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 CsPb_0.9K_0.1F_2.9 (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.