Basic Research On Enhanced Separation Of Lithium From Spent Lithium-ion Batteries By Microwave Pyrolysis Of Biomass

Lithium-ion batteries(LIBs)have been sought after by the scientific research and commercial circles due to their excellent electrochemical performance,and a large number of spent lithium-ion batteries have subsequently become new urban mines.Spent LIBs contain a large number of toxic substances and valuable metal elements.Over the past few decades,the backward treatment methods have continuously endangered the health of humans and the environment.On the contrary,the efficient and environmentally friendly recycling and extraction of valuable components in spent LIBs will bring huge environmental and economic benefits to people.This paper introduced the microwave heating method into the LIBs recycling process for the first time,systematically measured and analyzed the dielectric properties of the cathode material of the spent LIBs and the mixture(cathode material+reducing agen),and studied the thermodynamics and phase change of the system during microwave roasting;In this paper,biomass pyrolysis was used to strengthen the decomposition and reduction of ternary cathode materials for the first time,and the effects of pyrolysis temperature,biomass dose,roasting temperature and roasting time on the leaching rate of lithium were explored;At the same time,lattice collapse model and coupling reaction mechanism were used to reveal the effect of biomass pyrolysis on the decomposition of the cathode material during the roasting process.Finally,the Coats-Redfern model was used to study the kinetics of the pyrolysis of biomass under microwave heating to reduce the cathode material of the lithium-ion battery.The main findings are as follows:(1)Studies found that the cathode material of waste lithium-ion batteries has a high relative permittivity and loss tangent value,and it is a good absorbing material.At room temperature,the addition of biomass slightly reduced the dielectric performance of the cathode material,while the addition of anthracite increased the dielectric performance of the cathode material.The microwave absorbing performance of the cathode material,mixed powder A(cathode material+biomass),and mixed powder B cathode material+anthracite)reaches the maximum when the bulk density is 1.33 g/cm3,1.4g/cm3,and1.219 g/cm3;Temperature has a significant impact on the dielectric properties of the mixed powder.In the pre-reduction stage,the dielectric properties of the cathode material and the mixed powder B are better than those of the mixed powder A.In the reduction roasting stage,the absorbing effect of the mixed powder A has been improved due to the production of biochar.(2)Under the microwave heating,the cathode material in mixed powder A and mixed powder B starts to decompose at 300?and 530?,respectively.Compared with the traditional anthracite reducing agent,decomposition reaction of cathode material under the action of biomass has a lower temperature and the produced Li₂CO₃ has a good crystal form;the decomposition of the cathode material and the combustion reaction of biochar can form a coupling reaction,thereby it reduce the decomposition temperature of Li(Ni_xCo_yMn_z)O to 300?.In addition,the reduction of metal oxides and the formation of Li₂CO₃ can form a series of coupling reactions to promote the formation of Li₂CO₃.Finally,the lattice collapse model was used to describe the structural collapse of the cathode material during the roasting process and the bonding process of the new material.(3)The thermogravimetric data of the mixed powder A under different heating rates fit the Coats-Redfern equation very well,indicating that the reaction process of the biomass powder and the cathode powder under microwave heating is controlled by the chemical reaction.Fitting the thermogravimetric data of the pre-reduction stage and the reduction roasting stage under different heating rates,it was found that the activation energy(E)reaches the minimum value at 20K/min;the thermogravimetric data of the pre-reduction stage and the reduction roasting stage under different biomass content were fitted,and it was found that the E of the pre-reduction stage is basically concentrated at 35-40 k J/mol.While the reduction roasting stage,when the biomass content is 20%,the E is the smallest,and the reaction is the easiest to proceed at this time.(4)The effects of pyrolysis temperature(Pte),biomass dose(bio%),reduction roasting temperature(Rte)and reduction roasting time(Rti)on the leaching rate of lithium were studied,and the results indicated that 93.4%lithium could be leached under the following optimum conditions:bio%=24,Pte=500?,Rte=750?,and Rti=25min.