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Silicon-Germanium Heterostructure Nanowires As High Capacity Lithium-Ion Battery Anodes - an Electrochemical and Structural Investigation
Here we report the formation of high-performance and high-capacity lithium-ion battery anodes from high-density Si-Ge heterostructure nanowire arrays grown directly from the current collector. The unique morphology of the active material consists of Si NW branches grown from a Ge NW backbone. By tuning the ratio of Si to Ge in the material it is possible to design electrodes for either high-capacity applications (high Si : Ge mass ratio) or high rate capability applications (high Ge : Si mass ratio). We show by ex-situ high-resolution transmission electron microscopy (HRTEM) and high-resolution scanning electron microscopy (HRSEM) studies that the NW array transforms into a mechanically robust, porous network of Si and Ge ligaments. Once this network is formed it is highly stable, maintaining capacities of 1700 mAh/g over 200 cycles. The electrode material described here also has the advantage of being formed in a low energy, rapid synthetic protocol. Using a very simple reaction protocol, NW growth occurs by thermolytic decomposition of an organometallic precursor onto a preheated substrate in an inert atmosphere.
1. T. Kennedy, E. Mullane, H. Geaney, M. Osiak, C. O’Dwyer, K. M. Ryan, Nano Letters 14, 716-723 (2014),
2. E. Mullane, T. Kennedy, H. Geaney, K. M. Ryan, ACS Applied Materials & Interfaces, 6, 18800-18807 (2014).