Characterization and Identification of Precipitates Formed on the Cathode Surface in Static Zn-Br Battery

<b>Static zinc-bromine batteries (ZBBs) are a promising and low-cost grid electrochemical energy storage device for energy generation shifting to the use of renewable energy. The sacrifice of an externally forced flow source and membranes in the cell design lowers the battery manufacturing cost but leads to long-term cycling fading. Specifically, an unknown precipitation reaction at the cathode surface during charging forms a thin solid film raising the charge transfer resistance and lowering cycling efficiency and capacity. For the first time, the precipitate was characterized and identified as an insoluble polycrystalline zinc hydroxide bromide hydrate (ZHB) with a layered structure. By investigating the influence of different compositions and concentrations of electrolytes and charging conditions, we proposed that pH variation of electrolytes caused by electrolyte concentration polarization during charging are the immediate factors contributing to ZHB precipitates. In addition, in the long-term cycling, hydrogen and bromine loss also indirectly contributes to irreversible precipitation. In turn, optimization cycling protocols and control of pH are key to suppressing the formation of the precipitate. Overall, understanding and addressing long-term cycling fading is crucial for the advancement of rechargeable battery technologies, allowing for improved performance, extended cycle life, and enhanced reliability in grid energy storage systems.</b><br/>&lt;quillbot-extension-portal&gt;&lt;/quillbot-extension-portal&gt;