Cascade Defluorination of Perfluoroalkylated Catholytes Unlocks High Lithium Primary Battery Capacities
Haining Gao, Kosuke Yoshinaga, Katherine Steinberg, Timothy M. Swager, Betar M. Gallant
Abstract
Abstract Exceeding the energy density of lithium−carbon monofluoride (Li−CF x ), today's leading Li primary battery, requires an increase in fluorine content ( x ) that determines the theoretical capacity available from C−F bond reduction. However, high F‐content carbon materials face challenges such as poor electronic conductivity, low reduction potentials (<1.3 V versus Li/Li + ), and/or low C−F bond utilization. This study investigates molecular structural design principles for a new class of high F‐content fluoroalkyl‐aromatic catholytes that address these challenges. A polarizable conjugated system—an aromatic ring with an alkene linker—functions as electron acceptor and redox initiator, enabling a cascade defluorination of an adjacent perfluoroalkyl chain ( R F = −C n F 2n+1 ). The synthesized molecules successfully overcome premature deactivation observed in previously studied catholytes and achieve close‐to‐full defluorination (up to 15/17 available F), yielding high gravimetric capacities of 748 mAh g −1 fluoroalkyl‐aromatic and energies of 1785 Wh kg −1 fluoroalkyl‐aromatic . The voltage compatibility between fluoroalkyl‐aromatics and CF x enables design of hybrid cells containing C−F redox activity in both solid and liquid phases, with a projected enhancement of Li–CF x gravimetric energy by 35% based on weight of electrodes+electrolyte. With further improvement of cathode architecture, these “liquid CF x ” analogues are strong candidates for exceeding the energy limitations of today's primary chemistries.