Leaching of lithium cobaltate cathode material with phosphite eutectic solvent
Deep eutectic solvents (DES) have attracted significant attention within the areas of cathode material recovery from spent lithium-ion batteries (LIBs),owing to their remarkable properties of good dissolving capacity for metal oxides,simple synthesis procedures and low pollution. In this work,a novel deep eutectic solvent composed of choline chloride (hydrogen bond acceptor,ChCl) and phosphorous acid (hydrogen bond donor,PA) was synthesized,and the leaching performances of lithium and cobalt from lithium cobalt oxide (LiCoO2) using the DES as lixiviants were studied. The effects of DES composition,leaching time,temperature,and liquid-to-solid ratio on leaching efficiencies were investigated,and the leaching mechanism was analyzed by UV-Vis spectra,FTIR spectra and ion chromatography. The results indicate that the phosphite-based DES (n(PA):n(ChCl)=4∶1) exhibits an exceptionally low viscosity of 155 mPa·s at 20 ℃. Meanwhile,the leaching kinetics is fast and the leaching efficiency is high for leaching of LiCoO2 by the DES. At a leaching temperature of 80 ℃,a liquid-to-solid ratio of 80 g/g and a leaching time of only 20 min,the leaching efficiencies for lithium (Li) and cobalt (Co) reach 99％ and 97％,respectively. During the DES leaching process,Co3+in LiCoO2 is reduced to Co2+by phosphorous acid while it is oxidized to phosphoric acid,and Co2+is present as[CoCl4]2-in the leaching solutions.
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