CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application Nos. 10-2017-0135616, filed on Oct. 19, 2017, and 10-2018-0124981, filed on Oct. 19, 2018, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

Technical Field

The present invention relates to a method of preparing a negative electrode active material, and, specifically, the method of preparing a negative electrode active material may include forming a mixture by mixing Li2O and SiOx(0<x<2) particles including SiO2; forming a reaction product by performing a heat treatment on the mixture at 400° C. to 600° C.; and removing a portion of lithium silicate in the reaction product by washing the reaction product.

Background Art

Requirements for the use of alternative energy or clean energy have increased due to the rapid increase in the use of fossil fuels, and, as a part of this trend, power generation and electricity storage using an electrochemical reaction are the most actively researched areas.

Currently, a typical example of an electrochemical device using the electrochemical energy may be a secondary battery and there is a trend that its usage area is expanding more and more. In recent years, demand for secondary batteries as an energy source has been significantly increased as technology development and demand with respect to portable devices, such as portable computers, mobile phones, and cameras, have increased. Among these secondary batteries, lithium secondary batteries having high energy density, i.e., high capacity, have been subjected to considerable research and have been commercialized and widely used.

In general, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material in which lithium ions from the positive electrode are intercalated and deintercalated, and SiOx(0<x<2) having high discharge capacity may be used as the negative electrode active material. However, SiOx(0<x<2) reacts with a lithium source in the battery to form lithium silicate, and the lithium silicate is formed in an irreversible phase so that an amount of the lithium source contributing to charge and discharge of the battery is reduced. Thus, there is a limitation in that initial efficiency of the battery is reduced.

Accordingly, a technique for forming lithium silicate in advance by mixing SiOx(0≤x<2) with lithium metal and performing a heat treatment has been typically used. In this case, since the amount of the lithium source converted to the irreversible phase in the battery may be minimized, the initial efficiency of the battery may be improved.

However, a heat treatment at a high temperature of 900° C. or more is generally required to react the lithium metal with the SiOx(0≤x<2), and a grain size of silicon in the SiOx(0≤x<2) is excessively increased at such a high temperature. Since the grain size of the silicon is excessively increased, there is a limitation in that cycle characteristics of the battery are degraded.

Therefore, there is a need for a method of preparing a negative electrode active material which may prevent the grain size of the silicon from growing excessively while minimizing the formation of the irreversible phase due to the lithium source in the battery.

DISCLOSURE OF THE INVENTION

Technical Problem

An aspect of the present invention provides a method of preparing a negative electrode active material which may prevent a grain size of silicon from growing excessively while minimizing the formation of an irreversible phase due to a lithium source in a battery.

Technical Solution

According to an aspect of the present invention, there is provided a method of preparing a negative electrode active material which includes forming a mixture by mixing Li2O and SiOx(0<x<2) particles including SiO2; forming a reaction product by performing a heat treatment on the mixture at 400° C. to 600° C.; and removing a portion of lithium silicate in the reaction product by washing the reaction product.

Advantageous Effects

According to a method of preparing a negative electrode active material according to an embodiment of the present invention, since irreversible phase formation due to a lithium source provided from a positive electrode may be minimized by forming lithium silicate in advance by Li2O, initial efficiency of a battery may be improved. Also, since a heat treatment temperature is low at 400° C. to 600° C. during the formation of the lithium silicate, the growth of silicon grains in a negative electrode active material may be suppressed, and thus, life characteristics of the battery may be improved.

