Tailoring the NaI-rich solid electrolyte interphase for enhanced stability in sodium metal batteries

Abstract

Unlocking the potential of sodium metal batteries (SMBs) depends on the formation of a mechanically robust and ionically conductive solid electrolyte interphase (SEI) that prevents dendrite formation and maintains peak performance under challenging conditions. Our study presents an effective electrolyte additive called cetyltrimethylammonium iodide (CTAI), designed to enhance the durability of SEI by enriching it with a NaI-rich composition, I⁻ anion reduces surface diffusion barriers for sodium ions while boasting impressive ionic conductivity of 18 mS cm⁻¹, whereas CTA⁺ cation suppresses the dendrite formation on the sodium metal anodes (SMAs). Notably, the resulting SEI exhibits a thickness of ∼40 nm. Benefiting from the additive, the Na||Na symmetrical cell demonstrates remarkable cycling stability over 5000 h and minimal overpotential of around 35 mV under current density of 2 mA cm⁻² and capacity of 2 mAh cm⁻². Furthermore, our findings indicate significant enhancements in cycling stability and rate capability for Na-S batteries. Thus, our work represents a notable advancement in sodium metal batteries, offering a transformative approach to establishing stable SEIs and dendrite-free SMAs.