Binary silicon-based thin-film anodes for lithium-ion batteries: A review

Silicon has been considered a promising replacement anode material for carbon due to its high specific capacity (i.e., up to 11 times higher than that of carbon). However, the negative consequences of high electrical resistance and large volume change during charge/discharge cycling still hinder its widespread in (most) practical applications. To overcome these issues, binary Si-alloys with lithium-active or lithium-inactive materials have been explored. In this review, the addition of alloying materials in the form of composites and layers has been reviewed to understand its impact on electrochemical and cyclability performance. For lithium-active materials, the initial discharge capacity was dependent on the material type and concentration. The most promising materials were germanium, tin, and carbon due to their enhanced electrical conductivity, the formation of amorphous alloys with silicon, and mitigated volume expansion during charge/discharge cycling. The initial discharge capacity of silicon-alloy films was found to have an inverse relationship with the concentration of lithium-inactive materials. Silicon alloyed with copper, titanium, and vanadium showed enhanced capacity retention, due to their enhanced electrical conductivity and strong affinity towards silicon which produced mechanically robust anodes. However, the best alloying material, concentration, and structure (i.e., layered or composite) have yet to be conclusively identified.