Effect of substitution La by Mg on electrochemical and electronic properties in La$_{2-x}$Mg$_x$Ni$_7$ alloys: a combined experimental and ab initio studies
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arXiv
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| Format: | Preprint |
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2025
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| _version_ | 1866916656699146240 |
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| author | Werwiński, Mirosław Szajek, Andrzej Marczyńska, Agnieszka Smardz, Lesław Nowak, Marek Jurczyk, Mieczysław |
| author_facet | Werwiński, Mirosław Szajek, Andrzej Marczyńska, Agnieszka Smardz, Lesław Nowak, Marek Jurczyk, Mieczysław |
| contents | 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 multiphase 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 ($C_{max}$) increases with Mg concentration and that reach 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 $C_{max}$. 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 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. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2503_14952 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Effect of substitution La by Mg on electrochemical and electronic properties in La$_{2-x}$Mg$_x$Ni$_7$ alloys: a combined experimental and ab initio studies Werwiński, Mirosław Szajek, Andrzej Marczyńska, Agnieszka Smardz, Lesław Nowak, Marek Jurczyk, Mieczysław Materials Science Computational Physics 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 multiphase 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 ($C_{max}$) increases with Mg concentration and that reach 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 $C_{max}$. 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 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. |
| title | Effect of substitution La by Mg on electrochemical and electronic properties in La$_{2-x}$Mg$_x$Ni$_7$ alloys: a combined experimental and ab initio studies |
| topic | Materials Science Computational Physics |
| url | https://arxiv.org/abs/2503.14952 |