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The leaching and recycling of valuable metals via environmentally benign solvents is important because of the ever-increasing waste lithium-ion batteries, but it remains a challenge. Herein, a multi-functional deep eutectic solvent (DES) based on lactic acid (LA) and guanidine hydrochloride (GHC) was used to extract cobalt and lithium ions from LiCoO2 . Due to the strong acidity (protons) and abundant chlorine coordinating ions of LA/GHC, the solubility of LiCoO2 in LA/GHC could reach as high as 19.9 mg g-1 (stirred at 80 °C for 24 h), and a little LiCoO2 powder even could be dissolved at room temperature without stirring. Oxalic acid was used to strip and separate the oxalates of cobalt and lithium. Furthermore, LA/GHC could be recycled with a similar dissolving performance. This work avoided using corrosive acids and could be realized at low temperature (80 °C), making it energy-saving and cost-effective. It shows DESs have great potential in extracting strategically important metals from LiCoO2 cathodes and provides an efficient and green alternative for sustainable recycling of spent lithium-ion batteries.
Tian et al. (2022) studied this question.