Synergistic Modulation of Solid- and Cathode-Electrolyte Interphase via a Lithium Salt Additive toward Stable Sodium Metal Batteries

Constructing feasible sodium metal batteries (SMBs) faces complex challenges in stabilizing cathodes and sodium metal anodes. It is imperative, but often underemphasized, to simultaneously regulate the solid-electrolyte interphase (SEI) to counter dendrite growth and the cathode-electrolyte interphase (CEI) to mitigate cathode deterioration. Herein, we introduce lithium 2-trifluoromethyl-4,5-dicyanoimidazolide (LiTDI) as an efficacious additive in a carbonate-based electrolyte to extend cycle lifespan of full SMBs: the capacity retention reaches 77.8% after 8000 cycles at room temperature and 74.3% after 5000 cycles at 50 °C. Cryogenic transmission electron microscopy characterization reveals that LiTDI promotes formation of inorganics-condensed SEI and CEI. The former inhibits continuous electrolyte decomposition and ensures homogeneous sodium plating, while the latter shields cathode from transition metal dissolution. This study highlights the crucial role of LiTDI in stabilizing both anodes and cathodes in SMBs, and it provides insights into designing functional additives for synergistic modulation of SEI and CEI.