Hydrophobic Deep Eutectic Solvents in Lithium-Ion Battery Recycling Processes

The growth of metal-containing waste raises public concern due to its impact on the environment, human health, and the accelerated depletion of natural resources. In the context of a circular economy, metal recovery from secondary resources is attracting increasing research interest. Liquid–liquid extraction and leaching are the main processes used for separating and recovering metals from such sources. The extractants and solvents typically used in these processes often possess aggressive properties that can cause not only environmental problems but also damage to industrial equipment. Therefore, there is a need to make these processes safer and cleaner by using environmentally friendly solvents. In recent years, deep eutectic solvents have attracted attention due to their ease of preparation, biodegradability, low toxicity, and the ability to finely tune their physicochemical properties. Recently, studies have emerged on their use for metal recovery from electronic waste, minerals, biological materials, and other sources. This review provides an overview of hydrophobic deep eutectic solvents and their application in the recovery and separation of a wide range of metals, including those from lithium-ion batteries.