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

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 Aspergillus niger-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 Na3.9Mn0.9Al0.1V(PO4)3/AN (NMAVP/AN) exhibits 105.9 mA h g–1 at 0.5 C, and the as-prepared Na3.1MnV(PO3.7F0.3)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).