A Dual-Function Additive to Regulate Nucleation Behavior and Interfacial Chemistry for Ultra-Stable Na Metal Anodes beyond One Year

Sodium (Na) metal anodes suffer from dendrite formation and inferior reversibility, mainly induced by the inhomogeneous nucleation/growth and fragile solid electrolyte interphase (SEI), which hinders their commercial application. Optimizing nucleation behavior or SEI features can improve Na deposition/stripping process, as observed in most currently available approaches, but its long-term cyclic stability remains a great challenge because these issues are not fully optimized/solved in an individual method. Herein, a dual-role crown ether additive (CEA) is introduced into electrolytes to circumvent these challenges concurrently. As revealed by experiments and theoretical calculations, CEA possesses a strong affinity with Na+ and effectively regulates desolvation kinetics, leading to the uniform Na nucleation/growth. On the other hand, the resultant Na+/CEA complexes with a strong Lewis acid feature easily attract anions, which enables an anion-abundant solvation sheath, resulting in a NaF-rich SEI. Consequently, Na|Cu cells deliver a high average Coulombic efficiency of 99.95% beyond one year and stable cyclic stability over 3000 h even under a high depth of discharge (75%), surpassing most previous works. Furthermore, this concept is readily extended to zinc metal batteries, verifying that simultaneous nucleation control and interfacial chemistry regulation are promising ways to realize stable metal anodes.

Automated summary

Sodium metal anodes face challenges such as dendrite formation and poor reversibility due to inhomogeneous nucleation/growth and fragile solid electrolyte interphase (SEI). In this study, a dual-role crown ether additive (CEA) was introduced to improve the nucleation behavior and SEI features simultaneously. The CEA effectively regulated the desolvation kinetics to achieve uniform nucleation and growth of sodium, while also forming a NaF-rich SEI through the presence of Na+/CEA complexes. This approach resulted in stable cyclic stability for over 3000 hours, surpassing previous works.