Improving rate performances of Li-rich layered oxide by the co-doping of Sn and K ions

Abstract

The specific capacities and power performances of conventional cathode materials are still needed to improve in order to meet the demand for electrical vehicles. Li-rich layered oxide delivers a high specific capacity, but poor rate performances. Chemical doping is an effective way to address this challenge due to the expanded crystal lattice. Unlike a single ion substitution in the literature, here Li-rich layered oxides were doped by Sn and K to achieve the favorite rate performance, where Sn and K were assumed to replace transition metal ion and Li ion, respectively. Results indicate the co-doped samples result in an increasing capacity retention by more than 40% from 107.9 (contrast sample) to 151.5 mAh g−1 (co-doped sample) at 10 C-rate. Electrochemical impedance spectroscopy (EIS) and calculated diffusion coefficient of Li+ also confirmed the favorite rate performances for co-doped sample. Combining results of Rietveld structure refinement, we proposed that the reason for rate performances comes from the enlarged crystal lattices, which provides a smooth diffusion tunnel for Lithium ions during the charge/discharge processes. The as-adopted method provides a possibility to achieve the improved rate performances by co-doping big-size ions at the different crystal sites.