The preparation and characterization of samples of glass electrolyte for lithium/sodium-ion batteries

Energy storage has a place in the daily life and the industrial area. Batteries are basic energy storage systems because they can provide the electrical energy whenever and wherever they are needed. Secondary batteries are an important type of battery systems. In secondary batteries, the conventional electrolyte is a liquid which is the mix of organic solvent and ionic conducting salts. In spite of their high ionic conductivity, they have defects in terms of the usage and long duration performance such as risks of leakage, flaming, expansion, and even explosion. In order to eliminate these defects, solid electrolytes have gained importance to search instead of liquid electrolytes. Moreover, the electrolyte is needed to have high ionic conductivity with negligible electrical conductivity. Therefore, amorphous solids such as glasses and polymers are preferred as a solid electrolyte. However, they have low ionic conductivity in the literature. In this regard, the starting of this thesis is the development of ionic conductivity of glass materials and the studying of the effective factors in the ionic conductivity. In the literature, LIBs and SIBs are so popular in the battery study. Li-based systems have higher ionic conductivity than Na-based systems. Uneven, Li-based electrolytes don't have enough ionic conductivity. In this thesis, the first purpose is to improve the ionic conductivity of Li-based glass samples. However, limited Lithium source and its high-cost causes to need alternatives. At this point, Sodium-based systems are so attractive as a substitute because of the abundance and low cost of Sodium. In this context, the second purpose is to their ionic conductivity and compare them to Li-based glasses as a substitute. In the literature, oxide glasses have high stability. In order to obtain firstly high stability and secondly high conductivity, they were studied in the thesis. In the literature, so much experience has been done. They haven't obtained the ideal material for the industrial application. Hence, the object of this study is to improve their ionic conductivity by the changing of glass combinations and to investigate the effect of the formulation over the ionic conductivity and activation energy. In this study, glass-A, glass-B (LiPO3), glass-C (0.90LiPO3-0.10Li2MoO4), glass-D (0.50Si2O-0.15B2O3.0.15Al2O3.0.2Na2O.Na2SO4) and glass-E(0.50Si2O-0.15B2O3-0.15Al2O3-0.2Na2O-Na2SO4) were prepared. Glass-A is known as a Li-based glass and was used to compare to Li-based glasses in terms of the effect of Lithium content in the ionic conductivity. Its formulation wasn't done in this study. Glass-B and glass-C were prepared to compare to Li-based glasses in terms of the effect of MoO3 content in the ionic conductivity. In Na-based glasses, Si2O as a glass former and Na2O as a glass modifier have constant mole fraction in formulations of Na-based glasses, glass-D, and glass-E. The purpose is to observe the effect of mixed glass former in the ionic conductivity. In this regard, B2O3 ve Al2O3, glass formers, were used with different mole fraction. In order to investigate mixed anion effect, Na2SO4 was used slightly as a dopant salt apart from total mole fraction. Glasses were prepared by the conventional melt-quenching procedure. In the next step, they were characterized by XRF, PIGE, optical microscopy, SEM and EIS analyses. In EIS analysis, The Complex impedance measurement was performed under these conditions; the amplitude value was 200 mV, the frequency range was 10-2-106 Hz, the temperature was at 150, 200 and 250°C. Carbon from the graphite pencil was used to serve as an electrode. In conclusion, the ionic conductivity was obtained respectively (Glass-A, B, C, D, and E); 1.91x10-05, 6.06x10-05, 4.63x10-04, 4.13x10-06 4.81x10-06 S cm-1 at 250°C. In addition, the activation energy was obtained at 49.23, 58.94, 60.00, 60.88 and 76.44 kJ mol-1. Results generally show low ionic conductivity and high activation energy in spite of high operating temperature. It is figured out that high stability and endurance are obtained at high operating temperature. On the other hand, Na-based glasses have lower ionic conductivity and higher activation energy than of Li-based glasses. Glass-B has higher ionic conductivity than glass-A related to Lithium content. The effect of the Lithium content show a positive result. Glass-C has MoO3 compound, unlike glass-B. It shows that the mixed glass former gives obviously positive result in the ionic conductivity. In the next studies, a different combination of glass formers and higher Lithium content should be experienced to develop the ionic conductivity. In Na-based glasses, glass-E has lower ionic conductivity than glass-D. It shows that more fraction of Al2O3 in glass-E reduced the ionic conductivity and raised the activation energy. It is known that Al2O3 and B2O3 have an effect to reduce crystalline structure in the glass matrix. Because of that, the mole fraction of Si2O should be reduced and then of Al2O3 and B2O3 should be improved in the next studies. Furthermore, Na2SO4 as a dopant salt showed a positive effect in the ionic conductivity and especially the activation energy. Consequently, the positive effect of MoO3 in the ionic conductivity of Li-based glasses is shown and in Na-based glasses, the positive effect of Na2SO4 as a dopant salt is confirmed.