Maximizing the rate capability of carbon-based anode materials for sodium-ion batteries

Maximizing the rate capability of carbon materials optimizes sodium ion battery (SIB) performance. This study develops nanoscale nitrogen-doped carbon material (NNCM), in which nano-sized primary particles aggregate. These aggregates form a meso-macro-hierarchical porous structure, which facilitates Na+ diffusion from outside the aggregates into the primary nanoparticles. The large specific surface area of carbon black improves Na+ accessibility by forming large interfaces, and Na+ is easily solvated through defect sites and pores on the primary particle surfaces. Furthermore, primary nanoparticles have short Na+ diffusion pathways, while turbostratic structures provide broad pathways aiding Na+ diffusion. Nitrogen improves the electrical conductivity of the carbon matrix and provides abundant active sites by creating extrinsic defects. Together, these factors afford NNCM good capacity retention (38% at 100 A/g vs. 1 A/g), reversible capacity (similar to 101 mAh/g at 100 A/g), ultrahigh cycling stability (11,000 cycles at 100 A/g), high initial coulombic efficiency (80%), and remarkable rate capability.