Quaternary Transition Metal Oxide Layered Framework: O3-Type Na[Ni0.32Fe0.13Co0.15Mn0.40]O2 Cathode Material for High-Performance Sodium-Ion Batteries

Analogous compounds in lithium-ion batteries (LIBs), various ternary chemical compositions in O3-type layered oxides, have been introduced in sodium-ion batteries (SIBs). However, O3-type ternary transition metal oxide cathodes, including the NaNixCoyMnzO2 and NaNixFeyMnzO2 (x + y + z = 1) compounds, continue to face several challenges with respect to their low reversible capacity and poor cycle retention owing to their structural instability. Herein, we propose the well-balanced quaternary transition metal oxide structure of O3-type Na[Ni0.32Fe0.13Co0.15Mn0.40]O2 as cathode materials that have an average composition of both Na[Ni0.25Fe0.25Mn0.5]O2 and Na[Ni0.4Co0.3Mn0.3]O2 compounds. Compared to its respective ternary members, the Na[Ni0.32Fe0.13Co0.15Mn0.40]O2 cathode exhibits a higher specific capacity as well as improved cycling stability and rate capability. The post-mortem ex-situ X-ray diffraction (XRD) studies of a cycled electrode clearly show that coexistence of quaternary transition metals in a Na[Ni0.32Fe0.13Co0.15Mn0.40]O2 cathode could improve the structural stability. Moreover, quaternary transition metal oxide frameworks effectively prevent the dissolution of transition metals during cycling, thus improving the battery performances. The appealing physical properties and electrochemical performance of this material demonstrate its great promise for a high-performance O3-type cathode in sodium-ion batteries.