Improvement of electrochemical performance of layered manganese enriched electrode material with the coating of Ni0.25Mn0.75Ox composite oxides

• Composite oxides Ni0.25Mn0.75Ox are used as coating material for Li1.2Ni0.2Mn0.6O2.
• The electrochemical properties of Li1.2Ni0.2Mn0.6O2 are improved after coating.
• The composite metal oxides are more effective than single metal oxides or fluorides.

Layered solid solution cathode Li1.2Ni0.2Mn0.6O2 has been synthesized and coated by composite oxides Ni0.25Mn0.75Ox with varying amounts (2, 5 and 8 wt%) in this paper. The effect of coated Ni0.25Mn0.75Ox on the physical and electrochemical properties of the materials has been discussed through the characterizations of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), electrochemical impedance spectroscopy (EIS), discharge, cyclic performance and rate capability. The discharge capacities and coulombic efficiencies of Li1.2Ni0.2Mn0.6O2 in the first cycle have been improved and increase with the increasing content of coated Ni0.25Mn0.75Ox. The 8 wt% Ni0.25Mn0.75Ox coated Li1.2Ni0.2Mn0.6O2 delivers 298 mA h g−1 for the first discharge capacity and 91.9% for the first coulombic efficiency, compared with 228 mA h g−1 and 66.1% for pristine Li1.2Ni0.2Mn0.6O2. However, the 5 wt% Ni0.25Mn0.75Ox coated Li1.2Ni0.2Mn0.6O2 shows the best capacity retention (94.2% for 80 cycles) and rate capability (106 mA h g−1 at 10 °C). Electrochemical impedance spectroscopy (EIS) results show that the Rct of Li1.2Ni0.2Mn0.6O2 electrode decreases after coating, which is responsible for superior rate capability.