Zwitterionic surfactant–stabilized ionogel electrolytes with high ionic conductivity for lithium secondary batteries

Abstract

Considering the safety risks posed by the liquid organic electrolytes of conventional lithium-ion batteries, considerable attention has been drawn to the development of safer solid-state alternatives such as ionic liquid (IL)-containing ionogels. Although photocurable ionogels can entrap ILs without altering their primary properties and do not suffer from liquid outflow, the lithium salts dissolved in ILs form ion pairs rather than dissociate into free ions, which results in poor ion-transport properties. To address this problem, we herein immobilize a zwitterionic surfactant on the surface of a polymeric matrix to afford stabilized ionogels with the surfactant dipole structure oriented toward the IL-based electrolyte. The enhanced lithium-ion conductivity of these ionogels positively influences lithium plating/stripping behavior and performance in lithium iron phosphate half-cell tests, with the best rate capability (116.8 mAh g−1 at 1 C) and cycling performance (initial discharge capacity = 148.9 mAh g−1, capacity fading rate = 0.069% per cycle) obtained at a surfactant loading of only 2 wt%. Thus, this study paves the way to the design of high-performance zwitterion-containing ionogel electrolytes as less flammable and leakage-prone alternatives to conventional liquid organic electrolytes for lithium secondary batteries.