High-capacity sulfide all-solid-state lithium battery with a conversion-type iron fluoride cathode

Abstract

Transition metal fluoride-lithium batteries with low cost and high energy densities are considered hopeful candidates for next-generation rechargeable lithium batteries. However, conversion-type metal fluorides suffer from poor electronic conductivity, irreversible structural change, unfavorable dissolution of transition metal cations, high voltage hysteresis, and rapid capacity degradation upon cycling. In this study, reduced graphene oxide (rGO) sheets with uniformly anchored iron trifluoride (FeF₃) composites are prepared by an in situ solvothermal approach. The rGO-FeF₃ composites are combined with soft sulfide solid electrolytes to build sufficient electronic/ionic conductive pathways, which leads to substantial improvements in the electrochemical performances of FeF₃ cathodes. In this work, an unprecedented reversible capacity of 742.7 mA h g⁻¹ (569 mA h g⁻¹) with extraordinary 119% capacity retention at 0.1C (0.4C) for 50 (120) cycles is achieved. Moreover, an outstanding reversible capacity of 409 mA h g⁻¹ at 1C (1C = 500 mA g⁻¹) with excellent stability of 300 cycles is also realized, which substantially surpasses the state-of-the-art performance for the FeF₃ cathode in various battery systems at a similar current density. This research provides a novel strategy to overcome the limitations of transition metal fluorides and paves a new way for their practical applications in all-solid-state batteries.