Electrochemical lithiation of the CeNiC2 compound

Electrochemical lithiation of CeNiC2 was carried out in a Swagelok-type cell with a positive electrode containing LiCoO2 over 51/50 cycles of lithiation/delithiation. The crystal structure of CeNiC2 (structure type CeNiC2, Pearson symbol oS8, space group Amm2) before and after lithiation was investigated by X-ray diffraction. The electrodes containing the ternary carbide were examined by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The crystal structure of CeNiC2 remained very stable toward electrochemical lithiation. The volume of the unit cell after 51/50 lithiation/delithiation cycles decreased by only 0.06 %. A small amount of lithium, up to 0.115 Li per formula unit, was reversibly incorporated into CeNiC2. The electrochemical lithiation process included two reactions: 1) insertion of Li into suitable voids and channels of near-surface layers of CeNiC2, and 2) partial decarbonization of the electrode. The composition and morphology of the grains of the electrode material changed only slightly. Small amounts of LizCy, Ce22.7Ni21.6O55.7 and Li2O were detected as by-products of the lithiation. The lithiation mechanism of ternary carbides containing a rare earth and a 3d-element depends on the stoichiometry and peculiarities of the crystal structure.