TECHNICAL FIELD
The present application claims priority to Korean Patent Application No. 10-2020-
0120881 filed on September 18, 2020 in the Republic of Korea. The present disclosure
10 relates to a separator for an electrochemical device and a method for manufacturing the same.
Particularly, the present disclosure relates to a separator for an electrochemical device
including inorganic particles and having improved binding force to an electrode, and a
method for manufacturing the same.
15 BACKGROUND ART
Recently, lithium-ion secondary batteries have been used widely as power sources
of portable electronic instruments, such as notebook PCs, cellular phones, digital cameras,
camcorders, or the like. In addition, since such lithium-ion secondary batteries have high
energy density, they have been applied to transport means, such as electric vehicles.
20 As portable electronic instruments have been downsized and weight-lightened,
casings of nonaqueous secondary batteries have been simplified. Originally, battery cans
made of stainless steel were used as casings. However, after casings made of aluminum
cans have been developed, soft pack casings made of aluminum laminate packs have been
3
developed recently. In the case of a soft pack casing made of aluminum laminate, it is
flexible, and thus may form a gap between an electrode and a separator during
charge/discharge, resulting in the technical problem of degradation of cycle life. To solve
the problem, technologies of adhesion between an electrode and a separator are important,
5 and many technical attempts have been made.
In general, a separator for an electrochemical device has a structure including a
porous polymer film (separator substrate) and an inorganic coating layer formed on at least
one surface of the separator substrate. The inorganic coating layer includes inorganic
particles and a binder resin, and is introduced to provide the separator substrate with
10 durability (for preventing film from breakage) or heat resistance/stability (for preventing
heat shrinking). As a binder resin for such a separator, a polyvinylidene fluoride (PVdF)-
based resin has been used frequently, and the binder resin is migrated toward the separator
surface through a humidified phase separation process to form an adhesive top layer portion
having a high content of binder resin in the vicinity of the surface of the inorganic coating
15 layer. However, since the adhesion of a PVdF-based resin itself is low, it is difficult to
ensure a high level of binding force. To improve the adhesion, the content or coating
amount of the binder resin may be increased. However, in this case, the adhesive layer
becomes thick to cause a decrease in energy density and an increase in resistance undesirably.

WHAT IS CLAIMED IS:
1. A separator for an electrochemical device, comprising a porous polymer
substrate and an inorganic coating layer formed on at least one surface of the porous polymer
5 substrate,
wherein the inorganic coating layer comprises inorganic particles and a binder
polymer,
the inorganic particles comprise composite particles coated with a coupling
compound at least partially on the surfaces thereof,
10 the coupling compound comprises a functional group capable of being bound to
each of the inorganic particles and the binder polymer, and the functional group comprises
at least one selected from the group consisting of an alkyl group, an alkoxy group and and
an ester group,
the binder polymer includes an amorphous polymer and/or a semi-crystalline
15 polymer having a glass transition temperature (Tg) of 60°C or lower.
2. The separator for an electrochemical device according to claim 1, wherein
the binder polymer comprises at least one compound represented by the following Chemical
Formula 1:
20 [Chemical Formula 1]
38
wherein each R independently represents -H, -OR4, -C(=O)-R4, -C(=O)O-R4, -
OC(=O)-R4 or -C(=O)NH-R4; each R4 independently represents H, or a substituted or nonsubstituted C1-C5 alkyl group; m is an integer of 1 or more; and n is 0 or an integer of 1 or
5 more.
3. The separator for an electrochemical device according to claim 1, wherein
the binder polymer comprises at least one selected from polyvinyl acetate (PVAc) and
polyethylene-co-vinyl acetate.
10
4. The separator for an electrochemical device according to claim 1, wherein
the binder polymer has a weight average molecular weight (Mw) of 600,000 or less.
5. The separator for an electrochemical device according to claim 1, wherein
15 the coupling compound comprises a silane compound and/or a titanate compound.
6. The separator for an electrochemical device according to claim 1, wherein
the inorganic coating layer comprises the inorganic particles in an amount of 50 wt% or
39
more, based on 100 wt% of the total weight of the binder polymer and the inorganic particles,
and the inorganic coating layer has a porous structure formed from interstitial volumes
between the inorganic particles.
5 7. The separator for an electrochemical device according to claim 1, wherein
the inorganic coating layer has a top layer portion comprising an electrode adhesive portion
in which the binder polymer is distributed at a higher concentration as compared to the other
portions.
10 8. The separator for an electrochemical device according to claim 1, wherein
the binder polymer further comprises a crystalline binder resin.
9. A method for manufacturing the separator for an electrochemical device as
defined in any one of claims 1 to 8, comprising the steps of:
15 introducing a solvent and a binder polymer to prepare a polymer solution;
introducing inorganic particles to the polymer solution to prepare slurry for forming
an inorganic coating layer; and
applying the slurry to the surface of a porous polymer film substrate and carrying
out drying under a humidified condition to perform a humidified phase separation process,
20 wherein an electrode adhesive portion having a high content of binder polymer is
formed on the surface portion of the inorganic coating layer through the humidified phase
separation process.
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10. The method for manufacturing the separator for an electrochemical device
according to claim 9, wherein the inorganic particles comprise composite particles coated
with a coupling compound.