Ionic liquid crystal induced morphological control of solid composite polymer electrolyte for lithium-ion batteries

Abstract

A novel two-dimensional (2D) solid composite polymer electrolyte (SPE) was synthesized by co-assembling ionic liquid crystals [1-hexadecyl-3-methyl tetrafluoroborate ([C16mim]BF4)] and polycationic liquids [1-(hexyl methacrylate)-3-butyimidazolium tetrafluoroborate (PMOBIm-BF4)] along with the imidazolium moieties using a flexible spacer. Ionic liquid crystals were used to induce ion-conductive 2D pathways in the ionic liquid cationic polymer, and polymer cationic ionic liquids acted as ion-conductive media for lithium-ion batteries. Owing to its excellent thermal stability, non-inflammability, and high ionic conductivity, the PMPC0.5 electrolyte containing 3/1/0.5 ratio of polyMOBIm-BF4/PEGDA/[C16mim]BF4 exhibited anenhanced lithium-storage performance within a wide electrochemical window of up to 4.2 V vs. Li+/Li, and high ionic conductivity of 7.14 × 10−5 and 2.17 × 10−3 S cm−1 at 25 and 95 °C, respectively. The assembling ability of ionic liquid crystals can not only develop lamella structure and ordered channel for improved Li-ion transportation, but also could show efficient enhancement for ionic conductivity of the polyionic liquid. The Li/SPE/LiFePO4 coin cells using the PMPC0.5 as electrolyte delivered a specific capacity of 136.7 mAh g−1 in the first cycle and118.9 mAh g−1 in the 40th cycle at a rate of 0.1C.