Enhanced electrochemical performance of lithium rich layered cathode materials by Ca2+ substitution

Abstract

The poor cycling stability and large voltage decay in Li-rich cathode materials is related to the layer to spinel structural transformation. It is understood that the ease of structural transformation is correlated to the amount of oxygen gas released during the first charge above 4.5V. So one of the effective strategy to improve the electrochemical properties is by suppressing oxygen evolution through stabilizing oxygen radical intermediates by tuning metal-oxygen bond characteristics such as covalency, bond energy, iconicity, etc. through cation substitutions in Li rich phases. In this work we report that small amount of Ca substitution in Li layers of Li rich phases, Li1.2-2xCaxCo0.13Ni0.13Mn0.54O2 (x=0.005) improves the electrochemical cycling stability as well as the rate capability. With x=0.005 calcium substitution, the initial coulombic efficiency increased from 70% (for the pristine) to 83% and the capacity retention is improved from 71% to 87% after 100 cycles. Similarly Ca doping improves the rate capability especially at higher rates. The improved electrochemical performance of the Ca doped Li-rich cathode can be attributed to the fine-tuning of the crystal-chemical aspects manifested through enhanced structural stability and increased interlayer distance.