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

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.