Going Green By Going Blue: Recycling Li-Ion Batteries By Extracting Cobalt and Nickel Using Deep Eutectic Solvents
Authors: Tran Mai Kim , F. Rodrigues Marco-Tulio , Ganguli Babu , Kato Keiko , Ajayan Pulickel M 
Published: February 2020

With the ever-imminent electrification of the transportation sector, the growth of renewable energy systems requiring better storage units, and the desire for smaller, faster, and smarter consumer electronics, the demand for Li-ion batteries (LIBs) to power the needs of the world is higher than ever. Over the past ten years, while battery prices have plummeted by a factor of four going from about $800/kWh to now $200/kWh for current chemistries1,2, costs of valuable metals within the batteries themselves have surged—notably in the most expensive part of the battery, the cathode, commonly made of cobalt-rich compounds. Cobalt in particular poses not only an economical burden, but a social and environmental one as well, instigating efforts to reduce the reliance on the conflict mineral while still maintaining high performance. Such efforts have led to the development of chemistries using other metals such as manganese and nickel, and has also pushed researchers to pursue more battery recycling options.
In this work, a process to extract and reuse cobalt from LIBs containing lithium cobalt (III) oxide (LCO) has been developed using deep eutectic solvents (DESs), a “green” alternative to traditionally toxic solvents. DESs are solutions of two or more Lewis or Brønsted acids and bases that exhibit a deeply depressed freezing point; they can additionally made from cheap and potentially renewable materials3. Nickel metal was also tested in these eutectics, as the nickel manganese cobalt oxide (NMC) and lithium nickel cobalt aluminum oxide (NCA) batteries are projected to play a more prominent role in the future of Li-ion battery technology. The objective is to sustainably recycle these metals from LIBs and then repurpose it in other energy applications.
In dissolution experiments simulating the extraction of cobalt from the traditional LIBs, LCO powder was mixed directly with the DES under heat, resulting in a vibrant aqua-blue solution indicating the presence of Co2+ ions. The solubilized metal was filtered and subsequently electrodeposited. Inductively coupled plasma optical emission spectrometry results showed record solubility values for a metal oxide in the presence of a DES. Similarly, experiments done using the nickel-based compounds showed promise for further development, leading to the eventual testing on spent Li-ion cathodes as well. Usage of the recovered metal in a supercapacitor and a new LIB cell demonstrates that such recycling can indeed apply sustainable means to a sustainable end—or rather a new beginning.
References

Opitz, A. et al., Can Li-Ion batteries be the panacea for automotive applications? Renewable and Sustainable Energy Reviews
2017, 68 (1), 685-692.

“After electric cars, what more will it take for batteries to change the face of energy?” The Economist [London] 12 Aug. 2017. Electronic.

Smith, E., et al. Deep Eutectic Solvents (DESs) and Their Applications. Rev.
2014, 114, 11060-11082.