Damien Bregiroux

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 (Li1.3Al0.3Ti1.7(PO4)3 (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 10-5 to 10-4 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 × 10-4 mS/cm) at ambient temperature.

Effect of the sintering method on microstructure and thermal and mechanical properties of zirconium oxophosphate ceramics Zr 2 O(PO 4 ) 2

Due to an ultra-low thermal expansion, Zr2O(PO4)2 could find many applications as a thermal shock resistant material. To this end, ceramic processing is a key step in order to reach best properties. In this work, Zr2O(PO4)2 was sintered by conventional sintering and by the spark plasma sintering technique (SPS) with and without additive. Samples made by conventional sintering with ZnO as sintering aid have a maximum relative density of around 92 %. Microstructure is composed of large grains and microcracks can be observed. When doped 2 with 5 wt. % of MgO, samples can be densified by SPS up to 99.6 % of the relative density and the grain size maintained between 0.5 and 1.5 μm. Thermal conductivity and Vickers microhardness were investigated as a function of the microstructure. Best values were obtained for the ceramic doped with 5 wt.% MgO and sintered by SPS, thanks to a fine microstructure and a small amount of residual microcracks.