Hierarchical TaO2F microspheres assembled by nanosheets and their application in infrared and microwave transparency and lithium-ion batteries

Abstract

Transition metal oxyfluorides possess enormous promise as high-performance anodes for energy storage and transparent materials for modern communication systems. In this study, a series of hierarchical TaO₂F microspheres composed of single crystalline nanosheets, were synthesized via a straightforward hydrothermal method at 160 °C for 6–48 h. The growth of TaO₂F nanosheets is governed through hydrolysis-condensation reactions of tantalum ions, enhanced by the use of acetic acid, which leads to the formation of well-defined, hierarchical microsphere structures through aggregation and self-assembly. These TaO₂F microspheres exhibit high infrared and microwave transparency, with transmittance exceeding 90 % within the 2–18 GHz frequency range at a thickness of 1.5 mm, attributable to their low imaginary permittivity, low dielectric loss tangent and well-formed crystalline structure. As anodes for LIBs, TaO₂F microspheres demonstrate good lithium storage properties including a high reversible capacity, notable high-rate capability (107 mA h g⁻¹ at 1250 mA g⁻¹), and robust cyclic stability. This performance results from a synergistic effect of a large surface area (75 m² g⁻¹), sub-50 nm particle size, and porous structure, which contribute to efficient Li ion transport and lower bandgap energy.