Lithium ion conducting polymerized ionic liquid pentablock terpolymers as solid-state electrolytes

In this study, a lithium ion conducting polymerized ionic liquid pentablock terpolymer (PILPTP) was investigated as a solid polymer electrolyte (SPE) for lithium ion batteries. The ABCBA pentablock terpolymer, poly(tbS-b-EP-b-MS-b-EP-b-tbS) (tbS = tert-butyl-styrene; EP = ethylene-r-propylene; MS = 4-methylstyrene), was brominated and quaternized to covalently attach two different cations (methylimidazolium and methylpyrrolidinium) to the C block and subsequently ion exchanged to form two different TFSI-exchanged PILPTPs (MPyr-TFSI and MIm-TFSI; TFSI = bis(trifluoromethane)sulfonimide). Free standing, mechanically stable, transparent SPE films were produced with MPyr-TFSI and MIm-TFSI containing 1 M Li-TFSI/ionic liquid (IL) (IL = EMIm-TFSI or PYR14-TFSI; EMIm = 1-ethyl-3-methylimidazolium, PYR14 = 1-butyl-1-methylpyrrolidinium), referred to as MPyr-TFSI + Li-TFSI/PYR14-TFSI and MIm-TFSI + Li-TFSI/EMIm-TFSI. Both SPEs show promising ionic conductivities, electrochemical stabilities, and stripping and plating stabilities. Specifically, the MIm-TFSI + Li-TFSI/EMIm-TFSI SPE possessed an ionic conductivity of 0.1 mS cm−1 at 28 °C; the MPyr-TFSI + Li-TFSI/PYR14-TFSI SPE possessed an electrochemical stability window of 4.2 V versus Li/Li+ at room temperature; the MPyr-TFSI + Li-TFSI/PYR14-TFSI SPE exhibited stable stripping and plating overvoltage profiles over 500 cycles at 70 °C. These results demonstrate the feasibility of a PIL multiblock polymer as an SPE for lithium ion batteries.