Pyrosynthesis of Na3V2(PO4)3@C Cathodes for Safe and Low-Cost Aqueous Hybrid Batteries

Rechargeable hybrid aqueous batteries (ReHABs) have emerged as promising sustainable energy-storage devices because all components are environmentally benign and abundant. In this study, a carbon-wrapped sponge-like Na3V2(PO4)(3) nanoparticle (NVP@C) cathode is prepared by a simple pyrosynthesis for use in the ReHAB system with impressive rate capability and high cyclability. A high-resolution X-ray diffraction study confirmed the formation of pure Na ion superionic conductor (NASICON) NVP with rhombohedral structure. When tested in the ReHAB system, the NVP@C demonstrated high rate capability (66mAhg(-1) at 32C) and remarkable cyclability over 1000 cycles (about 72% of the initial capacity is retained at 30C). Structural transformation and oxidation change studies of the electrode evaluated by using insitu synchrotron X-ray diffraction and exsitu X-ray photoelectron spectroscopy, respectively, confirmed the high reversibility of the NVP@C electrode in the ReHAB system through a two-phase reaction. The combined strategy of nanosizing and carbon-wrapping in the NVP particles is responsible for the remarkable electrochemical properties. The pyrosynthesis technique appears to be a promising and feasible approach to prepare a high-performance electrode for safe and low-cost ReHAB systems as nextgeneration large-scale energy storage devices.