Research On The Direct Regeneration Technology And Mechanism Of Spent LiNi_xCo_yMn_1-x-yO₂ Cathode Materials

LiNi_xCo_yMn_1-x-yO₂ cathode material has been widely used in green-energy vehicles and other fields with its high theoretical capacity and high working voltage.With the rapid development of the new energy vehicle industry,a large number of spent lithium-ion batteries are facing the problem of decommissioning and recycling.Compared with traditional pyrometallurgy and hydrometallurgy techniques,the direct regeneration of spent lithium-ion batteries has lower energy consumption,higher recovery efficiency and lower environmental treatment cost.In this thesis,we take spent Li Ni_1/3Co_1/3Mn_1/3O₂as the object to first explore the effect of calcination process on the micro-structure and electrochemical performance of regenerated cathode materials.The form of surficial lithium impurities was studied as well,which were reused as lithium sources to regenerate spent cathode material,realizing the in-situ regeneration of spent lithium-ion batteries.At the same time,combined with high temperature nickel doping and Li₃PO₄coating,the regenerated materials were modified and further studied.The main research contents are as follows:（1）The lithium-containing impurities that covered on the surface of spent cathode materials were most in the form of Li₂CO₃.Spent Li Ni_1/3Co_1/3Mn_1/3O₂materials have defects such as Li vacancies and Ni O rock salts,and the integrity of the layered structure is low,which contributing to its poor electrochemical performance.Cathode materials were separated by heat treatment at 450℃,and then calcinated at 850℃in oxygen atmosphere for 12h,which show improved integrity of the layered structure and good electrochemical performance.The first discharge capacity at 0.5C is 145.6m Ah g^-1.（2）The effects of different kinds of nickel doping salts on the properties of spent Li Ni_1/3Co_1/3Mn_1/3O₂were studied also.The result shows that:Li₂CO₃impurities and Ni O rock-salt phase defects on the surface of the spent cathode materials were removed after regenerated with Ni CO₃.Besides,part of Li and Ni might mitigate and dope into the lattice during high-temperature calcination,and the electrochemical performance of regenerated material was significantly improved,exhibiting discharge capacity of 81.75m Ah g^-1at 5C.（3）Different amounts of（NH₄）₂HPO₄were added to form coating layers of different thickness over regenerated cathode materials,which would react with Li₂CO₃impurities that covered on the surface of spent Li Ni_1/3Co_1/3Mn_1/3O₂.Coated regenerated materials show best electrochemical performance with 1.0wt%（NH₄）₂HPO₄.The discharge specific capacity was 138.49m Ah g^-1after 200 cycles at 0.5C,with the capacity retention rate of 93.9%.Figures 49,Table 16,Reference 115.