Improved Cycling Stability and Fast Charge–Discharge Performance of Cobalt-Free Lithium-Rich Oxides by Magnesium-Doping

Layered Li-rich, Co-free, and Mn-based cathode material, Li 1.17 Ni 0.25– x Mn 0.58 Mg x O 2 (0 ≤ x ≤ 0.05), was successfully synthesized by a coprecipitation method. All prepared samples have typical Li-rich layered structure, and Mg has been doped in the Li 1.17 Ni 0.25 Mn 0.58 O 2 material successfully and homogeneously. The morphology and the grain size of all material are not changed by Mg doping. All materials have a estimated size of about 200 nm with a narrow particle size distribution. The electrochemical property results show that Li 1.17 Ni 0.25– x Mn 0.58 Mg x O 2 ( x = 0.01 and 0.02) electrodes exhibit higher rate capability than that of the pristine one. Li 1.17 Ni 0.25– x Mn 0.58 Mg x O 2 ( x = 0.02) indicates the largest reversible capacity of 148.3 mAh g –1 and best cycling stability (capacity retention of 95.1%) after 100 cycles at 2 C charge–discharge rate. Li 1.17 Ni 0.25– x Mn 0.58 Mg x O 2 ( x = 0.02) also shows the largest discharge capacity of 149.2 mAh g –1 discharged at 1 C rate at elevated temperature (55 °C) after 50 cycles. The improved electrochemical performances may be attributed to the decreased polarization, reduced charge transfer resistance, enhanced the reversibility of Li + ion insertion/extraction, and increased lithium ion diffusion coefficient. This promising result gives a new understanding for designing the structure and improving the electrochemical performance of Li-rich cathode materials for the next-generation lithium-ion battery with high rate cycling performance.