Mechanisms of the Ammonium Sulfate Roasting of Spent Lithium‐Ion Batteries

Abstract Ammonium sulfate ((NH 4 ) 2 SO 4 ) assisted roasting has been proven to be an effective way to convert spent lithium‐ion battery cathodes to water‐soluble salts. Herein, thermogravimetric (TG) experiments are performed to analyze the mechanism of the sulfation conversion process. First, the reaction activation energies of the sulfate‐assisted roasting are 88.87 and 95.27 kJ mol −1 , which are calculated by Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) methods, respectively. Then, nucleation and growth are determined and verified as the sulfation reaction model by the Šatava–Šesták method. Finally, sub‐reactions of the sulfation process are investigated and reaction controlling mechanisms are determined by the contribution of sub‐reaction. Based on the thermogravimetric analysis, the phase boundary reaction is found to dominate in the initial step of the roasting process (α < 0.6) while the nucleation reaction controlls the following step (α > 0.6), agreeing well with changing trend of activation energy. Overall, thermogravimetric analysis is a general way to study the mechanism of the various roasting processes.