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

ConspectusLithium-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.