Supermolecule-regulated synthesis strategy of general biomass-derived highly nitrogen-doped carbons toward potassium-ion hybrid capacitors with enhanced performances

Biomass-derived carbons are promising anodes in potassium-ion hybrid capacitors owing to their tunable structure and competitive cost-effectiveness. The intercalation of K+ ions into carbonaceous anode is a sluggish reaction due to the turbostratic structure and large radius of K+ ions, resulting in the inability to exploit its high capacity and high-rate capability. Nitrogen-doping strategy could enhance the K-ion storage performance by surface capacitive adsorption mechanism. Nevertheless, conventional nitrogen-doping strategies could only endow biomass-derived carbons with low nitrogen-doping levels (<10 at.%), owing to the general agglomeration issue of biomass molecules and the easy release of nitrogen dopant during carbonization. Herein, we proposed a supermolecule-regulated strategy, which enables the breakage of the agglomeration of lignin molecule and disperses lignin in Lewis alkali-acid coupled supermolecule through inter-molecule interactions between lignin and the supermolecule. The co-decomposition of supermolecule/lignin composite precursor could form a covalent-bonded graphitic carbon nitride/carbon intermediate, ensuring the high nitrogen doping level (17.0 at.%) in lignin-derived carbon. The obtained carbon anode delivered high reversible capacities and high-rate capability. All-carbon potassium-ion hybrid capacitors constructed by this carbon as both anode and cathode exhibited a high energy density and power density. This work proposes a general method for constructing highly nitrogen-doped carbon anodes with superior performances.