Гидротермальный редокс синтез шпинелей кобальта и марганца с использованием нитратов металлов

Abstract

The hydrothermal reduction of cobalt, manganese and lithium nitrates with ethylene glycol was studied in the temperature range 100-270 оС in order to obtain nanostructured spinels. The phase composition, particle sizes of the reaction products, and their morphology studied by using IR spectroscopy, X-ray diffractometry, and scanning electron microscopy. We found that the nature of the reaction product of manganese and cobalt nitrates with ethylene glycol (EG) depends on the reaction temperature, the ratio of metal nitrate: ethylene glycol and reaction time. In excess of the reducing agent at temperatures up to 140 оС, observed the formation of metal oxalates. The main product of hydrothermal reduction of manganese nitrate with ethylene glycol at temperatures of 150 оC and 180 оC is manganese oxide Mn3O4 (Hausmanite). At 200 оС obtained the mixture of manganese oxide (Mn3O4) and carbonate (MnCO3). In accordance with the data of X-ray phase analysis at 220 оС and 240 оС, the only reaction product in both cases is manganese carbonate. It was obtained two types of structures on electron-microscopic images of the non-calcined sample at 200 оC: needle-shaped and spherical clusters. It can be assumed that these structures belong to the phases Mn3O4 (Hausmanite) and manganese carbonate MnCO3, respectively. When reduced cobalt nitrate with ethylene glycol in the temperature range 120-220 оC, gives a main amorphous phase, and on X-ray diffraction patterns are observed weak reflections corresponding to cobalt oxide Co3O4. It was shown that upon calcination (at 750 оС) of the samples during the reduction of the mixture of cobalt and manganese nitrates, was obtained the spinel phase of the composition (Co,Mn)(Co,Mn)2O4. In a similar way were obtained Li2CoMn3O8 and LiCoO2 phases (with average particle sizes of 42 nm and 30 nm), which can be used as cathodes in lithium batteries.