Deciphering Molecular Structural Effect on Redox‐Mediated CO 2 Reduction Reaction Mechanisms for Aprotic Li‐CO 2 Batteries

ABSTRACT Redox mediators (RMs) emerge as critical enablers for unlocking the energy potentials of aprotic Li‐CO 2 batteries through solution‐mediated CO 2 reduction reaction (CO 2 RR). However, the structural effect of RMs on CO 2 RR pathways and catalytic efficiency remains insufficiently understood. Herein, through a comparative investigation of model quinone (Q)‐based RMs using in situ spectroscopic techniques coupled with theoretical calculations, it is revealed that reduced Q species chemically bind with CO 2 to form metastable Li n (Q‐xCO 2 ) adducts (n, x = 1 or 2), which subsequently dissociate into LiCO 2 intermediates and further generate Li 2 CO 3 and CO as discharge product while regenerating Li n Q (n = 0 or 1) for sustained redox cycling. The dissociation of Li n (Q‐xCO 2 ) adducts constitutes the rate‐determining step under non‐polarization conditions. The introduction of electron‐withdrawing groups (EWGs) into the Q moiety can enhance discharge potentials, but creates a kinetic trade‐off: increased dissociation kinetics of Li n (Q‐xCO 2 ) adducts and suppressed adduct formation due to diminished CO 2 binding affinity for reduced Q species. Strategic electronic modulation via optimized EWG substitution balances this CO 2 affinity and adducts dissociation equilibrium, achieving simultaneous improvements in discharge potential and capacity. Our work provides fundamental guidelines for the rational design of advanced RMs in next‐generation Li‐CO 2 batteries.