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DESCRIPTION
NON-AQUEOUS ELECTROLYTE INCLUDING ADDITIVE FOR NON-AQUEOUS
ELECTROLYTE, AND LITHIUM SECONDARY BATTERY INCLUDING THE
NON-AQUEOUS ELECTROLYTE
TECHNICAL FIELD
[0001] [Cross-reference to Related Applications]
[0002] This application claims the priority of Korean Patent
Application No. 10-2022-0005270 filed on January 13, 2022,
in the Korean Intellectual Property Office, the disclosure
of which is incorporated herein by reference.
[0003] [Technical Field]
[0004] The present invention relates to a non-aqueous
electrolyte including an additive for a non-aqueous
electrolyte, and a lithium secondary battery including the
non-aqueous electrolyte.
BACKGROUND ART
[0005] Recently, as application fields of a lithium
secondary battery have rapidly expanded to not only the power
supply of electronic devices such as electricity,
electronics, communications, and computers but also the
power storage supply of large-area devices such as
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automobiles and power storage devices, a demand for a
secondary battery having high capacity, high output, and
high stability has been increasing.
[0006] In particular, in a lithium secondary battery for
automobiles, high capacity, high output, and long-term
service life characteristics have been becoming important.
In order to increase the capacity of the secondary battery,
a high-nickel positive electrode active material having high
energy density but low stability can be used, or the
secondary battery can be driven with a high voltage.
[0007] However, when the secondary battery is driven under
the above conditions, as charge and discharge proceeds, the
surface structure of an electrode or a film formed on the
surface of positive/negative electrode deteriorates due to
a side reaction caused by the deterioration of an electrolyte,
and thus transition metal ions may be eluted from the surface
of the positive electrode. As described above, since the
eluted transition metal ions are electro-deposited on the
negative electrode, and reduce passivation ability of a solid
electrolyte interphase (SEI), there occurs a problem in that
the negative electrode is deteriorated.
[0008] This deterioration phenomenon of the secondary
battery tends to be further accelerated when the potential
of the positive electrode is increased or when the battery
is exposed to high temperatures.
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[0009] In addition, when the lithium ion battery is
continuously used for a long period of time or left to stand
at high temperatures, gas is generated, thereby causing a
so-called swelling phenomenon in which the thickness of the
battery increases, and it is known that the amount of gas
generated in this case depends on the state of the SEI.
[0010] Therefore, in order to solve such problems, research
and development on methods capable of suppressing the elution
of metal ions from the positive electrode and forming a
stable SEI film on the negative electrode, thereby reducing
the swelling phenomenon of the secondary battery and
increasing the stability at high temperatures have been
attempted.
DISCLOSURE OF THE INVENTION
TECHNICAL PROBLEM
[0011] An aspect of the present invention provides an
additive for a non-aqueous electrolyte capable of
suppressing the degradation of a positive electrode,
reducing side reactions between a positive electrode and an
electrolyte, and forming a stable SEI film on a negative
electrode.
[0012] Another aspect of present invention provides a non-
aqueous electrolyte having improved stability at high
temperatures by including the additive for a non-aqueous
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electrolyte.
[0013] Another aspect of the present invention provides a
lithium secondary battery having improved overall
performance by including the non-aqueous electrolyte,
thereby having improved high-temperature cycle
characteristics and high-temperature storage characteristics.
TECHNICAL SOLUTION
[0014] According to an aspect of the present invention,
there is provided a non-aqueous electrolyte including an
additive for a non-aqueous electrolyte, the additive
including a repeating unit represented by Formula 1 and
Formula 2 below:
[0015] [Formula 1]
RI
0
[0016] In Formula 1 above, X is a perfluoroalkyl group
having 1 to 10 carbon atoms, and R1 is any one selected from
the group consisting of H, an alkyl group having 1 to 10
carbon atoms, an alkenyl group having 2 to 20 carbon atoms,
an alkynyl group having 2 to 20 carbon atoms, an alkoxy group
having 1 to 20 carbon atoms, a cycloalkyl group having 3 to
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12 carbon atoms, a cycloalkenyl group having 3 to 12 carbon
atoms, an aryl group having 6 to 12 carbon atoms, a halogen
atom, and a nitrile group.
[0017] [Formula 2]
R2
0
[0018] In Formula 2 above, R is an alkyl group having 1 to
carbon atoms which is substituted with at least one
nitrile group, and R2 is any one selected from the group
consisting of H, an alkyl group having 1 to 10 carbon atoms,
10 an alkenyl group having 2 to 20 carbon atoms, an alkynyl
group having 2 to 20 carbon atoms, an alkoxy group having 1
to 20 carbon atoms, a cycloalkyl group having 3 to 12 carbon
atoms, a cycloalkenyl group having 3 to 12 carbon atoms, an
aryl group having 6 to 12 carbon atoms, a halogen atom, and
a nitrile group.
[0019] According to another aspect of the present invention,
there is provided a lithium secondary battery including the
non-aqueous electrolyte.
ADVANTAGEOUS EFFECTS
[0020] A polymer, which is provided as an additive for a
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non-aqueous electrolyte and contains a repeating unit
represented by Formula 1 and Formula 2, is capable of forming
an elastic and robust solid electrolyte interphase (SEI)
film on the surface of a negative electrode. Therefore, it
is possible to prevent the negative electrode from
deteriorating by maintaining the robust SEI layer even at
high temperatures, and suppress an additional SEI formation
reaction by solvent decomposition during cycles.
[0021] In addition, the polymer, which is provided as the
additive for a non-aqueous electrolyte of the present
invention, includes a perfluoroalkyl group in the repeating
unit of Formula 1, thereby a LiF inorganic material is easily
produced, and thus it is possible to form a stable polymer-
inorganic material-based SEI layer.
[0022] Moreover, the polymer, which is provided as the
additive for a non-aqueous electrolyte of the present
invention, includes a nitrile group in the repeating unit of
Formula 2, and thus is well electro-deposited on a negative
electrode, so that the SEI layer may be easily formed.
[0023] Therefore, when the non-aqueous electrolyte of the
present invention including the polymer provided as the
additive for a non-aqueous electrolyte of the present
invention is used, it is possible to form an electrode-
electrolyte interface which is stable and has strong
durability even at high temperatures, and thus high-
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temperature cycle characteristics and high-temperature
storage characteristics are improved, so that a lithium
secondary battery with improved overall performance may be
achieved.
MODE FOR CARRYING OUT THE INVENTION
[0024] It will be understood that terms or words used in
the present specification and claims shall not be construed
as being limited to having meanings defined in commonly used
dictionaries, but should be interpreted as having meanings
and concepts consistent with the technical idea of the
present invention based on the principle that an inventor
may appropriately define concepts of the terms to best
explain the invention.
[0025] It will be further understood that the terms
"include," "comprise," or "have" in this specification
specify the presence of stated features, numbers, steps,
elements, or combinations thereof, but do not preclude the
presence or addition of one or more other features, numbers,
steps, elements, or combinations thereof.
[0026] Also, the expressions "a" and "b" in the description
of "a to b carbon atoms" in the specification each denote
the number of carbon atoms included in a specific functional
group. That is, the functional group may include "a" to "b"
carbon atoms. For example, the expression "alkylene group
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having 1 to 5 carbon atoms" denotes an alkylene group
including 1 to 5 carbon atoms, that is, -CH2-, -CH2CH2-, -
CH2CH2CH2-, -CH2CH(CH3)-, -CH(CH3)CH2-, -CH(CH3)CH2CH2-, and
the like.
[0027] Furthermore, in the present specification, the
expression "alkyl group" denotes a branched or unbranched
monovalent saturated hydrocarbon group.
[0028] In addition, in the present specification, an alkyl
group, an alkenyl group, an alkynyl group, an alkoxy group,
a cycloalkyl group, a cycloalkenyl group and an aryl group
may be substituted or unsubstituted. Unless
otherwise
defined, the term "substituted" means that at least one
hydrogen bonded to carbon is substituted with an element
other than hydrogen, and for example, it means being
substituted with an alkyl group having 1 to 20 carbon atoms,
an alkenyl group having 2 to 20 carbon atoms, an alkynyl
group having 2 to 20 carbon atoms, an alkoxy group having 1
to 20 carbon atoms, a cycloalkyl group having 3 to 12 carbon
atoms, a cycloalkenyl group having 3 to 12 carbon atoms, a
heterocycloalkyl group having 3 to 12 carbon atoms, a
heterocycloalkenyl group having 3 to 12 carbon atoms, an
aryloxy group having 6 to 12 carbon atoms, a halogen atom,
a fluoroalkyl group having 1 to 20 carbon atoms, a nitro
group, an aryl group having 6 to 20 carbon atoms, a
heteroaryl group having 2 to 20 carbon atoms, a haloaryl
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group having 6 to 20 carbon atoms, etc.
[0029] Hereinafter, the present invention will be described
in more detail.
[0030] Non-aqueous Electrolyte
[0031] A non-aqueous electrolyte according to the present
invention may include a polymer containing a repeating unit
represented by Formula 1 and Formula 2 below. A secondary
battery including the non-aqueous electrolyte of the present
invention may have excellent high-temperature cycle
characteristics and high-temperature storage characteristics
since deterioration caused by interfacial reactions at high
temperatures is suppressed.
[0032] [Formula 1]
RI
0
[0033] [Formula 2]
R2
0
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[0034] In addition, the repeating unit of Formula 1
contained in the polymer, which is provided as the additive
for a non-aqueous electrolyte of the present invention,
includes a perfluoroalkyl group, thereby a LiF inorganic
material is easily produced, and thus it is possible to form
a SEI layer based on a stable polymer-inorganic material.
Therefore, it is possible to suppress the degradation in
passivation ability of SEI at high temperatures, thereby
preventing the negative electrode from deteriorating.
[0035] Moreover, the polymer, which is provided as the
additive for a non-aqueous electrolyte of the present
invention, includes a nitrile group in the repeating unit of
Formula 2, and thus is well electro-deposited on a negative
electrode, so that the SEI layer may be easily formed.
Therefore, it is possible to rapidly form a robust SEI layer.
[0036] In Formula 1 above, X may be a perfluoroalkyl group
having 1 to 10 carbon atoms. Preferably, X in Formula 1 above
may be a linear or branched perfluoroalkyl group having 1 to
5 carbon atoms, and most preferably, X in Formula 1 above
may be a linear perfluoroalkyl group having 1 to 3 carbon
atoms.
[0037] In Formula 2 above, R may be an alkyl group having 1
to 10 carbon atoms which is substituted with at least one
nitrile group. Preferably, R in Formula 2 above may be a
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linear or branched alkyl group having 1 to 5 carbon atoms
which is substituted with at least one nitrile group, and
most preferably, R in Formula 2 above may be an alkyl group
having 1 to 3 carbon atoms which is substituted with at least
one nitrile group.
[0038] In Formulae 1 and 2 above, R1 and R2 may be each
independently any one selected from the group consisting of
H, an alkyl group having 1 to 10 carbon atoms, an alkenyl
group having 2 to 20 carbon atoms, an alkynyl group having
2 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon
atoms, a cycloalkyl group having 3 to 12 carbon atoms, a
cycloalkenyl group having 3 to 12 carbon atoms, an aryl group
having 6 to 12 carbon atoms, a halogen atom, and a nitrile
group. Preferably, R1 and R2 in Formulae 1 and 2 above may
be each independently any one selected from the group
consisting of H and an alkyl group having 1 to 10 carbon
atoms. Most preferably, R1 and R2 in Formulae 1 and 2 above
may be H.
[0039] The non-aqueous electrolyte according to the present
invention may include a polymer represented by Formula 3
below as an additive.
[0040] [Formula 3]
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fl
0 0
[0041] In Formula 3 above, X may be a perfluoroalkyl group
having 1 to 10 carbon atoms. Preferably, X in Formula 3 above
may be a linear or branched perfluoroalkyl group having 1 to
5 carbon atoms, and most preferably, X in Formula 3 above
may be a linear perfluoroalkyl group having 1 to 3 carbon
atoms.
[0042] In Formula 3 above, R may be an alkyl group having 1
to 10 carbon atoms which is substituted with at least one
nitrile group. Preferably, R in Formula 3 above may be a
linear or branched alkyl group having 1 to 5 carbon atoms
which is substituted with at least one nitrile group, and
most preferably, R in Formula 3 above may be an alkyl group
having 1 to 3 carbon atoms which is substituted with at least
one nitrile group.
[0043] In Formula 3 above, m and n may be each independently
an integer of 1 to 100. Preferably, m may be an integer of
10 to 50, and n may be an integer of 60 to 100, and most
preferably, m may be an integer of 10 to 30, and n may be an
integer of 70 to 90. If m and n in Formula 3 above satisfies
the above range, there is an advantage in that an amount of
an inorganic material component such as LiF may be
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appropriately adjusted due to the additive of the present
invention when the SEI layer based on the polymer-inorganic
material is formed.
[0044] The additive for a non-aqueous electrolyte according
to the present invention may be included in an amount of
0.01 parts by weight to 5 parts by weight, preferably 0.05
parts by weight to 2 parts by weight, and more preferably,
0.10 parts by weight to 1.5 parts by weight based on 100
parts by weight of the non-aqueous electrolyte. When the
content of the polymer containing the repeating unit
represented by Formula 1 and Formula 2 above satisfies the
above range, the film-forming effect on the surface of the
negative electrode is sufficient, and thus there is an effect
of achieving excellent high-temperature service life
characteristics and high-temperature storage characteristics.
[0045] The non-aqueous electrolyte according to the present
invention may further include a lithium salt, an organic
solvent, or other electrolyte additives.
[0046] The lithium salt is used as an electrolyte salt in
the lithium secondary battery, wherein it is used as a medium
for transferring ions. Typically, for example, the lithium
salt may include Li + as a cation, and may include at least
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one selected from the group consisting of Br-, I-,
NO3-, N(CN)2-, BF4-, C104-, BI0C110-, A1C14-, A102-, PF6-, CF3S03-f
CH3CO2 f CF 3C 0 2 f ASF 6 f SbF 6 f CH 3S 0
3 f (CF 3CF 2S 0 2) 2N-,
(CF 3S 0 2) 2N-, (F SO 2) 2N-, HF 2C 20 4 f BC 4 8 PF 4C 20
4 r PF2C408 r
(CF3)2PF4 f (CF 3) 3P F 3 f (CF 3) 4P F 2 f (CF 3) 5P F (CF 3) 6P
C4F 9S03 r
CF 3CF 2S03 f CF 3CF 2 CF 3) 2C 0 f CF 3S 0 2) 2CH CF 3 (CF
2) 0 3 f and SCN
as an anion.
[0047] Specifically, the lithium salt may include a single
material selected from the group consisting of LiC1, LiBr,
LiI, LiBF4, LiC104, LiB10C110, LiA1C14, LiA102, LiPF6, LiCF3S03,
LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3S03, LiN(502F)2
(lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO2CF2CF3)2
(lithium bis(perfluoroethanesulfonyl)imide, LiBETI), and
LiN(502CF3)2 (lithium bis(trifluoromethanesulfonyl)imide,
LiTFSI) or a mixture of two or more thereof. In addition to
the above, any lithium salt commonly used in an electrolyte
of a lithium secondary battery may be used without limitation.
[0048] The lithium salt may be appropriately changed in a
normally usable range, but may be included in a concentration
of 0.5 M to 4.0 M, preferably, 1.0 M to 3.0 M, and more
preferably, 1.5 M to 2.0 M in the electrolyte in order to
obtain an optimum effect of forming a film for preventing
corrosion on the surface of an electrode. When the
concentration of the lithium salt satisfies the above range,
there is a sufficient effect of improving cycle
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characteristics during high-temperature storage of a lithium
secondary battery, and the viscosity of the non-aqueous
electrolyte is suitable, so that the impregnability of the
electrolyte may be improved.
[0049] The non-aqueous organic solvent may include at least
one organic solvent selected from the group consisting of a
cyclic carbonate-based organic solvent, a linear carbonate-
based organic solvent, a linear ester-based organic solvent,
and a cyclic ester-based organic solvent.
[0050] The additive according to the present invention is
effective particularly in the case of using the cyclic
carbonate solvent. When a conventional electrolyte additive
is used in conjunction with the cyclic carbonate solvent,
the SEI film formed by the decomposition of the cyclic
carbonate solvent has had a problem in that it is difficult
to maintain the SEI film due to a change in volume of the
negative electrode, which occurs during cycles, and thus the
solvent is continually decomposed. Thus, there has been a
problem in that the ionic conductivity of the electrolyte is
reduced, and thus the cycle characteristics are deteriorated.
However, when the polymer according to the present invention
is used as an additive in conjunction with the cyclic
carbonate solvent, it is possible to form a robust SEI film,
and thus there is an effect of maintaining cycle
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characteristics high.
[0051] The cyclic carbonate-based organic solvent is an
organic solvent which may well dissociate the lithium salt
in the electrolyte due to high permittivity as a highly
viscous organic solvent, wherein specific examples of the
cyclic carbonate-based organic solvent may be at least one
organic solvent selected from the group consisting of
ethylene carbonate (EC), propylene carbonate (PC), fluoro
ethylene carbonate (FEC), 1,2-butylene carbonate, 2,3-
butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene
carbonate, and vinylene carbonate, and, among them, the
cyclic carbonate-based organic solvent may include fluoro
ethylene carbonate.
[0052] Also, the linear carbonate-based organic solvent is
an organic solvent having low viscosity and low permittivity,
wherein typical examples of the linear carbonate-based
organic solvent may be at least one organic solvent selected
from the group consisting of dimethyl carbonate (DMC),
diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl
carbonate (EMC), methylpropyl carbonate, and ethylpropyl
carbonate, and the linear carbonate-based organic solvent
may specifically include diethyl carbonate (DEC).
[0053] Furthermore, the organic solvent may further include
at least one ester-based organic solvent selected from the
group consisting of a linear ester-based organic solvent and
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a cyclic ester-based organic solvent in addition to at least
one carbonate-based organic solvent selected from the group
consisting of the cyclic carbonate-based organic solvent and
the linear carbonate-based organic solvent, in order to
prepare an electrolyte having high ionic conductivity.
[0054] Specific examples of the linear ester-based organic
solvent may be at least one organic solvent selected from
the group consisting of methyl acetate, ethyl acetate, propyl
acetate, methyl propionate, ethyl propionate, propyl
propionate, and butyl propionate.
[0055] Also, the cyclic ester-based organic solvent may
include at least one organic solvent selected from the group
consisting of y-butyrolactone, y-valerolactone, y-
caprolactone, o-valerolactone, and c-caprolactone.
[0056] Meanwhile, if necessary, any organic solvent commonly
used in a non-aqueous electrolyte may be additionally used
without limitation as the organic solvent. For example, at
least one organic solvent among an ether-based organic
solvent, a glyme-based organic solvent, and a nitrile-based
organic solvent may be further included.
[0057] As the ether-based solvent, any one selected from the
group consisting of dimethyl ether, diethyl ether, dipropyl
ether, methyl ethyl ether, methyl propyl ether, ethyl propyl
ether, 1,3-dioxolane (DOL), and 2,2-bis(trifluoromethyl)-
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1,3- dioxolane (TFDOL) or a mixture of two or more thereof
may be used, but the ether-based solvent is not limited
thereto.
[0058] The glyme-based organic solvent is a solvent having
higher dielectric constant and lower surface tension than
the linear carbonate-based organic solvent and having lower
reactivity with metal, wherein the glyme organic solvent may
include at least one selected from the group consisting of
dimethoxyethane (glyme, DME), diglyme, triglyme, and
tetraglyme (TEGDME), but the glyme organic solvent is not
limited thereto.
[0059] The nitrile-based organic solvent may include at
least one selected from the group consisting of acetonitrile,
propionitrile, butyronitrile, valeronitrile, caprylonitrile,
heptanenitrile, cyclopentane carbonitrile, cyclohexane
carbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile,
difluorobenzonitrile,
trifluorobenzonitrile,
phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-
fluorophenylacetonitrile, but the nitrile organic solvent is
not limited thereto.
[0060] In addition, the non-aqueous electrolyte of the
present invention may further include, if necessary, an
electrolyte additive known in the art in the non-aqueous
electrolyte in order to prevent the non-aqueous electrolyte
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from being decomposed in a high-output environment and
causing a negative electrode to collapse, or to further
improve low-temperature high-rate discharge characteristics,
high-temperature stability, overcharge prevention, an effect
of suppressing battery expansion at high temperatures, and
the like.
[0061] Representative examples of the additional
electrolyte additive may include at least one additive for
forming an SEI film selected from the group consisting of a
cyclic carbonate-based compound, a halogen-substituted
carbonate-based compound, a sultone-based compound, a
sulfate-based compound, a phosphate-based compound, a
borate-based compound, a nitrile-based compound, a benzene-
based compound, an amine-based compound, a silane-based
compound, and a lithium salt-based compound.
[0062] The cyclic carbonate-based compound may include
vinylene carbonate (VC) or vinyl ethylene carbonate.
[0063] The halogen-substituted carbonate-based compound may
include fluoroethylene carbonate (FEC).
[0064] The sultone-based compound may include at least one
compound selected from the group consisting of 1,3-propane
sultone (PS), 1,4-butane sultone, ethene sultone, 1,3-
propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-
propene sultone.
[0065] The sulfate-based compound may include ethylene
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sulfate (Esa), trimethylene sulfate (TMS), or methyl
trimethylene sulfate (MTMS).
[0066] The phosphate-based compound may include at least one
compound selected from the group consisting of lithium
difluorobis(oxalato)phosphate, lithium difluorophosphate,
tetramethyl trimethylsilyl phosphate, trimethylsilyl
phosphite, tris(2,2,2-trifluoroethyl)phosphate, and
tris(trifluoroethyl)phosphite.
[0067] The borate-based compound may include
tetraphenylborate, lithium oxalyldifluoroborate (LiODFB),
and lithium bis(oxalato)borate (LiB(C204)2, LiBOB) .
[0068] The nitrile-based compound may include at least one
compound selected from the group consisting of
succinonitrile, adiponitrile, acetonitrile, propionitrile,
butyronitrile, valeronitrile,
caprylonitrile,
heptanenitrile,
cyclopentanecarbonitrile,
cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-
fluorobenzonitrile,
difluorobenzonitrile,
trifluorobenzonitrile, phenylacetonitrile, 2-
fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.
[0069] The benzene-based compound may include fluorobenzene,
the amine-based compound may include triethanolamine or
ethylenediamine, and the silane-based compound may include
tetravinylsilane.
[0070] The lithium salt-based compound is a compound
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different from the lithium salt included in the non-aqueous
electrolyte, and may be lithium difluorophosphate (LiDFP),
LiP02F2, LiBF4, or the like.
[0071] Among the additional electrolyte additives, when a
combination of vinylene carbonate (VC), 1,3-propane sultone
(PS), ethylene sulfate (Esa), and lithium difluorophosphate
(LiDFP) is further included, it is possible to form a more
robust SEI film on the surface of a negative electrode during
an initial activation process of a secondary battery, and to
suppress the generation of a gas which may be generated due
to the decomposition of an electrolyte at high temperatures,
thereby improving high-temperature stability of the
secondary battery.
[0072] Meanwhile, the additional additives may be used as a
mixture of two or more thereof, and may be included in an
amount of 0.050 wt% to 20 wt%, particularly 0.10 wt% to 15
wt%, and preferably 0.30 wt% to 10 wt% based on a total
weight of the non-aqueous electrolyte. When the content of
the additional electrolyte additives satisfies the above
range, there is a more excellent effect of improving ionic
conductivity and cycle characteristics.
[0073] Lithium Secondary Battery
[0074] The present invention also provides a lithium
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secondary battery including the non-aqueous electrolyte.
[0075] Specifically, the lithium secondary battery includes
a positive electrode including a positive electrode active
material, a negative electrode including a negative
electrode active material, a separator disposed between the
positive electrode and the negative electrode, and the above-
described non-aqueous electrolyte.
[0076] In this case, the lithium secondary battery of the
present invention may be prepared according to a typical
method known in the art. For example, after an electrode
assembly is formed by sequentially stacking a positive
electrode, a negative electrode, and a separator disposed
between the positive electrode and the negative electrode,
the lithium secondary battery of the present invention may
be prepared by inserting the electrode assembly into a
battery case, and injecting the non-aqueous electrolyte
according to the present invention.
[0077] (1) Positive Electrode
[0078] The positive electrode may be prepared by coating a
positive electrode collector with a positive electrode
material mixture slurry including a positive electrode
active material, a binder, a conductive agent, and a solvent.
[0079] The positive electrode collector is not particularly
limited so long as it has conductivity without causing
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adverse chemical changes in the battery, and, for example,
stainless steel, aluminum, nickel, titanium, fired carbon,
or aluminum or stainless steel that is surface-treated with
one of carbon, nickel, titanium, silver, or the like may be
used.
[0080] The positive electrode active material is a compound
capable of reversibly intercalating and deintercalating
lithium, wherein the positive electrode active material may
specifically include a lithium metal oxide including lithium
and at least one metal such as cobalt, manganese, nickel, or
aluminum. More specifically, the lithium metal oxide may
include a lithium-manganese-based oxide (e.g., LiMn02,
LiMn204, etc.), a lithium-cobalt-based oxide (e.g., LiCo02,
etc.), a lithium-nickel-based oxide (e.g., LiNi02, etc.), a
lithium-nickel-manganese-based oxide (e.g., LiNi1_yMny02
(where 0<y<1), LiMn2Niz04 (where 0<z<2), etc.), a lithium-
nickel-cobalt-based oxide (e.g., LiNi1_y1Coy102 (where O<Y1<1),
etc.), a lithium-manganese-cobalt-based oxide (e.g., LiCol_
y2Mny202 (where O<Y2<1), LiMn2_z1Coz104(where 0<z1<2), etc.), a
lithium-nickel-manganese-cobalt-based oxide (e.g.,
Li(NipCoqMnr)02 (where 0<p<1, 0<q<1, 0< r<1, and p+q+r=1) or
Li (NipiCogiMnri) 04 (where 0<p1<2, 0<q1<2, 0<r1<2, and
p1+q1+r1=2), etc.), or a lithium-nickel-cobalt-transition
metal (M) oxide (e.g., Li
(Nip2Coq2Mnr2Ms2)02 (where M is
23
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CA 03228292 2024-02-05
selected from the group consisting of Al, Fe, V, Cr, Ti, Ta,
Mg, and Mo, and p2, q2, r2, and s2 are atomic fractions of
each independent elements, wherein 0<p2<1, 0<q2<1, 0<r2<1,
0<s2<1, and p2+q2+r2+52=1), etc.), and any one thereof or a
compound of two or more thereof may be included.
[0081] Among these materials, in terms of the improvement
of capacity characteristics and stability of the battery,
the lithium metal oxide may include LiCo02, LiMn02, LiNi02,
a lithium nickel manganese cobalt oxide (e.g.,
Li (Ni1/3Mn1/3C01/3) 021 Li
(Ni0.6Mn0.2C00.2) 02, Li (Ni0.5Mno.3Coo.2) 021
Li(Ni0.7Mn0.15C00.15)02, Li(Ni0.8Mn0.1C00.1)02, etc.), a lithium
nickel cobalt aluminum oxide (e.g., Li(Ni0.8Coo.15A10A5)02,
etc.), or the like, and any one thereof or a mixture of two
or more thereof may be used.
[0082] The positive electrode active material may be
included in an amount of 60 wt% to 99 wt%, preferably 70 wt%
to 99 wt%, and more preferably 80 wt% to 98 wt% based on a
total weight of solids excluding the solvent in the positive
electrode material mixture slurry.
[0083] The binder is a component that assists in the binding
between the active material and the conductive agent and in
the binding with the current collector.
[0084] Examples of the binder may include polyvinylidene
fluoride, polyvinyl alcohol, starch, hydroxypropylcellulose,
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regenerated cellulose,
polyvinylpyrrolidone,
polytetrafluoroethylene, polyethylene (PE), polypropylene,
an ethylene-propylene-diene monomer, a sulfonated ethylene-
propylene-diene monomer, a styrene-butadiene rubber, a
fluoro rubber, various copolymers, and the like.
[0085] The binder may be commonly included in an amount of
1 wt% to 20 wt%, preferably 1 wt% to 15 wt%, and more
preferably 1 wt% to 10 wt% based on the total weight of solid
in excluding the solvent in the positive electrode material
mixture slurry.
[0086] The conductive agent is a component for further
improving the conductivity of the positive electrode active
material, and may be added in an amount of 1 wt% to 20 wt%
based on the total weight of the solid content in the
positive electrode material mixture slurry.The conductive
agent is not particularly limited as long as it has
conductivity without causing adverse chemical changes in the
battery, and, for example, a conductive material, such as:
carbon powder such as carbon black, acetylene black, Ketjen
black, channel black, furnace black, lamp black, or thermal
black; graphite powder such as natural graphite with a well-
developed crystal structure, artificial graphite, or
graphite; conductive fibers such as carbon fibers or metal
fibers; conductive powder such as fluorocarbon powder,
aluminum powder, and nickel powder; conductive whiskers such
Date Recue/Date Received 2024-02-05
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as zinc oxide whiskers and potassium titanate whiskers;
conductive metal oxide such as titanium oxide; or
polyphenylene derivatives, may be used.
[0087] The conductive agent may be commonly included in an
amount of 1 wt% to 20 wt%, preferably 1 wt% to 15 wt%, and
more preferably 1 wt% to 10 wt% based on the total weight of
solids excluding the solvent in the positive electrode
material mixture slurry.
[0088] The solvent may include an organic solvent, such as
N-methyl-2-pyrrolidone (NMP), and may be used in an amount
such that desirable viscosity is obtained when the positive
electrode active material as well as selectively the binder
and the conductive agent are included. For example, the
solvent may be included in an amount such that a
concentration of a solid content including the positive
electrode active material as well as selectively the binder
and the conductive agent is in a range of 50 wt% to 95 wt%,
preferably 70 wt% to 95 wt%, and more preferably 70 wt% to
90 wt%.
[0089] (2) Negative Electrode
[0090] The negative electrode, for example, may be prepared
by coating a negative electrode collector with a negative
electrode material mixture slurry including a negative
electrode active material, a binder, a conductive agent, and
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a solvent, or a graphite electrode formed of carbon (C) or
a metal itself may be used as the negative electrode.
[0091] For example, in a case in which the negative
electrode is prepared by coating the negative electrode
collector with the negative electrode material mixture
slurry, the negative electrode collector generally has a
thickness of 3 pm to 500 pm. The negative electrode collector
is not particularly limited so long as it has high
conductivity without causing adverse chemical changes in the
battery, and, for example, copper, stainless steel, aluminum,
nickel, titanium, fired carbon, copper or stainless steel
that is surface-treated with one of carbon, nickel, titanium,
silver, or the like, an aluminum-cadmium alloy, or the like
may be used. Also, similar to the positive electrode
collector, the negative electrode collector may have fine
surface roughness to improve bonding strength with the
negative electrode active material, and the negative
electrode collector may be used in various shapes such as a
film, a sheet, a foil, a net, a porous body, a foam body,
and a non-woven fabric body.
[0092] Furthermore, the negative electrode active material
may include at least one selected from the group consisting
of lithium metal, a carbon material capable of reversibly
intercalating/deintercalating lithium ions, metal or an
alloy of lithium and the metal, a metal composite oxide, a
27
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material which may be doped and undoped with lithium, and a
transition metal oxide.
[0093] As the carbon material capable of reversibly
intercalating/deintercalating lithium ions, a carbon-based
negative electrode active material generally used in a
lithium ion secondary battery may be used without particular
limitation, and, as a typical example, crystalline carbon,
amorphous carbon, or both thereof may be used. Examples of
the crystalline carbon may include graphite such as irregular,
planar, flaky, spherical, or fibrous natural graphite or
artificial graphite, and examples of the amorphous carbon
may be soft carbon (low-temperature sintered carbon) or hard
carbon, mesophase pitch carbide, and fired cokes.
[0094] As the metal or the alloy of lithium and the metal,
a metal selected from the group consisting of Cu, Ni, Na, K,
Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge,
Al, and Sn, or an alloy of lithium and the metal may be used.
[0095] As the metal or the alloy of lithium and the metal,
a metal selected from the group consisting of Cu, Ni, Na, K,
Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge,
Al, and Sn, or an alloy of lithium and the metal may be used.
[0096] One selected from the group consisting of Pb0, Pb02,
Pb203, Pb304, 5b203, 5b204, 5b205, GeO, Ge02, Bi203, Bi204 r Bi205 r
LixFe203 (0)(1), LixWO2 (0)(1), and SnxMei_xMe'yOz (Me: Mn,
Fe, Pb, Ge; Me': Al, B, P, Si, Groups I, II and III elements
28
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of the periodic table, or halogen; 0<x1; 1y3; 1zE3) may
be used as the metal composite oxide.
[0097] The material, which may be doped and undoped with
lithium, may include Si, SiOx (0<x2), a Si-Y alloy (where Y
is an element selected from the group consisting of alkali
metal, alkaline earth metal, a Group 13 element, a Group 14
element, transition metal, a rare earth element, and a
combination thereof, and is not Si), Sn, Sn02, and Sn-Y
(where Y is an element selected from the group consisting of
alkali metal, alkaline earth metal, a Group 13 element, a
Group 14 element, transition metal, a rare earth element,
and a combination thereof, and is not Sn), and a mixture of
SiO2 and at least one thereof may also be used. The element
Y may be selected from the group consisting of Mg, Ca, Sr,
Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg,
Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au,
Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po,
and a combination thereof.
[0098] The transition metal oxide may include lithium-
containing titanium composite oxide (LTO), vanadium oxide,
and lithium vanadium oxide.
[0099] The additive according to the present invention is
effective particularly when Si or SiOx (0<x2) is used as a
negative electrode active material. Specifically, when a Si-
based negative electrode active material is used, the
29
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degradation of service life characteristics is promoted by
extreme expansion/contraction of volume during cycles if a
robust SEI layer is not formed on the surface of a negative
electrode during an initial activation process. However, the
additive according to the present invention is capable of
forming an elastic and robust SEI layer, thereby making the
secondary battery using the Si-based negative electrode
active material have excellent service life and storage
characteristics.
[00100] The
negative electrode active material may be
included in an amount of 50 wt% to 99 wt%, preferably 60 wt%
to 99 wt%, and more preferably 70 wt% to 98 wt% based on a
total weight of the solid content in the negative electrode
material mixture slurry.
[00101] Examples
of the binder may include polyvinylidene
fluoride (PVDF), polyvinyl alcohol, starch,
hydroxypropylcellulose, regenerated
cellulose,
polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene,
polypropylene, an ethylene-propylene-diene monomer, a
sulfonated ethylene-propylene-diene monomer, a styrene-
butadiene rubber, a fluoro rubber, and various copolymers
thereof. Specifically, styrene butadiene rubber (SBR)-
carboxylmethyl cellulose (CMC) may be used in terms of high
thickening properties.
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[00102] The binder may be commonly included in an amount
of 1 wt% to 20 wt%, preferably 1 wt% to 15 wt%, and more
preferably 1 wt% to 10 wt% based on the total weight of
solids excluding the solvent in the negative electrode
material mixture slurry.
[00103] The conductive agent is a component for further
improving the conductivity of the negative electrode active
material, and may be added in an amount of 1 wt% to 20 wt%
based on the total weight of the solid content in the
negative electrode material mixture slurry. The conductive
agent is not particularly limited as long as it has
conductivity without causing adverse chemical changes in the
battery, and, for example, a conductive material, such as:
carbon powder such as carbon black, acetylene black, Ketjen
black, channel black, furnace black, lamp black, or thermal
black; graphite powder such as natural graphite with a well-
developed crystal structure, artificial graphite, or
graphite; conductive fibers such as carbon fibers or metal
fibers; conductive powder such as fluorocarbon powder,
aluminum powder, and nickel powder; conductive whiskers such
as zinc oxide whiskers and potassium titanate whiskers;
conductive metal oxide such as titanium oxide; or
polyphenylene derivatives, may be used.
[00104] The conductive agent may be included in an amount
of 1 wt% to 20 wt%, preferably 1 wt% to 15 wt%, and more
31
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preferably 1 wt% to 10 wt% based on the total weight of
solids excluding the solvent in the negative electrode
material mixture slurry.
[00105] The solvent may include water or an organic
solvent, such as N-methyl-2-pyrrolidone (NMP), and may be
used in an amount such that desirable viscosity is obtained
when the negative electrode active material as well as
optionally the binder and the conductive agent is included.
For example, the solvent may be included in an amount such
that a concentration of a solid content including the
negative electrode active material as well as optionally the
binder and the conductive agent is in a range of 50 wt% to
95 wt%, for example, 70 wt% to 90 wt%.
[00106] In a case in which the metal itself is used as
the negative electrode, the negative electrode may be
prepared by a method of physically bonding, rolling, or
depositing a metal on a metal thin film itself or the
negative electrode collector. The depositing method may use
an electrical deposition method or chemical deposition
method of metal.
[00107] For example, the metal bonded/rolled/deposited on
the metal thin film itself or the negative electrode
collector may include one metal selected from the group
consisting of lithium (Li), nickel (Ni), tin (Sn), copper
(Cu), and indium (In) or an alloy of two metals thereof.
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[00108] (3) Separator
[00109] Also, a typical porous polymer film used as a
typical separator, for example, a porous polymer film
prepared from a polyolefin-based polymer, such as an ethylene
homopolymer, a propylene homopolymer, an ethylene-butene
copolymer, an ethylene-hexene copolymer, and an ethylene-
methacrylate copolymer, may be used alone or in a lamination
therewith as the separator. Also, a typical porous nonwoven
fabric, for example, a nonwoven fabric formed of high melting
point glass fibers or polyethylene terephthalate fibers may
be used, but the present invention is not limited thereto.
Furthermore, a coated separator including a ceramic
component or a polymer material may be used to secure heat
resistance or mechanical strength, and the separator having
a single layer or multilayer structure may be optionally
used.
[00110] Specifically, a safety reinforced separator (SRS)
on which a coating layer including a ceramic component or a
polymer material is formed may be used as separators included
in the electrode assembly of the present invention in order
to secure heat resistance or mechanical strength.
[00111] Specifically, the separators included in the
electrode assembly of the present invention may include a
porous separator substrate, and a porous coating layer
33
Date Recue/Date Received 2024-02-05
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entirely coated on one surface or both surfaces of the
separator substrate, and the coating layer may include a
mixture of inorganic particles selected from a metal oxide,
a metalloid oxide, a metal fluoride, a metal hydroxide, and
a combination thereof, and a binder polymer for connecting
and fixing the inorganic particles to each other.
[00112] The coating layer may include, as the inorganic
particles, at least one selected from A1203, SiO2, TiO2, Sn02,
Ce02, MgO, NiO, CaO, zno, ZrO2, Y203, SrTiO3, BaTiO3, Mg(01-1)2,
and MgF. Here, the inorganic particles may improve thermal
stability of the separator. That is, the inorganic particles
may prevent the separator from being contracted at high
temperatures. In addition, the binder polymer may improve
mechanical stability of the separator by fixing the inorganic
particles.
[00113] A shape of the lithium secondary battery of the
present invention is not particularly limited, but a
cylindrical type using a can, a prismatic type, a pouch type,
or a coin type may be used.
[00114] Hereinafter, the present invention will be
described in more detail with reference to specific examples.
However, the following examples are merely presented to
34
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exemplify the present invention, and the scope of the present
invention is not limited thereto. It will be apparent to
those skilled in the art that various modifications and
alterations are possible within the scope and technical
spirit of the present invention. Such
modifications and
alterations fall within the scope of claims included herein.
[00115] Synthetic Examples
[00116] In an argon (Ar) environment, Ag0Tf (4.0 mmol),
KF (6.0 mmol), 2-fluoropyridine (4.0 mmol), and TMSCF3 (4.0
mmol) were added in Et0Ac solvent and the resulting mixture
was stirred at room temperature for 12 hours. Selectfluor
(3.0 mmol) was added thereto and reacted, and PVA-CN (0.02
mol) was then added thereto and reacted. After the reaction
was terminated, AgF by-products were filtered and the
remaining polymer solution was precipitated in distilled
water, and then the precipitate was dried in vacuum to obtain
a polymer. The obtained polymer was a material represented
by Formula 3.
[00117] [Formula 3]
0 0
X R (X is CF3, R is CH2CH2CN, m is 20,
and n is 80)
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[00118] Examples
[00119] Example 1
[00120] (Preparation of Non-aqueous Electrolyte)
[00121] A non-aqueous solvent was prepared by dissolving
LiPF6 to 1.5 M in an organic solvent (fluoro ethylene
carbonate (FEC):diethyl carbonate (DEC) = 10:90 volume
ratio), and 0.1 g of a polymer of Formula 3 below was
introduced to 99.9 g of the non-aqueous solvent, thereby
preparing a non-aqueous electrolyte.
[00122] [Formula 3]
0 0
(X is CF3, R is CH2CH2CN, m is 20,
and n is 80)
[00123] (Manufacture of Lithium Secondary Battery)
[00124] A positive electrode active material
(LiNi0.85Co0.05Mn0.08A10. 0202) r a conductive agent (carbon
nanotube), and a binder (polyvinylidene fluoride) were added
to N-methyl-2-pyrrolidone (NMP), which was a solvent, in a
weight ratio of 97.74:0.7:1.56 to prepare a positive
electrode slurry (solid content 75.5 wt%). The
positive
electrode slurry was applied on one surface of a positive
36
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electrode collector (Al thin film) having a thickness of 15
pm, dried, and roll-pressed to prepare a positive electrode.
[00125] A negative electrode active material (silicon;
Si), a conductive agent (carbon black), and a binder
(styrene-butadiene rubber(SBR)-carboxylmethyl cellulose
(CMC)) were added in a weight ratio of 70:20.3:9.7 to N-
methy1-2-pyrrolidone (NMP), which was a solvent, to prepare
a negative electrode slurry (solid content 26 wt%). The
negative electrode slurry was applied on one surface of a
negative electrode current collector (Cu thin film) having
a thickness of 15 pm, dried, and roll-pressed to prepare a
negative electrode.
[00126] In a dry room, a polyolefin-based porous
separator on which inorganic particles A1203 were applied was
disposed between the positive electrode and the negative
electrode prepared above, and then the prepared non-aqueous
electrolyte was injected thereto to manufacture a secondary
battery.
[00127] Example 2
[00128] A secondary battery was manufactured in the same
manner as in Example 1 except that 0.3 g of the polymer of
Formula 3 above was introduced to 99.7 g of the non-aqueous
solvent prepared in Example 1 to prepare a non-aqueous
electrolyte.
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[00129] Example 3
[00130] A secondary battery was manufactured in the same
manner as in Example 1 except that 0.5 g of the polymer of
Formula 3 above was introduced to 99.5 g of the non-aqueous
solvent prepared in Example 1 to prepare a non-aqueous
electrolyte.
[00131] Example 4
[00132] A secondary battery was manufactured in the same
manner as in Example 1 except that 1.0 g of the polymer of
Formula 3 above was introduced to 99.0 g of the non-aqueous
solvent prepared in Example 1 to prepare a non-aqueous
electrolyte.
[00133] Example 5
[00134] A non-aqueous solvent was prepared by dissolving
LiPF6 to 1.5 M in an organic solvent (fluoro ethylene
carbonate (FEC):diethyl carbonate (DEC) = 10:90 volume
ratio), and 0.1 g of a polymer of Formula 4 below was
introduced to 99.9 g of the non-aqueous solvent, thereby
preparing a non-aqueous electrolyte.
[00135] [Formula 4]
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R2
0 0
X R (R1 is CH3, R2 is OCH3, X is CF3, R
is CH2CH2CN, m=20, n=80)
[00136] A secondary battery was manufactured in the same
manner as in Example 1 except above mentioned non-aqueous
electrolyte was used.
[00137] Example 6
[00138] A non-aqueous solvent was prepared by dissolving
LiPF6 to 1.5 M in an organic solvent (fluoro ethylene
carbonate (FEC):diethyl carbonate (DEC) = 10:90 volume
ratio), and 0.1 g of a polymer of Formula 4 below was
introduced to 99.9 g of the non-aqueous solvent, thereby
preparing a non-aqueous electrolyte.
[00139] [Formula 4]
R1 R2
0 0
X R (R1 is F, R2 is CH2CHCH2, X is CF3, R
is CH2CH2CN, m=20, n=80)
A secondary battery was manufactured in the same manner as
39
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in Example 1 except above mentioned non-aqueous electrolyte
was used.
[00140] Comparative Example 1
[00141] A secondary battery was manufactured in the same
manner as in Example 1 except that 100 g of the non-aqueous
solvent prepared in Example 1 was used to prepare a non-
aqueous electrolyte.
[00142] Experimental Example 1 - Evaluation of High-
temperature Cycle Characteristics
[00143] For each of the secondary batteries manufactured
in Examples 1 to 6 and Comparative Example 1, cycle
characteristics were evaluated.
[00144] Specifically, each of the batteries manufactured
in Examples 1 to 6 and Comparative Example 1 was charged to
4.2 V with a constant current of 1 C at 45 C, and then
discharged to 3.0 V with a constant current of 0.5 C, which
was set as one cycle, and then 250 cycles of the charge and
discharge were performed, and then a capacity retention was
measured based on an initial capacity after one cycle. The
results are listed in Table 1 below:
[00145] [Table 1]
Capacity retention (%)
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Example 1 76.9
Example 2 77.8
Example 3 79.1
Example 4 79.5
Example 5 75.2
Example 6 77.3
Comparative Example 1 73.9
[00146] As shown in Table 1, Examples 1 to 6 in which the
additive for a non-aqueous electrolyte of the present
disclosure was used had higher capacity retention than that
of Comparative Example 1 in which the additive was not used,
and thus had excellent service life characteristics.
[00147] Experimental Example 2 - Evaluation of High-
temperature Storage Characteristics
[00148] For each of the secondary batteries manufactured
in Examples 1 to 6 and Comparative Example 1, high-
temperature storage characteristics were evaluated.
[00149] Specifically, the secondary batteries of Examples
1 to 6 and Comparative Example 1 were each fully charged to
4.2 V, and then stored at 60 C for 8 weeks.
[00150] Before the storage, the resistance of each of the
fully-charged secondary batteries was measured and then set
as an initial resistance of the secondary battery.
[00151] After 8 weeks, the resistance of each of the
stored batteries was measured to calculate a resistance
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increased during the 8-week storage period. The percentage
of the increased resistance to the initial resistance of the
secondary battery was calculated to derive a resistance
increase rate after 8 weeks. The results are listed in Table
2 below:
[00152] [Table 2]
Resistance increase rate (%)
Example 1 29.5
Example 2 22.6
Example 3 21.0
Example 4 8.3
Example 5 35.8
Example 6 26.4
Comparative Example 1 45.4
[00153] As shown in Table 2 above, it was confirmed that
the secondary batteries of Examples 1 to 6 had a lower
resistance increase rate after 8 weeks than that of the
secondary battery of Comparative Example 1, and thus had
stable performance at high temperatures.
42
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