In the present work, we provide a systematic analysis of the structural evolution of rayon-based carbon fibers (RCFs) induced by doping boron using scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD) and Raman spectroscopy. For the first time, boron-doped RCFs with tunable amounts of boron were fabricated by exposing the RCFs to a vapor of boron by the decomposition of boron carbide (B₄C). SEM and XRD results indicate that at the higher temperatures the strong erosion of boron vapor not only changed the original structure of RCFs, but also produced some flaws. Interestingly, when the temperature of doping boron is higher than 2200 °C, the graphite basal planes of RCFs are perpendicular to the fiber axis. Raman spectra also confirmed the presence of disorders and flaws in graphitic layers because of the displacement and solid solution of boron in the carbon lattice. Further, the chemical environment of boron species was ascertained by ¹¹B nuclear magnetic resonance, indicating that boron atoms exist in three chemical environments, including the substitutional boron (BC₃), boron clusters and B₄C. Moreover, the TGA data indicated that doping boron greatly improved the oxidation inhibition of RCFs, and is superior to increasing the heat treatment temperature for improving the oxidation resistance. Such a systematic analysis of the structural evolution and oxidation resistance of RCFs induced by doping boron thus provides industrial potential for preparing RCFs with higher oxidation resistance at up to 800 °C.

We demonstrate a new kind of silicon (Si)-based anode architecture consisting of Si nanoparticles and carbon nanocoils (CNCs). In such a hybrid structure, the conductive three-dimensional interpenetrating network of the CNCs can enhance the structural integrity of the electrode. Also, the CNCs afford a conductive network of lithium ion and electron pathways in the hybrids, thereby enabling efficient transport of electrons and the diffusion of lithium ions upon charging–discharging process. As a result, the hybrids exhibit much-improved cycling performance.

Paraffin is one of the most common and promising phase change materials to store and release thermal energy. The inadequacy of paraffin lies in its low thermal conductivity, which affects its further application on thermal energy storage. In this work, hollow fibers derived from pitch were spun. The graphitization (treated at 2773 K under argon atmosphere) induced the carbon atom arrangement and lattice order development, which endowed the hollow graphite fibers (HGFs) with good graphite structure. The HGFs applied as thermal additives into paraffin significantly improved its thermal conductivity. The high thermal conductivity of the HGFs/paraffin composite was achieved up to 2.50 W/(m·K) along the fiber axis, which displayed an over 680% enhancement as compared with that of the pure paraffin. The HGFs displayed significant improvement of the heat transfer rate and heat flow of paraffin, which indicated the promising potential application of the HGFs/paraffin PCM in thermal energy storage systems.