Nondestructive testing of defects in adhesive joints

eported that tortuosity decreases with the
increase in the porosity of the membranes [10].
AC impedance of PEs based on electrospun
P(VdF-HFP) membranes with different ceramic
fillers at a temperature varies from 0 to 60 °C
was determined. The bulk resistance Rb of the
electrolyte at 25 °C varies between 1.6, 2.2, 3.8
and 4.8, respectively, for BaTiO3, SiO2, Al2O3
and PE without filler, thus, denoting a
sufficiently high ionic conductivity. The
temperature dependence of ionic conductivities
of the NCPEs in the range of 0-60 ºC is
presented in Figure 5. It can be observed that
within the temperature range the Arrhenius plots
are almost linear.
Properties
Fiber diameter range
(μm)
Average fiber
diameter (μm)
Filler
Al 2O3 SiO2 BaTiO3
0.4-2.2 1-4.9 0.7-4.5 0.9-3.3
1.2 2.78 2.22 1.76
Porosity (%) 84 85 85 87
Electrolyte uptake
(%)
Ionic conductivity at
25 °C (mS/cm)
Electrolyte retention
ratio (R)
Tensile strength
(MPa)
425 459 459 462
4.21 5.92 6.45 7.21
0.86 0.88 0.88 0.89
6.5 9.2 10.3 12.5
Modulus (MPa) 9.2 15.8 16.9 17.3
Elongation at break
(%)
75 62 60 58
Tortuosity 14.81 12.56 12.04 11.52
Table 1. Properties of electrospun membranes and
nanocomposite polymer electrolytes based on the
membranes activated with 1M LiPF6 in EC/DMC.
3.5. Electrochemical properties
The electrochemical stability window of
electrospun P(VdF-HFP) based PE is shown in
Fig. 6. The PE based on P(VdF-HFP) without
ceramic filler exhibits an anodic stability up to
4.7 V. With the incorporation of filler particles in
the polymer matrix, the electrochemical stability
is enhanced. The stability order for the NCPEs
follows as: 4.8 V (Al2O3) = 4.8 V (SiO2) < 4.9 V
(BaTiO3). Thus, NCPEs have good anodic
stability above 4.7 versus Li/Li + , i.e., sufficient
- 4 -
to be compatible with most of the common
cathode materials used for lithium battery.
log σ (S/cm)
-1.8
-2.0
-2.2
-2.4
-2.6
-2.8
-3.0
No filler
Al 2 O 3
SiO 2
BaTiO 3
3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7
1000/T (K -1 )
Fig. 5. Temperature effect of the ionic conductivity
of PEs based on electrospun P(VdF-HFP)
membranes with different ceramic fillers.
The impedance behavior of NCPEs with 1 M
LiPF6 in EC/DMC on lithium metal is presented
in Fig. 7. Rf varies in the range 600-800 Ω with
lower values recorded for the NCPEs. This
indicates a good interface with the lithium
electrode.
Current (mA)
1. 4
2 1.
1. 0
8 0.
0. 6
4 0.
0. 2
0 0.
No filler
Al 2 O 3
SiO 2
BaTiO 3 O 2 (In-situ)
4.0 4.2 4.4 4.6 4.8 5.0 5.2
Voltage (V)
Fig. 6. Anodic stability by LSV of polymer
electrolytes based on electrospun P(VdF-HFP)
membranes with different ceramic fillers
(Li/NCPE/SS cells, 1 mV/s, 2 to 5.5 V).
The PEs with and without filler have been
evaluated for charge/discharge performance in
Li/LiFePO4 cells at room temperature. The first
cycle charge-discharge properties at a current
density corresponding to 0.1 C-rate are presented