KR20130137958A - Nonaqueous electrolyte and lithium secondary battery containing the same - Google Patents

Abstract

The present invention relates to a nonaqueous electrolyte and a lithium secondary battery containing the same and, in particular, to a nonaqueous electrolyte including an organic solvent, electrolyte salt, and an ester compound having a specific structure; and a lithium secondary battery containing the same. If the nonaqueous electrolyte according to the present invention is applied to a lithium secondary battery, the ignition or explosion of a battery induced by heat generation can be prevented by inhibiting the rise of temperature inside the battery and the stability of the battery can be improved by rapidly causing a short circuit in a current interruption device and enabling the rapid operation of a safety device in the battery in case of the overcharge of the battery.

Description

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte and a lithium secondary battery having the non-aqueous electrolyte,

The present invention relates to a nonaqueous electrolyte and a lithium secondary battery having the same, and more particularly, to a nonaqueous electrolyte and a lithium secondary battery having the same to ensure excellent safety when the battery is overcharged.

Recently, interest in energy storage technology is increasing. As the application fields of cell phones, camcorders, notebook PCs, and electric vehicles further expand, there is a growing demand for higher energy density of batteries used as power sources for such electronic devices. Lithium secondary batteries are the ones that can best meet these demands, and researches on them are actively under way.

However, such a lithium secondary battery has safety problems such as ignition and explosion caused by using an organic electrolyte, and has a disadvantage in that manufacturing is difficult. In particular, as the utilization range of the lithium secondary battery has been dramatically expanded, a lithium secondary battery is used in various conditions and environments, and accordingly, a demand for a higher capacity lithium secondary battery is gradually increasing. In order to provide a high capacity lithium secondary battery, the operating range of the electrode is gradually expanding, and the shift to high voltage can benefit from the capacity, but the safety problem is also highlighted.

Until now, it is difficult to achieve high capacity and high safety at the same time, and there is a problem that safety becomes weak as the capacity is increased. Therefore, it is very important to secure the safety and safety evaluation of the battery, and many solutions have been proposed to solve such safety problems.

For example, a cylindrical lithium secondary battery having a large capacity requires particular attention to safety. Therefore, in the case of a cylindrical battery, various safety devices such as a current interrupt device (CID) and a PTC are involved, and when the internal pressure increases, the CID may be shorted to prevent the interruption of the current.

More specifically, one of the main things in the safety assessment is overcharging. This is a case in which a constant current is continuously given to deviate from the normally used voltage. If the situation persists, the internal pressure increases due to temperature rise and gas generation by side reaction between the cathode active material and the electrolyte. Without safety devices, batteries can ignite or explode.

In order to prevent this, the CID is used. When the internal pressure reaches a predetermined pressure or more when the battery is overcharged, overcharging can be prevented by a short circuit of the CID. Therefore, rapid short circuit of CID during overcharging is very important for securing battery safety.

Accordingly, the problem to be solved by the present invention is to provide a lithium secondary battery which is excellent in basic battery performance, suppresses the temperature rise during overcharging, and in particular, induces a short circuit of the current blocking device to improve battery safety. .

In order to solve the above problems, according to an aspect of the present invention, an organic solvent; Electrolyte salts; And it provides a nonaqueous electrolyte containing an ester compound represented by the formula (1).

[Formula 1]

In Formula 1,

R ₁ is a substituted or unsubstituted linear or branched alkyl group having 1 to 5 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 30 carbon atoms,

R ₂ is a substituted or unsubstituted linear or branched alkylene group having 1 to 5 carbon atoms,

R ₃ is hydrogen, a substituted or unsubstituted linear or branched alkyl group having 1 to 5 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 20 carbon atoms,

At least one of R ₁ and R ₃ is an aryl group.

In the term of the substituent used in the present invention, the alkyl group may be a straight or branched alkyl group having 1 to 5 carbon atoms, or may be a straight or branched alkyl group having 1 to 3 carbon atoms. Examples of such unsubstituted alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, t-butyl, pentyl, isoamyl and the like. One or more hydrogen atoms included in the alkyl group include a halogen atom, a hydroxyl group, -SH, a nitro group, a cyano group, a substituted or unsubstituted amino group (-NH ₂ , -NH (R), -N (R ') (R ''), R 'and R "are independently of each other an alkyl group having 1 to 10 carbon atoms), amidino group, hydrazine, or hydrazone group carboxyl group, sulfonic acid group, phosphoric acid group, C1-C20 alkyl group, C1-C20 halogenated Alkyl group, C1-C20 alkenyl group, C1-C20 alkynyl group, C1-C20 heteroalkyl group, C6-C20 aryl group, C6-C20 arylalkyl group, C6-C20 heteroaryl group, or C6-C20 It may be substituted with a heteroarylalkyl group.

Among the terms of the substituents used in the present invention, an aryl group is used alone or in combination to mean a carbocycle aromatic system having 6 to 30 carbon atoms containing one or more rings, which rings may be attached or fused together in a pendant manner. The term aryl includes aromatic radicals such as phenyl, naphthyl, tetrahydronaphthyl, indane and biphenyl. At least one hydrogen atom of the aryl group may be substituted with the same substituent as in the alkyl group.

In the term of the substituent used in the present invention, an alkylene group means a straight or branched chain saturated divalent hydrocarbon moiety of 1 to 5, or 1 to 4, or 1 to 3 carbon atoms. One or more hydrogen atoms included in the alkylene group include a halogen atom, cyano group, hydroxy group, nitro group, amino group (-NH 2, -NH (R), -N (R ') (R' '), R' and R Is independently an alkyl group having 1 to 10 carbon atoms, an alkyl group having 1 to 12 carbon atoms, a halogenated alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, an alkynyl group having 2 to 12 carbon atoms, and a 6 to 12 carbon atoms. And optionally substituted with an aryl group Examples of alkylene groups include methylene, ethylene, propylene, butylene, hexylene and the like.

R ₁ and R ₃ are each independently a methyl group, an ethyl group, a propyl group, isopropyl group, a phenyl group, or a benzyl group, and R ₂ is a methylene group, an ethylene group, a propylene group, or an isopropylene group, and the R ₁ And at least one of R ₃ may be a phenyl group or a benzyl group.

The ester compound includes phenoxyethyl propionate, 2-phenoxyethyl isobutyrate, phenoxyethyl benzoate, 2-isobutoxyethyl benzoate (2- isobutoxyethyl benzoate), 2-ethoxyethyl benzoate, 2-methoxyethyl benzoate, and 2-methoxyethyl benzoate may be any one selected from the group consisting of or a mixture of two or more thereof.

In addition, the organic solvent is ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2 3-pentylene carbonate, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), Methylpropyl carbonate, ethylpropyl carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ It may be any one selected from the group consisting of -valerolactone and ε-caprolactone or a mixture of two or more thereof.

In addition, the electrolyte salt is a negative ^{ion, F -, Cl -, Br} -, I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 _{^{PF 4 -, (CF 3)}} 3 PF 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 _{^{-, (CF 3 SO 2)}} 2 N -, (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- It may include any one selected from the group consisting of SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- or two or more thereof.

In addition, the ester compound may include 0.5 parts by weight to 10 parts by weight based on 100 parts by weight of the organic solvent.

Meanwhile, according to another aspect of the present invention, there is provided a lithium secondary battery including an anode, a cathode, and a nonaqueous electrolyte, wherein the nonaqueous electrolyte is a nonaqueous electrolyte described above.

Here, the anode may be provided with an anode active material layer containing a lithium metal, a carbon material, a metal compound, and a mixture thereof.

The metal compound may be Si, Ge, Sn, Pb, P, Sb, Bi, Al, Ga, In, Ti, Mn, Fe, Co, Ni, Cu, Zn, Ag, Mg, Sr, and Ba. It may be any one selected from the group consisting of, or a compound containing two or more metal elements thereof, or a mixture thereof.

The cathode may include a cathode active material layer containing a lithium-containing oxide.

Here, the lithium-containing oxide may be a lithium-containing transition metal oxide.

In addition, the lithium-containing transition metal _{oxides, Li x CoO 2 (0.5 <} x <1.3), Li x NiO 2 (0.5 <x <1.3), Li x MnO 2 (0.5 <x <1.3), Li x Mn 2 _{O 4 (0.5 <x <1.3} ), Li x (Ni a Co b Mn c) O 2 (0.5 <x <1.3, 0 <a <1, 0 <b <1, 0 <c <1, a + b + c = 1), Li _x Ni _{1 -y} Co _y O ₂ (0.5 <x <1.3, 0 <y <1), Li _x Co _{1 -y} Mn _y O _{2 <1), Li x Ni 1} -y Mn y O 2 (0.5 <x <1.3, O≤y <1), Li x (Ni a Co b Mn c) O 4 (0.5 <x <1.3, 0 <a <2, 0 <b <2 , 0 <c <2, a + b + c = 2), Li x Mn 2 -z Ni z O 4 (0.5 <x <1.3, 0 <z <2), Li x Mn _{2 -z} Co _z O ₄ (0.5 <x <1.3, 0 <z <2), Li _x CoPO ₄ (0.5 <x <1.3) and Li _x FePO ₄ Any one or a mixture of two or more thereof may be used.

The lithium secondary battery may be a cylindrical battery having a current blocking device (CID).

When the nonaqueous electrolyte according to the present invention is applied to a lithium secondary battery, it is possible to prevent the battery from igniting or exploding due to heat generation by suppressing an increase in the internal temperature of the battery when the battery is overcharged. At the same time, the safety of the battery can be improved by inducing a quick short circuit of the current interrupt device (CID) to enable rapid operation of the safety device in the battery.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments of the invention and, together with the description of the invention, It should not be construed as limited.
1 is a graph showing the overcharge voltage and temperature change of the lithium secondary battery manufactured according to an embodiment of the present invention.
2 is a graph showing changes in overcharge voltage and temperature of a lithium secondary battery manufactured according to a comparative example of the present invention.

Hereinafter, the present invention will be described in detail. The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

As described above, the lithium secondary battery is threatened with safety during overcharging, and one of the main reasons is that the non-aqueous electrolyte causes side reactions at the cathode and the anode.

Specifically, during overcharging, the cathode may rapidly generate heat due to a side reaction between the cathode active material, which is a lithium-containing oxide, and the electrolyte. Overcharged cathodes are very unstable in structure, especially at high temperatures. The overcharged cathode, which has an unstable structure, causes an exothermic reaction with the electrolyte and simultaneously releases activated oxygen. Due to the exothermic reaction and the oxidation reaction by the released oxygen, rapid heat generation occurs in the battery, and the battery may be exploded in a short time.

In addition, the SEI collapses at the interface of the anode using the carbon material, and a side reaction between the electrolyte and the exposed anode surface occurs. In addition, Li plating proceeds during overcharging, causing reaction between Li plated metal and electrolyte, causing more gas generation and even explosion.

In a typical cylindrical battery, when gas is generated inside the battery to increase the internal pressure, the current is blocked through the CID to suppress the increase in the internal pressure. However, during overcharging, heat generation inside the battery cannot be solved. In addition, depending on the electrolyte, there is a small amount of gas generation, which may slow down the CID short time.

The nonaqueous electrolyte according to the present invention is an organic solvent; Electrolyte salts; And by including an ester compound represented by the following formula (1), this problem is solved.

[Formula 1]

In Formula 1, R ₁ is a substituted or unsubstituted linear or branched alkyl group having 1 to 5 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, and R ₂ is 1 to A substituted or unsubstituted linear or branched alkylene group having 5, R ₃ is hydrogen, a substituted or unsubstituted linear or branched alkyl group having 1 to 5 carbon atoms, or a substituted 6 to 20 carbon atoms Or an unsubstituted aryl group, at least one of R ₁ and R ₃ is an aryl group.

When at least one of the R ₁ and the R ₃ is an aryl group, when the battery is overcharged, the ester compound represented by Formula 1 is polymerized to form a film on the surface of the positive electrode, thereby increasing the resistance of the battery. Increase and simultaneously inhibit the oxidative exothermic reaction of the electrolyte. In addition, the gas is additionally generated by the polymerization to increase the internal pressure, which causes the CID short circuit to occur more quickly, thereby ensuring the safety of the battery. In Formula 1, R ₁ and R ₃ are each independently a methyl group, an ethyl group, a propyl group, an isopropyl group, a phenyl group, or a benzyl group, and R ₂ is a methylene group, an ethylene group, a propylene group, or an isopropylene group And at least one of R ₁ and R ₃ may be a phenyl group or a benzyl group.

The ester compound includes phenoxyethyl propionate, 2-phenoxyethyl isobutyrate, phenoxyethyl benzoate, 2-isobutoxyethyl benzoate (2- isobutoxyethyl benzoate), 2-ethoxyethyl benzoate and 2-methoxyethyl benzoate may be any one or a mixture of two or more thereof selected from the group consisting of It is not limited only to this.

In addition, as the organic solvent included in the nonaqueous electrolyte according to the present invention, those conventionally used in the lithium secondary battery electrolyte may be used without limitation. For example, ether, ester, amide, linear carbonate, cyclic carbonate, and the like may be used alone. Or it can mix and use 2 or more types.

Among them, a carbonate compound which is typically a cyclic carbonate, a linear carbonate, or a mixture thereof may be included.

Specific examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, Propylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and halides thereof, or a mixture of two or more thereof. Examples of such halides include, but are not limited to, fluoroethylene carbonate (FEC) and the like.

Specific examples of the linear carbonate compound include any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate and ethyl propyl carbonate And mixtures of two or more of them may be used as typical examples, but the present invention is not limited thereto.

In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, are high viscosity organic solvents and have a high dielectric constant, so that they can dissociate lithium salts in the electrolyte better, and cyclic carbonates such as dimethyl carbonate and diethyl carbonate When a low viscosity, low dielectric constant linear carbonate is mixed in an appropriate ratio, an electrolyte having a higher ionic conductivity can be produced.

As the ether in the organic solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether and ethyl propyl ether or a mixture of two or more thereof may be used , But is not limited thereto.

And esters in the organic solvent include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ Any one or a mixture of two or more selected from the group consisting of -valerolactone and ε-caprolactone may be used, but is not limited thereto.

The non-aqueous electrolyte solution for lithium secondary batteries of the present invention may further include a conventionally known additive for forming an SEI layer within the scope of the present invention. As the additive for forming the SEI layer usable in the present invention, cyclic sulfite, saturated sultone, unsaturated sultone, and acyclic sulfone may be used alone or in combination of two or more thereof, but is not limited thereto. In addition, among the aforementioned cyclic carbonates, vinylene carbonate and vinylethylene carbonate may also be used as additives for forming an SEI layer for improving battery life.

The cyclic sulfites include ethylene sulfite, methyl ethylene sulfite, ethyl ethylene sulfite, 4,5-dimethyl ethylene sulfite, 4,5-diethyl ethylene sulfite, propylene sulfite, 4,5-dimethyl propylene sulfide Pite, 4,5-diethyl propylene sulfite, 4,6-dimethyl propylene sulfite, 4,6-diethyl propylene sulfite, 1,3-butylene glycol sulfite, and the like. 1,3-propane sultone, 1,4-butane sultone, and the like, and unsaturated sultone include ethene sultone, 1,3-propene sultone, 1,4-butene sultone, 1-methyl-1,3-prop Pen sulfone etc. are mentioned, As acyclic sulfone, divinyl sulfone, dimethyl sulfone, diethyl sulfone, methyl ethyl sulfone, methyl vinyl sulfone, etc. are mentioned.

The electrolyte salt contained in the nonaqueous electrolyte of the present invention may be an anion selected from the group consisting of F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N (CN) ₂ ^- , BF ₄ ^- , ClO ₄ ^{- _{6 -, (CF 3) 2}} PF 4 -, (CF 3) 3 PF 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 _{^{-, CF 3 CF 2 SO 3}} -, (CF 3 SO 2) 2 N -, (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- It may include any one selected from the group consisting of SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- or two or more thereof. Examples of the electrolyte salt include LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, chloroborane lithium, lithium lower aliphatic carboxylate, lithium tetraphenylborate, and the like.

The ester compound according to the present invention may be selected in an appropriate amount according to the specific type of the organic solvent, the electrolyte salt, the electrode active material. For example, the solvent may include 0.5 parts by weight to 10 parts by weight, or 1 part by weight to 10 parts by weight based on 100 parts by weight of the organic solvent. When the content satisfies this range, the battery performance is prevented from being deteriorated, and at the same time, the effect of suppressing the temperature rise during overcharging is further improved, thereby improving the safety of the battery.

Meanwhile, the lithium secondary battery of the present invention comprises an anode, a cathode, and a non-aqueous electrolyte, and the non-aqueous electrolyte is the non-aqueous electrolyte according to the present invention.

The lithium secondary battery of the present invention can be produced by a conventional method known in the art. For example, a porous separator may be inserted between the cathode and the anode, and the nonaqueous electrolyte solution according to the present invention may be added to the separator.

In the separator of the present invention, the porous substrate on which the porous coating layer is formed may be any porous substrate commonly used in an electrochemical device. For example, a polyolefin porous membrane or a nonwoven fabric may be used, It is not particularly limited.

Examples of the polyolefin-based porous film include polyolefin-based polymers such as polyethylene, polypropylene, polybutylene, and polypentene, such as high density polyethylene, linear low density polyethylene, low density polyethylene and ultra high molecular weight polyethylene, One membrane can be mentioned.

The nonwoven fabric may be, for example, polyethylene terephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate, or polycarbonate. ), Polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfidro, polyethylenenaphthalene, etc. Or the nonwoven fabric formed from the polymer which mixed these is mentioned. The structure of the nonwoven fabric may be a spun bond nonwoven fabric or a meltblown nonwoven fabric composed of long fibers.

The anode has a structure in which the anode layer including the anode active material and the binder is supported on one or both surfaces of the current collector.

As the anode active material, a lithium metal, a carbon material, a metal compound, or a mixture thereof, which may normally occlude and release lithium ions, may be used.

Concretely, as the carbon material, low-crystallinity carbon and high-crystallinity carbon may be used. Examples of the low crystalline carbon include soft carbon and hard carbon. Examples of highly crystalline carbon include natural graphite, Kish graphite, pyrolytic carbon, liquid crystal pitch carbon fiber high temperature sintered carbon such as mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch derived cokes.

The metal compound may be at least one selected from the group consisting of Si, Ge, Sn, Pb, P, Sb, Bi, Al, Ga, In, Ti, Mn, Fe, Co, Ni, Cu, Zn, Ag, And compounds containing at least one metal element. These metal compounds may be a single substance, an alloy, an oxide (TiO ₂ , SnO ₂ Or the like), a nitride, a sulfide, a boride, an alloy with lithium, or the like, but an alloy with a single substance, an alloy, an oxide, and lithium can be increased in capacity. Among them, it may contain at least one element selected from Si, Ge and Sn, and it may further increase the capacity of the battery including at least one element selected from Si and Sn.

The cathode has a structure in which a cathode layer including a cathode active material, a conductive material and a binder is supported on one or both surfaces of the current collector.

The cathode active material may include a lithium-containing oxide, and the lithium-containing oxide may be a lithium-containing transition metal oxide. Li _x CoO ₂ (0.5 <x <1.3), Li _x NiO ₂ (0.5 <x <1.3), Li _x MnO ₂ (0.5 <x <1.3), Li _x Mn _{2 O 4 (0.5 <x <1.3} ), Li x (Ni a Co b Mn c) O 2 (0.5 <x <1.3, 0 <a <1, 0 <b <1, 0 <c <1, a + b + c = 1), Li _x Ni _1-y Co _y O ₂ (0.5 <x <1.3, 0 <y <1), Li _x Co _{1 -y} Mn _y O _{2 <1), Li x Ni 1} -y Mn y O 2 (0.5 <x <1.3, O≤y <1), Li x (Ni a Co b Mn c) O 4 (0.5 <x <1.3, 0 <a <2, 0 <b <2 , 0 <c <2, a + b + c = 2), Li x Mn 2 -z Ni z O 4 (0.5 <x <1.3, 0 <z <2), Li x Mn _{2 -z} Co _z O ₄ (0.5 <x <1.3, 0 <z <2), Li _x CoPO ₄ (0.5 <x <1.3) and Li _x FePO ₄ Any one or a mixture of two or more thereof may be used. The lithium-containing transition metal oxide may be coated with a metal such as aluminum (Al) or a metal oxide. In addition to the lithium-containing transition metal oxide, sulfide, selenide and halide may also be used.

The conductive material is not particularly limited as long as it is an electron conductive material that does not cause a chemical change in an electrochemical device. In general, carbon black, graphite, carbon fiber, carbon nanotube, metal powder, conductive metal oxide, organic conductive material and the like can be used. Commercially available products as the conductive material include acetylene black series (manufactured by Chevron Chemical Co., (Chevron Chemical Company or Gulf Oil Company products), Ketjen Black EC series (Armak Company), Vulcan XC-72 (Cabot Company) and Super P (MM (MMM)). For example, acetylene black, carbon black and graphite.

The binder used for the cathode and the anode has a function of holding the cathode active material and the anode active material in the current collector and also connecting the active materials, and a commonly used binder may be used without limitation.

For example, it is possible to use vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, styrene Various types of binder polymers such as styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), and the like can be used.

The current collector used for the cathode and the anode may be any metal having a high conductivity and a metal which can easily adhere to the slurry of the active material and is not reactive in the voltage range of the battery. Specifically, examples of the current collector for a cathode include aluminum, nickel, or a combination thereof. Examples of the current collector for an anode include copper, gold, nickel, or a copper alloy or a combination thereof And the like. In addition, the current collector may be used by laminating the substrates made of the above materials.

The cathode and the anode are kneaded using respective active materials, conductive materials, binders, and high boiling point solvents to form an electrode mixture, and then the mixture is applied to a copper foil of a current collector, dried, and press-molded. It can be manufactured by heat-processing under vacuum at about 250 degreeC for 2 hours, respectively.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape, a square shape, a pouch shape, a coin shape, or the like using a can. Preferably a cylindrical cell may be used, more preferably the cylindrical cell may have a CID.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example  One

(1) Preparation of non-aqueous electrolyte

After preparing an organic solvent mixed in a weight ratio of ethylene carbonate (EC): propylene carbonate (PC): dimethyl carbonate (DMC) = 3: 1: 6, 3% by weight of phenoxyethyl propionate was added to the organic solvent. Mix as much as possible. Then, LiPF ₆ is added as a lithium salt so that it may become 1M, and a nonaqueous electrolyte solution is manufactured.

(2) Manufacture of cathode

Conductive material:: _{0 .2} LiCo Ni Mn _{0 .53 0 .27} O ₂ as a cathode active material, a binder of 96: 2: the total aluminum (Al) foil as a home after 2 made of a slurry by mixing in a weight ratio of, conventional methods Coated and dried to produce the cathode.

(3) Manufacture of anode

Artificial graphite: binder is mixed in a weight ratio of 98: 2 to prepare an anode active material slurry, and then coated on a copper (Cu) foil current collector in a conventional manner to prepare an anode.

(4) Production of lithium secondary battery

A cylindrical battery is prepared by a conventional method using a jelly roll prepared by interposing a polyethylene porous membrane between the prepared cathode and anode.

Example  2

A cylindrical battery was prepared in the same manner as in Example 1 except for using 2-phenoxyethyl isobutyrate instead of phenoxyethyl propionate.

Example  3

Same method as Example 1 except using methyl propionate (MP) instead of dimethyl carbonate (DMC) and 4% by weight of 2-methoxyethyl benzoate instead of 3% by weight of phenoxyethyl propionate To prepare a cylindrical battery.

Comparative Example  One

A cylindrical battery was prepared in the same manner as in Example 1 except that no phenoxyethyl propionate was added.

Comparative Example  2

A cylindrical battery was prepared in the same manner as in Example 1 except that methyl propionate was used instead of dimethyl carbonate and phenoxyethyl propionate was not added.

Test Example : Overcharge safety evaluation

(1) The batteries of Examples 1 to 3 and Comparative Examples 1 and 2 prepared above were subjected to constant current / constant voltage condition charging and 0.02C cut off charging at 0.5C rate. After that, overcharging was performed again under constant current / constant voltage at 2C 18.5V. On the other hand, the outside of the battery of Examples and Comparative Examples was wrapped with a heat insulating material prior to the present evaluation.

The CID short time and the maximum temperature of each battery were measured and listed in Table 1 below.

CID short time (minutes) Maximum temperature (℃) Example 1 6.8 103 Example 2 7.0 110 Example 3 8.0 105 Comparative Example 1 13.0 280 (fire) Comparative Example 2 12.7 223 (fire)

As shown in Table 1, it can be seen that the embodiments according to the present invention have a faster CID short time than the comparative examples, and in particular, the temperature increase suppression effect is very excellent.

(2) Meanwhile, the batteries of Example 1 and Comparative Example 1 prepared above were subjected to constant current / constant voltage conditions and 0.02C cut off charging at 0.5C rate. Thereafter, in the process of performing the overcharge in the constant current / constant voltage method at 2C 18.5V, voltage and temperature were measured over time, and the results are shown in FIGS. 1 (Example 1) and 2 (Comparative Example 1). .

1 and 2, the battery of Example 1 has a CID short time of 6.8 minutes, the battery of Comparative Example 1 is 13.0 minutes, it can be confirmed that the short circuit time of the battery of Example 1 is nearly doubled. This can be confirmed that the battery of Example 1 induces a fast short circuit of the CID to cut off the current, thereby preventing the battery from igniting or exploding, thereby improving the safety of the battery.

In addition, looking at the temperature of the battery according to the overcharge time according to Example 1 and Comparative Example 1, in the case of Example 1 was raised to 103 ℃ relatively quickly to about 7 minutes, the CID short-circuited, so that the temperature gradually decreases On the contrary, although the temperature did not reach the ignition temperature, the temperature of Comparative Example 1 was relatively slower than that of Example 1, but it increased to a maximum of 280 ° C. For this reason, it was confirmed that the safety of the battery of Example 1 was improved.

Claims (13)

Organic solvent;
Electrolyte salts; And
A nonaqueous electrolyte containing an ester compound represented by the following formula (1):
[Chemical Formula 1]

In Formula 1,
R ₁ is a substituted or unsubstituted linear or branched alkyl group having 1 to 5 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 30 carbon atoms,
R ₂ is a substituted or unsubstituted linear or branched alkylene group having 1 to 5 carbon atoms,
R ₃ is hydrogen, a substituted or unsubstituted linear or branched alkyl group having 1 to 5 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 20 carbon atoms,
At least one of R ₁ and R ₃ is an aryl group. The method of claim 1,
R ₁ and R ₃ are each independently a methyl group, an ethyl group, a propyl group, isopropyl group, a phenyl group, or a benzyl group, and R ₂ is a methylene group, an ethylene group, a propylene group, or an isopropylene group, and the R ₁ And at least one of R ₃ is a phenyl group or a benzyl group. The method of claim 1,
The ester compound includes phenoxyethyl propionate, 2-phenoxyethyl isobutyrate, phenoxyethyl benzoate, 2-isobutoxyethyl benzoate (2- isobutoxyethyl benzoate), 2-ethoxyethyl benzoate, 2-methoxyethyl benzoate, and 2-methoxyethyl benzoate. Nonaqueous electrolyte. The method of claim 1,
The organic solvent is ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3 Pentylene carbonate, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl Carbonate, ethylpropyl carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valle Non-aqueous electrolyte, characterized in that any one or a mixture of two or more selected from the group consisting of rolactone and ε-caprolactone. The method of claim 1,
The electrolyte salt includes, as ^{anions, F -, Cl -, Br} -, I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF 4 ^{_{-, (CF 3) 3 PF}} 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, _{(CF 3 SO 2) 2 N} -, (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- Non ^- aqueous electrolyte solution containing any one selected from the group consisting of SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- or two or more thereof. The method of claim 1,
The ester compound, 0.5 parts by weight to 10 parts by weight based on 100 parts by weight of the organic solvent, characterized in that the non-aqueous electrolyte. A lithium secondary battery comprising an anode, a cathode and a nonaqueous electrolyte,
The nonaqueous electrolyte is a lithium secondary battery, characterized in that the nonaqueous electrolyte of any one of claims 1 to 6. The method of claim 7, wherein
The anode comprises an anode active material layer comprising a lithium metal, a carbon material, a metal compound and a mixture thereof. 9. The method of claim 8,
The metal compound is a group consisting of Si, Ge, Sn, Pb, P, Sb, Bi, Al, Ga, In, Ti, Mn, Fe, Co, Ni, Cu, Zn, Ag, Mg, Sr, and Ba Lithium secondary battery, characterized in that any one selected from or a compound containing two or more metal elements or a mixture thereof. The method of claim 7, wherein
Wherein the cathode comprises a cathode active material layer containing a lithium-containing oxide. The method of claim 10,
Wherein the lithium-containing oxide is a lithium-containing transition metal oxide. 12. The method of claim 11,
The lithium-containing transition metal oxide is Li _x CoO ₂ (0.5 <x <1.3), Li _x NiO ₂ (0.5 <x <1.3), Li _x MnO ₂ (0.5 <x <1.3), Li _x Mn ₂ O ₄ (0.5 <x <1.3), Li _x (Ni _a Co _b Mn _c ) O ₂ (0.5 <x <1.3, 0 <a <1, 0 <b <1, 0 <c <1, a + b + c = 1), Li _x Ni _{1 -y} Co _y O ₂ (0.5 <x <1.3, 0 <y <1), Li _x Co _{1 -y} Mn _y O ₂ (0.5 <x <1.3, 0≤y <1 ), Li _x Ni _{1 -y} Mn _y O ₂ (0.5 <x <1.3, O≤y <1), Li _x (Ni _a Co _b Mn _c ) O ₄ (0.5 <x <1.3, 0 <a <2 , 0 <b <2, 0 <c <2, a + b + c = 2), Li _x Mn _{2 -z} Ni _z O ₄ (0.5 <x <1.3, 0 <z <2), Li _x Mn _{2 -z} Co _z O ₄ (0.5 <x <1.3, 0 <z <2), Li _x CoPO ₄ (0.5 <x <1.3) and Li _x FePO ₄ (0.5 <x <1.3) Or a mixture of two or more of these lithium secondary batteries. The method of claim 7, wherein
The lithium secondary battery is a lithium secondary battery, characterized in that the cylindrical battery provided with a current blocking element.

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