Title of Invention	NON-AQUEOUS ELECTROLYTE AND ELECTROCHEMICAL DEVICE WITH AN IMPROVED SAFETY
Abstract	The present invention discloses a non-aqueous electrolyte comprising a lithium salt and a solvent, the electrolyte containing, based on the weight of the electrolyte, 1-5 wt% of a compound of Formula 1 or its decomposition product, and 1-3 wt% of an aliphatic di-nitrile compound of Formula 2: [Formula 1] wherein X is fluorine and Y is hydrogen, chlorine or fluorine, [Formula 2] N=C—R—C=N wherein R is (CH2)n (n is an integer of 2-12).

Title of Invention

NON-AQUEOUS ELECTROLYTE AND ELECTROCHEMICAL DEVICE WITH AN IMPROVED SAFETY

Abstract

The present invention discloses a non-aqueous electrolyte comprising a lithium salt and a solvent, the electrolyte containing, based on the weight of the electrolyte, 1-5 wt% of a compound of Formula 1 or its decomposition product, and 1-3 wt% of an aliphatic di-nitrile compound of Formula 2: [Formula 1] wherein X is fluorine and Y is hydrogen, chlorine or fluorine, [Formula 2] N=C—R—C=N wherein R is (CH2)n (n is an integer of 2-12).

Full Text	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(ex. lithium transition metal oxide), an anode (ex. 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 oC 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 both a fluoroethylene carbonate (FEC) compound and an aliphatic di-nitrile compound are used as electrolyte additive, these compounds show a synergic effect in terms of the performance of a battery, as well as in terms of the safety of the battery, for example in terms of the prevention of battery ignition at over-charged state and/or the prevention of ignition/explosion caused by internal short circuit of a battery at high temperatures above 150 °C. 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, 1-10 wt% of a compound of Formula 1 or its decomposition product, and 1-10 wt% of an aliphatic di- 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 a surface of a cathode active material and an aliphatic di-nitrile compound; and a non-aqueous electrolyte containing 1-10 wt% of a compound of Formula 1 or its decomposition product based on the weight of the electrolyte. In the present invention, the aliphatic di-nitrile compound is preferably succinonitrile. Moreover, in the present invention, the decomposition product of the compound of Formula 1 has an opened-ring structure. Brief Description of the Accompanying Drawings FIGS. 1 to 3 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 wliich the batteries are charged to 4.2V. Herein, FIG. 1 is for Example 1, FIG. 2 for Comparative Example 1, FIG. 3 for Comparative Example 2. FIG. 4 is a graphic diagram showing the results of heat generation analysis conducted using differential scanning calorimetry (DSC) in order to examine the thermal safety of each of the batteries manufactured in Example 1 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 FIGS. 1 to 3) . When the compound of Formula 1 or its decomposition product and the aliphatic di-nitrile compound are used in combination as additive, 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 such as a fluoroethylene carbonate 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 (CI) ) 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, the compound of Formula 1 such as a fluoroethylene carbonate is so thermally fragile to be easily decomposed at high temperature and to generate a large amount of gas. The generated gas can vent a pouch- typed or can-typed battery case, thereby accelerating the combustion of the electrolyte and causing the ignition and explosion of the battery due to internal short circuits That is, 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 FIG. 2). Accordingly, the present invention is characterized in that the aliphatic di-nitrile compound is used in combination with the compound of Formula 1 or its decomposition product. When the aliphatic di-nitrile compound is used in combination with the compound of Formula 1 or its decomposition product, the aliphatic di-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 (ex. linear carbonates or cyclic carbonates) 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. 4). Also, the continuous interaction chemically between the compound of Formula 1 and the cyano (-CN) functional group of the nitrile compound prevents a large amount of gas generation occurred when using the compound of Formula 1 alone. In short, 1) the compound of Formula 1 or its decomposition product and 2) an aliphatic di-nitrile compound such as succinonitrile 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 di-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 di-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(see Table 2). When considering this effect together with an improvement in the performance of a high-capacity battery, 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. 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 in the inventive electrolyte is preferably 1-10 wt%, and more preferably 1-5 wt%. The compound of Formula 1 has a high viscosity, and thus when the compound of Formula 1 is used in an excessive amount, the ion conductivity of the electrolyte can be reduced and the mobility of Li ion can be inhibited, causing to a reduction of the cycle life and capacity of battery. 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. The inventive electrolyte may contain as an additive an aliphatic mono-nitrile compound having one cyano (-CN) functional group such as R-CN, wherein R is aliphatic hydrocarbon etc.). The inventive non-aqueous electrolyte for lithium secondary batteries contain a general 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 LiCIOa, LiCF3S03, LiPF6, LiBF4, LiAsF6, LiSbF6, LiN (CF3S02) 2, LiN(C2F5S02)2, L1AIO4, LiAlCl4, LiS03CF3, and LiN (CxF2x+iS02) (CyF2y+iS02) (x and y = natural numbers). Meanwhile, the aliphatic di-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 di-nitrile compound is introduced into an electrolyte, and then a complex is formed between the surface of a cathode active material and the aliphatic di-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 di-nitrile compound is formed by dipping a cathode, comprising a cathode active material coated on a collector, into an electrolyte containing the aliphatic di-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 18 0 °C or lower. Otherwise, although the high-temperature heat treatment depends on the kind of the aliphatic di-nitrile compound, it may be performed at such a temperature range as to prevent excessive evaporation of the aliphatic di-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 4 0 °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 LiCo02, LiNi02, LiMn204, LiMn02, and LiNii-xCoxMy02 (wherein 0:2 X 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, Ti02 and Sn02) 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 1M LiPF6 solution having a composition of EC: EMC = 1: 2. To the electrolyte, 1 wt % of fluoroethylene carbonate and 2 wt % of succinonitrile were added. Artificial graphite c ■ • and LiCoC>2 were used as an anode active material and a cathode active material, respectively. Then, a 3443 size of lithium polymer battery was manufactured according to a conventional method and aluminum laminate was used as the battery package. Example 2 A lithium polymer battery was manufactured in the same manner as in Example 1, except that 3. wt% of fluoroethylene carbonate was used instead of 1 wt% of fluoroethylene carbonate. Example 3 A lithium polymer battery was manufactured in the same manner as in Example 1, except that 5 wt% of fluoroethylene carbonate was used instead of 1 wt% of fluoroethylene carbonate. Comparative Example 1 A lithium polymer battery was manufactured in the same manner as in Example 1, except that 1 wt% of fluoroethylene carbonate was added and succinonitrile was not added. Comparative Example 2 A lithium polymer battery was manufactured in the same manner as in Example 1, except that 2 wt% of succinonitrile was added and fluoroethylene carbonate was not added. Comparative Example 3 A lithium polymer battery was manufactured in the same manner as in Comparative Example 1, except that 3 wt% of fluoroethylene carbonate was used. Comparative Example 4 A lithium polymer battery was manufactured in the same manner as in Example 1, except that fluoroethylene carbonate and succinonitrile were not added. Comparative Example 5 A lithium polymer battery was manufactured in the same manner as in Comparative Example 1, except that 5 wt% of fluoroethylene carbonate was used. Comparative Example 6 A lithium polymer battery was manufactured in the same manner as in Comparative Example 2, except that 5 wt% of butyronitrile was used instead of succinonitrile. 1. Test for Safety (1) Each of the batteries manufactured in Example 1 and. Comparative Examples 1 and 2 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 3. As can be seen in FIG. 1, only the case of the battery containing 1 wt% of fluoroethylene carbonate (FEC) and 2 wt% of the succinonitrile compound (SN) added to the electrolyte solvent realized a thermally stable battery at high temperature for 1 hour or longer without ignition. On the other hand, in the case of adding fluoroethylene carbonate alone (FIG. 2) or the case of "lidding oh'ly succinonitrile (FIG. 3), it could be seen that the battery was ignited and exploded at a high temperature above 150 °C without mTiTrifaTnirfg high- temperature safety for 1 hour. 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. 2. Test for Safety (2) Each of the batteries manufactured in Example 1 and Comparative Example 4 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 "C/min to 400 'Cto measure temperature peaks corresponding to heat generation. As shown in FIG. 4, the battery (Comparative Example 4) manufactured without the aliphatic di-nitrile compound shows heat generation peaks at about 200 °C and about 240 °C. 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 13 indicates heat generation caused by combined factors including the reaction between the electrolyte and the cathode, and the structural collapse of the cathode. The battery comprising the non-aqueous electrolyte containing succinonitrile 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 and the cathode surface. 3. Test for Safety (3) Each battery obtained from Examples 1 and 2, and Comparative Examples 1, 2, 3, 4 and 6 was tested under the overcharge conditions of 12V/1C and 20V/1C in a CC/CV (Constant Current/Constant Voltage) manner. The above overcharge test was repeated many times and the average values for the test results are shown in the Table 1. As shown in Table 1, only the case of the battery containing fluoroethylene carbonate and succinonitrile compound added to the electrolyte solvent showed a excellent safety without ignition nor internal short circuits, by controlling the oxidation of the electrolyte and the exothermic reaction resulting from the structural collapse of the cathode. On the other hand, in the case of adding fluoroethylene carbonate alone such as Comparative Example 1 and 3 or the case of adding only aliphatic mono-nitrile compound or the aliphatic di-nitrile compound such as Comparative Example 2 and 6, it could be seen that the frequency of the battery ignition at over-charged state is not constant and is largely high. For example, batteries were ignited while a high temperature above 200 °C was detected inside the battery/ at surface of the battery. Meanwhile, the case of adding neither aliphatic mono-nitrile compound nor the aliphatic di-nitrile compound(Comparative Example 4), all the batteries were ignited. 4. Test for battery performance Each battery obtained from Example 3 and Comparative Examples 4 and 5 was stored at a high temperature of 80°C for 10 days and tested for battery performance. The test results are shown in the following table 2. Exmaple 3 comprising the non-aqueous electrolyte containing fluoroethylene carbonate and succinonitrile added thereto according to the present invention, showed excellent capacity restorability and battery performance even after a high-temperature storage. Industrial Applicability As can be seen from the foregoing, according to the present invention, when the compound of Formula 1 and the aliphatic di-nitrile compound are used in combination, they can show a synergic effect in terms of securing safety at over-charged condition or in case of a high-temperature storage, 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. We Claim: 1. A non-aqueous electrolyte comprising a lithium salt and a solvent, the electrolyte containing, based on the weight of the electrolyte, 1-5 wt% of a compound of Formula 1 or its decomposition product, and 1-3 wt% of an aliphatic di-nitrile compound of Formula 2: [Formula 1] wherein X is fluorine and Y is hydrogen, chlorine or fluorine, [Formula 2] N=C—R—C=N wherein R is (CH2)n (n is an integer of 2-12). 2. The non-aqueous electrolyte as claimed in claim 1, wherein the aliphatic di-nitrile compound is succinonitrile. 3. The non-aqueous electrolyte as claimed in claim 1, wherein the solvent includes cyclic carbonates or linear carbonates,wherein the cyclic carbonates are selected from the group consisting of ethylene carbonate(EC), propylene carbonate(PC) and gamma-butyrolactone(GBL), wherein the linear carbonates are selected from the group consisting of diethyl carbonate(DEC), dimethyl carbonate(DMC), ethyl methyl carbonate(EMC) and methyl propyl carbonate(MPC). 4. The non-aqueous electrolyte as claimed in claim 1, wherein the electrolyte includes an aliphatic mono-nitrile compound. 5. The non-aqueous electrolyte as claimed in claim 1, wherein the electrolyte includes a compound selected from alkylene compounds, sulfur- containing compounds and lactam-based compounds, which can form a passivation layer on an anode surface. 6. An electrochemical device comprising a cathode, an anode, and a non- aqueous electrolyte as claimed in any of claims 1 and 2 to 5. 7. The electrochemical device as claimed in claim 6, the cathode has a complex formed between a surface of a cathode active material and the aliphatic di- nitrile compound 8. The electrochemical device as claimed in claim 7, the complex between the cathode active material surface and the aliphatic di-nitrile compound is formed by high-temperature treating the electrochemical device manufactured from an electrolyte containing the aliphatic di-nitrile compound added thereto, or by dipping the cathode, comprising the cathode active material coated on a collector, into the electrolyte containing the aliphatic di-nitrile compound added thereto, followed by heat treatment at high temperature. 9. The electrochemical device as claimed in claim 10, wherein the high- temperature treatment is performed at a temperature of 30 °C or more before or after assemblage of the electrochemical device. ABSTRACT NON-AQUEOUS ELECTROLYTE AND ELECTROCHEMICAL DEVICE WITH AN IMPROVED SAFETY The present invention discloses a non-aqueous electrolyte comprising a lithium salt and a solvent, the electrolyte containing, based on the weight of the electrolyte, 1-5 wt% of a compound of Formula 1 or its decomposition product, and 1-3 wt% of an aliphatic di-nitrile compound of Formula 2: [Formula 1] wherein X is fluorine and Y is hydrogen, chlorine or fluorine, [Formula 2] N=C—R—C=N wherein R is (CH2)n (n is an integer of 2-12).

Full Text

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(ex. lithium transition metal oxide), an anode
(ex. 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 oC 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 both a
fluoroethylene carbonate (FEC) compound and an aliphatic
di-nitrile compound are used as electrolyte additive,
these compounds show a synergic effect in terms of the
performance of a battery, as well as in terms of the
safety of the battery, for example in terms of the
prevention of battery ignition at over-charged state
and/or the prevention of ignition/explosion caused by
internal short circuit of a battery at high temperatures
above 150 °C. 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, 1-10 wt% of a compound of Formula 1 or its
decomposition product, and 1-10 wt% of an aliphatic di-
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 a surface of a cathode active
material and an aliphatic di-nitrile compound; and a
non-aqueous electrolyte containing 1-10 wt% of a
compound of Formula 1 or its decomposition product based
on the weight of the electrolyte.
In the present invention, the aliphatic di-nitrile
compound is preferably succinonitrile.
Moreover, in the present invention, the
decomposition product of the compound of Formula 1 has
an opened-ring structure.
Brief Description of the Accompanying Drawings
FIGS. 1 to 3 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
wliich the batteries are charged to 4.2V. Herein, FIG. 1
is for Example 1, FIG. 2 for Comparative Example 1, FIG.
3 for Comparative Example 2.
FIG. 4 is a graphic diagram showing the results of
heat generation analysis conducted using differential
scanning calorimetry (DSC) in order to examine the
thermal safety of each of the batteries manufactured in
Example 1 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 FIGS. 1 to 3) .
When the compound of Formula 1 or its
decomposition product and the aliphatic di-nitrile

compound are used in combination as additive, 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 such as a fluoroethylene
carbonate 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 (CI) ) 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, the compound of Formula 1 such as a
fluoroethylene carbonate is so thermally fragile to be
easily decomposed at high temperature and to generate a
large amount of gas. The generated gas can vent a pouch-
typed or can-typed battery case, thereby accelerating
the combustion of the electrolyte and causing the

ignition and explosion of the battery due to internal
short circuits
That is, 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 FIG. 2).
Accordingly, the present invention is characterized in
that the aliphatic di-nitrile compound is used in
combination with the compound of Formula 1 or its
decomposition product.
When the aliphatic di-nitrile compound is used in
combination with the compound of Formula 1 or its
decomposition product, the aliphatic di-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 (ex. linear
carbonates or cyclic carbonates) 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. 4).
Also, the continuous interaction chemically
between the compound of Formula 1 and the cyano (-CN)
functional group of the nitrile compound prevents a
large amount of gas generation occurred when using the
compound of Formula 1 alone.
In short, 1) the compound of Formula 1 or its
decomposition product and 2) an aliphatic di-nitrile
compound such as succinonitrile 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 di-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 di-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(see Table 2).

When considering this effect together with an
improvement in the performance of a high-capacity
battery, 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.
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 in the inventive
electrolyte is preferably 1-10 wt%, and more preferably
1-5 wt%. The compound of Formula 1 has a high viscosity,
and thus when the compound of Formula 1 is used in an
excessive amount, the ion conductivity of the
electrolyte can be reduced and the mobility of Li ion
can be inhibited, causing to a reduction of the cycle
life and capacity of battery.
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.

The inventive electrolyte may contain as an
additive an aliphatic mono-nitrile compound having one
cyano (-CN) functional group such as R-CN, wherein R is
aliphatic hydrocarbon etc.).
The inventive non-aqueous electrolyte for lithium
secondary batteries contain a general 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 LiCIOa,
LiCF3S03, LiPF6, LiBF4, LiAsF6, LiSbF6, LiN (CF3S02) 2,
LiN(C2F5S02)2, L1AIO4, LiAlCl4, LiS03CF3, and
LiN (CxF2x+iS02) (CyF2y+iS02) (x and y = natural numbers).
Meanwhile, the aliphatic di-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 di-nitrile
compound is introduced into an electrolyte, and then a
complex is formed between the surface of a cathode
active material and the aliphatic di-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 di-nitrile

compound is formed by dipping a cathode, comprising a
cathode active material coated on a collector, into an
electrolyte containing the aliphatic di-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 18 0 °C or lower. Otherwise, although the
high-temperature heat treatment depends on the kind of
the aliphatic di-nitrile compound, it may be performed
at such a temperature range as to prevent excessive
evaporation of the aliphatic di-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 4 0 °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 LiCo02, LiNi02, LiMn204, LiMn02, and
LiNii-xCoxMy02 (wherein 0:2 X 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,
Ti02 and Sn02) 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 1M LiPF6
solution having a composition of EC: EMC = 1: 2. To the
electrolyte, 1 wt % of fluoroethylene carbonate and 2
wt % of succinonitrile were added. Artificial graphite
c ■ •

and LiCoC>2 were used as an anode active material and a
cathode active material, respectively. Then, a 3443 size
of lithium polymer battery was manufactured according to
a conventional method and aluminum laminate was used as
the battery package.
Example 2
A lithium polymer battery was manufactured in the
same manner as in Example 1, except that 3. wt% of
fluoroethylene carbonate was used instead of 1 wt% of
fluoroethylene carbonate.
Example 3
A lithium polymer battery was manufactured in the
same manner as in Example 1, except that 5 wt% of
fluoroethylene carbonate was used instead of 1 wt% of
fluoroethylene carbonate.
Comparative Example 1
A lithium polymer battery was manufactured in the
same manner as in Example 1, except that 1 wt% of
fluoroethylene carbonate was added and succinonitrile
was not added.
Comparative Example 2
A lithium polymer battery was manufactured in the
same manner as in Example 1, except that 2 wt% of
succinonitrile was added and fluoroethylene carbonate
was not added.
Comparative Example 3
A lithium polymer battery was manufactured in the
same manner as in Comparative Example 1, except that 3
wt% of fluoroethylene carbonate was used.
Comparative Example 4
A lithium polymer battery was manufactured in the
same manner as in Example 1, except that fluoroethylene
carbonate and succinonitrile were not added.
Comparative Example 5
A lithium polymer battery was manufactured in the

same manner as in Comparative Example 1, except that 5
wt% of fluoroethylene carbonate was used.
Comparative Example 6
A lithium polymer battery was manufactured in the
same manner as in Comparative Example 2, except that 5
wt% of butyronitrile was used instead of succinonitrile.

1. Test for Safety (1)
Each of the batteries manufactured in Example 1
and. Comparative Examples 1 and 2 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 3.
As can be seen in FIG. 1, only the case of the
battery containing 1 wt% of fluoroethylene carbonate
(FEC) and 2 wt% of the succinonitrile compound (SN)
added to the electrolyte solvent realized a thermally
stable battery at high temperature for 1 hour or longer
without ignition.
On the other hand, in the case of adding
fluoroethylene carbonate alone (FIG. 2) or the case of
"lidding oh'ly succinonitrile (FIG. 3), it could be seen
that the battery was ignited and exploded at a high
temperature above 150 °C without mTiTrifaTnirfg high-
temperature safety for 1 hour. 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.
2. Test for Safety (2)

Each of the batteries manufactured in Example 1
and Comparative Example 4 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 "C/min to 400 'Cto
measure temperature peaks corresponding to heat
generation.
As shown in FIG. 4, the battery (Comparative
Example 4) manufactured without the aliphatic di-nitrile
compound shows heat generation peaks at about 200 °C and
about 240 °C. 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 13 indicates heat generation caused by combined
factors including the reaction between the electrolyte
and the cathode, and the structural collapse of the
cathode. The battery comprising the non-aqueous
electrolyte containing succinonitrile 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 and the cathode surface.
3. Test for Safety (3)
Each battery obtained from Examples 1 and 2, and
Comparative Examples 1, 2, 3, 4 and 6 was tested under
the overcharge conditions of 12V/1C and 20V/1C in a
CC/CV (Constant Current/Constant Voltage) manner. The

above overcharge test was repeated many times and the
average values for the test results are shown in the
Table 1.
As shown in Table 1, only the case of the battery
containing fluoroethylene carbonate and succinonitrile
compound added to the electrolyte solvent showed a
excellent safety without ignition nor internal short
circuits, by controlling the oxidation of the
electrolyte and the exothermic reaction resulting from
the structural collapse of the cathode.
On the other hand, in the case of adding
fluoroethylene carbonate alone such as Comparative
Example 1 and 3 or the case of adding only aliphatic
mono-nitrile compound or the aliphatic di-nitrile
compound such as Comparative Example 2 and 6, it could
be seen that the frequency of the battery ignition at
over-charged state is not constant and is largely high.
For example, batteries were ignited while a high
temperature above 200 °C was detected inside the battery/
at surface of the battery.
Meanwhile, the case of adding neither aliphatic
mono-nitrile compound nor the aliphatic di-nitrile
compound(Comparative Example 4), all the batteries were
ignited.

4. Test for battery performance

Each battery obtained from Example 3 and
Comparative Examples 4 and 5 was stored at a high
temperature of 80°C for 10 days and tested for battery
performance. The test results are shown in the following
table 2. Exmaple 3 comprising the non-aqueous
electrolyte containing fluoroethylene carbonate and
succinonitrile added thereto according to the present
invention, showed excellent capacity restorability and
battery performance even after a high-temperature
storage.

Industrial Applicability
As can be seen from the foregoing, according to
the present invention, when the compound of Formula 1
and the aliphatic di-nitrile compound are used in
combination, they can show a synergic effect in terms of
securing safety at over-charged condition or in case of
a high-temperature storage, 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.

We Claim:
1. A non-aqueous electrolyte comprising a lithium salt and a solvent, the
electrolyte containing, based on the weight of the electrolyte, 1-5 wt% of a
compound of Formula 1 or its decomposition product, and 1-3 wt% of an aliphatic
di-nitrile compound of Formula 2:
[Formula 1]

wherein X is fluorine and Y is hydrogen, chlorine or fluorine,
[Formula 2]
N=C—R—C=N
wherein R is (CH2)n (n is an integer of 2-12).
2. The non-aqueous electrolyte as claimed in claim 1, wherein the aliphatic
di-nitrile compound is succinonitrile.
3. The non-aqueous electrolyte as claimed in claim 1, wherein the solvent
includes cyclic carbonates or linear carbonates,wherein the cyclic carbonates are
selected from the group consisting of ethylene carbonate(EC), propylene
carbonate(PC) and gamma-butyrolactone(GBL), wherein the linear carbonates are
selected from the group consisting of diethyl carbonate(DEC), dimethyl
carbonate(DMC), ethyl methyl carbonate(EMC) and methyl propyl
carbonate(MPC).

4. The non-aqueous electrolyte as claimed in claim 1, wherein the
electrolyte includes an aliphatic mono-nitrile compound.
5. The non-aqueous electrolyte as claimed in claim 1, wherein the
electrolyte includes a compound selected from alkylene compounds, sulfur-
containing compounds and lactam-based compounds, which can form a passivation
layer on an anode surface.
6. An electrochemical device comprising a cathode, an anode, and a non-
aqueous electrolyte as claimed in any of claims 1 and 2 to 5.
7. The electrochemical device as claimed in claim 6, the cathode has a
complex formed between a surface of a cathode active material and the aliphatic di-
nitrile compound

8. The electrochemical device as claimed in claim 7, the complex between
the cathode active material surface and the aliphatic di-nitrile compound is formed
by high-temperature treating the electrochemical device manufactured from an
electrolyte containing the aliphatic di-nitrile compound added thereto, or by
dipping the cathode, comprising the cathode active material coated on a collector,
into the electrolyte containing the aliphatic di-nitrile compound added thereto,
followed by heat treatment at high temperature.

9. The electrochemical device as claimed in claim 10, wherein the high-
temperature treatment is performed at a temperature of 30 °C or more before or
after assemblage of the electrochemical device.

ABSTRACT

NON-AQUEOUS ELECTROLYTE AND ELECTROCHEMICAL DEVICE WITH AN
IMPROVED SAFETY
The present invention discloses a non-aqueous electrolyte comprising a lithium salt and a
solvent, the electrolyte containing, based on the weight of the electrolyte, 1-5 wt% of a compound of
Formula 1 or its decomposition product, and 1-3 wt% of an aliphatic di-nitrile compound of Formula 2:
[Formula 1]

wherein X is fluorine and Y is hydrogen, chlorine or fluorine,
[Formula 2]
N=C—R—C=N
wherein R is (CH2)n (n is an integer of 2-12).

NON-AQUEOUS ELECTROLYTE AND ELECTROCHEMICAL DEVICE WITH AN IMPROVED SAFETY

Documents:

Inventors:

PCT Conventions: