Theoretical investigation on next-generation Mg-battery cathodes

Abstract

The Mg-ion battery is a promising alternative to the currently used Li-ion batteries in case of element shortcoming. However, poor cyclic stability and low energy density of cathode active materials for Mg-ion batteries remain as an assignment to solve for its commercialization. In this dissertation, garnet-type intercalation cathode active materials, MgxMo2(SiO4)3 and MgxFe2(SiO4)3, are investigated for high-performance Mg-ion battery applications through first-principle density functional theory calculations and the results are discussed through the five subsections. At first, the unique atomic structure of garnet is introduced briefly, and resulting three-dimensional Mg-ion migration mechanisms are discussed in the second part. In the third part, charge transfer during charging/discharging of battery is examined in detail through the density of states, crystal orbital overlap population, Bader charge, and magnetic moment to clarify the center of redox reaction in garnet. At fourth, the mechanical and thermodynamic stabilities are evaluated for newly proposed hypothetical garnets. Finally, the material- and cell-level energy densities are calculated and compared with state-of-the-art Li-ion batteries. The computation results and discussions about garnets as cathode active through this doctoral dissertation present a great potential of garnet cathodes for high-performance energy-storage-applications and suggest a new direction to develop Mg-ion batteries.