Enhancing the Compatibility of Lignin and Polyacrylonitrile through Carboxylation to Dually Boost the Electron and Ion Transport of Carbon Fiber Electrodes

Abstract Incorporating lignin into polyacrylonitrile (PAN) provides a sustainable and cost-effective strategy for fabricating carbon fiber electrodes. However, the poor compatibility between lignin and PAN induces phase separation and structural defects, thereby hindering charge transport and limiting capacitive performance. Herein, a carboxylation strategy is developed to regulate the interfacial interactions between lignin and PAN, enabling the fabrication of carboxylated lignin/PAN-derived carbon fibers (C-lignin/PAN-CF). The introduced carboxyl groups form hydrogen bonds with PAN cyano groups, suppressing phase separation and enabling the formation of continuous, more graphitized carbon fiber networks with improved electron transport. Meanwhile, the thermal decomposition of carboxyl-containing groups induces in situ self-activation, forming finer, mesopore-enriched carbon fiber networks that facilitate electrolyte penetration and accelerate ion diffusion. Benefiting from these synergistic effects, the C-lignin/PAN-CF electrode delivers a high specific capacitance of 478.17 F g–1, more than three times that of the unmodified lignin/PAN-CF electrode (147.85 F g–1). The C-lignin/PAN-CF-based symmetric supercapacitors further deliver a high energy density of 33.26 Wh kg–1, far exceeding that of the unmodified device (12.98 Wh kg–1), and exhibit excellent cycling stability with 92.48% capacitance retention after 5000 cycles. This work demonstrates that carboxylation-mediated compatibility engineering is an effective strategy for simultaneously enhancing electron and ion transport in lignin-derived carbon fiber electrodes for advanced energy-storage applications.