Thermodynamic Study On Roasting Process Of NaHSO₄-LiCoO₂ System

Lithium-ion battery is a new generation of secondary battery which is developing rapidly in the 1990 s. In mobile phones, laptops and other fields have a great market share. Cathode material is one of the key materials for making lithium-ion battery.Compared with other cathode materials, Li Co O2 has the best comprehensive performances in reversibility, discharge capacity, charge efficiency, voltage stability and so on. It is the maximum application of cathode materials for lithium-ion battery.After a long period of using, lithium-ion batteries will be discarded because of the capacity decrease. Along with the increasing of the spent lithium-ion batteries, the reasonable subsequent treatment is becoming an increasingly urgent problem.Recycling spent lithium-ion batteries can effectively eliminate the hazard to the environment and relieve the tension of the metal mineral resources about lithium and cobalt.In this paper, the research status of recycling and utilization of spent lithium-ion batteries are discussed, and the advantages and disadvantages of various recycling technologies are summarized. Next, the thermodynamic equilibrium of Na HSO4-Li Co O2 roasting system is studied, and the thermodynamic equilibrium diagram of this system is drawn. The results show that selecting a certain temperature can make every reaction in roasting system to the favorable direction. When the actual partial pressure of O2 in roasting system is lower than the equilibrium partial pressure,Li Co O2 will be decomposed. When the actual partial pressure of SO3 in roasting system is higher than the equilibrium partial pressure, occurrence of Li and Co elements will be transformed into the stable form of sulfate. With the increase of SO3 decomposition pressure, Li will remove from Li Co O2 prior to Co element, and it will exist stably in the form of sulfate. Therefore, selecting the appropriate condition, can be directed to control the elements migration of Li and Co. Besides, in view of the shortcomings of existing recycling technology, this paper proposes a roasting experiment that mixtures of Na HSO4·H2O and Li Co O2 extracted from spent lithium-ion batteries were prepared with different molar ratios. The changes, which mass-heat, phase composition and morphology of the roasting product, distribution of the elements and the electron bonding energy of Co element in the roasting products were studied by TG-DSC, XRD,SEM, EDS and XPS. Results showed that the evolution of Li Co O2 in the sulfating roasting process is chemical evolution, and the elements migration of Li, Co, S, O, Na are chemical migration. The chemical model for elements migration of Li, Co, S, O, Na are related to the system temperature and the mixtures of Li Co O2 and Na HSO4·H2Owith different mixing ratios. Under the roasting conditions of 600 o C and 0.5h, with the increase in the ratio of Na HSO4·H2O in the sample of Li Co O2 mixed with Na HSO4·H2O, the Li element evolved as follows:Li Co O2â†'Li2Oâ†'Li2SO4â†'Li Na(SO4), and the Co element evolved as follows:Li Co O2â†'Co3O4â†'Co Oâ†'Co SO4â†'Na6Co(SO4)4â†'Na2Co(SO4)2. The roasting products exhibited irregular shapes and dense structures, and the distribution of these particles were not uniform. With the increase in ratio of Na HSO4·H2O, the elements of Co, Na, O and S in the roasting products were mostly diffuse distribution and the electron bonding energy of Co was increased.