Enhanced electrochemical performances of silicon nanotube bundles anode coated with graphene layers

• Electrochemical performances of Si NBs were enhanced by coating graphene layers.
• Capacity after 600 cycles reached fivefold the case of without graphene layers.
• Graphene served as mechanical protecting layer improved structural sustainability.
• Formation of Li-rich Li15Si4 crystallites resulted in unexpected capacity increase.

Significant enhancement in electrochemical performances has been achieved in silicon nanotube bundles (Si NBs) via coating with graphene layers (denoted as Si NBs@G), which could be a promising anode material in Li-ions batteries. The synthesized Si NBs@G have tubular structure with a diameter of around 200 nm and a thickness about 80 nm and the tube walls are composed of Si nanocrystals with a size about several nanometers. Galvanostatic charge-discharge measurements showed that the Si NBs@G displayed gradual increasing in capacity after first 100 cycles and finally reached a capacity of ∼765 mAh g−1 at 600 cycles, which was almost fivefold the capacity of the parent Si NBs without graphene coating. The graphene outerlayer is considered to serve as the mechanical protecting layer to enhance structural sustainability of Si NBs anode by forming stable solid electrolyte interface. In addition, the formation of Li-rich Li15Si4 crystallites also contributes to the capacity improvement.

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