Preferential lithium extraction and regeneration of LiCoO2 cathodes from spent lithium-ion batteries via two-step (NH4)2SO4 roasting approach

The recovery of lithium from spent lithium-ion batteries offers a significant way to alleviate the shortage of lithium resources. In this work, the preferential extraction of lithium from the spent LiCoO2 (LCO) cathode through a two-step (NH4)2SO4 roasting was proposed, followed by regeneration LCO (r-LCO). Firstly, the LCO structure was destroyed, and parts of Li and Co were converted into Li2SO4 and CoSO4. At this time, the elemental sulfur was stored and recycled in the form of SO42-. Secondly, CoSO4 acted as a roasting agent and reacted with the residual LCO (R-LCO) to form water-soluble Li2SO4 with the increase in temperature, while CoSO4 was converted into water-insoluble Co3O4. Lithium was preferentially extracted through the subsequent water-leaching. No impurity cations were introduced in the whole roasting process which had a high sulfur atom economy of 54.4%. Finally, the effects of key parameters such as roasting temperature, w(LCO)/w((NH4)2SO4), and holding time on preferential lithium extraction were investigated. The results showed that 98.75% of the lithium was preferentially extracted and then successfully prepared as battery-grade Li2CO3. 99.32% of the Co was recovered in the form of Co3O4. The r-LCO with excellent structure and electrochemical performances and a high-capacity retention of 91.6% at 1C after 150 cycles.