AbstractFSI⁻‐based ionic liquids (ILs) are promising electrolyte candidates for long‐life and safe lithium metal batteries (LMBs). However, their practical application is hindered by sluggish Li⁺ transport at room temperature. Herein, it is shown that additions of bis(2,2,2‐trifluoroethyl) ether (BTFE) to LiFSI‐Pyr₁₄FSI ILs can effectively mitigate this shortcoming, while maintaining ILs′ high compatibility with lithium metal. Raman spectroscopy and small‐angle X‐ray scattering indicate that the promoted Li⁺ transport in the optimized electrolyte, [LiFSI]₃[Pyr₁₄FSI]₄[BTFE]₄ (Li₃Py₄BT₄), originates from the reduced solution viscosity and increased formation of Li⁺‐FSI⁻ complexes, which are associated with the low viscosity and non‐coordinating character of BTFE. As a result, Li/LiFePO₄ (LFP) cells using Li₃Py₄BT₄ electrolyte reach 150 mAh g⁻¹ at 1 C rate (1 mA cm⁻²) and a capacity retention of 94.6% after 400 cycles, revealing better characteristics with respect to the cells employing the LiFSI‐Pyr₁₄FSI (operate only a few cycles) and commercial carbonate (80% retention after only 218 cycles) electrolytes. A wide operating temperature (from −10 to 40 °C) of the Li/Li₃Py₄BT₄/LFP cells and a good compatibility of Li₃Py₄BT₄ with LiNi_0.5Mn_0.3Co_0.2O₂ (NMC532) are demonstrated also. The insight into the enhanced Li⁺ transport and solid electrolyte interphase characteristics suggests valuable information to develop IL‐based electrolytes for LMBs.