Theory of Transport in Highly Concentrated Electrolytes

TL;DR

This paper develops a comprehensive continuum transport theory for highly concentrated ionic liquids and their mixtures, enabling detailed analysis of bulk and interfacial behaviors in electrochemical systems.

Contribution

It introduces a unified, thermodynamically consistent framework for modeling transport in pure ionic liquids and their mixtures, covering bulk and interfacial phenomena.

Findings

Validated the theory with zinc-ion battery experiments.

Described dynamic bulk transport effects in ionic liquids.

Analyzed interfacial structures in electrochemical cells.

Abstract

Ionic liquids are promising candidates for novel electrolytes as they possess large electrochemical and thermodynamic stability and offer a high degree of tunability. As purely-ionic electrolyte without neutral solvent they exhibit characteristic structures near electrified interfaces and in the bulk, both being described theoretically via separate frameworks and methodologies. We present a holistic continuum theory applying to both regions. This transport theory for pure ionic liquids and ionic liquids-mixtures allows the systematic description of the electrolyte evolution. In particular, dynamic bulk-transport effects and interfacial structures can be studied. The theory is thermodynamically consistent and describes multi-component solutions (ionic liquids, highly concentrated electrolytes, water-in-salt electrolytes). Here, we give a detailed derivation of the theory and focus on bulk transport processes of ionic liquids as appearing in electrochemical cells. In addition, we validate our framework for a zinc-ion battery based on a mixture of ionic-liquid and water as electrolyte.