JP5365469B2 - Lithium air battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium air battery capable of preventing deactivation in advance by avoiding deposition of a solid material in an electrode. <P>SOLUTION: The lithium air battery includes at least an air electrode, a negative electrode, and aqueous electrolyte interposed between the air electrode and the negative electrode and partially dipped in the air electrode, wherein the lithium air battery includes a temperature regulating means of making the temperature of a portion of the aqueous electrolyte not dipped in the air electrode lower than a portion dipped in the air electrode. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a lithium-air battery that can prevent deactivation in advance by avoiding solid deposition in an electrode.

  The lithium-air battery is a chargeable / dischargeable battery using lithium metal or a lithium compound as a negative electrode active material and oxygen as a positive electrode active material. Since oxygen, which is a positive electrode active material, is obtained from air, there is no need to enclose the positive electrode active material in the battery, so in theory, a lithium-air battery has a larger capacity than a secondary battery using a solid positive electrode active material. Can be realized.

In a lithium-air battery, the reaction of formula (1) proceeds at the negative electrode during discharge.
2Li → 2Li ⁺ + 2e ⁻ (1)
The electrons generated by the equation (1) reach the positive electrode after working with an external load via an external circuit. Then, lithium ions (Li ⁺ ) generated in the formula (1) move from the negative electrode side to the positive electrode side by electroosmosis in the electrolyte sandwiched between the negative electrode and the positive electrode.

Further, during discharge, the reactions of the formulas (2) and (3) proceed at the positive electrode.
2Li ⁺ + O ₂ + 2e ⁻ → Li ₂ O ₂ (2)
2Li ⁺ + 1 / 2O ₂ + 2e ⁻ → Li ₂ O (3)
The generated lithium peroxide (Li ₂ O ₂ ) and lithium oxide (Li ₂ O) are accumulated in the air electrode as solids.
At the time of charging, the reverse reaction of the above formula (1) proceeds at the negative electrode, and the reverse reactions of the above formulas (2) and (3) proceed at the positive electrode, and the lithium metal is regenerated at the negative electrode. .

In the conventional lithium-air battery, solids composed of lithium peroxide (Li ₂ O ₂ ) and lithium oxide (Li ₂ O), which are reaction products of the above formulas (2) and (3), accumulate in the air electrode. As a result, the air electrode is clogged, the contact between the electrolyte and air is cut off, and this causes a problem in charging and discharging.
As a technique for eliminating such deactivation of a lithium-air battery, Non-Patent Document 1 discloses an organic electrolyte between a lithium ion conductive solid electrolyte and a negative electrode, and between the electrolyte and an air electrode. A technique for preventing precipitation of lithium oxide (Li ₂ O), which is a solid reaction product at the air electrode, by disposing an aqueous electrolytic solution in the air electrode is disclosed.

Zhou Goshin, 1 other, “Developing a high-performance“ lithium-air battery ”with a new structure”, [online], February 24, 2009, National Institute of Advanced Industrial Science and Technology, [October 28, 2009] Day search], Internet <URL: http: //www.aist.go.jp/aist_j/press_release/pr2009/pr20090224/pr20090224.html>

In the lithium-air battery disclosed in the above non-patent document, the reaction of the formula (4) proceeds at the negative electrode during discharge.
Li → Li ⁺ + e ⁻ (4)
According to the above formula (4), metallic lithium Li begins to dissolve in the organic electrolyte as lithium ions Li ⁺ , and electrons are supplied to the conducting wire. The dissolved lithium ion Li ⁺ passes through the solid electrolyte and moves to the aqueous electrolyte solution of the positive electrode.

On the other hand, in the lithium-air battery, the reaction of the formula (5) proceeds at the positive electrode during discharge.
O ₂ + 2H ₂ O + 4e ⁻ → 4OH ⁻ (5)
According to the above formula (5), electrons are supplied from the conducting wire, and oxygen and water in the air react with each other on the surface of the air electrode to generate hydroxide ions OH ⁻ . In the aqueous electrolyte solution on the air electrode side, the lithium ion Li ⁺ generated in the above formula (4) is encountered to form water-soluble lithium hydroxide LiOH.

As described above, the lithium-air battery disclosed in Non-Patent Document 1 is a lithium hydroxide that is a salt generated by an electrode reaction in an aqueous electrolyte disposed between a lithium ion conductive solid electrolyte and an air electrode. By dissolving LiOH, salt precipitation is prevented. However, in Non-Patent Document 1, no consideration is given to the saturation solubility of the salt in the aqueous electrolyte solution, and therefore, when the lithium hydroxide concentration exceeds the saturation solubility, precipitation of lithium hydroxide begins. Is expected. Therefore, the lithium air battery disclosed in Non-Patent Document 1 is not considered to be an invention that can sufficiently achieve the problems to be solved.
The present invention has been accomplished in view of the above circumstances, and an object of the present invention is to provide a lithium-air battery in which deactivation can be prevented in advance by avoiding solid precipitation in the electrode.

The lithium-air battery of the present invention is a lithium-air battery having at least an air electrode, a negative electrode, and an aqueous electrolytic solution interposed between the air electrode and the negative electrode and partially immersed in the air electrode, Of the aqueous electrolytic solution, a temperature adjusting means for lowering the temperature of the portion not immersed in the air electrode is lower than the temperature of the portion immersed in the air electrode, the air electrode, the negative electrode, and the aqueous solution A battery case for storing the electrolytic solution, a heat conductor, a heat receptor, and a Peltier element as the temperature adjusting means, further outside the battery case, and out of the aqueous electrolytic solution, on the air electrode One surface of the Peltier element is attached to a part where a non-immersed part is located, and the heat receptor is attached to a part outside the battery case and at least where the air electrode is located. It is other one of the surfaces of the Peltier element, characterized in that attached to the heat receptors through the heat conductor.

In the lithium air battery having such a configuration, the crystallization of the discharge product starts from the portion not immersed in the air electrode set at a lower temperature in the aqueous electrolyte by the temperature adjusting unit. Generation of discharge products in a portion of the aqueous electrolyte that is immersed in the air electrode is suppressed, and deterioration of battery performance due to clogging of the air electrode can be prevented. Further, the lithium-air battery having such a configuration adjusts the positive / negative of the Peltier element at the time of discharging, and makes the surface on the aqueous electrolyte side a cooling surface and the surface on the heat conductor side as a heat release surface. The aqueous electrolyte solution can be cooled and at least the air electrode can be heated. As a result, a temperature gradient is positively formed in the aqueous electrolyte solution, and convection is generated to improve lithium ion conductivity. At the same time, it is possible to prevent the precipitation of the discharge product solid at least in the vicinity of the air electrode, and to prevent a decrease in lithium ion conductivity. Further, the lithium-air battery having such a configuration reverses the heat release surface / cooling surface during discharge by reversing the polarity of the Peltier element during discharge during charging, and heats the aqueous electrolyte. At least the air electrode can be cooled, thereby accelerating charging by promoting the dissolution of the discharge product solid in the aqueous electrolyte and forming convection in the aqueous electrolyte. Conduction can be improved.

  As one form of the lithium-air battery of the present invention, a first thermocouple and a conductivity meter are attached to a portion of the aqueous electrolyte that is not immersed in the air electrode, and a second thermocouple is attached to the air electrode. It can be configured that a thermocouple is attached.

  The lithium air battery having such a configuration measures the temperature of each of the aqueous electrolyte and the air electrode using the first thermocouple and the second thermocouple, and the conductivity of the aqueous electrolyte using the conductivity meter. By measuring the electrical conductivity, the discharge product solid concentration in the electrolytic solution can be calculated in advance, and the temperature adjusting means can be executed before the concentration reaches the saturated concentration of the electrolytic solution.

  According to the present invention, in preparation for the case where the discharge product concentration exceeds the saturation solubility in the aqueous electrolyte solution, and solids are deposited and clogged, particularly at the air electrode, the temperature is adjusted in the electrolyte solution using the temperature adjusting means. By providing the gradient, it is possible to prevent a decrease in battery performance due to clogging of the air electrode.

It is the cross-sectional schematic diagram which showed the example of the lithium air battery which is the 1st structural example of this invention, and performs partial heating / cooling using a Peltier device. It is the cross-sectional schematic diagram which showed the example of the lithium air battery which is the 2nd structural example of this invention, and performs the heating by environmental heat / operation heat / resistance heating, and cooling by ventilation. It is the cross-sectional schematic diagram which showed the example of the lithium air battery which is the 3rd structural example of this invention, and cools with the refrigerant | coolant which flows through a refrigerant flow path. It is the cross-sectional schematic diagram which showed the example of the lithium air battery which is the 4th structural example of this invention, and performs partial cooling inside a battery. It is the cross-sectional schematic diagram which showed the example of the lithium air battery which is a 5th structural example of this invention, and performs automatic temperature control. It is the cross-sectional schematic diagram which was the 6th structural example of this invention, and showed the example of the Daniel battery.

  The lithium-air battery of the present invention is a lithium-air battery having at least an air electrode, a negative electrode, and an aqueous electrolytic solution interposed between the air electrode and the negative electrode and partially immersed in the air electrode, Of the aqueous electrolytic solution, a temperature adjusting means is provided for making the temperature of the portion not immersed in the air electrode lower than the temperature of the portion immersed in the air electrode.

In a metal-air battery using an aqueous electrolyte, it is common to use a gas diffusion electrode that reduces oxygen for the positive electrode, a metal (Li, Zn, Al, Fe, etc.) for the negative electrode, and an alkaline aqueous solution for the electrolytic solution.
Among metal-air batteries, for example, an aqueous lithium-type battery as disclosed in Non-Patent Document 1 described above has a Li ion permeable partition wall between the electrolyte and the negative electrode. During discharge, Li ⁺ and OH ⁻ as discharge products are stored in an aqueous solution, and during charging, Li ⁺ and OH ⁻ in the electrolyte are consumed to generate Li and oxygen.
In such a battery, discharge products can be accumulated as ions in the solution, and discharge is possible even if the saturation solubility of ions is exceeded. However, if the saturation solubility is exceeded, LiOH as a discharge product is considered to be an ionic crystal and precipitates in the solvent layer. The crystallized discharge product (hereinafter sometimes referred to as product solid) covers the electrode surface, which is a discharge reaction field, and may hinder subsequent discharge reactions. In particular, when the product solid is deposited in the pores of the air electrode, oxygen as the positive electrode active material is not supplied, so that the entire battery is deactivated and the discharge may be stopped.
In the air electrode, there is a three-phase interface of gas phase (oxygen), liquid phase (aqueous electrolyte), and solid phase (conductive material, catalyst), but once the product solid precipitates on the three-phase interface When it occurs, it is expected that not only discharging but also charging is difficult to occur. As can be seen from the reaction formulas of the above formulas (4) and (5), which are reaction formulas at the time of discharge, it is desirable that the product solid exists in the electrolytic solution at the time of discharge, and the product solid outside the electrolytic solution. It is not preferable that the be deposited. Further, the precipitation may inhibit the electrolyte diffusion in the electrolytic solution, promote the bias of the solution concentration distribution, and demerits that lithium ion conduction is inhibited.
As mentioned above, the disadvantage of the product solid precipitation has been explained by taking a lithium-air battery as an example, but such a disadvantage is that the discharge product is dissolved in a solvent, and the discharge is generated as a solid by dissolution equilibrium above the saturation solubility. This is a problem in all batteries that can store objects, for example, Daniel batteries (Cu | CuSO ₄ | ZnSO ₄ | Zn).

  When ions are precipitated in a solid state due to dissolution equilibrium, crystal growth occurs by the following mechanism. First, crystal formation nuclei are formed in the electrolytic solution in a supersaturated state. The formation of crystal nuclei is likely to be formed on a place with high energy, for example, particularly on a solid surface, and thus is likely to be formed on an electrode surface or a battery inner wall surface. If the atmospheric conditions necessary for crystal growth in the battery are uniform, product solids are particularly likely to precipitate on the air electrode surface. In the portion where the solid crystal is generated, both the ion conduction path and the oxygen introduction path are blocked, and as a result, the battery is deactivated.

The lithium-air battery of the present invention is configured based on the following five technical ideas, based on the mechanism of battery deactivation due to the precipitation of the product solid.
The first technical idea is an idea of inducing the precipitation site of the product solid during discharge by forming a temperature gradient inside the battery. More specifically, in the idea that the temperature of the portion of the aqueous electrolyte not immersed in the air electrode is lower than the temperature of the portion immersed in the air electrode, and as a result, a temperature gradient is formed. is there. By designing the battery based on this concept, the crystallization of the discharge product starts from the portion of the aqueous electrolyte that is not immersed in the air electrode, preventing the precipitation of product solids at the air electrode. it can.
In the lithium-air battery of the present invention, a product solid is obtained by providing a low-temperature portion by cooling from the outside at a position sufficiently separated from the air electrode and the negative electrode, at least a position sufficiently separated from the air electrode, on the wall surface of the aqueous solvent electrolyte layer. Lowers the local saturation solubility of LiOH, which promotes the precipitation of product solids.
In the case where the lithium-air battery according to the present invention is operated particularly near room temperature, a temperature gradient is realized by providing a part higher or lower than the temperature around the battery or both in the battery.

The second technical idea is an idea of heating the entire battery to activate the battery during charging. By designing the battery based on such a concept, at a high temperature, the dissolution of the discharge product solid is promoted, so that a high charge rate is possible.
When the internal temperature of the electrolytic solution is set high during charging, the discharge product can be quickly dissolved from the solid state due to the increase in solubility and dissolution rate of the discharge product solid. As a result, the transport of metal ions to the electrode that is a reaction field can be promoted, and a high charge rate is possible.
Depending on the structure of the lithium-air battery, the entire battery may not necessarily be heated. For example, as in a first configuration example described later, the dissolution of the discharge product solid in the aqueous electrolyte is promoted to accelerate charging, and the ionic conduction is improved by forming convection in the aqueous electrolyte. From this point of view, at the time of charging, it is possible to adopt a configuration in which at least the temperature of the aqueous electrolyte layer is set higher than the temperature of other parts of the battery.

The third technical idea is an idea of promoting convection in the electrolytic solution by forming a temperature distribution. By designing the battery based on this idea, the temperature distribution is formed in the electrolytic solution. As a result, ionic conduction is promoted by convection in the electrolytic solution, and the product concentration is locally increased. It is possible to prevent crystallization in a place where there is not.
If there is no convection in the electrolyte, the electrolyte concentration increases as the temperature rises, and the discharge product precipitates when the saturation solubility is exceeded. May be disturbed.
However, by promoting convection based on the third technical idea, sufficient ion conduction can be ensured and the reactants and products on the electrode surface can be transported.

The fourth technical idea is an idea of preparing a mechanism for forming a temperature gradient in the battery.
As a configuration of the battery that specifically realizes the temperature gradient as described above, for example, by using the surrounding excess heat, the part corresponding to the electrolyte of the battery is cooled from the outside, and the other part is kept warm. The structure of covering with a heat insulating material can be considered. In this case, air cooling, water cooling, or other refrigerants can be used for cooling.
As an example of a configuration for more actively forming a temperature gradient, a configuration in which different portions of the battery are heated and cooled can be considered. In order to efficiently perform heating and cooling simultaneously, for example, a Peltier element can be used. Specifically, a temperature gradient is formed between the positive electrode and the negative electrode by transferring heat generated in the Peltier element to the positive electrode and the negative electrode using a heat conductor. In the case where the vicinity of the electrode is heated using heat conduction with a heater such as a Peltier element, it is preferable to prevent leakage by sandwiching an insulating layer between the heater and the electrode.
As another example in which the temperature gradient inside the battery can be efficiently formed, a configuration in which the periphery of the electrode and the outer periphery of the solution layer are separated by a material having a high heat capacity can be considered.

The fifth technical idea is an idea of automatically controlling the temperature gradient. Energy saving can be realized by designing a battery based on such a concept.
According to the discussion so far, it is necessary to form a temperature gradient when the discharge product is saturated and deposited in the aqueous electrolyte at least during discharge. Therefore, extra energy can be saved by stopping the temperature adjusting means for forming the temperature gradient in cases other than discharging, specifically in charging.
Specifically, the concentration is monitored by measuring the conductivity of the aqueous electrolyte, and the cooling / heating system is activated when the LiOH concentration in the aqueous electrolyte approaches saturation solubility. The monitoring of the electrolyte solution temperature and the electrode temperature can be started, and the cooling / heating system can be stopped when a temperature gradient equal to or higher than the threshold is formed or when the discharge is stopped.

Of the above five technical ideas, in particular, as a specific form of the lithium-air battery for realizing the third to fifth technical ideas, the temperature adjusting means includes:
(1) Temperature setting means for setting the temperature of the portion immersed in the air electrode of the aqueous electrolyte solution of the lithium-air battery and the temperature of the portion not immersed in the air electrode that is lower than the temperature. ,
(2) Temperature control means for performing at least one of heating of a portion immersed in the air electrode and cooling of a portion not immersed in the air electrode in the aqueous electrolyte solution of the lithium-air battery,
(3) Temperature control monitoring means for monitoring the necessity of temperature control for the aqueous electrolyte of the lithium air battery,
(4) When the temperature control monitoring means determines that the temperature control of the aqueous electrolyte is necessary, the temperature control operation mode for starting the temperature control of the aqueous electrolyte is selected, and the temperature control monitoring means selects the aqueous electrolyte. And a temperature control mode switching unit that selects a temperature control stop mode for stopping the temperature control of the aqueous electrolyte solution and executes the selected temperature control mode when it is determined that the temperature control is not necessary. Can be mentioned.
In the lithium-air battery having such a configuration, the temperature of the portion of the aqueous electrolyte not immersed in the air electrode is set lower than the temperature of the portion immersed in the air electrode, and temperature control is performed. The actual temperature of the part not immersed in the air electrode is made to be higher than the actual temperature of the part immersed in the air electrode by appropriately controlling the temperature by the means, the temperature control monitoring means and the temperature control mode switching means. The temperature can be lowered, and the temperature gradient of the aqueous electrolyte can be appropriately formed.
Hereinafter, the temperature setting unit, the temperature control unit, the temperature control monitoring unit, and the temperature control mode switching unit will be described.

  Specifically, as the temperature setting means, the temperature data of the portion immersed in the air electrode and the temperature data of the portion not immersed in the air electrode of the aqueous electrolyte of the lithium air battery are stored. Examples thereof include a recording medium such as a disk, and an apparatus such as an electronic computer capable of transmitting the temperature data to a temperature control monitoring unit described later. However, as long as the temperature data is set before, during, or during the operation of the lithium air battery, and the temperature data can be used for temperature control of the lithium air battery, it is not necessarily limited to these recording media and devices. Any means can be adopted.

As the temperature control means, specifically, the Peltier element as described above can be used. As a Peltier device, a non-oxide type thermoelectric material or an oxide type thermoelectric material is roughly classified.
Examples of non-oxide thermoelectric materials include telluride thermoelectric materials represented by bismuth telluride (Bi ₂ Te ₃ ) compounds; silicon-germanium thermoelectric materials; silicide thermoelectric materials such as β-FeSi ₂ and CrSi ₂ ; Skutterudite-based thermoelectric materials typified by CoSb ₃ ; Half-Heusler metal-based thermoelectric materials such as ZrNiSn and ZrCoSn; Zinc / antimony-based thermoelectric materials typified by Zn ₄ Sb ₃ compounds; B ₄ C, β rhombohedral boron boron compounds such _{as; B 12} clusters, _{Si 20} clusters _include clusters solids such as _{C 60} clusters.
Examples of oxide thermoelectric materials include layered cobalt oxide thermoelectric materials such as NaCo ₂ O ₄ and Ca ₃ Co ₄ O ₉ , zinc oxide thermoelectric materials, and titanium oxide thermoelectric materials typified by SrTiO ₃ .
Peltier elements that can be used as temperature control means are not necessarily limited to the non-oxide thermoelectric material and the oxide thermoelectric material. In addition to the thermoelectric material, Si P known as an amorphous material is known. A -Ge-Au thermoelectric material or the like can also be used.
As the temperature control means, in addition to heating / cooling control using a Peltier element, heating control using a resistance heater, cooling control using air cooling, water cooling, and the like can be given.

As one form of temperature control monitoring means, as a temperature measurement device for monitoring the temperature of the lithium air battery, and as temperature data serving as a reference for determining the necessity of temperature control, among the aqueous electrolyte of the lithium air battery, The temperature data of the portion immersed in the air electrode and the temperature data of the portion not immersed in the air electrode can be held. By holding the temperature data, the temperature control monitoring means can determine whether or not the temperature control of the lithium air battery is necessary from the temperature of each part of the lithium air battery monitored by the temperature measuring device. .
The means for measuring the temperature of the lithium air battery is not particularly limited, and generally a method for measuring the temperature around the lithium air battery can be employed. As specific examples of the temperature measurement method, a glass thermometer using pure mercury, a metal thermometer using bimetal, an electric thermometer using a platinum wire, a temperature sensor using a thermocouple, and a thermistor were used. The measuring method using a resistance thermometer, a radiation thermometer, etc. can be mentioned.

  The configuration of the temperature control mode switching means is not particularly limited. Specifically, a switch for switching the temperature control means described above in conjunction with information on whether or not temperature control is necessary, and information on whether or not temperature control is necessary are provided. An apparatus such as an electronic computer that can be transmitted to a temperature control means or the like can be exemplified.

  Hereinafter, an air electrode, a negative electrode, and an aqueous electrolytic solution that is partially immersed in the air electrode, which are interposed between the air electrode and the negative electrode, which are components of the lithium-air battery according to the present invention, will be described in order. To do.

(Air electrode)
The air electrode of the lithium-air battery according to the present invention preferably has an air electrode layer. Usually, in addition to this, an air electrode current collector and an air electrode lead connected to the air electrode current collector It is what has.

(Air electrode layer)
The air electrode layer in the lithium-air battery according to the present invention contains at least a conductive material. Furthermore, you may contain at least one of a catalyst and a binder as needed.

  The conductive material used for the air electrode layer 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. However, in the present invention, the carbon material preferably has a porous structure. This is because the specific 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. As content of the electroconductive material in an air electrode layer, it is preferable to exist in the range of 65 mass%-99 mass%, for example in the range of 75 mass%-95 mass% especially. If the content of the conductive material is too small, the reaction field may decrease and the battery capacity may decrease. This is because it may not be possible to exert a proper catalytic function.

Examples of the catalyst used for the air electrode layer include cobalt phthalocyanine and manganese dioxide. The catalyst content in the air electrode layer is, for example, preferably in the range of 1% by mass to 30% by mass, and more preferably in the range of 5% by mass to 20% by mass. If the catalyst content is too low, sufficient catalytic function may not be achieved. If the catalyst content is too high, the content of the conductive material is relatively reduced, the reaction field is reduced, and the battery capacity is reduced. This is because there is a possibility that a decrease in the number of times will occur.
From the viewpoint that the electrode reaction is performed more smoothly, the conductive material described above preferably supports a catalyst.

  The air electrode layer only needs to contain at least a conductive material, but preferably further contains a binder for fixing the conductive material. Examples of the binder include polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE). Although it does not specifically limit as content of the binder in an air electrode layer, For example, it is preferable that it is in the range of 30 mass% or less, especially 1 mass%-10 mass%.

The thickness of the air electrode layer is different depending on the use of the air battery, for example, 2 μm to
It is preferable to be in the range of 500 μm, especially in the range of 5 μm to 300 μm.

(Air current collector)
The air electrode current collector in the lithium-air battery according to the present invention collects the air electrode layer. 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, titanium, and carbon. Examples of the shape of the air electrode current collector include a foil shape, a plate shape, and a mesh (grid) shape. In particular, in the present invention, the air electrode current collector is preferably mesh-shaped from the viewpoint of excellent current collection efficiency. In this case, usually, a mesh-shaped air electrode current collector is disposed inside the air electrode layer. Furthermore, the lithium-air battery according to the present invention has another air electrode current collector (for example, a foil-shaped current collector) that collects electric charges collected by the mesh-shaped air electrode current collector. Also good. In the present invention, a battery case to be described later may also have the function of an air electrode current collector.
The thickness of the air electrode current collector is, for example, preferably in the range of 10 μm to 1000 μm, and more preferably in the range of 20 μm to 400 μm.

(Negative electrode)
The negative electrode in the lithium-air battery according to the present invention preferably has a negative electrode layer containing a negative electrode active material. Usually, in addition to this, a negative electrode current collector, and a negative electrode connected to the negative electrode current collector It has a lead.

(Negative electrode layer)
The negative electrode layer in the lithium air battery according to the present invention contains at least a negative electrode active material having a lithium element.
The negative electrode active material in the lithium-air battery according to the present invention is preferably capable of occluding and releasing lithium ions. Such a negative electrode active material is not particularly limited as long as it has a lithium element, and examples thereof include simple metals, alloys, metal oxides, and metal nitrides. Examples of the alloy having a lithium element include a lithium aluminum alloy, a lithium tin alloy, a lithium lead alloy, and a lithium silicon alloy. Moreover, as a metal oxide which has a lithium element, lithium titanium oxide etc. can be mentioned, for example. Examples of the metal nitride containing a lithium element include lithium cobalt nitride, lithium iron nitride, and lithium manganese nitride.

  The negative electrode layer may contain only a negative electrode active material, or may contain at least one of a conductive material and a binder in addition to the negative electrode active material. For example, when the negative electrode active material is in the form of a foil, a negative electrode layer containing only the negative electrode active material can be obtained. On the other hand, when the negative electrode active material is in a powder form, a negative electrode layer having a negative electrode active material and a binder can be obtained. Note that the conductive material and the binder are the same as the contents described in the above-mentioned “air electrode” section, and thus the description thereof is omitted here.

(Negative electrode current collector)
The material for the negative electrode current collector in the lithium-air battery according to the present invention is not particularly limited as long as it has conductivity, and examples thereof include copper, stainless steel, nickel, and carbon. 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.

(Separator)
When the lithium air battery according to the present invention has a structure in which multiple layers of an air electrode, a negative electrode, and an aqueous electrolyte solution interposed between the air electrode and the negative electrode are stacked, safety is ensured. From this point of view, it is preferable to have a separator between the air electrode layer and the negative electrode layer belonging to different laminates. Examples of the separator include porous films such as polyethylene and polypropylene; and nonwoven fabrics such as a resin nonwoven fabric and a glass fiber nonwoven fabric.

(Battery case)
The lithium-air battery according to the present invention usually has a battery case that houses an air electrode, a negative electrode, and an aqueous electrolyte. Specific examples of the shape of the battery case include a coin type, a flat plate type, a cylindrical type, and a laminate type. The battery case may be an open-air battery case or a sealed battery case. An open-air battery case is a battery case having a structure in which at least the air electrode layer can sufficiently come into contact with the atmosphere. On the other hand, when the battery case is a sealed battery case, it is preferable to provide a gas (air) introduction pipe and an exhaust pipe in the sealed battery case. In this case, the gas to be introduced / exhausted preferably has a high oxygen concentration, and more preferably pure oxygen. In addition, it is preferable to increase the oxygen concentration during discharging and decrease the oxygen concentration during charging.

(Aqueous electrolyte)
The aqueous electrolytic solution in the lithium-air battery according to the present invention is a layer formed between the air electrode layer and the negative electrode layer and responsible for the conduction of lithium ions.
As the aqueous electrolytic solution, usually, water containing a lithium salt is used. Examples of the lithium salt include inorganic lithium salts such as LiPF ₆ , LiBF ₄ , LiClO _4, and LiAsF ₆ ; and LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ (Li-TFSI), LiN (SO ₂ C ₂ F ₅ ) ₂ , organic lithium salts such as LiC (SO ₂ CF ₃ ) _{3 and the} like.
The concentration of LiOH in the aqueous electrolyte is 0 to 5.12M. Note that 5.12M is a saturated concentration at room temperature. However, since the decrease in lithium ion conductivity becomes significant at an electrolyte concentration of less than 0.1M, in order to compensate for the operation in the LiOH concentration region, an additional 0.1 to 12M KOH or NaOH may be added. it can.
In the present invention, the aqueous electrolyte may contain a low volatile liquid such as an ionic liquid.

Hereafter, the structural example of the battery of this invention is shown.
As a first configuration example of the present invention, a battery case containing an air electrode, a negative electrode, and an aqueous electrolyte, a heat conductor, a heat receptor, and a Peltier element as a temperature adjusting means are further provided on the outside of the battery case. A portion of the aqueous electrolyte solution where the portion not immersed in the air electrode is located, one surface of the Peltier element is attached to the outside of the battery case, and at least the air electrode is located In addition, there is an example in which a heat receptor is attached and the other surface of the Peltier element is attached to the heat receptor via a heat conductor.

FIG. 1 is a schematic sectional view showing an example of a lithium-air battery which is a first configuration example of the present invention and performs partial heating / cooling using a Peltier element.
The lithium-air battery shown in FIG. 1 includes an air electrode 10, a negative electrode 11, and an aqueous electrolyte 12 that is interposed between the air electrode 10 and the negative electrode 11 and is partially immersed in the air electrode 10. ing. Further, the air electrode 10, the negative electrode 11, and the aqueous electrolyte solution 12 are accommodated in a battery case 13 so that the aqueous electrolyte solution 12 does not leak to the outside. In addition, although not shown in figure, you may provide the ventilation unit which sends air to the air electrode 10 separately. Further, it is preferable to provide a separator 14 so that the discharge product solid falls on the negative electrode 11 and accumulates and does not hinder ion conduction to the negative electrode surface.

In the first configuration example, one surface of the Peltier element 15 is attached to the outside of the battery case 13 where the electrolyte layer of the battery is located. On the other hand, the other surface of the Peltier element 15 is joined to the heat conductor 16, and the heat conductor 16 is a heat receptor attached to the outside of the battery case 13 where the air electrode 10 or the separator 14 is located. 17 respectively. The heat receptor 17 attached to the outside of the separator has an annular shape so as to surround the battery case 13.
At the time of discharging the battery, the electrolyte layer is cooled by adjusting the positive / negative of the Peltier element, the surface on the electrolyte layer side is used as a cooling surface, and the surface on the heat conductor 16 side is used as a heat release surface. The electrode 10 and the separator 14 can be heated respectively. As a result, a temperature gradient is positively formed in the electrolyte layer, and convection is generated to improve lithium ion conductivity. Precipitation of the discharge product solid in the vicinity can be prevented, and a decrease in lithium ion conductivity can be prevented. Although not shown, it is preferable to cover the Peltier element 15, the heat conductor 16, and the heat receptor 17 with a heat insulating material in order to perform efficient heating / cooling. In addition, an insulator 18 is preferably installed between the heat receptor 17 on the air electrode 10 side and the battery case 13 in order to prevent leakage.

  On the other hand, when the battery is charged, salt dissolution occurs in the electrolytic solution, so there is no need to cool the electrolytic solution. Further, at the time of charging, high temperature is not desirable because the formation of dendritic precipitates is promoted particularly in the negative electrode 11. For the above two reasons, it is preferable not to cool the electrolyte layer and heat the electrode during charging. At the time of charging, by reversing the polarity of the Peltier element at the time of discharging, the heat release surface / cooling surface can be reversed from that at the time of discharging, thereby heating the electrolyte during charging and cooling the air electrode 10 and the separator 14. can do. As a result, it is possible to accelerate the charging by promoting the dissolution of the discharge product solid in the electrolytic solution 12 and to improve the ionic conduction by forming a convection in the electrolytic solution 12.

  As a 2nd structural example of this invention, the example of having a means to air-cool the part which is not immersed in an air electrode among aqueous electrolytes as a temperature control means is mentioned. In addition, as an example of a more specific aspect of the second configuration example, the battery further includes a battery case that houses an air electrode, a negative electrode, and an aqueous electrolyte solution, and is outside the battery case and the aqueous electrolyte solution. Among them, there is an example in which a heat radiating plate is provided at a portion where a portion not immersed in the air electrode is located.

  FIG. 2 is a schematic cross-sectional view showing an example of a lithium-air battery that is a second configuration example of the present invention and performs heating by environmental heat / operational heat / resistance heating and cooling by air blowing. In the second configuration example, the configuration of the air electrode 10, the negative electrode 11, the aqueous electrolyte solution 12, and the battery case 13 is the same as that of the first configuration example shown in FIG. Also in the point which provides, it is the same as that of the 1st structural example.

In the second configuration example, cooling is partially performed by sending cold air by blowing from the outside of the battery case 13 where the electrolyte layer of the battery is located to a part that is particularly susceptible to heat from the surroundings. FIG. 2 illustrates the blower 20 and an arrow 21 indicating the direction of the cold air. In this case, it is preferable to attach the heat radiating plate 22 to the cooling portion from the viewpoint of efficient cooling.
The non-cooled portion, that is, the portion where no air cooling is performed is heated by heat from the surrounding environment or heat generated by the operation of the battery itself. When a sufficient temperature gradient cannot be formed even by such environmental heat, it is preferable to install the resistance heater 23 outside the battery case 13 where the air electrode 10 and the separator 14 are located. The resistance heater 23 attached to the outside of the separator 14 has an annular shape so as to surround the battery case 13.
Furthermore, it is preferable that a part such as an electrode that is not cooled by blowing or the like is covered with a heat insulating material 24 or the like as shown in the drawing or provided with a mechanism that blocks blowing.

Thus, by cooling the electrolyte layer with cold air and heating the air electrode 10 and the separator 14 with the resistance heater 23, a temperature gradient is positively formed in the electrolyte layer, and convection is generated. While improving lithium ion conductivity, precipitation of the discharge product solid in the air electrode 10 and separator 14 vicinity can be prevented, and the fall of lithium ion conductivity can be prevented.
On the other hand, as described above, during the charging of the battery, from the viewpoint that the dissolution of the salt in the electrolytic solution and the formation of dendritic precipitates in the negative electrode 11 are promoted, the cooling of the electrolytic solution layer is performed during the charging. It is preferable not to heat the electrodes.

  The third configuration example of the present invention further includes a battery case that houses an air electrode, a negative electrode, and an aqueous electrolytic solution. The temperature adjusting means is outside the battery case, and the aqueous electrolytic solution includes air. An example in which a coolant channel is provided at a portion where a portion not immersed in the electrode is located can be given.

FIG. 3 is a schematic sectional view showing an example of a lithium-air battery which is a third configuration example of the present invention and performs cooling by the refrigerant flowing in the refrigerant flow path. In the third configuration example, the configuration of the air electrode 10, the negative electrode 11, the aqueous electrolyte solution 12, and the battery case 13 is the same as that of the first configuration example shown in FIG. Also in the point which provides, it is the same as that of the 1st structural example.
In the third configuration example, the refrigerant flow path 30 is provided from the outside of the battery case 13 where the battery electrolyte layer is located, particularly in a region where heat is easily received from the surroundings. Although the details are not shown, the actual refrigerant flow path 30 has a structure that surrounds the outside of the battery case 13 and can sufficiently cool the electrolyte layer. It is preferable to provide a water jacket (not shown) in the battery case 13 in order to prevent mixing into the electrolyte in the battery due to refrigerant leakage, short circuit due to electrode leakage, and the like.
Furthermore, as shown in FIG. 3, it is preferable to install the resistance heater 23 outside the battery case 13 where the air electrode 10 and the separator 14 are located so that the entire battery does not reach a uniform temperature. The resistance heater 23 attached to the outside of the separator 14 has an annular shape so as to surround the battery case 13. In order to further increase the heating effect, it is preferable to cover with a heat insulating material 24 as shown in the figure.

In this way, the electrolyte layer is cooled by the refrigerant flow path 30, and the air electrode 10 and the separator 14 are heated by the resistance heater 23, so that a temperature gradient is positively formed in the electrolyte layer, and convection is generated. It is possible to improve the lithium ion conductivity and prevent the precipitation of the discharge product solid in the vicinity of the air electrode 10 and the separator 14 and prevent the lithium ion conductivity from being lowered.
On the other hand, as described above, during the charging of the battery, from the viewpoint that the dissolution of the salt in the electrolytic solution and the formation of dendritic precipitates in the negative electrode 11 are promoted, the cooling of the electrolytic solution layer is performed during the charging. It is preferable not to heat the electrodes.

  As a fourth configuration example of the present invention, a battery case containing an air electrode, a negative electrode, and an aqueous electrolyte, a first heat conductor, a second heat conductor, a heat receptor, and a Peltier element as a temperature adjusting means The first heat conductor is attached to the portion of the aqueous electrolyte solution where the portion not immersed in the air electrode is located so as to penetrate the outside and the inside of the battery case. One side of the Peltier element is attached to a part of the body that is located outside the battery case, and a heat receptor is attached to a part that is outside the battery case and at least where the air electrode is located. An example is given in which the other surface is attached to the heat receptor via a second heat conductor.

  FIG. 4 is a schematic cross-sectional view showing an example of a lithium-air battery that is a fourth configuration example of the present invention and performs partial cooling inside the battery. In the fourth configuration example, the configuration of the air electrode 10, the negative electrode 11, the aqueous electrolyte solution 12, and the battery case 13 is the same as that of the first configuration example shown in FIG. Also in the point which provides, it is the same as that of the 1st structural example.

In the fourth configuration example, the first heat conductor 40 is attached as a cooling point so as to penetrate from the inside of the battery electrolyte layer to the outside of the battery case 13. In the case of this configuration example, it is preferable to install a packing 41 between the first heat conductor 40 and the battery case 13 from the viewpoint of maintaining airtightness in the battery case. The first thermal conductor used for the cooling point is not particularly limited as long as it has a material that can withstand the electrolytic solution in addition to the thermal conductivity, and specific examples thereof include nickel and stainless steel. .
One surface of the Peltier element 42 is attached outside the cooling point. On the other hand, the other one surface of the Peltier element 42 is joined to the second heat conductor 43, and the second heat conductor 43 is disposed outside the battery case 13 where the air electrode 10 or the separator 14 is located. Each is attached to the attached heat receptor 44. The heat receptor 44 attached to the outside of the separator has an annular shape so as to surround the battery case 13. In addition, an insulator 45 is preferably installed between the heat receptor 44 on the air electrode 10 side and the battery case 13 in order to prevent leakage.

At the time of discharging the battery, by adjusting the positive / negative of the Peltier element, the surface on the first heat conductor 40 side serving as a cooling point is the cooling surface, and the surface on the heat conductor 16 side is the heat release surface, The electrolyte layer can be cooled, and the air electrode 10 and the separator 14 can be heated. As a result, a temperature gradient is positively formed in the electrolyte layer, and convection is generated to improve lithium ion conductivity. At the same time, the precipitation of the discharge product solid in the vicinity of the air electrode 10 and the separator 14 can be prevented, and the decrease in lithium ion conductivity can be prevented.
On the other hand, as described above, during the charging of the battery, from the viewpoint that the dissolution of the salt in the electrolytic solution and the formation of dendritic precipitates in the negative electrode 11 are promoted, the cooling of the electrolytic solution layer is performed during the charging. It is preferable not to heat the electrodes. At the time of charging, by reversing the polarity of the Peltier element at the time of discharging, the heat release surface / cooling surface can be reversed from that at the time of discharging, thereby heating the electrolyte during charging and cooling the air electrode 10 and the separator 14 can do. As a result, dissolution of the discharge product solid in the electrolytic solution 12 is promoted to accelerate charging, and ionic conduction can be improved by forming convection in the electrolytic solution 12.

  As a fifth configuration example of the present invention, a first thermocouple and a conductivity meter are attached to a portion of the aqueous electrolyte not immersed in the air electrode, and a second thermocouple is attached to the air electrode. An example can be given.

FIG. 5 is a schematic cross-sectional view showing an example of a lithium-air battery which is a fifth configuration example of the present invention and performs automatic temperature control. The fifth configuration example is a configuration in which a thermocouple and a conductivity meter are added based on the first configuration example shown in FIG.
As already described in the description of the first configuration example, it is sufficient that there is a temperature gradient in the battery at the time of discharge and at least when the discharge product solid is deposited. Therefore, the temperature adjusting means is stopped except during the deposition. In this way, excessive energy consumption can be suppressed.

The electrolyte allows for some degree of discharge product dissolution. However, since the precipitation of the product solid starts when the saturation concentration of the electrolytic solution is exceeded, it is preferable to start the temperature control immediately before reaching the saturation concentration.
The concentration of the lithium salt in the electrolytic solution can be determined from the electrical conductivity. In the lithium air battery, the saturated LiOH concentration is about 5M, and the conductivity at this time is 0.35 S · cm ⁻¹ . In the unsaturated electrolyte, taking into account that the higher the LiOH concentration, the higher the conductivity, when discharging and when the conductivity is ≧ 0.35 S · cm ⁻¹ (that is, when the LiOH concentration is ≧ 5 M), In addition, if the Peltier element 15 is controlled to operate only when the temperature of the liquid layer and the positive electrode satisfies {(air electrode temperature) − (electrolyte temperature)} <(threshold), the product solid is sufficiently precipitated. I can prevent it. The conductivity of the electrolytic solution can be measured by a conductivity meter 50, and the air electrode temperature or the electrolytic solution temperature can be measured by an air electrode side thermocouple 51 or an electrolyte side thermocouple 52, respectively. In the case of this configuration example, from the viewpoint of maintaining airtightness in the battery case, a packing is installed between the battery case 13 and the conductivity meter 50, the air electrode side thermocouple 51 or the electrolyte side thermocouple 52, respectively. Is preferred.
The control of the Peltier element at the time of discharging and charging the battery and the effect accompanying it are the same as in the first configuration example described above.

FIG. 6 is a schematic sectional view showing an example of a Daniel battery, which is a sixth configuration example of the present invention.
As shown in the figure, the Daniel battery includes a negative electrode in which a zinc electrode 60 is immersed in a zinc sulfate aqueous solution 61, and a positive electrode in which a copper electrode 62 is immersed in a copper sulfate aqueous solution 63. 63 is a battery in which 63 is partitioned by a porous diaphragm 64 such as an unglazed plate. In this configuration example, the entire Daniel battery is stored in the battery case 65.
The chemical reaction during the discharge of the Daniel battery is
Positive electrode: Cu ²⁺ 2e ⁻ → Cu (I)
Negative electrode: Zn → Zn ²⁺ + 2e ⁻ (II)
On the other hand, the chemical reaction when charging a Daniel battery is
Positive electrode: Cu → Cu ²⁺ + 2e ⁻ (III)
Negative electrode: Zn ²⁺ + 2e ⁻ → Zn (IV)
It is. That is, the Daniel battery is a battery that can be discharged and charged by a contrasting chemical reaction between the positive electrode and the negative electrode. As can be seen from the above formulas (I) to (IV), the concentration of zinc ions as the active material increases in the negative electrode side electrolyte during discharge, and precipitation due to saturation of the zinc salt occurs, and the same concentration change occurs during charging. Occurs on the positive side.

The sixth configuration example includes a mechanism capable of forming an independent temperature gradient between the positive electrode and the negative electrode based on the above consideration. That is, one surface of the Peltier element 66 is attached to the outside of the battery case 65 where the electrolyte solution layer on the negative electrode side of the Daniel battery is located. On the other hand, the other one surface of the Peltier element 66 is joined to the heat conductor 67, and the heat conductor 67 is further attached to the heat receptor 68 attached to the outside of the battery case 65 where the zinc electrode 60 is located. It is joined. An insulator 69 is preferably installed between the heat receptor 68 and the zinc electrode 60 to prevent leakage. The Peltier element 70, the heat conductor 71, the heat receptor 72, and the insulator 73 are also installed on the positive electrode side, similarly to the negative electrode side.
At the time of discharging the battery, the positive / negative of the Peltier element 66 for the negative electrode side electrolyte is adjusted, the surface on the electrolyte layer side is used as a cooling surface, and the surface on the heat conductor 67 side is used as a heat release surface. The layer can be cooled and the zinc electrode 60 can be heated. As a result, a positive temperature gradient is formed in the electrolyte layer, and convection is generated to improve the diffusibility of zinc ions. Precipitation of the discharge product solid (zinc sulfate) in the vicinity can be prevented, and a decrease in zinc ion diffusibility can be prevented. In order to perform efficient heating / cooling, it is preferable to cover a part or all of each of the Peltier element 66, the heat conductor 67, and the heat receptor 68 with a heat insulating material 74.
On the other hand, at the time of charging the battery, by adjusting the positive / negative of the Peltier element 70 for the electrolyte solution on the positive electrode side, the surface on the electrolyte layer side becomes the cooling surface, and the surface on the heat conductor 71 side becomes the heat release surface, The electrolyte layer can be cooled and the copper electrode 62 can be heated. As a result, a positive temperature gradient is formed in the electrolyte layer, and convection is generated to improve the diffusibility of copper ions. Precipitation of the discharge product solid (copper sulfate) in the vicinity of the electrode 62 can be prevented, and a decrease in diffusibility of copper ions can be prevented. In order to perform efficient heating / cooling, it is preferable to cover a part or all of each of the Peltier element 70, the heat conductor 71, and the heat receptor 72 with a heat insulating material 74.
In the case of the sixth configuration example, the negative electrode side electrolyte Peltier element 66 and the positive electrode side electrolyte Peltier element 70 are sufficiently spaced so as not to interfere with each other's electrolyte temperature, or between both Peltier elements, It is preferable to use a heat insulating material 74 incorporating a material having low thermal conductivity.

DESCRIPTION OF SYMBOLS 10 Air electrode 11 Negative electrode 12 Aqueous electrolyte 13 Battery case 14 Separator 15 Peltier element 16 Heat conductor 17 Heat receptor 18 Insulator 20 Blower 21 Arrow 22 which shows the direction of cold air Heat sink 23 Resistance heater 24 Heat insulating material 30 Refrigerant flow Path 40 First heat conductor 41 Packing 42 Peltier element 43 Second heat conductor 44 Heat receptor 45 Insulator 50 Conductivity meter 51 Air electrode side thermocouple 52 Electrolyte side thermocouple 60 Zinc electrode 61 Zinc sulfate aqueous solution 62 Copper electrode 63 Copper sulfate aqueous solution 64 Porous diaphragm 65 Battery case 66 Peltier element for negative electrode side electrolyte 70 Peltier element for positive electrode side electrolyte 67, 71 Thermal conductors 68, 72 Heat receptors 69, 73 Insulator 74 Insulating material

Claims (2)

A lithium-air battery having at least an air electrode, a negative electrode, and an aqueous electrolyte interposed between the air electrode and the negative electrode and partially immersed in the air electrode,
Of the aqueous electrolytic solution, comprising a temperature adjusting means for lowering the temperature of the portion not immersed in the air electrode lower than the temperature of the portion immersed in the air electrode ,
A battery case containing the air electrode, the negative electrode and the aqueous electrolyte, a heat conductor, a heat receptor, and a Peltier element as the temperature adjusting means;
One surface of the Peltier element is attached to the outside of the battery case, and the portion of the aqueous electrolyte solution where the portion not immersed in the air electrode is located,
The heat receptor is attached to the outside of the battery case and at least a portion where the air electrode is located,
The other surface of the Peltier element is attached to the heat receptor via the thermal conductor , and the lithium-air battery is characterized in that Of the aqueous electrolyte, a portion not immersed in the air electrode is attached with a first thermocouple and a conductivity meter,
The lithium air battery according to claim 1 , wherein a second thermocouple is attached to the air electrode.

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