Study On The Exploration And Performance Of Electrolytes For Rechargeable Magnesium Battery

Rechargeable magnesium（Mg）batteries have attracted much attention due to high theoretical volumetric capacity（3832 mAh cm^-33 for Mg vs.2062 mAh cm^-33 for Li）,improved safety（dendrite-free Mg deposition）,and low cost（the fifth most abundant element in the earth crust）.However,the research of high performance Mg batteries faces two challenges:the lack of high energy density cathodes and high voltage Mg-compatible electrolytes.In view of above problems,we develop boron-based Mg electrolyte with wide electrochemical window,high ionic conductivity and non-nucleophilic characteristic.Mg-S batteries was conducted using aforementioned boron-based Mg electrolytes.In addition,Mg-Cu₂Se battery have also been assembled and tested.The specific research contents are as follows:（1）Thenovelboron-basedelectrolyteissynthesizedfrom tris（2H-hexafluoroisopropyl）borate（THFPB）and MgO in 1,2-dimethoxyethane（DME）,which presents high reversibility for Mg plating/stripping,high anodic stability（up to 4.2 V vs.Mg）,non-corrosivity to stainless steel.In addition,by virtue of the non-nucleophilic characteristic,the electrolyte has good compatibility with conversion materials sulfur.The Mg-S batteries show a high stable discharge capacity of 1030 m Ah g^–1for 15 cycles and one well-defined voltage plateau of≈1.1 V vs.Mg,yielding a desirable energy density beyond 1100 Wh kg^–1.The active species[B（OCH₂（CF₃）₂）₄]^–were identified through NMR and MS.Wide electrochemical window and non-nucleophilic characteristic are significant to realize high-voltage and high-capacity Mg batteries.（2）The highly concentrated double boron complex electrolyte is simply prepared by dissolving Mg（BH₄）and THFPB in diglyme（DGM）solvent,which exhibits high ionic conductivity(3.72 mS cm^-1at 25°C),high coulombic efficiency（99%）,and superior oxidation stability（>2.8 V vs.Mg on stainless steel（SS））.The improved Mg plating/stripping performance seems to be partly due to the improved solubility of Mg（BH₄）.Raman spectra was used to characterize the effects of THFPB on the dissociation of Mg（BH₄）₂ by study of free states of borohydride.Mg-Mo₆S₈ cells employing the as-prepared electrolyte show excellent cycle life and impressive rate capability.It is surprising that the double boron complex electrolyte is successfully cycled as the electrolyte in a Mg-S coin cell,which delivers high specific capacity.（3）Coin cells were assembled using Mg disk anodes,Cu₂Se cathode,and above-mentioned electrolyte from the first part.The electrochemical reaction Cu₂Se+Mg²⁺+2e^-=MgSe+2Cu was inferred from the results of SEM,TEM and XRD.