Strategies for pH regulation in aqueous zinc ion batteries

Aqueous zinc ions batteries (AZIBs) using non-organic electrolytes have garnered sustained interest as a future energy storage technology, primarily due to their low cost, environmental friendliness, and intrinsic safety. However, zinc ion batteries suffer from a series of serious challenges, including hydrogen evolution reaction (HER) at the anode, surface passivation, dendrite formation, as well as limited operating voltage and comparatively low energy density. These factors are all influenced by the concentration of H+ in the electrolyte (i.e., the pH), and its fluctuations during the cycle process. To date, there remains a lack of systematic evaluation of the correlation between the pH value of electrolyte and the challenges faced by AZIBs, or a focused review of how pH influences the electrochemical performance of AZIBs and strategies that can be used to improve cell efficiency. In this review we emphasize the strong correlation between electrolyte pH and AZIBs challenges and detail the research progress made in recent years relating to electrolyte additives, separator modification, interfacial protective layers, and battery system design, with a particular focus on the regulatory mechanisms associated with pH control. On this basis, we propose important future research focuses and suggestions for the onward development of AZIBs.