Fluoro-Organosulfur Catholytes to Boost Lithium Primary Battery Energy

Discovery of new electrochemical redox motifs are essential to expand the design landscape for energy-dense batteries. We report a family of fluorinated reactants based on pentafluorosulfanyl arenes that allow for high electron-transfer numbers (up to 8-e−/reactant) by exploiting multiple coupled redox processes including extensive S–F bond breaking, yielding capacities of 861 mAh∙greactant-1 and voltages up to ~2.9 V when used as catholytes in primary Li cells. At a cell level, gravimetric energies of 1085 Wh/kg are attained at moderate temperatures of 50 ºC, with 853 Wh/kg delivered at >100 W/kg, exceeding all leading primary batteries based on electrode + electrolyte (sub-stack) mass. Voltage compatibility of R-Ph-SF5 reactants and carbon monofluoride (CFx) conversion cathodes further enabled investigation of a hybrid battery containing both fluorinated catholyte and cathode. The hybrid cells reach extraordinarily high cell active mass loading (~80%) and allow for significant boosting of sub-stack gravimetric energy of Li−CFx cells by at least 20% while exhibiting good shelf life and safety characteristics.