Flowerlike Mesoporous FeF₃·0.33H₂O with 3D Hierarchical Nanostructure: Size-Controlled Green-Synthesis and Application as Cathodes for Na-Ion Batteries

A flowerlike mesoporous FeF3·0.33H2O with three-dimensional (3D) hierarchical nanostructure is successfully prepared for the first time through a facile PEG-assisted solvothermal route. By rationally regulating and controlling the amount of PEG-400 in solvent, a series of nanostructured FeF3·0.33H2O materials with various morphologies and sizes is obtained. The probable formation mechanism related to the role of the PEG is explored. Furthermore, the electrochemical performances of the as-prepared samples for Na-ion battery (NIB) are investigated and discussed. The flower-like mesoporous FeF3·0.33H2O can deliver the noticeable initial discharge capacity of 283 mAh g–1 and retain 190 mAh g–1 after 100 cycles within a potential range of 1.5–4.5 V at 0.1 C. Particularly, even at a high rate of 2.0 C, the material can still exhibit a high capacity of 155 mAh g–1. The excellent electrochemical performances can be attributed to the unique 3D hierarchical porous nanostructure and the small particle size, which can provide large electrode/electrolyte contact area and abundant Na storage sites, facilitate rapid electronic and ionic transportation as well as electrolyte penetration, and accommodate the volume changes of the FeF3·0.33H2O cathode materials. Therefore, this work provides a facile and scalable strategy to prepare high-performance cathode active materials in the applications of high-capacity NIB.