Hierarchical Na3V2(PO4)2F3 Microsphere Cathodes for High-Temperature Li-Ion Battery Application

Abstract

Sodium superionic conductor (NASICON)-structured Na₃V₂(PO₄)₂F₃ cathode materials have received vast attention in the high-temperature storage performance due to their structural and thermal stability. Herein, hierarchical Na₃V₂(PO₄)₂F₃ microspheres (NVPF-HMSs) consisting of nanocubes were designed by a one-pot facial solvothermal method. The hierarchical Na₃V₂(PO₄)₂F₃ 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^-1 at 0.1 C and 85 mA h g^-1 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^-1 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.

Scheme 1. Schematic Representation of the Synthesis of NVPF-HMSs

Figure 1

(a) Powder XRD pattern of NVPF-HMS and (b) crystal structure of NVPF.

Figure 2

(a,b) Low–high magnification FE-SEM images of NVPF-HMSs.

Figure 3

(a,b) Low–high magnification HR-TEM images of NVPF-HMSs, (c) high-resolution image, and (d) SAED pattern.

Figure 4

(a) Survey spectra and (b) vanadium 2p and oxygen 1s peaks of NVPF-HMSs.

Figure 5

Electrochemical performance of the NVPF-HMS cathode at 25 °C; (a) CV profile at 0.2 mV s^–1, (b) galvanostatic charge–discharge curve at 0.1 C, (c) rate performance at different C values, (d) long cycle performance at 1 C, and (e) EIS spectra.

Figure 6

Electrochemical performance of the NVPF-HMS cathode at 55 °C, (a) galvanostatic charge–discharge curve at 1 C, (b) EIS spectra, and (c) long cycle performance at 1 C.