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

Potassium (K)-based layered oxides are potential candidates for K-ion storage but they suffer from chemical instability under ambient conditions that deteriorate their performance in rate-capability and cycle life. To tackle this issue, a facile hydration strategy is employed, in which H2O molecules are introduced into the K ion layers of P3-type K0.4Fe0.1Mn0.8Ti0.1O2, which induces a phase transition from the hexagonal to monoclinic symmetry accompanied by layer spacing expansion. The hydrated K0.4Fe0.1Mn0.8Ti0.1O2 center dot 0.16H(2)O has a strong tolerance to air and can be stored in lab air ambient for 60 days without a change in crystal structure or chemical composition. The K0.4Fe0.1Mn0.8Ti0.1O2 center dot 0.16H(2)O electrode shows improved K+ mobility and less volume change during potassiation/de-potassiation. Owing to these merits, K0.4Fe0.1Mn0.8Ti0.1O2 center dot 0.16H(2)O as the cathodes for both organic and aqueous potassium-ion full batteries attain outstanding rate capability and cycling stability (for example, capacity retention of 90% after 1000 cycles). This simple and potent hydration strategy has also been applied to improve the air stability of other K-based layered oxides, including P3-K0.4MnO2 and P2-K0.5Cu0.1Fe0.1Mn0.8O2, illustrating its usefulness in boosting layered oxides for durable potassium-ion storage.

Automated summary

This study presents a hydration strategy to enhance the stability of potassium-based layered oxides for potassium-ion storage, improving their rate capability and cycle life. The introduction of water molecules induces a phase transition and expands the layer spacing, leading to improved K+ mobility and less volume change during the ion storage process. The hydrated oxides exhibit outstanding rate capability and cycling stability, making them promising cathodes for potassium-ion batteries.