阅读说明：本技术 硅碳复合材料及其制备方法和应用 (Silicon-carbon composite material and preparation method and application thereof ) 是由 严大洲 温国胜 杨涛 李艳平 韩治成 刘诚 孙强 万烨 于 2021-07-08 设计创作，主要内容包括：本发明提供了一种硅碳复合材料及其制备方法和应用。该硅碳复合材料包括：中空硅球核层、氧化硅壳层和石墨烯壳层。氧化硅壳层包覆在中空硅球核层的外表面；石墨烯壳层包覆在氧化硅壳层的远离中空硅球核层的外表面。将本发明复合材料作为锂离子电池负极材料,材料的导电性较高、体积效应也得到了有效的改善,更重要的是其还有效地解决了硅基材料与电解液发生副反应的问题,从而使电池的循环性能得以有效提高。进而电池在满足较高有效容量及较快充放电速率的基础上,其循环性能更佳,比如循环效率及循环寿命均较高。(The invention provides a silicon-carbon composite material and a preparation method and application thereof. The silicon-carbon composite material comprises: the device comprises a hollow silicon spherical core layer, a silicon oxide shell layer and a graphene shell layer. The silicon oxide shell layer is coated on the outer surface of the hollow silicon sphere core layer; the graphene shell layer is coated on the outer surface of the silicon oxide shell layer far away from the hollow silicon sphere core layer. The composite material is used as the cathode material of the lithium ion battery, the conductivity of the material is higher, the volume effect is effectively improved, and more importantly, the problem of side reaction between the silicon-based material and the electrolyte is effectively solved, so that the cycle performance of the battery is effectively improved. On the basis of meeting the requirements of higher effective capacity and faster charge-discharge rate, the battery has better cycle performance, such as higher cycle efficiency and longer cycle life.)

1. A silicon carbon composite, comprising:

a hollow silicon sphere core layer;

the silicon oxide shell layer is coated on the outer surface of the hollow silicon sphere core layer;

and the graphene shell layer is coated on the outer surface of the silicon oxide shell layer far away from the hollow silicon sphere core layer.

2. The silicon-carbon composite material as claimed in claim 1, wherein the thickness of the silicon oxide shell layer is 5 to 10 nm; preferably, the silicon oxide shell layer is formed by oxidation reaction of an oxidant and silicon on the surface of the hollow silicon sphere; preferably, the oxidant is a gaseous oxidant; more preferably, the gaseous oxidant is oxygen or air.

3. The silicon-carbon composite material according to claim 1 or 2, wherein the hollow silicon sphere core layer has a particle size of 300 to 500nm and a wall thickness of 20 to 30 nm.

4. The silicon-carbon composite material according to any one of claims 1 to 3, wherein the graphene shell layer has a thickness of 0.35 to 1.2 nm; preferably, the graphene shell layer is formed by performing a hydrothermal reduction reaction on graphene oxide on the surface of the silicon oxide shell layer.

5. A method for preparing a silicon-carbon composite material according to any one of claims 1 to 4, characterized in that it comprises the following steps:

step S1, providing a hollow silicon ball, and coating a silicon oxide shell layer on the outer surface of the hollow silicon ball so as to form a hollow silicon ball core layer with the surface coated with the silicon oxide shell layer;

and step S2, coating a graphene shell layer on the outer surface of the silicon oxide shell layer far away from the hollow silicon sphere core layer, and further forming the silicon-carbon composite material.

6. The method for preparing a composite material according to claim 5, wherein the step S1 includes:

step S11, providing the hollow silicon spheres;

step S12, mixing the hollow silicon spheres with an oxidant to make silicon on the surfaces of the hollow silicon spheres perform oxidation reaction with the hollow silicon spheres, and further forming the hollow silicon sphere core layer with the surface coated with the silicon oxide shell layer, which is marked as Si/SiO₂An intermediate material.

7. The preparation method according to claim 6, wherein in the oxidation reaction process, the reaction temperature is 120-200 ℃, and the reaction time is 12-48 h; preferably, the oxidant is a gaseous oxidant; more preferably, the oxidant is oxygen or air; preferably, the flow rate of the gas oxidant is 0.25-4 mL/min.

8. The production method according to claim 6 or 7, wherein the step S2 includes:

step S21, mixing the Si/SiO₂Mixing the intermediate material, the graphene oxide and the surface modifier to form a mixed solution;

and step S22, adding a hydrazine hydrate solution into the mixed solution to perform a hydrothermal reduction reaction, thereby obtaining the silicon-carbon composite material.

9. The method of claim 8, wherein the Si/SiO is present in a coating solution₂The weight ratio of the intermediate material, the graphene oxide and the surface modifier is (0.8-2.4): (0.25-1): 1-6); preferably, the mass concentration of the hydrazine hydrate solution is 4-20%; preferably, in the hydrothermal reduction reaction process, the reaction temperature is 180-220 ℃, and the reaction time is 12-48 h; preferably, the surface modifier is polyvinylpyrrolidone and/or cetyltrimethylammonium bromide.

10. The method for preparing a composite material according to claim 6, wherein the step S11 includes:

mixing a silicon source, a template agent, a surfactant, a cosurfactant and water to form mixed emulsion, adding a catalyst into the mixed emulsion to perform hydrolysis reaction to obtain hollow SiO containing the template agent inside₂Then washing to remove the template agent to obtain the hollow SiO₂；

Subjecting the hollow SiO₂And mixing the hollow silicon spheres with a reducing agent and carrying out reduction reaction to obtain the hollow silicon spheres.

11. The method according to claim 10, wherein the silicon source is tetraethoxysilane; preferably, the template agent is one or more of xylene, polyethylene glycol octyl phenyl ether and TWEEN 80; preferably, the catalyst is ammonia water or hydrochloric acid; preferably the surfactant is sodium lauryl sulfate; preferably, the cosurfactant is n-butanol; preferably, in the washing process, the washing agent is ethanol, petroleum ether, kerosene, gasoline, toluene or diethyl ether;

preferably, the weight ratio of the silicon source to the template is (3:1) - (1: 3);

preferably, the volume ratio of the cosurfactant to the water is 1 (2-8);

preferably, the weight ratio of the surfactant to the silicon source is (2:1) - (1: 2);

more preferably, the reaction temperature in the hydrolysis process is 40-60 ℃, and the reaction time is 15-20 min.

12. The preparation method according to claim 10, wherein during the reduction reaction, the reducing agent is one or more of magnesium, sodium borohydride, potassium borohydride, lithium aluminum hydride and sodium sulfite; preferably, the reaction temperature in the reduction reaction process is 650-800 ℃, and the reaction time is 3-6 h.

13. A lithium ion battery negative electrode material, which is characterized by comprising the silicon-carbon composite material of any one of claims 1 to 4 or the silicon-carbon composite material prepared by the preparation method of any one of claims 5 to 12.

Technical Field

The invention relates to the field of lithium batteries, in particular to a silicon-carbon composite material and a preparation method and application thereof.

Background

The silicon negative electrode material has extremely high theoretical lithium storage capacity (3590mAh g)^-1) And the lithium alloying voltage is suitable and the production resources are rich, and the like, and the lithium alloying material is considered as a most potential new generation cathode material, but the application of the lithium alloying material is limited by the problems of structural damage, capacity loss and life decay caused by the huge volume change in the charging and discharging process, slow charging rate caused by poor conductivity and the like. In order to solve the inherent defects of the silicon negative electrode material, scientists have conducted a great deal of research, wherein the nano hollow structure is a very effective method in overcoming the problem of volume expansion; in addition, compounding silicon with other materials and utilizing the physical properties of the other materials to improve the electrochemical performance of the silicon negative electrode material is an effective way to solve the problem of poor conductivity. For example:

(1) "hollow Structure" -Preparation of SiO₂ Hollow Nanospheres by Using a Template Method and Their Heat-insulating Property[J]Shandong Chemical Industry,2017, the academic paper provides a method for preparing a hollow structure material, in which styrene, PVP and ethyl orthosilicate are used as raw materials, and hollow silica is prepared through a template. The method mainly comprises the following steps: firstly, mixing raw materials according to a certain proportion to prepare a polystyrene hard template; repeatedly adding tetraethoxysilane and ammonia water into the solution containing the hard template for many times, reacting for a period of time, and cooling to room temperature; and thirdly, centrifugally separating and drying to finally obtain the hollow silicon dioxide. Hard template method as main preparation method of nano hollow silicon structureBesides a series of other problems such as high-temperature removal or chemical etching, the treatment cost is high, even toxic chemical reagents are used, and the process has the problems of environmental protection and safety.

(2) "composite Material" -Cu₅J. Power Sources,2006,153(2):371-₅A Si-Si/C composite material. The preparation method mainly comprises the following steps: firstly, mixing copper powder and silicon powder in a vacuum ball milling tank according to a certain proportion, and ball milling under the atmosphere of argon to obtain Cu₅Si-Si; ② mixing Cu₅Reacting the Si-Si mixture for 4 hours at 600 ℃ under the argon atmosphere; thirdly, mixing the product of the last step with graphite, and continuously ball-milling to finally obtain Cu₅A Si-Si/C composite material.

In summary, in the prior art, the problems of serious volume effect and poor conductivity of the silicon-based negative electrode material are mainly solved by adopting a structural design and material compounding manner. However, the above two methods cannot effectively solve the problem of side reaction between the silicon material and the electrolyte, resulting in poor cycle performance of the battery.

Therefore, how to more effectively reduce the side reaction between the silicon negative electrode material and the electrolyte, and accordingly improve the cycle performance of the lithium battery, is a problem to be solved in the art.

Disclosure of Invention

The invention mainly aims to provide a silicon-carbon composite material and a preparation method and application thereof, and aims to solve the problem that the cycle performance of a lithium ion battery is poor when a silicon-based material is used as a negative electrode material of the lithium ion battery in the prior art.

In order to achieve the above object, according to one aspect of the present invention, there is provided a silicon carbon composite. The silicon-carbon composite material comprises: a hollow silicon sphere core layer; the silicon oxide shell layer is coated on the outer surface of the hollow silicon sphere core layer; and the graphene shell layer is coated on the outer surface of the silicon oxide shell layer far away from the hollow silicon sphere core layer.

Further, the thickness of the silicon oxide shell layer is 5-10 nm; preferably, the silicon oxide shell layer is formed by oxidation reaction of an oxidant and silicon on the surface of the hollow silicon sphere; preferably, the oxidant is a gaseous oxidant; more preferably, the gaseous oxidant is oxygen or air.

Furthermore, the particle size of the hollow silicon spherical core layer is 300-500 nm, and the wall thickness is 20-30 nm.

Further, the thickness of the graphene shell layer is 0.35-1.2 nm; preferably, the graphene shell layer is formed by performing a hydrothermal reduction reaction on the surface of the silicon oxide shell layer through graphene oxide.

Further, the preparation method comprises the following steps: step S1, providing a hollow silicon ball, and coating a silicon oxide shell layer on the outer surface of the hollow silicon ball so as to form a hollow silicon ball core layer with the surface coated with the silicon oxide shell layer; and step S2, coating a graphene shell layer on the outer surface of the silicon oxide shell layer far away from the hollow silicon sphere core layer, and further forming the silicon-carbon composite material.

Further, step S1 includes: step S11, providing hollow silicon balls; step S12, mixing the hollow silicon spheres with an oxidant to make silicon on the surfaces of the hollow silicon spheres perform oxidation reaction with the hollow silicon spheres, and further forming a hollow silicon sphere core layer with a surface coated with a silicon oxide shell layer, which is marked as Si/SiO₂An intermediate material.

Further, in the oxidation reaction process, the reaction temperature is 120-200 ℃, and the reaction time is 12-48 h; preferably, the oxidant is a gaseous oxidant; more preferably, the oxidant is oxygen or air; preferably, the flow rate of the gas oxidant is 0.25-4 mL/min.

Further, step S2 includes: step S21, mixing Si/SiO₂Mixing the intermediate material, the graphene oxide and the surface modifier to form a mixed solution; and step S22, adding a hydrazine hydrate solution into the mixed solution to perform a hydrothermal reduction reaction, thereby obtaining the silicon-carbon composite material.

Further, Si/SiO₂The weight ratio of the intermediate material, the graphene oxide and the surface modifier is (0.8-2.4): (0.25-1): 1-6); preferably, the mass concentration of the hydrazine hydrate solution is 4-20%; preferably, in the hydrothermal reduction reaction process, the reaction temperature is 180-220 ℃, and the reaction time is 12-48 h; preferably, the surface modifier is polyvinylpyrrolidone and/orCetyl trimethylammonium bromide.

Further, step S11 includes: mixing a silicon source, a template agent, a surfactant, a cosurfactant and water to form mixed emulsion, adding a catalyst into the mixed emulsion to perform hydrolysis reaction to obtain hollow SiO containing the template agent inside₂Then washing to remove the template agent to obtain hollow SiO₂(ii) a Hollow SiO₂And mixing with a reducing agent and carrying out reduction reaction to obtain the hollow silicon spheres.

Further, the silicon source is tetraethoxysilane; preferably, the template agent is one or more of xylene, polyethylene glycol octyl phenyl ether and TWEEN 80; preferably, the catalyst is ammonia water or hydrochloric acid; preferably the surfactant is sodium lauryl sulfate; preferably, the cosurfactant is n-butanol; preferably, in the washing process, the detergent is ethanol, petroleum ether, kerosene, gasoline, toluene or diethyl ether; preferably, the weight ratio of the silicon source to the template is (3:1) - (1: 3); preferably, the volume ratio of the cosurfactant to the water is 1 (2-8); preferably, the weight ratio of the surfactant to the silicon source is (2:1) - (1: 2); more preferably, the reaction temperature in the hydrolysis process is 40-60 ℃, and the reaction time is 15-20 min.

Further, in the reduction reaction process, the reducing agent is one or more of magnesium, sodium borohydride, potassium borohydride, lithium aluminum hydride and sodium sulfite; preferably, the reaction temperature in the reduction reaction process is 650-800 ℃, and the reaction time is 3-6 h.

In order to achieve the above object, according to one aspect of the present invention, there is provided a lithium ion battery anode material, including the above silicon-carbon composite material, or including the silicon-carbon composite material prepared by the above preparation method.

The composite material is used as the cathode material of the lithium ion battery, the conductivity of the material is higher, the volume effect is effectively improved, and more importantly, the problem of side reaction between the silicon-based material and the electrolyte is effectively solved, so that the cycle performance of the battery is effectively improved. On the basis of meeting the requirements of higher effective capacity and faster charge-discharge rate, the battery has better cycle performance, such as higher cycle efficiency and longer cycle life.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:

FIG. 1 shows a process flow diagram of a method of making a silicon carbon composite according to one embodiment of the invention;

FIG. 2 shows a TEM image of a silicon-carbon composite material in example 1 of the present invention;

fig. 3 shows an XRD pattern of the silicon carbon composite in example 1 of the present invention.

Detailed Description

It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.

As described in the background section, when the silicon-based material is used as a negative electrode material of a lithium ion battery in the prior art, there is a problem that the cycle performance of the battery is poor. In order to solve this problem, the present invention provides a silicon carbon composite material comprising: the device comprises a hollow silicon spherical core layer, a silicon oxide shell layer and a graphene shell layer. The silicon oxide shell layer is coated on the outer surface of the hollow silicon sphere core layer; the graphene shell layer is coated on the outer surface of the silicon oxide shell layer far away from the hollow silicon sphere core layer.

According to the silicon-carbon composite material, the outer surface of the hollow silicon ball is coated with the silicon oxide shell layer, and the silicon oxide forms the protective layer of the hollow silicon ball, so that the silicon-carbon composite material is higher in adaptability to the hollow silicon ball and more stable in practical application environment. Thus, when the silicon-carbon composite material is used as a negative electrode material of a lithium ion battery, the penetration of the electrolyte can be effectively prevented, so that the side reaction between the silicon active material and the electrolyte is reduced, and the cycle performance of the battery is improved. In addition, the hollow silicon spheres have the excellent performances of small density, large specific surface area, good thermal stability and large internal space. On one hand, the volume change in the process of lithium ion intercalation-deintercalation can be effectively buffered, and further the pulverization and agglomeration of silicon active substances are effectively avoided, so that the cycle life of the battery is prolonged. On the other hand, the effective diffusion distance of lithium ions can be shortened, so that the effective capacity of the battery is improved. The graphene has excellent conductivity, can improve the conductivity of the material, and can effectively relieve stress generated in the volume expansion process of silicon, so that the charge and discharge rate of the battery is improved. The silicon oxide shell layer is used as the intermediate layer of the hollow silicon sphere core layer and the graphene layer, and the excellent performances of the hollow silicon spheres and the graphene layer on the outer layer can be well balanced.

In a word, when the composite material is used as a lithium ion battery cathode material, the conductivity of the material is higher, the volume effect is effectively improved, and more importantly, the problem of side reaction between a silicon-based material and an electrolyte is effectively solved, so that the cycle performance of the battery is effectively improved. On the basis of meeting the requirements of higher effective capacity and faster charge-discharge rate, the battery has better cycle performance, such as higher cycle efficiency and longer cycle life.

Preferably, the thickness of the silicon oxide shell layer is 20-30 nm. Like this, the suitability of silicon oxide shell layer and cavity silicon sphere nuclear layer and graphite alkene layer is all better, and combined material's structural integrity is better, on keeping the above-mentioned excellent performance of cavity silicon sphere nuclear layer and graphite alkene layer basis, has reduced the side reaction of electrolyte with the silicon active material more effectively to the circulation efficiency of battery has further been improved. Preferably, the silicon oxide shell layer is formed by oxidation reaction of the oxidizing agent and silicon on the surface of the hollow silicon sphere. Preferably, the oxidant is a gaseous oxidant. More preferably, the gaseous oxidant is oxygen or air. Oxidizing agent and silicon on the surface of the hollow silicon ball to generate silicon oxide in situ. Based on this, the silicon oxide layer is stably and closely coated on the surface of the hollow silicon sphere, so that a hollow silicon sphere core layer with a surface coated with a silicon oxide shell layer is formed, the binding force between the two layers is larger, and the coating integrity and stability are better, so that the permeation of electrolyte is further prevented, the side reaction of the electrolyte and the active silicon material is reduced, and the cycle efficiency of the battery is further improved. In addition, oxygen or air is used as an oxidant, so that the raw materials are more easily obtained, and the coating process is safer, more convenient and more environment-friendly.

In order to further improve the performance stability of the hollow silicon sphere core layer, the particle size of the hollow silicon sphere core layer is preferably 300-500 nm, and the wall thickness is preferably 20-30 nm.

Preferably, the thickness of the graphene shell layer is 0.35-1.2 nm. The graphene shell layer is formed by carrying out hydrothermal reduction reaction on graphene oxide on the surface of the silicon oxide shell layer. Therefore, the graphene shell layer can be stably coated on the outer surface of the silicon oxide shell layer, and the graphene shell layer and the silicon oxide shell layer form a compact network conductive structure, so that the conductivity of the material is further improved. Meanwhile, the mode can also effectively relieve the stress generated in the volume expansion process of the silicon, and is favorable for further improving the charge and discharge rate of the battery. In addition, silicon particles are deposited on graphene, and the particles are adsorbed on the graphene by van der waals force between the particles to enhance mutual acting force, so that the function of reducing the adhesive can be achieved. The thickness of the graphene shell layer can be detected by a JY-HR 800 Raman spectrometer.

The invention also provides a preparation method of the silicon-carbon composite material, as shown in figure 1, the preparation method comprises the following steps: step S1, providing a hollow silicon ball, and coating a silicon oxide shell layer on the outer surface of the hollow silicon ball so as to form a hollow silicon ball core layer with the surface coated with the silicon oxide shell layer; and step S2, coating a graphene shell layer on the outer surface of the silicon oxide shell layer far away from the hollow silicon sphere core layer, and further forming the silicon-carbon composite material.

Based on the above reasons, the silicon-carbon composite material of the present invention has the advantages that the outer surface of the hollow silicon sphere is coated with the silicon oxide shell layer, and the silicon oxide is used as the protective layer of the hollow silicon sphere, such that the silicon-carbon composite material has high adaptability to the hollow silicon sphere, and is stable in practical application environment. Thus, when the silicon-carbon composite material is used as a negative electrode material of a lithium ion battery, the penetration of the electrolyte can be effectively prevented, so that the side reaction between the silicon active material and the electrolyte is reduced, and the cycle performance of the battery is improved. In addition, the hollow silicon spheres have the excellent performances of small density, large specific surface area, good thermal stability and large internal space. On one hand, the volume change in the process of lithium ion intercalation-deintercalation can be effectively buffered, and further the pulverization and agglomeration of silicon active substances are effectively avoided, so that the cycle life of the battery is prolonged. On the other hand, the effective diffusion distance of lithium ions can be shortened, so that the effective capacity of the battery is improved. The graphene has excellent conductivity, can improve the conductivity of the material, and can effectively relieve stress generated in the volume expansion process of silicon, so that the charge and discharge rate of the battery is improved. The silicon oxide shell layer is used as the middle layer of the hollow silicon sphere core layer and the graphene layer, and the performances of the hollow silicon spheres and the graphene layer on the outer layer can be well balanced. The thickness of each layer in the invention is detected by a JY-HR 800 Raman spectrometer.

Preferably, step S1 includes: step S11, providing hollow silicon balls; step S12, mixing the hollow silicon spheres with an oxidant to make silicon on the surfaces of the hollow silicon spheres perform oxidation reaction with the hollow silicon spheres, and further forming a hollow silicon sphere core layer with a surface coated with a silicon oxide shell layer, which is marked as Si/SiO₂An intermediate material. Thus, the oxidizing agent and the silicon on the surface of the hollow silicon ball are subjected to oxidation reaction, and the silicon oxide is generated in situ. Based on the operation, the silicon oxide layer is stably and tightly coated on the surface of the hollow silicon sphere, so that a hollow silicon sphere core layer with a surface coated with a silicon oxide shell layer is formed, the binding force between the two layers is larger, and the coating integrity and stability are better, so that the permeation of electrolyte is further prevented, the side reaction of the electrolyte and the active silicon material is reduced, and the cycle efficiency of the battery is further improved.

In order to further improve the performance stability of the silicon dioxide shell layer, preferably, in the oxidation reaction process, the reaction temperature is 120-200 ℃, and the reaction time is 1-2 h; preferably, the oxidant is a gaseous oxidant; more preferably, the oxidant is oxygen or air; preferably, the flow rate of the gas oxidant is 0.25-4 mL/min. Oxygen or air is used as an oxidant, so that the raw materials are more easily obtained, and the operation is safer and simpler.

Preferably, step S2 includes: step S21, mixing Si/SiO₂Mixing the intermediate material, the graphene oxide and the surface modifier to form a mixed solution; step S22, adding hydrazine hydrate solution to the mixed solution to perform hydrothermal reduction reaction, and furtherAnd obtaining the silicon-carbon composite material. The invention firstly prepares Si/SiO₂Mixing the intermediate material, the graphene oxide and the surface modifier. Wherein the surface modifier can be for SiO₂Hydrophilic modification is carried out, and the surface of the graphene oxide has a large number of hydrophilic groups such as-OH and-COOH, so that the graphene oxide and SiO on the surface of the silicon oxide layer can be prepared₂The particles are tightly adhered, and then under the subsequent hydrothermal reduction reaction, the graphene oxide is reduced on the surface of the silicon oxide layer to form a tightly-connected and compact graphene layer.

In order to further improve the coating stability and integrity of the silicon dioxide shell layer and the graphene layer, Si/SiO is preferred₂The weight ratio of the intermediate material, the graphene oxide and the surface modifier is (0.8-2.4): (0.25-1): 1-6); preferably, the mass concentration of the hydrazine hydrate solution is 4-20%; preferably, in the hydrothermal reaction process, the reaction temperature is 180-220 ℃, and the reaction time is 12-48 h; preferably, the surface modifier is polyvinylpyrrolidone (PVP) and/or cetyltrimethylammonium bromide.

Preferably, step S11 includes: mixing a silicon source, a template agent, a surfactant, a cosurfactant and water to form mixed emulsion, adding a catalyst into the mixed emulsion to perform hydrolysis reaction to obtain hollow SiO containing the template agent inside₂Then washing to remove the template agent to obtain hollow SiO₂(ii) a Hollow SiO₂And mixing with a reducing agent and carrying out reduction reaction to obtain the hollow silicon spheres. Thus, the hollow structure template is easier to construct, and the hollow SiO is₂The template that inside contained gets rid of more conveniently, and more green is difficult for leading to breaking of spherical shell after the template is got rid of simultaneously, and does not need complicated equipment. The method is simpler, has low cost, is easy for industrial production, and is suitable for large-scale production.

In order to further optimize the structure of the hollow silicon spheres, the silicon source is preferably tetraethoxysilane. Preferably, the templating agent is one or more of xylene, octyl phenyl ether of polyethylene glycol, and TWEEN 80. Preferably, the catalyst is ammonia or hydrochloric acid, and more preferably, the mass concentration of ammonia is 25%. Preferably, the surfactant is sodium lauryl sulfate. Preferably, the co-surfactant is n-butanol. Therefore, the average particle size of the hollow silicon spheres can be controlled to be 310-510 nm more effectively on the basis of ensuring the structural integrity of the hollow silicon spheres. Preferably, in the washing process, the detergent is alcohol, petroleum ether, kerosene, gasoline, toluene or diethyl ether. Preferably, the weight ratio of the silicon source to the template is (3:1) to (1:3), more preferably (2:1) to (1: 1); preferably, the volume ratio of the cosurfactant to the water is 1 (2-8); preferably, the weight ratio of the surfactant to the silicon source is (2:1) - (1: 2); more preferably, the reaction temperature in the hydrolysis process is 40-60 ℃, and the reaction time is 15-20 h. More preferably, the silicon source, the template agent, the surfactant, the co-surfactant and water are preheated and stirred at 30 to 60 ℃ when they are mixed to form a mixed emulsion.

Preferably, in the reduction reaction process, the reducing agent is magnesium, sodium borohydride, potassium borohydride, lithium aluminum hydride or sodium sulfite; the reaction temperature in the reduction reaction process is 650-800 ℃, and the reaction time is 3-6 h. Based on the above operation, the hollow SiO₂Can be more stably reduced into hollow silicon spheres, and the structural performance of the hollow silicon spheres can be better maintained.

The invention also provides a lithium ion battery cathode material which comprises the silicon-carbon composite material or the silicon-carbon composite material prepared by the preparation method.

Based on the above reasons, the composite material is used as the lithium ion battery cathode material, the conductivity of the material is higher, the volume effect is effectively improved, and more importantly, the problem of side reaction between the silicon-based material and the electrolyte is effectively solved, so that the electrical property of the battery is effectively improved, the battery has better cycle performance on the basis of higher effective capacity and high charge-discharge rate, for example, the cycle efficiency and the cycle life are higher.

The present application is described in further detail below with reference to specific examples, which should not be construed as limiting the scope of the invention as claimed.

Example 1

The preparation process of the silicon-carbon composite material comprises the following steps:

1. 4.5g of tetraethoxysilane are weighedAnd 4.5g of dimethylbenzene to prepare an oil phase, then 10g of surfactant lauryl sodium sulfate, 35mL of cosurfactant n-butanol and 140mL of deionized water are weighed to prepare a mixed solution, and the mixed solution is preheated and stirred at 50 ℃. Dripping the oil phase into the mixed solution, stirring to form colorless transparent microemulsion, immediately adding 4mL ammonia water (mass concentration is 30 wt%), reacting at 50 deg.C for 15min, centrifuging the solution to separate white precipitate, washing with deionized water and ethanol for 3 times, and vacuum drying at 60 deg.C to obtain hollow SiO₂. Wherein the weight ratio of the surfactant, the silicon source and the template agent is 2.2:1: 1; the volume ratio of the cosurfactant to the deionized water is 1: 4; the catalyst concentration was 5.5%.

2. Weighing 1.28g of the hollow SiO₂Mixing the mixture with 1g of reducing agent magnesium powder in a glove box, transferring the mixture into a tubular furnace, and reacting for 6 hours at 650 ℃ under the argon atmosphere to obtain the hollow silicon spheres. Wherein the average particle diameter of the hollow silicon spheres is 305 nm.

3. After the temperature of the tube furnace is cooled to the room temperature, introducing oxygen at the rate of 1L/min, reheating to 150 ℃, preserving heat for 1h, cooling and collecting the product to obtain Si/SiO₂An intermediate material.

4. 0.8g of the above Si/SiO solid was weighed₂And mixing the intermediate material with 0.5g of graphene oxide, stirring for 30min, keeping the temperature of 25 ℃ for ultrasonic treatment for 1h, adding 1g of PVP into the mixture, and continuing stirring for 1 h. Transferring the mixed solution into a vacuum reaction kettle, measuring 2mL of hydrazine hydrate, adding water to dilute the hydrazine hydrate to 20mL, adding the hydrazine hydrate into the reaction kettle, putting the reaction kettle into a forced air drying oven, reacting for 48 hours at 180 ℃, performing centrifugal separation, and collecting a product to obtain the silicon-carbon composite material Si/SiO₂/G。

The thickness of the hollow silicon spherical core layer is 20nm, the thickness of the silicon oxide shell layer is 5nm, and the average thickness of the graphene shell layer is 0.3 nm. FIG. 2 shows a TEM image of a silicon-carbon composite material in example 1 of the present invention; fig. 3 shows an XRD pattern of the silicon carbon composite in example 1 of the present invention. The model of a Transmission Electron Microscope (TEM) is JEM-2100F, and the magnification is 300 k; the X-ray powder diffraction analysis (XRD) model is BRYKER D8.

Mixing the silicon-carbon composite material with a conductive agent (Super P) and a polymer binder (polyvinylidene fluoride) according to a weight ratioPreparing electrode plates of the button cell at a ratio of 8:1:1, assembling the electrode plates into the button cell, and testing the initial capacity of the button cell to 1646 mAh.g by using an 8-channel cell tester BTS-5V^-1After 100 cycles, the concentration of the active ingredient is still 1040mAh g^-1The above. Charge and discharge rate: can still maintain 750 mAh.g under the 3C multiplying power^-1The above.

Example 2

The difference from example 1 is that:

in the step 1, the using amount of the tetraethoxysilane is 9 g; the dosage of the sodium dodecyl sulfate is 12 g; the dosage of the n-butanol is 40 mL; the dosage of the deionized water is 120 mL; preheating and stirring at 40 ℃; the dosage of ammonia water is 3 mL; the hydrolysis reaction temperature was 60 ℃. Wherein the weight ratio of the surfactant, the silicon source and the template agent is 2.7:2: 1; the volume ratio of the cosurfactant to the deionized water is 1: 3; the catalyst concentration was 7%.

In the step 2, the using amount of the magnesium powder is 2g, the reaction temperature is 700 ℃, and the reaction time is 5 hours. Wherein the average particle diameter of the hollow silicon spheres is 405 nm.

In the step 3, the introduction amount of oxygen is 3L/min, and the reaction temperature is 120 ℃.

In the step 4, the using amount of the graphene oxide is 0.3 g; the consumption of PVP is 2 g; adding deionized water into 2mL of hydrazine hydrate to dilute to 12 mL; in the hydrothermal reduction reaction, the reaction temperature is 200 ℃ and the reaction time is 24 hours.

The thickness of the hollow silicon spherical core layer is 25nm, the thickness of the silicon oxide shell layer is 5nm, and the average thickness of the graphene shell layer is 0.3 nm.

Preparing the silicon-carbon composite material, a conductive agent (Super P) and a high polymer binder (polyvinylidene fluoride) into electrode plates of a button cell according to the weight ratio of 8:1:1, assembling the electrode plates into the button cell, and testing the initial capacity of the button cell to 1760 mAh.g by using a cell analyzer^-1And after 100 cycles, the concentration of the active ingredient is still 1100mAh g^-1The above. Charge and discharge rate: can still maintain 845mAh g under the 3C multiplying power^-1The above.

Example 3

The difference from example 1 is that:

in the step 1, the using amount of the tetraethoxysilane is 9 g; the dosage of the sodium dodecyl sulfate is 15 g; the dosage of the n-butanol is 20 mL; the dosage of the deionized water is 160 mL; preheating and stirring at 60 ℃; the hydrolysis reaction temperature was 60 ℃. Wherein the weight ratio of the surfactant, the silicon source and the template agent is 3.3:2: 1; the volume ratio of the cosurfactant to the deionized water is 1: 8; the catalyst concentration was 8%.

In the step 2, the using amount of the magnesium powder is 1.5g, and the reaction time is 4 h. Wherein the average particle diameter of the hollow silicon spheres is 405 nm.

In the step 3, the introduction amount of oxygen was 0.5L/min, and the reaction temperature was 200 ℃.

In the step 4, the using amount of the graphene oxide is 0.25 g; the consumption of PVP is 3 g; the using amount of hydrazine hydrate is 3 mL; in the hydrothermal reduction reaction, the reaction temperature is 220 ℃ and the reaction time is 12 hours.

The thickness of the hollow silicon spherical core layer is 25nm, the thickness of the silicon oxide shell layer is 10nm, and the average thickness of the graphene shell layer is 0.6 nm.

Preparing the silicon-carbon composite material, a conductive agent (Super P) and a high polymer binder (polyvinylidene fluoride) into electrode plates of the button cell according to the weight ratio of 8:1:1, assembling the electrode plates into the button cell, and testing the initial capacity of the button cell to 1546mAh g by using a cell analyzer^-1After 100 cycles, the concentration of the active component is still 950mAh g^-1The above. Charge and discharge rate: can still maintain 687mAh g under the 3C multiplying power^-1The above.

Example 4

The difference from example 1 is that:

in the step 1, the using amount of the tetraethoxysilane is 13.5 g; the dosage of the sodium dodecyl sulfate is 8 g; the dosage of the n-butanol is 40 mL; the dosage of the deionized water is 120 mL; preheating and stirring at 30 ℃; the dosage of ammonia water is 2 mL; the hydrolysis reaction temperature was 40 ℃. Wherein the weight ratio of the surfactant, the silicon source and the template agent is 1.8:3: 1; the volume ratio of the cosurfactant to the deionized water is 1: 3; the catalyst concentration was 4.5%.

In the step 2, the using amount of the magnesium powder is 3g, the reaction temperature is 700 ℃, and the reaction time is 3 hours. Wherein the average particle diameter of the hollow silicon spheres is 505 nm.

In the step 3, the introduction amount of oxygen was 0.25L/min, and the reaction temperature was 160 ℃.

In the step 4, the using amount of the graphene oxide is 1 g; the consumption of PVP is 5 g; the amount of hydrazine hydrate used was 1 mL.

The thickness of the hollow silicon spherical core layer is 30nm, the thickness of the silicon oxide shell layer is 10nm, and the average thickness of the graphene shell layer is 0.6 nm.

Preparing the silicon-carbon composite material, a conductive agent (Super P) and a high polymer binder (polyvinylidene fluoride) into electrode plates of a button cell according to the weight ratio of 8:1:1, assembling the electrode plates into the button cell, and testing the initial capacity of the button cell to reach 1532mAh g by using a cell analyzer^-1After 100 cycles, the concentration of the active ingredient is still 840mAh g^-1The above. Charge and discharge rate: can still maintain 689mAh g under 3C multiplying power^-1The above.

Example 5

The difference from example 1 is that:

in the step 1, the dosage of the dimethylbenzene is 9 g; the dosage of the sodium dodecyl sulfate is 5 g; the dosage of n-butanol is 30 mL; the dosage of the deionized water is 100 mL; the dosage of ammonia water is 1 mL; the hydrolysis reaction temperature was 40 ℃. Wherein the weight ratio of the surfactant, the silicon source and the template agent is 1.1:1: 2; the volume ratio of the cosurfactant to the deionized water is 1: 3.3; the catalyst concentration was 4%.

In step 2, the reaction temperature was 800 ℃. Wherein the average particle diameter of the hollow silicon spheres is 305 nm.

In the step 3, the introduction amount of oxygen is 4L/min, and the reaction temperature is 180 ℃.

In the step 4, the using amount of the graphene oxide is 0.6 g; the consumption of PVP is 6 g; the using amount of hydrazine hydrate is 4 mL; in the hydrothermal reduction reaction, the reaction time was 24 hours.

The thickness of the hollow silicon spherical core layer is 20nm, the thickness of the silicon oxide shell layer is 10nm, and the thickness of the graphene shell layer is 0.3.

Preparing the silicon-carbon composite material, a conductive agent (Super P) and a high polymer binder (polyvinylidene fluoride) into electrode plates of the button cell according to the weight ratio of 8:1:1, assembling the electrode plates into the button cell, and testing the initial capacity of the button cell to 1360mAh g by using a cell analyzer^-1After 100 cycles, the concentration of the active ingredient is still maintained at 720mAh g^-1The above. Charge and discharge rate: can still maintain 610mAh g under the 3C multiplying power^-1The above.

Comparative example 1

Cu₅J.Power Sources,2006,153(2) 371-^-1And after 40 cycles, the concentration is kept at 456mAh g^-1The above.

The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes will occur to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.