KR20070010961A - Solid polymer electrolyte based on porous matrix and composition thereof - Google Patents

Abstract

Provided is a solid polymer electrolyte based on a porous matrix, which is applicable to conventional lithium secondary battery processes and has high ambient-temperature ion conductivity desirable for lithium polymer secondary batteries. The solid polymer electrolyte based on a porous matrix is obtained from a precursor consisting of a porous matrix used as a supporter with mechanical properties, a cross-linking agent for forming a cross-linked structure, a lithium salt for providing lithium ions, a low-viscosity additive capable of improving ion conductivity at ambient temperature and low temperature, and an initiator.

Description

Solid polymer electrolyte and composition thereof comprising a porous matrix {Solid Polymer Electrolyte Based on Porous Matrix and Composition Thereof}

1 shows a polyethylene nonwoven fabric (1) used as a porous matrix and a solid polymer electrolyte (2, 3) produced by the present invention.

2 is a view showing the ionic conductivity according to the temperature of the solid polymer electrolyte prepared in Example 1.

3 is a view showing the electrochemical stability of the solid polymer electrolyte prepared by the present invention.

4 is a view showing the thermal characteristics of the solid polymer electrolyte prepared by the present invention.

The present invention relates to a solid polymer electrolyte and its composition having excellent mechanical properties and excellent ion conductivity at room temperature and low temperature, and more particularly, using a porous matrix having excellent mechanical properties as a basic support, at least one type of crosslinking agent, lithium By introducing various low-viscosity additives that can increase the dissociation of salts and lithium salts and the mobility of lithium ions, they can exhibit excellent properties that can be applied to lithium polymer secondary batteries, while eliminating the problem of leakage. An improved solid polymer electrolyte is disclosed.

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 lithium polymer battery (LPB). Lithium polymer secondary batteries have higher energy density per unit weight than conventional batteries and have various forms. It can be manufactured with high voltage and large capacity battery by lamination, and it is environmentally friendly because it does not use heavy metals that pollute the environment such as cadmium or mercury.

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 its high crystallinity, it has very low ion conductivity at room temperature.

In order to solve this problem, the inorganic nanoparticles were introduced into the solid polymer electrolyte to obtain ionic 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 of ˜10 ⁻³ S / cm (M. Alamgir et al., J. power sources, 54, 40, 1995). 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.

A fundamental problem of the conventional solid polymer electrolyte is that increasing the mechanical properties of the electrolyte reduces the ion conductivity, and increasing the ion conductivity decreases the mechanical properties. This is because the matrix for transferring ions and the matrix for mechanical properties are the same in the solid polymer electrolyte.

In order to solve these problems, the present invention uses a porous matrix having excellent mechanical strength as a basic physical support in designing a matrix that is responsible for mechanical properties and a matrix that performs ion transfer, and conducts ions to the porous region of the porous matrix. It is to introduce a solid polymer electrolyte with excellent characteristics.

The present invention provides a porous matrix introduced into a support of mechanical properties, a crosslinking agent for forming a crosslinked structure, a lithium salt for providing lithium ions, a low viscosity additive capable of improving ionic conductivity at room temperature and low temperature, and disclosed And a solid polymer electrolyte obtainable from a precursor consisting of zero.

The porous matrix may be any one selected from an olefin resin, a fluorine resin, a polyester resin or a cellulose nonwoven fabric, a polymer separator, and glass fibers.

In this case, the porous matrix has a thickness of 10 to 200 µm and a pore size of 1 to 100 µm. The mechanical strength of the porous matrix is 1 MPa or more, preferably 5 MPa, more preferably 10 MPa or more. Porous matrices with tensile strength can be used.

In the above crosslinking agent, one or a mixture of at least two selected from the group of crosslinking agents represented by Formula 1 may be used.

Formula 1

In Formula 1, R ₁ and R ₂ are each an alkyl group having 1 to 10 carbon atoms, R ₃ and R ₄ are each a hydrogen atom, an alkyl group having 1 to 10 carbon atoms or an alkenyl group having 2 to 12 carbon atoms, X Is a hydrogen atom or a methyl group, n is an integer between 1 and 15.

The low viscosity additive may be any one selected from the materials represented by the formula (2) and (3) or may be used consisting of at least two or more mixtures.

Formula 2

In Formula 2, R ₅ and R ₆ are each a chain or branched alkyl group having 1 to 10 carbon atoms; R ₇ , R ₈ and R ₉ are each a hydrogen atom or a methyl group, and p, q and l are each an integer from 0 to 20.

Formula 3

In Formula 3, R ₁₀ , R _11, and R ₁₂ each represent a hydrogen atom or a methyl group, and n is an integer of 0 to 150, respectively.

Lithium salt in the above may be any one selected from the group consisting of LiClO ₄ , LiBF ₄ , LiCF ₃ SO ₃ , LiPF ₆ , LiAsF ₆ , or Li (CF ₃ SO ₂ ) ₂ N.

In the above, the initiator may use any one initiator selected from the group consisting of photoinitiation or thermal initiation.

In the above, the crosslinking agent content is 10 to 50% by weight, the content of the low viscosity additive is 30 to 90% by weight, the lithium salt content is 5 to 15% by weight, the initiator may be used from 0.1 to 5.0% by weight.

In the above-described solid polymer electrolyte, a solid polymer electrolyte can be obtained by inducing a crosslinking reaction by irradiating UV light at a wavelength of 300 to 600 nm for 1 to 10 minutes, more preferably at 350 nm wavelength for 3 minutes.

On the other hand, the present invention includes a lithium polymer secondary battery containing a solid polymer electrolyte containing the above-mentioned porous matrix.

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

The present invention uses a porous matrix as a basic support in order to secure the mechanical properties of the solid polymer electrolyte, the tensile strength of the porous matrix is preferably 1MPa or more in the MD (Machine Direction) direction, preferably 5MPa, More preferably 10 MPa or more tensile strength is required. In addition, if the tensile strength of the porous matrix is sufficiently secured, it may be directly applied to the winding or lamination process of the currently commercialized lithium secondary battery.

In addition, since the thickness of the solid polymer electrolyte also depends on the thickness of the porous matrix, the thickness of the porous matrix is preferably 100 µm or less, preferably 50 µm or less, and more preferably 30 µm or less.

Since the porous matrix itself does not have ion conduction properties, the pore size should be sufficiently secured, and thus, a solid polymer electrolyte may be manufactured in which a region through which ions can be transferred increases, thereby exhibiting higher ion conductivity. It is preferable that the average pore size is as small as several micrometers to as large as tens of micrometers.

As the porous matrix, a nonwoven fabric, a polyolefin separator, a polycarbonate membrane, a glass fiber, or the like may be used, and a polyolefin nonwoven fabric is most preferred. In particular, the polyethylene nonwoven fabric has excellent pore closing temperature required by the lithium secondary battery, which is excellent in terms of safety. Another advantage of the nonwoven fabric is that the price is low, thereby increasing the price competitiveness of the solid polymer electrolyte of the present invention.

The ion conduction properties of the solid polymer electrolyte prepared by the present invention are mainly determined by the electrolyte properties in the porous region. In order to improve the conductivity of the porous region, a method selected from the conventional solid polymer electrolyte may be introduced without the limitation of mechanical properties.

In order to dissociate the lithium salt properly, it is preferable to use a polyethylene glycol-based polymer as the main matrix, and to control the crosslinked structure in order to reduce the retention characteristics and crystallinity of the polymer in the porous matrix.

Representative crosslinking materials include polyalkylene glycol dimethacrylate and the content of the crosslinking materials is in the range of 0.1 to 95% by weight, preferably 10 to 50% by weight, based on the total composition. The amount can be adjusted accordingly.

In order to improve room temperature and low temperature properties, low viscosity low molecular weight polyethylene glycol and copolymers thereof are used as additives to act as plasticizers, and anion immobilization roles are performed to increase dissociation of lithium salts and increase mobility of lithium ions. An additional polyethylene glycol borate can be introduced. In particular, due to the mechanical properties secured by the use of a porous matrix it is possible to maximize the content of low viscosity additives. The content is used in the range of 0.1 to 99% by weight, preferably 30 to 90% by weight, alone or in combination of two or more of the additives, based on the characteristics of the electrolyte composition.

In the composition of the present invention, any lithium salt may be used as the lithium salt, as long as it is a lithium salt used for producing a conventional polymer electrolyte. Conventionally used lithium salts include lithium perchloroate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium hexafluorophosphate (LiPF ₆ ), lithium Hexafluoroacenate (LiAsF ₆ ), lithium trifluoromethanesulfonylimide (Li (CF ₃ SO ₂ ) ₂ N), and the like. 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.

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 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.

Such a present invention is described in more detail based on the following examples, but the present invention is not limited thereto. The following is a specific embodiment of the present invention.

<Example 1>

Polyethylene glycol dimethylmethacrylate crosslinker (Mn = 400 g / mol), polyethylene glycol dimethylether additive 1 (Mn = 250 g / mol), polyethylene glycol borate additive 2 (Mn = 1660 g / mol) , An electrolyte precursor containing lithium salt [Li (CF ₃ SO ₂ ) ₂ N] and methyl benzoyl formate as a photoinitiator was prepared in the composition shown in Table 1.

A precursor prepared in a glove box filled with argon gas was applied to a 60 μm thick nonwoven fabric made of polyethylene, and then irradiated with ultraviolet light having a wavelength of 350 nm for 3 minutes to induce a crosslinking reaction.

The precursor, which was in the liquid state by the above reaction, was solidified in a polyethylene nonwoven fabric to form a solid polymer electrolyte.

The nonwoven fabric used in this example and a photo of the prepared solid polymer electrolyte are shown in FIG. 1. In Figure 1 (1) represents a polyethylene nonwoven fabric used as a porous matrix, (2) and (3) is a photograph showing a solid polymer electrolyte prepared by the present invention.

It can be seen that the solid polymer electrolyte of the present invention exhibits excellent mechanical properties.

TABLE 1

division Crosslinking agent Additives1 Additive2 Lithium salt (EO: Li = 20: 1) Initiator Example 1-1 1.0 g 1.0 g 0.264 g 0.456 g 0.0123 g Example 1-2 0.6g 1.4 g 0.277 g 0.479 g 0.0123 g Example 1-3 0.4g 1.6 g 0.283 g 0.490 g 0.0123 g Example 1-4 0.2 g 1.8g 0.289 g 0.501 g 0.0123 g

<Example 2>

A solid polymer electrolyte was prepared by applying the same electrolyte precursor composition and the same manufacturing method, except that 100 µm thick glass fibers were used as the porous matrix. Table 2 shows the results of measuring the ion conductivity at room temperature of the electrolyte by the method of Test Example 1.

TABLE 2

division Crosslinking agent Additives1 Additive2 Lithium Salt (EO: Li = 20: 1) Initiator Ion Conductivity (S / cm) Example 2-1 1.0 g 1.0 g 0.264 g 0.456 g 0.0123 g 4.7 × 10 ^-5 Example 2-2 0.6g 1.4 g 0.277 g 0.479 g 0.0123 g 6.5 × 10 ^-5 Example 2-3 0.4g 1.6 g 0.283 g 0.490 g 0.0123 g 8.8 × 10 ^-5 Example 2-4 0.2 g 1.8g 0.289 g 0.501 g 0.0123 g 1.2 × 10 ^-4

Comparative Example

In order to confirm the effect of additive 2 in the solid polymer electrolyte, an electrolyte precursor in which additive 2 was not introduced in the composition of Examples 1-3 was prepared by the method of Example 1.

<Test Example 1>

After the solid polymer electrolyte prepared in Example 1 was laminated between stainless steel symmetric electrodes, cells were assembled, and the resistance of the electrolyte was measured using an alternating current impedance method to calculate ion conductivity. The ion conductivity results of the temperature change are shown in FIG. 2. It was confirmed that excellent ion conductivity characteristics were shown at room temperature as well as at low temperature.

<Test Example 2>

The electrochemical stability of the solid polymer electrolyte prepared in Comparative Example, Example 1-1 and Example 1-3 was measured. The solid polymer electrolyte and the stainless steel electrode

After stacking between lithium electrodes, the decomposition voltage of the electrolyte was measured at a scanning speed of 2 mV / sec using a linear scanning potential method, and is shown in FIG. 3. The introduction of additive 2 improved the electrochemical stability from 4.8V to 5.3V.

<Test Example 3>

Differential Scanning Calorimeter (DSC) was used to confirm the thermal stability of the prepared solid polymer electrolyte. The measurement temperature ranged from -100 ° C to 200 ° C, and the results obtained by increasing the temperature at a rate of 10 ° C / min are shown in FIG. 4. In the case of Example 1 in which a polyethylene nonwoven fabric was introduced, an endothermic reaction was observed at around 130 ° C., which showed that the thermal stability of the solid polymer electrolyte of the present invention was secured like a commercially available polyolefin separator.

Since the solid polymer electrolyte of the present invention uses a porous matrix having excellent mechanical properties as a basic support, at room temperature and low temperature capable of introducing an excessive amount of an additive of a low viscosity material that can increase the mobility of lithium ions and induce the dissociation of additional lithium salts. It is a novel solid polymer electrolyte exhibiting high ionic conductivity.

In addition, since the process can be applied to the existing lithium secondary battery process as it is advantageous to commercialization, it can be applied as a new electrolyte material of lithium secondary batteries to be applied to electronic devices or electric vehicles that require high safety in a short time.

Claims (9)

A precursor comprising a porous matrix introduced into a support of mechanical properties, a crosslinking agent for forming a crosslinked structure, a lithium salt for providing lithium ions, a low viscosity additive capable of improving ion conductivity at room temperature and low temperature, and an initiator Solid polymer electrolyte comprising a porous matrix, characterized in that obtained from The solid polymer electrolyte of claim 1, wherein the porous matrix is any one selected from an olefin resin, a fluorine resin, a polyester resin, a cellulose nonwoven fabric, a polymer separator, and a glass fiber. The porous matrix of claim 1, wherein the porous matrix has a thickness of 10 to 200 µm and a pore size of 1 to 100 µm. The porous matrix has a mechanical property of 1 MPa or more in tensile strength in the MD (Machine Direction) direction. Solid polymer electrolyte containing According to claim 1, wherein the crosslinking agent is a solid polymer electrolyte comprising a porous matrix, characterized in that consisting of one or at least two or more selected from the group of crosslinking agents represented by the formula (1) Formula 1

In Formula 1, R ₁ and R ₂ are each an alkyl group having 1 to 10 carbon atoms, R ₃ and R ₄ are each a hydrogen atom, an alkyl group having 1 to 10 carbon atoms or an alkenyl group having 2 to 12 carbon atoms, X Is a hydrogen atom or a methyl group, n is an integer between 1 and 15. The solid polymer electrolyte of claim 1, wherein the low viscosity additive comprises one or at least two mixtures selected from materials represented by Formulas 2 and 3. Formula 2

In Formula 2, R ₅ and R ₆ are each a chain or branched alkyl group having 1 to 10 carbon atoms; R ₇ , R ₈ and R ₉ are each a hydrogen atom or a methyl group, and p, q and l are each an integer from 0 to 20. Formula 3

In Formula 3, R ₁₀ , R _11, and R ₁₂ each represent a hydrogen atom or a methyl group, and n is an integer of 0 to 150, respectively. The method of claim 1, wherein the lithium salt comprises a porous matrix, characterized in that selected from the group consisting of LiClO ₄ , LiBF ₄ , LiCF ₃ SO ₃ , LiPF ₆ , LiAsF ₆ , or Li (CF ₃ SO ₂ ) ₂ N Solid polymer electrolyte  The solid polymer electrolyte of claim 1, wherein the initiator is selected from the group consisting of photoinitiation or thermal initiation. The method according to claim 1, wherein the crosslinking agent content is 10 to 50% by weight, the content of the low viscosity additive is 30 to 90% by weight, the lithium salt content is 5 to 15% by weight, and the initiator contains 0.1 to 5.0% by weight. Solid polymer electrolyte comprising a porous matrix characterized in that. A lithium polymer secondary battery containing a solid polymer electrolyte comprising the porous matrix of any one of claims 1 to 8.

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