Modulating Double‐Layer Solvation Structure via Dual‐Weak‐Interaction for Stable Sodium‐Metal Batteries

Abstract Sodium‐metal batteries are the most promising low‐cost and high‐energy‐density new energy storage technology. However, the sodium‐metal anode has poor reversibility, which can be optimized by constructing the robust solid electrolyte interphase (SEI). Here, a concept of dual‐weak‐interaction electrolyte (DWIE) is demonstrated, its double‐layer solvation structure is composed of weakly solvated tetrahydrofuran as the inner layer, and dipole interaction are introduced in the outer layer by dibutyl ether. This double‐layer solvation structure dominated by contact ion pairs and aggregates can promote to deriving of inorganic‐rich SEI film, resulting in smooth and dendrite‐free sodium‐metal deposition. By adjusting the molecular configuration of dibutyl ether to diisobutyl ether, the dipole interaction is further enhanced, resulting in stronger weakly solvating effect. Thus, the Na||Cu cells using the optimized DWIE achieved a high Coulombic efficiency of 99.22%, surpassing most electrolyte design strategies. Meanwhile, at 5C, the Na₃V₂(PO₄)₃ (NVP)||Na cell achieves stable cycling exceeding 3000 cycles. Even under rigorous conditions of ≈8.8 mg cm⁻² NVP loading and 50 µm thickness Na, the full cell can achieve a long cycling lifespan of 217 cycles. The pioneering concept paves the way for crafting readily achievable, cost‐effective, and eco‐friendly electrolytes tailored for SMBs, and offers potential applications in other battery systems.