The effect of nickel substitution on the electrochemical performance of a lanthanum silicide (LaSi 2 )/silicon (Si) composite electrode for lithium-ion batteries was studied. The results of X-ray diffraction analysis showed that LaSi 2 forms a substitutional solid solution with Ni, and that only the Si site in LaSi 2 is substituted by Ni, whereas elemental Si in the crystal structure is not substituted. Although the charge−discharge capacity of a LaNi x Si 2−x electrode (x = 0.06 and 0.12) was lower than that of a LaSi 2 electrode, the LaNi x Si 2−x electrode exhibited a high-rate performance. A LaNi 0.10 Si 1.90 /Si (70:30 wt %) composite electrode showed a large initial discharge capacity and a superior long-term cycle performance compared to electrodes composed of Si alone and LaSi 2 /Si composite, and suppressed the decrease in the initial Coulombic efficiency of the Si electrode. The LaNi 0.10 Si 1.90 /Si electrode also exhibited an excellent high-rate performance with a reversible capacity of 2240 mA h g(Si) −1 at a rate of 10 C. The results of computational chemistry demonstrated that LaNi 0.25 Si 1.75 favors Li migration in the pathway compared to LaSi 2 . These results indicate that Ni substitution in a LaSi 2 /Si composite negative electrode significantly improves its electrochemical performance.

We prepared composite electrodes of iron silicide/Si by using mechanical grinding for mixtures of ferrosilicon and Si followed by gas-deposition, and investigated their electrochemical properties as Li-ion battery anode. With increasing the mechanical grinding time, the phase transformation from FeSi to FeSi2 took place more significantly, and the composite electrode showed better cycle stabilities. There was no remarkable difference in mechanical properties and electronic conductivity between FeSi and FeSi2. On the other hand, the FeSi2 exhibited about three times larger capacities in comparison with the FeSi electrode. In addition, a result of our first principle calculation indicates that Li ion can diffuse more easily in FeSi2 lattice than in FeSi lattice. It is suggested that the better cyclability of the composite electrodes was attributed to the moderate reactivity of FeSi2 with Li and the smooth Li-ion diffusion in it.

A Ge x Si 1¹x alloy electrode is useful for addressing the shortcomings of a Si negative electrode for lithium-ion batteries. To further improve the electrochemical performance of a Ge x Si 1¹x negative electrode, a film-forming additive and the formation of a composite with LaSi 2 were applied. A Ge 0.1 Si 0.9 electrode exhibited better cyclability in the additive-containing electrolyte with a discharge capacity of 1240 mA h g ¹1 at the 400th cycle. In addition, a Ge 0.1 Si 0.9 /LaSi 2 composite electrode showed better cycle performance than a Ge 0.1 Si 0.9 electrode.