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

Abstract

Abstract 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 SO42– in the transition metal sulfate to form Li2SO4, and the sulfates of transition metals react to form Ni0.5Co0.2Mn0.3O1.4. Studies have shown sulfur can be recirculated thoroughly in the form of SO42–, 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.