Abstract

Deep eutectic solvents (DESs) have emerged as promising sustainable media for the recycling of lithium-ion batteries due to their low toxicity, low cost, and strong metal dissolution capabilities. However, a molecular-level understanding of metal dissolution and speciation in these complex media remains limited, hindering the rational optimization of recycling processes.

In this work, theoretical chemistry simulations were employed to investigate the leaching mechanisms of transition metals in choline chloride-based DESs combined with ethylene glycol, lactic acid, and malonic acid. In parallel, the speciation of transition metals in these DES environments was explored both as the thermodynamic outcome of the leaching process and in the context of their potential use as functional electrolytes in electrochemical energy storage devices, such as supercapacitors.

Particular emphasis was placed on nickel and cobalt as representatives of distinct physicochemical behaviors. Literature reports [1] reveal notable differences in their coordination chemistry: while cobalt adopts coordination environments commonly observed for transition metal ions, nickel exhibits markedly different speciation, suggesting unique thermodynamic preferences and coordination motifs.

Elucidating the fundamental reactivity and speciation of nickel and cobalt advances both the optimization of recycling processes and the valorization of the resulting leaching solutions, supporting more sustainable circular economy strategies.

References

[1] J.T.M. Amphlett, M.D. Ogden, W. Yang, and S. Choi, Journal of Molecular Liquids, 318 (2020).