Product control and a study of the structural change process during the recycling of lithium-ion batteries based on the carbothermic reduction method
Xuefeng She, Kewei Zhu, Jingsong Wang, Qingguo Xue
Abstract
Carbothermal reduction to recover lithium-ion batteries is an environmentally friendly recycling method. This work provides a theoretical analysis of the thermodynamics and an experimental verification process for the carbon thermal reduction recovery of lithium cobaltate (LiCoO 2 ), as well as an explanation of the microstructural changes. The reaction conditions are controlled to obtain the ideal recovery product. A thermodynamic graph of the possible reaction between LiCoO 2 and graphite (C) and the reduction of cobalt oxide (CoO, Co 2 O 3 , Co 3 O 4 ) by carbon monoxide (CO) is obtained by thermodynamic analysis. The feasibility of the carbothermic reduction reaction of LiCoO 2 at high temperature is studied under standard atmospheric pressure. By controlling the reaction temperature (800 °C) and the ratio of the reactants (LiCoO 2 /C = 4:5), the reduction products cobalt monoxide (CoO) and lithium carbonate (Li 2 CO 3 ) are obtained, and the recovery rates are 89% and 84%, respectively. From the perspective of the crystal structure, the reduction process of LiCoO 2 is analyzed. The Li-O bond in the LiCoO 2 crystal structure is destroyed by CO, which promotes destruction of the Li-O octahedral structure and the formation of a Co-O octahedron. The Li-O octahedron is transformed into a tetrahedral structure in Li 2 O, and Li 2 O then reacts with CO 2 to form Li 2 CO 3 ; the Co-O octahedrons combine to form a CoO crystal structure. When the temperature continues to rise, CoO is reduced to Co. The carbothermic reduction recovery method does not require any additional hazardous chemicals and can avoid secondary pollution during the recovery process. This research provides theoretical support for the industrial recycling of lithium-ion batteries.