Production of LiFePO₄ by Using Steelmaking Slag as a Phosphorus Source

Abstract

The usage of LiFePO₄ (LFP) battery cathodes for electric vehicles (EVs) has increased in recent years. Phosphorus for LFP will be required for a comparable amount of fertilizer. However, the economically minable phosphate rock mines are decreasing, and the market for phosphorus is already tight. Thus, it is urgently necessary to promote the production of LFP based on secondary phosphorus resources. In this study, the production of LFP using phosphorus recovered from steelmaking slag was investigated. After selective leaching of steelmaking slag, the phosphorus in the extract is precipitated as FePO₄ by titration with FeCl₃ at pH=3. The FePO₄ was mixed with LiOH·H₂O and glucose (C₆H₁₂O₆) and heat treated at 700°C to prepare LFP. The FeCl₃ titration amount should be controlled within 0.6 stoichiometric mole ratio of Fe³⁺ to phosphorus to avoid the Fe₃PO₇ generation. The glucose should be mixed at the mole ratio of FePO₄/C=1.0 to prevent the Fe³⁺ from being over-reduced to Fe. The other elements, Ca, Si, Mg, Al, and Mn in the slag extract, did not affect the crystallization process and the structure of FePO₄ and LFP. The present study confirmed the feasibility of using steelmaking slag as a source of phosphorus for the preparation of LFP.