Synthesis, structure and electrochemical properties of a new cation ordered layered Li-Ni-Mg-Mo oxide

Abstract

Lithium-rich oxides are attracting intense interest as the next generation cathode materials for lithium-ion batteries due to their high theoretical capacity. Nevertheless, these materials suffer from a number of shortcomings, such as oxygen loss at high voltage, large hysteresis and poor rate capability. In this work, we show that through a dual cation substitution strategy replacing Ti with Mo and Mg, the disordered rocksalt (DRS) Li1.2Ni0.4Ti0.4O2 is transformed into a new cation ordered layered phase Li1.2Ni0.4Mo0.2Mg0.2O2, with the high valence dopant Mo6+ on the (0,0,0) site. Li1.2Ni0.4Mo0.2Mg0.2O2 showed improved performance compared to that of the similarly prepared DRS Li1.2Ni0.4Ti0.4O2 material (∼190 mA h g−1vs. ∼105 mA h g−1 after 10 cycles, respectively). The characteristics of the electrochemical process were studied using ex situ XRD and XAS, which indicated the involvement of both Ni and Mo redox during the cycling as well as the electrochemical instability of the layered phase which changes to a disordered rocksalt phase on cycling.