Al/Ti Co-doped Fe/Mn-based layered oxide for high-performance sodium-ion storage

Abstract

Fe-Mn based layered transition metal oxides are compelling candidates for sodium-ion cathodes owing to their high specific capacity and cost-effectiveness. However, their practical application is hampered by inherent challenges including the Jahn-Teller effect, lattice oxygen loss, transition metal dissolution. In this study, Al/Ti co-doped Na0.67Fe0.4Mn0.4Al0.1Ti0.1O2 (FM-AT) cathode is proposed and prepared. The introduction of Al/Ti, creating strong Al-O and Ti-O bonds, effectively stabilizes the lattice oxygen and elevates the reversibility of anionic redox reactions. Furthermore, the stability of the transition metal layer is effectively enhanced, suppressing transition metal dissolution and the P2-OP4 phase transition associated with TMO2 layer slippage at deep charge states. The FM-AT demonstrates excellent cycling stability, with a capacity of 137.1 mAh g-1 under 20 mA g-1 and a capacity retention of 85.5% after 50 cycles (55.7% for the pristine FM cathode). Even after 200 cycles under 200 mA g-1, a capacity retention of 72.1% is achieved (versus 20.9% for the FM). This work offers a novel method for enhancing the structural stability of iron-manganese based electrode and designing cost-effective, high-performance sodium ion cathodes.