Study On Recycle And Reuse Of Ternary Cathode Materials From Waste Lithium-ion Batteries

Lithium-ion batteries are widely used in electric vehicles and communications due to their ultrahigh energy density and good cycle performance.The outputs of lithium-ion batteries increased year by year and showed a significant impact on our daily life.However,lithium batteries will always be discarded after they reach their useful life.If they are buried deeply by solidification or stored in waste mines,valuable metals such as Ni and Co,and other materials will be desert which cause huge waste of resources.In addition,toxic substances will cause serious environmental pollution and ecological destruction.All of the points mentioned above show that the recycling and reuse of discarded lithium-ion batteries is particularly important.Therefore,this subject has systematically studied the recovery and reuse of lithium nickel cobalt manganese oxide?hereinafter referred to as"ternary"?cathode materials used in lithium ion batteries.The main research contents are as follows:Separation of the positive electrode material and the current collector is accomplished by selecting a suitable solution.Firstly,the waste battery was discharged completely and then it was disassembled manually.The SEM,XRD,DSC and FT-IR characterization were carried out on the cathode material of the used battery.It was found that the binder used in the battery is PTFE,and the cathode material is lithium nickel cobalt manganese oxide.The positive electrode material and the aluminum foil were separated by means of alkali leaching.In order to avoid the pollution problem from recycling the cathode materials by using the inorganic acid,environmental and friendly citric acid is used as the leaching acid,and hydrogen peroxide is used as the reducing agent to extract the ternary cathode material.The effects of parameters such as leaching acid concentration,solid-liquid ratio,reaction temperature,reducing agent content and reaction time for the leaching efficiency of valuable metals were systematically studied.The leaching efficiency distribution of nickel,cobalt,manganese and lithium was 95.3%,94.2%,96.2%and98.2%under the optimal parameters?citric acid concentration is 1.5 mol/L,solid-liquid ratio is 20 g/L,reaction temperature is 70°C,reducing agent content is 2 vol%,reaction time is 60 min?.In order to obtain the ternary cathode materials with good morphology and electrochemical properties,the ternary cathode materials precursor Ni_0.8Co_0.1Mn_0.1?OH?₂were prepared by co-precipitation.The effects of feed rate,aging time,reaction pH and complexing agent concentration on the morphology of the precursor were studied systematically.The spherical precursor materials with good morphology and high density were obtained when the feed rate was 0.6 mL/min,the aging time was 16 h,and the reaction pH was 11.0 and the concentration of the complexing agent is 0.4 mol/L.LiNi_0.8Co_0.1Mn_0.1O₂?hereinafter referred to as NCM811?was prepared by two-stage calcination.The effects of calcination temperature,calcination time and heating rate on the morphology of NCM811 were studied systematically.The prepared product has the best morphology when the heating rate is 5°C/min,the calcination temperature was 750°C and the calcination time was 20 h.The SEM characterization results show that the surface morphology of the product is smooth and flat,the shape tends to be spherical,and the distribution of valuable metal elements is uniform.The XRD characterization results show that the product has higher crystallinity,lower ion mixing degree and better layered structure.The coin cell assembled using the calcined product was subjected to electrochemical performance testing at a voltage stage of 2.8 V to 4.3 V.The test results show that the first charge capacity of the battery is 176.9 mAh/g at 0.1 C rate and the first discharge capacity is 166.0 mAh/g which mean the first cycle Coulomb efficiency is 94.31%.The rate performance of batteries are also good.The specific capacities of0.5 C,1.0 C,2.0 C,5.0 C and 10 C were 144.7 mAh/g,131.5 mAh/g,125.5 mAh/g,102.3 mAh/g and 93.2 mAh/g,respectively.