Counteranion-Mediated Intrinsic Healing of Poly(ionic liquid) Copolymers

Fabrication of self-healing/healable materials using reversible interactions that are governed by their inherent chemical features is highly desirable because it avoids the introduction of extra groups that may present negative effects on their functions. The present study exploits the inherently featured electrostatic interactions of the ion pairs in polymeric ionic liquids (PILs) as the driving force to fabricate healable PIL copolymers. The healable PIL copolymers are fabricated through the copolymerization of the IL monomers with ethyl acrylate followed by the replacement of Br^- counteranions with bulkier ones such as bis(trifluoromethanesulfonyl)imide (TFSI^-). Without modifying the chemical structures of the PIL moieties, the healing performance of the as-prepared PIL copolymers can be effectively mediated by their counteranions. The PIL copolymers that do not possess healability when paired with Br^- counteranions become healable after exchanging the Br^- counteranions with larger-sized ones (e.g., TFSI^-). The PIL copolymers paired with bulky counteranions exhibit enhanced chain mobility and highly reversible ion-pair interactions, which facilitate the healing process. The PIL copolymers paired with TFSI^- anions can completely heal the damage/cut upon heating at 55 °C for 7.5 h. Meanwhile, the counteranions with larger sizes not only benefit the healing performance of the PIL copolymers but also enhance their ion conductivity. The ion conductivity of the PIL copolymers paired with TFSI^- is an order of magnitude higher than that of the PIL copolymers paired with Br^-. Therefore, the as-prepared healable PIL copolymers are potentially useful as solid electrolytes in PIL-based energy devices to improve their safety and reliability.