Lithiation-Dependent Micromechanical Response of Amorphous and Crystalline MoO3 Thin-Film Cathodes on Al Current Collectors.

In this study, the mechanical response of MoO3 thin-film cathodes deposited on aluminum substrates was systematically investigated using nanoindentation techniques under an inert atmosphere. Both amorphous and crystalline phases were examined across non-, partially, and fully lithiated states to elucidate the influence of lithium intercalation on elastic and plastic behavior. A range of indenter geometries, including spherical and Berkovich tips, were employed to extract plastic, elastic, and interfacial properties. The elasticity increased with lithium content, with partially lithiated systems exhibiting the highest values. Residual indentation depths were lowest for partially lithiated samples, indicating a distinct mechanical regime compared to both non- and fully lithiated states. The amorphous phase demonstrated higher stiffness, with deformation-induced cracks confined within the layer, while the crystalline phase accommodated deformation more uniformly via grain boundary sliding. The mechanical response in the crystalline phase suggests a significant role of grain-boundary-mediated deformation mechanisms. Furthermore, no degradation in layer adhesion was observed with increasing lithium content, indicating a mechanically stable interface across all lithiation states. These findings provide new insights into the mechanical integrity of cathode-current collector systems in solid-state lithium-ion batteries and underscore the critical role of intercalation state, structural phase, and microstructural pathways in determining mechanical performance.