Na‐Rich Na3V2(PO4)3 Cathodes for Long Cycling Rechargeable Sodium Full Cells

Abstract NASICON‐type sodium vanadium phosphate (Na 3 V 2 (PO 4 ) 3 , or NVP) cathode materials have great potential for fast charging and long cycling sodium‐ion batteries (SIBs) similar to lithium iron phosphate (LiFePO 4 , or LFP) cathode materials used in lithium‐ion batteries (LIBs). However, the cycle life and energy density in the full cell using NVP materials need to be significantly improved. This paper investigates the degradation mechanisms of NVP‐based SIBs and identifies the Na loss from the cathode to the anode solid electrolyte interphase (SEI) reactions as the main cause of capacity degradation. A new Na‐rich NVP cathode (e.g., Na 4 V 2 (PO 4 ) 3 , or Na 4 VP) is developed to address the Na loss problem. Conventional NVP can be easily transformed into the Na 4 VP by a facile and fast chemical solution treatment (30 s). Na‐free‐anode Na 4 VP and hard carbon‐Na 4 VP full cells are assembled to evaluate the electrochemical properties of the Na‐rich NVP cathode. The Na 4 VP cathode provides excess Na to compensate for the Na loss, resulting much longer cycle life in the full cells (>400 cycles) and a high specific energy and power density. Good low‐temperature performance is also observed.