Abstract text (incl. figure legends and references)

Understanding structure-composition-property-performance relationships is essential for the development of more powerful, long-lived and affordable lithium ion batteries. Raman imaging microscopy can visualize structural and chemical information acquired from the battery"s internal components, such as details of their molecular composition, grain fractures, and electrode degradation. A confocal Raman system integrated with an SEM (RISE microscope) provides sufficient resolution to evaluate variations within single particles that can be correlated with structure. The atomic composition of a Li-ion cathode can be determined using EDS, leading to a comprehensive understanding of the cathode material. Fig. 1 shows correlative SEM, EDS and RISE images acquired from the same sample area of a Li-ion battery cathode composed of various grains. Although the particles appear as uniform in the SEM image (Fig. 1a), the EDS image shows that the particles contain a high amount of oxygen, shown in green (Fig. 1b). Red in the EDS image corresponds to the carbon matrix in which fluoride atoms could be detected. The Raman image (Fig. 1c) visualizes grains that consist of LiCoO2 in blue and LiNixCoyMnzO2 grains in green.

During electrochemical cycling of Li-ion batteries, microstructural changes can lead to a loss of energy, especially under rapid charging. Changes in performance are often nonuniform as a result of inhomogeneous degradation in which some regions in battery electrodes may experience more significant degradation than others. Such inhomogeneous deterioration can be studied using RISE microscopy. SEM images show deterioration of the large uniform lithium metal oxide-containing grains of pristine cathodes into sub-grains after rapid charging-discharging cycles. Raman images, on the other hand, reveal that not all Li-Metal-Oxide grains are affected in the same way by such rapid charging cycles and changes in the concentration of Li-Metal-Oxide composition is observed [1].

The integration of SEM with Raman imaging and EDS provides the opportunity to explore electrode inhomogeneity in a unique way. These results reveal heterogeneous deterioration of structure in Li-ion oxide cathode particles that can contribute to reduced performance and longevity in lithium-ion cells.

[1] K. Hollricher, D. Strom, and U. Schmidt, G.I.T. Imaging & Microscopy 2 (2021), 14 Wiley-VCH GmbH, Weinheim, Germany

Fig. 1: Correlative SEM (left) – EDS (middle) – RISE (right) images of a Li-ion cathode.