A Li-S battery with safety configuration has been constructed by employing electrochemically prelithiated Si/C microspheres as an anode, S/C composites as a cathode, and a room temperature ionic liquid of n-Methyl-n-Allylpyrrolidinium bis(trifluoromethanesulfonyl)imide (RTIL P1A3TFSI) as an electrolyte. Galvanostatic discharge–charge tests show that the as-assembled Li-S battery could deliver a high discharge specific capacity of 1457mAhg−1 (based on the sulfur cathode) at 0.1C, indicating the high Li electroactivity of the system. The reversible capacity is 926.4mAhg−1 in the first cycle, and could remain as high as 670mAhg−1 after 50 cycles, revealing the favorable compatibility between the RTIL P1A3TFSI electrolyte and the two electrode materials in the Li-S battery. The as-assembled Li-S battery in the charged state can be used for energy output without activation process by charging. This green rechargeable Li-S battery typically gives an output voltage of 1.5V per cell, which raises the potential for directly replacing the widely used 1.5V primary alkaline batteries and dry cells without any change of external circuits of current electronic devices but more rechargeable and powerful.