KR100313560B1 - Graft solid polymer electrolyte and its manufacturing method - Google Patents

Abstract

The present invention is a solid polymer electrolyte mainly composed of a graft polymer and a lithium salt grafted with polyethylene glycol methyl ether by a sorbomer curation-demercuration reaction to a polyethylene oxide main chain having a double bond introduced therein, and It relates to a manufacturing method. The solid polymer electrolyte of the present invention exhibits excellent ionic conduction properties and excellent mechanical properties through crosslinking, and has a feature of easily controlling the length of the side chain and the degree of crosslinking. In addition, according to the present invention, the solid polymer electrolyte can appropriately control the flexibility and ionic conduction properties of the polymer chain by changing the components of each mixture, and does not contain any organic solvents, so there is no problem of electrolyte leakage and corrosion of the electrode. It may be usefully used in various electrochemical devices including secondary batteries.

Description

Graft form of solid polymer electrolyte and preparation method thereof

The present invention relates to a graft type solid polymer electrolyte and a method for preparing the same, which not only exhibit excellent ion conducting properties and excellent mechanical properties through crosslinking, but also easily control the length and degree of crosslinking of the side chain. More specifically, the present invention is based on the graft polymer and lithium salt grafted polyethylene glycol methyl ether by a sorbomer curation-demercuration reaction to a polyethylene oxide main chain in which a double bond is introduced. A solid polymer electrolyte and a linear polymer having a double bond introduced into the polyethylene oxide main chain were synthesized, and a polyethylene glycol methyl ether was grafted to the electric double bond by solbomercuring-demercuring to obtain a graft polymer. It relates to a method for producing a solid polymer electrolyte comprising the step of adding a lithium salt.

The rapid development of the electric, electronic, telecommunication and computer industries has led to an increasing demand for high performance, high stability secondary batteries. In particular, the thinning and miniaturization of electric and electronic products has resulted in the demand for thinning and miniaturizing secondary batteries, which are energy sources. In addition, there is a demand for the development of high-performance batteries due to the development of electric vehicles due to environmental problems. One representative system that meets these expectations is a lithium polymer secondary battery (hereinafter referred to as 'LPB'). The lithium polymer secondary battery is composed of a negative electrode, an electrolyte, and a positive electrode material. The negative electrode active material is lithium, a lithium-aluminum alloy, carbon, etc., the electrolyte is a solid polymer electrolyte, and the positive electrode active material is a transition metal compound. , Composite materials composed of polymer electrolyte and electron conductive material are mainly used.

In the above, the solid polymer electrolyte does not contain a heavy metal material, there is no problem of environmental pollution, and has a feature that can adjust the size or shape as desired. Therefore, as high performance and miniaturization of precision electronics and electronic devices require high performance, miniaturization and thinning of batteries, the flexible thin film battery can be used as a battery for smart card memory backup, which is the latest product of the next generation credit society. In addition, it is possible to easily develop a high-voltage large-capacity battery by lamination, which enables development of a power source for an electric vehicle.

In general, the polymer to be used as the solid polymer electrolyte has a polar group having an ion coordination ability in the polymer chain, ② the glass transition temperature is low, the flexibility of the chain is good, ③ the crystallinity that hinders ion conduction should be low ④ For the good solvation of salts, the structure of the polymer chain should be easy.

There are not many polymers that fully meet these requirements, and researches using polyethylene oxide are mainly progressing. However, pure polyethylene oxide has a disadvantage in that, despite the advantages of a structure capable of dissociating ions, the crystallinity is high and the ion conductivity at room temperature is very low. Therefore, many researchers have been researched to develop a solid polymer electrolyte such that the polyethylene oxide having the same characteristics as the electric exhibits excellent conductivity.

Representatively, as an example of a polymer electrolyte having a polyethylene oxide as a side chain, a method of preparing a solid polymer electrolyte by grafting polyether monoisocyanate to an acrylic copolymer containing a hydroxyl functional group and mixing with an alkali metal salt is disclosed. See US Patent No. 5,337,184). In this case, the flexibility can be obtained through the graft structure, but the acrylic copolymer, which is the main chain, does not contribute to the improvement of the ionic conductivity at all.

In addition, as an example of the preparation of a mixed polymer electrolyte containing polyethylene oxide as a main component, a mixture of propylene carbonate, dimethoxyethane, polyethylene oxide, lithium triplate, and irradiating crosslinking agent is impregnated with a Nomex aramid fabric. A method for preparing a polymer electrolyte by irradiating a mixture with ultraviolet rays or electron beams is disclosed (see US Patent No. 5,102,752). However, this method is difficult to manufacture and consumes a lot of time and cost, such as irradiating ultraviolet rays, and it is possible to prepare a mixture of polyethylene oxide / propylene carbonate / dimethoxyethane / lithium triflate mixture crosslinked by nomex aramid fabric and ultraviolet irradiation. There is a problem in terms of mechanical stability of the polymer electrolyte due to compatibility problems, and also contains a large amount of organic solvent, causing corrosion and safety problems of the electrode.

Recently, crosslinked polymer electrolytes having polar groups in the main and side chains have been reported through anionic polymerization (M. Andrei et al., Polymer, 35: 3592 (1994); K. Motogami et al., Electrochemica Acta, 37). : 1725 (1992). The polymer electrolyte thus prepared has excellent ionic conductivity at high temperature and low temperature, but has a polypropylene oxide structure in which the manufacturing process is complicated and the main chain structure at the graft reaction has better ionic conductivity than polyethylene oxide. There was a downside. In addition, the change in the length of the graft is limited due to the limitation of reactivity, the graft and the crosslinking reaction occurs at the same time there was a problem that difficult to control the degree of crosslinking.

Accordingly, the inventors of the present invention have made efforts to solve the above problems of the solid polymer electrolyte, which is the core of the lithium polymer secondary battery (LPB), and as a result, a linear polymer having a double bond introduced into the polyethylene oxide main chain Synthesized and grafted polyethylene glycol methyl ether to the electric double bond by solbomercuring-demercuring to obtain a graft polymer, and then a solid polymer prepared by adding lithium salt and controlling the presence or absence of crosslinking and degree of crosslinking. The electrolyte shows excellent ionic conductivity and excellent mechanical properties through crosslinking, can easily control the length and degree of crosslinking of the side chain, and it does not contain any organic solvents, so there is no problem of electrolyte leakage and electrode corrosion. The present invention has been completed.

After all, the main object of the present invention is to provide a solid polymer electrolyte mainly composed of a graft polymer and a lithium salt grafted polyethylene glycol methyl ether to a polyethylene oxide main chain in which a double bond is introduced by a solbomercuration-demercuring reaction. There is.

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

1 is a graph showing ionic conductivity according to lithium salt content of an uncrosslinked graft polymer electrolyte.

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

The present invention provides a graft polymer having a molecular weight of 120 to 750 and a graft ratio of 60 to 90% of the polyethylene glycol methyl ether grafted to the polyethylene oxide main chain to which a double bond is introduced by a solbomercuring-dimerization reaction. . In addition, the present invention provides a solid polymer electrolyte composed of 60 to 95 wt% of an electric graft polymer and 5 to 40 wt% of a lithium salt. In this case, the lithium salt may be lithium triplate (LiCF ₃ SO ₃ ), lithium perchlorate (LiClO ₄ ) or lithium bis (trifluoromethylsulfonyl) imide (LiN (CF ₃ SO ₂ )). In the above, the graft rate represents the ratio of the number of double bonds in the main chain before the graft reaction and the number of double bonds in the main chain after the grafting in percentage.

In addition, the graft polymer content of the initiator of the cross-linking reaction, for example, benzoyl peroxide or 2,2'-azobisisobutyronitrile (AIBN) in the composition of the solid polymer electrolyte It can be added in an amount corresponding to 1 to 20% by weight of to prepare a crosslinked solid polymer electrolyte.

Meanwhile, the solid polymer electrolyte of the present invention synthesizes a linear polymer in which a double bond is introduced into a polyethylene oxide main chain, and grafts a polyethylene glycol methyl ether to an electric double bond by solbomercuring-demercuring. It is then prepared by adding a lithium salt and adjusting the presence or absence of crosslinking and the degree of crosslinking.

The solid polymer electrolyte prepared as described above greatly improves the ionic conductivity because the polyethylene oxide structure exhibiting excellent ion conductivity is not only present in the main chain and the side chain at the same time, but also there is no deformation in the ethylene oxide structure of the main chain after the graft reaction; Crosslinkable functional groups are present in the main chain to exhibit excellent mechanical properties through crosslinking; The side chain length is easily controlled by grafting ethylene oxide to the linear polymer through a solbomercuring-demercuring reaction; And since the crosslinking reaction is possible after obtaining the graft reactant, the degree of crosslinking can be controlled. In addition, the solid polymer electrolyte of the present invention can be easily produced at low cost in a short time.

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, and it will be apparent to those skilled in the art that the scope of the present invention is not limited to these examples according to the gist of the present invention.

Example 1 :

Grafted polymer electrolyte using polyethylene glycol and CCMP (3-chloro-2-chloromethyl-propene) as a monomer was prepared by the following synthesis process:

In the above,

X is 2, 7.2, 11.8 or 16.3; And,

Y is 0.6.

To prepare the electrografted polymer electrolyte, first, 16 g of polyethylene glycol having an average molecular weight of 400 was dissolved in 150 ml chlorobenzene solvent with 10.8 g KOH, and then injected into the reactor, and 5 g of CCMP was dissolved in 50 ml chlorobenzene solvent. After the injection, the reaction was stirred at 43 ° C. for 24 hours while vigorously stirring with a stirrer. Subsequently, the product was filtered to remove by-products KCl and KOH salts, and the solvent was evaporated to obtain a gel-type linear polymer.

3 g of the linear polymer obtained above, 2 g of Mercury trifluoroacetate (Hg (CF ₃ CO ₂ ) ₂ ) and ₃ g of polyethylene glycol methyl ether were dissolved in 100 ml of tetrahydrofuran and injected into an Erlenmeyer flask, which was then sealed and kept for 6 hours. By stirring, 0.7 g of sodium borohydride (NaBH ₄ ) was slowly added and stirred for 24 hours. The product thus obtained was washed with diethyl ether to completely remove unreacted polyethylene glycol methyl ether. Through this method, a grafted polymer having a molecular weight of 120 and a graft ratio of 60 to 90% was obtained. In this case, the graft rate represents the ratio of the number of double bonds in the main chain before the graft reaction and the number of double bonds in the main chain after the grafting in percent.

77% by weight of the graft polymer obtained above and 23% by weight of lithium triplate were dissolved in a high-purity acetonitrile solvent, cast on a Teflon molder to volatilize the solvent for 8 hours in a high-purity nitrogen atmosphere, and then 48 hours in a 50 ° C vacuum oven. Drying to obtain a gel type, uncrosslinked polymer film completely free of solvent.

Examples 2-4 :

Except that 77% by weight of the graft polymer having a molecular weight of 350, 550, or 750 and a graft rate of 60 to 90% and 23% by weight of lithium triflate were added to and dissolved in a high-purity acetonitrile solvent. Then, a solid polymer electrolyte was prepared in the same manner as in the manufacturing method of Example 1 described above.

Examples 5-9 :

Grafted Polyethylene Glycol Methyl Ether Ether of 550 and Graft Rate of 60-90% Graft Polymers 76.4, 89.4, 94.2, 96.1, 98% by Weight and Lithium Triplate 23.6, 10.6, 5.8, 3.9, 2% by Weight A solid polymer electrolyte was prepared in the same manner as in Preparation Example 1, except that was added to a high-purity acetonitrile solvent to dissolve it.

Examples 10-13 :

Grafted grafted polyethyleneglycol methylmethyl ether obtained in the same manner as in Example 1, 77% by weight graft polymer having a molecular weight of 550 and a graft rate of 60 to 90%, 23% by weight of lithium triplate, and benzoyl peroxide as an initiator 5, 10, 15 and 20% by weight of the polymer content was added to the high-purity acetonitrile solvent to dissolve it, and cast in a Teflon molder at 50 ° C. or lower to volatilize the solvent for 1 hour in a high purity nitrogen atmosphere, and then the temperature was 70 ° C. The crosslinking reaction was carried out for 5 hours. This was finally dried in a vacuum oven to obtain a crosslinked polymer film from which solvent was completely removed.

The compositions and their mechanical properties of the solid polymer electrolytes prepared in Examples 1 to 13 are shown in Table 1 below. In addition, the ionic conductivity was measured over a range of temperature using a frequency response analyzer with a solid polymer electrolyte film between the stainless electrodes, the ionic conductivity of the cross-linked graft polymer electrolyte is shown in Table 2, Example 3 The ionic conductivity according to the lithium salt content of the uncrosslinked graft polymer electrolyte prepared in 5 to 9 is shown in FIG. 1. In Fig. 1, six samples having different EO / Li ratios are shown, and the graft polymer electrolytes prepared in Examples 5, 3, 6, 7, 8 and 9 from the left side are shown. Each represents; In addition, (●) is the ion conductivity measured at 25 ℃, (■) is the ion conductivity measured at 35 ℃, (▲) is ion conductivity measured at 45 ℃, (▼) is the ion conductivity measured at 55 ℃ Indicates the ion conductivity measured at 65 ℃.

Composition and Mechanical Properties of Solid Polymer Electrolyte division Composition of Solid Polymer Electrolyte Mechanical properties Graft polymer Lithium Tree Plate (wt%) Benzoyl peroxide (% by weight of graft polymer content) Content (% by weight) Molecular Weight of Grafted Polyethylene Glycol Example 1 77 120 23 Gel type Example 2 77 350 23 Gel type Example 3 77 550 23 Gel type Example 4 77 750 23 Gel type Example 5 76.4 550 23.6 Gel type Example 6 89.4 550 10.6 Gel type Example 7 94.2 550 5.8 Gel type Example 8 96.1 550 3.9 Gel type Example 9 98 550 2 Gel type Example 10 77 550 23 5 Freestanding film Example 11 77 550 23 10 Freestanding film Example 12 77 550 23 15 Freestanding film Example 13 77 550 23 20 Freestanding film

The solid polymer electrolyte prepared in Examples 1 to 13 was confirmed that the polyethylene oxide structure is present in the main chain and the side chain at the same time, there is no deformation in the ethylene oxide structure of the main chain even after the graft reaction, and there is a crosslinkable functional group in the main chain Also confirmed. Therefore, it was found that the solid polymer electrolyte of the present invention had greatly improved ionic conductivity and exhibited excellent mechanical properties through easy crosslinking.

Ion conductivity according to benzoyl peroxide content (unit: S / cm) division Ion conductivity measurement temperature (℃) Mechanical properties 25 40 Example 3 3.32 × 10 ^-5 9.58 × 10 ^-5 Gel type Example 10 2.59 × 10 ^-5 6.15 × 10 ^-5 Freestanding film Example 11 1.57 × 10 ^-5 2.76 × 10 ^-5 Freestanding film Example 13 3.84 × 10 ^-6 1.67 × 10 ^-5 Freestanding film

As shown in Table 2, in the conventional solid polymer electrolyte, since the decrease in flexibility of the polymer after crosslinking is suppressed, the ionic conductivity after crosslinking is reduced by about 10 to 100 times compared to before crosslinking. Through the graft structure peculiar to the invention, it was found that even after crosslinking, the ionic conductivity was not greatly reduced.

On the other hand, as shown in Figure 1, the conventional solid polymer electrolyte using polyethylene oxide shows the maximum ionic conductivity when the EO / Li ratio (oxyethylene unit / lithium ion ratio) is 20: 1, the solid of the present invention The polymer electrolyte showed a maximum ionic conductivity at 50: 1. Therefore, it was confirmed that the solid polymer electrolyte of the present invention can exhibit high ionic conductivity using a small amount of lithium salt.

As described and demonstrated in detail above, the present invention is a graft polymer in which a polyethylene glycol methyl ether is grafted to a polyethylene oxide main chain in which a double bond is introduced, and a solid polymer based on lithium salt. An electrolyte and a method for producing the same are provided. The solid polymer electrolyte of the present invention exhibits excellent ionic conduction properties and excellent mechanical properties through crosslinking, and has a feature of easily controlling the length of the side chain and the degree of crosslinking. In addition, according to the present invention, the solid polymer electrolyte can appropriately control the flexibility and ionic conduction properties of the polymer chain by changing the components of each mixture, and does not contain any organic solvents, so there is no problem of electrolyte leakage and corrosion of the electrode. It may be usefully used in various electrochemical devices including secondary batteries.

Claims (6)

A graft polymer having a molecular weight of 120 to 750 and a graft ratio of 60 to 90% of a polyethylene glycol methyl ether grafted to a polyethylene oxide main chain to which a double bond is introduced by a solbomercuration-demercuration reaction. Solid polymer electrolyte consisting of 60 to 95% by weight of the graft polymer of claim 1 and 5 to 40% by weight of lithium salt. The method of claim 2, The lithium salt is one kind selected from the group consisting of lithium triplate (LiCF ₃ SO ₃ ), lithium perchlorate (LiClO ₄ ) and lithium bis (trifluoromethylsulfonyl) imide (LiN (CF ₃ SO ₂ )). Solid polymer electrolyte. The method of claim 2 or 3, Benzoyl peroxide or 2,2'-azobisisobutyronitrile (2,2'-azobisisobutyronitrile) for the crosslinking reaction is further included in an amount corresponding to 1 to 20% by weight of the graft polymer content. Solid polymer electrolyte. A linear polymer having a double bond introduced into the polyethylene oxide main chain was synthesized using polyethylene glycol and CCMP (3-chloro-2-chloromethyl-propene) as a monomer, and a polyethylene glycol methyl ether was subjected to solbomerization-D in the double bond. A method for producing a solid polymer electrolyte comprising the step of grafting by mercuring to obtain a graft polymer having a molecular weight of 120 to 750 and a graft rate of 60 to 90%, and then adding a lithium salt. The method of claim 5, After the addition of the lithium salt, further comprising the step of cross-linking by adding benzoyl peroxide or 2,2'-azobisisobutyronitrile (2,2'-azobisisobutyronitrile) to prepare a solid polymer electrolyte, characterized in that Way.