Effect of Heteroatoms Doped Nanoporous Carbon for Aqueous Zinc–Bromine Battery

Abstract

As interest in renewable energy increases, the importance of batteries that store surplus power is also increasing. However, frequent ignition issues with the lithium-ion secondary battery arose. One of the next-generation batteries, Zinc-Bromine based aqueous flow batteries, are being actively studied based on advantages of high safety and environmental benignity. However, there is an exorbitant price for flow battery due to the use of a membrane, an electrolyte tank, and a pump. In order to eliminate the shortcomings, this research introduced a form of membraneless and flowless systems. In this study, a nanoporous carbon material doped with nitrogen and boron heteroatoms was synthesized and coated on graphite felt. Differences in electrochemical performance were observed when carbon was coated with different slurry compositions (activated carbon: conductive carbon: binder), dopant amount of heteroatoms, and carbon loading mass. Cyclic voltammetry was performed with a three-electrode system to observe the faradaic reaction of active materials according to the potential change. Besides the difference in contact angle for ZnBr 2 electrolyte, there are differences in single cell test at 20 mA/cm 2 & 2 mAh/cm 2 and performance test at 20 mA/cm 2 & 24.3 mAh/cm 2 . These causes can be explained not only by the effect of the different slurry compositions, but also by the interaction of the active material with the coated carbon. Also, the redox reactions of bromine anion during charging process could be a clue for the battery capacity. Cathodic reactions for polybromide [Br 2 + Br n – → Br n+2 – , (n=1,3,5...)] can be analyzed by Raman spectroscopy. The peak shift and deconvolution of the Raman data can measure the progress of cathodic reactions. The boron dopants can stabilize the reversibility of faradaic reactions and induce high resistance to strong acid electrolytes (For ZnBr 2 electrolyte of 2.0 M or higher, it has a value under the pH 4). Figure 1