Subnanometric Pores of the Solid Electrolyte Interphase Layer for Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) are promising next-generation batteries as a sustainable alternative to lithium-ion systems, yet an understanding of the solid electrolyte interphase (SEI) is far from sufficient. Here, we develop a probing approach using redox mediator molecules to characterize subnanometric SEI pores, revealing that Na⁺ transport occurs through diffusion channels. By electrochemical analysis, differential electrochemical mass spectrometry, and theoretical calculations, the influences of solvent salts on SEI architecture have been studied. These findings offer fundamental knowledge beyond classical SEI models and provide both a powerful characterization tool and principles for electrolyte choice for SIBs.