Conversion Mechanisms of Selective Extraction of Lithium from Spent Lithium-Ion Batteries by Sulfation Roasting

With the undergoing unprecedented development of lithium-ion batteries (LIBs), the recycling of end-of-life batteries has become an urgent task considering the demand for critical materials, environmental pollution, and ecological impacts. Selective recovery of targeted element(s) is becoming a topical field that enables metal recycling in a short path with highly improved material efficiencies. This research demonstrates a process of selective recovery of spent Ni-Co-Mn (NCM)-based lithium-ion battery by systematically understanding the conversion mechanisms and controlling the sulfur behavior during a modified-sulfation roasting. As a result, Li from complex cathode components can be selectively extracted with high efficiency by only using water. Notably, the sulfur driven recovery processes can be divided into two stages: (i) part of the structure of NCM523 was destroyed, and Ni, Co, and Mn were reduced to divalent in different degrees to form sulfate (NiSO₄, CoSO₄, MnSO₄) when reacting with H₂SO₄ at ambient temperature; (ii) with increasing temperature, Li ions in the unstable layered structure are released and combined with SO₄^2- in the transition metal sulfate to form Li₂SO₄, and the sulfates of transition metals react to form Ni_0.5Co_0.2Mn_0.3O_1.4. Studies have shown sulfur can be recirculated thoroughly in the form of SO₄^2-, which in principle avoids secondary pollutions. By controlling the appropriate conversion temperature, we envisage that the sulfation selective roasting recovery technology could be easily applied to other spent lithium-ion battery materials. Besides, this work may also provide a unique platform for further study on the efficient extracting of other mineral resources.