Localized High-Concentration Electrolytes Get More Localized Through Micelle-Like Structures

TL;DR

This paper uncovers micelle-like microstructures in localized high-concentration electrolytes, linking their unique microstructure to improved stability and performance in lithium-metal batteries.

Contribution

It reveals the formation of micelle-like structures in LHCE electrolytes and connects microstructural features with electrolyte stability and SEI formation.

Findings

Micelle-like structures exist in LHCE electrolytes.

Salt concentration peaks at room temperature.

Microstructure influences SEI stability.

Abstract

Liquid electrolytes in batteries are typically treated as macroscopically homogeneous ionic transport media despite having complex chemical composition and atomistic solvation structures, leaving a knowledge gap of microstructural characteristics. Here, we reveal a unique micelle-like structure in a localized high-concentration electrolyte (LHCE), in which the solvent acts as a surfactant between an insoluble salt in diluent. The miscibility of the solvent with the diluent and simultaneous solubility of the salt results in a micelle-like structure with a smeared interface and an increased salt concentration at the centre of the salt-solvent clusters that extends the salt solubility. These intermingling miscibility effects have temperature dependencies, wherein an exemplified LHCE peaks in localized cluster salt concentration near room temperature and is utilized to form a stable solid-electrolyte interphase (SEI) on Li-metal anode. These findings serve as a guide to predicting a stable ternary phase diagram and connecting the electrolyte microstructure with electrolyte formulation and formation protocols to form stable SEI for enhanced battery cyclability.