KR20070097864A - Lithium secondary battery of improved stability and high temperature properties - Google Patents

Abstract

A lithium secondary battery using a surface-coated cathode active material and an electrolyte containing an additive is provided to improve high-temperature characteristics, high-temperature continuous charging characteristics and safety against overcharge under a high-voltage and high-current condition. A lithium secondary battery comprises: (a) a cathode active material capable of reversible lithium intercalation/deintercalation, made of a lithium transition metal oxide and surface-coated with a metal oxide or halide; (b) an anode active material capable of reversible lithium intercalation/deintercalation; (c) a porous separator; and (d) a non-aqueous electrolyte comprising (i) a lithium salt, (ii) a non-aqueous organic solvent, and (iii) a halogenated aromatic compound as a overcharge- preventing agent.

Description

Lithium Secondary Battery of Improved Stability and High Temperature Properties

The present invention relates to a lithium secondary battery, and more particularly, in a lithium secondary battery including a cathode active material of a lithium transition metal oxide, a metal oxide or a metal halide is coated on a surface of the lithium transition metal oxide. Since the halogenated aromatic compound is contained in the non-aqueous lithium electrolyte, high temperature performance and safety are improved, and continuous charging characteristics at room temperature and high temperature are improved without deterioration of battery performance, and in particular, overcharge safety at overvoltage and overcurrent It provides an improved lithium secondary battery.

Recently, as interest in energy storage technology has increased and its fields of application have been expanded and diversified to not only mobile phones, camcorders, notebook computers, but also electric vehicles and hybrid electric vehicles, the demand for secondary batteries as an energy source is rapidly increasing. Among such secondary batteries, many studies have been conducted on lithium secondary batteries of high energy density and discharge voltage, and they are commercially used and widely used.

In general, a lithium secondary battery uses a transition metal oxide such as LiCoO ₂ as a positive electrode active material and a carbon material as a negative electrode active material, a polyolefin-based porous separator is inserted between the negative electrode and the positive electrode, and a non-aqueous electrolyte solution having a lithium salt such as LiPF ₆ is used. It is prepared by putting. During charging, lithium ions of the positive electrode active material are released and inserted into the carbon layer of the negative electrode, and during discharging, lithium ions of the carbon layer are released and inserted into the positive electrode active material, and the non-aqueous electrolyte moves lithium ions between the negative electrode and the positive electrode. Acts as a medium. Such a lithium secondary battery should basically be stable in the operating voltage range of the battery and have a performance capable of transferring ions at a sufficiently high speed.

In such a lithium secondary battery, safety evaluation and securing safety are very important, and there is an urgent need for a battery in which safety is secured for ignition and smoke in the battery.

In addition to the advantages of having a high energy density and a discharge voltage as described above, the lithium secondary battery has a high operating potential of the battery, so that high energy may flow momentarily, and during overcharging, a lithium metal dendrite may be formed on the surface of the negative electrode. ) Phases can form and cause battery explosion or fire.

One of the most dangerous situations during the overcharge is a high temperature overcharge, the lithium ion battery is overcharged to 4.2 V or more, the electrolyte begins to decompose, and the higher the temperature, the easier it is to reach the ignition point and more likely to ignite. However, since oxygen is not supplied in the sealed space of the battery, ignition is unlikely to occur. LiCoO ₂ used as a positive electrode active material in a battery has a layer structure of 'O-Co-O' in which a Co layer is located between oxygen atom layers, and 'O-Co-O-Li' in which Li is located between these structures. It forms a crystal structure of -O-Co-O '. Since this structure is not stable, it tends to change into a stable spinel structure at high temperatures. The spinel has a molecular formula of LiCo ₂ O ₄ , and has less oxygen per unit cell than the layered structure, so that excess oxygen is transferred to the electrolyte to supply oxygen to the electrolyte that reaches the ignition point, causing explosion due to ignition.

Therefore, a method of installing a protection circuit or using a heat shield by a separator has been proposed as a method for preventing the explosion of the battery at such a high temperature or an overcharged state. However, the use of the protection circuit requires a separate space inside the battery, thereby limiting the miniaturization and cost of the battery pack, and the heat blocking mechanism by the separator may not work effectively when heat is generated rapidly. It is difficult to expect reliable operating characteristics.

Therefore, recently, a solution through an organic electrolyte additive has been proposed as a solution to the above problem. For example, as described in US Pat. No. 6,074,776, the aromatic compound added to the electrolyte under a high voltage higher than the average voltage. Polymerization to increase the internal resistance in the battery to block the flow of current, or as described in Japanese Patent Application Laid-Open No. 2000-215909, when the battery is overcharged by including a polycyclic aromatic compound and a benzene compound having side chains in the electrolyte. There is known a technique for suppressing the heat generation so that they are rapidly oxidatively decomposed to thermally block the membrane by Joule heat due to its decomposition heat or an increase in internal resistance and cause thermal runaway. In addition, Japanese Patent Application Laid-Open No. 2000-123867 describes a technique of adding a small amount of an ester compound (for example, vinylene carbonate) having a cyclic molecular structure and having a C═C unsaturated bond in a ring to an electrolyte solution. It is assumed that these additives are decomposed at the cathode or the anode to form a film on the electrode surface to suppress decomposition of the electrolyte.

However, safety mechanisms by the electrolyte additives generally have a tendency to cause Joule heat generation to vary according to the current value at the time of charging or the internal resistance of the battery, irregular timing, and deterioration of the battery performance.

Moreover, the necessity for batteries capable of operating at high voltages and high currents is increasing with the high functionality and versatility of devices to which the batteries are applied. However, the electrolyte additive as described above generally has a problem in that overcharge safety under high voltage and high current is inferior.

Therefore, there is a high demand for the development of a more effective technology that can ensure the safety of the battery at high temperature and overcharge without degrading the performance of the battery, and in particular, the battery safety even under high voltage and high current. to be.

Accordingly, an object of the present invention is to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

After extensive research and various experiments, the inventors have prepared secondary batteries prepared by coating a surface of a positive electrode active material with a metal oxide or a metal halide and adding a halogenated aromatic compound to a lithium electrolyte, thereby deteriorating the electrical characteristics of the battery. Without this, it has been found that high temperature storage characteristics and normal temperature and high temperature continuous charging characteristics are improved, and overcharge can be prevented, and in particular, overcharge safety at high voltage and high current is excellent. The present invention has been completed based on this finding.

Lithium secondary battery according to the present invention for achieving this object,

(a) a positive electrode active material of a lithium transition metal oxide capable of reversible storage and release of lithium and whose surface is coated with a metal oxide or metal halide;

(b) a negative electrode active material capable of reversible storage and release of lithium;

(c) a porous separator; And

(d) a nonaqueous electrolyte containing (i) a lithium salt, (ii) a non-aqueous organic solvent and (iii) a halogenated aromatic compound as an overcharge inhibitor;

It is configured to include.

Therefore, the lithium secondary battery according to the present invention is characterized in that a metal oxide or metal halide is coated on the surface of the positive electrode active material, and a halogenated aromatic compound as an overcharge inhibitor is added to the electrolyte.

The metal oxide or metal halide coating layer improves the high temperature storage characteristics of the battery by the action of inhibiting the reaction between the positive electrode and the electrolyte, and also improves the trickle charge at room temperature and high temperature.

The halogenated aromatic compound improves the safety of the battery by reducing the amount of heat generated in the battery during overcharging to prevent thermal runaway phenomenon. In particular, at a high temperature, electrolyte decomposition on the surface of the positive electrode becomes active, thereby increasing the internal pressure of the battery, and the compound oxidizes and decomposes on the surface of the positive electrode before the non-aqueous organic solvent, and forms a film on the surface. Silver is effective in suppressing overcharge due to its ability to act as a resistor and difficult to re-dissolve in the electrolyte.

However, a secondary battery to which only one of the above components is applied, that is, a secondary battery in which only a coating layer of a metal oxide or a metal halide is formed on the surface of a positive electrode active material, and a secondary battery in which only a halogenated aromatic compound as an overcharge inhibitor is added to the electrolyte Batteries are not excellent in overcharge safety under high voltage and high current, respectively. On the other hand, the secondary battery including all of these components has been found to surprisingly improve the safety at high voltage, high current. This is an unexpected result.

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

As described above, the lithium secondary battery of the present invention has a positive electrode active material, a negative electrode active material, and a porous separator coated with a metal oxide or metal halide on the surface of a lithium transition metal oxide, a lithium salt, a non-aqueous organic solvent, and a halogenated aromatic It is comprised by containing the electrolyte solution of an oxide.

The positive electrode is prepared by, for example, applying a mixture of the positive electrode active material, the conductive agent, and the binder onto a positive electrode current collector, followed by drying, and optionally, a filler is further added to the mixture.

The positive electrode current collector is generally made to a thickness of 3 to 500 μm. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface treated with carbon, nickel, titanium, silver or the like can be used. The current collector may form fine irregularities on its surface to increase the adhesion of the positive electrode active material, and may be in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The lithium transition metal oxide may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + x} Mn _2-x O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO _2, and the like; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , Cu ₂ V ₂ O ₇ and the like; Ni-site type lithium nickel oxide represented by the formula LiNi _1-x M _x O ₂ , wherein M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x = 0.01 to 0.3; Formula LiMn _2-x M _x O ₂ (wherein M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (wherein M = Fe, Co, Lithium manganese composite oxide represented by Ni, Cu or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with alkaline earth metal ions; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ and the like can be used, but are not limited thereto.

Examples of the metal oxide or metal halide coated on the surface of the lithium transition metal oxide include Al ₂ O ₃ , ZrO ₂ , AlPO ₄ , MgO, SnO ₂ , and MgF ₂ , but are not limited thereto. Depending on the two or more of these may be used together. Among them, Al ₂ O ₃ is particularly preferable.

A method of coating a metal oxide or the like on the surface of the lithium transition metal oxide is known in the art, and examples thereof include sputtering, chemical vapor deposition (CVD), dip coating, and the like. have.

The coating layer may be formed on the entire surface of the lithium transition metal oxide or only part thereof. The thickness of the coating layer may be preferably 1 to 50 nm, and if the thickness of the coating layer is too thin, it is difficult to achieve desired high temperature storage characteristics, etc., while if the thickness is too thick, the performance of the battery decreases with increasing resistance. This is not so desirable.

The conductive agent is typically added in an amount of 1 to 50 wt% based on the total weight of the mixture including the positive electrode active material. Such a conductive agent is not particularly limited as long as it has conductivity without causing chemical change in the battery. Examples of the conductive agent include graphite such as natural graphite and artificial graphite; Carbon blacks such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used. In some cases, since the conductive second coating layer is added to the positive electrode active material, the addition of the conductive agent may be omitted.

The binder is a component that assists in bonding the active material and the conductive agent to the current collector, and is generally added in an amount of 1 to 50 wt% based on the total weight of the mixture including the positive electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, Polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers, and the like.

The filler is optionally used as a component for inhibiting expansion of the positive electrode, and is not particularly limited as long as it is a fibrous material without causing chemical change in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials, such as glass fiber and carbon fiber, are used.

The negative electrode is manufactured by coating and drying the negative electrode active material on a negative electrode current collector, and optionally, components of the positive electrode active materials as described above may be further included.

The negative electrode current collector is generally made to a thickness of 3 to 500 ㎛. Such a negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, the surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver, and the like, aluminum-cadmium alloy, and the like can be used. In addition, like the positive electrode current collector, fine concavities and convexities may be formed on the surface to enhance the bonding strength of the negative electrode active material, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

As said negative electrode active material, For example, carbon, such as hardly graphitized carbon and graphite type carbon; Li _x Fe ₂ O ₃ (0 ≦ _x ≦ 1), Li _x WO ₂ (0 ≦ _x ≦ 1), Sn _x Me _{1 - x} Me ' _y O _z (Me: Mn, Fe, Pb, Ge; Me' Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen, 0 <x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8); Lithium metal; Lithium alloys; Silicon-based alloys; Tin-based alloys; SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ , and oxides such as Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used. Preferably, graphitized carbon having a crystal surface distance constant d ₀₀₂ value of a carbonaceous material measured by X-ray diffraction method of 0.338 nm or less and a specific surface area of 10 m ² / g or less measured by BET method may be used.

The separator is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally from 0.01 to 10 ㎛ ㎛, thickness is generally 5 ~ 300 ㎛. As such a separator, for example, olefin polymers such as chemical resistance and hydrophobic polypropylene; Sheets or non-woven fabrics made of glass fibers or polyethylene are used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

As described above, the nonaqueous electrolyte contains a lithium salt, a nonaqueous organic solvent, and a halogenated aromatic compound.

The lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte, and for example, LiCl, LiBr, Lii, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , consisting of _{LiAsF 6, LiSbF 6, LiAlCl 4} , CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate, imide, etc. It is possible to mix and use 1 or 2 or more from a group.

As the non-aqueous organic solvent, for example, N-methyl-2-pyrrolidinone, propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), dimethyl carbonate Nate (DMC), diethyl carbonate (DEC), gamma-butylo lactone, 1,2-dimethoxy ethane, tetrahydroxyfuran (fran), 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3 Dioxolon, formamide, dimethylformamide, dioxolon, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxy methane, dioxolon derivatives, sulfolane, methyl sulfolane, 1 , 3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyroionate, ethyl propionate and the like can be used, but are not limited thereto. Preferably, a linear carbonate compound and a cyclic carbonate compound can be used in combination.

The halogenated aromatic compound as an overcharge preventing agent is a compound in which a substituent such as a halogen group or a halogen-substituted alkyl group is bonded to an aromatic structure such as phenyl, benzyl, naphthyl, preferably halogen-substituted toluene, and more preferably fluorine. -Substituted toluene. Preferred examples of the fluorine-substituted toluene include 4-FT (4-Fluoro toluene), 2-FT (2-Fluoro toluene), 3-FT (3-Fluoro toluene), and difluoro toluene. In some cases, two or more of them may be used together. Especially, 4-FT is especially preferable.

The amount of the halogenated aromatic compound added is 1 to 20% by weight, preferably 5 to 15% by weight based on the electrolyte. If the amount of the compound is too small, it is difficult to exert an effect of preventing overcharging. On the contrary, if the amount of the compound is too high, the amount of the electrolyte solution (content of the carbonate solvent) decreases, thereby deteriorating the rate characteristic and the cycle characteristic of the battery.

In addition to the above compounds, the nonaqueous electrolyte according to the present invention may be used for the purpose of improving charge and discharge characteristics, flame retardancy, and the like, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme , Hexaphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, trichloride Aluminum or the like may be added. In some cases, in order to impart nonflammability, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high temperature storage characteristics.

In the lithium secondary battery according to the present invention, the structure of the positive electrode, the negative electrode, and the separator is not particularly limited. For example, each of these sheets may be formed in a winding type or a stacking type to form a cylindrical or rectangular shape. Or it may be a form inserted into the case of the pouch type.

Hereinafter, the present invention will be described in detail by way of examples, but the scope of the present invention is not limited thereto.

Preparation Example 1 Preparation of Positive Electrode Active Material

Al ₂ O ₃ was coated on the surface of LiCoO ₂ , a lithium transition metal oxide, to a thickness of about 10 nm to synthesize a cathode active material for a lithium secondary battery.

Production Example 2 Preparation of Nonaqueous Electrolyte

5FT% of 4-FT (4-fluorotoluene: Aldrich's reagent) was added to an electrolyte of 1M LiPF ₆ EC / EMC = 1/2 (vol%) to prepare a nonaqueous electrolyte for lithium secondary batteries.

Example 1 Manufacture of Lithium Secondary Battery

95% by weight of the cathode active material synthesized in Preparation Example 1, 2.5% by weight of Super-P (conductor) and 2.5% by weight of PVDF (binder) were added to NMP (N-methyl-2-pyrrolidone) as a solvent to mix the positive electrode. After preparing the slurry, a positive electrode was prepared by coating, drying and pressing on an aluminum current collector.

95.5 wt% artificial graphite, 2.5 wt% Super-P (conductor) and 2 wt% PVDF (binder) were added to NMP as a solvent to prepare a negative electrode mixture slurry, which was then coated, dried and pressed onto a copper current collector. A negative electrode was prepared.

A lithium secondary battery was manufactured by using a nonaqueous electrolyte prepared in Preparation Example 2 with a porous separator (Celgard ^TM ) interposed between the positive electrode and the negative electrode.

Comparative Example 1 Fabrication of Lithium Secondary Battery

A lithium secondary battery was manufactured in the same manner as in Example 1, except that 4-FT was not added to the electrolyte.

Comparative Example 2 Fabrication of Lithium Secondary Battery

A lithium secondary battery was manufactured in the same manner as in Example 1, except that Bare-LiCoO ₂ , which was not coated with Al ₂ O ₃ , was used as the cathode active material.

Comparative Example 3 Fabrication of Lithium Secondary Battery

A lithium secondary battery was manufactured in the same manner as in Example 1, except that Bare-LiCoO ₂ , which was not coated with Al ₂ O ₃ , was used as a cathode active material and an electrolyte solution without adding 4-FT was used. .

Experimental Example 1

For the batteries of Example 1 and Comparative Examples 1 to 3, as shown in Table 1, the experiment to compare the high temperature storage characteristics, room temperature continuous charging, high temperature continuous charging, and overcharge safety was performed.

TABLE 1

As shown in Table 1, the battery of Example 1 according to the present invention is excellent in high temperature storage characteristics, swelling phenomenon was not observed even during continuous charging at room temperature and high temperature, problems in all battery cells even during overcharge It can be seen that does not occur.

On the other hand, in the battery of Comparative Example 1 in which Al ₂ O ₃ coated LiCoO ₂ was used as a positive electrode active material but 4-FT was not added to the electrolyte, swelling was observed during continuous high-temperature charging, and problems were observed in all batteries during overcharging. Occurred. In addition, Al ₂ O ₃ is the battery of Comparative Example 3 using a coating that is not LiCoO ₂ as the positive electrode active material, the swelling phenomenon even when the cell thickness change is also very large and room temperature continuous charging at the time of high-temperature storage has been observed. In addition, although the positive electrode active material was used for LiCoO ₂ without Al ₂ O ₃ coating, the battery of Comparative Example 1 in which 4-FT was added to the electrolyte was safe under normal temperature continuous charging and overcharge conditions, but the cell thickness at high temperature storage. The change was relatively large and swelling was observed during high temperature continuous charging.

Experimental Example 2

Experiments on the overcharge safety under high voltage and high current under the same conditions as in Table 2 for the batteries of Example 1 and Comparative Examples 1 to 3.

TABLE 2

As shown in Table 2, the battery of Example 1 according to the present invention was found to be safe at the time of overcharging under all the high voltage and the high current, but the batteries of Comparative Examples 1 to 3 can be seen that the safety is significantly reduced. have. In particular, it can be seen that the battery of Comparative Example 2, which was safe under the overcharge conditions of Experimental Example 1, could not secure the desired safety under high voltage and high current.

As described above, in the lithium secondary battery according to the present invention, the metal oxide is coated on the surface of the positive electrode active material and the halogenated aromatic compound is added to the lithium electrolytic solution, so that the high-temperature storage without deteriorating the electrical characteristics of the battery. The characteristics, the room temperature and high temperature continuous charging characteristics are improved, overcharge can be prevented, and in particular, the overcharge safety at high voltage and high current is excellent.

Those skilled in the art to which the present invention pertains will be able to perform various applications and modifications within the scope of the present invention based on the above contents.

Claims (12)

(a) a positive electrode active material of a lithium transition metal oxide capable of reversible storage and release of lithium and whose surface is coated with a metal oxide or metal halide; (b) a negative electrode active material capable of reversible storage and release of lithium; (c) a porous separator; And (d) a nonaqueous electrolyte containing (i) a lithium salt, (ii) a non-aqueous organic solvent and (iii) a halogenated aromatic compound as an overcharge inhibitor; Lithium secondary battery is configured to include. The lithium secondary battery of claim 1, wherein the metal oxide or metal halide is at least one selected from the group consisting of Al ₂ O ₃ , ZrO ₂ , AlPO ₄ , MgO, SnO _2, and MgF ₂ . The lithium secondary battery of claim 2, wherein the metal oxide or metal halide is Al ₂ O ₃ . The lithium secondary battery of claim 1, wherein the metal oxide or metal halide coating layer has a thickness of 1 to 50 nm. The lithium secondary battery of claim 1, wherein the halogenated aromatic compound is halogen-substituted toluene. The lithium secondary battery according to claim 5, wherein the halogen-substituted toluene is fluorine-substituted toluene. According to claim 6, The fluorine-substituted toluene is selected from the group consisting of 4-FT (4-Fluoro toluene), 2-FT (2-Fluoro toluene), 3-FT (3-Fluoro toluene) and Difluoro toluene Lithium secondary battery, characterized in that one or more than two. 8. The lithium secondary battery of claim 7, wherein the fluorine-substituted toluene is 4-FT. The lithium secondary battery of claim 1, wherein the halogenated aromatic compound is contained in an amount of 5 to 15 wt% based on the electrolyte. The method of claim 1, wherein the lithium transition metal oxide is LiCoO₂, LiNiO₂, LiMn₂O₄ And LiNi_1-XCo_XO₂Lithium secondary battery, characterized in that selected from the group consisting of. The method of claim 1, wherein the negative electrode active material is graphitized carbon having a crystal surface distance constant d ₀₀₂ of a carbonaceous material measured by X-ray diffraction method of 0.338 nm or less and a specific surface area of 10 m ² / g or less measured by a BET method. A lithium secondary battery characterized by the above. The method of claim 1, wherein the non-aqueous organic solvent is ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), diethyl carbonate (DEC), dimethyl carbonate (DMC) With ethyl methyl carbonate (EMC), gamma butyrolactone (GBL), sulfolane, methyl acetate (MA), ethyl acetate (EA), methyl propionate (MP) and ethyl propionate (EP) Lithium secondary battery, characterized in that the mixture of a linear carbonate compound and a cyclic carbonate compound selected from the group consisting of.