Method for manufacturing all-solid-state battery, and all-solid-state battery

Abstract

The present invention provides a method for manufacturing an all-solid-state battery with which it is possible to suppress warpage.　The present invention pertains to a method for manufacturing an all-solid-state battery provided with a positive electrode current collector layer 2, a pair of positive electrode active material layers 3, a pair of solid electrolyte layers 4, and a pair of negative electrode active material layers 5, the method including: a step for preparing the pair of solid electrolyte layers 4 which are formed of an oxide solid electrolyte and each have a first main surface 4a and a second main surface 4b that are opposite to each other; a positive electrode mixture layer formation step in which a positive electrode mixture layer that contains a positive electrode active material precursor is formed on respective first main surfaces 4a of the pair of solid electrolyte layers 4, thereby obtaining a pair of positive electrode mixture-equipped solid electrolyte layers; a positive electrode formation step for forming the pair of positive electrode active material layers 3 by arranging the pair of positive electrode mixture-equipped solid electrolyte layers so as to face each other with the positive electrode current collector layer 2 being sandwiched therebetween, while having main surfaces of the respective positive electrode mixture layers and main surfaces of the positive electrode current collector layer 2 in contact with each other, and subsequently firing the pair of positive electrode mixture-equipped solid electrolyte layers; and a negative electrode formation step for forming the negative electrode active material layers 5 on the respective second main surfaces 4b of the pair of solid electrolyte layers 4.

Description

All-solid-state battery manufacturing method and all-solid-state battery

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

[0002] Lithium-ion secondary batteries have established themselves as high-capacity, lightweight power sources essential for mobile devices, electric vehicles, and other applications. However, conventional lithium-ion secondary batteries primarily use flammable organic electrolytes, raising concerns about the risk of fire. To address this issue, development is underway on all-solid-state lithium-ion batteries, which use solid electrolytes instead of organic electrolytes. Furthermore, due to concerns about the rising cost of lithium raw materials worldwide, development is also underway on all-solid-state sodium-ion batteries.

[0003] Patent Document 1 listed below discloses an example of an all-solid-state lithium secondary battery. In this lithium secondary battery, a positive electrode composite layer, a solid electrolyte layer, and a negative electrode composite layer are stacked in this order. A positive electrode current collector is provided on the surface of the positive electrode composite layer. A negative electrode current collector is provided on the surface of the negative electrode composite layer. Examples of materials for the solid electrolyte layer include perovskite-type oxides, NASICON-type oxides, and LISICON-type oxides.

[0004] International Publication No. 2015 / 128982

[0005] However, when a composite layer serving as an electrode layer is formed on a solid electrolyte layer made of an oxide solid electrolyte, warping may occur in the laminate of the solid electrolyte layer and the electrode layer, which may impair the adhesion between the electrode layer and the current collector and deteriorate the battery characteristics of the all-solid-state battery.

[0006] An object of the present invention is to provide a method for manufacturing an all-solid-state battery and an all-solid-state battery capable of suppressing warpage.

[0007] A method for manufacturing an all-solid-state battery that solves the above problems and various aspects of the all-solid-state battery will be described.

[0008] A manufacturing method of an all-solid-state battery according to a first aspect of the present invention is a manufacturing method of an all-solid-state battery including a positive electrode current collector layer, a pair of positive electrode active material layers, a pair of solid electrolyte layers, and a pair of negative electrode active material layers, the method comprising: a step of preparing the pair of solid electrolyte layers made of an oxide solid electrolyte and having first and second main surfaces facing each other; a positive electrode composite layer forming step of forming a positive electrode composite layer containing a positive electrode active material precursor on each of the first main surfaces of the pair of solid electrolyte layers to obtain a pair of positive electrode composite-included solid electrolyte layers; a positive electrode forming step of arranging the pair of positive electrode composite-included solid electrolyte layers to face each other with the positive electrode current collector layer therebetween and such that each of the positive electrode composite layers is in contact with each of the main surfaces of the positive electrode current collector layer, and then firing the resultant to form the pair of positive electrode active material layers; and a negative electrode forming step of forming the negative electrode active material layer on each of the second main surfaces of the pair of solid electrolyte layers.

[0009] In the method for producing an all-solid-state battery of Aspect 2, in Aspect 1, it is preferable that the thickness of the positive electrode active material layer is greater than the thickness of the negative electrode active material layer.

[0010] In the method for producing an all-solid-state battery of Aspect 3, in Aspect 1 or Aspect 2, it is preferable that in the positive electrode forming step, the firing of the pair of stacked bodies of the positive electrode composite-attached solid electrolyte layer and the positive electrode current collector layer is performed while applying a load to the stacked body in a stacking direction.

[0011] A method for manufacturing an all-solid-state battery according to a fourth aspect of the present invention is a method for manufacturing an all-solid-state battery including an anode current collector layer, a pair of cathode active material layers, a pair of solid electrolyte layers, and a pair of anode active material layers, the method comprising: a step of preparing the pair of solid electrolyte layers made of an oxide solid electrolyte and having first and second main surfaces facing each other; an anode composite layer-forming step of forming an anode composite layer containing an anode active material precursor on each of the first main surfaces of the pair of solid electrolyte layers to obtain a pair of solid electrolyte layers with the anode composite; an anode-forming step of arranging the pair of solid electrolyte layers with the anode composite to face each other with the anode current collector layer therebetween and such that each anode composite layer is in contact with each main surface of the anode current collector layer, and then firing the resultant to form the pair of anode active material layers; and a cathode-forming step of forming the cathode active material layer on each of the second main surfaces of the pair of solid electrolyte layers.

[0012] In the method for producing an all-solid-state battery of Aspect 5, in Aspect 4, it is preferable that in the negative electrode forming step, the firing of the pair of stacked bodies of the negative electrode composite-attached solid electrolyte layer and the negative electrode current collector layer is performed while applying a load to the stacked body in a stacking direction.

[0013] In the method for producing an all-solid-state battery of Aspect 6, in any one of Aspects 1 to 5, it is preferable that the solid electrolyte layer consists of only a dense layer and has a thickness of 70 μm or less.

[0014] The method for producing an all-solid-state battery of Aspect 7 is preferably any one of Aspects 1 to 5, wherein the solid electrolyte layer has a dense layer and a porous layer, and the dense layer and the porous layer are laminated.

[0015] In the method for producing an all-solid-state battery of Aspect 8, in Aspect 7, it is preferable that the dense layer has a thickness of 70 μm or less.

[0016] In the method for producing an all-solid-state battery of Aspect 9, in Aspect 7 or Aspect 8, it is preferable that the total thickness of the dense layer and the porous layer is 170 μm or less.

[0017] In the method for producing an all-solid-state battery of Aspect 10, in any one of Aspects 1 to 9, it is preferable that the negative electrode forming step is performed before the positive electrode forming step.

[0018] A method for producing an all-solid-state battery according to Aspect 11 is any one of Aspects 1 to 10, wherein the positive electrode active material layer is a solid-state battery represented by the general formula Na ｘ M ｙ P ２ O ｚ wherein 1≦x≦2.8, 0.95≦y≦1.6, 6.5≦z≦8, and M is at least one element selected from the group consisting of Fe, Ni, Co, Mn, and Cr.

[0019] In the method for producing an all-solid-state battery of Aspect 12, in any one of Aspects 1 to 11, it is preferable that the anode active material layer contains an anode active material made of hard carbon.

[0020] In the method for producing an all-solid-state battery of Aspect 13, in any one of Aspects 1 to 12, it is preferable that the oxide solid electrolyte contains at least one selected from the group consisting of β-alumina, β″-alumina, and NASICON crystal.

[0021] A fourteenth aspect of the present invention provides an all-solid-state battery comprising one positive electrode current collector layer, two positive electrode active material layers, two solid electrolyte layers, and two negative electrode active material layers, wherein the positive electrode current collector layer has a first main surface and a second main surface facing each other, and the positive electrode active material layer is a compound represented by the general formula Na ｘ M ｙ P ２ O ｚwherein 1≦x≦2.8, 0.95≦y≦1.6, 6.5≦z≦8, and M is at least one crystal selected from the group consisting of Fe, Ni, Co, Mn, and Cr; the solid electrolyte layer is made of an oxide solid electrolyte containing at least one crystal selected from the group consisting of β-alumina, β″-alumina, and NASICON crystal; the anode active material layer includes an anode active material made of hard carbon; the cathode active material layer is laminated on each of the first main surface and the second main surface of the cathode current collector layer, and the solid electrolyte layer is laminated on each main surface of the cathode active material layer opposite to the side on which the cathode current collector layer is provided, and the anode active material layer is laminated on each main surface of the solid electrolyte layer opposite to the side on which the cathode active material layer is provided.

[0022] According to the present invention, it is possible to provide a method for manufacturing an all-solid-state battery and an all-solid-state battery capable of suppressing warpage.

[0023] FIG. 1 is a schematic cross-sectional view showing an all-solid-state battery according to one embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing an all-solid-state battery according to an embodiment of the present invention that is different from the embodiment shown in FIG. 1. FIG. 3 is a schematic cross-sectional view showing a solid electrolyte layer in the embodiment of the present invention that is shown in FIG. 1. FIGS. 4(a) to 4(c) are schematic cross-sectional views illustrating the second electrode formation step and the electrode mixture layer formation step in the manufacturing method for an all-solid-state battery according to the first embodiment of the present invention. FIGS. 5(a) to 5(c) are schematic cross-sectional views illustrating the first electrode formation step in the manufacturing method for an all-solid-state battery according to the first embodiment of the present invention. FIGS. 6(a) and 6(b) are schematic cross-sectional views illustrating a manufacturing method for an all-solid-state battery according to a comparative example. FIG. 7 is a photograph of an all-solid-state battery manufactured by the manufacturing method for an all-solid-state battery according to one embodiment of the present invention, taken from the negative electrode active material layer side. FIG. 8(a) is a photograph of an all-solid-state battery manufactured by the manufacturing method for an all-solid-state battery according to one embodiment of the present invention, taken from the negative electrode active material layer side. FIG. 8(b) is a photograph of the all-solid-state battery shown in FIG. 8(a) taken from the side. FIG. 9 is a schematic cross-sectional view illustrating the mutual cancellation of forces acting in an all-solid-state battery fabricated by the method for manufacturing an all-solid-state battery according to the first embodiment of the present invention. FIG. 10 is a schematic cross-sectional view illustrating an example in which, in the first electrode formation step, a stack of a pair of solid electrolyte layers with an electrode composite and a positive electrode current collector layer is fired while a load is applied in the stacking direction. FIGS. 11( a) to 11(d) are schematic cross-sectional views illustrating the second electrode formation step, the electrode composite layer formation step, the first electrode formation step, and the like in the method for manufacturing an all-solid-state battery according to a modified example of the first embodiment of the present invention. FIGS. 12( a) and 12(b) are schematic cross-sectional views illustrating the electrode composite layer formation step and the like in the method for manufacturing an all-solid-state battery according to the second embodiment of the present invention. FIGS. 13( a) and 13(b) are schematic cross-sectional views illustrating the first electrode formation step, the second electrode formation step, and the like in the method for manufacturing an all-solid-state battery according to the second embodiment of the present invention. FIG. 14 is a diagram illustrating a solid electrolyte layer used in the method for manufacturing an all-solid-state battery according to a third embodiment of the present invention.

[0024] Preferred embodiments will be described below. However, the following embodiments are merely examples, and the present invention is not limited to the following embodiments. In addition, in each drawing, components having substantially the same functions may be referred to by the same reference numerals.

[0025] (All-Solid-State Battery) FIG. 1 is a schematic cross-sectional view showing an all-solid-state battery according to one embodiment of the present invention.

[0026] The all-solid-state battery 1 of this embodiment is an all-solid-state secondary battery. The all-solid-state battery 1 may be, for example, an all-solid-state sodium ion secondary battery or an all-solid-state lithium ion secondary battery.

[0027] The all-solid-state battery 1 includes a positive electrode current collector layer 2, a pair of positive electrode active material layers 3, a pair of solid electrolyte layers 4, a pair of negative electrode active material layers 5, and a pair of negative electrode current collector layers 6. That is, the all-solid-state battery 1 includes one positive electrode current collector layer 2, two positive electrode active material layers 3, two solid electrolyte layers 4, two negative electrode active material layers 5, and two negative electrode current collector layers 6.

[0028] In this embodiment, the positive electrode current collector layer 2 is the current collector layer of the present invention. The positive electrode active material layer 3 is the first electrode active material layer of the present invention. The negative electrode active material layer 5 is the second electrode active material layer of the present invention. Note that the current collector layer of the present invention may be the negative electrode current collector layer, the first electrode active material layer may be the negative electrode active material layer, and the second electrode active material layer may be the positive electrode active material layer. In this case, a positive electrode current collector layer is provided on the second electrode active material layer. Note that a current collector layer does not necessarily have to be provided on the second electrode active material layer.

[0029] Each of the pair of solid electrolyte layers 4 has a first main surface 4a and a second main surface 4b. The first main surface 4a and the second main surface 4b face each other. A positive electrode active material layer 3, which is one of the pair of first electrode active material layers, is provided on the first main surface 4a of one of the solid electrolyte layers 4. A negative electrode active material layer 5, which is one of the pair of second electrode active material layers, is provided on the second main surface 4b of the solid electrolyte layer 4.

[0030] Similarly, a positive electrode active material layer 3, which is the other first electrode active material layer, is provided on the first main surface 4a of the other solid electrolyte layer 4. A negative electrode active material layer 5, which is the other second electrode active material layer, is provided on the second main surface 4b of the solid electrolyte layer 4. In other words, the solid electrolyte layer 4 is laminated on the main surface of each positive electrode active material layer 3 opposite to the side on which the positive electrode current collector layer 2 is provided. The negative electrode active material layer 5 is laminated on the main surface of each solid electrolyte layer 4 opposite to the side on which the positive electrode active material layer 3 is provided. These layers constitute a pair of laminated structures 7, each including the positive electrode active material layer 3, the solid electrolyte layer 4, and the negative electrode active material layer 5.

[0031] The positive electrode current collector layer 2 has a first main surface 2a and a second main surface 2b. The first main surface 2a and the second main surface 2b face each other. A positive electrode active material layer 3 serving as a first electrode active material layer in one of a pair of laminated structures 7 is laminated on the first main surface 2a of the positive electrode current collector layer 2. A positive electrode active material layer 3 serving as a first electrode active material layer in the other laminated structure 7 is laminated on the second main surface 2b.

[0032] One of a pair of anode current collector layers 6 is provided on the surface of the anode active material layer 5 serving as the second electrode active material layer in one of the laminated structure parts 7. Specifically, the surface of the anode active material layer 5 is the surface facing the solid electrolyte layer 4 side of the anode active material layer 5. Similarly, the other anode current collector layer 6 is provided on the surface of the anode active material layer 5 serving as the second electrode active material layer in the other laminated structure part 7. Note that the pair of anode current collector layers 6 does not necessarily have to be provided.

[0033] An extraction electrode may be connected to the positive electrode current collector layer 2 or each positive electrode active material layer 3 of the all-solid-state battery 1. Similarly, an extraction electrode may be connected to each negative electrode current collector layer 6 or each negative electrode active material layer 5. The extraction electrode electrically connects the all-solid-state battery 1 to the outside.

[0034] The all-solid-state battery 1 of this embodiment is characterized in that the pair of solid electrolyte layers 4 are arranged to face each other with the positive electrode current collector layer 2 interposed therebetween, and the positive electrode active material layer 3 is in contact with each main surface of the positive electrode current collector layer 2. In this case, when manufacturing the all-solid-state battery 1, the positive electrode active material layer 3 can be formed in a state in which the layers face each other with the positive electrode current collector layer 2 interposed therebetween. This makes it possible to suppress warping of the all-solid-state battery 1.

[0035] In the all-solid-state battery 1 of this embodiment, the positive electrode active material layers 3 in a pair of laminated structure portions 7 face each other with the positive electrode current collector layer 2 sandwiched therebetween. However, for example, the negative electrode active material layers 5 in a pair of laminated structure portions 7 may face each other with the negative electrode current collector layer 6 sandwiched therebetween. In this case, the negative electrode active material layer 5 is the first electrode active material layer, and the positive electrode active material layer 3 is the second electrode active material layer. This example will be described below as an embodiment of the present invention different from the embodiment shown in FIG. 1 .

[0036] FIG. 2 is a schematic cross-sectional view showing an all-solid-state battery according to an embodiment of the present invention that is different from the embodiment shown in FIG.

[0037] In this embodiment, the all-solid-state battery 1A includes a negative electrode current collector layer 6, a pair of negative electrode active material layers 5, a pair of solid electrolyte layers 4, a pair of positive electrode active material layers 3, and a pair of positive electrode current collector layers 2.

[0038] An anode active material layer 5 is provided on the first main surface 4a of each solid electrolyte layer 4. A cathode active material layer 3 is provided on the second main surface 4b of each solid electrolyte layer 4. These constitute a pair of laminated structures 7 in which the cathode active material layer 3, the solid electrolyte layer 4, and the anode active material layer 5 are respectively stacked.

[0039] The negative electrode current collector layer 6 has a first main surface 6a and a second main surface 6b. The first main surface 6a and the second main surface 6b face each other. The negative electrode active material layer 5 of one of the pair of laminated structures 7 is laminated on the first main surface 6a of the negative electrode current collector layer 6. The negative electrode active material layer 5 of the other laminated structure 7 is laminated on the second main surface 6b.

[0040] One of the pair of positive electrode current collector layers 2 is provided on the surface of the positive electrode active material layer 3 in one of the laminated structure parts 7. Specifically, the surface of the positive electrode active material layer 3 is the surface facing the solid electrolyte layer 4 side of the positive electrode active material layer 3. Similarly, the other positive electrode current collector layer 2 is provided on the surface of the positive electrode active material layer 3 in the other laminated structure part 7. Note that the pair of positive electrode current collector layers 2 does not necessarily have to be provided.

[0041] When manufacturing the all-solid-state battery 1A of this embodiment, the negative electrode active material layer 5 can be formed in a state where the layers face each other with the negative electrode current collector layer 6 sandwiched therebetween, thereby making it possible to suppress warping of the all-solid-state battery 1A.

[0042] Hereinafter, each layer in the all-solid-state battery of the present invention will be described in detail.

[0043] (Solid Electrolyte Layer) FIG. 3 is a schematic cross-sectional view showing the solid electrolyte layer in the embodiment shown in FIG.

[0044] The solid electrolyte layer 4 has a first solid electrolyte layer 8 and a pair of second solid electrolyte layers 9. The first solid electrolyte layer 8 has a third main surface 8a and a fourth main surface 8b. The third main surface 8a and the fourth main surface 8b face each other. One of the pair of second solid electrolyte layers 9, the second solid electrolyte layer 9, is provided on the third main surface 8a of the first solid electrolyte layer 8. The other second solid electrolyte layer 9 is provided on the fourth main surface 8b of the first solid electrolyte layer 8.

[0045] 1 , a pair of solid electrolyte layers 4 each include a first solid electrolyte layer 8 and a second solid electrolyte layer 9 provided on each of the two main surfaces of the first solid electrolyte layer 8. In this embodiment, the first main surface 4 a of the solid electrolyte layer 4 is the surface of one of the second solid electrolyte layers 9. The second main surface 4 b of the solid electrolyte layer 4 is the surface of the other of the second solid electrolyte layers 9.

[0046] The first solid electrolyte layer 8 shown in Fig. 3 is specifically a dense layer. On the other hand, the second solid electrolyte layer 9 is specifically a porous layer. The second solid electrolyte layer 9 has pores that are three-dimensionally connected. It is desirable that the first solid electrolyte layer 8 and the second solid electrolyte layer 9 are integrated.

[0047] The first solid electrolyte layer 8 has a denser structure than the second solid electrolyte layer 9. As a result, the first solid electrolyte layer 8 not only has a function of conducting ions but also a function as a base layer for ensuring the mechanical strength of the solid electrolyte layer 4.

[0048] In this embodiment, a positive electrode active material layer 3 is provided on one of the second solid electrolyte layers 9. A negative electrode active material layer 5 is provided on the other of the second solid electrolyte layers 9. In this case, an anchor effect acts between each second solid electrolyte layer 9, which is a porous layer, and the positive electrode active material layer 3 and the negative electrode active material layer 5.

[0049] More specifically, when the positive electrode active material layer 3 is formed on the surface of one second solid electrolyte layer 9, the active material powder constituting the positive electrode active material layer 3 easily enters the voids. Similarly, when the negative electrode active material layer 5 is formed on the surface of the other second solid electrolyte layer 9, the active material powder constituting the negative electrode active material layer 5 easily enters the voids. As a result, an anchor effect acts between each second solid electrolyte layer 9 and the formed positive electrode active material layer 3 and negative electrode active material layer 5. This can improve the adhesion between the solid electrolyte layer 4 and the positive electrode active material layer 3 and negative electrode active material layer 5. This can reduce the contact resistance between the solid electrolyte layer 4 and the positive electrode active material layer 3 and negative electrode active material layer 5.

[0050] The porosity of the first solid electrolyte layer 8 is smaller than the porosity of the second solid electrolyte layer 9. The porosity is defined by the following formula (1): In formula (1), p is the bulk density, and p0 is the true density.

[0051] Porosity = (1-p / p0) x 100 (%)...Formula (1)

[0052] The porosity of the first solid electrolyte layer 8 is preferably 20% or less, more preferably 10% or less, and even more preferably 5% or less. The lower limit of the porosity of the first solid electrolyte layer 8 is not particularly limited, but can be, for example, 0.1%.

[0053] The porosity of the second solid electrolyte layer 9 is preferably 25% or more, more preferably 30% or more, and even more preferably 40% or more. On the other hand, the porosity of the second solid electrolyte layer 9 is preferably 97% or less, more preferably 95% or less, and even more preferably 90% or less. When the porosity of the second solid electrolyte layer 9 is within the above range, three-dimensionally interconnected voids can be more easily formed, and the adhesion between the solid electrolyte layer 4 and the positive electrode active material layer 3 and the negative electrode active material layer 5 can be further improved.

[0054] The thickness of the first solid electrolyte layer 8 is preferably 0.01 μm or more, more preferably 0.1 μm or more, even more preferably 1 μm or more, and particularly preferably 5 μm or more. On the other hand, the thickness of the first solid electrolyte layer 8 is preferably 70 μm or less, more preferably 50 μm or less.

[0055] If the thickness of the first solid electrolyte layer 8 is too thin, the mechanical strength may decrease, or a short circuit may occur between the positive electrode active material layer 3 and the negative electrode active material layer 5. On the other hand, if the thickness of the first solid electrolyte layer 8 is too thick, the ionic conductivity in the first solid electrolyte layer 8 may easily decrease. In addition, the energy density per unit volume of the all-solid-state battery 1 tends to decrease.

[0056] When the thickness of the first solid electrolyte layer 8 is 70 μm or less, the all-solid-state battery is particularly likely to warp, as will be described later. Therefore, the manufacturing method according to the present invention is particularly suitable.

[0057] The thickness of the second solid electrolyte layer 9 is preferably 1 μm or more, more preferably 2 μm or more, even more preferably 5 μm or more, and particularly preferably 10 μm or more. On the other hand, the thickness of the second solid electrolyte layer 9 is preferably 100 μm or less, and more preferably 80 μm or less.

[0058] If the thickness of the second solid electrolyte layer 9 is too thin, the amount of material constituting the positive electrode active material layer 3 and the negative electrode active material layer 5 that enters the voids in the second solid electrolyte layer 9 will be small. As a result, the contact area between the solid electrolyte layer 4 and the positive electrode active material layer 3 and the negative electrode active material layer 5 will be small, and adhesion will likely decrease. In this case, the ion conduction paths at the interfaces between the solid electrolyte layer 4 and the positive electrode active material layer 3 and the negative electrode active material layer 5 will be reduced, and the internal resistance of the all-solid-state battery 1 will tend to increase. As a result, the rapid charge / discharge characteristics of the all-solid-state battery 1 will likely decrease.

[0059] On the other hand, if the thickness of the second solid electrolyte layer 9 is too thick, it becomes difficult to fill the entire voids of the second solid electrolyte layer 9 with the material constituting the positive electrode active material layer 3 or the negative electrode active material layer 5. This reduces the energy density per unit volume of the all-solid-state battery 1. In addition, the amount of shrinkage during the formation of the second solid electrolyte layer 9 increases, making the second solid electrolyte layer 9 more likely to peel off at the interface with the first solid electrolyte layer 8.

[0060] The thickness of the solid electrolyte layer 4, i.e., the total thickness of the first solid electrolyte layer 8 and the second solid electrolyte layer 9, is preferably 10 μm or more, more preferably 12 μm or more, even more preferably 15 μm or more, and particularly preferably 17 μm or more. On the other hand, the total thickness of the first solid electrolyte layer 8 and the second solid electrolyte layer 9 is preferably 170 μm or less, more preferably 150 μm or less.

[0061] When the thickness of the solid electrolyte layer 4 is equal to or greater than the above-mentioned lower limit, the mechanical strength can be further improved. In addition, it is possible to make it more difficult for a short circuit to occur between the positive electrode active material layer 3 and the negative electrode active material layer 5. On the other hand, when the thickness of the solid electrolyte layer 4 is equal to or less than the above-mentioned upper limit, the distance required for ion conduction in the solid electrolyte layer 4 is shortened, and the ion conductivity is further improved. In addition, it is possible to further increase the energy density per unit volume of the all-solid-state battery 1.

[0062] Furthermore, when the thickness of the solid electrolyte layer 4 is 50 μm or less, the all-solid-state battery is particularly likely to warp, as will be described later. Therefore, the manufacturing method according to the present invention is particularly suitable.

[0063] The same material can be used for the first solid electrolyte layer 8 and the second solid electrolyte layer 9 in the solid electrolyte layer 4. The solid electrolyte layer 4 is made of an oxide solid electrolyte.

[0064] When the all-solid-state battery 1 is an all-solid-state sodium-ion secondary battery, the oxide solid electrolyte used in the solid electrolyte layer 4 is a sodium ion conductive oxide. Examples of sodium ion conductive oxides include compounds containing at least one element selected from Al, Y, Zr, Si, and P, as well as Na and O. Specific examples of sodium ion conductive oxides include beta-alumina or NASICON crystal, which have excellent sodium ion conductivity. Among these, the sodium ion conductive oxide is preferably at least one sodium ion conductive oxide selected from the group consisting of β"-alumina, β-alumina, and NASICON crystal. It is more preferable that the sodium ion conductive oxide is β-alumina or β"-alumina. These have even better sodium ion conductivity. For these reasons, it is preferable that the oxide solid electrolyte constituting the solid electrolyte layer 4 contains at least one element selected from the group consisting of β-alumina, β"-alumina, and NASICON crystal.

[0065] Beta alumina has two types of crystal forms: β-alumina and β"-alumina. The theoretical composition formula of β-alumina is Na ２ O.11Al ２ O ３ The theoretical composition formula of β"-alumina is Na ２ O 5.3 Al ２ O ３ Since β″-alumina is a metastable material, it is usually ２ O or MgO is added as a stabilizer. Since β"-alumina has higher sodium ion conductivity than β-alumina, it is preferable to use β"-alumina alone or a mixture of β"-alumina and β-alumina. ２ It is more preferable to use LiO-stabilized β″-alumina or MgO-stabilized β″-alumina. ２The composition formula of O-stabilized β″-alumina is, for example, Na １．７ Li ０．３ Al １０．７ O １７ The composition formula of MgO-stabilized β″-alumina is, for example, (Al １０．３２ Mg ０．６８ O １６ ) (Na １．６８ O).

[0066] NASICON crystals include Na ３ Zr ２ Si ２ P.O. １２ , Na ３．２ Zr １．３ Si ２．２ P ０．８ O １０．５ , Na ３ Zr １．６ Ti ０．４ Si ２ P.O. １２ , Na ３ Hf ２ Si ２ P.O. 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 P.O. １２ , Na ３．６ Ti ０．２ Y ０．８ Si ２．８ O ９ , Na ３ Zr １．８８ Y ０．１２ Si ２ P.O. １２ , Na ３．１２ Zr １．８８ Y ０．１２ Si ２ P.O. １２ , Na ３．０５ Zr ２ Si ２．０６ P ０．９５ O １２ , Na ３．４ Zr ２ Si２．４ P ０．６ O １２ , Na ３．４ Zr １．９ Zn ０．１ Si ２．４ P ０．６ O １２ , Na ３．４ Zr １．９ Mg ０．１ Si ２．２ P ０．８ O １２ , Na ２．８ Zr ２ Si ２．４ P ０．６ O １２ , Na ３．６ Zr ０．１３ Yb １．６７ Si ０．１１ P ２．９ O １２ , Na ５ YSi ４ O １２ Among them, NASICON crystal is Na ３．４ Zr ２ Si ２．４ P ０．６ O １２ or Na ３．０５ Zr ２ Si ２．０６ P ０．９５ O １２ In this case, the sodium ion conductivity can be further improved.

[0067] When the all-solid-state battery 1 is an all-solid-state lithium ion secondary battery, the oxide solid electrolyte used in the solid electrolyte layer 4 is a lithium ion conductive oxide. In this case, the oxide solid electrolyte may be, for example, Li １．３ Al ０．３ Ti １．７ (P.O. ４ ) ３ , Li ７ La ３ Zr ２ O １２ , Li １．０７ Al ０．６ Ti １．４６ (P.O. ４ ) ３ , Li １．５ Al０．５ Ge １．５ (P.O. ４ ) ３ At least one selected from the following can be used.

[0068] A metal layer may be provided on each surface of the pair of second solid electrolyte layers 9. When the second electrode active material layer formed on the second solid electrolyte layer 9 is made of metallic sodium, metallic lithium, or the like, the adhesion between the second solid electrolyte layer 9, the metal layer, and the second electrode active material layer can be increased. This reduces the interfacial resistance, thereby increasing the discharge capacity.

[0069] The metal constituting the metal layer is not particularly limited, and examples thereof include Sn, Ti, Bi, Au, Al, Cu, Sb, and Pb. These metals constituting the metal layer may be used alone or in combination of two or more. The metal layer may also be made of an alloy of these metals.

[0070] The thickness of the metal layer is preferably 3 nm or more, more preferably 5 nm or more, even more preferably 10 nm or more, and particularly preferably 20 nm or more, while the thickness of the metal layer is preferably 5 μm or less, more preferably 3 μm or less, even more preferably 1 μm or less, and particularly preferably 500 nm or less.

[0071] The metal layer can be formed by, for example, a physical vapor deposition method such as vapor deposition or sputtering, or a chemical vapor deposition method such as thermal CVD, MOCVD, or plasma CVD. Alternatively, the metal layer can be formed by, for example, a liquid phase film formation method such as plating, a sol-gel method, or spin coating. Among these, it is preferable to use a vapor deposition method or a sputtering method for forming the metal layer. In this case, it is easy to form a thin metal layer, and the above-mentioned effects of providing the metal layer can be easily obtained.

[0072] 3 , in this embodiment, the second solid electrolyte layer 9 is provided on both the third main surface 8a and the fourth main surface 8b of the first solid electrolyte layer 8. However, the second solid electrolyte layer 9 may be provided on one of the third main surface 8a and the fourth main surface 8b of the first solid electrolyte layer 8. Alternatively, the solid electrolyte layer 4 may be composed only of the first solid electrolyte layer 8, which is a dense layer.

[0073] (Positive Electrode Active Material Layer) The positive electrode active material contained in the positive electrode active material layer 3 shown in FIG. 1 is not particularly limited, but may be a compound represented by the general formula Na ｘ M ｙ P ２ O ｚ In particular, the positive electrode active material is preferably a glass-ceramic material containing crystals represented by the general formula Na ｘ MP ２ O ７ It is more preferable that the positive electrode active material is made of crystallized glass containing crystals represented by the formula: where 1≦x≦2, and M is at least one selected from the group consisting of Fe, Ni, Co, Mn, and Cr. Examples of such positive electrode active material crystals include Na ２ FeP ２ O ７ , Na ２ CoP ２ O ７ , Na ２ NiP ２ O ７ etc. can be used.

[0074] In addition, crystallized glass means that precursor glass containing an amorphous phase is heated to precipitate crystals.In other words, crystallized glass means that precursor glass containing an amorphous phase is fired to crystallize the amorphous phase.All of the amorphous phase may be transformed into a crystalline phase, or the amorphous phase may remain.One type of crystal may be precipitated from the amorphous phase, or two or more types of crystals may be precipitated.Whether it is crystallized glass or not can be determined, for example, based on the peak angle shown by powder X-ray diffraction (XRD).

[0075] The positive electrode active material layer 3 may contain a solid electrolyte and a conductive additive. The proportions of the respective materials in the positive electrode active material layer 3, in mass %, can be, for example, 30% to 95% positive electrode active material, 5% to 70% solid electrolyte, and 0% to 20% conductive additive.

[0076] The solid electrolyte may be the same as that described in the "Solid Electrolyte Layer" section. The conductive additive may be, for example, conductive carbon. Examples of conductive carbon include acetylene black, carbon black, ketjen black, and vapor-grown carbon fiber (VGCF) conductive additive. The conductive additive is preferably a carbon-based conductive additive made of the above-mentioned materials.

[0077] It is preferable that the positive electrode active material layer 3 contains a solid electrolyte. In this case, the positive electrode active material and the solid electrolyte can be integrated. Alternatively, when the positive electrode active material layer 3 contacts the solid electrolyte layer 4, the two can be integrated. As a result, an ion conduction path is more effectively formed.

[0078] The thickness of the positive electrode active material layer 3 is preferably 10 μm or more, more preferably 50 μm or more, and even more preferably 100 μm or more. On the other hand, the thickness of the positive electrode active material layer 3 is preferably 1000 μm or less, and more preferably 700 μm or less. When the thickness of the positive electrode active material layer 3 is equal to or greater than the above lower limit, the charge / discharge capacity of the all-solid-state battery 1 can be further increased. On the other hand, when the thickness of the positive electrode active material layer 3 is too thick, resistance to electronic conduction increases, which may reduce the discharge capacity of the all-solid-state battery 1. Alternatively, the operating voltage of the all-solid-state battery 1 may decrease.

[0079] In the embodiment shown in FIG. 1 , when the positive electrode active material layers 3 in a pair of laminated structures 7 face each other with the positive electrode current collector layer 2 sandwiched therebetween, the positive electrode active material of each positive electrode active material layer 3 is preferably made of crystallized glass. However, for example, when the negative electrode active material layers 5 in a pair of laminated structures 7 face each other with the negative electrode current collector layer 6 sandwiched therebetween, the positive electrode active material of the positive electrode active material layer 3 may be made of, for example, a metal or an alloy. Specifically, the positive electrode active material may be, for example, aluminum, titanium, silver, copper, stainless steel, or an alloy containing at least one of these. The above-mentioned metals or alloys may be used alone or in combination. In this case, the positive electrode active material layer 3 may be a metal film or an alloy film.

[0080] (Negative electrode active material layer) The negative electrode active material contained in the negative electrode active material layer 5 is not particularly limited, and for example, a carbon electrode material such as hard carbon or soft carbon can be used. The carbon electrode material is preferably hard carbon. However, when the all-solid-state battery 1 is an all-solid-state sodium secondary battery, the negative electrode active material may contain metallic sodium or an alloy-based negative electrode active material capable of absorbing sodium, such as tin, bismuth, lead, or phosphorus. Note that the negative electrode active material layer 5 is preferably not metallic sodium or a negative electrode active material layer containing metallic sodium.

[0081] The negative electrode active material layer 5 may further contain a solid electrolyte and a conductive additive. The ratio of each material in the negative electrode active material layer 5 may be, for example, in mass %, 60% to 95% negative electrode active material, 5% to 35% solid electrolyte, and 0% to 5% conductive additive. The solid electrolyte may be, for example, the solid electrolyte described in the "Solid Electrolyte Layer" section. The conductive additive may be, for example, the conductive additive described in the "Cathode Active Material Layer" section.

[0082] The thickness of the negative electrode active material layer 5 is preferably 0.3 μm or more, more preferably 3 μm or more, and even more preferably 10 μm or more. On the other hand, the thickness of the negative electrode active material layer 5 is preferably 500 μm or less, more preferably 300 μm or less. When the thickness of the negative electrode active material layer 5 is equal to or greater than the above lower limit, the charge / discharge capacity of the all-solid-state battery 1 can be further increased. On the other hand, when the thickness of the negative electrode active material layer 5 is too thick, resistance to electronic conduction increases, which may reduce the discharge capacity of the all-solid-state battery 1. Alternatively, the operating voltage of the all-solid-state battery 1 may decrease.

[0083] In the embodiment shown in FIG. 1 , when the positive electrode active material layers 3 in a pair of laminated structure portions 7 face each other with the positive electrode current collector layer 2 sandwiched therebetween, the negative electrode active material of each negative electrode active material layer 5 may be made of, for example, a metal or an alloy. Specifically, the negative electrode active material may be, for example, aluminum, titanium, silver, copper, stainless steel, or an alloy containing at least one of these. The above-mentioned metals or alloys may be used alone or in combination. In this case, the negative electrode active material layer 5 may be a metal film or an alloy film.

[0084] (Positive Electrode Current Collector Layer and Negative Electrode Current Collector Layer) In the embodiment shown in FIG. 1 , the positive electrode current collector layer 2 and the negative electrode current collector layer 6 are aluminum foil. However, the material of each of the positive electrode current collector layer 2 and the negative electrode current collector layer 6 is not limited to aluminum, and may be, for example, aluminum, titanium, silver, copper, stainless steel, or an alloy containing at least one of these. The metals or alloys listed above may be used alone or in combination. The thicknesses of the positive electrode current collector layer 2 and the negative electrode current collector layer 6 are not particularly limited, but may be 0.01 μm or more and 1000 μm or less.

[0085] An example of a method for producing an all-solid-state battery according to the present invention will be described below.

[0086] (Manufacturing Method) (First Embodiment of Manufacturing Method) Figures 4(a) to 4(c) are schematic cross-sectional views for explaining a second electrode forming step and an electrode mixture layer forming step in the manufacturing method for an all-solid-state battery according to the first embodiment of the present invention. Figures 5(a) to 5(c) are schematic cross-sectional views for explaining a first electrode forming step and the like in the manufacturing method for an all-solid-state battery according to the first embodiment. In this embodiment, the first electrode forming step is a positive electrode forming step. The second electrode forming step is a negative electrode forming step.

[0087] As shown in Fig. 4(a), a pair of solid electrolyte layers 4 are prepared. Next, as shown in Fig. 4(b), a second electrode formation step is performed in which a negative electrode active material layer 5 is formed as a second electrode active material layer on each second main surface 4b of the pair of solid electrolyte layers 4.

[0088] Next, as shown in FIG. 4( c), an electrode mixture layer forming step is performed in which an electrode mixture layer 13 is formed on each first main surface 4 a of the pair of solid electrolyte layers 4. Specifically, first, a paste containing a positive electrode active material precursor is prepared. Next, the paste is applied to each first main surface 4 a of the pair of solid electrolyte layers 4, and the paste is then dried. In this way, an electrode mixture layer 13 is formed on each first main surface 4 a of the pair of solid electrolyte layers 4, thereby obtaining a pair of solid electrolyte layers 14 with an electrode mixture. The solid electrolyte layer 14 with an electrode mixture is a laminate of the solid electrolyte layer 4 and the electrode mixture layer 13.

[0089] In this embodiment, the electrode mixture layer forming step is specifically a positive electrode mixture layer forming step. The electrode mixture layer 13 is a positive electrode mixture layer. The electrode mixture-containing solid electrolyte layer 14 is a positive electrode mixture-containing solid electrolyte layer.

[0090] 5( a) is prepared. Next, the positive electrode current collector layer 2 is sandwiched between a pair of solid electrolyte layers 14 with an electrode mixture from both main surfaces of the positive electrode current collector layer 2. Specifically, the electrode mixture layer 13 of one of the solid electrolyte layers 14 with an electrode mixture is brought into contact with the first main surface 2a of the positive electrode current collector layer 2. The electrode mixture layer 13 of the other solid electrolyte layer 14 with an electrode mixture is brought into contact with the second main surface 2b of the positive electrode current collector layer 2.

[0091] Next, the stack of the pair of solid electrolyte layers 14 with electrode composite and the positive electrode current collector layer 2 is fired to form a pair of positive electrode active material layers 3 as a pair of first electrode active material layers shown in FIG. 5( b). Next, as shown in FIG. 5( c), a negative electrode current collector layer 6 is formed on each surface of the pair of negative electrode active material layers 5. In this manner, an all-solid-state battery 1 is obtained. Note that in the present invention, the negative electrode current collector layer 6 does not necessarily have to be formed.

[0092] A feature of the manufacturing method according to the present invention is that a pair of solid electrolyte layers 14 with an electrode mixture are arranged so as to face each other with a current collector layer sandwiched therebetween, and so that each electrode mixture layer 13 is in contact with each main surface of the current collector layer, and then fired to form a pair of first electrode active material layers. This makes it possible to suppress warping of the all-solid-state battery 1. This will be explained below by comparing one embodiment of the present invention and the first embodiment with a comparative example.

[0093] 6(a) and 6(b) are schematic cross-sectional views for explaining a manufacturing method of an all-solid-state battery of a comparative example. FIG. 7 is a photograph of an all-solid-state battery manufactured by the manufacturing method of the comparative example.

[0094] In the comparative example, as shown in FIG. 6( a), a solid electrolyte layer 4 is prepared in the same manner as in the first embodiment. Next, a negative electrode active material layer 5 is formed on the second main surface 4b of the solid electrolyte layer 4 in the same manner as in the first embodiment. Next, an electrode mixture layer 13 is formed on the first main surface 4a of the solid electrolyte layer 4 in the same manner as in the first embodiment. The electrode mixture layer 13 contains a positive electrode active material precursor. Next, the laminate of the negative electrode active material layer 5, the solid electrolyte layer 4, and the electrode mixture layer 13 is fired to obtain the all-solid-state battery shown in FIG. 6( b).

[0095] As shown in FIG. 7 , significant warpage occurs in the all-solid-state battery manufactured by the manufacturing method of the comparative example. In this case, the charge / discharge efficiency of the all-solid-state battery may be degraded, or the all-solid-state battery may malfunction. The warpage occurs when the cathode active material layer 3 (the first electrode active material layer shown in FIG. 6( b)) shrinks from the electrode mixture layer 13 shown in FIG. 6( a). More specifically, the shrinkage of the cathode active material layer 3 applies tensile stress to the solid electrolyte layer 4 side of the cathode active material layer 3, and contraction stress to the side of the cathode active material layer 3 farther from the solid electrolyte layer. This causes warpage throughout the entire all-solid-state battery. In contrast, the manufacturing method of the present invention can suppress warpage of the all-solid-state battery.

[0096] Fig. 8(a) is a photograph of an all-solid-state battery fabricated by a method for manufacturing an all-solid-state battery according to one embodiment of the present invention, taken from the negative electrode active material layer side. Fig. 8(b) is a photograph of the all-solid-state battery shown in Fig. 8(a) taken from the side. The all-solid-state batteries shown in Fig. 8(a) and Fig. 8(b) were fabricated by a method similar to that of the first embodiment, except that no negative electrode current collector layer was formed and that a lead wire was connected to the positive electrode current collector layer.

[0097] 8(a) and 8(b), it can be seen that warpage is suppressed in the all-solid-state battery manufactured by the manufacturing method of the present invention. This is because, taking the all-solid-state battery 1 manufactured by the manufacturing method of the first embodiment as an example, forces caused by contraction of a pair of positive electrode active material layers 3 cancel each other out, as schematically shown in FIG.

[0098] More specifically, in the manufacturing method of the first embodiment, as shown in FIG. 5( a), a pair of solid electrolyte layers 14 with an electrode mixture are arranged to face each other with the positive electrode current collector layer 2 therebetween, with each electrode mixture layer 13 in contact with each main surface of the positive electrode current collector layer 2, and then fired. As a result, the pair of positive electrode active material layers 3 contract while facing each other with the positive electrode current collector layer 2 therebetween. As shown in FIG. 9, in one laminate structure 7, a tensile stress is applied to the solid electrolyte layer 4 side of the positive electrode active material layer 3, and a contraction stress is applied to the positive electrode current collector layer 2 side of the positive electrode active material layer 3. Similarly, in the other laminate structure 7, a tensile stress is applied to the solid electrolyte layer 4 side of the positive electrode active material layer 3, and a contraction stress is applied to the positive electrode current collector layer 2 side of the positive electrode active material layer 3.

[0099] As a result, for example, a force that displaces both ends of the all-solid-state battery 1 in the left-right direction in FIG. 9 downward and a force that displaces both ends upward act simultaneously on the all-solid-state battery 1. Therefore, the forces that displace the both ends of the all-solid-state battery 1 cancel each other out. Therefore, warping of the all-solid-state battery 1 is suppressed. Therefore, in the first embodiment, deterioration of battery characteristics such as charge / discharge efficiency can be suppressed. The same applies to the embodiments shown in FIGS. 8( a) and 8(b).

[0100] As shown in FIG. 3 , the solid electrolyte layer 4 of the first embodiment has a first solid electrolyte layer 8 that is a dense layer and a second solid electrolyte layer 9 that is a porous layer. As described above, the thickness of the first solid electrolyte layer 8 is preferably 70 μm or less. Alternatively, the total thickness of the solid electrolyte layer 4 is preferably 170 μm or less. When the thickness of the first solid electrolyte layer 8 is 70 μm or less, or when the total thickness of the solid electrolyte layer 4 is 170 μm or less, warping of the all-solid-state battery as in the comparative example is particularly likely to occur. Therefore, the manufacturing method according to the present invention is particularly suitable.

[0101] It is preferable that the thickness of the positive electrode active material layer 3 as the first electrode active material layer is thicker than the thickness of the negative electrode active material layer 5 as the second electrode active material layer. In this case, the effect of stress due to contraction when the positive electrode active material layer 3 is formed is particularly large on the all-solid-state battery. Therefore, warping of the all-solid-state battery as in the comparative example is particularly likely to occur. Therefore, the manufacturing method according to the present invention is particularly suitable.

[0102] 10, in the first electrode formation step, the sintering of the stack of the pair of electrode composite-attached solid electrolyte layers 14 and the positive electrode current collector layer 2 is preferably performed while applying a load F to the stack in the stacking direction. This more reliably increases the adhesion between the positive electrode current collector layer 2 and the pair of positive electrode active material layers 3 serving as the first electrode active material layers shown in FIG. 1. The applied load F is preferably 500 g or less. In this case, the all-solid-state battery 1 is more reliably less likely to be damaged.

[0103] In the present invention, the electrode mixture layer forming step may be a negative electrode mixture layer forming step. The electrode mixture layer may be a negative electrode mixture layer. The electrode mixture-accompanying solid electrolyte layer may be a negative electrode mixture-accompanying solid electrolyte layer. The first electrode forming step may be a negative electrode forming step. The second electrode forming step may be a positive electrode forming step. This example is shown as a modified example of the first embodiment.

[0104] (Modification of First Embodiment of Manufacturing Method) FIGS. 11( a) to 11(d) are schematic cross-sectional views for explaining a second electrode forming step, an electrode mixture layer forming step, a first electrode forming step, and the like in a manufacturing method for an all-solid-state battery according to a modification of the first embodiment.

[0105] 11( a), a solid electrolyte layer 4 is prepared as in the first embodiment. Next, a positive electrode active material layer 3 is formed on each second main surface 4b of the pair of solid electrolyte layers 4.

[0106] Next, as shown in FIG. 11( b), an electrode mixture layer 15 is formed on each first main surface 4a of the pair of solid electrolyte layers 4. This results in a pair of solid electrolyte layers 14A with an electrode mixture. Specifically, the electrode mixture layer 15 is a negative electrode mixture layer containing a negative electrode active material precursor. Specifically, the solid electrolyte layer 14A with an electrode mixture is a solid electrolyte layer with a negative electrode mixture.

[0107] 11( c) is prepared. Next, the negative electrode current collector layer 6 is sandwiched between a pair of solid electrolyte layers 14A with an electrode mixture from both main surfaces of the negative electrode current collector layer 6. Specifically, the electrode mixture layer 15 of one of the solid electrolyte layers 14A with an electrode mixture is brought into contact with the first main surface 6a of the negative electrode current collector layer 6. The electrode mixture layer 15 of the other solid electrolyte layer 14A with an electrode mixture is brought into contact with the second main surface 6b of the negative electrode current collector layer 6.

[0108] Next, the stack of the pair of solid electrolyte layers 14A with electrode mixture and the negative electrode current collector layer 6 is fired to form a pair of negative electrode active material layers 5 shown in FIG. 11(d).

[0109] Although not shown, the positive electrode current collector layer 2 shown in FIG. 2 may then be formed on each surface of the pair of positive electrode active material layers 3 .

[0110] In this modification, too, in the anode formation step as the first electrode formation step, it is preferable to perform firing of the stack of the pair of solid electrolyte layers 14A with electrode composite and the anode current collector layer 6 while applying a load to the stack in the stacking direction, which can more reliably increase the adhesion between the anode current collector layer 6 and the anode active material layer 5 as the pair of first electrode active material layers.

[0111] Hereinafter, the method for forming each layer in the all-solid-state battery of the present invention will be described in more detail.

[0112] (Formation of Solid Electrolyte Layer) (a) Preparation of Green Sheet for Forming First Solid Electrolyte Layer First, a slurry is prepared by adding an organic vehicle containing a binder to at least one of the first solid electrolyte powder and the raw material powder of the first solid electrolyte powder. The raw material powder here refers to a powder that will react in a subsequent firing process to become a solid electrolyte. The binder is a material that binds together powder-like materials.

[0113] Next, the slurry is applied to a substrate and dried to prepare a green sheet for forming a first solid electrolyte layer. The drying temperature of the slurry can be, for example, 40°C or higher and 100°C or lower. The drying time of the slurry can be, for example, 3 minutes or higher and 24 hours or lower. Thereafter, the green sheet for forming the first solid electrolyte layer is peeled off from the substrate.

[0114] When an all-solid-state sodium ion secondary battery is manufactured as the all-solid-state battery 1, for example, at least one type selected from the group consisting of β″-alumina, β-alumina, and NASICON crystals can be prepared as the first solid electrolyte powder. As the β″-alumina, β-alumina, and NASICON crystals, the same materials as those described in the above section “First Solid Electrolyte Layer” can be used.

[0115] When an all-solid-state lithium ion secondary battery is manufactured as the all-solid-state battery 1, the first solid electrolyte powder may be, for example, Li １．３ Al ０．３ Ti １．７ (P.O. ４ ) ３ , Li ７ La ３ Zr ２ O １２ , Li １．０７ Al ０．６９ Ti １．４６ (P.O. ４ ) ３ , Li １．５ Al ０．５ Ge １．５ (P.O. ４ ) ３ At least one selected from the following can be prepared.

[0116] The raw material powder of the first solid electrolyte powder is, for example, a raw material powder of β″-alumina, containing, in mol %, Al ２ O ３ 65%-98%, Na ２ O 2% to 20%, MgO+Li ２ O 0.3% to 15%, ZrO ２ 0% to 20%, Y ２ O ３ The reason for limiting the composition as above will be explained below.

[0117] Al ２ O ３ is the main component of β″-alumina. ２ O ３ The content of Al is preferably 65% ​​to 98% by mole, and more preferably 70% to 95% by mole. ２ O ３ If the amount of Al is too small, the ionic conductivity of the solid electrolyte is likely to decrease. ２ O ３ If the amount is too large, α-alumina that does not have sodium ion conductivity remains, and the ion conductivity of the solid electrolyte tends to decrease.

[0118] Na ２ O is a component that imparts sodium ion conductivity to the solid electrolyte. ２ The O content is preferably 2% to 20%, more preferably 3% to 18%, and even more preferably 4% to 16%, in mole percent. ２ If the amount of O is too small, it becomes difficult to obtain the above-mentioned effect. ２ If there is too much O, the excess sodium will form NaAlO ２ As a result, compounds that do not contribute to ionic conductivity, such as ammonium nitrate, etc., are formed, and the ionic conductivity of the solid electrolyte is likely to decrease.

[0119] MgO and Li ２ O is a component that stabilizes the structure of β″-alumina, i.e., a stabilizer. MgO + Li ２The O content is preferably 0.3% to 15%, more preferably 0.5% to 10%, and even more preferably 0.8% to 8% in mole percent. ２ If the amount of O is too small, α-alumina remains in the solid electrolyte, which tends to reduce ionic conductivity. ２ Too much O resulted in MgO or Li that did not function as a stabilizer. ２ O remains in the solid electrolyte, which tends to reduce ionic conductivity.

[0120] ZrO ２ and Y ２ O ３ has the effect of suppressing abnormal grain growth of β"-alumina during firing and improving the adhesion between the individual particles of β"-alumina. As a result, the ionic conductivity of the solid electrolyte is easily improved. ZrO ２ The content of Y is preferably 0% to 20%, more preferably 0% to 15%, even more preferably 1% to 13%, and particularly preferably 2% to 10%, in mole percent. ２ O ３ The content of ZrO is preferably 0% to 5%, more preferably 0.01% to 4%, and even more preferably 0.02% to 3%, in mole percent. ２ or Y ２ O ３ If the amount is too large, the amount of β″-alumina produced decreases, and the ionic conductivity of the solid electrolyte tends to decrease.

[0121] The raw material powder of the first solid electrolyte powder is, for example, a raw material powder of NASICON crystal, which contains, in mol %, Na ２ O 17.5% to 50%, Al ２ O ３ +Y ２ O ３ +Yb ２ O ３ +Nd ２ O ３ +Nb ２ O ５ + TiO ２ +HfO ２ + ZrO ２ 12% to 45%, SiO２ +P ２ O ５ It is possible to prepare one containing 24% to 54%.

[0122] The average particle size of at least one of the first solid electrolyte powder and the raw material powder of the first solid electrolyte powder is preferably 0.01 μm or more, more preferably 0.05 μm or more, and even more preferably 0.1 μm or more. On the other hand, the average particle size of at least one of the first solid electrolyte powder and the raw material powder of the first solid electrolyte powder is preferably 10 μm or less, more preferably 5 μm or less, even more preferably 3 μm or less, even more preferably 1 μm or less, and particularly preferably 0.6 μm or less. In this case, peeling of the second solid electrolyte layer 9, which is a porous layer, from the first solid electrolyte layer 8 can be made less likely to occur in the subsequent firing step.

[0123] In this specification, the average particle size is the average particle size D measured by a laser diffraction particle size distribution analyzer. ５０ Refers to...

[0124] As the binder, for example, a resin binder such as polypropylene carbonate can be used. Furthermore, as the resin binder, for example, polyvinyl acetal such as polyvinyl alcohol (PVA) and polyvinyl butyral (PVB), polyvinylidene fluoride (PVDF), polytetrafluoroethylene, acrylic resin, ethyl methyl cellulose, carboxymethyl cellulose, ethyl cellulose, alginic acid, polyethylene glycol, polycarbonate resin such as polyethylene carbonate or polypropylene carbonate, or copolymers thereof can be used. These binders may be used alone or in combination. Among them, polyvinyl butyral (PVB), acrylic resin, polycarbonate resin such as polyethylene carbonate or polypropylene carbonate are preferred.

[0125] Alternatively, the binder may be a glass binder when an all-solid-state sodium ion secondary battery is manufactured as the all-solid-state battery 1. As the glass binder, for example, a sodium ion conductive glass powder can be used.

[0126] The organic vehicle may contain a solvent, a plasticizer, etc. in addition to the binder. Examples of solvents that can be used include water and organic solvents such as ethanol and acetone. However, when water is used as the solvent, alkaline components such as sodium may be eluted from the raw material powder, increasing the pH of the slurry and causing the raw material powder to aggregate. Therefore, it is preferable to use an organic solvent as the solvent.

[0127] The content of at least one of the first solid electrolyte powder and the raw material powder of the first solid electrolyte powder contained in the slurry is preferably 10% by mass or more, more preferably 30% by mass or more. On the other hand, the content of at least one of the first solid electrolyte powder and the raw material powder of the first solid electrolyte powder contained in the slurry is preferably 80% by mass or less, more preferably 50% by mass or less. The content of the binder contained in the slurry can be, for example, 5% by mass or more and 50% by mass or less.

[0128] The substrate to which the slurry is applied is not particularly limited, but for example, a resin film such as a PET (polyethylene terephthalate) film can be used.

[0129] (b) Preparation of Green Sheet for Forming Second Solid Electrolyte Layer First, a slurry is prepared by adding an organic vehicle containing a binder to a mixed powder containing at least one of the second solid electrolyte powder and the raw material powder of the second solid electrolyte powder, and a polymer powder. The polymer powder is a material for forming voids in the second solid electrolyte layer 9. Specifically, the polymer powder is burned and removed in a subsequent firing step, thereby forming the voids.

[0130] Next, the slurry is applied to a substrate and dried to prepare a green sheet for forming a second solid electrolyte layer. The drying temperature of the slurry can be, for example, 40° C. or higher and 100° C. or lower. The drying time of the slurry can be, for example, 5 minutes or higher and 24 hours or lower. Thereafter, the green sheet for forming a second solid electrolyte layer is peeled off from the substrate.

[0131] As at least one of the second solid electrolyte powder and the raw material powder of the second solid electrolyte powder, a powder similar to the first solid electrolyte powder and the raw material powder of the first solid electrolyte powder described above can be used.

[0132] The average particle size of at least one of the second solid electrolyte powder and the raw material powder of the second solid electrolyte powder is preferably 0.1 μm or more, more preferably 0.2 μm or more, even more preferably 0.5 μm or more, and particularly preferably 0.8 μm or more. On the other hand, the average particle size of at least one of the second solid electrolyte powder and the raw material powder of the second solid electrolyte powder is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 10 μm or less, even more preferably 5 μm or less, and particularly preferably 3 μm or less. In this case, peeling of the second solid electrolyte layer 9, which is a porous layer, from the first solid electrolyte layer 8 can be made less likely to occur in the subsequent firing step.

[0133] Examples of polymer powder materials include acrylic resin, polyacrylonitrile, polymethacrylonitrile, polystyrene, etc. Polymer powder made of one of these materials may be used alone, or multiple types of polymer powder made of different materials may be used in combination.

[0134] The average particle size of the polymer powder is preferably 0.1 μm or more, more preferably 1 μm or more, even more preferably 5 μm or more, and particularly preferably 10 μm or more. On the other hand, the average particle size of the polymer powder is preferably 100 μm or less, more preferably 80 μm or less, even more preferably 70 μm or less, and particularly preferably 50 μm or less. If the average particle size of the polymer powder is too small, it becomes difficult to form three-dimensionally interconnected voids in the resulting second solid electrolyte layer 9. On the other hand, if the average particle size of the polymer powder is too large, the resulting second solid electrolyte layer 9 may be insufficiently sintered, resulting in reduced ionic conductivity.

[0135] The blending ratio of at least one of the second solid electrolyte powder and the raw material powder of the second solid electrolyte powder to the polymer powder is preferably 75:25 to 3:97 by volume, more preferably 60:40 to 6:94, and even more preferably 40:60 to 9:91. If the content of the polymer powder is too low, it becomes difficult to form three-dimensionally interconnected voids in the resulting second solid electrolyte layer 9. On the other hand, if the content of the polymer powder is too high, the resulting second solid electrolyte layer 9 may be insufficiently sintered, resulting in reduced ionic conductivity.

[0136] The blending ratio of at least one of the second solid electrolyte powder and the raw material powder of the second solid electrolyte powder to the polymer powder is preferably 95:5 to 20:80 by mass, more preferably 90:10 to 30:70, and even more preferably 80:20 to 40:60.

[0137] As the components of the organic vehicle, such as the binder, solvent, and plasticizer, the same components as those explained in the section "Preparation of green sheet for forming first solid electrolyte layer" can be used.

[0138] The content of at least one of the second solid electrolyte powder and the raw material powder of the second solid electrolyte powder contained in the slurry is preferably 5% by mass or more, more preferably 10% by mass or more. On the other hand, the content of at least one of the second solid electrolyte powder and the raw material powder of the second solid electrolyte powder contained in the slurry is preferably 80% by mass or less, more preferably 60% by mass or less. The content of the binder contained in the slurry can be, for example, 5% by mass or more and 30% by mass or less.

[0139] The substrate to which the slurry is applied is not particularly limited, but for example, a resin film such as a PET (polyethylene terephthalate) film can be used.

[0140] (c) Preparation of Laminated Sheet Next, a second green sheet for forming a solid electrolyte layer is laminated on each of the two main surfaces of the first green sheet for forming a solid electrolyte layer to obtain a laminated sheet. Alternatively, the laminated sheet may be obtained by laminating the green sheets and pressing them with a hot press or the like. In this case, the adhesion between the green sheets can be further improved.

[0141] Alternatively, a slurry containing a mixed powder containing at least one of the second solid electrolyte powder and the raw material powder of the second solid electrolyte powder and a polymer powder, and an organic vehicle containing a binder may be applied to both main surfaces of the green sheet for forming the first solid electrolyte layer, and then the slurry may be dried to obtain a laminated sheet.

[0142] (d) Firing of Laminated Sheet Next, the obtained laminated sheet is fired, thereby forming the first solid electrolyte layer 8 and the second solid electrolyte layer 9. In this manner, the solid electrolyte layer 4 can be obtained, in which the second solid electrolyte layer 9, which is a porous layer, is provided on both main surfaces of the first solid electrolyte layer 8, which is a dense layer.

[0143] It is desirable to remove the binder from the green sheet for forming the first solid electrolyte layer when forming the first solid electrolyte layer 8. It is desirable to remove the binder and polymer powder from the green sheet for forming the second solid electrolyte layer when forming the second solid electrolyte layer 9.

[0144] The firing temperature may be appropriately selected depending on the type of solid electrolyte powder or raw material powder used. When the solid electrolyte powder contains β-alumina or β"-alumina, the firing temperature is preferably 1400°C or higher, more preferably 1450°C or higher, and even more preferably 1500°C or higher. On the other hand, the firing temperature is preferably 1750°C or lower, and more preferably 1700°C or lower. If the firing temperature is too low, sintering tends to be insufficient. Alternatively, the reaction of the raw material powder becomes insufficient, making it difficult to produce the desired crystals. On the other hand, if the firing temperature is too high, the amount of evaporation of sodium components and the like increases, causing precipitation of heterogeneous crystals, which tends to reduce the ionic conductivity of the resulting solid electrolyte layer 4.

[0145] When the solid electrolyte powder contains NASICON crystals, the firing temperature is preferably 1200°C or higher, more preferably 1210°C or higher. On the other hand, the firing temperature is preferably 1400°C or lower, more preferably 1300°C or lower. If the firing temperature is too low, sintering tends to be insufficient. Alternatively, the reaction of the raw material powder becomes insufficient, making it difficult to produce the desired crystals. On the other hand, if the firing temperature is too high, the amount of evaporation of sodium components and the like increases, causing the precipitation of heterogeneous crystals, which tends to reduce the ionic conductivity of the solid electrolyte layer 4.

[0146] The firing time is adjusted appropriately so that sintering proceeds sufficiently. Specifically, the sintering time may be set to, for example, 10 to 120 minutes. It is particularly preferable that the sintering time be set to 20 to 80 minutes.

[0147] It is not necessary to form a laminate sheet when forming the solid electrolyte layer 4. For example, a slurry containing a mixed powder containing a polymer powder and at least one of the second solid electrolyte powder and a raw material powder of the second solid electrolyte powder, and an organic vehicle containing a binder may be applied to both main surfaces of the first solid electrolyte layer 8. The slurry may then be dried to obtain a laminate of the first solid electrolyte layer 8 and the green sheets for forming the second solid electrolyte layer. The laminate may then be fired to obtain the solid electrolyte layer 4.

[0148] In the first embodiment, the second solid electrolyte layer 9, which is a porous layer, is formed on both main surfaces of the first solid electrolyte layer 8, which is a dense layer. However, the second solid electrolyte layer 9 may be formed on only one main surface of the first solid electrolyte layer 8.

[0149] (Formation of Positive Electrode Active Material Layer) A paste containing a positive electrode active material precursor and, if necessary, a solid electrolyte powder and a conductive additive is prepared. The paste may also contain, if necessary, a binder, a plasticizer, a solvent, or the like.

[0150] When the paste contains a binder, examples of the binder that can be used include cellulose derivatives such as carboxymethyl cellulose, hydroxypropyl methyl cellulose, hydroxypropyl cellulose, ethyl cellulose, hydroxyethyl cellulose, and hydroxymethyl cellulose, and water-soluble polymers such as polyvinyl alcohol; thermosetting resins such as thermosetting polyimide, phenolic resin, epoxy resin, urea resin, melamine resin, unsaturated polyester resin, and polyurethane; polycarbonate resins such as polypropylene carbonate; and polyvinylidene fluoride.

[0151] Next, the paste is applied to one main surface of the solid electrolyte layer 4, and the paste is dried. The drying temperature for the paste is not particularly limited, but can be, for example, 30°C or higher and 150°C or lower. The drying time for the paste is not particularly limited, but can be, for example, 5 minutes or higher and 600 minutes or lower. By drying the paste, an electrode mixture layer is formed on one main surface of the solid electrolyte layer 4. In this way, a solid electrolyte layer with an electrode mixture is obtained. The electrode mixture layer may be a compact.

[0152] Thereafter, the solid electrolyte layer with the electrode mixture is fired. The firing atmosphere is preferably a reducing atmosphere. The maximum temperature during firing can be, for example, 400°C to 600°C. The holding time at this temperature can be, for example, 5 minutes or more and less than 3 hours. By the above firing, a positive electrode active material layer 3 is obtained as a first electrode active material layer.

[0153] Unlike the embodiment shown in FIG. 1 , when manufacturing an all-solid-state battery in which the negative electrode active material layers 5 in a pair of laminated structure portions 7 face each other with the negative electrode current collector layer 6 sandwiched therebetween, the positive electrode active material layer 3 may be, for example, a metal film or an alloy film. In this case, the positive electrode active material layer 3 can be formed using, for example, a physical vapor deposition method such as vapor deposition or sputtering, a chemical vapor deposition method such as thermal CVD, MOCVD, or plasma CVD, or a liquid phase film formation method such as plating, a sol-gel method, or spin coating. Among these, vapor deposition or sputtering is preferably used to form the positive electrode active material layer 3. In this case, the adhesion of the positive electrode active material layer 3 to the solid electrolyte layer 4 can be easily improved.

[0154] (Positive electrode active material precursor and its preparation) The positive electrode active material precursor is, for example, a positive electrode active material precursor powder. The positive electrode active material precursor powder is preferably made of an amorphous oxide material that generates active material crystals upon firing. When the positive electrode active material precursor powder is made of an amorphous oxide material, active material crystals are generated during firing, and the material softens and flows, enabling the formation of a dense positive electrode active material layer 3.

[0155] In the present invention, the term "amorphous oxide material" is not limited to a completely amorphous oxide material, but also includes an oxide material containing a portion of crystals. An oxide material containing a portion of crystals is, for example, an oxide material with a crystallinity of 10% or less.

[0156] The positive electrode active material precursor powder contains, in mole percent in terms of oxide, Na ２ O 25% to 55%, Fe ２ O ３ +Cr ２ O ３ + MnO + CoO + NiO 10% to 30%, and P ２ O ５ It is preferable that the content be 25% to 55%. The reason for limiting the composition in this way will be explained below. In the following explanation of the content of each component, "%" means "mol %" unless otherwise specified.

[0157] Na ２ O is a group of the general formula Na ｘ M ｙ P ２ O ｚ where 1≦x≦2.8, 0.95≦y≦1.6, 6.5≦z≦8, and M is the main component of the active material crystal, which is at least one transition metal element selected from Cr, Fe, Mn, Co, and Ni. ２ The O content is preferably 25% to 55%, and more preferably 30% to 50%. ２ When the content of O is within the above range, the charge / discharge capacity of the all-solid-state battery 1 can be further increased.

[0158] Fe ２ O ３ , Cr ２ O ３ , MnO, CoO and NiO are also represented by the general formula Na ｘ M ｙ P ２ O ｚ The main component of the active material crystal is represented by the formula: ２ O ３ +Cr ２ O ３The content of Fe + MnO + CoO + NiO is preferably 10% to 30%, and more preferably 15% to 25%. ２ O ３ +Cr ２ O ３ When the content of Fe+MnO+CoO+NiO is equal to or greater than the lower limit, the charge / discharge capacity of the all-solid-state battery 1 can be further increased. ２ O ３ +Cr ２ O ３ When the content of +MnO + CoO + NiO is less than the above upper limit, unwanted Fe ２ O ３ , Cr ２ O ３ In this specification, for example, when the content is described as "a+b+c+...", it means the total amount of a, b, and c.

[0159] In order to further improve the cycle characteristics of the all-solid-state battery 1, Fe ２ O ３ It is preferable to positively contain Fe. ２ O ３ The content of Cr is preferably 1% to 30%, more preferably 5% to 30%, even more preferably 10% to 30%, and particularly preferably 15% to 25%. ２ O ３ The content of each of the components Fe, MnO, CoO and NiO is preferably 0% to 30%, more preferably 10% to 30%, and even more preferably 15% to 25%. ２ O ３ , Cr ２ O ３ When at least two or more components selected from MnO, CoO and NiO are contained, the total amount thereof is preferably 10% to 30%, and more preferably 15% to 25%.

[0160] P ２ O ５ Also, the general formula Na ｘ M ｙ P ２ Oｚ P is the main component of the active material crystals. ２ O ５ The content of P is preferably 25% to 55%, and more preferably 30% to 50%. ２ O ５ When the content of is within the above range, the charge / discharge capacity of the all-solid-state battery 1 can be further increased.

[0161] The positive electrode active material precursor powder contains, in addition to the above components, V ２ O ５ , Nb ２ O ５ , MgO, Al ２ O ３ , TiO ２ , ZrO ２ , or Sc ２ O ３ These components have the effect of increasing electrical conductivity. Specifically, electrical conductivity here refers to electronic conductivity. Therefore, when the positive electrode active material precursor powder contains these components, the rapid charge / discharge characteristics of the all-solid-state battery 1 are likely to be improved. The total content of the above components is preferably 0% to 25%, and more preferably 0.2% to 10%. When the content of the above components is equal to or less than the upper limit, heterogeneous crystals that do not contribute to the battery characteristics are unlikely to be generated, and the charge / discharge capacity of the all-solid-state battery 1 can be further increased.

[0162] In addition to the above components, the positive electrode active material precursor powder contains SiO ２ , B ２ O ３ , GeO ２ , Ga ２ O ３ , Sb ２ O ３ , or Bi ２ O ３The cathode active material precursor powder may contain these components. When the raw materials for the cathode active material precursor powder contain these components, the glass-forming ability is further improved when obtaining the cathode active material precursor powder. This makes it easier to obtain a more homogeneous cathode active material precursor powder. The total content of the above components in the cathode active material precursor powder is preferably 0% to 25%, and more preferably 0.2% to 10%. Because these components do not contribute to battery characteristics, if their content is too high, the charge / discharge capacity of the all-solid-state battery 1 tends to be small.

[0163] The positive electrode active material precursor powder is preferably prepared by melting and molding a raw material batch. This preparation method makes it easier to obtain an amorphous positive electrode active material precursor powder with excellent homogeneity. Specifically, the positive electrode active material precursor powder can be prepared as follows.

[0164] First, raw materials are prepared to have a desired composition to obtain a raw material batch. Next, the obtained raw material batch is melted. The melting temperature may be adjusted appropriately so that the raw material batch is homogeneously melted. For example, the melting temperature is preferably 800°C or higher, and more preferably 900°C or higher. The upper limit of the melting temperature is not particularly limited. However, if the melting temperature is too high, it may lead to energy loss and evaporation of sodium components, etc. For this reason, the melting temperature is preferably 1500°C or lower, and more preferably 1400°C or lower.

[0165] The resulting melt is then molded. The molding method is not particularly limited, and for example, the melt may be poured between a pair of chill rolls and molded into a film while being rapidly cooled. Alternatively, the melt may be poured into a mold and molded into an ingot.

[0166] The resulting compact is then pulverized to obtain a cathode active material precursor powder, which preferably has an average particle size of 0.01 μm or more and less than 0.7 μm, more preferably 0.03 μm or more and 0.6 μm or less, even more preferably 0.05 μm or more and 0.6 μm or less, and particularly preferably 0.1 μm or more and 0.5 μm or less.

[0167] (Formation of Negative Electrode Active Material Layer) The negative electrode active material layer 5 can be formed using, for example, a paste containing a negative electrode active material precursor powder and, as needed, a solid electrolyte powder and a conductive additive. The paste may contain, as needed, a binder, a plasticizer, a solvent, and the like.

[0168] When manufacturing an all-solid-state sodium-ion secondary battery as the all-solid-state battery 1, it is preferable to use a sodium ion-conductive solid electrolyte precursor solution to obtain the paste. Specifically, the sodium ion-conductive solid electrolyte precursor solution and the negative electrode active material precursor are mixed and then dried. This results in a powder mixture of the sodium ion-conductive solid electrolyte precursor and the negative electrode active material precursor. However, by mixing the sodium ion-conductive solid electrolyte precursor and the negative electrode active material precursor, a powder mixture of the sodium ion-conductive solid electrolyte precursor and the negative electrode active material precursor may be obtained without going through the drying step.

[0169] Next, the resulting mixture powder is pulverized and further mixed with a conductive additive and a binder in an organic solvent. When the negative electrode active material of the negative electrode active material layer 5 to be formed is hard carbon, hard carbon may be further added to the above-mentioned mixture powder and mixed. For example, N-methyl-2-pyrrolidone or the like can be used as the organic solvent. In this way, a paste is obtained.

[0170] As the binder, the binders explained in the section "Formation of the positive electrode active material layer" can be used.

[0171] The paste is applied to one main surface of the solid electrolyte layer 4, dried, and then fired to form the negative electrode active material layer 5.

[0172] When firing the laminate of the solid electrolyte layer 4 and the paste, for example, N ２ It is preferable to perform the firing at a temperature of more than 600°C and not more than 1300°C in an inert atmosphere. For example, the firing may be performed in an Ar, Ne or He atmosphere, or in a vacuum. Alternatively, the firing may be performed in a H ２When the firing is performed in an inert atmosphere or a reducing atmosphere, the initial charge-discharge efficiency of the all-solid-state battery 1 can be further improved.

[0173] The atmosphere may contain a small amount of oxygen as long as the negative electrode active material is not oxidized or oxidatively decomposed during firing. The oxygen concentration may be, for example, 1000 ppm or less, but is not limited thereto.

[0174] Alternatively, the negative electrode active material layer 5 may be formed by applying the paste onto a substrate such as PET (polyethylene terephthalate), drying the paste to form a green sheet, and then firing the green sheet.

[0175] As described above, the negative electrode active material layer 5 may be a metal film or an alloy film. In this case, the negative electrode active material layer 5 can be formed using, for example, a physical vapor deposition method such as vapor deposition or sputtering, a chemical vapor deposition method such as thermal CVD, MOCVD, or plasma CVD, or a liquid phase film formation method such as plating, a sol-gel method, or spin coating. Among these, it is preferable to use a vapor deposition method or a sputtering method to form the negative electrode active material layer 5. In this case, the adhesion of the negative electrode active material layer 5 to the solid electrolyte layer 4 can be easily improved.

[0176] (Negative Electrode Active Material Precursor) When sugar is used for the negative electrode active material precursor, examples thereof include cellulose, D-glucose, sucrose, etc. When biomass is used for the negative electrode active material precursor, examples thereof include corn stalks, sorghum stalks, pine cones, mangosteen, argan shells, rice husks, dandelions, cereal straw cores, ramie fiber, cotton, kelp, coconut endocarp, etc. When polymers are used for the negative electrode active material precursor, examples thereof include polyacrylonitrile (PAN), pitch, polyvinyl chloride (PVC), nanofibers, polyaniline, sodium polyacrylate, tires (polymers for tires), phosphorus-doped PAN, etc.

[0177] (Sodium ion conductive solid electrolyte precursor and its solution) When the sodium ion conductive solid electrolyte is beta-alumina, the sodium ion conductive solid electrolyte precursor can be obtained by mixing, for example, aluminum nitrate, sodium nitrate, and lithium nitrate, with the ratio of each material adjusted to achieve the composition ratio of the desired sodium ion conductive solid electrolyte.

[0178] The sodium ion conducting solid electrolyte is NASICON crystal or Na ５ XSi ４ O １２ When the sodium ion conductive solid electrolyte precursor solution is a crystalline structure in which X is at least one selected from Group 3 transition metal elements or rare earth elements, the sodium conductive solid electrolyte precursor solution may be a solution containing sodium and transition metal elements constituting the sodium ion conductive solid electrolyte, and carbonate ions. In the solution, the sodium element is contained in the form of sodium ions, and the transition metal element is contained in the form of transition metal ions. The sodium ion conductive solid electrolyte precursor is, for example, a gelled or dried product of the sodium ion conductive solid electrolyte precursor solution. The sodium ion conductive solid electrolyte is then formed from a calcined product of the sodium ion conductive solid electrolyte precursor. In addition, when the sodium ion conductive solid electrolyte is a sodium ion conductive solid electrolyte, the sodium ion conductive solid electrolyte may be formed from a sodium ion conductive solid electrolyte precursor. ５ XSi ４ O １２ In the case of a type crystal, X is preferably at least one element selected from rare earth elements.

[0179] As the sodium ion conductive solid electrolyte precursor solution, a solution containing nitrate ions instead of carbonate ions can also be used.

[0180] In the sodium ion conductive solid electrolyte precursor solution, carbonate ions are preferably bidentate to the transition metal element, which makes it easier for the transition metal element to exist stably in the solution.

[0181] In the sodium ion conductive solid electrolyte precursor solution, a compound represented by the general formula NR ４ ＋and each R is independently H, CH ３ , C ２ H ５ and CH ２ CH ２ It is preferable that the solution contains ions of at least one type of substituent selected from the group consisting of OH, in which case the transition metal element is more likely to exist stably in the solution.

[0182] The sodium ion conductive solid electrolyte precursor solution can be obtained by mixing, for example, water glass, sodium tripolyphosphate, and an aqueous solution of ammonium zirconium carbonate. The water glass is specifically sodium silicate.

[0183] (Positive Electrode Current Collector Layer and Negative Electrode Current Collector Layer) The method for forming the positive electrode current collector layer 2 and the negative electrode current collector layer 6 is not particularly limited, and may be, for example, a physical vapor deposition method such as vapor deposition or sputtering, or a chemical vapor deposition method such as thermal CVD, MOCVD, or plasma CVD. Alternatively, the positive electrode current collector layer 2 and the negative electrode current collector layer 6 may be formed by a liquid phase film formation method such as plating, a sol-gel method, or spin coating.

[0184] The positive electrode current collector layer 2 may be formed on a substrate by, for example, the method described above. The positive electrode current collector layer 2 may then be peeled off from the substrate. On the other hand, the negative electrode current collector layer 6 may be formed on the negative electrode active material layer 5 by the method described above. However, it is preferable to form the negative electrode current collector layer 6 on the negative electrode active material layer 5 by a sputtering method, as this provides excellent adhesion.

[0185] Note that, unlike the embodiment shown in FIG. 1 , when manufacturing an all-solid-state battery in which the anode active material layers 5 in a pair of laminated structure portions 7 face each other with the anode current collector layer 6 sandwiched therebetween, the anode current collector layer 6 may be formed on a substrate by, for example, the method listed above. Thereafter, the anode current collector layer 6 may be peeled off from the substrate. On the other hand, the cathode current collector layer 2 may be formed on the cathode active material layer 3 by the method listed above. However, in this case, it is preferable to form the cathode current collector layer 2 on the cathode active material layer 3 by a sputtering method, as this provides excellent adhesion.

[0186] In the first embodiment, the second electrode forming step of forming the negative electrode active material layer 5 is performed before the first electrode forming step of forming the positive electrode active material layer 3. However, the second electrode forming step may be performed after the first electrode forming step. This example is shown in the second embodiment.

[0187] 12(a) and 12(b) are schematic cross-sectional views for explaining an electrode mixture layer forming step and the like in a method for manufacturing an all-solid-state battery according to a second embodiment. 13(a) and 13(b) are schematic cross-sectional views for explaining a first electrode forming step and a second electrode forming step and the like in a method for manufacturing an all-solid-state battery according to the second embodiment.

[0188] This embodiment differs from the first embodiment in that a second electrode forming step is performed after the first electrode forming step, and also in that the negative electrode active material layer 25 as the second electrode active material layer is a metal film.

[0189] 12( a), a pair of solid electrolyte layers 4 are prepared in the same manner as in the first embodiment. Next, an electrode mixture layer 13 is formed on each first main surface 4 a of the pair of solid electrolyte layers 4 in the same manner as in the first embodiment. In this way, a pair of solid electrolyte layers 14 with an electrode mixture is obtained.

[0190] 12( b) is prepared. Next, the positive electrode current collector layer 2 is sandwiched between a pair of solid electrolyte layers 14 with an electrode mixture from both main surfaces of the positive electrode current collector layer 2. Specifically, the electrode mixture layer 13 of one of the solid electrolyte layers 14 with an electrode mixture is brought into contact with the first main surface 2 a of the positive electrode current collector layer 2. The electrode mixture layer 13 of the other solid electrolyte layer 14 with an electrode mixture is brought into contact with the second main surface 2 b of the positive electrode current collector layer 2.

[0191] Next, the stack of the pair of solid electrolyte layers 14 with electrode composite and the positive electrode current collector layer 2 is fired to form a pair of positive electrode active material layers 3 as a pair of first electrode active material layers shown in FIG. 13( a). Next, as shown in FIG. 13( b), a negative electrode active material layer 25 is formed on each second main surface 4 b of the pair of solid electrolyte layers 4. In this embodiment, the negative electrode active material layer 25 is a metal film. In this case, the negative electrode active material layer 25 can be formed by a sputtering method, a vapor deposition method, or the like.

[0192] The anode active material layer 25 may have the same configuration as the anode active material layer 5 in the first embodiment. In this case, the anode active material layer 25 may be obtained by applying a paste containing the anode active material precursor powder to the second main surface 4 b of the solid electrolyte layer 4, drying the paste, and firing the paste.

[0193] Next, similarly to the first embodiment, a negative electrode current collector layer is formed on each surface of the pair of negative electrode active material layers 25. Note that the formation of the negative electrode current collector layer is not necessarily required.

[0194] In this embodiment, a pair of solid electrolyte layers 14 with an electrode mixture are disposed so as to face each other with a current collector layer interposed therebetween, and so that each electrode mixture layer 13 is in contact with each main surface of the current collector layer, and then fired to form a pair of first electrode active material layers. This makes it possible to suppress warping of the all-solid-state battery, as in the first embodiment.

[0195] In the first and second embodiments, the solid electrolyte layer 4 has a first solid electrolyte layer 8 which is a dense layer and a second solid electrolyte layer 9 which is a porous layer, as shown in Fig. 3. However, the configuration of the solid electrolyte layer 4 is not limited to this. An example in which the solid electrolyte layer 4 does not have a porous layer is shown in the third embodiment.

[0196] Third Embodiment of Manufacturing Method FIG. 14 is a diagram showing a solid electrolyte layer used in a manufacturing method of an all-solid-state battery according to a third embodiment.

[0197] This embodiment differs from the first embodiment in that the solid electrolyte layer 34 is composed of only a dense layer. In other words, the solid electrolyte layer 34 is composed of the first solid electrolyte layer 8 in the first embodiment shown in FIG. 3 .

[0198] In the step of preparing the solid electrolyte layer 34, a method similar to the method for forming the first solid electrolyte layer 8 described above can be used. Alternatively, the solid electrolyte layer 34 may be formed by a sol-gel method. The subsequent steps can be performed in the same manner as in the first embodiment. Therefore, warping of the all-solid-state battery can be suppressed, similar to the first embodiment.

[0199] The thickness of the solid electrolyte layer 34 is preferably 70 μm or less, and more preferably 50 μm or less. On the other hand, the thickness of the solid electrolyte layer 34 is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more. If the thickness of the solid electrolyte layer 34 is too thin, the mechanical strength decreases and the layer becomes more susceptible to breakage, making internal short circuits more likely to occur. If the thickness of the solid electrolyte layer 34 is too thick, the distance of ion conduction during charging and discharging increases, increasing internal resistance. As a result, the discharge capacity tends to decrease. Alternatively, the operating voltage of the all-solid-state battery tends to decrease. In addition, the energy density per unit volume of the all-solid-state battery also tends to decrease.

[0200] When the thickness of the solid electrolyte layer 34 is 70 μm or less, the all-solid-state battery is particularly likely to warp as in the comparative examples shown in Figure 6(b) and Figure 7. Therefore, the manufacturing method according to the present invention is particularly suitable.

[0201] The present invention will be described in more detail below based on specific examples, but the present invention is not limited to the following examples and can be implemented with appropriate modifications within the scope that does not change the gist of the present invention.

[0202] (Example 1) (a) Preparation of green sheet for forming first solid electrolyte layer Sodium carbonate (Na ２ CO ３ ), aluminum oxide (Al ２ O ３), magnesium oxide (MgO), zirconium oxide (ZrO ２ ), and yttrium oxide (Y ２ O ３ ) as a raw material, and in mol %, Na ２ O 14.2%, Al ２ O ３ 75.4%, MgO 5.4%, ZrO ２ 4.9%, Y ２ O ３ A raw material powder was prepared so that the concentration of hydroxybenzoates was 0.1%, and the powder was calcined for 4 hours at 1250°C and then pulverized to an average particle size of 2 µm. Next, 12.5 parts by mass of polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., product name "BM-SZ") was added as a binder to 100 parts by mass of this powder, and the mixture was dispersed in N-methylpyrrolidone and thoroughly stirred in a planetary centrifugal mixer to form a slurry.

[0203] The obtained slurry was applied onto a polyethylene terephthalate film (PET film) using a doctor blade, dried at 70°C, and then peeled off from the PET film to obtain a green sheet for forming a first solid electrolyte layer.

[0204] (b) Preparation of green sheet for forming second solid electrolyte layer ２ CO ３ ), aluminum oxide (Al ２ O ３ ), magnesium oxide (MgO), zirconium oxide (ZrO ２ ), and yttrium oxide (Y ２ O ３ ) as a raw material, and in mol %, Na ２ O 14.2%, Al ２ O ３ 75.4%, MgO 5.4%, ZrO ２ 4.9%, Y ２ O ３A raw material powder was prepared so that the concentration was 0.1%, calcined at 1250°C for 4 hours, and then pulverized to an average particle size of 2 μm. Next, 35 parts by mass of this powder was mixed with 65 parts by mass of cross-linked polymethyl methacrylate particles (manufactured by Sekisui Chemical Co., Ltd., product number "MBX-50") having an average particle size of 50 μm as polymer particles. To 100 parts by mass of the resulting mixture, 12.5 parts by mass of polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., product name "BM-SZ") was added as a binder. The mixture was dispersed in N-methylpyrrolidone and then thoroughly stirred in a planetary centrifugal mixer to form a slurry.

[0205] The obtained slurry was applied onto a PET film using a doctor blade, dried at 70° C., and then peeled off from the PET film to obtain a green sheet for forming a second solid electrolyte layer.

[0206] (c) Preparation of Laminated Sheet The obtained green sheets for forming a second solid electrolyte layer were laminated on both main surfaces of the obtained green sheets for forming a first solid electrolyte layer, and the laminated sheets were isostatically pressed at 90°C and 40 MPa for 5 minutes to prepare laminated sheets.

[0207] (d) Firing of Laminated Sheet The obtained laminated sheet was punched into a square of 47.25 mm and then fired at 1550°C for 30 minutes. This produced a solid electrolyte layer in which a porous second solid electrolyte layer was provided on both main surfaces of a dense first solid electrolyte layer. The obtained solid electrolyte layer was 38 mm square and 70 μm thick.

[0208] In the obtained solid electrolyte layer, the thickness of the first solid electrolyte layer was 20 μm. The thickness of each of the pair of second solid electrolyte layers was 25 μm. The porosity of the first solid electrolyte layer was 5%, and the porosity of the second solid electrolyte layer was 78%. Two such solid electrolyte layers were produced.

[0209] (e) Preparation of paste for forming positive electrode active material layer. ２ O-20Fe ２ O ３ -40P ２ O ５The raw material prepared so as to have an average particle diameter D was melted at 1250°C for 45 minutes in the atmosphere and then cooled and formed using a twin roller to produce a glass film. The obtained glass film was pulverized using a ball mill and a planetary ball mill to produce a glass film having an average particle diameter D ５０ 0.2μm, BET specific surface area 30m ２ Thus, a positive electrode active material precursor powder was obtained, which was a glass powder having a particle size of 1 / g.

[0210] The obtained glass powder (86.5 mass%) and a solid electrolyte (45 m2) were mixed. ２ / g, and 12.9 mass % of β″-alumina having a BET specific surface area of ​​300 m ２ 0.6 mass% of carbon nanotubes (manufactured by C-nano Corporation, product number "LB116") with a molecular weight of 100000 / g, a diameter of 10 nm, and a length of 20 μm were mixed. This resulted in a positive electrode composite powder. Next, 20 parts by mass of polypropylene carbonate (PPC) as a binder was added to 100 parts by mass of the positive electrode composite powder, and N-methyl-2-pyrrolidone was added as a solvent so that the concentration of the positive electrode composite powder was 50% by mass. This was mixed in a rotation / revolution mixer to produce a positive electrode paste, which is a paste for forming a positive electrode active material layer.

[0211] (f) Preparation of a Paste for Forming a Negative Electrode Active Material Layer A mixture was obtained by mixing sucrose, a hard carbon source serving as a negative electrode active material precursor, and β-alumina powder in a weight ratio of 4:1 in a stirrer for 1 hour. The resulting mixture was then dried in a thermostatic chamber at 60°C for 12 hours. This mixture was then vacuum dried at 100°C for 6 hours to obtain a powder mixture of a sodium ion conductive solid electrolyte precursor and a negative electrode active material precursor. The resulting powder mixture was then pulverized in an agate mortar to obtain a powder.

[0212] a powder of a mixture of a sodium ion conductive solid electrolyte precursor and a negative electrode active material precursor, and an average particle diameter D ５０1 μm hard carbon powder and acetylene black as a conductive additive were weighed and mixed in a weight ratio of 57:40:3. This resulted in a negative electrode composite powder. Next, 15 parts by mass of polypropylene carbonate (PPC) as a binder was added to 100 parts by mass of the negative electrode composite powder, and N-methyl-2-pyrrolidone was added as a solvent so that the concentration of the negative electrode composite powder was 50% by mass. This was mixed using a rotation / revolution mixer to produce a negative electrode paste, which is a paste for forming a negative electrode active material layer.

[0213] (g) Formation of negative electrode active material layer The negative electrode paste was applied to the center of one main surface of the solid electrolyte layer so as to have a square of 33 mm and a thickness of 70 μm. Next, the negative electrode paste was dried in a thermostatic oven at 80° C. for 1 hour. Thereafter, the laminate of the solid electrolyte layer and the negative electrode paste was dried in a thermostatic oven at 80° C. for 1 hour. ２ The negative electrode active material layer was formed by baking at 800°C for 2 hours in a 99.99% RH atmosphere. The weight of the negative electrode active material layer was calculated by subtracting the weight of the solid electrolyte layer from the weight of the laminate after the formation of the negative electrode active material layer. The weight of the hard carbon active material serving as the negative electrode active material was calculated by multiplying the calculated weight by 0.8, the ratio of the negative electrode active material in the negative electrode active material layer. In addition, the capacity of the negative electrode active material layer was calculated by setting the capacity per gram of hard carbon at 385 mAh / g. As a result, the capacity per unit area of ​​the negative electrode active material layer was 0.3 mAh / cm. ２ It was.

[0214] A negative electrode active material layer was formed on one main surface of each of the two solid electrolyte layers.

[0215] (h) Formation of Positive Electrode Active Material Layer After forming a negative electrode active material layer on one main surface of the solid electrolyte layer in the above process, a positive electrode paste was applied to the center of the other main surface of the solid electrolyte layer to a size of 33 mm and a thickness of 300 μm. Next, the positive electrode paste was dried in a thermostatic chamber at 80°C for 2 hours. This formed an electrode composite layer. An electrode composite layer was formed on each of the other main surfaces of the two solid electrolyte layers. This resulted in two solid electrolyte layers with electrode composites. Each of the two solid electrolyte layers with electrode composites had a negative electrode active material layer laminated thereon.

[0216] On the other hand, one sheet of aluminum foil with a thickness of 20 μm was prepared as a positive electrode current collector layer. Next, two sheets of solid electrolyte layers with electrode composites and the aluminum foil were stacked together, with the aluminum foil sandwiched between the two sheets of solid electrolyte layers with electrode composites. At this time, the two solid electrolyte layers with electrode composites and the aluminum foil were stacked together so that each electrode composite layer was in contact with each main surface of the aluminum foil. Next, a 500 g weight was placed on the stack of two negative electrode active material layers, two solid electrolyte layers with electrode composites, and one aluminum foil. In this way, while loading the stack in the stacking direction, N was applied in volume %. ２ / H ２ The aluminum foil was baked at 500° C. for 30 minutes in a 96 / 4 atmosphere to form a positive electrode active material layer, thereby producing an all-solid-state battery in which two positive electrode active material layers were formed on one sheet of aluminum foil.

[0217] The weight of the positive electrode active material layer was calculated by subtracting the weight of the laminate before forming the positive electrode active material layer from the weight of the aluminum foil. The weight of the positive electrode active material layer was calculated by multiplying the weight by 0.865, which is the ratio of the positive electrode active material in the positive electrode active material layer. ２ FeP ２ O ７ The weight of the active material was calculated. ２ FeP ２ O ７ Na as an active material ２ FeP ２ O ７ The capacity of the positive electrode active material layer was calculated assuming that the capacity per 1 g of the crystallized glass was 97 mAh / g, which is the theoretical capacity. As a result, the capacity per unit area of ​​the positive electrode active material layer was 0.5 mAh / cm ２ In addition, the N / P ratio was calculated by dividing the capacity of the negative electrode active material layer by the capacity of the positive electrode active material layer, and was found to be 0.6.

[0218] Comparative Example 1 One sheet of the solid electrolyte layer with the electrode mixture laminated with the negative electrode active material layer in Example 1 and one sheet of aluminum foil with a thickness of 20 μm were prepared and stacked. At this time, the solid electrolyte layer with the electrode mixture and the aluminum foil were stacked so that the electrode mixture layer was in contact with the main surface of the aluminum foil. Next, a 500 g weight was placed on the stack of one negative electrode active material layer, one solid electrolyte layer with the electrode mixture, and one aluminum foil. In this way, while loading the stack in the stacking direction, N was applied in volume %. ２ / H ２ The mixture was baked at 500° C. for 30 minutes in a SiO2 / SiO2 atmosphere (Mg / Ni / Ni / O). This formed a positive electrode active material layer, and an all-solid-state battery was fabricated.

[0219] The capacity per unit area of ​​the positive electrode active material layer was calculated in the same manner as in Example 1, and the capacity was found to be 0.5 mAh / cm ２ In addition, the N / P ratio was calculated by dividing the capacity of the negative electrode active material layer by the capacity of the positive electrode active material layer, and was found to be 0.6.

[0220] (Charge / Discharge Characteristics) The all-solid-state battery was encapsulated using an aluminum laminate. Lead electrodes were electrically connected to the positive electrode active material layer and the negative electrode active material layer, respectively. The all-solid-state battery was then charged and discharged at 60°C and 0.02C.

[0221] (Evaluation) Warpage was suppressed in the all-solid-state battery of Example 1. The all-solid-state battery of Example 1 operated normally. On the other hand, the all-solid-state battery of Comparative Example 1 was significantly warped and did not operate.

[0222] DESCRIPTION OF SYMBOLS 1, 1A... All-solid-state battery 2... Positive electrode current collector layer 2a, 2b... First and second main surfaces 3... Positive electrode active material layer 4... Solid electrolyte layer 4a, 4b... First and second main surfaces 5... Negative electrode active material layer 6... Negative electrode current collector layer 6a, 6b... First and second main surfaces 7... Laminated structure portion 8... First solid electrolyte layer 8a, 8b... Third and fourth main surfaces 9... Second solid electrolyte layer 13... Electrode mixture layer 14, 14A... Solid electrolyte layer with electrode mixture 15... Electrode mixture layer 25... Negative electrode active material layer 34... Solid electrolyte layer

Claims

1. A method for manufacturing an all-solid-state battery comprising a positive electrode current collector layer, a pair of positive electrode active material layers, a pair of solid electrolyte layers, and a pair of negative electrode active material layers, the method comprising: a step of preparing a pair of solid electrolyte layers made of an oxide solid electrolyte and each having a first main surface and a second main surface facing each other; a positive electrode composite layer forming step of forming a positive electrode composite layer containing a positive electrode active material precursor on each first main surface of the pair of solid electrolyte layers to obtain a pair of positive electrode composite-attached solid electrolyte layers; a positive electrode forming step of arranging the pair of positive electrode composite-attached solid electrolyte layers to face each other with the positive electrode current collector layer therebetween and so that each positive electrode composite layer is in contact with each main surface of the positive electrode current collector layer, and then firing the resulting mixture to form the pair of positive electrode active material layers; and a negative electrode forming step of forming the negative electrode active material layer on each second main surface of the pair of solid electrolyte layers.

2. The method for producing an all-solid-state battery according to claim 1, wherein the thickness of the positive electrode active material layer is greater than the thickness of the negative electrode active material layer.

3. The method for producing an all-solid-state battery according to claim 1, wherein in the positive electrode forming step, the stack of the pair of the positive electrode composite-attached solid electrolyte layer and the positive electrode current collector layer is fired while applying a load to the stack in the stacking direction.

4. A method for manufacturing an all-solid-state battery comprising an anode current collector layer, a pair of cathode active material layers, a pair of solid electrolyte layers, and a pair of anode active material layers, the method comprising: a step of preparing a pair of solid electrolyte layers made of an oxide solid electrolyte and having first and second main surfaces facing each other; an anode composite layer forming step of forming an anode composite layer containing an anode active material precursor on each first main surface of the pair of solid electrolyte layers to obtain a pair of solid electrolyte layers with the anode composite; an anode forming step of arranging the pair of solid electrolyte layers with the anode composite to face each other with the anode current collector layer therebetween and so that each anode composite layer is in contact with each main surface of the anode current collector layer, and then firing the resultant to form the pair of anode active material layers; and a cathode forming step of forming the cathode active material layer on each second main surface of the pair of solid electrolyte layers.

5. The method for producing an all-solid-state battery according to claim 4, wherein in the negative electrode forming step, the stack of the pair of the negative electrode composite-attached solid electrolyte layer and the negative electrode current collector layer is fired while applying a load to the stack in the stacking direction.

6. The method for producing an all-solid-state battery according to claim 1 or 4, wherein the solid electrolyte layer consists of only a dense layer, and the thickness of the solid electrolyte layer is 70 μm or less.

7. The method for producing an all-solid-state battery according to claim 1 or 4, wherein the solid electrolyte layer has a dense layer and a porous layer, and the dense layer and the porous layer are laminated.

8. The method for producing an all-solid-state battery according to claim 7, wherein the dense layer has a thickness of 70 μm or less.

9. The method for producing an all-solid-state battery according to claim 7, wherein the total thickness of the dense layer and the porous layer is 170 μm or less.

10. The method for producing an all-solid-state battery according to claim 1 or 4, wherein the negative electrode forming step is carried out before the positive electrode forming step.

11. The positive electrode active material layer is a compound represented by the general formula Na ｘ M ｙ P ２ O ｚ wherein 1≦x≦2.8, 0.95≦y≦1.6, 6.5≦z≦8, and M is at least one element selected from the group consisting of Fe, Ni, Co, Mn, and Cr.

12. The method for producing an all-solid-state battery according to claim 1 or 4, wherein the negative electrode active material layer contains a negative electrode active material made of hard carbon.

13. The method for producing an all-solid-state battery according to claim 1 or 4, wherein the oxide solid electrolyte contains at least one selected from the group consisting of β-alumina, β″-alumina, and NASICON crystal.

14. An all-solid-state battery comprising one positive electrode current collector layer, two positive electrode active material layers, two solid electrolyte layers, and two negative electrode active material layers, wherein the positive electrode current collector layer has a first main surface and a second main surface facing each other, and the positive electrode active material layer is a cation-containing compound represented by the general formula Na ｘ M ｙ P ２ O ｚ wherein 1≦x≦2.8, 0.95≦y≦1.6, 6.5≦z≦8, and M is at least one crystal selected from the group consisting of Fe, Ni, Co, Mn, and Cr; the solid electrolyte layer is made of an oxide solid electrolyte containing at least one crystal selected from the group consisting of β-alumina, β″-alumina, and NASICON crystal; the anode active material layer includes an anode active material made of hard carbon; the cathode active material layer is laminated on each of the first main surface and the second main surface of the cathode current collector layer; the solid electrolyte layer is laminated on a main surface of each of the cathode active material layers opposite to a side on which the cathode current collector layer is provided; and the anode active material layer is laminated on a main surface of each of the solid electrolyte layers opposite to a side on which the cathode active material layer is provided.

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