Layered-tunnel structured cathode for high performance sodium-ion batteries

Sodium-ion batteries (SIBs) are promising candidates for large-scale energy storage applications. High-performance cathode material with high-energy density and long cycle life is of great interest. Here, an F-doped Na x [Formula: see text]F y with layered-tunnel intergrowth structure is synthesized by a facile solid-state reaction method. The microstructure and composition of prepared material was confirmed by X-ray diffraction, field emission scanning electron microscope and transmission electron microscopy. The aim of the structure design is to combine the complementary features of high capacity from P2 phase and excellent structural stability from tunnel phase, as well as to improve rate performance by F doping. When investigated as high-rate and long-life cathode materials for Na-ion batteries, the layered-tunnel intergrowth structure exhibits synergistic effect including high discharge capacity (194.0[Formula: see text]mAh[Formula: see text][Formula: see text]), good rate capability (86[Formula: see text]mAh[Formula: see text][Formula: see text] at 15 C) as well as good cycling stability (81.2% capacity retention after 100 cycles). The as-prepared layered-tunnel intergrowth Na x [Formula: see text]F y provides new insight into the development of intergrowth electrode materials and their application in rechargeable SIBs.