Dissociation mechanism of lithium salt by BaTiO3 with spontaneous polarization

In composite solid-state electrolytes, functional fillers with ferroelectric properties have demonstrated their ability to prompt the dissociation of lithium salt (LiFSI), thereby significantly enhancing ionic conductivity. However, the underlying mechanism has been challenging to fully comprehend, which hinders further improvement in electrolyte performance. Herein, we elucidate the dissociation mechanism of LiFSI induced by the ferroelectric fillers of BaTiO3. We find that the dipole's direction of tetragonal-BaTiO3 (T-BTO) can slightly deflect under an external electric field of a battery to enhance the polarization. The {001} planes of T-BTO, aligned along the polarization direction, exhibit a more pronounced ability to dissociate lithium salt and accumulate anions owing to the formation of surface-absorbed FSI− by binding between the O of FSI− and the Ti of T-BTO. Moreover, T-BTO3−x fillers with enhanced spontaneous polarization by oxygen vacancy defects can further amplify these effects, leading to an increased proportion of free Li+ from 19% to 72%. The ionic conductivity of T-BTO3−x–poly(vinylidene fluoride) composite electrolyte can reach a value as high as 8.4 × 10−4 S cm−1 at 25 °C. This work reveals the dissociation mechanism of lithium salt due to the introduction of ferroelectric fillers and highlights its great promise for developing practical solid-state composite electrolytes.