FePO 4 /FeF 3 Composites as High‐Capacity, Highly Reversible Cathodes for Li‐Ion Batteries

ABSTRACT Increasing the energy density of Li‐ion batteries requires cathodes that can store more than one electron per transition‐metal center. Iron‐based conversion cathodes such as FeF 3 are attractive due to their high theoretical capacity and low cost; however, their practical performance is limited by large voltage hysteresis, sluggish kinetics, and capacity loss during cycling. Here, we report a ball‐milled FeF 3 /FePO 4 composite cathode that combines the high capacity of FeF 3 with the superior reversibility of FePO 4 . Compared to pure FeF 3 , the composite retains high capacity while exhibiting improved rate capability, lower polarization, and markedly enhanced cycling stability. After prelithiation, the composite delivers a reversible discharge capacity of 572 mAh g −1 , corresponding to a specific energy of 1175 Wh kg −1 . These results show that integration of FeF 3 and FePO 4 offers an effective route to cathodes that combine high capacity with high reversibility.