A Nonfluorinated Diluent in Ether-Based Electrolyte for Low-Temperature Sodium-Ion Batteries

Linear ethers with multidentate chelate sites to Na⁺ usually have strong solvating power and poor film-forming ability at interfaces that increase the desolvation energy barrier in sodium-ion batteries (SIBs). Herein, we introduce a nonfluorinated and cost-effective diluent of cyclopentyl methyl ether (CPME) in 1,2-diethoxyethene electrolyte to enhance the percentage of anion-participating solvation structure, thus decreasing the desolvation energy and accelerating the ion transfer across the interfaces under cryogenic temperatures. The tame electrolyte exhibits a high reversibility in the Na deposition/stripping process with an average Coulombic efficiency of 99.95% for 1000 cycles. The Na||Na₃V₂(PO₄)₃ cell retained 99% capacity retention after 180 cycles at −40 °C. Moreover, the hard carbon||Na₃V₂(PO₄)₃ cell retained 92.7% capacity retention for 260 cycles under −20 °C, and the initial capacity at −50 °C is 53% of that at 30 °C. Therefore, such a cost-effective diluent shows great potential in promoting the widespread implementation of low-cost and low-temperature SIBs.