Effect of CVD carbon coatings on Si@CNF composite as anode for lithium-ion batteries

Lithium-ion battery (LIB) anodes with high capacity and binder free structure were synthesized from carbon nanofibers that contained silicon nanoparticles (Si@CNF). The particle filled nonwoven structures were produced by an electrospinning and subsequent carbonization process. Pristine Si@CNF composites had Si nanoparticles exposed on the fiber surface. As produced, the Si nanoparticles could become detached from the nanofiber surface during cycling, causing severe structural damage and capacity loss. In order to prevent Si from detaching from the nanofiber surface, the Si@CNF composite was then treated with a thermal chemical vapor deposition (CVD) technique to make Si completely coated with a carbon matrix. The carbon coated Si@CNF (Si@CNF-C) composites were synthesized with different Si contents (10, 30, and 50 wt%) for different CVD treatment times (30, 60, and 90 min). It was found that the initial coulombic efficiency of Si@CNF-C could be increased via the amorphous carbon by stabilizing solid-electrolyte-interface (SEI) formation on surface. The capacity and cyclic stability were improved by the CVD carbon coating, especially for the 30 wt% Si@CNF-C composite with 90 min CVD coating, a CVD amorphous carbon coating of less than 1% by weight on Si@CNF composites contributed to more than 200% improvement in cycling performance. Results indicate that the CVD carbon coating is an effective approach to improve the electrochemical properties of Si@CNF composites making this a potential route to obtain high-energy density anode materials for LIBs.