Synthesis and electrochemical studies of the 4 V cathode, Li(Ni_2/3Mn_1/3)O₂

Abstract

Layered Li(Ni_2/3Mn_1/3)O₂ compounds are prepared by freeze-drying, mixed carbonate and molten salt methods at high temperature. The phases are characterized by X-ray diffraction, Rietveld refinement, and other methods. Electrochemical properties are studied versus Li-metal by charge-discharge cycling and cyclic voltammetry (CV). The compound prepared by the carbonate route shows a stable capacity of 145 (±3) mAh g⁻¹ up to 100 cycles in the range 2.5-4.3 V at 22 mA g⁻¹. In the range 2.5-4.4 V at 22 mA g⁻¹, the compound prepared by molten salt method has a stable capacity of 135 (±3) mAh g⁻¹ up to 50 cycles and retains 96% of this value after 100 cycles. Capacity-fading is observed in all the compounds when cycled in the range 2.5-4.5 V. All the compounds display a clear redox process at 3.65-4.0 V that corresponds to the Ni^2+/3+-Ni^3+/4+ couple.