Fast lithium intercalation mechanism on surface-modified cathodes for lithium-ion batteries

Enhancing the understanding of fast lithium intercalation on cathode surfaces modified by oxides is crucial for the development of electrode materials that offer high-power and long-life operation. Herein, lithium transfer is elucidated by directly observing the structural changes within the cathode, through the interface, and into the electrolyte using in situ neutron reflectometry (NR). Two films are studied---a Li${}_2$ZrO${}_3$-modified and an unmodified LiCoO${}_2$ film---and it is found that the modified film exhibits a superior rate capability. In situ NR studies indicate that the surface modification facilitates the formation of a dense cathode-electrolyte interphase (CEI), primarily composed of inorganic species. In contrast, the unmodified surface is covered by a relatively sparse and electrolyte-impregnated CEI. These structural observations suggest that lithium desolvation during intercalation primarily occurs on the CEI and LiCoO${}_2$ surfaces for the modified and unmodified films, respectively. Fast desolvation of lithium on the CEI may contribute to the superior rate capability of the surface-modified cathodes. This suggests a mechanism of fast intercalation achieved by surface modification of low ionically conductive oxides. Simultaneous chemical composition and morphological information is a powerful way to elucidate the dynamics at cathode/liquid electrolyte interfaces suitable for high-power operation. (© 2023 The Authors. Advanced Energy Materials published by Wiley‐VCH GmbH)