The increased use of electronic devices and electric vehicles over the past decade has led to the development of advanced lithium-ion batteries. However, the intercalation electrode materials used in lithium-ion batteries have inherently low theoretical capacities. The use of metallic anodes provides a pathway to increased energy density. Metallic electrodes suffer from instabilities at the electrode-electrolyte interface, including unstable SEI formation, low coulombic efficiencies, and dendritic growth. This work studies the use of thin film ionomers as a protection layer between the electrolyte and the anode for lithium metal and magnesium metal batteries. The ionomer in use is a crosslinked polymer network with covalently bound anions that is coated onto a traditional microporous separator. We quantify the impact of the ionomer on cation transference number and on coulombic efficiency, overpotential, and cell lifetime while galvanostatic cycling. Post-mortem analysis is completed to evaluate dendrite formation and electrolyte decomposition. We find that the thin ionomeric coatings can influence the metal deposit morphology and that the composition of the coating influences the effectiveness as a protection layer.