Cobalt-catalyzed soft-hard carbon composite anodes for enhanced sodium-ion storage.

Hard carbon is expected to be a high-capacity anode material for sodium-ion batteries (SIBs). However, its Na+ storage performance, especially the low discharge capacity, remains a great challenge. Herein, the soft-hard carbon composite anodes with high degree of graphitization were synthesized via low-temperature pyrolysis (at only 900 °C) of Cobalt-catalyzed perylene tetracarboxylic dianhydride (PTCDA-Co) and cotton, with subsequent removal of cobalt. The composite resulting from a 2:3 mass ratio of soft to hard carbon exhibits a good discharge capacity of 355.81 mAh g−1 at a current density of 50 mA g−1 and an enhanced initial Coulombic efficiency (ICE) of 81.41%. The enhanced electrochemical storage performance of cotton is attributed to the introduction of PTCDA-Co, which creates low-defect graphitic layer, hierarchical porous channels, and carbon shielding coating on hard carbon. [Display omitted] • Highly graphitized carbon composite anodes synthesized from cotton carbon and PTCDA-Co at 900 °C. • PCo-HC 2–3 shows 355.81 mAh/g discharge capacity at 50 mA g−1 with ICE 81.41%. • The Na+ storage mechanism in PCo-HC 2–3 is an adsorption-insertion/filling mechanism. [ABSTRACT FROM AUTHOR]