IONIC LIQUID-MODIFIED CATHODE AND ELECTROCHEMICAL
DEVICE USING THE SAME
Technical Field
The present invention relates to a cathode
(positive electrode) capable of improving the safety of
batteries without deteriorating the battery performance,
and more particularly, to a cathode modified with an
ionic liquid, as well as an electrochemical device
including the same.
Background Art
Recently, interests in energy storage technology
are gradually increased. As the use of batteries is
enlarged to applications for the storage of energy for
portable telephones, camcorders, notebook computers,
personal computers and electric vehicles, efforts on the
research and development of the batteries are
increasingly embodied. In this view, the field of
electrochemical devices receives the greatest attention,
and among them, interests in the development of
chargeable/dischargeable secondary batteries are
focused.
Among secondary batteries which are now in use,
lithium secondary batteries developed in the early 1990s
are in the spotlight due to the advantages of higher
operation voltages and far greater energy densities than
those of conventional batteries, such as Ni-MH, Ni-Cd
and sulfuric acid-lead batteries. However, the lithium
secondary batteries are disadvantageous in that they
have safety problems, such as firing and explosion,
caused by the use of organic electrolytes, and their
preparation requires a complicated process.
Meanwhile, ionic liquid, also called "room
temperature molten salt", means a salt showing liquid

properties at room temperature. The ionic liquid
consists generally of organic cations and inorganic
anions and is characterized by having high evaporation
temperature, high ion conductivity, thermal resistance,
nonflammability and the like. The ionic liquid is
applied in solvents for organic synthesis, solvents for
separation and extraction, and the like, and recently,
there are studies on the possibility for the application
of the ionic liquid to an electrolyte solution for
electrochemical devices, such as capacitors, lithium ion
batteries, fuel batteries and the like. Most of such
studies concern electrolyte solutions for capacitors,
and many studies on the application of the ionic liquid
to an electrolyte solution for lithium ion batteries are
now conducted in Japan and USA as leaders, but not yet
put to practical use due to the problems of a reaction
between the ionic liquid and the carbon-based anode, and
an increase in the viscosity of the electrolyte
solution.
US Patent Application No. 2002-0110737 discloses
the application of the ionic liquid to an electrolyte
solution for lithium i'on batteries. This patent
application describes that, by the selection of a
suitable ionic liquid and the control of the ratio of
the selected ionic liquid to the existing electrolyte
solution, the ionic liquid can show nonflammability.
Also, it describes that the reaction between the ionic
liquid and the carbon-based anode can be inhibited by a
process for injecting the electrolyte solution in two
steps. However, the two-step process for injecting the
electrolyte solution has problems in that the process is
difficult to be actually applied and to produce an ionic
liquid whose reaction with an anode (negative electrode)
has been inhibited. Also, due to the high viscosity of
the ionic liquid, an increase in the viscosity of the

mixed electrolyte solution cannot be avoided, thus
causing the deterioration in the battery performance.
Furthermore, Japanese Patent Laid-Open Publication
Nos. Hei 11-86905 and 11-260400 disclose the application
of an imidazolium cation-containing liquid to an
electrolyte solution for ion batteries. However, the
ionic liquid used in such patents has a problem in that
it shows a higher reduction potential than that of
lithium ions so that it is reduced faster than lithium
ions in the anode.
In an attempt to solve the problem of the high
reduction potential of the ionic liquid as described
above, Japanese Patent Laid-Open Publication No. Hei 11-
297335 discloses an ionic liquid based on ammonium with
a lower reduction potential than that of lithium. In
this case, the reduction potential problem can be
overcome, but there is a problem in that the ionic
liquid is co-intercalated with lithium ions into the
carbon-based anode.
In an attempt to solve the problem of the co-
intercalation of the ionic liquid with the carbon-based
anode, Japanese Patent Laid-Open Publication No. 2002-
110225 discloses the use of a titanium-based anode.
However, even in this case, there is a problem in that,
due to the high viscosity of the ionic liquid, the high-
efficiency discharge performance of batteries will be
deteriorated when the ionic liquid is applied in the
batteries.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
FIG. 1 is a schematic diagram showing the
structure of a battery comprising a cathode introduced
with an ionic liquid, an anode, and a separator
interposed between the two electrodes.
FIG. 2 is a graphic diagram showing the comparison

between the ionic dispersion coefficients of BDMI+ and
Li+ in solutions which contain BDMI-PF6 and LiPF6
dissolved in propylene carbonate (PC), respectively.
FIG. 3 is a schematic diagram showing a reaction
between the anode of a lithium secondary battery and
electrolyte containing BDMI-PF6 and LiPF6 dissolved in
propylene carbonate (PC), respectively.
FIGS. 4 to 10 are graphic diagrams showing the
evaluation result of thermal safety by DSC analysis for
batteries fabricated in Examples 1 to 4 and Comparative
Examples 1 to 3, respectively.
Disclosure of the Invention
The present inventors have many studies to solve
the above-mentioned problems in the prior art, and
consequently, found that the use of an ionic liquid as
one component of a cathode (positive electrode) other
than use as an electrolyte solution can not only realize
the improvement of battery safety, but also prevent the
deterioration in battery performance caused by a
reaction between the ionic liquid and the carbon-based
anode (negative electrode) and an increase in the
electrolyte viscosity which occurs as a result of the
addition of the ionic liquid with high viscosity.
Accordingly, it is an object of the present
invention to provide a cathode modified with ionic
liquid, which can improve the safety of batteries
without deteriorating the battery performance, as well
as an electrochemical device including the cathode.
To achieve the above object, the present invention
provides a cathode produced from a cathode slurry
comprising: (a) a cathode active material based on a
lithium-containing metal composite oxide or a
chalcogenide compound; and (b) an ionic liquid.
Also, the present invention provides an

electrochemical device including said cathode, and
preferably a lithium secondary battery.
Hereinafter, the present invention will be
described in detail.
Although it is known that the use of the ionic
liquid as an electrolyte additive can improve the safety
of batteries, it is only known in this technical field
that this improvement is attributable to the inherent
high boiling point and nonflammability of the ionic
liquid, but the actual mechanism of the ionic liquid on
the improvement of the battery safety is not yet
precisely established. Moreover, the use of the ionic
liquid as the electrolyte additive could realize the
improvement of the battery safety as described in the
prior art, but necessarily caused the deterioration in
the battery performance due to a reaction between the
ionic liquid added and the carbon-based anode, and/or an
increase in the electrolyte viscosity by the ionic
liquid with high viscosity.
The present invention is characterized in that the
ionic liquid (IL) known to be able to improve the
battery safety upon use in an electrolyte solution is
used as one component of the cathode without use as an
electrolyte component.
By virtue of this characteristic, the cathode
according to the present invention can satisfy both the
improvement of the battery safety and the prevention of
deterioration in the battery performance as described
below.
First, the cathode prepared with the ionic liquid
as one component of the cathode can improve the battery
safety. As described above, the mechanism where the use
of the ionic liquid improves the battery safety is not
yet precisely established, but can be believed to be
attributable to the following factors. Namely, the prior

cathode active materials based on lithium-containing
metal oxides or chalcogenide compounds are lithium
intercalation compounds whose structural stability and
capacity are determined by the intercalation and
deintercalation reactions of lithium ions. With an
increase in charge potential, the capacity of such
compounds increase, whereas such compounds , become
structurally unstable, thus causing a rapid reduction in
the thermal stability of the electrode. If oxygen is
generated due to the structural instability of the
electrode as described above, the oxygen will be highly
exothermic so that it will cause thermal runaway in
batteries and provide a possibility for the oxygen to
react with the electrolyte within batteries so as to
explode the batteries.
However, in the present invention, a portion or
all of the surface of the cathode active material is
surrounded .by the ionic liquid with characteristics
including high boiling point, thermal resistance and
nonflammability. Thus, the oxygen generation by the
structural instability of the electrode can be prevented
so as to improve the safety, particularly thermal
safety, of batteries. Particularly, cations with
relatively less electrons in the ionic liquid can
inhibit the generation of highly exothermic oxygen by
attraction with oxygen enriched in unpaired electrons,
thus improving the battery safety.
Second, the cathode prepared using the ionic
liquid as one component of the cathode according to the
present invention can prevent the deterioration in the
battery performance occurring due to the ionic liquid
added. Namely, as described in the prior art, the use of
the ionic liquid in the electrolyte solution caused the
deterioration in the battery performance due to an
increase in the electrolyte viscosity by the ionic

liquid with high viscosity, and/or a reaction between
the ionic liquid and the anode.
Of the above-mentioned performance deteriorations,
the performance deterioration caused by the reaction
between the ionic liquid and the anode is generally
attributable to the following three factors. The first
factor occurs because the ionic liquid has a higher
reduction potential than that of lithium so that the
cations of the ionic liquid are reduced faster than
lithium ions in the anode. This factor can be solved by
limiting the kind of ionic liquid. The second factor
occurs because the ionic liquid is co-intercalated with
lithium ions into a carbon material constituting the
anode, and this factor can be solved by the use of an
anode material other than the carbon material. The third
factor fundamentally occurs regardless of the kinds of
the ionic liquid and the anode material. Namely, if
lithium ions are reduced in the anode, the ionic liquid
cations with a similar electrochemical window to
lithium, among ions present in the battery, will show a
tendency to also be competitively reduced. In this case,
it can be expected that the reduction of lithium ions
will be predominant since the reaction rate of lithium
ions with relatively small molecular weight is faster.
In practice, however, the contrary results were shown
(see FIG. 2) . Namely, the ionic liquid cations can reach
the anode faster than lithium ions solvated in the
electrolyte solution so that they can form a barrier
layer against lithium ions (see FIG. 3), thus the
deterioration in the battery performance can be caused.
The prior art has attempted to solve the first and
second factors easy to solve among the above-described
factors. However, in the present invention, in addition
to the first and second factors, the third factor that
is the most fundamental factor was found, and to solve

the third factor, the ionic liquid is localized only to
the cathode so that the deterioration in the battery
performance caused by the use of the ionic liquid can be
prevented.
Also, according to the present invention, even if
the ionic liquid present in the cathode flows out to the
electrolyte solution after a battery reaction
progressed, the deterioration in the battery performance
by a reaction between the ionic liquid and the anode can
be inhibited since a normal solid electrolyte interface
(SEI) was formed at the initial stage of charge cycles
by a reaction between the anode and the electrolyte
solution.
As a component which is added to a cathode slurry
comprising a cathode active material based on a lithium-
containing metal composite oxide or a chalcogenide
compound according to the present invention, any
conventional ionic. liquids known in. the art,- -which - can
realize both the improvement of battery safety and the
prevention of the deterioration in battery performance
as_ .described above,- may be- used. - Regarding concrete- -
examples of the ionic liquid, the cations of the ionic
liquid include imidazolium, pyrazolium, triazolium,
thiazolium, oxazolium, pyridazinium, pyrimidinium,
pyrazinium, ammonium, phosphonium, pyridinium or
pyrrolidinium, which may be substituted or unsubstituted
with a Ci-15 alkyl group, as well as mixtures thereof, and
the anions of the ionic liquid include PF6", BF4~, CF3SO3",
N(CF3SO2)2~, N(C2F5SO2)2~, C(CF2SO2)3~, AsF6", SbF6", A1C14"/
NbF6"/ HSO4", CIO4", CH3SO3", CF3CO2" or mixtures thereof.
Also, the ionic liquid may be a zwitterionic compound,
an ionic structure which is formed by the covalent
bonding of cations and anions so as to bear negative
electricity and positive electricity.
The amount of the ionic liquid to be introduced

into the cathode is preferably 0.1-30 parts by weight
based on 100 parts by weight of the cathode active
material, and can be controlled to a suitable amount
based on the design of final battery capacity. If it is
used at an amount of less than 0.1 part by weight, it
will show an insignificant effect on the improvement of
the thermal stability of the cathode, and if it is used
at an amount of more than 30 parts by weight, the
relative amount of the active material in the cathode
will be reduced, thus causing a reduction in the overall
capacity of the battery.
A method for preparing the cathode comprising
ionic liquid as one component thereof according to the
present invention is not limited to any specific method.
In one embodiment, the cathode may be prepared by any
conventional method known in the art, for example, by
applying on a current collector a cathode slurry
comprising an ionic liquid and a cathode active material
based on a lithium-containing metal composite oxide or
chalcogenide compound, which can store and release
lithium. In this case, a small amount of a conducting
agent and/or a binder may optionally be added.
Hereinafter, the method for preparing the cathode
according to the present invention will be described in
detail. Electrode materials, including a lithium-
containing metal composite oxide or chalcogenide
compound-based cathode active material, an ionic liquid,
and optionally a binder and/or a conducting agent, etc.,
are dispersed in solvent or dispersion medium, such as
N-methylpyrrolidone (NMP), so as to prepare a cathode
slurry. The prepared slurry is coated on a cathode
current collector and subjected to a heat treatment
process followed by a pressing process.
Among cathode components to be introduced with the
ionic liquid, the lithium-containing metal composite

oxide-based cathode active material is a lithium-
containing oxide including at least one element selected
from the group consisting of alkali metals, alkaline
earth metals, Group 13 elements, Group 14 elements,
Group 15 elements, transition metals and rare earth
elements. Examples thereof include, but are not limited
to, lithium manganese oxide (e.g., LiMn204), lithium
cobalt oxide (e.g., LiCoG*2), lithium nickel oxide (e.g.,
LiNi02), lithium iron oxide (e.g., LiFeP04) or
combinations thereof. Also, examples of the chalcogenide
compound-based cathode active material include, but are
not limited to, TiS2, Se02, MoS2, FeS2, Mn02, NbSe3, V205,
V6O13, CuCl2 or mixtures thereof.
As the conducting agent, any material may be used
as long as it is an electron-conducting material which
does not cause chemical changes within a constructed
battery. Examples of the conduction material include,
but are not limited to, carbon black, such as acetylene
black, ketzen black, furnace black or thermal black,
natural graphite, artificial graphite, conductive
fibers, and the like.
As the binder, thermoplastic resin, thermosetting
resin or a combination thereof may be used, and examples
of the binder include, but are not limited to,
polyvinylidene fluoride (PVdF), polytetrafluoroethylene
(PTFE) and the like.
The current collector may be made of any
conductive material, but in the case of the cathode, is
preferably a foil made of aluminum, nickel or a
combination thereof.
As shown in FIG. 1, in the cathode prepared as
described above, the ionic liquid is present either on
the surface of the cathode active material particles or
between the particles, so that not only the improvement
of the battery safety as described above is achieved but

also the deterioration of the battery performance is
prevented.
In another aspect, the present invention provides
an electrochemical device comprising: (a) a cathode
produced from a cathode slurry comprising a cathode
active material based on a lithium-containing metal
composite oxide or a chalcogenide compound, and an ionic
liquid; (b) an anode; (c) a separator; and (d) an
electrolyte solution.
The electrochemical devices according to the
present invention include all devices in which
electrochemical reactions occur. Specific examples of
such devices include primary and secondary batteries,
and the like.
A method of preparing the electrochemical device
using the electrode produced as described above may be
performed by any conventional method known in the art.
In one embodiment of . the method, the separator -is
interposed between the two electrodes to form an
assembly into which the electrolyte solution is then
inj ected.
In this case, the heat release of the cathode
containing the ionic liquid, to the electrolyte
solution, is preferably at least 0.01 J/g lower than
that of a cathode containing no ionic liquid. Also, the
temperature at which the heat release of the ionic
liquid-containing cathode to the electrolyte solution is
the highest upon the increase of the outside temperature
is preferably at least 0.01 °C lower than the temperature
at which the heat release of the cathode containing no
ionic liquid is the highest.
The electrochemical devices prepared by the above-
described method are preferably lithium secondary
batteries, including lithium metal secondary batteries,
lithium ion secondary batteries, lithium polymer

secondary batteries, lithium ion polymer secondary
batteries, etc.
In this case, the anode according to the present
invention may be prepared by settling an anode active
material to an anode current collector, according to any
conventional method known in the art. Particularly,
unlike the prior art, a carbon-based material may also
be used as the anode active material without
limitations. Examples of the anode active material
include, but are not limited to, lithium-adsorbing
materials, such as lithium metals or lithium alloys,
carbon, petroleum coke, activated carbon, graphite or
other carbons. Examples of the anode current collector
include, but are not limited to, foils made of copper,
gold, nickel, copper alloy, or a combination thereof.
A separator which can be used in the present
invention is not limited to any specific separator, but
a porous separator may be used- and examples thereof
include porous polypropylene, polyethylene or polyolefin
separators.
Examples of the electrolyte solution which can be
used in the present invention include, but are not
limited to, salts of a structure such as A+B", wherein A+
contains an ion selected from alkaline metal cations,
such as Li+, Na+ and K+, and combinations thereof, and B"
contains an ion selected from anions, such as PF6~, BF4~,
CI", Br", I", C104", ASF6", CH3CO2"r CF3SO3" N(CF3SO2)2", and
C(CF2SO2)3-/ and combinations thereof, are dissolved or
dissociated in an organic solvent selected from the
group consisting of propylene carbonate (PC), ethylene
carbonate (EC), diethyl carbonate (DEC), dimethyl
carbonate (DMC), dipropyl carbonate (DPC), dimethyl
sulfoxide, acetonitrile, dimethoxyethane,
diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone
(NMP), ethylmethyl carbonate (EMC), y-butyrolactone and a

mixture thereof.
The injection of the electrolyte solution may be
performed in a suitable stage during a manufacture
process of the electrochemical devices, depending on a
particular preparation process of a final product and
physical properties required for the final product.
Namely, the electrolyte solution may be injected before
the assembling of the electrochemical device or a final
stage during the assembling.
The external shape of the electrochemical device
is not limited to any specific shape, but may be a
cylindrical shape with a can, an angular shape, a pouch
shape, and a coin shape.
Best Mode for Carrying Out the Invention
Hereinafter, the present invention will be
illustrated by way of- the following examples. It is to
be understood, however,., that these - examples- are given
for illustrative purpose only and are not construed to
limit the scope of the present invention.
Reference,Example 1
Each of BDMI-PF6 and LiPF6 were dissolved in
propylene carbonate (PC) so as to prepare electrolyte
solutions. The electrolyte concentration of the
solutions was controlled to a range of 0.25M to 1.5M.
Each of the solutions was measured for ionic diffusion
coefficient by PMG-NMR (pulsed field gradient-NMR,
Bruker DRX-600 spectrometer).
It was expected that Li+ with low molecular weight
would have a greater ionic diffusion coefficient than
that of the cations of the ionic liquid, but actual test
results showed that the cation BDMI+ of BDMI-PF6 had a
significantly greater ionic diffusion coefficient than
lithium ions (see FIG. 2) . For this reason, it can be
expected that if Li+ and BDMI+ are contained in an

electrolyte solution for lithium secondary batteries, a
competitive reduction reaction in the anode can
progress.
[Examples 1 ~ 4: Preparations of cathodes and
lithium secondary batteries]
Example 1
1-1: Cathode
LiCo02 as a cathode active material, carbon black
as a conducting agent, and polyvinylidene fluoride
(PVdF) as a binder, were mixed at a weight ratio of 94 :
3 : 3, to which BDMI-PF6 as an ionic liquid was added at
an amount of 3 parts by weight based on 100 parts by
weight of the cathode active material. To the resulting
mixture, N-methyl pyrrolidone (NMP) was added to prepare
a cathode slurry. The prepared slurry was applied on an
aluminum foil, and thermally treated at 130 °C for 2
hours. The cathode thus prepared was pressed and punched
at 1.4875 cm2.
1-2: lithium secondary battery
The cathode prepared in Example 1-1 above, and an
anode made by punching a Li metal foil at 1.7 67 cm2, were
provided. A polyethylene resin separator was interposed
between the two electrodes (see FIG. 1), and then, an
electrolyte solution which contains 1 M LiPFg and has a
weight ration of EC : PC : DEC of 3 : 2 : 5 was injected
into the resulting structure, thus prepared a coin-type
battery.
Example 2
A cathode and a lithium secondary battery were
prepared in the same manner as in Example 1 except that
BMI-PF6 was used in place of BDMI-PF6 as an ionic liquid.
Example 3
A cathode and a lithium secondary battery were
prepared in the same manner as in Example 1 except that

TMHA-PF6 was used in place of BDMI-PF6 as an ionic
liquid.
Example 4
A cathode and a lithium secondary battery were
prepared in the same manner as in Example 1 except that
TMHA-TFSI was used in place of BDMI-PF6 as an ionic
liquid.
[Comparative Examples 1 ~ 4: Preparations of
cathodes and lithium secondary batteries]
A cathode and a lithium secondary battery were
prepared in the same manner as in Example 1 except that
a cathode slurry which contains no ionic liquid and has
a weight ratio of active material: conducting agent:
binder of 94: 3: 3 was used.
Comparative Example 2
A lithium secondary battery was fabricated in the
same manner as in Example 1 except that a cathode was
fabricated using a cathode slurry which contains no
ionic liquid and has a weight ratio of active material:
conducting agent: binder of 94: 3: 3, and then BMI-PF6
was added at an amount of 3 parts by weight based on 100
parts by weight of an EC : PC : DEC (weight ratio of 3 :
2 : 5)-based electrolyte solution containing 1M lithium
hexafluorophosphate (LiPFe) dissolved therein.
Comparative Example 3
A lithium secondary battery was prepared in the
same manner as in Example 1 except that a cathode was
made by using a cathode slurry which contains no ionic
liquid and has a weight ratio of active material:
conducting agent: binder of 94: 3: 3, and then BMI-PF6
was added at an amount of 10 parts by weight based on
100 parts by weight of an EC : PC : DEC (weight ratio of
3:2: 5)-based electrolyte solution containing 1M
lithium hexafluorophosphate (LiPFe) dissolved therein.

Test Example 1: Evaluation of performance of
lithium secondary battery
In order to evaluate the performance of the
lithium secondary batteries including the cathode which
have been modified with the ionic liquid according to
the present invention, the following test was performed.
The batteries of Examples 1 to 4 and Comparative
Examples 1 to 3 were evaluated for charge/discharge
characteristics, and the evaluation results are given in
Table 1 below.
The lithium secondary batteries which have been
prepared by adding the ionic liquid in the production of
the cathode according to the present invention showed
equal performance to the battery of Comparative Example
1 with no use of the ionic liquid (see Table 1) . This
suggests that the ionic liquid which had been added in
the production of the batteries in order to improve the
battery safety did not cause the deterioration- of the -
battery performance.
On the other hand, the batteries of Comparative
Examples 2 and 3 prepared.with the addition of the ionic
liquid to the electrolyte solution all showed the
deterioration in performance. Among them, the battery of
Comparative Example 2 prepared with the addition of the
ionic liquid at a relatively small amount of 3 parts by
weight did not show a great deterioration in
performance. However, the battery of Comparative Example
3 prepared with the addition of 10 parts by weight of
the ionic liquid to 100 parts by weight of the
electrolyte solution showed a great deterioration in
performance as compared to the battery of Example 1
prepared using the same kind of the ionic liquid and the
battery of Comparative Example 1 with no use of the
ionic liquid (see FIG. 1)


Test Example 2: Safety evaluation
In_ order to -evaluate the safety of lithium
secondary batteries including the cathode which has been
modified with the ionic liquid according to the present
invention,- the-following test was-performed.
Each of the batteries of Examples 1 to 4 and
Comparative Examples 1 to 3 was charged to 4.2V,
disassembled to separate only the cathode. The separated
cathode was evaluated for thermal stability with the
electrolyte by a differential scanning calorimeter
(DSC) . The DSC analysis was performed by scanning the
cathode at a heating rate of 5 °C/min up to 350 °C under
a nitrogen atmosphere.
The lithium secondary battery of Comparative
Example 1 with no use of the ionic liquid showed a heat
release of about 405.9 J/g (see FIG. 8), whereas the
lithium secondary battery of Examples 1 to 4 prepared
with the addition of the ionic liquid showed a heat
release up to about 200 J/g, indicating the effect of a

reduction of about 50% in heat release (see FIGS. 4, 5,
6 and 7) . This suggests that the lithium secondary
batteries made by using the ionic liquid as the cathode
additive have a greatly improved safety.
Meanwhile, the battery of Comparative Example 2
preparing with the addition of 3 parts by weight of the
ionic liquid to the electrolyte solution did not show a
great reduction in heat release, similarly with the case
of the above performance evaluation (see FIG. 9). On the
other hand, the battery of Comparative Example 3
prepared with the addition of 10 parts by weight of the
ionic liquid to the electrolyte solution showed a
reduction in heat release, which is equal to those of
the batteries prepared in Examples 1 to 4 (see FIG. 10).
Industrial Applicability
As described above, according to the present
invention, the cathode modified with the ionic liquid is
used in batteries, so that the safety of the batteries
can be improved without causing a significant
deterioration in the battery performance.

We Claim:
1 A cathode comprising as components:
(a) a cathode active material based on a lithium-containing metal composite oxide or a chalcogenide
compound; and
(b) an ionic liquid,
wherein the amount of (b) is 0.1 -30 parts by weight per 100 parts by weight of the (a),
and
wherein the cathode is obtainable from a cathode slurry comprising said components (a)
and(b).
2. The cathode as claimed in claim 1, wherein the cation of the iomc liquid is at least one selected
from the group consisting of imidazolium, pyrazolium, triazolium, thiazolium, oxazolium,
pyridazinium, pyrimidinium, pyrazinium, ammonium, phosphonium, pyridinium and pyrrolidinium,
which are substituted or unsubstituted with a C1-15 alkyl group.
3. The cathode as claimed in claim 1, wherein the anion of the ionic liquid is at least one selected
from the group consisting of PF6-, BF4_, CF3SO3", N(CF3SO2)2-, N(C2F5SO2)2 C(CF2SO2)3_, AsF6-,
SbF6-, AlCl4-, NbF6-, HSO4, ClO4, CH3SO3 and CF3CO2".
4. The cathode as claimed in claim 1, wherein the ionic liquid is a zwitterionic compound.

5. The cathode as claimed in claim 1, wherein the hthium-containing metal composite oxide is a
hthium-containing oxide including at least one element selected from the group consisting of alkali
metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, transition
metals and rare earth elements.
6. The cathode as claimed in claim 1, wherein the chalcogenide compound is at least one selected
from the group consisting of T1S2, Se02, MoS2, FeS2, Mn02, NbSe3, V2O5, V6O13, and CuCl2
7. An electrochemical device comprising:
(a) a cathode as claimed in any one of claims 1 to 6

(b) an anode;
(c) a separator; and
(d) an electrolyte solution not including an ionic liquids as an electrolyte component.
8. The electrochemical device as claimed in claim 7, which is a lithium secondary battery.

ABSTRACT

(54) Title: IONIC LIQUID-MODIFIED CATHODE AND ELECTROCHEMICAL DEVICE USING THE SAME
(57) Abstract: The present invention provides a cathode produced from a cathode slurry comprising' (a) a cathode active material
based on a lithium-containing metal composite oxide or a chalcogenide compound; and (b) an ionic liquid, as well as an electrochemical
device including the cathode. The inventive cathode can greatly improve the safety of batteries without causing a significant
deterioration in the battery performance.