Stable Sodium‐Metal Batteries in Carbonate Electrolytes Achieved by Bifunctional, Sustainable Separators with Tailored Alignment

Abstract Sodium (Na) is the most appealing alternative to lithium as an anode material for cost‐effective, high‐energy‐density energy‐storage systems by virtue of its high theoretical capacity and abundance as a resource. However, the uncontrolled growth of Na dendrites and the limited cell cycle life impede the large‐scale practical implementation of Na‐metal batteries (SMBs) in commonly used and low‐cost carbonate electrolytes. Herein, the employment of a novel bifunctional electrospun nanofibrous separator comprising well‐ordered, uniaxially aligned arrays, and abundant sodiophilic functional groups is presented for SMBs. By tailoring the alignment degree, this unique separator integrates with the merits of serving as highly aligned ion‐redistributors to self‐orientate/homogenize the flux of Na‐ions from a chemical molecule level and physically suppressing Na dendrite puncture at a mechanical structure level. Remarkably, unprecedented long‐term cycling performances at high current densities (≥1000 h at 1 and 3 mA cm −2 , ≥700 h at 5 mA cm −2 ) of symmetric cells are achieved in additive‐free carbonate electrolytes. Moreover, the corresponding sodium–organic battery demonstrates a high energy density and prolonged cyclability over 1000 cycles. This work opens up a new and facile avenue for the development of stable, low‐cost, and safe‐credible SMBs, which could be readily extended to other alkali‐metal batteries.