FeOF/TiO₂ Hetero-Nanostructures for High-Areal-Capacity Fluoride Cathodes

Iron fluoride compounds offer an exciting pathway toward low-cost and high-capacity conversion-type lithium-ion battery (LIB) cathodes. However, due to the sluggishness of the electronic and ionic transport in iron fluorides, mass loadings of active materials in previous studies are typically less than 2.5 mg cm–2, which is too low for practical applications. Herein, we improve the charge transport in fluoride electrodes at both nano- and mesoscales to enable high-mass-loading fluoride electrodes. At the nanoscale, we prepare electronically conducting LixTiO2 composites with FeOF nanoparticles to reduce electron transport distance to 5–10 nm, which is one of the shortest among reports. At the mesoscale, we design a percolating three-dimensional porous carbon nanotube (CNT) network to enable fast pathways for both electrons and ions. The resulting spongelike material, FeOF/TiO2@CNT, substantially enhances the kinetics of the conversion reaction in FeOF, boosts extra lithium storage capacity, and reduces the voltage hysteresis. Steady cycling over 300 cycles is achieved at a high mass loading of 8.7 mg cm–2 (FeOF/TiO2) (1.74 mAh cm–2). Such areal capacity of lithium storage is significantly higher than previously reported iron fluorides-based structures, a significant step forward toward the development of low-cost metal fluoride electrodes.