NaCrO₂/Coffee Waste–derived Nitrogen-doped Carbon Composite as High-Performance Cathode Material for Sodium Ion Batteries

Sodium-ion batteries (NIBs) are promising alternatives to lithium-ion batteries for large-scale energy applications such as energy storage systems, owing to the earth-abundance and low cost of sodium resources. Among layered oxide cathode materials for NIBs, O3-type NaCrO₂ has attracted considerable attention owing to its electrochemically active Cr^3+/4+, which is unlike that of LiCrO₂, and potential for carbon coating with a high thermal stability. In this study, we propose a new facile and eco-friendly method for applying nitrogen-doped carbon to NaCrO₂ using coffee waste as a carbon source. The synthesized O3-type NaCrO₂/coffee waste–derived N-doped carbon composite exhibits an outstanding electrochemical performance as an NIB cathode material. The sodium/composite cell achieved a 73.7% capacity retention after 500 charge/discharge cycles and an approximate 50% discharge capacity during 43 s of charge. The results demonstrate the potential use of coffee waste for battery materials with improved electrochemical performances.