(Invited) Solvometallurgy as a Sustainable Approach for Lithium-Ion Batteries Recycling
Authors: Ferrara Chiara 
Published: August 2024

Lithium-Ion Batteries, LIBs, are the core devices that made possible the diffusion of portable consumer electronics and, more recently, the booming of the electric vehicle market. [1] Their ubiquitous use and diffusion led to the well-known and urgent problem of spent LIBs management. Indeed, spent LIBs represent a complex and hazardous kind of waste for which specific regulation, disposal, and recycling routes are still missing. At the same time the continuous and growing production of LIBs involves the mandatory use of specific elements such as Li, Co, Ni, Cu, Al that are considered strategic or critical raw materials due to their limited availability, high costs, monopoly, and geological distribution. [2] The development of efficient and sustainable procedures for recycling of spent LIBs is the answer to these two main challenges as in enable to properly manage the LIBs waste and allow for the recovery of critical raw materials. While at industrial scale the high temperature pyrometallurgy and hydrometallurgy are the methods in use today, in the very last years, many approaches have been explored at research level, among them low temperature pyrometallurgy, soft hydrometallurgy, solvometallurgy, bioleaching. [3] Among them, the solvometallurgical approach exploiting Deep Eutectic Solvents (DESs) as leaching agents is particularly appealing thank to some specific features such as the low volatility, low flammability, low costs, ease of preparation combined with high leaching efficiencies.
DESs are mixture of based on the presence of a hydrogen bond donors and acceptors forming a eutectic mixture at ambient temperature; although their first conceptualization is recent, several compositions have been already appeared in literature for this specific application. [4] At the same time, a rationalization of the role of the mixture components and a specific design of the composition, tailored for the application in LIBs recycling is still missing. We here present the results of our work on the development of new DESs compositions enabling the close-loop recycling of different spent cathodes. The DES compositions have been designed considering the overall recycling process, the effect of the DES compositions in terms of hydrogen bond donors and acceptors has been evaluated and rationalized through a preliminary chemical-physical characterization through thermal, NMR, FTIR, viscosity analysis. The leaching of the most common cathode has been optimized against the dominant parameters (temperature, treatment duration, cathode-to-DES ratio) opening the ways for two possibilities: the recovery of critical raw materials and the direct resynthesis of new cathodes. All the steps and products have been fully characterized with a multi-technique approach including structural and chemical investigation through the electrochemical testing of the re-synthetized materials. Finally, these two options have been assessed through LCA analysis, being able to provide an overview of the global sustainability of the proposed processes.
[1] Ji et al., Chem Soc. Rev. (2023) doi 10.1039/d3cs00254c
[2] Global Supply Chains of EV Batteries report, International Energy Agency
[3] Yasa et al. J. En. Stor. 73 (2023) 109073
[4] Padwal et al. Adv. En. Sus. Res. 3 (2022) 2100133