Optimizing sodium storage mechanisms and electrochemical performance of high Nitrogen-Doped hard carbon anode materials Derived from waste plastics for Sodium-Ion batteries

Abstract

The development of high-performance hard-carbon (HC) anode materials for sodium-ion batteries was constrained by slow charge-transfer kinetics and sodium-storage mechanisms. In this paper, high nitrogen-doped (12.24 %) HC with an efficient interworking structure was synthesized in situ using waste plastics as precursors by utilizing the strong 2-D self-template effect of guanine. Elucidating the mechanism of sodium storage in heteroatom-doped carbon with coexisting heterocyclic and graphitic nitrogen, which synergistically enhances electrochemical activity, utilizing a range of in-situ and ex-situ characterization methods. Based on density functional theory (DFT), it has been discovered that the doping of pyrrole nitrogen (N5) and pyridinium nitrogen (N6) can effectively expand the interlayer spacing during the Na⁺ sodiated/de-sodiated process, thereby enhancing electrochemical activity. The optimized HC has increased the Na⁺ diffusion coefficient by 1.5 orders of magnitude (10^-8.2 cm² s⁻¹ vs 10^-9.76 cm² s⁻¹) and exhibits high reversible capacity (452 mAh/g@20 mA g⁻¹), high rate performance (388mAh/g@500 mA g⁻¹), superior cycling stability (87.6 % @500 mA g⁻¹ after 2,000 cycles). The full cell exhibits good cyclic stability (91.87 %@100 mA g⁻¹ after 2,00 cycles), while the designed pouch cell also demonstrates favorable cycle life (90.78 %@200 mA g⁻¹ after 100 cycles).