Fabrication of C@Si@G for flexible lithium-ion batteries

•A sandwich structure of C@Si@G is put out.•Every C@Si fiber is wrapped by single layer G (graphene) to constrain the volume expansion of Si (silicon).•Natural cocoon silk is applied as carbon-sourced substrate.•The as-prepared flexible C@Si@G composite is directly used as Li-ion anode without Copper foil (current collector).•The C@Si@G anode possesses an excellent discharge capacity of 1070 mAh g−1 at 0.2 A g−1 after 300 cycles. The commercial application of silicon is still impeded by poor conductivity and significant volume change. In this work, a C@Si@G composite was synthesized by a facile chemical solution reaction and carbonization procedure with cocoon silk as a natural carbon source. This composite has a sandwich structure, where Si nanoparticles as a sandwich middle layer and graphene (G) as an out layer. And it possesses the advantages of flexible, nitrogen-doped and is environmentally friendly. The optimized C@Si@G-15 composite is used as a self-supporting anode without a current collector, and it shows a reversible discharge capacity of 972 mAh g−1after 120 cycles at 1 A g−1 and a relatively high capacity of 1070 mAh g−1 after 300 cycles at 200 mA g−1, demonstrating the effect of coating the N-doped carbonized silk and the graphene synergistically to improve electrical connectivity and to constrain the pulverization of Si nanoparticles. Hence, it delivers great potential for application on wearable devices.