P2-type Na2/3Mn1/2Co1/3Cu1/6O2 as advanced cathode material for sodium-ion batteries: Electrochemical properties and electrode kinetics

Sodium-ion batteries (SIBs) have been considered as one of foremost promising alternatives for the widely used lithium-ion batteries. In order to assemble high-performance SIBs, cathode materials with stable structure and superior electrochemical properties are needed emphatically. In this work, we prepare a new layered oxide material, P2-type Na2/3Mn1/2Co1/3Cu1/6O2 (P2-MCC) with the morphology of hexagonal micro-prisms, by a sol-gel method. When used as cathode material for SIBs, the P2-MCC exhibits good cycling stability (e.g., >83.5% capacity retention after 100 cycles at 100 mA g−1) and superior high-rate performance. Moreover, it also owns an attractive ability of fast-charging, e.g., a high capacity retention of ∼66% after 100 cycles as charging at a high current density of 200 mA g−1 and discharging at a low current density of 10 mA g−1. Such good electrochemical properties can be originated from the synergetic improvement of selected multi-metallic ions and enhanced electrode kinetics (high apparent Na-diffusion kinetics) which is demonstrated by the galvanostatic intermittent titration technique, electrochemical impedance spectroscopy and cyclic voltammetry at various scan rates.