In-situ characterization for sodium/potassium-ion batteries: probing dynamic processes to unlock performance

Sodium/potassium-ion batteries (SIBs/PIBs) are promising for large-scale energy storage due to their abundant resources and lithium-ion compatibility. However, their practical application depends on optimizing electrochemical performance, particularly rate capability and cycling stability; therefore, elucidating key mechanisms like electrode evolution, phase transitions, and ion transport is essential for realizing their potential. Traditional ex-situ techniques fail to capture real-time changes in operating batteries, often providing incomplete insights into mechanisms such as capacity degradation and interfacial instability. In-situ characterization overcomes this limitation by enabling direct observation of material dynamics, thereby advancing both fundamental research and practical development of SIBs/PIBs. A comprehensive review of these techniques is crucial to address the increasing demand for sustainable energy storage solutions. This review provides an overview of in-situ techniques, detailing their principles, operational methods, advantages and limitations. It underscores that understanding the principles alone is insufficient; precise interpretation of experimental results is essential for analyzing electrochemical processes. Through examples, we aim to elucidate battery reaction mechanisms and offer strategies for addressing complex electrochemical systems. This article focuses on diffraction- and spectroscopy-based methods (in-situ XRD, XAS, Raman and FTIR), electron microscopy (in-situ TEM, SEM) and in-situ AFM, highlighting their applications in SIBs/PIBs research and offering guidance for future studies.