Coulombic self-ordering upon charging a large-capacity layered cathode material for rechargeable batteries

Abstract

Lithium- and sodium-rich layered transition-metal oxides have recently been attracting significant interest because of their large capacity achieved by additional oxygen-redox reactions. However, layered transition-metal oxides exhibit structural degradation such as cation migration, layer exfoliation or cracks upon deep charge, which is a major obstacle to achieve higher energy-density batteries. Here we demonstrate a self-repairing phenomenon of stacking faults upon desodiation from an oxygen-redox layered oxide Na₂RuO₃, realizing much better reversibility of the electrode reaction. The phase transformations upon charging A₂MO₃ (A: alkali metal) can be dominated by three-dimensional Coulombic attractive interactions driven by the existence of ordered alkali-metal vacancies, leading to counterintuitive self-repairing of stacking faults and progressive ordering upon charging. The cooperatively ordered vacancy in lithium-/sodium-rich layered transition-metal oxides is shown to play an essential role, not only in generating the electro-active nonbonding 2p orbital of neighbouring oxygen but also in stabilizing the phase transformation for highly reversible oxygen-redox reactions.

Here the authors report the evolution of stacking faults in Na₂RuO₃ showing that there is progressive cation ordering upon charging and notably the stacking faults can disappear. This behavior is driven by cooperative Coulombic interactions and can contribute to stabilizing the phase transformations.