N-methylpyrrolidone-based electrolyte modulated CF bond weakening and Interface optimization synergistically enhances Li/CFx batteries energy density.

Abstract

Lithium/fluorinated carbon (Li/CF_x) batteries have garnered substantial interest from researchers due to their superior energy density and low self-discharge characteristics. However, the strong covalent CF bond in the CF_x cathode limits its discharge kinetics, affecting the actual power density and operating voltage. In this work, N-methylpyrrolidone (NMP) with high donor number has proposed as the main solvent of the electrolyte to facilitate the breaking of the CF bond through a bimolecular nucleophilic substitution (S_N2) reaction. This strategy effectively reduces the energy barrier for Li⁺ embedding and improves interfacial reaction potential. Notably, NMP forms a nitrogen-rich cathode-electrolyte interface (CEI) membrane during the discharge process, which enhances interfacial ionic conductivity and stabilizes the electrode-electrolyte interface. The optimized electrolyte system achieves a discharge plateau of 2.7 V and an energy density of 2128 Wh kg^-1 at 50 mA g^-1, significantly surpassing that of the conventional electrolyte (COE). This study provides a low-cost electrolyte optimization strategy, offering a promising approach to maintaining the high energy density and discharge voltage of Li/CF_x batteries.