Elucidation of Active Oxygen Sites upon Delithiation of Li₃IrO₄

Abstract

Transformational increases in the storage capacity of battery cathodes could be achieved by tapping into the redox activity at oxide ligands in addition to conventional transition metal couples. Yet the key signatures that govern such lattice oxygen redox (LOR) have not been ascertained. Li 3 IrO 4 has the largest reversible LOR, rendering it a unique model system. Here, Xray spectroscopy and computational simulations reveal that LOR in Li 3 IrO 4 is selectively compensated via O sites with 3 lone pairs, which are activated by Li/Ir disorder. The 2-electron LOR can be reversed to regenerate the initial state without unlocking competing bulk reactions observed in many other compounds. We uncover an intricate interplay between stoichiometry, O coordination and non-bonding states in LOR and pinpoint spectroscopic signatures. This interplay is indispensable to design materials with 3d metals that fulfill the promise of LOR to overcome the bottlenecks of current cathodes for future implementation in practical batteries.

Oxygen-redox activity in non-Li-excess W-doped LiNiO2 cathode

“…[87] Secondly, the aforementioned O K-edge emission feature was not observed in Li3IrO4, wherein delithiation is compensated solely by bulk O 2− oxidation involving the generation of lone pairs. [88] Finally, as mentioned before, all O-redox-active charged stoichiometric layered, Li-excess and certain Na cathodes studied using RIXS thus far, despite the differences in their pristine structure and delithiation pathways, show the same ~523.7 eV emission feature and low-energy excitations close to the elastic line (i.e., asymmetric broadening) at an excitation energy of 531 eV during highefficiency RIXS mapping to varying degrees irrespective of the composition and cycling protocol. [9,10,27,28,[30][31][32]34,35,[38][39][40][41][42][43][44][45] Therefore, it is only rational that the same hr-RIXS feature is also seen in both stoichiometric layered and Li-excess cathode systems.…”

Mixed Cationic and Anionic Redox in Ni and Co Free Chalcogen-Based Cathode Chemistry for Li-Ion Batteries

“…The anion redox phenomenon was well investigated in practical Li-rich NMC material and Ru-, Ir-based model compounds, and it was proven that the oxygen redox stabilization is intrinsically improved by raising transition metal and oxygen ligand covalency as the Ru exhibited higher oxygen redox stabilization than Mn. 7,23,24 The driving force for improved anion redox reaction is metal−ligand covalency, and the property could be improved to achieve efficient anion redox stabilization in contrast to unstable oxygen anion redox in oxide cathodes. To improve the metal−ligand covalency, the strategy of replacing the oxide ligand with the chalcogen (S, Se) ligand is emerging, where the less electronegative nature of the chalcogen improves the ligand p band penetration into the metal d band with a combination of appropriate metals and chalcogen ligands.…”