Membrana protettiva per le batterie litio-aria per veicoli elettrici

Abstract The growing demand for rechargeable batteries in automotive industry and electronic devices creates interesting fields for research. Current Lithium-ion technologies provide specific energy about 100¿265 W¿h/kg. Lithium-Air batteries with theoretical energy density about 11,640W¿h/kgrepresents an exciting opportunity for further applications. Metallic lithium acts as anode electrode and oxygen as cathode where take place Oxygen Reduction Reaction(ORR) and Oxygen Evolution Reaction(OER).Currently most of the researches on the Lithium-air battery is based on pure oxygen feed while in real application for different reasons like cost, safety, bulky oxygen tanks can't be used. Unlimited available oxygen in surrounding air is an alternative solution for oxygen feeding but presence of humidity and other components like carbon dioxide may cause side reactions and corrosion that reduce efficiency and lifetime of the batteries. Protective membranes with high selectivity for oxygen and blocking humidity (hydrophobicity) and other air components were prepared via non-solvent induced phase separation. The facilitated transport seems to be the best option in comparison with active and passive transport for this particular application. In facilitated transport an appropriate carrier molecule transports oxygen from feeding side to cell side. Two types of polymeric membranes were prepared, via non solvent induced phase separation, with Poly(Vinylidene Fluoride -co-hexafluoropropylene) (PVDF-HFP) and different additives. First type was prepared with sacrificial silica nanoparticles (SiO2 NPs) and incorporated in the PVDF-HFP matrix. Homogeneous dispersion of SiO2 NPs and PVDF-HFP in DMF was casted as a thin film. Subsequently the membrane was immersed in Hydrofluoric Acid to obtain leached membrane.This last one was loaded with Silicon Oil The membrane surface morphology was examined using field-emission scanning electron microscopy.FESEM pictures confirm a controlled homogeneous and uniform porosity.Thermogravimetric analyses (TGA) were performed to investigate the thermal stability of the membranes and confirmed the absence of silica particles inside after HF treatment. Contact angles as well as oxygen and water permeability were measured to assess both hydrophobicity and selectivity of the membranes, giving encouraging results. Afterward the membrane was electrochemically tested in cell. The cell was assembled with metallic lithium as anode,TEGDME_LiClO4as electrolyte, GDL-24BC as air cathode and the oxygen selective membrane. Long time charge/discharge tests were carried out by potential/time controlled steps between 2.25V and 4.3V vs. Li+/Li at the current density of 0.05 mA.cm-2, with a cut-off time of 20h. During the tests, ambient air (inside a dry-room with a constant humidity of 17% RH) or dry O2 were continuously circulated at the air cathode. The Li-air cells were tested after 6 h of rest at the OCV. The discharge-charge performances with membrane in air (17% RH) were highly reproducible, with few signs of deterioration for the initial 16 cycles, which indicates a perfect cycling performance almost comparable to those of cells powered with pure oxygen. Second type was prepared with Cyclodextrin Based Nanosponges incorporated in the PVDF_HFP matrix. After homogeneous dispersion of NS in the polymer and the precursor solution was casted as a thin film. The membranes surface morphologies were examined using field-emission scanning elec