A High‐Capacity Cathode for Lithium Batteries Consisting of Porous Microspheres of Highly Amorphized Iron Fluoride Densified from Its Open Parent Phase

An FeF 3 cathode with very high reversible capacity, exceeding 200 mAh g −1 , is achieved by amorphizing of FeF 3 . The amorphization is achieved by densifying the open structure phase along with the removal of channel H 2 O at 0 °C in BmimBF 4 . This process is accompanied by a voltage increase of 200 mV. The generation of a hierarchical electron/ion wiring network, enabled by the interaction of ionic liquid with carbon nanotube and FeF 3 surfaces, significantly improves the reversibility.