This invention is the design of a high efficiency electrolyte that enables the stable cycling of lithium cobalt oxide (LiCoO2, or LCO) layered cathode under high voltages (e.g. 4.5 V vs. Li/Li+). Due to the structural instability of LCO cathode materials under high voltages ( >4.2 V), commercial Li-ion batteries (LIBs) using LCO cathode typically has a low cut-off charge voltage. The practical reversible capacity of LCO is only limited to ~140 mAh g-1. Nevertheless, in this new electrolyte, the LCO cathode could deliver a very high capacity about 190 mAh g-1 (at 0.1C) and realize excellent cycling stability under a charge cut-off voltage of 4.5 V, along with a cell Coulombic efficiency (CE) over 99.8%. In sharp contrast, in the conventional carbonate electrolyte (1 M LiPF6 in EC/EMC, 3:7 wt), the LCO cathode has a fast capacity fading (66% capacity retention after only 50 cycles) and a low cell CE about 97.5%. Therefore, this new electrolyte could significantly improve the energy densities and cycle lives of batteries with LCO cathodes.