Effects elucidation of carbon nanofibers structural evolution on sodium ion storage behavior

Hard carbon (HC) is a promising anode material for sodium-ion batteries (SIBs) due to its large capacity, highly abundant, and low cost. However, the lack of understanding for its sodium ion storage mechanism, especially in the low potential plateau region, hinders the design and development of high-performance HC anode materials. Herein, hard carbon nanofibers (CNFs) are prepared by electrospinning and a subsequent carbonization step. The correlation between the microstructure of CNFs and their sodium ion storage behaviors is systematically investigated, demonstrating that the electrochemical performance is closely related to their microstructure. CNFs carbonized at 1300 °C (CNF-1300) achieves excellent reversible capacity, rate performance and cycling stability. Furthermore, the sodium ion storage mechanism of CNF-1300 is elucidated by linking its microstructure and the electrochemical properties via galvanostatic intermittent titration technique measurements and in-situ Raman spectroscopy, demonstrating the capacity in the low potential plateau region is mainly contributed by pore filling. At last, a sodium ion storage mechanism based on adsorption-intercalation-pore filling is proposed, providing guidance for the design of high-performance HC anode materials in SIBs.