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, Na1.5VPO4.8F0.7, 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 (V(3.8+)/V(5+)). 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.

Manganese hexacyanomanganate open framework as a high-capacity positive electrode material for sodium-ion batteries

“…expand or shrink only o3% throughout the range of electrochemical cycling (Supplementary Table 1), which reflects the stable crystal structure of open-framework PBAs 12,33 . The overall volume expansion is 1.36%, which is the lowest value ever observed for NIBs 10 .…”

“…In the past, researchers have explored the possibility of adapting positive electrode materials of LIBs, including Na super ionic conductor structures 7 , layered oxides 5,8 , tunnel-structured oxides 9 and fluorophosphates 10 , for Na þ intercalation. However, close-packed, oxide-ion arrays connected by first-row transition metal elements do not have enough interstitial space in the structure for rapid Na þ diffusion 11 .…”

Polyanion‐Type Electrode Materials for Sodium‐Ion Batteries

“…b) Energy density of Na 1.5 VPO 4.8 F 0.7 compared with various cathode materials for NIBs and Li‐ion batteries. Reproduced with permission 94. Copyright 2013, American Chemical Society.…”

Phosphate Framework Electrode Materials for Sodium Ion Batteries

“…The reaction mechanisms during charge/discharge process include combinations of solid solution and two‐phase reaction behavior, but the structural motif was maintained throughout these reactions 223. The relationship among V 3+ /V 4+ /V 5+ redox reactions, Na + −Na + ordering, and Na + intercalation mechanisms of Na 3 (VO 1− x PO 4 ) 2 F 1+2 x in SIBs were investigated by Park et al through a combined theoretical and experimental approach 218, 224. They found that the redox mechanism and phase reactions varied with fluorine content.…”