Unveiling the lithium deintercalation mechanisms in spent lithium-ion batteries via sulfation roasting

Recovery of valuable metals from spent lithium-ion batteries (LIBs) is of great importance for resource sustainability and environmental protection. This study introduced pyrite ore (FeS₂) as an alternative additive to achieve the selective recovery of Li₂CO₃ from spent LiCoO₂ (LCO) batteries. The mechanism study revealed that the sulfation reaction followed two pathways. During the initial stage (550 °C-800 °C), the decomposition and oxidation of FeS₂ and the subsequent gas-solid reaction between the resulting SO₂ and layered LCO play crucial roles. The sulfation of lithium occurred prior to cobalt, resulting in the disruption of layered structure of LCO and the transformation into tetragonal spinel. In the second stage (over 800 °C), the dominated reactions were the decomposition of orthorhombic cobalt sulfate and its combination with rhombohedral Fe₂O₃ to form CoFe₂O₄. The deintercalation of Li from LCO by the substitution of Fe and conversion of Co(III)/Fe(II) into Co₃O₄/CoFe₂O₄ were further confirmed by density functional theory (DFT) calculation results. This fundamental understanding of the sulfation reaction facilitated the future development of lithium extraction methods that utilized additives to substantially reduce energy consumption.