Bromine trifluoride as an oxidizing solvent for lithium batteries

Properties of bromine trifluoride were investigated. Electrochemical measurements were made. The fast Fourier transform technique was used to measure AC impedance spectra below 5 Hz. A Teflon-coated platinum wire with only the end exposed to the solvent yielded a stable reference electrode potential for BrF₃ studies. A passivating fluoride film stabilizes the lithium anode in BrF ₃, and open-circuit potentials exceeding 5.1 V can be obtained for the Li/BrF₃/Pt cell. The Li/BrF₃/Pt cell shows good discharge performance up to 50 mA/cm² at 50°C. Higher current densities, however, lead to a rapid decline in potential that is attributed to the rate-limiting transport of lithium ions across the passivating film. The cathode reaction, involving the reduction of BrF₃ to form Br₂ and F^-, is markedly affected by the nature of the cathode substrate. Stable open-circuit potentials were observed on Pt and Ir, and the reduction of BrF₃ occurs readily. Mixed potentials are apparently established on Fe, Co, Ni and Cu electrodes due to the corrosion and passivation of these metals in BrF₃