Research On Magnesium Trifluoromethanesulfonate And Magnesium Bis (Diisopropyl) Amide-Based Electrolytes For Rechargeable Magnesium-Sulfur Battery

Magnesium metal anode has received extensive attention due to the high theoretical specific capacity,low redox potential,large abundance and low cost.Compared with lithium metal anode,it reveals no dendrite growth during discharge-charge cycles and thus maintains superior safety.However,coupled with high-specific-capacity sulfur cathodes,the conventional nucleophilic APC（0.4 M（Ph MgCl）₂-AlCl₃/THF）electrolyte is inclined to attack the electrophilic sulfur,resulting in poor electrochemical performance.To handle this issue,three novel non-nucleophilic or weakly nucleophilic electrolytes,which exhibit excellent Mg deposition-dissolution performance and prominent compatibility with sulfur-based cathodes,have been developed and applied to high-energy-density magnesium-sulfur batteries,.The specific research contents are as follows:（1）Magnesium trifluoromethanesulfonate（Mg（CF₃SO₃）₂）is a non-nucleophilic magnesium salt with low price,low moisture content and reveals easily soluble in ether solvents.We developed a novel electrolyte consisting of a mixture of Mg（CF₃SO₃）₂-AlCl₃.Moreover,MgCl₂ was adopted to accelerate the chemical reaction of electrolyte components while anthracene（ANT）was introduced as a ligand to stabilize Mg²⁺.The optimized electrolyte shows lower deposition-dissolution overpotential（0.1 V）,high coulombic efficiency（98.5%）,benign anode stability（3.25 V on platinum;2.5 V on stainless steel;2.0 V on copper and 1.85 V on aluminum,respectively）as well as moderate ionic conductivity(1.88 m S cm^-1).Fourier transform infrared spectrometer（FTIR）further explored the mechanism of each component in the electrolyte.Coupled with S@MC cathode,the Mg-S battery delivers excellent cycling performance.（2）Referring to the reported（HMDS）₂Mg-AlCl₃ electrolyte,we firstly proposed a magnesium bisamide compound magnesium bis（diisopropylamide）（denoted as MBA）and prepared a new electrolyte containning MBA-AlCl₃.The effects of different salt ratios and solvent variety were compared on the overpotential,cycling stability of Mg deposition-dissolution,and anode stability via abundant electrochemical characterization.The structure of the active species was confirmed via crystal X-ray diffraction（XRD）.In addition,compared with the traditional APC electrolyte,the electrolyte with lithium salt additives exhibits improved electrochemical performance,where the role of lithium salt was illuminated via X-ray photoelectron spectroscopy（XPS）.（3）The reverse Schlenk equilibrium mechanism leads to the reaction between the covalent magnesium compound（HMDS）₂Mg and the ionic-bond magnesium salt MgCl₂.The resulting electrolyte reveals nonflammable and no Lewis acids whereas still retains the merits of organic halogenated magnesium.Similarly,we developed a novel electrolyte based on MBA-MgCl₂ and applied it to Mg-S batteries.The structure of the active species in the electrolyte was confirmed via nuclear magnetic resonance（NMR）and density functional theory（DFT）.Designed MBA-2MgCl₂/THF electrolyte shows good compatibility with Mo₆S₈cathode.The addition of AlCl₃ could further broaden the electrochemical window to match sulfur cathode to construcct a high-energy density Mg-S battery.