Maximized Pseudo-Graphitic Content in Self-Supported Hollow Interconnected Carbon Foam Boosting Ultrastable Na-Ion Storage

Abstract Hard carbons are the most promising commercialized anodes for sodium-ion batteries (SIBs). However, it is still a great challenge to design highly stable hard carbon anodes coupled with a large reversible capacity. Herein, a self-supported hollow interconnected carbon foam (HICF) is developed by one-step pyrolysis of a commercial and low-cost melamine sponge. The integration of interconnected network and hollow feature can not only provide strong mechanical stability and additional inner space to effectively accommodate the structural deformation from Na+ insertion/extraction, but also enable fast electron and Na-ion transport to achieve a large reversible capacity. As a result, HICF delivers a large reversible capacity of 306 mAh g−1 at 100 mA g−1 and an ultralong cycle life with 86.4% capacity retention over 1000 cycles at 1000 mA g−1. The superior Na-storage performance is also contributed by the maximized content (63.24%) of pseudo-graphitic phase in HICF realized by tuning pyrolysis time, as the pseudo-graphitic phase could store more sodium ions and maintain more stable microstructure owing to its appropriate d -spacing than highly disordered phase. Furthermore, kinetic analysis based on cyclic voltammetry (CV) and galvanostatic intermittent titration technique (GITT) verifies the adsorption–intercalation mechanism. This work provides a low-cost and high-performance anode candidate for the future practical applications of SIBs.