Lithium-ion batteries are crucial to the global transition to sustainable energy and electric transportation. While gigafactories and recycling facilities focus on reclaiming batteries for electric vehicles (EVs), smaller-scale batteries, such as those in electric bicycles, require similar attention due to their rapidly growing market. Recycling these batteries differs from EV batteries due to their mixed composition of NMC (LiNixMnyCozO2) and LFP (LiFePO4) chemistries. Adaptable recycling processes are needed to recover cobalt, nickel, manganese, and lithium effectively, despite the challenges posed by varying iron concentrations.
This study optimizes hydrometallurgical recycling processes for LIBs containing mixed LFP and NMC cathodes. With rising global demand for LIBs driven by EVs and electronic devices, efficient recycling processes that recover critical metals—nickel (Ni), manganese (Mn), cobalt (Co), and lithium (Li)—are essential. Economic efficiency and environmental sustainability drive advancements in handling these mixed chemistries.
Two leaching approaches were assessed: acid-excess leaching and acid-deficient leaching with residue recirculation. A design of experiments (DoE) methodology evaluated parameters like sulfuric acid (H2SO4) and hydrogen peroxide (H2O2) concentrations and solid-to-liquid (S/L) ratios. Acid-excess leaching achieved over 95% dissolution yields for Ni, Mn, and Co but required additional purification to remove impurities like aluminum (Al), copper (Cu), and iron (Fe), increasing complexity and reagent use. The acid-deficient leaching approach proved more cost-effective and environmentally friendly. Using stoichiometric acid amounts and incorporating 60% residue recirculation improved dissolution yields by up to 12.5% over standard methods. The optimized process achieved yields of 89.2% for Ni, 88.8% for Mn, 89.1% for Co, and 91.0% for Li while reducing reagent use and eliminating extensive impurity removal. This aligns with European regulations targeting higher LIB recycling rates, offering a sustainable pathway for recycling.
The study also explored solvent extraction strategies for separating Mn, Co, and Ni from the pregnant leaching solution (PLS). DEHPA (bis-2,4,4-trimethylpentylphosphinic acid) and Cyanex®272 extractants enabled efficient metal separation with minimal impurities. Mn was selectively extracted at pH 1.6 using DEHPA, while Co was separated from Ni at pH 3.9 using Cyanex®272. Acid-deficient leaching produced a cleaner PLS with fewer impurities, simplifying solvent extraction and reducing costs. A comparative analysis highlighted the strengths and limitations of both methods. Acid-excess leaching achieved higher dissolution yields but required additional impurity management steps, increasing reagent consumption and waste. In contrast, acid-deficient leaching with residue recirculation offered lower operational costs and environmental impact, albeit with slightly reduced yields for some metals. These findings highlight acid-deficient leaching as a viable alternative for sustainable LIB recycling.