Stduy Of Chemical Reaction Mechanism And Rate Influencing Factors Of LiCoO₂ Roasting In SO₃ Atmosphere

It is imperative to recycle spent Li-ion batteries in order to advocate resource-economical and environment-friendly society and the need of sustainable development. More and more spent Li-ion batteries are coming were contributed to frequent replacement of a variety of PEDs(Portable Electronic Devices). LiCoO2 is the first commercial, large-scale industrial production and the most widely used cathode material for Li-ion batteries that used in PEDs. There is a large amount of cobalt and lithium in LiCoO2 cathode material. Previous studies have shown that chemical evolution would be occurred when LiCoO2 in the SO3 atmosphere and new substances would be generated. However, it is unacquainted for us to understand the kinetic reaction mechanism of LiCoO2 in SO3 atmosphere and the influence of temperature and other system conditions on reaction rate. Study of the reaction mechanism and rate influencing factors of LiCoO2-SO3 system were conductive to a new process design and parameter optimization for recovery of Li and Co from spent LiCoO2 in acid roasting process.On the basis of thermodynamic analysis of the reaction of LiCoO2-SO3 system,model fitting method was used to study kinetic reaction mechanism of LiCoO2-SO3 system and to study effects of reaction temperature, reaction time and Na2SO4 addition on chemical reaction.The thermodynamic results indicated that there are two chemical reactions in the LiCoO2-SO3 system range from 300? to 500?. The two reactions are as follows: (1)12LiCo02+6SO3=6Li2S04+4Co3O4+02; (2) 2Co304+6SO3=6CoS04+O2?When the SO3 content is low in system, the type (1) reaction occurs. When the SO3 content is higher in system, The reactions of type (1) and type (2) both occur. The two reactions all belongs to gas-solid reactions. The kinetic reaction mechanism of LiCoO2-SO3 system range from 300? to 500? are as follows: 1) SO3 gas diffusion through the product layer to the surface boundary layer; 2) SO3 gas diffusion to the surface of LiCoO2 through the product layer; 3) on the surface of LiCoO2, the interface chemical reaction occurred after being adsorbed by SO3; 4) O2 spread out through the product layer; 5) O2 spread out through the boundary layer. The kinetics results show that the optimal mechanism of LiCoO2-SO3 reaction is 1 - 2/3R -(1-R)2/3. The major step of SO3-LiCoO2 reaction was controlled by inner diffusion. The apparent activation energy of this reaction was 51.04kJ/mol.The results of TG-DSC shown that the reaction of LiCoO2-SO3 system is endothermic reaction range from 300? to 500?, and the reaction temperature is favorable to accelerate the reaction rate. If Na2So4 was added in the reaction system,the presence of Na2So4 breaks down Li2SO4 or other products layer, which made the diffusion of SO3 was facilitated and the reaction rate was accelerated. Li2So4, COSO4 and Na2SO4 exist in the phase form of Li2Co(S04)2,NaLiSo4,Na2Co(SO4)2 and Na6Co(SO4)4.