Research On The Recycling Of Waste Lithium Iron Phosphate Cathode Materials And The Effect Of Impurities On Material Performance

High-temperature regeneration and hydrometallurgy are the two mainstream ways to recover LiFePO₄cathode materials from failed lithium-ion batteries,however,the high-temperature regeneration process is accompanied by the disadvantages of high energy consumption and the influence of impurities,while hydrometallurgy consumes large amounts of acid and generates large amounts of wastewater.To address the shortcomings of the current recycling methods for used lithium iron phosphate cathode materials,this paper uses a combination of high-temperature regeneration and hydrometallurgy to recover used lithium iron phosphate cathode materials,with the innovative use of phosphoric acid-assisted roasting to recover Li,Fe,and P elements.In addition,based on the characteristics of Al,Fe,Cu itself,impurity removal treatment has been a difficult point of lithium-ion battery lithium iron phosphate recycling,so this paper also studied the effect of different metal cations Al³⁺,Cu²⁺and Fe³⁺fugitive state on the electrochemical properties of lithium iron phosphate cathode material,the main contents are:（1）Phosphoric acid-assisted roasting was used to recover used LiFePO₄cathode materials under oxygen atmosphere.with a molar ratio of H₃PO₄to LiFePO₄of 0.52:1,a roasting temperature of 350℃,a hydrochloric acid concentration of 0.5 mol/L,a leaching time of 2.5 h,a liquid-to-solid ratio of 12 mL/g,and a leaching temperature of 55°C,the leaching rates of was 80.12%and that of Fe was 3.55%.Li was recovered in the form of Li₃PO₄,and the recycled Li₃PO₄was used as the lithium source,the solid filtrate as the iron source to resynthesize the lithium iron phosphate cathode material by carbon thermal reduction.XRD shows that the regenerated lithium iron phosphate cathode material is a standard olivine structure,XPS shows that the regenerated lithium iron phosphate material contains Fe³⁺impurities,the first week discharge capacity of the regenerated LiFePO₄at a current density of 0.1 C is133.5 mAhg^-1,and the capacity retention rate is 87%after 100 cycles at a current density of 1 C.The regenerated LiFePO₄can still work normally under large multiplier charge/discharge conditions.（2）The introduction of metal cation impurities,including Al₂O₃,Fe₂O₃,CuO,AlPO₄,FePO₄,and Cu₃（PO₄）₂,into the lithium iron phosphate cathode material was investigated in this study.XRD,SEM,and XPS analysis indicated that the structure and morphology of the cathode material were not significantly affected by the introduced cation impurities.However,during the structural repair process,it was found that the impurities had a considerable impact on the electrochemical performance of the material.Electrochemical testing and analysis revealed that the phosphate impurity Fe PO₄had the least effect on the first week discharge specific capacity,cycling,and multiplier performance of the LiFePO₄battery,followed by AlPO₄.In contrast,the Cu₃（PO₄）₂impurity had a more significant effect on the multiplier performance,with a low discharge of 5 mAhg^-1at 5 C.Among the oxide class impurities,Al₂O₃had little effect on the first week Coulomb efficiency of LiFePO₄,but the first week charge/discharge specific capacity decreased to 119mAhg^-1,and the capacity retention was 96%after 100 cycles.The cyclic voltammetry curve shows that the potential difference between the oxidation and reduction peaks of Fe₂O₃impurity is the largest,indicating that the Fe₂O₃impurity has the greatest effect on the reversibility of lithium iron phosphate.the Cu O impurity has the greatest effect on the multiplicity of lithium iron phosphate,which cannot be charged and discharged normally at 5 C.Based on comprehensive analysis,oxide-type cation impurities had a more significant impact on the electrochemical performance of the lithium iron phosphate cathode material than phosphate-type cation impurities.