Study On Kinetics In The Recovering Process Of Spent LiNi_xCo_yMn_1-x-yO₂ Lithium-ion Battery Cathode Materials And Its Regeneration Of LiNi_0.5Co_0.2Mn_0.3O₂

Lithium-ion batteries?LIBs?have been widely used in consumer electronics and new energy vehicles due to their high energy density,low self-discharge effect,absence of memory effect,and widely operating temperature.However,the service life of LIB is generally 1?3 years.With the rapidly development of these fields,the treatment of spent LIBs has become a research hotspot.In this paper,the most widely used Li Ni_xCo_yMn_1-x-yO₂ material was selected as the research object,and the material was cycled and regenerated.For the recovery of Li Ni_xCo_yMn_1-x-yO₂ material,this work presents a technology of reduction roasting combined with stepwise leaching to recover the valuable metals in spent LIBs.The TG-DSC and XRD analysis of reduction roasting process of Li Ni_xCo_yMn_1-x-yO₂ material showed that the Li Ni_xCo_yMn_1-x-yO₂ material was decomposed to a mixture of Li₂CO₃,Ni O,Ni,Co,and Mn O when roasting temperature exceed 550 ?.The kinetics process of reduction roasting were analyzed by shrinking core model,the results showed: when the temperature exceed 500 ?,the Li₂CO₃ evolution reaction begin to occur,and its activation energy is 220.96 k J/mol;the Li Ni_xCo_yMn_1-x-yO₂ material crystal dissociation reaction is carried out at 550 ?,and its activation energy is 480.67 k J/mol.The single factor experiment was used to study the effect of roasting conditions on the leaching rate of metal elements in roasted products.The optimum roasting conditions were as follows: roasting temperature = 650 ?,roasting time = 30 min,carbon content = 10 wt.%.The roasted product was treated by stepwise leaching to recover Li⁺,Ni²⁺,Co²⁺,and Mn²⁺.Li⁺ was extracted by water leaching.The optimum water leaching conditions were: liquid-solid ratio = 30 ml/g,leaching time = 90 min.Under this conditions,Li+ leaching rate was as high as 93.23%.Ni²⁺,Co²⁺,and Mn²⁺ in water leaching residue were leached by surfuric acid.The optimum acid leaching conditions were: surfuric acid concentration = 4 mol/L,liquid-solid ratio = 10 ml/g,leaching time = 30 min,leaching temperature = 90 ?,under this conditions,the leaching rates of Ni²⁺,Co²⁺,and Mn²⁺ were 99.56%,99.87% and 99.9%,respectively.The kinetics of surfuric acid leaching process was analyzed by shrink core model,and its results indicated that the internal diffusion step of the reactants was the surfuric acid leaching process control step.The activation energy of surfuric acid react with Ni²⁺,Co²⁺,and Mn²⁺ were analyzed by Arrenius equatin,and the results were 29.35 k J/mol,24.00 k J/mol,and 23.29 k J/mol,respectively.It is proved that the surfuric acid leaching process is a diffusion control process in kinetics aspect.The surfuric acid leaching solution was used as a raw material for the co-precipitation reaction to obtain a regenerated Ni_0.5Co_0.2Mn_0.3?OH?₂ precursor.Afterwards,regenerated precursor calcinated with Li₂CO₃ to prepare a regenerated LiNi_0.5Co_0.2Mn_0.3O₂ material.The regenerated LiNi_0.5Co_0.2Mn_0.3O₂ material was compared with the LiNi_0.5Co_0.2Mn_0.3O₂ material prepared under the same process.The morphology,particle size distribution,dispersibility,crystallinity and lithium-nickel mixing degree of the two materials were basically the same.Electrochemical tests showed the electrochemical properties of the two materials.The structural stability,electrochemical reaction reversibility,and electrical conductivity are basically the same,which verifies the feasibility of the regeneration method.