JP2019032970A - Aqueous lithium - air secondary battery - Google Patents

Abstract

To provide an aqueous lithium - an air secondary battery, having a charge capacity.SOLUTION: An aqueous lithium - an air secondary battery 100 comprises: a metal lithium layer 1; a solid electrolyte layer 5; a reaction prevention layer 4 arranged between the metal lithium layer 1 and the solid electrolyte layer 5; a first organic liquid electrolyte layer 31 arranged between the metal lithium layer 1 and the reaction prevention layer 4; and a conductive porous layer 2 arranged between the metal lithium layer 1 and the first organic electrolyte layer 31. The conductive porous layer 2 comprises: a porous base 28 formed by an insulation body; and a conductive layer 29 coating an inner surface of the porous base 28.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an aqueous lithium-air secondary battery.

  Metal-air secondary batteries that use oxygen in the air as the positive electrode active material are known for their high energy density. In particular, a lithium-air secondary battery using metallic lithium (Li) as a negative electrode active material has been attracting attention because it has the largest theoretical weight energy density (charge capacity per unit weight).

As an electrolytic solution of the lithium-air secondary battery, there are a case where a non-aqueous solvent is used as an electrolytic solution and a case where an aqueous electrolytic solution is used.
When aqueous electrolyte is used, oxygen reduction reaction proceeds faster on the positive electrode side (air electrode side) during discharge than when non-aqueous electrolyte solution is used, and water oxidation reaction is possible during charging. It is advantageous for high output. However, metallic lithium has a problem because it has high reactivity with water. On the other hand, when an organic electrolytic solution is used, the growth of so-called lithium dendrite, in which metallic lithium precipitates and grows with charging, becomes a problem.

  Therefore, the surface of the metal lithium layer (metal lithium layer) as a negative electrode is covered with a water-impermeable (non-water-permeable) lithium ion conductor so that an aqueous electrolyte does not contact the metal lithium. ing. As the water-impermeable lithium ion conductor, for example, a glass ceramic (lithium ion conductive glass ceramic, hereinafter referred to as LATP) containing titanium (Ti) is used. However, when LATP comes into contact with metallic lithium, there is a problem that the titanium component of LATP is reduced and the lithium ion conductivity is lowered.

  Therefore, a device has been devised in which an inorganic solid electrolyte having lithium ion conductivity is inserted as a reaction preventing layer between the metallic lithium layer and the LATP layer. However, when a reaction prevention layer is inserted, there is a problem that resistance (interface resistance) at the interface between the metal lithium layer and the reaction prevention layer or at the interface between the reaction prevention layer and LATP increases. Also, during the discharge reaction, lithium ions move from the metal lithium layer toward the positive electrode, and the metal lithium layer contracts, creating voids at the interface between the metal lithium layer and the reaction preventing layer, reducing lithium ion conductivity. There is a problem that the discharge reaction is lowered (Patent Document 1).

  Therefore, a contrivance has been made to use a fluid electrolyte layer as the reaction preventing layer and to follow the volume change of the metal lithium layer accompanying charge / discharge while reducing the interface resistance. As the electrolyte layer having fluidity, for example, an organic electrolytic solution in which a lithium salt is dissolved in an organic solvent is used (Patent Document 2), and for the purpose of adjusting the fluidity of the organic electrolytic solution (decreasing fluidity), organic electrolysis In some cases, a gel electrolyte obtained by dissolving a polymer in a liquid is used (Patent Document 3). However, when an organic electrolyte is used, the growth of lithium dendrite becomes a problem.

  Therefore, an intrinsic polymer electrolyte in which a lithium salt is dispersed in a polymer such as polyethylene oxide (PEO) has been studied as a reaction prevention layer, and it is known that the growth of lithium dendrite can be suppressed by the crystallinity of the polymer. . However, since the intrinsic polymer electrolyte is solid at room temperature, it cannot follow the volume change of the metallic lithium layer accompanying charging / discharging as it is. Therefore, it is a problem because it is necessary to heat the lithium-air secondary battery to soften the intrinsic polymer electrolyte and to follow the volume change of metallic lithium (Patent Document 3).

  Therefore, in order to improve the followability to the volume change of the metallic lithium layer while reducing the interface resistance when using the intrinsic polymer electrolyte layer as the reaction preventing layer, a polymer is interposed between the intrinsic polymer electrolyte layer and the metallic lithium layer. A device has also been devised in which an organic electrolyte layer that does not dissolve is further arranged (Patent Document 4). However, the organic solvent in the organic electrolyte layer infiltrates into the polymer in the intrinsic polymer electrolyte layer, causing unevenness in the crystalline state in the intrinsic polymer electrolyte layer, resulting in a decrease in lithium dendride resistance, and lithium dendride locally Problems that occur and grow are known. In addition, there may be a problem that LATP is damaged by stress generated by local growth of lithium dendride.

  Therefore, by providing a conductive elastic layer formed of a conductive elastic material between the metal lithium layer and the organic electrolyte layer, the conductive elastic member functions as an electronic conduction auxiliary material, and lithium dendrite is generated. There has been proposed a technique for reducing the stress concentration on LATP as a solid electrolyte by using the elastic force of the conductive elastic member while suppressing the stress accompanying the growth of lithium dendrite. As the conductive elastic material, for example, an expanded metal made of titanium is used (Patent Document 5).

JP-T-2007-513464 Japanese Patent No. 5354580 Japanese Patent No. 5382573 Japanese Patent Laying-Open No. 2006-091856 JP 2017-091745 A

  However, when a conductive elastic layer is provided, lithium deposition during charging tends to occur on the positive electrode side (anti-reaction layer side) of the conductive elastic layer, while lithium dissolution (elution due to ionization) during discharge occurs. In some cases, it tends to occur on the negative electrode side (metal lithium layer side). That is, the metal lithium deposited at the time of charging cannot be eluted as lithium ions at the time of discharging, and the chargeable capacity (discharge capacity) cannot be increased.

  The present invention has been made in view of such a situation, and an object thereof is to provide an aqueous lithium-air secondary battery having a large charge capacity.

In order to achieve the above object, the characteristic configuration of the aqueous lithium-air secondary battery according to the present invention is as follows:
A metallic lithium layer;
A solid electrolyte layer;
A reaction preventing layer disposed between the metal lithium layer and the solid electrolyte layer;
An organic electrolyte layer disposed between the metal lithium layer and the reaction preventing layer;
A conductive porous layer disposed between the metal lithium layer and the organic electrolyte layer;
The said electroconductive porous layer exists in the point provided with the electroconductive layer which covers the porous base material formed with the insulator, and the inner surface of the said porous base material.

According to the said structure, a reaction prevention layer can be arrange | positioned between a metal lithium layer and a solid electrolyte layer, and a direct contact with metal lithium and a solid electrolyte layer can be avoided. And it can maintain, without reducing the lithium ion conductivity of a solid electrolyte layer. (* Since the solid electrolyte layer is not limited to include titanium, the relationship between avoidance of contact and prevention of titanium reduction is not shown)
Moreover, the followability with respect to the volume change of the metal lithium layer accompanying charging / discharging can be improved by the flow of organic electrolyte solution by arrange | positioning an organic electrolyte solution layer between a metal lithium layer and a reaction prevention layer. And the lithium ion electroconductivity between a metallic lithium layer and a reaction prevention layer can be improved.
In addition, by disposing the conductive porous layer between the metal lithium layer and the organic electrolyte layer, the conductive porous layer can function as an auxiliary material for electronic conduction and suppress the generation of lithium dendrite. it can. As a result, stress concentration on the solid electrolyte can be alleviated and direct contact between the lithium dendrite and the solid electrolyte can be avoided. And it can maintain, without reducing the lithium ion conductivity of a solid electrolyte layer.

Furthermore, since the conductive porous layer is a porous base material, the organic electrolyte is held inside, and the organic electrolyte can flow through the conductive porous layer, so that lithium is deposited during charging. Can be promoted on the negative electrode side (metal lithium layer side) of the conductive porous layer. As a result, a reduction in charge capacity can be avoided.
In addition, since the porous substrate is an insulator, only by changing or adjusting the thickness of the conductor layer covering the inner surface of the porous substrate, the electronic conductivity of the conductive porous layer, that is, the electric resistance ( The electrical resistivity) can be changed and adjusted. As a result, the electrical resistivity of the conductive porous layer can be easily adjusted to suppress the growth of lithium dendrite. And it can maintain, without reducing the lithium ion conductivity of a solid electrolyte layer.
Therefore, according to the above configuration, it is possible to provide an aqueous lithium-air secondary battery having a large charge capacity by avoiding a decrease in charge capacity and maintaining the lithium ion conductivity of the electrolyte layer without decreasing. Can do.

Here, the insulator means a material (substance) having an electrical resistivity of 10 8 Ωm or more.
Further, that the porous base material is an insulator means that the porous base material is substantially integrally formed of an insulator material, and the insulator material is made conductive. It does not include those formed integrally with the applied material.
The inner surface of the porous substrate refers to the surface of the pores of the porous substrate, and refers to the surface on which the porous substrate and the organic electrolyte can come into contact.
The conductor layer covering the inner surface of the porous substrate does not necessarily need to be one layer that continuously covers the entire inner surface of the porous substrate. Examples of the conductive layer include a case where the conductive layer is a discontinuous layer that covers a part of the inner surface of the porous base material in the form of a film as a layer, and these films are dotted in an island shape. Including cases. That is, the continuity of the film as a layer in the conductor layer is not limited.

Further features of the aqueous lithium-air secondary battery according to the present invention are as follows:
The porous substrate is a nonwoven fabric based on a polyamide resin as an insulator,
The conductor layer is a metal plating layer.

According to the said structure, the nonwoven fabric which made the polyamide resin a base material is equipped with elasticity, and can deform | transform easily with the stress accompanying the growth of lithium dendrite, and can receive the said stress by the deformation | transformation. As a result, stress concentration on the solid electrolyte can be relaxed. Polyamide resin is a polymer mainly composed of amide bonds, and includes nylon resin and aramid resin.
Moreover, by using a metal plating layer as the conductor layer, the thickness of the conductor layer and the continuity of the film as the conductor layer can be easily adjusted by changing the plating conditions. That is, the electrical resistivity of the conductive porous layer can be easily adjusted. Therefore, it is possible to provide an aqueous lithium-air secondary battery having a large charge capacity by appropriately adjusting the electrical resistivity of the conductive porous layer.

Further features of the aqueous lithium-air secondary battery according to the present invention are as follows:
The electrically conductive porous layer has an electrical resistivity of 3 Ωm or more and less than 70 Ωm.

According to the said structure, the growth of lithium dendrite can be suppressed especially well.
In addition, lithium deposition during charging can be particularly promoted on the negative electrode side (metal lithium layer side) of the conductive porous layer.
As a result, it is possible to provide a water-based lithium-air secondary battery having a large chargeable discharge capacity while avoiding a decrease in chargeable charge capacity.

Schematic cross-sectional view illustrating the basic configuration of an aqueous lithium-air secondary battery State explanatory drawing at the time of charge of the water based lithium-air secondary battery according to the present invention State explanatory diagram at the time of discharging of the water based lithium-air secondary battery according to the present invention State explanatory diagram at the time of charge of the conventional water-based lithium-air secondary battery State explanatory drawing at the time of discharge of the conventional water based lithium-air secondary battery Schematic configuration diagram of evaluation cell Figure showing the evaluation results of discharge characteristics Enlarged view of the surface of the nonwoven fabric (microscopic view) Enlarged view of non-woven fabric after plating in Example 1 (microscope observation view) Enlarged view of the nonwoven fabric after plating in Example 2 (microscopic observation view) Surface observation of conductive porous layer of Example 1 (after charging, working electrode side) Surface observation view of conductive porous layer of Example 1 (after charging, counter electrode side) Surface observation diagram of conductive porous layer of Example 1 (after discharge, working electrode side) Surface observation diagram of conductive porous layer of Example 1 (after discharge, counter electrode side) Surface observation diagram of conductive porous layer of Example 2 (after charging, working electrode side) Surface observation diagram of conductive porous layer of Example 2 (after charging, counter electrode side) Surface observation of conductive porous layer of Example 2 (after discharge, working electrode side) Surface observation drawing of conductive porous layer of Example 2 (after discharge, counter electrode side)

  A water based lithium-air secondary battery according to an embodiment of the present invention will be described with reference to FIGS.

[Schematic Configuration of Embodiment]
A schematic configuration of an aqueous lithium-air secondary battery according to an embodiment of the present invention will be described with reference to FIG.
An aqueous lithium-air secondary battery 100 according to an embodiment of the present invention includes a metal lithium layer 1, a solid electrolyte layer 5, a reaction prevention layer 4 disposed between the metal lithium layer 1 and the solid electrolyte layer 5, and The first organic electrolyte layer 31 (organic electrolyte layer 3) disposed between the metal lithium layer 1 and the reaction preventing layer 4 and the metal lithium layer 1 and the first organic electrolyte layer 31 are disposed. The conductive porous layer 2 includes a porous substrate 28 made of an insulator and a conductor layer 29 that covers the inner surface of the porous substrate 28. Yes.

The aqueous lithium-air secondary battery 100 according to the embodiment of the present invention further includes a second organic electrolytic solution layer 32, an aqueous electrolytic solution layer 6, and a positive electrode layer 7, and the positive electrode layer 7 from the metallic lithium layer 1 side. The metal lithium layer 1, the conductive porous layer 2, the first organic electrolyte layer 31, the reaction prevention layer 4, the second organic electrolyte layer 32, the reaction prevention layer 4, the solid electrolyte layer 5, The secondary battery cell is configured as an integral body in a state where the aqueous electrolyte layer 6 and the positive electrode layer 7 are layered in this order.
A negative electrode current collector (not shown) is connected to a surface 11 (see FIGS. 2 to 4) on the other side of the surface 12 facing the positive electrode layer 7 of the metallic lithium layer 1. A positive electrode current collector is connected to the other side of the surface facing the layer 1.
Air G is supplied to the positive electrode layer 7 as oxygen.
Moreover, although not shown in figure, this secondary battery cell is accommodated and used for a battery container.

[Detailed Description of Embodiment]
Hereinafter, the detailed configuration of the water based lithium-air secondary battery 100 will be described with reference to FIG.

The metal lithium layer 1 is a negative electrode of the water based lithium-air secondary battery 100.
The metallic lithium layer 1 is made of metallic lithium.
The metal lithium layer 1 is formed in a thin film shape or plate shape, and a thin film metal lithium foil is used in this embodiment. As the metal lithium layer 1, for example, a thin film or plate formed with a thickness of 30 μm to 300 μm is used.

The positive electrode layer 7 is a negative electrode of the water based lithium-air secondary battery 100.
As the positive electrode layer 7, one that can be normally used as the water based lithium-air secondary battery 100 can be used.
In the present embodiment, the positive electrode layer 7 includes a catalyst layer on the side facing the metal lithium layer 1 and a gas diffusion layer on the other side facing the metal lithium layer 1. As the catalyst layer, a layer formed by mixing platinum-supported carbon powder as a discharge catalyst and iridium dioxide powder as a charge catalyst is used. As the gas diffusion layer, a carbon paper subjected to water repellent treatment is used. That is, as the positive electrode layer 7 in this embodiment, a catalyst layer obtained by bonding a carbon paper to the catalyst layer can be used.

The aqueous electrolyte layer 6 is a lithium ion conductive aqueous electrolyte layer.
The aqueous electrolyte layer 6 can be a liquid electrolyte having high fluidity or a gel electrolyte solution to which a water-soluble polymer is added.
In this embodiment, the aqueous electrolyte layer 6 uses a layer in which an olefin separator is impregnated with an aqueous electrolyte. In addition, this aqueous electrolyte solution was prepared so that the density | concentration of lithium chloride might be 10 mol / L with respect to the saturated aqueous solution of lithium hydroxide.

The solid electrolyte layer 5 is a water-impermeable lithium ion conductor.
In the present embodiment, the solid electrolyte layer 5 uses a water-impermeable lithium ion conductive glass ceramic (LATP) as a water-impermeable lithium ion conductor.
As LATP, the following structure containing titanium is used. That is,
Li1 + X (M, Al, Ga) X (Ge1-yTiy) 2 -X (PO 4) 3
(Where X <0.8 and 0 <Y <1.0, and M is an element selected from the group consisting of Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb )
And / or
_{Li1 + X + yQxTi 2 -XSiyP 3} -yO 12
(Where 0 <X <0.4 and 0 <Y <0.6 are satisfied, and Q is Al or Ga)
What is represented by can be used suitably.

The reaction preventing layer 4 is an intrinsic polymer electrolyte layer in which a lithium salt is dispersed in a polymer, and is an electrolyte layer that does not contain an organic solvent.
The reaction preventing layer 4 is solid around room temperature (around 25 ° C.).
PEO, PPO, etc. can be used for the polymer used as the host (medium in which the lithium salt is dispersed) of the reaction preventing layer 4. Examples of the lithium salt include LiPF ₆ , LiClO ₄ , LiBF ₄ , LiTFSI (Li (CF ₃ SO ₂ ) ₂ N), Li (C ₂ F ₄ SO ₂ ) ₂ N, LiBOB (lithium bisoxalatoborate), and the like.
The reaction preventing layer 4 may include a PEO-LiTFSI electrolyte that is an intrinsic polymer electrolyte in which LiTFSI is dispersed in PEO that is a crystalline polymer as an intrinsic polymer. The PEO-LiTFSI electrolyte has a high mechanical strength and the highest lithium ion conductivity among the currently known intrinsic polymer electrolytes, and is preferable as the reaction preventing layer 4.

The organic electrolyte layer 3 is a liquid electrolyte layer using an organic solvent that does not dissolve the reaction preventing layer 4 as a solvent. As the organic electrolyte layer 3, an organic electrolyte using a chain ether solvent can be preferably used. Examples of the chain ether solvent include 1,2-dimethoxyethane (DME), 1,1-dimethoxypropane (DMP), 1,2-ethoxyethane (DEE), ethoxymethoxyethane (EME), and the like. .
In this embodiment, the organic electrolyte layer 3 is composed of the first organic electrolyte layer 31 on the metal lithium layer 1 side of the reaction preventing layer 4 and the second organic layer on the cathode layer 7 side of the reaction preventing layer 4. And an electrolytic solution layer 32.

When the first organic electrolyte layer 31 is used, the interface connectivity resulting from the surface roughness of the reaction preventing layer 4 and the metal lithium layer 1 can be improved.
That is, the liquid electrolyte solution of the first organic electrolyte layer 31 fills the irregularities on the surfaces of the metal lithium layer 1 and the reaction prevention layer 4, thereby reducing the interface resistance between the metal lithium layer 1 and the reaction prevention layer 4. And lithium ion conductivity can be improved.

When the second organic electrolyte layer 32 is used, interface connectivity due to the surface roughness of the reaction preventing layer 4 or the solid electrolyte layer 5 can be improved.
That is, the liquid electrolyte solution of the second organic electrolyte layer 32 fills the irregularities on the surfaces of the reaction preventing layer 4 and the solid electrolyte layer 5, thereby reducing the interface resistance between the reaction preventing layer 4 and the solid electrolyte layer 5. And lithium ion conductivity can be improved.

The conductive porous layer 2 is a layer of a porous base material capable of penetrating the electrolytic solution of the first organic electrolytic solution layer 31 therein. In addition, the conductive porous layer 2 is an electronic conductive material in which the porous base material 28 is an insulator, and the inner surface of the porous base material 28 is provided with a conductive layer 29 having electron conductivity. Layer.
The conductive porous layer 2 includes a porous substrate 28 made of an insulator and a conductor layer 29 that covers the inner surface of the porous substrate 28.

The porous substrate 28 is formed of a plastic insulator. As the insulator having plasticity, a material having elastic deformability is particularly preferable.
Here, the insulator means a material (substance) having an electrical resistivity of 10 8 Ωm or more.

The porous base material 28 is a base material portion that is substantially integrally formed of an insulating material and serves as a skeleton of the conductive porous layer 2.
As the insulator having elastic deformation that forms the porous substrate 28, a resin is preferable. As the resin for forming the conductive porous layer 2, a resin such as an olefin resin (polyolefin) or an amide resin (polyamide) can be used, and an amide resin is particularly preferable.
As the amide resin, an aramid resin or a nylon resin can be used, and a nylon resin is particularly preferable.

The porous base material 28 is a base material having pores that can be held by allowing the electrolyte solution of the first organic electrolyte layer 31 to permeate therein.
As the porous base material 28, for example, a sponge-like foam that is foamed inside the base material or a felt-like non-woven fabric formed by entwining fibers can be used.

The conductor layer 29 is a layer made of a material having electronic conductivity formed on the inner surface of the porous substrate 28.
Here, the inner surface of the porous substrate 28 refers to the surface of the pores of the porous substrate 28 and refers to the surface on which the porous substrate 28 and the organic electrolyte solution can come into contact.

  The material for forming the conductor layer 29 is a material having electronic conductivity, such as a metal, a carbon material, and a resin compound obtained by kneading the metal or the carbon material, and an organic solvent of the electrolyte solution of the organic electrolyte layer 3 Use those that are not dissolved, plasticized, or swollen.

  The conductor layer 29 is not necessarily an integral layer that continuously covers the entire inner surface of the porous substrate 28. The conductor layer 29 includes, for example, a discontinuous layer that covers a part of the inner surface of the porous substrate 28 in the form of a film as a layer, and these films are dotted like islands. Including the case where it exists. That is, the continuity of the film as a layer in the conductor layer 29 is not limited.

  In the present embodiment, as the porous base material 28 of the conductive porous layer 2, a non-woven fabric obtained by thermally bonding a complex entanglement of aramid resin fibers 25 is used. The bonded portion of the heat-bonded fibers 25 of the porous base material 28 that is a nonwoven fabric is heat-bonded to each other and is integrally formed as the porous base material 28.

The conductive layer 29 of the conductive porous layer 2 is made of nickel provided on the inner surface of the porous base material 28 that is a non-woven fabric, that is, on the surface of the fiber 25 that forms the porous base material 28 that is a non-woven fabric. A plating layer is used.
The nickel plating layer is formed by, for example, an electroless nickel plating method. Specifically, the porous base material 28 as a nonwoven fabric is formed by dipping in an electroless nickel plating solution. The plating layer formed by the electroless nickel plating method is formed on the surface portion of the fiber 25 in the porous substrate 28 through which the electroless nickel plating solution penetrates and contacts the electroless nickel plating solution.

The electrical resistivity of the conductive porous layer 2 is preferably 3 Ωm or more and less than 70 Ωm, and particularly preferably about 5 Ωm to 50 Ωm.
As described above, when the conductive porous layer 2 is formed of the porous base material 28 and the conductor layer 29 and is adjusted to the above electric resistivity range, the dissolution and precipitation of lithium at the time of charging and discharging is efficiently performed. Yes.

  Specifically, as shown in FIG. 2, lithium precipitates d at the time of charging can be uniformly generated over the entire surface of the metallic lithium layer 1 and the conductive porous layer 2. Further, at the time of discharging, as shown in FIG. 3, ionization (dissolution) of lithium in the metal lithium layer 1 and lithium precipitate d deposited on the surface of the conductive porous layer 2 is caused to occur in the metal lithium layer 1. It can be performed uniformly over the surface and the entire surface of the conductive porous layer 2.

  If the electrical resistivity of the conductive porous layer 2 is too small, the conductive porous layer 2 is more than the lithium ions that move the electrolyte solution of the first organic electrolyte layer 31 soaked in the conductive porous layer 2. The electrons that move are more easily moved.

  Therefore, the electrons supplied from the metal lithium layer 1 during charging are supplied with priority to the conductive porous layer 2. Then, the electrons supplied to the conductive porous layer 2 are supplied to the electrolyte solution of the first organic electrolyte layer 31 from the vicinity of the surface 22 of the conductive porous layer 2 facing the positive electrode layer 7 side.

Therefore, as shown in FIG. 4, the lithium ions in the first organic electrolyte layer 31 are preferentially deposited on the surface 22 of the conductive porous layer 2 to become a precipitate d. A part of the lithium deposited on the surface 22 grows as dendrite, and the capacity and cycle characteristics of the aqueous lithium-air secondary battery 100 are reduced.
On the other hand, at the time of discharge, electrons are taken from the metal lithium layer 1 and lithium ions are preferentially eluted from the surface 12 of the metal lithium layer 1 facing the positive electrode layer 7. Further, lithium ions are eluted from the vicinity of the surface 21 of the conductive porous layer 2 on the side close to the metallic lithium layer 1.

Therefore, when charging and discharging are repeated, the metal lithium layer 1 is selectively dissolved (eluting), and the surface 12 of the metal lithium layer 1 is eroded as shown in FIG. Further, in the vicinity of the surface 22 of the conductive porous layer 2, lithium dentite is likely to grow.
Since the surface 12 of the metal lithium layer 1 is eroded, a gap e is generated between the metal lithium layer 1 and the conductive porous layer 2. Due to the gap e, the number of electrical contacts between the metallic lithium layer 1 and the conductive porous layer 2 is reduced, and the conductivity of electrons between the metallic lithium layer 1 and the conductive porous layer 2 is further increased. descend. As a result, the erosion of the metal lithium layer 1 further proceeds, and the capacity and cycle characteristics of the water based lithium-air secondary battery 100 are reduced.

[Explanation of Examples]
Hereinafter, specific examples of the evaluation of the water based lithium-air secondary battery 100 according to the present application will be described.
In the following examples and comparative examples, instead of directly evaluating the aqueous lithium-air secondary battery 100, an evaluation cell 90 corresponding to the characteristics of the aqueous lithium-air secondary battery 100 is created and used for evaluation.

[Example 1]
[Creation of intrinsic polymer electrolyte]
For the reaction prevention layer 4, an electrolyte membrane of PEO-LiTFSI was used.
First, 55 g of acetonitrile (made by Wako Pure Chemicals, special grade) solvent is weighed. Then, 3.67 g of PEO (SIGMA-ALDRICH, MW: 600,000) as a polymer component and 1.33 g of LiTFSI (manufactured by SIGMA-ALDRICH) are charged as an electrolyte component in the solvent. And this is stirred well at room temperature and dissolved completely to obtain a solution.

Next, 0.56 g of barium titanate powder (manufactured by Alfa Aesar) is put into this solution, stirred, and well dispersed to obtain a dispersion solution.
Next, this dispersion solution is poured directly into a silicon casting container in which a polyamide nonwoven fabric (manufactured by Japan Vilene Co., Ltd .: FT-765, thickness: 150 μm) is placed in advance. And this dispersion solution was vacuum-dried at 120 degreeC for 3 hours, acetonitrile was removed completely, and the nonwoven fabric impregnation PEO-LiTFSI electrolyte (thickness: 150 micrometers) by which the PEO-LiTFSI electrolyte was filled in the pore of the nonwoven fabric. ) Is cut out into a circle having a diameter of 2.0 cm and used as the reaction preventing layer 4.

[Adjustment of organic electrolyte]
A chain ether organic electrolyte was used as the organic electrolyte 39 corresponding to the electrolyte of the organic electrolyte layer 3.
In this example, 1 mol / L LiTFSI DME electrolytic solution (battery grade manufactured by Kishida Chemical Co., Ltd.) is used as the organic electrolytic solution layer 3 as it is as the chain ether-based organic electrolytic solution.

(Creation of conductive porous layer)
As the conductive porous layer 2, a polyamide non-woven fabric (manufactured by Nippon Vilene Co., Ltd., FT-765, thickness 150 μm) is used as the porous base material 28. 29 was used.
First, the porous substrate 28 that has been subjected to alkali cleaning is immersed in a Pink Schummer solution (manufactured by Nippon Kanisen Co., Ltd.) diluted 10 times at room temperature (about 25 ° C.) for 3 to 10 minutes and then taken out.
Next, it is immersed in a Red Schumater solution diluted by 5 times (manufactured by Nippon Kanisen Co., Ltd.) at room temperature (about 25 ° C.) for 3 to 10 minutes and taken out.
Then, this was immersed in an electroless nickel plating solution diluted by a factor of 5 (manufactured by Nippon Kanisen Co., Ltd .: SE-680) at a plating solution temperature of 28 ° C. for 30 seconds, taken out, and nickel plated. A conductive nonwoven fabric (one embodiment of the metal plating layer) is obtained, cut into a circle having a diameter of 2.0 cm, and used as the conductive porous layer 2.
In the electroless nickel plating method, it is known that when a base material is immersed in an electroless nickel plating solution for a long time, the thickness of the plating layer formed on the surface of the base material increases.

A microscopic observation of the nonwoven fabric before nickel plating in Example 1 is shown in FIG.
Moreover, the microscopic observation figure of the nonwoven fabric (conductive porous layer 2) after the nickel plating of this Example 1 is shown in FIG.

  Table 1 shows the measurement results of the plating amount, electrical resistivity R, and lithium ion resistance RL of the conductive porous layer 2 of Example 1. In addition, the lithium ion resistance RL in Table 1 shows a value when the conductive porous layer 2 is impregnated with the organic electrolyte layer 3.

[Production of charge / discharge evaluation cell]
An HS flat cell (manufactured by Hosen Co., Ltd.) was used as the evaluation cell 90 for the purpose of charge / discharge evaluation. FIG. 6 shows a schematic configuration of the evaluation cell 90.
As a working electrode 15 for evaluating the efficiency, a copper foil (made by Nilaco Co., Ltd.) having a thickness of 50 μm serving as a negative electrode current collector, and a metal lithium foil having a thickness of 200 μm (Honjo Metal Co., Ltd.) as a counter electrode 14 supplying lithium metal Company).
The working electrode 15 and the counter electrode 14 are cut out into a circle having a diameter of 1.5 cm.

  In order to prevent direct contact between the working electrode 15 and the counter electrode 14, the reaction preventing layer 4 is disposed between the working electrode 15 and the counter electrode 14. Furthermore, the conductive porous layer 2 is disposed between the working electrode 15 and the reaction preventing layer 4 in order to promote the precipitation of lithium near the working electrode 15.

Then, as illustrated in FIG. 6, a stacked body 99 in which the working electrode 15, the conductive porous layer 2, the reaction preventing layer 4, and the counter electrode 14 are stacked in this order from the bottom is accommodated in a container 91 of the evaluation cell 90.
The container 91 includes an upper container 91a and a lower container 91b when the upper container 91a serving as a lid, a lower container 91b on which the evaluation cell 90 is placed, and the lower container 91b are closed with the upper container 91a closed. О ring 91c is provided. The laminated body 99 is accommodated in the container 91 in a state in which the spring 95 pushes the laminated body 99 from the back side of the counter electrode 14 toward the lower container 91b.
After closing the lower container 91b with the upper container 91a, the container 91 is filled with the organic electrolyte layer 3. When the container 91 is filled with the organic electrolyte 39, the pores of the conductive porous layer 2 are filled with the organic electrolyte 39.

The counter electrode 14 and the working electrode 15 are connected to a charging / discharging evaluation device 96 (potenti / galvanostat, manufactured by BioLogic: VMP3) via a container 91 with a wire 93 and a wire 94, respectively.
Then, the container 91 is closed in a state where the laminated body 99 is pressed by the spring 95 from the back side of the counter electrode 14 with a predetermined load (for example, 49.03 N as the predetermined load).

In this example, lithium deposited on the working electrode 15 corresponds to the metal lithium layer 1 of the present embodiment.
In this embodiment, the counter electrode 14 corresponds to the solid electrolyte layer 5, the aqueous electrolyte layer 6, and the positive electrode layer 7.
In this embodiment, the organic electrolyte 39 corresponds to the organic electrolyte layer 3.
Although not shown in FIG. 6, the organic electrolytic solution 39 penetrates into the pores of the conductive porous layer 2. Further, the organic electrolyte 39 penetrates into the interface portion between the conductive porous layer 2 and the reaction preventing layer 4 to substantially form the first organic electrolyte layer 31. Similarly, the organic electrolytic solution 39 permeates between the reaction preventing layer 4 and the counter electrode 14 to substantially form the second organic electrolytic solution layer 32.

[Charge / discharge evaluation]
The evaluation cell 90 is left still in a thermostat kept at 28 ° C., and a charge / discharge evaluation apparatus 96 is used to perform a charging operation of +0.2 mA / cm ² × 100 Hr (20 mAh / cm ² ). After metal lithium was deposited on the conductive porous layer 2, a discharge operation (footstep potential: -0.5 V) of 0.4 mA / cm2 × 50 Hr was performed.
The evaluation results of the discharge characteristics of this evaluation cell 90 are shown in FIG. Below, the evaluation cell 90 of Example 1 is called cell A1.
Moreover, the surface observation figure of the electroconductive porous layer 2 before and behind charging / discharging of this Example 1 is shown in FIGS.
7 represents the discharge capacity C (mAh / cm ² ) per unit area, and the vertical axis in FIG. 7 represents the voltage E (V) during discharge.

  Here, the discharge capacity means the amount of electric power that can be discharged out of the electric power stored in the secondary battery, and corresponds to the charge capacity when normally used as a so-called secondary battery. That is, the discharge capacity means the charge capacity that can be taken out from the secondary battery, and the larger this value, the better the secondary battery.

[Example 2]
In the evaluation cell 90 of Example 2, the dipping conditions in the electroless nickel plating solution in the process of forming the conductive porous layer 2 of Example 1 were changed, and this was plated at a temperature of 28 ° C. plating solution. It is the same except that the time is 90 seconds.
The microscope observation figure of the nonwoven fabric (conductive porous layer 2) after the nickel plating of this Example 2 is shown in FIG.
As in Example 1, the evaluation results such as the electrical resistivity R of the conductive porous layer 2 are shown in Table 1, and the evaluation results of the discharge characteristics of the evaluation cell 90 are shown in FIG. Hereinafter, the evaluation cell 90 of Example 2 is referred to as a cell A2.
Moreover, the surface observation figure of the electroconductive porous layer 2 before and behind charging / discharging of this Example 2 is shown in FIGS.

[Comparative Example 1]
Comparative Example 1 is the same as Example 1 except that the nonwoven fabric of the porous substrate 28 is used as it is instead of the conductive porous layer 2 of Example 1.
As in Example 1, the evaluation results of the discharge characteristics of the evaluation cell 90 are shown in FIG. Hereinafter, the evaluation cell 90 of Comparative Example 1 is referred to as a cell B1.

[Comparative Example 2]
Comparative Example 2 was carried out except that a titanium expanded metal having a thickness of 150 μm (manufactured by Nikken Las Industrial Co., Ltd .: No. NK0713S) was used as the conductive elastic layer instead of the conductive porous layer 2 of Example 1. Same as Example 1.
As in Example 1, the evaluation results are shown in Table 1 for the electrical resistivity R of the expanded metal made of titanium, and the evaluation results of the discharge characteristics of the evaluation cell 90 are shown in FIG. Hereinafter, the evaluation cell 90 of Comparative Example 2 is referred to as a cell B2.

〔Evaluation results〕
[Table 1]

According to FIG. 7, a predetermined amount of charge with respect to (20mAh / cm ^2), in order from the discharge capacity is large, the cell A2 (4.75mAh / ^cm 2), the cell A1 (1.99mAh / ^cm 2), Cell B2 (1.03 mAh / cm ² ), cell B1 (0.16 mAh / cm ² ), cell A1 and cell A2 having the configuration of the present invention, cell B1 having the configuration of the present invention, Compared with the cell B2, it has a relatively large discharge capacity. Therefore, according to this invention, it turns out that a lithium-air secondary battery with a large charge capacity can be provided.

Since the thickness of the nickel plating layer (conductor layer 29) of the conductive porous layer 2 of Example 2 is immersed in the electroless nickel plating solution for a longer time than the plating time of Example 1, the thickness of Example 1 It is considered that the thickness is relatively larger than the thickness of the nickel plating layer (conductor layer 29) of the conductive porous layer 2. Therefore, as shown in Table 1, the electrical resistivity of the conductive porous layer 2 of Example 2 is relatively smaller than the electrical resistivity of the conductive porous layer 2 of Example 1.
That is, the conductive porous layer 2 includes a porous substrate 28 and a conductor layer 29 that covers the inner surface of the porous substrate 28. When the thickness of the conductor layer 29 is changed, the conductive porous layer 2 It can be seen that the electrical resistivity of layer 2 can be changed. Specifically, when the thickness of the conductive layer 29 is increased, the electrical resistivity of the conductive porous layer 2 can be reduced, and when the thickness of the conductive layer 29 is decreased, the electrical conductivity of the conductive porous layer 2 is reduced. The resistivity can be increased.

Moreover, as shown in Table 1, the expanded metal made of titanium of Comparative Example 2 has the lowest electrical resistivity.
Although the measurement result of the electrical resistivity of the nonwoven fabric of the comparative example 1 is not shown, since this nonwoven fabric uses the aramid resin which is an insulator, it is thought that electrical resistivity is the highest.

When viewed individually, the discharge potential of the cell B1 using the non-woven fabric as it is instead of the conductive porous layer 2 has decreased from the beginning of discharge. Further, the discharge capacity of the cell B1 is the smallest.
The degree of decrease in the discharge potential of the cell B1 is as follows: the cell A1 using the conductive porous layer 2 having conductivity, the cell A2, and the cell B2 using titanium expanded metal instead of the conductive porous layer 2 It is significantly larger than
Therefore, in order to keep the discharge potential at a high value for a long time (to obtain a sufficient discharge capacity), it is considered that the conductive porous layer 2 needs a certain degree of conductivity.

On the other hand, compared with the discharge capacity of the cell B2 using the expanded metal made of titanium having the lowest electrical resistivity, the discharge capacities of the cells A1 and A2 using the conductive porous layer 2 having conductivity are significantly increased. ing.
Therefore, in order to obtain a sufficient discharge capacity, it is considered that the conductive porous layer 2 needs an appropriate resistance while having conductivity.

According to the comparison with the cell A1 and the cell A2 using the conductive porous layer 2 having conductivity, the discharge capacity of the cell A2 having a relatively small electric resistivity is significantly increased.
Therefore, it is considered that the electric resistivity value of the conductive porous layer 2 used in the cell A2 is a more preferable electric resistivity value at least in terms of the initial discharge capacity in the charge / discharge cycle.
It can also be seen that when the conductor layer 29 covering the inner surface of the porous substrate 28 is provided and the thickness of the conductor layer 29 is changed, the discharge capacity of the aqueous lithium-air secondary battery 100 changes.

If a conductive elastic layer such as a titanium expanded metal is used instead of the conductive porous layer 2, lithium elution is likely to occur at the working electrode 15 side (negative electrode side) and is deposited during charging. It is known that the lithium metal cannot be eluted as lithium ions during discharge, and the charge capacity cannot be increased.
However, looking at the surface observation views of the conductive porous layer 2 before and after charging / discharging (see FIGS. 11 to 18), the precipitation and dissolution states of lithium in the conductive porous layer 2 in both the cells A1 and A2 are as follows. It can be seen that it is uniform on the counter electrode 14 side and the working electrode 15 side. Therefore, by using the conductive porous layer 2 having a certain high electrical resistivity, the lithium deposition and dissolution state with respect to the conductive porous layer 2 before and after charge / discharge becomes uniform, and the discharge capacity increases. Conceivable. In other words, it is considered that lithium metal can be deposited (generated and deposited) in a portion that is easily used during discharge by using the conductive porous layer 2 having a certain high electrical resistivity.

  Moreover, according to the surface observation figure (refer FIG. 11 to FIG. 18) of the electroconductive porous layer 2 before and behind charging / discharging, it turns out that the remarkable lithium dendride growth has not arisen. Therefore, it is considered that the growth of lithium dendriide can be suppressed by using the conductive porous layer 2 having a somewhat high electrical resistivity.

According to the comparison between the cell A1 and the cell A2, it can be seen that in the cell A2 where the value of the electrical resistivity of the conductive porous layer 2 is small, lithium deposition on the counter electrode side after charging is relatively large. From this point, when the value of the electrical resistivity of the conductive porous layer 2 is larger than that in the case of the cell A2, the state of precipitation and dissolution of lithium with respect to the conductive porous layer 2 before and after charging and discharging becomes more uniform. This is considered to contribute to the improvement of the cycle characteristics of the secondary battery.
Accordingly, the discharge capacity of the cell A2 is greatly superior in terms of the initial discharge capacity in the charge / discharge cycle of the secondary battery, but the cell A1 may be superior to the cell A2 in terms of the cycle characteristics of the secondary battery. It is thought that there is.

  From the above results, it is considered that there is a preferable range for the electrical resistivity of the conductive porous layer 2. Specifically, the electrical resistivity of the conductive porous layer 2 needs to be 3 Ωm or more and less than 70 Ωm. Furthermore, it can be considered that the electrical resistivity of the conductive porous layer 2 is preferably 5 Ωm or more and less than 65 Ωm. Considering that the discharge capacity of the cell A2 is particularly outstanding and excellent (the discharge capacity is large), in order to increase the initial discharge capacity of the charge / discharge cycle, the electrical resistivity of the conductive porous layer 2 is: It is considered to be particularly preferable that it is 5 Ωm or more and less than 10 Ωm.

  As described above, the present invention can provide a lithium-air secondary battery having a large charge capacity.

[Another embodiment]
(1) Although the case where a nonwoven fabric is used as the porous substrate 28 has been exemplified in the above embodiment, a sponge-like foam may be used as the porous substrate 28 instead of using the nonwoven fabric. The nonwoven fabric is only an example of the porous substrate 28.

(2) In the above embodiment, the case where a nickel plating layer is used as the conductor layer 29 is exemplified. However, instead of using the plating layer, for example, a metal deposition film may be used as the porous substrate 28. The plating layer is only an example of the conductor layer 29.

(3) In the above embodiment, the case where a polyamide resin is used as the insulator forming the nonwoven fabric is exemplified. However, instead of using the polyamide resin, other electrochemically stable resins such as an olefin resin may be used. Good. Polyamide resin is only an example of an insulator.

  Note that the configurations disclosed in the above-described embodiments (including other embodiments, the same applies hereinafter) can be applied in combination with the configurations disclosed in the other embodiments as long as no contradiction arises. The embodiment disclosed in this specification is an exemplification, and the embodiment of the present invention is not limited to this. The embodiment can be appropriately modified without departing from the object of the present invention.

  The present invention can be usefully used for an aqueous lithium-air secondary battery.

1: Metal lithium layer 2: Conductive porous layer 3: Organic electrolyte layer 4: Reaction prevention layer 5: Solid electrolyte layer 28: Porous substrate 29: Conductor layer 31: First organic electrolyte layer (organic electrolysis Liquid layer)
32: Second organic electrolyte layer (organic electrolyte layer)
39: Organic electrolyte (organic electrolyte layer)
100: Water-based lithium-air secondary battery

Claims (3)

A metallic lithium layer;
A solid electrolyte layer;
A reaction preventing layer disposed between the metal lithium layer and the solid electrolyte layer;
An organic electrolyte layer disposed between the metal lithium layer and the reaction preventing layer;
A conductive porous layer disposed between the metal lithium layer and the organic electrolyte layer;
The conductive porous layer is an aqueous lithium-air secondary battery including a porous base material formed of an insulator and a conductor layer covering an inner surface of the porous base material. The porous substrate is a nonwoven fabric based on a polyamide resin as an insulator,
The water based lithium-air secondary battery according to claim 1, wherein the conductor layer is a metal plating layer.   The water based lithium-air secondary battery according to claim 1 or 2, wherein an electrical resistivity of the conductive porous layer is 3 Ωm or more and less than 70 Ωm.