An integrated process for recycling spent LiCoO2 cathode materials via sulfate roasting and stepwise precipitation

With the rapid development of new energy industry, the quantity of spent lithium-ion batteries (LIBs) is increasing accordingly. From the environmental protection and resource recovery standpoints, it is crucial to recover valuable metals from spent LIBs. In this study, an efficient and integrated process was proposed to extract the valuable metals from spent LIBs with inexpensive Fe₂(SO₄)₃ as a reagent. The effects of various process parameters including the mass ratio of Fe₂(SO₄)₃ to the cathode material (F/C), roasting temperature, and roasting time on the leaching efficiencies were investigated. The leaching efficiency of Li was approximately 100 %, and that of cobalt reached 96 %, while the iron was hardly leached under the optimal conditions. The reaction mechanism of sulfation roasting process was studied through thermodynamic behavior, phase transformation as well as valence state transition. When roasting at a low temperature (＜600 °C), the ion-exchange reaction dominated, which converted lithium into its soluble sulfate prior to cobalt. With increased temperature (600–700 °C), Fe₂(SO₄)₃ decomposed and generated SO₂, promoting the sulfation reaction through gas–solid interaction, and thus increasing the leaching efficiency of Li and Co. Once the temperature reached 800 °C, CoSO₄ decomposed and the resulting cobalt oxide reacted with Fe₂O₃ to create a spinel phase CoFe₂O₄, which is very difficult to dissolve, will reduce the recovery of cobalt. Furthermore, the recovery of Li and Co from the filtrate using H₂C₂O₄ and Na₂CO₃ was investigated, where the recovery efficiency of Co and Li from the filtrate reached 94 % and 88 %, respectively. The findings demonstrated that it is possible to recover valuable metals from the cathode materials of spent LiCoO₂ batteries through the sulfation roasting-water leaching process followed by stepwise precipitation.