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

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Abstract
NASICON‐type sodium vanadium phosphate (Na3V2(PO4)3, or NVP) cathode materials have great potential for fast charging and long cycling sodium‐ion batteries (SIBs) similar to lithium iron phosphate (LiFePO4, 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., Na4V2(PO4)3, or Na4VP) is developed to address the Na loss problem. Conventional NVP can be easily transformed into the Na4VP by a facile and fast chemical solution treatment (30 s). Na‐free‐anode Na4VP and hard carbon‐Na4VP full cells are assembled to evaluate the electrochemical properties of the Na‐rich NVP cathode. The Na4VP 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.
Funding Information
  • Program of Shanghai Academic Research Leader (21XD1420800)
  • National Natural Science Foundation of China (22005059)
  • China Postdoctoral Science Foundation (2019M661339)
  • National Science Foundation (NNCI 2025489, NNCI 1542101)
  • Molecular Engineering and Sciences Institute, University of Washington
  • Clean Energy Institute

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