Synergistic Enhancement of Ion Transport and Interfacial Stability in PVDF-HFP Gel Electrolytes via Regulation of Cross-Linking Density for Lithium Metal Batteries

Lithium metal is regarded as the most promising anode for next-generation batteries owing to its high theoretical capacity and low redox potential. However, severe lithium dendrite growth remains a major obstacle to the commercialization of lithium metal batteries. Gel polymer electrolytes (GPEs) have shown better dendrite suppression capability than liquid electrolytes. In this work, we demonstrate that the cross-linking density in a semi-interpenetrating polymer network (semi-IPN) of PVDF-HFP and PEGDA plays a critical role in regulating the solvation structure and interfacial stability of GPEs. By systematically tuning the cross-linking density via the PEGDA content, we construct a series of GPEs with well-controlled network structures. It is found that an optimal cross-linking density promotes the formation of contact ion pairs and aggregates (CIPs/AGGs) in the Li + solvation sheath, which facilitates the formation of a robust, LiF-rich solid electrolyte interphase (SEI). This stable interface effectively suppresses lithium dendrite growth and enhances electrochemical stability. Full cells with LiFePO 4 as the cathode deliver an excellent cycling performance, retaining 83.8% capacity after 400 cycles at 0.2C and 88.7% after 300 cycles at 0.5C. This study systematically reveals the crucial influence of cross-linking density on the Li + solvation structure and SEI properties, providing fundamental insights into the design of high-performance polymer electrolytes for advanced lithium metal batteries.