Conductivity enhancement in plastic-crystalline solid-state electrolytes

TL;DR

This study demonstrates that replacing molecules in succinonitrile plastic crystals with larger ones significantly enhances Li+ ion conductivity, offering a promising route for improved solid-state electrolytes in energy storage.

Contribution

It introduces a novel method of increasing conductivity in plastic-crystalline electrolytes by molecular substitution, supported by dielectric spectroscopy analysis.

Findings

Conductivity of Li+ ions increased by several decades.

Enhanced coupling between ionic and reorientational motions observed.

Supports the 'revolving door' mechanism for conductivity enhancement.

Abstract

Finding new ionic conductors that enable significant advancements in the development of energy-storage devices is a challenging goal of current material science. Aside of material classes as ionic liquids or amorphous ion conductors, the so-called plastic crystals (PCs) have been shown to be good candidates combining high conductivity and favourable mechanical properties. PCs are formed by molecules whose orientational degrees of freedom still fluctuate despite the material exhibits a well-defined crystalline lattice. Here we show that the conductivity of Li+ ions in succinonitrile, the most prominent molecular PC electrolyte, can be enhanced by several decades when replacing part of the molecules in the crystalline lattice by larger ones. Dielectric spectroscopy reveals that this is accompanied by a stronger coupling of ionic and reorientational motions. These findings, which can be understood in terms of an optimised "revolving door" mechanism, open a new path towards the development of better solid-state electrolytes.