KR100400215B1 - Polymer matrix, polymer solid electrolyte containing the matrix, and lithium secondary battery employing the electrolyte - Google Patents

Abstract

PURPOSE: A polymer matrix, a polymer solid electrolyte containing the matrix, and a lithium secondary battery employing the electrolyte are provided, to improve the ion conductivity at a room temperature, the affinity of a polymer matrix to an electrolyte solution and the binding force to an electrode for reducing the interface resistance between an electrode and an electrolyte. CONSTITUTION: The polymer matrix comprises a trimethylolpropane derivative represented by (H2C=CR1-CO2CH2)3CC2H5; a hydrophilic polymer; and a binding polymer, wherein R1 is H or CH3. Preferably the binding polymer is selected from the group consisting of polyethylene oxide, poly(vinyl chloride), poly(vinyl acetate) and poly(vinyl fluoride); and the hydrophilic polymer is represented by -(CH2-CR2H)n-, wherein R2 is 2-pyrrolidinonyl, OCOCH3, OCOCH=CH2, C6H5, CN or SO2CH=CH2; and n is 10-2,000. The polymer solid electrolyte comprises the polymer matrix; and an electrolyte solution contained in the polymer matrix.

Description

A polymer matrix, a polymer solid electrolyte containing the same, and a lithium secondary battery employing the polymer solid electrolyte

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, comprising a polymer matrix as a polymer solid electrolyte component of a lithium secondary battery, which is widely used as a power source for electronic devices, a polymer solid electrolyte including the same, and a lithium secondary battery employing the same. will be.

The ionic conductivity of the polymer solid electrolyte not only greatly affects the internal resistance during battery charging and discharging, but also has a very important effect on the efficiency and rate of the battery. Therefore, the electrolyte should basically be able to prevent the short circuit of the battery, to maintain a high ion conductivity by moistening a large amount of electrolyte solution and to be able to move the lithium ions smoothly.

U.S. Pat.Nos.4758483,4792504 and 4908284 disclose crosslinks of polyethylene oxide (PEO) as specific examples of the polymer matrix constituting the polymer solid electrolyte. The crosslinked product is easy to manufacture and can be mass-produced, but the polymer solid electrolyte containing such a polymer matrix has a low ionic conductivity of 10 ⁻⁵ S / cm or less at room temperature. Therefore, they cannot be used at room temperature and can only be used at temperatures above 60 ° C. That is, although it can be used as a high-temperature electrolyte, it has a disadvantage that it cannot be used at room temperature where general electronic devices are used, and it is still difficult to practically use.

In order to solve the above problems, a polymer matrix comprising a material comprising trimethylolpropane triacrylate (TMPTA) and polyvinylpyrrolidone (PVP) and an electrolyte solution contained therein Solid electrolytes have been proposed. Although the electrolyte has excellent ion conductivity at room temperature, it is difficult to process due to lack of flexibility, and there is a problem in that the interface resistance is increased due to insufficient adhesion of the electrolyte to the electrode.

The technical problem to be achieved by the present invention is to solve the above problems to provide a polymer matrix excellent in ion conductivity and flexibility.

Another technical problem to be achieved by the present invention is to provide a polymer solid electrolyte which is excellent in ionic conductivity at room temperature as well as excellent in flexibility and can reduce the interfacial resistance between electrode and electrolyte by including the polymer matrix.

Another technical problem to be achieved by the present invention is to provide a lithium secondary battery capable of smoothly operating at a high current density by reducing the internal resistance by employing the polymer solid electrolyte.

In order to achieve the first object, the present invention provides a polymer matrix comprising a material comprising a trimethylolpropane derivative represented by the formula (1), a hydrophilic polymer and a binding polymer.

<Formula 1>

In said formula, R <_1> is hydrogen or a methyl group.

The binding polymer is a material having low glass transition temperature and flexible characteristics at room temperature, and is selected from polyethylene oxide, polyvinyl chloride, polyvinylacetate, and polyvinyl fluoride.

The second object is a polymer matrix made of a material comprising a trimethylolpropane derivative represented by the formula (1), a hydrophilic polymer and a binding polymer; And

It is made by a polymer solid electrolyte comprising a; electrolyte contained in the polymer matrix.

<Formula 1>

In said formula, R <_1> is hydrogen or a methyl group.

A third object of the present invention is achieved by a lithium secondary battery employing the polymer solid electrolyte.

The polymer matrix of the present invention consists of a material comprising a trimethylolpropane derivative of formula (1), a hydrophilic polymer such as polyvinylpyrrolidone and a binding polymer such as polyethylene oxide. In more detail, the polymer matrix is composed of a homopolymer of a network structure formed by polymerizing a hydrophobic trimethylolpropane derivative represented by Formula 1, and a hydrophilic polymer and a binding polymer contained in the network structure of the homopolymer.

Alternatively, the polymer matrix is composed of a copolymer of a hydrophobic trimethylolpropane derivative represented by the formula (1) and a hydrophilic polymer, and is composed of a binding polymer contained in a network of the copolymer.

Or part of the homopolymer of the trimethylolpropane derivative of Formula 1 and a hydrophilic polymer and a binding polymer present between the network structure of the homopolymer, and the other part of the hydrophobic trimethylol of Formula 1 It consists of a copolymer of a propane derivative and a hydrophilic polymer, and consists of a binding polymer contained in a network of the copolymer.

The amount of the binder polymer is preferably 10 to 30% by weight based on the total weight of the trimethylolpropane derivative and the hydrophilic polymer. Here, when the content of the binding polymer exceeds 30% by weight relative to the total weight of the trimethylolpropane derivative and the hydrophilic polymer, the binding property is increased but the strength is lowered, so that it is difficult to maintain the shape as the polymer matrix, and when the content is less than 10% by weight. It is undesirable because it does not contribute at all to the desired improvement in binding and increase in conductivity.

It is preferable that the mixing weight ratio of the trimethylpropane derivative of Formula 1 and the hydrophilic polymer is 1: 1 to 1:10. When the content of the trimethylpropane derivative exceeds the above range, the electrochemical properties of the electrolyte are lowered. On the other hand, when the content of the trimethylolpropane derivative is less than the above range, the mechanical strength of the electrolyte is lowered, which is not preferable.

The trimethylolpropane derivative is trimethylolpropane triacrylate (TMPTA) or trimethylolpropane trimethacrylate (TMPTMA), as can be seen from the formula (1).

The hydrophilic polymer is not particularly limited. Preference is given to using compounds of the formula (2). These include polyvinylpyrrolidone {poly (vinyl pyrrolidone)}, polyvinyl acetate {poly (vinyl acetate)}, polyvinyl acrylate {poly (vinyl acrylate)}, polystyrene, polyacrylonitrile And polyvinyl sulfone {poly (vinyl sulfone)} and the like.

In addition, the weight average molecular weight of the hydrophilic polymer is preferably 1 × 10 ⁴ to 1 × 10 ⁵ , among which polyvinylpyrrolidone having a weight basis molecular weight of 5 × 10 ⁴ is most preferred.

In the formula, R ₂ is selected from the 2-pyrrolidino carbonyl _{(2-pyrrolidinonyl), OCOCH 3} , OCOCH = CH 2, C 6 H 5, the group consisting of CN and SO ₂ CH = CH _2;

n is a number from 10 to 2000

The polymer solid electrolyte of the present invention contains the above-described polymer matrix and the electrolyte solution contained in the polymer matrix. In this case, the hydrophilic polymer contained in the polymer matrix serves to increase the ion conductivity of the electrolyte by facilitating the electrolyte solution in which the lithium ions are dissociated, and the binding polymer increases the bonding strength to the electrode and the flexibility of the electrolyte. To improve.

In the polymer solid electrolyte of the present invention, it is important to appropriately adjust the weight ratio of the polymer matrix and the electrolyte solution. Preferably, the polymer matrix is 5 to 60% by weight and the electrolyte is 40 to 95% by weight. If the polymer matrix is less than 5% by weight based on the total weight of the electrolyte, the mechanical strength of the electrolyte is lowered. If the polymer matrix is more than 60% by weight, the mechanical strength of the electrolyte is improved, but the ion conductivity of the electrolyte is lowered.

The manufacturing method of the polymer solid electrolyte according to the present invention will be described.

First, the trimethylolpropane derivative represented by Chemical Formula 1 and the hydrophilic polymer of Chemical Formula 2 are mixed at a weight ratio of 1: 1 to 1:10, and a binder polymer, an ionic inorganic salt, a solvent, a polymerization initiator, and the like are added to the polymer solid. Prepare the electrolyte composition. A plasticizer may be added to the composition so that the organic electrolyte can be easily impregnated in a later step. At this time, dibutyl phthalate or the like is used as the plasticizer.

The polymer solid electrolyte composition is applied onto a support such as a Teflon thin film, a mylar film, etc. using a means such as a doctor blade or a bar coater, and then polymerized to polymer the polymer according to the present invention. Complete the solid electrolyte.

Here, the polymer solid electrolyte may be prepared by applying a polymer solid electrolyte composition directly on the electrode, as well as by coating on a separate support as described above.

In the present invention, as the solvent of the electrolytic solution, a non-aqueous solvent, particularly a non-aqueous solvent that is large in polarity with the dielectric constant and easily dissociated, is used.

The non-aqueous solvent may be used as long as it does not exhibit phase separation when mixed with a compound for forming a polymer matrix of Formulas 1 and 2. Among them, propylene carbonate (PC), ethylene carbonate (EC), γ-butyrolactone, 1,3-dioxolane (1,3-dioxolane), dimethoxyethane ( using at least one solvent selected from dimethoxyethane, dimethylcarbonate and diethylcarbonate, tetrahydrofuran (THF), dimethylsulfoxide and polyethyleneglycol dimethylether. It is preferable. And the content of the solvent is the usual level used in the polymer solid electrolyte.

The inorganic salt is not particularly limited as long as it is a lithium compound that dissociates in an organic solvent to give lithium ions, and specific examples thereof include lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), and hexafluoride. Group consisting of lithium hexafluorophosphate (LiPF ₆ ), lithium trifluoromethansulfonate (LiCF ₃ SO ₃ ) and lithium bistrifluoromethansulfonylamide.LiN (CF ₃ SO ₂ ) ₂ ) At least one ionic lithium salt selected from is used. When the organic electrolyte solution containing such an inorganic salt is introduced into the polymer matrix, it acts as a path for moving lithium ions along the direction of the current. And the content of the inorganic salt is the usual level used in the polymer solid electrolyte.

Hereinafter, a lithium secondary battery employing a polymer solid electrolyte and a method of manufacturing the same according to an exemplary embodiment of the present invention will be described.

First, lithium is contained in a polymer solid electrolyte composition according to the present invention, that is, a composition containing an electrolyte consisting of a trimethylolpropane derivative of Formula 1, a hydrophilic polymer, a binding polymer, a polymerization initiator, an inorganic salt, and a solvent. One selected from a lithium cathode active material such as manganese oxide, lithium nickel oxide, lithium cobalt oxide, and the like and a conductive agent are added, followed by sufficient mixing.

The reaction mixture is coated on top of the positive electrode current collector and then heated to form a composite positive electrode layer.

On the other hand, a mixture of the carbon powder and the polymer solid electrolyte composition is coated on a negative electrode current collector and heat is applied to form a composite negative electrode layer.

The composite negative electrode layer, the polymer solid electrolyte layer, and the composite positive electrode layer are stacked, and then bonded by applying a heat treatment or a predetermined pressure to complete the lithium secondary battery according to the present invention.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited only to the following Examples.

<Example 1>

6 g of PVP, 1 g of PEO, and 3 g of TMPTA were added to a clean glass bottle, and 15 g of an EC / PC solution of LiPF ₆ (1M, volume ratio of EC / PC = 1: 1) and 2.5 ml of acetonitrile were mixed well. . 0.1 g of BEE was added to the mixture and remixed, which was then cast to a thickness of about 100 μm on a Teflon substrate using a doctor blade.

The resultant was dried and irradiated with ultraviolet (350 nm) to photopolymerize for about 5 minutes to complete the polymer solid electrolyte.

<Example 2>

It was carried out in the same manner as in Example 1, except that 5 g PVP, 2 g PEO and 3 g TMPTA were used instead of 6 g PVP, 1 g PEO and 3 g TMPTA.

<Example 3>

Instead of using PVP 6g, PEO 1g and TMPTA 3g, PVP 4g, PEO 3g and TMPTA 3g were used in the same manner as in Example 1.

Comparative Example 1

It carried out according to the same method as Example 1, except that 7 g of PVP and 3 g of TMPTA were used instead of 6 g of PVP, 1 g of PEO and 3 g of TMPTA.

Comparative Example 2

The same procedure as in Example 1 was conducted except that instead of PVP 4g, PEO 3g and TMPTA 3g, 7g PEO and 3g TMPTA were used.

Ion conductivity and flexibility of the polymer solid electrolyte prepared by the above method were evaluated as follows.

(1) ion conductivity

As a sample, a gel film having a diameter of 13 mm was prepared from the polymer solid electrolyte prepared according to Example 1-3 and Comparative Example 1-2. After fixing this sample between two stainless discs, ion conductivity was measured at normal temperature using the alternating current impedance method.

(2) flexibility

The gel-like film was wound on a stainless rod 5 mm in diameter and then returned to its original state. The appearance of the film after repeating this process about 10 times was visually investigated.

Ion conductivity and flexibility of the polymer solid electrolyte prepared according to Examples 1-3 and Comparative Examples 1-2 were measured and shown in Table 1 below.

division Ion Conductivity (S / cm) flexibility Example 1 3.1 × 10 ^-3 Very good Example 2 2.8 × 10 ^-3 Very good Example 3 2.2 × 10 ^-3 Very good Comparative Example 1 3.2 × 10 ^-3 Bad Comparative Example 2 7.4 × 10 ^-4 Bad

From Table 1, it can be seen that when the three components of PVP, PEO and TMPTA are used in preparing the polymer matrix (Examples 1-3), both ionic conductivity and flexibility are excellent. On the other hand, when only PVP and TMPTA were used (Comparative Example 1), the ion conductivity was excellent, but the flexibility was poor, and when only PEO and TMPTA were used (Comparative Example 2), both the ion conductivity and the flexibility characteristics were poor.

Meanwhile, the interfacial resistance between the electrolyte and the composite electrode according to Example 1-3 and Comparative Example 1-2 was measured. As a result, it was found that the interface resistance of the electrolyte according to Example 1-4 was reduced as compared with the case of the comparative example. This is because the binding force of the electrolyte of Example 1-4 to the composite electrode is increased as compared with the case of the comparative example.

According to the present invention, the following effects are obtained.

First, since the ion conductivity at room temperature is very excellent, it can accelerate the practical use of the lithium secondary battery.

Second, since the polymer matrix of the present invention has excellent affinity for the electrolyte and has elasticity, a flexible structure is achieved. Therefore, the polymer solid electrolyte including the polymer matrix is very easy to be processed into a desired shape.

Third, the bonding force to the electrode can be improved to reduce the interface resistance between the electrode and the electrolyte. As a result, a battery capable of operating at a high current density can be produced.

Fourth, the polymer matrix of the present invention has a uniform pore distribution and can exhibit uniform reaction characteristics over the entire battery area. As a result, it can be used stably for a long time.

Claims (22)

A polymer matrix comprising a substance comprising a trimethylolpropane derivative represented by the formula (1), a hydrophilic polymer and a binding polymer. <Formula 1>

In said formula, R <_1> is hydrogen or a methyl group. The polymer matrix of claim 1, wherein the binding polymer is selected from the group consisting of polyethylene oxide, polyvinyl chloride, polyvinylacetate, and polyvinyl fluoride. The polymer matrix according to claim 1, wherein the content of the binding polymer is 10 to 30% by weight based on the total weight of the trimethylolpropane derivative represented by Formula 1 and the hydrophilic polymer. According to claim 1, wherein the trimethylolpropane derivative represented by Formula 1 is a homopolymer having a network (network) structure, Wherein said hydrophilic polymer and the associative polymer are present in the network of said homopolymer. The method of claim 1, wherein the trimethylolpropane derivative represented by Formula 1 and the hydrophilic polymer is copolymerized, The polymer matrix, characterized in that the binding polymer is present in the network of the copolymer. The method of claim 1, wherein a part of the trimethylolpropane derivative represented by the formula (1) is a homopolymer having a network (network), the hydrophilic polymer and the binding polymer is present in the network structure of the homopolymer or , The remainder of the polymer matrix is characterized in that the trimethylolpropane derivative represented by the formula (1) is copolymerized with a hydrophilic polymer, and a binding polymer is present in the copolymer network structure. 2. The polymer matrix of claim 1, wherein the hydrophilic polymer is a compound of formula (2). <Formula 2>

In the formula, R ₂ is selected from the 2-pyrrolidino carbonyl _{(2-pyrrolidinonyl), OCOCH 3} , OCOCH = CH 2, C 6 H 5, the group consisting of CN and SO ₂ CH = CH _2; n is a number from 10 to 2000 The polymer matrix according to claim 1, wherein the weight average molecular weight of the hydrophilic polymer is 1 × 10 ⁴ to 1 × 10 ⁵ . The polymer matrix of claim 1 wherein the hydrophilic polymer is polyvinylpyrrolidone. The polymer matrix according to claim 1, wherein the mixed weight ratio of the trimethylolpropane derivative represented by Chemical Formula 1 and the hydrophilic polymer is 1: 1 to 1:10. A polymer matrix made of a material containing a trimethylolpropane derivative represented by Formula 1, a hydrophilic polymer and a binding polymer; And An electrolyte solution contained in the polymer matrix. <Formula 1>

In said formula, R <_1> is hydrogen or a methyl group. 12. The polymer solid electrolyte of claim 11, wherein the binding polymer is selected from the group consisting of polyethylene oxide, polyvinyl chloride, polyvinylacetate, and polyvinyl fluoride. 12. The polymer solid electrolyte of claim 11, wherein the content of the binding polymer is 10 to 30% by weight based on the total weight of the trimethylolpropane derivative represented by Formula 1 and the hydrophilic polymer. The method of claim 11, wherein the trimethylolpropane derivative represented by Formula 1 is a homopolymer having a network (network) structure, Wherein said hydrophilic polymer and the associative polymer are present in the network structure of said homopolymer. The method of claim 11, wherein the trimethylolpropane derivative represented by Formula 1 and the hydrophilic polymer is copolymerized, A polymer solid electrolyte, characterized in that the binding polymer is present in the network structure of the copolymer, The method of claim 11, wherein a part of the trimethylolpropane derivative represented by the formula (1) is a homopolymer having a network (network), the hydrophilic polymer and the binding polymer is present in the network structure of the homopolymer or , The remainder of the polymer solid electrolyte is characterized in that the trimethylolpropane derivative represented by the formula (1) is copolymerized with a hydrophilic polymer, and a binding polymer is present in the network structure of the copolymer. 12. The polymer solid electrolyte of claim 11, wherein the hydrophilic polymer is a compound of formula (2). <Formula 2>

In the formula, R ₂ is selected from the 2-pyrrolidino carbonyl _{(2-pyrrolidinonyl), OCOCH 3} , OCOCH = CH 2, C 6 H 5, the group consisting of CN and SO ₂ CH = CH _2; n is a number from 10 to 2000 12. The polymer solid electrolyte of claim 11, wherein the weight average molecular weight of the hydrophilic polymer is 1 × 10 ⁴ to 1 × 10 ⁵ . 12. The polymer solid electrolyte according to claim 11, wherein the hydrophilic polymer is polyvinylpyrrolidone. The polymer solid electrolyte of claim 11, wherein the mixed weight ratio of the trimethylolpropane derivative represented by Chemical Formula 1 and the hydrophilic polymer is 1: 1 to 1:10. The polymer solid electrolyte of claim 11, wherein the polymer matrix is 5 to 60 wt% based on the weight of the electrolyte, and the electrolyte is 40 to 95 wt%. A lithium secondary battery employing the polymer solid electrolyte according to any one of claims 11 to 21.