Polymerized ionic liquid diblock copolymer as solid-state electrolyte and separator in lithium-ion battery

Abstract

A polymerized ionic liquid diblock copolymer (PILBCP-TFSI), poly(MMA-b-MUBIm-TFSI), consisting of an ionic liquid monomer, (1-[(2-methacryloyloxy)undecyl]-3-butylimidazolium bis(trifluoromethane)sulfonamide) (MUBIm-TFSI), and a non-ionic monomer, methyl methacrylate (MMA), was synthesized via reverse addition fragmentation chain transfer polymerization followed by anion exchange metathesis. Free standing, mechanically stable transparent solid polymer films were produced with PILBCP-TFSI containing 1 M lithium bis(trifluoromethane)sulfonamide in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (Li-TFSI/EMIm-TFSI). The resulting PILBCP-TFSI + Li-TFSI/EMIm-TFSI films possessed ion conductivities from 1 to 10 mS cm−1 from 25 °C to 105 °C. Solid-state lithium-ion coin cell batteries were assembled and tested at room temperature with PILBCP-TFSI + Li-TFSI/EMIm-TFSI films as the solid-state electrolyte and separator and resulted in a maximum discharge capacity of 112 mAh g−1 at 0.1 C with a Coulombic efficiency greater than 94% over 100 cycles. For the first time, these results demonstrate the feasibility of PIL block copolymers as solid-state electrolytes and separators in lithium-ion batteries.