HK1124625B - Solid electrolyte with high ion-conductivity and method for manufacturing the same, and electrochemical system using solid electrolyte - Google Patents

Description

High ion conductivity solid electrolyte, method of preparing the same and electrochemical system using the same

Technical Field

The present invention relates to a high ion-conductive solid electrolyte, which is a high ion-conductive solid electrolyte such as protons (hydrogen ions) or hydroxide ions, and which is particularly inexpensive, exhibits high conductivity despite being alkaline, and is capable of stably maintaining high conductivity because of little elution of a compound that acts as a conductivity even in a wet state, a method for producing the same, and a fuel cell and other electrochemical systems using the same.

Background

As an electrochemical system using a proton conductive solid electrolyte, an electrolytic device such as a fuel cell, a dehumidifier, or an electrolytic hydrogen generator has been put to practical use, and in particular, the application of a proton conductive solid electrolyte that operates at room temperature is widely involved. For example, a polymer electrolyte fuel cell obtains electric energy by flowing an electric current through an electrochemical oxidation reaction of hydrogen supplied to a negative electrode as represented by the following formula (1), an electrochemical reduction reaction of oxygen supplied to a positive electrode as represented by formula (2), and a reaction caused by proton transfer in an electrolyte therebetween.

H₂→2H⁺+2e^- ............(1)

1/2O₂+2H⁺+2e^-→H₂O .........(2)

There are also fuel cells using a substance other than hydrogen as a fuel, such as a direct methanol fuel cell in which the fuel supplied to the anode is methanol, but even in this case, the reaction in which the fuel is electrochemically oxidized at the anode to release protons proceeds in the same manner, and the fuel cell can be operated by a proton-conductive solid electrolyte.

As the electrolytic device, for example, an electrolytic hydrogen generator has been put to practical use. This electrolytic hydrogen generator generates hydrogen gas by a reaction reverse to the reaction of the above-described formulas (1) and (2) in the fuel cell, and has an advantage that a hydrogen gas tank is not required because high-purity hydrogen can be obtained on site only by water and electricity. Further, by using the solid electrolyte, electrolysis can be easily performed by introducing only pure water containing no electrolyte. In the field of paper making, it is also attempted to produce hydrogen peroxide for bleaching on site by the same system by electrolytic method using the following formula (3) (see non-patent document 1).

O₂+H₂O+2e^-→HO₂ ^-+OH^- ...............(3)

The dehumidifier is configured to sandwich a proton conductive solid electrolyte between positive and negative electrodes, and when a voltage is applied between the positive and negative electrodes, water is decomposed into oxygen and protons at the positive electrode by the following reaction of formula (4), and the protons that have moved to the negative electrode via the solid electrolyte are combined with oxygen in the air again by the reaction of formula (5) to form water, and as a result of these reactions, water moves from the positive electrode side to the negative electrode side, thereby dehumidifying at the positive electrode side.

H₂O→1/2O₂+2H⁺+2e^- .....................(4)

1/2O₂+2H⁺+2e^-→H₂O .....................(5)

An air conditioner that is combined with a moisture evaporation type air cooler and that can decompose and dehumidify water using the same operation principle as that of an electrolysis type hydrogen generator has also been proposed (see non-patent document 2).

Further, various sensors, electrochromic devices, and the like are systems based on the same operation principle as described above, and operate by the movement of protons in the electrolytes between 2 different redox pairs of the positive electrode and the negative electrode, and therefore, proton-conductive solid electrolytes can be used. Currently, confirmatory studies of these systems using proton-conductive solid electrolytes are also underway.

The hydrogen sensor can use, for example, the change in electrode potential due to the hydrogen concentration when hydrogen gas is introduced in the reaction of the above-described formula (4) or formula (5). Also, the use of a change in electrode potential or a change in ionic conductivity can also be applied in a humidity sensor.

Electrochromic devices using, for example, WO at the negative electrode₃And the principle of color development by the reaction of the following formula (6) when an electric field is applied, and the application to a display device or a light-shielding glass can be considered. This system also operates by the transfer of protons to and from the negative electrode, and can utilize a proton-conductive solid electrolyte.

WO₃+xH⁺+xe^-→HxWO₃(color generation)... (6)

Further, as an electrochemical system which operates by using a proton conductive solid electrolyte in principle, there are a primary battery, a secondary battery, an optical switch, an apparatus for producing electrolyzed water, and the like. A nickel-metal hydride battery, which is an example of a secondary battery, uses a hydrogen storage alloy for the negative electrode, nickel hydroxide for the positive electrode, and an alkaline electrolyte for the electrolyte, and electrochemical redox of protons and occlusion of hydrogen gas into the hydrogen storage alloy occur in the negative electrode during charge and discharge as shown in the following formulas (7) and (8).

[ Charge ] H₂O+e^-→ H (occlusion) + OH^- ......(7)

[ discharge ] H (occlusion) + OH^-→H₂O+e^- ......(8)

An electrochemical redox reaction of nickel hydroxide represented by the following formulae (9) and (10) occurs in the positive electrode.

[ Charge ] Ni (OH)₂+OH^-→NiOOH+H₂O+e^- ...(9)

[ discharge ] NiOOH + H₂O+e^-→Ni(OH)₂+OH^- ...(10)

The charge-discharge reaction of the battery is established by the movement of protons or hydroxide ions in the electrolyte, and a proton-conductive solid electrolyte may be used in principle, but not a solid electrolyte but an alkaline electrolyte has been used.

For example, a technique of using yttrium in the negative electrode has been proposed as an optical switch (see non-patent document 3). When an electric field is applied, yttrium is hydrogenated as in the following formula (11) to transmit light, and thus transmission and non-transmission can be switched by the electric field. In principle, this system can also use a proton-conducting solid electrolyte, but an alkaline electrolyte has been generally used.

Y+3/2H₂O+3e→YH₃+3OH ...............(11)

The electrolyzed water is water subjected to an electrolytic reaction, has different functions on the reduction side and the oxidation side, has an effect of being beneficial to health, an effect of sterilizing, an effect of washing, and an effect of promoting growth of crops, and has various uses such as drinking water, water for food, washing water, and water for agriculture. The electrolytic reaction is promoted because water contains an electrolyte, but if the electrolyte is dissolved in water, the electrolyte may need to be removed during use. When a solid electrolyte is used, the man-hour for removing the electrolyte is not required.

In many of the electrochemical systems that have been put into practical use such as the fuel cell, the electrolyzer, and the dehumidifier, a perfluorosulfonic acid electrolyte membrane sold by dupont under the trade name Nafion is used as the solid electrolyte. Further, the present applicant has proposed a solid electrolyte containing an inorganic/organic composite compound of a zirconic acid compound and polyvinyl alcohol (refer to patent documents 1 and 2). A main application of these solid electrolytes is a casting method in which a raw material aqueous solution is generally cast on a flat plate and water in a solvent is evaporated by heating to form a film (patent document 3). These composite compounds can be produced by neutralizing a zirconium salt or zirconyl salt (オキシジルコニウム salt) with an alkali in the presence of polyvinyl alcohol, and exhibit high proton (hydroxide ion) conductivity by impregnation with an alkali such as sodium hydroxide, sodium silicate, or sodium carbonate.

The applicant proposed a method for better producing these solid electrolytes by the following steps: a step of heating a solution in which a water-containing solvent, polyvinyl alcohol, and a zirconium salt or zirconyl salt coexist to 50 ℃ or higher at a pH of 7 or less to hydrolyze the zirconium salt or zirconyl salt, removing the solvent, and then contacting the hydrolyzed solution with an alkali (patent document 4).

On the other hand, as a substance capable of functioning as a hydroxide ion conductive substance, there are anion exchange membranes which have been conventionally used, and for example, an anion exchange membrane as an electrolyte for a fuel cell (patent document 5) or an anion exchange membrane to which an inorganic filler has been added (patent document 6) has been proposed. Further, an electrolyte composition containing a polymer matrix containing a nitrogen-containing organic compound and a metal hydroxide (patent document 7), or a general polymer solid electrolyte membrane containing inorganic fine particles, an electrolyte salt and a polymer, particularly not a so-called hydroxide ion conductive substance (patent document 8), is also disclosed.

Patent document 1: japanese patent laid-open No. 2003-242832

Patent document 2: japanese patent laid-open publication No. 2004-146208

Patent document 3: japanese patent laid-open publication No. 2004-285458

Patent document 4: japanese Special application No. 2007-84374

Patent document 5: japanese patent laid-open No. 2000-331693

Patent document 6: japanese patent laid-open publication No. 2004-217921

Patent document 7: japanese laid-open patent publication No. 2002-

Patent document 8: japanese patent laid-open publication No. 2004-339422

Non-patent document 1: electrochemistry 69, No3, 154-

Non-patent document 2: the Chinese congress lecture paper of the electrochemical society of 12 years, P3373(2000)

Non-patent document 3: J.electrochem.Soc., Vol.143, No.10, 3348-3353(1996)

Disclosure of Invention

However, the above-mentioned perfluorosulfonic acid electrolyte membrane has a problem of high price mainly due to the complexity of the production process. Moreover, there are difficulties: since the perfluorosulfonic acid electrolyte membrane is a strong acid, the materials that can be used as the electrode and other constituent materials of the system are limited to acid-resistant materials such as noble metals, and it is difficult to reduce the cost of the entire system. In addition, in some applications such as primary batteries and secondary batteries, an electrode active material cannot be stably present or does not function unless it is in an alkali, and therefore, there is a problem that an acidic solid electrolyte cannot be used.

On the other hand, the solid electrolyte containing an inorganic/organic composite compound of a zirconic acid compound and a polyvinyl alcohol described in patent documents 1, 2, and 4 proposed by the present applicant is a solid electrolyte that can remarkably improve water resistance, heat resistance, oxidation resistance, and alkali resistance by complexing inexpensive polyvinyl alcohol with a zirconic acid compound at a molecular level by the above-mentioned simple method, and can obtain a high performance although it is low in price. Further, according to patent document 4, the concentration of the raw material solution of the solid electrolyte can be maintained at a predetermined concentration to allow efficient film formation, and gelation of the raw material solution can be prevented.

These solid electrolytes are alkaline-type, but also function, and can be applied to applications using an alkali such as a primary battery and a secondary battery, and the electrodes and peripheral members thereof do not necessarily need to be expensive materials such as noble metals, and therefore contribute to cost reduction of the entire system. Further, since polyvinyl alcohol having the highest gas-shielding property among polymers is further compounded with a dense inorganic oxide, it is possible to realize an extremely high shielding property against the permeation of a substance as the whole solid electrolyte, and it is highly advantageous in applications requiring a high shielding property against the permeation of a substance, such as a fuel cell.

However, these solid electrolytes have a disadvantage that a sufficiently high conductivity is obtained after impregnation and absorption of the alkali component, and the alkali component is not sufficiently stably fixed and immobilized in the solid electrolyte. For example, when the electrolyte is used in a system such as a fuel cell which is used in a high humidity environment and in which the generated water is discharged to the outside of the system, the absorbed alkaline component may be dissolved in water and discharged, and there is a problem that the concentration of the alkaline component in the electrolyte gradually decreases and the conductivity decreases. Although the conductivity can be maintained by constantly supplying the discharged alkali component, the system becomes complicated.

On the other hand, all anion exchange membranes are produced by adding a nitrogen-containing organic compound such as a quaternary ammonium salt to an organic polymer serving as a skeleton, and making the organic polymer basic to generate hydroxide ion conductivity. The nitrogen moiety having hydroxide ion conductivity in these compounds is bound to the polymer which becomes the skeleton, and thereby fixed. Therefore, they do not flow out of the ion exchange membrane. However, unlike the above-mentioned materials, a general anion exchange membrane is not a complex compound with an inorganic oxide at a molecular level but a material based on a general organic polymer, and therefore has a limit in acid resistance and oxidation resistance. In order to improve chemical stability, for example, if a fluorine-based polymer is used in the skeleton, the price is increased. Further, if an organic polymer is used as a skeleton material, high shielding properties against permeation of a substance, such as the above inorganic/organic composite compound electrolyte, cannot be obtained in terms of compactness.

For example, the anion exchange membrane disclosed in patent document 5 uses a fluorine-based polymer as a skeleton polymer, and is chemically very stable, but is more expensive than the inorganic/organic composite compound electrolyte. Further, since denseness as in the case of an inorganic/organic composite compound electrolyte cannot be obtained, high shielding property against permeation of a substance cannot be obtained. The anion exchange membrane containing an inorganic filler disclosed in patent document 6 can be prepared by physically mixing an inorganic substance with a polymer that has been conventionally used as an anion exchange membrane to prepare a composite, but since the polymer has low compatibility with the inorganic substance and is difficult to be composited at the molecular level only by physical mixing, it is difficult to improve the performances relating to the properties at the molecular level, such as heat resistance and oxidation resistance.

Patent document 7 also discloses a simple mixture of a nitrogen-containing organic polymer having anion exchange ability, such as polydiallyldimethylammonium salt, and a metal hydroxide as an inorganic substance, as in the case of these anion exchange membranes. Patent document 8 describes that (CH) having anion exchange ability is simply mixed (solid-dissolved) with a composite of inorganic fine particles such as an inorganic oxide and a polymer such as polyvinyl alcohol₃)₄NBF₄And a quaternary ammonium salt, but in this case, the quaternary ammonium salt is not fixed and a problem of elution occurs, as in the case of a solid electrolyte composed of a conventional inorganic/organic composite compound. There is no disclosure of any method for fixing the quaternary ammonium salt.

The present invention has been made to solve the above-mentioned problems of the high ion-conductive solid electrolyte, and an object of the present invention is to provide a low-cost, alkali-type, high-conductivity solid electrolyte which is capable of stably maintaining high conductivity because the outflow of a compound that exhibits high conductivity even in a wet state is small, a method for producing the same, and a fuel cell and other electrochemical systems using the same.

The present invention provides the following basic contents for achieving the above object: a high ion-conductive solid electrolyte containing a composite compound containing at least polyvinyl alcohol and a zirconic acid compound as constituent components and a nitrogen-containing organic compound having an amine, quaternary ammonium compound or imine structure; a high ion-conductive solid electrolyte containing a composite compound which comprises at least a polyvinyl alcohol and a zirconic acid compound as components and a nitrogen-containing organic compound having an amine, quaternary ammonium compound or imine structure, and which is obtained by hydrolyzing a zirconium salt or zirconyl salt in a raw material solution in which a water-containing solvent, a polyvinyl alcohol, a zirconium salt or zirconyl salt and a nitrogen-containing organic compound having an amine, quaternary ammonium compound or imine structure coexist, removing the solvent, and then contacting the resultant with an alkali; and a method for producing these high ion-conductive solid electrolytes. The hydrolysis reaction is carried out by heating to 50 ℃ or higher, or by heating to 50 ℃ or higher in a state where the pH is 7 or lower.

Further, the following configuration is provided: a raw material solution in which an aqueous solvent, polyvinyl alcohol, a zirconium salt or an oxyzirconium salt, and a nitrogen-containing organic compound having an amine, quaternary ammonium compound or imine structure coexist, the raw material solution containing a salt of at least one of an alkaline earth metal, aluminum, or a rare earth metal; in the step of contacting with a base, the base contains a hydroxide or an oxysalt of at least one of an alkaline earth metal, aluminum, silicon, boron, and tungsten.

Further, the following configuration is provided: the nitrogen-containing organic compound at least comprises polydiallyldimethylammonium salt or hydroxide thereof, or polyallylamine; the nitrogen-containing organic compound contains at least an imidazole ring; the nitrogen-containing organic compound contains at least polyvinylpyrrolidone; the weight ratio of the nitrogen-containing organic compound to the polyvinyl alcohol is 0.18 or more; and the composite compound contains at least one element selected from alkaline earth metals, aluminum, silicon, boron, rare earth elements, and tungsten.

As a method for producing these high ion-conductive solid electrolytes, the following methods are provided: a high ion-conductive solid electrolyte is obtained by hydrolyzing a zirconium salt or a zirconyl salt in a raw material solution in which a water-containing solvent, polyvinyl alcohol, a zirconium salt or a zirconyl salt, and a nitrogen-containing organic compound having an amine, quaternary ammonium compound, or imine structure coexist to obtain a composite compound solution, removing the solvent from the composite compound solution to obtain a composite compound, and then contacting the composite compound with an alkali. Further, a raw material solution in which a water-containing solvent, polyvinyl alcohol, a zirconium salt or zirconyl salt, and a nitrogen-containing organic compound having an amine, quaternary ammonium compound, or imine structure coexist is heated to 50 ℃ or higher in a state where the pH is 7 or lower to hydrolyze the zirconium salt or zirconyl salt in the raw material solution and cause a polycondensation reaction of the zirconic acid compound to obtain a composite compound solution, and then the solvent is removed from the composite compound solution to obtain a composite compound, and the composite compound is brought into contact with a base to obtain a high ion-conductive solid electrolyte.

Further, in the polycondensation reaction of the zirconic acid compound, a complex compound of polyvinyl alcohol and the zirconic acid compound is formed, and at the same time, the nitrogen-containing organic compound is complexed with the polyvinyl alcohol or the zirconic acid compound at a molecular level ( み in う) to be incorporated into the complex compound, thereby containing the nitrogen-containing organic compound; the raw material solution contains at least one salt of alkaline earth metal, aluminum or rare earth metal; or a hydroxide or an oxysalt containing at least one of an alkaline earth metal, aluminum, silicon, boron, or tungsten in the alkali in contact with the composite compound.

In addition, an electrochemical system using a high ion-conductive solid electrolyte, which is configured such that a plurality of electrodes separated by the solid electrolyte are disposed in the high ion-conductive solid electrolyte, can be specifically provided as follows: a fuel cell, a steam pump, a dehumidifier, an air conditioner, an electrochromic device, an electrolysis-type hydrogen generator, an electrolytic hydrogen peroxide production device, an electrolytic water production device, a humidity sensor, a hydrogen sensor, a primary battery, a secondary battery, an optical switching system, or a battery system using a polyvalent metal.

According to the present invention, the complex compound containing at least polyvinyl alcohol and a zirconic acid compound as constituent components can impart hydroxide ion or proton conductivity by containing a nitrogen-containing organic compound having an amine, quaternary ammonium compound or imine structure. That is, when amines, which are derivatives of ammonia, are used as the nitrogen-containing organic compounds, they are coordinately bound to protons of water molecules to form cations, and dissociated hydroxide ions, which are counter ions, are generated, thereby having hydroxide ion conductivity. This conduction of hydroxide ions can be realized by a mechanism in which hydroxide ions abstract protons from adjacent water molecules when water molecules are present in the vicinity, and is actually considered to be proton conduction.

Further, when a quaternary ammonium hydroxide is used as the nitrogen-containing organic compound, the quaternary ammonium hydroxide has hydroxide ion conductivity or proton conductivity by the same mechanism as described above. Imines also have hydroxide ion or proton conductivity by the same mechanism as amines. When these nitrogen-containing organic compounds are, for example, polymers, they are not easily eluted due to complexation with the complex compound when they are introduced into the complex compound containing polyvinyl alcohol and a zirconic acid compound as constituent components. In addition, when the compound is a low molecular weight compound having a plurality of nitrogen moieties in the same molecule, such as imidazole, for example, a part of the nitrogen moieties is bonded to zirconium ions or zirconate ions in the complex compound, whereby the complex compound can be immobilized. Therefore, by containing the nitrogen-containing organic compound as in the present invention, unlike the conventional composite compound impregnated with sodium hydroxide, sodium silicate, and sodium carbonate, the cations are fixed in the composite compound, and therefore, the outflow together with the moisture is not easily caused.

The introduced nitrogen-containing organic compound is introduced into the composite compound containing at least polyvinyl alcohol and a zirconic acid compound as constituent components by complexing at the molecular level, whereby the problems of water resistance, heat resistance, oxidation resistance and alkali resistance of the compound itself are reduced, and water resistance, heat resistance, oxidation resistance and alkali resistance higher than those of conventional anion exchange membranes using the nitrogen-containing organic compound can be obtained. Further, as the characteristics of the composite compound, higher substance permeability blocking property than that of the anion-exchange membrane can be obtained.

As a method of containing the nitrogen-containing organic compound, it is only necessary to dissolve the nitrogen-containing organic compound in advance in a raw material solution of the complex compound, and the nitrogen-containing organic compound can be introduced into the complex compound extremely easily and at the same low cost as the conventional complex compound. That is, the nitrogen-containing organic compound generally has high solubility in water, and can be mixed with a composite compound material such as polyvinyl alcohol, a zirconium salt, or an zirconyl salt at a molecular level by mixing the compound material with a raw material solution containing water. When the reaction for forming the complex compound is carried out in this state, the nitrogen-containing organic compound automatically becomes a state of being complexed with the complex compound at a molecular level.

The solid electrolyte of the present invention has hydroxyl ion or proton conductivity, and can be used in a fuel cell, a steam pump, a dehumidifier, an air conditioner, an electrochromic device, an electrolysis-type hydrogen generator, an electrolytic hydrogen peroxide production device, an electrolytic water production device, a humidity sensor, a hydrogen sensor, a primary battery, a secondary battery, an optical switching system, a battery system using a polyvalent metal, or the like. Further, since the solid electrolyte of the present invention is of an alkaline type, unlike conventional acid-type solid electrolytes such as Nafion (trade name), it is possible to improve the corrosion resistance to metals, and therefore, it is not necessary to use expensive corrosion-resistant materials such as noble metals for peripheral members such as electrodes. The present invention can also be used in applications where the electrode active material cannot stably exist or function under acidic conditions, such as primary batteries, secondary batteries, optical switching systems, and battery systems using polyvalent metals.

Drawings

FIG. 1 shows the structural diagram of (A) an amine, (B) a quaternary ammonium compound, and (C) an imine, which are contained in the nitrogen-containing organic compound of the present invention.

Fig. 2 is a system diagram schematically showing a manufacturing process of the high ion-conductive solid electrolyte according to the present invention.

Detailed Description

The following describes specific embodiments of the high ion-conductive solid electrolyte of the present invention, a method for producing the same, and an electrochemical system using the same. The present invention is based on a high ion-conductive solid electrolyte containing a composite compound containing at least polyvinyl alcohol and a zirconic acid compound as constituent components and a nitrogen-containing organic compound having an amine, quaternary ammonium compound or imine structure.

The composite compound contained in the solid electrolyte of the present invention contains a zirconic acid compound as an essential component. The zirconic acid being ZrO₂Is a basic unit and contains H₂Compound of O of the formula ZrO₂·xH₂O represents, but the zirconic acid compound of the present invention means zirconic acid and derivatives thereof, or all compounds mainly composed of zirconic acid. Therefore, a part of other elements may be substituted within a range not to impair the characteristics of zirconic acid, and deviation from the stoichiometric composition or addition of additives may be also allowed. For example, zirconates, zirconium hydroxides and also ZrO₂Derivatives based on them, or compounds based on them, are also included in the zirconic acid compound as the basic unit.

The composite compound contained in the solid electrolyte of the present invention contains polyvinyl alcohol, which is an indispensable component, as a constituent component. The polyvinyl alcohol need not be a complete polyvinyl alcohol, and may be used as long as it functions as a polyvinyl alcohol in nature. For example, polyvinyl alcohol in which a part of the hydroxyl groups is substituted with other groups, or polyvinyl alcohol in which a part is copolymerized with other polymers may also function as polyvinyl alcohol. In addition, since the same effect can be obtained by using polyvinyl alcohol in the reaction process of the present invention, polyvinyl acetate or the like which is a raw material of polyvinyl alcohol can be used as a starting material.

Therefore, other polymers, for example, polyolefin polymers such as polyethylene and polypropylene, polyacrylic polymers, polyether polymers such as polyethylene oxide and polypropylene oxide, polyester polymers such as polyethylene terephthalate and polybutylene terephthalate, fluorine polymers such as polytetrafluoroethylene and polyvinylidene fluoride, sugar chain polymers such as methyl cellulose, polyvinyl acetate polymers, polystyrene polymers, polycarbonate polymers, epoxy resin polymers, and other organic and inorganic additives may be blended within the range where the effect of the polyvinyl alcohol of the present invention is sufficiently exhibited.

The polyvinyl alcohol and the zirconic acid compound of the present invention form a composite compound. That is, polyvinyl alcohol and a zirconic acid compound in the composite compound are complexed with each other at a molecular level, and the polyvinyl alcohol and the zirconic acid compound are firmly bonded to each other through hydrogen bonding and dehydration condensation via a hydroxyl group of the polyvinyl alcohol. The complex compound is a compound, which is distinguished from a mixture obtained by physically mixing polyvinyl alcohol and a zirconic acid compound. That is, unlike the mixture, the chemical properties of each constituent component in the composite compound are not necessarily maintained after the composite. For example, in the case of the present invention, polyvinyl alcohol which is a constituent component of the composite compound is water-soluble (hot water-soluble) by itself, but does not substantially dissolve in hot water after forming the composite compound with the zirconic acid compound. If the amount of zirconic acid relative to the amount of polyvinyl alcohol in the composite compound is too small, water resistance, heat resistance, oxidation resistance, alkali resistance, or strength cannot be obtained. In addition, when the amount of zirconic acid is too large, flexibility is impaired, and a problem arises in brittleness. Therefore, the weight ratio of the zirconic acid compound to the polyvinyl alcohol in the composite compound is preferably controlled to 0.01 to 1.

In the present invention, a composite compound containing at least polyvinyl alcohol and a zirconic acid compound as constituent components contains a nitrogen-containing organic compound having an amine, quaternary ammonium compound or imine structure. The nitrogen-containing organic compound having an amine, quaternary ammonium compound or imine structure is an organic compound having nitrogen-containing moieties in the molecule as shown in fig. 1(a), (B) and (C), respectively. In addition, amines are derivatives of ammonia, and are generally classified and named as primary amines, secondary amines, and tertiary amines according to structural differences as shown in fig. 1(a), but they all play a similar role in coordinating and binding with protons of water molecules to generate dissociated hydroxide ions, thereby having hydroxide ion conductivity. In order to more stably immobilize the nitrogen-containing organic compound in the composite oxide, the nitrogen-containing organic compound is preferably a polymer, and a polymer having an amino group such as polyallylamine, a polymer having a quaternary ammonium group such as polydiallyldimethylammonium salt and polyvinylbenzyltrimethylammonium salt, a polymer having a pyridine ring such as polyvinylpyridine and polyvinylmethylpyridine, a polymer having an imidazole ring such as polyvinylimidazole and polybenzimidazole, and other polyvinylpyrrolidone can be used. Among them, polydiallyldimethylammonium salts and polyallylamine are preferably used in view of ion conductivity. In addition, in order to suppress swelling of the solid electrolyte due to water absorption, polyvinylpyrrolidone is preferably used.

The low-molecular nitrogen-containing organic compound has good immobilization properties as long as it has a plurality of nitrogen moieties in the same molecule, and can be used. That is, when there are a plurality of nitrogen moieties, one nitrogen moiety may bind to zirconate ions, for example, while the other nitrogen moieties may function to conduct hydroxide ions. Examples of such compounds include imidazole.

The content of the nitrogen-containing organic compound is preferably 0.18 or more in terms of a weight ratio to the polyvinyl alcohol. If it is less than 0.18, high ion conductivity cannot be obtained. However, if the amount of the nitrogen-containing organic compound is too large, there arises a problem that the strength becomes weak, the oxidation resistance is lowered, and the water absorption of the whole solid electrolyte is increased to swell excessively, so that the content is preferably not more than 2 in terms of the weight ratio to the polyvinyl alcohol.

The composite compound of the present invention, which contains at least a polyvinyl alcohol and a zirconic acid compound as components and contains a nitrogen-containing organic compound having an amine, quaternary ammonium compound or imine structure, can be produced by the following steps: a solution containing a water-containing solvent, polyvinyl alcohol, a zirconate or zirconyl salt, and a nitrogen-containing organic compound, which are present together, is heated to 50 ℃ or higher in a pH of 7 or less to hydrolyze the zirconium salt or zirconyl salt, and then the solvent is removed and the solution is brought into contact with an alkali.

Fig. 2 is a system diagram schematically showing a production process of a composite compound. First, as raw materials, an aqueous solvent is prepared in step 1, polyvinyl alcohol is prepared in step 2, a zirconium salt or a zirconyl salt is prepared in step 3, and a nitrogen-containing organic compound is prepared in step 4, and these raw materials are mixed in step 5 to obtain a raw material solution in which polyvinyl alcohol, a zirconium salt or a zirconyl salt and a nitrogen-containing organic compound are co-present in an aqueous solvent. In order to evaporate water in the raw material solution within a practical time range during production and efficiently form a solid electrolyte membrane, the polyvinyl alcohol concentration of the raw material solution is preferably 5 wt% or more, and more preferably 10 wt% or more. The zirconium salt and the zirconyl salt may be any of those that can be dissolved in the aqueous solvent, and the ratio of oxygen to anions and the water content may be any values.

In addition, the present invention is carried out in a solvent in the presence of water, and therefore, it is not necessary to use a pure solvent of only water as long as water is present in the solvent. However, water is the most preferable solvent from the viewpoint of solubility of zirconium salt or zirconyl salt, or solubility of polyvinyl alcohol. Therefore, the aqueous solvent which is a constituent element of the present invention shown in step 1 may be any solvent which contains water and can coexist with water. Specifically, the solvent of the present invention may be present with water as long as the reaction can be carried out with a minimum amount of water that participates in the reaction even in the presence of other solvents, and the number of solvents that can coexist with water is not limited. That is, the solvent refers to all components in the raw material solution except the solutes of polyvinyl alcohol and zirconium salt, and since, for example, granulated sugar becomes a member of the solvent when dissolved, all substances that are considered to be liquid (including dissolved solids) that can coexist with water can actually be used as the solvent.

Next, in step 6, the raw material solution is heated to 50 ℃ or higher while maintaining the pH of 7 or lower. Thereby, the zirconium salt or zirconyl salt is hydrolyzed while the polycondensation of the zirconic acid compound occurs as shown in step 7. During the polycondensation reaction of the zirconic acid compound, complexation occurs at the molecular level between polyvinyl alcohol molecules coexisting in the raw material solution and the zirconic acid compound, and both are combined by hydrogen bonding or dehydration condensation via a hydroxyl group, to form a composite compound solution as shown in step 8. At this time, the nitrogen-containing organic compound dissolved in the raw material solution is also complexed with the polyvinyl alcohol or zirconic acid compound at a molecular level, and automatically enters the composite compound. When the pH of the raw material solution is more than 7, the hydrolysis of the zirconium salt and the subsequent condensation reaction of zirconic acid proceed vigorously, and gelation occurs when the polyvinyl alcohol concentration is high, and therefore the pH of the raw material solution is preferably 7 or less, and particularly preferably 2 or less.

If the heating temperature of the raw material solution is lower than 50 ℃, it is difficult to cause sufficient hydrolysis of the zirconium salt in a practical time frame in production. On the other hand, if the heating temperature is excessively increased to an extremely high temperature, hydrolysis of the zirconium salt and subsequent condensation reaction of zirconic acid excessively proceed, and gelation starts to occur, but in this case, the heating temperature is not particularly limited since the heating time can be controlled by adjusting the heating time. However, from the viewpoint of the need to raise and lower the temperature of the raw material solution in a uniform state, it is actually preferable that the temperature of the raw material solution is not more than about 80 ℃.

The heating time may be adjusted according to the selected heating temperature, but is preferably in the range of 20 minutes to 5 hours at 50 ℃. If the heating time is shorter than 20 minutes, the progress of hydrolysis of the zirconium salt becomes insufficient, and if it is longer than 5 hours, gelation may start. In addition, it is preferably from several minutes to about 30 minutes at 80 ℃.

Next, in step 9, the solvent is removed from the complex compound solution obtained in step 8, and the complex compound a to be a solid electrolyte shown in step 10 is formed. The compound A is not necessarily a completely hydrolyzed zirconium salt or zirconyl salt or a completely dehydrated and condensed zirconic acid compound. When the composite compound a is formed into a solid electrolyte without contacting with an alkali, only an incomplete solid electrolyte in which pores are opened when immersed in water can be obtained. Therefore, it is necessary to contact the complex compound a of step 10 obtained by volatilizing the solvent from the complex compound solution obtained in step 8 in step 9 and solidifying the complex compound solution with a base in step 11.

The alkali to be contacted with the composite compound a may be any alkali as long as it can neutralize the zirconium salt or the zirconyl salt, and ammonia, sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, strontium hydroxide, barium hydroxide, carbonate, or the like can be used. These may be used alone or in a mixture of two or more. Further, as a method of bringing the molded composite compound a into contact with an alkali, there are methods of dipping in an alkali solution, coating or spraying an alkali solution on the composite compound, or exposing to alkali vapor, and the like.

By contacting with an alkali in this manner, hydrolysis and dehydration condensation of the complex compound a are further promoted in step 12, and a stable alkali-type complex compound B (═ the high ion-conductive solid electrolyte of the present invention) is obtained in step 13. Further, the composite compound B is already formed into a solid when it comes into contact with the base, and therefore, the problem of gelation does not occur.

In the present invention, at least one element selected from the group consisting of an alkaline earth element, aluminum, silicon, boron, a rare earth element and tungsten may be introduced into a composite compound containing at least a polyvinyl alcohol and a zirconic acid compound as constituent components and a nitrogen-containing organic compound having an amine, quaternary ammonium compound or imine structure, but among these elements, the introduction of the alkaline earth metal element, aluminum and the rare earth element may be carried out by the following steps: a solution in which an aqueous solvent, polyvinyl alcohol, a zirconium salt or an zirconyl salt, and a nitrogen-containing organic compound having an amine, quaternary ammonium compound or imine structure coexist contains a salt of at least one of an alkaline earth metal, aluminum, and a rare earth metal. In this case, the salt of the alkaline earth metal, aluminum, and rare earth metal may be neutralized by finally contacting with an alkali, and introduced into the composite compound as an oxide or hydroxide, and for example, calcium chloride, strontium chloride, aluminum chloride, lanthanum chloride, yttrium chloride, or a hydrate thereof may be preferably used as the raw material.

In the step of contacting with an alkali in the above-mentioned production method, an alkaline earth metal element, aluminum, silicon, boron, or tungsten may be introduced into the composite compound by adding a hydroxide or an oxysalt containing at least one of an alkaline earth metal, aluminum, silicon, boron, and tungsten to the alkali, and calcium hydroxide, strontium hydroxide, aluminum hydroxide, sodium aluminate, sodium silicate, sodium borate, sodium tungstate, or a hydrate thereof may be used as a raw material.

The high ion-conductive solid electrolyte obtained by the present invention exhibits high proton or hydroxide ion conductivity of an alkaline type, and can be produced into an alkaline type, whereby relatively inexpensive materials such as nickel can be used as electrodes and other system constituent materials, and the cost of the entire system can be reduced.

Further, the alkaline type electrolyte can be applied to a primary battery and a secondary battery, and the possibility of liquid leakage can be eliminated by replacing the conventional alkaline electrolyte with the electrolyte material of the present invention. By using the alkaline solid electrolyte, a secondary battery which has been difficult to put into practical use in the past, for example, a high energy density battery using a polyvalent metal having a valence of 2 or more as a negative electrode can be put into practical use. Further, a nickel zinc battery using zinc oxide for the negative electrode and nickel hydroxide similar to the nickel hydrogen battery for the positive electrode is exemplified. As shown in the following formulas (12) and (13), in a nickel zinc battery, zinc oxide is reduced to metallic zinc during charging of a negative electrode, and conversely, zinc is electrochemically oxidized to zinc oxide during discharging.

[ charging]ZnO+H₂O+2e^-→Zn+2OH^- ......(12)

[ discharge of electric energy]Zn+2OH^-→ZnO+H₂O+2e^- ......(13)

The nickel zinc battery has a high energy storage density because zinc is divalent, but zinc oxide is easily dissolved in an alkaline electrolyte, zinc ions are eluted from an electrode, and the eluted zinc ions are reduced during charging, and at this time, needle-like metallic zinc (dendrite) is generated, which causes a problem that short circuit easily occurs when the zinc passes through a separator. Further, since zinc has a lower oxidation-reduction potential than hydrogen, zinc is easily oxidized by water to cause self-discharge when left in a charged state, and there is a problem that hydrogen is generated from a zinc electrode during charging to lower charging efficiency, and in particular, there is a problem that a battery using a liquid electrolyte is difficult to put into practical use. Further, water in the solid electrolyte is poor in reactivity, and thus self-discharge is not easily caused even with respect to a metal having a lower oxidation-reduction potential than hydrogen, and electrolysis of water, that is, reduction of protons, which competes with reduction of the metal is not easily caused, and thus the charging efficiency is improved. The above-described action of suppressing dissolution and diffusion of metal ions and the action of preventing generation of dendrites can provide the same action and effect even for a primary battery or a nickel-metal hydride battery. Further, the same advantages as described above are obtained in a zinc-air battery using an air electrode as a positive electrode, and a battery in which diffusion of oxygen into the zinc electrode is suppressed and charging can be easily performed can be obtained.

Metals having a valence of 2 or more include, in addition to zinc, a plurality of metals such as copper, cobalt, iron, manganese, chromium, vanadium, tin, molybdenum, niobium, tungsten, silicon, boron, and aluminum, and therefore, the application of the electrolyte of the present invention makes it possible to put secondary batteries using the above metals into practical use.

In an alkaline secondary battery such as a nickel-metal hydride battery, an alkaline electrolyte solution having a porous separator impregnated therein has been conventionally used, but the electrolyte of the present invention has functions of both the electrolyte solution and the separator, and therefore, the amount of the electrolyte solution can be reduced without using the electrolyte solution, and the energy density of the battery can be improved accordingly. Further, unlike a porous separator, since a short circuit can be prevented even when the separator is formed as a thin film, a thin film type electrode having a large surface area can be used.

Further, since the solid electrolyte of the present invention is of an alkaline type, when applied to a fuel cell, an organic compound liquid fuel having a C — C bond such as ethanol or ethylene glycol can be used. Conventionally, when an acid type electrolyte is used, a high catalytic activity for oxidative decomposition reaction of an organic compound having a C — C bond cannot be obtained, and therefore, methanol having no C — C bond is generally used as a liquid fuel, but the toxicity of methanol is a problem. However, since the use of the alkaline electrolyte can provide a high catalytic activity for the oxidative decomposition reaction of the organic compound having a C — C bond, a safer and more easily handled liquid fuel such as ethanol or ethylene glycol can be used.

The solid electrolyte of the present invention uses inexpensive raw materials and is based on a simple aqueous solution process, and therefore, the price thereof is significantly reduced as compared with conventional perfluorosulfonic acid electrolytes. Further, unlike inorganic solid materials, they are flexible and therefore can be easily processed into thin films. When a compound of polyethylene oxide and a silicon compound, which has been attempted in the past, is selected, a compound having hot water resistance cannot be obtained even by applying the present invention, and a method such as a sol-gel method, which is expensive, must be used. However, by selecting polyvinyl alcohol as in the present invention, an aqueous solution preparation method which is easy to produce and low in cost can be applied.

The solid electrolyte of the present invention is proton conductive, and thus can be applied to a fuel cell, a steam pump, a dehumidifier, an air conditioner, an electrochromic device, an electrolysis-type hydrogen generator, an electrolytic hydrogen peroxide generator, an electrolytic water generator, a humidity sensor, and a hydrogen sensor, as in the case of a conventional perfluorosulfonic acid ion-exchange membrane. The solid electrolyte material is alkaline but exhibits high ion conductivity, and therefore can be applied to electrochemical systems such as primary batteries, secondary batteries, and optical switching systems, or to novel battery systems using polyvalent metals.

Specific examples of the high ion-conductive solid electrolyte, the method for producing the same, and the electrochemical system using the same according to the present invention will be described below. However, the present invention is not limited to the contents described in these examples.

Example 1

In order to produce an electrolyte membrane of a high ion-conductive solid electrolyte according to the present invention, first, a 20 wt% aqueous solution of polydiallyldimethylammonium chloride having a molecular weight of 100000 to 200000 as a nitrogen-containing organic compound is mixed with 50cc of a 7 wt% aqueous solution of polyvinyl alcohol having a polymerization degree of 3100 to 3900 and a saponification rate of 86 to 90%, only in an amount of 0.06 weight ratio of polydiallyldimethylammonium chloride to polyvinyl alcohol, and zirconium oxychloride octahydrate (ZrCl)₂O·8H₂O) was added to 12g of a 16.7 wt% aqueous solution, and the mixture was heated at 50 ℃ for 1 hour while stirring to prepare a raw material solution. The raw material solution was defoamed, and then cast on a polyester film coated on a smooth pedestal of an applicator (RK Print Coat Instruments ltd, K control coater 202) equipped with a blade capable of adjusting a gap with the pedestal using a micrometer. At this time, the pedestal is controlled and heated to 50 to 60 ℃. Immediately after the raw material solution was cast on a stand, a blade having a gap adjusted to 0.6mm was swept over the raw material solution at a constant speed to be leveled to a certain thickness. The raw material solution was repeatedly cast from above at a stage where the fluidity was almost lost by directly heating and leaving at 50 to 60 ℃ and immediately, a blade having a gap adjusted to 0.6mm was again swept above the raw material solution at a constant speed to be leveled to a constant thickness. Then, the temperature of the pedestal was raised to 140 to 150 ℃ and the pedestal was kept in this state and subjected to heat treatment for 1.5 hours. Then, the film formed on the pedestal was peeled off, immersed in a 1.67 wt% aqueous ammonia solution at room temperature for 2 hours, washed with hot water at 60 to 70 ℃ for 30 minutes, and heated at 120 ℃ for 1 hour.

Example 2

An electrolyte membrane was produced by the same procedure as in example 1, except that polydiallyldimethylammonium chloride as the nitrogen-containing organic compound in example 1 was used only in an amount of 0.12 by weight relative to polyvinyl alcohol.

Example 3

An electrolyte membrane was produced by the same procedure as in example 1, except that polydiallyldimethylammonium chloride as the nitrogen-containing organic compound in example 1 was used only in an amount of 0.18 by weight relative to polyvinyl alcohol.

Example 4

An electrolyte membrane was produced by the same procedure as in example 1, except that polydiallyldimethylammonium chloride as the nitrogen-containing organic compound in example 1 was used only in an amount of 0.24 by weight relative to polyvinyl alcohol.

Example 5

An electrolyte membrane was produced by the same procedure as in example 1, except that polydiallyldimethylammonium chloride as the nitrogen-containing organic compound in example 1 was used only in an amount of 0.32 by weight relative to polyvinyl alcohol.

Example 6

An electrolyte membrane was produced by the same procedure as in example 1, except that polydiallyldimethylammonium chloride as the nitrogen-containing organic compound in example 1 was used only in an amount of 0.44 by weight relative to polyvinyl alcohol.

Example 7

An electrolyte membrane was produced by the same procedure as in example 1, except that a 20 wt% aqueous solution of polyallylamine hydrochloride was used in an amount such that the weight ratio of the polyallylamine hydrochloride to the polyvinyl alcohol was 0.06 instead of the 20 wt% aqueous solution of the polydiallyldimethylammonium chloride as the nitrogen-containing organic compound in example 1.

Example 8

An electrolyte membrane was produced by the same procedure as in example 7, except that polyallylamine hydrochloride as the nitrogen-containing organic compound in example 7 was used in an amount of 0.18 by weight based on the polyvinyl alcohol.

Example 9

An electrolyte membrane was produced by the same procedure as in example 1, except that a 10 wt% aqueous solution of imidazole hydrochloride was used in an amount such that the weight ratio of imidazole hydrochloride to polyvinyl alcohol was 0.06 instead of the 20 wt% aqueous solution of polydiallyldimethylammonium chloride as the nitrogen-containing organic compound in example 1.

Example 10

An electrolyte membrane was produced by the same procedure as in example 9, except that the imidazole hydrochloride as the nitrogen-containing organic compound in example 9 was used only in an amount of 0.20 by weight relative to the polyvinyl alcohol.

Example 11

An electrolyte membrane was produced by the same procedure as in example 1 except that a 10 wt% aqueous solution of polyvinylpyrrolidone was used in an amount such that the weight ratio of polyvinylpyrrolidone to polyvinyl alcohol was 0.29 instead of the 20 wt% aqueous solution of polydiallyldimethylammonium chloride as the nitrogen-containing organic compound in example 1.

Comparative example

A solid electrolyte was produced by the same procedure as in example 1, except that a 20 wt% aqueous solution of polydiallyldimethylammonium chloride as the nitrogen-containing organic compound in example 1 was not added. The results of measuring the ion conductivity of examples 1 to 11 and comparative examples are shown in table 1.

TABLE 1

Ionic conductivity of zirconic acid compound/polyvinyl alcohol composite compound containing nitrogen-containing organic compound having amine, quaternary ammonium compound or imine structure

The ion conductivity of the prepared solid electrolyte was measured by the following method. First, the solid electrolyte was cut into a circular shape having a diameter of 30mm, sandwiched between 2 platinum disks having a diameter of 28mm and nickel disks disposed on the outer sides of the platinum disks, and then sandwiched and fixed by insulating clips. An alternating voltage of 10mV was applied to a lead wire attached to a nickel disk using an LCR meter, and the response of current and phase angle was measured while changing the frequency from 5MHz to 50 Hz. The ionic conductivity was determined from the Cole-Cole plot as conventionally performed. The measurement was performed in a state where the solid electrolyte was immersed in pure water, and was performed in a constant temperature bath while controlling the temperature to 60 ℃. The measurement was performed after immersion in pure water for about 30 minutes.

As shown in table 1, in any of examples 1 to 11, the ion conductivity was significantly increased by containing the nitrogen-containing organic compound having an amine, quaternary ammonium compound or imine structure, and was shown to be 10^-5～10^-3High value of S/cm scale. When these solid electrolytes were washed with warm water after alkali treatment for 30 minutes and conductivity was measured, the solid electrolytes were immersed in pure water at 60 ℃ for about 30 minutes, but even in this case, high conductivity was maintained. This means that the basic nitrogen-containing organic compound is not eluted, but is immobilized within the composite compound constituting the solid electrolyte.

Example 12

Then, a 20 wt% aqueous solution of polydiallyldimethylammonium chloride having a molecular weight of 100000 to 200000 and a 10 wt% aqueous solution of polyvinylpyrrolidone having an average molecular weight of 35000 are mixed in an amount of 0.09 weight ratio of polyvinylpyrrolidone to polyvinyl alcohol only as nitrogen-containing organic compounds in 50cc of a 7 wt% aqueous solution of polyvinyl alcohol having a polymerization degree of 3100 to 3900 and a saponification rate of 86 to 90%, and then zirconium oxychloride octahydrate (ZrCl Cl I) is mixed after mixing the aqueous solutions only in an amount of 0.32 weight ratio of polydiallyldimethylammonium chloride to polyvinyl alcohol only as nitrogen-containing organic compounds₂O·8H₂O) was added to 12g of a 16.7 wt% aqueous solution, and the mixture was heated at 50 ℃ for 1 hour while stirring to prepare a raw material solution. By using the raw material solution,an electrolyte membrane was produced by the same procedure as in example 1.

The results of measuring the ionic conductivity of example 12 and the swelling ratios of examples 5, 11 and 12 are shown in Table 2. The swelling ratio is a swelling ratio due to water absorption obtained by measuring the diameter of the membrane in a state of just being immersed in pure water for 30 minutes at normal temperature and in a state of being dried at 80 ℃.

TABLE 2

Effect of polyvinylpyrrolidone in combination with other nitrogen-containing organic Compounds on inhibition of swelling

As shown in table 2, the membrane area of example 5 containing polydiallyldimethylammonium chloride but not containing polyvinylpyrrolidone was expanded by 59%, whereas the membrane area of example 11 containing polyvinylpyrrolidone but not containing polydiallyldimethylammonium chloride was 4%, and the swelling ratio of example 12 containing both polydiallyldimethylammonium chloride and polyvinylpyrrolidone was 33%, indicating that the swelling was significantly reduced by adding polyvinylpyrrolidone. The swelling is greatly reduced, and the problems of dimensional change and strength reduction when an electrolyte such as a fuel cell is used in a wet state are reduced. Although the effect of polyvinylpyrrolidone on improvement of ion conductivity is not so great, incorporation of polyvinylpyrrolidone in combination with another nitrogen-containing organic compound having a high effect of improving ion conductivity as in example 12 makes it possible to achieve high ion conductivity and to control the swelling ratio to a level that does not pose a practical problem.

Example 13

In 50cc of a 7 wt% aqueous solution of a polyvinyl alcohol having a polymerization degree of 3100 to 3900 and a saponification rate of 86 to 90%, the weight ratio of poly (diallyldimethylammonium chloride) to the polyvinyl alcohol is 0.32Adding a 20 wt% aqueous solution of polydiallyldimethylammonium chloride having a molecular weight of 100000 to 200000 as a nitrogen-containing organic compound, and then adding zirconium oxychloride octahydrate (ZrCl)₂O·8H₂O) 12g of a 16.7 wt% aqueous solution and a predetermined amount of a 20 wt% aqueous solution of lanthanum chloride heptahydrate were mixed, and the mixture was heated at 50 ℃ for 1 hour while stirring to prepare a raw material solution. Using this raw material solution, an electrolyte membrane was produced by the same procedure as in example 1.

Example 14

An electrolyte membrane was produced by the same procedure as in example 13, except that calcium chloride hexahydrate was used instead of lanthanum chloride heptahydrate in example 13.

Example 15

An electrolyte membrane was produced by the same procedure as in example 13, except that strontium chloride hexahydrate was used instead of lanthanum chloride heptahydrate in example 13.

Example 16

An electrolyte membrane was produced by the same procedure as in example 13, except that aluminum chloride hexahydrate was used instead of lanthanum chloride heptahydrate in example 13.

Example 17

An electrolyte membrane was produced by the same procedure as in example 13, except that yttrium chloride hexahydrate was used instead of lanthanum chloride heptahydrate in example 13.

The ionic conductivities of the electrolyte membranes of examples 13 to 17 and example 5 after immersion in pure water for 30 minutes are shown in table 3. Each of the examples to which the alkaline earth metal element, aluminum and the rare earth metal element were added showed higher conductivity than example 5 to which no different element was added.

TABLE 3

Ion conductivity when an element other than zirconium is added to a zirconic acid compound/polyvinyl alcohol composite compound containing a nitrogen-containing organic compound

Example 18

Adding a 20 wt% aqueous solution of polydiallyldimethylammonium chloride having a molecular weight of 100000 to 200000 as a nitrogen-containing organic compound to 50cc of a 7 wt% aqueous solution of polyvinyl alcohol having a polymerization degree of 3100 to 3900 and a saponification rate of 86 to 90%, in an amount such that the weight ratio of polydiallyldimethylammonium chloride to polyvinyl alcohol is 0.32, and mixing zirconium oxychloride octahydrate (ZrCl)₂O·8H₂O) was added to 12g of a 16.7 wt% aqueous solution, and the mixture was heated at 50 ℃ for 1 hour while stirring to prepare a raw material solution. Using this raw material solution, an electrolyte membrane was produced by the same procedure as in example 1.

Example 18-1

The electrolyte membrane was immersed in a solution containing 2.5g of calcium hydroxide and 4g of sodium hydroxide in 100cc of water, and subjected to alkali treatment.

Example 18-2

The electrolyte membrane was immersed in a solution containing 2.5g of aluminum hydroxide and 4g of sodium hydroxide in 100cc of water, and subjected to alkali treatment.

Examples 18 to 3

The electrolyte membrane was immersed in a solution containing 2.5g of sodium aluminate and 4g of sodium hydroxide in 100cc of water, and subjected to alkali treatment.

Examples 18 to 4

The electrolyte membrane was immersed in a solution prepared by adding 2.5g of sodium tetraborate decahydrate and 4g of sodium hydroxide to 100cc of water, and subjected to alkali treatment.

Examples 18 to 5

The electrolyte membrane was immersed in a solution prepared by adding 9g of 52 to 57 wt% sodium silicate (water glass) and 4g of sodium hydroxide to 100cc of water, and subjected to alkali treatment.

Examples 18 to 6

The electrolyte membrane was immersed in a solution prepared by adding 2.5g of sodium tungstate dihydrate and 4g of sodium hydroxide to 100cc of water, and subjected to alkali treatment.

The ionic conductivities of example 18-1 to example 18-3, in which the alkali treatment was performed in the alkali solution containing these different elements, are shown in Table 4. As shown in table 4, the electrolyte membrane treated with the alkali in the solution containing the aluminum and calcium elements showed higher conductivity than the electrolyte membrane of example 5, which was treated with only ammonia and had no addition of the dissimilar metal element, and which had the same composition.

TABLE 4

Ion conductivity of zirconic acid compound/polyvinyl alcohol composite compound containing nitrogen-containing organic compound when hydroxide and oxysalt are added to alkali treatment liquid

The swelling ratios of examples 18-4 to 18-6 obtained by subjecting the alkali solutions containing the dissimilar metal elements to alkali treatment are shown in Table 5. As shown in table 5, the electrolyte membrane treated with alkali in the solution containing boron, silicon and tungsten elements had a swelling ratio of 32% to 26% which was lower than that of 59% in example 5 in which the electrolyte membrane of the same composition was treated with ammonia alone and no dissimilar metal element was added, and had a significant swelling inhibition effect.

TABLE 5

Swelling ratio of zirconate compound/polyvinyl alcohol composite compound containing nitrogen-containing organic compound when each oxoacid salt is added to alkali treatment liquid

As described in detail above, according to the present invention, a composite compound containing at least a polyvinyl alcohol and a zirconic acid compound as constituent components contains a nitrogen-containing organic compound having an amine, quaternary ammonium compound or imine structure, and thus, a high ion-conductive solid electrolyte and a method for producing the same can be provided which can provide high hydroxide ion or proton conductivity, are inexpensive, exhibit high conductivity in spite of being of an alkaline type, and can stably maintain high conductivity because the compound having conductivity in a wet state flows out little.

Further, the nitrogen-containing organic compound having an amine, quaternary ammonium compound or imine structure can be introduced into the composite compound composed of at least the zirconic acid compound and polyvinyl alcohol by an extremely simple method, and is complexed with the zirconic acid compound at a molecular level, so that the anion exchange membrane is excellent in chemical stability and substance-shielding property compared with the conventional anion exchange membrane composed of a nitrogen-containing organic compound. The solid electrolyte of the present invention is proton-or hydroxide ion-conductive, and therefore can be used in fuel cells, steam pumps, dehumidifiers, air conditioning equipment, electrochromic devices, electrolytic hydrogen generators, electrolytic hydrogen peroxide generators, electrolytic water generators, humidity sensors, hydrogen sensors, primary batteries, secondary batteries, optical switching systems, battery systems using polyvalent metals, and the like. Further, since the solid electrolyte is alkaline, unlike conventional acid-type solid electrolytes such as Nafion (trade name), the solid electrolyte can improve the corrosion resistance to metals, and therefore, expensive corrosion-resistant materials such as noble metals are not necessarily used for peripheral parts such as electrodes. In addition, the polymer electrolyte can be used in applications where the electrode active material cannot stably exist or function under acidic conditions, such as primary batteries, secondary batteries, optical switching systems, and battery systems using polyvalent metals.

Claims (18)

1. A solid electrolyte having high ion conductivity, characterized by comprising a composite compound containing at least a polyvinyl alcohol and a zirconic acid compound as constituent components and a nitrogen-containing organic compound having an amine, quaternary ammonium compound or imine structure and being a polymer or a low-molecular-weight organic compound containing a plurality of nitrogen moieties in the molecule, wherein the weight ratio of the nitrogen-containing organic compound to the polyvinyl alcohol is 0.18 or more.

2. A solid electrolyte having high ion conductivity, characterized by comprising a composite compound containing at least a polyvinyl alcohol and a zirconic acid compound as constituent components and a nitrogen-containing organic compound having an amine, quaternary ammonium compound or imine structure and being a polymer or a low-molecular-weight organic compound containing a plurality of nitrogen moieties in the molecule, wherein the weight ratio of the nitrogen-containing organic compound to the polyvinyl alcohol is 0.18 or more, and the solid electrolyte is obtained by: in a raw material solution in which an aqueous solvent, polyvinyl alcohol, a zirconium salt or an oxyzirconium salt, and a low-molecular nitrogen-containing organic compound having an amine, quaternary ammonium compound, or imine structure and containing a polymer or a molecule containing a plurality of nitrogen moieties coexist, the solvent is removed after hydrolysis of the zirconium salt or the oxyzirconium salt, and then the zirconium salt or the oxyzirconium salt is brought into contact with an alkali.

3. The solid electrolyte of claim 2, wherein the zirconium salt or zirconyl salt is hydrolyzed by heating the raw material solution to 50 ℃ or higher.

4. The solid electrolyte with high ion conductivity according to claim 2, wherein the zirconium salt or zirconyl salt is hydrolyzed by heating the raw material solution to 50 ℃ or higher in a state where the pH is 7 or lower.

5. The solid electrolyte with high ion conductivity according to claim 2, wherein the raw material solution contains a salt of at least one of an alkaline earth metal, aluminum, or a rare earth metal.

6. The solid electrolyte of claim 2, wherein the base comprises a hydroxide or an oxysalt of at least one of an alkaline earth metal, aluminum, silicon, boron, or tungsten.

7. The solid electrolyte with high ionic conductivity according to claim 1, wherein the nitrogen-containing organic compound comprises at least polydiallyldimethylammonium salt or hydroxide thereof, or polyallylamine.

8. The solid electrolyte with high ionic conductivity according to claim 1, wherein the nitrogen-containing organic compound contains at least an imidazole ring.

9. The solid electrolyte with high ionic conductivity according to claim 1, wherein the nitrogen-containing organic compound comprises at least polyvinylpyrrolidone.

10. The solid electrolyte with high ion conductivity according to claim 1, wherein the composite compound contains at least one element selected from alkaline earth elements, aluminum, silicon, boron, rare earth elements, and tungsten.

11. A method for producing a solid electrolyte with high ion conductivity, characterized by hydrolyzing a zirconium salt or a zirconyl salt from a raw material solution in which a water-containing solvent, polyvinyl alcohol, a zirconium salt or a zirconyl salt, and a nitrogen-containing organic compound having an amine, quaternary ammonium compound or imine structure and being a polymer or a low-molecular-weight nitrogen-containing organic compound containing a plurality of nitrogen moieties in a molecule coexist, and the weight ratio of the nitrogen-containing organic compound to polyvinyl alcohol is 0.18 or more, removing the solvent, and then contacting with an alkali to obtain the solid electrolyte with high ion conductivity according to claim 1.

12. A method for producing a high ion conductivity solid electrolyte, characterized by heating a raw material solution, in which a water-containing solvent, polyvinyl alcohol, a zirconium salt or an oxyzirconium salt, and a nitrogen-containing organic compound having an amine, a quaternary ammonium compound or an imine structure and having a polymer or a low molecular weight containing a plurality of nitrogen moieties in the molecule are coexistent, and the weight ratio of the nitrogen-containing organic compound to polyvinyl alcohol is 0.18 or more, to 50 ℃ or higher in a state in which the pH is 7 or less, hydrolyzing the zirconium salt or the oxyzirconium salt in the raw material solution and initiating a polycondensation reaction of the zirconic acid compound to obtain a composite compound solution, removing the solvent from the composite compound solution to obtain a composite compound, and then contacting the composite compound with an alkali to obtain the high ion conductivity solid electrolyte according to claim 1.

13. The method for producing a solid electrolyte with high ion conductivity according to claim 12, wherein a composite compound of polyvinyl alcohol and a zirconic acid compound is formed during the polycondensation reaction of the zirconic acid compound, and the nitrogen-containing organic compound is complexed with the polyvinyl alcohol or the zirconic acid compound at a molecular level and incorporated into the composite compound to form a composite compound solution containing the nitrogen-containing organic compound.

14. The method for producing a solid electrolyte with high ion conductivity according to claim 11, wherein the raw material solution contains a salt of at least one of an alkaline earth metal, aluminum, and a rare earth metal.

15. The method for producing a solid electrolyte with high ion conductivity according to claim 11, wherein the alkali in contact with the composite compound contains a hydroxide or an oxysalt of at least one of an alkaline earth metal, aluminum, silicon, boron, and tungsten.

16. An electrochemical system using a solid electrolyte with high ion conductivity, characterized by comprising: in the high ion-conductive solid electrolyte according to claim 1, a plurality of electrodes separated by the solid electrolyte are arranged.

17. The electrochemical system using a high ion-conductive solid electrolyte according to claim 16, wherein the electrochemical system is a fuel cell, a steam pump, a dehumidifier, an air conditioning machine, an electrochromic device, an electrolysis device, a humidity sensor, a hydrogen sensor, a primary battery, a secondary battery, an optical switching system, or a battery system using a polyvalent metal.

18. The electrochemical system using a high ion-conductive solid electrolyte according to claim 17, wherein the electrolysis device is an electrolysis-type hydrogen generation device, an electrolytic hydrogen peroxide production device, or an electrolytic water production device.