N-doped porous carbon nanofibers sheathed pumpkin-like Si/C composites as free-standing anodes for lithium-ion batteries

Dramatic capacity fading and poor rate performance are two main obstacles that severely hamper the widespread application of the Si anode owing to its large volume variation during cycling and low intrinsic electrical conductivity. To mitigate these issues, free-standing N-doped porous carbon nanofibers sheathed pumpkin-like Si/C composites (Si/C-ZIF-8/CNFs) are designed and synthesized by electrospinning and carbonization methods, which present greatly enhanced electrochemical properties for lithium-ion battery anodes. This particular structure alleviates the volume variation, promotes the formation of stable solid electrolyte interphase (SEI) film, and improves the electrical conductivity. As a result, the as-obtained free-standing Si/C-ZIF-8/CNFs electrode delivers a high reversible capacity of 945.5 mA h g⁻¹ at 0.2 A g⁻¹ with a capacity retention of 64% for 150 cycles, and exhibits a reversible capacity of 538.6 mA h g⁻¹ at 0.5 A g⁻¹ over 500 cycles. Moreover, the full cell composed of a free-standing Si/C-ZIF-8/CNFs anode and commercial LiNi_1/3Co_1/3Mn_1/3O₂ (NCM) cathode shows a capacity of 63.4 mA h g⁻¹ after 100 cycles at 0.2 C, which corresponds to a capacity retention of 60%. This rational design could provide a new path for the development of high-performance Si-based anodes.