Abstract: Alkaline zinc–iron flow batteries (AZIFBs), known for their low cost, intrinsic safety, and high theoretical energy density, have emerged as promising candidates for large-scale energy storage applications. However, the non-ideal deposition behavior of zincate ions (Zn(OH)₄^2–) limits long-term cycling stability of AZIFBs. During repeated charge–discharge processes, zincate ions undergo uneven nucleation and growth on the electrode surface, which promotes the formation of zinc dendrites as well as electrically isolated “dead zinc.” These parasitic phenomena not only accelerate performance degradation but can also cause internal short circuits or permanent loss of active material, thereby significantly shortening the service life of the battery. Developing effective strategies to stabilize zinc deposition while preserving the system chemistry remains a critical research priority. To address these challenges, this study introduces 2-methylimidazole (2-Mel) as a functional electrolyte additive designed to regulate zinc electrodeposition at the molecular level and enhance the overall electrochemical performance of AZIFBs. The mechanism of action of 2-Mel is attributed to its ability to coordinate with zincate ions through its imidazole nitrogen sites. This coordination results in a more homogeneous distribution of zinc species near the electrode interface, promoting uniform nucleation and controlled crystal growth. Additionally, 2-Mel forms a stable adsorption layer on the electrode surface, which mitigates the localized current densities and suppresses the protrusive growth patterns that typically lead to dendrite formation. Morphological and crystallographic characterizations, including scanning electron microscopy (SEM) and X-ray diffraction (XRD), confirm that the presence of 2-Mel significantly alters the preferred zinc growth orientation. Although zinc predominantly grows along the (101) plane in additive-free electrolytes, fostering vertical and dendritic structures, its growth shifts to the (002) plane in the presence of 2-Mel, resulting in a planar, densely packed morphology that adheres more uniformly to the substrate. Electrochemical analyses further reveal that 2-Mel exerts only a minor influence on the intrinsic deposition kinetics of the zincate ions, indicating that the additive leaves the fundamental redox processes of the battery essentially unaffected. However, it substantially reduces the mass-transport resistance and suppresses the corrosion current, thereby improving the reaction reversibility and stabilizing the interfacial behavior at the zinc anode. Such improvements are vital for enabling long-duration operation in practical flow battery systems. These enhancements contribute to improved Coulombic efficiency, reduced side reactions, and greater long-term operational reliability. Under optimized conditions, the AZIFB containing 2-Mel achieves over 1050 stable charge–discharge cycles at a current density of 80 mA·cm^–2, far surpassing the durability of the baseline system. The battery also demonstrates excellent thermal adaptability across a wide temperature range (25–55 ℃), highlighting the robustness of the additive under practical operating conditions. Furthermore, the modified system delivers an impressive peak power density of 1133.7 mW·cm^–2 at 80% state of charge, reflecting improved electrochemical kinetics and reduced polarization. Overall, these findings demonstrate that 2-Mel is a highly effective electrolyte additive capable of simultaneously regulating zinc deposition, mitigating failure mechanisms, and concurrently enhancing performance and durability. This study provides a promising strategy for the practical deployment of high-performance alkaline zinc-based flow batteries.