Negative electrode active material, negative electrode including the same and lithium secondary battery including the same

Abstract

Disclosed is a negative electrode active material which includes: a silicon oxide composite including i) Si, ii) a silicon oxide represented by SiOx (0<x≤2), and iii) magnesium silicate containing Si and Mg; and a carbon coating layer positioned on the surface of the silicon oxide composite and including a carbonaceous material, wherein X-ray diffractometry of the negative electrode active material shows peaks of Mg2SiO4 and MgSiO3 at the same time and shows no peak of MgO; and the ratio of peak intensity, I (Mg2SiO4)/I (MgSiO3), which is intensity I (Mg2SiO4) of peaks that belong to Mg2SiO4 to intensity I (MgSiO3) of peaks that belong to MgSiO3 is smaller than 1, the peaks that belong to Mg2SiO4 are observed at 2θ=32.2±0.2°, and the peaks that belong to MgSiO3 are observed at 2θ=30.9±0.2°.

1 . A negative electrode active material comprising: a silicon oxide composite comprising
 i) Si,   ii) a silicon oxide represented by SiO x  (0<x≤2), and   iii) a magnesium silicate containing Si and Mg; and   a carbon coating layer disposed on a surface of the silicon oxide composite and comprising a carbonaceous material,   wherein X-ray diffractometry of the negative electrode active material includes peaks associated with Mg 2 SiO 4  and MgSiO 3  at the same time and no peak associated with MgO,   a ratio of peak intensity, I (Mg 2 SiO 4 )/I (MgSiO 3 ), is smaller than 1 wherein I (Mg 2 SO 4 ) is an intensity of peaks associated with Mg 2 SiO 4 , and I (MgSiO 3 ) is an intensity of peaks associated with MgSiO 3 ,   at least one of the peaks associated with Mg 2 SiO 4  is observed at 2θ=32.2±0.2°, and at least one of the peaks associated with MgSiO 3  is observed at 2θ=30.9±0.2°, and   a water content of the negative electrode active material is less than 200 ppm as determined by the Karl-Fischer method at 250° C.   
     
     
         2 . The negative electrode active material according to  claim 1 , wherein the carbon coating layer is present in an amount of 2.5-10 parts by weight based on 100 parts by weight of the silicon oxide composite. 
     
     
         3 . The negative electrode active material according to  claim 1 , wherein Mg is present in an amount of 4-16 wt % based on 100 wt % of the silicon oxide composite. 
     
     
         4 . The negative electrode active material according to  claim 1 , wherein an average particle diameter (D 50 ) of the silicon oxide composite powder is 0.1-20 μm. 
     
     
         5 . A method for preparing the negative electrode active material according to  claim 1 , comprising:
 carrying out a reaction of SiO x  (0<x<2) gas with Mg gas,   cooling the reaction mixture at 400-900° C. and depositing a silicon oxide composite;   pulverizing the deposited silicon oxide composite; and   injecting a carbonaceous material gas into the pulverized silicon oxide composite and carrying out a heat treatment at 800-1,150° C. for 30 minutes to 8 hours to form a carbonaceous material-containing coating layer on a surface of the silicon oxide composite.   
     
     
         6 . The method according to  claim 5 , wherein the SiO x  (0<x<2) gas is prepared by evaporating a mixture of Si and SiO 2  at 1,000-1,800° C., and the Mg gas is prepared by evaporating Mg at 800-1,600° C. 
     
     
         7 . The method according to  claim 5 , wherein the reaction of the SiO x  (0<x<2) gas with the Mg gas is carried out at 800-1,800° C. 
     
     
         8 . The method according to  claim 5 , wherein, in injecting a carbonaceous material gas, the carbonaceous material gas is injected to the pulverized silicon oxide composite, and then the heat treatment is carried out at 900-1,050° C. 
     
     
         9 . A negative electrode comprising:
 a negative electrode current collector; and   a negative electrode active material layer comprising the negative electrode active material according to  claim 1 , disposed on at least one surface of the negative electrode current collector.   
     
     
         10 . A lithium secondary battery comprising the negative electrode as defined in  claim 9 . 
     
     
         11 . The negative electrode active material according to  claim 1 , wherein the ratio of peak intensity, I (Mg 2 SiO 4 )/I (MgSiO 3 ), is from 0.1 to 0.9. 
     
     
         12 . The negative electrode active material according to  claim 1 , wherein the ratio of peak intensity, I (Mg 2 SiO 4 )/I (MgSiO 3 ), is from 0.2 to 0.7. 
     
     
         13 . The negative electrode active material according to  claim 1 , wherein the carbon coating layer is present in an amount of 2.5-7 parts by weight based on 100 parts by weight of the silicon oxide composite. 
     
     
         14 . The negative electrode active material according to  claim 1 , wherein the carbon coating layer is present in an amount of 3-5 parts by weight based on 100 parts by weight of the silicon oxide composite. 
     
     
         15 . The negative electrode active material according to  claim 1 , wherein Mg is present in an amount of 4-10 wt % based on 100 wt % of the silicon oxide composite. 
     
     
         16 . The method according to  claim 5 , wherein the reaction mixture is cooled at 500-800 ° C. 
     
     
         17 . The method according to  claim 5 , wherein the cooling is conducted for 1-6 hours. 
     
     
         18 . The method according to  claim 5 , wherein the heat treatment is conducted at 900-1,050° C. to form the carbonaceous material-containing coating layer. 
     
     
         19 . The method according to  claim 5 , wherein the heat treatment is conducted at 950-1,000° C. to form the carbonaceous material-containing coating layer. 
     
     
         20 . The method according to  claim 5 , wherein the heat treatment is conducted at a rate of 3-10° C./min to form the carbonaceous material-containing coating layer.