Simultaneous Incorporation of V and Mn Element into Polyanionic NASICON for High Energy‐Density and Long‐Lifespan Zn‐Ion Storage

Abstract Aqueous Zn‐ion battery (AZIB) has attracted huge attention due to its distinct advantages such as abundant zinc sources, low development cost, high security, and environmental friendliness compared to traditional commercialized batteries. Developing novel cathode materials with high energy density and long lifespan is very important for the practical application of AZIB in the coming years. Herein, V and Mn elements are simultaneously incorporated into the NASICON host to make use of the electrochemical redox reaction in both V and Mn transition metal elements for aqueous Zn‐ion storage. A significant increase in both capacity and working voltage has been observed after Mn doping into Na 3 V 2 (PO 4 ) 3 to form Na 4 VMn(PO 4 ) 3 . Taking advantage of the merits of both high capacity and high voltage, the Na 4 VMn(PO 4 ) 3 @Graphene cathode delivers an optimal energy density of 309.7 Wh kg −1 with very stable cycle performance (89.1% capacity retention after 3000 cycles at 5.0 A g −1 ). A two‐step electron transfer mechanism between V 4+ /V 3+ and Mn 3+ /Mn 2+ redox couple in Na 4 VMn(PO 4 ) 3 has been revealed during the electrochemical process for Zn‐ion storage.