Silicon carbon-graphite negative electrode material and preparation method thereof

Abstract

The present invention relates to the technical field of new energy batteries, and discloses a silicon-carbon-graphite negative electrode material and a preparation method thereof; a silicon-carbon-graphite negative electrode material, comprising an inner layer of SiO2, an outer layer of graphite, and g-C3N4 bonded between the inner layer and the outer layer. The present application utilizes a silicon-carbon-graphite negative electrode material forming a core-shell structure, and uniformly coats the surface of silicon dioxide with a graphite carbon layer, which can avoid contact with an electrolyte, thereby avoiding irreversible reactions generated during use. The present application bonds carbon nitride between nano-silicon dioxide and graphite, and utilizes the layered structure of carbon nitride to form a continuous, uniformly porous outward-spreading structure, which can well buffer the volume changes present during charge and discharge, and utilizes the structure of carbon nitride to further increase the specific surface area of ​​the negative electrode material. In addition, a tight bonding structure is formed between carbon nitride, silicon dioxide and graphite, which can avoid the pulverization and shedding problems of silicon materials, thereby improving the cycle stability of the electrode.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy batteries, and in particular to a silicon-carbon-graphite negative electrode material and a preparation method thereof. Background Art

[0002] Currently, the market has high requirements for the energy density of lithium-ion batteries. Among them, the negative electrode material is the key material of lithium-ion batteries. The capacity improvement of the negative electrode material can greatly increase the specific capacity of the whole battery. Therefore, the negative electrode material determines the improvement of battery performance to a large extent.

[0003] Silicon has the advantages of high theoretical capacity and abundant reserves, as well as a theoretical specific capacity that is ten times that of traditional graphite materials, making it a potential negative electrode material for lithium-ion batteries.

[0004] Then, in actual applications, silicon produces a volume expansion of up to 300% during the charging and discharging process. The problem caused by its huge volume expansion is that the huge mechanical stress it produces causes the silicon particles to crack and shatter, thus limiting the application areas of silicon negative electrodes.

[0005] Therefore, how to solve the volume expansion problem caused by the silicon negative electrode is a problem that needs to be solved at present. Summary of the invention

[0006] <Technical Problems Solved by the Invention>

[0007] The invention is used to solve the problem in the prior art that the battery capacity is affected due to the volume expansion of the silicon negative electrode.

[0008] <Technical solution adopted by the present invention>

[0009] In view of the above technical problems, the object of the present invention is to provide a silicon-carbon-graphite negative electrode material and a preparation method thereof.

[0010] The specific contents are as follows:

[0011] First, the present invention provides a silicon-carbon-graphite negative electrode material, including an inner layer of SiO2, an outer layer of graphite, and g-C3N4 bonded between the inner layer and the outer layer.

[0012] Second, the present invention provides a method for preparing the aforementioned silicon-carbon-graphite negative electrode material, comprising the following steps:

[0013] S1 uses silicon source and hexadecyltrimethylammonium bromide as raw materials to obtain mesoporous silica through a sol-gel method;

[0014] S2 disperses g-C3N4 in water to form a dispersion, adds a silane coupling agent and mesoporous silica to the dispersion, and transfers the dispersion to a Teflon-lined stainless steel autoclave to obtain an intermediate after reaction;

[0015] S3: adding graphite, dopamine hydrochloride and ammonium persulfate to the tris solution, mixing and reacting to obtain dopamine-modified graphite;

[0016] S4: adding the intermediate into water and dispersing to obtain a dispersion; then dissolving polyamic acid and triethanolamine into water, adding dopamine-modified graphite, and obtaining a silicon-carbon-graphite negative electrode material through ultrasonic stirring and vacuum filtration.

[0017] <Technical mechanism and beneficial effects of the present invention>

[0018] The present application utilizes a silicon-carbon-graphite negative electrode material that forms a core-shell structure, and uniformly coats the surface of silicon dioxide with a graphite carbon layer to prevent it from contacting the electrolyte, thereby avoiding irreversible reactions generated during use.

[0019] The present application bonds carbon nitride between nano-silicon dioxide and graphite, and utilizes the layered structure of carbon nitride to form a continuous, evenly distributed, outward-spreading structure, which can well buffer the volume changes during the charge and discharge process. The structure of carbon nitride can further increase the specific surface area of ​​the negative electrode material. In addition, a tight bonding structure is formed between carbon nitride, silicon dioxide and graphite, which can avoid the problem of pulverization and shedding of silicon materials, thereby improving the cycle stability of the electrode.

[0020] Since silicon cannot be used alone as a negative electrode material, the conductivity of the silicon-carbon negative electrode material can be improved by coating graphite to form a carbon layer and coating it on the surface of silicon dioxide. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0022] <Technical solution>

[0023] A silicon-carbon-graphite negative electrode material, comprising

[0024] SiO2 in the inner layer, graphite in the outer layer, and g-C3N4 bonded between the inner and outer layers.

[0025] In the present invention, g-C3N4 is doped with transition metal oxides.

[0026] In the present invention, the transition metal oxide includes at least one of MnO, Fe3O4, and MoO3.

[0027] In the present invention, the method of doping g-C3N4 with transition metal oxides is as follows:

[0028] Dispersing g-C3N4 in anhydrous ethanol and subjecting to ultrasonic treatment to obtain a first mixed solution;

[0029] Transition metal ions and melamine are added into deionized water, and then hydroxide is added to precipitate the transition metal ions. After drying and calcination, g-C3N4 doped with transition metal oxides is obtained.

[0030] In the present invention, the mass ratio of transition metal ions, melamine and hydroxide is 1:5-10:8-12.

[0031] In the present invention, the transition metal ions are added in the form of nitrates.

[0032] In the present invention, the hydroxide is sodium hydroxide or potassium hydroxide.

[0033] In the present invention, the calcination process parameters are 400-600° C. and 5-10 hours.

[0034] Second, the present invention provides a method for preparing the aforementioned silicon-carbon-graphite negative electrode material, comprising the following steps:

[0035] S1 uses silicon source and hexadecyltrimethylammonium bromide as raw materials to obtain mesoporous silica through a sol-gel method;

[0036] S2 disperses g-C3N4 in water to form a dispersion, adds a silane coupling agent and mesoporous silica to the dispersion, and transfers the dispersion to a Teflon-lined stainless steel autoclave to obtain an intermediate after reaction;

[0037] S3: adding graphite, dopamine hydrochloride and ammonium persulfate to the tris solution, mixing and reacting to obtain dopamine-modified graphite;

[0038] S4: adding the intermediate into water and dispersing to obtain a dispersion; then dissolving polyamic acid and triethanolamine into water, adding dopamine-modified graphite, and obtaining a silicon-carbon-graphite negative electrode material through ultrasonic stirring and vacuum filtration.

[0039] In the present invention, the silicon source is tetraethyl orthosilicate.

[0040] In the present invention, the mass ratio of the silicon source, hexadecyltrimethylammonium bromide, g-C3N4 and the silane coupling agent is 15-25:18-25:10-15:5-10.

[0041] In the present invention, the mass ratio of graphite, dopamine hydrochloride and ammonium persulfate is 18-25:10:3-8.

[0042] In the present invention, the mass ratio of polyamic acid, triethanolamine and dopamine modified graphite is 1-2:1-2:1.

[0043] <Example>

[0044] Example 1

[0045] A silicon-carbon-graphite negative electrode material, and a preparation method thereof, comprising the following steps:

[0046] S1: using tetraethyl orthosilicate and hexadecyltrimethylammonium bromide as raw materials to obtain mesoporous silica through a sol-gel method;

[0047] Dissolve hexadecyltrimethylammonium bromide in a mixed solution of ethanol and ammonia (the solvent is water, and the volume ratio is 50 ethanol: 5 ammonia water: 150 water). During the stirring process, add tetraethyl orthosilicate, react at a speed (1000r / min) for 18 to 24 hours, centrifuge, wash with ethanol, and dry to obtain mesoporous silica.

[0048] S2 disperses g-C3N4@MnO in water to form a dispersion, then adds a silane coupling agent and mesoporous silica to the dispersion, and transfers it to a Teflon-lined stainless steel autoclave to obtain an intermediate after reaction (150°C, 4.5h);

[0049] The preparation method of g-C3N4@MnO is as follows: Mn(NO3)2 and melamine are added into deionized water, and then NaOH is added, dried at 80°C, and calcined at 500°C for 4h to obtain g-C3N4@MnO; wherein, Mn 2+ The mass ratio of melamine and NaOH is 1:8:10.

[0050] S3: adding graphite, dopamine hydrochloride and ammonium persulfate to a tris (1.3-1.8 g / L) solution, mixing and reacting to obtain dopamine-modified graphite;

[0051] S4: adding the intermediate into water and dispersing to obtain a dispersion; then dissolving polyamic acid and triethanolamine into water, adding dopamine-modified graphite, and obtaining a silicon-carbon-graphite negative electrode material through ultrasonic stirring and vacuum filtration.

[0052] The mass ratio of silicon source, hexadecyltrimethylammonium bromide, g-C3N4 and silane coupling agent is 22:20:12:8.

[0053] The mass ratio of graphite, dopamine hydrochloride and ammonium persulfate is 22:10:6.

[0054] The mass ratio of polyamic acid, triethanolamine and dopamine modified graphite is 1:1:1.

[0055] Example 2

[0056] The difference between this embodiment and embodiment 1 is that g-C3N4@MnO is replaced by g-C3N4.

[0057] Example 3

[0058] The difference between this embodiment and embodiment 1 is that the mass ratio of the silicon source, hexadecyltrimethylammonium bromide, g-C3N4, and the silane coupling agent is 18:18:10:5.

[0059] <Comparative Example>

[0060] Comparative Example 1

[0061] The difference between this comparative example and Example 1 is that no g-C3N4 is added to the silicon-carbon-graphite negative electrode material.

[0062] <Test example>

[0063] The negative electrode materials prepared in Examples 1-3 and Comparative Example 1 were used as samples for testing to determine the electrochemical properties of the negative electrode materials. The results are shown in Table 1.

[0064] Table 1 Electrochemical performance results of samples

[0065]

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a silicon-carbon-graphite negative electrode material, characterized in that: The steps include: S1. Using silicon source and hexadecyltrimethylammonium bromide as raw materials, mesoporous silica is obtained by sol-gel method; S2: dispersing g-C3N4 in water to form a dispersion, adding a silane coupling agent and mesoporous silica to the dispersion, and transferring the dispersion to a Teflon-lined stainless steel autoclave to obtain an intermediate after reaction; S3: adding graphite, dopamine hydrochloride and ammonium persulfate to the tris solution, mixing and reacting to obtain dopamine-modified graphite; S4: adding the intermediate into water and dispersing to obtain a dispersion; dissolving polyamic acid and triethanolamine into water, adding dopamine-modified graphite, and obtaining a silicon-carbon-graphite negative electrode material through ultrasonic stirring and vacuum filtration.

2. The method for preparing the silicon-carbon-graphite negative electrode material according to claim 1, characterized in that: The silicon source is tetraethyl orthosilicate.

3. The method for preparing the silicon-carbon-graphite negative electrode material according to claim 1, characterized in that: The mass ratio of silicon source, hexadecyltrimethylammonium bromide, g-C3N4 and silane coupling agent is 15~25:18~25:10~15:5~10.

4. The method for preparing the silicon-carbon-graphite negative electrode material according to any one of claims 1 to 3, characterized in that: The mass ratio of graphite, dopamine hydrochloride and ammonium persulfate is 18~25:10:3~8.

5. The method for preparing the silicon-carbon-graphite negative electrode material according to any one of claims 1 to 3, characterized in that: The mass ratio of polyamic acid, triethanolamine and dopamine modified graphite is 1~2:1~2:

1.

6. A silicon-carbon-graphite negative electrode material obtained by the preparation method according to any one of claims 1 to 5, characterized in that: include SiO2 in the inner layer, graphite in the outer layer, and g-C3N4 bonded between the inner and outer layers.

7. The silicon-carbon-graphite negative electrode material according to claim 6, characterized in that: g-C3N4 is doped with transition metal oxides.

8. The silicon-carbon-graphite negative electrode material according to claim 7, characterized in that: The transition metal oxide includes at least one of MnO, Fe3O4, and MoO3.

9. The silicon-carbon-graphite negative electrode material according to claim 6 or 7, characterized in that: The method of doping g-C3N4 with transition metal oxides is: Dispersing g-C3N4 in anhydrous ethanol and subjecting to ultrasonic treatment to obtain a first mixed solution; Transition metal ions and melamine are added into deionized water, and then hydroxide is added to precipitate the transition metal ions. After drying and calcination, g-C3N4 doped with transition metal oxides is obtained.

10. The silicon-carbon-graphite negative electrode material according to claim 9, characterized in that: The mass ratio of transition metal ions, melamine and hydroxide is 1:5~10:8~12.

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