Near-Room-Temperature Quasi-Solid-State F-Ion Batteries with High Conversion Reversibility Based on Layered Structured Electrolyte

摘要

Solid-state fluoride ion batteries (SSFIBs) are anion-shuttle-driven andalkali-metal-free emerging energy storage systems, and have the advantagesof low cost, high safety, and energy density. However, the current major challengesof SSFIBs or quasi-SSFIBs are the lack of high-conductivity fluorideelectrolytes and the difficulty of mild-temperature operation of full cells. Here,a 2D fluoride conductor (KSn_2F_5) synthesized by mechanochemical method isemployed as the compatible solid electrolyte with a high F-ion conductivity of10~(?4) S cm~(?1) at 60℃. The high concentration and frequent hopping of chargecarriers in F-vacancy-rich KSn2F5 contribute to the higher ionic conductivitycompared to most reported fluoride structures. Integrating this layered electrolytewith high-voltage CuF_2 cathode and Sn/SnF_2 anode, a highly reversiblecycling of conversion-type quasi-SSFIBs with a discharge capacity of150 mAh g~(?1) for at least 70 cycles at 60℃ is achieved. The interface engineeringaided by tetra-n-butylammonium fluoride salt facilitates the F-iontransfer between cathode and electrolyte and fluorination/defluorinationconversion mechanism of CuF_2 cathode with optimized multiphase andnanodomain distributions.