TECHNICAL FIELD
The present disclosure relates to a separator and an electrochemical device
including the same. Particularly, the present disclosure relates to a separator which shows
5 reduced deformation during a lamination process, resulting in a decrease in lamination
short defect rate, and an electrochemical device including the same.
The present application claims priority to Korean Patent Application No. 10-2020-
0102806 filed on August 14, 2020 in the Republic of Korea, the disclosures of which are
incorporated herein by reference.
10
BACKGROUND ART
Recently, energy storage technology has been given an increasing attention.
Efforts into research and development for electrochemical devices have been actualized
more and more, as the application of energy storage technology has been extended to
15 energy for cellular phones, camcorders and notebook PC and even to energy for electric
vehicles. In this context, electrochemical devices have been most spotlighted. Among
such electrochemical devices, development of rechargeable secondary batteries has been
focused. More recently, active studies have been conducted about designing a novel
electrode and battery in order to improve the capacity density and specific energy in
20 developing such batteries.
Among the commercially available secondary batteries, lithium secondary
batteries developed in the early 1990’s have been spotlighted, since they have a higher
operating voltage and significantly higher energy density as compared to conventional
3
batteries, such as Ni-MH, Ni-Cd and sulfuric acid-lead batteries using an aqueous
electrolyte. However, such lithium-ion batteries cause safety-related problems, such as
ignition and explosion, due to the use of an organic electrolyte, and have a disadvantage in
that they are difficult to manufacture.
5 More recently, lithium-ion polymer batteries have improved such disadvantages of
lithium-ion batteries and have been expected as one of the next-generation batteries.
However, such lithium-ion polymer batteries still provide relatively lower capacity as
compared to lithium-ion batteries, and particularly show insufficient discharge capacity at
low temperature. Therefore, there is an imminent need for improving such a
10 disadvantage.
Although such electrochemical devices have been produced from many production
companies, safety characteristics thereof show different signs. Evaluation and
securement of safety of such electrochemical devices are very important. The most
important consideration is that electrochemical devices should not damage users upon their
15 malfunction. For this purpose, safety standards strictly control ignition and smoke
emission in electrochemical devices. With regard to safety characteristics of
electrochemical devices, there is great concern about explosion when an electrochemical
device is overheated to cause thermal runaway or perforation of a separator. Particularly,
a polyolefin-based porous substrate used conventionally as a separator for an
20 electrochemical device shows a severe heat shrinking behavior at a temperature of 100°C
or higher due to its material property and a characteristic during its manufacturing process,
including orientation, thereby causing a short-circuit between a cathode and an anode.
To solve the above-mentioned safety problems of an electrochemical device, there
4
has been suggested a separator having a porous organic-inorganic coating layer formed by
applying a mixture of an excessive amount of inorganic particles with a binder polymer
onto at least one surface of a porous polymer substrate having a plurality of pores.
Meanwhile, according to the related art, a battery has been manufactured by
5 adhering and laminating a separator with an electrode through a lamination process.
When the electrode is laminated with the separator and heat and pressure are applied
thereto during the lamination process, the binder layer having a pore structure with surface
irregularities is adhered to the electrode surface, wherein the adhesion to the electrode is
increased as the heat and pressure condition applied during the lamination process is
10 increased. Recently, since the processing rate is increased in order to improve the
productivity and the time during which heat is applied to the separator is reduced, the
adhesion is ensured by increasing the pressure. However, under these circumstances,
there is a concern about deformation caused by high pressure. When the porous polymer
substrate used in a separator is liable to heat and pressure during the lamination process,
15 the porous polymer substrate undergoes a significant decrease in thickness and the pores
thereof are damaged significantly so that the battery performance and the breakdown
voltage of the separator may be degraded, resulting in Hi-pot defects and low-voltage
defects. Therefore, there is a need for a solution for improving the above-mentioned
problems.
20
DISCLOSURE
Technical Problem
The present disclosure is designed to solve the problems of the related art, and
5
therefore the present disclosure is directed to providing a separator which shows reduced
deformation during a lamination process with an electrode, resulting in a decrease in
lamination short defect rate.
The present disclosure is also directed to providing an electrochemical device
5 including the separator.
Technical Solution
In one aspect of the present disclosure, there is provided a separator according to
any one of the following embodiments.
10 According to the first embodiment, there is provided a separator including:
a porous polymer substrate provided with a core portion substrate having a
plurality of pores, and skin portion substrates disposed on both surfaces of the core portion
substrate and having a plurality of pores,
wherein both the core portion substrate and the skin portion substrate include first
15 inorganic particles, or only the core portion substrate includes first inorganic particles, and
when both the core portion substrate and the skin portion substrate include the first
inorganic particles, the core portion substrate includes the first inorganic particles at a
higher weight percentage (wt%) as compared to the skin portion substrate; and
a porous coating layer disposed on at least one surface of the porous polymer
20 substrate, and including a plurality of second inorganic particles and a binder polymer
disposed partially or totally on the surfaces of the second inorganic particles so that the
second inorganic particles may be interconnected and fixed,
wherein the first inorganic particles have a higher Mohs hardness than the Mohs
6
hardness of the second inorganic particles.
According to the second embodiment, there is provided the separator as defined in
the first embodiment, wherein the first inorganic particles have a Mohs hardness of 5 or
more and the second inorganic particles have a Mohs hardness of less than 5.
5 According to the third embodiment, there is provided the separator as defined in
the first or the second embodiment, wherein the first inorganic particles include silicon
oxide (SiO), titanium dioxide (TiO2), zirconia (ZrO2), alumina (Al2O3), barium sulfate
(BaSO4), barium titanate (BaTiO3), boehmite, zinc oxide, magnesium oxide, magnesium
hydroxide, aluminum hydroxide, or a mixture of two or more of them.
10 According to the fourth embodiment, there is provided the separator as defined in
any one of the first to the third embodiments, wherein the second inorganic particles
include barium sulfate (BaSO4), barium titanate (BaTiO3), boehmite, zinc oxide,
magnesium oxide, magnesium hydroxide, aluminum hydroxide, or a mixture of two or
more of them.
15 According to the fifth embodiment, there is provided the separator as defined in
any one of the first to the fourth embodiments, wherein when both the core portion
substrate and the skin portion substrate include the first inorganic particles, the core portion
substrate includes the first inorganic particles at a weight percentage (wt%) 20-600 times
higher than the weight percentage of the first inorganic particles in the skin portion
20 substrate.
According to the sixth embodiment, there is provided the separator as defined in
any one of the first to the fifth embodiments, wherein the core portion substrate includes
the first inorganic particles at 10-20 wt%.
7
According to the seventh embodiment, there is provided the separator as defined in
any one of the first to the sixth embodiments, wherein the core portion substrate includes
the first inorganic particles at 10-20 wt%, and the skin portion substrate includes the first
inorganic particles at 0.1-10 wt%.
5 According to the eighth embodiment, there is provided the separator as defined in
any one of the first to the seventh embodiments, wherein the second inorganic particles
have a BET specific surface area of 5-20 m2
/g.
According to the ninth embodiment, there is provided the separator as defined in
any one of the first to the eighth embodiments, wherein each of the core portion substrate
10 and the skin portion substrate is a polyolefin-based porous polymer substrate.
According to the tenth embodiment, there is provided the separator as defined in
any one of the first to the ninth embodiments, wherein each of the core portion substrate
and the skin portion substrate has a melt index (MI) of 0.2 g/10 min. or less.
According to the eleventh embodiment, there is provided the separator as defined
15 in any one of the first to the tenth embodiments, wherein the binder polymer includes
polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-cotrichloroethylene, polymethyl methacrylate, polybutyl acrylate, polybutyl methacrylate,
polyacrylonitrile, polyvinyl pyrro1idone, polyvinyl acetate, polyethylene-co-vinyl acetate,
polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose
20 acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinylalchol, cyanoethyl cellulose,
cyanoethyl sucrose, pullulan, carboxymethyl cellulose, or a mixture of two or more of
them.
According to the twelfth embodiment of the present disclosure, there is provided
8
an electrochemical device including a cathode, an anode and a separator interposed
between the cathode and the anode, wherein the separator is the same as defined in any one
of the first to the eleventh embodiments.
According to the thirteenth embodiment, there is provided the electrochemical
5 device as defined in the twelfth embodiment, which is a lithium secondary battery.
Advantageous Effects
In the case of a separator provided with a porous coating layer including inorganic
particles and a binder polymer on a porous polymer substrate according to the related art,
10 the porous coating layer is compressed together with the porous substrate during the
lamination with an electrode. However, the separator according to an embodiment of the
present disclosure is provided with a porous coating layer using inorganic particles having
a low hardness so that deformation of the porous coating layer may occur predominantly,
thereby preventing deformation of the porous polymer substrate.
15 In addition, the separator according to an embodiment of the present disclosure
includes inorganic particles introduced to the porous polymer substrate, wherein the
inorganic particles function as supports to further prevent deformation of the porous
polymer substrate.
In the separator according to an embodiment of the present disclosure, since the
20 inorganic particles are introduced to the porous polymer substrate, the porous polymer
substrate shows increased wettability, and thus the amount of slurry for a porous coating
layer with which the porous polymer substrate is impregnated is increased relatively based
on the porous polymer substrate. In this manner, it is possible to protect deformation of
9
the porous polymer substrate, while providing enhanced insulation property.
BEST MODE
Hereinafter, preferred embodiments of the present disclosure will be described in
5 detail with reference to the accompanying drawings. Prior to the description, it should be
understood that the terms used in the specification and the appended claims should not be
construed as limited to general and dictionary meanings, but interpreted based on the
meanings and concepts corresponding to technical aspects of the present disclosure on the
basis of the principle that the inventor is allowed to define terms appropriately for the best
10 explanation.
In one aspect of the present disclosure, there is provided a separator including:
a porous polymer substrate provided with a core portion substrate having a
plurality of pores, and skin portion substrates disposed on both surfaces of the core portion
substrate and having a plurality of pores,
15 wherein both the core portion substrate and the skin portion substrate include first
inorganic particles, or only the core portion substrate includes first inorganic particles, and
when both the core portion substrate and the skin portion substrate include the first
inorganic particles, the core portion substrate includes the first inorganic particles at a
higher weight percentage (wt%) as compared to the skin portion substrate; and
20 a porous coating layer disposed on at least one surface of the porous polymer
substrate, and including a plurality of second inorganic particles and a binder polymer
disposed partially or totally on the surfaces of the second inorganic particles so that the
second inorganic particles may be interconnected and fixed,
10
wherein the first inorganic particles have a higher Mohs hardness than the Mohs
hardness of the second inorganic particles.
Particularly, the porous polymer substrate may be a porous polymer film substrate
or a porous polymer nonwoven web substrate.
5 The porous polymer film substrate may be a porous polymer film including
polyolefin, such as polyethylene, polypropylene, polybutene or polypentene. Such a
polyolefin porous polymer film substrate realizes a shut-down function at a temperature of
80-130°C.
Herein, the polyolefin porous polymer film may be formed of polymers including
10 polyolefin polymers, such as polyethylene, including high-density polyethylene, linear
low-density polyethylene, low-density polyethylene or ultrahigh-molecular weight
polyethylene, polypropylene, polybutylene, or polypentene, alone or in combination of two
or more of them.
In addition, the porous polymer film substrate may be obtained by molding various
15 polymers, such as polyesters, other than polyolefins, into a film shape.
Further, the porous polymer film substrate and porous polymer nonwoven web
substrate may be formed of polyethylene terephthalate, polybutylene terephthalate,
polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetherether ketone,
polyether sulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene,
20 or the like, alone or in combination, besides the above-mentioned polyolefins.
There is no particular limitation in the thickness of the porous polymer substrate,
the porous polymer substrate has a thickness of 1-100 μm, particularly 5-50 μm.
Although there is no particular limitation in the size of the pores present in the porous
11
polymer substrate and porosity, the pore size and porosity may be 0.01-50 μm and 10-95%,
respectively.
The porous polymer substrate has a tri-layer laminate structure including a core
portion substrate having a plurality of pores, and skin portion substrates disposed on both
5 surfaces of the core portion substrate and having a plurality of pores.
Each of the core portion substrate and the skin portion substrate may have a melt
index (MI) of 0.2 g/10 min. or less, 0-0.2 g/10 min, 0.02-0.2 g/10 min., or 0.06-0.2 g/10
min. When the melt index of each of the core portion substrate and the skin portion
substrate satisfies the above-defined range, the polymer resin used in the porous polymer
10 substrate may have a high weight average molecular weight to cause an increase in
modulus of the separator. Therefore, it is possible to minimize deformation of the porous
polymer substrate, and to improve short defects, which may occur after a lamination
process, and degradation of life caused by deformation of the separator due to the internal
pressure of the battery during the evaluation of the life.
15 The melt index (melt flow index) may be determined through the ejected amount
of the resin used in a porous polymer substrate molten under a pressure of 21.6 kg for 10
minutes.
Both the core portion substrate and the skin portion substrate include the first
inorganic particles, or only the core portion substrate includes the first inorganic particles.
20 When the first inorganic particles are introduced to the core portion substrate and the skin
portion substrate, impregnation of the porous polymer substrate with slurry for a porous
coating layer may be increased through the wettability of the porous polymer substrate
improved by the inorganic particles. In addition, when only the core portion substrate
12
includes the first inorganic particles, no inorganic particles exist on the surface of the
porous polymer substrate, and thus the separator may provide improved resistance
characteristics.
Since the porous polymer substrate includes inorganic particles therein, the
5 inorganic particles function as supports so that deformation of the porous polymer
substrate may be minimized during the lamination of an electrode with the separator to
prevent the pores from being damaged, and the problem of degradation of the performance
of an electrochemical device using the separator may be improved. In addition,
impregnation of the porous polymer substrate with slurry for a porous coating layer is
10 increased by the inorganic particles contained in the porous polymer substrate, and the
inorganic particles function as insulators in the porous polymer substrate after drying the
slurry. Therefore, it is possible to prevent a decrease in breakdown voltage of the
separator, and thus to improve Hi-pot defects and low-voltage defects.
When both the core portion substrate and the skin portion substrate include the
15 first inorganic particles, the core portion substrate includes the first inorganic particles at a
higher weight percentage (wt%) as compared to the skin portion substrate.
According to an embodiment of the present disclosure, the weight percentage of
the first inorganic particles in the core portion substrate may be 20-600 times higher or 30-
300 times higher than the weight percentage of the first inorganic particles in the skin
20 portion substrate. When the ratio of the weight percentage of the first inorganic particles
in the core portion substrate to the weight percentage of the first inorganic particles in the
skin portion substrate satisfies the above-defined range, it is possible to minimize
deformation of the porous polymer substrate, to improve the resistance of the separator,
13
and to improve the breakdown voltage characteristics.
Particularly, when only the core portion substrate includes the first inorganic
particles, the core portion may include the first inorganic particles in an amount of 10-20
wt%, or 12-18 wt%.
5 In addition, when both the core portion substrate and the skin portion substrate
include the first inorganic particles, the core portion may include the first inorganic
particles in an amount of 10-20 wt%, or 12-18 wt%, while the skin portion substrate may
include the first inorganic particles in an amount of 0.1-10 wt%, or 0.5-7 wt%.
The separator according to the present disclosure includes a porous coating layer
10 disposed on at least one surface of the porous polymer substrate, and including a plurality
of second inorganic particles and a binder polymer disposed partially or totally on the
surfaces of the second inorganic particles so that the second inorganic particles may be
interconnected and fixed.
In the separator according to an embodiment of the present disclosure, the binder
15 polymer used for forming the porous coating layer may be one used currently for forming a
porous coating layer in the art. Particularly, a polymer having a glass transition
temperature (Tg) of -200 to 200°C may be used. This is because such a polymer can
improve the mechanical properties, such as flexibility and elasticity, of the finally formed
porous coating layer. Such a binder polymer functions as a binder which connects and
20 stably fixes the inorganic particles with one another, and thus contributes to prevention of
degradation of mechanical properties of a separator having a porous coating layer.
In addition, it is not essentially required for the binder polymer to have ion
conductivity. However, when using a polymer having ion conductivity, it is possible to
14
further improve the performance of an electrochemical device. Therefore, a binder
polymer having a dielectric constant as high as possible may be used. In fact, since the
dissociation degree of a salt in an electrolyte depends on the dielectric constant of the
solvent for the electrolyte, a binder polymer having a higher dielectric constant can
5 improve the salt dissociation degree in an electrolyte. The binder polymer may have a
dielectric constant ranging from 1.0 to 100 (measured at a frequency of 1 kHz), particularly
10 or more.
In addition to the above-mentioned function, the binder polymer may be
characterized in that it is gelled upon the impregnation with a liquid electrolyte and thus
10 shows a high degree of swelling. Thus, the binder polymer has a solubility parameter (i.e.,
Hildebrand solubility parameter) of 15-45 MPa1/2 or 15-25 MPa1/2 and 30-45 MPa1/2
.
Therefore, hydrophilic polymers having many polar groups may be used more frequently
as compared to hydrophobic polymers, such as polyolefins. When the solubility
parameter is less than 15 MPa1/2 and more than 45 MPa1/2, it is difficult for the binder
15 polymer to be swelled with a conventional liquid electrolyte for a battery.
Non-limiting examples of the binder polymer include, but are not limited to:
polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-cotrichloroethylene, polymethyl methacrylate, polybutyl acrylate, polybutyl methacrylate,
polyacrylonitrile, polyvinyl pyrro1idone, polyvinyl acetate, polyethylene-co-vinyl acetate,
20 polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose
acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinylalchol, cyanoethyl cellulose,
cyanoethyl sucrose, pullulan, carboxymethyl cellulose, or a mixture of two or more of
them.
15
The first inorganic particles have a higher Mohs hardness as compared to the
second inorganic particles. Particularly, the first inorganic particles may have a Mohs
hardness of 5 or more, 5-10, or 5.5-9, and the second inorganic particles have a Mohs
hardness of less than 5, or 2.5-4.
5 As used herein, the term ‘Mohs hardness’ refers to a value of hardness evaluated
by comparing the hardness of a material to those of 10 types of minerals as standard
materials (Mohs hardness 1: talc, Mohs hardness 2: gypsum, Mohs hardness 3: calcite,
Mohs hardness 4: fluorite, Mohs hardness 5: apatite, Mohs hardness 6: orthoclase, Mohs
hardness 7: quartz, Mohs hardness 8: topaz, Mohs hardness 9: corundum, and Mohs
10 hardness 10: diamond). When rubbing a sample to be evaluated against a standard
material, the material generating scratches was judged to have a lower hardness. In
addition, when it is difficult to determine the Mohs hardness of a material directly, the
material is analyzed for its composition and its hardness may be determined from another
material having the same composition.
15 When the first inorganic particles have a higher Mohs hardness as compared to the
second inorganic particles, it is possible to prevent deformation of the porous polymer
substrate, caused by deformation of the porous coating layer using the second inorganic
particles.
When the second inorganic particles have a Mohs hardness of higher than 5, the
20 inorganic particles having such a high Mohs hardness and contained in the porous coating
layer reduces deformation of the porous coating layer during the lamination process of the
separator, but causes damages to the porous polymer substrate, resulting in degradation of
dielectric properties, deformation of the pores of the porous polymer substrate, and
16
degradation of the life characteristics of the electrochemical device using the separator.
When the second inorganic particles have a Mohs hardness of less than 5, it is
possible to prevent deformation of the porous polymer substrate relatively due to the
deformation of the second inorganic particles in the porous coating layer during the
5 lamination process, which is favorable in terms of the hi-pot characteristics and life
characteristics of the separator.
According to an embodiment of the present disclosure, any combination of the
first inorganic particles with the second inorganic particles may be selected with no
particular limitation, as long as the first inorganic particles have a higher Mohs hardness
10 than the Mohs hardness of the second inorganic particles.

WHAT IS CLAIMED IS:
1. A separator comprising:
a porous polymer substrate provided with a core portion substrate having a
5 plurality of pores, and skin portion substrates disposed on both surfaces of the core portion
substrate and having a plurality of pores,
wherein both the core portion substrate and the skin portion substrate comprise
first inorganic particles, or only the core portion substrate comprises first inorganic
particles, and when both the core portion substrate and the skin portion substrate include
10 the first inorganic particles, the core portion substrate comprises the first inorganic
particles at a higher weight percentage (wt%) as compared to the skin portion substrate;
and
a porous coating layer disposed on at least one surface of the porous polymer
substrate, and comprising a plurality of second inorganic particles and a binder polymer
15 disposed partially or totally on the surfaces of the second inorganic particles so that the
second inorganic particles are interconnected and fixed,
wherein the first inorganic particles have a higher Mohs hardness than the Mohs
hardness of the second inorganic particles.
20 2. The separator according to claim 1, wherein the first inorganic particles
have a Mohs hardness of 5 or more and the second inorganic particles have a Mohs
hardness of less than 5.
39
3. The separator according to claim 1, wherein the first inorganic particles
comprise silicon oxide (SiO), titanium dioxide (TiO2), zirconia (ZrO2), alumina (Al2O3),
barium sulfate (BaSO4), barium titanate (BaTiO3), boehmite, zinc oxide, magnesium oxide,
magnesium hydroxide, aluminum hydroxide, or a mixture of two or more of them.
5
4. The separator according to claim 1, wherein the second inorganic particles
comprise barium sulfate (BaSO4), barium titanate (BaTiO3), boehmite, zinc oxide,
magnesium oxide, magnesium hydroxide, aluminum hydroxide, or a mixture of two or
more of them.
10
5. The separator according to claim 1, wherein when both the core portion
substrate and the skin portion substrate comprise the first inorganic particles, the core
portion substrate comprises the first inorganic particles at a weight percentage (wt%) 20-
600 times higher than the weight percentage of the first inorganic particles in the skin
15 portion substrate.
6. The separator according to claim 1, wherein the core portion substrate
comprises the first inorganic particles at 10-20 wt%.
20 7. The separator according to claim 5, wherein the core portion substrate
comprises the first inorganic particles at 10-20 wt%, and the skin portion substrate
comprises the first inorganic particles at 0.1-10 wt%.
40
8. The separator according to claim 1, wherein the second inorganic particles
have a BET specific surface area of 5-20 m2
/g.
9. The separator according to claim 1, wherein each of the core portion
5 substrate and the skin portion substrate is a polyolefin-based porous polymer substrate.
10. The separator according to claim 1, wherein each of the core portion
substrate and the skin portion substrate has a melt index (MI) of 0.2 g/10 min. or less.
10 11. The separator according to claim 1, wherein the binder polymer comprises
polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-cotrichloroethylene, polymethyl methacrylate, polybutyl acrylate, polybutyl methacrylate,
polyacrylonitrile, polyvinyl pyrro1idone, polyvinyl acetate, polyethylene-co-vinyl acetate,
polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose
15 acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinylalchol, cyanoethyl cellulose,
cyanoethyl sucrose, pullulan, carboxymethyl cellulose, or a mixture of two or more of
them.
12. An electrochemical device comprising a cathode, an anode and a separator
20 interposed between the cathode and the anode, wherein the separator is the same as defined
in any one of claims 1 to 11.
13. The electrochemical device according to claim 12, which is a lithium
41
secondary battery.