Recent advances in lignin-based carbon fibers (LCFs): precursors, fabrications, properties, and applications

To meet the huge market demand for carbon fibers (CFs), great efforts have been focused on developing low-cost and sustainable CFs with comparable properties. Lignin, a polyaromatic heteropolymer in nature, is considered a promising precursor suitable for CFs fabrication due to its abundant, renewable, low-cost, high-carbon, thermostable, and thermoplastic characteristics. Although research on lignin-based carbon fibers (LCFs) has achieved impressive results, their mechanical properties are still inferior to those of commercialized CFs. In this review, the structural characteristics of the lignin polymers from different plant sources and isolation methods are introduced. The key factors affecting LCFs performances and the effective strategies aiming to improve the properties of LCFs are also summarized in detail, revealing the influences of structural features of lignin on the performances of LCFs. In particular, recent advances in precursors, spinning techniques, stabilization, carbonization, graphitization, and activization of LCFs since 2017 are systematically reviewed. Furthermore, to expand the new applications of LCFs, a comprehensive overview of LCFs applications in diverse fields (electrochemical energy storage, adsorption, catalysis, and other emerging fields) is provided. Finally, the current challenges and opportunities for the future development of LCFs are proposed.