Optimized design of 3D nitrogen-doped graphene-like carbon derived from g-C₃N₄ encapsulated nano-Si as high-performance anode for lithium-ion batteries

Silicon anode is attracted enormous attention due to ultra-high theoretical capacity. However, the volume change of nearly 300% and poor conductivity stymie the application of silicon anodes. It is of fundamental importance and challenge to solve this problem. Here, the porous Si/nitrogen-doped carbon nanosheets (Si/NCNS) composites are successfully synthesized by in situ growth of nano-silicon on a graphene-like carbon. The in-situ growth of nano-SiO₂ is introduced through the electrostatic interaction on the surface of g-C₃N₄ nanosheets (CNNS) by hydrolysis of tetraethyl orthosilicate (TEOS). Subsequently, SiO₂ nanoparticles are reduced to porous Si and the nitrogen of CNNS is partially removed to form nitrogen-doped carbon nanosheets (NCNS) via a magnesiothermic reduction route. Importantly, NCNS not only provides rapid transferring channels for electrons and lithium ions but also relieves volumetric changes of Si, which contributes to ameliorating electrochemical performance. The optimal Si/NCNS-1 composite exhibits excellent electrochemical performances of 1106.7 mAh g⁻¹ after 200 cycles with the capacity retentions of 93.6%, and the coulombic efficiency remains above 99.5%. This controllable synthesis method provides a potential building for the application of Si anode.