Bionic liquid–liquid phase separation phenomenon inspired lignin molecular aggregates toward highly nitrogen-doped nanocarbon anode for sodium-ion hybrid capacitors

Abstract

Sodium-ion hybrid capacitors (SHICs) are potentially low-cost and high-power energy storage devices. Developing novel anode materials with rapid kinetics is pivotal for propelling the advancement of SIHCs. Naturally renewable lignin is one of the ideal carbon sources for preparing anodes. However, lignin has an inherent tendency to aggregate. This aggregation poses a significant challenge in achieving a high nitrogen-doping level within lignin-derived carbon, limiting its sodium-ion storage capacity. In this work, we were inspired by the universal phenomenon that liquid–liquid phase separation (LLPS) in eukaryotic cells drives the self-assembly of biomacromolecules to form multi-component biomolecular aggregates. Lignin was used as the organic carbon precursor, nitrogen-containing supermolecules were used as the nitrogen source, and natural polyphenolic compounds were introduced to disperse lignin to reduce the aggregation of lignin and strengthen the weak intermolecular interactions. A three-dimensional, highly nitrogen-doped lignin-derived nanocarbon (termed TMLC) was synthesized by a one-step carbonization method as a high-rate sodium-ion storage anode. The high nitrogen doping content, abundant defects, and unique nanostructure endow TMLC with surface pseudocapacitance for rapid charge storage, facilitate Na⁺ transport, and guarantee structural stability. Consequently, TMLC exhibits remarkable rate performance (136 mA h g⁻¹ at a current density of 40 A g⁻¹) and excellent long-term cycling stability (1000 cycles, 99% capacity retention).