Unraveling the Enhancement of Confined Water on the Li‐Ion Transport of Solid Electrolytes

Abstract Oxide solid electrolytes are attractive for the implementation of solid‐state Li‐ion batteries. However, constrained by the large ion‐transport hindrance inside the densely packed lattice, their Li‐ion conductivity can hardly reach the level of liquid electrolytes. A strategy of introducing confined water into the lattice paves a new way for enhancing the Li‐ion transport, which has been reported in the previous studies. To further verify the universality of this strategy and unravel the facilitation mechanism, here this work establishes an ideal model using Li‐H‐Cl‐O quaternary compounds with a wide electrochemical stability window. As a major kind of confined water, the content and type of ─OH groups are crucial parameters affecting the Li‐ion conductivity. Through a controllable dehydration technique, the hydrogen‐bonded ─OH groups can be mostly removed, leaving the free ─OH groups in lattice, which is beneficial to the increase of free volume and acceleration of rotation response. The 1–2 orders of magnitude enhancement of Li‐ion conductivity ensures full cells good rate and cycling performance. This work not only addresses the controversy in Li‐H‐Cl‐O about the hydrogen effect on Li‐ion transport, but also provides detailed theoretical insights for the rational design of solid electrolytes.