Enhanced selective separation of valuable metals from spent lithium-ion batteries by aluminum synergistic sulfation roasting strategy

Recycling of spent lithium-ion batteries has become crucial due to the current situation of resource shortage and environmental pollution. Herein, the proposed process fully utilizes cheap ammonium sulfate as sulfating agent and aluminum foil of spent lithium-ion batteries itself as reducing agent for synergistically roasting the cathode material. Thermodynamic analysis and experimental results show that, different from conventional sulfation and thermite reduction roasting, aluminum synergistic sulfation roasting converts Li in the cathode material to water-soluble Li2SO4 instead of LiMn2O4 and LiAlO2, and reduces transition metals to acid-soluble low-valent oxides instead of high-valent oxides or metal elements. The effects of roasting temperature, ammonium sulfate dosage, and roasting time on the phase transformation were studied. Under the optimal roasting parameters (T = 600 °C, n[(NH4)2SO4]:n(2Li) = 1.4, t = 1.0 h) of spent ternary cathode, the water leaching efficiency of Li is 97.2 % with less than 0.5 % of Al and transition metals being co-leached. Subsequently, more than 96 % of Al and 99 % of transition metals can be extracted through alkaline and non-reducing agent acid leaching, respectively. This work provides a potential approach and valuable technical reference for the efficient and selective recovery of valuable metals directly from the spent ternary cathode with high aluminum content.