TECHNICAL FIELD
[0001] [Cross-reference to Related Application]􀁇
[0002] The present application claims priority to and the
benefits 􀁇 of Korean Patent Application No. 10-2014-0128882
filed with the Korean Intellectual Property Office on
September 26, 2014 and Korean Patent Application No. 10-2015-
0135259 filed with the Korean Intellectual Property Office on
September 24, 2015 the entire contents of which are
􀁘􀁗􀁇 incorporated herein by reference.􀁇
[0003] [Technical Field]􀁇
[0004] The present invention relates to a lithium secondary
battery comprising a non-aqueous electrolyte solution
comprising lithium bis(fluorosulfonyl)imide (LiFSI) and a
􀁘􀁜􀁇 phosphazene compound additive, a positive electrode
containing a lithium-nickel-manganese-cobalt-based oxide as a
positive electrode active material, a negative electrode and
a separator.􀁇
BACKGROUND ART
􀁙􀁗􀁇 [0005] According to the increase of technical development
and demand on mobile devices, the demand on secondary
batteries as an energy source has been rapidly increased.
Among the secondary batteries, lithium secondary batteries
having high energy density and voltage are commercially
􀁙􀁜􀁇 available and widely used.
3
􀁇
[0006] As a positive electrode active material of a lithium
secondary battery, a lithium metal oxide is used, and as a
negative electrode active material, a lithium metal, a
lithium alloy, crystalline or amorphous carbon or a carbon
composite is used. The 􀁇 active material is coated on a
current collector to an appropriate thickness and length, or
the active material itself is coated as a film shape and then
is wrapped or stacked with a separator that is an insulating
material, to form an electrode group. After that, the
􀁘􀁗􀁇 electrode group is inserted in a can or a vessel similar
thereto, and an electrolyte solution is injected therein to
manufacture a secondary battery.
[0007] In the lithium secondary battery, lithium ions repeat
intercalation and deintercalation from a lithium metal oxide
􀁘􀁜􀁇 of a positive electrode to a carbon electrode to conduct
charging and discharging. In this case, lithium is strongly
reactive and reacts with the carbon electrode to produce
Li2CO3, LiO, LiOH, etc. to form a coated layer on the surface
of a negative electrode. This coated layer is called a solid
􀁙􀁗􀁇 electrolyte interface (SEI). The SEI layer formed at the
beginning of charging may prevent the reaction of the lithium
ions with the carbon negative electrode or other materials
during charging and discharging. In addition, the SEI layer
performs the role of an ion tunnel and passes only the
􀁙􀁜􀁇 lithium ions. The ion tunnel may induce the solvation of the
4
􀁇
lithium ions, and organic solvents of an electrolyte solution
having high molecular weight may induce co-intercalation at
the carbon negative electrode, thereby preventing the
breaking of the structure of the carbon negative electrode.
[0008] Therefore, to improve 􀁇 prove the cycle properties at a high
temperature and the output at a low temperature of a lithium
secondary battery, a rigid SEI layer is necessary to be
formed at the negative electrode of the lithium secondary
battery. Once the SEI layer is formed during an initial
􀁘􀁗􀁇 charging, the SEI layer prevents the reaction of the lithium
ions with the negative electrode or other materials during
repeating charging and discharging while using the battery
later and plays the role of the ion tunnel for passing only
the lithium ions between an electrolyte solution and the
􀁘􀁜􀁇 negative electrode.
[0009] The improvement of the output properties at a low
temperature is not expected for a common electrolyte solution
not comprising an electrolyte additive or an electrolyte
solution comprising an electrolyte additive with inferior
􀁙􀁗􀁇 properties due to the formation of a non-uniform SEI layer.
In addition, even when an electrolyte additive is included,
in the case when the amount required thereof is not
controlled, the surface of the positive electrode may be
decomposed during performing a reaction at a high temperature
􀁙􀁜􀁇 due to the electrolyte additive, or an oxidation reaction of
5
􀁇
the electrolyte solution may be carried out, thereby
increasing the irreversible capacity and deteriorating the
output properties of a secondary battery.
DISCLOSURE OF THE INVENTION
􀁜􀁇 TECHNICAL PROBLEM
[0010] An aspect of the present invention provides a nonaqueous
electrolyte solution for a lithium secondary battery,
that may improve output properties and may increase lifespan
properties, and a lithium secondary battery comprising the
􀁘􀁗􀁇 same.
TECHNICAL SOLUTION
[0011] According to an aspect of the present invention,
there is provided a lithium secondary battery comprising a
non-aqueous electrolyte solution comprising lithium
􀁘􀁜􀁇 bis(fluorosulfonyl)imide (LiFSI) and a phosphazene compound
as additives, a positive electrode comprising a lithiumnickel-
manganese-cobalt-based oxide as a positive electrode
active material, a negative electrode and a separator.
[0012] The non-aqueous electrolyte solution may further
􀁙􀁗􀁇 comprise a lithium salt, and a mixing ratio of the lithium
salt and the lithium bis(fluorosulfonyl)imide by molar ratio
may be from 1:0.01 to 1:1. The concentration of the lithium
bis(fluorosulfonyl)imide in the non-aqueous electrolyte
solution may be from 0.01 mol/L to 2 mol/L.
􀁙􀁜􀁇 [0013] The lithium-nickel-manganese-cobalt-based oxide may
6
􀁇
be represented by the following Formula 1.
[0014] [Formula 1]
[0015] Li1+x(NiaCobMnc)O2
[0016] In the above Formula, the conditions of 0.55􀋺 a􀋺 0.65,
0.18􀋺 b􀋺 0.22, 0.18􀋺 c􀋺 0.22, -0.2􀋺 x􀁜􀁇 􀋺 0.2 and x+a+b+c=1 may be
satisfied.
ADVANTAGEOUS EFFECTS
[0017] According to the non-aqueous electrolyte solution for
a lithium secondary battery, a rigid SEI layer may be formed
􀁘􀁗􀁇 at a negative electrode during performing the initial
charging of the lithium secondary battery comprising the same,
flame retardant properties may be imparted in high
temperature environment, and the decomposition of the surface
of a positive electrode and the oxidation reaction of an
􀁘􀁜􀁇 electrolyte solution may be prevented, thereby improving the
output properties and the lifespan properties after storing
at high temperature of the lithium secondary battery.
BEST MODE FOR CARRYING OUT THE INVENTION
[0018] Hereinafter, the present invention will be described
􀁙􀁗􀁇 in more detail to assist the understanding of the present
invention. It will be understood that terms or words used in
the specification and claims, should not be interpreted as
having a meaning that is defined in dictionaries, but should
be interpreted as having a meaning that is consistent with
􀁙􀁜􀁇 their meaning in the context of the present invention on the
7
􀁇
basis of the principle that the concept of the terms may be
appropriately defined by the inventors for the best
explanation of the invention.
[0019] The non-aqueous electrolyte solution according to an
embodiment 􀁇 of the present invention comprises lithium
bis(fluorosulfonyl)imide (LiFSI).
[0020] The lithium bis(fluorosulfonyl)imide is added in the
non-aqueous electrolyte solution as a lithium salt to form a
rigid and thin SEI layer on a negative electrode and to
􀁘􀁗􀁇 improve output properties at a low temperature. Further, the
decomposition of the surface of a positive electrode, which
may be possibly generated during performing cycle operation
at high temperature, may be restrained, and the oxidation
reaction of the electrolyte solution may be prevented. In
􀁘􀁜􀁇 addition, since the SEI coated layer formed on the negative
electrode has a thin thickness, the movement of lithium ions
at the negative electrode may be performed smoothly, and the
output of a secondary battery may be improved.
[0021] According to an embodiment of the present invention,
􀁙􀁗􀁇 the concentration of the lithium bis(fluorosulfonyl)imide in
the non-aqueous electrolyte solution is preferably from 0.01
mol/L to 2 mol/L and more preferably, from 0.01 mol/L to 1
mol/L. In the case that the concentration of the lithium
bis(fluorosulfonyl)imide is less than 0.1 mol/L, the
􀁙􀁜􀁇 improving effects of the output at a low temperature and the
8
􀁇
cycle properties at high temperature may be insignificant,
and in the case that the concentration of the lithium
bis(fluorosulfonyl)imide exceeds 2 mol/L, side reactions in
the electrolyte solution during the charging and discharging
􀁜􀁇 of the battery may occur excessively, swelling phenomenon may
be generated, and the corrosion of a positive electrode or a
negative electrode collector formed by using a metal in the
electrolyte solution may be induced.
[0022] To prevent the above-described side reaction, a
􀁘􀁗􀁇 lithium salt may be further included in the non-aqueous
electrolyte solution of the present invention. The lithium
salt may comprise commonly used lithium salts in this field.
For example, one or a mixture of at least two selected from
the group consisting of LiPF6, LiAsF6, LiCF3SO3, LiBF6, LiSbF6,
􀁘􀁜􀁇 LiN(C2F5SO2)2, LiAlO4, LiAlCl4, LiSO3CF3 and LiClO4 may be used.
[0023] The mixing ratio of the lithium salt and the lithium
bis(fluorosulfonyl)imide is preferably from 1:0.01 to 1 by
the molar ratio. In the case that the mixing ratio of the
lithium salt and the lithium bis(fluorosulfonyl)imide is
􀁙􀁗􀁇 greater than the upper limit, the side reaction in the
electrolyte solution during the charging and discharging of
the battery may be excessively carried out, and swelling
phenomenon may be generated. In the case that the molar
ratio is less than the lower limit, the improvement of the
􀁙􀁜􀁇 output properties produced of the secondary battery may be
9
􀁇
deteriorated. Particularly, in the case that the mixing
ratio of the lithium salt and the lithium
bis(fluorosulfonyl)imide by the molar ratio is less than
1:0.01, irreversible reaction may be carried out a lot during
􀁜􀁇 the forming process of an SEI coated layer in a lithium ion
battery and the intercalation process of solvated lithium
ions by a carbonate-based solvent between negative electrodes,
and the improving effects of the output at a low temperature
and the cycle properties and capacity properties after
􀁘􀁗􀁇 storing at high temperature of the secondary battery may
become insignificant due to the exfoliation of the surface
layer of the negative electrode (for example, the surface
layer of carbon) and the decomposition of an electrolyte
solution. When the mixing ratio of the lithium salt and the
􀁘􀁜􀁇 lithium bis(fluorosulfonyl)imide by the molar ratio exceeds
1:1, excessive amount of lithium bis(fluorosulfonyl)imide may
be included in an electrolyte solution, and an electrode
collector may be corroded during performing charging and
discharging and the stability of the secondary battery may be
􀁙􀁗􀁇 deteriorated.
[0024] The positive electrode active material of the
lithium-nickel-manganese-cobalt-based oxide may comprise an
oxide represented by the following Formula 1.
[0025] [Formula 1]
􀁙􀁜􀁇 [0026] Li1+x(NiaCobMnc)O2
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􀁇
[0027] In the above Formula, the conditions of 0.55􀋺 a􀋺 0.65,
0.18􀋺 b􀋺 0.22, 0.18􀋺 c􀋺 0.22, -0.2􀋺 x􀋺 0.2 and x+a+b+c =1 are
satisfied.
[0028] By using the positive electrode active material of
􀁜􀁇 the lithium-nickel-manganese-cobalt-based oxide in the
positive electrode, synergistic effect may be attained
through the combination with the lithium
bis(fluorosulfonyl)imide. When the amount of Ni in the
positive electrode active material of the lithium-nickel􀁘
􀁗􀁇 manganese-cobalt-based oxide increases, cation mixing by
which the site of Li+1 ions and the site of Ni+2 ions are
exchanged in the lamella structure of the positive electrode
active material during charging and discharging may be
generated, and the structure thereof may be broken. Thus,
􀁘􀁜􀁇 the side reaction of the positive electrode active material
with the electrolyte may be performed, or the elution
phenomenon of a transition metal may be exhibited. The
cation mixing is carried out because the size of the Li+1 ion
and the size of the Ni+2 ion are similar. Through the side
􀁙􀁗􀁇 reaction, the electrolyte in the secondary battery may be
depleted, and the structure of the positive electrode active
material may be broken, thereby easily deteriorating the
performance of the battery.
[0029] Therefore, an electrolyte in which the lithium
􀁙􀁜􀁇 bis(fluorosulfonyl)imide is applied is used in the positive
11
􀁇
electrode active material of Formula 1 according to an
embodiment of the present invention to form a layer at the
surface of the positive electrode using a lithium
bis(fluorosulfonyl)imide induced component so as to restrain
the cation mixing phenomenon of the Li+1 ions and 􀁇 the Ni+2
ions while obtaining the range for securing the amount of a
nickel transition metal sufficient for securing the capacity
of the positive electrode active material. According to the
positive electrode active material comprising the oxide
􀁘􀁗􀁇 according to the above Formula 1 of the present invention,
side reaction with the electrolyte and metal eluting
phenomenon may be effectively restrained by using the
electrolyte in which the lithium bis(fluorosulfonyl)imide is
applied.
􀁘􀁜􀁇 [0030] In particular, in the case that the ratio of the Ni
transition metal in the oxide represented by the above
Formula 1 exceeds 0.65, an excessive amount of Ni is included
in the positive electrode active material, and the cation
mixing phenomenon of the Li+1 ions and the Ni+2 ions may not
􀁙􀁗􀁇 be restrained even by the layer formed using the lithium
bis(fluorosulfonyl)imide at the surface of the electrode.
[0031] In addition, in the case that an excessive amount of
the Ni transition metal is included in the positive electrode
active material, the oxidation number of Ni may be changed.
􀁙􀁜􀁇 When the nickel transition metal having a d orbital makes a
12
􀁇
coordination bond, a regular octahedron structure may be
formed, however in an environment comprising high temperature,
etc., the order of the energy level of the nickel transition
metal may be changed or the oxidation number thereof may be
􀁜􀁇 changed (disproportionation reaction) by the application of
external energy to form a twisted octahedron structure. Thus,
the crystal structure of the positive electrode active
material comprising the nickel transition metal may be
deformed, and the probability of the elution of the nickel
􀁘􀁗􀁇 metal in the positive electrode active material may be
increased.
[0032] As a result, the inventors of the present invention
confirmed that the high output, the stability at high
temperature and the good efficiency of capacity properties
􀁘􀁜􀁇 may be secured through the combination of the positive
electrode active material comprising the oxide according to
the above Formula 1 with a lithium bis(fluorosulfonyl)imide
salt.
[0033] In addition, a phosphazene compound may be included
􀁙􀁗􀁇 as an electrolyte additive according to an embodiment of the
present invention. Particularly, at least one selected from
the group consisting of the compounds represented by the
following Formulae 2 and 3 may be illustrated.
[0034] [Formula 2]
13
􀁇
􀁇
[0035] [Formula 3]
􀁇
[0036] In a lithium secondary battery, oxygen released from
􀁜􀁇 a positive electrode in high temperature environment may
promote the exothermic decomposition reaction of an
electrolyte solvent and induce the expansion of a battery, so
called, swelling phenomenon, to rapidly deteriorate the
lifespan and the efficiency of charging and discharging of
􀁘􀁗􀁇 the battery. In some cases, the battery may be exploded and
14
􀁇
the stability thereof may be largely deteriorated. Since the
phosphazene compound added in the electrolyte is a flame
retardant compound, the generation of a gas due to the
decomposition of the electrolyte at high temperature through
the 􀁇 reaction of the electrolyte with the surface of the
negative electrode and the positive electrode in the battery
may be restrained, and the generation of oxygen at the
positive electrode may be restrained, thereby improving the
lifespan properties of a lithium secondary battery. Thus,
􀁘􀁗􀁇 the output properties at high temperature and the lifespan
properties of the secondary battery comprising the
phosphazene compound according to an embodiment of the
present invention may be effectively increased.
[0037] In this case, the amount of the phosphazene compound
􀁘􀁜􀁇 may not be limited only if sufficient to accomplish the
effects of the present invention comprising the improvement
of the output properties at high temperature and the lifespan
properties of the battery. For example, the amount of the
phosphazene compound may be from 0.1 to 15 wt% and preferably
􀁙􀁗􀁇 may be from 3.0 to 10 wt% based on the total amount of the
electrolyte. In the case that the amount of the phosphazene
compound is less than 0.1 wt%, the flame retardant effect may
be insufficiently obtained. In the case that the amount of
the phosphazene compound exceeds 15 wt%, the increasing
􀁙􀁜􀁇 degree of the effects may be limited, however irreversible
15
􀁇
capacity may be increased or the resistance of the negative
electrode may be increased. Particularly, the amount of the
phosphazene compound may be controlled by the amount added of
the lithium bis(fluorosulfonyl)imide so as to efficiently
prevent the generation 􀁇 ration of side reaction possibly carried out
according to the addition of a large amount of the lithium
bis(fluorosulfonyl)imide.
[0038] In addition, a non-aqueous organic solvent that may
be included in the non-aqueous electrolyte solution is not
􀁘􀁗􀁇 limited only if the decomposition thereof due to oxidation
reaction, etc. during the charging and discharging of a
battery may be minimized and target properties may be
exhibited with the additive. For example, a nitrile-based
solvent, a cyclic carbonate solvent, a linear carbonate
􀁘􀁜􀁇 solvent, an ester solvent, an ether solvent or a ketone
solvent, etc. may be used. These solvents may be used alone
or as a combination of two or more.
[0039] In the organic solvents, a carbonate-based organic
solvent may be readily used. The cyclic carbonate solvent
􀁙􀁗􀁇 may be one selected from the group consisting of ethylene
carbonate (EC), propylene carbonate (PC) and butylene
carbonate (BC), or a mixture of at least two thereof. The
linear carbonate solvent may be one selected from the group
consisting of dimethyl carbonate (DMC), diethyl carbonate
􀁙􀁜􀁇 (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC),
16
􀁇
methyl propyl carbonate (MPC) and ethyl propyl carbonate
(EPC), or a mixture of at least two thereof.
[0040] 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-fluorophenyl acetonitrile and 4-
􀁘􀁗􀁇 fluorophenyl acetonitrile. The non-aqueous solvent according
to an embodiment of the present invention may be the
acetonitrile.
[0041] Meanwhile, the lithium secondary battery according to
an embodiment of the present invention may comprise a
􀁘􀁜􀁇 positive electrode, a negative electrode, a separator
disposed between the positive electrode and the negative
electrode and the non-aqueous electrolyte solution. The
positive electrode and the negative electrode may comprise
the positive electrode active material and the negative
􀁙􀁗􀁇 electrode active material, respectively, according to an
embodiment of the present invention.
[0042] Meanwhile, the negative electrode active material may
comprise amorphous carbon and crystalloid carbon and may use
carbon such as non-graphitized carbon, graphitized carbon,
􀁙􀁜􀁇 etc; a metal complex oxide such as LixFe2O3 (0≤x≤1), LixWO2
17
􀁇
(0≤x≤1), SnxMe1-xMe’yOz (Me: Mn, Fe, Pb and Ge; Me’: Al, B, P,
Si, elements in group 1, group 2 and group 3 on the periodic
table, and halogen; 0
22
􀁇
[0073] Using voltage difference generated when charging and
discharging the secondary batteries manufactured in Examples
1 to 6 and Comparative Examples 1 to 3 at -30°C with 0.5 C
for 10 seconds, the output thereof was calculated. In this
case, the output of Comparative Example 1 was 3.4 W. Th􀁜􀁇 e
output of Examples 1 to 6 and Comparative Examples 2 and 3
was calculated by percent based on that of Example 1, and the
results are illustrated in the following Table 1. The test
was performed at the state of charge (SOC) of 50%.
􀁘􀁗􀁇 [0074]
[0075] Using voltage difference generated when charging and
discharging the secondary batteries manufactured in Examples
1 to 6 and Comparative Examples 1 to 3 at 23°C with 0.5 C for
10 seconds, the output thereof was calculated. In this case,
􀁘􀁜􀁇 the output of Comparative Example 1 was 37.1 W. The output
of Examples 1 to 6 and Comparative Examples 2 and 3 was
calculated by percent based on that of Example 1, and the
results are illustrated in the following Table 1. The test
was performed at the SOC of 50%.
􀁙􀁗􀁇
[0076]
[0077] The secondary batteries manufactured in Examples 1 to
6 and Comparative Examples 1 to 3 were stored at 60°C for 20
􀁙􀁜􀁇 weeks, and the output thereof was calculated using voltage
23
􀁇
difference generated when charging and discharging at 23°C
with 5 C for 10 seconds. In this case, the output of
Comparative Example 1 was 35.9 W. The output of Examples 1
to 6 and Comparative Examples 2 and 3 was calculated by
􀁜􀁇 percent based on that of Example 1, and the results are
illustrated in the following Table 1. The test was performed
at the SOC of 50%.
[0078] [Table 1]
Output properties – based on Comparative Example 1
Output at low
temperature
Output at room
temperature
Output after
storing at high
temperature
Example 1 2.11 1.02 3.32
Example 2 4.36 2.93 8.73
Example 3 3.19 2.33 6.25
Example 4 2.31 1.61 4.01
Example 5 4.21 2.91 8.52
Example 6 1.84 0.86 1.27
Comparative
Example 1
- - -
Comparative
Example 2
-0.75 -0.47 -2.88
Comparative
Example 3
-2.99 -1.48 -7.42
􀁘􀁗􀁇 [0079] As shown in Table 1, the secondary batteries of
Examples 1 to 6 exhibited better output at a low temperature
or room temperature by up to about 5% when compared to that
of the secondary batteries of Comparative Examples 1 to 3.
Particularly, since the secondary batteries of Examples 1 to
􀁘􀁜􀁇 6 use the phosphazene compound as an additive, the stability
at high temperature may be increased, and the output
24
􀁇
properties after storing at high temperature may be better by
up to 14% or above when compared to that of the secondary
batteries of Comparative Examples 1 to 3.
[0080]
[0081] The 􀁇 secondary batteries manufactured in Examples 1 to
6 and Comparative Examples 1 to 3 were charged in constant
current (CC)/constant voltage (CV) conditions at 23°C to 4.2
V/38 mA with 1 C and discharged in CC conditions to 2.5 V
with 3 C, and the discharge capacity thereof was measured.
􀁘􀁗􀁇 This experiment was repeatedly performed from 1st to 1000th
cycles. The discharge capacity at the 1000th cycle was
calculated by percent based on the capacity at the 1st cycle
(capacity at 1000th cycle/capacity at 1st cycle*100(%)), and
data thus obtained are illustrated in the following Table 2.
􀁘􀁜􀁇 [0082]
[0083] The secondary batteries manufactured in Examples 1 to
6 and Comparative Examples 1 to 3 were charged in CC/CV
conditions at 45°C to 4.2 V/38 mA with 1 C and discharged in
CC conditions to 2.5 V with 3 C, and the discharge capacity
􀁙􀁗􀁇 thereof was measured. This experiment was repeatedly
performed from 1st to 1000th cycles. The discharge capacity
measured at the 1000th cycle was calculated by percent based
on the capacity at the 1st cycle (capacity at 1000th
cycle/capacity at 1st cycle*100(%)), and data thus obtained
􀁙􀁜􀁇 are illustrated in the following Table 2.
25
􀁇
[0084] [Table 2]
Lifespan properties (%)
Lifespan properties
at room temperature
Lifespan properties
at high temperature
Example 1 79.8 77.8
Example 2 83.9 80.8
Example 3 81.5 79.2
Example 4 80.3 77.8
Example 5 82.7 81.0
Example 6 80.4 74.8
Comparative Example
1
79.1 76.1
Comparative Example
2
79.6 74.2
Comparative Example
3
66.7 60.7
[0085] As shown in Table 2, it would be confirmed that the
lifespan properties at room temperature of the lithium
secondary 􀁇 batteries of Examples 1 to 6 are better than those
of the lithium secondary batteries of Comparative Examples 1
to 3, and it would be confirmed that the lifespan properties
at high temperature of the lithium secondary batteries of
Examples 1 to 5 are better than those of the lithium
􀁘􀁗􀁇 secondary batteries of Comparative Examples 1 to 3. The
lifespan properties at high temperature and the lifespan
properties at room temperature of the lithium secondary
battery of Comparative Example 3 using Li(Ni0.5Co0.3Mn0.2)O2 as
the positive electrode active material are found markedly low.
􀁘􀁜􀁇 Meanwhile, the lifespan properties at high temperature of the
lithium secondary battery of Example 6 were inferior to those
of the lithium secondary battery of Example 1 to 5.
26
􀁇
I/We Claim:
1. A lithium secondary battery comprising:
a non-aqueous electrolyte solution comprising lithium
bis(fluorosulfonyl)imide (LiFSI) and a phosphazene 􀁇 e compound
as additives;
a positive electrode comprising a lithium-nickelmanganese-
cobalt-based oxide as a positive electrode active
material;
􀁘􀁗􀁇 a negative electrode; and
a separator.
2. The lithium secondary battery of claim 1, wherein the
lithium-nickel-manganese-cobalt-based oxide is represented by
􀁘􀁜􀁇 the following Formula 1:
[Formula 1]
Li1+x(NiaCobMnc)O2
in the above Formula, 0.55􀋺 a􀋺 0.65, 0.18􀋺 b􀋺 0.22, 0.18
􀋺 c􀋺 0.22, -0.2􀋺 x􀋺 0.2 and x+a+b+c=1.
􀁙􀁗􀁇
3. The lithium secondary battery of claim 1, wherein the
non-aqueous electrolyte solution further comprises a lithium
salt.
􀁙􀁜􀁇 4. The lithium secondary battery of claim 3, wherein a
27
􀁇
mixing ratio of the lithium salt and the lithium
bis(fluorosulfonyl)imide by molar ratio is from 1:0.01 to 1:1.
5. The lithium secondary battery of claim 1, wherein a
concentration of the lithium 􀁇 bis(fluorosulfonyl)imide in the
non-aqueous electrolyte solution is from 0.01 mol/L to 2
mol/L.
6. The lithium secondary battery of claim 3, wherein the
􀁘􀁗􀁇 lithium salt is one or a mixture of at least two selected
from the group consisting of LiPF6, LiAsF6, LiCF3SO3,
LiN(CF3SO2)2, LiBF6, LiSbF6, LiN(C2F5SO2)2, LiAlO4, LiAlCl4,
LiSO3CF3 and LiClO4.
􀁘􀁜􀁇 7. The lithium secondary battery of claim 1, wherein the
phosphazene compound is at least one selected from compounds
represented by the following Formulae 2 and 3:
[Formula 2]
􀁙􀁗􀁇
28
􀁇
[Formula 3]
.
8. The lithium secondary battery of claim 1, wherein the
non-􀁇 aqueous organic solvent comprises a nitrile-based solvent,
a linear carbonate solvent, a cyclic carbonate solvent, an
ester solvent, an ether solvent, a ketone solvent or a
combination thereof.
􀁘􀁗􀁇 9. The lithium secondary battery of claim 8, wherein the
cyclic carbonate solvent is one or a mixture of at least two
selected from ethylene carbonate (EC), propylene carbonate
(PC) and butylene carbonate (BC), and the linear carbonate
solvent is one or a mixture of at least two selected from the
􀁘􀁜􀁇 group consisting of dimethyl carbonate (DMC), diethyl
carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl
carbonate (EMC), methyl propyl carbonate (MPC) and ethyl
29
􀁇
propyl carbonate (EPC).
10. The lithium secondary battery of claim 8, wherein the
nitrile-based solvent is 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-fluorophenyl
􀁘􀁗􀁇 acetonitrile and 4-fluorophenyl acetonitrile.
11. The lithium secondary battery of claim 1, wherein an
amount of the additive of the phosphazene compound is 0.1-15
wt% based on a total amount of the non-aqueous electrolyte
􀁘􀁜􀁇 solution.
12. The lithium secondary battery according to any one of
claims 1 to 11, wherein the secondary battery is a pouch type
lithium secondary battery.