Anion π–π Stacking for Improved Lithium Transport in Polymer Electrolytes

Polymer electrolytes (PEs) with excellent flexibility, processability, and good contact with lithium metal (Li°) anodes have attracted substantial attention in both academic and industrial settings. However, conventional poly­(ethylene oxide) (PEO)-based PEs suffer from a low lithium-ion transference number (T Li +), leading to a notorious concentration gradient and internal cell polarization. Here, we report two kinds of highly lithium-ion conductive and solvent-free PEs using the benzene-based lithium salts, lithium (benzenesulfonyl)­(trifluoromethanesulfonyl)­imide (LiBTFSI) and lithium (2,4,6-triisopropyl­benzenesulfonyl)­(trifluoromethanesulfonyl)­imide (LiTPBTFSI), which show significantly improved T Li + and selective lithium-ion conductivity. Using molecular dynamics simulations, we pinpoint the strong π–π stacking interaction between pairs of benzene-based anions as the cause of this improvement. In addition, we show that Li°∥Li° and Li°∥LiFePO4 cells with the LiBTFSI/PEO electrolytes present enhanced cycling performance. By considering π–π stacking interactions as a new molecular-level design route of salts for electrolyte, this work provides an efficient and facile novel strategy for attaining highly selective lithium-ion conductive PEs.