The development of electrocatalysts for the oxygen evolution reaction (OER) is one of the principal challenges in the area of renewable energy research.
Fluorine is known to be a key element for various components
of
batteries since current electrolytes rely on Li-ion salts having fluorinated
ions and electrode binders are mainly based on fluorinated polymers.
Metal fluorides or mixed anion metal fluorides (mainly oxyfluorides)
have also gained a substantial interest as active materials for the
electrode redox reactions. In this review, metal fluorides for cathodes
are considered; they are listed according to the dimensionality of
the metal fluoride subnetwork. The synthesis conditions and the crystal
structures are described; the electrochemical properties are briefly
indicated, and the nature of the electron transport agent is noted.
We stress the crucial importance of the elaboration processes to induce
the presence of cation disorders, of anion substitutions (mainly F–/O2– or F–/OH–) or vacancies. Finally, we show that an accurate structural
characterization is a key step to enable enhanced material performances
to overcome several lasting roadblocks, namely the large irreversible
capacity and poor energy efficiency that are frequently encountered.
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