Dual-Salt Low-Concentration Electrolyte for Low-Temperature Sodium Metal Batteries

The high theoretical capacity of 1165 mAh g^-1 and lower cost position sodium metal batteries (SMBs) as a promising alternative to lithium-based batteries. However, their application at ultralow temperatures is limited by conventional commercial electrolytes, which present challenges such as an unstable solid electrolyte interphase (SEI) and suboptimal ionic kinetic performance. Building on the significant impact of low concentration and the pivotal role of SEI films in enhancing the cycle stability of batteries, we develop a low-concentration and dual-salt carbonate electrolyte. This low-concentration electrolyte enhances the fluidity of the electrolyte, while the dual-salt system promotes the formation of a high proportion of anions solvated structure and robust inorganic SEI films. This innovative combination markedly improves the ionic kinetic performance and low temperature cycle life. Consequently, the Na||Na symmetric cell with this electrolyte exhibits a prolonged cycling life of 900 h, while the Na||Na₃V₂(PO₄)₃ full cell maintains a capacity of 70.5 mAh g^-1 over 100 cycles at -40 °C.