A Multifunctional Interphase Layer Enabling Superior Sodium‐Metal Batteries under Ambient Temperature and −40 °C

Abstract The sodium (Na)‐metal anode with high theoretical capacity and low cost is promising for construction of high‐energy‐density metal batteries. However, the unsatisfactory interface between Na and the liquid electrolyte induces tardy ion transfer kinetics and dendritic Na growth, especially at ultralow temperature (−40 °C). Herein, an artificial heterogeneous interphase consisting of disodium selenide (Na₂Se) and metal vanadium (V) is produced on the surface of Na (Na@Na₂Se/V) via an in situ spontaneous chemical reaction. Such interphase layer possesses high sodiophilicity, excellent ionic conductivity, and high Young's modulus, which can promote Na‐ion adsorption and transport, realizing homogenous Na deposition without dendrites. The symmetric Na@Na₂Se/V cell exhibits outstanding cycling life span of over 1790 h (0.5 mA cm⁻²/1 mAh cm⁻²) in carbonate‐based electrolyte. More remarkably, ab initio molecular dynamics simulations reveal that the artificial Na₂Se/V hybrid interphase can accelerate the desolvation of solvated Na⁺ at −40 °C. The Na@Na₂Se/V electrode thus exhibits exceptional electrochemical performance in symmetric cell (over 1500 h at 0.5 mA cm⁻²/0.5 mAh cm⁻²) and full cell (over 700 cycles at 0.5 C) at −40 °C. This work provides an avenue to design artificial heterogeneous interphase layers for superior high‐energy‐density metal batteries at ambient and ultralow temperatures.