Research On The Rapid Regeneration Of Waste LiNi_0.6Co_0.2Mn_0.2O₂ Cathode Materials By Enhanced Acid Leaching

Li Ni_xCo_yMn_1-x-yO₂ ternary materials has become the mainstream key material in the field of electric vehicles and energy storage due to its high energy density,excellent cycle performances,stable platform,etc.As its demand and output increase year by year,a large number of spent ternary lithium batteries has explosively produced.How to achieve their efficient and clean recycling is not only a realistic guarantee for the safe supply of resources,but also a strategic requirement for the construction of an ecological civilization.In order to solve the problems of the environment pollution of using inorganic acid in leaching system,and the long and complication of regeneration process in ternary materials recycling,this thesis focuses on the following:1.In view of environmental pollution of inorganic acid and difficulty treat of waste liquid in leaching system,a new method of leaching Li Ni_0.6Co_0.2Mn_0.2O₂material with ultrasound-assisted DL-malic acid was proposed.Li Ni_0.6Co_0.2Mn_0.2O₂materials were prepared from the leachate by carbonate co-precipitation solid phase sintering method.After the spent ternary materials obtained from pretreatment,the effect of various conditions on the metal leaching efficiency was investigated and the leaching kinetics were studied.The microscopic changes of the leaching filter residue were analyzed by SEM and FT-IR.The precursor that synthesized from the leaching filtrate at p H=8.5 was preheated at 450°C for 5 h and then sintered at 800-900°C for 12 h to regenerate Li Ni_0.6Co_0.2Mn_0.2O₂ materials.Then that was passed by XRD,SEM,electrochemical test,etc.The effects of the second stage calcination temperature on the structure,morphology,and electrochemical performance of Li Ni_0.6Co_0.2Mn_0.2O₂were studied.The results show that the optimal leaching conditions:ultrasound intensity of 90 W,DL-malic acid concentration of 1.0 mol/L,solid-liquid ratio of 5g/L,H₂O₂ concentration of 4 vol%,temperature of 80°C,leaching time of 30 min.Under these conditions,the leaching efficiencies of Ni,Co,Mn,and Li were 97.8%,97.6%,97.3%,and 98%,respectively.The leaching kinetics conforms to the log rate law model,and the leaching activation energy of Ni,Co,Mn,Li are 49.72 k J/mol,48.33 k J/mol,46.43 k J/mol,41.92 k J/mol,respectively.The electrochemical performance of the sample synthesized at 850°C is the best.The first discharge specific capacity at a current density of 0.1 C is 169.4 m A h g^-1,and the first discharge specific capacity at a rate of 1 C is 154.9 m A h g^-1.After 100 cycles,the discharge specific capacity was 131.8 m A h g^-1,and the capacity retention efficiency were 85.1%.2.In view of the shortcomings of complicated process control in the existing recycling process,a new method of Li Ni_0.6Co_0.2Mn_0.2O₂ was proposed by preparing precursor directly from the leaching solution and regenerating cathode materials with high temperature calcination.The precursor was directly prepared by spray drying from the leaching solution with the ratio of n(Ni):n(Co):n(Mn)=3:1:1,n(Li):n(Ni+Co+Mn)=1.05 controlled by adding the corresponding acetates.The calcination temperature,structure and morphology of Li Ni_0.6Co_0.2Mn_0.2O₂ precursor were characterized by TG/DSC,XRD,SEM.The precursor was preheated at 450°C for 5 h and then sintered at 800-900°C for 12 h to regenerate Li Ni_0.6Co_0.2Mn_0.2O₂materials.XRD,FTIR,SEM,HRTEM,and electrochemical tests were used to character the effects of the amount of malic acid and the calcination temperature on the structure,morphology,and electrochemical performance of the material.The electrochemical performance of Li Ni_0.6Co_0.2Mn_0.2O₂ was the better when the ratio of malic acid to(Ni+Co+Mn+Li)was 1:2 and the temperature was 850°C.The first discharge specific capacity is 165.3 m A h g^-1 at a current density of 0.1 C,and the specific discharge capacity is 158.9 m A h g^-1 for the first cycle at a rate of 1 C,and the charge and after 100 discharge cycles at a rate of 1 C,and the capacity retention rate is 86.7%.And it still can provide a specific discharge capacity of 136.1 m A h g^-1 at 5 C rate,this means it has a good rate performance.