Temperature-dependent electrochemical dynamics in zinc-bromine flow batteries

Abstract

Zinc‑bromine flow batteries (ZBFBs) are a promising technology for large-scale energy storage, yet the influence of operating temperature on their electrochemical performance and long-term stability remains poorly understood. In this study, we present a systematic investigation of the temperature-dependent behavior of ZBFBs across a wide temperature range. Results show that elevating the operating temperature from 30 to 70 °C significantly improves voltage efficiency from 76.6% to 83.7% at 80 mA cm−2 due to reduced polarization. However, this gain is offset by a decline in coulombic efficiency, which decreases from 99.3% to 95.3% as a result of increased bromine crossover and side reactions. Notably, when operated at 50 °C, the ZBFB exhibits the best cycling stability exceeding 1000 cycles due to rapid polybromide/bromide reaction kinetics and uniform zinc deposition. In situ optical monitoring and ex situ characterizations reveal that below 50 °C, poor mixing of polybromide and localized zinc accumulation near the membrane side lead to shortened cycle life, while above 50 °C, weakened bromine complexation and coarser zinc morphologies accelerate self-discharge and capacity decay. This study provides a comprehensive and mechanistically grounded understanding of how temperature simultaneously influences reaction kinetics, oil-water two-phase flow behavior, zinc deposition and parasitic side reactions, thereby affecting the overall battery performance and offering critical insights for the design of thermally adaptive and long-life ZBFB systems for next-generation energy storage.