High-Performance Rechargeable Aluminum-Ion Batteries Enabled by Composite FeF3 @ Expanded Graphite Cathode and Carbon Nanotube-Modified Separator

Rechargeable aluminum ion batteries (AIBs) are one of the most promising battery technologies for future large-scale energy storage due to their high theoretical volumetric capacity, low-cost, and high safety. However, the low capacity of the intercalation-type cathode materials reduces the competitiveness of AIBs in practical applications. Herein, a conversion-type FeF 3 -expanded graphite (EG) composite is synthesized as a novel cathode material for AIBs with good conductivity and cycle stability. Combined with the introduction of a single-wall carbon nanotube modified separator, the shuttle effect of the intermediate product, FeCl 2 , is significantly restrained. Moreover, enhanced coulombic efficiency and reversible capacity are achieved. The AIB exhibits a satisfying reversible specific capacity of 266 mAh g −1 at 60 mA g −1 after 200 cycles, and good Coulombic efficiency of nearly 100% after 400 cycles at a current density of 100 mA g −1 . Ex situ X-ray diffraction and X-ray photoelectron spectroscopy are applied to explore the energy storage mechanism of FeF 3 in AIBs. The results reveal that the intercalation of Al 3+ species and the reduction of Fe 3+ species occurrs in the discharge process. These findings are meaningful for the fundamental understanding of the FeF 3 cathode for AIBs and provide unprecedented insight into novel conversion type cathode materials for AIBs.