A NASICON‐Type Positive Electrode for Na Batteries with High Energy Density: Na4MnV(PO4)3

Abstract The mixed Mn 2+ /V 3+ Na‐super‐ionic‐conductor (NASICON) cathode material Na 4 MnV(PO 4 ) 3 is prepared by solid‐state reaction at 800 °C under argon. When used as a positive electrode in Na batteries, this material can exchange three electrons for two transition metals, that is, yielding a high gravimetric capacity of 156 mAh g −1 on charge when the upper cutoff voltage is set to 4.3 V versus Na + /Na. Operando X‐ray diffraction during battery operation is performed and it is shown that the mechanisms of Na + insertion/extraction are single or biphasic depending on the electrochemical cycling conditions.