Iron (II) fluoride cathode material derived from MIL-88A

Abstract

We report an eco-friendly, simple, and scalable method of FeF 2 cathode production. MIL-88A was synthesized in a water medium without any additives. It was used as a source of iron (3 +) ions during pyrolysis. The porous structure of such a sacrificial agent allowed us to incorporate poly-vinylidene fluoride molecules as a guest component into a host MIL-88A framework. Pyrolysis in Ar-flow results in two simultaneous processes: reducing Fe 3+ into Fe 2+ and forming porous carbon shells for FeF 2 nanoparticles. Applying complex analysis of high-resolution TEM images, porosity measurements, and XANES spectroscopy, we have revealed that obtained iron fluoride is composed of nanoparticles with elongated and hexagonal shapes. Both iron fluorides were attributed to tetragonal FeF 2 structure type, contained only Fe 2+ ions, and were covered with porous carbon shells. The obtained material was used as a cathode for a lithium-ion battery and showed good stability and a high capacity of 425–330 mA h/g. The proposed water-based synthesis of MIL-88A as a precursor in combination with mild pyrolysis conditions and good electrochemical performance make this material promising for cathode application. • We report the green and reproducible synthesis of MIL-88a. • For the first time, MIL-88a was applied as an iron and carbon source to produce FeF 2 . • MIL-88a was used as a host for polyvinylidene fluoride. • We obtained stable FeF 2 nanoparticles in a porous conductive carbon matrix. • This material was tested in a lithium-ion battery as a conversion cathode.