The presence of colossal dielectric constant in the low frequency region is observed in the strontium ferrite with hexagonal structure. This result can be explained in the framework of the "grain-layer" and the polarization of Maxwell - Wagner in the ceramic medium. The effect of negative capacitance in ceramic strontium hexaferrite at a frequency of less than 2.10 Hz has been detected.

Keywords: hexaferrite strontium, ferromagnetic, insulator, semiconductor, colossal dielectric constant, negative capacitance, high-temperature annealing, X-ray structural analysis, full-profile analysis, electron microscopy.

The composite cathode material of the core@shell type with the LiMn2O4@LiCoO2 formula of has been successfully synthesized using the solid-state reactions in several stages. Its structure has been studied by means of X-ray diffraction, scanning and transmission electron microscopy and vibrational infrared spectroscopy. Electrochemical investigation in two-electrode cell has been showed improvement of characteristics of the synthesized cathode material than the constituent components. The specific power of LiMn2O4@LiCoO2 is 650 mWh/g, against 450 and 500 mWh/g for LiCoO2 and LiMn2O4, respectively.

Keywords: lithium-ion batteries, cathode materials, Delafosse, X-ray structural analysis, electron microscopy, electrochemical properties

The solid solution of  LiMn1/3Cr1/3Fe1/3O2 with the structure of α-NaFeO2  isostructural with the widely used LiCoO2  has been synthesized and investigated as a cathode material. Rated voltage of LiMn1/3Cr1/3Fe1/3O2  relative to the lithium is 4 V.  The possibility of charging − discharging the material to a specific capacity of 220-250 mAh/g at currents of C/15-C/50 without phase transformations has been experimentally demonstrated. 

Keywords: lithium-ion batteries, cathode materials, Delafosse, solid solution, X-ray structural analysis, electrochemical properties