Optimizing high voltage Na3V2(PO4)2F3 cathode for achieving high rate sodium-ion batteries with long cycle life

Sodium-ion batteries have gained an intense attention as a promising alternate for Li-ion batteries due to their low cost, and abundant availability. To meet high energy density requirements, developing a high voltage cathode with ultra-long cycle life is of great importance. Na3V2(PO4)2F3 (NVPF) features a high working voltage, fast sodium-ion diffusion channels, and small volume change during the cycling process. However, the practical performance of NVPF cathode is currently hindered by poor Na+ ion diffusion at high voltage, low cycle life, and limited rate behavior. Herein, we evaluate the effect of synthesis conditions in sol–gel technique, binders (PVDF, PAI and CMC), and electrolytes (ether, and ester based solvents) to overcome the diffusion limitation in high voltage NVPF cathode. Benefiting from the synergistic effect of CMC binder, and DEGME electrolyte, and reduced graphene oxide composite, NVPF effectively overcome the potential barrier during Na+ ion insertion/extraction at high voltage. NVPF with CMC binder and DEGDME electrolyte displayed a high Na+ ion diffusion kinetics, low cell resistance, and delivered an excellent electrochemical performance. NVPF delivered a high coulombic efficiency (92%), long cycle life (10,000 cycles), and an excellent rate performance (50 C), outperforming the conventional PVDF binder, and carbonate based electrolytes. Furthermore, the full-cell constructed by NVPF cathode, and Na3V2(PO4)3 anode delivered an capacity retention. The current study provides new insights for overcoming the kinetic barrier during sodium ion storage in high voltage cathode that could direct the research development towards high energy sodium-ion batteries.