A team of researchers from The Hong Kong Polytechnic University, University of Sydney, University of Alberta, The University of Queensland, and Yale University have used the tailored deep eutectic solvent (DES) choline chloride–formic acid (ChCl–FA) to extract critical metals from mixed NCM and LFP cathode materials with high selectivity and efficiency.

A paper on their work is published in the ACS journal Environmental Science & Technology.

Deep eutectic solvents are a new class of ionic liquid (IL) analogues; they are formed from a eutectic mixture of Lewis or Brønsted acids and bases which can contain a variety of anionic and/or cationic species.

The mixed cathode materials (LiFePO₄:Li(NiCoMn)_1/3O₂ mass ratio of 1:1) were processed under mild conditions(80 °C, 120 min) with a solid–liquid mass ratio of 1:200.

The team noted that the leaching performance is further enhanced by mechanochemical processing because of particle size reduction, grain refinement, and internal energy storage.

Mechanochemical reactions effectively inhibited undesirable leaching of nontarget elements (iron and phosphorus), thus promoting the selectivity and leaching efficiency of critical metals.

This was achieved through the preoxidation of Fe and the enhanced stability of iron phosphate framework, which significantly increased the separation factor of critical metals to nontarget elements from 56.9 to 1475. The proposed combination of ChCl–FA extraction and the mechanochemical reaction can achieve a highly selective extraction of critical metals from multisource spent LIBs under mild conditions.

—Wang et al.

Resources

• Mengmeng Wang, Kang Liu, Zibo Xu, Shanta Dutta, Marjorie Valix, Daniel S. Alessi, Longbin Huang, Julie B. Zimmerman, and Daniel C. W. Tsang (2023) “Selective Extraction of Critical Metals from Spent Lithium-Ion Batteries” Environmental Science & Technology doi: 10.1021/acs.est.2c07689

• Emma L. Smith, Andrew P. Abbott, and Karl S. Ryder (2014) “Deep Eutectic Solvents (DESs) and Their Applications” Chemical Reviews 114 (21), 11060-11082 doi: 10.1021/cr300162p