High-Performance Cathode of Sodium-Ion Batteries Enabled by a Potassium-Containing Framework of KMnFeTiO.

Sodium-ion batteries (SIBs) are promising candidates for large-scale electric energy storage with abundant sodium resources. However, their development is challenged by the availability of satisfactory cathode materials with stable framework to accommodate the transportation of large-sized Na (1.02 Å), whose continuous insertion/extraction can easily cause irreversible volumetric deformation in the crystalline material, leading to inevitable structural failure and capacity fading. Here, different from the previous synthesis efforts targeting at Na containing compounds, we unveil the possibility of achieving a highly reversible sodiation/desodiation process by resorting to a K-based layered metal oxide formulated as KMnFeTiO (KMFT), which is a P2 type in structure with a wide interlayer spacing to sit K (1.38 Å). We demonstrate that an initial K/Na exchange can introduce Na into the lattice while a small amount of K remains inside, which plays a significant role in ensuring enlarged channels for a fast and stable Na diffusion. The KMFT electrode delivers a high initial discharge capacity of 147.1 mA h g at 10 mA g and outstanding long cycling stability with capacity retention of 71.5% after 1000 cycles at 500 mA g. These results provide a new design strategy for the development of stable SIBs cathodes to facilitate their future applications.