LAUSR

Abstract La-Mg-Ni-based alloys are promising negative electrode materials for 3rd generation of Ni-MH x batteries. In this work we investigate the effect of Mg substitution on the electrochemical and electronic properties of La 2− x Mg x Ni 7 materials. The mechanical alloying technique is used to produce a series of La 2− x Mg x Ni 7 alloys ( x  = 0.00, 0.25, 0.50 and 0.75). The X-ray diffraction measurements indicate multi-phase character of the samples with majority (La,Mg) 2 Ni 7 phases of hexagonal Ce 2 Ni 7 -type and rhombohedral Gd 2 Co 7 -type. Electrochemical measurements show how the maximum discharge capacity ( C m a x ) increases with Mg concentration and that it reaches the highest value of 304 mAh/g for La 1.5 Mg 0.5 Ni 7 ( x  = 0.5). The experimental efforts are followed by the density functional theory (DFT) calculations performed with the full-potential local-orbital minimum-basis scheme (FPLO). To simulate chemical disorder we use the coherent potential approximation (CPA). The calculations are focused on the La 1.5 Mg 0.5 Ni 7 composition with the highest measured value of C m a x . Additionally, several other structures are considered as reference points. We find that hexagonal and rhombohedral structures of La 2 Ni 7 have almost identical total energies which is in a good agreement with a measured coexistence of both phases in the samples. The calculated site preferences of Mg in both Ce 2 Ni 7 -type and Gd 2 Co 7 -type La 1.5 Mg 0.5 Ni 7 phases are consistent with the previous experimental data. Furthermore, the valence band of the nanocrystalline La 1.5 Mg 0.5 Ni 7 sample is investigated by X-ray photoelectron spectroscopy (XPS). The experimental XPS are interpreted based on the corresponding spectra calculated with DFT.