Enhanced performance of PVDF-based solid electrolytes via PEO-induced α-to-amorphous phase transition enabling stable lithium batteries

Abstract

Solid polymer electrolytes (SPEs) have attracted great interest due to their superior safety. However, in SPEs, high crystallinity reduces the amorphous regions in the polymer and restricts the mobility of polymer segments, thereby lowering ionic conductivity, severely hinder its practical application. In this study, polyvinylidene fluoride (PVDF) and polyethylene oxide (PEO) were crosslinked by stepwise stirring and solution casting to resolve the contradiction: intermolecular interactions induce the transformation of the non-polar α-phase into an amorphous phase, thereby reducing crystallinity. The resulting continuous dipole moments form efficient ion channels, while PEO’s amorphous regions provide transport pathways that promote lithium salt dissociation. Consequently, this process simultaneously reduces crystallinity and enhances conductivity. Crosslinked SPEs with good lithium salt solubility, low interfacial impedance, larger lithium-ion mobility number (0.51), wider electrochemical window (5.0 V (vs. Li⁺/Li)), higher ionic conductivity at room temperature (3.1 × 10^-4 S cm⁻¹ at 25 °C), and high mechanical strength (4.45 MPa) were formed. After assembling into a battery, the symmetric cell exhibits significantly enhanced cycle life, maintaining 97 % capacity retention after 300 h of cycling. These findings demonstrate the substantial potential of PVDF/PEO crosslinked SPE (PVDF-based SPEs) for applications in lithium batteries.