We have found remarkable ion-conductive properties in a novel polymer electrolyte composed of poly(ethylene carbonate) and Li bis-(fluorosulfonyl) imide. The self-diffusion coefficient of Li-ions exceeded 10⁻⁷ cm² s⁻¹ and the Li transference number was estimated to be more than 0.8 in composites filled with only 1 wt% of TiO₂ nanoparticles.

Poly(ethylene carbonate)-based polymer electrolytes with lithium salts (LiX; X = TFSI, ClO₄, BF₄ and PF₆) were prepared, and their lithium transference numbers (t₊) were measured to make comparison between different anion radius and salt concentrations. The LiTFSI electrolytes had the highest t₊ and Li-ion conductivities of all samples at 80°C; these values increased with increasing salt concentration. According to the results of FT-IR measurements for all concentrated samples, the changes of band fraction, which divide at around 1720 cm⁻¹ for carbonyl groups interact, with Li⁺ (C=O — Li⁺), are strongly related to the mobility of Li⁺ ions.

Ion-conductive behavior of a novel polymer electrolyte without oxyethylene units, poly(ethylene carbonate) (PEC)-Li salt system, was reported. Salt-concentration dependence revealed that the LiCF3SO3 and LiClO4 electrolytes exhibit typical polyether-like conduction behavior. However, the LiBETI, LiBF4 and LiTFSI electrolytes were much different, and the conductivity increased and Tg decreased with increasing salt concentration. This behavior of salt-rich PEC electrolytes relates to the ‘polymer-in-salt’ system. Li+ transference number of PEC-LiBF4 (44.4 wt%) electrolyte was measured, and the value was estimated to be ∼0.5 at 100 oC.