Application of in‐situ characterization techniques in modern aqueous batteries

Abstract The development of high‐performance aqueous batteries calls for an in‐depth knowledge of their charge–discharge redox and failure mechanism, as well as a systematic understanding of the dynamic evolution of microstructure, phase composition, chemical composition, and local chemical environment of the materials for battery. In‐situ characterization technology is expected to understand and reveal the problems faced by aqueous rechargeable batteries, such as the dissolution of electrode materials, the growth of metal negative electrode dendrites, passivation, corrosion, side reactions and a series of problems. Based on this, typical in‐situ characterization techniques and their basic mechanisms are summarized, including in‐situ optical visualization, in‐situ microscopy techniques (in‐situ scanning electron microscopy (SEM), in‐situ transmission electron microscopy (TEM)), in‐situ X‐ray techniques (in‐situ X‐ray diffraction (XRD), in‐situ X‐ray photoelectron spectroscopy (XPS), in‐situ near‐edge structural X‐ray absorption spectroscopy (XANES)), and in‐situ spectroscopy techniques (in‐situ Raman spectroscopy, in‐situ Fourier transform infrared (FTIR)). Moreover, some emerging techniques concerning aqueous battery research, especially gas evolution and materials dissolution issues, such as in‐situ electrochemical quartz crystal microbalance (EQCM), in‐situ fiber‐optic sensing, in‐situ gas chromatography (GC) are introduced. At last, the applications of advanced in‐situ characterizations in future research of aqueous batteries are emphasized and discussed, along with some of the remaining challenges and possible solutions.