Hybrid Li Ion Conducting Membrane as Protection for the Li Anode in an Aqueous Li-Air Battery: Coupling Sol-Gel Chemistry and Electrospinning.

Aqueous lithium-air batteries have very high theoretical energy densities, which potentially makes this technology very interesting for energy storage in electric mobility applications. However, the aqueous electrolyte requires the use of a watertight layer to protect the lithium metal, typically a thick NASICON glass-ceramic layer, which adds ohmic resistance and penalizes performance. This article deals with the replacement of this ceramic electrolyte by a hybrid organic-inorganic membrane. This new membrane combines an ionically conducting inorganic phase for Li ion transport (LiAlTi(PO) (LATP) and a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) polymer for water tightness and mechanical properties. The Li ion transport through the membrane is ensured by an interconnected 3-D network of crystalline LATP fibers obtained by coupling an electrospinning process with the sol-gel synthesis followed by thermal treatment. After an impregnation step with PVDF-HFP, hybrid membranes with different volumetric fractions of PVDF-HFP were synthesized. These membranes are watertight and have Li ion conductivities ranging from 10 to 10 mS/cm. The conductivity depends on the PVDF-HFP volume fraction and the fibers' alignment in the membrane thickness, which in turn can be tuned by adjusting the water content in the electrospinning chamber during the process. The alignment of fibers parallel to the membrane surface is conductive to poor conductivity values whereas a disordered fiber mat leads to interesting conductivity values (1 × 10 mS/cm) at ambient temperature.