KR101294763B1 - Electrolyte for lithium secondary battery and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a lithium secondary battery electrolyte and a lithium secondary battery comprising the same, the electrolyte is a non-aqueous organic solvent; Lithium salts; And 3,5-dicyclohexyl-3,4,5,6-tetrahydro-2-h-1,3,5-thiadiazine-2-thione compound of Formula 1 below.

[Formula 1]

Electrolyte solution of the present invention can provide a lithium secondary battery excellent in high temperature storage characteristics and life characteristics compared to the conventional carbonate-based electrolyte.

High temperature preservation, long life, cyclohexyl

Description

Electrolyte for lithium secondary battery and lithium secondary battery comprising same {Electrolyte for lithium secondary battery and lithium secondary battery comprising the same}

The present invention relates to a lithium secondary battery electrolyte and a lithium secondary battery comprising the same, and more particularly, to a lithium secondary battery electrolyte having excellent high temperature storage characteristics and lifetime characteristics and a lithium secondary battery comprising the same.

With the recent rapid development of the electronics, telecommunications, and computer industries, the use of portable electronic products such as camcorders, mobile phones, notebook PCs, etc., as well as the compactness, light weight, and high functionality of the devices are becoming common. The demand for it is increasing. In particular, the rechargeable lithium secondary battery has a high energy density per unit weight of about 3 times higher than conventional lead acid batteries, nickel-cadmium batteries, nickel-hydrogen batteries, and nickel-zinc batteries, and can be rapidly charged. Development is underway.

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. A 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 pouch 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, an organic electrolyte solution in which lithium salts are dissolved in a non-aqueous organic solvent is used as an electrolyte for a lithium secondary battery. In this case, it is preferable to use an organic solvent having high ionic conductivity and high dielectric constant and low viscosity. However, since there is no single non-aqueous organic solvent that satisfies all of these conditions, a mixed solvent of a high dielectric constant organic solvent and a low dielectric constant organic solvent or a mixture of a high dielectric constant organic solvent and a low viscosity organic solvent is used. Solvent is used.

US Patent No. 6,114,070 discloses a method of improving ionic conductivity of an organic solvent by mixing dimethyl carbonate or diethyl carbonate and ethylene carbonate or propylene carbonate as a mixed solvent of chain carbonate and cyclic carbonate. It is. However, these mixed solvents can be used usually below 120 ℃ but when the temperature is higher than the gas generated by the vapor pressure there is a problem that the battery is swelled and can not be used.

U.S. Patent 5,352,548 discloses an electrolyte comprising an organic solvent having a vinylene carbonate (VC) content of at least 20%. However, vinylene carbonate has a low dielectric constant compared to ethylene carbonate, propylene carbonate, and gamma butyrolactone, and thus has a problem in that charge and discharge characteristics and efficiency characteristics of a battery are reduced when used as a main solvent.

Accordingly, the present invention is to solve the above-mentioned disadvantages and problems of the prior art, and an object of the present invention is to provide a lithium secondary battery electrolyte having excellent high temperature storage characteristics and excellent life characteristics.

In order to achieve the object as described above, the present invention is a non-aqueous organic solvent; Lithium salts; And a 3,5-dicyclohexyl-3,4,5,6-tetrahydro-2-h-1,3,5-thiadiazine-2-thione compound of Chemical Formula 1, and an electrolyte for a lithium secondary battery, and the same It provides a lithium secondary battery comprising.

[Formula 1]

In addition, the present invention provides a lithium secondary battery electrolyte and a lithium secondary battery comprising the content of the compound of [Formula 1] is 0.2 to 1.5% by weight relative to the total 100% by weight of the electrolyte.

In addition, the present invention provides a lithium secondary battery electrolyte and a lithium secondary battery comprising the content of the compound of [Formula 1] is 0.2 to 1.0% by weight relative to the total 100% by weight of the electrolyte.

In addition, the present invention provides a lithium secondary battery electrolyte and a lithium secondary battery comprising the non-aqueous organic solvent is at least one material selected from the group consisting of carbonate, ester, ether and ketone.

In the present invention, the carbonate is dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC) ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate (BC) provides a lithium secondary battery electrolyte, and a lithium secondary battery comprising any one material selected from the group consisting of.

In the present invention, the lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiAlO At least one selected from the group consisting of ₄ , LiAlCl ₄ , LiN (C _x F _{2x +1} SO ₂ ) (CyF _{2x +1} SO ₂ ), wherein x and y are natural numbers, and LiSO ₃ CF ₃ It provides a lithium secondary battery electrolyte and a lithium secondary battery comprising the same, characterized in that the material.

Therefore, the lithium secondary battery electrolyte of the present invention and a lithium secondary battery comprising the same as an additive 3,5-dicyclohexyl-3,4,5,6-tetrahydro-2-h-1,3,5-thiadiazine-2-thione compound By including, there is an effect that can provide a lithium secondary battery excellent in high temperature storage characteristics and life characteristics.

Details of the above object and technical configuration of the present invention and the effects thereof will be more clearly understood by the following detailed description of the present invention.

The present invention, 3,5-dicyclohexyl-3,4,5,6-tetrahydro of the formula [1] as an additive to an electrolyte containing a non-aqueous organic solvent and lithium salt for the purpose of improving the high temperature storage characteristics and life characteristics It relates to an electrolyte solution containing a 2-h-1,3,5-thiadiazine-2-thione compound.

[Formula 1]

The electrolyte according to the present invention will be described in detail as follows.

First, the electrolyte according to the present invention includes a non-aqueous organic solvent, and the non-aqueous organic solvent may be carbonate, ester, ether or ketone. The carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC) ethylene carbonate (EC), Propylene carbonate (PC), butylene carbonate (BC) and the like can be used, and the ester is butyrolactone (BL), decanolide (decanolide), valerolactone, mevalonolactone (mevalonolactone) , Caprolactone, n-methyl acetate, n-ethyl acetate, n-propyl acetate, and the like may be used. The ether may be dibutyl ether, and the like, and the ketone may include polymethylvinyl ketone. The present invention is not limited to the type of nonaqueous organic solvent.

When the non-aqueous organic solvent is a carbonate-based organic solvent, it is preferable to use a mixture of a cyclic carbonate and a chain carbonate. In this case, the cyclic carbonate and the chain carbonate are preferably used by mixing in a volume ratio of 1: 1 to 1: 9, and more preferably used by mixing 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.

The electrolyte solution of the present invention may further include an aromatic hydrocarbon organic solvent in the carbonate solvent. An aromatic hydrocarbon compound may be used as the aromatic hydrocarbon organic solvent.

Specific examples of the aromatic hydrocarbon-based organic solvent include benzene, fluorobenzene, chlorobenzene, nitrobenzene, toluene, fluorotoluene, trifluorotoluene, xylene and the like. In the electrolyte containing an aromatic hydrocarbon-based organic solvent, the volume ratio of the carbonate solvent / aromatic hydrocarbon solvent is preferably 1: 1 to 30: 1. The performance of the electrolyte is preferable when mixed in the above volume ratio.

Next, the electrolyte according to the present invention comprises a lithium salt, the lithium salt acts as a source of lithium ions in the battery to enable the operation of the basic lithium battery, for example LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiAlO ₄ , LiAlCl ₄ , LiN (C _x F _{2x +1} SO ₂ ) ( CyF _{2x +1} SO ₂ ), where x and y are natural water and LiSO ₃ CF ₃ and include one or more or mixtures thereof.

At this time, the concentration of the lithium salt can be used in the range of 0.6 to 2.0M, preferably in 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 and the performance of the electrolyte is lowered. If the lithium salt is more than 2.0M, the viscosity of the electrolyte is increased, thereby reducing the mobility of lithium ions.

Next, the electrolyte according to the present invention contains a 3,5-dicyclohexyl-3,4,5,6-tetrahydro-2-h-1,3,5-thiadiazine-2-thione compound of [Formula 1] as an additive do.

[Formula 1]

Although it is not common to include additives in battery manufacturing, additives may be added depending on the purpose, especially in order to improve the characteristics of each sector, for example, life characteristics, low temperature high rate discharge characteristics, high temperature safety, overcharge prevention, and high temperature swelling. As added, in the present invention, it can be said that the additive is used to improve the high temperature storage characteristics and life characteristics.

The content of the additive of [Formula 1] is preferably added in 0.2 to 1.5% by weight relative to 100% by weight of the total electrolyte.

When the content is less than 0.2% by weight, there is no effect of improving the high temperature storage characteristics and lifespan characteristics, and when the content exceeds 1.5% by weight, the high temperature storage characteristics and lifetime characteristics are improved, but 1.5% by weight The high temperature storage characteristics and the service life characteristics tend to be rather poor while exceeding the above.

In addition, the content of the additive of [Formula 1] is more preferably added in 0.1 to 1.0% by weight relative to 100% by weight of the total electrolyte.

When the content is less than 0.2% by weight, there is no effect of improving the high temperature storage characteristics and lifespan characteristics, and when the content exceeds 1.0% by weight, the high temperature storage characteristics and life characteristics are improved than those without adding 1.0 wt%. The lifetime characteristic tends to be rather bad, exceeding%.

Next, the electrolyte according to the present invention may further include a carbonate derivative having a substituent selected from the group consisting of halogen, cyano group (CN) and nitro group (NO ₂ ) as an additive. Adding an additive of the carbonate derivative is preferable because it can provide a battery having excellent electrochemical characteristics such as high temperature swelling characteristics, capacity, lifespan, and low temperature characteristics. As such an additive, an ethylene carbonate derivative represented by the following Chemical Formula 2 is preferable, and fluoroethylene carbonate is most preferred.

[Formula 2]

(Wherein X is selected from the group consisting of halogen, cyano group (CN) and nitro group (NO ₂ ).)

The additive is preferably included in 0.1 to 10 parts by weight based on 100 parts by weight of the total electrolyte. When the amount of the additive is less than 0.1 part by weight, it is difficult to expect the effect of suppressing gas generation inside the battery. When the amount of the additive is used in excess of 10 parts by weight, the high temperature life is not good and the problem of swelling at high temperature occurs.

Next, the lithium secondary battery including the electrolyte solution of the present invention includes a positive electrode and a negative electrode.

The positive electrode includes a positive electrode active material capable of reversibly intercalating and deintercalating lithium ions. Representative examples of the positive electrode active material include LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , or LiNi _{1 −} Lithium-transition metal oxides such as _{x- y} Co xMyO ₂ (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1, M is a metal of Al, Sr, Mg, La, etc.) are used .

The negative electrode includes a negative electrode active material capable of intercalating and deintercalating lithium ions, and the negative electrode active material uses crystalline or amorphous carbon or a carbon-based negative electrode active material of a carbon composite.

Applying the positive electrode and the negative electrode active material to the current collector of a thin plate with a suitable thickness and length, respectively, wound or laminated with a separator as an insulator to make an electrode group, and then put it in a can or a similar container, and then inject the electrolyte solution of the present invention A lithium secondary battery is manufactured. As the separator, a resin such as polyethylene or polypropylene may be used.

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

Example 1

LiCoO2 as a positive electrode active material, polyvinylidene fluoride (PVDF) as a binder and carbon as a conductive agent were mixed in a weight ratio of 92: 4: 4, and then dispersed in N-methyl-2-pyrrolidone to prepare a positive electrode slurry. . The slurry was coated on an aluminum foil having a thickness of 20 μm, dried, and rolled to prepare a positive electrode. Synthetic graphite as a negative electrode active material, styrene-butadiene rubber as a binder, and carboxymethyl cellulose as a thickener were mixed in a weight ratio of 96: 2: 2, and then dispersed in water to prepare a negative electrode active material slurry. This slurry was coated on a copper foil having a thickness of 15 mu m, followed by drying and rolling to prepare a negative electrode.

A film separator made of a polyethylene (PE) material having a thickness of 20 μm was put between the prepared electrodes and then wound and compressed, and inserted into a rectangular can.

An electrolyte was injected into the square can to prepare a lithium secondary battery. The electrolyte solution was dissolved 1.3 M LiPF ₆ in ethylene carbonate / ethyl methyl carbonate / dimethyl carbonate mixed solvent (2: 2: 6 volume ratio), and then 3,5-dicyclohexyl-3,4,5,6-tetrahydro- as an additive Prepared by adding 2-h-1,3,5-thiadiazine-2-thione compound, wherein the 3,5-dicyclohexyl-3,4,5,6-tetrahydro-2-h-1,3,5 0.2 wt% of -thiadiazine-2-thione compound was added.

[Example 2]

Example 3 was carried out in the same manner as in Example 1 except that the 3,5-dicyclohexyl-3,4,5,6-tetrahydro-2-h-1,3,5-thiadiazine-2-thione compound was mixed at 0.3% by weight. It was.

[Example 3]

The same procedure as in Example 1 was conducted except that the 3,5-dicyclohexyl-3,4,5,6-tetrahydro-2-h-1,3,5-thiadiazine-2-thione compound was mixed at 0.5 wt%. It was.

Example 4

The same procedure as in Example 1 was conducted except that the 3,5-dicyclohexyl-3,4,5,6-tetrahydro-2-h-1,3,5-thiadiazine-2-thione compound was mixed at 0.8 wt%. It was.

[Example 5]

Example 3 was carried out in the same manner as in Example 1 except that the 3,5-dicyclohexyl-3,4,5,6-tetrahydro-2-h-1,3,5-thiadiazine-2-thione compound was mixed at 1.0% by weight. It was.

[Example 6]

Example 3 was carried out in the same manner as in Example 1, except that the 3,5-dicyclohexyl-3,4,5,6-tetrahydro-2-h-1,3,5-thiadiazine-2-thione compound was mixed at 1.5% by weight. It was.

Comparative Example 1

Same as Example 1, except that 3,5-dicyclohexyl-3,4,5,6-tetrahydro-2-h-1,3,5-thiadiazine-2-thione compound was not mixed, 0% by volume It was carried out.

Comparative Example 2

The same procedure as in Example 1 was conducted except that the 3,5-dicyclohexyl-3,4,5,6-tetrahydro-2-h-1,3,5-thiadiazine-2-thione compound was mixed at 2.0 wt%. It was.

The lithium batteries of Examples 1 to 6 and Comparative Examples 1 and 2 were charged with 4.2V at a 0.5C charge / discharge rate, and then left at 60 ° for one month to measure 0.2C discharge capacity to measure high temperature storage capacity (%). In addition, after charging 4.2V cut-off at 0.8C charge-discharge rate at 60 ° and performing 3.0V cut-off discharge at 1C charge-discharge rate, the 100th capacity retention rate was calculated by calculating the 100th capacity retention rate. %) Was measured.

The measurement results are shown in Table 1 below.

Remarks Additive (% by weight) High Temperature Storage Capacity (%) 100 times capacity (%) Example 1 0.2 85.9 88.1 Example 2 0.3 88.3 91.3 Example 3 0.5 90.1 91.4 Example 4 0.8 91.1 90.5 Example 5 1.0 92.1 91.0 Example 6 1.5 92.2 90.4 Comparative Example 1 0 82.1 85.4 Comparative Example 2 2.0 92.1 90.2

From the results shown in Table 1, the high-temperature storage capacity and the 100-time capacity of Examples 1 to 5 were 3,5-dicyclohexyl-3,4,5,6-tetrahydro-2-h-1,3,5-thiadiazine- It can be seen that the high temperature storage characteristics and lifespan characteristics were improved by remarkably superior to Comparative Example 1 without adding the 2-thione compound.

In the case of Comparative Example 2, in the case of Comparative Example 1 without addition of 3,5-dicyclohexyl-3,4,5,6-tetrahydro-2-h-1,3,5-thiadiazine-2-thione compound Although the high temperature storage capacity and 100 times the capacity is superior, when comparing Example 6 and Comparative Example 2, Comparative Example 2 is a greater amount of 3,5-dicyclohexyl-3,4,5 than Example 6 Despite the addition of, 6-tetrahydro-2-h-1,3,5-thiadiazine-2-thione compound, it can be seen that the high temperature storage capacity and the 100 doses are not as good as in Example 6, It can be seen that adding an additive in excess of 1.5% by weight is meaningless.

However, in the case of Example 6, in the case of Comparative Example 1 without addition of 3,5-dicyclohexyl-3,4,5,6-tetrahydro-2-h-1,3,5-thiadiazine-2-thione compound Although the high temperature storage capacity and the 100 times capacity is superior, when comparing Example 5 and Example 6, Example 6 is a greater amount of 3,5-dicyclohexyl-3,4,5 than Example 5 In spite of the addition of, 6-tetrahydro-2-h-1,3,5-thiadiazine-2-thione compound, the dose of 100 times is not as good as in Example 5, therefore, in the present invention, the additive It can be seen that it is preferable to add to 10.0% by weight or less.

Therefore, in the present invention, it is preferable to add the additive 3,5-dicyclohexyl-3,4,5,6-tetrahydro-2-h-1,3,5-thiadiazine-2-thione compound at 0.2 to 1.5% by weight. In addition, in the life characteristics, it is more preferable to add the additive at 0.2 to 1.0% by weight.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, Various changes and modifications will be possible.

Claims (12)

Non-aqueous organic solvents; Lithium salts; And 3,5-dicyclohexyl-3,4,5,6-tetrahydro-2-h-1,3,5-thiadiazine-2-thione compound of the general formula (1). [Formula 1]

The method of claim 1, The content of the compound of [Formula 1] is a lithium secondary battery electrolyte, characterized in that 0.2 to 1.5% by weight relative to the total 100% by weight of the electrolyte. The method of claim 1, The content of the compound of [Formula 1] is a lithium secondary battery electrolyte, characterized in that 0.2 to 1.0% by weight relative to the total 100% by weight of the electrolyte. The method of claim 1, The non-aqueous organic solvent is at least one material selected from the group consisting of carbonates, esters, ethers and ketones. 5. The method of claim 4, The carbonate is dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC) ethylene carbonate (EC), propylene Electrolyte for lithium secondary battery, characterized in that any one material selected from the group consisting of carbonate (PC) and butylene carbonate (BC). The method of claim 1, The lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiAlO ₄ , LiAlCl ₄ , LiN (C _x F _{2x +1} SO ₂ ) (CyF _{2x +1} SO ₂ ) (where x and y are natural numbers) and LiSO ₃ CF ₃ characterized in that at least one material selected from the group consisting of The electrolyte solution for lithium secondary batteries. An electrolytic solution containing a non-aqueous organic solvent, a lithium salt, and a 3,5-dicyclohexyl-3,4,5,6-tetrahydro-2-h-1,3,5-thiadiazine-2-thione compound represented by Chemical Formula 1 below; A positive electrode including a positive electrode active material capable of intercalating and deintercalating the lithium; And A lithium secondary battery comprising a negative electrode comprising a negative electrode active material capable of intercalating and deintercalating the lithium. [Formula 1]

The method of claim 7, wherein The content of the compound of [Formula 1] is a lithium secondary battery, characterized in that 0.2 to 1.5% by weight relative to the total 100% by weight of the electrolyte. The method of claim 7, wherein The compound of [Formula 1] is a lithium secondary battery, characterized in that 0.2 to 1.0% by weight relative to the total 100% by weight of the electrolyte. The method of claim 7, wherein The non-aqueous organic solvent is at least one material selected from the group consisting of carbonates, esters, ethers and ketones. 11. The method of claim 10, The carbonate is dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC) ethylene carbonate (EC), propylene Lithium secondary battery, characterized in that any one material selected from the group consisting of carbonate (PC) and butylene carbonate (BC). The method of claim 7, wherein The lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiAlO ₄ , LiAlCl ₄ , LiN (C _x F _{2x +1} SO ₂ ) (CyF _{2x +1} SO ₂ ) (where x and y are natural numbers) and LiSO ₃ CF ₃ characterized in that at least one material selected from the group consisting of Lithium secondary battery.