Silicon-based solid-state lithium batteries (Si-SSLBs) are of great interest due to their extremely high safety and energy density. However, the low ionic conductivity of solid electrolytes hinders their use in batteries, the volume expansion of the Si anode during Li⁺ insertion/extraction, and the high interfacial resistance between the solid electrolyte and electrodes. In this study, a composite solid electrolyte (CSE) with excellent ionic conductivity (1.20 × 10⁻⁴ S·cm⁻¹) at 60 °C was developed by introducing the plasticizer succinonitrile (SN) and the inorganic solid electrolyte Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) into poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP) matrix. A three-dimensional (3D) face-contact Si/PVHS-L/LFP (PVHS-L: PVDF-HFP/SN/LATP and LFP: LiFePO₄) solid-state battery model was constructed by a secondary coating process based on the use of PVHS-L. This approach forms a fully integrated electrode–electrolyte interface, enhancing Li⁺ transport efficiency compared to conventional mechanically assembled batteries. The integrated device achieves maximum interfacial contact, resulting in superior electrochemical performance. Specifically, the battery integrated with Si anode, PVHS-L CSE and LFP cathode delivers a discharge specific capacity of 122.6 mAh·g⁻¹ after 100 cycles, with a capacity retention rate of 81.5%. This work provides a new strategy to address the challenge of achieving stable and continuous interfacial contact in Si-SSLBs.