<p>Polymer-based solid-state electrolytes with high flexibility and excellent processability present great prospects in all-solid-state lithium batteries. However, when encountering interface stability problems, the application of polymer-based solid-state electrolytes in allsolid-state lithium batteries is puzzling. In this work, we proposed a lithium crosslinking strategy to regulate the interfacial chemistry by tailoring an effective Li₂O-rich solid electrolyte interphase layer attributed to introducing 15-crown-5 into the polymer matrix. Specifically, crosslinking the 15-crown-5 with Li⁺ in polymer-based solid-state electrolytes boosts the Li⁺ transport by weakening the coordination between Li⁺ and polymer chains. The crosslinked 15-crown-5 moves along with the Li⁺ to the anode and decomposes to form the Li₂O-rich solid electrolyte interphase with faster Li⁺ diffusion kinetics, resulting in uniform lithium deposition and suppressing the dendrite penetration. Therefore, the symmetric Li-Li cell could stably maintain cycling over 1100 h without shortcircuiting. The LiFePO₄∥Li full battery presents high retention of capacity (92.75%) over 500 cycles at 1 C. Also, the NCM811∥Li full battery can be well-operated in 300 cycles with the capacity retention of 81.44% at 1 C. This study inspires the development of high-performance all-solid-state lithium batteries by rationally tailoring interface chemistry components by regulating the coordinated structure of Li⁺ at the molecular level.</p>