• • 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.