Si@nitrogen-doped porous carbon derived from covalent organic framework for enhanced Li-storage

Due to ultra-high theoretical capacity (4200 mAh g^-1), silicon (Si) is an excellent candidate for the anode of lithium-ion batteries (LIBs). However, the application of Si is severely limited by its volume expansion of approximately 300% during the charge/discharge process. Herein, nitrogen-doped porous carbon (NC) capped nano-Si particles (Si@NC) composites with a core-shell structure were obtained by calcination of covalent organic frameworks (COFs) encapsulated nano-Si. COFs is a crystalline material with well-ordered structures, adjustable and ordered pores and abundant N atoms. After carbonization, the well-ordered pores and frameworks were kept well. Compared with other Si@NC composites, the well-ordered NC framework shell derived from COFs possesses high elasticity and well-ordered pores, which provides space for the volume expansion of nano-Si, and a channel to transfer Li⁺. The core-shell Si@NC composite exhibited good performances when applied as the anode of LIBs. At a current density of 100 mA g^-1, it exhibited a discharge-specific capacity of 1534.8 mAh g^-1 after 100 cycles with a first-coulomb efficiency of 69.7%. The combination of COFs with nano-Si is a better strategy for the preparation of anode materials of LIBs.