Local structural distortion and energy gradient enhance lithium ionic conductivity in high-entropy oxide

Abstract

Li-rich disordered rock-salt oxides have been extensively studied as electrode materials for lithium-ion batteries, however, their diffusion of lithium ions relies on the presence of excess lithium-ion content (>54.5 atom% relative to total metal ions). An emerging high-entropy strategy can reduce the lithium-ion content and enhance lithium-ion conductivity in sodium superionic conductor (e.g. Li(Ti,Zr,Sn,Hf)₂(PO₄)₃). However, the high ionic conductivity in Li-stuffed disordered rock-salt oxides with low lithium-ion content is generally attributed to its cocktail effect, and the underlying mechanisms remains unclear. Here, we develop a robust Li-poor disordered rock-salt high-entropy oxide, (MgCoNiCuZn)_0.75Li_0.25O (HEOLi) as an artificial solid electrolyte interphase coating layer to stabilize lithium metal anodes, achieving an impressive cycling stability of over 15000 h. We elucidate a cocktail effect of HEOLi arising from its disordered structure of HEOLi, with unique crystallographic local structural distortions, delocalized electron structure, and energy gradients, enabling high Li-ion conductivity. These energy gradients reduce the overall energy barrier and promote Li⁺ hopping through preferential pathways within the HEOLi. This work offers insight into the cocktail effect of high-entropy and the Li-ion conduction mechanism, facilitating the rational design of conductive high-entropy ceramics.