Study On Recycling Mechanism Of Waste Lithium Cobalt Oxide Battery Cathode Material

Lithium-ion batteries are widely used in various industries due to their unique superior performance such as high energy density,high operating voltage,no memory effect,and wide application temperature range.However,due to the lithium-ion battery material itself,the battery will have a certain service life,so in the next few years,a considerable number of wastes lithium-ion batteries will be eliminated by the market.At present,LiCoO₂is currently the most widely used cathode material for lithium-ion batteries,and the resources of lithium and cobalt are in a state of less supply and greater demand in China;if the lithium and cobalt elements are disposed of at will,they will cause a great deal of pollution and harm to the environment and human body.It is therefore imperative to investigate lithium-ion battery recycling and reuse,which not only has high economic value but is also consistent with China’s concept of the green cycle and sustainable development.Our research group proposed an innovative closed-loop route for the recycling and resynthesis of waste lithium-ion batteries.The products Co₂O₃ and Li₂CO₃ were obtained by carbothermal reduction of the pretreated LiCoO₂cathode material.On this basis,Li OH·H₂O was prepared by electrolysis of Li₂CO₃ by cation membrane electrolysis.The experimental process of synthesizing high-performance lithium-ion battery cathode material LiCoO₂ with Li OH·H₂O and Co₂O₃as raw materials and Li Cl-KCl as mixed molten salt medium was studied by molten salt synthesis method.The electrochemical performance of the product LiCoO₂ cathode material battery was tested.Finally,the kinetics of the synthesis process was analyzed and calculated.This thesis concludes as follows:（1）It is preliminarily feasible to prepare Li OH·H₂O by using a cationic membrane electrolytic cell with two electrolytic chambers.The obtained products are all Li OH·H₂O,with uniform particle size,particle size range between 60-90μm and uniform distribution range.According to the results of orthogonal experiment and single factor experiment,the effect of current density and power consumption per unit product on electrolysis experiment is:current density>initial concentration of cathode electrolyte>initial concentration of anode electrolyte.Considering the influence of various factors on the electrolysis process,the optimum process parameters were selected as follows:the initial electrolyte concentration of anode was Li NO₃ 0.5mol·L^-1,the initial concentration of cathode electrolyte was Li OH 1%（wt%）,and the current density was 70 m A·cm^-2.Under this condition,the current efficiency in the electrolysis process was 78.66%,and the unit DC power consumption was 7.24 k W·h·kg^-1.（2）LiCoO₂ with uniform crystal size,complete crystal phase and regular crystal plane shape was synthesized by using molten Li Cl-KCl as molten salt medium,Co₂O₃and self-made precursor Li OH·H₂O as raw materials.According to XRD and SEM characterization,the synthesized LiCoO₂ particle size is about 1μm and has a good hexagonal lattice structure.The single factor experiment was carried out with the electrode performance as the evaluation index.The LiCoO₂ electrode synthesized at Li/Co=1.1 and 750℃ for 6 h had the best performance.The first charge and discharge specific capacities were 150 m Ah/g and 146 m Ah/g,respectively.The coulombic efficiency was 97%.After 50 cycles,the discharge specific capacity was still 129m Ah/g,and the capacity retention rate was 87.76%.After the rate performance test,the experimental results show that the battery prepared by the LiCoO₂ synthesized under the optimal conditions can still have better charge and discharge performance after experiencing different rate charge and discharge.These results show that LiCoO₂synthesized by molten salt method has good charge-discharge performance,cycle performance and rate performance.（3）Based on the thermal analysis method,combined with the differential Kissinger method,the activation energy of the three endothermic peaks in the molten salt synthesis reaction process was calculated.The apparent activation energy of each peak was 34.212 k J·mol^-1,168.53925 k J·mol^-1 and 221.26181 k J·mol^-1,respectively.The reaction order n of each endothermic peak calculated by Kissinger method is1.516,1.607 and 1.221,and the pre-exponential factor A is 3.187×10^-4,2.191×10^-3 and2.306×10^-3,respectively.