Adjusting anion–solvent dipole interactions in ether-based electrolytes for wide temperature range applications of sodium-ion batteries

Ether-based electrolytes have superior low-temperature performance, however, their instability at high temperatures hinders their commercial application. Therefore, it is crucial to conduct further studies to enable their use in practical batteries. In this work, we demonstrate that the coordination of anion–solvent dipole interactions with weak solvation improves interface transmission and reduces the kinetic barrier for Na⁺ desolvation, leading to a significant improvement in the rate capability and cycling stability of batteries over a wide temperature range (−50–55 °C). The Na‖Na symmetrical cell demonstrates outstanding stripping/plating cycling durability for over 4000 h at −20 °C and 0.5 mA cm⁻². The Na₄Fe₃(PO₄)₂P₂O₇ ‖Na half cells present an ultra-high capacity retention of 99.9% after 1000 cycles at −20 °C and 0.3C, with an average coulombic efficiency (CE) of 99.8%. Additionally, the Na₄Fe₃(PO₄)₂P₂O₇‖hard carbon pouch batteries exhibit superior high-temperature cycling performance with a capacity retention of 87.8% after 1000 cycles and excellent low-temperature stability compared to commercial electrolytes with a capacity retention of 98.3% after 500 cycles. Our strategy in expanding the working temperature range of sodium-ion batteries accelerates the practical application of ether-based electrolytes.