A Flexible Lithium-Ion-Conducting Membrane with Highly Loaded Titanium Oxide Nanoparticles to Promote Charge Transfer for Lithium-Air Battery.

In this research, we aim to investigate a flexible composite lithium-ion-conducting membrane (FC-LICM) consisting of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and titanium dioxide (TiO 2 ) nanoparticles with a TiO 2 -rich configuration. PVDF-HFP was selected as the host polymer owing to its chemically compatible nature with lithium metal. TiO 2 (40-60 wt%) was incorporated into the polymer matrix, and the FC-LICM charge transfer resistance values (R ct ) were reduced by two-thirds (from 1609 Ω to 420 Ω) at the 50 wt% TiO 2 loading compared with the pristine PVDF-HFP. This improvement may be attributed to the electron transport properties enabled by the incorporation of semiconductive TiO 2 . After being immersed in an electrolyte, the FC-LICM also exhibited a R ct that was lower by 45% (from 141 to 76 Ω), suggesting enhanced ionic transfer upon the addition of TiO 2 . The TiO 2 nanoparticles in the FC-LICM facilitated charge transfers for both electron transfer and ionic transport. The FC-LICM incorporated at an optimal load of 50 wt% TiO 2 was assembled into a hybrid electrolyte Li-air battery (HELAB). This battery was operated for 70 h with a cut-off capacity of 500 mAh g -1 in a passive air-breathing mode under an atmosphere with high humidity. A 33% reduction in the overpotential of the HELAB was observed in comparison with using the bare polymer. The present work provides a simple FC-LICM approach for use in HELABs.