Ternary metal fluorides as high-energy cathodes with low cycling hysteresis

• Published in: Nature communications Vol. 6; no. 1; p. 6668
• Main Authors: Wang, Feng, Kim, Sung-Wook, Seo, Dong-Hwa, Kang, Kisuk, Wang, Liping, Su, Dong, Vajo, John J., Wang, John, Graetz, Jason
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 26.03.2015; Nature Publishing Group; Nature Pub. Group
• Subjects: 639/301/1023/1026; 639/301/299/161/891; 639/301/930/1032; 639/638/440; Humanities and Social Sciences; MATERIALS SCIENCE; multidisciplinary; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms7668

Transition metal fluorides are an appealing alternative to conventional intercalation compounds for use as cathodes in next-generation lithium batteries due to their extremely high capacity (3–4 times greater than the current state-of-the-art). However, issues related to reversibility, energy efficiency and kinetics prevent their practical application. Here we report on the synthesis, structural and electrochemical properties of ternary metal fluorides (M 1 y M 2 1- y F x : M 1 , M 2 =Fe, Cu), which may overcome these issues. By substituting Cu into the Fe lattice, forming the solid–solution Cu y Fe 1- y F 2 , reversible Cu and Fe redox reactions are achieved with surprisingly small hysteresis (<150 mV). This finding indicates that cation substitution may provide a new avenue for tailoring key electrochemical properties of conversion electrodes. Although the reversible capacity of Cu conversion fades rapidly, likely due to Cu + dissolution, the low hysteresis and high energy suggest that a Cu-based fluoride cathode remains an intriguing candidate for rechargeable lithium batteries. Transition metal fluorides have high theoretical specific capacities as cathodes for lithium ion batteries, but low working potentials and poor energy efficiency limit their practical applications. Here, the authors report a group of ternary metal fluorides, which may overcome these problems.