SECONDARY BATTERY AND METHOD FOR MANUFACTURING THE SAME

The invention provides a secondary battery and a preparation method thereof.The preparation method comprises the steps that a lithium source, an iron source, a phosphorus source, a transition metal salt source, a bismuth source and a solvent are mixed to obtain an intermediate solution, and the pH of the intermediate solution is 1.0-4.0; performing hydrothermal reaction on the intermediate solution, and drying to obtain a precursor; performing heat treatment on the precursor to obtain an inner core which comprises lithium iron phosphate and bismuth salt; and coating the inner core with a coating material to obtain the positive electrode material which comprises the inner core and a conductive polymer coating layer arranged on at least the surface of the inner core. The positive electrode material disclosed by the invention has the advantages of high compaction density and high conductivity, and the energy density, the cycle performance and the high and low temperature performance of the positive electrode mat