Interconnected porous carbon fibers (pCF) are an innovative class of materials for energy storage and conversion. They exhibit a high specific surface area, tunable porosity, cost efficiency and scalability, which makes them competitive with carbon nanotubes and nanofibers. This study focuses on the development and optimization of pCF for applications in supercapacitors and lithium-ion batteries, while providing detailed insights into their microstructure and morphology.
The fabrication process is comprised of four critical steps: fiber spinning, electron beam (EB) irradiation, stabilization and carbonization. Polyacrylonitrile (PAN) serves as the primary precursor, with optional additives such as cellulose acetate (CA), nanocellulose (NC) and lignosulfonate (LS) to enhance porosity. The optimized spinning parameters, including coagulant bath temperature and fiber stretching, have been demonstrated to achieve a reduction in fiber density of up to 38.5% (from 1.04 g/cm³ to 0.64 g/cm³), thereby ensuring high porosity in the precursor fibers. EB irradiation induced structural modifications, enhancing porosity and surface chemistry. The stabilization and carbonization processes were fine-tuned to preserve the integrity of the carbon structure and to regulate the pore distribution. Carbonization at temperatures ranging from 700 to 900°C resulted in fibers with specific surface areas ranging from 150 to 200 m²/g. Increased carbonization temperatures led to improved microporosity and mechanical strength, while lowered temperatures resulted in enhanced mesoporosity.
To characterize these pCF at each stage of the production process (precursor fiber, EB cross-linked fiber, stabilized fiber, and carbonized fiber), a combination of classical and advanced analytical methods was employed. Classical investigations included measurements of density, porosity, strength, and modulus of elasticity. Structural and imaging techniques such as scanning electron microscopy (SEM) and atomic force microscopy (AFM) were complemented by Raman spectroscopy and X-ray diffraction (XRD), providing insights into surface roughness, bonding states and overall structure. Focussed Ion Beam (FIB) sections facilitated cross-sectional analysis, while nanotomography (nCT) provided 3D representations of the fibers’ pore systems. The utilization of transmission electron microscopy (TEM) facilitated a high-resolution examination of pore distribution and interconnectivity.
Prototypes from optimized fibers demonstrated outstanding performance. Lithium-sulfur battery cathodes achieved a discharge capacity of 850 mAh/g S over 100 cycles with excellent stability. Additionally, the hierarchical pore distribution satisfied the requirements for supercapacitor applications.
These findings highlight the transformative role of pCF in energy systems, emphasizing application-specific optimization and thorough structural characterization.