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

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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.
Funding Information
  • U.S. Department of Energy
  • Office of Science
  • Basic Energy Sciences (DE‐SC0023408)
  • Basic Energy Sciences (DE‐AC0276SF00515)

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