Carbon-coated silicon-based negative electrode material and preparation method thereof, negative electrode plate and lithium ion battery
By forming a carbon-coated silicon-based anode material with a multi-layered core-shell structure through hydroxyl modification treatment on the surface of silicon powder and reaction with aminosilane, the problem of the imbalance between battery capacity and cycle life after silicon-carbon materials are combined with graphite is solved, and a lithium-ion battery with high initial reversible capacity and long cycle life is realized.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- BLUE OCEAN & BLACK STONE TECH CO LTD (FUJIAN)
- Filing Date
- 2025-11-25
- Publication Date
- 2026-04-17
AI Technical Summary
In existing technologies, it is difficult to achieve a balance between battery capacity and cycle life when silicon-carbon materials are combined with graphite in lithium-ion batteries. The volume effect of silicon-carbon materials leads to poor cycle life, while graphite has a long cycle life but low theoretical capacity.
By forming hydroxyl groups on the surface of silicon powder, a multi-layered core-shell structure of carbon-coated silicon-based anode material is formed by reacting aminosilanes with specific organic compounds, and then compounded with graphite to prepare lithium-ion batteries.
It significantly improves the initial reversible capacity and first coulombic efficiency of lithium-ion batteries, while achieving the best balance between battery capacity and cycle life, with a capacity retention rate of over 80%.
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Figure CN121885571A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of battery anode material technology, and in particular to carbon-coated silicon-based anode materials and their preparation methods, anode sheets, and lithium-ion batteries. Background Technology
[0002] Graphite is commonly used as an anode material in lithium-ion batteries, but its low specific capacity (372 mAh / g) makes it difficult to meet the demands of high-capacity lithium-ion batteries. Silicon has an extremely high specific capacity (4200 mAh / g), which can significantly improve the energy density of lithium-ion batteries. However, silicon as an anode material has many problems, such as easy agglomeration, large volume changes during charge and discharge (volume expansion greater than 300%), poor conductivity, and poor cycle stability, which limit its commercial application. Currently, silicon-based anodes generally use silicon-carbon materials, and their preparation techniques are mainly mechanical ball milling and chemical vapor deposition (CVD) of silicon-carbon. The former produces silicon-carbon samples with large and non-uniform particle sizes and is prone to introducing impurities, resulting in low purity. The latter can obtain samples with high purity and good uniformity, but still has problems such as the complexity of the equipment required for the process, the flammability and explosiveness of silanes, and the high cost of porous carbon frameworks.
[0003] Silicon-carbon materials have a high theoretical specific capacity, but their volume effect leads to poor cycle life; graphite has a long cycle life, but its theoretical capacity is low. Currently, commercially available anode materials are prepared by mixing silicon-carbon materials with commercial graphite in a certain proportion. The specific capacity of the electrode prepared by the composite anode material increases with the increase of the proportion of silicon-carbon materials, but it also reduces its cycle stability to a certain extent, making it difficult to achieve a good balance between battery capacity and cycle life.
[0004] Application content The purpose of this application is to address the shortcomings of existing technologies that use silicon-carbon materials combined with graphite, which struggle to maintain a balance between battery capacity and cycle life. This application proposes a carbon-coated silicon-based anode material, its preparation method, anode sheet, and a lithium-ion battery. First, silicon powder is treated with a modifying liquid to form hydroxyl groups on its surface, increasing its hydrophilicity and reactivity, yielding an intermediate product. This intermediate product is then treated with an aminosilane to obtain amino-modified silicon powder. Next, the amino-modified silicon powder, a specific organic compound containing phenolic hydroxyl groups, and an aqueous solution containing an amino polymer are reacted to form a carbon-coated silicon-based anode material with a multi-layered core-shell structure. Using this carbon-coated silicon-based anode material to prepare a lithium-ion battery significantly improves the initial reversible capacity and initial coulombic efficiency. Furthermore, the battery prepared by combining this carbon-coated silicon-based anode material with graphite achieves an optimal balance between capacity and cycle life.
[0005] Firstly, the method for preparing a carbon-coated silicon-based anode material provided in this application adopts the following technical solution: the preparation method includes the following steps, such as... Figure 1 As shown: (1) Silicon powder is dispersed in a modification liquid for treatment to form a hydroxyl-modified silicon dispersion system. Then, the hydroxyl-modified silicon dispersion system is filtered to obtain an intermediate product. The intermediate product is dispersed with aminosilane in a solvent and reacted. The reacted product is filtered, washed, and dried to obtain amino-modified silicon powder. The modification liquid contains sulfuric acid and hydrogen peroxide. (2) Disperse the amino-modified silica powder in an aqueous solution of pyrogallol and / or catechol, and adjust the pH of the dispersed system to 8.0 to 9.5. Specifically, for example, the pH can be 8.0, 8.5, 9.0 or 9.5. Then add an aqueous solution containing amino polymer to react. After the reaction is completed, separate the system into solid and liquid components. (3) The solid product obtained by solid-liquid separation in step (2) is calcined to obtain carbon-coated silicon-based anode material (Si@C material).
[0006] The above technical solution involves treating silicon powder with a modification liquid containing specific components. This process forms abundant hydroxyl groups on the silicon powder surface, increasing its hydrophilicity and reactivity, making it easier to undergo further functional group modification. In the dispersion system, the alkoxy group at one end of the aminosilane hydrolyzes to form silanol groups, which then undergo hydrolysis-condensation reaction with the hydroxyl groups on the silicon powder surface, thus obtaining amino-modified silicon powder. The amino group of the aminosilane is a strongly polar functional group, which can react with the phenolic groups of pyrogallol or catechol under weakly alkaline conditions (pH = 8.0–9.5) through hydrogen bonding and electrostatic interactions. Hydroxyl groups are deprotonated to form phenoxy anions, which are easily oxidized by oxygen to generate highly reactive intermediates, o-benzoquinone. O-benzoquinone contains highly reactive carbon-carbon double bonds that can be interconnected through Michael addition to form carbon-carbon covalent bonds. The amino groups in the polymer containing amino groups exist as free bases and are nucleophilic. The highly nucleophilic amino groups can efficiently attack the electron-deficient centers (carbon-oxygen double bonds) on o-benzoquinone, undergoing a Schiff base reaction to generate stable carbon-nitrogen covalent bonds, thereby forming a stable cross-linked network. After calcination, the final carbon-coated silicon-based anode material is obtained.
[0007] When the pH of the dispersed system is adjusted to less than 8.0, the phenolic hydroxyl groups of pyrogallol or catechol are extremely difficult to deprotonate, making it impossible to obtain the key intermediate, o-benzoquinone. Consequently, the subsequent efficient covalent cross-linking reaction cannot be initiated. Furthermore, the amino groups on the polymer chains containing amino groups will react with H+. + It combines and is protonated, and its lone pair electrons are then... +When the nucleophilicity of the pyrogallol or catechol is occupied, its nucleophilicity decreases sharply, and it cannot form a stable cross-linked network. When the pH of the dispersed system is adjusted to greater than 9.5, the oxidation of pyrogallol or catechol becomes very violent and uncontrollable in a strongly alkaline environment and in the presence of oxygen. Over-oxidation may occur, leading to ring-opening reactions and the formation of complex oxides.
[0008] Optionally, the average particle size of the silicon powder is 80-200 nm; the modification solution is a mixture of sulfuric acid and hydrogen peroxide solution, wherein the volume ratio of the sulfuric acid to the hydrogen peroxide solution is 1.0-1.5:1.0, specifically, for example, it can be 1.0:1.0, 1.2:1.0 or 1.5:1.0.
[0009] By using the above technical solution, by limiting the average particle size of the silicon powder and synergistically controlling the volume ratio of sulfuric acid to hydrogen peroxide solution in the modification solution, the carbon-coated silicon-based anode material can achieve the optimal size. At the same time, by adjusting the silicon content in the carbon-coated silicon-based anode material, the initial reversible capacity and initial coulombic efficiency of the battery prepared using the carbon-coated silicon-based anode material are significantly improved. Furthermore, the capacity retention rate of the battery after combining the carbon-coated silicon-based anode material with graphite is higher than 80% (after 200 cycles).
[0010] In a specific embodiment of the preparation method described in this application, in step (1), the specific process of dispersing silicon powder in the modification liquid is as follows: dispersing silicon powder in the modification liquid and stirring for 1 to 2 hours, wherein the ratio of silicon powder to the modification liquid is 1.0g: 50 to 150mL, specifically, for example, it can be 1.0g: 50mL, 1.0g: 100mL or 1.0g: 150mL.
[0011] In a specific embodiment of the preparation method described in this application, in step (1), before filtering the hydroxyl-modified silicon dispersion system to obtain the intermediate product, the pH value of the hydroxyl-modified silicon dispersion system is first adjusted to neutral (in this article, the pH value for neutrality is 7.0 to 7.5). The purpose is to ensure that the subsequent reaction of pyrogallol and / or catechol with the aqueous solution containing amino polymer is carried out in a weakly alkaline environment (pH = 8.0 to 9.5).
[0012] In a specific embodiment of the preparation method described in this application, the mass ratio of silicon powder to aminosilane in step (1) is 100:1 to 5, specifically, for example, it can be 100:1, 100:2, 100:3, 100:4 or 100:5; in a preferred embodiment, the mass ratio of silicon powder to aminosilane is 100:1 to 3.
[0013] In a specific embodiment of the preparation method described in this application, the solvent in step (1) must be able to fully dissolve the aminosilane and effectively wet and disperse the silicon powder; it must be able to allow and promote the hydrolysis of the aminosilane to generate the key silanol; and its boiling point, toxicity, ease of removal, and other factors must be considered.
[0014] In the specific implementation process, the purpose of washing in step (1) is to remove water-soluble and organic-soluble impurities and by-products, and to replace the solvent to facilitate subsequent drying and obtain a sample with better dispersion performance.
[0015] In a specific embodiment of the preparation method described in this application, the drying conditions in step (1) are: a temperature of 70 to 90°C, specifically, for example, 70°C, 75°C, 80°C, 85°C or 90°C, and a time of 10 to 14 hours, specifically, for example, 10 hours, 12 hours or 14 hours.
[0016] In a specific embodiment of the preparation method described in this application, the mass ratio of the amino-modified silicon powder, pyrogallol and / or catechol and the aqueous solution containing the amino polymer in step (2) is 10:1 to 4:1 to 4. Specifically, for example, it can be 10:1:1, 10:2:2, 10:3:3 or 10:4:4. In a preferred embodiment, the mass ratio of the amino-modified silicon powder, pyrogallol or catechol and the amino-containing polymer is 10:2 to 3:2 to 3.
[0017] In a specific embodiment of the preparation method described in this application, in step (2), the aqueous solution of pyrogallol and / or catechol is a mixed solution of pyrogallol and / or catechol with a solvent. Specifically, the solvent is deionized water, which is a participant and promoter in the reaction, playing a role in dissolving oxygen and providing protons (H+). + The transfer environment allows pyrogallol and / or catechol to dissolve efficiently in water simultaneously with the aqueous solution of the amino-containing polymer, enabling subsequent reactions to proceed fully and forming a uniform, highly cross-linked three-dimensional network structure. There is no particular limitation on the amount of solvent used in step (2), as long as the solvent can effectively dissolve the amino-modified silica powder, pyrogallol and / or catechol, and the aqueous solution of the amino-containing polymer.
[0018] In a specific embodiment of the preparation method described in this application, in step (2), the aqueous solution containing the amino polymer is a mixture of the amino polymer and a solvent. The amino polymer is selected from one or more of polylysine, polyamide-amine dendritic polymer (Shanghai Maclean Biochemical Technology Co., Ltd., P920718-250mg), ethylenediamine, hexamethylenediamine and polyethyleneimine.
[0019] Optionally, the amino-containing polymer is polyethyleneimine, wherein the weight-average molecular weight of the polyethyleneimine is 10,000 to 100,000 g / mol. More preferably, the weight-average molecular weight of the polyethyleneimine is 70,000 g / mol.
[0020] Through the above technical solution, polyethyleneimine (PEI) provides a carbon source on the one hand, and can also serve as a crosslinking agent and structural scaffold for polymer networks on the other. Multiple amino groups on a PEI molecular chain can react with multiple pyrogallol / benzoquinone molecules simultaneously, thereby "stitching" countless small molecules into a huge, three-dimensional crosslinked polymer network. This is the basis for forming gels or robust coatings. At the same time, the long-chain structure of PEI itself provides toughness, flexibility and a certain strength to the final material.
[0021] In a preferred embodiment of the preparation method described in this application, step (2) is specifically performed as follows: a: Disperse the amino-modified silica powder obtained in step (1) in an aqueous solution of pyrogallol and / or catechol, adjust the pH of the dispersed system to 8.0-9.5, then add an aqueous solution containing amino polymer to react, and then separate the reacted system into solid and liquid components. b: Disperse the solid product obtained from solid-liquid separation in an aqueous solution of pyrogallol and / or catechol, and adjust the pH of the dispersed system to 8.0–9.5; c: Then, an aqueous solution containing an amino polymer is added to the system to adjust the pH value and reacted. The system after reaction is then separated into solid and liquid components to obtain a solid product. d: Repeat steps (2b) and (2c) 1 to 2 times. Each time, when operating step (2b), use the solid product obtained in the previous step (2c) as the raw material for the next step (2b). The purpose of repeating steps (2b) and (2c) is to make the coating layer of the carbon-coated silicon-based anode material finally prepared thicker.
[0022] Optionally, in step (3), the specific method for calcining the solid product obtained by solid-liquid separation is as follows: the solid product is heated to 750-850°C at a heating rate of 4-6°C / min under the protection of an inert atmosphere, and held at 750-850°C for 1-3 hours. Specifically, for example, the heating rate can be 4°C / min, 5°C / min or 6°C / min, for example, the temperature can be raised to 750°C, 800°C or 850°C, for example, it can be held at 750°C, 800°C or 850°C for 1 hour, 2 hours or 3 hours.
[0023] The purpose of the above technical solution is to transform the precursor into a stable and efficient functionalized structure, form a strong interfacial bond, thereby constructing a robust composite material that can withstand the huge volume changes of silicon. It also improves the conductivity of the material, forms a stable SEI film, decomposes and removes impurities such as organic solvents and residual functional groups introduced during the preparation process, and purifies the material.
[0024] Secondly, this application provides a carbon-coated silicon-based anode material prepared according to the above-described preparation method.
[0025] Thirdly, this application provides a negative electrode sheet, comprising a copper foil and a negative electrode slurry coated on at least one side of the copper foil. The raw materials for preparing the negative electrode slurry include a negative electrode material, a binder, a conductive agent, and water. The negative electrode material is a carbon-coated silicon-based negative electrode material obtained by the preparation method described above, and the binder is a combination of carboxymethyl cellulose and styrene-butadiene emulsion.
[0026] Optionally, the mass ratio of the negative electrode material, the binder, and the conductive agent is 6-8:1-3:1. Specifically, for example, it can be 6:3:1, 7:2:1, or 8:1:1. In a preferred case, the mass ratio of the negative electrode material, the binder, and the conductive agent is 7:2:1; and the mass ratio of carboxymethyl cellulose and styrene-butadiene emulsion is 1.0:1.0-1.5.
[0027] Through the above technical solution, the hydroxyl (-OH) and carboxyl (-COOH) groups in CMC molecules can form strong hydrogen bonds and van der Waals forces with the active material and current collector surface, providing a certain degree of adhesion. The carboxyl groups of CMC can interact with the subsequently added SBR (styrene-butadiene emulsion) particles, helping the SBR to be more uniformly distributed in the slurry and jointly contributing to the adhesion. CMC acts as a dispersant and structural framework, while SBR acts as a toughening agent. If only CMC is added, although a uniform slurry and electrode can be obtained, the electrode is too brittle, prone to cracking during processing, and has an unsatisfactory cycle life. If only SBR is added, the slurry cannot be stored and coated stably, and the electrode adhesion strength is insufficient.
[0028] The negative electrode material provides the battery capacity and determines the battery energy density. If too little binder is added, it will not provide sufficient bonding force, while adding too much will hinder lithium-ion transport, increase internal resistance, and introduce unnecessary side reactions. The role of the conductive agent is to form a highly efficient and stable conductive network. If too little is added, the conductivity will be too poor, while adding too much will crowd out the space of the active material and binder, reduce the energy density, and affect the wetting of the electrolyte. Adjusting the mass ratio of the negative electrode material, the binder, and the conductive agent to 6-8:1-3:1 is a balance point achieved between high energy density and acceptable processability and stability.
[0029] In a specific embodiment of the negative electrode sheet described in this application, the solid content of the negative electrode slurry is 30% to 40%, specifically, for example, 30%, 32%, 34%, 36%, 38%, or 40%.
[0030] Optionally, the loading of the carbon-coated silicon-based negative electrode material on the negative electrode sheet is 0.7–1.0 mg / cm³. 2 Specifically, for example, it could be 0.7 mg / cm³. 2 0.8 mg / cm 2 0.9 mg / cm 2 Or 1.0 mg / cm 2 .
[0031] Through the above technical solutions, a trade-off exists between loading and battery performance. Pursuing high energy density requires high loading, but excessive loading increases ion and electron transport impedance, limiting reaction kinetics and leading to poorer rate performance. Furthermore, high loading means greater expansion and contraction stress on the entire electrode layer, exacerbating side reactions and polarization accumulation, posing challenges to initial coulombic efficiency (ICE) and cycle life. Simultaneously, it places higher demands on processes such as slurry coating (requiring higher surface density for single coating, prone to uneven thickness, streaks, and cracking), electrode drying (solvents evaporate quickly on the surface, forming a hard shell, while internal solvents struggle to escape, resulting in a "skinning" effect and damaging the internal electrode structure), electrolyte wetting (potential for incomplete wetting), and rolling (requiring greater pressure, more prone to problems like crushing, rebound, or binder migration, affecting pore structure). Therefore, a loading of 0.7–1.0 mg / cm³ is selected. 2 This allows for a balance between the battery's electrochemical performance and manufacturing requirements.
[0032] Optionally, the raw materials for preparing the negative electrode slurry also include graphite. Based on the total mass of the carbon-coated silicon-based negative electrode material and graphite as 100% by weight, the content of the carbon-coated silicon-based negative electrode material is 20-30% by weight, specifically, for example, 20%, 22%, 24%, 26%, 28%, or 30% by weight, and the content of graphite is 70-80% by weight, specifically, for example, 70%, 72%, 74%, 76%, 78%, or 80% by weight.
[0033] The reason for adding graphite to the raw materials for preparing the negative electrode slurry through the above technical solution is that the carbon-coated silicon-based negative electrode material has a high theoretical capacity but poor cycle stability, while graphite has a long cycle life but a low theoretical capacity. Mixing them with graphite achieves a balance between high energy density and long cycle life. Taking the total mass of the carbon-coated silicon-based negative electrode material and graphite as 100% by weight, when the content of the carbon-coated silicon-based negative electrode material is less than 20% by weight and the content of graphite is greater than 80% by weight, the electrode energy density is too low. When the content of the carbon-coated silicon-based negative electrode material is greater than 30% by weight and the content of graphite is less than 70% by weight, its cycle stability deteriorates and its cycle life shortens.
[0034] Fourthly, this application provides a lithium-ion battery, which includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode is the aforementioned negative electrode.
[0035] In the specific embodiments of the lithium-ion battery described in this application, the positive electrode, separator, and electrolyte can be conventional choices in the art.
[0036] In summary, this application includes at least one of the following beneficial technical effects: 1. In this application, silicon powder is first treated with a modification liquid to form hydroxyl groups on the surface of the silicon powder, thereby increasing its hydrophilicity and reactivity, and obtaining an intermediate product. The intermediate product is then treated with aminosilane. During this process, the alkoxy group at one end of the aminosilane hydrolyzes into silanol, which then undergoes a hydrolysis-condensation reaction with the hydroxyl groups on the surface of the silicon powder to form a silicon-carbon precursor. The amino group in the aminosilane interacts strongly with the silicon-carbon precursor to obtain amino-modified silicon powder. Under certain conditions, pyrogallol or catechol generates an active intermediate, o-benzoquinone. The polymer containing amino groups reacts with o-benzoquinone to form a stable cross-linked network, ultimately forming a carbon-coated silicon-based anode material with a core-shell structure. Using this carbon-coated silicon-based anode material to prepare lithium-ion batteries can significantly improve the initial reversible capacity, initial coulombic efficiency, and cycle capacity retention of the battery. 2. In a preferred embodiment, by limiting the raw material composition in the preparation of carbon-coated silicon-based anode material and synergistically controlling the calcination conditions, the initial reversible capacity of the battery prepared using carbon-coated silicon-based anode material can reach more than 2000 mAh / g, and the initial coulombic efficiency is higher than 90%. 3. In a preferred embodiment, when preparing the negative electrode sheet, the carbon-coated silicon-based negative electrode material prepared in this application is compounded with graphite to prepare the battery, which can achieve the best balance between battery capacity and cycle life, and the battery capacity retention rate is higher than 80%. Attached Figure Description
[0037] Figure 1This is a flowchart illustrating the preparation process of the carbon-coated silicon-based anode material described in this application. Figure 2 SEM image of the carbon-coated silicon-based anode material prepared in Example 1; Figure 3 The images shown are TEM images of the carbon-coated silicon-based anode material prepared in Example 1, where a is a TEM image magnified 25,000 times and b is a TEM image magnified 98,000 times. Figure 4 The graphs show the first charge-discharge curves of the carbon-coated silicon-based anode material and the pure silicon anode material prepared in Example 1 at a current density of 100 mA / g. Detailed Implementation
[0038] The following is in conjunction with the appendix Figures 1-4 The present application will be further described in detail with reference to specific embodiments.
[0039] The following examples further illustrate the carbon-coated silicon-based anode material and its preparation method, anode sheet, and lithium-ion battery described in this application. These examples are implemented based on the technical solution of this application, providing detailed implementation methods and specific operating procedures; however, the scope of protection of this application is not limited to the following examples.
[0040] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.
[0041] Silicon powder: Purchased from Zhejiang Zhongning Silicon Industry Co., Ltd., with an average particle size of 80-200nm; Silicon powder: Purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., product number: S130843, average particle size is 20-60nm; Aminosilane: γ-aminopropyltriethoxysilane, purchased from Shanghai Amore Biotechnology Co., Ltd., product number: 919-30-2; Aminosilane (non-amino): Tetra(dimethylsiloxy)silane, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., item number: T102295; Polyethyleneimine: 50% polyethyleneimine aqueous solution, purchased from Shanghai Jizhi Biochemical Technology Co., Ltd., product number: E54373-100g; Chitosan: Purchased from Shanghai Yuanye Biotechnology Co., Ltd., product number: V32356; Polyethylene: Purchased from Shanghai Yuanye Biotechnology Co., Ltd., Item No.: V34065; Carboxymethyl cellulose: Purchased from Dongguan Kelude Experimental Equipment Technology Co., Ltd., Item No.: MA-EN-BI-09010W; Styrene-butadiene emulsion: Purchased from Dongguan Kelude Experimental Equipment Technology Co., Ltd., Item No.: MA-EN-BI-03020R; Conductive agent: Super P, purchased from TIMCAL Graphite & Carbon, Item No.: Super P carbon black for high-lithium batteries; Positive electrode sheet: Purchased from Suzhou Shengernuo Technology Co., Ltd., 16*0.6mm; Separator: Cellulose separator, purchased from Suzhou Duoduo Chemical Technology Co., Ltd., item number: NE-000264; Electrolyte: Purchased from Suzhou Duoduo Chemical Technology Co., Ltd., Product No.: LB-370.
[0042] Test case SEM test: Images were taken using a Hitachi SU-70 thermal field emission scanning electron microscope with an accelerating voltage of 5 kV; TEM test: Images were taken using a Philips-FEI Tecnai F30 field emission high-resolution transmission microscope with an accelerating voltage of 300 kV. First coulomb efficiency: Xinwei CT-4008Tn tester, ratio of discharge capacity to charge capacity; Initial reversible capacity: The amount of charge that the battery can store or release during the first charge-discharge cycle, as measured by the Xinwei CT-4008Tn tester. 3rd reversible capacity and 205th reversible capacity: The 3rd reversible capacity is the reversible capacity after 200 cycles at a current density of 1 A / g, and the capacity after the 3rd charge-discharge cycle with a recovery current of 0.1 A / g. The 205th reversible capacity is the reversible capacity after 200 cycles at a current density of 1 A / g, and the capacity after the 205th charge-discharge cycle with a recovery current of 0.1 A / g. The voltage range of the charge-discharge cycle is 0.01 to 3.00 V. Capacity retention rate after compounding: The ratio of reversible capacity after 205 cycles to reversible capacity after 3 cycles using the Xinwei CT-4008Tn tester.
[0043] Example 1 A method for preparing a carbon-coated silicon-based anode material, the method comprising the following steps: (1) 1.0 g of silicon powder with an average particle size of 80-200 nm was dispersed in 100 mL of modification solution (the volume ratio of sulfuric acid to hydrogen peroxide solution was 1:1, the mass concentration of sulfuric acid was 99.7%, and the mass concentration of hydrogen peroxide solution was 30%) and stirred for 1 h to form a hydroxyl-modified silicon dispersion system. The hydroxyl-modified silicon dispersion system was then washed with deionized water to adjust the pH value to 7.0 and then filtered. The intermediate product was then reacted with 0.03 g of γ-aminopropyltriethoxysilane in a mixed solution of ethanol and deionized water (volume ratio of 1:1) and magnetically stirred for 12 h. The product after reaction was filtered and the solid product obtained was washed with anhydrous ethanol (volume concentration of 99.7%) and then dried at 80 °C for 12 h to obtain amino-modified silicon powder. (2)a: Disperse 1.00g of amino-modified silica powder prepared in step (1) and 0.20g of pyrogallol in 100mL of deionized water, add NaOH solution (4% by mass) dropwise to the dispersed system, adjust the pH of the dispersed system to 8.5, stir for 12h, add 0.40g of 50% polyethyleneimine aqueous solution, stir at room temperature (25℃) for 6h to mix, filter the mixed system with deionized water to obtain the filtered product; b: Disperse the obtained filtrate with 0.20 g pyrogallol in 100 mL of deionized water, add NaOH solution (4% by mass) dropwise to the dispersed system, and adjust the pH of the dispersed system to 8.5; c: After stirring for 12 hours, add 0.40 g of 50% polyethyleneimine aqueous solution and stir at room temperature (25℃) for 6 hours to mix. Filter the mixed system with deionized water to obtain the filtered product. d: Use the filtration product obtained in step (2c) as the raw material for step (2b), and repeat steps (2b) and (2c) once; (3) Dry the solid product after filtration in step (2d) at 80°C for 12 hours, place the product in a tube furnace, heat it to 800°C at a heating rate of 5°C / min under nitrogen protection, hold it for 2 hours, and then cool it naturally to room temperature (25°C) to obtain carbon-coated silicon-based anode material.
[0044] The carbon-coated silicon-based anode material prepared in Example 1 was tested by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The test results are as follows: Figures 2-3 As shown, from Figure 2 It can be seen that the carbon-coated silicon-based anode material prepared in Example 1 has a spherical morphology with a size of 200-300 nm. Figure 3It can be seen that the carbon-coated silicon-based anode material prepared in Example 1 has a core-shell structure. The outer carbon shell coating layer has a thickness of 10-15 nm. After calcination, a robust porous carbon layer is formed, which provides a buffer space for the volume expansion of silicon during charging and discharging and improves conductivity. The interior is crystalline silicon with obvious lattice stripes.
[0045] Example 2 The process was carried out in accordance with Example 1, except that 1.0g of silicon powder with an average particle size of 80-200nm was replaced with 1.0g of silicon powder with an average particle size of 20-60nm to obtain a carbon-coated silicon-based anode material.
[0046] Example 3 The process was carried out in accordance with Example 1, except that the volume ratio of sulfuric acid to hydrogen peroxide solution in the modified solution was 7:3, resulting in a carbon-coated silicon-based anode material.
[0047] Example 4 The process was carried out in accordance with Example 1, except that in step (2), the dried product was placed in a tube furnace and heated to 800°C at a heating rate of 10°C / min under nitrogen protection, held for 2 hours, and then naturally cooled to room temperature (25°C) to obtain carbon-coated silicon-based anode material.
[0048] Example 5 The process was carried out in accordance with Example 1, except that in step (2), the dried product was placed in a tube furnace and calcined at 800°C for 4 hours under nitrogen protection, and then naturally cooled to room temperature (25°C) to obtain a carbon-coated silicon-based anode material.
[0049] Comparative Example 1 The modification was carried out in accordance with Example 1, except that the modified liquid was replaced with a mixed solution of deionized water and anhydrous ethanol, wherein the volume ratio of deionized water to anhydrous ethanol was 1:1, to obtain the negative electrode material.
[0050] Comparative Example 2 The method was implemented in accordance with Example 1, except that 0.03g of γ-aminopropyltriethoxysilane was replaced with 0.03g of tetra(dimethylsiloxy)silane to obtain the negative electrode material.
[0051] Comparative Example 3 The process was carried out in accordance with Example 1, except that in step (2), the pH value of the dissolved system was adjusted to 7.0 to obtain the negative electrode material.
[0052] Comparative Example 4 The process was carried out in accordance with Example 1, except that in step (2), the pH value of the dissolved system was adjusted to 10.0 to obtain the negative electrode material.
[0053] Comparative Example 5 The process was carried out in accordance with Example 1, except that 0.40g of 50% polyethyleneimine aqueous solution was replaced with 0.20g of polyethylene to obtain the negative electrode material.
[0054] Comparative Example 6 The procedure was carried out as described in Example 1, except that in step (2), 0.40 g of 50% polyethyleneimine aqueous solution (a polymer containing amino groups) was replaced with 0.20 g of chitosan. The specific operation was as follows: (1) 1.0 g of silicon powder with an average particle size of 80-200 nm was dispersed in 100 mL of modification solution (the volume ratio of sulfuric acid to hydrogen peroxide solution was 1:1, the mass concentration of sulfuric acid was 99.7%, and the mass concentration of hydrogen peroxide solution was 30%) and stirred for 1 h to form a hydroxyl-modified silicon dispersion system. The hydroxyl-modified silicon dispersion system was then washed with deionized water to adjust the pH value to 7.0 and then filtered. The intermediate product was then reacted with 0.03 g of γ-aminopropyltriethoxysilane in a mixed solution of ethanol and deionized water (volume ratio of 1:1) and magnetically stirred for 12 h. The product after reaction was filtered and the solid product obtained was washed with anhydrous ethanol (volume concentration of 99.7%) and then dried at 80 °C for 12 h to obtain amino-modified silicon powder. (2)a: Disperse 1.00g of amino-modified silica powder prepared in step (1) and 0.20g of pyrogallol in 100mL of deionized water, add acetic acid solution (mass concentration of 10%) dropwise to the dispersed system, adjust the pH value of the dispersed system to 6.5, stir for 12h, add 0.20g of chitosan, stir at room temperature (25℃) for 6h to mix, filter the mixed system with deionized water to obtain the filtered product; b: Disperse the obtained filtrate with 0.20 g of pyrogallol in 100 mL of deionized water, add acetic acid solution (mass concentration of 10%) dropwise to the dispersed system, and adjust the pH of the dispersed system to 6.5. c: After stirring for 12 hours, add 0.20 g of chitosan and stir at room temperature (25°C) for 6 hours to mix. Filter the mixed system with deionized water to obtain the filtered product. d: Use the filtration product obtained in step (2c) as the raw material for step (2b), and repeat steps (2b) and (2c) once; (3) The solid product after filtration in step (2d) is dried at 80°C for 12 hours. The product is placed in a tube furnace and heated to 800°C at a heating rate of 5°C / min under nitrogen protection. The temperature is maintained for 2 hours and then naturally cooled to room temperature (25°C) to obtain carbon-coated silicon-based anode material.
[0055] Application Example 1 A negative electrode sheet is prepared by mixing the carbon-coated silicon-based negative electrode material prepared in Example 1, a binder, and Super P (conductive agent) in a mass ratio of 7:2:1. The mixture is then added to deionized water and stirred for 24 hours to obtain a slurry. The binder is a combination of carboxymethyl cellulose and styrene-butadiene emulsion in a mass ratio of 1:1. The solid content of the slurry is 35%. The slurry is coated onto a single-sided copper foil and dried in an oven at 80°C for 12 hours. The dried negative electrode sheet is then cut into 12 mm round pieces. The loading of the carbon-coated silicon-based negative electrode material on the negative electrode sheet is 0.8 mg / cm³. 2 .
[0056] Lithium-ion coin cell battery: A lithium-ion coin cell battery is assembled by combining a positive electrode, the negative electrode prepared in Application Example 1, a separator, and an electrolyte. The lithium-ion coin cell battery prepared in Application Example 1 and a lithium-ion coin cell battery prepared using pure silicon as the negative electrode material (the only difference from Application Example 1 is the negative electrode material) were subjected to charge-discharge performance tests. The test conditions were: constant current charge-discharge, current density of 100 mA / g, and voltage range of 0.01V to 3.00V. The test results are as follows: Figure 4 As shown, from Figure 4 As can be seen, the curve of voltage decrease represents the charging process, and the curve of voltage increase represents the charging process. For pure silicon anode materials, the curve smoothly decreases from about 1.00V, and after falling below 0.20V, it quickly enters a very long and flat plateau (close to 0.01V). This is a typical characteristic of pure silicon, indicating that its electrochemical reaction is almost entirely concentrated at extremely low potentials. For carbon-coated silicon-based anode materials, the curve has a distinct "slope" or "bulge" between 0.80 and 0.20V. This feature strongly indicates the presence of carbon materials (especially graphite). The lithiation process of graphite is completed through a series of step-like phase transitions, contributing capacity in the form of a slope above 0.10V. The curve of carbon-coated silicon-based anode materials is a superposition of the slope of carbon (0.80–0.20V) and the plateau of silicon (0.10–0.01V), clearly revealing its composite material nature.
[0057] Application Example 2 The application was carried out in the manner described in Example 1, except that the carbon-coated silicon-based anode material prepared in Example 1 was replaced with the carbon-coated silicon-based anode material prepared in Example 2 when preparing the anode sheet.
[0058] Application Example 3 The application was carried out in the manner described in Example 1, except that the carbon-coated silicon-based anode material prepared in Example 1 was replaced with the carbon-coated silicon-based anode material prepared in Example 3 when preparing the anode sheet.
[0059] Application Example 4 The application was carried out in the manner described in Example 1, except that the carbon-coated silicon-based anode material prepared in Example 1 was replaced with the carbon-coated silicon-based anode material prepared in Example 4 when preparing the anode sheet.
[0060] Application Example 5 The application was carried out in the manner described in Example 1, except that the carbon-coated silicon-based negative electrode material prepared in Example 1 was replaced with the carbon-coated silicon-based negative electrode material prepared in Example 5 when preparing the negative electrode sheet.
[0061] Application Comparative Example 1 The application was carried out in the manner described in Example 1, except that the carbon-coated silicon-based negative electrode material prepared in Example 1 was replaced with the negative electrode material prepared in Comparative Example 1 when preparing the negative electrode sheet.
[0062] Application Comparative Example 2 The application was carried out in the manner described in Example 1, except that the carbon-coated silicon-based negative electrode material prepared in Example 1 was replaced with the negative electrode material prepared in Comparative Example 2 when preparing the negative electrode sheet.
[0063] Application Comparative Example 3 The application was carried out in the same manner as in Example 1, except that the carbon-coated silicon-based negative electrode material prepared in Example 1 was replaced with the negative electrode material prepared in Comparative Example 3 when preparing the negative electrode sheet.
[0064] Application Comparative Example 4 The method of application example 1 was followed, except that when preparing the negative electrode sheet, the carbon-coated silicon-based negative electrode material prepared in example 1 was replaced with the negative electrode material prepared in comparative example 4.
[0065] Application Comparative Example 5 The application was carried out in the manner described in Example 1, except that the carbon-coated silicon-based negative electrode material prepared in Example 1 was replaced with the negative electrode material prepared in Comparative Example 5 when preparing the negative electrode sheet.
[0066] Application Comparative Example 6 The application was carried out in the manner described in Example 1, except that the carbon-coated silicon-based negative electrode material prepared in Example 1 was replaced with the negative electrode material prepared in Comparative Example 6 when preparing the negative electrode sheet.
[0067] Application Comparative Example 7 The application was carried out in accordance with Example 1, except that, in the preparation of the negative electrode sheet, all the styrene-butadiene emulsion was replaced with carboxymethyl cellulose in the binder.
[0068] The initial reversible capacity and first coulombic efficiency of the lithium-ion coin cells prepared in Examples 1-5 and the lithium-ion coin cells prepared in Comparative Examples 1-7 were tested respectively. The test results are shown in Table 1.
[0069] When preparing negative electrode sheets using Examples 1-5, the carbon-coated silicon-based negative electrode materials prepared in Examples 1-5 were compounded with graphite, and the compounded negative electrode sheets were assembled into batteries according to the method of Application Example 1 to obtain lithium-ion coin batteries compounded using Examples 1-5. The specific compounding is as follows: the carbon-coated silicon-based negative electrode materials, graphite, binder, and Super P (conductive agent) prepared in Examples 1-5 were mixed, wherein the total mass ratio of the carbon-coated silicon-based negative electrode material to graphite, the mass of the binder, and the mass of Super P was 7:2:1, the mass ratio of the carbon-coated silicon-based negative electrode material to graphite was 13:37, and the binder was a composition of carboxymethyl cellulose and styrene-butadiene emulsion with a mass ratio of 1:1.
[0070] When preparing negative electrode sheets using Comparative Examples 1-6, the negative electrode materials prepared in Comparative Examples 1-6 were compounded with graphite, and the compounded negative electrode sheets were assembled into batteries according to the method of Application Example 1 to obtain lithium-ion coin batteries compounded using Comparative Examples 1-6. The specific compounding is as follows: the negative electrode materials, graphite, binder and Super P (conductive agent) prepared in Comparative Examples 1-6 were mixed, wherein the mass ratio of the total mass of the negative electrode material and graphite, the mass of the binder and the mass of Super P was 7:2:1, the mass ratio of the negative electrode material to graphite was 13:37, and the binder was a composition of carboxymethyl cellulose and styrene-butadiene emulsion with a mass ratio of 1:1.
[0071] When preparing the negative electrode sheet using Comparative Example 7, the carbon-coated silicon-based negative electrode material prepared in Example 1 was combined with graphite, and the combined negative electrode sheet was assembled into a battery in the manner of Application Example 1 to obtain the lithium-ion coin cell battery after combination in Application Example 7. The specific combination is as follows: the negative electrode material, graphite, binder and SuperP (conductive agent) prepared in Example 1 were mixed, wherein the mass ratio of the total mass of the negative electrode material and graphite, the mass of the binder and the mass of SuperP was 7:2:1, the mass ratio of the negative electrode material to graphite was 13:37, and the binder was carboxymethyl cellulose.
[0072] The lithium-ion coin cells of Application Examples 1-5 and Comparative Examples 1-7, after being compounded with graphite, were tested for their 3rd reversible capacity, 205th reversible capacity, and capacity retention, respectively. The test results are shown in Table 1. Table 1 As can be seen from the results in Table 1, the electrodes prepared by the silicon-carbon material prepared by the above method have excellent electrochemical performance. While maintaining high capacity, they significantly improve first-efficiency. Furthermore, the material can still maintain high capacity and capacity retention rate when combined with graphite.
[0073] The embodiments described in this specific implementation are preferred embodiments of this application and are not intended to limit the scope of protection of this application. Identical components are represented by the same reference numerals. Therefore, all equivalent changes made to the structure, shape, and principle of this application should be included within the scope of protection of this application.
Claims
1. A method for preparing a carbon-coated silicon-based anode material, characterized in that, The preparation method includes the following steps: (1) Disperse silicon powder in a modification liquid for treatment to form a hydroxyl-modified silicon dispersion system. Then filter the hydroxyl-modified silicon dispersion system to obtain an intermediate product. Disperse the intermediate product with aminosilane in a solvent and react. Filter, wash and dry the product after reaction to obtain amino-modified silicon powder. The modification liquid contains sulfuric acid and hydrogen peroxide. (2) Disperse the amino-modified silica powder in an aqueous solution of pyrogallol and / or catechol, adjust the pH of the dispersed system to 8.0~9.5, then add an aqueous solution containing amino polymer to react, and then separate the reacted system into solid and liquid components. (3) The solid product obtained by solid-liquid separation in step (2) is calcined to obtain carbon-coated silicon-based anode material.
2. The method for preparing the carbon-coated silicon-based anode material according to claim 1, characterized in that, The average particle size of the silicon powder is 80~200 nm; The modified solution is a mixture of sulfuric acid and hydrogen peroxide solution, wherein the volume ratio of sulfuric acid to hydrogen peroxide solution is 1.0~1.5:1.
0.
3. The method for preparing the carbon-coated silicon-based anode material according to claim 1 or 2, characterized in that, The amino-containing polymer is polyethyleneimine, and the weight-average molecular weight of the polyethyleneimine is 10,000 to 100,000 g / mol.
4. The method for preparing the carbon-coated silicon-based anode material according to claim 1 or 2, characterized in that, In step (3), the specific method for calcining the solid product obtained by solid-liquid separation is as follows: the solid product is heated to 750-850 ℃ at a heating rate of 4-6 ℃ / min under the protection of an inert atmosphere, and held at 750-850 ℃ for 1-3 h.
5. A carbon-coated silicon-based anode material obtained by the preparation method according to any one of claims 1 to 4.
6. A negative electrode sheet, comprising a copper foil and a negative electrode paste coated on at least one surface of the copper foil, wherein the raw materials for preparing the negative electrode paste include a negative electrode material, a binder, a conductive agent, and water, characterized in that, The negative electrode material is a carbon-coated silicon-based negative electrode material obtained by the preparation method of any one of claims 1 to 4, and the binder is a combination of carboxymethyl cellulose and styrene-butadiene emulsion.
7. The negative electrode sheet according to claim 6, characterized in that, The mass ratio of the negative electrode material, the binder, and the conductive agent is 6~8:1~3:
1.
8. The negative electrode sheet according to claim 6 or 7, characterized in that, On the negative electrode sheet, the loading of the carbon-coated silicon-based negative electrode material is 0.7~1.0 mg / cm³. 2 .
9. The negative electrode sheet according to claim 6 or 7, characterized in that, The raw materials for preparing the negative electrode slurry also include graphite. Based on the total mass of the carbon-coated silicon-based negative electrode material and graphite as 100% by weight, the content of the carbon-coated silicon-based negative electrode material is 20-30% by weight, and the content of the graphite is 70-80% by weight.
10. A lithium-ion battery, the lithium-ion battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The negative electrode sheet is the negative electrode sheet described in any one of claims 6 to 9.