Freestanding and Consecutive Intermixed N‑Doped Hard Carbon@Soft Carbon Fiber Architectures as Ultrastable Anodes for High-Performance Li-Ion Batteries

Freestanding N-doped hard carbon fibers and consecutive intermixed N-doped hard carbon@soft carbon composite fibers were successfully prepared by a simple electrospinning technique that used polyacrylonitrile and coal tar pitch as precursors. The electrochemical properties of these N-doped carbon fibers as anode materials for Li-ion batteries are studied. The prepared freestanding N-doped carbon fiber can be directly used as the anode without adding any binder and collector. The addition of coal tar pitch as a soft carbon source can reduce environmental pollution, improve the utilization of secondary resources, and improve the electrical conductivity of carbon fibers. Especially, intermixed N-doped hard carbon@soft carbon fibers with diameters of 200–300 nm were synthesized by electrospinning, followed by carbonization at 800 °C (CCNF-800), which displayed the best electrochemical performance among all samples. The high reversible capacity and ultrastable cycling stability can be ascribed to the reduced charge-transfer resistance and improved Li+ diffusion coefficient of CCNF-800 caused by a modification of coal tar pitch-based soft carbon. Ex situ X-ray diffraction (XRD) patterns also confirm that CCNF-800 possesses high structural stability and reversibility during cycling. This work provides an effective approach for the design of high-performance carbon-based electrodes and offers a new pathway to reduce dependence on fossil fuels.