Fall and Rise: Disentangling Cycle Life Trends in Atmospheric Plasma-Synthesized FeOOH/PANI Composite for Conversion Anodes in Lithium-Ion Batteries

Various iron oxides have been proven to be promising anode materials for metal-ion batteries due to their natural abundance, high theoretical capacity, ease of preparation, and environmental friendliness. However, the synthesis of iron oxide-based composites requires complex approaches, especially when it comes to composites with intrinsically conductive polymers. In this work, we propose a one-step microplasma synthesis of polyaniline-coated urchin-like FeOOH nanoparticles (FeOOH/PANI) for applications as anodes in lithium-ion batteries. The material shows excellent electrochemical properties, providing an initial capacity of ca. 1600 mA∙h∙g⁻¹ at 0.05 A∙g⁻¹ and 900 mA∙g⁻¹ at 1.2 A∙g⁻¹. Further cycling led to a capacity decrease to 150 mA∙h∙g⁻¹ by the 60th cycle, followed by a recovery that maintained the capacity at 767 mA∙h∙g⁻¹ after 2000 cycles at 1.2 A∙g⁻¹ and restored the full initial capacity of 1600 mA∙h∙g⁻¹ at a low current density of 0.05 A∙g⁻¹. Electrochemical milling—the phenomenon we confirmed via a combination of physico-chemical and electrochemical techniques—caused the material to exhibit interesting behavior. The anodes also exhibited high performance in a full cell with NMC532, which provided an energy density of 224 Wh∙kg⁻¹, comparable to the reference cell with a graphite anode (264 Wh∙kg⁻¹).