JP2009032415A - Air battery system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an air battery system having a favorable cycle characteristic. <P>SOLUTION: The problem is solved by providing the air battery system including an air battery cell having: an air electrode having an air electrode layer containing a conductive material and an air electrode power collector for collecting electric power from the air electrode layer; a negative electrode having a negative electrode layer containing a negative electrode active material that adsorbs and releases Li ions and a negative electrode power collector for collecting electric power from the negative electrode layer; a separator provided between the air electrode layer and the negative electrode layer; and the fluorine-containing electrolyte with which at least the separator is impregnated, and also including a discharge controller that terminates the discharge of the air battery cell, wherein a discharge final voltage of the discharge controller is 2.3 V or higher based on an Li metal. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an air battery system having good cycle characteristics.

The air battery is a nonaqueous battery using air (oxygen) as a positive electrode active material, and has advantages such as high energy density, easy size reduction, and weight reduction. In order to improve the characteristics of such an air battery, various developments have been conventionally made. For example, Patent Document 1 discloses an air battery using a hydrophobic nonaqueous electrolyte such as a room temperature molten salt. This technique suppresses the dissolution of oxygen and moisture in the electrolyte by using a hydrophobic non-aqueous electrolyte, and prevents the metal negative electrode from being deteriorated by an oxidation reaction or a hydrolysis reaction.

  On the other hand, in a secondary battery type air battery, improvement in cycle characteristics is desired. For example, Patent Document 2 discloses a sealed oxygen lithium secondary battery in which a gas such as pressurized oxygen is enclosed. In this technique, a sealed oxygen lithium secondary battery is used to prevent moisture from entering from the outside world and improve cycle characteristics. Patent Document 3 discloses a nonaqueous electrolyte air battery using a nonaqueous electrolytic solution in which carbon dioxide is dissolved. In this technique, by using a nonaqueous electrolytic solution in which carbon dioxide is dissolved, oxygen and moisture are prevented from reacting directly with the negative electrode active material, and cycle characteristics are improved.

As described above, although oxygen and moisture can be one factor that deteriorates the cycle characteristics of the air battery, in reality, it is considered that a decrease in cycle characteristics occurs due to the overlap of a plurality of factors. As factors that cause the cycle characteristics to deteriorate, for example, factors attributable to the air electrode member configuration, factors attributable to the air electrode density, factors attributable to various side reactions, and the like are conceivable. However, these factors have not been studied, and there has been a fact that the improvement of cycle characteristics is often not clarified.
JP 2005-116317 A Japanese Patent No. 3764623 JP 2003-7357 A

  The present invention has been made in view of the above circumstances, and has as its main object to provide an air battery system having good cycle characteristics.

  The present inventors diligently studied to achieve the above object. As a result, the air battery cell using an electrolyte containing Li ions as an ionic conductor and containing fluorine was discharged until a low voltage was reached. As a result, it was found that the cycle characteristics are greatly reduced. Although this reason is not necessarily clear, it is thought that it is because the side reaction mentioned later occurs and LiF etc. arise. The present invention has been made based on this finding, and it has been found that by providing a discharge control unit that prevents the voltage of the air battery cell from becoming too low during discharge, it is possible to suppress deterioration in cycle characteristics. The invention has been completed.

  That is, the present invention contains an air electrode having an air electrode layer containing a conductive material and an air electrode current collector that collects the air electrode layer, and a negative electrode active material that absorbs and releases Li ions. A negative electrode including a negative electrode layer and a negative electrode current collector that collects current from the negative electrode layer, a separator disposed between the air electrode layer and the negative electrode layer, and a fluorine-containing fluorine impregnated in at least the separator and containing fluorine An air battery cell having an electrolyte solution, and a discharge control unit for terminating discharge of the air battery cell, and a discharge end voltage of the discharge control unit is 2.3 V or more based on Li metal An air battery system is provided.

  According to the present invention, by providing a discharge control unit and preventing the voltage of the air battery cell from becoming too low during discharge, generation of LiF or the like as a side reaction product can be suppressed, and deterioration of cycle characteristics can be suppressed. can do.

  In the said invention, it is preferable that the said discharge final voltage is 2.6 V or less on the basis of Li metal. This is because if the discharge end voltage is too high, the discharge capacity may be lowered.

  In the said invention, it is preferable that the said fluorine-containing electrolyte solution contains a fluorine-containing electrolyte. This is because LiF or the like, which is a side reaction product, is easily generated, and the effects of the present invention can be sufficiently exhibited.

In the above invention, the fluorine-containing electrolyte is preferably LiPF _6. This is because LiPF ₆ is easily decomposed, so that LiF as a side reaction product is particularly easily generated.

  The present invention also includes an air electrode having an air electrode layer containing a conductive material and an air electrode current collector that collects the air electrode layer, and a negative electrode active material that absorbs and releases Li ions. A negative electrode including a negative electrode layer and a negative electrode current collector that collects current from the negative electrode layer, a separator disposed between the air electrode layer and the negative electrode layer, and a fluorine-containing fluorine impregnated in at least the separator and containing fluorine A method for controlling an air battery cell, comprising: using an air battery cell having an electrolyte solution; and stopping charging at a stage where the voltage of the air battery cell is 2.3 V or more on the basis of a Li metal. I will provide a.

  According to the present invention, by stopping the discharge at a specific voltage, generation of LiF or the like as a side reaction product can be suppressed, and deterioration of cycle characteristics can be suppressed.

  In this invention, there exists an effect that it can suppress that the cycling characteristics of an air battery system fall.

  Hereinafter, an air battery system and an air battery cell control method of the present invention will be described in detail.

A. Air Battery System First, the air battery system of the present invention will be described. An air battery system of the present invention includes an air electrode having an air electrode layer containing a conductive material and an air electrode current collector that collects the air electrode layer, and a negative electrode active material that absorbs and releases Li ions. A negative electrode having a negative electrode current collector and a negative electrode current collector for collecting current of the negative electrode layer, a separator disposed between the air electrode layer and the negative electrode layer, and at least a fluorine impregnated in the separator and containing fluorine And a discharge control unit for terminating the discharge of the air battery cell, and a discharge end voltage of the discharge control unit is 2.3 V or more on the basis of Li metal. It is characterized by this.

According to the present invention, by providing a discharge control unit and preventing the voltage of the air battery cell from becoming too low during discharge, generation of LiF or the like as a side reaction product can be suppressed, and deterioration of cycle characteristics can be suppressed. can do. Here, in an air battery using Li ions as an ion conductor, it is known that the following reaction (1) occurs at the air electrode during discharge.
_{^{Li + + e - + O 2}} → Li 2 O or Li 2 O 2 reaction (1)

On the other hand, in the present invention, if discharge is performed to a low voltage with respect to an air battery cell using Li ion as an ionic conductor and an electrolyte containing fluorine, cycle characteristics are significantly reduced. I found out. The reason for this is not necessarily clear, but it is probably because a side reaction represented by the following reaction (2) occurs and LiF is generated.
Li ⁺ + F ⁻ → LiF reaction (2)

  Since this LiF is difficult to be decomposed at the time of charging, only a smaller electric capacity than the discharging electric capacity can be charged. As a result, by repeating charge and discharge, LiF is accumulated, and it is considered that cycle characteristics deteriorate. Therefore, in the present invention, the discharge is stopped at a voltage that does not cause a side reaction such as the above reaction (2), thereby suppressing the generation of LiF and providing an air battery system with good cycle characteristics. Can do it.

  Note that the above side reaction is a phenomenon that is unlikely to occur in a lithium secondary battery or the like having a similar structure, although it is found in an air battery using Li ion as an ion conductor and using an electrolyte containing fluorine. is there. The reason for this is not necessarily clear, but it is thought to be due to the fact that the charge / discharge reaction occurs in an oxygen-rich atmosphere. That is, it is presumed that the decomposition of the fluoride electrolyte salt is promoted because of the large amount of oxygen. For this reason, the reduction in cycle characteristics due to the side reaction is considered to be a problem peculiar to air batteries using an electrolytic solution containing oxygen as a reaction source and containing fluorine.

  In the present invention, the discharge end voltage of the discharge control unit is normally set to 2.3 V or more on the basis of Li metal. That is, when the voltage of the air battery cell becomes lower than the discharge end voltage, the discharge control unit operates to stop the discharge. Especially, in this invention, it is preferable that the discharge end voltage of a discharge control part is 2.4 V or more on the basis of Li metal. This is because generation of LiF or the like as a side reaction product can be further suppressed, and cycle characteristics can be improved.

  On the other hand, the discharge end voltage of the discharge controller is preferably 2.6 V or less on the basis of Li metal. This is because if the discharge end voltage is too high, the discharge capacity may be lowered. From the viewpoint of discharge capacity, the discharge end voltage of the discharge control unit is more preferably 2.5 V or less on the basis of Li metal.

  Next, the air battery cell used for this invention is demonstrated using drawing. Fig.1 (a) is a schematic sectional drawing which shows an example of the air battery cell used for this invention. FIG.1 (b) is a perspective view which shows the external appearance of the air battery cell shown by Fig.1 (a). An air battery cell 10 shown in FIG. 1A includes a negative electrode current collector 2 formed on the inner bottom surface of a lower insulating case 1a, a negative electrode lead 2 'connected to the negative electrode current collector 2, and a negative electrode current collector. A negative electrode layer 3 made of Li metal formed on the body 2, an air electrode layer 4 containing carbon, an air electrode mesh 5 and an air electrode current collector 6 for collecting the air electrode layer 4, and an air electrode current collector Upper insulating case having an air electrode lead 6 ′ connected to the electric body 6, a separator 7 installed between the negative electrode layer 3 and the air electrode layer 4, and a microporous film 8 provided for supplying oxygen. 1b, the negative electrode layer 3 and the air electrode layer 4, and a fluorine-containing electrolytic solution 9 containing fluorine.

FIG. 2 is an explanatory view illustrating the air battery system of the present invention. The air battery system 20 shown in FIG. 2 includes the air battery cell 10 and the discharge control unit 11. The discharge controller 11 has a function of terminating the discharge of the air battery cell 10.
Hereinafter, the air battery system of the present invention will be described separately for the members of the air battery system and the configuration of the air battery system.

1. First, members of the air battery system of the present invention will be described. The air battery system of the present invention usually has air battery cells and a discharge controller. Hereinafter, the members of the air battery system of the present invention will be described separately for (1) air battery cells and (2) discharge control units.

(1) Air battery cell First, the air battery cell used for this invention is demonstrated. The air battery cell used in the present invention usually has an air electrode, a negative electrode, a separator, a fluorine-containing electrolyte and a battery case.

(I) Negative electrode The negative electrode used in the present invention has a negative electrode layer containing a negative electrode active material that absorbs and releases Li ions, and a negative electrode current collector that collects current from the negative electrode layer.

  The negative electrode active material is not particularly limited as long as it can occlude and release Li ions. As said negative electrode active material, the thing similar to the negative electrode active material used for a general lithium ion battery can be used. Specific examples include carbon materials such as metal lithium, lithium alloys, metal oxides, metal sulfides, metal nitrides, and graphite. Among these, metal lithium and carbon materials, particularly metal lithium are preferable.

  In the present invention, the negative electrode layer may contain at least a negative electrode active material, but may contain a binder for immobilizing the negative electrode active material, if necessary. The type and amount of the binder used are the same as those described later in “(ii) Air electrode”, and thus the description thereof is omitted here.

  The material for the negative electrode current collector is not particularly limited as long as it has conductivity, and examples thereof include copper, stainless steel, and nickel. Examples of the shape of the negative electrode current collector include a foil shape, a plate shape, and a mesh (grid) shape. In the present invention, a battery case, which will be described later, may have the function of a negative electrode current collector.

(Ii) Air electrode The air electrode used in the present invention has an air electrode layer containing a conductive material and an air electrode current collector that collects the air electrode layer. In the present invention, oxygen reacts with Li ions in the air electrode, and lithium oxide is generated on the surface of the conductive material. For this reason, the air electrode layer has a void enough to allow the fluorine-containing electrolyte, which is a carrier of oxygen and Li ions, to move sufficiently.

  The conductive material is not particularly limited as long as it has conductivity, and examples thereof include a carbon material. Furthermore, the carbon material may have a porous structure or may not have a porous structure, but in the present invention, the carbon material preferably has a porous structure. This is because the surface area is large and many reaction fields can be provided. Specific examples of the carbon material having a porous structure include mesoporous carbon. On the other hand, specific examples of the carbon material having no porous structure include graphite, acetylene black, carbon nanotube, and carbon fiber. Further, the conductive material may carry a catalyst. Examples of the catalyst include cobalt phthalocyanine and manganese dioxide.

  In the present invention, the air electrode layer only needs to contain at least a conductive material, but preferably further contains a binder for immobilizing the conductive material. Examples of the binder include polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). The content of the binder contained in the air electrode layer is not particularly limited. For example, it is preferably 30% by weight or less, and more preferably 1% by weight to 10% by weight.

  The material for the air electrode current collector is not particularly limited as long as it has conductivity, and examples thereof include stainless steel, nickel, aluminum, iron, and titanium. Examples of the shape of the air electrode current collector include a foil shape, a plate shape, and a mesh (grid) shape. Among these, in the present invention, the shape of the air electrode current collector is preferably a mesh shape. This is because the current collection efficiency is excellent. In this case, usually, a mesh-shaped air electrode current collector is disposed inside the air electrode layer. Furthermore, the air battery cell may have another air electrode current collector (for example, a foil-shaped current collector) that collects charges collected by the mesh-shaped air electrode current collector. In the present invention, a battery case to be described later may also have the function of an air electrode current collector.

(Iii) Fluorine-containing electrolyte The fluorine-containing electrolyte used in the present invention contains at least one fluorine-containing material. The fluorine-containing material may be an electrolyte (fluorine-containing electrolyte), a solvent (fluorine-containing solvent), or an additive (fluorine-containing additive). Especially, in this invention, it is preferable that the fluorine-containing material contained in a fluorine-containing electrolyte solution is a fluorine-containing electrolyte and / or a fluorine-containing solvent.

Examples of the fluorine-containing electrolyte include inorganic lithium salts such as LiPF ₆ , LiBF ₄ , and LiAsF ₆ ; and LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , Organic lithium salts such as LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ) and LiC (CF ₃ SO ₂ ) ₃ can be mentioned, and among them, LiPF ₆ is preferable. This is because LiPF ₆ is easily decomposed, so that LiF as a side reaction product is easily generated, and the effects of the present invention can be sufficiently exhibited.

On the other hand, examples of the electrolyte other than the fluorine-containing electrolyte include LiClO ₄ and LiBOB (Lithium Bis (Oxalato) Borate).

  Examples of the fluorine-containing solvent include methyl difluoroacetate, ethyl difluoroacetate, dimethyldifluoromalonate, and methylpentafluoropropionate. Among them, methyl difluoroacetate is preferable. In addition, since the said fluorine-containing solvent generally has favorable oxygen solubility, it is useful as a solvent of electrolyte solution.

  On the other hand, examples of the solvent other than the fluorine-containing solvent include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), butylene carbonate, and γ-butyrolactone. , Sulfolane, acetonitrile, 1,2-dimethoxymethane, 1,3-dimethoxypropane, diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran and the like. Among them, in the present invention, a mixed solvent in which EC or PC and DEC or EMC are combined is preferable.

  Examples of the fluorine-containing additive include fluoroethylene carbonate, fluorobenzene, trifluoromethanepropylene carbonate, and the like.

  The concentration of the electrolyte contained in the fluorine-containing electrolytic solution is the same as that in a general air battery electrolytic solution, for example, in the range of 0.5 mol / l to 2 mol / l. The fluorine-containing electrolytic solution used in the present invention may be at least impregnated in the separator, but is usually injected so as to fill the air electrode layer and the negative electrode layer.

(Iv) Separator The separator used in the present invention is installed between the air electrode layer and the negative electrode layer. The separator is not particularly limited as long as it has a function of separating the air electrode layer and the negative electrode layer and holding the fluorine-containing electrolyte solution. For example, a porous film such as polyethylene or polypropylene; Nonwoven fabrics such as glass fiber nonwoven fabrics; and polymer materials used in lithium polymer batteries.

(V) Battery Case The shape of the battery case used in the present invention is not particularly limited as long as the above-described air electrode, negative electrode, separator, and fluorine-containing electrolyte can be accommodated. Examples thereof include a mold, a flat plate type, and a cylindrical type. The battery case used in the present invention may be an open battery case or a sealed battery case.

(2) Discharge control part Next, the discharge control part used for this invention is demonstrated. The discharge controller used in the present invention has a function of terminating the discharge of the air battery cell. In the present invention, the discharge end voltage of the discharge control unit is normally set to 2.3 V or more on the basis of Li metal. That is, when the voltage of the air battery cell becomes lower than the discharge end voltage, the discharge control unit operates to stop the discharge. The preferable range of the discharge end voltage is as described above.

  The discharge control unit usually includes a monitor unit that monitors the voltage of the air battery cell, and a discharge termination unit that terminates the discharge when the voltage obtained from the monitor unit is less than the discharge termination voltage.

2. Configuration of Air Battery System Next, the configuration of the air battery system of the present invention will be described. The air battery system of this invention has an air battery cell and a discharge control part. Hereinafter, the configuration of the air battery system of the present invention will be described by dividing it into (1) the configuration of the air battery cell and (2) the arrangement of the discharge control unit.

(1) Configuration of Air Battery Cell First, the configuration of the air battery cell in the present invention will be described. The configuration of the air battery cell in the present invention is not particularly limited as long as it has the above-described air electrode, negative electrode, separator, fluorine-containing electrolytic solution, and battery case, and can take any configuration. In addition, the shape of the electrode body (air electrode, negative electrode and separator) used in the present invention is not particularly limited, and specific examples include a flat plate type, a cylindrical type, and a wound type. it can.

In the air battery cell used in the present invention, it is preferable that the air electrode layer and the negative electrode layer are always filled with the fluorine-containing electrolyte when the volume change of the electrode accompanying charge / discharge occurs. This is because it is possible to suppress an increase in internal resistance due to the electrolyte shortage. The conventional air battery cell has a problem in that the volume of the electrodes (air electrode and negative electrode) changes greatly with charge and discharge, resulting in a situation where the electrolyte is insufficient. For example, when considering an air battery cell using lithium metal as a negative electrode active material, Li elutes as Li ions at the negative electrode during discharge, and lithium oxide precipitates at the air electrode. At this time, since the density of lithium oxide (Li ₂ O ₂ ) is larger than the density of Li, the entire electrode contracts by about 35% in volume ratio. As a result, there is a problem in that the amount of the electrolytic solution is insufficient at the end of discharge, and a part of the air electrode or the like is not immersed in the electrolytic solution, thereby increasing the internal resistance. On the other hand, when the air electrode layer and the negative electrode layer are always filled with the electrolytic solution, an increase in internal resistance due to the shortage of the electrolytic solution can be suppressed.

  In the present invention, the “volume change of the electrode accompanying charge / discharge” means that when metal ions move between the air electrode layer and the negative electrode layer due to charge / discharge, the difference in the density of the product, etc. It means the volume change of the resulting electrode (air electrode and negative electrode).

  An example of a configuration in which the air electrode layer and the negative electrode layer are always filled with the fluorine-containing electrolyte when a volume change associated with charge / discharge occurs is, for example, a configuration in which the fluorine-containing electrolyte is circulated. it can. By circulating the fluorine-containing electrolyte, charging and discharging can be performed without causing the gas-liquid interface that existed when using conventional air battery cells, and even when the volume of the electrode changes, This is because the air electrode layer and the negative electrode layer can always be filled with the fluorine-containing electrolyte. In addition, there is an advantage that a decrease in the fluorine-containing electrolyte due to volatilization can be prevented. Further, by circulating the fluorine-containing electrolyte during charging, it is possible to efficiently remove oxygen generated by the charging reaction from the air electrode layer.

  Specifically, as shown in FIG. 3, the fluorine-containing electrolyte 9 is circulated by using the electrolyte-transfer means 21 such as a motor, the fluorine-containing electrolyte 9, the anode layer 3, the separator 7, and the air. A configuration in which the polar layer 4 is circulated in this order can be given. At the time of discharge, oxygen 23 is supplied to the air electrode layer 4 using oxygen supply means 22 such as bubbling, and excess oxygen is removed by the exhaust means 24. If the oxygen supply means 22 can appropriately increase the oxygen concentration dissolved in the fluorine-containing electrolytic solution 9, the exhaust means 24 is not particularly necessary. Further, at the time of charging, the fluorine-containing electrolyte may be circulated in the direction opposite to the flow of the fluorine-containing electrolyte shown in FIG. In FIG. 3, for convenience, the air electrode current collector and the negative electrode current collector are omitted, but current collection may be performed by an appropriate method.

  Another configuration in which the air electrode layer and the negative electrode layer are always filled with the fluorine-containing electrolyte when a volume change associated with charge / discharge occurs is a configuration using a large amount of the fluorine-containing electrolyte. it can. By using a sufficiently large amount of the fluorine-containing electrolyte, it is possible to prevent the air electrode layer and the like from becoming insufficient.

  That is, in the present invention, when the liquid level of the fluorine-containing electrolyte solution changes due to the volume change of the electrode accompanying charge / discharge, the position where the liquid level of the fluorine-containing electrolyte solution is lowest is the air. It is preferable that the position is higher than the positions of the top surfaces of the polar layer and the negative electrode layer. It is because it can prevent that a fluorine-containing electrolyte solution runs short by setting the quantity of a fluorine-containing electrolyte solution to become said position. For example, when Li metal is used for the negative electrode layer, a reaction in which lithium is eluted by discharge occurs, and the volume of the entire electrode is reduced. Therefore, normally, the surface of the fluorine-containing electrolyte at the end of discharge corresponds to the lowest position.

  “The uppermost surfaces of the air electrode layer and the negative electrode layer” means the uppermost surface of the air electrode layer, the uppermost surface of the negative electrode layer, the air electrode layer, and the negative electrode layer, depending on the configuration of the air battery cell. It may mean the top surface. Each case will be described with reference to FIG. For convenience, the air electrode current collector and the negative electrode current collector are omitted.

  FIG. 4A is a schematic cross-sectional view showing an aspect in which the position where the liquid level of the fluorine-containing electrolyte is lowered is higher than the uppermost surface of the air electrode layer. The air battery cell shown in FIG. 4A is an air battery cell formed in the order of the negative electrode layer 3, the separator 7 and the air electrode layer 4 from the inner bottom surface of the battery case 1. The lowest position is a position higher than the uppermost surface of the air electrode layer 4. This air battery cell has an advantage that oxygen can be easily supplied.

  FIG. 4B is a schematic cross-sectional view showing an aspect in which the position where the liquid level of the fluorine-containing electrolyte is lowered is higher than the uppermost surface of the negative electrode layer. The air battery cell shown in FIG. 4B is an air battery cell formed in the order of the air electrode layer 4, the separator 7 and the negative electrode layer 3 from the inner bottom surface of the battery case 1. The lowest position is a position higher than the uppermost surface of the negative electrode layer 3. Furthermore, since this air battery cell has a structure in which the air electrode layer is below the negative electrode layer, an oxygen supply means 22 and an exhaust means 24 may be provided as necessary.

  FIG. 4C is a schematic cross-sectional view showing an aspect in which the position where the liquid level of the fluorine-containing electrolyte is lowered is higher than the uppermost surfaces of the air electrode layer and the negative electrode layer. The air battery cell shown in FIG. 4C includes a separator 7, a negative electrode layer 3 disposed on one surface of the separator 7, and an air electrode layer 4 disposed on the other surface of the separator 7. In the cylindrical air battery cell, the lowest position of the fluorine-containing electrolyte 9 is higher than the uppermost surfaces of the negative electrode layer 3 and the air electrode layer 4.

  In the present invention, it is preferable that the position where the fluorine-containing electrolyte is lowered is higher than the positions of the uppermost surfaces of the air electrode layer and the negative electrode layer. The difference in height between the position where the fluorine-containing electrolyte is lowered and the position of the uppermost surface of the air electrode layer and the negative electrode layer varies depending on the volume of the battery case used, for example, 1 mm. It is preferable to be within a range of ˜30 mm, especially within a range of 3 mm to 10 mm. If the difference in height is too small, the electrolyte may be insufficient due to volatilization of the solvent, etc., and if the difference in height is too large, the supply of oxygen may be delayed and high-rate discharge characteristics may deteriorate. Because there is. In addition, it is preferable that the initial input amount of the fluorine-containing electrolyte is determined by measuring or calculating in advance the volume change of the electrode accompanying charge / discharge, and determining the optimal input amount.

(2) Arrangement of Discharge Control Unit Next, the arrangement of the discharge control unit in the present invention will be described. FIG. 5 is an explanatory diagram illustrating a discharge control unit used in the present invention. The air battery cell 101 is connected to the external terminal −V105 and the external terminal + V104 via a switch circuit 103 (discharge termination portion). A load 107 is connected to the external terminal −V105 and the external terminal + V104. Further, a charge / discharge control circuit 102 is connected in parallel to the air battery 101. The charge / discharge control circuit 102 has a function of monitoring the voltage of the air battery 101 (monitor unit). When the air battery 101 reaches a certain discharge voltage, a signal is output from the charge / discharge circuit 102 so that the switch circuit 103 is turned off. Thereby, it will be in a discharge end state. In FIG. 5, reference numeral 108 denotes an air electrode terminal of the air battery, and reference numeral 109 denotes a negative terminal of the air battery.

B. Next, a method for controlling the air battery cell of the present invention will be described. The air battery cell control method of the present invention includes an air electrode having an air electrode layer containing a conductive material and an air electrode current collector that collects the air electrode layer, and a negative electrode active material that absorbs and releases Li ions. A negative electrode layer containing a substance, a negative electrode having a negative electrode current collector for collecting the negative electrode layer, a separator disposed between the air electrode layer and the negative electrode layer, and at least the separator is impregnated with fluorine. An air battery cell having a fluorine-containing electrolyte solution, and the discharge of the air battery cell is terminated at a stage where the voltage of the air battery cell is 2.3 V or more on the basis of Li metal, and charging is performed. is there.

  According to the present invention, by stopping the discharge at a specific voltage, generation of LiF or the like as a side reaction product can be suppressed, and deterioration of cycle characteristics can be suppressed. In addition, about the production | generation etc. of LiF, and about the air battery cell used, since it is the same as that of the content described in said "A. air battery system", description here is abbreviate | omitted.

  In the present invention, the discharge is usually stopped when the voltage of the air battery cell is 2.3 V or higher with respect to the Li metal. In particular, it is preferable to stop the discharge at a stage of 2.4 V or more based on Li metal. This is because generation of LiF or the like as a side reaction product can be further suppressed, and cycle characteristics can be improved. As described above, the end-of-discharge voltage is based on Li metal.

  On the other hand, in the present invention, it is preferable to stop the discharge when the voltage of the air battery cell is 2.6 V or less on the basis of Li metal. This is because if the discharge is terminated at a high voltage, the discharge capacity may be lowered. From the viewpoint of the discharge capacity, it is more preferable to stop the discharge at a stage of 2.5 V or less on the basis of Li metal.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

Hereinafter, the present invention will be described in more detail with reference to examples.
[Example 1]
(Production of air battery cells)
In this example, a coin cell type air lithium battery was produced. The following coin cells were assembled in an argon box.
A schematic diagram of a coin cell is shown in FIG. Both the negative electrode case 32 and the air electrode case 30 are made of SUS material, and the air electrode case 30 has a plurality of through holes 39 having a diameter of 2 mm. A metal lithium foil 34 is installed on the negative electrode case 32. As the metallic lithium 34, a sheet having a thickness of 250 μm punched out with a diameter of 18 mm was used. A polyethylene separator 35 was placed on the metal lithium foil 34. The separator 35 was punched to a diameter of 19.5 mm with a thickness of 25 μm.

Next, the fluorine-containing electrolytic solution 33 was injected from above the separator 35 with a dropper. The fluorine-containing electrolyte solution 33, ethylene carbonate and diethyl carbonate 1: 1 in a mixed solvent were mixed at a volume ratio was used LiPF ₆ electrolytic solution prepared by dissolving 1M (manufactured by Kishida Chemical). Thereafter, an air electrode was installed on the separator 35. The air electrode used was an air electrode mesh 36 pressed into the air electrode mesh 36 by pressing the air electrode mixture 37 against the air electrode mesh 36. The air electrode mesh 36 is a Ni mesh having a thickness of 150 μm and a diameter of 15 mm. The air electrode mixture 37 was kneaded in a mortar with 82 parts by weight of ketjen black and 15 parts by weight of manganese dioxide, and then 3 parts by weight of polytetrafluoroethane (hereinafter abbreviated as PTFE) was added. A kneaded product was used. An air electrode case 30 was put in pellets of the air electrode mixture 37. The air electrode current collector 38 is installed in the air electrode case 30 by welding. The air electrode current collector 38 was a nickel mesh having a thickness of 150 μm and a diameter of 15 mm. A gasket 31 was fitted into the air electrode case 30 to obtain an air electrode plate.

  This air electrode plate is put on a separator immersed in a fluorine-containing electrolyte solution 33, combined, and then the negative electrode case and the air electrode case are joined using a coin cell caulking machine (manufactured by Hosen) to obtain a coin cell. It was. Next, after putting the obtained coin cell in a glass container in an argon box and sealing it, oxygen gas was introduced into the glass container to replace the argon gas with oxygen gas.

(Cycle test)
A cycle test was performed using the obtained coin cell. The conditions of the cycle test are as follows.
Charging conditions: 10 mA / g (current per carbon), 4.8 Vcut (vs Li metal)
Discharge condition: 10 mA / g (current per carbon)
End-of-discharge voltage: 2.3 V (vs Li metal)
The results of the cycle test are shown in Table 1. The capacity retention rate was obtained by dividing the discharge capacity at the 50th cycle by the discharge capacity at the 1st cycle.

[Example 2]
A cycle test was performed in the same manner as in Example 1 except that the same coin cell as in Example 1 was used and the final discharge voltage was 2.5 V.

[Example 3]
A cycle test was conducted in the same manner as in Example 1 except that the same coin cell as in Example 1 was used and the final discharge voltage was 2.6V.

[Example 4]
A cycle test was performed in the same manner as in Example 1 except that the same coin cell as in Example 1 was used and the final discharge voltage was 2.7 V.

[Comparative Example 1]
A cycle test was performed in the same manner as in Example 1 except that the same coin cell as in Example 1 was used and the final discharge voltage was set to 2.0V.

[Evaluation]
The results of the cycle tests conducted in Examples 1 to 4 and Comparative Example 1 are shown in Table 1 below.

  As shown in Table 1, when the discharge end voltage was 2.3 V or more on the basis of Li metal, a good capacity retention rate was shown (Examples 1 to 4). On the other hand, when the end-of-discharge voltage was 2.0 V on the basis of Li metal, the capacity retention rate was extremely low at 55.1% (Comparative Example 1). Thereby, when the discharge end voltage was 2.3 V or more on the basis of Li metal, it was confirmed that the deterioration of the cycle characteristics could be suppressed. Moreover, although Example 3 and Example 4 showed the favorable capacity | capacitance maintenance factor, it is thought that it is preferable from the viewpoint of discharge capacity that discharge end voltage is 2.6V or less on the basis of Li metal. .

It is explanatory drawing explaining the air battery system of this invention. It is explanatory drawing explaining the air battery system of this invention. It is explanatory drawing explaining the method of circulating a fluorine-containing electrolyte solution. It is explanatory drawing explaining the positional relationship of the liquid level of a fluorine-containing electrolyte solution, and uppermost surfaces, such as an air electrode layer. It is explanatory drawing explaining the discharge control part used for this invention. It is explanatory drawing explaining the air battery cell produced in the Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Battery case 1a ... Lower insulating case 1b ... Upper insulating case 2 ... Negative electrode collector 2 '... Negative electrode lead 3 ... Negative electrode layer 4 ... Air electrode layer 5 ... Air electrode mesh 6 ... Air electrode current collector 6' ... Air Electrode lead 7… Separator 8… Microporous membrane 9… Fluorine-containing electrolyte

Claims (5)

An air electrode having an air electrode layer containing a conductive material and an air electrode current collector for collecting the air electrode layer, a negative electrode layer containing a negative electrode active material that absorbs and releases Li ions, and the negative electrode layer Air having a negative electrode having a negative electrode current collector for collecting current, a separator disposed between the air electrode layer and the negative electrode layer, and a fluorine-containing electrolyte solution that is impregnated in at least the separator and contains fluorine A battery cell;
A discharge controller for terminating the discharge of the air battery cell,
An air battery system, wherein an end-of-discharge voltage of the discharge controller is 2.3 V or more based on Li metal.   2. The air battery system according to claim 1, wherein the discharge end voltage is 2.6 V or less on the basis of Li metal.   The air battery system according to claim 1 or 2, wherein the fluorine-containing electrolyte contains a fluorine-containing electrolyte. Air battery system according to any one of claims to claims 1 to 3, wherein the fluorine-containing electrolyte, characterized in that it is a LiPF _6. An air electrode having an air electrode layer containing a conductive material and an air electrode current collector for collecting the air electrode layer, a negative electrode layer containing a negative electrode active material that absorbs and releases Li ions, and the negative electrode layer Air having a negative electrode having a negative electrode current collector for collecting current, a separator disposed between the air electrode layer and the negative electrode layer, and a fluorine-containing electrolyte solution that is impregnated in at least the separator and contains fluorine Using battery cells,
The method of controlling an air battery cell, wherein the discharge of the air battery cell is stopped and charging is performed when the voltage of the air battery cell is 2.3 V or higher with respect to a Li metal.

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