Enhanced Interphase Ion Transport via Charge‐Rich Space Charge Layers for Ultra‐Stable Solid‐State Lithium Metal Batteries

Abstract The significant interfacial resistance between solid electrolyte‐electrode interfaces is a major bottleneck for the practical application of solid‐state lithium batteries. This resistance is primarily caused by the formation of space charge layers (SCLs), resulting from the redistribution of ionic carriers at the interface between dissimilar materials with varying chemical potentials, which lead to insufficient carriers and sluggish lithium‐ion transport. In this study, a conjugated structure polymer is constructed through in situ polymerization onto the oxide electrolyte, forming charge‐rich SCLs on the organic/inorganic interface, and enabling the interfacial layer to maintain superior ion transfer and contact. The Li solid NMR spectra and computational study suggest that optimized SCLs offer effective pathways for Li + conduction in the electrolyte, thereby enhancing the interfacial conduction. Furthermore, the designed electrolyte induces the formation of an inorganic‐rich interphase layer on the lithium anode, enabling rapid lithium‐ion transport and uniform Li deposition. Consequently, the lithium symmetric cell with this electrolyte operates for more than 5100 h, while LiFePO 4 /Li solid‐state batteries can stably cycle up to 800 times at 5 C. This interfacial modification strategy provides a new perspective for the rational design of the charge‐rich SCLs and advances the understanding of the SCLs inside the electrolyte.