Study on sodium storage properties of manganese‐doped sodium vanadium phosphate cathode materials

Na+ superionic conductor (NASICON)-structured Na4VMn(PO4)3 (NVMP) possesses stable cycling performance at 2.5–3.8 V by replacing with lower cost Mn but suffers rapid capacity decay when further widening the voltage to 2.5–4.2 V, owing a less V4+/V5+ redox couple. Herein, stabilize couple and improve reversibility, series of carbon-coated NVMP (NVMP@C) different V/Mn ratios are compared, among which, Na3.25V1.75Mn0.25(PO4)3@C delivers an additional reversible 7 mAh g−1 3.9–4.2 V. Based on this, activate V4+/V5+, Al-doped Na3.25V1.75−yMn0.25Aly(PO4)3 structures synthesized. When 0.5 Al is doped, 15 corresponding can be released. In addition, it found that activation not conducive electrochemical reversibility C-rate performance, shrinkage whole framework structure oxidization V4+ V5+.