Organic radical functionalized graphene as a superior anode material for lithium-ion batteries

Abstract

We report organic radical functionalized graphene via a simple etherification of carboxylic groups on graphene oxide with the hydroxyl group on 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (4-hydroxy-TEMPO). The resultant 4-hydroxy-TEMPO functionalized graphene (TEMPO-G) is revealed to consist of an electrically conducting network of graphene sheets with abundant electrochemically active nitroxide radical functionalities. As a consequence, when applied as the anode material for lithium ion batteries (LIBs), TEMPO-G exhibits a high reversible capacity with excellent cycling stability for lithium storage in terms of 1080 mA h g⁻¹ at a current density of 100 mA g⁻¹ after 400 cycles. The superior lithium storage performance of TEMPO-G can be attributed to the synergistic effect of graphene and abundant nitroxide radicals for ultrahigh lithium storage due to the two types of reservoirs (graphene and nitroxide radicals). Meanwhile, the unwanted dissolution of nitroxide radicals in the electrolyte can be avoided due to chemical bonding between the graphene sheets and 4-hydroxy-TEMPO. Moreover, the interconnected graphene sheet network can not only provide a large interfacial area for fast lithium ion diffusion from electrolyte to electrode but also shortens the diffusion length of lithium ions and electrons, as well as accommodating the volume change during the charge–discharge process.