Hierarchical NaV(PO)F Microsphere Cathodes for High-Temperature Li-Ion Battery Application.

Sodium superionic conductor (NASICON)-structured NaV(PO)F cathode materials have received vast attention in the high-temperature storage performance due to their structural and thermal stability. Herein, hierarchical NaV(PO)F microspheres (NVPF-HMSs) consisting of nanocubes were designed by a one-pot facial solvothermal method. The hierarchical NaV(PO)F microsphere size is 2-3 μm, which is corroborated by FE-SEM and HR-TEM analyses. The NVPF-HMSs have been demonstrated as a cathode in Li-ion batteries at both low and elevated temperatures (25 and 55 °C, respectively). The NVPF-HMS cathode in a Li-ion cell exhibits reversible capacities of 119 mA h g at 0.1 C and 85 mA h g at 1 C with an 82% retention after 250 cycles at 25 °C. At elevated temperatures, the NVPF-HMS cathode exhibits a superior capacity of 110 mA h g at 1 C along with a retention of 90% after 150 cycles at 55 °C. Excellent capacity and cyclability were achieved at 55 °C due to its hierarchical morphology with a robust crystal structure, low charge-transfer resistance, and improved ionic diffusivity. The Li-ion storage performance of the NVPF-HMS cathode material at elevated temperatures was analyzed for the first time to understand the high-temperature storage property of the material, and it was found to be a promising candidate for elevated-temperature energy storage applications.