Anion-Cation Targeted Regulation Enables Ultrafast and Stable Sodium Metal Batteries at Low Temperatures.

Abstract

Anion-dominated solvation and artificial interfacial engineering have been intensively pursued for low-temperature sodium-metal batteries (SMBs), yet they face constraints from temperature-sensitive solvation dynamics and interfacial control. Here we propose anion-cation-targeted regulation via Sn(OTf)2 that simultaneously constructs a solvent-reinforced solvation structure and electrochemically induces an alloy-based solid electrolyte interphase (SEI) (Na15Sn4), which goes beyond the prevailing anion-centric strategy to address the critical challenges of SMBs at subzero temperatures. Competitive Sn2+-Na+ coordination excludes PF6 - from the primary solvation sheath, while OTf- and the ether groups of diethylene glycol dimethyl ether (DEGDME) coupling foster a solvent-dominated configuration, substantially reducing the Na+ desolvation energy barrier at low temperatures. This design enables Na||Na3V2(PO4)3 cells to deliver a recorded 1050 cycles at -20°C and 20 C, and nearly 700 cycles at -50°C. Ah-scale pouch cells sustain durable 450 cycles at -20°C, with a 6 Ah cell reaching 215 Wh kg-1 at 25°C (total cell mass). Our findings resolve the longstanding trade-off between low-temperature kinetics and stability in SMBs, offering a new design rationale beyond conventional interfacial engineering.