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

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, and transition metal dissolution. In this study, an Al/Ti co-doped Na_0.67Fe_0.4Mn_0.4Al_0.1Ti_0.1O₂ (FM-AT) cathode is proposed and prepared. The introduction of Al/Ti effectively stabilizes the lattice oxygen structure by forming strong Al-O and Ti-O bonds, thereby suppressing oxygen redox activity and enhancing its reversibility. 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 in deep charge states. The FM-AT demonstrated excellent cycling stability, with a capacity of 137.1 mAh g^-1 at 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 at 200 mA g^-1, a capacity retention of 72.1% was achieved (versus 20.9% for the FM). This work offers a novel method for enhancing the structural stability of iron-manganese based electrodes and designing cost-effective, high-performance sodium ion cathodes.