A non-nucleophilic electrolyte based on all-inorganic salts with conditioning-free characteristic for rechargeable magnesium batteries

Conditioning-free electrolytes with high reversibility of Mg plating/stripping are of vital importance for the commercialization of the superior rechargeable magnesium batteries (RMBs). In the present work, a non-nucleophilic electrolyte (denoted as MLCH) based on all-inorganic salts of MgCl₂, LiCl and CrCl₃ for RMBs is prepared by a straightforward one-step reaction. As a result, the MLCH electrolyte shows the noticeable performance of high ionic conductivity (3.40 mS cm⁻¹), low overpotential (∼46 mV vs Mg/Mg²⁺), high Coulombic efficiency (∼93%), high anodic stability (SS, ∼2.56 V vs Mg/Mg²⁺) and long-term (more than 500 h) cycling stability, especially the conditioning-free characteristic. The main equilibrium species in the MLCH electrolyte are confirmed to be the tetracoordinated anions of [LiCl₂(THF)₂]⁻ and solvated dimers of [Mg₂(µ-Cl)₃(THF)₆]⁺. The addition of LiCl can assist the dissolution of MgCl₂ and activation of the electrode/electrolyte interface, resulting in a superior Mg plating/stripping efficiency. The synergistic effect of LiCl, CrCl₃, a small amount of HpMS and the absence of polymerization THF enable the conditioning-free characteristic of the MLCH electrolyte. Moreover, the MLCH electrolyte exhibits decent compatibility with the cathodic materials of CuS. The Mg/CuS full cell using the MLCH electrolyte presents a discharge specific capacity of 215 mAh g⁻¹ at 0.1 C and the capacity can retain ∼72% after 40 cycles. Notably, the MLCH electrolyte has other superiorities such as the broad sources of materials, low-cost and easy-preparation, leading to the potential prospect of commercial application.