Tez özetleri Astronomi ve Uzay Bilimleri Anabilim Dalı

Preparation of Polymer Gel Electrolytes and Investigation

of Their Conductivities
In this thesis study, polymer gel electrolytes whicih can be used in lithium batteries, dye sensitized solar cells etc. were prepared. Thesis study consists of two independent studies. In the first part of the thesis, poly(ethylene glycol)/poly(2-acrylamido-2-methyl-1-propane sulfonic acid) (PEG/PAMPS) polymer gel was prepared in deionized water in the presence of amonium persulfate (APS) as initiator. APS was used in the amount of 1 mol % of AMPS monomer in the feed. Polymerization reaction was taken place in a water bath with temperature controller at 70 °C for 24 h. Polymeric gels were dried under vacuum at 70 °C for 24 h. The prepared liquid electrolyte was added into dried polymer gel. Homogen and immobile polymer gel electrolyte (PGE) was attained at room temperature. In the second part of the thesis, poly(ethylene glycol)/poly(glycidyl methacrylate) (PEG/PGMA) polymer gel was prepared in the presence of amonium persulfate (APS) as initiator. APS was used in the amount of 1 weight % of GMA monomer in the feed. Polymerization reaction was taken place in a water bath with temperature controller at 70 °C for 24 h. The prepared liquid electrolyte were added to prepared PEG/PGMA gels Homogen and mobile polymer gel electrolyte (PGE) was attained at room temperature. In the thesis study, PEG/PAMPS and PEG/PGMA polymer gels was prepared, used as polymer gel electrolytes and characterized for the first time.
During preparing PEG/PAMPS-based polymer gel elektrolytes, 1-methyl-2- pyrrolidone (NMP) and γ-butyrolactone (GBL) were chosen as organic solvents Sodium iodide (NaI)/iodine (I₂) were used as redox couples and were dissolved in this organic solvent/ solvent mixtures. In all of the polymer gel electrolytes, alkali iodide salt/iodine mole concentration was kept 10/1. The effect of the concentration of alkali metal iodide salt was investigated on ionic conductivity (σ) and liquid electrolyte uptake (Q_e) and a maxiumum point was obtained at 0.4M NaI. Polymer gel electrolytes which had 1 M or 1.5 M AMPS monomer concentration, higher σ and higher Q_e values were obtained for 1.5M. Ionic conductivity and liquid electrolyte uptake values of PGE’s in different volume ratio of NMP:GBL organic solvent mixtures were compared, the highest ionic conductivity and the highest liquid electrolyte uptake value, was observed when NMP:GBL volume ratio was 7:3. When the different type of alkali metal iodide salts (NaI or LiI) was investigated, higher σ and higher Q_e values were obtained for NaI. Besides, ionic conductivity depending on the temperature was measured and conductivity mechanism of PGE was discussed. With the measured ionic conductivities at 20-70°C, lnσ-1/T curve was fitted and it was determined that polymer gel electrolyte indicated Arrhenius type conductivity. PEG/PAMPS(1.5M)-0.4 polymer gel electrolye which had the maximum ionic conductivity (2.58mS/cm), had the minimum activation energy (E_a=18.17 kJ mol^-1 K^-1).Structural and termal characterization of dried gels and polymer gel electrolytes were carried out using Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry and Thermal Gravimetric Analysis (TGA), respectively. The morphological properties of PEG/PAMPS polymers was investigated using Scanning Electron Microscopy (SEM). The structural properties of polymer gel elekctrolytes were studied by X-Ray Diffraction (XRD) and UV-Vis Absorption Spectroscopy (UV-Vis).
During preparing PEG/PGMA-based polymer gel electrolytes, solvents with high boiling points, ethylene carbonate (EC) and propylene carbonate (PC) were chosen as organic solvent mixture in order to overcome volatilization. And dielectric constants of these solvents are high to help ion dissociation. To hinder crystallization of EC, PC was added and volume ratio of EC:PC was kept 8:2. Sodium iodide/iodine (NaI/I₂) and potassium iodide/iodine (KI/I₂) were used as redox couples and were dissolved in this organic solvent mixture. The liquid electrolyte were added to prepared PEG/PGMA gels Homogen and mobile polymer gel electrolyte (PGE) was attained at room temperature. In all of the PGE’s, iodide salt/iodine mole concentration was kept 10/1. The effect of polymer content in polymer gel electrolyte was investigated, poylmer content of polymer gel electrolyte was changed form %10 to %20 weight, ionic conductivity decreased. It was determined that polymer chains blocked ion transfer. When the samples which were prepared with NaI or KI compared, KI-based samples showed higher ionic conductivity. Besides, ionic conductivity depending on the temperature was measured and conductivity mechanism of PGE was discussed. With the measured ionic conductivities at 20-70°C, lnσ-1/T curve was fitted and it was determined that polymer gel electrolyte indicated Arrhenius type conductivity. PEG/PGMA-10K polymer gel electrolye which had the maximum ionic conductivity (5.39mS/cm), had the minimum activation energy (E_a=15.12 kJ mol^-1 K^-1). Structural and thermal characterization of gels and polymer gel electrolytes were carried out using Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry and Thermal Gravimetric Analysis (TGA), respectively. The morphological properties of PEG/PGMA polymer was investigated using Scanning Electron Microscopy (SEM).