Controllable synthesis of spinel lithium nickel manganese oxide cathode material with enhanced electrochemical performances through a modified oxalate co-precipitation method

A spinel lithium nickel manganese oxide (LiNi_0.5Mn_1.5O₄) cathode material is synthesized with a modified oxalate co-precipitation method by controlling pH value of the precursor solution and introducing excessive Li source in the precursor. All the samples synthesized through this method are of Fd3m phase with a small amount of P4₃32 phase. It is found that pH value of the precursor solution considerably affects the morphology, stoichiometry and crystallographic structure of the target material, thereby resulting in different amounts of Mn³⁺ (i.e., different degree of disorder). 5% excessive Li source in the precursor may compensate for the lithium loss during the high-temperature sintering process and eliminate the Li_xNi_1-xO impurity phase. Under the optimized synthesis conditions, the obtained high-purity LiNi_0.5Mn_1.5O₄ spinel exhibits enhanced electrochemical performances. A reversible capacity of ca. 140 mAh g^-1 can be delivered at 0.1C and the electrode retains 106 mAh g^-1 at 10C rate. When cycled at 0.2C, a capacity retention of more than 98% is obtained in the initial 50 electrochemical cycles.