Reversible densification in nano-Li2MnO3 cation disordered rock-salt Li-ion battery cathodes

Abstract

The full structure of nano-Li₂MnO₃ with superior reversible capacities of 290 mA h g⁻¹ for over 10 cycles was investigated by neutron and X-ray total scattering, which demonstrate that contrary to previous claims, a phase transformation occurs during synthesis forming a disordered cubic MnO-type rock-salt with nanodomains of Li/Mn layering of ∼1 nm. A comprehensive study of the structural and charge evolution combining in operando X-ray total scattering with advanced spectroscopic methods at the Mn K-edge such as High Energy Resolved Fluorescence Detected XANES, EXAFS and Emission Spectroscopies including main and valence-to-core transitions, point to a lattice densification with an effective loss of Li₂O, with the subsequent electrochemical activation of Li₂O as the main responsible mechanism for the exchanged capacity. Interestingly, and unlike previous studies, no capacity losses could be associated to the material's densification.