• • Mg2+ doping suppresses Jahn-Teller distortion by shortening Mn–O bond length, as evidenced by charge density analysis, leading to enhanced structural stability and capacity retention of 90.4% after 200 cycles at 0.1 C.
• • The NFMPP-Mg@CNTs cathode achieves a discharge capacity of 126 mAh g−1 at 0.1 C, close to the theoretical capacity of 129 mAh g−1, and maintains 80% capacity after 3000 cycles at 0.5 C, demonstrating excellent long-term cycling stability.
• • Mg2+ doping widens Na+ diffusion channels, reducing the migration barrier from 0.566 eV to 0.398 eV, as calculated by first-principles, which enhances Na+ diffusion kinetics and ionic conductivity.
• • The material delivers an energy density of 401 Wh kg−1, among the highest reported for mixed phosphate cathodes, positioning it as a strong candidate for large-scale energy storage applications.