Research On Low-temperature Crushing,Grinding And Flotation Of Spent Lithium-ion Battery Electrode Materials

Lithium-ion batteries are widely used,and their demand is growing rapidly.At the same time,the amounts of spent lithium-ion batteries are also increasing.The efficient recycling of spent lithium-ion batteries has become a major problem that China urgently needs to solve.It is of great significance for protecting the environment and recycling resources.In the recycling process of spent lithium batteries,the efficient dissociation of electrode materials and the separation of positive and negative electrode materials are the key links to achieve efficient recycling of electrode materials.In this paper,the positive and negative electrode plates of spent lithium-ion batteries are taken as the research object.The electrode material has low peeling-off efficiency during the conventional crushing process,the current collector material is easy to be crushed and mixed into the electrode material particles.The organic binder film on the surface of the positive and negative electrode material particles makes it difficult to separate them by flotation.A new process of using low temperature selective crushing to achieve efficient dissociation of electrode material particles,low temperature grinding to quickly remove the organic film on the surface of electrode material particles,and then efficient flotation separation,and carried out related research work.The cryo-mill was used to carry out the low-temperature crushing experimental of the spent lithium-ion battery electrode plates.The results showed that the selective crushing index of the positive and negative plates at normal temperature was 7.05 and 1.97,and the low-temperature crushing positive and negative plates were respectively 1.09 and 0.25.The smaller the selective crushing index,the better the selective crushing effect.The results show that the positive and negative plates have better selectivity at low temperature.When the crushing temperature is 93 K,the peeling-off efficiency of the positive electrode material reaches 87.29%,which is 4.28 times the peeling-off efficiency when crushing at room temperature;and the peeling-off efficiency of the negative electrode material increases from 38.53% to 93.16% at room temperature.The low temperature crushing greatly improves the peeling-off efficiency of the electrode material particles.The presence of the organic binder hinders the peeling-off of the electrode materials during the crushing process and affects the flotation separation efficiency of the electrode materials.The low-temperature characteristics of the organic binder PVDF was analyzed by DSC.The results show that the PVDF binder undergoes a crystalline transformation at 235 K,from a highly elastic state to a glass state,which leads to embrittlement and failure of the binder.The macro-mechanical properties of electrode materials were analyzed using a universal material testing machine(CTM),a low-temperature impact testing machine(JBD-300B)and a peel strength test device.The results show that when the temperature is 77 K,the tensile strength of the positive electrode current collector aluminum foil is 1.66 times that at normal temperature.The tensile strength of the negative electrode current collector copper foil is 1.97 times that at normal temperature.The impact strength of the aluminum foil of the positive electrode current collector material is 77.8% higher than that under normal temperature conditions.The impact strength of the copper foil of the negative electrode current collector material is 1.55 times that at normal temperature.The difference in the lowtemperature performance of the material leads to the key factor of selective crushing at low temperature.With the help of SEM,SEM-EDX and 3D-XRM,the microstructure of the electrode plates after low temperature treatment were analyzed.The results showed that many cracks appeared on the surface of the electrode plate after low temperature treatment,and at the same time,the interlayer cracked glue structure failed,and the electrode material was more likely to fall off under the action of external force.Therefore,the electrode material with low temperature crushing has a higher peelingoff efficiency.The cryogenic grinding test of electrode material particles was carried out using a cryogenic ball mill.Through the combination of SEM-EDX,XPS,FE-EPMA and other analytical techniques,the effect of low temperature grinding on the element distribution on the electrode material surface was analyzed.As a result,it was found that the content of fluorine element on the surface of the electrode material particles was significantly reduced after low temperature grinding,indicating that the grinding can effectively remove the organic film on the surface of the particles.Particle size analysis and contact angle analysis show that the average particle size of particles after low-temperature grinding is smaller and the difference in particle contact angle becomes larger.The flotation separation experimental shows that the flotation efficiency of electrode material particles is greatly improved after low temperature grinding.The grade and recovery rate of lithium cobaltate in the flotation concentrate reached 91.75% and 87.28%,respectively,while under normal temperature grinding conditions were 55.36% and 72.80%,respectively.There are 48 figures,9 tables and 94 references in this thesis.