Uniaxially Aligned Relaxor Ferroelectric polymer electrolyte for high-performance solid-state lithium batteries

Abstract

Owing to their flexibility and cost-effectiveness, solid polymer electrolytes (SPEs) offer a promising alternative to inorganic solid electrolytes. Here, we present a highly oriented relaxor ferroelectric SPE based on a polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene (PVDF-TrFE-CFE) matrix achieved through external elongation. The incorporation of a large Cl atom into the ferroelectric polymer chain effectively increases the amorphous regions, allowing for up to 300 % stretching and facilitating the alignment of the polymer chains. This enhanced orientation, confirmed by 2D wide-angle X-ray diffraction, reduces tortuosity and improves Li-ion transport compared to the unstretched sample. Moreover, molecular dynamics (MD) simulations and electrochemical evaluations further demonstrate the advantages of this structure. The aligned amorphous regions, as revealed by MD simulations, provide favorable and continuous pathways for Li-ion transport, facilitating the stable electrochemical performance observed in both Li//Li symmetric cells and full cells with Li iron phosphate cathodes. Additionally, the incorporation of tantalum-doped Li lanthanum zirconate as an active filler further enhances the mechanical strength and electrochemical properties of the SPE, achieving a high ionic conductivity of approximately 3.63 x 10-4 S cm-1 and extended cycling stability. These results highlight the potential of highly oriented PVDF-based SPEs for next-generation Li-ion battery applications.