Artificial Organo-Fluoro-Rich Anode Electrolyte Interface and Partially Sodiated Hard Carbon Anode for Improved Cycle Life and Practical Sodium-Ion Batteries.

In this work, a strategy is introduced wherein without keeping any excess cathode, a practical full-cell sodium-ion battery has been demonstrated by utilizing a hard carbon (HC) anode and sodium vanadium fluorophosphate and carbon nanotube composite (NVPF@C@CNT) cathode. A thin, robust, and durable solid electrolyte interface (SEI) is created on the surface of HC through its incubation wetted with a fluoroethylene carbonate (FEC)-rich warm electrolyte in direct contact with Na metal. During the incubation, the HC anode is partially sodiated and passivated with a thin SEI layer. The sodium-ion full cell fabricated while maintaining N/P ∼1.1 showed the first cycle Coulombic efficiency of ∼97% and delivered a stable areal capacity of 1.4 mAh cm at a current rate of 0.1 mA cm realized for the first time to the best of our knowledge. The full cell also showed a good rate capability, retaining 1.18 mAh cm of its initial capacity even at a high current rate of 0.5 mA cm, and excellent cycling stability, giving a capacity of ∼1.0 mAh cm after 500 cycles. The current strategy presents a practical way to make a sodium-ion full cell, utilizing no excess cathode material, significantly saving cost and time.