Effective enhancement of the electrochemical performance of layered cathode Li1.5Mn0.75Ni0.25O2.5via a novel facile molten salt method

Abstract

A series of nanocrystalline lithium-rich cathode materials Li_1.5Mn_0.75Ni_0.25O_2.5 have been prepared by a novel synthetic process, which combines the co-precipitation method and a modified molten salt method. By using a moderate excess of 0.5LiNO₃–0.5LiOH eutectic salts as molten media and reactants, the usage of deionized water or alcohol in the subsequent wash process is successfully reduced, compared with the traditional molten salt method. The materials with different excess Li salt content, Li/M (M = Ni + Mn) = 1.55, 1.65, 1.75, 1.85, 1.95, 2.05, molar ratio, show distinct differences in their structure and charge–discharge characteristics. The structural characterization demonstrates that the sample with a ratio of Li/M = 1.85 has a more well-defined α-NaFeO₂ structure and a more enlarged Li layer spacing. It also exhibits the best comprehensive electrochemical behavior with the highest coulombic efficiency, the best rate capability and optimal cycling stability. More specifically, it delivers a dramatically improved initial coulombic efficiency of 87.86%, and a discharge capacity of 129 mA h g⁻¹ even at an ultra-high current density of 2000 mA g⁻¹ (10C). Meanwhile a superior cycling stability is also observed with a high discharge capacity of 251 mA h g⁻¹ and a retention of 98% at 0.2C after 50 cycles. Our results reveal that this method is facile and feasible to synthesize a high rate and high capacity lithium-rich material.