Effect of substitution La by Mg on electrochemical and electronic properties in LaMgNi alloys: a combined experimental and ab initio studies
arXiv:2503.14952 · doi:10.1016/j.jallcom.2018.05.299
Abstract
La-Mg-Ni-based alloys are promising negative electrode materials for 3rd generation of Ni-MH batteries. In this work, we investigate the effect of Mg substitution on the electrochemical and electronic properties of LaMgNi materials. The mechanical alloying technique is used to produce a series of LaMgNi alloys ( = 0.00, 0.25, 0.50 and 0.75). The X-ray diffraction measurements indicate multiphase character of the samples with majority (La,Mg)Ni phases of hexagonal CeNi-type and rhombohedral GdCo-type. Electrochemical measurements show how the maximum discharge capacity () increases with Mg concentration and that reach the highest value of 304 mAh/g for LaMgNi ( = 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 LaMgNi composition with the highest measured value of . Additionally, several other structures are considered as reference points. We find that hexagonal and rhombohedral structures of LaNi have almost identical total energies, which is in a good agreement with a coexistence of both phases in the samples. The calculated site preferences of Mg in both CeNi-type and GdCo-type LaMgNi phases are consistent with the previous experimental data. Furthermore, the valence band of the nanocrystalline LaMgNi sample is investigated by X-ray photoelectron spectroscopy (XPS). The experimental XPS are interpreted based on the corresponding spectra calculated with DFT.