Solid-state lithium-metal batteries (SSLMBs) with a Li₇La₃Zr₂O₁₂-based composite solid electrolyte (CSE) show great potential for overcoming the safety and specific energy concerns of conventional liquid-electrolyte Li-ion batteries. Nevertheless, achieving a satisfactory connection between a solid electrolyte and the cathode and anode materials is a major challenge. Three strategies have been adopted in this work to improve the performance of SSLMBs. First, the Ga concentration in Ga-doped Li₇La₃Zr₂O₁₂ (LGLZO) was adjusted. We first revealed the strong impact of the Ga stoichiometry on the battery performance. Second, a spin-coating method was used to fabricate an LGLZO CSE layer directly on top of a LiFePO₄ (LFP) cathode. This practice can improve the cathode/CSE interfacial contact and establish a Li⁺ conducting network within the cathode. Third, the ionic liquid (IL) connection interlayer was applied between the Li metal electrode and the CSE to facilitate the Li⁺ transport across the interface, homogenize the Li⁺ flux, and form a robust SEI for suppressing side reactions. The IL also functioned as a plasticizer to enhance the segmental motion of the polymer chains, increasing the Li⁺ conductivity. We found that the TFSI⁻ IL anion is superior to FSI⁻ for the rate capability and cycling stability of the cell. We believe that the proposed dual interface design can be utilized to cost-effectively address the electrode//electrolyte interface problems, which are crucial for the practical application of SSLMBs.