LFP Cathode Recycling: a comparison between traditional and greener methods

This thesis investigates the recycling of cathode active powder from LiFePO4 (LFP) Li-ion batteries, with a focus on hydrometallurgical methods, specifically acid leaching. The work addresses the growing need for sustainable and environmentally responsible ways to recycle Li-ion batteries. This topic is becoming increasingly important due to the growth of the electric vehicle market and the European Union's commitment to reducing greenhouse gas emissions. The objective of this study is to recover the main elements of lithium, iron, and phosphorus from LFP batteries using both traditional and greener hydrometallurgical methods, and to compare the efficiency of four different leaching agents. The traditional methods use sulfuric acid (1 M) and hydrochloric acid (0.6 M with NaClO as an oxidizing agent), while the greener methods use citric acid (0.5 M with H2O2 as oxidizing agent) and hydrogen peroxide (20% w/w). The recycling steps involved four phases: pretreatment, leaching, precipitation, and lithium recovery. In the pretreatment phase, cathode active powder was subjected to a heat treatment at 300°C, followed by a passage in a ball mill and manual sieving to separate the active powder from the aluminum current collector. In the leaching phase, the powder was subjected to acid leaching using the four mentioned leaching agents. In the precipitation phase, the dissolved metals were precipitated out of solution using a sodium hydroxide (10 M) solution. Finally, in the lithium recovery phase, the lithium was extracted from the precipitate using a solution of sodium carbonate at concentration of 30%. The results of the study indicate that sulfuric acid provided the best overall leaching and lithium recovery performance, with high efficiencies for all three main elements: 73% for iron, 73% for phosphorus, and 74% for lithium. In contrast, the selective leaching agents, citric acid and hydrochloric acid, showed very low efficiencies for iron and phosphorus, which is desirable, but lower lithium leaching efficiencies of 66% and 34%, respectively. The results of the lithium recovery phase showed that the best method for lithium recovery was the sulfuric acid route, where lithium was recovered in form of lithium phosphate. Citric acid and hydrochloric acid routes did not provide satisfactory results for lithium recovery, as the final solutions contained relatively high concentrations of lithium. In conclusion, this study provides valuable insights into the feasibility of using hydrometallurgical methods to recycle cathode active powder from LFP batteries. However, given the relatively low efficiencies observed for the selective leaching agents, citric acid and hydrochloric acid, and the need to improve the lithium recovery for these routes, further research is needed to optimize and develop greener methods for recycling Li-ion batteries.