Thermal pyrolysis of Si@ZIF-67 into Si@N-doped CNTs towards highly stable lithium storage

Silicon is attracting considerable attention as an active anode material for advanced lithium-ion batteries due to its ultrahigh theoretical capacity. However, the reversible utilization of silicon-based anode materials is still hindered by the rapid capacity decay, as a consequence of the huge volume change of silicon during cycling. Herein, we use a Co-zeolitic imidazole framework (ZIF-67) to prepare silicon-wrapped nitrogen-doped carbon nanotubes (Si@N-doped CNTs) by controllable thermal pyrolysis. The as-prepared nanocomposites can effectively prevent pulverization and accommodate volume fluctuations of silicon during cycling. It can deliver a highly reversible capacity of 1100 mAh g^-1 even after 750 cycles at a current density of 1000 mA g^-1. As confirmed by an in situ transmission electron microscopy experiment, the remarkable electrochemical performance of Si@N-doped CNTs is attributed to the high electronic conductivity and flexibility of cross-linked N-doped CNTs network as a cushion to mitigate the mechanical stress and volume expansion. Furthermore, a full cell consisting of Si@N-doped CNTs anode and LiFePO₄ cathode delivers a high reversible capacity of 1264 mAh g^-1 and exhibits good cycling stability (>85% capacity retention) over 140 cycles at 1/4 C (1 C = 4000 mA g^-1) rate.