Enabling robust anionic redox structure via tuning the symmetry of locally ordered lattice in Li-rich Li-Mn-O cathodes

Abstract

Li-rich Li-Mn-O (LR-LMO) oxides are promising cathodes for low-lost and high-energy–density Li-ion batteries owing to their accessible anionic redox reaction (ARR) chemistry. However, the unstable ARR structure can result in inferior electrochemical properties, restricting practical applications of LR-LMO oxides. In this study, we demonstrate that the symmetry of locally ordered lattice can be tuned to enable robust ARR structure in LR-LMO cathodes. By employing a twofold symmetry locally ordered lattice in the LR-LMO oxide (denoted as tLR-LMO), a reversible capacity of 260 mAh/g at 0.1C and capacity retention of 78 % after 100 cycles at 1C were observed. The tLR-LMO has retarded cationic migrations during the ARR process when compared to this with a sixfold symmetry locally ordered lattice (denoted as sLR-LMO), as indicated by in-situ X-ray diffraction and ex-situ scanning transmission electron microscopy studies. The tLR-LMO also shows superior stability in its ARR structure as revealed by ex-situ X-ray absorption spectra and neutron pair distribution function results and supported by theoretical calculations. More broadly, this work highlights the role of local-structure symmetry in designing high-performance Li-rich cathodes with ARR activity.