Advanced in situ methods for the characterization of practical electrodes in lithium-ion batteries

In this paper, an overview of the progress recently achieved in our laboratory in the development and application of four in situ methods, namely in situ X-ray diffraction measurements (XRD), differential electrochemical mass spectrometry (DEMS), infrared spectroscopy, and Raman microscopy, is presented. For bulk investigations during cycling, in situ XRD measurements are used, and explained here in the instance of the reaction of graphite with lithium. Next, three surface-sensitive in situ methods are discussed, namely DEMS, infrared spectroscopy, and Raman microscopy. As an illustration of in situ infrared spectroscopy and DEMS, we show results for both the oxidative and reductive decomposition of electrolyte solutions. Finally, a cell for in situ Raman microscopy is described. This method is well suited, e.g., for an analysis of the structural properties of carbon materials, for a characterization of positive electrodes, and electrolytes of lithium-ion cells. As an example, Raman spectra measured in situ at a single LiCoO2 particle selected on the surface of a commercial electrode are discussed.