JP5453055B2 - Lithium air battery - Google Patents

Description

  The present invention relates to a lithium air battery, and more particularly, to a positive electrode of a lithium air battery using a solid electrolyte.

  An air battery having a positive electrode using oxygen in the air as an active material can charge and discharge the battery by oxidizing and reducing oxygen at the positive electrode. For example, a positive electrode that oxidizes and reduces oxygen containing lithium peroxide or lithium oxide, a negative electrode that contains a carbonaceous material that occludes and releases lithium ions, an electrolyte layer that is interposed between the positive electrode and the negative electrode, and stores these There has been proposed an air lithium secondary battery comprising a container having air holes opened therein and an oxygen permeable membrane disposed between the opened surface and the positive electrode ( For example, Patent Document 1). Here, an electrolyte layer to which an organic solvent is added is used, and the positive electrode is formed by rolling a film containing a solid electrolyte, a carbonaceous material, a lithium peroxide, and a binder into a current collector, and oxygen. As the permeable membrane, a water-repellent porous membrane that permeates oxygen in the air and prevents water from entering is used. However, since the positive electrode is porous, the water repellency is insufficient and water that has passed through the oxygen permeable membrane may enter the electrolyte as it is and deactivate the negative electrode.

  For this reason, a non-aqueous metal-air battery has been proposed in which oxygen in the atmosphere is supplied from an oxygen pump (for example, Patent Document 2). However, attaching such functional parts complicates the battery and increases the manufacturing cost.

  Meanwhile, a first cell including a first positive electrode, a first negative electrode, and a first electrolyte that generate / decompose and discharge / charge a metal oxide or metal peroxide, and a metal oxide or metal peroxide generated / A second positive electrode, a second negative electrode, and a second electrolyte, which are decomposed and discharged / charged, have an oxygen permeable portion between the first positive electrode and the second positive electrode, and charge / discharge the first cell / second cell. An air battery is also disclosed that is configured to be able to supply oxygen gas to be used for the oxygen permeation section (for example, Patent Document 3). However, since the positive electrode of the cell disposed outside is eventually exposed to the atmosphere, it cannot sufficiently prevent the negative electrode from being deactivated by water in the atmosphere.

Further, in order to enable charging at a low voltage and discharging at a high voltage, a catalyst for a positive electrode used for a positive electrode of a lithium-air secondary battery having a negative electrode made of a non-aqueous electrolyte and metal Li, There has been proposed one containing a metal oxide containing at least CeO ₂ having the ability to absorb and release (for example, Patent Document 4). With such a catalyst, even if the overvoltage is reduced and discharging is performed more efficiently at the positive electrode, the oxygen of the positive electrode active material and the electrolyte of the positive electrode are not in contact with the catalyst in the vicinity of the current collector. The ability is not fully demonstrated.

Japanese Patent Laid-Open No. 2005-166585 JP 2009-230981 A JP 2008-91248 A JP 2008-1112724 A

  That is, in the positive electrode of an air battery containing an organic electrolytic solution or the like, water in the atmosphere may pass through the porous positive electrode and dissolve in the electrolytic solution, leading to the negative electrode and deactivating the negative electrode. It is difficult to use for a long time, and mainly stays in dry air.

  Thus, an air battery capable of preventing the permeation of water can be configured by using an inorganic solid electrolyte. In this way, for example, even if the positive electrode contains an aqueous solution that serves as an electrolyte, the deterioration of the negative electrode can be effectively prevented. Moreover, when an aqueous solution is contained or brought into contact with the positive electrode, a reaction promoting effect by the liquid is expected, and a high current density can be achieved. Furthermore, if a catalyst compatible with the aqueous solution is used in combination, the negative electrode can be prevented from being deteriorated and used for a long period of time, and a higher current density can be expected.

  On the other hand, batteries using such inorganic solid electrolytes are expected to be used at high temperatures. Particularly in a battery using an organic electrolyte, use at a high temperature is not always preferable. Further, when an aqueous solution is contained in or brought into contact with the positive electrode, a reaction promoting effect by the liquid as described above can be expected, but use at a high temperature may cause loss of water from the aqueous solution due to evaporation. Therefore, it is desired that the air battery using the inorganic solid electrolyte as described above is a non-aqueous air battery that does not contain or contact the aqueous solution with the positive electrode.

  Therefore, it is more preferable to construct an air battery that does not contain the aqueous solution as described above in the positive electrode, and to form a positive electrode structure that can promote the electrode reaction. In other words, the catalyst and the first solid electrolyte layer can be included and combined with the negative electrode capable of occluding / releasing lithium ions via the second solid electrolyte layer. The positive electrode structure concerning this can be provided.

Hereinafter, what can be specifically provided in the present invention will be described.
(1) A negative electrode having the ability to occlude and release lithium ions or the ability to release lithium ions, a catalyst for at least oxygen reduction, a catalyst for oxygen reduction and generation, and a first solid electrolyte layer There can be provided a lithium-air battery including a positive electrode including a negative electrode and a second solid electrolyte layer disposed between the negative electrode and the positive electrode.

  Here, the first and second solid electrolyte layers may each be a layer containing the same or different solid electrolyte. Further, the first and second solid electrolyte layers may not be physically separated. That is, it may include continuously changing from the first solid electrolyte layer to the second solid electrolyte layer. Such a solid electrolyte layer may be a uniform compound for each of the first and second solid electrolyte layers or the whole of the first and second solid electrolyte layers, and various compounds may be mixed. It may also be a mixture. The thickness of the first solid electrolyte layer may be 10 to 2 mm, for example, and may be particularly thin. For example, in the bulk of the solid electrolyte, the depth from the surface that can contact oxygen molecules as the active material to the point where the electrode reaction as the positive electrode can occur may be used as the positive electrode. In this case, the portion deeper than that belongs to the second solid electrolyte layer and functions as an electrolyte disposed between the negative electrode and the positive electrode of the air battery. Here, for example, LiN, LISICON, a substance having a perovskite structure, a substance having a NASICON type structure, or a sulfide can be used as the solid electrolyte. It is preferable that these solid electrolyte layers can be handled as one bulk body. The solid electrolyte layer may include a laminate in which thin layers are laminated. Further, the catalyst is not particularly limited, and may be a small piece, particle, or powder of a metal such as platinum or nickel, or may be a green compact, sintered body, particle, or powder of an inorganic compound. Good. In particular, a perovskite-type inorganic compound may be included. There are also phthalocyanine-based catalysts. Such a lithium-air battery may be a so-called primary battery or a secondary battery. The second solid electrolyte layer may be pressed and held between the negative electrode and the positive electrode with a predetermined force, and may be formed integrally with the negative electrode and / or the positive electrode. The first and / or second electrolyte layers are preferably substantially impermeable to water vapor and / or water.

(2) The lithium air battery according to (1), wherein the first solid electrolyte layer has an ionic conductivity of 1 × 10 ⁻⁵ S / cm or more at 25 ° C.

The first solid electrolyte layer may have an ionic conductivity of 1 × 10 ⁻⁵ S / cm or more in the atmosphere at 25 ° C., more preferably 5 × 10 ⁻⁵ S / cm or more, Preferably, it may be 8 × 10 ⁻⁵ S / cm or more. In consideration of application in a wider temperature range, the ion conductivity is preferably 1 × 10 ⁻⁵ S / cm or more in the range of −10 ° C. or more and the upper limit temperature that can actually be used.

(3) In the positive electrode, the shape of the positive electrode is formed by the first solid electrolyte layer, and the catalyst is attached to the surface of the positive electrode shape that can be exposed to oxygen. ) Or (2) can be provided.

(4) The lithium-air battery according to (3) above, wherein the surface area of the shape of the positive electrode that can be exposed to oxygen is at least three times the area of the apparent surface.

  Here, the apparent surface area can mean an area along a reference surface of a surface defined as an electrode surface described later. For example, if the shape of the surface of the positive electrode that can react with oxygen (for example, a plane) is square, the square of one side is the apparent area, and if it is circular, the radius is squared. The apparent area is multiplied by the circumference. The surface area of the shape of the positive electrode can be determined, for example, by covering the other surface and measuring the surface area by BET. Further, if there is a standard surface whose surface is substantially flat due to BET adsorption, the ratio of the surface area of the shape of the positive electrode can also be obtained based on the standard surface.

(5) The lithium-air battery according to (3), wherein the surface of the positive electrode shape that can be exposed to oxygen includes at least 2 holes / cm ² having an opening having a maximum width of 30 nm to 3 mm. Can be provided.

(6) The positive electrode-shaped surface that can be exposed to oxygen is a projection having a maximum cross-sectional width of 30 nm or more and 3 mm or less, and a height from the reference surface of 10 μm or more and 500 μm or less. / cm ² comprise able to provide a lithium air battery according to (3), wherein the.

  Here, the reference surface is the surface of the first electrolyte layer constituting the positive electrode, and constitutes the main surface on the outer surface of the cell composed of the negative electrode / second electrolyte layer / positive electrode (first electrolyte layer). Can mean what to do. More specifically, the surface on the atmosphere side of the positive electrode that can contribute to the electrode reaction is defined as the electrode surface. Next, a plane or a curved surface that follows the defined electrode surface is defined as a rough surface or a rough curved surface. When the approximate surface or approximate curved surface is pressed against the electrode surface, the electrode surface is uniformly adhered and covered. Then, the distance from the rough surface or the rough curved surface to the actual electrode surface is mapped on the electrode surface. At this time, the reference surface can be obtained by smoothly connecting the most frequent distances. If the electrode surface can be defined as a substantially flat surface, the reference surface is a flat reference plane, and the distance from the reference plane to the actual electrode surface when this reference plane is pressed against the electrode surface is the same. The reference surface can be obtained by mapping on the reference plane and connecting the most frequent distance to the plane. For example, when there is a surface profile as shown in FIG. 10, the frequency distribution can be measured, and a place with high frequency can be used as a reference plane. Such a profile can be performed by a stylus type three-dimensional measuring apparatus. For example, in the surface profile measured by running a plurality of scanning lines with a stylus type three-dimensional measuring apparatus, the surface shape and long-period undulations in each scanning line are removed (for example, if the electrode surface is a plane, the surface is inclined) The shape is defined by correction, and the waviness having a period of, for example, 1/10 of the reference length that defines the electrode surface (for example, the short side when the electrode surface is rectangular) is removed by Fourier analysis or the like. The reference surface is obtained from the frequency distribution. At the same time, an approximate surface including a swell based on such a long period is obtained, and the apparent area is obtained.

  The holes and protrusions can also extend substantially perpendicular to the reference surface. When these holes and protrusions are cut at the reference surface, the cross section may exhibit a closed line shape. This cross-sectional shape substantially matches the opening shape from the above assumption. The maximum width of the closed line shape is referred to as the maximum width of the hole and the protrusion, respectively. For example, if the closed line shape is a perfect circle, the maximum width is a diameter, and if it is an ellipse, the maximum width is a long diameter. Here, these holes and protrusions can also be handled approximately as flat bottoms and tops. When dealing with the depth of the hole and the height of the protrusion, it is preferable to perform a flat approximation.

The positive electrode-shaped surface may include the electrode surface described above. The positive electrode-shaped surface is preferably provided with at least 2 holes / cm ² having openings having a maximum width of 30 nm or more and 3 mm or less, more preferably 5 holes / cm ² or more, and further preferably 10 holes / cm ^2. That's it. Naturally, the total area of the hole openings is smaller than the apparent surface area, and there is an upper limit on the number of holes. In particular, when the total area of the openings of holes with the same depth becomes more than half of the apparent area, the reference surface described above becomes the bottom surface of the hole, so in that case, the shape of the surface is rather than having a hole in the reference surface A wall having a predetermined height extends upward from the reference surface. The predetermined height corresponds to the depth of the hole. In this case, it can be said that the surface has a continuous convex portion as described later. In addition, the opening of the hole provided with at least 2 holes / cm ² preferably has a maximum width of 30 nm or more, more preferably 100 nm or more, and further preferably 1 μm or more. In addition, the opening of the hole provided with at least 2 holes / cm ² preferably has a maximum width of 3 mm or less, more preferably 2 mm or less, and further preferably 1.5 mm or less. The sizes of the openings of all the holes may be the same or substantially the same, or may be different. The maximum width of the opening of the hole may vary according to a normal distribution, for example. For convenience, the lower limit and the upper limit of the number can be defined in the same manner as described above by using the average maximum width of the hole openings.

The positive electrode-shaped surface preferably includes at least 2 protrusions / cm ² having a cross-sectional shape with a maximum width of 30 nm or more and 3 mm or less, more preferably 6 protrusions / cm ² or more, and still more preferably 12 protrusions / cm ^{2. 2} or more. In addition, the opening of the hole provided with at least 2 holes / cm ² preferably has a maximum width of 30 nm or more, more preferably 1 μm or more, and further preferably 5 μm or more. In addition, the opening of the hole provided with at least 2 holes / cm ² preferably has a maximum width of 3 mm or less, more preferably 2 mm or less, and further preferably 1.5 mm or less.

(7) The surface of the positive electrode shape that can be exposed to oxygen is provided with a mesh pattern by continuous convex portions or concave portions, and the height or depth from the reference surface of the convex portions or concave portions is 5 μm or more and 500 μm or less. It is possible to provide the lithium-air battery as described in (3) above.

  The mesh pattern is not particularly limited, and the mesh whose size or shape changes regularly or irregularly may be substantially continuously formed as irregularities on the electrode surface. For example, a convex or concave portion that outlines a regular hexagon of the same size may extend over the electrode plane, and a hexagon or other polygon of a mixed size may be used as the electrode surface by such a convex or concave portion. It may spread to. The height or depth of the convex part or the concave part may be constant, and may change regularly or irregularly. Here, the continuous convex portions or concave portions are mainly described. However, these convex portions and concave portions do not necessarily have to be continuous over the entire surface. That is, it may be interrupted or may be isolated. In the case of a convex part, the above-mentioned reference surface becomes a surface that spreads out on the ridge, and in the case of a concave part, it becomes a surface that spreads on the top. For example, when the total area of the tops of the protrusions having the same height is more than half of the apparent area, the top surface becomes the reference surface, and the surface form is provided with the recesses having a depth corresponding to the height. . Conversely, when the total area of the bottom surface of the concave portion having the same depth is more than half of the apparent area, the bottom surface becomes the reference surface, and the surface form is provided with the convex portion having a height corresponding to the depth.

  Moreover, you may provide the surface form provided with the recessed part isolated only on the surface like a porous body. At this time, the solid electrolyte functioning as the electrolyte side layer or the second electrolyte layer of the positive electrode should not substantially transmit water vapor and water so that water vapor or water in the atmosphere does not reach the negative electrode. Is preferred. For example, if the entire positive electrode is a porous body, water vapor or water in the atmosphere may pass through the positive electrode, but a solid electrolyte (for example, an inorganic solid electrolyte such as glass ceramics) disposed between the negative electrode Therefore, the permeation to these negative electrodes is substantially prevented.

(8) The first solid electrolyte layer is Li _{1 + x + z} M _x (Ge _1-y , Ti _y ) _2−x Si _z P _3−z O ₁₂ (where 0 ≦ x ≦ 0.8, 0 ≦ y Lithium air according to any one of (1) to (7) above, which contains a crystal of ≦ 1.0, 0 ≦ z ≦ 0.6, M = Al or one selected from Ga and Ga) A battery can be provided.

The first solid electrolyte is Li _{1 + x + z} M _x (Ge _1−y , Ti _y ) _2−x Si _z P _3−z O ₁₂ (where 0 ≦ x ≦ 0.8, 0 ≦ y ≦ 1.0, 0 ≦ z ≦ 0.6, M = Al or one selected from Al and Ga) is preferable because it has excellent chemical stability and high ion conductivity. Further, the first solid electrolyte may be a glass ceramic bulk body in which the crystals are deposited, or a glass ceramic powder in which the crystals are deposited or a glass powder in which the crystals are precipitated by heat treatment, etc. It is more preferable that the material is molded and sintered by the above method. The same applies to the second solid electrolyte.

(9) The first solid electrolyte layer is mol% based on oxide,
Li ₂ O 10-25%,
Al ₂ O ₃ and / or _Ga 2 _O 3 _0.5~15%,
TiO ₂ and / or GeO ₂ 25-50%,
SiO ₂ 0~15%,
P ₂ O ₅ 26~40%
The lithium air battery according to any one of the above (1) to (8), which contains each of the above components, can be provided.

_{Li 1 + x + z M x} (Ge 1-y, Ti y) 2-x Si z P 3-z O 12 ( where, 0 ≦ x ≦ 0.8,0 ≦ y ≦ 1.0,0 ≦ z ≦ 0.6 , M = Al, one or more kinds selected from Ga) are precipitated,
Li ₂ O 10-25%,
Al ₂ O ₃ and / or _Ga 2 _O 3 _0.5~15%,
TiO ₂ and / or GeO ₂ 25-50%,
SiO ₂ 0~15%,
P ₂ O ₅ 26~40%
It can produce by heat-processing the glass containing each component of these.

  Here, “mol% based on oxide” means that oxides, composite salts, etc. used as raw materials of glass constituents are all decomposed at the time of melting, and oxides combined with oxygen corresponding to their respective charges. And each component contained by the molar ratio (%) of the generated oxide based on the assumption that it is present in the glass in the form of its oxide. The “glass ceramic” is a material obtained by precipitating crystals in a glass phase by heat-treating glass, and can be a material composed of an amorphous solid and crystals.

(10) The lithium-air battery according to any one of (1) to (9), wherein the second solid electrolyte layer is the same type as the first solid electrolyte. .

(11) The lithium-air battery according to any one of (1) to (10), wherein the positive electrode further includes an electrolyte composed of a polymer and an aqueous solution.

  In the lithium-air battery of the present invention, since the inorganic solid electrolyte is disposed as the second electrolyte layer between the negative electrode and the positive electrode, deterioration of the negative electrode due to atmospheric water vapor or water that can enter from the air positive electrode can be effectively suppressed. is there. Therefore, in order to accelerate the electrode reaction, it is possible to arrange an electrolyte made of an aqueous solution on the surface of the positive electrode. In addition, for example, in a battery that requires output particularly when used in a special environment such as a dry atmosphere, an electrolyte (gel electrolyte) made of a polymer and an aqueous solution is formed on the surface of the positive electrode made of the first solid electrolyte layer. The gel electrolyte may be disposed around the catalyst particles on the surface of the positive electrode so that the catalyst is fixed to the surface. Furthermore, in order to apply such a lithium-air battery at a higher temperature, it is preferable that an electrolyte made of an aqueous solution is not disposed on the positive electrode. In this way, the activity of the positive electrode is not lost even during continuous use at high temperatures, and it is possible to effectively prevent suppression of the electrode reaction due to water evaporation at the positive electrode, thereby obtaining high discharge performance or charge / discharge performance. Is possible.

  As described above, in the lithium-air battery of the present invention, since the electrode surface area of the positive electrode is larger than the apparent area, the contact area with the catalyst attached to the surface can be increased, and a high current density is obtained. be able to.

The schematic diagram which shows the form of the surface by the side of the air phase of a positive electrode regarding one Example of this invention. The schematic diagram which shows the form of the surface by the side of the air phase of a positive electrode regarding 2 Example of this invention. The schematic diagram which shows the form of the surface by the side of the air phase of a positive electrode regarding 3 Example of this invention. The schematic diagram which shows the form of the surface by the side of the air phase of a positive electrode regarding the 4th Example of this invention. The schematic diagram which shows the form of the surface by the side of the air phase of a positive electrode regarding the 5th Example of this invention. The schematic diagram which shows the structure of a positive electrode regarding another Example of this invention. The schematic diagram which shows the structure of a positive electrode regarding another Example of this invention. The schematic diagram illustrating the whole structure of the lithium air battery of this invention. The schematic diagram illustrating the state of a positive electrode with the aqueous solution of a lithium air battery, and an electrode reaction. The schematic diagram illustrating the state of a positive electrode without the aqueous solution of a lithium air battery, and an electrode reaction. The schematic diagram illustrating the method of calculating | requiring a reference | standard surface from a surface form.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the following description is made for explaining the embodiments of the present invention, and the present invention is limited to these embodiments. It is not a thing. The same or the same type of elements are denoted by the same or related symbols, and redundant description is omitted.

  FIG. 1 is a schematic view of a cell 10 of a lithium air battery showing one embodiment of the present invention. A negative electrode protective layer 13 and a solid electrolyte layer 16 (corresponding to a second solid electrolyte layer) are disposed on the negative electrode 12 having the ability to occlude and release lithium ions or the ability to release lithium ions, and at least oxygen A cathode 14 including a catalyst for reduction or a catalyst for oxygen reduction and generation, and a first solid electrolyte layer is laminated. Here, Li—Al alloy foil is used for the negative electrode 12. The solid electrolyte layer 16 is made of glass ceramics and does not substantially transmit water vapor or water. The positive electrode 14 is also made of the same kind or different kind of glass ceramics. Details will be described later. Electrons of the negative electrode and the positive electrode are taken out of the cell by a current collector (not shown).

In general, in a lithium-air battery, for example, when the negative electrode active material is Li metal and the liquid that serves as the active material and the electrolyte is water, the following battery reaction is considered to have occurred.
Li + H ₂ O = LiOH + 1 / 2H ₂
Or
Li + 1 / 2H ₂ O + 1 / 4O ₂ = LiOH
For each of the negative electrode side and the positive electrode side,
The negative electrode: ^Li = Li + + e ^-
Positive electrode: e ⁻ + H ₂ O = OH ⁻ + 1 / 2H ₂
Or
e ⁻ + 1/2 H ₂ O + 1/4 O ₂ = OH ⁻
Can be expressed as In order to activate such a battery reaction and obtain a battery with high output, the positive electrode preferably has the ability to reduce and decompose water or oxygen in order to promote electron transfer to water or oxygen.

  In FIG. 8, the above reaction at the positive electrode is illustrated. A catalyst 15 (for example, a metal such as platinum, nickel, gold, other noble metals, and an inorganic compound such as an oxide containing a perovskite oxide) is attached to the surface of the positive electrode 14, and the electrode reaction occurs. Facilitate. There is an aqueous solution 50 around the catalyst 15, and the oxygen existing around the positive electrode can be dissolved and the above reaction can be caused therein. Oxygen as an active material reacts in the aqueous solution 50 in contact with the surface of the catalyst 15 to generate hydroxide ions. And it couple | bonds with the floating lithium ion and precipitates as lithium hydroxide (or lithium oxide).

  However, when there is no aqueous solution 50 in this way, as shown in FIG. 9, oxygen or water vapor directly contacts the surface of the catalyst 15 from the gas phase, and the interface 52 with the positive electrode 14 (catalyst, oxygen, water, positive electrode). ) To react with electrons and lithium ions brought from the current collector (not shown) to the positive electrode to produce lithium hydroxide (lithium oxide). When there is an aqueous solution as shown in FIG. 8, a large area of the catalyst surface can be utilized. However, when there is no aqueous solution and a gas phase acts on a solid-solid contact portion, the area of the contact portion is small. Small and slow reaction rate. Therefore, as shown in FIG. 1, a hole having a diameter Di1 and a depth De1 is formed on the surface of the positive electrode 14 on the gas phase side to create a larger area than the apparent area L1 × L2. be able to. This hole does not penetrate the positive electrode 14, and the positive electrode 14 is made of glass ceramics and has substantially no gas permeability. If these holes are assumed to be opened vertically, the area of the side surface increases. Therefore, if n holes are opened per unit area 20, the area increased per unit area. Is n × π × Di1 × De1. Here, when there is a distribution in the diameter and depth of the holes, this formula can be applied by taking an average (for example, arithmetic average).

  Here, the opening shape of the hole 18 is not limited, and may be a closed linear shape including a circle, an ellipse, a polygon, or a concave shape. It may be a mixture of these shapes. Therefore, the maximum width can be used to define such an opening shape. The maximum width is preferably 10 to 20 μm if it is relatively small, and 200 to 300 μm if it is relatively large. The depth does not need to be uniform, and typically 200 to 300 μm is preferable.

  FIG. 2 is a schematic view of a lithium-air battery cell showing a second embodiment of the present invention. The basic structure of the cell 10 'is the same as that shown in FIG. On the gas phase side surface of the positive electrode 14, a column 22 having a diameter Di2 and a height H1 is provided in a circular approximation. Assuming that the pillars 22 are standing vertically, the area of the side surfaces of the pillars 22 increases. Therefore, if n pillars stand per unit area 20, the pillars 22 increase per unit area. The area is n × π × Di2 × H1. Here, when there is a distribution in the diameter and height of the protrusions (columns), this formula can be applied by taking an average (for example, arithmetic average).

  Here, the shape of the pillar 22 in a plan view is not limited, and may be a closed linear shape including a circle, an ellipse, a polygon, or a concave shape. It may be a mixture of these shapes. Therefore, the maximum width can be used to define such a planar view shape. The maximum width is preferably 10 to 20 μm if it is relatively small, and 200 to 300 μm if it is relatively large. The height does not need to be uniform, and typically a height of 300 to 500 μm is preferable.

  FIG. 3 is a schematic diagram of a lithium-air battery cell showing a third embodiment of the present invention. The basic structure of the cell 11 is the same as in FIG. On the surface of the positive electrode 14 on the gas phase side, a mesh pattern composed of continuous convex portions is formed. The height of the convex part 24 is H2. If it is assumed that the convex portion 24 stands vertically, the area of the side surface of the convex portion 24 is increased. Therefore, if the length per unit area of the convex portion 24 is LL1, the area increased per unit area. Is 2 × H2 × LL1. Here, when there is a distribution in the height of the convex portion, an average (for example, arithmetic average) can be taken and this formula can be applied.

  FIG. 4 is a schematic diagram of a lithium-air battery cell showing a fourth embodiment of the present invention. The basic structure of the cell 11 'is the same as that in FIG. On the surface on the gas phase side of the positive electrode 14, a mesh pattern composed of continuous concave portions is formed contrary to FIG. 3. The depth of the recess 26 is De2. Assuming that the recess 26 is a vertical groove, the area of the side surface thereof increases. Therefore, if the length per unit area of the recess 26 is LL2, the area increasing per unit area is 2 × De2 × LL2. Here, when there is a distribution in the depth of the recess, this formula can be applied by taking an average (for example, arithmetic average).

FIG. 5 is a schematic diagram of a lithium-air battery cell showing a fifth embodiment of the present invention. The basic structure of the cell 10 '' is the same as that in FIG. A hemispherical protrusion 19 is formed on the surface of the positive electrode 14 on the gas phase side. Such protrusions can be realized by embedding a slightly larger glass ceramic sphere on the surface half in the process of manufacturing the positive electrode green sheet. The diameter of such a projection 19 and Di3, if the number per unit area is n, the area increases per unit area becomes n × π × (Di3) 2 /2. Here, when there is a distribution in the diameter of the protrusion 19, this equation can be applied by taking an average (for example, arithmetic average).

  FIG. 6A shows a slightly modified embodiment, and shows only the positive electrode. Here, the concave portion 19 ′ is one in which pores in the porous body appear on the surface.

  FIG. 6B is a schematic diagram illustrating a configuration including a surface of the positive electrode, a catalyst, and a gel electrolyte 54 in the vicinity of the surface in the cross-sectional view of the positive electrode. Here, the surface of the positive electrode 14 is provided with unevenness, and the surface area is enlarged. Thereby, more contact points with the catalyst 15 attached to the surface and reaction points in the vicinity thereof are provided. Further, these catalysts 15 are fixed to the surface of the positive electrode 14 by a gel electrolyte (gel electrolyte 54) made of a polymer and an aqueous solution. Since the aqueous solution of the gel electrolyte 54 is absorbed by the polymer as compared with the aqueous solution shown in FIG. 8, it is difficult to evaporate and difficult to dry. And since the catalyst 15 adheres to the surface of the positive electrode 14, the contact area with the aqueous solution contained becomes large. As a result, the number of reaction points for electrode reaction increases, and the current density can be increased.

  FIG. 7 schematically shows a case where a battery is configured by using the cells of FIGS. 1 to 5 and using the cell having the positive electrode of FIG. 6A or 6B. The negative electrode 12, the negative electrode protective layer 13, the electrolyte 16, and the positive electrode 14 are laminated in this order, and current collectors 34 and 36 are in close contact with the negative electrode 12 and the positive electrode 14, respectively. These are stored in a case 30 forming a battery. A plurality of air holes 32 (two in the figure) are formed on the positive electrode side of the case 30. The current collectors 34 and 36 are electrically connected to a load or a power source through leads, and are discharged or charged. In addition, this battery may be a primary battery only for discharging without charging.

  As a method for producing a surface shape for increasing the surface area of the first solid electrolyte, a method of mechanically processing the bulk body of the solid electrolyte, a method of processing by etching, or a precursor of the solid electrolyte (sintering) Examples thereof include a method of transferring a desired shape to a previous green sheet) by stamping and sintering.

[Example 1]
More specific examples will be described below.
(Preparation of solid electrolyte layer)
As raw materials, H ₃ PO ₄ , Al (PO ₃ ) ₃ , Li ₂ CO ₃ , SiO ₂ , and TiO ₂ were used, and these raw materials were mol% in terms of oxide, and P ₂ O ₅ 33.8%. , Al ₂ O ₃ 7.6%, Li ₂ O 14.5%, SiO ₂ 2.8%, TiO ₂ 41.3% were weighed and mixed uniformly. The mixture was put in a platinum pot and heated and dissolved in an electric furnace at 1450 ° C. for 3 hours with stirring. The obtained glass melt was dropped into running water to obtain flaky glass. By pulverizing this glass with a jet mill, glass particles having an average particle diameter of 1.9 μm were obtained.

(Creation of green sheet for second solid electrolyte layer)
The glass particles were finely pulverized with a wet ball mill using ethanol, and the obtained slurry was spray-dried to obtain glass fine particles having an average particle diameter of 0.3 μm.
A slurry 1 was prepared by adding a dispersant to an acrylic resin dispersed in water to glass fine particles and stirring the mixture with a ball mill for 48 hours. The content of glass fine particles in this slurry was 65.5% by mass, and the content of acrylic resin was 13.5% by mass. The slurry was molded at a thickness of 45 μm on a PET film that had been subjected to a release treatment by the doctor blade method, and was subjected to primary drying at 80 ° C. and further secondary drying at 95 ° C. to obtain a sheet-like material. . A dense green sheet 1 is produced by superposing 8 sheets of sheet material after peeling the PET film and applying pressure at 196.1 MPa for 10 minutes using an isotropic pressure device (CIP). did. Green sheet 1 was cut into 30 mm square.

(Creation of green sheet of first solid electrolyte layer)
A slurry 2 obtained by heat-treating the glass particles to glass ceramic particles, further pulverizing them to an average particle diameter of 1 μm, adding a dispersant to an acrylic resin dispersed in water, and stirring the mixture for 12 hours with a ball mill Adjusted. The content of glass ceramic particles in this slurry was 45% by mass and acrylic resin 17.5% by mass. This slurry was molded to a thickness of 60 μm on a PET film that had been subjected to a release treatment by the doctor blade method, and was subjected to primary drying at 80 ° C. and further secondary drying at 95 ° C. to obtain a sheet-like material. Four sheets of sheet material after peeling the PET film were superposed, and these green sheets 2 were pressed at 70 ° C. and 60 kgf / cm 2 with a hot press to obtain green sheets 2. The green sheet 2 was cut into φ12.

(Solid electrolyte production process)
These green sheets 1 and 2 were again made into a laminate by hot pressing at 70 ° C. and a pressure of 60 kgf / cm ² . After heating at 480 ° C. for 2 hours (degreasing), the temperature was rapidly raised to 930 ° C., maintained at 930 ° C. for 2 hours (sintering), and then naturally cooled to room temperature.

(Identification of crystal phase)
In order to confirm the state of the produced solid electrolyte, the green sheets 1 and 2 were separately subjected to the same heat treatment conditions as described above. When the fired product of the green sheet 1 was examined by an X-ray diffraction method, the main crystal phase was Li _{1 + x + y} AlTi _2-x Si _y P _3-y O ₁₂ (wherein 0 ≦ x ≦ 0.4, 0 <y ≦ 0.6). Moreover, the ionic conductivity obtained by performing impedance measurement was 1.8 × 10 ⁻⁴ Scm ⁻¹ . Further, when the fired product of the green sheet 2 was examined by an X-ray diffraction method, the fired product had a main crystal phase similar to that of the fired product of the green sheet 1, and the apparent ionic conductivity was 2.1 × 10 ^−4. S / cm. The bulk density was 67%.

[Example 2]
(Production of solid electrolyte)
As raw materials, H ₃ PO ₄ , Al (PO ₃ ) ₃ , Li ₂ CO ₃ , SiO ₂ manufactured by Nichetsu Co., Ltd., TiO ₂ manufactured by Sakai Chemical Industry Co., Ltd., GeO manufactured by Sumitomo Metal Mining Co., Ltd. _2. ZrO ₂ made by NIPPON Denko was used. These were expressed in terms of mass% in terms of oxides, Li ₂ O component 14.2%, Al ₂ O ₃ component 8.0%, SiO ₂ component 1.0%, P ₂ O ₅ component 42.3%, The GeO ₂ component was measured to be 18.1%, the TiO ₂ component was 15.2%, the ZrO ₂ component was 1.2%, and mixed uniformly, and then placed in a platinum pot and placed in an electric furnace at 1350 ° C. The glass melt was obtained by heating and melting for 3 hours while stirring at a temperature of 5 ° C. Thereafter, the glass melt was poured from a platinum pipe attached to the pot into a metal mold made of INCONEL600 (INCONEL is a registered trademark) heated to 300 ° C. Thereafter, the glass was allowed to cool to a surface temperature of 600 ° C. or lower, then placed in an electric furnace heated to 550 ° C., and gradually cooled to room temperature, thereby producing a glass block from which thermal strain was removed. Thereafter, the resulting subjected to 12 hours heat treatment the glass block at 890 ° C., have rows crystallization treatment, to produce a glass ceramic.

The above glass ceramic was cut and ground to a 25 mm square and a thickness of 0.3 mm, and then drilled with a diameter of 100 μm, a depth of 100 μm, and a pitch interval of 100 μm on 1 cm ² on one side of the glass ceramic. Here, such drilling is performed on a processing line that is 100 μm apart. Therefore, 100 × 100 holes are opened in a unit area of 1 cm square, and the number thereof is 10,000. Thus, the area increases per unit area of 1 cm ^2, in the n × π × Di1 × De1, n = 10000, Di1 = 100μm, since it is De1 = 100 [mu] m, with ^{3.14 × 10 8 μm 2 = 3.14cm} 2 Yes, it has increased about 3 times.

(Production of lithium-air battery cells)
The solid electrolyte produced in Examples 1 and 2 was used and laminated in the order of negative electrode / negative electrode protective layer / solid electrolyte. Platinum-supported carbon was used for the positive electrode catalyst. After applying a mixed slurry of platinum-supporting carbon and Nafion to the surface of the solid electrolyte, drying treatment was performed in a reduced-pressure atmosphere.
Negative electrode: Li metal foil 1 cm ² 0.1 mm (thickness t)
Negative electrode protective layer: EC (ethylene carbonate): DEC (diethyl carbonate) = 1: 1 vol LiPF ₆ 1M
Cathode catalyst: Platinum-supported carbon

[Comparative example]
The same negative electrode, electrolyte, and positive electrode as in Example 2 were used, and a positive electrode that was not drilled as in Example 2 was prepared.

[Test example]
Each of the Li / air batteries using the solid electrolytes of Examples 1 and ² was tested at a discharge current density of 0.5 mA / cm ² at room temperature. The result was 86% in Example 1 and 77% in Example 2 with respect to the electric capacity of Li metal.
In the comparative example, it was 5%.

10, 11 Lithium-air battery cell 12 Negative electrode 13 Negative electrode protective layer 14 Positive electrode 15 Catalyst 16 Electrolyte
18 hole 20 unit area 22 pillar 24 convex part
26 Concave part 50 Aqueous solution 52 Electrode reaction part

Claims (10)

A negative electrode having the ability to occlude and release lithium ions, or the ability to release lithium ions;
A positive electrode comprising at least a catalyst for oxygen reduction, or a catalyst for oxygen reduction and generation, and a first solid electrolyte layer;
A second solid electrolyte layer disposed between the negative electrode and the positive electrode ,
In the positive electrode, the shape of the positive electrode is formed by the first solid electrolyte layer, and the surface area thereof is larger than the apparent surface area,
The lithium-air battery , wherein the catalyst is attached to a surface in the shape of the positive electrode that can be exposed to oxygen . 2. The lithium-air battery according to claim 1, wherein the first solid electrolyte layer has an ionic conductivity of 1 × 10 ⁻⁵ S / cm or more at 25 ° C. 3. The surface area of the shape of the positive electrode, lithium-air battery according to claim 1 or 2, characterized in that there are at least 3 times the area of the apparent surface that may be exposure to oxygen. 3. The lithium-air battery according to claim 1, wherein the positive electrode-shaped surface that can be exposed to oxygen includes at least two holes / cm ² having an opening having a maximum width of 30 nm to 3 mm. The positive electrode-shaped surface that can be exposed to oxygen is a protrusion having a maximum cross-sectional width of 30 nm or more and 3 mm or less, and a height from the reference surface of 10 μm or more and 500 μm or less is at least 2 / cm ^2. The lithium-air battery according to claim 1 , comprising: a lithium-air battery. The surface of the positive electrode shape that can be exposed to oxygen has a mesh pattern with continuous convex portions or concave portions, and the height or depth from the reference plane of the convex portions or concave portions is 5 μm or more and 500 μm or less. The lithium-air battery according to claim 1 or 2 , characterized in that: The first solid electrolyte layer includes Li _{1 + x + z} M _x (Ge _1-y , Ti _y ) _2−x Si _z P _3−z O ₁₂ (where 0 ≦ x ≦ 0.8, 0 ≦ y ≦ 1. 0,0 ≦ z ≦ 0.6, M = Al, lithium-air battery according to any one of claims 1 to 6, characterized in that it comprises a crystal of one or more selected from Ga). The first solid electrolyte layer is mol% based on oxide,
Li ₂ O 10-25%,
Al ₂ O ₃ and / or _Ga 2 _O 3 _0.5~15%,
TiO ₂ and / or GeO ₂ 25-50%,
SiO ₂ 0~15%,
P ₂ O ₅ 26~40%
The lithium air battery according to any one of claims 1 to 7 , comprising each of the following components. Said second solid electrolyte layer, lithium-air battery according to any one of claims 1 to 8, wherein a first solid electrolyte and the like. The positive electrode further lithium-air battery according to any one of claims 1-9, characterized in that it comprises an electrolyte comprising a polymer and an aqueous solution.

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