Spent lithium-ion battery recycling: multi-stage synergistic deep removal of impurities and lithium extraction

Abstract Nowadays, the recycling of spent lithium-ion batteries is a key concern in the energy field. Among them, for the purification of Li-containing mother liquor, the targeted multi-means coupling impurity removal methods are mostly employed, which however, inevitably lead to a Li loss of 3~5%, and high costs. In this study, a multi-stage hydrolysis method, combining with the residual P and Al, Mg, Cu, Zn, Ni, Fe, forming hydroxide-phosphate co-precipitation for the synergistic impurity separation, was adopted. Thermodynamic calculations show that Li+ and Mg2+ are insensitive to pH when pH <10, and Al, Cu, Zn, Ni, Fe behave similarly in nature. Impurities should be precipitated as: Fe3+＞Al3+＞Cu2+＞Ni2+＞Zn2+＞Mg2+, with phosphate precipitating first, followed by converting into hydroxide as pH rising. Actual results showed that the order was P＞Fe & Al & Cu & Ni & Zn＞Mg, and the process was divided into three steps, with separation points at pH = 2.37, 8.66, and 11.00, respectively. All the impurity removal efficiencies were close to 100%, the loss of Li was 1.74%. The optimal conditions for Li2CO3 precipitation were determined: an Na2CO3 addition of 1.5 times the theoretical amount, a temperature of 90 oC, a reaction time of 4 hours, and a one-time addition of dosing method. Li precipitation efficiency reaches 90.10%, with a 99.95% purity. The results effectively reduced Li losses and provided a practically feasible basis for the industrial purification of Li-containing mother liquor.