Effect\nof Temperature on Intermediate Phases of Na<sub>3</sub>V<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub> during Cycling by <i>Operando</i> X‑ray Diffraction

Na<sub>3</sub>V<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub> (NVP) has\ngained a lot of attention due to its remarkable properties, such as\nits robust crystal structure, cycle life, rate capabilities, and so\non. Nevertheless, NVP undergoes a substantial decrease in its rate\ncapability at low temperatures, which limits its practical applications.\nIn this study, the performance of NVP at low, room, and high temperatures\nduring cycling is thoroughly investigated using synchrotron <i>operando</i> X-ray diffraction. The (de)insertion of two sodium\nions from Na<sub>3</sub>V<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub> to\nNa<sub>1</sub>V<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub> appeared\nto occur via two intermediate phases (Na<sub>2</sub>V<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub> and Na<sub>1.64</sub>V<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub>). The Na<sub>1.64</sub>V<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub> phase which is observed for the first-time during <i>operando</i> XRD measurements of NVP, exhibited limited stability\nat high temperatures. The increase in the quantity of these intermediate\nphases from high to low temperatures, especially at high C-rates,\ncould be anticipated to be one of the contributing factors of poor\nrate capabilities of NVP at low temperatures. This study encourages\nthe exploration of suitable strategies to enhance the performance\nof NVP at low temperatures and high C-rates.