Dual-site substitution enables high-voltage P2-Na0.67Ni0.33Mn0.67O2 cathodes with superior wide-temperature performance and enhanced ambient stability for sodium-ion batteries

Abstract

P2-type NaxNiyMnzO2 cathodes, while promising for rapid Na + transport, suffer from irreversible phase transitions, severe high-voltage degradation, and intrinsic hygroscopicity. To address these limitations, a synergistic doping strategy is applied to synthesize the P2-Na0.61Ca0.03Ni0.23Mg0.10Mn0.67O2 cathode with enhanced sodium storage performance and excellent ambient stability. The material achieves a compaction density of 3.16 g/cm 3 under 260 MPa, rivaling ternary lithium cathodes.Through Ca incorporation in Na layers and Mg substitution in transition metal framework, the cathode expands Na + pathways, suppresses P2-O2 phase transition, and promotes highly reversible Ni 2+ /Ni 4+ redox activity. It maintains 82.32 % capacity after 200 cycles at 1 C and delivers 64.62 mAh g -1 at 15 C within 2.0-4.3 V, vastly surpassing the 6.58 % retention and 27.91 mAh g -1 of the undoped Na 0.67 Ni 0.33 Mn 0.67 O 2 . While increasing the voltage to 4.5 V, 73.25 % capacity retention is maintained, far exceeding the pristine cathode (5.04 %). Notably, exceptional wide-temperature performance is achieved, with 90.73 % capacity retention after 200 cycles at -15 °C and 65.69 % after 2 150 cycles at 55 °C. Moreover, in full-cells the material still sustains 259.32 Wh•kg -1 after 150 cycles, underscoring the practical potential for advanced storage applications.