Electrochemical synthesis of the LixCa0.5Pr0.5FeO3 phase

The composition, structure and properties of the cathode material based on Ca 0.5 Pr 0.5 FeO 3 (structure type CaTiO 3 , space group Pm -3 m , Pearson`s symbol cP 5) were studied by X-ray powder diffraction, scanning electron microscopy, and energy-dispersion X-ray spectroscopy. Electrochemical lithiation of the ceramic phase, which was used as cathode material, was carried out in the two-electrode prototype of the battery “Swagelok-cell”. Li-metal was used as anode material. As an electrolyte for battery was used an commercial 1 M Li[PF 6 ] solution and a mixture of aprotic solvents ethylene carbonate and dimethyl carbonate (1:1 vol. ratio). Morphology of the surface of the complex oxides was studied using scanning electron microscope TESCAN Vega3 LMU. SE-detector characterizes the morphological contrast of the studied surface, BSE-detector characterizes the contrast of the surface phases with different distribution of elements. Phase analysis and quantitative composition of the polycrystalline samples (before and after lithiation) were studied using Oxford Instruments energy dispersive X-ray analyser (Aztec ONE system). The structure analysis of the samples was carried out by powder X-ray diffraction using a diffractrometer STOE STADI P (Cu K α 1 -radiation, λ = 1.54060 Å, 5° ≤ 2 θ ≤ 100°, monochromator Ge(111), room temperature). The phase based on cubic perovskite Li x Ca 0.5 Pr 0.5 FeO 3 ( x = 0.062) was synthesized by electrochemical method. The unit cell parameters increase because of the inclusion of lithium in the free space of the structure: а = 3.8494(1)→3.8520(1) Å, V = 57.0399(1)→57.1556(1) Å 3 . Small aggregates of the Li x Ca 0.5 Pr 0.5 FeO 3 phase have sizes in the range from 200 to 500 nm. The total composition of the electrode before and after electrochemical Li-intercalation is practically unchanged and is equal Ca 11.2 Pr 10.2 Fe 21.2 O 57.4 and Li x Ca 9.0 Pr 8.7 Fe 18.9 O 63.4 , respectively. An increasing of porosity of the electrode surface and aggregation of small particles on the base of the electrode with electrolyte components is observed after lithium intercalation/deintercalation processes. Keywords: complex oxides, electrochemical synthesis, CaTiO 3 -type, cathode material, Li-ion batteries.