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-SF 5 ) 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·g reactant −1 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·kg −1 are attained at 5 W·kg −1 and moderate temperatures of 50 °C, with 853 Wh·kg −1 delivered at >100 W·kg −1 , exceeding all leading primary batteries based on electrode + electrolyte (substack) mass. Voltage compatibility of R-Ph-SF 5 reactants and carbon monofluoride (CF x ) 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·kg −1 ), allowing for significant boosting of substack gravimetric energy of Li−CF x cells by at least 20% while exhibiting good shelf life and safety characteristics.