| Lithium-ion batteries have been widely used due to their high specific capacity and good cycle life.With the great increasing demand of used lithium batteries,it is an urgent need for recovering valuable metals from the spend lithium ion batteries and reducing environmental pollution.This thesis reports the direct roasting of ammonium sulfate and ternary anode materials,followed by water leaching to obtain nickel-cobalt-manganese mother liquor.Precursor was prepared by precipitation and aging processes by the rection of mother solution and sodium carbonate-sodium bicarbonate solution.Finally,a ternary material was prepared by calcining the precursor and lithium carbonate.The main works of this thesis are as follows:(1)Using the difference in absorption wavelengths of Ni2+ and Co2+ions,a dual-wave length method was used to determine the Ni2+ and Co2+contents by a spectrophotometer,and the total amount of Ni,Co,and Mn was measured by EDTA titration,and Mn was determined by a subtraction method.(2)After dismantling the used lithium battery by hand to obtain the battery core,the positive electrode material powder is obtained by mechanically agitating and sieving in dilute acid.Then,the roasting process of the positive electrode material and ammonium sulfate was studied systematically.The optimal calcination conditions were found to be that the calcination temperature was 470 ? and the calcination time was 90 min.The leaching process of the calcined product showed that the leaching rates of the Ni,Co,and Mn salts after the positive electrode material was calcined by the new method were both above 99%,and the leachate was almost neutral,avoiding the use of a large amount of alkali to neutralize the subsequent steps.(3)This paper studied the impurity removal process of iron and aluminum impurities in the leaching mother liquor.The two-step method was established to achieve efficient removal of iron and aluminum ions.Hydrogen peroxide and sodium hydroxide were sequentially added to the leaching mother liquor,and the pH of the solution was adjusted to 3.2 to oxidize most of the Fe2+ to Fe3+,thereby forming Fe(OH)3 precipitates;in addition,water was used under the control of pH 4.5.The residual aluminum ions were removed by thermal methods.Experiments showed that the removal rate of aluminum was 99.9%.The loss of nickel,cobalt,manganese in the process of impurity removal is all small,and the recovery rate can reach more than 99%.(4)In this dissertation,precursors were prepared by using Na2CO3 and NaHCO3 mixed buffer as precipitants,and the effects of reaction process and aging process on the precursors were studied.The results show that the aging process of the reaction product is beneficial to obtain a better precursor.When the aging temperature was 70 ? and the aging time was 10 h,the prepared precursor particles exhibited spherical particles with a diameter of 2 ?m.(5)The paper studied the process of preparing ternary materials by recycling precursors.The results show that the ?-NaFeO2 layered structure material can be obtained at a calcination temperature of 900 ? and a calcination time of 10 h.The material particles can still maintain spherical shape,and the particle size distribution is uniform,about 200 nm.The first charge specific capacities of the materials at 2.5-4.6 V and 0.2 C,0.5 C,and 1 C(1 C=200 mA g-1)discharge rates were 229.7,190.1,and 172.7 mAh g-1,respectively.The initial discharge specific capacities were 224.1,177.8,and 153.7 mAh g-1,and the first Coulomb efficiency was 97.5%,93.5%,and 89.0%.After 40 cycles,the corresponding specific discharge capacities were 198.2,153.5 and 119.3 mAh g-1,respectively,and the capacity retention rates were 88.4%,86.3%and 77.6%,respectively,showing good cycle stability. |
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