Three-dimensional nitrogen-doped carbon coated hierarchically porous silicon composite as lithium-ion battery anode

Three-dimensional (3D) Nitrogen-doped carbon coated hierarchically porous silicon (hp-Si@NC) composite with cocontinuous skeletons and abundant interconnected macropores was prepared by a sol-gel route, followed by a magnesiothermic reduction and a polydopamine pyrolyzation. The BET specific surface area and pore volume of the obtained hp-Si@NC composite are calculated to be around 220.4 m 2 ·g ─1 and 0.247 cm 3 ·g ─1 , respectively. Both hierarchically porous Si monolith and hp-Si@NC composite possess great electrochemical performances. The hierarchically porous Si monolith exhibits an initial discharge and charge capacity of about 1943 and 1621 mAh·g ─1 , and maintains a reversible capacity of about 125 mAh·g ─1 in the 100th cycle. The hp-Si@NC composite reveals a discharge capacity of about 1077 mAh·g ─1 and a charge capacity of 723 mAh·g ─1 in the first cycle, and a reversible capacity of around 700 mAh·g ─1 remains after 100 cycles. The coulombic efficiency increases from 67.1% in the first cycle to 97% in the second cycle and to 99% in the 100th cycle, with a great rate performance. All these favorable electrochemical characterizations benefit from unique pore structure and N-doped carbon layer. The hp-Si@NC composite obtained by integrating with sol-gel process, magnesiothermic reduction and polydopamine pyrolyzation can be promisingly applied as an anode in Li-ion batteries with a bright prospect.