Investigations On High-Performance Magnesium Alloy Anode Material For Seawater Batteries

With the rapid development of society,people's demand for various types of energy is ever-increasing.The development of a large number of non-renewable fossil energy resources has made land resources gradually scarce,so it is particularly important to find a new kind of green,clean and renewable energy.People are gradually turning their attention to the ocean.Magnesium seawater batteries can meet the power supply demands for deep-sea exploration equipment,and are safe and environmentally friendly.Researchers make full use of the ocean's own conditions to develop magnesium seawater batteries.However,despite its many advantages,magnesium also has some problems such as low discharge activity and serious self-corrosion when used as an anode material.In this paper,quantum chemical calculation method based on first principles is used to study the quantum chemistry of the system composed of alloy elements and pure magnesium.Appropriate alloying elements were screened out and some experimental phenomena were explained.Combined with the binary alloy phase diagram,the crystal models of some intermetallic compounds and solid solution alloys were established using Materials Studio quantum chemistry calculation software.The binding energy and phase-to-phase potential difference of the corresponding magnesium alloy system were calculated.The results showed that the binding energy values of the three intermetallic compounds Mg₂Cu,Mg Co and Mg₂Ni were negative,but their absolute values were relatively small,indicating that they are not stable enough to exist in magnesium alloys.And the potential difference between the phases of the corresponding solid solution alloy was too large,which theoretically increased the driving force of micro-galvanic corrosion effect,which is not conducive to improve the corrosion resistance of magnesium alloys,so Cu,Co,Ni were excluded.In contrast,the alloy system formed by magnesium and some rare earth elements such as Yb and common elements such as Al,Zn,Sn and Bi has a more negative binding energy,indicating that the corresponding second phase,which can affect the properties of the alloy,can be stable in the magnesium alloy,and the influence mainly depends on the volume fraction and distribution of the second phase in the alloy.The calculation results also showed that the phase-to-phase potential difference between the intermetallic compounds formed by the five elements of Yb,Al,Zn,Sn,Bi and Mg and the corresponding solid solution alloy was small,so it is not easy to cause the micro-galvanic corrosion that may exist in the alloy,which is beneficial to improve the corrosion resistance of magnesium alloy.Based on the above theoretical calculation results,five elements Yb,Al,Zn,Sn,Bi were selected for alloying and a series of alloys were prepared for electrochemical and self-corrosion tests.The results of galvanostatic discharge showed that different alloying elements had different effects on the discharge activity of magnesium,and the effect was mainly influenced by the content of alloying elements.The addition amount of Al element is generally large,and when the content is 8.0%,the average discharge potential of binary Mg-Al alloy reached the most negative value.The addition amount of Sn and Bi elements should not be too high,and the discharge potential shifted positively with the increase of the content of both elements,and the optimal content was 0.2%.The optimum content of Zn and Yb was 1.0%.The results of polarization curve were consistent with the results of galvanostatic discharge.Based on the optimum content of each element,a series of quaternary magnesium alloys were prepared,and compared with pure magnesium,the optimum quaternary alloys were Mg-8.0%Al-0.2%Sn-1.0%Yb,the discharge potential was negatively shifted by 56m V compared with pure magnesium,and the anodic utilization was increased by nearly 45%,showing both high discharge activity and high anodic utilization efficiency,so it is a suitable anode material used for seawater battery.