Flexible coal-derived carbon fibers via electrospinning for self-standing lithium-ion battery anodes

A series of flexible and self-standing coal-derived carbon fibers (CCFs) were fabricated through electrospinning coupled with carbonization using bituminous coal and polyacrylonitrile (PAN) as the carbon precursors. These CCFs were utilized as free-standing lithium-ion battery (LIB) anodes. Optimizing carbonization temperature reveals that the CCFs exhibit a one-dimensional solid linear structure with a uniform distribution of graphite-like microcrystals. These fibers possess a dense structure and smooth surface, with averaging diameter from approximately 125.0 to 210.0 nm at carbonization temperatures ranging from 600 to 900 °C. During electrospinning and carbonization, the aromatic rings enriched in bituminous coal crosslink with PAN chains, forming a robust three-dimensional (3D) framework. This 3D microstructure significantly enhances the flexibility and tensile strength of CCFs, while increasing the graphite-like sp² microcrystalline carbon content, thus improving electrical conductivity. The CCFs carbonized at 700 °C demonstrate an optimal balance of sp³ amorphous and sp² graphite-like carbons. The average diameter of CCFs-700 is 177 nm and the specific surface area (SSA) is 7.2 m²·g⁻¹. Additionally, the fibers contain oxygen-containing functional groups, as well as nitrogen-containing functional groups, including pyridinic nitrogen and pyrrolic nitrogen. Owing to its characteristics, the CCFs-700 showcases remarkable electrochemical performance, delivering a high reversible capacity of 631.4 mAh·g⁻¹. CCFs-700 also exhibit outstanding cycle stability, which retains approximately all of their first capacity (400.1 mAh·g⁻¹) after 120 cycles. This research offers an economical yet scalable approach for producing flexible and self-supporting anodes for LIBs that do not require current collectors, binders and conductive additives, thereby simplifying the electrode fabrication process.