To seek the promising candidate for 5 V electrolytes, fluorine-free lithium bis(oxalato)borat (LiBOB) is chosen as the lithium salt, γ-butyrolactone (GBL) as well as sulfolane (SL) with the property of stability against oxidative decomposition is chosen as supporting electrolyte solvents, and linear diethyl carbonate (DMC) is chosen as the third supporting electrolyte solvent to lower viscosity. After systematical analytical studies, it indicates that SL solvent is the main and key reason for the improvement of electrochemical performance, which not only improves the stability of electrolyte system against oxidative decomposition, but also decreases the electrode polarization resistance. More than that, 1.0molL−1 LiBOB–SL/GBL/DMC electrolyte shows good compatibilities with both intercalation hosts as LiNi0.5Mn1.5O4 cathode and carbonaceous anode. It suggests that this novel electrolyte would be an alternative electrolyte for 5 V high-voltage rechargeable lithium-ion batteries based upon LiNi0.5Mn1.5O4 cathode.