Solvent-exchange strategy induced robust eutectic solvent-based gel polymer electrolytes for lithium metal batteries

Abstract

Instability resulting from inferior mechanical properties and the growth of lithium dendrites hinders the application of gel polymer electrolytes (GPEs) in lithium metal batteries. In this work, a solvent exchange strategy was developed to fabricate a polyvinylidene fluoride (PVDF)-based gel polymer electrolyte (PFGPE-x). This process induces conformational changes in the extended PVDF chains, enhancing polymer-polymer interactions and promoting microcrystal formation, which leads to a uniform and robust physical crosslinking network. The fabricated PFGPE-x electrolyte exhibits robust mechanical properties with a Young's modulus up to 47.9 MPa, which is much higher than the modulus of the previously reported PVDF-based GPEs. The N-methyl acetamide (MAc)/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)-derived deep eutectic solvents are integrated in the polymer backbone via hydrogen bonding, forming continuous ion channels and facilitating the formation of β crystal phase in PFGPE-x. Li symmetric cells with PFGPE-4 electrolyte exhibited a long lifespan of over 650 h at a current density of 0.05 mA cm⁻². The LFP|PFGPE-4|Li cell shows an initial discharge capacity of 98.7 mAh g⁻¹, and maintains 90.7% of initial capacity after 50 cycles at 25 °C. This work presents a novel approach to constructing GPE with high modulus for high performance lithium metal batteries.