Anion-Rectifying Polymeric Single Lithium-Ion Conductors

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.