| In this thesis, a mixture of acetonitrile (AN) and gamma-butyrolactone (gammaBL) are used as the solvent in combination with LiClO4 or LiBF4 as the salt of the electrolyte studied for Li-ion capacitors. The electrolyte with various ratios of AN and gammaBL with different salts are investigated, and visual observation shows that metallic lithium is stable in LiClO4 or LiBF4 in 1:1 (wt.) AN/gammaBL electrolyte. The ionic conductivity of the electrolyte as a function of LiClO4 salt is optimized, and it is shown that 1M LiClO4 in 1:1 (wt.) AN/gammaBL electrolyte has the highest conductivity which is much higher than a commercial electrolyte (1M LiPF6 in 1:1:1 (wt.) ethylene carbonate (EC)/Dimethyl carbonate (DMC)/diethyl carbonate (DEC)) used in Li-ion batteries, over the whole temperature range from -30°C to 65°C. The electrochemical stability windows of three electrolytes, 1M LiPF6 1:1:1 (wt.) EC/DMC/DEC, 1.1M LiClO4 in 1:1 (wt.) AN/gammaBL and 1M LiBF4 in 1:1 (wt.) AN/gammaBL, on three kinds of electrodes (GC, AC and HC) are different from each other, and the results are compared and discussed. The discharge and charge cycling results show that Li/AC cells with both 1.1M LiClO4 in 1:1 AN/gammaBL and 1M LiBF 4 in 1:1 AN/gammaBL electrolytes have fast capacity decay due to the increased impedance. The capacity of the latter was higher initially but decayed more rapidly which can be probably attributed to the product covered on the surface of the AC electrode. |
