Résumé
The mixed Mn2+/V3+ Na-super-ionic-conductor (NASICON) cathode material Na4MnV(PO4)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.