Study On Hydrometallurgical Recovery And Lithium Supplementation Mechanism Of Cathode Materials For Power Battery

Environmental pollution and energy shortage have promoted the sustained and explosive growth of the new energy vehicle.As the power source of new energy vehicles,the number of lithium-ion power batteries has also soared.Waste power batteries belong to the category of serious pollution solid waste.If waste batteries are not properly treated,it will cause serious environmental pollution and waste of resources,such as waste of valuable metal resources,heavy metal pollution,electrolyte and organic solvent pollution.Therefore,efficient recycling of used power batteries is an important measure to achieve efficient use of resources and mitigate environmental pollution.This article mainly focuses on the recycling of cathode materials for two mainstream lithium-ion batteries for new energy vehicles:ternary lithium-ion batteries and lithium iron phosphate batteries.The main contents are generalized as follows:?1?For different cathode materials,different methods of stripping collection were used to establish a pre-treatment process?deep discharge,dismantling,classification and peeling,etc.?of the waste power batteries.The waste cathode materials were characterized by relevant tests to verify the failure mechanism of ternary materials and LiFePO₄.And according to the failure mechanism of different materials,corresponding recycling processes are designed.?2?"Hydrothermal leaching"was adopted to recycle scrapped ternary material LiNi_0.6Co_0.2Mn_0.2O₂.The high temperature and high pressure conditions of the hydrothermal reaction are used to improve the leaching efficiency of valuable metals.The effects of process conditions on the leaching rate of valuable metals in waste ternary materials were studied.The results show that when the hydrothermal temperature,leaching time and solid-liquid ratio are 150?,8 h and 20 g L^-1,respectively,in 0.5 M H₂SO₄ solution,the leaching efficiency of Ni,Co,and Mn valuable metals is higher than 90%.?3?The regenerated ternary material LiNi_0.6Co_0.2Mn_0.2O₂ was successfully synthesized by closed-loop recovery of valuable metals in the leaching solution by co-precipitation.The effects of calcination process and Na-F ion doping on material properties were studied.The experimental results show that the gradient calcination can effectively slow down the crystalline transition speed of ternary material,reduce lattice defects,improve the integrity and stability of the layered structure.Among them,the ternary material synthesized by the optimal process has the initial discharge of 177.9 mAh g^-1 and the capacity retention rate up to 82.07%?0.2 C cycle for 100 times?.Na-F doping can reduce the cation mixing of materials,stabilize the layered structure,improve the cycle and rate performance.When the doping amount is 0.02,the regenerated ternary material Li_1-xNa_xNi_0.6Co_0.2Mn_0.2O_2-xF_x has the highest initial discharge capacity of 176.37 mAh g^-1 and the best rate performance and higher capacity retention rate of 87.48%?0.2 C cycle for 100 times?.?4?The scrapped LiFePO₄ materials are repair by the replenishment of lithium with two processes:solid-phase and hydrothermal reaction.In the former case,the lithium of Li₂CO₃is replenished into scrapped LiFePO₄ through the traditional method of solid-phase carbon reduction.In the latter case,the lithium in LiOH solution is is replenished into scrapped LiFePO₄ through hydrothermal reaction,and the crystallinity of regenerated material is increased by annealing after hydrothermally reaction.The Research results show that the materials regenerated by the hydrothermal reaction+annealing process are superior to the traditional solid-phase reaction in terms of purity,crystal structure,and electrochemical performance.Among them,the first discharge capacity and capacity retention rate?0.2 C cycle for 100 times?of LiFePO₄ regenerated by the hydrothermal reaction were 144.02 mAh g^-1 and 92.36%,respectively,while the performance of LiFePO₄ regenerated by solid-phase reaction were 135.13 mAh g^-1 and 89.5%,respectively.