Preparation And Electrochemical Performance Of Magnesium Based Anode For Magnesium Sulfur Battery

Magnesium is rich in resources,low in price,high in safety,and non-toxic,and at the same time,magnesium and lithium exhibit diagonally similar properties.Therefore,magnesium-based chemical power sources have great potential.But in fact,the chemical properties of magnesium are very active,and the surface is very easy to form a passivation film,resulting in"voltage hysteresis"phenomenon.In addition,magnesium also has the disadvantages of high corrosion rate and severe anodic polarization.In response to these problems,a variety of magnesium-based composite materials were prepared by doping a small amount of other elements in a magnesium negative electrode by coating,vapor deposition,and the like.At the same time,magnesium-based alloys with different compositions are used as the negative electrode of the magnesium-sulfur battery.The electrochemical test method was combined with SEM and XRD to analyze the effects of composite anode on the performance of charge and discharge and cycle stability of magnesium-sulfur batteries.Three kinds of Super C65 magnesium carbon materials were prepared by mixing the magnesium powder with Super C65 under three different ball milling times by ball milling.The ball milling method serves to reduce the polarization of the magnesium negative electrode and enhance the cycle stability of the battery by refining the crystal grains.The addition of Super C65 can reduce the polarization of the negative electrode of the magnesium negative electrode and improve the utilization of the negative electrode.When the magnesium carbon material containing10%Super C65 prepared by ball milling for 14 h is used as the negative electrode,the performance of the battery is optimal.At this time,the discharge platform of the magnesium-sulfur battery is about 1.2¹.3 V,and the first discharge specific capacity reaches 600 mAh/g.Considering that lithium metal has a relatively high energy density and electrochemical activity,lithium is added to magnesium by three methods of tableting,coating and evaporation to prepare a magnesium-lithium material as a negative electrode of a magnesium-sulfur battery.The addition of lithium in the tableting method can effectively alleviate the"voltage hysteresis"phenomenon of the magnesium electrode and inhibit the polarization of the negative electrode of the magnesium-sulfur battery.In the coating method,the cold press film rupture treatment of the hydraulic press can cause the passivation film to be broken due to a relatively large pressure,thereby enhancing the chemical reaction between the electrode and the solution.Although the lithium plating prepared by the vapor deposition method is not uniform,the activity of the battery is remarkably improved.Not only has the magnesium discharge platform been improved,but also magnesium and lithium have played their respective roles;a high platform of lithium appears around 1.7 V,a low platform of magnesium appears around 1.3 V,and a discharge specific capacity of up to 1400 mAh/g.In general,the addition of lithium can reduce the"voltage hysteresis"phenomenon caused by the presence of the passivation film on the magnesium surface,thereby increasing the theoretical specific capacity and discharge potential of the alloy as the negative electrode of the battery,thereby improving the utilization of the negative electrode.The commercial lithium-magnesium alloy is used as the negative electrode of the magnesium-sulfur battery,and the discharge platform and discharge specific capacity of the battery are obviously improved.The high platform of the magnesium-sulfur battery using the magnesium-lithium alloy as the negative electrode appears near 2.0 V,the low platform appears at about 1.3 V,and the first discharge specific capacity reaches about 1000 mAh/g.When the magnesium rare earth alloy is used as the negative electrode,the discharge platform and specific capacity of the battery can be improved,and the cycle stability of the battery can be improved.The three magnesium-lithium alloy materials with different lithium contents synthesized by molten salt electrolysis are not suitable for the electrochemical performance of the Mg?TFSI?₂ electrolyte system.LiTFSI with a concentration of 0.5 mol/L was added to it,and it was found that the discharge platform and specific capacity of the battery were greatly improved.The discharge platform had an increase of about 0.4 V,and the first discharge specific capacity of the battery was also increased by about 400 mAh/g.