Single-step pyrolysis of Stipa Tenacissima fibers to hard carbon: A potential route for sodium-ion battery anodes

Abstract

Hard Carbon (HC) has emerged as a viable candidate for the negative electrode material in sodium-ion batteries (SIBs). This study focuses on the development of a novel HC-negative electrode derived from the pyrolysis of Stipa tenacissima fibers (STF). Prior to pyrolysis, STF underwent a hot water wash pre-treatment, and various pyrolysis temperatures (800 °C, 1000 °C, and 1300 °C) were investigated to elucidate their influence on HC properties and performance. Structural analysis revealed significant differences in the HC structure, highlighting a direct correlation between capacity improvement and the size of accessible micropores for sodium insertion. Composite electrodes were assembled and evaluated in non-aqueous sodium half-cells to assess HC's performance. Notably, increasing the pyrolysis temperature resulted in higher reversible capacity (RC). Specifically, HC prepared at 1300 °C exhibited an RC of 270 mAh g⁻¹, initial coulombic efficiency (ICE) of approximately 60 %, and exceptional reversibility with 99 % capacity retention after 90 cycles at a 25 mA g⁻¹ of current density (CD). These results surpassed those obtained with HC prepared at 800 °C and 1000 °C. Moreover, this study explores the biological, biochemical, biophysical, and structural advantages conferred by STF, making it a promising component in SIBs, with the ultimate goal of establishing long-lasting, high-performance battery systems.