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).
Highlights
With the development of lithium-ion batteries in various fields, abundant disadvantages such as insufficient resources, high costs, and safety issues have gradually emerged, prompting people to explore sustainable alternative energy sources to meet energy storage needs (Kundu et al, 2015; Kim et al, 2016; Li et al, 2017)
When the volume of polyethylene glycol (PEG)-400 reaches 20 ml, the shape of the products turns into amethyst-like submicrospheres (∼300 nm) with porous structure (P-20, Figures 1E,F)
The particle size of FeF3·0.33H2O sub-microspheres (P-30; Supplementary Figures S1A,B) does not further decrease when the volume of PEG-400 reaches to 30 ml, which is related to chain entanglement and particle agglomeration caused by longer molecular chains of PEG-400 and excessive viscosity in the solvent (Niu and Li, 2014)
Summary
With the development of lithium-ion batteries in various fields, abundant disadvantages such as insufficient resources, high costs, and safety issues have gradually emerged, prompting people to explore sustainable alternative energy sources to meet energy storage needs (Kundu et al, 2015; Kim et al, 2016; Li et al, 2017). When the volume of PEG-400 reaches 20 ml, the shape of the products turns into amethyst-like submicrospheres (∼300 nm) with porous structure (P-20, Figures 1E,F).
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