The second calcining mainly results in the oxidation of divalent nickel. Accordingly, if the calcining time is too short, it may lead to insufficient oxidation reaction, resulting in an excessive amount of divalent nickel. Accordingly, it may result in severe Li/Ni disordering and thereby a decrease in performances of the obtained positive electrode material. If the calcining time is too long, it may lead to a large degree of crystallization. Accordingly, it may result in poor cycle performance of the obtained positive electrode material and an increase in cost. In this regard, an appropriate calcining time shall be determined based on the flow rate of oxygen during the calcining. Consequently, it may control the oxidation of divalent nickel, reduce the content of divalent nickel in the Li layer, inhibit Li/Ni disordering, and avoid excessive crystallization in the positive electrode material. Ultimately, the charging and discharging capacity, rate performance, and cycle performance of lithium-ion batteries containing the positive electrode material may be improved.

The first calcining may be operated at a constant temperature or a variable temperature. For example, the first calcining may be composed of maintaining at a temperature selected from 300 to 500° C. for 1-10 hours, preferably 4-8 hours. Alternatively, the first 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 1-10 hours, preferably 4-8 hours. In a variant, there may be a step of maintaining at the temperature between the heating and cooling.