Silicon-carbon negative electrode material and preparation method thereof, negative electrode plate and electrochemical device

Abstract

The invention relates to the technical field of batteries, and discloses a silicon-carbon negative electrode material and a preparation method thereof, a negative electrode plate and an electrochemical device. The silicon-carbon negative electrode material provided by the invention comprises a porous carbon matrix, the oxygen content of the porous carbon matrix is A, and 0.3 wt% < = A < = 3 wt%; the nano silicon is at least partially positioned in the pores of the porous carbon matrix; and the carbon coating layer wraps at least part of the surface of the porous carbon substrate. And the electrochemical performance is excellent.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to silicon-carbon anode materials and their preparation methods, anode sheets, and electrochemical devices. Background Technology

[0002] With the global emphasis on clean energy and the rapid development of new energy industries such as electric vehicles, photovoltaic power generation, and wind power, the demand for electrochemical devices such as lithium batteries in the energy storage field has experienced explosive growth. While silicon anode materials possess a high theoretical specific capacity advantage, their volume undergoes significant changes during the charging and discharging process of lithium batteries. This drastic volume change can lead to the shedding and pulverization of electrode active materials, and even damage to the electrode structure, resulting in rapid capacity decay. This technological bottleneck severely restricts the widespread application of silicon anode materials in industrial production. Carbon anode materials, on the other hand, exhibit smaller volume changes during charging and discharging due to their stable structural characteristics, demonstrating excellent cycle stability. Furthermore, carbon materials have similar chemical properties to silicon, exhibiting good compatibility. Based on this, the industry commonly employs a method of combining silicon and carbon materials to prepare silicon-carbon anode materials. Silicon-carbon anode materials can effectively improve the volume effect of silicon and enhance its electrochemical stability.

[0003] However, in the composite system of silicon and porous carbon, the deposition of silicon source on the surface of porous carbon has many drawbacks. For example, silicon deposition on the surface can lead to silicon crystallization, which intensifies expansion, blocks the pore channels of porous carbon substrate, aggravates electrochemical performance defects, restricts cycle stability, causes SEI film instability, and continuously consumes lithium source. These problems are intertwined and jointly restrict the practical application of gas-phase silicon-carbon anode materials in lithium-ion batteries, and have become one of the key technical bottlenecks that urgently need to be overcome in the field of new energy materials.

[0004] It should be noted that the above statements are only used to provide background information related to this application and do not necessarily constitute prior art. Summary of the Invention

[0005] In a first aspect of this application, a silicon-carbon anode material is provided, comprising: a porous carbon matrix having an oxygen content of A of 0.3wt% ≤ A ≤ 3wt%; nano-silicon, at least partially located within the pores of the porous carbon matrix; and a carbon coating layer that coats at least a portion of the surface of the porous carbon matrix.

[0006] In some embodiments, the hydrogen content of the porous carbon matrix is ​​B, wherein 0.05wt%≤B≤0.5wt%, and A>B.

[0007] In some embodiments, 1.5 wt% ≤ A ≤ 2 wt%, 0.1 wt% ≤ B ≤ 0.25 wt%.

[0008] In some embodiments, the specific surface area of ​​the porous carbon matrix is ​​1600 m². 2 / g~2400m 2 / g.

[0009] In some embodiments, the microporosity of the porous carbon matrix is ​​80% to 97%.

[0010] In some embodiments, the pore volume of the porous carbon matrix is ​​0.6 cm³. 3 / g-1.2cm 3 / g.

[0011] In some embodiments, the average pore size of the porous carbon matrix is ​​1.5 nm to 2.3 nm.

[0012] In some embodiments, the particle size of the porous carbon matrix is ​​3μm≤Dv50≤10μm.

[0013] In a second aspect of this application, a method for preparing a silicon-carbon anode material is proposed, comprising: performing a first carbonization treatment on a resin carbon source to obtain a first intermediate; performing an activation treatment on the first intermediate to obtain a second intermediate; performing a second carbonization treatment on the second intermediate to obtain a porous carbon matrix, wherein the temperature of the second carbonization treatment is 800°C to 1000°C; and performing a vapor deposition treatment on the porous carbon matrix using a silicon source and a carbon source to obtain the silicon-carbon anode material.

[0014] In some embodiments, the temperature of the first carbonization treatment is 400°C to 600°C.

[0015] In some embodiments, the activator used in the activation process includes at least one of KOH, NaOH, CO2, and water vapor.

[0016] In some embodiments, the activation treatment temperature is 400°C to 800°C.

[0017] In a third aspect of this application, a negative electrode sheet is provided, the negative electrode sheet comprising the silicon-carbon negative electrode material proposed in this application, or the silicon-carbon negative electrode material prepared by the method proposed in this application.

[0018] In a fourth aspect, this application provides an electrochemical device comprising the negative electrode sheet proposed in this application.

[0019] The beneficial effects of the technical solution proposed in this application include at least the following: The silicon-carbon anode material proposed in this application exhibits high bonding strength between nano-silicon and the porous carbon matrix, with the nano-silicon possessing a suitable spatial distribution. This helps reduce the shedding of nano-silicon particles during lithium-ion battery cycling, thereby improving cycle stability. Furthermore, the carbon coating layer, combined with the aforementioned porous carbon matrix and nano-silicon, further enhances the conductivity and structural stability of the silicon-carbon anode material.

[0020] The method for preparing silicon-carbon anode materials proposed in this application achieves suitable micro-oxygen content and low hydrogen content in the porous carbon matrix through precise control of relevant process parameters. This is beneficial for preparing silicon-carbon anode materials with uniform nano-silicon distribution, small silicon volume effect, and good electrochemical stability. Attached Figure Description

[0021] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a voltage-to-capacity curve of the silicon-carbon anode material prepared in one embodiment of this application; Figure 2 This is a scanning electron microscope (SEM) image of the silicon-carbon anode material prepared in one embodiment of this application; Figure 3 This is a pore size distribution diagram of the porous carbon matrix prepared in Example 7 of this application. Detailed Implementation

[0022] The embodiments of this application are described in detail below, with examples of these embodiments shown in the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0023] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0024] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are open-ended expressions, meaning they include what is specified in this application but do not exclude other aspects.

[0025] In the description of this application, all figures disclosed herein, whether or not the words "approximately" or "about" are used, are approximate values. Each figure may vary by less than 10% or by a difference that is considered reasonable by one of the art, such as 1%, 2%, 3%, 4%, or 5%.

[0026] 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 also 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 "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0027] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0028] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0029] Taking lithium batteries as an example, when silicon-carbon materials are used as negative electrode active materials, silicon undergoes a huge volume change after lithium intercalation, causing the original SEI film to rupture. The exposed fresh silicon surface will react with the electrolyte again, continuously generating new and thicker SEI films, thereby consuming a large amount of lithium and electrolyte, which in turn significantly reduces the initial coulombic efficiency of lithium-ion batteries.

[0030] Therefore, in a first aspect of this application, a silicon-carbon anode material is proposed, comprising: a porous carbon matrix, wherein the oxygen content of the porous carbon matrix is ​​A, wherein 0.3wt%≤A≤3wt%; nano-silicon, wherein at least a portion of the nano-silicon is located within the pores of the porous carbon matrix; and a carbon coating layer, wherein the carbon coating layer coats at least a portion of the surface of the porous carbon matrix. The porous carbon matrix has an oxygen content of A and a hydrogen content of B, wherein the oxygen content is the percentage of oxygen in the porous carbon by its total weight, and the hydrogen content is the percentage of hydrogen in the porous carbon by its total weight.

[0031] Within the aforementioned range, oxygen in porous carbon matrices primarily exists as polar functional groups such as hydroxyl (-OH), carboxyl (-COOH), and carbonyl (C=O). These functional groups can interact with silicon or the silicon oxide layer SiO2. x The formation of Si-OC covalent bonds or strong hydrogen bonds can significantly enhance the interfacial bonding between nano-silicon and the porous carbon matrix, reducing the shedding of nano-silicon from the silicon-carbon anode material during the charge-discharge cycle of lithium batteries. The aforementioned chemical bonding also improves the direct bonding strength between nano-silicon and the porous carbon matrix, reducing multilayer adsorption of nano-silicon. Furthermore, oxygen-containing functional groups such as carboxyl groups are fully consumed in the bonding with silicon, thereby reducing side reactions between the active oxygen-containing functional groups and substances such as the electrolyte in lithium batteries. This includes side reactions with lithium ions, such as lithium ion (Li...) + The reaction -COOH + Li + →-COOLi+H + This reduces the additional lithium consumption in lithium batteries. Therefore, the aforementioned silicon-carbon anode material can exhibit superior initial efficiency and lithium intercalation capacity in lithium batteries.

[0032] As an example, the oxygen content A is 0.3wt%, 0.5wt%, 0.7wt%, 1wt%, 1.3wt%, 1.5wt%, 1.7wt%, 2wt%, 2.3wt%, 2.5wt%, 2.7wt%, 3wt%, etc.

[0033] In some embodiments, the hydrogen content of the porous carbon matrix is ​​B, wherein 0.05wt%≤B≤0.5wt%, and A>B.

[0034] Hydrogen exists primarily as nonpolar CH bonds in porous carbon matrices. These CH bonds are connected to silicon via van der Waals forces, resulting in a relatively weak interaction and limited anchoring effect on nano-silicon. When A > B, oxygen dominates over hydrogen in the porous carbon matrix, leading to a stronger "binding" ability of the porous carbon matrix to nano-silicon, which is beneficial for maintaining high structural stability in silicon-carbon anode materials. Consequently, the uniform distribution of nano-silicon within the pores of the porous carbon matrix provides active sites for lithium-ion storage, reducing the shedding of nano-silicon particles during lithium-ion battery cycling and improving cycle stability and lithium intercalation capacity. Furthermore, the carbon coating layer, combined with the aforementioned porous carbon matrix and nano-silicon, further enhances the conductivity and structural stability of the silicon-carbon anode material.

[0035] As an example, the hydrogen content B is 0.05wt%, 0.07wt%, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, etc.

[0036] In some embodiments, 1.5wt%≤A≤2wt%, 0.1wt%≤B≤0.25wt%.

[0037] Within the aforementioned oxygen and hydrogen content ranges, the adsorption state of nano-silicon is optimized, which can improve the uniformity of nano-silicon distribution, enhance the stability of the silicon-carbon composite structure, and strengthen its bonding strength. This, in turn, is beneficial for improving the initial charge-discharge efficiency and cycle performance of silicon-carbon anode materials.

[0038] In some embodiments, the specific surface area of ​​the porous carbon matrix is ​​1600 m². 2 / g~2400m 2 / g. Therefore, on the aforementioned porous carbon matrix, nano-silicon can have suitable dispersibility, which is beneficial to reducing the structural damage caused by local expansion stress concentration to silicon-carbon anode materials.

[0039] In some embodiments, the microporosity of the porous carbon matrix is ​​80%–97%. Micropores are pores with a diameter of less than 2 nm, and are the smallest of the three common types of pores (micropores < 2 nm, mesopores 2 nm–50 nm, and macropores > 50 nm). Within the aforementioned microporosity range, the porous carbon matrix can accommodate a moderate amount of nano-silicon deposition, which is beneficial for achieving high lithium-ion capacity while reducing the impact of silicon volume changes on the stability of silicon-carbon anode materials. The microporosity is calculated using the "adsorption-desorption" behavior of small molecule gases (such as N2 and CO2) in micropores at low temperatures (e.g., N2 at -196 °C). Pore parameters are calculated through adsorption isotherms. Common models include the t-plot method, the DR (Dubinin-Radushkevich) method, and the HK (Horvath-Kawazoe) method.

[0040] In some embodiments, the pore volume of the porous carbon matrix is ​​0.6 cm³. 3 / g-1.2cm 3 / g. This helps to reduce the impact of volume changes in nano-silicon during lithium insertion and delithiation on the structural stability of silicon-carbon anode materials.

[0041] In some embodiments, the average pore size of the porous carbon matrix is ​​1.5 nm to 2.3 nm. This facilitates the uniform distribution of nano-silicon within the pores.

[0042] In some embodiments, the particle size of the porous carbon matrix is ​​3 μm ≤ Dv50 ≤ 10 μm. Therefore, the porous carbon matrix exhibits high structural stability and can buffer volume changes during the lithium-ion insertion / extraction process on nano-silicon.

[0043] In some embodiments, the specific surface area of ​​the silicon-carbon anode material is 2 cm². 2 / g~30cm 2 / g. Therefore, the silicon-carbon anode material has an appropriate contact area with the electrolyte in the lithium battery, which can improve the lithium-ion insertion / extraction rate in the lithium battery.

[0044] In a second aspect of this application, a method for preparing a silicon-carbon anode material is proposed, comprising: performing a first carbonization treatment on a resin carbon source to obtain a first intermediate; performing an activation treatment on the first intermediate to obtain a second intermediate; performing a second carbonization treatment on the second intermediate to obtain a porous carbon matrix, wherein the temperature of the second carbonization treatment is 800°C to 1000°C; and performing a vapor deposition treatment on the porous carbon matrix using a silicon source and a carbon source to obtain the silicon-carbon anode material.

[0045] The method proposed in this application involves the decomposition and removal of some thermally unstable oxygen-containing functional groups in the resin carbon source during the first carbonization process. For example, carboxyl groups decompose into CO2 and H2O at 400℃~500℃, and hydroxyl groups dehydrate at 500℃~600℃, resulting in the retention of a large number of thermally stable ether bonds (-COC-) and carbonyl groups (C=O) in the resin carbon source. Therefore, the hydrogen content can be adjusted during the first carbonization process to obtain a first intermediate that is "mildly deoxygenated" while retaining strongly bonded oxygen.

[0046] In the activation process, an activating agent (such as KOH) is used to chemically activate the first intermediate. At a low to medium temperature (400℃~800℃), the activating agent reacts with the carbon in the first intermediate to generate an activating substance. This facilitates the introduction of hydroxyl (-OH), carboxyl (-COOH), and other groups onto the carbon pore wall surface, increasing the oxygen content of the second intermediate. The second carbonization process is at a higher temperature than the first. During this process, the second intermediate can remove heteroatoms from the porous structure, repair the carbon framework structure, and thus control the pore structure of the prepared porous carbon matrix. The conditions for the second carbonization process, within the aforementioned range, are conducive to the formation of a richer pore structure in the porous carbon matrix, increasing microporosity and facilitating the deposition of nano-silicon. Therefore, through the aforementioned process, a porous carbon matrix with moderate pore size and controllable oxygen and hydrogen content can be prepared. This results in sufficient reaction sites on the surface of the porous carbon matrix for bonding with silicon and reduces the volume effect caused by excessive nano-silicon deposition.

[0047] Vapor deposition treatment of the porous carbon matrix allows silanes to react with appropriate oxygen-containing functional groups (such as -OH, -O-, etc.) on the surface of the porous carbon matrix to form stable Si-O covalent bonds, which is beneficial to improving the deposition efficiency of silanes. This process prepares uniformly distributed and appropriately sized nano-silicon, improving the volume effect of silicon and thus enhancing the electrochemical stability of the prepared silicon-carbon anode material. Furthermore, organic functional groups, such as amino and epoxy groups, can be introduced into the silicon source during silicon deposition treatment. These organic functional groups (such as amino and epoxy groups) extend outward from the silicon source, forming a dense organic structure on the surface of the nano-silicon. This structure can further cover the active sites on the surface of the nano-silicon. In the battery, the aforementioned organic structure can physically isolate the nano-silicon from direct contact with the electrolyte, reducing side reactions (such as electrolyte decomposition, nano-silicon and Li) from the source. + (Side reactions, etc.). This further reduces the interaction between nano-silicon and the electrolyte, preventing lithium-ion consumption or damage to the nano-silicon structure, thereby improving the first-efficiency and other electrical properties of silicon-carbon anode materials.

[0048] As an example, the temperature of the second carbonization process is 1000°C.

[0049] As an example, the second carbonization process takes 20 minutes.

[0050] In some embodiments, the temperature of the first carbonization treatment is 400°C to 600°C, and the time of the first carbonization treatment is 0.5 h to 2 h. Conditions within the aforementioned range for the first carbonization treatment are beneficial for controlling the specific surface area and pore volume of the porous carbon matrix, thereby promoting the formation of a richer pore structure, increasing the microporosity, facilitating the deposition of nano-silicon, and reducing the impact on the silicon-carbon anode material structure caused by the large volume expansion of nano-silicon during lithium insertion / extraction through spatial buffering.

[0051] As an example, the temperatures for the first carbonization treatment are 400°C, 450°C, 500°C, 550°C, and 600°C.

[0052] As an example, the first carbonization treatment time is 0.5h, 1h, 1.5h, and 2h.

[0053] In some embodiments, during the activation treatment, the molar ratio of the first intermediate to the activator is 1:(2~4), and the activator includes at least one of KOH, NaOH, CO2, and water vapor. Thus, the pore structure and surface functional group composition of the carbon structure can be improved through the chemical action of the activator.

[0054] In some embodiments, the second intermediate is subjected to acid washing. This removes unreacted activator.

[0055] In some embodiments, the activation treatment temperature is 400°C to 800°C, and the activation treatment time is 1 hour to 2 hours.

[0056] As an example, the activation treatment temperature is 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, or 800℃.

[0057] In some embodiments, the vapor deposition process includes silicon deposition and carbon deposition.

[0058] As an example, the vapor deposition process includes: S1: Start the fluidized bed, weigh a certain amount of porous carbon matrix and add it to the fluidized bed feed tank. While heating and introducing carrier gas, feed the material into the reactor. The carrier gas is an inert gas (argon, etc.) or nitrogen. The heating rate is 3°C / min~10°C / min. Weigh 6kg~10kg of porous carbon. S2: After reaching a certain temperature, hold the temperature for a certain time. After the temperature stabilizes, introduce silane to perform silicon deposition. Raise the temperature to 480°C~530°C, hold the pressure for 10min~50min, and the deposition reaction time is 4-8h. S3: Turn off the silane and maintain the pressure for a period of time while continuing to raise the temperature. Introduce acetylene for carbon deposition treatment. The pressure holding time is 10 min to 30 min. Raise the temperature to 600°C to 700°C and introduce acetylene for 1 h to 5 h. After cooling to room temperature, collect the target silicon-carbon anode material.

[0059] In some embodiments, the gas used in the silicon deposition process includes silane.

[0060] In some embodiments, the carbon-coated gas includes at least one of methane, ethane, propane, butane, ethylene, propylene, butene, acetylene, propyne, butyne, pentane, hexane, pentene, and pentyne.

[0061] In a third aspect of this application, a negative electrode sheet is proposed, comprising the silicon-carbon negative electrode material proposed in this application, or the silicon-carbon negative electrode material prepared by the method proposed in this application.

[0062] The negative electrode includes a negative current collector and a negative electrode film layer located on at least one side of the negative current collector. The negative electrode film layer contains a negative electrode active material, which includes a silicon-carbon negative electrode material prepared by the method proposed in this application.

[0063] In some embodiments, the current collector includes any one of copper foil, nickel foil, copper-nickel composite foil, aluminum foil, carbon-based current collector, and foamed metal current collector.

[0064] In some embodiments, the active film layer further includes a binder and a conductive agent.

[0065] In some embodiments, the binder is sodium carboxymethyl cellulose (CMC), sodium alginate (SA), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), sodium polyacrylate (PAAS), styrene-butadiene rubber (SBR), polyimide (PI), polydopamine (PDA), polyvinyl alcohol (PVA), or any combination thereof.

[0066] In some embodiments, the conductive agent includes graphite, carbon black, acetylene black, Ketjen black, graphene, metal powder, or any combination thereof.

[0067] In some embodiments, the negative electrode sheet can be obtained by the following method: The negative electrode active material, conductive agent and binder are uniformly stirred in a solvent to prepare a negative electrode slurry; and the slurry is coated on the negative electrode current collector.

[0068] In some embodiments, the solvent is either deionized water or N-methylpyrrolidone (NMP).

[0069] In a fourth aspect, this application provides an electrochemical device comprising the negative electrode sheet proposed in this application.

[0070] The electrochemical device proposed in this application includes a lithium battery, which may include secondary batteries such as lithium-ion batteries. Therefore, the silicon-carbon anode material proposed in this application exhibits excellent volume expansion uniformity, which is beneficial for improving the stability of the electrode structure, thereby enhancing the cycle performance and other electrical properties of the electrochemical device.

[0071] The following specific embodiments illustrate the solution of this application. It should be noted that these embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0072] Example 1 Thermoplastic resin was subjected to a first carbonization treatment at 400°C for 1 hour in a rotary kiln to obtain a first intermediate. The first intermediate (resin carbon powder) was mixed with KOH at a mass ratio of 1:2 and placed in a rotary kiln at 700°C for 3 hours for activation treatment to obtain a second intermediate. The second intermediate was acid-washed for 5 hours, washed with water until neutral, and dried. The second intermediate underwent a second carbonization treatment at 800°C for 20 minutes to remove oxygen, resulting in a porous carbon matrix. The porous carbon matrix can be further finely crushed. The porous carbon matrix was then placed in a fluidized bed for vapor deposition. The reactor air was replaced with nitrogen, and the temperature was raised to 550°C. A mixture of silane and nitrogen gas at a flow rate of 50 L / min was introduced and held for 6 hours for silicon deposition. The silane flow was stopped, and a mixture of acetylene and nitrogen gas at a flow rate of 50 L / min was introduced and held for 4 hours for carbon deposition to obtain a silicon-carbon anode material.

[0073] Example 2 Example 2 is the same as Example 1, except that the first carbonization treatment temperature is 500°C.

[0074] Example 3 Example 3 is the same as Example 1, except that the first carbonization treatment temperature is 600°C.

[0075] Example 4 Example 4 is the same as Example 1, except that the second carbonization temperature is 900°C.

[0076] Example 5 Example 5 is the same as Example 1, except that the second carbonization temperature is 1000°C.

[0077] Example 6 Example 6 is the same as Example 2, except that the second carbonization temperature is 900°C.

[0078] Example 7 Example 7 is the same as Example 2, except that the second carbonization temperature is 1000°C.

[0079] Example 8 Example 8 is the same as Example 3, except that the second carbonization temperature is 900°C.

[0080] Example 9 Example 9 is the same as Example 3, except that the second carbonization temperature is 1000°C.

[0081] Comparative Example 1 Comparative Example 1 is the same as Example 2, except that the second carbonization temperature is 1100°C.

[0082] Comparative Example 2 Comparative Example 2 is the same as Example 2, except that the second carbonization temperature is 1200°C.

[0083] Test method: 1. Scanning electron microscopy (SEM) test: Scanning electron microscopy characterization was performed using a Philips XL-30 field emission scanning electron microscope at 10 kV and 10 mA.

[0084] 2. Specific surface area specification: The specific surface area of ​​the prepared silicon-carbon anode material was tested using a JW-BK100C specific surface area and pore size analyzer to obtain the specific surface area data of the anode material after deposition.

[0085] 3. Particle size distribution characterization: The particle size distribution of the prepared gas-phase silicon-carbon anode material was tested using a Malvern Mastersizer 2000 / 3000 laser particle size analyzer to obtain particle size distribution curves and key parameters.

[0086] 4. Electrochemical performance testing: (1) Preparation of button lithium batteries Preparation of negative electrode sheet: The mass ratio of silicon-carbon negative electrode material active material, conductive agent (carbon black or carbon nanotubes) and binder lithium polyacrylate (PAALi) is set to (6~8):1:1. Add an appropriate amount of deionized water and place it on a ball mill for 1h~3h to ensure that the homogenization effect reaches the best state. Cut copper foil with a width of 10 cm and a length of 20 cm with a utility knife, place it on a heated flat plate coating machine for coating, and then place the copper foil loaded with slurry in a vacuum drying oven at a drying temperature of 60°C~80°C for 12h~24h. Take out the dried electrode sheet and punch out a 12mm~14mm negative electrode sheet.

[0087] Electrolyte preparation: First, place the sealed ethylene carbonate (EC) solvent in a 50°C constant temperature drying oven and heat until it becomes liquid. Measure the required amounts of EC and propylene carbonate (PC) solvents, and add the appropriate amount of fluoroethylene carbonate (FEC) additive according to the formula requirements. Stir on a magnetic stirrer for 4-6 hours. Take an appropriate amount of LiPF6 salt and add it to a glass bottle to prepare a 1M LiPF6 solvent EC:PC (n:n=1:1) + 5% FEC electrolyte.

[0088] Separator: The lithium battery separator is made of polyolefin polyethylene (PE) or polypropylene (PP).

[0089] Battery assembly: (a) Wipe the operating table inside the glove box clean with a paper towel, use metal tweezers to pick up the negative electrode shell onto the operating table, and then pick up the spring sheet and the gasket in turn, placing them in the center inside the negative electrode shell.

[0090] (b) Using a lithium metal sheet as the counter electrode, in order to avoid the lithium metal sheet from slipping, a drop of electrolyte is added to the center of the pad using a pipette before the lithium metal sheet is placed on the pad.

[0091] (c) First, add 40 μL of electrolyte to the lithium metal sheet, then place a PP or PE membrane, and then add another 40 μL of electrolyte.

[0092] (d) Place the negative electrode sheet with the active material coated on it facing the separator, and finally put the positive electrode shell on.

[0093] (e) Then, the assembled coin cells are packaged. Finally, the packaged cells are left to stand at room temperature for 10 hours to allow the electrolyte, active materials, and separator to fully impregnate before electrochemical testing can be carried out.

[0094] (2) Performance testing methods The battery was charged and discharged using a LAND system. After resting for 10 hours, it was discharged at 0.05C to 0.005V, then rested for five minutes before being discharged at 50μA to 0.005V. After resting for 5 minutes, it was discharged again at 10μA to 0.005V, and finally charged at a constant current of 0.05C to 2V. This process was repeated once. The charge-discharge capacity curve was obtained. The initial efficiency was calculated as the capacity at the lithium insertion cutoff voltage of 2V divided by the capacity at the lithium extraction cutoff voltage of 0.005V. Specifically, the electrochemical characteristics of the anode material were investigated within a defined voltage range using constant current charge-discharge tests. This testing procedure aimed to obtain a series of key data, including specific capacity, coulombic efficiency, charge-discharge voltage curves, and cycle stability, to provide a preliminary and comprehensive evaluation of the electrochemical performance of the anode material.

[0095] 5. Silane utilization rate test Set the silicon deposition ratio to C, weigh xg of the deposited silicon-carbon anode material, place it in a tube furnace, and burn it at 900°C for 8 hours. After cooling, weigh the material after burning and set it to yg. The silane utilization rate is calculated as [(y÷60×28) / x%]÷C.

[0096] Test results: The characteristic test results of silicon-carbon anode materials are shown in Table 1.

[0097] The electrical performance test results of the silicon-carbon anode material are shown in Table 2.

[0098] Table 1

[0099] Table 2

[0100] As shown in Tables 1 and 2, the silicon-carbon anode material proposed in this application exhibits superior electrochemical performance.

[0101] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. "First feature" and "second feature" may include one or more of the indicated feature.

[0102] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0103] In this application, the order in which the steps are written does not imply a strict execution order and does not limit the implementation process. The specific execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps in this application can 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) can 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.

[0104] 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 silicon-carbon anode material, characterized in that, include: A porous carbon matrix, wherein the oxygen content of the porous carbon matrix is ​​A, 0.3wt%≤A≤3wt%; Nano-silicon, wherein the nano-silicon is at least partially located within the pores of the porous carbon matrix; A carbon coating layer that covers at least a portion of the surface of the porous carbon matrix.

2. The silicon-carbon anode material according to claim 1, characterized in that, The hydrogen content of the porous carbon matrix is ​​B, wherein 0.05wt%≤B≤0.5wt%, and A>B.

3. The silicon-carbon anode material according to claim 2, characterized in that, 1.5 wt%≤A≤2wt%, 0.1wt%≤B≤0.25wt%.

4. The silicon-carbon anode material according to claim 1 or 2, characterized in that, The specific surface area of ​​the porous carbon matrix is ​​1600 m². 2 / g~2400m 2 / g; and / or, The microporosity of the porous carbon matrix is ​​80%~97%.

5. The silicon-carbon anode material according to claim 1 or 2, characterized in that, At least one of the following conditions must be met: The porous carbon matrix has a pore volume of 0.6 cm³. 3 / g-1.2cm 3 / g; The average pore size of the porous carbon matrix is ​​1.5 nm to 2.3 nm; The particle size of the porous carbon matrix is ​​3μm≤Dv50≤10μm.

6. A method for preparing the silicon-carbon anode material according to any one of claims 1 to 5, characterized in that, include: The resin carbon source is subjected to a first carbonization treatment to obtain a first intermediate; The first intermediate is activated to obtain the second intermediate; The second intermediate is subjected to a second carbonization treatment to obtain a porous carbon matrix. The temperature of the second carbonization treatment is 800°C to 1000°C. The porous carbon matrix is ​​subjected to vapor phase deposition using silicon and carbon sources to obtain the silicon-carbon anode material.

7. The method according to claim 6, characterized in that, The temperature of the first carbonization treatment is 400°C to 600°C.

8. The method according to claim 6 or 7, characterized in that, The activating agent used in the activation process includes at least one of KOH, NaOH, CO2, and water vapor. The activation treatment temperature is 400°C to 800°C.

9. A negative electrode sheet, characterized in that, The negative electrode sheet comprises the silicon-carbon negative electrode material according to any one of claims 1 to 5, or the silicon-carbon negative electrode material prepared by the method according to any one of claims 6 to 8.

10. An electrochemical device, characterized in that, The electrochemical device includes the negative electrode as described in claim 9.

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