Role of transition metals in a charge transfer mechanism and oxygen removal in Li1.17Ni0.17Mn0.5Co0.17O2: experimental and first-principles analysis

Abstract

Oxygen removal from high capacity Li-rich layered oxide Li_1.17Ni_0.17Mn_0.5Co_0.17O₂ affects the charge transfer process during cycling. During de-lithiation, oxygen removal takes place with the reduction in oxygen binding energy. Co substitution affects oxygen removal by shifting the O-p orbital closer to the Fermi energy. A convex hull plot is used to analyse single-phase and two-phase reactions during de-lithiation in Li_1.17Ni_0.17Mn_0.5Co_0.17O₂ and Li₂MnO₃. Experimentally, the single-phase and two-phase reactions are identified based on the characteristics of the charge curve. In the charge transfer process more than 80% of lithium charge is transferred to oxygen in both the compounds. Effective charge and cyclic voltammetry reveal the redox centers in the compounds which help to understand the role of oxygen and transition metals in de-lithiation. A detailed explanation of oxygen removal and the charge transfer mechanism of Li_1.17Ni_0.17Mn_0.5Co_0.17O₂ and Li₂MnO₃ is provided in the current experimental and density functional theory based study.