Nitrogen-doped holey graphene additive for high-performance electric double-layer supercapacitors

A facile and cost-effective method is developed to produce nitrogen (N)-doped holey graphene nanosheets (NHGNSs) using rapid heating under an NO atmosphere. This is a single-step and residual-free process wherein the holey structure and N doping are simultaneously created. In this study, we employ three kinds of additives, namely graphene (GNSs), holey graphene (HGNSs), and NHGNSs, in activated carbon (AC) electrodes. The conventional GNS additive though improves electronic conductivity of the AC electrode greatly hinders the ionic conductivity, decreasing supercapacitive performance in propylene carbonate electrolyte. HGNSs with large accessible surface area and efficient ion transport pathways outperform the GNS electrode additive. The NHGNSs, owing to the dual benefits of the holey structure and high electronic conductivity, is the best additive for the AC electrode. The NHGNSs improve electrode wettability toward electrolyte, enhance ion diffusion, and reduce interfacial contact resistance, thereby promoting rate capability of the AC cell. In addition, the effects of electrode additives on reliability of AC cells are investigated for the first time. The NHGNSs effectively suppress the leakage current and electrode gassing under operation. An effective strategy to improve charge-discharge performance, cyclability, and reliability of electric double-layer supercapacitors is proposed.