Traditional Electrochemical Zn2+ Intercalation/Extraction Mechanism Revisited: Unveiling Ion‐Exchange Mediated Irreversible Zn2+ Intercalation for the δ‐MnO2 Cathode in Aqueous Zn Ion Batteries

Abstract Rechargeable aqueous Zn/δ‐MnO 2 batteries are extensively investigated owing to the low cost, safety and eco‐friendliness. However, the charge storage mechanism of δ‐MnO 2 electrode is still in debate. In this paper, it is revealed that the Zn 2+ intercalation in δ‐MnO 2 electrode is an ion exchange process rather than the commonly‐conceived electrochemical process for the first time. Before the discharge/charge process, Zn 2+ irreversibly intercalates into the structure of δ‐MnO 2 . The ion‐exchange mediated irreversible Zn 2+ intercalation in δ‐MnO 2 has no contribution to the capacity of δ‐MnO 2 electrode during cycles. This study further reveals that the electrochemical H + intercalation/extraction, the electrodissolution of δ‐MnO 2 and the electrodissolution‐electrodeposition of vernadite dominate the charge storage process of δ‐MnO 2 electrode. These findings shed new light on the fundamental understanding for the reaction mechanism of δ‐MnO 2 electrode in aqueous batteries.