scanning electron microscope image of the cross-section of the negative electrode sheet, the number of silicon-carbon particles in the first negative electrode film is ≥10, and the number of silicon-carbon particles in the second negative electrode film is <10.

[0078] The test methods for the number of silicon-carbon particles in the first negative electrode film and the second negative electrode film are as follows: The negative electrode sheet was prepared using a Japanese electronic ion polisher. The sample preparation voltage was 7.5 kV, the argon flow rate was 5.5 L / min, and the time was 80 min. The prepared cross-sectional electrode sheet was characterized using a Thermo Fisher Apreo 2s microscope to obtain scanning electron microscope images. The scanning electron microscope images were magnified 500 times. In backscatter mode, silicon-carbon particles were bright white and graphite particles were dark gray. The number of bright white particles in the first and second negative electrode films were counted respectively.

[0079] As an example, in the scanning electron microscope image of the cross-section of the negative electrode sheet, the number of silicon-carbon particles in the first negative electrode film layer can be 10, 12, 15, 18, 20, 22, 25, 28 or 30, and the number of silicon-carbon particles in the second negative electrode film layer can be 0, 1, 2, 5, 7 or 9.

[0080] Optionally, the number of silicon-carbon particles in the first negative electrode film is ≥15, and the number of silicon-carbon particles in the second negative electrode film is ≤5.

[0081] This application, by ensuring that the number of silicon-carbon particles in the first and second negative electrode films in the scanning electron microscope images of the negative electrode cross-section are within the aforementioned range, facilitates the placement of more silicon-carbon composite materials in the first negative electrode film, shortens the lithium-ion transport distance, reduces the polarization degree of the negative electrode, and thereby improves the deterioration of DC resistance of the battery cell after discharge to 10% SOC.

[0082] In some implementations, the mass percentage of silicon in the negative electrode film is greater than 0 and less than or equal to 9 wt%.

[0083] The mass percentage of silicon in the negative electrode film refers to the percentage of the mass of silicon in the negative electrode film.

[0084] As an example, the mass percentage of silicon in the negative electrode film can be 0.1wt%, 0.2wt%, 0.5wt%, 0.8wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, or 9wt%.

[0085] Optionally, the mass percentage of silicon in the negative electrode film is 1wt% to 5wt%.

[0086] Optionally, the mass percentage of silicon in the negative electrode film is 2wt% to 4wt%.

[0087] By ensuring that the mass percentage of silicon in the negative electrode film is within the aforementioned range, this application is beneficial in increasing the energy density of lithium phosphate-containing battery cells without significantly reducing cycle performance.

[0088] The mass percentage of silicon in the first negative electrode film is greater than 0 and less than or equal to 9 wt%, while the mass percentage of silicon in the second negative electrode film is 0 to 3 wt%.

[0089] Optionally, the mass percentage of silicon in the first negative electrode film is 0.67wt% to 5wt%, and the mass percentage of silicon in the second negative electrode film is 0 to 1.67wt%.

[0090] Optionally, the mass percentage of silicon in the first negative electrode film layer is 1.33wt% to 4wt%, and the mass percentage of silicon in the second negative electrode film layer is 0% to 1.33wt%.

[0091] In some embodiments, the mass percentage of silicon in the first negative electrode film is 2wt% to 3wt%, and the mass percentage of silicon in the second negative electrode film is 0% to 1wt%.

[0092] As an example, the mass percentage of silicon in the first negative electrode film layer can be 2wt%, 2.1wt%, 2.2wt%, 2.3wt%, 2.4wt%, 2.5wt%, 2.6wt%, 2.7wt%, 2.8wt%, 2.9wt%, or 3wt%, and the mass percentage of silicon in the second negative electrode film layer can be 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, or 1wt%.

[0093] Optionally, the mass percentage of silicon in the negative electrode film is 1.5 wt%.

[0094] This application, by ensuring that the mass percentage of silicon in the first negative electrode film and the mass percentage of silicon in the second negative electrode film are within the aforementioned ranges, facilitates the placement of more silicon-carbon composite material in the first negative electrode film, shortens the lithium-ion transport distance, reduces the polarization degree of the negative electrode sheet, and thereby improves the deterioration of DC resistance of the battery cell after discharge to 10% SOC.

[0095] In some implementations, the capacity of the negative electrode is greater than 370 mAh / g and less than or equal to 700 mAh / g.

[0096] The capacity of the negative electrode can be measured by the following methods:

[0097] After wiping one side of the double-sided coated electrode with alcohol, the electrode is dried in an oven to obtain a single-sided electrode. The single-sided electrode is then cut into a circular piece with a diameter of 14mm to obtain the negative electrode.

[0098] The electrolyte was prepared as follows: ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 20:20:60. LiPF6 was then uniformly dissolved in the mixture, and fluoroethylene carbonate (FEC) was added as an additive to obtain the electrolyte. The concentration of LiPF6 was 1 mol / L, and the mass percentage of FEC in the electrolyte was 5%.

[0099] The coin cell was prepared as follows: using the aforementioned negative electrode as the working electrode, lithium metal as the counter electrode, and a polypropylene film as the separator, the negative electrode, separator, and lithium metal were stacked in sequence, with the separator positioned between the working electrode and the counter electrode. Electrolyte was then injected to assemble the coin cell. The assembled coin cell was placed in a 25°C constant temperature chamber and allowed to stand for 30 minutes. It was then discharged at a constant current of 0.1C to 5mV, followed by a constant voltage discharge to 0.05C to obtain the discharge capacity C1 of the electrode.

[0100] Optionally, the capacity of the negative electrode is 400mAh / g to 500mAh / g.

[0101] In some embodiments, the capacity of the first negative electrode film is 435 mAh / g to 470 mAh / g, and the capacity of the second negative electrode film is 370 mAh / g to 400 mAh / g.

[0102] As an example, the capacity of the first negative electrode film can be 435mAh / g, 440mAh / g, 445mAh / g, 450mAh / g, 455mAh / g, 460mAh / g, 465mAh / g, or 470mAh / g, and the capacity of the second negative electrode film can be 370mAh / g, 375mAh / g, 380mAh / g, 385mAh / g, 390mAh / g, 395mAh / g, or 400mAh / g.

[0103] The capacity of the first negative electrode film and / or the capacity of the second negative electrode film can be measured by the following methods:

[0104] The single-sided electrode is fixed to the tape, and the first film layer is peeled off by using the adhesive properties of the tape. The capacity C2 of the second active layer is tested using the above method for testing the capacity of the negative electrode. The capacity C3 of the first film layer is C1-C2.

[0105] This application, by ensuring that the capacity of the first negative electrode film and the capacity of the second negative electrode film are within the aforementioned ranges, facilitates the placement of more silicon-carbon composite material in the first negative electrode film, shortens the lithium-ion transport distance, reduces the polarization degree of the negative electrode sheet, and thereby improves the deterioration of DC resistance of the battery cell after discharge to 10% SOC.

[0106] This application also provides a method for preparing a battery cell, comprising: preparing a positive electrode sheet and a negative electrode sheet respectively, wherein the positive electrode sheet includes a positive active material, the positive active material includes a lithium phosphate, the negative electrode sheet includes a negative electrode film and a negative electrode current collector, the negative electrode film includes a silicon-carbon composite material and graphite, the silicon-carbon composite material includes a porous carbon matrix and silicon-containing materials distributed in the porous carbon matrix, the Dv50 particle size of the silicon-carbon composite material is 3μm~8.5μm, and the silicon-carbon composite material is prepared by chemical vapor deposition; the negative electrode film includes a first negative electrode film and a second negative electrode film, the second negative electrode film is disposed between the first negative electrode film and the negative electrode current collector, and the mass proportion of the silicon-carbon composite material in the first negative electrode film is higher than the mass proportion of the silicon-carbon composite material in the second negative electrode film.

[0107] It should be noted that this application is not limited to the method of preparing silicon-carbon composite materials by chemical vapor deposition. This application provides a specific method for preparing silicon-carbon composite materials, the steps of which are as follows:

[0108] Step 1: Weigh 500g of porous carbon and place it in a reactor (rotary kiln or fluidized bed). Heat it to 500℃ under argon protection and keep it at that temperature for 2 hours to allow the air adsorbed inside the porous carbon to be fully desorbed.

[0109] Step 2: Introduce a mixture of silane and argon gas (silane to argon volume ratio 1:4) into the rotary kiln at a flow rate of 4 L / min, maintain a slight positive pressure of 200 Pa, and rotate the rotary kiln at a rotation frequency of 20 Hz to obtain silicon-carbon particles.

[0110] Step 3: Heat the rotary kiln to 600℃, introduce a mixture of acetylene and argon gas at a flow rate of 3L / min, and rotate the rotary kiln at a rotation frequency of 20Hz to coat the silicon carbide particles.

[0111] Step 4: After natural cooling, the silicon-carbon composite material is obtained by passing it through a 200-mesh sieve.

[0112] This application includes lithium phosphate-containing battery cells where the Dv50 particle size of the silicon-containing material in the negative electrode film is within the aforementioned range, and at least half of the silicon-containing material is disposed in the region of the negative electrode film close to the positive electrode. However, conventional silicon-carbon negative electrodes expand significantly, repeatedly expanding and contracting during cycling, with fresh interfaces repeatedly forming and continuously consuming lithium ions, thus deteriorating the cycle life of the single cell. The silicon-carbon negative electrode material used in this application comprises a porous carbon matrix and silicon-containing material distributed within the porous carbon matrix. The residual pores in the porous carbon matrix provide space for the volume expansion of silicon, reducing mechanical stress, thereby exhibiting lower volume expansion during charge and discharge, compensating for the aforementioned cycle disadvantages of the battery cell. Furthermore, the poor thermodynamic and kinetic properties of silicon-carbon negative electrode materials worsen the DC internal resistance of the battery. Therefore, this application uses silicon-carbon particles with smaller Dv50 and places at least half of the silicon-carbon negative electrode in the first film layer, shortening the lithium-ion transport distance of the silicon-carbon negative electrode material, improving the polarization of the battery, and reducing the DC internal resistance of the battery.

[0113] In some embodiments, carbon coating is performed by chemical vapor deposition when preparing lithium phosphate.

[0114] It should be noted that this application is not limited to using chemical vapor deposition to carbon-coat lithium-containing phosphates. This application provides a specific method for carbon-coating lithium-containing phosphates, the steps of which are as follows:

[0115] S1, Heating Stage:

[0116] Nitrogen gas is introduced to purge the air from the reactor.

[0117] The reactor temperature is increased to 800°C at a rate of 5-10°C / min.

[0118] S2, Encapsulation Stage:

[0119] A mixture of methane and nitrogen gas is slowly introduced, with a methane to nitrogen flow rate ratio of 1:3, and the reaction time is 3 hours.

[0120] S3, Cooling Phase:

[0121] After the reaction is complete, stop the flow of methane gas, continue to flow nitrogen gas, and slowly cool to room temperature.

[0122] This application employs chemical vapor deposition to carbon-coat lithium phosphates, which improves the uniformity of carbon coating, thereby enhancing the conductivity and kinetic performance of lithium phosphates, and ultimately mitigating the deterioration of DC resistance in battery cells after discharge to 10% SOC.

[0123] In some embodiments, preparing the positive electrode sheet includes coating the surface of the positive current collector with a positive active slurry, wherein the coating amount of the positive active slurry is 16 mg / cm2 to 32.5 mg / cm2.

[0124] As an example, the coating amount of the positive electrode active slurry can be 16 mg / cm2, 18 mg / cm2, 20 mg / cm2, 22 mg / cm2, 25 mg / cm2, 28 mg / cm2, 30 mg / cm2 or 32.5 mg / cm2.

[0125] Optionally, the coating amount of the positive electrode active slurry is 23 mg / cm2 to 26 mg / cm2.

[0126] This application reduces the diffusion distance of lithium ions from the surface to the interior by ensuring that the coating amount of the positive electrode active slurry is within the above-mentioned range, thereby reducing the diffusion resistance and making it easier for lithium ions to be inserted into the negative electrode active material. This is beneficial for the battery cell to balance energy density and improve the DC resistance degradation of the battery cell after discharge to 10% SOC.

[0127] In addition, the following description, with appropriate reference to the accompanying drawings, describes a battery cell, its preparation method, the battery, and the power-consuming device of this application.

[0128] [Battery cell]

[0129] This application does not impose any particular restrictions on the type of battery cell; for example, the battery cell can be a lithium-ion battery, etc.

[0130] Typically, a battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0131] This application does not impose any particular limitation on the type of electrolyte, which can be selected according to actual needs. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions). This includes battery cells using electrolyte solutions and some battery cells using solid electrolytes.

[0132] [Positive electrode plate]

[0133] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0134] 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.

[0135] 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.).

[0136] In some embodiments, when the battery cell is a lithium-ion battery, the positive electrode active material may use a positive electrode active material for lithium-ion batteries well known in the art. By way of example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphate with olivine structure, lithium transition metal oxide and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive electrode active material for batteries can also be used. These positive electrode active materials include at least lithium-containing phosphate, which may be used alone or in combination of two or more. Among them, examples of the lithium transition metal oxide include, but are not limited to, at least one of lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., LiNi1 / 3Co1 / 3Mn1 / 3O2 (also abbreviated as NCM333), LiNi0.5Co0.2Mn0.3O2 (also abbreviated as NCM523), LiNi0.5Co0.25Mn0.25O2 (also abbreviated as NCM211), LiNi0.6Co0.2Mn0.2O2 (also abbreviated as NCM622), LiNi0.8Co0.1Mn0.1O2 (also abbreviated as NCM811)), lithium nickel cobalt aluminum oxide (e.g., LiNi0.8Co0.15Al0.05O2) and modified compounds thereof. Examples of the lithium-containing phosphate with olivine structure include, but are not limited to, at least one of lithium iron phosphate (e.g., LiFePO4 (also abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (e.g., LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

[0137] In some embodiments, in order to further increase the energy density of the battery cell, the positive electrode active material for a lithium-ion battery may include one or more of a lithium transition metal oxide with the general formula LiaNibCocMdOeAf and a modified compound thereof, wherein 0.8 ≤ a ≤ 1.2, 0.5 ≤ b < 1, 0 < c < 1, 0 < d < 1, 1 ≤ e ≤ 2, 0 ≤ f ≤ 1, M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A is selected from one or more of N, F, S and Cl.

[0138] In some embodiments, as an example, the positive electrode active material for lithium-ion batteries may include one or more of LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi1 / 3Co1 / 3Mn1 / 3O2 (NCM333), LiNi0.5Co0.2Mn0.3O2 (NCM523), LiNi0.6Co0.2Mn0.2O2 (NCM622), LiNi0.8Co0.1Mn0.1O2 (NCM811), LiNi0.85Co0.15Al0.05O2, LiFePO4, and LiMnPO4.

[0139] In this application, the modified compounds of the above-mentioned positive electrode active materials may be those that have undergone doping modification and / or surface coating modification of the positive electrode active materials.

[0140] As an optional technical approach in this application, the polyanionic compound can be Li1+xMn1-yAyP1-zRzO4; wherein x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R includes one or more elements selected from B, S, Si and N;

[0141] As an optional technical approach in this application, the polyanionic compound may be LiaAeMn1-fBfP1-gCgO4-nDn, wherein A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; B includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; C includes one or more elements selected from B, S, Si, and N; D includes one or more elements selected from S, F, Cl, and Br; a is selected from the range of 0.9 to 1.1, e is selected from the range of 0.001 to 0.1, f is selected from the range of 0.001 to 0.5, g is selected from the range of 0.001 to 0.1, n is selected from the range of 0.001 to 0.1, and the second positive electrode active material is electrically neutral.

[0142] During the charging and discharging process of a battery, Li undergoes insertion / extraction and consumption, resulting in varying molar Li content at different discharge states. In the examples of cathode materials in this application, the molar Li content refers to the initial state of the material, i.e., the state before feeding. When the cathode material is applied to the battery system, the molar Li content changes after charge-discharge cycles.

[0143] In the examples of cathode materials in this application, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0144] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0145] 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.

[0146] 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.

[0147] [Negative electrode plate]

[0148] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector.

[0149] 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.

[0150] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0151] In some embodiments, the negative electrode film layer may optionally include an adhesive. The adhesive may be selected from 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).

[0152] In some embodiments, the negative electrode film may optionally include a conductive agent. 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.

[0153] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0154] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0155] In other embodiments, the current collector of the negative electrode sheet typically includes a current collector body and a base coating. The base coating can be disposed on at least one side of the current collector body. The base coating basically does not contain negative electrode active material, and may include a small amount of carbon material. However, the carbon material forms a thin coating and cannot function as a negative electrode active material. In this embodiment, the negative electrode sheet can be an electrode sheet without a negative electrode active material layer. For a negative electrode sheet without a negative electrode active material layer, when the current collector of the negative electrode sheet does not contain a base coating, the film layer can be disposed on the surface of at least one side of the current collector; when the current collector of the negative electrode sheet includes a base coating, the film layer can be disposed on the surface of the base coating away from the current collector.

[0156] In some embodiments, the film layer may further include a binder for fixing the additive to the negative electrode sheet. The type of binder is not particularly limited, and those skilled in the art can choose flexibly according to actual needs.

[0157] [Electrolytes]

[0158] 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.

[0159] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0160] 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.

[0161] 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.

[0162] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0163] [Isolation membrane]

[0164] In some embodiments, the battery cell also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0165] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0166] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0167] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0168] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0169] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 shows a square battery cell 5 as an example.

[0170] In some embodiments, referring to FIG4, the outer packaging may include a housing 51 and a cover plate 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 cover plate 53 can be placed over the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0171] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0172] Figure 5 shows a battery module 4 as an example. Referring to Figure 5, 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, the multiple battery cells 5 can be fixed in place using fasteners.

[0173] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0174] 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.

[0175] Figures 6 and 7 illustrate a battery pack 1 as an example. Referring to Figures 6 and 7, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0176] In addition, this application also provides an electrical device, which includes at least one of the battery cell, battery module, or battery pack provided in this application. The battery cell, battery module, or battery pack 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.

[0177] As the electrical device, a single battery cell, a battery module, or a battery pack can be selected according to its usage requirements.

[0178] Figure 8 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 individual battery cells, a battery pack or battery module can be used.

[0179] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0180] Example

[0181] 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.

[0182] The relevant parameters of the battery cells of Examples 1-12 and Comparative Examples 1-10 are shown in Table 1 below.

[0183] Table 1. Relevant parameters of the battery cells in Examples 1-12 and Comparative Examples 1-10

[0184]

[0185] Figure 9 is a scanning electron microscope image of the cross-section of the negative electrode sheet in Embodiment 12 of this application.

[0186] Silicon-carbon composite materials are prepared by the following methods:

[0187] Step 1: Weigh 500g of porous carbon and place it in a reactor (rotary kiln or fluidized bed). Heat it to 500℃ under argon protection and keep it at that temperature for 2 hours to allow the air adsorbed inside the porous carbon to be fully desorbed.

[0188] Step 2: Introduce a mixture of silane and argon gas (silane to argon volume ratio 1:4) into the rotary kiln at a flow rate of 4 L / min, maintain a slight positive pressure of 200 Pa, and rotate the rotary kiln at a rotation frequency of 20 Hz to obtain silicon-carbon particles.

[0189] Step 3: Heat the rotary kiln to 600℃, introduce a mixture of acetylene and argon gas at a flow rate of 3L / min, and rotate the rotary kiln at a rotation frequency of 20Hz to coat the silicon carbide particles.

[0190] Step 4: After natural cooling, the silicon-carbon composite material is obtained by passing it through a 200-mesh sieve.

[0191] Silicon-oxygen composite materials are prepared by the following methods:

[0192] Step 1: Provide a raw material composition according to the content of Al and Mg elements in the target product. The raw material composition includes elemental silicon, silicon oxide, aluminum source (aluminum nitrate), and magnesium source (metallic magnesium).

[0193] Step 2: In a helium atmosphere with an absolute pressure of 30 Pa, the raw material composition is heated to 1300°C to form vapor by vapor deposition, and then the vapor is cooled to 900°C to form a deposit.

[0194] Step 3: Collect the sediment and crush it into powder;

[0195] Step 4: Place the powder in the reaction chamber of the vapor deposition equipment, introduce a mixture of carbon source gas (acetylene) and nitrogen into the reaction chamber, with acetylene accounting for 20% by volume, heat to 750°C, maintain for 2 hours, and obtain carbon-coated product.

[0196] Step 5: Mix the carbon-coated product with a lithium source (lithium ammonia) at a ratio of 100:30 (mass ratio), heat to 650°C, keep warm for 2 hours to carry out the lithiation reaction, collect the product, and obtain the silicon-oxygen composite material.

[0197] In Examples 1-8, 12 and Comparative Examples 1, 4-5, the DV10 particle size of the silicon-containing material was 2.4 μm and the DV90 particle size was 8.8 μm. In Example 9, the DV10 particle size of the silicon-containing material was 2 μm and the DV90 particle size was 5.2 μm. In Example 10, the DV10 particle size of the silicon-containing material was 3 μm and the DV90 particle size was 11 μm. In Example 11, the DV10 particle size of the silicon-containing material was 3.5 μm and the DV90 particle size was 12.6 μm. In Comparative Example 2, the DV10 particle size of the silicon-containing material was 0.5 μm and the DV90 particle size was 4 μm. In Comparative Example 3, the DV10 particle size of the silicon-containing material was 4.3 μm and the DV90 particle size was 15.3 μm. The cumulative particle size distribution map of the silicon-containing material was obtained by using a laser particle size analyzer of model Mastersizer3000. The Dv10, DV50 and DV90 particle sizes of the silicon-containing material can be obtained from the peaks in the cumulative particle size distribution map.

[0198] The number of bright white particles in the first negative electrode film layer and / or the second negative electrode film layer was determined by the following method:

[0199] The negative electrode was prepared using a Japanese electronic ion polisher. The preparation voltage was 7.5 kV, the argon flow rate was 5.5 L / min, and the preparation time was 80 min. The prepared cross-sectional electrode was characterized using a Thermo Fisher Apreo 2s microscope to obtain scanning electron microscope (SEM) images. The SEM images were magnified 500 times. In backscattered light mode, silicon carbon particles were bright white and graphite particles were dark gray. The number of bright white particles in the first and second negative electrode films was counted.

[0200] Lithium iron phosphate was used as the positive electrode active material in Examples 1-12 and Comparative Examples 1-5. The coating amount of the positive electrode active slurry in Examples 1-11 and Comparative Examples 1-5 was 24 mg / cm2, and the coating amount of the positive electrode active slurry in Example 12 was 33 mg / cm2.

[0201] The battery cells of Examples 1-12 and Comparative Examples 1-3, 5-8, and 10 of this application and their preparation methods include the following steps:

[0202] S1. Preparation of the positive electrode sheet

[0203] Lithium iron phosphate (LiFePO4), a positive electrode active material, acetylene black, a conductive agent, and polyvinylidene fluoride, a binder, were mixed in a weight ratio of 97.9:0.5:1.6 and dissolved in the solvent N-methylpyrrolidone (NMP) to prepare a positive electrode slurry. The positive electrode slurry was then uniformly coated onto a 15μm aluminum foil, thoroughly dried, cold-pressed, die-cut, and slit to obtain the positive electrode sheet.

[0204] S2. Preparation of negative electrode sheet

[0205] The negative electrode active material includes graphite and silicon-containing materials (or only graphite). The negative electrode active material, conductive agent carbon black, thickener CMC, binder, and carbon nanotubes are mixed in a weight ratio of 96.4:0.5:1:2:0.1, and deionized water is added. The mixture is stirred evenly under vacuum to obtain a first negative electrode slurry. A second negative electrode slurry is obtained in the same manner. The silicon content in the negative electrode active material of the first and second negative electrode slurries differs. The second negative electrode slurry is then coated onto a 6μm copper foil and dried to form a first negative electrode film precursor. The first negative electrode slurry is then coated onto the surface of the first negative electrode film precursor. After drying, cold pressing, die-cutting, and slitting, a negative electrode sheet is obtained. The coating quality of the first and second negative electrode slurries is the same.

[0206] S3. Preparation of the isolation membrane

[0207] Using a conventional PE base film with a thickness of 5μm, ceramic fiber, styrene-butadiene rubber, polyvinylidene fluoride and water are mixed evenly in a mass ratio of 4:0.9:0.1:5 to obtain a ceramic fiber slurry. The slurry is then uniformly coated onto the surface of the base film using a gravure coating method to form a ceramic fiber layer, and dried at 45℃ to obtain a separator membrane.

[0208] S4. Preparation of electrolyte

[0209] In an argon atmosphere glove box with a water content of <10ppm, ethylene carbonate (EC), ethyl methyl carbonate, and dimethyl carbonate (DMC) are mixed in a volume ratio of 3:3:4. Then, lithium hexafluorophosphate (LiPF6) is uniformly dissolved in the solvent, and FEC is added to obtain the electrolyte.

[0210] S5, Assembly

[0211] The positive electrode, separator, and negative electrode are prepared in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then wound, hot-pressed and shaped by applying pressure to the flat area, and welded to obtain the electrode assembly. The electrode assembly is placed in a square aluminum shell, vacuum dried, and then injected with electrolyte. After standing, formation testing, aging, and capacity testing, a battery cell with a final volume of 0.411L is obtained.

[0212] The battery cells of Comparative Examples 4 and 9 of this application and their preparation methods include the following steps:

[0213] S1. Preparation of the positive electrode sheet

[0214] Lithium iron phosphate (LiFePO4), a positive electrode active material, acetylene black, a conductive agent, and polyvinylidene fluoride, a binder, were mixed in a weight ratio of 97.9:0.5:1.6 and dissolved in the solvent N-methylpyrrolidone (NMP) to prepare a positive electrode slurry. The positive electrode slurry was then uniformly coated onto a 15μm aluminum foil, thoroughly dried, cold-pressed, die-cut, and slit to obtain the positive electrode sheet.

[0215] S2. Preparation of negative electrode sheet

[0216] The negative electrode active material includes graphite and silicon-containing materials. The negative electrode active material, conductive agent carbon black, thickener CMC, binder, and carbon nanotubes are mixed in a weight ratio of 96.4:0.5:1:2:0.1, and deionized water is added. The mixture is stirred evenly under vacuum to obtain a negative electrode slurry. The negative electrode slurry is then coated onto a 6μm copper foil, dried, cold-pressed, die-cut, and slit to obtain the negative electrode sheet.

[0217] S3. Preparation of the isolation membrane

[0218] Using a conventional PE base film with a thickness of 5μm, ceramic fiber, styrene-butadiene rubber, polyvinylidene fluoride and water are mixed evenly in a mass ratio of 4:0.9:0.1:5 to obtain a ceramic fiber slurry. The slurry is then uniformly coated onto the surface of the base film using a gravure coating method to form a ceramic fiber layer, and dried at 45℃ to obtain a separator membrane.

[0219] S4. Preparation of electrolyte

[0220] In an argon atmosphere glove box with a water content of <10ppm, ethylene carbonate (EC), ethyl methyl carbonate, and dimethyl carbonate (DMC) are mixed in a volume ratio of 3:3:4. Then, lithium hexafluorophosphate (LiPF6) is uniformly dissolved in the solvent, and FEC is added to obtain the electrolyte.

[0221] S5, Assembly

[0222] The positive electrode, separator, and negative electrode are prepared in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then wound, hot-pressed and shaped by applying pressure to the flat area, and welded to obtain the electrode assembly. The electrode assembly is placed in a square aluminum shell, vacuum dried, and then injected with electrolyte. After standing, formation testing, aging, and capacity testing, a battery cell with a final volume of 0.411L is obtained.

[0223] In addition, the cycle performance and DC resistance of the battery cells prepared in Examples 1-12 and Comparative Examples 1-10 were measured, and the results are shown in Table 2.

[0224] The testing method is as follows:

[0225] 1. Cyclic performance

[0226] At 25℃, the secondary battery was left to stand for 30 minutes, then charged at a 0.5C rate to 3.8V, and further charged at a constant voltage of 3.8V to a current of 0.05C. It was then left to stand for 5 minutes, and finally discharged at a 0.5C rate to a voltage of 2.0V. The resulting capacity was recorded as the initial capacity C0. This constitutes one charge-discharge cycle. The above steps were repeated for the same secondary battery, recording the discharge capacity Cn at each cycle. The battery capacity retention rate after each cycle was Pn = Cn / C0 * 100%, continuing until Pn ≦ 80%, at which point the test was stopped, and the number of cycles was recorded.

[0227] 2. DC resistance

[0228] Set the constant temperature chamber to 25℃, place the battery cell inside, and let it stand for 30 minutes. Then, charge it to 3.8V using a constant voltage of 0.33C, followed by charging at 3.8V until the current is less than 0.05C, and let it stand for 5 minutes. Discharge it with a constant current of 1C for 54 minutes, adjust the battery cell charge to 10% SOC, and let it stand for 60 minutes. Record the battery cell voltage V0. Discharge it with a constant current of 4C for 30 seconds, and record the battery cell voltage V1 at this time. Calculate the DC resistance: DCR = (V1 - V0) / 4C current.

[0229] Table 2. Cycle performance and DC resistance of the battery cells prepared in Examples 1-12 and Comparative Examples 1-10

[0230]

[0231] As shown in Examples 1-4 and Examples 5-8, when the silicon content in the negative electrode film is 1.5 wt%, the number of cycles to 80% SOC for a single battery cell is 2500-2830 cls, and the DC resistance at 10% SOC is 1800-1925 mΩ; when the silicon content in the negative electrode film is 3 wt%, the number of cycles to 80% SOC for a single battery cell is 1800-2300 cls, and the DC resistance at 10% SOC is 1885-2000 mΩ. Furthermore, the greater the difference in silicon content between the first and second negative electrode films, the smaller the DC resistance at 10% SOC, but the lower the number of cycles to 80% SOC for the single battery cell.

[0232] As shown in Examples 1 and 9-11, when the Dv50 particle size of the silicon-carbon composite material is 3μm to 8.5μm, the number of cycles for a single cell to reach 80% SOC is 2430 to 2870cls, and the DC resistance at 10% SOC is 1657 to 1920mΩ. Furthermore, as the Dv50 particle size of the silicon-carbon composite material increases, the number of cycles for a single cell to reach 80% SOC increases, but the DC resistance at 10% SOC also increases.

[0233] Comparing Examples 1 and 12, it can be seen that the coating amount of the positive electrode active slurry in Example 1 is 24 mg / cm2, while the coating amount of the positive electrode active slurry in Example 12 is 33 mg / cm2. The DC resistance at 10% SOC of Example 12 is higher than that at 10% SOC of Example 1.

[0234] Comparing Comparative Example 1 and Example 1, it can be seen that Comparative Example 1 uses silicon-oxygen composite material as silicon-containing material. The number of cycles of the battery cell of Comparative Example 1 to 80% SOC is only 1300cls, which is much lower than that of Example 1. The DC resistance of Comparative Example 1 at 10% SOC is 3023mΩ, which is much higher than that of Example 1.

[0235] Comparing Comparative Example 2 and Example 1, it can be seen that the Dv50 particle size of the silicon-carbon composite material used in Comparative Example 2 is only 2 μm, and the number of cycles of the battery cell in Comparative Example 2 to 80% SOC is only 1500 cls, which is much lower than that in Example 1.

[0236] Comparing Comparative Example 3 and Example 1, it can be seen that the Dv50 particle size of the silicon-carbon composite material used in Comparative Example 3 is 10 μm, and the DC resistance of Comparative Example 3 at 10% SOC is 2783 mΩ, which is much higher than that of Example 1.

[0237] As can be seen from the comparison between Comparative Example 4 and Example 1, the negative electrode film layer of Comparative Example 4 does not include the first negative electrode film layer and the second negative electrode film layer, but is a whole, wherein the silicon-containing material is uniformly distributed in the negative electrode film layer. The DC resistance of Comparative Example 4 at 10% SOC is 1935mΩ, which is higher than that of Example 1.

[0238] As can be seen from the comparison between Comparative Example 5 and Example 1, the mass ratio of silicon-carbon composite material in the first negative electrode film layer of Comparative Example 5 is less than that in the second negative electrode film layer. The silicon content in the first negative electrode film layer is 1 wt%, and the silicon content in the second negative electrode film layer is 2 wt%. The DC resistance of Comparative Example 5 at 10% SOC is 2300 mΩ, which is much higher than that of Example 1.

[0239] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A battery cell, wherein, The battery cell includes a positive electrode and a negative electrode. The positive electrode includes a positive active material, which includes a lithium phosphate. The negative electrode includes a negative film and a negative current collector. The negative film includes a silicon-carbon composite material and graphite. The silicon-carbon composite material includes a porous carbon matrix and silicon-containing materials distributed in the porous carbon matrix. The Dv50 particle size of the silicon-carbon composite material is 3μm~8.5μm. The negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. The second negative electrode film layer is disposed between the first negative electrode film layer and the negative electrode current collector. The mass percentage of silicon-carbon composite material in the first negative electrode film layer is W1, and the mass percentage of silicon-carbon composite material in the second negative electrode film layer is W2, where W1 > W2.

2. The battery cell of claim 1, wherein, The Dv50 particle size of the silicon-carbon composite material is 3μm~7.5μm.

3. The battery cell of claim 1 or 2, wherein, The diameter of the silicon-carbon composite material is ≤1.

1.

4. The battery cell of claim 3, wherein, The silicon-carbon composite material has a Dv10 particle size ≥ 2 μm and a Dv90 particle size ≤ 18 μm.

5. The battery cell of any one of claims 1-4, wherein, W1 > 2W2.

6. The battery cell of any one of claims 1-5, wherein, At least two-thirds of the silicon-carbon composite material in the negative electrode film is located in the first negative electrode film.

7. The battery cell of any one of claims 1-6, wherein, In the scanning electron microscope image of the cross-section of the negative electrode sheet, the number of silicon-carbon particles in the first negative electrode film is ≥10, and the number of silicon-carbon particles in the second negative electrode film is <10. The test methods for the number of silicon-carbon particles in the first negative electrode film and the number of silicon-carbon particles in the second negative electrode film are as follows: The negative electrode was prepared using a Japanese electronic ion polisher. The preparation voltage was 7.5 kV, the argon flow rate was 5.5 L / min, and the preparation time was 80 min. The prepared cross-sectional electrode was characterized using a Thermo Fisher Apreo 2s microscope to obtain scanning electron microscope (SEM) images. The SEM images were magnified 500 times. In backscattered light mode, silicon carbon particles were bright white and graphite particles were dark gray. The number of bright white particles in the first negative electrode film and the second negative electrode film were counted.

8. The battery cell of any one of claims 1-7, wherein, The mass percentage of silicon in the negative electrode film is greater than 0 and less than or equal to 9 wt%.

9. The battery cell of claim 8, wherein, The silicon element in the first negative electrode film layer accounts for 2wt% to 3wt% by mass, and the silicon element in the second negative electrode film layer accounts for 0wt% to 1wt% by mass.

10. The battery cell of any one of claims 1-9, wherein, The capacity of the negative electrode sheet is greater than 370mAh / g and less than or equal to 700mAh / g.

11. The battery cell of claim 10, wherein, The capacity of the first negative electrode film is 435mAh / g to 470mAh / g, and the capacity of the second negative electrode film is 370mAh / g to 400mAh / g.

12. A method of producing a battery cell, wherein, The method for preparing the battery cell includes: preparing a positive electrode sheet and a negative electrode sheet respectively, wherein the positive electrode sheet includes a positive active material, the positive active material includes a lithium phosphate, the negative electrode sheet includes a negative electrode film and a negative current collector, the negative electrode film includes a silicon-carbon composite material and graphite, the silicon-carbon composite material includes a porous carbon matrix and silicon-containing materials distributed in the porous carbon matrix, the Dv50 particle size of the silicon-carbon composite material is 3μm~8.5μm, and the silicon-carbon composite material is prepared by chemical vapor deposition; The negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. The second negative electrode film layer is disposed between the first negative electrode film layer and the negative electrode current collector. The mass ratio of silicon-carbon composite material in the first negative electrode film layer is higher than the mass ratio of silicon-carbon composite material in the second negative electrode film layer.

13. The method of claim 12, wherein the battery cell is a lithium-ion battery cell. In the preparation of the lithium-containing phosphate, carbon coating was performed using chemical vapor deposition.

14. The method of producing a battery cell according to claim 12 or 13, wherein, The preparation of the positive electrode sheet includes coating the surface of the positive current collector with a positive active slurry, wherein the coating amount of the positive active slurry is 16 mg / cm2 to 32.5 mg / cm2.

15. A battery, wherein, The battery comprises a battery cell according to any one of claims 1 to 11 or a battery cell prepared by a method according to any one of claims 12 to 14.

16. An electrical device, comprising: The electrical device includes the battery of claim 15, the battery being used to provide electrical energy.

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