Fluoro-organosulfur catholytes to boost lithium primary battery energy

Abstract

Discovery of new electrochemical redox motifs is essential to expand the design landscape for energy-dense batteries.We report a family of fluorinated reactants based on pentafluorosulfanyl arenes (R-Ph-SF5) that allow for high electron-transfer numbers (up to 8-e2/ reactant) by exploiting multiple coupled redox processes, including extensive S-F bond breaking, yielding capacities of 861 mAh greactant 21 and voltages up to ∼2.9 V when used as catholytes in primary Li cells. At a cell level, gravimetric energies of 1,085 Wh kg21 are attained at 5 W kg21 and moderate temperatures of 50°C, with 853 Wh kg21 delivered at >100 W kg21, exceeding all leading primary batteries based on electrode + electrolyte (substack) 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 energy (1,195 Wh kg21), allowing for significant boosting of substack gravimetric energy of Li2CFx cells by at least 20% while exhibiting good shelf life and safety characteristics.