Development of polymer gel electrolytees for solid lithium air cells

Among rechargeable batteries, lithium oxygen (Li-O2) batteries offer one of the highest theoretical specific energy density (about 11.5 kWh / kg). It consists of a conventional, anhydrous rechargeable lithium-oxygen battery (LOB), lithium metal anode, a porous cathode, Li + conductive liquid electrolyte, and a separator used to prevent a short circuit between the two electrodes. However, it prevents the use of liquid electrolytes in LOBs; There are various problems such as low evaporation temperature, passivation of the metal anode surface and decomposition of the electrolyte at higher potentials after 4.0 V. Replacing volatile, flammable and leaking liquid electrolytes with gel polymer electrolytes (GPE) is generally considered an effective approach to solving problems. Polyvinylidenfluoride-hexafluoropropylene (PVDF-HFP), one of the important matrices for the production of GPE, has been successfully applied to the Li-O2 battery, utilizing its high solubility, low crystallinity, good electrochemical and mechanical properties. Our aim in this study; replacing volatile, flammable and leaking liquid electrolytes with polyvinylidenfluoride-hexafluoropropylene (PVDF-HFP) based GPEs. Gel-polymer electrolytes were prepared by dissolving the PVDF-HFP polymer in Acetone, Dimethylformamide and dissolved type lithium salts and their different concentrations. We prepared LiTFSI / PVDF-HFP, LiClO4 / PVDF-HFP and LiPF6 / PVDF-HFP GPEs containing concentrations of lithium salts changed from 1.0 M to 2.0 M. GPEs in lithium-oxygen batteries of lithium salts and different concentrations; We investigated its effect on ionic conductivity and electrochemical performance. In this study, we synthesized highly conductive GPEs using Al2O3, TiO2 and LATP nano powders as ceramic fillers. Composite GPEs were prepared by mixing 16% by weight PVDF-HFP polymer dissolved in acetone and Dimethylformamide and 1M LiTFSI dissolved in TEGDME solvent. By adding Al2O3, TiO2 and LATP fillers in different proportions, the effect of ceramic fillers and weight changes has been investigated as a composite gel polymer in LOBs. Electrochemical performance of GPEs was tested using the ECC-Air test cell. In this cell, lithium foil was used as anode, gas diffusion layer (GDL, Sigracet 24BC) as cathode and GPEs were used as electrolyte. The reaction potential of Li-O2 cells was investigated by cycling voltammetry (CV) and ionic conductivity of gel polymer electrolytes by electrochemical impedance spectroscopy (EIS) methods. The galvanostatic charge-discharge profile of the cells was realized between 2 V-4.5 V at 0.1 mA / cm2. Our results show compositions with high ionic conductivity and best cycle life. In our results, we determined the optimum salt concentration and ceramic filler type.