JP6410137B2 - Metal air battery - Google Patents

Description

  The present invention relates to a metal-air battery, and more particularly to a metal-air battery that suppresses discharge inhibition by battery reaction products and can improve discharge capacity even when the current density is high.

The metal-air battery uses oxygen in the air as a positive electrode active material, and does not need to have a positive electrode active material in the battery, so it can contain more negative electrode active materials than other batteries. It is possible and the energy density can be increased.
However, in the metal-air battery, the reactions of the following formulas 1 and 2 occur at the positive electrode and the negative electrode, respectively, due to discharge, and the hydroxide ions generated at the positive electrode react with the ions (M ⁺ ) of the negative electrode active material. A hydroxide is formed. And since the produced | generated hydroxide adheres to an electrode or drifts between electrodes and inhibits battery discharge, a negative electrode active material cannot fully be utilized.

For example, a positively charged battery reaction product at a pH equal to or lower than the isoelectric point is easily attracted to the negatively charged hydroxide ions or electrons generated in the vicinity of the positive electrode, and easily adheres to the electrode surface. It is presumed that the battery reaction is inhibited by covering the surface, that is, the reaction field, and on the other hand, in the vicinity of the negative electrode, it repels the positive charge of the metal ions dissolved from the negative electrode and hinders the dissolution of the metal ions.
Moreover, when the precipitated hydroxide drifts in the electrolyte, the conductivity is lowered and the battery output is lowered.

  In Patent Document 1, by using a citric acid aqueous solution as an electrolytic solution, citrate ions and magnesium ions eluted from the negative electrode are complexed, so that the solubility of magnesium ions is increased and the deposition of magnesium oxide on the negative electrode is suppressed. Thus, it has been disclosed that continuous electrolysis of magnesium is possible.

Japanese Patent No. 5358533

However, since there is a limit to the amount of magnesium complexed with citric acid, magnesium in the negative electrode cannot be fully utilized, and the effect in a region where the current density is high is small.
That is, since citric acid neutralizes the charge of Mg ions, two molecules of citric acid are used to trap one molecule of Mg ions, and the Mg ions generated by the discharge are sufficiently complexed. I can't.

The present invention has been made in view of such problems of the prior art, and its object is to inhibit the battery reaction by the battery reaction product in the metal-air battery even in a region where the current density is high. It is an object of the present invention to provide a metal-air battery that prevents the discharge capacity and the battery output from decreasing.

  As a result of intensive studies to achieve the above object, the present inventors have peeled off deposits generated by the battery reaction adhering to the electrodes and removed the battery reaction products floating between the electrodes, so that the discharge capacity and The inventors have found that the battery output can be prevented from decreasing, and have completed the present invention.

This invention is based on the said knowledge, Comprising: The metal air battery of this invention is a metal air battery containing the electrolyte solution which has ionic conductivity between an air electrode and a negative electrode.
And the electrolytic solution contains an aggregating agent that aggregates and precipitates the battery reaction product,
The battery reaction product in the metal-air battery is such that the pH of the electrolyte is a pH at which the battery reaction product is positively charged, and the flocculant is an inorganic flocculant having a negative charge in the electrolyte at the pH. It contains an aggregating agent that aggregates and precipitates.

According to the present invention, since the battery reaction product is peeled off from the electrode and aggregated and precipitated, it is possible to prevent the battery reaction product from reducing the area of the electrode reaction field where the battery reaction is performed. Furthermore, since floating particles floating between the electrodes are removed and the ionic conductivity of the electrolyte is prevented from being lowered, a battery-air reaction is promoted, and a metal-air battery with improved discharge capacity and battery output can be provided.

It is a figure which shows an example of the metal air battery of this invention. It is a photograph which shows the precipitation state of the battery reaction product by a flocculant. It is a figure which shows the discharge characteristic of the cell using the electrolyte solution of an Example and a comparative example.

The metal-air battery of the present invention will be described.
The metal-air battery of the present invention aggregates and precipitates the precipitate generated by the battery reaction, thereby preventing the precipitate from covering the electrode surface and drifting in the electrolyte, thereby preventing battery reaction inhibition. Is.

FIG. 1 shows an example of a metal-air battery of the present invention. As shown in FIG. 1, the metal-air battery of the present invention has an electrolyte 3 between a negative electrode 1 and an air electrode 2, and both the negative electrode 1 and the air electrode 2 have a substantially reactive surface. The deposit storage section 4 is provided below the negative electrode 1 and the air electrode 2 and stores aggregates / precipitates of metal reaction products.
By having the deposit storage part 4, the aggregated battery reaction product and the battery reaction product which peeled off from the electrode do not accumulate between electrodes, and it can prevent that a battery reaction product inhibits a battery reaction. Here, the term “substantially vertical” means that the aggregation / precipitate of the metal reaction product does not hinder the sedimentation in the sediment reservoir.

<Electrolyte>
The electrolytic solution of the present invention contains a flocculant, a supporting electrolyte, and water, and may contain other additives as necessary.

(Flocculant)
The flocculant of the present invention agglomerates and precipitates the product produced by the battery reaction, that is, the hydroxide produced by combining the metal ions of the negative electrode active material and the hydroxide ions generated at the positive electrode.
By aggregating and precipitating the above battery reaction product, the battery reaction product covers the electrode surface, reducing the reaction field of the battery reaction, and the battery reaction product drifts in the electrolyte and decreases the conductivity. By preventing the battery reaction, the battery reaction can be prevented from being inhibited, and the discharge capacity and the battery output are improved.

As the aggregating agent, conventionally known aggregating agents can be used as long as the battery reaction product can be agglomerated and precipitated, and examples thereof include inorganic aggregating agents and anionic polymer aggregating agents.
However, since the surface charge of the battery reaction product varies depending on the pH of the electrolyte, it is necessary to select an aggregating agent according to the charge of the battery reaction product.
Specifically, when the battery reaction product is a positively charged electrolyte solution, a flocculant having a negative charge is added to the electrolyte solution, and conversely, the battery reaction product is negatively charged. In some cases, a positively charged flocculant is added.

For example, when the active material of the negative electrode is magnesium, the isoelectric point of magnesium hydroxide produced and precipitated by the battery reaction is about pH = 12. Therefore, at pH lower than this, hydrogen ions are adsorbed to the OH group. The battery reaction product is positively charged.
In addition, when the active material of the negative electrode is aluminum, the isoelectric point of aluminum hydroxide produced and deposited by the battery reaction is about pH = 8. Therefore, at a pH lower than this, the battery reaction product is similarly positive. Is charged. The isoelectric point of zinc oxide is about pH = 9.5.

As described above, when the pH of the electrolytic solution is such that the battery reaction product is positively charged, the inorganic flocculant has an isoelectric point of the oxide derived from the flocculant of the oxide of the negative electrode active material. Use one that is lower than the isoelectric point.
Specifically, when the active material of the negative electrode is magnesium, one that forms an oxide having an isoelectric point of 12 or less is used, and when the active material of the negative electrode is aluminum, the isoelectric point is 8 or less. A material that forms an oxide is used.

The isoelectric point is the pH value when the zeta potential becomes 0, and the isoelectric point of the oxide derived from the inorganic flocculant is measured in advance with an ultrasonic zeta potential measuring device or the like. I can know.

Examples of the oxide having an isoelectric point of 10 or less include aluminum oxide (isoelectric point pH 8) and iron oxide (isoelectric point pH 6.5).
Examples of the inorganic flocculant that forms aluminum oxide include polyaluminum chloride, aluminum chloride, aluminum sulfate, iron-containing aluminum sulfate, polyaluminum sulfate, sodium aluminate, and the like, and these include one kind or two or more kinds. You may mix and use.
Examples of the inorganic flocculant that forms iron oxide include ferrous sulfate, ferric sulfate, ferric chloride, copper chloride, polyiron sulfate, and the like. You may mix and use the above.

Anionic polymer flocculants include sodium polyacrylate, dimethylaminoethyl polyacrylate, polyacrylate amide, polyacrylamide partial hydrolyzate, polyacrylamide sulfonation derivative, polystyrene sulfonate sodium, maleate An acid polymer can be mentioned, These may mix 1 type (s) or 2 or more types.
These anionic polymer flocculants preferably have a molecular weight of 100,000 or more.

The content of the flocculant in the electrolytic solution depends on the flocculant used and the like, but is preferably 10 mg / L or more and 500 mg / L or less, and more preferably 50 mg / L or more and 200 mg / L or less.
If it is less than 10 mg / L, the coagulation / precipitation effect is small and the discharge capacity may not be sufficiently improved, and if it exceeds 500 mg / L, the initial voltage may be lowered.

(Supporting electrolyte)
The electrolyte for metal-air batteries of the present invention contains an electrolyte that increases conductivity.
If the supporting electrolyte does not interact with the active material of the negative electrode, does not cause side reactions on the electrode surface, has sufficient solubility in the solvent, and is sufficiently dissociated at that concentration, the supporting electrolyte can be used as a metal-air battery. A conventionally known supporting electrolyte to be applied can be used.

  Examples of the supporting electrolyte include sodium chloride, potassium chloride, sodium sulfate, and potassium sulfate. These may be used alone or in combination of two or more, but sodium chloride is easy to handle. Since the ionic conductivity is high and the output can be increased, it can be preferably used. The content of the supporting electrolyte in the electrolytic solution is preferably 1 mol / L or more and 10 mol / L or less, although it depends on the electrolyte used, the negative electrode active material, and the like.

  Moreover, it is preferable that the electrolyte solution of this invention is a water-system electrolyte solution. The presence of polar water molecules in the electrolytic solution stably causes agglomerates, promotes agglomeration / sedimentation, and improves the discharge capacity.

<Negative electrode>
The negative electrode 1 can be used as long as it is a substance that generates magnesium ions or aluminum ions and electrons by an oxidation reaction, and examples thereof include a metal material containing magnesium or aluminum as a main component.
Here, the main component in this invention means the component containing 50 mass% or more.
The metal material containing magnesium or aluminum as a main component may contain not only an alloy of magnesium and aluminum but also other metals.
Examples of the other metals include zinc, manganese, silicon, rare earth elements, calcium, strontium, tin, germanium, lithium, zirconium, and beryllium, and these may be used alone or in combination.

In general, an alloy is a generic term for a metal element having one or more metal elements or non-metal elements added and having metallic properties. Specifically, a material obtained by adding one or more metal elements or non-metal elements to the above metal element can be given.
In addition, the alloy structure is composed of eutectic alloys in which the component elements become separate crystals, so-called a mixture; the component elements are completely melted into a solid solution; the component elements are intermetallic compounds or metals and nonmetals. And the like that form a compound of
In this embodiment, any alloy structure may be used. However, the material is not limited to these, and a conventionally known material applied to an air battery can be used.

<Air electrode>
As the air electrode 2, any substance can be used as long as it receives electrons generated at the negative electrode and reduces oxygen. Examples thereof include manganese lower oxides such as Mn ₂ O ₃ and Mn ₃ O ₄ , carbon materials such as activated carbon, and perovskite complex oxides such as lanthanum manganite.
The air electrode 2 has a water repellent film (not shown) on the side to which an oxygen-containing gas such as air is supplied. As the water repellent film, for example, a porous film made of a polymer having water repellency such as polytetrafluoroethylene (PTFE) is used, and the electrolytic solution is prevented from leaking out of the air electrode through the electrode.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to the following Example.

First, it was confirmed whether or not the battery reaction product was precipitated in the electrolytic solution.
To the 4 mol / L NaCl electrolyte, 0.34 g (0.3 mol / L) of Mg (OH) ₂ powder (particle size <75 μm) is added instead of the battery reaction product, and the electrolyte containing the battery reaction product Was made. The electrolyte had a pH of 9.7.
After adding polyaluminum chloride powder (manufactured by Taki Chemical Co., Ltd .: PAC250AD: purity 30% by mass) to this electrolytic solution so as to be 33 mg / L, 100 mg / L, and 333 mg / L, respectively, Mg (OH) It was confirmed that ₂ precipitated.
The pH was 9.2 at a PAC concentration of 333 mg / L and pH 9.6 at a PAC concentration of 33 mg / L.
FIG. 2 shows the state after standing for 5 minutes together with the case where polyaluminum chloride was not added.

[Example 1]
Polyaluminum chloride powder (manufactured by Taki Chemical: PAC250AD: purity 30% by mass) was added to a 4 mol / L sodium chloride aqueous solution so as to have a concentration of 33 mg / L to prepare [Electrolytic Solution 1].

[Example 2]
Polyaluminum chloride powder (manufactured by Taki Chemical Co., Ltd .: PAC250AD: purity 30% by mass) was added to a 4 mol / L sodium chloride aqueous solution to a concentration of 100 mg / L to prepare [Electrolytic Solution 2].

[Example 3]
Polyaluminum chloride powder (manufactured by Taki Chemical Co., Ltd .: PAC250AD: purity 30% by mass) was added to a 4 mol / L sodium chloride aqueous solution to a concentration of 333 mg / L to prepare [Electrolytic Solution 3].

[Comparative Example 1]
[Electrolytic solution 4] was prepared without adding polyaluminum chloride powder to a 4 mol / L sodium chloride aqueous solution.

An Mg alloy (AM60: aluminum 6%, manganese 1%) in which a portion other than 9 mm × 11.2 mm (about 1 cm ² ) is masked with a polytetrafluoroethylene (PTFE) tape is placed in an acrylic container to form a negative electrode. .
In addition, a 9 mm × 11.2 mm (about 1 cm ² ) window was opened in the acrylic container, and a positive electrode was provided by attaching a MnO ₂ / C layer + polytetrafluoroethylene (PTFE) layer to prepare an evaluation cell.

2 ml each of [Electrolytic Solution 1] to [Electrolytic Solution 4] was injected into the evaluation cell, connected to a galvanostat, and started discharging at room temperature (25 ° C.) under a current density of 100 A / cm ^2. The cell voltage with respect to time was measured.
The evaluation results are shown in FIG.
[Electrolytic solution 1] and [Electrolytic solution 3] had the same discharge characteristics.

From the results shown in FIG. 3, Examples 1 to 3 using the electrolytic solution containing the flocculant have an increased discharge capacity and higher current density than the comparative example using the electrolytic solution not containing the flocculant. It was also confirmed that cell reaction inhibition was prevented.
Further, in Example 2 in which the concentration of the flocculant was 100 mg / L, the discharge time was longer than in Examples 1 and 3 in which the concentrations of the flocculant were 33 mg / L and 333 mg / L, respectively.

DESCRIPTION OF SYMBOLS 1 Negative electrode 2 Air electrode 3 Electrolyte solution 4 Deposit storage part

Claims (3)

A metal-air battery including an ionic conductive electrolyte between an air electrode and a negative electrode, the electrolyte containing an aggregating agent that aggregates and precipitates a battery reaction product ,
A metal-air battery, wherein the pH of the electrolytic solution is a pH at which a battery reaction product has a positive charge, and the flocculant is an inorganic flocculant having a negative charge in the electrolytic solution at the pH . The electrolytic solution is an aqueous electrolytic solution containing at least one selected from the group consisting of sodium chloride, potassium chloride, sodium sulfate, and potassium sulfate,
The negative electrode contains magnesium or a magnesium alloy, and the inorganic flocculant is polyaluminum chloride, aluminum chloride, aluminum sulfate, iron-containing aluminum sulfate, polyaluminum sulfate, sodium aluminate, ferrous sulfate, ferric sulfate. 2. The metal-air battery according to claim 1, wherein the metal-air battery is at least one selected from ferric chloride, copper chloride, and iron polysulfate. The electrolytic solution is an aqueous electrolytic solution containing at least one selected from the group consisting of sodium chloride, potassium chloride, sodium sulfate, and potassium sulfate,
The negative electrode includes aluminum or an aluminum alloy, and the inorganic flocculant is selected from sodium aluminate, ferrous sulfate, ferric sulfate, ferric chloride, copper chloride, and polyiron sulfate. It is the above, The metal air battery of Claim 1 characterized by the above-mentioned.

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