Study On High Value Recycling Technology Of Spent Lithium Iron Phosphate Black Powder

Lithium iron phosphate（LiFePO₄）batteries are widely used in electric vehicles,large-scale energy storage and other fields because of their low cost,high safety and long life.As its production and use increases year by year,there will inevitably be a large number of LiFePO₄ batteries at end-of-life in the future.If not effectively recycled,it will not only cause waste of resources,but also bring serious environmental pollution.Therefore,it is important to develop a low-cost and high-value recovery technology for LiFePO₄ black powder.Based on this,two resourceful reuse technologies for dry remediation and wet recovery of LiFePO₄ black powder are investigated in this paper.Firstly,the dry repair strategy of LiFePO₄ black powder was investigated.The effects of ball milling method,calcination temperature,sucrose content and lithium carbonate addition on the properties of the regenerated material were investigated.The discharge specific capacities of the regenerated material obtained at calcination temperature of 700℃,sucrose addition of 20 wt.%and lithium carbonate addition of0.4 wt.%was 152.4 and 113.9 m Ah g^-1 at 0.2 and 2 C and the capacity retention rate of 91.7%for 100 cycles at 0.2 C.The difference in performance between the dry-repaired LiFePO₄ black powder and commercial LiFePO₄ may be due to the high impurity content in the LiFePO₄ black powder,which reduces the electrochemical performance of the material.Secondly,the wet regeneration process was used to regenerate the LiFePO₄material.To avoid the influence of impurities in the black powder on the performance of the regenerated LiFePO₄ material,as well as to avoid the corrosion of the equipment and the problem of acidic waste water generated by conventional acidic solvents,ammonium sulfate was directly used as leaching agent and the solution recycling was adopted to obtain lithium carbonate and iron phosphate.At a solids content of 150 g L^-1 in the spent LiFePO₄ and deionised water and 1.3 times the theoretical addition of ammonium persulphate,the purity of the lithium carbonate obtained was greater than 99%,and the recovery of lithium carbonate was increased to 96%and the recovery of iron phosphate was stabilised at 97%in the seventh closed-loop recovery.The LiFePO₄ was regenerated by adding anhydrous glucose to the obtained ferric phosphate and lithium carbonate,and the specific capacity of the regenerated material was 163.9 and 124 m Ah g^-1 at 0.1 and 4 C,respectively,and155.1 m Ah g^-1 after 95 weeks at 0.2 C.The electrochemical properties of the materials obtained by wet regeneration were superior to those obtained by dry restoration.In summary,to achieve low cost and high value recovery of LiFePO₄ black powder,two technical routes,dry remediation and wet recovery,were developed in this thesis.The effect of heat treatment temperature and different material ratios on the performance of the rehabilitated LiFePO₄ material in dry repair was investigated,and a direct recovery route using ammonium persulphate as leaching agent to extract iron phosphate and lithium carbonate was developed,avoiding the problems of corrosion of equipment and difficult treatment of wastewater by conventional acidic solvents,and avoiding the effect of impurities in the black powder on the performance of the rehabilitated material,resulting in a high performance rehabilitated The final result is a high performance regenerated lithium iron phosphate.This thesis provides a useful reference for the low-cost and high-value recovery of LiFePO₄ black powder.