Directional Regulation of Surface Chemistry of Graphene Using Carbon Dots for Sodium-Ion Battery Anodes

In this study, we have fabricated carbon dot/reduced graphene oxide (CDs/rGO) composites using oxygen-functionalized CDs and conductive graphene oxide (GO) by a hydrothermal method and calcination at 250 °C. The CDs can manipulate the surface functional groups of the composites by consuming C–O bonds and introducing C═O bonds. As sodium-ion battery anodes, CDs/rGO with a high C═O group content exhibits a great reversible capacity of 308 mAh g–1 at 0.05 A g–1, which is up to 1.8 times that of rGO (173 mAh g–1). It retains a capacity of 116 mAh g–1 after 2000 cycles at 2 A g–1. When assembled into a full cell, the activated anode and NVP@C display a higher initial discharge capacity of 291 mAh ganode–1 with an average working voltage of 2.5 V. The good performance of CDs/rGO is mainly due to the synergistic effects of the CDs with abundant Na storage sites and rGO with a conductive network. The improved electrochemical properties are dominated by the capacitive Na storage mechanism. This work implies that the oxygen-functionalized CDs could serve as medium to regulate the surface chemistry of carbon materials.