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In energy storage devices, materials evolve from their initial state either due to electrochemical reactions or instabilities at interfaces, and such transformations must be understood and controlled for improved electrochemical behavior. This manuscript discusses multiscale in situ techniques that are designed to reveal reaction mechanisms, degradation processes, and interfacial transformations in energy storage materials to guide the development of better batteries. Our recent work has used a combination of in situ transmission electron microscopy (TEM) and in situ X-ray diffraction/spectroscopy to elucidate phase transformation pathways in high capacity electrode materials for alkali ion batteries. For instance, Cu2S electrode materials show similar global transformations during reaction with alkali metal ions, but the nanoscale reaction pathways differ significantly, which influences the electrochemical behavior. Other research is focused on using X-ray photoelectron spectroscopy (XPS) to understand reaction mechanisms at solid-state interfaces. Finally, synchrotron X-ray diffraction investigations have revealed strain evolution in individual alloying anode particles. This work demonstrates the importance of utilizing in situ techniques to understand dynamic processes in energy devices so as to guide the synthesis of new materials with high energy density and long lifetime.
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