Extending Cycle Life of Mg/S Battery by Activation of Mg Anode/Electrolyte Interface through an LiCl‐Assisted MgCl 2 Solubilization Mechanism

Non‐nucleophilic electrolytes that can reversibly plate/strip Mg are essential for realizing high‐performance rechargeable Mg/S batteries. In contrast to organometallic electrolytes, all‐inorganic electrolytes based on MgCl 2 ‐AlCl 3 complexes are more cost‐effective and hold better stability to air and moisture. A recently developed electrolyte that contains tetrahydrofuran solvated divalent Mg cation, [Mg·6THF][AlCl 4 ] 2 , has exhibited decent compatibility with the sulfur cathode. However, it suffers a large overpotential and short cycle life, which hinders its applications in Mg/S batteries. Here, an efficient plating/stripping of Mg is realized successfully by using LiCl to dissolve MgCl 2 from the electrolyte/electrode interface. As a result, the overpotential of Mg plating/stripping is remarkably reduced to 140/140 mV at a current density of 500 µA cm −2 . Both experiments and density functional theory (DFT) calculations reveal that the LiCl‐assisted solubilization of MgCl 2 facilitates the exposure of fresh surface on the Mg anode. Utilizing such an LiCl‐activation strategy, Mg/S full batteries with a significantly extended cycle life of over 500 cycles, as well as coulombic efficiency close to 100%, are achieved successfully. This work demonstrates the role of LiCl‐assisted interface activation on extending the cycle‐life Mg/S batteries with all‐inorganic electrolytes.