ADVANCED MATERIALS & PROCESSES | JULY/AUGUST 2023 21 includes reducing the cost and energy use of each processing step as much as possible while recovering as many components of the battery as possible. In addition to start-up companies refining this technique, the ReCell Center is a consortium of national laboratories and universities funded by the U.S. Department of Energy’s Vehicle Technology Office, which conducts research in the battery recycling field. The goal is to reduce financial risks associated with introducing new direct recycling technologies and to help facilitate development of a robust recycling market for EOL electric vehicle batteries. Figure 3 shows a schematic created by the ReCell Center that provides an example of a series of processes for a possible direct recycling operation[4]. DIRECT RECYCLING PROCESS Lithium-ion batteries consist of layers of composite electrodes bound to metal foils with a polymer binder, plastic separators, and liquid electrolyte all encased in large, complex automotive battery packs. As a result, some amount Fig. 3 – Example of direct recycling processes provided by the ReCell Center[4]. of disassembly is required for every battery recycling process. This remains an important area of study because manual disassembly is labor-intensive and there is currently no standardization of battery pack designs across different electric vehicles. A typical series of direct recycling processes starts with a set of disassembly, shredding, or other size reduction procedures, followed by liquid electrolyte recovery and various component separation processes. The methods for separating anode, cathode, current collector, and separator materials are unique to the direct recycling process and are a subject of focused research, because contaminants introduced by incomplete separation can interfere with essential processes further down the direct recycling line. Some options for separating EOL battery feedstocks include froth flotation for separating anode and cathode materials, solvent-based delamination of composite electrodes from the current collector, magnetic separation of ferrous metal materials, or a combination thereof[7-9]. After this stage of the separation process, the recovered material often contains cathode active material, carbon black, and polyvinylidene fluoride (PVDF) binder. The next step is to remove the PVDF binder and carbon black from this mixture (often referred to as “black mass”) so that only the transition metal oxide active material remains. Options for removing the carbon black and PVDF from the black mass include thermal binder removal or solvent- based extraction combined with filtration[10,11]. After the PVDF and carbon black have been removed, the recovered product will ideally be a contaminant- free—though lithium-deficient—nickel manganese cobalt (NMC) cathode powder. This spent cathode material is then relithiated to re- store lithium ions back into the Li-deficient structure through a variety of techniques including hydrothermal, ionothermal, redox mediator, and solid state relithiation[12-15]. At this point, the material should be fully rejuvenated and ready to return to the cathode production stream. However, many cathode active materials entering the waste stream have been phased out of current LIBs for electric vehicles because they are no longer the most advanced or highest performing option. For this reason, transforming the EOL cathode material to a more economically viable option through upcycling processes must be part of the direct recycling process as well[16]. DIRECT RECYCLING ROADBLOCKS The reason direct recycling is not yet widely adopted in industry is due to several remaining challenges inherent to the processes described above. These include unwanted metal or fluorine species contamination, production of environmentally harmful
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