A lithium secondary battery with high-output/high-input characteristics which has a long life, and is highly safe contains a negative electrode of a negative-electrode active material. In a dispersion prepared by dispersing 100 g of the active-material powder in 200 g of water together with 2 g of carboxymethyl cellulose, the particle diameter at which particles begin to appear is 50 .mu.m or smaller when the dispersion is examined by the grind gauge method for determining the degree of dispersion in accordance with JIS K5400.