Study On Regeneration Of Lithium Cobaltate Cathode Material From Spent Lithium-ion Batteries

Lithium-ion batteries are favored by the manufacturing industry because of their high energy density,high working voltage and long service life,and are widely used in the fields of new energy vehicles,portable electronic equipment and large energy storage equipment.Due to the limited cycle life of lithium-ion batteries,the number of spent lithium-ion batteries has soared in recent years.Spent lithium-ion batteries contain many high-value metal elements,while there is a risk of soil and water pollution,so recycling of spent lithium ion batteries is of great significance to resource conservation and environmental protection.This study takes the ineffective LCO material from spent Samsung mobile phone batteries as the research object,explores the possibility of using hydrothermal method to regenerate electrode material and the best experimental conditions in the regeneration process,and researchs the mechanism of spent LCO regeneration.Finally the electrochemical performance of the cathode material after the initial regeneration is improved by the heat treatment method.The main contents are as follows:（1）It is found that Co₃O₄ is contained in spent LCO material.Through thermodynamic calculation,it is realized that Co₃O₄ has the theoretical feasibility to regenerate as lithium cobaltate under hydrothermal conditions.In order to regenerate the Co₃O₄ in the spent lithium cobalt oxide material to Li Co O₂,the orthogonal test and univariate optimization experiment were carried out in Li OH solution with pure Co₃O₄as the test object and the Li Co O₂ yieldγas the evaluation index.The orthogonal test results show that the order of influencing factors on the yield of lithium cobaltate is as follows:H₂O₂ dosage>hydrothermal temperature>reaction time>Li⁺concentration.The optimum conditions for the reaction of Co₃O₄ to Li Co O₂ under hydrothermal conditions are as follows:hydrothermal temperature 220℃,reaction time 6 h,dosage of H₂O₂ 0.3 m L·g^-1,initial concentration of Li⁺3 mol·L^-1,the yield of Li Co O₂ is80.72%.The results of SEM analysis shows that the Co₃O₄ spherical particles were destroyed by hydrothermal reaction and new flake products are formed.XRD pattern shows that the reaction products contains layered lithium cobaltate phase.In the XPS spectrum of Co element,the characteristic peak area of Co²⁺decreases and that of Co³⁺increases,indicating that Co²⁺is oxidized to Co³⁺.The results show that the hydrothermal method is feasible to regeneration Co₃O₄ from spent lithium cobaltate cathode material to lithium cobaltate.（2）The study on the regeneration of spent lithium cobaltate cathode material by hydrothermal method is carried out.It is found that the lithium cobalt ratio R_Li/Co of spent lithium cobaltate cathode material recovers from 0.75 to 1.00 nearly after hydrothermal reaction.The results of single factor optimization experiment show that the optimal conditions of hydrothermal regeneration experiment are as follows:H₂O₂dosage 0.1 m L·g^-1,hydrothermal temperature 220℃,holding time 4 h,Li⁺concentration 3 mol·L^-1.The electrochemical performance test of the regenerated lithium cobalt oxide material shows that its electrochemical performance is greatly improved compared with the original waste material.And the specific capacity of initial discharge at 0.1C rate reaches 159.2 m Ah·g^-1.The discharge specific capacity at 1 C rate is 134.9 m Ah·g^-1,and the capacity retention rate after 100 cycles was 90.8%.At the same time,the electrochemical performance test shows that the electrochemical properties of the regenerated LCO material are affected by the dosage of H₂O₂ and the hydrothermal temperature,in which the hydrothermal temperature has a greater impact on the electrochemical properties.The results of SEM shows that the particle surface of lithium cobalt oxide material is cleaner,the residual binder and aluminum foil are reduced,and the phenomenon of particle fracture and fragmentation is reduced after the hydrothermal reaction.XRD and XPS tests shows that the phase of Co₃O₄ is removed and the layered structure is more stable.（3）The regeneration electrode material is heat treated to improve its electrochemical performance.It is found that the electrochemical performance of cathode materials after heat treatment is better in oxygen atmosphere.And the electrochemical performance gradually increases with the increase of temperature.However,with the extension of heat treatment time,the electrochemical performance of electrode materials raises first and then lower.The optimum conditions for heat treatment are as follows:at 850℃for 4 h in oxygen atmosphere.The specific capacity of initial discharge of lithium cobalt oxide material is 169.9 m Ah·g^-1 at 0.1C,and the specific discharge capacity at 1 C rate is 155.7 m Ah·g^-1,and the capacity retention rate was 95.3%after 100 times of cycling.The results of SEM show that the micro debris of lithium cobaltate material decreases and the agglomeration phenomenon arises after heat treatment.XPS analysis showed that Co²⁺is basically converted to Co³⁺in the heat treated lithium cobalt acid material.The XRD data is refined by GSAS software,and the lattice parameters a,c,c/a and I（003）/I（104）of lithium cobaltate material after heat treatment are obtained.It was found that the layered structure is better and the crystallinity is improved after heat treatment.Therefore,heat treatment is an effective method to improve the electrochemical performance of the regeneration lithium cobaltate materials.The thesis has 43 pictures,12 tables and 92 references.