Spatial-temporally resolved optical imaging of electroplating/stripping processes in anode-free secondary batteries

Metal batteries with enhanced safety, long lifespan, and high energy density, are crucial for future cutting-edge energy storage applications. In view of recent developments, anode-free secondary batteries (AFSBs) are emerging as potential alternatives of conventional batteries due to their lower costs (reduced material consumption), simplified structure (anode side with bare current collector), and high theoretical energy density. However, AFSBs face challenges including severe metal dendrite growth, significant volume change, low coulombic efficiency, low plating-stripping efficiency, and unstable solid electrolyte interphase (SEI), which impede their safety and lifespan. Recent developments in optical imaging techniques are beneficial for the in situ/operando, real-time, and spatial-temporally resolved in-depth understanding of the electroplating/stripping processes and monitoring (inside batteries) the interfacial phenomena, helping to tackle such challenges. This review article presents an overview and analysis of recent developments in employing advanced optical imaging techniques to directly visualize and quantify these processes, contributing to a deeper understanding of metal deposition and dissolution at the nanoscale. Importantly, practical strategies for different (e.g., zinc, lithium, sodium) AFSBs are presented to overcome the aforementioned challenges. Finally, the potential of optical imaging techniques in AFSBs is envisioned, with an emphasis on overcoming current limitations and unveiling their full potential in developing efficient AFSBs.