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Abstract Lattice oxygen redox yields anomalous capacity and can significantly increase the energy density of layered Li‐rich transition metal oxide cathodes, garnering tremendous interest. However, the mechanism behind O redox in these cathode materials is still under debate, in part due to the challenges in directly observing O and following associated changes upon electrochemical cycling. Here, with17O NMR as a direct probe of O activities, it is demonstrated that stacking faults enhance O redox participation compared with Li2MnO3domains without stacking faults. This work is concluded by combining both ex situ and in situ17O NMR to investigate the evolution of O at 4i, 8j sites from monoclinicC2/mand 6c(1), 6c(2), 6c(3) sites from the stacking faults (P3112). These measurements are further corroborated and explained by first‐principles calculations finding a stabilization effect of stacking faults in delithiated Li2MnO3. In situ17O NMR tracks O activities with temporal resolution and provides a quantitative determination of reversible O redox versus irreversible processes that form short covalent OO bonds. This work provides valuable insights into the O redox reactions in Li‐excess layered cathodes, which may inspire new material design for cathodes with high specific capacity.
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This content will become publicly available on April 10, 2026
Tailoring Oxygen Redox Activity and Accelerating Li + Diffusion via Ti Substitution Within Li‐O‐Vacancy Configurations
Abstract Layered oxide cathode with a Li‐O‐vacancy configuration offers high capacity by leveraging additional oxygen redox reactions. However, it faces severe challenges of sluggish kinetics of oxygen redox reactions and lattice oxygen loss, resulting in slow Li+diffusion and rapid electrochemical degradation. Herein, Ti is introduced as electrochemical inactive element into Li‐O‐vacancy configuration to form Mn/vacancy/Ti arrangement within transition metal layers of layered oxide, achieving a marked increase in average output voltage at high current density compared with Ti‐free counterpart. Not only voltage hysteresis between charge and discharge processes can be significantly reduced, but rate capability can be heightened in Li4/7[□1/7Ti1/7Mn5/7]O2by means of retrained over‐potential and improved Li+diffusivity. Furthermore, theoretical calculations suggest that these improvements stem from Ti substitution, which elongates the Li─O bond and lowers the Li+migration energy barrier. Besides, in situ differential electrochemical mass spectrometry and soft X‐ray absorption spectroscopy reveal the modified Li‐O‐vacancy configuration enables reversible anionic and cationic redox behaviors during cycling. These findings provide a promising strategy for tailoring oxygen redox activity and accelerating Li+diffusion kinetics in layered cathode materials with oxygen redox chemistry.
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- Award ID(s):
- 2118020
- PAR ID:
- 10647395
- Publisher / Repository:
- Advanced Functional Materials
- Date Published:
- Journal Name:
- Advanced Functional Materials
- Volume:
- 35
- Issue:
- 38
- ISSN:
- 1616-301X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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