Effects of Components in Solvent-Enhanced PVDF-HFP-Based Polymer Electrolyte on Its Electrochemical Performance

Lithium (Li) metal has been considered as a potential substitute for the graphite anode in Li-ion batteries to further boost their energy density. Polymer electrolytes (PEs) are expected to be applied in Li metal batteries (LMB) to replace liquid electrolytes due to safety concerns. Among others, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)-based electrolytes offer clear advantages such as improved processability and chemical/electrochemical stability. However, Li dendrite growth in LMBs and the low Li-ion conductivity of solid polymer electrolytes (SPEs) still hinder their practical applications. To address this issue, it has been proposed that solvent-enhanced PVDF-HFP-based polymer electrolytes (SPPEs) with a tuned amount of residual N-methyl-2-pyrrolidone (NMP) could provide improved ionic conductivity and outstanding chemical/electrochemical stability. We report herein the effects of different salts, polymer, and additives on the electrochemical performance and interface stability of SPPEs. We demonstrate that lithium salts and blended polymers play a pivotal role in the electrochemical performance of SPPEs. In addition, additives exert a remarkable effect on the stripping/plating behaviors of metallic lithium anode in SPPEs. SPPEs with adequate LiNO₃ are found to be stable with lower overpotentials at 0.5 mA cm⁻² on cycling of symmetrical Li cells. These results highlight novel SPPE strategies for optimizing the ionic conductivity and stabilizing the lithium metal anodes.