KR19990012519A - Polymer electrolyte composition comprising an ionomer having a copolymer of methyl methacrylate and maleic acid metal salt and a process for producing the same - Google Patents

Abstract

The present invention relates to a polymer electrolyte composition comprising an ionomer copolymerized with methyl methacrylate and a maleic acid metal salt, and a process for producing the same. The polymer electrolyte composition of the present invention comprises 20 to 25% by weight of an ionomer copolymerized with methyl methacrylate and maleic acid metal salt and having an ion concentration of 1 to 8 mol%; 65 to 75% by weight plasticizer; And 5 to 10% by weight of a lithium salt. The polymer electrolyte composition of the present invention is easily prepared by copolymerizing methyl methacrylate and maleic acid, titrating with an alkaline metal salt solution to synthesize an ionomer, and mixing with a plasticizer and a lithium salt. The polymer electrolyte composition of the present invention is excellent in mechanical properties, ionic conductivity and compatibility, and is transparent and can be used not only as an electrolyte of a lithium polymer secondary battery but also as an electrochromic device. Particularly, when used as an electrolyte for a lithium polymer secondary battery, a battery having excellent charging / discharging efficiency and small interface resistance between a polymer electrolyte and a negative electrode active material is produced.

Description

Polymer electrolyte composition comprising an ionomer copolymerized with methyl methacrylate and maleic acid metal salt and a process for producing the same

The present invention relates to a polymer electrolyte composition comprising an ionomer in which methyl methacrylate and a maleic acid metal salt are copolymerized, and a process for producing the same. More particularly, the present invention relates to a polymer electrolyte composition comprising an ionomer, a plasticizer and a lithium salt copolymerized with methyl methacrylate and a maleic acid metal salt, and a process for easily producing an electro-polymeric electrolyte composition.

As the electric, electronic, communication, and computer industries rapidly develop, the demand for high performance and high stability secondary batteries has been gradually increasing. Particularly, due to the thinness and simplicity of electric and electronic products, A secondary battery such as a lithium secondary battery has been required to be thinner and smaller.

In response to these demands, the flexible thin film battery can be used not only as a memory back-up battery for a smart card, which is a high-end product of the next generation credit society, but also because it is easy to make high voltage and large capacity by stacking, It can also be developed as a vehicle power source. Particularly, a lithium polymer secondary battery (LPB) is one of the most popular high performance battery systems in recent years, and a lithium polymer secondary battery is a lithium polymer secondary battery in which lead (Pb) and cadmium (Cd) It does not contain any heavy metal substances and has no advantage of environmental pollution. The lithium polymer secondary battery is composed of a negative electrode active material, an electrolyte and a positive electrode active material. Examples of the negative electrode active material include lithium, a lithium-aluminum alloy or carbon, a solid polymer electrolyte (SPE) , A polymer electrolyte, and an electronic conductive material.

Thus, by using a solid polymer electrolyte as an electrolyte, a battery can be made thin, and its size and shape can be controlled as desired. An attempt to develop a solid polymer electrolyte exhibiting excellent conduction characteristics owing to the characteristics of such solid polymer electrolyte .

Recently, a method has been reported in which a polymer having an amorphous structure, a plasticizer such as ethylene carbonate or propylene carbonate, and a lithium salt are mixed to prepare a solid polymer electrolyte having a high ionic conductivity of 10 ^-3 S / cm at room temperature .

For example, U.S. Patent No. 5,219,679 discloses a method of preparing a solid polymer electrolyte by mixing polyacrylonitrile, ethylene carbonate, propylene carbonate, and lithium perchlorate (LiClO ₄ ). However, when the polyelectrolyte is prepared using polyacrylonitrile, the ionic conductivity and mechanical properties of the polymer electrolyte are excellent, but the compatibility of the plasticizer and the polymer is not good, so that the plasticizer impregnated in the polymer flows to the polymer surface There was a problem. In addition, when the content of the plasticizer as a polar solvent is increased in order to obtain a high ionic conductivity, the mechanical properties of the solid polymer electrolyte deteriorate.

(O. Bohnke et al., Solid State Ionics, 66: 97 (1993)) disclose a method of preparing solid polymer electrolytes by mixing polymethyl methacrylate, ethylene carbonate, propylene carbonate and lithium perchlorate. ). However, when the polymer electrolyte is prepared using polymethyl methacrylate, the content of the plasticizer, which is a polar solvent, must be increased in order to obtain a high ionic conductivity, so that the mechanical properties of the polymer electrolyte deteriorate, There was no disadvantage. In addition, there is a disadvantage that the charge / discharge efficiency of a battery manufactured using an electric electrolyte is reduced due to the presence of an immobilized anion which does not contribute to charging / discharging of the polymer electrolyte.

Accordingly, there has been a desperate need to develop a polymer electrolyte which is excellent in mechanical properties and can be produced in the form of a film, but has excellent ionic conductivity and compatibility. Particularly, when a polymer electrolyte is prepared by using polymethyl methacrylate, which is superior in compatibility with a plasticizer than polyacrylonitrile, the mechanical properties and ionic conductivity of the polymer electrolyte and the structure The development of improved polymethylmethacrylate has been urgently required.

Accordingly, the present inventors have made extensive efforts to overcome the problems of the solid polymer electrolyte which is a core component of the lithium polymer secondary battery (LPB) produced using the above-mentioned polymethyl methacrylate, and as a result, it has been found that methyl methacrylate and maleic acid metal salt The polymer electrolyte comprising the copolymerized ionomer, the plasticizer and the lithium salt has excellent mechanical properties, ionic conductivity and compatibility and is excellent in the charge and discharge efficiency of a battery produced using the electrolyte. The polymer electrolyte having an interface resistance between the polymer electrolyte and the negative electrode active material And the present invention has been completed.

As a result, a main object of the present invention is to provide a polymer electrolyte composition comprising an ionomer, a plasticizer and a lithium salt copolymerized with methyl methacrylate and a maleic acid metal salt.

Another object of the present invention is to provide a method for producing an electric polymer electrolyte composition.

FIG. 1 is a graph showing the ionic conductivity according to the ion concentration of the ionomer in the polymer electrolyte composition comprising the ionomer copolymerized with methyl methacrylate and maleic acid metal salt of the present invention.

FIG. 2 is a graph showing the interfacial resistance according to the ion concentration of the ionomer in the polymer electrolyte composition comprising the ionomer copolymerized with the methyl methacrylate and the maleic acid metal salt of the present invention.

Hereinafter, a polymer electrolyte composition comprising an ionomer copolymerized with methyl methacrylate and a maleic acid metal salt according to the present invention and a method for producing the same will be described in more detail.

In the present invention, the ionic conductivity of the polymer electrolyte is improved by introducing a lithium salt of maleic acid, which is an ionic group, into the main chain of the polymer, and the content of the plasticizer as a polar solvent is reduced to prevent deterioration of the mechanical properties of the polymer electrolyte. But also reduces the interfacial resistance between the polymer electrolyte and the negative electrode active material of the battery using the polymer electrolyte of the present invention. In addition, since the cation of the ion group introduced into the polymer main chain interacts with the anion in which the ion is dissolved, the migration of the anion which does not contribute to the substantial charge and discharge is prevented, so that the battery produced using the polymer electrolyte of the present invention Thereby improving charge and discharge efficiency.

The polymer electrolyte composition of the present invention comprises 20 to 25% by weight of an ionomer of the structural formula (I) copolymerized with methyl methacrylate and maleic acid metal salt and having an ion concentration of 1 to 8 mol%; 65 to 75% by weight plasticizer; And 5 to 10% by weight of a lithium salt.

As the maleic acid metal salt, lithium maleate or sodium maleate, most preferably lithium maleate is used.

When the ionomer concentration is 1 to 8 mol% and less than 1 mol% or more than 8 mol%, the ionic conductivity of the prepared polymer electrolyte is small and the interface resistance is large. Thus, the produced polymer electrolyte is an electrolyte of a lithium polymer secondary battery Can not be used. In addition, the content of the ionomer in the polymer electrolyte composition is 20 to 25% by weight. When the content is less than 20% by weight, the film-type polymer electrolyte can not be produced. When the content is more than 25% by weight, Can not be.

As the plasticizer, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate or dimethoxyethane, most preferably ethylene carbonate is used, and the content of the plasticizer in the polymer electrolyte composition is 65 to 75% by weight. When the content is less than 65% by weight, the ionic conductivity is low. When the content is more than 75% by weight, the polymer electrolyte in the form of a film can not be produced, so that the produced polymer electrolyte can not be put to practical use.

LiClO ₄ , LiCF ₃ SO ₃ , LiBF ₄ or LiPF ₆ , and most preferably LiClO ₄ are used as the lithium salt, and when the content of the lithium salt in the polymer electrolyte composition is less than 5% by weight, the ionic conductivity of the polymer electrolyte Can not be practically used.

The process for producing the polymer electrolyte composition of the present invention will be described below.

Step 1: Synthesis of copolymer of methyl methacrylate and maleic acid

96.0 to 99.5 mol% of methyl methacrylate and 0.5 to 4.0 mol% of maleic acid are dissolved in an organic solvent, preferably tetrahydrofuran, and injected into the reactor to remove dissolved oxygen contained in the reactants and the organic solvent. Then, an initiator, preferably hydrogen peroxide, benzoylperoxide (BPO), or 2,2'-azobisisobutyronitrile (IBN), in an amount of 1 to 5 wt% , More preferably 2,2'-azobisisobutyronitrile is dissolved in a solvent, preferably tetrahydrofuran, and the mixture is stirred and reacted at 50 to 80 ° C, and the reaction product is treated with a non-solvent, Precipitated in methanol and then dried to synthesize a copolymer of methyl methacrylate and maleic acid.

Step 2: Synthesis of ionomer

The acidic copolymer synthesized in the electrical process is titrated with an alkaline metal salt solution having a concentration of 0.02 to 0.5N, preferably an aqueous lithium hydroxide solution having a concentration of 0.02 to 0.2N, and dried to obtain an ionic compound having an ionic concentration of 1 to 8 mol% (I).

Step 3: Production of polymer electrolyte composition

20 to 25% by weight of the ionomer synthesized in the electric process is dissolved in a polar solvent, preferably tetrahydrofuran, mixed with 65 to 75% by weight of a plasticizer and 5 to 10% by weight of a lithium salt, ), Preferably on a Teflon plate, and the solvent is volatilized to prepare a film-type transparent polymer electrolyte composition.

As the plasticizer, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate or demethoxyethane, most preferably ethylene carbonate is used. As the lithium salt, LiClO ₄ , LiCF ₃ SO ₃ , LiBF ₄ or LiPF ₆ , And most preferably LiClO ₄ .

Hereinafter, the present invention will be described in more detail with reference to examples.

It is to be understood by those skilled in the art that these embodiments are merely illustrative of the present invention and that the scope of the present invention is not limited to these embodiments in accordance with the gist of the present invention.

[Example 1-7]

Preparation of Polymer Electrolyte Composition

Methyl methacrylate and maleic acid were dissolved in 250 ml of tetrahydrofuran, respectively, in the amounts shown in Table 1, and the high-purity nitrogen was flowed into the reactor at a flow rate of 50 cc / min for about 1 hour. Then, 0.05 g of 2,2'-azobisisobutyronitrile as an initiator was dissolved in 10 ml of tetrahydrofuran, and the mixture was stirred. The mixture was reacted at 60 ° C for about 5 hours, and the reaction product was precipitated in methanol And dried in a vacuum oven at 120 캜 for 24 hours to synthesize a copolymer of methacrylate and maleic acid. The acidic copolymers synthesized in the prior art were each titrated with a 0.05 N lithium hydroxide aqueous solution and dried in a vacuum oven at 150 캜 for 15 hours to synthesize ionomers having ion concentrations as shown in Table 1 below.

[Table 1]

23.2% by weight of the ionomer synthesized above was dissolved in tetrahydrofuran, sufficiently mixed with 69.8% by weight of ethylene carbonate and 7.0% by weight of lithium perchlorate with stirring for about 12 hours, and the mixture was cast on a Teflon plate The solvent was volatilized to prepare a film-type transparent polymer electrolyte composition.

[Example 8]

Ionic conductivity of polymer electrolyte

The film type polymer electrolyte prepared in each of Examples 1 to 8 was cut with a punch to prepare a disk shaped specimen having a diameter of 12 mm and ion conductivity was measured using a frequency response analyzer (Solatron 1225, Germany) The results are shown in FIG. 1. In FIG. 1, the X-axis shows the ionic concentration of the ionomer and the Y-axis shows the ionic conductivity. As shown in FIG. 1, the polymer electrolyte of the present invention has excellent ion conductivity at room temperature, and ion conductivity of the polymer electrolyte can be controlled by changing the ion concentration of the ionomer. In addition, the ion conductivity of the polymer electrolyte of the present invention is largest when the ion concentration of the ionomer is 4.5 mol%, and decreases continuously when the ion concentration is further increased. When the ion concentration exceeds 8 mol%, the produced polymer electrolyte is lithium It can not be used as an electrolyte of a polymer secondary battery.

[Example 9]

Interfacial Resistance Measurement of Polymer Electrolyte

The film-shaped polymer electrolyte prepared in each of Examples 1 to 8 was cut with a punch to prepare a disk-shaped specimen having a diameter of 12 mm. Using the prepared specimen as an electrolyte and lithium as a negative electrode active material and a positive electrode active material, . Impedance of a battery manufactured by using a frequency response analyzer (Solatron 1225, Germany) and sweeping in a frequency range of 10 nm to 10 MHz was measured, and the interface resistance immediately after the battery production and the interface resistance in the steady state were analyzed, The results are shown in FIG. As shown in FIG. 2, the polymer electrolyte of the present invention is superior in the interfacial resistance to the polymer electrolyte containing polymethyl methacrylate corresponding to an ion concentration of 0 mol% on the graph. In addition, the interfacial resistance of the polymer electrolyte according to the present invention is the smallest when the ion concentration of the ionomer is 4.5 mol%, and increases continuously when the ion concentration is further increased. When the ion concentration exceeds 8 mol% It can not be used as an electrolyte of a lithium polymer secondary battery.

As described and demonstrated in detail above, the present invention provides a polymer electrolyte composition comprising an ionomer, a plasticizer, and a lithium salt copolymerized with methyl methacrylate and a maleic acid metal salt, and a process for producing the same. The polymer electrolyte composition of the present invention is excellent in mechanical properties, ionic conductivity and compatibility, and is transparent and can be used not only as an electrolyte of a lithium polymer secondary battery but also as an electrochromic device. Particularly, when used as an electrolyte for a lithium polymer secondary battery, a battery having excellent charging / discharging efficiency and small interface resistance between a polymer electrolyte and a negative electrode active material is produced. In addition, the polymer electrolyte composition of the present invention can be easily produced, and ion conductivity can be controlled by changing the ion concentration of the ionomer.

Claims (6)

From 20 to 25% by weight of an ionomer of structural formula (I), wherein the copolymer is methyl methacrylate and maleic acid metal salt and has an ion concentration of 1 to 8 mol%; 65 to 75% by weight plasticizer; And 5 to 10% by weight of a lithium salt. The method according to claim 1, Wherein the maleic acid metal salt is lithium maleate. The method according to claim 1, The plasticizer is preferably ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate or dimethoxyethane. Polymer electrolyte composition. The method according to claim 1, Lithium salt, characterized in that _{LiClO 4, LiCF 3 SO 3,} LiBF 4 or LiPF ₆ Polymer electrolyte composition. (i) 96.0 to 99.5 mol% of methyl methacrylate and 0.5 to 4.0 mol% of maleic acid are dissolved in an organic solvent and injected into a reactor to remove dissolved oxygen contained in the reactants and the organic solvent, Adding 5% by weight of an initiator and reacting at 50 to 80 캜 to synthesize a copolymer of methyl methacrylate and maleic acid; (ii) titrating the copolymer synthesized in the electrical process with an alkaline metal salt solution having a concentration of 0.02 to 0.5 N to synthesize an ionomer having an ion concentration of 1 to 8 mol%; And (iii) 20 to 25% by weight of the ionomer synthesized in the electric process is dissolved in a polar solvent, mixed with 65 to 75% by weight of a plasticizer and 5 to 10% by weight of a lithium salt, and then the mixture is cast in a mold and the solvent is volatilized Wherein the polymer electrolyte composition is a polymer electrolyte. 6. The method of claim 5, Wherein the alkaline metal salt solution is an aqueous solution of lithium hydroxide having a concentration of 0.02 to 0.2N A method for producing a polymer electrolyte composition.