Tracking Battery Dynamics by Operando Synchrotron X-ray Imaging: Operation from Liquid Electrolytes to Solid-State Electrolytes

Lithium-ion batteries have been widely applied in portable electronics due to their high energy density (300 Wh kg(-1)). However, their potential applications in electric vehicles and grid energy storage call for higher energy density toward 500 Wh kg(-1). Solid-state batteries, employing highly safe electrolytes to replace flammable liquid electrolytes, probably achieve this aim by reviving the metallic lithium anode. However, the sluggish lithium transport across the solid-solid interfaces seriously influences the actual battery electrochemistry in applications. Unlike the relatively complete basic theories of solid-liquid electrochemistry, the electrochemical fundamentals and models in the solid-state batteries are still ambiguous, which cannot give a guideline for optimizing strategies for high battery performance. Therefore, building better batteries for next-generation electrochemical energy storage remains a great challenge. Synchrotron X-ray imaging techniques are currently catching increasing attention due to their natural advantages, which are nondestructiveness, chemically responsiveness, elementally sensitivity, and high penetrability to enable operando investigation of a real battery. Based on the derived nanotomography techniques, it can provide 3D morphological information including thousands of slice morphologies from the bulk to the surface. Combined with X-ray absorption spectroscopy, X-ray imaging can even present chemical and phase mapping information, including the oxidation state, local environment, etc., with sub-30 nm spatial resolution, which addresses the issues that we only obtain as averaged information in traditional X-ray absorption spectroscopy. Through an operando charging/discharging setup, X-ray imaging enables the study of the correlation between the morphology change and the chemical evolution (mapping) under different states of charge and cycling. In addition, X-ray imaging breaks up the size limit of nanoscale samples for the in-situ transmission electron microscope imaging, which enables a large, thick sample with a broad field of view, truly uncovering the behavior inside a real battery system. In this Account, we focus on the topic of operando synchrotron X-ray imaging methodology and the emerging applications in the battery operation from liquid electrolytes to solid-state electrolytes, aiming to probe battery dynamics from the classic solid-liquid electrochemistry to emerging solid-solid electrochemistry. First, operando synchrotron X-ray imaging methodology and challenges of characterization in the real-time battery operation are discussed, including operando imaging principles, setup design, and impact factors in the actual experiment. Second, challenges facing operando synchrotron X-ray imaging in the battery development from liquid electrolytes to solid-state electrolytes have been summarized. Third, we highlight the fundamental issues in the battery dynamics obtained by the operando transmission X-ray imaging. Especially, we describe our recent progresses and new findings in probing real-time battery dynamics operation from liquid electrolytes to solid-state electrolytes. Overall, we provide a deep understanding from fundamentals to applications of operando imaging techniques in both battery systems, which will guide the investigation in developing next-generation battery devices.

Automated summary

Lithium-ion batteries have high energy density, but there is a need for further improvement in the field of electric vehicles and grid energy storage. Solid-state batteries may achieve higher energy density by using safer electrolytes, but the slow lithium transport across solid-solid interfaces remains a challenge. Synchrotron X-ray imaging techniques have the potential to provide in-depth insights into real battery systems.