Negative electrode material for lithium ion secondary batteries, method for manufacturing the same, paste for negative electrode, negative electrode sheet, and lithium ion secondary

A method for manufacturing a negative electrode material for lithium ion secondary batteries made of composite material particles, comprising the steps of:

• pulverizing a mixture obtained by mixing nanosilicon particles having a 50% particle diameter (Dn50) in a number-based cumulative particle size distribution of primary particles of 5 to 100 nm and a carbon precursor at a softening point or higher temperature of the carbon precursor to obtain nanosilicon-containing particles comprising the nanosilicon particles covered with only amorphous carbon material (step 1),
• treating a mixture, obtained by mixing the nanosilicon-containing particles and graphite particles, in an inert gas atmosphere at a temperature of 900° C. or more and 1200° C. or less and then pulverizing the processed mixture to obtain composite material particles (composite material particles 1) (step 2), and
• treating a mixture, obtained by further mixing the composite material particles 1 with the nanosilicon-containing particles, in an inert gas atmosphere at a temperature of 900° C. or more and 1200° C. or less and then pulverizing the processed mixture to obtain composite material particles (composite material particles 2) (step 3),
• wherein the composite material particles have an exothermic peak temperature in DTA measurement of 830° C. to 890° C. and no exothermic peak temperature in DTA measurement of less than 830° C.