Process for obtaining ferric phosphate and lithium iron phosphate, and applications

Abstract

The present invention relates to a process for obtaining high-purity ferric phosphate (FePO4) from ferric polysulfate (PSF), and its use as a precursor for the preparation of an iron-lithium phosphate material with a NASICON-type structure. The process comprises adding a ferric polysulfate solution to a phosphorus source in an aqueous medium, forming a ferric phosphate suspension, followed by solid / liquid separation, washing, hydrothermal treatment, and calcination, yielding high-purity ferric phosphate with a near-stoichiometric phosphorus-to-iron molar ratio and an α-quartz crystal structure. This ferric phosphate can then be subjected to a conversion step in the presence of at least one lithium source and at least one reducing agent, under controlled pH conditions, an inert atmosphere, and hydrothermal treatment, to obtain an iron-lithium phosphate material with the formula Li3Fe2(PO4)3 and a NASICON-type structure.The material thus obtained is useful in the manufacture of electrodes or cathodes for electrochemical devices and in electrochemical extraction processes of lithium from brines.