Insight into the decay mechanism of non-ultra-thin silicon film anode for lithium-ion batteries

Silicon thin-film is one of the most promising silicon anode materials for lithium-ion batteries, with the advantages of high cycle stability and initial coulombic efficiency. The excellent performance of silicon thin-films is due to their ultra-thin thickness (< 200 nm), but this results in their areal capacity too low to be compatible with commercial cathode materials, and only films thicker than 500 nm are practical. However, frequent volume changes in non-ultra-thin silicon films during cycling may cause layer misalignment and separation of the film from substrate. In this paper, silicon films with a thickness of similar to 700 nm are prepared by magnetron sputtering on the inhomogeneous surface of a copper foil. The properties of the silicon films and mechanisms involved in the cycling process is investigated by combining experimental means during cycling with calculations of the atomic-scale amorphous lithium-silicon Zintl Phases' structural volumes before and after cycling. The results show that the volume of silicon doesn't recover after delithiation and there is still significant swelling. The cyclic process causes a superimposed expansion of the volume, but the non-uniform film substrate causes the lateral expansion stresses to offset each other, thereby retaining a relatively stable structure. At the end of 100 cycles, the specific capacity of the silicon film electrode is 1461.5 mAh g(-1) (areal capacity 0.242 mAh cm(-2)), with a capacity retention of 64.35%, and the silicon film thickness becomes 8.5 mu m. We believe that by reducing the longitudinal expansion volume or stress of the silicon film, the cycle life of the silicon film can be further optimized.