Nano-interface engineering in all-solid-state lithium metal batteries: Tailoring exposed crystal facets of epitaxially grown LiNi0.5Mn1.5O4 films

Abstract

Understanding the solid electrolyte/cathode nano-interfacial kinetics is critical in designing advanced all-solid-state lithium metal batteries with improved performance and stability. However, the correlation between crystallographic features of cathodes and the solid nano-interface behaviour remains controversial due to the difficulty in eliminating the impact of other factors. Here, we systematically investigated the effect of exposed crystal facets of LiNi 0.5 Mn 1.5 O 4 on the solid nano-interface using the substrate orientation-dependent epitaxial growth of thin films as a model study. (100), (110), and (111)-oriented Pt/MgO substrates were used to make selective high-quality epitaxial LiNi 0.5 Mn 1.5 O 4 films with different {100}/{111}-exposed facet ratios. The atomic arrangement of the exposed facets was found to affect the electrochemical performance. Loosely packed {100} facets and densely packed {111} facets were beneficial for lithium ion diffusion and cycle stability, respectively. In particular, stable {111} facets effectively suppressed the dissolution and diffusion of transition metals at the solid nano-interface during charge-discharge, enabling a 99.6% retention after 100 cycles. In addition, this model study reveals that an amorphous cathode surface layer and a twin boundary inside the cathode are crystallographic origins that hinder the electrochemical performance of batteries. These findings suggest that crystallographic modifications of cathodes can be a key to improving the solid nano-interface. • Precise epitaxial growth creates different exposed crystal facets of LiNi 0.5 Mn 1.5 O 4. • Loosely packed {100} facets induces high capacity via fast lithium ion diffusion. • {111} facets blocks mutual diffusion across the nano-interface, enhancing stability. • Thin film model reveals crystallographic origins of the solid interface degradation.