High-Value Utilization of Lignin To Prepare Functional Carbons toward Advanced Lithium-Ion Capacitors

Lithium-ion capacitor (LIC) bridging the gap between the lithium ion battery and electrochemical capacitor has attracted myriad interest. Lignin, the second most abundant natural polymer, is also the main byproduct treated as a waste in pulp and paper industry, which causes severe pollution to the aerosphere, water, and soil. Herein, for the purpose of constructing high-performance LICs and high-value utilization of biomass waste, by regulating the porous framework and graphitic degree, lignin is converted to two kinds of functional carbons that serve as the electrode materials in LICs. Lignin-derived hierarchical porous carbon (LPC-3) prepared via the combination of freeze drying and activation displays a large specific surface area of 2490 m2 g–1 and a high fraction (54%) of pores in size more than 1.25 nm. As a result, a high specific capacitance of 145 F g–1 and a superior cyclic stability of 87% retention after 5000 cycles at 1 A g–1 are achieved. Simultaneously, lignin-derived graphitic carbon (LGC-1500) synthesized with the aid of a catalyst (Fe). Thanks to a high fraction of extended graphitic structure embedded in the amorphous phase, LGC-1500 exhibits high plateau capacity (182 mA h g–1 below 0.2 V) and superior rate capability (131 mA h g–1 at 5 A g–1). Additionally, with optimization, the assembled LGC-1500//LPC-3 LIC delivers a high-energy density of 97 W h kg–1, a high power density of 11.4 kW kg–1, and a superior cyclic stability of 92.3% retention after 5000 cycles at 1 A g–1. This strategy realizes the high-value utilization of lignin and provides insights into the design of high-performance LICs and other energy storage systems.