AbstractHigh Li⁺ conductivity, good interfacial compatibility and high mechanical strength are desirable for practical utilization of all‐solid‐state electrolytes. In this study, by introducing Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) with surface defects into poly(ethylene oxide) (PEO), a composite solid electrolyte (OV‐LLZTO/PEO) is prepared. The surface defects serve as anchoring points for oxygen atoms of PEO chains, forming a firmly bonded polymer‐ceramic interface. This bonding effect effectively prevents the agglomeration of LLZTO particles and crystallization of PEO domains, forming a homogeneous electrolyte membrane exhibiting high mechanical strength, reduced interfacial resistance with electrodes as well as improved Li⁺ conductivity. Owing to these favorable properties, OV‐LLZTO/PEO can be operated under a high current density (0.7 mA cm⁻²) in a Li–Li symmetric cell without short circuit. Above all, solid‐state full‐cells employing OV‐LLZTO/PEO deliver state‐of‐the‐art rate capability (8 C), power density and capacity retention. As a final proof of concept study, flexible pouch cells are assembled and tested, exhibiting high cycle stability under 5 C and excellent safety feature under abusive working conditions. Through manipulating the interfacial interactions between polymer and inorganic electrolytes, this study points out a new direction to optimizing the performance of all‐solid‐state batteries.