Electrode structure and method for manufacturing an electrode structure

Abstract

This technology provides a way to make the current collector of an electrode structure less susceptible to damage. [Solution] The electrode structure comprises a current collector and an electrode layer containing a solid electrolyte and disposed on the current collector. The electrode layer comprises a first surface in contact with the current collector and a second surface opposite to the first surface. The oxygen concentration in the region of the electrode layer on the first surface side, including the first surface, is higher than the oxygen concentration in the region of the electrode layer on the second surface side, including the second surface.

Description

[Technical Field]

[0001] The technologies disclosed herein relate to electrode structures and methods for manufacturing electrode structures. More specifically, to electrode structures for use in batteries. [Background technology]

[0002] Batteries have undergone various improvements to enhance their performance. For example, Patent Document 1 discloses an electrode structure that constitutes the positive and negative electrodes used in a battery. The electrode structure comprises a current collector and an electrode layer placed on the current collector. In the battery of Patent Document 1, an electrolyte is placed between the positive and negative electrodes, which are composed of the electrode structure. In addition, in this type of battery, a solid electrolyte may be included inside the electrode layer of the electrode structure. The inclusion of a solid electrolyte inside the electrode layer facilitates the movement of ions within the electrode layer, thereby improving the performance of the battery. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2019 / 044382 [Overview of the project] [Problems that the invention aims to solve]

[0004] If a solid electrolyte is included within the electrode layer of an electrode structure, ions can easily move within the electrode layer, potentially reaching the current collector. When ions reach the current collector, depending on the type of metal and ions contained in the current collector, an alloying reaction may occur between the metal and ions, potentially damaging the current collector.

[0005] This specification discloses techniques for making the current collectors of electrode structures less susceptible to damage. [Means for solving the problem]

[0006] In a first aspect of this technology, the electrode structure comprises a current collector and an electrode layer containing a solid electrolyte and disposed on the current collector. The electrode layer comprises a first surface in contact with the current collector and a second surface opposite to the first surface. The oxygen concentration in the region of the electrode layer on the first surface side, including the first surface, is higher than the oxygen concentration in the region of the electrode layer on the second surface side, including the second surface.

[0007] In this configuration, the oxygen concentration is higher in the region of the electrode layer on the current collector side (first surface side), which reduces the activity of the solid electrolyte located on the first surface side of the electrode layer. As a result, ions are less likely to move to the current collector via the solid electrolyte, making the current collector less susceptible to damage.

[0008] In a second aspect of this technology, in the first aspect described above, the solid electrolyte may be a sulfide-based solid electrolyte.

[0009] This configuration allows for improved ion conductivity within the electrode layer by using a sulfide-based solid electrolyte. Therefore, while the high oxygen concentration in the first-surface region of the electrode layer reduces the ion conductivity of the solid electrolyte located on the first-surface side, the ion conductivity of the solid electrolyte in other regions of the electrode layer can be improved.

[0010] In a third aspect of this technology, the method for manufacturing an electrode structure comprises a current collector and an electrode layer containing a solid electrolyte and disposed on the current collector. The method for manufacturing an electrode structure comprises an exposure step of exposing a first surface of the electrode layer to one of water vapor, alcohol, and an organic solvent, and an adhesion step of bonding the electrode layer to the current collector such that the first surface exposed to one of water vapor, alcohol, and an organic solvent in the exposure step comes into contact with the current collector.

[0011] With this configuration, the activity of the solid electrolyte located near the first surface of the electrode layer can be reduced by exposing the first surface of the electrode layer to one of water vapor, alcohol, and an organic solvent. Therefore, the activity of the solid electrolyte located near the first surface of the electrode layer can be reduced by a simple method.

[0012] In a fourth aspect of this technology, in the third aspect described above, the exposure step may involve exposing the first surface of the electrode layer to one of water vapor and alcohol.

[0013] This configuration allows for efficient reduction of the activity of the solid electrolyte located near the first surface of the electrode layer. [Brief explanation of the drawing]

[0014] [Figure 1] A diagram showing the schematic configuration of the electrode structure according to the embodiment. [Figure 2] A flowchart showing an example of a method for manufacturing an electrode structure according to the embodiment. [Modes for carrying out the invention]

[0015] The electrode structure 10 of this embodiment will be described with reference to the drawings. The electrode structure 10 is used as an electrode when manufacturing a battery. As shown in Figure 1, the electrode structure 10 comprises a current collector 12 and an electrode layer 14.

[0016] The current collector 12 is made of metal foil. In this embodiment, the metal foil is aluminum foil, and the electrode structure 10 is used as the negative electrode. The metal foil may be made of any metal with high conductivity, and may be made of other metals such as copper, nickel, or stainless steel. The current collector 12 may also be a metal-coated resin foil in which the surface of a resin layer (the type of resin is not particularly limited) is coated with a metal (for example, the metal mentioned above).

[0017] The electrode layer 14 is disposed on the current collector 12. Hereinafter, in the electrode layer 14, the surface 16 (the lower surface in FIG. 1) in contact with the current collector 12 may be referred to as the "first surface 16", and the surface 18 on the opposite side of the first surface 16 (the upper surface in FIG. 1) may be referred to as the "second surface 18". In the electrode layer 14, the oxygen concentration in the region close to the first surface 16 including the first surface 16 (hereinafter, also simply referred to as the "region on the first surface 16 side") is made higher than the oxygen concentration in the region close to the second surface 18 including the second surface 18 (hereinafter, also simply referred to as the "region on the second surface 18 side").

[0018] The electrode layer 14 contains an electrode active material 20, a conductive assistant 22, and solid electrolytes 24a and 24b. The type of the electrode active material 20 is not particularly limited. When the electrode structure 10 is used as a positive electrode, the electrode active material 20 can be formed of an NCM-based material such as LCO (LiCoO2), LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc., LFP (LiFePO4), LiMn2O4, etc., but is not limited thereto. When the electrode structure 10 is used as a negative electrode, the electrode active material 20 can be formed of Si, SiO, graphite, LTO (Li4Ti5O 12 ), etc., but is not limited thereto. Further, the electrode active material 20 contained in the electrode layer 14 may be of one type, or a plurality of types of electrode active materials may be combined in an arbitrary ratio. Further, the electrode active material 20 may be solid particles, porous particles, or other shapes.

[0019] The conductive assistant 22 is disposed between the electrode active materials 20. The type of the conductive assistant 22 is not particularly limited. For example, the conductive assistant 22 can be formed of a carbon material or a metal material. The carbon material has various shapes such as particulate (solid, hollow, porous), fibrous, tubular, brush-shaped, chip-shaped (or flat-shaped), etc., and any of them may be used. The metal material has shapes such as particulate and fibrous, and any of them may be used. Further, metal-coated carbon may be used as the conductive assistant 22. Further, the conductive assistant 22 contained in the electrode layer 14 may be of one type, or a plurality of types of conductive assistants may be combined in an arbitrary ratio.

[0020] The solid electrolytes 24a and 24b are in particulate form and are disposed between the electrode active materials 20. Hereinafter, the solid electrolyte located in the region on the first surface 16 side may be referred to as solid electrolyte "24a", and the other solid electrolytes may be referred to as solid electrolyte "24b". At least a part of the solid electrolyte 24a is in contact with the current collector 12. The solid electrolytes 24a and 24b are formed of a sulfide-based material, and in this embodiment, they are formed mainly of Li7SiPS8. Note that the main components of the solid electrolytes 24a and 24b are not particularly limited. For example, the solid electrolytes 24a and 24b may be formed mainly of other sulfide-based materials such as Li 10 GeP2S 12 or Li6PS5Cl. Also, the solid electrolytes 24a and 24b may be Li 0.34 La 0.51 TiO 2.94 (LLT) or Li7La3Zr2O 12 (LLZ) and other oxide-based materials. Sulfide-based solid electrolytes tend to have higher ion conductivity than oxide-based solid electrolytes. In the case of these materials, the ion conductivity refers to the lithium ion conductivity. Hereinafter, when referring to the ion conductivity of the solid electrolytes 24a and 24b, it indicates the lithium ion conductivity. By using the sulfide-based solid electrolytes 24a and 24b, the resistance value of the battery manufactured using the electrode structure 10 can be reduced, and it becomes difficult to lose electrical energy during charging and discharging.

[0021] Further, as described above, the oxygen concentration in the region on the first surface 16 side of the electrode layer 14 is made higher than the oxygen concentration in the region on the second surface 18 side. Therefore, the solid electrolyte 24a located in the region on the first surface 16 side contains more oxygen than the solid electrolyte 24b not located in the region on the first surface 16 side. For this reason, while the solid electrolyte 24b has a high ionic conductivity, the solid electrolyte 24a has a low ionic conductivity. The amount of oxygen contained in the electrode layer 14 (for example, the ratio of sulfur element and oxygen element, etc.) can be measured using a known method such as scanning electron microscope energy dispersive X-ray spectroscopy (SEM-EDX) mapping.

[0022] In this embodiment, the ionic conductivity of the solid electrolyte 24a located in the region on the first surface 16 side is made lower than the ionic conductivity of the solid electrolyte 24b not located in the region on the first surface 16 side. For example, in the entire electrode layer 14, if the ionic conductivity of the solid electrolyte contained in the electrode layer 14 is high, ions will easily move between the solid electrolytes in the entire electrode layer 14. Ions may move to the solid electrolyte located in the region on the first surface 16 side and reach the current collector 12 through the solid electrolyte located in the region on the first surface 16 side. Then, the metal (for example, aluminum) constituting the current collector 12 and the ions (for example, lithium ions) may alloy, and the current collector 12 may be damaged. In this embodiment, the ionic conductivity of the solid electrolyte 24a located in the region on the first surface 16 side is made low. Therefore, even if ions move from the solid electrolyte 24b not located in the region on the first surface 16 side to the solid electrolyte 24a, since the solid electrolyte 24a has a low ionic conductivity, it is difficult for ions to move to the current collector 12 through the solid electrolyte 24a. Therefore, it is possible to suppress the current collector 12 from being damaged by the ions that have moved through the solid electrolytes 24a and 24b.

[0023] Next, a method for manufacturing the electrode structure 10 will be described. Hereinafter, when the solid electrolytes 24a and 24b contained in the electrode layer 14 are not distinguished, the alphabetic subscript may be omitted and the solid electrolyte may be referred to as "24".

[0024] As shown in Figure 2, first, the electrode layer 14 is formed (S12). Specifically, a slurry is prepared by mixing the electrode active material 20, conductive additive 22, and solid electrolyte 24 with a solvent. The slurry may also contain additives such as binders, thickeners, and dispersants. Next, the slurry is applied to a base (not shown) for fabricating the electrode layer 14 and dried. This forms the electrode layer 14 on the base. The electrode layer 14 formed in step S12 contains only the unoxidized solid electrolyte 24.

[0025] Next, one surface of the electrode layer 14 formed in step S12 is exposed to water vapor (S14). Specifically, the upper surface of the electrode layer 14 formed on the base (the surface opposite to the surface in contact with the base) is exposed to water vapor. As a result, the oxygen concentration increases in the region of the electrode layer 14 including the surface exposed to water vapor and its vicinity. At this time, the solid electrolyte 24 exposed on the surface exposed to water vapor is oxidized, and the ionic conductivity of the solid electrolyte 24 decreases. This results in the production of an electrode layer 14 with a high oxygen concentration in the region including the surface exposed to water vapor and its vicinity (the region that becomes the region on the first surface 16 side when the electrode structure 10 is manufactured). Note that, when this electrode layer 14 is located on the base, the oxygen concentration is low on the lower surface (the surface in contact with the base) and high on the upper surface (the surface not in contact with the base).

[0026] Next, the electrode layer 14 is bonded to the current collector 12 so that the surface exposed to water vapor is in contact with the current collector 12. Specifically, the electrode layer 14 is positioned on the current collector 12 so that the surface exposed to water vapor is in contact with the current collector 12. That is, the electrode layer 14 is inverted from its position on the base and positioned on the current collector 12. Then, the surface of the electrode layer 14 exposed to water vapor (the first surface 16 with a high oxygen concentration) comes into contact with the current collector 12. Then, the electrode layer 14 is pressurized toward the current collector 12, and after that, the base is removed. As a result, the electrode layer 14 is bonded to the current collector 12 with the surface exposed to water vapor (the first surface 16 with a high oxygen concentration) in contact with the current collector 12, and the electrode structure 10 is manufactured. Note that the water vapor exposed to the electrode layer 14 (i.e., the solid electrolyte 24) may be diluted with argon gas or the like as appropriate.

[0027] In this embodiment, one surface of the electrode layer 14 (the surface that becomes the first surface 16) was exposed to water vapor, but the configuration is not limited to this. For example, instead of water vapor, an alcohol-based solvent may be exposed to one surface of the electrode layer 14. A liquid alcohol-based solvent may be exposed, or the vapor of the solvent may be exposed. The vapor of the solvent may be diluted with argon gas or the like as appropriate. As the alcohol-based solvent, for example, methanol, ethanol, isopropanol, etc. may be used, or other alcohol-based solvents may be used. Even when an alcohol-based solvent is used, the ionic conductivity of the solid electrolyte 24a exposed to one surface (the surface that becomes the first surface 16) can be reduced. In particular, when the electrode layer 14 contains a sulfide-based solid electrolyte 24, exposing one or more alcohol-based solvents from methanol, ethanol, and isopropanol to one surface of the electrode layer 14 can efficiently reduce the ionic conductivity of the solid electrolyte 24a exposed to one surface (the surface that becomes the first surface 16). Alternatively, instead of water vapor and alcohol-based solvents, an organic solvent may be exposed to one surface of the electrode layer 14. Examples of organic solvents other than alcohol-based solvents include toluene, acetonitrile, anisole, 1,2-dimethoxyethane, and tetramethylamine. These organic solvents may be used, or other organic solvents may be used. When exposing with other organic solvents, the solvent may be exposed in liquid form, or the solvent vapor may be exposed. The solvent vapor may also be diluted with argon gas or the like as appropriate. Even when an organic solvent is used, the ionic conductivity of the solid electrolyte 24a exposed to one surface (the surface that becomes the first surface 16) can be reduced.

[0028] The specific examples of the technology disclosed herein have been described in detail above, but these are merely illustrative and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes to the specific examples described above. Furthermore, the technical elements described herein or in the drawings exhibit technical usefulness individually or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology illustrated herein or in the drawings achieves multiple objectives simultaneously, and achieving even one of these objectives itself constitutes technical usefulness. [Explanation of symbols]

[0029] 10: Electrode structure 12: Current collector 14: Electrode layer 16: 1st page 18:Second side 20: Electrode active material 24a, 24b: Solid electrolyte

Claims

1. Current collector and, It comprises an electrode layer containing a solid electrolyte and disposed on the current collector, The electrode layer comprises a first surface that contacts the current collector and a second surface opposite to the first surface. An electrode structure in which the oxygen concentration in the region on the first surface side, including the first surface of the electrode layer, is higher than the oxygen concentration in the region on the second surface side, including the second surface of the electrode layer.

2. The electrode structure according to claim 1, The solid electrolyte is a sulfide-based solid electrolyte in the electrode structure.

3. A method for manufacturing an electrode structure comprising a current collector and an electrode layer containing a solid electrolyte and disposed on the current collector, An exposure step in which the first surface of the electrode layer is exposed to one of water vapor, alcohol, and an organic solvent, A method for manufacturing an electrode structure, comprising: an bonding step of bonding the electrode layer onto a current collector such that the first surface exposed in the exposure step to one of water vapor, alcohol, and an organic solvent comes into contact with the current collector.

4. A method for manufacturing an electrode structure according to claim 3, A method for manufacturing an electrode structure, wherein the exposure step involves exposing the first surface of the electrode layer to one of water vapor and alcohol.

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