Solvent-Anion Counterpoised Electrolyte Enables High-Rate Magnesium Metal Batteries

Magnesium batteries are compelling post-lithium energy storage candidates but suffer from sluggish charge transfer kinetics, fundamentally restricted by the high energy barrier of Mg²⁺ desolvation. Herein, we address the compact and tenacious solvation sheath induced by the high charge density of Mg²⁺, characterized by strong electrostatic binding. To effectively weaken the coordination strength and lower the desolvation barrier, we utilize machine learning to identify electrolytes that energetically balance Mg²⁺-solvent and Mg²⁺-anion interactions. This counterpoise state leads to a comprehensive weakening of the solvation shell. As corroborated by in situ Raman spectroscopy, this environment facilitates a synchronous desolvation pathway and induces a robust MgH₂-based solid-electrolyte interphase, fundamentally accelerating interfacial kinetics. The screened amine-based electrolyte empowers low-overpotential Mg²⁺ reduction of 0.06 V at 1 mA cm^-2, and full cells with high-rate performance sustain 50 C cycling, and a Mg/fluorinated carbon cell delivers 918 mAh g^-1 at 0.5 C. This paradigm shifts the design focus from individual solvation to collective energy equilibration in multivalent electrolytes.