Spatially and temorally resolved in situ Raman spectroscopy of cathode materials of Li-ion batteries

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Li-ion batteries have been used as mobile energy storage devices for a variety of modern IT applications. Li-ion batteries are also of great interest for future applications in electro mobility (electrical and hybrid vehicles) and for use as stationary energy sources. However, in particular regarding the latter applications, further technological developments will be necessary. A rational development of Li-ion batteries with higher energy density and stability is based on a fundamental understanding of their mode of operation. This requires the development and application of new experimental approaches allowing for a detailed analysis of the battery under working conditions. It has been shown that Raman microscopy has the potential to provide new insight into the mode of operation of Li-ion batteries, in particular, when it is used for spatially-resolved analysis.The goal of the project is to gain new insight into the mode of operation of LiCoO2 and Li(NiMnCo)O2 (NMC) cathode materials for Li-ion batteries using spatially-resolved analysis under working conditions of the battery. Emphasis will be put on studies of individual particles besides studies on the dynamics of the cathode materials. To take the influence of the carbon additive and binder material into account, cathode materials will be investigated as cathode mixes consisting of active mass, carbon additive and polyvinylidendifluoride binder. The main method of investigation will be resonance-enhanced in situ Raman microscopy, which will be employed for both spatially-resolved experiments (Raman mapping) and measurements on individual particles. A significant increase in the sensitivity of the method is expected from the optimization of the resonance enhancement as well as the use of surface-enhanced Raman spectroscopy (SERS) and changes in the in situ-cell design. These studies will be supported by other methods such as IR, UV-Vis and X-ray photoelectron spectroscopy.One focus of the investigations is the analysis of individual particles under working conditions. In this way, we intend to explore the differences in the state of charge and dynamics of the individual particles. Such fundamental studies are of great interest regarding the observed fatigue of LiCoO2 and NMC cathode materials. Another focus of the envisaged investigations is the heterogeneity of the cathode materials as well as its dynamics. In this context, we intend to explore, to which extent the behavior is influenced by different cathode mixes (i.e. variation in type of carbon). As an alternative approach to gain insight into the mode of operation of LiCoO2 and NMC cathode materials, atomic layer deposition (ALD) will be employed to prepare defined Al2O3 coatings. To this end, by using in situ analysis, we expect to be able to elucidate the origin of the positive influences of the coatings on the behavior of the cathode materials by comparison with uncoated materials.