JP5646104B1 - Magnesium air battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolyte for a magnesium air battery excellent in terms of power generation duration and discharge capacity. SOLUTION: In a case 11, four cells 20 are laminated, and a conductive metal plate 28 is laminated at one end, and the lower surface is sealed with a cap 15 in which a through hole 16 is formed. The magnesium air battery 10 is configured. Each cell 20 includes a stainless positive electrode 21, a positive electrode active body 22 including activated carbon, an electrolyte layer 23 formed of a separator sheet holding an electrolyte, and a negative electrode 24 formed of a magnesium alloy AZ31. The electrolyte layer 23 is formed by impregnating ethylenediaminetetraacetic acid tetrasodium (EDTA4Na) with an aqueous solution containing 0.2% potassium chloride and then drying. By using ethylenediaminetetraacetic acid tetrasodium as an electrolytic solution, the production of magnesium hydroxide can be suppressed, and the power generation duration and the discharge capacity can be improved. [Selection] Figure 2

Description

  The present invention relates to a magnesium-air battery that generates power using magnesium and oxygen.

In recent years, magnesium-air batteries using magnesium or a magnesium alloy on the negative electrode side and oxygen in the air on the positive electrode side have been developed. The reaction at the positive electrode and the negative electrode in the magnesium-air battery is as follows.
Positive electrode side: O ₂ + 2H ₂ O + 4e ⁻ → 4OH ⁻
Negative electrode side: 2Mg + 3OH ⁻ → 2Mg ²⁺ + 4e ⁻

Regarding magnesium-air batteries, the following problems have been pointed out in relation to the pH of the electrolyte. When the electrolytic solution is acidic, a phenomenon occurs in which self-discharge, that is, electrons eluted from magnesium or magnesium alloy on the negative electrode side react with hydrogen ions on the negative electrode to generate hydrogen gas. On the other hand, when the electrolytic solution is alkaline, magnesium hydroxide, that is, Mg (OH) ₂ is generated on the magnesium surface, and a passive film that does not allow electricity and ions to pass therethrough is formed, so that no current flows.
Patent Document 1 and Patent Document 2 disclose that polyvalent carboxylates such as citrate and succinate are used in order to solve the above-described problems. According to Patent Document 1, as an effect of using a polyvalent carboxylate, “the ions of the polyvalent carboxylate are chelate-bonded to the magnesium ions and bonded to the magnesium ions, so the magnesium ions are bonded to the hydroxide ions. It is said that the solubility of magnesium ions can be drastically improved ”and“ the aqueous electrolyte can be easily prevented from changing to alkaline by the buffering action of polyvalent carboxylate ions ”.

Japanese Patent No. 5192163 JP 2010-182435 A

However, as described above, the electrolyte of the magnesium-air battery has a problem that self-discharge occurs when it is acidic, and a passive film is formed when it is alkaline. In the technique 2 as well, it is necessary to adjust the pH within a range where these problems can be avoided, and it is not easy to generate power stably.
Moreover, although citric acid is considered to be effective in Patent Document 1, “capacitance cannot be measured because the voltage was reduced to 0.1 V or less before the negative electrode was completely dissolved in the electrolytic solution to which citric acid was added. (Take Yasuda et al., “Development of Magnesium Fuel Cell” http://www.tonio.or.jp/koryu/ronbunsyu-27/H25-045.pdf) There was still room for improvement.
An object of this invention is to provide the electrolyte solution of the magnesium air battery excellent in the surface of electric power generation continuation time and discharge capacity in this condition.

The present invention is a magnesium air battery that generates electricity using magnesium and oxygen,
A negative electrode made of magnesium or a magnesium alloy;
A positive electrode made of a conductive material;
A positive electrode active body arranged in contact with the positive electrode and supplying oxygen;
It can be comprised as a magnesium air battery provided with the electrolyte layer which is arrange | positioned between the said positive electrode active body and the said negative electrode, and hold | maintains the electrolyte solution containing the aqueous solution of the aminopolycarboxylate which shows alkalinity.

The aminopolycarboxylate has at least one —N (CH ₂ COOH) ₂ and can stably chelate with magnesium ions. In the present invention, among various aminopolycarboxylates, an alkaline solution is used.
According to the present invention, the aminopolycarboxylate can chelate bond with magnesium ions, so that the generation of magnesium hydroxide can be suppressed and the formation of a passive film can be suppressed. In the present invention, since the electrolytic solution becomes alkaline, the problem of self-discharge that occurs under acidic conditions can be naturally avoided.
That is, the present invention avoids the problem that the electrolyte of the magnesium-air battery is acidic under the condition that the electrolyte is made alkaline, and is alkaline by using an aminopolycarboxylate that forms a chelate bond with magnesium ions. It also tries to avoid the problems that occur below. By doing so, the magnesium-air battery of the present invention can improve the power generation duration and the discharge capacity.

In the magnesium air battery of the present invention,
Examples of the aminopolycarboxylate include ethylenediaminetetraacetic acid tetrasodium (EDTA4Na), ethylenediaminetetraacetic acid trisodium (EDTA3Na), nitrilotriacetic acid trisodium (NTA3Na), diethylenetriaminepentaacetic acid pentasodium (DTPA5Na), hydroxyethylethylenediaminetriacetic acid triacetate. Sodium (HEDTA3Na), triethylenetetramine-N, N, N ′, N ″, N ″, N ″ ′ hexadium (TTHA6Na), N- (2-hydroxyethyl) iminodisodium (HIDA2Na), N, N— Using at least one of di (2-hydroxyethyl) glycine-sodium (DHEGNa), tetrasodium glutamate diacetate (GLDA4Na), and ethylenediamine-N, N′-trisodium disuccinate (EDDSH3Na) It is good.
These may be used alone or in combination. fa
In these aminopolycarboxylates, sodium hydroxide may be added when the alkalinity is very weak.

In the magnesium-air battery of the present invention,
It is preferable that the electrolytic solution during power generation is adjusted to pH 8 or more and pH 13 or less.
By adjusting the pH in this way, self-discharge that occurs under acidic conditions can be reliably avoided. The pH can be adjusted by the concentration of the electrolytic solution or the addition of an alkaline substance such as sodium hydroxide.

In the magnesium air battery of the present invention,
The electrolytic solution preferably contains at least one of sodium chloride and potassium chloride in the range of 0.05% by weight to 18% by weight.
By carrying out like this, the electrical conductivity of electrolyte solution can be improved.

In the present invention, the electrolyte layer can have various configurations.
As a first configuration of the electrolyte layer,
The electrolyte layer may be configured by a tank that stores the electrolytic solution in a state in which at least a part of the negative electrode and the positive electrode active body is immersed.
The electrolytic solution may be stored in the tank from the beginning, or the electrolytic solution may be injected into the tank at the start of power generation. Alternatively, a solid aminopolycarboxylate may be stored in the tank, and water may be injected into the tank at the start of power generation.

As a second configuration of the electrolyte layer,
The electrolyte layer may be constituted by a water retaining body that contacts at least part of the negative electrode and the positive electrode active body and absorbs and holds the electrolytic solution.
According to such a configuration, since the electrolytic solution is held in the water retaining body, there is an advantage that liquid leakage is easily suppressed. Even in such a configuration, the electrolytic solution may be held in the water holding body from the beginning of the assembly of the magnesium-air battery, or the electrolytic solution may be supplied from the outside to the water holding body at the start of power generation.

In the case of the second configuration, that is, the configuration using the water retaining body,
The electrolyte is held as a solid at a site that can be eluted in the water holding body in a state before the start of power generation,
The water holding body may be provided with a supply mechanism for supplying an amount of water capable of realizing the elution from the outside.
By doing so, since only the solid exists in the battery before the start of power generation, it can be stored without worrying about liquid leakage. In addition, power generation can be started simply by supplying water from the outside.
Possible parts for holding the electrolyte before the start of power generation include the surface or inside of the water retention body, the contact surface between the negative electrode and the water retention body, the contact surface between the positive electrode active body and the water retention body, and the like.

As a supply mechanism for supplying electrolyte or water from the outside,
In the case of including a case that encloses the negative electrode, the positive electrode, the positive electrode active body, and the water retaining body,
The supply mechanism may be a through hole formed in the lower surface of the case. The size and number of the through holes are arbitrary.
By so doing, when the lower surface of the magnesium-air battery is immersed in a container storing water or the like, water can be sucked into the water retaining body due to the water absorption of the water retaining body, and power generation can be started. Compared to a mechanism that supplies water etc. from the top surface of the magnesium air battery, it is only necessary to immerse the magnesium air battery, so it is simple and avoids leakage of water etc. during supply, and a short circuit caused by leaked water etc. There is also an advantage that can be suppressed.

In addition, when a through hole is provided on the lower surface,
An external connection terminal connected to the negative electrode and the positive electrode may be formed above the center of the case.
In this way, the circuit can be connected to the terminal even when the magnesium-air battery is immersed in water or the like.

The water retaining body can have various configurations, for example,
The water-retaining body may have a weight density of 100 g / square meter or more and 1000 g / square meter or less based on pulp.
The water retaining body may be formed only from pulp, or may be formed by combining pulp and nonwoven fabric. By setting the above-described weight density, water absorption sufficient to start power generation of the magnesium-air battery can be ensured.

Regardless of the configuration of the electrolyte layer, in the magnesium-air battery of the present invention,
The positive electrode active material may use at least a part of activated carbon and manganese dioxide.
Activated carbon can store oxygen in the air and supply it. Manganese dioxide can liberate oxygen atoms by reacting with water. Therefore, a positive electrode active body can be comprised by using these substances.
These may be used alone or in combination. Further, it may be used in a solid state or may be used after being powdered and laminated on a sheet.

  In the present invention, the above-described features are not necessarily all provided, and some of them may be omitted or combined as appropriate. In addition to the magnesium-air battery, the present invention can take various forms. For example, a manufacturing method for manufacturing the above-described magnesium-air battery, a power generation method using the above-described magnesium-air battery, an electrolyte used for the magnesium-air battery, and an electrolyte that holds the electrolyte used for the magnesium-air battery in a solid state For example, a method for producing a layer.

It is explanatory drawing which shows the external appearance of the magnesium air battery in an Example. It is explanatory drawing which shows the internal structure of the magnesium air battery in an Example. It is a graph which shows the measurement result of the power generation continuation time of the magnesium air cell in an example. It is a graph which shows the measurement result of the discharge capacity of the magnesium air cell in an Example. 6 is an explanatory diagram showing an internal structure of a magnesium-air battery in Example 2. FIG.

  FIG. 1 is an explanatory view showing the appearance of a magnesium-air battery 10 in the example. The magnesium-air battery 10 of the embodiment is configured to start power generation by immersing the lower part in water. The structure and power generation capacity will be described below.

A. Overall structure:
The magnesium-air battery 10 has a structure in which a plurality of cells are incorporated in a resin case 11. A recess 12 that is recessed in the width direction is formed above the case 11, and a terminal 13 for connecting to an external circuit is provided here. In this embodiment, the terminal 13 has a structure in which a part of the conductive metal constituting the electrode of the cell is exposed. You may make it provide the terminal 13 separately from the electrode of a cell.

  The state which looked at the magnesium air battery 10 from the downward direction was shown in the lower side of the figure. As shown in the figure, a step portion 11s is formed on the lower surface of the case 11, and a cap 15 in which a plurality of through holes 16 are formed is fitted and sealed. By standing the magnesium-air battery 10 in a container or the like in which water is stored with the cap 15 as the bottom surface, water penetrates into the case 11 through the through hole 16 and power generation can be started.

  In this embodiment, since the terminal 13 for connecting to an external circuit is provided on the upper side, even when the magnesium air battery 10 is soaked in water as described above, the battery is connected to the external circuit without worrying about a short circuit or the like. Can be connected. In the present embodiment, the terminal 13 is formed at the upper end. However, from the viewpoint of avoiding the terminal 13 being immersed in water, the terminal 13 may be provided above the water level during power generation. It can be provided at any position above the half of the case 11.

  On the side surface of the case 11, a reference line 14 serving as a reference for immersing the magnesium-air battery in water at the start of power generation is drawn. However, the reference line 14 is only a guideline, and power generation can be started even if the water level is slightly lower than the reference line 14.

FIG. 2 is an explanatory diagram showing the internal structure of the magnesium-air battery 10 in the example. The state of the AA cross section in a perspective view (FIG. 1) was typically shown.
As shown in the figure, the magnesium-air battery 10 is sealed with four cells 20 stacked in a case 11 and a conductive metal plate 28 stacked on one end. The number of cells 20 can be arbitrarily set. The lower side of the case 11 is sealed with a cap 15 in which a through hole 16 is formed.

An enlarged view of each cell 20 is shown on the lower side of the figure. The cell 20 has a structure in which four layers are stacked.
The positive electrode 21 can be formed of a conductive metal such as stainless steel or copper. In this embodiment, stainless steel is used.
The positive electrode active body 22 is a layer in which activated carbon powder is laminated. Instead of activated carbon, manganese dioxide or the like may be used.
The electrolyte layer 23 is composed of a separator sheet holding an electrolyte.
The negative electrode 24 is made of a magnesium alloy AZ31. Magnesium may be used.
The four cells are arranged in series such that the positive electrode 21 is in contact with the negative electrode 24. The positive electrode 21 of the cell 20 located at the left end in the drawing and a part of the upper end of the metal plate 28 are configured to be exposed from the case 11 and function as the terminal 13 described in FIG.

The structure of the electrolyte layer 23 will be described in more detail.
The separator sheet is a hybrid material of pulp and nonwoven fabric, and its weight density is about 100 to 1000 grams / square meter.
In this embodiment, an aqueous solution obtained by adding 0.2% of potassium chloride to ethylenediaminetetraacetic acid tetrasodium (EDTA4Na) is used as an electrolytic solution. When manufacturing the magnesium-air battery 10, the above electrolyte solution is infiltrated into the separator sheet and then dried to form the electrolyte layer 23. Since the electrolyte layer 23 manufactured in this way does not contain a liquid before the start of power generation, there is no concern that liquid leakage occurs when the magnesium-air battery 10 is stored.
When the magnesium-air battery 10 is immersed in water at the start of power generation, the separator sheet absorbs water, and the preliminarily retained tetrasodium ethylenediaminetetraacetate (EDTA4Na) is eluted, so that it functions as an electrolytic solution.

The aqueous solution of ethylenediaminetetraacetic acid tetrasodium (EDTA4Na) used in this example exhibits an alkalinity of about pH 8-13. Therefore, it is possible to avoid self-discharge that occurs when the electrolyte is acidic.
In addition to this, for the electrolyte layer 23, ethylenediaminetetraacetic acid trisodium (EDTA3Na), nitrilotriacetic acid trisodium (NTA3Na), diethylenetriaminepentaacetic acid pentasodium (DTPA5Na), hydroxyethylethylenediaminetriacetic acid trisodium (HEDTA3Na), triethylenetetramine -N, N, N ', N ", N", N "' hexasodium (TTHA6Na), N- (2-hydroxyethyl) imino disodium (HIDA2Na), N, N-di (2-hydroxyethyl) glycine Monosodium (DHEGNa), tetrasodium glutamate diacetate (GLDA4Na), ethylenediamine-N, N′-trisuccinate (EDDSH3Na), etc. may be used, and the pH of the electrolyte is 8 or less. In such cases, an alkali such as sodium hydroxide It may be held in accordance with the sexual material.

B. Power generation duration:
FIG. 3 is a graph showing the measurement results of the power generation duration time of the magnesium-air battery in the example. The vertical axis represents current value, and the horizontal axis represents elapsed time. In this example, 6% ethylenediaminetetraacetate (EDTA4Na) was added to potassium chloride O.D. An aqueous solution mixed at a weight ratio of 2% is used as the electrolytic solution, and the result is shown by a curve C1 in the figure. As a comparative example, the measurement result when the electrolytic solution is a 10% aqueous solution of potassium chloride is shown by a curve C2. As an external circuit, a bullet-type white LED (Vf = 2.8 V, 53 lumens / w, a current range where practical brightness can be obtained is 2 mA or more) was connected.
As shown in the figure, the comparative example (curve C2) can obtain a high current value at the beginning of the measurement, but the current value suddenly decreases after 4 hours, and becomes less than 2 mA after about 10 hours. I can't get the brightness. On the other hand, in this example, as shown by the curve C1, a current value of 10 mA or more is obtained even after 24 hours have elapsed, and it can be seen that the power generation duration time is significantly improved.

C. Discharge capacity:
FIG. 4 is a graph showing the measurement results of the discharge capacity of the magnesium-air battery in the example. The result of this example is shown in a curve C11, and the result of the comparative example is shown in a curve C12. The structure of the magnesium-air battery in the examples and comparative examples is the same as in the case of the power generation duration (FIG. 3). A 10 ohm fixed resistor was connected as a load by an external circuit. In the comparative example (curve C12), a high output voltage was obtained at the beginning of the measurement, but the discharge capacity was about 450 mAh / g because the power generation continuation time was short. On the other hand, in the case of this example (curve C11), the discharge capacity is about 1900 mAh / g, which is about four times that of the comparative example.

D. Effects and variations:
As described above, according to the magnesium-air battery 10 of the present example, it was confirmed that the power generation duration and the discharge capacity are greatly improved as compared with a general magnesium battery using potassium chloride as an electrolyte. did it.
The above-mentioned improvement is obtained for the following reason. That is, ethylenediaminetetraacetic acid tetrasodium (EDTA4Na) used in the electrolytic solution of the example is a kind of aminopolycarboxylate, and can stably chelate bond with magnesium ions. As a result, it can suppress that magnesium ion reacts with hydroxide ion and generates magnesium hydroxide, and can suppress formation of a passive film. In the present invention, since the electrolytic solution becomes alkaline, the problem of self-discharge that occurs under acidic conditions can be naturally avoided.

The magnesium air battery 10 described in the embodiment can take various modifications as shown below.
(1) In the Example, the example which hold | maintains the solid electrolyte in the electrolyte layer 23 in the state before electric power generation was shown. Instead, the electrolyte can be held at various sites that can be eluted into the electrolyte layer 23, for example, the contact surface between the negative electrode 24 and the electrolyte layer 23, or the contact surface between the positive electrode active body 22 and the electrolyte layer 23. Or the like.
(2) In the embodiment, the solid electrolyte is held in the electrolyte layer 23 and power generation is started by adding water. However, the electrolyte solution may be held in the electrolyte layer 23 in advance. Good.
(3) Although the example which used the separator sheet for the electrolyte layer 23 was shown in the Example, the electrolyte layer 23 is good also as a tank which stores a liquid as shown below.

FIG. 5 is an explanatory diagram showing the internal structure of the magnesium-air battery 10A according to a modification. In the modified magnesium-air battery 10A, as in the embodiment, four cells 20A are stacked in series inside resin cases 11A and 11B, and a metal plate 28A serving as an electrode is stacked on the negative electrode side.
However, the cases 11A and 11B are in the shape of a container whose bottom surface is also closed, and the cell 20A and the metal plate 28A are enclosed by covering the lower case 11A with the upper case 11B and bonding them.
A through hole 18 is provided on the upper surface of the case 11B, from which an electrolytic solution can be injected.

  The structure of the cell 20A is shown at the bottom of the figure. The positive electrode 21, the positive electrode active body 22, and the negative electrode 24 are the same as those in the example. In the modification, a spacer 23A is attached instead of the electrolyte layer in the embodiment. In the modification, the cylindrical spacer 23A is stopped by a pin 23B penetrating from the positive electrode 21 to the negative electrode 24. For convenience of illustration, the head of the pin 23B is drawn so as to protrude from the surfaces of the positive electrode 21 and the negative electrode 24, but the head of the pin 23B is connected to the positive electrode 21 so that the positive electrode 21 and the negative electrode 24 of the adjacent cell 20A can be easily contacted. It is preferable to process so as not to protrude from the negative electrode 24. The spacer 23A can be mounted in various structures such as adhesion, in addition to using the pin 23B.

The spacer 23A forms a predetermined gap between the positive electrode active body 22 and the negative electrode 24, and functions as a tank that stores the electrolyte together with the cases 11A and 11B. When the electrolytic solution is injected from the through hole 18, the entire inside of the case 11 </ b> A is filled with the electrolytic solution, so that the portion between the positive electrode active body 22 and the negative electrode 24 functions as an electrolyte layer that contributes to power generation.
Also in the modification, for example, in a state before power generation, a solid electrolyte may be held on any part in the case 11 or on the surfaces of the positive electrode 21, the positive electrode active body 22, and the negative electrode 24. . In this way, when water is injected from the through hole 18, the electrolyte retained in advance is melted and becomes an electrolytic solution, so that power generation can be started.
The spacer 23A is not necessarily provided between the positive electrode active body 22 and the negative electrode 24, and a groove for fixing the positive electrode active body 22 and the negative electrode 24 with a predetermined interval may be provided on the inner surface of the case 11B. Good.

  In the above, the Example and modification of this invention were demonstrated. The present invention need not have all the features described in the embodiments and the like, and some of them may be omitted or combined as appropriate.

  The present invention can be used to improve the power generation duration and discharge capacity of a magnesium-air battery.

DESCRIPTION OF SYMBOLS 10, 10A ... Magnesium air battery 11, 11A, 11B ... Case 11s ... Step part 12 ... Recess 13 ... Terminal 14 ... Reference line 15 ... Cap 16 ... Through-hole 20, 20A ... Cell 21 ... Positive electrode 22 ... Positive electrode active body 23 ... Electrolyte layer 23A ... Spacer 23B ... Pin 24 ... Negative electrode 28, 28A ... Metal plate

Claims (10)

A magnesium-air battery that generates electricity using magnesium and oxygen,
A negative electrode made of magnesium or a magnesium alloy;
A positive electrode made of a conductive material;
A positive electrode active body arranged in contact with the positive electrode and supplying oxygen;
An electrolyte layer disposed between the positive electrode active body and the negative electrode and holding an electrolytic solution containing an aqueous solution of an aminopolycarboxylate salt exhibiting alkalinity ,
Examples of the aminopolycarboxylate include ethylenediaminetetraacetic acid tetrasodium (EDTA4Na), ethylenediaminetetraacetic acid trisodium (EDTA3Na), nitrilotriacetic acid trisodium (NTA3Na), hydroxyethylethylenediaminetriacetic acid trisodium (HEDTA3Na), triethylenetetramine- A magnesium-air battery using at least one of N, N, N ′, N ″, N ″, N ″ ′ hexasodium (TTHA6Na) and ethylenediamine-N, N′-trisuccinate (EDDSH3Na) . The magnesium-air battery according to claim 1 ,
A magnesium-air battery in which the electrolyte during power generation is adjusted to pH 8 or more and pH 13 or less. The magnesium-air battery according to claim 1 or 2 ,
The said electrolyte solution is a magnesium air battery containing 0.05 weight% or more and 18 weight% or less of at least one of sodium chloride and potassium chloride. It is a magnesium air battery in any one of Claims 1-3 ,
The said electrolyte layer is a magnesium air battery comprised by the tank which stores the said electrolyte solution in the state which immersed at least one part of the said negative electrode and positive electrode active body. It is a magnesium air battery in any one of Claims 1-3 ,
The said electrolyte layer is a magnesium air battery comprised by the water holding body which contacts the said negative electrode and positive electrode active body at least partially, and absorbs and hold | maintains the said electrolyte solution. The magnesium-air battery according to claim 5 ,
The electrolyte is held as a solid at a site that can be eluted in the water holding body in a state before the start of power generation,
A magnesium-air battery comprising a supply mechanism for supplying from the outside an amount of water capable of realizing the elution to the water retaining body. The magnesium-air battery according to claim 6 ,
A case for enclosing the negative electrode, the positive electrode, the positive electrode active body, and the water retention body,
The supply mechanism is a magnesium-air battery, which is a through hole formed in the lower surface of the case. The magnesium-air battery according to claim 7 ,
A magnesium-air battery, wherein an external connection terminal connected to the negative electrode and the positive electrode is formed above the center of the case. It is a magnesium air battery in any one of Claims 5-8 ,
The water-retaining body is a magnesium-air battery having a weight density of 100 grams / square meter or more and 1000 grams / square meter or less based on pulp. It is a magnesium air battery in any one of Claims 1-9, Comprising :
The positive electrode active material is a magnesium air battery using at least a part of activated carbon and manganese dioxide.

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