Metal oxide materials for solid-state fluoride ion batteries

Abstract

This study explores the potential of metal oxide fluorides as cathode materials for solid-state fluoride-ion batteries (FIBs), aiming to combine the stability of intercalation-based electrode materials with the high energy density of conversion-based materials. Through comprehensive experimental investigations using techniques such as electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), linear sweep voltammetry (LSV), and X-ray diffraction (XRD), the compatibility and electrochemical performance of transition metal oxides (Cu2O, FeO, and Mn2O3) with CsPb0.9K0.1F2.9 (PK10) solid electrolyte and Pb/PbF2 composite anode are evaluated. Results indicate negligible room temperature capacity for Cu2O, FeO, and Mn2O3, suggesting potential limitations related to the cathode fluorination reaction. Additionally, PK10 electrolyte displays slight instability at room temperature, indicating potential electrochemical activity. Symmetric cell testing using Pb/PbF2 composite electrodes confirms the suitability of the Pb/PbF2 composite as both counter and reference electrodes. Notably, Cu2O full cells show enhanced specific capacity at elevated temperatures (60 °C), reaching 310.24 mAh/g during the first cycle, equivalent to 82.96% of the theoretical specific capacity. This considerable increase in capacity due to only a slightly higher temperature is attributed to reduced overpotential and enhanced fluoride ions diffusion rates. However, observation of capacity fade between cycles for the Cu2O cell at 60 °C suggests irreversible reactions, necessitating further investigation. In conclusion, this study highlights the potential of metal oxide cathode materials in solid-state FIBs, emphasizing the importance of understanding electrolyte stability and cathode compatibility for battery performance enhancement.