Fully Realizing the Bipolar Energy Storage Capability of Radical Polymer-Grafted Graphene Sheets for Zinc-Organic Battery Cathodes.

Radical polymers, containing stable nitroxyl radical, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), within their repeating units, are considered as bipolar cathode materials capable of undergoing both oxidation and reduction in the redox process. However, in most cases, TEMPOcontaining radical polymers are exclusively employed as p-type cathode materials, initially oxidized to a positively charged state, with only one electron being stored or released in the redox process of TEMPO units. Here, a kind of composite material, poly(2,2,6,6-tetramethylpiperidin-1-oxyl-4-yl methacrylate) (PTMA) grafted to reduced graphene oxide, rGO-g-PTMA, is applied as cathode material for zinc-organic battery. Its high specific capacity (>220 mAh g^-1) and two well-resolved voltage plateaus confirmed the participation of TEMPO reduction in energy storage, as well as the bipolar energy storage capability of PTMA. Its electrochemical reaction mechanism and energy storage performance are also investigated in detail. This first full and distinct utilization of its p- and n-type redox reaction of PTMA opens a new avenue for nitroxyl radicals as high-performance cathode materials for zinc-organic batteries.