KR20010037901A - New blended porous polymer electrolyte(Ⅱ) and a method for manufacturing thereof - Google Patents

Abstract

PURPOSE: A porous polymer electrolyte composition and a method for manufacturing the same are provided which has superior ionic conductivity, electrochemical stability and interface property. CONSTITUTION: In a polymer electrolyte composition for a secondary battery, the porous polymer electrolyte composition comprises a porous polymer matrix in which an ionomer copolymerized by methylmethacrylate and basic salt maleate is blended with vinylidene fluoride polymer; and a liquid electrolyte in which lithium salts are added to an organic solvent impregnating pores of the porous polymer matrix. In a method for manufacturing the polymer electrolyte composition for a secondary battery, the method comprises the steps of blending the ionomer copolymerized by methylmethacrylate and basic salt maleate and the vinylidene fluoride polymer using a cosolvent; obtaining a polymer film after adding a plasticizer to the blended solution for producing porous structures, casting a homogeneous solution manufactured by adding inorganic materials to the solution onto a glass plate and evaporating the cosolvent from the casted solution; obtaining a porous polymer film by impregnating the polymer film into methanol or diethylether, thereby selectively melting the plasticizer only in the film; and impregnating the porous polymer film into a liquid electrolyte manufactured by dissolving a lithium salt of 5 to 30 wt.% based on the polymer weight of one salt selected from the group consisting of lithium perchloride, lithium hexafluoro phosphate, lithium triflate, lithium bistrifluoro methylsulfonyl amide and lithium tetrafluoroborate into a solvent of 50 to 300 wt.% based on the polymer weight of one or more mixed solvents selected from the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, ethylmethyl carbonate, dimethoxy ethane, diethoxy ethane and 2-methyl tetrahydrofuran.

Description

New blended porous polymer electrolyte (II) and a method for manufacturing according}

The present invention relates to a novel porous polymer electrolyte composition and a preparation method thereof, and more particularly, to a porous polymer based on a blend of a vinylidene fluoride-based polymer and an ionomer copolymerized with methyl methacrylate and maleic acid alkali salt. It relates to an electrolyte composition.

With the rapid development of the electrical, electronics, telecommunications and computer industries, the demand for high performance and high safety secondary batteries has been gradually increasing. Secondary batteries are also required to be lighter and smaller.

In addition, as the necessity of new forms of energy supply and demand due to air pollution and noise caused by mass distribution of automobiles and the depletion of oil has emerged, the necessity of developing electric vehicles to solve this problem has increased. As a result, development of batteries having high power and high energy density has been demanded.

In order to meet such demands, one of the high-performance, next-generation advanced new batteries, which has recently attracted the most attention, is a lithium polymer battery (LPB). LPB is largely composed of an anode, a polymer electrolyte, and a cathode. Lithium and carbon are used as the anode active material, and the polymer electrolyte is composed of a polymer, a salt, a non-aqueous organic solvent, and other additives. The positive electrode active material is composed of a transition metal oxide, a metal chalcogen compound, a conductive polymer, and the like.

Lithium ion batteries (LIBs) using liquid electrolytes have raised safety issues, and methods of mounting electrode materials and safety devices to supplement them have been developed. However, manufacturing costs are expensive and large secondary batteries There is a problem that is difficult to apply.

On the contrary, LPB using a polymer electrolyte can be manufactured at a lower cost, can be adjusted in size or shape as desired, and is safe and has a high energy density per unit weight. Accordingly, the flexible thin film LPB can be easily developed as a power source for an electric vehicle because it is easy to develop high voltage and large capacity batteries by lamination in addition to portable cordless electronic products.

In order to commercialize LPB having such excellent advantages, many studies have been conducted to develop polymer electrolytes that satisfy excellent ion conduction properties, electrochemical stability, and interfacial properties with electrodes.

Initially, research has been conducted on solvent-free polymer electrolytes prepared by adding salt to polyethylene oxide, polypropylene oxide, and melting in a co-solvent (US Pat. No. 5,102,752). polyacrylonitrile, polymethyl methacrylate, polyvinyl chloride, polyvinylidene a polymer such as fluoride, ethylene carbonyl marinade, prepared in the form of a film is dissolved with an organic solvent such as propylene carbonate and a salt and co-solvent 10 ^- Studies on gel polymer electrolytes showing high ionic conductivity of ³ S / cm or more are being conducted (KM Abraham et al., J. Electrochem. Soc., 142, 1789, 1995).

However, these gel polymer electrolytes have a disadvantage in that mechanical properties deteriorate depending on the amount of the added organic solvent, and there are many problems in the part related to the automated process such as the removal of a common solvent and special process conditions when applied to LPB. Is being raised.

Recently, a method of first preparing a matrix polymer containing no organic solvent, laminating it with an anode and a cathode, and impregnating the obtained film with an organic solvent has been proposed (JM Tarascon et al., Solid State Ionics, 86-88, 49, 1996, US Patent No. 5,456,000). However, the vinylidene fluoride-based polymer is electrochemically stable but has a disadvantage in that the impregnating property of the liquid electrolyte is poor due to low surface energy and low affinity with the organic solvent.

Continuous bleeding or volatilization of the liquid electrolyte due to time and charge and discharge in the battery due to the low affinity with the liquid electrolyte results in not only a decrease in the ionic conductivity in the polymer matrix, but also an increase in the overall resistance in the battery. As a result, it is a fundamental cause of the continuous decrease in capacity after a long time and deterioration of high rate charge / discharge characteristics.

Accordingly, the present inventors conducted a study to solve the above problems, and introduced a porous structure by introducing an ionomer copolymerized with methyl methacrylate and maleic acid alkali salt having excellent compatibility with an organic solvent in a vinylidene fluoride-based polymer. It was found that the polymer electrolyte can be prepared by directly producing the polymer matrix and impregnating the liquid electrolyte to complete the present invention.

Accordingly, an object of the present invention is to provide a novel porous polymer electrolyte composition excellent in ion conductivity, electrochemical stability and interfacial properties.

It is another object of the present invention to provide a method for preparing a novel porous polymer electrolyte composition having excellent ion conductivity, electrochemical stability and interfacial properties.

1 is a comparison of the content of the vinylidene fluoride-based polymer and the liquid electrolyte in the porous polymer film according to the present invention,

2 is a comparison of the ion conductivity characteristics according to the temperature of the porous polymer electrolyte prepared through the blend of vinylidene fluoride-based polymer and ionomer,

3 (a) shows the interfacial resistance with the lithium electrode of the porous polymer electrolyte according to the present invention, Figure 3 (b) shows the interfacial resistance with the lithium electrode of the vinylidene fluoride-based polymer.

In the polymer electrolyte composition for secondary batteries, a porous polymer matrix in which an ionomer copolymerized with methyl methacrylate and an alkali maleic acid salt and a vinylidene fluoride-based polymer are blended, and lithium in an organic solvent in the pores of the porous polymer matrix. It is characterized in that the porous polymer electrolyte composition impregnated with the liquid electrolyte to which the salt is added.

In addition, the present invention is a method of manufacturing a polymer electrolyte composition for a secondary battery, the step of blending the polymer of the ionomer and vinylidene fluoride-based polymer copolymerized with methyl methacrylate and maleic acid alkali salt using the co-solvent, After adding a plasticizer for generating porous structure to the solution, casting a uniform solution prepared by adding an inorganic substance to the electric solution on a glass plate to evaporate the co-solvent to obtain a polymer film, and the polymer film is methanol or di Selectively dissolving only the plasticizer in the film by impregnating with ethyl ether to obtain a porous polymer film, and impregnating the porous polymer film with a liquid electrolyte prepared by dissolving a lithium salt in an organic solvent. Characterized in that the manufacturing method.

The porous polymer electrolyte composition according to the present invention is a polyvinylidene fluoride, a copolymer of vinylidene fluoride and nucleus fluoropropylene, a copolymer of vinylidene fluoride and trifluoroethylene, a vinylidene fluoride and tetrafluoroethylene Plasticizers such as dimethyl phthalate, dibutyl phthalate, and dioctyl phthalate were added to a polymer matrix prepared through a blend of a vinylidene fluoride-based polymer such as a copolymer of ethylene and an ionomer copolymerized with methyl methacrylate and an alkali maleic acid salt. To form a porous structure by using the present invention is prepared by impregnating a liquid electrolyte prepared by adding a salt such as lithium perchlorate, lithium hexafluorophosphate to a mixed solvent such as ethylene carbonate, propylene carbonate, dimethyl carbonate, etc.One alkali metal salt is a Group I alkali lane acid salts are both available, a lithium salt, sodium salt or potassium salt is preferred.

Hereinafter, the present invention will be described in detail.

First, in order to prepare an ionomer, methylmethacrylate and maleic anhydride monomer are added at a constant ratio to synthesize copolymers of various kinds of methyl methacrylate and maleic anhydride having the chemical structure of general formula (I).

X = mol% maleic anhydride

(Ⅰ)

In order to synthesize the above polymer, tetrahydrofuran is used as a solvent, methyl methacrylate and maleic anhydride, which are a certain amount of monomer, are put together in a reactor and stirred under a nitrogen atmosphere.

After stirring, a certain amount of initiator is injected to react, and the reaction is precipitated in a methanol solvent to obtain a copolymer by filtration. The copolymer thus obtained is dried at room temperature and then dried in a vacuum oven to completely remove the solvent.

Alkali metal hydroxides, preferably lithium hydroxide, sodium hydroxide or potassium hydroxide, prepared by dissolving a copolymer of the synthesized methyl methacrylate with maleic anhydride in a methanol solvent to a concentration of 0.1 normal to prepare as ionomer. The copolymer of methacrylic acid and maleic anhydride is neutralized using a lockside solution to obtain an ionomer copolymerized with a desired methyl methacrylate and maleic acid alkaline salt having the chemical structure of general formula (II).

The copolymer ionomer of methyl methacrylate and maleic acid alkali salt thus obtained is a polymer having a molecular weight of 10,000-200,000 and a content of maleic acid alkali salt in the ionomer of 0 to 50 mol%, preferably 2 to 30 mol%.

M = Li ⁺ , Na ⁺ , K ⁺

X = mol of maleic acid alkaline salt

(Ⅱ)

Synthesized ionomer, polyvinylidene fluoride having a molecular weight of 100,000 to 350,000, a copolymer of vinylidene fluoride and hexafluoropropylene having a composition of 1 to 30 mol%, and a composition of trifluoroethylene 1 1 type selected from the group consisting of a copolymer of vinylidene fluoride and trifluoroethylene having ˜30 mol% or a copolymer of vinylidene fluoride and tetrafluoroethylene having a composition of 1 to 30 mol% and tetrafluoroethylene The vinylidene fluoride-based polymer of the quantitative weight ratio of 1: 1 to 1: 9 is dissolved in a co-solvent tetrahydrofuran to make a uniform solution.

After adding one plasticizer selected from the group consisting of dimethyl phthalate, dibutyl phthalate or dioctyl phthalate to 10 to 350% by weight, preferably 50 to 300% by weight, based on the polymer weight, the aluminum oxide , A uniform solution prepared by adding 1 to 100% by weight, preferably 5 to 50% by weight, based on the weight of the polymer, is added to the inorganic material selected from lithium aluminum oxide, silica or zeolite, and the co-solvent is evaporated. After the polymer film is obtained. When the polymer film thus obtained is again impregnated in methanol, only the plasticizers in the film are selectively extracted to obtain a porous polymer film. The obtained porous polymer film was transferred into an argon atmosphere glove box, and then ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and gamma were 10 to 350% by weight, preferably 50 to 300% by weight based on the weight of the polymer. Lithium perchlorate in an amount of 5 to 30% by weight based on the polymer in one or two or more mixed organic solvents selected from the group consisting of butyrolactone, ethylmethyl carbonate, dimethoxyethane, diethoxyethane, or 2-methyltetrahydrofuran, Impregnated with 1 mol of a liquid electrolyte prepared by dissolving one lithium salt selected from the group consisting of lithium hexafluorophosphate, lithium triflate, lithium bistrifluoromethylsulfonylimide or lithium tetrafluoroborate salt. A porous polymer electrolyte is prepared in which polymer electrolytes are filled with liquid electrolytes.

The amount of the liquid electrolyte impregnated into the porous film of the prepared polymer blend is 10 to 350% by weight, preferably 50 to 300% by weight based on the weight of the polymer.

The content of the liquid electrolyte into the porous polymer film prepared by the above method is shown in FIG. 1, which is a vinylidene fluoride and hexafluoropropylene copolymer among vinylidene fluoride-based polymers, and In the copolymer ionomer of methyl methacrylate and maleic acid alkali salt, a porous structure is formed in each polymer in which the methyl methacrylate and lithium maleate salt are copolymerized with the vinylidene fluoride-based polymer in a 2: 8 (weight ratio) blend. After impregnation, the impregnation characteristics of the liquid electrolytes were compared.

At this time, despite the short impregnation time within a few minutes, the content of the liquid electrolyte is more than 100% by weight based on the polymer film, which can be confirmed that the improved properties than the case of using only a vinylidene fluoride-based polymer.

Figure 2 shows the ion conduction properties for the temperature range from the low temperature to room temperature of the prepared porous polymer electrolyte, the room temperature ion conductivity characteristics of 10 ^-3 S / cm or more even containing only about 100% by weight based on the weight of the polymer It can be seen that the low-temperature characteristic shows a relatively high level even at -25 ° C, and thus the ion conducting characteristics are improved compared to the case of using only vinylidene fluoride-based polymer.

Figure 3 shows the interfacial resistance with the lithium electrode of the polymer electrolyte prepared by the above method, it can be expected to exhibit excellent interfacial properties due to very small interfacial resistance value. Because of this, the polymer electrolyte prepared in the above manner may be usefully used as a material of the polymer electrolyte for lithium polymer secondary batteries.

Hereinafter, the present invention will be described in detail through Examples and Test Examples. However, these examples and test examples are provided only to explain the present invention in detail, and the scope of the present invention is not limited thereto.

<Example 1>

Among the ionomers copolymerized with methyl methacrylate and maleic acid alkali salts, copolymerized ionomers of methyl methacrylate and lithium maleate salts containing 4 mol% of lithium maleate salts are vinylidene fluoride and hexafluoro in vinylidene fluoride-based polymers. After mixing with a copolymer of propylene to a weight ratio of 2: 8, dibutyl phthalate is added so as to 1.5: 1 in a weight ratio with the polymer, and silica is added to 20% by weight based on the total weight of the polymer to tetrahydro After dissolving in a furan solvent, it was cast on a glass plate to evaporate the solvent to obtain a composite film.

This was again impregnated with methanol solvent to selectively extract dibutylphthalate, a plasticizer in the composite film, and then the dried film was transferred to an argon atmosphere glove box, where lithium hexafluorophosphate was added to a mixed solvent of ethylene carbonate and dimethyl carbonate 1: 1 mole. It was impregnated again into the prepared 1 mol liquid electrolyte to prepare a porous polymer electrolyte.

<Example 2>

It was carried out using a mixture having the same constituents and composition as in Example 1, except that a copolymer ionomer of methyl methacrylate and lithium maleate with 4 mol% of polyvinylidene fluoride and lithium maleate was used. A porous polymer electrolyte was prepared in the same manner as in Example 1.

<Example 3>

The same composition as in Example 1 except for the use of a copolymer of vinylidene fluoride and tetrafluoroethylene and a copolymer ionomer of methyl methacrylate and lithium maleate with a content of 4 mol% of lithium maleate salt and Using the mixture having a composition, a porous polymer electrolyte was prepared in the same manner as in Example 1.

<Example 4>

The above-mentioned implementation was carried out except that the blend composition ratio of the copolymer ionomer of methyl methacrylate and lithium maleate with 4 mol% of lithium maleate salt and the copolymer of vinylidene fluoride and hexafluoropropylene was 3: 7 by weight. A porous polymer electrolyte was prepared in the same manner as in Example 1, using a mixture having the same ingredients and composition as in Example 1.

<Example 5>

The above-mentioned implementation was carried out except that the blend composition ratio of the copolymer ionomer of methyl methacrylate and lithium maleate salt having a content of lithium maleate of 4 mol% and the copolymer of vinylidene fluoride and hexafluoropropylene was 5: 5 by weight. A porous polymer electrolyte was prepared in the same manner as in Example 1, using a mixture having the same ingredients and composition as in Example 1.

<Test Example 1>

In order to examine the ion conduction characteristics of the porous polymer electrolyte prepared in Examples 1 to 5, each polymer electrolyte film was bonded with a stainless steel electrode, and then sealed with a polyethylene-coated aluminium packaging material and then a frequency response analyzer. Using the (Frequency Response Analyzer, FRA) the ion conductivity was measured by calculating the resistance value from the change of current according to the frequency of the input voltage between 1 MHz ~ 100 Hz.

<Test Example 2>

In order to examine the interfacial properties of the porous polymer electrolytes prepared in Examples 1 to 5, the lithium electrodes were attached to both sides of the polymer electrolyte film as a current collector using a lithium electrode, and then 1 MHz using the frequency response analyzer. The interfacial resistance was observed within the frequency range of 1 KHz or less from the change of current according to the frequency change of the input voltage between ˜50 mHz.

The porous polymer electrolyte composition according to the present invention has the advantage that the compatibility with the organic solvent is improved to improve the ion conductivity characteristics, interfacial stability, etc. in the bulk, and also electrochemically stable.

That is, it is easier to manufacture than the existing gel polymer electrolyte, and high ion conductivity can be obtained even with a small amount of plasticizer, and it has excellent mechanical properties, and also improves the impregnation characteristics of the liquid electrolyte by introducing the ionomer and impregnates the liquid electrolyte solution. It has the advantage that it can be stably maintained in the polymer matrix for a long time without coming out.

Therefore, when the porous polymer electrolyte composition according to the present invention is applied to a conventional lithium secondary battery, it is possible to secure an advantage in the existing secondary battery market with sufficient competitiveness.

Claims (17)

In the polymer electrolyte composition for a secondary battery, A porous polymer matrix in which an ionomer copolymerized with methyl methacrylate and an alkali maleic acid salt and a polymer of vinylidene fluoride series are blended; Porous polymer electrolyte composition, characterized in that the liquid electrolyte in which lithium salt is added to the organic solvent is impregnated into the pores of the porous polymer matrix. The composition ratio according to claim 1, wherein the composition ratio in the porous polymer matrix in which the ionomer copolymerized with methyl methacrylate and the maleic acid alkali salt and the vinylidene fluoride-based polymer is blended is 1: 1 by 1: 9 by weight. Porous polymer electrolyte composition. According to claim 1, The vinylidene fluoride-based polymer is a copolymer of vinylidene fluoride and hexafluoropropylene having a composition of polyvinylidene fluoride and hexafluoropropylene of 1 to 30 mol%, trifluoro A copolymer of vinylidene fluoride and trifluoroethylene having a composition of ethylene of 1 to 30 mol% or a copolymer of vinylidene fluoride and tetrafluoroethylene having a composition of 1 to 30 mol% of tetrafluoroethylene Porous polymer electrolyte composition, characterized in that one selected from the group. The organic solvent of claim 1, wherein the organic solvent is selected from the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, gamma butyrolactone, ethyl methyl carbonate, dimethoxyethane, diethoxyethane or 2-methyltetrahydrofuran. Porous polymer electrolyte composition, characterized in that one or two or more selected mixed solvents. The porous polymer electrolyte composition according to claim 1, wherein the lithium salt is one selected from lithium perchlorate, lithium hexafluorophosphate, lithium triflate, lithium bistrifluoromethylsulfonylamide or lithium tetrafluoroborate salt. . The porous polymer electrolyte composition according to claim 1, wherein the amount of the liquid electrolyte impregnated into the porous polymer matrix is 50 to 300% by weight based on the weight of the polymer. The porous polymer electrolyte composition according to claim 1, wherein the ionomer is a polymer obtained by copolymerizing methyl methacrylate and maleic acid alkali salt having a molecular weight of 10,000 to 200,000 and an amount of ionic groups in the ionomer of 2 to 30 mol%. . The porous polymer electrolyte composition according to claim 1 or 3, wherein the vinylidene fluoride-based polymer has a molecular weight of 100,000 to 350,000. The porous polymer electrolyte composition according to claim 1 or 4, wherein the organic solvent is 50 to 300% by weight based on the weight of the polymer. The porous polymer electrolyte composition according to claim 1 or 5, wherein the lithium salt is 5 to 30% by weight based on the weight of the polymer. 8. The porous polymer electrolyte composition according to claim 1 or 7, wherein the maleic acid alkali salt is lithium maleate salt, potassium maleate salt or sodium maleate salt. The porous polymer electrolyte composition according to claim 1, wherein the porous polymer matrix is in the form of a thin thin plate. In the manufacturing method of the polymer electrolyte composition for secondary batteries, Blending an ionomer and a vinylidene fluoride-based polymer copolymerized with methyl methacrylate and maleic acid alkali salt using a cosolvent; Adding a plasticizer for porous structure generation to the blended solution, and then casting a uniform solution prepared by adding inorganic material to the electric solution on a glass plate to evaporate the cosolvent to obtain a polymer film; Impregnating the polymer film with methanol or diethyl ether to selectively melt only the plasticizer in the film to obtain a porous polymer film; And And impregnating the porous polymer film with a liquid electrolyte prepared by dissolving the lithium salt of the following (II) in a solvent of the following (I). (I) One or two selected from the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, gamma butyrolactone, ethyl methyl carbonate, dimethoxyethane, diethoxyethane or 2-methyltetrahydrofuran As a mixed solvent of the phase, 50 to 300% by weight based on the weight of the polymer. (II) Lithium perchlorate, lithium hexafluorophosphate, lithium triflate, lithium bistrifluoromethylsulfonylamide or lithium tetrafluoroborate salt, selected from the group consisting of 5 to 5 based on the weight of the polymer. 30% by weight. 14. The vinylidene fluoride-based polymer according to claim 13, wherein the vinylidene fluoride-based polymer is a copolymer of vinylidene fluoride and hexafluoropropylene having a composition of 1 to 30 mol% of polyvinylidene fluoride and hexafluoropropylene, and trifluoro A copolymer of vinylidene fluoride and trifluoroethylene having a composition of ethylene of 1 to 30 mol% or a copolymer of vinylidene fluoride and tetrafluoroethylene having a composition of 1 to 30 mol% of tetrafluoroethylene Method for producing a porous polymer electrolyte composition, characterized in that one selected from the group. The porous polymer electrolyte composition according to claim 13, wherein the plasticizer is one selected from the group consisting of dimethyl phthalate, dibutyl phthalate or dioctyl phthalate, and is added at 50 to 300 wt% based on the polymer. Manufacturing method. The method of claim 13, wherein the inorganic material is one selected from the group consisting of aluminum oxide, lithium aluminum oxide, silica or zeolite, and the preparation of the porous polymer electrolyte composition, characterized in that 5 to 50% by weight based on the polymer is added. Way. The method of claim 13, wherein the cosolvent is tetrahydrofuran or acetone.