The electrochemical properties of Al-Si-Ni alloys composed of nanocrystal and metallic glass for lithium-ion battery anodes

Melt-spun Al75-X Si25Ni (X) (X = 2, 4, 7, and 10 mol%) alloys were investigated as anode materials for lithium-ion batteries. The Al68Si25Ni7 anode showed a maximum capacity of 840 mA h g(-1) at the fifth cycle and maintained 661 mA h g(-1) after 40 cycles with a high coulumbic efficiency of 93%. The specific capacity increased as the decrease in the Ni content during the first 20 cycles, but the cycle performance became poorer. For the Al65Si25Ni10 anode, the specific capacity increased slowly as the cycles increased and reached 370 mA h g(-1) after 40 cycles. When the Al68Si25Ni7 ribbons were annealed, their initial capacity became higher, but much poorer cycle performance and low coulumbic efficiency occurred. Except Al65Si25Ni10, the AlLi compound could be detected in the anodes after lithiation. However, the capacity faded rapidly due to the formation of excessive AlLi in the Al73Si25Ni2 and annealed Al68Si25Ni7 anodes. The experiments revealed that the as-quenched ribbons consisted of the nanoscaled alpha-Al, metallic glass and alpha-Si, and their fractions were dependent on the Ni content. The alpha-Al was a supersaturated solid solution of Si and Ni in fcc-Al. For the as-quenched Al68Si25Ni7 ribbons, the alpha-Al grains were embedded in the amorphous matrix. It can be understood that metallic glass can store Li, and the supersaturated solid solution can store Li even more easily compared with other known Al-Si-based alloys. A conclusion can be drawn that the microstructure that the nanoscaled alpha-Al embedded in the metallic glass matrix is beneficial to improve the structure stability, restrain serious structural evolution, and limit the volume variation and pulverization during electrochemical cycles.