TECHNICAL FIELD
The present application claims priority to Korean Patent Application No. 10-2020-
0131460 filed on October 12, 2021 in the Republic of Korea. The present disclosure
relates to a negative electrode for a lithium-ion secondary battery and a secondary battery
10 including the same. Particularly, the present disclosure relates to a negative electrode that
may be used effectively in a battery for quick charging and a second battery including the
same.
BACKGROUND ART
15 As technical development and needs for mobile instruments have been increased,
secondary batteries that is rechargeable and can be downsized and provided with high
capacity have been increasingly in demand. In addition, among such secondary batteries,
lithium secondary batteries having high energy density and operating voltage have been
commercialized and used widely.
20 A lithium secondary battery has a structure including an electrode assembly
having a positive electrode and a negative electrode, each of which includes an active
material coated on an electrode current collector, and a porous separator interposed
between both electrodes; and a lithium salt-containing electrolyte injected to the electrode
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assembly. The electrode is obtained by applying slurry including an active material, a
binder and a conductive material dispersed in a solvent to a current collector, followed by
drying and pressing.
In addition, the fundamental performance characteristics, such as capacity, output
5 and life, of a lithium secondary battery are significantly affected by the negative electrode
material. To maximize the performance of a battery, it is required for the negative
electrode active material to meet several requirements, including an electrochemical
reaction potential close to that of lithium metal, high reversibility of reaction with lithium
ions and a high lithium-ion diffusion rate in the active material. Graphite has been used
10 frequently as a material satisfying such requirements.
To satisfy various electrochemical characteristics of a battery, there has been
suggested a combination of multiple kinds of graphite or a negative electrode having a
multilayer structure. In the case of the conventional electrode having a multilayer
structure, each layer includes only one type of electrode active material, and for example,
15 the upper layer and the lower layer include a negative electrode active material different
from each other (upper layer material a/lower layer material b), or the upper layer and the
lower layer include the same negative electrode active material (upper layer material
a/lower layer material a, or upper layer material b/lower layer material b). However, in
the case of the negative electrode including a stack of layers each including a single type of
20 material, there are problems in that quick charge characteristic are poor, or hightemperature characteristics and capacity are degraded rapidly. There is another problem
in that cracks are generated in the electrode layer, while drying the electrode.
Particularly, when using artificial graphite as a negative electrode active material
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in a battery for high-rate (2 C rate or higher) quick charging, there is a problem of low
conductivity. To improve the conductivity, a method for coating the surface of artificial
graphite with carbon (soft carbon or hard carbon) has been considered. However, in this
case, the electrode active material shows increased strength due to the carbon coating so
5 that the electrode active material may be deformed (the degree of orientation is increased,
or the active material is broken) during the process for manufacturing a battery (pressing
step), resulting in the problems of side reactions and deterioration of high-temperature
characteristics.
Meanwhile, particularly, as the thickness of the electrode active material is
10 increased, the electrode binder migrates toward the top layer according to the evaporation
of a solvent, while the electrode is dried, and thus the electrode binder is distributed
predominantly in the top layer portion to cause a problem of degradation of the binding
force between the electrode and the current collector.
15 DISCLOSURE
Technical Problem
The present disclosure is designed to solve the problems of the related art, and
therefore the present disclosure is directed to providing a negative electrode having a
multilayer structure, which includes a carbon-coated artificial graphite and a non-coated
20 artificial graphite as a negative electrode active material. The present disclosure is also
directed to providing a lithium-ion secondary battery including the negative electrode.
These and other objects and advantages of the present disclosure may be understood from
the following detailed description and will become more fully apparent from the exemplary
5
embodiments of the present disclosure. Also, it will be easily understood that the objects
and advantages of the present disclosure may be realized by the means shown in the
appended claims and combinations thereof.
5 Technical Solution
According to the first embodiment of the present disclosure, there is provided a
negative electrode for a lithium ion secondary battery, including a negative electrode
current collector and a negative electrode active material layer formed on at least one
surface of the negative electrode current collector, wherein the negative electrode active
10 material layer includes a lower layer formed on the surface of the current collector and an
upper layer formed on the top of the lower layer, each of the lower layer and the upper
layer independently includes a negative electrode mixture containing a negative electrode
active material, a conductive material and a binder, each of the upper layer and the lower
layer independently includes a negative electrode active material a and a negative electrode
15 active material b, the negative electrode active material a is an artificial graphite surfacecoated with a carbonaceous material, and the negative electrode active material b is an
artificial graphite and is not coated.
According to the second embodiment of the present disclosure, there is provided
the negative electrode for a lithium-ion secondary battery as defined in the first
20 embodiment, wherein the content of the negative electrode active material b in the upper
layer is 40-60 wt% based on the total content of the negative electrode active material a
and the negative electrode active material b.
According to the third embodiment of the present disclosure, there is provided the
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negative electrode for a lithium-ion secondary battery as defined in the first or the second
embodiment, wherein the proportion of the content of the binder in the negative electrode
mixture of the lower layer is relatively higher than the proportion of the content of the
binder in the negative electrode mixture of the upper layer.
5 According to the fourth embodiment of the present disclosure, there is provided
the negative electrode for a lithium-ion secondary battery as defined in any one of the first
to the third embodiments, wherein each of the artificial graphite of the negative electrode
active material a and the artificial graphite of the negative electrode active material b
independently has a degree of orientation (ratio of I110 to I004 of particles) of 3-25.
10 According to the fifth embodiment of the present disclosure, there is provided the
negative electrode for a lithium-ion secondary battery as defined in any one of the first to
the fourth embodiments, wherein each of the artificial graphite of the negative electrode
active material a and the artificial graphite of the negative electrode active material b
independently has a specific surface area of 0.5-5 m2
/g.
15 According to the sixth embodiment of the present disclosure, there is provided the
negative electrode for a lithium-ion secondary battery as defined in any one of the first to
the fifth embodiments, wherein the carbonaceous material of the negative electrode active
material a includes a low-crystallinity carbonaceous material and/or an amorphous
carbonaceous material.