KR100709207B1 - A lithium secondary battery - Google Patents

Abstract

The present invention relates to a lithium secondary battery having excellent safety and high temperature storage property. The lithium secondary battery includes a positive electrode and a negative electrode capable of reversible intercalation / deintercalation of lithium, and an electrolyte, and includes at least one of a positive electrode and a negative electrode. Silver active material; Water-soluble polymer binders; And a water-soluble thickener, wherein the electrolyte includes a non-aqueous organic solvent including a lactone compound having a cyclic carbonate and an alkyl substituent, an ester compound having an electron withdrawing group, and two or more lithium salts, wherein at least one of the lithium salts is Lithium tetrafluoroborate.

Lactone, gamma valerolactone, gamma caprolactone, high temperature storage, safety

Description

Lithium Secondary Battery {A LITHIUM SECONDARY BATTERY}

1 is an exploded perspective view of a lithium secondary battery.

2 is a view showing the results of measuring the coulombic efficiency of the organic solvent used in the preparation of the electrolyte of the present invention.

<Description of the symbols for the main parts of the drawings>

1: lithium secondary battery 2: negative electrode

3: anode 4: separator

5: battery container

[Industrial use]

The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery comprising the same, and more particularly, to an electrolyte for a lithium secondary battery and a lithium secondary battery including the same, which may improve battery safety, high temperature storage, and electrochemical characteristics. .

[Prior art]

Lithium secondary batteries using nonaqueous electrolytes have high voltage and high energy density, and are excellent in storage performance and low temperature operation, and are widely used in portable consumer electronics products. In addition, research and development have been actively conducted to increase the size of the battery and to utilize it as an electric vehicle or a home nighttime power storage device. Moreover, in recent years, the battery of especially thin shape and high capacity is calculated | required, and the demand of the polymer battery or the thin lithium secondary battery of a laminated exterior is increasing.

However, since most of the solvents used in these solvents have a low flash point and high combustibility, there is a risk of ignition or explosion due to overcharging, heating, or the like. Therefore, in recent years, proposals for securing the safety of this battery have been increasing. For example, Japanese Unexamined Patent Application Publication No. 10-189043 discloses that non-aqueous electrolyte exhibits sufficient battery performance along with high-temperature characteristics, low-temperature characteristics, and cycle characteristics, by reducing halogenated carbonate in a nonaqueous electrolyte. An electrolytic solution is described.

Japanese Unexamined Patent Application Publication No. 11-40199 proposes to ensure safety by operating a safety valve by increasing the internal pressure of a battery when overcharged by mixing a halogenated carbonate with a nonaqueous electrolyte.

However, when a lithium secondary battery containing a halogenated carbonate mixed with a nonaqueous electrolyte is stored at a temperature of about 60 ° C. for several days, the film formed on the negative electrode surface is decomposed to generate gas, and the internal pressure of the battery is greatly increased. . In particular, in the thin lithium secondary battery of a polymer battery or a laminate exterior, it is a fatal problem that battery thickness increases by decomposition gas. In addition, in a polymer battery or a thin lithium secondary battery of a laminated exterior, there is a problem that the battery expands and deforms due to excessively rapid withstand pressure increase due to overcharging, thereby generating an internal short. In particular, when overcharged from a discharged state to a large current, the internal shortage is likely to occur due to lithium precipitation, and thus there is a problem that securing of safety is also difficult.

In addition, a method of ensuring safety by using a flash point containing propylene carbonate, gamma butyrolactone, or the like, or a nonaqueous electrolyte having a high combustion heat has been proposed, but a negative electrode produced by the propylene carbonate or gamma butyrolactone by these solvents Due to the poor durability of the coating, it is impossible to secure the life characteristics, which are the basic characteristics of the lithium secondary battery, and to ensure the reliability of the lithium secondary battery due to the swelling phenomenon of the battery when the life is deteriorated. do.

The present invention is to provide a lithium secondary battery excellent in safety, high temperature storage, and electrochemical properties in order to solve the above problems.

The present invention to achieve the above object,

In a lithium secondary battery comprising a positive electrode, a negative electrode, and an electrolyte capable of reversible intercalation / de-intercalation of lithium,

At least one of the positive electrode and the negative electrode is an active material; Water-soluble polymer binders; And water soluble thickeners,

The electrolyte comprises a non-aqueous organic solvent containing a lactone compound having a cyclic carbonate and an alkyl substituent, an ester compound having an electron withdrawing group, and two or more lithium salts, wherein at least one of the lithium salts is lithium tetrafluoroborate Provided is a lithium secondary battery.

Hereinafter, the present invention will be described in more detail.

The lithium secondary battery of the present invention comprises a positive electrode, a negative electrode, and an electrolyte capable of reversible intercalation / deintercalation of lithium, and at least one of the positive electrode and the negative electrode includes an active material, a water-soluble polymer binder, and a water-soluble thickener. .

Generally as the active material, any material capable of reversible intercalation / deintercalation of lithium used in a lithium secondary battery may be used. Preferred examples of the positive electrode active material include a composite compound of at least one selected from cobalt, manganese, and nickel and lithium, and specifically, a lithium-containing compound described below may be preferably used: Li _x Mn _1-y M _y A ₂ (1); Li _x Mn _1-y M _y O _2-z X _z (2); Li _x Mn ₂ O _4-z X _z (3); Li _x Mn _2-y M _y M'z A ₄ (4); Li _x Co _1-y M _y A ₂ (5); Li _x Co _1-y M _y O _2-z X _z (6); Li _x Ni _1-y M _y A ₂ (7); Li _x Ni _1-y M _y O _2-z X _z (8); Li _x Ni _1-y Co _y O _2-z X _z (9); Li _x Ni _1-yz Co _y M _z A _α (10); Li _x Ni _1-yz Co _y M _z O _2-α X _α (11); Li _x Ni _1-yz Mn _y M _z A _α (12); Li _x Ni _1-yz Mn _y M _z O _2-α X _α (13); Li _x Mn _2-yz M _y M'z A ₄ (14).

Wherein 0.9 ≦ x ≦ 1.1, 0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.5, and 0 ≦ α ≦ 2; M and M 'are the same or different, Mg, Al, Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Ni, Mn, Cr, Fe, Sr, V is selected from the group consisting of rare earth elements, A is selected from the group consisting of O, F, S and P, and X is selected from the group consisting of F, S and P.

Furthermore, lithium Fe, such as LiFeO ₂ , V ₂ O _5, TiS, MoS, an organic disulfide compound or an organic polysulfide compound, can be used.

Examples of the negative electrode active material include a carbonaceous material selected from the group consisting of artificial graphite, natural graphite, graphitized carbon fiber, graphitized mesocarbon microbeads, fullerene, amorphous carbon, or mixtures thereof. The carbonaceous material has a d ₀₀₂ interplanar distance of 3.35 to 3.38 and an Lc (crystallite size) by X-ray diffraction at least 20 nm and an exothermic peak at 700 ° C. or more. This is preferable. Moreover, the metallic substance which can be alloyed with lithium, or the composite containing this metallic substance and carbonaceous material can also be illustrated as a negative electrode active material. Examples of the metal that can be alloyed with lithium include Al, Si, Sn, Pb, Zn, Bi, In, Mg, Ga, and Cd.

It is preferable to have a non-fluorine-type organic polymer of the copolymer which has butadiene group as said water-soluble high molecular binder. Copolymers having a butadiene group include styrene-butadiene rubber (SBR), carboxy-modified styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), and acrylate-butadiene rubber. In addition, sodium polyacrylate, copolymers of propylene and olefins having 2 to 8 carbon atoms, copolymers of (meth) acrylic acid and alkyl esters of (meth) acrylic acid, and the like can also be used.

A water-soluble thickener is added to the water-soluble polymer binder to improve binding property.

As the water-soluble thickener, a cellulose compound such as carboxymethyl cellulose-alkali metal salt, hydroxypropylmethyl cellulose-alkali metal salt or methyl cellulose-alkali metal salt can be used. In the alkali metal salt, Na, K or Li may be used as the alkali metal. Thus, when the cellulose compound to which the alkali metal salt is added is used, when the cellulose compound is used alone, the water-soluble polymer binder and the cellulose compound Since both are nonconductors, the electron conduction path and the ion conduction path may be reduced, resulting in an increase in battery internal resistance, and consequently, a problem of deterioration of the high rate discharge characteristic of the battery may be prevented. Polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, polymethacrylic acid, polyethylene oxide, polyacrylamide, poly-N-isopropylacrylamide, poly-N, N-dimethylacrylamide, polyethyleneimine, polyoxy Ethylene, poly (2-methoxyethoxyethylene), poly (3-molpyridylethylene), polyvinylsulfonic acid, polyvinylidene fluoride, amylose, poly (acrylamide-co-diallyldimethyl Ammonium chloride) and the like can also be used as a thickener.

In the lithium secondary battery of the present invention, the content of the water-soluble polymer binder is preferably 0.5 to 10% by weight based on the total amount of the active material and the binder (hereinafter referred to as "mixing"). If the content of the binder is less than 0.5% by weight, the amount of the binder is insufficient, the physical properties of the electrode plate is lowered, so that the active materials in the electrode plate is dropped off, if larger than 10% by weight, the ratio of the active material and the conductive agent is reduced to decrease the battery capacity There is a problem.

The content of the water-soluble thickener is preferably 0.1 to 10% by weight of the mixture weight. If the content of the water-soluble thickener is less than 0.1% by weight, there is a problem that the coating of the active material composition is difficult because the viscosity of the active material composition is too low, and if the content of more than 10% by weight, the coating of the active material composition is difficult.

The positive electrode and the negative electrode of the present invention may further include an electrically conductive conductor. Specific examples thereof include nickel powder, cobalt oxide, titanium oxide, carbon, and the like. As carbon, Ketjen black, acetylene black, furnace black, graphite, carbon fiber, fullerene, etc. can be illustrated.

The positive electrode and the negative electrode are prepared by dispersing an active material powder, a water-soluble polymer binder and a water-soluble thickener in water to prepare a slurry, applying the slurry onto a metal current collector, and then drying and rolling the same. Furthermore, after dipping a metal current collector in the said slurry, it can also manufacture by drying. The form of the positive electrode and the negative electrode is generally a sheet-shaped negative electrode, but is not limited thereto, and may also be manufactured in a columnar shape, a disk shape, a plate shape, or a columnar shape.

In the case of using the conventional organic solvent-based binder-dispersion solution by using the water-soluble binder and the water-soluble thickener dispersed in the aqueous dispersion, it is excellent in terms of the environment at a low price since no special equipment for treating the organic solvent is required. In particular, excellent binding properties can be provided to carbon-based powders such as graphite used as the negative electrode active material.

The present invention also provides a lithium secondary battery having the positive electrode and the negative electrode. The lithium secondary battery includes a positive electrode, a negative electrode, and an electrolyte, and may include a separator as necessary. As the separator, any one can be used as long as it is used in a lithium secondary battery, and examples thereof include polyethylene, polypropylene, or a multilayer film thereof, polyvinylidene fluoride, polyamide, glass fiber, and the like.

The electrolyte of the lithium secondary battery of the present invention consists of a non-aqueous organic solvent and a lithium salt containing a lactone compound having a cyclic carbonate and an alkyl substituent.

The cyclic carbonate in the electrolyte is preferably ethylene carbonate, propylene carbonate, vinylene carbonate, butylene carbonate or mixtures thereof, more preferably ethylene carbonate. Since these cyclic carbonates are easily solvated with lithium ions, the ionic conductivity of the electrolyte can be increased.

The cyclic carbonate is 50% by volume or less, preferably 5% by volume to 30% by volume, more preferably 5% by volume to 20% by volume, most preferably 5% by volume to 15% by volume with respect to the non-aqueous organic solvent. Used.

The lactone compound having an alkyl substituent is a compound having an alkyl group as a substituent in the lactone cyclic compound. Preferred examples thereof include beta butyrolactone, gamma valerolactone, gamma caprolactone, gamma heptanolactone, gamma octanolactone, Gamanonalactone, gamma decanolactone, deltacaprolactone, deltaheptanolactone, deltaoctanolactone, deltanonlactone, deltadecanolactone, deltadodecanolactone, and the like. The lactone compound is used in an amount of 0.1 to 80% by volume, preferably 0.5 to 60% by volume with respect to the nonaqueous organic solvent.

In addition, the electrolyte further includes a low viscosity solvent, it is preferable that the low viscosity solvent is added in the range of 1% by volume to 50% by volume relative to the non-aqueous organic solvent. The low viscosity solvent is dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), tetrahydrofuran , 2-methyl tetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, acetonitrile, methyl pyroionate, dimethyl formamide, fluoroether and the like. As the fluoroether, HCF ₂ (CF ₂ ) ₃ CH ₂ OCF ₂ CF ₂ H, CF ₃ CF ₂ CH ₂ OCF ₂ CFHCF ₃ , HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H, HCF ₂ CF ₂ CH One or more of ₂ OCF ₂ CFHCF ₃ , HCF ₂ (CF ₂ ) ₃ CH ₂ OCF ₂ CFHCF ₃ may be preferably used.

In addition, the electrolyte may further include an unsubstituted lactone compound, it is preferably added in the range of 1% by volume to 60% by volume with respect to the non-aqueous organic solvent. As the unsubstituted lactone compound, beta propiolactone, gamma butyrolactone, delta valerolactone, epson caprolactone, or the like may be used.

The electrolyte of the present invention may further include an ethylene carbonate derivative represented by the following Chemical Formula 1.

[Formula 1]

Wherein X and Y are each independently an electron withdrawing group selected from the group consisting of hydrogen, halogen, cyano group (CN) and nitro group (NO ₂ ) and at least one of X and Y is halogen, cyano group (CN) and is an electron withdrawing group selected from the group consisting of a nitro group (NO ₂₎ is preferred.

Preferred examples of the ethylene carbonate derivatives include fluoroethylene carbonate, difluoroethylene carbonate, fluoropropylene carbonate, difluoropropylene carbonate, trifluoropropylene carbonate, fluorogamma butyrolactone, difluorogamma butyrolactone , Chloroethylene carbonate, dichloroethylene carbonate, chloropropylene carbonate, dichloropropylene carbonate, trichloropropylene carbonate, chloro gamma butyrolactone, dichloro gamma butyrolactone, bromoethylene carbonate, dibromoethylene carbonate, bromopropylene carbonate, Dibromopropylene carbonate, tribromopropylene carbonate, bromogamma butyrolactone, dibromo gamma butyrolactone, nitroethylene carbonate, nitropropylene carbonate, nitrogamma butyrolactone, cyanoethyl Carbonate, cyano and the like lactone as propylene carbonate, gamma -butyrolactone cyano.

The ester compound is added in an amount of 0.1 wt% or more and 25 wt% or less, preferably 0.5 wt% or more and 10 wt% or less with respect to the electrolyte. When the amount of the ester compound is less than 0.1% by weight, it is difficult to expect the effect of suppressing gas generation inside the battery, and when the amount of the ester compound exceeds 25% by weight, a thick conductive film is formed to impair the reversibility of the battery. The problem that the battery performance deteriorates occurs.

Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiSbF ₆ , LiAlO ₄ , LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ) (where x and y are natural water), LiCl, LiI, etc. As a lithium salt for lithium secondary batteries, what is conventionally known can be used. The lithium salt is preferably 0.1 mol / L or more and 2.0 mol / L or less, and more preferably 0.1 mol / L or more and 1.5 mol / L or less.

In addition, the electrolyte of the present invention includes lithium tetrafluoroborate (LiBF ₄ ) as the negative electrode film forming material. The LiBF ₄ is preferably used in the range of 0.001 mol / L or more and 1 mol / L or less with respect to the electrolyte. Further, if the amount of addition of LiBF ₄ is 0.001mol / less than L, it is not preferable because it is not possible to suppress the decomposition of the coating film high temperature during storage, the content of LiBF ₄ is more than 1mol / L, it is not preferable since the deterioration of the cycle characteristics.

According to the electrolyte configuration of the present invention, it is possible to improve the safety of the lithium secondary battery by improving the nonflammability of the electrolyte. In addition, a film of a lactone compound is formed on the surface of the negative electrode, and the film can suppress decomposition of the organic solvent, thereby improving cycle life characteristics of the lithium secondary battery. In addition, since the durability of the film formed on the surface of the negative electrode is not decomposed during high temperature storage, it is possible to suppress the generation of gas, so the high temperature storage characteristics are superior to the non-aqueous electrolyte made of a conventional carbonate solvent. LiBF ₄ also reforms the film during film formation on the cathode surface, preventing film decomposition during high temperature storage and suppressing gas generation. In addition, excessively rapid gas generation at the time of overcharging is suppressed, and internal short circuit caused by expansion deformation of the laminate exterior battery can be prevented to increase safety.

The lithium secondary battery of the present invention is manufactured by encapsulating the negative electrode, the positive electrode, the electrolyte, and the separator as necessary in a battery case. 1 is an exploded perspective view of a lithium secondary battery 1 which is one embodiment of the present invention. The lithium secondary battery 1 is cylindrical and has a negative electrode 2, a positive electrode 3, a separator 4 disposed between the negative electrode 2 and the positive electrode 3, a negative electrode 2, a positive electrode 3, and The main body consists of the sealing member which encloses the electrolyte, the cylindrical battery container 5, and the battery container 5 impregnated with the separator 4 as a main part. The lithium secondary battery 1 is configured by stacking the negative electrode 2, the positive electrode 3, and the separator 4 in order, and then storing the lithium secondary battery 1 in the battery container 5 in a state of being wound in a spiral shape.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only one preferred embodiment of the present invention and the present invention is not limited to the following examples.

(Examples and Comparative Examples: Production of Lithium Secondary Battery)

An electrolyte was prepared in the composition shown in Table 1 below. In Table 1, the composition of the non-aqueous organic solvent was expressed by volume ratio, and 1.3 mol / L LiPF ₆ and LiBF ₄ were used as lithium salts _. In Table 1, EC is ethylene carbonate, DEC is diethyl carbonate, EMC is ethyl methyl carbonate, GBL is gamma butyrolactone, GCL is gamma caprolactone, GVL is gamma valerolactone, and FEC is monofluoroethylene carbonate.

Non-aqueous organic solvent combination (% volume) Electrolyte salt Lactone Compounds (Volume%) EC DEC GBL GCL GVL LiPF ₆ LiBF ₄ Comparative Example 1 30 70 1.3M Comparative Example 2 30 70 1.3M Comparative Example 3 30 40 30 1.3M Example 1 30 70 1.3M Example 2 30 70 1.3M Example 3 30 40 30 1.3M GCL 3% Example 4 30 40 30 1.3M GVL 3% Example 5 30 40 30 1.3M 0.03M GCL 3% Example 6 30 40 30 1.3M 0.03M GVL 3%

For the positive electrode active material made of lithium cobalt oxide (LiCoO ₂ ), carbon black was mixed to prepare a mixture. In addition, an N-methylpyrrolidone solution in which polyvinylidene fluoride was dissolved was prepared. And the said mixture was mixed with N-methylpyrrolidone solution to make a slurry, and this slurry was apply | coated to aluminum foil by the doctor blade method. After apply | coating a slurry, it dried and cut | disconnected to rectangle, and produced the positive electrode in which the positive electrode is formed on the aluminum foil which is an electrical power collector.

Next, styrene-butadiene rubber, sodium carboxymethylcellulose, and artificial graphite were dispersed in water in water, and the slurry thus prepared was applied to copper foil by a doctor blade method. After apply | coating a slurry, it dried and cut | disconnected to rectangle to manufacture the negative electrode in which the negative electrode is formed on the copper foil which is an electrical power collector.

A polypropylene porous separator was inserted between the positive electrode and the negative electrode, and the cells were fabricated by swirling them in a spiral shape, which was inserted into a battery container made of aluminum laminate. Then, a predetermined amount of electrolyte was injected into the battery container in which the cell was inserted. The lithium secondary battery was manufactured by sealing a battery container after pouring and leaving it to stand for 24 hours. In addition, the size of the battery used for experiment used the aluminum laminated exterior of thickness 3.8mm, width 35mm, and height 62mm, and design capacity was 800 mAh.

Test Example 1: Coulomb Efficiency Analysis

Coulomb efficiency analysis results of the organic solvents used in the electrolytes of the lithium secondary batteries of Comparative Examples 1 to 3 and Examples 1 to 6 are shown in FIG. 2.

As shown in FIG. 2, GBL (gamma butyrolactone), GVL (gamma valerolactone), GCL (gamma caprolactone), and the like also have an initial charging time as in EC (ethylene carbonate), which is a typical negative electrode film former of a lithium ion battery. It can be seen that the material to form a film on the cathode. Thus, the negative film forming agent initially formed plays an important role in the lithium secondary battery. That is, the material forming the film on the surface of the cathode is Comparative Example 1 is EC, Comparative Example 2 and Comparative Example 2 is GBL, Example 1, Example 3, Example 5 is GCL, Example 2, Example 4 , Example 6 is GVL.

(Test Example: Characteristics of Organic Solvent)

The vaporization point, flash point and combustion heat of the organic solvents used in the electrolytes of Comparative Examples and Examples were measured and described in Table 2 below.

Vaporization Point (℃) Flash point (℃) Combustion (KJ / Kg) EC 243 160 14,695 EMC 93 24 19,780 DEC 126 31 21,114 GBL 205 98 24,110 GCL 219 98 31,072 GVL 210 100 29,870 FEC 250 122 10,672

Test Example 2: Battery Characteristic Evaluation

Experimental conditions of the Comparative Examples 1 to 3 and Examples 1 to 6 are the following table by measuring the shelf life characteristics, high temperature (60 ℃) life, overcharge characteristics, and storage stability at high temperature (80 ℃) It described in 3. Evaluation of each battery characteristic was performed as follows.

The normal temperature life characteristics and the high temperature life characteristics were evaluated by repeatedly charging and discharging the lithium secondary battery at room temperature or 60 ° C. The charging conditions were constant current-constant voltage charging, and constant current charging was performed at a current of 1 C until the voltage reached 4.2 V, followed by constant voltage charging at 4.2 V for 2 hours. In addition, discharge conditions were made into constant current discharge, and were made to discharge until the voltage reached 3.0V at 1C. Dose retention after 100 cycles is shown in Table 2. The capacity remaining ratio after 100 charge / discharge is a ratio of the discharge capacity at 100 charge / discharge to the discharge capacity at the time of charge / discharge once in a lifetime.

       The high temperature storage stability was evaluated by measuring the thickness of the battery after leaving it in a constant temperature oven at 80 ° C. for 5 days and measuring the thickness of the battery before the temperature cooled down.

      The overcharge characteristics were 0.5C constant current charge to 4.2V, followed by constant voltage charging at 4.2V for 2 hours, and after standing for 3 hours at room temperature, overcharge for 5 hours to 12V with a constant current of 2A.

Remaining discharge capacity (%) after 100 cycles 80% increase in thickness after 5 days Overcharge Characteristics in Charge (1.0C 12V) Comparative Example 1 97 23 explosion Comparative Example 2 30 270 No explosion Comparative Example 3 33 250 No explosion Example 1 84 13 No explosion Example 2 85 10 No explosion Example 3 94 16 No explosion Example 4 94 15 No explosion Example 5 95 2 No explosion Example 6 94 3 No explosion

As shown in Table 3, in Comparative Example 1 in which the negative electrode film was formed by EC, the life characteristics were excellent, but it can be seen that an explosion occurred during overcharging. As shown in Table 2, since 70% by volume of DEC having high combustion heat and low flash point was used, it can be seen that the amount of heat generated during overcharging reached the explosion stage. In the case of Comparative Example 2 and Comparative Example 3, since the electrolyte used used 60 to 100% by volume of solvents (EC and GBL) of high combustion heat and low flash point, which are more stable than the conditions of Comparative Example 1 in terms of flash point and combustion heat, The explosion does not occur during charging, but the service life is very poor. This shows that the negative electrode films formed under the conditions of Comparative Examples 2 and 3 are not suitable for the lithium ion secondary batteries in which charge and discharge are continuously performed.

On the other hand, in the case of Examples 1 to 4 using GCL, GVL, or the like as the cathode coating, it was found that not only did the explosion phenomenon occur during the overcharge experiment, but also the life characteristics were good. In addition, it can be seen that also excellent characteristics in comparison with Comparative Example 2 using gamma butyl lactone in the life characteristics and high temperature standing characteristics. This suggests that gamma valerolactone and gamma caprolactone can be used as a flame retardant solvent.

However, in the case of Examples 5 to 6 in which the electrolyte of the lithium ion battery is composed of mixed salts, it can be seen that the high temperature leaving characteristic is further improved.

That is, it can be seen that in the configuration using the mixed electrolyte salt as in Examples 5 and 6, a lithium ion battery system having both heat resistance and durability can be obtained.

The electrolyte for a lithium secondary battery of the present invention is excellent in safety during overcharging, excellent life characteristics at room temperature and high temperature, and improved high temperature storage property by mixing and using a lactone compound having an alkyl substituent group in an existing non-aqueous organic solvent.

Claims (28)

In a lithium secondary battery comprising a positive electrode, a negative electrode, and an electrolyte capable of reversible intercalation / de-intercalation of lithium, At least one of the positive electrode and the negative electrode is an active material; Water-soluble polymer binders; And water soluble thickeners, The electrolyte includes a non-aqueous organic solvent including a cyclic carbonate and a lactone compound having an alkyl substituent, an ester compound having an electron withdrawing group, and two or more lithium salts, and at least one of the lithium salts is lithium tetrafluoroborate (LiBF ₄ ), The cyclic carbonate is used in 5 to 50% by volume with respect to the non-aqueous organic solvent, The lactone compound having an alkyl substituent is beta butyrolactone, gamma caprolactone, gamma heptanolactone, gamma octanolactone, gamma nalactone, gamma decanolactone, deltacaprolactone, deltaheptanolactone, deltaoctano Selected from the group consisting of lactones, delta nolacactone, delta decanolactone, delta dodecanolactone, and mixtures thereof, Lactone-based compound having an alkyl substituent is a lithium secondary battery that is contained in 0.1 to 80% by volume relative to the non-aqueous organic solvent. The lithium secondary battery of claim 1, wherein the cathode comprises at least one compound selected from the group consisting of the following compounds as a cathode active material: Li _x Mn _1-y M _y A ₂ (1); Li _x Mn _1-y M _y O _2-z X _z (2); Li _x Mn ₂ O _4-z X _z (3); Li _x Mn _2-y M _y M'z A ₄ (4); Li _x Co _1-y M _y A ₂ (5); Li _x Co _1-y M _y O _2-z X _z (6); Li _x Ni _1-y M _y A ₂ (7); Li _x Ni _1-y M _y O _2-z X _z (8); Li _x Ni _1-y Co _y O _2-z X _z (9); Li _x Ni _1-yz Co _y M _z A _α (10); Li _x Ni _1-yz Co _y M _z O _2-α X _α (11); Li _x Ni _1-yz Mn _y M _z A _α (12); Li _x Ni _1-yz Mn _y M _z O _2-α X _α (13); Li _x Mn _2-yz M _y M'z A ₄ (14). Wherein 0.9 ≦ x ≦ 1.1, 0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.5, and 0 ≦ α ≦ 2; M and M 'are the same or different, Mg, Al, Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Ni, Mn, Cr, Fe, Sr, V is selected from the group consisting of rare earth elements, A is selected from the group consisting of O, F, S and P, and X is selected from the group consisting of F, S and P. The method of claim 1, wherein the cathode is a carbonaceous material selected from the group consisting of artificial graphite, natural graphite, graphitized carbon fiber, graphitized mesocarbon microbeads, fullerene, amorphous carbon, or a mixture thereof. Secondary battery. The method of claim 1, wherein the water-soluble polymer binder is a styrene-butadiene rubber (SBR), carboxy-modified styrene-butadiene rubber, sodium polyacrylate, copolymers of propylene and olefins of 2 to 8 carbon atoms, (meth) acrylic acid and (meth A lithium secondary battery which is at least one selected from the group consisting of a copolymer of alkyl acrylate ester, acrylonitrile-butadiene rubber (NBR), and acrylate-butadiene rubber. The method of claim 1, wherein the water-soluble thickener is a cellulose compound, polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, polymethacrylic acid, polyethylene oxide, polyacrylamide, poly-N-isopropyl acrylamide, poly- N, N-dimethylacrylamide, polyethyleneimine, polyoxyethylene, poly (2-methoxyethoxyethylene), poly (3-molpyridylethylene), polyvinylsulfonic acid, polyvinylidene fluoride, amylose ( amylose), and at least one lithium secondary battery selected from the group consisting of poly (acrylamide-co-diallyldimethylammonium chloride). The lithium secondary battery of claim 5, wherein the cellulose-based compound is at least one selected from the group consisting of cellulose-alkali metal salts, hydroxypropylmethyl cellulose-alkali metal salts, and methyl cellulose-alkali metal salts. The lithium secondary battery of claim 1, wherein the content of the water-soluble polymer binder is 0.5 to 10 wt% based on the total amount of the active material and the binder (hereinafter referred to as “mixing”). The lithium secondary battery of claim 1, wherein the content of the water-soluble thickener is 0.1 to 10 wt% of the weight of the mixture. The lithium secondary battery of claim 1, wherein the positive electrode and the negative electrode further include an electrically conductive conductive agent. The lithium secondary battery of claim 1, wherein the cyclic carbonate is at least one selected from the group consisting of ethylene carbonate, propylene carbonate, vinylene carbonate, butylene carbonate, and mixtures thereof. delete The lithium secondary battery of claim 1, wherein the cyclic carbonate is used in an amount of 5 to 30% by volume based on the non-aqueous organic solvent. The lithium secondary battery of claim 12, wherein the cyclic carbonate is used in an amount of 5 to 15% by volume based on the non-aqueous organic solvent. delete delete The lithium secondary battery of claim 1, wherein the lactone compound is used in an amount of 0.5 to 60 vol% based on the non-aqueous organic solvent. The lithium secondary battery of claim 1, wherein the ester compound having an electron withdrawing group is an ethylene carbonate derivative represented by Formula 1 below: [Formula 1]

Wherein X and Y are each independently an electron withdrawing group selected from the group consisting of hydrogen, halogen, cyano group (CN) and nitro group (NO ₂ ). The lithium secondary battery of claim 17, wherein at least one of X and Y is an electron withdrawing group selected from the group consisting of halogen, cyano group (CN), and nitro group (NO ₂ ). 18. The method of claim 17, wherein the ethylene carbonate derivative is fluoroethylene carbonate, difluoroethylene carbonate, fluoropropylene carbonate, difluoropropylene carbonate, trifluoropropylene carbonate, fluorogamma butyrolactone, difluorogamma Butyrolactone, Chloroethylene carbonate, Dichloroethylene carbonate, Chloropropylene carbonate, Dichloropropylene carbonate, Trichloropropylene carbonate, Chloro gamma butyrolactone, Dichloro gamma butyrolactone, Bromoethylene carbonate, Dibromoethylene carbonate, Bromo Propylene Carbonate, Dibromopropylene Carbonate, Tribromopropylene Carbonate, Bromogamma Butyrolactone, Dibromogamma Butyrolactone, Nitroethylene Carbonate, Nitropropylene Carbonate, Nitrogamma Butyrolactone, Cyanoethyl At least one lithium secondary battery selected from the group consisting of carbonate, cyanopropylene carbonate, cyanogammabutyrolactone and mixtures thereof. The lithium secondary battery of claim 1, wherein the ester compound having an electron withdrawing group is used in an amount of 0.1 wt% or more and 25 wt% or less with respect to the electrolyte. The lithium secondary battery of claim 1, wherein the electrolyte further comprises a low viscosity solvent. The lithium secondary battery of claim 21, wherein the low viscosity solvent is used in an amount of 1 to 50% by volume based on the nonaqueous organic solvent. The method of claim 21, wherein the low viscosity solvent is dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC ), Tetrahydrofuran, 2-methyl tetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, acetonitrile, methyl pyrionate, dimethyl formamide, fluoro At least one lithium secondary battery selected from the group consisting of ethers and mixtures thereof. The method of claim 1, wherein the lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiSbF ₆ , LiAlO ₄ , LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ) (where x and y are natural water), LiCl, LiI and mixtures thereof At least one lithium secondary battery. The lithium secondary battery of claim 1, wherein LiBF ₄ is used in an amount of 0.001 mol / L or more and 1 mol / L or less with respect to the electrolyte. The lithium secondary battery of claim 1, wherein the electrolyte further comprises an unsubstituted lactone compound. The lithium secondary battery of claim 26, wherein the unsubstituted lactone compound is at least one selected from the group consisting of beta propiolactone, gamma butyrolactone, deltavalerolactone, epsoncaprolactone, and mixtures thereof. The lithium secondary battery of claim 26, wherein the unsubstituted lactone compound is used in an amount of 1% by volume to 60% by volume with respect to the nonaqueous organic solvent.

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