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.