Decoupling Segmental Dynamics and Particle–Polymer Interactions in Poly(vinylidene Fluoride-co-hexafluoropropylene) [PVDF-HFP]/Li1.3Al0.3Ti1.7(PO₄)₃ Composite Solid Electrolyte

Understanding the lithium-ion dynamics in a composite polymer electrolyte (CPE) system is necessary for its application toward all-solid-state batteries. In this study, the dynamic properties of CPE with a poly(vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) polymer as the host and Li1.3Al0.3Ti1.7(PO4)3 (LATP) as the filler with different concentrations (0%, ∼4.4%, ∼7.6%, and ∼14.2%) are investigated for Li-ion transport via a temperature-dependent broadband dielectric spectroscopy technique. The estimations on ionic conductivity indicate that CPEs with filler concentration up to ∼7.6% exhibit two different conduction mechanisms (viz., Vogel–Fulcher–Tammann and Arrhenius conduction) within the temperature range of 180 to 360 K. However, for CPEs with ∼14% filler concentration, a single Arrhenius-like ion conduction mechanism was observed. The ionic conductivity increases with filler concentration until a particular threshold and then leads to a decrease in ionic mobility. To understand the possible reasons behind the enhancement of the ionic conduction, segmental and chain relaxation dynamics were fitted using the Havriliak–Negami functions. The estimated relaxation time constants reveal that for CPE samples with 4.4% and 7.6% of LATP fillers, segmental relaxation becomes slower by four orders than that of the pristine sample, while the CPE with ∼14.2% filler exhibits significantly faster relaxation. On the other hand, relaxation times corresponding to chain relaxation in the CPEs increase compared to the pristine sample. The enhancement in ionic conduction for CPEs with 4.4% and 7.6% LATP fillers can be attributed to the slower segmental relaxation, whereas higher filler concentration (∼14.2%) results in suppressed motion with the LATP percolation path being the dominant ion conduction medium. Further, the particle–polymer interaction in these CPEs is probed by examining the distribution of the relaxation times. The appearance of faster relaxation modes is attributed to chain entanglements and interdiffusion, leading to the enhancement of ion conduction through more free volume at the interfacial zone of the filler and polymer. This work highlights the significant importance of understanding the polymer–particle interface to design CPEs for future battery applications.