Biodegradable Redox-Active Organic Radical Cathode Material for Lithium-Ion Batteries

Organic redox-active polymer electrodes offer cost-effective, flexible, and sustainable alternatives to scarce, toxic, and expensive metal-based materials for lithium-ion batteries (LIBs). However, conventional polymers are usually incinerated after use, causing environmental hazards. To promote eco-friendly batteries, degradable polymers should be explored, although research in this area has remained limited. Existing degradable polymer electrodes struggle to balance electrochemical performance with mild degradation. To address these limitations, this study introduces a biodegradable polymer for cathodes in LIBs by attaching a redox-active nitroxide radical, 2,2,6,6-tetramethylpiperidin-1-yl oxyl (TEMPO), to an ester-based polycaprolactone (PCL) backbone. The developed radical polymer can be degraded under accelerated acidic (1 M HCl, 80 °C) and basic (KOH, 90 °C) conditions yielding water-soluble byproducts, verified by proton nuclear magnetic resonance analysis, ensuring eco-friendly disposal. This polymer cathode demonstrated a high initial Coulombic efficiency (99%), excellent high-rate charging/discharging performance (1 C–30 C), and ∼93% capacity recovery after high-rate cycling, confirming its structural stability. These findings can offer a sustainable pathway for LIBs by reducing their environmental impact.