Non-aqueous direct leaching using a reusable nickel-selective amic-acid extractant for efficient lithium-ion battery recycling

Abstract

The demand for lithium-ion secondary batteries (LiBs) is rapidly increasing in pursuit of the Sustainable Development Goals. In particular, the recycling of nickel-based cathodes is attracting attention owing to the growth of the electric vehicle market. There are concerns surrounding conventional LiB recycling processes regarding environmental pollution because of their complexity and the discharge of large amounts of acidic wastewater. In this study, we used an alternative recycling process that directly leaches the cathode materials using a non-aqueous hydrophobic solvent instead of inorganic acids. This method enables simultaneous leaching and extraction, which are typically performed in two stages in conventional recycling, to be performed in a single step. To enhance the leaching of nickel-based cathodes, N-[N,N-di(2-ethylhexyl) aminocarbonyl methyl] glycine (D2EHAG), which has high affinity for nickel and cobalt, was used to prepare the leaching solvent. More than 96% of the nickel and cobalt in a nickel-based cathode was successfully leached into the D2EHAG solvent system, while typical industrial metal extractants showed very poor leaching performance. The addition of ascorbic acid and water into the leaching solvent synergistically enhanced the leaching efficiency, demonstrating a crucial role in the leaching process. After leaching, the leached metals could be selectively separated and recovered by stripping. Furthermore, the reusability of the leaching solvent was demonstrated for at least three leaching-stripping cycles. These findings will contribute to the development of a more simple recycling process for nickel-based automotive LiBs with a reduced amount of acidic wastewater.