KR20060014280A - Non-aqueous electrolyte for secondary batteries and secondary batteries containing the same - Google Patents

Abstract

The present invention provides a non-aqueous electrolyte solution for a lithium secondary battery comprising an additive which inhibits the oxidative decomposition reaction of the electrolyte on the surface of the cathode by first oxidizing and forming a passivation layer on the surface of the cathode.

More specifically, the present invention provides a lithium secondary battery nonaqueous electrolyte and a lithium secondary battery comprising the nonaqueous electrolyte, characterized in that it comprises a lithium salt, a non-aqueous organic solvent and a halogenated phosphate ester.

According to the present invention, it is possible to suppress the thickness expansion of the battery even at high temperature storage after full charge without affecting the battery characteristics, thereby improving the reliability when the battery set is mounted. In addition, it is possible to prevent thermal runaway during overcharging and to improve the flame retardancy of the flammable electrolyte, thereby improving the safety of the lithium secondary battery.

Secondary Battery, Non-Aqueous Electrolyte, Halogenated Phosphate Ester

Description

Non-Aqueous Electrolyte for Lithium Secondary Battery and Lithium Secondary Battery Containing It {Non-Aqueous Electrolyte for Secondary Batteries and Secondary Batteries containing the Same}

1 is a result of high temperature inflation at 90 ° C. for 8 hours.

FIG. 2 shows the results of reactivity experiments of electrodes through cyclic voltammetry. FIG.

3 is a result of comparing the calorific value of the positive electrode through DSC.

4 is a result of comparing the calorific value of the cathode through DSC.

5 is a 3C-rate, 10V overcharge test results.

Recently, with the development of the high-tech electronic industry, it is possible to reduce the weight and weight of electronic equipment, thereby increasing the use of portable electronic devices. The need for a battery having a high energy density as a power source for such a portable electronic device has been increasing, and research on lithium secondary batteries has been actively conducted.

Lithium metal oxide is used as a positive electrode active material of a lithium secondary battery, and lithium metal, a lithium alloy, (crystalline or amorphous) carbon or a carbon composite material is used as a negative electrode active material.

The lithium secondary battery may be classified into a lithium ion battery, a lithium ion polymer battery, and a lithium polymer battery according to the type of separator and electrolyte used, and may be cylindrical, square or coin type depending on the form.

The average discharge voltage of the lithium secondary battery is about 3.6 to 3.7 V, and high power can be obtained as compared with other alkaline batteries, Ni-MH batteries, Ni-Cd batteries and the like. However, in order to produce such a high driving voltage, an electrochemically stable electrolyte composition is required in the charge and discharge voltage range of 0 to 4.2 V. For this reason, a mixture of non-aqueous carbonate solvents such as ethylene carbonate, dimethyl carbonate and diethyl carbonate is used as the electrolyte solution. However, the electrolytic solution having such a composition has a problem in that the battery characteristics are lowered at high rate charge / discharge compared to the aqueous electrolytic solution used in Ni-MH batteries or Ni-Cd batteries.

During the initial charging of the lithium secondary battery, lithium ions from the lithium metal oxide as the positive electrode move to the carbon electrode as the negative electrode and are intercalated with carbon. At this time, since lithium is highly reactive, it reacts with the carbon electrode to generate Li ₂ CO _3, LiO, LiOH, and the like to form a film on the surface of the negative electrode.

Such a coating is called a SEI (Solid Electrolyte Interface) film. The SEI film formed at the beginning of charging prevents the reaction of lithium ions with a carbon anode or other material during charging and discharging. It also acts as an ion tunnel to pass only lithium ions. The ion tunnel serves to prevent the organic solvents of the large molecular weight electrolytes that solvate lithium ions and move together to be co-intercalated with the carbon anode to collapse the structure of the carbon anode.

Therefore, once the SEI film is formed, lithium ions do not react sideways with the carbon negative electrode or other materials again, so that the amount of lithium ions is reversibly maintained. That is, the carbon of the cathode reacts with the electrolyte at the initial stage of charge to form a passivation layer such as an SEI film on the surface of the cathode to maintain stable charge and discharge without further decomposition of the electrolyte (J. Power Sources, 51 (1994), 79-104.

For this reason, the lithium secondary battery may maintain a stable cycle life after exhibiting no reaction of forming an irreversible passivation layer after the initial charging reaction.

However, there is a problem in that gas is generated inside the battery due to decomposition of the carbonate-based organic solvent during the SEI film formation reaction (J. Power Sources, 72 (1998), 66-70). Such gases include H ₂ , depending on the type of the non-aqueous organic solvent and the negative electrode active material. CO, CO ₂ , CH ₄ , C ₂ H ₆ , C ₃ H ₈ , C ₃ H ₆ and the like. Due to the gas generation inside the battery, the thickness of the battery is expanded during charging.

In addition, as time passes during high temperature storage after full charge, the passivation layer is gradually collapsed by the increased electrochemical energy and thermal energy, so that side reactions in which the exposed cathode surface reacts with the surrounding electrolyte continuously occur.

At this time, gas is continuously generated to increase the pressure inside the battery. The increase in the internal pressure causes a phenomenon in which the center portion of the specific surface of the battery is deformed, such as the rectangular battery and the lithium polymer battery (PLI) swelling in a specific direction. As a result, a local difference occurs in the adhesion between the electrode plates in the electrode group of the battery, thereby degrading performance and safety of the battery and making it difficult to install the lithium secondary battery.

As a method for solving the above problems, there is a method of improving the safety of a secondary battery including a non-aqueous electrolyte by installing a vent or a current breaker for ejecting an internal electrolyte when the internal pressure rises above a predetermined level. However, this method has a problem of causing a risk of malfunction due to the increase in internal pressure.

In addition, a method of changing the SEI formation reaction by injecting an additive into the electrolyte in order to suppress an increase in the internal pressure is known. For example, Japanese Patent Laid-Open No. 9-73918 discloses a method of improving the high temperature storage property of a battery by adding 1% or less of a diphenyl picrylhydrazyl compound, and Japanese Patent Laid-Open No. 8-321312 No. 1 discloses a method of improving the service life performance and long-term shelf life by using a compound of 1 to 20% N-butyl amines in an electrolytic solution. Japanese Patent Application Laid-Open No. 8-64238 discloses 3 × 10 _^-4 to 3 × 10. A method of improving the shelf life of a battery by adding _^-2 moles of calcium salt is disclosed. Japanese Patent Laid-Open No. 6-333596 discloses a method of improving the shelf life of a battery by adding an azo compound to suppress the reaction between the electrolyte and the negative electrode. A method is disclosed.

In addition, Japanese Patent Laid-Open No. 7-176323 discloses a method of adding CO ₂ to an electrolyte, and Japanese Patent Laid-Open No. 7-320779 describes a method of suppressing decomposition of an electrolyte by adding a sulfide compound to the electrolyte. have.

As such, a small amount of organic matter or By adding an inorganic substance, the method of inducing an appropriate film formation on the surface of a cathode like an SEI film is used. However, the added compound, depending on its intrinsic electrochemical properties, interacts with carbon, which is a cathode during initial charge and discharge, to form a decomposed or unstable film, resulting in deterioration of ion mobility in the electrons and generation of gas in the cell. Rather, by increasing the internal pressure, there is a problem of worsening the storage and stability, life performance and capacity of the battery.

In non-aqueous electrolyte secondary batteries, if the power circuit or charging device of the electronic device breaks down and the battery is overcharged, abnormal heat generation occurs in the battery, and in extreme cases, the battery may be damaged or ignited. It has become an important subject to effectively suppress heat generation and to ensure the stability of the battery so as not to cause it.

As a countermeasure against bursting and ignition of a battery during overcharging, a method of controlling the charging voltage by a charger has become mainstream. However, in the present state, since the use of the protection circuit and the protection element places great restrictions on the miniaturization and cost reduction of the battery pack, it is desirable to secure the stability without the protection circuit and the protection element.

In order to solve such a problem, it was intended to add a small amount of aromatic compounds as an additive to the electrolyte of a lithium secondary battery to ensure stability against overcharging of the battery. It is proposed in Japanese Unexamined Patent Publication No. 9-106835, Patent No. 2939469, and the like. In Japanese Patent Application Laid-Open No. 7-302614 and Japanese Patent Laid-Open Publication No. 1, an anisole having an reversible redox potential and having a π electron orbit as an additive in an electrolyte solution having a molecular weight of 500 or less and a positive electrode potential at the time of full charge of a secondary battery. It is proposed to use organic low molecular weight compounds such as (Anisole), which is an additive called redox shuttle, which consumes overcharge current during overcharging and establishes a protective mechanism. In Japanese Patent Laid-Open No. 9-106835, it is proposed that an additive starts a polymerization reaction at a voltage in an overcharge state, and acts as a resistor to protect the battery during overcharge. However, the anisole proposed in Japanese Patent Laid-Open Nos. 7-302614 and 9-50822 clearly functions as a redox shuttle during overcharging, but reacts in a general battery operating voltage range. This has been known to adversely affect the cycle characteristics of the discharge capacity.

In addition, when the demand for high energy density and high power density is increasing, it has been proposed to add flame retardant phosphate esters to the electrolyte in order to increase the flame retardancy of the carbonate-based flammable electrolyte to improve the safety of the battery. (Japanese Patent Application Laid-Open No. 4-184870, Japanese Patent Application Laid-Open No. 8-88023, and Japanese Patent Application Laid-Open No. Hei 10-189038-189040).

However, when this kind of compound is added, flame retardancy can be imparted, but electrical conductivity is lowered, and electrolyte characteristics are greatly degraded. In addition, due to the high permeability of the phosphate ester, it penetrates into the film formed on the surface of the negative electrode and surface reaction occurs at the electrode. As a result, battery characteristics such as charge and discharge efficiency, energy density, and output density are also significantly inferior to those before the addition of phosphate esters, making them difficult to be used. In addition, the silane compounds (Japanese Patent Laid-Open Publication Nos. 3-236168 to 236171) and fluorine compounds (Japanese Patent Laid-Open Publications No. Hei 8-138737 and Hei 10-116629) similarly deteriorate the characteristics of the electrolyte and the battery when added. It is hard to be practical.

In order to solve the above problems, an object of the present invention is to provide a nonaqueous electrolyte solution for a lithium secondary battery comprising an additive that inhibits the oxidative decomposition reaction of the electrolyte on the surface of the cathode by oxidatively decomposing first on the surface of the cathode. do.

According to the present invention, it is possible to suppress the expansion of the thickness of the battery during high temperature storage after full charge without reducing the battery characteristics such as low temperature characteristics and storage characteristics of the battery, thereby improving reliability when the battery set is mounted.

In addition, an object of the present invention is to prevent thermal runaway phenomenon and to improve the flame retardancy of the flammable electrolyte, thereby improving the safety of the lithium secondary battery.

In order to achieve the above object, the present invention provides a lithium secondary battery non-aqueous electrolyte, characterized in that it comprises a lithium salt, a non-aqueous organic solvent and the compound of formula (1) or formula (2).

(However, R1 to R3 is a C = 1-5 alkyl group in which part or all of the hydrogen atoms are substituted with halogen elements, or a benzene group in which part or all of the hydrogen atoms are substituted with halogen elements.)

(Wherein R4 is a C = 1-5 alkyl group in which part or all of hydrogen atoms are substituted with halogen elements or a benzene group in which part or all of hydrogen atoms are substituted with halogen atoms, and R5 is part or all of hydrogen atoms) C = 1-5 alkyl group substituted with halogen.)

In one embodiment, 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 , LiAlO At least one selected from the group consisting of ₄ , LiAlCl ₄ , 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 It provides a nonaqueous electrolyte solution for a lithium secondary battery.

In one embodiment, the lithium salt provides a non-aqueous electrolyte for a lithium secondary battery, characterized in that the concentration of 0.6 to 2M.

The concentration of the lithium salt is more preferably used within the range of 0.7 to 1.6M. If the concentration of the lithium salt is less than 0.6M, the conductivity of the electrolyte is lowered, the performance of the electrolyte is lowered, if it exceeds 2M, the viscosity of the electrolyte is increased, there is a problem that the mobility of lithium ions is reduced and low-temperature performance is also reduced.

In one embodiment, the non-aqueous organic solvent provides a non-aqueous electrolyte for a lithium secondary battery, characterized in that at least one selected from the group consisting of carbonate, ester, ether and ketone.

In one embodiment, the carbonate is dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC ) Non-aqueous lithium secondary battery, characterized in that at least one selected from the group consisting of ethylene carbonate (EC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), propylene carbonate (PC) and butylene carbonate (BC) Provide an electrolyte solution.

The present invention provides a non-aqueous electrolyte solution for a lithium secondary battery, wherein the carbonate is used by mixing a cyclic carbonate and a chain carbonate.

In this case, the cyclic carbonate and the chain carbonate are preferably used in a volume ratio of 1: 1 to 1: 9, more preferably used in a volume ratio of 1: 1.5 to 1: 4. The performance of the electrolyte is preferable when mixed in the above volume ratio.

In one embodiment, the non-aqueous organic solvent provides a non-aqueous electrolyte for a lithium secondary battery, characterized in that the mixed solvent of a carbonate solvent and an aromatic hydrocarbon organic solvent.

In one embodiment, the aromatic hydrocarbon-based organic solvent provides a non-aqueous electrolyte for a lithium secondary battery, characterized in that the compound of formula (3).

(Wherein R is a halogen or an alkyl group of C = 1 to 10, and n is 1 to 5)

In one embodiment, the aromatic hydrocarbon-based organic solvent is at least one selected from the group consisting of benzene, fluorobenzene, toluene, fluorotoluene, trifluorotoluene and xylene Provide a nonaqueous electrolyte.

In one embodiment, the carbonate-based solvent and the aromatic hydrocarbon-based organic solvent provides a non-aqueous electrolyte solution for a lithium secondary battery, characterized in that mixed in a volume ratio of 1: 1 to 50: 1. The performance of the electrolyte is preferable when mixed in the above volume ratio.

In one embodiment, the ester is butyrolactone, decanolide (decanolide), valerolactone, mevalonolactone (mevalonolactone), caprolactone (caprolactone), n-methyl acetate, n-ethyl acetate, And it provides a non-aqueous electrolyte for lithium secondary battery, characterized in that selected from the group consisting of n-propyl acetate.

Dibutyl ether and the like may be used as the ether, but is not limited thereto.

In one embodiment, the compound of formula 1 is a lithium secondary, characterized in that the trifluoroethyl phosphate (TFEP) of Formula 4 or the trifluorophenyl phosphate (TFPP) of the formula (5) A nonaqueous electrolyte solution for batteries is provided.

In one embodiment, the compound of Formula 1 or Formula 2 provides a non-aqueous electrolyte solution for a lithium secondary battery, characterized in that contained in a volume ratio of 1: 1 to 1:50 relative to carbonate.

When the compound of Formula 1 or Formula 2 is less than 1:50 volume ratio with respect to carbonate, it is difficult to expect the effect of suppressing gas generation inside the battery or improving the safety of the battery due to flame retardancy. Since a thick conductive film is formed to impair the reversibility of the battery, battery performance such as cycle characteristics deteriorates.

The present invention provides a non-aqueous electrolyte solution for a lithium secondary battery comprising the compound of Formula 4 or Formula 5 in a volume ratio of 1:50 to 1: 5 relative to the non-aqueous organic solvent.

In another embodiment, the non-aqueous electrolyte for lithium secondary batteries; It provides a lithium secondary battery comprising a positive electrode containing a lithium intercalation compound and a negative electrode containing carbon, carbon composite, lithium metal, or lithium alloy.

In one embodiment, the lithium secondary battery provides a lithium secondary battery, characterized in that the lithium ion battery or a lithium polymer battery.

When the battery voltage reaches the overcharge voltage, the compound of Formula 1 or Formula 2 starts a decomposition reaction, generates gas, and simultaneously starts an electrochemical polymerization reaction to form a conductive polymer film on the surface of the positive electrode. This polymer film acts as a resistor and suppresses overcharge since it is a substance that is hardly re-dissolved in the electrolyte.

In addition, by reducing the amount of heat generated during overcharging to prevent thermal runaway phenomenon to improve the safety of the battery.

The nonaqueous electrolyte for lithium secondary batteries of the present invention is generally stable at a temperature range of -20 to 60 ° C., and maintains stable characteristics even at a voltage of 4 V, thereby improving safety and reliability of the lithium secondary battery.

In the present invention, the positive electrode active material of the lithium secondary battery is LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , or LiNi _1-xy Co _x M _y O ₂ (0 ≦ x ≦ 1, 0 ≦ _y ≦ 1, 0 ≤ x + y ≤ 1, M is a lithium metal oxide such as a metal such as Al, Sr, Mg, La, etc. or a lithium intercalation compound such as a lithium chalcogenide compound, crystalline or amorphous Carbon, carbon composites, lithium metals, or lithium alloys are used. In addition, any material used as a cathode active material and an anode active material of a lithium secondary battery may be used.

In the lithium secondary battery of the present invention, a slurry containing an active material is coated on a current collector and then molded into a predetermined shape to form a positive electrode and a negative electrode, and the electrode and negative electrode are wound or laminated together with a separator which is an insulator to form an electrode assembly. After the electrode assembly is placed in a battery case, the electrolyte is injected through an electrolyte injection hole, and then manufactured through a step of assembling a battery.

As the separator, a polyethylene separator, a polypropylene separator, a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may be used.

Hereinafter, the present invention will be described in more detail with reference to examples, but these examples are for illustrative purposes only and should not be construed as limiting the present invention.

Example 1

Ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC) are mixed in a ratio of 1: 1: 1 and trifluoroethyl phosphate (TFEP) is a volume ratio of 50: 1 as a non-aqueous organic solvent. 1 M LiPF ₆ was added as a solute to a solvent mixed with each other to prepare a nonaqueous electrolyte solution for a lithium secondary battery.

A square 423048 cell was fabricated using LiCoO ₂ as the positive electrode, graphite as the negative electrode, PVDF as the binder, and acetylene black as the conductive agent.

Example 2

A battery was prepared in the same manner as in Example 1 except that a solvent in which trifluoroethyl phosphate (TFEP) was mixed at a volume ratio of 20: 1 was prepared. Then, battery characteristic evaluation and limit oxygen index were measured.

Example 3

A battery was prepared in the same manner as in Example 1 except for using a solvent in which trifluoroethyl phosphate (TFEP) was mixed at a volume ratio of 10: 1, and then battery characteristics evaluation and limit oxygen index were measured.

Example 4

A battery was prepared in the same manner as in Example 1 except that a solvent in which trifluoroethyl phosphate (TFEP) was mixed at a volume ratio of 5: 1 was used, and then battery characteristic evaluation and limit oxygen index were measured.

Example 5

A battery was prepared in the same manner as in Example 1 except that a solvent in which trifluorophenyl phosphate (TFPP) was mixed at a volume ratio of 50: 1 was used. The cell characteristics were evaluated and the limit oxygen index was measured.

Example 6

Except for using a solvent in which trifluorophenyl phosphate (TFPP) was mixed in a volume ratio of 20: 1, the same method as in Example 1 was prepared, and then the battery characteristic evaluation and the limit oxygen index were measured.

Example 7

A battery was prepared in the same manner as in Example 1 except that a solvent in which trifluorophenyl phosphate (TFPP) was mixed at a volume ratio of 10: 1 was prepared. The cell characteristics were evaluated and the limit oxygen index was measured.

Example 8

A battery was prepared in the same manner as in Example 1 except that a solvent in which trifluorophenyl phosphate (TFPP) was mixed at a volume ratio of 5: 1 was used, and then battery characteristic evaluation and limit oxygen index were measured.

Comparative Example 1

A battery was prepared in the same manner as in Example 1 except for using a solvent in which triethyl phosphate (TEP) was mixed at a volume ratio of 10: 1, and then battery characteristic evaluation and limit oxygen index were measured.

Comparative Example 2

A non-aqueous organic solvent was used except that an electrolyte prepared by using ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a ratio of 1: 1: 1 was used as a solvent. The same procedure as in Example 1 was made, and the battery characteristics were evaluated and the limit oxygen index was measured.

The characteristics and limit oxygen index of the battery were measured by the following method.

Battery characteristic evaluation

(1) Mars charge and discharge test

After charging with a current of 170 mA and a charging voltage of 4.2 V under constant current-constant voltage conditions, the battery was discharged to 2.75 V with a current of 170 mA after being left for 1 hour and left for 1 hour (3 repetitions).

(2) Standard charge and discharge experiment

The battery was charged to a charging voltage of 1C and 4.2V under constant current-constant voltage conditions and discharged to 3V under 1C constant current conditions. The capacity retention rate (residual discharge capacity compared to the initial capacity) was measured by repeating 300 times under these standard charge and discharge conditions.

Limit oxygen index measurement

The JIS K7201 method limit oxygen index was measured. Table 3 shows the result.

Next, the following experiments were performed.

Comparison of C-rate discharge voltage

Under a constant current-constant voltage condition, a current of 170 mA (0.2 C-rate) was charged to a charging voltage of 4.2 V, and discharged to 3 V under respective constant current conditions (0.2 C, 0.5 C, 1.0 C). When the discharge capacity was 100%, the voltage at the discharge capacity of 50% was taken as the discharge voltage. The results are shown in Table 2.

High Temperature Inflation Experiment

The degree of swelling of the electrode at high temperature was measured by leaving it at 90 ° C. for 8 hours under a 4.2 V full charge state. The results are shown in FIG. The battery using the nonaqueous electrolyte of the present invention can be confirmed that there is no change in the thickness of the electrode even after 8 hours.

Cyclic voltammetry

Oxidation-reduction reactivity of the electrolyte and the electrode was tested five times with a voltage range of 2.5 ~ 0V and a scan rate of 1mV / s. The results are shown in FIG. 2, which shows that Example 3 is much less reactive between the negative electrode and the electrolyte than Comparative Example 2.

Calorific value measurement of electrode

The calorific value of the positive electrode and the negative electrode of Example 3 and Comparative Example 2 was measured during full charge at 4.2V through DSC. The measuring method is to extract the positive and negative electrodes from a battery fully charged at 4.2V after chemical charge and discharge using the corresponding electrolyte, and then put them into a DSC measurement cell, and then generate heat and heat generation from 50 ° C to 350 ° C at a temperature rising rate of 5 ° C per minute. The temperature was measured and the results are shown in FIGS. 3 and 4.

Overcharge Experiment

The results of overcharging experiments up to 10V with 3C-rate current are shown in FIG. 5. Compared with Comparative Example 2, it could be confirmed that Example 3 and Example 7 did not have an explosion and fire when overcharged. This is presumably because trifluoroethyl phosphate (TFEP) reduces the amount of heat generated during overcharging and prevents thermal runaway.

division Mars Charging (mAh) Mars discharge (mAh) Chemical Efficiency (%) △ IR (mΩ) 100cys. Capacity retention rate (%) 300cys. Capacity retention rate (%) Example 1 1035.8 934.2 90.2 2.6 96 91 Example 2 1032.4 928.6 89.9 2.8 96 90 Example 3 1025.0 922.8 90.0 3.0 95 89 Example 4 1013.5 917.6 90.5 3.9 94 86 Example 5 1027.2 928.1 90.4 3.2 95 90 Example 6 1019.9 922.8 90.5 3.4 94 88 Example 7 1008.5 909.5 90.2 3.5 93 87 Example 8 1000.2 900.2 90.0 3.7 93 85 Comparative Example 1 1000.9 629.4 62.9 17.1 9 - Comparative Example 2 1026.9 930.3 90.6 3.0 95 90

△ IR (mΩ): change in battery internal resistance

division Discharge voltage 0.2C-rate 0.5C-rate 1.0C-rate Example 3 3.77 3.71 3.65 Example 7 3.77 3.72 3.66 Comparative Example 2 3.76 3.69 3.56

division Marginal oxygen index (% by volume) Example 1 18.4 Example 2 20.5 Example 3 22.9 Example 4 25.1 Example 5 18.3 Example 6 20.2 Example 7 22.6 Example 8 24.7 Comparative Example 1 23.1 Comparative Example 2 16.7

From Tables 1 and 2, Examples 1 to 8 including TFEP and TFPP of the present invention in battery characteristic evaluation showed the same results as Comparative Example 2, and the addition of the compound did not affect the battery characteristics. Could be confirmed.

On the other hand, from Table 3, the non-aqueous electrolyte containing TFEP and TFPP of the present invention can increase the limit oxygen index of the electrolyte solution to ensure flame retardancy.

However, in Comparative Example 1 containing a phosphate ester not substituted with fluorine, the limiting oxygen index was high, but it was found that serious problems occurred in the battery characteristics (initial capacity / efficiency, internal resistance, and lifespan characteristics).

The nonaqueous electrolyte containing the halogenated trialkylphosphate for lithium secondary batteries of the present invention did not affect battery characteristics, and was able to suppress the thickness expansion of the battery even at high temperature storage after full charge. In addition, it was possible to prevent thermal runaway during overcharging and to improve the flame retardancy of the flammable electrolyte, thereby improving the safety of the lithium secondary battery.

Claims (16)

A non-aqueous electrolyte solution for a lithium secondary battery, comprising a lithium salt, a non-aqueous organic solvent, and a compound represented by the following general formula (1) or (2). [Formula 1]

(However, R1 to R3 is a C = 1-5 alkyl group in which part or all of the hydrogen atoms are substituted with halogen elements, or a benzene group in which part or all of the hydrogen atoms are substituted with halogen elements.) [Formula 2]

(Wherein R4 is a C = 1-5 alkyl group in which part or all of hydrogen atoms are substituted with halogen elements or a benzene group in which part or all of hydrogen atoms are substituted with halogen atoms, and R5 is part or all of hydrogen atoms) C = 1-5 alkyl group substituted with halogen.) 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 , LiAlO ₄ , LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ), provided that at least one selected from the group consisting of LiCl and LiI Non-aqueous electrolyte for lithium secondary batteries. The non-aqueous electrolyte solution for lithium secondary batteries according to claim 2, wherein the lithium salt has a concentration of 0.6 to 2 M. The nonaqueous electrolyte of claim 1, wherein the nonaqueous organic solvent is at least one selected from the group consisting of carbonate, ester, ether and ketone. The method of claim 4 wherein the carbonate is dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC) ethylene Non-aqueous electrolyte for lithium secondary batteries, characterized in that at least one selected from the group consisting of carbonate (EC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), propylene carbonate (PC) and butylene carbonate (BC). The non-aqueous electrolyte for lithium secondary battery according to claim 4, wherein a cyclic carbonate and a chain carbonate are used as the carbonate. The nonaqueous electrolyte solution for lithium secondary batteries according to claim 1, wherein the nonaqueous organic solvent is a mixed solvent of a carbonate solvent and an aromatic hydrocarbon organic solvent. 8. The non-aqueous electrolyte for lithium secondary batteries according to claim 7, wherein the aromatic hydrocarbon organic solvent is a compound represented by the following Chemical Formula 3. [Formula 3]

(Wherein R is a halogen or an alkyl group of C = 1 to 10, and n is 1 to 5) The non-aqueous electrolyte for lithium secondary battery according to claim 7, wherein the aromatic hydrocarbon organic solvent is at least one selected from the group consisting of benzene, fluorobenzene, toluene, fluorotoluene, trifluorotoluene, and xylene. . 8. The nonaqueous electrolyte of claim 7, wherein the carbonate solvent and the aromatic hydrocarbon organic solvent are mixed in a volume ratio of 1: 1 to 50: 1. The method of claim 4, wherein the ester is butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, n-methylacetate, n-ethyl acetate, and n Non-aqueous electrolyte solution for lithium secondary batteries, characterized in that selected from the group consisting of -propyl acetate. The non-aqueous lithium secondary battery according to claim 1, wherein the compound of Formula 1 is Trifluoroehtly phosphate (TFEP) of Formula 4 or Trifluorophenyl phosphate (TFPP) of Formula 5. Electrolyte solution. [Formula 4]

[Formula 5]

The non-aqueous electrolyte for lithium secondary battery according to claim 4, wherein the compound of Formula 1 or Formula 2 is included in a volume ratio of 1: 1 to 1:50 with respect to carbonate. The nonaqueous electrolyte of claim 12, wherein the compound of Formula 4 or Formula 5 is included in a volume ratio of 1:50 to 1: 5 with respect to the non-aqueous organic solvent. Non-aqueous electrolyte for lithium secondary battery according to any one of claims 1 to 14; A positive electrode comprising a lithium intercalation compound; And Lithium secondary battery, characterized in that consisting of a negative electrode containing carbon, carbon composites, lithium metal, or lithium alloy. The lithium secondary battery according to claim 15, wherein the lithium secondary battery is a lithium ion battery or a lithium polymer battery.

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