Reviving lithium: a sustainable approach to recover lithium metal from spent lithium-ion batteries using deep eutectic solvents

In this work, we investigated the effects of a single covalent link between hydrogen bond donor species on the behavior of deep eutectic solvents (DESs) and shed light on the resulting interactions at molecular scale that influence the overall physical nature of the DES system. We have compared sugar-based DES mixtures, 1:2 choline chloride/glucose [DES(g)] and 1:1 choline chloride/trehalose [DES(t)]. Trehalose is a disaccharide composed of two glucose units that are connected by an α-1,4-glycosidic bond, thus making it an ideal candidate for comparison with glucose containing DES(g). The differential scanning calorimetric analysis of these chemically close DES systems revealed significant difference in their phase transition behavior. The DES(g) exhibited a glass transition temperature of -58°C and behaved like a fluid at higher temperatures, whereas DES(t) exhibited marginal phase change behavior at -11°C and no change in the phase behavior at higher temperatures. The simulations revealed that the presence of the glycosidic bond between sugar units in DES(t) hindered free movement of sugar units in trehalose, thus reducing the number of interactions with choline chloride compared to free glucose molecules in DES(g). This was further confirmed using quantum theory of atoms in molecule analysis that involved determination of bond critical points (BCPs) using Laplacian of electron density. The analysis revealed a significantly higher number of BCPs between choline chloride and sugar in DES(g) compared to DES(t). The DES(g) exhibited a higher amount of charge transfer between the choline cation and sugar, and better interaction energy and enthalpy of formation compared to DES(t). This is a result of the ability of free glucose molecules to completely surround choline chloride in DES(g) and form a higher number of interactions. The entropy of formation for DES(t) was slightly higher than that for DES(g), which is a result of fewer interactions between trehalose and choline chloride. In summary, the presence of the glycosidic bond between the sugar units in trehalose limited their movement, thus resulting in fewer interactions with choline chloride. This limited movement in turn diminishes the ability of the hydrogen bond donor to disrupt the molecular packing within the lattice structure of the hydrogen bond acceptor (and vice versa), a crucial factor that lowers the melting point of DES mixtures. This inability to move due to the presence of the glycosidic bond in trehalose significantly influences the physical state of the DES(t) system, making it behave like a semi-solid material, whereas DES(g) behaves like a liquid material at room temperature.

The recycling of lithium-ion batteries (LIBs) is of critical importance due to the increasing demand for electric vehicles and portable electronic devices. It also helps address supply risks of critical raw materials and reduces the environmental impact of mining. Traditional recycling methods are often inefficient and environmentally damaging. This study investigates the use of deep eutectic solvents (DES), made from citric acid and choline chloride, for leaching valuable metals from black mass derived from spent LIBs. The research focuses on optimizing the leaching parameters, such as temperature, DES ratio, and solid-to-liquid ratio, to maximize the extraction efficiency of lithium, cobalt, nickel, and manganese. A key aspect of the study was the examination of the rheological properties of the DES system, as these properties significantly impact the leaching process. The viscosity and pH of the DES were measured, providing insights into their behavior under various conditions. Understanding the viscosity and flow characteristics of these DES systems is crucial for developing scalable and effective recycling methods. The DES mixture with a 2:1 ratio of citric acid to choline chloride, mixed with 50% water, showed the best performance. At 90 °C for 24 h, this DES mixture achieved leaching efficiencies of 77.5% for lithium, 79.9% for cobalt, 80% for manganese, 66.2% for nickel, 82.5% for copper, and 93.8% for aluminum. These findings suggest the potential of citric acid-choline chloride DES as a sustainable and environmentally friendly reagent for recycling LIBs.

Molecular dynamic (MD) simulation and density function theory (DFT) calculation relevant to green leaching of metals from spent lithium-ion battery cathode materials using glucose-based deep eutectic solvent (DES)

Metal organic frameworks (MOFs) are a class of porous polymeric material composed of metal ions or clusters linked together by organic bridging ligands. Their large surface areas accompanied by uniform pores, open metal sites, and diverse available post-synthesis functionalization routes make MOFs promising candidate materials for gas storage, separation, and heterogeneous catalysis. MOFs are typically synthesized by solvothermal reactions in organic solvents or in water, but have also been prepared in ionic liquids (ILs) recently; examples of the latter include Cu-BTC (BTC: 1,3,5-benzenetricarboxylate), Ln-BTC, Cd-BTC, Zn-BTC, and others. ILs have been attracting increasing attention as a solvent of choice for chemical synthesis, because of their unique integration of various properties such as essentially zero vapor pressure, excellent solvating properties, easy recyclability, and high thermal stability. The majority of the reports dealing with MOF synthesis have focused on ILs derived from 1-alkyl-3-methylimidazolium. However, deep eutectic solvents (DESs), mixtures of two or more compounds that have melting points lower than that of either of their constituents, are known to exhibit solvent properties very similar to those of ILs and have been employed for MOF synthesis. They have advantages over other types of ILs such as ease of preparation as pure phases from easily available components, low prices, and relative unreactivity towards atmospheric moisture. DES can act as both a solvent and a ligand during the MOF synthesis. MOFs can be synthesized by sonochemical method which has exhibited rapid synthesis kinetics, uniform particle morphology, and excellent phase purity in inorganic materials synthesis. The sonochemical method promotes homogeneous nucleation and reduces crystallization time considerably via the creation, growth, and collapse of an acoustic cavity, generating extremely high temperature (5000-25000 K)/pressure as well as fast heating and cooling rates. In the sonochemical synthesis route, in connection with this reaction mechanism, DESs are thought to create cavitation easily at relatively high temperatures due to their low vapor pressures, and thus have good potential as a reaction medium in the sonochemical synthesis of nanomaterials. In this work, we have chosen the widely investigated Cu3(BTC)2 as a representative MOF material for sonochemical synthesis using choline chloride/dimethylurea DES as a solvent (designated as S-CuBTC). To the best of our knowledge, this is the first report of sonochemical synthesis of a MOF structure in a DES. Effects of various synthesis parameters on the crystallization process of Cu3(BTC)2 were examined, and the properties of the sample were compared to those of Cu3(BTC)2 prepared via a conventional ionothermal synthesis route in an oven (designated as C-CuBTC). In order to use MOFs for adsorption, rigorous guest removal from the pores has to be performed so as to achieve the highest possible surface area (and pore volume). This is typically accomplished by solvent washing and vacuum treatment. Since the mixture of choline chloride and 1,3dimethylurea in a molar ratio of 1:2 used in this work has a eutectic temperature of around 70 C, removal of the solvent guest before it solidifies inside the pores is challenging. Thus, an effective activation procedure for Cu3(BTC)2 samples obtained under ionothermal synthesis conditions was briefly examined by conducting repeated sample washing with de-ionized water and ethanol in the manner described in entries I to V in Table 1. No apparent PXRD patterns or morphology changes were observed after washing step II (see Figure S1 and S2). The corresponding SEM images after different washing steps did not reveal any noticeable differences either, except that the DES coated at the external surface in the Cu3(BTC)2 sample was removed. However, repeated washing (200 mL × 2) by de-ionized water and ethanol was necessary to obtain the BET surface area of a high quality Cu3(BTC)2, as shown in Table 1. Elemental analysis of the C-CuBTC sample after washing treatment IV confirmed the virtual elimination of DES; The

Green lithium extraction and recovery using a task-specific deep eutectic solvent.

The use of deep eutectic solvents (DESs) has been proposed as a novel technique for environmentally benign mineral processing, with utility in the reprocessing of legacy tailings in a process known as solvometallurgy. These solvents can leach a wide range of metals while having many advantages, such as low volatility, high target metal selectivity, lower production costs and potentially low ecotoxicity. We aimed to determine the capacity of different DESs to mobilise copper (Cu) and other metals from Cu mine tailings. They were: DES 1 (oxaline) – choline chloride + oxalic acid; DES 2 (ethaline) – choline chloride + ethylene glycol; DES 3 – betaine + acetic acid; and DES 4 – betaine + acetic acid + phosphoric acid. In a follow-up experiment, Plantago lanceolata seedlings were transplanted to the tailings after DES application in order to determine phytotoxic responses. Our results showed that Cu extraction from tailings increases with DES concentration and pointed to DES 3 and 4 (betaine-based) as more efficient in Cu leaching, although oxaline was more capable of enhancing nutrient availability. Almost all plants died 24 hours after transplanting to DES-treated tailings, except the ones treated with oxaline, which is possibly linked to the remarkable macronutrient mobilisation – an element known to alleviate Cu phytotoxicity. However, only the diluted oxaline (1:128, DES:water) was able to improve plant growth in tailings as it mobilised more nutrients, leading to greater plant biomass and chlorophyll content. Thus it is clear that hazardous effects will depend on the DES formulation, concentration and exposure route, which may promote extreme phytotoxicity by enhancing metal availability in mine tailings. Yet diluted oxaline showed promising beneficial effects in plant health and growth, indicating that some diluted DESs, at concentrations anticipated after application and leaching, may have a role in promoting land rehabilitation.

Recyclable water-modified deep eutectic solvents for removal of multiple heavy metals from soil

Study on the method and mechanism of As and Cd removal from brown rice flour using a deep eutectic solvent-soyasaponin system.

Deep eutectic solvents (DESs) show promise in pharmaceutical applications, most prominently as excellent solubilizers. Yet, because DES are complex multi-component mixtures, it is challenging to dissect the contribution of each component to solvation. Moreover, deviations from the eutectic concentration lead to phase separation of the DES, making it impractical to vary the ratios of components to potentially improve solvation. Water addition alleviates this limitation as it significantly decreases the melting temperature and stabilizes the DES single-phase region. Here, we follow the solubility of β-cyclodextrin (β-CD) in DES formed by the eutectic 2:1 mole ratio of urea and choline chloride (CC). Upon water addition to DES, we find that at almost all hydration levels, the highest β-CD solubility is achieved at DES compositions that are shifted from the 2:1 ratio. At higher urea to CC ratios, due to the limited solubility of urea, the optimum composition allowing the highest β-CD solubility is reached at the DES solubility limit. For mixtures with higher CC concentration, the composition allowing optimal solvation varies with hydration. For example, β-CD solubility at 40 wt% water is enhanced by a factor of 1.5 for a 1:2 urea to CC mole ratio compared with the 2:1 eutectic ratio. We further develop a methodology allowing us to link the preferential accumulation of urea and CC in the vicinity of β-CD to its increased solubility. The methodology we present here allows a dissection of solute interactions with DES components that is crucial for rationally developing improved drug and excipient formulations.

To meet the high demand for lithium-ion batteries (LIBs) and their corresponding challenges, effective and sustainable recycling methods are necessary. This research explores the use of deep eutectic solvents (DES) based on polycarboxylic acid to recover critical metals, such as lithium (Li), cobalt (Co), nickel (Ni), and manganese (Mn) from spent LIBs. The leaching efficiency of 3 DES was evaluated under various conditions by synthesizing them with succinic acid, malonic acid, and maleic acid using choline chloride. Optimal recovery was achieved with ChCl: Maleic acid, yielding 99.18 wt. % Li, 65.36 wt. % Co, 94.97 wt. % Ni, and 67.88 wt. % Mn at a S/L ratio of 20 g/L at 80 °C with constant stirring. Higher S/L ratios led to reduced recovery rates due to mass transfer limitations and solution saturation. Kinetic modeling revealed that the Jander model best described the leaching mechanism, suggesting a diffusion-controlled process. The activation energy calculation on DES ChCl: Maleic acid produces Li 38.57 kJ/mol, Co 63.09 kJ/mol, Ni 64.87 kJ/mol, and Mn 52.64 kJ/mol. The use of DES derived from eco-friendly polycarboxylic acids (succinic, malonic, and maleic acids) in this study represents an innovative way to recover critical metals from spent lithium-ion batteries (LIBs) in a sustainable and effective manner. Future studies are advised to examine the DES composition and investigate how agitation influences the recovery of specific metals. HIGHLIGHTS Lithium-ion battery leaching using deep eutectic solvent as leaching agent The results obtained from the leaching of lithium-ion batteries were the recovery of 99.18 % Li, 65.36 % Co, 67.88 % Mn, and 94.97 % Ni with the optimum leaching condition used was a solid/liquid ratio of 20gr/L with a temperature of 80 °C for 2 h. The kinetic mechanism of the leaching process follows Jander kinetics. GRAPHICAL ABSTRACT

Electrodeposition of NiCo on stainless steel substrate using deep eutectic solvent for efficient hydrogen evolution and methanol oxidation reactions

High-efficiency recycling of spent lithium-ion batteries: A double closed-loop process

This study aimed to develop an efficient and environmentally sustainable method for extracting bioactive compounds from juçara palm (Euterpe edulis Mart.) fruit residues using deep eutectic solvents (DES) and conventional solvents, combined with ultrasound-assisted extraction (UAE). Seven DES formulations based on choline chloride (ChCl) and different hydrogen bond donors (glycerol, glucose, and organic acids) were prepared, and their performance was compared with water, ethanol, and ethanol/water mixtures. The phenolic composition, anthocyanins and antioxidant activity of the extracts were determined using spectrophotometric assays (Folin-Ciocalteu, DPPH, ABTS, and FRAP) and ESI-MS/MS analysis. The results showed that DES exhibited higher efficiency in recovering total phenolic compounds, anthocyanins and ABTS compared to conventional solvents, particularly in the ChCl-glycerol system. ESI-MS/MS analyses monitored around 40 phenolic compounds, including phenolic acids, flavanones, flavonoids, and anthocyanins. Acidic solvents favored anthocyanin extraction and stability, while ethanol- and glycerol-based systems provided broader compound profiles. The use of DES proved to be a green and selective alternative for obtaining extracts rich in bioactive compounds, enhancing the value of juçara residues and contributing to the sustainability of the species production chain.

Solvometallurgical recycling of spent LiNixCoyMnzO2 (NCM) cathode material using ternary choline chloride-ethylene glycol-p-toluenesulfonic acid deep eutectic solvent

The surging demand for lithium-ion batteries (LIBs) has intensified the need for sustainable recovery of critical metals such as lithium, manganese, cobalt, and nickel from spent cathodes. While conventional hydrometallurgical and pyrometallurgical methods are widely used, they involve high energy consumption, hazardous waste generation, and complex processing steps, underscoring the urgency of developing eco-friendly alternatives. This study presents a novel, water-enhanced deep eutectic solvent (DES) system composed of choline chloride and D-glucose for the efficient leaching of valuable metals from spent LiMn-based battery cathodes. The DES was synthesized under mild conditions and applied to dissolve cathode powder, with leaching performance optimized by varying temperature and duration. Under optimal conditions (100 °C, 24 h), exceptional recovery efficiencies were achieved: 98.9% for lithium, 98.4% for manganese, and 71.7% for nickel. Material characterization using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and inductively coupled plasma mass spectrometer (ICP-MS) confirm effective phase dissolution and metal release. Although this DES system requires relatively higher temperature and longer reaction time compared to traditional acid leaching, it offers clear advantages in terms of non-toxicity, biodegradability, and elimination of strong oxidizing agents. These results demonstrate the potential of water-enhanced choline chloride–glucose DES as a green alternative for future development in sustainable battery recycling, supporting circular economy objectives.