Abstract
<jats:p>Hybrid solvents have been widely adopted in multifunctional electrolytes design by leveraging the complementary properties of their constituents. While research has traditionally focused on the physical properties of single solvents, we identify the largely overlooked role of geometric compatibility between co-solvents as a decisive factor in achieving synergistic effects for wide-temperature anode-free sodium batteries. Using diglyme-based electrolytes as a benchmark, we first extend the terminal group of the linear diglyme molecule to enhance oxidative stability. More importantly, we demonstrate that the unique asymmetric geometry of the resulting solvent enables cyclic 1,3-dioxane (DX), which cannot solvate Na+ by itself, to enter the primary solvation shell. This structural reconfiguration triggers the preferential degradation of DX to prevent the generation and crossover of attacking species, as revealed via implanted optical fiber sensing technique. The formulated electrolyte ensures the long-term stability of anode-free C-Al||Na3V2(PO4)3 full cells across a broad temperature range, realizing 91% capacity retention after 300 cycles at -20 °C and maintain 81% retention after 100 cycles under thermal stress at 50 °C. This work establishes molecular geometric compatibility as a critical new dimension in cosolvent engineering for designing customized solvation structures and interfacial regulation.</jats:p>