FeF3·0.33H2O@C nanocomposites derived from pomegranate structure as high-performance cathodes for sodium- and lithium-ion batteries

Iron fluoride is an excellent cathode material for alkali metal-ion batteries due to its high operating voltage and extremely high specific discharge capacity. To overcome its voltage hysteresis and compensate for capacity fading due to volume change and electrode dissolution, a FeF3·0.33H2[email protected] nanocomposite with a pomegranate-like structure (FeF3·0.33H2[email protected]) is designed and successfully synthesized via hydrothermal synthesis followed by a solid-phase process. The FeF3·0.33H2[email protected] nanocomposite derived from pomegranate structure effectively can reduce electrode polarization via its unique hierarchical carbon-coated architecture. Additionally, combining other structural advantages (e.g., coordination of volume expansion, reduction of Fe dissolution, and inhibition of nanoparticle coarsening) can result in high reversibility and rate performance. For Lithium-ion battery, the nanocomposite cathode demonstrates a discharging capacity of 225 mA h g−1 at 0.1C, as well as an excellent long-cycle performance with a capacity retention rate of 93% after 200 cycles. When the cathode materials are used in sodium-ion batteries, the nanocomposite cathode achieves an exceptionally high energy density of 1015 Wh kg−1, which is more than twice that of the commercial LiCoO2 cathode (504 Wh kg−1).