NEGATIVE ELECTRODE MATERIAL FOR LITHIUM-ION SECONDARY BATTERY, AND LITHIUM-ION SECONDARY BATTERY

摘要

PROBLEM TO BE SOLVED: To provide a lithium-ion secondary battery suppressed in deterioration of battery characteristics caused by a change in volume of silicon associated with charging and discharging.SOLUTION: A negative electrode has such a structure that a film of a mixture of a negative electrode material made by mixing/kneading silicon/carbon composite material powder, carbon black, and carbon nanofiber is formed on the surface of a current collector. The carbon black and carbon nanofiber coexist between grains of the silicon/carbon composite material powder. The silicon/carbon composite material has such a structure that the surface of silicon powder grains are coated with a carbon film. The average grain size of primary grains of the carbon black is smaller than that of the silicon/carbon composite material powder. The average size of the carbon nanofiber is longer than the average grain size of the primary grains of the carbon black. The average diameter of the carbon nanofiber is smaller than the average grain size of the primary grains of the silicon/carbon composite material powder and carbon black.