The ether's chain length effect in electrolyte for hard carbon towards efficient sodium storage at low temperature

The synergy between ether-based electrolytes (EBEs) and hard carbon (HC) in sodium-ion batteries (SIBs) enhances Coulombic efficiency, durability, and rate capability. Despite these advantages, the intricate relationship of how the molecular structure of ether solvents modifies electrolyte properties and, subsequently, sodium storage performance remains inadequately explored, especially for low-temperature applications, limiting the advancement of EBEs. Our study investigates ethylene glycol ether-based electrolytes with varying chain lengths to understand their influence on reaction kinetics and sodium storage. Notably, HC electrodes paired with NaPF6/ethylene 6 /ethylene glycol dimethyl ether exhibit superior performance, achieving 247.5 mAh g- 1 after 2000 cycles at 1.0 A g- 1 . Even at-20 degrees C, these cells exhibit impressive endurance, retaining capacities of 257.5 mAh g- 1 in half cells and 75.5 mAh g- 1 in full cells at 0.1 A g- 1 after 100 cycles, considering the entire mass of active material. Our thorough analysis indicates that the ether solvent with shorter chain length, distinguished by its low solvation-free energy and accelerated ionic kinetics, promotes rapid de-solvation and the formation of an inorganic-rich interface. Through this study, we illuminate the pivotal influence of solvent chain length on sodium storage in hard carbon, contributing to foundational insights towards the design of sophisticated electrolytes for SIBs.