Mobile-ion and matrix dynamics in dinitrile- and cycloalcohol-based lithium electrolytes studied by solid-state NMR, dielectric spectroscopy and rheology

Abstract

Dinitrile-based lithium electrolytes were investigated through a comprehensive approach integrating nuclear magnetic resonance (NMR), dielectric spectroscopy, and viscosimetry. The reorientational motion within the succinonitrile-glutaronitrile (SN-GN) matrix was elucidated and the impact of lithium salt additions examined. Effect of enhanced molecular rigidity was investigated by incorporating fumaronitrile (FN) molecules with double central bond (C=C). Additionally, deuterated SN facilitated 2H NMR investigations of the reorientational dynamics, while 7Li NMR probed the charge carrier's dynamics. Viscosimetry, along with proton and lithium diffusion NMR measurements, offered insights interpreted via a paddle-wheel mechanism. Moreover, an exhaustive compilation and comparison of all available conductivity data for nitrile-based electrolytes was performed, with a specific focus on contextualizing the findings of this research. Ultimately, a comparative analysis was undertaken between the SN-GN matrix and an alternative hosting matrix comprised of cyclohexanol and cyclooctanol (HEX-OCT). This project involved dielectric spectroscopy and NMR investigations on various HEX-OCT-based electrolyte samples, expanding the approach employed for the SN-GN matrix on another substance class. In contrast to the dinitrile mixture, the HEX-OCT-based Li electrolytes were found to exhibit a revolving door mechanism, with volume effects playing a lesser role.