Reversible and Fast (De)fluorination of High-Capacity Cu2O Cathode: One Step Toward Practically Applicable All-Solid-State Fluoride-Ion Battery

All-solid-state fluoride-ion batteries (FIBs) are regarded as promising energy storage devices; however, currently proposed cathodes fail to meet the requirements for practical applications in terms of high energy density and high rate capability. Herein, the first use of stable and low-cost cuprous oxide (Cu2O) as a cathode material for all-solid-state FIBs with reversible and fast (de)fluorination behavior is reported. A phase-transition reaction mechanism involving Cu+/Cu2+ redox for charge compensation is confirmed, using the combination of electrochemical methods and X-ray absorption spectroscopy. The first discharge capacity is approximately 220 mAh g(-1), and fast capacity fading is observed in the first five cycles, which is ascribed to partial structural amorphization. Compared with those of simple metal/metal fluoride systems, the material shows a superior rate capability, with a first discharge capacity of 110 mAh g(-1) at 1 C. The rate-determining step and probable structural evolutions are investigated as well. It is believed that the comprehensive investigations of Cu2O as a cathode material described in this work can lead to an improved understanding of all-solid-state FIBs.

Automated summary

This study reports the first use of stable and low-cost cuprous oxide as a cathode material for all-solid-state fluoride-ion batteries, showing reversible and fast defluorination behavior. The phase-transition reaction mechanism involving Cu+/Cu2+ redox for charge compensation is confirmed using electrochemical methods and X-ray absorption spectroscopy. Despite fast capacity fading observed in the initial cycles, the material exhibits superior rate capability compared to simple metal/metal fluoride systems.