TECHNICAL FIELD
The present application claims priority to Korean Patent Application No. 10-2020-
0157007 filed on November 20, 2020 in the Republic of Korea. The present disclosure
relates to a lithium secondary battery which shows low dissolution of a binder resin during
10 the operation thereof and is prevented from an increase in viscosity of an electrolyte, and a
method for manufacturing the same.
BACKGROUND ART
A lithium secondary battery is an energy storage system which has a fundamental
15 structure of positive electrode/negative electrode/separator/electrolyte, is rechargeable
through the reversible conversion between chemical energy and electrical energy, and
shows high energy density. Such a lithium secondary battery has been used widely for
compact electronics, such as cellular phones and notebook computers. Recently,
application of the lithium secondary battery has been extended rapidly to hybrid electric
20 vehicles (HEV), plug-in electric vehicles (EV), electric bikes (e-bikes) and energy storage
systems (ESS) as a countermeasure for environmental problems, high oil price and energy
efficiency and storage.
When manufacturing and using such a lithium secondary battery, it is an important
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technical problem to ensure the safety of a lithium secondary battery. Particularly, a
separator used conventionally for a lithium secondary battery shows a severe heat
shrinking behavior at high temperature due to its material property and a characteristic
during its manufacturing process, thereby causing a safety problem, such as an internal
5 short-circuit. Recently, there has been suggested an organic-inorganic composite porous
separator prepared by coating a mixture of inorganic particles with a binder resin on a
porous polymer substrate to ensure the safety of a lithium secondary battery. In general,
the binder resin used for such a separator includes a PVDF-based binder resin. However,
in this case, the interlayer adhesion between an electrode and the separator is insufficient to
10 cause a high risk of separation between the electrode and the separator. As a result, there
is a problem in that the inorganic particles separated from the porous coating layer during
such interlayer separation may function as local defects in the lithium secondary device.
To solve the problem, introduction of a non-crystalline polymer material, such as polyvinyl
acetate (PVAc) has been suggested. However, such a non-crystalline polymer material
15 shows high solubility to an electrolyte, and thus it may be dissolved out from the
electrolyte during the operation of a battery to cause a decrease in adhesion of the separator
and separation of the inorganic particles, and degradation of the resistance characteristics
of a battery caused by an increase in viscosity of an electrolyte. Therefore, there is a need
for designing a battery in which the viscosity of an electrolyte is controlled to a
20 predetermined level or lower.
DISCLOSURE
Technical Problem
4
The present disclosure is designed to solve the problems of the related art, and
therefore the present disclosure is directed to providing a method for manufacturing a
battery in which the viscosity of an electrolyte is controlled to a predetermined level or
lower during the operation of the battery. The method for manufacturing a battery
5 according to the present disclosure is characterized by preparing an analysis specimen for a
separator in advance to determine how the viscosity of an electrolyte is increased, and
applying a selected material to the manufacture of a battery.
These and other objects and advantages of the present disclosure may be
understood from the following detailed description. Meanwhile, it will be easily
10 understood that the objects and advantages of the present disclosure may be realized by the
means shown in the appended claims and combinations thereof.
Technical Solution
According to the first embodiment of the present disclosure, there is provided a
15 method for manufacturing a battery, including the steps of:
(S1) preparing an analysis specimen including a binder resin composition selected
as an object to be analyzed;
(S2) dipping the analysis specimen in an organic solvent selected as an object to be
analyzed and allowing the analysis specimen to stand therein for a predetermined time;
20 (S3) removing the analysis specimen from the organic solvent, and determining
the viscosity of the organic solvent; and
(S4) comparing the viscosity of the organic solvent with a reference value.
According to the second embodiment of the present disclosure, there is provided
5
the method for manufacturing a battery as defined in the first embodiment, wherein step
(S2) includes allowing the analysis specimen in the organic solvent to stand therein at 23-
28°C for 24 hours or more.
According to the third embodiment of the present disclosure, there is provided the
5 method for manufacturing a battery as defined in the first or the second embodiment,
wherein the analysis specimen in step (S2) includes the binder resin composition at a ratio
of 1-10 wt% based on 100 wt% of the total weight of the organic solvent and the binder
resin composition.
According to the fourth embodiment of the present disclosure, there is provided
10 the method for manufacturing a battery as defined in any one of the first to the third
embodiments, wherein when the viscosity of the organic solvent is lower than the reference
value in step (S4), the binder resin composition to be analyzed and the organic solvent to
be analyzed are applied to the manufacture of a battery.
According to the fifth embodiment of the present disclosure, there is provided the
15 method for manufacturing a battery as defined in the fourth embodiment, wherein the
reference value is selected from a range of 15-20 cP.
According to the sixth embodiment of the present disclosure, there is provided the
method for manufacturing a battery as defined in the fifth embodiment, wherein the
reference value is 17 cP.
20 According to the seventh embodiment of the present disclosure, there is provided
the method for manufacturing a battery as defined in the fourth embodiment, wherein the
organic solvent is used as an electrolyte in the manufacture of a battery.
According to the eighth embodiment of the present disclosure, there is provided
6
the method for manufacturing a battery as defined in any one of the fourth to the seventh
embodiments, wherein the binder resin composition is used as a binder for a separator in
the manufacture of a battery.
According to the ninth embodiment of the present disclosure, there is provided the
5 method for manufacturing a battery as defined in any one of the first to the eighth
embodiments, wherein the analysis specimen is obtained by dissolving the binder resin
composition in acetone at a concentration of 1-10 wt%, applying the resultant solution to a
release film, and carrying out drying under a humidified condition.
According to the tenth embodiment of the present disclosure, there is provided the
10 method for manufacturing a battery as defined in the ninth embodiment, wherein the
humidified condition includes a relative humidity ranging from 30% to 60%.
According to the eleventh embodiment of the present disclosure, there is provided
the method for manufacturing a battery as defined in any one of the first to the tenth
embodiments, wherein the analysis specimen includes a porous substrate for a separator
15 and a porous coating layer formed on the surface of the porous substrate, the porous
coating layer includes inorganic particles and a binder resin, and the binder resin includes a
polymer resin.
According to the twelfth embodiment of the present disclosure, there is provided
the method for manufacturing a battery as defined in any one of the first to the eleventh
20 embodiments, which further includes a step of manufacturing a separator for a battery by
using the binder resin composition as an ingredient forming the separator.
According to the thirteenth embodiment of the present disclosure, there is provided
the method for manufacturing a battery as defined in any one of the first to the twelfth
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embodiments, which further includes step (S5) of forming an electrode assembly including
a negative electrode, a positive electrode, a separator interposed between the negative
electrode and the positive electrode and an electrolyte, wherein the separator includes the
selected binder resin composition, and the electrolyte includes the selected organic solvent.
5 According to the fourteenth embodiment of the present disclosure, there is
provided the method for manufacturing a battery as defined in any one of the first to the
twelfth embodiments, wherein the organic solvent in step (S2) includes a lithium salt.
Advantageous Effects
10 According to the present disclosure, a binder resin showing a low degree of
dissolution in an electrolyte is used for manufacturing a battery, and thus it is possible to
prevent degradation of adhesion of battery devices, and an increase in resistance caused by
an increase in viscosity of an electrolyte.
15 DESCRIPTION OF DRAWINGS
The accompanying drawings illustrate a preferred embodiment of the present
disclosure and together with the foregoing disclosure, serve to provide further
understanding of the technical features of the present disclosure, and thus, the present
disclosure is not construed as being limited to the drawing. Meanwhile, shapes, sizes,
20 scales or proportions of some constitutional elements in the drawings may be exaggerated
for the purpose of clearer description.
FIG. 1 is a graph illustrating the high-temperature charge/discharge characteristics
and capacity retention of the battery according to each of Examples and Comparative
8
Examples.
FIG. 2 is a graph illustrating the room-temperature charge/discharge characteristics
and capacity retention of the battery according to each of Examples and Comparative
Examples.
5
BEST MODE
Hereinafter, preferred embodiments of the present disclosure will be described in
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
10 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
explanation. Therefore, the description proposed herein is just a preferable example for
the purpose of illustrations only, not intended to limit the scope of the disclosure, so it
15 should be understood that other equivalents and modifications could be made thereto
without departing from the scope of the disclosure.