Peroxo Species Formed in the Bulk of Silicate Cathodes.

Zhenlian Chen,Lirong Zheng,Xianhui Zhang,Deyu Wang,Ailing Tian,Liyuan Huai,Wenqiang Du,Ying Zhang,Jun Li,Zhifeng Zhang,Xiao Cheng Zeng,Bjoern Schwarz,Zhiyong Zhang,Helmut Ehrenberg,Jinlei Wu

doi:10.1002/anie.202100730

Abstract

Oxygen redox in Li‐rich oxides may boost the energy density of lithium‐ion batteries by incorporating oxygen chemistry in solid cathodes. However, oxygen redox in the bulk usually entangles with voltage hysteresis and oxygen release, resulting in a prolonged controversy in literature on oxygen transformation. Here, we report spectroscopic evidence of peroxo species formed and confined in silicate cathodes amid oxygen redox at high voltage, accompanied by Co2+/Co3+ redox dominant at low voltage. First‐principles calculations reveal that localized electrons on dangling oxygen drive the O‐O dimerization. The covalence between the binding cation and the O‐O dimer determines the degree of electron transfer in oxygen transformation. Dimerization induces irreversible structural distortion and slow kinetics. But peroxo formation can minimize the voltage drop and volume expansion in cumulative cationic and anionic redox. These findings offer insights into oxygen redox in the bulk for the rational design of high‐energy‐density cathodes.

Highlights

Oxygen redox in Li-rich oxide cathodes offers a new way to increase the energy density of lithium-ion batteries for applications in battery-driven electric vehicles and green power grid stations.[1]
The two sets of pre-edge peaks from the lattice metal-oxo ligand and peroxo moiety O22À can be distinguished in the spectra. Their relative positions agree very well with the experimental O K-edge X-ray absorption near edge structure (XANES) spectroscopy shown in C-4 of Figure 2 a, confirming the DO signature is from the excitation of the O-1s electron to the s* orbital of the dinuclear peroxo moiety formed in the bulk amid oxygen redox
The overall spectroscopic and structural evolution with nearly two Li+ extractions can be described by two oxidations, somewhat successive but overlapped with: 1) the cationic oxidation Co2+!Co3+ dominating the solid-solution-like reaction within Orth-1 phase; 2) anionic oxidation 2 O2À!O22À accompanied by the phase transition from Orth-1 to Orth-2 and medium-range distortion within the Orht-2 phase

Summary

Introduction

Oxygen redox (or anionic redox) in Li-rich oxide cathodes offers a new way to increase the energy density of lithium-ion batteries for applications in battery-driven electric vehicles and green power grid stations.[1]. Angewandte Chemie International Edition published by Wiley-VCH GmbH. The agreement between experimental and first-principles simulated X-ray absorption near edge structure (XANES) suggests a criterion to ascertain which oxidized oxygen species dominates the oxygen redox reaction. With clarification of oxidized species, a new paradigm can be established for rational designs of cumulative cationic and anionic redox to achieve reversible high energy-density by incurring peroxo formation

Results and Discussion

Conclusion

Conflict of interest