Temperature‐dependent Battery Performance of a Na3V2(PO4)2F3@MWCNT Cathode and In‐situ Heat Generation on Cycling

Excellent structural stability, high operating voltage, and high capacity have made Na3V2(PO4)2F3 a promising cathode material for sodium‐ion batteries. However, high‐temperature battery performances and heat generation measurements have not been systematically reported yet. Carbon‐coated Na3V2(PO4)2F3@MWCNT (multi‐walled carbon nanotube) samples are fabricated by a hydrothermal‐assisted sol‐gel method and the electrochemical performances are evaluated at three different temperatures (25, 45, and 55 °C). The well‐crystallized Na3V2(PO4)2F3@MWCNT samples exhibit good cycling stability at both low and high temperatures; they deliver an initial discharge capacity of 120–125 mAhg−1 at a 1 C rate with a retention of 53 % capacity after 1,400 cycles with 99 % columbic efficiency. The half‐cell delivers a capacity of 100 mAhg−1 even at a high rate of 10 C at room temperature. Furthermore, the Na3V2(PO4)2F3@MWCNT samples show good long‐term durability; the capacity loss is an average of 0.05 % per cycle at a 1 C rate at 55 °C. Furthermore, ionic diffusivity and charge transfer resistance are evaluated as functions of state of charge, and they explain the high electrochemical performance of the Na3V2(PO4)2F3@MWCNT samples. In‐situ heat generation measurements reveal reversible results upon cycling owing to the high structural stability of the material. Excellent electrochemical performances are also demonstrated in the full‐cell configuration with hard carbon as well as antimony Sb/C anodes. (Not) feeling the heat: A composite Na3V2(PO4)2F3@MWCNT electrode is synthesized by a sol‐gel method, and its electrochemical performances are examined in half‐ and full‐cell configurations. A Na3V2(PO4)2F3@MWCNT/Na coin‐type half‐cell cathode and activated hard carbon anode full‐cell demonstrates a promising cathode and associated full‐cell configuration for high power and thermally safe energy‐storage applications.