Engineering interfacial molecular bridge APTES enhancing Li+ transport and interface stability in Al2O3/PVDF-HFP composite solid-state electrolytes.

To address the demand for safe, high-energy-density lithium-metal batteries, we developed a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)-based composite electrolyte via an "interfacial molecular bridge" strategy. γ-aminopropyltriethoxysilane (APTES) molecules are covalently anchored onto Aluminum oxide (Al2O3) fillers, where the terminal NH2 groups act as Lewis base sites to immobilize bis(trifluoromethanesulfonyl)imide anion(TFSI-) anions, releasing free Li+ and boosting the transference number from 0.42 to 0.66. Concurrently, the uniformly dispersed fillers suppress PVDF-HFP crystallization, creating continuous amorphous pathways that deliver a high ionic conductivity of 7.02 × 10-4 S cm-1 with a low activation energy of 0.11 eV. A "more is less" effect of grafting density is revealed: insufficient grafting fails to inhibit agglomeration, while excessive silane forms an insulating polysiloxane barrier that degrades performance. The optimized electrolyte exhibits a wide electrochemical window (∼5.0 V), robust Li plating/stripping for over 1000 h at 0.1 mA cm-2, and stable cycling in LFP||Li full cells with 86.6% capacity retention over 500 cycles at 0.5C. This work establishes a surface-engineering paradigm for designing high-performance composite solid-state electrolytes.