Investigation of Fluorine Distribution and Pre-Defluorination in Hydrometallurgical Recycling Processes for Lithium-Ion Batteries

The growing demand for lithium-ion batteries (LIBs), particularly in the field of electromobility, is leading to an increasing need for efficient and sustainable recycling processes. In addition to the recovery of strategically important metals, such as lithium, nickel, cobalt, and manganese, the fluorine content also poses a challenge. Fluorine enters the battery system primarily via the conductive salt lithium hexafluorophosphate (LiPF6) and via fluorine-containing binders, such as polyvinylidene fluoride (PVDF). During hydrometallurgical recycling, fluorine can transfer into the leaching solution, where it can negatively impact metal recovery and product quality, e.g., by forming stable fluoride compounds. Furthermore, this halogen exhibits environmentally problematic and health-hazardous properties. This study investigates the distribution of fluorine and the influence of defluorination strategies on hydrometallurgical recycling processes for end-of-life lithium-ion batteries. For this purpose, the fluorine content in each process step from two different black masses, one pyrolysed and one unpyrolysed sample, are analysed. To determine their behaviour and the effect of pretreatment, these experiments are also conducted with defluorinated black masses. Wet-chemical defluorination in an alcoholic potassium hydroxide solution was used as the defluorination method, which was then compared to the untreated variants as a reference. After pretreatment, the hydrometallurgical recycling process of the black masses starts by leaching with sulphuric acid, as well as the addition of hydrogen peroxide as a reducing agent. The pregnant leach solutions are further processed using multi-stage precipitation processes to selectively recover nickel, cobalt, manganese, and lithium. The fluorine content in the individual process steps is measured in order to evaluate the fluorine distribution throughout the process. In combination with the effects of the respective pretreatments on the fluorine distribution, a broader understanding of fluorine behaviour in hydrometallurgical recycling of lithium-ion batteries can be gained.