Boosting sodium storage performance of biomass-derived porous carbon anodes by surface functionalized strategy

In order to enhance the sodium ion storage performance of biomass-derived carbon anode materials, a surface functionalization strategy was employed through a simple acid etching method on porous carbon. The resulting functionalized carbon exhibits a hierarchically porous structure, expanded interlayer spacing, and oxygencontaining functional groups. The redox reactions occurring at the surface between Na ions and carbonyl groups provide additional sites for sodium ion storage, thereby improving cycling capacity and rate capability. Theoretical calculations and electrochemical tests further demonstrate that the functionalized carbon can increase the surface-controlled sodium storage capacity by modifying the transport and adsorption processes of sodium ions. After 200 cycles at a current density of 100 mA g-1, the carbon anode, which was surfacefunctionalized with an etching time of 6 h, achieve a high reversible capacity of 273 mA h g-1. Furthermore, it displays improved rate performance with a capacity of 194 mA h g-1 at a high current density of 2 A g-1 for sodium-ion batteries. This study introduces an effective and general strategy for the cost-effective and large-scale synthesis of carbon anode materials for sodium-ion batteries.