In situ cross-linking construction of 3D mesoporous bimetallic phosphide-in-carbon superstructure with atomic interface toward enhanced sodium ion storage performance

•Atomic-heterointerface is successfully fabricated, which could maximize the Na+ storage.•The electrode demonstrates ultrahigh stability and superior rate capability.•DFT calculations were performed to provide in-depth insights on the charge storage mechanism. Constructing heterostructures are capable of offering fascinating performance for electronics owing to the built-in charge transfer driving force. However, exploring a universal methodology to rationally design and controllable synthesis of heterostructure with high stability of interface is a big challenge. Also the synergistic effect of the heterointerface in the composites remains to be clarified. Here, we report three-dimensional (3D) FeP/CoP heterostructure embedded within N-doped carbon aerogel (FeP/CoP-NA) through an in situ cross-linking and phosphorization process. In such a 3D hybrid, the FeP/CoP heterocrystals are wrapped by N-doped carbon which form a core-shell structure. Benefiting from the unique porous network induced by N-doped carbon, the conducting highway is built to promote the ion and electron fast diffusion. This structure can accommodate the volume change of FeP/CoP, which prevent the agglomeration and act as the protecting layer to maintain the integrity of the interface. Impressively, the atomic interface between FeP/CoP is successfully constructed, which could not only introduce enhanced capacitive contribution to facilitate electron transport, but also provide extra active sites to adsorb more Na+ proved by both experiments and density functional theory (DFT) calculations. As expected, FeP/CoP-NA electrode demonstrates an excellent rate capability of 342 mAh g−1 at a current of 5 A g−1, a high specific capacity of 525 mAh g−1 at 0.2 A g−1, and a long cycling stability over 8000 cycles at high current density.