Cascade Defluorination of Perfluoroalkylated Catholytes Unlocks High Lithium Primary Battery Capacities

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.