In-Situ/Operando Characterization Techniques for Rechargeable Batteries: Electrodes and Electrolytes Origins

Rechargeable batteries are essential to satisfy the increasing needs generated by electric vehicles, portable devices, and large-scale energy storage systems. A comprehensive understanding of the realistic operating conditions in batteries is necessary for performance, safety, and cycle life enhancement. In-situ/operando characterization techniques are currently essential instruments to investigate the structural, chemical, and morphological changes of electrode and electrolyte materials in real-time under actual operating conditions. Here, recent advancements in using in-situ/operando techniques to emphasize the origins and behaviors of electrodes and electrolytes in metal-ion, solid-state, and aqueous batteries are examined. State-of-the-art techniques offer significant advantages in battery research. In-situ X-ray diffraction (XRD) is utilized to explore phase transition, crystal structure evolution, and degradation mechanisms of electrodes. In-situ electron microscopy techniques like scanning electron microscopy (SEM) and transmission electron microscopy (TEM) enable direct visualization of electrode morphology changes, Li dendrite formation, and composition transformations at the Micro to atomic scale. These imaging techniques allow for detecting defects or cracks within the active material particles. In-situ atomic force microscopy (AFM) offers valuable information on the interface, such as mechanical properties, SEI morphology, and the growth of Li dendrite. In-situ neutron-related methods unravel lithium distribution and transport path in electrode materials. Additionally, the application of in-situ X-ray absorption spectroscopy (XAS), which has been used to elucidate redox reactions, electronic structure changes, and local atomic arrangements, is discussed. Critical challenges are highlighted, including the necessity of improving spatial and temporal resolution, the complexity of interpreting data from multi-component systems, and the compatibility of techniques with commercial cells. Opportunities are also explored for integrating multiple in-situ/operando techniques, developing a stable SEI layer, and achieving reversible Li plating. The experimental setup and working principles are comprehensively explained. This work guides future research directions for next-generation rechargeable batteries by providing a detailed understanding of the fundamental processes at the electrode and electrolyte levels. Keywords: in-situ/operando, lithium-ion batteries, solid-state batteries, characterization techniques, aqueous batteries