Effect of a bromine complex agent on electrochemical performances of zinc electrodeposition and electrodissolution in Zinc–Bromide flow battery

To stabilize bromine during charging in zinc-bromide flow batteries, bromine-complexing agent is typically used as a supporting material in electrolyte. This paper describes the influences of the bromine-complexing agent on the electrochemical performances of the zinc deposition and dissolution process during charge and discharge. The surface morphologies before and after the zinc electrodissolution process are compared when using 1-Ethyl-1-methyl-pyrrolidinium bromide as a bromine-complexing agent in electrolyte, and the several measurements including surface chemical analysis are also performed in conjunction with the charge–discharge cell tests. Experimental results show that employing 1-Ethyl-1-methyl-pyrrolidinium bromide in electrolyte, through the formation of an electrostatic shield of 1-Ethyl-1-methyl-pyrrolidinium cations in-and-around the zinc dendrite during charging, provides powerful and effective effects yielding the uniformly flat formation of zinc as well as the prevention of zinc-dendrite growth. It also appears that the diffusion of 1-Ethyl-1-methyl-pyrrolidinium bromide on electrodeposited zinc produces not only two type morphologies of a melting-slurry agglomerate and a furrow ripple but also the change of chemical elemental composition, resulting in higher redox reaction reversibility and activity. Consequently, these results indicate that the propagation of zinc dendrite is mostly controlled by the diffusion rate of the 1-Ethyl-1-methyl-pyrrolidinium species on the zinc metallic surface.