Internal Magnetic Fields for Improved Cyclability in Aqueous Zn-Br2 Static Batteries

Abstract

Owing to their high safety and low-cost, aqueous zince-bromine batteries (AZBBs) are envisioned as being highly applicable in both portable and stationary energy storage. The highly reversible Zn/Zn2+ (-0.76 V vs. RHE) and Br-/Br2 (1.08 V vs. RHE) redox couples have been employed in Zn-Br2 flow batteries (1.84 V vs. RHE), although widespread implementation has not been realized. This is largely because parasitic losses in overall battery performance rapidly occur due to i) dendritic growth of Zn deposits during the repetitive discharge process, leading to internal short circuits and ii) the cross-diffusion of highly soluble Br- (Br3 -) ions causing severe self-discharge and reduced cycle life. Common approaches to mitigate these problems include electrode engineering and incorporating additives and ion-selective membranes into the system for improving cycle life and coulombic efficiency. This talk will highlight the benefits of fabricating an aqueous Zn-Br2 static battery with internally contained magnetic fields, (~ 30, 40, 50 and 60 mT) at the anode and cathode by incorporating 1 mm thick Nd permanent magnets. Here we show that moderate internal magnetic fields are capable of simultaneously mitigating dendrite growth while drastically reducing cross-diffusion, leading to enhanced cycle life and improved energy and voltage efficiency. Operando UV-Vis spectroscopy, scanning electro microscopy (SEM), and electrochemical methods (electrochemical impedance spectroscopy and cyclic voltammetry) were used to to rationalize the effect of magnetic fields on the performance and cyclability of AZBBs.