The synthesis and electrochemical properties of LixCa0.5Sm0.5MnO3 phase

Abstract

The composition and properties of the cathode material based on Ca 0.5 Sm 0.5 MnO 3 (structure type GdFeO 3 , space group Pnma ) were studied by X-ray powder diffraction, scanning electron microscopy, energy dispersion and X-ray fluorescence X-ray spectroscopy. Electrochemical lithiation of the 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. The anode and cathode materials were separated by pressed cellulose to avoid contact between them. An electrolyte for batteries consisted of 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 oxides was studied using scanning electron microscopes TESCAN Vega3 LMU. Quantitative composition of the powders (before and after lithiation) was studied using Oxford Instruments energy dispersive X-ray analyser (Aztec ONE system). X-ray fluorescent spectroscopy (spectrometer ElvaX Pro) was used for investigation of the integral composition of electrodes before and after electrochemical procesess. The phase and structural 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 orhorhombic perovskite Li x Ca 0.5 Sm 0.5 MnO 3 ( x = 0.088) was, synthesized by electrochemical method. The unit cell parameters increase because of the inclusion of lithium in the free space of the structure: a = 5.4054 (10) → 5.4050 (5) Å, b = 7.5477 (16) → 7.5520 (8) Å, c = 5.3552 (10) → 5.3567 (5) Å, V = 218.48 (7) → 218.65 (4) Å 3 . The size of spherical microcrystallites in the original sample reaches from 0.3 to 2.5 μm. The surface of the electrode actively adsorbs the components of the electrolyte, resulting in the formation of block-like aggregates, 2–4 μm in size. The particle size in the aggregates is in the range of 100–300 nm. The total composition of the electrode before and after electrochemical Li-intercalation is practically unchanged and is Ca 9.8 Sm 9.5 Mn 21.3 O 59.4 and Ca 9.5 Sm 9.3 Mn 21.1 O 60.1 , respectively. Keywords: complex oxides, structure of orhorhombic perovskite cathode material, Li-ion batteries.