【Technical Field】
The present disclosure relates to a gel polymer
electrolyte and a lithium secondary battery including 5 the
same. More particularly, the present disclosure relates to
a gel polymer electrolyte including an imide salt, and a
lithium secondary battery including the same and having a
protective film formed on a cathode tab.
10
【Background Art】
In general, a secondary battery means a battery
capable of charging/discharging, unlike a non-rechargeable
primary battery, and is used widely in the field of
15 advanced electronic instruments such as cellular phones,
notebook computers and camcorders.
Such a lithium secondary battery uses a lithium-based
oxide as a cathode active material and a carbonaceous
material as an anode active material. In addition, a non20
aqueous electrolyte is used as an electrolyte because of
the reactivity between lithium and water. Lithium
secondary batteries may be classified into lithium ion
batteries using a liquid electrolyte and lithium polymer
batteries using a polymer electrolyte, depending on the
25 type of electrolyte. The polymer electrolyte may include
3
an all-solid type polymer electrolyte containing no organic
electrolyte solution and a gel type polymer electrolyte
containing an organic electrolyte solution.
With regard to an electrolyte solution for lithium
secondary batteries, when using an 5 imide-based salt as an
electrolyte salt, an electrolyte containing an imide-based
salt having low viscosity shows a small increase in
viscosity of organic solvent at low temperature, thereby
maintaining lithium ion mobility, resulting in significant
10 improvement of high-temperature storability and lowtemperature
output characteristics. However, as compared
to LiPF6 used currently as an electrolyte salt, an imidebased
salt may corrode aluminum (Al) as a cathode
collector, and thus is limited in application to secondary
15 batteries.
When using an imide salt for an electrolyte solution,
there are several opinions about the causes of degradation
of inhibition against corrosion of metal, i.e., aluminum as
a cathode collector.
20 For example, according to an opinion, imide anion
directly causes corrosion of aluminum. However, according
to another opinion, aluminum itself is highly corrosive
material and the use of an imide salt does not form a
coating film capable of inhibiting corrosion of aluminum to
25 fail in inhibition against corrosion of aluminum, while the
4
use of LiPF6 forms such a coating film.
In other words, the cause of degradation of
inhibition against corrosion of aluminum as a cathode
collector when using an imide salt as an electrolyte salt
has not been shown clearly to date. However, 5 there is a
need for a method for preventing corrosion of a cathode
collector such as aluminum, while using an imide-based salt
effective for improvement of output characteristics and
high-temperature storability.
10 The present inventors have found that when using an
imide salt for a gel polymer electrolyte, corrosion of an
aluminum collector is reduced significantly, and thus it is
possible to provide a secondary battery having excellent
stability and quality. The present disclosure is based on
15 this finding.
【Disclosure】
【Technical Problem】
A technical problem to be solved by the present
20 disclosure is to provide an electrolyte that allows the
production of a secondary battery having excellent quality
with no corrosion of a cathode, while using, as an
electrolyte salt, an imide-based salt effective for
improvement of output quality and high-temperature
25 storability, as well as a secondary battery including the
5
same.
【Technical Solution】
In one general aspect, there is provided a gel
polymer electrolyte obtained by polymerizing a 5 composition
for a gel polymer electrolyte including a polymerizable
monomer, a polymerization initiator, an electrolyte salt
and an electrolyte solvent, wherein the electrolyte salt is
an imide salt.
10 In another general aspect, there is provided a
secondary battery including the gel polymer electrolyte.
【Advantageous Effects】
According to the embodiments of the present
15 disclosure, it is possible to provide an electrolyte that
allows the production of a secondary battery having
excellent quality with no corrosion of a cathode, while
using, as an electrolyte salt, an imide-based salt
effective for improvement of output quality and high20
temperature storability, as well as a secondary battery
including the same.
【Description of Drawings】
Fig. 1A shows a plane view of a cathode having a
25 cathode tab that protrudes from a cathode collector, and
6
Fig. 1B shows a lateral sectional view of Fig, 1A.
Fig. 2A shows a plane view of a cathode including a
protective film on a cathode tab which is a non-coated
portion, and Fig. 2B shows a lateral sectional view of Fig,
2A, according 5 ording to an embodiment.
Fig. 3 is a photo illustrating a composition for a
gel polymer electrolyte obtained according to the present
disclosure, after gelling.
Fig. 4 and Fig. 5 are graphs showing the results of
10 Test Example 1 and Test Example 2.
Fig. 6 is a graph showing the results of Test Example
3.
Fig. 7 is a photo illustrating the polymer cells
obtained according to Example 10 and Example 11, after
15 carrying out the test of Test Example 3.

10: cathode active material-coated portion
20: cathode tab
20 30: cathode collector
40: protective film
ℓ: length of protective film
w: width of protective film
T: thickness of protective film
25 A: cathode tab portion of polymer cell according to
7
Example 10
B: enlarged view of cathode tab to which protective
film is attached in polymer cell according to Example 11
【Best Mode5 】
In one aspect, the present disclosure provides a gel
polymer electrolyte obtained by polymerizing a composition
for a gel polymer electrolyte including a polymerizable
monomer, a polymerization initiator, an electrolyte salt
10 and an electrolyte solvent, wherein the electrolyte salt is
an imide salt.
Preferably, the imide salt is a compound represented
by the following Chemical Formula 1:
[Chemical Formula 1]
15 R1-SO2-N-(Li+)-SO2-R2
wherein each of R1 and R2 independently represents
fluorine (F) or a perfluoroalkyl.
The compound represented by Chemical Formula 1 may
include lithium bis(fluorosulfonyl)imide (LiFSI), lithium
20 bis(trifluoromethanesulfonyl)imide (LiTFSI) or lithium
bis(perfluoroethanesulfonyl)imide (LiBETI). Preferably,
the compound represented by Chemical Formula 1 is
bis(fluorosulfonyl)imide (LiFSI).
As an electrolyte salt for use in the electrolyte
25 according to the present disclosure, the composition for a
8
gel polymer electrolyte may further include a lithium salt
other than the imide salt represented by Chemical Formula
1. The electrolyte salt may be used in a concentration of
0.5M-2.0M based on the composition for a gel polymer
5 electrolyte.
In the gel polymer electrolyte according to the
present disclosure, the molar ratio of the lithium salt
other than the imide salt : imide salt may be 1:10 to 8:2,
preferably 2:8 to 7:3.
10 Meanwhile, the polymerizable monomer preferably
includes an acrylate compound, but is not limited thereto.
Particularly, the polymerizable monomer may be a
compound such as 2-cyanoethyl acrylate, tetraethyleneglycol
diacrylate, polyethyleneglycol diacrylate, 1,4-butanediol
15 diacrylate, 1,6-hexanediol diacrylate, trimethylolpropane
triacrylate, trimethylolpropane ethoxylate triacrylate,
trimethylolpropane propoxylate triacrylate,
ditrimethylolpropane tetraacrylate, pentaerythritol
tetraacrylate, pentaerythritol ethoxylate tetraacrylate,
20 dipentaerythritol pentaacrylate, dipentaerythritol
hexaacrylate, polyethyleneglycol diglycidyl ether, 1,5-
hexadiene diepoxide, glycerol propoxylate triglycidyl
ether, vinylcyclohexene dioxide, 1,2,7,8-diepoxyoctane, 4-
vinylcyclohexene dioxide, butylglycidyl ether, diglycidyl
25 1,2-cyclohexanedicarboxylate, ethyleneglycol diglycidyl
9
ether, glycerol triglycidyl ether or glycidyl methacrylate.
These monomers may be used alone or in combination upon
polymerization.
In addition, the polymerizable monomer may further
include a monomer containing a functional group, 5 oup, such as
phosphate or sulfate group, capable of inhibiting corrosion
to carry out polymerization.
The monomer containing a functional group capable of
inhibiting corrosion may be at least one compound selected
10 from the group consisting of ethyleneglycol methacrylate
phosphate, Mevinphos, 2-methacryloyloxyethyl
phosphorylcholine, bis[2-(methacryloyloxy)ethyl]phosphate,
Crotoxyphos, methyl (2E)-3[(dimethoxyphosphoryl)oxy]but-2-
enoate, monoacryloxyethyl phosphate, 10-(phosphonoxy)decyl
15 methacryate, 2-((diethoxyphosphinyl)oxy)ethyl methacrylate,
(phosphonoxy)propane-1,3-diyl bismethacrylate, 2-sulfoethyl
methacrylate, [2-(methacryloyloxy)ethyl]dimethyl-(3-
sulfopropyl)ammonium hydroxide, 2-propenoic acid, 4-
[(methylsulfonyl)oxy]butyl ester, 2-
20 (methanesulfonyloxy)ethyl methacrylate and 2-
(methanesulfonyloxy)ethyl acrylate, but is not limited
thereto.
In addition, the composition for a gel polymer
electrolyte may further include a corrosion inhibitor as an
25 additive.
10
The corrosion inhibitor may be selected from the
group consisting of the compounds represented by the
following Chemical Formula 2 to Chemical Formula 6. The
following compounds may be used alone or in combination.
[5 Chemical Formula 2]
[Chemical Formula 3]
(In Chemical Formula 2 and Chemical Formula 3, each
10 of R1, R2 and R3 independently represents H, a C1-C10 linear
or branched alkyl group, a C1-C10 linear or branched alkyl
ester group, Na or Si(CH3)3.)
11
[Chemical Formula 4]
(In Chemical Formula 4, R1 is a C1-C6 linear or
branched alkylene group, a C6-C12 arylene group or a C2-C6
alkenylene group, and n is an 5 integer of 1-10.)
[Chemical Formula 5]
(In Chemical Formula 5, each of R2-R5 independently
represents a C1-C6 linear or branched alkylene group, O or
10 -SO2- group.)
[Chemical Formula 6]
(In Chemical Formula 6, each of R6-R11 independently
represents a C1-C6 linear or branched alkylene group, a C6-
15 C12 arylene group or a C2-C6 alkenyl group, and m is an
integer of 0-3.)
12
More particularly, the compound that may be used as a
corrosion inhibitor may include, but is not limited to:
tris(trimethylsilyl) phosphate, tris(triethylsilyl)
phosphate, NaH2PO4 (sodium phosphate monobasic), Na2HPO4,
Na3PO4, NaHSO3, Na2SO3, methylene methanedisulfonate5 ,
propane sultone, propene sultone, ethylene sulfate or
ethylene sulfite.
It can be said that the composition for a gel polymer
electrolyte according to the present disclosure is an
10 electrolyte precursor solution that is injected into a
battery subsequently and subjected to polymerization
(gelling) so that it is converted into a gel polymer
electrolyte.
In another aspect, the present disclosure provides a
15 secondary battery including a cathode, an anode and the
above-described gel polymer electrolyte.
Preferably, the cathode includes: a cathode
collector; a cathode tab that protrudes from the cathode
collector; and a protective film formed on the cathode tab.
20 The protective film may include any one or a
combination of two or more selected from the group
consisting of a polyethylene terephthalate (PET) film,
polyimide (PI) film and a polypropylene (PP) film. The
protective film may have a thickness of 1 μm to 100 μm.
25 Preferably, the cathode tab is a non-coated portion
13
having no cathode active material-coated portion.
In addition, the protective film is present
preferably in a ratio of 10%-90% based on the total length
of the cathode tab along the protruding direction of
cathode tab with the same width as the width 5 of the cathode
tab perpendicular to the protruding direction of cathode
tab.
In the case of a battery using a gel polymer
electrolyte as in the present disclosure, the gel polymer
10 electrolyte has little flowability as compared to a liquid
electrolyte solution. Thus, it is possible to maximize the
effect of taping a protective film.
Hereinafter, the present disclosure will be explained
in detail with reference to the accompanying drawings
15 illustrating an exemplary embodiment wherein the gel
polymer electrolyte disclosed herein is used and the
protective film capable of interrupting a physical contact
with the gel polymer electrolyte is provided on at least
one surface of the cathode tab.
20 Fig. 1A shows a plane view of a cathode having a
cathode tab that protrudes from a cathode collector, and
Fig. 1B shows a lateral sectional view of Fig. 1A.
Particularly, as shown in Fig. 1A and Fig. 1B, a
cathode active material-coated portion 10 is present on
25 either surface or both surfaces of a cathode collector 30.
14
In addition, one end to the cathode collector 30 may be
formed as a cathode tab 20 in the form of a non-coated
portion having no cathode-active material-coated portion.
According to an embodiment of the present disclosure,
the cathode tab may be formed by notching a continuou5 s
cathode sheet having an active material coated on either
surface or both surfaces of the cathode collector at
intervals of a unit electrode by using molds.
According to the present disclosure, the cathode tab
10 formed after such notching may be formed as a non-coated
portion having no cathode active material-coated portion,
as shown in Fig. 1A and Fig. 1B.
Meanwhile, the protective film provided on at least
one surface of the cathode tab according to an embodiment
15 of the present disclosure may be varied according to
various factors, such as the structure of a secondary
battery, but is not limited thereto. A particular
embodiment of the protective film will be explained with
reference to Fig. 2 A and Fig. 2B.
20 Fig. 2A shows a plane view of a cathode including a
protective film on a cathode tab formed as a non-coated
portion, and Fig. 2B shows a lateral sectional view of Fig.
2A, according to an embodiment.
Referring to Fig. 2A and Fig. 2B, a cathode active
25 material-coated portion 10 is formed on either surface of
15
both surfaces of a cathode collector 30, and one end to the
collector 30 is provided as a cathode tab 20 in the form of
a non-coated portion having no cathode active materialcoated
portion. In addition, the cathode tab 20 has a
protective film 40 on either surface or both 5 oth surfaces
thereof.
According to an embodiment of the present disclosure,
as shown in Fig. 2A, the protective film 40 is attached in
such a manner that it covers the cathode tab 20, and is
10 present in a ratio of 10%-90%, preferably 20%-70%, based on
the total length (d+ℓ) of the cathode tab along the
protruding direction L of the cathode tab 20 for the
purpose of connection with an external circuit. For
example, the protective film may have a length ℓ of 1 mm-10
15 mm but the length may be varied according to the shape or
size of a cathode and those of a secondary battery. It is
preferred that the width w of the protective film 40
perpendicular to the protruding direction L of the cathode
tab 20 is the same as the width of the cathode tab 20, but
20 is not limited thereto.
Meanwhile, the protective film 40 formed on at least
one surface of the cathode tab 20 may have a thickness T of
1 μm-100 μm. When the thickness T of the protective film
is excessively small, it is not possible to provide a
25 sufficient effect of protecting the cathode tab from a gel
16
polymer electrolyte. On the other hand, when the thickness
is excessively large, the total thickness increases
undesirably.
According to an embodiment of the present disclosure,
attaching the protective film onto the cathode tab may b5 e
carried out in any step of the process for producing a
secondary battery with no particular limitation.
For example, according to an embodiment of the
present disclosure, a continuous cathode sheet having a
10 cathode active material coated on either surface or both
surfaces of a cathode collector is subjected to notching at
intervals of a unit electrode in the form of a desired
cathode by using molds to form a cathode tab, and a
protective film is attached onto the cathode tab. In this
15 manner, it is possible to obtain a cathode tab having a
protective film.
According to another embodiment, a cathode active
material is applied onto either surface or both surfaces of
a cathode collector, and a protective film is attached to
20 the non-coated portion of the cathode collector, followed
by notching with molds into the form of a desired cathode
tab. In this manner, it is possible to obtain a cathode
tab having a protective film.
Meanwhile, the cathode may further include an
25 insulating layer and the insulating layer may be present
17
between the cathode tab and the protective film or on the
protective film.
The insulating layer may include at least one
selected from the group consisting of polyethylene
terephthalate, polypropylene, polyester, 5 r, polyphenylene
sulfide, polyimide, acetate, glass fabric, polyvinylidene
fluoride, polyvinylidene fluoride-co-hexafluoropropylene,
epoxy resins and polyamide resins.
Meanwhile, according to an embodiment of the present
10 disclosure, the cathode collector is preferably aluminum
and the cathode active material used herein may be any one
selected from lithium-containing transition metal oxides or
equivalents thereof. Particularly, the cathode active
material may include a manganese-based spinel active
15 material, lithium metal oxide or a mixture thereof.
Further, the lithium metal oxide may be selected from the
group consisting of lithium-manganese oxides, lithiumnickel-
manganese oxide, lithium-manganese-cobalt oxides and
lithium-nickel-manganese-cobalt oxides. More particularly,
20 the lithium metal oxide may be LiCoO2, LiNiO2, LiMnO2,
LiMn2O4, Li(NiaCobMnc)O2 (wherein 0＜a＜1, 0＜b＜1, 0＜c＜1,
a+b+c=1), LiNi1-YCoYO2, LiCo1-YMnYO2, LiNi1-YMnYO2 (wherein
0≤Y＜1), Li(NiaCobMnc)O4 (0＜a＜2, 0＜b＜2, 0＜c＜2, a+b+c=2),
LiMn2-zNizO4, or LiMn2-zCozO4 (wherein 0＜Z＜2).
25 According to an embodiment of the present disclosure,
18
the anode collector is preferably copper. As an anode
active material, a carbonaceous anode material such as
crystalline carbon, amorphous carbon or carbon composite
may be used alone or in combination, but is not limited
5 thereto.
Each of the cathode collector and anode collector may
have a thickness of about 10 μm-100 μm and each electrode
active material coated on the collector may have a
thickness of about 50 μm-200 μm. However, the present
10 disclosure is not limited thereto.
According to an embodiment of the present disclosure,
the anode may be produced with a larger size as compared to
the cathode in order to prevent a physical short between
both electrodes.
15 In addition, a separator may be inserted between the
cathode and anode in order to prevent a physical short
between both electrodes. The separator may include a
porous polymer film, such as a single film or laminate of
two or more of porous polymer films including a polyolefin20
based polymer, such as ethylene homopolymer, propylene
homopolymer, ethylene/butene copolymer, ethylene/hexene
copolymer and ethylene/methacrylate copolymer. In addition
to the above, the separator may include conventional porous
non-woven fabrics, such as those formed of high-melting
25 point glass fibers or polyethylene terephthalate fibers,
19
but is not limited thereto.
The appearance of a battery container in which the
secondary battery according to the present disclosure is
received is not limited particularly, but particular
examples of the appearance may include a cylindrical 5 indrical shape,
prismatic shape or pouch-like shape.
【Mode for Invention】
The examples and experiments will now be described.
10 The following examples and experiments are for illustrative
purposes only and not intended to limit the scope of this
disclosure.
Example 1
15
First, lithium bis(fluorosulfonyl)imide (LiFSI) is
dissolved into a non-aqueous electrolyte solvent containing
ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in
20 a volume ratio of EC:EMC=1:2 to a concentration of 1M to
provide an electrolyte solution. To 100 parts by weight of
the electrolyte solution, 5 parts by weight of mixed
polymerizable monomers (2.5 wt% of 2-cyanoethyl acrylate
and ditrimethylolpropane tetraacrylate) and 0.25 parts by
25 weight of tert-butylperoxy-2-ethylhexanoate as a
20
polymerization initiator are added to obtain a composition
for a gel polymer electrolyte.

Production of Cathode
First, 94 wt% of Li[Li0.29Ni0.14Co0.11Mn0.46]O2 as a cathod5 e
active material, 3 wt% of carbon black as a conductive
agent and 3 wt% of PVdF as a binder are added to N-methyl-
2-pyrrolidone (NMP) as a solvent to provide a cathode
mixture slurry. The cathode mixture slurry is applied onto
10 aluminum (Al) foil having a thickness of about 20 μm as a
cathode collector, followed by drying, to obtain a cathode.
Then, roll pressing is carried out to finish the production
of a cathode.
Production of Anode
15 Carbon-coated SiO and graphite are mixed with a weight
ratio of 10:90 to provide an anode active material. Then,
the anode active material, carbon black as a conductive
agent, SBR and CMC are mixed with a weight ratio of
94:2:2:2. The materials are introduced into distilled
20 water as a solvent, followed by mixing, to obtain
homogeneous anode slurry.
The anode slurry is applied onto copper (Cu) foil
having a thickness of 10 μm as an anode collector, followed
by drying, rolling and punching, to obtain an anode.
25 Production of Battery
21
The cathode, anode and a separator having three layers
of polypropylene/polyethylene/polypropylene (PP/PE/PP) are
used to assemble a battery. Then, the composition for a
gel polymer electrolyte prepared as described above is
injected to the battery thus assembled, followed by heat5 ing
at 80°C under nitrogen atmosphere for 2-30 minutes, thereby
providing a coin type secondary battery.
When the composition for a gel polymer electrolyte is
injected to a battery and then heated, it is polymerized
10 (gelled) so that it forms a gel polymer electrolyte in the
battery. Fig. 3 is a photo illustrating a composition for
a gel polymer electrolyte obtained according to the present
disclosure, after gelling.
15 Example 2
A composition for a gel polymer electrolyte is
obtained in the same manner as described in Example 1,
except that lithium bis(fluorosulfonyl)imide (LiFSI) is
used at a concentration of 1.2M instead of 1M. Then, a
20 coin type secondary battery is obtained by using the
composition for a gel polymer electrolyte.
Example 3
A composition for a gel polymer electrolyte is
25 obtained in the same manner as described in Example 1,
22
except that a mixture of 0.5M of lithium
bis(fluorosulfonyl)imide (LiFSI) with 0.5M of LiPF6 is used
instead of 1M of LiFSI. Then, a coin type secondary
battery is obtained by using the gel polymer electrolyte.
5
Example 4
A gel polymer electrolyte is obtained in the same
manner as described in Example 3, except that 0.5M of LiBF4
is used instead of 0.5M of LiPF6. Then, a coin type
10 secondary battery is obtained by using the gel polymer
electrolyte.
Example 5
A gel polymer electrolyte is obtained in the same
15 manner as described in Example 1, except that 0.5 parts by
weight of tris(trimethylsilyl)phosphate is further added as
a corrosion inhibitor. Then, a coin type secondary battery
is obtained by using the gel polymer electrolyte.
20 Example 6
A gel polymer electrolyte is obtained in the same
manner as described in Example 1, except that 0.5 parts by
weight of sodium phosphate monobasic is further added as a
corrosion inhibitor. Then, a coin type secondary battery
25 is obtained by using the gel polymer electrolyte.
23
Example 7
A gel polymer electrolyte is obtained in the same
manner as described in Example 1, except that propylene
oxide is used as a polymerizable monomer instead 5 stead of the
mixed polymerizable monomers containing 2.5 wt% of 2-
cyanoethyl acrylate and ditrimethylolpropane tetraacrylate.
Then, a coin type secondary battery is obtained by using
the gel polymer electrolyte.
10
Example 8
A gel polymer electrolyte is obtained in the same
manner as described in Example 1, except that lithium
bis(trifluoromethanesulfonyl)imide (LiTFSI) is used instead
15 of lithium bis(fluorosulfonyl)imide (LiFSI). Then, a coin
type secondary battery is obtained by using the gel polymer
electrolyte.
Example 9
20 A gel polymer electrolyte is obtained in the same
manner as described in Example 2, except that lithium
bis(trifluoromethanesulfonyl)imide (LiTFSI) is used instead
of lithium bis(fluorosulfonyl)imide (LiFSI). Then, a coin
type secondary battery is obtained by using the gel polymer
25 electrolyte.
24
Example 10
A polymer cell (capacity: 1350 mAh) is obtained by
using the composition for a gel polymer electrolyte
obtained according to Example 2 and the 5 he same electrodes as
the production of a coin type battery.
Example 11
A polymer cell (capacity: 1350 mAh) is obtained by
10 forming a polyethylene terephthalate protective film on the
cathode tab of the polymer cell according to Example 10.
Comparative Example 1
A composition for a gel polymer electrolyte and a
15 coin type secondary battery are obtained in the same manner
as described in Example 1, except that the polymerizable
monomers and polymerization initiator are not used.
Comparative Example 2
20 A composition for a gel polymer electrolyte and a
coin type secondary battery are obtained in the same manner
as described in Example 2, except that the polymerizable
monomers and polymerization initiator are not used.
25 The above Examples and Comparative Examples are shown
25
in brief in the following Table 1.
[Table 1]
Electrolyte
salt
Electrolyte
type
Corrosion
inhibitor
Battery type
Ex. 1 1M LiFSI gel _
coin type
secondary
battery
Ex. 2 1.2M LiFSI gel _
coin type
secondary
battery
Ex. 3
0.5M LiFSI +
0.5M LiPF6
gel _
coin type
secondary
battery
Ex. 4
0.5M LiFSI +
0.5M LiBF4
gel _
coin type
secondary
battery
Ex. 5 1M LiFSI gel
Tris(trimethy
lsilyl)
phosphate
coin type
secondary
battery
Ex. 6 1M LiFSI gel
sodium
phosphate
monobasic
coin type
secondary
battery
Ex. 7 1M LiFSI gel _
coin type
secondary
battery
Ex. 8 1M LiTFSI gel _
coin type
secondary
battery
Ex. 9 1.2M LiTFSI gel _
coin type
secondary
battery
Ex. 10 1M LiFSI gel _
polymer cell
(cathode tab
protective
film is not
attached)
26
Ex. 11 1M LiFSI gel _
polymer cell
(cathode tab
protective
film is
attached)
Comp.
Ex. 1
1M LiFSI liquid _
coin type
secondary
battery
Comp.
Ex. 2
1.2M LiFSI liquid _
coin type
secondary
battery
Test Example 1
Each of the lithium secondary batteries (capacity:
3.0 mAh) according to Examples 1-9 and Comparative Examples
1 and 2 is charged to 4.2V under a constant 5 t current
condition of 0.1C, and then under a constant voltage
condition of 4.2V. The charging is stopped when the
charged current reaches 1/20C. Then, each battery is
allowed to stand for 10 minutes and discharged to 2.7V
10 under a constant current condition of 0.1C. Then, each
battery is charged to 4.2V under a constant current
condition of 0.7C, and then charged under a constant
voltage condition of 4.2V. After that, the charging is
stopped when the charged current reaches 1/20C. Then, each
15 battery is allowed to stand for 10 minutes and discharged
to 2.7V under a constant current condition of 0.5C. The
above charge/discharge cycles are carried out 10 times.
27
Test Example 2
After carrying out Test Example 1, each of the
lithium secondary batteries (capacity: 3.0 mAh) according
to Examples 1-9 and Comparative Examples 1 and 2 is charged
to 4.35V under a constant current condition 5 n of 0.1C, and
then charged under a constant voltage condition of 4.35V.
The charging is stopped when the charged current reaches
1/20C. Then, each battery is allowed to stand for 10
minutes and discharged to 2.7V under a constant current
10 condition of 0.1C. Then, each battery is charged to 4.35V
under a constant current condition of 0.7C, and then
charged under a constant voltage condition of 4.35V. After
that, the charging is stopped when the charged current
reaches 1/20C. Then, each battery is allowed to stand for
15 10 minutes and discharged to 2.7V under a constant current
condition of 0.5C. The above charge/discharge cycles are
repeated.
The results of Test Examples 1 and 2 are shown in
20 Fig. 4 and Fig. 5.
As shown in Fig. 4, the battery according to Example
1 shows normal voltage behaviors during charge/discharge
cycles with the lapse of time, while the battery according
to Comparative Example 1 shows unstable behaviors due to
25 corrosion.
28
In addition, as shown in Fig. 5, each of the
batteries according to Examples 1-8 allows normal
charge/discharge cycles at a charge cut-off voltage of 4.2V
and even at a higher charge cut-off voltage of 4.35V, while
each of the batteries according to Comparative 5 mparative Examples 1
and 2 does not allow charge/discharge cycles even at 4.2V.
Meanwhile, when using LiFSI as an imide salt, the
corrosion inhibition and charge/discharge characteristics
are better as compared to LiTFSI. When using LiFSI in
10 combination with another lithium salt (Examples 3 and 4),
the use of LiFSI in combination with a corrosion inhibitor
provides the best corrosion inhibition and charge/discharge
characteristics.
In addition, when using an acrylate monomer as a
15 polymerizable monomer for electrolyte composition (Examples
1-6), the corrosion inhibition and charge/discharge
characteristics are better as compared to a propylene oxide
monomer (Example 7).
20 Test Example 3
Each of the polymer cells according to Examples 10
and 11 is charged to 4.2V under a constant current
condition of 0.5C, and then charged under a constant
voltage condition of 4.2V. The charging is stopped when the
25 charged current reaches 1/20C. Then, each polymer cell is
29
allowed to stand for 10 minutes and discharged to 2.7V
under a constant current condition of 0.5C. The above
charge/discharge cycles are carried out 400 times.
The test results are shown in Fig. 6. As shown in
Fig. 6, Example 11 shows little change in capacity 5 acity up to
400 cycles, and Example 10 also shows little change in
capacity up to 250 cycles.
Meanwhile, Fig. 7 shows the photo of the cathode tab,
after subjecting Examples 10 and 11 to the test.
10 In the case of the polymer cell having no protective
film on the cathode tab according to Example 10, it is
observed that a portion of the tab causes short due to
corrosion after repeating charge/discharge cycles (see Part
A of Fig. 7), resulting in a drop of capacity at about 300
15 cycles (see Fig. 6). Meanwhile, in the case of the polymer
cell having a protective film on the cathode tab according
to Example 11, it is observed that the cathode tab causes
no corrosion even after repeating charge/discharge cycles
(see Part B of Fig. 7).

I/We claim:
【Claim 1】
A gel polymer electrolyte obtained by polymerizing a
composition for a gel polymer electrolyte comprising a
polymerizable monomer, a polymerization initiator, 5 iator, an
electrolyte salt and an electrolyte solvent, wherein the
electrolyte salt is an imide salt.
【Claim 2】
10 The gel polymer electrolyte according to claim 1,
wherein the imide salt is a compound represented by the
following Chemical Formula 1:
[Chemical Formula 1]
R1-SO2-N-(Li+)-SO2-R2
15 wherein each of R1 and R2 independently represents
fluorine (F) or a perfluoroalkyl.
【Claim 3】
The gel polymer electrolyte according to claim 2,
20 wherein the compound represented by Chemical Formula 1 is
at least one selected from the group consisting of lithium
bis(fluorosulfonyl)imide, lithium
bis(trifluoromethanesulfonyl)imide and lithium
bis(perfluoroethanesulfonyl)imide.
25
31
【Claim 4】
The gel polymer electrolyte according to claim 1,
wherein the polymerizable monomer is an acrylate-based
compound.
5
【Claim 5】
The gel polymer electrolyte according to claim 1,
wherein the polymerizable monomer is at least one selected
from the group consisting of 2-cyanoethyl acrylate,
10 tetraethyleneglycol diacrylate, polyethyleneglycol
diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol
diacrylate, trimethylolpropane triacrylate,
trimethylolpropane ethoxylate triacrylate,
trimethylolpropane propoxylate triacrylate,
15 ditrimethylolpropane tetraacrylate, pentaerythritol
tetraacrylate, pentaerythritol ethoxylate tetraacrylate,
dipentaerythritol pentaacrylate, dipentaerythritol
hexaacrylate, polyethyleneglycol diglycidyl ether, 1,5-
hexadiene diepoxide, glycerol propoxylate triglycidyl
20 ether, vinylcyclohexene dioxide, 1,2,7,8-diepoxyoctane, 4-
vinylcyclohexene dioxide, butylglycidyl ether, diglycidyl
1,2-cyclohexanedicarboxylate, ethyleneglycol diglycidyl
ether, glycerol triglycidyl ether and glycidyl
methacrylate, or a mixture of two or more of them.
25
32
【Claim 6】
The gel polymer electrolyte according to claim 1,
wherein the polymerizable monomer further comprises a
monomer containing a functional group capable of inhibiting
5 corrosion.
【Claim 7】
The gel polymer electrolyte according to claim 6,
wherein the functional group capable of inhibiting
10 corrosion is at least one selected from a phosphate group
and sulfate group.
【Claim 8】
The gel polymer electrolyte according to claim 6,
15 wherein the monomer containing a functional group capable
of inhibiting corrosion is at least one compound selected
from the group consisting of ethyleneglycol methacrylate
phosphate, Mevinphos, 2-methacryloyloxyethyl
phosphorylcholine, bis[2-(methacryloyloxy)ethyl]phosphate,
20 Crotoxyphos, methyl (2E)-3[(dimethoxylphosphoryl)oxy]but-2-
enoate, monoacryloxyethyl phosphate, 10-(phosphonoxy)decyl
methacryate, 2-((diethoxyphosphinyl)oxy)ethyl methacrylate,
(phosphonoxy)propane-1,3-diyl bismethacrylate, 2-sulfoethyl
methacrylate, [2-(methacryloyloxy)ethyl]dimethyl-(3-
25 sulfopropyl)ammonium hydroxide, 2-propenoic acid, 4-
33
[(methylsulfonyl)oxy]butyl ester, 2-
(methanesulfonyloxy)ethyl methacrylate and 2-
(methanesulfonyloxy)ethyl acrylate.
【5 Claim 9】
The gel polymer electrolyte according to claim 1,
which further comprises a corrosion inhibitor as an
additive.
10 【Claim 10】
The gel polymer electrolyte according to claim 9,
wherein the corrosion inhibitor is at least one selected
from the group consisting of the compounds represented by
the following Chemical Formula 2 to Chemical Formula 6:
15 [Chemical Formula 2]
[Chemical Formula 3]
(In Chemical Formula 2 and Chemical Formula 3, each
20 of R1, R2 and R3 independently represents H, a C1-C10 linear
34
or branched alkyl group, a C1-C10 linear or branched alkyl
ester group, Na or Si(CH3)3.)
[Chemical Formula 4]
(In Chemical Formula 4, R1 is a C1-C6 linear 5 r or
branched alkylene group, a C6-C12 arylene group or a C2-C6
alkenylene group, and n is an integer of 1-10.)
[Chemical Formula 5]
10 (In Chemical Formula 5, each of R2-R5 independently
represents a C1-C6 linear or branched alkylene group, O or
-SO2- group.)
[Chemical Formula 6]
15 (In Chemical Formula 6, each of R6-R11 independently
35
represents a C1-C6 linear or branched alkylene group, a C6-
C12 arylene group or a C2-C6 alkenyl group, and m is an
integer of 0-3.)
【5 Claim 11】
The gel polymer electrolyte according to claim 9,
wherein the corrosion inhibitor is at least one selected
from the group consisting of tris(trimethylsilyl)
phosphate, tris(triethylsilyl) phosphate, NaH2PO4 (sodium
10 phosphate monobasic), Na2HPO4, Na3PO4, NaHSO3, Na2SO3,
methylene methanedisulfonate, propane sultone, propene
sultone, ethylene sulfate or ethylene sulfite.
【Claim 12】
15 The gel polymer electrolyte according to claim 1,
which further comprises a lithium salt other than the imide
salt as an electrolyte salt.
【Claim 13】
20 The gel polymer electrolyte according to claim 12,
wherein the lithium salt is at least one selected from the
group consisting of LiPF6, LiClO4, LiCl, LiBr, LiI, LiCoO2,
LiBF4, LiB10Cl10, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4,
LiAlO4, CH3SO3Li, CF3SO3Li, chloroborane lithium, lithium
25 lower aliphatic carbonate and lithium 4-phenylborate.
36
【Claim 14】
The gel polymer electrolyte according to claim 12,
wherein the molar ratio of the lithium salt other than the
imide salt : imide 5 e salt is 1:10 to 8:2.
【Claim 15】
The gel polymer electrolyte according to claim 12,
wherein the molar ratio of the lithium salt other than the
10 imide salt : imide salt is 2:8 to 7:3.
【Claim 16】
The gel polymer electrolyte according to claim 1,
wherein the electrolyte salt is used in a concentration of
15 0.5M-2.0M based on the composition for a gel polymer
electrolyte.
【Claim 17】
A secondary battery comprising a cathode, an anode
20 and the gel polymer electrolyte as defined in any one of
claims 1 to 16.
【Claim 18】
The secondary battery according to claim 17, wherein
37
the cathode comprises: a cathode collector; a cathode tab
protruding from the cathode collector; and a protective
film formed on the cathode tab.
【5 Claim 19】
The secondary battery according to claim 18, wherein
the protective film comprises any one or a mixture of two
or more selected from the group consisting of a
polyethylene terephthalate (PET) film, polyimide (PI) film
10 and a polypropylene (PP) film.
【Claim 20】
The secondary battery according to claim 18, wherein
the protective film has a thickness of 1 μm to 100 μm.
15
【Claim 21】
The secondary battery according to claim 18, wherein
the cathode tab is a non-coated portion having no cathode
active material-coated portion.
20
【Claim 22】
The secondary battery according to claim 18, wherein
the protective film is present in a ratio of 10%-90% based
on the total length of the cathode tab along the protruding
25 direction of cathode tab.
38
【Claim 23】
The secondary battery according to claim 18, wherein
the protective film has the same width as the width of the
cathode tab perpendicular to the protruding direction 5 n of
cathode tab.
【Claim 24】
The secondary battery according to claim 18, wherein
10 the cathode further comprises an insulating layer.
【Claim 25】
The secondary battery according to claim 24, wherein
the insulating layer is present between the cathode tab and
15 the protective film or on the protective film.
【Claim 26】
The secondary battery according to claim 24, wherein
the insulating layer comprises at least one selected from
20 the group consisting of polyethylene terephthalate,
polypropylene, polyester, polyphenylene sulfide, polyimide,
acetate, glass fabric, polyvinylidene fluoride,
polyvinylidene fluoride-co-hexafluoropropylene, epoxy
resins and polyamide resins.
25
39
【Claim 27】
The secondary battery according to claim 17, which
has a cylindrical shape, prismatic shape or pouch-like
shape.