Molecular Ionic Composite Polymer Electrolytes for High-Voltage Batteries

Polymer electrolytes are promising candidates for enabling safe, high-energy lithium batteries, particularly when paired with high-voltage layered oxide cathodes and lithium metal anodes. However, challenges at electrode|electrolyte interfaces, such as parasitic side reactions and electrolyte decomposition, have hindered the widespread adoption of polymer electrolyte-based high-voltage lithium batteries. To address these issues, this study introduces molecular ionic composites (MICs) as free-standing polymer electrolyte membranes, eliminating the need for any additional liquid electrolytes during cell assembly. MICs consist of a charged rigid-rod ionic polymer, poly-2,2″-disulfonyl-4,4'-benzidine terephthalamide (PBDT), combined with mobile ions from ionic liquids, lithium salts, and functional additives. The associative interactions between PBDT and these ions create a tunable platform with exceptional mechanical strength, moderate ionic conductivity, and enhanced electrochemical stability of polymer electrolyte over a wide temperature range. The optimized MIC electrolytes exhibit high ionic conductivity (3.21 mS cm^-1 at 60 °C), a wide electrochemical stability window (5 V vs Li|Li⁺ based on linear sweep voltammetry), and excellent mechanical properties (tensile strength of 6.3 MPa, elastic modulus of 450 MPa). Furthermore, MICs enable good cycling stability in NMC811||Li metal cells, delivering an initial specific discharge capacity of 212 mAh g^-1 and 93% capacity retention after 100 cycles at 2.8-4.4 V, C/3, and 60 °C. These results underscore the potential of MICs as a promising electrolyte platform for next-generation high-voltage lithium batteries and broader electrochemical energy storage applications.