A New High-Energy Cathode for a Na-Ion Battery with Ultrahigh Stability

Abstract

Large-scale electric energy storage is a key enabler for the use of renewable energy. Recently, the room-temperature Na-ion battery has been rehighlighted as an alternative low-cost technology for this application. However, significant challenges such as energy density and long-term stability must be addressed. Herein, we introduce a novel cathode material, Na 1.5VPO4.8F0.7, for Na-ion batteries. This new material provides an energy density of ∼600 Wh kg-1, the highest value among cathodes, originating from both the multielectron redox reaction (1.2 e- per formula unit) and the high potential (∼3.8 V vs Na+/Na) of the tailored vanadium redox couple (V3.8+/ V5+). Furthermore, an outstanding cycle life (∼95% capacity retention for 100 cycles and ∼84% for extended 500 cycles) could be achieved, which we attribute to the small volume change (2.9%) upon cycling, the smallest volume change among known Na intercalation cathodes. The open crystal framework with two-dimensional Na diffusional pathways leads to low activation barriers for Na diffusion, enabling excellent rate capability. We believe that this new material can bring the low-cost room-temperature Na-ion battery a step closer to a sustainable large-scale energy storage system. © 2013 American Chemical Society.