CA 03229040 2024-02-09
DESCRIPTION
NON-AQUEOUS ELECTROLYTE INCLUDING ADDITIVES FOR NON-AQUEOUS
ELECTROLYTE, AND LITHIUM SECONDARY BATTERY INCLUDING THE SAME
TECHNICAL FIELD
[0001] [Cross-reference to Related Applications]
[0002] This application claims the priority from Korean Patent
Application No. 10-2022-0007153 filed on January 18, 2022, 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 same.
BACKGROUND ART
[0005] Recently, as the application field of lithium secondary
batteries has rapidly expanded to power supply of electronic
equipment such as electrical devices, electronic devices,
communication devices, and computers, as well as power storage
supply of large-area devices such as automobiles and power storage
devices, demand for high-capacity, high-output and high-stability
secondary batteries is increasing.
[0006] In particular, high capacity, high output, and long life
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characteristics are becoming important in lithium secondary
batteries for automotive applications. In order to increase the
capacity of the secondary battery, a positive electrode active
material having a high energy density but low stability may be
used, or the secondary battery may be driven at a high voltage.
[0007] However, in the case of driving a secondary battery under
the above conditions, as charging and discharging proceeds, the
film formed on the positive/negative electrode surface or the
electrode surface structure deteriorates due to side reactions
caused by the deterioration of the electrolyte, and transition
metal ions from the positive electrode surface may be eluted. As
described above, since the eluted transition metal ions are
electro-deposited on the negative electrode and lower the
passivation capability of the SEI, a problem of deterioration of
the negative electrode occurs.
[0008] The deterioration of the secondary battery tends to be
accelerated when the potential of the positive electrode increases
or the battery is exposed to high temperatures.
[0009] In addition, when a lithium ion battery is used
continuously for a long time or left at a high temperature,it is
known that a so-called swelling phenomenon occurs in which gas is
generated and the thickness of the battery is increased, and the
amount of gas generated at this time depends on the state of the
SEI.
[0010] Therefore, in order to solve this problem, research and
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development of a method for suppressing the elution of metal ions
from the positive electrode and forming a stable SEI film on the
negative electrode, thereby reducing the swelling of the secondary
battery, and increasing the stability at high temperature are
being tried.
DISCLOSURE OF THE INVENTION
TECHNICAL PROBLEM
[0011] As a result of various studies conducted to solve the above
problem, the present invention intends to provide an additive for
a non-aqueous electrolyte capable of inhibiting the degradation
of the positive electrode, reducing the side reaction between the
positive electrode and the electrolyte, and forming a stable SEI
film on the negative electrode.
[0012] Further, in the present invention, it is an object of the
present invention to provide a non-aqueous electrolyte having
improved stability at a high temperature by including the additive
for a non-aqueous electrolyte.
[0013] Further, in the present invention, it is an object of the
present invention to provide a lithium secondary battery with
improved overall performance by improving high-temperature cycle
characteristics and high-temperature storage characteristics by
including the non-aqueous electrolyte.
[0014] In order to achieve the above object, the present invention
provides a non-aqueous electrolyte including an additive for a
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non-aqueous electrolyte represented by the following Chemical
Formula 1:
[0015] [Chemical Formula 1]
X
\r/
\\µ`,
[0016] In Chemical Formula 1, A may be a cyclic phosphate group
having 2 or 3 carbon atoms, R may be an alkylene group or
alkenylene group having 1 to 5 carbon atoms, and X may be a
perfluoroalkyl group having 1 to 5 carbon atoms.
[0017] According to another embodiment, the present invention
provides a lithium secondary battery including the non-aqueous
electrolyte.
ADVANTAGEOUS EFFECTS
[0018] The compound represented by Chemical Formula 1, which is
provided as an additive for a non-aqueous electrolyte of the
present invention is a compound based on a cyclic phosphate
structure, and when the negative electrode SEI layer is formed, a
ring opening reaction proceeds, resulting in poly-
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phosphoesterification.
Accordingly, it is possible to form a
solid electrolyte interphase (SEI) film that is flexible and
strong on the surface of the negative electrode. Therefore, it
is possible to suppress deterioration of the passivation ability
of the SEI at a high temperature, thereby preventing deterioration
of the negative electrode.
[0019] In addition, in the compound represented by Chemical
Formula 1 provided as an additive for a non-aqueous electrolyte
of the present invention, since the perfluoroalkyl group is not
directly substituted with the alkylene group connected to the
oxygen of the phosphate group, but is substituted through oxygen,
-CF3 at the terminal is easily reduced to the form of LiF.
Accordingly, a polymer-inorganic film rich in inorganic substances
such as LiF can be formed, and deterioration due to an interfacial
reaction is suppressed.
[0020] Therefore, when the non-aqueous electrolyte of the present
invention including the compound of Chemical Formula 1 is used,
since it is possible to form an electrode-electrolyte interface
that is stable even at high temperatures and has low resistance,
high-temperature cycle characteristics and high-temperature
storage characteristics are improved, therefore a lithium
secondary battery having an improved overall performance can be
implemented.
MODE FOR CARRYING OUT THE INVENTION
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[0021] The terms or words used in the specification and claims
should not be interpreted as being limited to conventional or
dictionary meanings, and the terms or words should be interpreted
as a meaning and a concept that are consistent with the technical
concept of the present invention based on the principle that the
inventor can appropriately define the concepts of terms in order
to explain his/her own invention in the best way.
[0022] In this specification, the terms "includes," "comprises,"
or "has" and the like are intended to designate the presence of
the features, numbers, steps, components, or combinations thereof
that are implemented, and are not to be understood as precluding
the possibility of the presence or addition of one or more other
features or numbers, steps, components or combinations thereof.
[0023] In addition, in the description of "carbon number a to b"
in the present specification, "a" and "b" mean 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,
"alkylene group having 1 to 5 carbon atoms" refers to an alkylene
group containing 1 to 5 carbon atoms, i.e. -CH2-, -CH2CH2-, -
CH2CH2CH2-, -CH2CH(CH3)-, -CH(CH3)CH2- and -CH(CH3)CH2CH2-, etc.. In
addition, in the present specification, the term "alkylene group"
means a branched or unbranched divalent saturated hydrocarbon
group.
[0024] Also, in the present specification, both the alkylene group
and the alkenylene group may be substituted or unsubstituted.
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Unless otherwise defined, the term "substituted" means that at
least one hydrogen bonded to carbon is substituted with an element
other than hydrogen, for example, it means "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 group having 6 to 20 carbon atom, etc.
[0025] Hereinafter, the present invention will be described in
more detail.
[0026] Non-aqueous Electrolyte
[0027] The non-aqueous electrolyte according to an embodiment of
the present invention includes a compound represented by the
following Chemical Formula 1 as an additive. The compound of
Chemical Formula 1 below is a compound based on a cyclic phosphate
structure, and when the negative electrode SEI layer is formed, a
ring opening reaction proceeds, resulting in poly-
phosphoesterification.
Accordingly, it is possible to form a
solid electrolyte interphase (SEI) film that is flexible and
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strong on the surface of the negative electrode.
[0028] [Chemical Formula 1]
X
o
\\e/
µ4.
[0029] In Chemical Formula 1, A may be a cyclic phosphate group
having 2 or 3 carbon atoms, R may be an alkylene group or
alkenylene group having 1 to 5 carbon atoms, and X may be a
perfluoroalkyl group having 1 to 5 carbon atoms.
[0030] In Chemical Formula 1, A may be a cyclic phosphate group
having 2 or 3 carbon atoms, preferably a cyclic phosphate group
having 2 carbon atoms. When A is a cyclic phosphate group having
2 carbon atoms, the ring strain is relatively high and the ring
opening reaction occurs easily.
[0031] In Chemical Formula 1, R may be an alkylene group or
alkenylene group having 1 to 5 carbon atoms, preferably an alkylene
group having 1 to 5 carbon atoms, and most preferably an alkylene
group having 1 to 3 carbon atoms.
[0032] In Chemical Formula 1, X may be a perfluoroalkyl group
having 1 to 5 carbon atoms, preferably CF3 or CF2CF3. Since the
additive of Chemical Formula 1 contains a perfluoroalkyl group,
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an inorganic LiF material can be easily formed to form a stable
polymer-inorganic-based SEI layer. Specifically, in the compound
represented by Chemical Formula 1, since the perfluoroalkyl group
is not directly substituted with the alkylene group connected to
the oxygen of the phosphate group, but is substituted through
oxygen, -CF3 at the terminal is easily reduced to the form of LiF.
Accordingly, a polymer-inorganic film rich in inorganic substances
such as LiF can be formed, and deterioration due to an interfacial
reaction is suppressed.
[0033] Specifically, the compound represented by Chemical Formula
1 of the present invention may be a compound represented by the
following Chemical Formula 1-1.
[0034] [Chemical Formula 1-1]
C) /O R
'""*""' 0 C F3
/1r,
PN
%,
[0035] In Chemical Formula 1-1, R may be an alkylene group having
1 to 5 carbon atoms, and most preferably, an alkylene group having
1 to 3 carbon atoms.
[0036] Specifically, the compound represented by Chemical Formula
1 of the present invention may be any one of compounds represented
by Chemical Formulas 2-1 to 2-4 below.
[0037] [Chemical Formula 2-1]
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o ri/1\0CF3
[0038] [Chemical Formula 2-2]
/VCICF3
0
PNri
[0039] [Chemical Formula 2-3]
1"...1c,,F (7,4,F
0µ. 2 3
/
0." P%\ =0
[0040] [Chemical Formula 2-4]
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OCF2CF3
N%1/4 rt
\-1
[0041] In the present invention, the additive for a non-aqueous
electrolyte may be included in an amount 0.01 parts by weight to
parts by weight, preferably 0.1 parts by weight to 4 parts by
5 weight, more preferably 0.8 parts by weight to 3.5 parts by weight,
based on 100 parts by weight of the non-aqueous electrolyte. When
the content of the compound represented by Chemical Formula 1 is
less than 0.01 parts by weight, as the driving time increases,
the effect of forming a positive/negative electrode film may be
insignificant, and thus the effect of inhibiting transition metal
elution may be lowered. In
addition, when the content of the
compound represented by Chemical Formula 1 exceeds 5 parts by
weight, not only the viscosity of the electrolyte increases due
to the excess additive, but also ionic conductivity decreases due
to the increase in viscosity, which adversely affects the mobility
of ions in the battery, and storage characteristics or lifespan
characteristics may be lowered. In
addition, due to the
decomposition of excessive additives, battery resistance may
increase, and side reactions and by-products may be caused.
[0042] The non-aqueous electrolyte according to the present
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invention may further include a lithium salt, an organic solvent
and optionally other electrolyte additives.
[0043] The lithium salt is used as an electrolyte salt in a
lithium secondary battery, and is used as a medium for transferring
ions.
Typically, lithium salts contain, for example, Li+ as
cations and at least one selected from the group consisting of F-,
Cl-, Br-, I-, NO3-, N(CN)2-, BF4-, C104-, B10C110-, A1C14-, A102-, PF6-,
CF3S03 f CH3C 0 2 f CP 3C 0 2 f ASP 6 f SbF 6
CH3S 0 3 f (CP 3CF 2S 0 2) 2N f
(CP 3S 0 2) 2N, S 0 2) 2N, BP 2C 20 4 f BC 40 f P 4C 2 4 PF
2C 40 8 r (CF 3) 2PF 4 r
(CF 3) 3PF 3 (CF 3) 4P 2 f (CF 3) 5P F, (CF 3) 6P, C 4P 9S 0 3 f
CP 3CP 2S 3
CF 3CF 2 (CF 3) 2C0 (CP 3S 0 2) 2CH f CP 3 (CP 2) 7S03 and SCN as anions.
[0044] Specifically, the lithium salt may include a single
substance or a mixture of two or more selected from the group
consisting of LiC1, LiBr, LiI, LiBF4, LiC104, LiB10C110, LiA1C14,
LiA102, LiPF LiCF SO LiCH CO LiCF CO LiA _ 6,
__ 3_ _ ____3 _ _ 3_ _ 2f - 6 f LiSbP 6 f LiCH3S03f
LiN(502F)2 (lithium bis(fluorosulfonylflimide; LiFSI), LiN(502CF3)2
(lithium bis(perfluoroethanesulfonyl)imide; LiBETI)
and
LiN(502CF3)2 (lithium bis(trifluoromethanesulfonyl) imide; LiTFSI).
In addition to these, lithium salts commonly used in electrolytes
of lithium secondary batteries may be used without limitation.
[0045] The lithium salt may be appropriately changed within the
range that can be used in general, but in order to obtain an
optimal effect of forming a film for preventing corrosion on the
electrode surface, the lithium salt may be included at a
concentration of 0.5 M to 5.0 M, preferably, 0.8 M to 2.5 M, more
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preferably 1.0 M to 2.0 M in the electrolyte.
When the
concentration of the lithium salt is less than 0.5 M, the lithium
amount is insufficient and the capacity and cycle characteristics
of the lithium secondary battery are inferior, and when the
concentration exceeds 5.0 M, there may be a problem that as the
viscosity of the non-aqueous electrolyte increases, the
electrolyte impregnation ability decreases, ion conductivity
decreases, and battery resistance increases.
[0046] 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.
[0047] The additive according to the invention is particularly
effective when a cyclic carbonate solvent is used. When
a
conventional electrolyte additive is used together with a cyclic
carbonate solvent, it is difficult for the SEI film formed by
decomposition of the cyclic carbonate solvent to be maintained as
an SEI film due to the volume change of the negative electrode
occurring during cycle progression. As a result, there was a
problem in that the ionic conductivity of the electrolyte is
lowered and cycle characteristics are deteriorated. However, when
the polymer according to the present invention is used as an
additive together with a cyclic carbonate solvent, a strong SEI
film can be formed, thereby maintaining high cycle characteristics.
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[0048] The cyclic carbonate-based organic solvent is a high-
viscosity organic solvent that has a high dielectric constant and
can dissociate lithium salts in the electrolyte well, and specific
examples thereof may include at least one organic solvent selected
from the group consisting of ethylene carbonate (EC), propylene
carbonate (PC), fluoroethylene carbonate (FEC), 1,2-butylene
carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-
pentylene carbonate and vinylene carbonate, and among them,
fluoroethylene carbonate may be included.
[0049] In addition, the linear carbonate-based organic solvent is
an organic solvent having a low viscosity and a low dielectric
constant, and representative examples thereof may include at least
one organic solvent selected from the group consisting of dimethyl
carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate,
ethylmethyl carbonate (EMC), methylpropyl carbonate and
ethylpropyl carbonate, and specifically, diethyl carbonate (DEC).
[0050] In addition, in order to prepare an electrolyte having
high ionic conductivity, the organic solvent may include at least
one carbonate-based organic solvent selected from the group
consisting of a cyclic carbonate-based organic solvent and a
linear carbonate-based organic solvent together with at least one
ester-based organic solvent selected from the group consisting of
a linear ester-based organic solvent and a cyclic ester-based
organic solvent.
[0051] Specific examples of the linear ester-based organic
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solvents may include one or more organic solvents selected from
the group consisting of methyl acetate, ethyl acetate, propyl
acetate, methyl propionate, ethyl propionate, propyl propionate
and butyl propionate.
[0052] In addition, the cyclic ester-based organic solvent may
include one or more organic solvents selected from the group
consisting of y-butyrolactone, y-valerolactone, y-caprolactone,
o-valerolactone and c-caprolactone.
[0053] Meanwhile, as the organic solvent, an organic solvent
commonly used in the non-aqueous electrolyte may be added without
limitation, as needed. For example, one or more organic solvents
among an ether-based organic solvent, a glyme-based solvent, and
a nitrile-based organic solvent may be further included.
[0054] Examples of the ether-based solvent may include any one or
a mixture of two or more selected from the group consisting of
dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether,
methylpropyl ether, ethylpropyl ether, 1,3-dioxolane (DOL) and
2,2-bis(trifluoromethyl) -1,3-dioxolane (TFDOL), but is not
limited thereto.
[0055] The glyme-based solvent has a higher dielectric constant
and lower surface tension than the linear carbonate-based organic
solvent, is a solvent with less reactivity with metal, and may
include at least one selected from the group consisting of
dimethoxyethane (glyme, DME), diethoxyethane, digylme, triglyme,
and tetraglyme (TEGDME), but is not limited thereto.
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[0056] The nitrile-based solvent may be 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 is
not limited thereto.
[0057] In addition, the non-aqueous electrolyte of the present
invention prevents negative electrode collapse due to
decomposition of the non-aqueous electrolyte under a high-output
environment, or if necessary, a known electrolyte additive may be
further included in the non-aqueous electrolyte to further improve
low-temperature high-rate discharge characteristics, high-
temperature stability, overcharge prevention, and a battery
expansion inhibition effect at high temperatures.
[0058] Representative examples of these other electrolyte
additives may include at least one additive for forming an SEI
layer selected from the group consisting of cyclic carbonate-based
compounds, halogen-substituted carbonate-based compounds,
sultone-based compounds, sulfate-based compounds, phosphate-based
compounds, borate-based compounds, nitrile-based compounds,
benzene-based compounds, amine-based compounds, silane-based
compounds and lithium salt-based compounds.
[0059] The cyclic carbonate-based compound may include vinylene
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carbonate (VC) or vinylethylene carbonate.
[0060] The halogen-substituted carbonate-based compound may be
fluoroethylene carbonate (FEC).
[0061] The sultone-based compound may include at least one
compounds 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.
[0062] The sulfate-based compound may include ethylene sulfate
(Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate
(MTMS).
[0063] The phosphate-based compound may include one or more
compounds selected from the group consisting of lithium difluoro
(bisoxalato) phosphate, lithium difluoro phosphate, tetramethyl
trimethyl silyl phosphate, trimethyl silyl phosphite, tris(2,2,2-
trifluoroethyl) phosphate and tris(trifluoroethyl) phosphite.
[0064] The borate-based compound may include tetraphenylborate,
lithium oxalyldifluoroborate (LiODFB), and
lithium
bisoxalatoborate (LiB(C204)2, LiBOB) .
[0065] The nitrile-based compound may include one or more
compounds selected from the group consisting of succinonitrile,
adiponitrile, acetonitrile, propionitrile,
butyronitrile,
valeronitrile, caprylonitrile, heptanenitrile, cyclopentane
carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile, 4-
fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile,
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phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-
fluorophenylacetonitrile.
[0066] The benzene-based compound may include fluorobenzene, the
amine-based compound may include triethanolamine or
ethylenediamine, and the silane-based compound may include
tetravinylsilane.
[0067] The lithium salt-based compound is a compound different
from the lithium salt included in the non-aqueous electrolyte,
and may include lithium difluorophosphate (LiDFP), LiP02F2 or LiBF4.
[0068] Among these other electrolyte additives, when a
combination of vinylene carbonate (VC), 1,3-propane sultone (PS),
ethylene sulfate (Esa), and lithium difluorophosphate (LiDFP) is
further included, during the initial activation process of the
secondary battery, a stronger SEI film can be formed on the surface
of the negative electrode, gas generation that can be generated
due to decomposition of the electrolyte at high temperature can
be suppressed, and the high-temperature stability of a secondary
battery can be improved.
[0069] Meanwhile, two or more of the other electrolyte additives
may be mixed and used, and may be included in an amount of 0.01
to 20 wt%, specifically 0.01 to 10 wt%, preferably 0.05 to 5 wt%
based on the total weight of the non-aqueous electrolyte. When
the content of the other electrolyte additives is less than 0.01
wt%, the effect of improving the high-temperature storage
characteristics and high-temperature lifespan characteristics of
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the battery is insignificant, and when the content of the other
electrolyte additives exceeds 20 wt%, side reactions in the
electrolyte during charging and discharging of the battery are
likely to excessively occur.
In particular, when the other
electrolyte additives are added in excess, they may not be
sufficiently decomposed at a high temperature, and thus may remain
unreacted or precipitated in the electrolyte at room temperature.
Accordingly, a side reaction in which the lifespan or resistance
characteristic of the secondary battery is lowered may occur.
[0070] Lithium Secondary Battery
[0071] The present invention also provides a lithium secondary
battery including the non-aqueous electrolyte.
[0072] 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 interposed between the positive electrode
and the negative electrode, and the aforementioned non-aqueous
electrolyte.
[0073] In this case, the lithium secondary battery of the present
invention may be manufactured according to a conventional method
known in the art. For example, the lithium secondary battery of
the present invention can be manufactured as follows:after a
positive electrode, a negative electrode, and a separator between
the positive and negative electrodes are sequentially stacked to
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form an electrode assembly, the electrode assembly is inserted
into the battery case, and the non-aqueous electrolyte according
to the present invention is injected.
[0074] (1) Positive Electrode
[0075] The positive electrode may be manufactured by coating a
positive electrode mixture slurry including a positive electrode
active material, a binder, a conductive material, and a solvent
on a positive electrode current collector.
[0076] The positive electrode current collector is not
particularly limited as long as it has conductivity without
causing a chemical change in the battery, and for example,
stainless steel; aluminum; nickel; titanium; calcined carbon; or
aluminum or stainless steel surface-treated with carbon, nickel,
titanium, silver, etc. may be used.
[0077] The positive electrode active material is a compound
capable of reversibly intercalating/deintercalating lithium, and
specifically, may specifically include a lithium metal oxide
including lithium and one or more metals such as cobalt, manganese,
nickel, or aluminum. For example, as the lithium metal oxides,
lithium-manganese-based oxides (for example, LiMn02, LiMn204, etc.),
lithium-cobalt-based oxides (for example, LiCo02, etc.), lithium-
nickel-based oxides (for example, LiNi02, etc.), lithium-nickel-
manganese-based oxides (for example, LiNi1_yMny02 (where, O<Y<l),
LiMn2_zNiz04 (where, O<Z<2), etc.), lithium-nickel-cobalt-based
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oxides (for example,LiNi1_y1Coy102 (where, O<Y1<1), etc.), lithium-
manganese-cobalt-based oxides (for example, LiCo1_y2Mny202 (where,
O<Y2<1), LiMn2_z1Con04 (where, O<Z1<2), etc.), lithium-nickel-
manganese-cobalt-based oxides (for example, Li(NipCoqMnr)02 (where,
0<p<1, 0<q<1, 0<r<1, p+q+r=1)or Li (NipiCogiMnri)04 (where, 0<p1<2,
0<q1<2, 0<r1<2, p1+q1+r1=2), etc.), or lithium-nickel-cobalt-
transition metal (M) oxides (for example, Li (Nip2Coq2Mhr2Ms2)02,
where M is selected from the group consisting of Al, Fe, V, Cr,
Ti, Ta, Mg and Mo, and p2, q2, r2 and s2 each are an atomic
fraction of each independent element, 0<p2<1, 0<q2<1, 0<r2<1,
0<s2<1, p2+ q2+r2+52=1), etc.) may be used, and any one or two or
more of these compounds may be included.
[0078] Among them, in terms of enhancing the capacity
characteristics and stability of the battery, the lithium metal
oxide may be LiCo02, LiMn02, LiNi02, lithium nickel-manganese-
cobalt oxides (for example, Li
(Ni1/3Mn1/3C01/3) 02
Li(Ni0.6Mn0.2Co0.2)02,Li(Ni0.5Mn0.3Coo.2)02,
Li(Ni0.7Mno.15Coo.15)02and
Li(Ni0.8Mn0.1C00.1)02, etc.), or lithium nickel cobalt aluminum
oxides (for example, Li(Ni0.8C00.15A10A5)02, etc.), and taking into
consideration the remarkable improvement effect by controlling the
type and content ratio of the constituent elements forming the
lithium composite metal oxide, the lithium composite metal oxide
may be Li(Ni0.6Mn0.2Co0.2)02, Li(Ni0.5Mn0.3Co0.2)02, Li(Ni0.7Mno.15Coo.15)02
and Li(Ni0.8Mn0.1C00.1)02, etc., and any one of these or a mixture
of two or more may be used.
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[0079] The positive electrode active material may be included in
an amount of 80 wt% to 99 wt%, specifically, 90 wt% to 99 wt%,
based on the total weight of solids in the positive electrode
mixture slurry.
[0080] The binder is a component that assists in bonding the
active material and the conductive material to the current
collector.
[0081] Examples of such binders may include polyvinylidene
fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch,
hydroxypropyl cellulose, regenerated
cellulose,
polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene (PE),
polypropylene,ethylene-propylene-diene, sulfonated ethylene-
propylene-diene, styrene-butadiene rubber, fluororubber, or
various copolymers thereof.
[0082] Typically, the binder may be included in an amount of 1 to
wt%, preferably 1 to 15 wt%, more preferably 1 to 10 wt% based
on the total weight of solids in the positive electrode mixture
slurry.
[0083] The conductive material is a component for further
20 improving the conductivity of the positive electrode active
material.
[0084] The conductive material 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 solids in the negative electrode slurry.
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The conductive material is not particularly limited as long as it
has conductivity without causing a chemical change in the battery,
and for example, may include 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,
artificial graphite;conductive fibers such as carbon fibers,
carbon nanotubes, or metal fibers; conductive powders such as
carbon fluoride powder, aluminum powder, or nickel powder;
conductive whiskers such as zinc oxide or potassium titanate;
conductive metal oxides such as titanium oxide; or conductive
materials such as a polyphenylene derivative.
[0085] Typically, the conductive material may be included in an
amount of 1 to 20 wt%, preferably 1 to 15 wt%, more preferably 1
to 10 wt% based on the total weight of solids in the positive
electrode mixture slurry.
[0086] The solvent may include an organic solvent such as NMP (N-
methy1-2-pyrrolidone), and may be used in an amount to achieve a
desirable viscosity when the positive electrode active material
and, optionally, a binder and a conductive material are included.
For example, it may be included so that the concentration of the
solids including the positive electrode active material, and
optionally the binder and the conductive material is 50 to 95 wt%,
preferably 70 to 95 wt%, more preferably 70 to 90 wt%.
[0087] (2) Negative Electrode
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[0088] The negative electrode is, for example, manufactured by
coating a negative electrode mixture slurry containing a negative
electrode active material, a binder, a conductive material and a
solvent on the negative electrode current collector, or a graphite
electrode made of carbon (C) or metal itself may be used as the
negative electrode.
[0089] For example, when the negative electrode is manufactured
by coating the negative electrode mixture slurry on the negative
electrode current collector, the negative electrode current
collector generally has a thickness of 3 to 500 pm. The negative
electrode current collector is not particularly limited as long
as it has conductivity without causing a chemical change in the
battery, and for example, copper; stainless steel; aluminum;
nickel; titanium; calcined carbon; or copper or stainless steel
surface-treated with carbon, nickel, titanium, silver, etc.; or
an aluminum-cadmium alloy may be used. In
addition, like the
positive electrode current collector, fine irregularities may be
formed on a surface of the negative electrode current collector
to strengthen the adhesion with the negative electrode active
material, and the negative electrode current collector may take
various forms such as films, sheets, foils, nets, porous materials,
foam, non-woven materials, etc.
[0090] In addition, the negative electrode active material may
include at least one selected from the group consisting of lithium
metal, a carbon material capable of reversibly
24
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intercalating/deintercalating lithium ions; metals or alloys of
these metals and lithium; metal composite oxides; materials
capable of doping and dedoping lithium; and transition metal
oxides.
[0091] As a carbon material capable of reversibly
intercalating/deintercalating lithium ions, any carbon-based
negative active material generally used in lithium ion secondary
batteries may be used without particular limitation, and a
representative example thereof is crystalline carbon, amorphous
carbon or a combination thereof.
Examples of the crystalline
carbon include graphite such as amorphous, plate-like, flake,
spherical or fibrous natural graphite or artificial graphite, and
examples of the amorphous carbon include soft carbon (soft carbon:
low-temperature calcined carbon), hard carbon, mesophase pitch
carbide, calcined coke, etc.
[0092] Examples of the above metals or alloys of these metals
with lithium include metals 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 these metals and lithium.
[0093] Examples of the metal composite oxide include one or more
selected from the group consisting of Pb0, Pb02, Pb203, Pb304, 5b203,
5b204, 5b205, GeO, Ge02, Bi203, Bi204, Bi205, LixFe203(0x1),
LixWO2(0x1) and SnxiMelõMe'yOx (Me: Mn, Fe, Pb, Ge; Me': Al, B, P,
Si, elements of groups 1, 2 and 3 of the periodic table, halogens;
0<x1;
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[0094] Examples of the material capable of doping and dedoping
lithium include Si, SiOx (0<x2), an Si-Y alloy (wherein Y is an
element selected from the group consisting of alkali metals,
alkaline earth metals, group 13 elements, group 14 elements,
transition metals, rare earth elements and combinations thereof,
but is not Si), Sn, 5n02, Sn-Y (wherein Y is an element selected
from the group consisting of alkali metals, alkaline earth metals,
group 13 elements, group 14 elements, transition metals, rare
earth elements, and combinations thereof and is not Sn), and one
or more of these and 5i02 may be mixed and 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 combinations thereof.
[0095] Examples of the transition metal oxide can include a
lithium-containing titanium composite oxide (LTO), vanadium oxide,
lithium vanadium oxide, etc.
[0096] The additive according to the present invention is
particularly effective when Si or SiOx (0<x2) is used as a
negative electrode active material. Specifically, in the case of
using a Si-based negative electrode active material, when a strong
SEI layer is not formed on the surface of the negative electrode
during initial activation, deterioration of lifespan
characteristics is promoted due to extreme volume expansion-
contraction during cycle progression. However, since the additive
26
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according to the invention can form a resilient yet robust SEI
layer, the lifespan characteristics and storage characteristics
of the secondary battery using the Si-based negative electrode
active material can be excellent.
[0097] The negative electrode active material may be included in
an amount of 50 to 99% by weight, preferably 60 to 99% by weight,
and more preferably 70 to 98% by weight based on the total weight
of solids in the negative electrode mixture slurry.
[0098] The binder is a component that assists in bonding between
the conductive material, the active material, and the current
collector. Examples of such binders may include polyvinylidene
fluoride(PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC),
starch, hydroxypropyl cellulose, regenerated cellulose,
polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene,
polypropylene, ethylene-propylene-diene, sulfonated ethylene-
propylene-diene, styrene-butadiene rubber, fluororubber, or
various copolymers thereof.
[0099] Typically, the binder may be included in an amount of 1 to
wt%, preferably 1 to 15 wt%, more preferably 1 to 10 wt% based
20 on the total weight of solids in the negative electrode mixture
slurry.
[00100]
The conductive material 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 solids in the negative electrode slurry.
27
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The conductive material is not particularly limited as long as it
has conductivity without causing a chemical change in the battery,
and for example, may include 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,
artificial graphite;conductive fibers such as carbon nanotubes,
carbon fibers or metal fibers; conductive powders such as carbon
fluoride powder, aluminum powder, or nickel powder; conductive
whiskers such as zinc oxide or potassium titanate; conductive
metal oxides such as titanium oxide; or conductive materials such
as a polyphenylene derivative.
[00101] The conductive material may be included in an amount
of 1 to 20 wt%, preferably 1 to 15 wt%, more preferably 1 to 10
wt% based on the total weight of solids in the negative electrode
mixture slurry.
[00102] The solvent may include water or an organic solvent
such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount
to achieve a desirable viscosity when the negative active material
and, optionally, a binder and a conductive material are included.
For example, it may be included so that the concentration of the
solids including the negative electrode active material, and
optionally the binder and the conductive material is 50 wt% to 95
wt%, preferably 70 wt% to 90 wt%.
[00103] When a metal itself is used as the negative electrode,
it may be manufactured by physically bonding, rolling, or
28
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depositing a metal on the metal thin film itself or the negative
electrode current collector.
As the deposition method, an
electrical deposition method or a chemical vapor deposition method
for metal may be used.
[00104] For
example, the metal to be bonded/rolled/deposited
on the metal thin film itself or the negative electrode current
collector may include one type of metal or an alloy of two types
of metals selected from lithium (Li), nickel (Ni), tin (Sn), copper
(Cu), and indium (In).
[00105] (3) Separator
[00106]
In addition, as the separator, a conventional porous
polymer film conventionally used as a separator, for example, a
porous polymer film made of 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 as a laminate
thereof,ora conventional porous nonwoven fabric, for example, a
nonwoven fabric made of high melting point of glass fiber,
polyethylene terephthalate fiber, etc. may be used, but is not
limited thereto.
In addition, a coated separator including a
ceramic component or a polymer material may be used to secure heat
resistance or mechanical strength, and may optionally be used in
a single-layer or multi-layer structure.
[00107] The
external shape of the lithium secondary battery of
29
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the present invention is not particularly limited, but may be a
cylindrical type using a can, a prismatic type, a pouch type, or
a coin type.
[00108] Hereinafter, the present invention will be described
in more detail through specific examples. However, the following
examples are only examples to help the understanding of the present
invention, and do not limit the scope of the present invention.
It is obvious to those skilled in the art that various changes
and modifications are possible within the scope and spirit of the
present disclosure, and it goes without saying that such
variations and modifications fall within the scope of the appended
claims.
[00109] Examples
[00110] Example 1
[00111] (Preparation of non-aqueous electrolyte)
[00112] A non-aqueous solvent was prepared by dissolving LiPF6
in fluoroethylenecarbonate (FEC) and diethyl carbonate (DEC) in a
volume ratio of 10:90 as an organic solvent to 1.5 M, and 0.1 g
of the compound of Formula 2-1 was added to 99.9 g of the non-
aqueous solvent to prepare a non-aqueous electrolyte.
[00113] [Chemical Formula 2-1]
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CA 03229040 2024-02-09
o ri/\OCF3
[00114] (Manufacture of lithium secondary battery)
[00115] A positive electrode active
material
(LiNi0.85Coo.o5Mno.08A10.0202), a conductive material (carbon nanotube),
and a binder (polyvinylidene fluoride) were added to N-methy1-2-
pyrrolidone (NMP) as a solvent in a weight ratio of 97.74:0.7:1.56
to prepare a positive electrode slurry (solids: 75.5 wt%). The
positive electrode slurry was applied on one surface of a positive
electrode current collector (Al thin film) having a thickness of
15 pm, and dried and roll pressed to manufacture a positive
electrode.
[00116] A negative electrode active material (silicon; Si), a
conductive material (carbon black), and a binder (styrene-
butadiene rubber (SBR)-carboxymethyl cellulose (CMC)) were added
to N-methyl-2-pyrrolidone (NMP) as a solvent to prepare a negative
electrode slurry (solids: 26 wt%). The negative electrode slurry
was applied on a negative electrode current collector (Cu thin
film) having a thickness of 15 pm, dried and rolled to manufacture
a negative electrode.
[00117] A polyolefin-based porous separator coated with
31
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inorganic particles A1203 was interposed between the manufactured
positive electrode and the negative electrode in a dry room, and
then the prepared non-aqueous electrolyte was injected to
manufacture a secondary battery.
[00118] Example 2
[00119] A secondary battery was manufactured in the same manner
as in Example 1, except that 0.3 g of the compound of Formula 2-
1 was added to 99.7 g of the non-aqueous solvent prepared in
Example 1 to prepare a non-aqueous electrolyte.
[00120] Example 3
[00121] A secondary battery was manufactured in the same manner
as in Example 1, except that 0.5 g of the compound of Formula 2-
1 was added to 99.5 g of the non-aqueous solvent prepared in
Example 1 to prepare a non-aqueous electrolyte.
[00122] Example 4
[00123] A secondary battery was manufactured in the same manner
as in Example 1, except that 1.0 g of the compound of Formula 2-
1 was added to 99.0 g of the non-aqueous solvent prepared in
Example 1 to prepare a non-aqueous electrolyte.
[00124] Example 5
[00125] A secondary battery was manufactured in the same manner
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as in Example 1, except that 3.0 g of the compound of Formula 2-
1 was added to 97.0 g of the non-aqueous solvent prepared in
Example 1 to prepare a non-aqueous electrolyte.
[00126] Comparative Example 1
[00127] A secondary battery was manufactured in the same manner
as in Example 1, except that a non-aqueous electrolyte was prepared
using 100 g of the non-aqueous solvent prepared in Example 1.
[00128] Comparative Example 2
[00129] A secondary battery was manufactured in the same manner
as in Example 1, except that 0.1 g of the compound of the following
Chemical Formula A was added to 99.9 g of the non-aqueous solvent
prepared in Example 1 to prepare a non-aqueous electrolyte.
[00130] [Chemical Formula A]
0 O'CH2CF3
PiNIN
ird
[00131] Experimental Example 1 - Evaluation of high-
temperature cycle characteristics
[00132] For each of the secondary batteries manufactured in
33
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Examples 1 to 5 and Comparative Examples 1 and 2, cycle
characteristics were evaluated.
[00133] Specifically, each of the batteries manufactured in
Examples 1 to 5 and Comparative Examples 1 and 2 was charged to
4.2V at 45 C at 1C constant current, and discharged to 3.11V at
0.5C constant current as 1 cycle, and after 600 cycles of charging
and discharging, the capacity retention rate compared to the
initial capacity after 1 cycle was measured.
The results are
shown in Table 1 below.
[00134] [Table 1]
Capacity retention rate (%)
Example 1 80.0
Example 2 81.1
Example 3 81.5
Example 4 82.7
Example 5 88.6
Comparative Example 1 78.4
Comparative Example 2 79.5
[00135] As shown in Table 1, Examples 1 to 5 in which the
additive for a non-aqueous electrolyte of the present invention
was used had a higher capacity retention rate and superior lifespan
characteristics compared to Comparative Examples 1 and 2 in which
the additive was not used. In particular, in the case of compound
A used in the secondary battery of Comparative Example 2, CF3 at
the terminal is directly connected to an alkylene group, and thus
it is different from the additive of the present invention in
which CF3 at the terminal is connected to an alkylene group via
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oxygen. -CF3 is a strong electron withdrawing group (EWG), and
when it is directly linked to an alkylene group, it is thought
that it is difficult to reduce to the LiF form. Meanwhile, when
the terminal is present in the form of -0CF3 as in the additive
of the present invention, it is considered that as a weak EWG is
obtained, the LiF formation reaction is easy, and it is easy for
the polymer-inorganic composite film to be formed on the negative
electrode, and thus the capacity retention rate at high
temperature is excellent.
[00136] Experimental Example 2 - Evaluation of high temperature
storage characteristics
[00137] For each of the secondary batteries manufactured in
Examples 1 to 5 and Comparative Examples 1 and 2, high temperature
storage characteristics were evaluated.
[00138] Specifically, the secondary batteries of Examples 1 to
5 and Comparative Examples 1 and 2 were fully charged to 4.2V,
respectively, and then stored at 60 C for 6 weeks.
[00139] Before storage, the capacity of the fully charged
secondary battery was measured and set as the initial capacity of
the secondary battery.
[00140] After 6 weeks, the capacity of the stored secondary
battery was measured to calculate the capacity decrease during
the storage period of 6 weeks. The capacity retention rate was
derived after 6 weeks by calculating the percentage ratio of the
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reduced capacity to the initial capacity of the secondary battery.
The results are shown in Table 2 below.
[00141] [Table 2]
Capacity retention rate (%)
Example 1 91.9
Example 2 92.1
Example 3 92.3
Example 4 93.7
Example 5 97.2
Comparative Example 1 87.9
Comparative Example 2 90.7
[00142] As shown in Table 2, it was confirmed that the
secondary batteries of Examples 1 to 5 had a higher capacity
retention rate after 6 weeks than the secondary batteries of
Comparative Examples 1 and 2, and thus had stable performance at
high temperature. In particular, in the case of compound A used
in the secondary battery of Comparative Example 2, CF3 at the
terminal is directly connected to an alkylene group, and thus it
is different from the additive of the present invention in which
CF3 at the terminal is connected to an alkylene group via oxygen.
-CF3 is a strong electron withdrawing group (EWG), and when it is
directly linked to an alkylene group, it is thought that it is
difficult to reduce to the LiF form. Meanwhile, when the terminal
is present in the form of -0CF3 as in the additive of the present
invention, it is considered that as a weak EWG is obtained, the
LiF formation reaction is easy, and it is easy for the polymer-
inorganic composite film to be formed on the negative electrode,
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and thus the capacity retention rate during long-term storage at
high temperature is excellent.
37
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