Tailoring Mg2+ Solvation Structure in a Facile All‐Inorganic [MgxLiyCl2x+y·nTHF] Complex Electrolyte for High Rate and Long Cycle‐Life Mg Battery

A high‐performance all‐inorganic magnesium–lithium chloride complex (MLCC) electrolyte is synthesized by a simple room‐temperature reaction of LiCl with MgCl2 in tetrahydrofuran (THF) solvent. Molecular dynamics simulation, density functional theory calculation, Raman spectroscopy, and nuclear magnetic resonance spectroscopy reveal that the formation of [MgxLiyCl2x+y·nTHF] complex solvation structure significantly lowers the coordination number of THF in the first solvation sheath of Mg2+, which significantly enhances its de‐solvation kinetics. The MLCC electrolyte presents a stable electrochemical window up to 3.1 V (vs Mg/Mg2+) and enables reversible cycling of Mg metal deposition/stripping with an outstanding Coulombic efficiency up to 99% at current densities as high as 10 mA cm−2. Utilizing the MLCC electrolyte, a Mg/Mo6S8 full cell can be cycled for over 10 000 cycles with a superior capacity retention of 85 mA h g−1 under an ultrahigh rate of 50 C (1 C = 128.8 mA g−1). The facile synthesis of high‐performance MLCC electrolyte provides a promising solution for future practical magnesium batteries. An all‐inorganic magnesium–lithium chloride complex (MLCC) electrolyte, with a unique solvation structure and fast surficial redox kinetics, was synthesized using a simple reaction of MgCl2 and LiCl salts in THF solvent at room temperature. The Mg/Mo6S8 full cells using the MLCC electrolyte achieved a superior capacity retention of 85 mA h g−1 after 10 000 cycles at an ultrahigh rate of 50 C.