Activating graphite with defects and oxygenic functional groups to boost sodium-ion storage

摘要

Sodium-ion batteries have been one of the most promising alternatives for lithium-ion batteries (LIBs) for large-scale energy storage systems due to cost-efficiency and rich resources of sodium. However, graphite, a commercial anode material of LIBs, shows a very low reversible capacity for sodium-ion storage because of the weak binding between sodium and graphite. Herein, an activated graphite (AG) material with abundant defects including edges and vacancies with oxygenic functional groups is well-designed and fabricated by a facile and eco-friendly ball-milling method. The structural evolutions during the ball-milling process and their effects on electrochemical sodium-ion storage performance are investigated. A stable reversible capacity of 139.1 mA h g−1 can be achieved at 1.0 A g−1 even after 4500 cycles for the AG-50 electrode with the 50-hour ball-milling treatment, amounting to a very low decay ratio of 0.0034 per cycle. Based on physical characterizations and density functional theory calculations, the greatly improved specific capacity and cycling stability of the AG anode for sodium-ion storage can be attributed to the enlarged interlayer space, increased specific surface area, and introduced defects caused by ball-milling treatment, which provide vast active sites for reversible sodium-ion storage based on a adsorption/desorption mechanism, thus leading to great improvement in the specific capacity of the AG electrode. These results can provide a meaningful reference for the application of modified graphite for high-performance sodium storage.