Dual-layer carbon protected coaxial cable-like Si-based composites as high-performance anodes for lithium-ion batteries

•The NC@Si@CNTs electrode has coaxial cable structure.•The N doping into the carbon framework can be synchronized with the preparation procedure, which not only generate more defects and active sites, but also introduce porous microstructures and increase the specific surface area.•The double-layer carbon structure not only provides high conductivity, but also acts as a buffer to reduce volume expansion during cycling and stabilize the structure.•The composites have high capacity and good cyclic. [Display omitted] The double-layer carbon protected coaxial cable-like silicon-based composites exhibit excellent electrochemical performance and cycle stability. The Si-based composites (NC@Si@CNTs) are synthesized successfully by a facile route. Using tetraethylorthosilicate as Si-source, carbon nanotubes (CNTs) and polydopamine as C-source, a dual-layer carbon protected coaxial cable-like structure is achieved. As an anode for Li-ion battery, the dual-layer carbon protection to Si layer gives a initial specific discharge and reversible specific discharge capacity of 2804 and 1752 mAh g−1 at 200 mA g−1 after 150 cycles. Even at 2 A g−1, the NC@Si@CNTs electrode can still display an initial and reversible specific capacities of 2297 mAh g−1 and 910 mAh g−1. The dual-layer carbon protected coaxial cable-like structure also improves the rate performance and cycling stability greatly compared to Si. This might be ascribed mainly to high conductivity and buffer effect of two carbon layers during cycling, which provide more effective transmission paths for electrons and promote fast diffusion for Li ions. In addition, the N-doping of carbon layer for extra Li ions and more stable structure of the as-prepared coaxial cable also contribute to the enhanced specific capacity and cycle stability during the charging/discharging process.