Tailored Deep Eutectic Solvents for Effective Leaching and Electrochemical Recovery of Spent Li-Ion Battery Cathode Materials

The increase in demand for Lithium-ion battery (LIB) raw materials such as cobalt, nickel and lithium are expected to exacerbate exploitative resource extraction and have negative geopolitical implications. A solution to ameliorate this issue is to recycle LIBs. Unfortunately, the existing LIB recycling market is dominated by energy inefficient and environmentally harmful processes such as pyrometallurgy and hydrometallurgy which produce products that require further processing before downstream use. Deep Eutectic Solvents (DESes) are a class of compounds that are formed by mixing hydrogen bond donors and acceptors and exhibit high capability for dissolving metal oxides. In this work, we tailored the electrochemical stability window of selected, high leaching efficiency DESes by incorporating additives (such as ammonium salts and glymes), thereby expanding their electrochemical window and gaining the ability to electrochemical plate out dissolved metals from the DES in addition to facilitating leaching at high recovery rates. The electrochemical window of our baseline DES, the extensively studied system consisting of choline chloride and ethylene glycol (ChCl: EG), is ca 1-3 V (vs AgCl). This system can be tailored with additives to yield DESes with extended electrochemical stability window of ca 4-5 V (vs AgCl) while retaining its excellent leaching. The ability of this class of DESes to efficiently leach metals from LiCoO 2 (LCO) and LiMn x Ni y Co (1-x+y) O 2 (LMNCO) cathodes and corresponding leaching efficiencies for Li, Co, Mn and Ni was examined over a range of temperatures and by subjecting the mixture to microwave or sonication in addition to (or in lieu of) heating. Selective tailored DES were shortlisted depending on the high leaching efficiency and leached elements were electrochemically recovered. The microstructure of the electrodeposited material was examined using x-ray diffraction and scanning electron microscopy for phase identification, purity, and stability of the individual elements. Keywords : LIB, Cathode, Electrodeposition, Leaching, Sonication, DES Figure 1. Effect of additives on the electrochemical window of a ChCl:EG DES (left); Photograph of leach liquors of different cathode materials (LCO, LNO, LMO and LNMCO from left to right) dissolved in selected DES (right) Figure 1