Recent progress of layered structured P2-and O3-type transition metal oxides as cathode material for sodium-ion batteries

The demand for grid-scale energy storage devices is increasing extensively nowadays. However, existing energy storage devices, consisting of Nickel-cadmium batteries, Lithium-ion batteries, and Nickel-metal hydride batteries, cannot meet future demands due to irregular dispersal and the high price of the reserves. In this regard, sodium-ion batteries (SIBs) that utilize Na-ions in their charge storage mechanism have gained significant consideration due to price advantage and extensive dispersal of sodium reserves in the earth's crust. Due to its significant effect on the electrochemical performance, the cathode materials are considered a key component for SIBs. Up to now, Polyanionic compounds, Prussian blue analogues, Organic materials, and Layered transition metal oxides (LTMOs) have been investigated as cathode materials for SIBs. LTMOs are considered potential cathode materials for SIBs due to their feasible synthesis, excellent specific capacity, and environmental friendliness. Layered P2-and O3-types are found to be promising candidates for their use as cathode material in SIBs commercialization. This review features the current development in LTMOs (mainly P2-and O3-types) as cathode candidates for SIBs, their synthesis techniques, the present challenges faced by this technology, modification approaches to enhance the electrochemical performance, and future aspects of developing fully functional SIBs.