4. Type
Ion
conductivity
Mechanical
strength
Safety Price
Liquid Good Poor Unsafe Expensive
Gel Good Good Unsafe Not cheap
Polymer Poor Good Safe Cheap
Glass Poor Good Safe Not cheap
Solid polymer electrolyte is an ionically conducting but electronically
insulating solution of a salt in a polymer.
Ionic conductivity
SPEs: 10-6-10-9 S/cm(room temperature), 10-4-10-5S/cm (80-100 °C)
Liquid electrolyte: 10-2-10-3 S/cm (room temperature)
5. Both cations and anions in polymer electrolyte may contribute to its
conductivity, but their transport mechanisms are different.
Cations-each lithium-ion is complexed to PEO through roughly five ether
oxygens. The transport of lithium-ion is connected with the movement of
the complexing segment of the PEO chain.
Anions- hopping mechanism between different occupied sites and
vacancies, which are large enough to hold the ion.
6. C uI
B r/P M D E TA C uII
B r/P M D E TA +
+ e-
H 3C
O
C
C H
O
C H 3
B r
+ e- H 3C
O
C
C
O
C H 3
H
+ B r-
B r-
+ C uII
B r/P M D E TA +
B r-C uII
B r/P M D E TA
Initiator
transition m etalcatalyst/ligand
7. H 3C
O
C
C
O
C H 3
H
+
O
O
H 3C
O
C
C H
O
C H 3
C
H 2
C O
O
H
( R ') ( M 1) ( R '-M 1)
M 2 =
C H 2
C
O O
O H6
M 3=
C H 2
C
O O
O
C H 3
8.5
R '-M 1 + M R '-M 1-M
R '-M 1-M + n M R '-M 1-M n
IN ITIA TIO N
P R O P A G A TIO N M = M 1,M 2 orM 3
R adicalcoupling:
R 1-C H 2-C X H + H X C -C H 2-R 2 R 1-C H 2-C X H -H X C -C H 2-R 2
R adicaldisproportionation:
R 1-C H 2-C X H + H X C -C H 2-R 2 R 1-C H 2-C X H 2 + X H C =C H -R 2
TE R M IN A TIO N
10. The PMAPEGOH-70-30 polymer could not be dissolved in
chloroform, even after stirring for 10 days at 50 °C. This can
possibly be due to that the increased amount of hydroxyl (-OH)
end-group monomers formed much more hydrogen bonds in
the polymer, making it more difficult to dissolve.
*PMAPEGCH3-90-10, which had a molecular weight of 20000
g/mol. The polymer was too difficult to handle in any of the
following steps due to its severe stickiness and somewhat
liquid-like state. Perhaps since no hydrogen bond can form in
the polymers with methoxy-group (-OCH3) end-capped side-chains,
these hydrophilic side chains present high stickiness.
11.
12. The structures of the polymers are somewhat complex and contain
several protons which have similar chemical shift coupled with
each other. Furthermore, they are random copolymers, i.e., the
protons are placed in slightly different chemical environments when
their neighbors are different, which may lead to different chemical
shifts of the protons even if they originate from similar functional
groups. These factors make it difficult to analyze the NMR spectra in
more detail.
14. The influences on Tg come from several factor:
the lithium ions in the salt (LiTFSI) leads to the formation
of cross-links in the PEO part, and should thus increase
Tg due to increased rigidity;
the anions (TFSI-) from the salt is a common plasticizer
and will decrease Tg;
while high amounts of methacrylate monomers and
hydrogen bond formation in the polymers will raise the
Tg.
All of the factors are work at the same time, and it is
difficult to say which is stronger or weaker. There is no
obvious trend in changes in Tg when the salt is dissolved
in the polymer matrix.
15. The impedance of the cell was measured
by applying a sinusoidal potential
excitation in the frequency range between
1×10-2 Hz and 1×107 Hz, and the AC
current signal was recorded. The AC
root-mean-square voltage was set to 1V,
and the measurements were performed at
room temperature, 30 °C, 40 °C, 50 °C and
60 °C. Thereafter, the AC frequency (F),
and the real (Cp’) and imaginary (Cp’’) parts
of the capacitance is given by the
computer.
19. The ionic conductivities of
PMAPEGOH-90-10 and
PMAPEGCH3-90-10 are
lower than for the PEO
electrolyte for all investigated
temperatures, probably due
to the low content of the
PEO-based monomer –
only 10 %. This also means
that there is much lower
salt concentration in the co-
polymer electrolyte.
20. When comparing the two
systems, it can be seen that the
methoxy-group end-capped
generally show higher
conductivity. This could well be
due to that they have longer
PEO-side chains, hence
higher salt concentration.
Furthermore, the hydroxyl-
group can form hydrogen
bonds in the systems, which
then decrease the mobility of
the side-chains and thus
result in lower ionic
conductivity.
21. The ionic conductivity of a polymer
electrolyte can be calculated from the
equation:
23. The overall ionic mobility can be estimated from:
The lithium-ion mobility
is very low in PEO
system at room
temperature, but
relatively high above
its melting temperature
(Tm = 52°C) at 60 °C.
The reason is that the
ion mobility is much
higher in the liquid state
than in the solid state.
24. The overall ionic mobility can be estimated from:
The ion mobility for the
bipolar system is much higher
than the PEO system,
because the dual polarity of
the SPE system promotes a
nano-scale separation and
ordering of the
macromolecular
constituents, thus offer
structures which have shown
to significantly promote ionic
transport.
25. The overall ionic mobility can be estimated from:
The ion mobility
increases with higher
portion of the PEO-
based monomers
because the ion
transport generally
occurred in the
amorphous portions of
PEO.
26. The overall ionic mobility can be estimated from:
The PMAPEGCH3
system higher ion
mobility, due to its
longer EO units side-
chains and no
hydrogen bonds
formed in this system.
28. SEM images of cross-section view of polymer electrolytes (PMAPEGOH-80-20,
left; PMAPEGCH3-80-20, right) coated onto LiFePO4 electrode.
29.
30. The special characteristic of this polymer is that it comprises both
hydrophobic polymethacrylate backbones, and short (6 or 8.5 EO
units) PEO side-chains, which are hydrophilic. The bipolar structure
could result in a nano-scale phase-separation, which can offer higher
ionic conductivity than linear amorphous PEO, as suggested in previous
Molecular Dynamic studies.
From the results, it is seen that the lithium-ion mobility is
comparatively low in a conventional PEO electrolyte system at
room temperature, but relatively high above its melting
temperature (Tm = 52°C) at 60 °C. The ionic mobility is much
higher in the synthesized bipolar systems at ambient
temperatures, in accordance with previous MD simulation studies.
Problems with the half-cell batteries: pinholes & contamination
During discharge, the oxidation reaction occurs within the anode, hence lithium-ions are transported across the electrolyte towards the cathode, while the electrons pass through the external circuit to the cathode. During charging, the reverse reactions take place.
Both cations and anions in polymer electrolyte may contribute to its conductivity, but their transport mechanisms are different.
Mtn-Y/Ligand is the transition metal complexes, where Mtn is the transition metal and Y is either a ligand or a counterion; R is the polymer chain; and R-X is the initiator for the reaction, where X is a halogen atom. Radicals are generated from a reversible redox process of the transition metal ion: Mtn+1/ Mtn. There is a dynamic equilibrium between the alkyl halide (R-X) and the corresponding active site (R•) with the transition metal complex. The equilibrium is kept shifted towards the left side in Fig. 6 in order to maintain the concentration of radicals as small as possible, thereby restricting the radical termination reactions
Mtn-Y/Ligand is the transition metal complexes, where Mtn is the transition metal and Y is either a ligand or a counterion; R is the polymer chain; and R-X is the initiator for the reaction, where X is a halogen atom. Radicals are generated from a reversible redox process of the transition metal ion: Mtn+1/ Mtn. There is a dynamic equilibrium between the alkyl halide (R-X) and the corresponding active site (R•) with the transition metal complex. The equilibrium is kept shifted towards the left side in Fig. 6 in order to maintain the concentration of radicals as small as possible, thereby restricting the radical termination reactions
All monomers were passed through a column of neutral aluminum oxide to remove inhibitors directly before the polymerization.
CuBr (270.5 mg) was first added to a 50-mL flask. Thereafter, the mixture of monomers (10mL), PMDETA (0.4 mL), and 2-MBP (0.11mL) were added to the flask. These steps were taken in the glove-box, since the whole polymerization process is sensitive to water and oxygen.
The flask was put into a water bath with a thermostat at 50℃ for several hours. The reaction time was different for different polymers, as discussed above (see Fig. 5). The polymerization was terminated by putting the flask into liquid nitrogen.
Chloroform was used to dissolve the product, after which the dissolved polymer solution was filtered through a neutral aluminum oxide column to remove the copper catalyst.
The resulting solution was concentrated and precipitated in hexane three times.
The reasons for this lack of any obvious trend are probably similar to the –OH end-capped systems, i.e., TFSI- decreases Tg while lithium ions increases Tg, and the different effects are differently strong depending on the monomer composition.
