KR100335649B1 - Composition of Gel-Type Polymer Electrolytes Comprising Vinylidenefluoride and Acrylate Polymers and Process for Preparing the Same - Google Patents

Abstract

The present invention relates to a polymer electrolyte composition prepared by adding an organic solvent, a lithium salt and an inorganic substance to a vinylidene fluoride-based polymer and an acrylate-based polymer. The gel polymer electrolyte prepared according to the present invention has excellent ion conductivity and wider interface stability than a gel polymer electrolyte composed of only a vinylidene fluoride-based polymer. Therefore, the gel polymer electrolyte prepared in the present invention may be usefully used as a material of the polymer electrolyte for lithium polymer secondary batteries.

Description

Composition of Gel-Type Polymer Electrolytes Comprising Vinylidenefluoride and Acrylate Polymers and Process for Preparing the Same}

The present invention relates to a novel gel polymer electrolyte. More specifically, the present invention is a gel polymer prepared by adding an organic solvent, a lithium salt, and an inorganic material to a vinylidene fluoride-based polymer and an acrylate polymer blend, and having excellent ion conductivity and improved interface stability with an electrode. An electrolyte and a method for producing the same.

With the rapid development of the electrical, electronics, telecommunications and computer industries, the demand for high-performance, high-safety secondary batteries has been gradually increasing, especially in light of the shortening and portability of electrical and electronic products. Secondary batteries, which are components, are also required to be lighter and smaller. In addition, as the necessity of a new form of energy supply and demand due to the exhaustion of oil and environmental pollution, such as air pollution and noise, due to the mass distribution of automobiles, the need for the development of electric vehicles that can solve this has increased. As a power source, development of a battery having high power and high energy density is required.

In response to these demands, one of the latest high-performance, next-generation new batteries that has received the most attention in recent years 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.

Conventional lithium ion batteries using liquid electrolytes have raised safety problems, and methods for mounting electrode materials and safety devices have been developed. However, manufacturing costs are expensive and difficult to apply to large secondary batteries. . On the contrary, LPB using a polymer electrolyte can be manufactured more inexpensively, can be adjusted in size or shape as desired, is safe, and has an 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 a high-voltage large-capacity battery by stacking 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 satisfying excellent ion conducting properties, electrochemical stability, and excellent interfacial properties with electrodes. Initially, studies on solvent-free polymer electrolytes mainly based on polyethylene oxide, polypropylene oxide, and the like have been conducted for a long time (see European Patent No. 78505; US Patent No. 5,102,752), due to a problem of low temperature conductivity. Currently, high ions of 10 ^-3 S / cm or more are added to a polymer such as polyacrylonitrile, polyvinyl chloride, polyvinylidene fluoride or polymethyl methacrylate by adding an organic solvent such as ethylene carbonate or propylene carbonate together with a salt. Research is underway on gelated plasticized polymer electrolytes that exhibit conductivity (O. Bohnke et al., Solid State Ionics, 66, 97 (1993); US Pat. No. 5,219,697). Among them, the gel polymer electrolyte film based on polyacrylonitrile, polyvinyl chloride or polyvinylidene fluoride has excellent mechanical properties but poor compatibility between the added organic solvent and the polymer, so that the organic solvent leaks out. ), Gel ionic electrolytes based on acrylate-based polymers such as polymethyl methacrylate have excellent compatibility with plasticizers, but have problems with ion conducting properties and interfacial stability with electrodes. Due to the weak physical properties, there is a disadvantage that the film is deteriorated according to the content of the organic solvent.

Therefore, there is a continuous need for the development of a new polymer electrolyte having excellent mechanical properties, ion conducting properties, and interfacial stability with an electrode, which can be used in a lithium polymer secondary battery.

Accordingly, the present inventors have made diligent efforts to develop a new polymer electrolyte having excellent mechanical properties, ion conductivity, and interfacial stability with an electrode that can be used in a lithium polymer secondary battery. By mixing the acrylate-based polymer having excellent compatibility with the organic solvent, it is possible to suppress the increase in internal resistance and the decrease in ionic conductivity due to the leakage of the organic solvent generated in the gel polymer electrolyte. In addition, it was confirmed that the stability at the interface can be increased by suppressing the reactivity between the polymer electrolyte and the electrode, thereby completing the present invention.

As a result, a main object of the present invention is to provide a polymer of a vinylidene fluoride-based polymer and an acrylate-based polymer, and to provide a gel polymer electrolyte composition having excellent ion conductivity and improved interfacial stability.

Another object of the present invention is to provide a method for preparing a gel polymer electrolyte composition comprising a vinylidene fluoride-based polymer and an acrylate-based polymer.

1 is a graph showing ionic conductivity characteristics of a gel polymer electrolyte containing polyvinylidene fluoride and polymethyl methacrylate in a weight ratio of 10: 0 or 7: 3, respectively.

FIG. 2 is a graph showing ion conductivity characteristics of a gel polymer electrolyte having a copolymer of vinylidene fluoride and hexafluoropropylene and a polymethyl methacrylate in a weight ratio of 10: 0 or 7: 3, respectively.

3 is a graph showing interfacial resistance with a lithium electrode of a gel polymer electrolyte containing polyvinylidene fluoride and polymethyl methacrylate in a weight ratio of 10: 0 or 7: 3, respectively.

4 is a graph showing interfacial resistance with a lithium electrode of a gel polymer electrolyte including a copolymer of vinylidene fluoride and hexafluoropropylene and a polymethyl methacrylate in a weight ratio of 10: 0 or 7: 3, respectively.

The gel polymer electrolyte composition of the present invention is prepared by mixing an organic solvent, a lithium salt, and an inorganic substance in a polymer blend composed of a vinylidene fluoride polymer and an acrylate polymer.

The polymer blend is a vinylidene fluoride-based polymer and an acrylate-based polymer in a 99: 1 to 20:80 weight ratio, preferably 90:10 to 50:50 weight ratio, and dissolved in tetrahydrofuran as a cosolvent. To obtain. At this time, the vinylidene fluoride-based polymer is a copolymer of polyvinylidene fluoride having a weight average molecular weight of 100,000 to 350,000, hexafluoropropylene and vinylidene fluoride having a composition ratio of 5 to 25 mol% of hexafluoropropylene. A copolymer of trifluoroethylene and vinylidene fluoride having a composition ratio of trifluoroethylene of 5 to 25 mol%, or tetrafluoroethylene and vinylidene fluoride having a composition ratio of 5 to 25 mol% of tetrafluoroethylene. Polymers, such as a copolymer, can be used. Examples of the acrylate-based polymer include polymethyl acrylate, polyethyl acrylate, polymethyl methacrylate, polyethyl methacrylate, polybutyl acrylate or polybutyl methacrylate having a weight average molecular weight of 100,000 to 500,000. Can be used.

In addition, the organic solvent is one or more solvents selected from the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, gamma butyrolactone, methyl ethyl carbonate, etc. To 500 parts, preferably 100 to 350 parts are used.

And, the lithium salt is a salt of one of lithium perchlorate, lithium hexafluorophosphate, lithium triplate, lithium bistrifluoromethylsulfonylimide or lithium tetrafluoroborate, based on the weight ratio of 100 parts of the polymer blend, lithium Salts from 1 to 50 parts, preferably from 2 to 25 parts are used.

Finally, the inorganic material is an inorganic material such as aluminum oxide, lithium aluminum oxide, silica or zeolite, 1 to 50 parts, preferably 5 to 25 parts by weight relative to 100 parts of the polymer blend.

Hereinafter, the present invention will be described in more detail with reference to Examples. These examples are only for illustrating the present invention in more detail, it will be apparent to those skilled in the art that the scope of the present invention is not limited by these examples in accordance with the gist of the present invention. .

Example 1 :

Polyvinylidene fluoride and polymethyl methacrylate are mixed in a weight ratio of 7: 3 and dissolved in tetrahydrofuran, a cosolvent, and a mixed organic solvent of ethylene carbonate and propylene carbonate in a 1: 1 molar ratio based on the mixed polymer, lithium Perchlorate and silica were added in a weight ratio of 100: 300: 10: 10 to prepare a uniform solution, which was then cast on Teflon plate and the cosolvent was evaporated to prepare a gel polymer electrolyte in the form of a film.

Example 2 :

The same method as in Example 1, except that a copolymer of vinylidene fluoride having a hexafluoropropylene content of 12 mol%, hexafluoropropylene, and polymethyl methacrylate were mixed at a weight ratio of 7: 3. To prepare a gel polymer electrolyte in the form of a film.

Comparative Example 1 :

A gel polymer electrolyte was prepared in the same manner as in Example 1, except that polyvinylidene fluoride was used alone.

Comparative Example 2 :

A gel polymer electrolyte was prepared in the same manner as in Example 1, except that a copolymer of vinylidene fluoride and hexafluoropropylene was used alone.

Measurement of Ion Conductivity :

Ion conductivity was measured for the gel polymer electrolytes prepared in Examples 1 and 2 and Comparative Examples 1 and 2. Ionic conductivity is obtained by measuring the resistance values in the high frequency region by using a frequency response analyzer (FRA) by bonding each polymer electrolyte film to a stainless steel electrode and then vacuum-sealing it with a polyethylene-coated aluminum package. And it was calculated using the ion conductivity calculation formula (see Figs. 1 and 2).

In Figure 1,-(■)-is a graph showing the ion conductivity characteristics according to the temperature of the gel polymer electrolyte composition using a polymer blend having a weight ratio of polyvinylidene fluoride and polymethyl methacrylate of 7: 3,-( ●)-is a graph showing the ion conductance characteristics of the gel polymer electrolyte using polyvinylidene fluoride according to the temperature. As shown in FIG. 1, by mixing methyl methacrylate with polyvinylidene fluoride, ionic conductivity was improved in a wide temperature range, and in particular, ionic conductivity in a low temperature range was a conventional gel-type polymer without methacrylate mixing. Significantly improved over the electrolyte.

In FIG. 2,-(■)-is a copolymer of vinylidene fluoride and hexafluoropropylene, a vinylidene fluoride-based polymer, and a polymer having a weight ratio of polymethyl methacrylate of 7: 3, an acrylate-based polymer. It is a graph showing the ion conductivity characteristics according to the temperature of the gel polymer electrolyte composition using the blend,-(●)-is a graph showing the ion conductivity characteristics according to the temperature of the copolymer of vinylidene fluoride and hexafluoropropylene only. As shown in FIG. 2, the room temperature ion conductivity is 2.17 × 10 ⁻³ S / cm, which is superior to or similar to that of the conventional gel-type polymer electrolyte in which polymethyl methacrylate is not mixed. Maintained ^-4 S / cm level was very good.

Measurement of Interface Resistance :

In addition, the interfacial resistance of the gel polymer electrolytes prepared in Examples 1 and 2 and Comparative Examples 1 and 2 was measured. The interfacial resistance was compared by attaching lithium electrodes to both sides of the polymer electrolyte film and then measuring resistance values in the low frequency region using a frequency response analyzer (see FIGS. 3 and 4).

In Figure 3,-(□)-is a graph measuring the interfacial resistance between the gel polymer electrolyte composition and the lithium electrode using a polymer blend having a weight ratio of polyvinylidene fluoride and polymethyl methacrylate of 7: 3,- (Circle)-is a graph which measured the interface resistance between the gel polymer electrolyte composition using polyvinylidene fluoride, and a lithium electrode. As shown in FIG. 3, it can be seen that the interfacial resistance of the polymer electrolyte and the lithium electrode of the present invention in which polymethyl methacrylate is mixed is significantly reduced compared to the interfacial resistance of the electrolyte in which the polymethyl methacrylate is not mixed.

In Fig. 4,-(□)-is a copolymer of vinylidene fluoride and hexafluoropropylene, a vinylidene fluoride-based polymer, and a polymer having a weight ratio of polymethyl methacrylate of 7: 3, an acrylate-based polymer. It is a graph which measured the interfacial resistance between the gel polymer electrolyte composition and the lithium electrode using the blend, and-(○)-is a graph showing the interfacial resistance of the copolymer of vinylidene fluoride and hexafluoropropylene. As shown in FIG. 4, it can be seen that the interfacial resistance of the polymer electrolyte and the lithium electrode of the present invention in which polymethyl methacrylate is mixed is significantly reduced compared to the interfacial resistance of the electrolyte in which the polymethyl methacrylate is not mixed.

As described and demonstrated in detail above, the present invention provides a gel polymer electrolyte composition prepared by mixing an organic solvent, a lithium salt, and an inorganic material in a blend of a vinylidene fluoride-based polymer and an acrylate-based polymer. The gel polymer electrolyte prepared according to the present invention has superior ion conductivity characteristics and improved interfacial stability over a wide temperature range, compared to a conventional gel polymer electrolyte composed only of a vinylidene fluoride series polymer. Therefore, the gel polymer electrolyte prepared in the present invention may be usefully used as a material of the polymer electrolyte for lithium polymer secondary batteries.

Claims (7)

Copolymer of hexafluoropropylene and vinylidene fluoride having a composition ratio of hexafluoropropylene of 5 to 25 mol%, and air of trifluoroethylene and vinylidene fluoride having a composition ratio of trifluoroethylene of 5 to 25 mol% A vinylidene fluoride-based polymer and an acrylate-based polymer selected from the group consisting of a copolymer and a copolymer of tetrafluoroethylene and vinylidene fluoride having a composition ratio of tetrafluoroethylene of 5 to 25 mol%. The polymer blend was dissolved in a co-solvent in a weight ratio of 99: 1 to 20:80, and then 50 to 500 parts of an organic solvent, 1 to 50 parts of lithium salt, and 1 to 50 parts of inorganic salt based on 100 parts by weight of the polymer blend. Mixing the parts with the polymer blend dissolved in the cosolvent to obtain a uniform solution; And, Casting the obtained solution to evaporate the co-solvent manufacturing method of a gel polymer electrolyte composition. delete The method of claim 1, The acrylate-based polymer has a weight average molecular weight of 100,000 Polymethyl acrylate, polyethyl acrylate, polymethyl meth from 500,000 Methacrylate, polyethyl methacrylate, polybutyl acrylate or poly Butyl methacrylate, characterized in that Method for preparing a gel polymer electrolyte composition. The method of claim 1, Organic solvents include ethylene carbonate, propylene carbonate, dimethyl carbonate, Consisting of diethyl carbonate, gamma butyrolactone, and methyl ethyl carbonate At least one solvent selected from the group Method for preparing a gel polymer electrolyte composition. The method of claim 1, Lithium salt is lithium perchlorate, lithium hexafluoro phosphate, lithium triple Yttrium, lithium bistrifluoromethylsulfonylimide or lithium tetrafluoro Characterized in that it is a borate salt Method for preparing a gel polymer electrolyte composition. The method of claim 1, Inorganic materials are aluminum oxide, lithium aluminum oxide, silica or zeolite Characterized by Method for preparing a gel polymer electrolyte composition. 100 parts of polymer blend in which vinylidene fluoride-based polymer and acrylate-based polymer are mixed in a weight ratio of 99: 1 to 20:80, 50 to 500 parts of organic solvent, 1 to 50 parts of lithium salt and 1 to 50 parts of inorganic material Gel polymer electrolyte composition comprising.