Cation/Anion Doping Strategy for Na₄MnV(PO₄)₃ with High Energy Density and Long Cycling Life through Construction by <i>Aspergillus niger</i>

Na₄MnV(PO₄)₃ (NMVP) has gained attention for its high redox potential, good cycling stability, and competitive price but suffers from poor intrinsic electronic conductivity and Jahn-Teller effect from Mn³⁺. In this work, cation/anion doping strategy was used for <i>Aspergillus niger-</i>bioderived carbon-coated NMVP (NMVP/AN) to improve the structural stability and electrochemical performance, where Al³⁺ doping inhibited the dissolution of Mn and enhanced the Mn³⁺/Mn²⁺ redox pair activity; besides, F^- doping not only weakens the Na₂-O bond but also endows the hierarchical and porous structure of NMVP/AN, which led to a more rapid and fluid transfer of Na⁺. The elaborately designed Na_3.9Mn_0.9Al_0.1V(PO₄)₃/AN (NMAVP/AN) exhibits 105.9 mA h g^-1 at 0.5 C, and the as-prepared Na_3.1MnV(PO_3.7F_0.3)₃/AN (NMVPF/AN) delivers 104.1 mA h g^-1 at 5 C. Further demonstration of the hard carbon//NMAVP/AN full cell manifests the good potential of Al³⁺-doped NMVP/AN for practical applications (100.6 mA h g^-1 at 1 C). These findings open up the possibility of unlocking the high-performance Na superionic conductor (NASICON).