Tailoring Loose Mg ²⁺ Solvation Structure by Steric and Competitive Solvent Coordination for Fast‐Charging Magnesium Batteries

Magnesium batteries are attracting growing interest as next‐generation energy storage technology due to their high safety, cost‐effectiveness, and resource abundance. However, their development remains limited by sluggish Mg 2+ transport kinetics at the electrode/electrolyte interface. Herein, we propose an electrolyte design strategy that modulates the Mg 2+ solvation structure by introducing tetrahydrofuran (THF) as a co‐solvent into a borate‐based electrolyte, Mg[B(hfip) 4 ] (MBF) in dimethoxyethane (DME). THF, selected from a series of linear and cyclic ethers, has a comparable dielectric constant and donor number to DME, but its cyclic structure introduces steric hindrance that induces competitive coordination with Mg 2+ . This competition weakens Mg 2+ − solvent interactions, yielding a more labile solvation structure and enhanced desolvation kinetics. As a result, Mg||Mg cells employing the optimized MBF/1D1T electrolyte (DME: THF = 1:1, v:v) exhibit a significantly reduced Mg plating/stripping overpotential of 120 mV at 10 mA cm −2 , compared with 316 mV at 8 mA cm −2 with MBF/DME, along with exceptional cycling stability exceeding 1200 h. Furthermore, representative sulfide cathodes such as CuS and VS 4 demonstrate faster activation and improved high‐rate performance in the presence of MBF/1D1T.