KR101944009B1 - Electrolyte composition for secondary battery and method for producing the same - Google Patents

Abstract

상기 화학식 1에서, R₁ 및 R₂ 는, 각각 독립적으로, 탄소수 1 내지 2의 탄화수소기 또는 할로겐화 탄화수소기이며, R₁ 및 R₂는 단일결합 또는 이중결합으로 연결되어, 고리 구조를 형성한다.
[화학식 2]

상기 화학식 2에서, X는 수소, 시아노기(CN) 또는 불소기(F)이다.Disclosed is an electrolyte composition for a secondary battery having improved stability by preventing decomposition of an organic carbonate used as a solvent of an electrolyte composition, and a method for producing the same. The electrolyte for the secondary battery may be a non-aqueous solvent; Lithium salts; And a carbonate compound represented by the following formula (1) and a pyridine compound represented by the following formula (2) as an additive.
[Chemical Formula 1]

In Formula 1, R ₁ and R ₂ are each independently a hydrocarbon group or halogenated hydrocarbon group having 1 to 2 carbon atoms, and R ₁ and R ₂ are connected to each other through a single bond or a double bond to form a ring structure.
(2)

In the above formula (2), X is hydrogen, a cyano group (CN) or a fluorine group (F).

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolyte composition for a secondary battery,

The present invention relates to an electrolyte composition for a secondary battery, and more particularly, to an electrolyte composition for a secondary battery having improved stability by preventing decomposition of an organic carbonate used as a solvent of an electrolyte composition and a method for producing the same.

The lithium secondary battery has advantages of high energy density and small self-discharge, and thus it is usefully used as a power source for mobile devices such as a smart phone and a notebook, and as a power source for electric vehicles. In the lithium secondary battery, an electrolyte composed of a lithium salt as an electrolyte and a non-aqueous solvent is used. Examples of the non-aqueous solvent include a carbonate solvent (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) (VEC), vinylene carbonate (VC), fluorinated ethylene carbonate (FEC), and the like are used. As the electrolyte, lithium salts such as LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ and LiN (CF ₃ SO ₂ ) ₂ are mainly used. The electrolyte for a lithium secondary battery must have an electrochemically stable potential range as well as a high ionic conductivity and an excellent thermal stability. The solvent should have a high dielectric constant to dissolve the lithium salt and have a high ion conductivity at a wide temperature range. However, since it is difficult to satisfy all of these various characteristics with a single material, two or more carbonate solvents are mixed and used. Examples of the electrolyte include cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC) which can increase the solubility of electrolytes due to their high dielectric constant, and organic solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC) (EMC) and other linear carbonate which can lower the viscosity of electrolyte.

In order to improve the characteristics of the lithium secondary battery, for example, initial capacity, cycle characteristics, high temperature storage characteristics, low temperature characteristics, self discharge characteristics, overcharging characteristics, various additives may be added to the electrolyte. For example, in order to increase the capacity and cycle life of a lithium secondary battery, a vinylene carbonate-based additive has been used since the 1990s. The vinylene carbonate-based additive forms a SEI (Solid Electrolyte interface) film that is stable in the initialization process of the battery, and suppresses reduction of the battery capacity even when the battery is repeatedly charged and discharged. In addition, cyclic carbonate-based additives (VC, VEC, FEC) having a lower decomposition potential than EC or PC are widely used for improving battery characteristics. However, when the above additives are used, there is a problem that the cyclic carbonate solvent having a high dielectric constant such as EC and PC is decomposed and the EC or PC content in the electrolytic solution is continuously decreased. That is, when the vinylene carbonate-based additive is used, an oligomerization reaction or a transesterification reaction that forms polyethylene carbonate, polypropylene carbonate, polyoxyethylene carbonate or the like as the number of cycles of charge / , PC, EMC, DMC, and other carbonate solvents. When the carbonate solvent is decomposed in this way, not only the solubility of the lithium salt as the electrolyte is reduced but also other byproducts (for example, inorganic or organic lithium salts such as Li ₂ CO ₃ , LiF, Li ₂ O and LiOR, Is a hydrocarbon group) salt to increase the resistance in the cell, decrease the electric capacity, and degrade cycle characteristics of the battery.

In order to overcome such disadvantages, Korean Patent Registration No. 511517 discloses a technique of adding an additive such as pyridine, pyrimidine and triazine to an electrolyte to increase the safety of the battery, and U.S. Patent No. 6841303 discloses a technique for improving ionic conductivity A high gel polymer electrolyte composition is disclosed. Also disclosed in the Electrochemical Society (2005, volume 152, issue 7, A1361-A1365, ECS KM, Abraham) Additives for Stabilizing LiPF ₆ Electrolyte Against thermal Decomposition is a technique for improving the thermal stability of electrolytes at high temperatures. As described above, the performance of the battery can be partially improved by forming the SEI film by using the carbonate-based additives (VC, VEC, FEC). However, as the charge / discharge cycle is increased, And the polymer reaction progresses more seriously at a high temperature, the content of the solvent is remarkably decreased, and the cell performance is deteriorated.

Accordingly, an object of the present invention is to provide an electrolyte composition for a secondary battery and a method of manufacturing the same, capable of suppressing decomposition and / or polymerization of an electrolyte to improve cycle characteristics, charge / discharge capacity characteristics, electric resistance characteristics, and the like of the secondary battery .

Another object of the present invention is to provide an electrolyte composition for a secondary battery, which is excellent in heat resistance and stability and can improve cycle characteristics, charge / discharge capacity characteristics, electric resistance characteristics, and the like of a secondary battery even in a high- .

In order to achieve the above object, the present invention provides a nonaqueous solvent; Lithium salts; And an electrolyte for a secondary battery comprising a carbonate compound represented by the following formula (1) and a pyridine compound represented by the following formula (2) as an additive.

[Chemical Formula 1]

In Formula 1, R ₁ and R ₂ are each independently a hydrocarbon group or halogenated hydrocarbon group having 1 to 2 carbon atoms, and R ₁ and R ₂ are connected to each other through a single bond or a double bond to form a ring structure.

(2)

In the above formula (2), X is hydrogen, a cyano group (CN) or a fluorine group (F).

In addition, the present invention relates to a method for producing a compound represented by the formula (1), wherein the carbonate compound represented by the formula (1) and the pyridine compound represented by the formula (2) are stirred for 3 hours or more at a temperature of 40 to 100 캜, Producing; And mixing the aged additive with a non-aqueous solvent and a lithium salt. The present invention also provides a method for producing an electrolyte for a secondary battery.

INDUSTRIAL APPLICABILITY The electrolyte composition for a secondary battery according to the present invention can suppress the decomposition and / or polymerization of an electrolyte even at a high temperature storage and use environment, and can improve cycle characteristics, charge / discharge capacity characteristics, electric resistance characteristics, and the like of the secondary battery .

Hereinafter, the present invention will be described in detail.

The electrolyte for a secondary battery according to the present invention is for improving the high-temperature stability of a secondary battery, particularly, a lithium secondary battery, and includes a non-aqueous solvent; Lithium salts; And additives represented by the following formulas (1) and (2).

Wherein R ₁ and R ₂ are each independently a hydrocarbon group or halogenated hydrocarbon group having 1 to 2 carbon atoms, and R ₁ and R ₂ are a single bond or a double bond (that is, a carbon-carbon single bond or a double bond) Bond) to form a ring structure. The halogenated hydrocarbon group is exemplified by a fluoro hydrocarbon group.

In the above formula (2), X is hydrogen, a cyano group (CN) or a fluorine group (F).

The non-aqueous solvent preferably has a high solubility with respect to the lithium salt and the additive, and includes, but is not limited to, propylene carbonate (PC), ethylene carbonate (EC), ethylmethyl carbonate (DEC), gamma-butyrolactone (GBL), and diethyl carbonate (DEC) may be used alone or in combination. Preferably linear carbonates such as ethyl methyl carbonate (EMC), dimethyl carbonate (DMC) and diethyl carbonate (DEC), and cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate have. In addition, the lithium salt is, as to improve the ionic conductivity of the electrolyte, without _{limitation, LiClO 4, LiCF 3 SO 3} , LiPF 6, LiBF 4, LiAsF 6, LiN (CF 3 SO 2) 2 , etc., alone or Can be mixed and used. In the electrolyte for a secondary battery according to the present invention, the concentration (content) of the lithium salt is 0.9 M to 1.2 M (mol / liter), preferably 0.95 M to 1.1 M. If the content of the lithium salt is less than 0.9 M, the ionic conductivity of the electrolytic solution may be too low. If the content exceeds 1.2 M, the increase of the ionic conductivity is not remarkable, which is economically undesirable.

The electrolyte additive represented by the above formulas (1) and (2) prevents the decomposition of the carbonate solvent contained in the electrolytic solution and suppresses the polymerization of the carbonate solvent. Specific examples of the carbonate compound represented by Formula 1 include vinylene carbonate (VC: 86.05), fluoroethylene carbonate (FEC: molecular weight: 106.05), mixtures thereof, and the like , And specific examples of the pyridine compound represented by the formula (2) include pyridine (molecular weight: 79.10). The compounds represented by the formulas (1) and (2) may be prepared by various conventional organic synthesis methods or may be commercially available. In particular, the compounds represented by the formulas (1) and (2) may be used in an anhydrous state Is also commercially available. In the electrolytic solution for a secondary battery according to the present invention, the total content of the additives represented by the formulas (1) and (2) is 0.1 to 10% by weight, preferably 1 to 6% by weight, more preferably 1.5 to 5% by weight. If the total content of the additive is too small, the stability of the electrolyte at high temperature can not be improved. If the total content of the additive is too large, the properties of the electrolyte (ionic conductivity, etc.) . In the electrolyte for a secondary battery according to the present invention, the amount of the pyridine compound represented by Formula 2 is preferably 0.2 to 1.0 mole, more preferably 0.3 to 0.8 mole, per 1.0 mole of the carbonate compound represented by Formula 1 And most preferably 0.4 to 0.6 mol. In the electrolytic solution, the content of the carbonate compound represented by Formula 1 is 1.2 to 4% by weight, and the content of the pyridine compound represented by Formula 2 is more preferably 0.6 to 2% by weight. If the amount of the pyridine compound represented by the formula (2) is too small (for example, less than 0.4 mol) or too large (for example, more than 0.6 mol), the stability of the electrolyte composition lowers, , The electrolytic solution may be discolored to blackish brown. In the electrolyte solution for a secondary battery according to the present invention, the above components other than the lithium salt, additives and the like are the non-aqueous solvents.

The electrolyte solution for a secondary battery according to the present invention can be produced by a common method such as mixing and stirring each component. Preferably, the carbonate compound represented by the formula (1) and the pyridine compound represented by the formula (2) are mixed at the above-mentioned ratios and the oxygen-shielded state and the temperature of 40 to 100 ° C, preferably 40 to 60 ° C For 3 hours to 3 hours, preferably 3 hours to 5 hours, to prepare an aged additive. The aged additive is then mixed with a non-aqueous solvent and a lithium salt, An electrolyte solution for a secondary battery according to the invention can be produced. Here, if the aging temperature of the additive is too high or the aging time is too long, the carbonate compound of the formula 1 itself may be polymerized. If the aging temperature is too low or the aging time is too short, Is insufficient, there is a fear that the activity of the additive is lowered. The thus-aged additive may be mixed with the non-aqueous solvent and the lithium salt to prepare an electrolyte solution for a secondary battery according to the present invention.

In the electrolyte for a secondary battery according to the present invention, when the carbonate compound represented by Formula 1 and the pyridine compound represented by Formula 2 are used as an electrolyte additive, the decomposition of the carbonate solvent is suppressed and the heat resistance and stabilization of the electrolyte Thereby improving the high temperature service life and capacity characteristics of the battery in which the electrolyte solution is used. A secondary battery in which an electrolyte according to the present invention is used is a secondary battery having a normal structure. The secondary battery includes a positive electrode, a negative electrode, a separation membrane physically separating the positive electrode and the negative electrode and allowing lithium ions to pass therethrough, And the like.

Hereinafter, the present invention will be described in more detail by way of specific examples and comparative examples. The following examples are intended to further illustrate the present invention and are not intended to limit the scope of the present invention.

[Example 1] Preparation of electrolyte solution

In a globe box where water and oxygen are controlled, 396 g of melted ethylene carbonate (EC) and 707 g of ethyl methyl carbonate (EMC) are mixed and then 50 g of molecular sieve is added , Stirred for 12 hours or longer, and filtered to prepare an electrolyte solvent having a water content of 20 ppm or less. 152 g of LiPF ₆ (molecular weight: 151.91) was added to the water-removed electrolyte solvent to prepare 1250 g of a 1 M LiPF ₆ electrolyte solution. On the other hand, 17.2 g of vinylene carbonate (VC) and 8.0 g of pyridine were fed into a flask equipped with a stopper, the flask was filled with nitrogen to prevent oxygen from entering the flask, and then the temperature inside the flask was adjusted to 60 캜 While stirring, the mixture was stirred for 3 hours to agitate the additive. All of the aged additive was added to the electrolyte solution to prepare an electrolyte solution having an additive content of about 2% by weight.

[Example 2] Preparation of electrolyte solution

An electrolytic solution was prepared in the same manner as in Example 1, except that 18.5 g of fluorinated ethylene carbonate (FEC) and 6.5 g of pyridine were used instead of 17.2 g of vinylene carbonate (VC) and 8.0 g of pyridine.

[Comparative Example 1] Preparation of electrolyte solution

An electrolytic solution was prepared in the same manner as in Example 1 except that 25 g of vinylene carbonate was used alone instead of 17.2 g of vinylene carbonate (VC) and 8.0 g of pyridine.

[Comparative Example 2] Preparation of electrolyte solution

An electrolytic solution was prepared in the same manner as in Example 1, except that 25 g of fluorinated ethylene carbonate (FEC) was used alone instead of 17.2 g of vinylene carbonate (VC) and 8.0 g of pyridine.

[Comparative Example 3] Electrolyte preparation

An electrolytic solution was prepared in the same manner as in Example 1 except that 25 g of pyridine was used alone instead of 17.2 g of vinylene carbonate (VC) and 8.0 g of pyridine.

[Comparative Example 4] Preparation of electrolyte solution

An electrolytic solution was prepared in the same manner as in Example 1 except that 8.6 g of vinylene carbonate (VC) and 16.4 g of pyridine were used instead of 17.2 g of vinylene carbonate (VC) and 8.0 g of pyridine.

[Comparative Example 5] Preparation of electrolyte solution

An electrolytic solution was prepared in the same manner as in Example 1, except that 20 g of vinylene carbonate (VC) and 5 g of pyridine were used instead of 17.2 g of vinylene carbonate (VC) and 8.0 g of pyridine.

[Comparative Example 6] Preparation of electrolyte solution

An electrolytic solution was prepared in the same manner as in Example 1, except that 22 g of fluorinated ethylene carbonate (FEC) and 3 g of pyridine were used instead of 17.2 g of vinylene carbonate (VC) and 8.0 g of pyridine.

[Comparative Example 7] Preparation of electrolyte solution

An electrolytic solution was prepared in the same manner as in Example 1, except that 3 g of fluorinated ethylene carbonate (FEC) and 22 g of pyridine were used instead of 17.2 g of vinylene carbonate (VC) and 8.0 g of pyridine.

Performance evaluation of electrolyte and secondary battery

50 ml of the electrolytic solution prepared in Examples 1 to 2 and Comparative Examples 1 to 7 was placed in a transparent container and stored in a thermostatic oven at 65 ° C for 2 weeks. (Gardner value) of the electrolyte solution was measured using a Gardner index. The change in the carbonate content in the electrolyte solution (EC residual ratio (%)) was measured using NMR (600 MHz) and gas chromatography, EC content / initial EC content after 2 weeks) was measured. A 1000 mAh pouch cell was manufactured in the usual manner by using the electrolyte prepared in Examples 1 and 2 and Comparative Examples 1 to 7, lithium cobalt oxide (LCO) active material as an anode, and graphite as a cathode. Respectively. The prepared battery was charged to 4.2 V at 1 C at high temperature (60 캜), discharged to 3 V, and charged and discharged 100 times. Table 1 shows the discharge capacity (%) after 100 charge / discharge cycles compared with the initial discharge capacity.

additive Chromaticity
change EC
Remaining rate Discharge
Volume Example 1 17.2 g of vinylene carbonate (VC) and
Pyridine 8.0 g One 99% 98% Example 2 18.5 g of fluorinated ethylene carbonate (FEC) and
Pyridine 6.5 g One 99% 97% Comparative Example 1 25 g of vinylene carbonate (VC) 3 92% 93% Comparative Example 2 25 g of fluorinated ethylene carbonate (FEC) 3 91% 92% Comparative Example 3 25 g 2 94% 80% Comparative Example 4 8.6 g of vinylene carbonate (VC) and
Pyridine 16.4 g 7 92% 86% Comparative Example 5 20 g of vinylene carbonate (VC) and
5 g 7 91% 90% Comparative Example 6 22 g of fluorinated ethylene carbonate (FEC) and
Pyridine 3 g 8 90% 90% Comparative Example 7 3 g of fluorinated ethylene carbonate (FEC) and
22 g 10 90% 88%

As shown in Table 1, when the mole ratio of pyridine to vinylene carbonate used as an additive was 0.51 (Example 1), the molar ratio of pyridine to vinylene carbonate was 2.07 (Comparative Example 4) and 0.27 (Comparative Example 5), the EC content in the electrolytic solution was kept high and the chromaticity change of the electrolytic solution was changed as compared with the case of using only vinylene carbonate (Comparative Example 1) and the case of using only pyridine (Comparative Example 3) And the battery discharge performance was also excellent. The molar ratio of pyridine to ethylene fluorocarbonate was 9.83 (Comparative Example 7) and 0.18 (Comparative Example 6) in the case where the molar ratio of pyridine to ethylene fluorocarbonate used as an additive was 0.47 (Example 2) , The EC content in the electrolytic solution was kept high and the chromaticity change of the electrolytic solution was small as compared with the case where only fluorinated ethylene carbonate was used (Comparative Example 2) and the case where only pyridine was used (Comparative Example 3) Performance. It can be seen from the above Examples and Comparative Examples that by controlling the molar ratio of pyridine: vinylene carbonate or ethylene carbonate to about 1: 2, the high temperature characteristics of the electrolyte and the secondary battery can be improved.

Claims (6)

delete delete delete delete delete A carbonate compound represented by the following formula 1 and a pyridine compound represented by the following formula 2 are stirred for 3 hours or more at a temperature of 40 to 100 DEG C in a state where oxygen is blocked to prepare an aged additive,
[Chemical Formula 1]

In Formula 1, R ₁ and R ₂ are each independently a hydrocarbon group or halogenated hydrocarbon group having 1 to 2 carbon atoms, and R ₁ and R ₂ are connected to each other through a single bond or a double bond to form a ring structure.
(2)

In Formula 2, X is hydrogen, a cyano group (CN) or a fluorine group (F); And
And mixing the aged additive with a non-aqueous solvent and a lithium salt.