Preparation method of double-layer carbon modified silicon negative electrode material

Abstract

This invention discloses a method for preparing a bilayer carbon-modified silicon anode material. It belongs to the field of energy conversion and storage technology. It includes the following steps: (1) ultrasonically treating silicon-based particles in an organic solvent, then adding a silane coupling agent to the above dispersion, heating and stirring, centrifuging and drying to obtain a silicon-based material A modified with a silane coupling agent on the surface; (2) dispersing A in an organic solvent, then adding an ionic liquid dropwise to the above dispersion, heating and stirring to obtain an ionic liquid-grafted material B; (3) dispersing material B and rGO material in ethanol, ultrasonically mixing, heating and stirring, and finally washing and drying the product to obtain material C; (4) mixing material C with graphite, degassing and stirring, then performing temperature-controlled sintering, and cooling to room temperature to obtain a bilayer carbon-modified silicon anode material with a first layer of strong linkage between rGO and silicon substrate, and a second layer of graphite carbon homogeneously coating rGO. The method of this invention uses ionic liquids, silane coupling agents, or a combination of the two as interfacial bonding materials to improve the interfacial bonding force of the coating material, thereby reducing the volume expansion of the silicon anode material during charge-discharge cycles, forming a continuously connected buffer layer to overcome the breakage of silicon particles, and improving the interfacial conductivity. It has a significant effect on improving the structural stability of the anode active material in lithium-ion batteries or lithium slurry batteries, and improves the long cycle life of the material.

Description

Technical Field

[0001] This invention relates to a method for preparing a double-layer carbon-modified silicon anode material. Specifically, this invention involves using highly conductive reduced graphene oxide (rGO) as the first coating layer, carbon material as the second coating layer, silicon-based particles as the matrix, and ionic liquid, silane coupling agent, or a combination of both as the interface bonding material. This method improves the interfacial bonding force of the coating material, thereby reducing the volume expansion of the silicon anode material during charge-discharge cycles. It also improves the conductivity of the inner and outer coating interfaces, thus enabling the practical application of high-capacity silicon materials.

[0002] This invention belongs to the field of energy conversion and storage technology, and particularly relates to the modification of the surface of silicon anode materials in lithium-ion batteries for electrochemical energy storage technology. Background Technology

[0003] Lithium-ion batteries or lithium slurry flow batteries are typical electrochemical energy storage technologies. The anode active material is a core and crucial component. Currently, the widely used graphite anode material has a relatively low theoretical specific capacity of only 372 mAh / g. Silicon, on the other hand, boasts an ultra-high theoretical specific capacity (4200 mAh / g) and enormous development potential, but suffers from poor conductivity and severe volume expansion (>300%), leading to particle cracking, collapse, and pulverization. This, in turn, results in poor contact with the conductive agent and detachment from the current collector, ultimately hindering its electrochemical performance and limiting its application. The theoretical specific capacity and structural stability of the anode material play a critical role in the overall battery capacity and lifespan.

[0004] rGO is a nano-carbon material that combines electrical conductivity and ion transport properties after reduction and certain structural repair of graphene oxide. Furthermore, it possesses flexibility and excellent mechanical properties, making it a good coating material for silicon-based anode materials. Currently, coating strategies are an important method to address key issues in silicon anode materials. For example, patent CN 114824201 A provides a core-shell structured carbon-silicon anode material for lithium-ion batteries and its preparation method, using physical methods such as ball milling to achieve carbon coating on silicon, but subsequent high-temperature sintering (400-1000°C) is required. o (C) This method suffers from poor coating uniformity and high energy consumption. Patent CN114284494 A provides a nano-silicon composite material and its preparation method. The core is nano-silicon crystals, the first coating layer is a porous material including metasilicate and deoxidized silicon suboxide, and the second coating layer includes deoxidized silicon dioxide. However, since the coating material is also silicon-based, its resistance to volume expansion still needs improvement. Patent CN 114914430 A also provides a silicon anode material and its preparation method. The core is silicon, the first coating layer is TiO2 or partially replaced by Ti5Si3, and the second coating layer is carbon. Its first coating layer and silicon substrate are in rigid contact at a heterogeneous interface, therefore the substrate and interface are still prone to cracking.

[0005] While the aforementioned methods have achieved some modification effects, their coating strength is generally weak, and the carbon layer is prone to detachment under strong external fields. Therefore, this invention uses ionic liquids, silane coupling agents, or a combination of both as interfacial bonding materials to strongly bond rGO to silicon-based particles, while simultaneously providing a buffer space for the expansion of the silicon-based particles. A second carbon coating layer strengthens the external force of the graphene coating layer, and this homogeneous interface is another important guarantee for the performance of this double-layered silicon-carbon composite anode material. This invention will facilitate the practical application of silicon anode materials in complex multi-physics environment systems such as lithium-ion batteries or lithium slurry flow batteries. Summary of the Invention

[0006] The purpose of this invention is to provide a novel method for preparing a double-layer carbon-modified silicon anode material. Specifically, this invention relates to using highly conductive rGO as the first coating layer, carbon material as the second coating layer, silicon-based particles as the matrix material, and ionic liquid, silane coupling agent, or a combination of both as the interfacial bonding material. This method improves the interfacial bonding force of the coating material, thereby mitigating the volume expansion of the silicon anode material during charge-discharge cycles, forming a continuously connected buffer layer to overcome the breakage of silicon particles, and simultaneously improving interfacial conductivity, thus enabling the practical application of high-specific-capacity silicon-based materials.

[0007] The technical solution adopted in this invention is as follows:

[0008] A coated composite silicon-carbon material with high interfacial bonding strength is prepared by using highly conductive rGO as the first coating layer, carbon material as the second coating layer, silicon-based particles as the matrix material, and ionic liquid, silane coupling agent, or a combination of both as the interfacial bonding material to improve the interfacial bonding strength of the coating material. The preparation method includes the following steps:

[0009] A method for preparing a double-layer carbon-modified silicon anode material, characterized by comprising:

[0010] (1) The silicon-based particles were ultrasonically treated in an organic solvent, and then a silane coupling agent was added to the above dispersion and heated and stirred. The mixture was then centrifuged and dried to obtain silicon-based material A modified with a silane coupling agent on the surface; (2) A was dispersed in an organic solvent, and then an ionic liquid was added dropwise to the above dispersion. The mixture was heated and stirred to obtain material B grafted with an ionic liquid; (3) Material B and reduced graphene oxide rGO were dispersed in ethanol, ultrasonically mixed, heated and stirred, and finally the product was washed and dried to obtain material C; (4) Material C was... The mixture is stirred and degassed with graphite, then sintered at a controlled temperature and cooled to room temperature to obtain a first layer consisting of a strong bond between rGO and the silicon matrix, with an ionic liquid, a silane coupling agent, or a combination of both as the interface connecting material to form a continuously connected buffer layer, maintaining structural stability and stress uniformity. The second layer is a bilayer carbon-modified silicon anode material with graphite carbon homogeneously coated with rGO. In step (1), the silicon-based material is one or more of pure silicon, silicon oxide, and silicon-carbon composite, with a spherical or near-spherical shape and a particle size of 0.01~10 μm. The silane coupling agent added in step (1) has the following structure: R is a non-hydrolyzable group including one or more of methyl, ethyl, propyl, mercapto, mercaptoethyl, mercaptopropyl, vinyl, propenyl, amino, aminoethyl, aminopropyl, epoxy, cyano, haloalkyl, acryloyloxy, and glycidyl etheroxypropyl; X is a hydrolyzable group including one or more of halogen, acyloxy, alkoxy, aryloxy, and acyl; the amount added is 0.1~10wt%; the organic solvent in steps (1,2) is one or more of toluene, acetonitrile, acetone, chloroform, carbon tetrachloride, methanol, ethanol, and N-methylpyrrolidone; the ultrasonic time in steps (1,3) is 3~60min; the stirring time in steps (1,2,3) is 1~20h, and the stirring temperature is 40~120℃. o C; In step (2), the ionic liquid is selected from one or more of the following general structural formulas of ionic liquids. In the formula, Z represents imidazole, pyridine, or pyrrolidine; X represents 1-ethyl-3-methyl, 1-propyl-3-methyl, 1-butyl-3-methyl, 1-pentyl-3-methyl, 1-hexyl-3-methyl, 1-heptyl-3-methyl, 1-octyl-3-methyl, 1-allyl-3-methyl, 1-vinyl-3-ethyl, 1-benzyl-3-methyl, 1,3-xylyl, 1-hexadecyl-3-methyl, 1-aminoethyl-2,3-dimethyl, or 1-(3-aminopropyl)-3-methyl; Y represents sulfate, hydrogen sulfate, phosphate, dihydrogen phosphate, halide, tetrafluoroborate, hexafluorophosphate, or bis(trifluoromethanesulfonyl)imide; the amount added is 0.1~20wt%; in step (3), the rGO sheet diameter is 0.05~20μm, the thickness is 0.35~30nm, and the content added is 0.1~ 30 wt%, the oxygen-containing functional groups carried on the surface include one or more of hydroxyl, carboxyl, carbonyl, epoxy, amino / amine, nitro, sulfonic acid, ester and nitrile groups; in step (3), rGO is a doped material, and the doping element includes one or more of B, N, P, S, Cl, Br and F; in step (4), the graphite is artificial graphite, amorphous carbon, or doped carbon; the doping element includes one or more of B, N, P, S, Cl, Br and F; the content added is 1~60 wt%; the degassing stirring time in step (4) is 0.1~5h, and the rotation speed is 200~10000 rpm; the low-temperature sintering atmosphere in step (4) is one or more of nitrogen, argon, helium, oxygen and hydrogen; the temperature is 100~600℃. o C; sintering time is 0.1~6h.

[0011] This application provides an internal interface-connected composite silicon-carbon anode material with double-layer carbon-coated modified silicon-based particles obtained by the above preparation method.

[0012] A lithium-ion battery electrode is prepared by using the above-mentioned interface-connected composite silicon-carbon composite anode material as the anode active material.

[0013] The method of the present invention has the following advantages compared with the prior art:

[0014] (1) The present invention uses ionic liquid, silane coupling agent or a combination of the two as interface connecting materials. The covalent bond force greatly improves the uniformity and stability of the heterostructure bonding. At the same time, the organic linker provides a buffer space for the volume expansion of silicon particles, continuously connecting the first coating layer rGO to the silicon matrix, maintaining structural stability and stress uniformity. In addition, the silane coupling agent contains silicon components, which can provide more space for lithium-ion storage.

[0015] (2) The present invention uses rGO as the first coating layer material, which can synergistically exert its conductivity, flexibility and ion transport channel characteristics.

[0016] (3) The second graphite coating layer further enhances the stability of the carbon coating layer structure. The constructed double carbon coating can effectively suppress the volume expansion of composite silicon particles.

[0017] (4) This method has a significant effect on improving the stability of lithium-ion battery slurry and the structural stability of negative electrode active material in slurry flow system. Its mechanical and electrical coupling has a significant effect on improving electrochemical capacity and long cycle life. Attached Figure Description

[0018] Figure 1 XRD pattern of graphite used in this invention

[0019] Figure 2 This is a schematic diagram of the double-layer carbon-coated silicon-based anode composite material structure in this invention. Detailed Implementation

[0020] The invention will be further described below with reference to embodiments, but these should not be construed as limiting the scope of protection of the invention.

[0021] Example 1:

[0022] (1) Take 5g of silicon dioxide and sonicate it in 10mL of methanol solution for 30 minutes. Then add 0.1g of silane coupling agent 3-chloroethyl-trimethylsiloxane to the above dispersion and heat it to 80°C. o C. Stir for 2 hours, centrifuge and dry to obtain modified material A with silane coupling agent on the surface of silicon suboxide; (2) Disperse material A in 10 mL toluene solvent, then add 0.2 g of 1-ethyl-3-methylimidazolium bromide (EmimBr) to the above dispersion, and heat to 80 °C. o C. Stir for 2 hours, centrifuge and dry to obtain silane coupling agent silicon-based material B for further ionic liquid surface modification; (3) Disperse material B in 10 mL of ethanol by ultrasonication for 10 minutes, add 0.25 g of nitrogen-doped rGO to the system, and heat to 90°C. o C, stir for 2 hours, and finally cool the system to room temperature, wash and dry to obtain material C; (4) Disperse the obtained material C with 1g of graphite in methanol, degas and stir for 20 minutes, the degassing machine speed is 7000r / min, finally centrifuge and dry and put it in a tube furnace in a nitrogen environment for 200 minutes. o The product was obtained by calcination at C for 1 hour. A coin cell was fabricated using lithium metal as the counter electrode and assembled at room temperature. The resulting coin cell had an initial specific capacity of 850 mAh / g and a capacity retention of 85.3% after 50 charge-discharge cycles.

[0023] Example 2:

[0024] Repeat Example 1, except that the silicon suboxide in step 1 is replaced with a porous silicon material. The obtained interface-connected rGO and graphite bilayer coated silicon material are used as active materials, and lithium metal is used as the counter electrode to assemble a coin cell. The initial discharge capacity was tested to be 2490 mAh / g, and the capacity retention rate after 50 charge-discharge cycles was 88.5%.

[0025] Example 3:

[0026] Example 2 was repeated, except that 3-chloroethyl-trimethylsiloxane in step 1 was replaced with 3-chloropropyl-trimethylsiloxane. The resulting interface-linked rGO and graphite bilayer coated silicon material were used as active materials, and lithium metal was used as the counter electrode to assemble a coin cell. The initial discharge capacity was tested to be 2595 mAh / g, and the capacity retention rate after 50 charge-discharge cycles was 92.2%.

[0027] Example 4:

[0028] Example 3 was repeated, except that the ionic liquid 1-ethyl-3-methylimidazolium bromide (EmimBr) in step 2 was replaced with 1-ethyl-3-methylimidazolium chloride (EmimCl). The resulting interface-linked rGO and graphite bilayer coated silicon material were used as active materials, and lithium metal was used as the counter electrode to assemble a coin cell. The initial discharge capacity was tested to be 2681 mAh / g, and the capacity retention rate after 50 charge-discharge cycles was 93.8%.

[0029] Example 5:

[0030] Example 4 was repeated, except that the amount of rGO added in step 3 was changed to 0.75g. The obtained interface-connected rGO and graphite bilayer coated silicon material were used as active materials, and lithium metal was used as the counter electrode to assemble a coin cell. The initial discharge capacity was tested to be 2752 mAh / g, and the capacity retention rate after 50 charge-discharge cycles was 93.9%.

[0031] Example 6:

[0032] Example 5 was repeated, except that the amount of graphite added in step 4 was changed to 1.5g. The resulting interface-connected rGO and graphite double-layer coated silicon material were used as active materials, and lithium metal was used as the counter electrode to assemble a coin cell. The initial discharge capacity was tested to be 2659 mAh / g, and the capacity retention rate after 50 charge-discharge cycles was 96.2%.

[0033] Example 7:

[0034] Repeat Example 6, except that the sintering temperature of the tubular furnace in step 4 is changed to 300°C. o C, using interface-connected rGO and graphite bilayer coated silicon material as active materials and lithium metal as counter electrode to assemble coin cells, the initial discharge capacity was tested to be 2708 mAh / g, and the capacity retention rate after 50 charge-discharge cycles was 97.6%.

[0035] Example 8:

[0036] Example 7 was repeated, except that the sintering time of the tube furnace in step 4 was changed to 2 hours. The obtained interface-connected rGO and graphite double-layer coated silicon material were used as active materials, and lithium metal was used as the counter electrode to assemble a coin cell. The initial discharge capacity was tested to be 2729 mAh / g, and the capacity retention rate after 50 charge-discharge cycles was 99.0%.

Claims

1. A method for preparing a double-layer carbon-modified silicon anode material, characterized in that, include: (1) The silicon-based particles were ultrasonically treated in an organic solvent, and then a silane coupling agent was added to the above dispersion and heated and stirred. The mixture was then centrifuged and dried to obtain silicon-based material A modified with a silane coupling agent on the surface; (2) A was dispersed in an organic solvent, and then an ionic liquid was added dropwise to the above dispersion. The mixture was heated and stirred to obtain material B grafted with an ionic liquid; (3) Material B and reduced graphene oxide rGO were dispersed in ethanol, ultrasonically mixed, heated and stirred, and finally the product was washed and dried to obtain material C; (4) Material C was mixed with... Graphite is mixed, degassed, and stirred, then sintered at a controlled temperature. After cooling to room temperature, a first layer is obtained, consisting of a strong bond between rGO and the silicon matrix, with an ionic liquid, a silane coupling agent, or a combination of both as the interface connecting material, forming a continuously connected buffer layer to maintain structural stability and stress uniformity. The second layer is a bilayer carbon-modified silicon anode material with graphite carbon homopolymer coating rGO. In step (1), the silicon-based material is one or more of pure silicon, silicon oxide, and silicon-carbon composite, with a spherical or near-spherical shape and a particle size of 0.01~10 μm. The silane coupling agent added in step (1) has the following structure: R is a non-hydrolyzable group including one or more of methyl, ethyl, propyl, mercapto, mercaptoethyl, mercaptopropyl, vinyl, propenyl, amino, aminoethyl, aminopropyl, epoxy, cyano, haloalkyl, acryloyloxy, and glycidyl etheroxypropyl; X is a hydrolyzable group including one or more of halogen, acyloxy, alkoxy, aryloxy, and acyl; the amount added is 0.1~10wt%; the organic solvent in steps (1, 2) is one or more of toluene, acetonitrile, acetone, chloroform, carbon tetrachloride, methanol, ethanol, and N-methylpyrrolidone; the ultrasonic time in steps (1, 3) is 3~60min; the stirring time in steps (1, 2, 3) is 1~20h, and the stirring temperature is 40~120℃. o C; In step (2), the ionic liquid is selected from one or more of the following general structural formulas of ionic liquids. In the formula, Z represents imidazole, pyridine, or pyrrolidine; X represents 1-ethyl-3-methyl, 1-propyl-3-methyl, 1-butyl-3-methyl, 1-pentyl-3-methyl, 1-hexyl-3-methyl, 1-heptyl-3-methyl, 1-octyl-3-methyl, 1-allyl-3-methyl, 1-vinyl-3-ethyl, 1-benzyl-3-methyl, 1,3-xylyl, 1-hexadecyl-3-methyl, 1-aminoethyl-2,3-dimethyl, or 1-(3-aminopropyl)-3-methyl; Y represents sulfate, hydrogen sulfate, phosphate, dihydrogen phosphate, halide, tetrafluoroborate, hexafluorophosphate, or bis(trifluoromethanesulfonyl)imide; the amount added is 0.1~20wt%; in step (3), the rGO sheet diameter is 0.05~20μm, the thickness is 0.35~30nm, and the content added is 0.1~ 30 wt%, the oxygen-containing functional groups carried on the surface include one or more of hydroxyl, carboxyl, carbonyl, epoxy, amino / amine, nitro, sulfonic acid, ester and nitrile groups; in step (3), rGO is a doped material, and the doping element includes one or more of B, N, P, S, Cl, Br and F; in step (4), the graphite is artificial graphite, amorphous carbon, or doped carbon; the doping element includes one or more of B, N, P, S, Cl, Br and F; the content added is 1~60 wt%; the degassing stirring time in step (4) is 0.1~5h, and the rotation speed is 200~10000 rpm; the temperature-controlled sintering atmosphere in step (4) is one or more of nitrogen, argon, helium and hydrogen; the temperature is 100~600℃. o C; sintering time is 0.1~6h.

2. A bilayer carbon-modified silicon anode material obtained by the preparation method of claim 1.

3. A lithium-ion battery electrode, characterized in that, It is prepared using the double-layer carbon-modified silicon anode material as described in claim 2 as the anode active material.

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