Compositional and structural heterogeneity of solid-electrolyte interphase (SEI) layer arising from multitude of interfacial constituents and external stimuli is a major challenge in analyzing electrochemical interfaces. For example, the anode surface is typically filled with native oxide, hydroxide and carbonate layers with varying composition and thickness due to its high reactivity with environment. As the multitude of solvates (i.e. ionic solvation structures) from electrolyte interact with chemically inhomogeneous anode surface, the heterogeneity in SEI layer is inevitable. The challenge is to delineate each electrolyte constituent interactions with specific anode surface chemistry under realistic electrochemical conditions. Our team recently developed a unique ion soft-landing capability that can isolate ions (either solvated or bare) from liquid electrolyte based on their charge-to-mass ratio and selectively soft-land these ions (with kinetic energies of 1-100 eV) on metal electrode with tunable surface chemistry. This unique capability is equipped with in situ vibrational and X-ray photoelectron spectroscopy measurements, providing an unprecedented ability to isolate and analyze electrode-electrolyte interactions. We isolated Mg²⁺ ions with variant solvate structure and composition (e.g. varying number of counter anions as part of primary solvation sheath) and soft-landed on Mg metal electrodes with selected surface chemistry. The spectroscopic signatures of transient and decomposed products were analyzed in combination with first principle based calculations. This presentation will discuss the reaction pathways and products of interfacial reaction between selective Mg²⁺ based electrolyte components and Mg metal electrodes under variable temperature conditions.