Solid-state batteries (SSBs) with metallic lithium (Li) anodes are regarded as the next-generation energy storage devices with high energy and power densities. However, the issues of the Li dendrite growth and poor interfacial contact between the solid electrolyte and electrodes severely limit their wide practical applications. Therefore, it is of great importance to develop an electrolyte with high modulus to inhibit the growth of lithium dendrites and achieve a close contact with the electrodes. Herein, we fabricated a thin asymmetrical composite electrolyte (CPE), which integrates a ceramic-rich layer on the anode side and a polymer-rich layer on the cathode side by utilizing the natural settlement of Li_6.28La₃Zr₂Al_0.24O₁₂ (LLZAO) during the in situ polymerization process. In such unique architecture, the rigid ceramic-rich layer is towards the Li metal and can effectively suppress the growth of Li dendrites, and the soft polymer-rich layer could wet the cathode to endow connected interface simultaneously. As a result, this asymmetric CPE possesses a high ionic conductivity of 8.43 × 10⁻⁴ S cm⁻¹ and a wide electrochemical window up to 5.0 V at room temperature. The cycle of lithium symmetric cells renders a low charging voltage polarization and outstanding stability. Moreover, LiNi_0.5Co_0.2Mn_0.3O₂/Li batteries using this CPE exhibit excellent cyclic stability, superior rate capability, and a high initial discharge capacity of 149.1 mA h g⁻¹ at room temperature.