Hydration Enables Air-Stable and High-Performance Layered Cathode Materials for both Organic and Aqueous Potassium-Ion Batteries

摘要

Potassium (K)-based layered oxides are potential candidates for K-ion storagebut they suffer from chemical instability under ambient conditions that deterioratetheir performance in rate-capability and cycle life. To tackle this issue,a facile hydration strategy is employed, in which H_2O molecules are introducedinto the K ion layers of P3-type K_(0.4)Fe_(0.1)Mn_(0.8)Ti_(0.1)O_2, which induces aphase transition from the hexagonal to monoclinic symmetry accompaniedby layer spacing expansion. The hydrated K_(0.4)Fe_(0.1)Mn_(0.8)Ti_(0.1)O_2 · 0.16H_2Ohas a strong tolerance to air and can be stored in lab air ambient for60 days without a change in crystal structure or chemical composition. TheK_(0.4)Fe_(0.1)Mn_(0.8)Ti_(0.1)O_2 · 0.16H_2O electrode shows improved K+ mobility andless volume change during potassiation/de-potassiation. Owing to thesemerits, K_(0.4)Fe_(0.1)Mn_(0.8)Ti_(0.1)O_2 · 0.16H_2O as the cathodes for both organic andaqueous potassium-ion full batteries attain outstanding rate capability andcycling stability (for example, capacity retention of 90% after 1000 cycles).This simple and potent hydration strategy has also been applied to improvethe air stability of other K-based layered oxides, including P3-K_(0.4)MnO_2 andP2-K_(0.5)Cu_(0.1)Fe_(0.1)Mn_(0.8)O_2, illustrating its usefulness in boosting layered oxidesfor durable potassium-ion storage.