Negative electrode material for lithium ion secondary battery

摘要

The invention provides an anode material for lithium ion secondary battery using a coated graphite powder as a raw material. The coated graphite powder is coated with carbonized material of thermoplastic resin of a carbonization yield of not more than 20 wt % in a proportion of not more than 10 parts by weight the carbonized material per 100 parts by weight graphite powder. The graphite powder as coated with thermoplastic resin increases 5% or more in accumulative pore volume of the graphite powder having a pore size of 0.012 mum to 40 mum as measured by a mercury porosimeter method, as compared with the graphite powder before coated with the thermoplastic resin. The coated graphite powder has a mesopore volume defined by IUPAC of 0.01 cc/g or less as calculated with the BJH method as viewed from desorption isotherm, which is also equal to 60% or less of the pore volume of the graphite powder before coated with the thermoplastic resin, an average particle size ranging from 10 mum to 50 mum, as measured by a laser-scattering-particle-size-distribution measuring device, and a ratio of standard deviation to the average particle size (sigma/D) of 0.02 or less.