Understanding the Role of Zinc Hydroxide Sulfate and its Analogues in Mildly Acidic Aqueous Zinc Batteries: A Review

Abstract

Mildly acidic aqueous zinc batteries (AZBs) have attracted tremendous attention for grid storage applications with the expectation to tackle the issues of Li‐ion batteries on high cost and poor safety. However, the performance, particularly energy density and cycle stability of AZBs are still unsatisfactory when compared with LIBs. To help the development of AZBs, a lot of effort have been made to understand the battery reaction mechanisms and precedent microscopic and spectroscopic analyses have shown flake‐like large particles of zinc hydroxide sulfate (ZHS) and its analogues formed on the surfaces of cathodes and anodes in sulfate and other electrolyte systems during cycling. However, because of the complexity of the thermodynamics and kinetics of aqueous reactions to understand different battery conditions, controversies still exist. This article will review the roles of ZHS discussed in recent representative references aiming to shine light on the fundamental mechanisms of AZBs and pave ways to further improve the battery performance.

Activating iodine redox by enabling single-atom coordination to dormant nitrogen sites to realize durable zinc–iodine batteries

“…18–21 Additionally, the conversion reaction of iodine can facilitate a faster redox reaction than that of traditional metal-oxide-based cathodes and does not involve protons during the redox reaction, thereby maintaining the pH value in the vicinity of the cathode surface. 22,23 Nevertheless, similar to lithium–sulfur batteries, the intrinsic insulating properties of iodine and the formation of soluble polyiodide intermediates can lead to sluggish redox kinetics and shuttling, thereby having a detrimental effect on power density and durability. 24,25…”

Building a Rechargeable Voltaic Battery via Reversible Oxide Anion Insertion in Copper Electrodes

“…Along this line of thinking, if we can create a “locally alkaline” condition from a near-neutral solution, the pH demands of Cu and Zn should be satisfied simultaneously. We noticed that zinc sulfate hydroxide (Zn 4 SO 4 (OH) 6 ) precipitation is a common phenomenon in ZnSO 4 electrolytes, − which contains abundant hydroxide (OH – ) anions in its structure, thus pertaining to an alkaline substance. Therefore, we may take advantage of this precipitation to mitigate the Cu 2+ dissolution issue.…”