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 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. The 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 °C, a reaction time of 4 h, 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.