High entropy fluorides as conversion cathodes with tailorable electrochemical performance

Abstract

With the recent development of high entropy materials, an alternative approach to develop advanced functional materials with distinctive properties that show improved values compared to conventional materials has been provided. The high entropy concept was later successfully transferred to metal fluorides and high entropy fluorides (HEFs) were successfully synthesized. Owing to their high theoretical specific capacities in energy storage applications, HEFs were utilized as cathode materials for lithium-ion batteries (LIBs) and their underlying storage mechanisms were investigated. Instead of a step-by-step reduction of each individual metal cation, the HEFs seem to exhibit a single-step reduction process, indicating a solid solution compound instead of merely a mixture of different metal fluorides. It was also observed that the electrochemical behavior of the HEFs depends on each individual incorporated element. Therefore, by altering the elemental composition, new materials that exhibit improved electrochemical properties can be designed. Remarkably, HEFs with seven incorporated metal elements exhibited a better cycling stability as well as a lower hysteresis compared to binary metal fluorides. These findings offer new guidelines for material design and tailoring towards high performance LIBs.