Electrochemical Recovery of Lithium-Ion Battery Materials from Molten Salts: Microstructural Characterisation Using X-Ray Imaging

Abstract

Recycling spent Li-ion batteries (LiBs) guarantees the conservation of important metal resources by reducing demands on raw supply and offsetting the energy and environmental costs associated with its manufacture. However, selecting practical end of life solutions for battery waste management remains a challenge. Molten salts, on the other hand, are a well-established group of inorganic compounds and are understood to be one of the leading candidates in the recovery of valuable metals. They offer a much greener and simpler route to metal recovery by electrochemical means compared with the use of reducing agents for hydrometallurgical recovery [1]. Yet, the current mechanistic understanding of the electrochemical recovery of metals in molten salts needs to be improved.SEM, EDS and XRD are some of the most employed characterisation techniques used to reveal material composition and surface topography; however, they are known to expose the final product to air and moisture obscuring the results. X-ray computed tomography offers a non-destructive approach for 3D microstructure visualisation and subsequent quantification [2]. This technique can be used to study the morphological evolution of metal deposits from their oxide particles in a representative high-temperature medium to provide a wealth of information on the fundamentals of the electrochemical reduction process.Here, we demonstrate a study into the electrochemical deposition of recovered Co metal from lithium cobalt oxide, LiCoO2 in LiCl-KCl eutectic (LKE) which has been previously studied by the authors’ using a fluidised cathode arrangement [3]. This novel diagnostic approach has been applied to LiCoO2-LKE samples before and after electrolysis at 450 °C, yielding key insights into the morphological evolution of product formation. Different morphologies of recovered Co metal such as dendrite features and agglomerates have been captured and quantified. It has also been observed that CO/CO2 gas formation occurs in copious quantities at the anode surface leading to operational consequences such as the required overpotential needed to drive the reaction. For the first time, the application of X-ray imaging offers the ability to understand the role of process conditions and cell configurations to optimise a pyro-electrochemical reprocessing technology that can play a key role in sustainable battery recycling as well as refractory metal recovery.[1] B. Zhang, H. Xie, B. Lu, X. Chen, P. Xing, J. Qu, Q. Song, H. Yin, A Green Electrochemical Process to Recover Co and Li from Spent LiCoO2-Based Batteries in Molten Salts, ACS Sustain Chem Eng. 7 (2019) 13391–13399.[2] P.J. Withers, C. Bouman, S. Carmignato, V. Cnudde, D. Grimaldi, C.K. Hagen, E. Maire, M. Manley, A. du Plessis, S.R. Stock, X-ray computed tomography, Nature Reviews Methods Primers. 1 (2021) 1–21.[3] M. Mirza, R. Abdulaziz, W.C. Maskell, C. Tan, P.R. Shearing, D.J.L. Brett, Recovery of cobalt from lithium-ion batteries using fluidised cathode molten salt electrolysis, Electrochim Acta. 391 (2021) 138846.