One-step radiation synthesis of gel polymer electrolytes with high ionic conductivity for lithium-ion batteries

Article abstract of DOI:10.1039/c7ta02291c

We demonstrated a one-step synthesis method for a novel gel polymer electrolyte (named PDMP-Li GPE) based on 3-(dimethylamino) propyl methacrylate, poly(ethylene glycol) diacrylate and 1 M LiPF₆ liquid electrolyte solution by a γ-radiation technique for lithium-ion batteries. The resultant PDMP-Li GPE exhibited good thermal stability, excellent mechanical strength and high ionic conductivity, and the highest ionic conductivity reached 8.88 × 10^-3 S cm^-1 at 25 °C. The LiFePO₄/PDMP-Li GPE/graphite pouch-type cell exhibited more than 97% columbic efficiency and the capacity retention was about 86% after 50 cycles at 0.1C. With these outstanding characteristics, it is expected to be a promising candidate for the application in polymer lithium-ion batteries.

Full text of DOI:10.1039/c7ta02291c

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January 2016 Pages 1–330
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ISSN 2050-7488
PAPER
Kun Chang, Zhaorong Chang et al.
Bubble-template-assisted synthesis of hollow fullerene-like
MoS nanocages as a lithium ion battery anode material
2
rsc.li/materials-a

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ARTICLE
One-step radiation synthesis of gel polymer electrolyte with high
ionic conductivity for lithium-ion batteries
Received 00th January 20xx,
Accepted 00th January 20xx
a
b
a
a
a*
Yimeng Wang, Jingyi Qiu, Jing Peng, Jiuqiang Li and Maolin Zhai
DOI: 10.1039/x0xx00000x
We demonstrated a one-step synthesis method for a novel gel polymer electrolyte (named as PDMP-Li GPE) based on 3-
dimethylamino) propyl methacrylate, poly(ethylene glycol) diacrylate and 1 M LiPF liquid electrolyte solution by γ-
radiation technique for lithium-ion battery. The resultant PDMP-Li GPE exhibited good thermal stability, excellent
(
6
www.rsc.org/
-3
-1
o
mechanical strength and high ionic conductivity, and the highest ionic conductivity reached 8.88×10 S cm at 25 C. The
LiFePO /PDMP-Li GPE/graphite pouch-type cell exhibited more than 97% columbic efficiency and the capacity retention
4
was about 86% after 50 cycles at 0.1 C. With the outstanding characteristics, it is expected to be a potential candidate for
the application in polymer lithium-ion batteries.
the uptake amount of the liquid electrolyte within the polymer
1
6
Introduction
matrix. However, the increase of liquid electrolyte uptake
brings the low mechanical properties of GPEs, that is, the
conductivity and mechanical stability of GPEs are mutually
exclusive. Notably, PMMA has received considerable attention
due to its similar structure to carbonate-based solvents
applied in the conventional liquid electrolytes, which suggests
that it may have good compatibility with the lithium salts as
well as offer a good interfacial contact with commonly used
electrodes. Meanwhile, its amorphous structure is beneficial to
Lithium-ion batteries have gained an unprecedented
importance in the last several decades as the energy storage of
portable devices such as cell phones, laptop computers and so
1
-4
on. However, some serious problems including leakage,
flame and explosion have been reported to happen in the
application of lithium-ion batteries with liquid electrolytes,
because of the existence of highly flammable organic liquid
5
electrolytes. The solvent-free solid electrolyte is the ideal way
-3
-1
the ionic conductivity (1×10 S cm at ambient temperature),
but still can not meet the needs of practical applications.
Besides, the GPEs can be prepared by ultraviolet-curing
to solve the current safety problem of liquid electrolyte, but
this advantage goes along with a considerably reduced
6
conductivity. To combine the positive properties of liquid and
1
7, 18
19, 20
16, 21
(
UV)
, solvent-casting technique
2
, thermal method
solid polymer electrolytes, gel polymer electrolytes (GPEs)
have been introduced, which have higher ionic conductivity
and more stability than solid polymer electrolytes and liquid
electrolytes, respectively, and consequently they could provide
an alternative solution to safety problem of lithium-ion
2-25
and electrospinning technique
. Compared with traditional
methods, γ-radiation is a simpler, cleaner and more effective
technique which is suitable for large-scale industrial
production. It can be carried out at room temperature without
initiators and catalysts. In the case of in situ polymerization
technique, the preparation of the gel electrolyte and the
assembly of the batteries could be achieved in one step,
improving the production efficiency and reducing the costs.
Depending on the method of packaging, batteries can have
a coin, cylindrical, prismatic, or pouch shape. According to Li’s
7
, 8
battery. Furthermore, compared with the commercial liquid
electrolytes, the main advantages of GPEs in lithium-ion
batteries are its non-leakage nature, higher thermal stability,
and it can be used to prepare the flexible, thinner and smaller
electrochemical devices.
9
,
Recently, various polymers such as poly(acrylonitrile) (PAN)
11, 12
2
6
1
0
work, the large format pouch-type cells are widely used for
high power applications. Compared with the coin-type half
cells whose anode electrode is lithium metal, the pouch-type
full cells are cheaper, safer, more practical and relevant to Li-
,
poly(vinylidene fluoride) (PVDF)
1
and poly(methyl
3-15
methacrylate) (PMMA)
have been widely used as polymer
matrices for the preparation of GPEs in the lithium-ion
batteries. The ionic conductivity of these systems was around
2
7
-
5
-3
-1
0 -10 S cm at room temperature, which was influenced by
ion battery devices. Besides, the Al-plastic pouch has
advantages of light weight, hermetic shielding, and freedom
1
2
8
for use in various device designs.
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In this work, a novel GPE based on 3-(dimethylamino) propyl
methacrylate (DMAPMA), poly(ethylene glycol) diacrylate
PEGDMA) and 1 M LiPF liquid electrolyte solution was
(
6
prepared by γ-radiation technique through a one-step
synthesis method, called PDMP-Li GPE. The thermal stability
and the mechanical properties of the resultant gels have been
tested. And the ionic conductivity of the gel samples was
studied by impedance spectroscopy. Finally, in order to
confirm the possibility of PDMP-Li GPE usage in lithium-ion
batteries, we tested its electrochemical properties in the
pouch-type full cells.
Experimental
Materials
2-Dimethylaminomethacrylate (98%), methacryloyl chloride
(
98%), lithium hexafluorophosphate (LiPF 98%) and
6
,
poly(ethylene glycol) diacrylate (PEGDMA, average Mn = 400)
were bought from J&K and used without further purification.
-
1
6
Liquid electrolyte (1 M LiPF in EC/DEC 1:1 v:v) without any dose rate of 80 Gy min at room temperature. The resulting
other additives (such as safety agents or fire retardant gels were cut into cylindrical pieces and dried in the air at 25
additives) was purchased from Tinci Company and used as
o
C for one day. For comparison, PDMAPMA gels (short for
supplied. Other chemicals were analytic-grade reagents PDMP) were prepared under the same gelation condition only
obtained from Beijing Chemical Company and used as without the addition of LiPF6.
received.
Characterization of PDMP-Li GPE
Synthesis of 3-(dimethylamino) propyl methacrylate (DMAPMA)
Micro-FTIR and thermogravimetric analysis (TGA) were used to
The 3-(dimethylamino) propyl methacrylate (DMAPMA) was characterize the composition and thermal stability of the resultant
prepared and purified according to the procedure published gels. Micro-FTIR analysis was performed using a Nicolet (Magna-IR
2
9
-1
earlier by P. van de Wetering (Scheme 1). Briefly, to an ice- 750) spectrometer in the range of 5000-600 cm . TGA was carried
cooled solution of DMAP-OH (3.60 mL, 30 mmol) in CH Cl (300 out using a TA Q600 thermal analyzer under a nitrogen atmosphere,
2
2
o
o
mL) were added triethylamine (8.32 mL, 60 mmol) under over a temperature range of 25-600 C with a heating of 5 C/min.
magnetic stirring, then added methacryloyl chloride (5.38 mL, The gel fraction (GF) is defined as:
5
4 mmol) by dropwise in 30 minutes. After stirred for 5 h at
ambient temperature, the orange liquid was washed by
saturated NaHCO solution, then the organic layer was dried
on Na SO and filtered. The product was isolated by
evaporation under reduced pressure, giving a 80% yield. H
NMR (400 MHz, CDCl , TMS standard, r.t.): δ (ppm) 6.10 (s, 1H, gel which was cut into cylindrical pieces (d = 10 mm), and then the
C=CH), 5.55 (s, 1H, C=CH), 4.20 (t, 2H, OCH ), 2.37 (t, 2H, compression strength test was performed by Instron 3365 material
), 1.85 (m, 2H, test system at room temperature.
Gel fraction (%) = W
is the weight of the gel part and W
dry weight.
The mechanical properties were measured using as-synthesized
g
/W
o
×100
(1)
where W
g
o
is the original total
3
2
4
1
3
2
NCH
OCH
2
), 2.24 (s, 6H, N(CH
3 2 3
) ), 1.95 (s, 3H, C=CCH
2
CH CH N).
2
2
The electrochemical measurements were carried out on an
electrochemical instrument (CHI-660D, Shanghai). The ionic
conductivity of the GPE was measured with a symmetrical cell
SS/GPE/SS by EIS. The GPE was sandwiched between two SS discs
(
diameter Ø=16 mm). The ionic conductivity of the GPE was
calculated from the bulk electrolyte resistance (R) according to:
ꢁ
σ ꢀ
(2)
Synthesis of PDMP-Li GPE
ꢂꢃ
where l is the thickness of the GPE, and S is the contact area
between GPE and SS disc. The bulk electrolyte resistance was
obtained from the complex impedance diagram. In all the
measurement for electrochemical impedance spectrum, the
alternative current signal is from 100 kHz to 0.1 Hz with potential
amplitude of 10 mV.
Synthesis route of PDMP-Li GPE is shown in Scheme 2. The
concentrations of DMAPMA (monomer) and PEGDMA (cross-
-1
-1
linker) were 0.75 mol L and 0.05 mol L , respectively. The
DMAPMA/PEGDMA were placed in a glass tube of 10 mm
diameter and dissolved in the liquid electrolyte. The mixture
was bubbled with nitrogen for 15 min. Finally, the tube was
sealed and irradiated to form the gel with 10 kGy dose at a
2
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In situ synthesis and characterization of PDMP-Li GPE in pouch-
type Li-ion cells
Preparation and characterization of PDMP-Li GPE
It has been widely known that radiation-induced polymerization
In situ synthesis and characterization of PDMP-Li GPE were carried and crosslinking is an efficient and clean method, which needs no
out in LiFePO /graphite pouch-type cells. The production process of initiators and can be done at room temperature. In the process, the
4
the pouch-type cells was similar to the commercial ones. The polymerization and crosslinking of the monomer is initiated by the
positive electrodes were obtained by coating the mixing slurry radicals generated from the radiation. As shown in Scheme 2, a
containing 92 wt.% commercial-grade LiFePO4 active material, 3 certain percentage of DMAPMA and PEGDMA were dissolved in the
wt.% Super P, 1 wt.% conductive graphite KS6 and 4 wt.%
poly(vinylidene fluride) (PVDF) onto an aluminium foil collector. The
negative electrodes were prepared by coating the mixing slurry of
9
4
3 wt.% commercial-grade man-made graphite, 3 wt.% Super P and
wt.% poly(vinylidene fluride) (PVDF) onto a copper foil. The
separator was chosen commercial-grade. The negative electrode,
positive electrode, and separators (Celgard 2325, USA, 25 μm in
thickness) were subsequently rolled together to make a cell core.
o
The cell core was dried at 85 C overnight and put into cell shells
made from aluminium film. The structure of pouch-type Li-ion cell
and preparation process of PDMP-Li GPE was shown in Scheme S1.
The injection of the excessive mixture liquid electrolyte (1 M LiPF
6
-1
in EC/DEC 1:1 v:v) containing DMAPMA/PEGDMA (0.75 mol L and
-
1
0
.05 mol L , respectively) was carried out in an Ar-filled glovebox,
after resting for 30 min, then the excess electrolyte and the
formation gas were removed with a vacuum degassing machine to
facilitate the diffusion of electrolyte into the cell core, finally
remaining the content of electrolyte about 5 g/Ah. Subsequently,
the cells were sealed with a sealing machine and the assembled
liquid electrolyte, then after the system being irradiated, the
DMAPMA monomer and the PEGDMA crosslinker formed an orange
gel with the liquid electrolyte involved. The crosslinking network
ensured the organic solvents won’t leakage which improved the
safety of the lithium-ion battery with the gel electrolyte.
o
cells were put in an oven (40 C) for 24 h, ensuring that the
electrolyte was fully absorbed.
Then the cells were irradiated with 10 kGy dose at a dose rate of
8
0 Gy/min at room temperature. In this process, the radiation-
induced polymerization and crosslinking of DMAPMA and PEGDMA
in the liquid electrolyte took place. Since the absorbed dose was
only 10 kGy, during the irradiation, there was no significant change
in the separators, which are mainly composed of polypropylene and
Gel fractions (GF) of PDMP-Li GPE and PDMP gels as a function of
absorbed dose are shown in Fig. 1. Similar to other gels, the
formation of gels starts at a critical absorbed dose (gelation dose),
and the gel fraction increases sharply with the increasing absorbed
3
0, 31
polyethylene.
Meanwhile, the PDMP-Li GPE was prepared in
32
dose in a narrow range and then levels off. It was found that the
situ inside the cells by one-step method.
PDMP-Li GPEs were synthesized at lower absorbed dose and the gel
fractions were much higher compared with that of PDMP gel
The cell performances including charge-discharge curve and
cyclic property were examined by using the charge-discharge
testing device (NEWARE CT-3008-5V500 mA, Shenzhen, China).
without LiPF . It is worth noting that high GF could be gained by
6
relatively low absorbed dose, which brings advantages for avoiding
the radiation side effects. And the radiation-induced polymerization
o
Cycle performance of the cells was evaluated at 0.1 C and 25 C
between 2.3 V to 3.6 V. All the cells were charged at room
temperature by the constant-current/constant-voltage (CC-CV)
protocol. That is, the cells were charged at a certain current rate
until the voltage reached to a limited voltage, followed by holding
the voltage until the current dropped to 10 mA.
Electrochemical impedance spectroscopy (EIS) was measured
using a frequency response analyser (CHI-660D, Shanghai) with an
electrochemical interface in the frequency range from 100 kHz to
o
0
.1 Hz at an amplitude of 5 mV and 25 C.
Morphology study of the electrode was observed using a
scanning electron microscope (SEM, Hitachi S-4800, Japan), and the
o
electrodes here were dried in vacuum at 60 C for three days.
Results and discussion
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o
and crosslinking was much more efficient for PDMP-Li GPE system, and when the temperature arrives at 80 C, the liquid electrolyte
obtaining GF of ca. 93% at only 5 kGy, maybe the LiPF inside the remains 80% of its initial weight. A decomposition at temperature
6
o
system as an additive improved the formation of crosslinking above 80 C may occur according to reaction 4. As shown in curve 1,
3
3
o
network.
pure PDMAPMA gel is thermally stable up to 250 C, the first
decomposition is related to the dimethylamino in the structure of
PDMAPMA. Another decomposition is observed in the range of
FTIR and TGA were carried out to characterize the chemical
structure and thermal stability of the resultant gels, respectively.
Herein, the FTIR spectra of PDMP-Li GPE, PEGDMA crosslinker and
DMAPMA monomer are shown in Fig. 2. For PEGDMA crosslinker
o
o
temperature from 350 C to 400 C, probably due to the
3
5
carbonization loss of the backbone segments. Compared with
-1 curve 3 and curve 4, it is obvious that PDMP-Li GPE expresses more
-1
and DMAPMA monomer, the peaks of 1637.3 cm and 1720.3 cm
are ascribed to the functional groups of C=C and C=O, respectively.
Compared with the FTIR spectra of PEGDMA and DMAPMA, it can
be found that PDMP-Li GPE remained the absorption peak at 1720.3
o
excellent thermal stability(curve 2), i.e, before 100 C, PDMP-Li GPE
6
does not lose any weight, indicating the LiPF and organic solvents
in the gelled network are more stable; for the temperature range of
complete thermal decomposition, all the systems are similar.
-
1
cm for C=O, while the absorption peak of C=C group disappeared.
The FTIR results suggest that the crosslinking network is obtained
through opening the C=C double bonds in the monomer and
crosslinker, while the main functional groups are remained.
o
Although the PDMP-Li GPE starts to decompose at 120 C, which is
17, 19
at the same level with others’ works,
and this degradation
temperature is still high enough for the practical use.
Fig. 3 shows the TGA curves of LiPF , liquid electrolyte (1 M LiPF6
6
in EC:DEC 1:1 v:v), PDMAPMA gel and PDMP-Li GPE. By comparing
the weight loss as a function of temperature, the order of thermal
stability is liquid electrolyte < LiPF < PDMP-Li GPE < PDMAPMA gel.
6
It is well known that the commercial LiPF6 is very unstable at
elevated temperature as shown in curve 3. LiPF decomposes in two
6
steps, the first decomposition step is attributed to the traces of
3
4
water and its decomposition occurs according to reaction 3.
LiPF ꢅ H O → LiF ꢅ POF ꢅ 2HF
(3)
ꢄ
ꢆ
ꢇ
o
The main decomposition starts at 85 C, and its decomposition
path is a simple dissociation producing lithium fluoride (LiF) as solid
3
4
and PF as gaseous products according to reaction 4.
5
LiPF → LiF ꢅ PFꢈ
(4)
ꢄ
In curve 4, the liquid electrolyte shows the worst thermal
stability: the organic solvents start to volatilize at the beginning,
4
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3
6
The ionic conductivity of the GPEs plays an important role on the by the higher lithium-ion concentration per repeating unit. Huang
+
electrochemical performance. In Fig. 4, we studied the influence reported that the Li ions within the GPEs were mainly solvated by
factors against the ionic conductivity of PDMP-Li GPE, and the C=O because of their high electronegativity which dissociated
-
determined the optimal synthesis conditions. When the absorbed lithium salt and hindered the movement of large PF
6
anions.
dose and dose rate are 10 kGy, 80 Gy/min, the concentration of Therefore, because of the strong interaction, the carbonyl oxygen
-
1
-1
+
-
DMAPMA and PEGDMA are 0.75 mol L , 0.05 mol L , respectively, can separate the Li and PF ions in the PDMP-Li GPE which may
6
+
-
the highest ionic conductivity of the resultant PDMP-Li GPE reaches prevent the reunion between Li and PF
6
ions concurrently and
-3
-1
+
8
.88×10 S cm at room temperature, which is higher than the create more free Li ions. Fig. 4a and Fig. 4b indicated that when the
most results that have been reported in literatures and competitive samples were irradiated for a long time, the high ionic conductivity
to the liquid electrolyte that has been widely used in lithium-ion may be scarified, but all the order of magnitude of the ionic
-
3
-1
6
battery. As the ion transport in the LiPF EC/DEC solution is mainly conductivity was about 10 S cm which is still higher than most
+
achieved by Li ions, the high conductivity in PDMP-Li GPE is caused reports as shown in Table 1.
Table 1 Ionic conductivities of various GPEs reported in literatures.
Gel composition
Ionic conductivity
[mS/cm]
a
Ref.
(
polymer/electrolyte)
o
PVDF-LiPAAOB/LiPF
6
-EC-DMC-EMC
-EC-DMC
BC-PVDF/LiTFSI-EC-DEC
0.35 (25 C)
11
17
o
OEGMA-CCMA/LiPF
6
2.30 (25 C)
o
4.20 (30 C)
18
o
P(AN-VAc)-PMMA/LiPF
CA-PLLA-HNT/LiPF
PVDF-PPC/LiPF
6
-EC-DMC-DEC
3.50 (30 C)
22
o
6
-EC-DMC
1.52 (25 C)
25
o
6
-EC-DMC
4.05 (30 C)
36
o
P(MMA-AN-VAc)/LiPF
6
6
-EC-DMC-DEC
-EC-DEC
3.48 (25 C)
37
o
PDMAPMA/LiPF
8.88 (25 C)
this work
a
LiPF
DMC, dimethyl carbonate; PVDF, poly(vinylidene fluoride); LiPAAOB, lithium polyacrylic acid oxalate borate; OEGMA, oligo(ethylene glycol) methyl ether
methacrylate; CCMA, cyclic carbonate methacrylate; BC, boron-containing crosslinker; P(AN-VAc), poly(acrylonitrile-co-vinyl acetate); CA, cellulose acetate; PLLA,
poly- -lactic acid; HNT, halloysite nanotube; PPC, poly(propylene carbonate); P(MMA-AN-VAc), poly(methyl methacrylate-co-acrylonitrile-co-vinyl acetate);
6
, lithium hexafluorophosphate; LiTFSI, lithium bis(trifluoromethane sulfonimide); EC, ethylene carbonate; EMC, ethyl methyl carbonate; DEC, diethyl carbonate;
L
-
3
-1
Fig. 4c shows the ionic conductivity of PDMP-Li GPE as a function when the ionic conductivity reaches 8.88×10
S cm , the
of DMAPMA concentration. The ionic conductivity first increased compressive stress is about 0.4 MPa which is high enough to meet
with increasing concentration of DMAPMA due to the denser gel
network and high degree of gelation which remained the liquid
electrolyte inside the gel network, and the maximum ionic
conductivity was observed at the DMAPMA concentration of 0.75
-1
mol L . Then, the ionic conductivity began to decrease with further
increase of the DMAPMA concentration, because the much denser
network caused less liquid electrolyte inside the gel, then led to the
3
8
decrease.
According to Fig. 4, the monomer concentration influences the
ionic conductivity most. So in Fig. 5, we observed the stress-strain
curves of the resultant PDMP-Li GPE against the monomer
concentration at room temperature. Usually, for solid state
materials, after soaked liquid, the mechanical property becomes
3
9
worse. The compressive stress and the elastic modulus increased
with DMAPMA concentration, while compressive strain decreased.
The order of magnitude of compressive stress was about 1 MPa,
-1
-1
among the monomer concentration from 0.6 mol L to 3.0 mol L .
The reasonable explanation for this phenomenon is that the higher
the needs of flexible batteries.
the monomer concentration, the denser the gel network, which In situ synthesis and properties of PDMP-Li GPE in pouch-type Li-
means less liquid electrolyte was absorbed in the network. This ion cell
makes the gel tougher and hard to be compressed. As we can see,
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From the above discussion, it can be notified that the PDMP-Li GPE These results are in line with the EIS spectra as shown in Figure S1.
exhibited good thermal stability, excellent mechanical strength and The decrease in discharge capacities of the pouch-type cell with
-3
-
especially presented high ionic conductivity around 8.88×10 S cm
1
.
To exam the actual application effort of the PDMP-Li GPE on the
lithium-ion batteries, the LiFePO electrode was chosen as cathode
and the LiFePO /PDMP-Li GPE/graphite pouch-type cells were
assembled. For comparison, the liquid-state LiFePO /graphite cells
4
4
4
were also assembled by using Celgard 2325 porous membrane as
separator.
In order to prove that PDMP-Li GPE was truly generated inside
the pouch-type full cells, we removed the cell’s shell and observed
that there was few orange gel on the aluminium film. The thickness
of PDMP-Li GPE was ca. 25 μm. We compared the SEM of the
electrodes before and after radiation in Fig. 6. It can be seen from
Fig. 6a and Fig. 6c that the surface of untreated electrodes was
rough and the morphology of the electrodes could be seen clearly.
However, the surface of the irradiated electrodes in Fig. 6b and Fig.
6
d became extremely flat and seemed like the surface was covered
evenly by the gelled layer which confirmed the PDMP-Li GPE truly
existed.
PDMP-Li GPE may occur due to the formation of passive layers over
the electrode surface during cycling. Taking the pouch-type cell with
PDMP-Li GPE for example, the detailed charge and discharge curves
are demonstrated in Fig. 7b. The characteristic voltage plateau of
4
LiFePO at about 3.3 V was quiet stable. Therefore, the application
of PDMP-Li GPE in pouch-type full cells will not sacrifice the cycling
It was found that there were some white spots on the surface of
stability of LiFePO
conductivity.
4
cathode, resulted from its high ionic
6
electrode in Fig. 6d. We speculate that LiPF may be precipitated on
the surface of GPE. In order to confirm our thought, the obtained
cathode in Fig. 6d was further washed with DEC several times and
died under vacuum. As shown in Fig. 6e, it can be seen that there Conclusions
were some small holes in the surface uniformly which confirmed
PDMP-Li GPE consisted of 1 M LiPF EC/DEC (1:1 in volume)
6
6
that the holes were produced in situ after the dissolution of LiPF .
and PDMAPMA gel was synthesized successfully by one-step
method with γ-radiation induced polymerization and
crosslinking. The resultant PDMP-Li GPE exhibited high ionic
Therefore, the liquid electrolyte with DMAPMA and PEGDMA
additives was totally gelled uniformly to form PDMP-Li GPE after
radiation in the pouch-type full cells and the high ionic conductivity
-3
-1
conductivity around 8.88×10 S cm , good thermal stability,
may be attributed to the evenly distributed LiPF
Fig. 7a presents the cyclic performances of the LiFePO
pouch-type cells. The cells were cycled with a constant current of assembled LiFePO /PDMP-Li GPE/graphite pouch-type cell
6
within the GPE.
excellent mechanical integrity and strength to allow the safe
4
/graphite operation in lithium-ion batteries. After 50 cycles, the
4
0
.1 C rate between 3.6 and 2.3 V. After 50 cycles, the capacity showed a very stable discharge behavior and little capacity loss
retention of the pouch-type cell with PDMP-Li GPE achieved a value under current constant voltage conditions, at rate of 0.1 C and
o
of 86%, slightly lower than that of the pouch-type cell with liquid 25 C. Considering these results, the cell with PDMP-Li GPE
electrolyte, which retained 93% of its initial discharge capacity. appears as a promising candidate for lithium-ion batteries.
6
| J. Name., 2012, 00, 1-3
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We thank Wei Wei and Yue Wang from Institute of Chemical
Defense for providing testing pouch-type cells. The National
Natural Science Foundation of China (Project No. 11375019) is 28.
acknowledged for supporting this research.
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Journal of Materials Chemistry A
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Table of Contents Entry
One-step radiation synthesis of gel polymer electrolyte with high ionic conductivity for lithium-ion batteries