Solid-state lithium batteries have attracted significant attention recently due to their superior safety and energy density. Nevertheless, the large interfacial resistance has limited the development of SSLBs. To tackle this problem, a general strategy is to add liquid electrolytes (LE) at the interface to form a solid-liquid hybrid electrolyte. However, the effects and interfacial properties of LE in the solid-liquid hybrid electrolyte have not been well-understood. In this work, we quantitatively add LE at the interface to eliminate the large interfacial resistance and study its interfacial properties. As little as 2 µL of LE at the interface enables a hybrid LiFePO4/LATP/Li battery to deliver a specific capacity of 125 mA h g−1 at 1 C and 98 mA h g−1 at 4 C. Excess LE has no further contribution to the electrochemical performance. Furthermore, the rigid SSE could suppress the formation of lithium dendrites, especially in the case with a high cathode loading (9.1 mg/cm2), suggesting the feasibility of high energy density SSLBs using Li metal anodes. The interfacial analysis reveals that an interfacial solid-liquid electrolyte interphase (SLEI) was formed at the interface, preventing the reduction of LATP by Li metal, thus ensuring the long-term durability of LATP in LE.