Highly Efficient p-Toluenesulfonic Acid-Based Deep-Eutectic Solvents for Cathode Recycling of Li-Ion Batteries

Abstract

The common use of Li-ion batteries (LIBs) in portable devices and electric vehicles is promoting an exponential growth of the rechargeable batteries market. Their use in electric vehicles while not yet so common will be favored in the near future by government incentives aiming to mitigate global warming effects coming from combustion engines. Despite the remote risk of cobalt (Co) and lithium (Li) supplies running low, metals recovery from “postconsumer” scrap is a rapidly expanding topic in the political agenda within the context of the circular economy. Among other recycling technologies, processes using mild conditions and providing high recycling efficiencies are gaining increased interest. For instance, organic acids are particularly interesting for LiCoO2 dissolution even though they typically need the additional use of reducing agents. Herein, we explore the Co (and Li) recovery from spent LIBs using deep eutectic solvents (DESs) at temperatures as low as 90 °C, at times of dissolution as short as 15 min and without the use of any additional reducing agent. In particular, we used the eutectic mixture composed of p-toluenesulfonic acid (PTSA) monohydrate and choline chloride (ChCl) (e.g., PTSA·H2O·ChClDES with a 1:1:1 molar ratio) and aqueous dilutions thereof (e.g., PTSA·2H2O·ChClDES and PTSA·3H2O·ChClDES with 1:2:1 and 1:3:1 molar ratios, respectively). Compared to organic acids, PTSAChCl-based DESs offered a significant reduction of the solute to solvent ratio (in g/L) needed for full Co dissolution. This brings benefits both in economic and sustainable terms that handling low solvent volumes has in industrial processes. Interestingly, Co recovery efficiencies from spent LIBs reached figures of up to 94% over the whole process relating to the extraction from spent LIBs using PTSAChCl-based DESs, the precipitation with either Na2CO3 or (NH4)2CO3, and the final calcination to obtain Co3O4.

Deep Eutectic Solvents for Boosting Electrochemical Energy Storage and Conversion: A Review and Perspective

“…[ 134 ] The strong reducibility of reline enables the extraction at a mild condition (180 °C) with a short reaction time of 12 h. They also found Co can be recycled as Co 3 O 4 using H 2 C 2 O 4 and NaOH precipitants through a dilution–precipitation–calcination process. Other DES systems such as ChCl/citric acid, [ 135 ] p‐toluenesulfonic acid monohydrate/ChCl, [ 136 ] and polyethylene glycol/thiourea [ 137 ] were also studied for the recycling of LiCoO 2 from spent LIBs. In addition to the extraction of metal ions, Wang et al.…”

Sustainable Li‐Ion Batteries: Chemistry and Recycling

“…A comparable recovery of 94% for Co from used LIBs, covering the entire process from battery disassembly to metal precipitation, was demonstrated when using a deep eutectic solvent consisting of p-toluenesulfonic acid monohydrate and choline chloride. [156] An economic feasibility was suggested based on the short extraction time of 15 min at 90 °C for cobalt from the expended cathode. The cobalt recovery from the deep eutectic solvent solution could be achieved by precipitation as cobalt carbonate.…”

Progress in the sustainable recycling of spent lithium‐ion batteries

“…In this case, some researchers shift perspectives to novel solvents. Deep eutectic solvent (DES) is one type of new solvents with low toxicity and great ability of dissolving metal oxides 31,32 . Compared with ionic liquids (ILs), DESs are obtained more cheaply and easily.…”