Improved Electrochemical Performance of RbxLi1.27-xCr0.2Mn0.53O2 Cathode Materials via Incorporation of Rubidium Cations into the Original Li Sites

Abstract

Rubidium doped cathode materials RbxLi1.27-xCr0.2Mn0.53O2 (x = 0, 0.01, 0.03 and 0.05) were prepared via a solid state reaction method. The influences of the amount of Rb+ incorporated in the cathodes on the electrochemical performance were investigated in detail. It was found that the initial specific capacity, coulombic efficiency and rate performance were improved by Rb doping. Among the prepared cathode samples, the Rb0.03Li1.24Cr0.2Mn0.53O2 material presented the best results. The material showed an initial discharging capacity of 224.9 mAh·g−1, a capacity retention of 98.8% after 50 cycles and excellent high-rate performance of 92.0 mAh·g−1 at 5C rate. The improved diffusion coefficient of Li ions in the Rb+ incorporated cathodes was confirmed by electrochemical impedance measurement. The changes in diffusion coefficient are in good accordance with the changes in lattice parameter of c axis obtained from XRD Rietveld refinement. With the increase in Rb concentration, the interlayer spacing increases, then the diffusion of Li ions is enhanced and finally the electrochemical properties is improved. However, when x reaches 0.05, the lattice distorsion happened, c axis begins to shrink, the Li ion diffusion is restricted, and therefore the electrochemical performance is reduced with further increase in Rb concentration.