Study On Recycling Of Valuable Metals In Ternary Cathode Materials Of Spent Lithium Batteries

Under the strategic goal of"carbon dioxide emission peak and carbon neutrality",the new energy industry is strongly supported by national policies.China’s lithium-ion new energy industry is developing rapidly,and the output and scrap of lithium-ion batteries which are the core components of new energy vehicles,continue to increase.Spent ternary lithium batteries contain a large number of valuable metals and hazardous waste,and their comprehensive recycling has both economic and environmental benefits.At present,the traditional thermal process has the disadvantages of high energy consumption,high lithium loss rate and heavy pollution,while the conventional hydrometallurgical process also has the problems of long process,complex purification process,low lithium recovery efficiencies and a large amount of wastewater.In this paper,the typical Li Ni_0.815Co_0.15Al_0.035O₂（NCA）and Li Ni_0.5Co_0.2Mn_0.3O₂（NCM）ternary cathode materials are used as raw materials,and the"selective roasting transformation-water leaching"method is used to recover the valuable metals from waste lithium batteries.At the same time,the prepared lithium carbonate is used to reprepare the battery cathode material.These developed processes can realize the recycling of valuable metals from spent lithium batteries.The main research results are as follows.（1）The NCA materials were treated with carbon reduction roasting selective lithium extraction process,and the extraction rates of Li,Ni,Co,and Al were 97.8%,0.45%,0.36%,and 0.75%under the conditions of carbon content of 15.0%,temperature of 700℃,and roasting time of 90 min,respectively.The extraction efficiencies of Li and Al were 98.0%and 10.0%from spent NCA materials by using hydrogen reduction roasting process under the conditions of roasting time of 90 min,hydrogen flow rate of300 m L/min and roasting temperature of 500℃,while the extraction rates of Ni and Co were less than 0.5%.The selective separation of lithium can also be realized by ammonium sulfate roasting,the extraction of Li,Ni,Co,and Al were 97.0%,0.5%,0.8%,and 1.2%respectively with the roasting temperature of 975℃,roasting time of90 min,and molar ratio（ammonium sulfate to raw material）of 1.2:1.0.The extraction efficiencies of Li reaches 97.0%by using aluminum-carbon synergistic roasting process to treat NCM materials under the conditions of 14.7%carbon content,7.0%aluminum content,roasting temperature of 650℃,and time of 90 min.However,the extraction rates of Ni,Co,Mn,and Al were<1%.The aluminum carbon synergistic reduction process can use the carbon and aluminum of raw materials to realize the efficient and economic recovery of lithium batteries,which has great industrial application potential.（2）The leaching residues of spent LIBs after lithium extraction is rich in nickel,cobalt,aluminum and manganese,which have great recovery value,but most of these metals exist in refractory metal elements or oxides,so it is difficult to make comprehensive utilization.Therefore,the two-step leaching process was used to treat the lithium residue.For this reason,a stepwise leaching process was adopted to treat the priority lithium extraction residue.In first sodium hydroxide leaching stage,more than 99%of aluminum can be removed by alkali leaching under the conditions of Na OH concentration of 2 mol/L at L/S of 30 m L/g,leaching time of 70 min and temperature of 90℃,while the leaching rate of Ni,Co and Mn are all less than 0.5%.After the removal of aluminum,the extraction of Ni,Co and Mn were 99.0%,99.0%and 98.5%respectively by using oxidation acid leaching with H₂SO₄ concentration of 2 mol/L and H₂O₂ concentration of 1.24 mol/L at L/S of 10 m L/g and 50℃within 70 min.The comprehensive recycling of valuable metals from waste lithium batteries by developing stepwise leaching process can be realized.（3）The leachate of preferential lithium extraction can prepare lithium carbonate with purity above 99.5%.The prepared lithium carbonate can be mixed and calcined with ternary precursors to reprepare Li Ni_0.5Co_0.2Mn_0.3O₂ cathode material.The first discharge specific capacity of the prepared cathode material is 165 m Ah·g^-1,the efficiency of the first charge/discharge reaches 91.7%,and the capacity retention rate after cycling was 88.4%after 100 cycles at a multiplicity of 1C.The charge/discharge test and CV test were performed under different multiplier cycles,indicating that this cathode material has good multiplier cycle performance and structural stability.