A method for modifying a positive electrode material for a lithium-ion battery. The method includes: a) grinding a mixture of manganese dioxide and lithium carbonate, and calcining the mixture at no less than a temperature of 600° C. for no less than 20 hrs in the presence of air, to yield a powdery lithium manganese oxide (LiMn2O4); b) adding a precursor for forming a graphene-like structure to the powdery LiMn2O4, mixing, curing at a constant temperature of no less than 180° C. for between 2 and 4 hrs, grinding, and calcining at no less than a temperature of 500° C. for between 1 and 50 hrs in the presence of an inert gas, to yield a composite powder comprising a graphene-like structure and LiMn2O4; and c) collecting and sintering the composite powder at a temperature of between 300 and 500° C. for between 1 and 10 hrs in the presence of air.