Galaguz V. Synthesis of LiFePO4/C nanocomposites and physicochemical properties of cathode material on their basis.

The thesis is devoted to the study of the impact of physicochemical factors on the formation of LiFePO4/C nanocomposite and its functional properties. For the first time, LiFePO4 nanocrystals were synthesized in the medium of saline melts and ionic liquid ChCl-DEG. Depending on the selection of precursors, composition of the reaction medium, mechanism of heating and temperature, samples with different properties were obtained. The use of CH3COOLi and NH4FePO4∙H2O as precursors and the reaction medium, ChCl-DEG, allowed to obtain monophasic nanocrystalline LiFePO4 samples of lamellar morphology for 1 hour at 245°C. With the influence of microwave radiation on the reaction medium (ChCl-DEG ionic liquid or solid phase reaction), the process of formation of LiFePO4 nanocrystals with admixture of amorphous LiFePO4 is intensified. Synthesis in ChCl-DEG with (NH4)2Fe(SO4)2∙6H2O, (C6H11O7)2Fe or FeC2O4∙2H2O as the precursor of the Iron (II) results in the formation of fractal texture precipitates and increases the interaction time to 14 hours. Using Raman and XPS-spectroscopy, the conditions for the formation of a conductive coating on sp2 carbon on LiFePO4. The dependence of the electrochemical parameters of the cathode on the physical and chemical properties of the synthesized samples is shown. Samples synthesized in ionic liquid of ChCl-DEG composition using CH3COOLi and NH4FePO4∙H2O show the best capacitance parameters Q=135 mAh/g, DLi=1.5∙10-10 cm2/s, average coulomb efficiency ~ 98%.