Full Article:https://doi.org/10.1063/5.0203665

In the face of global challenges such as energy shortages and environmental pollution, coupled with the widespread adoption of mobile devices, the development of high-performance electrochemical energy storage systems has become particularly crucial. Supercapacitors hold a significant position in the field of energy storage due to their high power density, rapid charge/discharge capabilities, and excellent cycling stability. However, to further enhance the performance of supercapacitors, it’s essential to gain a deeper understanding of their microscopic behaviors under actual operating conditions, including charge storage mechanisms, charge/ion transport processes, and interfacial reactions.

Traditional analytical techniques have significant limitations in directly observing these dynamic processes, especially concerning the changes in electronic and atomic structures, and the modulation of interfacial physical and chemical properties during actual charge and discharge. Therefore, the development and application of advanced in situ characterization techniques, particularly synchrotron X-ray spectroscopy, have become key technologies for studying the operating mechanisms of supercapacitors in recent years.

This review paper summarizes the application of synchrotron X-ray absorption spectroscopy (XAS) in the study of various supercapacitors, with a particular focus on the crucial role of in situ XAS techniques in exploring the evolution of electrode materials’ electronic and local atomic structures. Through multiple typical research cases, it illustrates how these techniques effectively reveal key scientific information, such as changes in the active element valence state, modulation of the local coordination environment, and the evolution of active sites during the charge and discharge processes of electrode materials. Specifically, the fundamental differences between the double-layer capacitance (EDLC) and pseudocapacitive energy storage mechanisms can be directly confirmed by in situ XAS techniques.

The combination of in situ soft X-ray and hard X-ray techniques can comprehensively analyze the correlation and changes in the electronic states and atomic structures of electrode materials. These spectroscopic advantages provide an important scientific basis for designing novel high-performance electrode materials. Furthermore, this article also looks ahead to future development directions, including the potential application of cutting-edge techniques such as ultrafast time-resolved X-ray spectroscopy and scanning transmission X-ray microscopy (STXM). These techniques will offer new perspectives for a deeper understanding of the physical and chemical nature of electrochemical energy storage processes, thereby laying a scientific foundation for the development of next-generation high-performance supercapacitors.