Exfoliation of LiCoO₂ into Nanosheets for Cobalt-Ion Extraction and Cathode Recycling

In recent years, methods for recycling Li-ion battery cathode materials such as lithium cobalt oxide (LiCoO₂, LCO) have attracted more and more attention. Since the cobalt in LCO is a limited resource, developing better ways to extract and recycle cobalt from the cathode materials becomes a critical issue. Traditional methods include pyrometallurgy and hydrometallurgy, which involve high temperatures and reaction of spent LCO with acid, respectively. Here, a new approach investigates cobalt extraction from nanosheets of LCO based on the rationale that cobalt extraction is more facile from high surface area LCO nanosheets compared to bulk LCO particles. To obtain LCO nanosheets, two exfoliation methods are used: 1) an oxidation-reduction assisted method, and 2) proton-exchange assisted method. Both approaches are aided by the intercalation of bulky ammonium cations into the interlayer space of the LCO structure, which facilitates exfoliation of LCO to form nanosheet suspensions in water upon sonication. The last step is to mix the nanosheet suspensions with cation solutions with the goal of achieving ion exchange and extraction of cobalt. The process is dependent on the pH of the solution and the choice of cation used to exchange for cobalt. This process is also demonstrated for other Co-containing cathodes such as LiNiMnCoO₂(NMC) and LiNiCoAlO₂ (NCA). The effectiveness of cobalt extraction and ion-exchange are characterized using Raman and X-ray photoelectron spectroscopy, electron microscopy, and inductively coupled plasma spectroscopic analysis. Further research will focus on different kinds of ion exchange and the reassembly of nanosheet backs into functional cathode materials.