Constructing robust interphase via anion-enhanced solvation structure for high-voltage fast charging sodium metal batteries

Abstract

Regulating the electrolyte solvation structure to establish a durable electrode-electrolyte interphase and broaden the electrochemical window is essential for advancing high-energy-density sodium metal batteries (SMBs). Despite the significant progress, the relationship between the precise control of the solvated structure of the electrolyte and interphases at the electrode-electrolyte remains ambiguous. In this work, a sodium salt is used to trigger a weak solvation effect, diethylene glycol dimethyl ether is introduced as a co-solvent to weaken the ion-dipole interactions between the solvent and Na⁺. Benefiting from this, anion-enhanced solvation structures are constructed, which facilitate the rapid transport and dissolution of Na⁺, as well as form a robust inorganic-rich electrolyte interface. As a result, the Na||Na₃V₂(PO₄)₂F₃ pouch cell assembled with the optimized electrolyte exhibits over 86.4 % capacity retention after 280 cycles at a charge voltage of 4.5 V. The Na||Na₃V₂(PO₄)₂F₃ coin cell exhibits stable cycling for 5000 cycles at a high current density of 20 C. This approach not only broadens the voltage window of sodium metal batteries but also ensures long-term stability and durability, providing new insights for the development of high energy density batteries.