Cathode Active Material Recycling from Spent Lithium Batteries: A Green (Circular) Approach Based on Deep Eutectic Solvents

Abstract

The transition to a circular economy vision must handle the increasing request of metals required to satisfy the battery industry; this can be obtained by recycling and feeding back secondary raw materials recovered through proper waste management. Here, a novel and green proof‐of‐concept was developed, based on deep eutectic solvents (DESs) to fully and easily recover valuable metals from various cathode active materials, including LiMn2O4, LiNi0.5Mn1.5O4, and LiNi0.8Co0.2O2. DES composed of choline chloride and lactic acid could leach Li, Mn, Co, and Ni, achieving efficiency of 100 % under much milder conditions with respect to the previous literature. For the first time, to our best knowledge, a two‐step approach was reported in the case of LiNi0.8Co0.2O2 for selective recovery of Li, Co, and Ni with high yield and purity. Furthermore, other cathode components, namely aluminum current collector and binder, were found to be not dissolved by the proposed DES, thus making a simple separation from the active material possible. Finally, this strategy was designed to easily regenerate and reuse the leaching solvents for more than one extraction, thus further boosting process sustainability.

Decomposition of Deep Eutectic Solvent Aids Metals Extraction in Lithium‐Ion Batteries Recycling

“…[8] Morina et al reported the reuse of a DES with an organic acid as hydrogen bond donor. [4] In their work, LIBs cathode materials were leached at temperatures up to 170 °C and for 24 h. Again, in this latter works, no results about DES decomposition were reported, though Rodriguez et al demonstrated the decomposition of DESs based on organic acid at milder condition (80 °C; 2 h). [19] In this work, thermally treated DES was used in the leaching of LIBs black mass allowing for extraction yields greater than 90 % after only 4 h. Among the degradation products, the trichloride anion Cl 3…”

“…[2] A competitive green alternative is represented by solvometallurgical processes, where deep eutectic solvents (DESs) are used to dissolve LIB metal oxides. [3,4] DES are mixtures of two or more components with a melting point lower than those of its individual components, which include a hydrogen bond acceptor (HBA; typically a quaternary ammonium salt) and a hydrogen bond donor (HBD; e. g., alcohol or carboxylic acid). Synthesis of DESs is generally straightforward, and biodegradability, safety, and low price can be ensured by the proper selection of the DES components.…”

“…Hydrometallurgical recycling allows effective recovery of electrode metals but is characterized by a negative environmental footprint, mainly determined by the application of toxic mineral acids and by the generation of large wastewater volumes [2] . A competitive green alternative is represented by solvometallurgical processes, where deep eutectic solvents (DESs) are used to dissolve LIB metal oxides [3,4] …”

“…Recently, attracted by these peculiarities, researchers have extended the application of DESs to the recycling of LIBs as metal leaching agents [5] . Different combinations of hydrogen bond donor and hydrogen bond acceptor in DES formulation were tested with the aim to maximize the metal extraction yields [4,6–11] . However, despite this interest of the scientific community, only very few studies attempted to develop a description of the mechanisms driving the dissolution of metal oxides in the employed DESs [12,13] .…”

“…The high cost of DESs combined with the lack of results about their possible reuse are the major obstacles to overcome their application on scale larger than laboratory. It is worth noting that the vast majority of the works reported in the literature involve the use of organic acid as hydrogen bond donor and, according to the above‐described leaching mechanism, imply the consumption of proton with formation of water during the metal oxide leaching [4,7,9–11] . To all effects, DES is acting as reagent and is irreversibly consumed, compromising its reuse in following metal extraction cycles.…”