Esters co-solvent has been used in ternary system electrolytes for electrochemical storage using LiTFSI as salt. Three linear esters have been studied: methyl propanoate (MP), ethyl propanoate (EP) and ethyl butanoate (EB). The ionic conductivity, viscosity, and electrochemical performances of ethylene carbonate (EC)/ester/dimethyl carbonate (DMC) mixtures have been determined and compared to the reference ternary mixture: EC/propylene carbonate (PC)/DMC in proportion (1/1/3) by volume. These electrolytes have been tested in half cells of the type: Li vertical bar electrolyte vertical bar activated carbon (AC) or graphite (Gr). These active materials are designed to be used in hybrid Li-ion capacitors. Electrochemical results show that MP presents the best performances at the AC electrode in terms of capacitance, especially at low temperatures (-10 degrees C). However, MP based electrolytes give the higher irreversible capacity when used with the Gr electrode, and are the most corrosive toward the aluminum current collector. This problem has been resolved by adding a small amount of LiPF6 (1% in mol) to the electrolyte solution as a passivating additive. Thus, MP based electrolytes exhibit the best performances in terms of capacity at the Gr electrode and capacitance at the AC electrode. (C) 2012 Elsevier Ltd. All rights reserved.