Civil Engineering Reference
In-Depth Information
2.5 Electrolyte Layers, Especially Functionalized Polymer
Electrolytes
The centrally positioned electrolyte is an indispensible part of an electrochromic
device. It can be a thin film, and Ta
2
O
5
(Franke et al.
2000
; Ahn et al.
2002
,
2003
;
Subrahmanyam et al.
2007
; Abe et al.
2009
; Wang et al.
2011
; Noguchi et al.
2012
) as well as ZrO
2
(Larsson and Niklasson
2004
) are well-known options.
Other alternatives include polymer electrolytes and hybrid materials (Thakur et al.
2012
) as well as polymerized ionic liquids (Sydam et al.
2012
), which, in principle,
allow a superior electrical insulation between the anodic and cathodic parts of the
device.
Nanoparticles can be used for functionalization of polymer electrolytes, and
recent work has studied these possibilities with regard to a ''model electrolyte''
consisting of polyethyleneimine-lithium bis(trifluoromethylsulfonyl) imide (PEI:
LiTFSI) (Bayrak Pehlivan et al.
2012a
,
b
) as well as to a proprietary electrolyte
developed for roll-to-roll manufacturing of electrochromic devices (Bayrak Peh-
livan et al.
2013
). Figure
12
shows how the ion conductivity—which influences
the coloration and bleaching speeds of an electrochromic device—is altered as a
result of adding *7-nm-diameter SiO
2
nanoparticles (fumed silica) (Bayrak
Pehlivan et al.
2012a
). Clearly, the ion conductivity goes up monotonically as the
SiO
2
content rises. The diffuse optical transmittance remained at *1 % up to 8 wt
%ofSiO
2
, implying that the sample was almost haze free, which is essential for
glazing products.
Adding nanoparticles comprised of a transparent conductor instead of SiO
2
can
produce strong near-infrared absorption, which then invokes a ''solar control''
function to the electrochromic glazing. Figure
13
reports spectral transmittance for
PEI:LiTFSI with *13-nm-diameter ITO nanoparticles and shows that a strong
Fig. 12 Ion conductivity at
the shown temperatures for
SiO
2
-containing (PEI-
SiO
2
):(LiTFSI) electrolytes.
Data points are connected by
straight lines for convenience.
From Bayrak Pehlivan et al.
(
2012a
)
10
-4
10
-5
20°C
30°C
40°C
50°C
60°C
70°C
10
-6
0
1
2
3
4
5
6
7
8
wt.% SiO
2
