TECHNICAL FIELD
[0001] The present invention relates to a non-aqueous
electrolyte solution and a cathode which include a phosphatebased
compound, and a lithium secondary battery including 5 g the
non-aqueous electrolyte solution and the cathode.
BACKGROUND ART
[0002] Recently, in line with the development of information
and telecommunications industry, electronic devices are being
10 miniaturized, light-weighted, reduced in thickness, and
portable. As a result, the need for high energy density
batteries used as power sources of such electronic devices
has increased. Currently, research into lithium secondary
batteries, as batteries that may best satisfy the above need,
15 has actively conducted.
[0003] A lithium secondary battery is a battery which is
composed of a cathode, an anode, and an electrolyte and a
separator which provide movement paths of lithium ions
between the cathode and the anode, wherein electrical energy
20 is generated by oxidation and reduction reactions that occur
when lithium ions are stored in and released from the cathode
and the anode.
[0004] A lithium secondary battery has an average discharge
voltage of about 3.6 V to about 3.7 V, and one of the
25 advantages of the lithium secondary battery is that it has a
3
higher discharge voltage than other alkaline batteries and a
nickel-cadmium battery. In order to achieve such a high
operating voltage, an electrolyte composition, which is
electrochemically stable in a charge and discharge voltage
range of 5 f 0 V to 4.2 V, is required.
[0005] Lithium ions released from a cathode active material,
such as lithium metal oxide, during initial charging of a
lithium secondary battery move to an anode active material,
such as a graphite-based material, to be intercalated into
10 interlayers of the anode active material. In this case,
since lithium is highly reactive, lithium reacts with an
electrolyte and carbon constituting the anode active material
on a surface of the anode active material, such as a
graphite-based material, to form a compound such as Li2CO3,
15 Li2O, or LiOH. These compounds may form a solid electrolyte
interface (SEI) on the surface of the anode active material
such as a graphite-based material.
[0006] The SEI may only pass lithium ions by acting as an
ion tunnel. Due to the effect of the ion tunnel, the SEI may
20 prevent the destruction of an anode structure due to the
intercalation of organic solvent molecules having a high
molecular weight, which move with lithium ions in the
electrolyte, into the interlayers of the anode active
material. Thus, the decomposition of the electrolyte does
25 not occur by preventing the contact between the electrolyte
4
and the anode active material, and stable charge and
discharge may be maintained by reversibly maintaining the
amount of lithium ions in the electrolyte.
[0007] Typically, with respect to an electrolyte solution
which does not include an electrolyte solution additive 5 itive or
includes an electrolyte solution additive having poor
characteristics, it is difficult to expect the improvement of
lifetime characteristics due to the formation of a nonuniform
SEI. Furthermore, even if an electrolyte solution
10 additive is included, in the case that the addition amount
thereof is not controlled to the required amount, the surface
of a cathode may be decomposed or an oxidation reaction of
the electrolyte may occur during a high temperature reaction
due to the electrolyte solution additive. Thus, eventually,
15 irreversible capacity of a secondary battery may increase and
lifetime characteristics may degrade.
[0008] [Prior Art Documents]
[0009] [Patent Document]
[0010] Korean Patent Application Laid-Open Publication No.
20 KR 2012-0132811 A1
DISCLOSURE OF THE INVENTION
TECHNICAL PROBLEM
[0011] The present invention provides a non-aqueous
electrolyte solution which may improve lifetime
25 characteristics of a secondary battery at high temperature
5
and high voltage by adding a small amount of an additive to
the non-aqueous electrolyte solution of the secondary battery.
[0012] The present invention also provides a cathode which
may improve lifetime characteristics of a secondary battery
at high temperature and high voltage by 5 adding a small amount
of an additive to the cathode of the secondary battery.
[0013] The present invention also provides a lithium
secondary battery including the non-aqueous electrolyte
solution or the cathode.
10 TECHNICAL SOLUTION
[0014] According to an aspect of the present invention,
there is provided a non-aqueous electrolyte solution
including: a lithium salt; an electrolyte solution solvent;
and a compound represented by Chemical Formula 1:
15 [0015]
[0016] in the above chemical formula,
[0017] Y1 and Y2 are each independently silicon (Si) or tin
(Sn),
[0018] R1 to R6 are each independently hydrogen or a C1-C10
20 alkyl group, and
6
[0019] A is ,
[0020] where Y3 is Si or Sn,
[0021] R7 to R9 are each independently hydrogen or a C1-C10
alkyl group, and
[0022] n 5 is between 2 and 4.
[0023] According to another aspect of the present invention,
there is provided a cathode including a lithium transition
metal oxide and a compound represented by Chemical Formula 1.
ADVANTAGEOUS EFFECTS
10 [0024] According to a non-aqueous electrolyte solution and a
cathode which include a compound of Chemical Formula 1
according to an embodiment of the present invention, lifetime
characteristics of a lithium secondary battery may be
improved, and in particular, lifetime characteristics at a
15 high temperature of 45°C or more and a high voltage of 4.3 V
or more. Also, stable and excellent lifetime characteristics
at high temperature and high voltage may be achieved
regardless of the moisture content or the presence of drying
and pressing processes of an electrode.
20 BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a graph illustrating the results of the
measurement of lifetime characteristics at 45°C of secondary
7
batteries not subjected to roll-pressing of a cathode in
lithium secondary batteries of Examples 3 and 4 and
Comparative Examples 6 to 8;
[0026] FIG. 2 is a graph illustrating the results of the
measurement of lifetime characteristics at 45°C of secondar5 y
batteries subjected to roll-pressing of a cathode in the
lithium secondary batteries of Examples 3 and 4 and
Comparative Examples 6 to 8;
[0027] FIG. 3 is a graph illustrating the results of the
10 measurement of lifetime characteristics at 45°C of secondary
batteries not subjected to both drying and roll-pressing of a
cathode in lithium secondary batteries of Example 3 and
Comparative Examples 9 and 10;
[0028] FIG. 4 is a graph illustrating the results of the
15 measurement of lifetime characteristics at 45°C of secondary
batteries subjected to drying of a cathode and not subjected
to roll-pressing of the cathode in the lithium secondary
batteries of Example 3 and Comparative Examples 9 and 10;
[0029] FIG. 5 is a graph illustrating the results of the
20 measurement of lifetime characteristics at 45°C of secondary
batteries subjected to both drying and roll-pressing of a
cathode in the lithium secondary batteries of Example 3 and
Comparative Examples 9 and 10;
[0030] FIG. 6 is a graph illustrating the results of the
25 measurement of lifetime characteristics at 45°C according to
8
the presence of drying and roll-pressing processes of a
cathode in the lithium secondary batteries of Example 3;
[0031] FIG. 7 is a graph illustrating the results of the
measurement of lifetime characteristics at 45°C according to
the presence of drying and roll-pressing processes of 5 a
cathode in the lithium secondary batteries of Comparative
Example 9;
[0032] FIG. 8 is a graph illustrating the results of the
measurement of lifetime characteristics at 45°C according to
10 the presence of drying and roll-pressing processes of a
cathode in the lithium secondary batteries of Comparative
Example 10; and
[0033] FIG. 9 is a graph illustrating the results of the
measurement of lifetime characteristics at 45°C of lithium
15 secondary batteries of Examples 5 and 6 and Comparative
Examples 11 and 12.
MODE FOR CARRYING OUT THE INVENTION
[0034] Hereinafter, the present invention will be described
in more detail to allow for a clearer understanding of the
20 present invention. It will be understood that words or terms
used in the specification and claims shall not be interpreted
as the meaning defined in commonly used dictionaries. It
will be further understood that the words or terms should be
interpreted as having a meaning that is consistent with their
25 meaning in the context of the relevant art and the technical
9
idea of the invention, based on the principle that an
inventor may properly define the meaning of the words or
terms to best explain the invention.
[0035] According to an embodiment of the present invention,
the present invention may provide a non-aqueous 5 eous electrolyte
solution including a lithium salt; an electrolyte solution
solvent; and a compound represented by Chemical Formula 1.
[0036]
[0037] in the above chemical formula,
10 [0038] Y1 and Y2 are each independently silicon (Si) or tin
(Sn),
[0039] R1 to R6 are each independently hydrogen or a C1-C10
alkyl group, and
[0040] A is ,
15 [0041] where Y3 is Si or Sn,
[0042] R7 to R9 are each independently hydrogen or a C1-C10
alkyl group, and
10
[0043] n is between 2 and 4.
[0044] According to an embodiment of the present invention,
in the case that n is 3 or 4 in A of Chemical Formula 1, A
may be formed by connecting phosphor (P) of one repeating
unit and oxygen (O) of another adjacent repeating unit 5 it to
each other to form a linear chain, a cyclic chain, or both
linear and cyclic chains.
[0045] The compound represented by Chemical Formula 1
according to an embodiment of the present invention, for
10 example, may be any one selected from the group consisting of
compounds of (1) to (6), or a mixture of two or more thereof:
11
12
.
[0046] In general, in a non-aqueous electrolyte solution
used in a lithium secondary battery, since an electrolyte
solution solvent may be decomposed on the surface of an
electrode during 5 uring charge and discharge of the battery or may
destruct an anode structure by co-intercalating into
interlayers of a carbon material anode, the electrolyte
13
solution solvent may decrease the stability of the battery.
[0047] It is known that the above limitations may be
addressed by a solid electrolyte interface (SEI) that is
formed on the surface of an anode by the reduction of the
electrolyte solution solvent during 5 g initial charge of the
battery. However, since it is generally not sufficient for
the SEI to act as a continuous protective layer of the anode,
lifetime and performance may eventually degrade when a charge
and discharge cycle of the battery is repeated. In
10 particular, since a SEI of a typical lithium secondary
battery is not thermally stable, the SEI may be easily
destructed due to thermal energy that is increased according
to the elapsed time when the battery is operated or left
standing at high temperature. As a result, the battery
15 performance may further degrade at high temperature, and in
particular, gas, such as CO2, may be continuously generated
due to the destruction of the SEI and the decomposition of
the electrolyte solution. Thus, the internal pressure and
thickness of the battery may be increased.
20 [0048] According to an embodiment of the present invention,
in the case that the compound represented by Chemical Formula
1 is added to a non-aqueous electrolyte solution or electrode
of a lithium secondary battery, the thickness increase and
performance degradation of the battery due to the destruction
25 of the SEI of the lithium secondary battery may not only be
14
improved, but the lifetime characteristics of the secondary
battery, particularly, at a high temperature of 45°C or more
and a high voltage of 4.3 V or more may also be improved.
[0049] In particular, the non-aqueous electrolyte solution
including the additive may exhibit stable and excellen5 t
lifetime characteristics at high temperature and high voltage
regardless of a moisture content of the electrode or the
presence of drying and pressing processes of the electrode
during the preparation of the secondary battery.
10 [0050] Specifically, the additive of Chemical Formula 1 may
act to stabilize anions of the lithium salt. For example, in
the case that the electrolyte solution includes a fluorine
(F)-containing material such as LiPF6, the fluorine may react
with water or lithium impurities during charge and discharge
15 to form hydrofluoric acid (HF), and an electrode cycle may be
degraded due to corrosion caused by the HF. In this case,
the additive may suppress the formation of HF which may be
formed due to side reactions between the electrolyte solution
and water formed during the charge and discharge.
20 [0051] Also, since the compound of Chemical Formula 1 with a
less stable structure than a typical phosphate-based compound
having a simple structure, for example, a structure of a
phosphate-based compound in which n in Chemical Formula 1 is
2 or more, is electrochemically unstable, the compound may be
25 easily broken to participate in the formation of a film of
15
the electrode and in particular, the compound may form a
conductive film. Thus, the above two factors may
significantly affect the performance improvement when the
compound is used in the secondary battery.
5
[0052] Furthermore, according to an embodiment of the
present invention, the non-aqueous electrolyte solution may
further include a compound represented by the following
Chemical Formula 2:
10 [0053]
[0054] in the above chemical formula,
[0055] R10 to R18 are each independently hydrogen or a C1-C10
alkyl group.
[0056] According to an embodiment of the present invention,
15 the compound represented by Chemical Formula 2, for example,
may be tris(trimethylsilyl)phosphate (TMSPa).
[0057] A mixing ratio of the compound represented by
Chemical Formula 1 to the compound represented by Chemical
16
Formula 2 is in a range of 1:0.1 to 1:2, may be in a range of
1:0.2 to 1:1, and for example, may be in a range of 1:0.2 to
1:0.6 as a weight ratio.
[0058] Also, the compound represented by Chemical Formula 1
may be included in an amount of 0.01 wt% 5 to 5 wt%, for
example, 0.1 wt% to 2 wt%, based on a total weight of the
non-aqueous electrolyte solution.
[0059] In the case that the amount of the compound
represented by Chemical Formula 1 is excessively small, the
10 compound may be entirely consumed during an initial operation
of the secondary battery, and thus, lifetime may degrade
during charge and discharge or long-term storage. In the
case in which the amount of the compound represented by
Chemical Formula 1 is excessively large, the capacity and
15 stability characteristics of the battery may be adversely
affected by side reactions of the remaining additive.
[0060] Any lithium salt typically used in the art may be
used as the lithium salt that is included in the non-aqueous
electrolyte solution according to the embodiment of the
20 present invention. For example, the lithium salt may include
any one selected from the group consisting of LiPF6, LiAsF6,
LiCF3SO3, LiN(CF3SO2)2, LiBF4, LiBF6, LiSbF6, LiN(C2F5SO2)2,
LiAlO4, LiAlCl4, LiSO3CF3, and LiClO4, or a mixture of two or
more thereof.
25 [0061] Also, any electrolyte solution solvent typically used
17
in an electrolyte solution for a lithium secondary battery
may be used as the electrolyte solution solvent used in the
present invention without limitation, and for example, ether,
ester, amide, linear carbonate, or cyclic carbonate may be
used alone or in a mixture of 5 two or more thereof.
[0062] Among these materials, the cyclic carbonate, the
linear carbonate, or a carbonate compound as a mixture
thereof may be typically included. Specific examples of the
cyclic carbonate may be any one selected from the group
10 consisting of ethylene carbonate (EC), propylene carbonate
(PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-
pentylene carbonate, 2,3-pentylene carbonate, vinylene
carbonate, and a halide thereof, or a mixture of two or more
thereof.
15 [0063] Also, specific examples of the linear carbonate may
be any one selected from the group consisting of dimethyl
carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate
(DPC), ethylmethyl carbonate (EMC), methylpropyl carbonate
(MPC), and ethylpropyl carbonate (EPC), or a mixture of two
20 or more thereof. However, the present invention is not
limited thereto.
[0064] In particular, the cyclic carbonate among the
carbonate-based electrolyte solution solvents may include
propylene carbonate, ethylene carbonate, and a mixture
25 thereof. Since the propylene carbonate, ethylene carbonate,
18
and mixture thereof are highly viscous organic solvents and
have high dielectric constants, the propylene carbonate,
ethylene carbonate, and mixture thereof may well dissociate
the lithium salt in the electrolyte solution. Thus, the
propylene carbonate, ethylene carbonate, and mixture thereo5 f
may be used.
[0065] Also, linear carbonates, such as diethyl carbonate,
dimethyl carbonate, ethylmethyl carbonate, and a mixture
thereof, may be used by being mixed with the cyclic carbonate.
10 Since an electrolyte solution having high electrical
conductivity may be prepared when the above cyclic carbonate
is mixed with low viscosity, low dielectric constant linear
carbonate in an appropriate ratio, the cyclic carbonates, for
example, may be used.
15 [0066] Also, any one selected from the group consisting of
methyl acetate, ethyl acetate, propyl acetate, ethyl
propionate (EP), methyl propionate (MP), γ-butyrolactone, γ-
valerolactone, γ-caprolactone, σ-valerolactone, and ε-
caprolactone, or a mixture of two or more thereof may be used
20 as the ester among the electrolyte solution solvents. Among
them, low viscous EP, MP, and a mixture thereof may be
particularly used.
[0067] According to another embodiment of the present
25 invention, the present invention may provide a cathode
19
including a lithium transition metal oxide and a compound
represented by Chemical Formula 1.
[0068] According to an embodiment of the present invention,
in the case that n is 3 or 4 in A of Chemical Formula 1, 5 A
may be formed by connecting P of one repeating unit and O of
another adjacent repeating unit to each other to form a
linear chain, a cyclic chain, or both linear and cyclic
chains.
10 [0069] In the compound of Chemical Formula 1, the compound,
for example, may be any one selected from the group
consisting of compounds of (1) to (6), or a mixture of two or
more thereof:
20
21
.
[0070] Also, according to an embodiment of the present
invention, the cathode may further include a compound
represented by Chemical Formula 2.
[0071] According to an embodiment of the 5 e present invention,
the compound represented by Chemical Formula 2, for example,
22
may be tris(trimethylsilyl)phosphate (TMSPa).
[0072] In this case, a mixing ratio of the compound
represented by Chemical Formula 1 to the compound represented
by Chemical Formula 2 is in a range of 1:0.1 to 1:2, may be
in a range of 1:0.2 to 1:1, and for example, 5 ple, may be in a
range of 1:0.2 to 1:0.6 as a weight ratio.
[0073] According to an embodiment of the present invention,
in the case that the compound represented by Chemical Formula
1 is included as an additive in the cathode, the lifetime
10 characteristics of the lithium secondary battery may be
improved, and the lifetime characteristics, particularly, at
a high temperature of 45°C or more and a high voltage of 4.3
V or more may be improved. Also, stable and excellent
lifetime characteristics at high temperature and high voltage
15 may be achieved regardless of the moisture content or the
presence of drying and pressing processes of the electrode.
[0074] Furthermore, since the compound of Chemical Formula 1
with a less stable structure than a typical phosphate-based
compound having a simple structure, for example, a structure
20 of a phosphate-based compound in which n in Chemical Formula
1 is 2 or more, is electrochemically unstable, the compound
may be easily broken to participate in the formation of a
film of the electrode and in particular, the compound may
form a conductive film. Thus, the above factors may
25 significantly affect the performance improvement,
23
particularly, the lifetime characteristics, when the compound
is used in the secondary battery.
[0075] According to an embodiment of the present invention,
the compound represented by Chemical Formula 1 may be
included in an amount of 0.01 wt% to 5 wt%, for example, 5 ample, 0.1
wt% to 2 wt%, based on a total amount of a cathode mixture
slurry including a cathode active material, an additive, a
conductive agent, and a binder.
[0076] The cathode active material, for example, the lithium
10 transition metal oxide, may be a compound represented by
Chemical Formula 3 below:
[0077]
Li[LixNiaCobMnc]O2 (-0.05≤x≤+0.5, 0
[0088] Example 1
[0089] LiPF6 was dissolved in an electrolyte solution
20 solvent having a composition, in which a volume ratio of
ethylene carbonate (EC):dimethyl carbonate (DMC):ethylmethyl
carbonate (EMC) was 3:4:3, to obtain a LiPF6 concentration of
1 M. Also, as an additive for a non-aqueous electrolyte
solution, tetra(trimethylsilyl)pyrophosphate (compound (1))
25 and tris(trimethylsilyl)phosphate (TMSPa) were prepared at a
26
weight ratio of 3:1, and a non-aqueous electrolyte solution
was prepared by adding the additive in an amount of 2 wt%
based on a total weight of the non-aqueous electrolyte
solution to the above mixture.
5
[0090] Example 2
[0091] A non-aqueous electrolyte solution was prepared in
the same manner as in Example 1 except that
tetra(trimethylsilyl)pyrophosphate was added alone as an
10 additive for a non-aqueous electrolyte solution in the
preparation of the non-aqueous solution of Example 1.
[0092] Comparative Example 1
[0093] A non-aqueous electrolyte solution was prepared in
15 the same manner as in Example 1 except that, instead of the
mixed additive of tetra(trimethylsilyl)pyrophosphate and
tris(trimethylsilyl)phosphate (TMSPa), propane sultone (PS)
and vinylene carbonate (VC) were prepared at a weight ratio
of 1.5:1 and added as an additive for a non-aqueous
20 electrolyte solution in the preparation of the non-aqueous
solution of Example 1.
[0094] Comparative Example 2
[0095] A non-aqueous electrolyte solution was prepared in
25 the same manner as in Example 1 except that, instead of the
27
mixed additive of tetra(trimethylsilyl)pyrophosphate and
tris(trimethylsilyl)phosphate (TMSPa), propane sultone (PS),
vinylene carbonate (VC), and ethylene sulfate (ESa) were
prepared at a weight ratio of 0.5:3:1 and added as an
additive for a non-aqueous electrolyte solution in 5 the
preparation of the non-aqueous solution of Example 1.
[0096] Comparative Example 3
[0097] A non-aqueous electrolyte solution was prepared in
10 the same manner as in Example 1 except that, instead of the
mixed additive of tetra(trimethylsilyl)pyrophosphate and
tris(trimethylsilyl)phosphate (TMSPa), propane sultone (PS)
and vinylene carbonate (VC) were prepared at a weight ratio
of 1.5:3 and added as an additive for a non-aqueous
15 electrolyte solution in the preparation of the non-aqueous
solution of Example 1, and LiPF6 was used at a concentration
of 1.3 M in the preparation of the non-aqueous solution of
Example 1.
20 [0098] Comparative Example 4
[0099] A non-aqueous electrolyte solution was prepared in
the same manner as in Example 1 except that, instead of the
mixed additive of tetra(trimethylsilyl)pyrophosphate and
tris(trimethylsilyl)phosphate (TMSPa), propane sultone (PS),
25 vinylene carbonate (VC), and LiBF4 were prepared at a weight
28
ratio of 1.5:1:2 and added as an additive for a non-aqueous
electrolyte solution in the preparation of the non-aqueous
solution of Example 1.
[00100] Comparative 5 ive Example 5
[00101] A non-aqueous electrolyte solution was prepared in
the same manner as in Example 1 except that, instead of the
mixed additive of tetra(trimethylsilyl)pyrophosphate and
tris(trimethylsilyl)phosphate (TMSPa), TMSPa was added alone
10 as an additive for a non-aqueous electrolyte solution in the
preparation of the non-aqueous solution of Example 1.
[00102] [Preparation of Lithium Secondary Battery]
[00103] Example 3
15 [00104] A cathode mixture slurry was prepared by adding 94
wt% of Li(Li0.2Mn0.55Ni0.15Co0.1)O2 as a cathode active material,
3 wt% of carbon black as a conductive agent, and 3 wt% of
polyvinylidene fluoride (PVdF) as a binder to N-methyl-2-
pyrrolidone (NMP) as a solvent. An about 20 μm thick
20 aluminum (Al) thin film as a cathode collector was coated
with the cathode mixture slurry and dried to prepare a
cathode.
[00105] Also, an anode mixture slurry was prepared by adding
96 wt% of carbon powder as an anode active material, 3 wt% of
25 PVdF as a binder, and 1 wt% of carbon black as a conductive
29
agent to NMP as a solvent. A 10 μm thick copper (Cu) thin
film as an anode collector was coated with the anode mixture
slurry and dried, and the Cu thin film was then roll-pressed
to prepare an anode.
[00106] A polymer type battery was prepared by a ty5 pical
method using a polyethylene (PE) separator with the cathode
and anode thus prepared, and a lithium secondary battery was
then completed by injecting the non-aqueous electrolyte
solution prepared in Example 1.
10
[00107] Example 4
[00108] A lithium secondary battery was prepared in the same
manner as in Example 3 except that the non-aqueous
electrolyte solution prepared in Example 2 was used as a non15
aqueous electrolyte solution.
[00109] Comparative Example 6
[00110] A lithium secondary battery was prepared in the same
manner as in Example 3 except that the non-aqueous
20 electrolyte solution prepared in Comparative Example 1 was
used as a non-aqueous electrolyte solution.
[00111] Comparative Examples 7 to 10
[00112] Lithium secondary batteries were prepared in the same
25 manner as in Example 3 except that the non-aqueous
30
electrolyte solutions prepared in Comparative Examples 2 to 5
were respectively used as a non-aqueous electrolyte solution.
[00113] Experimental Example 1
[00114]
[00115] The lithium secondary batteries (based on a battery
10 capacity of 3.26 mAh) prepared in Examples 3 and 4 and
Comparative Examples 6 to 8 were charged at a constant
current of 1 C to a voltage of 4.35 V at 45°C, and thereafter,
the secondary batteries were charged at a constant voltage of
4.35 V and the charge was terminated when the charge current
15 was 0.163 mAh. After the batteries were left standing for 10
minutes, the batteries were discharged at a constant current
of 2 C to a voltage of 2.94 V. This charge and discharge
cycle was repeated 1 to 100 times and 1 to 200 times. The
results thereof are respectively presented in FIGS. 1 and 2.
20 [00116] Specifically, FIG. 1 is the results of lifetime
characteristics of the lithium secondary batteries using a
cathode not subjected to roll-pressing during the preparation
of the cathode, and FIG. 2 is the results of lifetime
characteristics of the lithium secondary batteries using a
25 cathode subjected to roll-pressing.
31
[00117] Referring to FIGS. 1 and 2, the lithium secondary
batteries of Examples 3 and 4 of the present invention
including tetra(trimethylsilyl)pyrophosphate (compound (1))
as an additive of a non-aqueous electrolyte solution had a
moderate slope to the 100th cycle regardless of the presenc5 e
of a roll-pressing process during the preparation of the
cathode.
[00118] In contrast, with respect to Comparative Examples 6
to 8, in the case that roll pressing was not performed on a
10 cathode, slopes were rapidly reduced after the first cycle
and the measurement was not possible after a 70th cycle. In
the case in which the roll pressing was performed on the
cathode, it may be confirmed that moderate slopes were
maintained to about a 25th cycle and the slopes were then
15 significantly reduced to about a 50th cycle as the number of
cycles was increased.
[00119] Thus, as a result of the lifetime characteristics of
FIGS. 1 and 2, in the case that
tetra(trimethylsilyl)pyrophosphate was used alone or the
20 mixed additive of tetra(trimethylsilyl)pyrophosphate and
tris(trimethylsilyl)phosphate (TMSPa) was used as in the
examples of the present invention, it was confirmed that
excellent lifetime characteristics were obtained to the 200th
cycle regardless of the presence of a roll-pressing process
25 of the cathode.
32
[00120] Experimental Example 2
[00121]
[00122] The lithium secondary batteries (based on a battery
capacity of 3.26 mAh) prepared in Example 3 and Comparative
Examples 9 and 10 were charged at a constant current of 1 C
10 to a voltage of 4.35 V at 45°C, and thereafter, the secondary
batteries were charged at a constant voltage of 4.35 V and
the charge was terminated when the charge current was 0.163
mAh. After the batteries were left standing for 10 minutes,
the batteries were discharged at a constant current of 2 C to
15 a voltage of 2.94 V. This charge and discharge cycle was
repeated 1 to 30 times.
[00123] In this case, the presence of drying and rollpressing
processes of a cathode, which were used in the
lithium secondary batteries prepared in Example 3 and
20 Comparative Examples 9 and 10, is presented in Table 1 below.
[00124] [Table 1]
Drying Roll-pressing
(A) Set x x
(B) Set ○ x
33
(C) Set ○ ○
[00125] The results of the lifetime characteristics according
to Table 1 are presented in FIGS. 3 to 5.
[00126] FIG. 3 is the results of lifetime characteristics of
the lithium secondary batteries using a cathode not subjecte5 d
to both drying and roll-pressing during the preparation of
the cathode (A), FIG. 4 is the results of lifetime
characteristics of the lithium secondary batteries using a
cathode subjected to drying and not subjected to roll10
pressing (B), and FIG. 5 is the results of lifetime
characteristics of the lithium secondary batteries subjected
to both drying and roll-pressing (C).
[00127] Specifically, as a result of the lifetime
characteristics of the lithium secondary batteries using a
15 cathode not subjected to both drying and roll-pressing as in
FIG. 3, a slope of a graph illustrating the results of
lifetime characteristics of Example 3 was moderate to a 30th
cycle. In contrast, it may be confirmed that slopes of
graphs of the secondary batteries of Comparative Examples 9
20 and 10 were significantly reduced from a 10th cycle. In
particular, with respect to the lithium secondary battery of
Comparative Example 10 using only TMSPa as an electrolyte
solution additive, it may be understood that the slope was
rapidly reduced from a 5th cycle.
34
[00128] Similarly, in FIGS. 4 and 5, the lithium secondary
battery of Example 3 exhibited stable lifetime
characteristics regardless of the presence of drying and
roll-pressing processes. In contrast, with respect to the
lithium secondary batteries of Comparative 5 rative Examples 9 and 10,
the lifetime characteristics were degraded in comparison to
the lifetime characteristics of Example 3 due to the effects
of the drying and roll-pressing.
[00129] FIGS. 6 to 8 are graphs separating the graphs of FIGS.
10 3 to 5 for each lithium secondary battery.
[00130] FIG. 6 is a graph of the lithium secondary batteries
of Example 3 according to the presence of drying and rollpressing
processes. It may be confirmed that the lifetime
characteristics of the lithium secondary batteries of Example
15 3 were all excellent to the 30th cycle regardless of the
presence of drying and roll-pressing processes.
[00131] In contrast, FIG. 7 is a graph of the lithium
secondary batteries of Comparative Example 9 according to the
20 presence of drying and roll-pressing processes. With respect
to the lithium secondary batteries of Comparative Example 9,
in the case that both drying and roll-pressing were performed,
the lifetime characteristics were excellent to the 30th cycle.
However, in the case in which the drying or roll-pressing was
25 not performed, the lifetime characteristics were reduced.
35
[00132] FIG. 8 is a graph of the lithium secondary batteries
of Comparative Example 10 according to the presence of drying
and roll-pressing processes. With respect to the lithium
secondary batteries of Comparative Example 10, in the case
that both drying and roll-pressing were performed, 5 the
lifetime characteristics were excellent to the 30th cycle.
However, in the case in which the drying or roll-pressing was
not performed, the lifetime characteristics were reduced. In
particular, it may be understood that the lithium secondary
10 batteries of Comparative Example 10 were more affected by the
presence of drying and roll-pressing processes in comparison
to Comparative Example 9.
[00133]
15 [00134] Example 5
[00135] An additive mixture was prepared by mixing
tetra(trimethylsilyl)pyrophosphate (compound (1)) and
tris(trimethylsilyl)phosphate (TMSPa) at a weight ratio of
3:1, and a cathode mixture slurry was prepared by adding 2
20 wt% of the additive mixture, 92.12 wt% of
Li(Li0.2Mn0.55Ni0.15Co0.1)O2 as a cathode active material, 2.94
wt% of carbon black as a conductive agent, and 2.94 wt% of
polyvinylidene fluoride (PVdF) as a binder, based on a total
weight of the cathode mixture slurry, to N-methyl-2-
25 pyrrolidone (NMP) as a solvent. An about 20 μm thick
36
aluminum (Al) thin film as a cathode collector was coated
with the cathode mixture slurry and dried to prepare a
cathode.
[00136]
[00137] Also, an anode mixture slurry was prepared by adding
96 wt% of carbon powder as an anode active material, 3 wt% of
PVdF as a binder, and 1 wt% of carbon black as a conductive
agent to NMP as a solvent. A 10 μm thick copper (Cu) thin
10 film as an anode collector was coated with the anode mixture
slurry and dried, and the Cu thin film was then roll-pressed
to prepare an anode.
[00138] LiPF6 was dissolved in an electrolyte solution
solvent having a composition, in which a volume ratio of
15 ethylene carbonate (EC):dimethyl carbonate (DMC):ethylmethyl
carbonate (EMC) was 3:4:3, to obtain a LiPF6 concentration of
1 M. As an additive for a non-aqueous electrolyte solution,
vinylene carbonate (VC) and propane sultone (PS) were added
at a weight ratio of 1:1.5 to prepare a non-aqueous
20 electrolyte.
[00139] A polymer type battery was prepared by a typical
method using a polyethylene (PE) separator with the cathode
and anode thus prepared, and a lithium secondary battery was
then completed by injecting the prepared non-aqueous
25 electrolyte solution.
37
[00140] Example 6
[00141] A cathode and a lithium secondary battery were
prepared in the same manner as in Example 5 except that
tetra(trimethylsilyl)pyrophosphate was used alone 5 e instead of
using an additive mixture during the preparation of the
cathode of Example 5.
[00142] Comparative Example 11
10 [00143] A cathode and a lithium secondary battery were
prepared in the same manner as in Example 5 except that an
additive mixture was not used during the preparation of the
cathode of Example 5.
15 [00144] Comparative Example 12
[00145] A cathode and a lithium secondary battery were
prepared in the same manner as in Example 5 except that TMSPa
was used alone instead of using an additive mixture during
the preparation of the cathode of Example 5.
20
[00146] Experimental Example 3
[00147]
[00148] The lithium secondary batteries (based on a battery
25 capacity of 3.26 mAh) prepared in Examples 5 and 6 and
38
Comparative Examples 11 and 12 were charged at a constant
current of 1 C to a voltage of 4.35 V at 45°C, and thereafter,
the secondary batteries were charged at a constant voltage of
4.35 V and the charge was terminated when the charge current
was 0.163 mAh. After the batteries were left standing 5 nding for 10
minutes, the batteries were discharged at a constant current
of 2 C to a voltage of 2.94 V. This charge and discharge
cycle was repeated 1 to 100 times.
[00149] In this case, both dying and roll-pressing were
10 performed on the cathodes used in the lithium secondary
batteries which were prepared in Examples 5 and 6 and
Comparative Examples 11 and 12. The results of the lifetime
characteristics are presented in FIG. 9.
[00150] Referring to FIG. 9, the lithium secondary batteries
15 of Examples of 5 and 6 of the present invention including
tetra(trimethylsilyl)pyrophosphate (compound (1)) in the
cathode as an additive had a moderate slope to the 100th
cycle.
[00151] Also, the lifetime characteristics of Example 5 using
20 the additive mixture, in which
tetra(trimethylsilyl)pyrophosphate (compound (1)) and TMSPa
were mixed, were better than those of Example 6 using
tetra(trimethylsilyl)pyrophosphate (compound (1)) alone to
the 100th cycle. However, Example 5 exhibited a significant
25 difference from Comparative Examples 11 and 12 which did not
39
include tetra(trimethylsilyl)pyrophosphate in the cathodes.
[00152] Specifically, discharge capacities of Examples 5 and
6 of the present invention were improved by about 25% at a
90th cycle in comparison to Comparative Example 11 in which a
cathode additive was not used, and were 5 re improved by about
150% or more at the 100th cycle in comparison to Comparative
Example 12 in which tetra(trimethylsilyl)pyrophosphate was
not included and only TMSPa was added.
[00153] Therefore, as a result of the lifetime
10 characteristics of the lithium secondary batteries of FIG. 9,
in the case that tetra(trimethylsilyl)pyrophosphate (compound
(1)) was used alone or a mixed additive of
tetra(trimethylsilyl)pyrophosphate (compound (1)) and
tris(trimethylsilyl)phosphate (TMSPa) was used as in the
15 examples of the present invention, it may be confirmed that
excellent lifetime characteristics at high temperature and
high voltage were obtained in comparison to the comparative
examples which did not include the compound represented by
Chemical Formula 1.

I/We Claim:
1. A non-aqueous electrolyte solution comprising:
a lithium salt;
an electrolyte 5 te solution solvent; and
a compound represented by Chemical Formula 1,

where Y1 and Y2 are each independently silicon (Si) or
tin (Sn),
10 R1 to R6 are each independently hydrogen or a C1-C10
alkyl group, and
A is ,
where Y3 is Si or Sn,
R7 to R9 are each independently hydrogen or a C1-C10
15 alkyl group, and
n is between 2 and 4.
2. The non-aqueous electrolyte solution of claim 1,
41
wherein, in a case where n is 3 or 4 in A of Chemical Formula
1, A is formed by connecting phosphor (P) of one repeating
unit and oxygen (O) of another adjacent repeating unit to
each other to form a linear chain, a cyclic chain, or both
linear 5 and cyclic chains.
3. The non-aqueous electrolyte solution of claim 1,
wherein the compound represented by Chemical Formula 1 is any
one selected from the group consisting of compounds of (1) to
10 (6), or a mixture of two or more thereof:
42
.
4. The non-aqueous electrolyte solution of claim 1,
further comprising a compound represented by Chemical Formula
5 2:
43

where R10 to R18 are each independently hydrogen or a C1-
C10 alkyl group.
5
5. The non-aqueous electrolyte solution of claim 4,
wherein the compound represented by Chemical Formula 2 is
tris(trimethylsilyl)phosphate (TMSPa).
10 6. The non-aqueous electrolyte solution of claim 4,
wherein a mixing ratio of the compound represented by
Chemical Formula 1 to the compound represented by Chemical
Formula 2 is in a range of 1:0.1 to 1:2 as a weight ratio.
15 7. The non-aqueous electrolyte solution of claim 1,
wherein the compound represented by Chemical Formula 1 is
included in an amount of 0.01 wt% to 5 wt% based on a total
weight of the non-aqueous electrolyte solution.
44
8. The non-aqueous electrolyte solution of claim 1,
wherein the lithium salt comprises any one selected from the
group consisting of LiPF6, LiAsF6, LiCF3SO3, LiN(CF3SO2)2,
LiBF4, LiBF6, LiSbF6, LiN(C2F5SO2)2, LiAlO4, LiAlCl4, LiSO3CF3,
and LiClO4, or a mixture 5 of two or more thereof.
9. The non-aqueous electrolyte solution of claim 1,
wherein the electrolyte solution solvent comprises linear
carbonate, cyclic carbonate, ester, or a combination thereof.
10
10. The non-aqueous electrolyte solution of claim 9,
wherein the linear carbonate comprises any one selected from
the group consisting of dimethyl carbonate, diethyl carbonate,
dipropyl carbonate, ethylmethyl carbonate, methylpropyl
15 carbonate, and ethylpropyl carbonate, or a mixture of two or
more thereof; the cyclic carbonate comprises ethylene
carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-
butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene
carbonate, vinylene carbonate, and a halide thereof, or a
20 mixture of two or more thereof; and the ester comprises any
one selected from the group consisting of methyl acetate,
ethyl acetate, propyl acetate, ethyl propionate (EP), methyl
propionate (MP), γ-butyrolactone, γ-valerolactone, γ-
caprolactone, σ-valerolactone, and ε-caprolactone, or a
25 mixture of two or more thereof.
45
11. A cathode comprising:
a lithium transition metal oxide; and
a compound represented by Chemical Formula 1:
<5 Chemical Formula 1>
where Y1 and Y2 are each independently silicon (Si) or
tin (Sn),
R1 to R6 are each independently hydrogen or a C1-C10
alkyl group, and
10 A is ,
where Y3 is Si or Sn,
R7 to R9 are each independently hydrogen or a C1-C10
alkyl group, and
n is between 2 and 4.
15
12. The cathode of claim 11, wherein, in a case where n is
3 or 4 in A of Chemical Formula 1, A is formed by connecting
46
phosphor (P) of one repeating unit and oxygen (O) of another
adjacent repeating unit to each other to form a linear chain,
a cyclic chain, or both linear and cyclic chains.
13. The cathode of claim 11, wherein the com5 pound
represented by Chemical Formula 1 is any one selected from
the group consisting of compounds of (1) to (6), or a mixture
of two or more thereof:
47
.
14. The cathode of claim 11, further comprising a compound
represented by Chemical Formula 2:
5
48

where R10 to R18 are each independently hydrogen or a C1-
C10 alkyl group.
15. The cathode of claim 14, wherein the com5 pound
represented by Chemical Formula 2 is
tris(trimethylsilyl)phosphate (TMSPa).
16. The cathode of claim 14, wherein a mixing ratio of the
10 compound represented by Chemical Formula 1 to the compound
represented by Chemical Formula 2 is in a range of 1:0.1 to
1:2 as a weight ratio.
17. The cathode of claim 11, wherein the compound
15 represented by Chemical Formula 1 is included in an amount of
0.01 wt% to 5 wt% based on a total weight of the lithium
transition metal oxide.
49
18. The cathode of claim 11, wherein the lithium transition
metal oxide is a compound represented by Chemical Formula 3:

Li[LixNiaCobMnc]O2 (-0.05≤x≤+0.5, 0