Effect Of Alloying Elements On Electrochemical Performance Of Magnesium Anode In Magnesium Ion Battery

The problem of energy security and ecological environment is becoming more and more serious,and resources such as lithium,cobalt,and nickel are increasingly depleted.MIBs are expected to become a new generation of battery energy storage technology due to their low cost,high safety,environmental friendliness,and high volume specific capacity.the uneven deposition/dissolution of Mg will cause problems such as high overpotential and poor cycle stability,which limit the industrialization of MIBs.Based on the important influence of alloying elements on the electrochemical properties of metals,pure Mg and binary alloys containing Gd,Sn,Mn,Zn,and Al with an atomic percentage of 1%were prepared by smelting and extrusion,which are anodes for MIBs.Anodes are assembled into button batteries which were tested for cyclic voltammetry,charge and discharge,and combined with FESEM and CLSM to analyze the polarization phenomenon of alloy elements on Mg,cycle life and the influence of the surface morphology after Mg deposition/dissolution.And then,the effects of five alloying elements on the self-diffusion behavior of Mg atoms were analyzed by first-principles,and the effects and laws of alloying elements on the electrochemical performance of Mg anode for MIBs were comprehensively studied.Gd can significantly improve the electrochemical performance of Mg anode,and Sn,Mn,Zn,and Al play the opposite role.The test results of the symmetrical battery show that the overpotential of Mg-1 at.%Gd is the lowest,only 70%of that of Pure Mg,and the overpotential of other four alloys are higher than that of Pure Mg.And the long-term cycling stability of Mg-1at.%Gd is better than that of Pure Mg,and the long-term cycling stability of other four alloys are worse than that of Pure Mg.At 5 m A/cm~2,the Mg-1 at.%Gd symmetric battery can cycle for up to 220 h,while Pure Mg symmetric battery can cycle for less than 120 h.And in this case,cycle time of other four alloys symmetric batteries are less than 80 h.After charging and discharging,the surface morphology of Mg-1 at.%Gd is relatively uniform and smooth,and its roughness value is the lowest among six anodes,which is also the reason for the low overpotential and excellent long-term cycling performance of Mg-1 at.%Gd.The test results of half battery show that,compared with Pure Mg,the Mg-1 at.%Gd has better stability of cycle Coulomb efficiency,while other four alloys are poor.At 5m A/cm~2,Gd improves the cycle life of Pure Mg,after cycling 210 h,only the Cu||Mg-1at%.Gd half battery was still in normal charging and discharging state,Cu||Pure Mg half battery was short-circuited after cycling 107 h,and cycling time of other alloys half battery did not exceed 80h.The law of the cycle life of six anodes and density of its deposition-dissolution layer:Mg-1 at.%Gd>Pure Mg>Mg-1 at.%Sn>Mg-1 at.%Mn>Mg-1 at.%Zn>Mg-1 at.%Al.The test results of the full battery show that,Gd increases the specific discharge capacity of the full battery at 20 m A/g,the Cu S||Mg-1 at.%Gd full cell has the highest discharge specific capacity,and Sn,Mn,Zn,and Al reduce the discharge specific capacity of the full battery.The law of merits and demerits of the electrochemical properties of the six anodes in the above tests of symmetrical battery,half battery and full battery:Mg-1at.%Gd>Pure Mg>Mg-1 at.%Sn>Mg-1 at.%Mn>Mg-1 at.%Zn>Mg-1 at.%Al.The self-diffusion behavior of Mg atoms in Pure Mg and five binary magnesium alloys was analyzed by first-principles simulation.When Gd element is added,the self-diffusion energy barrier value of Mg atom is the lowest,and the lower self-diffusion energy barrier is conducive to the uniform and smooth deposition/dissolution morphology of Mg,which is consistent with the smooth and flat surface morphology of Mg-Gd after charging and discharging in the experiment.However,the law of self-diffusion barrier of six anodes is not completely consistent with the law of electrochemical performance in the experiment.Because the level of self-diffusion barrier is only one of the influencing factors of electrochemical performance,and the deposition sequence of Mg and alloy elements is also one of the influencing factors.This study provides a novel design idea for the anode of MIBs and provides a strong support for the industrial development of MIBs.