Mechanism Of Pyrolysis And Reduction Of LiCoO₂ In Spent Lithium Ion Batteries And Recovery Of Cobalt

In recent years,with the development of large-scale energy storage commodities such as electronic products and new energy vehicles,lithium-ion batteries(LIBs)have become a highly efficient energy storage device,their application scale and output have increased rapidly,and a large number of spent LIBs have emerged.The spent LIBs contain heavy metal elements inside.Improper disposal can easily lead to waste of recourses,environmental pollution,and harm to human health.Achieving harmless treatment and recycling of spent LIBs has certain social value.In this paper,the typical spent 18650 battery of LIBs were taken as the research object,and the cobalt in the spent LIBs is recovered by high-temperature pyrolysis combined with chemical precipitation.Firstly,the experimental research on the discharge,crushing and screening process of the spent LIBs pretreatment process was carried out,and the best conditions were obtained.Secondly,the thermodynamic theory was used to analyze the reduction mechanism of LiCo02 and graphite under nitrogen environment,and the reaction process was inferred.The experimental design was carried out to verify the mechanism of the carbothermal reduction reaction.Then,the "kinetic three factors" of LiCo02 carbothermal reduction reaction were calculated by thermal analysis kinetics.Finally,combined with the response surface optimization method,the process conditions of Co recovery by chemical method were optimized.In the process of high-temperature thermal decomposition,cathode materials(LiCoO2)was reduced by using the anode materials(graphite).The recovery method avoids the separation of cathode materials and cathode materials from spent LIBs.And the graphite is recycled.It provides a theoretical basis for industrial application.The main conclusions of this paper are as follows:1.The best discharge condition was to discharge the spent LIBs in 20%NaCl for 300 min.LiCoO2 is mainly concentrated in battery materials with a crushing particle size range of 0.425 mm or less.The electrode material should be screened by 60 mesh sieve and the crushing time should be 3 min.2.Under the atmosphere of nitrogen,the reduction reaction can reacted between LiCoO2 and graphite.And as the temperature increases,the reaction can be processed more easily.And the reaction products are Li2C03 and Co.The recovery rate of Co and Li can reach 94.75%and 92.24%respectively.3.Using the multiple heating rate method in the non-isothermal method,namely flynn-wall-ozawa method and Kissinger method,the activation energy E of the thermal decomposition reaction of LiCoO2 mixture in the atmosphere of nitrogen was 275.68 kJ/mol.The pre-exponential factor A was 1.8125×107 s-1.Coats-Redfern integral formula was used to deduce that the mechanism of thermal decomposition reaction of LiCo02 mixture was the three-dimensional diffusion mechanism of the anti-jander equation.4.The concentration of H2SO4,the liquid-solid ratio of H2O2 to anode material,the leaching time and the leaching temperature have significant effects on the leaching efficiency of Co.By the response surface optimization analysis,the influence of liquid-solid ratio,leaching temperature and H2SO4 concentration on the leaching rate was significant,and the influence of the interaction term on the leaching rate was not significant.The optimum experimental conditions for the leaching of Co were 6.2 mL-g-1 of liquid-solid ratio,96 ℃ of leaching temperature,45 min of leaching time,and 1.2 mol·L-1 H2SO4,respectively.5.The optimum conditions for the Co precipitation reaction were:the pH of the leachate was 1.5,the ratio of[C2O42-]/[Co2+]was 1.10,the reaction temperature was 70℃,and the precipitation time was 50 min.The CoC2O4 crystal obtained by this process has good crystal structure and higher purity.