The third calcining may be operated at a constant temperature or a variable temperature. For example, the third calcining may be composed of maintaining at a temperature selected from 250 to 500° C., for 1-24 hours, preferably 6-12 hours. Alternatively, the third calcining may comprise heating and cooling between two or more temperatures selected from 300 to 500° C. (for example, heating and cooling at a constant rate, preferably at a rate of 1-10° C./min, such as 1° C./min, 2° C./min, 4° C./min, 5° C./min, 7° C./min or 10° C./min), for a total time of 1-24 hours, preferably 6-12 hours. In a variant, there may be a step of maintaining at the temperature between the heating and cooling. There is no special limitation on the rate for heating to the required temperature for the third calcining. Preferably, the rate may be 1-10° C./min, for example 1° C./min, 2° C./min, 4° C./min, 5° C./min, 7° C./min or 10° C./min.

The third calcined product is the positive electrode material in accordance with the present disclosure. Optionally, the third calcined product may be subjected to cooling, sieving and removing iron impurities.

The inventor of the present application surprisingly found during the research that, when a positive electrode material is incorporated with a plurality of dopant elements and subjected to programmed calcining during its preparation, the obtained positive electrode material may have a stable lattice structure and improved particle strength. The positive electrode material may impart lithium batteries with better electrochemical performances, such as improved rate performance and cycling stability.