Spray-assisted synthesis of layered P2-type Na_0.67Mn_0.67Cu_0.33O₂ powders and their superior electrochemical properties for Na-ion battery cathode

Layered oxide materials are considered as prospective candidates for sodium-ion battery (SIB) cathode owing to their high operating voltage and theoretical capacity; however, their structural instability and vulnerability to environmental moisture prohibit their practical application. In this study, a synthesis method of layered P2-type Na_0.67Mn_0.67Cu_0.33O₂ (NMCO) powder with high crystallinity, possessing hexagonal layered structure with space group of P63/mmc, via spray pyrolysis is introduced. Moreover, Na-ion storage kinetics in NMCO cathode are systematically investigated using cyclic voltammetry, in-situ electrochemical impedance spectroscopy, and ex-situ X-ray diffraction spectroscopy. Through these analyses, the prepared cathode powders demonstrate that there is no additional induced stress during charge and discharge process owing to an elimination of phase transformation during the cycles. Furthermore, the optimized crystallinity of NMCO cathode post-treated at 750 °C (NMCO_750) leads to fast Na⁺ transport kinetics, thereby enhancing electrochemical performance. When applied as Na-ion cathode, NMCO_750 exhibits high gravimetric capacity of 84 mA h g⁻¹ at a rate of 0.5C and rate capabilities (62.5 mA h g⁻¹ at 15C).