NOVELTY - Preparation of cobalt oxide-graphene-carbon nanotube composite material involves adding graphite oxide in water, ultrasonically dispersing, adding cobalt hydroxide to graphite oxide suspension, ultrasonically mixing, stripping graphite oxide to graphene oxide, adding carbon nanotubes, ultrasonically mixing, filtering obtained cobalt hydroxide-graphene-carbon nanotube suspension, drying, and heating at rate of 15-25 degrees C/minute to 500-700 degrees C for 0.5-2 hours in protective gas atmosphere such that graphene oxide is reduced to graphene and cobalt hydroxide is decomposed to cobalt oxide.    USE - Preparation of cobalt oxide-graphene-carbon nanotube composite material used for preparing lithium ion battery (all claimed).    ADVANTAGE - The method enables preparation of cobalt oxide-graphene-carbon nanotube composite material with high energy storage potential, using less equipment, by simple process. The cobalt oxide-graphene-carbon nanotube composite material improves cycle performance and stability of the lithium ion battery, without generation of lithium dendrites, when used as an electrode material.    DETAILED DESCRIPTION - Preparation of cobalt oxide-graphene-carbon nanotube composite material involves adding graphite oxide in water, ultrasonically dispersing, adding cobalt hydroxide to obtained graphite oxide suspension, ultrasonically mixing uniformly, stripping graphite oxide to graphene oxide, adding carbon nanotubes, ultrasonically mixing uniformly, filtering obtained cobalt hydroxide-graphene-carbon nanotube suspension, drying, and heating at rate of 15-25 degrees C/minute to 500-700 degrees C for 0.5-2 hours in protective gas atmosphere such that graphene oxide is reduced to graphene and cobalt hydroxide is decomposed to cobalt oxide. The mass ratio of graphite oxide, cobalt oxide and carbon nanotubes is 10:4-20:1-10. INDEPENDENT CLAIMS are included for the following:    (1) lithium ion battery; and    (2) preparation of lithium ion battery.