KR100728180B1 - Non-aqueous electrolyte, lithium secondary battery, and secondary battery apparatus for lithium secondary battery - Google Patents

Abstract

Provided are a nonaqueous electrolyte having excellent withstand voltage resistance and a conductivity of lithium ions equivalent to that of the conventional one, and a lithium secondary battery and a secondary battery system provided with the nonaqueous electrolyte. When the counter electrode with respect to the platinum working electrode is made of metallic lithium, a nonaqueous electrolyte solution for a lithium secondary battery is used which contains at least one or more of aromatic compounds polymerizable at a working electrode potential of 4.2 V to 4.5 V.

Lithium secondary battery, nonaqueous electrolyte, lithium secondary battery system, negative electrode film improving additive, free fluorinated compound, aromatic compound

Description

Non-aqueous electrolyte, lithium secondary battery and secondary battery device for lithium secondary battery {NON AQUEOUS ELECTROLYTE, RECHARGEABLE LITHIUM BATTERY AND RECHARGEABLE BATTERY DEVICE}

1: is a schematic diagram which shows the structure of the secondary battery system which is embodiment of this invention.

[Description of Symbols for Main Parts of Drawing]

1 DC power supply,

2 ... lithium secondary battery,

4 ... switch means,

5 ... Control

[Industrial use]

TECHNICAL FIELD This invention relates to the nonaqueous electrolyte solution for lithium secondary batteries, a lithium secondary battery, and a secondary battery system.

[Prior art]

In a conventional lithium secondary battery, it is common to set the charge end voltage at about 4.2V with respect to lithium from the viewpoint of oxidation resistance and the like of the nonaqueous electrolyte. This is because when the lithium is charged to 4.2 V or more, the potential of the positive electrode rises to decompose the nonaqueous electrolyte, resulting in a decrease in cycle characteristics and deterioration of battery characteristics at high temperatures. However, if the charging voltage is 4.2V or more and the average operating voltage is increased, the energy density can be further improved.

In recent years, as shown in Japanese Patent Laid-Open No. 9-167635, a technique capable of realizing a nonaqueous electrolyte having a high withstand voltage by adding sulfite ester having a halogenated alkyl group as an electrolyte solvent has been proposed.

However, in the said patent document, although the withstand voltage resistance of electrolyte solution improves by adding sulfite ester, there exists a problem that the conductivity of lithium ion falls significantly.

This invention is made | formed in view of the said situation, Comprising: It aims at providing the lithium secondary battery and secondary battery system provided with the nonaqueous electrolyte which is excellent in a withstand voltage resistance, and whose conductivity of lithium ion is equivalent to the conventional thing, and this nonaqueous electrolyte.

In order to achieve the above object, the present invention adopts the following configuration.

The nonaqueous electrolyte solution for lithium secondary batteries of the present invention contains at least one or more of the aromatic compounds polymerizable at a working electrode potential of 4.2 V to 4.5 V when the counter electrode to the platinum working electrode is made of metal lithium.

By using said non-aqueous electrolyte solution as electrolyte solution of a lithium secondary battery, an aromatic compound superposes | polymerizes on the positive electrode surface of a lithium secondary battery at the time of initial charge, and forms a film. This film formation prevents the positive electrode from directly contacting the nonaqueous electrolyte. Thereby, the oxidative decomposition of the nonaqueous electrolyte solution by the anode can be prevented, and the breakdown voltage characteristic of the nonaqueous electrolyte solution can be improved. In addition, the high temperature characteristics of the lithium secondary battery can also be improved.

Moreover, in the nonaqueous electrolyte solution for lithium secondary batteries of this invention, it is preferable that the said aromatic compound is any 1 or more types of phenanthrene, terphenyl, and dimethyl biphenyl, Especially either or both of phenanthrene and terphenyl is preferable. Is preferred.

Next, the nonaqueous electrolyte solution for a lithium secondary battery of the present invention comprises one or both of the organofluorinated compounds represented by the following general formula (1) or (2):

[Formula 1]

R ¹ -OR ²

[Formula 2]

R ¹ -O-CO-OR ²

In Formulas 1 and 2, R ¹ and R ² are an alkyl group or a fluoroalkyl group.

More preferably, at least one of R ¹ and R ² in Formulas 1 and 2 is a fluoroalkyl group.

The organofluorinated compound is not decomposed with respect to oxidation by the positive electrode of the lithium secondary battery. Thus, by containing an organic fluorinated compound, the nonaqueous electrolyte excellent in the withstand voltage characteristic can be comprised.

In the nonaqueous electrolyte solution for lithium secondary batteries of the present invention, the organic fluorinated compound is preferably at least one selected from the following compounds: HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H, CF ₃ CH ₂ OCOOCH ₂ CF ₃ , CH ₃ OCOOCH ₂ CHFCH ₃ , CH ₃ OCOOCH (CH ₃ ) CH ₂ F, CH ₃ OCOOCH ₂ CH ₂ CH ₂ F. In particular, the organofluorinated compound is HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H, CH ₃ Preference is given to either or both of OCOOCH ₂ CHFCH ₃ .

In addition, the nonaqueous electrolyte solution for lithium secondary batteries of the present invention is the nonaqueous electrolyte solution described above, and at least one negative electrode film of fluoroethylene carbonate, vinylene carbonate, propane sultone, trifluoropropylmethyl sulfone, fluorobenzene, and LiBF ₄ . Improvement additives.

In addition to the above aromatic compound or organofluorinated compound, by adding a negative electrode film improving additive, the film formed on the negative electrode surface of the lithium secondary battery can be protected. As a result, the rapid reaction between the negative electrode and the nonaqueous electrolyte solution is particularly suppressed during charge and discharge at high temperatures, and thermal runaway of the lithium secondary battery can be prevented in advance.

Next, the lithium secondary battery of this invention is equipped with the nonaqueous electrolyte solution mentioned above.

According to the above arrangement, since the nonaqueous electrolyte having excellent withstand voltage characteristics is provided, the nonaqueous electrolyte is not decomposed even when the battery voltage at full charge is 4.2V to 4.5V, and there is no fear of thermal runaway at high temperature. It is possible to realize a lithium secondary battery having high stability at high capacity.

Next, the secondary battery system of this invention is equipped with the lithium secondary battery mentioned above and the charging apparatus which set the battery voltage at the time of full charge of this lithium battery to 4.2V-4.5V.

According to the said structure, since the lithium secondary battery of the said structure is provided and the battery voltage at the time of full charge of this lithium secondary battery can be controlled to 4.2V-4.5V, there exists a possibility that the nonaqueous electrolyte solution of a lithium secondary battery may decompose. There is no fear of thermal runaway at high temperature, and a secondary battery system having high stability at high capacity can be realized.

ADVANTAGE OF THE INVENTION According to this invention, the nonaqueous electrolyte excellent in voltage resistance, the lithium secondary battery provided with this nonaqueous electrolyte, and a secondary battery system can be provided.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

The lithium secondary battery of the present embodiment, the positive electrode capable of occluding and releasing lithium; A negative electrode capable of occluding and releasing lithium; A separator disposed between the positive electrode and the negative electrode; And a nonaqueous electrolyte, and are schematically configured.

In the positive electrode active material powder, a binder such as polyvinylidene fluoride and a conductive assistant such as carbon black are mixed to form a sheet or the like. This positive electrode is bonded to the positive electrode current collector. Examples of the positive electrode current collector include metal foils or metal nets such as aluminum and stainless steel.

As the positive electrode active material, at least one selected from cobalt, manganese and nickel and at least one selected from the group consisting of lithium and lithium, specifically, LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , LiCoNiMnO ₂ , LiFeO ₂ , V ₂ O ₅ and the like are preferred, and LiCoO ₂ , LiNiO ₂ or LiCoNiMnO ₂ is particularly preferred. Moreover, you may use the thing which can occlude | release and discharge | release lithium, such as TiS, MoS, an organic disulfide compound, and an organic poly sulfide compound.

The negative electrode is formed by mixing a binder such as polyvinylidene fluoride with a conductive assistant such as carbon black and the like into a negative electrode active material powder if necessary. This negative electrode is bonded to the negative electrode current collector. As a negative electrode electrical power collector, the metal foil or metal mesh which consists of Cu or Cu alloy can be illustrated.

Moreover, carbonaceous materials, such as artificial graphite, natural graphite, graphitized carbon fiber, graphitized mesocarbon bead, and amorphous carbon, can be illustrated as a negative electrode active material. Moreover, the metallic substance which can be alloyed with lithium, or the composite containing this metallic substance and carbonaceous material can also be illustrated as a negative electrode active material. Examples of the metal that can be alloyed with lithium include Al, Si, Sn, Pb, Zn, Bi, In, Mg, Ga, and Cd. Metal lithium foil can also be used as a negative electrode active material.

Moreover, a separator can use suitably well-known separators, such as a porous polypropylene film and a porous polyethylene film.

Next, the nonaqueous electrolytic solution conducts lithium ions. As an example, a nonaqueous electrolyte includes a nonaqueous solvent, a lithium salt, and a polymerizable aromatic compound.

The polymerizable aromatic compound is an aromatic compound polymerizable at the surface of the working electrode when the working electrode potential is 4.2 V to 4.5 V when the counter electrode to the platinum working electrode is made of metal lithium, and specifically, phenanthrene, terphenyl, dimethyl Any one or more types of biphenyls are preferable, and either or both of phenanthrene and terphenyl are particularly preferable.

By using said nonaqueous electrolyte as an electrolyte solution of a lithium secondary battery, an aromatic compound superposes | polymerizes on the surface of the positive electrode (corresponding to the said working electrode) of a lithium secondary battery at the time of initial charge, and forms a film. This film formation prevents the positive electrode from directly contacting the nonaqueous electrolyte. Thereby, the oxidative decomposition of the nonaqueous electrolyte solution by the anode can be prevented, and the breakdown voltage characteristic of the nonaqueous electrolyte solution can be improved. In addition, the high temperature characteristics of the lithium secondary battery can be improved.

The range of 0.01 mass%-5 mass% is preferable, and, as for the addition amount of the said aromatic compound in a nonaqueous electrolyte, the range of 0.1 mass%-0.5 mass% is more preferable. When the amount of the aromatic compound added is 0.1% by mass or more, a sufficient amount of film can be formed on the surface of the positive electrode, and oxidative decomposition of the nonaqueous electrolyte solution by the positive electrode can be prevented. Moreover, when the addition amount of an aromatic compound is 0.5 mass% or less, the charge / discharge efficiency of a lithium secondary battery can be improved, without reducing the conductivity of lithium ion of a nonaqueous electrolyte solution.

Next, as another example of a nonaqueous electrolyte, Non-aqueous solvent; Lithium salts; And any one or both of the organofluorinated compounds of Formula 1 or 2 may be contained:

[Formula 1]

R ¹ -OR ²

[Formula 2]

R ¹ -O-CO-OR ²

In Formulas 1 and 2, R ¹ and R ² are an alkyl group or a fluoroalkyl group.

More preferably, in Formulas 1 and 2, at least one of R ¹ and R ² is a fluoroalkyl group.

As said organofluorinated compound, HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H, CF ₃ CH ₂ OCOOCH ₂ CF ₃ , CH ₃ OCOOCH ₂ CHFCH ₃ , CH ₃ OCOOCH (CH ₃ ) CH ₂ F, CH ₃ It is preferable to use any one or more of OCOOCH ₂ CH ₂ CH ₂ F, and in particular, any one or both of HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H and CH ₃ OCOOCH ₂ CHFCH ₃ is preferable.

The organic fluorinated compound is not decomposed with respect to oxidation by the positive electrode of the lithium secondary battery. Thus, by containing an organic fluorinated compound, the nonaqueous electrolyte excellent in the withstand voltage characteristic can be comprised.

The range of 0.1 mass%-50 mass% is preferable, and, as for the addition amount of the said organic fluorinated compound in a non-aqueous electrolyte, the range of 1 mass%-20 mass% is more preferable. When the amount of the organofluorinated compound added is 1% by mass or more, the breakdown voltage characteristic of the nonaqueous electrolyte can be improved, and oxidative decomposition of the nonaqueous electrolyte by the positive electrode can be prevented. Moreover, when the addition amount of an organic fluorinated compound is 20 mass% or less, the charge / discharge efficiency of a lithium secondary battery can be improved, without the conductivity of the lithium ion of a nonaqueous electrolyte solution falling.

Further, in the above two kinds of nonaqueous electrolyte solution containing an aromatic compound or an organic fluorinated compound, in the group consisting of fluoroethylene carbonate, vinylene carbonate, propane sultone, trifluoropropylmethyl sulfone, fluorobenzene and LiBF ₄ , respectively. You may add 1 or more types of negative electrode film improvement additives chosen.

By adding the negative electrode film improving additive, it is possible to protect the film formed on the negative electrode surface of the lithium secondary battery with charging and discharging. As a result, the rapid reaction between the negative electrode and the nonaqueous electrolyte solution is particularly suppressed during charge and discharge at high temperatures, and thermal runaway of the lithium secondary battery can be prevented in advance.

The range of 0.05 mass%-20 mass% is preferable, and, as for the addition amount of the said negative electrode film improvement additive in a non-aqueous electrolyte solution, the range of 0.5 mass%-10 mass% is more preferable. When the amount of the negative electrode film improving additive added is 0.5% by mass or more, the film formed on the surface of the negative electrode can be sufficiently protected. Moreover, when the addition amount of a negative electrode film improvement additive is 10 mass% or less, the charge / discharge efficiency of a lithium secondary battery can be improved, without reducing the conductivity of lithium ion of a nonaqueous electrolyte solution.

Next, as a solvent contained in said non-aqueous electrolyte solution, the mixture of a cyclic carbonate and a linear carbonate can be illustrated.

As cyclic carbonate, it is preferable to contain any 1 or more types of ethylene carbonate, butylene carbonate, a propylene carbonate, and (gamma) -butyrolactone, for example. Since these cyclic carbonates are easily solvated with lithium ions, the ionic conductivity of the electrolyte itself can be increased.

Moreover, as linear carbonate, it is preferable to contain 1 or more types of dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate, for example. Since these linear carbonates have low viscosity, the conductivity of the electrolyte itself can be lowered to increase the ionic conductivity. However, since these linear carbonates have a low flash point, it is necessary to be careful not to overadd them because excessive flashing lowers the flash point of the electrolyte.

As the lithium salt, LiPF ₆ , LiBF ₄ , Li [N (SO ₂ C ₂ F ₅ ) ₂ ], Li [B (OCOCF ₃ ) ₄ ] or Li [B (OCOC ₂ F ₅ ) ₄ ] can be used. have. The concentration of these lithium salts in the electrolyte is preferably 0.5 mol / L to 2.0 mol / L. By including these lithium salts in the electrolyte, the ionic conductivity of the electrolyte itself can be increased.

According to the lithium secondary battery of the present embodiment, since the nonaqueous electrolyte having excellent withstand voltage characteristics is provided, the nonaqueous electrolyte is not decomposed even when the battery voltage at full charge is 4.2V to 4.5V, and thermal runaway occurs at high temperature. There is no concern, and a lithium secondary battery with high stability at high capacity can be realized.

Moreover, a secondary battery system can be comprised by combining the lithium secondary battery of this embodiment and the charging device which set the battery voltage at the time of full charge of this lithium battery to 4.2V-4.5V. According to this secondary battery system, since the battery voltage at the time of full charge of a lithium secondary battery can be controlled to 4.2V-4.5V, there is no possibility that a nonaqueous electrolyte solution of a lithium secondary battery may decompose, and thermal runaway will arise at high temperature. There is no concern, and a secondary battery system with high stability and high stability can be realized.

An example of a secondary battery system is shown in FIG. In Fig. 1, reference numeral 1 denotes a DC power supply, reference numeral 2 denotes a lithium secondary battery according to the present invention to be charged, reference numeral 4 denotes a switch means inserted in series into a constant current circuit, and reference numeral 5 denotes a control device. In the DC power supply 1, a charging voltage adjusting mechanism is assembled, and the charging end voltage is set to 4.2 to 4.5V. The switch means 4 is controlled by the control apparatus 5. The controller 5 monitors the voltage of the battery 2 and controls the charging current by turning on / off the switch means 4 in accordance with the battery voltage. In this secondary battery system, the charging current is supplied from the DC power supply 1 to the lithium secondary battery 2 via the switch means 4, and constant current charging is performed. After the battery voltage reaches the end-of-charge voltage of 4.2 to 4.5 V, the battery is switched to constant voltage charging and charged until a predetermined time.

By the above structure, the battery voltage at the time of full charge of a lithium secondary battery can be controlled to 4.2V-4.5V.

EXAMPLE

Hereinafter, the present invention will be described in more detail with reference to the experimental examples.

Experimental Example 1

 In this Experimental Example 1, a trielectrode cell was prepared by adding a polymerizable aromatic compound or an organofluorinated compound to a nonaqueous electrolyte solution, and performing a Cyclic Voltammogram test to measure a current voltage curve. And the reaction potential of the organofluorinated compound was measured.

The production of the three-electrode cell was performed as follows. First, the working electrode which consists of a platinum wire of diameter 0.5mm, the counter electrode which consists of metal lithium, and the reference electrode were prepared.

Moreover, the electrolyte solution which mixed LiPF ₆ of 1.3 mol / L in density | concentration was prepared in the mixed solvent which ethylene carbonate (EC) and diethyl carbonate (DEC) mix in the ratio of EC: DEC = 30: 70. 0.2 mass% of phenanthrene, 0.2 mass% of m-terphenyl, and 10 mass% of CF ₃ CH ₂ OCOOCH ₂ CF ₃ were added alone to this electrolyte solution to prepare the nonaqueous electrolyte solutions of Examples 1 to 3. In addition, as Comparative Example 1, EC, DEC, LiPF ₆ A nonaqueous electrolyte solution without any addition was prepared.

Next, the nonaqueous electrolyte was injected into the glass container, and the working electrode, the counter electrode and the reference electrode were inserted into the nonaqueous electrolyte to assemble the three-electrode cell. After assembling the cells, the cells were left at 25 ° C. for 15 hours, and at a rate of 5 mV / sec from an open circuit voltage (OCV) (about 3 V (vs Li)) to 8 V (vs Li) for a working electrode having an area of 0.31 cm ² . After the potential injection, the current voltage curve was measured by carrying out potential scanning at a speed of 5 mV / sec from 8 V (vs Li) to 0 V (vs Li). However, about the nonaqueous electrolyte solution to which the aromatic compound was added, it hold | maintained for 8 hours at the electric potential which the peak by the aromatic compound showed in the middle of electric potential injection.

In Table 1 below, the slope of the current value and the current voltage curve at the voltage 7V and the voltage (peak voltage) at which the derivative coefficient of the current voltage curve is maximized are shown.

As shown in Table 1, in Examples 1-3, the peak voltage is higher than the comparative example 1, and it turned out that the decomposition potential of electrolyte solution is rising by the additive. Moreover, it turned out that the electric current value in 7V of Examples 1-3 is smaller than the case of the comparative example 1. Therefore, in Examples 1 to 3, it was found that the decomposition of the electrolyte solution at around 7 V was suppressed by the addition of phenanthrene, m-terphenyl and CF ₃ CH ₂ OCOOCH ₂ CF ₃ .

additive Holding voltage Voltage 7V Peak voltage (V) Current (mA) Slope dI / dE Example 1 Penances 4.20V 0.001 0.0017 8 or more Example 2 m-terphenyl 4.50 V 0.001 0.0015 8 or more Example 3 CF ₃ CH ₂ OCOOCH ₂ CF ₃ - 0.005 0.013 7.5 Comparative Example 1 none - 0.008 0.022 7.3

Experimental Example 2

In Experimental Example 2, a coin-type lithium secondary battery was prepared by adding a polymerizable aromatic compound or an organic fluorinated compound to the nonaqueous electrolyte solution, and evaluated various battery characteristics.

The manufacturing of a lithium secondary battery was performed as follows. First, LiNiO ₂ having an average particle diameter of 10 μm and LiCoO ₂ having an average particle diameter of 10 μm were prepared, and these were mixed in a ratio of LiNiO ₂ : LiCoO ₂ = 30: 70 in a mass ratio to prepare a cathode active material. In addition, the positive electrode active material was also prepared containing only LiCoO _2. These positive electrode active materials, a binder made of polyvinylidene fluoride, and a conductive aid made of carbon powder having an average particle diameter of 3 µm were mixed, and N-methyl-2-pyrrolidone was further mixed to prepare a positive electrode slurry. The positive electrode slurry was coated on a positive electrode current collector made of aluminum foil having a thickness of 20 μm by the doctor blade method, dried at 120 ° C. for 24 hours in a vacuum atmosphere, and then volatilized N-methyl-2-pyrrolidone. Rolled. Thus, the positive electrode which consists of a positive electrode active material, a binder, and a conductive support material was formed on the positive electrode collector.

Next, 5 parts by weight of a binder made of polyvinylidene fluoride was mixed with 95 parts by weight of artificial graphite having an average particle diameter of 15 μm, and N-methyl-2-pyrrolidone was further mixed to prepare a negative electrode slurry. . After apply | coating this negative electrode slurry on the negative electrode collector which consists of 14-micrometer-thick Cu foil by the doctor blade method, it is made to dry at 120 degreeC for 24 hours in vacuum atmosphere, and volatilizes N-methyl- 2-pyrrolidone, Rolled. Thus, the negative electrode which consists of a negative electrode active material and a binder was formed on the negative electrode collector.

Next, an electrolyte solution in which LiPF ₆ with a concentration of 1.3 mol / L was added to a mixed solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a ratio of EC: DEC = 30: 70 was prepared. 10 mass% of a mixture of 0.2 mass% of phenanthrene, 0.2 mass% of 3,3'-dimethylbiphenyl, 0.15 mass% of phenanthrene, and 0.05 mass% of 3,3'-dimethylbiphenyl to this electrolyte solution HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H, 0.2% by mass of m-terphenyl and 10% by mass of CF ₃ CH ₂ OCOOCH ₂ CF ₃ were added to prepare the nonaqueous electrolyte solutions of Examples 4 to 9, respectively. Also as a comparative example, EC, DEC and LiPF ₆ A nonaqueous electrolyte solution without any addition was prepared.

Next, by placing a polypropylene porous separator between the positive electrode and the negative electrode and laminating them, and storing them in a coin-type battery case, and injecting the non-aqueous electrolyte solution and then sealing the battery case, The lithium secondary batteries of Examples 4 to 9 and Comparative Examples 2 and 3 were prepared. In addition, the set value of the discharge capacity of each battery is 5mAh. The structure of each battery is shown in Table 2.

About the obtained lithium secondary battery, after charging / discharging was repeated 2 cycles and it was set to the charged state, it stored in the 90 degreeC thermostat for 4 hours, and measured the discharge capacity (storage capacity) after storage. Next, after the measurement of the discharge capacity, charge and discharge of one cycle at room temperature were performed to measure the discharge capacity (recovery capacity). In addition, charging and discharging are performed under constant current charging until the battery voltage becomes 4.2 V to 4.5 V at a charging current of 0.5 C, followed by constant voltage charging for 2 hours, and constant current discharge to 3.0 V at a current of 0.2 C. did.

Table 3 shows OCV (Open Circuit Voltage) and the percentages of the storage capacity and the recovery capacity when the initial capacity is 100%.

additive anode Example 4 Penances LiNiO ₂ + LiCoO ₂ (30:70) Example 5 3,3'-dimethylbiphenyl LiNiO ₂ + LiCoO ₂ (30:70) Example 6 Phenanthrene 3,3'-dimethylbiphenyl LiNiO ₂ + LiCoO ₂ (30:70) Example 7 HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H LiNiO ₂ + LiCoO ₂ (30:70) Example 8 m-terphenyl LiCoO ₂ Example 9 CF ₃ CH ₂ OCOOCH ₂ CF ₃ LiCoO ₂ Comparative Example 2 none LiNiO ₂ + LiCoO ₂ (30:70) Comparative Example 3 none LiCoO ₂

Charge voltage Retention capacity Recovery capacity Example 4 4.20V 90% 99% Example 5 4.20V 82% 94% Example 6 4.20V 89% 97% Example 7 4.20V 78% 96% Example 8 4.50 V 89% 98% Example 9 4.50 V 78% 95% Comparative Example 2 4.20V 75% 93% Comparative Example 3 4.50 V 73% 91%

As shown in Table 3, it can be seen that the lithium secondary batteries of Examples 4 to 9 have higher storage capacity and recovery capacity and better high temperature characteristics than Comparative Examples 2 and 3. In particular, in Examples 8 and 9, it can be seen that favorable high temperature characteristics are exhibited even when the charging voltage is set to 4.5V.

Experimental Example 3

In this Experimental Example 3, a negative electrode film improving additive and a polymerizable aromatic compound or an organofluorinated compound were added to the nonaqueous electrolyte to prepare a cylindrical lithium secondary battery, and various battery characteristics were evaluated.

The manufacturing of a lithium secondary battery was performed as follows. First, in the same manner as in Experiment 2, a positive electrode and a negative electrode were prepared.

Next, an electrolyte solution in which LiPF ₆ with a concentration of 1.3 mol / L was added to a mixed solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a ratio of EC: DEC = 30: 70 was prepared. The nonaqueous electrolyte solutions of Examples 10 to 18 were prepared by adding a negative electrode film improving additive and a polymerizable aromatic compound or an organic fluorinated compound to this electrolyte solution. Moreover, as a comparative example, the nonaqueous electrolyte solution which added nothing other than EC, DEC, and LiPF ₆ was prepared.

Next, a polypropylene porous separator is disposed between the positive electrode and the negative electrode, and these are laminated, and then, these are wound in a cylindrical shape and stored in a cylindrical battery case, and after pouring the nonaqueous electrolyte solution, the battery case is sealed. By doing this, the lithium secondary batteries of Examples 10 to 18 and Comparative Examples 4 to 6 were produced. Moreover, the setting value of the discharge capacity of each battery is 2400-2600 mAh. The structure of each battery is shown in Table 4. In Table 4, FEC is fluoroethylene carbonate and VC is vinylene carbonate.

About the obtained lithium secondary battery, charging / discharging was repeated 2 cycles, and it stored in the 90 degreeC thermostat for 4 hours, and the operation state of the current cutoff valve was investigated. Moreover, about the obtained lithium secondary battery, charging / discharging was repeated 2 cycles, and it was stored in a 150 degreeC thermostat, and the presence or absence of the rupture of the battery was investigated. The results are shown in Table 5.

Aromatic compounds or organofluorinated compounds Cathode Improvement Agent anode Example 10 Phenanthrene (0.2% by mass) FEC (3 mass%) VC (1 mass%) LiNiO ₂ + LiCoO ₂ (30:70) Example 11 m-terphenyl (0.2 mass%) none LiNiO ₂ + LiCoO ₂ (30:70) Example 12 Phenanthrene (0.2% by mass) FEC (3 mass%) VC (1 mass%) LiNiO ₂ + LiCoO ₂ (30:70) Example 13 HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H (10 mass%) FEC (4 mass%) LiBF ₄ (0.15 mass%) LiNiO ₂ + LiCoO ₂ (30:70) Example 14 m-terphenyl (0.2 mass%) none LiCoO ₂ Example 15 CF ₃ CH ₂ OCOOCH ₂ CF ₃ (10 mass%) none LiCoO ₂ Example 16 CH ₃ OCOOCH ₂ CHFCH ₃ (10 mass%) FEC (5 mass%) VC (1 mass%) LiCoO ₂ Example 17 CH ₃ OCOOCH (CH ₃ ) CH ₂ F (10 mass%) FEC (5 mass%) VC (1 mass%) LiCoO ₂ Example 18 CH ₃ OCOOCH ₂ CH ₂ CH ₂ F (10 mass%) FEC (5 mass%) VC (1 mass%) LiCoO ₂ Comparative Example 4 none none LiNiO ₂ + LiCoO ₂ (30:70) Comparative Example 5 none none LiNiO ₂ + LiCoO ₂ (30:70) Comparative Example 6 none none LiCoO ₂

Charging voltage Current blocking valve Rupture test Example 10 4.20V Not working No burst Example 11 4.35V Not working No burst Example 12 4.35V Not working No burst Example 13 4.35V Not working No burst Example 14 4.50 V Not working No burst Example 15 4.50 V Not working No burst Example 16 4.50 V Not working No burst Example 17 4.50 V Not working No burst Example 18 4.50 V Not working No burst Comparative Example 4 4.20V Operation (after 7 hours) rupture Comparative Example 5 4.35V After 3 hours rupture Comparative Example 6 4.50 V After 35 minutes rupture

As shown in Table 5, for Comparative Examples 4 to 6, the current blocking valve was operated, and battery rupture occurred due to storage at 150 ° C. In Examples 10 to 18, there was no particular abnormality.

Experimental Example 4

In this Experimental Example 4, the negative electrode film improving additive alone or the negative electrode film improving additive and the aromatic compound were added to the nonaqueous electrolyte solution to prepare a cylindrical lithium secondary battery, and various battery characteristics were evaluated.

In the production of the lithium secondary battery, all of the positive electrodes were LiCoO ₂ , and the same procedure as in Experiment 3 was performed except that the structure of the nonaqueous electrolyte solution was shown in Table 6. Moreover, all the setting values of the discharge capacity of each battery are 2600 mAh. The structure of each battery is shown in Table 6. In Table 6, FEC is fluoroethylene carbonate, VC is vinylene carbonate, PS is propanesultone, TFPMS is trifluoropropylmethylsulfone, FB is fluorobenzene, and TP is m-terphenyl.

About the obtained lithium secondary battery, charge and discharge were repeated 100 cycles in the 45 degreeC thermostat, and the discharge capacity of the 100th cycle was measured.

In Table 6, the discharge capacity at the 100th cycle when the initial capacity is 100% is indicated as a percentage.

additive Charging voltage After 100 cycles Example 19 FEC (2 mass%), VC (1 mass%) 4.50 V 97% Example 20 VC (1 mass%) 4.50 V 92% Example 21 PS (1 mass%) 4.50 V 96% Example 22 TFPMS (1 mass%) 4.50 V 93% Example 23 FB (5 mass%), FEC (5 mass%), VC (1 mass%) 4.50 V 95% Example 24 TP (0.2 mass%), FEC (5 mass%), VC (1 mass%) 4.50 V 95% Example 25 CF ₃ CH ₂ OCOOCH ₂ CF ₃ (10 mass%), FEC (5 mass%), VC (1 mass%) 4.50 V 95% Comparative Example 7 none 4.50 V 88%

As shown in Table 6, compared with Comparative Example 7, Examples 19 to 25 exhibited excellent high temperature cycle characteristics.

ADVANTAGE OF THE INVENTION According to this invention, the nonaqueous electrolyte excellent in voltage resistance, the lithium secondary battery provided with this nonaqueous electrolyte, and a secondary battery system can be provided.

Claims (10)

When the counter electrode with respect to the platinum working electrode is made of metal lithium, an aromatic compound polymerizable at a working electrode potential of 4.2 V to 4.5 V; And A negative electrode film improving additive selected from the group consisting of fluoroethylene carbonate, vinylene carbonate, propanesultone, trifluoropropylmethylsulfone, fluorobenzene, LiBF ₄ and mixtures thereof; The aromatic compound is phenanthrene; Or a mixture of a compound selected from the group consisting of terphenyl, dimethylbiphenyl and mixtures thereof and phenanthrene, and a nonaqueous electrolyte solution for a lithium secondary battery. delete The method of claim 1, The aromatic compound is a nonaqueous electrolyte solution for a lithium secondary battery that is contained in an amount of 0.01% by mass to 5% by mass relative to the total mass of the nonaqueous electrolyte. An organofluorinated compound of Formula 2; And A non-aqueous electrolyte solution for a lithium secondary battery comprising a negative electrode film improving additive selected from the group consisting of fluoroethylene carbonate, vinylene carbonate, propanesultone, trifluoropropylmethylsulfone, fluorobenzene, LiBF ₄ and mixtures thereof. [Formula 2] R ¹ -O-CO-OR ² (In Formula 2, R ¹ and R ² is an alkyl group or a fluoroalkyl group.) The method of claim 4, wherein The organofluorinated compound is selected from the group consisting of CH ₃ OCOOCH ₂ CHFCH ₃ , CH ₃ OCOOCH (CH ₃ ) CH ₂ F, CH ₃ OCOOCH ₂ CH ₂ CH ₂ F and mixtures thereof. . The method of claim 4, wherein The organic fluorinated compound is a non-aqueous electrolyte solution for a lithium secondary battery that is contained in an amount of 0.1% by mass to 50% by mass relative to the total mass of the nonaqueous electrolyte. delete The method according to claim 1 or 4, The negative electrode film improvement additive is a non-aqueous electrolyte solution for a lithium secondary battery that is contained in an amount of 0.05% by mass to 20% by mass relative to the total mass of the nonaqueous electrolyte. A lithium secondary battery comprising the nonaqueous electrolyte according to claim 1 or 4. A lithium secondary battery according to claim 9; And The charging device which set the battery voltage at the time of full charge of the said lithium battery to 4.2V-4.5V Secondary battery device comprising a.

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