On-site-coagulation gel polymer electrolytes with a high dielectric constant for lithium-ion batteries

This paper reports a gel polymer electrolyte (GPE) that is synthesized as a liquid solution and transforms into a gel on-site after injection into lithium-ion batteries (LIBs). The GPE is produced by mixing poly (acrylonitrile-co-methacrylate) (P(AN-co-MA)) and polyethylene glycol (PEG) with a conventional carbonate-solvated LiPF6 liquid electrolyte (LE). P(AN-co-MA) dissociates counter-ion pairs and PEG promotes polymer-crosslinking for electrolyte gelation. The GPE has a high dielectric constant and low dielectric loss because of ion-pair dissociation and facilitated ion motion. When incorporated with a separator, the GPE exhibits an ionic conductivity of 1.7 × 10−3 S cm−1 and a Li transference number (tLi+) of 0.62. The corresponding values for the LE are 9.1 × 10−4 S cm−1 and 0.37, respectively. The high dielectric permittivity and tLi+ render the GPE stable at 5.2 V (vs. Li/Li+). The GPE outperforms the LE when assembled into Li||LiFePO4 batteries, exhibiting superior capacity, high rate retention, and cycling stability. Moreover, the GPE has low flammability such that a graphite|GPE|LiFePO4 pouch-cell battery operates smoothly under folding or after truncation. The on-site coagulation design ensures that the developed GPE can be used in existing LIB assembly lines to produce high-quality LIBs that can be applied in diverse power devices.