Sponge silicon powder and its preparation method and lithium ion battery

Abstract

The invention discloses spongy silicon powder which can be used in the negative electrode of a lithium ion battery and a preparation method of the spongy silicon powder. The preparation method of thespongy silicon powder comprises the following steps: coating the surface of magnesium-silicon-calcium composite powder with a zinc-bismuth alloy layer; carrying out solid-phase diffusion heat treatment on the magnesium-silicon-calcium composite powder coated with the zinc-bismuth alloy layer; oxidizing the magnesium-silicon-calcium composite powder after the solid-phase diffusion heat treatment; pickling the oxidized magnesium-silicon-calcium composite powder to remove zinc, bismuth, magnesium and calcium, and carrying out ball milling and calcining in a medium containing carbon-containing organic matters to obtain spongy silicon powder with a microporous structure with a carbon conductive layer on the surface. The spongy silicon powder overcomes the safety risks of ignition and explosionof workshop magnesium powder dust in the prior art, and is suitable for industrial batch production. The spongy silicon powder has a microporous structure with a carbon conductive layer on the surface, microporous gaps are uniform, the crystallinity of silicon particles is high, and the total oxygen content of the powder is less than 5%; the spongy silicon powder has relatively good conductivity and relatively high first charge-discharge coulombic efficiency when being used as a negative electrode material.

Description

technical field [0001] The disclosure belongs to the technical field of battery material preparation, and relates to a spongy silicon powder, a preparation method thereof, and a lithium ion battery. Background technique [0002] Since silicon has a theoretical specific capacity more than ten times higher than that of graphite anode (the theoretical specific capacity value of silicon is: 4200mAh / g), the use of silicon to replace the commonly used graphite anode has become the goal of high energy density power battery research. Silicon has the following disadvantages in use as a negative electrode: large volume expansion, easy cracking and pulverization of silicon particles; low coulombic efficiency for the first charge and discharge; high impedance; in response to the above shortcomings, a series of improvement methods have been proven effective, such as the use of nanoscale Silicon particles can reduce the breakage of bulk silicon, the use of porous structure silicon particl...

AI Technical Summary

Problems solved by technology

Silicon has the following disadvantages in use as a negative electrode: large volume expansion, easy cracking and pulverization of silicon particles; low coulombic efficiency for the first charge and discharge; high impedance; in response to the above shortcomings, a series of improvement methods have been proven effective, such as the use of nanoscale Silicon particles can reduce the breakage of bulk silicon, the use of porous structure silicon particles can alleviate the volume expansion during charging, and the surface coating carbon layer can improve the conductivity of silicon, etc.

The high-energy ball milling method is widely applicable, but it is time-consuming to prepare nano-silicon powder, and it is difficult to form a porous structure on the powder surface

The equipment of the plasma heating evaporation condensation method is complex, and there are certain limitations in the selection of raw materials and the selection of subsequent processes. Combined to form secondary polymerized silicon particles with a large number of voids, which is not conducive to subsequent processing; in some studies, the manufactured nano-silicon powder has a large specific surface area, but the use of silane to manufacture nano-silicon powder requires high raw material costs

There is a problem of chemical reagents polluting the environment in the preparation of nano-silicon powder by chemical methods. Some studies have used hydrofluoric acid to treat the mixture of silicon dioxide and silicon to obtain nano-silicon. The hydrofluoric acid used is highly corrosive, difficult to operate, and pollutes the environment. The problem is also difficult to solve

[0004] In the method for preparing porous silicon powder, the silicon powder prepared by some methods has the disadvantages of large silicon particles, large primary particle size, and poor uniformity; some methods use a large amount of magnesium powder in the process of synthesizing silicon-magnesium alloy powder. The production process must have strict environmental control measures such as helium protection to reduce the explosion risk of magnesium dust; in the process of magnesium removal, the temperature is often higher than the ignition point of magnesium, which makes magnesium easy to ignite, burn and oxidize, causing the overall high temperature of the powder Spontaneous combustion and over-burning lead to silicon oxidation and rapid growth of silicon particles. Therefore, it is very difficult to control the process of industrial production of porous nano-silicon powder by this method, especially it is difficult to control the particle size of nano-silicon powder; there are also studies using metal chloride molten salt medium Long-term heat preservation (10h~15h) method to decompose silicon-magnesium alloy powder, and then obtain porous silicon by hydrochloric acid pickling. This method eliminates the risk of magnesium ignition and combustion in industrial production, but the process requires long time heat preservation, and the powder preparation efficiency is low. The problem

Some studies have also disclosed a method of obtaining porous silicon with a core-shell structure by using alkali, hydrocarbon compounds and pickling after ball milling silicon-calcium alloy. Although this method has no fire risk of metal magnesium, silicon-calcium alloy is used in Amorphous sodium silicate is easily formed during the alkali reaction, and a large amount of massive silica will be formed when it reacts directly with acid, making the powder unsuitable for use as a negative electrode material for lithium batteries

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