Covalency does not suppress O2 formation in 4d and 5d Li-rich O-redox cathodes

Abstract

Layered Li-rich transition metal oxides undergo O-redox, involving the oxidation of the O2− ions charge compensated by extraction of Li+ ions. Recent results have shown that for 3d transition metal oxides the oxidized O2− forms molecular O2 trapped in the bulk particles. Other forms of oxidised O2− such as O22− or (O–O)n− with long bonds have been proposed, based especially on work on 4 and 5d transition metal oxides, where TM–O bonding is more covalent. Here, we show, using high resolution RIXS that molecular O2 is formed in the bulk particles on O2‒ oxidation in the archetypal Li-rich ruthenates and iridate compounds, Li2RuO3, Li2Ru0.5Sn0.5O3 and Li2Ir0.5Sn0.5O3. The results indicate that O-redox occurs across 3, 4, and 5d transition metal oxides, forming O2, i.e. the greater covalency of the 4d and 5d compounds still favours O2. RIXS and XAS data for Li2IrO3 are consistent with a charge compensation mechanism associated primarily with Ir redox up to and beyond the 5+ oxidation state, with no evidence of O–O dimerization.

Facilitating Reversible Cation Migration and Suppressing O2 Escape for High Performance Li‐Rich Oxide Cathodes

“…The interval between two vibrated peaks for both materials is 0.2 eV, indicating that the products of local O 2 are generated in both materials. [ 49–51 ]…”

“…The interval between two vibrated peaks for both materials is 0.2 eV, indicating that the products of local O 2 are generated in both materials. [49][50][51] Operando differential electrochemical mass spectrometry (DEMS) exhibits the oxygen release in the first charge and discharge process for LMNO and LMNPO-V O (Figure 4i,j). The capacity when O 2 begins to release for LMNPO-Vo is higher than that for LMNO.…”

Anionic Redox Regulated via Metal–Ligand Combinations in Layered Sulfides

“…In NaCr 2/3 V 1/3 S 2 case, the integrated XANES area ratio fluctuates around 100 ± 4% (Figure S7, Supporting Information), and the fully discharged sample returned to 100% of the pristine state when integrated from 2465 to 2480 eV, which showed more reversible nature than previous reports on oxygen redox. Except for O K‐edge XAS areas, commonly, the pre‐edge peak intensity or the K‐edge slope show obvious irreversible changes after being fully discharge, [ 1a,b,d,21 ] indicating the changes in electronic structure and variation of local chemical environment for oxides.…”

“…[44] Recently, House et al reported 4d and 5d Li-rich O-redox cathodes with covalent interaction still exhibit TM migration, voltage hysteresis and formation of O 2 . [21] To explain the differences in theoretical prediction and experimentally observed anion dimer formation, here, we analogize 4d and 5d Li-rich O-redox cathodes to transition metal sulfides. In previous reports, general transition metal chalcogenides are considered as highly covalent, but the hole concentration on anions that can be stabilized by covalency is related to the extent of covalent interaction, when the concentration exceed the limit of stabilization, catenation of anions would leads to polymerization of the anions.…”

A Novel Self-Assembly Strategy for the Fabrication of Nano-Hybrid Satellite Materials with Plasmonically Enhanced Catalytic Activity

“…Considerable research effort has been devoted to improve the photo-catalytic efficiency of existing semiconductor materials by applying top down and bottom up nano-engineering approaches [ 5 ]. Major improvements have been achieved by increasing the complexity of the materials at the nanoscale, favouring local charge separation and directing the systems towards specific reaction pathways [ 6 , 7 ]. One area of particular interest is plasmon enhanced catalysis, where only a few examples relevant to hydrogen evolution photo-chemistry have been explored [ 8 , 9 , 10 ].…”