Spatially resolved structural order in low-temperature liquid electrolyte.

Xie, Yujun; Wang, Jingyang; Savitzky, Benjamin H; Chen, Zheng; Wang, Yu; Betzler, Sophia; Bustillo, Karen; Persson, Kristin et al. · Sci Adv · 2023

basic_science · Level V

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Abstract

Determining the degree and the spatial extent of structural order in liquids is a grand challenge. Here, we are able to resolve the structural order in a model organic electrolyte of 1 M lithium hexafluorophosphate (LiPF<sub>6</sub>) dissolved in 1:1 (v/v) ethylene carbonate:diethylcarbonate by developing an integrated method of liquid-phase transmission electron microscopy (TEM), cryo-TEM operated at -30°C, four-dimensional scanning TEM, 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<sup>+</sup>-(PF<sub>6</sub><sup>-</sup>)<i><sub>n</sub></i> (<i>n</i> > 2) local structural order induced by high LiPF<sub>6</sub> salt concentration.