Doped and reactive silicon thin film anodes for lithium ion batteries: A review

Silicon is touted as a replacement for the commercially utilized carbon anode in lithium ion batteries. However, two drawbacks have hindered its use: low electronic conductivity and significant volume changes during lithiation/delithiation. Numerous studies have examined ways to improve silicon thin films with doped and reactive (i.e., oxidized, nitrated, and hydrogenated) forms summarized herein. Factors affecting electrochemical performance and cycling stability are compared against pure silicon, with the two alternatives generally showing better results. Most of the improvements for doped silicon have been attributed to higher electronic conductivity. Treatment gases such as: oxygen, nitrogen, and hydrogen, have been used to produce reactive silicon films. For oxidized silicon reaction products (i.e., lithium silicate, lithiated silicon, and lithium oxide) during cycling were found to serve as a buffer layer and/or matrix, helping to negate volume changes during charge/discharge. Improvements in nitrated silicon films were attributed to large lithiation capacity, high lithium ion conductivity, and mechanical stability. The improvement in cyclability performance for hydrogenated silicon films has yet to be fully developed and further systematic investigations are warranted.