Beyond the Conventional Leaching: Exploring Pyruvic Acid-Based Deep Eutectic Solvents for Sustainable Recycling of Spent Lithium-Ion Battery Cathode Material

Abstract

In the relentless pursuit of technological advancement, the world is steering toward groundbreaking progress, particularly in the domain of energy production and storage. In the energy storage domain, the role of Li-ion batteries (LIBs) is indispensable, which leads to their propelling surge and, consequently, an upswing in scrap generation. Considering the environmental impact and the exorbitant value of lithium and heavy metals in spent LIBs, a less hazardous and more efficient recovery is imperative. Herein, a deep eutectic solvent (DES) was devised to efficiently extract valuable metals from spent LIBs under optimized experimental conditions, notably without any additional reducing agents. We proposed two different choline chloride (ChCl)-based DESs, employing pyruvic acid (PA) and glyoxilic acid (GLY) as hydrogen bond donors. Through the vertical ionization potential (VIP) calculations, it was observed that PA manifests a lower VIP than GLY, indicating its propensity as a favored reductant for leaching cathode materials. Experimental findings further validated this assertion, demonstrating that ChCl/PA (1:1) effectively extracts 99% of both Co and Li from spent LIB cathode materials at 80 °C within a 5 h leaching duration. Compared to conventional lixiviants, this approach using ChCl/PA offered a significant leaching efficiency and brings benefits to the sustainable economy. Interestingly, the Co and Li recovery from the DES reached >99% after precipitation with oxalic acid and ensuring the reusability of DES for further three consecutive cycles.