Promoting combined AFM-electrochemistry techniques for analysis of charge transport at grain boundaries of ceramic components in electrochemical cells

For decades, the differences between the transport properties of grains and grain boundaries in polycrystalline oxides have been widely discussed in the scientific community. The reason is that grain boundaries, although representing a much smaller fraction of a given material than the grain interior, can greatly influence the performance of ceramic materials, which is a major drawback for the industrial application of these materials. Detailed knowledge of the chemical and physical parameters at the interfaces between adjacent grains is required in order to develop targeted synthesis strategies that specifically influence the transport properties of grain boundaries. Atomic force microscopy (AFM)-based electrochemical methods use an nm-sized tip as a probe and are able to image, for example, band bending at grain boundaries or variations in electrical conductivity with extremely high local resolution, thus providing small-scale insights into the physical and electrochemical conditions at grain boundaries. The results obtained by AFM-based electrochemical experiments are complementary to conventional electrochemical measurements and facilitate detailed modeling of grain boundary parameters in different materials. In this work, the differences between grain boundaries and grain interiors with respect to charge transport properties are first discussed with a special focus on oxide ion conducting and proton conducting materials. In a second step, a broader perspective on current research and potential applications of AFM-based grain boundary analysis in the field of lithium-ion battery materials is given.