Enabling polymeric ionic liquid electrolytes with high ambient ionic conductivity by polymer chain regulation

Abstract

• 1-vinyl-3-(2-ethylhexyl)imidazolium bistrifluoromethanesulfonimide (IL) is synthesized. • A novel borate-containing acrylate (BA) monomer is synthesized. • A copolymeric P(IL-BA) solid polymer electrolyte (SPE) is fabricated. • The P(IL-BA) SPE exhibits good ambient ionic conductivity. • An all-solid-state LFP| P(IL-BA)|Li battery exhibits good electrochemical performance at 30 °C. Polymeric ionic liquid (P(IL)) electrolytes, containing excellent mechanical performances, good processability, chemical stability, and non-flammability, are a kind of potential solid polymer electrolytes (SPEs). However, Li + migration is not easy in homo-polymeric P(IL) SPEs due to the order structure in the polymer chains. Herein, a branched ionic liquid (IL) monomer of 1-vinyl-3-(2-ethylhexyl)imidazolium bis(trifluoromethanesulphonyl)imide and a borate-containing acrylate (BA) monomer are designed and synthesized. Subsequently, their copolymeric P(IL-BA) SPE is fabricated which exhibits lower crystallinity and glass transition temperature, better dissociation ability of Li + salt and improved ambient ionic conductivity. The prepared P(IL-BA) SPE exhibits high ionic conductivity (2.46 × 10 −4 S cm −1 , 30 °C), robust electrochemical stability (4.75 V vs Li + /Li), and excellent thermal stability and non-flammability. The all-solid-state LiFePO 4 (LFP)|P(IL-BA) SPE|Li battery displays a reversible specific capacity of 142 mAh g −1 and Coulombic efficiency of approximately 100% at 0.2C at 30 °C. It is of great significance for designing ambient workable SPEs by regulating polymer chains to improve their ionic conductivity.