JP6673759B2 - Manufacturing method of magnesium air battery - Google Patents

Description

  The present invention relates to a method for manufacturing a magnesium-air battery using oxygen as a positive electrode active material.

  In a magnesium-air battery using oxygen in the air as a positive electrode active material, oxygen is constantly supplied from the outside of the battery, and a large amount of metallic magnesium, which is a negative electrode active material, can be filled in the battery. For this reason, it is reported that the value of the discharge capacity per unit volume of the battery can be extremely increased.

Further, transition metal oxides and noble metals are being studied as an electrode catalyst for a gas diffusion type air electrode serving as a positive electrode. For example, transition metal oxides such as MnO ₂ (see Non-Patent Document 1) and noble metals such as Pd (see Non-Patent Document 2) have been studied.

Y. Xue et al., "Template-directed fabrication of porous gas diffusion layer for magnesium air batteries", Journal of Power Sources, Vol.297, pp.202-207, 2015. W. Yang et al., "Comparison of CNF and XC-72 carbon supported palladium electrocatalysts for magnesium air fuel cell", Carbon, Vol. 45, pp. 397-401, 2007.

Incidentally, in the reports non-patent document 1, the discharge voltage at a current density of 25mA / cm ² is a 1.2V, the discharge voltage at a current density of 100 mA / cm ² has dropped to 0.8V and about 67% And the current density characteristics were low. Also in the reported non-patent document 2, although 25mA / cm ² current density at discharge voltage is relatively high and 1.4V, discharge voltage at a current density of 100 mA / cm ² within 0.7V and about 50% Is declining. As described above, in the related art, there has been a problem that the discharge voltage decreases with the discharge.

  The present invention has been made to solve the above problems, and has as its object to suppress a decrease in discharge voltage of a magnesium-air battery.

  The method for manufacturing a magnesium-air battery according to the present invention comprises an air electrode, a negative electrode including magnesium, an electrolyte interposed between the air electrode and the negative electrode, and a conductive material forming the air electrode. A method for producing a magnesium-air battery comprising: a catalyst comprising a metal oxide supported on a carrier; and a catalyst production step for producing a catalyst by oxidizing bacteria, which are bacteria that oxidize metals and proliferate.

  In the method for producing a magnesium-air battery, the oxidizing bacterium may be any one of the genera Leptostrix, Galionella, Siderocapsa, Thiobacillus, and mutants thereof.

  In the method for manufacturing a magnesium-air battery, the oxidizing bacterium is an iron oxidizing bacterium or a manganese oxidizing bacterium, and the metal oxide is at least one of iron oxide and manganese oxide.

In the method for producing a magnesium-air battery, a gel production step of producing a cellulose gel by a cellulose-producing bacterium that is a cellulose-producing bacterium, a freezing step of freezing the produced cellulose gel, and subjecting the frozen cellulose gel to a vacuum. a drying step of drying the cellulose gel is dried by carbonizing Ru and a carbonization step of preparing a carrier.

In the method for producing a magnesium-air battery, the bacteria-containing step of containing the oxidizing bacteria in a carrier prepared by carbonizing the cellulose gel, and a catalyst-containing step of containing a catalyst produced by the oxidizing bacteria in a carrier containing the oxidizing bacteria. with Ru.

  As described above, according to the present invention, an air electrode catalyst is produced by oxidizing bacteria, which are bacteria that oxidize and grow by oxidizing metals, so that a reduction in the discharge voltage of a magnesium-air battery can be suppressed. The effect is obtained.

FIG. 1 is a flowchart illustrating a method for manufacturing a magnesium-air battery according to an embodiment of the present invention. FIG. 2 is a flowchart for explaining a more detailed manufacturing method of the magnesium-air battery according to the embodiment of the present invention. FIG. 3 is a configuration diagram showing a configuration of the magnesium-air battery according to the embodiment of the present invention. FIG. 4 is a cross-sectional view showing a more detailed configuration example of the magnesium-air battery. FIG. 5 is a characteristic diagram illustrating a discharge state of the magnesium-air battery in Example 1.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a flowchart illustrating a method for manufacturing a magnesium-air battery according to an embodiment of the present invention. First, in step S101, an oxidizing bacterium that oxidizes and proliferates a metal to produce a catalyst made of a metal oxide (a catalyst production step). Next, in step S102, an air electrode is produced in which the produced catalyst is supported on a carrier made of a conductive material forming the air electrode.

  For example, powder of iron oxide or manganese oxide as a catalyst obtained in the catalyst production process, carbon powder, and if necessary, a binder powder such as polytetrafluoroethylene (PTFE) are mixed, and the mixture is mixed with titanium mesh or the like. The air electrode can be formed by pressure bonding on the support of the above.

  The air electrode can be formed by dispersing the above mixture in a solvent such as an organic solvent to form a slurry, applying the slurry on a metal mesh or a carbon cloth or a carbon sheet, and drying the slurry. In addition, by applying not only a cold press but also a hot press in order to increase the strength of the electrode and prevent leakage of the electrolyte, a more stable air electrode can be produced. A magnesium air battery is manufactured from the obtained air electrode.

  Further, a magnesium-air battery may be manufactured by the following example. As shown in the flowchart of FIG. 2, in step S111, a cellulose gel is produced by a cellulose producing bacterium that produces cellulose, and carbonized to produce a carrier (carrier producing step). Next, in step S112, the prepared carrier contains oxidizing bacteria (bacteria-containing step). Next, in step S113, the oxidizing bacteria are cultured in a metal-containing medium to produce a catalyst, so that the carrier contains the catalyst produced by the oxidizing bacteria to form an air electrode (catalyst containing step). A magnesium-air battery is manufactured from the air electrode thus manufactured.

  As described in detail below, the porosity of a carrier obtained by carbonizing a cellulose gel produced by a cellulose-producing bacterium is 95% or more, and has excellent water absorption. Therefore, an excellent medium can be obtained by adding a liquid medium to the carrier. The liquid medium is not particularly limited as long as iron oxidizing bacteria and manganese oxidizing bacteria can be cultured, but in 1 L of sterilized groundwater, 0.076 g of disodium hydrogen phosphate decahydrate, potassium dihydrogen phosphate dihydrate are contained. 0.03 g, HEPES [4- (2-hydroxyethyl) -1-piperazineethanesulfonic acid: buffer substance] 2.383 g, iron sulfate 0.01 mmol / L, pH adjusted to 7.0 with sodium hydroxide aqueous solution Liquid media are preferred.

  For example, a carrier and a liquid medium obtained by carbonizing the above-described cellulose gel are taken in an appropriate container such as a test tube, and iron oxidizing bacteria are put into the container together with iron pieces, and culturing may be performed in this state. . An air electrode is obtained using a carrier on which a catalyst made of iron oxide is supported. In addition, for example, the carrier and the liquid medium obtained by carbonizing the cellulose gel are placed in an appropriate container such as a test tube, and the manganese-oxidizing bacteria are added thereto together with the manganese small pieces, and the culture may be performed in this state. . An air electrode is obtained using a carrier on which a catalyst made of manganese oxide is supported.

  The culture time is preferably at least 6 hours, more preferably at least 12 hours. Further, by simultaneously culturing the iron oxidizing bacteria and the manganese oxidizing bacteria, it is possible to include a catalyst in which iron oxide and manganese oxide are mixed in carbonized bacterial cellulose. Bacteria contain the catalyst inside the carrier obtained by carbonizing the cellulose gel, so that the catalyst can be contained in a highly dispersed manner. The magnesium-air battery with the air electrode thus produced exhibits high performance.

  The manufacturing method described above is a method for manufacturing the magnesium-air battery shown in FIG. The magnesium-air battery includes a gas diffusion type air electrode 101 serving as a positive electrode, a negative electrode 102 including magnesium, and an electrolyte 103 interposed between the air electrode 101 and the negative electrode 102. One surface of the cathode 101 is exposed to the atmosphere, and the other surface is in contact with the electrolyte 103. The surface of the negative electrode 102 on the side of the electrolyte 103 is in contact with the electrolyte 103. Note that the electrolyte 103 may be either an electrolytic solution or a solid electrolyte. Electrolyte refers to the case where the electrolyte is in liquid form. Further, a solid electrolyte refers to a case where the electrolyte is in a gel form or a solid form.

  The magnesium-air battery of the present invention is characterized in that the catalyst of the air electrode 101 is composed of a metal oxide produced by oxidizing bacteria by culturing oxidizing bacteria that oxidize and grow the metal together with the corresponding metal. There is.

  Next, the air electrode 101 serving as a positive electrode will be described. As is well known, the air electrode 101 is formed of a carrier made of a conductive material, and a catalyst is supported on the carrier. Further, a binder or the like is added for use. The carrier composed of a conductive material is, for example, a cocontinuous body having a three-dimensional network configuration composed of fibrous fibers of 50 nm or less. For example, it can be obtained by carbonizing a cellulose gel produced by a well-known acetic acid bacterium. The co-continuous body having a three-dimensional network structure made of fine fibers having a fiber diameter of 50 nm or less has a structure in which a bonding portion between fibers and a fiber portion are deformable, and has elasticity.

  Next, the catalyst will be described. The catalyst added to the air electrode 101 (supported on a carrier) is produced by oxidizing bacteria, which are bacteria that oxidize metals and proliferate. For example, iron oxide produced by iron oxidizing bacteria or manganese oxide produced by manganese oxidizing bacteria serves as a catalyst.

  At the air electrode 101, an electrode reaction proceeds at a three-phase portion (three-phase interface) of electrolyte / electrode catalyst / gas (oxygen). The electrolyte 103 permeates into the air electrode 101 and is supplied with oxygen gas in the atmosphere, thereby forming a three-phase portion where the electrolyte, the electrode catalyst, and the gas (oxygen) coexist. If the electrode catalyst has high activity, oxygen reduction (discharge) and oxygen generation (charge) proceed smoothly, and the battery performance is greatly improved.

  The discharge reaction at the air electrode 101 can be expressed as follows.

(1/2) H ₂ O + (1/2) O ₂ + e ⁻ → OH ⁻ (1)

The hydroxide ion (OH ⁻ ) in the above formula is dissolved in the electrolyte 103 such as an aqueous electrolyte from the air electrode 101 by electrochemical reduction, and moves through the electrolyte 103 to the surface of the negative electrode 102. Oxygen (O ₂ ) is taken into the air electrode 101 from the atmosphere (air). The material (Mg ²⁺ ) dissolved from the negative electrode 102, the material [Mg (OH) ₂ ] deposited on the negative electrode 102, and air (O ₂ ) are shown together with the components in FIG.

  Catalysts such as iron oxide produced by iron oxidizing bacteria and manganese oxide produced by manganese oxidizing bacteria have strong interaction with oxygen and can adsorb many oxygen species on the catalyst surface. The oxygen species adsorbed on the surface of the catalyst is used in the oxygen reduction reaction as an oxygen source (active intermediate reactant) of the above formula (1), so that the reaction easily proceeds. Thus, iron oxide and manganese oxide function effectively as catalysts.

  In a magnesium-air battery, it is desirable that more reaction sites [three-phase portion of electrolyte / electrocatalyst / air (oxygen)] to cause an electrode reaction exist in order to reduce the discharge overvoltage of the battery. In response to this requirement, according to the present invention, a catalyst having a high specific surface area can be produced, and an air electrode of a magnesium-air battery having a large amount of the above-described three-phase portion on the surface of the electrode catalyst can be obtained.

Specifically, according to the present invention, iron oxide and manganese oxide having a specific surface area of 50 m ² / g or more can be obtained as a catalyst. The specific surface area of the catalyst used for the air electrode of the magnesium-air battery is preferably 30 m ² / g or more, but the above value satisfies this condition. The specific surface area was measured by a BET method using a commercially available measuring device to adsorb nitrogen gas at the temperature of liquid nitrogen.

  Next, the oxidizing bacteria used for preparing the catalyst will be described. The oxidizing bacterium may be any one of the genera Leptostrix, Galionella, Siderocapsa, and Thiobacillus. Alternatively, mutant strains obtained by subjecting these to mutation treatment by a known method using nitrosoguanidine (NTG) or the like may be used.

  For example, iron oxide is obtained by throwing iron oxidizing bacteria together with small pieces of iron into a liquid medium and culturing them. In addition, manganese oxide can be obtained by introducing a manganese oxidizing bacterium into a liquid medium together with small pieces of manganese and culturing it. The liquid medium is not particularly specified as long as it can culture iron-oxidizing bacteria and manganese-oxidizing bacteria. For example, as described above, a JOP liquid medium is preferable.

  The culture time is preferably at least 6 hours, more preferably at least 12 hours. In addition, by simultaneously culturing iron-oxidizing bacteria and manganese-oxidizing bacteria, it is also possible to obtain a catalyst in which iron oxide and manganese oxide are mixed. The thus obtained iron oxide and manganese oxide exhibit high performance as described above when used as a catalyst for the air electrode of the magnesium-air battery of the present invention.

Next, a conductive material (carrier) used for the air electrode 101 will be described. The conductive material is, for example, carbon. For example, carbon such as Ketjen black and acetylene black, and carbon such as activated carbon, graphite and carbon fiber can be used as the conductive material. In order to secure sufficient reaction sites in the air electrode 101, carbon having a large specific surface area is suitable. Specifically, a material having a BET specific surface area of 300 m ² / g or more is desirable. These carbons can be obtained, for example, as commercial products or by known synthesis.

  Further, the conductive material may be manufactured by carbonizing a cellulose gel produced by a cellulose-producing bacterium.

Here, preparation of a conductive material using cellulose gel will be described.
First, cellulose-producing bacteria are caused to produce a cellulose cell (gel production step).
Second, the produced cellulose gel is frozen (freezing step).
Third, the frozen cellulose gel is dried in a vacuum (drying step).
Fourth, the dried cellulose gel is heat-treated in an inert gas atmosphere and carbonized (carbonization step).

  By drying the cellulose gel produced in the gel production step by the freezing step and the drying step, a co-continuous body having a three-dimensional network structure composed of cellulose can be obtained. In the gel production step, a cellulose-producing bacterium produces a co-continuous body of nanofibrous cellulose integrated into a network by the cellulose-producing bacteria, and the shape is maintained by the freezing step. Is done.

A nanofiber is a fibrous substance having a diameter of 1 nm to 1 μm and a length of 100 times or more the diameter. The nanofiber may be hollow or coiled, and is not limited in shape. In addition, the gel refers to a solid in which the dispersion medium loses fluidity due to a three-dimensional network structure of the dispersoid (cellulose) and becomes solid. Specifically, it means a dispersion having a shear modulus of 10 ² to 10 ⁶ Pa.

The dispersion medium of the gel may be an aqueous system such as water (H ₂ O) or a carboxylic acid, methanol (CH ₃ OH), ethanol (C ₂ H ₅ OH), propanol (C ₃ H ₇ OH), n-butanol, iso- Organic compounds such as butanol, n-butylamine, dodecane, unsaturated fatty acids, ethylene glycol, heptane, hexadecane, isoamyl alcohol, octanol, isopropanol, acetone, and glycerin, may be used in combination of two or more.

As described above, the carrier of the cathode 101 preferably has a high specific surface area. The gel produced by the cellulose-producing bacteria has a basic structure of fibers of the order of nm, and has a high specific surface area. Specifically, it is possible to synthesize a support for the air electrode 101 having a specific surface area of 300 m ² / g or more.

Cellulose gel produced by cellulose-producing bacteria has a structure in which cellulose fibers are entangled in a coil or mesh, and further has a structure in which nanofibers are branched based on the growth of cellulose-producing bacteria. An excellent specific surface area of ² / g or more is realized. Such a nanofiber material is suitable as a conductive material of the air electrode 101.

  Cellulose-producing bacteria include, for example, Acetobacter xylinum subspecies schlofermenta, Acetobacter xylinum ATCC 23768, Acetobacter xylinum ATCC 23769, Acetobacter pasteurianus ATCC 10245, Acetobacter xylinum ATCC 14851, Acetobacter xylinum ATCC 11142, There are acetic acid bacteria such as Acetobacter xylinum ATCC10821.

  In addition, cellulose-producing bacteria include Agrobacterium, Rhizobium, Sarsina, Pseudomonas, Achromobacter, Alcaligenes, Aerobacterium, Azotobacter, Zugrea, Enterobacter, Kluvela, and NTG. Various mutant strains obtained by performing a mutation treatment by a known method using (nitrosoguanidine) or the like may be used.

  Freezing of the cellulose cell produced by the cellulose-producing bacterium may be carried out by placing the cell in an appropriate container such as a test tube and cooling the periphery of the test tube in a coolant such as liquid nitrogen. The freezing is not particularly limited as long as the dispersion medium of the cellulose-producing bacterial cellulose gel can be cooled below the freezing point, and may be carried out by cooling in a freezer.

  The shape is fixed by freezing, but when not freezing, in the drying step, since the dispersoids coagulate with the evaporation of the dispersion medium, a sufficient specific surface area cannot be obtained, and sufficient performance is obtained. Can not. By drying in a frozen state, the shape can be maintained. In the drying step, the dispersoid maintaining the network-like nanofiber cellulose is separated from the dispersion medium by sublimating the frozen dispersion medium from the solid state.

Drying can be performed by placing the frozen cellulose gel in a vacuum. For example, the frozen cellulose may be placed in a suitable container such as a flask, and the inside of the flask may be evacuated. By placing the frozen cellulose gel in a vacuum atmosphere, the sublimation point of the dispersion medium is lowered, and the dispersion medium can be sublimated even with a substance that does not sublime at normal pressure. The degree of vacuum varies depending on the dispersion medium used, but is not particularly limited as long as the dispersion medium sublimates. For example, when water is used as the dispersion medium, the degree of vacuum may be reduced to 0.06 MPa or less. Therefore, when water is used as the dispersion medium, the degree of vacuum may be set to 1.0 × 10 ^{−6 to} 1.0 × 10 ⁻² Pa. Further, heat may be applied by a heater or the like during drying.

  In the conventionally known method of drying in the atmosphere, the dispersion medium goes through a liquid state. For this reason, the nanofiber cellulose obtained in the form of a network becomes fluid in a liquid dispersion medium, deforms and agglomerates, and the specific surface area of the obtained conductive material (carrier) is greatly reduced. Would. For this reason, a method of drying in the air cannot provide a conductive material having a high specific surface area.

  Next, the carbonization step will be described. Cellulose gel is made of cellulose and has no conductivity, and is carbonized to provide conductivity. Carbonization is performed by heating in an inert gas so that cellulose is not oxidized to carbon dioxide. A conductive material obtained by carbonizing cellulose gel has high conductivity, corrosion resistance, and high specific surface area, and is suitable as the air electrode 101 of a magnesium-air battery.

  The carbonization of the cellulose gel is carried out after the drying step by firing the obtained cellulose gel in an inert gas atmosphere at 500 ° C to 2000 ° C, more preferably 900 ° C to 1800 ° C. The inert gas used in carbonization is not particularly limited as long as it is a gas that does not burn cellulose. For example, a nitrogen gas, an argon gas, a hydrogen gas, a carbon dioxide gas, or the like may be used. Alternatively, carbonization may be performed by using a reducing gas such as a carbon monoxide gas and heating in a reducing gas atmosphere. For example, it is more preferable to carbonize using a carbon dioxide gas or a carbon monoxide gas which has an activating effect on cellulose gel and can be expected to be highly activated.

  Next, a binder (binder) that can be added to the air electrode 101 will be described. The binder is not particularly limited, and examples thereof include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and polybutadiene rubber. These binders can be used as a powder or as a dispersion.

  Next, the negative electrode 102 will be described. The negative electrode 102 is made of a negative electrode active material. This negative electrode active material is not particularly limited as long as it can be used as a negative electrode material of a magnesium-air battery. For example, metal magnesium can be mentioned. Alternatively, as the magnesium-containing substance, a magnesium alloy capable of releasing magnesium ions can be mentioned as an example.

  The reaction at the time of discharging in the negative electrode 102 made of metallic magnesium can be expressed as follows.

(Discharge reaction)
^{Mg → Mg 2+ + 2e - ···} (2)

  The negative electrode 102 can be formed by a known method. For example, when a magnesium metal is used as the negative electrode, the negative electrode may be manufactured by cutting and forming a metal magnesium foil into a predetermined size and shape.

  Next, the electrolyte 103 will be described. The electrolyte 103 may be any substance capable of moving hydroxide ions between the air electrode 101 and the negative electrode 102. For example, an aqueous solution containing ions may be used as the electrolyte 103. Specifically, an aqueous solution of sodium chloride, an aqueous solution of potassium chloride, seawater, urine, sodium hydroxide, potassium hydroxide, hydrochloric acid, acetic acid, and a solvent in which two or more of these are mixed [for example, sodium chloride and potassium chloride (1: 1 volume ratio).

  In addition, the electrolyte 103 is a solid electrolyte that allows hydroxide ions to pass through, a polymer electrolyte that allows hydroxide ions to pass (for example, a polyethylene oxide-based material, specifically, for example, a substance in which the above-described aqueous solution and polyethylene oxide are composited) and the like. May be configured. The material constituting the electrolyte 103 is not limited to these, and any known solid electrolyte or polymer electrolyte that allows hydroxide ions to be used in a magnesium-air battery can be suitably used.

  Note that, in addition to the above configuration, the magnesium-air battery can include a separator, a battery case, structural members such as a metal mesh (for example, titanium mesh), and elements required for the magnesium-air battery. These can be conventionally known ones.

  For example, a magnesium-air battery can be configured as shown in FIG. The magnesium-air battery includes an air electrode 201, a negative electrode 202, an electrolyte 203, a separator 204, an air electrode support 205, an air electrode fixing ring 206, a negative electrode fixing ring 207, a negative electrode fixing washer 208, a negative electrode support 209, and a fixing member. A screw 210, an O-ring 211, an air electrode terminal 221, and a negative electrode terminal 222 are provided.

  The air electrode 201, the negative electrode 202, the electrolyte 203, and the separator 204 are housed in a cylindrical air electrode support 205. The air electrode support 205 has a partition 251 at the center in the cylinder, and is partitioned into a first area 205a where the air electrode 201 is arranged and a second area 205b where the negative electrode 202 and the separator 204 are arranged. ing. The partition 251 has an opening at the center, and the opening connects the first region 205a and the second region 205b.

The liquid electrolyte 203 is disposed at the opening of the partition 251 and is sandwiched between the air electrode 201 and the separator 204 serving as a salt bridge. The separator 204 is impregnated with the electrolyte 203. The electrolyte 203 is also arranged around the separator 204. The electrolyte 203 is, for example, a 2 mol / l aqueous solution of sodium chloride (NaCl / H ₂ O).

The air electrode 201 is sandwiched between an air electrode fixing ring 206 made of polytetrafluoroethylene (PTFE) and a partition 251 and is fixed to a first region 205 a in a cylinder of the air electrode support 205. I have. Within the opening of the air electrode fixing ring 206, the effective area of the electrode in contact with the air electrode 201 and air is 2 cm ² . On the other hand, the separator 204 is fixed to the second region 205 b in the cylinder of the air electrode support 205 by being sandwiched between the negative electrode fixing ring 207 made of PTFE and the partition 251. In this manner, the liquid electrolyte 203 is sealed between the air electrode 201 and the separator 204 at the opening of the partition 251.

In the negative electrode 202, a negative electrode fixing washer 208 is laminated inside a negative electrode fixing ring 207, and a negative electrode support 209 made of metal is put on the negative electrode fixing washer 208. The negative electrode 202 is made of a 500-μm-thick metal magnesium foil, and is crimped to the negative electrode fixing washer 208. The negative electrode 202 has an effective area of 2 cm ² . The negative electrode support 209 is fixed to the air electrode support 205 by fixing screws 210. An O-ring 211 is arranged between the cathode support 205 and the anode support 209.

  The negative electrode 202 is pressed in the direction of the separator 204 via the negative electrode fixing washer 208 by the negative electrode support 209 pressed against the air electrode support 205 by the fixing screw 210, and is pressed against the separator 204. The magnesium-air batteries having these configurations are manufactured in dry air having a dew point of −60 ° C. or less.

  The air electrode support 205 is made of metal, but is not shown, but is coated with PTFE and is insulated and separated from the electrolyte 203, the separator 204 and the like. The portion where the air electrode 201 and the air electrode support 205 are in contact with each other is not coated with PTFE for electrical contact. The fixing screw 210 made of metal is also covered with PTFE, though not shown, so that the air electrode support 205 and the negative electrode support 209 are electrically separated.

  Hereinafter, the present invention will be described in more detail with reference to examples.

[Example 1]
First, a first embodiment will be described. Example 1 is an example in which iron oxide produced by iron-oxidizing bacteria is used as a catalyst.

  First, Leptothrix ochracea, an iron-oxidizing bacterium, was put into a JOP liquid medium in a test tube together with iron pieces (purity of 99.9% or more, manufactured by High Purity Chemical Laboratory), and shaken with a shaker. The cells were cultured at 20 ° C. for 14 days. Leptotrix Ochracea was purchased from the ATCC (American Type Culture Collection). The JOP liquid medium was prepared by dissolving disodium hydrogen phosphate dodecahydrate 0.076 g, potassium dihydrogen phosphate dihydrate 0.02 g, HEPES 2.383 g, iron sulfate 0.01 mmol / L in 1 L of sterile groundwater. The pH was adjusted to 7.0 with an aqueous sodium hydroxide solution.

  After culturing for 14 days, iron pieces were removed, and the obtained iron oxide was washed in pure water for 24 hours using a shaker. In this cleaning, the pure water was replaced three times. The washed iron oxide was dried at 80 ° C. for 24 hours, and then pulverized using a mortar and a pestle to obtain an iron oxide powder produced by iron-oxidizing bacteria. The obtained iron oxide powder was evaluated by X-ray diffraction (XRD) measurement and BET specific surface area measurement.

As a result of the evaluation, it was confirmed that the iron oxide powder produced by the iron-oxidizing bacteria was iron oxide (Fe ₂ O ₃ ) by XRD measurement. The specific surface area of the iron oxide powder measured by the BET method was 68 m ² / g.

  Next, the obtained iron oxide powder was mixed with Ketjen black and polytetrafluoroethylene (PTFE) powder in a weight ratio of 50:30:20, and sufficiently pulverized and mixed using a grinder to obtain a mixture. The obtained slurry was roll-formed to produce a sheet-like electrode (thickness: 0.5 mm). This sheet-shaped electrode was cut into a circle having a diameter of 23 mm and pressed on a titanium mesh to obtain a gas diffusion type air electrode 201.

  Next, using the produced air electrode 201, a magnesium-air battery cell was produced in dry air having a dew point of −60 ° C. or less according to the following procedure. The produced cathode 201 was arranged in the first region 205 a of the cathode support 205 in a state of being in contact with the partition 251, and was fixed with the cathode fixing ring 206. The portion where the air electrode 201 and the air electrode support 205 are in contact with each other is not coated with PTFE for electrical contact.

Next, in the second region 205 b of the cathode support 205, the separator 204 was arranged in contact with the partition 251. Next, a 500-μm-thick metal magnesium foil (effective area: 2 cm ² ) was pressure-bonded to the negative electrode fixing ring 207 as the negative electrode 202. Next, the negative electrode fixing ring 207 was arranged in the second region 205b of the air electrode support 205, and the negative electrode fixing ring 207 to which the negative electrode 202 was crimped was fitted to the center.

  Next, an electrolytic solution constituting the electrolyte 203 is filled between the air electrode 201 and the negative electrode 202. In this state, an O-ring 211 is arranged on the bottom surface of the air electrode support 205, and the negative electrode support 209 is covered. It was fixed to the cathode support 205 with fixing screws 210. As the electrolytic solution, a 2 mol / l sodium chloride aqueous solution was used. Thereafter, the cathode terminal 221 was connected and fixed to the cathode support 205, and the anode terminal 222 was connected and fixed to the anode support 209.

  Next, the battery performance of the manufactured magnesium air battery of Example 1 was measured. In the battery performance measurement test, the air electrode terminal 221 and the negative electrode terminal 222 were used. As a battery discharge test, the charge / discharge measurement system (manufactured by BioLogic, VMP-3) was used to measure the discharge voltage until the battery voltage dropped from the open circuit voltage to 0V. The battery discharge test was performed in a normal living environment. The charge / discharge capacity was represented by a value (mAh / g) per weight of the negative electrode (magnesium).

FIG. 3 shows a discharge curve when a current density per effective area of the air electrode 201 of 25 mA / cm ² was applied as the battery performance of the magnesium-air battery of Example 1. As shown in FIG. 3, when iron oxide produced by iron-oxidizing bacteria was used as the air electrode catalyst, the average discharge voltage was 1.50 V and the discharge capacity was 1900 mAh / g. Here, the average discharge voltage is defined as a discharge voltage at an intermediate value of the total discharge capacity in FIG.

  The current density characteristics are shown in Table 1 below as the battery performance of the magnesium-air battery of Example 1. The current density shown in Table 1 is a current density per effective area of the air electrode 201. In Example 1, even when a current of 100 mA / cm 2 was applied, a large discharge capacity (mAh / g) and a decrease in the discharge voltage were not observed, and excellent current density characteristics were obtained. Thus, it was found that the iron oxide produced by the iron-oxidizing bacteria had a very excellent activity as a catalyst for an air electrode of a magnesium-air battery.

[Example 2]
Next, a second embodiment will be described. Example 2 is an example in which manganese oxide produced by manganese oxidizing bacteria is used as a catalyst.

  First, a manganese oxidizing bacterium, Leptothrix discophora, is introduced into a JOP liquid medium in a test tube together with manganese fragments (purity of 99.9% or more, manufactured by Kojundo Chemical Laboratory), and then shaken. And maintained at 20 ° C. for 14 days. Leptotrix discophora was purchased from ATCC (American Type Culture Collection).

  After culturing for 14 days, manganese small pieces were removed, and the obtained manganese oxide was washed in pure water for 24 hours using a shaker. In this cleaning, the pure water was replaced three times. The washed manganese oxide was dried at 80 ° C. for 24 hours, and then pulverized using a mortar and pestle to obtain manganese oxide powder produced by manganese oxidizing bacteria. The obtained manganese oxide powder was evaluated by X-ray diffraction (XRD) measurement and BET specific surface area measurement.

XRD measurement confirmed that the manganese oxide powder produced by the manganese oxide bacteria was manganese oxide (MnO ₂ ). The specific surface area of the manganese oxide powder measured by the BET method was 52 m ² / g.

  Next, in the same manner as in Example 1 described above, an air electrode 201 was manufactured using the obtained manganese oxide powder, and a magnesium-air battery of Example 2 was manufactured.

  Next, the battery performance of the manufactured magnesium air battery of Example 2 was measured in the same manner as in Example 1. The current density characteristics of the magnesium-air battery of Example 2 are shown in Table 1 below. As shown in Table 1, the discharge capacity of Example 2 was 1960 mAh / g, which was larger than the iron oxide produced by the iron-oxidizing bacteria of Example 1. Further, as shown in Table 1, the discharge voltage also showed a decrease in overvoltage as compared with Example 1, and the current density characteristics could be improved. It is considered that the improvement of these properties is due to the fact that the manganese oxide generated by the manganese oxidizing bacteria worked as an active center in the battery reaction, and thus the oxygen reduction (discharge) reaction was performed smoothly.

[Example 3]
Next, a third embodiment will be described. In Example 3, manganese oxide produced by manganese oxidizing bacteria was used as a catalyst, and cellulose gel (bacterial cellulose) was carbonized and used as a conductive material.

  First, manganese oxide powder was produced (produced) in the same manner as in Example 2 described above.

  Next, in Example 3, Natadoko (manufactured by Fujikko) was used as bacterial cellulose. Natadoko (Fujikko) is a cellulose gel produced by Acetobacter xylinum, which is an acetic acid bacterium. This nata de coco was placed in a test tube, and the test tube was immersed in liquid nitrogen for 30 minutes to completely freeze the nata de coco (bacterial cellulose gel).

After completely freezing the bacterial cellulose gel, the frozen bacterial cellulose gel is taken out into an eggplant flask and dried by a freeze dryer (manufactured by Tokyo Rikakiki Co., Ltd.) in a vacuum of 10 Pa or less to obtain bacterial cellulose. Was obtained. Next, the obtained nanofiber cellulose was carbonized by firing at 1200 ° C. for 2 hours in a nitrogen atmosphere. The specific surface area of the air electrode conductive material (carrier) thus obtained was 520 m ² / g when measured by the BET method.

  Next, manganese oxide powder produced in the same manner as in Example 2 was mixed and supported on the produced carrier. Next, the carrier sheet supporting manganese oxide was cut into a circular shape having a diameter of 23 mm using a punching blade, a laser cutter, or the like, to obtain a gas diffusion type air electrode. By using the obtained air electrode in the same manner as described above, a magnesium air battery was assembled as the air electrode 201.

  Next, the battery performance of the manufactured magnesium air battery of Example 3 was measured in the same manner as in Example 1. The current density characteristics are shown in Table 1 below as the battery performance of the magnesium-air battery of Example 3. As shown in Table 1, the discharge capacity of Example 3 was 2000 mAh / g, which was a value larger than that of the magnesium air battery with the air electrode 201 using Ketjen black of Example 2 as a conductive material.

  Further, as shown in Table 1, the discharge voltage also showed a decrease in overvoltage as compared with Example 2, and the current density characteristics were able to be improved. It is considered that these properties are improved because the conductive material obtained by carbonizing bacterial cellulose has a high specific surface area and high activity.

[Example 4]
Next, a fourth embodiment will be described. In Example 4, manganese oxide produced by manganese oxidizing bacteria was used as a catalyst, and cellulose gel (bacterial cellulose) was used as a conductive material by carbonization.

  First, an air electrode conductive material (carrier) was produced using nata de coco as a raw material in the same manner as in Example 3 described above. Next, the prepared carrier was put into a JOP liquid medium containing the manganese oxidizing bacteria and manganese fragments of Example 2, and in this state, the manganese oxidizing bacteria were cultured to produce manganese oxide serving as a catalyst. Contains manganese oxide produced by bacteria. The carrier sheet impregnated with manganese oxide in this manner was cut into a circular shape having a diameter of 23 mm using a punching blade, a laser cutter, or the like to obtain a gas diffusion type air electrode. By using the obtained air electrode in the same manner as described above, a magnesium air battery was assembled as the air electrode 201.

  Next, the battery performance of the manufactured magnesium air battery of Example 4 was measured in the same manner as in Example 1. The current density characteristics are shown in Table 1 below as the battery performance of the magnesium air battery of Example 4. As shown in Table 1, the discharge capacity of Example 4 was 2100 mAh / g, which was larger than that of Example 3.

  Further, as shown in Table 1, the discharge voltage also showed a decrease in overvoltage as compared with Example 3, and the current density characteristics could be improved. The improvement of these characteristics is due to the fact that in the air electrode 201 of Example 4, manganese oxide is highly dispersed and supported inside the carrier obtained by carbonizing bacterial cellulose, so that the number of reaction sites is increased and the activity is increased. it is conceivable that.

[Comparative Example 1]
Next, Comparative Example 1 will be described. In Comparative Example 1, using a commercially available iron oxide (Fe ₂ O ₃ ) (manufactured by Wako Pure Chemical Industries, Ltd.), a magnesium-air battery cell was produced in the same manner as in Example 1 described above. The battery test conditions are the same as in Example 1.

  As shown in Table 1, in Comparative Example 1, the discharge capacity was 1900 mAh / g, which was smaller than that of Example 1, for example. Further, as can be seen from Table 1, the discharge voltage of Comparative Example 1 is clearly lower than those of Examples 1 to 4, and when a large current is applied, the overvoltage clearly increases.

  From the above results, it was confirmed that the magnesium-air battery manufactured by the manufacturing method of the present invention was superior in discharge voltage and current density characteristics as compared with the related art, and was effective.

  As described above, according to the present invention, a catalyst produced by oxidizing bacteria, which are bacteria that oxidize and grow by oxidizing metals, is used for the air electrode, so that a decrease in the discharge voltage of the magnesium-air battery is suppressed. become able to. According to the present invention, a magnesium-air battery having excellent charge-discharge cycle performance can be manufactured, and the manufactured magnesium-air battery can be effectively used as a drive source for various electronic devices.

  Note that the present invention is not limited to the above-described embodiments, and many modifications and combinations can be made by those having ordinary knowledge in the art without departing from the technical concept of the present invention. That is clear.

  101: air electrode, 102: negative electrode, 103: electrolyte.

Claims (3)

An air electrode, a negative electrode containing magnesium, an electrolyte interposed between the air electrode and the negative electrode, and a metal oxide supported on a carrier made of a conductive material forming the air electrode A method for producing a magnesium-air battery comprising a catalyst comprising:
A catalyst production step of producing the catalyst by oxidizing bacteria, which are bacteria that grow by oxidizing metals ,
A gel production step of producing a cellulose gel by a cellulose-producing bacterium that is a bacterium that produces cellulose,
A freezing step of freezing the produced cellulose gel,
A drying step of drying the frozen cellulose gel in a vacuum,
Carbonization step of carbonizing the dried cellulose gel to produce the carrier,
A bacteria-containing step of containing the oxidizing bacteria in the carrier produced by carbonizing the cellulose gel,
A catalyst-containing step of causing the carrier containing the oxidizing bacteria to contain the catalyst produced by the oxidizing bacteria;
Manufacturing method of the magnesium-air battery, characterized in Rukoto equipped with. The method for manufacturing a magnesium-air battery according to claim 1,
The method for producing a magnesium-air battery, wherein the oxidizing bacterium is any one of a genus Leptotrix, a genus Galionella, a genus Siderocapsa, a genus Thiobacillus, and a mutant thereof. The method for manufacturing a magnesium-air battery according to claim 1 or 2,
The oxidizing bacterium is an iron oxidizing bacterium or a manganese oxidizing bacterium,
The method for manufacturing a magnesium-air battery, wherein the metal oxide is at least one of iron oxide and manganese oxide.

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