JP2008098075A - Air battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an air battery capable of preventing occurrence of short circuit by preventing growth of a dendrite in a negative electrode. <P>SOLUTION: The air battery 1 comprises a positive electrode 2 to oxidize and reduce oxygen, a negative electrode 3 consisting of a metal electrode, and an electrolyte layer 4 interposed between these. This air battery 1 is structured so that the surface 35 of at least electrolyte layer side of the metal electrode becomes at least temporarily liquid state. It is preferable that the surface 35 of at least electrolyte layer side of the metal electrode 3 is made of a metal having a melting point of 50°C or less. It is also preferable that the surface 35 of at least the electrolyte layer side is made of a metal which becomes liquid by the heat generated at the time of charging the air battery. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an air battery having a positive electrode using oxygen as an active material.

An air battery is a battery that performs charge and discharge using oxygen in the air as an active material in a positive electrode. The air battery is expected as a next-generation battery because it has an excellent feature of large capacity.
Heretofore, as an air battery, development of an air metal battery using a metal as a negative electrode active material has been performed. In particular, as a practical air metal battery, there is an air zinc battery including an air electrode (positive electrode) using oxygen as a positive electrode active material and a zinc electrode (negative electrode) using zinc as a negative electrode active material (Patent Literature). 1).

  However, an air metal battery such as an air zinc battery has a problem of forming a so-called dendrite when a metal such as zinc is deposited on the negative electrode during charging. When this dendrite grows, there is a possibility that a short circuit occurs. Therefore, the conventional air metal battery cannot be charged, and its secondary battery is difficult to make. The air zinc battery currently in practical use is only a disposable primary battery.

JP-A-2005-63702

  The present invention has been made in view of such conventional problems, and an object of the present invention is to provide an air battery capable of preventing dendrite growth in a negative electrode and preventing occurrence of a short circuit.

The present invention relates to an air battery having a positive electrode that oxidizes and reduces oxygen, a negative electrode made of a metal electrode, and an electrolyte layer interposed between the positive electrode and the negative electrode.
The air battery is an air battery characterized in that at least the surface on the electrolyte layer side of the metal electrode is at least temporarily in a liquid state (claim 1).

The most notable point in the air battery of the present invention is that at least the surface of the metal electrode on the side of the electrolyte layer is configured to be at least temporarily in a liquid state.
That is, in the air battery, at least the surface on the electrolyte layer side of the metal electrode can be at least temporarily in a liquid state. Therefore, it is possible to prevent a metal having a dendrite structure from being deposited on the surface of the metal electrode on the electrolyte layer side by electrodeposition. Moreover, even if the metal of a dendrite structure precipitates, a dendrite structure can be destroyed by making it into a liquid state as mentioned above.

  In general, in an air battery having a positive electrode that oxidizes and reduces oxygen, a negative electrode composed of a metal electrode, and an electrolyte layer interposed therebetween, the metal dendrite produced by electrodeposition contacts the electrolyte layer of the metal electrode. Occurs on the surface. And dendrite occurs when the metal is preferentially oriented during electrodeposition, and generally the crystal plane of the metal is not equivalent, so that the metal is preferentially oriented during electrodeposition.

  As in the present invention, when at least the surface on the electrolyte layer side of the metal electrode is in a liquid state, the crystal plane can be eliminated. Therefore, formation of dendrite can be prevented. In the present invention, even if the dendrite is once formed, the dendrite can be eliminated by making the liquid state as described above.

  Thus, the air battery of the present invention can prevent dendrite growth in the negative electrode and prevent the occurrence of a short circuit. Therefore, the air battery can be charged, and a secondary battery that is repeatedly charged and discharged can be formed.

Next, a preferred embodiment of the present invention will be described.
The air battery of the present invention is configured such that at least the surface of the metal electrode on the electrolyte layer side is in a liquid state at least temporarily during charge / discharge, for example. In the metal electrode, at least the surface on the electrolyte layer side (hereinafter referred to as “electrolyte side surface” as appropriate) may be in a liquid state, but the entire metal electrode may be in a liquid state.

  The air battery can be configured such that, for example, the electrolyte side surface is at least temporarily in a liquid state by heat during charging or external heating. Further, in applications such as automobiles, the liquid state can be obtained by the heat of the engine or the like. Further, the electrolyte side surface may always be in a liquid state at the use temperature of the air battery, or may be temporarily in a liquid state during charging or discharging.

  The electrolyte side surface is preferably in a liquid state at least when the air battery is charged. In this case, the occurrence of dendrite itself can be prevented, and the occurrence of a short circuit can be reliably prevented.

  Moreover, it is preferable that the said electrolyte side surface is a liquid state at least at the time of discharge of the said air battery. In this case, the discharge life of the air battery can be improved and the discharge can be performed for a longer period. That is, in general, in an air metal battery having a metal electrode on the negative electrode, an insulating layer made of a metal oxide is formed on the surface of the metal electrode (negative electrode) when the discharge is performed for a long time. Therefore, in the conventional air battery, the output voltage is liable to decrease during discharge, and it is difficult to perform long-term discharge. In the present invention, as described above, the electrolyte side surface of the metal electrode can be in a liquid state even during discharge. In this case, exposure of the metal oxide to the surface can be suppressed by the fluidity of the electrolyte-side surface that has become a liquid state. Therefore, as described above, the discharge time of the air battery can be improved and the discharge can be performed for a longer period.

It is preferable that at least the surface on the electrolyte layer side of the metal electrode is made of a metal having a melting point of 50 ° C. or less.
In this case, when the air battery is used, the electrolyte side surface can be easily brought into a liquid state. That is, in this case, at least the surface of the metal electrode on the side of the electrolyte layer can be easily brought into a liquid state in an environment where the temperature of the air battery is higher than 50 ° C. In this case, the electrolyte side surface of the metal electrode can be easily made into a liquid state by heat generated during charging.
That is, in this case, the air battery of the present invention can be easily realized.

Moreover, it is preferable that at least the surface on the electrolyte layer side of the metal electrode is made of a metal that becomes a liquid by heat generated when the air battery is charged.
In this case, the air battery of the present invention can be easily realized without using heating means such as a heating device.

The metal electrode is preferably made of a metal having a higher ionization tendency than hydrogen at least on the surface of the metal electrode on the electrolyte layer side.
In this case, the discharge voltage of the air battery can be improved.
In the metal electrode, only the electrolyte side surface is made of a metal having a higher ionization tendency than hydrogen, and the other part can be made of a metal having a lower ionization tendency than hydrogen. Further, the entire metal electrode can be formed of a metal having a higher ionization tendency than hydrogen.

Next, at least the surface on the electrolyte layer side of the metal electrode is preferably made of a metal containing Ga or Cs as a main component.
In this case, the melting point of the electrolyte side surface of the metal electrode can be lowered to about room temperature. Therefore, at the time of charging, at least the electrolyte side surface of the metal electrode can be more surely brought into a liquid state by the heat generation. Furthermore, the liquid state of the electrolyte side surface can be maintained even during discharge. That is, the surface on the electrolyte side can be maintained in a substantially liquid state under a normal use environment such as room temperature. Therefore, in this case, the formation of dendrite can be prevented more reliably and the discharge life can be improved.

Further, as described above, when the electrolyte side surface is made of a metal containing Ga or Cs as a main component, at least the surface of the metal electrode on the electrolyte layer side is at least selected from Zn, Sn, In, and Hg. It is preferably made of an alloy having one kind of metal as an accessory component (claim 6).
In the case of containing at least one metal selected from Zn, Sn, and In, the melting point of the electrolyte side surface of the metal electrode can be further lowered. Therefore, at the time of charging, the electrolyte side surface can be more reliably brought into a liquid state by the heat generation. Moreover, the said electrolyte side surface can be maintained in a substantially liquid state under normal use environment (room temperature). Therefore, in this case, the formation of dendrites can be prevented more reliably and the discharge life can be improved.

In an alloy containing Ga or Cs as a main component and at least one metal selected from Zn, Sn, and In as a minor component, the melting point can be controlled by adjusting the compounding ratio of the alloy. Therefore, the said metal electrode can be adjusted according to a use environment and a use.
Specific melting points of typical metals and alloys are shown below.
That is, Ga: 29.8 ° C., Ga / Zn (95/5): 25 ° C., Ga / Sn (92/8): 20 ° C., Ga / In (75.5 / 24.5): 15.7 ° C. Ga / In / Zn: (67/29/4): 13 ° C., Ga / In / Sn (62/25/13): 5 ° C., Cs: 28.4 ° C. The values in parentheses are the compounding ratio (weight ratio) of the alloy.

  Moreover, when Hg is contained as a subcomponent, the overvoltage of hydrogen can be increased. Therefore, generation of hydrogen, which is a side reaction during charge / discharge, can be prevented.

The metal electrode can be entirely formed of a metal that is in a liquid state as described above.
In addition, the metal electrode can be formed of a metal that is in a liquid state only on the electrolyte side surface. In this case, for example, the metal electrode can be formed by forming a layer made of a metal in a liquid state as described above on the surface of a zinc electrode or a current collector.
Further, the metal electrode can be formed by impregnating a mesh-like or sponge-like porous metal electrode or current collector with the metal in the liquid state.

As the detailed structure of the air battery, various structures of air batteries known at the present stage can be adopted.
Specifically, for example, in the battery case, a positive electrode that oxidizes and reduces oxygen and a negative electrode made of a metal electrode are disposed, and an electrolyte layer is disposed between the positive electrode and the negative electrode, whereby the air A battery can be constructed. In addition, the positive electrode has an air contact surface that comes into contact with air on the side facing the electrolyte layer, and an oxygen permeable membrane having oxygen permeability and water repellency is disposed on the air contact surface. be able to.

  The positive electrode can be formed by, for example, pressing a positive electrode material containing a carbon material and an organic binder onto a current collector. As the carbon material, it is preferable to use a porous carbon material having a large surface area. In this case, the contact area with oxygen is increased, and the charge / discharge capacity of the air electrode can be improved. Specifically, for example, activated carbon, graphite, carbon black, coke, and carbon fiber can be used.

Examples of the organic binder include polytetrafluoroethylene, polyvinylidene fluoride, and ethylene butadiene rubber.
Examples of the current collector include Ni mesh, stainless steel mesh, gold mesh, copper mesh, and platinum mesh.
In addition, as the oxygen permeable membrane, for example, a porous membrane made of polypropylene, polyethylene, polytetrafluoroethylene, polyester, polyphenylene sulfide, or the like can be used.

  The electrolyte layer can be composed of an electrolytic solution or a separator impregnated with the electrolytic solution. As the electrolytic solution, an alkaline electrolytic solution, a neutral salt aqueous solution electrolytic solution, an organic electrolytic solution, or the like can be used. As the separator, for example, a sheet-like porous body made of polyethylene, polypropylene, polyamide or the like can be used.

  As the shape of the air battery, there are various shapes such as a coin shape, a cylindrical shape, and a square shape. Cases corresponding to these shapes can be used as the battery case that houses the positive electrode, the negative electrode, the electrolyte layer, and the like.

(Example 1)
Next, an embodiment of the present invention will be described with reference to FIGS.
In this example, an air battery according to an example of the present invention is manufactured, and characteristics as a secondary battery are examined.

  As shown in FIG. 1, the air battery 1 of this example includes a positive electrode 2 that oxidizes and reduces oxygen, a negative electrode 3 made of a metal electrode, and an electrolyte layer 4 that is interposed between the positive electrode 2 and the negative electrode 3. The air battery 1 is configured such that at least the electrolyte-side surface 35 of the metal electrode 3 is at least temporarily in a liquid state. Specifically, in this example, the electrolyte side surface 35 is formed of an alloy containing Ga metal 31 as a main component.

Hereinafter, the air battery 1 of this example will be described in detail.
As shown in FIG. 1, the air battery 1 of this example includes a positive electrode 2, a negative electrode 3, and an electrolyte layer 4 disposed in a battery case 6. The positive electrode 2 is formed by pressure bonding a carbon catalyst carrying Pt to a current collector made of Ni mesh. The negative electrode 3 is composed of a copper current collector 32 and a metal layer 31 laminated thereon. The metal layer 31 is made of an alloy of Ga metal and Hg (Hg content 3 wt%). The electrolyte layer 4 is formed by impregnating a porous separator with an electrolytic solution.

  The positive electrode 2, the negative electrode 3, and the electrolyte layer 4 are disposed in the battery case 6 with the electrolyte layer 4 sandwiched between the positive electrode 2 and the negative electrode 3. The positive electrode 2 and the negative electrode 3 are disposed such that the side of the positive electrode 2 on which the carbon catalyst is supported (not shown) and the metal layer 31 side of the negative electrode 3 face the electrolyte layer 4 side.

  The battery case 6 includes a main body portion 61 having a concave cross section that is open at the top, and a cap portion 62 that closes the opening portion of the main body portion. The cap part 62 has a through hole 65 for supplying air into the battery at the central part thereof. The body portion 61 and the cap portion 62 are sealed with an insulating seal material 7. The positive electrode 2, the negative electrode 3, and the electrolyte layer 4 are housed in the battery case 6 with the negative electrode 3 facing the bottom of the main body 61. Further, the surface facing the surface in contact with the electrolyte layer 4 in the positive electrode 2 is an air contact surface 25 in contact with air. On the air contact surface 25 side on the positive electrode 2, an oxygen permeable membrane made of a polyester porous membrane is disposed.

Next, a method for manufacturing the air battery 1 of this example will be described.
Specifically, first, a Pt-supported carbon catalyst (20 wt% Pt / VULCAN XC-72R Carbon-supported catalyst, model number EC-20-PTC manufactured by Toyo Corporation) and polytetrafluoroethylene were each 9: 1 ( (Weight ratio), and then pressed to obtain a thin film positive electrode material. This positive electrode material contains platinum having a concentration of 20 wt% at 1 mg / cm ² . Next, a positive electrode material containing 5 mg of activated carbon was pressure-bonded to a metal mesh made of Ni and vacuum-dried to obtain a plate-like positive electrode 2.

Next, the negative electrode 3 was produced by applying a Ga alloy 31 containing 3 wt% of Hg on a plate-like current collector 32 made of copper.
Further, a gallium oxide saturated 6NKOH aqueous solution was prepared as an electrolytic solution, and a separator made of a polyamide nonwoven fabric was immersed in the electrolytic solution. In this way, a separator impregnated with the electrolytic solution was obtained as the electrolyte layer 4.

Next, as shown in FIG. 1, a battery case 6 for coin cells was prepared, and the negative electrode 3 was disposed in the main body 61. The negative electrode 3 was disposed in the main body 61 such that the current collector 32 side was directed to the bottom of the main body 61 and the metal layer 31 made of Ga alloy was directed to the opening side of the main body 61.
Next, the electrolyte layer 4 was disposed on the metal layer 31 of the negative electrode 3, and the positive electrode 2 was further disposed on the electrolyte layer 4. The positive electrode 2 was disposed with the surface on which the positive electrode material was pressure-bonded facing the electrolyte layer 4 side. Next, an oxygen permeable membrane 5 made of a polypropylene porous membrane was disposed on the positive electrode 2.

  Next, the opening of the main body 61 of the battery case 6 was closed with a cap 62 having a through hole 65. At this time, as shown in FIG. 1, the insulating sealing material 7 was disposed in the gap between the main body 61 and the cap, and the battery case 6 was sealed. Thus, the air battery 1 was produced. This is referred to as a battery E1. When the open circuit voltage of the battery E1 was measured, the open circuit voltage was 1.3V.

Next, a discharge test was performed on the battery E1.
Specifically, the battery E1 was discharged at a discharge current of 8 mA under the condition of a temperature of 30 ° C., and the battery voltage at this time was measured. The result is shown in FIG. In FIG. 2, the horizontal axis indicates the time since the start of discharge, and the vertical axis indicates the battery voltage.

  As is known from FIG. 2, the battery E1 was able to discharge for a long time of 100 minutes at a current of 8 mA. Further, in the battery E1, recovery of output was observed during discharge (see the portion indicated by the arrow in FIG. 2). This is considered to be because the insulating layer made of a metal oxide formed on the negative electrode was destroyed.

Next, a charge / discharge test of the battery E1 was performed.
Specifically, the battery E1 was discharged at a discharge current of 5 mA for 30 minutes under a temperature of 30 ° C., and thereafter charged and discharged repeatedly at a charge current of 5 mA for 30 minutes. And the battery voltage at this time was measured. The result is shown in FIG. FIG. 3 is a graph partially showing the relationship between the elapsed time from the start of the charge / discharge test and the battery voltage. That is, FIG. 3 shows the result of the charge / discharge test near the 20th time. In FIG. 3, the horizontal axis indicates the time since the start of the charge / discharge test, and the vertical axis indicates the battery voltage.

  As is known from FIG. 3, in the battery E1, no rapid voltage drop was observed even when charging / discharging was repeated 20 times. Therefore, it can be seen that, in the battery E1, generation of a leak current due to dendrite is prevented.

In this example, an air battery (battery E2) having a negative electrode configuration different from that of the battery E1 was produced.
The battery E2 is the same as the battery E1 except that the battery E2 has a negative electrode in which a metal layer made of an alloy of Ga metal and Zn (Zn content: 5 wt%) is formed on a copper current collector. An air battery having a configuration. The air battery of the battery E2 was produced in the same manner as the battery E1 except that a negative electrode produced by applying a Ga alloy containing 5 wt% Zn on a current collector made of copper was used.

Next, a discharge test was performed on the battery E2 in the same manner as the battery E1. As a result, the battery E2 could be discharged for a long time of 80 minutes at a current of 8 mA (not shown). Further, in the battery E2, as in the battery E1, recovery of output was observed during discharge (not shown).
Further, the battery E2 was subjected to a charge / discharge test in which the charge / discharge was repeated at a current of 5 mA for 30 minutes in the same manner as the battery E1. The result is shown in FIG. FIG. 4 is a graph partially showing the relationship between the elapsed time from the start of the charge / discharge test and the battery voltage, and shows the results near the 12th charge / discharge.

  As can be seen from FIG. 4, in the battery E2, a rapid voltage drop was not observed even when charging / discharging was repeated 12 times. Therefore, it can be seen that also in the battery E2, like the battery E1, generation of a leak current due to dendrites is prevented.

Moreover, in this example, the air battery (battery C) which has the negative electrode which does not become a liquid state at the time of charging / discharging was produced for the comparison with the said battery E1 and the said battery E2.
The battery C has, as a negative electrode, an electrode in which a metal layer made of Zn is laminated on a copper current collector. Other configurations are the same as those of the battery E1. The air battery of battery C was produced in the same manner as battery E1 except that a negative electrode produced by laminating Zn metal on a current collector made of copper was used.

  The battery C was also subjected to a charge / discharge test in which charge / discharge was repeated for 30 minutes at a current of 5 mA, similarly to the battery E1. The result is shown in FIG. FIG. 5 is a graph partially showing the relationship between the elapsed time from the start of the charge / discharge test and the battery voltage, and shows the results near the seventh charge / discharge.

  As can be seen from FIG. 5, in the battery C, when the charging / discharging was repeated seven times, a rapid voltage drop due to the leakage current was observed (see the part indicated by the arrow in FIG. 5). Therefore, in the battery C, it turns out that dendrite is formed.

  As described above, according to this example, the air battery (battery E1 and battery E2) configured such that at least the electrolyte side surface of the metal electrode is at least temporarily in a liquid state causes dendrite growth in the negative electrode. It can be seen that the occurrence of a short circuit can be prevented. Moreover, in the battery E1 and the battery E2 of this example, the electrolyte side surface of the negative electrode is in a liquid state even during discharge. Therefore, it can be seen that the insulating film made of a metal oxide can be broken and long-term discharge can be performed.

(Example 2)
In Example 1 described above, an air battery having an aqueous electrolyte was manufactured. However, this example is an example of manufacturing an air battery having an organic electrolyte.

First, the positive electrode and the negative electrode were produced in the same manner as the battery E1 of Example 1.
Next, a gallium perchlorate organic electrolytic solution was prepared as an electrolytic solution, and a separator made of a polyamide nonwoven fabric was immersed in the electrolytic solution. In this way, a separator impregnated with an organic electrolyte as an electrolyte layer was obtained.

  Next, in the same manner as in Example 1, a negative electrode, an electrolyte layer, and a positive electrode were disposed in a battery case for coin cells, and the battery case 6 was sealed. In this way, an air battery was produced. This is designated as battery E3. Battery E3 has a configuration similar to that of battery E1 except that the electrolyte layer has a gallium perchlorate organic electrolyte.

Next, the battery E3 was examined for the presence or absence of dendrite formation during charging and discharging.
That is, charging and discharging were repeatedly performed by charging the battery E3 with a current of 0.5 mA for 30 minutes under a temperature of 30 ° C., and then discharging the battery E3 to a discharge lower limit voltage of 0.1 V at 0.5 mA. The amount of charge electricity and the amount of discharge electricity at this time were measured, and the relationship between the number of charge / discharge and the ratio of the amount of discharge electricity to the amount of charge electricity (discharge electricity amount / charge electricity amount) was examined. The result is shown in FIG.

  As can be seen from FIG. 6, in the battery E3, even when charging / discharging was repeated 60 times, the electric quantity ratio between charging and discharging (discharge electric quantity / charge electric quantity) was almost balanced. Therefore, it can be seen that leakage current due to dendrites can be prevented even when an organic electrolyte is used as the electrolyte.

1 is a cross-sectional view of an air battery showing a configuration of an air battery according to Example 1. FIG. The diagram which shows the relationship between the discharge time of an air battery (battery E1) and battery voltage concerning Example 1. FIG. The diagram which shows the relationship between the elapsed time from the start of charging / discharging of an air battery (battery E1), and battery voltage concerning Example 1. FIG. The diagram which shows the relationship between the elapsed time from the start of charging / discharging of an air battery (battery E2), and battery voltage concerning Example 1. FIG. The diagram which shows the relationship between the elapsed time from the start of charging / discharging of an air battery (battery C), and battery voltage concerning Example 1. FIG. The diagram which shows the relationship between the charging / discharging frequency | count of the air battery (battery C) concerning Example 2, and ratio (discharge electricity amount / charge electricity amount) of the amount of discharge electricity with respect to charge electricity amount.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Air battery 2 Positive electrode 3 Negative electrode 31 Metal layer (metal which will be in a liquid state)
32 Current collector 35 Electrolyte side surface 4 Electrolyte layer

Claims (6)

In an air battery having a positive electrode that oxidizes and reduces oxygen, a negative electrode made of a metal electrode, and an electrolyte layer interposed between the positive electrode and the negative electrode,
The air battery is configured such that at least a surface of the metal electrode on the side of the electrolyte layer is at least temporarily in a liquid state.   2. The air battery according to claim 1, wherein at least a surface of the metal electrode on the electrolyte layer side is made of a metal having a melting point of 50 ° C. or less.   3. The air battery according to claim 1, wherein at least a surface of the metal electrode on the electrolyte layer side is made of a metal that becomes a liquid by heat generated when the air battery is charged.   The air battery according to claim 1, wherein at least a surface of the metal electrode on the electrolyte layer side is made of a metal having a higher ionization tendency than hydrogen.   5. The air battery according to claim 1, wherein at least a surface of the metal electrode on the electrolyte layer side is made of a metal containing Ga or Cs as a main component.   6. The air battery according to claim 5, wherein at least the surface on the electrolyte layer side of the metal electrode is made of an alloy having at least one metal selected from Zn, Sn, In, and Hg as a subcomponent. .

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