JP2004172346A - Polymer solid electrolyte and electric double-layer capacitor using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polymer solid electrolyte with excellent mechanical strength and film forming properties, and also to provide an electric double-layer capacitor using the same with excellent safety. <P>SOLUTION: The polymer solid electrolyte is constituted of: the polymer solid electrolyte comprising a polymer compound containing syndiotactic poly-methylmethacrelate, and isotactic poly-methylmethacrelate; at least one kind of electrolyte salt compound selected from a group comprising nitrogen-containing phloroborates, nitrogen-containing perchlorates, and nitrogen-containing phlorophosphates; and an organic electrolyte solvent, and the electric double-layer capacitor uses the electrolyte. <P>COPYRIGHT: (C)2004,JPO

Description

【００４７】
【発明の効果】
本発明により、機械的強度及び製膜性に優れた高分子固体電解質を提供することができる。本発明の高分子固体電解質を、電気二重層キャパシタに適用すると、キャパシタの静電容量を低下させることなく、また、電解質溶液がゲル化され、さらに機械的強度に優れていることから電解液の漏れ性を低減化、ショートの可能性を少なくすることができる。
【００４８】
【図面の簡単な説明】
【図１】電気二重層キャパシタの一例を示す概略図である。
【符号の説明】
１ 集電部材
２ 集電部材
３ 分極性電極
４ 分極性電極
５ セパレーター
６ ガスケット
７ ケース[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a polymer solid electrolyte and an electric double layer capacitor using the same. More specifically, the present invention relates to a polymer solid electrolyte comprising polymethyl methacrylate, an electrolyte salt compound, and an organic electrolyte solvent and having excellent mechanical strength and film-forming properties, and an electric double layer capacitor using the same.
[0002]
[Prior art]
2. Description of the Related Art In recent years, electric double-layer capacitors have attracted attention as backup power supplies, auxiliary power supplies, and the like, and developments that focus on the performance of activated carbon as electrodes for electric double-layer capacitors have been made widely. An electric double layer capacitor using activated carbon as a polarizable electrode generally has excellent capacitance. Therefore, with the development of the electronics field, demand for electric devices in addition to conventional adsorption applications is rapidly growing. Further, recently, in addition to the miniaturization of the conventional memory backup power supply and the like, development of a large-capacity product used for a power supply of a motor and the like has been performed.
[0003]
As described above, electric double layer capacitors are widely used, and a highly reliable capacitor is required for each application. However, when an organic solvent in which an electrochemically stable electrolyte salt is dissolved is used in an electric double layer capacitor, the electrolyte solution easily leaks, and there is a risk of ignition. In response to such a problem, a polymer solid electrolyte (also referred to as a gel electrolyte), which is a composite of a polymer, an electrolyte, and an organic solvent, has recently attracted attention. RES. Soc. Symp. Prc. Vol. 575 (2000), p. 423 exemplifies a polymer solid electrolyte obtained by combining polyvinylidene fluoride (hereinafter abbreviated as PVdF), an electrolyte and an electrolyte solvent.
[0004]
However, since such a solid polymer electrolyte has a somewhat poor mechanical strength, the thickness of the solid polymer electrolyte cannot be reduced, and therefore the capacity of the active material per cell cannot be greatly increased. Further, if the mechanical strength of the solid polymer electrolyte is low, the solid polymer electrolyte may be crushed, and the possibility that the positive electrode and the negative electrode come into contact and short-circuit increases.
[0005]
Matsuda et al., J. Mol. Electrochem. Soc. , Vol. 141, No. 7 (1994), P1730-1734, discloses a polymer solid electrolyte chemically crosslinked through polyoxyethylene.
[0006]
Further, as an example using isotactic polymethyl methacrylate (hereinafter abbreviated as i-PMMA) and syndiopolymethyl methacrylate (hereinafter abbreviated as s-PMMA), a negative electrode using a light metal as an active material, an i-PMMA An example of application to an organic electrolyte battery having an organic electrolyte gelled with s-PMMA and a positive electrode is described in JP-A-55-21862.
[0007]
[Problems to be solved by the invention]
The above-mentioned Matsuda et al. Polymer solid electrolyte containing PMMA as a constituent unit is a chemically cross-linked polymer solid electrolyte and thus has a problem in film-forming properties. Further, the organic electrolyte battery described in JP-A-55-21862 describes an organic electrolyte gelled with i-PMMA and s-PMMA, but this is an example applied to a lithium battery. Of course, there is no description or suggestion as to whether or not the capacitor can be used in combination with an electrolyte salt compound and an organic electrolyte solvent to form a capacitor. Therefore, an object of the present invention is to provide a polymer solid electrolyte excellent in mechanical strength and film forming property and an electric double layer capacitor using such a polymer solid electrolyte.
[0008]
[Means for Solving the Problems]
The present inventors have conducted intensive studies focusing on the excellent characteristics of PMMA, and as a result, have been composed of a polymer material of a stereocomplex comprising s-PMMA and i-PMMA, an electrolyte salt compound, and an organic electrolyte solvent. It has been found that the above object can be achieved by a solid polymer electrolyte and an electric double layer capacitor using the same, and the present invention has been accomplished. That is, the present invention provides a polymer compound comprising s-PMMA and i-PMMA, and at least one selected from the group consisting of nitrogen-containing fluoroborates, nitrogen-containing perchlorates and nitrogen-containing fluorophosphates. It is a polymer solid electrolyte composed of various kinds of electrolyte salt compounds and an organic electrolyte solvent.
[0009]
Another invention of the present invention is an electric double layer capacitor using such a polymer solid electrolyte.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
The polymer compound constituting the polymer solid electrolyte of the present invention comprises s-PMMA and i-PMMA. For i-PMMA and s-PMMA, PMMA containing i-PMMA and s-PMMA generated by synthesizing and polymerizing MMA may be used, but the mechanical properties and heat resistance of the solid polymer electrolyte are not limited. It is easy and preferred to use a high and readily available polymer mixture of i-PMMA and s-PMMA.
[0011]
Preferably, the isotacticity of i-PMMA is in the range of 50% to 100%, and the syndiotacticity of s-PMMA is in the range of 50% to 100%. The isotacticity of i-PMMA is 70% or more, preferably 80% or more, and most preferably 90% or more, and the syndiotacticity of s-PMMA is 50% to 70%. And it is more preferable because it is inexpensive.
[0012]
The mixing ratio of i-PMMA and s-PMMA is preferably determined from the viewpoint of the possibility of pseudo-crosslinking between polymer chains, that is, mechanical strength, and s-PM in the total weight of i-PMMA and s-PMMA. It is preferable that the mixing ratio of PMMA is in the range of 20 to 90% by weight. More preferably, it is 30 to 80% by weight, more preferably 40 to 70% by weight.
[0013]
s-PMMA can be synthesized by general radical polymerization or anionic polymerization using organolithium as an initiator in the presence of triethylaluminum, but commercially available products are also readily available. i-PMMA can be obtained by anionic polymerization using a Grignard reagent as an initiator, or coordination anionic polymerization using Yb [C (SiMe ₃ ) ₃ ] ₂ as a polymerization initiator.
[0014]
The molecular weight of the polymeric compound, processability, moldability, mechanical strength, is in the range of 5 × 10 ³ ~10 ⁷ the number average molecular weight in terms of flexibility is preferred. Moreover, strength improvement, according to the purpose, such as increased flexibility, without compromising the ionic conductivity of the solid polymer electrolyte, or be copolymerized with other monomers, may also be or crosslinking treatment, SiO ₂ And a filler such as TiO ₂ may be added.
[0015]
The electrolyte used in the present invention is composed of an electrolyte salt compound and an organic electrolyte solvent. Examples of the electrolyte salt compound include tetraethylammonium tetrafluoroborate, tetramethylammonium tetrafluoroborate, tetrapropylammonium tetrafluoroborate, tetrabutylammonium tetrafluoroborate, trimethylethylammonium tetrafluoroborate, triethylmethylammonium tetrafluoroborate, and diethyldimethylammonium Ammonium tetrafluoroborate such as tetrafluoroborate, N-ethyl-N-methylpyrrolidinium tetrafluoroborate, N, N-tetramethylenepyrrolidinium tetrafluoroborate, 1-ethyl-3-methylimidazolium tetrafluoroborate , Tetraethyl ammonium perchlorate, tetramethyl ammonium perchlorate, tetrapro Luammonium perchlorate, tetrabutylammonium perchlorate, trimethylethyl perchlorate, triethylmethylammonium perchlorate, diethyldimethylammonium perchlorate, N-ethyl-N-methylpyrrolidinium perchlorate, N, N-tetramethylenepyrrolidinium Perchlorate, ammonium perchlorates such as 1-ethyl-3-methylimidazolium perchlorate, tetraethylammonium hexafluorophosphate, tetramethylammonium hexafluorophosphate, tetrapropylammonium hexafluorophosphate, tetrabutylammonium hexafluorophosphate, Trimethylethylammonium hexafluorophosphate, triethylmethylammonium Sa fluoroalkyl phosphate, ammonium hexafluorophosphate, such as diethyl dimethyl ammonium hexafluoro phosphate.
[0016]
Examples of the organic electrolyte solvent include dimethyl carbonate, diethyl carbonate, ethylene carbonate, carbonates such as propylene carbonate, acetonitrile, nitriles such as propionitrile, γ-butyrolactone, α-methyl-γ-butyrolactone, β-methyl Lactones such as -γ-butyrolactone, γ-valerolactone, 3-methyl-γ-valerolactone, sulfoxides such as dimethyl sulfoxide and diethyl sulfoxide, amides such as dimethylformamide and diethylformamide, and tetrahydrofuran And ethers such as dimethoxyethane, dimethylsulfolane, sulfolane and the like. These organic solvents are usually used alone, but may be used as a mixed solvent of two or more kinds.
[0017]
In the present invention, the concentration of the electrolyte salt compound is not particularly limited as long as the electrolyte salt crystals do not precipitate at the stage of preparing the polymer solid electrolyte. Since the capacity may be reduced, the concentration with respect to the organic electrolyte solvent is preferably 0.1 mol / L (M / L) or more, more preferably 0.5 M / L or more.
[0018]
In the present invention, the proportion of the polymer compound in the polymer solid electrolyte is not particularly limited, but if it is too small, the mechanical strength may not be maintained, and if it is too large, the ionic conductivity tends to decrease. Usually, it is carried out at 2% by weight to 50% by weight, preferably 3% by weight to 20% by weight, more preferably 4% by weight to 15% by weight.
[0019]
Although the method for preparing the polymer solid electrolyte of the present invention is not particularly limited, a mixture of s-PMMA and i-PMMA becomes a uniform solution in an electrolytic solution heated to about 60 ° C to 120 ° C, and cooled to room temperature. Since has a gel-like form, processing such as film formation is easy.
[0020]
As a method for preparing a polymer solid electrolyte, a method of impregnating a polymer compound with an electrolyte solution comprising an electrolyte salt compound and an organic electrolyte solvent, a method of kneading an electrolyte salt compound, an organic electrolyte solvent and a polymer compound with a kneader or an open roll A method of mechanically mixing under an inert gas atmosphere with an extruder, a method of dissolving a polymer compound and an electrolyte salt compound in an organic electrolyte solvent, and a method of partially evaporating the organic electrolyte solvent after dissolution to obtain a concentration. And a method in which a polymer compound is dissolved in another solvent and then mixed with an electrolyte salt compound and an organic electrolyte solvent. The organic solvent used for the mixing is removed after preparing the solid polymer electrolyte.
[0021]
Specifically, there is a method in which a solution in which a polymer compound and an electrolyte salt are dissolved in an organic electrolyte solvent is applied on a smooth substrate or an electrode. As a coating method, a doctor blade method, a screen printing method, a gravure coating method, a roll coating method, a spray coating method, a dip coating method, a metal mask printing method, an electrostatic coating method, or the like can be used. Rolling may be performed by a flat plate press, a calender roll, or the like, if necessary. After the application, the organic electrolyte solvent is partially evaporated, or after application in a heated state, and then returned to room temperature, whereby a gel electrolyte can be obtained.
[0022]
The polymer solid electrolyte of the present invention is excellent in mechanical strength and film-forming properties, and is excellent in ionic conductivity, so that it is suitable for electric double layer capacitors, for example, an electric double layer capacitor containing no polymer solid electrolyte. After assembling, the polymer solid electrolyte heated and fluidized is introduced into the electric double layer capacitor, and cooled to room temperature, whereby the electric double layer capacitor using the polymer solid electrolyte can be manufactured. .
[0023]
Electric double layer capacitors can be classified into coin type, cylinder type, square type, and even laminate type, but generally, a structure having a pair of polarizable electrodes in a case and a separator between them is used. The polarizable electrode and the separator have a structure wetted with the electrolyte solution. Further, a current collector is provided on the case side of the polarizable electrode, and the case is sealed with a sealing material between the upper lid and the lower case so that the electrolyte solution does not leak.
[0024]
FIG. 1 is a schematic diagram showing an example of the electric double layer capacitor. In FIG. 1, 1 and 2 are current collecting members made of aluminum mesh or the like, 3 and 4 are polarizable electrodes, 5 is a separator made of a polypropylene nonwoven fabric or the like, 6 is a gasket made of a material such as polypropylene, 7 is a stainless steel case.
[0025]
As long as the solid polymer electrolyte is present alone between the polarizable electrodes, a solid polymer electrolyte and a separator made of a nonwoven fabric or a porous membrane may be used. The material of the separator is not particularly limited, and for example, polyethylene, polypropylene, polyamide, polyester and the like are used. The thickness between the polarizable electrodes is usually set to about 10 μm to 2 mm.
[0026]
Activated carbon is preferably used as the polarizable electrode material, and as a raw material of such activated carbon, plant materials such as coconut shell and bamboo, synthetic resin materials such as phenolic resin and polyvinyl alcohol, synthetic mesophase pitch, coal, natural pitch, Pitch-based materials such as isotropic pitch are exemplified. Activated carbon produced by gas activation of such a material or chemical activation with potassium hydroxide, zinc chloride or the like can be used as a polarizable material. The shape of the activated carbon is arbitrary, such as granular, cloth, crushed fiber, or fibrous.
[0027]
Such activated carbon can be used as it is in the case of a cloth-like shape, and in the case of granulated or crushed fibers, for example, a binder such as polytetrafluoroethylene, or a conductive material such as carbon black. And a mixture with an organic solvent may be applied on the current collecting member and dried. Alternatively, the mixture may be kneaded and then stretched to form a sheet, thereby forming a polarizable electrode. The thickness of the polarizing electrode is usually about 20 μm to 1 mm.
[0028]
The weight ratio between the polarizable electrode and the solid polymer electrolyte is, for example, 5/95 to 95/5. Examples of the current collecting member include aluminum and nickel. In order to reduce the resistance of the current collecting member, a metal foil serving as the current collecting member and the polarizable electrode may be bonded with a mixture of a synthetic resin and a conductive material, or aluminum may be sprayed on the polarizable electrode. As the sealing material, for example, an insulator such as polypropylene, butyl rubber, polyamide, or polyester is used. Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited thereto.
[0029]
【Example】
Synthesis Example 1 of i-PMMA
After purging with nitrogen in a 300 ml three-necked flask, toluene (28 ml), cyclohexane (112 ml), and phenylmagnesium bromide (0.77 M in ether solution, 7.4 ml) were added, and the mixture was cooled to 10 ° C.
[0030]
Methyl methacrylate (30 ml) was added dropwise over 90 minutes. After stirring for 6 hours, methanol (0.5 ml) was added to stop the reaction. After filtering the reaction solution, the residue was washed with methanol and then dried to obtain i-PMMA. As a result of GPC measurement, Mw of i-PMMA was 100,000. As a result of ¹ H-NMR measurement, the isotacticity was 93%.
[0031]
Synthesis Example 2 of i-PMMA:
I-PMMA was synthesized in the same manner as in Synthesis Example 1, except that cooling to 10 ° C was changed to heating to 40 ° C. As a result of GPC measurement, Mw of i-PMMA was 100,000, and as a result of ¹ H-NMR measurement, isotacticity was 80%.
[0032]
Preparation of Polarized Electrode 1.6 g of activated carbon (Kuraray Chemical Co., Ltd. BP-20), 0.2 g of carbon black and 0.2 g of polytetrafluoroethylene were mixed and stretched to obtain a polarizable electrode having a thickness of 300 μm. Obtained. The polarizable electrode was punched out to a diameter of 13 mm, attached using an aluminum current collector and a conductive paste, dried at 260 ° C. for 15 minutes, further dried at 200 ° C. in a vacuum drier for 12 hours, and then subjected to a dew point temperature of −70. Brought to a dry box below ℃.
[0033]
Example 1
1 g of i-PMMA obtained in Synthesis Example 1, 2 g of s-PMMA (Kuraray Parapet LW-500, Mw 38,000, syndiotacticity 60%), and 2 g of tetraethylammonium tetrafluorocarbon in a dry box having a dew point of -70 ° C. or less 4.5 g of borate and 22.5 g of propylene carbonate were introduced into a glass tube and dissolved by heating to 120 ° C. to obtain a polymer electrolyte. The weight ratio of i-PMMA and s-PMMA was 1: 2. The obtained polymer electrolyte was a thin white transparent gel at room temperature.
[0034]
Measurement of tensile strength:
A polymer solid electrolyte heated to 120 ° C. was cast on a polyester film so as to have a thickness of 3 mm to form a film. Five pieces were cut out at a length of 5 cm and a width of 1 cm, and the maximum tensile strength was measured using an autograph manufactured by Shimadzu Corporation under the conditions of 2 cm between jigs and a pulling speed of 5 mm / min. The average value of five test pieces was defined as the maximum tensile strength, and the results are shown in Table 1.
[0035]
Fabrication of electric double layer capacitor:
In a dry box, a polarizable electrode having an aluminum current collector attached to a CR2032 type coin-type electric double layer capacitor as shown in FIG. 1 heated to 100 ° C. and a glass filter paper separator are introduced. Then, the solid polymer electrolyte of Example 1 heated to 120 ° C. was injected, and a polarizable electrode to which an aluminum current collector was attached was further laminated, followed by sealing.
[0036]
Evaluation of capacitor performance:
After leaving the electric double layer capacitor at room temperature for 72 hours, constant current charging was performed at a constant current of 3 mA to 2.7 V, and further constant voltage charging was performed at 2.7 V for 30 minutes. Then, the battery was discharged at a constant current of 3 mA. This cycle of charge and discharge was repeated, and at the time of discharging in the eleventh cycle, the time required for the inter-terminal voltage to rise from 1.2 V to 1.0 V was measured to determine the discharge capacity. Table 1 shows the results of the discharge capacity.
[0037]
Evaluation of discharge capacity:
After allowing the electric double layer capacitor to stand at room temperature for 24 hours, the capacitor was charged at a constant current of 3 mA to a constant current of 2.7 V, and further charged at a constant voltage of 2.7 V for 30 minutes. Then, the battery was discharged at a constant current of 3 mA. This cycle of charge and discharge was repeated, and at the time of discharge in the third cycle, the time required for the inter-terminal voltage to rise from 1.2 V to 1.0 V was measured to determine the discharge capacity. Table 1 shows the results.
[0038]
Example 2
A polymer solid electrolyte was prepared in the same manner as in Example 1 except that the i-PMMA prepared in Synthesis Example 2 was used, and the tensile strength and the capacitance were measured. Table 1 shows the results.
[0039]
Example 3
A solid polymer electrolyte was prepared in the same manner as in Example 1, except that the weight ratio of i-PMMA to s-PMMA was 6: 4, and the tensile strength and the capacitance were measured. Table 1 shows the results.
[0040]
Example 4
A solid polymer electrolyte was prepared in the same manner as in Example 1, except that the weight ratio of i-PMMA to s-PMMA was 7: 3, and the tensile strength and the capacitance were measured. Table 1 shows the results.
[0041]
Example 5
A solid polymer electrolyte was prepared in the same manner as in Example 1, except that the weight ratio of i-PMMA to s-PMMA was 2: 8, and the tensile strength and the capacitance were measured. Table 1 shows the results.
[0042]
Example 6
A solid polymer electrolyte was prepared in the same manner as in Example 1 except that the weight ratio of i-PMMA to s-PMMA was 8: 2, and the tensile strength and the capacitance were measured. Table 1 shows the results.
[0043]
Example 7
A solid polymer electrolyte was prepared in the same manner as in Example 1 except that the weight ratio of i-PMMA to s-PMMA was 1: 9, and the tensile strength and the capacitance were measured. Table 1 shows the results.
[0044]
Comparative Example 1
A solid polymer electrolyte was produced in the same manner as in Example 1, except that only the same s-PMMA as in Example 1 was used. The obtained electrolyte was a viscous liquid, and it was impossible to measure the tensile strength. Table 1 shows the results of measuring the capacitance by the same method as in Example 1.
[0045]
Comparative Example 2
In a dry box having a dew point of −70 ° C. or less, 2 g of polyvinylidene fluoride (manufactured by Aldrich), 3 g of tetraethylammonium tetrafluoroborate, and 15 g of propylene carbonate are introduced into a glass tube, and heated to 120 ° C. to dissolve the polymer electrolyte. Obtained. The prepared polymer electrolyte was a transparent gel at room temperature. The capacitance value of the obtained solid polymer electrolyte was determined in the same manner as in Example 1. An attempt was made to produce a test piece for measuring tensile strength in the same manner as in Example 1, but the test piece was brittle and could not be cut out. Table 1 shows the results.
[0046]
[Table 1]

[0047]
【The invention's effect】
According to the present invention, a solid polymer electrolyte having excellent mechanical strength and film-forming properties can be provided. When the polymer solid electrolyte of the present invention is applied to an electric double layer capacitor, the electrolyte solution is gelled without lowering the capacitance of the capacitor, and the electrolyte solution is excellent in mechanical strength. Leakage can be reduced, and the possibility of a short circuit can be reduced.
[0048]
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an example of an electric double layer capacitor.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Current collection member 2 Current collection member 3 Polarized electrode 4 Polarized electrode 5 Separator 6 Gasket 7 Case

Claims (5)

A polymer compound comprising syndiotactic polymethyl methacrylate and isotactic polymethyl methacrylate; and at least one selected from the group consisting of nitrogen-containing fluoroborate, nitrogen-containing perchlorate, and nitrogen-containing fluorophosphate A solid polymer electrolyte composed of various kinds of electrolyte salt compounds and an organic electrolyte solvent. The solid polymer electrolyte according to claim 1, wherein the isotactic polymethyl methacrylate has an isotacticity of 50 to 100%. 3. The solid polymer electrolyte according to claim 1, wherein the syndiotactic polymethyl methacrylate has a syndiotacticity of 50 to 100%. The polymer compound according to any one of claims 1 to 3, wherein a weight ratio of the syndiotactic polymethyl methacrylate to the total weight of the syndiotactic polymethyl methacrylate and the isotactic polymethyl methacrylate is 20% by weight to 90% by weight. Is a solid polymer electrolyte. An electric double layer capacitor using the solid polymer electrolyte according to claim 1.

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