Synergistic Bulk and Interface Engineering of Layered Oxide Cathodes for Na-Ion Batteries

Na-ion batteries (NIBs) hold promise for large-scale energy storage due to the abundance and low cost of Na resources, but their practical applications are still limited by the energy density and cycling stability of the cathodes. This study develops a synergistic bulk and interfacial modification strategy for O3-type NaNi1/3Fe1/3Mn1/3O2 (NFM) cathode using CaHPO4 (CP), integrating Ca doping and uniform NaPO3 coating to enhance structural stability and interfacial robustness. The modified cathode (2%CP@NFM) delivers excellent performance, retaining 92% capacity over 300 cycles at 2 C, no capacity decay after 400 cycles at 5 C, and 83% capacity retention over 1000 cycles at 1 C in full-cells. Structural analyses reveal remarkable suppression of irreversible phase transitions, gas evolution, and transition metal ion dissolution issues of layered oxide cathodes. These findings highlight the potential of a low-cost CP modification strategy in achieving high-performance NIBs for sustainable energy storage.