In Situ Defect Healing Suppresses Mn Dissolution Chain Reactions in Aqueous Sodium-Ion Cathodes

A degradation chain reaction triggered by Mn dissolution is revealed, clarifying the continuous performance deterioration caused by Mn dissolution. A strategy for in situ surface repair is proposed, which achieves long-term stability through the synergistic action of high-concentration electrolyte and Fe 3+ filling of Mn vacancies. After 20,000 cycles at a current density of 2 A g −1 , the repaired electrode exhibited a capacity retention rate of 80%, outperforming most previously reported manganese-based aqueous sodium-ion battery cathodes.