Negative electrode active material, negative electrode and method for producing them

A method for producing a negative electrode active material containing negative electrode active material particles comprising the steps of:

• producing silicon compound particles containing a silicon compound,
• coating at least a part of the silicon compound particles with a carbon layer,
• inserting Li into the silicon compound particles to make the silicon compound particles contain Li2SiO3, and
• making a surface layer of the negative electrode active material particles contain a substance having a carboxylic acid structure by performing surface modification of the negative electrode active material particles containing the silicon compound particles coated with the carbon layer,
• wherein the negative electrode active material particles are that in which a negative fragment derived from a carboxylic acid structure is detected by measurement by TOF-SIMS,
• wherein a spectral intensity of Six+ (0<x<4) of a negative electrode containing the negative electrode active material after charging is higher than that of the negative electrode after discharging in a spectrum of K absorption edge XANES of Si obtained from the XAFS measurement of the negative electrode taken out from a charged secondary battery, and the negative electrode taken out from the charged secondary battery after complete discharge, and
• wherein the XANES spectrum of the negative electrode after the charge spectral intensity of Six+ (2≤x<4) is higher than spectral intensity of Six+ (0<x<2).

A method for producing a negative electrode containing negative electrode active material particles comprising the steps of:

• producing silicon compound particles containing a silicon compound,
• coating at least a part of the silicon compound particles with a carbon layer,
• forming a negative electrode containing the silicon compound particles coated with the carbon layer,
• inserting Li into the silicon compound particles contained in the formed negative electrode and making the silicon compound particles contain Li2SiO3, and
• making a surface layer of the negative electrode active material particles contained in the negative electrode contain a substance having a carboxylic acid structure by performing surface modification of the negative electrode active material particles containing the silicon compound particles coated with the carbon layer,
• wherein the negative electrode active material particles are that in which a negative fragment derived from a carboxylic acid structure is detected by measurement by TOF-SIMS,
• wherein a spectral intensity of Six+ (0<x<4) of a negative electrode containing the negative electrode active material after charging is higher than that of the negative electrode after discharging in a spectrum of K absorption edge XANES of Si obtained from the XAFS measurement of the negative electrode taken out from a charged secondary battery, and the negative electrode taken out from the charged secondary battery after complete discharge, and
• wherein the XANES spectrum of the negative electrode after the charge spectral intensity of Six+ (2≤x<4) is higher than spectral intensity of Six+ (0<x<2).