Negative electrode active material for lithium secondary battery and method of preparing the same

Abstract

The present specification relates to a negative electrode active material including an amorphous silicon-based composite represented by SiO a (0<a<1); and a carbon coating layer distributed on a surface of the silicon-based composite, and provides a negative electrode active material in which the crystal growth of crystalline silicon in a silicon-based composite prepared by thermal reduction with a metal reducing agent is suppressed in a state where a carbon coating layer is formed, and the ratio of silicon in the composite is high, and a method of preparing the same.

1 . A negative electrode active material, comprising:
 a silicon-based composite represented by SiO a  (0<a<1); and   a carbon coating layer distributed on a surface of the silicon-based composite;   wherein the silicon-based composite includes amorphous silicon.   
     
     
         2 . The negative electrode active material according to  claim 1 , wherein the silicon-based composite further includes crystalline silicon having a crystal size of 10 nm or less. 
     
     
         3 . The negative electrode active material according to  claim 1 , wherein the silicon-based composite further includes a crystalline silicon oxide. 
     
     
         4 . The negative electrode active material according to  claim 2 , wherein an amount of the crystalline silicon in the silicon-based composite is 10 wt % or less based on the total weight of silicon. 
     
     
         5 . The negative electrode active material according to  claim 1 , wherein a thickness of the carbon coating layer is in a range of 0.003 to 3.0 μm. 
     
     
         6 . The negative electrode active material according to  claim 1 , wherein an average particle diameter of the negative electrode active material is in a range of 0.1 to 20 μm. 
     
     
         7 . The negative electrode active material according to  claim 1 , wherein an average particle diameter of the negative electrode active material is in a range of 0.5 to 10 μm. 
     
     
         8 . The negative electrode active material according to  claim 1 , wherein a content of the carbon coating layer is in a range of 1 to 50 wt % of a total weight of the negative electrode active material. 
     
     
         9 . The negative electrode active material according to  claim 1 , wherein the carbon coating layer includes one or more selected from the group consisting of natural graphite, artificial graphite, mesocarbon microbeads (MCMB), carbon fibers and carbon black. 
     
     
         10 . The negative electrode active material according to  claim 1 , wherein the silicon-based composite further includes crystalline silicon having a crystal size of 10 nm or less. 
     
     
         11 . The negative electrode active material according to  claim 1 , wherein the negative electrode active material is formed by a method including:
 forming a carbon coating layer on a silicon-based precursor represented by SiO x  (0<x<2);   thermally treating the silicon-based precursor on which the carbon coating layer is formed; and   preparing a silicon-based composite represented by SiO a  (0<a<1) and having a surface on which a carbon coating layer is distributed by removing impurities;   wherein the silicon-based composite includes an amorphous silicon,   the thermal treatment includes thermally reducing a silicon-based precursor with a metal reducing agent in an inert atmosphere, and   the thermal treatment is performed in a temperature range of 350 to 650° C.   
     
     
         12 . The negative electrode active material according to  claim 11 , wherein the thermal treatment is performed in a rotary kiln. 
     
     
         13 . The negative electrode active material according to  claim 11 , wherein the metal reducing agent includes one selected from the group consisting of Ti, Al, Mg, Ca, Be, Sr, Ba and a combination thereof. 
     
     
         14 . The negative electrode active material according to  claim 11 , wherein a molar ratio of the silicon-based precursor to the metal reducing agent is in a range of 1:0.001 to 1:1. 
     
     
         15 . The negative electrode active material according to  claim 11 , wherein the preparing of the silicon-based composite includes removing impurities using an acidic aqueous solution. 
     
     
         16 . The negative electrode active material according to  claim 11 , wherein the acidic aqueous solution includes one or more selected from the group consisting of hydrochloric acid, nitric acid and sulfuric acid. 
     
     
         17 . The negative electrode active material according to  claim 11 , wherein the impurities include one or more materials selected from the group consisting of a metal oxide, a metal silicide and a metal silicate, and the metal is one selected from the group consisting of Ti, Al, Mg, Ca, Be, Sr, Ba and a combination thereof. 
     
     
         18 . A negative electrode comprising the negative electrode active material of  claim 1 . 
     
     
         19 . A secondary battery comprising the negative electrode of  claim 18 .