Stepwise recycling valuable metals from spent lithium-ion batteries cathode: high-efficient leaching by deep eutectic solvent and selective separation by recrystallization and electrostatic interaction

With the rapid expansion of electric device and vehicle markets, the huge amount of spent Lithium-ion batteries (LIBs) will be produced and pose a serious challenge to environmental safety. The complexity and similar characteristics for multiple valuable metals presented in LIBs cathode materials result in difficulties in their extraction and separation. In this study, a deep eutectic solvent (DES) was prepared by mixing chloroacetic acid (CAA) and betaine hydrochloride (BeCl), and used to extract valuable metals from spent cathode material. The maximum leaching efficiencies of Li, Ni, Co and Mn meet 99.64 %, 99.56 %, 98.92 % and 99.82 % under optimal conditions. Furthermore, the addition of ethanol alters the polarity of the leaching solution, leading to the recrystallization of [C₅H₁₂NO₂]⁺ within the solution. [CoCl₄]²⁻, [MnCl₄]²⁻ form stable compounds with [C₅H₁₂NO₂]⁺ through electrostatic interaction and were separated from the leaching solution. Subsequently, valuable metal ions were stepwise selectively precipitated and recovered by adding oxalic acid (OA) and adjusting pH. Ni and Co was recovered in NiC₂O₄·2H₂O and CoC₂O₄·2H₂O, Mn and Li was recycled in the form of Mn(OH)₂ and Li₂CO₃. The acidity, reducibility and coordination capabilities provided by CAA and BeCl ensure efficient extraction of valuable metals under relatively mild reaction conditions. The selective recrystallization and electrostatic interaction avoid the shortcomings of co-precipitation, and realize selective separation of valuable metals. The whole recovery efficiencies of Li, Ni, Co and Mn from LIBs cathode achieved around 86.1 %, 98.78 %, 93.15 % and 91.97 %, respectively. This study provides a green method for recovering valuable metals from spent LIBs.