U.S. patent application number 14/418059 was filed with the patent office on 2015-10-22 for organic/inorganic complex coating porous separator and secondary battery using the same.
This patent application is currently assigned to SAMSUNG TOTAL PETROCHEMICALS CO., LTD. The applicant listed for this patent is SAMSUNG TOTAL PETROCHEMICALS CO., LTD.. Invention is credited to Chang Hyun CHOI, Jae Yong HYUN, Do Hoon LEE, Jin A YOO.
Application Number | 20150303427 14/418059 |
Document ID | / |
Family ID | 49220932 |
Filed Date | 2015-10-22 |
United States Patent
Application |
20150303427 |
Kind Code |
A1 |
HYUN; Jae Yong ; et
al. |
October 22, 2015 |
Organic/Inorganic Complex Coating Porous Separator And Secondary
Battery Using The Same
Abstract
There is provided an organic/inorganic complex coating porous
separator including a porous substrate, and an organic/inorganic
complex coating layer formed in a single layer or multiple layers
on a single surface or both surfaces of the porous substrate or at
least a part of a pore portion of the porous substrate using a
coating solution comprising a binder dispersed or suspended in a
certain size and selectively comprising inorganic particles, and a
secondary battery including the same. According to the present
invention, since the coating solution comprising the binder
dispersed in a certain size or less in a solvent is coated/dried on
the porous substrate, a organic/inorganic complex coating porous
separator having excellent air permeability and adhesive strength
and a secondary battery including the organic/inorganic complex
coating porous separator are provided.
Inventors: |
HYUN; Jae Yong; (Dangjin-si,
KR) ; YOO; Jin A; (Incheon, KR) ; LEE; Do
Hoon; (Seosan-si, KR) ; CHOI; Chang Hyun;
(Seoul, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SAMSUNG TOTAL PETROCHEMICALS CO., LTD. |
Seosan-si |
|
KR |
|
|
Assignee: |
SAMSUNG TOTAL PETROCHEMICALS CO.,
LTD
Seosan-si
KR
|
Family ID: |
49220932 |
Appl. No.: |
14/418059 |
Filed: |
November 7, 2013 |
PCT Filed: |
November 7, 2013 |
PCT NO: |
PCT/KR2013/010038 |
371 Date: |
January 28, 2015 |
Current U.S.
Class: |
429/145 ;
429/144 |
Current CPC
Class: |
H01M 2/166 20130101;
H01M 10/0525 20130101; H01M 2220/20 20130101; H01M 10/052 20130101;
H01M 2/1606 20130101; H01M 2/1646 20130101; H01M 2/145 20130101;
H01M 2/18 20130101; H01M 2220/30 20130101; H01M 2/1686
20130101 |
International
Class: |
H01M 2/16 20060101
H01M002/16; H01M 10/052 20060101 H01M010/052 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 12, 2013 |
KR |
10-2013-0015059 |
Claims
1. A coating porous separator comprising: a porous substrate; and a
coating layer formed in a single layer or multiple layers on one or
more regions selected from the group consisting of a single surface
or both surfaces of the porous substrate or at least a part of a
pore portion of the porous substrate using a coating solution
comprising a binder dispersed or suspended in the form of particles
in a solvent, wherein a mean particle diameter of the binder
dispersed or suspended in the solvent is less than one and a half
times a mean pore diameter of the porous substrate.
2. The coating porous separator of claim 1, wherein the coating
solution further comprises dispersed inorganic particles.
3. The coating porous separator of claim 2, wherein the mean
particle diameter of the binder is a half or less of a mean
diameter of the inorganic particles.
4. The coating porous separator of claim 1, wherein the binder is
one or two or more selected from latex or emulsions or suspensions
formed by dispersing polymer compounds selected from the group
consisting of polystyrene-based, styrene butadiene-based,
nitrile-based, polyvinyl chloride-based, polyolefin-based,
acryl-based, acetate-based, polyvinylidene fluoride-based,
ethylene-vinyl acetate-based, polyvinyl butyral-based,
polytetrafluoro ethylene-based, polyimide-based, polyethylene
oxide-based, cellulose-based, polyvinyl alcohol-based, and
starch-based polymers and copolymers, in an organic solvent or a
water-based solvent.
5. The coating porous separator of claim 1, wherein the inorganic
particles include one or two or more selected from the group
consisting of SnO.sub.2, BaTiO.sub.2, Al.sub.2O.sub.3, CeO.sub.2,
SiO.sub.2, TiO.sub.2, Li.sub.3PO.sub.4, NiO, ZnO, MgO,
Mg(OH).sub.2, CaO, ZrO.sub.2, and Y.sub.2O.sub.3, and have a sphere
shape, a plate shape, or an irregular shape having a mean particle
diameter of 0.1 to 5 .mu.m.
6. The coating porous separator of claim 1, wherein in the coating
solution, a weight ratio of the inorganic particles:the binder is
4:1 to 140:1.
7. The coating porous separator of claim 1, wherein the coating
solution further comprises a second organic binder to be dissolved
in the solvent, and wherein the second organic binder includes one
or two or more selected from the group consisting of phosphoric
ester, phosphoric acryl-based copolymer, modified
polyacrylate-based copolymer, modified polyacrylic acid-based
copolymer, polyester- and amine amide-based copolymer,
polycarboxylic acid-based copolymer, polyalkylol- and amino
amide-based copolymer, siloxane- and acryl-based copolymer,
siloxane- and carboxylic acid-based copolymer, polyalkoxylate-based
copolymer, acryl- and ether-based copolymer, and metallic salts
thereof.
8. The coating porous separator of claim 1, wherein the coating
solution further comprises one or more additives selected from the
group consisting of a polymer dispresion agent, a wetting agent, an
antifoaming and defoaming agent, a leveling agent, a thickener, a
rheology additive, an adhesion promoter, an additive for surface,
and a UV absorber.
9. The coating porous separator of claim 1, wherein the porous
substrate has a thickness of 1 to 100 .mu.m and a porosity of 5 to
90%.
10. A secondary battery comprising the coating separator according
to claim 1.
11. The secondary battery of claim 10, wherein the secondary
battery is a lithium secondary battery.
12. The secondary battery comprising the coating separator
according to claim 2.
13. The secondary battery of claim 12, wherein the secondary
battery is a lithium secondary battery.
14. The secondary battery comprising the coating separator
according to claim 3.
15. The secondary battery of claim 14, wherein the secondary
battery is a lithium secondary battery.
16. The secondary battery comprising the coating separator
according to claim 4.
17. The secondary battery of claim 16, wherein the secondary
battery is a lithium secondary battery.
18. The secondary battery comprising the coating separator
according to claim 5.
19. The secondary battery of claim 18, wherein the secondary
battery is a lithium secondary battery.
20. The secondary battery comprising the coating separator
according to claim 6.
21. The secondary battery of claim 20, wherein the secondary
battery is a lithium secondary battery.
22. The secondary battery comprising the coating separator
according to claim 7.
23. The secondary battery of claim 22, wherein the secondary
battery is a lithium secondary battery.
24. The secondary battery comprising the coating separator
according to claim 8.
25. The secondary battery of claim 24, wherein the secondary
battery is a lithium secondary battery.
26. The secondary battery comprising the coating separator
according to claim 9.
27. The secondary battery of claim 26, wherein the secondary
battery is a lithium secondary battery.
Description
TECHNICAL FIELD
[0001] The present invention relates to a separator used in a
secondary battery and more particularly, to a porous separator in
which an organic/inorganic complex coating layer is applied to a
porous substrate, and a secondary battery including the same.
BACKGROUND ART
[0002] Lithium ion secondary batteries are basically comprised of
an anode, a cathode, a separator, and an electrolyte, and have been
widely applied to small-sized electronic devices, for example,
mobile phones, notebook computers, and the like, as high energy
density energy storage devices which can be charged and discharged
by reversible conversion between chemical energy and electric
energy. In recent years, in order to deal with environmental
issues, high oil prices, and energy efficiency and storage,
application of the lithium ion batteries has been rapidly expanded
to hybrid electric vehicles (HEV), plug-in EV, e-bikes, and energy
storage systems (ESS).
[0003] Although the lithium ion batteries are stable
electrochemical devices insulated by separators, short circuit
between an anode and a cathode may be caused by internal or
external abnormalities of the batteries or by shocks and there is a
possibility of heating and explosion. Therefore, ensuring
thermal/chemical stability of the separators as insulators is the
most important consideration.
[0004] Further, in recent years, along with an increasing demand
for high capacity and high power output, stability of batteries,
that is, stability in explosion and fire, becomes more important.
In order to ensure stability of a battery, voltage, current,
impedance, temperature, and the like, of a battery cell are
generally controlled by an electronic protection circuit or a
battery management system (BMS), thereby such attempts responding
to abnormalities, such as over charge and over current, of the
battery have been made.
[0005] A polyolefin-based separator commercially used a lot in
lithium secondary batteries is a porous film that prevents short
circuit between an anode and a cathode and provides pores serving
as a passage of lithium ions. Polyolefin-based separators
manufactured by a wet method or a dry method have been widely used
commercially.
[0006] The wet method is a method including mixing, melting,
extruding inorganic particles or oil components with polyolefin in
an extruder to prepare a sheet, and forming a thin film by
simultaneous or successive biaxial orientation using a roller or a
tenter, and extracting the inorganic particles or oil components
with a solvent to form a porous film. In this method, polyethylene
(PE) among polyolefins is mainly used to form a film. On the other
hand, the dry method is a method of forming a porous film by
melting and extruding a resin and then orienting the resultant with
a roller or a tenter without using an organic solvent, and
generally uses polypropylene (PP) and may use polyethylene as
necessary.
[0007] In a process for preparing a porous separator, except a
non-woven separator, a polyolefin porous separator, in which a
porous substrate is generally prepared by a film orientation
process, cannot avoid a change in volume such as contraction or
fusion of its separator when a temperature of a battery is
increased to 100.degree. C. or more due to an internal or external
stimulus, and, thus, an electrical short circuit between an anode
and a cathode may cause explosion. Further, if the separator is
broken due to dendrite growth within the battery, an internal short
circuit may induce explosion of the battery. There is disclosed a
coating separator in which in order to suppress thermal contraction
caused by high temperature and instability of the battery caused by
dendrite, inorganic particles together with a binder are coated on
one or both surfaces of the substrate of the porous separator, and,
thus, the inorganic particles suppresses a contraction rate of the
substrate and the separator is more stable due to the inorganic
coating layer.
[0008] In this case, if an organic/inorganic coating layer applied
to the porous substrate is not uniformly coated on the porous
substrate, when the coating layer is assembled in a secondary
battery or within the battery, a part of the inorganic coating
layer can be easily separated due to coating defects on the
surface. Such separation can decrease stability of the battery.
Therefore, a coating system for more uniform organic/inorganic
coating is needed to form a uniform inorganic coating layer and
ensure an excellent battery property.
[0009] As a conventionally well-known technology of an
organic/inorganic coating separator, a method for preparing an
organic/inorganic coating porous separator by coating
organic/inorganic slurry (PVDF-CTFE/BaTiO.sub.3 or
PVDF-CTFE/Al.sub.2O.sub.3) with an organic solvent is described in
Korean Patent No. 10-0775310. A process of this patent is identical
with a conventional electrode solution molding process using a
great amount of an N-methylpyrrolidone (NMP) solvent or acetone as
a dispersion medium.
[0010] Typically, an organic solvent dissolves a binder (PVDF-CTFE)
to provide an excellent adhesive property between inorganic
particles in powder form when it evaporates. Slurry prepared from a
binder solution in an organic solvent provides interconnectivity
among a porous substrate, an organic/inorganic coating layer, and
inorganic particles within the inorganic coating layer. The
components connected as such can endure contraction of a porous
separator caused by heating and an external physical shock (event)
without losing the interconnectivity during a battery is assembled
and operated.
[0011] Further, inorganic particles typically has a certain
distribution size, and when a binder is completely dissolved in a
solvent and the binder has an excellent compatibility with surfaces
of the inorganic particles, as the solvent evaporates, the binder
sufficiently covers the surfaces of the inorganic particles. Thus,
a sufficient adhesive strength between the inorganic particles can
be obtained, and even if the binder completely dissolved in the
solvent does not have a high wettability with respect to a porous
substrate, the binder solution infiltrates into a porous structure
and has a sufficient physical adhesive strength with respect to the
porous substrate. However, in this case, in order for the binder
solution to easily infiltrate into pores of the porous structure
and exhibit a relatively sufficient adhesive strength between the
inorganic substance and a surface of the porous substrate, the
binder in a sufficient amount may be needed, or gel is formed as
the solvent volatilizes. Thus, a solvent-impermeable space is
generated, resulting in non-uniformity of an organic/inorganic
coating layer, which may cause deterioration in battery property.
Further, if a concentration of the binder in slurry is increased, a
viscosity of the slurry is highly increased, which makes it
difficult to prepare an organic/inorganic complex layer of a thin
film, and a drying process may require a high temperature. If a low
viscosity of the slurry is maintained, an adhesive strength with
respect to a porous substrate or between inorganic substances is
decreased. Thus, the inorganic particles are easily separated. For
this reason, in many cases, a binder dispersed in a certain size in
a solvent has been used in the form of an emulsion or suspension,
and a binder dispersed in a certain size in an organic (oil-based)
solvent may be used, and particularly, a binder dispersed in a
certain size in water-based solvent (water) is preferred since it
is eco-friendly and has many processing advantages in coating
inorganic particles.
[0012] However, only with a typically dispersed binder, a
sufficient adhesive strength between the inorganic particles or
between the inorganic particles and the porous substrate cannot be
obtained.
[0013] As described above, a coating method based on a binder
composition soluble in an organic solvent has some problems.
Firstly, a binder soluble in an organic solvent is formed into gel
as the organic solvent volatilizes during a drying process, and,
thus, a solvent-impermeable space is generated, resulting in
non-uniformity of an organic/inorganic coating layer. Thus, a
battery property may be reduced. In order to overcome this problem,
the binder needs to undergo a secondary drying process in a vacuum
at a glass transition temperature (Tg) or higher. If a residual
solvent is present in a product due to insufficient drying, a part
of the binder is dissolved and gel may be formed. Thus, if a
surface of the coating layer becomes sticky, dust from the outside
or unnecessary particles may adhere thereto and a defect rate of
products may be increased due to adhesion between coating layers or
with a substrate when a product is wrapped. Secondly, if a
concentration of the binder in the slurry is increased, a viscosity
of the slurry is highly increased, which makes it difficult to
prepare an organic/inorganic complex layer of a thin film. Further,
since air permeability is low and a boiling point is high, a drying
process requires a high temperature. Thirdly, if a low viscosity of
the slurry is maintained, an adhesive strength with a porous
substrate or between inorganic substances is decreased. Thus, the
inorganic particles are easily separated. Fourthly, in a process
based on an organic solvent, a dry zone of a drying line is
elongated due to a critical explosion limit while being dried, and,
thus, it is difficult to improve a machining speed. Fifthly, since
the organic solvent has volatility, from the moment the slurry is
exposed to the external environment, the organic solvent
continuously volatilizes. Therefore, a concentration and a
rheological property of the slurry are changed due to evaporation
of the solvent while the slurry is prepared, transferred, and
coated, which may affect a coating quality of a final product.
Sixthly, when a coating separator is prepared, risk factors for
safety, healthy, and environment are inherent. The organic solvent
has toxicity, inflammability, and volatility due to its
characteristics. In order to lower the risks of the organic solvent
and reduce environmental pollution, the organic solvent needs to be
specially prepared and managed. As such, the preparation method of
the organic/inorganic coating separator using the binder soluble in
the organic solvent has limitations in view of characteristics of
the battery and characteristics of the process.
[0014] As a method for improving an adhesive strength between a
porous substrate and a coating layer, Korean Patent Laid-open
Publication No. 10-2012-0052100 describes a technology of preparing
a coating separator having two coating layers, comprising: forming
an organic/inorganic complex layer by casting a slurry, in which
styrene-butadiene rubber (SBR) and carboxyl methyl cellulose (CMC)
are dissolved in acetone as an organic solvent, onto a polyethylene
porous film; and performing an electric radiation on a polymer
compound solution. However, if an organic/inorganic complex layer
is formed by this method, the above-described problems of the
coating method using the organic solvent also occur. There has been
suggested a technology of forming a coating separator in three
layers by radiation onto an inorganic coating layer in order to
solve the problem caused by separation of inorganic substances due
to a low adhesive strength with a substrate. However, in this case,
since a film is formed by radiation, it is difficult to overcome
the problem of a thickness control of a coating layer at this point
in time where a coating separator is demanded to be thinner.
Further, due to low uniformity in pore, a current cannot be
uniformly distributed but concentrated on a single point when being
applied to a battery, and, thus, partial heating, degradation, and
explosion may occur. Therefore, it does not provide a fundamental
technical suggestion of an organic/inorganic coating separator.
[0015] In order to solve a problem that coating materials are
easily separated due to a low adhesive strength between a porous
substrate and a coating layer when an organic/inorganic coating
separator is prepared by the conventional methods, Korean Patent
No. 10-1125013 describes a method for preparing a cross-linked
ceramic-coated separator using a water-soluble ionic polymer. This
method also uses an ionic polymer which can be dissolved in water,
but the ionic polymer is not dispersed in water but completely
dissolved in water, and, thus, it cannot avoid confinement of the
solvent. Since dimethylacetamide as an organic solvent is used 15
times more than water, it does not provide a fundamental suggestion
of a coating method using water. In order to induce chemical
crosslinking after coating for the purpose of improving an adhesive
strength with a substrate, a crosslinking agent and an initiator
need to be added together with the organic solvent during a
preparation process of slurry, and during a drying process, a heat
or UV treatment for 20 hours or more is essentially required.
However, if a crosslinking agent and an initiator are added to a
slurry solution, before the slurry is applied to the porous
substrate, the slurry is partially cross-linked by itself by heat
and energy externally applied while a coating solution is stored
and transferred, resulting in solidification of the slurry. Thus,
uniformity of the coating separator is finally decreased. Further,
since a heat treatment and a UV treatment are needed a long time
even during a drying process, production yield may be very limited,
and a porous substrate of a thin film may be damaged due to high
temperature/high energy during the drying process, which may cause
deterioration in property and air permeability.
DISCLOSURE
Technical Problem
[0016] The present invention is contrived to solve the conventional
problems as described above. An object of the present invention is
to provide a separator capable of improving thermal and chemical
stability of a porous substrate by forming an organic/inorganic
complex coating porous layer excellent in air permeability and
adhesive strength by coating the porous substrate with a coating
solution in which a binder and selectively added inorganic
particles are dispersed in a specific size, and exhibiting a
sufficient adhesive strength between the inorganic particles or
between the inorganic particles and the substrate if the inorganic
particles are contained, and a secondary battery using the
same.
Technical Solution
[0017] An organic/inorganic complex coating porous separator
according to the present invention comprises a coating layer coated
with a coating solution which contains a binder and selectively
inorganic particles dispersed in the form of particle having a
certain particle size in a solvent, in a single layer or multiple
layers on a single surface or both surfaces of a porous substrate
or at least a part of a pore portion of the porous substrate.
[0018] The binder used in the present invention refers to two types
of binders including an oil-based binder dispersed in a certain
size in an organic solvent and a water-based binder dispersed in a
certain size in water. Herein, the expression "dispersed in a
certain size" means that binder particles are dispersed with a
certain distribution size and are present as an emulsion or a
suspension at the time of initial polymerization or by a
post-process. An adhesive strength between the inorganic particles
or between the inorganic particles and the substrate can be more
effectively regulated by regulating a particle size of the
dispersed binder by a temperature, a pH, or a concentration of an
emulsifier during a preparation process.
[0019] In the present invention, the term "certain size" of the
binder particles means that a mean particle diameter d.sub.50 of
the binder is a half or less of a mean diameter of the inorganic
particles and also less than one and a half times a mean pore
diameter of the porous substrate. When this condition is satisfied,
a specific surface area of the binder is increased and the binder
effectively infiltrate into an inner surface of the porous
substrate, thereby effectively improving an adhesive strength
between the porous substrate and the binder on an outer surface and
an adhesive strength between the substrate and the inorganic
particles during a drying process. Therefore, an adhesive strength
between the binder and the substrate is more effectively improved,
and if the inorganic particles are contained, a sufficient adhesive
strength between the inorganic particles or between the inorganic
particles and the substrate can be exhibited. If a binder having a
specific particle size is used as illustrated in the present
invention, it is possible to obtain a higher adhesive strength
between a binder and a substrate and a higher adhesive strength
between inorganic particles or between the inorganic particles and
the substrate, as compared with a case of using a binder which can
be chemically crosslinked and ionically crosslinked.
[0020] The present invention can be applied, without limitation, to
a coating separator for secondary battery that does not contain
inorganic particles. If a coating solution does not contain
inorganic particles, when a mean particle diameter d.sub.50 of a
binder is less than one and a half times a mean pore diameter of
the porous substrate, an excellent adhesive strength with respect
to the substrate can be exhibited.
[0021] In the present invention, if a coating solution uses
inorganic particles and a binder, an additional binder or a
dispersion agent (low molecular or high molecular dispersion agent)
for dispersing the inorganic particles or an antifoaming/defoaming
agent, a wetting agent, a leveling agent, a rheology modifier, and
the like, for improving a coating property of the coating solutoin
may be additinally contained, but preferably, for battery
properties, such additives may be added as small as possible.
[0022] According to the present invention, when the coating
solution is coated on the porous substrate, a polyolefin-based
porous film having low surface energy has a low wettability, which
may cause non-uniformity in coating. For uniformity in coating,
there may be used a surface treatment technology such as a corona,
plasma, or high-energy radiation treatment generally used to
increase surface energy and a surface roughness of the porous
substrate. By such a surface treatment, the coating solution can be
uniformly coated on the porous substrate with more efficiency.
However, according to the present invention, even if the surface
treatment is not carried out, high air permeability and adhesive
strength can be obtained, but if a surface treatment is carried
out, higher permeability and adhesive strength can be obtained, and
it is more advantageous to carry out the surface treatment in order
to improve wettability with respect to an electrolyte within the
battery.
[0023] According to the present invention, in the case of using
inorganic particles, a preferable exemplary embodiment of a method
for preparing a separator comprises:
[0024] (a) a step of dispersing inorganic particles by mixing the
inorganic particles with a solvent;
[0025] (b) a step of preparing a coating solution by mixing a
binder in the form of particle with the mixed solution obtained in
the step (a);
[0026] (c) a step of coating and drying the coating solution
obtained in the step (b) on one or more regions selected from the
group consisting of a one surface, both surfaces of a porous
substrate, and at least a part of a pore portion of the substrate
in a single layer or multiple layers.
[0027] In the present invention, when the coating solution is
coated on the porous substrate, a coating method is not
specifically limited, and various coating methods such as typically
used dip coating, die coating, Gravure coating, comma coating, may
be used.
[0028] Hereinafter, the present invention will be explained in more
detail.
[0029] <Porous Separator>
[0030] The porous separator of the present invention includes a
porous separator in which an organic/inorganic complex coating
layer is formed in a single layer or multiple layers on one or more
regions selected from the group consisting of a single surface,
both surfaces, and at least a part of a pore portion of a porous
substrate using the porous substrate and a coating solution
containing a binder dispersed in a solvent and selectively added
inorganic particles.
[0031] The porous substrate may employ any porous substrate
generally used in an electrochemical device such as a lithium
secondary battery. The porous substrate may include, for example, a
film or non-woven fabric formed using one or a mixture of two or
more polymer compounds such as high-density polyethylene,
low-density polyethylene, linear low-density polyethylene, ultra
high-molecular weight polyethylene, polypropylene, polyethylene
terephthalate, polybutylene terephthalate, polyester, polyacetal,
polyamide, polycarbonate, polyimide, polyetherether ketone,
polyether sulfone, polyphenylene oxide, polyphenylene sulfide, and
polyethylene naphthalene.
[0032] The porous substrate may be prepared to have a thickness
ranging from 1 to 100 .mu.m, and preferably, 1 to 30 .mu.m. Along
with a recent trend of high power output/high capacity of a
battery, it is advantageous to use a thin film as the porous
substrate. A pore diameter of the porous substrate is in a range of
0.01 to 50 .mu.m, and a porosity is 5 to 90% and preferably 20 to
80%. However, these numerical ranges can be easily modified
depending on an embodiment or as necessary.
[0033] A pore of the porous substrate may have various pore
structures. If any one of a mean pore diameter measured using a
porosimeter or a mean pore diameter observed from an FE-SEM image
satisfies the above-described conditions, it can be included in the
present invention. Herein, as for an uniaxially oriented separator
manufactured by a dry method, a central pore diameter in a TD
direction rather than an MD direction in an FE-SEM image becomes a
reference (refer to FIG. 1), and as for other porous substrates
(for example, a wet PE separator) having a network structure, a
pore diameter measured with a porosimeter typically becomes a
reference, but the present invention is not limited thereto.
[0034] If the coating solution contains inorganic particles, the
binder enables adhesion and fixation between the inorganic
particles and between the inorganic particles and the surface of
the porous substrate, thereby preventing physical deformation and
deterioration of properties of the porous substrate.
[0035] The binder refers to a binder in the form of an emulsion or
suspension in which particles of a polymer compound are dispersed
in an organic solvent or water, and specifically, the dispersed
binder is in an emulsion form or a suspension form of which a mean
pore diameter d.sub.50 is a half or less of a mean pore diameter
d.sub.50 of the inorganic particles and also less than one and a
half times a mean pore diameter d.sub.50 of the porous substrate.
For example, the binder may be one or a mixture of two or more
selected from the group consisting of latex, emulsions and
suspensions formed by dispersing polymer compounds, such as
polystyrene-based, styrene butadiene-based, nitrile-based,
polyvinyl chloride (PVC)-based, polyolefin-based, acryl-based,
acetate-based, polyvinylidene fluoride (PVDF)-based, ethylene-vinyl
acetate (EVA)-based, polyvinyl butyral-based,
polytetrafluoroethylene (PTFE)-based, polyimide-based, polyethylene
oxide-based, cellulose-based, polyvinyl alcohol-based, and
starch-based polymers or copolymers, in an organic solvent or a
water-based solvent such as water.
[0036] As a particle diameter of the binder is decreased, a
specific surface area is increased and an amount of the binder
passing through the porous substrate is increased. Thus, it is more
effective in increasing an adhesive strength between the inorganic
particles and between the substrate and the inorganic particles.
When a mean particle diameter d.sub.50 of the binder is a half or
less of a mean diameter of the inorganic particles and also less
than one and a half times a mean pore diameter of the porous
substrate, an organic/inorganic complex coating separator having an
excellent adhesive strength as an object of the present invention
can be obtained.
[0037] For example, as for a porous separator typically used in a
secondary battery, a PE separator formed by a wet method and a PP
separator formed by a dry method have mean pore diameters of 100 to
700 nm (400 to 700 nm in the case of using a three component system
and 100 to 300 nm in the case of using a two component system, and
a pore diameter may vary depending on a film forming condition, the
pore diameter described herein is not provided to limit a pore
diameter) and 50 to 200 nm, respectively. An effective mean
particle diameter of the binder for each film may vary. For
example, in an uniaxially oriented PP separator manufactured by a
dry method, a width of a pore in a TD direction may be in a range
of about 50 to about 200 nm, and, thus, a binder having a mean
particle diameter of 100 nm or less is preferred. In particular, a
binder which has a mean particle diameter of 100 nm or less and can
be bonded by ions or bonded by a crosslinking agent exhibited a
more effective adhesive strength and a thermal property between the
inorganic particles and the substrate, but it was found that if a
mean particle diameter is great, an adhesive strength is
decreased.
[0038] In the present invention, as the dispersed binder, binders
of many kinds having different mean particle diameters may be used.
In this case, if a mean particle diameter of any one of the binders
satisfies the above-described conditions, it is included in the
present invention.
[0039] In the coating solution of the present invention, besides
the binder, in order to more effectively improve an adhesive
strength with respect to the substrate and a coating property by
inducing an attraction force between the binder and the polymer, as
a second organic binder to be dissolved in the solvent, phosphoric
ester, phosphoric acryl-based copolymer, modified
polyacrylate-based copolymer, modified polyacrylic acid-based
copolymer, polyester amine amide-based copolymer, polycarboxylic
acid-based copolymer, polyalkylol amino amide-based copolymer,
siloxane- and acryl-based copolymer, siloxane- and carboxylic
acid-based copolymer, polyalkoxylate-based copolymer, acryl- and
ether-based copolymer, and metallic salts thereof may be used, and
one or two or more of them may be used.
[0040] The inorganic particles used in the coating solution of the
present invention may employ any inorganic particles typically used
in preparing a conventional coating separator for battery. The
inorganic particles may include one or a mixture of two or more
substances of SnO.sub.2, BaTiO.sub.2, Al.sub.2O.sub.3, CeO.sub.2,
SiO.sub.2, TiO.sub.2, Li.sub.3PO.sub.4, NiO, ZnO, MgO,
Mg(OH).sub.2, CaO, ZrO.sub.2, Y.sub.2O.sub.3, and talc, and the
inorganic particles may have a shape such as a sphere shape, a
plate shape, or an irregular shape.
[0041] The inorganic particles are not limited in diameter, but for
preparing slurry with good dispersion stability and for forming a
coating layer having a uniform thickness, the inorganic particles
may have a diameter of preferably 0.001 to 10 .mu.m, and most
preferably 0.1 to 5 .mu.m. If a mean diameter of the inorganic
particles is less than 0.01 .mu.m, dispersibility of the inorganic
particles may be decreased, or the inorganic particles may be
distributed within the already-formed pores, and, thus, air
permeability may be decreased. If a diameter of the inorganic
particles is more than 5 .mu.m, a thickness of the
organic/inorganic complex coating layer is increased, resulting in
deterioration in mechanical property, or the possibility of an
internal short circuit during charge and discharge of the battery
is increased due to the excessively large pores. Further, due to an
increase in overall thickness of the organic/inorganic complex
coating separator, there may be a limitation in manufacturing a
middle or large-sized battery cell which is thin and has high
capacity.
[0042] As for the inorganic particles, various inorganic particles
having different mean particle diameters may be mixed and used. If
a particle distribution of any one kind of inorganic particles
satisfies the above-described conditions, it is included in the
present invention. Further, a diameter of the inorganic particles
can be measured using a device configured to measure a particle
diameter and distribution using a laser or a light scattering
method.
[0043] In the coating solution used in the present invention, for
the purpose of regulating viscosity or improving ionic conductivity
and for the purpose of a coating property or dispersibility of the
inorganic particles, a low-molecular or high-molecular organic
compound soluble in the solvent may be further contained in
addition to the binder.
[0044] In the separator of the present invention, the coating layer
can be formed with a coating solution that contains only particles
of the binder but not contains the inorganic particles under the
above-described conditions. In this case, if the binder satisfies a
condition that a mean particle diameter thereof is less than one
and a half times a mean pore diameter of the porous substrate, a
coating separator having an excellent adhesive strength can be
prepared.
[0045] In the coating solution of the present invention, if
inorganic particles are used, preferably, a weight ratio of the
inorganic particles:the binder (P/B ratio) is 4:1 to 140:1. If a
weight ratio of the inorganic particles to the binder is less than
4:1 an amount of the binder resin with respect to the inorganic
particles is great, and, thus, air permeability is reduced and
performance of a battery deteriorates. If a weight ratio is more
than 140:1 and an amount of the binder is small and an amount of
the inorganic particles is too great, an adhesive strength between
the inorganic particles or between the porous substrate and the
inorganic particles is decreased and separation may occur.
[0046] In the separator of the present invention, preferably, the
coating layer has a thickness of 0.1 to 50 .mu.m, a pore diameter
of 0.001 to 10 .mu.m, and a porosity of 30 to 80%.
[0047] If a pore diameter is less than 0.001 .mu.m, or porosity is
less than 30%, pores are filled with a small amount of an
electrolyte, and, thus, a lithium ion transfer capability is
decreased or performance of a cell deteriorates. If a pore diameter
is more than 10 .mu.m, or porosity is more than 80%, a mechanical
property of the porous separator may deteriorate.
[0048] In the separator of the present invention, the method for
coating the coating solution on the porous substrate may employ a
typical coating method known in the art. For example, various
processes such as dip coating, die coating, roll coating, comma
coating, Gravure coating, or a combination thereof may be used.
[0049] <Preparation Method of Porous Separator>
[0050] The organic/inorganic complex porous separator according to
the present invention can be prepared by a typical method known in
the art, and a preferable exemplary embodiment of using inorganic
particles comprises:
[0051] (a) a step of dispersing inorganic particles by adding and
mixing the inorganic particles with a solvent;
[0052] (b) a step of preparing a coating solution by adding and
mixing a binder in the form of particle with the mixed solution
obtained in the step (a);
[0053] (c) a step of coating and drying the coating solution
obtained in the step (b) on one or more regions selected from the
group consisting of a one surface, both surfaces of a porous
substrate, and at least a part of a pore portion of the substrate
in a single layer or multiple layers.
[0054] In the step (a), the inorganic particles may be dispersed
using a typical dispersion method known in the art with, for
example, an ultrasonic homogenizer, a ball-mill, a disperser, a
mixer, and the like, and particularly preferably a ball-mill. In
this step, a dispersion processing time may vary depending on a
capacity, and preferably, it is 1 to 20 hours. A particle diameter
of the crushed inorganic particles can be controlled depending on a
size of a bead used for the ball-mill and a time for the ball-mill,
and preferably, it is about 0.001 to about 10 .mu.m as described
above. In this step, a particle dispersion state may deteriorate
depending on a size, a shape and a chemical structure of a surface
of the inorganic particles. If a polymer dispresion agent is added
as necessary, the inorganic particles can be more effectively
dispersed. Generally, an amount of the dispresion agent may vary
depending on a size, a chemical strucure, and a surface area of
inorganic particles, but appropriately, it is 0 to 3 parts by
weight with respect to 100 parts by weight of the inorganic
particles.
[0055] In the step (b), the organic/inorganic complex coating
solution is prepared by adding the binder to the mixed solution in
the form of slurry in which the inorganic particles are
dispersed.
[0056] In the step (c), before the porous substrate is coated with
the coating solution, a wetting agent for improving wettability of
the organic/inorganic complex coating solution with respect to the
porous substrate, a leveling agent for improving surface flatness
of the coating layer, an adhesion promoter for improving an
adhesive strength between the separator substrate and the coating
solution, an antifoaming and defoaming agent, and additives
applicable for improving a coating property such as a thickener, a
rheology additive, and a UV absorber may be selectivley added in
appropriate amounts depending on viscosity or surface energy of the
finally obtained coating solution. A kind of the additives can be
approprately selected and used depending on a desired coating
method and a coating characteristic.
[0057] In the step (c), the final coating separator according to
the present invention can be prepared by coating and drying the
coating solution on the porous substrate. In this step, the method
for coating the coating solution on the porous substrate may employ
a typical coating method known in the art. For example, by dip
coating, die coating, roll coating, comma coating, Gravure coating,
bar coating, or a combination thereof, the coating layer of a
single layer or multiple layers may be coated on a single surface
or both surfaces, and at least a part of the pore portion of the
porous substrate.
[0058] <Electrochemical Device Comprising Porous
Separator>
[0059] In an electrochemcial device comprising an anode, a cathode,
and an electrolyte, the organic/inorganic complex coating porous
separator according to the present invention may be used as a
separator between the anode and the cathode.
[0060] The electrochemical device includes all devices that make
electrochemical reactions. Specific examples of the electrochemical
device may include all kinds of primary/secondary batteries, fuel
cells, solar cells, or super capacitors. In particular, a lithium
secondary battery of the secondary batteries is the most
preferable.
[0061] The secondary battery device can be manufactured by a
typical method known in the art, and can be manufactured by
interposing the separator according to the present invention
between the anode and the cathode and injecting the
electrolyte.
[0062] A cathode, an anode, and an electrolyte to be applied as
well as the separator of the present invention are not specifically
limited and may empoly those typically used in the art.
Advantageous Effects
[0063] According to the present invention, when a binder in a form
of particles dispersed in a certain size in an oil-based or
water-based solvent is selectively mixed with inorganic particles
and then coated and dried on a porous substrate, a thus formed
organic/inorganic complex coating separator can exhibit a
sufficient adhesive strength without crosslinking by heat or UV,
and has a higher adhesive strength with respect to the substrate as
compared with the case where crosslinking caused by heat or UV
occurs. Further, the organic/inorganic complex coating separator
has excellent air permeability, thereby suppressing a thermal
contraction rate at a high temperature, and also exhibits excellent
processability.
[0064] Further, since the organic/inorganic complex coating
separator of the present invention is improved in wettability with
respect to an electrolyte, and, thus, ionic conductivity of lithium
and electrolyte uptake can be improved.
[0065] If the separator of the present invention is applied to a
battery and an electrochemical device, it is possible to
manufacture an excellent secondary battery device having improved
performance of a battery and improved thermal and electrochemical
stability.
DESCRIPTION OF DRAWINGS
[0066] FIG. 1 illustrates a method of measuring a pore diameter of
an uniaxially oriented porous separator manufactured by a dry
method.
[0067] FIG. 2 is an FE-SEM image of an organic/inorganic coating
porous separator prepared in Example 1.
[0068] FIG. 3 is a photo illustrating a result of a thermal
contraction experiment on separators, and illustrates
organic/inorganic complex coating porous separators prepared in
Example 1 and Comparative Example 7 after being left at 150.degree.
C. for 1 hour.
[0069] FIG. 4 illustrates a measurement result of a C-rate of
organic/inorganic complex coating porous separators prepared in
Example 1 and Comparative Example 3.
BEST MODE
[0070] The present invention can be modified and changed in various
ways and may include various exemplary embodiments. Although
preferred Examples are provided as follows for easy understanding
of the present invention, the following Examples are provided just
for illustrating the present invention but not for limiting the
scope of the present invention.
EXAMPLES AND COMPARATIVE EXAMPLES
[0071] The property measurement methods of organic/inorganic
complex coating separator prepared in the following Examples and
Comparative Examples are as follows.
[0072] 1. Coating Thickness Measurement Method
[0073] As a coating thickness gauge, a digimatic thickness gage
547-401 (.PHI.6.3 mm flat tip type, pressure of 3.5 N or less for
measurement) manufactured by Mitutoyo was used for measurement, and
a difference between a thickness of a coating separator and a
thickness of an original film before coating was calculated.
[0074] 2. Adhesive Strength Measurement Method
[0075] After a tape of 18 mm.times.20 mm (adhesion area) was
attached onto the coating separator, a load of 2 kgf was applied
thereto for 10 minutes. Then, an adhesive strength was measured
with a LLOYD U.TM.. Herein, as for the adhesive strength, a force
(gf) applied to pull a tape at a speed of 2 mm/min until the tape
was detached was measured using a 180 degree peel test.
[0076] 3. Gurley Measurement Method
[0077] As for gurley, a permeation time of 100 cc of air was
measured using a densometer manufactured by Toyoseiki Co., Ltd.
(ISO 5635/5).
[0078] 4. Thermal Contraction Rate Measurement Method
[0079] A sample was cut into a size of 50 mm.times.50 mm, and
vertical and horizontal lines (3 cm.times.3 cm) were drawn on a
central portion of the sample. Then, the sample was left in an oven
at a temperature of 150.+-.5.degree. C. for 1 hour. Thereafter, the
sample was taken out of the oven and left at room temperature for 5
minutes or more to be cooled to room temperature. Then, lengths of
the lines drawn on the central portion of the sample were measured
to calculate a contraction rate with respect to the lengths before
contraction.
Example 1
1-1. Preparation of Organic/Inorganic Complex Coating Porous
Separator
[0080] Alumina (Al.sub.2O.sub.3) as inorganic particles was added
to water to be solid content 30 weight %, and a modified polyacryl
polyether copolymer as a second organic binder was added in amount
of 1 weight % with respect to the amount of alumina, and then, the
inorganic particles were crushed to a mean particle diameter of 0.5
.mu.m using the ball-mill for 2 hours or more and dispersed so as
to prepare waterborne inorganic slurry. A waterborne styrene
butadiene latex (SBL) emulsion having a mean particle diameter of
dispersed binder of 80 nm is added as a binder to the slurry such
that a ratio of the inorganic particles/the binder (P/B ratio) is
Al.sub.2O.sub.3/SBL=40/1 (weight ratio), and with stirring for
about 2 hours or more, the emulsion is uniformly dispersed within
the slurry, thereby preparing a coating solution. As a porous
substrate, a corona-treated uniaxially oriented polypropylene
separator (porosity of 45%) having a mean pore diameter of 100 nm
in a TD direction and a thickness of 14 .mu.m was used. The coating
solution was coated on both surfaces of the separator by a dip
coating method, so that an organic/inorganic complex coating porous
separator having a thickness of 20 .mu.m was finally prepared. An
FE-SEM image of the prepared separator was as illustrated in FIG.
1. Further, FIG. 3 illustrates a photo illustrating a result of a
thermal contraction experiment on the separator.
[0081] 1-2. Preparation of Lithium Secondary Battery
[0082] A coin cell type lithium secondary battery was prepared
using a LiNiCoMnO.sub.2-based electrode as an anode, a graphite
electrode as a cathode, and an ethylene carbonate/ethyl methyl
carbonate/diethyl carbonate (EC/EMC/DEC=3:2:5)-based electrolyte
wherein lithium hexafluoro phosphate (LiPF.sub.6) was dissolved, as
an electrolyte.
Example 2
[0083] An organic/inorganic complex coating porous separator and a
lithium secondary battery including the same were prepared in the
same manner as Example 1 except that a mean pore diameter in a TD
direction of a polypropylene separator used as a porous substrate
was 130 nm.
Example 3
[0084] An organic/inorganic complex coating porous separator and a
lithium secondary battery including the same were prepared in the
same manner as Example 1 except that a mean pore diameter in a TD
direction of a polypropylene separator used as a porous substrate
was 80 nm and a mean particle diameter of a binder was 60 nm.
Example 4
[0085] An organic/inorganic complex coating porous separator and a
lithium secondary battery including the same were prepared in the
same manner as Example 1 except that a polyethylene separator
having a mean pore diameter of 400 nm in a TD direction was used as
a porous substrate.
Example 5
[0086] An organic/inorganic complex coating porous separator and a
lithium secondary battery including the same were prepared in the
same manner as Example 1 except that a polyethylene separator
having a mean pore diameter of 400 nm in a TD direction was used as
a porous substrate, and a mean particle diameter of crushed alumina
was 0.8 .mu.m and a mean particle diameter of the binder was 100
nm.
Example 6
[0087] An organic/inorganic complex coating porous separator and a
lithium secondary battery including the same were prepared in the
same manner as Example 1 except that a polyethylene separator
having a mean pore diameter of 400 nm in a TD direction was used as
a porous substrate, and a mean particle diameter of crushed alumina
was 1 .mu.m and a mean particle diameter of the binder was 100
nm.
Example 7
[0088] An organic/inorganic complex coating porous separator and a
lithium secondary battery including the same were prepared in the
same manner as Example 1 except that a mean particle diameter of
the binder was 50 nm.
Example 8
[0089] An organic/inorganic complex coating porous separator and a
lithium secondary battery including the same were prepared in the
same manner as Example 1 except that a mean particle diameter of
the binder was 100 nm.
Example 9
[0090] An organic/inorganic complex coating porous separator and a
lithium secondary battery including the same were prepared in the
same manner as Example 1 except that a polypropylene separator was
used as a porous substrate without a corona treatment.
Example 10
[0091] An organic/inorganic complex coating porous separator and a
lithium secondary battery including the same were prepared in the
same manner as Example 1 except that a polyethylene separator
having a mean pore diameter of 100 nm in a TD direction was used as
a porous substrate, and a mean particle diameter of the binder was
80 nm.
Example 11
[0092] An organic/inorganic complex coating porous separator and a
lithium secondary battery including the same were prepared in the
same manner as Example 1 except that a polyethylene separator
having a mean pore diameter of 400 nm in a TD direction was used as
a porous substrate, and an acryl emulsion having a mean particle
diameter of dispersed binder of 150 nm was used as binder.
Example 12
[0093] An organic/inorganic complex coating porous separator and a
lithium secondary battery including the same were prepared in the
same manner as Example 1 except that a polyethylene separator
having a mean pore diameter of 400 nm in a TD direction was used as
a porous substrate, and a PVDF emulsion having a mean particle
diameter of dispersed binder of 180 nm was used as binder.
Example 13
[0094] An organic/inorganic complex coating porous separator and a
lithium secondary battery including the same were prepared in the
same manner as Example 1 except that as a binder, SBL (styrene
butadiene latex) and CMC (carboxyl methyl cellulose) soluble in a
solvent were used together.
Example 14
[0095] An organic/inorganic complex coating porous separator and a
lithium secondary battery including the same were prepared in the
same manner as Example 1 except that a weight ratio of alumina to a
binder was 80:1.
Example 15
[0096] An organic/inorganic complex coating porous separator and a
lithium secondary battery including the same were prepared in the
same manner as Example 1 except that a weight ratio of alumina to a
binder was 20:1.
Comparative Example 1
[0097] A lithium secondary battery was prepared in the same manner
as Example 1 except that there was used a polypropylene (PP)
separator (porosity of 45%) having a thickness of about 14 .mu.m on
which a coating layer was not formed.
Comparative Example 2
[0098] A lithium secondary battery was prepared in the same manner
as Example 1 except that there was used a polyethylene (PE)
separator (porosity of 48%) having a thickness of about 14 .mu.m on
which a coating layer was not formed.
Comparative Example 3
[0099] PVDF-HFP was added in an amount of 5 weight % to acetone and
then dissolved at 40.degree. C. for about 2 hours or more, thereby
preparing a polymer compound solution. Al.sub.2O.sub.3 powder was
added to this polymer compound solution such that a weight ratio
(P/B ratio) of Al.sub.2O.sub.3 powder/PVDF-HFP could be 9/1 to
crush and disperse inorganic particles using the ball-mill for 3
hours or more, thereby preparing a coating solution in the form of
slurry. A particle diameter of the Al.sub.2O.sub.3 in the slurry
after crushing can be controlled depending on a particle diameter
of beads used for the ball-mill and a time for the ball-milling,
but in Comparative Example 3, the slurry was prepared by crushing
the inorganic particles to have a mean diameter of 0.5 .mu.m. As a
porous substrate, a corona-treated polypropylene separator
(porosity of 45%) having a thickness of 14 .mu.m was used, and the
coating solution was coated on the porous substrate by a dip
coating method. In this case, the dip coating method was carried
out at a line speed of 5 m/min, and a coating separator
(PVDF/Al.sub.2O.sub.3) having a thickness of 20 .mu.m was finally
prepared. A lithium secondary battery was prepared using the
prepared organic/inorganic complex coating porous separator in the
same manner as Example 1.
Comparative Example 4
[0100] An organic/inorganic complex coating porous separator and a
lithium secondary battery including the same were prepared in the
same manner as Example 1 except that a weight ratio of
Al.sub.2O.sub.3 powder/SBL was 1/1.
Comparative Example 5
[0101] An organic/inorganic complex coating porous separator and a
lithium secondary battery including the same were prepared in the
same manner as Example 1 except that a weight ratio of
Al.sub.2O.sub.3 powder/SBL was 150/1.
Comparative Example 6
[0102] An organic/inorganic complex coating porous separator and a
lithium secondary battery including the same were prepared in the
same manner as Example 1 except that a second organic binder was
not used.
Comparative Example 7
[0103] An organic/inorganic complex coating porous separator and a
lithium secondary battery including the same were prepared in the
same manner as Example 1 except that that a mean particle diameter
of a binder was 170 nm. FIG. 3 illustrates a photo illustrating a
result of a thermal contraction experiment on the prepared
separator.
Comparative Example 8
[0104] An organic/inorganic complex coating porous separator and a
lithium secondary battery including the same were prepared in the
same manner as Example 1 except that that a mean pore diameter of a
porous substrate was 150 nm, an acryl emulsion having a mean
particle diameter of dispersed binder of 250 nm was used as a
binder, and a P/B ratio was 20/1.
[0105] The properties of the materials used in Examples and
Comparative Examples and the properties of the prepared separators
were as illustrated in the following Tables 1 to 5.
TABLE-US-00001 TABLE 1 Example 1 Example 2 Example 3 Example 4
Example 5 Example 6 Porous substrate PP PP PP PE PE PE Substrate 14
14 14 14 14 14 thickness (.mu.m) Mean pore 100 130 80 400 400 400
diameter (nm) Corona .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. treatment Alumina mean
0.5 0.5 0.5 0.5 0.8 1.0 particle diameter (.mu.m) Binder SB SB SB
SB SB SB Binder mean 80 80 60 80 100 100 particle diameter d.sub.50
(nm) P/B ratio 40/1 40/1 40/1 40/1 40/1 40/1 Coated surface Both
Both Both Both Both Both surfaces surfaces surfaces surfaces
surfaces surfaces Coating 20 20 20 20 20 20 separator thickness
(.mu.m) Gurley 240 300 220 240 250 250 (sec/100 cc) Adhesive 340
360 380 460 470 500 strength (gf) MD thermal 3.8 3.5 2.0 2.5 2.8
contraction rate (% @ 150.degree. C., 1 hr)
TABLE-US-00002 TABLE 2 Exam- Exam- Example Example 7 ple 8 ple 9 10
Porous substrate PP PP PP PE Substrate thickness (.mu.m) 14 14 14
14 Mean pore diameter (nm) 100 100 100 100 Corona treatment
.largecircle. .largecircle. X .largecircle. Alumina mean particle
0.5 0.5 0.5 0.5 diameter (.mu.m) Binder SB SB SB SB Binder mean
particle diameter 50 100 80 80 d.sub.50 (nm) P/B ratio 40/1 40/1
40/1 40/1 Coated surface Both Both Both Both surfaces surfaces
surfaces surfaces Coating separator thickness 20 20 20 20 (.mu.m)
Gurley (sec/100 cc) 240 260 240 250 Adhesive strength (gf) 360 300
180 500 MD thermal contraction rate 3.8 4.5 5.0 2.0 (% @
150.degree. C., 1 hr)
TABLE-US-00003 TABLE 3 Exam- Exam- Exam- Exam- Exam- ple 11 ple 12
ple 13 ple 14 ple 15 Porous substrate PE PE PP PP PP Substrate
thickness 14 14 14 14 14 (.mu.m) Mean pore diameter 400 400 100 100
100 (nm) Corona treatment .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. Alumina mean particle 0.5 0.5 0.5 0.5
0.5 diameter (.mu.m) Binder Acryl PVDF SB + SB SB CMC Binder mean
particle 150 180 80 80 80 diameter d.sub.50 (nm) P/B ratio 40/1
40/1 40/1 80/1 20/1 Coated surface Both Both Both Both Both
surfaces surfaces surfaces surfaces surfaces Coating separator 20
20 20 20 20 thickness (.mu.m) Gurley (sec/100 cc) 250 250 250 240
250 Adhesive strength (gf) 340 340 310 320 380 MD thermal
contraction 4.4 5.5 5.7 4.2 3.8 rate (% @ 150.degree. C., 1 hr)
TABLE-US-00004 TABLE 4 Comparative Comparative Comparative Example
1 Example 2 Example 3 Porous substrate PP PE PP Substrate thickness
(.mu.m) 14 14 14 Mean pore diameter (nm) 100 400 100 Corona
treatment -- -- .largecircle. Alumina mean particle -- -- 0.5
diameter (.mu.m) Binder -- -- PVDF-HFP Binder mean particle -- --
-- diameter d.sub.50 (nm) P/B ratio -- -- 9/1 Coated surface -- --
Both surfaces Coating separator thickness -- -- 20 (.mu.m) Gurley
(sec/100 cc) 210 230 300 Adhesive strength (gf) -- -- 80 MD thermal
contraction 40 melted 14 rate (% @ 150.degree. C., 1 hr)
TABLE-US-00005 TABLE 5 Comparative Comparative Comparative
Comparative Comparative Example 4 Example 5 Example 6 Example 7
Example 8 Porous PP PP PP PP PP substrate Substrate 14 14 14 14 14
thickness (.mu.m) Mean pore 100 100 100 100 150 diameter (nm)
Corona .largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. treatment Alumina 0.5 0.5 0.5 0.5 0.5 mean particle
diameter (.mu.m) Binder SB SB SB SB Acryl Binder 80 80 80 170 250
mean particle diameter d.sub.50 (nm) P/B ratio 1/1 150/1 40/1 40/1
20/1 Coated Both Both Both Both Both surface surfaces surfaces
surfaces surfaces surfaces Coating 20 20 20 20 20 separator
thickness (.mu.m) Gurley 1500 220 220 220 280 (sec/100 cc) Adhesive
490 30 180 150 80 strength (gf) MD thermal 3.2 10 8 17 24
contraction rate (% @ 150.degree. C., 1 hr)
Experimental Example
Performance Evaluation of Lithium Secondary Battery
[0106] In order to evaluate performance of lithium secondary
batteries prepared in Example 1 and Comparative Example 3, a
capacity and a C-rate of each battery were measured.
[0107] A cycle was carried out five times at a battery discharge
speed of 0.2 C, 0.5 C, 1 C, 3 C, and 5 C, and discharge capacities
thereof were schematized by C-rate characteristics as illustrated
in FIG. 4.
[0108] According to a result of the experiment, as illustrated in
FIG. 4, the lithium secondary battery of Example 1 including the
coating separator of the present invention exhibited an excellent
C-rate characteristic as compared with the battery of Comparative
Example 3.
* * * * *