Ni_xSi_1-x alloys prepared by mechanical milling as negative electrode materials for lithium ion batteries

Ni_xSi_1-x (0 ≤ x ≤ 0.5, Δx = 0.05) alloys were prepared by ball milling and studied as anode materials for lithium ion batteries. Nanocrystalline Si/NiSi₂ phases were formed for x ≤ 0.25. The NiSi phase was observed for samples with higher Ni content. Increasing the Ni content was found to gradually lower the lithiation voltage, while delithiation voltage was not affected for x ≤ 0.25. As a result, Li15Si4 did not form during cycling for x > 0.15. The capacity trend of Ni_xSi_1-x alloys with composition suggested that the nanocrystalline NiSi₂ phase had some activity toward Li, while the NiSi phase had no capacity toward Li. In situ XRD studies confirmed the activity of nanocrystalline NiSi₂. The best cycling performance of NixSi_1-x alloys was obtained for x = 0.20 with 94% capacity retention after 50 cycles.