Comprehensive Utilization Of Valuable Components In Spent Lithium Iron Phosphate Cathode Materials

With global technological,economic and industrial development,the demand for energy is increasing in all countries,and the growing scarcity of non-renewable resources is driving the rapid development of the new energy vehicle sector.With this comes the massive use and end-of-life of lithium-ion batteries,which brings new challenges to resource pressure and environmental protection.Used lithium-ion batteries are rich in metal resources,and recycling can relieve the pressure on domestic resources while achieving economic benefits.Among lithium-ion batteries,lithium iron phosphate batteries have become the mainstay due to their low cost,good safety,long cycle life,small size and light weight.However,in the recycling process,used lithium iron phosphate battery cathode material often requires multi-stage processing to extract more valuable lithium,which leads to a longer recycling process and reduces the economic benefits.In addition,there is a lack of recycling of iron and phosphorus resources in used lithium iron phosphate batteries,and current research mostly converts them into low value-added substances such as iron phosphate.Therefore,this paper takes the waste iron phosphate lithium battery cathode material as the research object,aiming to shorten the process and efficiently recycle the resources and carry out relevant basic research.The main findings are as follows:First,the thermodynamic analysis shown that the total leaching of Li,Fe and P can be achieved under strong acid/strong acid reducing conditions;the oxidative leaching under weak acid/neutral aqueous solution environment can selectively extract Li.Suitable conditions for hydrothermal synthesis of LFP:high temperature,low redox potential,weak alkaline range and excess amount of Li.The leaching rates of Li,Fe,P and Al were 99.98%,99.12%,99.16%and22.44%under the conditions of sulfuric acid concentration of 1.5 mol/L,leaching temperature of 50°C,leaching time of 90 min and liquid-solid ratio of 7:1,respectively.The material phase in the slag consisted of aluminum foil and carbon compounds that were not leached by acid.Subsequently,to improve the utilization of valuable elements in the leach solution,the loss of lithium,iron and phosphorus can be reduced while selectively precipitating aluminum,which provides a reference for the optimization of the aluminum precipitation process.By formulating simulated solutions containing different ions,the possible interactions between the ions and the mechanism of aluminum precipitation were investigated.The order of ion precipitation in the PO₄^3-system was Fe³⁺>Al³⁺>Fe²⁺>Li⁺,and the lithium loss increased at higher p H and higher precipitation amount at the end point.The phosphate in the solution is easy to generate phosphate precipitation with Al³⁺,which makes the precipitation endpoint p H smaller,indicating that phosphate removal is better than the neutralization method,which can reduce the amount of alkali in the test process while facilitating the process of aluminum precipitation.Finally,the experiment achieved selective removal of aluminum from the solution in the phosphate system by using sufficient phosphate in the solution.Under the optimal precipitation conditions:the aluminum removal rate can reach more than 99.71%,while lithium and iron lose3.77%and 13.25%respectively,which achieves selective precipitation of aluminum to a large extent.The purification solution is hydrothermally regenerated into lithium iron phosphate material according to a certain Li:Fe:P ratio to achieve a closed-loop process.The physical phase and electron microscopic energy spectrum analysis of the precipitated aluminum slag shows that the precipitated aluminum slag is mainly composed of aluminum phosphate,with a small amount of iron-containing compounds interspersed.