Dual-Function Electrolyte Additive Design for Long Life Alkaline Zinc Flow Batteries.

Alkaline zinc-based flow batteries (AZFBs) have emerged as a promising electrochemical energy storage technology owing to Zn abundance, high safety, and low cost. However, zinc dendrite growth and the formation of dead zinc greatly impede the development of AZFBs. Herein, we propose a dual-function electrolyte additive strategy to regulate zinc nucleation and mitigate the hydroxide corrosion of zinc depositions for stable AZFBs. This strategy, as exemplified by urea, introduces an electrolyte additive to coordinate with Zn 2+ /Zn with proper strength, slowing zinc deposition kinetics to induce uniform nucleation and protecting the deposited zinc surface from attack by hydroxide ions through preferable adsorption. The zincate complexes with urea were identified to be Zn(OH) 2 (urea)(H 2 O) 2 and Zn 2 (OH) 4 (H 2 O) 4 (urea), which exhibit slow zinc deposition kinetics, allowing instantaneous nucleation. Our results reveal an additional energy barrier of 1.29 eV for the subsequent adsorption of an OH - group when a urea molecule absorbs on the zinc cluster, significantly mitigating the formation of dead zinc. Consequently, prolonged cell cycling of the prototype alkaline zinc-iron flow battery demonstrates stable operation for over 130 hours and an average coulombic efficiency of 98.5%. We anticipate that this electrolyte additive strategy will pave the way for developing highly stable AZFBs. This article is protected by copyright. All rights reserved.