High‐Strength Ultrathin Solid‐State Electrolyte with Ion‐Rectifying Honeycomb‐Like Skeleton for Lithium Metal Batteries Free from External Pressure

Abstract This work breaks the long‐standing thickness‐performance trade‐off in solid‐state electrolytes by designing an ultrathin (10 µm) membrane featuring an ion‐rectifying honeycomb‐like skeleton. The composite skeleton integrates boron nitride nanofibers (BNNFs) and lithiated nafion (Linafion) mosaics, simultaneously enabling rapid Li ⁺ transport and reinforcing mechanical robustness. The BNNFs provide abundant Lewis acid sites to anchor TFSI ^‐ anions, while Linafion domains facilitate rapid cation exchange via sulfonic acid groups, synergistically promoting Li ⁺ dissociation from both lithium salts and poly(ester‐ether). This unique ion‐rectification mechanism achieves ultrafast Li⁺ conduction with a low activation energy (0.099 eV), yielding a remarkable room‐temperature ionic conductivity of 5.5 × 10 ⁻⁴ S cm ⁻¹ and a high Li ⁺ transference number of 0.85. The all solid‐state electrolyte membrane simultaneously exhibits exceptional tensile strength (30 MPa) and compatibility with high‐loading NCM811 cathodes (12 mg cm ⁻² ) and ultrathin lithium anodes (40 µm). The pouch‐type full cells deliver high energy densities (316.6 Wh kg ⁻¹ , 838.1 Wh L ⁻¹ ) and cycling stability (92.2% retention after 100 cycles) at 25 °C. Notably, the full cell can work in a wide temperature range, while maintaining 120.6 mAh g ⁻¹ at ‐10 °C without external pressure. This strategy enables practical high‐energy solid‐state batteries using ultrathin electrolytes with robust mechanics, rapid conduction, and interfacial stability.