CO2-etching creates abundant closed pores in hard carbon for high-plateau-capacity sodium storage

• Main Authors: Zheng, Zhi, Hu, Sijiang, Yin, Wenji, Peng, Jiao, Wang, Rui, Jin, Jun, He, Beibei, Gong, Yansheng, Wang, Huanwen, Fan, Hong Jin
• Other Authors: School of Physical and Mathematical Sciences
• Format: Article
• Language: English
• Published: 2024
• Subjects: Physics; Closed pore; CO2-etching
• Online Access: https://hdl.handle.net/10356/173948
• Institution: Nanyang Technological University

Hard carbon (HC) has become the most promising anode material for sodium-ion batteries (SIBs), but its plateau capacity at ≈0.1 V (Na+/Na) is still much lower than that of graphite (372 mAh g−1) in lithium-ion batteries (LIBs). Herein, a CO2-etching strategy is applied to generate abundant closed pores in starch-derived hard carbon that effectively enhances Na+ plateau storage. During CO2 etching, open pores are first formed on the carbon matrix, which are in situ reorganized to closed pores through high-temperature carbonization. This CO2-assisted pore-regulation strategy increases the diameter and the capacity of closed pores in HC, and simultaneously maintains the microsphere morphology (10–30 µm in diameter). The optimal HC anode exhibits a Na-storage capacity of 487.6 mAh g−1 with a high initial Coulomb efficiency of 90.56%. A record-high plateau capacity of 351 mAh g−1 is achieved, owing to the abundant closed micropores generated by CO2-etching. Comprehensive in situ and ex situ tests unravel that the high Na+ storage performance originates from the pore-filling mechanism in the closed micropores.