Solvation engineering of high-entropy ether-based electrolytes for high-voltage sodium-ion batteries

Overcoming the poor oxidation stability of ether-based electrolytes at the cathode is essential for the practical application of high-voltage sodium-ion batteries (SIBs). This work proposes a strategy for preparing high-entropy ether-based electrolytes by incorporating sodium tetrafluoroborate (NaBF₄) and 1,3-dioxolane (DOL) into conventional concentrated ether-based systems. The high-entropy effect modulates the solvation structure, leading to an anion-reinforced configuration that facilitates the formation of a stable cathode electrolyte interphase (CEI). Moreover, this effect enhances sodium-ion (Na⁺) migration within the electrolyte and lowers the desolvation energy barrier, thereby ensuring cycling stability under high-voltage. The cell employing layered oxide cathode delivers a high initial specific capacity of 120 mAh g^-1 at 0.5C and retains 70% of its capacity after 300 cycles. Furthermore, it maintains a high specific capacity of 80 mAh g^-1 even at 5C, substantially outperforming conventional SIBs. This work provides important insights for design and application of high-voltage ether-based electrolytes.