CN110902667B - Preparation method of porous Si/C negative electrode material - Google Patents

Abstract

The invention discloses a preparation method of a porous Si/C negative electrode material, which comprises the following steps of (1) dispersing lignocellulose in an alkaline aqueous solution, and performing ball milling dispersion to obtain a lignocellulose dispersion liquid; (2) adjusting the pH value of the lignocellulose dispersion liquid to 5-7; (3) Mixing Si powder and the lignocellulose dispersion liquid after pH adjustment, and placing the mixture in a ball milling tank for ball milling and dispersion; (4) Carrying out negative pressure suction filtration on the dispersion liquid after ball milling, and separating a paper-like solid mixture; (5) And (3) carrying out heat treatment on the separated paper-like solid mixture in an inert atmosphere to carbonize the mixture, cooling to room temperature after the carbonization, washing with water, and drying to obtain the Si/C negative electrode material. According to the invention, by changing the mass ratio of Si powder to wood fiber and other factors, the quantity ratio of Si to carbon and the properties of pore channels and the like in the Si/C cathode material can be regulated and controlled to adapt to the huge volume change in the Si charge-discharge process, so that the volume effect problem of the Si electrode material is solved.

Description

A kind of preparation method of porous Si/C negative electrode material

technical field

The invention relates to the technical field of lithium ion batteries, in particular to a preparation method of a porous Si/C negative electrode material.

Background technique

High specific capacity electrode materials are the key to improving the energy density of lithium-ion batteries. Compared with the theoretical specific capacity of the existing graphite negative electrode of 372mAh/g, Si as the negative electrode theoretically has a specific capacity of 4200mAh/g, so its application in lithium-ion batteries has attracted much attention. However, the practical use of Si in Li-ion batteries suffers from enormous volume expansion (up to 300% volume change rate) and low electronic conductivity. In order to solve these problems of Si, the economical and feasible way is to combine carbon with good electronic conductivity with Si to improve the electronic conductivity of the material while improving the structural stability, so as to achieve the purpose of improving the cycle charge and discharge stability of Si materials. . At present, there are mainly two types of methods for compounding Si and carbon: one is to cover carbon on the surface of Si particles by vapor deposition; The mixture is then carbonized at high temperature to form the Si/C negative electrode material. However, the gas-phase carbon deposition method has harsh preparation conditions, low efficiency and high cost, and is difficult to be used in large-scale industrialization; small molecular organics such as sucrose melt during the heating process, and are easy to form a dense coating on the Si surface. The decarburization process is very easy to form a dense Si/C anode material, which is not good for buffering volume change and stabilizing the structure, so it cannot effectively improve the cycle stability of Si materials.

Contents of the invention

The purpose of the present invention is to overcome the above-mentioned deficiencies in the prior art, and to provide a preparation method of a porous Si/C negative electrode material. By changing the mass ratio of Si powder to wood fiber and other factors, Si and carbon in the Si/C negative electrode material can be regulated. The volume ratio and the properties of the pores are used to adapt to the huge volume change during the charging and discharging process of Si, so as to solve the volume effect problem of Si electrode materials.

In order to achieve the above object, the present invention adopts the following technical solutions:

A preparation method of porous Si/C negative electrode material, comprising the following steps:

(1) Disperse lignocellulose in an alkaline aqueous solution, and disperse through ball milling to obtain a lignocellulose dispersion;

(2) adjust the pH of the lignocellulose dispersion to 5-7;

In this step, considering that Si powder is easily soluble in alkaline solution, in order to avoid its dissolution, the pH of the lignocellulose dispersion is adjusted to the above range;

(3) Si powder is mixed with the lignocellulose dispersion after adjusting the pH and placed in a ball milling tank for ball milling to disperse;

(4) Negative pressure suction filtration is carried out on the dispersion liquid after ball milling, and the paper-like solid mixture is separated;

(5) Under an inert atmosphere, heat-treat the separated paper-like solid mixture to make it carbonized, cool to room temperature after completion, wash with water, and dry to obtain a Si/C negative electrode material. The negative electrode material constitutes the lithium ion battery negative electrode material.

In step (1), the alkaline aqueous solution is prepared by alkali and distilled water in a ratio of 1/20-1/50 by volume, and the addition of the lignocellulose is to make the concentration of lignocellulose 1% to 1%. 2%.

The alkali is concentrated ammonia water with a mass concentration of 25%. In this step, the alkali used can also use other alkaline substances such as sodium hydroxide and sodium carbonate, but other impurities will be introduced, based on the reason that ammonia water is easy to remove, so the present invention chooses to use concentrated ammonia water.

In step (1), the ball milling time is 0.5-2 hours.

In step (2), a liquid organic acid is used to adjust the pH of the lignocellulose dispersion. Wherein, the liquid organic acid is acetic acid or formic acid.

In step (3), the mass ratio of lignocellulose to Si powder is 5-10:1. In this step, if the mass ratio of lignocellulose and Si powder is too high, the discharge specific capacity of the negative electrode material obtained will become low, and if the mass ratio of lignocellulose and Si powder is too low, the Si/C negative electrode material obtained will The low C content is not conducive to the stability of the structure during charge and discharge.

In step (3), the average particle size of the Si powder is below 200nm.

In step (3), the ball milling time is 2-5 hours.

In step (5), the gas used in the inert atmosphere is nitrogen or argon; the carbonization temperature is 500-800° C., and the time is 5-10 hours.

In step (5), the heat treatment is carried out in a tube furnace, and the tube furnace is raised to the carbonization temperature at a heating rate of 1-8° C./min.

This application first mixes lignocellulose and ammonia solution, then ball mills to swell the lignocellulose, and then further ball mills with Si powder to form a uniform dispersion, and then suction filters to obtain a uniformly dispersed precursor of Si and lignocellulose, followed by High temperature heat treatment to obtain Si/C negative electrode material. By changing the ratio of Si powder to lignocellulose and other factors, the ratio of Si to carbon in the Si/C anode material can be adjusted to adapt to the huge volume change during the charging and discharging process of Si, thereby solving the volume effect problem of Si electrode materials. .

Compared with the prior art, the present invention has the following advantages and beneficial effects:

(1) Lignocellulose is swollen by the action of ammonia water to obtain uniform dispersion of Si powder and lignocellulose, and then the precursor is obtained by suction filtration, followed by high-temperature carbonization to prepare Si/C negative electrode materials. The process is simple and suitable for industrial production;

(2) Lignocellulose molecules contain a large number of negatively charged oxygen-containing groups, which are easy to generate electrostatic interactions with Si and promote the uniform dispersion of Si in lignocellulose, which helps to realize the dispersion of Si in carbon supports Uniform, which is conducive to its electrochemical performance;

(3) Lignocellulose is a natural product with a wide range of sources and is cheap and easy to obtain, which is extremely beneficial to the industrial preparation of Si/C anode materials.

Description of drawings

Fig. 1 is the scanning electron micrograph of the Si/C negative electrode material precursor that embodiment 1 prepares;

Fig. 2 is the scanning electron micrograph of the Si/C negative electrode material that embodiment 1 prepares;

Fig. 3 is the charge-discharge curve diagram of the Si/C negative electrode material prepared in embodiment 1;

Fig. 4 is the charge-discharge curve diagram of the Si/C negative electrode material prepared in embodiment 2;

5 is a charge-discharge curve diagram of the Si/C negative electrode material prepared in Example 3.

Detailed ways

The present invention will be further described below in conjunction with accompanying drawing and specific embodiment:

Example 1

A preparation method of porous Si/C negative electrode material, comprising the following steps:

(1) Add 0.3 g of lignocellulose and 1 ml of 25% concentrated ammonia into 20 ml of distilled water, and disperse through ball milling for 1 hour to obtain a lignocellulose dispersion;

(2) using acetic acid to adjust the pH of the lignocellulose dispersion to 7;

(3) 60 mg of Si powder with an average particle size of 100 nm was mixed with the lignocellulose dispersion after pH adjustment and placed in a ball mill tank for ball milling for 5 hours;

(4) Negative pressure suction filtration is carried out on the dispersion liquid after ball milling, and the paper-like solid mixture is separated;

(5) Put the solid mixture in a tube furnace, heat it up to 700°C for 5 hours at a rate of 2°C/min under a nitrogen atmosphere, cool to room temperature, wash with water, and dry to obtain Si/C negative electrode materials.

In the above process, Si is uniformly dispersed in lignocellulose to form a precursor. The structure of the precursor is shown in Figure 1; the structure of the Si/C negative electrode material obtained after the heat treatment of the precursor is shown in Figure 2, from which it can be seen Results: Si is uniformly dispersed in carbon, and there are abundant pores in the negative electrode material. The charge-discharge curve of the Si/C negative electrode material is shown in Figure 3. The Si/C negative electrode material has a discharge specific capacity of about 960mAh/g at a current density of 200mA/g.

Example 2

A preparation method of porous Si/C negative electrode material, comprising the following steps:

(1) Add 0.414g of lignocellulose and 1ml of 25% concentrated ammonia into 40ml of distilled water, and disperse through ball milling for 0.5h to obtain a lignocellulose dispersion;

(2) using formic acid to adjust the pH of the lignocellulose dispersion to 5;

(3) 60 mg of Si powder with an average particle size of 20 nm is mixed with the lignocellulose dispersion after pH adjustment and placed in a ball mill tank for ball milling for 2 h;

(4) Negative pressure suction filtration is carried out on the dispersion liquid after ball milling, and the paper-like solid mixture is separated;

(5) Put the solid mixture in a tube furnace, heat it up to 500°C for 10h at a rate of 1°C/min under nitrogen atmosphere, cool to room temperature, wash with water, and dry to obtain Si/C negative electrode material.

The charge-discharge curve of the Si/C negative electrode material prepared in this embodiment is shown in FIG. 4 . The Si/C negative electrode material has a discharge specific capacity of about 1250mAh/g at a current density of 200mA/g.

Example 3

A preparation method of porous Si/C negative electrode material, comprising the following steps:

(1) Add 1.04g of lignocellulose and 1ml of concentrated ammonia water with a concentration of 25% into 50ml of distilled water, and disperse through ball milling for 2h to obtain a lignocellulose dispersion;

(2) using acetic acid to adjust the pH of the lignocellulose dispersion to 7;

(3) 104mg of Si powder with an average particle size of 200nm was mixed with the lignocellulose dispersion after pH adjustment and placed in a ball mill jar for ball milling and dispersion for 5h;

(4) Negative pressure suction filtration is carried out on the dispersion liquid after ball milling, and the paper-like solid mixture is separated;

(5) The solid mixture was placed in a tube furnace, heated to 800°C for 5 hours at a rate of 8°C/min in an argon atmosphere, cooled to room temperature, washed with water, and dried to obtain a Si/C negative electrode material.

The charge-discharge curve of the Si/C negative electrode material prepared in this embodiment is shown in FIG. 5 . The Si/C negative electrode material has a discharge specific capacity of about 1070mAh/g at a current density of 200mA/g.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection of the present invention. within range.

Claims (7)

1. a preparation method of porous Si/C negative electrode material, is characterized in that: comprise the following steps: (1) Disperse lignocellulose in an alkaline aqueous solution, and disperse through ball milling to obtain a lignocellulose dispersion; the alkaline aqueous solution is prepared by a volume ratio of 1/20-1/50 of alkali and distilled water, Described alkali is the strong ammoniacal liquor that mass concentration is 25%; (2) Adjust the pH of the lignocellulose dispersion to 5-7; (3) Mix the Si powder with the lignocellulose dispersion after adjusting the pH and place it in a ball mill tank for ball milling to disperse; the mass ratio of lignocellulose to Si powder is 5-10:1; the average particle size of the Si powder is Below 200nm; (4) The dispersion liquid after ball milling is subjected to negative pressure suction filtration, and the paper-like solid mixture is separated; (5) Under an inert atmosphere, heat-treat the separated paper-like solid mixture to carbonize it, cool to room temperature after the end, wash with water, and dry to obtain the Si/C negative electrode material. 2. The preparation method of a kind of porous Si/C negative electrode material as claimed in claim 1, is characterized in that: in step (1), the addition amount of described lignocellulose is such that the concentration of lignocellulose is 1%～2 %. 3 . The method for preparing a porous Si/C negative electrode material according to claim 1 , wherein in step (1), the ball milling time is 0.5 to 2 hours. 4 . The method for preparing a porous Si/C negative electrode material according to claim 1 , wherein in step (2), a liquid organic acid is used to adjust the pH of the lignocellulose dispersion. 5 . The method for preparing a porous Si/C negative electrode material according to claim 1 , wherein in step (3), the ball milling time is 2 to 5 hours. 6. A method for preparing a porous Si/C negative electrode material as claimed in claim 1, characterized in that: in step (5), the gas used in the inert atmosphere is nitrogen or argon; the carbonization temperature is 500-800°C, and the time is 5~10h. 7. A method for preparing a porous Si/C negative electrode material as claimed in claim 1, characterized in that: in step (5), the heat treatment is carried out in a tube furnace, and the tube furnace heats up at a rate of 1-8°C/min rate up to the carbonization temperature.

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