Recent progress of in-situ characterization of LiNi_1−x−yCo_xMn_yO₂ cathodes for lithium metal batteries: A mini review

In the context of the gradual popularity of electric vehicles (EVs), the development of lithium battery systems with high energy density and power density is regarded as the foremost way to improve the range of EVs. LiNi_1−x−yCo_xMn_yO₂ (NCM) cathodes have been the focus of researchers due to their high energy density, excellent power performance, and low-temperature resistance. However, the elaboration of the decay mechanism of NCM cathode based on lithium metal batteries (LMBs) is still being restricted to the primary level. In the past decades, the development and application of advanced in-situ characterization tools have facilitated researchers' understanding of the internal operation mechanism of batteries during charging and discharging. In this minireview, the latest progress of in-situ observation of the NCM cathode by X-ray diffraction (XRD), fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, atomic force microscopy (AFM), transmission electron microscope (TEM), optical microscope, and other characterization tools is summarized. The mechanisms of structural degradation, cathode-electrolyte interfaces (CEIs) composition, and dynamic changes of NCM, electrolyte breakdown, and gas production are elaborated. Finally, based on the existing research progress, the opportunities and challenges for future in-situ characterization technology in the study of the mechanism of LMBs are discussed in depth. Therefore, the purpose of this minireview is to summarize recent work that focuses on the outstanding application of in-situ characterization techniques in the mechanistic study of LMBs, and pointing the way to the future development of high energy density and power density LMBs systems.