Enabling Multi-electron Reactions in NASICON Positive Electrodes for Aqueous Zinc-Metal Batteries

Sodium superionic conductor (NASICON)-structured compounds with a robust polyanionic framework, e.g., Na 3 V 2 (PO 4 ) 3, have been considered as promising cathode candidates for rechargeable batteries due to their open 3D structure and high thermal stability. However, their practical implementation in aqueous batteries is hindered by their structural instability during the charge/discharge process. Herein, Na 3 V 2- x Cr x (PO 4 ) 3 is investigated as a cathode material for aqueous zinc-metal batteries. It is identified that the Cr substitution has a significant effect on improving its rate capability and cycling stability. As a result, the optimal Na 3 V 1.5 Cr 0.5 (PO 4 ) 3 electrode delivers an ultra-stable cycling performance (68% capacity retention after 10,000 cycles at 1000 mA g –1 ). A two-electron reaction mechanism between V 4+ /V 3+ and V 5+ /V 4+ redox couples has been revealed during the electrochemical process for Zn-ion storage. This work verifies the feasibility of multi-electron reactions in NASICON-type cathodes for aqueous zinc batteries and sheds light on designing advanced cathode materials for other aqueous batteries.