KR100706654B1 - Nonaqueous electrolyte and lithium secondary battery comprising it - Google Patents

Abstract

A non-aqueous electrolyte solution and a lithium secondary battery comprising the same are provided.

The non-aqueous electrolyte solution includes an organic solvent, a lithium salt, and an additive containing an α-halogen substituted-xylene compound represented by the following Chemical Formula 1.

[Formula 1]

Wherein X ₁ , X ₂ and X ₃ are the same as or different from each other, are hydrogen or halogen, and at least one of X ₁ , X ₂ and X ₃ is halogen; n is an integer of 1-5.

Lithium secondary battery, electrolyte solution, α-halogen substituted-xylene-based compound

Description

Non-aqueous electrolyte solution and lithium secondary battery comprising same {NONAQUEOUS ELECTROLYTE AND LITHIUM SECONDARY BATTERY COMPRISING IT}

1 illustrates lithium _{secondary using} LiCoO ₂ as an active material of the positive electrode 100 and carbon (C) as an active material of the negative electrode 110, respectively, and using a non-aqueous electrolyte according to an embodiment of the present invention as the electrolyte solution 130. It is a schematic diagram of a battery.

2 is a graph showing the results of cyclic voltametry (CV) measurement of an electrolyte solution containing α-bromo-o-xylene.

3 is a graph showing the CV measurement results of the electrolyte solution added with o-xylene.

It is a graph which shows the CV measurement result of the electrolyte solution which does not add the (alpha)-halogen substitution- xylene type compound.

5 to 10 are measurements of voltage and current when the lithium secondary batteries of Examples 3 and 9 and Comparative Examples 1, 3, 4 and 5 were respectively overcharged at 780mA to 12V for 2 hours and 30 minutes respectively at 4.2V. A graph showing the results.

The present invention relates to a non-aqueous electrolyte and a lithium secondary battery comprising the same. More specifically, the present invention relates to a non-aqueous electrolyte that can improve the life characteristics and high temperature characteristics with stability during overcharging of a lithium secondary battery, and a lithium secondary battery comprising the same.

Secondary batteries are chemical cells that can be used semi-permanently because they can be recharged unlike primary batteries. These secondary batteries are exponentially increasing in size due to the recent mass distribution of laptops, mobile communication devices, and digital cameras. Doing.

Secondary batteries include lead-acid batteries, nickel-cadmium (Ni-Cd) batteries, nickel-hydrogen (Ni-MH) batteries, and lithium batteries, depending on the negative electrode material and the positive electrode material. The density is determined. Among these, lithium secondary batteries have been widely used as driving power sources for portable electronic devices because of their high energy density due to their low oxidation / reduction potential and molecular weight.

Among these lithium secondary batteries, a lithium secondary battery using a nonaqueous electrolyte includes a positive electrode active material such as a lithium metal mixed oxide coated on a metal as a positive electrode, and a negative electrode active material such as carbon material or metal lithium is coated on a metal as a negative electrode. It includes what has become. In addition, an electrolyte solution in which lithium salts are dissolved in an organic solvent is disposed between these positive and negative electrodes.

In such a lithium secondary battery, lithium ions (Li +) present in an ionic state in the electrolyte are moved from the positive electrode to the negative electrode during charging, and from the negative electrode to the positive electrode during discharge (the electrons are the positive electrode and the negative electrode at this time). It moves opposite to lithium ions along the connecting wire.) Generates electricity.

The average discharge voltage of the lithium secondary battery is about 3.6 to 3.7 V, and higher power can be obtained than other secondary batteries such as alkaline batteries, Ni-MH batteries, or Ni-Cd batteries. Electrochemically stable electrolyte is required in the voltage range of 0 to 4.2V.

In the lithium secondary battery, the electrolyte is a medium for transferring lithium ions between the positive electrode and the negative electrode, as described above, and must be stable in the operating voltage range of the battery, and have the ability to transfer ions at high speed.

In general, a non-aqueous carbonate-based organic solvent such as ethylene carbonate, dimethyl carbonate, diethyl carboate or the like is used as the solvent contained in the electrolyte of the lithium secondary battery. However, these organic solvents may be oxidatively decomposed by contact with the positive electrode at a voltage of about 6 V or more, for example, when the lithium secondary battery is overcharged to 4.2 V or more, thereby generating abnormal heat, and thus, explosion , There is a problem that does not ensure the stability of the lithium secondary battery due to the ignition.

Accordingly, many attempts have been made to secure stability during overcharging of a lithium secondary battery.

First, Japanese Patent Application Laid-Open No. 2000-156243 discloses an electrolyte solution containing an organic compound, such as an anisole derivative, biphenyl, or 4,4'-dimethylbiphenyl, having certain characteristics as an additive. In addition, this publication discloses that organic compounds, such as the anisole derivatives or biphenyl derivatives, produce redox shuttles in the cell to ensure the stability of the cell.

In addition, Japanese Patent Laid-Open No. 9-106835 discloses an electrolyte solution containing about 1 to 4% of a monomer such as biphenyl, 3-R-thiophene, 3-chlorothiophene or furan as an additive. This publication also discloses that monomers such as biphenyl are polymerized at a voltage exceeding the maximum operating voltage of the battery, thereby ensuring stability of the battery under conditions of overcharging.

In addition, Japanese Patent Laid-Open No. 10-275632 discloses a configuration in which a nonionic aromatic compound having an alkyl group is added as an additive to a secondary electrolytic solution containing a linear ester organic solvent, and cyclone as the nonionic aromatic compound. Hexylbenzene, toluene, hexyl trimellitate, dimethyl phthalate, dibutyl phthalate, butylbenzene, etc. are illustrated.

However, the additives such as biphenyl or cyclohexylbenzene used in the above-described prior arts do not guarantee satisfactory stability upon overcharging of the secondary battery, and also adversely affect the lifetime characteristics and high temperature characteristics of the secondary battery. Can be crazy

In more detail, the biphenyl or cyclohexylbenzene and the like may be oxidatively decomposed at a relatively low temperature of just over 40 ° C. and a relatively low voltage of just over 4.4 V, and the reaction product may accumulate on the surface of the positive electrode. Therefore, even when the secondary battery is operated under a normal operating voltage, when the secondary battery is stored under a high temperature or a condition of high voltage occurs locally in the secondary battery, the biphenyl or cyclohexylbenzene or the like is oxidized to decompose Can continue to accumulate on the surface. Therefore, when the secondary battery is used for a long time and the charge / discharge operation of many cycles is repeated, the content of the biphenyl or cyclohexylbenzene, etc. contained in the electrolyte decreases, so that the degree to which the secondary battery is overcharged is desired. It's hard to guarantee satisfactory stability. In addition, even when the secondary battery is not overcharged, as the biphenyl or cyclohexylbenzene continues to accumulate on the surface of the positive electrode under high temperature conditions or local high voltage conditions, the capacity of the secondary battery is greatly reduced, thereby reducing the secondary battery. The lifespan characteristics and the high temperature characteristics of are also significantly reduced.

Accordingly, the present invention is to provide a non-aqueous electrolyte that can sufficiently secure the stability during overcharging of a lithium secondary battery, and can improve the life characteristics and high temperature characteristics of the lithium secondary battery.

In addition, another object of the present invention to provide a lithium secondary battery containing the non-aqueous electrolyte.

The technical problems to be achieved by the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

In order to achieve the above object, the present invention provides a non-aqueous electrolyte solution containing an organic solvent, a lithium salt and an additive containing an α-halogen substituted-xylene-based compound represented by the following formula (1).

[Formula 1]

Wherein X ₁ , X ₂ and X ₃ are the same as or different from each other, are hydrogen or halogen, and at least one of X ₁ , X ₂ and X ₃ is halogen; n is an integer of 1-5.

In order to achieve the above another object, the present invention is a non-aqueous electrolyte solution containing an additive containing an organic solvent, a lithium salt and α-halogen substituted-xylene-based compound represented by the formula (1); An electrode part including positive and negative electrodes positioned to face each other with the non-aqueous electrolyte interposed therebetween; And it provides a lithium secondary battery comprising a separator for electrically separating the positive electrode and the negative electrode.

[Formula 1]

Wherein X ₁ , X ₂ and X ₃ are the same as or different from each other, are hydrogen or halogen, and at least one of X ₁ , X ₂ and X ₃ is halogen; n is an integer of 1-5.

Other specific details of the embodiments of the present invention are included in the following detailed description and the accompanying drawings.

Hereinafter, specific embodiments of the present invention will be described in detail to enable those skilled in the art to clearly appreciate. However, this is presented as an example of the present invention, whereby the present invention is not limited and the present invention is defined only by the scope of the claims to be described later.

The present invention basically provides a non-aqueous electrolyte solution containing an additive containing an organic solvent, a lithium salt and an α-halogen substituted-xylene compound represented by the following formula (1).

[Formula 1]

Wherein X ₁ , X ₂ and X ₃ are the same as or different from each other, are hydrogen or halogen, and at least one of X ₁ , X ₂ and X ₃ is halogen; n is an integer of 1-5.

The non-aqueous electrolyte solution includes an additive containing an α-halogen substituted-xylene compound represented by Chemical Formula 1. As will be described in more detail in the following examples, the α-halogen substituted-xylene-based compound is oxidized at a voltage at which the organic solvent of the electrolyte is oxidatively decomposed, that is, lower than about 6 V, but at a relatively high voltage of at least about 4.7 V or more. It decomposes and accumulates on the surface of the positive electrode.

Therefore, during overcharging of the lithium secondary battery, before the organic solvent is oxidatively decomposed by contact with the positive electrode to generate abnormal heat, the α-halogen substituted-xylene-based compound is first oxidatively decomposed and the reaction product of the positive electrode Since accumulated on the surface, it is possible to suppress the oxidative decomposition reaction of the organic solvent to ensure the stability during overcharging of the lithium secondary battery.

In addition, since the α-halogen substituted-xylene-based compound is oxidatively decomposed at a relatively high voltage of at least about 4.7 V and a correspondingly high temperature, the lithium secondary battery may be subjected to a high temperature when used at a normal operating voltage. Even if conditions of high voltage are preserved or locally occur in the lithium secondary battery, the additives can be oxidized and decomposed to continue to accumulate on the surface of the positive electrode. Therefore, even during long-term use of the lithium secondary battery, it is possible to reduce the decrease of the content of the additive and the capacity reduction of the lithium secondary battery due to the accumulation of the additive, thereby ensuring satisfactory stability during overcharging of the lithium secondary battery. It is possible to further improve the life characteristics and the high temperature characteristics of the lithium secondary battery.

The configuration of the non-aqueous electrolyte solution is as follows.

First, the non-aqueous electrolyte solution contains an organic solvent. At this time, the non-aqueous electrolyte solution does not contain water (H ₂ O) as defined by the term non-aqueous, but only an organic solvent.

Here, as the organic solvent, a carbonate organic solvent, an ester organic solvent, an ether organic solvent, a ketone organic solvent or an aromatic organic solvent may be used.

More specifically, the carbonate organic solvent is dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC ), Ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), fluoroethylene carbonate (FEC), vinylene carbonate (VC) or vinyl ethylene carbonate (VEC).

In addition, the ester organic solvents include γ-butylolactone (BL), decanolide, valerolactone, mevalolactone, caprolactone, n-methyl acetate, n-ethyl acetate, n-propyl acetate, and the like. The ether organic solvent may include dibutyl ether and the like.

The aromatic organic solvent may include fluorobenzene, 4chloro toluene (4CT), 4fluoro toluene (4FT), and the like.

Preferably, the organic solvent is at least one linear carbonate solvent selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC) and methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC ) And butylene carbonate (BC) may include one or more cyclic carbonate solvent selected from the group consisting of, wherein the linear carbonate solvent and the cyclic carbonate solvent in a mixing ratio of 1: 1 to 4: 1 Can be.

The cyclic carbonate-based solvent is large in polarity and sufficiently dissociates lithium ions, but has a disadvantage in that its ionic conductivity is small due to its large viscosity. Therefore, when the linear carbonate solvent having a small polarity but low viscosity is mixed with the cyclic carbonate solvent in a preferable ratio and included in the basic organic solvent of the non-aqueous electrolyte solution, the characteristics of the lithium secondary battery can be optimized.

In addition, the organic solvent is fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), γ- butyrolactone (BL), decanolide, valerolactone together with such carbonate solvent Selected from the group consisting of mevalolactone, caprolactone, n-methyl acetate, n-ethyl acetate, n-propyl acetate, dibutyl ether, fluorobenzene, 4chloro toluene (4CT) and 4fluoro toluene (4FT) It may further comprise one or more solvents.

In addition, various organic solvents usable for the lithium secondary battery can be used without limitation.

The non-aqueous electrolyte solution also contains a lithium salt as a solute.

More specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (C ₂ F ₅ SO _{3 ) 2, LiN (C 2 F} 5 SO 2) 2, LiN (CF 3 SO 2) 2. Using one salt selected from the group consisting of LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ) (where x and y are natural numbers), LiCl and LiI, or It can be mixed and used. In addition, various lithium salts usable for the lithium secondary battery can be used without limitation.

At this time, the lithium salt may be included in the non-aqueous electrolyte at a concentration of 0.6-2.0M with respect to the above-described organic solvent, it is more preferably contained at a concentration of 0.7 ~ 1.6M. If the concentration of the lithium salt is less than 0.6M, the electrical conductivity of the non-aqueous electrolyte solution containing the same decreases, so that the performance of the non-aqueous electrolyte which transfers ions at high speed between the positive electrode and the negative electrode of the lithium secondary battery decreases, and 2.0 M When exceeded, the viscosity of the non-aqueous electrolyte is increased, so that the mobility of lithium ions is reduced, and the low temperature performance is lowered.

On the other hand, the non-aqueous electrolyte solution, together with the organic solvent and the lithium salt contains an additive containing an α-halogen substituted-xylene compound represented by the following formula (1).

[Formula 1]

Wherein X ₁ , X ₂ and X ₃ are the same as or different from each other, are hydrogen or halogen, and at least one of X ₁ , X ₂ and X ₃ is halogen; n is an integer of 1-5.

Examples of the α-halogen substituted-xylene-based compound include α-fluoro-o-xylene, α-fluoro-m-xylene, α-fluoro-p-xylene, and α-chloro-o-xylene , α-chloro-m-xylene, α-chloro-p-xylene and α-bromo-o-xylene may be used, or a mixture of two or more compounds may be used. In addition, any conventionally known α-halogen substituted-xylene-based compound may be used without limitation.

In addition, the additive, together with the α-halogen substituted-xylene-based compound, includes a substance such as biphenyl, cyclohexylbenzene, chloro toluene, or fluorotoluene, which has conventionally been used as an additive in a non-aqueous electrolyte of a lithium secondary battery. Or it may contain two or more.

In addition, the α-halogen substituted-xylene-based compound is preferably included in an amount of 0.5-30 parts by weight based on 100 parts by weight of the organic solvent and the lithium salt, and more preferably 1-15 parts by weight. If the α-halogen substituted-xylene-based compound is included in less than 0.5 parts by weight, the improvement effect such as stability, life characteristics or high temperature characteristics at the time of overcharging of the lithium secondary battery is insignificant, and if included in excess of 30 parts by weight, Rather, the life characteristics of the lithium secondary battery are reduced.

On the other hand, in the non-aqueous electrolyte solution, the specific action exhibited by using the additive containing the α-halogen substituted-xylene-based compound is as follows.

In the case of using a lithium secondary battery under a normal operating voltage, the oxidative decomposition reaction caused by the contact between the negative electrode and the electrolyte and the resulting increase in the internal pressure of the gas and the battery are problematic. Therefore, the negative electrode is mainly formed by forming a film on the negative electrode. The method of preventing the reaction of the electrolyte solution has been considered. However, during overcharging of a lithium secondary battery or under high temperature conditions, oxidative decomposition of the electrolyte solution actively proceeds mainly on the surface of the positive electrode, which is a major cause of abnormal heat generation or an increase in the internal pressure of the battery.

To solve this problem, the non-aqueous electrolyte solution contains an α-halogen substituted-xylene-based compound which is oxidatively decomposed at a voltage of about 4.7V or more lower than the voltage at which the organic solvent is oxidatively decomposed (that is, about 6V). These additives first oxidize and generate gas while accumulating the reaction product on the surface of the positive electrode before the organic solvent is oxidatively decomposed by contact with the positive electrode to generate abnormal heat during overcharging of the lithium secondary battery. .

This accumulation reaction product forms a film, i.e., a passivation layer, on the surface of the positive electrode, thereby suppressing the oxidative decomposition reaction of the non-aqueous electrolyte solution containing the organic solvent. In particular, such a coating acts as a resistor and at the same time, it is difficult to re-dissolve in the electrolyte, so it effectively works to suppress overcharge. Therefore, the non-aqueous electrolyte solution may include an α-halogen substituted-xylene-based compound as an additive to reduce the amount of heat generated during overcharging, thereby preventing thermal runaway, thereby improving battery safety.

In addition, since the α-halogen substituted-xylene-based compound is oxidatively decomposed at a relatively high voltage of at least about 4.7 V and a correspondingly high temperature, the lithium secondary battery may be subjected to a high temperature when used at a normal operating voltage. Even if conditions of preservation or locally high voltage occur, the additives can be reduced to oxidatively decompose and continue to accumulate on the surface of the positive electrode. Therefore, even during long-term use of the lithium secondary battery, it is possible to reduce the decrease of the content of the additive and the capacity reduction of the lithium secondary battery due to the accumulation of the additive, thereby further improving the life characteristics and high temperature characteristics of the lithium secondary battery. Can be.

On the other hand, the above-mentioned non-aqueous electrolyte is stable in the temperature range of -20 ~ 60 ℃ and maintains stable characteristics even at a voltage of 4V, thereby improving the safety and reliability of the lithium secondary battery. Therefore, the non-aqueous electrolyte solution can be applied to any lithium secondary battery such as a lithium ion battery, a lithium polymer battery, without limitation.

The present invention also provides a non-aqueous electrolyte solution comprising an additive containing an organic solvent, a lithium salt and an α-halogen substituted-xylene compound represented by the following formula (1); An electrode part including positive and negative electrodes positioned to face each other with the non-aqueous electrolyte interposed therebetween; And it provides a lithium secondary battery comprising a separator for electrically separating the positive electrode and the negative electrode.

[Formula 1]

Wherein X ₁ , X ₂ and X ₃ are the same as or different from each other, are hydrogen or halogen, and at least one of X ₁ , X ₂ and X ₃ is halogen; n is an integer of 1-5.

FIG. 1 shows a schematic diagram of such a lithium secondary battery. In particular, LiCoO _{2 is used} as the active material of the positive electrode 100 and carbon (C) is used as the active material of the negative electrode, respectively. An embodiment of a lithium secondary battery used as) is schematically shown.

As shown in FIG. 1, a lithium secondary battery according to an exemplary embodiment of the present invention includes a positive electrode 100, a negative electrode 110, an electrolyte solution 130, and a separator 140.

However, since the non-aqueous electrolyte, which has been sufficiently described above, is used as the electrolyte 130 for the lithium secondary battery, further detailed description of the configuration of the non-aqueous electrolyte will be omitted.

On the other hand, the positive electrode 100, for example, using a positive electrode active material coated on a metal such as aluminum. In this case, although LiCoO ₂ is used as the positive electrode active material in FIG. 1, LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO _2, or LiNi _1-xy Co _x M _y O ₂ (0 ≦ _x ≦ ₁ , 0 ≤ y ≤ 1, 0 ≤ x + y ≤ 1, M may be a lithium intercalation compound such as a lithium metal oxide such as Al, Sr, Mg or La) or a lithium chalcogenide compound. In addition, without being limited thereto, any material usable as a positive electrode active material in a lithium secondary battery may be used.

In addition, the negative electrode 110 uses, for example, a negative electrode active material coated on a metal such as copper. In this case, in FIG. 1, for example, carbon (crystalline carbon or amorphous carbon) is used as the negative electrode active material. In addition, carbon composite, lithium metal, lithium alloy, and carbon-metal composite may be used. Without being limited to this, any material usable as a negative electrode active material in a lithium secondary battery can be used.

At this time, the metal used for the positive electrode 100 and the negative electrode 110 is a voltage applied from the outside during charging, and serves to supply a voltage to the outside during discharge, the positive electrode active material is a current collector that collects positive charges ( collector), the negative electrode active material serves as a current collector to collect negative charges.

On the other hand, the separator 140 serves to electrically separate the positive electrode 100 and the negative electrode 110.

As the separator 140, a single-layer separator made of polyethylene or polypropylene, a two-layer separator laminated with polyethylene / polypropylene, a three-layer separator laminated with polyethylene / polypropylene / polyethylene or polypropylene / polyethylene / polypropylene, and the like can be used. have.

Hereinafter, the configuration and operation of the present invention through the preferred embodiment of the present invention will be described in more detail. However, this is presented as a preferred example of the present invention and in no sense can be construed as limiting the present invention.

<Examples 1-9 and Comparative Examples 1-5>

A positive electrode slurry was prepared by mixing LiCoO ₂ as a positive electrode active material, polyvinylidene fluoride (PVDF) as a binder, and carbon as a conductive agent at a weight ratio of 92/4/4, and then dispersing it in N-methyl-2-pyrrolidone. It was. The slurry was coated on an aluminum foil having a thickness of 20 μm, dried, and rolled to prepare a positive electrode.

Crystalline artificial graphite as a negative electrode active material and PVDF as a binder were mixed at a weight ratio of 92/8, and then dispersed in N-methyl-2-pyrrolidone to prepare a negative electrode slurry. The slurry was coated on a copper foil having a thickness of 15 μm, dried, and rolled to prepare a negative electrode.

The positive electrode and the negative electrode thus prepared were wound and compressed using a polyethylene separator having a thickness of 16 μm and placed in a rectangular can of 30 mm × 48 mm × 6 mm. In addition, 1 M LiPF ₆ was added as a lithium salt to a non-aqueous organic solvent in which ethylene carbonate / ethyl methyl carbonate (EC / EMC) was mixed in half, and an additive was added to the electrolyte in the amount shown in Table 1 below. A liquid nonaqueous electrolyte was prepared. The non-aqueous electrolyte was injected into the electrolyte inlet of the square can, and then the inlet was sealed to prepare a square battery. At this time, the content of the additive shown in Table 1 is in parts by weight of the additive added to 100 parts by weight of the organic solvent and lithium salt.

TABLE 1

additive Addition amount (part by weight) Example 1 Alpha Bromo Ortho Xylene 1.0 Example 2 Alpha Bromo Ortho Xylene 5 Example 3 Alpha Bromo Ortho Xylene 10 Example 4 Alpha Bromo Ortho Xylene 20 Example 5 Alpha Bromo Ortho Xylene 30 Example 6 Alpha fluoro ortho xylene 5 Example 7 Alpha Chloro Ortho Xylene 5 Example 8 Alpha chloro meta xylene 5 Example 9 Alpha chloro para xylene 5 Comparative Example 1 - - Comparative Example 2 Orsso Xylene 5 Comparative Example 3 Biphenyl 3 Comparative Example 4 Cyclohexylbenzene 3 Comparative Example 5 Biphenyl / cyclohexylbenzene 3/3

Decomposition start voltage measurement

The ratio of Examples 2, 6, 7, 8, 9 and Comparative Examples 1, 2, 3, 4, to which the α-halogen substituted-xylene compound was added in the same amount in Examples 1-9 and Comparative Examples 1-5 The decomposition initiation voltage was measured by LSV (Linear sweep voltametry) of the aqueous electrolyte and is shown in Table 2 below.

Decomposition starting voltage measurement conditions were Pt as a working electrode, Li-metal as a reference electrode, Li-metal as a counter electrode, and measured at a scan rate of 1.0 mV / s in the voltage range of 3 ~ 7V.

TABLE 2

additive Breakdown Voltage (V) Alpha Bromo Ortho Xylene 4.72 Alpha fluoro ortho xylene 4.78 Alpha Chloro Ortho Xylene 4.75 Alpha chloro meta xylene 4.72 Alpha chloro para xylene 4.77 - 6.00 Orsso Xylene 4.60 Biphenyl 4.45 Cyclohexylbenzene 4.60 (4.50)

As shown in Table 2, the α-halogen substituted-xylene-based compound starts to decompose at a lower voltage than the organic solvent of the non-aqueous electrolyte, and therefore, will be oxidatively decomposed before the organic solvent upon overcharging of the lithium secondary battery. The fact was confirmed. The film is formed on the surface of the positive electrode by the oxidative decomposition of the α-halogen substituted-xylene-based compound, and since the film can prevent decomposition of the organic solvent, gas generation due to decomposition of the organic solvent can be suppressed. By reducing the pressure, the thickness of the battery after being fully charged can be reduced, and stability during overcharging of the lithium secondary battery can be ensured.

Of course, biphenyl and cyclohexylbenzene may also be helpful to some degree in ensuring the stability at the time of overcharge since decomposition starts to occur at a lower voltage than the organic solvent. However, the biphenyl and cyclohexylbenzene are decomposed at relatively low voltages of 4.45 V and 4.6 V (actually, even at about 4.5 V, a fine oxidative decomposition reaction was detected) so that the reaction product can accumulate on the surface of the positive electrode. It was confirmed that.

Therefore, even when the lithium secondary battery is operated under normal voltage, when stored under high temperature or when a condition of high voltage occurs locally, these additives decompose and the reaction product continues to accumulate on the surface of the positive electrode. Therefore, when the lithium secondary battery is used for a long time, it is difficult to ensure satisfactory stability at the time of overcharging because the content of the additive continues to decrease, and moreover, even under normal use conditions, the reaction product due to the decomposition of the additive is formed on the surface of the positive electrode. Since it continues to accumulate, the capacity | capacitance of a secondary battery is greatly reduced by that much, and also the life characteristic and high temperature characteristic also fall remarkably.

On the other hand, FIG. 2 shows the result of CV measurement of the electrolyte solution added with α-bromo-o-xylene, FIG. 3 shows the result of CV measurement of the electrolyte solution added with o-xylene, and FIG. The CV measurement result of the electrolyte solution which does not add the halogen substitution-xylene type compound is shown.

2 and 3, the oxidation potential is 4.72V when α-bromo-o-xylene is added and the oxidation potential is 4.65V when o-xylene is added. It can be seen that it is very low compared to the oxidation potential of the basic electrolyte (EC / EMC 1/2 by vol with 1M LiPF ₆ ).

For this reason, if α-bromo-o-xylene or o-xylene is added to the non-aqueous electrolyte, the above additives are first oxidized before the electrolyte is oxidized, thus forming a film on the positive electrode to decompose the electrolyte. Inhibition improves the safety of the lithium secondary battery in an overcharged state.

For reference, even in the case of the basic electrolyte, even though the oxidation reaction occurs, the organic solvent is decomposed without forming a film, so that only the gas is generated, so that the change of the surface of the positive electrode is insignificant. For this reason, the second cycle of FIG. 4 is also not much different from the first cycle. However, when α-bromo-o-xylene is added, the oxidation reaction product accumulates in the black tar shape on the positive electrode above the oxidation potential. Moreover, referring to FIG. 2, after the first cycle and the second cycle, an oxidation peak larger than the first cycle is formed, which causes the oxidation reaction product accumulated in the first cycle to promote the oxidation reaction in the second cycle. Because. Because of this, as the cycle is repeated, the oxidation reaction is accelerated and the continuous reaction occurs, so that the reaction product on the surface of the positive electrode is rapidly increased, so that the current is continuously consumed in the overcharge state of the lithium secondary battery and the electrolyte decomposition reaction is suppressed to improve safety. Secure. .

<Evaluation of battery thickness and life after charge>

After charging the lithium secondary battery prepared by injecting the non-aqueous electrolyte solution of Example 1-9 and Comparative Example 1-5 with a current of 166mA and a charging voltage of 4.2V under constant current-constant voltage (CC-CV) conditions, After standing for 1 hour, the battery was discharged to 2.75V with a current of 166mA and left for 1 hour.

After repeating this process three times, the battery was charged with 4.2V charging voltage for 2 hours and 30 minutes at a current of 780mA. Then, it was left for 4 days in a high temperature chamber of 85 ℃ and after the initial cell assembly was measured in the thickness change rate after the charge to the thickness of the cell is shown in Table 3 below. In addition, the lithium secondary batteries prepared by injecting the electrolyte solutions of Examples 1-9 and Comparative Examples 1 to 5 were charged to a charging voltage of 1C and 4.2V under CC-CV conditions, and cut-off voltages of 1C and 3V under CC conditions. To discharge. The charge and discharge were repeated 100 times and 300 times to measure the capacity retention rate (residual capacity relative to the initial capacity), and the results are shown in Table 3 below.

TABLE 3

additive Addition amount (part by weight) Thickness increase rate (85 ℃, 4day) Capacity maintenance rate (100 cycles) Capacity maintenance rate (300cycle) Example 1 Alpha Bromo Ortho Xylene 1.0 15% 85% 80% Example 2 Alpha Bromo Ortho Xylene 5 5% 87% 85% Example 3 Alpha Bromo Ortho Xylene 10 5% 90% 85% Example 4 Alpha Bromo Ortho Xylene 20 5% 85% 82% Example 5 Alpha Bromo Ortho Xylene 30 5% 75% 65% Example 6 Alpha fluoro ortho xylene 5 5% 87% 82% Example 7 Alpha Chloro Ortho Xylene 5 5% 87% 83% Example 8 Alpha chloro meta xylene 5 5% 87% 82% Example 9 Alpha chloro para xylene 5 5% 87% 84% Comparative Example 1 - - 35% 75% 70% Comparative Example 2 Orsso Xylene 5 25% 75% 70% Comparative Example 3 Biphenyl 3 55% 70% 65% Comparative Example 4 Cyclohexylbenzene 3 45% 75% 70% Comparative Example 5 Biphenyl / cyclohexylbenzene 3/3 42% 70% 62%

Referring to Table 3, Examples 1 to 9, compared with Comparative Examples 1 to 5, the lithium secondary battery has a small thickness increase rate and a small capacity decrease even during long-term use, even when stored at a high temperature, thereby significantly improving high temperature and life characteristics. It was found to indicate.

This is because biphenyl and cyclohexylbenzene used in Comparative Examples 1 to 5 are decomposed at a relatively low voltage, so that even when the lithium secondary battery is operated under a normal voltage, it is stored under a high temperature or a high voltage condition occurs locally. This is because the reaction product continues to accumulate on the surface of the positive electrode and the capacity of the secondary battery is greatly reduced by that amount.

<Overcharge characteristic evaluation>

5 to 10, respectively, measurements of voltage and current when the lithium secondary batteries of Examples 3 and 9 and Comparative Examples 1, 3, 4, and 5 were overcharged at 12C at 12C at 12C under 4.4V full charge The results are shown.

As shown in FIG. 5, in the case of Example 3, when the battery voltage reached 4.4 V and then overcharged to become an overcharged state, α-bromo-o-xylene started the decomposition reaction at 4.7 V and reached a voltage of 5.3 V. Rises and then decreases to 5.2V. In addition, as shown in Fig. 6, the α-chloro-p-xylene starts the decomposition reaction at 4.8 V, the voltage rises to 5.1 V, and then decreases to 5.0 V. These are respectively α-bromo-o- This is due to the oxidation reaction of xylene and α-chloro-p-xylene, which initiates the polymerization reaction and accumulates the polymerization reaction product on the positive electrode and generates heat of polymerization.

This heat causes the separator to shut down. Further overcharging in this state causes the conductive reaction product to accumulate in micropores that are not shut down, resulting in a micro short circuit between the positive electrode and the negative electrode, causing a current to flow, thereby increasing the voltage again. In addition, the temperature does not increase above a certain temperature and becomes a stable state.

Thus, in Examples 3 and 9 in which the α-halogen substituted-xylene-based compound was added, an internal short circuit was induced compared to Comparative Example 1 in which the α-halogen substituted-xylene-based compound was not added. This suppresses the voltage rise and thereby prevents thermal runaway during overcharging even if the current is continuously applied, and when charging stops, the voltage naturally drops to ensure sufficient stability of the lithium secondary battery.

Meanwhile, referring to FIGS. 8 to 10, when biphenyl or cyclohexylbenzene according to the prior art is used, it is impossible to secure stability at the time of overcharging alone, and when the two materials are mixed, stability at the time of overcharging to some extent is required. It was found to be possible.

Ten lithium secondary batteries of Example 2-9 and Comparative Example 1-5 were prepared, respectively, charged to 4.2V, and evaluated for stability against overcharge of 780mA / 12V. When the lithium secondary battery was overcharged at 780 mA / 12V for 2 hours and 30 minutes under CC / CV conditions, the state of the battery was evaluated and shown in Table 4 below.

TABLE 4

additive Addition amount (part by weight) 780mA / 2.5hr Example 2 Alpha Bromo Ortho Xylene 5 9L0, 1L5 Example 3 Alpha Bromo Ortho Xylene 10 9L0, 1L5 Example 4 Alpha Bromo Ortho Xylene 20 10L0 Example 5 Alpha Bromo Ortho Xylene 30 10L0 Example 6 Alpha fluoro ortho xylene 5 9L0, 1L5 Example 7 Alpha Chloro Ortho Xylene 5 8L0, 2L5 Example 8 Alpha chloro meta xylene 5 10L0 Example 9 Alpha chloro para xylene 5 10L0 Comparative Example 1 - - 10L5 Comparative Example 2 Orsso Xylene 5 10L5 Comparative Example 3 Biphenyl 3 2L0, 8L5 Comparative Example 4 Cyclohexylbenzene 3 10L5 Comparative Example 5 Biphenyl / cyclohexylbenzene 3/3 10L0

However, the number in front of L means the number of test cells.

Overcharge safety assessment criteria are as follows:

(L0: good, L1: leakage, L2: flash, L2: flame, L3: smoke, L4: fire, L5: burst)

As shown in Table 4, in the battery of Example 2-9, the α-halogen substituted-xylene-based compound dissolved in the non-aqueous electrolyte consumes an overcharge current, but the battery of Comparative Example 1 uses the α-halogen in the non-aqueous electrolyte. Since the substituted-xylene compound is not dissolved, the overcharge current is accumulated in the electrode as it is.

For this reason, in Comparative Example 1, the electrode becomes unstable and reacts with the organic solution of the non-aqueous electrolyte to generate heat. After the onset of heat generation, the temperature rises sharply, and even when the current is cut off, the battery temperature continuously increases, leading to ignition and explosion.

In contrast, in Example 2-9, in which the α-halogen substituted-xylene-based compound was added to the non-aqueous electrolyte solution, current blocking was promoted during overcharging and the polymerization reaction product accumulated on the surface of the positive electrode, resulting in polymerization of the positive electrode and the negative electrode. It acts as an electrical bridge between them to form a fine short. This causes a constant current to flow and the voltage to remain at a constant potential to stabilize the temperature of the battery. For this reason, the safety of the lithium secondary battery during overcharging was ensured. In addition, it has been found that after the current is interrupted, a fine short circuit occurs so that the voltage is not high even though the current flows, thereby reducing the heat generation of the battery. Further, the α-halogen substituted-xylene-based compound is oxidized when the lithium secondary battery is overcharged, consumes an overcharge current, generates heat, and the heat of the separator causes the separator to be thermally fused. In addition, the reaction product precipitates a solid on the separator, which also closes the pores of the separator and has conductivity, thereby forming a fine short circuit to stabilize the cell.

According to the present invention, while providing sufficient stability during overcharging of a lithium secondary battery, a non-aqueous electrolyte solution capable of improving the life characteristics and high temperature characteristics of a lithium secondary battery and a lithium secondary battery comprising the same are provided. can do.

Claims (10)

A non-aqueous electrolyte solution containing an organic solvent, a lithium salt, and an α-halogen substituted-xylene compound represented by the following general formula (1). [Formula 1]

Wherein X ₁ , X ₂ and X ₃ are the same as or different from each other, are hydrogen or halogen, and at least one of X ₁ , X ₂ and X ₃ is halogen; n is an integer of 1-5. The α-halogen substituted-xylene-based compound according to claim 1, wherein the α-halogen substituted-xylene-based compound is α-fluoro-o-xylene, α-fluoro-m-xylene, α-fluoro-p-xylene, α-chloro-o A non-aqueous electrolyte comprising at least one compound selected from the group consisting of -xylene, α-chloro-m-xylene, α-chloro-p-xylene and α-bromo-o-xylene. The non-aqueous electrolyte of claim 1, wherein the α-halogen substituted-xylene-based compound contains 0.5 to 30 parts by weight based on 100 parts by weight of the organic solvent and the lithium salt. According to claim 1, wherein the organic solvent is at least one linear carbonate solvent selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC) and methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate Non-aqueous electrolyte solution containing at least one cyclic carbonate solvent selected from the group consisting of (PC) and butylene carbonate (BC) in a mixing ratio of 4: 1 to 1: 1. The method of claim 4, wherein the organic solvent is fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), γ- butyrolactone (BL), decanolide, valerolactone, At least one selected from the group consisting of valerolactone, caprolactone, n-methylacetate, n-ethylacetate, n-propylacetate, dibutylether, fluorobenzene, 4chloro toluene (4CT) and 4fluoro toluene (4FT) A non-aqueous electrolyte solution further comprising a solvent. The method of claim 1, wherein the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (C ₂ F ₅ SO ₃ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ . LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ) (wherein x and y are natural numbers), LiCl and LiI, at least one selected from the group consisting of 0.6 to 2.0 in the organic solvent. Non-aqueous electrolyte solution contained in the concentration of M. Non-aqueous electrolyte solution of any one of Claims 1-6; An electrode part including positive and negative electrodes positioned to face each other with the non-aqueous electrolyte interposed therebetween; And Lithium secondary battery comprising a separator for electrically separating the positive electrode and the negative electrode. The method of claim 7, wherein the positive electrode is LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ and LiNi _1-xy Co _x M _y O ₂ (0≤x≤1, 0≤y≤1, 0≤x + y ≤ 1, M is Al, Sr, Mg or La) Lithium secondary battery is coated with an active material selected from the group consisting of. The method of claim 7, wherein the negative electrode is crystalline carbon, amorphous carbon, carbon composite, lithium metal, lithium alloy And a lithium secondary battery coated with an active material selected from the group consisting of carbon-metal composites. 8. The separator according to claim 7, wherein the separator is a single-layer separator made of polyethylene or polypropylene, a two-layer separator laminated with polyethylene / polypropylene, and a three-layer separator laminated with polyethylene / polypropylene / polyethylene or polypropylene / polyethylene / polypropylene. Lithium secondary battery selected from the group consisting of.

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