Impact of Nickel Impurities on Lithium Iron Phosphate Cathodes Synthesized from Iron Sulfate Recovered from Stainless-Steel Scrap

초록

As global demand for Li-ion batteries (LIBs) rises, sustainable production of battery materials has become an critical challenge. Lithium iron phosphate (LiFePO₄, LFP) is particularly promising cathode material due to its safety, cost-effectiveness, and scalability for large-scale applications. This study investigates the synthesis of LFP cathodes using iron sulfate, a byproduct of stainless-steel recycling. While recycling stainless steel recovers essential elements like iron, nickel, and chromium, nickel impurities are unavoidably introduced during these processes, potentially affecting the structural and electrochemical properties of LFP. The Significant amount of Stainless-steel scrap creates both environmental challenges and opportunities for resource recovery, necessitating effective impurity management. Our findings revealed that nickel incorporation into the LFP crystal lattice causes structure distortion and remains electrochemically inactive within the operating voltage range of LFP, leading to reduced specific capacity. Across a range of nickel concentrations, no beneficial effects on LFP performance were observed. Instead, nickel consistently acted as a detrimental impurity. By carefully controlling nickel levels in the recovered iron sulfate, we demonstrated that minimizing nickel impurities below a critical threshold is essential to achieving acceptable electrochemical performance in LFP. This research highlights the importance of rigorous impurity management in recycled materials to ensure sustainable cathode production. Leveraging iron sulfate from stainless steel recycling, we establish a framework for integrating resource recovery into energy material production, addressing environmental challenges, and promoting a circular economy.