Lithium insertion in Si electrodes studied by first principles method

Abstract

Si has been considered as one of the most potential new-generation anode materials for high-capacity lithium-ion batteries. However, the lithiation and delithiation of lithium ions during the charge-discharge processes of the Si electrode would give rise to almost four-fold volume expansion, causing structural changes and cracks of the conductive network, limiting the application of Si-based anode material. In this paper, the lithium ions inserting into Si material at various positions and at different doping concentrations of lithium ions was studied by first-principles method. The stability of different insertion sites, the structural changes, band structures and density of States after Li insertion were analyzed. It has been found that the lithium ions doping is an interstitial doping rather than a substitutional one and the tetrahedral center (Td) site is the most stable insertion position. From the band structure analysis, it can be seen that the Si material with the insertion of lithium ions becomes metal-like, and as the concentration changes, silicon changes from an indirect gap semiconductor to a direct gap semiconductor. When the concentration reaches 12.5%, the structural expansion rate increases obviously. This work provides a strategy for the improvement of the Si based anode material used in high-capacity lithium-ion batteries.