Operando SAXS/WAXS Unveils Solvated Structure Dynamics in PVDF-co-HFP Solid-State Electrolytes

Abstract

Solvation effectively enhances the Li⁺ transport and optimizes the mechanical properties of solid-state polymer electrolytes (SPE). However, operando characterization of the solvation formation process and the dynamic evolution of solvated structure during Li⁺ transport remains very challenging. Here, we developed an operando X-ray scattering device for the first time to reveal the effect of Li⁺ migration on the solvated structure during charging and discharging processes. The observed variations in operando small-angle X-ray scattering (SAXS) curves reveal that the conversion of AGG to n-AGG and contact ion pairs (CIP) with Li⁺ increases or decreases. n-AGG is formed by multiple AGG attractively bound together. The obstruction of Li⁺ transport pathways due to the degradation of chain segments, results in capacity decay. Operando grazing incidence wide-angle X-ray scattering (GIWAXS) shows that the crystalline regions of PVDF-co-HFP are gradually eroded during dimethyl sulfoxide (DMSO) evaporation, leading to a significant decrease in mid-term crystallinity. Due to the precise control of the process, PVDF-co-HFP SPE achieves a high conductivity of 2.08 × 10⁻⁴ S cm⁻¹ and a Li⁺ transference number of 0.58. The insights gained from this work provide opportunities for more precise control of SPE processing and optimizing Li⁺ transport channels to improve capacity decay.