Differential Extraction Behavior Of Metal Elements In 523-type Lithium Battery Cathode Material Under Acidic Roasting Conditions

Building a sustainable,low-energy,high recycling efficiency power lithium-ion battery recycling system is the only way for China and other countries in the world to achieve sustainable development,energy conservation and emission reduction,especially in China’s carbon peak and carbon neutral Under the condition that the target period has been set,the field of new energy is bound to usher in vigorous development,and it is particularly important to solve the problem of resource shortage and sustainability for the development of new energy.At present,researches on acidic aqueous systems and high-temperature reduction roasting systems are concentrated,and there are also microbial environments and non-aqueous systems involved.However,there are few reports on low-temperature roasting systems.The reason is that the ternary materials are stable at low temperatures.The valuable metal elements in it are difficult to escape.Based on the advantage that the acidic roasting system can effectively reduce valuable metal elements,the research group has established the roasting and leaching conditions for the complete leaching of the Li MO₂-Na HSO₄·H₂O（M=Ni,Co,Mn）system through preliminary research,with a high leaching rate and a simplified method.However,the phase transitions,thermodynamic changes,morphology changes,element migration and changes in the corresponding leaching rate under different temperatures and ratios are still not involved.Therefore,this article aims at the above problems and discusses the Li Ni_0.5Co_0.2Mn_0.3O₂-Na HSO₄·H₂O system at different temperatures and ratios.Establish the system of thermodynamics,phase,morphology,element migration and leaching rate,and study the reasons for the differential extraction of different metal elements.The following conclusions are concluded:（1）TG-DSC results show that the Li Ni_0.5Co_0.2Mn_0.3O₂-Na HSO₄·H₂O system has three obvious weight loss platforms at different mass ratios.The difference is that as the ratio increases,the endothermic peak that appears at the original high temperature is at low temperature.And it loses some of the endothermic peaks at low temperatures,indicating that the increase in the ratio has a greater impact on the thermal effect of the reaction,and the reaction to form compound sulfate can be achieved at a lower temperature.Thermal analysis kinetics research on the same mass ratio Li Ni_0.5Co_0.2Mn_0.3O₂-Na HSO₄·H₂O system under different heating rates shows that this process belongs to the nucleation process（N1）.（2）The XRD results of the proportional increase process at different temperatures show that the product phase has a gradual sulfation trend.Through the analysis of the overall reaction,the transformation process of the crystal system is obtained:Hexagonal?Tetragonal?Orthorhombic?Cubic?Monoclinic this transformation process.The phase evolution diagrams were made for the phase transitions of the heating at different ratios,and the effects of different ratios and temperatures on the formation of bimetallic sulfate were obtained.（3）The morphology change of the calcined product of the system is obtained through the microscopic morphology change:spherical particles?massive particles with agglomeration of small particles?smaller and uniform particles.The ICP-OES leaching results show that the differential leaching behavior of different elements is affected by both temperature and ratio.Using thermodynamic analysis and valence bond theory to study this differential behavior,the results show that 1)when SO₃ is sufficient,Mn⁴⁺is the most difficult to be released from Li Ni_0.5Co_0.2Mn_0.3O₂.After removal,it will be oxidized by combining high-valent oxides with SO₃.Reduction reaction;Ni²⁺bond is weak,and only Ni O exists in the product,which can be combined with SO₃ to form Ni SO₄;while Co has a stronger+2 bond and a weaker+3 bond,and+3 directly reacts with SO₃,and the?_rG^θis smaller,the order of formation is that Li is better than Ni is better than Co is better than Mn;2)In the case of insufficient SO₃,the high valence oxides of Mn and Co will be preferentially reduced to form low valence oxides and then oxidized at their low valence.The material form reacts with SO₃.When the mass ratio is less than 1:2.85,the leaching rates of Ni,Mn,and Co are similar,and the difference becomes obvious as the ratio increases,that is,Li is better than Ni,Co then better than Mn.It shows that the deep reason for the differential release behavior of Li,Ni,Co,Mn lies in its valence in Li Ni_0.5Co_0.2Mn_0.3O₂,which is affected by the temperature and ratio,and shows the difference in the acidic roasting and leaching process,and the roasting conditions can be optimized accordingly.In order to realize the step-by-step leaching and separation of metal elements.Hydrometallurgy recovers valuable metal elements through the leaching of H₂SO₄,HCl,H₃PO₄,citric acid,etc.from the anode materials of scrap lithium-ion batteries.The current problem in the recycling process is that the recovery rate of lithium is low and the recovery cost is high.The reason is that in the acid leaching process,lithium will be transferred into the acid leaching solution together with nickel,cobalt and manganese in the form of ions.In the subsequent stages of impurity removal and sequential extraction and separation of nickel,cobalt,and manganese,a large amount of reagents floods will cause the volume of the raffinate expanding after the extraction of nickel,cobalt and manganese.As the acid leaching solution was further diluted,the concentration of lithium will decrease.This multi-stage loss and dilution reduces the concentration of lithium,making the economic cost of recovery higher,and the recovery rate of lithium is usually about 80-90%.If lithium can be selectively extracted from the cathode material of waste lithium-ion batteries before acid leaching,and nickel,cobalt,and manganese elements can be extracted step by step,the formation of low-concentration lithium-ion solutions and the loss of lithium can be avoided,and recycling costs can be reduced,which improves the recovery rate of lithium.This article uses Na HSO₄·H₂O as a substitute reagent for the sulphating roasting process to achieve no harmful gas output during the roasting process and the process is more simplified,which can realize the preferential leaching of lithium,and lay a good theoretical foundation for the stepwise leaching of nickel,cobalt and manganese..