Battery cell and preparation method therefor, and electric device

Abstract

A battery cell and a preparation method therefor, and an electric device. The battery cell comprises a negative electrode sheet. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material film layer provided on at least one side of the negative electrode current collector. The negative electrode active material film layer comprises graphite and a silicon-carbon material, wherein the silicon-carbon material has an average sphericity Φ of 0.8-1.0. The electric device comprises the battery cell.

Description

Battery cells, their preparation methods, and electrical devices

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese patent application 202410813492.X, filed on June 21, 2024, entitled “Battery cell and method of preparation thereof and electrical device thereof”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application belongs to the field of battery cell technology, specifically relating to a battery cell, its preparation method, and an electrical device thereof. Background Technology

[0004] A battery cell, also called a rechargeable battery cell, is a single battery unit that can be repeatedly charged and discharged for multiple uses. In recent years, with the increasingly widespread application of battery cells, represented by lithium-ion battery cells, people have placed higher demands on their performance, especially their cycle performance.

[0005] However, the current problem is that when increasing the energy density of a single battery cell, the cycle performance of that cell is significantly affected.

[0006] Summary of the Invention

[0007] The purpose of this application is to provide a battery cell whose negative electrode comprises graphite and silicon-carbon materials. During use, the silicon-carbon material exhibits a high average sphericity, thereby improving the cycle performance and reliability of the high-energy-density battery cell. A further purpose of this application is to provide an electrical device incorporating this battery cell, thereby achieving improved cycle performance of the battery cell.

[0008] In a first aspect, embodiments of this application provide a battery cell comprising a negative electrode sheet, the negative electrode sheet comprising a negative current collector and a negative active material film layer disposed on at least one side of the negative current collector, the negative active material film layer comprising graphite and silicon-carbon materials, wherein the average sphericity Φ of the silicon-carbon material is 0.8 to 1.0.

[0009] The battery cell in this embodiment includes a negative electrode sheet, which comprises silicon-carbon material and graphite. The average sphericity Φ of the silicon-carbon material powder is 0.8 to 1.0, indicating that the particles in the silicon-carbon material have high roundness, which is beneficial to reducing the cycle degradation problem caused by lithium plating, thereby improving battery reliability. The silicon-carbon material with high average sphericity has a natural slippage effect between the silicon-carbon material and the graphite particles, which is beneficial to the fracture elongation of the negative electrode sheet and to reducing the microcracks in the negative electrode sheet during the cycle of the battery cell, thereby improving the cycle performance of the high-energy-density battery cell and thus improving the reliability of the battery cell.

[0010] The natural slippage between silicon-carbon materials with high average sphericity and graphite particles is also reflected in the degree of particle breakage. If the silicon-carbon material with sharp edges breaks, compared with the silicon-carbon material with an average sphericity Φ of 0.8 to 1.0 in this application, the silicon-carbon material with sharp edges has a larger specific surface area. This results in a decrease in the initial coulombic efficiency of the battery cell containing the silicon-carbon material with sharp edges and the formation of an SEI film by active ions, which increases the loss of active ions, such as lithium ions, and affects the initial coulombic efficiency and cycle performance. Therefore, the silicon-carbon material of this application can improve the initial coulombic efficiency and cycle performance in the battery cell.

[0011] In addition, the negative electrode sheet in the battery cell contains graphite and silicon-carbon materials. The silicon-carbon materials with high average sphericity and roundness have a natural slippage effect with the graphite particles, which helps to reduce the probability of internal breakage of the electrode assembly containing the negative electrode sheet during the preparation and winding process, thereby improving the yield of the battery cell.

[0012] In some alternative implementations, the average sphericity Φ of the silicon-carbon material is 0.85≤B≤0.95.

[0013] According to the embodiments of this application, the average sphericity of the silicon-carbon material is within the above-mentioned range. During the preparation and use of the negative electrode sheet containing the silicon-carbon material, it is beneficial to further reduce the internal breakage of the electrode assembly containing the negative electrode sheet during winding, and further improve the yield of the battery cell.

[0014] In addition, the negative electrode sheet contains silicon-carbon material with high average sphericity, which further improves the cycle capacity stability of the high energy density battery cell containing the negative electrode sheet, thereby improving the reliability of the battery cell.

[0015] In some alternative embodiments, the silicon-carbon material includes:

[0016] A carbon matrix having a porous structure, the carbon matrix comprising silicon-based materials located within the porous structure;

[0017] A carbon coating layer, at least partially coating the surface of a carbon matrix.

[0018] According to embodiments of this application, the silicon-based material is located on a carbon matrix. The carbon matrix restricts the volume deformation of the silicon-based material, enhances the structural stability of the silicon-carbon material, reduces the volume change rate of the silicon-based material, and helps maintain the structural stability of the negative electrode active material film, thereby improving the cycle performance and electrical reliability of the battery cell. The presence of the carbon coating layer helps reduce the contact area with the electrolyte, thus reducing the risk of lithium plating.

[0019] This application does not impose specific limitations on the types and structures of silicon-based materials. In some optional embodiments, silicon-based materials include one or more of elemental silicon, silicon oxide, silicon-carbon composite materials, and silicon alloy materials.

[0020] In some alternative embodiments, the tap density of the silicon carbide material is 0.9 g / cm³. 3 Up to 1.15 g / cm 3 The option is 1.03 g / cm³. 3 Up to 1.14 g / cm 3 When the tap density of silicon-carbon material is within the above range, due to the suitable sphericity of the silicon-carbon material, there is more silicon-carbon material in the relative volume, which can improve the tap density and elongation of the negative electrode active material film layer, thereby further improving the energy density and cycle performance of the battery cell.

[0021] In some alternative implementations, the volumetric particle size Dv of the silicon-carbon material 1 50 is available in sizes from 4μm to 12μm, with options from 4μm to 6μm and from 8μm to 12μm.

[0022] The volumetric particle size Dv of silicon-carbon materials 1 When 50 is within the above range, the natural slippage between silicon-carbon material with high average sphericity and graphite particles in the negative electrode active material film layer is enhanced, further reducing the internal breakage of the electrode assembly containing the negative electrode sheet during winding, further improving the cell yield, further improving the cycle performance of high energy density battery cells, and thus improving the reliability of battery cells.

[0023] In some alternative embodiments, the particle size distribution span (SPAN) of the silicon-carbon material is 1.2 to 1.6; optionally 1.2 to 1.4; optionally 1.5 to 1.6.

[0024] When the particle size distribution span (SPAN) of silicon-carbon material is within the above range, it indicates that the particle size distribution of silicon-carbon material powder is relatively narrow. The natural slippage between silicon-carbon material with high average sphericity and graphite particles in the negative electrode active material film layer is enhanced, further reducing the internal breakage of the electrode assembly containing the negative electrode sheet during winding, further improving the yield of the battery cell, further improving the cycle performance of high energy density battery cells, and thus improving the reliability of the battery cells.

[0025] In some alternative embodiments, the silicon-carbon material comprises 40% to 60% silicon and 40% to 60% carbon by mass percentage.

[0026] According to embodiments of this application, silicon can improve the overall capacity and energy density of silicon-carbon materials, while carbon, as a conductive agent, helps improve the conductivity of individual battery cells, but its specific capacity is generally relatively low. When the silicon and carbon content in silicon-carbon materials are within the aforementioned ranges, it can maintain the structural stability of the silicon-carbon material, which is beneficial for improving cycle performance, and also increase the overall capacity of the silicon-carbon material and the energy density of individual battery cells.

[0027] In some alternative implementations, the peak intensity ID of the D peak and the peak intensity IG of the G peak in the Raman spectrum of the silicon-carbon material satisfy 1.5 < ID / IG < 2.5.

[0028] According to the embodiments of this application, if the ID / IG ratio of carbon in the Raman spectrum of silicon-carbon material is within the above range, the carbon phase structure in silicon-carbon material can be evaluated, indicating that the degree of carbon graphitization is high, and silicon-carbon material has good electrical conductivity and mechanical stability, which is beneficial to the cycle performance of battery cells.

[0029] In some alternative embodiments, the average strength of the silicon-carbon material is from 20 MPa to 50 MPa, and optionally from 41 MPa to 48 MPa.

[0030] The silicon-carbon material has the above-mentioned average strength, indicating that it has suitable softness and hardness, and the maximum stress that the material can withstand is within a suitable range. Therefore, during the preparation and use of the negative electrode containing this silicon-carbon material, the particle breakage rate of the silicon-carbon material is reduced, which is beneficial to maintaining the structural stability of the negative electrode active material film layer and enabling the battery to have better cycle performance.

[0031] In some alternative implementations, the volumetric particle size Dv of graphite 2 50 is 14μm to 18μm, and can be selected from 15μm to 17μm.

[0032] Graphite volumetric particle size Dv 2 When 50 is within the above range, the negative electrode active material film layer contains silicon-carbon material with high average sphericity and graphite with the above volume particle size. The slippage between the two is enhanced, further reducing the internal breakage of the electrode assembly containing the negative electrode sheet during winding, further improving the cell yield, further improving the cycle performance of high energy density battery cells, and thus improving the reliability of battery cells.

[0033] In some alternative embodiments, the mass ratio of graphite to silicon carbide is 1:(0.66 to 1.5).

[0034] Optionally, the mass ratio of graphite to silicon carbide can be any value or a range of combinations thereof from 1:0.66, 1:0.7, 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5.

[0035] According to embodiments of this application, graphite typically has a layered structure at the microscopic level, exhibiting good conductivity and structural stability. Silicon-carbon materials have a higher specific capacity, but their volume expansion rate is relatively larger than that of graphite. When the mass ratio of graphite to silicon-carbon materials is within the aforementioned range, it can maintain the structural stability of the negative electrode active material film, which is beneficial for improving cycle capacity performance. Furthermore, it can increase the specific capacity of the negative electrode active material film, thereby increasing the energy density of the battery cell.

[0036] In some optional embodiments, the silicon-carbon material includes a first silicon-carbon material and a second silicon-carbon material, wherein the volumetric particle size Dv of the first silicon-carbon material is... 3 50 is smaller than the volumetric particle size Dv of the second silicon-carbon material 4 50.

[0037] According to the embodiments of this application, combining a first silicon-carbon material and a second silicon-carbon material with different volume particle sizes is beneficial to improving the compaction density of the negative electrode active material film layer and further improving the energy density of the battery cell.

[0038] In some alternative embodiments, the volumetric particle size Dv of the first silicon-carbon material 3 50 is 4μm to 6μm; the volumetric particle size Dv of the second silicon-carbon material 4 50 ranges from 8μm to 12μm.

[0039] According to the embodiments of this application, the first silicon-carbon material and the second silicon-carbon material with different volume particle sizes are combined to further improve the compaction density of the negative electrode active material film layer and further improve the energy density of the battery cell.

[0040] In some alternative embodiments, the particle size distribution span (SPAN) of the first silicon carbide material is 1.5 to 1.6; and the particle size distribution span (SPAN) of the second silicon carbide material is 1.2 to 1.4.

[0041] According to the embodiments of this application, the first silicon-carbon material and the second silicon-carbon material with different particle size distribution spans are combined to indicate that the particle size distribution of the first silicon-carbon material and the second silicon-carbon material is relatively narrow, which further improves the compaction density of the negative electrode active material film layer and further improves the energy density of the battery cell.

[0042] In some alternative embodiments, the mass ratio of the first silicon carbide material to the second silicon carbide material is (1-4):1.

[0043] According to the embodiments of this application, the mass ratio of the first silicon-carbon material to the second silicon-carbon material is within the above range, and the negative electrode active material film layer includes the first silicon-carbon material and the second silicon-carbon material, which further improves the compaction density of the negative electrode active material film layer and further improves the energy density of the battery cell.

[0044] In some alternative embodiments, the negative electrode active material film layer includes a binder and a conductive agent.

[0045] In this application embodiment, the type of binder is not explicitly limited; any binder that can be applied to the slurry of the negative electrode sheet and has a certain binding effect can be used in this application embodiment. In some optional embodiments, the negative electrode active material film layer includes a binder. Optionally, the binder includes one or more of the following: carboxymethyl cellulose, polyacrylic acid and its modified derivatives, polyacrylamide and its modified derivatives, polyvinyl alcohol and its modified derivatives, polyacrylonitrile and its modified derivatives, polyethyleneimine and its modified derivatives, styrene-butadiene rubber and its modified derivatives, styrene-acrylic emulsion and its modified derivatives, polyacrylate and its modified derivatives, polyurethane and its modified derivatives, sodium alginate and its modified derivatives, guar gum and its modified derivatives, xanthan gum and its modified derivatives, gum arabic and its modified derivatives, β-cyclodextrin polymers, and carrageenan and its modified derivatives. In some optional embodiments, the negative electrode active material film layer includes a thickener. The thickener may be carboxymethyl cellulose and its salts.

[0046] In this application embodiment, the type of conductive agent is not explicitly limited. Any conductive agent that can be applied to the slurry of the negative electrode sheet and has a good conductive effect can be used in this application embodiment. In order to further improve the conductivity of the negative electrode sheet and reduce its internal resistance, in some optional embodiments, the conductive agent includes one or more of carbon nanotubes, graphene, carbon nanofibers, superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, and carbon dots.

[0047] In some alternative embodiments, the compaction density of the negative electrode active material film is 1.3 g / cm³. 3 Up to 1.8 g / cm 3 1.4g / cm³ is an optional value. 3 Up to 1.6 g / cm 3 The compaction density of the negative electrode active material film layer is within the above range, which can further improve the energy density of the battery cell; the negative electrode active material film layer contains silicon-carbon material, which has a suitable pore structure, improving the wetting and retention characteristics of the negative electrode active material film layer to the electrolyte, thereby further improving the cycle performance of the battery cell.

[0048] In some alternative embodiments, the elongation at break of the negative electrode sheet under pressures of 1.3 MPa to 1.6 MPa is 1% to 3.5%. An elongation at break of the negative electrode sheet within this range can improve the flexibility of the electrode sheet, reduce the probability of brittle fracture, and thus improve the reliability of the battery.

[0049] In some alternative embodiments, in order to improve the performance of the negative electrode in the battery cell and improve the charge and discharge performance of the battery cell, the battery cell includes an electrolyte with a viscosity of 2 to 15 mPa*S.

[0050] In some alternative embodiments, in order to improve the performance of the negative electrode in the battery cell and improve the charge and discharge performance of the battery cell, the battery cell includes an electrolyte with a conductivity of 9 to 15 mS / cm.

[0051] The viscosity and conductivity of the electrolyte can be adjusted using methods commonly used in the art. In some alternative embodiments, the battery cell includes an electrolyte comprising an acetate compound, wherein the acetate compound includes one or more of methyl acetate, ethyl acetate, and propyl acetate.

[0052] Secondly, embodiments of this application provide a method for preparing a battery cell, comprising: winding a component including a negative electrode sheet to obtain a battery cell, wherein the negative electrode sheet includes a negative current collector and a negative active material film layer disposed on at least one side of the negative current collector, the negative active material film layer including graphite and silicon-carbon material, wherein the average sphericity Φ of the silicon-carbon material is 0.8 to 1.0.

[0053] Thirdly, embodiments of this application provide an electrical device comprising a battery cell according to the first aspect or a battery cell prepared by the second aspect. The electrical device of this application comprises a battery cell according to the first aspect or a battery cell prepared by the second aspect, and therefore possesses at least the corresponding advantages of a battery cell. Attached Figure Description

[0054] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0055] Figure 1 shows a schematic diagram of one embodiment of the battery cell of this application.

[0056] Figure 2 shows an exploded view of the battery cell shown in Figure 1.

[0057] Figure 3 shows a schematic diagram of one embodiment of an electrical device that uses the battery cell of this application as a power source.

[0058] Figure 4 shows the elongation at break of the negative electrode sheet in the embodiments and comparative examples of this application.

[0059] Figure 5 shows the specific capacity of negative electrode sheets with different compaction densities in the embodiments and comparative examples of this application.

[0060] Figure 6 shows the silicon-carbon material in a fresh negative electrode sheet, which is a comparative example of this application.

[0061] Figure 7 illustrates the silicon-carbon material in a fresh negative electrode sheet according to an embodiment of this application.

[0062] The accompanying drawings are not necessarily drawn to scale. Detailed Implementation

[0063] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the battery cell, its preparation method, and the electrical device thereof. 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 for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0064] 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 the 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 specific parameters, it is understood that ranges of 60–110 and 80–120 are also expected. 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 "a–b" represents a shortened representation of any combination of real numbers between a and b, characterized in that a and b are both 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.

[0065] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0066] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0067] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0068] Unless otherwise specified, in this application, the terms "first," "second," "third," "fourth," etc., are used to distinguish different objects, rather than to describe a specific order or primary / secondary relationship.

[0069] Unless otherwise specified, in this application, the term "active ion" refers to ions that can be inserted and extracted back and forth between the positive and negative electrodes of a battery cell, including but not limited to lithium ions.

[0070] In this application, "several" or "multiple" refers to two or more (including two). In this application, "several items" or "multiple items" refers to two or more (including two, three, etc.).

[0071] The battery cells mentioned in the embodiments of this application may be lithium-ion battery cells, lithium metal battery cells, etc., and the embodiments of this application are not limited to this.

[0072] Cycle performance is a key performance indicator for individual battery cells. Generally, increasing the energy density of a battery cell may lead to a decrease in cycle performance, or vice versa. This is because pursuing higher energy density may require certain material or structural designs. For example, adding angular silicon materials to increase the energy density of a battery cell can affect its cycle capacity.

[0073] Therefore, how to make high-energy-density battery cells also have good cycle performance is a technical problem that urgently needs to be solved.

[0074] As a crucial component of a battery cell, the performance of the negative electrode sheet has a significant impact on the overall performance of the cell. Currently, graphite is the most commonly used negative electrode active material, but the energy density of cells using it is already close to the theoretical value. Silicon materials have the advantage of high theoretical energy density, which can significantly improve the energy density of battery cells; however, this affects the cycle performance of the battery cells and requires further improvement.

[0075] In view of this, the technical solution of the present application provides a battery cell, a method for preparing the same, and an electrical device, which enables the battery cell to achieve both high energy density and good cycle performance.

[0076] Specifically, this application provides a single battery cell.

[0077] This application does not impose any particular limitation on the type of battery cell; it can be any battery cell, such as a lithium-ion battery cell, a lithium metal battery cell, etc. The embodiments of this application are not limited in this regard. Typically, a battery cell includes an electrode assembly and an electrolyte. The electrode assembly may include a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes. During the charging and discharging process of the battery cell, active ions move back and forth between the positive and negative electrodes, inserting and extracting, and the electrolyte plays the role of conducting ions. This application does not impose any particular limitation on the type of electrolyte; it can be selected according to actual needs. For example, the electrolyte can be selected from one or more of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0078] battery cell

[0079] In a first aspect, embodiments of this application provide a battery cell including a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative active material film layer disposed on at least one side of the negative current collector, the negative active material film layer including graphite and silicon-carbon materials, wherein the average sphericity Φ of the silicon-carbon material is 0.8 to 1.0.

[0080] Sphericity refers to the degree to which the shape of a particle closely approximates an ideal sphere, and is usually calculated as the ratio of the particle's surface area to the surface area of ​​a sphere of equal volume. The mean sphericity is the average sphericity value for powder materials such as silicon-carbon. The formula for sphericity can be:

[0081] Φ=A particle / A sphere

[0082] Where: Φ represents sphericity; A sphere A represents the surface area of ​​an ideal sphere with the same volume as the particle; particle This represents the actual surface area of ​​the particle.

[0083] The average sphericity of silicon-carbon materials can be tested using methods known in the art. As an example, characterization can be performed using the Malvern Morphologi G3-ID instrument and its accompanying graphics software. For instance, a series of two-dimensional images of silicon-carbon powder particles with equal thickness and diameter are captured using a microscope, and the volume of the powder particles is estimated using their area and perimeter. The surface area of ​​an equal-volume sphere is calculated from the volume, and this is compared with the actual detected surface area of ​​the powder particles to obtain the sphericity.

[0084] Graphite can include one or both of artificial and natural graphite. Graphite is a material with good electrical conductivity and chemical stability. It can adsorb and release active ions, such as lithium ions. These active ions are inserted into or extracted within the graphite lattice, enabling the charging and discharging process of a battery cell. Graphite has a stable crystal structure, which helps maintain the shape and stability of the electrodes, contributing to extending the lifespan of battery cells and improving cycle stability.

[0085] Compared to graphite, silicon-carbon materials have superior specific capacity and a greater volume change rate due to the presence of silicon.

[0086] The negative electrode sheet in the battery cell of this application embodiment contains silicon-carbon material and graphite. The average sphericity Φ of the silicon-carbon material powder is 0.8 to 1.0, indicating that the particles in the silicon-carbon material have high roundness. The high average sphericity and roundness of the silicon-carbon material have a natural sliding effect with the graphite particles. Moreover, the relatively rounded particles in the silicon-carbon material are beneficial to improving the fracture elongation rate of the negative electrode sheet at the corner of the cell, reducing the battery capacity decay caused by lithium plating, thereby improving the cycle performance of the high-energy-density battery cell and thus improving the reliability of the battery cell.

[0087] Research has revealed that existing silicon-carbon materials generally require crushing processes, such as air jet milling, resulting in powders with distinct edges and corners. Furthermore, the cold pressing process during the fabrication of the negative electrode sheet can cause particle breakage, and the sharp edges can damage the negative electrode sheet, leading to breakage and affecting the battery's initial coulombic efficiency and cycle performance. In contrast, the silicon-carbon material with higher sphericity described in this application is prepared via emulsion polymerization. This silicon-carbon material is naturally formed during synthesis, eliminating the need for crushing processes, and contains a smaller proportion of angular silicon-carbon material.

[0088] High-energy-density battery cells typically use silicon-carbon particles with sharp edges. During the fabrication of the negative electrode sheet, the cold-pressing process damages this type of substrate. When the electrode assembly containing this negative electrode sheet is wound, the sharp edges of the silicon-carbon particles make the cell prone to internal breakage, reducing the yield of the electrode assembly. In the wound electrode sheet, the corners are particularly fragile; the sharp edges of the silicon-carbon particles in existing technologies can cause corner breakage, leading to lithium plating, cycle degradation, and even a significant drop in the battery cell's capacity, resulting in low battery cell reliability.

[0089] The natural slippage between silicon-carbon materials with high average sphericity and graphite particles is also reflected in the degree of particle breakage. If the silicon-carbon material with sharp edges breaks, compared with the silicon-carbon material with an average sphericity Φ of 0.8 to 1.0 in this application, the silicon-carbon material with sharp edges has a larger specific surface area, resulting in a decrease in initial coulombic efficiency and the formation of an SEI film by active ions, which increases the loss of active ions, such as lithium ions, and affects the initial coulombic efficiency and cycle performance. Therefore, the silicon-carbon material of this application can improve the initial coulombic efficiency and cycle performance in battery cells.

[0090] The negative electrode sheet in the battery cell of this application contains graphite and silicon-carbon materials. The silicon-carbon materials with high average sphericity and roundness have a natural slippage effect with the graphite particles, which is beneficial to improving the corner fracture elongation rate or the tolerance of the electrode sheet extension state. This helps to reduce the probability of corner fracture of the electrode assembly containing the negative electrode sheet during cell manufacturing and improve the cell yield.

[0091] Optionally, the average sphericity Φ of the silicon-carbon material can be any value or a range of combinations thereof from 0.80, 0.82, 0.84, 0.86, 0.88, 0.90, 0.92, 0.94, 0.96, 0.98, 1.00.

[0092] In some alternative implementations, the average sphericity Φ of the silicon-carbon material is 0.85≤B≤0.95.

[0093] According to the embodiments of this application, the average sphericity of the silicon-carbon material is within the above-mentioned range. During the preparation and use of the negative electrode sheet containing the silicon-carbon material, it is beneficial to further reduce the internal breakage of the electrode assembly containing the negative electrode sheet during winding, and further improve the yield of the battery cell.

[0094] In addition, the negative electrode in the battery cell contains silicon-carbon material with high average sphericity, which further improves the elongation of the negative electrode and enhances the cycle performance of the high-energy-density battery cell containing the negative electrode, thereby improving the reliability of the battery cell.

[0095] In some alternative embodiments, the silicon-carbon material includes:

[0096] A carbon matrix having a porous structure includes a silicon-based material located within the porous structure. According to embodiments of this application, the silicon-based material is located within the carbon matrix. The carbon matrix restricts the volumetric deformation of the silicon-based material, enhancing the structural stability of the silicon-carbon material, reducing the volume change rate of the silicon-based material, which is beneficial for maintaining the structural stability of the negative electrode active material film layer, improving the cycle performance and electrical reliability of the battery cell.

[0097] In some alternative embodiments, the silicon-carbon material includes:

[0098] A carbon matrix having a porous structure, the carbon matrix comprising silicon-based materials located within the porous structure;

[0099] A carbon coating layer, at least partially coating the surface of a carbon matrix.

[0100] According to embodiments of this application, the silicon-based material is located on a carbon matrix. The carbon matrix restricts the volumetric deformation of the silicon-based material, enhancing its structural stability and reducing its volume change rate. This helps maintain the structural stability of the negative electrode active material film, improving the cycle performance and electrical reliability of the battery cell. The presence of the carbon coating layer reduces the contact area between the silicon-carbon material and the electrolyte, lowering the risk of lithium plating. Furthermore, the carbon coating layer helps maintain the stability of the silicon-carbon material's performance and facilitates its storage and transportation.

[0101] The presence of a carbon coating on the surface of silicon-carbon materials can be determined using a transmission electron microscope.

[0102] Silicon-carbon materials consist of a carbon coating layer, a carbon matrix containing a porous structure, and silicon-based materials inside the porous structure. These can be comprehensively identified using transmission electron microscopy and XPS elemental analysis.

[0103] This application does not impose specific limitations on the types and structures of silicon-based materials. In some optional embodiments, silicon-based materials include one or more of elemental silicon, silicon oxide, silicon-carbon composite materials, and silicon alloy materials.

[0104] In some alternative embodiments, the tap density of the silicon carbide material is 0.9 g / cm³. 3 Up to 1.15 g / cm 3 The option is 1.03 g / cm³. 3 Up to 1.14 g / cm 3 When the tap density of silicon-carbon material is within the above range, due to the suitable sphericity of the silicon-carbon material, there is more silicon-carbon material in the relative volume, which can improve the tap density and elongation of the negative electrode active material film layer, thereby further improving the energy density and cycle performance of the battery cell.

[0105] The tap density of silicon carbide materials is a well-known concept in the art and can be determined using instruments and methods known in the field. For example, it can be determined using a powder tap density tester according to GB / T5162-2006. The testing instrument can be the Dandong Baite BT-301, with the following test parameters: vibration frequency 250±15 times / minute, amplitude 3±0.2mm, number of vibrations 5000 times, and graduated cylinder capacity 25mL.

[0106] In some alternative implementations, the volumetric particle size Dv of the silicon-carbon material 1 50 is available in sizes from 4μm to 12μm, with options from 4μm to 6μm and from 8μm to 12μm.

[0107] The volumetric particle size Dv of silicon-carbon materials 1 When 50 is within the above range, the natural slippage between silicon-carbon material with high average sphericity and graphite particles in the negative electrode active material film layer is enhanced, further reducing the internal breakage of the electrode assembly containing the negative electrode sheet during winding, further improving the cell yield, further improving the cycle performance of high energy density battery cells, and thus improving the reliability of battery cells.

[0108] In some alternative embodiments, the particle size distribution span (SPAN) of the silicon-carbon material is 1.2 to 1.6; optionally 1.2 to 1.4; optionally 1.5 to 1.6.

[0109] When the particle size distribution span (SPAN) of silicon-carbon material is within the above range, it indicates that the particle size distribution of silicon-carbon material powder is relatively narrow. The natural slippage between silicon-carbon material with high average sphericity and graphite particles in the negative electrode active material film layer is enhanced, further reducing the internal breakage of the electrode assembly containing the negative electrode sheet during winding, further improving the yield of the battery cell, further improving the cycle performance of high energy density battery cells, and thus improving the reliability of the battery cells.

[0110] Span of particle size distribution (SPAN) is a parameter that describes the range of particle size distribution. It reflects the breadth of the particle size distribution. SPAN = (Dv90 - Dv10) / Dv50, where Dv50 represents the particle size greater than 50% of the particle volume distribution (i.e., the median particle size), while Dv90 and Dv10 represent the particle sizes greater than 90% and 10% of the particle volume distribution, respectively.

[0111] The volume distribution particle sizes Dv10, Dv50, and Dv90 of silicon-carbon materials are known in the art, representing the particle sizes corresponding to a cumulative volume distribution percentage of 10%, 50%, and 90%, respectively, and can be measured using instruments and methods known in the art. Volume distribution particle size Dv 150. Dv 2 The value 50 has a well-known meaning in the art, representing the particle size corresponding to a cumulative volumetric distribution percentage of 50%. For example, it can be determined using a laser particle size analyzer, referring to GB / T 19077-2016. The testing instrument can be the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0112] In some alternative embodiments, the silicon-carbon material comprises 40% to 60% silicon and 40% to 60% carbon by mass percentage.

[0113] According to embodiments of this application, silicon can improve the overall capacity and energy density of silicon-carbon materials, while carbon, as a conductive agent, helps improve the conductivity of individual battery cells, but its specific capacity is generally relatively low. When the silicon and carbon content in silicon-carbon materials are within the aforementioned ranges, it can maintain the structural stability of the silicon-carbon material, which is beneficial for improving cycle performance, and also increase the overall capacity of the silicon-carbon material and the energy density of individual battery cells. In some cases, silicon-carbon materials may also include other elements such as oxygen, hydrogen, nitrogen, and boron.

[0114] In some alternative embodiments, the peak intensities ID of the D peak and IG of the G peak in the Raman spectrum of the silicon-carbon material satisfy 1.5 < ID / IG < 2.5, where the D peak is located at 1340 cm⁻¹. -1 ~1360cm -1 The G peak is located at 1570cm. -1 ~1590cm -1 For example, the D peak can be located at 1350 cm⁻¹. -1 The G peak can be located at 1580 cm. -1 .

[0115] According to the embodiments of this application, if the ID / IG ratio of carbon in the Raman spectrum of silicon-carbon material is within the above range, the carbon phase structure in silicon-carbon material can be evaluated, indicating that the degree of carbon graphitization is high, and silicon-carbon material has good electrical conductivity and mechanical stability, which is beneficial to the cycle performance of battery cells.

[0116] In some alternative embodiments, the average strength of the silicon-carbon material is from 20 MPa to 50 MPa, and optionally from 41 MPa to 48 MPa.

[0117] The silicon-carbon material has the above-mentioned average strength, indicating that it has suitable softness and hardness, and the maximum stress that the material can withstand is within a suitable range. Therefore, during the preparation and use of the negative electrode containing this silicon-carbon material, the particle breakage rate of the silicon-carbon material is reduced, which is beneficial to maintaining the structural stability of the negative electrode active material film layer and enabling the battery to have better cycle performance.

[0118] Average strength refers to the average strength of a single particle in powder materials such as silicon carbide. Average single particle strength is the average of the maximum stress that multiple powder particles can withstand under external force. It depends on factors such as the shape, size, structure and composition of the powder particles. Different types of powders have different average single particle strengths.

[0119] The average strength can be determined using testing methods known in the art. For example, silicon-carbon powder or silicon-carbon material comprising multiple particles is passed through a Shimazu MCT series micro-compression testing machine (Japan). A single-particle sample is sandwiched between two indicators, and the diameter d of the single-particle sample is recorded. The sample is tested in 200-micrometer increments until 0.1 micrometers, with a test compressive force of 9.8-4903 mN, until the silicon-carbon material fractures. The experimental force P at this point is recorded. The average strength is calculated as the average value. Average strength = 2.8 × P / (πd) 2 ).

[0120] In some alternative implementations, the volumetric particle size Dv of graphite 2 50 is 14μm to 18μm, and can be selected from 15μm to 17μm.

[0121] Graphite volumetric particle size Dv 2 When 50 is within the above range, the negative electrode active material film layer contains silicon-carbon material with high average sphericity and graphite with the above volume particle size. The slippage between the two is enhanced, further reducing the internal breakage of the electrode assembly containing the negative electrode sheet during winding, further improving the cell yield, further improving the cycle performance of high energy density battery cells, and thus improving the reliability of battery cells.

[0122] In some alternative embodiments, the graphite particle size distribution span (SPAN) is 1.7 to 2.0, optionally 1.8 to 1.9.

[0123] When the particle size distribution span (SPAN) of graphite is within the above range, it indicates that the particle size distribution of graphite powder is relatively narrow. The negative electrode active material film layer contains silicon-carbon material with high average sphericity and graphite with narrow particle size distribution. The slippage effect between these two is enhanced, which further reduces the internal breakage of the electrode assembly containing the negative electrode sheet during winding, further improves the yield of the battery cell, further improves the cycle performance of high energy density battery cells, and thus improves the reliability of the battery cell.

[0124] In some alternative embodiments, the mass ratio of graphite to silicon carbide is 1:(0.66 to 1.5).

[0125] Optionally, the mass ratio of graphite to silicon carbide can be any value or a range of combinations thereof from 1:0.66, 1:0.7, 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5.

[0126] According to embodiments of this application, graphite typically has a layered structure at the microscopic level, exhibiting good conductivity and structural stability. Silicon-carbon materials have a higher specific capacity, but their volume expansion rate is relatively larger than that of graphite. When the mass ratio of graphite to silicon-carbon materials is within the aforementioned range, it can maintain the structural stability of the negative electrode active material film, which is beneficial for improving cycle capacity performance. Furthermore, it can increase the specific capacity of the negative electrode active material film, thereby increasing the energy density of the battery cell.

[0127] In some optional embodiments, the silicon-carbon material includes a first silicon-carbon material and a second silicon-carbon material, wherein the volumetric particle size Dv of the first silicon-carbon material is... 3 50 is smaller than the volumetric particle size Dv of the second silicon-carbon material 4 50.

[0128] According to the embodiments of this application, combining a first silicon-carbon material and a second silicon-carbon material with different volume particle sizes is beneficial to improving the compaction density of the negative electrode active material film layer and further improving the energy density of the battery cell.

[0129] In some alternative embodiments, the volumetric particle size Dv of the first silicon-carbon material 3 50 is 4μm to 6μm; the volumetric particle size Dv of the second silicon-carbon material 4 50 ranges from 8μm to 12μm.

[0130] According to the embodiments of this application, the first silicon-carbon material and the second silicon-carbon material with different volume particle sizes are combined to further improve the compaction density of the negative electrode active material film layer and further improve the energy density of the battery cell.

[0131] In some alternative embodiments, the particle size distribution span (SPAN) of the first silicon carbide material is 1.5 to 1.6; and the particle size distribution span (SPAN) of the second silicon carbide material is 1.2 to 1.4.

[0132] According to the embodiments of this application, the first silicon-carbon material and the second silicon-carbon material with different particle size distribution spans are combined to indicate that the particle size distribution of the first silicon-carbon material and the second silicon-carbon material is relatively narrow, which further improves the compaction density of the negative electrode active material film layer and further improves the energy density of the battery cell.

[0133] In some alternative embodiments, the mass ratio of the first silicon carbide material to the second silicon carbide material is (1-4):1.

[0134] According to the embodiments of this application, the mass ratio of the first silicon-carbon material to the second silicon-carbon material is within the above range, and the negative electrode active material film layer includes the first silicon-carbon material and the second silicon-carbon material, which further improves the compaction density of the negative electrode active material film layer and further improves the energy density of the battery cell.

[0135] In some alternative embodiments, the negative electrode active material film layer includes a binder and a conductive agent.

[0136] In this application embodiment, the type of binder is not explicitly limited; any binder that can be applied to the slurry of the negative electrode sheet and has a certain binding effect can be used in this application embodiment. In some optional embodiments, the negative electrode active material film layer includes a binder. Optionally, the binder includes one or more of the following: carboxymethyl cellulose, polyacrylic acid and its modified derivatives, polyacrylamide and its modified derivatives, polyvinyl alcohol and its modified derivatives, polyacrylonitrile and its modified derivatives, polyethyleneimine and its modified derivatives, styrene-butadiene rubber and its modified derivatives, styrene-acrylic emulsion and its modified derivatives, polyacrylate and its modified derivatives, polyurethane and its modified derivatives, sodium alginate and its modified derivatives, guar gum and its modified derivatives, xanthan gum and its modified derivatives, gum arabic and its modified derivatives, β-cyclodextrin polymers, and carrageenan and its modified derivatives. In some optional embodiments, the negative electrode active material film layer includes a thickener. The thickener may be carboxymethyl cellulose and its salts.

[0137] In this application embodiment, the type of conductive agent is not explicitly limited. Any conductive agent that can be applied to the slurry of the negative electrode sheet and has a good conductive effect can be used in this application embodiment. In order to further improve the conductivity of the negative electrode sheet and reduce its internal resistance, in some optional embodiments, the conductive agent includes one or more of carbon nanotubes, graphene, carbon nanofibers, superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, and carbon dots.

[0138] In some alternative embodiments, the compaction density of the negative electrode active material film is 1.3 g / cm³. 3 Up to 1.8 g / cm 3 1.4g / cm³ is an optional value. 3 Up to 1.6 g / cm 3 The compaction density of the negative electrode active material film layer is within the above range, which can further improve the energy density of the battery cell; the negative electrode active material film layer contains silicon-carbon material, which has a suitable pore structure, improving the wetting and retention characteristics of the negative electrode active material film layer to the electrolyte, thereby further improving the cycle performance of the battery cell.

[0139] The areal density of the negative electrode active material film is a term known in the art and can be tested using methods known in the art. For example, a negative electrode sheet coated on one side and cold-pressed (if it is a double-sided coated negative electrode sheet, the negative electrode active material film on one side can be wiped off first) can be punched into a small circular sheet with an area of ​​S1, and its weight recorded as M1. Then, the negative electrode active material film on the weighed negative electrode sheet is wiped off, and the weight of the negative electrode current collector is measured and recorded as M0. The areal density of the negative electrode sheet = (M1 - M0) / S1.

[0140] The compaction density of the negative electrode active material film layer is a term known in the art and can be tested using methods known in the art. The compaction density of the negative electrode active material film layer = areal density of the negative electrode active material film layer / thickness of the negative electrode active material film layer. The thickness of the negative electrode active material film layer is a term known in the art and can be tested using methods known in the art, such as a micrometer (e.g., Mitutoyo 293-100, with an accuracy of 0.1 μm).

[0141] In some optional embodiments, the elongation at break of the negative electrode sheet under pressures of 1.3 MPa to 1.6 MPa is 1% to 3.5%. It can be any value or a range of combinations thereof from 1.00%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, and 3.5%. An elongation at break of the negative electrode sheet within the above range can improve the flexibility of the electrode sheet, reduce the probability of brittle fracture, and thus improve the reliability of the battery.

[0142] It should be noted that the above-mentioned parameter tests for silicon-carbon materials, graphite, or negative electrode active material films can be performed by sampling and testing from the prepared battery cells according to the following steps.

[0143] The battery cell is discharged (for safety reasons, it is generally left fully discharged); after disassembling the battery cell, the negative electrode is removed and soaked in dimethyl carbonate for a certain period of time (e.g., 2-10 hours); then the negative electrode is removed and dried at a certain temperature and time (e.g., 60°C for more than 4 hours), and then the negative electrode is removed. At this point, samples can be taken from the dried negative electrode to test various parameters related to the negative electrode active material film, such as the areal density, compaction density, and porosity of the negative electrode active material film.

[0144] In some optional embodiments, to improve the performance of the negative electrode in the battery cell and enhance the charge-discharge performance of the battery cell, the battery cell includes an electrolyte with a viscosity of 2 to 15 mPa*S. The viscosity of the electrolyte is any value or a range thereof from 2 mPa*S, 3 mPa*S, 4 mPa*S, 5 mPa*S, 6 mPa*S, 7 mPa*S, 8 mPa*S, 9 mPa*S, 10 mPa*S, 11 mPa*S, 12 mPa*S, 13 mPa*S, 14 mPa*S, and 15 mPa*S.

[0145] The viscosity of the electrolyte can be tested by measuring the shear force exerted on the rotor as it rotates continuously at a constant speed within the sample at a certain temperature. This shear force causes the spring to generate torque, which is proportional to the viscosity, thus yielding the viscosity value. Specifically, a Bollefeld (DV-2TLV) viscometer was used to test the viscosity of the finished electrolyte. The ambient temperature was controlled at 25℃ and the ambient humidity at <80%. 30 mL of electrolyte was taken and kept at a constant temperature of 25℃ in a water bath for at least 30 minutes. The rotor was placed in the sample cup, and the sample was added to a depth of approximately 0.3 cm from the rim of the cup. The connected viscometer was then started, and the setting was 70 RPM.

[0146] In some optional embodiments, to improve the performance of the negative electrode in the battery cell and enhance the charge-discharge performance of the battery cell, the battery cell includes an electrolyte with a conductivity of 9 to 15 mS / cm. Optionally, the conductivity of the electrolyte can be any value or a range thereof from 9 mS / cm, 10 mS / cm, 11 mS / cm, 12 mS / cm, 13 mS / cm, 14 mS / cm, and 15 mS / cm.

[0147] Ionic conductivity refers to the conductivity of an electrolyte for ions, reflecting the electrolyte's ability to conduct electricity to ions.

[0148] For ionic conductivity testing, take approximately 100 mL of electrolyte sample in a dry, clean, corrosion-resistant sample bottle, seal it, and place it in a constant-temperature water bath. Shake the sample occasionally and maintain the temperature at 25℃ (deviation ±0.5℃). After the sample temperature stabilizes, test its conductivity using a commercially available conductivity meter. Clean and dry the conductivity meter with calibration solution, then vertically immerse it in the liquid to be tested. Click to start the test, and record the test results after the data has stabilized for at least 10 seconds.

[0149] The lithium secondary battery provided in this application has an ionic conductivity within the above-mentioned range, and therefore has good fast-charging performance.

[0150] The viscosity and conductivity of the electrolyte can be adjusted using methods commonly used in the art. In some alternative embodiments, the battery cell includes an electrolyte comprising an acetate compound, wherein the acetate compound includes one or more of methyl acetate, ethyl acetate, and propyl acetate.

[0151] In some alternative embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. As an example, the metal material may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0152] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode active material film layer. For example, in some optional embodiments, the negative electrode sheet of this application further includes a conductive undercoat layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode active material film layer and disposed on the surface of the negative electrode current collector; in some optional embodiments, the negative electrode sheet of this application further includes a protective layer covering the surface of the negative electrode active material film layer.

[0153] The negative electrode current collector has two surfaces opposite each other in its thickness direction, and the negative electrode active material film layer is disposed on either or both of these opposing surfaces. It should be noted that the negative electrode active material film layer parameters (e.g., compacted density, areal density, porosity, etc.) given in this application refer to the parameters of the negative electrode active material film layer on one side of the negative electrode current collector. When the negative electrode active material film layer is disposed on both sides of the negative electrode current collector, if the parameters of the negative electrode active material film layer on either side meet the requirements of this application, it is considered to fall within the protection scope of this application.

[0154] In some embodiments, the negative electrode active material film layer may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc.

[0155] In some optional embodiments, the thickness of the negative electrode active material film is 50–250 μm; alternatively, it is 50–150 μm. Controlling the thickness of the negative electrode active material film within the above range, while taking into account the stability of the negative electrode sheet, is beneficial to improving the capacity of the negative electrode sheet and thus to improving the energy density of the battery cell.

[0156] The specific composition and structure of the negative electrode sheet can be selected according to the type of battery cell, and the embodiments of this application are not limited in this regard.

[0157] For example, when the battery cell is a lithium-ion battery cell, the negative electrode sheet includes a negative current collector and a negative active material film layer disposed on at least one surface of the negative current collector and including a negative active material. For example, the negative current collector has two surfaces opposite to each other in its thickness direction, and the negative active material film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0158] The negative electrode active material is a material capable of extracting and inserting active ions (such as lithium ions), and can be any material known in the art. As examples, negative electrode active materials include, but are not limited to, one or more of soft carbon, hard carbon, tin-based materials, and lithium titanate. Tin-based materials may include one or more of elemental tin, tin oxides, and tin alloys. This application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials may also be used.

[0159] When the battery cell is a lithium metal battery cell, the negative electrode sheet may not include a negative electrode active material capable of extracting and embedding active ions. For example, in some alternative embodiments, the negative electrode sheet may include a lithium sheet or a lithium alloy sheet; in other embodiments, the negative electrode sheet includes a mesh or foam-like three-dimensional framework layer, such as foamed copper (or copper alloy), foamed nickel (or nickel alloy), copper (or copper alloy) mesh, nickel (or nickel alloy) mesh, etc.

[0160] Methods for preparing silicon-carbon materials include:

[0161] S10. Phenolic and aldehyde substances are mixed and reacted in a solvent under acidic or alkaline conditions to obtain a mixture containing organic particles;

[0162] S20. Carbonize the mixture to prepare a carbon substrate;

[0163] S30. Perform a pore-forming treatment on the carbon substrate to obtain a carbon matrix with a porous structure;

[0164] S40. Deposit silicon-based material within the porous structure of a porous carbon matrix to prepare a silicon-carbon core;

[0165] S50. A silicon-carbon material with a carbon coating layer is prepared by coating carbon onto the surface of a silicon-carbon core.

[0166] Research has revealed that the silicon-carbon materials produced using related technologies typically consist of silicon-carbon particles with sharp edges. During the fabrication of the negative electrode sheet, the cold pressing process damages this type of substrate. This causes internal breakage in the electrode assembly containing the negative electrode sheet during winding and cell improvement, reducing the yield of the electrode assembly. Furthermore, the battery cell containing this negative electrode sheet experiences significant stretching loss during cycling, leading to a sharp drop in battery cell capacity and low battery cell reliability.

[0167] The preparation method of this application embodiment uses phenolic and aldehyde substances to prepare organic particles, which are then carbonized to obtain a carbon matrix. The carbon matrix powder has a suitable average sphericity, indicating that the particles in the carbon matrix powder have a high degree of roundness. By coating the surface of the silicon-carbon core with carbon, the roundness and average sphericity of the particles are further improved. The negative electrode sheet is prepared using silicon-carbon material with a high average sphericity and graphite. Since there is a good sliding effect between the silicon-carbon material with a high average sphericity and the graphite particles, it is beneficial to reduce the internal breakage of the electrode assembly containing the negative electrode sheet during winding, improve the cell yield, improve the cycle performance of the battery cell, and thus improve the reliability of the battery cell.

[0168] In some optional embodiments, S10. Phenolic and aldehyde substances are mixed and reacted in a solvent under acidic or alkaline conditions to obtain a mixture containing organic particles, which may specifically include:

[0169] Phenolic resin microspheres, or organic particles, are prepared by emulsion polymerization of phenolic and aldehyde substances under acidic or alkaline conditions.

[0170] According to embodiments of this application, the solvent can be a mixed solution of water and alcohol. The water content can be 30% to 40% by mass, and the alcohol content can be 60% to 70% by mass.

[0171] Alcohols can be substances such as ethanol and polyvinyl alcohol. Phenolic substances can be one or more of phenol, hydroquinone, and naphthol. Aldehydes can be one or more of formaldehyde, acetaldehyde, and benzaldehyde. Acidic and alkaline conditions can be obtained by adding acids or bases known in the art, such as adding hydrochloric acid or hydrofluoric acid to obtain acidic conditions, and adding sodium hydroxide to obtain alkaline conditions.

[0172] In some alternative embodiments, in S20, the mixture is carbonized at 700°C to 1000°C to prepare a carbon substrate.

[0173] The carbonization temperature can be any value or range of 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, and 1000℃. Carbonizing the mixture within the above temperature range yields a carbon substrate with a high degree of graphitization, facilitating the subsequent production of silicon-carbon materials.

[0174] In some optional embodiments, in step S20, the coke raw material is carbonized at a temperature of 700-1000°C to prepare a carbon substrate. This process may specifically include: carbonizing at 700-1000°C, chemically activating it under alkaline conditions in a protective atmosphere for 6-8 hours, and then physically activating it by introducing carbon dioxide for 10-12 hours. The protective atmosphere can be nitrogen, and the alkaline conditions can be adjusted by adding substances such as NaOH.

[0175] In some optional embodiments, in step S30, the carbon substrate is subjected to a pore-forming process to obtain a carbon matrix with a porous structure, which may specifically include:

[0176] Pretreatment of carbon-based materials removes impurities and surface contaminants, thereby ensuring the effectiveness of subsequent treatments.

[0177] Choose a suitable hole-forming method; common methods include chemical, physical, and biological methods. Physical methods include laser etching and electrochemical etching.

[0178] The material after pore-forming treatment is washed to remove residual treatment fluid and products.

[0179] In some alternative embodiments, after washing the material after the pore-forming treatment to remove residual treatment liquid and products in S30, the method may further include drying it to ensure that the material surface is clean.

[0180] In some alternative embodiments, the average sphericity Φ of the carbon matrix is ​​0.8 to 1.0, optionally 0.85 to 0.95.

[0181] The average sphericity of the carbon matrix within the aforementioned range is beneficial for obtaining higher roundness and average sphericity of particles in the subsequently produced silicon-carbon materials. Higher average sphericity in silicon-carbon materials enhances slippage between the silicon-carbon material and graphite, further reducing the risk of internal breakage of the electrode assembly containing the negative electrode sheet during winding, further improving the cell yield, and further enhancing the cycle capacity stability of high-energy-density battery cells, thereby improving the reliability of the battery cells.

[0182] In some alternative embodiments, the volumetric particle size Dv of the carbon matrix 4 50 is available in sizes from 4 μm to 12.5 μm, with options from 4 μm to 6 μm and from 8 μm to 12 μm. The volumetric particle size Dv of the carbon matrix is ​​also available. 4 When 50 is within the above range, it is beneficial to prepare silicon-carbon materials with a suitable volumetric particle size Dv50, which is beneficial to the anode active material film layer having a suitable porosity and the silicon-carbon material having good particle packing performance, which is beneficial to improve the compaction density of the anode active material film layer, thereby further improving the energy density of the battery cell.

[0183] In some optional embodiments, the particle size distribution span (SPAN) of the carbon matrix is ​​1.2 to 1.8, optionally 1 / 4 to 1.6. When the particle size distribution span (SPAN) of the carbon matrix is ​​within the above range, it is beneficial to prepare silicon-carbon materials with a suitable particle size distribution span, thereby enhancing the slip between the silicon-carbon material and graphite, further reducing the internal breakage of the electrode assembly containing the negative electrode sheet during winding, further improving the cell yield, further improving the cycle performance of high-energy-density battery cells, and thus improving the reliability of the battery cells.

[0184] In some alternative embodiments, the specific surface area of ​​the carbon matrix is ​​1900 m². 2 / g to 2500m 2 / g, 1950m can be selected. 2 / g to 2400m 2 When the specific surface area of ​​the carbon matrix is ​​within the above-mentioned range, it is beneficial for the deposition of silicon-based materials within the carbon matrix, resulting in a silicon-carbon material with a suitable specific surface area. This increases the ion insertion channels in the negative electrode active material film, facilitating the rapid diffusion of ions from the particle surface to the bulk phase, thereby further optimizing the fast-charging performance of the battery cell. Furthermore, when the specific surface area of ​​the carbon matrix is ​​within the above-mentioned range, the resulting silicon-carbon material has a suitable specific surface area, which helps reduce side reactions, thus also enabling the battery cell to have better cycle performance.

[0185] In some alternative embodiments, the porosity of the carbon matrix is ​​75% to 90%, optionally 75% to 85%. This facilitates the deposition of a suitable amount of silicon in the carbon matrix's pore structure, resulting in a silicon-carbon material with suitable porosity and silicon-carbon composition. This allows the negative electrode active material film to achieve both high capacity and a suitable pore structure, thereby benefiting the battery cell in achieving both high energy density and good cycle performance.

[0186] In some optional embodiments, in the Raman spectrum of the carbon matrix, the peak intensity ID of the D peak and the peak intensity IG of the G peak satisfy 1.5 < ID / IG < 2.5, which can be selected as 1.8 to 2.0; wherein the D peak is located at 1340 cm⁻¹. -1 ~1360cm -1 The G peak is located at 1570cm. -1 ~1590cm -1 .

[0187] According to the embodiments of this application, the ID / IG ratio of carbon in the Raman spectrum of the carbon matrix is ​​within the above range, indicating that it has a good degree of graphitization, which further improves the capacity of silicon-carbon materials.

[0188] In some optional embodiments, in S30, the tap density of the carbon matrix is ​​0.25 g / cm³. 3Up to 0.5; optionally 0.3 g / cm³ to 0.35 g / cm³. 3 When the tap density of the carbon matrix is ​​within the above range, it is beneficial to obtain silicon-carbon materials with suitable tap density after silicon deposition, thereby increasing the tap density of the negative electrode active material film, which can further improve the energy density and cycle performance of the battery cell.

[0189] The specific surface area of ​​carbon-based materials is a well-known concept in the art and can be determined using instruments and methods known in the field. For example, it can be measured using the nitrogen adsorption specific surface area analysis method according to GB / T19587-2017, and calculated using the BET (Brunauer Emmett Teller) method. The testing instrument can be the Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0190] In some optional embodiments, in S30, the porosity of the carbon matrix is ​​70% to 95%, optionally 75% to 90%. This facilitates the deposition of a suitable amount of carbon in the pore structure of the carbon matrix, thereby enabling the prepared silicon-carbon material to have a suitable specific capacity, allowing the negative electrode active material film to achieve both high capacity and a suitable pore structure, which in turn helps the battery cell to achieve both high energy density and good cycle performance.

[0191] The porosity of carbon-based materials can be determined using methods known in the art. For example, the true density ρr of a carbon matrix with secondary particles can be measured using a true density meter (e.g., AccuPycⅡ1340). Specifically, the steps include: weighing a sample of a certain mass (denoted as m), placing it in the true density meter, sealing the testing system, and introducing helium gas according to a program; measuring the gas pressure in the sample chamber and expansion chamber, and then calculating the true volume Vr of the carbon matrix according to Bohr's Law (PV = nRT), thus the true density ρr = m / Vr. The apparent density of the carbon matrix can be obtained by loading a sample of a certain mass (denoted as m) into a cylindrical mold with an inner diameter of 10 mm and applying a pressure of 200 MPa to obtain the apparent volume V0 of the carbon matrix, thus the apparent density ρ0 = m / V0. The porosity of the carbon matrix is ​​denoted as P, then P = (1 - ρ0 / ρr) × 100%.

[0192] In some optional embodiments, in S40, silicon is deposited within the porous structure of the carbon matrix to prepare a silicon-carbon material, which can be performed using chemical vapor deposition (CVD) or physical vapor deposition (PVD). In CVD, a gaseous silicon source is deposited onto the surface or within the pores of the carbon-based material through a chemical reaction to form a silicon layer. In PVD, silicon atoms are deposited within the porous structure of the carbon-based material under vacuum conditions by evaporating or sputtering a silicon source. In some optional embodiments, the gaseous silicon source may include one or more of silanes, silanes, trimethylsilane, silane, propane, dichlorosilane, trichlorosilane, and tetrachlorosilane.

[0193] In some alternative embodiments, in the chemical vapor deposition (CVD) method, a gaseous silicon source is vapor-deposited in a rotary kiln, tube furnace, or fluidized bed using either nitrogen or argon as a protective gas; wherein the flow rate of the gaseous silicon source is 0.5–5 L / min; the flow rate of the protective gas is 0.5–30 L / min; the vapor deposition temperature is 500°C–700°C; and the time is 6–12 h.

[0194] In some alternative embodiments, following chemical vapor deposition (CVD), a carbon layer is coated using solid-phase or vapor-phase deposition or other methods to improve the stability between the material and the electrolyte. The carbon source for the CVD-formed carbon layer can be one or a combination of methane, ethylene, and acetylene. The CVD-formed carbon layer can be deposited at 500-650 degrees Celsius for 2-4 hours, followed by shutting off the gas source and cooling to obtain spherical silicon-carbon materials.

[0195] In some optional embodiments, in S50, coating the surface of the silicon-carbon core with carbon to obtain a silicon-carbon material with a carbon coating layer can specifically include:

[0196] Silicon-carbon materials with a carbon coating layer are prepared by coating the surface of a silicon-carbon core with carbon using solid-phase or vapor-phase deposition or other methods. This coating is used to improve the stability between the material and the electrolyte. The carbon source for vapor-phase deposition can be one or more combinations of methane, ethylene, and acetylene. The carbon layer can be formed by vapor-phase deposition at 500-650 degrees Celsius for 2-4 hours, followed by cooling with the gas source turned off to obtain spherical silicon-carbon materials.

[0197] This application provides a method for preparing a negative electrode sheet, including:

[0198] We provide slurries containing silicon carbide materials and graphite.

[0199] The slurry is coated on at least one side of the negative electrode current collector to form a negative electrode active material film layer, thus obtaining the negative electrode sheet.

[0200] In some alternative embodiments, a slurry comprising silicon carbon material and graphite is provided, which may specifically include: dispersing the silicon carbon material and graphite, a negative electrode binder, optional negative electrode conductive agent, and optional other additives in a solvent and stirring until homogeneous to form a slurry. The solvent may be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.

[0201] In some alternative embodiments, the mass ratio of graphite to silicon carbide is 1:(0.66 to 1.5).

[0202] According to embodiments of this application, graphite typically has a layered structure at the microscopic level, exhibiting good conductivity and structural stability. Silicon-carbon materials have a higher specific capacity, but their volume expansion rate is relatively larger than that of graphite. When the mass ratio of graphite to silicon-carbon materials is within the aforementioned range, it can maintain the structural stability of the negative electrode active material film, which is beneficial for improving cycle capacity performance. Furthermore, it can increase the specific capacity of the negative electrode active material film, thereby increasing the energy density of the battery cell.

[0203] In some alternative embodiments, the slurry is coated on at least one side of the negative electrode current collector to form a negative electrode active material film layer, thereby obtaining a negative electrode sheet. This may specifically include: coating the slurry onto the negative electrode current collector, and then performing processes such as drying and cold pressing to form a negative electrode sheet.

[0204] [Positive electrode plate]

[0205] In some alternative embodiments, the positive electrode includes a positive current collector and a positive active material film layer disposed on at least one surface of the positive current collector and comprising a positive active material. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive active material film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0206] The positive electrode active material film layer includes a positive electrode active material, which may be a positive electrode active material known in the art for use in battery cells.

[0207] For example, when the battery cell is a lithium-ion battery cell or a lithium metal battery cell, the positive electrode active material may include one or more of lithium transition metal oxides, lithium-containing phosphates, and their respective modified compounds. Examples of lithium transition metal oxides may include one or more of lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their respective modified compounds. Examples of lithium-containing phosphates may include one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their respective modified compounds. This application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials may also be used.

[0208] In some alternative embodiments, to further improve the energy density of the battery cell, the positive electrode active material may include materials of the general formula Li. a Ni b Co c M d O e A f One or more of lithium transition metal oxides and their modified compounds. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M includes one or more selected from Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A includes one or more selected from N, F, S and Cl.

[0209] As an example, positive electrode active materials may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.80 Co 0.15 Al 0.05 One or more of O2, LiFePO4 and LiMnPO4.

[0210] The modified compounds for the above-mentioned positive electrode active materials can be obtained by doping and / or surface coating of the positive electrode active materials.

[0211] In some optional embodiments, the positive electrode active material film layer may also optionally include a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode conductive agent; as an example, the positive electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0212] In some optional embodiments, the positive electrode active material film layer may also optionally include a positive electrode binder. This application does not impose any particular limitation on the type of positive electrode binder. As an example, the positive electrode binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0213] In some alternative embodiments, the positive current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. As an example, the metal material may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0214] The positive electrode active material film layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to this.

[0215] [Isolation membrane]

[0216] The separator is positioned between the positive and negative electrodes, primarily serving to prevent short circuits between the positive and negative electrodes. This application does not impose any particular restriction on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0217] In some alternative embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0218] In summary, the aforementioned negative electrode, positive electrode, and separator disposed between the negative electrode and positive electrode can form an electrode assembly, which also possesses the advantages of the aforementioned negative electrode.

[0219] [Electrolytes]

[0220] In some embodiments, the battery cell includes an electrolyte. The electrolyte acts as a conductor of active ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte, which can be selected according to requirements. For example, the electrolyte can be selected from one or more of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0221] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0222] The type of electrolyte salt is not specifically limited and can be selected according to actual needs. For example, electrolyte salts include one or more selected from lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0223] The type of solvent is not specifically limited and can be selected according to actual needs. In some optional embodiments, as an example, the solvent may include one or more selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0224] In some alternative embodiments, the electrolyte may also optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain properties of the battery cell, such as additives that improve the overcharge performance of the battery cell, additives that improve the high-temperature performance of the battery cell, and additives that improve the low-temperature power performance of the battery cell.

[0225] In some alternative embodiments, the battery cell includes the electrode assembly described above and the electrolyte described above.

[0226] In some alternative embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0227] In some alternative implementations, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, aluminum shell, or 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, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0228] This application does not impose any particular restrictions on the shape of the battery cell; it can be a flat body, a cuboid, or other shapes. Figure 1 shows a cuboid battery cell 5 as an example.

[0229] In some optional embodiments, as shown in FIG2, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The electrode assembly 52 of the first aspect of the present application or the electrode assembly 52 prepared according to the method of the second aspect of the present application is encapsulated in the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be adjusted according to requirements.

[0230] In some embodiments of this application, the battery cells according to this application can be assembled into a battery cell module. The number of battery cells contained in the battery cell module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery cell module.

[0231] Optionally, the battery cell module may also include a housing with a receiving space in which multiple battery cells are housed.

[0232] In some alternative implementations, the aforementioned battery cell modules can also be assembled into a battery cell pack, and the number of battery cell modules contained in the battery cell pack can be adjusted according to the application and capacity of the battery cell pack.

[0233] Preparation method of battery cell

[0234] Secondly, embodiments of this application provide a method for preparing a battery cell, comprising: winding a component including a negative electrode sheet to obtain a battery cell, wherein the negative electrode sheet includes a negative current collector and a negative active material film layer disposed on at least one side of the negative current collector, the negative active material film layer including graphite and silicon-carbon material, wherein the average sphericity Φ of the silicon-carbon material is 0.8 to 1.0.

[0235] In some optional embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a battery cell. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding process and / or a stacking process. The electrode assembly is placed in an outer package, dried, and then injected with electrolyte. After processes such as encapsulation, settling, formation, and shaping, a battery cell is obtained. Multiple battery cells can further be connected in series, parallel, or a combination thereof to form a battery cell module. Multiple battery cell modules can also be connected in series, parallel, or a combination thereof to form a battery cell pack. In some optional embodiments, multiple battery cells can also be directly assembled into a battery cell pack.

[0236] In some alternative implementations, the electrode assembly can be placed in an outer package, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a battery cell is obtained.

[0237] Electrical appliances

[0238] Thirdly, embodiments of this application provide an electrical device comprising a battery cell according to the first aspect or a battery cell prepared by the second aspect. The electrical device of this application comprises a battery cell according to the first aspect or a battery cell prepared by the second aspect, and therefore possesses at least the corresponding advantages of a battery cell.

[0239] A single battery cell can be used as a power source for an electrical device or as an energy storage unit for that device. Electrical devices can be, but are not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0240] Figure 3 is a schematic diagram of an example 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 this device, battery packs or battery modules can be used.

[0241] Another example of an electrical 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.

[0242] Example

[0243] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0244] Example 1

[0245] Preparation of negative electrode sheet:

[0246] Preparation of silicon-carbon materials: Phenol and formaldehyde were mixed at a molar ratio of 1:1.15 in a mixed solution of polyvinyl alcohol (65% by mass) and water, wherein the water content of the mixed solution was 35% by mass. The mixed solution contained 1% polyvinylpyrrolidone (PVP) by mass. The mixture was reacted at 60℃ for 5.5 h to obtain a mixed solution containing phenolic resin microspheres.

[0247] Phenolic resin microspheres were carbonized and activated at 900℃ under nitrogen protection for 11 hours to obtain a carbon substrate.

[0248] A porous carbon matrix is ​​obtained by performing a pore-forming treatment on a carbon substrate. Specifically, this includes: activating the matrix with steam to create pores, and then using a TriStar II surface area analyzer to measure the BET (Boiler Equivalent) of the carbon matrix to be 2000 μm. 2 / g, the pore volume of the carbon matrix is ​​0.95g / cm3; the proportion of micropores smaller than 2nm to the total pore volume is 90%.

[0249] The preparation of silicon-carbon cores involves depositing silicon-based materials within the porous structure of a porous carbon matrix. Specifically, this includes: using silane as the silicon source and nitrogen as the protective gas, performing vapor-phase deposition in a rotary kiln, tube furnace, or fluidized bed; the silane flow rate is 4.5 L / min; the protective gas flow rate is 20 L / min; the vapor-phase deposition temperature is 560 °C, and the time is 8 hours, to obtain the silicon-carbon material.

[0250] A silicon-carbon material with a carbon coating layer was prepared by coating a silicon-carbon core with carbon. Specifically, this involved passing acetylene gas through a container containing the silicon-carbon core at a flow rate of 0.01-0.03 L / min for 2.5 h, followed by vapor deposition at 600°C for 3 h. The silicon-carbon material comprised 47% silicon and 53% carbon by mass. The silicon-carbon material had a DV50 of 8 μm, a span of 1.4, and an I0. D / I G It is version 2.0.

[0251] A slurry containing silicon carbide and graphite is provided. The negative electrode active material, conductive agent carbon black, carbon nanotubes (CNTs), binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are mixed in a mass ratio of 94.5:1:0.375:2.8:1.325, wherein the negative electrode active material is a mixture of artificial graphite and silicon carbide, with a mass ratio of artificial graphite to silicon carbide of 6:4. Deionized water is then added, and the mixture is stirred for 0.5-6 hours to obtain the slurry. The solid content of the slurry is 53%.

[0252] A slurry is coated on both sides of the negative electrode current collector to form a structure of a first negative electrode active material film layer - negative electrode current collector - second negative electrode active material film layer, thus obtaining a negative electrode sheet. Specifically, this includes: coating the slurry on both sides of the negative electrode current collector, coating the slurry onto a copper foil with a thickness of 6 μm, and then drying, cold pressing, and slitting to obtain the negative electrode sheet, wherein the thickness of the negative electrode active material film layer is 110 μm.

[0253] Preparation of the positive electrode sheet:

[0254] Nickel-cobalt-manganese (LiNi) 0.96 Co 0.3 Mn 0.1 O2) ternary material, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 97:1:2. N-methylpyrrolidone is added and the mixture is stirred and mixed thoroughly to prepare a positive electrode slurry. Then, it is uniformly coated on a 13μm aluminum foil, dried, cold-pressed, and slit to obtain a positive electrode sheet.

[0255] Separating membrane:

[0256] A 1-micron thick CCS coating and a 1-micron thick PCS coating are applied to one side of a 7 cm thick polypropylene film as the base film. The main component of the CCS coating is alumina, and the main component of the PCS coating is polyvinylidene fluoride.

[0257] Electrolyte (types and formulation of solvents, lithium salts, and additives):

[0258] LiPF6 and LIFSI were dissolved in a solvent, which included a mixed solution of ethylene carbonate, methyl ethyl carbonate, diethyl carbonate and fluoroethylene carbonate, with a volume ratio of ethylene carbonate, methyl ethyl carbonate, diethyl carbonate and fluoroethylene carbonate of 1:1:1:1. The resulting electrolyte had concentrations of 0.6 mol / L for LiPF6 and 0.4 mol / L for LIFSI.

[0259] The above-mentioned positive electrode sheet, separator, and negative electrode sheet are wound in sequence to obtain a bare cell; the bare cell is placed in a packaging shell, dried, and then injected with electrolyte. After vacuum sealing, standing, formation, and shaping, a lithium-ion battery cell is obtained.

[0260] Examples 2-1 to 2-5

[0261] The difference between this embodiment and Embodiment 1 is that the molar ratio of phenol and formaldehyde is different, and the average sphericity of the silicon carbon material is different. The average sphericity of the silicon carbon material is shown in Table 1.

[0262] Examples 3-1 to 3-2

[0263] The difference between this embodiment and Embodiment 1 is that the silicon content of the silicon-carbon material is different, as shown in Table 1.

[0264] Examples 4-1 to 4-2

[0265] The difference between this embodiment and Embodiment 1 is that the volume average particle size D of the silicon-carbon material is... V 1 The differences are 50, see Table 1.

[0266] Examples 5-1 to 5-2

[0267] The difference between this embodiment and Embodiment 1 is that the average strength of the silicon-carbon material is different, as shown in Table 1.

[0268] Examples 6-1 to 6-7

[0269] The difference between this embodiment and Embodiment 1 is that the negative electrode sheet is prepared using a first silicon-carbon material, a second silicon-carbon material, and natural graphite as the negative electrode active material. The negative electrode active material is a mixture of artificial graphite and silicon-carbon material, with a mass ratio of artificial graphite to the sum of the masses of the first and second silicon-carbon materials of 6:4. The first and second silicon-carbon materials in Embodiments 6-1 to 6-7 respectively comprise 47% silicon and 53% carbon by mass percentage. The volume average particle size D of Embodiments 6-7 to 5-6 is... V 3 Table 2 shows the SPAN value, quality, and other parameters.

[0270] Examples 7-1 to 7-3

[0271] The difference between this embodiment and Example 1 lies in the composition, content, viscosity, and conductivity of the electrolyte. In Example 7-3, the electrolyte includes lithium salts and a solvent. The lithium salts include LiPF6 and LIFSI, with concentrations of 0.6 mol / L and 0.4 mol / L, respectively. The solvent is ethyl acetate:EC:FEC:DEC, with a volume ratio of 3:1:3:3. In Example 7-2, the electrolyte includes lithium salts and a solvent. The lithium salts include LiPF6 and LIFSI, with concentrations of 0.64 mol / L and 0.36 mol / L, respectively. The solvent is ethyl acetate:EC:FEC:DEC, with a volume ratio of 2.5:1.5:3.3:2.7. In Example 7-1, the electrolyte includes lithium salts and a solvent. The lithium salts include LiPF6 and LIFSI, with concentrations of 0.68 mol / L and 0.32 mol / L, respectively. The solvent is ethyl acetate:EC:FEC:DEC, with a volume ratio of 2.3:1.7:3.5:2.5. The viscosity and conductivity of the electrolytes in the above examples differ, as shown in Table 3.

[0272] Comparative Example 1

[0273] The difference between this comparative example and Example 1 lies in the preparation of the silicon-carbon material: coconut shells, a type of biomass, are used as the raw material.

[0274] Comparative Example 2

[0275] The difference between this comparative example and Example 1 lies in the preparation of the silicon-carbon material: the parameters for preparing the phenolic resin microspheres are different, resulting in different average sphericity of the silicon-carbon material, as shown in Table 1.

[0276] Test section

[0277] 1) Methods for testing the sphericity of silicon-carbon materials:

[0278] Characterization was performed using a Malvern Morphologi G3-ID instrument and its accompanying graphics software. A series of two-dimensional images of silicon-carbon powder particles were captured using a microscope. The thickness and diameter of each particle were equal, and the volume of the particles was estimated using their area and perimeter. The surface area of ​​an equal-volume sphere was calculated based on the volume, and this was compared with the actual detected surface area of ​​the powder particles to obtain the sphericity. The calculation formula is as follows: Method for detecting the sphericity of silicon-carbon materials:

[0279] Φ=A particle / A sphere Where: Φ represents sphericity; A sphere A represents the surface area of ​​an ideal sphere with the same volume as the particle; particleThis represents the actual surface area of ​​the particle.

[0280] 2) Method for testing the compaction density of the negative electrode sheet: Take the coated and cold-pressed negative electrode sheet, remove the negative electrode active material film layer on one side, and punch it into a small circular piece with an area of ​​S1. Weigh it and record its weight as M1. Then wipe off the negative electrode active material film layer of the weighed negative electrode sheet, weigh the negative electrode current collector, and record it as M0. The areal density of the negative electrode sheet = (M1-M0) / S1. The compaction density of the negative electrode active material film layer = areal density of the negative electrode active material film layer / thickness of the negative electrode active material film layer. The thickness of the negative electrode active material film layer has a meaning known in the art, and a Mitutoyo 293-100 micrometer with an accuracy of 0.1 μm is used.

[0281] 3) Method for testing the elongation at break of the negative electrode: Remove the negative electrode from the battery cell, add electrolyte to completely immerse the electrode in the electrolyte, and store it at 90℃ for at least 48 hours. Then remove the electrode; the film layer of the negative electrode will peel off from the current collector. Take the negative electrode and remove the current collector. Prepare a sample with a width of 15 mm and a length of 50 mm from the film layer after removing the current collector. Set the equipment pressure to 2 MPa, then fix the sample on a tensile testing machine (model AI7000). Attach a layer of yellow Teflon to the upper and lower clamps, changing it once per shift to prevent electrode slippage. Record the initial length L0. Start the tensile testing machine and test under a pressure of 1.3-1.6 MPa until the sample breaks. Read the displacement L1 of the sample at the time of breakage from the tensile testing machine. Elongation = (L1-L0) / L0*100%.

[0282] 4) Method for detecting the volumetric energy density of a single battery cell: At 25°C, the secondary battery cells prepared in each example and comparative example are charged and discharged at 1 / 3C-1 / 3C (the testing instrument can be a Xinwei testing machine), with a voltage range of 2.8V to 4.3V. The energy released by the battery cell in the first cycle is recorded and then divided by the volume of the battery cell to obtain the volumetric energy density of the battery cell, with the unit being Wh / kg.

[0283] 5) Method for testing the cycle performance of individual battery cells: The individual battery cells prepared in the examples and comparative examples were placed in the test channel of the Chenhua electrochemical workstation and charged at a constant current rate of 1C to the charging cutoff voltage of 3.7V. After standing for 5 minutes, they were discharged at a constant current rate of 1C to the discharge cutoff voltage of 2.0V. The number of cycles was recorded, and then they were allowed to stand for another 5 minutes. This cycle was repeated until the capacity decayed to 80% of the capacity of the first discharge cycle, and the number of battery cell cycles was recorded.

[0284] The test results are shown in Tables 1 and 2.

[0285] As can be seen from the results in Table 1, the sphericity of the embodiment is relatively larger than that of the comparative example. The silicon-carbon material of the negative electrode sheet of the embodiment has higher roundness and is not easily broken. Therefore, the negative electrode sheet of the embodiment contains silicon-carbon material and graphite. The silicon-carbon material with high average sphericity and roundness has a natural sliding effect with the graphite particles. Moreover, the particles in the silicon-carbon material are relatively round, which is beneficial to improving the fracture elongation rate of the negative electrode sheet at the corner of the cell, reducing the large capacity decay caused by lithium plating, thereby improving the cycle performance of the high energy density battery cell and thus improving the reliability of the battery cell.

[0286] Compared with Comparative Examples 1-2, by implementing Examples 1 and Examples 2-1 to 2-5, silicon-carbon materials with higher sphericity can achieve improved elongation at break and compaction density in the negative electrode sheet, thereby improving the energy density and cycle performance of the battery.

[0287] Examples 1, 3-1 to 3-2, 4-1 to 4-2, and 5-1 to 5-2 demonstrate that the sphericity, silicon content, particle size DV150, and average strength of silicon-carbon materials affect the compaction density and elongation at break of the negative electrode sheet, thereby affecting the energy density and cycle performance of the battery.

[0288] As can be seen from Examples 6-1 to 6-7, using two silicon-carbon materials with different volumetric particle sizes and SPAN values ​​to prepare negative electrode sheets can increase the compaction density of the negative electrode sheets, thereby further improving the energy density and cycle performance of the battery.

[0289] In Examples 7-1 to 7-3, the negative electrode sheet of Example 1 was used, and electrolytes with different compositions and addition ratios were used, resulting in different viscosities and conductivity of the electrolytes. The electrolytes of Examples 7-1 to 7-3 had higher viscosity and higher conductivity than the electrolyte of Example 1, thus improving the charge and discharge performance of the battery.

[0290] Figure 4 shows the elongation at break of the negative electrode sheet of the embodiments and comparative examples of this application, referred to as elongation. The left side shows the elongation at break of the negative electrode sheet of Comparative Example 1, and the right side shows the elongation at break of the negative electrode sheet of Embodiment 1. It shows that the negative electrode sheet of the embodiments has a better elongation at break than the comparative example, which is beneficial to the cycle performance of the battery and reduces the probability of capacity drop during the cycle of the battery cell.

[0291] Figure 5 shows the specific capacity of negative electrode sheets with different compaction densities in the embodiments and comparative examples of this application. A is the negative electrode sheet of Comparative Example 2, B is the negative electrode sheet of Comparative Example 1. The compaction density in A is larger, and the compaction density in B is smaller. C is the negative electrode sheet of Example 5-1, and D is the negative electrode sheet of Example 5-2. The compaction density in C is larger, and the compaction density in D is smaller. This illustrates that when the embodiments have the same compaction density as the comparative examples, the negative electrode sheets of the embodiments have a larger specific capacity, which is beneficial to improving the energy density of the battery.

[0292] Figure 6 shows the silicon-carbon material in the fresh negative electrode sheet of Comparative Example 1 of this application. After the cold pressing process, the silicon-carbon material powder particles in the fresh negative electrode sheet of the Comparative Example were broken, which affected the electrochemical performance of the battery cell.

[0293] Figure 7 shows the silicon-carbon material in the fresh negative electrode sheet of Example 1 of this application. After the cold pressing process, the silicon-carbon material powder particles in the fresh negative electrode sheet of the example are more rounded, which is beneficial to the electrochemical performance of the battery cell.

[0294] 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, characterized in that, The device includes a negative electrode sheet, which includes a negative current collector and a negative active material film layer disposed on at least one side of the negative current collector. The negative active material film layer includes graphite and silicon carbide materials, wherein the average sphericity Φ of the silicon carbide material is 0.8 to 1.

0.

2. The battery cell according to claim 1, characterized in that, The average sphericity Φ of the silicon-carbon material is 0.85≤B≤0.

95.

3. The battery cell according to claim 1 or 2, characterized in that, The silicon-carbon material includes: A carbon matrix having a porous structure, the carbon matrix comprising a silicon-based material located within the porous structure; A carbon coating layer, at least partially coating the surface of the carbon matrix.

4. The battery cell according to claim 3, characterized in that, The silicon-based materials include one or more of elemental silicon, silicon oxide, silicon-carbon composite materials, and silicon alloy materials.

5. The battery cell according to any one of claims 1-4, characterized in that, The silicon-carbon material satisfies any one or more of the following conditions: 1) The tap density of the silicon carbide material is 0.9 g / cm³. 3 Up to 1.15 g / cm 3 ; 2) The volumetric particle size Dv of the silicon-carbon material 1 50 ranges from 4μm to 12μm; 3) The particle size distribution span (SPAN) of the silicon-carbon material is 1.2 to 1.

6. 4) The silicon-carbon material comprises 40% to 60% silicon and 40% to 60% carbon by mass percentage; 5) In the Raman spectrum of the silicon-carbon material, the peak intensity ID of the D peak and the peak intensity IG of the G peak satisfy 1.5 < ID / IG < 2.5; 6) The average strength of silicon-carbon materials is 20 MPa to 50 MPa.

6. The battery cell according to any one of claims 1 to 5, characterized in that, The volumetric particle size Dv of the graphite 2 50 is 14μm to 18μm.

7. The battery cell according to any one of claims 1 to 6, characterized in that, The mass ratio of the graphite to the silicon carbide material is 1:(0.66~1.5).

8. The battery cell according to any one of claims 1 to 7, characterized in that, The silicon-carbon material includes a first silicon-carbon material and a second silicon-carbon material, wherein the volumetric particle size Dv of the first silicon-carbon material is... 3 50 is less than the volumetric particle size Dv of the second silicon-carbon material 4 50.

9. The battery cell according to claim 8, characterized in that, The volumetric particle size Dv of the first silicon-carbon material 3 50 is 4μm to 6μm; the volumetric particle size Dv of the second silicon-carbon material 4 50 ranges from 8μm to 12μm.

10. The battery cell according to claim 8 or 9, characterized in that, The particle size distribution span (SPAN) of the first silicon-carbon material is 1.5 to 1.6; the particle size distribution span (SPAN) of the second silicon-carbon material is 1.2 to 1.

4.

11. The battery cell according to any one of claims 8 to 10, characterized in that, The mass ratio of the first silicon-carbon material to the second silicon-carbon material is (1-4):

1.

12. The battery cell according to any one of claims 1 to 11, characterized in that, The negative electrode sheet satisfies one or more of the following conditions: 1) The negative electrode active material film layer includes a binder and a conductive agent; 2) The compacted density of the negative electrode sheet is 1.3 g / cm³. 3 Up to 1.8 g / cm 3 ; 3) The elongation at break of the negative electrode sheet under pressure of 1.3 MPa to 1.6 MPa is 1% to 3.5%.

13. The battery cell according to any one of claims 1 to 12, characterized in that, The battery cell includes an electrolyte, and the electrolyte satisfies one or more of the following conditions: 1) The viscosity of the electrolyte is 2 to 15 mPa*S; 2) The conductivity of the electrolyte is 9 to 15 mS / cm; 3) The electrolyte includes acetate esters, which include one or more of methyl acetate, ethyl acetate, and propyl acetate.

14. A method for preparing a single battery cell, characterized in that, include: A battery cell is obtained by winding a component containing a negative electrode sheet. The negative electrode sheet includes a negative current collector and a negative active material film layer disposed on at least one side of the negative current collector. The negative active material film layer includes graphite and silicon carbon materials, wherein the average sphericity Φ of the silicon carbon material is 0.8 to 1.

0.

15. An electrical appliance, characterized in that, Includes the battery cell described in any one of claims 1 to 13 or the battery cell prepared by the method of claim 14.

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