JP2022015292A - Powder containing iron oxide particles and negative electrode material for metal air battery - Google Patents

Abstract

To provide powder containing iron oxide particles which are cheaper and which can maintain the reaction efficiency even after repeated redox reactions.SOLUTION: A powder containing iron oxide particles of the present invention contains: 80 mass% or more of iron oxide particles containing iron oxide consisting of at least one of Fe2O3 and Fe3O4; and 3 mass% or more of oxide particles containing an oxide having a standard free energy of formation in the temperature range of 200°C to 600°C lower than the standard free energy of formation of Fe3O4 if the iron oxide contains Fe3O4, or if the iron oxide does not contain Fe3O4, the standard free energy of formation of this oxide is lower than the standard free energy of formation of Fe2O3 at the same temperature range.SELECTED DRAWING: Figure 1

Description

The present invention relates to an iron oxide particle-containing powder having a small decrease in reaction activity with respect to repeated redox reactions, and a negative electrode material for a metal-air battery using the iron oxide particle-containing powder.

Since iron is an inexpensive and stable metal, metal-air batteries using the redox reaction of iron shown below are being developed. Here, M is metallic iron and MO is iron oxide.
M + H ₂ O → MO + H ₂ (discharge)
MO + H ₂ → M + H ₂ O (charging)

In order to activate the redox reaction, fine iron particles having a particle size of several tens to several hundreds of nm are usually used. Heat of reaction is generated when iron is oxidized, but when the specific surface area of iron particles is large, the sintering reaction of iron particles occurs even at a relatively low temperature of about 400 to 600 ° C., and the iron particles become coarse. As a result, since the specific surface area of the iron particles is reduced, there is a problem that the reaction efficiency of the redox reaction is significantly reduced by repeated use.

In order to solve the above problem, in Patent Document 1, in iron or iron oxide, a platinum group metal or the platinum group metal is used, and Ti, Zr, V, Nb, Cr, Mo, Al are used as a second additive metal. , Ga, Mg, Mg, Mg, Sc, Ni and Cu are disclosed as reaction media to which at least one of them is compound-added.

International Publication No. 2004/002881

However, in Patent Document 1, since the reaction efficiency is insufficient only with the second additive metal, it is necessary to use it in combination with an expensive platinum group. Another problem is that the manufacturing cost is high because a chemical solution treatment such as a coprecipitation method is used as a method for alloying the added metal with the iron particles.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a powder containing iron oxide particles, which is cheaper and can maintain the reaction efficiency even if the redox reaction is repeated.

In order to solve the above problems, the inventors have diligently studied a material that is cheaper and can maintain the reaction efficiency even if the redox treatment is repeated. As a result, it was found that iron oxide particle-containing powder containing a predetermined amount of an oxide more stable than iron oxide as a sintering inhibitor is effective in a temperature range of 200 ° C. or higher and 600 ° C. or lower under atmospheric pressure. The present invention has been completed. The gist of the present invention is as follows.

[1] 80 mass% or more of iron oxide particles containing iron oxide composed of at least one of Fe ₂ O ₃ and Fe ₃ O ₄ , and Fe ₃ O ₄ when the iron oxide contains Fe ₃ O ₄ . When iron oxide does not contain Fe ₃ O ₄ , an oxide containing an oxide having a smaller standard free energy in the temperature range than the standard free energy of Fe ₂ O ₃ in the temperature range of 200 ° C. or higher and 600 ° C. or lower. Iron oxide particle-containing powder containing 3 mass% or more of particles.

[2] The oxide particles are selected from the group consisting of chromium oxide, silicon oxide, zirconium oxide, manganese oxide, zinc oxide, aluminum oxide, magnesium oxide, calcium oxide, niobium oxide, titanium oxide, and vanadium oxide. Or the iron oxide particle-containing powder according to the above [1], which contains two or more.

[3] The iron oxide particles according to the above [1] or [2], which contain 10 vol% or more of plate-like particles having a thickness of 0.01 μm or more and 1 μm or less and an aspect ratio of 2.0 or more. Containing powder.

[4] The iron oxide particle-containing powder according to the above [3], wherein the plate-shaped particles are composite particles containing the iron oxide particles and the oxide particles.

[5] The iron oxide particle-containing powder according to any one of [1] to [4] above, wherein the oxide has a density difference from iron oxide within ± 1.0 g / m ³ .

[6] A negative electrode material for a metal-air battery, which comprises the iron oxide particle-containing powder according to any one of the above [1] to [5].

[7] Iron oxide composed of at least one of Fe ₂ O ₃ and Fe ₃ O ₄ , Fe 3 O 4 when the iron oxide contains Fe ₃ O ₄ , and Fe ₃ O ₄ when the iron oxide contains Fe ₃ O ₄ . In some cases, an oxide having a smaller standard free energy in the temperature range than the standard free energy in the temperature range of 200 ° C. or higher and 600 ° C. or lower of Fe ₂ O ₃ is used, and iron oxide is added to 80 mass% or more and the oxide is used. In the compounding process of obtaining a compound by blending with a blending ratio of 3 mass% or more,
A method for producing iron oxide particle-containing powder, which comprises a pulverization step of crushing the compound to obtain an iron oxide particle-containing powder containing iron oxide particles and oxide particles.

According to the present invention, it is possible to provide an iron oxide particle-containing powder that is cheaper and can maintain the reaction efficiency even if the redox reaction is repeated.

It is a figure for demonstrating the morphology of a plate-like particle. It is a figure for demonstrating a metal-air battery. It is a figure for demonstrating the cell used for evaluating the performance of the negative electrode material in an Example.

Hereinafter, preferred embodiments of the present invention will be described. The present invention is not limited to the following embodiments. Further, in the present specification, the numerical range represented by using "-" means a range including the numerical values before and after "-" as the lower limit value and the upper limit value.

The iron oxide particle-containing powder according to the present embodiment contains 80 mass% or more of iron oxide particles containing iron oxide composed of at least one of Fe ₂ O ₃ and Fe ₃ O ₄ , and the iron oxide contains Fe ₃ O ₄ . In the case of Fe ₃ O ₄ , if the iron oxide does not contain Fe ₃ O ₄ , the standard generation free energy in the temperature range of 200 ° C or higher and 600 ° C or lower of Fe ₂ O ₃ is higher than the standard generation free energy in the temperature range. It contains 3 mass% or more of oxide particles containing oxides having low energy.

[Iron oxide particles]
The iron oxide particles that are the base material of the iron oxide particle-containing powder contain at least one of Fe ₂ O ₃ (hematite) and Fe ₃ O ₄ (magnetite) that are stably produced by the iron oxidation reaction. The content of the iron oxide particles shall be 80 mass% or more with respect to the entire iron oxide particle-containing powder. When the content of iron oxide particles with respect to the entire iron oxide particle-containing powder is less than 80 mass%, the amount of iron oxide that contributes to the redox reaction is small, so that it can be recovered by the redox reaction using the iron oxide particle-containing powder. The amount of charge is reduced. Therefore, the content of iron oxide particles with respect to the entire iron oxide particle-containing powder is set to 80 mass% or more. The content of iron oxide particles with respect to the entire iron oxide particle-containing powder is preferably 85 mass% or more, more preferably 90 mass% or more. The upper limit of the content of iron oxide particles with respect to the entire iron oxide particle-containing powder is 97 mass% or less in relation to the content of the sintering inhibitor.

The ratio of the contents of Fe ₂ O ₃ and Fe ₃ O ₄ contained in the iron oxide particles is not particularly limited. That is, the iron oxide particles may contain only Fe ₂ O ₃ as iron oxide, or may contain only Fe ₃ O ₄ as iron oxide.

The shape of the iron oxide particles is not particularly limited, and may be spherical, polyhedral, or plate-shaped. When the particle shape is spherical or polyhedral, the particle diameter (primary particle diameter) is preferably 0.01 μm or more, and preferably 1 μm or less, from the viewpoint of reaction efficiency.

Further, the iron oxide particles may be single particles or may form composite particles together with oxide particles as described later. In this embodiment, the iron oxide particles are composed of iron oxide and unavoidable impurities. However, iron oxide particles may contain trace amounts of additive elements in addition to iron oxide and unavoidable impurities.

[Sintering inhibitor]
The sintering inhibitor has an effect of suppressing the sintering of the iron oxide particles described above. In order to effectively exert this effect, as a sintering inhibitor, the atmospheric temperature at which iron oxidation-reduction is generated is set to a temperature range of 200 ° C. or higher and 600 ° C. or lower, and the standard free energy for oxide formation under atmospheric pressure is set. ΔG ⁰ is smaller than the standard generation free energy ΔG ⁰ (Fe ₂ O ₃ : −450 to −400 kJ / mol, Fe ₃ O ₄ : -470 to 425 kJ / mol) of the iron oxide in the same temperature range, that is, Select an oxide that is stable at the ambient temperature at which iron oxidation reduction occurs. As described above, iron oxide consists of at least one of Fe ₂ O ₃ and Fe ₃ O ₄ , but among Fe ₂ O ₃ and Fe ₃ O ₄ contained in iron oxide, the standard generation free energy ΔG ⁰ in the above temperature range. It suffices if the standard free energy ΔG ⁰ of the oxide in the above temperature range is smaller than that of the smaller one. That is, when iron oxide contains Fe ₃ O ₄ , the standard free energy ΔG ⁰ of the oxide in the above temperature range may be smaller than Fe ₃ O ₄ . When iron oxide does not contain Fe ₃ O ₄ , the standard free energy generated in the temperature range of 200 ° C. or higher and 600 ° C. or lower may be smaller than that of Fe ₂ O ₃ . As for the standard free energy of formation, for example, the values of ΔG ⁰ at 200 ° C. and 600 ° C. of each oxide are used from the Ellingham diagram of Reference 1.

When the atmospheric temperature is lower than 200 ° C., the redox reaction of iron does not proceed, while when it is higher than 600 ° C., sintering becomes remarkable. Therefore, it is preferable that the atmospheric temperature at which the redox reaction is caused by using the oxide particle-containing powder according to the present embodiment is 200 ° C. or higher and 600 ° C. or lower. As the sintering inhibitor, as a stable oxide at 200 ° C. or higher and 600 ° C. or lower, as shown in Table 1, chromium oxide (Cr ₂ O ₃ ), silicon oxide (SiO ₂ ), zirconium oxide (ZrO ₂ ), and oxidation Manganese (MnO), Zinc Oxide (ZnO), Aluminum Oxide (Al ₂ O ₃ ), Magnesium Oxide (MgO), Calcium Oxide (CaO), Niobide Oxide (Nb ₂ O ₃ ), Titanium Oxide (TIO ₂ , TIO), It is preferable to select any one or more oxides selected from the group consisting of vanadium oxide and vanadium oxide (V ₂ O ₃ ) as the sintering inhibitor.

As the sintering inhibitor, an oxide having a difference in density (true density) from iron oxide within ± 1.0 g / m ³ is preferable. This is because an oxide having a density difference of ± 1.0 g / m ³ or less from the iron oxide particles can be easily dispersed uniformly in the iron oxide particle-containing powder. As such an oxide, it is preferable to select any one or two or more selected from the group consisting of chromium oxide, zirconium oxide, manganese oxide, zinc oxide, niobium oxide, titanium oxide, and vanadium oxide. From the viewpoint of the stability and uniform dispersibility of the oxide, it is more preferable that the oxide is one or more selected from the group consisting of chromium oxide, zirconium oxide, and manganese oxide.

The content of the oxide (sintering inhibitor) with respect to the entire iron oxide particle-containing powder shall be 3 mass% or more. When the oxide content with respect to the entire iron oxide particle-containing powder is less than 3 mass%, the sintering suppressing effect is insufficient. The content of the sintering inhibitor with respect to the entire iron oxide particle-containing powder may be more than 5% or 6% or more. The upper limit of the oxide content with respect to the entire iron oxide particle-containing powder is 20 mass% or less in relation to the iron oxide particle content.

The particle shape of the sintering inhibitor is not particularly limited, and may be spherical, polyhedral, or plate-shaped. The sintering inhibitor can be adsorbed on the surface of the iron oxide particles or dispersed in the gaps between the iron oxide particles to exert the effect of suppressing the sintering of the iron oxide particles. In order to obtain such an effect, when the oxide particles are spherical or polyhedral particles, the primary particle diameter is preferably 5 nm or more, and more preferably 30 nm or less.

In this embodiment, the oxide particles are composed of oxides and unavoidable impurities. However, the oxide particles may contain trace amounts of additive elements in addition to oxides and unavoidable impurities.

The iron oxide particle-containing powder preferably contains plate-like particles having a thickness of 0.01 μm or more and 1 μm or less and an aspect ratio of a long piece to a short piece of 2.0 or more. As shown in FIG. 1, the plate-shaped particles are composite particles containing iron oxide particles and oxide particles, and are aggregates in which oxides having a diameter of several nm to several hundred nm and primary particles of iron oxide are aggregated. .. By adopting such a plate-like aggregate structure, the surface area can be increased as compared with the spherical or polyhedral-shaped aggregate particles (secondary particles) having the same volume, and the sintering inhibitor is finely and uniformly dispersed. By doing so, the effect of suppressing sintering can be enhanced. As a result, since the iron oxide particles are less likely to be sintered even by repeated redox, it is considered that the iron oxide particle-containing powder exhibits particularly excellent characteristics when used as the negative electrode material of the iron-air battery. In order to obtain the above effect, the content of the plate-like particles in the entire iron oxide particle powder is preferably 10 vol% or more. It is more preferable that the content of the plate-like particles in the entire iron oxide particle-containing powder is 21 vol% or more. The upper limit of the content of the plate-shaped particles in the entire iron oxide particle-containing powder is not particularly limited and may be 100 vol%. The primary particle diameter (sphere equivalent diameter) of the plate-shaped particles is preferably 5 nm or more, and more preferably 30 nm or less. The particle size of the iron oxide particles, the oxide particles, and the plate-like particles formed by combining them is measured by the method shown in the examples.

The iron oxide particle-containing powder according to the present embodiment can suppress the sintering of iron oxide particles when the redox treatment is repeated, and can maintain the reaction efficiency. Therefore, the iron oxide particle-containing powder according to this embodiment is suitable as an active material for a negative electrode material of a metal-air battery. When the iron oxide particle-containing powder is used as the active material of the negative electrode material of the metal-air battery, the atmospheric temperature at which the redox reaction occurs is preferably 200 to 600 ° C. as described above.

The metal-air battery (iron-air battery) containing the iron oxide particle-containing powder according to the present embodiment as the active material of the negative electrode will be described with reference to FIG. As shown in FIG. 2, in the metal-air battery 7, when discharging, a current flows in the direction of the arrow in the figure. First, in the air electrode 5, O ₂ is combined with an electron to generate O ^2- . Next, in the iron oxide particle-containing powder 1 of the negative electrode, an iron oxidation reaction occurs and hydrogen is generated. The hydrogen combines with O ^2- to generate water, and electrons flow out from the negative electrode side. Conversely, during charging, current flows in the direction of the arrow in the figure. In the iron oxide particle-containing powder 1 of the negative electrode, an iron reduction reaction occurs due to the inflowing electrons. Hydrogen and O ^2- are generated by the reduction reaction. The generated O ^2- emits electrons at the air electrode 5 to become O ₂ , and is emitted to the outside.

Next, a method for producing the iron oxide particle-containing powder will be described.
The method for producing the iron oxide particle-containing powder according to the present embodiment includes iron oxide composed of at least one of Fe ₂ O ₃ and Fe ₃ O ₄ , and Fe _{3 O 4 when the iron oxide contains Fe 3 O 4 .} When the iron oxide does not contain Fe ₃ O ₄ , the oxide having a smaller standard free energy in the temperature range than the standard free energy in the temperature range of 200 ° C. or higher and 600 ° C. or lower of Fe ₂ O ₃ is used. A compounding step of blending the iron oxide in a blending ratio of 80 mass% or more and the oxide in a blending ratio of 3 mass% or more to obtain a blend, and iron oxide containing iron oxide particles and oxide particles by crushing the blend. It includes a pulverization step for obtaining a particle-containing powder.

As the iron oxide as the main raw material, iron oxide (at least one of Fe ₂ O ₃ and Fe ₃ O ₄ ) available as an industrial material such as a pigment and a ferrite raw material can be used. Alternatively, iron oxide particles having the above particle size can be produced from ferrous sulfate or ferrous chloride by a general production method such as a wet method or a dry method. The particle size of iron oxide as a raw material is not particularly limited, and may be about several tens of nm to several μm, which is easily available. As the sintering inhibitor, oxide particle powder available as an industrial material can be used in addition to the reagent. The particle size of the sintering inhibitor as a raw material is not particularly limited, and may be about several tens of nm to several μm.

The above iron oxide and the sintering inhibitor are blended in a blending ratio of 80 mass% or more of iron oxide and 3 mass% or more of oxide to obtain a blend, which is then transferred to a crusher and oxidized for mixing. The formulation is ground until the primary particle size of the iron and oxide particles is the specified size. The primary particle diameters of the iron oxide particles and the oxide particles are as described above. The crusher may be any equipment having the ability to pulverize particles to the nm level, and for example, a jet mill crusher, a ball mill crusher, or the like is preferable.

The above-mentioned plate-shaped particles can be obtained, for example, by pulverizing and mixing the compound with a high-energy ball mill. Further, the content of the plate-shaped particles with respect to the entire iron oxide particle-containing powder can be adjusted by the rotation speed of the high-energy ball mill when the iron oxide powder and the sintering inhibitor are pulverized and mixed. The content of the plate-shaped particles with respect to the entire iron oxide particle-containing powder can also be adjusted by extracting the plate-shaped particles from the entire iron oxide particle-containing powder obtained after pulverization and mixing.

Iron oxide and oxide were blended in the blending ratio shown in Table 2 to prepare a raw material powder. Put the raw material powder in a pot, add 50 ml of ethanol to 10 g of the raw material powder, and use a high-energy ball mill (Fritsch, Inc .: pulverisette 7) to grind the iron oxide particles at the rotation speed and time shown in Table 3. The contained powder was prepared. For No. 21, the iron oxide particle-containing powder sample after pulverization was dispersed in a solvent and filtered through a filter having a hole diameter of 3 μm to extract plate-shaped particles. Next, the iron oxide particle-containing powder was taken out from the pot, and the particle diameters of the iron oxide particles and the oxide particles were determined. In addition, the particle size, volume fraction, and redox characteristics of the plate-shaped particles were determined.

(Measurement of particle size)
Regarding the particle size of iron oxide and oxide particles, a 20,000-fold mapping image was obtained in three fields by scanning transmission electron microscope (STEM) and characteristic X-ray spectroscopy (EDX). Then, 20 particles were arbitrarily selected for each particle, and the particle diameter was measured.
The morphology and body integration ratio of the plate-like particles contained in the obtained iron oxide particle-containing powder were determined by using a scanning electron microscope (SEM) and a scanning transmission electron microscope (STEM). I asked for it as follows. From the 2000 times SEM image, select several particles with a length of about 10 μm that look linear, and measure the thickness of these particles by STEM observation at 2 million times, and all of them have a thickness of 0.01 to 1 μm. It was confirmed that the particles were plate-like particles. Next, 20 plate-like particles present in the 2000-fold SEM image were arbitrarily selected, the short and long sides thereof were measured, and the aspect ratio was obtained from the average value. The diameter and composition of the primary particles constituting the plate-like particles were confirmed by STEM of 2 million times and characteristic X-ray spectroscopy (EDX). As for the ratio of the plate-shaped particles present in the iron oxide powder, STEM-EDX is used to obtain a mapping image of 20,000 times in 3 fields, and the plate-shaped particles and other particles are separated by image processing to obtain the plate-like particles. The ratio was calculated as the volume ratio.

(Redox characteristics)
In order to measure the redox characteristics of the iron oxide particle-containing powder, a device in which the cell 6 shown in FIG. 3 was arranged on a heat balance capable of introducing gas and heating was used. 50 mg of iron oxide particle-containing powder 1 was introduced into a 20 cc cell 6. The cell 6 was kept at 400 ° C., and the reduction treatment of iron oxide by introducing hydrogen gas at 100 ml / min for 60 min and the oxidation treatment of iron by introducing 2.8 vol% steam for 180 min were repeated. The iron oxide particles become Fe by the reduction treatment, and Fe is oxidized by the oxidation treatment to become Fe ₃ O ₄ . Therefore, the weight of the iron oxide particle-containing powder 1 changes due to redox. The weight change ΔM of the iron oxide particle-containing powder 1 after each reduction treatment and after the oxidation treatment was measured.

Starting from the time when all of them became Fe in the first reduction treatment, one oxidation and reduction treatment was regarded as one cycle, and the weight change ΔM ₁₀ due to oxidation and reduction in the 10th cycle was measured as a repeated weight change. If the weight change ΔM ₁₀ in the 10th cycle is 90% or more of the weight change ΔM ₁ in the 1st cycle, it is ◎, if it is less than 90%, if it is 70% or more, it is 〇, it is less than 70%, and if it is 50% or more, it is △. , If it is less than 50%, it is marked as x. The results are shown in Table 3.

As for the amount of change, when the theoretical weight change ΔM _R due to the redox treatment is 100%, if the weight change ΔM ₁₀ due to the redox in the 10th cycle is 90% or more, ⊚, less than 90%, 70%. If it is above, it is evaluated as 〇, less than 70%, if it is 50% or more, it is evaluated as Δ, and if it is less than 50%, it is evaluated as ×. The results are shown in Table 3.

<Reference 1> Steel Handbook 3rd Edition I, The Iron and Steel Institute of Japan (Maruzen) 1981, p4.

The present invention is an iron oxide particle-containing powder that suppresses sintering during redox. By using the iron oxide particle-containing powder according to the present invention, it is possible to produce a negative electrode material for an iron-air battery at low cost and with a long life, so that the present invention is useful for constructing a hydrogen energy society in the future.

1 Iron oxide particle-containing powder 2 Iron oxide particles 3 Oxide particles 4 Plate-shaped particles 5 Air electrode 6 Cell 7 Metal-air battery

Claims (7)

80 mass% or more of iron oxide particles containing iron oxide composed of at least one of Fe ₂ O ₃ and Fe ₃ O ₄ , and Fe ₃ O ₄ when the iron oxide contains Fe ₃ O ₄ , and the iron oxide is When Fe ₃ O ₄ is not contained, 3 mass of oxide particles containing an oxide having a smaller standard free energy in the temperature range than the standard free energy of Fe ₂ O ₃ in the temperature range of 200 ° C. or higher and 600 ° C. or lower. % Or more, iron oxide particle-containing powder. The oxide particles are one or two selected from the group consisting of chromium oxide, silicon oxide, zirconium oxide, manganese oxide, zinc oxide, aluminum oxide, magnesium oxide, calcium oxide, niobium oxide, titanium oxide, and vanadium oxide. The iron oxide particle-containing powder according to claim 1, which contains the above. The iron oxide particle-containing powder according to claim 1 or 2, which contains 10 vol% or more of plate-like particles having a thickness of 0.01 μm or more and 1 μm or less and an aspect ratio of 2.0 or more. The iron oxide particle-containing powder according to claim 3, wherein the plate-shaped particles are composite particles containing the iron oxide particles and the oxide particles. The iron oxide particle-containing powder according to any one of claims 1 to 4, wherein the oxide has a density difference from iron oxide within ± 1.0 g / m ³ . A negative electrode material for a metal-air battery, which comprises the iron oxide particle-containing powder according to any one of claims 1 to 5. Iron oxide consisting of at least one of Fe ₂ O ₃ and Fe ₃ O ₄ , Fe 3 O 4 when the iron oxide contains Fe ₃ O ₄ , and Fe ₃ O ₄ when the iron oxide does not contain Fe ₃ O ₄ . The oxide having a smaller standard free energy in the temperature range than the standard free energy in the temperature range of 200 ° C. or higher and 600 ° C. or lower of Fe ₂ O ₃ is 80 mass% or more of the iron oxide and 3 mass% of the oxide. The compounding process of compounding with the above compounding ratio to obtain a compound and
A method for producing iron oxide particle-containing powder, which comprises a pulverization step of crushing the compound to obtain an iron oxide particle-containing powder containing iron oxide particles and oxide particles.

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