Impedance diagrams of PTFE-bonded TiS
2 electrodes on which lithium intercalation reactions were proceeding were measured at various cathodic potentials in LiBF
4/tetrahydrofuran(THF), LiClO
4/THF and LiClO
4/propylenecarbonate(PC) solutions. It was found that the diagram was basically composed of a distorted capacitive semicircle at higher frequncies and two straight lines with different slopes at lower frequencies. The semicircle was ascribed to the combination of the double layer capacitance, the charge transfer resistance and an additional constant phase impedance due to the effect of electrode porosity, and the lines with slopes of π/4 and π/2 to the semi-infinite and finite diffusion effects of Li
+ ions in Li
xTiS
2, respectively. The charge transfer resistance,
Rct, increased from 0.005 Ω·m
2 at 2.5 V to 0.25 Ω·m
2 at 1.8 V with decreasing potential in 2 kmol·m
−3 LiBF
4/THF, showing that the intercalation rate is controlled by the charge transfer process at lower potentials in this solution. In 1 kmol·m
−3 LiClO
4/THF and 1 kmol·m
−3 LiClO
4/PC, however, values of
Rct were less than 0.01 Ω·m
2 at all potentials examined. Diffusion coefficients of Li
+ ions in Li
xTiS
2, \ ilde
D, were strongly dependent on the composition of electrolyte; their values in 2 kmol·m
−3 LiBF
4/THF, 1 kmol·m
−3 LiClO
4/THF and 1 kmol·m
−3 LiClO
4/PC were 2×10
−15-1×10
−14, 5×10
−14-5×10
−13 and 3×10
−13-2×10
−12 m
2s
−1, respectively. The increased value of \ ilde
D in 1 kmol·m
−3 LiClO
4/PC seems to be attributed to the solvent-intercalation effects which leads to an increase in the basal plane spacing and the electrode porosity, and thus the effective electrode area for the intercalation.
抄録全体を表示