Endogenous MoC/Mo ₂ C Nanoscale Heterostructures Confined in Hollow Porous Carbon Spheres Toward Sodium‐Ion Capacitors

Abstract Transition metal carbides (TMCs) are considered highly promising anode materials for sodium‐ion capacitors (SICs) due to their intrinsic high electrical conductivity and stability. However, severe agglomeration and significant volume expansion over electrochemical sodium‐storage lead to the inactivation of active sites and structural collapse, thereby causing inferior electrochemical performance. For this, a double‐layered carbon coating involved a templating strategy is devised to in situ fabricate endogenous MoC/Mo ₂ C nanoscale heterostructures confined in hollow porous carbon spheres (MoC/Mo ₂ C@HPC) toward SICs. The solid‐solution charge‐storage mechanism is rationally put forward for MoC/Mo ₂ C@HPC. Moreover, a global “refining‐recombination” process involved nanoparticles (NPs) refinement occurs during prolonged cycling of MoC/Mo ₂ C, inducing a gradual increase in graphitical degree of the surrounded nano‐graphite domains, which results in an “abnormal progressive growth” in capacity. The boosted extrinsic pseudo‐capacitance behavior, NPs refinement induced abundant active sur‐/interfaces, and the built‐in electric field within nano heterostructures, as authenticated by comprehensive physicochemical characterizations and theoretical simulation calculation, synergistically guarantee efficient sodium‐storage of the MoC/Mo ₂ C@HPC anode. Benefiting from these appealing structural/compositional merits, the assembled MoC/Mo ₂ C@HPC‐based SICs, exhibit remarkable energy density along with exceptional cycle life. More essentially, the contribution here provides fundamental insights into precise phase regulation and structural design of TMCs toward advanced next‐generation SICs.