Engineering Solvent–Anion Interactions via Asymmetric Ethers for 200 Wh Kg ⁻¹ Low‐Temperature Anode‐Free Sodium Pouch Cells

Abstract

ABSTRACT Achieving highly reversible Na plating/stripping is crucial for the stable operation of low‐temperature anode‐free sodium metal batteries (LT‐AFSMBs), yet simultaneously realizing ultra‐high Coulombic efficiency (CE) and long‐term durability, accompanied by high energy density, remains a formidable challenge. Herein, by regulating the molecular side chain, we design an asymmetric chain‐like ether solvent that elegantly balances weak Na + ‐dipole and strong anion‐dipole interactions. This rationally tailored electrolyte fosters an anion‐rich Na + coordination environment, which significantly lowers the desolvation barrier and drives the formation of a robust, anion‐derived solid electrolyte interphase with rapid interfacial dynamics. Consequently, the optimized electrolyte delivers an unprecedented average CE of 99.96% over 500 cycles at −20°C. Remarkably, even under stringent conditions of an ultra‐high cathode loading (28.05 mg cm −2 ) and areal capacity (2.48 mAh cm −2 ), the LT‐AFSMBs retain 85.9% of their initial capacity over 600 cycles at −20°C. Moreover, practical Ah‐level anode‐free pouch cells demonstrate stable operation for 300 cycles, yielding a high energy density exceeding 200 Wh kg −1 (based on the mass of entire pouch cell). This paradigm‐shifting solvation strategy provides a highly viable and scalable blueprint for the next‐generation, extreme‐temperature energy storage systems.