The present disclosure relates to a solid electrolyte battery and a battery module
including the same. More particularly, the present disclosure relates to a solid electrolyte
battery, which can reduce the interfacial resistance between a negative electrode active
material layer and a separator, while increasing the adhesion to a negative electrode current
collector, and a battery module including the same.
10 The present application claims priority to Korean Patent Application No. 10-2018-
0048585 filed on April 26, 2018 in the Republic of Korea, the disclosures of which
including the specification and drawings are incorporated herein by reference.
BACKGROUND ART
15 A lithium ion battery using a liquid electrolyte has a structure in which a negative
electrode and positive electrode are defined by a separator, and thus may cause a shortcircuit when the separator is damaged by deformation or external impact, resulting in a risk,
such as overheating or explosion. Therefore, it can be said that development of a solid
electrolyte capable of ensuring safety is a very important problem in the field of lithium
20 ion secondary batteries.
A lithium secondary battery using a solid electrolyte has enhanced safety, prevents
leakage of an electrolyte to improve the reliability of a battery, and facilitates manufacture
of a thin battery. In addition, lithium metal may be used as a negative electrode to
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improve energy density. Thus, such a lithium secondary battery using a solid electrolyte
has been expected to be applied to a high-capacity secondary battery for electric vehicles in
addition to a compact secondary battery, and has been spotlighted as a next-generation
battery.
5 Meanwhile, in the case of a battery using a solid electrolyte, its electrodes and
polymer-based separator (membrane) are totally in a solid state and it includes no liquid
electrolyte. Thus, a void generated at the interface between an electrode and a separator
is present as a dead space. Particularly, when the electrode surface is irregular due to the
shape of an active material, aggregation of a conductive material and swelling of a binder,
10 more voids are generated to cause an increase in resistance between an electrode and a
separator, thereby adversely affecting the life characteristics of a battery. Particularly,
when using a graphite-based negative electrode active material, a significant change in
volume of the active material occurs during charge/discharge and the voids are developed
more during the progress of cycles, thereby accelerating degradation of life.
15 In addition, it is known that a solid electrolyte interface layer (SEI layer) formed
during the initial charge process of a conventional lithium ion battery is an important
protective layer that protects a negative electrode active material from side reactions during
the progress of cycles of the battery. The main source for forming such a SEI layer
includes a solvent of a non-aqueous electrolyte or additive, such as vinylene carbonate
20 (VC). However, in the case of a solid electrolyte battery using a solid electrolyte, it has
no solvent or additive, unlike a battery using a liquid electrolyte, and thus it is difficult to
form a SEI layer on the surface of the negative electrode active material. Therefore,
while the solid electrolyte battery repeats cycles, side reactions occur continuously to
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accelerate degradation of the negative electrode active material and to cause a decrease in
life of the battery.
To solve the above-mentioned problem, many attempts have been made to add a
liquid ion conductive material (or electrolyte) in a solid electrolyte battery so that the
5 interface between an electrode and a separator may be filled therewith. To use such a
liquid material, a liquid injection step is to be carried out after the assemblage of a cell.
However, there is a disadvantage in that an excessive amount of a liquid material should be
injected so that it may be present at the interface between a separator and an electrode.
To overcome this, a liquid material, such as an electrolyte or additive, may be
10 absorbed preliminarily into a polymer-based separator. Then, the polymer-based
separator to which the electrolyte is absorbed may be softened to reduce the interfacial
resistance between a separator and an electrode. However, the softened separator has
poor mechanical properties, thereby making it difficult to perform assemblage, and makes
the adhesion between an electrode active material and a current collector weak. As a
15 result, there is a difficulty in practical application of the above-mentioned method.
DISCLOSURE
Technical Problem
The present disclosure is designed to solve the problems of the related art, and
20 therefore the present disclosure is directed to providing a solid electrolyte battery or all
solid state battery, which allows a liquid material to be present only in an electrode so as to
soften a separator, with no separate liquid injection step of an electrolyte, thereby
improving the performance of a battery by retaining the adhesion between an electrode
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active material and a current collector, while reducing the interfacial resistance between a
separator and an electrode, and enables formation of a SEI layer on the surface of a
negative electrode active material even in a solid electrolyte battery system, like in a liquid
electrolyte battery. The present disclosure is also directed to providing a battery module
5 including the battery.
Technical Solution
In one aspect of the present disclosure, there is provided a solid electrolyte battery
according to any one of the following embodiments.
10 According to the first embodiment, there is provided a solid electrolyte battery
including a positive electrode, a negative electrode and a separator interposed between the
positive electrode and the negative electrode,
wherein the negative electrode includes: a negative electrode current collector; a
first negative electrode active material layer formed on at least one surface of the negative
15 electrode current collector and including a first negative electrode active material, a first
solid electrolyte and a first electrolyte salt; and a second negative electrode active material
layer formed on the first negative electrode active material layer and including a second
negative electrode active material, a second solid electrolyte, a second electrolyte salt and a
plasticizer having a melting point of 30-130°C,
20 the solid electrolyte battery is activated at a temperature between the melting point
of the plasticizer and 130°C, and
a solid electrolyte interface (SEI) layer is formed on the surface of the second
negative electrode active material.
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According to the second embodiment, there is provided the solid electrolyte
battery as defined in the first embodiment, wherein the plasticizer has a melting point of
35-65°C.
According to the third embodiment, there is provided the solid electrolyte battery
5 as defined in the first or the second embodiment, wherein the plasticizer is ethylene
carbonate (EC), polyethylene glycol (PEG) having a weight average molecular weight of
1,000 or more, succinonitrile (SN), cyclic phosphate (CP) or at least two of them.
According to the fourth embodiment, there is provided the solid electrolyte battery
as defined in any one of the first to the third embodiments, wherein the plasticizer is used
10 in an amount of 0.1-30 wt% based on the total weight of the second negative electrode
active material layer.
According to the fifth embodiment, there is provided the solid electrolyte battery
as defined in any one of the first to the fourth embodiments, wherein each of the first
negative electrode active material layer and the second negative electrode active material
15 layer further includes a conductive material and a binder.
According to the sixth embodiment, there is provided the solid electrolyte battery
as defined in any one of the first to the fifth embodiments, wherein the weight ratio of the
first negative electrode active material layer to the second negative electrode active
material layer is 1:99-99:1.
20 According to the seventh embodiment, there is provided the solid electrolyte
battery as defined in any one of the first to the sixth embodiments, wherein the plasticizer
is present in a liquid state after the solid electrolyte battery is activated.
According to the eighth embodiment, there is provided the solid electrolyte battery
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as defined in any one of the first to the seventh embodiments, wherein each of the first
negative electrode active material and the second negative electrode active material is a
graphite-based negative electrode active material.
According to the ninth embodiment, there is provided the solid electrolyte battery
5 as defined in any one of the first to the eighth embodiments, wherein the voids in the
second negative electrode active material layer are filled with the liquid-state plasticizer.
According to the tenth embodiment, there is provided the solid electrolyte battery
as defined in any one of the first to the ninth embodiments, wherein the separator includes
a solid electrolyte membrane.
10 According to the eleventh embodiment, there is provided the solid electrolyte
battery as defined in any one of the first to the tenth embodiments, wherein the solid
electrolyte membrane includes a polymer solid electrolyte, an oxide-based solid electrolyte,
a sulfide-based solid electrolyte, or at least two of them.
According to the twelfth embodiment, there is provided the solid electrolyte
15 battery as defined in the eighth embodiment, wherein the graphite-based negative electrode
active material includes natural graphite, artificial graphite, mesocarbon microbeads
(MCMB), carbon fibers, carbon black, soft carbon, hard carbon, or at least two of them.
In another aspect of the present disclosure, there is also provided a battery module
according to the following embodiment.
20 According to the thirteenth embodiment, there is provided a battery module
including the solid electrolyte battery as defined in any one of the first to the twelfth
embodiments, as a unit cell.
In still another aspect of the present disclosure, there is provided a battery pack
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according to the following embodiment.
According to the fourteenth embodiment, there is provided a battery pack
including the battery module as defined in the thirteenth embodiment.
5 Advantageous Effects
According to an embodiment of the present disclosure, since the first negative
electrode active material layer facing the negative electrode current collector includes no
plasticizer, no softening of the solid electrolyte occurs so that the mechanical properties of
the active material layer may be maintained and the adhesion to the negative electrode
10 current collector may be retained. In addition, since the second negative electrode active
material layer facing the separator includes a plasticizer, softening of the solid electrolyte
occurs to reduce the interfacial resistance between the active material layer and the
separator.
Further, the specific plasticizer contained in the second negative electrode active
15 material layer causes reaction on the negative electrode active material surface, during the
initial charge of the solid electrolyte battery, so that a SEI layer may be formed.
In addition, the formed SEI layer functions as a protective layer for the negative
electrode active material and prevents degradation of the negative electrode, thereby
improving the life characteristics of a battery.
20 Further, the plasticizer remaining after the formation of the SEI layer has high ion
conductivity and oxidation reactivity, and thus additionally improves the performance of a
battery Hereinafter, preferred embodiments of the present disclosure will be described in
15 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
20 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 should
be understood that other equivalents and modifications could be made thereto without
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departing from the scope of the disclosure.
In one aspect of the present disclosure, there is provided a solid electrolyte battery
including a positive electrode, a negative electrode and a separator interposed between the
5 positive electrode and the negative electrode, wherein the negative electrode includes: a
negative electrode current collector; a first negative electrode active material layer formed
on at least one surface of the negative electrode current collector and including a first
negative electrode active material, a first solid electrolyte and a first electrolyte salt; and a
second negative electrode active material layer formed on the first negative electrode
10 active material layer and including a second negative electrode active material, a second
solid electrolyte, a second electrolyte salt and a plasticizer having a melting point of 30-
130°C, the solid electrolyte battery is activated at a temperature between the melting point
of the plasticizer and 130°C, and a solid electrolyte interface (SEI) layer is formed on the
surface of the second negative electrode active material.
15 Since the plasticizer has a melting point of 30-130°C, it is present in a solid state at
room temperature of about 15-25°C. Meanwhile, the plasticizer is converted into a liquid
state at a temperature equal to or higher than its melting point and has fluidity.
Subsequently, the plasticizer phase-transformed into a liquid state may form a solid
electrolyte interface (SEI) layer on the surface of the second negative electrode active
20 material through chemical reaction during the initial charge of the battery.
In general, once a battery is manufactured, the battery is finished as commercially
available one after being subjected to an activation step.
Herein, the high-temperature activation step should be carried out at a temperature
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equal to or higher than the melting point of the plasticizer. The activation step may be
carried out by allowing a battery to stand for a predetermined time at a temperature higher
than room temperature, for example 30°C or higher, preferably 35°C or higher, and more
preferably 50°C or higher, and 130°C or lower, preferably 100°C or lower, and more
5 preferably 90°C or lower, while the battery is charged/discharged or not.
The predetermined time may be 10 seconds to 48 hours, preferably 1 minute to 24
hours, more preferably about 1-8 hours.
Meanwhile, when the activation temperature is higher than 130°C, the binder that
may be contained in the electrode active material layer may be cured, thereby making it
10 difficult to realize performance as an electrode. Therefore, the activation temperature
should be 130°C or lower. Accordingly, the plasticizer should have a melting point of
130°C or lower.
According to the present disclosure, after the solid electrolyte battery is
manufactured, it is subjected to an activation step. Herein, the high-temperature
15 activation step may be carried out by allowing the battery to stand at a temperature
between the melting point of the plasticizer and 130°C for a predetermined time, such as
10 seconds to 48 hours, while the battery is not charged/discharged. Then, the plasticizer
forms a SEI layer on the surface of the second negative electrode active material through
chemical reaction during the initial charge of the battery. In this manner, it is possible to
20 prevent degradation of the negative electrode and to improve the life characteristics of the
battery.
Particularly, according to the present disclosure, the first negative electrode active
material layer facing the negative electrode current collector includes no plasticizer and the
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second negative electrode active material layer facing the separator includes a plasticizer.
FIG. 1 is a schematic sectional view illustrating the negative electrode using the
conventional solid electrolyte, and FIG. 2 is a schematic sectional view illustrating the
negative electrode using the solid electrolyte according to an embodiment of the present
5 disclosure. Referring to FIGS. 1 and 2, in the case of the battery using the conventional
solid electrolyte, voids 4 present at the interface between a negative electrode active
material layer 2 and a separator 3 are present as a dead space having no ion conductivity.
Particularly, when the electrode surface is irregular due to the shape of an active material,
aggregation of a conductive material and swelling of a binder, more voids are generated to
10 cause an increase in resistance between the electrode and the separator, thereby adversely
affecting life characteristics of a battery.
However, according to the present disclosure, no softening of the solid electrolyte
occurs in the first negative electrode active material layer 20 so that the active material
layer may retain mechanical properties and the physical adhesion to a current collector 10
15 may be retained. In the second negative electrode active material layer 22, softening of
the solid electrolyte occurs to reduce the interfacial resistance between the second negative
electrode active material layer 22 and the separator 30.
Particularly, when using a graphite-based negative electrode active material,
significant swelling/shrinking of the active material occurs during the charge/discharge
20 cycles of the battery, thereby causing detachment at the interface between the negative
electrode active material layer and the separator. However, since the second negative
electrode active material layer includes a plasticizer according to the present disclosure,
softened solid electrolyte is positioned at the interface between the negative electrode
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active material layer and the separator, and thus breakage of lithium ion conduction paths
may be prevented. As a result, it is possible to improve the life of a battery using a
graphite-based negative electrode active material.
According to an embodiment of the present disclosure, the graphite-based negative
5 electrode active material may include natural graphite, artificial graphite, mesocarbon
microbeads (MCMB), carbon fibers, carbon black, soft carbon, hard carbon, or at least two
of them.
The plasticizer is characterized in that it has a melting point of 30-130°C,
preferably 35-65°C. More particularly, the plasticizer may be any material, as long as it
10 is present in a solid state at room temperature but is transformed into a liquid state at high
temperature. Specifically, the plasticizer may be ethylene carbonate (EC) having a
melting point of about 37°C, polyethylene glycol (PEG) having a weight average
molecular weight of 1,000 or more and a melting point of about 35°C, succinonitrile (SN)
having a melting point of about 57°C, cyclic phosphate (CP) having a melting point of
15 about 65°C, or at least two of them.
Meanwhile, since propylene carbonate (PC) having a melting point of about -49°C,
polyethylene glycol (PEG) having a weight average molecular weight of 600 or less,
polyethylene glycol dimethyl ether (PEGDME) having a melting point of about -23°C,
dioctyl phthalate (DOP) having a melting point of about -50°C, and diethyl phthalate
20 (DEP) having a melting point of about -4°C are present in a liquid state at room
temperature, they cannot be applied as a plasticizer according to the present disclosure.
As one examples of the plasticizer according to the present disclosure, ethylene
carbonate has a melting point of about 37°C. The second negative electrode active
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material slurry containing ethylene carbonate has a melting point slightly higher than the
melting point of ethylene carbonate but is prepared at a temperature lower than the
subsequent activation temperature. Thus, ethylene carbonate can be present in a liquid
state in the slurry, and thus ethylene carbonate can be dispersed homogeneously in the
5 slurry. When the slurry is coated and dried on the first negative electrode active material
layer subsequently, the dispersion medium is removed through evaporation, but ethylene
carbonate remains without evaporation and is transformed into a solid state at room
temperature so that it may be distributed homogeneously around the second negative
electrode active material. Herein, since drying of the second negative electrode active
10 material slurry is carried out by vacuum drying at a temperature equal to or lower than the
melting point of ethylene carbonate, preferably at room temperature, ethylene carbonate is
not transformed into a liquid state but is present in a solid state.
In addition, the solid electrolyte battery including the second negative electrode
active material layer prepared from the second negative electrode active material slurry is
15 exposed to a high temperature higher than 37°C, the melting point of ethylene carbonate,
through the high-temperature activation step. Thus, ethylene carbonate distributed around
the second negative electrode active material is transformed into a liquid state again and
reacts with the electrolyte salt in the negative electrode, and then is present in a liquid state
subsequently even at a temperature of 37°C or lower, thereby forming a solid electrolyte
20 interface (SEI) layer on the negative electrode active material surface through chemical
reaction. Such a SEI layer functions as a protective layer for the negative electrode active
material during the progress of cycles of the solid electrolyte battery, and thus prevents
degradation of the negative electrode active material.
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Further, ethylene carbonate transformed into a liquid state reacts with the second
solid electrolyte, thereby softening the second solid electrolyte. The softened second
negative electrode active material layer has high ion conductivity by itself and is attached
well to the separator to reduce the interfacial resistance between the second negative
5 electrode active material layer and the separator.
Ethylene carbonate is used for the conventional non-aqueous electrolyte and is
advantageous in that it may be applied to most batteries and has no impurities.
Particularly, such ethylene carbonate has high ion conductivity and high oxidation
reactivity (6.2V) in a non-aqueous electrolyte. Thus, ethylene carbonate remaining after
10 the formation of the solid electrolyte interface (SEI) layer has an advantage in that it can
additionally improve the performance of a battery.
In addition to ethylene carbonate, polyethylene glycol having a weight average
molecular weight of 1,000 or more, succinonitrile (SN) and cyclic phosphate (CP) used as
a plasticizer according to the present disclosure can provide effects similar to the above15 described effects of ethylene carbonate. Herein, the temperature at which the second
negative electrode active material slurry is prepared and the temperature in the subsequent
battery activation step may be varied with the type of plasticizer, and may be selected
suitably depending on the melting point of a plasticizer.
Meanwhile, the plasticizer may be used in an amount of 0.1-30 wt%, 0.5-25 wt%,
20 or 0.7-20 wt%, based on the total weight of the second negative electrode active material
layer.
When the plasticizer is used in an amount less than the above-defined range, it is
not possible to provide the effects of plasticizer sufficiently. When the plasticizer is used
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in an amount larger than the above-defined range, the resultant battery becomes similar to
a battery using a liquid electrolyte and improvement of safety is not sufficient.
In addition, the plasticizer may be dissolved and dispersed in a liquid state in the
second negative electrode active material slurry, or may be dispersed in a solid state.
5 Meanwhile, the first negative electrode active material and the second negative
electrode active material may satisfy a weight ratio of 1:99-99:1, preferably 30:70-70:30,
and more preferably 30:70-50:50. It is possible to modify the performance of a battery
suitably by varying the ratio of the negative electrode active material layers.
In addition, the first negative electrode active material layer and the second
10 negative electrode active material layer may include a different negative electrode active
material, may further include a different type of conductive material and binder, and may
have a different compositional ratio of the ingredients.
Meanwhile, the first negative electrode active material layer or the second negative
electrode active material layer may further include a conductive material and binder
15 depending on the type of solid electrolyte or desired performance. Herein, the conductive
material may be used in an amount of 0.1-20 wt%, preferably 1-10 wt%, based on the total
weight of the first and the second negative electrode active material layers. In addition,
the binder may be used in an amount of 0.1-20 wt%, preferably 1-10 wt%, based on the
total weight of the first and the second negative electrode active material layers.
20 The conductive material is not particularly limited, as long as it causes no
chemical change in the corresponding battery and has conductivity. For example, the
conductive material include any one selected from: graphite, such as natural graphite or
artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black,
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furnace black, lamp black or thermal black; conductive fibers, such as carbon fibers or
metallic fibers; metal powder, such as carbon fluoride, aluminum or nickel powder;
conductive whisker, such as zinc oxide or potassium titanate; conductive metal oxide, such
as titanium oxide; and conductive materials, such as polyphenylene derivatives, or a
5 mixture of two or more of them.
In addition, particular examples of the binder include various types of binders,
such as polyvinylidene fluoride-co-hexafluoropropylene (PVDF-co-HFP), polyvinylidene
fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, styrene-butadiene rubber
(SBR), carboxymethyl cellulose (CMC), or the like.
10 In addition, it is preferred to use a solid electrolyte having excellent reduction
stability according to the present disclosure. Since the solid electrolyte mainly functions
to transport lithium ions in the electrodes according to the present disclosure, any solid
electrolyte having high ion conductivity, such as 10-5 S/cm or more, preferably 10-4 S/cm
or more, may be used with no particular limitation.
15 Herein, the solid electrolyte may be a polymer solid electrolyte formed by adding a
polymer resin to a solvated electrolyte salt, or a polymer gel electrolyte formed by
incorporating an organic electrolyte containing an organic solvent and an electrolyte salt,
an ionic liquid, monomer or oligomer to a polymer resin. In addition, the solid electrolyte
may be a sulfide-based solid electrolyte having high ion conductivity or an oxide-based
20 solid electrolyte having high stability.
For example, the polymer solid electrolyte may include a polyether polymer,
polycarbonate polymer, acrylate polymer, polysiloxane polymer, phosphazene polymer,
polyethylene derivatives, alkylene oxide derivatives, phosphate polymer, polyagitation
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lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, polymer containing an
ionically dissociable group, or the like. In addition, the solid polymer electrolyte may
include a polymer resin, such as a branched copolymer including polyethylene oxide
(PEO) backbone copolymerized with a comonomer including an amorphous polymer, such
5 as PMMA, polycarbonate, polydimethylsiloxane (pdms) and/or phosphazene, comb-like
polymer, crosslinked polymer resin, or the like, and may be a mixture of such polymers.
In addition, the polymer gel electrolyte includes an electrolyte salt-containing
organic electrolyte and a polymer resin, wherein the organic electrolyte is used in an
amount of 60-400 parts by weight based on the weight of the polymer resin. There is no
10 particular limitation in the polymer used for the gel electrolyte, and particular examples of
the polymer include polyether polymers, PVC polymers, PMMA polymers,
polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-cohexafluoropropylene: PVDF-co-HFP), or the like. In addition, a mixture of such
polymers may be used.
15 In addition, the electrolyte salt is an ionizable lithium salt and may be represented
by Li+X
-
. Preferably, the lithium salt may be any one selected from the group consisting
of LiTFSI, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB10Cl10, LiPF6, LiAsF6, LiSbF6, LiAlCl4,
LiSCN, LiCF3CO2, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC4F9SO3,
LiC(CF3SO2)3, (CF3SO2)·2NLi, lithium chloroborate, lithium lower aliphatic carboxylate,
20 lithium imide 4-phenylborate and combinations thereof. More preferably, the electrolyte
salt may be lithium bistrifluoromethanesulfonamide (LiTFSI).
In addition, the dispersion medium for the negative electrode active material slurry
according to the present disclosure is not particularly limited, as long as it is used currently
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for preparing negative electrode active material slurry. Particularly, the dispersion
medium may be isopropyl alcohol, N-methyl pyrrolidone (NMP), acetone, water, or the
like.
Meanwhile, the negative electrode for a solid electrolyte battery according to the
5 present disclosure is obtained by coating the first negative electrode active material slurry
onto a negative electrode current collector, followed by drying, to form the first negative
electrode active material layer, and then coating the second negative electrode active
material slurry onto the first negative electrode active material layer, followed by drying,
to provide a negative electrode having the first and the second negative electrode active
10 material layers.
Herein, the coating may be carried out by using any known coating process, such
as slot die coating, gravure coating, spin coating, spray coating, roll coating, curtain
coating, extrusion, casting , screen printing, inkjet printing, or the like.
In addition, the negative electrode active material slurry may be dried by
15 irradiating heat, electron beams (E-beams), gamma rays, or UV (G, H, I-line), or the like,
to vaporize the solvent. Preferably, the second negative electrode active material slurry
may be vacuum dried at room temperature. It is possible for the plasticizer to be present
in a solid state, not a liquid state, through the vacuum drying at room temperature.
Although the dispersion medium is removed through evaporation by the drying
20 step, the other ingredients do not evaporate and remain as they are to form a negative
electrode active material layer.
In addition, according to the present disclosure, the negative electrode current
collector may be a metal plate having conductivity, and may be selected suitably
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depending on the polarity of an electrode used therewith as known in the field of secondary
batteries.
Further, according to the present disclosure, the positive electrode may include any
positive electrode active material with no particular limitation, as long as it can be used as
5 a positive electrode active material for a lithium secondary battery. Particular examples
of the positive electrode active material include, but are not limited to: layered compounds
such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or those
compounds substituted with one or more transition metals; lithium manganese oxides such
as those represented by the chemical formula of Li1+xMn2-xO4 (wherein x is 0-0.33),
10 LiMnO3, LiMn2O3 and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as
LiV3O8, LiV3O4, V2O5 or Cu2V2O7; Ni-site type lithium nickel oxides represented by the
chemical formula of LiNi1-xMxO2 (wherein M is Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x is
0.01-0.3); lithium manganese composite oxides represented by the chemical formula of
LiMn2-xMxO2 (wherein M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01-0.1) or Li2Mn3MO8
15 (wherein M = Fe, Co, Ni, Cu or Zn); lithium manganese composite oxides having a spinel
structure and represented by the formula of LiNixMn2-xO4; LiMn2O4 in which Li is
partially substituted with an alkaline earth metal ion; disulfide compounds; Fe2(MoO4)3;
LiNi0.8Co 0.1Mn0.1O2; or the like.
In addition, the separator is interposed between the negative electrode and the
20 positive electrode and functions to electrically insulate the negative electrode and the
positive electrode from each other while allowing lithium ions to pass therethrough. The
separator may be any solid electrolyte membrane used conventionally in the field of solid
electrolyte batteries with no particular limitation.
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For example, the solid electrolyte membrane may be a polymer solid electrolyte
membrane, oxide-based solid electrolyte membrane, or a sulfide-based solid electrolyte
membrane.
According to an embodiment of the present disclosure, the polymer solid
5 electrolyte may include a polyether polymer, polycarbonate polymer, acrylate polymer,
polysiloxane polymer, phosphazene polymer, polyethylene derivatives, alkylene oxide
derivatives, phosphate polymer, polyagitation lysine, polyester sulfide, polyvinyl alcohol,
polyvinylidene fluoride, polymer containing an ionically dissociable group, or the like.
According to an embodiment of the present disclosure, the sulfide-based solid
10 electrolyte includes Li, X and S, wherein X may include at least one of P, Ge, B, Si, Sn, As,
Cl, F and I.
According to an embodiment of the present disclosure, the oxide-based solid
electrolyte includes Li, A and O, wherein A may include at least one of La, Zr, Ti, Al, P
and I.
15 According to an embodiment of the present disclosure, the solid electrolyte
membrane may further include a lithium salt.
According to an embodiment of the present disclosure, the lithium salt include Li+
as cation, and may include, as anion, at least one of F
-
, Cl-
, Br-
, I-
, NO3
-
, N(CN)2
-
, BF4
-
,
ClO4
-
, AlO4
-
, AlCl4
-
, PF6
-
, SbF6
-
, AsF6
-
, F2C2O4
-
, BC4O8
-
, (CF3)2PF4
-
, (CF3)3PF3
-
,
(CF3)4PF2
-
, (CF3)5PF-
, (CF3)6P
-
, CF3SO3
-
, C4F9SO3
-
, CF3CF2SO3
-
, (CF3SO2)2N
-
, (F2SO2)2N
-
20 ,
CF3CF2(CF3)2CO-
, (CF3SO2)2CH-
, CF3(CF2)7SO3
-
, CF3CO2
-
, CH3CO2
-
, SCN-
, and
(CF3CF2SO2)2N
-
.
Meanwhile, in still another aspect of the present disclosure, there is provided a
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battery module including the lithium secondary battery as a unit cell, a battery pack
including the battery module, and a device including the battery pack as a power source.
Herein, particular examples of the device may include, but are not limited to:
electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, or electric
5 power storage systems.
Hereinafter, the present disclosure will be explained in detail with reference to
examples. However, the following examples are for illustrative purposes only and the
scope of the present disclosure is not limited thereto.
10
1. Example 1
(1) Manufacture of Negative Electrode
First, 3 parts by weight of styrene butadiene rubber (SBR) and 1.5 parts by weight
of carboxymethyl cellulose (CMC) as binders were dissolved in acetonitrile as a solvent to
15 prepare a binder solution, and 3 parts by weight of carbon black (Super C65) as a
conductive material was introduced to the binder solution to obtain a mixed solution.
Next, 80 parts by weight of artificial graphite as the first negative electrode active
material, 8 parts by weight of polyethylene oxide (PEO) as the first solid electrolyte and
3.5 parts by weight of bis-trifluoromethanesulfonimide (LiTFSI) as the first electrolyte salt
20 were mixed at 60°C to obtain homogeneous slurry for the first negative electrode active
material.
Then, slurry was prepared in the same manner as the first negative electrode active
material slurry, and 1 part by weight of ethylene carbonate (melting point: 37°C) as a
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plasticizer was further introduced thereto at room temperature and mixed. After that,
additional solvent was added thereto considering the viscosity to obtain the second
negative electrode active material slurry.
The first negative electrode active material slurry was applied to a copper current
5 collector having a thickness of 20 μm and vacuum-dried at 120°C for 24 hours to form the
first negative electrode active material layer.
Then, the second negative electrode active material slurry was applied onto the
first negative electrode active material layer and vacuum-dried at room temperature for 24
hours to form the second negative electrode active material layer, thereby providing a
10 negative electrode.
Herein, the first negative electrode active material layer and the second negative
electrode active material layer were controlled to a weight ratio of about 30:70.
After drying, ethylene carbonate in the second negative electrode active material
layer was present in a solid state at room temperature.
15
(2) Manufacture of Battery
The negative electrode obtained as described above and lithium metal as a counter
electrode were used to obtain a coin-type half-cell. Particularly, a polymer separator
membrane, i.e. a polymer solid electrolyte membrane (PEO + Lithium bis (fluorosulfonyl)
20 imide (LiFSI), 20:1 (molar ratio)) having a thickness of 50 μm was interposed between
lithium metal and the negative electrode to obtain a half-cell.
(3) High-Temperature Activation Step of Battery
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The obtained battery was stored at 60°C for 10 minutes. After that, ethylene
carbonate used as a plasticizer was transformed into a liquid state.
2. Example 2
5 A negative electrode and a battery were obtained in the same manner as Example 1,
except that 8.5 parts by weight of polyethylene oxide was used instead of 8 parts by weight
of polyethylene oxide as the first and the second solid electrolytes, and 0.5 parts by weight
of succinonitrile (melting point: 57°C) was mixed instead of 1 part by weight of ethylene
carbonate as a plasticizer incorporated to the second negative electrode active material
10 slurry. After drying, succinonitrile contained in the second negative electrode active
material layer was present in a solid state at room temperature.
Next, under the same condition as Example 1, the battery was subjected to a hightemperature activation step. Then, succinonitrile was transformed into a liquid state.
15 3. Comparative Example
A negative electrode and a battery were obtained in the same manner as Example 1,
except that the second negative electrode active material slurry includes no ethylene
carbonate as a plasticizer.
Then, the battery was subjected to a high-temperature activation step under the
20 same condition as Example 1.
4. Determination of Capacity Retention of Battery
Each of the batteries according to Examples 1 and 2 and Comparative Example
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was charged/discharged and the capacity retention was determined. The results are
shown in FIG. 3. Herein, charge/discharge was carried out at a temperature of 25°C and
0.05C., wherein the charge voltage was 1.5V and the discharge voltage was 0.05V.
Referring to FIG. 3, while the batteries repeat charge/discharge cycles, the
5 batteries according to Examples show higher capacity retention as compared to
Comparative Example and the difference in capacity retention tends to increase as the
cycle number is increased.
It can be seen from the above results that the plasticizer used in Examples forms a
SEI layer on the surface of the second negative electrode active material through chemical
10 reaction during the charge of the battery.
The present disclosure has been described in detail with reference to particular
embodiments and drawings. However, it should be understood that the detailed
description and specific examples, while indicating preferred embodiments of the
15 disclosure, are given by way of illustration only, since various changes and modifications
within the scope of the disclosure will become apparent to those skilled in the art from this
detailed description.
[Description of Drawing Numerals]
20 1, 10: Current collector
2: Negative electrode active material layer
3, 30: Separator
4: Void
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20: First negative electrode active material layer
22: Second negative electrode active material layer

1. A solid electrolyte battery comprising a positive electrode, a negative
electrode and a separator interposed between the positive electrode and the negative
5 electrode,
wherein the negative electrode comprises: a negative electrode current collector; a
first negative electrode active material layer formed on at least one surface of the negative
electrode current collector and comprising a first negative electrode active material, a first
solid electrolyte and a first electrolyte salt; and a second negative electrode active material
10 layer formed on the first negative electrode active material layer and comprising a second
negative electrode active material, a second solid electrolyte, a second electrolyte salt and a
plasticizer having a melting point of 30-130°C,
the solid electrolyte battery is activated at a temperature between the melting point
of the plasticizer and 130°C, and
15 a solid electrolyte interface (SEI) layer is formed on the surface of the second
negative electrode active material.
2. The solid electrolyte battery according to claim 1, wherein the plasticizer
has a melting point of 35-65°C.
20
3. The solid electrolyte battery according to claim 1, wherein the plasticizer is
ethylene carbonate (EC), polyethylene glycol (PEG) having a weight average molecular
weight of 1,000 or more, succinonitrile (SN), cyclic phosphate (CP) or at least two of them.
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4. The solid electrolyte battery according to claim 1, wherein the plasticizer is
used in an amount of 0.1-30 wt% based on the total weight of the second negative
electrode active material layer.
5
5. The solid electrolyte battery according to claim 1, wherein each of the first
negative electrode active material layer or the second negative electrode active material
layer further comprises a conductive material and a binder.
10 6. The solid electrolyte battery according to claim 1, wherein the weight ratio
of the first negative electrode active material layer to the second negative electrode active
material layer is 1:99-99:1.
7. The solid electrolyte battery according to claim 1, wherein the plasticizer is
15 present in a liquid state after the solid electrolyte battery is activated.
8. The solid electrolyte battery according to claim 1, wherein each of the first
negative electrode active material and the second negative electrode active material is a
graphite-based negative electrode active material.
20
9. The solid electrolyte battery according to claim 1, wherein the voids in the
second negative electrode active material layer are filled with the liquid-state plasticizer.
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10. The solid electrolyte battery according to claim 1, wherein the separator
comprises a solid electrolyte membrane.
11. The solid electrolyte battery according to claim 10, wherein the solid
5 electrolyte membrane comprises a polymer solid electrolyte, an oxide-based solid
electrolyte, a sulfide-based solid electrolyte, or at least two of them.
12. The solid electrolyte battery according to claim 8, wherein the graphitebased negative electrode active material comprises natural graphite, artificial graphite,
10 mesocarbon microbeads (MCMB), carbon fibers, carbon black, soft carbon, hard carbon,
or at least two of them.
13. A battery module comprising the solid electrolyte battery as defined in any
one of claims 1 to 12, as a unit cell.
15
14. A battery pack comprising the battery module as defined in claim 13