Quasi-solid-state electrolytes that possess high ionic conductivity, excellent interface stability, and low interfacial resistance, are required for practical solid-state batteries. Herein, a heterogeneous quasi-solid-state hybrid electrolyte (QSHE) with a robust lithium-ion transport layer composed of Li1+xAlxTi2-x(PO4)3 (LATP) nanoparticles (NPs) at the anode/electrolyte interface was fabricated using electrospun nanofibers as a skeleton via a facile in situ polymerization approach. The QSHE exhibits a high ionic conductivity (0.98 mS cm-1), a wide electrochemical window (4.76 V vs. Li/Li+), and favorable compatibility with lithium metal (maintaining stability over 2000 h in a symmetrical cell) at room temperature. When coupled with a Li|LiFePO4 battery, the QSHE enables the battery to retain 95.4% of its capacity after 300 cycles at 2 C. Moreover, the atomic force microscopy verifies the high Young’s modulus of the LATP-dominated bottom layer, while numerical simulation validates the effective distribution of lithium ions at the interface facilitated by LATP NPs, hence contributing to dendrite-free lithium plating/stripping morphology. This straightforward strategy could pave the way for the development of high-performance and interfacially stable lithium metal batteries.