U.S. patent application number 14/418785 was filed with the patent office on 2015-06-04 for separation membrane comprising coating layer and battery using same.
This patent application is currently assigned to SAMSUNG SDI CO., LTD.. The applicant listed for this patent is SAMSUNG SDI CO., LTD.. Invention is credited to Jun Ho Chung, In Sik Jeon, Mok Yun Jin, Jin Kyu Park, Tae Joon Park.
Application Number | 20150155542 14/418785 |
Document ID | / |
Family ID | 50028247 |
Filed Date | 2015-06-04 |
United States Patent
Application |
20150155542 |
Kind Code |
A1 |
Jeon; In Sik ; et
al. |
June 4, 2015 |
SEPARATION MEMBRANE COMPRISING COATING LAYER AND BATTERY USING
SAME
Abstract
Disclosed herein is a high thermal resistant polyolefin-based
separator including a coating layer containing polyamic acid.
Specifically, the separator includes a polyolefin-based substrate
film, and a coating layer containing polyamic acid formed on one or
both surfaces of the polyolefin-based substrate film, wherein the
polyamic acid contains one or more functional groups selected from
the group consisting of a sulfone group, a trifluoromethyl group,
an alkyl group, and a phenyl ether group. Also, disclosed herein is
an electrochemical battery having improved thermal stability by
using the separator including a coating layer containing polyamic
acid.
Inventors: |
Jeon; In Sik; (Suwon-si,
KR) ; Park; Jin Kyu; (Suwon-si, KR) ; Park;
Tae Joon; (Suwon-si, KR) ; Chung; Jun Ho;
(Suwon-si, KR) ; Jin; Mok Yun; (Suwon-si,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SAMSUNG SDI CO., LTD. |
Yongin-si, Gyeonggi-do |
|
KR |
|
|
Assignee: |
SAMSUNG SDI CO., LTD.
Yongin-si, Gyeonggi-do
KR
|
Family ID: |
50028247 |
Appl. No.: |
14/418785 |
Filed: |
July 31, 2013 |
PCT Filed: |
July 31, 2013 |
PCT NO: |
PCT/KR2013/006894 |
371 Date: |
January 30, 2015 |
Current U.S.
Class: |
429/144 |
Current CPC
Class: |
C08G 73/105 20130101;
Y02E 60/10 20130101; C09D 179/08 20130101; H01M 2220/30 20130101;
H01M 2/1653 20130101; H01M 2/1686 20130101; C08G 73/1067 20130101;
C08G 73/1082 20130101; H01M 2/166 20130101; C08G 73/1039 20130101;
C08G 73/1042 20130101; C08G 73/1071 20130101; C08G 73/1064
20130101; H01M 10/052 20130101; C08G 73/1078 20130101 |
International
Class: |
H01M 2/16 20060101
H01M002/16; H01M 10/052 20060101 H01M010/052 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 1, 2012 |
KR |
10-2012-0084536 |
Nov 9, 2012 |
KR |
10-2012-0126384 |
Claims
1. A separator, comprising: a polyolefin-containing substrate film;
and a coating layer including polyamic acid on at least one surface
of the substrate film, wherein the polyamic acid is represented by
the following Chemical Formula 1 or 2: ##STR00044## wherein:
R.sub.1, R.sub.5 and R.sub.7 are, independently of one another, an
unsubstituted or substituted aromatic hydrocarbon having 6 to 30
carbon atoms; an unsubstituted or substituted aliphatic hydrocarbon
having 2 to 20 carbon atoms; or an unsubstituted or substituted
alicyclic hydrocarbon having 3 to 24 carbon atoms; R.sub.2, R.sub.6
and R.sub.8 are, independently of one another, an unsubstituted or
substituted aromatic hydrocarbon having 6 to 30 carbon atoms; an
unsubstituted or substituted aliphatic hydrocarbon having 2 to 20
carbon atoms; an unsubstituted or substituted alicyclic hydrocarbon
having 3 to 24 carbon atoms; --R.sub.3--Ar.sub.5--R.sub.4--,
wherein R.sub.3 and R.sub.4 are, independently of each other, an
alkylene having 1 to 5 carbon atoms; and Ar.sub.5 is an arylene
having 6 to 15 carbon atoms that is unsubstituted or mono- to
tri-substituted by CH.sub.3, OH, SH or NH.sub.2; n is an integer of
30 to 10000; and x is an integer of 15 to 5000, and y is an integer
of 15 to 5000.
2. The separator as claimed in claim 1, wherein R.sub.1, R.sub.5
and R.sub.7 are, independently of one another, an aromatic
hydrocarbon represented by the following Chemical Formula 3, and
R.sub.2, R.sub.6 and R.sub.8 are, independently of one another, an
aromatic hydrocarbon represented by the following Chemical Formula
4: ##STR00045## wherein, in Chemical Formula 3: Ar.sub.1 to
Ar.sub.4 are, independently of one another, an unsubstituted or
substituted arylene having 6 to 15 carbon atoms; X.sub.1 to X.sub.3
are, independently of one another, a single bond, O, S, C(.dbd.O),
S(.dbd.O).sub.2, C(.dbd.O)NH, an unsubstituted or substituted
alkylene having 1 to 10 carbon atoms, or an unsubstituted or
substituted silylene; and m, l and o are, independently of one
another, 0 or 1; with the provisos that: if m is 1, and l and o are
0, X.sub.2 and X.sub.3 are a single bond, and Ar.sub.2 is an
unsubstituted or substituted trivalent arylene having 6 to 15
carbon atoms; if m and l are 1, and o is 0, X.sub.3 is a single
bond, and Ar.sub.3 is an unsubstituted or substituted trivalent
arylene having 6 to 15 carbon atoms; and if m, l and o are all 0,
X.sub.1 to X.sub.3 are a single bond, and Ar.sub.1 is an
unsubstituted or substituted tetravalent arylene having 6 to 15
carbon atoms;
--(Ar.sub.6)--X.sub.4--(Ar.sub.7).sub.p--X.sub.5--(Ar.sub.8).sub.-
q--X.sub.6--(Ar.sub.9).sub.r [Chemical Formula 4] wherein, in
Chemical Formula 4: Ar.sub.6 to Ar.sub.9 are, independently of one
another, an unsubstituted or substituted arylene having 6 to 15
carbon atoms; X.sub.4 to X.sub.6 are, independently of one another,
a single bond, O, S, C(.dbd.O), S(.dbd.O).sub.2, C(.dbd.O)NH, an
unsubstituted or substituted alkylene having 1 to 10 carbon atoms,
or an unsubstituted or substituted silylene; and p, q and r are,
independently of one another, 0 or 1; with the provisos that: if p
is 1, and q and r are 0, X.sub.5 and X.sub.6 are a single bond; if
p and q are 1, and r is 0, X.sub.6 is a single bond; and if p, q
and r are all 0, X.sub.4 to X.sub.6 are a single bond.
3. The separator as claimed in claim 1, wherein the polyamic acid
contains a sulfone group.
4. The separator as claimed in claim 3, wherein the sulfone group
is a meta-aryl sulfone group.
5. The separator as claimed in claim 1, wherein the polyamic acid
contains a sulfone group and a trifluoromethyl group.
6. The separator as claimed in claim 1, wherein the polyamic acid
includes a first repeating unit containing a phenyl ether group and
a second repeating unit containing a sulfone group, and a ratio of
the first repeating unit to the second repeating unit is 5:5 to
1:9.
7. The separator as claimed in claim 1, wherein the polyamic acid
includes a first repeating unit containing a sulfone group and a
second repeating unit containing a trifluoromethyl group, and a
ratio of the first repeating unit to the second repeating unit is
9:1 to 7:3.
8. The separator as claimed in claim 1, wherein the polyamic acid
has a structure of following Chemical Formula 9: ##STR00046##
wherein a ratio of repeating units x to y is 9:1 to 7:3.
9. The separator as claimed in claim 8, wherein one or more aryl
sulfone groups in the repeating unit x or y of the Chemical Formula
9 are a meta-aryl sulfone group.
10. The separator as claimed in claim 1, wherein the coating layer
contains inorganic particles.
11. The separator as claimed in claim 10, wherein the inorganic
particles include one or more of Al.sub.2O.sub.3, SiO.sub.2,
B.sub.2O.sub.3, Ga.sub.2O.sub.3, TiO.sub.2 or SnO.sub.2.
12. The separator as claimed in claim 1, wherein the separator has
a breaking temperature of 180.degree. C. or more under a condition
of 0.005 N, and a heating rate of 5.degree. C./min.
13. An electrochemical battery, comprising: a cathode, an anode,
the separator as claimed in claim 1, and an electrolyte.
14. The electrochemical battery as claimed in claim 13, wherein the
electrochemical battery is a lithium secondary battery.
Description
TECHNICAL FIELD
[0001] The present invention relates to a separator including a
coating layer, and an electrochemical battery using the same.
BACKGROUND ART
[0002] A separator for an electrochemical battery refers to an
intermediate membrane segregating a cathode and an anode from each
other in a battery, while continuously maintaining ion
conductivity, thereby allowing battery charging and
discharging.
[0003] Recently, along with weight lightening and miniaturization
trend of an electrochemical battery for high portability of an
electronic device, a battery is also required to have high power
and large capacity in order to be used for an electric car, and the
like. Thus, a separator for a battery is required to be thin and
have light weight, and at the same time, to have excellent thermal
shape stability for production of a high power battery.
[0004] Particularly, in case where a polyolefin-based film is used
as a substrate film of the separator, the film may melt down even
at relatively low temperature, and thus, in order to compensate for
such a problem, a study to improve the thermal resistance of the
substrate film has proceeded. It is suggested in Korean Patent
Registration No. 10-0775310, etc. that a coating layer of a mixture
of organic and inorganic materials is formed on one or both
surfaces of a substrate film of a separator, in order to improve
the thermal resistance of a substrate film.
[0005] Meanwhile, an attempt has been made to improve thermal
stability of a coating layer, by using an organic binder having
excellent thermal resistance such as polyimide as a coating agent
component of a separator. However, the organic binder having high
thermal resistance does not dissolve in a low boiling point
solvent, which later causes a problem of not properly performing a
drying process of the solvent after coating a separator. Moreover,
this not only decreases air permeability of a separator, but also
reduces compatibility with other coating agent components added
together so as to make it difficult to be substantially utilized as
a coating agent.
[0006] Therefore, the development of a separator for a battery
having excellent thermal resistance and air permeability, by
coating the separator with an organic binder having high thermal
resistance and also high solubility in a low boiling point solvent
as a coating agent component, is needed.
DISCLOSURE OF INVENTION
Technical Problem
[0007] An object of the present invention is to provide a separator
having excellent thermal resistance and drying processability, by
utilizing polyamic acid having excellent solubility in a low
boiling point solvent as a coating agent component of a
separator.
[0008] Another object of the present invention is to provide a
separator having a less solvent residual amount in a coating layer
so as to have excellent air permeability, and improved thermal
resistance.
[0009] Another object of the present invention is to provide an
electrochemical battery having excellent thermal stability, by
using the separator.
[0010] Another object of the present invention is to provide a
separator maintaining an excellent shutdown function of a
polyolefin-based separator, and having improved thermal resistance
and air permeability.
Technical Solution
[0011] In one general aspect, a polyolefin-based separator includes
a coating layer containing polyamic acid.
[0012] Specifically, the separator includes a polyolefin-based
substrate film, and a coating layer containing polyamic acid formed
on one or both surfaces of the polyolefin-based substrate film,
wherein the polyamic acid has the structure of following Chemical
Formula 1 or 2.
##STR00001##
[0013] wherein
[0014] R.sub.1, R.sub.5 and R.sub.7 are, independently of one
another, an unsubstituted or substituted aromatic hydrocarbon
having 6 to 30 carbon atoms; an unsubstituted or substituted
aliphatic hydrocarbon having 2 to 20 carbon atoms; or an
unsubstituted or substituted alicyclic hydrocarbon having 3 to 24
carbon atoms. R.sub.1, R.sub.5 and R.sub.7 may be identical to or
different from one another.
[0015] In another general aspect, an electrochemical battery
includes the separator, a cathode, an anode, and electrolyte.
[0016] In another general aspect, a lithium secondary battery
includes the separator.
Advantageous Effects
[0017] The separator of the present invention maintains a shutdown
property as it is, while having improved melt-down temperature and
excellent thermal resistance.
[0018] Further, the separator of the present invention has a less
solvent residual amount in a coating layer of the dried separator,
thereby not reducing air permeability, and compensates for the
thermal sensitivity of polyolefin, thereby enhancing the thermal
resistance of the separator.
[0019] The coating composition for a separator of the present
invention may have excellent solubility in a low boiling point
solvent, and mitigate a drying condition, so that simplification of
a process and cost saving are possible.
[0020] Further, the separator of the present invention has strong
resistance to thermal shrinkage which occurs upon overheating of a
battery, and thus, in case of utilizing the separator in a battery,
the battery has improved stability and extended life.
[0021] Further, the polyamic acid used in the coating composition
of the present invention may maintain the dispersibility of
inorganic particles in an inorganic dispersion, so as to improve
the preparation processability of a coating layer of a mixture of
organic and inorganic materials.
[0022] The effects according to the present invention are not
limited by the illustration above, and various effects are included
herein.
BRIEF DESCRIPTION OF DRAWINGS
[0023] FIG. 1 is a graph showing capacity change with the number of
cycle of a battery using the separator according to an exemplary
embodiment of the present invention.
[0024] FIG. 2 is a graph showing the measurement of shutdown
temperature of the separator according to Example 1 (Graph B) and
Comparative Example 1 (Graph A).
[0025] FIG. 3 is a graph showing the result of thermal mechanical
analysis (TMA) measurement of the separator according to Example 1
(Graph B) and Comparative Example 1 (Graph A).
[0026] FIG. 4 is a graph showing the measurement of a high-rate
discharge property (C-rate) of a separator according to Example 1
and Comparative Example 1.
BEST MODE
[0027] Hereinafter, the present invention will be described in
detail. Since the part not disclosed herein may be sufficiently
recognized and inferred by a person skilled in the art to which the
invention pertains or in the similar art, a description thereof
will be omitted.
[0028] The separator according to an exemplary embodiment of the
present invention includes a coating layer containing high thermal
resistant polyamic acid. Specifically, the separator according to
an exemplary embodiment of the present invention includes a
polyolefin-based substrate film, and a coating layer containing
polyamic acid formed on one or both surfaces of the
polyolefin-based substrate film, wherein the polyamic acid has the
structure of following Chemical Formula 1 or 2.
##STR00002##
[0029] wherein
[0030] R.sub.1, R.sub.5 and R.sub.7 are, independently of one
another, an unsubstituted or substituted aromatic hydrocarbon
having 6 to 30 carbon atoms; an unsubstituted or substituted
aliphatic hydrocarbon having 2 to 20 carbon atoms; or an
unsubstituted or substituted alicyclic hydrocarbon having 3 to 24
carbon atoms. R.sub.1, R.sub.5 and R.sub.7 may be identical to or
different from one another.
[0031] Specifically, the aromatic hydrocarbon having 6 to 30 carbon
atoms may be represented by following Chemical Formula 3:
##STR00003##
[0032] wherein Ar.sub.1 to Ar.sub.4 are, independently of one
another, unsubstituted or substituted arylene having 6 to 15 carbon
atoms, and Ar.sub.1 to Ar.sub.4 may be identical to or different
from one another; and X.sub.1 to X.sub.3 are, independently of one
another, a single bond, O, S, C(.dbd.O), S(.dbd.O).sub.2,
C(.dbd.O)NH, unsubstituted or substituted alkylene having 1 to 10
carbon atoms, specifically alkylene having 1 to 4 carbon atoms, or
unsubstituted or substituted silylene. For example, the substituted
alkylene or silylene may be mono- or di-substituted by F, OH,
CH.sub.3, CF.sub.3 and the like.
[0033] m, l and o are, independently of one another, 0 or 1.
Specifically, if m is 1, and l and o are 0, X.sub.2 and X.sub.3 are
a single bond, and Ar.sub.2 is unsubstituted or substituted
trivalent arylene having 6 to 15 carbon atoms, and if m and l are
1, and o is 0, X.sub.3 is a single bond, and Ar.sub.3 is
unsubstituted or substituted trivalent arylene having 6 to 15
carbon atoms. If m, l and o are all 0, X.sub.1 to X.sub.3 are a
single bond, and Ar.sub.1 is unsubstituted or substituted
tetravalent arylene having 6 to 15 carbon atoms, for example,
unsubstituted or substituted tetravalent phenylene or
naphthylene.
[0034] In the Chemical Formula 1 or 2, R.sub.2, R.sub.6 and R.sub.8
are, independently of one another, an unsubstituted or substituted
aromatic hydrocarbon having 6 to 30 carbon atoms; an unsubstituted
or substituted aliphatic hydrocarbon having 2 to 20 carbon atoms;
an unsubstituted or substituted alicyclic hydrocarbon having 3 to
24 carbon atoms; or --R.sub.3--Ar.sub.5--R.sub.4-- (wherein R.sub.3
and R.sub.4 are, independently of each other, alkylene having 1 to
5 carbon atoms; and Ar.sub.5 is unsubstituted or substituted
arylene having 6 to 15 carbon atoms, and if Ar.sub.5 is
substituted, it is mono- to tri-substituted by CH.sub.3, OH, SH or
NH.sub.2.). R.sub.2, R.sub.6 and R.sub.8 may be identical to or
different from one another.
[0035] Specifically, in R.sub.2, R.sub.6 and R.sub.8, the
unsubstituted or substituted aromatic hydrocarbon having 6 to 30
carbon atoms may be represented by following Chemical Formula
4:
--(Ar.sub.6)--X.sub.4--(Ar.sub.7).sub.p--X.sub.5--(Ar.sub.8).sub.q--X.su-
b.6--(Ar.sub.9).sub.r [Chemical Formula 4]
[0036] wherein Ar.sub.6 to Ar.sub.9 are, independently of one
another, arylene having 6 to 15 carbon atoms, and Ar.sub.6 to
Ar.sub.9 may be identical to or different from one another; and
X.sub.4 to X.sub.6 are, independently of one another, a single
bond, O, S, C(.dbd.O), S(.dbd.O).sub.2, C(.dbd.O)NH, unsubstituted
or substituted alkylene having 1 to 10 carbon atoms, specifically
alkylene having 1 to 4 carbon atoms, or unsubstituted or
substituted silylene. For example, the substituted alkylene or
silylene may be mono- or di-substituted by F, OH, CH.sub.3,
CF.sub.3 and the like.
[0037] p, q and r are, independently of one another, 0 or 1. If p
is 1, and q and r are 0, X.sub.5 and X.sub.6 are a single bond, and
Ar.sub.6 and Ar.sub.7 are, independently of each other,
unsubstituted or substituted phenylene or naphthylene. If p and q
are 1, and r is 0, X.sub.6 is a single bond. If p, q and r are all
0, X.sub.4 to X.sub.6 are a single bond.
[0038] In the Chemical Formula 4, X.sub.4 may be in an ortho-,
meta-, or para-position to an amine group (--NH--) of the Chemical
Formula 1 or 2. Specifically, it may be in a meta-position, and in
case of being in a meta-position to an amine group, its solubility
may be improved.
[0039] In the Chemical Formula 1, n is an integer of 30 to 10000,
an integer of 100 to 1000, an integer of 50 to 500, or an integer
of 50 to 300.
[0040] In the Chemical Formula 2, x is an integer of 15 to 5000,
and y is an integer of 15 to 5000, specifically, x is an integer of
50 to 500, and y is an integer of 50 to 500, and more specifically,
x is an integer of 25 to 250, and y is an integer of 25 to 250.
[0041] According to an exemplary embodiment of the present
invention, in the Chemical Formula 1 or 2, R.sub.1, R.sub.2,
R.sub.5, R.sub.6, R.sub.7 and R.sub.8 may be, independently of one
another, an unsubstituted or substituted aromatic hydrocarbon
having 6 to 18 carbon atoms; an unsubstituted or substituted
alicyclic hydrocarbon having 6 to 24 carbon atoms; or an
unsubstituted or substituted aliphatic hydrocarbon having 2 to 17
carbon atoms, and in the aromatic hydrocarbon of the Chemical
Formula 3 or 4, Ar.sub.1 to Ar.sub.4, or Ar.sub.6 to Ar.sub.9 may
be, independently of one another, an unsubstituted or substituted
arylene having 4 to 10 carbon atoms, specifically phenylene or
naphthylene Herein, in the Chemical Formula 3, m, l and o may be
all 0, or m may be 1, and l and o may be 0, and in the Chemical
Formula 4, p, q and r may be all 1, or q may be 1, and q and r may
be 0
[0042] The polyamic acid compound according to another exemplary
embodiment of the present invention may be the compound wherein in
the aromatic hydrocarbon of the Chemical Formula 3 or 4, Ar.sub.1
to Ar.sub.4 are unsubstituted, and Ar.sub.6 to Ar.sub.9 are,
independently of one another, unsubstituted or substituted. If any
one or more of Ar.sub.6 to Ar.sub.9 are substituted, they may be
substituted by CH.sub.3, CF.sub.3, OH, F or the like, for example,
CH.sub.3 or CF.sub.3.
[0043] The polyamic acid compound according to another exemplary
embodiment of the present invention may be the compound wherein in
the Chemical Formula 1 or 2, R.sub.1, R.sub.5 and R.sub.7 are an
unsubstituted or substituted phenylene or naphthylene, an
unsubstituted or substituted alicyclic hydrocarbon having 4 to 12
carbon atoms, an aliphatic hydrocarbon having 4 to 7 carbon atoms,
or two or three unsubstituted or substituted phenyl groups in the
form of being connected by a single bond, O, S, C(.dbd.O),
S(.dbd.O).sub.2, C(.dbd.O)NH, unsubstituted or substituted alkylene
having 1 to 10 carbon atoms, unsubstituted or substituted silylene,
and the like. The two or three unsubstituted or substituted phenyl
groups may be, specifically, independently of each other, in the
form of being connected by a single bond; C(.dbd.O);
S(.dbd.O).sub.2; alkylene having 1 to 3 carbon atoms unsubstituted
or mono- or di-substituted by CH.sub.3 or CF.sub.3; or silylene
unsubstituted or mono- or di-substituted by CH.sub.3 or CF.sub.3.
More specifically, the connecting group of the two or three phenyl
groups may be a single bond, C(.dbd.O), C(CH.sub.3).sub.2 or
C(CF.sub.3).sub.2. Alternatively, two phenyl groups may be
connected by the connecting group. R.sub.2, R.sub.6 and R.sub.8 may
be an unsubstituted or substituted alicyclic hydrocarbon having 4
to 12 carbon atoms, an unsubstituted or substituted aliphatic
hydrocarbon having 4 to 17 carbon atoms, or two to four
unsubstituted or substituted phenyl groups in the form of being
connected by a single bond, O, S, C(.dbd.O), S(.dbd.O).sub.2,
C(.dbd.O)NH, unsubstituted or substituted alkylene having 1 to 10
carbon atoms, unsubstituted or substituted silylene, and the like.
The two to four unsubstituted or substituted phenyl groups may be,
specifically, independently of each other, in the form of being
connected by a single bond; S(.dbd.O).sub.2; O; C(.dbd.O); alkylene
having 1 to 3 carbon atoms unsubstituted or mono- or di-substituted
by CH.sub.3 or CF.sub.3; or silylene unsubstituted or mono- or
di-substituted by CH.sub.3 or CF.sub.3. More specifically, the
connecting group of the two to four phenyl groups may be a single
bond, C(.dbd.O), S(.dbd.O).sub.2, O, C(CH.sub.3).sub.2 or
C(CF.sub.3).sub.2. In particular, the connecting group may be
C(.dbd.O), S(.dbd.O).sub.2 or O. For example, two phenyl groups may
be connected by the connecting group.
[0044] The polyamic acid compound according to another exemplary
embodiment of the present invention may be the compound wherein in
the Chemical Formula 1 or 2, R.sub.1 and R.sub.5 are unsubstituted
or substituted phenylene or naphthylene, and R.sub.2, R.sub.6,
R.sub.7 and R.sub.8 are two to four unsubstituted or substituted
phenyl groups in the form of being connected by a single bond, O,
S, C(.dbd.O), S(.dbd.O).sub.2, C(.dbd.O)NH, unsubstituted or
substituted alkylene having 1 to 10 carbon atoms, unsubstituted or
substituted silylene, or the like.
[0045] The polyamic acid having the structure of the Chemical
Formula 1 or 2 may represent adequate solubility in the low boiling
point solvent (the solvent having a boiling point less than
150.degree. C.). Specifically, if an organic binder component of
the separator coating agent has low solubility in the low boiling
point solvent, the preparation of the coating agent usable in a
general coating method itself may be difficult, and on the
contrary, if it has unduly high solubility in the low boiling point
solvent, battery safety may be rather decreased due to the risk of
dissolving the separator in the electrolyte solution of a battery.
The polyamic acid having the structure of the Chemical Formula 1 or
2 has adequately controlled solubility in a low boiling point
solvent, and thus, is suitable as a coating composition of a
separator. The polyamic acid having the structure of the Chemical
Formula 1 or 2 has excellent thermal resistance and solubility in a
low boiling point solvent, thereby securing the thermal resistance
of the separator with polyamic acid itself without proceeding with
imidation separately, and also dispenses with carrying out
imidation at high temperature, thereby avoiding the damage of a
polyolefin layer which is a lower substrate, and thus, a coating
layer may be formed on a polyolefin-based substrate. Further, since
its solubility in a low boiling point solvent is excellent, a high
temperature drying process under a severe condition for removing a
high boiling point solvent is not necessary, and thus, a coating
layer may be formed on a polyolefin substrate. Though polyimide has
excellent thermal resistance, it does not dissolve in a low boiling
point solvent, so that it has not been substantially utilized as a
coating agent component of the separator. Specifically, in a
separator including a coating layer, if a large amount of solvent
remains in the coating layer after drying, the separator will have
reduced adhesion, and also decreased air permeability, and thus,
not function properly as a separator. Therefore, in case where the
separator is intended to be coated by a general coating method (in
particular, dip coating), a low boiling point solvent has been used
as a coating agent solvent, in order to facilitate drying of the
solvent. However, in case of polyimide, since it does not dissolve
in the low boiling point solvent, it has been difficult to be
utilized in a separator coating layer in the prior art, in spite of
its excellent thermal resistance. Thus, the problems in the prior
art are intended to be solved in the present invention by
introducing polyamic acid which has excellent thermal resistance
and easily dissolves in a low boiling point solvent.
[0046] The term used herein, `aromatic hydrocarbon having 6 to 30
carbon atoms` includes all the cases where the aromatic hydrocarbon
is present alone, two aromatic hydrocarbons are joined to form a
condensed ring, or two or more aromatic rings are not joined to
each other, but connected by another connecting group. The aromatic
hydrocarbon present alone is exemplified by a divalent or
tetravalent phenylene group, and two aromatic hydrocarbons joined
to each other to form a condensed ring are exemplified by a
divalent or tetravalent naphthylene group.
[0047] The term used herein, `arylene having 6 to 15 carbon atoms`
includes an aromatic hydrocarbon having 6 to 15 carbon atoms
wherein the aromatic hydrocarbon is present alone, or two aromatic
hydrocarbons are joined to each other to form a condensed ring, and
the arylene is exemplified by a phenylene or naphthylene group. The
arylene may be di-, tri- or tetravalent, herein.
[0048] The term used herein, `alicyclic hydrocarbon having 3 to 24
carbon atoms` refers to a saturated or partially unsaturated
hydrocarbon group containing 1 to 3 rings having 3 to 8 carbon
atoms, respectively. For example, as the alicyclic hydrocarbon
having 6 to 20 carbon atoms, a cyclohexyl, cycloheptyl,
cyclohexenyl, or 1,2,3,4-tetrahydronaphthalene group may be
mentioned.
[0049] The term used herein, `aliphatic hydrocarbon having 2 to 20
carbon atoms` refers to a saturated or partially unsaturated,
straight-chained or branched-chained, di- or tetravalent
hydrocarbon group. Specifically, it may refer to a saturated,
straight-chained or branched-chained, di- or tetravalent
hydrocarbon group. As an example of the aliphatic hydrocarbon
having 2 to 20 carbon atoms, ethyl, butyl, pentyl, hexyl,
1,1-dimethylbutyl or the like may be used.
[0050] In case where the term, `unsubstituted or substituted` is
used herein, unless otherwise stated, a group may be unsubstituted
or substituted several times by F, OH, SH, CH.sub.3, CF.sub.3,
NH.sub.2 or the like. For example, a group may be mono- to
tri-substituted by F, OH, SH, CH.sub.3, CF.sub.3, NH.sub.2 or the
like.
[0051] In case where R.sub.2, R.sub.6 or R.sub.8 is phenylene, or
R.sub.2, R.sub.6 or R.sub.8 contains a phenylene group as a part
herein, it may be, independently of one another, connected in an
ortho-, meta- and para-position.
[0052] Specifically, in the Chemical Formulae 1 and 2, R.sub.1,
R.sub.5 and R.sub.7 may be selected from the group consisting of
following Chemical Formulae A1 to A43.
##STR00004## ##STR00005## ##STR00006## ##STR00007## ##STR00008##
##STR00009##
[0053] Specifically, in the Chemical Formulae 1 and 2, R.sub.2,
R.sub.6 and R.sub.8 may be selected from the group consisting of
following Chemical Formulae B1 to B74.
##STR00010## ##STR00011## ##STR00012## ##STR00013## ##STR00014##
##STR00015## ##STR00016## ##STR00017## ##STR00018##
[0054] The polyamic acid compound according to another exemplary
embodiment of the present invention may include one or more
functional groups selected from the group consisting of a sulfone
group, a trifluoromethyl group, an alkyl group and a phenyl ether
group. For example, one or more sulfone, trifluoromethyl, alkyl
and/or phenyl ether groups may be included in the molecule, and
both sulfone and trifluoromethyl groups may be included. If the
polyamic acid includes one or more sulfone, trifluoromethyl, alkyl
and/or phenyl ether groups, it may have more increased solubility
in a low boiling point solvent. Specifically, the polyamic acid
represented by any one of following Chemical Formulae 5 to 7 may be
used.
##STR00019##
[0055] The polyamic acid having the structure of the Chemical
Formula 5 has excellent solubility in a low boiling point solvent,
and specifically it may represent excellent solubility in a solvent
composition containing acetone being a low boiling point solvent
and N,N-dimethyl acetamide (DMAc) being a high boiling point
solvent in a weight ratio of about 9.5:0.5 or less, that is, in a
weight ratio of acetone to DMAc of 9.5:0.5 or less. More
specifically it may represent excellent solubility in a solvent
composition containing acetone and DMAc in a weight ratio of
acetone to DMAc of 9:1 or less, or 8.75:1.25 or less.
##STR00020##
[0056] The polyamic acid having the structure of the Chemical
Formula 6 has excellent solubility in a low boiling point solvent,
and specifically it may represent excellent solubility in a solvent
composition containing acetone being a low boiling point solvent
and DMAc being a high boiling point solvent in a weight ratio of
about 8:2 or less, that is, in a weight ratio of acetone to DMAc of
8:2 or less. More specifically, it may represent excellent
solubility in a solvent composition containing acetone and DMAc in
a weight ratio of acetone to DMAc of 7.5:2.5 or less.
##STR00021##
[0057] The polyamic acid having the structure of the Chemical
Formula 7 has excellent solubility in a low boiling point solvent,
and specifically it may represent excellent solubility in a solvent
composition containing acetone being a low boiling point solvent
and DMAc being a high boiling point solvent in a weight ratio of
about 7.5:2.5 or less, that is, in a weight ratio of acetone to
DMAc of 7.5:2.5 or less. More specifically, it may represent
excellent solubility in a solvent composition containing acetone
and DMAc in a weight ratio of acetone to DMAc of 6:4 or less.
[0058] Further, polyamic acid having the structure wherein an amic
acid repeating unit containing a phenyl ether group (x)
(hereinafter, referred to as a `unit`) and an amic acid unit
containing a sulfone group (y) are repeated, or polyamic acid
having the structure wherein an amic acid unit containing a sulfone
group but not containing a trifluoromethyl group (x) and an amic
acid unit containing sulfone and trifluoromethyl groups (y) are
repeated, may be used. Specifically, the polyamic acid represented
by following Chemical Formula 8 or 9 may be used:
##STR00022##
[0059] wherein more specifically, a ratio x:y is 5:5 to 1:9. Within
the range of the ratio, the polyamic acid solubility in the low
boiling point solvent (e.g., acetone) may be increased.
[0060] The polyamic acid having the structure of the Chemical
Formula 8 may specifically, represent excellent solubility in a
solvent composition containing acetone being the low boiling point
solvent and DMAc being the high boiling point solvent in a weight
ratio of about 8:2 or less. More specifically, it may represent
excellent solubility in a solvent composition containing acetone
and DMAc in a weight ratio of acetone to DMAc of 7.5:2.5 or
less.
##STR00023##
[0061] wherein a ratio x:y is 9:1 to 7:3. The polyamic acid within
the range of the ratio may have not too high solubility in an
electrolyte solution and the like, and only sufficiently high
solubility in the low boiling point solvent. The polyamic acid
having the structure of the Chemical Formula 9 has excellent
solubility in the low boiling point solvent, and specifically, may
represent excellent solubility in a solvent composition containing
acetone being the low boiling point solvent and DMAc being the high
boiling point solvent in a weight ratio of about 9.5:0.5 to
5:5.
[0062] In the Chemical Formulae 5 to 9, the sulfone group may be a
substituent in an ortho-, meta- or para-position to an amine group,
for example, in a meta-position. In case where the sulfone group is
a substituent in the meta-position, polyamic acid solubility in the
low boiling point solvent may be increased.
[0063] The polyamic acid according to exemplary embodiments of the
present invention may have a weight average molecular weight (Mw)
of 50,000 to 100,000. In case of having the molecular weight range,
it may have increased solubility in the low boiling point solvent,
and improved thermal resistance.
[0064] The polyamic acid of the Chemical Formula 1 may be prepared
by a method known in the art to react an anhydride containing
R.sub.1 with diamine containing R.sub.2. The polyamic acid of the
Chemical Formula 2 may be prepared by a method known in the art to
react an anhydride containing R.sub.5 with diamine containing
R.sub.6, and an anhydride containing R.sub.7 with diamine
containing R.sub.8.
[0065] The non-limiting example of the anhydride containing
R.sub.1, R.sub.5 or R.sub.7 may include pyromellitic dianhydride,
4,4'-(hexafluoroisopropylidene)diphthalic dianhydride,
3,3',4,4'-benzophenonetetracarboxylic dianhydride,
4,4'-carbonyldiphthalic dianhydride, 1,2,3,4-butanetetracarboxylic
dianhydride, 4,4'-oxydiphthalic dianhydride,
3,3',4,4'-biphenyltetracarboxylic dianhydride,
bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride,
3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride,
4,4'-isopropylidenediphthalic dianhydride,
1,2,4,5-cyclohexanetetracarboxylic dianhydride,
1,2,3,4-cyclopentanetetracarboxylic dianhydride, or the like.
[0066] The non-limiting example of the diamine containing R.sub.2,
R.sub.6 or R.sub.8 may include 3,3'-diaminodiphenylsulfone,
4,4'-diaminodiphenyl sulfone, 1,6-hexamethylenediamine,
4,4'-oxydianiline, 4,4'-methylenedianiline, 1,3-phenylenediamine,
1,4-phenylenediamine,
2,2-bis(3-amino-4-methylphenyl)hexafluoropropane,
meta-xylenediamine, para-xylenediamine,
3,3'-(hexafluoroisopropylidene)dianiline,
4,4'-(hexafluoroisopropylidene)dianiline),
3-[3-(3-aminophenyl)sulfonylphenyl]sulfonylaniline,
2,2'-bis(trifluoromethyl)benzidine, 1,16-hexadecanediamine,
1,4-cyclohexyldiamine, 3,3'-bis(trifluoromethyl)benzidine,
ortho-tolidine, 2,3,5,6-tetramethyl-1,4-phenylenediamine,
2,5-dimethyl-1,4-phenylenediamine,
4,4'-diamino-3,3'-dimethyldiphenylmethane,
2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, or the like
[0067] The polyamic acid having the structure of the Chemical
Formula 1 or 2 may represent adequate solubility in the low boiling
point solvent (the solvent having a boiling point less than
150.degree. C.)
[0068] Specifically, if an organic binder component of the
separator coating agent has low solubility in the low boiling point
solvent, the preparation of the coating agent usable in a general
coating method itself may be difficult, and on the contrary, if it
has unduly high solubility in the low boiling point solvent,
battery safety may be rather decreased due to the risk of
dissolving the separator in the electrolyte solution of a
battery.
[0069] Thus, in one exemplary embodiment of the present invention,
there is provided a coating composition having adequately
controlled solubility in the low boiling point by using the
polyamic acid having the structure of the Chemical Formula 1 or
2.
[0070] The polyamic acid used in the present invention may be
contained in 1 to 30% by weight, more specifically 1 to 20% by
weight, and for example, 1 to 15% by weight, based on the weight of
the coating composition. Within the range, the polyamic acid may
sufficiently serve as an organic binder component of the coating
agent, and sufficiently impart high thermal resistance to the
coating composition.
[0071] The low boiling point solvent used in the present invention
refers to a solvent having a boiling point less than 150.degree. C.
The non-limiting examples of the low boiling point solvent usable
in the present invention may include acetone, tetrahydrofuran
(THF), and the like. These may be used alone or in a mixture of two
or more, and for example, acetone may be used. Since acetone has a
significantly low boiling point of about 56.5.degree. C., if it is
used as a solvent of a coating agent, the coating layer may be
easily dried, so that the air permeability of the separator becomes
excellent, and also deterioration of the physical properties due to
the residual solvent may be prevented.
[0072] According to one embodiment of the present invention,
additionally to the low boiling point solvent, a high boiling point
solvent may be used together as the solvent of the coating
composition.
[0073] The high boiling point solvent usable in the present
invention refers to a solvent having boiling point of 150.degree.
C. or more. The non-limiting example of the high boiling point
solvent usable in the present invention may include
dimethylformamide (DMF), dimethylsulfoxide (DMSO),
dimethylacetamide (DMAc), dimethylcarbonate (DMC),
N-methylpyrrolidone (NMP), or the like. These may be used alone or
in a mixture of two or more.
[0074] As to the contents of the low boiling point solvent and the
high boiling point solvent, the weight ratio of the low boiling
point solvent (X) to the high boiling point solvent (Y) (X:Y) may
be 9.5:0.5 to 5:5, specifically 9.0:1.0 to 5:5, and more
specifically 8:2 to 5:5.
[0075] In case of adjusting the content ratio of the low boiling
point solvent and the high boiling point solvent to the above
range, the polyamic acid may be sufficiently dissolved to
facilitate the preparation of the coating agent, and the coating
layer formed on the substrate film may also be easily dried. That
is, the solvent may remain in a small amount in the dried coating
layer of the separator (for example, 500 ppm or less), so that the
air permeability of the separator will not be decreased.
[0076] The total content of the solvent including the low boiling
point solvent and the high boiling point solvent may be 20 to 99%
by weight, specifically 50 to 95% by weight, and more specifically
70 to 95% by weight, based on the weight of the coating
composition. If the solvent is contained within the range, the
coating agent may be easily prepared, and the drying process of the
coating layer may be performed well.
[0077] The inorganic particles used in the present invention are
not specifically limited, and any inorganic particles generally
used in the art may be used. The non-limiting examples of the
inorganic particles usable in the present invention include
Al.sub.2O.sub.3, SiO.sub.2, B.sub.2O.sub.3, Ga.sub.2O.sub.3,
TiO.sub.2, SnO.sub.2 or the like. These may be used alone or in a
mixture of two or more. The inorganic particles used in the present
invention may be, for example, Al.sub.2O.sub.3 (alumina).
[0078] The size of the inorganic particle used in the present
invention is not specifically limited, and the average particle
diameter may be 1 to 2,000 nm, or 100 to 1,000 nm. In case of using
the inorganic particles within the size range, dispersibility and
coating processability of the inorganic particles in a coating
solution may be prevented from being reduced, and the thickness of
the coating layer may be appropriately adjusted to prevent
mechanical property deterioration and increase in electric
resistance. Further, the size of the pores produced in the
separator may be appropriately adjusted to lower a probability of
causing an internal short-circuit upon charging and discharging a
battery.
[0079] In the preparation of the coating composition, the inorganic
particles may be used in the form of an inorganic dispersion being
dispersed in an appropriate solvent. The appropriate solvent is not
specifically limited, and any solvent generally used in the art may
be used. As an appropriate solvent to disperse the inorganic
particles, acetone may be used, for example.
[0080] The inorganic dispersion may be prepared by a general method
without a special limitation, and for example, in a manner of
adding Al.sub.2O.sub.3 in a proper amount to acetone, and milling
it to be dispersed with a beads mill.
[0081] In the preparation of the inorganic dispersion, the content
of the inorganic particles may be 10 to 40% by weight, specifically
20 to 30% by weight, based on the weight of the dispersion. If the
inorganic particles are contained within the range, their heat
dissipation property may be sufficiently exhibited, and the
separator coated using them may have effectively suppressed thermal
shrinkage.
[0082] The content of the inorganic dispersion may be 10 to 70% by
weight, specifically 20 to 60% by weight, and more specifically 30
to 50% by weight, based on the weight of the coating composition of
the present invention. Within the range, the inorganic particles
may be expected to show a sufficient heat dissipation property, and
the content of an organic binder is also relatively properly
adjusted, and thus, the adhesion of the separator may be secured
above a certain level.
[0083] According to an exemplary embodiment of the present
invention, the coating composition may further include a binder in
addition to the polyamic acid. The binder may be one selected from
the group consisting of polyvinylidene fluoride (PVdF) homopolymer,
polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP),
polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone,
polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene
oxide, cellulose acetate, cellulose acetate butyrate, cellulose
acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol,
cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl
cellulose and acrylonitrilestyrene-butadiene copolymer, alone or in
a mixture thereof. Specifically, polyvinylidene fluoride
homopolymer and/or polyvinylidene fluoride-hexafluoropropylene
copolymer may be included.
[0084] In case of further including polyvinylidene fluoride
homopolymer, the viscosity and adhesion of the coating composition
may be improved to assist the inorganic particles to be uniformly
dispersed, and also, a coating layer having high adhesion may be
formed on a substrate film to increase the stability of the
separator. The weight average molecular weight of the
polyvinylidene fluoride-hexafluoropropylene copolymer usable in the
present invention may be 1,000,000 g/mol or less, or for example,
1,000,000 to 1,200,000 g/mol, but not specifically limited thereto.
Within the molecular weight range, the adhesion between the coating
layer and the polyolefin-based substrate film may be enhanced, so
that the heat-sensitive polyolefin-based substrate film may be
effectively prevented from shrinking by heat, and additionally, the
adhesion between the coating layer and an electrode may also be
improved to prevent the short-circuit of a cathode and an anode.
Further, in case of using the polyvinylidene fluoride homopolymer
within the molecular weight range, the polyvinylidene fluoride
homopolymer may dissolve well even with a small amount of DMF,
thereby facilitating the drying of the coating layer.
[0085] Further, for example, in case of coating the separator with
a coating agent further containing polyvinylidene
fluoride-hexafluoropropylene copolymer, the electrolyte
impregnation property of the separator may be improved to produce a
battery having excellent electrical output. The weight average
molecular weight of the polyvinylidene fluoride copolymer usable in
the present invention may be 800,000 g/mol or more, or for example,
600,000 to 800,000 g/mol, but not specifically limited thereto. In
case of using the polyvinylidene fluoride-hexafluoropropylene
copolymer within the molecular weight range, a separator having a
sufficiently improved electrolyte impregnation property may be
prepared, and using the separator, a battery efficiently generating
electrical output may be produced.
[0086] In the polyvinylidene fluoride-hexafluoropropylene copolymer
used in the present invention, each content of the polyvinylidene
fluoride and hexafluoropropylene is not specifically limited, but
the hexafluoropropylene may be contained in 0.1 to 40% by weight,
based on the total weight of the copolymer.
[0087] The method of preparing a coated separator according to one
exemplary embodiment of the present invention may include applying
a coating composition containing polyamic acid, a low boiling point
solvent, and a high boiling point solvent on one or both surfaces
of a polyolefin-based substrate film, and drying it to form a
coating layer.
[0088] The preparation of a coating composition containing polyamic
acid, a low boiling point solvent, and a high boiling point solvent
in the present invention may include mixing 1 to 30% by weight of
the polyamic acid, based on the total weight of the coating
composition, with 70 to 99% by weight of the low boiling point
solvent and the high boiling point solvent, based on the total
solvent, and stirring it at 10 to 40.degree. C. for 30 minutes to 5
hours.
[0089] The coating composition may further include inorganic
particles. Therefore, the preparation of the coating composition
may include mixing the polyamic acid, the low boiling point
solvent, the high boiling point solvent, and the inorganic
particles, and stirring it at 10 to 40.degree. C. for 30 minutes to
5 hours. Herein, the content of the inorganic particles may be 10
to 40% by weight, based on the total weight of the coating
composition.
[0090] Alternatively, the coating composition may be prepared by
dispersing the inorganic particles in a dispersion medium to
prepare an inorganic dispersion, and mixing it with a high
molecular solution containing the polyamic acid, the low boiling
point solvent and the high boiling point solvent. In case of
separately preparing the inorganic dispersion as such, the
dispersion property and solution stability of the inorganic
particles and the polyamic acid may be improved. Therefore, in
another embodiment, the coating composition of the present
invention may be prepared by mixing the polyamic acid ingredient
and the inorganic particles prepared in the state of being
dissolved or dispersed in an appropriate solvent, respectively.
[0091] For example, the coating composition may be prepared in a
manner of preparing solutions of polyamic acid, polyvinylidene
fluoride homopolymer and/or polyvinylidene
fluoride-hexafluoropropylene copolymer each dissolved in an
appropriate solvent, and an inorganic dispersion in which inorganic
particles are dispersed, respectively, then mixing them with an
appropriate solvent.
[0092] After mixing the polyamic acid solution, the inorganic
dispersion, and the solvent, the mixture may be sufficiently
stirred using a ball mill, a beads mill, a screw mixer, or the like
to prepare a coating composition in the form of a mixture.
[0093] According to another embodiment of the present invention,
there is provided a separator in which the coating composition is
coated on one or both surfaces of the polyolefin-based substrate
film.
[0094] The method to coat the polyolefin-based substrate film with
the coating agent is not specifically limited, and any method
generally used in the art may be used. The non-limiting example of
the coating method may include a dip coating, a die coating, a roll
coating, a comma coating method, or the like. These methods may be
applied alone or in a combination of two or more. The coating layer
of the separator of the present invention may be formed by, for
example, a dip coating method.
[0095] The coating layer of a mixture of organic and inorganic
materials of the present invention may have a thickness of 0.01 to
20 .mu.m, specifically 1 to 15 .mu.m. Within the thickness range,
the coating layer may be formed to have an adequate thickness to
obtain excellent thermal stability and adhesion, and the separator
may be prevented from being unduly thick entirely, thereby
suppressing an increase of internal resistance of a battery.
[0096] The coating layer may be dried by warm air, hot air or low
humidity air, or vacuum dried, or dried by irradiating far-infrared
radiation, electron beam or the like in the present invention. In
addition, the drying temperature depends on the kind of the
solvent, but may be generally 60 to 120.degree. C. The drying time
also depends on the kind of the solvent, but may be generally 1
minute to 1 hour. In a specific example, the drying may be carried
out at 90 to 120.degree. C. for 1 to 30 minutes, or 1 to 10 minutes
In the present invention, the solvent may be effectively removed
even under a condition of reduced drying time and lower drying
temperature as the above by using the polyamic acid having
excellent solubility in the low boiling point solvent as a coating
composition component.
[0097] After drying, the residual amount of the low boiling point
solvent and the high boiling point solvent in the coated separator
may be 500 ppm or less. Specifically, the residual amount of the
low boiling point solvent and the high boiling point solvent in the
coated separator may be 400 ppm or less. For example, after drying,
the low boiling point solvent may not remain, and the high boiling
point solvent may remain in 500 ppm or less in the coating
layer.
[0098] It is preferred that the substrate film used in the
separator of the present invention is polyolefin-based. The
non-limiting example of the polyolefin-based substrate film may
include a polyethylene substrate film, a polypropylene substrate
film, or the like.
[0099] In case of the separator for a secondary battery, a
substrate film having a shutdown function is preferred, and the
polyolefin-based substrate film used in the separator of the
present invention corresponds to the substrate film having an
excellent shutdown function.
[0100] The polyolefin-based substrate film used in the present
invention may be selected from the group consisting of for example,
a single polyethylene membrane, a single polypropylene membrane, a
double-layered polyethylene/polypropylene membrane, a
triple-layered polypropylene/polyethylene/polypropylene membrane,
and a triple-layered polyethylene/polypropylene/polyethylene
membrane.
[0101] The polyolefin-based substrate film may have a thickness of
1 to 40 .mu.m, more specifically 1 to 30 .mu.m, and still
specifically 1 to 20 .mu.m. In case of using the substrate film
within the thickness range, the prepared separator may have an
adequate thickness which is enough to prevent a short-circuit of a
cathode and an anode of a battery, but not enough to increase the
internal resistance of a battery.
[0102] The polyamic acid of the present invention is not imidated
in the coating layer, and may be present in the form of polyamic
acid.
[0103] The residual amount of the organic solvent in the dried
coating layer of the separator of the present invention may be 500
ppm or less. The organic solvent residual amount refers to a sum of
the residual amounts of the low boiling point solvent and the high
boiling point solvent, if both solvents are used.
[0104] The solvent residual amount in the dried coating layer of
500 ppm or less in the present invention does not numerically
include a value less than zero, and technically refers to a
positive (+) value of 0 to 500 ppm.
[0105] The dried coating layer of the separator of the present
invention refers to a coating layer dried by the drying process at
70 to 120.degree. C., specifically 100 to 120.degree. C. for 1 to
20 minutes, or 1 to 10 minutes, more specifically 1 to 2 minutes,
or dried at 10 to 30.degree. C. for 6 to 48 hours, after coating
the coating agent on the polyolefin-based substrate film.
[0106] In case where the solvent residual amount in the dried
coating layer of the separator is 500 ppm or less, the followings
may be prevented: a problem caused by an excessive amount of the
solvent remaining in the coating layer, that is, an organic binder
component not representing sufficient adhesion, and a problem of
not effectively suppressing the thermal shrinkage of the substrate
film due to reduced adhesion of the coating layer, which
accordingly functions as a factor hindering battery performance
upon charging/discharging a battery which causes the short-circuit
of an electrode when a battery overheats.
[0107] The organic solvent remaining in the dried coating layer of
the present invention may have a boiling point higher than the
melting point of the substrate film of the present invention.
[0108] When measuring a temperature at which a separator breaks by
pulling the separator coated with the polyamic acid with a force of
0.005 N at a heating rate of 5.degree. C./rain (see ASTM E 831),
the breaking temperature may be 180.degree. C. or more. Within the
range, the separator does not shrink well even at high temperature,
so that the stability of the separator and a battery may be
improved. Therefore, in another exemplary embodiment of the present
invention, there is provided a separator including a
polyolefin-based substrate film; and a coating layer containing
polyamic acid formed on one or both surfaces of the substrate film,
wherein the separator has a breaking temperature of 180.degree. C.
or more under a condition of 0.005 N, and a heating rate of
5.degree. C./min.
[0109] The separator coated with the polyamic acid of the present
invention may have, after being left at 200.degree. C. for 1 hour,
thermal shrinkage in a machine direction (MD) or a transverse
direction (TD) of 20% or less, specifically 10% or less, more
specifically 5% or less, respectively. The thermal shrinkage may be
5% or less, for example. Within the range, the short-circuit of an
electrode may be effectively prevented to improve the stability of
a battery.
[0110] The separator coated with the polyamic acid of the present
invention may have, after being left at 150.degree. C. for 1 hour,
thermal shrinkage in a machine direction (MD) or a transverse
direction (TD) of 15% or less, specifically 13% or less, more
specifically 10% or less, respectively. The thermal shrinkage may
be 5% or less, for example. Within the range, the short-circuit of
an electrode may be effectively prevented to improve the stability
of a battery.
[0111] The method to measure the thermal shrinkage of the separator
is not specifically limited, and any method generally used in the
art may be used.
[0112] The non-limiting example of the method of measuring the
thermal shrinkage of the separator is as follows: After a prepared
separator is cut into a size of about 5 cm (MD) x about 5 cm (TD),
and stored in a chamber at 200.degree. C. for 1 hour, the shrinkage
in MD and TD directions of the separator is measured to calculate
the thermal shrinkage.
[0113] The thermal shrinkage at 150.degree. C. may be measured in
the same manner as the above method, except that the chamber at
200.degree. C. is replaced with the chamber at 150.degree. C.
[0114] The separator of the present invention may have thermal
resistance temperature of 200.degree. C. or more. If the separator
has the thermal resistance temperature of 200.degree. C. or more,
an electrode short-circuit phenomenon by heat may be effectively
suppressed, thereby manufacturing a battery having high thermal
safety. `Thermal resistance temperature` used herein, refers to
temperature to which when the separator is exposed for 10 minutes,
the shrinkage of the separator in MD/TD directions is less than
5%.
[0115] According to another embodiment of the present invention,
there is provided an electrochemical battery including a porous
polyolefin-based separator containing the coating layer of a
mixture of organic and inorganic materials, and a cathode and an
anode, and filled with electrolyte.
[0116] The kind of the electrochemical battery is not specifically
limited, and may be any kind known to the art.
[0117] The electrochemical battery of the present invention may be,
specifically, a lithium secondary battery such as a lithium metal
secondary battery, a lithium ion secondary battery, a lithium
polymer secondary batter, a lithium ion polymer secondary battery,
or the like.
[0118] The method of manufacturing the electrochemical battery of
the present invention is not specifically limited, and any method
generally used in the art may be used.
[0119] The non-limiting example of the method of manufacturing the
electrochemical battery is as follows: The battery may be
manufactured in a manner of disposing the polyolefin-based
separator including the coating layer of a mixture of organic and
inorganic materials between a cathode and an anode of the battery,
and then filling it with an electrolyte solution.
[0120] The electrode forming the electrochemical battery of the
present invention may be prepared in the form of binding an
electrode active material to an electrode current collector by a
method generally used in the art.
[0121] The cathode active material of the electrode active material
used in the present invention is not specifically limited, and any
cathode active material generally used in the art may be used.
[0122] The non-limiting example of the cathode active material may
include lithium manganese oxide, lithium cobalt oxide, lithium
nickel oxide, lithium iron oxide, a lithium complex oxide combining
those oxides, or the like.
[0123] The anode active material of the electrode active material
used in the present invention is not specifically limited, and any
anode active material generally used in the art may be used.
[0124] The non-limiting example of the anode active material may
include a lithium adsorption material such as a lithium metal or
lithium alloy, carbon, petroleum coke, activated carbon, graphite,
or other carbons.
[0125] The electrode current collector used in the present
invention is not specifically limited, and any electrode current
collector generally used in the art may be used.
[0126] The non-limiting example of the materials of the cathode
current collector of the electrode current collector may include
foil prepared from aluminum, nickel or a combination thereof, or
the like.
[0127] The non-limiting example of the materials of the anode
current collector of the electrode current collector may include
foil prepared from copper, gold, nickel, a copper alloy or a
combination thereof, or the like.
[0128] The electrolyte solution used in the present invention is
not specifically limited, and any electrolyte for an
electrochemical battery generally used in the art may be used.
[0129] The electrolyte solution may be one wherein a salt having a
structure such as A.sup.+B.sup.- is dissolved or dissociated in an
organic solvent.
[0130] The non-limiting example of A.sup.+ may include a cation
selected from the group consisting of an alkali metal cation such
as Li.sup.+, Na.sup.+ or K.sup.+, or a combination thereof.
[0131] The non-limiting example of B.sup.- may include an anion
selected from the group consisting of an anion such as
PF.sub.6.sup.-, BF.sub.4.sup.-, Cl.sup.-, Br.sup.-, I.sup.-,
ClO.sub.4.sup.-, AsF.sub.6.sup.-, CH.sub.3CO.sub.2.sup.-,
CF.sub.3SO.sub.3.sup.-, N(CF.sub.3SO.sub.2).sub.2.sup.- or
C(CF.sub.2SO.sub.2).sub.3.sup.-, or a combination thereof.
[0132] The non-limiting example of the organic solvent may include
propylene carbonate (PC), ethylene carbonate (EC), diethyl
carbonate (DEC), dimethyl carbonate (DMC), dipropylcarbonate (DPC),
dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane,
tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethylcarbonate
(EMC), .gamma.-butyrolactone, or the like. These may be used alone
or in a mixture of two or more.
[0133] Hereinafter, the present invention is described in more
detail, by describing the following Examples, Comparative Examples,
and Experimental Examples. However, the Examples, Comparative
Examples, and Experimental Examples are only illustrative of the
present invention, and the disclosure of the present invention is
not construed as being limited thereto.
Examples 1 to 20
Preparation of Separator Having a Coating Layer Containing Polyamic
Acid Formed Thereon
Example 1
(1) Preparation of Coating Composition
[0134] 0.5 mol of 3,3'-diamino diphenyl sulfone (DDS), and
N,N-dimethylacetamide (DMAc) were placed in a four-neck flask
equipped with a stirrer, a temperature controlling device, a
nitrogen gas injection device, and a condenser while passing
nitrogen therethrough, and dissolved with stirring. Next, 0.5 mol
of pyromellitic dianhydride (PMDA) in a solid state was added to
the solution, and the solution was vigorously stirred. Herein, the
solid content by mass ratio was 20% by weight, and the reaction
proceeded for 24 hours while maintaining the temperature less than
25.degree. C. to prepare a polyamic acid solution.
[0135] In order to prepare an inorganic dispersion, 25% by weight
of Al.sub.2O.sub.3 (LS235, Nippon Light Metal Company, Ltd.) was
added to acetone (Daejung Chemical & Metals Co., Ltd.), and
milled at 25.degree. C. for 3 hours using a beads mill to be
dispersed, thereby preparing an inorganic dispersion.
[0136] The thus prepared, polyamic acid solution and inorganic
dispersion were mixed in a weight ratio of polyamic acid
solution:inorganic dispersion:N,N-dimethylacetamide
(DMAc):acetone=1:4.8:0.8:3.4, and stirred at 25.degree. C. for 2
hours with a power mixer to prepare a coating composition.
(2) Preparation of Separator Having Coating Layer Containing
Polyamic Acid Formed Thereon
[0137] The above prepared coating composition was coated on both
surfaces of the polyethylene substrate film having a thickness of
12 .mu.m in a manner of dip coating, and then dried at room
temperature for 24 hours to prepare a separator.
Example 2
[0138] The separator was prepared by the same method as in above
Example 1, except that 1,6-hexamethylenediamine was placed in the
four-neck flask instead of 3,3'-diaminodiphenylsulfone, and the
mixing was carried out in a weight ratio of the prepared polyamic
acid solution:N,N-dimethylacetamide (DMAc):inorganic
dispersion:acetone=0.9:1.5:4.1:3.5, in the preparation of the
coating composition.
Example 3
[0139] The separator was prepared by the same method as in above
Example 1, except that 4,4'-oxydianiline was placed in the
four-neck flask instead of 3,3'-diaminodiphenylsulfone, the solid
content of the polyamic acid solution by mass ratio was 10% by
weight, and the mixing was carried out in a weight ratio of the
prepared polyamic acid solution:N,N-imethylacetamide
(DMAc):inorganic dispersion:acetone=0.9:2.8:4.1:2.2, in the
preparation of the coating composition.
Example 4
[0140] The separator was prepared by the same method as in above
Example 1, except that 0.2 mol of 4,4'-oxydianiline and 0.3 mol of
3,3'-diaminodiphenylsulfone were placed in the four-neck flask
instead of 0.5 mol of 3,3'-diaminodiphenylsulfone, and the mixing
was carried out in a weight ratio of the prepared polyamic acid
solution:N,N-dimethylacetamide (DMAc):inorganic dispersion:
acetone=0.9:1.5:4.1:3.5, in the preparation of the coating
composition.
Example 5
[0141] The separator was prepared by the same method as in above
Example 1, except that 4,4'-diaminodiphenylsulfone was placed in
the four-neck flask instead of 3,3-diaminodiphenylsulfone, in the
preparation of the coating composition.
Example 6
[0142] The separator was prepared by the same method as in above
Example 1, except that 0.375 mol of pyromellitic dianhydride and
0.125 mol of 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride
were used instead of 0.5 mol of pyromellitic dianhydride, and the
mixing was carried out in a weight ratio of the prepared polyamic
acid solution:N,N-dimethylacetamide (DMAc):inorganic
dispersion:acetone=0.9:0.2:4.1:4.7, in the preparation of the
coating composition.
Example 7
[0143] The separator was prepared by the same method as in above
Example 1, except that polyvinylidene fluoride homopolymer
(hereinafter, referred to as `PVdF homopolymer`) solution was
further included, and the mixing was carried out in a weight ratio
of the prepared polyamic acid solution:PVdF homopolymer solution:
N,N-dimethylacetamide (DMAc):inorganic dispersion:
acetone=0.5:0.7:0.7:4.1:4.0, in the preparation of the coating
composition.
[0144] The PVdF homopolymer solution was prepared by adding 10% by
weight of PVdF homopolymer (5130, Solvay) to DMF (Daejung Chemical
& Metals Co., Ltd.), and stirring it at 25.degree. C. for 4
hours using a stirrer.
Example 8
[0145] The separator was prepared by the same method as in above
Example 1, except that polyvinylidene fluoride-hexafluoropropylene
copolymer (hereinafter, referred to as `PVdF-HFP copolymer`)
solution was further included, and the mixing was carried out in a
weight ratio of the prepared polyamic acid solution:PVdF-HFP
copolymer solution:N,N-dimethylacetamide (DMAc):inorganic
dispersion: acetone=0.5:0.7:1.4:4.1:3.3, in the preparation of the
coating composition.
[0146] The PVdF-HFP copolymer solution was prepared by adding 10%
by weight of PVdF-HFP copolymer having a weight average molecular
weight of 700,000 g/mol (21216, Solvay) to acetone (Daejung
Chemical & Metals Co., Ltd.), and stirring it at 25.degree. C.
for 4 hours using a stirrer.
Example 9
[0147] The separator was prepared by the same method as in above
Example 1, except that 0.45 mol of pyromellitic dianhydride and
0.05 mol of 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride
were used instead of 0.5 mol of pyromellitic dianhydride, and the
mixing was carried out in a weight ratio of the prepared polyamic
acid solution:N,N-dimethylacetamide (DMAc):inorganic
dispersion:acetone=0.9:0.3:4.1:4.7, in the preparation of the
coating composition.
Example 10
[0148] The separator was prepared by the same method as in above
Example 1, except that 0.35 mol of pyromellitic dianhydride and
0.15 mol of 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride
were used instead of 0.5 mol of pyromellitic dianhydride, and the
mixing was carried out in a weight ratio of the prepared polyamic
acid solution:N,N-dimethylacetamide (DMAc):inorganic
dispersion:acetone=0.9:0.1:4.1:4.7, in the preparation of the
coating composition.
Example 11
[0149] The separator was prepared by the same method as in above
Example 1, except that 0.3 mol of pyromellitic dianhydride and 0.2
mol of 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride were
used instead of 0.5 mol of pyromellitic dianhydride, and the mixing
was carried out in a weight ratio of the prepared polyamic acid
solution:inorganic dispersion:acetone=0.9:4.1:4.7, in the
preparation of the coating composition.
Example 12
[0150] The separator was prepared by the same method as in above
Example 1, except that 1,2,3,4-Butanetetracarboxylic dianhydride
was used instead of pyromellitic dianhydride, in the preparation of
the coating agent.
Example 13
[0151] The separator was prepared by the same method as in above
Example 1, except that 1,2,4,5-cyclohexanetetracarboxylic
dianhydride was used instead of pyromellitic dianhydride, in the
preparation of the coating agent.
Example 14
[0152] The separator was prepared by the same method as in above
Example 1, except that 4,4'-carbonyldiphthalic dianhydride was used
instead of pyromellitic dianhydride, in the preparation of the
coating agent.
Example 15
[0153] The separator was prepared by the same method as in above
Example 1, except that 4,4'-(hexafluoroisopropylidene)diphthalic
dianhydride, and 1,16-hexadecanediamine were used instead of
pyromellitic dianhydride, and 3,3'-diamino diphenyl sulfone,
respectively, in the preparation of the coating agent.
Example 16
[0154] The separator was prepared by the same method as in above
Example 1, except that 4,4'-(hexafluoroisopropylidene)diphthalic
dianhydride, and 1,4-cyclohexyldiamine were used instead of
pyromellitic dianhydride, and 3,3'-diamino diphenyl sulfone,
respectively, in the preparation of the coating agent.
Example 17
[0155] The separator was prepared by the same method as in above
Example 6, except that 4,4'-diamino diphenyl sulfone was used
instead of 3,3'-diamino diphenyl sulfone, in the preparation of the
coating agent.
Example 18
[0156] The separator was prepared by the same method as in above
Example 6, except that 1,2,4,5-cyclohexanetetracarboxylic
dianhydride was used instead of pyromellitic dianhydride, in the
preparation of the coating agent.
Example 19
[0157] The separator was prepared by the same method as in above
Example 6, except that 4,4'-isopropylidenediphthalic dianhydride
was used instead of 4,4'-(hexafluoroisopropylidene)diphthalic
dianhydride, in the preparation of the coating agent.
Example 20
[0158] The separator was prepared by the same method as in above
Example 1, except that
3-[3-(3-aminophenyl)sulfonylphenyl]sulfonylaniline was used instead
of, and 0.375 mol of pyromellitic dianhydride and 0.125 mol of
4,4'-(hexafluoroisopropylidene)diphthalic dianhydride were used
instead of 0.5 mol of pyromellitic dianhydride, in the preparation
of the coating agent.
[0159] The solvent ratios used in the above Examples are shown in
the following Table 1.
TABLE-US-00001 TABLE 1 Acetone DMAc Example 1 8.15 1.85 Example 2
7.3 2.7 Example 3 6 4 Example 4 7.3 2.7 Example 5 8.15 1.85 Example
6 8.94 1.06 Example 9 8.85 1.15 Example 10 9.04 0.96 Example 11
9.15 0.85 Example 12 8.15 1.85 Example 13 8.15 1.85 Example 14 8.15
1.85 Example 15 8.15 1.85 Example 16 8.15 1.85 Example 17 8.94 1.06
Example 18 8.94 1.06 Example 19 8.94 1.06 Example 20 8.15 1.85
Comparative Examples 1 and 2
Preparation of Separator Having a Coating Layer not Containing
Polyamic Acid Formed Thereon
Comparative Example 1
[0160] A coating agent prepared by mixing in a compositional ratio
of the PVdF-HFP copolymer solution of Example 8: the inorganic
dispersion of Example 1: acetone=2:4.8:3.2, and stirring it at
25.degree. C. for 2 hours with a power mixer, was coated on both
surfaces of a polyethylene substrate film having a thickness of 14
.mu.m in a manner of dip coating, and dried to prepare the
separator.
Comparative Example 2
[0161] The separator was prepared in the same method as in
Comparative Example 1, except that the PVdF homopolymer solution of
Example 7 was used instead of the PVdF-HFP copolymer solution.
TABLE-US-00002 TABLE 2 Molecular Polyamic acid weight Ex- ample 1
##STR00024## 40,000~60,000 Ex- ample 2 ##STR00025## 60,000~80,000
Ex- ample 3 ##STR00026## 90,000~110,000 Ex- ample 4 ##STR00027##
80,000~100,000 x:y = 4:6 Ex- ample 5 ##STR00028## 60,000~80,000 Ex-
ample 6 ##STR00029## 60,000~80,000 x:y = 7.5:2.5 Ex- ample 7
##STR00030## 40,000~60,000 Ex- ample 8 ##STR00031## 40,000~60,000
Ex- ample 9 ##STR00032## 60,000~80,000 x:y = 9:1 Ex- ample 10
##STR00033## 60,000~80,000 x:y = 7:3 Ex- ample 11 ##STR00034##
60,000~80,000 x:y = 6:4 Ex- ample 12 ##STR00035## 40,000~60,000 Ex-
ample 13 ##STR00036## 50,000~70,000 Ex- ample 14 ##STR00037##
60,000~80,000 Ex- ample 15 ##STR00038## 40,000~60,000 Ex- ample 16
##STR00039## 60,000~80,000 Ex- ample 17 ##STR00040## 70,000~90,000
x:y = 7.5:2.5 Ex- ample 18 ##STR00041## 70,000~90,000 x:y = 7.5:2.5
Ex- amples 19 ##STR00042## 60,000~80,000 x:y = 7.5:2.5 Ex- ample 20
##STR00043## 70,000~90,000 x:y = 7.5:2.5
Experimental Example 1
Solubility in Low Boiling Point and High Boiling Point Solvents
According to Structure of Polyamic Acid
[0162] In order to evaluate the solubility of the polyamic acids
prepared according to the above Examples each having different
structure in a low boiling point solvent and a high boiling point
solvent, the ratios of the low boiling point solvent and the high
boiling point solvent at which the solvents are maintained in the
most clear state when each of the polyamic acid is dissolved
therein, were measured. Acetone (Daejung Chemical & Metals Co.,
Ltd) was used as the low boiling point solvent, and
N,N-dimethylacetamide (DMAc) was used as the high boiling point
solvent.
[0163] As to the low boiling point solvent and the high boiling
point solvent of each of the polyamic acids, the results of
measuring the acetone: DMAc ratios at which the most clear state is
maintained, are shown in the following Table 3:
TABLE-US-00003 TABLE 3 Examples Acetone:DMAc 1 8.75:1.25 2 7.5:2.5
3 6:4 4 6.66:3.34 5 8.33:1.67 6 9.09:0.91 9 8.88:.1.12 10 9.44:0.56
11 Dissolved in an electrolyte solution 12 9:1 13 8.88:.1.12 14 9:1
15 9.33:0.67 16 9.23:0.77 17 9.33:0.67 18 9.41:0.59 19 9.41:0.59 20
9.47:0.53
[0164] As shown in the above Table 3, it was confirmed that the
polyamic acids prepared in above Examples 1 to 20 have excellent
solubility in acetone which is the low boiling point solvent, and
thus, are suitable for being utilized in the coating composition of
the separator.
[0165] In particular, the polyamic acid having the highest
solubility in acetone was those prepared according to Examples 6,
9, 10 and 11, and when comparing these polyamic acids, it was
confirmed that as the ratio of
4,4'-(hexafluoroisopropylidene)diphthalic dianhydride increases,
the solubility of the polyamic acid in acetone increases.
[0166] However, it was observed that the polyamic acid of Example
11 dissolved also in an electrolyte solution of a battery, as a
result of its excessively increased solubility in the low boiling
point solvent.
Experimental Example 2
Measurement of Thickness and Coated Weight of Coating Layer
[0167] The following method was carried out in order to measure the
thicknesses and the coated weights of the coating layers of the
separators prepared in above Examples 1 to 20, and Comparative
Examples 1 and 2.
[0168] First, the thickness of each coating layer was measured
using a SEM cross section image of each coating layer and micro
calipers. Then, each coating layer was cut into a size of 10 cm
(MD).times.20 cm (TD) and its weight was measured with an
electronic scale to calculate the coated weight. The results of
measuring the thicknesses and the coated weights are shown in the
following Table 5.
Experimental Example 3
Measurement of Thermal Shrinkage of Separator
[0169] The following method was carried out in order to measure the
thermal shrinkage of the separators prepared in above Examples 1 to
20, and Comparative Examples 1 and 2.
[0170] Each separator prepared according to the above Examples and
Comparative Examples was cut into a size of 5 cm (MD).times.5 cm
(TD), thereby producing a total of seven samples. Each of the
samples was stored in chambers at 150.degree. C. and 200.degree. C.
for 1 hour, and then shrinkage amounts in MD and TD directions of
each sample were measured to calculate the thermal shrinkage. The
results of measuring the thermal shrinkage are shown in the
following Table 5.
Experimental Example 4
Measurement of Air Permeability
[0171] The air permeability of the separators prepared in above
Examples 1 to 20, and Comparative Examples 1 and 2 was measured by
determining the time to pass 100 cc of air through the separator
using EG01-55-1MR (Asahi Seiko Co., Ltd.).
Experimental Example 5
Electrolyte Solution Wettability of Separator
[0172] The following method was carried out in order to measure the
electrolyte solution wettability of the separators prepared in
above Examples 1 to 20, and Comparative Examples 1 and 2.
[0173] Each separator prepared according to the above Examples and
Comparative Examples was cut into a square of 3 cm (MD).times.3 cm
(TD), thereby producing a total of seven samples. After each sample
was floated on the surface of an electrolyte solution in a beaker,
time to be completely soaked by the electrolyte solution was
measured.
[0174] The time to be soaked by the electrolyte solution is shown
in the following Table 5.
Experimental Example 6
Measurement of DMAc Solvent Residual Amount in Coating Layer of
Separator
[0175] In order to measure the organic solvent residual amounts in
the coating layers of the dried separators prepared in above
Examples 1 to 20, and Comparative Examples 1 and 2, gas
chromatography (HP-6890) was performed under conditions described
in the following Table 4, and the results are shown in Table 5.
TABLE-US-00004 TABLE 4 Parameters Conditions Column Front:
HP-INNOWax (length 30M, ID 0.53 mm, film thickness 1.00 .mu.m)
Back: HP-1 (length 30M, ID 0.53 mm, film thickness 0.88 .mu.m)
Temperature 40.degree. C. (4 min.) .fwdarw.20.degree. C./min
.fwdarw. 250.degree. C. (4 min.) and time Flow rate 10 mL/min
Injector S/SL Injector Split ratio 5:1 Detector FID Injection 1
volume Injector 200.degree. C. temperature
TABLE-US-00005 TABLE 5 Thick- Coated nesses of weights of Solvent
Electrolyte Air Coating coating residual solution permeability
Thermal shrinkage of separator (%) layer layer amount wettability
(Sec/100 150.degree. C., 1 hour 200.degree. C., 1 hour (.mu.m)
(g/m.sup.2) (ppm) (sec) cc) TD MD TD MD Example 1 6.1 7.3 120 30
550 0.5 0.6 0.9 1.0 Example 2 6.6 7.5 115 40 650 0.5 0.6 0.9 1.0
Example 3 6.9 7.7 310 45 790 0.3 0.6 0.8 0.9 Example 4 6.8 7.6 180
35 650 0.4 0.5 0.9 1.0 Example 5 6.4 7.6 125 34 600 0.5 0.5 1.0 1.0
Example 6 6.2 7.2 55 31 403 0.5 0.7 1.1 1.3 Example 7 8.1 8.4 80 55
426 1.1 1.1 2.0 2.1 Example 8 7.8 8.1 85 38 438 1.4 1.3 2.5 3.0
Example 9 6.9 7.8 55 32 380 0.5 0.7 0.9 1.0 Example 10 6.3 7.5 56
32 380 0.5 0.6 1.0 1.1 Example 11 6.0 7.0 55 30 350 0.6 0.7 1.1 1.2
Example 12 6.2 7.3 115 35 360 0.7 0.5 0.9 0.8 Example 13 6.7 7.5
120 37 340 0.6 0.7 0.9 1.0 Example 14 6.5 7.4 120 40 330 0.5 0.8
0.8 1.1 Example 15 6.1 7.1 120 41 290 0.6 1.0 0.9 1.2 Example 16
6.3 7.3 115 40 295 0.5 0.7 1.0 1.3 Example 17 6.0 7.0 60 38 270 1.3
1.4 2.0 2.5 Example 18 6.0 7.0 55 37 265 1.4 1.5 2.5 3.5 Example 19
6.0 7.0 60 32 280 0.6 0.8 1.2 1.3 Example 20 6.0 7.0 95 40 295 1.0
1.2 1.9 2.1 Comparative 8.8 8.5 -- 65 414 21.5 26.0 -- -- Example 1
Comparative 9.0 9.0 -- >300 455 10.0 12.5 -- -- Example 2
[0176] As shown in the above Table 5, it is confirmed that the
separators of Examples 1 to 20 containing polyamic acid in the
coating layers have less thermal shrinkage amounts, and thus, have
excellent thermal resistance, as compared with those of Comparative
Examples 1 and 2 not containing polyamic acid.
[0177] Further, when comparing the separators of Examples 6, 9, 10
and 11, as the ratio of 4,4'-(hexafluoroisopropylidene)diphthalic
dianhydride increases, the solubility of the polyamic acid in
acetone increases (see Table 1), and thus, it was confirmed that as
the solvent is easily volatilized, drying performance is improved,
and as a result, the solvent residual amount of the coating layer
is small, so that the air permeability becomes excellent.
[0178] Meanwhile, after a lithium secondary battery was
manufactured using the separator according to Example 1, battery
capacity change by the use of the battery was observed, and as a
result, it was confirmed that a battery capacity was hardly changed
even after about 350 cycles (FIG. 1).
[0179] Accordingly, it is considered that in case of utilizing the
separator of the present invention in an electrochemical battery,
thermal stability of the battery may be improved, such that a
battery life is extended over a long term.
Experimental Example 7
Measurement of Shutdown Function of Separator
[0180] In order to measure the shutdown function of each separator
according to above Example 1 and Comparative Example 1, the
impedance of the separators prepared in Example 1 and Comparative
Example 1 was measured at 1 kHz and a heating rate of 10.degree.
C./min using 3522-50 LCR HiTester (HIOKI) (FIG. 2).
[0181] It is shown in FIG. 2 that the shutdown temperatures of
Example 1 and Comparative Example 1 were similar, and when
comparing it with the results of Experimental Example 3, it was
confirmed that the separator of Example 1 having a coating layer
containing polyamic acid formed thereon had improved thermal
resistance, while still maintaining the shutdown function
excellent, and thus, the high temperature safety of the separator
may be secured.
Experimental Example 8
Measurement of TMA (Thermal Mechanical Analysis)
[0182] In order to measure TMA of each separator according to above
Examples and Comparative Examples, the temperature at which each
separator breaks was measured using TA Instruments (TMA Q400) by
pulling each separator with a force of 0.005 N at a heating rate of
5.degree. C./min (see ASTM E 831) (FIG. 3). The results are shown
in the following Table 6.
[0183] It is shown in FIG. 3 that the separator of Comparative
Example 1 was observed to have pore shrinkage in the vicinity of
shutdown temperature (about 130.degree. C.), and represented a
breaking property at about 150.degree. C. or more. On the contrary,
the separator of Example 1 hardly showed shrinkage up to
191.degree. C., due to the high temperature safety of the coating
layer containing polyamic acid. Further, according to Table 6, the
separator including the polyamic acid coating layer showed a
breaking temperature of 180.degree. C. or more.
TABLE-US-00006 TABLE 6 Breaking temperature (.degree. C.) Example 1
191 Example 2 190 Example 3 188 Example 4 187 Example 5 190 Example
6 188 Example 7 176 Example 8 179 Example 9 188 Example 10 190
Example 11 189 Example 12 188 Example 13 187 Example 14 190 Example
15 190 Example 16 189 Example 17 187 Example 18 188 Example 19 191
Example 20 188 Comparative 145 Example 1 Comparative 144 Example
2
Experimental Example 9
Measurement of High-Rate Discharge Property (C-Rate)
[0184] The high-rate discharge property of each separator according
to Example 1 and Comparative Example 1 was measured (FIG. 4). The
high-rate discharge property was measured by observing a capacity
change rate by determining the capacities of a battery having a
capacity of 850 mAh, wherein the capacity was determined after
charging for 2 hours and then discharging for 5 hours (0.2 C),
after charging for 2 hours and then discharging for 2 hours (0.5
C), after charging for 2 hours and then discharging for hour (1 C),
and after charging for 2 hours and then discharging for 30 minutes
(2 C), using a charge/discharge tester (TOSCAT-3600, TOYO Systems
Co., Ltd.).
[0185] It is shown in FIG. 4 that the separator of Example 1
represented a much excellent high-rate discharge property as
compared with the separator of Comparative Example 1. As the
high-rate discharge property is superior, the output property of a
battery is improved, and thus, the separator of Example 1 may
significantly contribute to improved safety of a battery, and also
development of a higher output battery, due to an excellent high
temperature property.
* * * * *