FePO₄/FeF₃ Composites as High-Capacity, Highly Reversible Cathodes for Li-Ion Batteries

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 FeF₃ 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 FeF₃/FePO₄ composite cathode that combines the high capacity of FeF₃ with the superior reversibility of FePO₄. Compared to pure FeF₃, 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 FeF₃ and FePO₄ offers an effective route to cathodes that combine high capacity with high reversibility.