Asymmetric bulk toward energy-dense fast-charging sodium metal batteries

The desolvation energy barrier and the solid electrolyte interphase are crucial factors for fast-charging sodium metal batteries. Here, we construct an asymmetric bulk through separator design, featuring opposing surface potentials on each side. We observe stepwise desolvation within the asymmetric bulk, which results in enhanced Na+ transfer kinetics and reduced nucleation energy barrier. Additionally, the bulk in contact with the Na metal interface induces electron transfer from the solvent environment to anions, accelerating the cleavage kinetics of P–F bonds. Consequently, the resulting solid electrolyte interphase is enriched with inorganic components, exhibiting robust and low-resistance characteristics. The Na₃V₂(PO₄)₃-based pouch cell (213.6 Wh kg−1) can stably cycle over a thousand times at a rate of 10C. The NaNi_0.3Fe_0.4Mn_0.3O₂-based pouch cell with high energy density (221.9 Wh kg−1) satisfies the discharge requirements for electric vertical take-off and landing operations and delivers sufficient power for drones at a charging rate of 5C.