Local Redox Reaction of High Valence Manganese in Li₂MnO₃-Based Lithium Battery Cathodes

Highlights

• The trend for cationic/anionic redox at different stages of delithiation in Li₂MnO₃

• High valence Mn⁶⁺ and Mn⁷⁺ in the form of MnO₄ tetrahedrons

• Local redox reaction between Mn⁶⁺ or Mn⁷⁺ and their surrounding oxygen atoms

• A comprehensive understanding to the electron transfer in Li_xMnO₃ during delithiation

Summary

Li₂MnO₃ endows Li-rich layered oxides with a superior energy density; however, its electron transfer mechanism is still unclear. Here, the electronic and thermodynamic behavior of Li_xMnO₃ (x = 0.5–2) is determined using first-principles computations. The cationic redox, anionic redox, and local electron exchange in Mn-O polyhedron are revealed. An obvious electron donation inclination of manganese is demonstrated when the Li⁺ content is low. Through ab initio molecular dynamics, high valence Mn⁶⁺ and Mn⁷⁺ are generated in the form of MnO₄ tetrahedrons with structural transformation toward a disordered structure, controlled by the Li⁺ content and dynamic energy barrier. Furthermore, a local redox reaction between Mn⁶⁺ or Mn⁷⁺ and their surrounding oxygen atoms is elucidated. Consequently, a comprehensive understanding regarding the electron transfer in Li_xMnO₃ is provided. Our results bring insight regarding the electron transfer mechanism in Li-rich layered oxide cathode materials and encourage further reconsideration and investigation into its redox mechanism.