A secondary battery and its preparation method, the secondary battery having a negative electrode containing a negative current collector and no negative active material; an electrolyte having an electrolyte salt and an organic solvent; a separator; a positive electrode having a positive active material layer containing a positive active material, wherein the positive active material comprises a material having a layered crystal structure; and a battery case used for packaging. Main active component of the secondary battery is the positive active material having a layered crystal structure, which is environmentally-friendly and low in cost; meanwhile, negative active material is not needed by the second battery system, thereby remarkably reducing the weight and cost of the battery and improving the battery energy density. The reaction mechanism adopted by the secondary battery significantly increases the working voltage of the battery and further improves the energy density of the battery.