Fabrication And Electrochemical Properties Of Functionalized Ionic Liquid-Based Non-Nucleophilic Mg Electrolytes

Rechargeable magnesium battery with metal magnesium as anode is widely regarded as the most potential new energy battery technology in the post-lithium-ion battery technologies because of its high theoretical specific capacity,rich resources,environment-benign and difficult formation of magnesium dendrites in the process of magnesium deposition and dissolution.However,the magnesium electrolyte based on commercial simple magnesium salt can easily react with active magnesium metal to form a dense non conducting magnesium passivation film,so it cannot be used as the electrolyte of magnesium secondary battery.Therefore,the search for new magnesium electrolyte materials is the key to the development of rechargeable magnesium battery technology.Among them,mononuclear magnesium cationic non-nucleophilic magnesium electrolyte salt is considered to be an ideal salt for the development of high-performance magnesium electrolyte because of its reversible deposition and dissolved magnesium ability,relatively wide electrochemical window and non-nucleophilic properties.In this paper,new magnesium electrolytes based on mononuclear magnesium cationic non-nucleophilic magnesium electrolyte salt Mg[AlCl₄]₂were obtained by Lewis acid-base reaction of magnesium chloride and aluminum chloride,and their electrochemical properties were studied.（1）Mononuclear magnesium cationic non-nucleophilic magnesium electrolyte salt Mg[AlCl₄]₂was synthesized by Lewis acid-base reaction of anhydrous magnesium chloride and anhydrous aluminum chloride in the molar ratio of 1:2 with1-Butyl-1-methylpyrrolidinium bis（trifluoromethylsulfonyl）-imide（PYR14TFSI）as solvent.A new conditioning-free non-nucleophilic magnesium electrolyte Mg（AlCl₄）₂-PYR14TFSI-DG/Li I was obtained through further solvent optimization and electrolyte additive optimization.The electrochemical experimental results show that the electrolyte with Li I additive can significantly reduce the overpotential of Mg deposition/dissolution and realize the reversible deposition and dissolution of magnesium in the first cycle.The mechanism study shows that using Li I as electrolyte additive not only is favorable to the dissolution of magnesium chloride,which is insoluble on the surface of magnesium,but also helps to form a Mg I₂-rich magnesium conductive layer on the surface of magnesium anode,so as to effectively activate the metal magnesium/electrolyte interface and promote the Mg deposition and dissolution.Using the conditioning-freenon-nucleophilicmagnesiumelectrolyteof Mg（AlCl₄）₂-PYR14TFSI-DG/Li I,a rechargeable Mg battery coupled with V₂O₅-PANi cathode and Mg anode delivers a stable discharge specific capacity of nearly 50 m A h·g^-1after an impressively prolonged cycle life of 500 cycles at a current density of 60 m A·g^-1.（2）PYR14TFSI,nitrogenfunctionalionicliquidsof1-（3-dibutylaminopropyl）-3-methylpyridiumbis（trifluoromethylsulfonyl）-imide（NMEITFSI）and1-（3-dibutylaminopropyl）-1-methylpyrrolidiumbis（trifluoromethylsulfonyl）-imide（NPYR14TFSI）,oxygen functional ionic liquid of N,N-diethyl-N-methyl-N-（2-methoxyethyl）ammonium bis（trifluoromethylsulfonyl）-imide（OMEITFSI）were used as solvents,through the Lewis acid-base reaction of anhydrous magnesium chloride and anhydrous aluminum chloride in the molar ratio of 1:2,four ionic liquidelectrolytesofMg[AlC1₄]₂-PYR14TFSI,Mg[AlC1₄]₂-NMEITFSI,Mg[AlC1₄]₂-NPYR14TFSI and Mg[AlC1₄]₂-OMEITFSI based on mononuclear magnesium cationic non-nucleophilic magnesium electrolyte salt Mg[AlC1₄]₂were synthesized.The further results show that the ionic liquid electrolyte of Mg[AlC1₄]₂-PYR14TFSI cannot reversibly deposit and dissolve Mg without organic cosolvent,while reversible deposition and dissolution of magnesium of the magnesium electrolytes of Mg[AlC1₄]₂-NMEITFSI and Mg[AlC1₄]₂-NPYR14TFSI can be achieved at room temperature.The new non-nucleophilic magnesium electrolyte Mg[AlC1₄]₂-OMEITFSI-DME/THF based on OMEITFSI developed through solvent optimization shows better performance than Mg[AlC1₄]₂-PYR14TFSI-DME/THF.The overpotential of Mg-Mg symmetrical battery can be maintained below 300 m V at 5m A·cm^-2current density.These results preliminarily demonstrate the application potential of functionalized ionic liquids in magnesium electrolyte.