KR100838060B1 - Electrolytic solution for overcharge protection of lithium secondary batteries and lithium secondary batteries using the same - Google Patents

Abstract

The present invention relates to an electrolyte and a lithium secondary battery using the same, which improves the stability of the battery by polymerizing at a voltage of 100 ° C. or higher or 4.3 V or higher to disable electrical communication.

In the present invention, a mixture of 5 to 55% by weight of 1,3-dioxolane and 45 to 95% by weight of MEC / DEC is used as an electrolyte of a lithium secondary battery, and further trimethylamine, triethylamine, tributylamine, tri Propylamine, tribenzylamine and the like can be added at 5% by weight or less of the total 1,3-dioxolane. The organic electrolyte according to the present invention can suppress the risk of overheating and ignition of the battery when the battery is exposed to high temperature or overcharged.

Electrolyte for lithium secondary battery, 1,3-dioxolane, MEC / DEC

Description

Overcharge prevention electrolyte for lithium secondary battery and lithium secondary battery using same {Electrolytic solution for overcharge protection of lithium secondary batteries and lithium secondary batteries using the same}

The present invention relates to an overcharge preventing electrolyte for a lithium secondary battery and a lithium secondary battery using the same. More particularly, the polymerization at a voltage of 100 ° C. or higher or 4.3 V or higher prevents electrical communication of the battery, thereby improving stability of the battery. It relates to an electrolyte solution.

There have been many attempts to suppress the overcharging of lithium secondary batteries by changing the composition of the electrolyte or by adding an additive to the electrolyte. In US Pat. No. 5,580,684, 1-10 wt% of trimethyl phosphate, 10-20 wt% of tris (trifluoroethyl) phosphate, tris (2-chloroethyl) phosphate, etc. are added to the electrolytic solution as a phosphate ester-based material. Increasing self-extinguishing has been reported to increase stability in case of battery abnormalities. US Pat. No. 5,776,627 adds thiophene, biphenyl, furan and the like to polymerize them in case of battery abnormalities, thereby preventing the movement of lithium. As a gas generated at this time, the vent of the battery can be easily opened to increase the stability of the battery.

Similarly, 1,2-dimethoxy-4-bromo-benzene is described in US Pat. No. 5,573,119, 2-chloro-p-xylene, 4-chloro-anisole in U.S. Pat. Patent 5858573 reports that the safety of a battery can be improved by adding 2,7-diacetyl thianthrene or the like to the electrolyte, respectively. However, these electrolyte additives have been limited in their use by polymerizing under normal operating conditions of the battery, or by degrading the overall performance such as high rate characteristics, low temperature characteristics, and lifetime characteristics of the batteries.

Accordingly, an object of the present invention is to provide an overcharge preventing electrolyte solution for a lithium secondary battery that can suppress the risk of overheating and ignition of a battery when the battery is exposed to high temperatures or overcharged.

In order to achieve the above object, the present invention provides an electrolyte solution that improves the stability of the battery by polymerizing at a voltage of 100 ° C or higher or 4.3 V or higher to disable electrical conduction of the battery.

The electrolyte solution for a lithium secondary battery according to the present invention includes a chain carbonate and 1,3-dioxolane.

The chain carbonate is preferably a mixture of methyl ethyl carbonate and diethyl carbonate (MEC / DEC), and the weight ratio thereof is preferably from 2: 8 to 8: 2.

The proportion of the chain carbonate in the electrolyte is preferably 45 to 95% by weight and the proportion of 1,3-dioxolane is 5 to 55% by weight. If the ratio of the 1,3-dioxolane is 5% by weight or less, the battery protection function is hardly exhibited. If the ratio of 1,3-dioxolane is 55% by weight or more, the mixture may not be completely mixed with the electrolyte and may be impaired under the electrolyte when left for a long time.

In addition, the electrolyte for a lithium secondary battery according to the present invention may further include a polymerization inhibitor. Such a polymerization inhibitor is preferably used when the proportion of the chain carbonate in the electrolyte is within 45 to 65% by weight and the proportion of 1,3-dioxolane is 35 to 55% by weight, which is 35% by weight in the electrolyte. When only 1,3-dioxolane is used, the electrolyte may polymerize even during normal battery operation due to the impact of battery shock or battery temperature rise. The polymerization inhibitor is preferably selected from the group consisting of tertiary aman, more specifically trimethylamine, triethylamine, tripropylamine, tributylamine and tribenzylamine.

According to this invention, the lithium secondary battery using the said electrolyte solution is provided, It does not specifically limit about structural members other than the said electrolyte solution which comprises a secondary battery, The conventional structural member used conventionally can be used. In addition, the structure of the lithium secondary battery according to the present invention is also not particularly limited.

Hereinafter, the present invention will be described in more detail.

The electrolyte is closely related to the safety of the battery. It should not cause decomposition or other reactions within the operating voltage range of the battery, and should have good mobility of lithium ions and not be greatly influenced by temperature. In addition, if the battery is exposed to an external risk factor or if the battery's charge / discharge function can be stopped during abnormal operation of the battery, the function of the protection circuit can be supplemented or replaced, thereby greatly improving the safety of the battery. The temperature at which abnormal operation of the battery occurs is usually 100 ° C. or higher, and battery malfunction occurs even at a voltage of 4.3 V or higher. Therefore, the battery protection action only occurs in the above conditions, and should not adversely affect the performance of the battery in the normal battery operating period. This property can be specified by adding a large amount of 1,3-dioxolane to the electrolyte. In this case, a mixture of MEC / DEC is used as the main component of the electrolyte in order not to affect overall performance such as low-temperature discharge characteristics of the battery. Salts of the electrolytic solution used in the present invention include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ and the like LiPF ₆ , LiAsF ₆ desirable.

Experimental results showed that 1,3-dioxolane polymerized by reacting with electrolyte at a temperature of 100 ℃ or higher or voltage of 4.3V or higher. do.

However, when more than 35% by weight of 1,3-dioxolane is added, the electrolyte may polymerize even during normal battery operation due to the impact of battery use or the increase of battery temperature. At the same time, a substance capable of inhibiting the polymerization of 1,3-dioxolane is added. That is, tertiary amines, specifically trimethylamine, triethylamine, tributylamine, tripropylamine, tribenzylamine, etc., are added to 5% by volume or less of the total 1,3-dioxolane, thereby polymerizing in normal operation of the battery. It is possible to sufficiently suppress the phenomena that become unnatural.

Hereinafter, the present invention will be described in more detail with reference to preferred examples and test examples, but the present invention is not limited thereto.

LiPF ₆ used in the following Example was used without a battery reagent grade product of Hashimoto, Japan, without purification, the solvent used in the preparation of the organic electrolyte solution was a battery reagent grade product of Merck, all experiments were argon gas (99.9999% or more) atmosphere It was carried out under.

Example 1

It was to hold the electrolytic solution into the LiPF ₆ of the content to create a 1M LiPF ₆ solution in a plastic barrel've then given into vigorous shaking, methyl ethyl carbonate and diethyl carbonate dissolving the lithium salt, at this time, methyl ethyl carbonate: D The weight ratio of ethyl carbonate was 2: 8. Next, 1,3-dioxolane was added in an amount of 5% by weight based on the total weight of the prepared electrolyte, thereby preparing an organic electrolyte according to the present invention.

Example 2

An organic electrolyte solution according to the present invention was prepared in the same manner as in Example 1, except that 1,3-dioxolane was added to 10 wt% based on the total weight of the electrolyte in Example 1 above.

Example 3

Example 1 and 1 except that the weight ratio of methyl ethyl carbonate to diethyl carbonate is 5: 5 and 1,3-dioxolane is added so as to be 35% by weight relative to the total weight of the electrolyte. In the same manner, an organic electrolyte solution according to the present invention was prepared.

Example 4

In Example 1 described above, 1,3-dioxolane was added at 40% by weight relative to the total weight of the electrolyte solution, and trimethylamine was added as 3% by volume of the total 1,3-dioxolane as a polymerization inhibitor. Except for the organic electrolyte according to the present invention was prepared in the same manner as in Example 1.

Example 5

In Example 4 described above, 1,3-dioxolane was added at 55% by weight relative to the total weight of the electrolyte solution, and tribenzylamine was added as 5% by volume of the total 1,3-dioxolane as a polymerization inhibitor. An organic electrolyte solution according to the present invention was prepared in the same manner as in Example 4.

Comparative Examples 1 to 3

Comparative Example 1, 10 wt% of thiophene was added to Comparative Example 1, 5 wt% of thiophene, to which the organic electrolyte solution of Example 1 was added 5 wt% of trimethyl phosphate instead of 1,3-dioxolane as an additive. What was added was made into the comparative example 3.

Test Example 1

Using the organic electrolyte solution of Example 1-5 and Comparative Example 1-3 described above to prepare a lithium secondary battery containing the gel polymer electrolyte as follows to measure the degree of overcharge protection for each.                     

To an organic solvent mixed with 250 ml of cyclo-hexanone and 250 ml of acetone, 20 g of vinylidene fluoride / hexafluoropropylene copolymer (wherein the hexafluoropropylene content is 15% by weight) was added for 2 hours in a ball mill. Mixed to dissolve. 1000 g of LiCoO ₂ as a cathode active material and 20 g of carbon black as a conductive agent were added to the mixture, which was then mixed for 8 hours to form a cathode active material composition.

Vinylidene fluoride / hexafluoropropylene copolymer of the cathode active material composition using a doctor blade having a 320 μm gap and a thickness of 147 μm and a width of 4.9 cm and an organic solvent mixed with 250 ml of cyclo-hexanone and 250 ml of acetone (The content of hexafluoropropylene is 15% by weight.) 20 g and 20 g of carbon black are added, and the pretreatment composition prepared by mixing for 8 hours is coated with a spray coating method and coated on a pretreated aluminum thin film and dried to form a cathode electrode. Made a plate.

Meanwhile, the anode electrode plate was manufactured according to the following procedure.

To the organic solvent in which 300 ml of N-methylpyrrolidone and 100 ml of acetone were mixed, 20 g of vinylidene fluoride / hexafluoropropylene copolymer (wherein the hexafluoropropylene content was 15% by weight) was added as a binder. Dissolve by mixing for hours. 1000 g of mesocarbon fiber (MCF) was added to the mixture as an anode active material, and then mixed for 3 hours to form an anode active material composition.

The anode active material composition was 178 µm thick and 5.1 cm wide using a 420 µm gap doctor blade, and vinylidene fluoride / hexafluoro in an organic solvent in which 300 ml of N-methylpyrrolidone and 100 ml of acetone were mixed. 50 g of propylene copolymer (where the content of hexafluoropropylene is 15% by weight) and 5 g of carbon black are added and mixed for 2 hours, followed by coating and drying on a pretreated copper thin film by spray coating. To make an anode electrode plate.

On the other hand, 15 g of vinylidene fluoride / hexafluoropropylene copolymer (wherein the hexafluoropropylene content is 15% by weight) was added to 500 ml of the organic electrolyte solution of Examples 1 to 5 and Comparative Examples 1 to 3, and 40 g of silica was used as the inorganic filler. Was added and heated to 90 ° C. to prepare a gel polymer electrolyte.

 The gel-type polymer electrolyte was coated between the cathode electrode plate and the anode electrode plate, and then wound in a jellyroll manner to form an electrode assembly. This electrode assembly was placed in a pouch to complete a lithium secondary battery.

The degree of overcharge protection for each of the lithium secondary batteries thus obtained was measured and shown in Table 1 below.

[Table 1] 12V overcharge safety test results

safety rupture Fire Sum Example 1 18 20 12 50 Example 2 20 19 11 50 Example 3 39 11 0 50 Example 4 42 8 0 50 Example 5 40 10 0 50 Comparative Example 1 10 26 15 50 Comparative Example 2 13 28 9 50 Comparative Example 3 11 23 16 50

When the battery is exposed to high temperature, or when the temperature of the battery rises rapidly due to abnormal operation of the battery, or when the battery is charged to more than 4.3V due to malfunction of the charger or battery protection circuit or user's carelessness, etc. The safety of the battery can be ensured by stopping the. In addition, since the temperature of the battery increases even when charged or discharged with an overcurrent, the risk of rupture and ignition of the battery due to the overcurrent can be sufficiently suppressed.

Claims (9)

An electrolyte solution for a lithium secondary battery comprising a mixture of methyl ethyl carbonate and diethyl carbonate (MEC / DEC), 1,3-dioxolane, a polymerization inhibitor, and a LiPF ₆ salt in a weight ratio in the range of 2: 8 to 8: 2. delete delete The electrolyte solution for a lithium secondary battery according to claim 1, wherein the proportion of the carbonate mixture in the electrolyte is 45 to 95% by weight and the proportion of 1,3-dioxolane is 5 to 55% by weight. delete The electrolyte solution for a lithium secondary battery according to claim 1, wherein the proportion of the carbonate mixture in the electrolyte is 45 to 65% by weight and the proportion of 1,3-dioxolane is 35 to 55% by weight. The electrolyte of claim 1, wherein the polymerization inhibitor is selected from the group consisting of trimethylamine, triethylamine, tripropylamine, tributylamine, and tribenzylamine. The electrolyte solution for a lithium secondary battery according to claim 7, wherein the material added as the polymerization inhibitor is 5 vol% or less of the total 1,3-dioxolane. The lithium secondary battery using the electrolyte solution in any one of Claims 1, 4, or 6-8.