| In recent years,the consumption of the new energy vehicles and other electronic products powered by lithium-ion batteries?LIBs?have increased dramatically with the development of infrastructure and people's living standards together with environmental protection consciousness,which significantly promotes the rapid growth of LIBs industry chains.However,mass production and the limited service life of LIBs lead to a sharp number increase of spent LIBs.Therefore,it is quite important to improve the spent LIBs recycling system and establish a technical support system to realize low-cost,green and efficient recycling of spent LIBs.At present,the properties and recycling of cathode materials are studied systematically in acidic aqueous solutions,aqueous solution environmen ts with microorganisms and non-aqueous environment.However,the basic properties of LiMO2?M=Ni,Co,Mn?cathode materials in other medium environments remain unclear.In this thesis,the modes of occurrence,evolution law,distribution characteristics and evolution and control mechanism of elements are studied in LiCoO2-NaHSO4·H2O and LiNi1/3Co1/3Mn1/3O2-NaHSO4·H2O system.Then,chemical evolution characteristics of chemical substances in this system and their chemical pathways for the related elements transformation are revealed.The LiCoO2-NaHSO4·H2O system exhibits thermodynamic instability and chemical conversion compared with the single cathode material powder LiCoO 2during roasting process.As the proportion of NaHSO4·H2O in mixtures increases,the phase composition evolved as follows:LiCoO2 and Co3O4?LiCoO2,Co3O4,LiNa?SO4??Co3O4,LiNa?SO4?.After roasting,the original layered structure of LiCoO2 completely destroyed and the serious sintered phenomenon together with irregular blocky particles are observed.Meanwhile,the cobalt compounds are interactively distributed with sodium salts.After being roasted and washed,the Co element existed in the residues in form of insoluble Co3O4,which can be used to separate Li and Co elements directionally through roasting and water leaching in a mass ratio of 1:1.40.This selective sulfating roasting process might be reactions:12LiCoO2+6SO3?g?=6Li2SO4+4Co3O4+O2?g?,Li2SO4+Na2SO4=2LiNa?SO4?.In the LiCoO2-NaHSO4·H2O co-roasting system,the phase composition evolved as follows:LiCoO2,NaHSO4·H2O?LiNa?SO4?,Co3O4,when roasted at 600?in a stoichiometric mass ratio of NaHSO4·H2O.The destruction and transformation of LiCoO2 layered structure are related to the decrease of thermodynamic stability of LiCoO2 in the system.During roasting process,the removal of Li from LiCoO 2 plays a key role on its breaking of layered structure and the occurrence of the Li and Co elements evolves as follows:LiCoO2?Li2SO4?LiNa?SO4?and LiCoO2?Li?1-x?CoO2?Co3O4.LiNi1/3Co1/3Mn1/3O2 exhibited obvious thermodynamic stability variations under different roasting conditions.The occurrence of Li,Ni,Co and Mn could generate the corresponding sulfates in the atmosphere of LiNi1/3Co1/3Mn1/3O2-NaHSO4·H2O system under 425°C.The bimetallic sulfates show various dominant occurrence forms under different temperature ranges.Also,with the continuous increasing of roasting temperature,the Na6Me?SO4?4?Me=Ni,Co?will be transformed into Na2Me?SO4?2?Me=Ni,Co?and the intimate intergrowth of sulfates are generated above 550°C.With temperature cooling to room temperature,the complex sulfates broken into different forms of bimetallic sulfates.The corresponding sulfates generation order is Li>Ni,Co>Mn in this system,and the valence state changes of Co and Mn are+3?+2 and+4?+3?+2,respectively. |
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