Enabling High Lithium Conductivity in Polymerized Ionic Liquid Block Copolymer Electrolytes

Abstract Herein, the use of a novel block copolymer host, based on a polymerized ionic liquid block copolymer, is proposed. Mechanically robust solid polymer electrolytes (SPEs) with high lithium conductivity are developed using a ternary polymer electrolyte system, consisting of a poly(styrene-b-1-((2-acryloyloxy)ethyl)-3-butylimidazolium bis(trifluoromethanesulfo-nyl)imide) (S-PIL64-16) block copolymer, a N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide (C3mpyrFSI) ionic liquid (IL) and a lithium bis (fluorosulfonyl) imide (LiFSI) salt. The impact of both IL and lithium salt concentration on the morphology, ion migration processes and electrochemical performance of the electrolytes is characterized. High lithium ion conductivity is achieved when anion to Li+ molar ratio was kept below a value of 1.5, resulting in a lithium transport number ( ) as high as 0.53 at 50?°C. Finally, the cycling performance in a Li|LiFePO4 full cell is assessed using an in-house formulated solid-state high loading cathode (LiFePO4 loading=10?mg?cm?2, 1.8?mAh?cm?2). 98?% of the theoretical discharge capacity (167?mA?g?1) is achieved for the first cycle at a C-rate of C/20 at 50?°C. The results herein reported are the first demonstration of a PIL block copolymer-IL-salt composite electrolyte operating at near-practical levels, making them a promising choice of electrolyte for the next generation of solid-state high capacity lithium-metal batteries.