A halogen-containing precursor silicon-carbon composite negative electrode material and its preparation method and application

Abstract

The present invention discloses a halogen-containing precursor silicon-carbon composite negative electrode material, and its preparation method and application. It relates to the technical field of silicon-carbon materials. The silicon-carbon composite material comprises the following components: a silicon material; the silicon material is nano-silicon particles containing silicon-halogen bonds on the surface; graphene, the graphene coating the silicon material; the graphene having a wrinkled structure. The silicon-carbon composite material of the present invention is a material with a coating structure, in which the graphene carbon layer is coated on the surface of the silicon material, which can improve the conductivity of the material. When the material is used in a battery, the coating of the graphene carbon layer can inhibit the volume expansion of silicon, prevent direct contact between silicon and the electrolyte, reduce the excessive growth of the SEI film, and reduce the damage to the electrode structure caused by the volume change of silicon.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon-carbon materials, and in particular to a halogen-containing precursor silicon-carbon composite negative electrode material, and a preparation method and application thereof. Background Art

[0002] As the core of energy storage devices and electric vehicles, the energy storage performance and safety of batteries are particularly important, which determines the future development of energy storage devices and electric vehicles. Therefore, the development of safe, stable and long-lasting energy storage batteries can effectively change the current energy system based on fossil fuels. Among the many batteries currently in use, lithium-ion batteries are considered to be the most promising batteries because of their high operating voltage, long cycle life and low environmental pollution. At present, the negative electrode materials of commercial lithium-ion batteries are mostly graphite, and its low theoretical capacity can no longer meet the actual needs. Among all the alternative negative electrode materials for lithium-ion batteries, silicon-based negative electrodes exhibit high theoretical capacity (4200mAh g -1 ), with its high abundance and low lithium insertion potential, is considered one of the most promising anode materials. However, the commercial application of silicon-based anodes still faces significant obstacles. First, silicon undergoes a significant volume expansion during lithium insertion and extraction, which can cause material pulverization, electrode structure collapse, and continuous growth of the SEI film, ultimately leading to rapid battery capacity degradation. Second, the low intrinsic conductivity also leads to poor rate performance of silicon anodes.

[0003] Combining silicon with carbon materials is one of the most commonly used methods to improve the performance of silicon-based negative electrodes. Carbon materials can act as a buffer layer for silicon volume changes and enhance silicon's conductivity. Graphene is a two-dimensional carbon material with a high specific surface area. The combination of silicon material and graphene can effectively reduce the damage to the electrode structure caused by silicon materials during expansion and contraction. At the same time, the high conductivity of graphene can enhance the conductivity of silicon-based materials. However, for silicon-carbon composite materials with a coating structure, the carbon layer is easily separated from the silicon surface during a long cycle, resulting in a decrease in the material's ionic and electronic conductivity, an unstable negative electrode structure, and a decrease in the battery's cycle stability.

[0004] Therefore, developing a stable composite structure is one of the difficult problems to be solved in the preparation of high-capacity silicon-carbon negative electrode materials. Summary of the Invention

[0005] The first technical problem to be solved by the present invention is:

[0006] Provided is a silicon-carbon composite material.

[0007] The second technical problem to be solved by the present invention is:

[0008] Provided is a method for preparing a silicon-carbon composite material.

[0009] The third technical problem to be solved by the present invention is:

[0010] Provided is an application of a silicon-carbon composite material, specifically, a battery.

[0011] In order to solve the first technical problem, the technical solution adopted by the present invention is:

[0012] A silicon-carbon composite material comprising the following components:

[0013] Silicon materials;

[0014] The silicon material is nano silicon particles with silicon-halogen bonds on the surface;

[0015] Graphene, wherein the graphene covers the silicon material;

[0016] The graphene has a wrinkled structure.

[0017] According to the embodiments of the present invention, one of the technical solutions has at least one of the following advantages or beneficial effects:

[0018] 1. The silicon-carbon composite material of the present invention is a material with a coated structure. A graphene carbon layer coats the surface of the silicon material, enhancing the material's electrical conductivity. When used in batteries, the graphene carbon layer coating inhibits silicon volume expansion, preventing direct contact between silicon and the electrolyte, reducing excessive growth of the SEI film, and minimizing damage to the electrode structure caused by silicon volume changes.

[0019] 2. The graphene coating has a wrinkled structure, which is conducive to releasing the stress generated by silicon during the expansion process, so that when the silicon-carbon composite material is loaded onto the battery as the negative electrode material, it is beneficial to improve the cycle stability of the battery.

[0020] 3. In the silicon-carbon composite material, the silicon material is nano-silicon particles with silicon-halogen bonds on their surfaces. These nano-silicon particles with silicon-halogen bonds on their surfaces are actually due to the fact that during the preparation of the silicon-carbon composite material, halogenated graphene easily produces active halogen atoms during high-temperature reduction. These active halogen atoms have a strong etching effect on silicon. During the reduction process, some of these active halogen atoms react with silicon to form silicon-halogen bonds, resulting in a stronger interface between the graphene carbon layer and the silicon surface, and closer contact between them. This further improves the ionic and electronic conductivity between the silicon and carbon layers, maintains the stability of the coating structure, and thus achieves better rate performance and cycling stability.

[0021] According to one embodiment of the present invention, the silicon-halogen bond comprises at least one of a silicon-fluorine bond, a silicon-chlorine bond, a silicon-bromine bond, and a silicon-iodine bond. Furthermore, the compound corresponding to the silicon-halogen bond comprises at least one of silicon fluoride, silicon chloride, silicon bromide, and silicon iodide. Furthermore, the silicon halide is preferably silicon fluoride, but silicon chloride, silicon bromide, and silicon iodide can all induce the graphene coating to produce a wrinkled structure.

[0022] According to one embodiment of the present invention, the mass ratio of the silicon material to the graphene is 1-2:0.05-1.0.

[0023] In order to solve the second technical problem, the technical solution adopted by the present invention is:

[0024] Provided is a battery comprising a positive electrode, a negative electrode and an electrolyte; wherein the negative electrode comprises the silicon-carbon composite material.

[0025] In order to solve the third technical problem, the technical solution adopted by the present invention is:

[0026] A method for preparing the silicon-carbon composite material comprises the following steps:

[0027] S1: mixing silicon material and graphene oxide, and drying to obtain a silicon-graphene oxide coating structure;

[0028] S2 placing the silicon-graphene oxide coating structure in a mixed gas containing a halogen gas to perform a substitution reaction to obtain silicon-halogenated graphene;

[0029] S3 reduces the silicon-halogenated graphene to obtain a silicon-carbon composite material.

[0030] According to the embodiments of the present invention, one of the technical solutions has at least one of the following advantages or beneficial effects:

[0031] 1. During the halogenation process in step S2, the halogen gas reacts with the silicon particles to produce silicon halide gas. The generated silicon halide gas overflows from the silicon surface and impacts the outer graphene oxide layer, causing the graphene coating layer to produce a wrinkled structure, which can effectively release the stress generated by the silicon during the volume expansion process. In addition, the wrinkled structure will still be retained after the reduction in step S3.

[0032] 2. In step S3, halogenated graphene easily produces active halogen atoms during high-temperature reduction. The active halogen atoms have a strong etching effect on silicon. During the reduction process, some active halogen atoms react with silicon to produce silicon-halogen bonds, so that the graphene carbon layer and the silicon surface form a stronger interface effect and the mutual contact is closer, further improving the ionic and electronic conductivity between the silicon and carbon layers, and maintaining the stability of the coating structure. When the silicon-carbon composite material is used to prepare a battery, the battery can obtain better cycle stability.

[0033] 3. The preparation process of the present invention is simple and suitable for large-scale preparation. It can effectively alleviate the volume effect caused by silicon expansion, maintain the stability of the electrode structure, and effectively improve the conductivity and cycle stability of silicon-based negative electrode materials.

[0034] According to one embodiment of the present invention, the halogenated graphene is preferably fluorinated graphene. The active fluorine atoms generated by the fluorinated graphene during high-temperature reduction have a better etching effect on silicon.

[0035] According to one embodiment of the present invention, in step S1, before mixing the silicon material and graphene oxide, the following steps are further included: dispersing the graphene oxide in an organic solvent to obtain a graphene oxide dispersion; and mixing the silicon material and the graphene oxide dispersion to obtain a silicon-graphene oxide mixed dispersion.

[0036] According to one embodiment of the present invention, the organic solvent includes at least one of acetone, N,N-dimethylformamide, ethanol and N-methylpyrrolidone.

[0037] According to one embodiment of the present invention, the concentration of the graphene oxide dispersion is 1-20 g / L.

[0038] Graphene oxide concentrations in the range of 1-20 g / L are beneficial for coating silicon particles. If the concentration is too low, the graphene oxide coating is incomplete. If the concentration is too high, the graphene oxide solution is too viscous, which is not conducive to the dispersion of silicon particles.

[0039] According to one embodiment of the present invention, the method further includes the following steps: mixing silicon material, graphene oxide dispersion and dispersant, wherein the dispersant includes ionic liquid C n MIMSiO3 (n = 2-12). Wherein, MIM represents an imidazole ionic liquid. In the present invention, the ionic liquid C n MIMSiO3 (n=2-12) is also used as a surfactant. Graphene oxide solution is generally weakly acidic, and some commonly used surfactants are not effective in acidic environments. Ionic liquid C n MIMSiO3 (n=2-12) is a silicon-containing ionic liquid that decomposes during thermal reduction, leaving only silicon and carbon elements, which can provide lithium storage capacity.

[0040] According to one embodiment of the present invention, in a mixed solution comprising silicon material and graphene oxide dispersion, 1‰-5% of the mixed solution of ionic liquid C is added. n One or a mixture of MIMSiO3 (n=2-12).

[0041] According to one embodiment of the present invention, the following steps are also included: drying the silicon-graphene oxide mixed dispersion to obtain a silicon-graphene oxide powder with a coating structure; placing the silicon-graphene oxide powder in a halogen-containing mixed gas for a substitution reaction to obtain a silicon-halogenated graphene powder; and reducing the silicon-halogenated graphene powder at a high temperature under an inert atmosphere to obtain a silicon-carbon composite material.

[0042] According to one embodiment of the present invention, the following steps are also included: drying the silicon-graphene oxide mixed dispersion to obtain a silicon-graphene oxide powder with a coating structure; placing the silicon-graphene oxide powder in a mixed gas containing fluorine gas for a substitution reaction to obtain silicon-fluorinated graphene powder; and reducing the silicon-fluorinated graphene powder at a high temperature under an inert atmosphere to obtain a silicon-carbon composite material.

[0043] According to one embodiment of the present invention, the inert atmosphere is a mixture of inert gas and hydrogen (4% hydrogen), and the gas flow rate is 40-80 mL / min.

[0044] According to one embodiment of the present invention, the drying method includes at least one of a spray drying method and a flash evaporation method.

[0045] According to one embodiment of the present invention, the flake size of the graphene oxide is 0.5-30 μm.

[0046] According to one embodiment of the present invention, the particle size of the silicon material is 0.1-1 μm.

[0047] According to one embodiment of the present invention, the mass ratio of silicon material to graphene oxide is 1-2:0.1-1.0.

[0048] The mass ratio of silicon material to graphene oxide is 1-2:0.1-1.0. If the silicon material content is lower than this value, the specific capacity will not be significantly improved after the composite. If the silicon material content is higher than this value, the coating is not thorough and the cycle performance is reduced.

[0049] According to one embodiment of the present invention, in the mixed gas containing halogen gas, the volume ratio of halogen gas is 1-30%.

[0050] According to one embodiment of the present invention, in step S2, the temperature of the substitution reaction is 50-300° C., and the time is 0.5-12 h.

[0051] According to one embodiment of the present invention, in step S3, the reaction parameters of the reduction are as follows: calcination at 600-1000° C. for 2-8 hours.

[0052] Another aspect of the present invention relates to the use of the silicon-carbon composite material in an ion battery vehicle. This includes the silicon-carbon composite material described in the first embodiment. Because this application utilizes all of the technical solutions of the silicon-carbon composite material, it possesses at least all of the beneficial effects of the technical solutions of the aforementioned embodiments.

[0053] Other features and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments with reference to the following drawings, in which:

[0055] Figure 1 Schematic diagram of the structure of the silicon-carbon composite material of Example 1. DETAILED DESCRIPTION

[0056] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts are within the scope of the present invention.

[0057] Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0058] Example 1

[0059] A silicon-carbon composite material, such as Figure 1 As shown, it includes the following components:

[0060] Silicon materials;

[0061] The silicon material is a nano-silicon particle with silicon-fluorine bonds on its surface;

[0062] Graphene, wherein the graphene covers the silicon material;

[0063] The graphene has a wrinkled structure.

[0064] A method for preparing the silicon-carbon composite material comprises the following steps:

[0065] (1) Graphene oxide with an average sheet size of 5 μm was dispersed in ethanol and ultrasonically stirred for 60 min to obtain a graphene oxide ethanol dispersion with a concentration of 10 g / L after uniform dispersion;

[0066] (2) adding silicon nanoparticles with a particle size of 500 nm and C5MIMSiO3 to the graphene oxide ethanol dispersion according to the mass ratio of silicon nanoparticles, ionic liquid and graphene oxide of 100:1:10, and stirring at a speed of 300-500 r / min using a polytetrafluoroethylene stirring paddle for 2 h to obtain a uniformly dispersed silicon-graphene oxide mixed ethanol dispersion;

[0067] (3) spray drying the silicon-graphene oxide mixed ethanol dispersion to obtain a silicon-graphene oxide powder with a coating structure;

[0068] (4) placing the silicon-graphene oxide powder in a mixture of fluorine and argon for a substitution reaction, wherein the volume ratio of fluorine gas is 10%, the reaction temperature is 100° C., and the reaction time is 2 h to obtain silicon-fluorinated graphene powder;

[0069] (5) The silicon-fluorinated graphene powder was placed in a tubular furnace at a temperature of 800°C for thermal reduction for 2 h, and an argon-hydrogen mixture (4% hydrogen) was passed through at a flow rate of 60 mL / min to obtain a silicon-carbon composite material with a coating structure.

[0070] Example 2

[0071] A silicon-carbon composite material comprises the following components:

[0072] Silicon materials;

[0073] The silicon material is a nano-silicon particle with silicon-fluorine bonds on its surface;

[0074] Graphene, wherein the graphene covers the silicon material;

[0075] The graphene has a wrinkled structure.

[0076] A method for preparing the silicon-carbon composite material comprises the following steps:

[0077] (1) Graphene oxide with an average sheet size of 5 μm was dispersed in ethanol and ultrasonically stirred for 60 min to obtain a graphene oxide ethanol dispersion with a concentration of 10 g / L after uniform dispersion;

[0078] (2) adding silicon nanoparticles with a particle size of 500 nm and C5MIMSiO3 to the graphene oxide ethanol dispersion according to the mass ratio of silicon nanoparticles, ionic liquid and graphene oxide of 100:1:50, and stirring at a speed of 300-500 r / min using a polytetrafluoroethylene stirring paddle for 2 h to obtain a uniformly dispersed silicon-graphene oxide mixed ethanol dispersion;

[0079] (3) spray drying the silicon-graphene oxide mixed ethanol dispersion to obtain a silicon-graphene oxide powder with a coating structure;

[0080] (4) placing the silicon-graphene oxide powder in a mixture of fluorine and argon for a substitution reaction, wherein the volume ratio of fluorine gas is 20%, the reaction temperature is 150° C., and the reaction time is 6 h to obtain silicon-fluorinated graphene powder;

[0081] (5) The silicon-fluorinated graphene powder was placed in a tubular furnace at a temperature of 800°C for thermal reduction for 4 hours, and an argon-hydrogen mixture (4% hydrogen) was passed through at a flow rate of 60 mL / min to obtain a silicon-carbon composite material with a coating structure.

[0082] Example 3

[0083] A silicon-carbon composite material comprises the following components:

[0084] Silicon materials;

[0085] The silicon material is a nano-silicon particle with silicon-fluorine bonds on its surface;

[0086] Graphene, wherein the graphene covers the silicon material;

[0087] The graphene has a wrinkled structure.

[0088] A method for preparing the silicon-carbon composite material comprises the following steps:

[0089] (1) Graphene oxide with an average sheet size of 5 μm was dispersed in ethanol and ultrasonically stirred for 60 min to obtain a graphene oxide ethanol dispersion with a concentration of 10 g / L after uniform dispersion;

[0090] (2) adding silicon nanoparticles with a particle size of 500 nm and C5MIMSiO3 to the graphene oxide ethanol dispersion according to the mass ratio of silicon nanoparticles, ionic liquid and graphene oxide of 100:1:100, and stirring at a speed of 300-500 r / min using a polytetrafluoroethylene stirring paddle for 2 h to obtain a uniformly dispersed silicon-graphene oxide mixed ethanol dispersion;

[0091] (3) spray drying the silicon-graphene oxide mixed ethanol dispersion to obtain a silicon-graphene oxide powder with a coating structure;

[0092] (4) placing the silicon-graphene oxide powder in a mixture of fluorine and argon for a substitution reaction, wherein the volume ratio of fluorine gas is 30%, the reaction temperature is 200° C., and the reaction time is 12 h to obtain silicon-fluorinated graphene powder;

[0093] (5) The silicon-fluorinated graphene powder was placed in a tubular furnace at a temperature of 800° C. for thermal reduction for 6 h, and an argon-hydrogen mixture (4% hydrogen) was passed through at a flow rate of 60 mL / min to obtain a silicon-carbon composite material with a coating structure.

[0094] Example 4

[0095] The difference between Example 4 and Example 1 is that in Example 4, the silicon material is nano-silicon particles having silicon-chlorine bonds on the surface; while in Example 1, the silicon material is nano-silicon particles having silicon-fluorine bonds on the surface.

[0096] Silicon materials;

[0097] The silicon material is a nano-silicon particle with silicon-chlorine bonds on its surface;

[0098] Graphene, wherein the graphene covers the silicon material;

[0099] The graphene has a wrinkled structure.

[0100] A method for preparing the silicon-carbon composite material comprises the following steps:

[0101] (1) Graphene oxide with an average sheet size of 5 μm was dispersed in ethanol and ultrasonically stirred for 60 min to obtain a graphene oxide ethanol dispersion with a concentration of 10 g / L after uniform dispersion;

[0102] (2) adding silicon nanoparticles with a particle size of 500 nm and C5MIMSiO3 to the graphene oxide ethanol dispersion according to the mass ratio of silicon nanoparticles, ionic liquid and graphene oxide of 100:1:10, and stirring at a speed of 300-500 r / min using a polytetrafluoroethylene stirring paddle for 2 h to obtain a uniformly dispersed silicon-graphene oxide mixed ethanol dispersion;

[0103] (3) spray drying the silicon-graphene oxide mixed ethanol dispersion to obtain a silicon-graphene oxide powder with a coating structure;

[0104] (4) placing the silicon-graphene oxide powder in a mixture of chlorine and argon for a substitution reaction, wherein the volume ratio of chlorine is 10%, the reaction temperature is 100° C., and the reaction time is 2 h to obtain silicon-graphene chloride powder;

[0105] (5) The silicon-chlorinated graphene powder was placed in a tubular furnace at a temperature of 800°C for thermal reduction for 2 hours, and an argon-hydrogen mixture (4% hydrogen) was passed through at a flow rate of 60 mL / min to obtain a silicon-carbon composite material with a coating structure.

[0106] Example 5

[0107] The difference between Example 5 and Example 1 is that in Example 5, the silicon material is nano-silicon particles having silicon-bromine bonds on the surface; while in Example 1, the silicon material is nano-silicon particles having silicon-fluorine bonds on the surface.

[0108] Silicon materials;

[0109] The silicon material is a nano-silicon particle with silicon-bromine bonds on its surface;

[0110] Graphene, wherein the graphene covers the silicon material;

[0111] The graphene has a wrinkled structure.

[0112] A method for preparing the silicon-carbon composite material comprises the following steps:

[0113] (1) Graphene oxide with an average sheet size of 5 μm was dispersed in ethanol and ultrasonically stirred for 60 min to obtain a graphene oxide ethanol dispersion with a concentration of 10 g / L after uniform dispersion;

[0114] (2) adding silicon nanoparticles with a particle size of 500 nm and C5MIMSiO3 to the graphene oxide ethanol dispersion according to the mass ratio of silicon nanoparticles, ionic liquid and graphene oxide of 100:1:10, and stirring at a speed of 300-500 r / min using a polytetrafluoroethylene stirring paddle for 2 h to obtain a uniformly dispersed silicon-graphene oxide mixed ethanol dispersion;

[0115] (3) spray drying the silicon-graphene oxide mixed ethanol dispersion to obtain a silicon-graphene oxide powder with a coating structure;

[0116] (4) placing the silicon-graphene oxide powder in a mixture of bromine and argon for a substitution reaction, wherein the volume ratio of bromine gas is 10%, the reaction temperature is 200° C., and the reaction time is 2 h to obtain silicon-brominated graphene powder;

[0117] (5) The silicon-brominated graphene powder was placed in a tube furnace at a temperature of 800° C. for thermal reduction for 2 h, and an argon-hydrogen mixture (4% hydrogen) was passed through at a flow rate of 60 mL / min to obtain a silicon-carbon composite material with a coating structure.

[0118] Example 6

[0119] The difference between Example 6 and Example 1 is that in Example 6, the silicon material is nano-silicon particles having silicon-iodine bonds on the surface; while in Example 1, the silicon material is nano-silicon particles having silicon-fluorine bonds on the surface.

[0120] Silicon materials;

[0121] The silicon material is a nano-silicon particle with silicon-iodine bonds on its surface;

[0122] Graphene, wherein the graphene covers the silicon material;

[0123] The graphene has a wrinkled structure.

[0124] A method for preparing the silicon-carbon composite material comprises the following steps:

[0125] (1) Graphene oxide with an average sheet size of 5 μm was dispersed in ethanol and ultrasonically stirred for 60 min to obtain a graphene oxide ethanol dispersion with a concentration of 10 g / L after uniform dispersion;

[0126] (2) adding silicon nanoparticles with a particle size of 500 nm and C5MIMSiO3 to the graphene oxide ethanol dispersion according to the mass ratio of silicon nanoparticles, ionic liquid and graphene oxide of 100:1:10, and stirring at a speed of 300-500 r / min using a polytetrafluoroethylene stirring paddle for 2 h to obtain a uniformly dispersed silicon-graphene oxide mixed ethanol dispersion;

[0127] (3) spray drying the silicon-graphene oxide mixed ethanol dispersion to obtain a silicon-graphene oxide powder with a coating structure;

[0128] (4) placing the silicon-graphene oxide powder in a mixture of iodine gas and argon gas for substitution reaction, wherein the volume ratio of iodine gas is 10%, the reaction temperature is 300° C., and the reaction time is 2 h to obtain silicon-iodinated graphene powder;

[0129] (5) The silicon-iodinated graphene powder was placed in a tubular furnace at a temperature of 800° C. for thermal reduction for 2 h, and an argon-hydrogen mixture (4% hydrogen) was passed through at a flow rate of 60 mL / min to obtain a silicon-carbon composite material with a coating structure.

[0130] Comparative Example 1

[0131] The difference between Comparative Example 1 and Example 1 is that the silicon-carbon composite material of Comparative Example 1 is not treated with fluorine gas, while the silicon-carbon composite material of Example 1 is treated with fluorine gas.

[0132] A method for preparing the silicon-carbon composite material comprises the following steps:

[0133] (1) Graphene oxide with an average sheet size of 5 μm was dispersed in ethanol and ultrasonically stirred for 60 min to obtain a graphene oxide ethanol dispersion with a concentration of 10 g / L after uniform dispersion;

[0134] (2) adding silicon nanoparticles with a particle size of 500 nm and C5MIMSiO3 to the graphene oxide ethanol dispersion according to the mass ratio of silicon nanoparticles, ionic liquid and graphene oxide of 100:1:10, and stirring at a speed of 300-500 r / min using a polytetrafluoroethylene stirring paddle for 2 h to obtain a uniformly dispersed silicon-graphene oxide mixed ethanol dispersion;

[0135] (3) spray drying the silicon-graphene oxide mixed ethanol dispersion to obtain a silicon-graphene oxide powder with a coating structure;

[0136] (4) The silicon-graphene oxide powder was placed in a tubular furnace at a temperature of 800°C for thermal reduction for 2 h, and an argon-hydrogen mixture (4% hydrogen) was passed through at a flow rate of 60 mL / min to obtain a silicon-carbon composite material with a coating structure.

[0137] Comparative Example 2

[0138] The difference between Comparative Example 2 and Example 1 is that in step (2) of Comparative Example 2, the ionic liquid C5MIMSiO3 is not added.

[0139] A method for preparing the silicon-carbon composite material comprises the following steps:

[0140] (1) Graphene oxide with an average sheet size of 5 μm was dispersed in ethanol and ultrasonically stirred for 60 min to obtain a graphene oxide ethanol dispersion with a concentration of 10 g / L after uniform dispersion;

[0141] (2) adding silicon nanoparticles with a particle size of 500 nm to the graphene oxide ethanol dispersion at a mass ratio of 100:10, and stirring the mixture at a speed of 300-500 r / min using a polytetrafluoroethylene stirring paddle for 2 h to obtain a uniformly dispersed silicon-graphene oxide mixed ethanol dispersion;

[0142] (3) spray drying the silicon-graphene oxide mixed ethanol dispersion to obtain a silicon-graphene oxide powder with a coating structure;

[0143] (4) placing the silicon-graphene oxide powder in a mixture of fluorine and argon for a substitution reaction, wherein the volume ratio of fluorine gas is 10%, the reaction temperature is 100° C., and the reaction time is 2 h to obtain silicon-fluorinated graphene powder;

[0144] (5) The silicon-fluorinated graphene powder was placed in a tubular furnace at a temperature of 800°C for thermal reduction for 2 h, and an argon-hydrogen mixture (4% hydrogen) was passed through at a flow rate of 60 mL / min to obtain a silicon-carbon composite material with a coating structure.

[0145] Comparative Example 3

[0146] The difference between Comparative Example 3 and Example 3 is that the mass ratio of the nanoparticles to the graphene oxide in step (2) is different. Specifically, in Comparative Example 3, the mass ratio of the silicon nanoparticles, the ionic liquid, and the graphene oxide is 100:1:1; and specifically, in Example 3, the mass ratio of the silicon nanoparticles, the ionic liquid, and the graphene oxide is 100:1:100.

[0147] Among them, the mass ratio of silicon nanoparticles to graphene oxide in Comparative Example 3 is 100:1; the mass ratio of silicon nanoparticles to graphene oxide in Example 1 is 100:10.

[0148] A method for preparing the silicon-carbon composite material comprises the following steps:

[0149] (1) Graphene oxide with an average sheet size of 5 μm was dispersed in ethanol and ultrasonically stirred for 60 min to obtain a graphene oxide ethanol dispersion with a concentration of 10 g / L after uniform dispersion;

[0150] (2) adding silicon nanoparticles with a particle size of 500 nm and C5MIMSiO3 to the graphene oxide ethanol dispersion according to the mass ratio of silicon nanoparticles, ionic liquid and graphene oxide of 100:1:1, and stirring at a speed of 300-500 r / min for 2 h using a polytetrafluoroethylene stirring paddle to obtain a uniformly dispersed silicon-graphene oxide mixed ethanol dispersion;

[0151] (3) spray drying the silicon-graphene oxide mixed ethanol dispersion to obtain a silicon-graphene oxide powder with a coating structure;

[0152] (4) placing the silicon-graphene oxide powder in a mixture of fluorine and argon for a substitution reaction, wherein the volume ratio of fluorine gas is 10%, the reaction temperature is 100° C., and the reaction time is 2 h to obtain silicon-fluorinated graphene powder;

[0153] (5) The silicon-fluorinated graphene powder was placed in a tubular furnace at a temperature of 800°C for thermal reduction for 2 h, and an argon-hydrogen mixture (4% hydrogen) was passed through at a flow rate of 60 mL / min to obtain a silicon-carbon composite material with a coating structure.

[0154] Performance testing:

[0155] The materials prepared in Examples 1-3 and Comparative Examples 1-3 were assembled into button cells for electrochemical performance testing and analysis. The specific scheme is as follows: the prepared materials, conductive agent SP, and binder LA136 were mixed in a ratio of 8:1:1 to form a button cell of model 2032. The counter electrode was a lithium sheet, the separator was a Celgard 2400 microporous polypropylene film, the voltage range was 0.01-1.5V, and the 0.1Ag -1 The current density is used for constant current charge and discharge.

[0156] The test results are shown in Table 1.

[0157] Table 1

[0158]

[0159] As can be seen from Table 1, by comparing the electrochemical properties of Examples 1-3 with Comparative Examples 1-3, compared with the silicon-carbon negative electrode material with fluorine-free graphene oxide as a carbon source, the lithium ion battery assembled by the silicon-carbon composite material prepared by Example 1-3 using the present invention, the cycle stability is significantly improved. This is because in the fluorination process, fluorine gas reacts with silicon to produce silicon fluoride gas, and the volatilization of the gas prompts the graphene coating to produce a wrinkled structure, which is conducive to releasing the stress generated by silicon during expansion. Moreover, fluorine atoms have a strong etching effect on silicon, and the active fluorine atoms produced by fluorinated graphene in the thermal reduction process react with silicon, so that the graphene carbon layer after reduction forms a stronger interface effect with the silicon surface, and the mutual contact is also more close, and the stability of the coating structure is maintained during charge and discharge, so as to obtain better cycle stability. By comparing Example 1 with Comparative Example 2, it can be seen that the addition of ionic liquid C5MIMSiO3 significantly improves the cycle performance of the battery, because ionic liquid, as a dispersant and surfactant, enhances the uniform dispersion of silicon particles and graphene oxide, which is conducive to silicon particles and graphene oxide forming a coating structure.

[0160] The results of Examples 4 to 6 are similar to those of Example 1 and are not shown one by one to avoid redundancy.

[0161] The above are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention specification, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing a silicon-carbon composite material, characterized in that: The following steps are involved: S1: mixing silicon material, graphene oxide and dispersant, and drying to obtain silicon-graphene oxide coating structure; S2 placing the coated silicon-graphene oxide structure in a mixed gas containing a halogen gas to perform a substitution reaction, wherein the temperature of the substitution reaction is 50-300° C. and the time is 0.5-12 hours to obtain silicon-halogenated graphene; S3 reducing the silicon-halogenated graphene, wherein the reaction parameters for the reduction are: calcining at 600-1000° C. for 2-8 hours to obtain a silicon-carbon composite material; The dispersant includes ionic liquid C n MIMSiO3, n=2-12; The silicon-carbon composite material comprises the following components: Silicon materials; The silicon material is nano silicon particles with silicon-halogen bonds on the surface; Graphene, wherein the graphene covers the silicon material; The graphene has a wrinkled structure.

2. The method according to claim 1, wherein: The silicon-halogen bond includes at least one of a silicon-fluorine bond, a silicon-chlorine bond, a silicon-bromine bond and a silicon-iodine bond.

3. The method according to claim 1, wherein: The mass ratio of the silicon material to the graphene is 1-2:0.05-1.

0.

4. The method according to claim 1, wherein: In step S1, before mixing the silicon material and graphene oxide, The method comprises the following steps: dispersing graphene oxide in an organic solvent to obtain a graphene oxide dispersion liquid; and mixing a silicon material and the graphene oxide dispersion liquid to obtain a silicon-graphene oxide mixed dispersion liquid.

5. The method according to claim 4, characterized in that: The concentration of the graphene oxide dispersion is 1-20 g / L.

6. The method according to claim 1, wherein: The mass ratio of the silicon material to graphene oxide is 1-2:0.1-1.

0.

7. The method according to claim 1, wherein: In the halogen-containing gas mixture, the volume proportion of halogen gas is 1-30%.

8. A battery, characterized in that: The invention comprises a positive electrode, a negative electrode and an electrolyte; wherein the negative electrode comprises a silicon-carbon composite material prepared by the method according to any one of claims 1 to 3.

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