Si nanotubes array sheathed with SiN/SiOxNy layer as an anode material for lithium ion batteries

Silicon has received high interest as an anode material for lithium ion batteries due to its large theoretical Li storage capacity. However, poor cyclability and low coulombic efficiency of the Si based electrode, caused by the pulverization of the active material and the continuous formation of unstable solid electrolyte interphase (SEI) due to large volume change associated with Li, limits its practical use as an anode material. We have developed a Si nanotube array sheathed with silicon nitride compound to improve the mechanical integrity, resulting in improved electrochemical performance. The SiN/SiOxNy outer shell has excellent mechanical properties, such as a high elastic modulus and hardness. This guides the volume expansion of the Si into the hollow inner space of the tubular structure during charge, which prevents both the pulverization of the Si active material, as well as continuous SEI layer formation by protecting the exposure of fresh Si surface to the electrolyte. Si nanotube array sheathed with silicon nitride electrode compound exhibits improved electrochemical performance, including stable capacity retention and high coulombic efficiencies, over the analogous homogeneous Si nanotube system.