Study On Recovery Of Spent Ternary Cathode Material And Re-synthesis And Modification Of Li-rich Mn-based Materials

The development of the electric vehicle market is driving the continuously increase in the sales of power-type lithium-ion batteries.It is expected that the cumulative national end-of-life battery will reach 120-200 thousand tons from 2018 to 2020.If so many spent lithium-ion batteries are not handled properly,they will bring tremendous pressure to the environment in China.Therefore,it is crutial to recover spent lithiumion batteries.Compared to traditional lithium-ion battery cathode materials,lithiumrich manganese-based cathode materials have attracted wide attention because of their low cost and high specific capacity of more than 250 m A h g-1.Nevertheless,they still face many drawbacks,for they always exhibit poor cycle performance,low rate capability and serious voltage decay,which have limited the use of lithium-rich materials.In this paper,aluminum foil and positive active material are separated by thermalshock & ultrasonic method and then Al3+ impurity is further extracted by A extraction system and Li_1.2Mn_0.56Ni_0.16Co_0.08O₂ is re-synthesised by co-precipitation method.In addition,accroding to the properties of lithium-rich materials,supercritical CO₂ and Ni Fe2O4 coating are used to modify the particles' surface and to improve the electrochemical performance of Li-rich material.In order to reduce Al3+ impurities and recover aluminum foil directly,the thermal-shock & ultrasonic method is used to separate aluminum foil and positive active material and the treatment process is optimized.The best heat treatment temperature and time are 450 °C,60 min,selected by the shedding effect of active material.A acid extraction system is used to further remove Al3+ impurities.By optimizing the saponification value of extraction agent,p H value of leaching liquor and the O/A ratio,it is found that the saponification value of extractant has a significant impact on the extraction of Al3+ ion impurities.Removal rate of Al3+ ion can reach 98% after saponification.The increase in p H value of leaching liquor will reduce the recovery of Ni2+,Co2+ and Mn2+ and the optimized O/A is 1:1.Re-synthesized lithium-rich material is prepared by a hydroxide co-precipitation method using the recovered solution and is further characterized by physical and electrochemical characterization.The results show that the the re-synthesized lithium-rich material also delivers a discharge capacity of 260 m A h g-1 and its rate capacity and cycle stability are equivalent to the lithiumrich material prepared by the commercial medicine.Via supercritical CO₂ treatment,oxygen is extracted,leaving oxygen vacancies on the surface of Li-rich materials.The initial coulombic efficiency raises from 75.97% for pristine material to 82.24% for modified material,which can be attributed to the effect of pre-activation of the Li2 Mn O3 component,leading an increase in the content of trivalent manganese and reversible oxygen.The modified material also performs better rate performance and cycle stability.Ni Fe2O4 nanoparticles are coated on the surface of Li-rich materials,introducing new electrochemical active sites.The coated layer not only protects internal electrode materials,improving cyclic stability,but also stores excess Li+ ions that can not embedded in the Li-rich material during the first discharge process.The initial Coulomb efficiency of the Ni Fe2O4 coated materials are more than 94%,and the rate capability of the coated material is also greatly improved,delivering over 200 m A h g-1 in 5C discharge current density.