Silicon-carbon composite material with core-shell structure, preparation method and application thereof

Abstract

The application provides a kind of silicon-carbon composite material with core-shell structure, a preparation method and application thereof, and belongs to the field of lithium battery, with nano-silicon as content, silicon-carbon core-shell structure composite material powder is prepared by dispersion polymerization. The method first disperses silicon powder in tertiary amine oxide, adds monomers such as acrylonitrile and peroxide initiator in the system, and prepares silicon-polyacrylonitrile core-shell structure material through dispersion polymerization and thermal oxidation process, and finally obtains silicon-carbon composite material with core-shell structure through carbonization treatment. When the composite material prepared by the application is used for lithium battery negative electrode test, the reversible specific capacity is 2426 mAh / g under the current density of 200 mA / g, and the initial coulombic efficiency can reach 88%; the preparation process of the application is simple and easy to mass production.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of silicon-carbon composite material with core-shell structure, preparation method and its application, belong to lithium battery field, with silicon material as core, dispersion polymerization is prepared silicon-carbon core-shell structure composite material powder. BACKGROUND

[0002] The theoretical specific capacity of silicon-based material is large, and the discharge potential is low, which is a popular candidate material for the next generation of high-energy-density lithium-ion battery anode. However, during the charging and discharging process, the silicon-based material expands greatly, the electrode material is easily pulverized, the electrode stability is low, and the reversible specific capacity decreases significantly, which affects the widespread application of silicon-based materials in high-capacity batteries.

[0003] To solve this problem, currently, conductive carbon materials are introduced to inhibit the expansion of silicon-based materials. CN110061198B proposes a method for preparing a silicon-carbon composite material by mixing bituminous coal and pre-oxidized silicon nanoparticles and then sintering at high temperature. CN110739446A proposes a method for preparing a silicon-carbon composite material by mixing a chelating agent, a transition metal salt, and water, heating and stirring, and then evaporating to obtain a modified silicon-based gel and carbonizing. CN113666354A proposes a method for preparing a porous silicon-carbon composite material by ultrasonic dispersion, ball milling, and magnesium thermal reduction reaction under argon protection, followed by hydrochloric acid purification. CN106784732B proposes a method for preparing a carbon-coated nanosilicon composite material by oxygen diffusion of micron-sized silicon powder with an oxide layer, carbon coating by vapor deposition, and removal of silicon oxide by immersion in a hydrofluoric acid solution. However, the above methods still have problems such as poor dispersion of silicon and carbon, difficulty in uniform molding of core-shell structure, and poor stability of silicon-carbon materials during charging and discharging. SUMMARY

[0004] To solve the problems of the prior art, the present application provides a silicon-carbon composite material with core-shell structure, a preparation method, and its application.

[0005] To achieve the above-mentioned purpose, the technical solution adopted by the present application is as follows:

[0006] A method for preparing a silicon-carbon composite material with core-shell structure, which uses a tertiary amine oxide as a solvent and adopts a dispersion polymerization method to disperse monomers on the surface of nanosilicon cores, and finally carbonizes to obtain a silicon-carbon composite material with core-shell structure. The specific steps are as follows:

[0007] Step one: add an amphiphilic tertiary amine oxide as a solvent to a reaction kettle, then add nanosilicon powder, and stir and mix at room temperature to form a stable silicon-tertiary amine oxide dispersion system.

[0008] Step two, monomer polymer and peroxide initiator are added into the dispersion system obtained in step one, and the reaction is carried out under nitrogen protection at 60-80℃ for 2-24h, to form a silicon-single monomer core-shell dispersion liquid in the silicon-tertiary amine oxide dispersion system; the monomer polymer is dissolved in the tertiary amine oxide.

[0009] Step three, the dispersion liquid obtained in step two is heated to 150-400℃, and a solvothermal oxidation reaction is carried out for 0.5-8h to form a silicon-polyimidazene dispersion liquid; after the solvothermal oxidation reaction, the solid product is collected and ball milled for 2-6h, and then washed with ethanol and the solid product is collected.

[0010] Step four, the solid product in step three is subjected to carbonization treatment under inert gas protection, the heating rate is kept at 1-10℃ / min, the carbonization treatment temperature is 600-1000℃, and the constant temperature carbonization treatment time is 2-6h, and then the carbonization treatment is cooled (to room temperature), ground and sieved to obtain a silicon-carbon composite material suitable for lithium ion battery negative electrode material.

[0011] Further, in step three, the silicon-polyimidazene dispersion liquid in step three can be directly mixed with pitch carbon source and ball milled for 2-6h, and then washed with ethanol for multiple times, and the solid product is collected and subjected to carbonization treatment, the heating rate is kept at 1-10℃ / min, the final carbonization temperature is 600-1000℃, and the constant temperature carbonization time is 2-6h, and then the product is taken out after being cooled to room temperature; ground and sieved through a 325 mesh screen to obtain a silicon-carbon composite material suitable for lithium ion battery negative electrode material. The pitch carbon source includes coal tar pitch, ethylene tar, and a mixture of one or more than two of the coating pitch.

[0012] Further, in step one, the nano silicon powder includes nano silicon powder, micro silicon powder, and micro silicon monoxide powder.

[0013] Further, in step one, the structure of the amphiphilic tertiary amine oxide is as follows: wherein, one or two of the three functional groups of R1, R2 and R3 are hydrophobic groups, and the rest are hydrophilic groups; the hydrophobic group can be C2-C 28 straight chain or branched chain saturated alkyl, C2-C 28 straight chain or branched chain unsaturated alkyl, wherein the unsaturated alkyl contains one to four alkenyl or alkynyl groups, C7-C 38 straight chain or branched chain saturated alkyl-aryl functional group, C8-C 38 straight chain or branched chain unsaturated alkyl-aryl functional group, wherein the unsaturated alkyl contains one to four alkenyl or alkynyl groups; the hydrophilic group is polyethylene oxide, polypropylene oxide or an ethylene oxide-propylene oxide block copolymer, and the average polymerization of the polyethylene oxide, polypropylene oxide or ethylene oxide-propylene oxide block copolymer is between 1-100.

[0014] Further, in the step one, the amount of the nano-silicon powder added is 10-20wt% of the amount of the amphiphilic tertiary amine oxide.

[0015] Further, in the step two, the amount of the monomer polymer is 50-100wt% of the amount of the nano-silicon powder, and the amount of the initiator is 0.5-3.3wt% of the amount of the monomer polymer.

[0016] Further, in the step two, the monomer polymer includes one or more than two of polypropylene, polystyrene, polymethyl acrylate, polyethyl acrylate, polymethyl methacrylate, polyethyl methacrylate, polypropyl methacrylate, polybutyl methacrylate, polyisoprene, polyacrylonitrile-methyl acrylate copolymer, acrylonitrile-methyl acrylate copolymer, acrylonitrile-isoprene copolymer, and epoxy resin.

[0017] Further, in the step two, the peroxide initiator includes ammonium persulfate, potassium persulfate, sodium persulfate, and dibenzoyl peroxide.

[0018] Further, in the step three, the inert protective atmosphere is nitrogen and argon.

[0019] A silicon-carbon composite material with a core-shell structure is obtained by the preparation method.

[0020] The silicon-carbon composite material with a core-shell structure is applied in the field of lithium ion batteries as a negative electrode material, and the first coulomb efficiency is higher than 50%.

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] (1) The present application uses a tertiary amine oxide-nano-silicon powder dispersion system, and the tertiary amine oxide is used as a solvent to realize fine dispersion of the silicon material in the solvent.

[0023] (2) The present application uses the tertiary amine oxide as a solvent to efficiently control the radical polymerization process of acrylonitrile and other monomers on the surface of silicon atoms to form a polymer shell-silicon core composite material.

[0024] (3) The tertiary amine oxide solvent system and the solvent thermal oxidation reaction control the cyclization process of polyacrylonitrile, and the carbonization process is controllable and adjustable. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 X-ray diffraction pattern of the silicon-carbon composite material in Example 1.

[0026] Figure 2 Scanning electron microscope image of the silicon-carbon composite material in Example 1.

[0027] Figure 3 Transmission electron micrograph of the silicon-carbon composite material in Example 1.

[0028] Figure 4 Graph of the first charge-discharge curve of the silicon-carbon negative electrode in Example 1.

[0029] Figure 5 Graph of the first charge-discharge curve of the silicon-carbon negative electrode in Example 7.

[0030] Figure 6 Graph of the cycle charge-discharge of the silicon-carbon negative electrode in Example 7. DETAILED DESCRIPTION

[0031] The technical solution of the present application achieves the preparation target of the silicon-carbon composite material through the following examples.

[0032] Example 1

[0033] Step one, take 60g octadecylamine polyoxyethylene ether (average polymerization degree is 5) oxide, mix 12g nano silicon powder under stirring at room temperature, and form a stable nano silicon powder-tertiary amine oxide dispersion system;

[0034] Step two, add 12g acrylonitrile and 0.4g ammonium persulfate initiator into the above dispersion system, and react at 70℃ for 24h under nitrogen protection, so as to form a silicon-polyacrylonitrile core-shell dispersion liquid in the tertiary amine oxide system;

[0035] Step three, heat the above dispersion liquid to 150℃, and perform solvothermal oxidation reaction for 4h, so as to form a silicon-polyimidazene dispersion liquid, collect the solid product after the solvothermal oxidation reaction, then ball mill for 4h, and wash with ethanol for multiple times, and then collect the solid product;

[0036] Step four, perform carbonization treatment on the solid product, keep the heating rate at 1℃ / min under inert atmosphere, and keep the final carbonization temperature at 800℃ for 3h, and then perform cooling, grinding and sieving, so as to obtain a silicon-carbon composite material. The results of XRD, scanning electron microscope and transmission electron microscope analysis are shown in Figures 1-4 When used for lithium ion battery negative electrode test, the specific capacity of the first discharge is 2695mAh / g, the specific capacity of the charge is 2102mAh / g, and the first coulombic efficiency is 78%.

[0037] Example 2

[0038] Step one, take 60g octadecylamine polyoxyethylene ether (average polymerization degree is 5) oxide, mix 12g micron silicon powder under stirring at room temperature, and form a stable micron silicon powder-tertiary amine oxide dispersion system;

[0039] Step two, 12 g of acrylonitrile and 0.4 g of ammonium persulfate initiator were added into the above dispersion system, and the reaction was carried out at 60°C for 24 h under nitrogen protection, and a silicon-polyacrylonitrile core-shell dispersion was formed in the tertiary amine oxide system;

[0040] Step three, the above dispersion was heated to 200°C, and the solvothermal oxidation reaction was carried out for 0.5 h, and a silicon-polyimidazene dispersion was formed, and after the solvothermal oxidation reaction, the solid product was collected, and then ball-milled for 4 h, and washed with ethanol for multiple times, and then the solid product was collected;

[0041] Step four, the solid product was subjected to carbonization treatment, the heating rate was kept at 1°C / min under inert atmosphere, the final carbonization temperature was kept at 800°C for 2 h, and then the temperature was lowered, the product was ground and sieved, and a silicon-carbon composite material was obtained. When used for lithium ion battery negative electrode test, the specific capacity of the first charge-discharge was 3098 mAh / g, the charge specific capacity was 1301 mAh / g, and the first coulombic efficiency was 52%.

[0042] Example 3

[0043] Step one, 60 g of octadecyl amine polyoxyethylene ether (average polymerization degree is 5) oxide was mixed with 12 g of silicon monoxide powder under stirring at room temperature, and a stable silicon monoxide-tertiary amine oxide dispersion system was formed;

[0044] Step two, 12 g of acrylonitrile and 0.4 g of ammonium persulfate initiator were added into the above dispersion system, and the reaction was carried out at 80°C for 12 h under nitrogen protection, and a silicon-polyacrylonitrile core-shell dispersion was formed in the tertiary amine oxide system;

[0045] Step three, the above dispersion was heated to 200°C, and the solvothermal oxidation reaction was carried out for 4 h, and a silicon-polyimidazene dispersion was formed, and after the solvothermal oxidation reaction, the above dispersion was ball-milled for 4 h, and washed with ethanol for multiple times, and then the solid product was collected;

[0046] Step four, the solid product was subjected to carbonization treatment, the heating rate was kept at 5°C / min under inert atmosphere, the final carbonization temperature was kept at 800°C for 6 h, and then the temperature was lowered, the product was ground and sieved, and a silicon-carbon composite material was obtained. When used for lithium ion battery negative electrode test, the specific capacity of the first charge-discharge was 1154 mAh / g, the charge specific capacity was 773 mAh / g, and the first coulombic efficiency was 67%.

[0047] Example 4

[0048] Step one, 60 g of octadecyl amine polyoxyethylene ether (average polymerization degree is 10) oxide was mixed with 12 g of nano silicon powder under stirring at room temperature, and a stable nano silicon powder-tertiary amine oxide dispersion system was formed;

[0049] Step two, 12 g of acrylonitrile and 0.4 g of ammonium persulfate initiator were added into the above dispersion system, and the system was reacted at 70°C for 24 h under nitrogen protection, and a silicon-polyacrylonitrile core-shell dispersion was formed in the tertiary amine oxide system;

[0050] Step three, the above dispersion was heated to 400°C, and the solvent-thermal oxidation reaction was carried out for 0.5 h, and a silicon-polyimidazene dispersion was formed. After the solvent-thermal oxidation reaction, the solid product was collected, and then ball-milled for 2 h. After being washed with ethanol for multiple times, the solid product was collected.

[0051] Step four, the solid product was subjected to carbonization treatment, the heating rate was kept at 1°C / min under inert atmosphere, and the final carbonization temperature was kept at 800°C for 3 h. After cooling, grinding and sieving, a silicon-carbon composite material was obtained. When used for lithium ion battery negative electrode test, the specific capacity of the first discharge was 2268 mAh / g, the specific capacity of the charge was 1542 mAh / g, and the first coulombic efficiency was 68%.

[0052] Example 5

[0053] Step one, 60 g of octadecyl amine polyoxyethylene ether (average polymerization degree was 50) oxide was mixed with 12 g of nano silicon powder under stirring at room temperature, and a stable nano silicon powder-tertiary amine oxide dispersion system was formed.

[0054] Step two, 6 g of acrylonitrile, 6 g of styrene and 0.4 g of ammonium persulfate initiator were added into the above dispersion system, and the system was reacted at 70°C for 24 h under nitrogen protection, and a silicon-polyacrylonitrile core-shell dispersion was formed in the tertiary amine oxide system.

[0055] Step three, the above dispersion was heated to 150°C, and the solvent-thermal oxidation reaction was carried out for 8 h, and a silicon-polyimidazene dispersion was formed. After the solvent-thermal oxidation reaction, the solid product was collected, and then ball-milled for 6 h. After being washed with ethanol for multiple times, the solid product was collected.

[0056] Step four, the solid product was subjected to carbonization treatment, the heating rate was kept at 1°C / min under inert atmosphere, and the final carbonization temperature was kept at 800°C for 3 h. After cooling, grinding and sieving, a silicon-carbon composite material was obtained. When used for lithium ion battery negative electrode test, the specific capacity of the first discharge was 2268 mAh / g, the specific capacity of the charge was 1542 mAh / g, and the first coulombic efficiency was 68%.

[0057] Example 6

[0058] Step one, 60 g of octadecyl amine polyoxyethylene ether (average polymerization degree was 50) oxide was mixed with 12 g of nano silicon powder under stirring at room temperature, and a stable nano silicon powder-tertiary amine oxide dispersion system was formed.

[0059] Step two, 12g of styrene and 0.4g of ammonium persulfate initiator were added into the above dispersion system, and the reaction was carried out at 70°C for 24h under nitrogen protection, and a silicon-poly (styrene) core-shell dispersion was formed in the tertiary amine oxide system.

[0060] Step three, the above dispersion was heated to 150°C, and the solvothermal oxidation reaction was carried out for 4h, and a silicon-poly (imidazoline) dispersion was formed. After the solvothermal oxidation reaction, the solid product was collected, and then ball-milled for 4h. After being washed with ethanol for several times, the solid product was collected.

[0061] Step four, the solid product was subjected to carbonization treatment, the heating rate was kept at 1°C / min under inert atmosphere, and the final carbonization temperature was kept at 600°C for 3h. After cooling, grinding and sieving, a silicon-carbon composite material was obtained. When used as a negative electrode for lithium ion battery test, the specific capacity of the first charge-discharge was 2964mAh / g, the charge specific capacity was 1541mAh / g, and the first coulombic efficiency was 52%.

[0062] Example 7

[0063] Step one, 60g of carboxylate anionic surfactant C 18 H 37 O(CH2CH2) n COONa (average degree of polymerization 5) was stirred at room temperature, and 12g of nano-silicon powder was mixed to form a stable nano-silicon powder-tertiary amine oxide dispersion system.

[0064] Step two, 12g of styrene and 0.4g of ammonium persulfate initiator were added into the above dispersion system, and the reaction was carried out at 70°C for 24h under nitrogen protection, and a silicon-poly (styrene) core-shell dispersion was formed in the tertiary amine oxide system.

[0065] Step three, the above dispersion was heated to 150°C, and the solvothermal oxidation reaction was carried out for 4h, and a silicon-poly (imidazoline) dispersion was formed. After the solvothermal oxidation reaction, the solid product was collected, and then ball-milled for 4h. After being washed with ethanol for several times, the solid product was collected.

[0066] Step four, the solid product was subjected to carbonization treatment, the heating rate was kept at 1°C / min under inert atmosphere, and the final carbonization temperature was kept at 600°C for 3h. After cooling, grinding and sieving, a silicon-carbon composite material was obtained. When used as a negative electrode for lithium ion battery test, the specific capacity of the first charge-discharge was 2964mAh / g, the charge specific capacity was 1541mAh / g, and the first coulombic efficiency was 52%.

[0067] Example 8

[0068] Step one, 60g of octadecyl amine polyoxyethylene ether (average degree of polymerization 5) oxide was stirred at room temperature, and 12g of nano-silicon powder was mixed to form a stable nano-silicon powder-tertiary amine oxide dispersion system.

[0069] Step two, 12 g of methyl acrylate and 0.4 g of ammonium persulfate initiator were added to the above dispersion system, and the reaction was carried out at 80°C for 24 h under nitrogen protection, forming a silicon-poly (methyl acrylate) core-shell dispersion in the tertiary amine oxide system.

[0070] Step three, the above dispersion was heated to 150°C, and solvent thermal oxidation was carried out for 4 h, forming a silicon-poly (imidazoline) dispersion. After solvent thermal oxidation, the solid product was collected, then ball-milled for 4 h, and washed with ethanol multiple times to collect the solid product.

[0071] Step four, the solid product was subjected to carbonization treatment, the heating rate was kept at 1°C / min under inert atmosphere, and the final carbonization temperature was kept at 1000°C for 3 h. After cooling, grinding, and sieving, a silicon-carbon composite material was obtained. When used as a negative electrode for lithium ion batteries, the specific capacity of the first charge-discharge was 2617 mAh / g, the specific capacity of the charge was 1465 mAh / g, and the first coulombic efficiency was 56%.

[0072] Example 9

[0073] Step one, 60 g of octadecyl amine polyoxyethylene ether (average degree of polymerization 5) oxide was mixed with 12 g of nano-silicon powder under stirring at room temperature, forming a stable nano-silicon powder-tertiary amine oxide dispersion system.

[0074] Step two, 6 g of acrylonitrile and 0.2 g of ammonium persulfate initiator were added to the above dispersion system, and the reaction was carried out at 70°C for 24 h under nitrogen protection, forming a silicon-poly (acrylonitrile) core-shell dispersion in the tertiary amine oxide system.

[0075] Step three, the above dispersion was heated to 150°C, and solvent thermal oxidation was carried out for 4 h, forming a silicon-poly (imidazoline) dispersion. After solvent thermal oxidation, the solid product was collected, then ball-milled for 4 h, and washed with ethanol multiple times to collect the solid product.

[0076] Step four, the silicon-poly (imidazoline) composite material in step three was mixed with 6 g of medium-temperature coal pitch, ball-milled for 4 h, and washed with ethanol to collect the solid product. Carbonization treatment was carried out at a heating rate of 1°C / min, and the final carbonization temperature was kept at 800°C for 3 h. After cooling, grinding, and sieving, a silicon-carbon composite material was obtained. When used as a negative electrode for lithium ion batteries, the specific capacity of the first charge-discharge was 2426 mAh / g, the specific capacity of the charge was 2134 mAh / g, the first coulombic efficiency was 88%, the specific capacity attenuated to 1974 mAh / g after 100 charge-discharge cycles, and the capacity retention rate compared to the second cycle capacity was 82%.

[0077] Example 10

[0078] Step one, take 60g octadecyl amine polyoxyethylene ether (average degree of polymerization of 5) oxide, under stirring at room temperature, mix 12g nano silicon powder, form a stable nano silicon powder-tertiary amine oxide dispersion system;

[0079] Step two, add 6g acrylonitrile and 0.2g ammonium persulfate initiator to the above dispersion system, under nitrogen protection, react at 70℃ for 24h, form a silicon-polyacrylonitrile core-shell dispersion liquid in the tertiary amine oxide system;

[0080] Step three, heat the above dispersion liquid to 150℃, solvothermal oxidation reaction for 4h, form a silicon-polyimidazene dispersion liquid, after solvothermal oxidation reaction, collect the solid product, then ball mill for 4h, wash with ethanol for several times, collect the solid product;

[0081] Step four, mix the silicon-polyimidazene composite material in step three with 6g ethylene tar (softening point 250℃), ball mill for 4h, collect the solid product after washing with ethanol, carbonization treatment, heating rate 1℃ / min, final carbonization temperature 800℃, constant temperature for 3h, cooling, grinding, sieving, get silicon-carbon composite material. When tested as anode of lithium ion battery, the specific capacity of first charge-discharge is 3249mAh / g, the charge specific capacity is 2111mAh / g, the first coulombic efficiency is 65%.

[0082] Example 11

[0083] Step one, take 60g octadecyl amine polyoxyethylene ether (average degree of polymerization of 5) oxide, under stirring at room temperature, mix 12g nano silicon powder, form a stable nano silicon powder-tertiary amine oxide dispersion system;

[0084] Step two, add 6g acrylonitrile and 0.2g ammonium persulfate initiator to the above dispersion system, under nitrogen protection, react at 70℃ for 24h, form a silicon-polyacrylonitrile core-shell dispersion liquid in the tertiary amine oxide system;

[0085] Step three, heat the above dispersion liquid to 150℃, solvothermal oxidation reaction for 4h, form a silicon-polyimidazene dispersion liquid, after solvothermal oxidation reaction, collect the solid product, then ball mill for 4h, wash with ethanol for several times, collect the solid product;

[0086] Step four, mix the silicon-polyimidazene composite material in step three with 6g coated pitch, ball mill for 4h, collect the solid product after washing with ethanol, carbonization treatment, heating rate 1℃ / min, final carbonization temperature 800℃, constant temperature for 3h, cooling, grinding, sieving, get silicon-carbon composite material. When tested as anode of lithium ion battery, the specific capacity of first charge-discharge is 3046mAh / g, the charge specific capacity is 1797mAh / g, the first coulombic efficiency is 59%.

[0087] Example 12

[0088] Step one, take 60g octadecyl amine polyoxyethylene ether (average degree of polymerization is 5) oxide, under stirring at room temperature, mix 12g nano silicon powder, form a stable nano silicon powder-tertiary amine oxide dispersion system;

[0089] Step two, add 6g acrylonitrile and 0.2g ammonium persulfate initiator into the above dispersion system, under nitrogen protection, react at 70℃ for 24h, form a silicon-polyacrylonitrile core-shell dispersion liquid in the tertiary amine oxide system;

[0090] Step three, heat the above dispersion liquid to 150℃, and perform solvothermal oxidation reaction for 4h to form a silicon-polyimidazene dispersion liquid, collect the solid product after the solvothermal oxidation reaction, then ball mill for 4h, wash with ethanol for several times, and collect the solid product;

[0091] Step four, mix the silicon-polyimidazene composite material in step three with 3g medium temperature coal pitch and 3g ethylene tar (softening point 250℃), ball mill for 4h, collect the solid product after washing with ethanol, perform carbonization treatment, heat at a speed of 1℃ / min, and finally heat at 800℃ for 3h, cool, grind, and sieve to obtain a silicon-carbon composite material. When tested as a negative electrode of a lithium ion battery, the specific capacity of the first charge-discharge is 2617mAh / g, the specific capacity of the charge is 1439mAh / g, and the first coulombic efficiency is 55%.

[0092] The electrochemical performance of the silicon-carbon composite material prepared in the above example is shown in Table 1 below:

[0093]

[0094]

[0095] The above examples only express the embodiments of the present application, but cannot be understood as a limitation on the scope of the patent of the present application. It should be pointed out that, for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which all belong to the protection scope of the present application.

Claims

1. A method for preparing a silicon-carbon composite material having a core-shell structure, characterized by, The preparation method uses a tertiary amine oxide as a solvent, adopts a dispersion polymerization method, performs dispersion polymerization of monomers on the surface of a nano silicon core, and finally carbonizes to obtain a silicon-carbon composite material with a core-shell structure.

2. The method for preparing a core-shell structured silicon-carbon composite material according to claim 1, characterized in that, The specific steps are as follows: Step one: an amphiphilic tertiary amine oxide is used as a solvent, and nano silicon powder is added, and the mixture is stirred at room temperature to obtain a silicon-tertiary amine oxide dispersion system; Step two: monomer polymers and a peroxide initiator are added to the dispersion system obtained in step one, and the reaction is carried out at 60-80 DEG C for 2-24 h under nitrogen protection, so that a silicon-monomer core-shell dispersion liquid is formed in the silicon-tertiary amine oxide dispersion system; Step three: the dispersion liquid obtained in step two is heated to 150 DEG C-400 DEG C, and a solvothermal oxidation reaction is carried out for 0.5-8 h, so that a silicon-polyimidazoline dispersion liquid is formed; after the solvothermal oxidation reaction, the solid product is collected and subjected to ball milling, washing, and collection of the solid product in sequence; Step four: the solid product in step three is subjected to carbonization treatment under inert gas protection, the carbonization treatment temperature is 600-1000 DEG C, the isothermal carbonization treatment time is 2-6 h, and after the carbonization treatment, cooling, grinding, and sieving are carried out to obtain a silicon-carbon composite material with a core-shell structure.

3. The method for preparing a core-shell structured silicon-carbon composite material according to claim 2, characterized in that, In step three, the silicon-polyimidazoline dispersion liquid obtained in step three can be directly mixed with a pitch carbon source, subjected to ball milling for 2-6 h, washed, and then the solid product is collected and subjected to carbonization treatment, the carbonization temperature is 600-1000 DEG C, the carbonization time is 2-6 h, and after the carbonization treatment, cooling, grinding, and sieving are carried out to obtain a silicon-carbon composite material with a core-shell structure.

4. The method for preparing a core-shell structured silicon-carbon composite material according to claim 2, characterized in that, In step three, the ball milling time is 2-6 h, and ethanol is used for washing.

5. The preparation method of the silicon-carbon composite material with a core-shell structure according to claim 2, characterized in that: In step one, the nano silicon powder includes nano silicon powder, micro silicon powder, and micro silicon monoxide powder; The structure of the amphiphilic tertiary amine oxide in step one is: wherein one or two of the three functional groups R1, R2, R3 are hydrophobic groups and the rest are hydrophilic groups; the hydrophobic groups can be C2-C 28 linear or branched saturated alkyl, C2-C 28 linear or branched unsaturated alkyl, wherein the unsaturated alkyl contains one to four alkenyl, alkynyl groups, C7-C 38 linear or branched saturated alkyl-aryl functional groups, C8-C 38 linear or branched unsaturated alkyl-aryl functional groups, wherein the unsaturated alkyl contains one to four alkenyl, alkynyl groups; the hydrophilic groups are polyethylene oxide, polypropylene oxide or ethylene oxide propylene oxide block copolymers, the average polymerization of the polyethylene oxide, polypropylene oxide or ethylene oxide propylene oxide block copolymers is between 1-100; In step one, the addition amount of the nano silicon powder is 10-20 wt% of the mass of the amphiphilic tertiary amine oxide.

6. The preparation method of the silicon-carbon composite material with a core-shell structure according to claim 2, characterized in that: In step two, the amount of the monomer polymers is 50-100 wt% of the mass of the nano silicon powder, and the amount of the initiator is 0.5-3.3 wt% of the mass of the monomer polymers; In step two, the monomer polymers include one or a mixture of two or more of polypropylene, polystyrene, polymethyl acrylate, polyethyl acrylate, polymethyl methacrylate, polyethyl methacrylate, polypropyl methacrylate, polybutyl methacrylate, polyisoprene, polyacrylonitrile-methyl acrylate copolymer, acrylonitrile-methyl acrylate copolymer, acrylonitrile-isoprene copolymer, and epoxy resin; In step two, the peroxide initiator includes ammonium persulfate, potassium persulfate, sodium persulfate, and dibenzoyl peroxide.

7. The method for preparing a core-shell structured silicon-carbon composite material according to claim 2, characterized in that: In step three, the inert protective atmosphere is nitrogen and argon.

8. A silicon-carbon composite material having a core-shell structure, characterized by, The preparation method is obtained by any of claims 1-7.

9. Use of the silicon-carbon composite material having a core-shell structure according to claim 8, characterized in that, It is applied to the field of lithium ion batteries and used as a negative electrode material.

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