KR19990024598A - Non-aqueous electrolyte solution for lithium ion batteries and lithium ion battery comprising same - Google Patents

Abstract

The present invention provides an organic electrolyte solution for a lithium ion battery including a lithium salt and a mixed organic solvent, wherein the mixed organic solvent includes a high dielectric constant solvent, a low viscosity solvent, and a compound represented by the following Formula 1 The present invention relates to an organic electrolyte and a lithium ion battery employing the same, and the non-aqueous electrolyte solution for a lithium ion battery according to the present invention has advantages of excellent ion conductivity and low temperature storage characteristics and a wide potential window region. Therefore, the lithium ion battery employing the electrolyte solution of the present invention not only shows stable charge and discharge characteristics even when the battery has a large capacity and cycles, but also has excellent life characteristics of the battery.

Wherein R ₁ and R ₂ are each independently of each other, a linear or cyclic alkyl group having 1 to 5 carbon atoms, and x is 0 to 3;

Description

Non-aqueous electrolyte solution for lithium ion batteries and lithium ion battery comprising same

The present invention relates to a lithium ion battery, and more particularly, to an organic electrolyte solution for a lithium ion battery capable of improving battery capacity, low temperature resistance, and a charge / discharge cycle, and a lithium ion battery including the same.

In recent years, the miniaturization, thinning, and weight reduction of electronic devices have been made rapidly, and in the field of office automation, in particular, small size and light weight have been reduced from desktop computers to laptop and notebook computers. In addition, with the emergence of electronic notebooks, electronic still cameras, and the like, the miniaturization of conventional hard disks and floppy disks, and the development of memory cards, which are new small memory media, are also in progress.

In accordance with the trend of light and short reduction of such battery devices, high performance is also required for secondary batteries that supply power to them.

In response to this demand, the development of lithium secondary batteries as a high energy density battery to replace lead batteries or nickel-cadmium batteries is rapidly progressing.

In the lithium secondary battery, transition metal compounds such as TiO ₂ , MoS ₂ , CoO ₂ , V ₂ O ₅ , FeS, NbS ₂ , MnO ₂ , or oxides of these and lithium are used as active materials, As the negative electrode, lithium metal, an alloy thereof, or a carbon material is used as the active material.

In addition, as the separator, a low resistance and excellent solution retention property with respect to the ion migration of the electrolyte is mainly used. At least one nonwoven fabric selected from glass fiber, polyester, Teflon, polypropylene, polytetrafluoroethylene (PTFE), and the like is used. Or a woven fabric.

Meanwhile, lithium secondary batteries are classified into liquid electrolyte batteries and polymer electrolyte batteries according to the type of electrolyte used. Generally, batteries using liquid electrolytes are lithium ion batteries and batteries using polymer electrolytes are lithium polymer batteries. do.

Of these, as the liquid electrolyte, an organic electrolyte solution in which lithium salt is dissolved in an organic solvent rather than an aqueous solution is used because lithium reacts violently upon contact with water. In this case, it is preferable to use an organic solvent having high ionic conductivity and low dielectric constant and low viscosity. Since there is no single organic solvent that satisfies all of these conditions, the organic solvent having a high dielectric constant and a low viscosity organic solvent are used. Mixed solvent systems are commonly used.

Examples of such a mixed organic solvent include a carbonate ester mixed solvent of propylene carbonate and diethyl carbonate, a three component mixed solvent of ethylene carbonate, dimethyl carbonate, and diethyl carbonate.

However, these mixed solvents have a problem that the low temperature storage characteristics and the charge and discharge cycle characteristics are not satisfactory.

It is an object of the present invention to provide an organic electrolyte solution for a lithium ion battery having improved low-temperature storage characteristics and charge / discharge cycle characteristics.

Another object of the present invention is to provide a lithium ion battery having improved low-temperature storage characteristics and charge / discharge cycle characteristics by employing the organic electrolyte.

1 is a cross-sectional view of a cell for measuring ion conductivity.

2 is a cross-sectional view of the cell for measuring the potential window.

3 is a graph showing a cyclic voltametry for the conventional non-aqueous electrolyte and the non-aqueous electrolyte according to the present invention.

Explanation of symbols for the main parts of the drawings

11, 25 electrolyte 12 platinum electrode

13: platinum lead wire 21: nickel lead wire

22: Teflon sealing 23: working electrode

24: Nickel Foil 26: Luggin capillary

27: nickel chip

Technical problem of the present invention is that in the organic electrolyte solution for a lithium ion battery comprising a lithium salt and a mixed organic solvent, the mixed organic solvent comprises a high dielectric constant solvent, a low viscosity solvent and a compound represented by the formula (1) It can be made by organic electrolyte for lithium ion batteries:

[Formula 1]

Wherein R ₁ and R ₂ are each independently of each other, a linear or cyclic alkyl group having 1 to 5 carbon atoms, and x is 0 to 3;

In addition, another technical problem of the present invention is an anode comprising an oxide of a lithium-containing metal; A negative electrode including a material selected from the group consisting of metal lithium, lithium alloy or carbon material; And a lithium salt may be made by a lithium ion battery comprising a non-aqueous electrolyte solution dissolved in a mixed organic solvent consisting of a high dielectric constant solvent, a low boiling point solvent and the compound represented by the formula (1).

Here, the mixing volume% of the high dielectric constant solvent, the low viscosity solvent, and the compound represented by Chemical Formula 1 is preferably 30-50: 30-40: 20-30.

In addition, the high dielectric constant solvent may be ethylene carbonate, propylene carbonate or gamma butyrolactone, the low boiling point solvent may be dimethyl carbonate, diethyl carbonate, dimethoxyethane or fatty acid ester derivative, the compound of Formula 1 is dimethyl mal Nate, diethylmalonate or diethyloxalate.

Since the compound represented by Chemical Formula 1 has a low melting point and a low viscosity and no decomposition occurs at a high voltage, the compound may contribute to low temperature storage resistance, ion conductivity, cycle characteristics, and oxidation resistance.

Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in detail, this invention is not limited to this.

Example 1

An active material paste was prepared by mixing polytetrafluoroethylene dissolved in LiMn ₂ O ₄ as an active material, Super-P carbon as a conductive agent, and N-methylpyrrolidone as a binder, and then, onto an aluminum foil having a thickness of 200 μm. After casting, drying, pressing, and cutting to cut for a 2016 type coin-type battery to prepare a positive electrode.

Further, an active material paste was prepared by mixing graphite powder (manufactured by Osaka Gas Co., MCMB 2528 graphite powder) as the active material, Super-P carbon as the conductive agent, and polytetrafluoroethylene dissolved in N-methylpyrrolidone as the binder. After manufacturing, it was cast in an aluminum foil having a thickness of 200 μm, dried, pressed, and cut to cut for a 2016 type coin-type battery, thereby preparing a negative electrode.

Subsequently, electrolyte solution was prepared by the following method.

First, a reagent bottle containing ethylene carbonate (manufactured by Mitsubishi Chem.) In a solid state was placed in an electric mantle, and then slowly heated to 70-80 ° C. to liquefy. Subsequently, LiPF ₆ was placed in a plastic container to store the electrolyte, and then dimethyl carbonate solvent (manufactured by Mitsubishi Chem.) Was added and shaken vigorously to dissolve the lithium salt. The liquefied ethylene carbonate solution is added to the mixture using a pipette to shake the mixture, and dimethylmalonate (from Aldrich Chem. Co., purity: 99% or more) is added thereto, followed by vigorous shaking to mix the solution evenly. It was prepared to an organic electrolyte solution.

At this time, in order to completely remove the effect of the moisture contained in the dimethylmalonate, the dimethylmalonate is simply distilled, and then, in a reagent container containing the dimethylmalonate under an argon gas atmosphere of 99.9999% or more, the Molecular Sieve 4A ( molecular sieve 4A) was placed in a vacuum oven and dried at 120 ° C. for 24 hours. The mixed volume ratio of ethylene carbonate, dimethyl carbonate and dimethyl malonate was 40:40:30.

After preparing the electrolyte in the same manner as described above, cover the lid of the plastic barrel, wrap around the lid again with a paraffin sheet, store in a dry box for 10 days, and then according to Karl Fisher Titration As a result of measuring the amount of water contained in the electrolyte solution over time, the average value was 60 ppm and found to contain a very small amount of water.

Subsequently, the ion conductivity, potential window, and low temperature storage characteristics of the prepared electrolyte were measured by the following method:

First, the ion conductivity of the electrolyte was measured using the cell for measuring ion conductivity as shown in FIG. 1, and the results are shown in Table 1 below.

Next, prepare two 30 ml plastic containers for each cold storage property, put 15 ml of electrolyte into each container, close the lid, and wind the paraffin film around the lid to completely block air contact. The vessel was then placed in a TABAI thermo-hygrostat and left for 24 hours at temperatures of -30 ° C and -40 ° C, respectively. Then, it was visually observed whether the solvent and the lithium salt were phase separated and whether the electrolyte was frozen. The experimental results are shown in Table 1 below.

Finally, in order to determine whether the prepared electrolyte solution is stable in the operating voltage range, potential injection was performed at a rate of 1 kHz / s at a frequency of 1 MHz using a three-pole measuring cell as shown in FIG. 2. The results are shown in FIG. 3.

Subsequently, five coin-type cells of the complete 2016 type were prepared using the positive electrode, the negative electrode, and the electrolyte prepared as described above, and then the capacity change rate with respect to the capacity of these cells and the initial capacity values after 100 and 200 cycles. Calculate the average value. The results are shown in Table 1.

In this case, the battery capacity and the charge and discharge characteristics were used as a charge-discharger (manufactured by Maccor) with a capacity of 1A, charging and discharging were carried out at 0.2C at 25 ℃, respectively, and the charging voltage was 3.0-4.3V.

In addition, the initial dose and the dose change after 100 cycles and 200 cycles are expressed as a ratio with respect to the initial dose value, respectively, and the results are shown in Table 2.

Example 2

An electrolyte was prepared in the same manner as in Example 1 except that diethylmalonate was used instead of dimethylmalonate, the cell was constructed, and then ion conductivity, potential window, low temperature storage characteristics, battery capacity, and 100 cycles. And the rate of change of dose relative to the initial dose after 200 cycles. The results are shown in Table 1 and FIG. 3.

Example 3

An electrolyte was prepared in the same manner as in Example 1 except that diethyloxalate was used instead of dimethylmalonate, and the battery was constructed, followed by ion conductivity, potential window, low temperature storage characteristics, battery capacity, and 100 cycles. And the rate of change of dose relative to the initial dose after 200 cycles. The results are shown in Table 1 and FIG. 3.

Example 4-6

The mixing volume ratios of ethylene carbonate, dimethyl carbonate and dimethyl malonate are 40:40:20 (Example 4), 30:40:30 (Example 5) and 50:30:20 (Example 6), respectively. Then, the electrolyte was prepared in the same manner as in Example 1, the battery was constructed, and then the ion conductivity, low temperature storage characteristics, battery capacity, and capacity change rate with respect to the initial capacity values after 100 and 200 cycles were measured. The results are shown in Table 1 below.

Comparative Example 1

An electrolyte was prepared in the same manner as in Example 1 except that dimethylmalonate was not added to the mixed organic solvent, the cell was constructed, and then the ion conductivity, potential window, low temperature storage characteristics, capacity of the cell, and 100 cycles were obtained. And the rate of change of dose relative to the initial dose after 200 cycles. The results are shown in Table 1 and FIG. 3.

Comparative Example 2

An electrolyte solution was prepared in the same manner as in Example 1 except that the mixed volume ratio of ethylene carbonate, dimethyl carbonate, and dimethyl malonate was 60:20:20, and the battery was formed, followed by ion conductivity, low temperature storage characteristics, and battery. The dose change rate with respect to the capacity of and the initial dose value after 100 and 200 cycles was measured. The results are shown in Table 1 below.

Ion Conductivity (25 ℃, s / cm) Freezing at -30 ℃ Freeze at -40 ℃ Initial capacity (mAh) Capacity change rate after 100 cycles Capacity change rate after 200 cycles Example 1 1.124 × 10 ^-2 Non-freezing Non-freezing 2.89 92% 87% Example 2 1.226 × 10 ^-2 〃 〃 2.91 90% 85% Example 3 1.137 × 10 ^-2 〃 〃 2.88 90% 85% Example 4 1.311 × 10 ^-2 〃 〃 2.86 90% 85% Example 5 1.116 × 10 ^-2 〃 〃 2.77 86% 81% Example 6 1.133 × 10 ^-2 〃 〃 2.87 91% 85% Comparative Example 1 freezing freezing 2.88 90% 82% Comparative Example 2 1.475 × 10 ^-2 〃 〃 2.91 81% 70%

In addition, referring to Figure 3, it can be seen that the electrolytic solution according to the present invention has a wider potential window area than the two-component electrolytic solution composed of conventional ethylene carbonate and dimethyl carbonate.

From the results of Table 1 and FIG. 3, it can be seen that the electrolyte according to the present invention and the lithium ion battery employing the same have high ion conductivity and excellent low temperature storage characteristics. In addition, it can be seen that the cycle characteristics are very excellent in view of the large capacity of the battery and the small capacity change rate according to the progress of the cycle, and the wide potential window region can maintain stable battery characteristics even in a wide voltage range.

The non-aqueous electrolyte solution for lithium ion batteries according to the present invention has the advantage of excellent ion conductivity and low temperature storage characteristics and wide potential window area. Therefore, the lithium ion battery employing the electrolytic nucleus of the present invention not only shows stable charge / discharge characteristics even when the battery has a large capacity and cycles, but also has good life characteristics of the battery.

Claims (10)

In the organic electrolyte solution for lithium ion batteries containing a lithium salt and a mixed organic solvent, The mixed organic solvent comprises a high dielectric constant solvent, a low viscosity solvent and a compound represented by the following formula (1). [Formula 1] In the above formula, R ₁ and R ₂ are independent of each other, a linear or cyclic alkyl group having 1 to 5 carbon atoms, x is 0-3. The organic electrolyte solution for a lithium ion battery according to claim 1, wherein the mixed volume% of the high dielectric constant solvent, the low boiling point solvent, and the compound of Formula 1 is 30-50: 30-40: 20-30. The organic electrolyte solution for a lithium ion battery according to claim 1 or 2, wherein the high dielectric constant solvent is selected from the group consisting of ethylene carbonate, propylene carbonate, and gamma butyrolactone. The organic electrolyte solution for a lithium ion battery according to claim 1 or 2, wherein the low boiling point solvent is selected from the group consisting of dimethyl carbonate, diethyl carbonate, dimethoxyethane and fatty acid ester derivatives. The organic electrolyte solution for a lithium ion battery according to claim 1 or 2, wherein the compound of Formula 1 is selected from the group consisting of multimethylmalonate, diethylmalonate and diethyloxalate. An anode comprising an oxide of a lithium-containing metal; A negative electrode including a material selected from the group consisting of metal lithium, lithium alloy or carbon material; And A lithium ion battery comprising a non-aqueous electrolyte solution in which a lithium salt is dissolved in a mixed organic solvent consisting of a high dielectric constant solvent, a low boiling point solvent, and a compound represented by the following Formula 1. [Formula 1] In the above formula, R ₁ and R ₂ are independent of each other, a linear or cyclic alkyl group having 1 to 5 carbon atoms, x is 0-3. The organic electrolyte solution for a lithium ion battery according to claim 6, wherein the mixing volume% of the high dielectric constant solvent, the low boiling point solvent, and the compound of Formula 1 is 30-50: 30-40: 20-30. The organic electrolyte solution for lithium ion batteries according to claim 6 or 7, wherein the high dielectric constant solvent is selected from the group consisting of ethylene carbonate, propylene carbonate, and gamma butyrolactone. 8. The organic electrolyte solution for lithium ion batteries according to claim 6 or 7, wherein the low boiling point solvent is selected from the group consisting of dimethyl carbonate, diethyl carbonate, dimethoxyethane and fatty acid ester derivatives. The organic electrolytic solution for lithium ion battery according to claim 6 or 7, wherein the compound of Formula 1 is selected from the group consisting of multimethylmalonate, diethylmalonate and diethyloxalate.