Ilnytskyi R. Intercalated Current-Formation in the TiO2, TiO2/С Modified Nanodispersed Systems

This dissertation deals with the investigation of the joint effect of thermal annealing, laser irradiation and doping on physicochemical properties of nanocomposites formed on the basis of nanodispersed ТіО2, doped with Zr, Nb, Fe and nanoporous carbon. The interrelations have been determined between the conditions and modes of obtaining and modifying constituents of the composite and electrochemical process regularities in electrical energy storage and generation devices. The optimal conditions of laser modification when this material provides high specific capacity properties of lithium power sources have been found. It has been demonstrated that the specific capacity of the electrochemical system formed on the basis of the modified composite TiО2/С when the current is 1-5 mA is 15-50 times higher than the similar capacity for the primary composite, which shows the formation of the matrix with a considerable number of guest positions capable of substantially intensifying charging/discharging processes. Based on the overall tests, the influence of the intercalated Zr and Nb and the thermal annealing on the crystalline structure, surface morphology of TiО2 has been shown. It has been discovered that doping TiО2 with niobium provides anatase phase stability toward the temperatures of 1123 К. According to the results of X-ray analysis of ТіО2 doped with zirconium, the content of rutile after annealing is ~ 30 %. This material is characterized by the porous structure with the specific area of 260 m2/g, which is by 40% bigger in comparison with the results obtained for TiО2 undoped and doped with niobium. With the help of the thermogravimetric method, it has been found that its content of water is up to 20% of its initial mass. According to the results of the ultraviolet spectroscopy, the width of the titanium dioxide bandgap decreases from 3.5 eV to 2.5 eV when ТіО2 is doped with zirconium and annealed at the temperature of up to 1123 K respectively, the cause of which is appearance of energy levels in the ТіО2 bandgap because of the formation of oxygen vacancies after annealing, which has been confirmed by the X-ray photoelectron spectroscopy. For the first time, the ТіО2 doped with zirconium and niobium and annealed at 673 and 1123 K has been used as a cathode material in lithium power sources. The efficiency of combining these methods of modification in order to improve the intercalation of lithium ioniums into the titanium dioxide structure has been demonstrated. The value of specific energy characteristics of the lithium power sources has increased by 50% and 20% when ТіО2 is doped with zirconium and niobium respectively with their subsequent annealing at 1123 К. It has been experimentally proved that the electrochemical intercalation of lithium ioniums into the rutile structure of magnesium fluoride is a two-stage process. The first one involves filling the hollowness of structural channels in surface layers, accumulation of lithium metal on the surface; the second - filling free "guest" positions in the cathode matrix structure at the expense of lithium diffusion. The kinetics of lithium diffusion in the structure of MgF2 and MgF2/С has been studied. It has been determined that in the process of accumulating lithium intercalated by seleit matrix with the rutile structure, the diffusion coefficient changes in a non-monotone way depending on the established cathode-anode difference in potentials while its total reduction is observed.