Seeking experimental proof of anionic redox in high capacity cathodes 1.

The high capacities (> 250 mAh g–1) of Li-cathode materials have been attributed to reversible anionic redox stabilized by the formation of ‘peroxo-like’ O-O dimers in layered (Li/Na)2RuO3 and 3D β-Li2IrO3 structures. The formation of peroxo-like dimers is believed to stabilize O2-/O1.5- redox by the sharing of one electron hole between each oxygen in the pair. Peroxo-like distances have been proposed by Bragg diffraction, TEM or EXAFS. Unlike PDF, these techniques are not a direct probe of actual distribution of 𝑑 interatomic distances, and large uncertainties surround the estimated distances or existence of peroxo-like dimers. We propose to study the origin of anionic redox in Li0.5RuO3 and Na0.5RuO3 c by a new and comprehensive approach combining PDF and advanced spectroscopies that we have been successfully implemented in the characterization Mn-based high capacity cathodes.