AUTHOR=Song Weibing , Lu Hongyu , Zhao Wenlong , Cao Xiaofei , Yan Lei , Zhao Jingxin , Li Neng , Tang Yuxin , Hu Jun TITLE=Control of Shape and Size in Iron Fluoride Porous Sub-Microspheres: Consequences for Steric Hindrance Interaction JOURNAL=Frontiers in Nanotechnology VOLUME=3 YEAR=2021 URL=https://www.frontiersin.org/journals/nanotechnology/articles/10.3389/fnano.2021.710348 DOI=10.3389/fnano.2021.710348 ISSN=2673-3013 ABSTRACT=

Iron-based fluorides are promising alternates for advanced sodium-free battery cathodes due to their large theoretical capacity. However, the rational structural control on the iron-based fluorides toward high-performance batteries is still challenging. To this end, a controllable porous structure on FeF3·0.33H2O sub-microspheres is achieved by a polyethylene glycol (PEG)-assisted hydrothermal method via adjusting the volume of PEG-400. Experimental and molecular dynamic results verify that the formation of small amethyst-like sub-microspheres is mainly ascribed to the steric hindrance reaction of PEG-400, which makes it difficult for F− to combine with Fe3+ to form coordination bonds, and partially hinders the nucleation and growth of FeF3·0.33H2O nanospheres. As a sodium-free battery cathode, the FeF3·0.33H2O sub-microspheres with porous structure and smaller particle size exhibit excellent electrochemical performance with regard to cycle capacity and rate capability (a remaining capacity of 328 mAh g−1 and up to 95.3% retention rate when backs to 0.1 C after 60 cycles).