KR20040008787A - Gel polymer electrolyte forming composition having excellent storage property - Google Patents

Abstract

PURPOSE: A composition for the preparation of a gel polymer electrolyte, its preparation method and a method for removing oxygen from the composition are provided, to improve storage stability in ungelled state. CONSTITUTION: The composition comprises a monomer capable of changing into gel phase by polymerization or crosslinking, a prepolymer or their mixture; a polymerization initiator generating radicals by heat or radiation; an alkali metal salt; a nonaqueous solvent; and the oxygen capable of suppressing the initiation of polymerization or crosslinking of the monomer, the prepolymer or their mixture by the polymerization initiator. The content of the oxygen is determined according to the content of the polymerization initiator and the desired storage period.

Description

Gel polymer electrolyte forming composition having excellent storage property}

The present invention relates to a composition for forming a gel polymer electrolyte having excellent storage properties, and more particularly, to a composition for forming a gel polymer electrolyte capable of long-term storage in an ungelled state.

The electrolytes used in the battery include liquid electrolytes and polymer electrolytes. Compared with liquid electrolytes, polymer electrolytes have characteristics such as thin film thickness, good electrolyte holding power, good productivity, free shape, and high safety. have.

In addition, polymer electrolytes include a dry polymer electrolyte containing no electrolyte and a gel polymer electrolyte containing an electrolyte. Compared with a dry polymer electrolyte, a gel polymer electrolyte has a very high ion conductivity and even ions of a liquid electrolyte. Close to conductivity.

There are many methods for preparing a gel polymer electrolyte, but a representative method is to apply the composition by applying heat or light to a composition for forming a gel polymer electrolyte including a monomer or a pre-polymer, a polymerization initiator, a metal salt, and an organic solvent. It is a method of gelation. In this case, the polymerization initiator forms a radical by heat or light, and the radical initiates polymerization of the monomer or prepolymer.

There are two typical ways in which the gel polymer electrolyte is implemented in a lithium battery. The first method is to apply a composition for forming a gel polymer electrolyte onto an arbitrary planar support, and then apply heat or light to obtain a gel polymer electrolyte membrane, which is included as an electrolyte in the cell assembly. The second method is a method of gelling the composition by impregnating the composition for forming a gel polymer electrolyte in a battery assembly including a porous separator and applying heat.

However, the composition for forming a gel polymer electrolyte cannot be stored for a long time because the polymerization reaction proceeds at a slow rate even at room temperature. Therefore, the composition must be made by mixing a monomer or prepolymer, a polymerization initiator, a lithium salt, and an organic solvent immediately before being used in the battery manufacturing process, which is very troublesome in the battery manufacturing process.

Therefore, the technical problem to be solved by the present invention is to make the process of preparing a composition for forming a gel polymer electrolyte in order to simplify the battery manufacturing process to be made independently of the battery manufacturing process. Another object of the present invention is to provide a composition for forming a gel polymer electrolyte, which has the same storage characteristics as that of a liquid electrolyte, and enables long-term storage.

In order to solve the above technical problem, in the present invention,

Monomers, prepolymers or mixtures thereof that can be changed into a gel by polymerization or crosslinking; Polymerization initiators that generate radicals by heat or light; Alkali metal salts; In the composition for forming a gel polymer electrolyte comprising a non-aqueous solvent,

The composition provides a composition for forming a gel polymer electrolyte further comprising oxygen capable of inhibiting the polymerization initiator from initiating a polymerization reaction or a crosslinking reaction of the monomer, prepolymer or a mixture thereof.

At this time, the content of the oxygen in the composition may be determined according to the content of the polymerization initiator and the desired storage period in the composition.

Usually, the content of oxygen in the composition is preferably 2.0 to 10.0 mg per liter of the composition.

Further, in the present invention, monomers, prepolymers or mixtures thereof that can be changed into a gel by polymerization or crosslinking; Polymerization initiators that generate radicals by heat or light; Alkali metal salts; And preparing a mixture comprising a non-aqueous solvent;

Closing the container after injecting the mixture into a closed container having an inlet and a gas inlet through which the mixture can be introduced; And

It provides a method for producing a composition for forming a gel polymer electrolyte comprising the step of injecting an oxygen-containing gas through the inlet in a sealed container containing the mixture.

At this time, dry air, oxygen or a mixture thereof may be used as the oxygen-containing gas.

In addition, in the present invention, the composition according to the present invention in order to be compatible with the battery manufacturing process,

Injecting a composition for forming a gel polymer electrolyte according to the present invention into a battery assembly;

Maintaining the battery assembly in which the composition is injected for a predetermined time sufficient to reduce the content of dissolved oxygen so that gelation is not prevented under reduced pressure; And

Thereafter, sealing the cell assembly provides a method for removing oxygen from the composition for forming a gel polymer electrolyte according to the present invention.

At this time, the reduced pressure is 1 to 40 torr, the predetermined time is preferably 5 to 30 seconds.

Hereinafter, the technical configuration of the present invention in more detail.

In the present invention, monomers, prepolymers or mixtures thereof that can be changed into a gel by polymerization or crosslinking; Polymerization initiators that generate radicals by heat or light; Alkali metal salts; And it provides a gel polymer electrolyte composition for forming long-term storage in the ungelled state by further including oxygen in a gel polymer electrolyte composition for forming a composition containing a non-aqueous solvent.

The composition of the present invention can be applied for the preparation of all kinds of gel polymer electrolytes.

Accordingly, as the material which can be changed into a gel phase by the polymerization or crosslinking, it is possible to undergo polymerization or crosslinking by a free group, and all kinds of monomers or prepolymers or mixtures thereof which can be used for forming a gel polymer electrolyte are used. Can be. For example, for a gel polymer electrolyte for a lithium secondary battery, an isocyanate monomer, an epoxide monomer, an acrylate monomer, an ethylene oxide monomer, a prepolymer thereof, or a mixture thereof may be used.

In addition, as the polymerization initiator can be easily decomposed by heat or light to generate radicals, any polymerization initiator that can be used to form a gel polymer electrolyte can be used. For example, benzophenone, benzoyl peroxide, acetyl peroxide, lauroyl peroxide, dibutyl tin diacetate, azobisisobutyronitrile, or a mixture thereof may be used.

In addition, as the alkali metal salt, various metal salts may be used according to the type of battery, and all kinds of salts of alkali metal may be used in the battery and its ions may be transferred through the gel polymer electrolyte. For example, for application to lithium batteries, lithium salts such as lithium perchlorate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium trifluoride methanesulfonate, lithium bistrifluoromethanesulfonylamide, or mixtures thereof may be used. Can be.

In addition, all organic solvents commonly used in the gel polymer electrolyte may be used as the organic solvent. For example, in the case of a lithium battery, propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate, fluorobenzene (FB), tetrahydrofuran, 2-methyl tetrahydrofuran, diethoxyethane, methyl formate, ethyl formate, γ-butyrolactone, or a mixture thereof may be used.

The characteristic action in the composition for gel polymer electrolyte formation which can be stored for a long time in the ungelled state provided by this invention is as follows.

The polymerization initiator decomposes when subjected to heat or light (including microwaves and ultraviolet rays) to generate radicals. These radicals serve to polymerize or crosslink monomers or prepolymers and the like in the composition and thus change the composition into a gel state. However, the radical reaction proceeds at a slow speed even under normal temperature conditions, and the gelled composition cannot be used in the battery manufacturing process. In order to solve this problem, in the present invention, by including oxygen in the composition, even once a radical is generated from the polymerization initiator during storage, it is recombined with oxygen dissolved in the composition to lose activity as a radical, and thus the composition gelates during storage. It can be prevented.

At this time, the content of the oxygen to be included in the composition for forming the gel polymer electrolyte is changed according to the content of the polymerization initiator in the composition for forming the gel polymer electrolyte and the desired storage period. Typically, as the content of the polymerization initiator increases, or as the desired shelf life increases, the oxygen content should also increase. However, depending on the composition there will be a saturation point and therefore no oxygen content above that saturation point. And the determination of the appropriate oxygen content can be easily determined by a person of ordinary skill in the art through several experiments on the composition desired.

Usually, the content of oxygen in the composition is preferably 2.0 to 10.0 mg per liter of the composition. At this time, the gelation reaction may occur even at room temperature if it is less than 2.0, and when it exceeds 10.0, it does not melt any more.

In addition, in the present invention, in order to prepare a composition for forming a gel polymer electrolyte capable of long-term storage in the ungelled state,

Monomers, prepolymers or mixtures thereof that can be changed into a gel by polymerization or crosslinking; Polymerization initiators that generate radicals by heat or light; Alkali metal salts; And preparing a mixture comprising a non-aqueous solvent;

Closing the container after injecting the mixture into a closed container having an inlet and a gas inlet through which the mixture can be introduced; And

It provides a method for producing a composition for forming a gel polymer electrolyte comprising the step of injecting an oxygen-containing gas through the inlet in a sealed container containing the mixture.

At this time, dry air, oxygen or a mixture thereof may be used as the oxygen-containing gas.

On the other hand, in order for the composition for forming a gel polymer electrolyte capable of long-term storage in the ungelled state according to the present invention to be compatible with a battery manufacturing process, the composition may be removed from the composition immediately before the composition is used in the process or at an appropriate time during the battery manufacturing process. Oxygen must be able to be removed effectively. As a preferred example of the oxygen removal method, the present invention provides the following method.

That is, after injecting the composition for forming a gel polymer electrolyte according to the present invention into the battery assembly, the battery assembly is maintained for a predetermined time sufficient to lower the content of dissolved oxygen so as not to interfere with gelation under reduced pressure. The battery assembly is then sealed.

While the cell assembly is maintained under reduced pressure, oxygen dissolved in the composition is vaporized by a change in solubility, and the content of dissolved oxygen in the composition is extremely low. Therefore, the gelation of the composition is not disturbed at all in the heat treatment step of the battery assembly performed after the sealing of the battery assembly.

At this time, the reduced pressure is preferably 1 to 40 torr. If the reduced pressure exceeds 40 torr, it takes a long time to sufficiently lower the dissolved oxygen content, which hinders the rapid progress of the battery manufacturing process. In addition, if the reduced pressure condition is less than 1 torr, not only the cost for forming the reduced pressure condition greatly increases, but also the vaporization of the non-aqueous solvent and oxygen occurs violently, and thus the reliability of the battery manufacturing process is lowered. On the other hand, the time to maintain the battery assembly in which the composition according to the present invention is injected under reduced pressure conditions can be appropriately adjusted according to the pressure value of the reduced pressure conditions, it is usually preferably 5 to 30 seconds.

Hereinafter, through the embodiment of the composition for forming a gel polymer electrolyte for a lithium-ion polymer battery that can be an embodiment of the present invention to reveal the long-term storage characteristics of the composition according to the present invention. However, as mentioned above, the scope of the present invention is not limited only to the composition for forming a gel polymer electrolyte for a lithium ion polymer battery.

How to measure gelation

Long-term storage characteristics of the composition according to the present invention can be revealed through the degree of gelation of the composition for forming a gel polymer electrolyte. As gelation of the composition for forming a gel polymer electrolyte proceeds, the viscosity of the composition increases and transparency decreases. Therefore, the degree of gelation can be performed through the measurement of the viscosity of the composition and the observation of transparency. Viscosity measurement may be performed using a general viscosity measuring device, and transparency may be performed by visual observation.

The degree of gelation is determined by two grades of "gelling" or "gelling", in which "gelling" is a case where there is no change in viscosity that is outside the range of viscosity measurement and no change in transparency is observed. Is a case where a change in viscosity occurs outside the error range of the viscosity measurement or a change in transparency is observed.

Example 1

To 1000 g of non-aqueous solvent in which EC / EMC / PC / FB was mixed at a weight ratio of 4: 4: 1: 1, LiPF ₆ was added as a metal salt to a concentration of 1.3 M. To this mixture was prepared a mixture in which 3 g of a multifunctional acrylate as a monomer and 0.03 g of lauroyl peroxide as an initiator were prepared. The multifunctional group acrylate is added with 0.01% by weight of a tetrapropyl titanate catalyst to a mixture of 1 mol of dipentaerythritol, 2 mol of ε- captolactone, and toluene solvent, and reacted at 50 ° C. to provide a terminal hydroxyl group. Synthesizing a monomer of a variant of dipentaerytriol in which a part of the structure is substituted with pentyl alcohol, and then reacting 4 moles of acrylic acid and 2 moles of butylcarboxylic acid to 1 mole of the monomer to produce two hydroxyl groups present at the terminal of the monomer ( Polyester hexa substituted with -OC (= O) (CH2) 5OC (= O) CH = CH2 instead of -OH) and -OC (= O) (CH2) 3CH3 instead of the other four hydroxyl groups (-OH) It is an acrylate compound.

Subsequently, the mixture was placed in a hermetically sealed container equipped with a gas inlet and sealed. Subsequently, an oxygen cylinder is connected to the gas inlet so that oxygen can be injected from the bottom of the mixture, and oxygen is quantitatively supplied so that 1 mg of dissolved oxygen is present with respect to 1 liter of the mixture.

The gelation degree according to the storage period was measured while storing the composition for forming a gel polymer electrolyte according to the present invention thus prepared at a temperature of 20 ° C., and the results are shown in Table 1 below.

Example 2

Except that the concentration of dissolved oxygen to 2mg per 1L of the mixture, the gel polymer electrolyte composition for preparing a composition according to the present invention was prepared in the same manner as in Example 1 and then stored at a temperature of 20 ℃ during the storage period According to the gelation degree was measured, the results are shown in Table 1.

Example 3

Except that the concentration of dissolved oxygen to 4mg per 1L of the mixture, in the same manner as in Example 1 to prepare a composition for forming a gel polymer electrolyte according to the present invention and stored at a temperature of 20 ℃ during storage period According to the gelation degree was measured, the results are shown in Table 1.

Comparative Example 1

After preparing a mixture containing the same non-aqueous solvent, metal salt, monomer, and polymerization initiator as in Example 1, the mixture was placed in a cylindrical sealed container equipped with a gas inlet and sealed. Subsequently, a nitrogen cylinder was connected to the gas inlet to fill the sealed container containing the mixture with nitrogen.

The gelation degree according to the storage period was measured while storing the mixture thus prepared at a temperature of 20 ℃, the results are shown in Table 1.

Gas in container Oxygen dissolved amount, mg / l Gel degree according to storage period Early 4 days 7 days 14 days 21st 30 days Example 1 Oxygen 1.0 Miguel Miguel Gelation Gelation - - Example 2 Oxygen 2.0 Miguel Miguel Miguel Miguel Gelation Gelation Example 3 Oxygen 4.0 Miguel Miguel Miguel Miguel Miguel Miguel Comparative Example 1 nitrogen - Miguel Gelation Gelation Gelation - -

As shown in Table 1, compared with the storage period of the gel polymer electrolyte-forming composition containing no oxygen is less than 5 days, the gel polymer electrolyte-forming composition according to the present invention is of course not less than 7 days depending on the content of oxygen It can be seen that it extends beyond 30 days.

Therefore, by using the gel polymer electrolyte composition according to the present invention, the preparation method thereof, and the oxygen removing method according to the present invention, the process of preparing the composition for forming the gel polymer electrolyte can be independent from the battery manufacturing process, and thus the battery manufacturing process. Can be simplified.

Claims (7)

Monomers, prepolymers or mixtures thereof that can be changed into a gel by polymerization or crosslinking; Polymerization initiators that generate radicals by heat or light; Alkali metal salts; In the composition for forming a gel polymer electrolyte comprising a non-aqueous solvent, The composition is a composition for forming a gel polymer electrolyte, the polymerization initiator further comprises oxygen capable of inhibiting the polymerization or crosslinking reaction of the monomer, prepolymer or a mixture thereof. The method of claim 1, wherein the content of oxygen in the composition, The composition for forming a gel polymer electrolyte, characterized in that determined according to the content of the polymerization initiator and the desired storage period in the composition. The method of claim 2, wherein the content of oxygen in the composition, The composition for forming a gel polymer electrolyte, characterized in that 2.0 to 10.0 mg per 1L of the composition. Monomers, prepolymers or mixtures thereof that can be changed into a gel by polymerization or crosslinking; Polymerization initiators that generate radicals by heat or light; Alkali metal salts; And preparing a mixture comprising a non-aqueous solvent; Closing the container after injecting the mixture into a closed container having an inlet and a gas inlet through which the mixture can be introduced; And Injecting the oxygen-containing gas through the inlet to the sealed container containing the mixture, A method for preparing a composition for forming a gel polymer electrolyte according to any one of claims 1 to 3. 5. The method of claim 4, wherein the oxygen-containing gas is at least one selected from dry air and oxygen. Injecting a composition for forming a gel polymer electrolyte according to any one of claims 1 to 3 into a battery assembly; Maintaining the battery assembly in which the composition is injected for a predetermined time sufficient to reduce the content of dissolved oxygen so that gelation is not prevented under reduced pressure; And A method for removing oxygen from the composition for forming a gel polymer electrolyte according to any one of claims 1 to 3, which then comprises sealing the cell assembly. The method of claim 6, wherein the decompression conditions are 1 to 40 torr, and the predetermined time is 5 to 30 seconds.