Recovery Of Valuable Metals From Spent Lithium Battery Positive Plates And Preparation Of LiNi_0.6Co_0.2Mn_0.2O₂ Cathode Materials

Lithium ion batteries are widely used in the field of new energy vehicles because of their excellent comprehensive performance and the rapid development of new energy vehicle industry leads to the explosive growth of production and sales of lithium ion batteries.The service life of ordinary lithium-ion batteries is only 4～6 years.Since 2018,the first batch of lithium-ion batteries,which have been widely used in new energy industry,have been retired.Retired lithium-ion batteries contain a large number of Ni,Co,Mn,Li,and other metal elements,as well as corrosive and volatile organic electrolytes,which pose great security risks and even threaten the ecological environment and human health.At the same time,the content of metal elements in the retired lithium-ion batteries is much higher than the grade of metal ores in nature,which is a valuable resource.Facing the dual characteristics of retired lithium-ion batteries,how to use them as resources scientifically has become a research hotspot.However,the current recycling technology can only deal with a single type of retired batteries,and the recycling products are single.In the face of complex types of lithium-ion batteries,it is urgent and necessary to develop a recycling technology that can be used in multiple types of lithium-ion batteries.In this paper,retired lithium-ion battery cathode materials are used as raw materials,and the mixture of cathode materials is obtained after high-temperature roasting and screening.Under the action of leaching agent H₂SO₄ and reducing agent H₂O₂,the solution rich in Ni²⁺,CO²⁺,Mn²⁺,and Li⁺is obtained.After adjusting the ion ratio of leaching solution,the leaching solution is directly prepared into ternary precursor,and the high-purity lithium carbonate is recovered from the filtrate;It is easy to introduce al impurities in the previous process,so the process of synthesizing ternary cathode material from aluminum leaching solution is simulated,and the tolerance level of electrochemical performance of regenerated cathode material to Al impurity content is determined;In order to avoid the introduction of Al impurities,we separate the cathode active material from the Al foil by electrolytic stripping,which ensures the integrity of the Al foil after separation and gives priority to the recovery of most lithium,while the impurity Cu will deposit on the cathode surface of the electrolytic cell without affecting the recovery process.The whole process was characterized by SEM,TEM,XRD,XPS and electrochemical test,and the mechanism was described.The main achievements of this paper are as follows:1.The mixture of cathode active materials separated from Al foil is leached in the mixed system of H₂SO₄～H₂O₂.Through the investigation of the type of leaching agent,the concentration of leaching agent,the leaching temperature,the leaching time and other factors,the optimal parameters of the reduction leaching process are obtained,the leaching temperature is 90℃,the leaching time is 2.5 h,and the concentration of sulfuric acid is 2.5h.Under the optimal conditions,the leaching rate of all metals is above 99%;after adjusting the ion ratio,the leaching solution coprecipitated to synthesize Li Ni_0.6Co_0.2Mn_0.2O₂material with good electrochemical performance,and the first charge discharge specific capacity reaches 196.260 m Ah·g^-1and 180.072 m Ah·g^-1 at 0.2 C.The filtrate is evaporated and concentrated to recover high-purity lithium carbonate under the action of saturated sodium carbonate.The mechanism of coprecipitation is also studied.2.Li(Ni_0.6Co_0.2Mn_0.2)O₂and Li(Ni_0.6Co_0.2Mn_0.2)Al_xO₂（Al%=0.01%、0.1%、1%and 5%）with different Al contents are synthesized by hydroxide coprecipitation and calcination.And the process of synthesizing ternary cathode materials from leaching solution containing aluminum was simulated,the mechanism of the effect of aluminum on the properties of the materials is studied.The results show that the electrochemical performance of ternary cathode materials with higher Al content deteriorates sharply with the increase of Al content,while the electrochemical performance of ternary cathode materials with 0.01%Al content is close to that of ordinary ternary materials,so the leaching solution with less than 0.01%Al content does not need to remove Al.3.Taking the positive plate of the retired lithium-ion battery as the anode of the electrolytic cell and sodium sulfate solution as the electrolyte,through the investigation of external voltage,electrode spacing,electrolyte concentration and cathode material,the optimal parameters of the electrolytic stripping process were obtained as follows:external voltage 30 V,electrode spacing 15 cm,electrolyte sodium sulfate concentration 1.5 g·L^-1 and the cathode is pure aluminum plate,On the premise of ensuring the integrity of Al foil,the complete separation of ternary cathode material and Al foil can be realized.At the same time,about 75%of lithium dissolves in the electrolyte but nickel,cobalt,manganese,etc.do not dissolve.In addition,due to the special behavior of Cu impurities,the impurity removal process can be omitted and most of the lithium can be preferentially recovered.Finally,the separated cathode material is used to prepare a cathode material with excellent electrochemical performance.