JP3270117B2 - Electrochemical element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrochemical device using an electrolyte solution, and more particularly to a device capable of controlling electric conductivity, comprising: The present invention relates to an electrochemical device having a polymer electrolyte layer made of a polymer material and a second electrode arranged apart from the polymer electrolyte layer.

[0002]

2. Description of the Related Art It has long been pointed out that the behavior of ions as charge carriers in an electrolyte solution is similar to the behavior of electrons and holes as carriers in a semiconductor.
Electrochemical rectifiers and amplifiers such as solution diodes and solution transistors have been proposed as electrochemical elements (for example, LETAW &BARDEEN; J. Appl.
hys., 25 (5), 600 (1954), OSHIDA; J. Phys. Soc. Japa
n, 15 (12), 2288 (1960), LANE &CAMERON; Electronic
s, 32 (9), 53 (1959), etc.).

In order for such an electrochemical device to perform the same electrical conductivity control as that of a semiconductor device, it is necessary to regulate the concentration distribution of charge carriers inside the device by an appropriate method. Early proposals for this method involved controlling the concentration of charge carriers, ie, ions, near the electrode by passing an electric current through the electrode to cause an electrochemical reaction, thereby causing concentration polarization. Thereafter, a method of forming an ion concentration distribution in a state where no electric current is passed by contacting a cation exchange resin with an anion exchange resin has been reported (for example, LOVRECEK, DESPIC &BOCKRIS; J. Phys. Chem., 63 ,
750 (1959), LOVRECEK &KUNST; Nature, 189 , 804 (196
1) etc.).

[0004]

The above-described conventional electrochemical devices have a drawback that when the electrolyte is a simple liquid, the electrolyte easily flows and is easily affected by vibration. In the case of a device using a solid electrolyte such as a polymer electrolyte, the movement of ions serving as charge carriers is slower than in the case of a liquid electrolyte,
There was a disadvantage that response was slow. In addition, when the electrolyte medium contains water and hydrogen ions and hydroxide ions are used as charge carriers, carrier movement is faster than other commonly used ions. There has been a problem that a gas is generated by the reaction and the gas is accumulated inside the element.

An object of the present invention is to reduce the influence of vibration,
An object of the present invention is to provide an electrochemical device which has no problem of gas generation from an electrode and has a fast response.

[0006]

According to the present invention, there is provided an electrochemical device, wherein the gap between the polymer electrolyte layer and the second electrode is filled with a medium mainly composed of a liquid, and the ionic species contained in the medium is filled. Ions common to the polymer electrolyte are contained as free ions in the polymer electrolyte layer at a higher concentration than the concentration in the medium, and the liquid is contained in the polymer electrolyte layer.

[0007]

The voltage-current characteristics of the electrochemical device of the present invention are asymmetric with respect to the origin as described below. That is,
The polymer constituting the polymer electrolyte layer has an ion-dissociating part in the molecular structure, swells with a solvent having a high dielectric constant, and forms a polymer ion (a part directly connected to the polymer structure and charged). It dissociates into free ions having the opposite polarity to the polymer ions. The free ions are bound by the electrostatic field force of the polymer ions fixed by the crosslinking, and most of them are confined inside the polymer electrolyte layer and distributed almost uniformly inside the polymer electrolyte layer. From the surface of the layer, some free ions leak into the external medium to an extent corresponding to the Debye length of the electrolyte solution at that location. Therefore, a free ion concentration gradient is generated near the surface of the polymer electrolyte layer. Since the first electrode is in close contact with the polymer electrolyte layer, the free ion concentration on the surface of the first electrode is substantially equal to the free ion concentration in the polymer electrolyte layer. On the other hand, in the medium, if the second electrode is positioned about the Debye length away from the polymer electrolyte layer, the free ion concentration on the surface of the second electrode is higher than the value on the surface of the first electrode. Lower. In the case where the free ions are generally charge carriers that are electrochemically reversibly oxidized and reduced on the electrodes, when an alternating voltage is applied between the first and second electrodes, the free ions are in either direction. Current can also flow. However, in practice, since the free ion concentrations on the surfaces of the first and second electrodes are different as described above, the magnitude of the concentration overvoltage differs depending on the direction of the current. As a result, the direction of the voltage applied to the electrochemical device Therefore, the amount of current flowing differs, and rectification appears.

Since the amount of ions leaking from the polymer electrolyte layer into the medium determines the characteristics of the electrochemical device of the present invention, the profile of the ion concentration distribution generated in the medium without passing an electric current can be adjusted appropriately. State
It is indispensable to guarantee stable operation of this electrochemical device. As mentioned earlier, this profile depends on the Debye length, which depends on the ion concentration in the medium. Therefore, the ion concentration profile can be controlled by dissolving an appropriate amount of electrolyte in the medium. The dissolved electrolyte desirably has the same ions as the free ions present in the polymer electrolyte layer. If the dissolved electrolyte is as high as the ion concentration of the polymer electrolyte, the ion concentration distribution between the first and second electrodes becomes almost uniform, and the element cannot operate effectively. It is not preferable because the Debye length becomes short, the range of leakage of free ions from the polymer electrolyte layer to the medium becomes narrow, and the influence on the second electrode becomes small. If the ion dissociation of the solvent itself constituting the electrolyte solution cannot be ignored or if the solvent used is difficult to purify and the presence of the electrolyte as some impurities cannot be ignored, these unavoidable ions (for example, water is used as the solvent) (Eg, H ₃ O ⁺ and OH ⁻ ), the influence of unavoidable ions on the device characteristics should be reduced. From the above points, the ion concentration in the medium is 1 ×
It should be 10 ⁻⁶ mol / l or more and 1 × 10 ⁻² mol / l or less.

Here, consider the case where the distance between the polymer electrolyte layer and the second electrode is much larger than the Debye length. In such a case, the portion formed near the surface of the polymer electrolyte layer and having a concentration gradient of free ions,
It does not substantially affect the electrochemical characteristics of the device.
As a result, this electrochemical element is regarded as a concentration battery including a polymer electrolyte layer having a high free ion concentration and a medium having a low free ion concentration, and it is difficult to exhibit desired characteristics. As described above, the Debye length depends on the ion concentration. In the case of monovalent ions, for example, if the ion concentration is 1 μmol / l in a solvent having a relative dielectric constant of 80, the Debye length is about 300 nm. The range in which the ion concentration significantly changes near the polymer electrolyte layer interface is up to about 20 times the Debye length.
The gap between the electrodes should generally be 6 μm or less. In the electrochemical device of the present invention, as described above, since the distance between the polymer electrolyte layer and the second electrode is small, it is possible to make the entire device small, thereby improving the response speed of the device. It is possible.

[0010] The electrochemical element of the present invention is a device in which ions in the electrolytic solution are used as charge carriers and the conductivity is controlled by controlling the concentration of ions near the electrodes. Is not preferred. It is desirable that the solvent used in the medium has a high dielectric constant and practically does not dissociate, and acetonitrile, propylene carbonate, dimethylformamide and the like can be used. However, even a solvent that slightly dissociates ions can be used as long as the ions generated from the solvent do not substantially participate in the electrode reaction under the operating conditions of the device. For example, even if water is used as a solvent, the electrolyte ions used as charge carriers are 1
A practical device can be manufactured if it is added in an amount of × 10 ⁻⁶ mol / l or more and the electrode reaction of the carrier proceeds in preference to the electrolytic reaction of water.

The medium mainly composed of a liquid in the electrochemical device of the present invention may be composed of only a usual liquid, but it is necessary to maintain a stable distance between the polymer electrolyte layer and the second electrode. Since it is effective for stabilizing the operating characteristics of the element,
A material obtained by inserting a suitable solid spacer or a porous body into a liquid, a cross-linked polymer swollen with a liquid, or the like may be used.

[0012] From practical demands, it should be ensured that the electrochemical device of the present invention does not wear out even when current is continuously applied. In order to achieve this, the electrochemical element has no deterioration or elution of the electrode due to energization,
It is required that there is no decomposition and consumption of the electrolyte due to energization. In order to prevent deterioration of the electrodes, the electrodes used in the device of the present invention need to be made of a conductor which is electrochemically inactive in a normal use state of the device. Materials satisfying such conditions include electrochemically noble metals such as gold, platinum, rhodium and alloys thereof, graphite and amorphous carbon. In order to prevent the deterioration of the electrolyte, the charge carriers present in the electrolyte undergo a reversible electrochemical reaction on the above-mentioned inactive electrode, and the carriers oxidized at the anode of the device are subjected to a reverse reaction at the cathode. Should be reduced. A carrier suitable for such a reversible oxidation / reduction reaction is iron.
Transition metal ions having multiple oxidation states such as (III) / iron (II), copper (II) / copper (I), cerium (IV) / cerium (III) and halogen ions such as rare earth ions, iodine and bromine And quinone compounds such as hydroquinone and naphthohydroquinone, and phenothiazine compounds such as thionin, N-methylphenothiazine and methylene blue.
These ions may form a complex in the presence of the ligand. Of course, be careful of the combination of the carrier, the electrode material, and the electrolyte solvent so that the components of the electrolyte other than the electrode material and the carrier do not deteriorate at the oxidation-reduction potential at which the oxidation or reduction reaction involving these ions proceeds. You should choose. That is, the substance used as the carrier must be reduced at a noble potential and oxidized at a lower potential than the electrode material and the electrolyte solvent.

The crosslinked polymer constituting the polymer electrolyte layer is used for the purpose of holding the electrolytic solution and for fixing the ion having the opposite charge to the carrier ion in the electrolytic solution. By holding the electrolyte and preventing its flow,
Even if shock or vibration is applied to the element, stirring of the electrolyte does not occur. Therefore, the carrier concentration in the vicinity of the electrode is prevented from being disturbed by vibration and impact, and the operation of the element is stabilized. Further, by holding a layer having a high carrier concentration in the element, the electric resistance (internal resistance) of the element can be reduced. Further, by using the crosslinked polymer electrolyte, a layer having a high carrier concentration can be formed with good reproducibility in the vicinity of the second electrode of the device without contacting the second electrode, and the carrier near the second electrode can be formed. Can be appropriately maintained. Such a polymer electrolyte layer is composed of a crosslinked polymer electrolyte and a liquid that swells the polymer electrolyte. The crosslinked polymer electrolyte plays a role of supplying ions at an appropriate concentration into the polymer electrolyte layer, preventing flow inside the polymer electrolyte layer, and stabilizing the position of the polymer electrolyte layer in the device. In order not to slow down the movement of the carriers in the polymer electrolyte layer, the smaller the ratio of the polymer to the liquid, the better. When the proportion of the polymer in the polymer electrolyte layer increases, the number of liquid molecules that are adsorbed around the polymer chain and whose movement is restricted is increased, and the dissolved carrier ions are difficult to move. In order to allow carrier ions to move in the same manner as in a free liquid, it is necessary that the liquid be present in the polymer at least in the same weight or more. When the weight ratio of the liquid to the polymer is 100 times or more, the polymer electrolyte becomes very soft, and the purpose of stabilizing the position of the polymer electrolyte layer cannot be achieved. For the reasons described above, the polymer electrolyte layer is required to be composed of a crosslinked polymer electrolyte swelled by a liquid at a weight ratio of 1 to 100 times.

The polymer constituting the polymer electrolyte layer has an ion dissociable portion in the molecule. For the operation of the electrochemical device of the present invention, as described above, it is essential to bind free ions, which are charge carriers, in the polymer electrolyte layer. The charge having the opposite sign to the free ions in the polymer electrolyte layer must appear on the polymer side. This condition is satisfied if a polymer that is a salt of the above-mentioned free ion is used as a crosslinkable polymer material. Further, free ions used as charge carriers may be introduced by an ion exchange operation after the formation of the polymer electrolyte layer.

As the anion constituting the ion dissociable portion, a sulfonic acid group, a phosphoric acid group, a carboxyl group and the like can be used. As the cation,
Quaternary ammonium, amine, and the like can be used.

The electrochemical device of the present invention preferably has a container for holding the first and second electrodes, the polymer electrolyte layer and the medium in order to stabilize the operation.
This container firstly prevents liquid from being lost from the element, secondly prevents moisture and other electrolyte ions from entering the inside of the element from the outside, and thirdly determines the relative position of each part in the element. Takes the role of fixed holding. The material of the container must be a material such as a solvent such as water or an electrolytic solution, electrolyte ions, etc., which is difficult to penetrate, is electrochemically inert, has appropriate hardness, and is an electrically insulating material. From this point of view, glass and various ceramics,
You can choose plastic and so on.

[0017]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic sectional view showing an example of the basic configuration of the electrochemical device of the present invention.

This electrochemical element has a first electrode 1 in the form of a flat plate, a polymer electrolyte layer 3 which is closely and uniformly laminated on the first electrode 1, and is opposed to the polymer electrolyte layer 3 and A second electrode 2 is provided at a predetermined distance from the polymer electrolyte layer 3, and a liquid having a high dielectric constant is mainly disposed between the polymer electrolyte layer 3 and the second electrode 2. Medium 4 is filled. The first electrode 1 and the second electrode 2 are parallel. The electrodes 1 and 2, the polymer electrolyte layer 3 and the medium 4 are sealed in a container 5. The polymer electrolyte layer 3 is made of a crosslinked ion-dissociative polymer substance,
The liquid constituting the medium 4 is contained in a large amount (for example, 50% by weight or more). The medium 4 is an electrolyte, and ions common to the ionic species contained in the medium 4
It is contained as a free ion in the polymer electrolyte layer 3 at a concentration higher than that in the inside. The gap between the polymer electrolyte layer 3 and the second electrode 2 is made equal to or less than the Debye length of the medium 4 as an electrolyte solution.

In this electrochemical device, as described in the above-mentioned "action" section, a small amount of free ions leak from the surface of the polymer electrolyte layer 3 into the medium 4 to the extent of the Debye length. As a result, a free ion concentration gradient is generated near the surface of the polymer electrolyte layer 3, and the first and second electrodes 1, 2
The free ion concentration on the surface of
The concentration overvoltage differs depending on the direction of the current,
Rectification characteristics appear in this electrochemical element.

The form of the electrochemical device of the present invention is not limited to that shown in FIG. In particular, when a small-sized element with a small capacity is formed, for example, as shown in FIGS. 2 (a) and 2 (b), the first and second electrodes 1, 2 are formed on the same surface of the inner wall of the container 5. It is good to be arranged in. The polymer electrolyte layer 3 is provided so as to cover the entire first electrode 1, and the side surface of the polymer electrolyte layer 3 and the side surface of the second electrode 2 are arranged close to each other in the order of the Debye length. Will be done. In this case, each of the electrodes 1 and 2 can be easily formed as an electrode pattern using a printing technique.
This electrochemical device is different from the electrochemical device shown in FIG. 1 in that carriers flow in the lateral direction, but the principle that voltage-current characteristics appear asymmetrically with respect to the origin is the same as in the above-described case.

Further, as shown in FIG. 3, a plurality of first electrodes 1 and a plurality of second electrodes 2 may be arranged on the same plane to form the electrochemical device of the present invention. Each of the electrodes 1 and 2 has an elongated shape. Also in this case, similarly to the electrochemical device shown in FIG. 2, the polymer electrolyte layer 3 is provided so as to cover the entire first electrode 1, and the side surface of the polymer electrolyte layer 3 and the second electrode The two side surfaces are arranged close to each other by the Debye length. With such a configuration, the cross-sectional area of the portion where the polymer electrolyte layer 3 and the second electrode 2 face each other can be increased, and the current capacity can be increased as compared with that shown in FIG. It becomes possible.

Further, the electrodes 1 and 2 can be arranged coaxially. FIG. 4 is a schematic cross-sectional view showing the configuration of such an electrochemical device. In this electrochemical device, a cylindrical second electrode 2 is provided at the center, and the polymer electrolyte layer 3, the first electrode 1, and the side wall of the container 5 are coaxially arranged with respect to the second electrode 2. Are arranged in a direction from the outside to the outside. Of course, a gap of approximately the Debye length is provided between the second electrode 2 and the polymer electrolyte layer 3, and the gap is filled with the medium 4. Thus, each electrode 1,
By arranging 2 coaxially, the end portion of the electrode is not substantially present, and the carrier concentration distribution is not disturbed by the existence of the end portion, so that good operation can be expected.

Next, an example in which the electrochemical device of the present invention is actually prepared will be described.

Example 1 In a nitrogen atmosphere, two glass plates were horizontally opposed at a distance of 50 μm using a polyester film as a spacer. Between these two glass plates, N, N-dimethylacrylamide, acryloylaminopropyltrimethylammonium chloride, N, N-methylenebisacrylamide, N, N, N ', N'-tetramethylethylenediamine, ammonium persulfate and water 800: 8: 100: 1:
A solution mixed at a ratio of 2: 3200 (weight ratio) was filled, allowed to stand, and polymerized. The obtained water-containing film was sufficiently washed with a 1:30 solution (weight ratio) of potassium iodide and water, and then immersed in 1000-fold volume of pure water for 3 hours or more.

Next, two glass plates having a platinum pattern with a width of 100 μm and a length of 10 mm formed on the surface thereof were prepared, one of the glass plates was wetted with water, and the other was placed on the other glass plate with a knife. 5μ thick with a cut of about 2mm
m polyester films were superimposed such that the positions of the platinum patterns and the cuts were substantially the same.

The above-mentioned hydrated film was placed on the polyester film, and another glass plate was overlaid thereon such that the platinum pattern almost coincided with the position of the platinum pattern on the lower glass plate. As a result, FIG. 1 shows that the platinum pattern of the upper glass plate is the first electrode, the platinum pattern of the lower glass plate is the second electrode, the hydrated film is the polymer electrolyte layer, and the iodine ion is the carrier ion. An electrochemical device of the configuration was formed.

When a voltage of 0.1 V is applied between the two electrodes of this element so that the first electrode becomes positive, 800 μA is applied.
Current flowed. Conversely, when a voltage of 0.1 V was applied so that the first electrode became negative, a current of 70 μA flowed. From this, it was found that this electrochemical element had asymmetrical voltage / current characteristics with respect to the origin and had rectifying properties.
FIG. 5 shows a voltage-current curve of the device.

Example 2 Polyvinyl alcohol and 2,6-di- (4'-
A mixture of (diazidobenzal) -4-methylcyclohexane and formic acid was spin-coated, dried, and then irradiated with ultraviolet light from a high-pressure mercury lamp for photocrosslinking. Thereafter, the platinum plate was sufficiently washed with water, a water-containing film prepared in the same manner as in Example 1 was placed on the coated surface of the platinum plate, and another platinum plate was further placed. The device thus obtained was left in a glass container overnight to be stabilized, and an electrochemical device having the configuration shown in FIG. 1 was completed. In this electrochemical device, a medium formed on a platinum plate by photo-crosslinking at first becomes a medium, and since this medium is sufficiently washed with water, it contains a large amount of water.

Example 3 Two striped platinum electrodes having a width of 50 μm and a length of 5 mm were formed in parallel on a glass plate at a distance of 10 μm from each other. γ
1: 1 methacryloxypropyltrimethoxysilane and water
After the glass plate was immersed in the mixed solution for 3 hours,
Heat treatment was performed at 00 ° C. for 5 minutes. Next, a window having a size of 0.5 mm × 4 mm was cut out on a polyester film having a thickness of 5 μm, and the window was aligned with the platinum electrode.
This polyester film was overlaid on the glass plate.

Subsequently, acrylamide, 3-methacrylaminopropyltrimethylammonium chloride, N, N'-methylenebisacrylamide and N, N, N ', N'-
5000: 30: 1250: 120: 1: 100 by weight of tetramethylethylenediamine, riboflavin and water
The solution was mixed at a ratio of 000 to make a solution, and the solution was dropped into the hole portion of the polyester film film on the above-mentioned glass plate, and pressed with another glass plate from above. And
The solution sealed in the window portion was irradiated with light having a wavelength of 366 nm using an optical mask, and a predetermined portion of the solution was photopolymerized to form a polymer electrolyte layer as shown in FIG. After that, remove the upper glass plate and wash with water to remove the unpolymerized solution, and then add 1:10 potassium iodide and water.
It was immersed in a solution (weight ratio). In addition, one of potassium iodide
After washing with a μmol / l solution, the resultant was covered with a polycarbonate resin and sealed with a small amount of the solution to complete an electrochemical device.

[0031]

As described above, according to the present invention, a medium mainly composed of a liquid is filled between a polymer electrolyte layer and a second electrode, and ions common to ionic species contained in the medium are contained in the medium. It is contained as a free ion in the polymer electrolyte layer at a higher concentration than the concentration in the medium, and the liquid is contained in the polymer electrolyte layer, thereby exhibiting a rectifying action at a low voltage and a small current, and the structure is reduced. It is relatively simple, does not require high-purity components, can be made small using printing technology, is not easily affected by vibration, has no problem of gas generation from electrodes, and responds There is an effect that an electrochemical element having a high speed can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of a basic configuration of an electrochemical device of the present invention.

FIG. 2A is a schematic cross-sectional view illustrating a configuration of an electrochemical device according to another embodiment of the present invention, and FIG. 2B is a schematic plan view illustrating an arrangement of each electrode in the electrochemical device.

FIG. 3 is a schematic plan view showing a configuration of an electrochemical device according to still another embodiment of the present invention.

FIG. 4 is a schematic cross-sectional view showing a configuration of an electrochemical device of the present invention in which each electrode is coaxially arranged.

FIG. 5 is a graph showing the voltage of the electrochemical device according to the first embodiment of the present invention.
It is a figure showing a current curve.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st electrode 2 2nd electrode 3 Polymer electrolyte layer 4 Medium 5 Container

Claims (3)

(57) [Claims] 1. A first electrode, a polymer electrolyte layer formed of a crosslinked polymer substance disposed in close contact with the first electrode, and a second electrolyte layer disposed apart from the polymer electrolyte layer. In an electrochemical device having an electrode, a gap between the polymer electrolyte layer and the second electrode is filled with a liquid-based medium, and ions common to ion species contained in the medium are An electrochemical device, wherein the liquid is contained as free ions in the polymer electrolyte layer at a concentration higher than the concentration in the medium, and the liquid is contained in the polymer electrolyte layer. 2. The method according to claim 1, wherein the content of the liquid in the polymer electrolyte layer is 5%.
The electrochemical device according to claim 1, wherein the content is 0% by weight or more. 3. A gap between the polymer electrolyte layer and the second electrode is 6 μm or less, and an ion concentration in a medium filling the gap is 1 × 10 ⁻⁶ mol / l or more and 1 × 10 ^−2. mo
3. The electrochemical device according to claim 1, wherein the ratio is 1 / l or less.