JP2013134838A - Negative electrode mixture for iron-air secondary battery, negative electrode mixture slurry, negative electrode for iron-air secondary battery, method of manufacturing the same, and iron-air secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an iron-air secondary battery which has a sufficient discharge capacity and is excellent in cycle characteristic.SOLUTION: A negative electrode mixture for an iron-air secondary battery contains iron oxide and binder, with the binder containing polyethylene as main component and having a peak originated from the polyethylene showing maximum heat absorption amount in differential scan calorimetry and a peak showing heat absorption amount next to the former within a measurement temperature range of 80-90°C. A negative electrode mixture slurry for an iron-air secondary battery includes the negative electrode mixture and solvent. A method of manufacturing a negative electrode for the iron-air secondary battery includes steps of painting the negative electrode mixture slurry and removing solvent in the negative electrode mixture slurry having been painted. The negative electrode for the iron-air secondary battery is obtained by the manufacturing method. The iron-air secondary battery includes the negative electrode, a positive electrode, and an electrolyte.

Description

  The present invention relates to a negative electrode mixture and a negative electrode mixture slurry for an iron-air secondary battery, a negative electrode for an iron-air secondary battery using the negative electrode mixture slurry, a method for producing the same, and iron using the negative electrode -It relates to an air secondary battery.

  For various uses such as for electric vehicles, secondary batteries with high energy density are required. Lithium ion secondary batteries have been put to practical use as secondary batteries so far, but lithium ion secondary batteries require approximately the same volume as the positive and negative electrodes, and the volume of these electrodes in the battery However, there is a limit to increasing the energy density. Therefore, in order to achieve further higher energy density, it is necessary to develop both a new positive electrode active material and a negative electrode active material.

  On the other hand, since the metal-air secondary battery can use oxygen in the atmosphere as the positive electrode, most of the battery can be constituted by the negative electrode, so that the energy density can be increased relatively easily. Therefore, new metal-air secondary batteries have been developed for the purpose of increasing the energy density.

As a metal-air secondary battery, for example, a zinc-air secondary battery using zinc as a negative electrode active material is known. However, the electrolyte is decomposed at the time of charging, and a dendritic crystal is formed. There was a problem.
In contrast, an iron-air secondary battery using iron as a negative electrode active material can use a high-concentration alkaline aqueous solution as an electrolytic solution, so that it is theoretically charged without a decomposition reaction of the electrolytic solution. It is possible to form a dendrite-like crystal, and the charge / discharge cycle has a relatively long life.

  In the electrolyte of the iron-air secondary battery, iron as the negative electrode active material reacts as follows.

  The negative electrode of an iron-air secondary battery is usually prepared by coating a negative electrode mixture slurry containing a negative electrode mixture containing powdered iron oxide and a binder and a viscosity adjusting solvent on the negative electrode current collector. It is manufactured by working and removing the solvent. And as said binder, it is disclosed that polyethylene can be used, for example (refer nonpatent literature 1).

H. Kitamura, S. Okada, J. Yamaki, Effect of binder on cycle performance of an Fe2O3 electrode, Ninth International Symposium on Advances in Electrochemical Science and Technology, 2010.12.02.

  However, normal polyethylene is insoluble in a solvent, and when a negative electrode mixture slurry is applied on a negative electrode current collector and the solvent is dried to produce a negative electrode, the binding force of the negative electrode mixture is insufficient. In addition, powdered iron and polyethylene are separated, a part of the negative electrode mixture is dropped from the negative electrode, and the iron-air secondary battery has insufficient cycle characteristics. was there.

  This invention is made | formed in view of the said situation, and makes it a subject to provide an iron-air secondary battery which has sufficient discharge capacity and was excellent in cycling characteristics.

To solve the above problem,
The present invention is a negative electrode mixture for an iron-air secondary battery containing iron oxide and a binder, wherein the binder is mainly composed of polyethylene, and the binder is used in differential scanning calorimetry. In addition to the peak derived from the polyethylene showing the maximum amount of heat absorption, the iron-air secondary battery has a peak showing the next amount of heat absorption in the measurement temperature range of 80 to 90 ° C. The negative electrode mixture is provided.
In the negative electrode mixture for an iron-air secondary battery of the present invention, the binder preferably has an average particle size of less than 20 μm.
In the negative electrode mixture for an iron-air secondary battery of the present invention, the binder is preferably spherical.
The negative electrode mixture for an iron-air secondary battery of the present invention preferably further contains a conductive agent.

The present invention also provides a negative electrode mixture slurry for an iron-air secondary battery comprising the negative electrode mixture for an iron-air secondary battery of the present invention and a solvent.
The present invention also includes a step of applying the negative electrode mixture slurry for the iron-air secondary battery of the present invention to a current collector, and a step of removing the solvent in the coated negative electrode mixture slurry. A method for producing a negative electrode for an iron-air secondary battery is provided.
In the manufacturing method of the negative electrode for iron-air secondary batteries of this invention, it is preferable to remove the said solvent by drying the said coated negative mix slurry at 115-135 degreeC.

Moreover, this invention provides the negative electrode for iron-air secondary batteries characterized by the above-mentioned by the manufacturing method of this invention.
The present invention also provides an iron-air secondary battery comprising the negative electrode, positive electrode and electrolyte for the iron-air secondary battery of the present invention.
In the iron-air secondary battery of the present invention, the electrolytic solution preferably contains a hydrogen generation inhibitor.

  According to the present invention, an iron-air secondary battery having a sufficient discharge capacity and excellent cycle characteristics can be provided.

1 is a schematic cross-sectional view illustrating a laminated structure in which an anode, a separator, a cathode, and an oxygen diffusion film are laminated in an iron-air secondary battery according to the present invention. It is a figure which shows the measurement result of the differential scanning calorie | heat amount of the binder used in the Example.

<Negative electrode mixture for iron-air secondary battery>
The negative electrode mixture for an iron-air secondary battery according to the present invention (hereinafter sometimes referred to as “negative electrode mixture”) is referred to as iron oxide and a binder (hereinafter referred to as “negative electrode binder”). The negative electrode binder is mainly composed of polyethylene, and the negative electrode binder is derived from the polyethylene showing the maximum heat absorption amount in differential scanning calorimetry. In addition to the peak (hereinafter sometimes referred to as “first peak”), a peak (hereinafter also referred to as “second peak”) indicating the heat absorption amount next to this is 80 to 90 ° C. It is characterized by having in the measurement temperature zone. By using the specific binder as described above, an iron-air secondary battery having a sufficient discharge capacity and excellent cycle characteristics can be obtained.

  Iron oxide is a negative electrode active material, preferably in the form of particles, and may be spherical. In addition, in this specification, when iron oxide is particles other than a spherical shape, let the maximum length in particle | grains be the particle size.

The iron oxide preferably has a D ₉₀ , that is, a particle size of 50 nm or less when the cumulative amount in the cumulative particle size distribution of the particles is 90%. In the electrode reaction of the negative electrode, Fe (OH) ₂ (iron hydroxide (II)) is generated as a reaction intermediate, which has a low electron transfer property, but covers the surface of iron oxide that is the negative electrode active material. The internal iron oxide away from the negative electrode surface hardly reacts. However, by making the D ₉₀ of iron oxide as described above, the electron transfer property when the iron oxide is coated with Fe (OH) ₂ is further improved. D ₉₀ is a value obtained from each particle diameter (diameter) measured by arbitrarily selecting 100 particles with a transmission electron microscope (TEM).

For the same reason, the iron oxide D ₁₀₀ is preferably 50 nm or less, more preferably 30 nm or less, and still more preferably 10 nm or less. Here, “D _{100 of} iron oxide is 50 nm or less” means that the particle size of all iron oxides is 50 nm or less. D ₁₀₀ is obtained from the particle size of particles measured using a transmission electron microscope, as in D ₉₀ .

  The particle size of iron oxide is preferably 1 nm or more, more preferably 2 nm or more. Iron oxide tends to increase the electrode reaction activity because the effective surface area through which the electrochemical reaction proceeds increases as the particle size decreases. However, if the particle size is too small, the density of iron oxide decreases, resulting in a battery. The energy density may decrease. On the other hand, by making the particle diameter equal to or greater than the above lower limit value, the electrode reaction activity can be further increased without reducing the energy density. The particle size can be measured by using a transmission electron microscope.

  The binder for negative electrode contains polyethylene as a main component. Here, “having polyethylene as a main component” means that the proportion of polyethylene in the binder for negative electrode is 90% by mass or more, and may be 100% by mass, that is, only composed of polyethylene. .

  When the negative electrode binder is subjected to differential scanning calorimetry (DSC), in addition to the first peak showing the maximum heat absorption amount, the heat following the first peak is obtained. And a second peak indicating the amount of absorption. And it has the said 2nd peak in a 80-90 degreeC measurement temperature range.

The first peak is derived from polyethylene, and the same measurement temperature is obtained when the negative electrode binder after the differential scanning calorimetry is cooled and the differential scanning calorimetry (re-measurement) is performed again. Observed in the belt.
On the other hand, even if the second peak is cooled after the differential scanning calorimetry and the negative electrode binder is cooled and the differential scanning calorimetry (re-measurement) is performed again, the second peak is in the measurement temperature range of 80 to 90 ° C. It is not observed. The second peak is presumed to be derived from polyethylene having a lower molecular weight than that from which the first peak is derived, and becomes high molecular weight by heating during the first measurement of the differential scanning calorific value. At the time of re-measurement, it is estimated that it is not observed in the measurement temperature range of 80 to 90 ° C.
In the negative electrode binder, the ratio of all components derived from the first and second peaks is preferably 90% by mass or more.

  As the negative electrode binder, a commercially available product may be used, or a product produced by a known method may be used. The binder for negative electrodes can be obtained, for example, by mixing polyethylenes obtained by polymerization under different conditions.

  The negative electrode binder is preferably particulate, and more preferably spherical. In addition, in this specification, when the binder for negative electrodes is particles other than a spherical form, let the largest length in particle | grains be the particle size.

The negative electrode binder preferably has an average particle size of less than 20 μm, more preferably 15 μm or less. By doing in this way, the binding force of a negative electrode mixture improves more. Here, the average particle diameter, the grain falls 50% weight percentage obtained by sieving test diameter, means that the effective particle size (D _50).

  The negative electrode mixture may contain other components in addition to the iron oxide and the negative electrode binder as long as the effects of the present invention are not hindered. Preferable examples of the other components include a conductive agent (negative electrode conductive agent).

  The negative electrode conductive agent may be a known one, and examples thereof include carbon materials such as acetylene black and ketjen black.

  The content of iron oxide in the negative electrode mixture is preferably 25 to 95% by mass, more preferably 35 to 55% by mass. By setting it to the lower limit value or more, the charge / discharge capacity of the iron-air secondary battery is further improved. Moreover, by making it into the upper limit value or less, the binding force of the negative electrode mixture is improved, and the cycle characteristics of the iron-air secondary battery are further improved.

  The content of the negative electrode binder in the negative electrode mixture is preferably 0.5 to 20% by mass, more preferably 5 to 15% by mass. By setting it to the lower limit value or more, the binding force of the negative electrode mixture is improved, and the cycle characteristics of the iron-air secondary battery are further improved. Moreover, the charging / discharging capacity | capacitance of an iron-air secondary battery improves more by setting it as an upper limit or less.

  The content of the negative electrode conductive agent in the negative electrode mixture is preferably 0 to 150 parts by mass, more preferably 0 to 120 parts by mass with respect to 100 parts by mass of iron oxide. The charge / discharge capacity tends to improve as the content of the negative electrode conductive agent increases. However, by setting it to the upper limit or less, the binding force of the negative electrode mixture is improved and the cycle characteristics of the iron-air secondary battery are further improved. To do.

  The negative electrode mixture can be produced by mixing the iron oxide, the negative electrode binder, and other components as necessary, all at once or in an appropriate order. The mixing method of these components is not particularly limited, and may be a known method using a ball mill or a mixer.

<Negative electrode slurry for iron-air secondary battery>
The negative electrode mixture slurry for an iron-air secondary battery according to the present invention (hereinafter sometimes referred to as “negative electrode mixture slurry”) contains the negative electrode mixture and a solvent. .
The solvent is preferably an organic solvent, and examples thereof include N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, ethanol, toluene, xylene, hexane and the like. . These solvents may be used by heating as necessary.
As said solvent, 1 type may be used independently and 2 or more types may be used together.
The viscosity of the negative electrode mixture slurry can be adjusted by adjusting the type and amount of the solvent.

The negative electrode mixture slurry according to the present invention can be produced by mixing the negative electrode mixture and a solvent. The mixing method of these components is not particularly limited, and may be a known method.
In addition to the iron oxide, the binder for the negative electrode, and other components as necessary, the solvent may be mixed in a lump or in an appropriate order when the negative electrode mixture is manufactured. Good.

  The content of the solvent in the negative electrode mixture slurry is preferably 25 to 65% by mass, more preferably 35 to 55% by mass. By setting it to the lower limit value or more, the viscosity of the negative electrode mixture slurry is moderately lowered and the handleability becomes better, and by setting it to the upper limit value or less, the negative electrode for an iron-air secondary battery described later is manufactured. Removal of the solvent becomes easier.

<Negative electrode for iron-air secondary battery and method for producing the same>
The method for producing a negative electrode for an iron-air secondary battery (hereinafter sometimes referred to as “negative electrode”) according to the present invention is a step of applying the negative electrode mixture slurry to a current collector (negative electrode current collector). And a step of removing the solvent in the coated negative electrode mixture slurry. Such a production method can be the same as the production method of the conventional negative electrode except that the negative electrode mixture slurry is replaced with the above-mentioned one instead of the conventional one.

The material of the negative electrode current collector may be any material as long as it has electrical conductivity, and is preferably a metal. Examples thereof include simple metals such as copper and nickel, and alloys such as stainless steel. Copper is preferable from the viewpoint that it can be easily processed into a shape.
The shape of the negative electrode current collector is preferably a sheet shape or a plate shape. A three-dimensional network may be used, and an example of a three-dimensional network metal is “Celmet” manufactured by Sumitomo Electric.

  The negative electrode mixture slurry may be applied to the negative electrode current collector by a known method such as a doctor blade method.

By removing the solvent in the coated negative electrode mixture slurry, a negative electrode in which a negative electrode mixture layer containing a negative electrode active material is formed on the negative electrode current collector is obtained.
The solvent in the negative electrode mixture slurry is preferably removed by evaporation, and a method of evaporating any one of heating, reduced pressure and ventilation alone or in combination of two or more can be exemplified, and evaporates at least by heating. It is preferable to make it.

The heating temperature of the negative electrode mixture slurry when the solvent is evaporated is preferably 115 to 135 ° C, more preferably 115 to 125 ° C. By setting it as such a range, the binding force of a negative electrode mixture improves and the cycling characteristics of an iron-air secondary battery improve more. For example, by setting the lower limit value or more, the residual amount of the solvent can be easily reduced, and the negative electrode mixture can be more firmly fixed to the negative electrode current collector. Moreover, the fall of the iron oxide from a negative electrode is suppressed by setting it as an upper limit or less.
The heating time of the negative electrode mixture slurry when the solvent is evaporated may be adjusted according to the heating temperature, but is preferably 1 to 24 hours.

The negative electrode mixture layer formed by removing the solvent is preferably further pressed onto the negative electrode current collector by pressing. By doing so, a negative electrode with better characteristics can be obtained.
For example, when the negative electrode current collector has a diameter of 10 mm, the pressure during pressing is preferably 3 to 20 Pa, and more preferably 5 to 15 Pa. By setting it to the lower limit value or more, the effect by pressing can be sufficiently obtained, and by setting the lower limit value or less, the structure of the negative electrode mixture layer can be maintained more stably. The pressing is preferably performed at room temperature (for example, 15 to 25 ° C.).

The negative electrode according to the present invention is characterized by being obtained by the above-described manufacturing method, wherein a negative electrode mixture layer is formed on a negative electrode current collector, and the conventional iron--, except that the negative electrode mixture layer is different. It can be set as the structure similar to the negative electrode for air secondary batteries.
For example, the negative electrode is preferably in the form of a sheet or plate, and the thickness is preferably 5 to 500 μm.

Anode mixture the amount of on the negative electrode current collector (the weight of the negative electrode mixture layer) is preferably 0.5 to 50 mg / cm ^2, more preferably 1.5~15mg / cm ² .

A negative electrode lead wire may be connected to the negative electrode as an external connection terminal. And it is preferable that a negative electrode lead wire is connected to the site | part in which the negative mix layer of a negative electrode collector is not formed.
The material of the negative electrode lead wire may be any material as long as it has conductivity, and is preferably a metal. Examples thereof include simple metals such as nickel, chromium, iron, and titanium, and two or more of these simple metals. Alloys such as nickel and stainless steel (iron-nickel-chromium alloy) are preferable.

  The negative electrode according to the present invention uses a negative electrode mixture containing the specific negative electrode binder having the first peak and the second peak in the differential scanning calorimetry, so that the negative electrode mixture layer is bonded. The adhesion is excellent, and the components such as iron oxide and the negative electrode mixture itself are prevented from falling off from the negative electrode mixture layer and the negative electrode current collector, and the structure of the negative electrode is stably maintained.

<Iron-air secondary battery>
An iron-air secondary battery according to the present invention includes the negative electrode, a positive electrode, and an electrolytic solution, and may have a configuration similar to that of a conventional iron-air secondary battery except that the negative electrode is different. it can.

  The positive electrode is formed by forming a positive electrode catalyst layer on a current collector (positive electrode current collector).

The material of the positive electrode current collector may be any material as long as it has conductivity, and is preferably a metal. Examples thereof include simple metals such as nickel, chromium, iron, and titanium, and two or more of these simple substances. Examples of the alloy include metals, and nickel and stainless steel (iron-nickel-chromium alloy) are preferable.
The shape of the positive electrode current collector is preferably a mesh shape or a porous plate shape.

  It is preferable that the said positive electrode catalyst layer contains a positive electrode catalyst, and also contains a electrically conductive agent (positive electrode electrically conductive agent) and a binder (binder for positive electrodes) in addition to this. By containing the positive electrode binder, the positive electrode catalyst layer is stably fixed by the positive electrode current collector.

The positive electrode catalyst may be any material that can reduce oxygen, and examples thereof include non-oxide materials and oxide materials.
Examples of the non-oxide material include carbon materials such as activated carbon; platinum; iridium and the like.
Examples of the oxide material include manganese oxide such as manganese dioxide; iridium oxide containing one or more metals selected from the group consisting of titanium, tantalum, niobium, tungsten, and zirconium; iridium other than the iridium oxide Oxides: perovskite complex oxides represented by the general formula “ABO ₃ (wherein A and B are different metal elements)”.

  The positive electrode catalyst is preferably manganese dioxide, platinum, or the perovskite complex oxide. The perovskite complex oxide has at least two elements selected from the group consisting of La (lanthanum), Sr (strontium) and Ca (calcium) at the A site, and Mn (manganese) and Fe ( Those having at least one element selected from the group consisting of (iron), Cr (chromium) and Co (cobalt) are preferred. Among these, platinum is preferable because of its high catalytic activity for oxygen reduction. The perovskite complex oxide is preferable because it has an oxygen storage / release capability.

  The positive electrode conductive agent may be any material that can improve the conductivity of the positive electrode catalyst layer, and examples thereof include the same as the negative electrode conductive agent.

  The positive electrode binder may be any material that does not dissolve in the electrolyte solution. Examples of the material include polytetrafluoroethylene (PTFE), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene / Examples of the fluororesin include hexafluoropropylene copolymer, tetrafluoroethylene / ethylene copolymer, polyvinylidene fluoride, polychlorotrifluoroethylene, and chlorotrifluoroethylene / ethylene copolymer.

  The positive electrode is, for example, applied to the positive electrode current collector by adding a solvent to the positive electrode catalyst, and if necessary, a positive electrode conductive agent and / or a binder for the positive electrode, and mixing the mixture, It is obtained by removing the solvent to form the positive electrode catalyst layer. The solvent at this time may be the same as the solvent in the negative electrode mixture slurry, but is preferably selected as appropriate according to the type of the positive electrode conductive agent. The composition may be applied in the same manner as the application of the negative electrode mixture slurry during the production of the negative electrode, and the solvent may be removed in the same manner as the removal of the solvent in the negative electrode mixture slurry.

A positive electrode lead wire may be connected to the positive electrode as an external connection terminal. And it is preferable that a positive electrode lead wire is connected to the site | part in which the positive electrode catalyst layer of a positive electrode electrical power collector is not formed.
The material of the positive electrode lead wire may be any material as long as it has conductivity, and is preferably a metal. Examples thereof include simple metals such as nickel, chromium, iron, and titanium, and two or more of these simple metals. Alloys such as nickel and stainless steel (iron-nickel-chromium alloy) are preferable.

The electrolyte solution is preferably one in which an electrolyte is dissolved in an aqueous solvent or a non-aqueous solvent.
Examples of the electrolytic solution using an aqueous solvent include an aqueous solution in which at least one selected from the group consisting of sodium hydroxide (NaOH), potassium hydroxide (KOH), and ammonium chloride (NH ₄ Cl) is dissolved as an electrolyte. It is done. In this case, the concentration of the electrolyte in the aqueous solution is preferably 1 to 99% by mass, more preferably 3 to 60% by mass, and further preferably 5 to 40% by mass.

The electrolytic solution preferably contains a hydrogen generation inhibitor in addition to the electrolyte. When the electrolytic solution contains the hydrogen generation inhibitor, the hydrogen generation reaction that is a side reaction is suppressed, and as a result, the charge / discharge capacity of the iron-air secondary battery is increased.
Examples of the hydrogen generation inhibitor include metal sulfides. Among them, alkali metal sulfides are preferable, and potassium sulfide (K ₂ S) is more preferable.
What is necessary is just to adjust suitably the density | concentration of the hydrogen-generation inhibitor in electrolyte solution in the range which does not impair battery reaction.

  The iron-air secondary battery is configured by, for example, laminating the negative electrode, the separator, and the positive electrode in this order, and filling the electrolyte solution so as to contact the negative electrode, the separator, and the positive electrode. The negative electrode is arranged so that the negative electrode mixture layer faces the separator, and the positive electrode is arranged so that the positive electrode current collector faces the separator.

  Further, the iron-air secondary battery is preferably one in which the negative electrode, the separator, the positive electrode, and the oxygen diffusion film are laminated in this order. In this case, the oxygen diffusion film is disposed so as to face the positive electrode catalyst layer of the positive electrode. The oxygen diffusion film promotes the supply of oxygen (air) to the positive electrode.

The separator may be made of any material as long as the electrolyte is permeable and has insulating properties. Examples thereof include polyolefins such as polyethylene and polypropylene; and fluorine resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride. It is done. When the electrolytic solution is an aqueous solution, those obtained by hydrophilicizing these polyolefins or fluororesins may be used.
The separator is preferably a nonwoven fabric or a porous membrane.

The oxygen diffusion film may be made of any material that can transmit oxygen (air). Examples thereof include polyolefins such as polyethylene and polypropylene; and fluorine resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride. Can be mentioned.
The oxygen diffusion membrane is preferably porous.

FIG. 1 is a schematic cross-sectional view illustrating a laminated structure in which the negative electrode, separator, positive electrode, and oxygen diffusion film are laminated in an iron-air secondary battery according to the present invention.
The laminated structure 1 shown here includes a negative electrode 2, a separator 3, a positive electrode 4, and an oxygen diffusion film 5 laminated in this order.
The negative electrode 2 is formed by forming a negative electrode mixture layer 22 on a negative electrode current collector 21. The positive electrode 4 is formed by forming a positive electrode catalyst layer 42 on a positive electrode current collector 41. The negative electrode 2 is disposed such that the main surface of the negative electrode mixture layer 22 opposite to the contact surface with the negative electrode current collector 21 is opposed to and in contact with one main surface of the separator 3. The main surface of the positive electrode current collector 41 opposite to the contact surface with the positive electrode catalyst layer 42 faces and contacts the other main surface of the separator 3 (the surface opposite to the “one main surface”). Are arranged.
One main surface of the oxygen diffusion film 5 is disposed so as to face and contact the main surface of the positive electrode catalyst layer 42 opposite to the contact surface with the positive electrode current collector 41.
An electrolytic solution (not shown) is filled along the peripheral edge of the laminated structure 1 so as to contact the negative electrode 2, the separator 3, and the positive electrode 4.
In addition, the laminated structure in this invention is not limited to what is shown here, For example, in the range which does not prevent the effect of this invention, a part of structure shown in FIG. 1 may be changed.

  Since the iron-air secondary battery according to the present invention includes the negative electrode, the iron-air secondary battery has a sufficient discharge capacity, and even when charging and discharging are repeated, a decrease in the discharge capacity is suppressed, and the cycle characteristics are excellent.

  Hereinafter, the present invention will be described in more detail with reference to specific examples. However, the present invention is not limited to the following examples. In the following examples, “SUS” means “stainless steel”.

In this example, the following polyethylene was used as the binder for the negative electrode.
Binder (1): spherical polyethylene particles (“LE-1080” manufactured by Sumitomo Seika Co., Ltd., average particle size: 6 μm)
Binder (2): spherical polyethylene particles (“LE-2080” manufactured by Sumitomo Seika Co., Ltd., average particle size 10 μm)

<Measurement of Differential Scanning Calorie of Binder>
The differential scanning calorific value of the binder was measured by the following method. That is, using “Thermal Plus TG 8100” manufactured by Rigaku, 5 mg of the binder was placed in a SUS pan, and the binder was heated to 150 ° C. at a heating rate of 15 ° C./min.
As a result, in the binder (1), a peak (first peak) derived from polyethylene showing the maximum heat absorption amount was observed in the measurement temperature range of 105 to 110 ° C. Further, following this heat absorption amount, A peak (second peak) showing a large heat absorption amount was observed in the measurement temperature range of 80 to 90 ° C. The measurement results are shown in FIG. After completion of the measurement, the binder (1) used for the measurement was cooled, and the differential scanning calorific value was measured again under the same conditions. As a result, the peak observed in the measurement temperature range of 80 to 90 ° C. in the previous measurement (second) ) Was not observed.
On the other hand, in the binder (2), a peak derived from polyethylene was observed around the measurement temperature of 105 ° C., but no additional peak was observed in the measurement temperature range of 80 to 90 ° C.

<Manufacture of negative electrode mixture slurry>
[Example 1]
50 parts by mass of iron oxide (Fe ₂ O ₃ manufactured by Aldrich, product number 544884-5G, average particle size less than 50 nm) and 50 parts by mass of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) were dry mixed by a ball mill for 24 hours.
Next, 90 parts by mass of the obtained mixture and 10 parts by mass of the binder (1) as a binder were mixed to form a negative electrode mixture, and further N-methyl-2-pyrrolidone (NMP) 90 parts by mass here. By adding and mixing parts, an ink-like negative electrode mixture slurry (1) was obtained.

[Comparative Example 1]
A negative electrode mixture slurry (R1) was produced in the same manner as in Example 1 except that the binder (2) was used in place of the binder (1).

<Manufacture of negative electrode>
[Example 2]
The negative electrode mixture slurry (1) was applied on a SUS304 sheet and dried at 120 ° C. for 12 hours to obtain a coated electrode. The amount of the negative electrode mixture (weight of the negative electrode mixture layer) placed on the SUS304 sheet of this coated electrode was 2 mg / cm ² . In addition, the amount of the negative electrode mixture is the same in Comparative Examples 2 to 5 shown below.
Further, after punching this coated electrode into a disk shape having a diameter of 10 mm, the obtained disk electrode was pressed against SUS304 mesh at a pressure of 10 Pa to obtain a negative electrode (1) pressure-bonded to the SUS304 mesh. The thickness of the negative electrode (1) excluding the SUS304 mesh was 50 to 100 μm.

[Comparative Example 2]
A negative electrode (R1) was produced in the same manner as in Example 2, except that the negative electrode mixture slurry (R1) was used instead of the negative electrode mixture slurry (1).

[Comparative Example 3]
A negative electrode (R2) was produced in the same manner as in Example 2, except that the drying temperature of the negative electrode mixture slurry (1) was 140 ° C. instead of 120 ° C.

[Comparative Example 4]
A negative electrode (R3) was produced in the same manner as in Example 2 except that the drying temperature of the negative electrode mixture slurry (1) was changed to 160 ° C instead of 120 ° C.

[Comparative Example 5]
Except that the drying temperature of the negative electrode mixture slurry (1) was changed to 110 ° C. instead of 120 ° C., production of the negative electrode was attempted in the same manner as in Example 2, but the negative electrode mixture peeled off from the SUS304 sheet. The negative electrode could not be manufactured.

<Evaluation of cycle characteristics of iron-air secondary battery>
A three-electrode electrochemical cell (hereinafter abbreviated as “cell”) is constructed using each of the SUS mesh negative electrodes obtained above, and the charge and discharge test is performed. -The cycle characteristics of the air secondary battery were evaluated. Specifically, it is as follows.

(Production of three-electrode electrochemical cell)
For each SUS mesh-attached negative electrode (negative electrode (1), (R1) to (R3)), one end of the SUS304 wire (manufactured by Niraco, 1.0 mm in diameter) is attached to the part of the SUS mesh only where the negative electrode is not crimped. A working electrode was formed by welding. Then, using this working electrode, a platinum mesh (100 mesh) manufactured by Nilaco as a counter electrode, and an Hg / HgO electrode (manufactured by Interchemi) as a reference electrode, respectively, 8 mol / L of hydroxide as an electrolytic solution. Cells (1) and (R1) to (R3) were constructed using an aqueous potassium solution. The potassium hydroxide aqueous solution was used after bubbling with nitrogen gas for 30 minutes in advance in order to eliminate the influence of dissolved oxygen.

(Charge / discharge test of three-electrode electrochemical cell)
The obtained cells (1) and (R1) to (R3) were subjected to a charge / discharge test by the following method to evaluate cycle characteristics.
A charge / discharge test apparatus “BTS2004H” manufactured by Nagano Co., Ltd. was used for the charge / discharge test. The cell was left open circuit for 24 hours after fabrication in order to allow the electrolyte to fully penetrate the electrode. And charging / discharging was performed on the following conditions.
Charging is performed at a constant current of 0.5 mA / cm ² , and when the voltage reaches −1.15 V with respect to the reference electrode (Hg / HgO electrode), the charge capacity is −1.15 V until the charge capacity reaches 1007 mAh / g in total. Performed at a constant voltage. The discharge was performed at a constant current of 0.2 mA / cm ² until the voltage was −0.1 V with respect to the reference electrode (Hg / HgO electrode). The test is performed in a nitrogen gas atmosphere at 25 ° C., charged (in the direction in which the voltage decreases, that is, corresponding to a reduction reaction of iron), discharged after completion of charging, and repeated as one cycle. A discharge test was conducted. There was a one hour rest period between charging and discharging. The first to fourth cycles were aged, and the electric capacity (mAh / g) was measured from the fifth cycle. Capacitance, all of the iron element contained in the negative electrode is assumed to constitute the Fe ₂ O _3, was determined as the capacity per Fe 2 _O 3 _1g. The content of Fe ₂ O ₃ (mass), the content of iron element (mass) determined by atomic absorption spectroscopy, it was determined by converting the amount of _Fe 2 _{O 3.} Table 1 shows the measurement results of the discharge capacity at the fifth and tenth cycles.

As is clear from the above results, the cell (1) using the negative electrode (1) of Example 2 is excellent in both the discharge capacity at the 5th and 10th cycles, has a high capacity retention rate, and has cycle characteristics. It was excellent. On the other hand, the cell (R1) using the negative electrode (R1) of Comparative Example 2 had insufficient discharge capacity at both the fifth and tenth cycles. Thus, it was confirmed that an iron-air secondary battery having a sufficient discharge capacity and excellent cycle characteristics can be obtained by using a specific binder in the negative electrode.
On the other hand, the cell (R2) using the negative electrode (R2) of Comparative Example 3 and the cell (R3) using the negative electrode (R3) of Comparative Example 4 have no discharge capacity at the fifth and tenth cycles. The cycle characteristics were inferior. In the cells (R2) and (R3), it was estimated that the iron oxide was detached from the negative electrode, and this was the cause of the decrease in the discharge capacity.

(Production and charge / discharge test of three-electrode electrochemical cell in which electrolyte contains hydrogen generation inhibitor)
The negative electrode (1) is used as the negative electrode, and the electrolyte solution contains 0.1 / mol L of potassium sulfide (K ₂ S), which is a hydrogen generation inhibitor, instead of an 8 mol / L potassium hydroxide aqueous solution. The cell (2) is constructed as a three-electrode electrochemical cell in the same manner as described above except that an 8 mol / L potassium hydroxide aqueous solution is used, and a charge / discharge test is performed to evaluate the discharge capacity and cycle characteristics. did.
As a result, the discharge capacity at the 5th cycle is 610 mAh / g, the discharge capacity at the 10th cycle is the maximum at 672 mAh / g, and the discharge capacity and cycle are further increased than in the cell (1) using no hydrogen generation inhibitor. Excellent characteristics. This was presumed to be because the use of a hydrogen generation inhibitor suppressed the generation of hydrogen inside the electrode during charging, and the iron oxide from falling off the electrode was highly suppressed.

  The present invention can be used in the energy field.

  DESCRIPTION OF SYMBOLS 1 ... Laminated structure, 2 ... Negative electrode, 21 ... Negative electrode collector, 22 ... Negative electrode mixture layer, 3 ... Separator, 4 ... Positive electrode, 41 ... Positive electrode collector Electric current body 42... Positive electrode catalyst layer 5... Oxygen diffusion film

Claims (10)

A negative electrode mixture for an iron-air secondary battery containing iron oxide and a binder,
The binder is mainly composed of polyethylene,
In the differential scanning calorimetry, the binder has, in addition to the peak derived from the polyethylene showing the maximum heat absorption amount, a peak showing the heat absorption amount next to this in the measurement temperature range of 80 to 90 ° C. A negative electrode mixture for an iron-air secondary battery.   2. The negative electrode mixture for an iron-air secondary battery according to claim 1, wherein the binder has an average particle size of less than 20 μm.   The negative electrode mixture for an iron-air secondary battery according to claim 1 or 2, wherein the binder is spherical.   Furthermore, a conductive agent is contained, The negative mix for iron-air secondary batteries as described in any one of Claims 1-3 characterized by the above-mentioned.   A negative electrode mixture slurry for an iron-air secondary battery, comprising the negative electrode mixture for an iron-air secondary battery according to any one of claims 1 to 4 and a solvent.   A step of coating the current collector with the negative electrode mixture slurry for an iron-air secondary battery according to claim 5 and a step of removing the solvent in the coated negative electrode mixture slurry. The manufacturing method of the negative electrode for iron-air secondary batteries characterized by these.   The method for producing a negative electrode for an iron-air secondary battery according to claim 6, wherein the solvent is removed by drying the coated negative electrode mixture slurry at 115 to 135 ° C.   A negative electrode for an iron-air secondary battery obtained by the production method according to claim 6 or 7.   An iron-air secondary battery comprising the negative electrode for the iron-air secondary battery according to claim 8, a positive electrode, and an electrolytic solution.   The iron-air secondary battery according to claim 9, wherein the electrolyte contains a hydrogen generation inhibitor.

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