TECHNICAL FIELD
The present disclosure relates to a separator applicable to an electrochemical
10 device, such as a lithium secondary battery, a method for manufacturing the same, and a
lithium secondary battery including the same.
The present application claims priority to Korean Patent Application No. 10-2020-
0127233 filed on September 29, 2020 and Korean Patent Application No. 10-2020-
0127237 filed on September 29, 2020 in the Republic of Korea, the disclosures of which
15 are incorporated herein by reference.
BACKGROUND ART
Recently, energy storage technology has been given an increasing attention.
Efforts into research and development for electrochemical devices have been actualized
20 more and more, as the application of energy storage technology has been extended to
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
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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
developing such batteries.
Among the commercially available secondary batteries, lithium secondary
5 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
batteries, such as Ni-MH, Ni-Cd and sulfuric acid-lead batteries using an aqueous
electrolyte.
Although such electrochemical devices have been produced from many production
10 companies, safety characteristics thereof show different signs. Evaluation and
securement of safety of such electrochemical devices are very important. For example, a
separator prevents a short-circuit between a positive electrode and a negative electrode and
provides a channel for transporting lithium ions. Therefore, such a separator is an
important element affecting the safety and output characteristics of a battery.
15 Such a separator frequently includes a polyolefin-based porous polymer substrate.
In order to prevent the porous polymer substrate from heat shrinking and to enhance
adhesion to an electrode, there has been frequently used a separator provided with a porous
coating layer including inorganic particles and a binder polymer on at least one surface of a
porous polymer substrate.
20 The separators may be classified broadly into aqueous coating separators using an
aqueous solvent and organic coating separators using an organic solvent, depending on the
porous coating layer. Particularly, the aqueous coating separators allow uniform thin film
coating and show high heat resistance.
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However, there is still a need for a separator showing increased adhesion (Lami
strength) to an electrode, while maintaining high porosity in the porous coating layer.
DISCLOSURE
5 Technical Problem
The present disclosure is designed to solve the problems of the related art, and
therefore the present disclosure is directed to providing an aqueous coating separator which
has excellent heat resistance, includes a porous coating layer having high porosity and
shows improved adhesion to an electrode, a method for manufacturing the same, and a
10 lithium secondary battery including the same.
However, objects to be accomplished by the present disclosure are not limited to
the above-mentioned problem, and other objects of the present disclosure may be
understood from the following detailed description and will become more fully apparent
from the exemplary embodiments of the present disclosure.
15
Technical Solution
In one aspect of the present disclosure, there is provided a separator for a lithium
secondary battery, a method for manufacturing the same and a lithium secondary battery
including the same according to any one of the following embodiments.
20 According to the first embodiment, there is provided a separator for a lithium
secondary battery, including:
a porous polymer substrate; and
a porous coating layer formed on at least one surface of the porous polymer
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substrate, and including inorganic particles, a particle-type binder polymer and a dispersant,
wherein the dispersant includes a carboxyl group and a glycol group, and
when the porous coating layer is divided into a top layer, an intermediate layer and
a bottom layer in the thickness direction, the content of the particle-type binder polymer in
5 the top layer is higher than the content of the particle-type binder polymer in the bottom
layer.
According to the second embodiment, there is provided the separator for a lithium
secondary battery as defined in the first embodiment, wherein the top layer is the
outermost layer, when the porous coating layer is cut into n pieces in the thickness
10 direction; the bottom layer is the layer facing the porous polymer substrate, when the
porous coating layer is cut into n pieces in the thickness direction; the intermediate layer is
the remaining layer except the top layer and the bottom layer in the porous coating layer;
and n is an integer of 3-10.
According to the third embodiment, there is provided the separator for a lithium
15 secondary battery as defined in the first or the second embodiment, wherein the content of
the particle-type binder polymer has a concentration gradient with which it increases from
the bottom layer to the top layer based on the thickness direction of the porous coating
layer, and the content of the inorganic particles has a concentration gradient with which it
increases from the top layer to the bottom layer based on the thickness direction of the
20 porous coating layer.
According to the fourth embodiment, there is provided the separator for a lithium
secondary battery as defined in any one of the first to the third embodiments, wherein the
intermediate layer in the porous coating layer has a gradual concentration gradient of the
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particle-type binder polymer, or has no specific concentration gradient.
According to the fifth embodiment, there is provided the separator for a lithium
secondary battery as defined in any one of the first to the fourth embodiments, wherein the
weight ratio of the inorganic particles to the dispersant is 99.5:0.5-95:5.
5 According to the sixth embodiment, there is provided the separator for a lithium
secondary battery as defined in any one of the first to the fifth embodiments, wherein the
content of the particle-type binder polymer is 10-50 parts by weight based on 100 parts by
weight of the porous coating layer.