Mechanistic understanding and strategies to design interfaces of solid electrolytes: insights gained from transmission electron microscopy

Abstract

Solid electrolytes (SEs) have garnered increased attention for their promise to enable higher volumetric energy density and enhanced safety required for future battery systems. SEs are not only a key constituent in all-solid-state batteries, but also are important "protectors" of Li-metal anodes in next-generation battery configurations, such as Li-air, Li-S, redox flow batteries, among others. The impedance at interfaces associated with SEs, e.g. internal grain/phase boundaries and their interfacial stability with electrodes, represent two key factors limiting the performance of SEs, yet analyzing these interfaces experimentally at the nano/atomic scale is generally challenging. A mechanistic understanding of the possible instability at interfaces and propagation of interfacial resistance will pave the way to the design of high-performance SE-based batteries. In this review, we briefly introduce the fundamentals of SEs and challenges associated with their interfaces. Next, we discuss experimental techniques that allow for atomic-to-microscale understanding of ion transport and stability in SEs and at their interfaces, specifically highlighting the applications of state-of-art and emerging ex situ and in situ transmission electron microscopy (TEM) and scanning TEM (STEM). Representative examples from current literature that exemplify recent fundamental insights gained from these S/TEM techniques are highlighted. Applicable strategies to improve ion conduction and interfaces in SE-based batteries are also discussed. This review concludes by highlighting opportunities for future research that will significantly promote the fundamental understanding of SEs, specifically further developments in S/TEM techniques that will bring new insights into the design of high-performance interfaces for future electrical energy storage.

Solvent-Mediated Synthesis of Amorphous Li3PS4/Polyethylene Oxide Composite Solid Electrolytes with High Li+ Conductivity

“…TEM was employed to further probe: (i) the contact between the Li 3 PS 4 and PEO and (ii) nanocrystalline domains which may exist in these amorphous materials. Lithium thiophosphates are notoriously difficult to study via TEM at room temperature because of their high beam sensitivity. , Therefore, this study utilized cryo-TEM (holder cooled by liquid nitrogen) and low electron dose fluxes (<1000 e – Å –2 s –1 ) to minimize beam damage. Figure a and b show representative cryo-TEM images of Li 3 PS 4 + PEO composites containing 1 and 56 wt % polymer, respectively.…”

Investigation the sodium storage kinetics of H1.07Ti1.73O4@rGO composites for high rate and long cycle performance

“…The above operation was carried out in an argon‐filled glove box. A thin Na 2 O layer was expected to form on the surface of Na metal during the loading process of the TEM‐STM specimen holder into the TEM specimen chamber, which was served as the solid electrolyte in the following in‐situ TEM experiment 54,55 . The W tip with Na 2 O/Na was driven to contact with the HTO sample on the Cu rod, and an appropriate bias voltage was applied on the W tip to drive the sodiation reaction.…”

“…A thin Na 2 O layer was expected to form on the surface of Na metal during the loading process of the TEM-STM specimen holder into the TEM specimen chamber, which was served as the solid electrolyte in the following in-situ TEM experiment. 54,55 The W tip with Na 2 O/Na was driven to contact with the HTO sample on the Cu rod, and an appropriate bias voltage was applied on the W tip to drive the sodiation reaction. In order to minimize the influence of the electron beam, the electron beam was blocked except for imaging and video recording during the sodiation process.…”

Recent advancements in solid electrolytes integrated into all-solid-state 2D and 3D lithium-ion microbatteries

“…[213][214][215] The composition of this layer with N and P concentration gradients and their unique spatial distribution acts as an effective passivation layer. [214][215][216] LiPON/LCO interface, its composition, and electronic structure have been also studied by such techniques as X-ray photoemission spectroscopy, scanning transmission electron microscopy (STEM) coupled with electron energy loss spectroscopy (EELS). It was observed that the interface of a 10Å layer is usually formed with nitrogen-containing species.…”