阅读说明：本技术 一种类夹心棒硅碳负极材料及其制备方法 (Sandwich rod-like silicon-carbon negative electrode material and preparation method thereof ) 是由 田军 李国敏 于 2019-04-02 设计创作，主要内容包括：本发明公开了一种类夹心棒硅碳负极材料及其制备方法,所述的硅碳负极材料形状类似夹心棒,从内至外由碳纳米管层、硅层、聚多巴胺碳层、石墨烯层组成,其制备方法包括以下步骤：S1：碳纳米管/二氧化硅复合物的制备；S2：碳纳米管/硅复合物的制备；S3：碳纳米管/硅/聚多巴胺复合物的制备；S4：碳纳米管/硅/聚多巴胺/氧化石墨烯复合物的制备；S5：类夹心棒硅碳负极材料的制备。本发明的类夹心棒硅碳负极材料可有效抑制SEI膜的过度生长,提高库伦效率,同时可显著提高材料的导电性,改善硅负极材料的体积膨胀以及防止硅层暴露在电解液中而被粉化,提高锂离子电池的循环性能及能量密度。(The invention discloses a sandwich rod-like silicon-carbon cathode material and a preparation method thereof, wherein the silicon-carbon cathode material is similar to a sandwich rod in shape and consists of a carbon nanotube layer, a silicon layer, a polydopamine carbon layer and a graphene layer from inside to outside, and the preparation method comprises the following steps: s1: preparing a carbon nano tube/silicon dioxide compound; s2: preparing a carbon nano tube/silicon compound; s3: preparing a carbon nano tube/silicon/polydopamine compound; s4: preparing a carbon nano tube/silicon/polydopamine/graphene oxide compound; s5: and (3) preparing a silicon-carbon cathode material similar to the sandwich rod. The sandwich rod-like silicon-carbon negative electrode material can effectively inhibit the overgrowth of an SEI film, improve the coulombic efficiency, obviously improve the conductivity of the material, improve the volume expansion of the silicon negative electrode material, prevent a silicon layer from being pulverized after being exposed in electrolyte, and improve the cycle performance and energy density of a lithium ion battery.)

1. The sandwich rod-like silicon-carbon cathode material is characterized in that the silicon-carbon cathode material is similar to a sandwich rod in shape and consists of a carbon nanotube layer, a silicon layer, a polydopamine carbon layer and a graphene layer from inside to outside, and the preparation method comprises the following steps:

s1: dispersing carbon nanotubes in a mixed solution containing deionized water, ethanol and ammonia water, adding tetraethyl orthosilicate, stirring at room temperature for 30-60 min, and then washing with deionized water and ethanol for several times to obtain a carbon nanotube/silicon dioxide compound;

s2: depositing a layer of silicon on the surface of the carbon nano tube/silicon dioxide compound through chemical vapor deposition, then adopting 3-10 wt% hydrofluoric acid to etch for 2-5 h, removing the silicon dioxide layer, and cleaning with deionized water and ethanol for several times to obtain the carbon nano tube/silicon compound;

s3: adding dopamine hydrochloride into a buffer solution to prepare a certain concentration, then adding the carbon nano tube/silicon composite, adjusting the pH value to 8.5, stirring for 12-24 h, washing with deionized water and ethanol for several times, and drying in vacuum to obtain a carbon nano tube/silicon/poly-dopamine composite;

s4: dispersing graphene oxide in deionized water to prepare graphene oxide dispersion liquid with a certain concentration, adding the carbon nano tube/silicon/polydopamine composite, heating to 50-80 ℃, stirring for 5-12 h, washing with deionized water and ethanol for several times, and drying in vacuum to obtain a carbon nano tube/silicon/polydopamine/graphene oxide composite;

s5: and (3) placing the carbon nano tube/silicon/polydopamine/graphene oxide compound in a muffle furnace with inert gas, heating at a heating rate of 2-5 ℃/min, and carrying out heat treatment for 2-5 h to obtain the silicon-carbon cathode material similar to the sandwich rod.

2. The sandwich rod-like silicon-carbon negative electrode material and the preparation method thereof according to claim 1, wherein the diameter of the carbon nanotube is 20-80 nm.

3. The sandwich rod-like silicon-carbon negative electrode material and the preparation method thereof according to claim 1, wherein the thickness of the silicon layer is 20-50 nm.

4. The sandwich rod-like silicon-carbon negative electrode material and the preparation method thereof as claimed in claim 1, wherein the thickness of the hollow layer between the carbon nanotube and the silicon layer is 30-60 nm.

5. The sandwich rod-like silicon-carbon negative electrode material and the preparation method thereof according to claim 1, wherein the mass ratio of the carbon nanotube/silicon composite to the dopamine hydrochloride in step S3 is 2: 1-1: 3.

6. The sandwich rod-like silicon-carbon negative electrode material and the preparation method thereof according to claim 1, wherein the concentration of the dopamine hydrochloride solution in the step S3 is 0.05-1 mg/mL.

7. The sandwich rod-like silicon-carbon anode material and the preparation method thereof of claim 1, wherein the concentration of the graphene oxide dispersion liquid in the step S4 is 0.1-2 mg/mL.

8. The sandwich rod-like silicon-carbon anode material and the preparation method thereof according to claim 1, wherein the heat treatment temperature in the step S5 is 500-800 ℃.

Technical Field

The invention belongs to the technical field of lithium ion battery cathode materials, and particularly relates to a sandwich rod-like silicon-carbon cathode material and a preparation method thereof.

Background

The lithium ion battery is a green high-energy environment-friendly battery, and has the outstanding advantages of high energy density, environmental friendliness, no memory effect, long cycle life, small self-discharge and the like, so that the lithium ion battery is widely applied and paid attention to the applications of mobile phone batteries, mobile power supplies, electric automobiles and the like. The lithium ion battery is widely applied to new energy automobiles as a power battery, and as the safety performance, the energy density, the high rate performance and the cycle life of the lithium ion battery are further improved, no material can completely meet the requirements of an automobile power system on the lithium ion battery at present.

In order to develop a lithium ion battery suitable for a new energy automobile, researchers mainly focus on anode and cathode materials at the present stage. At present, graphite is mainly used as a negative electrode material, but the specific capacity and the lithium removal potential of the negative electrode material are low, and the low lithium removal potential (only 0.05V) causes a safety problem, so that the application of the graphite in a large-capacity battery is limited. The appearance of silicon gives great hope to new energy automobiles, has the characteristics of the highest theoretical specific capacity (4200 mAh & g < -1 >), moderate lithium removal potential (< 0.5V vs Li +/Li) and abundant reserve of 27.6 percent and the like, and is greatly valued by researchers. However, silicon has poor conductivity, and when the highest specific capacity is reached, the volume expansion of silicon is as high as more than 300%, which seriously affects the cycle performance of the lithium ion battery, and finally leads to the vicious cycle of electrochemical performance, thereby limiting the commercial application of silicon.

Therefore, the prior art has yet to be improved.

Disclosure of Invention

Aiming at the problems in the prior art, the invention aims to provide a sandwich rod-like silicon-carbon negative electrode material and a preparation method thereof, and aims to improve the conductivity and coulombic efficiency of the silicon-based material, improve the volume expansion of the silicon negative electrode material and improve the cycle performance and energy density of a lithium ion battery.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows: the silicon-carbon cathode material is similar to a sandwich rod in shape and consists of a carbon nanotube layer, a silicon layer, a polydopamine carbon layer and a graphene layer from inside to outside, and the preparation method comprises the following steps:

s1: dispersing carbon nanotubes in a mixed solution containing deionized water, ethanol and ammonia water, adding tetraethyl orthosilicate, stirring at room temperature for 30-60 min, and then washing with deionized water and ethanol for several times to obtain a carbon nanotube/silicon dioxide compound;

s2: depositing a layer of silicon on the surface of the carbon nano tube/silicon dioxide compound through chemical vapor deposition, then adopting 3-10 wt% hydrofluoric acid to etch for 2-5 h, removing the silicon dioxide layer, and cleaning with deionized water and ethanol for several times to obtain the carbon nano tube/silicon compound;

s3: adding dopamine hydrochloride into a buffer solution to prepare a certain concentration, then adding the carbon nano tube/silicon composite, adjusting the pH value to 8.5, stirring for 12-24 h, washing with deionized water and ethanol for several times, and drying in vacuum to obtain a carbon nano tube/silicon/poly-dopamine composite;

s4: dispersing graphene oxide in deionized water to prepare graphene oxide dispersion liquid with a certain concentration, adding the carbon nano tube/silicon/polydopamine composite, heating to 50-80 ℃, stirring for 5-12 h, washing with deionized water and ethanol for several times, and drying in vacuum to obtain a carbon nano tube/silicon/polydopamine/graphene oxide composite;

s5: and (3) placing the carbon nano tube/silicon/polydopamine/graphene oxide compound in a muffle furnace with inert gas, heating at a heating rate of 2-5 ℃/min, and carrying out heat treatment for 2-5 h to obtain the silicon-carbon cathode material similar to the sandwich rod.

In the technical scheme, in the steps of the sandwich rod-like silicon-carbon negative electrode material and the preparation method thereof, the diameter of the carbon nano tube is 20-80 nm, and preferably, the diameter of the carbon nano tube is 30-50 nm.

The thickness of the silicon layer is 20-50 nm, and preferably, the thickness of the silicon layer is 30-40 nm.

The thickness of the hollow layer between the carbon nano tube and the silicon layer is 30-60 nm, and preferably, the thickness of the hollow layer between the carbon nano tube and the silicon layer is 30-50 nm.

The mass ratio of the carbon nanotube/silicon composite to the dopamine hydrochloride in the step S3 is 2: 1-1: 3, and preferably, the mass ratio of the carbon nanotube/silicon composite to the dopamine hydrochloride in the step S3 is 1: 1-1: 2.

The concentration of the dopamine hydrochloride solution in the step S3 is 0.05-1 mg/mL, and preferably, the concentration of the dopamine hydrochloride solution in the step S3 is 0.1-0.8 mg/mL.

The concentration of the graphene oxide dispersion liquid in the step S4 is 0.1-2 mg/mL, preferably, the concentration of the graphene oxide dispersion liquid in the step S4 is 0.5-1.5 mg/mL.

The heat treatment temperature in the step S5 is 500-800 ℃, preferably, the heat treatment temperature in the step S5 is 700-800 ℃.

The sandwich rod-like silicon-carbon negative electrode material is prepared by the preparation method.

The invention has the beneficial effects that:

(1) according to the invention, the carbon nano tube is used as a matrix, the silicon dioxide is used as a sacrificial template, and a silicon layer is generated by a CVD method to prepare the carbon nano tube/silicon coaxial hollow structure, so that the volume expansion of a silicon-based material can be relieved, the overgrowth of an SEI film can be inhibited, and the coulombic efficiency can be improved;

(2) according to the invention, the surface of the silicon layer is coated with the polydopamine layer and the graphene oxide layer, the polydopamine layer and the graphene oxide layer are carbonized and reduced through high-temperature heat treatment, the conductivity of the material can be obviously improved, meanwhile, the polydopamine carbon layer has enough elasticity, the silicon layer is tightly fixed on the reduced graphene oxide sheet through covalent bonds or hydrogen bonds, a good buffer space can be provided for the volume expansion of silicon, and the silicon layer can be effectively prevented from being pulverized after being exposed in electrolyte;

(3) the sandwich rod-like silicon-carbon cathode material prepared by the invention can effectively improve the conductivity and the coulombic efficiency of the silicon-based material, improve the volume expansion of the silicon cathode material and improve the cycle performance and the energy density of a lithium ion battery.

Detailed Description

The present invention is described in detail below with reference to specific embodiments, and the description in this section is only exemplary and explanatory and should not be construed as limiting the scope of the present invention in any way.