Key Takeaways & Executive Findings
- •• • P3-type Na2/3Cu1/3Mn2/3O2 exhibits reversible oxygen redox with an exceptionally low voltage hysteresis of 0.05 V, compared to >0.5 V in conventional systems, directly addressing a critical barrier to energy-efficient cycling. • • Spectroscopic analyses confirm a reversible O2−→O− evolution without O–O dimerization, ensuring structural stability and mitigating irreversible capacity loss. • • Multilateral non-invasive magnetic methods demonstrate that strong Cu-O-Mn superexchange interactions delocalize O− species, inhibiting irreversible O–O bonding and enabling ultralow voltage hysteresis. • • Magnetic exchange engineering is established as a transformative strategy to unlock reversible oxygen redox, offering a new design paradigm for high-energy battery electrodes.
Abstract
The instability of oxygen redox activity in layered oxide cathodes, particularly the formation of localized electron holes on oxygen (O−) and subsequent anion dimerization, has been demonstrated to trigger rapid capacity degradation and severe voltage hysteresis. Our study primarily focuses on P3-type Na2/3Cu1/3Mn2/3O2, which demonstrates reversible oxygen redox with an exceptionally low voltage hysteresis of 0.05 V. Spectroscopic analyses demonstrate a reversible O2−→O− evolution in Na2/3Cu1/3Mn2/3O2 without O–O dimerization. Furthermore, Multilateral non-invasive magnetic methods reveal that strong Cu-O-Mn superexchange interactions during the metal-ligand redox process lead to delocalization of O− species and inhibition of irreversible O–O bonding, thereby enabling ultralow voltage hysteresis. This work establishes magnetic exchange engineering as a transformative strategy to unlock reversible oxygen redox in high-energy battery electrodes.
1. Introduction
Conventional layered oxide cathodes relying solely on cationic redox are approaching theoretical capacity limits, necessitating the integration of anionic redox reactions (ARR) to boost energy density. However, the inherent instability of electron holes on oxygen (O−) leads to O–O dimerization, triggering irreversible transition metal migration, oxygen loss, and severe voltage hysteresis exceeding 0.5 V. Existing mitigation strategies—cationic substitution, surface coating, and structural design—fail to address the intrinsic localization of O− at the electronic level, leaving a critical bottleneck in ARR commercialization.
This work introduces magnetic exchange engineering as a novel approach to stabilize anionic redox. By designing a P3-type Na2/3Cu1/3Mn2/3O2 cathode with strong Cu-O-Mn superexchange interactions, the study demonstrates that these interactions delocalize O− species, preventing O–O dimerization and achieving an ultralow voltage hysteresis of 0.05 V. This mechanism directly tackles the root cause of ARR instability, offering a transformative pathway for high-energy, long-cycle-life battery cathodes.
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Chunjing Hu, Jiefan Liu, Xiaobing Lou, Ming Shen, Bingwen Hu, Chao Li (2026). Metal-ligand redox assisted by strong Cu-O-Mn superexchange interaction in a prototype layered oxide cathode. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3975-2
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Frequently Asked Questions
What is the specific voltage hysteresis value achieved in Na2/3Cu1/3Mn2/3O2, and how does it compare to conventional anionic redox cathodes?
The voltage hysteresis is 0.05 V, which is an order of magnitude lower than the >0.5 V typically observed in conventional systems, indicating significantly reduced energy loss during charge/discharge.
How does the Cu-O-Mn superexchange interaction prevent O–O dimerization at the atomic level?
Strong Cu-O-Mn superexchange interactions delocalize the O− holes, reducing their localization on specific oxygen sites and thereby inhibiting the formation of O–O bonds, as confirmed by magnetic and spectroscopic analyses.
What experimental techniques were used to confirm the reversible O2−/O− redox without dimerization?
Spectroscopic analyses (likely including X-ray photoelectron spectroscopy or X-ray absorption spectroscopy) and multilateral non-invasive magnetic methods were employed to track oxygen redox evolution and confirm the absence of O–O dimerization.
What are the implications of this work for the scalability of high-energy sodium-ion batteries?
By demonstrating a stable anionic redox mechanism with ultralow hysteresis, this work provides a design principle for cathodes that could enable higher energy densities and longer cycle life, addressing key barriers to commercial adoption of sodium-ion batteries.
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