Silicon-carbon composite material and preparation method thereof, battery monomer, battery device and power utilization device

Abstract

The invention relates to a silicon-carbon composite material and a preparation method thereof, a battery monomer, a battery device and an electric device. And the battery monomer negative electrode film layer comprises a silicon-carbon composite material. The silicon-carbon composite material is composed of an inner core and a double-layer shell, wherein the inner core comprises porous carbon and silicon deposited in the porous carbon; the shell comprises a first shell layer containing a carbon coating layer and a second shell layer containing a polymer coating layer (the polymer contains M functional groups such as nitrile groups, amide groups, carboxyl groups or organic boric acid). The first shell layer isolates electrolyte from active silicon, relieves side reaction and improves conductivity; the functional group of the second shell layer forms an intermolecular force with the carbon layer of the first shell layer, reducing carbon defect activity in the first shell layer and reducing electrolyte permeation. Through physical buffering, interface stability and double-layer synergistic effect, the defect problem of a traditional carbon-containing coating layer is solved, and the storage performance of the battery is remarkably improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a silicon-carbon composite material and its preparation method, a battery cell, a battery device, and an electrical device. Background Technology

[0002] Batteries are widely used in electronic devices such as mobile phones, laptops, electric vehicles, electric cars, electric airplanes, electric ships, electric car toys, electric toy ships, electric toy airplanes, and power tools.

[0003] In the development of battery cells, improving the storage performance and cycle performance of battery cells is one of the urgent problems to be solved. Summary of the Invention

[0004] To address the aforementioned technical problems, this application provides a silicon-carbon composite material and its preparation method, a battery cell, a battery device, and an electrical device.

[0005] In a first aspect, embodiments of this application provide a silicon-carbon composite material. The silicon-carbon composite material includes a core and a shell supported on the surface of the core. The core includes porous carbon and silicon deposited in the porous carbon. The shell includes a first shell layer and a second shell layer. The first shell layer is supported on the surface of the core, and the second shell layer is supported on the surface of the first shell layer away from the core. The first shell layer includes a carbon-containing coating layer. The second shell layer includes a polymer-containing coating layer. The polymer includes one or more of an aliphatic polymer containing an M functional group or a polymer containing an organoboronic acid. The M functional group includes one or more of a nitrile group, an amide group, an alkoxy group, a carboxyl group, or an amino group.

[0006] This multi-layered structural design ensures both the conductivity and integrity of the outer shell while effectively addressing the defects inherent in traditional carbon-containing coatings, thereby improving the material's storage performance. Specifically, porous carbon not only provides a suitable spatial structure to accommodate silicon deposition and buffer against silicon volume expansion, but also acts as a conductive network, effectively enhancing the conductivity of silicon. The outer shell comprises a first shell layer and a second shell layer. The first shell layer is mounted on the core surface, and the second shell layer is mounted on the side of the first shell layer furthest from the core. The first shell layer, including a carbon-containing coating, not only isolates the electrolyte from direct contact with the active silicon in the core, effectively mitigating side reactions, but also acts as a physical buffer layer to mitigate structural damage caused by the volume expansion and contraction of silicon during charging and discharging, and further improves the material's electronic conductivity. The second shell includes a polymer-containing coating layer. The functional groups in the aliphatic polymer containing the M functional group or the polymer containing organoboronic acid generate intermolecular forces with the oxygen-containing functional groups at the carbon defect sites in the first shell. By interacting with the carbon defects, the activity of the carbon defects can be reduced, thereby reducing the number of channels through which the electrolyte enters the core through the carbon defects, and ultimately improving the storage performance of the battery cell.

[0007] In some embodiments, the silicon deposited in porous carbon may optionally include amorphous silicon with a grain size of 0.5 nm to 3 nm. Porous carbon not only provides a good spatial structure to accommodate the deposition of amorphous silicon, providing buffer space for silicon volume expansion, but also acts as a conductive network, effectively improving the conductivity of silicon. Amorphous silicon exhibits isotropic expansion characteristics, while crystalline silicon exhibits anisotropic expansion behavior. Since the expansion characteristics of crystalline silicon easily lead to stress problems, and silicon materials experience significant expansion and contraction during cycling, using amorphous silicon has a clear advantage: its volume expansion is smaller than that of crystalline silicon, and its cycle stability is better. Amorphous silicon with a grain size within this range can not only be uniformly dispersed in porous carbon to enhance conductivity, but also has a smaller degree of expansion itself. Simultaneously, the porous carbon structure can effectively buffer the expansion effect, ultimately significantly improving the storage performance and cycle performance of the battery cell.

[0008] In some embodiments, the carbon-containing coating may optionally comprise amorphous carbon.

[0009] By introducing amorphous carbon into a carbon-containing coating layer, the amorphous state of silicon can be effectively maintained without high-temperature graphitization, while mitigating the reaction between carbon and silicon during high-temperature graphitization. Furthermore, this carbon-containing coating layer acts as a physical barrier, limiting direct contact between the electrolyte and the core silicon to some extent, thus maintaining the material's cycle stability. More importantly, amorphous carbon possesses excellent electronic conductivity, significantly improving the conductivity of silicon-carbon composite materials, thereby effectively enhancing the storage and cycle performance of individual battery cells.

[0010] In some embodiments, optionally, the aliphatic polymer containing the M functional group includes one or more of polyacrylonitrile, polyethylene glycol dipropyl cyanide, polyacrylamide, polyurethane, polyacrylic acid, or 3-(azidopropyl)triethoxysilane.

[0011] By selecting aliphatic polymers containing these M functional groups, such as polyacrylonitrile, polyethylene glycol dipropylene glycol, polyacrylamide, polyurethane, polyacrylic acid, or 3-(azidopropyl)triethoxysilane, the functional groups in these polymers generate intermolecular forces with oxygen-containing functional groups (such as hydroxyl, carbonyl, or carboxyl groups) at carbon defect sites in the first shell. By interacting with carbon defects, the activity of carbon defects is reduced, thereby reducing the number of channels for electrolyte to enter the core through carbon defects, further mitigating electrolyte decomposition. In addition, aliphatic polymers containing M functional groups themselves polymerize on the material surface, improving the stability of the coating layer, and ultimately improving the storage performance and cycle performance of the battery cell.

[0012] In some embodiments, optionally, the polymer containing organoboronic acid includes a polymer containing phenylboronic acid, wherein the polymer containing phenylboronic acid includes one or more of phenylboronic acid, 4-trifluoromethylphenylboronic acid, 3-cyanoboronic acid, 4-cyanoboronic acid, tetrafluorophenylboronic acid, triaminophenylboronic acid, or tetraaminophenylboronic acid. The functional groups in these organoboronic acid-containing polymers generate intermolecular forces with oxygen-containing functional groups (such as hydroxyl, carbonyl, or carboxyl groups) at carbon defect sites in the first shell, inducing the formation of a boron-containing solid electrolyte membrane (SEI), improving SEI stability, and enhancing the overall kinetics of the coating layer; furthermore, by interacting with carbon defects, the activity of carbon defects can be reduced, thereby reducing the number of channels through which the electrolyte enters the core, further mitigating electrolyte decomposition, and ultimately improving the storage and cycle performance of the battery cell.

[0013] In some embodiments, optionally, the polymer content is 0.2% to 3.0%, preferably 0.5% to 1.6%, based on the total mass of the negative electrode material. By setting the polymer content, the functionality of the polymer and the overall material performance can be effectively balanced. An appropriate amount of polymer not only generates intermolecular forces between the functional groups in aliphatic polymers containing M functional groups or polymers containing organoboronic acids and the oxygen-containing functional groups (such as hydroxyl, carbonyl, or carboxyl groups) at the carbon defect sites in the first shell, thereby reducing the activity of carbon defects through interaction with them, but also significantly alleviates the problems of conductivity degradation and increased structural rigidity caused by excessive polymer content by rationally controlling the polymer content. Thus, while ensuring the stability of the second shell coating, the material performance is optimized, ultimately improving the storage performance and cycle performance of the battery cell.

[0014] In some embodiments, the silicon content is optionally 25% to 55%, preferably 35% to 48%, based on the total mass of the negative electrode material. By setting the silicon content, a certain capacity is ensured while increasing the proportion of carbon. The carbon per unit mass reduces the stress caused by silicon expansion, thereby improving the storage performance and cycle performance of the battery cell.

[0015] In some embodiments, the thickness of the casing is optionally 8nm~40nm, preferably 10nm~30nm. By reasonably controlling the casing thickness, the physical isolation of the casing is ensured, effectively reducing the side reactions of the electrolyte at carbon defects; in addition, it can effectively suppress capacity loss and first-efficiency reduction caused by excessive casing thickness, thereby significantly improving the storage performance and cycle performance of the battery cell.

[0016] In some embodiments, the thickness of the first shell layer is optionally 4nm~30nm, preferably 8nm~20nm. By setting the thickness of the first shell layer, the function of the first shell layer and the overall material performance can be effectively balanced. The first shell layer can provide sufficient thickness to isolate the electrolyte from direct contact with the core, preventing side reactions, and can also mitigate the structural damage caused by volume changes in silicon during charging and discharging, while maintaining the electronic conductivity of the material. In addition, it can effectively suppress capacity loss and first-time efficiency reduction caused by excessive thickness of the first shell layer, further significantly improving the storage performance and cycle performance of the battery cell.

[0017] In some embodiments, the thickness of the second shell layer is optionally 4nm-15nm, preferably 5nm-12nm. By setting the thickness of the second shell layer, the function of the second shell layer and the overall material performance can be effectively balanced. The second shell layer not only generates intermolecular forces between the functional groups in the aliphatic polymer containing the M functional group or the polymer containing organoboronic acid and the oxygen-containing functional groups (such as hydroxyl, carbonyl, or carboxyl groups) at the carbon defect sites in the first shell layer, thereby reducing the activity of carbon defects through interaction with carbon defects, but also significantly alleviates the problems of conductivity degradation and increased structural rigidity caused by excessive thickness of the second shell layer by reasonably controlling the thickness of the second shell layer. Thus, while ensuring the stability of the coating, the material performance is optimized, ultimately improving the storage performance and cycle performance of the battery cell.

[0018] In some embodiments, optionally, the polymer includes a polymer containing organoboronic acid, and the boron content in the negative electrode material is 0.01% to 0.1%, preferably 0.02% to 0.05%, based on the mass of the negative electrode material. By using a polymer containing organoboronic acid and controlling the boron content, the functionality of the polymer and the overall performance of the material can be effectively balanced. An appropriate amount of polymer not only generates intermolecular forces between the functional groups in the organoboronic acid polymer and the oxygen-containing functional groups (such as hydroxyl, carbonyl, or carboxyl groups) at the carbon defect sites in the first shell, thereby reducing the activity of carbon defects through interaction with carbon defects, but also significantly alleviates the problems of conductivity degradation and increased structural rigidity caused by excessive polymer content by rationally controlling the polymer content, ultimately improving the storage performance and cycle performance of the battery cell.

[0019] In some embodiments, optionally, the polymer comprises an aliphatic polymer containing an M functional group, wherein the M functional group includes one or more of nitrile, amide, or amino groups, and the nitrogen content in the negative electrode material is 0.02% to 1.5%, preferably 0.03% to 0.3%, based on the mass of the negative electrode material. By using an aliphatic polymer containing an M functional group and controlling the nitrogen content, the functionality of the polymer and the overall performance of the material can be effectively balanced. An appropriate amount of polymer not only generates intermolecular forces between the functional groups in the aliphatic polymer containing the M functional group and the oxygen-containing functional groups (such as hydroxyl, carbonyl, or carboxyl groups) at the carbon defect sites in the first shell, thereby reducing the activity of carbon defects through interaction with carbon defects, but also significantly alleviates the problems of conductivity degradation and increased structural rigidity caused by excessive polymer content by rationally controlling the polymer content, ultimately improving the storage performance and cycle performance of the battery cell.

[0020] In some embodiments, the average particle size of the silicon-carbon composite material is optionally 7 μm to 11 μm. By controlling the average particle size of the silicon-carbon composite material within this range, on the one hand, the reduction in specific surface area caused by particle agglomeration during the polymer coating process can be alleviated; on the other hand, the problem of deterioration in bulk dynamics caused by excessively large particles can be effectively reduced. Therefore, controlling the average particle size between 7 μm and 11 μm improves the dispersibility of the material, thereby significantly improving the storage performance and cycle performance of the battery cell.

[0021] In some embodiments, optionally, the BET specific surface area of ​​the silicon-carbon composite material is 0.5 m². 2 / g~2m 2 / g. By reasonably controlling the range of BET specific surface area, it is helpful to reduce the consumption of active lithium during the formation of SEI (solid electrolyte interface), thereby improving the first efficiency of the battery and reducing the continuous consumption of active lithium in subsequent cycles, significantly improving the storage performance and cycle performance of the battery cell.

[0022] In some embodiments, optionally, the BET specific surface area of ​​the negative electrode material is 0.5 m². 2 / g~4m 2 / g. By reasonably controlling the range of BET specific surface area, it is helpful to reduce the consumption of active lithium during the formation of SEI (solid electrolyte interface), thereby improving the first efficiency of the battery and reducing the continuous consumption of active lithium in subsequent cycles, significantly improving the storage performance and cycle performance of the battery cell.

[0023] Secondly, embodiments of this application provide a method for preparing a silicon-carbon composite material, comprising the following steps: Core preparation: Silicon was deposited on porous carbon using chemical vapor deposition to obtain sample A containing a core. The temperature of the chemical vapor deposition method was 500℃~640℃, and the deposition time was 1h~7h. Carbon coating: Sample A is coated with carbon using chemical vapor deposition to form carbon-coated sample B. The temperature of the chemical vapor deposition method is 540℃~640℃, and the deposition time is 1h~6h. Polymer coating: Sample B is added to a solvent, a certain proportion of polymer is added, the solid content of the solution is controlled, and after stirring and mixing, the solvent is evaporated by spray drying to obtain sample C. The solvent includes one or more of water, NMP or ethanol, and the solid content of the solution is in the range of 20% to 50%. The polymer includes one or more of aliphatic polymers containing M functional groups or polymers containing organoboronic acids. The M functional group includes one or more of nitrile, amide, alkoxy, carboxyl or amino groups. Calcination treatment: Sample C is transferred to an inert atmosphere furnace for calcination treatment to obtain the final silicon-carbon composite material. The calcination treatment temperature is 100℃~400℃ and the calcination treatment time is 1h~6h.

[0024] Thirdly, embodiments of this application provide a battery cell including a positive electrode, a negative electrode, and a separator, wherein the separator is located between the positive electrode and the negative electrode; the negative electrode includes a negative current collector and a negative electrode film disposed on at least one side of the negative current collector, wherein the negative electrode film includes a silicon-carbon composite material of the first aspect of this application or a silicon-carbon composite material prepared according to the method of the second aspect of this application.

[0025] Fourthly, embodiments of this application provide a battery device, including a single battery cell from the third aspect of this application.

[0026] Fifthly, embodiments of this application provide an electrical device, including a battery cell according to the third aspect of this application or a battery device according to the fourth aspect of this application. Attached Figure Description

[0027] 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.

[0028] Figure 1 The diagram shows a schematic of a battery cell provided in some embodiments of this application.

[0029] Figure 2A schematic diagram of an electrical device provided in some embodiments of this application is shown.

[0030] Figure 3 The images show scanning electron microscope (SEM) images and energy dispersive spectroscopy (EDS) elemental analysis diagrams of the negative electrode sheets provided in some embodiments of this application.

[0031] Figure 4 The following are scanning electron microscope (SEM) images and energy dispersive spectroscopy (EDS) elemental analysis diagrams of the negative electrode sheets provided in this application.

[0032] Figure 5 The following are scanning electron microscope (SEM) images and energy dispersive spectroscopy (EDS) elemental analysis diagrams of the negative electrode sheets provided in this application. Detailed Implementation

[0033] The following detailed description, with appropriate reference to the accompanying drawings, discloses the silicon-carbon composite material and its preparation method, battery cell, battery device, and electrical device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually 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.

[0034] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0035] 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.

[0036] 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.

[0037] Unless otherwise specified, all steps in 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.

[0038] Unless otherwise specified, in this application, the terms "first," "second," etc., are used to distinguish different objects, rather than to describe a specific order or primary / secondary relationship.

[0039] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0040] In the description of the embodiments of this application, unless otherwise specified, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0041] Unless otherwise stated, the test temperature for all parameters mentioned in this application is 25°C.

[0042] The secondary battery cell mentioned in the embodiments of this application can independently perform charging and discharging functions. After discharging, it can be recharged to activate the active materials and continue to be used. The battery cell can be cylindrical, cuboid, or other shapes, etc., and the embodiments of this application are not limited in this respect. Figure 1 The example shown is a rectangular battery cell 5.

[0043] The battery cells provided in the embodiments of this application may include, but are not limited to, lithium battery cells and sodium battery cells, such as lithium-ion battery cells, sodium-ion battery cells, lithium metal battery cells, sodium metal battery cells, etc.

[0044] The battery cell provided in the embodiments of this application includes an electrode assembly. The electrode assembly can be a wound structure or a stacked structure, and the embodiments of this application are not limited in this regard. The battery cell also includes an outer packaging, which can be used to encapsulate the electrode assembly. The outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, such as one or more of aluminum-plastic film, polypropylene, polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0045] The battery apparatus mentioned in the embodiments of this application may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple battery cells, which are connected in series, parallel, or mixed connections via busbars.

[0046] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells.

[0047] As an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple battery cells together to form an independent module. As another example, a battery module can be formed by bundling multiple battery cells together with cable ties.

[0048] In some embodiments, the battery device may be a battery pack, which includes a housing and one or more individual battery cells housed within the housing.

[0049] As an example, the battery cell assembly can be a battery module, which can be housed in a housing by fixing the battery module in the housing.

[0050] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple battery cells to the housing.

[0051] As an example, the enclosure may include a first enclosure and a second enclosure. The first enclosure and the second enclosure are fastened together to form a closed space inside the enclosure to house the individual battery cells. Here, "closed" refers to covering or closing, and can be either sealed or unsealed. The first enclosure may be a top cover or a bottom plate.

[0052] As an example, the enclosure may include a top cover, a frame, and a bottom plate. The top cover and bottom plate are connected to the frame, creating an enclosed space inside the enclosure to house the individual battery cells.

[0053] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0054] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use battery cells or battery devices, such as, but not limited to, mobile devices (e.g., mobile phones, tablets, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc. Battery cells and battery devices are used to store or provide electrical energy.

[0055] Figure 2 This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.

[0056] Electrode assemblies generally include a positive electrode, a negative electrode, and an isolator. The isolator is located between the positive and negative electrodes and serves to isolate the positive and negative electrodes to prevent short circuits.

[0057] [Silicon-carbon composite materials] In the field of lithium-ion batteries, silicon-based anode materials have attracted much attention due to their extremely high theoretical capacity (4200 mAh / g) and are considered an ideal choice for next-generation high-energy-density batteries. However, silicon materials undergo significant volume changes (approximately 300%) during charge and discharge. This massive volume expansion not only leads to structural damage but also affects their storage and cycle performance. Therefore, effectively mitigating the volume change problem of silicon materials and improving their storage and cycle performance has become a current research hotspot.

[0058] To address this issue, researchers have proposed a series of surface coating technologies. Among them, carbon coatings effectively suppress structural damage caused by silicon volume changes through physical buffering. Furthermore, carbon coatings are widely used for surface modification of silicon materials due to their excellent physical insulation properties and electronic conductivity. However, carbon coatings inevitably contain defects (such as unsaturated carbon bonds and atomic vacancies). These defects, due to their unsaturated electronic structure and high surface and active site energies, become preferential adsorption sites for water or CO2 from the air. These adsorbed molecules undergo dissociation and recombination at the defective active sites, thereby generating oxygen-containing functional groups (such as hydroxyl, carbonyl, or carboxyl groups) on the carbon surface. The electrolyte may penetrate into the silicon core through these carbon defects, leading to side reactions. Moreover, the oxygen-containing functional groups enriched near the carbon defects can also induce electrolyte reactions, resulting in electrolyte decomposition and further affecting the material's storage performance.

[0059] To address the aforementioned issues, this application provides a silicon-carbon composite material comprising a core and a shell loaded on the surface of the core. The core comprises porous carbon and silicon deposited in the porous carbon. The shell comprises a first shell layer and a second shell layer. The first shell layer is loaded on the surface of the core, and the second shell layer is loaded on the side of the first shell layer away from the core. The first shell layer comprises a carbon-containing coating layer. The second shell layer comprises a polymer-containing coating layer. The polymer comprises one or more of an aliphatic polymer containing an M functional group or a polymer containing an organoboronic acid. The M functional group comprises one or more of a nitrile group, an amide group, an alkoxy group, a carboxyl group, or an amino group.

[0060] This multi-layered structural design ensures both the conductivity and integrity of the outer shell while effectively addressing the defects inherent in traditional carbon-containing coatings, thereby improving the material's storage performance. Specifically, porous carbon not only provides a suitable spatial structure to accommodate silicon deposition and buffer against silicon volume expansion, but also acts as a conductive network, effectively enhancing the conductivity of silicon. The outer shell comprises a first shell layer and a second shell layer. The first shell layer is mounted on the core surface, and the second shell layer is mounted on the side of the first shell layer furthest from the core. The first shell layer, including a carbon-containing coating, not only isolates the electrolyte from direct contact with the active silicon in the core, effectively mitigating side reactions, but also acts as a physical buffer layer to mitigate structural damage caused by the volume expansion and contraction of silicon during charging and discharging, and further improves the material's electronic conductivity. The second shell includes a polymer-containing coating layer. The functional groups in the aliphatic polymer containing the M functional group or the polymer containing organoboronic acid generate intermolecular forces with the oxygen-containing functional groups at the carbon defect sites in the first shell. By interacting with the carbon defects, the activity of the carbon defects can be reduced, thereby reducing the number of channels through which the electrolyte enters the core through the carbon defects, and ultimately improving the storage performance of the battery cell.

[0061] Test methods for aliphatic polymers containing M functional groups or polymers containing organoboronic acids: (1) Preparation of negative electrode material: 1) Battery disassembly: Disassemble the battery in an inert atmosphere glove box (argon or nitrogen protection) and remove the negative electrode. This prevents air and moisture from affecting sensitive materials (such as silicon and carboxyl groups).

[0062] 2) Material Separation: Cut the electrode into small pieces and place them in a container. Add a solvent, such as deionized water, and ultrasonically disperse for 10 minutes or soak for 24 hours to dissolve the water-based binder and disperse the active material particles. Wash, filter, dry, and dissolve again, repeating this process three times until the binder and active material are separated.

[0063] 3) Cleaning and drying: The material is gently cleaned with anhydrous solvents (such as DMC, DEC) to remove residual electrolyte and byproducts such as LiF. Then it is dried in a vacuum environment to obtain the negative electrode material. The negative electrode material includes the silicon-carbon composite material, conductive carbon, and other active negative electrode materials such as graphite.

[0064] (2) Testing of aliphatic polymers containing M functional groups or polymers containing organoboronic acids: 1) Preliminary morphological observation (SEM): • Technology: Scanning electron microscope • Objective: To observe the overall morphology of the active material. In silicon-carbon composites, nano-sized silicon particles (tens to hundreds of nanometers) embedded within a hard carbon matrix are typically observed. If the polymer coating is sufficiently thick (usually a few to tens of nanometers), a different contrast between the silicon particle surface and the hard carbon, or a blurred coating layer, may be visible under high-resolution SEM. However, this is only a preliminary indication and does not confirm the chemical composition.

[0065] 2) X-ray photoelectron spectroscopy (XPS) characterization Determination of the M functional group: XPS identifies chemical bonds by detecting changes in the binding energy (BE) of elements on the sample surface. The core principle is that different chemical bonds cause shifts in the electron binding energy of the same element. For example: C 1s: The chemical environment of carbon (such as C–C, C–O, C=O) corresponds to different BE.

[0066] N 1s: The chemical environment of nitrogen (e.g., –NH2, –C≡N, –CONH2) corresponds to different BE.

[0067] O 1s: The chemical environment of oxygen (such as –C–O–, –C=O, –OH) corresponds to different BE.

[0068] Sample preparation: The sample must be dry, non-volatile, and have a smooth surface (powder can be pressed into tablets or coated).

[0069] Non-conductive samples need to be plated with gold or carbon (to prevent charge accumulation).

[0070] Instrument calibration: The binding energy zero point was calibrated using the C 1s peak (BE = 284.8 eV).

[0071] Scan parameters: Full spectrum scan: Al Kα X-ray source (1486.6 eV), resolution 0.1 eV, scan range 0–1200 eV.

[0072] High-Resolution Scan: C 1s: 280–300 eV, resolution 0.05 eV.

[0073] N 1s: 395–410 eV, resolution 0.05 eV.

[0074] O 1s: 525–540 eV, resolution 0.05 eV.

[0075] Data processing: The peaks of different chemical states were separated by fitting the Gaussian-Lorentzian curve.

[0076] Calculate the area ratio of each peak and analyze the proportion of functional groups.

[0077] Characteristic peak positions and chemical state analysis 1. Nitrile (-C≡N) Amide (-CONH2) Amino (-NH2) N 1s: ~400.0-401.5 eV (C≡N bond) ~398.5-400.0 eV (-NH2 or -NH- group).

[0078] C 1s: ~288.0-289.5 eV (related to triple bond carbon). ~287.5-288.5 eV (amide carbonyl) ~531.0-533.0 eV (C=O oxygen) ~284.8-285.5 eV (CN bond) 2. Alkoxy groups (-OR, such as -OH, -OC2H5) C 1s: ~286.0-287.0 eV (CO bond).

[0079] O 1s: -CO-: ~531.0533.0 eV.

[0080] 3. Carboxyl group (COOH) C 1s: C=O: ~288.0-289.0 eV (carboxyl carbonyl). C-OH: ~286.0-287.0 eV (hydroxyl carbon).

[0081] O 1s: C=O: ~531.5-533.0 eV. –OH: ~533.5-535.0 eV.

[0082] Tests for organoboronic acids: XPS characterization: 1. Sample preparation steps: Conductivity treatment: The sample is deposited with a conductive carbon layer of 10-30 nm thickness under an inert atmosphere (such as argon) or coated with a conductive adhesive (such as silver paste) to reduce the charging effect.

[0083] Surface cleaning: using low-temperature ion sputtering (Ar) + Sputtering (1 keV energy, sputtering time ≤30 s) removes surface contaminants and avoids thermal decomposition of organoboronic acids.

[0084] 2. XPS parameter settings: Full spectrum scanning: Al Kα radiation source (1486.6 eV), energy resolution ≤0.1 eV, scanning range 0-1300 eV.

[0085] High-resolution B 1s scan: energy resolution ≤0.05 eV, step size 0.01 eV, analysis range 188-192 eV.

[0086] Charge correction: The B 1s energy level shift is corrected based on the binding energy of organic carbon (CC) in C 1s (284.8 eV).

[0087] 3. Data processing and chemical state identification: B 1s peak fitting: Using an asymmetric Gaussian-Lorentzian mixing function, the following chemical states were distinguished: B-OH: Binding energy 190.2 ± 0.2 eV (FWHM 1.0-1.5 eV); BOC: Binding energy 190.5-190.8 eV (substituent type affects offset).

[0088] In some embodiments, the silicon deposited in porous carbon may optionally include amorphous silicon with a grain size of 0.5 nm to 3 nm. Porous carbon not only provides a good spatial structure to accommodate the deposition of amorphous silicon, providing buffer space for silicon volume expansion, but also acts as a conductive network, effectively improving the conductivity of silicon. Amorphous silicon exhibits isotropic expansion characteristics, while crystalline silicon exhibits anisotropic expansion behavior. Since the expansion characteristics of crystalline silicon easily lead to stress problems, and silicon materials experience significant expansion and contraction during cycling, using amorphous silicon has a clear advantage: its volume expansion is smaller than that of crystalline silicon, and its cycle stability is better. Amorphous silicon with a grain size within this range can not only be uniformly dispersed in porous carbon to enhance conductivity, but also has a smaller degree of expansion itself. Simultaneously, the porous carbon structure can effectively buffer the expansion effect, ultimately significantly improving the storage performance and cycle performance of the battery cell.

[0089] As a non-limiting example, the grain size of amorphous silicon includes, but is not limited to: 3nm, 2.99nm, 2.8nm, 2.7nm, 2.6nm, 2.5nm, 2.4nm, 2.3nm, 2.2nm, 2.1nm, 2.0nm, 1.9nm, 1.8nm, 1.7nm, 1.6nm, 1.5nm, 1.4nm, 1.3nm, 1.2nm, 1.0nm, 0.8nm, and 0.5nm.

[0090] Amorphous silicon refers to a semiconductor material with a short-range ordered structure, belonging to the amorphous form of silicon-based materials. Its atomic arrangement does not possess the long-range ordered structure of crystalline silicon, but it does have a short-range atomic arrangement, resulting in electron transport properties that fall between those of a conductor and a semiconductor.

[0091] Methods for testing amorphous silicon and its grain size: (1) Preparation of negative electrode material Refer to the above-mentioned method for preparing anode materials.

[0092] (2) XRD test Based on XRD testing of the anode material, the grain size is obtained by fitting the peak with a diffraction angle of approximately 28.5° (2θ) and then substituting the obtained peak width and peak position into the Scherrer equation.

[0093]

[0094] K is the Scherrer constant. If B is the full width at half maximum (FWHM) of the diffraction peak, then K = 0.89; if B is the integral width at half maximum (FWHM) of the diffraction peak, then K = 1. D is the average thickness of the grain perpendicular to the crystal plane (Å); B is the measured FWHM of the diffraction peak in the sample; θ is the Bragg diffraction angle, in degrees; γ is the X-ray wavelength, typically 1.54056 Å for Cu kα. Silicon grains with a size ≤ 5 nm are defined as amorphous silicon.

[0095] In some embodiments, the carbon-containing coating may optionally comprise amorphous carbon.

[0096] By introducing amorphous carbon into a carbon-containing coating layer, the amorphous state of silicon can be effectively maintained without high-temperature graphitization, while mitigating the reaction between carbon and silicon during high-temperature graphitization. Furthermore, this carbon-containing coating layer acts as a physical barrier, limiting direct contact between the electrolyte and the core silicon to some extent, thus maintaining the material's cycle stability. More importantly, amorphous carbon possesses excellent electronic conductivity, significantly improving the conductivity of silicon-carbon composite materials, thereby effectively enhancing the storage and cycle performance of individual battery cells.

[0097] Test methods for amorphous carbon: (1) Preparation of negative electrode material Referring to the above-described method for preparing the negative electrode material, the negative electrode material comprises the aforementioned silicon-carbon composite material, conductive carbon, and other active negative electrode materials such as graphite.

[0098] (2) Pre-processing: Surface observation: The surface of the above-mentioned negative electrode material was observed under a scanning electron microscope, and silicon-carbon composite material and other particles were distinguished by EDS.

[0099] Micromanipulation: Using a micromanipulator (such as NanoManipulator), the silicon-carbon composite material is picked up from the surface of the negative electrode material and transferred to a TEM copper grid.

[0100] Thickness reduction: If the silicon-carbon composite particles are thick, FIB (fiber-insulated glass) is used to further thin them to an electron-transmitting thickness (<100 nm). The atomic layer thickness of the coating layer is directly measured using a bright-field (BF) or high-resolution (HRTEM) mode of a TEM. Lattice fringes cannot be observed in the carbon layer.

[0101] In some embodiments, optionally, the aliphatic polymer containing the M functional group includes one or more of polyacrylonitrile, polyethylene glycol dipropyl cyanide, polyacrylamide, polyurethane, polyacrylic acid, or 3-(azidopropyl)triethoxysilane.

[0102] By selecting aliphatic polymers containing these M functional groups, such as polyacrylonitrile, polyethylene glycol dipropylene glycol, polyacrylamide, polyurethane, polyacrylic acid, or 3-(azidopropyl)triethoxysilane, the functional groups in these polymers generate intermolecular forces with oxygen-containing functional groups (such as hydroxyl, carbonyl, or carboxyl groups) at carbon defect sites in the first shell. By interacting with carbon defects, the activity of carbon defects is reduced, thereby reducing the number of channels for electrolyte to enter the core through carbon defects, further mitigating electrolyte decomposition. In addition, aliphatic polymers containing M functional groups themselves polymerize on the material surface, improving the stability of the coating layer, and ultimately improving the storage performance and cycle performance of the battery cell.

[0103] In some embodiments, optionally, the polymer containing organoboronic acid includes a polymer containing phenylboronic acid, which includes one or more of phenylboronic acid, 4-trifluoromethylphenylboronic acid, 3-cyanoboronic acid, 4-cyanoboronic acid, tetrafluorophenylboronic acid, triaminophenylboronic acid, or tetraaminophenylboronic acid. The functional groups in these organoboronic acid-containing polymers interact with oxygen-containing functional groups (such as hydroxyl, carbonyl, or carboxyl groups) at carbon defect sites in the first shell, inducing the formation of a boron-containing solid electrolyte membrane (SEI), improving SEI stability, and enhancing the overall kinetics of the coating layer. Furthermore, by interacting with carbon defects, the activity of carbon defects can be reduced, thereby reducing the number of channels through which the electrolyte enters the core, further mitigating electrolyte decomposition, and ultimately improving the storage and cycle performance of the battery cell.

[0104] In some embodiments, optionally, the polymer content is 0.2% to 3.0%, preferably 0.5% to 1.6%, based on the total mass of the negative electrode material. By setting the polymer content, the functionality of the polymer and the overall material performance can be effectively balanced. An appropriate amount of polymer not only generates intermolecular forces between the functional groups in aliphatic polymers containing M functional groups or polymers containing organoboronic acids and the oxygen-containing functional groups (such as hydroxyl, carbonyl, or carboxyl groups) at the carbon defect sites in the first shell, thereby reducing the activity of carbon defects through interaction with them, but also significantly alleviates the problems of conductivity degradation and increased structural rigidity caused by excessive polymer content by rationally controlling the polymer content. Thus, while ensuring the stability of the second shell coating, the material performance is optimized, ultimately improving the storage performance and cycle performance of the battery cell.

[0105] As a non-limiting example, the polymer content includes, but is not limited to: 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, based on the total mass of the anode material.

[0106] Methods for testing polymer content: (1) Preparation of negative electrode material Refer to the above-mentioned method for preparing anode materials.

[0107] (2) Thermogravimetric analysis test: Thermogravimetric analysis [GB / T 13464-2008] was used to measure the percentage of heat loss of the negative electrode material between 100-450℃, and the percentage of the polymer coating was obtained.

[0108] In some embodiments, the silicon content is optionally 25% to 55%, preferably 35% to 48%, based on the total mass of the negative electrode material. By setting the silicon content, a certain capacity is ensured while increasing the proportion of carbon. The carbon per unit mass reduces the stress caused by silicon expansion, thereby improving the storage performance and cycle performance of the battery cell.

[0109] As a non-limiting example, the silicon content includes, but is not limited to: 25%, 30%, 35%, 40%, 45%, 48%, 50%, and 55%, based on the total mass of the anode material.

[0110] Methods for testing silicon content: (1) Preparation of negative electrode material Referring to the above-mentioned anode material preparation method (2) Silicon content test Quantitative analysis of total silicon content in silicon-carbon composites using XRF method I. Instrument Preparation XRF spectrometer type: Energy-dispersive radiofrequency (EDXRF) Calibration standard sample: Instrument calibration was performed using standard samples with known silicon content.

[0111] II. Sample Preparation The key to sample preparation is uniformity and surface smoothness, avoiding pores or particle accumulation that could affect X-ray excitation efficiency. Powder samples (such as silicon-based materials and ceramics) are pressed into sheets (20-25 mm in diameter and 5-10 mm in thickness) under a pressure of 10-20 MPa. X-ray tube voltage and current: The Kα line energy of silicon is 1.74 keV, so a voltage of 40-50 kV and a current of 50-100 µA are typically selected. Measurement time: 50-300 seconds. Sample testing: Place the prepared sample in the sample chamber, ensuring the surface is perpendicular to the X-ray beam. Start the testing program and record the characteristic X-ray spectrum of silicon (Kα line near 1.74 keV). Matrix correction: If other elements (such as iron or aluminum) are present in the sample, matrix effects (such as absorption and enhancement effects) need to be corrected using empirical coefficients or basic parameter methods.

[0112] Characteristic peak identification: The Kα line (1.74 keV) and Kβ line (1.89 keV) of silicon are the main characteristic peaks. The silicon content is calculated based on the peak intensities.

[0113] Quantitative analysis: Silicon content is calculated using the standard curve method (comparing the peak intensity of the test sample with that of a standard sample) or a built-in software algorithm (such as the FP method or empirical coefficient method).

[0114] Repeatability verification: Repeat the test 3 times for the same sample to ensure that the relative standard deviation (RSD) is <5%.

[0115] In some embodiments, the thickness of the casing is optionally 8nm~40nm, preferably 10nm~30nm. By reasonably controlling the casing thickness, the physical isolation of the casing is ensured, effectively reducing the side reactions of the electrolyte at carbon defects; in addition, it can effectively suppress capacity loss and first-efficiency reduction caused by excessive casing thickness, thereby significantly improving the storage performance and cycle performance of the battery cell.

[0116] As a non-limiting example, the thickness of the casing includes, but is not limited to: 8nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, and 40nm.

[0117] Test method for shell thickness: (1) Preparation of negative electrode material Referring to the above-described method for preparing the negative electrode material, the negative electrode material comprises the aforementioned silicon-carbon composite material, conductive carbon, and other active negative electrode materials such as graphite.

[0118] (2) Pre-processing: Surface observation: The surface of the above-mentioned negative electrode material was observed under a scanning electron microscope, and silicon-carbon composite material and other particles were distinguished by EDS.

[0119] Micromanipulation: Using a micromanipulator (such as NanoManipulator), the silicon-carbon composite material is picked up from the surface of the negative electrode material and transferred to a TEM copper grid.

[0120] Thickness reduction: If the particles are thick, FIB (fiber-insulated electrode) is used to further thin them to the electron-transmitting thickness (<100 nm). The outer shell thickness is directly measured using bright-field (BF) or high-resolution (HRTEM) mode of TEM.

[0121] In some embodiments, the thickness of the first shell layer is optionally 4nm~30nm, preferably 8nm~20nm. By setting the thickness of the first shell layer, the function of the first shell layer and the overall material performance can be effectively balanced. The first shell layer can provide sufficient thickness to isolate the electrolyte from direct contact with the core, preventing side reactions, and can also mitigate the structural damage caused by volume changes in silicon during charging and discharging, while maintaining the electronic conductivity of the material. In addition, it can effectively suppress capacity loss and first-time efficiency reduction caused by excessive thickness of the first shell layer, further significantly improving the storage performance and cycle performance of the battery cell.

[0122] As a non-limiting example, the thickness of the first shell layer includes, but is not limited to: 4nm, 8nm, 10nm, 12nm, 14nm, 16nm, 18nm, 20nm, 25nm, and 30nm.

[0123] Methods for testing the thickness of the first shell layer: Refer to the above-mentioned test method for shell thickness.

[0124] In some embodiments, the thickness of the second shell layer is optionally 4 nm to 15 nm, preferably 5 nm to 12 nm. By setting the thickness of the second shell layer, the function of the second shell layer and the overall material performance can be effectively balanced. The second shell layer not only generates intermolecular forces between the functional groups in the aliphatic polymer containing the M functional group or the polymer containing organoboronic acid and the oxygen-containing functional groups (such as hydroxyl, carbonyl, or carboxyl groups) at the carbon defect sites in the first shell layer, thereby reducing the activity of carbon defects through interaction with carbon defects, but also significantly alleviates the problems of conductivity degradation and increased structural rigidity caused by excessive thickness of the second shell layer by reasonably controlling the thickness of the second shell layer. Thus, while ensuring the stability of the coating, the material performance is optimized, ultimately improving the storage performance and cycle performance of the battery cell.

[0125] As a non-limiting example, the thickness of the second shell includes, but is not limited to: 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, and 15nm.

[0126] Methods for testing the thickness of the second shell: Refer to the above-mentioned test method for shell thickness.

[0127] In some embodiments, optionally, the polymer includes a polymer containing organoboronic acid, and the boron content in the negative electrode material is 0.01% to 0.1%, preferably 0.02% to 0.05%, based on the mass of the negative electrode material. By using a polymer containing organoboronic acid and controlling the boron content, the functionality of the polymer and the overall performance of the material can be effectively balanced. An appropriate amount of polymer not only generates intermolecular forces between the functional groups in the organoboronic acid polymer and the oxygen-containing functional groups (such as hydroxyl, carbonyl, or carboxyl groups) at the carbon defect sites in the first shell, thereby reducing the activity of carbon defects through interaction with carbon defects, but also significantly alleviates the problems of conductivity degradation and increased structural rigidity caused by excessive polymer content by rationally controlling the polymer content, ultimately improving the storage performance and cycle performance of the battery cell.

[0128] As a non-limiting example, the B element content in the negative electrode material includes, but is not limited to: 0.01%, 0.02%, 0.04%, 0.05%, 0.06%, 0.08%, and 0.1%, based on the mass of the negative electrode material.

[0129] Test method for boron (B) content in anode materials: (1) Preparation of negative electrode material Referring to the above-mentioned anode material preparation method (2) Determination of element B content Quantitative analysis of element B: The negative electrode material was digested according to EPA-3052-1996, "Microwave Acid Digestion of Silicates," and then the content of the target element was determined using an ICAP-7000 inductively coupled plasma atomic emission spectrometer (ICP-OES) from Thermo Fisher Scientific, in accordance with EPA 6010D-2014, "Inductively Coupled Plasma Atomic Emission Spectrometry." The specific testing method was as follows: 0.5 g of the negative electrode material sample was microwave-digested using 10 mL of nitric acid and 10 mL of hydrofluoric acid. After digestion, the sample was added to a 50 mL volumetric flask and diluted to volume. The content of the target element was then determined using an ICAP-7000 ICP-OES instrument.

[0130] In some embodiments, optionally, the polymer comprises an aliphatic polymer containing an M functional group, wherein the M functional group includes one or more of nitrile, amide, or amino groups, and the nitrogen content in the negative electrode material is 0.02% to 1.5%, preferably 0.03% to 0.3%, based on the mass of the negative electrode material. By using an aliphatic polymer containing an M functional group and controlling the nitrogen content, the functionality of the polymer and the overall performance of the material can be effectively balanced. An appropriate amount of polymer not only generates intermolecular forces between the functional groups in the aliphatic polymer containing the M functional group and the oxygen-containing functional groups (such as hydroxyl, carbonyl, or carboxyl groups) at the carbon defect sites in the first shell, thereby reducing the activity of carbon defects through interaction with carbon defects, but also significantly alleviates the problems of conductivity degradation and increased structural rigidity caused by excessive polymer content by rationally controlling the polymer content, ultimately improving the storage performance and cycle performance of the battery cell.

[0131] As a non-limiting example, the nitrogen content in the negative electrode material includes, but is not limited to: 0.02%, 0.04%, 0.06%, 0.08%, 0.10%, 0.15%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, and 1.5%, based on the mass of the negative electrode material.

[0132] Test method for nitrogen content in negative electrode materials: (1) Preparation of negative electrode material Refer to the above-mentioned method for preparing anode materials.

[0133] (2) Determination of N element content CHNS test: Weigh directly (usually 2-3 mg) and place in a tin can. Test by oxygen combustion method. Refer to (JY / T0580-2020) for testing standards.

[0134] In some embodiments, the average particle size of the silicon-carbon composite material is optionally 7 μm to 11 μm. By controlling the average particle size of the silicon-carbon composite material within this range, on the one hand, the reduction in specific surface area caused by particle agglomeration during the polymer coating process can be alleviated; on the other hand, the deterioration of bulk dynamics caused by excessively large particles can be effectively reduced. Therefore, controlling the average particle size between 7 μm and 11 μm improves the dispersibility of the material, thereby significantly improving the storage performance and cycle performance of the battery cell.

[0135] As a non-limiting example, the average particle size of silicon-carbon composites includes, but is not limited to, 7 μm, 8 μm, 9 μm, 10 μm, and 11 μm.

[0136] Test method for average particle size of silicon-carbon composite materials: (1) Preparation of negative electrode material Refer to the above-mentioned method for preparing anode materials.

[0137] (2) Average particle size test of silicon-carbon composite materials: The negative electrode material is dispersed on a conductive substrate, and a two-dimensional distribution map of silicon elements is generated by energy dispersive X-ray spectroscopy (EDS). 2) Based on the EDS distribution map, mark the regions of the silicon-carbon composite material and draw lines to measure the longest axis length of the particles; 3) Calculate the average particle size by counting the longest axis length of all marked particles.

[0138] In some embodiments, optionally, the BET specific surface area of ​​the silicon-carbon composite material is 0.5 m². 2 / g~2m 2 / g. By reasonably controlling the range of BET specific surface area, it is helpful to reduce the consumption of active lithium during the formation of SEI (solid electrolyte interface), thereby improving the first efficiency of the battery and reducing the continuous consumption of active lithium in subsequent cycles, significantly improving the storage performance and cycle performance of the battery cell.

[0139] As a non-limiting example, the BET specific surface area of ​​silicon-carbon composite materials includes, but is not limited to, 0.5 m². 2 / g, 1m 2 / g, 1.5m 2 / g、2m 2 / g. Silicon-carbon composite materials within this BET range are beneficial for improving the storage and cycle performance of individual battery cells.

[0140] In some embodiments, optionally, the BET specific surface area of ​​the negative electrode material is 0.5 m². 2 / g~4m 2 / g. By reasonably controlling the range of BET specific surface area, it is helpful to reduce the consumption of active lithium during the formation of SEI (solid electrolyte interface), thereby improving the first efficiency of the battery and reducing the continuous consumption of active lithium in subsequent cycles, significantly improving the storage performance and cycle performance of the battery cell.

[0141] As a non-limiting example, the BET specific surface area of ​​the negative electrode material includes, but is not limited to, 0.5 m². 2 / g, 1m 2 / g, 1.5m 2 / g、2m 2 / g. Negative electrode materials within this BET range are beneficial for improving the storage and cycle performance of individual battery cells.

[0142] Test method for BET specific surface area of ​​negative electrode materials: (1) Preparation of negative electrode material Referring to the above-mentioned anode material preparation method (2) BET specific surface area test: Gas specific surface area analysis, reference standard [GB / T 19587-2017] 1) Pretreatment: Take an appropriate amount of sample in a special sample tube, heat and degas for 2 hours, and weigh the total weight after cooling to room temperature. Subtract the mass of the sample tube to obtain the sample mass.

[0143] 2) Testing: The sample tube is placed in the workstation and the amount of gas adsorbed on the solid surface under different adsorption pressures is measured at a constant low temperature. Based on the BET multilayer adsorption theory and its formula, the amount of monolayer adsorption of the sample is obtained, and the specific surface area of ​​the solid sample per unit mass is calculated.

[0144] 3) Adsorbed gas: nitrogen, adsorption pressure points: 0.05 / 0.10 / 0.15 / 0.20 / 0.25 / 0.30, test atmosphere: high-purity liquid nitrogen atmosphere.

[0145] After the first charge and discharge cycle, the battery was disassembled, the electrodes were cleaned, samples were prepared, and the CP element distribution of the electrodes was tested using SEM / EDS. Figure 3 EDS elemental analysis diagrams of negative electrode sheets in some embodiments of this disclosure are shown. Figure 4 and Figure 5 EDS elemental analysis diagrams of the negative electrode materials in some comparative examples of this disclosure are shown. Figure 4 It contains only a shell with a polymer coating. Figure 5 A shell containing only a carbon coating. Figure 3 and Figure 4 or Figure 5 The comparison shows that in silicon-carbon composite materials with a first shell containing a carbon coating and a second shell containing a polymer coating (the polymer contains M functional groups such as nitrile, amide, carboxyl, or organoboronic acid), the aggregation of O elements is significantly reduced. This proves that the first shell isolates the electrolyte from the active silicon, alleviates side reactions, and improves conductivity; the functional groups of the second shell form intermolecular forces with the oxygen-containing groups at the carbon defects, reducing defect activity and electrolyte penetration.

[0146] [Preparation Methods for Silicon-Carbon Composite Materials] Another embodiment of this application provides a method for preparing a silicon-carbon composite material, comprising the following steps S100 to S400: S100. Core preparation: Silicon is deposited on porous carbon using chemical vapor deposition to obtain sample A containing a core. The temperature of the chemical vapor deposition method is 500℃~640℃, and the deposition time is 1h~7h. S200. Carbon coating: Carbon coating of sample A is performed using chemical vapor deposition to form carbon-coated sample B. The temperature of the chemical vapor deposition method is 540℃~640℃, and the deposition time of the chemical vapor deposition method is 1h~6h. S300. Polymer Coating: Sample B is added to a solvent, a certain proportion of polymer is added, the solid content of the solution is controlled, and after stirring and mixing, the solvent is evaporated by spray drying to obtain sample C. The solvent includes one or more of water, NMP or ethanol, and the solid content of the solution is in the range of 20% to 50%. The polymer includes one or more of aliphatic polymers containing M functional groups or polymers containing organoboronic acids. The M functional group includes one or more of nitrile, amide, alkoxy, carboxyl or amino groups. S400. Calcination treatment: Sample C is transferred to an inert atmosphere furnace for calcination treatment to obtain the final silicon-carbon composite material. The calcination temperature is 100℃~400℃, and the calcination time is 1h~6h. In the S100 core preparation step, the low-temperature preparation of silicon reduces the consumption of active silicon, thereby mitigating capacity loss.

[0147] [Positive electrode plate] In some embodiments, the positive electrode may include a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector and comprising a positive electrode active material. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0148] Taking a lithium-ion battery cell as an example, the positive electrode active material may include, but is not limited to, one or more of lithium transition metal oxides, lithium-containing phosphates, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their respective modified compounds. Examples of lithium-containing phosphates may include, but are not limited to, 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. In some embodiments, to further improve the energy density of the battery cell, the positive electrode active material may include materials with the general formula Li a Ni b Co c M d O e A fOne 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 but is not limited to one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A includes but is not limited to one or more of N, F, S and Cl.

[0149] As an example, the positive electrode active material may include, but is not limited to, 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 0.85 Co 0.1 Al 0.05 One or more of O2, LiFePO4, and LiMnPO4.

[0150] During the charging and discharging process, lithium (Li) undergoes insertion / extraction and consumption within a single battery cell, resulting in varying molar Li content at different discharge states. In the examples of positive electrode active materials in this application, the molar Li content represents the initial state of the material, i.e., the state before material addition. As the positive electrode active material is applied to the battery cell, the molar Li content changes after charge-discharge cycles. Similarly, in the examples of positive electrode active materials in this application, the molar O content is only a theoretical value. Lattice oxygen release causes changes in the molar O content, leading to fluctuations in the actual molar O content.

[0151] Taking sodium-ion battery cells as an example, the positive electrode active material can be one or more of the following, including but not limited to sodium-containing transition metal oxides, polyanionic materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian blue materials. For example, the positive electrode active material can be, but is not limited to, NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, and NaNi 1 / 2Ti 1 / 2 O2, NaNi 1 / 2 Mn 1 / 2 O2, Na 2 / 3 Fe 1 / 3 Mn 2 / 3O2, NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, NaFePO4, NaMnPO4, NaCoPO4, Prussian blue materials, with the general formula X p M' q (PO4) r O x Y 3-x One or more of the materials. In general formula X p M' q (PO4) r O x Y 3-x In this case, 0 < p ≤ 4, 0 < q ≤ 2, 1 ≤ r ≤ 3, 0 ≤ x ≤ 2, and X includes, but is not limited to, H. + Li + Na + K + and NH4 + One or more of the following, M' is a transition metal cation, optionally including but not limited to one or more of V, Ti, Mn, Fe, Co, Ni, Cu and Zn, and Y is a halide anion, optionally one or more of F, Cl and Br.

[0152] The modified compounds for the positive electrode active materials of the aforementioned lithium battery cells and sodium battery cells can be obtained by doping and / or surface coating modifications of the positive electrode active materials.

[0153] In some embodiments, the positive electrode film layer may further include a positive electrode conductive agent. As an example, the positive electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0154] In some embodiments, the positive electrode film layer may further include a positive electrode binder. As an example, the positive electrode binder may include, but is not limited to, one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0155] In some embodiments, the positive current collector may be a metal foil or a composite current collector. An example of a metal foil is aluminum foil. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include, but is not limited to, one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include, but is not limited to, one or more of polypropylene, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene, and polyethylene.

[0156] The positive electrode film 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 positive electrode active materials, positive electrode conductive agents, positive electrode binders, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to this.

[0157] [Isolation Component] The insulating element is placed between the positive and negative electrode plates to isolate the positive and negative electrodes and prevent short circuits.

[0158] In some embodiments, the separator includes a separator membrane. This application does not impose any particular limitation on the type of separator membrane; any known porous membrane with good chemical and mechanical stability can be selected.

[0159] In some embodiments, the material of the separator may include at least one selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation. The separator may be a single component located between the positive and negative electrodes, or it may be attached to the surfaces of the positive and negative electrodes. An inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating may also be applied to the surface of the separator.

[0160] In some embodiments, the separator is a solid electrolyte. The solid electrolyte is disposed between the positive and negative electrode plates, serving both to transport ions and to isolate the positive and negative electrodes.

[0161] In some embodiments, the battery cell may further include an outer packaging for accommodating the negative electrode, separator, and positive electrode assembly. The outer packaging may be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. Alternatively, the outer packaging may be a flexible package, such as a pouch. The flexible package may be made of plastic, such as aluminum-plastic film, polypropylene, polybutylene terephthalate (PBT), or polybutylene succinate (PBS).

[0162] [Negative electrode plate] In some embodiments, the negative electrode sheet may include a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector and comprising a negative electrode active material. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0163] The negative electrode active material includes the silicon-carbon composite material of the first aspect of this application or the silicon-carbon composite material prepared according to the method of the second aspect of this application.

[0164] In some embodiments, the negative electrode film layer may further include a negative electrode conductive agent. As an example, the negative electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0165] In some embodiments, the negative electrode film layer may further include a negative electrode binder. As an example, the negative electrode binder may include, but is not limited to, one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0166] In some embodiments, the negative electrode film layer may also include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0167] In some 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 polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include, but is not limited to, one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include, but is not limited to, one or more of polypropylene, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene, and polyethylene.

[0168] The negative electrode film 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, negative electrode conductive agent, negative electrode 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.

[0169] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet also 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 film layer and disposed on the surface of the negative electrode current collector.

[0170] In some embodiments, the negative electrode sheet can be made of foamed metal. The foamed metal can be foamed nickel, foamed copper, foamed aluminum, foamed alloy, foamed carbon, etc. When foamed metal is used as the negative electrode sheet, the surface of the foamed metal may or may not contain a negative electrode active material.

[0171] [Electrolytes] The electrolyte plays a role in conducting ions between the positive and negative electrode plates.

[0172] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and an organic solvent.

[0173] Taking a lithium battery cell as an example, the electrolyte salt can be one or more of the following: 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).

[0174] Taking sodium battery cells as an example, the electrolyte salt can be one or more of the following: sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoroarsenate (NaAsF6), sodium difluorosulfonylimide (NaFSI), sodium difluoromethanesulfonylimide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalate borate (NaDFOB), sodium dioxalate borate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorodioxalate phosphate (NaDFOP), and sodium tetrafluorooxalate phosphate (NaTFOP).

[0175] In some embodiments, the organic solvent may include, but is not limited to, one or more of the following: ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl ester carbonate (BC), 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), diethyl sulfone (ESE), ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyl tetrahydrofuran, diphenyl ether, and crown ether.

[0176] In some embodiments, the electrolyte may also include additives. For example, the 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 overcharge performance, additives that improve high-temperature performance, additives that improve low-temperature performance, etc.

[0177] Optionally, the additive may include one or more of fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propanesulfonate lactone (PS), and vinyl sulfate (DTD).

[0178] Methods for preparing battery cells are well known. In some 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 packaging, dried, and then injected with the electrolyte. After vacuum sealing, settling, and formation processes, a battery cell is obtained.

[0179] Example 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.

[0180] Example 1 Preparation of silicon-carbon composite materials Core preparation: Silicon was deposited on porous carbon using chemical vapor deposition to obtain sample A containing a core. The chemical vapor deposition temperature was 520℃ and the chemical vapor deposition time was 6h. Carbon coating: Sample A was coated with carbon using chemical vapor deposition to form carbon-coated sample B. The chemical vapor deposition temperature was 600℃ and the chemical vapor deposition time was 2.5h.

[0181] Polymer coating: Sample B is added to a solvent, a certain proportion of polyacrylonitrile is added, the solid content of the solution is controlled, and after stirring and mixing, the solvent is evaporated by spray drying to obtain sample C. The solvent includes one or more of water, the solid content of the solution is 40%, the polymer includes one or more of aliphatic polymers containing M functional groups or polymers containing organoboronic acids, the M functional group includes nitrile groups, and the polymer includes polyacrylonitrile.

[0182] Calcination treatment: Sample C was transferred into an inert atmosphere furnace for calcination treatment to obtain the final silicon-carbon composite material. The calcination treatment temperature was 260℃ and the calcination treatment time was 2h.

[0183] Positive electrode sheet LiNi, the positive electrode active material 0.91 Co 0.08 Mn 0.01 O2 (9-series), conductive carbon black, and polyvinylidene fluoride (PVDF) binder are thoroughly mixed in an appropriate amount of N-methylpyrrolidone (NMP) solvent at a weight ratio of 97:1:2 to form a uniform positive electrode slurry. The positive electrode slurry is coated onto the surface of the positive electrode current collector, and after drying, cold pressing, and cutting, the positive electrode sheet is obtained.

[0184] Negative electrode sheet The above-mentioned silicon-carbon composite material was mixed with graphite, conductive carbon black and carbon nanotubes, and polyacrylic acid binder in a mass ratio of 17:78:1.9:0.1:3. The mixture was then added to deionized water and stirred under the action of a high-speed mixer until the system was homogeneous, resulting in a negative electrode slurry with a solid content of 45%. The negative electrode slurry was uniformly coated on the copper foil of the negative electrode current collector and dried at 85°C. After cold pressing, the negative electrode sheet was obtained.

[0185] electrolyte Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed uniformly in a mass ratio of 30:30:40 to serve as an organic solvent. LiPF6 was then dissolved in the organic solvent, and fluoroethylene carbonate (FEC) was added. The concentration of LiPF6 in the electrolyte was 1 mol / L, and the mass percentage of FEC was 5 wt%.

[0186] Isolation component A 12 μm thick polyethylene film was selected as the separator.

[0187] battery cell The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then wound to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a single battery cell is obtained.

[0188] Examples 2-8 The preparation method of the battery cell is similar to that in Example 1, except that the preparation parameters of the silicon-carbon composite material are adjusted. For details of the parameter adjustments, please refer to Table 1.

[0189] Example 9 The preparation method of the battery cell is similar to that of Example 1. The difference is that the chemical vapor deposition temperature for core preparation is different. In this comparative example, the silicon deposited at this temperature has a higher degree of crystallinity and tends to have the characteristics of crystalline silicon. For specific parameter adjustments, please refer to Table 1.

[0190] Comparative Example 1 The preparation method of the battery cell is similar to that in Example 1, except that there is no polymer coating step and no calcination treatment.

[0191] Comparative Example 2 The preparation method of the battery cell is similar to that of Comparative Example 1. The difference is that the chemical vapor deposition temperature of the carbon coating step is different. When the deposition is carried out at this temperature, the graphitization degree of the amorphous carbon coating layer is improved. For specific parameter adjustments, please refer to Table 1.

[0192] Comparative Example 3 The preparation method of the battery cell is similar to that of Example 9, except that there is no polymer coating step and calcination treatment.

[0193] Comparative Example 4 The preparation method of the battery cell is similar to that in Example 1, except that the polymer type is different. For details of the parameter adjustments, please refer to Table 1.

[0194] The specific parameters for each of the above embodiments and comparative examples are shown in Table 1.

[0195] Table 1

[0196] In Table 1, "\" indicates that the parameter does not exist.

[0197] Test section 1. Electrolyte permeation experiment: Step 1: First charge and discharge cycle of the battery: Let stand at 25°C for 5 minutes; charge at 0.33C0 to 4.25V, then charge at 4.25V constant voltage to 0.05C0; let stand for 5 minutes; discharge at 0.33C to 2.5V.

[0198] Step Two: Extreme Film CP: Disassemble the negative electrode at 0%~5% SOC, retaining the negative electrode sheet, and soak DMC to remove the side reaction layer.

[0199] Step 3: SEM / EDS test the CP element distribution of the electrode.

[0200] (1) Sample preparation: a. Use ceramic scissors to cut the electrode into 6mm*6mm pieces, attach them to the sample stage coated with paraffin, and make the sample protrude slightly (<1mm) from the edge of the sample stage.

[0201] b. Set the polishing voltage and time for polishing (50 min at 7.5 KV for a 150 μm thick positive electrode sheet, and 100 min at 7.5 KV for a 150 μm thick negative electrode sheet).

[0202] (2) Parameter settings: Mode: In-lens, Voltage: 20KV, Aperture: 60um, Working distance: 8.5mm.

[0203] (3) Testing Procedure: Map at approximately 1K (within the entire field of view on the current collector side) to observe the distribution of silicon and oxygen elements.

[0204] 2. Cycle performance test of individual battery cells At 25℃, a single battery cell is charged to 4.3V at a constant current of 1 / 3C, then charged to 0.05C at a constant voltage of 4.3V, rested for 5 minutes, and then discharged to 2.8V at a constant current of 1 / 3C. The resulting discharge capacity is recorded as the initial capacity C0. This charging and discharging process is repeated, and the discharge capacity Cn of the battery cell after the nth cycle is recorded. The capacity retention rate of the battery cell after each cycle is Pn = (Cn / C0) × 100%. The capacity retention rate of the battery cell after 500 cycles can be used to reflect the difference in cycle performance of the battery cells.

[0205] 3. Storage performance test of individual battery cells Step 1: Let stand at 25℃ for 5 minutes; charge at 0.33C0 to 4.25V, then charge at 4.25V constant voltage to 0.05C0; let stand for 5 minutes; discharge at 0.33C to 2.5V, and record the capacity at this point as Cz (the capacity of the cell after storage is the reversible capacity, marked as Ct, where t is the storage time). Charge at 0.33C0 to 4.25V, then charge at 42.5V constant voltage to 0.05C0. At this point, the cell is fully charged.

[0206] Step 2: Place the fully charged secondary battery in a 60℃ environment and store it for a period of time. Then, take out the battery cells and test them according to the procedure in Step 1. Repeat the above operation until t=180 days. Calculate the reversible capacity retention rate F2, F2=Ct÷Cz*100%.

[0207] The test results of the above embodiments and comparative examples are shown in Table 2.

[0208] Table 2

[0209] In Table 2, "\" indicates that the parameter does not exist.

[0210] Comparing Examples 1 to 8 with Comparative Examples 1 and 2 reveals that a single shell containing only a carbon coating layer is insufficient to improve the battery's storage and cycle performance. By adding a second shell layer containing an aliphatic polymer with M functional groups or a polymer containing organoboronic acid, the functional groups in the aliphatic polymer with M functional groups or the polymer containing organoboronic acid interact with the oxygen-containing functional groups at the carbon defect sites in the first shell layer, reducing the activity of the carbon defects. This reduces the number of channels through which the electrolyte enters the core via the carbon defects, ultimately improving the storage and cycle performance of the battery cell.

[0211] Example 1 and Comparative Example 4 illustrate that the polymer in Comparative Example 4 lacks interaction with the carbon layer. Therefore, the polymer in the second shell layer needs to generate intermolecular forces with the oxygen-containing functional groups at the carbon defect sites in the first shell layer in order to reduce carbon defect activity, reduce electrolyte penetration, and ultimately improve the storage performance and cycle performance of the battery cell.

[0212] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A battery cell, characterized in that, It includes a positive electrode, a negative electrode, and a separator, wherein the separator is located between the positive electrode and the negative electrode; The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode material, and the negative electrode material includes a silicon-carbon composite material. The silicon-carbon composite material includes a core and a shell loaded on the surface of the core. The core includes porous carbon and silicon deposited in the porous carbon. The shell includes a first shell layer and a second shell layer. The first shell layer is loaded on the surface of the core, and the second shell layer is loaded on the side of the first shell layer away from the core. The first shell layer includes a carbon-containing coating layer; The second shell layer includes a polymer-containing coating layer, the polymer including one or more of an aliphatic polymer containing an M functional group or a polymer containing an organoboronic acid, wherein the M functional group includes one or more of a nitrile group, an amide group, an alkoxy group, a carboxyl group or an amino group.

2. The battery cell according to claim 1, characterized in that, The silicon includes amorphous silicon, and the grain size of the amorphous silicon is 0.5nm to 3nm.

3. The battery cell according to claim 1, characterized in that, The carbon-containing coating layer includes amorphous carbon.

4. The battery cell according to any one of claims 1-3, characterized in that, The aliphatic polymer containing the M functional group includes one or more of polyacrylonitrile, polyethylene glycol dipropyl cyanide, polyacrylamide, polyurethane, polyacrylic acid, or 3-(azidopropyl)triethoxysilane.

5. The battery cell according to any one of claims 1-3, characterized in that, The polymer containing organic boric acid includes polymers containing phenylboronic acid, which include one or more of phenylboronic acid, 4-trifluoromethylphenylboronic acid, 3-cyanobenzonic acid, 4-cyanobenzonic acid, tetrafluorophenylboronic acid, triaminophenylboronic acid, or tetraaminophenylboronic acid.

6. The battery cell according to any one of claims 1-3, characterized in that, The polymer content is 0.2% to 3%, based on the total mass of the negative electrode material.

7. The battery cell according to any one of claims 1-3, characterized in that, The polymer content is 0.5% to 1.6%, based on the total mass of the negative electrode material.

8. The battery cell according to any one of claims 1-3, characterized in that, The silicon content is 25% to 55%, based on the total mass of the negative electrode material.

9. The battery cell according to any one of claims 1-3, characterized in that, The silicon content is 35% to 48%, based on the total mass of the negative electrode material.

10. The battery cell according to any one of claims 1-3, characterized in that, The thickness of the outer shell is 8nm~40nm.

11. The battery cell according to any one of claims 1-3, characterized in that, The thickness of the outer shell is 10nm~30nm.

12. The battery cell according to any one of claims 1-3, characterized in that, The thickness of the first shell layer is 4nm~30nm.

13. The battery cell according to any one of claims 1-3, characterized in that, The thickness of the first shell layer is 8nm~20nm.

14. The battery cell according to any one of claims 1-3, characterized in that, The thickness of the second shell is 4nm~15nm.

15. The battery cell according to any one of claims 1-3, characterized in that, The thickness of the second shell is 5nm~12nm.

16. The battery cell according to any one of claims 1-3, characterized in that, The polymer includes the polymer containing organoboric acid, and the B element content in the negative electrode material is 0.01% to 0.1%, based on the mass of the negative electrode material.

17. The battery cell according to any one of claims 1-3, characterized in that, The polymer includes the polymer containing organoboronic acid, and the B element content in the negative electrode material is 0.02% to 0.05%, based on the mass of the negative electrode material.

18. The battery cell according to any one of claims 1-3, characterized in that, The polymer includes an aliphatic polymer containing an M functional group, wherein the M functional group includes one or more of nitrile, amide, or amino groups, and the N element content in the negative electrode material is 0.02% to 1.5%, based on the mass of the negative electrode material.

19. The battery cell according to any one of claims 1-3, characterized in that, The polymer includes an aliphatic polymer containing an M functional group, wherein the M functional group includes one or more of nitrile, amide, or amino groups, and the N element content in the negative electrode material is 0.03% to 0.3%, based on the mass of the negative electrode material.

20. The battery cell according to any one of claims 1-3, characterized in that, The average particle size of the silicon-carbon composite material is 7 μm to 11 μm.

21. The battery cell according to any one of claims 1-3, characterized in that, The BET specific surface area of ​​the silicon-carbon composite material is 0.5 m². 2 / g~2m 2 / g.

22. The battery cell according to any one of claims 1-3, characterized in that, The BET specific surface area of ​​the negative electrode material is 0.5 m². 2 / g~4m 2 / g.

23. A battery device, characterized in that, Includes the battery cell according to any one of claims 1-22.

24. An electrical appliance, characterized in that, Includes the battery cell according to any one of claims 1-22 or the battery device according to claim 23.

25. A silicon-carbon composite material, characterized in that, The silicon-carbon composite material includes a core and a shell loaded on the surface of the core. The core includes porous carbon and silicon deposited in the porous carbon. The shell includes a first shell layer and a second shell layer. The first shell layer is loaded on the surface of the core, and the second shell layer is loaded on the side of the first shell layer away from the core. The first shell layer includes a carbon-containing coating layer. The second shell layer includes a polymer-containing coating layer. The polymer includes one or more of an aliphatic polymer containing an M functional group or a polymer containing an organoboronic acid. The M functional group includes one or more of a nitrile group, an amide group, an alkoxy group, a carboxyl group, or an amino group.

26. A method for preparing a silicon-carbon composite material, characterized in that, Includes the following steps: Core preparation: Silicon was deposited on porous carbon using chemical vapor deposition to obtain sample A containing a core. The temperature of the chemical vapor deposition method was 500℃~640℃, and the deposition time was 1h~7h. Carbon coating: Sample A is coated with carbon using chemical vapor deposition to form carbon-coated sample B. The temperature of the chemical vapor deposition method is 540℃~640℃, and the deposition time is 1h~6h. Polymer coating: Sample B is added to a solvent, a certain proportion of polymer is added, the solid content of the solution is controlled, and after stirring and mixing, the solvent is evaporated by spray drying to obtain sample C. The solvent includes one or more of water, NMP or ethanol, and the solid content of the solution is in the range of 20% to 50%. The polymer includes one or more of aliphatic polymers containing M functional groups or polymers containing organoboronic acids. The M functional group includes one or more of nitrile, amide, alkoxy, carboxyl or amino groups. Calcination treatment: Sample C is transferred to an inert atmosphere furnace for calcination treatment to obtain the final silicon-carbon composite material. The calcination treatment temperature is 100℃~400℃ and the calcination treatment time is 1h~6h.

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