Molten lithium sulfonimide salt having poly(propylene oxide) tail

Poly(propylene oxide) (PPO) tailed lithium(trifluoromethyl sulfonylimide)s (TFSI–PPO) were prepared as non-onium type ionic liquid polymers. Introduction of PPO chain to the TFSI salt group resulted in lower the glass transition temperature (Tg) and induce the salt dissociation. The TFSI–PPO showed relatively high ionic conductivity owing to the high dissociation degree of the TFSI salt group. The maximum ionic conductivity of 3.3×10−6 S cm−1 was observed at 30 °C for TFSI salt having PPO tail with number average molecular weight of 850. On the other hand, PPOs having the same salt moiety on both chain ends ((TFSI)2–PPO) showed higher Tg than that of TFSI–PPOs. The lithium transference number of the (TFSI)2–PPO with PPO chain length of Mn=2000 was 0.74 in spite of slightly lower ionic conductivity.