A Promising Carbon/g‐C3N4 Composite Negative Electrode for a Long‐Life Sodium‐Ion Battery

2D graphitic carbon nitride (g‐C3N4) nanosheets are a promising negative electrode candidate for sodium‐ion batteries (NIBs) owing to its easy scalability, low cost, chemical stability, and potentially high rate capability. However, intrinsic g‐C3N4 exhibits poor electronic conductivity, low reversible Na‐storage capacity, and insufficient cyclability. DFT calculations suggest that this could be due to a large Na+ ion diffusion barrier in the innate g‐C3N4 nanosheet. A facile one‐pot heating of a mixture of low‐cost urea and asphalt is strategically applied to yield stacked multilayer C/g‐C3N4 composites with improved Na‐storage capacity (about 2 times higher than that of g‐C3N4, up to 254 mAh g−1), rate capability, and cyclability. A C/g‐C3N4 sodium‐ion full cell (in which sodium rhodizonate dibasic is used as the positive electrode) demonstrates high Coulombic efficiency (ca. 99.8 %) and a negligible capacity fading over 14 000 cycles at 1 A g−1. Flachlandkomposite: Kostengünstige Komposite aus Kohlenstoff und graphitischem Kohlenstoffnitrid können als negative Elektroden für langlebige Natrium‐Ionen‐Batterien verwendet werden.