Nanoscale mapping of spatial fluctuations in oxygen redox activity within a charged single particle of Li-rich layered oxide

Abstract

Direct visualization of the spatial distribution of oxygen redox activity in single (primary) particles of Li-rich layered oxide (LLO) is essential for a deeper understanding of its reaction mechanism. In this study, we propose a real-space mapping approach for identifying oxygen redox-active domains using scanning transmission electron microscopy (STEM)-based electron energy-loss spectroscopy (EELS). Electron-released oxygen (oxidized oxygen) was clearly detected by EELS and soft X-ray absorption spectroscopy (S-XAS) in the charged state of Li_1+x(Ni_0.3Mn_0.7)_1-xO₂ (0 < x < 1/3). STEM-EELS spectrum imaging clarified that the fluctuations in oxygen redox activity closely correlate with the Ni distribution within LLO particles, found that oxidized oxygen species distribution was well correlated with Ni-poor region. The heterogeneous distribution of transition metals leads to non-uniform activation of oxygen in the particles, with Ni-rich domains suppressing oxygen redox activity. This real-space mapping of oxygen activity domains at the LLO single-particle level contributes to understanding the material's mechanism.