Described herein are solid solution composites that are used as cathode materials for lithium-ion batteries. The solid solution composite of α LiMVO4-βLiNi1-x-yCoxMnyO2, in which LiMVO4 has cubic close-packed structure, LiNi1-x-yCoxMnyO2 has hexagonal layered structure, and both share an oxygen lattice fully or partly. The new solid solution materials have advantage for lithium-ion batteries that the working voltage of the composite is adjustable by controlling the molar ratio of α and β and have higher working voltage than current secondary battery materials.Also described herein are methods of preparing such composite.