Abstract
The properties of succinonitrile-based
electrolytes can be enhanced
by the addition of an ionic liquid (IL). Here, we have reported the
relationship between the electrical transport properties and the structure
of a new [(1 –
x
)succinonitrile:
x
IL]–LiI–I
2
electrolyte, where the mole fraction
(
x
) of the IL (1-butyl-3-methyl imidazolium iodide)
was varied from 0 to 40%. Compositional variation revealed the optimum
conducting electrolyte (OCE) at
x
= 10 mol %, possessing
an electrical conductivity (σ
25°C
) of ∼7.5
mS cm
–1
with an enhancement of ∼369%. The
partial replacement of succinonitrile by the IL eliminated the abrupt
change in the slope of the log σ vs
T
–1
plot at the melting temperature of the succinonitrile–LiI–I
2
system, showing the Vogel–Tamman–Fulcher-type
behavior owing to molecular chain disorder. Raman spectroscopy showed
the I
3
–
concentration nearly twice the
I
5
–
concentration for the OCE. Vibrational
spectroscopy exhibited red shifts in the ν
C≡N
, ν
CH
2
, ν
a,CC
, ν
a,N-CH
3
, and ν
s,N-butyl
modes, indicating an interaction between succinonitrile and the
IL. The area ratio
A
CH
2
/
A
C≡N
increased slightly for
x
= 10 mol % (OCE) and largely for
x
> 10 mol
%,
indicating an increase in the C–H bond length. These observations
indicated that the interaction between succinonitrile and the IL was
enhanced at
x
> 10 mol %, which decreased the
electrical
conductivity of these electrolytes. Owing to fast ion transport, an
OCE-based dye-sensitized solar cell showed a 40–55% decrease
in the charge-transfer and Warburg resistances, resulting in ∼139
and ∼122% increases in
J
SC
and
η, respectively.