Operando widefield optical imaging of electrochemical systems: a practical tutorial for battery materials research

Abstract Operando widefield optical imaging enables real-time, non-destructive observation of electrochemical systems functioning under realistic operating conditions, providing critical insights into dynamic processes that determine device performance and failure mechanisms. These methods employ light in the visible, or near-infrared regions to visualise morphological, structural, and chemical changes as they occur, bridging the gap between static ex-situ characterisation and actual device operation. The spatial and temporal resolution of optical approaches means they excel at capturing processes such as metal dendrite nucleation and growth in batteries and state-of-charge evolution in electrode materials during cycling. This tutorial provides guidance on implementing operando widefield optical imaging for electrochemical energy materials research, with a focus on battery electrode systems, as well as important practical considerations for addressing common pitfalls. Critical operational practices encompass optical path optimisation, vibration isolation, environmental stability control, and synchronisation of imaging with device performance data to enable correlation between microscopic events and macroscopic electrochemical behaviour. Systematic data analysis workflows are presented for extracting quantitative information from time-series images, including feature tracking, growth rate measurements, intensity analysis for state-of-charge mapping, and correlation with electrochemical data. The tutorial emphasises that while widefield optical imaging faces spatial resolution limitations compared to electron microscopy techniques, its accessibility, temporal resolution, and non-destructive nature make it particularly well suited to mechanistic studies of electrochemical processes. Greatest scientific value emerges through integration with complementary characterisation techniques to achieve comprehensive understanding of electrode material behaviour during operation.