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, 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.