Analysis Of Thermal Reduction Effect Of Typical Organic Components In Waste Ternary Materials On Cathode Materials

In order to improve the adhesion between electrode material and current collector and increase the electronic conductivity between electroactive substances,a certain proportion of conductive agent(acetylene black)and binder(polyvinylidene fluoride PVDF,styrene butadiene rubber SBR)are usually added in the battery manufacturing process.Existing studies have confirmed that the reducibility of the above typical organic matter makes it have the potential to destroy the stable layered structure of the cathode material during heat treatment.However,the thermal reduction effect and mechanism of typical organic components and their mixtures on cathode materials are still unclear.This study adheres to the concept of " treating waste with waste," and uses the typical organic components of waste ternary lithium batteries to carry out in-situ thermal reduction of transition metals in cathode materials,and explores the thermal reduction effects of different organic components and their mixtures on cathode active materials.The weight of each organic component in the thermal reduction process is clarified,and the reduction mechanism of each organic component and its mixture in the thermal reduction process is deeply analyzed.By constructing simulated materials,the effect of PVDF coating on the leaching efficiency of transition metals in cathode materials and the effect of structural differences on the thermal reduction effect of ternary lithium batteries during cyclic charging and discharging were investigated.The results of the thermal reduction effect of typical organic components on the cathode materials of ternary lithium batteries show that under the same conditions,the reduction effect of three typical organic components(PVDF,acetylene black and SBR)from high to low is : acetylene black > SBR > PVDF.In addition,due to the high initial valence state(+ 4 valence)of manganese,it consumes more reducing agents than the other two metals during the thermal reduction process.In the case of the same reducing agent and the same amount,the reduction effect of high nickel cathode material NCM811 is better than that of low nickel cathode material NCM111 with higher manganese content.The results of the thermal reduction effect of the typical organic component mixture on the ternary lithium battery cathode material show that the thermal reduction effect increases with the increase of the main reducing agent content in the mixed thermal reduction process of the typical organic component of the cathode,and the mixed thermal reduction effect when PVDF is the main body is stronger than when acetylene black is the main body.In addition,the addition of acetylene black to PVDF as the main body has a positive gain effect on the thermal reduction reaction,while the thermal reduction effect decreases after adding a small amount of PVDF to acetylene black as the main body;in the mixed thermal reduction process of typical organic components of positive and negative electrodes,the content of each metal ion and its leaching efficiency change relatively small,indicating that SBR has a limited role in promoting mixed thermal reduction.In the process of exploring the thermal reduction mechanism of single and mixed typical organic components of ternary lithium batteries,TG test results show that acetylene black does not have weight loss during the heating process,indicating that its reduction form of cathode materials is based on carbothermal reduction under solid-solid reaction system.PY-GC-MS analysis showed that the pyrolysis products of PVDF were mainly fluorinated compounds such as vinylidene fluoride and fluorobenzene.The pyrolysis products of SBR are mainly polymers polymerized by olefin compounds such as retene and cycloethylene.The reduction of the cathode materials is mainly achieved by the reducing gas produced by pyrolysis and a small amount of residual pyrolysis carbon.In addition,the mixed organic components are exactly the same as the pyrolysis products of their single organic components.It shows that no cross reaction occurs between the organic components during the mixed thermal reduction process.According to the analysis of the thermal reduction process of the cathode material and the pyrolysis products of each typical organic component,it is speculated that the gain or inhibition effect of different reducing agents in the mixed thermal reduction process is mainly related to the reaction form of PVDF and acetylene black with the cathode material.Roasting can significantly improve the leaching efficiency of transition metal elements in real/simulated materials.The in-situ thermal reduction method can use organic binders that can negatively impact the leaching process as reducing agents.This not only breaks the layered structure of the positive electrode material to achieve the reduction of transition metals but also eliminates the negative impact of organic binders on the recovery process.The efficient recovery of waste ternary lithium batteries is achieved through this dual action.The stress damage suffered by positive electrode material particles during the cycle of charge and discharge of ternary lithium batteries reduces the contact effect of acetylene black and positive electrode materials,leading to a decrease in the reduction ability of acetylene black based on the solid-solid reaction system to break the structure of the positive electrode material,ultimately resulting in lower leaching efficiency of transition metal elements in real materials than in simulated materials.Grinding operations can eliminate the negative impact of structural changes on the thermal reduction.After the impact of structural changes in positive electrode material particles during the cycle of charge and discharge is eliminated by grinding,real materials can achieve ideal leaching efficiency.The leaching efficiency of lithium,nickel,cobalt,and manganese metallic elements are as high as 86.79%,99.87%,99.78%,and 98.71%,respectively.