JPH03145004A - Membranous electrolyte - Google Patents

Abstract

PURPOSE:To prevent a leakage of solution and to improve the ion conductivity by composing a membranous electrolyte by filling an ion conductor in the hollows of a solid high polymer porous membrane with a specific penetration hole diameter. CONSTITUTION:The membranous electrolyte is composed by filling an ion conductor in the hollows of a solid high polymer porous membrane with the mean penetration hole diameter more than 0.1mum and 0.7mum and less. In this case, as the solid high polymer porous membrane with the mean penetration hole diameter more than 1mum and 0.7mum and less, polyethylene, polypropylene, polycarbonate, or the like is used. And as the ion conductor, a composite of an alkali salt or proton acid and polyester, or the like is used. Consequently, an electrolyte membrane with no solution leakage, with an excellent dynamic strength, a flexibility, and a low resistance can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to 1 m of electrolyte. Electrolyte thin films can be widely used in fields that require low electrical resistance and excellent mechanical strength, such as primary batteries, secondary batteries, electrochromic devices, and sensors.

[Conventional technology]

Solid polymer electrolyte membranes include ion exchange membranes such as perfluorocarbon membranes with sulfonic acid groups (trade name: Naflon@) and polyethylene oxide membranes (hereinafter referred to as P).
There are ion-conductive materials represented by composites of EO (hereinafter referred to as EO) and alkali metal salts, which have been widely studied and some have been put into practical use. Since these membranes are solid, they have the advantage of not leaking, are easy to process, and are compact.

Ion exchange membranes made of perfluorosulfonic acid or perfluorocarboxylic acid have excellent chemical and thermal properties, and can be integrated with positive and negative electrodes to form a compact cell, so they are used in salt electrolysis, as well as in fuel cells and water electrolysis. Applications are also being considered. PEO and alkali metal salt CLiChS
Composites with O1+ LiCI Oar LiAsF6, etc.) are expected to be applied to secondary and primary batteries, electrochromic elements, and sensors with high output density and energy density.

(ff1lJ to be Solved by the Invention) A system using a solid polymer electrolyte membrane has a problem in that the electrical energy efficiency decreases due to ohmic loss caused by the electrical resistance of the membrane. P
A solid polymer electrolyte membrane using an ionic conductor such as a composite of EO and an alkali metal salt has the advantage of being solid, but it is relatively weak at room temperature compared to aqueous solutions such as mineral acids, alkalis, and salts. The conductivity is two to three orders of magnitude lower, and its applications are limited due to the ohmic loss of the film. For example, the effective resistance of an electrolyte membrane with a film thickness of 50 nm and a specific conductivity of 10'''S-cm-' at room temperature is 5000 ohm·Cl11.

One solution to lowering electrical resistance is to make the film thinner, but there are limitations mainly due to constraints on mechanical strength.

In view of these circumstances, the present inventors have considered solving the above problems by filling the pores of a solid polymer porous thin film with an ionic conductor to form an electrolyte thin film, and have found success. However, in order to put the electrolyte thin film into practical use and expand its applications, it is desirable to further increase the ionic conductivity.

(Means for Solving Problem 1) In the process of pursuing the above problem, the present inventors discovered that even if the pore diameter of a solid polymer porous thin film was made larger, the pores were filled with an ionic conductor. They also discovered that it is possible to prevent and prevent liquid leakage, and thereby improve the ionic conductivity of the thin film, and have completed the present invention.

Thus, according to the present invention, the average through hole diameter is 0, 1-1
An electrolyte thin film is provided in which the pores of a solid polymer porous membrane having a diameter of 0.74 or less are filled with an ionic conductor.

For example, polyethylene, polypropylene, polycarbonate, polyimide, polyester, tetrafluoropolyethylene, etc. can be used as the solid polymer porous membrane having an average through-pore diameter of 0.1 umB 0.7- or less.

When the average through-hole diameter exceeds 0.1, the ionic conductivity through the ionic conductor immobilized in such a hole is greatly improved compared to the case where the through-hole has a small diameter. However, when the average through-hole diameter exceeds the 0.7 mark, it becomes difficult to fill the holes with the ionic conductor and prevent leakage.

The average through-pore diameter of the porous polymer used in the present invention can be measured using mercury porosimeter method, electron microscopy method, particle permeation method,
A method such as a gas adsorption method can be used.

In addition, the porosity of the solid polymer porous thin film is 0.1 to 90%.
It is preferably within the range of . If it is less than 0.1%, the amount of ionic conductor that can be filled is too small and the ionic conductivity of the thin film is not sufficient. On the other hand, if it exceeds 90%, it becomes difficult to maintain a practical thin film strength.

The thickness of the thin film is preferably within the range of 1 to 100 squares. Although it depends on the membrane material and manufacturing method, in general, if it is less than 1, it will be disadvantageous in terms of practical strength and handling workability, while if it is 100 m1, the effective resistance will be large.

As the ionic conductor used in the present invention, a complex of an alkali metal salt or a protonic acid and a polyether, or a complex of a network or crosslinked polymer containing these polymers as segments can be used. can. Polyethers such as polyethylene oxide, polypropylene oxide, or copolymers thereof are commercially available as liquid and powder reagents with different molecular weights and degrees of polymerization, and can be easily used. Namely, polyethylene glycol, polyethylene glycol monoether, polyethylene glycol diether, polypropylene glycol, polypropylene glycol
Polyethers such as monoether, polypropylene glycol diether, or copolymers of these polyethers such as poly(oxyethylene/oxypropylene) glycol, poly(oxyethylene/oxypropylene) glycol monoether, or Poly(oxyethylene/oxypropylene) glycol diether, condensates of these polyoxyalkylenes and ethylenecyamine, phosphoric acid esters, saturated fatty acids, aromatic esters, etc. can be used.

An alkali metal or alkaline earth metal salt or a protonic acid can be used to form a complex with these polymer compounds. Examples of anions include halogen ions, perchlorate ions, thiocyanate ions, trifluoromethanesulfonate ions, and borofluoride ions. Sodium fluoride (LiF), sodium iodide (N
al), lithium iodide (LH), lithium perchlorate (LiCi, 04), sodium thiocyanate (NaSCN), lithium trifluoromethanesulfonate (LiCFiSOz), lithium borofluoride (LiB)
F4), lithium hexafluorophosphate (LiPFi)
, phosphoric acid (l(, POshima), sulfuric acid ()I!5O4)
, ) litzated methanesulfonic acid, tetrafluorinated ethylene sulfonic acid (CzFm(SOJ:h)), hexafluorinated butanesulfonic acid (C4h(SOri4)), and the like.

Particularly preferred ionic conductors are complexes of polymers of ethylene oxide and propylene oxide, each alone or in combination, and an alkali metal or alkaline earth metal salt or a protonic acid. As a complex, ethylene oxide,
For example, propylene oxide has the chemical formula CH1+0CzHa
-+r-f-OC3H8→, m-0~1 at 0Ctls
0. It is a polyether with a molecular weight of 1 to 8, and is particularly excellent as a solvent for forming ionic conductors.In addition, the smaller the molecular weight, the better the fluidity, so it is possible to improve the ionic conductivity. A molecular weight in the range of 150 to 500 is preferred because if it is too small, it will be difficult to immobilize it in the pores.

The method for producing the electrolyte thin film of the present invention is as follows: (i) An ionic conductor in solution form, an ionic conductor dissolved in a solvent, or an ionic conductor finely dispersed in a solvent in the form of a sol or gel is prepared using a porous solid polymer. 1. In the manufacturing process of porous thin films, solutions of ionic conductors or their sol or gel molecules are impregnated into porous thin films, or the solvent is removed after coating or spraying. After mixing the solution! ! (2) Impregnating, coating or spraying a solid polymer porous thin film with an ionic conductor monomer or soluble precursor, and then reacting within the pores.

In the impregnation, coating, or spraying method, the solid polymer porous material of the present invention has an average through-pore diameter of 0.1 to 0.7 tna, and a solution having a contact angle of 90° or less is taken into the pores by capillary condensation action. It is an application of properties.

Therefore, it can be widely applied to systems in which the contact angle of the solution to the solid polymer is 90° or less, preferably 60' or less, without surface modification treatment. Assuming that the surface tension of the ionic conductor dissolved in the solvent is T, the contact angle with respect to the solid polymer is θ, and the hole is a cylindrical capillary with a radius R, a solution of the ionic conductor is condensed in the capillary, Holding force ΔP
It can be approximated by a pigeon. Therefore, in order to fill the pores with an ionic conductor, it is important that the contact angle is 90" or less and that the porous membrane has a small pore diameter as shown in the present invention. For example, the pore diameter can be changed from 1 jM to 0. By lowering the value to .1-, ΔP increases by one order of magnitude.

The surface tension of organic compounds used as solvents is lower than that of water or alkali metal salts. For example, in air at 20°C, acetonitrile at 20 dyne/cm, methylene chloride at 28
dyne/c1n, benzene 29 dyne/cm, and ethylene glycol, diethylene glycol, and triethylene glycol 44 to 46 dyne/c.
It is m.

Although the surface tension generally tends to increase by adding an alkali metal or alkaline earth metal salt or a protic acid, the effect of increasing ΔP is relatively small. Control of the contact angle is also important in order to fill a porous polymer with a solution of an ionic conductor by impregnation, coating, or spraying by capillary condensation. A contact angle of 90° or less can be achieved by selecting a solvent or by treating the surface of the porous polymer.
Formamide: 77°, glycerin: 79°.

Furthermore, when using a polyolefin porous membrane as an example of surface treatment of a porous polymer membrane, it may be subjected to immersion treatment with alcohol or acrylic acid, or plasma treatment, or graft polymerization (especially Kaisho 61-106
640), it is possible to control the wetting characteristics of the solution used.

Among the methods for producing the three-electrolyte membrane of the present invention, impregnation, coating, and spraying methods are particularly preferred because they are simple and can yield a homogeneous thin film. An example in which an alkali metal salt and polyethylene glycol are used as the ionic conductor will be explained below.

The alkali metal salt and polyethylene glycol can be filled into the pores of the polymer membrane by preparing a homogeneous solution and then impregnating, coating or spraying the solution. The alkali metal salt and polyethylene glycol are dissolved in a solvent such as dichloromethane, methanol, water, acetonitrile, acetone, chloroform methyl ethyl ketone, etc., and then mixed, or
Alternatively, the alkali metal salt is directly dissolved in a solution of low molecular weight polyethylene glycol to form a homogeneous solution.

The impregnation method involves immersing a porous polymer membrane in the solution, replacing the remaining air in the porous membrane with the solution by ultrasonic cavitation or vacuum degassing, removing excess solution, and then air drying the solvent as necessary. Or remove by heating. In the coating or spraying method, the porous membrane is placed on a filter cloth, filter paper, filter, etc., the solution is coated or sprayed, and then dried under reduced pressure or in the air.
The solvent is removed by heating or other operations.

Furthermore, in the present invention, one of the noteworthy features is that the ionic conductor filled into the pores of the porous membrane may be in a solid state or a liquid state. Polyethylene glycols having a molecular weight of 500 or less and their complexes with alkali metal salts can remain liquid at room temperature. Further, many of polyethylene oxide, polypropylene oxide, and copolymers thereof having monool, diol, and polyol structures are liquid polyethers. These liquid polymers such as liquid polyethers and their alkali metal or alkaline earth metal salts or complexes of protonic acids are produced by applying capillary condensation force into the pores of the solid polymer porous membrane of the present invention. and immobilize it,
A substantially solid TN membrane electrolyte can be embodied. In order to prepare an immobilized liquid electrolyte membrane, the surface tension of the liquid and the contact angle between the liquid and the solid polymer porous membrane are important.
-cm-' or less, preferably 45 dyne" Cm-
' and the contact angle at 20°C is 60'' or less, preferably 70° or less.

Applications of the electrolyte thin film of the present invention include secondary batteries, secondary batteries, electrochromic devices, large capacity capacitors, sensors, etc. In these electrochemical processes, the electrical energy consumed and the energy generated are largely related to ohmic loss due to the electrical resistance of the electrolyte, so an electrolyte membrane with low resistance is required. The resistance of the membrane is expressed by the following equation.

R-to-1/A Here, l is the film thickness (Cm), A is the cross-sectional area (cff
l) K is a proportionality constant, and the length of the minus side indicates the electrical resistance of a cube of unit length, generally one film m, and is called specific resistance (Ω·d). A practical characteristic value is expressed as an effective resistance R' (Ω·cffl), which is a resistance value per unit area of the film.

R'-A-R--42 The effective resistance of a conductive thin film is determined by the resistivity and film thickness as shown in the above equation, but is also influenced by temperature and coexisting substances. From a practical point of view, it is necessary that the R' value at room temperature be low, and even if a large area ratio is possible, for example, t,
It is desirable that it be less than oooΩ·d.

〔Example〕

A polypropylene porous membrane with a film thickness of 25 Ina, an effective radius of 0.14 m, and a porosity of 45% (commercially available Duraguard 2500)
A solution with a surface tension of 33.2 dyne-cm-' obtained by dissolving 10-t% of lithium perchlorate in poly(oxyethylene/oxypropylene) glycol monoether with an average molecular weight of 240 was added to the pores of @). It was fixed by an impregnation method, and the specific conductivity at room temperature (24°C) was measured.

Urajo base = main film thickness 6! ! m, average pore diameter 0.10-1, porosity 2% (Example 2), and membrane thickness 10-1, average pore diameter 0.44, porosity 10% (Example 3). Lithium perchlorate 1 for dimethoxypolyethylene oxide with an average molecular weight of 240 in the pores of the bore (■)
The surface tension obtained by dissolving 1-t% is 37.8 dyne.
A solution of -cln-' was immobilized by immersion at room temperature (
The specific conductivity was measured at 24°C.

Polypropylene porous membrane with a five-layer membrane thickness of 25n, effective radius of 0.072m, and porosity of 38% (commercially available Duraguard 2400@)
An immobilized liquid film similar to that in the example was obtained and its specific conductivity was measured.

The pores of the porous membrane of Comparative Example 1 were impregnated with a solution of 13-t% lithium perchlorate dissolved in polyethylene glycol with an average molecular weight of 400 and had a surface tension of 46.5 dyne-cm-', followed by vacuum desorption. I felt it, but I couldn't get it fixed. Porous membrane and related? The contact angle with the liquid was 61.2°.

Although the main film thickness of the stop plate was 104 mm, the average pore diameter was 0.80 marks, and the porosity was 15%, it could not be fixed even though it was degassed.

Table 1 summarizes the results.

Table 1 Example 1 Example 2 Example 3 Comparative example 1 Comparative example 2 Comparative example 3 25 0.4X0.04 0.14 6 0.10 10 0.40 25 0.2X0.02 0°0?2 25 0 0.2 , 8 61.2 Ah, 1 2.1X10-'4.2X10" 1.5X10-4 3.4X10-' Note) Average pore diameter is 0.4 Jll X O,04- means major axis 0
．． 4-1 means that the minor axis is 0.04-, and the effective radius is the radius determined by calculating the cross-sectional area of the hole assuming that the hole is rectangular and then assuming that the cross-section is a perfect circle.

〔Effect of the invention〕

According to the present invention, an electrolytic film is produced by filling an ionic conductor into a solid polymer permeable thin film having an average through-pore diameter of more than 0.1 and less than or equal to 0.7. A flexible, low-resistance electrolyte thin film with excellent mechanical strength and no leakage can be obtained.

Claims (2)

[Claims] 1. An electrolyte thin film comprising an ionic conductor filled in the pores of a solid polymer porous membrane having an average through-pore diameter of more than 0.1 μm and 0.7 μm or less. 2. The ionic conductor is made of a composite of a single or composite polymer of ethylene oxide and propylene oxide and an alkali metal or alkaline earth metal salt or protonic acid, and is a liquid with a surface tension of 45 dyne cm or less. The electrolyte thin film according to claim 1.