Cascade Defluorination of Perfluoroalkylated Catholytes Unlocks High Lithium Primary Battery Capacities

Abstract

<jats:title>Abstract</jats:title><jats:p>Exceeding the energy density of lithium−carbon monofluoride (Li−CF<jats:sub>x</jats:sub>), today's leading Li primary battery, requires an increase in fluorine content (<jats:italic>x</jats:italic>) 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 (&lt;1.3 V versus Li/Li<jats:sup>+</jats:sup>), 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 (<jats:italic>R</jats:italic><jats:sub>F</jats:sub> = −C<jats:sub>n</jats:sub>F<jats:sub>2n+1</jats:sub>). 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<jats:sup>−1</jats:sup><jats:sub>fluoroalkyl‐aromatic</jats:sub> and energies of 1785 Wh kg<jats:sup>−1</jats:sup><jats:sub>fluoroalkyl‐aromatic</jats:sub>. The voltage compatibility between fluoroalkyl‐aromatics and CF<jats:sub>x</jats:sub> enables design of hybrid cells containing C−F redox activity in both solid and liquid phases, with a projected enhancement of Li–CF<jats:sub>x</jats:sub> gravimetric energy by 35% based on weight of electrodes+electrolyte. With further improvement of cathode architecture, these “liquid CF<jats:sub>x</jats:sub>” analogues are strong candidates for exceeding the energy limitations of today's primary chemistries.</jats:p>