The lithiated nickel-cobalt oxide LiNi 0.5 Co 0.5 O 2 used as cathode material was grown at low-temperature using different aqueous solution methods. The wet chemistry involved the mixture of metal salts (acetates or nitrates) with various carboxylic acid-based aqueous solutions. Physicochemical and electrochemical properties of LiNi 0.5 Co 0.5 O 2 products calcined at 400-600°C were extensively investigated. The four methods used involved complexing agents such as either citric, oxalic, aminoacetic (glycine), or succinic acid in aqueous medium which functioned as a fuel, decomposed the metal complexes at low temperature, and yielded the free impurity LiNi 0.5 Co 0.5 O 2 compounds. Thermal (TG-DTA) analyses and XRD data show that powders grown with a layered structure ( space group) have been obtained at temperatures below 400°C by the acidification reaction of the aqueous solutions. The local structure of synthesized products was characterized by Fourier transform infrared (FTIR) spectroscopy. The electrochemical properties of the synthesized products were evaluated in rechargeable Li cells using a non-aqueous organic electrolyte (1 M LiClO 4 in propylene carbonate, PC). The LiNi 0.5 Co 0.5 O 2 positive electrodes fired at 600°C exhibited good cycling behavior.
Comprehensive dielectric measurements have been performed on the mixed-crystal system K1−xLixTaO3 in order to check the hypotheses done about the ferroelectric and the dipole glass behaviours and identify their respective origins. These have been made for a series of concentrations (1.5% < x < 5%), spanning the critical concentration xc ≅ 2%, and over the frequency range from 20 Hz to 2 MHz. The broad frequency and temperature ranges have allowed us to cover, in the same study, both Li-related dielectric relaxations as well as the transition for x > xc and to investigate their relationship. We have gathered new strong supports (quasi-discontinuity in the dielectric constant, thermal hysteresis) of first-order character of the transition for x = 3.5% and 5% and studied the kinetics within this hysteresis for x = 5%. We have also identified the high-temperature relaxation with an activation energy of about 2700 K, which we attribute to Li pairs undergoing π flips at high temperatures. It is argued that, at low temperatures, these pairs are sources of static random fields responsible for the disorder of the low-temperature phase.
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