Regeneration Preparation Of LiFe₅O₈ By Calcination Of Na₂C₂O₄ And Spent LiFePO₄

Lithium iron phosphate（LiFePO₄）batteries have been widely used in the new energy vehicle industry in recent years.With the advent of the retirement period,their recycling and utilization as resources,economy,and ecology have attracted widespread attention.Sodium salt assisted roasting is commonly used as a dephosphorizing agent in pyrometallurgical recovery,and can separate each other by generating water-soluble sodium salts and insoluble target products.LiFe₅O₈ has the advantages of high saturation magnetization,strong thermal stability and environmental friendliness.Based on this,this paper was used spent LiFePO₄ as raw material and Na₂C₂O₄ as auxiliary material to regenerate and prepare LiFe₅O₈ using the"sodium roasting+water washing"method.The roasting recovery process and roasting process mechanism are studied,and the magnetic and electrochemical properties of LiFe₅O₈ and RGO/LiFe₅O₈are explored.The carbon footprint of the Na₂C₂O₄ roasting spent LiFePO₄ regeneration process is calculated using the full life cycle impact assessment method.The main research conclusions of this paper are as follows:（1）Using Na₂C₂O₄ as an auxiliary calciner to regenerate spent LiFePO₄ to prepare LiFe₅O₈ material,the calcination process was studied.According to TG-DSC and XRD analysis,calcination chemical reaction equations,thermodynamic analysis,and first principles calculations,it is concluded that the liquid phase of calcination water washing is Na₃PO₄,and the solid phase transformation of insoluble matter in water washing is LiFePO₄→Fe₂O₃→LiFe₅O₈→LiFe O₂.Fe₂O₃ is an important intermediate product in the calcination process.The optimal preparation conditions for LiFe₅O₈ are n（LiFePO₄）:n（Na₂C₂O₄）:n（Fe₂O₃）=1:1.5:2,with a roasting time of 3 hours and a roasting temperature of 900℃.At this time,the recovery rates of LiFe₅O₈ and Na₃PO₄ can reach 99.65%and 96.91%,respectively.（2）The RGO/LiFe₅O₈ composite material was prepared by mixing LiFe₅O₈ and RGO through ultrasound,and its magnetic and electrochemical properties were studied.The results show that the saturation magnetization of LiFe₅O₈ and RGO/LiFe₅O₈ are58.11emu/g and 60.07emu/g,respectively,and the coercivity is 72 Oe and 67 Oe,respectively,showing excellent soft magnetic properties.The electrochemical impedances of LiFe₅O₈ and RGO/LiFe₅O₈ are 158.2Ωand 105.2Ω,respectively;At1C magnification,its first discharge specific capacity as a negative electrode material is 1159.57 m A h/g and 1401.14 m A h/g,and after 50 cycles,its discharge specific capacity is 194.41 m A h/g and 252.38 m A h/g,demonstrating excellent conductivity,high discharge specific capacity,and good cycle stability.（3）Using the life cycle assessment method,the carbon footprint of Na₂C₂O₄roasted spent LiFePO₄ regenerated LiFe₅O₈ material was analyzed.Clarify the goals and scope of carbon footprint accounting for the regeneration process,analyze the life cycle inventory,establish a carbon footprint calculation model,and calculate the carbon footprint of each stage.The results showed that the carbon footprint emissions during the regeneration process of preparing 1 kg LiFe₅O₈ ranged from 8.11 to 32.48 kg CO₂eq.