Self-assembled FeF₃ nanocrystals clusters confined in carbon nanocages for high-performance Li-ion battery cathode

With the revival of lithium metal anodes, there is an urgent need for matching cathodes to form the next generation batteries with high-capacity and low-cost. A porous hierarchical structure containing FeF₃ nanocrystals (3–9 nm) capsulated in conductive carbon nanocages (40–110 nm) was fabricated. The morphology and size of the FeF₃ nanocrystals were influenced by the existence of carbon nanocage. During the preparation process, the carbon nanocage inhibited the growth of FeF₃ crystals. During the dis/charge process, the carbon nanocages not only restricted the complex conversion reaction (Fe³⁺ ⇄ Fe²⁺ ⇄ Fe) within the confined space, but also functioned as a bridge for the transmission of electrons, thus enhancing the electrochemical performance of the electrode. As a result, the FeF₃/C electrode delivered an excellent reversible capacity of 410 mA h g⁻¹ over 120 cycles at 100 mA g⁻¹.