Computational Insights into Anion Storage Mechanisms in Transition Metal Oxide Cathodes

Abstract

The growing demand for sustainable and high-performance energy storage has driven extensive research into battery chemistries beyond conventional lithium-ion systems. Anion batteries, which store charge using anions rather than cations, hold significant promise due to their high theoretical energy density, abundant material resources, and novel redox mechanisms. This dissertation aims to provide atomistic insights into advanced cathode design for anion-storage batteries by employing density functional theory (DFT) calculations to elucidate the mechanisms of anion storage in transition-metal-oxide cathodes. Transition metal oxides offer a diverse platform for cathodes, featuring multiple redox-active transition metals and versatile crystal structures. We explored anion-storage mechanisms in Mn3O4 (a representative binary oxide) and ABO3 perovskites (a prototypical complex oxide). First, we investigated reversible chloride-ion (Cl⁻) storage in Zn2+-inserted Mn3O4. The insertion of Zn2+ significantly distorts the Mn3O4 lattice, facilitating a novel Cl-/Cl0 redox mechanism through polychloride formation instead of traditional Mn-based redox, in agreement with experimental validations. Next, we demonstrated that Mn3O4 can also accommodate hydroxide ions (OH-), enabling pure-water batteries. DFT calculations indicate thermodynamically feasible OH- insertion into Mn3O4, accompanied by structural rearrangements and novel vibrational features, consistent with experimental identification of hydroxide-related phases. Further, we extended our study to perovskite oxides as potential cathodes for Cl2/Cl- redox batteries due to their structural flexibility. By computationally screening Cl adsorption on a series of SrBO3 perovskites (B = Ti, V, Cr, Mn, Fe, Co), we identified SrCoO3 as optimal for chlorine evolution based on the theoretical overpotential plot. Using an interpretable machine learning method, we identified electronic descriptors critical for Cl adsorption, clarifying the underlying structure–property relationships. Finally, we expanded this analysis to a medium-entropy perovskite oxide, LaMn0.25Fe0.25Co0.25Ni0.25O3, featuring multiple active sites. The disordered structure yields a diverse range of adsorption environments, many of which exhibit intrinsically low chlorine evolution reaction overpotentials and enhanced catalytic performance, surpassing the simple-component counterparts through synergistic effects. Collectively, these findings deepen the fundamental understanding of anion storage in transition metal oxides and offer design strategies for next-generation anion storage cathode materials.