Rational Electrolyte Molecular Design Regulates Donor Number for Stable Cycling of Li–CF x Batteries

ABSTRACT The irreversible nature of Li–CF x discharge chemistry, governed by the formation of insoluble LiF, fundamentally limits the development of rechargeable ultra‐high energy density batteries. Here, we report an electrolyte design strategy based on amide solvents with rationally tailored donor numbers to regulate Li + solvation and LiF dissolution. By systematically comparing N,N‐dimethylpropionamide (DMPA), N,N‐dimethyltrifluoroacetamide (DMTFA), and N,N‐diethyltrifluoroacetamide (DETFA), we demonstrate that modifying electron‐withdrawing and steric substituent groups enable a fine balance between oxidative stability and LiF solubility. Through combined molecular screening, donor number analysis, and LiF solubility tests, DETFA was identified as the optimal solvent for dissolving discharge‐generated LiF while maintaining compatibility with lithium metal, thereby mitigating cathode passivation and enabling stable cycling. The optimized electrolyte enables up to 40 discharge–charge cycles with high‐capacity retention in Li–CF x cells, using unmodified commercial CF x cathodes. Combined spectroscopic and electrochemical analyses reveal that the enhanced LiF solubility in the electrolyte is central to suppressing cathode passivation. These findings offer a molecular‐level design guideline for improving cycling stability in Li–CF x systems, highlighting electrolyte design as a key lever for electrolyte‐enabled rechargeability.