Mechanism Research On Preparation Of Mg-Li Alloys By Electrolysis In Molten Salt

The mechanism of preparing Mg-Li alloys by cathodic alloying and codeposition in molten salt were studied in this thesis.The main contents and conclusions are as follows:The deposition mechanism of lithium(Li) on magnesium(Mg) electrode was studied by cyclic voltammetry,potential step and X-ray diffraction(XRD),etc. Surface morphology of alloying electrodes was charactered by scanning electron microscopy(SEM).The intermediate reaction products and reduction potentials of Li ion on Mg electrode in eutectic LiCl-KCl were determined.Results showed that the reduction potentials of formingα-Mg solid solution andβ-MgLi alloy by deposition Li on Mg electrode were about -2.10 V and -2.30 V,respectively.The formation ofα-Mg solid solution was controlled by the diffusion of Li within the Mg substance.Neucleation polarization during the process of formingβ-MgLi alloy was observed and the process of polarization was instantaneaus.The results of SEM image showed that when deposited Li,the surface morphologies of Mg electrode were different from the situation without deposition.When Mg was electrolyzed at -2.10 V,the deposited Li atoms entered the crystal lattice of Mg substance and formed uniformα-Mg solid solutoin.The codeposition mechanism of Li and Mg on Mo electrode in eutectic LiCl-KCl-MgCl₂-KF-BaCl₂ was also studied by cyclic voltammetry,potential step and current step,etc.The reduction potentials of Li ion and Mg ion on molybdenum(Mo) electrode were determined.Main factors such as temperature, different cathodic limits and scanning speed etc.that affect electrode process were analyzed.Results showed that the technology of preparing Mg-Li alloy by codeposition in molten salt proved to be feasible.On Mo electrode,underpotential deposition of Mg(â…¡) were found at about -1.80 V and deposition of Mg(â…¡) were found at about -2.0 V.Then at about -2.40 V,Mg-Li solid alloy was formed by underpotential deposition of Li on the Mg deposited already covering the Mo electrode.This electrode process was controlled by the diffusion of Li within the Mg substance.From caculating the number of electron transfer,the author found out that the underpotential deposition of Mg(â…¡) on Mo electrode is a reversible and simple charge-transfer reaction.The diffusion coefficient of Mg(â…¡) on Mo electrode is about 1.99×10^-5cm²Â·s^-1.The effection of temperature during electrode process showed that the activation energy of forming Mg-Li alloy by codeposition was 28.72kJ·mol^-1 in this experimental conditions.