Oxygen Vacancy-Driven Water Dissociation for High-Performance Potassium-Ion Storage.

Aqueous potassium-ion batteries (AKIBs) are attractive for low-cost and sustainable energy storage, yet their performance is limited by water-induced electrode degradation. Herein, we identify a previously unrecognized water-dissociation-regulated cointercalation mechanism in a P3-type K0.46MnO2 (KMO) cathode. We found that oxygen vacancies in KMO interact with neighboring lattice oxygens and promote water dissociation during charging, generating -OH groups which subsequently react with water to form H3O+. The resulting H3O+ cointercalates with K+, contributing to a gradual increase in capacity, while the -OH···H2O configuration serves as an interlayer pillar that stabilizes the layered structure. Benefiting from this water-driven charge-carrier regulation, KMO delivers an enhanced discharge capacity of 89.4 mAh g-1 with a record-high 96.0% capacity retention over 25,000 cycles. Furthermore, a KMO-based pouch full cell demonstrates the best capacity retention of 88.8% after 9000 cycles reported to date, highlighting the potential of hydration chemistry to enable durable and high-performance AKIBs.