Sulfonylimide-Based Single-Ion-Conducting Porous Organic Polymer Electrolytes for Enhanced Performance of Solid-State Lithium Batteries

The development of solid-state electrolytes with high ionic conductivity and interfacial stability is vital for next-generation lithium-ion batteries. Concentration polarization in conventional electrolytes accelerates solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) growth, thereby limiting cycle life and reliability. Here, we report a lithium sulfonylimide-based single-ion-conducting porous organic polymer (Li-SSP) electrolyte designed to suppress anion mobility and enhance Li⁺ transport. The Li-SSP was synthesized via Sonogashira coupling of 4-bromo-<i>N</i>-((4-aminophenyl)sulfonyl)benzenesulfonamide with 1,3,5-triethynylbenzene. Fourier-transform infrared spectroscopy confirmed its chemical structure, while Brunauer-Emmett-Teller analysis revealed coexisting mesoporous and microporous architectures with a high surface area of 271 m² g^-1. The immobilized anionic groups in the porous framework provide continuous Li⁺ conduction pathways, effectively reducing concentration polarization and improving electrochemical stability. The lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)/poly(vinylidene fluoride-<i>co</i>-hexafluoropropylene) (PVDF-HFP)/Li-SSP composite electrolyte exhibits a high ionic conductivity of 4.04 × 10^-4 S cm^-1 at 30 °C and a high Li⁺ transference number of 0.70, significantly higher than that of LiTFSI/PVDF-HFP electrolytes (0.18). A Li||Li symmetric cell demonstrates stable Li plating/stripping for over 400 h with low overpotential, confirming excellent interfacial compatibility. A LiFePO₄ half-cell with the Li-SSP composite electrolyte delivers high capacities of 148.1 mAh g^-1 at 0.2 C and 86.7 mAh g^-1 at 5 C, along with 96.1% capacity retention after 300 cycles at 0.5 C. Scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy analyses further confirm the formation of thinner and chemically stable CEI films, resulting in reduced interfacial resistance. These results highlight that rational design of Li-SSP electrolytes enables high Li⁺ transference, robust interfacial stability, and extended cycle life, offering a promising pathway toward safe and durable solid-state lithium-ion batteries.