Extraction of valuable metals from the waste of Li-ion batteries

Abstract

The production and use of the Li-ion batteries is growing rapidly, entailing a future surge of the related scrap mass. It justifies the investigation and development of their processing, enabling the recovery of the valuable metals and avoiding the environmental hazards. The special features (long life, high number of efficient cycling, fast charging, high energy density, stable voltage) of the most developed types guarantee their bright future in such important applications as consumer electronics and electric vehicles. Depending on the actual type, the cathode material usually contains critical – thus highly valuable – metals, like Co, Ni, and Li. The carrier of these materials, the Cu and the Al current collector foils are also of economic interest to be recovered. The best performing batteries are based on the more expensive common transition metals, whose primary supply is limited. Thus recycling is getting a key issue in achieving the ambitious plans of electrification. Hydrometallurgical processing of the black mass, containing the active electrode materials and obtained by physical separation of the shredded and ground scrap, offers the recovery of the valuable metals either in compound or elemental states. The fi ne black mass powder of mixed vehicle Li-ion batteries may contain 4–22% Co, 10–18% Ni, 0.5–15% Mn, and 3.5–4% Li in the complex Li-transition metals oxide cathode material, beside 1–2% Al and Cu as residues of the metal foils, also a few per cent of Fe and 20–30% graphite from the anode. The latter is inert in the aqueous processing and can be easily separated as a by-product. In order to recycle the valuable transition metals (Ni, Co, and Mn) for producing new cathode materials, it is also possible to adjust the final steps of the hydrometallurgical procedure to obtain just the required composition of the mixed hydroxides or oxides of these metals. Due to less stringent economic and environmental conditions, the recovery of Li from the cathode material is not common yet, although it is also possible by a multi-step hydrometallurgical scheme, in either the carbonate or the hydroxide forms, however it requires more energy input. The hydrometallurgical procedure starts with leaching in usually sulphuric acid of moderate concentrations, requiring the addition of a mild reducing agent to bring the higher oxidation states of the transition metals to the soluble divalent sate. According to our laboratory results, however, hydrochloric acid can be an even more efficient lixiviant and the contained chloride ions act as reducing agents. However, it also implies the use of more expensive structural materials. An important further advantage of the chloride solution is the possibility of controlled complex formation, which can convert the targeted metals into anionic species to be sorbed by strongly basic anion-exchange resins. Such a scheme has been developed in our laboratory to produce a pure Co-chloride solution, while Ni and Mn are released from the anion-exchange column during the loading and the first rinsing steps. Cobalt can be precipitated as a pure hydroxide compound from the eluate, while Mn and Ni are separately obtained as oxide and hydroxide products in a subsequent oxidative precipitation treatment. After re-dissolution, pure electrolytes can be produced from these precipitated compounds for depositing metals, as alternative products, by cathodic reduction, also optimised in our laboratory.