Tailoring Mg²⁺ Solvation Structure in a Facile All‐Inorganic [Mg_xLi_yCl_2x+y·<i>n</i>THF] Complex Electrolyte for High Rate and Long Cycle‐Life Mg Battery

Abstract

A high‐performance all‐inorganic magnesium–lithium chloride complex (MLCC) electrolyte is synthesized by a simple room‐temperature reaction of LiCl with MgCl 2 in tetrahydrofuran (THF) solvent. Molecular dynamics simulation, density functional theory calculation, Raman spectroscopy, and nuclear magnetic resonance spectroscopy reveal that the formation of [Mg x Li y Cl 2x+y · n THF] complex solvation structure significantly lowers the coordination number of THF in the first solvation sheath of Mg 2+ , which significantly enhances its de‐solvation kinetics. The MLCC electrolyte presents a stable electrochemical window up to 3.1 V (vs Mg/Mg 2+ ) 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/Mo 6 S 8 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.