Covalent Quantum Bridging Enables Bicontinuous Electron–Ion Highways in Hard Carbon for Ultrafast Sodium Storage

As one of the best alternatives to anodes for sodium-ion batteries, hard carbon holds strong promise for commercial application. However, its inherently slow ion diffusion and poor electronic conductivity fundamentally limit the rate capability and cycling stability. Herein, inspired by biological vascular bundles, we design a bicontinuous network within a carbon framework via a bridging strategy using bamboo powder (BP) and carbon quantum dots (CQDs), which achieves the ultrafast transfer of electrons and ions from graphite-like domains (interlayer adsorption/conversion) to closed-pore (filling). Specifically, through stepwise pyrolysis, CQDs acting as "transport highways" were covalently grafted onto BP, and the resulting "quantum-bridge" precursor was topologically reconstructed into a bicontinuous carbon framework. This process generates interconnected graphene nanodomains (GNDs) that facilitate electron transport, while concurrently creating topological defects and sites for pyridinic/pyrrolic N to enable efficient Na⁺ adsorption and surface migration. The designed hard carbon achieves a high specific capacity (391.1 mAh g^-1 at 0.1 C), excellent initial Coulombic efficiency (92%), outstanding rate capability (83.5% capacity retention after 15,000 cycles at 20 C), and remarkable low-temperature performance (90.2% capacity retention after 400 cycles at 1 C and -20 °C). This work establishes a general design principle for energy storage materials requiring simultaneous, rapid electron-ion migration.