Boosting the cycling stability of P2-type layered oxide cathodes via a synergistic high sodium and Li/Mg co-doping strategy
Sodium-ion batteries (SIBs) are emerging as a cost-effective alternative to lithium-ion batteries due to the abundance of sodium resources. Among cathode materials, P2-type layered oxides (Na_xTMO_2) offer high ionic conductivity and rate capability but suffer from low initial sodium content and Na+/vacancy ordering, leading to structural degradation and capacity fading. This study proposes a synergistic strategy combining high sodium content with Li/Mg co-doping to enhance the cycling stability of P2-type cathodes. The high sodium content increases the sodium reservoir, reducing the depth of desodiation for a given capacity, while Li/Mg co-doping mitigates Na+/vacancy ordering and stabilizes the crystal structure. The optimized cathode exhibits significantly improved cycling performance, retaining 82.3% of its initial capacity after 500 cycles at 1C, compared to 65.4% for the undoped counterpart. Furthermore, the co-doped material demonstrates enhanced rate capability, delivering 112 mAh/g at 5C, and suppressed phase transitions, as evidenced by in-situ X-ray diffraction. This work provides a rational design pathway for high-performance P2-type cathodes, addressing key bottlenecks in SIB commercialization.