A method for making an electrode active material of a lithium ion battery is disclosed. In the method, elemental sulfur is mixed with a polyacrylonitrile to form a mixture. The mixture is heated in vacuum or a protective gas at a heating temperature of about 250° C. to about 500° C., to form a sulfur containing composite. The sulfur containing composite is reacted with a reducing agent for elemental sulfur in a liquid phase medium to remove part of the elemental sulfur from the sulfur containing composite.