Solid‐state lithium‐metal batteries attract great attention due to their high energy density and superior safety. However, the sluggish Li⁺ kinetics of solid electrolyte and poor interface compatibility between electrolyte and lithium anode lead to unsatisfied performance at room temperature, which severely limit their practical application. Herein, a Janus quasi‐solid electrolyte (JSE) design is reported, which modifies the Li⁺ solvation environment in succinonitrile (SN) plastic crystal electrolyte and creates 1D Li⁺ transportation channels. Density functional theory calculations and Raman results reveal that Li_1.3Al_0.3Ti_1.7(PO₄)₃ changes the Li⁺ solvation environment from SN units to aggregated ion pairs, which accelerates the diffusion rate of Li⁺. As a result, JSE presents excellent ionic conductivity (0.73 mS cm⁻¹) and high lithium transference number (0.72). With this efficient JSE, Li symmetric cells deliver excellent cycle stability over 600 h with a low over potential of 60 mV. LiFePO₄|JSE|Li solid‐state battery delivers an impressive performance with a specific discharge capacity of 152 mAh g⁻¹ after 100 cycles at room temperature under 0.5 C. Moreover, the corresponding pouch cell also shows outstanding performance (140 mAh g⁻¹ under 0.5 C) and withstands abuse tests such as bending and cutting, demonstrating its superior safety for future utilization.