A flexible and free-standing silicon-based anode with a rational yolk-shell structure for high-performance lithium-ion batteries

Silicon is arousing considerable interest as a potential material for the anode of lithium-ion batteries (LIBs) owing to its proper discharge voltage and outstanding specific capacity. However, the inferior electrical conductivity, enormous volume variation, and slow Li+ propagation kinetics of Si severely hinder its application. Here, a free-standing and flexible silicon/carbon nanofibers composite with a yolk-shell structure (Si@void@CNFs) is designed, which consists of a yolk synthesized by sodiothermic reduction of SiO2 at a comparatively low temperature (450 ºC), a shell generated via electrospinning technique, and a void formed through etching atomic layer deposition (ALD) Al2O3 coating with dilute HCl. The as-prepared Si@void@CNFs anode employed in LIBs displays a large initial discharge capacity of 2828 mAh g-1 with a perfect Coulombic efficiency of 71% at 0.2 A g-1, significantly improved cycle stability retaining a large specific capacity of 952 mAh g-1 after 200 cycles, and remarkable rate performance (1725, 1567, 1391, 1121, and 719 mAh g-1 at 0.2, 0.5, 1, 2, and 4 A g-1). The superior electrochemical behaviour of the free-standing Si@void@CNFs is imputed to the cooperative effects of the mechanically robust CNFs shell, the porous silicon yolk, and the rational yolk-shell structure.