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The separation of electrode active materials from spent Li-ion batteries (LIBs) by froth flotation is challenging due to the changes in surface properties of electrode active materials from cycling as well as the presence of organic binders. In this work, the froth flotation separation of aged anode and cathode composite materials from spent LIBs was systematically investigated after the materials were heat treated. The results show that aged anode and cathode materials from spent LIBs can be well separated from each other after a heating process in air at 400 °C and at which some of the PVDF binder remains intact. The underlying mechanism was investigated by X-ray photoelectron spectroscopy (XPS), contact angle measurements, and scanning transmission electron microscopy (STEM) coupled with energy-dispersive X-ray spectroscopy (EDX). The results from the XPS and contact angle measurements show that there is a hydrophilic and oxygen-rich layer on the surface of aged anode materials. This hydrophilic surface, associated with the solid electrolyte interface (SEI) layer, impacts the froth flotation process significantly. The results also show that both the SEI layers and PVDF binder residues on the surface are removed at 400 °C for an hour, restoring the hydrophobicity of the anode materials, which, in turn, benefits the separation of anode and cathode materials. The STEM/EDX elemental analysis data confirms that there are 20 nm-thick oxygen-rich SEI layers on the surfaces, which can be removed after a heating process. The present result illustrates the significance of the SEI layers in flotation separation of electrode materials and sheds new lights into the future development of the recycling processes for the separation of anode and cathode composite materials from spent Li-ion batteries.

With the rapid growth of the volume of spent Li-ion batteries (LIBs), recycling of spent LIBs has attracted significant attention in recent years for future sustainability. In particular, there remains a great need for the development of a scalable and environmentfriendly separation process to recycle valuable cathode active materials from spent LIBs and electrode scraps. In this work, froth flotation technique was adopted to separate cathode active materials from a mixture of cathode and anode materials. To evaluate whether the recovered cathode materials maintain their functional integrity after the developed separation process, a variety of electrochemical analyses have been conducted systematically. The present work demonstrated that froth flotation process with kerosene enhanced separability of mixed electrode materials and the recycled cathode materials almost preserved their original electrochemical reactivity. Cycle performance (up to 200 cycles) and rate capability (up to 1 C) of the recycled cathodes were comparable to those of a pristine cathode. However, the higher polarization observed in the recycled cathodes was identified as a key challenge, and it needs to be addressed further. This work provides valuable insights into further development of a scalable froth flotation-based recycling process which can be implemented in a direct recycling process.

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.