Fundamental Research On Microwave Assisted Extraction And Reconstruction Of Valuable Metals Derived From Electrode Material Of Spent Lithium-ion Battery

Lithium-ion batteries(LIBs)have been widely used in consumer electronics,stationary energy storage and electric vehicles as a kind of excellent storage carrier of electric energy.Currently,the fast-growing market of new energy vehicles has spurred a surge demand and output of electric vehicles batteries.It is predicted that there will be a huge growth for spent LIBs in the future due to their limited life span and the rapid upgrading of electronic products.In view of the environmental preservation and valuable resources conservation,the recycling of spent LIBs is highly desirable around the world.Gorvement ministries of China have issued poolicies to gradually promote the spent batteries recycling into the standardization and industrialization storage.Pyrometallurgy and hydrometallurgy processes of spent electrode materials play an important role in spent LIBs recycling process.Faced with the problems that conventional recycling processes are usually complicated and the external heating method leads to blocked reaction,this research aims to recycle valuable metals from electrode material of spent LIBs.The mechanisms of liberation and recovery were studied based on surficial and micro properties of raw material.Microwave enhanced carbothermal reduction and leaching of electrode materilas were proposed and combined to accomplish the recovery of metals.Meanwhile,the regeneration of cathode material was also conducted based on the optimized recycling of electrode materials.This study revealed the dissipative behavior and transfer mechanism of phase in recycling process.Meanwhile,it focuses on studying the key scientific issues of microwave-aided collaborative recovery of valuable metals from electrode material and its control process.The main obtained achievements and progress are listed below:Firstly,the resource properties of the electrode materials of spent LIBs were clarified based on the surface and microscopic properties,and the internal reasons for the difficulty of dissociation and leaching of the electrode materials were revealed.The surface coating of organic binder and high valued valences of transition metals of cathode materials make it difficult to recycle valuable components by metallurgy recycling.In order to enhance the efficiency of metal migration and transformation in the reduction roasting and leaching process,the advantages of microwave heating in aspects of the integrity and uniformity on materials,as well as its activation and polarization effects on polar molecules are used to promote their recycling efficiency.It is revealed that the heating rate of materials in microwave field is mainly affected by microwave power and materilal mass.The enhancement of heating rate can lead to local high temperature which improve the reduction ability of graphite.The basic thermodynamic data of Li Ni_0.5Co_0.2Mn_0.3O₂ were obtained based on thermodynamic calculation,and the feasibility of carbothermal reduction of electrode materials was accordingly predicted.The reduction reaction of cathode material and graphite would take place when temperature increased to 755°C as predicted by thermodynamic study.Secondly,the phase dissipation and transfer mechanism of electrode materials during reduction roasting process were revealed from the dynamic level,and the effect of key factors on the reduction roasting behavior of electrode materials was also investigated.Results show that there are three phase transition stages during reduction reaction of electrode materials in which electrolyte decompose at temperature below120°C.Then organic binder was decomposed when temperature increased to the region of 400-600°C,and thus fluorobenzene and vinylidene fluoride were generated.The reduction of cathode and anode materials occurred under 700°C.With the increase of temperature,it showed disordered lamellar phase with a mixture of lithium and metal ions between the slab and the interclub space.When temperature increased to 800°C,the Li Ni_0.5Co_0.2Mn_0.3O₂ phase disappeared completely,and reduction products of Ni O,Co O,Mn O,Co,and Ni were produced.The agglomeration of electrode particles was reduced attributed that organic binder PVDF were removed.The optimal microwave reduction parameters are 900°C reaction temperature,25 min reaction time and 10wt.%graphite.The reduction efficiencies of Ni,Co and Mn reach 94.86%?92.45%and88.76%,respectively.Then,microwave enhance leaching of valuable metals from electrode mater ials was studied and the optimized conditions of metal leaching was proposed.BBD response surface method was used to analyze the influence of key factors on the leaching efficiency of electrode materials and the second order model of Y=?₀+?₁X₁+?₂X₂+?₃X₃+?₁₂X₁X₂+?₁₃X₁X₃+?₂₃X₂X₃+?₁₁X₁²+?₂₂X₂²+?₃₃X₃² was th erefore proposed.It showed that microwave power,temperature and leaching ti me are the most significant role to improve metals leaching.The optimal leach ing efficiencies of 97.84%,98.01%,98.16%and 98.29%for Ni,Co,Mn and Li were obtained under the conditions of 640W microwave power,500 rpm stt ring speed and 35 min.The leaching kinetics was analyzed based on the solid-liquid reaction properties,and then the kinetics model of 1-(1-(3)^-1/3-1/3ln(1-(3)=was accordingly proposed.The validity and generalization of the model was evaluated by the actual leaching data and the microscopic properties of the leaching residue.The apparent energy E_a and the characterization result s of leaching residues show that the whole leaching process is controlled by c hemical reaction and diffusion,and the effect of microwave induced activation,polarization and coupling resonance of polar molecules result in the increase of activated molecule and effective collisions.This leads to the decrease of appar ent energy E_a for all metals,and thus the leaching performance of electrode m aterial was promoted under microwave field.Finally,sol-gel method was used to synthesis new cathode material Li Ni_1/3Co_1/3Mn_1/3O₂ on the basis of fully understanding the improvement of reduction roasting and leaching of electrode material.The synthesized cathode material kept?-Na Fe O₂ layered structure with well-indexed for an R(?)m space group.The internal lattice fringes are clear and orderly,and the lattice is well developed.The electrodes regenerated with shorter leaching time exhibit better performances.It exhibits the best initial discharge apacity of 157.5 m A h g^-1,and maintains at 137.2 m A h g^-1 after 160cycles with the highest capacity retention of 87.1%,and the coulomb efficiency kept99%during the whole charge-discharge process.The Discharge platform voltage still kept around 3.7V after many times discharge.The obtained cathode materials show excellent reversible discharge capacity and cycle stability through reductive roasting,leaching and regeneration process,which means the proposed collaborative recovery process of this study is proved to have high theoretical and practical value.This dissertation contains 89 figures,23 tables and 182 references.