Tuning Diluent‐Solvent Interactions via Optimal Diluent Fluorination for Favorable Graphite Anode Interface

ABSTRACT Localized high concentration electrolytes (LHCEs) have garnered significant attention in the past decade due to their unique cation‐solvate microstructure, which effectively stabilizes the graphite anodes. However, a long battery (anode) cycle life demands simultaneous optimization of Li + solvation structure, Li + desolvation kinetics, composition of the crucial solid‐electrolyte interphase (SEI), interfacial stability, and Li + diffusion across SEI, factors which are challenging to balance. Though the diluents play a key role in governing LHCE solvation environments, the influence of diluent fluorination and diluent‐solvent intermolecular interactions on graphite SEI formation remains underexplored. This work demonstrates that controlled fluorination of the diluent, rather than heavy fluorination, results into effective Li + (de)‐intercalation at graphite anodes. The optimally fluorinated diluent, difluoromethoxybenzene (DFMB), induces the most favorable diluent‐solvent interactions with triethyl phosphate (TEP) as compared to methoxybenzene (MB) and trifluoromethoxybenzene (TFMB). Moreover, the identification and quantification of the diluent‐solvent intermolecular interactions by the Diffusion‐Ordered spectroscopy (DOSY) and Nuclear Overhauser Effect Spectroscopy (NOESY) nuclear magnetic resonance (NMR) techniques establishes 1 H‐ 1 H interactions between diluent and solvent to be the key factor driving the solvation dynamics of LHCE. Such a molecular tuning of diluent‐solvent interactions produces a cascading impact on solvation microstructure, Li + desolvation kinetics, interphase characteristics, and interfacial stability of graphite anodes.