JP4265191B2 - Lithium ion conductive all solid electrolyte and lithium ion conductive gel electrolyte - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium ion conductive polymer electrolyte capable of realizing excellent ion conductivity and a high transportation rate for lithium ions. <P>SOLUTION: In a matrix polymer constituting this lithium ion conductive polymer electrolyte, the excellent ion conductivity and the high transportation rate for lithium ions can be realized by introducing a monomer containing lithium capable of releasing lithium ions by being dissociated, and by simultaneously adding a salt monomer having an ionic interaction for facilitating the dissociation of lithium ions from the monomer containing lithium. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a lithium ion conductive all solid electrolyte and a lithium ion conductive gel electrolyte.
[0002]
[Prior art]
As electronic devices become smaller and lighter and more portable, lithium secondary batteries having the characteristics of high voltage and high energy density have attracted attention in recent years and are actively researched and developed. It is also a highly anticipated field in the development of electric vehicles and the like. Against this background, it is expected that a lithium secondary battery capable of realizing higher voltage and higher energy density will be required in the future.
[0003]
As an electrolyte of a conventional electric device, generally a liquid electrolyte, in particular, an ionic compound dissolved in an organic electrolytic solution has been used, but the liquid electrolyte is liquid leakage to the outside, volatilization, Since elution of the electrode material is likely to occur, long-term reliability has been a problem. Further, in order to solve these problems, a strong material such as a steel can is required as a package, but it is heavy and is not suitable for making electronic devices lighter and more portable. The use of aluminum cans as a packaging material is very effective for reducing the weight of the battery, but it is inferior in strength compared to steel cans. It is necessary also from the point of safety such as, and various studies have been conducted.
[0004]
The ion conductive polymer electrolyte is used as a method for making the electrolyte non-liquefied, but the ion conductive polymer electrolyte is often classified into two types for convenience. One is a gel electrolyte in which the electrolyte is gelled with a polymer compound to eliminate the fluidity of the electrolyte as an electrolyte. In this case, a battery with excellent reliability such as leakage resistance and storage can be configured. Has the advantage. As another method, there is an all-solid-state solid electrolyte that does not use an organic solvent at all, or uses an organic solvent having a low boiling point at the time of electrolyte synthesis, and then removes the organic solvent having a low boiling point by heating or the like.
[0005]
The gel electrolyte, for example, a semi-solid polymer electrolyte membrane is proposed, the ion conductivity of 10- ⁴ S / cm has been achieved (e.g., Patent Document 1). There are also cases where the lithium ion conductive gel electrolyte comprising a lithium salt and a polymer polymer has been proposed, ionic conductivity of 10- ⁴ S / cm has been achieved (e.g., Patent Document 2). On the other hand, the all-solid electrolyte, for example, imidazolium molten salt electrolyte is proposed, ion conductivity of the polymer 10- ⁷ S / cm has been achieved (e.g., Patent Document 3). The high ionic conductivity of polymer electrolytes is one of the most important items for improving battery performance. If an electrolyte with a low conductivity is incorporated in the battery, the internal resistance increases, causing a significant loss of battery capacity. It becomes. In addition to ionic conductivity, it is also very important that the lithium ion transport number is high in order to improve battery performance, and the lithium ion transport number is low, that is, it contributes to the conductivity of ions other than lithium ions. Is large, the anion accumulates in the vicinity of the negative electrode at the time of discharging (positive electrode at the time of charging), so that the charge on the electrode is canceled and the electrode reaction is significantly inhibited. Similarly, cations other than lithium accumulate near the positive electrode during discharge (near the negative electrode during charging), leading to inhibition of the electrode reaction. As a result, the electrode at the time of charging / discharging is largely polarized, the battery voltage is lowered, and the capacity is impaired.
[0006]
Generally, salts such as LiClO ₄ and LiPF ₆ used as lithium salts dissociate into ions in an organic solvent and contribute to conductivity. However, when these salts are used, since the ion conduction mechanism is generally based on biions (anions and cations), the transport number of lithium ions becomes small. In order to increase the transport number of lithium ions, single ion conduction type electrolytes have been developed, but no electrolyte that satisfies both the ionic conductivity and the transport number of lithium ions has been realized. Development of a simple electrolyte is desired.
[0007]
[Patent Document 1]
Japanese Patent No. 2715309 (page 3-4)
[Patent Document 2]
Japanese Examined Patent Publication No. 7-32022 (page 4-5)
[Patent Document 3]
Japanese Unexamined Patent Publication No. 2000-11753 (page 4, table 2)
[0008]
[Problems to be solved by the invention]
The present invention has been made in view of the above problems, and an object of the present invention is to provide a polymer electrolyte capable of realizing high ion conductivity and high lithium ion transport number.
[0009]
[Means for Solving the Problems]
As a result of intensive efforts to solve such problems, the present inventors do not have a polymerizable functional group, such as LiClO ₄ or LiPF ₆ , and dissociate into an ion in an organic solvent. A salt monomer that uses a lithium-containing monomer capable of introducing lithium ions into the system without using a salt, and further has an ionic interaction to promote dissociation of the lithium ion from the lithium-containing monomer It has been found that the addition of can simultaneously improve the ionic conductivity and the transport number of lithium ions, and further studies have been made to complete the present invention.
[0010]
That is, the present invention
(1) Obtained from a lithium salt monomer having a polymerizable functional group, a monomer having an acid component having a double bond, and a polyfunctional salt monomer composed of a monomer having a quaternary ammonium salt having a double bond. Lithium ion conductive all solid electrolyte, characterized by
(2) Furthermore, the lithium ion conductive all solid electrolyte according to item (1) obtained by including a chemical crosslinking component,
(3) The lithium salt monomer having a polymerizable functional group is a carboxylic acid lithium salt monomer having a polymerizable functional group, a sulfonic acid lithium salt monomer having a polymerizable functional group, and a phenol lithium salt monomer having a polymerizable functional group. The lithium ion conductive all solid electrolyte according to item (1) or (2), selected from:
(4) Provided is a lithium ion conductive gel electrolyte obtained by including a component used in the lithium ion conductive all solid electrolyte according to any one of items (1) to (3) and an organic solvent. It is.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Examples of the lithium salt monomer having a polymerizable functional group used in the present invention include a lithium carboxylate having a polymerizable functional group, a lithium sulfonate having a polymerizable functional group, and a phenol lithium salt having a polymerizable functional group. preferable. Preferred examples of the polymerizable functional group include an acryl group, a methacryl group, and a vinyl group, and specific examples of the preferable lithium salt monomer having these include lithium acrylate, lithium methacrylate, and lithium 2-vinylbenzenesulfonate. Lithium 3-vinylbenzenesulfonate, lithium 4-vinylbenzenesulfonate, lithium 2-methyl-1-pentene-1-sulfonate, lithium 1-octene-1-sulfonate, lithium 4-vinylbenzenemethanesulfonate, Examples include lithium 2-acrylamido-2-methyl-1-propanesulfonate, 2-vinylphenol lithium salt, 3-vinylphenol lithium salt, and 4-vinylphenol lithium salt. The lithium salt monomer having a polymerizable functional group is used to introduce lithium ions into the polymer electrolyte, but the polymer electrolyte was formed because the component serving as the counter ion contains a polysynthetic functional group. Thereafter, it is taken into the polymer matrix, and counter ions can be prevented from moving to the electrode during charging and discharging. As a result, accumulation near the electrodes can be prevented, and a decrease in battery capacity or a significant decrease in cycle characteristics can be prevented.
[0012]
As an example of synthesis of a lithium salt monomer having a polymerizable functional group, when a carboxylic acid is used, a methanol solution of a carboxylic acid having a double bond is prepared, lithium hydroxide is added thereto, and a stirring reaction is performed. A method in which the carboxyl group is lithiated and acetone is added to precipitate the product.
[0013]
Furthermore, polyfunctional salt monomer consisting of monomers having quaternary ammonium salt monomer having a double bond with an acid component having a double bond used in the present invention includes a quaternary ammonium salt having a double bond Ru polyfunctional salt monomer der synthesized from an acid component having a double bond. The quaternary ammonium salts having a double bond, among its chloride and the like. Examples thereof include 2-ethyltrimethylammonium chloride chloride, 3-acrylamidopropyltrimethylammonium chloride, 2-ethyltrimethylammonium acrylate chloride, 3-methacrylamidopropyltrimethylammonium chloride, and dimethylaminoethylbenzyl chloride methacrylate. Preferred examples of the acid component having a double bond include carboxylic acids and sulfonic acids having a double bond, and any acid component capable of forming an ionic bond with an amine component having a double bond is particularly preferable. It is not limited. Among them, a sulfonic acid having a double bond with a high acidity is preferable from the viewpoint of the magnitude of polarization when introduced into a gel and ease of synthesis of a salt monomer. For example, 2-vinylbenzenesulfonic acid, 3-vinylbenzenesulfonic acid, 4-vinylbenzenesulfonic acid, 2-methyl-1-pentene-1-sulfonic acid, 1-octene-1-sulfonic acid, 4- Vinylbenzenemethanesulfonic acid, 2-acrylamido-2-methyl-1-propanesulfonic acid, and the like can be used.
[0014]
An example of a method for synthesizing a multifunctional salt monomer comprising a monomer having an acid component having a double bond and a monomer having a quaternary ammonium salt having a double bond used in the present invention has a double bond. Dissolve the sulfonic acid in water, add 0.6 equivalent of silver carbonate to the sulfonic acid to silverize the sulfonic acid, and filter the resulting solution to obtain a silver sulfonate having a double bond. An aqueous solution is obtained. A quaternary ammonium chloride aqueous solution having a double bond is dropped into this solution, and the reaction is carried out while tracking the conductivity. As the reaction proceeds, the silver chloride precipitated is removed by filtration, and the resulting solution is concentrated and recrystallized. Or the method of depositing the polyfunctional monomer which has ionic interaction by adding tetrahydrofuran is mentioned.
[0015]
Examples of chemical crosslinking components used in the present invention include N, N′-methylenebisacrylamide, ethylene glycol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol diacrylate, 1,6-hexanediol diacrylate. , Neopentyl glycol diacrylate, tripropylene glycol diacrylate, polypropylene glycol diacrylate, trimethylol propane trimethacrylate, trimethylol propane triacrylate, tetramethylol methane tetraacrylate, triethylene glycol dimethacrylate, polyethylene glycol imethacrylate, 1,3-butylene glycol dimethacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate Rate and so on. Addition of chemical cross-linking components improves the thermal stability of gel electrolytes, but gel electrolytes such as polyacrylonitrile and polyvinylidene fluoride that do not contain chemical cross-linking moieties and enable gel formation by intermolecular force are stable at high temperatures. Therefore, it is preferable to add a chemical cross-linking component to the gel electrolyte containing the chemical cross-linking component.
[0016]
Furthermore, examples of the organic solvent used in the present invention include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethoxyethane, tetrahydrofuran, γ-butyrolactone, and N-methyl-2-pyrrolidone. It can use individually or in mixture of 2 or more types.
[0017]
In order to form a polymer network in the electrolyte of the present invention, various methods such as a method of applying heat, a method of irradiating light in the visible and ultraviolet regions, and a method of irradiating radiation such as an electron beam can be applied. In the polymerization by heat, a thermal polymerization initiator can be added as necessary. Examples of the thermal polymerization initiator include azo polymerization initiators such as azobisisobutyronitrile, peroxide polymerization initiators such as benzoyl peroxide, and the like.
[0018]
Examples of a method of obtaining a lithium ion conductive polymer electrolyte of the present invention, a lithium salt monomer having a polymerizable functional group, and a monomer with quaternary ammonium salt having a double bond with an acid component having a double bond A multifunctional salt monomer comprising a monomer having a chemical crosslinking component, if necessary, is added to an organic solvent and stirred at room temperature until uniform to obtain solution 1. In parallel with the preparation of Solution 1, an azo polymerization initiator such as azobisisobutyronitrile or a peroxide polymerization initiator such as benzoyl peroxide dissolved in a solvent is added to Solution 1 and stirred. Thus, solution 2 is obtained. The solution 2 thus obtained is placed in an oven at 60 to 80 ° C. for about 10 minutes to 2 hours, whereby a lithium salt monomer having a polymerizable functional group, a monomer having an acid component having a double bond, and a double A polyfunctional salt monomer composed of a monomer having a quaternary ammonium salt having a bond, a copolymer composed of a chemical crosslinking component is obtained, and at the same time, a polymer is formed, and at the same time, it is gelled with an organic solvent and is a single ion conduction type Lithium ion conductive gel electrolyte can be obtained. When no solvent is used in the above, a single ion conduction type lithium ion conductive all solid electrolyte is obtained.
[0019]
In the lithium ion conductive gel electrolyte and the lithium ion conductive all solid electrolyte of the present invention, as an example of the ratio of each component, a lithium salt monomer having a polymerizable functional group is preferably 5 mmol / L to 5 mol / L. More preferably, for 10 mmol / L to 2 mol / L, a polyfunctional salt monomer composed of a monomer having a salt monomer acid component and a monomer having a base component is preferably 10 mmol / L to 2 mol / L, more preferably , 50 mmol / L to 1 mol / L, and the chemical crosslinking component is preferably 5 mmol / L to 500 mmol / L, more preferably 10 mmol / L to 200 mmol / L. The polymerization initiator is preferably 5 mmol / L to 100 mmol / L.
[0020]
The lithium ion conductive gel electrolyte and the lithium ion conductive all solid electrolyte of the present invention are useful as batteries, electric double layer capacitors, electrochromic and other materials for electrochemical devices.
[0021]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention in more detail, this invention is not limited at all by this.
[0022]
[Example 1]
<Synthesis of a lithium salt monomer having a polymerizable functional group>
Acrylic acid 3.61 g (50 mmol) and lithium hydroxide 1.0 g (42 mmol) were dissolved in 25 ml of methanol and reacted at room temperature for 2 hours. When the obtained solution was dropped into 500 ml of acetone, a white precipitate was formed. The resulting white precipitate was washed several times with acetone and collected by filtration. It was dried using a vacuum dryer at room temperature to obtain 2.8 g of lithium acrylate (white powder). The yield was 85.5%.
[0023]
<Synthesis of a polyfunctional salt monomer (hereinafter referred to as a polyfunctional salt monomer) comprising a monomer having an acid component and a monomer having a base component>
Dissolve 10.36 g (50 mmol) of 2-acrylamido-2-methyl-1-propanesulfonic acid in 500 ml of water, add 8.27 g (30 mmol) of silver carbonate to the solution, stir for 8 hours, and after filtration, colorless and transparent Liquid was obtained. An aqueous solution of 3-methacrylic acid amidopropyltrimethylammonium chloride was prepared so as to be 100 mmol / L, and the obtained liquid was subjected to a drop reaction. As the reaction proceeded, a silver chloride white solid precipitated. The reaction was carried out while measuring the conductivity with a conductivity meter. When 492.0 ml of an aqueous solution of 3-methacrylic acid amidopropyltrimethylammonium chloride was dropped, the conductivity showed the minimum value, and this point was regarded as the end point. Silver chloride precipitated by filtration was removed to obtain a colorless and transparent aqueous solution. The filtrate was concentrated by an evaporator to obtain a slightly viscous aqueous solution.
After diluting the obtained aqueous solution with ethanol, tetrahydrofuran was added, and when a white crystalline substance started to appear, the addition was stopped and the mixture was cooled in a refrigerator. White crystals obtained by filtration were vacuum-dried and the melting point of the product was confirmed by differential scanning calorimetry (DSC) to confirm that the obtained compound was a single polyfunctional salt monomer.
[0024]
<Synthesis and evaluation of single ion conductive gel electrolyte>
0.117 g (0.3 mmol) of the above polyfunctional salt monomer, 0.117 g (1.5 mmol) of lithium acrylate, and 0.023 g (0.15 mmol) of methylenebisacrylamide were placed in a test tube, and N-methyl- Add 2.5 ml of 2-pyrrolidone (hereinafter NMP) solvent and dissolve by stirring. The obtained solution was degassed, and 0.5 ml of 0.029 g (0.12 mmol) of benzoyl peroxide dissolved in 1.0 ml of NMP was added thereto. After stirring, the obtained uniform transparent solution was heated to 80 ° C., and after 15 minutes, a milky white gel electrolyte was obtained. The gel electrolyte was produced in an argon atmosphere.
The conductivity of the lithium ion conductive gel electrolyte obtained above was measured at room temperature by the AC impedance method. The measured frequency range was 50 Hz to 30 MHz, and the voltage was 0.5 V. The measurement result was 2.5 × 10 ⁻⁴ S / cm. Moreover, the transport number of lithium ions was measured using DC polarization measurement and AC impedance measurement together ("Conductive polymer", edited by Naoya Ogata). When the DC polarization voltage was 10 mV, a result of 0.98 was obtained.
[0025]
[Example 2]
<Synthesis and evaluation of single ion conductive gel electrolyte>
In the preparation of the gel electrolyte in Example 1, 0.570 g (0.3 mmol) of lithium 4-vinylbenzenesulfonate was used instead of lithium acrylate, and a white gel electrolyte was prepared in the same manner as in Example 1. Obtained. The ionic conductivity of the obtained lithium ion conductive gel electrolyte was 1.7 × 10 ⁻⁴ S / cm. The lithium ion transport number was 0.99.
[0026]
[Example 3]
<Synthesis and evaluation of single ion conductive gel electrolyte>
In preparation of the gel electrolyte in Example 1, a white gel electrolyte was obtained in the same manner as in Example 1 except that 0.378 g (0.3 mmol) of 4-vinylphenol lithium salt was used instead of lithium acrylate. It was. The obtained lithium ion conductive gel electrolyte had an ionic conductivity of 1.2 × 10 ⁻⁴ S / cm. The lithium ion transport number was 0.98.
[0027]
[Example 4]
<Synthesis and Evaluation of Single Ion Conductive All Solid Electrolyte>
0.117 g (0.3 mmol) of a polyfunctional salt monomer obtained in the same manner as in Example 1 and 0.117 g (1.5 mmol) of lithium acrylate were placed in a test tube, and 2.5 ml of methyl alcohol was added thereto. Stir to dissolve. The obtained solution was degassed, and 0.5 ml of 0.029 g (0.12 mmol) of benzoyl peroxide dissolved in 1.0 ml of methyl alcohol was added thereto. After stirring, the obtained uniform transparent solution was applied on a Teflon (registered trademark) plate and polymerized by heating at 80 ° C. for 1 hour. Furthermore, it put into the vacuum dryer at 100 degreeC for 1 hour, and methanol was removed completely. In this way, a film having a thickness of about 300 μm was produced. The all solid electrolyte membrane was produced under an argon atmosphere. The ionic conductivity of the obtained all solid electrolyte membrane was 1.1 × 10 ⁻⁶ S / cm. The lithium ion transport number was 0.99.
[0028]
[Comparative Example 1]
<Synthesis and evaluation of ionic conductivity of biion conductive lithium ion conductive gel electrolyte>
0.117 g (0.3 mmol) of the polyfunctional salt monomer of Example 1, 0.430 g (5.0 mmol) of methyl acrylate, and 0.023 g (0.15 mmol) of methylenebisacrylamide were placed in a test tube, and LiClO was added thereto. Add 2.5 ml of a solution prepared by dissolving ₄ in NMP to a concentration of 1 mol / L, and dissolve by stirring. The resulting solution was degassed, and 0.5 ml of 0.029 g (0.12 mmol) of benzoyl peroxide dissolved in 1.0 ml of the above-described LiClO ₄ NMP solution was added thereto. After stirring, the obtained uniform transparent solution was heated to 80 ° C., and after 15 minutes, a milky white lithium ion conductive gel electrolyte was obtained. The gel electrolyte was produced under an argon atmosphere.
The lithium ion conductive gel electrolyte obtained above had an ionic conductivity of 3.3 × 10 ⁻³ S / cm and a lithium ion transport number of 0.25. The ionic conductivity of Comparative Example 1 was as high as 3.3 × 10 ⁻³ S / cm, but the lithium ion transport number was as low as 0.25 because of the biionic conduction type mechanism. .
[0029]
[Comparative Example 2]
<Synthesis and evaluation of ionic conductivity of all-solid electrolytes of biionic conductivity type>
0.117 g (0.3 mmol) of the polyfunctional salt monomer of Example 1, 0.430 g (5.0 mmol) of methyl acrylate, and 0.160 g (1.5 mmol) of LiClO ₄ were put in a test tube, and methyl alcohol was added thereto. Add 2.5 ml and stir to dissolve. The resulting solution was degassed, and 0.5 ml of 0.029 g (0.12 mmol) of benzoyl peroxide dissolved in 1.0 ml of methyl alcohol was added thereto. After stirring, the obtained uniform transparent solution was applied on a Teflon (registered trademark) plate and polymerized by heating at 80 ° C. for 1 hour. Furthermore, it put into the vacuum dryer at 100 degreeC for 1 hour, and methanol was removed completely. Thus, a film having a thickness of about 300 μm was obtained. The all solid electrolyte membrane was produced under an argon atmosphere. The ionic conductivity of the obtained all solid electrolyte membrane was 1.0 × 10 ⁻⁶ S / cm. The lithium ion transport number was 0.40.
[0030]
【The invention's effect】
According to the present invention, both high ionic conductivity and high ionic transport number are compatible. Particularly, since the ionic transport number is very high at 0.98, it is considered that the discharge capacity is increased. Such polymer electrolytes are useful as materials for batteries, electric double capacitors and other electrochemical devices.

Claims (4)

It is obtained from a lithium salt monomer having a polymerizable functional group, a monomer having an acid component having a double bond, and a polyfunctional salt monomer composed of a monomer having a quaternary ammonium salt having a double bond. Lithium ion conductive all solid electrolyte. The lithium ion conductive all solid electrolyte according to claim 1 obtained by containing a chemical crosslinking component. The lithium salt monomer having a polymerizable functional group is selected from a carboxylic acid lithium salt monomer having a polymerizable functional group, a sulfonic acid lithium salt monomer having a polymerizable functional group, and a phenol lithium salt monomer having a polymerizable functional group The lithium ion conductive all solid electrolyte according to claim 1 or 2. The lithium ion conductive gel electrolyte obtained by including the component and organic solvent which are used for the lithium ion conductive all solid electrolyte in any one of Claims 1-3.