Herein, we report the synthesis of a novel imidazolium-based ionic salt, lithium (fluorosulfonyl) ((3-(1-methyl-1H-imidazol-3-ium-3-yl)propyl)sulfonyl) bis(fluorosulfonyl)imide (LiFSMIPFSI) as an electrolyte for the application in lithium-ion battery (LIB). The as-synthesized LiFSMIPFSI exhibited high purity and yield, which was characterized by various spectroscopic techniques. The LiFSMIPFSI electrolyte with a mixed solvent of ethylene carbonate (EC) and dimethyl sulfoxide (DMSO) (75:25 v/v) showed a wide electrochemical stability (ca. 4.5 V vs. Li/Li+) and high thermal stability (300 °C), good Li+ conductivity (ca. 8.02 mS/cm at 30 °C), and low intrinsic viscosity, which concurrently delivered a specific discharge capacity of ca. 125 mAhg−1 at 0.1 C with the full LIB configuration of LiFePO4/electrolytes/graphite. The performance of this LiFSMIPFSI electrolyte was enhanced further by the addition of conventional lithium bis(fluoro-sulfonyl)imide (LiFSI) and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) ionic salts (20% each) as additives with the specific discharge capacity of ca. 147 and 139 mAhg−1, respectively, at 0.1 C. This is mainly due to the additional enhancement of Li+ conductivity and its concentrations in the electrolytes induced by the additives. The LiFSMIPFSI electrolyte with LiFSI additive based LIB showed the highest cycling stability (capacity retention ca. 97%) among the electrolytes after 500 charge-discharge cycles. Thus, the present work contributes to the development of new ionic salts and its effects upon the addition of additives on LIB performance.