Hydrometallurgical Recovery Of LiNi_xCo_yMn_1-x-yO₂ Material From Spent Libs And Its Application For Regenerating Cathode Materials Of Lithium/Sodium-Ion Batteries

With the promotion of new energy vehicles in China and the rapid development of mobile communication equipment,there will be an explosion of retired lithium ion batteries in next few years.Ternary cathode materials(NCM:Li Ni_xCo_yMn_1-x-yO₂),as the main cathode material of current lithium ion batteries,contains a large amount of valuable metals such as lithium（2-5%）and cobalt（5-20%）,with a very high recycling value.In order to alleviate the harm to environment and solve the problem of resources shortage,it is essential to begin recycling and reuse of NCM cathode materials.Hydrometallurgy has been widely used in lithium battery recovery due to its advantages of high extraction efficiency,high separation accuracy,low energy consumption and low cost.However,traditional hydrometallurgy using sulfuric acid and other inorganic strong acid as leaching agent will produce harmful gas and wastewater that causing serious secondary pollution.The precursor Ni_1/3Co_1/3Mn_1/3（OH）₂that precipitated via Na OH is unstable and easy to be oxidized,with an amorphous structure.Therefore,in order to solve the problem of lithium resource shortage,a mild recovery method based on organic acids was proposed in this study,and a recycled cathode material with good performance were obtained as well.At the same time,transition metals are extracted from waste ternary materials for the synthesis of ternary layered cathode material for sodium ion batteries,and improve the rate performance and capacity of P2-phase cathode materials for sodium storage.The main contents of this dissertation are as follows:1.The mild phosphoric acid and citric acid were used in leaching NCM,where citric acid was used as reducing agent to promote the leaching of Mn⁴⁺and Co²⁺,forming a green and efficient leaching system.At the same time,using environmentally friendly oxalic acid as precipitator,the spherical precursor with stable oxidation state is formed by the complexation of C₂O₄^2-ions with the transition metal ions.A secondary sphere structure with high rate performance can be obtained by using the spherical precursor as the self-supporting template,avoids the oxidation of Mn（OH）₂and the destruction of the original structure.The final recovery rates of Li,Ni,Co,Mn were 99.9%,93.3%,101.3%and 99.1%,respectively.At the same time,the recycled ternary materials with good cycle stability and rate performance were obtained.2.The transition metal elements in the waste ternary materials were leached and precipitated,and then mixed and calcined with Na₂CO₃to obtain Na_0.67Mn_0.67Ni_0.17Co_0.17O₂,a kind of P2-phase ternary sodium electrical material.Through the composite of spinel-phase and P3-phase,the rate performance and specific capacity of the material have been greatly improved.The reversible capacity of the composite is up to 165 m Ah g^-1after 50 cycles at 0.2 C,which is 43.5%higher than that before composite,and the capacity retention is 91.9%.3.The morphology of P2-phase sodium electric ternary cathode material was improved.By changing the coprecipitation mode and liquid addition rate,single crystal ternary sodium electric materials can be synthesized controllably to avoid the crushing of secondary spherical materials in the process of cycling.After 250 cycles at 2 C,the capacity is maintained at 126.85m Ah g^-1,and the capacity retention is more than 80%.