Autonomous ion-highways quasi-solid electrolytes toward high-voltage lithium metal batteries

Electrolyte solidification holds great promise in addressing safety concerns. Nevertheless, integrating high electrochemical stability and intrinsic interfacial compatibility remains challenging for high-voltage lithium metal batteries. Herein, we report an ion-percolative quasi-solid electrolyte via concentration-driven self-assembly. At a concentration threshold (LiFSI(FEC)_x, x = 0.37), the system triggers spontaneous crystallization of LiFSI to form a rigid, nonflammable framework at room temperature and generates dispersed [LiFSI-FEC] ionic clusters that simultaneously percolate within grain boundaries. This unique ion-percolative architecture (nano-LiFSI skeleton + [LiFSI-FEC] cluster network) enables autonomous Li-ion highways between dynamic clusters along grain boundaries of salt. The optimized electrolyte achieves a high ionic conductivity of 2.3 × 10^-4 S/cm and an exceptional Li⁺ transference number (0.75) at room temperature. This electrolyte provides a satisfying tradeoff between nonflammability, electrochemical windows, ionic conductivity, and mechanical properties, simultaneously achieving perfect compatibility with the lithium metal anode and 4.6 V high-voltage cathodes.