Fading Mechanisms and Voltage Hysteresis in FeF2–NiF2 Solid Solution Cathodes for Lithium and Lithium‐Ion Batteries. Issue 6 (15th January 2019) - Huang, Qiao
Abstract: The rapid development of ultrahigh‐capacity alloying or conversion‐type anodes in rechargeable lithium (Li)‐ion batteries calls for matching cathodes for next‐generation energy storage devices. The high volumetric and gravimetric capacities, low cost, and abundance of iron (Fe) make conversion‐type iron fluoride (FeF2 and FeF3 )‐based cathodes extremely promising candidates for high specific energy cells. Here, the substantial boost in the capacity of FeF2 achieved with the addition of NiF2 is reported. A systematic study of a series of FeF2 –NiF2 solid solution cathodes with precisely controlled morphology and composition reveals that the presence of Ni may undesirably accelerate capacity fading. Using a powerful combination of state‐of‐the‐art analytical techniques in combination with the density functional theory calculations, fundamental mechanisms responsible for such a behavior are uncovered. The unique insights reported in this study highlight the importance of careful selection of metals and electrolytes for optimizing electrochemical properties of metal fluoride cathodes. Abstract : Addition of NiF2 to FeF2 and formation of FeF2 –NiF2 solid solution cathodes boost the capacity in rechargeable Li and Li‐ion batteries. Unfortunately, the presence of Ni accelerates capacity fading. By using analytical techniques in combination with modeling and simulations, the in situ formed LiNiO2 induces excessive electrolyte decomposition, which hinders the transport of ions and electrons to electrochemical reaction sites.