Investigation On Bismuth-Based Artificial Interfacial Films And Their Magnesium Metal Deposition/Dissolution Properties

Lithium-ion batteries with graphite anodes have been commercialized for 30years.However,the frequent safety accidents and the shortage of lithium resources imped their further development.Secondary magnesium（Mg）batteries have attracted much attention due to the less propensity to grow dendrites,the high safety and the low price for Mg metal anodes.Nevertheless,the surface passivation of the Mg metal anodes by magnesium oxide has always plagued the development of secondary Mg batteries.In this dissertation,from the perspective of constructing functional artificial protective layer on Mg metal anodes,the interface materials have been designed and prepared in terms of composition and structure that are conducive to the Mg nucleation and migration.Three kinds of artificial protective layer materials include the bismuth-based,the bismuth-indium-based and the gallium-indium-tin-based composites.These interface materials improve the nuclear overpotential,plateau overpotential,and long stable cycling performance in Mg//Mg symmetric battery and Mg//Cu asymmetric batteries.The specific research contents are as follows:（1）Bismuth-based artificial protective layers have been prepared via a simple chemical replacement reaction.These interfaces show continuous granular microscopic morphology,which compose of Bi and Bi O_x.The average thicknesses are 8.3μm and4.0μm,respectively.Density functional theory calculations indicate the better magnesiophilic property of Bi and Bi O_x.The artificial protective layer was still tightly adhered to the surface of the magnesium foil after 50 charge-discharge cycles.The modified Mg metal anodes with these bismuth-based artificial protective layers display low nucleation overpotentials of 23 m V and low plateau overpotentials of 69 m V（93m V and 93 m V for pristine Mg anode）at 10μA cm^-2.（2）The bismuth/indium-based artificial protective layer has been prepared by a simple chemical replacement reaction.The main component of the artificial protective layer is a mixture phase of Bi metal and In metal,which has a continuous granular microscopic morphology.The average thickness is 3.0μm.With the help of the synergy of Bi and In,the preferential adsorption and promoted nucleation of Mg can be achieved.The artificial protective layer was still tightly adhered to the surface of the magnesium foil after 50 charge-discharge cycles.At a current density of 1.0 m A cm^-2at room temperature,low nucleation overpotentials and polarization voltages of 189m V and 160 m V（583 m V and 169 m V for pure magnesium）have been obtained,respectively.Ultra-long stable cycles of over 360 h and 1200 h（120 h and 292 h for pure magnesium）have been obtained at high temperature of 50°C and low temperature of 10°C,respectively.（3）The gallium-indium-tin-based artificial protective layer with an average thickness of 10μm has been prepared by the chemical magensiation method.The artificial protective layer contains Mg-alloys and Ga-,In-,and Sn-based oxides.The artificial protective layer undergoes structural reorganization that is beneficial to the Mg-atoms migration during the charge-discharge cycle.At a current density of 1.0 m A cm^-2,a stable cycle of more than 4000 h（1600 h for pure magnesium）has been obtained,and the polarization voltages at the 100th cycle for the modified and pure magnesium anodes are 185 m V and 207 m V,respectively.The above results demonstrate that the interface protective layer derived from the chemical magnesium reaction between gallium-indium-tin alloy and Mg metal can effectively reduce the nucleation overpotential of Mg and improve the deposition/dissolution reversibility.