Cu-doped P2-Na0.5Ni0.33Mn0.67O2 encapsulated with MgO as a novel high voltage cathode with enhanced Na-storage properties

Abstract

We report a novel P2-type Na_0.5Ni_0.26Cu_0.07Mn_0.67O₂ (NCM) mixed oxide obtained by conventional solid-state method as a prospective cathode for sodium-ion battery (SIB) applications. X-ray diffraction analysis shows that NCM exhibits a hexagonal structure with a P6₃/mmc (No. 194) space group, in which Na-ions are located in a prismatic environment. The introduction of Cu into the lattice enhances its structural stability, showing a capacity retention of 83% after 100 cycles, which is much better than its native compound. MgO encapsulation was performed to further improve the interfacial kinetics and suppress P2–O2 phase transition. MgO coating significantly improves the electrochemical activity at high cut-off voltages, for instance, highest capacity of 131 mA h g⁻¹ was noted with superior rate performance of 83 and 51 mA h g⁻¹ at 5 and 20C, respectively. As expected, dual modification by Cu-ion doping and MgO coating provides a novel strategy for designing high-rate SIB cathodes.