Unraveling Synergistic Regulation Mechanism in Nitrogen/Sulfur Co-Doped Biomass-Derived Hard Carbon Toward Durable Sodium-Ion Battery Anodes

Abstract

Hard carbon (HC) materials featuring well-defined short-range ordered architectures have emerged as promising anode materials for sodium-ion batteries (SIBs). Nevertheless, due to the limited diffusion rate of sodium ions within the carbon structure, the rate capability of hard carbon at high current densities and long-term cycling stability remains a challenge. Herein, an innovative nitrogen/sulfur co-doping strategy is developed for loofah-derived hard carbon (LHC-N-S), synergistically regulating the electron defect and spatial structure. The synergistic charge regulation is attributed to the introduction of N atoms for ion adsorption and the improvement of electron conductivity. The spatial structure regulation mainly comes from the S doping to optimize the layer spacing and pore size, which facilitates the rapid ion diffusion kinetics. The obtained LHC-N-S anodes maintain a high reversible specific capacity (317.5 mAh g⁻¹ at 0.1 C) and ultralong lifespan (76% retention after 2000 cycles). Through the correlation analysis of the structural parameters and the Na⁺ storage performance, the N/S co-doping mechanism is further clarified. This work provides deep insights into the design of high-performance biomass-derived hard carbon anodes for SIBs by leveraging the synergistic charge and space regulation through heteroatom doping, paving the way for the development of durable and sustainable sodium-ion battery technologies.