Green synthesis of high-quality V₂O₅/single-walled carbon nanotube composites via Trachyspermum Ammi leaf extract: A sustainable approach to sodium-ion battery anodes

Abstract

High-performance sodium-ion batteries (NIBs) are an essential alternative for sustainable energy storage amid growing concerns about limited lithium resources. Two-dimensional transition metal oxides (TMOs) particularly vanadium pentoxide (V₂O₅)-show great promise as electrode materials for NIBs. In this work, we report the first-ever sol-gel-assisted green synthesis of V₂O₅ using Trachyspermum ammi (L.) leaf extract, offering an eco-friendly route free from hazardous chemicals. The green-synthesized V₂O₅ (GS-V₂O₅) and its composite with single-walled carbon nanotubes (SWCNT) (GS-V₂O₅/SWCNT) exhibited reduced crystallite size and lower agglomeration compared to chemically synthesized V₂O₅ (CS-V₂O₅), demonstrating superior structural properties. The GS-V₂O₅/SWCNT composite exhibits a remarkable specific capacity of 527 mAh g⁻¹ at a current density of 50 mA g⁻¹, significantly outperforming pristine GS-V₂O₅ (193 mAh g⁻¹). It also achieves a 60.46 % initial coulombic efficiency (ICE), significantly higher than the 6.14 % for GS-V₂O₅ alone. Electrochemical impedance spectroscopy (EIS) reveals a sharp reduction in charge transfer resistance (R_ct) from 1822 Ω to 31 Ω upon SWCNT addition, and GITT analysis confirms a Na-ion diffusion coefficient of 1.53 × 10⁻¹⁰ cm² s⁻¹. Postmortem studies indicate that SWCNT incorporation preserves electrode integrity, enhances electrical percolation, and maintains stability during cycling. Collectively, these findings highlight the strong potential of bio-synthesized nanocomposites for safer, long-lasting, and higher-performance energy storage applications.