Spatially Resolved Structural Order in Low-Temperature Liquid Electrolyte

Abstract

Determining the degree and the spatial extent of structural order in liquids is a significant grand challenge. Here, we are able to resolve the structural order in a model organic electrolyte of 1 M lithium hexafluorophosphate (LiPF6) dissolved in 1:1 (v/v) ethylene carbonate (EC):dimethyl carbonate (DEC) by developing an integrated method of liquid-phase TEM, cryogenic transmission electron microscopy (cryo-TEM) operated at -30°C, four-dimensional scanning transmission electron microscopy (4D-STEM), and data analysis based on deep learning. This study reveals the presence of short-range order (SRO) in the high salt-concentration domains of the liquid electrolyte from liquid phase separation at the low temperature. Molecular dynamics simulations suggest the SRO originates from the Li + -(PF6 -)n (n>2) local structural order induced by high LiPF6 salt concentration. TeaserAn integrated advanced transmission electron microscope operated at -30°C reveals short-range order in liquid electrolyte.