“Ionic Tug‐of‐War” Effect Decoupling Li ⁺ ‐Coordination Enables High Ion Conductivity and Interface Stability for Solid‐State Electrolytes

ABSTRACT The strong and excessive Li + ‐coordination with ethylene oxide (EO) chains induces an inadequate Li + conduction and poor interfacial stability in polyethylene oxide (PEO)‐based electrolytes. Herein, we introduce an “ionic tug‐of‐war” strategy to decouple Li + ‐coordination by leveraging other metal ions to compete with Li + for coordination. This design is realized by grafting Lewis‐acidic Mg 2 + sites, which possess moderate positive charge and coordination ability, onto the surface of triethoxy‐3‐(2‐imidazolin‐1‐yl)propylsilane (DI)‐bridged Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 fillers (denoted as LLZTO‐DI‐Mg). With the homogeneous dispersion of LLZTO‐DI‐Mg within PEO matrix, Mg 2+ sites readily chelate with EO and bis(trifluoromethanesulphonyl)imide (TFSI − ) anions, inducing competitive Mg 2+ ‐EO‐Li + and Mg 2+ ‐TFSI − ‐Li + coordination structures. The resulting loosened Li + ‐coordination environment enables high ionic conductivity (7.4 × 10 −4 S cm −1 ) and Li + transference number (0.63), both essential for efficient ion transport in battery systems. Moreover, the preferentially formed Mg 2+ ‐TFSI − promotes the generation of a robust solid electrolyte interphase (SEI) layer enriched with LiF/Li 3 N, thereby improving interfacial stability. When applied in LiFePO 4 ||Li and high‐voltage LiNi 0.83 Co 0.07 Mn 0.1 O 2 ||Li full cells, the customized electrolyte demonstrates superior rate capability and long‐term cycling performance. This work highlights the significant potential of “ionic tug‐of‐war” effect in regulating Li + conduction and tailoring interphase chemistry for high‐performance solid‐state composite electrolytes.