KR20020041645A - Non-aqueous electrolyte solution for lithium battery - Google Patents

Abstract

PURPOSE: Provided is a non-aqueous electrolyte for a lithium battery, which can improve a set mounting rate when preparing the lithium battery and can also improve capacity storage property of the battery at a high temperature. CONSTITUTION: The non-aqueous electrolyte is produced by adding 0.1-10.0pts.wt. of 3,6-dimethyl-1,4-dioxane-2,5-dione(formula I) to 100pts.wt. of a mixed organic solvent, in which 0.8-2.0M of lithium salts are dissolved, comprising a cyclic carbonate-based organic solvent and a linear carbonate-based organic solvent, wherein the cyclic carbonate-based organic solvent is ethylene carbonate, propylene carbonate, or a mixture thereof and the linear carbonate-based organic solvent is dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, or a mixture thereof.

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. Lithium prepared by adding 0.1 to 10.0 parts by weight of 3,6-dimethyl-1,4-dioxane-2,5-dione (3,6-dimethyl-1,4-dioxane-2,5-dione) A nonaqueous electrolyte solution for batteries.

[Formula 1]

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).

Thus, 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, gas generation in the cell is reduced, initial irreversible capacity, capacity storage characteristics at high temperatures, and charge and discharge cycle characteristics. There is an urgent need to develop an additive for a non-aqueous electrolyte of a lithium battery capable of improving the back and the like.

An object of the present invention is to solve the problems of the prior art as described above, 3,6-dimethyl-1,4-dioxane-2,5-dione (3,6-dimethyl-) in the conventional non-aqueous electrolyte for lithium batteries The addition of 1,4-dioxane-2,5-dione) suppresses the decomposition of the electrolyte solution, thereby providing a novel nonaqueous electrolyte solution for lithium batteries, which significantly reduces the thickness increase rate of the battery at high temperatures and improves the storage capacity at high temperatures. will be.

That is, in the present invention, 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 is dissolved at 0.8 to 2.0 M is represented by 3,6-dimethyl-1, Non-aqueous electrolyte solution for lithium batteries prepared by adding 0.1 to 10.0 parts by weight of 4-dioxane-2,5-dione is provided.

[Formula 1]

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 one or more selected from the group of linear carbonate organic solvents consisting of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate and ethyl propyl, are used in combination, more preferably Preferably, ethylene carbonate and dimethyl 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 0.1 to 10.0 parts by weight, preferably 3,6-dimethyl-1,4-dioxane-2,5-dione represented by the following formula (1) in the mixed organic solvent in which lithium salt is dissolved: It is prepared by adding 0.5 to 5.0 parts by weight, more preferably 1.0 to 5.0 parts by weight.

[Formula 1]

The lithium battery may be manufactured according to a conventional method using the nonaqueous electrolyte solution for lithium batteries of the present invention, and the lithium battery thus prepared may suppress gas generation inside the battery due to decomposition of the electrolyte when left at a high temperature (85 ° C.). Therefore, the swelling phenomenon in which the thickness of the battery is expanded is prevented and the capacity storage characteristic at high temperature is also excellent.

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

3,6-dimethyl-1,4-dioxane-2 in 100 parts by weight of a mixed organic solvent (hereinafter referred to as "basic nonaqueous electrolyte") in which ethylene carbonate: dimethyl carbonate = 1: 1 dissolved in LiPF ₆ is 1.0 M 0.5 parts by weight of, 5-dione (3,6-dimethyl-1,4-dioxane-2,5-dione) was added to prepare a nonaqueous electrolyte solution for a lithium battery. Using the nonaqueous electrolyte solution thus prepared, a 063048 square battery was manufactured according to a conventional method. That is, after mixing LiCoO _{2 as a} positive electrode active material, polyvinylidene fluoride as a binder (hereinafter referred to as “PVDF”), and graphite as a conductive agent in a weight ratio of 92: 4: 4, N-methyl-2-pyrroli A positive electrode slurry was prepared by dispersing with Mn-N-methyl-2-pyrrolydone. The positive electrode slurry was coated on an aluminum foil having a thickness of 20 μm, dried, and rolled to prepare a positive electrode of the battery. On the other hand, crystalline artificial graphite as a negative electrode active material and PVDF as a binder were mixed in a weight ratio of 92: 8, and then dispersed using N-methyl-2-pyrrolidone to prepare a negative electrode slurry. The negative electrode slurry was coated on a copper foil having a thickness of 15 μm, dried, and rolled to prepare a negative electrode of the battery. The positive and negative electrodes prepared as described above and a separator of 25 μm thick PE were wound and compressed and inserted into a rectangular can of 30 mm x 48 mm x 6 mm, and then filled with the nonaqueous electrolyte to fill a 063048 square cell. To complete.

Example 2

A non-aqueous electrolyte solution for lithium batteries was prepared in the same manner as in Example 1, except that 1.0 part by weight of 3,6-dimethyl-1,4-dioxane-2,5-dione was added, and a 063048 square battery was used thereto. Was prepared.

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 3,6-dimethyl-1,4-dioxane-2,5-dione was added thereto, and a 063048 square battery was used thereto. Was prepared.

Example 4

A non-aqueous electrolyte solution for lithium batteries was prepared in the same manner as in Example 1, except that 5.0 parts by weight of 3,6-dimethyl-1,4-dioxane-2,5-dione was added, and a 063048 square battery was used thereto. Was prepared.

Comparative Example 1

A 063048 square battery was prepared in the same manner as in Example 1, except that a basic nonaqueous electrolyte solution without using 3,6-dimethyl-1,4-dioxane-2,5-dione was used.

Each of the 063048 square cells obtained from Examples 1 to 4 and Comparative Example 1 was charged under constant current-constant voltage conditions up to 4.2V at a current of 160mA, and then discharged to 2.5V with a current of 160mA after being left for 1 hour. It was left for hours. After repeating this process three times, it was charged to 4.2V for 2 hours and 30 minutes with a current of 600mA. The thickness increase rate of each cell was calculated by comparing the thicknesses of the cells immediately after the completion of charge and the thicknesses measured every 4 hours or 24 hours while the battery was left in a high temperature chamber at 85 ° C. for 4 days after charging was completed. The results are summarized in Table 1 below.

0 hours 4 hours 24 hours 48 hours 72 hours 96 hours Example 1 5.3% 6.1% 8.9% 10.5% 15.1% 18.1% Example 2 4.6% 5.2% 6.7% 8.9% 12.9% 14.9% Example 3 3.3% 4.0% 5.2% 7.8% 11.8% 14.2% Example 4 3.4% 3.9% 5.4% 8.3% 13.1% 15.8% Comparative Example 1 7.9% 8.8% 11.6% 13.4% 17.4% 21.5%

As can be seen from Table 1, when the non-aqueous electrolyte of the present invention is used, the thickness increase rate of the battery when left at a high temperature after charging to 4.2V is significantly reduced to a maximum of 66% level compared with the case of using the conventional basic non-aqueous electrolyte.

On the other hand, after 4 days in the high temperature chamber, the discharge capacity of each battery was measured according to a conventional method, the results are summarized in Table 2 below.

Discharge capacity Example 1 82.8% Example 2 84.1% Example 3 85.0% Example 4 83.3% Comparative Example 1 82.0%

As can be seen from Table 2, when the nonaqueous electrolyte of the present invention is used, the capacity storage characteristic at a high temperature is somewhat improved compared with the case of using the conventional basic nonaqueous electrolyte.

As described above in detail, the use of the nonaqueous electrolyte for lithium batteries of the present invention reduces gas generation due to decomposition of the electrolyte when the lithium battery is left at a high temperature, thereby suppressing the swelling of the battery, thereby greatly improving the set mounting rate of the lithium battery. In addition, the capacity storage characteristics of the battery at high temperatures are also improved.

Claims (4)

3,6-dimethyl-1,4-dioxane- 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 is dissolved at 0.8 to 2.0 M A non-aqueous electrolyte solution for lithium batteries prepared by adding 0.1 to 10.0 parts by weight of 2,5-dione (3,6-dimethyl-1,4-dioxane-2,5-dione). [Formula 1] 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 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.