A New Class of High-Capacity Fe-Based Cation-Disordered Oxide for Li-Ion Batteries: Li-Fe-Ti-Mo Oxide

Low-cost Fe can be used for forming cation-disordered rocksalt Li-excess (DRX) materials instead of high-cost d(0)-species and then the Fe-based DRX can be promising electrode materials because they can theoretically achieve high capacity, resulting from additional oxygen redox reaction and stable cation-disordered structure. However, Fe-based DRX materials suffer from large voltage hysteresis, low electrochemical activity, and poor cyclability, so it is highly challenging to utilize them as practical electrode materials for a cell. Here, novel high-capacity Li-Fe-Ti-Mo electrode materials (LFTMO) with high average discharge voltage and reasonable stability are reported. The effect of Ti/Mo on electrochemical reactions in Fe-based DRX materials (LFTMO) is studied by controlling its composition ratio and using techniques for analyzing the local environment to find the key factors that improve its activity. It is found out that the introduction of appropriate quantity of redox-active Mo4+/5+ to Fe-based DRX materials can help stabilize the oxygen redox reaction via changing a local structure and can suppress a Fe redox reaction, which can cause poor performance. The understandings will help develop high capacity and long cyclability Fe-based DRX electrode materials.

Automated summary

Low-cost Fe can be used as an alternative to high-cost d(0)-species for the formation of cation-disordered rocksalt Li-excess (DRX) materials. However, Fe-based DRX materials have several challenges, such as large voltage hysteresis, low electrochemical activity, and poor cyclability. In this study, a novel Li-Fe-Ti-Mo electrode material (LFTMO) with high capacity and reasonable stability is reported. The introduction of redox-active Mo4+/5+ into Fe-based DRX materials helps stabilize the oxygen redox reaction and suppress the Fe redox reaction, improving the performance of the electrode material.