Ultrafast thermal shock synthesis of nitrogen-doped expanded graphite for high-performance sodium-ion battery anodes

Graphite materials have been highly successful as anode materials for lithium-ion batteries (LIBs), but they show limited performance in sodium-ion batteries (SIBs) due to the insufficient interlayer spacing, which restricts Na+ insertion and diffusion. In this work, we report the rapid synthesis of expanded graphite (EG) via a hightemperature shock reduction method and enhance its sodium storage capacity through nitrogen doping (EGN). The ultrafast nonequilibrium thermal shock generates a defect-rich structure in EGN, expanding the interlayer distance to 0.44 nm while maintaining the layered ordered structure characteristic of graphite-like materials. Spectroscopic analysis and theoretical calculations indicate that the successful incorporation of nitrogen atoms into expanded graphite increases the active sites and enhances Na+ adsorption capability. Consequently, SIBs with EGN anodes achieve a reversible specific capacity of 295 mA h g- 1 at 0.1 A g-1. This work presents a cost-effective and efficient method for EG synthesis, offering a new strategy for designing advanced sodium-ion anode materials.