Charging/discharging mechanism in Mg3Bi2 anode for Mg-ion batteries; The role of the spin-orbit coupling

Using density functional calculations, we examine insertion/extraction of Mg ions in Mg3Bi2, an interesting Mg ion battery anode. We found that a (110) facet is the most stable termination. Vacating a Mg2+ ion from the octahedral site is more favourable for both surface and bulk regions of the material. However, the diffusion barriers among the tetrahedral sites are ~3 times smaller than those among octahedral sites. Consequently, during the magnesiation/demagnesiation process, Mg ions first vacate the octahedral sites and then diffuse through the tetrahedral sites. The spin-orbit interaction lowers Mg's vacancy formation energy but has a minor effect on diffusion barriers.

Automated summary

Using density functional calculations, the insertion/extraction of Mg ions in Mg3Bi2 as a Mg ion battery anode was studied. The (110) facet was found to be the most stable termination and vacating a Mg2+ ion from the octahedral site was more favorable for both surface and bulk regions. The diffusion barriers among the tetrahedral sites were approximately three times smaller than those among octahedral sites, resulting in the sequential vacancy of octahedral sites and diffusion through tetrahedral sites during the magnesiation/demagnesiation process. The spin-orbit interaction had a minor effect on diffusion barriers but lowered the vacancy formation energy of Mg.