Mixed-Lignin Precursor Engineering for Hierarchically Porous Pseudo-Graphitic Carbon Toward High-Performance Supercapacitors

Developing biomass-derived carbon electrodes with simultaneously optimized pore architecture, graphitic ordering, and surface chemistry remains a challenge for high-performance supercapacitors. Herein, a dual-lignin precursor engineering strategy based on lignosulfonate and alkaline lignin is proposed to construct hierarchically porous carbons via an ex situ method. Benefiting from the complementary characteristics and cooperative interactions of the two lignins, the optimized carbon exhibits a well-balanced porous architecture composed of interconnected carbon nanosheets with predominantly pseudo-graphitic domains accompanied by locally graphitized regions. The mixed-lignin strategy effectively regulates sulfur retention and removal during carbonization, while the coexistence of oxygen- and sulfur-containing functional groups may improve electrode wettability and contribute to charge storage, thereby favoring substantial outer-surface charge accessibility with contributions from other charge-storage processes. Among all samples, the optimized 2L1A electrode delivers a high specific capacitance of 386.7 F g−1 at 1 A g−1 in a three-electrode configuration. The assembled symmetric supercapacitor delivers an energy density of 40.4 Wh kg−1 together with 97.4% capacitance retention after 10,000 charge–discharge cycles. Comprehensive kinetic analyses further demonstrate rapid electron/ion transport, predominant surface-controlled charge storage, and excellent reversibility. This work demonstrates the potential of mixed-lignin precursor engineering for the rational design of high-performance carbon electrodes for advanced supercapacitors.