A NASICON-typed Na4Mn0.5Fe0.5Al(PO4)3 cathode for low-cost and high-energy sodium-ion batteries

Developing low-cost and high-voltage manganese (Mn)-based Na superionic conductor (NASICON) cathode materials have attracted extensive interest. The low capacity and cycling instability of Na 4 MnAl(PO 4 ) 3 (NMAP), however, limits its performance in sodium-ion batteries (SIBs). Herein, a binary Na 4 Mn 0.5 Fe 0.5 Al(PO 4 ) 3 (MNFAP) is fabricated to ease the structural instability and, in turn, deliver an improved reversible capacity of 102 mAh g −1 at 0.1 C and a high energy density of 287.7 Wh kg −1 . The synergistic interaction of Fe and Mn in Na 4 Mn 0.5 Fe 0.5 Al(PO 4 ) 3 /C composite leads to a one-phase solid-solution reaction mechanism with high structural reversibility. Theoretical calculations have also been performed to explain the upshifted voltage platform of both Fe 2+ /Fe 3+ and Mn 3+ /Mn 4+ redox potentials. The rational design of NASICON-type cathodes by regulating their composition with dual metal ions provides new perspectives for developing high-performance SIBs.