Capacitance-enhanced sodium-ion storage in nitrogen-rich hard carbon

Abstract

We demonstrate an approach to prepare nitrogen-rich hard carbon (N-HCS) from biomass as a robust anode material for sodium-ion batteries. A reversible capacity of ∼520 mA h g⁻¹ at a current density of 20 mA g⁻¹ along with an excellent rate performance was obtained. When cycled at a high current density of 1 A g⁻¹, the N-HCS was stable for over 1000 cycles delivering a capacity of ∼204 mA h g⁻¹. Density functional theory (DFT) computations verified that nitrogen doping enhances the interaction of sodium ions with the carbon, leading to a significantly improved storage capacity. This work provides new physical insights into the relationship between sodium-ion storage and nitrogen-containing hard carbon materials.