Preparation method of uniformly coated silicon-carbon negative electrode material

Abstract

The invention discloses a preparation method of a uniformly-coated silicon-carbon negative electrode material, and belongs to the technical field of lithium battery negative electrode materials. The preparation method comprises the following steps: (1) preparing large-aperture porous carbon; and (2) synthesizing the silicon-carbon negative electrode material. By preparing large-aperture porous carbon and combining a degassing mode, small-particle-size sand-milled nano silicon particles can enter apertures conveniently, and the coating uniformity of the material is improved, so that the cycle performance of the material is improved. An amine catalytic structure is selected and combined with tannic acid to construct a polymerization pore channel, so that small-particle nano silicon can enter the pore channel; hydrogen bonds of the solvent and the raw materials are combined to enhance interface interaction, so that hierarchical pore structure regulation and control are realized. Meanwhile, a coupling agent is introduced, so that carboxyl reacts with hydroxyl on the surface of nano silicon, and long-chain alkyl enhances the compatibility with porous carbon; the epoxy group can react with hydroxyl on the surface of the porous carbon or silicon hydroxyl on the surface of the nano silicon, so that the dispersity of the filler is improved, and effective combination of the porous carbon and the nano silicon is realized.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lithium battery negative electrode materials, and particularly relates to a preparation method of a uniformly coated silicon-carbon negative electrode material. BACKGROUND

[0002] Lithium ion batteries are concerned due to the advantages of low self-discharge rate, fast charging and discharging, long cycle life and the like. According to the data in the China Lithium Ion Battery Industry Development White Paper (2025), the global total shipment of lithium ion batteries was 1545.1 GWh in 2024, with a year-on-year increase of 28.5%. In terms of the power battery market, the large-scale production of 4680 large cylindrical batteries and long-range fast-charging vehicles will promote the high specific capacity negative electrode material to enter the explosive growth channel. At present, China is the largest producer and consumer of lithium battery negative electrode materials in the world. Graphite is still the main negative electrode, but the energy density has approached its development limit. The theoretical specific capacity of silicon negative electrode is as high as 4200 mAh / g, which is more than 10 times that of traditional graphite materials. Therefore, silicon is considered to be the most competitive next-generation negative electrode material. Although silicon-based negative electrode materials have obvious advantages, the material has a large volume expansion (up to 300%) and poor conductivity, which easily leads to material pulverization, destruction of the integrity of the electrode sheet, instability of the SEI film and the like in the charging and discharging process, thereby affecting the electrochemical performance such as the initial efficiency and cycle life of the material, and hindering the commercialization process. Therefore, it is necessary to develop a preparation method capable of effectively improving the uniformity of the coating of the silicon-based negative electrode material. SUMMARY

[0003] In order to solve the above-mentioned deficiencies existing in the prior art, the purpose of the present application is to provide a preparation method of a uniformly coated silicon-carbon negative electrode material, so as to improve the uniformity of the coating of the silicon-carbon negative electrode material.

[0004] The technical solution of the present application for solving the above-mentioned technical problems is as follows: A preparation method of a uniformly coated silicon-carbon negative electrode material is provided, which comprises the following steps: (1) dispersing a carbon source, a template agent, tannic acid, carbon nanotubes and a pore catalyst in a solvent, and then drying the obtained product; (2) sintering the product obtained in step (1) in a nitrogen atmosphere, and obtaining a carbon skeleton structure containing a template agent after cooling; (3) soaking the product obtained in step (2) in hydrofluoric acid, and drying after water washing, to obtain a porous carbon material; (4) dissolving micron silicon and a surfactant in an ethanol solvent, and then performing ball milling dispersion to obtain monodisperse nanosilicon; (5) adding the porous carbon material of step (3) and a coupling agent to the product obtained in step (4), and continuing to perform ball milling, and then drying the obtained product after mixing; (6) After adding pitch to the product obtained in step (5), and then sintering in a nitrogen atmosphere, a uniformly coated silicon-carbon negative electrode material is prepared.

[0005] Further, the carbon source is at least one of wood, coconut shell and bagasse; the pore catalyst is at least one of ethylenediamine, N-methylethylenediamine and diethylenetriamine; the template agent is a mixture of silica nanoparticles and small-size microspheres; wherein the diameter of the silica nanoparticles is < 50 nm; the diameter of the small-size microspheres is ≤ 1 μm; and the solvent is a mixed solvent of ethanol and water.

[0006] Further, the mass ratio of the carbon source, the template agent, tannic acid, carbon nanotubes and the pore catalyst is 1:2:0.3-0.9:0.02-0.06:0.0003-0.001.

[0007] Further, the sintering temperature in step (2) is 600-1000 ℃, and the sintering time is 1-5 h.

[0008] Further, the mass ratio of the micron silicon and the surfactant is 1:0.1-0.2; and the surfactant is at least one of polyvinylpyrrolidone, polyethylene glycol and cetyltrimethylammonium bromide.

[0009] Further, the D50 of the monodisperse nanosilicon is ≤ 50 nm.

[0010] Further, the mass ratio of the porous carbon material and the coupling agent is 1:0.005-0.02; and the coupling agent is γ-glycidoxypropyltrimethoxysilane or stearic acid.

[0011] Further, the sintering temperature in step (6) is 1000-1200 ℃; and the sintering time is 10-12 h.

[0012] The present application has the following beneficial effects: (1) The present application prepares a macroporous porous carbon, and combines a degassing mode, so that small-particle-size sand-milled nanosilicon particles can enter the pore diameter, the uniformity of material coating is improved, and the cycle performance of the material is improved. (2) The present application selects an amine catalytic structure during preparation, combines tannic acid to construct a polymerized pore, facilitates the infiltration of nanosilicon slurry in the later stage, is conducive to the entry of small-particle-size nanosilicon into the pore, combines the hydrogen bonds of the solvent and the raw material to enhance the interface interaction, and realizes the regulation of a multi-level pore structure. (3) The present application introduces a coupling agent during preparation, realizes the reaction of carboxyl groups (-COOH) and hydroxyl groups on the surface of nanosilicon, and simultaneously enhances the compatibility with the porous carbon by long-chain alkyl groups; the epoxy groups (-CH2OCH-) can react with the hydroxyl groups on the surface of the porous carbon or the silicon hydroxyl groups on the surface of nanosilicon, are suitable for improving the dispersity of fillers, and realize the effective combination of the porous carbon and nanosilicon. BRIEF DESCRIPTION OF DRAWINGS

[0013] Fig. 1 SEM image of the silicon-carbon negative electrode material prepared for Example 1; Fig. 2 SEM image of the silicon-carbon negative electrode material prepared for Comparative Example 1. DETAILED DESCRIPTION

[0014] The following examples are presented to illustrate the application and are not intended to limit the scope of the application. In the examples, unless otherwise noted, conventional conditions or manufacturer's recommended conditions were used. Unless otherwise noted, the reagents or instruments used were conventional products available commercially.

[0015] Example 1: A method for preparing a uniformly coated silicon-carbon negative electrode material, comprising the following steps: (1) 100 g of coconut shell, 50 g of a template agent (containing 40 g & 30 nm nano-SiO2 and 10 g & 1 μm small size SiO2 microspheres), 15 g of tannic acid, 1 g of carbon nanotubes, and 0.015 g of ethylenediamine were mechanically stirred in a mixed solvent of ethanol and water, and the dispersion time was 2 h. After being mixed uniformly, the slurry was dried at 80°C; (2) The product obtained in step (1) was sintered in a nitrogen atmosphere at 800°C, and the sintering holding time was 3 h. After cooling to room temperature, it was taken out and used, to obtain a carbon skeleton structure containing a template agent; (3) The above material was soaked in 10 wt% HF for 24 h to remove the SiO2 template agent. After repeated water washing to remove surface impurities, drying was performed, to realize the preparation of a mesopore-macropore multi-level structure porous carbon material; (4) 20 g of micron silicon and 2 g of polyvinylpyrrolidone were dissolved in an ethanol solvent, and ball milling dispersion was performed, to realize nano-silicon particles D50≤50 nm, and monodisperse nano-silicon was prepared; (5) 20 g of the mesopore-macropore multi-level structure porous carbon material obtained in step (3) and 0.1 g of γ-glycidyloxypropyltrimethoxysilane were mixed into the product obtained in step (4), and degassing was simultaneously performed during the ball milling. After being mixed uniformly, the obtained product was subjected to spray drying; (6) Pitch (the mass of pitch was 25% of the mass of the product obtained in step (5)) was added to the product obtained in step (5), and after being mixed uniformly, sintering was performed in a nitrogen atmosphere at 1000°C, and the sintering time was 10 h. Finally, a silicon-carbon negative electrode material was obtained.

[0016] Example 2: A method for preparing a uniformly coated silicon-carbon negative electrode material, comprising the following steps: (1) 100 g coconut shell, 50 g template (containing 40 g 30 nm nano-SiO2 and 10 g 1 μm small-sized SiO2 microspheres), 45 g tannic acid, 3 g carbon nanotubes and 0.05 g N-methylethylenediamine were mechanically stirred in a mixed solvent of ethanol and water for 2 h. After uniform mixing, the slurry was dried at 100 °C. (2) sintering the product obtained in step (1) at 850° C. in a nitrogen atmosphere for 3 h, cooling it to room temperature, and then taking it out for standby use to obtain a carbon skeleton structure containing a template; (3) The above materials were immersed in 10 wt% HF for 24 h to remove the SiO2 template, and then washed with water repeatedly to remove surface impurities and dried to prepare a mesoporous-macroporous hierarchical porous carbon material. (4) Dissolve 20 g of micron silicon and 4 g of polyethylene glycol in ethanol solvent and perform ball milling dispersion to achieve D50 ≤ 50 nm of nano silicon particles to obtain monodisperse nano silicon; (5) Weigh 20 g of the mesoporous-macroporous hierarchical structure porous carbon material obtained in step (3) and 0.1 g of γ-glycidyloxypropyltrimethoxysilane and mix them into the product obtained in step (4). Degassing is performed during ball milling. After mixing evenly, the obtained product is spray-dried. (6) Add asphalt to the product obtained in step (5) (the mass of the asphalt is 25% of the mass of the product obtained in step (5)), mix well, and sinter in a nitrogen atmosphere at 1000°C for 10 hours to finally obtain a silicon-carbon negative electrode material.

[0017] Example 3: A method for preparing a uniformly coated silicon-carbon negative electrode material comprises the following steps: (1) 100 g of bamboo, 50 g of template (containing 40 g of 30 nm nano-SiO2 and 10 g of 1 μm small-sized SiO2 microspheres), 22 g of tannic acid, 2 g of carbon nanotubes, and 0.03 g of diethylenetriamine were mechanically stirred in a mixed solvent of ethanol and water for 2 h. After uniform mixing, the slurry was dried at 100 °C. (2) sintering the product obtained in step (1) at 900° C. in a nitrogen atmosphere for 3 h. After cooling to room temperature, the product is taken out for standby use to obtain a carbon skeleton structure containing a template; (3) The above materials were immersed in 10 wt% HF for 24 h to remove the SiO2 template, and then washed with water repeatedly to remove surface impurities and dried to prepare a mesoporous-macroporous hierarchical porous carbon material. (4) Dissolving 20 g of micron silicon and 3 g of hexadecyltrimethylammonium bromide in ethanol solvent and performing ball milling dispersion to achieve nano-silicon particles D50 ≤ 50 nm, thereby obtaining monodispersed nano-silicon; (5) 20 g of the mesoporous-macroporous multi-level structure porous carbon material obtained in step (3) and 0.4 g of stearic acid are mixed into the product obtained in step (4), and degassing is carried out during the ball milling process; after being uniformly mixed, the obtained product is subjected to spray drying; (6) Bitumen (the mass of the bitumen is 25% of the mass of the product obtained in step (5)) is added to the product obtained in step (5), and after being uniformly mixed, sintering is carried out in a nitrogen atmosphere at 1000°C for 10 h, and finally a silicon-carbon negative electrode material is obtained.

[0018] Example 4: A preparation method of a uniformly coated silicon-carbon negative electrode material, comprising the following steps: (1) 100 g of bamboo, 50 g of a template agent (containing 40 g of & 30 nm nano-SiO2 and 10 g of & 1 μm small-size SiO2 microspheres), 30 g of tannic acid, 1.5 g of carbon nanotubes, and 0.04 g of diethylenetriamine are subjected to mechanical stirring in an ethanol and water mixed solvent, and the dispersion time is 2 h; after being uniformly mixed, the slurry is subjected to drying at 100°C; (2) The product obtained in step (1) is subjected to sintering in a nitrogen atmosphere at 950°C for 3 h; after being cooled to room temperature, it is taken out for standby, and a carbon skeleton structure containing a template agent is obtained; (3) The above material is soaked in 10 wt% HF for 24 h to remove the SiO2 template agent; after being repeatedly washed with water, surface impurities are removed, and drying is carried out, so as to realize the preparation of a mesoporous-macroporous multi-level structure porous carbon material; (4) 20 g of micron silicon and 3 g of polyethylene glycol are dissolved in an ethanol solvent, and ball milling dispersion is carried out, so as to realize nano-silicon particles D50≤50 nm, and monodisperse nano-silicon is prepared; (5) 20 g of the mesoporous-macroporous multi-level structure porous carbon material obtained in step (3) and 0.1 g of γ-glycidoxypropyltrimethoxysilane are mixed into the product obtained in step (4); degassing is carried out during the ball milling process; after being uniformly mixed, the obtained product is subjected to spray drying; (6) Bitumen (the mass of the bitumen is 25% of the mass of the product obtained in step (5)) is added to the product obtained in step (5), and after being uniformly mixed, sintering is carried out in a nitrogen atmosphere at 1000°C for 10 h, and finally a silicon-carbon negative electrode material is obtained.

[0019] Example 5: A preparation method of a uniformly coated silicon-carbon negative electrode material, comprising the following steps: (1) 100 g pine wood, 50 g template agent (containing 40 g & 30 nm nano-SiO2 and 10 g & 1 μm small size SiO2 microspheres), 38 g tannic acid, 1.5 g carbon nanotubes and 0.04 g diethylene triamine are mechanically stirred in a mixed solvent of ethanol and water, the dispersion time is 2 h, after mixing uniformly, the slurry is dried at 100°C; (2) The product obtained in step (1) is sintered at 1000°C in a nitrogen atmosphere, the sintering holding time is 3 h, after cooling to room temperature, it is taken out for standby, and a carbon skeleton structure containing a template agent is obtained; (3) The above material is soaked in 10 wt% HF for 24 h to remove the SiO2 template agent, repeatedly washed with water to remove surface impurities, dried, and a mesoporous-macroporous multi-level structure porous carbon material is prepared; (4) 20 g of micron silicon and 4 g of polyethylene glycol are dissolved in an ethanol solvent, ball-milled and dispersed to achieve nano-silicon particles with D50≤50 nm, and monodisperse nano-silicon is prepared; (5) 20 g of the mesoporous-macroporous multi-level structure porous carbon material obtained in step (3) and 0.1 g of stearic acid are mixed into the product obtained in step (4), degassing is carried out during ball milling, and after mixing uniformly, the obtained product is spray dried; (6) Bitumen (the mass of bitumen is 25% of the mass of the product obtained in step (5)) is added to the product obtained in step (5), mixed uniformly, and sintered at 1000°C in a nitrogen atmosphere for 11 h, and finally a silicon-carbon negative electrode material is obtained.

[0020] Example 6: A preparation method of a uniformly coated silicon-carbon negative electrode material, comprising the following steps: (1) 100 g pine wood, 50 g template agent (containing 40 g & 30 nm nano-SiO2 and 10 g & 1 μm small size SiO2 microspheres), 45 g tannic acid, 1.5 g carbon nanotubes and 0.04 g diethylene triamine are mechanically stirred in a mixed solvent of ethanol and water, the dispersion time is 2 h, after mixing uniformly, the slurry is dried at 100°C; (2) The product obtained in step (1) is sintered at 1000°C in a nitrogen atmosphere, the sintering holding time is 3 h, after cooling to room temperature, it is taken out for standby, and a carbon skeleton structure containing a template agent is obtained; (3) The above material is soaked in 10 wt% HF for 24 h to remove the SiO2 template agent, repeatedly washed with water to remove surface impurities, dried, and a mesoporous-macroporous multi-level structure porous carbon material is prepared; (4) 20 g of micron silicon and 4 g of polyethylene glycol are dissolved in an ethanol solvent, ball-milled and dispersed to achieve nano-silicon particles with D50≤50 nm, and monodisperse nano-silicon is prepared; (5) 20 g of the mesoporous-macroporous multi-level structure porous carbon material obtained in step (3) and 0.1 g of γ-glycidoxypropyltrimethoxysilane are mixed into the product obtained in step (4), and degassing is carried out during the ball milling, and after mixing uniformly, the obtained product is subjected to spray drying; (6) Bitumen (the mass of the bitumen is 25% of the mass of the product obtained in step (5)) is added to the product obtained in step (5), and after mixing uniformly, sintering is carried out at 1000°C in a nitrogen atmosphere, and the sintering time is 12 h, and finally a silicon-carbon negative electrode material is obtained.

[0021] Comparative Example 1: A preparation method of a silicon-carbon negative electrode material comprises the following steps: (1) 100 g of coconut shell and 50 g of a template agent (containing 40 g of & 30 nm nano-SiO2 and 10 g of & 1 μm small-size SiO2 microspheres) are mechanically stirred in an ethanol and water mixed solvent, and the dispersion time is 2 h, and after mixing uniformly, the slurry is dried at 80°C; (2) The product obtained in step (1) is sintered at 800°C in a nitrogen atmosphere, and the sintering holding time is 3 h, and after cooling to room temperature, it is taken out for standby, and a carbon skeleton structure containing a template agent is obtained; (3) The above material is soaked in 10 wt% HF for 24 h to remove the SiO2 template agent, and after repeated water washing, surface impurities are removed, and drying is carried out to realize the preparation of a mesoporous-macroporous multi-level structure porous carbon material; (4) 20 g of micron silicon and 2 g of polyvinylpyrrolidone are dissolved in an ethanol solvent, and ball milling dispersion is carried out to realize nano-silicon particles with D50≤50 nm; (5) 20 g of the mesoporous-macroporous multi-level structure porous carbon material obtained in step (3) and 0.1 g of γ-glycidoxypropyltrimethoxysilane are mixed into the product obtained in step (4), and after ball milling, the obtained product is subjected to spray drying; (6) Bitumen (the mass of the bitumen is 25% of the mass of the product obtained in step (5)) is added to the product obtained in step (5), and after mixing uniformly, sintering is carried out at 1000°C in a nitrogen atmosphere, and the sintering time is 10 h, and finally a silicon-carbon negative electrode material is obtained.

[0022] Comparative Example 2: A preparation method of a silicon-carbon negative electrode material comprises the following steps: (1) 100 g of coconut shell and 50 g of a template agent (containing 40 g of & 30 nm nano-SiO2 and 10 g of & 1 μm small-size SiO2 microspheres) are mechanically stirred in an ethanol and water mixed solvent, and the dispersion time is 2 h, and after mixing uniformly, the slurry is dried at 80°C; (2) sintering the product obtained in step (1) at 800 DEG C under a nitrogen atmosphere, the sintering holding time being 3h, after cooling to room temperature, taking out for standby, obtaining a carbon skeleton structure containing a template agent; (3) soaking the above material in 10wt% HF for 24h, removing the SiO2 template agent, repeatedly washing with water to remove surface impurities, drying, realizing the preparation of a mesopore-macropore multi-level structure porous carbon material; (4) dissolving 20g micron silicon and 2g polyvinylpyrrolidone in an ethanol solvent, ball-milling and dispersing, realizing nano silicon particles D50≤50nm; (5) mixing 20g of the mesopore-macropore multi-level structure porous carbon material obtained in step (3) into the product obtained in step (4), after ball-milling, spray drying the obtained product; (6) adding pitch (the mass of pitch is 25% of the mass of the product obtained in step (5)) to the product obtained in step (5), mixing uniformly, sintering at 1000 DEG C under a nitrogen atmosphere, the sintering time being 10h, finally obtaining a silicon-carbon negative electrode material.

[0023] The materials prepared in Examples 1-6 and Comparative Examples 1-2 are subjected to electrochemical performance tests, one is to assemble a button to test the specific capacity of the material; two is to mix the material with graphite to 500mAh / g, and to test the full battery performance with ternary positive electrode material. The performance is shown in Table 1.

[0024] Table 1 Electrochemical performance test of the materials prepared in Examples 1-6 and Comparative Examples As can be seen from Table 1, through the preparation of macroporous carbon, combined with degassing treatment, the infiltration effect of nano silicon can be effectively improved, small particle nano silicon successfully enters the pore size, realizing the uniformity of silicon coating, improving the material performance, and reducing the volume expansion of the material. Figs. 1-2 As can be seen from Table 1, through the preparation of macroporous carbon, combined with degassing treatment, the infiltration effect of nano silicon can be effectively improved, small particle nano silicon successfully enters the pore size, realizing the uniformity of silicon coating, improving the material performance, and reducing the volume expansion of the material.

[0025] The above only describes the preferred embodiments of the present application, and is not intended to limit the present application, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a uniformly coated silicon-carbon negative electrode material, characterized in that: The following steps are involved: (1) dispersing a carbon source, a template, tannic acid, carbon nanotubes, and a pore catalyst in a solvent, and then drying the resulting product; (2) sintering the product obtained in step (1) in a nitrogen atmosphere, and obtaining a carbon skeleton structure containing a template after cooling; (3) soaking the product obtained in step (2) in hydrofluoric acid, washing with water and then drying to obtain a porous carbon material; (4) dissolving micron silicon and surfactant in ethanol solvent and then performing ball milling dispersion to obtain monodisperse nano silicon; (5) adding the porous carbon material and coupling agent from step (3) to the product obtained from step (4) and continuing ball milling, mixing well, and drying the obtained product; (6) Asphalt is added to the product obtained in step (5), and then sintered in a nitrogen atmosphere to obtain a uniformly coated silicon-carbon negative electrode material.

2. The preparation method according to claim 1, characterized in that The carbon source is at least one of wood, coconut shell and bagasse; the pore catalyst is at least one of ethylenediamine, N-methylethylenediamine and diethylenetriamine; the template is a mixture of silica nanoparticles and small-sized microspheres; the diameter of the silica nanoparticles is less than 50nm; the diameter of the small-sized microspheres is ≤1μm; and the solvent is a mixed solvent of ethanol and water.

3. The preparation method according to claim 1, characterized in that The mass ratio of the carbon source, the template, the tannic acid, the carbon nanotubes and the pore catalyst is 1:2:0.3-0.9:0.02-0.06:0.0003-0.

001.

4. The preparation method according to claim 1, characterized in that The sintering temperature in step (2) is 600-1000°C, and the sintering time is 1-5h.

5. The preparation method according to claim 1, characterized in that The mass ratio of the micron silicon to the surfactant is 1:0.1-0.2; the surfactant is at least one of polyvinyl pyrrolidone, polyethylene glycol and cetyltrimethylammonium bromide.

6. The preparation method according to claim 1, characterized in that The D50 of the monodisperse nano-silicon is ≤50nm.

7. The preparation method according to claim 1, characterized in that The mass ratio of the porous carbon material to the coupling agent is 1:0.005-0.02; the coupling agent is γ-glycidyloxypropyltrimethoxysilane or stearic acid.

8. The preparation method according to claim 1, characterized in that The sintering temperature in step (6) is 1000-1200°C; the sintering time is 10-12h.

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