The role of in situ and operando techniques in unraveling local electrochemical supercapacitor phenomena

In response to the escalating demands for efficient energy storage solutions, the enhancement of current supercapacitor electrode materials and the innovation of advanced alternatives are paramount. Traditional electrochemical methods, which have their limitations in offering a deep understanding of local electrochemical activities, such as ion adsorption, intercalation as well as transport. To truly grasp, manage, and enhance the electrochemical capabilities within energy materials, it's vital to use in situ and operando characterization techniques. These sophisticated techniques are key to gaining a thorough understanding of reaction pathways, mechanisms of degradation, and how materials behave when subjected to real-world conditions. In situ and operando techniques provide important information on how materials change over time, their redox reactions, the formation of the solid-electrolyte interface, other reactions occurring, and how ions move during operation. This article delves into the newest developments in these techniques, with a focus on their use in studying the structural integrity, dynamic characteristics, changes in chemical environment, and the physical changes of supercapacitor materials. It covers a range of experimental strategies, including X-ray, electron, neutron, optical, and scanning probe methods. The review provides detailed descriptions of each technique's methodology and operating principles, with particular emphasis on the design of in situ cells. Representative studies utilizing these techniques are highlighted to offer a comprehensive overview of the current state of the field. By integrating these advanced characterization methods, researchers can gain deeper insights into local electrochemical phenomena, leading to the optimization and enhancement of supercapacitor performance. This review serves as a crucial resource for scientists and engineers dedicated to advancing the capabilities and reliability of energy storage systems. Additionally, it addresses current challenges and identifies future opportunities for further development in this rapidly evolving field.