Elucidating the mechanism of discharge performance improvement in zinc-air flow batteries : a combination of experimental and modeling investigations

Abstract

The zinc-air flow battery demonstrates a bright prospect as the next-generation large-scale energy storage devices. Compared with conventional static zinc-air batteries, the electrochemical performance can be significantly improved, whereas the intrinsic mechanism is still unclear. Herein, the mechanism of the discharge performance improvement from the flowing electrolyte is systematically investigated by combining experimental and modeling methods. The experimental results demonstrate that the flowing electrolyte has an apparent effect on the discharge polarization performance, especially on the concentration polarization region. Compared with the static condition, the peak power density is improved by ~10% to 136 mW cm−2 at a flow rate of 5 mL min−1. Further numerical calculations reveal that this enhancement mainly comes from the transfer enhancement of hydroxide ions caused by the flowing electrolyte. Besides, the specific discharge capacity is improved from 623 to 767 mAh gZn−1 due to the alleviation of zinc oxide passivation in the presence of flowing electrolyte. Therefore, the performance improvement in zinc-air flow batteries is attributed to the enhanced transport of hydroxide and zincate ions rather than oxygen. The revealed mechanism can serve as the basis to design proper flow field and battery structure, and promote zinc-air flow batteries toward practical applications.