JP6352884B2 - Anode material for metal-air secondary battery, metal-air secondary battery comprising the same, and method for producing anode material for metal-air secondary battery - Google Patents

Description

  The present invention relates to a negative electrode material for a metal-air secondary battery, a metal-air secondary battery including the same, and a method for producing a negative electrode material for a metal-air secondary battery.

  Among secondary batteries in practical use, the one having the highest energy density (the amount of electric power that can be discharged with respect to the mass of the battery) is regarded as a lithium ion battery. As a secondary battery exceeding the energy density of this lithium ion battery, a metal-air secondary battery has attracted attention. In the metal-air secondary battery, the reactant of the positive electrode is oxygen in the air, and the reactant of the negative electrode is a metal. The greatest feature of this metal-air secondary battery is that, since oxygen in the atmosphere is utilized at the positive electrode, the mass of the reactant in the positive electrode can theoretically be zero. The mass of the battery occupies most of the mass of the reactant at the positive and negative electrodes and the mass of the electrolyte that mediates the reaction. For this reason, the metal-air secondary battery capable of reducing the mass of the reactant on one electrode to zero may greatly improve the energy density.

As a metal-air secondary battery, a combination of a conductive material such as carbon powder and an oxygen reduction catalyst is used as a positive electrode (air electrode), and zinc, aluminum, iron, hydrogen, or the like is configured as a negative electrode (metal electrode). Things are common. Among the negative electrode materials, iron is excellent in terms of cost and the like. For example, a metal-air all solid secondary battery having a negative electrode in which iron oxide nanoparticles as a negative electrode active material are supported on the surface of a KOH-ZrO ₂ based solid electrolyte. It has been developed (see JP 2012-74371 A). By using such a negative electrode, the characteristics of the metal-air all-solid secondary battery are improved as compared with the case of using a negative electrode made only of iron powder. However, the maximum discharge capacity of the secondary battery having the negative electrode is not sufficient, and the development of a negative electrode material for metal-air secondary batteries having higher performance is strongly desired.

JP 2012-74371 A

  The present invention has been made based on the above circumstances, and the object thereof is a negative electrode material for a metal-air secondary battery, which can exhibit good charge / discharge performance of the metal-air secondary battery, It is providing the manufacturing method of the metal-air secondary battery provided with this as a metal electrode, and the negative electrode material for metal-air secondary batteries.

  The invention made in order to solve the above problems is a negative electrode material used for a metal-air secondary battery, comprising a current collector and iron or iron oxide supported by the current collector. A negative electrode material for a metal-air secondary battery.

  Another invention made to solve the above problems is a metal-air secondary battery comprising the metal-air secondary battery negative electrode material as a metal electrode.

  Still another invention made in order to solve the above-described problem includes a step of supporting iron or iron oxide on a current collector, and the support of the iron or iron oxide is a metal-air secondary by an electrostatic adsorption composite method. It is a manufacturing method of the negative electrode material for batteries.

  According to the present invention, a metal-air secondary battery can exhibit good charge / discharge performance.

2 is a SEM image of the negative electrode material of Example 1. 3 is a graph showing a charge / discharge curve of the metal-air secondary battery of Example 1. FIG. FIG. 6 is a schematic diagram illustrating a production procedure of a metal-air secondary battery (metal-air all solid secondary battery) of Example 2. It is a graph which shows the change of the charging / discharging curve of the metal-air secondary battery (metal-air all-solid-state secondary battery) of Example 2, and discharge capacity. 6 is a graph showing changes in discharge capacity of the metal-air secondary battery of Example 3. 6 is a flowchart showing a procedure for producing a negative electrode material of Example 4. FIG. 4 is an X-ray diffraction spectrum of a negative electrode material of Example 4. 4 is a SEM image of a negative electrode material of Example 4. It is a graph which shows the change of the charging / discharging curve and discharge capacity of the metal-air secondary battery (liquid electrolyte) of Example 4. It is a graph which shows the change of the charging / discharging curve and discharge capacity of the metal-air all-solid-state secondary battery of Example 4. 6 is a partial cross-sectional SEM image of the metal-air all solid state secondary battery of Example 4. FIG. 6 is a partial cross-sectional SEM image of the negative electrode material of Example 5. 6 is a graph showing a charge / discharge curve of a metal-air secondary battery of Example 5. 7 is a partial cross-sectional SEM image of the negative electrode material of Example 6. 7 is a graph showing a charge / discharge curve of a metal-air secondary battery of Example 6. It is a graph which shows the charging / discharging curve of the metal-air all-solid-state secondary battery of Example 6. 7 is a partial cross-sectional SEM image of the negative electrode material of Example 7. 7 is a graph showing a charge / discharge curve of a secondary battery using the negative electrode material of Example 7.

[Anode material for metal-air secondary batteries]
A negative electrode material for a metal-air secondary battery according to an embodiment of the present invention includes a current collector and iron or iron oxide supported on the current collector.

(Current collector)
The current collector is not particularly limited, and a known current collector having conductivity can be used. The material forming the current collector is preferably formed from a metal material and a carbon material that do not contribute to the oxidation-reduction reaction, and more preferably from a carbon material.

  The shape of the current collector is not particularly limited, but a sheet shape is preferable. By setting it as a sheet, a metal-air secondary battery in which the positive electrode, the electrolyte, and the negative electrode are formed in layers can be easily formed. The average thickness of the sheet-like current collector is not particularly limited, but the lower limit is, for example, 0.01 mm, and preferably 0.1 mm. On the other hand, the upper limit is, for example, 10 mm, preferably 3 mm, and more preferably 1 mm. By setting it as such thickness, a more sufficient function as a negative electrode can be exhibited.

  The current collector preferably has electron conductivity and porosity. The porosity refers to a degree of porosity that allows the liquid electrolyte or solid electrolyte to contact the supported iron or iron oxide. When the current collector has such a property, in a metal-air secondary battery, the contact area between the negative electrode material (metal electrode) and the electrolyte is widened, so that the reaction efficiency is increased, and electrons generated by the oxidation-reduction reaction are quickly removed. Can be carried to. Therefore, this enhances the electrochemical characteristics and enables efficient charging and discharging.

  Further, when iron or iron oxide is used as a negative electrode material of a metal-air secondary battery, this iron or iron oxide does not elute unlike zinc or magnesium. For this reason, the area | region where iron or iron oxide contributes to an oxidation-reduction reaction efficiently is limited to the surface vicinity (for example, about 100 nm from the surface) of iron or iron oxide. Therefore, in order to increase the reaction efficiency, it is necessary to enlarge the surface area by making iron or iron oxide into a small particle size or a thin film, and the advantage of using a porous current collector is great.

  Specific structures of the porous current collector include (a) a mesh structure in which fibers having electron conductivity are regularly arranged, (b) a nonwoven structure in which the fibers are randomly arranged, and (c) independent pores. Or the three-dimensional network structure which has a continuous hole, and (d) the structure where these structures were combined are preferable. In such a structure, there are many contact points between fibers, or the whole is connected as a three-dimensional network structure, so that electrons can sufficiently move in the current collector. On the other hand, for example, in the case of a current collector formed by compressing conductive powder (carbon black, iron powder, etc.), movement of electrons is hindered, and sufficient charge / discharge characteristics cannot be obtained as compared with the above structure.

  Examples of the fiber having electron conductivity include metal fiber and carbon fiber, and carbon fiber is preferable. The lower limit of the average diameter of the fibers having electron conductivity is, for example, 0.5 μm, and preferably 2 μm. On the other hand, the upper limit is, for example, 100 μm, and preferably 50 μm. When metal fibers are used, titanium, nickel, stainless steel, etc. having corrosion resistance may be used. Moreover, the quantity of iron to carry | support can be reduced by using iron for a metal fiber.

  Among the porous current collectors, carbon paper is particularly preferable. Carbon paper has a nonwoven fabric structure in which carbon fibers are randomly arranged. By using the carbon paper, the above-described redox reactivity of iron or iron oxide and electron mobility become better. Furthermore, it is preferable that a powder having electron conductivity is embedded (filled) inside a porous body such as carbon paper (inside the pores). Examples of the powder include carbon black having a large surface area (for example, ketjen black). Thus, the surface area of the current collector can be further increased by combining carbon paper or the like with carbon black or the like.

  As the porous current collector, other than those formed from electronically conductive fibers, for example, activated carbon, independent pores or continuous pores obtained by a sintering method, a phase separation method, a solvent extraction method, etc. Those having a three-dimensional network structure can be used.

  The porosity of the porous current collector is, for example, 10% by volume or more and 80% by volume or less. The porosity means the ratio of the total volume of pores to the apparent volume of the current collector. The average pore diameter of the porous current collector is, for example, from 0.1 μm to 100 μm. The average pore diameter (average pore diameter) is a value measured by the mercury intrusion method described in JIS-K1150 (1994).

(Iron or iron oxide)
Part or all of iron or iron oxide supported on the current collector exists as a metal (Fe) or a metal oxide (for example, Fe ₂ O ₃ , Fe ₃ O ₄ ) depending on a charge-discharge state. Iron is a metal that is abundant in nature and can be expected to improve battery voltage. In addition, the cost is overwhelmingly lower than other metals, which helps the spread of metal-air secondary batteries.

  Here, iron has a broad meaning including not only iron itself but also iron alloys and iron-containing substances. Although the absolute value of the oxidation-reduction potential is relatively small, iron has an advantage that the metal electrode is stabilized even when repeatedly charged and discharged because the ionized product (iron ion) does not move. In addition, iron is inexpensive and has a large reserve, and dendrite formation does not occur even when used as a secondary battery, so that a safe secondary battery can be provided.

The iron or iron oxide to be supported is preferably in the following aspects (1) and (2).
(1) A mode in which iron or iron oxide is formed (coated) directly and partially (discontinuously) on the surface of the current collector (2) Iron or iron oxide is directly and continuously formed on the surface of the current collector The above-mentioned current collector “surface” is not limited to the outer surface, but also includes the surface of each fiber (for example, carbon fiber) inside the current collector.

  In any case, it can be used as a metal-air secondary battery. However, in the case of (1), it is possible to absorb strain caused by volume change during charging / discharging, and repeat charging / discharging. Is advantageous. On the other hand, in the case of (2), the absolute amount of iron or iron oxide to be carried increases, so that it is suitable for applications that require capacity. Which case should be selected may be selected according to the required characteristics.

  Examples of supported iron or iron oxide sizes are as follows. When iron or iron oxide is particulate, the lower limit of the average particle size is preferably 20 nm, more preferably 30 nm. On the other hand, the upper limit is preferably 2 μm, more preferably 600 nm, and even more preferably 200 nm. When iron or iron oxide is in the form of a film, the lower limit of the average film thickness is preferably 1 nm, and more preferably 10 nm. On the other hand, the upper limit is preferably 1 μm, more preferably 100 nm, and even more preferably 50 nm. Charge / discharge performance is further improved by reducing the average particle diameter or average film thickness of the iron or iron oxide to be supported within the above range. The “average particle size” means a 50% value (50% particle size, D50) of a volume-based cumulative particle size distribution curve measured by a laser diffraction method or the like.

  The negative electrode material for a metal-air secondary battery is obtained by a production method including a step of supporting iron or iron oxide on a current collector. The support of iron or iron oxide on the current collector is not particularly limited, and a known method can be used. Examples of the supporting method include a PVD method (vacuum deposition, sputtering, etc.), a CVD (plasma CVD, thermal CVD, atmospheric open CVD, etc.) method, a solution method, a coating method, an electrostatic adsorption composite method, and an electrodeposition method. . Among these, the CVD method and the electrostatic adsorption composite method performed under atmospheric pressure are preferable, and the electrostatic adsorption composite method is more preferable. A solution method is also preferable. When these methods are used, the porous current collector can be sufficiently supported inside.

  The electrostatic adsorption composite method is a method of adsorbing iron or iron oxide particles to a current collector using electrostatic interaction. Supporting by the electrostatic adsorption composite method can be performed, for example, by the following method. First, a positive or negative charge is imparted to the current collector surface by adsorbing a cationic polymer, an anionic polymer, or the like on the current collector surface. Here, the above-mentioned current collector “surface” is not limited to the outer surface, but also includes the surface of each fiber (for example, carbon fiber) inside the current collector (the same applies hereinafter). On the other hand, an ionic polymer is similarly used on the surface of the iron or iron oxide particle, and a charge opposite to that on the current collector surface is imparted. Cationic polymers and anionic polymers can be adsorbed alternately to adjust the surface charge to positive or negative. Next, by dipping a current collector (carbon paper or the like) in the liquid in which the oxide particles are dispersed, iron or iron oxide particles are adsorbed on the surface of the current collector by electrostatic interaction. Cationic polymers and anionic polymers can be removed by heat treatment after adsorption.

  Examples of the cationic polymer include a polymer having a quaternary ammonium group such as polydiallyldimethylammonium chloride (PDDA). Examples of the anionic polymer include a polymer having a sulfonic acid group such as sodium polystyrene sulfonate (PSS).

It is also possible to carry iron oxide particles on the current collector by the following method. In alcohol, iron oxide (Fe ₃ O ₄ ) has a positive surface potential, and carbon paper has a negative surface potential. For this reason, it is possible to adsorb the iron oxide on the carbon paper by immersing the carbon paper in the iron oxide suspension, stirring the magnetic iron oxide using magnetic force, and using the electrostatic force. By using this method, the current collector can be supported without containing a polymer between iron oxide and carbon.

  Furthermore, the current collector may be supported by electrodeposition. In the electrodeposition method, for example, iron can be deposited on carbon paper by applying a voltage using carbon paper as the cathode, a platinum rod as the anode, and a mixed solution of ethanol and iron chloride as the electrolyte.

The amount of iron or iron oxide supported is not particularly limited. When the current collector is in the form of a sheet, the lower limit of the supported amount per unit area is, for example, 0.01 mg / cm ² , and preferably 0.03 mg / cm ² . On the other hand, as this upper limit, it is 5 mg / cm < ² >, for example, and 1 mg / cm < ² > is preferable. By setting it as such a load, more sufficient function as a negative electrode can be exhibited.

  In some cases, iron or iron oxide is not carried in the voids of the porous current collector, but is carried (laminated) on one surface side of the sheet-like current collector. A single layer of iron or iron oxide particles adheres on the fiber, and by adjusting the particle size of the iron or iron oxide and the pore size of the porous body (current collector), the gaps in the current collector are not blocked. Can be formed into a state.

  The negative electrode material for a metal-air secondary battery can further include a solid electrolyte (first solid electrolyte) disposed so as to be in contact with iron or iron oxide. This solid electrolyte is disposed by applying a solid electrolyte solution on both sides of a sheet-like current collector carrying iron or iron oxide, and a sheet-like current collector carrying iron or iron oxide in the solid electrolyte solution. It can be performed by dipping the electric body. By drying after application or immersion, a sheet body (negative electrode material) in which the current collector is impregnated with the current collector is obtained. It does not specifically limit as a solid electrolyte, It is the same as that of what is illustrated as what is used for the metal-air secondary battery mentioned later. Thus, according to the negative electrode material in which the solid electrolyte is combined, a metal-air secondary battery can be easily manufactured by combining with the positive electrode (air electrode).

  According to the negative electrode material for a metal-air secondary battery, preferably, the current collector has an electronic conductivity and a porosity in which a liquid or solid electrolyte can come into contact with iron or iron oxide. For example, the current collector has the structures (a) to (d) described above, whereby the charge / discharge performance of the metal-air secondary battery can be improved. Thereby, the metal-air secondary battery which shows a plateau area | region (potential flat part) on a discharge curve can also be obtained.

[Metal-air secondary battery]
The metal-air secondary battery which concerns on one Embodiment of this invention is equipped with the said negative electrode material for metal-air secondary batteries as a metal electrode. Other configurations of the metal-air secondary battery can be the same as those of a general metal-air secondary battery. That is, the metal-air secondary battery includes an air electrode and an electrolyte interposed between the metal electrode and the air electrode in addition to the metal electrode. A separator may be provided between the metal electrode and the air electrode.

The air electrode functions as a positive electrode of the metal-air secondary battery. As the air electrode, a reaction represented by the following formula (1) occurs, and those used in ordinary metal-air secondary batteries can be used, but it is preferable to include a carbon and oxygen reduction catalyst. A sheet-like thing can be used for an air electrode, and it is preferable to use a carbon layer with a catalyst.
O ₂ + 2H ₂ O + 4e ⁻ → 4OH ⁻ (1)

Examples of the catalyst (oxygen reduction catalyst) include Pt and MnO ₂ . As the form of the carbon layer (carbon sheet) constituting the catalyst-attached carbon layer, for example, a green powder compact or carbon paper can be used.

  The lower limit of the average thickness of the air electrode is preferably 0.05 mm, and more preferably 0.1 mm. By setting the average thickness of the air electrode to the above lower limit or more, a sufficient reaction can be caused. On the other hand, the upper limit is, for example, 0.3 mm, and preferably 0.2 mm. If the air electrode becomes too thick, it tends to be difficult to efficiently form a three-phase interface of electrolyte, catalyst, and air.

  As the electrolyte, those usually used for metal-air secondary batteries, such as a liquid electrolyte and a solid electrolyte (second solid electrolyte), can be used. A plurality of types of electrolytes may be used, and a plurality of electrolytes may be used in multiple layers.

Examples of the liquid electrolyte include a solution in which a salt is dissolved in a solution and an ionic liquid. The liquid electrolyte in solution may be an alkaline aqueous solution such as a potassium hydroxide aqueous solution or a sodium hydroxide aqueous solution, or an organic solvent solution of a lithium salt such as LiPF ₆ or LiBF ₄ . Examples of the organic solvent include carbonate solvents such as ethylene carbonate, and ester solvents such as γ-butyrolactone and methyl acetate. The electrolyte may contain an additive such as potassium sulfide (K ₂ S).

  When a solid electrolyte is used as the electrolyte, the metal-air secondary battery is usually configured as a metal-air all-solid secondary battery having a layer structure including a metal electrode layer, a solid electrolyte layer, and an air electrode layer. The

Solid electrolyte refers to an electrolyte that does not have fluidity, and is composed of a polymer such as a polyethylene oxide polymer or an inorganic substance such as Li ₂ S—SiS ₂ , or a salt such as a basic hydroxide. The thing of the gel body hold | maintained at the gel can be mentioned. Examples of the salt in the gel solid electrolyte include basic hydroxides such as potassium hydroxide and sodium hydroxide, and examples of the gel include zirconia gel. A binder such as polyvinylidene fluoride (PVdF) may be mixed in the solid electrolyte.

  When the solid electrolyte is layered, it is preferable that the average film thickness is 0.1 mm or more in order to sufficiently exhibit the action of conducting hydroxide ions and to prevent short circuit. However, since the actual resistance (battery internal resistance) increases when the thickness is too large, the average film thickness is preferably set to 0.3 mm or less, for example.

  In addition, as one aspect | mode of a metal-air all-solid-state secondary battery, it can also be set as the form which impregnated the solid electrolyte (1st solid electrolyte) in the porous collector which forms a negative electrode. In this case, the solid electrolyte is impregnated into the current collector so as to be in contact with the iron or iron oxide supported on the current collector and continuously supplied with hydroxide ions generated at the air electrode. Yes. That is, the negative electrode material (metal electrode) in this embodiment is a negative electrode material further provided with the solid electrolyte (first solid electrolyte) disposed so as to be in contact with the iron or iron oxide described above. Such a negative electrode material and an air electrode constitute a metal-air all-solid secondary battery. In this case, the second solid electrolyte may not be further disposed between the negative electrode material (metal electrode) and the air electrode, but may be disposed.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, and can be implemented with modifications within a range that can be adapted to the gist of the present invention, all of which are included in the technical scope of the present invention. .

[Example 1]
In Example 1, iron was supported on carbon paper by an electrostatic adsorption composite method. The specific procedure is as follows. The surface of the carbon paper is hydrophilized using sodium deoxycholate (SDC), which is a surfactant, and finally polydiallyldimethylammonium chloride (PDDA) and sodium polystyrene sulfonate (PSS) are adsorbed in this order. Surface charge was adjusted to negative. On the other hand, the iron oxide particles (Fe ₃ O ₄ ) were positively adjusted in surface charge by adsorbing PDDA, PSS and PDDA in this order. Next, the carbon paper was immersed in a liquid in which the iron oxide particles were dispersed, so that both were combined by electrostatic interaction. Thus, the carbon paper carrying iron oxide particles was heat-treated at 350 ° C. to vaporize the surfactant and the polymer electrolyte (SDC, PDDA and PSS). Thereby, the negative electrode material was completed.

FIG. 1 shows an SEM (scanning electron microscope) image of the obtained negative electrode material. It was confirmed that iron oxide particles having a particle size of about 500 nm were adsorbed on the carbon fiber in a large amount and evenly. Moreover, the load of iron oxide particle was 0.227 mg / cm < ² > (Fe conversion). The supported amount was calculated from the mass of the residual material (Fe ₂ O ₃ ) after heat treatment at 950 ° C. in air (the same applies hereinafter). The oxidation-reduction behavior in an 8M aqueous potassium hydroxide solution of a metal-air secondary battery produced using this negative electrode material was observed by cyclic voltammetry. A metal-air secondary battery (test cell) was made of the following materials. The metal electrode (negative electrode) is a prepared negative electrode material, the electrolyte is an 8M potassium hydroxide aqueous solution, and the air electrode is a water-repellent carbon paper coated with electrolytic manganese dioxide (MnO ₂ ) as a redox catalyst to form a catalyst layer. The test cell was subjected to a charge / discharge test at a charge rate of 3 mA / cm ² and a discharge rate of 0.2 mA / cm ² .

  FIG. 2 shows the results of the charge / discharge test. In the charge curve, a reduction plateau of iron from trivalent to divalent and divalent to zero was observed. From this, it can be judged that reduction to iron is performed. Similarly, two distinct plateaus were observed in the discharge curve. Although the discharge capacity decreased as the cycle progressed, a large discharge capacity of 420 mAh / g (Fe) at the maximum was obtained in the initial cycle. This is a very large value corresponding to about 44% of the theoretical capacity of 960 mAh / g (Fe). It was shown that iron oxide was able to achieve good contact with an electrolyte or the like by supporting a negative electrode active material on porous carbon paper.

[Example 2]
A metal-air all-solid secondary battery was produced using the negative electrode material produced in the same manner as in Example 1 and a solid electrolyte. The procedure is shown in FIG. First, the electrolyte slurry 2 pulverized by a jet mill was applied to both sides of the negative electrode material 1 produced in the same manner as in Example 1. The solid content in the electrolyte slurry 2 is a mixture of 90 wt% of KOH—ZrO ₂ powder and 10 wt% of polyvinylidene fluoride (PVdF). After the application of the electrolyte slurry 2, it was dried to obtain an electrolyte sheet 3. Subsequently, the carbon papers 4 and 5 with a catalyst as an air electrode were piled up on both surfaces of the electrolyte sheet 3, and it was set as the all-solid-state battery. The amount of catalyst supported on the carbon papers 4 and 5 with catalyst used is 1 mg / cm ² , and the catalyst is electrolytic manganese dioxide (MnO ₂ ). FIG. 4 shows the charge / discharge results. As shown in FIG. 4, a sufficient function as an all solid state battery was confirmed.

[Example 3]
In Example 3, iron was supported on carbon paper by a sputtering method using a sputtering apparatus “HSR-542S” manufactured by Shimadzu Corporation. The average film thickness (supported amount) of iron was 30 nm (0.0354 mg), 100 nm (0.118 mg), 300 nm (0.354 mg), and 600 nm (0.709 mg), respectively. Negative electrode materials having the above average film thickness were obtained by adjusting the film formation time under the following film formation conditions and deposition rate.
Deposition conditions: Ar = 30 sccm, 200 W-10 mTorr_stationary deposition Deposition: 0.69 cm / s

  Using the obtained negative electrode material, a battery was produced in the same manner as in Example 1, and the characteristics were evaluated. The results are shown in FIG. A capacity of up to 500 mAh / g was obtained at an average film thickness of 30 nm. Moreover, the capacity | capacitance of 300 mAh / g or more was obtained even after repeating. Good charge / discharge was also observed at other average film thicknesses.

[Example 4]
In Example 4, iron oxide was supported on carbon paper by a solution method. A specific procedure is shown in FIG. First, carbon paper hydrophilized with SDC was immersed in an ethanol solution of acetylacetone iron complex (Fe (acac) ₃ ), and subjected to ultrasonic treatment for 30 minutes. Then, it left still for 1 hour in the 100 degreeC immersion state. Thereafter, heat treatment was performed at 400 ° C. for 1 hour in a nitrogen gas atmosphere to obtain a negative electrode material carrying iron oxide. The amount of iron oxide supported was 0.26 mg / cm ² (converted to Fe).

FIG. 7 shows an X-ray diffraction result of the obtained negative electrode material. It was confirmed that the precipitate (supported material) was Fe ₃ O ₄ .

  FIG. 8 shows an SEM image of the obtained negative electrode material. It was confirmed that iron oxide having a particle size of about 100 to 200 nm was supported.

  Using the obtained negative electrode material, a metal-air secondary battery was produced in the same manner as in Example 1, and the characteristics were evaluated. The evaluation results are shown in FIG. From FIG. 9, sufficient charge / discharge performance was confirmed.

  Using the obtained negative electrode material, a metal-air all solid secondary battery was produced in the same manner as in Example 2, and the characteristics were evaluated. The evaluation results are shown in FIG. Moreover, the partial cross section SEM image of the obtained metal-air all-solid-state secondary battery is shown in FIG. From FIG. 10, sufficient charge / discharge performance was confirmed. Further, from FIG. 11, it was confirmed that the solid electrolyte sufficiently penetrated into the carbon paper.

[Example 5]
In Example 5, iron oxide was supported by an electrostatic adsorption method to produce a negative electrode material. Specifically, first, 2 g of iron oxide was added to 60 ml of ethanol to prepare a suspension. Next, the carbon paper was immersed in a suspension of iron oxide, placed on a stirrer, and stirred at 500 rpm. At this time, since iron oxide has a magnetic force, the particles themselves were rotated and stirred in the suspension. Iron oxide was supported on carbon paper by stirring for 10 minutes to obtain a negative electrode material. FIG. 12 shows a partial cross-sectional SEM image of the obtained negative electrode material. From FIG. 12, it was confirmed that iron oxide particles of about 500 nm could be supported on carbon paper.

Further, a metal-air secondary battery using the negative electrode material, an air electrode similar to that in Example 1, and an 8M aqueous potassium hydroxide solution to which 0.03M potassium sulfide (K ₂ S) is added as an electrolyte. to prepare a charge rate 30 mA / cm ^2, the evaluation of the charge and discharge characteristics was performed by the discharge rate 3mA / cm ² 3-electrode method. The evaluation results are shown in FIG. From FIG. 13, sufficient charge / discharge performance was confirmed, and a large discharge capacity of 200 mAh / g (Fe) or more was obtained in the first cycle.

[Example 6]
In Example 6, a negative electrode material was produced by an electrodeposition method. Specifically, first, an electrolyte solution prepared by mixing 0.8 g of iron chloride with 100 ml of ethanol was prepared. Next, electrolytic treatment was performed for 30 minutes at a pulse applied voltage of 20 V using carbon paper as the cathode and a platinum rod as the anode. The pulse was applied for 120 seconds and rested for 20 seconds. As a result, iron oxide was precipitated on the carbon paper, and a negative electrode material was obtained. FIG. 14 shows a partial cross-sectional SEM image of the obtained negative electrode material.

Using the obtained negative electrode material (electrode area 1.5 cm ² ), a metal-air secondary battery was produced in the same manner as in Example 5, and the charge / discharge cycle was performed 3 cycles at a charge current of 5 mA and a discharge current of 0.2 mA. The charge / discharge characteristics were evaluated by the three-electrode method. The evaluation results are shown in FIG. From FIG. 15, sufficient charge / discharge performance was confirmed.

  Further, using the obtained negative electrode material, a metal-air all solid state secondary battery was produced in the same manner as in Example 2, and the charge / discharge cycle was performed three times at a charge current of 5 mA and a discharge current of 0.2 mA, thereby performing the three-electrode method. Thus, the charge / discharge characteristics were evaluated. The evaluation results are shown in FIG. From FIG. 16, it was confirmed that the initial cycle was 14 mAh / g (Fe), and sufficient charge / discharge performance was confirmed.

[Example 7]
In Example 7, a negative electrode material was produced by depositing iron on a metal incombustible cloth by electrodeposition. Specifically, a non-combustible cloth made of stainless steel (average thickness 5 mm) was prepared as a metal incombustible cloth. The diameter of the stainless steel wire constituting this nonwoven fabric was about 10 μm. As in Example 6, a solution prepared by mixing 0.8 g of iron chloride with 100 ml of ethanol was prepared as an electrolytic solution. Next, an electrolytic treatment was performed for 3 hours at a pulse applied voltage of 10 V using a platinum rod as the anode. The pulse was applied for 20 seconds and rested for 20 seconds. As a result, iron oxide was deposited on the metal incombustible cloth, and a negative electrode material was obtained. FIG. 17 shows a partial cross-sectional SEM image of the obtained negative electrode material. In FIG. 17, the left image is a 100 × enlarged image, and the right image is a 1000 × enlarged image obtained by further enlarging a part of the left image. From FIG. 17, it was confirmed that iron adhered to almost the entire surface of the nonwoven fabric by the electrodeposition method.

The obtained negative electrode material (electrode area 1.5 cm ² ) was used to evaluate the electrode. Since the characteristics when this negative electrode material is used for an air battery can be estimated from the results of the above examples, the charge / discharge characteristics were evaluated by the three-electrode method in order to compare only the characteristics of the iron negative electrode. Specifically, an Hg / HgO (1M-NaOH) electrode was used for the reference electrode, and a Pt electrode was used for the counter electrode. An 8M potassium hydroxide aqueous solution was used as the electrolyte, and the evaluation was performed with a charging current of 5 mA and a discharging current of 0.2 mA. The result is shown in FIG. As shown in FIG. 18, sufficient charge / discharge performance was confirmed. In particular, the plateau in the vicinity of -1 V (relative to the standard potential) corresponding to oxidation from zero valence to divalence was almost the same in three cycles, and it was found that this electrode was excellent in repetition characteristics.

  The negative electrode material for a metal-air secondary battery of the present invention can be suitably used as a metal electrode (negative electrode) of a metal-air secondary battery.

DESCRIPTION OF SYMBOLS 1 Negative electrode material 2 Electrolyte slurry 3 Electrolyte sheet 4, 5 Carbon paper with a catalyst

Claims (9)

A negative electrode material used for a metal-air secondary battery,
A current collector,
With iron or iron oxide carried on the current collector ,
The current collector has electronic conductivity, and a porous liquid or solid electrolyte can contact the iron or iron oxide;
A negative electrode material for a metal-air secondary battery , wherein the iron or iron oxide is further carried inside the current collector . The negative electrode material for a metal-air secondary battery according to claim 1, wherein the current collector is formed of a carbon material. The current collector is
(A) a mesh structure in which fibers having electron conductivity are regularly arranged;
(B) a nonwoven fabric structure in which the fibers are arranged randomly;
The negative electrode for a metal-air secondary battery according to claim 1 or 2, wherein (c) has a three-dimensional network structure having independent holes or continuous holes, or (d) a structure in which these structures are combined. material.   The negative electrode material for a metal-air secondary battery according to claim 3, wherein the current collector is carbon paper.   The negative electrode material for a metal-air secondary battery according to any one of claims 1 to 4, further comprising a first solid electrolyte disposed so as to contact the iron or iron oxide.   A metal-air secondary battery comprising the metal-air secondary battery negative electrode material according to any one of claims 1 to 5 as a metal electrode. An air electrode containing carbon and oxygen reduction catalysts;
The metal-air secondary battery according to claim 6, further comprising: a liquid electrolyte interposed between the air electrode and the metal electrode. An air electrode containing carbon and oxygen reduction catalysts;
The metal-air secondary battery according to claim 6, further comprising: a second solid electrolyte interposed between the air electrode and the metal electrode. Comprising a step of supporting iron or iron oxide on a current collector;
A method for producing a negative electrode material for a metal-air secondary battery in which the iron or iron oxide is supported by an electrostatic adsorption composite method.