All-solid-state battery and method for manufacturing same

Abstract

Provided is an all-solid-state battery in which an energy storage element is less likely to be damaged even when the energy storage element is housed inside an exterior body and the pressure inside the exterior body is made lower than the atmospheric pressure, thus making it possible to achieve stable battery performance.　An all-solid-state battery 1 comprises: an energy storage element 2 that has a solid electrolyte layer 6, a positive electrode layer 7, a negative electrode layer 8, and current collector layers 9, 10; a housing 3 that houses the energy storage element 2; and an exterior body 4 that houses the housing 3. The housing 3 has openings 5A, 5B overlapping at least a portion of the energy storage element 2 in a plan view. The housing 3 has a side wall 3c facing a side surface 2c of the energy storage element 2.

Description

All-solid-state battery and method for manufacturing the same

[0001] This invention relates to an all-solid-state battery and a method for manufacturing the all-solid-state battery.

[0002] Lithium-ion secondary batteries are essential for mobile devices and electric vehicles, and have established themselves as a high-capacity, lightweight power source. However, current lithium-ion secondary batteries mainly use flammable organic electrolytes, raising concerns about the risk of fire. To solve this problem, development is underway on all-solid-state batteries, such as all-solid-state lithium-ion secondary batteries and all-solid-state sodium-ion secondary batteries, which use solid electrolytes instead of organic electrolytes (for example, Patent Document 1).

[0003] Japanese Patent Publication No. 2010-15782

[0004] When using all-solid-state batteries, the energy storage elements, which are the constituent components, are sometimes housed inside an outer casing such as a vacuum pack. However, if the energy storage elements constituting the all-solid-state battery are made of brittle materials, especially in oxide-based secondary batteries, the energy storage elements may be damaged if the inside of the casing is depressurized and the energy storage elements are pressed from above by atmospheric pressure. On the other hand, if the pressure applied to the components constituting the energy storage elements from the stacking direction is insufficient, it may be difficult to make contact between the components, and stable battery characteristics may not be obtained.

[0005] The object of the present invention is to provide an all-solid-state battery and a method for manufacturing the all-solid-state battery, which house an energy storage element inside an outer casing and make it possible to obtain stable battery performance by preventing damage to the energy storage element even when the pressure inside the outer casing is lower than atmospheric pressure.

[0006] The following describes various embodiments of a solid-state battery and a method for manufacturing the solid-state battery that solve the above problems.

[0007] A solid-state battery according to embodiment 1 of the present invention comprises a storage element having a solid electrolyte layer, a positive electrode layer, a negative electrode layer, and a current collector layer, a housing for housing the storage element, and an outer casing for housing the housing, wherein the housing has an opening that overlaps with at least a portion of the storage element in a plan view, and the housing has a side wall facing the side surface of the storage element.

[0008] In the all-solid-state battery according to embodiment 2, it is preferable that the pressure inside the outer casing is lower than atmospheric pressure in embodiment 1.

[0009] In the all-solid-state battery according to embodiment 3, in embodiment 2, it is preferable that the energy storage element is pressed by the outer casing through the opening of the housing.

[0010] In the all-solid-state battery according to embodiment 4, it is preferable that in any one embodiment from embodiment 1 to embodiment 3, the housing has an upper housing portion and a lower housing portion, and the upper housing portion and the lower housing portion are fitted together at the side wall of the housing.

[0011] In the all-solid-state battery according to embodiment 5, in embodiment 4, it is preferable that the upper housing portion and the lower housing portion each have a stepped portion at the fitting portion of the upper housing portion and the lower housing portion, and that the stepped portions of the upper housing portion and the lower housing portion are fitted together.

[0012] In the all-solid-state battery according to embodiment 6, it is preferable that in any one embodiment from embodiment 1 to embodiment 5, the side wall of the housing has an outlet for the tab lead extending from the energy storage element.

[0013] In the all-solid-state battery according to embodiment 7, in any one embodiment from embodiment 1 to embodiment 6, it is preferable that the housing has an upper wall and a lower wall, and that the opening is provided in at least one of the upper wall and the lower wall of the housing.

[0014] In the all-solid-state battery according to embodiment 8, in embodiment 7, it is preferable that the area ratio of the opening to the entire surface of at least one of the upper and lower surfaces of the housing, including the opening, is 10% or more and 95% or less.

[0015] In the all-solid-state battery according to embodiment 9, it is preferable that the housing is composed only of the side walls in any one embodiment from embodiment 1 to embodiment 6.

[0016] In the all-solid-state battery according to embodiment 10, it is preferable that the solid electrolyte layer constituting the energy storage element is made of an oxide-based solid electrolyte in any one embodiment from embodiment 1 to embodiment 9.

[0017] A method for manufacturing an all-solid-state battery according to embodiment 11 of the present invention is a method for manufacturing an all-solid-state battery according to any one embodiment from 1 to 10, characterized by comprising the steps of: housing the energy storage element inside the housing such that the side surface of the energy storage element faces the side wall of the housing; housing the housing containing the energy storage element inside the outer casing; and depressurizing the inside of the outer casing to seal the energy storage element.

[0018] According to the present invention, it is possible to provide an all-solid-state battery and a method for manufacturing the all-solid-state battery, which house an energy storage element inside an outer casing, and even when the pressure inside the outer casing is lower than atmospheric pressure, damage to the energy storage element is less likely to occur, making it possible to obtain stable battery performance.

[0019] Figure 1 is a schematic cross-sectional view showing an all-solid-state battery according to a first embodiment of the present invention. Figure 2 is a schematic perspective view showing the housing and energy storage element constituting the all-solid-state battery according to a first embodiment of the present invention. Figures 3(a) to 3(c) are schematic perspective views for explaining the manufacturing method of the all-solid-state battery according to a first embodiment of the present invention. Figure 4 is a schematic cross-sectional view showing an all-solid-state battery according to a second embodiment of the present invention. Figure 5 is a schematic cross-sectional view showing an all-solid-state battery according to a third embodiment of the present invention. Figure 6 is a schematic perspective view showing the housing and energy storage element constituting the all-solid-state battery according to a third embodiment of the present invention. Figure 7(a) is a schematic plan view showing the upper housing portion used in the experimental example, and Figure 7(b) is a schematic plan view showing the lower housing portion used in the experimental example. Figure 8 is a schematic perspective view showing the housing in which the energy storage element of the experimental example is housed. Figure 9 is a photograph of the all-solid-state battery obtained in the experimental example by vacuum purging the inside of the housing to 0.5 kPa. Figure 10 is a graph showing the relationship between the pressure inside the housing obtained in the experimental example and the contact resistance of the all-solid-state battery.

[0020] Preferred embodiments of the present invention will be described below. However, the following embodiments are merely illustrative, and the present invention is not limited to these embodiments. In addition, in each drawing, components having substantially the same function may be referred to by the same reference numerals.

[0021] [First Embodiment] Figure 1 is a schematic cross-sectional view showing an all-solid-state battery according to the first embodiment of the present invention. Figure 2 is a schematic perspective view showing the housing and energy storage element constituting the all-solid-state battery according to the first embodiment of the present invention.

[0022] As shown in Figure 1, the all-solid-state battery 1 comprises a storage element 2, a housing 3, and an outer casing 4. The housing 3 houses the storage element 2. The outer casing 4 houses the housing 3. Therefore, the outer casing 4 houses the storage element 2 via the housing 3.

[0023] Examples of all-solid-state batteries 1 include all-solid-state lithium-ion secondary batteries, all-solid-state sodium-ion secondary batteries, and all-solid-state magnesium-ion secondary batteries. The following description will use an all-solid-state sodium-ion secondary battery as an example, but the following embodiments are applicable to all-solid-state batteries in general.

[0024] The energy storage element 2 has a first main surface 2a and a second main surface 2b that are opposite to each other. The energy storage element 2 also has a side surface 2c connecting the first main surface 2a and the second main surface 2b.

[0025] In this embodiment, the energy storage element 2 includes a solid electrolyte layer 6, a positive electrode layer 7, a negative electrode layer 8, a positive electrode side current collector layer 9, and a negative electrode side current collector layer 10.

[0026] In this embodiment, the solid electrolyte layer 6 is composed of an oxide-based solid electrolyte. More specifically, the solid electrolyte layer 6 is composed of a sodium ion conductive oxide.

[0027] A positive electrode layer 7 is provided on one main surface 6a of the solid electrolyte layer 6. In this embodiment, the positive electrode layer 7 contains a positive electrode active material capable of adsorbing and releasing sodium. A positive electrode current collector layer 9 is provided on the main surface of the positive electrode layer 7 opposite to the side on which the solid electrolyte layer 6 is located. In this embodiment, the main surface of the positive electrode current collector layer 9 opposite to the side on which the positive electrode layer 7 is located constitutes the first main surface 2a of the energy storage element 2.

[0028] A negative electrode layer 8 is provided on the other main surface 6b of the solid electrolyte layer 6. In this embodiment, the negative electrode layer 8 contains a negative electrode active material capable of adsorbing and releasing sodium. Furthermore, a negative electrode side current collector layer 10 is provided on the main surface of the negative electrode layer 8 opposite to the side on which the solid electrolyte layer 6 is located. In this embodiment, the main surface of the negative electrode side current collector layer 10 opposite to the side on which the negative electrode layer 8 is located constitutes the second main surface 2b of the energy storage element 2.

[0029] The housing 3 houses the energy storage element 2. In this embodiment, the housing 3 has an upper wall 3a, a lower wall 3b, and a side wall 3c. The side wall 3c of the housing 3 has a frame-like shape. The side wall 3c of the housing 3 connects the upper wall 3a and the lower wall 3b. The side wall 3c of the housing 3 is provided so as to face the side surface 2c of the energy storage element 2. The side wall 3c of the housing 3 may be provided so as to be in contact with the side surface 2c of the energy storage element 2, or it may be provided with a gap between it and the side surface 2c of the energy storage element 2. If the side wall 3c of the housing 3 is provided so as to be in contact with the side surface 2c of the energy storage element 2, the space inside the housing 3 can be utilized more effectively. On the other hand, if the side wall 3c of the housing 3 is provided with a gap between it and the side surface 2c of the energy storage element 2, damage caused by the side surface 2c of the energy storage element 2 can be made even less likely.

[0030] An opening 5A is provided in the upper wall 3a of the housing 3. The opening 5A is provided so as to overlap with the first main surface 2a of the energy storage element 2 in a plan view. The opening 5A may be provided so as to overlap with a part of the first main surface 2a of the energy storage element 2 in a plan view, or it may be provided so as to overlap with the entire first main surface 2a of the energy storage element 2.

[0031] As shown in Figure 2, the planar shape of the opening 5A in the upper wall 3a is approximately rectangular. However, the planar shape of the opening 5A in the upper wall 3a may be approximately circular, approximately elliptical, or approximately polygonal in any other way, and is not particularly limited.

[0032] An opening 5B is provided in the lower wall 3b of the housing 3. The opening 5B in the lower wall 3b is provided so as to overlap with the second main surface 2b of the energy storage element 2 in a plan view. The opening 5B may also be provided so as to overlap with a part of the second main surface 2b of the energy storage element 2 in a plan view, or it may be provided so as to overlap with the entire second main surface 2b of the energy storage element 2.

[0033] Although not shown in the diagram, the planar shape of the opening 5B in the lower wall 3b is approximately rectangular. However, the planar shape of the opening 5B in the lower wall 3b may be approximately circular, approximately elliptical, or an approximately polygonal shape other than a rectangle, and is not particularly limited.

[0034] In this embodiment, the housing 3 has an upper housing portion 3A and a lower housing portion 3B. The upper housing portion 3A is provided with an upper wall 3a and an opening 5A. The lower housing portion 3B is provided with a lower wall 3b and an opening 5B. Furthermore, the upper housing portion 3A and the lower housing portion 3B are fitted together at the side wall 3c of the housing 3.

[0035] The outer casing 4 houses the housing 3. The outer casing 4 also houses the energy storage element 2 via the housing 3. In this embodiment, the interior 4a of the outer casing 4 is depressurized, and the energy storage element 2 is sealed inside the interior 4a of the outer casing 4.

[0036] In this embodiment, the pressure inside the outer casing 4a is lower than atmospheric pressure. As a result, the energy storage element 2 is pressed against the outer casing 4. More specifically, the first main surface 2a of the energy storage element 2 is pressed against by the outer casing 4 through the opening 5A of the housing 3. Also, the second main surface 2b of the energy storage element 2 is pressed against by the outer casing 4 through the opening 5B of the housing 3.

[0037] Since the all-solid-state battery 1 of this embodiment has the above configuration, even when the energy storage element 2 is housed inside the outer casing 4a and the pressure inside the outer casing 4a is lower than atmospheric pressure, damage to the energy storage element 2 is less likely to occur, and stable battery performance can be obtained.

[0038] Conventionally, when the energy storage elements constituting an all-solid-state battery are made of brittle materials, such as oxide-based secondary batteries, the elements may break if the inside of the casing is evacuated and the elements are pressed from above by atmospheric pressure. On the other hand, if the pressure applied to the components constituting the energy storage elements from the stacking direction is insufficient, it may be difficult to make contact between the components, resulting in unstable battery characteristics.

[0039] In contrast, in the all-solid-state battery 1 of this embodiment, the side wall 3c of the housing 3 is provided so as to face the side surface 2c of the energy storage element 2, making it difficult for pressure to be applied to the side surface 2c of the energy storage element 2 by the side wall 3c of the housing 3. Therefore, damage to the energy storage element 2 caused by the side surface 2c of the energy storage element 2 can be made less likely. In particular, when the energy storage element 2 is made of an oxide-based material, damage to the energy storage element 2 caused by the side surface 2c of the energy storage element 2 is more likely to occur, so the effects of the present invention can be exhibited even more effectively when the energy storage element 2 is made of an oxide-based material.

[0040] Furthermore, in the all-solid-state battery 1 of this embodiment, the first main surface 2a and the second main surface 2b of the energy storage element 2 are pressed by the outer casing 4 through the openings 5A and 5B of the housing 3. This makes it possible to suppress damage to the energy storage element 2 while facilitating contact between the various components constituting the energy storage element 2, thereby obtaining stable battery characteristics.

[0041] In this embodiment, the area ratio of the opening 5A to the total area of ​​the upper surface 3a1 including the opening 5A of the housing 3 is preferably 10% or more, more preferably 20% or more, even more preferably 25% or more, preferably 95% or less, more preferably 80% or less, and even more preferably 70% or less. Also in this embodiment, the area ratio of the opening 5B to the total area of ​​the lower surface 3b1 including the opening 5B of the housing 3 is preferably 10% or more, more preferably 20% or more, even more preferably 25% or more, preferably 95% or less, more preferably 80% or less, and even more preferably 70% or less.

[0042] When the area ratio of openings 5A and 5B is greater than or equal to the lower limit, contact between each component constituting the energy storage element 2 can be made easier, and more stable battery characteristics can be obtained. Also, when the area ratio of openings 5A and 5B is less than or equal to the upper limit, damage to the energy storage element 2 can be made even less likely.

[0043] In this embodiment, the atmospheric pressure outside the all-solid-state battery 1 at 25°C is P １ The atmospheric pressure inside the outer casing 4a at 25°C is P ２ When this is the case, the difference (P１ -P ２ The pressure is preferably 0.01 kPa or more, more preferably 0.1 kPa or more, even more preferably 1 kPa or more, particularly preferably 10 kPa or more, preferably 70 kPa or less, more preferably 60 kPa or less, even more preferably 55 kPa or less, particularly preferably 50 kPa or less. The difference (P １ -P ２ If the above-mentioned difference (P) is greater than or equal to the lower limit, the outer casing 4 can more reliably press the first main surface 2a and the second main surface 2b of the energy storage element 2. １ -P ２ If the value is below the above upper limit, damage to the energy storage element 2 can be made even less likely.

[0044] The interior 4a of the outer casing 4 may be a vacuum, or it may be filled with an inert gas, or a mixture of an inert gas and a reducing gas. As the inert gas, for example, a noble gas, nitrogen gas, or carbon dioxide gas can be used, or these inert gases can be mixed and used. Among these, a noble gas is preferred as the inert gas. In this case, even more stable battery characteristics can be obtained in the all-solid-state battery 1. Examples of noble gases include helium, neon, and argon, and these noble gases can be mixed and used. Among these, argon is preferred as the noble gas. As the mixture of the inert gas and the reducing gas, for example, a mixture of hydrogen gas and nitrogen gas can be used.

[0045] Furthermore, even if the storage element is housed inside the casing, and the inside of the casing is evacuated, and pressure is applied to the storage element through the casing, if the storage element constituting the all-solid-state battery is made of a brittle material like that used in oxide-based secondary batteries, the storage element may be damaged.

[0046] In contrast, in the case of the all-solid-state battery 1 of this embodiment, where the upper housing portion 3A and the lower housing portion 3B are fitted together at the side wall 3c of the housing 3, even if pressure is applied to the housing 3 from the stacking direction of the energy storage elements 2, after the upper housing portion 3A and the lower housing portion 3B are fitted together, it becomes even more difficult for further pressure to be applied to the housing 3. Therefore, in this case, damage to the energy storage elements 2 caused by being pressed through the housing 3 can be made even less likely.

[0047] In particular, in this embodiment, a first stepped portion 3d is provided on the upper housing portion 3A of the side wall 3c of the housing 3. Also, a second stepped portion 3e is provided on the lower housing portion 3B of the side wall 3c of the housing 3. The first stepped portion 3d of the upper housing portion 3A and the second stepped portion 3e of the lower housing portion 3B are fitted together. In this case, even if pressure is applied to the housing 3 from the stacking direction of the energy storage elements 2, after the stepped portions of the upper housing portion 3A and the lower housing portion 3B are fitted together, it becomes even more difficult for further pressure to be applied to the housing 3. Therefore, in this case, damage to the energy storage elements 2 caused by being pressed through the housing 3 can be made even more difficult.

[0048] Furthermore, as in this embodiment, if the first stepped portion 3d of the upper housing portion 3A is positioned further outward than the second stepped portion 3e of the lower housing portion 3B, damage to the energy storage element 2 caused by pressure on the energy storage element 2 through the housing 3 can be made even less likely. However, the first stepped portion 3d of the upper housing portion 3A may also be positioned further inward than the second stepped portion 3e of the lower housing portion 3B, and is not particularly limited.

[0049] In this embodiment, as shown in Figure 2, the side wall 3c of the housing 3 has a tab lead 2A extraction section 3f extending from the energy storage element 2. In other words, the tab lead 2A is extracted from the energy storage element 2 via this extraction section 3f.

[0050] The following describes the details of each layer that makes up the all-solid-state battery 1.

[0051] (Solid electrolyte layer) The solid electrolyte layer 6 can be formed of an ion-conductive material such as a sodium-ion conductive oxide. Examples of the sodium-ion conductive oxide include compounds containing at least one selected from Al, Y, Zr, Si, and P, Na, and O. Specific examples of the sodium-ion conductive oxide include beta-alumina or NASICON crystal having excellent sodium-ion conductivity. Among them, from the viewpoint of further excellent sodium-ion conductivity, the sodium-ion conductive oxide is preferably beta-alumina.

[0052] Beta-alumina includes two crystal forms: β-alumina (theoretical composition formula: Na ２ O·11Al ２ O ３ ) and β”-alumina (theoretical composition formula: Na ２ O·5.3Al ２ O ３ ). Since β”-alumina is a metastable substance, usually, those added with Li ２ O or MgO as a stabilizer are used. Since β”-alumina has a higher sodium-ion conductivity than β-alumina, as beta-alumina, it is preferable to use β”-alumina alone or a mixture of β”-alumina and β-alumina, and Li ２ O-stabilized β”-alumina (Na １．７ Li ０．３ Al １０．７ O １７ ) or MgO-stabilized β”-alumina ((Al １０．３２ Mg ０．６８ O １６ )(Na １．６８ O)) is more preferably used.

[0053] Examples of NASICON crystal include Na ３ Zr ２ Si ２ PO １２ , Na ３．２ Zr １．３ Si ２．２ P ０．７ O １０．５ , Na ３ Zr １．６ Ti０．４ Si ２ PO １２ Na ３ HF ２ Si ２ PO １２ Na ３．４ Zr ０．９ HF １．４ Al ０．６ Si １．２ P １．８ O １２ Na ３ Zr １．７ Nb ０．２４ Si ２ PO １２ Na ３．６ Ti ０．２ Y ０．７ Si ２．８ O ９ Na ３ Zr １．８８ Y ０．１２ Si ２ PO １２ Na ３．１２ Zr １．８８ Y ０．１２ Si ２ PO １２ Na ３．４ Zr ２ Si ２．４ P ０．６ O １２ , or Na ３．６ Zr ０．１３ Yb １．６７ Si ０．１１ P ２．９ O １２ Examples include Na. From the viewpoint of superior sodium ion conductivity, NaSICON crystals are used. ３．４ Zr ２ Si ２．４ P ０．６ O １２ It is preferable to use [this].

[0054] The solid electrolyte layer 6 can be manufactured by mixing raw material powders, molding the mixed raw material powders, and then firing them. For example, the solid electrolyte layer 6 can be manufactured by slurrying the raw material powders to create a green sheet, and then firing the green sheet. Alternatively, the solid electrolyte layer 6 may be manufactured by the sol-gel method.

[0055] The thickness of the solid electrolyte layer 6 is preferably 5 μm or more, more preferably 10 μm or more, still more preferably 15 μm or more, and preferably 1000 μm or less, more preferably 200 μm or less, still more preferably 100 μm or less. When the thickness of the solid electrolyte layer 6 is not less than the above lower limit value, the mechanical strength of the all-solid-state battery 1 can be further enhanced, making it difficult to break and difficult to cause an internal short circuit. Also, when the thickness of the solid electrolyte layer 6 is not more than the above upper limit value, the internal resistance can be made smaller, and the capacity and operating voltage of the all-solid-state battery 1 can be further improved. Further, the energy density per unit volume of the all-solid-state battery 1 can be further improved.

[0056] (Positive electrode layer) The positive electrode active material contained in the positive electrode layer 7 is not particularly limited. For example, a positive electrode active material composed of crystallized glass containing a crystal represented by the general formula Na ｘ M ｙ P ２ O ｚ (1 ≤ x ≤ 2.8, 0.95 ≤ y ≤ 1.6, 6.5 ≤ z ≤ 8, M is at least one selected from the group consisting of Fe, Ni, Co, Mn, and Cr) can be used. Among them, crystallized glass containing a positive electrode active material crystal represented by the general formula Na ｘ MP ２ O ７ (1 ≤ x ≤ 2, M is at least one selected from the group consisting of Fe, Ni, Co, Mn, and Cr), or a positive electrode active material composed of Na ４ M ３ (PO ４ ) ２ (P ２ O ７ ) (M is at least one selected from the group consisting of Fe, Ni, Co, Mn, and Cr) is preferred. Examples of the positive electrode active material crystal include Na ２ FeP ２ O ７ 、Na ２ CoP ２ O ７ 、Na ２ NiP ２ O ７ 、Na ４ Fe ３ (PO４ ) ２ (P ２ O ７ ) etc. can be used.

[0057] In this specification, crystallized glass refers to a precursor glass containing an amorphous phase that has been heated (fired) to precipitate crystals (crystallize). In crystallized glass, the entire amorphous phase may have transitioned to a crystalline phase, or some amorphous phase may remain. Furthermore, in crystallized glass, one type of crystal may be precipitated, or two or more types of crystals may be precipitated. Crystallized glass can be determined, for example, by the peak angle shown by powder X-ray diffraction (XRD).

[0058] The positive electrode layer 7 may contain, in addition to the positive electrode active material, a sodium ion conductive solid electrolyte and a conductive additive. For example, the positive electrode layer 7 may contain, by mass%, 60% to 99.9% of the positive electrode active material, 0% to 30% of the sodium ion conductive solid electrolyte, and 0.1% to 10% of the conductive additive.

[0059] As the sodium ion conductive solid electrolyte, for example, those described in the section on solid electrolyte layer 6 can be used. Furthermore, as the conductive additive, for example, conductive carbon can be used. Examples of conductive carbon include acetylene black, carbon black, Ketjenblack, vapor-phase carbon fiber conductive additive (VGCF), or carbon nanotubes.

[0060] The positive electrode layer 7 can be formed, for example, by forming an electrode material layer on one main surface 6a of the solid electrolyte layer 6 and firing the electrode material layer. The electrode material layer can be obtained, for example, by applying a paste containing a positive electrode active material precursor and, optionally, sodium ion conductive solid electrolyte powder and a conductive additive, and then drying it. The paste may optionally contain a binder, plasticizer, or solvent. The electrode material layer may also be in the form of compacted powder.

[0061] The thickness of the positive electrode layer 7 is preferably 10 μm or more, more preferably 20 μm or more, even more preferably 30 μm or more, preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 200 μm or less. When the thickness of the positive electrode layer 7 is greater than or equal to the lower limit, the capacity of the all-solid-state battery 1 can be further improved. Also, when the thickness of the positive electrode layer 7 is less than or equal to the upper limit, the capacity and operating voltage of the all-solid-state battery 1 can be further improved, the positive electrode layer 7 is less likely to shrink due to firing during its formation, and the positive electrode layer 7 is less likely to peel off.

[0062] Furthermore, a thin metal film may be provided on the main surface of the positive electrode layer 7 on the positive electrode side current collector layer 9. In this case, the electronic conductivity at the interface between the positive electrode layer 7 and the positive electrode side current collector layer 9 can be further enhanced. Examples of thin metal films include aluminum films. The thin metal film can be formed by methods such as sputtering or vacuum deposition. In particular, from the viewpoint of improving adhesion with the positive electrode layer 7, it is preferable that the thin metal film is a sputtered film formed by sputtering.

[0063] (Negative electrode layer) The negative electrode active material contained in the negative electrode layer 8 is not particularly limited, but for example, carbon electrode materials such as hard carbon or soft carbon can be used. Hard carbon is preferred as the carbon electrode material. However, the negative electrode active material may be an alloy-based negative electrode active material that can absorb sodium, such as tin, bismuth, lead, or phosphorus, and may also contain metallic sodium. Alternatively, the negative electrode active material may be an oxide-based negative electrode active material that can absorb sodium, such as anatase-type titanium oxide, rutile-type titanium oxide, or brookite-type titanium oxide. It is preferable that the negative electrode layer 8 is not a negative electrode layer consisting of a single phase of metallic sodium.

[0064] The negative electrode layer 8 may contain, in addition to the negative electrode active material, a sodium ion conductive solid electrolyte and a conductive additive. For example, the negative electrode layer 8 may contain, by mass%, 60% to 95% of the negative electrode active material, 5% to 35% of the sodium ion conductive solid electrolyte, and 0% to 5% of the conductive additive.

[0065] For example, the sodium ion conductive solid electrolyte can be the one described in the section on solid electrolyte layer 6. For example, the conductive additive can be the one described in the section on positive electrode layer 7.

[0066] The negative electrode layer 8 can be formed, for example, by forming an electrode material layer on the other main surface 6b of the solid electrolyte layer 6 and firing the electrode material layer. The electrode material layer can be obtained, for example, by applying a paste containing a carbon electrode material precursor (a carbon electrode material precursor made of hard carbon), and optionally a sodium ion conductive solid electrolyte and a conductive additive, and then drying it. The paste may optionally contain a binder, plasticizer, or solvent. The electrode material layer may also be in the form of compacted powder.

[0067] The thickness of the negative electrode layer 8 is preferably 3 μm or more, more preferably 7 μm or more, even more preferably 10 μm or more, preferably 300 μm or less, more preferably 200 μm or less, and even more preferably 100 μm or less. When the thickness of the negative electrode layer 8 is greater than or equal to the lower limit, the deposition of sodium metal in the negative electrode layer 8 during charging of the all-solid-state battery 1 can be suppressed, and the cycle performance of the all-solid-state battery 1 can be improved. Furthermore, when the thickness of the negative electrode layer 8 is less than or equal to the upper limit, the capacity and operating voltage of the all-solid-state battery 1 can be further improved.

[0068] Furthermore, a thin metal film may be provided on the main surface of the negative electrode layer 8 on the negative electrode side current collector layer 10. In this case, the electronic conductivity at the interface between the negative electrode layer 8 and the negative electrode side current collector layer 10 can be further enhanced. Examples of thin metal films include aluminum films. The thin metal film can be formed by methods such as sputtering or vacuum deposition. In particular, from the viewpoint of improving adhesion with the negative electrode layer 8, it is preferable that the thin metal film is a sputtered film formed by sputtering.

[0069] (Positive electrode current collector layer and negative electrode current collector layer) The materials for the positive electrode current collector layer 9 and the negative electrode current collector layer 10 are not particularly limited, and metallic materials such as aluminum, titanium, silver, copper, stainless steel (SUS), nickel, or alloys thereof can be used, respectively. These metallic materials may be used individually or in combination of multiple types. The above-mentioned alloy is an alloy containing at least one of the above-mentioned metals.

[0070] The thickness of the positive electrode current collector layer 9 and the negative electrode current collector layer 10 is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 12 μm or more, preferably 200 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less. When the thickness of the positive electrode current collector layer 9 and the negative electrode current collector layer 10 is within the above range, the current collection function as a current collector can be further improved.

[0071] (Tab Lead) For tab lead 2A, for example, aluminum, nickel, stainless steel (SUS), titanium, iron, copper, silver, gold, etc. can be used.

[0072] (Housing) The material of housing 3 is not particularly limited, and for example, resin or metal can be used. In particular, the material of housing 3 is preferably a resin that has insulating properties. Examples of such resins include ABS resin (acrylonitrile butadiene styrene resin), PPS resin (polyphenylene sulfide resin), PLA resin (polylactic acid resin), PE resin (polyethylene resin), PP resin (polypropylene resin), PC resin (polycarbonate resin), PVC resin (polyvinyl chloride resin), PET resin (polyethylene terephthalate resin), epoxy resin, or PI resin (polyimide resin). As for metals, for example, stainless steel (SUS), nickel (Ni), titanium (Ti), aluminum (Al), copper (Cu), Inconel, or iron (Fe) can be used. In the case of metal, a coating layer may be formed on its surface to provide insulating treatment. The coating agent used to form the coating layer can be an insulating coating agent, such as resins like acrylic resin, epoxy resin, or urethane resin, or ceramics like water glass or boron nitride. The walls (upper wall 3a, lower wall 3b, and side walls 3c) that make up the housing 3 may have a mesh-like shape. In this case, the housing 3 can be made even lighter.

[0073] The thickness of the upper wall 3a of the housing 3 can be, for example, 0.2 mm or more and 5 mm or less. The thickness of the lower wall 3b of the housing 3 can be, for example, 0.2 mm or more and 5 mm or less. Also, the thickness of the side wall 3c of the housing 3 can be, for example, 0.2 mm or more and 5 mm or less.

[0074] (Outer casing) For the outer casing 4, for example, a laminate film can be used. Specifically, for the outer casing 4, for example, an aluminum laminate film can be used.

[0075] The thickness of the outer casing 4 can be, for example, 50 μm or more and 250 μm or less.

[0076] The following describes an example of a manufacturing method for the all-solid-state battery 1.

[0077] (Method for Manufacturing an All-Solid-State Battery) First, prepare an energy storage element 2. At this time, one energy storage element 2 may be prepared, or a laminate in which multiple energy storage elements 2 are stacked may be prepared. In the following, both of the above cases will be referred to as energy storage element 2. The method for manufacturing an all-solid-state battery 1 will be described below with reference to Figures 3(a) to (c).

[0078] First, prepare the lower housing portion 3B as shown in Figure 3(a). Next, house the energy storage element 2 in the lower housing portion 3B as shown in Figure 3(b). Then, fit the upper housing portion 3A into the lower housing portion 3B as shown in Figure 3(c). This houses the energy storage element 2 inside the housing 3. When housing the energy storage element 2, house it inside the housing 3 so that the side surface 2c of the energy storage element 2 faces the side wall 3c of the housing 3, as shown in Figure 1.

[0079] Next, the housing 3 containing the energy storage element 2 is placed inside the outer casing 4 (not shown in Figure 3). Then, the inside 4a of the outer casing 4 is depressurized to seal the energy storage element 2. This allows us to obtain the all-solid-state battery 1 shown in Figure 1. The inside 4a of the outer casing 4 may be a vacuum, or it may be filled with an inert gas, or a mixture of an inert gas and a reducing gas.

[0080] In the manufacturing method of this embodiment, the internal pressure 4a of the outer casing 4 is reduced to a pressure lower than atmospheric pressure. As a result, the first main surface 2a and the second main surface 2b of the energy storage element 2 are pressed by the outer casing 4 through the openings 5A and 5B of the housing 3, thereby suppressing damage to the energy storage element 2 and facilitating contact between the various components constituting the energy storage element 2, thereby obtaining stable battery characteristics.

[0081] [Second Embodiment] Figure 4 is a schematic cross-sectional view showing an all-solid-state battery according to a second embodiment of the present invention.

[0082] As shown in Figure 4, in the all-solid-state battery 21 of the second embodiment, the opening 25A is provided only in the upper wall 23a of the housing 23. Therefore, there is no opening in the lower wall 23b of the housing 23. Other aspects are the same as in the first embodiment.

[0083] In the second embodiment as well, the first main surface 22a of the energy storage element 22 is pressed by the outer casing 24 through the opening 25A of the housing 23. This suppresses damage to the energy storage element 22 while facilitating contact between the various components constituting the energy storage element 22, thereby achieving good battery characteristics.

[0084] As in the second embodiment, the opening 25A may be provided only in the upper wall 23a of the housing 23. In this case, the mechanical strength of the housing 23 can be further increased. Alternatively, as in the first embodiment, openings 5A and 5B may be provided in both the upper wall 3a and the lower wall 3b of the housing 3. In this case, the first main surface 2a and the second main surface 2b of the energy storage element 2 are pressed by the outer casing 4 through the openings 5A and 5B of the housing 3, making it easier to make contact between the various components constituting the energy storage element 2, and thus enabling more stable battery characteristics. Thus, in the present invention, it is sufficient that openings are provided in at least one of the upper wall and the lower wall of the housing.

[0085] [Third Embodiment] Figure 5 is a schematic cross-sectional view showing an all-solid-state battery according to the third embodiment of the present invention. Figure 6 is a schematic perspective view showing the housing and energy storage element constituting the all-solid-state battery according to the third embodiment of the present invention.

[0086] As shown in Figures 5 and 6, in the all-solid-state battery 31 of the third embodiment, there is no upper wall on the upper side of the housing 33, and the housing 33 has an opening 35A that opens upward. Also, there is no lower wall on the lower side of the housing 33, and the housing 33 has an opening 35B that opens downward. Therefore, in the all-solid-state battery 31, the housing 33 is composed only of side walls 33c. Other aspects are the same as in the first embodiment.

[0087] In the third embodiment as well, the first main surface 32a and the second main surface 32b of the energy storage element 32 are pressed by the outer casing 34 through the openings 35A and 35B of the housing 33. This suppresses damage to the energy storage element 32 while facilitating contact between the various components constituting the energy storage element 32, thereby achieving good battery characteristics.

[0088] As in the third embodiment, the housing 33 may not have an upper wall and a lower wall, and the housing 33 may be composed only of side walls 33c. Since most of the first main surface 32a and the second main surface 32b of the energy storage element 32 can be pressed by the outer casing 34, contact between each component constituting the energy storage element 32 can be made even easier, and more stable battery characteristics can be obtained. In addition, the housing 33 can be made even lighter. However, as in the first embodiment, the housing 3 may be provided with an upper wall 3a and a lower wall 3b. In this case, damage to the energy storage element 2 can be made even less likely, and the mechanical strength of the housing 3 can be further increased.

[0089] [Experimental Example] The following explanation will use an experimental example.

[0090] Specifically, first, an upper housing portion 43A, as shown in Figure 7(a), was prepared. The upper housing portion 43A is a lid member. The upper housing portion 43A has a circular opening 45A in its upper wall 43a. The area ratio of the opening 45A to the entire upper surface of the upper housing portion 43A, including the opening 45A, is 35%. Next, a lower housing portion 43B, as shown in Figure 7(b), was prepared. The lower housing portion 43B is a bottomed container with no opening in its lower wall 43b. The material of the upper housing portion 43A and the lower housing portion 43B is ABS resin, and the thickness of each wall is 1 mm.

[0091] Next, the energy storage element 42 was housed in the lower housing portion 43B. The energy storage element 42 had the same structure as the energy storage element 2 of the first embodiment. The solid electrolyte constituting the solid electrolyte layer 6 is β''-alumina, and the thickness of the solid electrolyte layer 6 is 200 μm. The positive electrode active material constituting the positive electrode layer 7 is Na ２ FeP ２ O ７ The positive electrode layer 7 has a thickness of 80 μm. The negative electrode active material constituting the negative electrode layer 8 is hard carbon, and the thickness of the negative electrode layer 8 is 40 μm. The material constituting the positive electrode side current collector layer 9 is aluminum, and the thickness of the positive electrode side current collector layer 9 is 15 μm. The material constituting the negative electrode side current collector layer 10 is aluminum, and the thickness of the negative electrode side current collector layer 10 is 15 μm.

[0092] Next, the first stepped portion 43d of the upper housing portion 43A was fitted into the second stepped portion 43e of the lower housing portion 43B to obtain a housing 43 in which the energy storage element 42 shown in Figure 8 was housed. When housing the energy storage element 42, the energy storage element 42 was housed in the housing 43 so that its side surface faced the side wall 43c of the housing 43. The tab lead 42A extending from the side surface of the energy storage element 42 was taken out from the outlet portion 43f in the side wall 43c of the housing 43. The material of the tab lead 42A is nickel.

[0093] Next, the housing 43 containing the energy storage element 42 was placed inside the outer casing. The outer casing is made of aluminum laminate film, and its thickness is 120 μm. Then, the inside of the outer casing was depressurized to seal the energy storage element 42. This obtained the all-solid-state battery of the experimental example.

[0094] Figure 9 is a photograph of an all-solid-state battery obtained in an experimental example by purging the inside of the casing to a vacuum of 0.5 kPa. As shown in Figure 9, it can be seen that in the all-solid-state battery obtained in the experimental example, the energy storage element is pressed by the casing through the opening of the casing.

[0095] Figure 10 is a graph showing the relationship between the internal pressure of the casing and the contact resistance of the all-solid-state battery obtained in the experimental example. Figure 10 also shows the results of an all-solid-state battery obtained in a comparative experiment where the energy storage element was not housed in the casing but directly in the casing. In the figure, black circles represent the results of the experimental example, and white circles represent the results of the comparative experiment. In the all-solid-state battery of the comparative experiment, the energy storage element was damaged, but the contact resistance test was performed anyway. No damage to the energy storage element was observed in any of the all-solid-state batteries obtained in the experimental example. In the case where the energy storage element was damaged, as in the comparative experiment, a short circuit was observed during charging, causing the battery to malfunction.

[0096] The contact resistance of the all-solid-state battery was measured by AC impedance measurement. Of the Cole-Cole plots obtained from the AC impedance measurement, the straight lines that do not form circles but instead lie along the real axis were evaluated as the contact resistance.

[0097] As shown in Figure 10, the all-solid-state battery obtained in the experimental example shows that the contact resistance is sufficiently reduced by reducing the pressure inside the casing from a pressure equivalent to atmospheric pressure. Furthermore, it was confirmed that the all-solid-state battery obtained in the experimental example did not experience any short circuits even after repeated use, and that the contact resistance remained stably reduced.

[0098] 1, 21, 31… All-solid-state battery 2, 22, 32, 42… Energy storage element 2A, 42A… Tab lead 2a, 22a, 32a… First main surface 2b, 22b, 32b… Second main surface 2c… Side surface 3, 23, 33, 43… Housing 3A, 43A… Upper housing section 3B, 43B… Lower housing section 3a, 23a, 43a… Upper wall 3a1… Top surface 3b, 23b, 43b… Lower wall 3b1… Bottom surface 3c, 33c, 43c… Side wall 3d, 43d… First stepped section 3e, 43e… Second stepped section 3f, 43f… Removal section 4, 24, 34… Outer casing 4a… Interior 5A, 5B, 25A, 35A, 35B, 45A... Openings 6... Solid electrolyte layer 6a... Main surface on one side 6b... Main surface on the other side 7... Positive electrode layer 8... Negative electrode layer 9... Positive electrode side current collector layer 10... Negative electrode side current collector layer

Claims

1. A solid-state battery comprising: an energy storage element having a solid electrolyte layer, a positive electrode layer, a negative electrode layer, and a current collector layer; a housing for housing the energy storage element; and an outer casing for housing the housing, wherein the housing has an opening that overlaps with at least a portion of the energy storage element in a plan view, and the housing has side walls facing the side surface of the energy storage element.

2. The all-solid-state battery according to claim 1, wherein the pressure inside the outer casing is lower than atmospheric pressure.

3. The all-solid-state battery according to claim 2, wherein the energy storage element is pressed by the outer casing through the opening of the housing.

4. The all-solid-state battery according to any one of claims 1 to 3, wherein the housing has an upper housing portion and a lower housing portion, and the upper housing portion and the lower housing portion are fitted together at the side wall of the housing.

5. The all-solid-state battery according to claim 4, wherein the upper housing portion and the lower housing portion each have a stepped portion at the fitting portion of the upper housing portion and the lower housing portion, and the stepped portions of the upper housing portion and the lower housing portion are fitted together.

6. The all-solid-state battery according to any one of claims 1 to 3, wherein the side wall of the housing has an outlet for a tab lead extending from the energy storage element.

7. The all-solid-state battery according to any one of claims 1 to 3, wherein the housing has an upper wall and a lower wall, and the opening is provided in at least one of the upper wall and the lower wall of the housing.

8. The all-solid-state battery according to claim 7, wherein the area ratio of the opening to the entire surface of at least one of the upper and lower surfaces of the housing, including the opening, is 10% or more and 95% or less.

9. The all-solid-state battery according to any one of claims 1 to 3, wherein the housing is composed only of the side walls.

10. The all-solid-state battery according to any one of claims 1 to 3, wherein the solid electrolyte layer constituting the energy storage element is composed of an oxide-based solid electrolyte.

11. A method for manufacturing an all-solid-state battery according to any one of claims 1 to 3, comprising: a step of housing the energy storage element inside the housing such that the side surface of the energy storage element faces the side wall of the housing; a step of housing the housing containing the energy storage element inside the outer casing; and a step of depressurizing the inside of the outer casing to seal the energy storage element.

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