Passivation Layers in Mg‐Metal Batteries: Robust Interphases for Li‐Metal Batteries

Abstract In advanced batteries, interphases serve as the key component in stabilizing the electrolyte with reactive electrode materials far beyond thermodynamic equilibria. While an active interphase facilitates the transport of working ions, an inactive interphase obstructs ion flow, constituting the primary barrier to the realization of battery chemistries. Here, a successful transformation of a traditionally inactive passivating layer on Mg‐metal anode, characteristic of Mg‐metal batteries with typical carbonate electrolytes, into an active and robust interphase in the Li‐metal scenario is presented. By further strategically designing magnesiated Li⁺ electrolytes, the in situ development of this resilient interphase on Li‐metal anodes, imparting enduring stability to Li‐metal batteries with nickel‐rich cathodes is induced. It is identified that the strong affinity between Mg²⁺ and anions in magnesiated Li⁺ electrolytes assembles ionic clusters with a bias for reducibility, thereby catalyzing the creation of anion‐derived interphases rich in inorganic constituents. The prevalence of ionic clusters induced by magnesiation of electrolytes has brought properties only available in high‐concentration electrolytes, suggesting a fresh paradigm of tailing electrolytes for highly reversible LMBs.