• • The 3D EC matrix reduces nucleation overpotential and induces horizontal sodium deposition, achieving dendrite-free anodes; symmetric cells show ultralow polarization of 12 mV over 1000 h at 5 mA cm−2 and 5 mA h cm−2, critical for long-cycle stability in grid-scale storage.
• • Exceptional high-rate endurance: stable operation for 500 h at an ultrahigh current density of 30 mA cm−2 and areal capacity of 30 mA h cm−2, with voltage hysteresis of only 50 mV, demonstrating viability for fast-charging applications.
• • Full cells with Na3V2(PO4)3 cathode deliver an initial discharge capacity of 108.1 mA h g−1 at 1 C and retain 94.4% capacity after 500 cycles, indicating robust commercial potential for sodium-ion batteries.
• • The EC framework achieves high Coulombic efficiency of 99.5% over 1000 cycles at 3 mA cm−2, ensuring minimal side reactions and enhanced safety, while utilizing harmful algal biomass to reduce marine pollution and carbon footprint.