Functionalized Carbon Based Electrodes for High-Performance Energy Storage Devices

Abstract

Rechargeable Li-ion batteries have become the main power sources for portable electronic devices by utilizing transition metal oxides or metal phosphates as the positive electrode materials. However, large-scale energy storage applications, such as electric vehicle, smart grid, and renewable energy storage, stimulate the need for the development of more sustainable and affordable organic based electrode materials. Recent research showed that oxygen functional groups on the surface of carbon materials, such as carbon nanotube and graphene oxide, can react with Li ions at ~3 V vs Li. In addition, these surface redox reactions have been utilized to develop carbon based positive electrodes for the Li rechargeable batteries or Li-hybrid capacitors. To further advance the surface redox reactions of carbon materials, we have assembled highly porous nanostructured electrodes employing the functionalized carbons based on simple and versatile processing techniques. There are two key advantages in the assembled electrodes: the porous carbon support can support fast electron conduction and ionic diffusion, while redox-active functional groups on the carbon support can store a large number of Li or Na ions. Consequently, the functionalized carbon electrodes deliver high gravimetric capacities over ~150 mAh/g with high redox potentials over ~3 V vs. Li, proposing promising positive electrodes for rechargeable batteries or hybrid capacitors. In addition, these functionalized carbon electrodes can sustain capacities over 1,000 cycles without significant capacity decay. Moreover, we incorporated external redox-active materials, such as organic molecules and polymers, into the porous carbon electrodes to further increase energy density of the electrodes.