The Study On The Transition Metal Sulfides Cu₂Mo₆S_8-nSe_n And CoS As Rechargeable Magnesium Batteries Cathode Materials

Due to the diagonal position in periodic table, the chemicalproperties of magnesium and lithium are similar. In comparison to lithium,magnesium has lower cost and higer safety. As the anode material forbatteries, Mg has a high theoretical specific capacity of2205mAh g-1,thus magnesium battery may be a candidate of high energy densitypowers for large load such as electric vehicles.The studies on rechargeable magnesium battery systems are stillunder early stage. The research is mainly focused on suitable cathodematerials for Mg2+intercalation and electrolyte in which Mg can bedeposited and dissolved. This paper systematically studies the phasestructures and electrochemical behaviors of the Chevrel phaseCu2Mo6S8-nSen(n=0,0.5,1.5) and sulfide CoS as the cathode materials forMg rechargeable batteries.The Chevrel Phase materials Cu2Mo6S8-nSen(n=0,0.5,1.5) weresynthesized by the molten salt method. Se-substituted Cu2Mo6S8-nSenkeptits Chevrel Phase, but the lattice parameters became larger. SEM imagesshowed that the Cu2Mo6S8-nSenparticle was well crystallized with smallsize. The studies of the electrochemical properties suggested that theshape of voltammetric peaks in the region0.5-0.8V changed. The steadyspecific capacity increased to103.5mAh/g and the cycling performancewere improved because of Se substitution in Cu2Mo6S8. All these resultsproved that the reversible intercalation of Mg ions into these hosts werefacilitated. The CoS microspheres composed of nanoflakes were synthesized bysolvothermal method.During the experiment,the parameters were changedto obtain CoS with best crystal structure and morphology.the parametersincluding the reaction temperature,the concentration of the solution,thecontents of organic solvent in the solution and the sulfides as reactants.Inthe condition of V(H2O):V(EG)=4:1,the steady specific capacity was125.5mAh/g and the cycling performance was good.After60cycles,thespecific capacity fade slowly and the efficiency of charging/dischagingstill kept above90%.All these results proved that the intercalation of Mgions into CoS was reversible and steady.Using in situ carbon coating, theelectronic conductivity of CoS was improved,thus the discharge specificcapacity of the electrode also incresed.