Imaging solid–electrolyte interphase dynamics using operando reflection interference microscopy

Abstract

The quality of solid-electrolyte-interphase (SEI) dictates the performances of most battery chemistries, especially lithium (Li)-metal, but its formation processes as well as evolution during battery operation remain little understood due to the lack of reliable in-operando characterization tools of sufficient spatial and temporal resolutions. Herein, we report an in-operando reflection interference microscope (RIM) that enables the real-time imaging of SEI during formation and evolution in state-of-the-art electrolyte based on LiPF6 dissolved in organic carbonates. By mapping the minimal and localized optical signals generated from interphasial events, RIM reveals with extremely high sensitivity that the stratified structure of SEI formed during four distinct steps, including the emergence of a permanent inner inorganic layer enriched in LiF, the transient assembly of an interfacial structure of an electrified double layer, and the consequent emergence of a temporary outer organic-rich layer, whose presence is reversible with electrochemical cycling. Comparing the morphologies of SEIs, we identify an inverse correlation between the thicknesses of two interphasial sub-components: the thicker the LiF-rich inner layer, the thinner the organic-rich outer layer, implying that the permanent inorganic-rich inner layer dictates the organic-rich outer layer formation and Li nucleation. We also find that trace presence of water (50 ppm) in the electrolyte induces a much thicker and higher quality LiF-rich layer and a much thinner organic-rich layer in SEI, which leads to less electrolyte consumption, and more uniform Li nucleation on the electrode surface. The real-time visualization of SEI dynamics achieved for the first time in this work provides a guideline for the rational design of interphases, a battery component that has been the least understood and most challenging barrier to developing electrolytes for future batteries.

Dynamic Molecular Investigation of the Solid-Electrolyte Interphase of an Anode-Free Lithium Metal Battery Using In Situ Liquid SIMS and Cryo-TEM

“…However, the voltage drops relatively fast after Li metal is stripped, and this observation also supports that part of the SEI layer can be electrochemically dissolved. Our explanation is supported by a recent paper, in which the SEI was studied using operando reflection interference microscopy and similar SEI dynamics was reported …”

“…Our explanation is supported by a recent paper, in which the SEI was studied using operando reflection interference microscopy and similar SEI dynamics was reported. 39 However, it is well-known that the SIMS sputter rates may vary on different materials. Furthermore, another interesting question is if the electrochemically undissolved (i.e., irreversible) SEI, which might contribute to the major functions of the SEI (conducting Li + ions and blocking electrons), fully forms at 3.0 V or not.…”

Interphases in aqueous rechargeable zinc metal batteries

“…The extensive characterization techniques discussed in this section provide a fundamental understanding toward the structures and properties of the SEI, benefiting further optimization of aqueous electrolytes and artificial SEI to achieve a stable and robust interphase in aqueous RZMBs. More in situ techniques, such as operando reflection interference microscopy, 140 are required to further understand the dynamic formation mechanism of the SEI and its physicochemical properties to realize the practical applications of aqueous RZMBs. Moreover, the advanced SEI characterization techniques for aqueous Zn batteries may also be applicable for other energy storage devices to investigate the interfacial structures and improve the battery performance.…”

In‐Situ‐Generated Electron‐Blocking LiH Enabling an Unprecedented Critical Current Density of Over 15 mA cm−2 for Solid‐State Hydride Electrolytes

“…[3] SEs also exhibit higher electrochemical stability to match high-voltage cathodic materials and Li-metal anodes to improve the energy density of the battery systems. [2] Inorganic SEs (e.g., sulfide, halide, oxide, hydride, etc.) have been extensively studied, [4] and most of them are highly reactive with Li anode, resulting in a severe deterioration of structures and performances.…”