JP2003208814A - High ion conductive solid electrolyte and electrochemical system using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive high ion conductive solid electrolyte using an organic-inorganic composite compound having both water absorbing property and water resisting property, and an electrochemical system using it. <P>SOLUTION: This high ion conductive solid electrolyte comprising a composite compound of a stannic acid compound containing water and polyvinyl alcohol is a basic constituent. After neutralizing aqueous solution obtained by dissolving alkali metal salt of stannic acid and polyvinyl alcohol by acid and removing water serving as a solvent, unnecessary salt is removed to obtain the stannic acid compound, and the high ion conductive solid electrolyte comprising the stannic acid compound, polyvinyl alcohol and water, and various kinds of electrochemical systems using it are provided. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a proton (hydrogen ion) high conductivity solid electrolyte or hydroxide ion high conductivity solid electrolyte applicable to fuel cells and the like, and a fuel using the high ion conductivity solid electrolyte. It relates to batteries and other electrochemical systems.

[0002]

2. Description of the Related Art Conventionally, as an electrochemical system using a proton conductive solid electrolyte, an electrolytic device such as a fuel cell, a dehumidifier or an electrolysis type hydrogen generator has been put into practical use. The battery has an electrochemical oxidation reaction of hydrogen supplied to the negative electrode as shown in the following formula (1), an electrochemical reduction reaction of oxygen supplied to the positive electrode as shown in the formula (2), and An electric current flows by the reaction consisting of proton transfer in the electrolyte, and electric energy is taken out. H ₂ → 2H ⁺ + 2e ⁻ ………………………… (1) 1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O ………… (2)

Some fuel cells use a fuel other than hydrogen, such as methanol, as the fuel supplied to the negative electrode. Even in this case, the reaction in which the fuel is electrochemically oxidized at the negative electrode to release a proton is similarly performed. And can be operated using a proton conductive solid electrolyte.

As an electrolysis device, for example, an electrolysis type hydrogen generation device has been put into practical use. This electrolysis-type hydrogen generator produces hydrogen by a reaction opposite to the reactions of the above formulas (1) and (2) in the fuel cell, and hydrogen of high purity is produced on-site only by water and electric power. Therefore, there is an advantage that a hydrogen cylinder is unnecessary. Further, by utilizing the solid electrolyte, electrolysis can be easily carried out only by introducing fresh water containing no electrolyte. In the field of paper manufacturing, an attempt has been made to produce hydrogen peroxide for bleaching on-site by an electrolytic method using the following formula (3) by a similar system (Electrochemistry, 69, No. 3, 154).
-159 (2001)). O ₂ + H ₂ O + 2e ⁻ → HO ₂ ⁻ + OH ⁻ ……………… (3)

The dehumidifier has a structure in which a proton conductive solid electrolyte membrane is sandwiched between positive and negative electrodes like a fuel cell and a hydrogen generator, and when a voltage is applied between the positive and negative electrodes, the positive electrode is subjected to the reaction of the following equation (4). Water is decomposed into oxygen and protons, and the protons that have moved to the negative electrode through the solid electrolyte are again bound to oxygen in the air by the reaction of formula (5) and returned to water. As a result of these reactions, the positive electrode side moves to the negative electrode side. Since the water has moved to the side, it is dehumidified on the positive electrode side. H ₂ O → 1 / 2O ₂ + 2H ⁺ + 2e ⁻ ……………… (4) 1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O ………… (5)

[0006] It is also possible to decompose water to dehumidify it by the same operating principle as that of the electrolysis type hydrogen generator, and an air conditioner combined with a moisture evaporative cooler has also been proposed (the 2000 Annual Conference of the Institute of Electrical Engineers of Japan). Proceedings, P3373 (2
000)).

In all of the systems put to practical use as described above, a perfluorosulfonic acid ion exchange membrane represented by Nafion membrane is used as a solid electrolyte. Also, various sensors, electrochromic devices, etc. are essentially a system based on the same operation principle as described above, and operate by moving protons in the electrolyte between two types of redox couples having different positive and negative electrodes. Therefore, a proton conductive solid electrolyte can be used. At present, empirical studies on systems using these proton-conducting solid electrolytes are also being conducted.

The hydrogen sensor utilizes a change in electrode potential depending on hydrogen concentration, and a solid electrolyte mainly composed of polyvinyl alcohol has been proposed as an electrolyte material (Sensors and Actuators, 11, 377-).
386 (1987)). Further, it can be applied to a humidity sensor by utilizing a change in electrode potential or a change in ionic conductivity.

The electrochromic device utilizes, for example, that when an electric field is applied to the negative electrode by using WO ₃ or the like, color is developed by the reaction of the following formula (6), and it is considered to be used as a display device or a light-shielding glass. There is. In this system, Sn, which is an inorganic compound, is used as the solid electrolyte.
(HPO ₄ ) .H ₂ O etc. have been proposed (Bull.Chem.So
c. Jpn., 60, 747-752 (1987)). WO ₃ + xH ⁺ + xe ⁻ → HxWO ₃ (coloring) ……………… (6)

In addition to the above, as an electrochemical system which operates in principle using a proton conductive solid electrolyte, there are primary batteries, secondary batteries, optical switches, electrolyzed water producing devices and the like. For example, a nickel hydrogen battery as a secondary battery is
A hydrogen storage alloy is used for the negative electrode, nickel hydroxide is used for the positive electrode, and an alkaline electrolyte is used as the electrolytic solution.
As shown in the formula (8), at the time of charging and discharging, electrochemical oxidation-reduction of protons and storage of hydrogen in the hydrogen storage alloy occur in the negative electrode. [Charge] H ₂ O + e ⁻ → H (storage) + OH ⁻ ··· (7) [Discharge] H (storage) + OH ⁻ → H ₂ O + e ⁻ ··· (8)

At the positive electrode, an electrochemical redox reaction of nickel hydroxide occurs as shown in the following equations (9) and (10). [Charging] ^{_{Ni (OH) 2 + OH -}} → NiOOH + H 2 O + e - ...... (9) [discharge] ^{_{NiOOH + H 2 O + e -}} → Ni (OH) 2 + OH - ...... (10) The charge and discharge reaction in the electrolyte of the battery It is established by the movement of protons or hydroxide ions, and in principle a proton conductive solid electrolyte can be used, but conventionally, an alkaline electrolyte that is not a solid electrolyte has been used.

As an optical switch, one using yttrium as a negative electrode has been proposed (J. Electrochem.
Soc., Vol. 143, No. 10, 3348-3353 (1
996)). By applying an electric field, yttrium is hydrogenated and transmits light as shown in the following equation (11), so that transmission and non-transmission of light can be switched by the electric field. In principle, this system can also utilize a proton conductive solid electrolyte, but conventionally an alkaline electrolyte has been used. Y + 3 / 2H ₂ O + 3e → YH ₃ + 3OH …………… (11)

Electrolyzed water is water that has undergone an electrolysis reaction, and has different effects on the reducing side and the oxidizing side, but it has a good health effect, a bactericidal effect, a cleaning effect, and an effect of promoting the growth of agricultural products. It has various uses such as food water, washing water, and agricultural water. The electrolytic reaction is promoted by the fact that water contains an electrolyte, but when the electrolyte is dissolved in water, it may be necessary to remove the electrolyte during use. When the solid electrolyte is used, the trouble of removing the electrolyte is unnecessary.

[0014]

However, the fuel cell, the electrolysis-type hydrogen generator, the dehumidifier, etc. which have been put into practical use as an electrochemical system using a proton conductive solid electrolyte has been used. The fluorosulfonic acid-based electrolyte has a problem that it is expensive mainly due to the complexity of the manufacturing process. Although it is expected that the price will be reduced to some extent due to the mass production effect of these electrolytes, there is a limit, and under the present circumstances, the advent of an inexpensive alternative material is desired.

By the way, in the normal-temperature-acting proton-conducting solid electrolyte, protons are transported at high speed by the action of the water contained in the solid, and therefore, a sufficient water absorption is required for the substitute material. Especially, most of them are used in a wet environment, and therefore must be water resistant. In the conventional perfluorosulfonic acid-based electrolyte, water absorbed around the highly hydrophilic sulfonic acid group carries ions at high speed,
The polyfluoroethylene skeleton plays a role in maintaining water resistance, chemical stability, and high temperature durability.

As an example of a hydrocarbon-based polymer material having high hydrophilicity and low cost, there is the above-mentioned polyvinyl alcohol, and a material having proton conductivity by mixing phosphoric acid can be used as a hydrogen sensor or the like. is there. In this example, the high water absorption of polyvinyl alcohol enables high-speed proton transfer. However, since polyvinyl alcohol is soluble in water, the material stability in a wet environment is low.

As another material having high hydrophilicity and water resistance, an inorganic hydrous compound can be mentioned. For example, the P ₂ O ₅ —ZrO ₂ —SiO ₂ hydrated glass produced by the sol-gel manufacturing method has a characteristic that it exhibits high proton conductivity by absorbing a large amount of water and does not dissolve in water, and is unique to inorganic compounds. It has the advantage of high temperature stability (J. Electrochem. Soc. Vol. 144, No. 6, 2175-
2178 (1997)).

However, a common weak point of these inorganic hydrous compounds is that they are brittle, and there is a problem that it is difficult to process a thin film, which is required particularly in the application of a solid electrolyte. Further, the sol-gel manufacturing method uses an expensive metal alkoxide as a raw material, and since it is manufactured using an organic solvent such as alcohol, there is a problem that it is difficult to reduce the cost in terms of equipment. The Sn (HPO ₄ ) .H ₂ O, which has been tried in electrochromic devices, can be processed by applying powder, but it has the gas diffusion suppressing function and high strength required for fuel cells and other applications. It is difficult to process it into a film that has it. _{Further, H 3 MoPO 40 · 29H 2} O molybdophosphate and _H and represented by a composition formula of 3 _{WPO 40} · 2
It has been reported that tungstophosphoric acid represented by the composition formula of 9H ₂ O has high conductivity (Chem. Lett., 1
7 (1979)), there is a problem in processability even when these molybdophosphoric acid and tungstophosphoric acid are used.

As a method for overcoming the drawbacks of the hydrophilic organic polymer and the inorganic compound, a means for compounding them can be considered. For example, Japanese Patent Application Laid-Open No. 2000-90946 proposes a proton conductive material in which a silicon compound and polyethylene oxide are chemically bonded at the nano level. Polyethylene oxide is an inexpensive and highly hydrophilic organic polymer like polyvinyl alcohol, but it dissolves in water by itself. However, it is said that a compound having a high temperature strength can be obtained by making it composite with a silicon compound by the sol-gel manufacturing method, so that it can have water resistance. However, it is difficult to obtain the composite material by a method other than the sol-gel manufacturing method, and no other method is disclosed. Therefore, there is a problem that the effect of reducing raw materials or manufacturing costs is low. Also,
Japanese Patent Application Laid-Open No. 2001-35509 also proposes an ion conductive material in which an inorganic compound such as a silicon compound and a proton conductivity-imparting agent such as tungstophosphoric acid or molybdophosphoric acid and an organic compound such as polyethylene oxide are combined. However, only the composite method by the sol-gel manufacturing method is disclosed.

All of the above conventional solid electrolytes are acidic, and the materials that can be used as electrodes and other system constituent materials are limited to acid-resistant materials such as precious metals, and it is difficult to reduce the cost of the entire system. is there. There is also a problem that the acidity of the solid electrolyte makes it difficult to apply it to some applications such as primary batteries, secondary batteries and optical switches due to the deterioration action of electrodes and active materials. Alkaline liquid electrolytes that have been conventionally used in, for example, have a drawback that there is a risk of liquid leakage.

Therefore, the present invention solves the problems of the above-mentioned ion conductive solid electrolyte, and uses the organic-inorganic composite compound having both water absorption and water resistance at a low cost and a high ion conductive solid. It is intended to provide an electrolyte and an electrochemical system using the high ion conductive solid electrolyte.

[0022]

In order to achieve the above object, the present invention provides a high ion conductive solid electrolyte composed of a composite compound of a stannic acid compound containing water and polyvinyl alcohol, and an alkali metal salt of stannic acid. A high ionic conductive solid electrolyte which is a complex compound of a stannic acid compound and polyvinyl alcohol and water obtained by neutralizing an aqueous solution in which polyvinyl alcohol is dissolved with an acid, removing water as a solvent, and then removing unnecessary salts. And various electrochemical systems using this high ion conductive solid electrolyte.

The composite compound composed of a stannic acid compound, polyvinyl alcohol and water contains at least one kind of silicic acid compound, boric acid compound, molybdic acid compound, tungstic acid compound and phosphoric acid compound. When produced by the neutralization method in an aqueous solution, the raw material aqueous solution is silicic acid, boric acid,
At least one kind of alkali metal salt selected from molybdic acid, tungstic acid, and phosphoric acid is contained, and the produced complex compound contains at least one kind of silicic acid compound, boric acid compound, molybdic acid compound, tungstic acid compound, and phosphoric acid compound. Contains. The ratio of the weight of the stannic acid compound calculated as SnO ₂ to the weight of polyvinyl alcohol is 0.08 or more. The composite compound is immersed in an acid solution or an alkaline solution.

As the electrochemical system, a fuel cell, a steam pump, a dehumidifier, an air conditioner, an electrochromic device, an electrolysis device, an electrolysis hydrogen generator, an electrolytic hydrogen peroxide production device, an electrolyzed water production device, a humidity sensor, hydrogen It can be applied to sensors, primary batteries, secondary batteries, optical switch systems, or new battery systems using polyvalent metals.

According to such a high ion conductive solid electrolyte and an electrochemical system using the solid electrolyte, a simple process of neutralizing stannate and other added salts in an aqueous solution coexisting with polyvinyl alcohol is performed. It is possible to prepare a high ionic conductive solid electrolyte by the above, and by the above neutralization reaction and the subsequent heat treatment, a polycondensation reaction of a compound generated from stannic acid and other added salts occurs, and a micro level with polyvinyl alcohol. Entanglement occurs and it becomes possible to form a composite. Since polyvinyl alcohol and stannic acid compounds and other additive compounds are hydrophilic, the composite compounds of both have the ability to enclose a large amount of water, and this entrapped water serves as a medium for rapid diffusion of protons or hydroxide ions. .

The polyvinyl alcohol, the stannic acid compound and the other added compounds are firmly bound to each other by hydrogen bond or dehydration condensation. Even though they are hydrophilic, they do not dissolve in hot water and are stable even in a hot and humid environment. Physical properties can be maintained. This composite material has strength and flexibility, and can be easily processed into a thin film. High ionic conductivity is exhibited even with stannic acid compounds alone, but high ionic conductivity can be maintained by further compounding silicic acid compounds, boric acid compounds, molybdic acid compounds, tungstic acid compounds, and phosphoric acid compounds. Can be increased. This composite material has high ionic conductivity even in the alkaline type.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Specific embodiments of a high ion conductive solid electrolyte and an electrochemical system using the solid electrolyte according to the present invention will be described below. The present invention is based on a micro-level composite compound of polyvinyl alcohol and a stannic acid compound and other silicic acid compounds, boric acid compounds, molybdic acid compounds, tungstic acid compounds, and phosphoric acid compounds produced in an aqueous solution, and is inexpensive. The basic means is to provide a proton or hydroxide ion-conducting solid electrolyte exhibiting high ionic conductivity and having sufficient water resistance, and an electrochemical system using the solid electrolyte.

In the present invention, an aqueous solution in which an alkali metal salt of stannic acid and polyvinyl alcohol are dissolved is neutralized with an acid,
After removing water as a solvent, the unnecessary salt is removed to obtain a composite compound of a stannic acid compound, polyvinyl alcohol, and water, specifically, a composite compound of a stannic acid compound and polyvinyl alcohol containing water. It is characterized by creating a solid electrolyte. In addition, the raw material aqueous solution in which stannate and polyvinyl alcohol are dissolved optionally contains an alkali metal salt such as silicic acid, boric acid, molybdic acid, tungstic acid, phosphoric acid, etc., and the produced composite compound is a silicic acid compound or boric acid compound. , Molybdic acid compounds, tungstic acid compounds, and phosphoric acid compounds.

Specific embodiments of the present invention will be described below. The invention of the present application is not limited to the description of these embodiments.

Example 1 To prepare an electrolyte membrane, first, polyvinyl alcohol having an average molecular weight of 120,000 to 190,000 and a saponification degree of 87 to 89%, and an average molecular weight of 18,000 to 26,000 were used. And saponification degree is 100
% Polyvinyl alcohol in a proportion of 50% by weight, a predetermined amount of sodium stannate trihydrate is dissolved in 80 cc of a 2% by weight aqueous solution to prepare a raw material aqueous solution. PH of aqueous solution of hydrochloric acid
Was dropped to 3 or less to neutralize. After that, the aqueous solution was poured into two petri dishes having a diameter of 90 mm and dried at 50 ° C. to remove water as a solvent. After drying, peel off the film remaining on the petri dish and put it in an oven for 10 minutes in air.
Heat treatment was performed at 0 ° C. for 3 hours, and washing was sufficiently performed in hot water at 70 to 80 ° C.

The electrolyte membrane produced by the above method was subjected to an acid immersion treatment to promote protonation or an alkaline solution immersion treatment to promote alkalinization. In the acid immersion treatment, the electrolyte membrane was immersed in 1.2 M hydrochloric acid at room temperature for 3 hours and then thoroughly washed with water. In the alkaline solution immersion treatment, the sample surface was wiped by immersing in 0.02 M sodium hydroxide at room temperature for 3 hours, drying without washing with water.

The samples prepared in this manner are sample No. 1 in Table 1. The amount of stannic acid compound was 1 to 12 and was converted to SnO ₂ in Table 1 and shown in the form of weight ratio to polyvinyl alcohol. In the table, those with the symbol (a) are those subjected to hydrochloric acid immersion treatment, those with the symbol (b) are those subjected to alkaline solution immersion treatment, and those without the symbol are acid or alkaline solutions. The one that has not been subjected to the immersion treatment is shown.

[0033]

[Table 1]

All of these samples in which a stannic acid compound having a SnO ₂ conversion weight ratio of 0.08 or more is combined with polyvinyl alcohol do not dissolve even if washed in hot water of 70 ° C. or more for 1 hour. Maintains the film shape and has excellent water resistance. For the purpose of comparison, a sample containing only polyvinyl alcohol containing no stannic acid compound was formed into a film by the same method, but only the one having low water resistance which was immediately dissolved in hot water could be formed. From these results, the compounding with the stannic acid compound has the effect of significantly improving the water resistance of polyvinyl alcohol.

The ionic conductivity of the prepared sample film was measured by the following method. First, a sample film is cut out into a circular shape having a diameter of 30 mm, sandwiched between two platinum disks having a diameter of 28 mm and a brass disk arranged outside the platinum disk, and further sandwiched and fixed by an insulated clip. Use a LCR meter on the lead wire attached to a brass disc to measure the voltage 1
An AC voltage of 0 mV was applied while changing the frequency from 5 MHz to 50 Hz, and the response of current and phase angle was measured. The ionic conductivity was obtained from the diameter of a semicircle of a Cole-Cole plot that is generally performed. The measurement was carried out by placing the sample in a high temperature and high humidity tank and controlling the humidity at 50 ° C. and the relative humidity at 90%. The measurement results of ionic conductivity are shown in Table 1.

A composite electrolyte sample of a stannic acid compound and polyvinyl alcohol was 10 ⁻⁷ S in the as-prepared state.
It showed only low ionic conductivity in the order of / cm.
The ionic conductivity was not significantly improved by the acid immersion treatment, but the ionic conductivity was significantly improved when alkali-typed by the alkali solution immersion treatment.
A high value of 0 ⁻⁵ S / cm order was exhibited.

In the above-mentioned production method, the results of adding sodium silicate, sodium borate, sodium molybdate, sodium tungstate, and sodium triphosphate to the raw material aqueous solution were obtained. 13 to 24. In Table 1, the symbols (Si), (B), (Mo),
(W) and (P) are a silicic acid compound, a boric acid compound,
It shows that a molybdic acid compound, a tungstic acid compound, and a phosphoric acid compound are added, and the amount of each compound is SiO ₂ , B ₂ O ₃ , MoO ₃ , WO ₃ , P _{2 respectively.}
It is converted to the weight of O ₅ and is shown in the form of a weight ratio to polyvinyl alcohol. From these results, silicic acid compounds,
It can be seen that even when a boric acid compound or a molybdic acid compound is added, a high ionic conductivity of the order of 10 ⁻⁵ S / cm can be maintained in the alkali type conversion. Moreover, when a tungstic acid compound or a phosphoric acid compound is added, it is 10
^It showed an extremely high ionic conductivity of the order of ⁻⁵ to 10 ⁻⁴ S / cm. The effect of these added compounds is shown in Sample No.
It is also expressed when two or more kinds of compounds such as 23 and 24 are added in combination.

Most of the samples shown in Table 1 are 100
When the heat treatment was not carried out at ℃, the strength was considerably lowered in the subsequent washing process with hot water, and the film shape could not be maintained. Therefore, in the electrolyte material of the present invention, 1
It is preferable to perform heat treatment at 00 ° C. or higher.

The above-mentioned polyvinyl alcohol does not have to be perfect, and any polyvinyl alcohol that essentially functions as polyvinyl alcohol can be used. For example, those in which a part of hydroxyl groups is substituted with other groups, and those in which other polymers are copolymerized in part can also function as polyvinyl alcohol. Further, since similar effects can be obtained by passing through polyvinyl alcohol in the reaction process of the present invention, polyvinyl acetate, which is a raw material of polyvinyl alcohol, can be used as a starting raw material.

Other polymers, for example, polyolefin polymers such as polyethylene and polypropylene, polyacrylic acid polymers, polyether oxide polymers such as polyethylene oxide and polypropylene oxide, as long as the function of the polyvinyl alcohol in the present invention is sufficiently exhibited. , Fluoropolymers such as polytetrafluoroethylene and polyvinylidene fluoride, sugar chain polymers such as methylcellulose, polyvinyl acetate polymers, polystyrene polymers, polycarbonate polymers, epoxy resin polymers and other organic and inorganic additives, etc. Can also be mixed.

As the alkali metal salt of stannic acid, any kind of alkali metal salt, ratio of alkali metal ions, tin and oxygen, and water content may be used as long as it is soluble in water.

The aqueous solution in the present invention means that water is essentially a solvent, and there may be other solvent components in a smaller amount than the water content. A silicic acid compound, a boric acid compound, a molybdic acid compound, a tungstic acid compound, and a phosphoric acid compound can be added to the material.
These compounds are added to the raw material aqueous solution by silicic acid, boric acid,
It is carried out by dissolving an alkali metal salt of molybdic acid, tungstic acid, or phosphoric acid. As the phosphate, any of the first, second and third phosphates can be used, but when the silicate or borate coexists, the first
Phosphates are not preferred because they already neutralize the salts when they are added to the raw material aqueous solution.

With regard to silicates, borates, molybdates, and tungstates, any kind and composition of alkali metal ions, water content and the like can be used. For example, in the case of silicate, water glass or the like can be used. Two or more kinds of these salts may be mixed and added. In addition, it is preferable to use a salt of a heteropoly acid such as tungstophosphoric acid, molybdophosphoric acid, silicotungstic acid, silicomolybdic acid, tungstoboric acid, molybdoboric acid, in which tungstic acid or molybdic acid is combined with phosphoric acid, silicic acid, boric acid, as a raw material. it can.

The type of acid added to the raw material aqueous solution may be any acid as long as it can neutralize stannate or other added salts, and hydrochloric acid, sulfuric acid, phosphoric acid and the like can be used. In addition, by adding boric acid, phosphoric acid, or the like to the acid to be added, the boric acid compound or phosphoric acid compound can be introduced into the material. Incidentally, the neutralization step with an acid in the present invention, contrary to the operation of adding an acid to the raw material aqueous solution,
It can also be carried out by the operation of adding the raw material aqueous solution to the acid.

The aqueous solution neutralized with an acid is processed into a desired shape such as a thin film by removing water as a solvent by heating and drying. The composite compound after processing is subjected to a heat treatment at a temperature of 100 ° C. or higher to cause a polycondensation reaction of the stannic acid compound itself and a bond with a silicic acid compound, a boric acid compound, a molybdic acid compound, a tungstic acid compound, a phosphoric acid compound and polyvinyl alcohol. It can accelerate production and increase strength, water resistance, and high temperature stability. If the heat treatment is not carried out, problems such as a decrease in strength in high temperature water occur. The heating atmosphere in the heat treatment may be air, an inert gas atmosphere, or a vacuum. However, it is 1 for the sample containing the silicic acid compound to the polyvinyl alcohol ratio of 0.032 or more.
Sufficient heat resistance can be obtained even by heat treatment at a temperature lower than 00 ° C.

By washing the complex compound with a solvent such as water before or after the heat treatment step, unnecessary salts in the complex compound are removed. In any electrochemical system using a solid electrolyte, a redox reaction occurs at the electrode, but among the anions introduced by the acid in the neutralization process, free ions not fixed to the solid electrolyte adversely affect the redox reaction. Therefore, it is necessary to remove unnecessary salts, which are free ions, by washing.

The ratio of the weight of the stannic acid compound in the composite compound converted to SnO ₂ to the weight of polyvinyl alcohol is limited to 0.08 or more. If the weight ratio is lower than these values, there arises a problem that sufficient water resistance cannot be obtained or sufficient ionic conductivity cannot be obtained.

In the case of obtaining an acid-type proton-conducting solid electrolyte, the produced composite compound is immersed in an acid to completely protonate the proton sites in the material, and the proton concentration is increased to increase the ionic conductivity. You can increase the degree. Any acid that can be protonated can be used, and hydrochloric acid, sulfuric acid, phosphoric acid or the like can be used. The electrolyte containing a tungstic acid compound and a phosphoric acid compound is more effective in the acid immersion treatment.

When an alkali-type proton or hydroxide ion-conducting solid electrolyte is obtained, the composite compound thus formed is subjected to a treatment of immersing it in an alkali solution so that it is more completely alkali-typed and its ionic conductivity is increased. be able to. Any alkali dipping treatment can be used as long as it can be alkali-typed, and a solution of sodium hydroxide, potassium hydroxide, lithium hydroxide or the like can be used. The alkali immersion treatment is effective when the inorganic compound contained in the electrolyte is a stannic acid compound alone, or when it is a silicic acid compound, a boric acid compound, or a molybdic acid compound. The treatment of dipping in the acid or alkali does not necessarily have to be an aqueous solution.

The high ionic conductive solid electrolyte obtained by the present invention can be easily converted into an alkali type by converting a proton site in a compound into an alkali metal ion, and a high proton or hydroxide in the alkali type. Shows ionic conductivity. By using the alkaline type, it becomes possible to use a relatively inexpensive material such as nickel as an electrode and other system constituent materials, and it is possible to reduce the cost of the entire system.

Further, by making it alkaline type, it can be applied to primary batteries and secondary batteries, and by using a conventional alkaline electrolyte as the electrolyte material of the present invention, the possibility of leakage can be eliminated. By using this alkaline solid electrolyte, it is possible to put a secondary battery, which has been difficult to put into practical use, into practical use, for example, a high energy density battery using a polyvalent metal having a valence of 2 or more as a negative electrode. . For example, a nickel zinc battery using zinc oxide for the negative electrode and nickel hydroxide, which is the same as nickel hydroxide battery for the positive electrode, can be given as an example.
In a nickel-zinc battery, as shown in the following formulas (12) and (13), zinc oxide is reduced to metallic zinc at the time of charging at the negative electrode, and zinc is electrochemically oxidized to zinc oxide at the time of discharging. Return. [Charging] ^{_{ZnO + H 2 O + 2e -}} → Zn + 2OH - ......... (12) [discharge] ^{Zn + 2OH - → ZnO + H} 2 O + 2e - ......... (13)

The nickel-zinc battery has a high storage energy density because zinc is divalent, but zinc oxide is easily dissolved in the alkaline electrolyte, and zinc ions are eluted from the electrode and the eluted zinc ions are reduced during charging. There is a problem in that acicular metal zinc (dendrites) is generated during the treatment, which penetrates the separator and causes a short circuit. Furthermore, since the redox potential of zinc is lower than that of hydrogen, zinc is easily oxidized by water during storage in a charged state and self-discharge occurs, and hydrogen is generated from the zinc electrode during charging, resulting in reduced charging efficiency. However, there is a problem that it is particularly difficult to put into practical use a battery using a liquid electrolyte, but when the high ion conductive solid electrolyte of the present invention is used, the dissolution of metal ions is suppressed and slightly dissolved. However, since the rate at which the metal ions diffuse from the electrode is slow, it is unlikely that metal dendrites are generated, and even if dendrites are generated, the solid electrolyte itself can be prevented from penetrating from the negative electrode to the positive electrode. Furthermore, the water in the solid electrolyte is poorly reactive, and the problem of self-discharging is less likely to occur even for metals having a lower redox potential than hydrogen, and the electrolysis of water that competes with the reduction reaction of metals, that is, the reduction of protons. Since the reaction does not easily occur, the charging efficiency is also improved. The effect of suppressing the dissolution and diffusion of the metal ions and the effect of preventing the generation of dendrites can exert the same effect on the primary battery or the nickel hydrogen battery. Further, the zinc-air battery using the air electrode as the positive electrode has the same merits as described above, and it is possible to obtain a battery that can be easily charged because the diffusion of oxygen to the zinc electrode is suppressed.

In addition to zinc, there are many divalent or higher valent metals such as copper, cobalt, iron, manganese, chromium, vanadium, tin, molybdenum, niobium, tungsten, silicon, boron, and aluminum. When applied, a secondary battery using the above metal can be put into practical use.

In alkaline secondary batteries such as nickel-hydrogen batteries, an alkaline electrolyte impregnated in a porous separator is conventionally used, but the electrolyte according to the present invention has both the functions of the electrolyte and the separator. Since the electrolyte solution is not necessary or the amount thereof can be reduced, the energy density of the battery can be improved accordingly. Further, unlike a porous separator, even if it is a thin film, it is possible to prevent a short circuit, so that a thin film type electrode having a large surface area can be used.

The solid electrolyte of the present invention uses inexpensive raw materials and is based on a simple aqueous solution process.
It is significantly cheaper than existing perfluorosulfonic acid-based electrolytes. Further, unlike an inorganic solid material, it has flexibility, so that thin film processing is easy. When the composite of polyethylene oxide and a silicon compound, which has been tried so far, is selected, a composite compound having hot water resistance cannot be prepared even if the method of the present invention is applied, resulting in high cost as in the sol-gel manufacturing method. It is necessary to use the method. However, by selecting polyvinyl alcohol as in the present invention, an aqueous solution manufacturing method that is easy to manufacture and low in cost can be applied.

Since the solid electrolyte according to the present invention has proton conductivity, the solid electrolyte according to the present invention is similar to the conventional perfluorosulfonic acid type ion exchange membrane in that it has a fuel cell, a steam pump, a dehumidifier, an air conditioner, an electrochromic device, an electrolyzer It can be applied to electrolysis type hydrogen generator, electrolytic hydrogen peroxide production device, electrolyzed water production device, humidity sensor, hydrogen sensor. Since this solid electrolyte material exhibits high ionic conductivity even in alkaline type, it can be applied to electrochemical systems such as primary batteries, secondary batteries, and optical switch systems, or new battery systems using polyvalent metals.

[0057]

As described in detail above, according to the present invention, it is unnecessary to neutralize the stannate and the added salt with an acid in an aqueous solution in which polyvinyl alcohol coexists, and after removing water as a solvent, unnecessary. The major feature is to remove the salt to form a composite compound.Since an organic-inorganic composite compound that has both water absorption and water resistance can be easily prepared by an aqueous solution manufacturing method, it is low cost and high cost. An ion conductive solid electrolyte and an electrochemical system using the high ion conductive solid electrolyte can be provided.

Particularly, if only the neutralization reaction of the aqueous stannate solution occurs, the polycondensation reaction of stannic acid simply occurs. However, the coexistence of polyvinyl alcohol causes the entanglement of polyvinyl alcohol and stannic acid at a micro level to form a composite. The condensation polymerization reaction is promoted by heating and is strong,
In addition, a flexible composite compound can be obtained. Moreover, although the single polyvinyl alcohol dissolves in hot water, the composite compound does not dissolve in hot water due to the strong entanglement with the stannic acid compound, and it is possible to stably maintain the physical properties even in a high temperature humid environment, In addition, since both the polyvinyl alcohol and the stannic acid compound are highly hydrophilic, the composite compound can absorb a large amount of water even though it is water resistant, and can impart high ionic conductivity. Therefore, the water contained in the composite compound of the stannic acid compound and polyvinyl alcohol serves as a medium for the rapid diffusion of protons or hydroxide ions.

Further, silicate, borate, molybdate, tungstate, phosphate or the like is allowed to coexist in a raw material aqueous solution containing stannate and polyvinyl alcohol, or an acid for neutralizing the raw material aqueous solution. By adding boric acid or phosphoric acid as a component of the above, a silicic acid compound, a boric acid compound, a molybdic acid compound, a tungstic acid compound, or a phosphoric acid compound can be easily compounded. By combining these third and fourth components, the characteristics can be improved and the cost can be reduced.

The high ion conductive solid electrolyte of the present invention is used for a fuel cell, a steam pump, a dehumidifier, an air conditioner, an electrochromic device, an electrolysis type hydrogen generator, an electrolytic hydrogen peroxide production apparatus, an electrolyzed water production apparatus, and humidity. It can be applied to various electrochemical systems such as sensors, hydrogen sensors, primary batteries, secondary batteries, optical switch systems or new battery systems using polyvalent metals, and contributes to lowering the price of these electrochemical systems. be able to. Further, by making the electrolyte material alkaline, it is possible to use a low-priced material as a material for peripheral members such as electrodes used in the above electrochemical system.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01M 10/30 H01M 10/30 AF term (reference) 4J002 BE021 DE186 DE187 DH047 DJ007 DK007 GQ00 5G301 CA02 CA30 CD01 5H024 AA02 AA14 BB01 BB08 BB10 BB11 FF21 GG04 HH01 HH11 5H026 AA06 BB03 CX05 EE13 EE18 HH05 HH08 5H028 AA06 BB03 BB05 BB06 BB10 EE02 EE05 EE06 EE08 FF09 HH01 HH08

Claims (10)

[Claims] 1. A high ion conductive solid electrolyte comprising a composite compound of a stannic acid compound containing water and polyvinyl alcohol. 2. A stannic acid compound, polyvinyl alcohol and water obtained by neutralizing an aqueous solution of an alkali metal salt of stannic acid and polyvinyl alcohol with an acid to remove water as a solvent and then removing unnecessary salts. A high-ion-conducting solid electrolyte, which is a composite compound comprising 3. 100 before or after removing unnecessary salts
The high ion conductive solid electrolyte according to claim 2, which is subjected to a treatment of heating at a temperature of ℃ or more. 4. The high ion conductive solid electrolyte according to claim 1, wherein the ratio of the weight of the stannic acid compound calculated as SnO ₂ to the weight of polyvinyl alcohol is 0.08 or more. 5. The high ion conductive solid electrolyte according to claim 1, 2, 3 or 4, containing at least one of a silicic acid compound, a boric acid compound, a molybdic acid compound, a tungstic acid compound and a phosphoric acid compound. 6. The raw material aqueous solution contains at least one kind of alkali metal salt selected from silicic acid, boric acid, molybdic acid, tungstic acid and phosphoric acid, and the produced complex compound is a silicic acid compound, a boric acid compound, a molybdic acid compound. The high-ion-conducting solid electrolyte according to claim 2, 3, 4, or 5, containing at least one of: a tungstic acid compound and a phosphoric acid compound. 7. The high ion conductive solid electrolyte according to claim 1, 2, 3, 4, 5, or 6, wherein the composite compound is immersed in an acid solution. 8. The high ion conductive solid electrolyte according to claim 1, 2, 3, 4, 5 or 6, wherein the composite compound is immersed in an alkaline solution. 9. An electrochemical system using a high ion conductive solid electrolyte, wherein the high ion conductive solid electrolyte according to any one of claims 1 to 8 is used. 10. The electrochemical system is a fuel cell,
Steam pump, dehumidifier, air conditioner, electrochromic device, electrolysis device, electrolysis hydrogen generator, electrolytic hydrogen peroxide production device, electrolyzed water production device, humidity sensor,
The electrochemical system using a high ion conductive solid electrolyte according to claim 9, which is a new battery system using a hydrogen sensor, a primary battery, a secondary battery, an optical switch system or a polyvalent metal.