Integrated channel positive electrode for metal secondary battery and method for manufacturing the same, and metal secondary battery

Abstract

To provide a metal secondary battery that has superior output and capacity characteristics than conventional one, and can significantly improve discharge characteristics in the atmosphere.SOLUTION: A channel-integrated positive electrode for a metal secondary battery includes a gas diffusion channel layer made of a porous layer made of a fibrous carbon material, and a positive electrode layer of the porous layer, which is made of a fibrous carbon material that is the same as or different from the carbon material, a part of the channel layer includes hollow pores that are developed by entanglement of the fibrous carbon material in the channel layer and the fibrous carbon material of the positive electrode layer that enters the channel layer, the pores provided by the channel layer and the positive electrode layer have a continuous pore size distribution of 10 nm or more and 200 μm or less, the channel layer and the positive electrode layer are integrated by the continuous pore size distribution.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a flow path integrated positive electrode for a metal secondary battery, a manufacturing method thereof, and a metal secondary battery including the positive electrode.

Background Art

[0002] In recent years, due to the spread of renewable energy and the demand for automotive electrification, the development of a lightweight and large-capacity battery, that is, a battery (specifically, a metal secondary battery) having a higher energy density has been demanded. Among the batteries under development, the lithium-air battery in particular has the highest theoretical energy density and is expected to be realized as a battery having an energy density far exceeding that of the currently popular lithium-ion battery.

[0003] The lithium-air battery is a battery that uses lithium metal as the negative electrode active material and atmospheric oxygen as the positive electrode active material. During discharge, lithium metal elutes at the negative electrode, and at the positive electrode, it reacts with oxygen absorbed from the atmosphere and lithium peroxide precipitates. During charging, the reverse reaction occurs, and these reactions are repeated for charge and discharge. When expressing this charge and discharge by a chemical reaction formula, at the negative electrode, JPEG0007900039000001.jpg1137 and at the positive electrode, JPEG0007900039000002.jpg1166 Here, since the positive electrode has the function of absorbing and discharging atmospheric oxygen according to discharge and charging, it is also called an air electrode.

[0004] To improve the output and capacity of a lithium-air battery and to improve its discharge characteristics in the atmosphere, the positive electrode must have sufficient conductivity as an electrode, have an electrochemical active surface where the battery reaction occurs, and have a diffusion path that can supply oxygen and lithium ions, which are battery reactants, to the electrochemical active surface. This diffusion path also serves to provide a space where a large amount of solid products (specifically, lithium peroxide (Li2O2)) deposited by the discharge reaction can accumulate without inhibiting their growth. Therefore, in addition to having a continuous pore structure that allows for easy diffusion supply of reactants (oxygen O2 and lithium ions Li + ), the positive electrode is required to have as large a pore volume and surface area (i.e., effective electrode area) as possible.

[0005] Therefore, as a positive electrode that can improve the output and capacity of a metal secondary battery (especially a lithium-air battery) and also improve its discharge characteristics in the atmosphere, the development of a positive electrode using porous carbon (e.g., carbon nanotubes) with a high porosity (i.e., high porosity) and a large surface area has been carried out.

[0006] In Non-Patent Document 1, carbon nanotubes (CNTs) having a wavy (wave) structure are processed into a sheet as a raw material and used as a positive electrode, enabling the production of a porous carbon positive electrode with a porosity increased up to 94% while having sufficient self-supporting ability, mechanical strength, and conductivity. It has been reported that when this is used as a lithium-air battery positive electrode, the capacity and output of the battery are improved.

[0007] In Non-Patent Document 2, as a flow path layer in a stack cell, a metal thin film of SUS foil or Al foil with a wavy shape and gas diffusibility in the cross-sectional direction is used and sandwiched between the positive electrode layers of porous carbon and laminated (i.e., a stack cell is fabricated), enabling the scaling up of the effective electrode area. As a result, it has been reported that the capacity and output as a lithium-air battery are improved.

[0008] Patent Document 1 reports that, in order to solve the problems that arise when applying a conventional positive electrode (specifically, a positive electrode made of carbon nanotubes) to a lithium-air battery cell (i.e., a single cell), namely the difficulty in processing and handling the positive electrode and the resulting instability of battery characteristics, and the difficulty in improving the capacity and output of the battery because it is not possible to design a stacked battery using the lithium-air battery cell (i.e., fabricate a stack cell), a channel-integrated positive electrode was developed by using a gas diffusion layer made of carbon fiber, which is lighter than a metal thin-film channel layer, as the channel layer in the stack cell, and integrating the carbon nanotube positive electrode layer with the gas diffusion layer (i.e., channel layer). [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2021-2437 [Non-patent literature]

[0010] [Non-Patent Document 1] Akihiko Nomura et. al., “Highly-porous Super-Growth carbon nanotube sheet cathode develops high-power Lithium-Air Batteries”, Electrochimica Acta 400 (2021) 139415 [Non-Patent Document 2] Yoshimi Kubo et. al., “Multicell Stack of Nonaqueous Lithium-Air Batteries”, ECS Transactions, 62 (1) pp. 129-135 (2014) [Overview of the project] [Problems that the invention aims to solve]

[0011] However, the porous carbon cathode described in Non-Patent Document 1 is not an integrated cathode layer and flow channel layer. Non-Patent Document 1 only evaluates and confirms the expression of battery characteristics by the cathode layer alone. In order to obtain a practical battery module using the porous carbon cathode described in Non-Patent Document 1, it is necessary to fabricate a stack cell, but the Non-Patent Document does not contain any information necessary for application to a stack cell (specifically, information on how the porous carbon cathode described in the Non-Patent Document can actually be used when fabricating a stack cell, what kind of flow channel layer structure is appropriate to combine it with, etc.). Therefore, designing and fabricating a stack cell using the porous carbon cathode described in Non-Patent Document 1 based on the Non-Patent Document is extremely difficult for those skilled in the art, and there is a problem in that it is not easy to scale up the effective electrode area by using a stack cell.

[0012] Furthermore, as mentioned above, Non-Patent Document 2 utilizes a thin metal film of SUS foil or Al foil, which has been processed to be corrugated to provide gas diffusivity in the cross-sectional direction, as the flow channel layer in a stacked cell. By sandwiching this between positive electrode layers and stacking them, it is possible to scale up the effective electrode area. However, since thin metal films are generally heavy, Non-Patent Document 2 has the problem that the gravimetric energy density of the stacked cell is significantly reduced compared to that of a single cell without stacking. Also, the positive electrode layer and the flow channel layer in Non-Patent Document 2 are not integrated. Therefore, in the stack design of Non-Patent Document 2, it is necessary to stack a large number of components with high precision in the order of flow channel layer, positive electrode layer, separator, negative electrode layer, and current collector, which presents the problem of a complicated process.

[0013] Furthermore, as described above, Patent Document 1 achieves weight reduction and thinning of the channel layer by using carbon fibers instead of a thin metal film as the channel layer. In addition, by integrating the channel layer using carbon fibers with the cathode layer using carbon nanotubes, the handling and processing of carbon nanotube cathodes, which were previously difficult, are made easier, enabling the stabilization of the battery characteristics of lithium-air battery cells. Furthermore, it is possible to fabricate stack cells using these lithium-air battery cells, thereby improving the capacity and output of the storage battery (specifically, lithium-air battery). On the other hand, although Patent Document 1 reports that the integration of the channel layer and the cathode layer means that the entire carbon nanotube cathode layer has penetrated (entered) into the channel layer of the conductive porous substrate, there is a problem that the battery characteristics achieved by this integration are limited to the battery characteristics that can be achieved by the cathode layer alone (i.e., they do not exceed the battery characteristics that can be achieved by the cathode layer alone). To elaborate, in the positive electrode described in Patent Document 1, in which the flow channel layer and the positive electrode layer are integrated, the flow channel layer is provided solely to enable the function of the positive electrode layer in the stack structure, and does not aim to improve battery characteristics by enabling new functions of the flow channel layer itself. Therefore, there is a problem that the effect of improving the capacity and output of the storage battery itself is limited to the battery characteristics that can be achieved by the positive electrode layer alone.

[0014] Thus, the conventional metal thin-film channel layers and carbon fiber channel layers described above are merely intended for supplying oxygen gas to the positive electrode layer and maintaining the stack structure in the fabrication of metal secondary batteries (especially lithium-air batteries), and are not expected to provide any effect beyond the role of a conventional channel layer. Therefore, the battery characteristics of a stack cell designed as a metal secondary battery are limited to the battery characteristics that can be achieved by the positive electrode layer alone. For these reasons, conventional positive electrodes for metal secondary batteries are still not sufficient in terms of improving the output and capacity of the metal secondary battery, as well as improving the discharge characteristics in air, and there is still a strong need for the development of new positive electrodes for metal secondary batteries (especially lithium-air batteries). [Means for solving the problem]

[0015] As a result of diligent study of the above problems, the present inventors have discovered for the first time that a metal secondary battery with an integrated channel cathode for a channel battery can be provided that has superior output and capacity characteristics compared to conventional batteries, and that can significantly improve discharge characteristics in air, by providing a channel cathode for a metal secondary battery that includes a gas diffusion channel channel layer made of a porous layer made of a fibrous carbon material and a positive electrode layer made of a porous layer made of the same or different fibrous carbon material as the carbon material, wherein a part of the channel channel layer includes pores of cavities formed by the entanglement of the fibrous carbon material in the channel channel layer and the fibrous carbon material of the positive electrode layer that enters the channel channel layer, and the pores provided by the channel channel layer and the positive electrode layer (including the pores of the cavities) have a continuous pore size distribution of 10 nm to 200 μm, and the channel channel layer and the positive electrode layer are integrated by the continuous pore size distribution, and

[0016] The present invention has, in particular, the following embodiments [1] to

[14] .

[0017] [1] A gas diffusion channel layer consisting of a porous layer made of fibrous carbon material, A positive electrode layer consisting of a porous layer made of the same or different fibrous carbon material as the carbon material, Includes, A portion of the channel layer includes pores formed by the entanglement of the fibrous carbon material in the channel layer and the fibrous carbon material of the positive electrode layer that enters the channel layer. The pores provided by the channel layer and the positive electrode layer have a continuous pore size distribution of 10 nm to 200 μm, and the channel layer and the positive electrode layer are integrated by this continuous pore size distribution. Integrated channel positive electrode for metal secondary batteries. [2] The positive electrode according to [1], wherein a portion of the flow channel layer has a thickness of at least 5 μm. [3] The positive electrode according to [1] or [2], wherein the pores of the cavity have a continuous pore size distribution of 10 μm to 50 μm. [4] The pores of the cavity have a pore volume of 0.5 cm³ per gram of weight of the positive electrode layer. 3 / g or more 5.0cm3 The positive electrode according to any one of [1] to [3], having a value of less than or equal to / g. [5] The positive electrode according to any one of [1] to [4], wherein the fibrous carbon material is carbon fiber and / or carbon nanotube. [6] The positive electrode according to any one of [1] to [5], wherein the fibrous carbon material of the flow path layer is carbon fiber and the fibrous carbon material of the positive electrode layer is carbon nanotube. [7] 250m 2 / g or more and 1400m 2 The positive electrode according to any one of [1] to [6], having a BET specific surface area of less than or equal to / g and greater than or equal to 0.1μm and less than or equal to 10μm, and having pores with a pore size distribution of: 1.0 cm 3 / g or more and 10.0 cm 3 / g or less, as the pore volume per gram weight of the positive electrode layer. [8] The positive electrode according to any one of [1] to [7], wherein the density of the flow path layer is greater than or equal to 0.01 g / cm 3 and less than or equal to 0.30 g / cm 3 . [9] The positive electrode according to any one of [1] to [8], wherein the peel strength between the positive electrode layer and the flow path layer is 1 mN / 5 mm or more in a 90-degree peel test.

[10] The positive electrode according to any one of [1] to [9], wherein the pore size distribution of the positive electrode is measured by mercury intrusion porosimetry.

[11] The positive electrode according to any one of [1] to

[10] , wherein the pores of the voids are visually observed by observation using an electron microscope or an X-ray computed tomograph.

[12] A metal secondary battery including a positive electrode, a negative electrode containing a metal, and an electrolytic solution between the positive electrode and the negative electrode, wherein the positive electrode is the positive electrode according to any one of [1] to

[11] .

[13] Including a negative electrode active material and a positive electrode active material, wherein the negative electrode active material is lithium, zinc, sodium, aluminum, magnesium, calcium, iron, or potassium, and the positive electrode active material is oxygen or carbon dioxide.

[12] A metal secondary battery as described above.

[14] A dispersion in which fibrous carbon material is dispersed in a solvent as a raw material for the cathode layer of a porous layer, A porous substrate made of fibrous carbon material is used as a channel layer for gas diffusion in the porous layer, Steps to prepare, The steps include: filtering the dispersion on the porous substrate to form the positive electrode layer on the channel layer; Includes, The fibrous carbon material used in the dispersion has a specific surface area of ​​350 m² by the BET method. 2 / g or more 1400m 2 / g or less, The porous substrate has a pore size of 30 μm or more and a density of 0.01 g / cm³. 3 More than 0.30g / cm 3 Having the following density, A method for manufacturing a positive electrode as described in any of [1] to

[11] . [Effects of the Invention]

[0018] According to one aspect of the present invention, a novel positive electrode for a metal secondary battery, different from existing positive electrodes, specifically a channel-integrated positive electrode for a metal secondary battery and a method for manufacturing the same, can be provided.

[0019] According to one aspect of the present invention, a metal secondary battery can be provided that has superior output and capacity characteristics compared to conventional metal secondary batteries, and that can significantly improve discharge characteristics in air, as described below.

[0020] According to one aspect of the present invention, a channel-integrated positive electrode for a metal secondary battery is provided, in which the channel layer and the positive electrode layer are integrated. Therefore, with a metal secondary battery using this positive electrode, the effective electrode area can be easily scaled up by stacking planar single cells. Therefore, according to the present invention, a metal secondary battery with superior output and capacity characteristics compared to conventional metal secondary batteries can be provided.

[0021] According to one aspect of the present invention, a gas diffusion layer made of a fibrous carbon material such as carbon fiber is used as the flow channel layer, making it possible to provide a thin and light flow channel layer. Therefore, with a metal secondary battery using this positive electrode, when stacking planar single cells to scale up the effective electrode area and obtain output and capacity, the gravimetric energy density can be improved compared to conventional metal secondary batteries that use metal as the flow channel layer for supplying oxygen gas between stacked positive electrode layers. In particular, in conventional metal secondary batteries that substitute the flow channel layer with a fuel cell separator made of metal or graphite carbon (this is not a separator for secondary batteries, but a component for stacking cells while supplying fuels such as hydrogen or methanol to fuel cell cells), the fuel cell separator is heavy (specifically, 50 mg / cm³). 2 Because it becomes extremely thick (specifically, more than 500 μm), the present invention makes it possible to dramatically improve the gravimetric energy density and volumetric energy density compared to such conventional metal secondary batteries.

[0022] According to one aspect of the present invention, a channel-integrated positive electrode for a metal secondary battery can be provided, which has a pore structure in which the boundary between the positive electrode layer and the channel layer cannot be clearly distinguished, that is, a pore structure having a continuous pore size distribution advantageous for oxygen supply. Therefore, according to the present invention, by manufacturing a metal secondary battery (for example, a lithium-air battery stack cell) using this channel-integrated positive electrode, it is possible to provide a metal secondary battery with superior battery capacity and output compared to a metal secondary battery that uses a simple laminate in which the positive electrode layer and the channel layer are simply stacked, or a laminate in which the positive electrode layer and the channel layer are bonded together with significant adhesive strength but do not achieve the continuous pore size distribution described above.

[0023] According to one aspect of the present invention, a channel-integrated positive electrode for a metal secondary battery is provided, which has a pore structure having a continuous pore size distribution between the positive electrode layer and the channel layer. Therefore, according to the present invention, by manufacturing a metal secondary battery (for example, a lithium-air battery stack cell) using this channel-integrated positive electrode, a metal secondary battery with excellent discharge capacity even in an atmosphere with a relatively low oxygen concentration (oxygen concentration of about 20%) can be provided. In other words, according to the present invention, even when operating in the atmosphere, a battery capacity equivalent to or greater than that under a pure oxygen atmosphere can be obtained. Therefore, a metal secondary battery that can significantly improve discharge characteristics in the atmosphere can be provided.

[0024] According to one aspect of the present invention, a channel-integrated positive electrode for a metal secondary battery is provided, which has a pore structure having a continuous pore size distribution between the positive electrode layer and the channel layer. Therefore, according to the present invention, by manufacturing a metal secondary battery (for example, a lithium-air battery stack cell) using this channel-integrated positive electrode, a metal secondary battery with excellent gas exchange function can be provided. Accordingly, according to the present invention, improvements in charge-discharge cycle characteristics (for example, low charge overvoltage and increased discharge cycles) can be achieved.

[0025] According to one aspect of the present invention, a channel-integrated positive electrode for a metal secondary battery can be provided, which has a pore structure having a continuous pore size distribution between the positive electrode layer and the channel layer. Therefore, it is possible to provide a metal secondary battery with a larger capacity and higher energy density compared to currently popular metal secondary batteries (e.g., lithium-ion batteries). For this reason, the present invention is expected to provide a metal secondary battery that is practically advantageous. [Brief explanation of the drawing]

[0026] [Figure 1] Figure 1 is a schematic diagram showing the method for fabricating a laminate from a flow channel layer in the example. [Figure 2] Figure 2 is a schematic diagram of the test specimen and peel test apparatus used for the peel test. [Figure 3]Figure 3 shows a scanning electron microscope image of a cross-section of a "CNT1w / CP1 laminate," which is a specific embodiment of the present invention. [Figure 4] Figure 4 shows a scanning electron microscope image of the delamination surface on the CP1 (channel layer) side of a "CNT1w / CP1 laminate," which is a specific embodiment of the present invention, after a delamination test. [Figure 5] Figure 5 shows an XCT (X-ray computed tomography) image of a cross-section of a "CNT1w / CP1 laminate," which is a specific embodiment of the present invention. [Figure 6] Figure 6 is a plot of the proportion of the occupied volume of the CNT (carbon nanotube) portion, the carbon fiber (CF) portion, and the void portion (Void) portion that constitute the "CNT1w / CP1 laminate" obtained in Figure 5, plotted against the thickness direction. [Figure 7] Figure 7 shows the results of measurements performed by the mercury intrusion method for a "CNT1w / CP1 laminate" (positive electrode sheet of Example 1), which is a specific embodiment of the present invention, and a "simple laminate" in which the positive electrode sheet of Example 3 is simply stacked as the positive electrode layer and CP1 as the flow channel layer. [Figure 8] Figure 8 shows the results of measurements performed using the mercury intrusion method for the "CNT4p / CP4 laminate," which is the positive electrode sheet of Example 8, and the "simple laminate," which is simply a stack of the positive electrode sheet of Example 9 as the positive electrode layer and CP4 as the flow channel layer. [Figure 9] Figure 9 is a schematic diagram showing the configuration of one embodiment of a lithium-air battery cell (wherein (a) in the figure is a schematic diagram showing the configuration of a lithium-air battery cell (Cell Examples 1, 2, 4, 6, 8, 10) in which a laminate in which the flow channel layer and the positive electrode layer are integrated is used as the positive electrode, and (b) is a schematic diagram showing the configuration of a conventional lithium-air battery cell (Cell Examples 3, 5, 7, 9, 11) in which a simple laminate in which only the positive electrode layer and the flow channel layer are simply stacked is used as the positive electrode). [Figure 10] Figure 10 shows the discharge test results of lithium-air battery stack cells for Cell Example 1 and Cell Example 3. [Figure 11]Figure 11 shows the charge-discharge cycle test results for lithium-air battery stack cells of cell examples 10 and 11 (where (a) in the figure shows the charge-discharge curve of the lithium-air battery stack cell of cell example 10; (b) in the figure shows the charge-discharge curve of the lithium-air battery stack cell of cell example 10; and (c) in the figure shows the voltage at the end of discharge and the end of charge with respect to the number of cycles for lithium-air battery stack cells of cell examples 10 and 11). [Modes for carrying out the invention]

[0027] The embodiments for carrying out the present invention will be described in detail below. However, it should be noted that the present invention is not limited to the embodiments described below, and can be implemented in various ways within the scope of its gist. For example, in order to help understand the present invention, the case in which the metal secondary battery is a lithium-air battery may be described as an example, but it should be noted that the application of the channel-integrated positive electrode for metal secondary batteries of the present invention is not limited to lithium-air battery positive electrodes, and can also be applied to positive electrodes for batteries equipped with a positive electrode that has a mechanism for absorbing and discharging external gas (so-called open-type batteries).

[0028] One aspect of the present invention, a "channel-integrated positive electrode for metal secondary batteries" (hereinafter also referred to as "the positive electrode of the present invention"), includes, as described above, a gas diffusion channel layer made of a porous layer of fibrous carbon material, and a positive electrode layer made of a porous layer of the same or different fibrous carbon material as the carbon material, wherein a portion of the channel layer includes pores formed by the entanglement of the fibrous carbon material in the channel layer and the fibrous carbon material of the positive electrode layer that enters the channel layer, and the pores provided by the channel layer and the positive electrode layer have a continuous pore size distribution of 10 nm to 200 μm, and the channel layer and the positive electrode layer are integrated by the continuous pore size distribution, thus forming a channel-integrated positive electrode for metal secondary batteries.

[0029] The "gas diffusion channel layer of the porous layer" constituting the positive electrode of the present invention only needs to have a gas diffusion mechanism capable of drawing in and exhausting external gases such as oxygen and carbon dioxide in a metal secondary battery, and the channel layer is a porous layer made of fibrous carbon material. The fibrous carbon material is not particularly limited as long as it is used as a material for a gas diffusion layer in a metal secondary battery (for example, an air battery such as a lithium-air battery or a fuel cell), and examples include carbon fibers, carbon nanotubes, and graphitized carbon fibers. These may also be used in combination, for example, carbon fibers and carbon nanotubes may be used in combination. Typically, it is preferable to use carbon fibers and / or carbon nanotubes, and it is more preferable to use carbon fibers.

[0030] The fibrous carbon material must be porous, and the lower limit of its porosity is preferably 85% or more, and more preferably 90% or more. The upper limit of its porosity is preferably 99.5% or less, and more preferably 98.5% or less, from the viewpoint of ensuring the physical strength of the flow channel layer. However, the present invention is not limited to these porosities as long as the objectives of the present invention can be achieved.

[0031] The density of the flow channel layer is not particularly limited as long as the objectives of the present invention are achieved, but is 0.01 g / cm³. 3 More than 0.30g / cm 3 Preferably, it is 0.02 g / cm³. 3 More than 0.20g / cm 3 It is more preferable that the following is the case: 0.05 g / cm³ 3 More than 0.15g / cm 3 The following is even more preferable:

[0032] The thickness of the flow channel layer is not particularly limited as long as the objectives of the present invention are achieved, but is typically preferably in the range of 50 μm to 500 μm, and more preferably 120 μm to 400 μm. It is desirable to appropriately adjust the thickness of the flow channel layer considering the thickness of the metal secondary battery to be designed, the thickness of the positive electrode layer, etc.

[0033] The "positive electrode layer" constituting the positive electrode of the present invention is a porous layer made of a fibrous carbon material. The fibrous carbon material is not particularly limited as long as it is a fibrous carbon material used as a positive electrode layer in metal secondary batteries (e.g., air batteries such as lithium-air batteries or fuel cells). For example, like the fibrous carbon material used in the "channel layer" constituting the positive electrode of the present invention, examples include carbon fibers, carbon nanotubes, and graphitized carbon fibers. Alternatively, a combination of carbon fibers and carbon nanotubes may be used. Thus, the fibrous carbon material used in the "positive electrode layer" constituting the positive electrode of the present invention may be the same as or different from the fibrous carbon material used in the "channel layer" constituting the positive electrode. Specifically, for example, the same type of carbon nanotube can be used in both the "channel layer" and the "positive electrode layer," and it is also possible to use carbon fibers in the "channel layer" and carbon nanotubes different from carbon fibers in the "positive electrode layer." Typically, the use of carbon fibers and / or carbon nanotubes is preferred, and the use of carbon nanotubes is more preferred. The carbon nanotube may be a single-walled carbon nanotube (SWNT), a double-walled carbon nanotube (DWNT), a multi-walled carbon nanotube (MWNT), or a mixture thereof.

[0034] The specific surface area of ​​the fibrous carbon material used in the positive electrode layer, as measured by the BET method, is 350 m². 2 / g or more 1400m 2 It is preferable that it be less than / g, and 400m 2 / g or more 1300m 2 It is more preferable that it be less than / g, and 500m 2 / g or more 1250m 2 It is even more preferable that the amount be less than or equal to / g.

[0035] The pore volume of the fibrous carbon material used in the positive electrode layer, measured by the BJH method, is 1.1 cm³, where the pore volume occupied by pores with a diameter of 2 nm to 1000 nm is 1.1 cm³. 3 / g or more 20cm 3 It is preferable that the amount be less than or equal to 1.2 cm.3 / g or more 15cm 3 It is more preferable that it be less than or equal to / g, and 1.5cm 3 / g or more 12cm 3 It is even more preferable that the amount be less than or equal to / g.

[0036] The thickness of the positive electrode layer is not particularly limited as long as the objectives of the present invention are achieved, but is typically preferably in the range of 10 μm to 500 μm, more preferably 50 μm to 300 μm, and even more preferably 100 μm to 200 μm. The thickness of the positive electrode layer should be appropriately adjusted considering the thickness of the metal secondary battery to be designed, the thickness of the flow channel layer, etc. Specifically, it is preferable to adjust the combined thickness of the positive electrode layer and the flow channel layer to be 60 μm to 1000 μm, more preferably 100 μm to 600 μm, and even more preferably 140 μm to 450 μm.

[0037] The positive electrode of the present invention is a "channel-integrated positive electrode for metal secondary batteries" as described above. Here, "metal secondary battery" refers to one that uses a metal as the negative electrode active material and an external gas such as oxygen or carbon dioxide as the positive electrode active material. Examples of metals for the negative electrode active material include, but are not limited to, lithium, zinc, sodium, aluminum, magnesium, calcium, iron, and potassium. Specific examples of metal secondary batteries include, but are not limited to, lithium-air batteries, zinc-air batteries, sodium-air batteries, aluminum-air batteries, magnesium-air batteries, calcium-air batteries, iron-air batteries, potassium-air batteries, and lithium-carbon dioxide batteries. However, the positive electrode of the present invention is preferably used as a positive electrode for a metal-air battery using oxygen as the positive electrode active material, and is more preferably used as a positive electrode for a lithium-air battery. As the oxygen for the positive electrode active material, pure oxygen, atmospheric oxygen, or a gas containing any oxygen partial pressure can be used. From the viewpoint of the output characteristics during discharge of a metal secondary battery, a higher oxygen concentration is generally preferable.

[0038] Furthermore, in the positive electrode of the present invention, a portion of the channel layer includes pores formed by the entanglement of fibrous carbon material in the channel layer and fibrous carbon material in the positive electrode layer that enters the channel layer, and the pores provided by the channel layer and the positive electrode layer have a continuous pore size distribution of 10 nm to 200 μm, and the channel layer and the positive electrode layer are integrated by this continuous pore size distribution. In other words, the positive electrode of the present invention has a laminated structure in which a channel layer is stacked on top of a positive electrode layer. Moreover, a portion of the channel layer on the side in contact with the positive electrode layer (specifically, the surface portion of the channel layer in contact with the positive electrode layer) has a structure in which pores are formed by the entanglement of fibrous carbon material in the channel layer and fibrous carbon material in the positive electrode layer that enters the channel layer. Here, the pores provided by the channel layer, excluding the pores corresponding to the cavities appearing in a part of the channel layer, specifically have a pore diameter of approximately 100 μm to 200 μm. The pores provided by the positive electrode layer, specifically have a pore diameter of approximately 10 nm to 10 μm. The pores corresponding to the cavities appearing in a part of the channel layer, specifically have a pore diameter of approximately 10 μm to 100 μm. Therefore, in the positive electrode of the present invention, the pores provided by the channel layer and the positive electrode layer have a continuous pore diameter distribution of 10 nm to 200 μm, and the channel layer and the positive electrode layer become integrated by this continuous pore diameter distribution. In this application, such integration is also referred to as the channel layer and the positive electrode layer being integrated from the viewpoint of pore diameter distribution.

[0039] On the other hand, simply stacking the channel layer and the positive electrode layer, as in the conventional method, does not produce the aforementioned cavities (i.e., pores). In this case, the pores provided by the channel layer and the positive electrode layer consist only of pores provided by the channel layer (specifically, pores with a diameter of approximately 100 μm to 200 μm) and pores provided by the positive electrode layer (specifically, pores with a diameter of approximately 10 nm to 10 μm). Therefore, pores corresponding to the aforementioned cavities (specifically, pores with a diameter of approximately 10 μm to 100 μm) do not appear in the pores provided by the channel layer and the positive electrode layer, and this effect appears as a discontinuous pore size distribution in the pore size distribution between 10 nm and 200 μm. As a result, the continuous pore size distribution described above is not achieved. In other words, the channel layer and the positive electrode layer are not integrated from the viewpoint of pore size distribution.

[0040] As described above, the "integrated channel" in the "channel-integrated positive electrode for metal secondary batteries," which is one aspect of the present invention, means that the pores provided by the channel layer and the positive electrode layer, which include some pores of cavities formed by the entanglement of the fibrous carbon material in the channel layer and the fibrous carbon material in the positive electrode layer that enters the channel layer, have a continuous pore size distribution of 10 nm to 200 μm, and the channel layer and the positive electrode layer are integrated by this continuous pore size distribution. This is understood to be because the fibrous carbon material of the positive electrode layer component enters the channel layer that is in contact with the positive electrode layer, cavities are formed by the entanglement with the fibrous carbon material of the channel layer component, and a portion (so-called layer) is formed in a part of the channel layer on the side in contact with the positive electrode layer that has the fibrous carbon material of the positive electrode layer component, the fibrous carbon material of the channel layer component and cavities formed by the entanglement of the two, and these cavities provide pores that connect the pores of the positive electrode layer and the pores of the channel layer.

[0041] The pore size distribution of the positive electrode of the present invention is measured by a known mercury intrusion method. The mercury intrusion method is a method that utilizes the high surface tension of mercury to apply pressure to infiltrate mercury into the pores of a powder, and then determines the specific surface area and pore size distribution from the pressure and the amount of mercury injected.

[0042] According to the positive electrode of the present invention, since it has the above-described "integrated flow channel" structure, the flow channel layer and the positive electrode layer are integrated in terms of pore size distribution. In this case, the adhesion between the positive electrode layer and the flow channel layer exhibits significant adhesive strength (specifically, 1 mN / 5 mm or more in a 90-degree peel test) that allows the flow channel layer and the positive electrode layer to remain attached to each other even when cut with a cutting tool such as scissors or a cutter. In this application, such integration is also referred to as the flow channel layer and the positive electrode layer being integrated in terms of adhesive strength. Thus, according to the positive electrode of the present invention, the positive electrode layer and the flow channel layer are integrated in terms of both adhesive strength and pore size distribution.

[0043] On the other hand, it should be noted that even if the adhesion between the positive electrode layer and the channel layer shows a significant adhesive strength of 1 mN / 5 mm or more in a 90-degree peel test, this does not necessarily mean that the channel layer and the positive electrode layer are integrated from the viewpoint of pore size distribution. This is because even if adhesion with significant adhesive strength is achieved by the fibrous carbon material of the positive electrode layer entering the channel layer, the pore size of both the fibrous carbon material of the channel layer and the fibrous carbon material of the positive electrode layer is small, so the fibrous carbon material of the positive electrode layer cannot penetrate deep into the channel layer, resulting in insufficient entanglement with the fibrous carbon material of the channel layer, and thus no cavity formation due to entanglement between the two may occur.

[0044] As described above, the "part of the flow channel layer" constituting the positive electrode of the present invention is a portion (so-called layer) having a fibrous carbon material of the positive electrode layer component, a fibrous carbon material of the flow channel layer component, and a cavity formed by the entanglement of the two. The thickness of the layer is preferably at least 5 μm, more preferably 10 μm, and even more preferably 20 μm. The upper limit of the thickness of the layer is not more than or equal to the thickness of the flow channel layer itself.

[0045] As described above, the "void pores" constituting the positive electrode of the present invention refer to pores that are cavities formed on the surface portion of the flow channel layer in contact with the positive electrode layer, due to the entanglement of the fibrous carbon material in the flow channel layer and the fibrous carbon material of the positive electrode layer that enters the flow channel layer. The pore size distribution of these "void pores" is not particularly limited as long as the objective of the present invention is achieved, but it is generally preferable to have a continuous pore size distribution of 10 μm to 50 μm.

[0046] Furthermore, the aforementioned "pores in the cavity" can be visually observed using an electron microscope or X-ray computed tomography. For example, in electron microscope observation, they are observed as images using a scanning electron microscope, and in X-ray computed tomography observation, they are observed as images using an X-ray CT (X-ray computed tomography) device.

[0047] The specific surface area of ​​the positive electrode of this invention, as determined by the BET method, is 250 m². 2 / g or more 1400m 2 It is preferable that it be less than / g, and 400m 2 / g or more 1300m 2 It is more preferable that it be less than / g, and 500m 2 / g or more 1250m 2 It is even more preferable that the amount be less than or equal to / g.

[0048] In the positive electrode of the present invention, the pores having a pore size distribution of 0.1 μm to 10 μm have a pore volume of 1.0 cm³ per gram of weight of the positive electrode layer (specifically, per gram of weight of CNTs (carbon nanotubes), which are components of the positive electrode layer). 3 / g or more 10.0cm 3 Preferably, the value is less than or equal to / g, and 1.2cm 3 / g or more 6.0cm 3 It is more preferable that it be less than or equal to / g, and 1.5cm 3 / g or more 5.0cm 3 It is even more preferable that the amount be less than or equal to / g.

[0049] One aspect of the present invention, a "metal secondary battery" (hereinafter also referred to as "the metal secondary battery of the present invention"), comprises a positive electrode, a negative electrode containing a metal, and an electrolyte between the positive electrode and the negative electrode, and uses the above-mentioned "channel-integrated positive electrode for metal secondary batteries" as the positive electrode. Components other than the positive electrode may be those used in conventional metal secondary batteries. For example, the negative electrode containing a metal uses a metal as the negative electrode active material. Specifically, examples of metals used as the negative electrode active material include lithium, zinc, sodium, aluminum, magnesium, calcium, iron, or potassium. Examples of positive electrode active materials include oxygen or carbon dioxide.

[0050] As described above, the positive electrode of the present invention is preferred as a positive electrode for a metal-air battery using oxygen as the positive electrode active material, and more preferably as a positive electrode for a lithium-air battery. Therefore, for a negative electrode containing metal, it is preferable to use lithium as the metal that is the negative electrode active material. Lithium may be pure lithium metal or a lithium alloy. Elements that form a lithium alloy with lithium include, but are not limited to, magnesium, titanium, tin, lead, aluminum, indium, silicon, zinc, antimony, bismuth, gallium, germanium, and yttrium. Furthermore, there are no particular restrictions on the type of electrolyte, and those used in conventional metal secondary batteries can be used, and a separator may be provided in the electrolyte.

[0051] An example of the metal secondary battery of the present invention is shown in a schematic diagram in Figure 9(a). The "metal secondary battery" shown in Figure 9(a) comprises a lithium metal foil as a negative electrode active material and a negative electrode current collector in contact with the lithium metal foil, and uses the "channel-integrated positive electrode for metal secondary batteries" described above as the positive electrode. The negative electrode current collector is made of a conductive metal material or carbon, and may have terminals (not shown) for external connection. In the negative electrode, the negative electrode active material and the negative electrode current collector may be constructed separately or as an integrated unit. Also, as shown in the figure, a separator may be provided between the lithium metal foil as the negative electrode active material and the positive electrode. In the positive electrode, the positive electrode layer (referred to as the "positive electrode layer integrated with the channel layer" in the figure) and the positive electrode current collector may be constructed separately or as an integrated unit. The positive electrode current collector may be made of a metal material such as aluminum, nickel, or stainless steel, and among these, aluminum is preferred because it is easy to process and inexpensive.

[0052] One aspect of the present invention, "Method for Manufacturing a Channel-Integrated Positive Electrode for Metal Secondary Batteries," includes the steps of: preparing a dispersion liquid in which a fibrous carbon material is dispersed in a solvent as a raw material for the positive electrode layer of the porous layer; and preparing a porous substrate made of a fibrous carbon material as a channel layer for gas diffusion in the porous layer; and forming the positive electrode layer on the channel layer by filtering the dispersion liquid on the porous substrate, wherein the fibrous carbon material used in the dispersion liquid has a BET specific surface area of ​​350 m². 2 / g or more 1400m 2 The porous substrate has a pore size of 30 μm or more and a concentration of 0.01 g / cm³ or less. 3 More than 0.30g / cm 3 It has the following density:

[0053] As the "fibrous carbon material" used as the raw material for the cathode layer of the porous layer, the "fibrous carbon material" already described in the "cathode layer" constituting the cathode of the present invention may be used. There are no particular restrictions on the solvent used to disperse the "fibrous carbon material" as long as the objective of the present invention can be achieved, but typically, water or 2-propanol is preferred.

[0054] The gas diffusion channel layer of the porous layer is specifically as described in the section on the "gas diffusion channel layer of the porous layer" that constitutes the positive electrode of the present invention. A "porous substrate made of fibrous carbon material" is used as the gas diffusion channel layer of the porous layer, but there are no particular restrictions on the porous substrate as long as it is a substrate made of fibrous carbon material that is used as a gas diffusion layer (i.e., a channel layer) in metal secondary batteries (for example, air batteries such as lithium-air batteries or fuel cells). Examples include aggregates of carbon fibers (specifically, carbon paper, carbon cloth, or carbon felt, etc.) and aggregates of carbon nanotubes or graphitized carbon fibers (specifically, sheets or nonwoven fabrics of carbon nanotubes, etc.). Preferably, it is an aggregate of carbon fibers and / or carbon nanotubes, and more preferably, it is carbon paper which is an aggregate of carbon fibers.

[0055] The filtration in the step of forming the positive electrode layer on the channel layer by filtering the dispersion on the porous substrate can be carried out using a known method. For example, the dispersion is an aqueous dispersion of carbon nanotubes which is filtered by suction onto carbon paper (CP) and then dried. This forms the positive electrode layer on the channel layer.

[0056] The fibrous carbon material used in the dispersion has a specific surface area of ​​350 m² by the BET method. 2 / g or more 1400m 2 It is preferable that it be less than / g, and 400m 2 / g or more 1300m 2 It is more preferable that it be less than / g, and 500m 2 / g or more 1250m 2 It is even more preferable that the amount be less than or equal to / g.

[0057] The porous substrate preferably has a pore diameter of 30 μm or more, more preferably 50 μm or more, and even more preferably 70 μm or more.

[0058] The density of the porous substrate is as already described in "Density of the flow channel layer," which is 0.01 g / cm³. 3 More than 0.30g / cm 3 Preferably, it is 0.02 g / cm³. 3 More than 0.20g / cm 3 It is more preferable that the following is the case: 0.05 g / cm³ 3 More than 0.15g / cm 3 The following is even more preferable:

[0059] With regard to conditions not specified in this application, there are no particular restrictions as long as the objectives of the present invention are achieved. [Examples]

[0060] Next, embodiments of the present invention will be described in more detail, but embodiments of the present invention are not limited to the following examples unless they exceed the gist of the invention.

[0061] <Cathode layer raw material> Table 1 shows the properties of the fibrous carbon material (hereinafter also referred to as "cathode carbon material") used as a cathode layer raw material in the examples. The fibrous carbon material used was a porous single-walled carbon nanotube (hereinafter also referred to as "CNT" or "fibrous CNT") as described below.

[0062] Single-walled carbon nanotube 1 (hereinafter also referred to as "CNT1") was produced using ZEONANO SG101 purchased from Zeon Corporation of Japan. Single-walled carbon nanotube 2 (hereinafter also referred to as "CNT2") was produced by the supergloss method in accordance with the description in Non-Patent Document 1 mentioned above and used as a raw material. Specifically, a silicon substrate coated with Fe (2 nm) / Al2O3 (40 nm) by sputter deposition was sealed in a ring furnace and annealed at 750°C for 6 minutes under 1 atmospheric pressure while supplying a He / H2 mixed gas (mixing ratio 1 / 9) at a flow rate of 1000 sccm. Next, a He / H2 mixed gas containing water (150 ppm) and ethylene (10%) was supplied at a flow rate of 1000 sccm for 10 minutes to grow a carbon nanotube aggregate on the silicon substrate, which was used as the raw material for single-walled CNT2. Single-walled carbon nanotube 3 (hereinafter also referred to as "CNT3") was purchased as Tuball® single-walled carbon nanotube manufactured by OCSiAl and used as a raw material. Single-walled carbon nanotube 4 (hereinafter also referred to as "CNT4") was purchased as single-walled carbon nanotube (product name: EC2.0) manufactured by Meijo Nanocarbon Co., Ltd. and used as a raw material.

[0063] [Table 1]

[0064] <Preparation of cathode carbon material dispersion> The cathode carbon materials listed in Table 1 were dispersed in water or 2-propanol under the conditions described below to prepare cathode carbon material dispersions. Table 2 shows the combinations of cathode carbon materials and dispersion solvents for the prepared cathode carbon material dispersions.

[0065] CNT1w, CNT2w, and CNT3w in Table 2 were prepared by mixing CNT1, CNT2, and CNT3, respectively, as CNT (i.e., carbon nanotube) samples in small amounts of pure water, pre-dispersing them with a mixer (conditions: SMT Corporation Highflex homogenizer HF93, rotation speed 9000 rpm, 3 minutes), and then adding pure water to achieve a CNT sample concentration of 0.05 wt%. These CNT aqueous dispersions were then ultrasonically treated at room temperature (conditions: Branson 450D, output 50W, 50 seconds) to obtain cathode carbon material dispersions (i.e., CNT1w, CNT2w, and CNT3w). CNT4 could not be dispersed at all in water and therefore could not be prepared as a dispersion.

[0066] CNT1p, CNT2p, CNT3p, and CNT4p were prepared by mixing CNT1, CNT2, CNT3, and CNT4, respectively, in a small amount of isopropanol, pre-dispersing them with a mixer (conditions: SMT Corporation Highflex homogenizer HF93, rotation speed 9000 rpm, 3 minutes), and then adding isopropanol to achieve a CNT sample concentration of 0.05% by weight. These CNT isopropanol dispersions were then sonicated in an ice bath (conditions: Branson 450D, output 20W, 180 minutes) to obtain cathode carbon material dispersions.

[0067] [Table 2]

[0068] <Flow channel layer> Table 3 shows the properties of the flow channel layers used in the examples. The fibrous carbon material used as the flow channel layer was the following porous carbon paper (hereinafter also referred to as "CP"), which is mainly composed of carbon fibers (hereinafter also referred to as "CF") (in other words, an aggregate of carbon fibers). Flow channel layer 1 (hereinafter also referred to as "CP1") used Kureha Corporation's Kureka Paper E704. Flow channel layer 2 (hereinafter also referred to as "CP2") used Technical Fibre Products' Carbon Veil Optiveil® 20352A. Flow channel layer 3 (hereinafter also referred to as "CP3") used Mitsubishi Chemical Corporation's Pyrofil MFL. Flow channel layer 4 (hereinafter also referred to as "CP4") used Toray Industries' carbon paper TGP-H-030.

[0069] [Table 3]

[0070] <Fabrication of a laminate consisting of a channel layer and a cathode layer> Each cathode carbon material dispersion, which forms the cathode layer as shown in Table 2, was filtered by suction onto carbon paper (CP) (specifically, CP1-CP4 in Table 3) which forms the channel layer, and then dried to obtain a laminate in which the channel layer and the cathode layer are bonded to each other. The term "bonding" as used here includes not only cases where the laminate exhibits significant bonding strength (specifically, 1 mN / 5 mm or more in a 90-degree peel test), as described later, but also cases where it is merely attached (specifically, less than 1 mN / 5 mm in a 90-degree peel test). Figure 1 shows a schematic diagram of the method for producing the laminate.

[0071] <Evaluation of integration between the flow channel layer and the cathode layer by peeling tests> The adhesive strength between the channel layer and the positive electrode layer in the obtained laminate was evaluated using the peel test apparatus shown in Figure 2, according to a 90-degree peel test. Specifically, the obtained laminate was cut into strips measuring 5 mm (width) x 15 mm (length), and the channel layer side (carbon paper side) was attached to one end of a glass piece using double-sided tape to form a test specimen. A weight (0.1 g = approximately 0.1 gf = approximately 1.0 mN) was fixed vertically to the positive electrode layer side (CNT side) of this test specimen using adhesive tape, and weights were added until the positive electrode layer peeled off the test specimen. This was repeated five or more times, and the average value of the load corresponding to the number of weights just before the positive electrode layer peeled off was determined as the adhesive strength. Since a significant adhesive strength of 1 mN / 5 mm or more in a 90-degree peel test indicates that the flow channel layer and the positive electrode layer are integrated as a laminate in terms of adhesive strength, if the measured adhesive strength is 1 mN / 5 mm or more in a 90-degree peel test, the laminate is evaluated as being integrated in terms of adhesive strength between the flow channel layer and the positive electrode layer (○). If the measured adhesive strength is less than 1 mN / 5 mm in a 90-degree peel test, the laminate is evaluated as not being integrated in terms of adhesive strength between the flow channel layer and the positive electrode layer (×).

[0072] As a result, it was confirmed that when CNT1w, CNT2w, or CNT3w is used as the cathode carbon material dispersion for the cathode layer and CP1 or CP2 is used as the channel layer, the above-mentioned significant adhesive strength is obtained (i.e., the evaluation is ○), and also when CNT3p or CNT4p is used as the cathode carbon material dispersion for the cathode layer and CP3 or CP4 is used as the channel layer, the above-mentioned significant adhesive strength is obtained (i.e., the evaluation is ○). In these cases, it was also confirmed that the channel layer and the cathode layer remain adhered to each other even when cut with cutting tools such as scissors or cutters.

[0073] When CNT1w, CNT2w, CNT3w, CNT1p, or CNT2p is used as the positive electrode carbon material dispersion and CP3 or CP4 is used as the channel layer, it was confirmed that delamination between the channel layer and the positive electrode layer is easy, and the significant adhesive strength described above cannot be obtained (i.e., the evaluation is ×). Similarly, when CNT2p is used as the positive electrode carbon material dispersion and CP1 or CP2 is used as the channel layer, it was confirmed that delamination between the channel layer and the positive electrode layer is easy, and the significant adhesive strength described above cannot be obtained (i.e., the evaluation is ×). Furthermore, when CNT1p, CNT3p, or CNT4p is used as the positive electrode carbon material dispersion and CP1 or CP2 is used as the channel layer, it was confirmed that the positive electrode carbon material components pass through the channel layer, and a laminate in which the channel layer and the positive electrode layer are adhered to each other cannot be obtained (i.e., the evaluation is ×).

[0074] <Evaluation of integration between the channel layer and the cathode layer using microscopic images> Figure 3 shows a scanning electron microscope image of a cross-section of a laminate (hereinafter also referred to as the "CNT1w / CP1 laminate") fabricated by the above method, where CNT1w is used as the cathode carbon material dispersion for the cathode layer and CP1 is used as the channel layer, after being cut with scissors. This indicates that the channel layer and the cathode layer were evaluated to be integrated in terms of adhesive strength in the peel test described above. As shown in Figure 3, it was confirmed that a CNT1 layer (a single-walled carbon nanotube CNT1 layer that forms the cathode layer, derived from the cathode carbon material dispersion CNT1w) with a thickness of approximately 80 μm was attached to a CP1 layer with a thickness of approximately 300 μm. In addition, as shown in Figure 3, it was confirmed that in the portion where the channel layer CP1 is in contact with the CNT1 layer of the cathode layer, the fibrous CNT (specifically, CNT1) component of the CNT1 layer penetrates the channel layer CP1, intertwines with the carbon fibers of CP1, and forms pores. In other words, with respect to the laminate that was evaluated in the above peel test as having an integrated channel layer and cathode layer, it was confirmed that a portion of the channel layer contains pores formed by the entanglement of carbon fibers in the channel layer and fibrous CNTs from the cathode layer that enter the channel layer.

[0075] Figure 4 shows a scanning electron microscope image of the delamination surface on the CP1 side of the CNT1w / CP1 laminate after the delamination test. From the microscope image of the delamination surface, it was observed that the fibrous CNT (specifically, CNT1) component from the CNT1 layer, which is the positive electrode layer that penetrated into the channel layer (CP1), remained on the CP1 side even after delamination, as indicated by the dotted circle. This residue of fibrous CNTs (specifically, CNT1) on the delamination surface on the channel layer side was also confirmed by visual observation. Although not shown in the figures, in all other laminates in this embodiment that showed a significant adhesive strength of 1 mN / 5 mm or more in the 90-degree delamination test, it was confirmed by microscope or visual observation that the positive electrode was composed of fibrous CNTs (specifically, CNT1) from the positive electrode layer that penetrated into the channel layer.

[0076] Figure 5 shows a cross-sectional image of a CNT1w / CP1 laminate taken with an X-ray CT (X-ray computed tomography) device (Carl Zeiss XRadia520Versa). Although the X-ray CT image in Figure 5 differs from the electron microscope cross-sectional observation in Figure 3 in that it is a non-destructive observation of the sample cross-section, as shown in the figure, it was confirmed that the fibrous CNT (specifically CNT1) component on the CNT1 layer side, which is the positive electrode layer, penetrates the channel layer and intertwines with the carbon fibers of the channel layer (specifically CP1), visually creating many cavities (i.e., pores). Although not shown in the figure, in the examples of this application, similar findings were observed in other laminates that showed a significant adhesive strength of 1 mN / 5 mm or more in the 90-degree peel test, except for the laminate prepared by the above method when CNT4p was used as the positive electrode carbon material dispersion liquid for the positive electrode layer and CP4 was used as the channel layer (hereinafter also referred to as "CNT4p / CP4 laminate"). In other words, with respect to the laminates in which the channel layer and the cathode layer were evaluated as being integrated in terms of adhesive strength in the above peel test, it was confirmed that, except for the CNT4p / CP4 laminate, a portion of the channel layer contains pores formed by the entanglement of carbon fibers in the channel layer and fibrous CNTs from the cathode layer that enter the channel layer.

[0077] Figure 6 plots the proportion of the occupied volume of the CNT portion (specifically, the CNT1 portion), the carbon fiber portion (specifically, the carbon fiber portion of CP1), and the void portion (specifically, the pore portion of the void formed when the fibrous CNT1 component on the CNT1 layer side, which is the positive electrode layer, penetrates the CP1 channel layer and intertwines with the carbon fibers of the channel layer) against the thickness direction. In the figure, the CNT portion, carbon fiber portion, and void portion are denoted as CNT portion (carbon nanotube portion), carbon fiber portion (CF portion), and void portion (Void portion), respectively. In the CNT1w / CP1 laminate, it was confirmed that the clear interface separating the positive electrode layer of CNT1 and the channel layer of CP1 disappears, and a portion where the CNT portion, carbon fiber portion, and void portion are mixed together (a so-called layer) is formed with a thickness of 100 μm or more. In the embodiments of this application, for all other laminates that showed a significant adhesive strength of 1 mN / 5 mm or more in the 90-degree peel test, it was confirmed that, with the exception of the CNT4p / CP4 laminate, similar parts (so-called layers) were formed in which the CNT parts, carbon fiber parts, and cavities were mixed together.

[0078] <Measurement of sheet properties of laminates composed of a flow channel layer and a cathode layer, and a single cathode layer> In the peel test described above, among the laminates in which the flow channel layer and the positive electrode layer were evaluated to be integrated in terms of adhesive strength, the following were used as positive electrode sheets: CNT1w / CP1 laminate, CNT1w / CP2 laminate (i.e., a laminate prepared by the above method using CNT1w as the positive electrode carbon material dispersion liquid for the positive electrode layer and CP2 as the flow channel layer), CNT2w / CP1 laminate (i.e., a laminate prepared by the above method using CNT2w as the positive electrode carbon material dispersion liquid for the positive electrode layer and CP1 as the flow channel layer), CNT3w / CP1 laminate (i.e., a laminate prepared by the above method using CNT3w as the positive electrode carbon material dispersion liquid for the positive electrode layer and CP1 as the flow channel layer), and CNT4p / CP4 laminate. The properties of these sheets were measured. Here, for convenience, the laminates used as positive electrode sheets are also referred to as Example 1, Example 2, Example 4, Example 6, and Example 8, respectively.

[0079] In addition, a standalone positive electrode layer was also used as a positive electrode sheet in cases where it was not integrated with the flow channel layer, and the properties of this sheet were also measured. The standalone positive electrode layers used as positive electrode sheets were positive electrode layers obtained solely from dispersions of CNT1w, CNT2w, CNT3w, and CNT4p (referred to here, for convenience, as Examples 3, 5, 7, and 9, respectively). Specifically, these standalone positive electrode layers were obtained by filtering each of the above-mentioned dispersions of positive electrode carbon materials onto an omnipore membrane filter (pore size: 1.0 μm), vacuum drying at 60°C, and then peeling off the filter.

[0080] Incidentally, the positive electrode sheet of the CNT4p / CP4 laminate (Example 8) was prepared according to the method described in Example 1 of Patent Document 1, and for the positive electrode sheet of the CNT4p positive electrode single layer (Example 9), the dispersion liquid described in Example 1 of Patent Document 1 was used as the positive electrode carbon material dispersion liquid.

[0081] The sheet properties of the above-mentioned laminate and the cathode single layer were measured by the following method.

[0082] (1) Measurement of specific surface area using the BET method The isotherms were determined using the BET method from adsorption isotherms obtained by nitrogen adsorption using 3Flex (manufactured by Micromeritics Instrument Corp.). (2) Measurement of pore volume occupied by pores with a diameter of 2 nm or more and 1000 nm or less The adsorption isotherms were obtained using the nitrogen adsorption method with 3Flex (manufactured by Micromeritics Instrument Corp.) and then determined using the BJH method. (3) Measurement of pore volume occupied by pores with a diameter of 0.1 μm or more and 10 μm or less Using the mercury intrusion method with AutoPoreIV (manufactured by Micromeritics Instrument Corp.), pore volumes in the range of pore diameters from 10 nm to 200,000 nm (0.01 μm to 200 μm) were measured, and the pore volume values ​​for pore diameters from 0.1 μm to 10 μm were used. (4) Measurement of pore volume occupied by pores with a diameter of 10 μm or more and 50 μm or less Using the mercury intrusion method with AutoPoreIV (manufactured by Micromeritics Instrument Corp.), pore volumes in the range of pore diameters from 10 nm to 200,000 nm (0.01 μm to 200 μm) were measured, and the pore volume values ​​for pore diameters from 10 μm to 50 μm were used.

[0083] The results are shown in Table 4. Note that the BET method specific surface area and pore volume in Table 4 are expressed as values ​​per gram of positive electrode layer (specifically, per gram of CNT (carbon nanotube), which is a component of the positive electrode layer). Therefore, all units (g) for the BET method specific surface area and pore volume in Table 4 refer to per gram of positive electrode layer (specifically, per gram of CNT (carbon nanotube), which is a component of the positive electrode layer).

[0084] [Table 4]

[0085] As shown in Table 4, among the cathode sheets, which are laminates in which the flow channel layer and cathode layer were evaluated as being integrated in terms of adhesive strength in the above peel test, the cathode sheets (i.e., Examples 1, 2, 4, and 6), excluding Example 8, showed that the mercury intrusion pore volume per unit weight of CNTs in the 10-50 μm cathode layer (unit: mLg) -1 The value of (this value has been converted to the value per unit weight of CNTs in the positive electrode layer) is 1.5 mLg -1 The above results clearly confirmed the presence of pores with a pore diameter of 10-50 μm. On the other hand, in the above peel test, the cathode sheets that are so-called simple laminates in which the channel layer and cathode layer were evaluated as not being integrated from the viewpoint of adhesive strength (i.e., Examples 3, 5, 7, and 9), and the cathode sheets that are laminates in which the channel layer and cathode layer were evaluated as being integrated from the viewpoint of adhesive strength (i.e., Example 8), showed the above mercury intrusion pore volume (unit: mLg). -1 The value of ) is 0.8 mLg -1The following were observed, and it was confirmed that pores with a diameter of 10-50 μm were not present. In particular, in the positive electrode sheets of Example 3 and Example 9, which are simple laminates, and the positive electrode sheet of Example 8, which is a laminate in which the flow channel layer and the positive electrode layer were evaluated to be integrated in terms of adhesive strength, the pore volume (unit: mLg) measured by the mercury intrusion method was small. -1 The value of ) is 0.1 mLg -1 It was confirmed that pores with extremely small diameters, less than 10-50 μm, were almost nonexistent. From these results, it was found that among the cathode sheets, which are laminates in which the channel layer and cathode layer were evaluated as being integrated in terms of adhesive strength, pores with a diameter of 10-50 μm were clearly present in all cathode sheets except Example 8 (i.e., Examples 1, 2, 4, and 6), while pores with a diameter of 10-50 μm were not present in the cathode sheets that are simple laminates (i.e., Examples 3, 5, 7, and 9), and in the cathode sheet, which is a laminate in which the channel layer and cathode layer were evaluated as being integrated in terms of adhesive strength (i.e., Example 8).

[0086] Figure 7 shows the results of measurements performed by the mercury intrusion method for the CNT1w / CP1 laminate, which is the positive electrode sheet of Example 1, and for a simple laminate consisting of the positive electrode sheet of Example 3 as the positive electrode layer and CP1 as the flow channel layer. Note that the vertical axis of Figure 7 is "mLg -1 This means that the pore volume (V) (unit: mL) has been converted to a value per gram of positive electrode layer weight (specifically, per gram of CNT1). In addition, "pores in positive electrode layer" and "pores in flow channel layer" in the figure indicate the pore diameter of each layer before stacking.

[0087] As shown in Figure 7, in the above simple laminate, the pore size distribution provided by the positive electrode sheet of Example 3 (i.e., the positive electrode sheet in which the positive electrode layer is CNT1) is observed in the range of pore size 0.1-10 μm, and at the same time, the pore size distribution provided by the flow channel layer CP1 is observed around 100 μm in pore size, but there is almost no pore size distribution observed in the range of 10-100 μm between the two, confirming that a pore size distribution is provided that clearly distinguishes the positive electrode layer and the flow channel layer.

[0088] On the other hand, as shown in Figure 7, in the CNT1w / CP1 laminate of Example 1, the pore size distribution provided by the CNT1 in the positive electrode layer extends to a region of approximately 10-100 μm, and forms a continuous pore size distribution up to approximately 100 μm provided by the CP1 in the flow channel layer. It was confirmed that this provides a pore size distribution in which the positive electrode layer and the flow channel layer cannot be clearly distinguished. In other words, in the pore size distribution of the CNT1w / CP1 laminate of Example 1, a pore size distribution of approximately 10-100 μm, which is not observed in the above-mentioned simple laminate, is observed, and it was confirmed that a continuous pore size distribution is formed from the pore size provided by the CNT1 in the positive electrode layer to the pore size provided by the CP1 in the flow channel layer.

[0089] From these findings, it was found that in the above-mentioned simple laminate, the positive electrode layer CNT1 and the flow channel layer CP1 are merely in contact with each other and are not integrated from the viewpoint of pore size distribution. On the other hand, in the above-mentioned CNT1w / CP1 laminate, the positive electrode layer CNT1 and the flow channel layer CP1 are integrated from the viewpoint of pore size distribution.

[0090] Figure 8 shows the results of measurements performed by the mercury intrusion method for the CNT4p / CP4 laminate, which is the positive electrode sheet of Example 8, and for a simple laminate consisting of the positive electrode sheet of Example 9 as the positive electrode layer and CP4 as the flow channel layer. Note that the vertical axis of Figure 8 is "mLg -1 This means that the pore volume (V) (unit: mL) has been converted to a value per gram of positive electrode layer (specifically, per gram of CNT4). In addition, "pores of the positive electrode layer" and "pores of the flow channel layer" in the figure indicate the pore diameter of the pores in each layer before lamination. Furthermore, as mentioned above, the CNT4p / CP4 laminate in Example 8 was manufactured according to the method described in Example 1 of Patent Document 1.

[0091] As shown in Figure 8, in the above simple laminate, the pore size distribution provided by the positive electrode sheet of Example 9 (i.e., the positive electrode sheet in which the positive electrode layer is CNT4) is observed in the range of pore size 0.1-10 μm, and at the same time, the pore size distribution provided by the CP4 flow channel layer is observed from around 30 μm in pore size. However, in the 10-30 μm range between the two, there is almost no pore size distribution like that observed in the CNT1w / CP1 laminate in Figure 7, confirming that it provides a pore size distribution that clearly distinguishes between the positive electrode layer and the flow channel layer. Furthermore, the pore size distribution of the CNT4p / CP4 laminate of Example 8 is similar to that of Example 9, confirming that it also provides a pore size distribution that clearly distinguishes between the positive electrode layer and the flow channel layer. From these findings, it was found that, from the viewpoint of adhesive strength, the CNT4p / CP4 laminate of Example 8 shows that the positive electrode layer and the flow channel layer are bonded together and integrated, as indicated by the peel test results above. However, from the viewpoint of pore size distribution, unlike the CNT1w / CP1 laminate of Example 1 shown in Figure 7, a continuous pore size distribution is not formed between the pore size provided by the CNT4 of the positive electrode layer and the pore size provided by the CP4 of the flow channel layer. In other words, in the CNT4p / CP4 laminate of Example 8, a continuous pore size distribution is not formed due to the integration of the positive electrode layer and the flow channel layer. Therefore, from the viewpoint of pore size distribution, it was found that the CNT4p / CP4 laminate of Example 8 is not an integrated structure of the positive electrode layer and the flow channel layer.

[0092] Considering these results along with the other results mentioned above, in the CNT4p / CP4 laminate of Example 8, As a result of the CNT4 in the positive electrode layer entering the CP4 in the flow channel layer, a layer in which the carbon fibers of CNT4 and CP4 are mixed exhibits significant adhesive strength. However, this is understood to be because, in this layer, the pores that form between the CNT4 in the positive electrode layer and the CP4 in the flow channel layer, as shown in the CNT1w / CP1 laminate of Example 1 in Figure 7, are not formed due to the entanglement of the CNT1 component of the positive electrode layer and the carbon fibers (CF) of the CP1 in the flow channel layer. The reason why no pores are formed in the cavity is that, compared to the CNT1w / CP1 laminate in Example 1, the pore diameter of the positive electrode layer is very small, approximately 1 / 10 or less, as shown by the comparison of the highest peaks in the pore diameter distribution of the positive electrode layer in Figures 7 and 8. Similarly, the pore diameter of the flow channel layer is also small, approximately 1 / 3, as shown by the comparison of the highest peaks in the pore diameter distribution of the flow channel layer in Figures 7 and 8. Therefore, the CNT4 in the positive electrode layer cannot penetrate deeply into the CP4 in the flow channel layer, and cavity formation due to entanglement between the CNT4 and the carbon fibers (CF) of the CP4 component of the flow channel layer does not occur.

[0093] The formation of a continuous pore size distribution in a cathode where the cathode layer and the channel layer are integrated (i.e., a channel-integrated cathode) can be confirmed by the increase in the volume of pore sizes that deviate from the pore size distribution provided by the cathode layer and the channel layer (CP) made of CNTs, respectively. For example, since the pore size distribution around 20 μm is not inherently present in either the cathode layer or the channel layer (CP) made of CNTs, if an increase in the volume of the pore size distribution in this range (more specifically, an increase in the cumulative pore volume of 10-50 μm) is observed, it can be confirmed that a continuous pore size is formed between the two layers due to the integration of the cathode layer and the channel layer (CP) made of CNTs.

[0094] The formation of a continuous pore size distribution in a channel-integrated cathode is achieved by combining a cathode layer and a channel layer with high porosity and large pore sizes. In one preferred embodiment, the density is 0.30 gcm³. -3 A cathode carbon material dispersion of CNTs that can create a cathode layer with the following characteristics (in other words, a porosity of 85% or more), with a pore size of 30 μm or more and a density of 0.01 g / cm³ -3 More than 0.30gcm -3One possible method is to filter the material directly into the following flow channel layer (CP).

[0095] <Discharge and Cycle Characteristics Evaluation> Lithium-air battery stack cells were fabricated using the stacks of the positive electrode sheets shown in Examples 1 to 9 in Table 4, and their discharge and cycle characteristics were evaluated.

[0096] The lithium-air battery stack cell was fabricated by the following method. Each of the above stacks was cut to a diameter of 16 mm, and after vacuum drying at 100°C for 12 hours or more, as shown in Figure 9(a), a lithium metal foil (diameter 16 mm), a lithium-ion secondary battery separator, and the cut stack (diameter 16 mm) were stacked in that order between the positive electrode and the negative electrode current collector, and an electrolyte (tetraethylene glycol dimethyl ether (TEGDME) solution containing 1 M lithium bistrifluoromethanesulfonylimide (LiTFSI), or a TEGDME solution containing 0.5 M LiTFSI, 0.5 M lithium nitrate (LiNO3), and 0.2 M lithium bromide (LiBr)) was permeated to create a lithium-air battery cell. Here, the absorption and discharge of external oxygen gas necessary for discharge and charging are performed in the cross-section of the flow channel layer.

[0097] When using the positive electrode sheets of Examples 3, 5, 7, and 9, which are standalone positive electrode layers not integrated with the flow channel layer, the flow channel layer corresponding to the positive electrode sheets of Examples 1, 4, 6, and 8 was introduced between them and the positive electrode current collector to fabricate a lithium-air battery stack cell. Figure 9(b) shows a schematic diagram of the fabricated lithium-air battery stack cell. It is the same as Figure 9(a) except that a standalone positive electrode layer not integrated with the flow channel layer is used.

[0098] Table 5 shows the configuration of each lithium-air battery stack cell that was fabricated. Here, Cell Example 1 to Cell Example 9, which are shown as lithium-air battery stack cells, correspond to lithium-air battery stack cells fabricated using each of the positive electrode sheet stacks from Example 1 to Example 9.

[0099] Although not illustrated here, we have confirmed that in lithium-air battery stack cells, if a flow channel layer is not provided between the positive electrode layer and the positive electrode current collector, the oxygen necessary for discharge cannot be supplied, and the battery characteristics cannot be obtained.

[0100] [Table 5]

[0101] Discharge tests were performed on lithium-air battery stack cells 1 to 9. A battery charge / discharge system (Hokuto Denko, HJ1001SD8) was used for the discharge tests under room temperature and constant current conditions (discharge rate: 0.1 mA / cm²). 2 , 0.4mA / cm 2 or 2.0 mA / cm 2 Discharge was performed under a cutoff voltage of 2V, in a pure oxygen flow or in dry air (oxygen: approximately 20%, dew point: -60 to -50°C). Figure 10 shows the discharge curves of the lithium-air battery stack cells of Cell Example 1 and Cell Example 3, which are the results of the discharge tests. From this figure, it was confirmed that under both discharge conditions, in a pure oxygen flow and in dry air, the lithium-air battery stack cell of Cell Example 1, which uses a positive electrode layer integrated with the flow channel layer, exhibited a larger discharge capacity.

[0102] Table 6 shows the maximum discharge capacity exhibited by lithium-air battery stack cells of cell examples 1 to 9. In all cases except for lithium-air battery stack cells 8 and 9, it was confirmed that lithium-air battery stack cells using a positive electrode integrated with the flow channel layer (specifically, cell examples 1, 2, 4, and 6) exhibited a larger discharge capacity than lithium-air battery stack cells where the positive electrode was stacked individually without integration with the flow channel layer (specifically, cell examples 3, 5, and 7). This is understood to be because, since the positive electrode layer and the flow channel layer are integrated in terms of pore size distribution, a continuous pore size distribution is formed between the positive electrode layer and the flow channel layer, allowing for more effective oxygen supply from the flow channel layer to the positive electrode layer made of CNTs.

[0103] On the other hand, the lithium-air battery stack cells of cell examples 8 and 9 showed similar discharge rates regardless of whether they were integrated or not. In the lithium-air battery stack cell of cell example 9, although more stable capacity development is expected due to the integration of the positive electrode layer and the flow channel layer, just as in the case of simple stacking of the positive electrode layer and the flow channel layer, a continuous pore size distribution is not formed between the positive electrode layer and the flow channel layer, and integration does not occur from the viewpoint of pore size distribution. Therefore, it is understood that the effect of improving the capacity of the cell itself is low.

[0104] [Table 6]

[0105] Charge-discharge cycle tests were also performed on the lithium-air battery stack cells of cell examples 10 and 11 listed in Table 5. A battery charge-discharge system (Hokuto Denko, HJ1001SD8) was used, under room temperature and constant current conditions (0.4 mA / cm²). 2 Under a pure oxygen flow, the cells were repeatedly discharged and charged for 5 hours between cutoff voltages of 2-4.5V. Figure 11 shows the charge-discharge curves of lithium-air battery stack cells for cell examples 10 and 11. Although the discharge voltages were similar for both, the lithium-air battery stack cell for cell example 10, which uses a positive electrode integrated with the flow channel layer, showed a lower charge voltage and a lower specified capacity (2.0mAh / cm²). 2 It was also confirmed that the number of discharges (cycles) could be exceeded. This is understood to be because the positive electrode layer and the flow channel layer are integrated in terms of pore size distribution, forming a continuous pore size distribution between the positive electrode layer and the flow channel layer, which allows for smoother absorption and discharge of oxygen during charging and discharging, thus improving the cycle characteristics. [Industrial applicability]

[0106] The integrated channel positive electrode for metal secondary batteries of the present invention can be suitably used as a positive electrode for metal secondary batteries (particularly lithium-air batteries), and its application to such batteries is highly promising. Therefore, it has potential applications in a wide variety of industries (for example, the electrical and telecommunications equipment industry, the energy industry, the transportation industry, the medical equipment industry, etc.).

Claims

1. A gas diffusion channel layer made of a porous layer of fibrous carbon material, A positive electrode layer consisting of a porous layer made of the same or different fibrous carbon material as the carbon material, Includes, A portion of the channel layer includes pores formed by the entanglement of fibrous carbon material in the channel layer and fibrous carbon material in the positive electrode layer that penetrates the channel layer, and has a thickness of at least 5 μm. The pores provided by the channel layer and the positive electrode layer have a continuous pore size distribution of 10 nm to 200 μm, and the channel layer and the positive electrode layer are integrated by this continuous pore size distribution. Integrated channel positive electrode for metal secondary batteries.

2. The positive electrode according to claim 1, wherein the pores of the cavity have a continuous pore size distribution of 10 μm to 50 μm.

3. The pores of the aforementioned cavity have a pore volume of 0.5 cm³ per gram of weight of the positive electrode layer. ３ / g or more 5.0cm ３ The positive electrode according to claim 1, having a value of less than or equal to / g.

4. The positive electrode according to claim 1, wherein the fibrous carbon material is carbon fiber and / or carbon nanotube.

5. The cathode according to claim 1, wherein the fibrous carbon material of the channel layer is carbon fiber, and the fibrous carbon material of the cathode layer is carbon nanotube.

6. 250m ２ / g or more 1400m ２ Having a BET specific surface area of ​​less than or equal to / g, Pores having a pore size distribution of 0.1 μm to 10 μm constitute a pore volume of 1.0 cm³ per gram of weight of the positive electrode layer. ３ / g or more 10.0cm ３ The positive electrode according to claim 1, having a value of less than or equal to / g.

7. The density of the aforementioned channel layer is 0.01 g / cm³. ３ 0.30g / cm or more ３ The positive electrode according to claim 1, which is as follows:

8. The positive electrode according to claim 1, wherein the peel strength between the positive electrode layer and the flow channel layer is 1 mN / 5 mm or more in a 90-degree peel test.

9. The positive electrode according to claim 1, wherein the pore size distribution of the positive electrode is measured by the mercury intrusion method.

10. The positive electrode according to claim 1, wherein the pores of the cavity are visually observed by observation using an electron microscope or X-ray computed tomography.

11. A metal secondary battery comprising a positive electrode, a negative electrode containing a metal, and an electrolyte between the positive electrode and the negative electrode, A metal secondary battery in which the positive electrode is the positive electrode described in any one of claims 1 to 10.

12. It contains a negative electrode active material and a positive electrode active material, The negative electrode active material is lithium, zinc, sodium, aluminum, magnesium, calcium, iron, or potassium. The positive electrode active material is oxygen or carbon dioxide. The metal secondary battery according to claim 11.

13. A method for manufacturing a channel-integrated positive electrode for a metal secondary battery, The aforementioned integrated channel-type positive electrode for a metal secondary battery includes a gas diffusion channel layer made of a porous layer of fibrous carbon material and a positive electrode layer made of the same or different fibrous carbon material as the carbon material, wherein a portion of the channel layer includes pores formed by the entanglement of the fibrous carbon material in the channel layer and the fibrous carbon material of the positive electrode layer that enters the channel layer, and the pores provided by the channel layer and the positive electrode layer have a continuous pore size distribution of 10 nm to 200 μm, and the channel layer and the positive electrode layer are integrated by this continuous pore size distribution. The steps include: preparing a dispersion of fibrous carbon material in a solvent as the raw material for the positive electrode layer of the porous layer, and preparing a porous substrate made of fibrous carbon material as the gas diffusion channel layer of the porous layer; The steps include: filtering the dispersion on the porous substrate to form the positive electrode layer on the channel layer; Includes, The fibrous carbon material used in the dispersion liquid has a BET specific surface area of 350 m ２ / g or more and 1400 m ２ / g or less, and The porous substrate has a pore size of 30 μm or more and a density of 0.01 g / cm³. ３ 0.30g / cm or more ３ A method for manufacturing a positive electrode having the following density.

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