Objective

Lithium-ion (Li-ion) batteries are a crucial enabler to a wide range of civil and military technologies. Manufacturing of Li-ion batteries relies on critical materials including lithium, cobalt, and nickel, for which the demand is predicted to significantly increase in the near future. Therefore, developing efficient, low-cost, and environmentally benign Li-ion batteries recycling technologies is critical for the U.S. In this project, the project team aimed to demonstrate the feasibility and to understand the reaction mechanism of a new Li-ion batteries recycling method using reusable and environmentally friendly metal-extracting reagents containing chloroaluminate ions. The objectives were to investigate the reaction mechanisms between Li-ion battery cathode materials (lithium transition metal oxides) and the chloroaluminate ions and demonstrate the technological feasibility of the recycling method under practical conditions.

This is a video showing the demonstration of this new Li-ion battery recycling method.

Technical Approach

The first metal extracting reagents investigated in this project is an ionic liquid containing imidazolium cations and tetrachloroaluminate anions. The reaction mechanism between lithium cobalt oxide and the tetrachloroaluminate anions was revealed through spectroscopic characterizations and computational study. Based on the findings from the ionic liquid reagent, the project team developed the second metal-extracting reagent which is an aluminum chloride solution in ethanol. The reaction mechanism between lithium cobalt oxide and the aluminum chloride solution in ethanol was also identified and confirmed through a series of spectroscopic characterizations. The project team also preliminarily demonstrated the feasibility of this new recycling method using used commercial Li-ion batteries and the aluminum chloride solution in ethanol as the extracting reagent.

Results

The investigations indicated that the reactive species in the metal-extracting reagents are chloroaluminate ions: tetrachloroaluminate anions in the ionic liquid and dichloroaluminate cations in the aluminum chloride solution in ethanol. The strong chemical affinity between chloride and lithium cation can chemically extract lithium from the lithium transition metal cathodes to form lithium chloride. Disproportionation subsequently occurs to the transition metal oxides framework after lithium extraction. As a result, transition metals are reduced from the insoluble high oxidation state to soluble low oxidation state. Li and transition metals can be readily separated through aqueous reactions and the aluminum in the reagents can be separated and discarded as insoluble aluminum hydroxide byproduct.  

Benefits

The Li-ion battery recycling method demonstrated in this project is unprecedented. The aluminum chloride solution in ethanol can extract the high-value metals including lithium, cobalt, nickel, and manganese with relatively low temperature, short reaction time, and perfect extraction efficiency. Ethanol can be completely recycled and reused after the recycling reaction. Comparing to the conventional pyrometallurgical and hydrometallurgical recycling methods, no toxic or greenhouse gases are emitted, and no acidic discharge is generated in this new recycling method. The preliminary demonstration using commercial Li-ion batteries clearly shows the practical potential of this method. However, further studies on the scalability emphasizing products separation efficiency and products purity is needed for potential commercialization of this new Li-ion batteries recycling technology.