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Carbon Nanotube‐Enhanced Growth of Silicon Nanowires as an Anode for High‐Performance Lithium‐Ion Batteries

Advanced lithium-ion batteries with high energy density, highrate capability, and excellent cycling performance are critically important for automotive and stationary energy storage applications such as electric vehicles, portable electronics, power tools, and energy storage for many types of renewable energy sources.[1–3] From the materials point of view, silicon is one of the most promising candidates as an anode material for these lithium-ion batteries owing to its abundance in nature, relatively low working potential, and highest known theoretical charge capacity of 4200 mAh g−1, 11 times higher than that of commercialized graphite.[4,5] One major challenge is that the dramatic volume change (>300%) for Si during lithium insertion and extraction processes causes capacity fading due to severe pulverization and electrical disconnection from the current collector, thus hindering practical applications.[5–8] In order to overcome these drawbacks, it is highly desirable to explore nanostructured silicon anodes with more robust architectures.[9–13] So far, silicon nanostructures (and their composites) with a variety of different dimensionalities, including nanoparticles,[14–18] nanospheres,[19] nanowires,[8,20–29] nanotubes,[30–32] nanoscale thin films,[7,33–35] and three-dimensional porous particles[36] have been reported to provide improved electrochemical performance over bulk silicon materials. These results are encouraging for the development of Si nanomaterials as potential building blocks for high-performance anode materials in lithium-ion batteries. Yet, scale-up and industrial implementation of these silicon nanostructures still lag behind and further improvements in overall performance, scalability, and cost are critically required. For example, silicon thin films exhibit highly improved cycling performance,[33,34] thanks to the anisotropy of their volume change. However, the optimized film thickness is usually a few hundred nanometers, which results in an areal capacity of ≈0.1 mAh cm−2, which is insufficient for application. Anodes made from one-dimensional silicon-based nanostructures can provide open space while remaining electrically connected to current collectors, allowing designs[8,12,13,30] which accommodate the volume change of silicon during lithium insertion. These nanostructures offer good contact with the current collectors at medium charge/discharge rate without