A Scalable Froth-Flotation Separation Process for Direct Recycling of Li-Ion Batteries and Its Technical Feasibility

Abstract

The increasing demand for Li-ion batteries (LIBs) in hybrid and electric vehicles had led to a significant increase in the volume of new and end-of-life LIBs. For this reason, recycling of spent LIBs has attracted significant attention in recent years for future sustainability. Different from existing recycling methods such as pyrometallurgical and hydrometallurgical methods, direct recycling method recovers cathode and anode active materials directly in reusable forms at a low cost. This process consists of two steps: 1) liberation and separation, and 2) re-functionalization (or re-lithiation). Many previous studies have been focusing on the second step only. To successfully implement the direct recycling process, development of a scalable and environmentally friendly separation process for battery active materials while preserving their functional integrity is necessary. To date, no studies have been conducted to evaluate the technical feasibility of such a scalable separation process for the direct recycling method. In this work, a water-based recycling process was developed to recover cathode active materials from LIBs. In this recycling process, froth flotation technique was used to separate cathode active materials from a mixture of cathode and anode materials. A variety of electrochemical analyses of the recycled cathode active materials were systematically conducted to evaluate technical feasibility and understand current challenges of this recycling process. The present research demonstrated that the use of kerosene as the collector in the froth flotation process improved the purity of produced cathode active materials, and the recycled cathode materials preserved their original electrochemical reactivity. Cycle performance (up to 200 cycles) and rate capability (up to 1C) of the recycled cathodes were comparable to those of a pristine cathode. However, the reversible capacity of the recycled cathodes was slightly lower than that of a pristine cathode because of cell polarization. The polarization caused by electrode wettability and surface impurities on the recycled cathodes was identified as a key challenge that needs to be addressed further. This work will provide valuable insights into further development of a froth flotation-based recycling process which can be implemented in the direct recycling process.