Interdigitated-electrode thin-film model systems to quantify sheet and contact resistance in LiMn2O4 cathodes with TiO2 interlayers

Abstract

Understanding the interplay between electronic and ionic transport in lithium-ion battery cathodes is essential for optimizing their performance. In this work, we develop and refine a methodology for decoupling these contributions by leveraging thin-film model systems with precisely patterned metallic contacts. This approach enables quantitative characterization of single interfaces, providing valuable input parameters for mathematical modeling of electrode structures. Through the systematic development of this method, we identified key factors influencing electronic conductivity in lithium manganese oxide (LiMn2O4, LMO) thin films. The choice of material was found to impact the nature of the contact, highlighting the importance of material selection beyond its role as a current collector. Furthermore, we observed a strong dependence of LMO conductivity and contact resistance on its microstructure and surface roughness, which could be systematically measured using this technique. These findings indicate the capability of our methodology to investigate how structural features, such as morphology and grain size, influence the electronic properties of battery materials. After establishing the technique, we applied it to investigate the effect of protective coatings on charge transport. Specifically, we examined the role of an atomic layer-deposited titanium dioxide (TiO2) layer on LMO films, assessing how its thickness influences both contact resistance and lithium-ion insertion/extraction dynamics. While TiO2 is a semiconductor and not expected to enhance electronic conductivity directly, our results illustrate its significant impact on interfacial charge transfer. This analysis provides a framework for understanding charge transport in active cathode materials and optimizing protective coatings to balance their ability to mitigate degradation while maintaining efficient charge transport.