Development of safe, rechargeable, and high energy density batteries is crucial for transitioning from fossil fuels to renewable energy resources which are available intermittently. Zinc metal batteries are a promising candidate for this owing to their low cost, high theoretical energy density and environmental friendliness. However, one of the major challenges to their development is unstable metal deposition which leads to formation of ramified, low-density, fragile structures called dendrites. During cell charging, these dendrites can cause rapid loss of storage capacity by breaking away from the electrode mass to form electrically disconnected or “dead” metal. Over time, they can also grow through the separators causing an internal short circuit, leading to poor reversibility and premature failure of the metal anodes. To overcome these challenges, polymers have been widely used as electrolyte additives in batteries to stabilize electrodeposition. In this work, we look at the effects of polymers in two scenarios - a fundamental study of hydrodynamic instability, and secondly in a more application-oriented study on zinc iodide systems.In the first part, we investigate the effect of salt concentration and polymer additive on electroconvection which is a hydrodynamic instability occurring at high voltages. We perform electrochemical measurements and direct flow visualization, which reveals that electroconvection is delayed and suppressed at all voltages in the presence of oligomers. Our experiments also indicate the importance of considering the interfacial effects of PEG adsorption in addition to the bulk effects of oligomer additives. To corroborate our experimental results, we also present a perturbation analysis study, which reveals that the underlying stability mechanism involves the formation of an oligomer layer at the interface, which in response to perturbation is believed to exert an opposing body force on the surrounding fluid to preserve the layer structure and in so doing suppresses electroconvection. In the second part, we use these oligomers to improve the cycling performance of aqueous zinc metal batteries. Although numerous past studies have talk about the effectiveness of polymeric additives, few go into detail about the design principles for choosing a particular polymer, its Mw or its concentration in the electrolyte. To fill this knowledge gap, in this work we systematically vary the Mw and concentration of linear PEG additives to optimize these parameters for extending the cycle life of Zinc iodide batteries. Our experiments reveal that when varying additive concentration, some polymer helps in improving the cycle life of the Zn anode but too much polymer additive in the electrolyte has the undesirable effect of increasing interfacial resistance which ultimately leads to a cell failure. Furthermore, when varying additive Mw, we find that the cycling performance initially increased with Mw, however, for PEG Mw > 1000 Da, the effect saturates and a further increase in PEG Mw produces negligible improvements in Zn anode lifetime. This saturation transition is also mirrored in the surface morphology and crystal orientation of the freshly electrodeposited zinc as observed by SEM and XRD respectively. To corroborate our experimental results, we also present a theoretical model which attributes this transition to a possible saturation in the thickness of the PEG layer at the interface with increasing Mw. Lastly, to assess the practical applicability of our findings, we demonstrate the effectiveness of the optimized additive (Mw = 1000 Da and concentration = 5wt%) in long duration, fast charging pouch cells.