Highly Efficient Recovery and Recycling of Cobalt from Spent Lithium-Ion Batteries Using an N-Methylurea-Acetamide Nonionic Deep Eutectic Solvent

Abstract

The growing demand for lithium-ion batteries (LiBs) for the electronic and automobile industries combined with the limited availability of key metal components, in particular cobalt, drives the need for efficient methods for the recovery and recycling of these materials from battery waste. Herein, we introduce a novel and efficient approach for the extraction of cobalt, and other metal components, from spent LiBs using a nonionic deep eutectic solvent (ni-DES) comprised of N-methylurea and acetamide under relatively mild conditions. Cobalt could be recovered from lithium cobalt oxide-based LiBs with an extraction efficiency of >97% and used to fabricate new batteries. The N-methylurea was found to act as both a solvent component and a reagent, the mechanism of which was elucidated.

Scheme 1. Schematic Representation Denoting the Recovery and Recycling of Cobalt from the Cathode Materials of Spent LiBs

(A) Dismantlement of discharged LiB to separate cathode layers; (B) sonication of cathode layers in N-methyl-2-pyrrolidone (NMP); (B′) separation of the aluminum layer; (C) centrifugation; (D) removal of supernatant NMP containing the PvDF binder; (E) drying of the pelleted cathode material (LCO) in a hot air oven at 120 °C for 2 h; (F) dispersion of collected LCO in NMU-A ni-DES; (G) heat treatment of collected LCO with NMU-A ni-DES at 180 °C for 24 h; (G′) dissolution of the leachate in 1% acetic acid, followed by the addition of KNO₃ (0.1 M) and the electrodeposition of cobalt hydroxide (see section 4.2.9); (H) dissolution of the leachate in Milli-Q grade water, followed by centrifugation to recover the cobaltous precipitate and drying in a hot air oven at 120 °C for 12 h; (I) calcination of the recovered cobaltous powder at 500 °C for 5 h; (J) addition of the required amount of lithium hydroxide, followed by calcination at 500 °C for 5 h; and (K) fabrication of a new LiB (see section 4.2.10).

Figure 1

Extraction of cobalt from LiCoO₂ using various ni-DESs comprising acetamide and urea derivatives. Briefly, 20 mg of the LCO powder was dispersed in 2 mL of the ni-DES, and the mixture was heated at 180 °C for 24 h (photograph taken directly after removal from the heating source).

Figure 2

(A) Color change observed upon heating LiCoO₂ in NMU-A ni-DES at 50–180 °C (±3 °C) for 24 h. (B) Extraction efficiency of cobalt as determined by the ICP-AES measurement upon heating LiCoO₂ at different temperatures in NMU-A ni-DES for 24 h.

Figure 3

Self-reaction of NMU when heated above 100 °C.

Figure 4

Infrared spectra of pure NMU and the NMU after heating containing the biuret derivative.

Figure 5

IR spectra of extracted, annealed (120 °C for 12 h), and calcinated (500 °C for 5 h) cobaltous powder extracted from LCO using the NMU-A ni-DES. For comparison, the IR spectrum of pure Co(OH)₂ (β-form) is also given.

Figure 6

(A) Image, (B) electron micrograph, (C) powder XRD pattern, and (D and E) binding energy profiles (Co 2p and Li 1s, respectively) of recovered cobalt oxide.

Figure 7

(A) Galvanostatic charge–discharge profile (inset shows the fabricated coin cell) and (B) cycling stability of a LCO-R coin cell at a 0.2 C rate (inset shows the coin cell testing).