Battery cell and preparation method therefor, silicon-carbon material and preparation method therefor, and electric device

Abstract

A battery cell and a preparation method therefor, a silicon-carbon material 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, and the negative electrode active material film layer comprises a silicon-carbon material, wherein the average strength of the silicon-carbon material is 2 MPa to 15 MPa, and the powder resistivity of the silicon-carbon material is 1 to 5 Ω·cm. Also provided are a silicon-carbon material and a preparation method therefor, and an electric device comprising the battery cell.

Description

Battery cells and their preparation methods, silicon-carbon materials and their preparation methods, and electrical devices

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese Patent Application No. 202410814334.6, filed on June 21, 2024, entitled “Battery Cell and Method for 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 and its preparation method, silicon-carbon materials and their preparation method, and an electrical device. 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, higher requirements have been placed on their performance, especially cycle performance. For example, battery cells are required to balance high energy density and good 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 and a method for preparing the same. The battery cell includes a negative electrode sheet containing a silicon-carbon material. The silicon-carbon material has suitable average strength and low powder resistivity, thus reducing the particle breakage rate of the silicon-carbon material during the charge-discharge cycle of the battery cell. This is beneficial for maintaining the structural stability of the negative electrode active material film layer and improving the volumetric energy density, cycle life, and charge-discharge performance of the battery cell. A further purpose of this application is to provide an electrical device incorporating the battery cell, thereby achieving improved volumetric energy density, cycle life, and charge-discharge performance.

[0008] In a first aspect, embodiments of this application provide a battery cell, the 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 silicon-carbon material, wherein the average strength of the silicon-carbon material is 2MPa to 15MPa; the powder resistivity of the silicon-carbon material is 1 to 5Ω·cm.

[0009] The negative electrode sheet of this application embodiment contains silicon-carbon material. The silicon-carbon material has a suitable 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 sheet containing the 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 cell to have a better cycle life.

[0010] The fact that the resistivity of silicon-carbon powder is within the above range indicates that silicon-carbon material has good conductivity, which is beneficial to improving the charge and discharge performance of battery cells.

[0011] Furthermore, the negative electrode sheet contains silicon-carbon material with suitable average strength, indicating that it has suitable softness. When a higher content of silicon-carbon material is added to the negative electrode sheet, the negative electrode active material film layer can have a suitable compaction density, thereby improving the volumetric energy density of the battery cell containing the negative electrode sheet.

[0012] In some alternative implementations, the silicon-carbon material has an average strength of 5 MPa to 8 MPa.

[0013] According to the embodiments of this application, the silicon-carbon material has a preferred average strength. During the preparation and use of the negative electrode containing the silicon-carbon material, the particle breakage rate of the silicon-carbon material is further reduced, which further improves the cycle life of the battery cell.

[0014] Furthermore, when a higher content of silicon-carbon material is added to the negative electrode sheet, the negative electrode active material film layer has a suitable compaction density, which further improves the volumetric energy density of the battery cell containing the negative electrode sheet.

[0015] In some alternative embodiments, the silicon-carbon material includes a carbon matrix having a porous structure and a silicon-based material located within the porous structure of the carbon matrix.

[0016] According to the embodiments of this application, silicon-based materials are deposited on a carbon matrix. The carbon matrix restricts the volume deformation of the silicon-based materials, enhances the structural stability of the silicon-carbon materials, reduces the particle breakage rate in the silicon-carbon materials, which is beneficial to maintaining the structural stability of the negative electrode active material film and improving the cycle life of the battery cell.

[0017] 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 materials, and silicon alloy materials.

[0018] In some alternative embodiments, the tap density of the silicon carbide material is 0.96 g / cm³. 3 Up to 1.10 gc / m 3 The option is 0.99 g / cm³. 3Up to 1.0 g / cm 3 When the tap density of silicon-carbon materials is within the above-mentioned range, the tap density of the negative electrode active material film can be increased, thereby further improving the energy density of the battery cell; it also helps the negative electrode active material film to have a suitable pore structure, reducing the difficulty of ion liquid phase transport, improving the wetting and retention characteristics of the negative electrode film to the electrolyte, and thus further improving the cycle performance of the battery cell.

[0019] In some alternative embodiments, the volumetric particle size Dv50 of the silicon-carbon material is 3 μm to 11 μm, optionally 4 μm to 9 μm.

[0020] When the volumetric particle size Dv50 of silicon-carbon materials is within the above range, it can increase the ion insertion channels in the negative electrode active material film layer, which is conducive to the rapid diffusion of ions from the particle surface to the bulk phase, thereby facilitating further optimization of the cycle performance of the battery cell; at the same time, it can also reduce the risk of silicon-carbon material particle breakage.

[0021] In some optional embodiments, the particle size distribution span (SPAN) of the silicon-carbon material is 0.9 to 2, optionally 1.2 to 1.8. When the particle size distribution span (SPAN) of the silicon-carbon material is within the above range, it is beneficial for the negative electrode active material film layer to have suitable porosity, and the silicon-carbon material has good particle packing performance, which is beneficial for improving the compaction density of the negative electrode active material film layer, thereby further improving the energy density of the battery cell.

[0022] In some optional embodiments, the average sphericity B of the silicon-carbon material is 0.9 ≤ B < 1, and can be optionally 0.92 to 0.95. An average sphericity within this range indicates that the silicon-carbon material has nearly spherical particles, resulting in a more uniform stress distribution. Compared to sheet-like or rod-shaped particles, spherical particles experience more uniform stress during charging and discharging, helping to reduce stress concentration between particles and thus improving the cycle performance of the battery cell.

[0023] 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 .

[0024] According to the embodiments of this application, the ID / IG ratio of carbon in the Raman spectrum of silicon-carbon material is within the above range, indicating that it has a good degree of graphitization, which is beneficial for the extraction and insertion of active ions and improves the capacity of silicon-carbon material.

[0025] In some alternative embodiments, the silicon-carbon material comprises 40% to 60% silicon and 40% to 60% carbon by mass percentage, optionally 47% to 50% silicon and 50% to 53% carbon.

[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 embodiments, the negative electrode active material film layer includes graphite, and the mass ratio of graphite to silicon carbide is 1:(0.66 to 1.5).

[0028] 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 performance. Furthermore, it can increase the specific capacity of the negative electrode active material film, thereby improving the energy density and cycle performance of the battery cell.

[0029] In some alternative embodiments, the negative electrode active material film layer includes a binder and a conductive agent.

[0030] In the embodiments of this application, the type of binder is not obviously limited. Any binder that can be applied to the slurry of the negative electrode sheet and has a certain bonding effect can be applied to the embodiments of this application.

[0031] In the embodiments of this application, the type of conductive agent is not obviously limited. Any conductive agent that can be applied to the slurry of the negative electrode sheet and has a good conductive effect can be applied to the embodiments of this application.

[0032] In some alternative embodiments, the compaction density of the negative electrode active material film is 1.3 g / cm³. 3 Up to 1.7 g / cm 3 1.4g / cm³ is an optional value. 3 Up to 1.6 g / cm3. A compaction density of the negative electrode active material film within this range can further improve the energy density of the battery cell. The negative electrode active material film contains silicon-carbon material, which has a suitable pore structure, enhancing the wettability and retention characteristics of the negative electrode active material film to the electrolyte, thereby further improving the cycle performance of the battery cell.

[0033] In some alternative embodiments, the elongation at break of the negative electrode sheet under a pressure of 1.3 MPa to 1.6 MPa is 1.5% to 3%, optionally 2.0% to 2.8%.

[0034] During the charging and discharging process of a battery cell, the electrode undergoes expansion and contraction. When the elongation of the negative electrode is within the aforementioned range, it can reduce stress concentration and crack formation in the electrode material, thereby improving the cycle performance of the battery cell and the reliability of the electrode. Furthermore, an elongation within this range can also reduce the probability of cracks or fissures appearing at the electrode corners, thus reducing corner lithium plating and improving the stability of the battery cell.

[0035] 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.

[0036] 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.

[0037] 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, which includes one or more of methyl acetate, ethyl acetate, and propyl acetate.

[0038] Secondly, embodiments of this application provide a method for preparing a single battery cell, comprising:

[0039] 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 a silicon-carbon material, wherein the average strength of the silicon-carbon material is 2 MPa to 15 MPa and the powder resistivity of the silicon-carbon material is 1 to 5 Ω·cm.

[0040] According to the embodiments of this application, silicon-carbon materials with suitable average strength and powder resistivity are used in the negative electrode sheet. Therefore, during the preparation and use of the negative electrode sheet containing the silicon-carbon material, the particle breakage rate of the silicon-carbon material is reduced, the resistivity is small, and the conductivity is good. This is beneficial to maintaining the structural stability of the negative electrode active material film layer, so that the battery cell has a better cycle life.

[0041] The fact that the resistivity of silicon-carbon powder is within the above range indicates that silicon-carbon material has good conductivity, which is beneficial to improving the charge and discharge performance of battery cells.

[0042] In addition, the negative electrode sheet contains silicon-carbon material with suitable average strength. When a higher content of silicon-carbon material is added to the negative electrode sheet, the negative electrode active material film layer can have a suitable compaction density, thereby improving the volumetric energy density of the battery cell containing the negative electrode sheet.

[0043] 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 the aforementioned battery cell, and therefore has at least the advantage of application with a negative electrode sheet. Attached Figure Description

[0044] 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.

[0045] Figure 1 shows a schematic diagram of one embodiment of the battery cell of this application.

[0046] Figure 2 shows an exploded view of the battery cell shown in Figure 1.

[0047] 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.

[0048] Figure 4 shows a scanning electron microscope image of a silicon-carbon material according to an embodiment of this application.

[0049] Figure 5 shows the charge-discharge curves of a battery according to an embodiment of this application and a comparative example.

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

[0051] The reference numerals in the attached drawings are explained as follows: 5, battery cell; 51, casing; 52, electrode assembly; 53, cover plate. Detailed Implementation

[0052] 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.

[0053] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is 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, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0058] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0059] Unless otherwise specified, the terms "connected" and "linked" in this application should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0060] Unless otherwise specified, in this application, the term "attachment" refers to a connection made by means of adhesion, coating, or other similar methods.

[0061] 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.

[0062] 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.

[0063] In this application, "multiple" or "more than" refers to two or more (including two). In this application, "several items" or "multiple items" refers to two or more (including two).

[0064] 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.

[0065] Energy density and cycle performance are two key performance indicators for 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, which can affect the cycle life of the battery cell. High-energy-density battery cells have high electrode compaction density, high film thickness, and low porosity, which may hinder ion transport and thus adversely affect the cycle performance of the battery cell.

[0066] Therefore, how to make high-energy-density battery cells also have good cycle performance is a technical problem that urgently needs to be solved.

[0067] As a crucial component of a battery cell, the performance of the negative electrode sheet significantly impacts 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-based materials offer 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 cells, requiring further improvement.

[0068] In view of this, the technical solution of the present application provides a battery cell and a method for preparing the same, which enables the battery cell to achieve both high energy density and good cycle performance.

[0069] Specifically, this application provides a lithium battery cell.

[0070] 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 a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process of the battery cell, ions move back and forth between the positive and negative electrode cells, inserting and extracting, and the electrolyte plays a role in conducting ions. This application does not impose any particular limitation on the type of electrolyte and it can be selected according to actual needs. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions). Battery cells using liquid electrolytes, and some battery cells using solid electrolytes, may also include a separator membrane, which is disposed between the positive and negative electrode cells and mainly serves a separating function.

[0071] battery cell

[0072] In a first aspect, embodiments of this application provide a battery cell, the battery cell including a negative electrode sheet, the negative electrode 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 silicon-carbon material, wherein the average strength of the silicon-carbon material is 2MPa to 15MPa; the powder resistivity of the silicon-carbon material is 1 to 5Ω·cm.

[0073] 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.

[0074] The negative electrode sheet of this application embodiment contains silicon-carbon material, wherein the silicon-carbon material has a suitable 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 sheet containing the 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, so that the battery cell has a better cycle life.

[0075] In addition, the negative electrode sheet contains silicon-carbon material with suitable average strength. When a higher content of silicon-carbon material is added to the negative electrode sheet, the negative electrode active material film layer can have a suitable compaction density, thereby improving the volumetric energy density of the battery cell containing the negative electrode sheet.

[0076] The fact that the resistivity of silicon-carbon powder is within the above range indicates that silicon-carbon material has good conductivity, which is beneficial to improving the charge and discharge performance of battery cells.

[0077] The fact that the average strength and powder resistivity of silicon-carbon materials are within the above range indicates that the silicon-carbon materials are prepared from specific raw materials, such as petroleum coke.

[0078] Optionally, the average strength of the silicon-carbon material is any value or a range of combinations thereof from 2MPa, 2.5MPa, 3.0MPa, 3.5MPa, 4.0MPa, 4.5MPa, 5MPa, 6MPa, 7MPa, 8MPa, 9MPa, 10MPa, and 15MPa.

[0079] The average strength can be determined using testing methods known in the art. For example, silicon-carbon material 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 in mm. The sample is tested in 200-micrometer increments until 0.1 micrometers, with a test compression force of 9.8-4903 mN, until the silicon-carbon material fractures. The experimental force P at this point is recorded in N. The average strength is taken as the average value, in MPa. Average strength = 2.8 × P / (πd) 2 ).

[0080] In some alternative implementations, the silicon-carbon material has an average strength of 5 MPa to 8 MPa.

[0081] According to the embodiments of this application, the silicon-carbon material has a preferred average strength. During the preparation and use of the negative electrode containing the silicon-carbon material, the particle breakage rate of the silicon-carbon material is further reduced, which further improves the cycle life of the battery cell.

[0082] Furthermore, when a higher content of silicon-carbon material is added to the negative electrode sheet, the negative electrode active material film layer has a suitable compaction density, which further improves the volumetric energy density of the battery cell containing the negative electrode sheet.

[0083] In some alternative embodiments, the resistivity of the silicon-carbon powder is 1.2 to 2 Ω·cm. A resistivity within this range indicates that the silicon-carbon material has good electrical conductivity, which is beneficial for improving the charge-discharge performance of individual battery cells.

[0084] The resistivity of silicon carbide powder has a well-known meaning in the art and can be tested using instruments and methods known in the field. For example, a resistivity meter (such as the ST2722 powder resistivity meter from Suzhou Jingge Electronics Co., Ltd.) can be used. During testing, a 1g powder sample is placed between the electrodes of the resistivity meter, and a constant pressure (e.g., 4 MPa) is applied using an electronic pressure gauge for 15-25 seconds to obtain a sheet-like sample. The powder resistivity δ is calculated using the formula δ=(S×R) / h, with units of Ω·cm. h is the height of the sheet-like sample in cm; R is the resistance in Ω; and S is the area of ​​the sheet-like sample in cm². 2 .

[0085] In some alternative embodiments, the silicon-carbon material includes a carbon matrix having a porous structure and a silicon-based material located within the porous structure of the carbon matrix.

[0086] According to the embodiments of this application, silicon-based materials are deposited on a carbon matrix. The carbon matrix restricts the volume deformation of the silicon-based materials, enhances the structural stability of the silicon-carbon materials, reduces the particle breakage rate in the silicon-carbon materials, which is beneficial to maintaining the structural stability of the negative electrode active material film and improving the cycle life of the battery cell.

[0087] Silicon-carbon materials are carbon-based materials with porous structures, and silicon-based materials with deposits inside the porous structures can be comprehensively identified through transmission electron microscopy and XPS elemental analysis.

[0088] 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 materials, and silicon alloy materials.

[0089] In some alternative embodiments, the tap density of the silicon carbide material is 0.96 g / cm³. 3 Up to 1.10 g / cm 3 The option is 0.99 g / cm³. 3 Up to 1.07 g / cm 3 to.

[0090] The rounded corners of this silicon-carbon material are beneficial for increasing its tap density. When the tap density of the silicon-carbon material is within the aforementioned range, it can increase the compaction density of the negative electrode active material film, thereby further improving the energy density of the battery cell. It also helps the negative electrode active material film to have a suitable pore structure, reducing the difficulty of ion liquid phase transport, improving the wetting and retention characteristics of the negative electrode film to the electrolyte, and thus further improving the cycle performance of the battery cell.

[0091] 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 art. For example, it can be determined using a powder tap density tester according to GB / T5162-2006. The testing instrument can be Dandong Baite BT-301, with the following test parameters: vibration frequency 250±15 times / minute, amplitude 3±0.2mm, number of vibrations 3, and graduated cylinder capacity 25mL.

[0092] In some alternative embodiments, the volumetric particle size Dv50 of the silicon-carbon material is 3 μm to 11 μm, optionally 4 μm to 9 μm.

[0093] When the volumetric particle size Dv50 of silicon-carbon materials is within the above range, it can increase the ion insertion channels in the negative electrode active material film layer, which is conducive to the rapid diffusion of ions from the particle surface to the bulk phase, thereby facilitating further optimization of the cycle performance of the battery cell; at the same time, it can also reduce the risk of silicon-carbon material particle breakage.

[0094] In some optional embodiments, the particle size distribution span (SPAN) of the silicon-carbon material is 0.9 to 2, optionally 1.2 to 1.8. When the particle size distribution span (SPAN) of the silicon-carbon material is within the above range, the silicon-carbon material has good particle packing performance, which is beneficial for the negative electrode active material film layer to have suitable porosity, and is beneficial for improving the compaction density of the negative electrode active material film layer, thereby further improving the energy density of the battery cell.

[0095] 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.

[0096] The volumetric particle sizes Dv10, Dv50, and Dv90 of silicon-carbon materials are well-known in the art, representing the particle sizes corresponding to a cumulative volumetric distribution percentage of 10%, 50%, and 90%, respectively. These sizes can be determined using instruments and methods known in the art. For example, they 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.

[0097] In some alternative embodiments, the average sphericity B of the silicon-carbon material is 0.9 ≤ B < 1, and can be 0.92 to 0.95.

[0098] Sphericity refers to the ratio of the minimum diameter to the maximum diameter of a particle. The closer a particle's morphology is to a sphere, the closer its sphericity is to 1. Average sphericity refers to the average sphericity of silicon-carbon materials in the negative electrode active material.

[0099] The average sphericity of silicon-carbon materials falls within the aforementioned range, indicating that the particles in these materials are nearly spherical, resulting in a more uniform stress distribution. Compared to sheet-like or rod-shaped particles, spherical particles experience more uniform stress during charging and discharging, which helps reduce stress concentration between particles and thus improves the cycle performance of individual battery cells.

[0100] 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, its accompanying graphics software, and Raman spectroscopy accessories.

[0101] 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 .

[0102] According to the embodiments of this application, the ID / IG ratio of carbon in the Raman spectrum of silicon-carbon material is within the above range, indicating that it has a good degree of graphitization, which is beneficial for the extraction and insertion of active ions and improves the capacity of silicon-carbon material.

[0103] The peak intensities of the D peak (ID) and G peak (IG) in the Raman spectra of silicon-carbon materials can be detected using an NGSLabspec Raman spectrometer with a scanning range of 100 cm⁻¹. -1 ~3200cm -1As an example, the method for detecting the graphitization intensity of silicon-carbon materials is as follows: The method for detecting the graphitization intensity of the medium-carbon matrix in silicon-carbon materials involves smearing or dropping a sample of the silicon-carbon material onto a glass slide, focusing the image, and following the parameters: Signal-to-noise ratio: Single-crystal silicon signal-to-noise ratio ≥30:1; Wavenumber range: 100cm². -1 ~3200cm -1； Resolution: 1cm -1 Repeatability: 0.05cm -1 I was measured using a Raman spectrometer. D / I G The value of .

[0104] In some alternative embodiments, the silicon-carbon material comprises 40% to 60% silicon and 40% to 60% carbon by mass percentage, optionally 47% to 50% silicon and 50% to 53% carbon.

[0105] 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.

[0106] In some alternative embodiments, the silicon-carbon material includes:

[0107] A carbon matrix having a porous structure, the carbon matrix comprising silicon-based materials located within the porous structure;

[0108] A carbon coating layer, at least partially coating the surface of a carbon matrix.

[0109] 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.

[0110] The presence of a carbon coating on the surface of silicon-carbon materials can be determined using a transmission electron microscope.

[0111] 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.

[0112] 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.

[0113] In some alternative embodiments, the negative electrode active material film layer includes graphite. Graphite can include artificial graphite and natural graphite. Graphite is a material with good electrical conductivity and chemical stability, capable of adsorbing and releasing 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 the battery cell. Graphite has a stable crystal structure, which helps maintain the shape and stability of the electrode, contributing to extending the lifespan of the battery cell and improving cycle stability.

[0114] Silicon-carbon materials have superior specific capacity and a greater rate of volume change compared to graphite due to the presence of silicon.

[0115] In some alternative embodiments, the negative electrode active material film layer includes graphite, and the mass ratio of graphite to silicon carbide is 1:(0.66 to 1.5).

[0116] 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 performance. Furthermore, it can increase the specific capacity of the negative electrode active material film, thereby improving the energy density and cycle performance of the battery cell.

[0117] In some alternative embodiments, the negative electrode active material film layer includes a binder and a conductive agent.

[0118] In this application embodiment, the type of binder is not explicitly limited. Any binder that has a certain bonding effect in the negative electrode active material film layer of the negative electrode sheet 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 forms, polyacrylamide and its modified forms, polyvinyl alcohol and its modified forms, polyacrylonitrile and its modified forms, polyethyleneimine and its modified forms, styrene-butadiene rubber and its modified forms, styrene-acrylic emulsion and its modified forms, polyacrylate and its modified forms, polyurethane and its modified forms, sodium alginate and its modified forms, guar gum and its modified forms, xanthan gum and its modified forms, gum arabic and its modified forms, β-cyclodextrin polymers, and carrageenan and its modified forms. In some optional embodiments, the negative electrode active material film layer includes a thickener. The thickener may be carboxymethyl cellulose and its salts.

[0119] In this application embodiment, the type of conductive agent is not explicitly limited. Any conductive agent that can be applied to the negative electrode active material film layer 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.

[0120] In some alternative embodiments, the compaction density of the negative electrode active material film is 1.3 g / cm³. 3 Up to 1.7 g / cm 3 1.4g / cm³ is an optional value. 3 Up to 1.6 g / cm 3 The rounded corners of the silicon-carbon material in the negative electrode active material film layer are beneficial to improving the compaction density of the film layer. When the compaction density of the negative electrode active material film layer is within the above-mentioned range, the energy density of the battery cell can be further improved. The inclusion of silicon-carbon material in the negative electrode active material film layer has a suitable pore structure, which improves the wetting and retention characteristics of the film layer with electrolyte, thereby further improving the cycle performance of the battery cell.

[0121] Please refer to Figure 4, which shows an electron microscope scan of the silicon-carbon material according to an embodiment of this application. The silicon-carbon material has rounded corners, which is beneficial to improving the compaction density of the negative electrode active material film.

[0122] 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.

[0123] 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).

[0124] 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.

[0125] During the charging and discharging process of a battery cell, the electrode undergoes expansion and contraction. When the elongation of the negative electrode is within the aforementioned range, it can reduce stress concentration and crack formation in the electrode material, thereby improving the cycle performance of the battery cell and the reliability of the electrode. Furthermore, an elongation within this range can also reduce the probability of cracks or fissures appearing at the electrode corners, thus reducing corner lithium plating and increasing the volumetric energy density of the battery cell.

[0126] The elongation at break of the negative electrode sheet is a well-known concept in the art, often simply referred to as elongation, and can be tested using methods known in the art. For example, the method for testing the elongation at break of the negative electrode sheet is as follows: Remove the negative electrode sheet from the battery cell, add electrolyte to completely immerse the sheet in the electrolyte, store it at 90°C for at least 48 hours, then remove the electrode sheet; the film layer of the negative electrode sheet will peel off from the current collector. Take the negative electrode sheet 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%.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] Ionic conductivity refers to the conductivity of an electrolyte for ions, reflecting the electrolyte's ability to conduct electricity to ions.

[0131] 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.

[0132] The lithium secondary battery provided in this application has an ionic conductivity within the above-mentioned range, and therefore has good fast-charging performance.

[0133] 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, which includes one or more of methyl acetate, ethyl acetate, and propyl acetate.

[0134] 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).

[0135] 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.

[0136] 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.

[0137] 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 specific capacity of the negative electrode sheet and thus to improving the energy density of the battery cell.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] The negative electrode active material film layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[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] Preparation method of battery cell

[0145] Secondly, embodiments of this application provide a method for preparing a single battery cell, comprising:

[0146] 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 a silicon-carbon material, wherein the average strength of the silicon-carbon material is 2 MPa to 15 MPa and the powder resistivity of the silicon-carbon material is 1 to 5 Ω·cm.

[0147] According to the embodiments of this application, a silicon-carbon material with suitable average strength and powder resistivity is used in the negative electrode sheet. Therefore, during the preparation and use of the negative electrode sheet containing the silicon-carbon material, the particle breakage rate of the silicon-carbon material is reduced, the powder resistivity is small, and it has good conductivity, which is beneficial to maintaining the structural stability of the negative electrode active material film layer and enabling the battery cell to have better cycle life.

[0148] The fact that the resistivity of silicon-carbon powder is within the above range indicates that silicon-carbon material has good conductivity, which is beneficial to improving the charge and discharge performance of battery cells.

[0149] In addition, the negative electrode sheet contains silicon-carbon material with suitable average strength. When a higher content of silicon-carbon material is added to the negative electrode sheet, the negative electrode active material film layer can have a suitable compaction density, thereby improving the volumetric energy density of the battery cell containing the negative electrode sheet.

[0150] Preparation method of negative electrode sheet

[0151] This application provides a method for preparing a negative electrode sheet, including:

[0152] S10. Carbonize the coke raw material to prepare a carbon substrate;

[0153] S20. Perform a pore-forming treatment on the carbon substrate to obtain a carbon matrix with a porous structure;

[0154] S30. Silicon is deposited within the porous structure of a carbon matrix to prepare silicon-carbon materials, wherein the powder resistivity of the silicon-carbon materials is 1 to 5 Ω·cm;

[0155] S40. Provide a slurry containing silicon carbide materials;

[0156] S50. The slurry is coated onto the negative electrode current collector to form a negative electrode active material film layer, thereby obtaining a negative electrode sheet.

[0157] According to embodiments of this application, the coke raw material can be petroleum coke. Carbon substrates are prepared by carbonization of the coke raw material. The resulting carbon substrate has a high degree of graphitization, suitable softness and hardness, and the maximum stress it can withstand is within a suitable range. Pore formation and silicon deposition are then performed on the substrate to give the resulting silicon-carbon material suitable average strength. 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 helps maintain the structural stability of the negative electrode active material film and gives the battery cell a better cycle life.

[0158] In addition, the negative electrode sheet contains silicon-carbon material and graphite with suitable average strength. When a higher content of silicon-carbon material is added to the negative electrode sheet, the negative electrode active material film layer can have a suitable compaction density, thereby improving the volumetric energy density of the battery cell containing the negative electrode sheet.

[0159] In some alternative embodiments, the corners of the carbon substrate can be shaped to make the corners rounded, which facilitates the subsequent production of silicon-carbon materials with high sphericity.

[0160] In some optional embodiments, in S10, the coke feedstock is a petroleum coke feedstock.

[0161] In some implementations, the type of coke feedstock and D can be adjusted. v The parameters such as 50 make it easier to improve the subsequent shaping and granulation processes when the coke raw material is within the given range, so that the final carbon matrix has an appropriate volume particle size.

[0162] Coke feedstock can be obtained commercially or by crushing coke materials; it can be petroleum coke. In some embodiments, the coke materials can be crushed to control the density (D) of the coke feedstock. v Parameters such as 50 are within the required range. Coke materials can be pulverized using equipment and methods known in the art, such as air jet mills, mechanical mills, or roller mills. The pulverization process often produces a large number of excessively small particles, and sometimes excessively large particles as well. Therefore, after pulverization, grading can be performed as needed to remove excessively small and excessively large particles from the pulverized powder. Grading treatment yields coke raw materials with the desired particle size distribution. Grading treatment can be carried out using equipment and methods known in the art, such as grading sieves, gravity classifiers, centrifugal classifiers, etc.

[0163] In some embodiments, S10, carbonizing the coke raw material to prepare a carbon substrate may include the following steps:

[0164] a) Provide coke raw materials;

[0165] b) Carbonize the coke raw material to obtain a carbon substrate.

[0166] Coke material crushing can be carried out in a process unit that includes a crusher, a classifier, and an induced draft fan. During the crushing process, the density (D) of the resulting coke raw material can be controlled by adjusting the feeding frequency, crushing frequency, classification frequency, and induced draft fan frequency. v The parameters, such as 50, are within the required range. Compared to the low classification frequency in traditional grinding processes, the method of this application can increase the classification frequency, which is beneficial for removing excessively small particles.

[0167] In some embodiments, the coking feedstock may include one or more of petroleum-based non-needle coke and petroleum-based needle coke. Optionally, the coking feedstock may include petroleum green coke.

[0168] The volatile matter content of coke feedstock can be tested using methods known in the art. For example, it can be determined according to SH / T 0026-1990.

[0169] In some embodiments, in step b), the edges and corners of the coke raw material particles can be polished by shaping, which is beneficial to the subsequent granulation process and gives the secondary particles in the resulting negative electrode active material higher structural stability. The coke raw material can be shaped using equipment and methods known in the art, such as shaping machines or other shaping equipment.

[0170] In some embodiments, after the coking raw material is shaped, it undergoes further grading to ensure that the final silicon-carbon material has appropriate particle size and other parameters. Grading can be performed using equipment and methods known in the art, such as grading sieves, gravity classifiers, and centrifugal classifiers.

[0171] Shaping and grading processes can be performed within a process unit comprising a shaping machine, a grading machine, and an induced draft fan. During the shaping and grading process, the Do of the resulting precursor can be controlled by adjusting the shaping frequency (e.g., the main and auxiliary frequencies of the shaping machine), the grading frequency, and the induced draft fan frequency. v Parameters such as 50 are within the required range. Compared to traditional shaping and grading processes, the method in this application increases the shaping frequency and appropriately extends the shaping time, while reducing the grading frequency and airflow frequency, resulting in a higher D content in the obtained precursor. v The 50 level adjustment is within the target range.

[0172] In the above preparation process, the coke raw material usually contains some impurity elements (such as iron, nickel, chromium, zinc, sulfur, silicon, etc.). The equipment used in the crushing, shaping and granulation process will also introduce some impurity elements (such as iron, copper, etc.). Under normal circumstances, the content of impurity elements in the core is very small, generally less than 1 ppm.

[0173] In some embodiments, the carbon substrate may be ball-milled to adjust its sphericity, etc.

[0174] In some optional embodiments, in step S10, the coke raw material is carbonized at a temperature of 900-1100°C to prepare a carbon substrate. The carbonization temperature can be any value or a range of combinations of 900°C, 950°C, 1000°C, 1050°C, and 1100°C. Carbonizing the coke raw material within the above temperature range yields a carbon substrate with a high degree of graphitization, which facilitates the subsequent preparation of silicon-carbon materials.

[0175] In some optional embodiments, in S10, the coke raw material is carbonized at a temperature of 900-1100°C to prepare a carbon substrate. This can specifically include: carbonizing at 900-1100°C, chemically activating it under alkaline conditions in a containing atmosphere for 6-8 hours, and then physically activating it by introducing carbon dioxide for 10-12 hours. The containing atmosphere can be nitrogen, and the alkaline conditions can be adjusted by adding substances such as NaOH.

[0176] In some optional embodiments, in S20, the average strength of a single carbon matrix particle is 1 MPa to 5 MPa, optionally 3 MPa to 4 MPa. An average strength of the carbon matrix within this range is beneficial for the prepared silicon-carbon material to have a suitable average strength. 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, maintaining the structural stability of the negative electrode active material film and enabling the battery cell to have a better cycle life.

[0177] In some optional embodiments, in S20, the tap density of the carbon matrix is ​​0.2 kg / m³. 3 Up to 0.4 kg / m 3 0.25kg / m 3 Up to 0.35kg / m 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 layer, which can further improve the energy density of the battery cell; it is also beneficial to further improve the cycle performance of the battery cell.

[0178] In some optional embodiments, in S20, the volumetric particle size Dv50 of the carbon matrix is ​​3 μm to 11 μm, optionally 4 μm to 9 μm. When the volumetric particle size Dv50 of the carbon matrix is ​​within the above range, it is beneficial to prepare silicon-carbon materials with a suitable volumetric particle size Dv50. Silicon-carbon materials have good particle packing properties, which is beneficial for the negative electrode active material film layer to have suitable porosity, and for increasing the compaction density of the negative electrode active material film layer, thereby further improving the energy density of the battery cell.

[0179] In some optional embodiments, in S20, the particle size distribution span (SPAN) of the carbon matrix is ​​0.9 to 2. When the particle size distribution span (SPAN) of the carbon matrix is ​​within this range, it is beneficial to prepare silicon-carbon materials with a suitable volumetric particle size (Dv50). The carbon material has good particle packing properties, which is beneficial for the negative electrode active material film to have suitable porosity. Silicon is beneficial for increasing the compaction density of the negative electrode active material film, thereby further improving the energy density of the battery cell.

[0180] 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, optionally 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 -1According 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 is beneficial for the extraction and insertion of active ions and improves the capacity of silicon-carbon materials.

[0181] In some optional embodiments, in S20, the average sphericity A of the carbon matrix is ​​0.8 ≤ A < 1, and can be selected as 0.92 to 0.95.

[0182] Sphericity refers to the ratio of the minimum diameter to the maximum diameter of a particle. The closer a particle's morphology is to a sphere, the closer its sphericity is to 1. Average sphericity refers to the average sphericity of a carbon matrix. The sphericity of silicon-carbon materials described above can be used for measurement.

[0183] The average sphericity of the carbon matrix is ​​within the above range, indicating that the particles of this type of carbon matrix powder are nearly spherical, resulting in a more uniform stress distribution. Compared to sheet-like or rod-shaped particles, spherical particles experience more uniform stress during charging and discharging, which helps reduce stress concentration between particles and thus improves the cycle performance of individual battery cells.

[0184] In some optional embodiments, in S20, the specific surface area of ​​the carbon matrix is ​​1900 m². 2 / g to 2500m 2 When the specific surface area of ​​the carbon matrix is ​​within the above-mentioned range, it is beneficial for silicon deposition on 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] 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.

[0186] In some optional embodiments, in S20, 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.

[0187] 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%.

[0188] In some optional embodiments, in S20, the carbon substrate is subjected to a pore-forming process to obtain a carbon matrix with a porous structure, which may specifically include:

[0189] Carbon-based materials are pretreated to remove impurities and surface contaminants to ensure the effectiveness of subsequent treatments;

[0190] Choose a suitable hole-forming method for hole formation. Common methods include chemical, physical, and biological methods. Physical methods include laser etching and electrochemical etching.

[0191] The material after pore-forming treatment is washed to remove residual treatment liquid and products. It is then dried to ensure the material surface is clean.

[0192] In some optional embodiments, in S30, 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 includes 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 hours.

[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 cooling with the gas source turned off to obtain spherical silicon-carbon material.

[0195] In some optional embodiments, in S40, providing a slurry containing the silicon-carbon material may specifically include: dispersing the silicon-carbon material, 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 to these.

[0196] In some optional embodiments, in S50, the slurry is coated onto the negative electrode current collector to form a negative electrode active material film layer to obtain the negative electrode sheet. This may specifically include: coating the slurry onto the negative electrode current collector, and then drying, cold pressing, and other processes to form the negative electrode sheet.

[0197] [Positive electrode plate]

[0198] 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.

[0199] 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.

[0200] 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, olivine-structured 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 olivine-structured 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.

[0201] 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.

[0202] 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.

[0203] 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.

[0204] 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.

[0205] 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.

[0206] 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).

[0207] 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.

[0208] [Isolation membrane]

[0209] 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.

[0210] 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.

[0211] [Electrolytes]

[0212] 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 at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0213] In some alternative embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0214] The type of electrolyte salt is not specifically limited and can be selected according to actual needs. For example, the electrolyte salt includes one or more lithium salts selected from those used in lithium-ion battery cells. As an example, the lithium salt includes 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).

[0215] 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).

[0216] 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.

[0217] 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.

[0218] 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 soft pack, such as a pouch. The soft pack can be made of plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0219] 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.

[0220] 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 this application or the electrode assembly 52 prepared according to the method of the second aspect of this 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.

[0221] This application provides a single battery cell. A single battery cell can be understood as a battery cell module or a battery cell pack.

[0222] 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.

[0223] Optionally, the battery cell module may also include a housing with a receiving space in which multiple battery cells are housed.

[0224] 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.

[0225] [Preparation Method]

[0226] The method for preparing the battery cell of this application is well known, and the method includes at least the step of preparing the electrode assembly according to the second aspect of the embodiments of this application.

[0227] 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.

[0228] 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.

[0229] Electrical appliances

[0230] This application provides an electrical device including the aforementioned battery cell.

[0231] 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.

[0232] 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.

[0233] 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.

[0234] Example

[0235] 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.

[0236] Example 1

[0237] Preparation of negative electrode sheet:

[0238] Preparation of silicon-carbon materials: S10. Carbonize the coke raw material to prepare a carbon substrate; specifically, this includes: using 1 kg of petroleum coke as a carbon source for carbonization activation at 960℃, and then adding 45 g of sodium hydroxide to the activated petroleum coke under nitrogen protection at 960℃ for chemical activation for 6-8 h to obtain the carbon substrate.

[0239] S20. The carbon substrate is subjected to a pore-forming treatment to obtain a carbon matrix with a porous structure; specifically, this includes: steam activation for pore-forming only, to obtain a carbon matrix, and using a TriStar II surface area analyzer, the BET of the carbon matrix is ​​measured to be 2010m. 2 / g, the pore volume of the carbon matrix is ​​0.95. Micropores smaller than 2nm account for 90% of the total pore volume.

[0240] S30. Silicon is deposited within the porous structure of the carbon matrix to prepare silicon-carbon material. Silane is used as the silicon source, and nitrogen is used as the protective gas. Vapor deposition is performed in a rotary kiln. The silane flow rate is 4.5 L / min, the protective gas flow rate is 20 L / min, the vapor deposition temperature is 560℃, and the time is 8 hours to obtain the silicon-carbon core.

[0241] A silicon-carbon material with a carbon-coated layer is prepared by coating carbon onto the surface of a silicon-carbon core. Specifically, this involves 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 comprises 47% silicon and 53% carbon by mass percentage. The DV50 of the silicon-carbon material is 8 μm, the span is 1.4, and the I... D / I G It is version 2.0.

[0242] S40. Provide a slurry comprising the silicon-carbon material and graphite; add artificial graphite, the silicon-carbon material prepared above, conductive agent carbon black, carbon nanotubes (CNTs), binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) to deionized water in a mass ratio of 58:37:0.8:0.2:2.8:1.2, mix and stir for 0.5-6 hours to obtain the slurry; the solid content of the slurry is 45%.

[0243] S50. The slurry is coated onto the negative electrode current collector to form a negative electrode active material film layer, thereby obtaining the negative electrode sheet. Specifically, this includes: uniformly coating the slurry onto one side of the negative electrode current collector, coating the slurry onto a copper foil with a thickness of 6 μm, then drying, cold pressing with a 50T roller, and slitting to obtain the negative electrode sheet, wherein the thickness of the negative electrode active material film layer is 110 μm.

[0244] Preparation of the positive electrode sheet:

[0245] Nickel-cobalt-manganese (LiNi) 0.96 Co 0.03 Mn 0.01 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 for 0.5-6 hours to obtain a positive electrode slurry. The solid content of the positive electrode slurry is 60%. The positive electrode slurry is coated on an Al foil with a thickness of 13 μm. After drying, cold pressing, and slitting, a positive electrode sheet is obtained, wherein the thickness of the positive electrode active material film layer is 151 μm.

[0246] Separating membrane:

[0247] A 7-micron-thick polypropylene film is used as the base film, with a 1-micron-thick CCS coating and a 1-micron-thick PCS coating applied to one side. The main component of the CCS coating is alumina, and the main component of the PCS coating is polyvinylidene fluoride.

[0248] Electrolyte:

[0249] LiPF6 and LIFSI were dissolved in a mixed solution of ethylene carbonate (EC), methyl ethyl carbonate (DEC), diethyl carbonate, and fluoroethylene carbonate (FEC), with a volume ratio of ethylene carbonate, methyl ethyl carbonate, diethyl carbonate, and fluoroethylene carbonate of 1:1:1:1. The concentrations of LiPF6 and LIFSI were 0.6 mol / L and 0.4 mol / L, respectively, to prepare the electrolyte.

[0250] 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 processes, a lithium-ion battery cell with dimensions of 148mm×97.5mm×28mm is obtained.

[0251] Examples 2-1 to 2-4

[0252] The difference between this embodiment and Embodiment 1 is that the carbonization activation temperature of petroleum coke, the concentration of sodium hydroxide added, and the physical activation time are adjusted as shown in Table 1 to obtain silicon-carbon materials with different average strengths. The average strength of the silicon-carbon materials is shown in Table 1.

[0253] Examples 3-1 to 3-2

[0254] The difference between this embodiment and Embodiment 1 is that the silicon-carbon content of the silicon-carbon material varies depending on the flow rate and time of silicon deposition, controlled at a flow rate of 4L / min, as shown in Table 1.

[0255] Examples 4-1 to 4-4

[0256] The difference between this embodiment and Embodiment 1 is that the silicon-carbon material in Embodiment 1 is used to prepare the negative electrode sheet. By changing the rollers of different masses used during the rolling process to control the rolling pressure, the negative electrode sheets prepared have different compaction densities and elongations, as shown in Table 1.

[0257] Implementation 5-1 to Example 5-3

[0258] The difference between this embodiment and Example 1 lies in the composition, content, viscosity, and conductivity of the electrolyte. In Example 5-3, 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 5-2, 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 5-1, 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 2.

[0259] Comparative Example 1

[0260] The difference between this comparative example and Example 1 lies in the preparation of the silicon-carbon material: coconut shells, a type of biomass, were used as raw materials, and the carbonization activation temperature of the coconut shells, the concentration of sodium hydroxide added, and the physical activation time were adjusted, as shown in Table 1.

[0261] Comparative Example 2

[0262] The difference between this comparative example and Example 1 lies in the preparation of the silicon-carbon material: phenolic resin was used as the raw material, and the carbonization activation temperature of the phenolic resin, the concentration of sodium hydroxide added, and the physical activation time were adjusted, as shown in Table 1.

[0263] Comparative Example 3

[0264] The difference between this comparative example and Example 1 lies in the preparation of the silicon-carbon material: by adjusting the carbonization activation temperature of petroleum coke, the concentration of sodium hydroxide added, and the physical activation time, silicon-carbon materials with different average strengths were prepared, as shown in Table 1.

[0265] Test section

[0266] 1) Method for testing the resistivity of silicon-carbon powder: Take 1g of silicon-carbon powder sample and place it between the electrodes of a resistivity tester. Apply constant pressure (e.g., 4 MPa) using an electronic pressure gauge and maintain it for 15-25 seconds to obtain a sheet-like sample. Calculate the powder resistivity δ of the material using the formula δ=(S×R) / h, in Ω·cm. h is the height of the sheet-like sample in cm; R is the resistance in Ω; and S is the area of ​​the sheet-like sample in cm². 2 .

[0267] 2) Test method for average strength of silicon-carbon materials: Silicon-carbon material powder is passed through a Shimazu MCT series micro-compression tester (Japan). A single powder particle sample is clamped between two indicators, and the diameter d of the single particle sample is recorded in mm. The sample is tested in 200-micrometer increments until 0.1 micrometers, with a test compression force of 9.8-4903 mN, until the silicon-carbon material fractures. The experimental force P at this point is recorded in N. The average strength is taken as the average value in MPa. Average strength = 2.8 × P / (πd) 2 ).

[0268] 3) Method for testing the compaction density of the negative electrode sheet: Take the coated and cold-pressed negative electrode sheet, remove the negative 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 active material film layer of the weighed negative electrode sheet, weigh the negative current collector, and record it as M0. The areal density of the negative electrode sheet = (M1-M0) / S1. The compaction density of the negative active material film layer = areal density of the negative active material film layer / thickness of the negative active material film layer. The thickness of the negative 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.

[0269] 3) Test method for the elongation at break of negative electrode sheet: Remove the negative electrode sheet from the cell, add electrolyte to completely immerse the electrode sheet in the electrolyte, store it at 90°C for more than 48 hours, and then remove the electrode sheet. The film layer of the negative electrode sheet can be peeled off from the current collector.

[0270] Remove the negative electrode and the current collector. Prepare a sample with a width of 15 mm and a length of 50 mm from the membrane 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 fracture from the tensile testing machine. Elongation = (L1-L0) / L0*100%.

[0271] 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). The voltage range is 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 / L.

[0272] 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.

[0273] 6) Battery cell fast charging performance test: Perform charge and discharge tests on the battery according to the following test procedure:

[0274] 1) Rest for 60 minutes at 25 degrees Celsius for 10 seconds.

[0275] 2) 1 / 3C0 DC 2.5V 25 10S (1 / 3C constant current discharge to 2.5V)

[0276] 3) Rest for 5 minutes at 25 degrees Celsius for 10 seconds.

[0277] 4) 0.4C0 CC 4.25V 25 10S (Anode potential reaches 0mV and jumps)

[0278] 5) Rest for 5 minutes at 25 degrees Celsius for 10 seconds.

[0279] 6) 1 / 3C DC 2.5V 25 degrees Celsius 10s (1 / 3C constant current discharge to 2.5V)

[0280] 7) Rest for 5 minutes at 25 degrees Celsius for 10 seconds.

[0281] 8) 0.6C0 CC 4.25V 25 degrees 10s (Anode potential reaches 0mV and then jumps)

[0282] 9) Rest for 5 minutes at 25 degrees Celsius for 10 seconds.

[0283] 10) 1 / 3C DC 2.5V 25 degrees Celsius 10s (1 / 3C constant current discharge to 2.5V)

[0284] 11) Rest for 5 minutes at 25 degrees Celsius for 10 seconds.

[0285] 12) 0.8C0 CC 4.25V 25 degrees 10s (Anode potential reaches 0mV and then jumps)

[0286] 13) Rest for 5 minutes at 25 degrees Celsius for 10 seconds.

[0287] 14) 1 / 3C0 DC 2.5V 25 10S (1 / 3C constant current discharge to 2.5V)

[0288] 15) Rest for 5 minutes at 25 degrees Celsius for 10 seconds.

[0289] 16) 1.0C0 CC 4.25V 25 10S (Anode potential reaches 0mV and jumps)

[0290] 17) Rest for 5 minutes at 25 degrees Celsius for 10 seconds.

[0291] 18) 1 / 3C0 DC 2.5V 25 degrees Celsius 10s (1 / 3C constant current discharge to 2.5V)

[0292] 19) Rest for 5 minutes at 25 degrees Celsius for 10 seconds, then fit the data to obtain the charging time in Table 1 and the curve in Figure 5. This test procedure is performed with 5% charging capacity, and the charging process ensures that the amount of lithium plating is extremely low.

[0293] The test results are shown in Table 1.

[0294] Table 2

[0295] As shown in Table 1, silicon-carbon materials produced from petroleum coke using a specific process have an average strength and powder resistivity within a suitable range, enabling battery cells to have excellent volumetric energy density, cycle life, and charge / discharge performance.

[0296] Example 2-1 uses petroleum coke as raw material. Compared with Comparative Example 1, even though coconut shell has the same average strength as Example 2-1, the powder resistivity of Comparative Example 1 is higher, the graphitization strength of carbon is lower, and the coconut shell has sharp edges. Therefore, its volumetric energy density, cycle life and charge / discharge performance are relatively lower.

[0297] Example 2-1 uses petroleum coke as raw material. Compared with Comparative Example 2, even though the raw material phenolic resin has the same average strength as that of Example 2-1, the powder resistivity of Comparative Example 1 is higher, the graphitization strength of carbon is lower, and the coconut shell has sharp edges. Therefore, the volumetric energy density, cycle life and charge-discharge performance of the battery are relatively smaller.

[0298] Example 1 uses petroleum coke as raw material. Compared with Comparative Example 3, the silicon-carbon material of Comparative Example 3 has higher average strength, but the powder resistivity of Comparative Example 3 is higher, the graphitization strength of carbon is lower, and the coconut shell has sharp edges. Therefore, the volumetric energy density, cycle life and charge-discharge performance of the battery are relatively small.

[0299] In Examples 1 and 2-1 to 2-4, the silicon-carbon material has a higher average strength and different powder resistivity. Compared with Comparative Example 3, the battery still has good volumetric energy density, cycle life and charge / discharge performance.

[0300] In Examples 3-1 to 3-2, the silicon content of the silicon-carbon material is different, which affects the volumetric energy density, cycle life and charge / discharge performance of the battery compared with Example 1.

[0301] In Examples 4-1 to 4-4, the silicon-carbon material in Example 1 was used to prepare negative electrode sheets with different compaction densities. Batteries containing negative electrode sheets with different compaction densities and elongation at break have improved volumetric energy density, cycle life, and charge / discharge performance.

[0302] In Examples 5-1 to 5-3, 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 5-1 to 5-3 had higher viscosity and higher conductivity than the electrolyte of Example 1, thus improving the charge and discharge performance of the battery.

[0303] The lithium plating window of the battery containing the silicon-carbon material in Example 2-1 and Comparative Example 2 is shown in Figure 5. The test method was obtained by the fast charging performance test of the battery cell described above, which shows that Example 2-1 has better rate performance than Comparative Example 2.

[0304] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A battery cell, wherein, The 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 a silicon-carbon material, wherein the average strength of the silicon-carbon material is 2 MPa to 15 MPa, and the powder resistivity of the silicon-carbon material is 1 to 5 Ω·cm.

2. The battery cell according to claim 1, wherein, The average strength of the silicon-carbon material is 5 MPa to 8 MPa.

3. The battery cell according to claim 1 or 2, wherein, The silicon-carbon material includes a carbon matrix with a porous structure and a silicon-based material located within the porous structure of the carbon matrix.

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

5. The battery cell according to any one of claims 1 to 4, wherein, The silicon-carbon material satisfies any one or more of the following conditions: 1) The tap density of the silicon carbide material is 0.96 g / cm³. 3 Up to 1.10 g / cm 3 ; 2) The volumetric particle size Dv50 of the silicon-carbon material is 3 μm to 11 μm; 3) The particle size distribution span (SPAN) of the silicon-carbon material is 0.9 to 2; 4) The average sphericity B of the silicon-carbon material is 0.9 ≤ B < 1; 5) In the Raman spectrum of the silicon-carbon material, the peak intensities ID of the D peak and IG of the G peak satisfy 1.5 < I. D / I G <2.5; 6) The silicon-carbon material comprises 40% to 60% silicon and 40% to 60% carbon by mass percentage.

6. The battery cell according to any one of claims 1 to 5, wherein, The negative electrode active material film layer includes graphite, and the mass ratio of graphite to silicon-carbon material is 1:(0.66~1.5).

7. The battery cell according to any one of claims 1 to 6, wherein, The negative electrode active material film layer includes a binder and a conductive agent.

8. The battery cell according to any one of claims 1 to 7, wherein, The negative electrode sheet satisfies any one or two of the following conditions: 1) The compaction density of the negative electrode active material film is 1.3 g / cm³. 3 Up to 1.7 g / cm 3 ; 2) The elongation at break of the negative electrode sheet under pressure of 1.3 MPa to 1.6 MPa is 1.5% to 3%.

9. The battery cell according to any one of claims 1 to 8, wherein, 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.

10. A method for preparing a single battery cell, wherein, include: A battery cell is obtained by winding an assembly 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 a silicon-carbon material, wherein the average strength of the silicon-carbon material is 2 MPa to 15 MPa, and the powder resistivity of the silicon-carbon material is 1 to 5 Ω·cm.

11. A silicon-carbon material, wherein, The silicon-carbon material comprises a carbon matrix with a porous structure and a silicon-based material located in the porous structure of the carbon matrix; the average strength of the silicon-carbon material is 2 MPa to 15 MPa; the powder resistivity of the silicon-carbon material is 1 to 5 Ω·cm.

12. A method for preparing a silicon-carbon material, comprising: A porous carbon matrix is ​​obtained by performing a pore-forming treatment on a carbon substrate. Silicon is deposited within the porous structure of the carbon matrix to prepare a silicon-carbon material, wherein the powder resistivity of the silicon-carbon material is 1 to 5 Ω·cm; and the average strength of the silicon-carbon material is 2 MPa to 15 MPa.

13. An electrical appliance, wherein, Includes the battery cell described in any one of claims 1-9 or the battery cell prepared by the preparation method described in claim 10.

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