C O M M U N I C A T I O N S
This implies that significant liquidlike character still exists at -35
°C. Studies down to -65 °C are in progress.
In summary, a nanostructured, liquid-electrolyte-filled polymer
material has been developed that has many of the best features of
gelled polymers and LC-based electrolytes plus very stable,
liquidlike ion conductivity over a wide temperature range that has
not been observed in either of those other types of materials.
Conductivity and NMR DOSY studies on this material over a wider
temperature range are underway. We are also exploring ways to
improve the conductivity of this material by removing the film
surface layer/crust, increasing the amount of PC solution and its
Li salt concentration in the films, and varying the type of liquid
electrolyte used. New Q-phase LLC monomer designs are also being
explored.
Figure 2. (a) XRD profile (inset: PLM image) and (b) photo of a cross-
linked QII-phase film of 1 with 15 wt % 0.245 M LiClO4-PC.
Supporting Information). The resulting colorless, transparent films
were flexible and mechanically robust, and showed no sign of PC
solution leaching even upon contact or blotting.
Table 1 shows RT ion conductivity values for the cross-linked
QII films and several comparison materials obtained using conven-
tional AC impedance analysis methods (Nyquist plots) (see the
Supporting Information).15 The RT conductivity of the QII network
of 1 with 15 wt % pure PC was only (6 ( 2) × 10-7 S cm-1. This
value is consistent with that reported for Li salts of ionic polymers
(i.e., polyelectrolytes) containing no added free salt (e10-6 S cm-1),
where polymer-bound anions afford limited Li+ mobility.1c In
contrast, the RT conductivity of the QII network of 1 with 15 wt %
Acknowledgment. This work was funded by the U.S. Depart-
ment of Energy via an STTR Grant to TDA Research with a
subcontract to CU Boulder (DE-FG02-04ER84093) and by the NSF
LC Materials Research Center at CU Boulder (DMR-0213918 and
DMR-0820579).
Supporting Information Available: Preparation and polymerization
of 1 and its LLC phases, phase diagrams, ion conductivity measurement
methods, VT conductivity and NMR DOSY data, and initial thermal
analysis data. This material is available free of charge via the Internet
0.245 M LiClO4-PC was found to be (9 ( 4) × 10-4 S cm-1
,
which is similar to that of gelled PEO systems containing
substantially more (40-60 wt %) liquid electrolyte with a higher
Li salt concentration (1 M).1c This value is also similar to that of
a film of 0.245 M LiClO4-PC solution measured by the same
method, suggesting liquidlike mobility in the QII channels. Nafion-
1135 was used as a calibration standard, and its observed
conductivity matched reported values.16 It was not possible to
directly confirm the importance of the QII phase with respect to
ion transport. Attempts to prepare 1/LiClO4-PC films with the same
composition as the QII films but in a different phase were
unsuccessful (because 1 has such a strong tendency to form the QII
phase; see the Supporting Information).
References
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film sample
conductivity (S cm-1
)
1 + 15% pure PC (QII network)
1 +15% 0.245 M LiClO4-PC (QII network)
Nafion-1135
(6 ( 2) × 10-7
(9 ( 4) × 10-4
(7.0 ( 0.3) × 10-3
0.245 M LiClO4-PC solution
(1.79 ( 0.01) × 10-3
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Preliminary variable-temperature (VT) conductivity studies
revealed that the conductivity of the QII-phase 1-(0.245 M
LiClO4-PC) films drops less than 1 order of magnitude as the
temperature goes from RT to -35 °C (and even down to -65 °C).
It also remains within the same order of magnitude upon heating
to 55 °C (see the Supporting Information). This behavior is not
observed in gelled PEO-Li salt or LC-based materials but is
important for good battery performance over a wide temperature
range. Retention of liquidlike behavior at low temperatures was
corroborated by VT-NMR DOSY measurements. The diffusion
constant (D) of the PC in a QII composite containing 15 wt % 0.245
Li salt-PC was found to be very similar to that of pure PC and
0.245 M LiClO4-PC at RT. At -35 °C, D for the PC in the QII
composite was 58% of that for pure liquid PC and 66% of that for
0.245 M LiClO4-PC at -35 °C (see the Supporting Information).
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references therein. Also see the Supporting Information for additional
references.
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