Study Of Electrolyte Solutions For Rechargeable Magnesium Battery

Rechargeable magnesium battery is a new promising battery systemdeveloped in recent years. It possesses advantages of low cost, high safety,high energy density and environment-amity. The development ofrechargeable magnesium battery is still in its early stage, which is mainlyconstrained by the electrolyte and cathode material. Similar to lithium,magnesium is covered by surface films in most of the relevant electrolytesolutions for batteries. However, in contrast to lithium where the surfacefilms covering the active metal are Li+conductors, surface films formedon magnesium can not conduct Mg2+. A reversible process ofdeposition-dissolution magnesium can not be achieved. In order to makebreakthrough in rechargeable magnesium battery, we should develop thesuitable electrolyte systems.In this paper, we systematically studied the electrochemicalperformance of （PhMgCl）₂-AlCl₃/mixed ether electrolytes and newphenolate-based magnesium ion conducting electrolytes for rechargeablemagnesium battery. The main research contents are as follows:（1）（PhMgCl）₂-AlCl₃was prepared and the electrochemicalperformance of its electrolytes containing co-solvents of DME+THF,Diglyme （DG）+THF and Tetraglyme （TG）+THF with different proportionswas studied. Compared with （PhMgCl）₂-AlCl₃/THF,（PhMgCl）₂-AlCl₃/DG+THF（3:2） still has high ionic conductivity (1.605mS·cm^-1), reversibleMg deposition behavior and acceptable anodic anti-oxidation performance （electrochemical window wider than2.8V）. A big advantage of DG+THFco-solvent is its low saturation vapor pressure （reduced from23.46kPa to9.41kPa）, which suppresses volatilization of the electrolyte and improvesthe battery safety on the whole. On the other hand, for potential currentcollectors, it is found that Pt offers the best electrochemical performanceand Al the worst of Pt、Ni、Cu and Al.（2）A new magnesium ion conducting electrolyte was prepared usinga simple reaction between AlCl₃and2-tert-butyl-4-methylphenolatemagnesium chloride （BMPMC）. The solution was characterized in term ofreversibility of magnesium deposition and dissolution，air stability andcompatibility with cathode material. The electrolyte solution shows highionic conductivity (2.56mS·cm^-1), good anodic stability （2.6V vs.Mg RE）,high reversibility of Mg deposition-dissolution and excellent air stability.Furthermore, the coin cell was constructed using the0.5M（BMPMC）₂–AlCl₃/THF solution as the electrolyte, a Mg disc as a negativeelectrode, and Mo₆S₈as a positive electrode. The discharge capacity wasca.100mAh·g^-1at room temperature and120mAh·g^-1at65℃, close tothe theoretic value of Mo₆S₈material. Moreover, the rechargeability of thecell is better at elevated temperature. This electrolyte system makes ithighly promising for opening up a new approach to other highenergy-density rechargeable Mg battery systems （e.g. Mg/air battery）.