Study On Discharge Characteristics And Pyrolysis Pretreatment Of Waste Lithium Batterie

The rapid development of the new energy automobile industry drives the increasing consumption of lithium ion batteries（LIBs）,which directly leads to an exponential increase in the output of decommissioned LIBs in the future.Therefore,its recycling has attracted wide attention.The recycling mainly includes pyrometallurgy,hydrometallurgy and other methods,and the spent lithium battery before the fire process and hydrometallurgy need to be pretreated to get the black powder material enrichment cathode material,spent lithium battery pretreatment is an indispensable link in the recycling process of spent LIBs,this pretreatment process can greatly improve the efficiency of recycling resources.It is also an essential part of recycling.The pretreatment process of spent lithium battery mainly includes classification,discharge,disassembly,crushing,separation and removal of organic binder and so on.Finally,black powder rich in positive electrode material is obtained.In this paper,the new process of fire recovery of spent LIBs proposed by our research group is designed to simplify the traditional pretreatment process of spent lithium battery,which mainly includes discharge process and pyrolysis pretreatment process.Firstly,a series of experiments were carried out on the chemical discharge and physical discharge of spent LIBs.It was found that the spent LIBs would have a voltage rebound phenomenon after static 48h after discharge,especially the use of Na₂SO₄solution and Na₂CO₃ solution would have a jump voltage rebound after static 48h after discharge.The rebounded battery voltage exceeds the safe disassembly voltage（2.5V）.However,there is no significant voltage rebound in the battery voltage after using Na Cl solution and flake graphite discharge.Therefore,this phenomenon is explained and the environmental protection and effectiveness of different discharge media are evaluated in five aspects at the end of the paper.Second,the separation of anode material and aluminum foil from used lithium-ion batteries is a key step in recycling.Compared with chemical dissolution and decomposition,pyrolysis pretreatment is a simple and feasible method.In this paper,thermogravimetric analysis of battery materials was conducted by TG.The pyrolysis process of spent lithium batteries is mainly divided into three stages:the first stage is volatile electrolyte,the second stage is thermal decomposition of diaphragm,and the third stage is thermal decomposition of organic binder（PVDF）.The pyrolysis process and pyrolysis behavior of spent LIBs materials were studied.FWO,Friedman,KAS and other methods were used to compare the pyrolysis kinetics of positive electrode materials.The activation energy（Eα）calculated by three model-free methods is best fitted by FWO method.During the pyrolysis process,the concentration of F decreases gradually with the increase of temperature,while the concentrations of Ni,Mn and Co remain stable.Most of the harmful elements F in battery materials are converted into HF gas,which can be adsorbed by alkaline solution.Therefore,pyrolysis pretreatment can not only separate and remove the organic binder,but also greatly reduce the content of harmful element F,which is a simple and effective method.Finally,aiming at the new pyrometallurgical process proposed by our research group,this paper proposes to simplify the pretreatment process flow.By eliminating the three main steps of classification,disassembly and crushing in the pretreatment process of spent lithium battery,the paper adopts the processing process which only includes discharge and pyrolysis,which not only greatly saves manpower,material and financial resources.It also highlights the advantages of large capacity and strong inclusivity of our new fire recovery process.