Anion‐Rectifying Polymeric Single Lithium‐Ion Conductors

Abstract Polymeric single lithium (Li)‐ion conductors (SICs), along with inorganic conducting materials such as sulfides and oxides, have received significant attention as promising solid‐state electrolytes. Yet their practical applications have been plagued predominantly by sluggish ion transport. Here, a new class of quasi‐solid‐state SICs based on anion‐rectifying semi‐interpenetrating polymer networks (semi‐IPNs) with reticulated ion nanochannels are demonstrated. This semi‐IPN SIC (denoted as sSIC) features a bicontinuous and nanophase‐separated linear cationic polyurethane (cPU), which supports single‐ion conducting nanochannels, and ultraviolet‐crosslinked triacrylate polymer, which serves as a mechanical framework. The cPU phase is preferentially swollen with a liquid electrolyte and subsequently allows anion‐rectifying capability and nanofluidic transport via surface charge, which enable fast Li⁺ migration through ion nanochannels. Such facile Li⁺ conduction is further enhanced by tuning ion‐pair (i.e., freely movable anions and cations tethered to the cPU chains) interaction. Notably, the resulting sSIC provides high Li⁺ conductivity that exceeds those of commercial carbonate liquid electrolytes. This unusual single‐ion conduction behavior of the sSIC suppresses anion‐triggered interfacial side reactions with Li‐metal anodes and facilitates electrochemical reaction kinetics at electrodes, eventually improving rate performance and cycling retention of Li‐metal cells (comprising LiNi_0.8Co_0.1Mn_0.1O₂ cathodes and Li‐metal anodes) compared to those based on carbonate liquid electrolytes.