KR100746347B1 - Solid polymer electrolyte comprising porous matrix and lithium-polymer secondary batteries using the same - Google Patents

Abstract

The present invention relates to a polymer electrolyte and a composition based on a porous matrix and a multifunctional crosslinking agent, and more particularly, to complement the weak mechanical properties of the high ion conductive polymer electrolyte with a porous matrix and to provide a box-type multifunctional crosslinking agent. It is a novel polymer electrolyte that maximizes the addition of plasticizer by introducing a crosslinking density in the polymer electrolyte.

In addition to introducing a porous matrix made of polyethylene or polypropylene, which can serve as a support for the polymer electrolyte, a cross-linking structure is formed by introducing a box-type multifunctional crosslinking agent to increase the mechanical strength of the polymer film, and the dissociation ability of lithium ions is improved. The present invention relates to a novel solid polymer electrolyte which exhibits high ionic conductivity even at room temperature and low temperature without excessively adding an excellent polyalkylene glycol plasticizer.

The solid polymer electrolyte prepared according to the present invention is an electrolyte system that not only has a room temperature ion conductivity value high enough to be applied to a lithium polymer secondary battery, but also improves safety problems such as leakage, thereby replacing the existing lithium secondary battery. Of course, it can be easily applied to a battery system that requires high safety.

Description

 Solid polymer electrolyte comprising porous matrix and lithium-polymer secondary batteries using the same

1 is a schematic diagram of a solid polymer electrolyte matrix structure of the present invention.

2 is a graph showing the ion conductivity characteristics according to the temperature of the solid polymer electrolyte of the present invention.

3 is a graph showing the electrochemical stability of the solid polymer electrolyte of the present invention.

The present invention relates to a solid polymer electrolyte comprising a porous matrix and a lithium-polymer secondary battery using the same, and more particularly, to the fragile mechanical properties of a high ion conductive polymer electrolyte with a porous matrix and at the same time a box-type multifunctional crosslinking agent. The present invention relates to a novel polymer electrolyte which maximizes the addition of plasticizer by increasing the crosslinking density in the polymer electrolyte.

With the rapid development of the electric, electronic, communication and computer industries, the demand for high-performance, high-safety secondary batteries has gradually increased. Secondary batteries are also required to be lighter and smaller. In addition, the necessity of the development of electric vehicles to solve this problem has been increasing as the necessity of a new type of energy supply and demand caused by the exhaustion of oil and the depletion of oil due to the air pollution and noise caused by the mass distribution of automobiles has increased. There is a demand for development of a battery having a high output and a high energy density.

One of the new high-performance, next-generation advanced batteries that has recently been in the spotlight in response to such demands is the lithium polymer battery (LPB), which has a higher energy density per unit weight than the conventional battery and has various forms. It is possible to manufacture, easy development of high voltage and large capacity battery by lamination, and does not use heavy metals that pollute the environment such as cadmium or mercury, which is environmentally friendly.

Lithium polymer secondary battery is largely composed of an anode (anode), a polymer electrolyte (polymer electrolyte), a cathode (cathode), lithium, carbon, etc. are used as the negative electrode active material, transition metal oxide, metal chalcogen compound as the positive electrode active material , Conductive polymers and the like are used. At this time, the polymer electrolyte is composed of a polymer, a salt, a non-aqueous organic solvent (optional), and other additives, and exhibits an ionic conductivity of about 10 ⁻³ to 10 ⁻⁸ S / cm at room temperature. Initial researches on polymer electrolytes have mainly been conducted on solid polymer electrolytes prepared by adding lithium salts to polyethylene oxide and polypropylene oxide, melting them in a co-solvent (Europe Patent No. 78505 and U.S. Patent No. 5,102,752). Due to the high crystallinity of, the ion conductivity was very low at room temperature.

In order to solve this problem, the inorganic nanoparticles were introduced into the solvent-free polymer electrolyte to obtain ion conductivity of ˜10 ^-5 S / cm at room temperature, but they are low values for commercialization. In contrast, plasticized polymer electrolytes prepared by adding organic solvents and lithium salts to polymers such as polymethyl methacrylate, polyacrylonitrile, polyvinyl chloride, and polyvinylidene fluoride, dissolved in a co-solvent and cast at room temperature High ion conductivity (M. Alamgir et al., J. power sources, 54, 40, 1995) of ˜10 ⁻³ S / cm. However, plasticized polymer electrolytes are difficult to apply to commercialization systems due to the fundamental problems of safety due to the use of organic solvents and low mechanical properties due to the introduction of excess organic solvents. Meanwhile, the related arts related to the present invention are disclosed in US Patent 2003/0180625 (Solid Polymer Electrolyte and Method of Preparation) and Song et al (J. of Power Sources, 10-16, 2004, 125 "Composite polymer electrolytes reinforced by non-woven fabrics ), But the technical configuration is different from the present invention.

The solid polymer electrolyte of the present invention is to introduce a porous matrix and at the same time introduce a box-type multifunctional group crosslinking agent to compensate for the weak mechanical properties of the high ion conductive polymer electrolyte. Physical strength is obtained by the porous matrix, and a network structure is formed by the multifunctional crosslinking agent, thereby increasing the crosslinking density than the existing polyethylene glycol crosslinking agent, thereby obtaining more excellent mechanical properties. Based on such excellent mechanical properties, the plasticizer can increase the dissociation degree of lithium salts and contribute to the movement of lithium salts, thereby maximizing the addition of low molecular weight polyethylene glycol, thereby exhibiting high ionic conductivity at room temperature and low temperature without deteriorating mechanical properties. .

The solid polymer electrolyte proposed in the present invention is a solid polymer electrolyte using a porous matrix as a support of the polymer electrolyte and introducing a novel polyfunctional crosslinking agent of box type. The crosslinking agent is terminated in a box-shaped cage based on siloxane as shown in Formula (1). The functional group consists of 8, 10 or 12 methacrylate mixtures.

 In the present invention, the porous matrix may use any one or more selected from olefin resin, fluorine resin, polyester resin, cellulose nonwoven fabric, polymer separator, and glass fiber.

In the present invention, the porous matrix has a thickness of 10 to 200 µm and a pore size of 1 to 100 µm. The porous matrix may have a mechanical property of 1 MPa or more in tensile strength in the MD (Machine Direction) direction.

In the present invention, the crosslinking density is controlled by introducing polyethylene glycol methacrylate or polyethylene glycol acrylate-based materials for higher dissociation and mobility of lithium salts. The crosslinking reaction is carried out with a box-type multifunctional crosslinking agent having one terminal having the same or similar functional groups, and the dissociation of lithium salts as well as mechanical strength can be increased. In addition, based on the strong mechanical properties secured by introducing a porous matrix and a box-type polyfunctional crosslinking agent, the low molecular weight polyethylene glycol plasticizer is introduced to obtain higher ion conductivity at room temperature and low temperature, thereby maximizing its ion conductivity. It features.

The present invention provides a box-shaped multifunctional crosslinking agent PSS (Formula 1), a polyethylene glycol acrylate (Formula 2), and a polyalkylene glycol dialkyl ether (Formula 3) substituted with methacrylate groups as representative plasticizers. .

(Formula 1)

In Formula 1, R1 is the same dimethacrylate group and the number of R1 is 8, 10, 12 mixtures.

(Formula 2)

In Formula 2, R ₂ is a hydrogen atom or a methyl group, n is an integer from 0 to 30.

 In addition, the present invention (i) 0.1 to 95% by weight of the crosslinking agent represented by the formula (1); (ii) 0.1 to 95% by weight of polyethylene glycol acrylate represented by the above formula (2); (iii) 0.1 to 80% by weight of a single or two or more plasticizers selected from polyalkylene glycol dialkyl ethers represented by the following formula (3) and polyethylene glycol borate represented by the formula (4); (iv) 3 to 30 weight percent of a lithium salt; And (v) a solid polymer electrolyte composition containing 0.5 to 5% by weight of an initiator.

(Formula 3)

In Formula 3, R ₃ , R ₄ , R ₅ , R _6, and R ₇ each represent a hydrogen atom or a methyl group, and p, q, and l each represent an integer between 0 and 30, respectively.

(Formula 4)

In Formula 4, m is an integer from 0 to 20.

To describe in more detail the configuration of the present invention as follows.

The present invention relates to a system capable of implementing high temperature and low temperature ionic conductivity without introducing a deterioration of mechanical properties by introducing a novel crosslinking agent with a porous matrix and a box-type multifunctional group in a solid polymer electrolyte. In the case of the general solid polymer electrolyte, in order to increase the ionic conductivity, the content of the low molecular weight plasticizer must be increased in the electrolyte, and the mechanical properties of the prepared solid polymer electrolyte are inevitably weakened. In order to solve this problem, in the present invention, a porous matrix having a porosity of 20 to 80% or more is used as a physical support, and the pore region includes 8 or 10 or 12 acrylates or methacrylates, etc. A novel crosslinking agent of a box-type polyfunctional group substituted with a functional group capable of thermal crosslinking and photocrosslinking reaction was introduced. In addition, in the present invention, polyethylene glycol methacrylate or polyethylene glycol acrylate-based materials were introduced to control the crosslinking density of the polymer electrolyte for higher dissociation and mobility of lithium salts. By having one end have the same or similar functional groups, crosslinking reaction with the box-type multifunctional crosslinking agent is performed, and the dissociation of lithium salts as well as mechanical strength can be increased. In addition, a low molecular weight polyethylene glycol plasticizer was introduced to obtain higher ion conductivity at room temperature and low temperature.

The greatest advantage in the present invention is to maximize the content of the plasticizer for dissociation of lithium salts and the movement of lithium ions without deterioration of mechanical properties because it is based on the strong mechanical properties secured by introducing a porous matrix and a box-type multifunctional crosslinking agent. Is that there is.

The reasons for selecting various crosslinking agent box-type multifunctional crosslinking agents that can constitute a solid polymer electrolyte are as follows. Solid polymer electrolytes generally exhibit very low ionic conductivity at room temperature. In order for the polymer electrolyte to be commercialized in a lithium secondary battery, the polymer electrolyte should have high ionic conductivity similar to that of the liquid electrolyte at room temperature and low temperature. In order to increase the low ion conductivity of the polymer electrolyte, it is necessary to add a low molecular weight plasticizer to the polymer matrix to increase the mobility of the polymer chain.

However, increasing the content of these plasticizers inevitably weakens the mechanical strength of the polymer film, which is another major problem in the commercialization of the polymer electrolyte. Therefore, in the present invention, a porous matrix is introduced to compensate for mechanical properties. However, even if the porous matrix is introduced, there is a limit to the amount of plasticizer that can be included in the electrolyte as a conventional crosslinking agent. Therefore, in the present invention, by introducing a box-type multifunctional crosslinking agent together with such a porous matrix, the crosslinking density can be increased to obtain strong mechanical properties, and has the advantage that the content of the plasticizer can be further maximized based on the improved physical properties.

The composition components of each crosslinking agent, plasticizer, lithium salt and initiator contained in the solid polymer electrolyte composition according to the present invention will be described in detail as follows.

<Bridge school>

In the composition of the present invention, the crosslinking agent of the formula (1) is contained at an appropriate ratio as the crosslinking agent. The box-shaped crosslinking agent represented by Formula 1 is based on polysiloxane having a flexible chain and has 8, 10, or 12 functional groups at its end to increase the crosslinking density to compensate for mechanical properties. In addition, dissociation of lithium salts and transfer of lithium ions by introducing a polyethylene glycol-based material substituted with a double bond capable of thermal reaction and photoreaction at one end represented by Formula 2 to form a crosslinking matrix with a polyfunctional crosslinking agent. By increasing the degree, higher ion conductivity can be exhibited.

In the case of the multifunctional crosslinking agent of Chemical Formula 1, 0.1 to 95% by weight of the electrolyte composition of the present invention may be contained, preferably 1 to 50% by weight, more preferably 1 to 10% by weight. In the case of Formula 2, the electrolyte composition of the present invention may be contained in an amount of 0.1 to 95% by weight, preferably 0.1 to 50% by weight, and more preferably 0.1 to 10% by weight.

<Plasticizer>

In the composition of the present invention alone or in the polyalkylene glycol dialkyl ether and polyalkylene glycol borate represented by the formula (3) and formula (4) to improve the dissociation of lithium salts and the mobility of lithium ions to improve the ionic conductivity It contains two or more plasticizers. In the composition of the present invention, the plasticizer may be contained in an amount of 0.1 to 99% by weight, preferably 1 to 50% by weight, more preferably 1 to 10% by weight.

<Lithium salt>

Any lithium salt may be used in the composition of the present invention as long as it is a lithium salt used for producing a conventional polymer electrolyte as a lithium salt. Lithium salts that have been conventionally used include, for example, LiClO ₄ , LiBF ₄ , LiCF ₃ SO ₃ , LiPF ₆ , LiAsF ₆ , Li (CF ₃ SO ₂ ) ₂ N. These lithium salts are used in the range of 3 to 30% by weight, preferably 5 to 15% by weight based on the total composition of the electrolyte, but the amount thereof may be appropriately adjusted according to the characteristics of the electrolyte composition.

<Initiator>

Since the curable initiator is contained in the composition of the present invention, both a photoinitiation type and a thermal initiation type may be used as the type of initiator. Examples of photocurable initiators include methylbenzoyl formate, igacure 250, ethylbenzoin ether, isopropylbenzoin ether, α-methylbenzoin ethylether, benzoin phenylether, α-acyl oxime ester, α, α-die Methoxy acetophenone, 1,1-dichloroacetophenone, 2-hydroxy-2methyl-1-phenylpropan-1-one [Darocur 1173 from Ciba Geigy], 1-hydroxycyclo Hexyl phenyl ketone (Irgacure 184 from Ciba Geigy), Darocure 1116, Igacure 907 and the like and anthraquinone, 2-ethyl anthraquinone, 2-chloro anthraquinone, thioxanthone, isopropyl thi Oxanthone, chlorothioxanthone, benzophenone, p-chlorobenzophenone, benzyl benzoate, benzoyl bonzoate, mychler ketone and the like. Thermosetting initiators include peroxide and azoisobutyronitrile. The initiator is contained in the range of 0.1 to 5.0% by weight in the total composition, the amount can be adjusted according to the mixing ratio of the electrolyte composition.

On the other hand, the present invention includes a lithium-polymer secondary battery containing the one prepared using the above-mentioned polymer electrolyte composition.

The present invention described above will be described in more detail based on the following examples, but the present invention is not limited thereto, but is only one embodiment.

Example 1 Preparation of Polymer Electrolyte Based on Porous Matrix and Box-Type Multifunctional Crosslinking Agent (Examples 1-1, 1-2, 1-3)

1,3,5,7,9,11,13,15-octa (propylmethacryl) pentacyclo- [9.5.1.1.1.1] octasiloxane and polyethylene glycol acrylate (Mn = 475 g / mol), polyethylene glycol dimethyl ether (Mn = 250 g / mol), and polyethylene glycol borate are mixed in the ratio shown in Table 1.

Lithium bistrifluorosulfonylimide (Li (CF ₃ SO ₂ ) ₂ N) was added to the mixture so that the EO: Li ratio was 20: 1 with a lithium salt, and then methylbenzoylformate was introduced as an acrylate initiator. After stirring to complete mixing. The mixture was applied onto a non-woven matrix of PE placed on a Teflon substrate in a glove box, and then irradiated with UV light at 350 nm for about 5 minutes in a closed state to prepare a solid polymer electrolyte.

The prepared solid polymer electrolyte was laminated between stainless steel symmetric electrodes to assemble a cell, and then the resistance of the electrolyte was measured by using an alternating current impedance method, and the ion conductivity was calculated using the same. The results are shown in Table 1.

Comparative Example 1-1 is a polyethylene glycol dimethacrylate (Mn = 400 g / mol) 0.2g, polyethylene glycol dimethyl ether (Mn = 250 g / mol) as a PE non-woven matrix and a conventional crosslinking agent. ) 0.8g, lithium bistrifluorosulfonylimide (Li (CF ₃ SO ₂ ) ₂ N) 0.2532g, 0.004g methylbenzoylformate as an initiator, the results are shown in Table 2.

[Table 1] Comparison of properties by crosslinking agent

division Crosslinking agents; g Characterization; (25 ℃), S / cm Formula 1 Formula 2 Formula 3 Formula 4 Ion conductivity Mechanical property Example 1-1 0.05 0 0.95 0 6.7 × 10 ^-4 Great Example 1-2 0.04 0.01 0.95 0 7.2 × 10 ^-4 Great Example 1-3 0.05 0 0.95 0.0257 6.3 × 10 ^-4 Great

[Table 2] Comparison of properties according to the amount of crosslinking agent added

 division Crosslinking agent; g Plasticizer; g Lithium salt; g Characterization; (25 ° C), S / cm Polyethylene Glycol Dimethacrylate Polyethylene Glycol Dimethyl Ether Lithium bistrifluorosulfonylimide Ion conductivity Mechanical properties Comparative Example 1-1 0.2 0.8 0.2532 2.7 × 10 ^-4 usually

<Example 2>

For the solid polymer electrolyte of Example 1-1, the ion conductivity according to the temperature change was measured. The measured result was shown in FIG.

<Example 3>

The polymer electrolyte was prepared in the same manner as in Example 1, and the electrochemical stability was measured. The results are shown in FIG. 3.

The solid polymer electrolyte according to the present invention maintains excellent mechanical properties based on the porous matrix and the multifunctional crosslinking agent. In addition, due to excellent mechanical properties, it is possible to induce an additional ion conductivity increase by maximizing the plasticizer content.

Therefore, the solid polymer electrolyte prepared according to the present invention not only has a high temperature ion conductivity value that can be applied to a lithium polymer secondary battery, but also improves safety problems such as leakage, and thus, a conventional lithium secondary battery. As a replacement, it can be provided as a new electrolyte material for lithium secondary batteries to be applied to electronic devices or electric vehicles requiring high safety.

Claims (7)

A porous matrix introduced into the support of mechanical properties; 0.1 to 50% by weight of a box-shaped multifunctional crosslinking agent represented by the following Chemical Formula 1, 0.1 to 30% by weight of polyethylene glycol acrylate or polyethylene glycol methacrylate represented by the following Chemical Formula 2, and 3 to 30% by weight of lithium salt , 0.1 to 96.7 wt% plasticizer and 0.1 to 5 wt% initiator; Solid polymer electrolyte comprising a. (Formula 1)

In Formula 1, R ₁ is the same dimethacrylate group and the number of R ₁ is a mixture of 8, 10, 12. (Formula 2)

In Formula 2, R ₂ is a hydrogen atom or a methyl group, n is an integer from 0 to 30. The solid polymer electrolyte of claim 1, wherein the porous matrix is any one selected from a nonwoven fabric, a polymer separator, and glass fiber of an olefin resin, a fluorine resin, a polyester resin, or a cellulose resin. The method of claim 1, wherein the porous matrix has a thickness of 10 to 200㎛, the pore size of 1 to 100㎛, a solid polymer, characterized in that the mechanical strength of the tensile strength in the direction of MD (Machine Direction) 1MPa or more Electrolyte. delete The solid polymer electrolyte of claim 1, wherein the plasticizer is one or two selected from a polyalkylene glycol plasticizer represented by the following Chemical Formula 3 and a borate plasticizer represented by the Chemical Formula 4. (Formula 3)

In Formula 3, R ₃ and R ₇ each represent a chain or branched alkyl group having 1 to 10 carbon atoms; R ₄ , R ₅ and R ₆ are each a hydrogen atom or a methyl group, and p, q and l are each an integer between 0 and 20. (Formula 4)

In Formula 4, m is an integer from 0 to 20. The solid polymer electrolyte of claim 1, wherein the lithium salt is selected from the group consisting of LiClO ₄ , LiBF ₄ , LiCF ₃ SO ₃ , LiPF ₆ , LiAsF _6, and Li (CF ₃ SO ₂ ) ₂ N. 7. A lithium-polymer secondary battery prepared using the solid polymer electrolyte of claim 1.

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