Organic/Inorganic Hybrid Block Copolymer Electrolytes with Nanoscale Ion-Conducting Channels for Lithium Ion Batteries

A series of organic/inorganic hybrid block and random copolymers were prepared by reversible addition–fragmentation chain transfer (RAFT) polymerization using poly(ethylene glycol) methyl ether methacrylate (PEGMA) and 3-(3,5,7,9,11,13,15-heptaisobutylpentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane-1-yl)propyl methacrylate (MA-POSS) as monomers in order to study the effect of polymer morphology and POSS content on the properties of polymer electrolytes. Flexible and dimensionally stable free-standing films were made from the hybrid block and random copolymers mixed with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) when the contents of MA-POSS unit were larger than 31 and 16 mol %, respectively. The ionic conductivity of the solid-state block copolymer (PBP) electrolyte was found to be 1 order of magnitude higher than that of the random copolymer (PRP) electrolyte when they had similar MA-POSS content, although their glass transition temperature values of their ion-conducting segments were quite close. Moreover, the ionic conductivity of the PBP electrolyte was not much different from that of the wax state poly(poly(ethylene glycol) methyl ether methacrylate) (P(PEGMA)) electrolyte. For example, the ionic conductivity values for the PBP electrolyte containing 31 mol % of MA-POSS, the PRP electrolyte containing 29 mol % of MA-POSS, and P(PEGMA) electrolyte were 2.05 × 10–5, 3.00 × 10–6, and 4.23 × 10–5 S cm–1, respectively, at 30 °C. The large ionic conductivity value of the block copolymer electrolyte is ascribed to the nanophase separation forming the ion-conducting channels.