Tailoring electroactive P-C bonds in pitch-based soft carbon toward sodium-ion batteries

Pitch serves as an economical substance characterized by a high carbon output, rendering it appropriate for employment as negative electrode components in Na-ion batteries, thereby facilitating enhanced value-added utilization. However, through direct thermal decomposition of pitch, the resulting carbon materials characterized by high graphitization, reduced interlayer spacing, and challenges in sodium ion deintercalation, ultimately leading to limited electrochemical performance. To expand the carbon interlayer spacing, this study adopted the phosphorus doping strategy, using NaH 2 PO 2 as the phosphorus source, which interacts with the aromatic molecules in pitch to form P-C bonds. The introduction of P-C bonds effectively suppressed graphite microcrystal development during high-temperature carbonization, resulting in decreased graphitization levels and expanded interlayer distances in the carbon matrix. Besides, P-C bonds demonstrate dual functionality by improving sodium ion adsorption while simultaneously reacting with alkali metal Na  +  to form Na x PC y , which directly participated in sodium storage. Consequently, the soft carbon material that has been doped with phosphorus showcases enhances sodium storage capabilities when compared to traditional soft carbon material obtained through direct pyrolysis, achieving a discharge capacity of 138.56 mAh g −1 when tested over 3500 cycles at 1 A g −1 . Therefore, this research demonstrates a simple and effective method for utilizing pitch in the sodium-ion batteries.