Modelling structure and ionic diffusion in a class of ionic liquid crystal-based solid electrolytes

TL;DR

This study designs and analyzes novel liquid crystal electrolytes for solid-state Li-ion batteries, demonstrating how molecular structure influences ionic conductivity and highlighting their potential for safer, high-performance energy storage.

Contribution

The paper introduces a new class of liquid crystal electrolytes with tunable ionic conductivity based on molecular self-organization and ion interactions, supported by simulations and experiments.

Findings

Conductivity depends on nanochannel formation influenced by alkyl chain length.

Ion pair interactions significantly affect ionic conduction.

Highly ordered lamellar phases achieved at 99% purity.

Abstract

Next-generation high-efficiency Li-ion batteries require an electrolyte that is both safe and thermally stable. A possible choice for high performance all-solid-state Li-ion batteries is a liquid crystal, which possesses properties in-between crystalline solids and isotropic liquids. By employing molecular dynamics simulations together with various experimental techniques, we have designed and analyzed a novel liquid crystal electrolyte composed of rigid naphthalene-based moieties as mesogenic units, grafted to flexible alkyl chains of different lengths. We have synthesized novel highly ordered lamellar phase liquid crystal electrolytes at 99% purity and have evaluated the effect of alkyl chain length variation on ionic conduction. We find that the conductivity of the liquid crystal electrolytes is directly dependent on the extent of the nanochannels formed by molecule self-organization, which itself depends non-monotonously on the size of the alkyl chains. In addition, we show that the ion pair interaction between the anionic center of the liquid crystal molecules and the Li+ ions plays a crucial role in the overall conductivity. Based on our results, we suggest that further improvement of the ionic conductivity performance is possible, making this novel family of liquid crystal electrolytes a promising option for the design of entirely solid-state Li+ ion batteries.