Experimental Study On Recovery Of Valuable Metals From Waste Lithium Battery Cathode Materials

Lithium-ion batteries（LIBS）are the best batteries with high specific energy,high cycle life,small volume,light weight,no memory effect,no pollution and other characteristics.They have rapidly developed into a new generation of energy storage power supply for power support in the fields of information technology,electric vehicles,hybrid vehicles,aerospace and so on.Among them,Li Co O₂battery has outstanding comprehensive performance and wide application.With the wide application,a large number of spent batteries need to be recycled.（1）Due to the limited thermodynamic data of Li-Co-o system,the relevant thermodynamic parameters are estimated and corrected,and then the Gibbs free energy of Li Co O₂ vacuum thermal decomposition and Li Co O₂ carbothermal reduction reaction was calculated.According to the thermodynamic calculation results,Li Co O₂ can be decomposed into lithium oxide and cobalt oxide under vacuum condition,and the decomposition reaction begins to take place at 973k and1Pa,producing Co₃O₄.With the increase of temperature,Li Co O₂ can be decomposed to Co O and Li₂O at 1223K and 1Pa.The thermodynamic calculation of vacuum carbothermal reduction of Li Co O₂ shows that at 973K and 1Pa,the reduction reaction begining.With the increase of temperature,Li Co O₂-C reduction system can generate Li₂CO₃,Li₂O,Co O and Co.when the temperature is higher than 1123K,Li Co O₂-C can be obtained Cobalt and lithium oxides in gaseous form.（2）The results of thermodynamic calculation are verified by experimental study in vacuum.The results of vacuum thermal decomposition of Li Co O₂ showed that at 1223K and 1Pa,the decomposition products were Co O and Li₂O,and Li₆Co O₄ was produced at the same time with high temperature,Li₆Co O₄ was difficult to decompose at 1223K-1423K.The results of vacuum carbothermal reduction experiment of Li Co O₂ showed that carbothermal reduction was beneficial to the separation of cobalt and lithium.Under the condition of 973K and1Pa,Li₂CO₃,Li₂O and Co O were produced.With the increase of temperature（1223K-1423K）,Li₂CO₃ was decomposed into Li₂O,and Co O was further reduced to Co.（3）Experimental study on the vacuum carbothermal reduction process of Li Co O₂ with different influencing factors was carried out.The experimental results of different reduction temperatures show that,Li Co O₂ decomposed into lithium compounds,and the reaction degree was quantified by the dissolution rate.The dissolution rate increases from 70.37%to 75.60%at 973 K-1223K.With the increase of temperature,lithium reduces to low-cost oxides,and the removal rate of 1323K and 1423 K were 39.11%,and 89.25%.The experimental results of different reduction time showed that the dissolution rate increased from 75.60%to85.38%after holding for 1h-2h.With the increase of temperature,lithium is reduced to form low-cost oxides,which are removed by gas form.After 1h of heat preservation,the removal rate of lithium was 39.11%,2h,and the removal rate of lithium was increased to 95.70%.（4）Under the condition of 1423K,1.5h,2MPa pressures and 1Pa vacuum degree,the products of carbothermal reduction were separated from carb on by magnetic separation for 5min under the condition of 1B magnetic field strength.The recovery of cobalt was more than 99.0%.（5）The effect factors of the Li Co O₂vacuum carbothermal reduction were studied.The results showed that different carbonaceous materials had great influence on the carbothermal reduction of Li Co O₂.Comparative analysis of graphite,graphene,carbon black and carbon nanotubes showed that the higher the carbon specific surface area and carbon content,the higher the dissolution rate of lithium and the higher the removal rate of lithium.Under the conditions of 1323K reduction temperature,1h and 1Pa vacuum degree,the removal rate of lithium was the highest when carbon nanotubes was used as reducing agent.（6）In this paper,a comparative experimental study on deeping lithium removal by vacuum thermal decomposition and vacuum carbothermal reduction were carried out for lithium slag produced by pyrometallurgical process.And it provided by the National Metallurgical Research Institute of Sweden.The results showed that the removal rate of Li was 77.43%at 1373K,2h and 1Pa,and 83.85%at 1373K,2h and 1Pa,respectively.