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Silicon suffers from high volume variation and poor conductivity, which limits its commercial application in lithium-ion battery anode materials. To improve the stability of Si-based electrodes, the porous structure was designed for both Si and carbon fiber. Furthermore, heteroatom doping was adopted to enhance the conductivity of carbon fiber. Three freestanding porous silicon@heteroatom-doped porous carbon fiber was successfully prepared by coaxial electrospinning. The impact of sulfur/boron doping on the electrochemical properties of anodic materials is systematically researched. The porous structure of both silicon and carbon fiber efficiently relieves the volume expansion of silicon and provides diffusion channels for ion transportation, while the S doping can increase active sites. Relying on the distinctive structure, the porous silicon@sulfur-doped porous carbon fiber (PSi@ SPCF) exhibits virtually the highest reversible capacities over the reported silicon@carbon fiber composites, with an excellent reversible capacity of 1112.7 mAh•g −1 after 1000 cycles at 2.0 A•g −1 , indicating the potential application of the PSi@SPCF composites in advanced energy storage.

Bifunctional comonomer 2-methylenesuccinamic acid (MLA) was designed and synthesized to prepare acrylonitrile copolymer P (AN-co-MLA) using mixed solvent polymerization as a carbon fiber precursor. The effect of monomer feed ratios on the structure and stabilization were characterized by elemental analysis (EA), Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), X-ray diffraction (XRD), proton nuclear magnetic (1H NMR), and differential scanning calorimetry (DSC) for the P (AN-co-MLA) copolymers. The results indicated that both the conversion and molecular weight of polymerization reduce gradually when the MLA content is increased in the feed and that bifunctional comonomer MLA possesses a larger reactivity ratio than acrylonitrile (AN). P (AN-co-MLA) shows improved stabilization compared to the PAN homopolymer and poly (acrylonitrile-acrylic acid-methacrylic acid) [P (AN-AA-MA)], showing features such as lower initiation temperature, smaller cyclic activation energy, wider exothermic peak, and a larger stabilization degree, which are due to the ionic cyclization reaction initiated by MLA, confirming that the as-prepared P (AN-co-MLA) is the potential precursor for high-performance carbon fiber.