Military operations increasingly utilize lithium-ion batteries (LIBs) such as conformal wearable batteries for soldiers and power supplies for radio communication, surveillance equipment, etc. Therefore, environmentally benign and economically feasible processes for recycling decommissioned LIBs become pressingly important for a sustainable future. In this project, the project team will demonstrate the feasibility of a new and efficient approach to deactivate and recycle LIBs using nonflammable and nonvolatile chloroaluminate ionic liquids (CILs) at mild conditions. The objectives of this project are:

• Investigating chemical deactivation of LIBs through electrolyte solidification catalyzed by Lewis acidic CIL.
• Demonstrating the feasibility and investigating the mechanisms to extract valuable metals (cobalt, nickel, lithium, and manganese) from LIBs using CILs.

The project team plans to first demonstrate the feasibility to solidify the Li-ion electrolyte by mixing with the CIL containing Lewis acidic Al₂Cl₇^- anion. The project team hypothesizes that the carbonate solvents in Li-ion electrolytes including ethylene carbonate, diethyl carbonate, and dimethyl carbonate can be solidified via cationic polymerization in the presence of Al₂Cl₇^- anion as the catalyst. The project team will further demonstrate that the same CILs are highly effective reagents to extract cobalt, nickel, manganese, and lithium from spent LIBs with high efficiency and low energy consumption. The preliminary studies indicate that lithium cobalt oxide (LiCoO₂) cathode reacts to CILs containing Lewis acidic Al₂Cl₇^- and Lewis neutral AlCl₄^- anions, respectively, under different mechanisms:

1. In the Lewis acidic Al₂Cl₇^- ionic liquid, water is used as the reducing agent to directly produce Co(II) chloride (CoCl₂) precipitate. CoCl₂ can be easily converted to Co(OH)₂, which is the precursor for Li cathode synthesis, through room-temperature aqueous precipitation reaction.
2. In the Lewis neutral AlCl₄^- ionic liquid, the preliminary result indicates that Co(III) is reduced to soluble Co(II) with Cl^- as the reducing agent. The dissolved Co(II) can be easily extracted via either electrowinning or aqueous precipitation reaction.

In both types of CILs, LiCoO₂ dissolves in very high concentration at slightly elevated temperature. Based on these promising results, the project team will systematically investigate the mechanisms and optimal processes of metal extractions form cathode materials including LiCoO₂ and LiNi_0.6Mn_0.2Co_0.2O₂ (NMC622), both of which will be extracted from real spent LIBs provided by Oak Ridge National Laboratory.

The LIBs recycling strategy is distinctly different from all the known methods to date with significant advantages in recycling efficiency, energy consumption, and environmental benignity. The project team expects the outcome of this project will be a game-changer to LIBs recycling technologies, not only benefiting military operations but also the entire LIB industry and general society.