Deep Eutectic Solvents: Green Approach for Cathode Recycling of Li‐Ion Batteries

Abstract

Lithium-ion batteries (LIBs) are highvoltage, high-energy, and high-power density energy storage devices with long cycle life, therefore intensively applied in full and hybrid electric vehicles, portable electronic devices (computers, mobile phones, and tablet), and renewable (solar and wind) sector. [1,2] Typically, LIBs for such applications with estimated lifetime of around 3-10 years generate a vast amount of waste at their end-of-life. [3,4] It is estimated that over 11 million tonnes of spent LIBs will be discarded through to 2030, and only less than 5% of them are being recycled. [4] Moreover, due to rapidly increasing demand of LIBs, the price of crucial element resources (Li, Ni, and Co) is also significantly increasing. In contrast, the health and environmental concerns may arise in the event of large, accumulated quantities of cobalt and lithium metals, which typically constitutes up to 20 and 7 wt%, respectively, of LIB cathodes, as well as toxic and flammable electrolytes (e.g., lithium hexafluorophosphate, LiPF 6 ). [3][4][5] Therefore, efficient recovery of such raw materials in spent LIBs is extremely crucial.At present, LIBs are recycled commercially using well-known processes such as pyrometallurgy, hydrometallurgy, and direct recycling. [4] However, these processes do not extract the maximum value from their feedstock. For instance, pyrometallurgy, or smelting operate at very high temperature (over 1100 C), which eliminates several materials (carbon anode, plastic separator, and electrolyte solvents) through vaporization (electrolyte), combustion, and melting. The final product is a mixed alloy of cobalt, nickel, and copper. The concept of direct recycling is simple: keep the cathode crystal structure intact. The definition of direct recycling is the recovery, regeneration, and reuse of battery components directly without breaking down the chemical structure. It has also been called direct cathode recycling and cathode-to-cathode recycling. By recovering cathode material, several energy-intensive and costly processing steps can be avoided. Not only does recovery of more materials offer potential additional revenues, but also costs and other impacts from waste treatment can be avoided. Advantages include low temperatures and low energy consumption, and the avoidance of most impacts from virgin material production.

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

“…Consequently, the extraction of metals using ethaline takes place without oxygen protonation, differently from the mechanism proposed by Hartley and co‐workers regarding DESs formulated with organic acids [14] . In addition, DESs are characterized by high metal extraction rate, low toxicity, safety, and biodegradability, but they have a cost much larger than traditional mineral acid‐based metal extraction systems [3] . Therefore, the extensive reuse of DES is mandatory to ensure the economic feasibility of the recycling process, and this aspect is not addressed in the literature.…”

“…[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] …”

Ternary Deep Eutectic Solvent (DES) with a Regulated Rate-Determining Step for Efficient Recycling of Lithium Cobalt Oxide

“…Still, the leaching efficiency needs improvement to meet the demand for the LIBs recycling at large scale. The complete leaching of cathode powders using binary DES composed of a HBD and a HBA species generally require tens of hours or even days. ,, Fundamentally, the leaching process of the solid materials in solvents involves the chemical reaction process and the mass transfer process. The chemical reaction rate is limited by the reaction kinetics while the mass transfer rate is limited by the mobility of the substance.…”

New Bifunctional Deep-Eutectic Solvent for In Situ Selective Extraction of Valuable Metals from Spent Lithium Batteries

“…), and their melting points are lower than any of the individual components. , Till now, the major application areas of DESs have mainly focused on metal electrodeposition and synthesis media due to the high solubility of metal salts, wide potential windows, low vapor pressure, and tunable compositions. In particular, some unique advantages of DESs, including the different coordination ability between the components and metals, great reusability, and inexpensive components, endow the solvents the potential to selectively extract metals from complex resources on a large scale with low-cost green strategies. , In 2005, the DESs as-prepared by 1 mol choline chloride and 2 mol urea helped realize certain selective dissolving transition-metal oxides, and the solubilities of ZnO, PbO 2 , and Fe 2 O 3 were 8466, 9157, and 49 ppm in the solvent (60 °C). Subsequently, non-aqueous DESs were introduced into the field of solvent metallurgy in 2009, solving the problem of wastewater discharge in traditional hydrometallurgy .…”