JPH04204522A - Electrolytic thin film - Google Patents

Abstract

PURPOSE:To obtain hgh ionic conductivity in an electrolytic thin film filling vacant holes of a solid high polymeric porous thin film with ionic conductive material, by treating the surface of the vacant holes of the electrolytic thin film by surfactants. CONSTITUTION:A perfluoroalkyl amine oxide of 5wt.% is dissolved into the mixed solvent of water and iso-propanol (mixing ratio of 4:1 in volume ratio), and a polyethylene fine porous film (25mum in thickness) is immersed into the obtained solution for two hours, and washed by pure water. The film is dried at 50 deg.C in vacuum, and a surface treated film is formed. The film is charged with the electrolytic liquid which is formed by dissolving LiClO4 into the mixed solution of polypropylene carbonate and dimethoxy ethane (mixing ratio of 1:1 in volume ratio) and obtaining a concentration of 1mol/l. The ionic conductivity of this film is 3.2X10<-3>OMEGA<-1>cm<-1>. Since the surface of the vacant hole on the solid high polymeric porous thin film is treated by surfactants, the mobility of the ionic conductive body for charge is improved, and the ionic conductivity of the electrolytic thin film is improved, and the electrolytic liquid charge is facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrolyte thin film, and more particularly to an electrolyte thin film formed by filling the pores of a solid polymer porous thin film with an ionic conductor. 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]

The present applicant has previously disclosed an electrolyte thin film formed by filling the pores of a solid polymer porous membrane with an ionic conductor (Japanese Unexamined Patent Publication No. 1-158051).

[Problem to be solved by the invention]

Although the electrolyte thin film described above has the properties of a solid when handled, it also has a much higher conductivity than a solid polymer electrolyte membrane, and its effectiveness is extremely wide and high.

However, even in this electrolyte thin film, higher ionic conductivity may be desired depending on the application or in the combination of the same porous solid polymer membrane and an ionic conductor. In some cases, filling was difficult.

Therefore, the present invention aims to solve such problems.

[Means to solve the problem]

In order to solve the above problems, the present invention provides an electrolyte thin film formed by filling the pores of a porous solid polymer thin film with an ionic conductor, in which the surface of the pores of the porous solid polymer thin film contains a surfactant. It is characterized by being processed.

The solid polymer porous thin film used in the present invention is not limited to, but has a thickness of 0.1p to 50p, a porosity of 40% to 90%, and a breaking strength of 200kg/cut or more;
Those having an average through-hole diameter of O.0OIJ- to 0.7p are preferably used.

The thickness of the thin film is generally 0.1 to 50 m, preferably 0.1 to 25 m. If the thickness is less than 0.1, it is difficult to put it to practical use because of the reduced mechanical strength as a support film and the ease of handling. On the other hand, if the number of houses exceeds 50, it is not preferable from the viewpoint of keeping the effective resistance low. The porosity of the porous thin film is preferably in the range of 40% to 90%, preferably in the range of 60% to 90%. If the porosity is less than 40%, the ionic conductivity as an electrolyte will be insufficient, while if it exceeds 90%, the functional strength as a support membrane will be low, making it difficult to put it into practical use.

The average diameter of the through-holes is generally 0.5mm, as long as the ionic conductor can be immobilized in the pores. It is on the OOC~0.7 side. The preferred average through-hole diameter depends on the material of the polymer membrane and the shape of the pores. The breaking strength of polymer membranes is generally 200kg/c++
I or more, preferably 500kg/Cn! Having the above properties makes it suitable for practical use as a support membrane.

The porous thin film used in the present invention functions as a support for the ion conductor as described above, and is made of a polymeric material with excellent mechanical strength.

From the viewpoint of chemical stability, for example, polyolefin, polytetrafluoroethylene, polyhynylidene fluoride can be used, but from the viewpoint of the design of the porous structure of the present invention and the ease of achieving both thin film thickness and mechanical strength, suitable materials are used. One example of a polymeric material is a polyolefin, especially one with a weight average molecular weight of 5 x 105 or more. That is, a crystalline linear polyolefin, which is an olefin homopolymer or copolymer, and whose weight average molecular weight is 5 x 105 or more, preferably 1 x 1
06 to 1×107. Examples include polyethylene, polypropylene, ethylene-propylene copolymer, polybutene-1, poly-4-methylpentene-1, and the like. Among these, the weight average molecular weight is 5 x 105
The above polyethylene or polypropylene is preferred.

The weight average molecular weight of the polyolefin influences the mechanical strength of the resulting permeable membrane. Ultra-high molecular weight polyolefins are
Ultra-stretching enables the formation of ultra-thin and high-strength films, which can be used as supports for highly ionic conductive thin films with low effective resistance. Although a polyolefin having a weight average molecular weight of less than 5 x 10 5 can be used at the same time, an ultra-thin and high strength film cannot be obtained by ultra-stretching in a system that does not contain a polyolefin having a weight average molecular weight of 5 x 10 5 or more.

The porous thin film as described above can be manufactured by the following method. Ultra-high molecular weight polyolefin is heated and dissolved in a solvent such as liquid paraffin in an amount of 1% to 15% by weight to form a uniform solution. A sheet is formed from this solution and rapidly cooled to form a gel-like sheet. The amount of solvent contained in this gel-like sheet is extracted with a volatile solvent such as methylene chloride.
0% to 90% by weight. This gel-like sheet is heated at a temperature below the melting point of the polyolefin and stretched to an areal magnification of 10 times or more. The solvent contained in this stretched film is extracted and removed with a volatile solvent such as methylene chloride, and then dried.

Another example of a suitable polymeric material is polycarbonate, in which the solid polymer porous thin film is made by irradiating the polycarbonate thin film with charged particles in a nuclear reactor and etching the tracks of the charged particles with alkali to form pores. It can also be produced by a method of forming. Such membranes are coated with polycarbonate and polyester products, for example as Nuclepore membranes.

In addition, polyester, polymethacrylate, polyacetal, polyvinylidene chloride, tetrafluoropolyethylene, etc. can be used.

The present invention is characterized in that the pore surface of such a solid polymer porous thin film is treated with a surfactant. Methods for treating the surface of the pores with a surfactant include: (1) kneading a surfactant during the production of a porous thin film, (2) treating the inner surface of the pores with a surfactant after thin film production, etc. can.

As the surfactant, nonionic surfactants can be preferably used, although there are no limitations, such as sorbitonohepentaerythritonopeglycerin, glycols, fatty acid esters of higher fatty acids or alkylene oxides, and perfluoroalkylamine oxides. etc. can be mentioned.

Treatment with such a surfactant increases the surface activity of the pore surface of the solid polymer porous thin film, improves wetting by the electrolyte, and improves the mobility of the electrolyte. There are effects such as ease of use of solvents that were difficult to fill in the past.

The ionic conductor used in the present invention is a composite of an alkali metal salt or protonic acid and a polar polymer such as polyether, polyester, or polyimine, or a network or crosslinked polymer containing these polymers as segments. Complexes with molecules can also be used. Polyether solvents such as polyethylene glycol, polypropylene glycol, or copolymers thereof are commercially available in liquid and powder forms with different molecular weights and degrees of polymerization.
It can be used easily. That is, polyethylene glycol, polyethylene glycol φ monoether, polyethylene glycol dietenopepolypropylene glycol, polypropylene glycol monoether,
Polyethers such as polypropylene glycol diether, or copolymers of these polyethers such as poly(oxyethylene/oxypropylene) glyconepoly (oxyethylene/oxypropylene) glycol monoether, or poly(oxyethylene/oxypropylene) glycol monoether;
(oxypropylene) glycol, dietenope, condensates of these polyoxyalkylenes and ethylenediamine, phosphoric acid esters, saturated fatty acids, aromatic esters, etc. can be used. Furthermore, copolymers of polyethylene glycol and dialkyl siloxane (for example, Naruse et al., Polymer Preprints, Japan
n Vol, 34. No, 7. 2021-202
4 (1985) and JP-A-60-217263), copolymers of polyethylene glycol and maleic anhydride (e.g. C, C, Lee et al., Polymer,
1982. Vow.

23 May 681-689), and copolymers of monomethyl ether of polyethylene glycol and methacrylic acid, e.g., N., Kobayashi et al., J.
Physical Chem-istry, Vol.
89. No. 6.987-9901985)) are known to form complexes with alkali metal ions and have ionic conductivities of 10-5 to 10'S-cm-' at room temperature, and this study It is suitable as a material constituting a thin film electrolyte useful in the invention.

The above-mentioned polyethers may have a low molecular weight of 150 or more, and the above-mentioned polymers include propylene carbonate, T-butyrolactone, ethylene carbonate, methylfuran, dimethoxyethane, dioxolane, tetrahydrofuran, acetonitrile, dimethylformamide, One or more solvents such as dimethylsulfoxide, methyltetrahydrofuran, sulfolane, methylthiophene, methylthiazole, and ethoxymethoxyethane may be added.

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. Lithium fluoride (LiF), sodium iodide (
NaI), lithium iodide (LiI), lithium perchlorate (L+Cj204), sodium thiocyanate (
NaSCN),) Lithium methanesulfonate (LiCF3SO3), Lithium borofluoride (LIBF)
4) Lithium hexafluorophosphate (LIPF6)
, phosphoric acid (■3P03), sulfuric acid (H2SO,) , ) litzated methanesulfonic acid, tetrafluorinated ethylene sulfonic acid [:C2F, (SO31t)2 ), hexafluorinated butanesulfonic acid [C4F6 (SO311)4 ],
Specific examples include:

As a method of filling ionic conductors into a polymer thin film,
■Remove the solvent after immersing, coating or spraying an ionic conductor dissolved in a solvent, or an ionic conductor finely dispersed in a solvent in the form of a sol or gel, into a solid polymer porous thin film; ■In the manufacturing process of porous thin films, a film is formed after mixing a solution of an ionic conductor or its sol or gel-like dispersion solution. ■A monomer or soluble precursor of an ionic conductor is made into a solid polymer porous thin film. Or immerse it in
A method such as applying or spraying and then reacting within the pores can be used.

〔Example〕

Example 1 Water and Improper Tool mixed solvent (mixing ratio 4:1 volume ratio)
A microporous polyethylene membrane (25R1 thickness) was immersed in a solution containing 5% by weight of perfluoroalkylamine oxide for 2 hours, and then washed with pure water. The same litter was dried at 50° C. in vacuum to obtain a surface-treated film. For the same litter, dissolve LiCβ04 in a mixed solution of propylene carbonate and dimethoxyethane (mixing ratio 1:1 volume ratio) and obtain 1 moR/f! It was filled with an electrolyte solution with a certain concentration.

The ionic conductivity of this membrane is 3.2 x 40-3Ω-1cm
'-1.

Comparative Example The ionic conductivity of a membrane that was not surface-treated by the method of Example 1 was 6. OXl0-'Ω-1 cm l.

Example 2 1i Ethylene oxide adduct of perfluoroalkylamine (C8H,7SO2NF-C112-
A polyethylene microporous membrane surface-treated with (CH20), lI) was filled with an electrolytic solution in which L+PFs was dissolved in a mixed solution of ethylene carbonate and dimethoxyethane (mixing ratio 7:3 by volume) to a concentration of 1 moff/l. . The ionic conductivity of this membrane was 1.9 Xl0-3Ω-1cm-1.

Comparative Example 2 A membrane that was not surface-treated by the method of Example 2 could not be filled with an electrolyte.

〔Effect of the invention〕

According to the present invention, by treating the surface of the pores of the solid polymer porous thin film with a surfactant, the mobility of the filled ionic conductor is improved, and the ionic conductivity of the electrolyte thin film is improved. There are effects such as facilitating the filling of the electrolytic solution, which was difficult to fill in the past.

Claims (2)

[Claims] 1. An electrolyte thin film formed by filling the pores of a solid polymer porous thin film with an ionic conductor, characterized in that the pore surface of the solid polymer porous thin film is treated with a surfactant. . 2. The electrolyte thin film according to claim 1, wherein the solid polymer porous thin film is a polyolefin.