NON-AQUEOUS ELECTROLYTE AND ELECTROCHEMICAL DEVICE WITH
AN IMPROVED SAFETY
Technical Field
The present invention relates to a non-aqueous
electrolyte having improved safety and to an
electrochemical device comprising the same.
Background Art
Recently, as electronic instruments have become
wireless and portable, non-aqueous electrolyte-based
secondary batteries with high capacity and high energy
density have been practically used as drive sources for
the electronic instruments. A lithium secondary battery,
which is a typical example of the non-aqueous secondary
batteries, comprises a cathode, an anode and an
electrolyte and is chargeable and dischargeable because
lithium ions coming out from a cathode active material
during a charge process are intercalated into an anode .
active material and deintercalated during a discharge
process, so that the lithium ions run between both the
electrodes while serving to transfer energy. Such a
high-capacity lithium secondary battery has an advantage
in that it can be used for a long period of time due to
high energy density. However, the lithium secondary
battery has problems in that when the battery is exposed
to high temperatures for a 'long period of time due to
internal heat generation during the driving thereof, the
stable structure of the battery, comprising a
cathode(lithium transition metal oxide), an anode
(crystalline or non-crystalline carbon) and a separator,
will be changed due to gas generation caused by the
oxidation of the electrolyte to deteriorate the
performance of the battery or, in severe cases, to cause
the ignition and explosion of the battery due to

internal short circuits in severe cases.
To solve such problems, there have been many-
recent attempts to improve the high-temperature safety
of the battery by (1) using a porous polyolefin-based
separator having a high melting point, which does not
easily. melt in the internal/external thermal
environments or (2) adding a non-flammable organic
solvent to a non-aqueous electrolyte comprising a
lithium salt and a flammable organic solvent.
However, the polyolefin-based separator has a
disadvantage in that it should generally have high film
thickness in order to achieve high-melting point and to
prevent internal short circuits. This high film
thickness relatively reduces the loading amount of the
cathode and the anode, thus making it impossible to
realize a high capacity of the battery, or deteriorating
the performance of the battery in severe cases. Also,
the polyolefin-based separator consists of a polymer
such as PE or PP, which has a melting point of about
150 "C, and thus, when the battery is exposed to high
temperatures above 150 °C for a long period of time, the
separator will melt, causing short circuits inside the
battery, thus causing the ignition and explosion of the
battery.
Meanwhile, a lithium secondary battery comprising
a flammable non-aqueous electrolyte containing a lithium
salt, cyclic carbonate and linear carbonate has the
following problems at high temperatures: (1) a large
amount of heat is generated due to the reaction between
lithium transition metal oxide and the carbonate solvent
to cause the short circuit and ignition of the battery,
and (2) a thermally stable battery cannot be realized
due to the flammability of the non-aqueous electrolyte
itself.
Recently, efforts to solve the problems associated

with the flammability of the electrolyte by adding a
phosphorus (P)-based compound having flame retardancy
have been made, but the compound causes a problem of
accelerating irreversible reactions, including Li
corrosion, in a battery, thus significantly reducing the
performance and efficiency of the battery.
Disclosure of the Invention
The present inventors have found that when a
fluoroethylene carbonate (FEC) compound is used as an
electrolyte solvent, and an aliphatic mono- or di-
nitrile compound is used as an electrolyte additive,
these compounds show a synergic effect in terms of the
prevention of battery ignition caused by external
physical shock (e.g., thermal shock) and/or the
prevention of ignition/explosion caused by internal
short circuit of a battery at high temperatures above
150 °C, that is, in terms of the safety of the battery.
The present invention is based on this finding.
The present invention provides a non-aqueous
electrolyte comprising a lithium salt and a solvent, the
electrolyte containing, based on the weight of the
electrolyte, 10-40 wt% of a compound of Formula 1 or its
decomposition product, and 1-40 wt% of an aliphatic
nitrile compound, as well as an electrochemical device
comprising the non-aqueous electrolyte:
[Formula 1]

wherein X and Y are each independently hydrogen,
chlorine or fluorine, except that both X and Y are not
hydrogen.
In another aspect, the present invention provides
an electrochemical device comprising: a cathode having a

complex formed between the surface of a cathode active
material and an aliphatic nitrile compound; and an anode
having formed thereon a coating layer containing a
decomposition product of the compound of Formula 1.
In still another aspect, the present invention
provides an electrochemical device comprising: a cathode
having a complex formed between the surface of a cathode
active material and an aliphatic nitrile compound; and a
non-aqueous electrolyte containing the compound of
Formula 1 or its decomposition product.
In yet another aspect, the present invention
provides an electrochemical device comprising: an anode
having formed thereon a coating layer containing a
decomposition product of the compound of Formula 1; and
a non-aqueous electrolyte containing an aliphatic
nitrile compound.
In the present invention, the aliphatic nitrile
compound may be an aliphatic mono-nitrile compound, an
aliphatic di-nitrile compound, or a mixture thereof,
wherein the aliphatic mono-nitrile compound may be
represented by Formula 2 below, and the aliphatic di-
nitrile compound may be represented by Formula 3 below:
[Formula 2]
N≡C-R
wherein R is (CH2)n-CH3 (n is an integer of 1-11); and
[Formula 3]
N≡C-R-C≡N
wherein R is (CH2)n (n is an integer of 2-12).
In the present invention, the aliphatic nitrile
compound is preferably succinonitrile, butyronitrile,
valeronitrile, or a mixture thereof.
Moreover, in the present invention, the
decomposition product of the compound of Formula 1 has
an opened-ring structure.

Brief Description of the Drawings
FIGS. 1 to 7 are graphic diagrams showing whether
the ignition and explosion of batteries occur after the
batteries are stored in an oven at 150 °C in a state in
which the batteries are charged to 4.2V. Herein, FIG. 1
is for Example 1, FIG. 2 for Example 2, FIG. 3 for
Example 3, FIG. 4 for Comparative Example 1, FIG. 5 for
Comparative Example 3, FIG. 6 for Comparative Example 2,
and FIG. 7 for Comparative Example 4.
FIG. 8 is a graphic diagram showing the results of
heat generation analysis conducted using differential
scanning calorimetry (DSC) in order to examine the
thermal stability of each of the batteries manufactured
in Examples 1 and 3 and Comparative Example 1.
Mode for Carrying Out the Invention
Hereinafter, the present invention will be
described in detail.
The present inventors have found through
experiments that the compound of Formula 1 and a nitrile
compound having a cyano (-CN) functional group show a
synergic effect in terms of securing battery safety
associated with thermal shock and in terms of high-
temperature cycle life (see Experiment 1 and FIGS. 1 to
7).
When the compound of Formula 1 and the aliphatic
nitrile compound are used in combination, they can show
a synergic effect in terms of the safety of a battery,
and the mechanism thereof is as follows.
The ignition and explosion reactions of a lithium
ion battery can occur due to a rapid exothermic reaction
between a charged cathode and an electrolyte, and if the
capacity of the battery increases, only controlling the
exothermic reaction between the cathode and the
electrolyte cannot secure the safety of the battery.

Generally, when the charge voltage of the cathode
is high or the capacity of the battery is increased (an
increase in the number of stacks (pouch type batteries,
etc.) or the number of electrode windings of jelly-rolls
(cylindrical or prismatic batteries, etc.)), the energy
level of the battery will be increased, and thus the
battery will tend to generate heat due to physical shock
(e.g., heat, temperature, pressure, etc.), or in severe
cases, explode, thus reducing the safety of the battery.
The compound of Formula 1 can prevent or delay the
battery from being ignited by the exothermic reaction,
compared to ethylene carbonate. This is because the
compound of Formula 1 consists of a halogen-based
compound (e.g., one introduced with at least one of
fluorine (F) and chlorine (Cl)) having a high flame-
retardant effect, and in particular, the compound can
form an SEI layer (protective layer) on the anode
surface upon charge to delay micro- or macro-thermal
short circuits occurring inside the battery.
However, when the compound of Formula 1 or its
decomposition product is used alone, the safety of the
battery, particularly the high-temperature safety of the
battery, cannot be sufficiently secured (see FIGS. 4 and
5), and thus the present invention is characterized in
that the aliphatic nitrile compound is used in
combination with the compound of Formula 1 or its
decomposition product.
When the aliphatic nitrile compound is used in
combination with the compound of Formula 1 or its
decomposition product, the aliphatic nitrile compound
can form a complex on the. surface of a cathode
consisting of lithium-transition metal oxide so as to
inhibit the reaction between the electrolyte and the
cathode, thus controlling heat generation and
controlling an increase in the temperature of the

battery. Also, the complex formation can prevent the
combustion of the electrolyte, which is accelerated by
oxygen liberated due to the structural collapse of the
cathode, prevent thermal runaway phenomena, and prevent
the internal short circuit of the battery from occurring
due to heat generation (see FIG. 8).
In short, 1) the compound of Formula 1 or its
decomposition product and 2) the resulting protective
layer which is made of a complex formed between an
aliphatic di-nitrile compound such as succinonitrile or
an aliphatic mono-nitrile compound such as butyronitrile
and the surface of a cathode active material, can show a
synergic effect, thus improving the safety of the
battery.
Furthermore, when the compound of Formula 1 or its
decomposition product and the aliphatic nitrile compound
are used in combination, they can show a synergic effect
in terms of the performance of a battery, and the
mechanism thereof is as follows.
The compound of Formula 1 or its decomposition
product forms a dense and close passivation layer on the
anode upon the initial charge cycle (which is generally
referred as formation of a battery). The passivation
layer prevents co-intercalation of the carbonate solvent
into the layered structure of active materials and
decomposition of the carbonate solvent, and thus reduces
irreversible reactions in the battery. Additionally, the
passivation layer allows only Li+ to be
intercalated/deintercalated through the layer, thereby
improving the life characteristics of the battery.
However, the passivation layer (SEI layer) formed
by the compound is easily decomposed at high temperature
(above 60 °C) to generate a large amount of gas (CO2 and
CO), and particularly in the case of a cylindrical
battery, the generated gas breaks a current interruptive

device (CID), an electrochemical device at a cylindrical
cap region, to interrupt electric current, thus reducing
the function of the battery. In severe cases, the
generated gas opens the cap region, so that the
electrolyte leaks to corrode the appearance of the
battery or to cause a significant reduction in the
performance of the battery.
According to the present invention; gas generation
resulting from the compound of Formula 1 or its
decomposition product can be inhibited through the use
of the aliphatic nitrile compound by the chemical
interaction between the compound of Formula 1 or its
decomposition and a cyano (-CN) functional group, thus
improving the high-temperature cycle life
characteristics of the battery.
When considering this effect together with an
improvement in the performance of a high-capacity
battery, butyronitrile or valeronitrile is most suitable
as aliphatic mono-nitrile, and succinonitrile is most
suitable as aliphatic di-nitrile.
Among aliphatic di-nitrile compounds, those having
long chain length have no great effect on the
performance and safety of the battery or adversely
affect the performance of the battery, and thus those
having short chain length are preferable. However,
malononitrile (CN-CH2-CN) having an excessively short
chain length causes side reactions such as gas
generation in the battery, and thus it is preferable to
use those having 2-12 aliphatic hydrocarbons (CN-(CH2)n-
CN, n=2-12), including succinonitrile. Among them, it is
more preferable to select nitrile having small carbon
number. Most preferred is succinonitrile.
Aliphatic mono-nitrile compounds show the same
tendency as mentioned above for the aliphatic di-nitrile
compounds, but when considering side reactions in the

battery, it is preferable to select those having 2-12
aliphatic carbons (CN-(CH2)n-CH3, n=1-11). Among them, it
is more preferable to select nitrile having small carbon
number. Butyronitrils and valeronitrile are most
preferable.
Meanwhile, among compounds containing a cyano
functional group, aromatic nitriles and fluorinated
aromatic nitrile compounds are not preferable because
they are electrochemically easily decomposed in the
battery to interfere with the migration of Li ions, thus
deteriorating the performance of the battery.
The content of the compound of Formula 1 or its
decomposition product for use as a solvent in the
inventive electrolyte is preferably 10-40 wt%.
The compound of Formula 1 is a compound introduced
with at least one of fluorine (F) and chlorine (C1)
having high electronegativity, and has high oxidation
voltage, i.e., high oxidation resistance, because it is
difficult to oxidize due to the strong electron
withdrawing effect of fluorine or chlorine. Accordingly,
the compound of Formula 1 is not decomposed even at a
high charge voltage of more than 4.2V, for example, a
high charge voltage of more than 4.35V, and thus can
sufficiently function as an electrolyte solvent.
Therefore, if the compound of Formula 1 is used as an
electrolyte solvent in a battery, the battery will show
excellent cycle life characteristics, even when it is
charged to 4.35 V and discharged.
Meanwhile, the compound of Formula 1 or its
decomposition product is first consumed for the
formation of a passivation layer. Herein, the consumed
amount of the compound of Formula 1 or its decomposition
product is proportional to the electric capacity of the
anode. Also, the compound of Formula 1 remaining after
use in the formation of the passivation layer on the

anode serves as an electrolyte solvent to exhibit
battery safety such as flame retardancy. Thus, another
characteristic of the present invention is to use the
compound of Formula 1 or its decomposition product in an
amount that can remain in an electrolyte even after the
formation of the anode passivation layer, for example,
in an amount of 10 wt% or more based on the weight of
the electrolyte.
As described above, it is preferable to use a
large amount of the compound of Formula 1 in terms of
battery safety such as flame retardancy, but the
compound of Formula 1 can reduce the cycle life and
capacity of a battery because it has high viscosity to
reduce the ion conductivity of an electrolyte and to
interfere with the migration of Li ions. For this
reason, it is preferable to use the compound of Formula
1 in an amount of 40 wt% or less based on the weight of
the electrolyte.
In the content of the aliphatic di-nitrile
compound is preferably 1-10 wt%, more preferably 1-5
wt%, and most preferably 1-3 wt%, in view of the
performance of the electrolyte.
Also, the aliphatic mono-nitrile compounds,
particularly butyronitrile and valeronitrile, have the
effects of increasing the ion conductivity of the
electrolyte and reducing the viscosity of the
electrolyte, and for this reason, the content of the
aliphatic mono-nitrile compound in the electrolyte is
preferably 1-40 wt%, more preferably 1-20 wt%, and most
preferably 1-10 wt%.
The inventive non-aqueous electrolyte for lithium
secondary batteries generally contain, in addition to
the compound of Formula 1, flammable non-aqueous organic
solvents, including cyclic carbonates, linear carbonates
and combinations thereof. Typical examples of the cyclic

carbonates include ethylene carbonate (EC), propylene
carbonate (PC), gamma-butyrolactone (GBL) and the like,
and typical examples of the linear carbonates include
diethyl carbonate (DEC), dimethyl carbonate (DMC),
ethylmethyl carbonate (EMC) and the like.
The non-aqueous electrolyte contains a lithium
salt, non-limiting examples of which include LiClO4,
LiCF3SO3, LiPF6, LiBF4, LiAsF6, LiSbF5, LiN(CF3SO2)2,
LiN(C2F5SO2)2, LiA1O4, LiAlCl4, LiSO3CF3, and
LiN (CxF2x+1SO2) (CyF2y+1SO2) (x and y = natural numbers).
Meanwhile, the aliphatic nitrile compounds can
form a bond with a transition metal, such as cobalt,
contained in the cathode active material through their
cyano functional groups having high dipole moment.
Particularly, the cyano functional groups can form
stronger bonds with the surface of the cathode at high
temperature, thereby forming a complex structure.
In order to simplify a manufacturing process of a
battery, it is preferable that the aliphatic nitrile
compound is introduced into an electrolyte, and then a
complex is formed between the surface of a cathode
active material and the aliphatic nitrile compound.
However, it is also possible to separately prepare a
cathode having a complex formed on the surface thereof,
before the assemblage of a battery.
Preferably, the complex between the surface of a
cathode active material and the aliphatic nitrile
compound is formed by dipping a cathode, comprising a
cathode active material coated on a collector, into an
electrolyte containing the aliphatic nitrile compound
added thereto, followed by heat treatment at high
temperature. The high-temperature heat treatment may be
performed in such a temperature range as not to affect
electrode active materials and a binder, generally at a
temperature of 180 °C or lower. Otherwise, although the

high-temperature heat treatment depends on the kind of
the aliphatic nitrile compound, it may be performed at
such a temperature range as to prevent excessive
evaporation of the aliphatic nitrile compound, generally
at a temperature of 100 °C or lower. In general, the
high-temperature treatment is suitably performed at a
temperature between 60 °C and 90 °C. Long-term treatment
at a temperature between 30 °C and 40 °C may provide the
same effect.
In addition, in the present invention, a compound
capable of forming a passivation layer on the surface of
an anode may additionally be used to prevent side
reactions where a passivation layer formed on the anode
from the compound of Formula 1, such as fluoroethylene
carbonate, emits a large amount of gas at high
temperature. Non-limiting examples of the compound
include alkylene compounds, such as vinylene carbonate
(VC) , sulfur-containing compounds, such as propane
sulfone, ethylene sulfite and 1,3-propane sultone, and
lactam-based compounds, such as N-acetyl lactam.
Furthermore, the electrolyte according to the
present invention may comprise vinylene carbonate,
propane sulfone and ethylene sulfite at the same time,
but only a sulfur-containing compound may also be
selectively added to the electrolyte to improve the
high-temperature cycle life characteristics of the
battery.
A typical example of electrochemical devices,
which can be manufactured according to the present
invention, is a lithium secondary battery, which may
comprise: (1) a cathode capable of intercalating and
deintercalating lithium ions; (2) an anode capable of
intercalating and deintercalating lithium ions; (3) a
porous separator; and (4) a) a lithium salt, and b) an
electrolyte solvent.

In general, as a cathode active material for use
in a lithium secondary battery, lithium-containing
transition metal oxides may be used. The cathode active
material can be at least one material selected from the
group consisting of LiCoO2, LiNiO2, LiMn2O4, LiMnO2, and
LiNi1-xCoxMyO2 (wherein 0≤ X ≤1, 0≤ Y ≤1, 0≤ X+Y ≤1, M is a
metal such as Mg, Al, Sr or La). Meanwhile, as an anode
active material for use a lithium secondary battery,
carbon, lithium metal or lithium alloy may be used. In
addition, other metal oxides capable of lithium
intercalation/deintercalation and having an electric
potential of less than 2V based on lithium (for example,
TiO2 and SnO2) may be used as the anode active material.
The lithium secondary battery according to the
present invention may have a cylindrical, prismatic or
pouch-like shape.
Hereinafter, the present invention will be
described in further detail with reference to examples.
It is to be understood, however, that these examples are.
illustrative only and the present invention is not
limited thereto.
Examples
Example 1
An electrolyte used in this Example was a 0.8M
LiPF6 solution having a composition of FEC: PC: DMC = 2:
1: 7. To the electrolyte, 2 wt % of succinonitrile was
added. Artificial graphite and LiCoO2 were used as an
anode active material and a cathode active material,
respectively. Then, a cylindrical battery was
manufactured according to a conventional method.
Example 2
A cylindrical battery was manufactured in the same
manner as in Example 1, except that the composition
ratio of the carbonate solvent containing fluoroethylene
carbonate (FEC) was 30: 5: 65.

Example 3
A cylindrical battery was manufactured in the same
manner as in Example 1, except that 5 wt% of
butyronitrile was used instead of succinonitrile.
Comparative Example 1
A 0.8M LiPF6 solution having a composition of FEC:
PC: DMC =2: 1: 7 was used as an electrolyte. Artificial
graphite and LiCoO2 were used as an anode active material
and a cathode active material, respectively. Then, a
cylindrical battery was manufactured according to a
conventional method.
Comparative Example 2
A 0.8M LiPF6 solution having a composition of EC:
PC: DMC = 2: 1: 7 was used as an electrolyte. To the
electrolyte, 2 wt% of succinonitrile was added.
Artificial graphite and LiCoO2 were used as an anode
active material and a cathode active material,
respectively. Then, a cylindrical battery was
manufactured according to a conventional method.
Comparative Example 3
A cylindrical battery was manufactured in the same
manner as in Comparative Example 1, except that the
composition ratio of the carbonate solvent containing
fluoroethylene carbonate (FEC) was 30: 5: 65.
Comparative Example 4
A cylindrical battery was manufactured in the same
manner as in Comparative Example 2, except that 5 wt% of
butyronitrile was used instead of succinonitrile.
The batteries obtained from the above Examples and
Comparative Examples were all subjected to heat
treatment at 60 °C for 12 hours or more.
Experiment 1
Each of the batteries manufactured in Examples 1-3
and Comparative Examples 1-4 was charged to 4.25V and
stored in an oven at 150 °C, and then whether the

ignition and explosion of the batteries occurred was
observed. The observation results are shown in FIGS. 1
to 7.
As can be seen in FIGS. 1, 2 and 3, only the case
of the battery employing fluoroethylene carbonate as the
electrolyte solvent and containing 2 wt% of the
succinonitrile compound added to the electrolyte
solvent, or the battery employing fluoroethylene
carbonate as the electrolyte solvent and containing 5
wt% of the butyronitrile compound added to the
electrolyte solvent, realized a thermally stable battery
at high temperature for 3-10 hours or longer without
ignition.
On the other hand, in the case of adding
fluoroethylene carbonate alone (FIGS. 4 and 5), the case
of adding only succinonitrile (FIG. 6), or the case of
adding only butyronitrile (FIG. 7) , it could be seen
that the battery was ignited and exploded at high
frequency at a high temperature above 150 °C without
maintaining high-temperature safety. In the case of FIG.
7, a short circuit occurred within 1 hour to reduce
voltage from 4.2V to 0V and to cause the explosion of
the battery.
However, the battery comprising the electrolyte
containing only succinonitrile added thereto had an
advantage in that the time for the battery to explode
was long because the battery was superior to the battery
comprising the electrolyte containing fluoroethylene
carbonate alone with respect to controlling heat
generation resulting from the reaction between the
cathode and the electrolyte and the structural collapse
of the cathode.
Experiment 2
Each of the batteries manufactured in Examples 1
and 2 and Comparative Example 1 was charged to 4.2V. A

general thermogravimetric analyzer, DSC (Differential
Scanning Calorimeter), was used, wherein two high-
pressure pans capable of resisting the vapor pressure of
the electrolyte were used as pans for measurement. To
one pan, about 5-10 mg of the cathode sample separated
from each of the batteries charged to 4.2V was
introduced, while the other pan was left empty. The
calorific difference between the two pans was analyzed
while the pans were heated at a rate of 5 oC/min to
400 °Cto measure temperature peaks corresponding to heat
generation.
As shown in FIG. 8, the battery (Comparative
Example 1) manufactured without the aliphatic mono- or
di-nitrile compound shows heat generation peaks at about
200 oC. Generally, the peak at about 200 °C indicates
heat generation caused by the reaction between the
electrolyte and the cathode, while the peak at about
240 oC indicates heat generation caused by combined
factors including the reaction between the electrolyte
and the cathode, and the structural collapse of the
cathode. However, it could be seen that Comparative
Example 1 showed a strong peak at about 200 oC together
with heat generation caused by combined factors at about
240 °C. On the other hand, the battery comprising the
non-aqueous electrolyte containing succinonitrile or
butyronitrile added thereto showed a remarkable
reduction in heat generation without showing the above
two temperature peaks. This indicates that heat
generation caused by the reaction between the
electrolyte and the cathode was controlled due to the
formation of a protective layer through a strong bond
between succinonitrile/butyronitrile and the cathode
surface.
Industrial Applicability

As can be seen from the foregoing, according to
the present invention, when the compound of Formula 1
and the aliphatic nitrile compound are used in
combination, they can show a synergic effect in terms of
securing safety associated with thermal shock and in
terms of high-temperature cycle life, even in the case
of a high-capacity battery, and also can provide
excellent battery performance.
Although the preferred embodiment of the present
invention has been described for illustrative purposes,
those skilled in the art will appreciate that various
modifications, additions and substitutions are possible,
without departing from the scope and spirit of the
invention as disclosed in the accompanying claims.

Claims
1. A non-aqueous electrolyte comprising a lithium
salt and a solvent, the electrolyte containing, based on
the weight of the electrolyte, 10-40 wt% of a compound
of Formula 1 or its decomposition product, and 1-40 wt%
of an aliphatic nitrile compound:
[Formula 1]

wherein X and Y are each independently hydrogen,
chlorine or fluorine, provided that both X and Y are not
hydrogen.
2. The non-aqueous electrolyte of Claim 1, wherein
the aliphatic nitrile compound is an aliphatic mono-
nitrile compound, an aliphatic di-nitrile compound, or a
mixture thereof.
3. The non-aqueous electrolyte of Claim 2,
wherein the aliphatic di-nitrile compound is contained
in an amount of 1-10 wt% based on the weight of the
electrolyte.
4. The non-aqueous electrolyte of Claim 2, wherein
the aliphatic mono-nitrile compound is represented by
Formula 2, and the aliphatic di-nitrile compound is
represented by Formula 3:
[Formula 2]
N≡C-R
wherein R is (CH2)n-CH3 (n is an integer of 1-11); and
[Formula 3]
N≡C-R-C≡N
wherein R is (CH2)n (n is an integer of 2-12) .

5. The non-aqueous electrolyte of Claim 1, wherein
the aliphatic nitrile compound is succinonitrile,
butyronitrile, valeronitrile or a mixture thereof.
6. The non-aqueous electrolyte of Claim 1, wherein
the solvent includes either or both of at least one
cyclic carbonate selected from the group consisting of
ethylene carbonate (EC), propylene carbonate (PC) and
gamma-butyrolactone (GBL), and at least one linear
carbonate selected from the group consisting of diethyl
carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl
carbonate (EMC) and methyl propyl carbonate (MPC).
7. The non-aqueous electrolyte of Claim 1, wherein
a compound selected from alkylene compounds, sulfur-
containing compounds and lactam-based compounds, which
can form a passivation layer on an anode surface, is
added to the electrolyte.
8. An electrochemical device comprising a cathode,
an anode, and a non-aqueous electrolyte according to any
one of Claims 1 to 7.
9. An electrochemical device comprising: a cathode
having a complex formed between a cathode active
material surface and an aliphatic nitrile compound; and
an anode having formed thereon a coating layer
containing a decomposition product of a compound of
Formula 1:
[Formula 1]

wherein X and Y are each independently hydrogen,
chlorine or fluorine, provided that both X and Y are not

hydrogen.
10. The electrochemical device of Claim 9, wherein
the aliphatic nitrile compound is an aliphatic mono-
nitrile compound, an aliphatic di-nitrile compound, or a
mixture thereof.
11. The electrochemical device of Claim 10,
wherein the aliphatic mono-nitrile compound is
represented by Formula 2, and the aliphatic di-nitrile
compound is represented by Formula 3:
[Formula 2]
N≡C-R
wherein R is (CH2)n-CH3 (n is an integer of 1-11); and
[Formula 3]
N≡C-R-C≡N
wherein R is (CH2)n (n is an integer of 2-12).
12. The electrochemical device of Claim 9, wherein
the complex between the cathode active material surface
and the aliphatic nitrile compound is formed either by
high-temperature treating a battery manufactured from an
electrolyte containing the aliphatic nitrile compound
added thereto, or by dipping the cathode, comprising the
cathode active material coated on a collector, into the
electrolyte containing the aliphatic nitrile compound
added thereto, followed by heat treatment at high
temperature.
13. The electrochemical device of Claim 12,
wherein the high-temperature treatment is performed at a
temperature of 30 oC or more before or after assemblage
of the battery.
14. The electrochemical device of Claim 9, wherein

the aliphatic nitrile compound is succinonitrile,
butyronitrile, valeronitrile, or a mixture thereof.
15. An electrochemical device comprising: a
cathode having a complex formed between a surface of a
cathode active material and an aliphatic nitrile
compound; and a non-aqueous electrolyte containing a
compound of Formula 1 or its decomposition product:
[Formula 1]

wherein X and Y are each independently hydrogen,
chlorine or fluorine, provided that both X and Y are not
hydrogen.
16. The electrochemical device of Claim 15,
wherein the aliphatic nitrile compound is an aliphatic
mono-nitrile compound, an aliphatic di-nitrile compound,
or a mixture thereof.
17. The electrochemical device of Claim 16,
wherein the aliphatic mono-nitrile compound is
represented by Formula 2, and the aliphatic di-nitrile
compound is represented by Formula 3:
[Formula 2]
N≡C-R
wherein R is (CH2)n-CH3 (n is an integer of 1-11); and
[Formula 3]
N≡C-R-C≡N
wherein R is (CH2)n (n is an integer of 2-12).
18. The electrochemical device of Claim 15,
wherein the compound of Formula 1 or its decomposition
product is contained in an amount of 10-40 wt% based on

the weight of the electrolyte.
19. The electrochemical device of Claim 15, the
complex between the cathode active material surface and
the aliphatic nitrile compound is formed either by high-
temperature treating a battery manufactured from an
electrolyte containing the aliphatic nitrile compound
added thereto, or by dipping the cathode, comprising the
cathode active material coated on a collector, into the
electrolyte containing the aliphatic mono-nitrile
compound added thereto, followed by heat treatment at
high temperature.
20. The electrochemical device of Claim 19,
wherein the high-temperature treatment is performed at a
temperature of 30 oC or more before or after assemblage
of the battery.
21. The electrochemical device of Claim 15,
wherein the aliphatic nitrile compound is
succinonitrile, butyronitrile, valeronitrile, or a
mixture thereof.
22. An electrochemical device comprising: an anode
having formed thereon a coating layer containing a
decomposition product of a compound of Formula 1; and a
non-aqueous electrolyte containing an aliphatic nitrile
compound:
[Formula 1]

wherein X and Y are each independently hydrogen,
chlorine or fluorine, provided that both X and Y are not
hydrogen.

23. The electrochemical device of Claim 22,
wherein the aliphatic nitrile compound is an aliphatic
mono-nitrile compound, an aliphatic di-nitrile compound,
or a mixture thereof.
24. The electrochemical device of Claim 23,
wherein the aliphatic mono-nitrile compound is
represented by Formula 2, and the aliphatic di-nitrile
compound is represented by Formula 3:
[Formula 2]
N≡C-R
wherein R is (CH2)n-CH3 (n is an integer of 1-11); and
[Formula 3]
N≡C-R-C≡N
wherein R is (CH2)n (n is an integer of 2-12).
25. The electrochemical device of Claim 23,
wherein the aliphatic mono-nitrile compound is contained
in an amount of 1-40 wt% based on the weight of the
electrolyte, or the aliphatic di-nitrile compound is
contained in an amount of 1-10 wt% based on the weight
of the electrolyte.
26. The electrochemical device of Claim 22,
wherein the aliphatic nitrile compound is
succinonitrile, butyronitrile, valeronitrile, or a mixture thereof.

Disclosed are a non-aqueous electrolyte comprising a lithium salt and a solvent, the electrolyte containing, based on the weight of the electrolyte, 10- 40 wt% of a compound of Formula 1 or its decomposition product, and 1-40 wt% of an aliphatic nitrile compound, as well as an electrochemical device comprising the non-aqueous electrolyte. Also disclosed is an electrochemical device comprising: a cathode having a complex formed between the surface of a cathode active material and an aliphatic nitrile
compound; and an anode having formed thereon a coating layer containing a decomposition product of the compound of Formula 1. Moreover, disclosed is an electrochemical device comprising: a cathode having a complex formed between the surface of a cathode active material and an aliphatic nitrile compound; and a non-aqueous electrolyte containing the compound of Formula 1 or its decomposition product. In addition, disclosed is an electrochemical device comprising: an anode having formed thereon a coating layer containing a decomposition product of the compound of Formula 1; and a non-aqueous electrolyte containing the compound of Formula 1 or its decomposition product.