Formation of NaF-Rich Solid Electrolyte Interphase on Na Anode through Additive-Induced Anion-Enriched Structure of Na+ Solvation

Abstract

High-capacity sodium (Na) anodes suffer from dendrite growth due to the high reactivity, which can be overcome through inducing a stable NaF-rich solid electrolyte interphase (SEI). Herein, we propose an additive strategy for realizing the anion-enriched structure of Na⁺ solvation to obtain a NaF-rich SEI. The electron-withdrawing acetyl group in 4-acetylpyridine (4-APD) increases the coordination number of PF₆ ^- in the Na⁺ solvation sheath to facilitate PF₆ ^- to decompose into NaF. Thus, the NaF-rich SEI with high mechanical stability and interfacial energy is formed to repress the growth of Na dendrites. With the 4-APD-contained electrolyte, the symmetric Na||Na cells show excellent cycling performance over 360 h at 1.0 mA cm^-2 . Meanwhile, excellent stability is also achieved for Na||Na₃ V₂ (PO₄ )₂ O₂ F full cells with high Coulombic efficiency (97 %) and capacity retention (91 %) after 200 cycles.

Keywords: 4-Acetylpyridine; Sodium Fluoride; Sodium-Metal Anodes; Solid Electrolyte Interphase; Solvation Sheath Regulation.