KR20020042224A - Non-aqueous electrolyte solution for lithium battery - Google Patents

Abstract

PURPOSE: Provided is a non-aqueous electrolyte for a lithium battery, which can prevent the battery from swelling, therefore, can improve a set mounting rate remarkably when preparing the lithium battery. CONSTITUTION: The non-aqueous electrolyte is produced by adding 0.1-10.0pts.wt. of a sulfoxide compound represented by the formula 1 to 100pts.wt. of a mixed organic solvent in which 0.8-2.0M of lithium salts are dissolved, wherein the mixed organic solvent comprises a cyclic carbonate-based organic solvent selected from ethylene carbonate, propylene carbonate, or a mixture thereof and a linear carbonate-based organic solvent selected from dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, or a mixture thereof. And the sulfoxide compound is perfluoro butane sulfonyl fluoride or perfluoro octane sulfonyl fluoride. In the formula, R is C1-C10 perfluoroalkyl and R' is C1-C10 fluoroalkyl or fluoro.

Description

Non-aqueous electrolyte solution for lithium battery

The present invention relates to a non-aqueous electrolyte for lithium batteries, and more particularly, to 100 parts by weight of a mixed organic solvent of a cyclic carbonate organic solvent and a linear carbonate organic solvent in which lithium salt is dissolved at 0.8 to 2.0 M. The present invention relates to a nonaqueous electrolyte solution for a lithium battery prepared by adding 0.1 to 10.0 parts by weight of the sulfoxide compound.

[Formula 1]

In the above, R is a perfluoroalkyl group having 1 to 10 carbon atoms, and R 'is a fluoroalkyl group or fluoro group having 1 to 10 carbon atoms.

The miniaturized and slimmed lithium secondary battery used in notebook computers, camcorders, mobile phones, etc. is a positive electrode active material made of lithium metal mixed oxide capable of detaching and intercalating lithium ions, a negative electrode made of carbon material or metal lithium, and mixed It consists of electrolyte solution in which lithium salt was melt | dissolved in the organic solvent. Coins, 18650 cylinders, 063048 squares, and the like are generally used as the lithium battery.

The average discharge voltage of about 3.6 to 3.7 V of the lithium battery is one of the biggest advantages of obtaining high power compared to other alkaline batteries or Ni-MH or Ni-Cd batteries. In order to achieve such a high driving voltage, an electrochemically stable electrolyte composition is required in the charge / discharge voltage range of 0 to 4.2 V. Therefore, ethylene carbonate (hereinafter referred to as "EC") and dimethyl carbonate (hereinafter referred to as "DMC") are required. Carbonate organic solvents such as " diethylcarbonate " (hereinafter referred to as " DEC ") are suitably mixed and used as a solvent of the electrolyte solution. As the solute of the electrolyte, lithium salts such as LiPF ₆ , LiBF ₄ , and LiClO ₄ are usually used, and these act as a source of lithium ions in the battery to enable basic operation of the lithium battery. However, the non-aqueous electrolyte prepared in this way may have disadvantages in high rate charge and discharge because the conductivity of the nonaqueous electrolyte is significantly lower than that of the aqueous electrolyte used in Ni-MH or Ni-Cd batteries.

In the initial charging of a lithium battery, lithium ions from the lithium metal oxide used as the positive electrode move to the graphite (crystalline or amorphous) electrode used as the negative electrode and are intercalated between the layers of the graphite electrode. At this time, since lithium has a high reactivity, the electrolyte and the carbon constituting the cathode react on the surface of the graphite anode to generate compounds such as Li ₂ CO ₃ , Li ₂ O, and LiOH. These compounds form a kind of passivation layer on the surface of the graphite cathode, which is called a solid electrolyte interface (SEI) film. Once formed, the SEI film functions as an ion tunnel to pass only lithium ions.

The SEI film solvates lithium ions by the effect of this ion tunnel, and organic solvent molecules having large molecular weight, such as EC, DMC, or DEC, which move together with lithium ions in the electrolyte are inserted together in the graphite anode ( cointercalation) prevents the structure of graphite cathodes from collapsing. Once the SEI film is formed, lithium ions again do not react sideways with the graphite cathode or other material, and the amount of charge consumed to form the SEI film has a property of not reversibly reacting upon discharge with an irreversible capacity. Accordingly, no further decomposition of the electrolyte occurs and the amount of lithium ions in the electrolyte is reversibly maintained to maintain stable charge and discharge (see J. Power Sources (1994) 51:79 to 104).

However, in the thin rectangular battery, there is a problem that the thickness of the battery is expanded during charging due to the generation of gases such as CO, CO ₂ , CH ₄ , and C ₂ H ₆ generated from decomposition of the carbonate-based organic solvent during the above-described SEI formation reaction. (See J. Power Sources (1998) 72: 66-70). In addition, when stored at high temperature in a fully charged state (for example, left at 85 ° C. for 4 days after 100% charge to 4.2V), the SEI film gradually decays due to increased electrochemical energy and thermal energy, and is exposed. The side reaction where the negative electrode surface reacts with the surrounding electrolyte continuously occurs. In this case, the internal pressure of the battery increases due to the continuous gas generation. As a result, in the case of the square battery and the polymer lithium ion (PLI) battery, the thickness of the battery increases, which causes a problem in that the set mounting itself becomes difficult.

In order to suppress such an increase in the internal pressure of the battery, studies have been conducted to change the aspect of the SEI formation reaction by adding an additive to the electrolyte. For example, Japanese Patent No. 95-176323 discloses a technique for adding CO ₂ to an electrolyte, and Japanese Patent No. 95-320779 discloses a technique for suppressing decomposition of an electrolyte by adding a sulfide compound to the electrolyte. In Japanese Patent No. 97-73918, diphenyl picrylhydrazyl was added to improve the high temperature storage of the battery. In Japanese Patent No. 96-321313, a specific compound was added to the electrolyte to charge and discharge the battery. Improved properties.

However, it is known so far that when certain compounds are added to the electrolyte to improve battery performance, the performance of some items is improved, while the performance of other items is accompanied by a decrease in performance (eg, low temperature performance is improved, but Discharge cycles were often reduced).

Therefore, by acting as an inhibitor of decomposition of the electrolyte in the cell and as a regulator of the SEI film formation reaction occurring on the surface of the graphite anode, it is possible to reduce the amount of gas generated in the battery and improve the charge / discharge cycle characteristics. The development of additives is urgently needed.

An object of the present invention is to solve the problems of the prior art as described above, by suppressing the decomposition of the electrolyte by adding a sulfoxide compound to the conventional non-aqueous electrolyte for lithium batteries to reduce the amount of gas generated at room temperature and high temperature significantly It is providing a nonaqueous electrolyte solution for lithium batteries.

That is, the present invention is 0.1 to 10.0 weight of the sulfoxide compound represented by the following formula (1) to 100 parts by weight of a mixed organic solvent of a cyclic carbonate organic solvent and a linear carbonate organic solvent in which lithium salt is dissolved at 0.8 to 2.0 M. It provides a nonaqueous electrolyte solution for lithium batteries prepared by addition.

[Formula 1]

In the above, R is a perfluoroalkyl group having 1 to 10 carbon atoms, and R 'is a fluoroalkyl group or fluoro group having 1 to 10 carbon atoms.

Hereinafter, the component of the nonaqueous electrolyte solution for lithium batteries of this invention is demonstrated in detail.

The organic solvent used in the preparation of the non-aqueous electrolyte lithium battery of the present invention is used by mixing a cyclic carbonate organic solvent and a linear carbonate organic solvent, preferably from a cyclic carbonate organic solvent group composed of ethylene carbonate and propylene carbonate. One or more selected, and a mixture of two or more selected from the group of linear carbonate organic solvents consisting of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate and ethyl propyl, more preferably Preferably, ethylene carbonate, dimethyl carbonate and diethyl carbonate are mixed and used. In addition, one or more selected from the group consisting of propyl acetate, methyl acetate, ethyl acetate, butyl acetate, methyl propionate and ethyl propionate may be further mixed and used as necessary. The mixing ratio of the organic solvent selected from each group is not particularly limited as long as the object of the present invention is not impaired, and the mixing ratio in the production of a nonaqueous electrolyte solution for a lithium battery is followed.

On the other hand, as the lithium salt contained in the nonaqueous electrolyte of the present invention, it is preferable to use one or more selected from the group consisting of LiPF ₆ , LiClO ₄ , LiAsF _6, and LiBF ₄ , and more preferably LiPF ₆ . use.

The non-aqueous electrolyte solution of the present invention is a sulfoxide compound represented by the following formula (1), preferably perfluorobutanesulfonyl fluoride or perfluorooctanesulfonyl fluoride, in the mixed organic solvent in which lithium salt is dissolved. To 10.0 parts by weight, preferably 0.5 to 2.0 parts by weight.

[Formula 1]

In the above, R is a perfluoroalkyl group having 1 to 10 carbon atoms, and R 'is a fluoroalkyl group or fluoro group having 1 to 10 carbon atoms.

The lithium battery can be manufactured according to a conventional method using the nonaqueous electrolyte solution for lithium batteries of the present invention, and the lithium battery thus produced can suppress gas generation inside the battery during normal charge and at high temperature (85 ° C.). The swelling phenomenon in which the thickness of the battery is expanded is prevented.

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

Example 1

Perfluoro-1-butanesulfur in 100 parts by weight of a mixed organic solvent (hereinafter referred to as "basic nonaqueous electrolyte") in which ethylene carbonate: dimethyl carbonate: diethyl carbonate = 1: 1: 1 dissolved in LiPF ₆ is 1.0 M 0.5 parts by weight of perfluoro-1-butanesulfonylfluoride was added to prepare a nonaqueous electrolyte solution for a lithium battery. Using the nonaqueous electrolyte thus prepared, an 18650 cylindrical battery and a 063048 square battery were manufactured according to a conventional method. In manufacturing the battery, graphite and LiCoO ₂ were used as the negative electrode active material and the positive electrode active material, polyvinylidene fluoride was used as the binder, and acetylene black was used as the conductive agent.

Example 2

A nonaqueous electrolyte solution for a lithium battery was prepared in the same manner as in Example 1, except that 1.0 part by weight of perfluoro-1-butanesulfonylfluoride was added, thereby preparing an 18650 cylindrical battery and a 063048 square battery. .

Example 3

A nonaqueous electrolyte solution for a lithium battery was prepared in the same manner as in Example 1, except that 2.0 parts by weight of perfluoro-1-butanesulfonylfluoride was added, thereby preparing an 18650 cylindrical battery and a 063048 square battery. .

Example 4

A non-aqueous electrolyte solution for lithium batteries was prepared in the same manner as in Example 1, except that 2.0 parts by weight of perfluoro-1-octanesulfonylfluoride was added instead of perfluoro-1-butanesulfonyl fluoride. This was used to prepare 18650 cylindrical cells and 063048 square cells.

Comparative Example 1

An 18650 cylindrical battery and a 063048 square battery were manufactured in the same manner as in Example 1, except that a basic nonaqueous electrolyte solution without added perfluoro-1-butanesulfonylfluoride was used.

The physical properties of each of the 18650 cylindrical batteries obtained from Examples 1 to 4 and Comparative Example 1 were measured by the following method, and the results are summarized in Table 1 below.

Gas generation amount (25 ℃, after 1 time charge and discharge) High temperature performance (85 ° C, left for 4 hours) Example 1 0.65 0.64 Example 2 0.68 0.85 Example 3 0.54 0.86 Example 4 0.78 0.91 Comparative Example 1 One One

[Measurement Method]

1) Gas generation amount: After the full charge from 0.2C to 4.2V at 25 ℃ constant temperature conditions, the volume of the gas generated at this time was measured while discharging from 0.2C to 2.75V. The amount of gas generated is shown as a relative value based on the amount of generated in Comparative Example 1.

2) High temperature performance: After the full charge to 0.2V at 0.2C under a constant temperature of 25 ℃, it was left for 4 hours at 85 ℃ to measure the volume of the gas generated at this time. The amount of gas generated is shown as a relative value based on the amount of generated in Comparative Example 1.

As can be seen from Table 1, when the nonaqueous electrolyte of the present invention was used, the amount of gas generated at room temperature (25 ° C) or high temperature (85 ° C) was significantly reduced.

Meanwhile, each of the 063048 square cells obtained from Examples 1 to 4 and Comparative Example 1 was fully charged from 0.2C to 4.2V at a constant temperature of 25 ° C., and then discharged from 0.2C to 2.75V at the same temperature, or 85 After standing for 4 hours at ℃, the thickness increase rate of the battery was measured. The results are summarized in Table 2 below.

Thickness increase rate after full charge (25 ℃, after 1 time charge and discharge) Thickness increase rate after full charge (85 ℃, left for 4 hours) Example 1 2.4% 4.8% Example 2 2.5% 6.4% Example 3 2.0% 6.6% Example 4 2.9% 6.9% Comparative Example 1 3.7% 7.5%

As can be seen from Table 2, when the nonaqueous electrolyte of the present invention is used, the degree of thickness expansion at room temperature (25 ° C.) and high temperature (85 ° C.) after the full charge of the square battery is significantly higher than that of the conventional basic nonaqueous electrolyte. Decreased.

As described in detail above, the use of the nonaqueous electrolyte for lithium batteries of the present invention greatly reduces the amount of gas generated due to decomposition of the electrolyte during charging and discharging of the lithium battery and at high temperature, thereby preventing swelling of the battery. The rate can be greatly improved.

Claims (5)

It was prepared by adding 0.1 to 10.0 parts by weight of a sulfoxide compound represented by the following formula (1) to 100 parts by weight of a mixed organic solvent of a cyclic carbonate organic solvent and a linear carbonate organic solvent in which a lithium salt was dissolved at 0.8 to 2.0 M. Non-aqueous electrolyte solution for lithium batteries. [Formula 1] In the above, R is a perfluoroalkyl group having 1 to 10 carbon atoms, and R 'is a fluoroalkyl group or fluoro group having 1 to 10 carbon atoms. The method of claim 1, The cyclic carbonate organic solvent is ethylene carbonate, propylene carbonate, or a mixture thereof, and the linear carbonate organic solvent is dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, or a mixture thereof. A nonaqueous electrolyte solution for lithium batteries. The method of claim 1, The non-aqueous electrolyte solution for lithium batteries, characterized in that the mixed organic solvent further comprises one or more selected from the group consisting of propyl acetate, methyl acetate, ethyl acetate, butyl acetate, methyl propionate and ethyl propionate. The method of claim 1, The lithium salt is at least one selected from the group consisting of LiPF ₆ , LiClO ₄ , LiAsF ₆ and LiBF _{4 Non-} aqueous electrolyte solution for lithium batteries. The method of claim 1, The sulfoxide compound is a perfluorobutanesulfonyl fluoride or a perfluorooctane sulfonyl fluoride, characterized in that the non-aqueous electrolyte for lithium batteries.