Synergistic Trimethylsilyl‐Engineered Ether and Weakly‐Coordinating Diluent Enables Compact Solvation for Robust Interphases in Practical Li‐SPAN Batteries

Sulfurized polyacrylonitrile (SPAN) is a highly applicable cathode material in lithium‐metal batteries for its low cost and high theoretical capacity. However, the polysulfide dissolution and shuttle effects in ether electrolytes pose a challenge to its long‐term stability. Here, based on the strategy of molecular structure design, an ion‐compact electrolyte is engineered through synergistically combining bis[2‐(trimethylsilyloxy)ethyl] ether (BTEE) with a weakly coordinating diluent difluorobenzene (DFBn). The bulky trimethylsilyl (TMS) groups of BTEE impose steric hindrance to weaken solvent dipole interactions, while DFBn further tailors the solvation environment, collectively driving the formation of an ion‐rich solvation structure. This unique solvation chemistry not only accelerates Li⁺ transport but also promotes the in situ construction of robust LiF‐rich interphases on both electrodes. As a result, the Li‐SPAN cells employing employing dipole modulated compact electrolyte DMCE demonstrate exceptional long‐term performance with 86.2% capacity retention over 800 cycles, and maintain stable cycles even under demanding operational conditions characterized by high cathode loading (≈3.88 mAh cm − 2 ) and lean electrolyte configuration (E/S ratio = 4.55) at both room temperature and 60 °C. This research confirms the feasibility of modulating the solvation environment by altering the ion‐dipole interaction through molecular structure design, giving new insights into the ether electrolyte design for practical Li‐SPAN batteries.