All-solid-state secondary batteries

Abstract

An all-solid-state secondary battery (100) of the present invention is provided with a plurality of positive electrode layers (1) including a positive-electrode active material layer (1B), a plurality of negative electrode layers (2) including a negative-electrode active material layer (2B), and a plurality of solid electrolyte layers (5) including a solid electrolyte, the all-solid secondary battery having a laminate (10) in which the positive electrode layers (1) and the negative electrode layers (2) are alternatingly laminated with the solid electrolyte layers (5) interposed therebetween. The plurality of solid electrolyte layers have an outermost solid electrolyte layer (5A) that is disposed on both end sides of the laminate (10) in the direction of lamination and is the thinnest of the plurality of solid electrolyte layers, and an inner solid electrolyte layer (5B) that is disposed farther inward relative to the outermost solid electrolyte layer and is thicker than the outermost solid electrolyte layer.

Description

[Technical Field]

[0001] The present invention relates to an all-solid-state secondary battery. This application claims priority based on Japanese Patent Application No. 2021-045819, filed on March 19, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] In recent years, electronics technology has made remarkable advances, leading to efforts to make portable electronic devices smaller, lighter, thinner, and more multifunctional. Accordingly, there is a strong demand for smaller, lighter, thinner, and more reliable batteries, which serve as the power source for such electronic devices. Currently, commonly used lithium-ion secondary batteries have traditionally used an electrolyte (electrolytic solution) such as an organic solvent as a medium for ion migration. However, batteries with the above-described configuration have the risk of electrolyte leakage.

[0003] In addition, since organic solvents and the like used in electrolytes are flammable substances, further improvement in the safety of batteries is required. Therefore, one measure to improve the safety of batteries has been proposed, which is to use a solid electrolyte instead of an electrolyte. Furthermore, development of all-solid-state secondary batteries that use a solid electrolyte as the electrolyte and also have other components made of solids is underway.

[0004] For example, Patent Document 1 describes that by providing two types of electrolytes with different porosities, the internal stress applied to the solid electrolyte layer due to volume expansion and contraction can be alleviated, thereby improving charge-discharge cycle characteristics. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2013 / 175993 [Non-patent literature]

[0006] [Non-Patent Document 1] Electric Power Research Institute Report 2004 T03036 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in all-solid-state secondary batteries, heat is generated during charging and discharging (Non-Patent Document 1). It is suggested that the center of the battery becomes hotter than the outer (peripheral) parts due to the difficulty in dissipating this heat. Generally, the higher the temperature of an all-solid-state secondary battery, the greater the capacity, but the faster it deteriorates, and the worse the cycle characteristics tend to be. This problem cannot be solved by Patent Document 1.

[0008] An object of the present invention is to provide an all-solid-state secondary battery having good cycle characteristics. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention provides the following means.

[0010] (1) An all-solid-state secondary battery according to a first aspect of the present invention is an all-solid-state secondary battery comprising a plurality of positive electrode layers including a positive electrode active material layer, a plurality of negative electrode layers including a negative electrode active material layer, and a plurality of solid electrolyte layers including a solid electrolyte, the positive electrode layers and the negative electrode layers being alternately stacked with the solid electrolyte layers interposed therebetween, the plurality of solid electrolyte layers being arranged on both end sides in the stacking direction of the stack, and comprising an outermost solid electrolyte layer (having a thickness of ta) having the thinnest thickness among the plurality of solid electrolyte layers, and an inner solid electrolyte layer (having a thickness of t) being arranged inside the outermost solid electrolyte layer and having a thickness greater than that of the outermost solid electrolyte layer. bn (1≦n)>t a ) and

[0011] (2) The all-solid-state secondary battery according to the above aspect may include a plurality of inner solid electrolyte layers that are thicker than the outermost solid electrolyte layer, and among the plurality of inner solid electrolyte layers, the inner solid electrolyte layers that are closer to a center in the stacking direction may have a greater thickness.

[0012] (3) The all-solid-state secondary battery according to the above aspect includes a plurality of inner solid electrolyte layers that are thicker than the outermost solid electrolyte layer, and the thickness of the n-th inner solid electrolyte layer counting from the inner solid electrolyte layer arranged at the center in the stacking direction among the plurality of inner solid electrolyte layers is t bn When t b(n+1) <t bn <t b(n+1) ×2 may be.

[0013] (4) In the all-solid-state secondary battery according to the above aspect, when the total number of the outermost solid electrolyte layers and the inner solid electrolyte layers is p and the number of the inner solid electrolyte layers is q, 3≦q≦p-2 may be.

[0014] (5) In the all-solid-state secondary battery according to the above aspect, the solid electrolyte may have any one of a Nasicon type, a garnet type, and a perovskite type crystal structure. [Effects of the Invention]

[0015] According to the present invention, an all-solid-state secondary battery having good cycle characteristics can be provided. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is an external view of an all-solid-state secondary battery according to one embodiment of the present invention. FIG. [Figure 2] 1 is an external view of a laminate according to an embodiment of the present invention. [Figure 3] 1 is a cross-sectional view schematically illustrating an example of an all-solid-state secondary battery according to an embodiment of the present invention. [Figure 4]FIG. 2 is a cross-sectional view schematically illustrating another example of an all-solid-state secondary battery according to an embodiment of the present invention. [Figure 5] FIG. 2 is a cross-sectional view schematically illustrating yet another example of an all-solid-state secondary battery according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] An embodiment of the present invention will be described in detail below with reference to the accompanying drawings. The drawings used in the following description may be simplified for the sake of convenience in order to clearly illustrate the features of the present embodiment, and the dimensional ratios of the components may differ from the actual ones. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present embodiment is not limited thereto. Appropriate modifications can be made within the scope of the effects of the present invention. For example, the configurations described in different embodiments can be appropriately combined.

[0018] Examples of all-solid-state secondary batteries include all-solid-state lithium-ion secondary batteries, all-solid-state sodium-ion secondary batteries, all-solid-state magnesium-ion secondary batteries, etc. Although the following description will be given using an all-solid-state lithium-ion secondary battery as an example, the present invention is applicable to all-solid-state secondary batteries in general.

[0019] (All-solid-state secondary battery) The all-solid-state secondary battery includes a laminate having a first electrode layer, a second electrode layer, and a solid electrolyte layer. Hereinafter, one of the first electrode layer and the second electrode layer functions as a positive electrode, and the other functions as a negative electrode. For ease of understanding, the following description will be given assuming that the first electrode layer is the positive electrode layer and the second electrode layer is the negative electrode layer.

[0020] The all-solid-state secondary battery of this embodiment will be described with reference to FIGS. As shown in Fig. 1, the all solid state secondary battery 100 of the first embodiment has a laminate 10, a positive external electrode 60, and a negative external electrode 70. As shown in Fig. 2, the laminate 10 is a hexahedron and has four side surfaces 21, 22, 23, and 24, an upper surface 25, and a lower surface 26. Furthermore, a positive external electrode 60 and a negative external electrode 70 are formed on either of a pair of opposing side surfaces. Note that the embodiment of the all solid state secondary battery 100 in Fig. 1 is one in which the positive external electrode 60 is formed on the side surface 21 of the laminate 10 in Fig. 2, and the negative external electrode 70 is formed on the side surface 22.

[0021] Next, the all-solid-state secondary battery 100 of this embodiment will be described with reference to the cross-sectional view of Fig. 3. In Fig. 3, LL is a line indicating the center (middle) position of the laminate 10 in the stacking direction (z direction). The all-solid-state secondary battery 100 has a laminate 10 in which a plurality of positive electrode layers 1, each having a positive electrode current collector layer 1A, a positive electrode active material layer 1B, and a side margin layer 3, and a plurality of negative electrode layers 2, each having a negative electrode current collector layer 2A, a negative electrode active material layer 2B, and a side margin layer 3, are alternately stacked with a solid electrolyte layer 5 interposed therebetween. The multiple solid electrolyte layers 5 are arranged on both ends (top surface 25 side and bottom surface 26 side) of the stack 10 in the stacking direction (z direction), respectively. The multiple solid electrolyte layers 5 include an outermost solid electrolyte layer 5A, which is the thinnest among the multiple solid electrolyte layers, and an inner solid electrolyte layer 5B, which is arranged more inward (closer to the center line L-L) than the outermost solid electrolyte layer 5A and is thicker than the outermost solid electrolyte layer 5A. Here, the "solid electrolyte layer" in "multiple solid electrolyte layers" refers to one interposed between the positive electrode layer and the negative electrode layer. Therefore, the "outer layer (reference numeral 4 in FIG. 1)" described below is not included in the "solid electrolyte layer" in "multiple solid electrolyte layers." The outermost solid electrolyte layer 5A refers to the solid electrolyte layer arranged on the outermost +z side and the outermost -z side of the multiple solid electrolyte layers 5 in the stacking direction (z direction) of the stack 10. 3, outer layers 4 are provided at both ends as the outermost layers in the stacking direction (z direction) of the laminate 10. In this example, the outer layers 4 at both ends have the same thickness.

[0022] In all-solid-state secondary batteries, heat is generated during charging and discharging. When comparing the area near the outer layer with the area located inside (for example, near the center), the outer layer dissipates heat more easily, while the inner layer dissipates heat more difficultly, resulting in the inner layer becoming hotter. Therefore, in the all-solid-state secondary battery of the present invention, a configuration is adopted in which a solid electrolyte layer (inner solid electrolyte layer) thicker than the outermost solid electrolyte layer is disposed inside the outermost solid electrolyte layer, thereby suppressing charge / discharge and heat generation in the portion closer to the center, thereby achieving a more uniform temperature distribution throughout the entire all-solid-state secondary battery, and thereby improving the cycle characteristics.

[0023] In this specification, the "inner solid electrolyte layer" refers to a solid electrolyte layer that is thicker than the "outermost solid electrolyte layer" and is located more inward than the outermost solid electrolyte layer. Therefore, a solid electrolyte layer that is located more inward than the outermost solid electrolyte layer but has the same thickness as the "outermost solid electrolyte layer" does not fall under the category of the "inner solid electrolyte layer." Hereinafter, a solid electrolyte layer that is located more inward than the outermost solid electrolyte layer and has the same thickness as the "outermost solid electrolyte layer" may be referred to as a "same-thickness solid electrolyte layer" to distinguish it from the "inner solid electrolyte layer" and the "outermost solid electrolyte layer." Furthermore, the number of layers of the "outermost solid electrolyte layer" is two, including one layer each on the upper surface 25 side and the lower surface 26 side, since these are solid electrolyte layers arranged on both end sides (upper surface 25 side and lower surface 26 side) in the stacking direction (z direction) of the laminate 10. Note that the "outermost solid electrolyte layer" is the thinnest solid electrolyte layer among the plurality of solid electrolyte layers, and therefore a configuration including a solid electrolyte layer thinner than the outermost solid electrolyte layer inside the outermost solid electrolyte layer does not fall under the category of the all-solid-state secondary battery of the present invention. There is no limit to the number of "inner solid electrolyte layers" as long as there is at least one. The "inner solid electrolyte layer" may be located inside the "outermost solid electrolyte layer," and there is no limit to the arrangement of multiple "inner solid electrolyte layers."

[0024] The all-solid-state secondary battery 100 shown in Fig. 3 has a configuration in which five inner solid electrolyte layers 5B of the same thickness are arranged symmetrically in the stacking direction (z direction) with respect to a center line LL. In Fig. 3, the center line LL is a line indicating the center (middle) position in the stacking direction (z direction) of the laminate 10, and also indicates the center (middle) position in the stacking direction (z direction) of the laminate 10 excluding the outer layers 4 because the outer layers 4 at both ends have the same thickness.

[0025] In the all-solid-state secondary battery 100 shown in FIG. 3, the thickness of the outermost solid electrolyte layer 5A is t a The thickness of the five inner solid electrolyte layers 5B (5B3, 5B2, 5B1, 5B2, 5B3) is, in order from the center line to the outside, t b1 , t b2 , t b3 Then, t a <t b3 <t b2 <t b1 The thickness of the inner solid electrolyte layer 5B is at least 1 time the thickness of the outermost solid electrolyte layer 5A, and preferably 1.2 times or more. There is no upper limit to the thickness of the inner solid electrolyte layer 5B, but in practice it is expected to be no more than 2 times the thickness of the outermost solid electrolyte layer 5A.

[0026] In the all-solid-state secondary battery 100 shown in FIG. 3, the multiple solid electrolyte layers 5 are composed of an outermost solid electrolyte layer 5A and an inner solid electrolyte layer 5B, and do not include a solid electrolyte layer that does not fall into either the outermost solid electrolyte layer 5A or the inner solid electrolyte layer 5B. However, as shown in an example in FIG. 4, the all-solid-state secondary battery 100 may include a solid electrolyte layer that has the same thickness as the outermost solid electrolyte layer and is arranged more inward than the outermost solid electrolyte layer (i.e., a "same-thickness solid electrolyte layer"). That is, in the all-solid-state secondary battery 101 shown in FIG. 4, the plurality of solid electrolyte layers 15 include, in addition to the outermost solid electrolyte layer 15A and the inner solid electrolyte layer 15B, a solid electrolyte layer 15a that has the same thickness as the outermost solid electrolyte layer and is arranged more inward than the outermost solid electrolyte layer 15A. In the all-solid-state secondary battery 101 shown in FIG. 4, the thickness of the outermost solid electrolyte layer 15A and the thickness of the adjacent solid electrolyte layer 15a are ta Then, the thickness t b12 (>t a ) inner solid electrolyte layer 15B2, thickness t b11 (>t b12 ) an inner solid electrolyte layer 15B1 is disposed.

[0027] In the all-solid-state secondary battery 100 shown in Fig. 3 and the all-solid-state secondary battery 101 shown in Fig. 4, the inner solid electrolyte layers disposed closer to the center (the portion including the center line LL) are configured to be thicker. That is, in the all-solid-state secondary battery 100 and the all-solid-state secondary battery 101, the thicknesses of the multiple inner solid electrolyte layers gradually increase (in steps) from the outside toward the inside. By configuring the multiple inner solid electrolyte layers so that their thicknesses gradually increase, charging / discharging and heat generation can be controlled more uniformly. The all-solid-state secondary battery 100 and the all-solid-state secondary battery 101 are examples in which the inner solid electrolyte layer has five layers, but the number of layers of the inner solid electrolyte layer is not limited to this.

[0028] Among the multiple inner solid electrolyte layers, the thickness of the inner solid electrolyte layer located at the nth position on the outside, counting from the inner solid electrolyte layer located at the center in the stacking direction, is defined as t bn When t b(n+1) <t bn <t b(n+1) ×2 It is preferable that: Here, the inner solid electrolyte layer placed in the center of the stacking direction is defined as the first inner solid electrolyte layer, and its thickness is t b1 It states that: The inequality sign on the left indicates that the inner solid electrolyte layer located on the outside is thicker than the inner solid electrolyte layer located in the center. The inequality sign on the right indicates that the thickness of the inner solid electrolyte layer located in the center is less than twice the thickness of the inner solid electrolyte layer adjacent to the inner solid electrolyte layer located on the outside of that inner solid electrolyte layer. If the difference in thickness between adjacent inner solid electrolyte layers is too large, it is difficult to achieve a uniform temperature distribution throughout the all-solid-state secondary battery, so a more continuous change is preferable. By providing a solid electrolyte layer that is thicker than the outermost solid electrolyte layer on the inner side than the outermost solid electrolyte layer and by providing a thickness gradient, it is possible to uniform the temperature distribution within the chip, suppress localized deterioration, and improve cycle characteristics.

[0029] When the total number of outermost solid electrolyte layers and inner solid electrolyte layers is p and the number of inner solid electrolyte layers is q, 3≦q≦p-2 It is preferable that: By having three or more thick inner solid electrolyte layers that suppress heat generation, heat generation inside the chip is suppressed, resulting in a more uniform temperature distribution throughout the entire solid-state secondary battery, which suppresses localized deterioration and improves cycle characteristics.

[0030] The all-solid-state secondary battery 100 shown in FIG. 3 and the all-solid-state secondary battery 101 shown in FIG. 4 are configured such that inner solid electrolyte layers of the same thickness are arranged symmetrically in the stacking direction (z direction) with respect to the center line LL, but as an example shown in FIG. 5, the inner solid electrolyte layers may be arranged asymmetrically in the stacking direction (z direction) with respect to the center line LL. That is, in the all-solid-state secondary battery 102 shown in FIG. 5, the plurality of solid electrolyte layers 25 include an outermost solid electrolyte layer 25A, an inner solid electrolyte layer 25B1 disposed in the center, and an inner solid electrolyte layer 15B2 disposed only on one side (the lower side in the drawing) of the inner solid electrolyte layer 25B1. Also, one side (the lower side in the drawing) of the inner solid electrolyte layer 25B1 includes one layer (25a3) of same-thickness solid electrolyte layer 25a having the same thickness as the outermost solid electrolyte layer, and two layers (25a1, 25a2) of same-thickness solid electrolyte layer 25a on the other side (the upper side in the drawing). In the all-solid-state secondary battery 102 shown in FIG. 5, the thickness of the outermost solid electrolyte layer 25A, the thickness of the adjacent same-thickness solid electrolyte layers 25a1 and 25a3, and the thickness of the same-thickness solid electrolyte layer 25a2 adjacent to the same-thickness solid electrolyte layer 25a1 are t a and the thickness t b22 (>t a ) is disposed in the center of the inner solid electrolyte layer 25B2 having a thickness t b21 (>t b22 ) an inner solid electrolyte layer 25B1 is disposed.

[0031] 5 has an inner solid electrolyte layer in the central portion (portion including the center line LL), but it may not be provided in the central portion. That is, it may have an inner solid electrolyte layer in the central portion, and the arrangement of the inner solid electrolyte layers may be asymmetric with respect to the center line LL, or it may not have an inner solid electrolyte layer in the central portion, and the arrangement of the inner solid electrolyte layers may be asymmetric with respect to the center line LL.

[0032] The outermost solid electrolyte layer and the inner solid electrolyte layer preferably comprise solid electrolytes of the same crystal structure.

[0033] The solid electrolyte constituting the outermost solid electrolyte layer and the inner solid electrolyte layer preferably has one of the following crystal structures: Nasicon, garnet, or perovskite, which exhibit high ionic conductivity. In addition, when a uniform-thickness solid electrolyte layer is provided, the solid electrolyte constituting the uniform-thickness solid electrolyte layer also preferably has one of the following crystal structures: Nasicon, garnet, or perovskite.

[0034] When the outermost solid electrolyte layer and the inner solid electrolyte layer have a solid electrolyte with the same crystal structure, the ionic conductivity is the same, and therefore the charge / discharge reaction occurs uniformly in both layers, improving the cycle characteristics of the battery.

[0035] Hereinafter, each layer constituting the all-solid-state secondary battery according to this embodiment will be described in detail. In the following explanation, either or both of the positive electrode active material and the negative electrode active material may be collectively referred to as the active material, either or both of the positive electrode current collector layer and the negative electrode current collector layer may be collectively referred to as the current collector layer, either or both of the positive electrode active material layer and the negative electrode active material layer may be collectively referred to as the active material layer, either or both of the positive electrode and the negative electrode may be collectively referred to as the electrode, and either or both of the positive electrode external electrode and the negative electrode external electrode may be collectively referred to as the external electrode.

[0036] (solid electrolyte layer) The solid electrolyte layer (the outermost solid electrolyte layer, the inner solid electrolyte layer, and the uniform-thickness solid electrolyte layer, if any) is not particularly limited, and may include a solid electrolyte having any one crystal structure selected from the group consisting of Nasicon-type, garnet-type, perovskite-type, and lysiccon-type crystal structures. For example, general solid electrolyte materials such as oxide-based lithium ion conductors having Nasicon-type, garnet-type, perovskite-type, and lysiccon-type crystal structures can be used. An ion conductor having a Nasicon-type crystal structure containing at least Li (lithium), M (M is at least one of Ti (titanium), Zr (zirconium), Ge (germanium), Hf (hafnium), and Sn (tin)), P (phosphorus), and O (oxygen) (for example, Li 1+x Al x Ti 2-x (PO4)3; LATP), and ionic conductors having a garnet-type crystal structure containing at least Li (lithium), Zr (zirconium), La (lanthanum), and O (oxygen) (e.g., Li7La3Zr2O 12 ;LLZ), or ion conductors having a garnet-like structure, and ion conductors having a perovskite-type structure containing at least Li (lithium), Ti (titanium), La (lanthanum), and O (oxygen) (for example, Li 3x La 2 / 3-x TiO3; LLTO), and lithium ion conductors having a lithicon-type crystal structure containing at least Li, Si, P, and O (e.g., Li 3.5 Si 0.5 P 0.5 O 3.5 In other words, these ion conductors may be used alone or in combination of two or more.

[0037] As the solid electrolyte material of this embodiment, it is preferable to use a lithium ion conductor having a Nasicon-type crystal structure, for example, Li 1+x Al x Ti 2-x(PO4)3 (LATP, 0 < x ≤ 0.6), LiZr2(PO4)3 (LZP), LiTi2(PO4)3 (LTP), Li 1+x Al x Ge 2-x (PO4)3 (LAGP, 0 < x ≤ 0.6), Li 1+x Y x Zr 2-x Preferably includes a solid electrolyte material represented by (PO4)3 (LYZP, 0 < x ≤ 0.6).

[0038] (Positive electrode layer and negative electrode layer) The positive electrode layer 1 and the negative electrode layer 2 are each provided with a plurality in the laminate 10, for example, and face each other through the solid electrolyte layer.

[0039] The positive electrode layer 1 has a positive electrode current collector layer 1A, a positive electrode active material layer 1B, and a side margin layer 3. The negative electrode layer 2 has a negative electrode current collector layer 2A and a negative electrode active material layer 2B.

[0040] (Positive electrode active material layer and negative electrode active material layer) The positive electrode active material layer 1B and the negative electrode active material layer 2B according to this embodiment contain known materials capable of at least occluding and releasing lithium ions as the positive electrode active material and the negative electrode active material. In addition, a conductive aid and an ion-conducting aid may be included. It is preferable that the positive electrode active material and the negative electrode active material can efficiently insert and desorb lithium ions. The thicknesses of the positive electrode active material layer 1B and the negative electrode active material layer 2B are not particularly limited, but for example, can be in the range of 0.5 μm or more and 5.0 μm or less.

[0041] Examples of the positive electrode active material and the negative electrode active material include transition metal oxides and transition metal composite oxides. Specifically, for example, the positive electrode active material and the negative electrode active material are lithium manganese composite oxides Li2Mn a Ma 1-a O3 (0.8 ≤ a ≤ 1, Ma = Co, Ni), lithium cobaltate (LiCoO2), lithium nickelate (LiNiO2), lithium manganese spinel (LiMn2O4), general formula: LiNi x Co y Mn zComposite metal oxides represented by O2(x + y + z = 1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1), lithium vanadium compounds (LiV2O5), olivine-type LiMbPO4 (where Mb is one or more elements selected from Co (cobalt), Ni (nickel), Mn (manganese), Fe (iron), Mg (magnesium), Nb (niobium), Ti (titanium), Al (aluminum), Zr (zirconium)), lithium vanadium phosphate (Li3V2(PO4)3 or LiVOPO4), Li-excess solid solution cathodes represented by Li2MnO3-LiMcO2 (Mc = Mn, Co, Ni), lithium titanate (Li4Ti5O 12 )、titanium oxide (TiO2), Li s Ni t Co u Al v Composite metal oxides represented by O2(0.9 < s < 1.3, 0.9 < t + u + v < 1.1), etc.

[0042] As the cathode active material and anode active material of this embodiment, it is preferable to contain a phosphate compound as a main component. For example, olivine-type LiMbPO4 (where Mb is one or more elements selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, Zr), lithium vanadium phosphate (LiVOPO4, Li3V2(PO4)3, Li4(VO)(PO4)2), lithium vanadium pyrophosphate (Li​​​​​​​​​​Here, there is no clear distinction between the active materials constituting the positive electrode active material layer 1B and the negative electrode active material layer 2B, and by comparing the potentials of two types of compounds, the compound in the positive electrode active material layer and the compound in the negative electrode active material layer, the compound showing a more noble potential can be used as the positive electrode active material, and the compound showing a more base potential can be used as the negative electrode active material. Furthermore, the same material may be used to constitute the positive electrode active material layer 1B and the negative electrode active material layer 2B, as long as the compound has the ability to simultaneously release and store lithium ions.

[0045] Examples of the conductive aid include carbon materials such as carbon black, acetylene black, ketjen black, carbon nanotubes, graphite, graphene, and activated carbon, and metal materials such as gold, silver, palladium, platinum, copper, and tin.

[0046] The ion-conducting aid is, for example, a solid electrolyte. Specifically, the solid electrolyte may be the same material as that used for the solid electrolyte layer 50.

[0047] When a solid electrolyte is used as the ion-conducting aid, it is preferable that the ion-conducting aid and the solid electrolyte used in the outermost solid electrolyte layer, the inner solid electrolyte layer, and, if a uniform-thickness solid electrolyte layer is included, the uniform-thickness solid electrolyte layer be made of the same material.

[0048] (Positive electrode current collector and negative electrode current collector) The materials constituting the positive electrode current collector layer 1A and the negative electrode current collector layer 2A are preferably materials with high electrical conductivity, such as silver, palladium, gold, platinum, aluminum, copper, and nickel. Copper is particularly preferred because it is less likely to react with oxide-based lithium ion conductors and has the effect of reducing the internal resistance of all-solid-state secondary batteries. The materials constituting the positive electrode current collector layer 1A and the negative electrode current collector layer 2A may be the same or different. There are no particular limitations on the thickness of the positive electrode current collector 1A and the negative electrode current collector 2A, but as a guideline, they can be in the range of 0.5 μm to 30 μm.

[0049] Furthermore, the positive electrode current collector layer 1A and the negative electrode current collector layer 2A preferably contain a positive electrode active material and a negative electrode active material, respectively.

[0050] It is desirable that the positive electrode current collector layer 1A and the negative electrode current collector layer 2A contain a positive electrode active material and a negative electrode active material, respectively, because this improves the adhesion between the positive electrode current collector layer 1A and the positive electrode active material layer 1B, and between the negative electrode current collector layer 2A and the negative electrode active material layer 2B.

[0051] The ratio of the positive electrode active material to the negative electrode active material in the positive electrode current collector layer 1A and the negative electrode current collector layer 2A of this embodiment is not particularly limited as long as they function as current collectors. However, it is preferable that the volume ratio of the positive electrode current collector to the positive electrode active material, or the volume ratio of the negative electrode current collector to the negative electrode active material, is in the range of 90 / 10 to 70 / 30.

[0052] (Side margin layer) The side margin layer 3 is preferably provided to eliminate the step between the solid electrolyte layer and the positive electrode layer 1, and the step between the solid electrolyte layer and the negative electrode layer 2. Therefore, the side margin layer 3 refers to the region other than the positive electrode layer 1. The presence of such a side margin layer 3 eliminates the step between the solid electrolyte layer and the positive electrode layer 1 and the negative electrode layer 2, thereby increasing the density of the electrode and making it less likely for delamination or warpage to occur during firing of the all-solid-state secondary battery.

[0053] The material constituting the side margin layer 3 preferably includes, for example, the same material as that of the solid electrolyte layer. Therefore, it is preferable to include an oxide-based lithium ion conductor having a Nasicon-type, garnet-type, or perovskite-type crystal structure. Examples of lithium ion conductors having a Nasicon-type crystal structure include ion conductors having a Nasicon-type crystal structure containing at least Li, M (M is at least one of Ti (titanium), Zr (zirconium), Ge (germanium), Hf (hafnium), and Sn (tin)), P, and O; ion conductors having a garnet-type crystal structure or a garnet-like structure containing at least Li, Zr, La, and O; and ion conductors having a perovskite-type structure containing at least Li, Ti, La, and O. In other words, these ion conductors may be used alone or in combination.

[0054] (outer layer) The outer layer 4 is disposed in one or both of the regions (both in FIG. 3 ) that are outer than either the positive electrode layer 1 (positive electrode current collector layer 1A) or the negative electrode layer 2 (negative electrode current collector layer 2A) in the stacking direction. The outer layer 4 may be made of the same material as the solid electrolyte layer. In this embodiment, the stacking direction corresponds to the z direction in FIG. 3 .

[0055] The thickness of the outer layer 4 is not particularly limited, but is, for example, 20 μm to 100 μm. When the thickness is 20 μm or more, the positive electrode layer 1 or the negative electrode layer 2 closest to the surface in the stacking direction of the laminate 10 is less likely to be oxidized by the atmosphere in the firing process, resulting in a high capacity and a highly reliable all-solid-state secondary battery with sufficient moisture resistance even in high-temperature and high-humidity environments. Furthermore, when the thickness is 100 μm or less, the all-solid-state secondary battery has a high volumetric energy density.

[0056] (Manufacturing method of all-solid-state secondary battery) The all-solid-state secondary battery of the present invention can be manufactured by the following procedure. A co-firing method or a sequential firing method may be used. The co-firing method is a method in which materials for forming each layer are stacked and then fired all at once to produce a laminate. The sequential firing method is a method in which each layer is produced in order, and a firing step is performed after each layer is produced. The co-firing method can reduce the number of work steps required for the all-solid-state secondary battery. Furthermore, the co-firing method results in a denser laminate. Below, an example of using the co-firing method will be described.

[0057] The co-firing method includes the steps of preparing a paste of each material that constitutes the laminate, applying and drying the paste to prepare a green sheet, and stacking the green sheets and co-firing the resulting laminate.

[0058] First, the materials for the positive electrode current collector layer 1A, positive electrode active material layer 1B, outermost solid electrolyte layer, inner solid electrolyte layer, negative electrode current collector layer 2A, negative electrode active material layer 2B, and side margin layer 3 are formed into a paste. The method for forming the paste is not particularly limited, but for example, a paste can be obtained by mixing powders of the materials in a vehicle. Here, the term "vehicle" refers to a liquid medium, including solvents, binders, etc. The binder contained in the paste for forming the green sheet or printed layer is not particularly limited, but examples include polyvinyl acetal resin, cellulose resin, acrylic resin, urethane resin, vinyl acetate resin, and polyvinyl alcohol resin, and the slurry can contain at least one of these resins.

[0059] The paste may also contain a plasticizer. The type of plasticizer is not particularly limited, but phthalate esters such as dioctyl phthalate and diisononyl phthalate may be used.

[0060] By this method, a paste for a positive electrode current collector layer, a paste for a positive electrode active material layer, a paste for a solid electrolyte layer, a paste for a negative electrode active material layer, a paste for a negative electrode current collector layer, and a paste for a side margin layer are prepared.

[0061] Next, a green sheet is prepared. The green sheet is obtained by applying the prepared paste to a substrate such as PET (polyethylene terephthalate) in a desired order, drying it as necessary, and then peeling off the substrate. The method for applying the paste is not particularly limited. For example, known methods such as screen printing, coating, transfer, and doctor blade can be used. The prepared solid electrolyte layer paste is applied to a substrate such as polyethylene terephthalate (PET) in a desired thickness and dried as necessary to prepare a solid electrolyte green sheet (outermost solid electrolyte layer). A similar procedure is also used to prepare a solid electrolyte green sheet (inner solid electrolyte layer) for an inner solid electrolyte layer that is thicker than the outermost solid electrolyte layer. If necessary, a similar procedure is also used to prepare a solid electrolyte green sheet (same thickness solid electrolyte layer) for a solid electrolyte layer of the same thickness.

[0062] The method for producing the solid electrolyte green sheet is not particularly limited, and known methods such as a doctor blade method, a die coater, a comma coater, or a gravure coater can be used.

[0063] Next, a cathode active material layer 1B, a cathode current collector layer 1A, and a cathode active material layer 1B are printed and laminated in this order on the solid electrolyte green sheet by screen printing to form a cathode layer 1. Furthermore, in order to fill the gap between the solid electrolyte green sheet and the cathode layer 1, a side margin layer 3 is formed by screen printing in the area other than the cathode layer 1 to produce a cathode unit (a solid electrolyte layer on which the cathode layer 1 and side margin layer 3 are formed). Positive electrode units are produced for each of the outermost solid electrolyte layer, the inner solid electrolyte layer, and, if necessary, the same-thickness solid electrolyte layer.

[0064] The negative electrode unit can be fabricated in the same manner as the positive electrode unit.

[0065] The positive electrode unit and the negative electrode unit are alternately offset so that one end of the positive electrode and one end of the negative electrode do not coincide with each other, and stacked up to a predetermined number of layers to produce a laminated substrate composed of elements of an all-solid-state secondary battery. The laminated substrate may have outer layers on both main surfaces of the laminate, as needed. The outer layers may be made of the same material as the solid electrolyte layers, such as a green sheet for a solid electrolyte. The inner solid electrolyte layer may be provided in a single layer or in multiple layers (in multiple locations). It is preferable to provide the inner solid electrolyte layers so that the number of layers of the elements is equally or approximately equally divided. For example, if a 31-layer laminate includes one inner solid electrolyte layer, the 16th layer may include one inner solid electrolyte layer. In this case, the laminated body may have an all-solid-state secondary battery having a configuration of one outermost solid electrolyte layer / 14 equal-thickness solid electrolyte layers / one inner solid electrolyte layer / 14 equal-thickness solid electrolyte layers / one outermost solid electrolyte layer. Similarly, when three inner solid electrolyte layers are provided, the inner solid electrolyte layers may be provided on the 16th layer and the 15th and 17th layers sandwiching it. In this case, an all-solid-state secondary battery is obtained in which the stack has the following structure: 1 outermost solid electrolyte layer / 13 equal-thickness solid electrolyte layers / 3 inner solid electrolyte layers / 13 equal-thickness solid electrolyte layers / 1 outermost solid electrolyte layer.

[0066] Furthermore, the stacking positions at which the inner solid electrolyte layers are provided do not need to be divided equally or approximately equally in number, and it is sufficient that the inner solid electrolyte layers, which are thicker than the outermost solid electrolyte layer, are provided at stacking positions inside the outermost solid electrolyte layer. By providing the inner solid electrolyte layer, a more uniform temperature distribution is achieved compared to an all-solid-state secondary battery having only a solid electrolyte layer of the same thickness.

[0067] The above-described manufacturing method is for producing a parallel-type all-solid-state secondary battery, but a manufacturing method for a series-type all-solid-state secondary battery can be achieved by stacking the positive electrodes so that one end of the positive electrode and one end of the negative electrode coincide with each other, that is, without offset.

[0068] Furthermore, the produced laminated substrate can be pressed collectively using a mold press, hot isostatic press (WIP), cold isostatic press (CIP), isostatic press, etc. Pressurization is preferably performed while heating, and can be performed at, for example, 40 to 95°C.

[0069] The produced laminated substrate can be cut into laminated bodies of unfired all-solid-state secondary batteries using a dicing device.

[0070] The laminate of the all-solid-state secondary battery is sintered by removing the binder and firing. The binder removal and firing can be performed, for example, in a nitrogen atmosphere at a temperature of 600°C to 1000°C. The retention time for the binder removal and firing is, for example, 0.1 to 6 hours.

[0071] Barrel polishing is performed to chamfer the corners of the laminate to prevent chipping and to expose the current collector layer at the end surface. It may be performed on the laminate 10 of an unsintered all-solid-state secondary battery, or on the laminate 10 after sintering. Barrel polishing methods include dry barrel polishing, which does not use water, and wet barrel polishing, which uses water. When wet barrel polishing is performed, an aqueous solution such as water is separately introduced into the barrel polishing machine.

[0072] The barrel treatment conditions are not particularly limited and can be adjusted as appropriate, provided that the treatment is carried out within a range that does not cause defects such as cracks or chips in the laminate.

[0073] Furthermore, external electrodes (positive external electrode 60 and negative external electrode 70) can be provided to efficiently extract current from the laminate 10 of the all-solid-state secondary battery. The positive external electrode 60 and negative external electrode 70 are formed on a pair of opposing side surfaces 21 and 22 of the laminate 10. Methods for forming the external electrodes include sputtering, screen printing, and dip coating. In the screen printing and dip coating methods, an external electrode paste containing metal powder, resin, and solvent is prepared and used to form the external electrodes. Next, a baking process is performed to remove the solvent, and a plating process is performed to form terminal electrodes on the surfaces of the external electrodes. On the other hand, the sputtering method can directly form the external electrodes and terminal electrodes, eliminating the need for the baking and plating processes.

[0074] The laminate 10 of the all-solid-state secondary battery may be sealed, for example, in a coin cell to improve moisture resistance and impact resistance. The sealing method is not particularly limited, and the fired laminate may be sealed with a resin, for example. Alternatively, the laminate may be sealed by applying or dip-coating an insulating paste such as Al2O3 around the periphery of the laminate and then heat-treating the insulating paste.

[0075] In the above embodiment, the method for manufacturing an all-solid-state secondary battery including the step of forming a side margin layer using a paste for the side margin layer has been exemplified, but the method for manufacturing an all-solid-state secondary battery according to this embodiment is not limited to this example. For example, the step of forming a side margin layer using a paste for the side margin layer may be omitted. The side margin layer may be formed, for example, by deformation of the paste for the solid electrolyte layer during the manufacturing process of the all-solid-state secondary battery.

[0076] Although the embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment and can be modified in various ways. [Example]

[0077] The present invention will be described in more detail below based on the above-described embodiment using examples and comparative examples, but the present invention is not limited to these examples. Note that the "parts" used for the amounts of materials used in preparing a paste mean "parts by mass" unless otherwise specified.

[0078] Example 1 (Preparation of Positive Electrode Active Material and Negative Electrode Active Material) The positive and negative electrode active materials were prepared using the following procedure. Li2CO3, V2O5, and NH4H2PO4 were used as starting materials. They were wet-mixed in a ball mill for 16 hours and then dehydrated and dried. The resulting powder was calcined at 850°C for 2 hours in a nitrogen-hydrogen mixed gas. After calcination, the mixture was wet-pulverized again in a ball mill for 16 hours and finally dehydrated and dried to obtain the positive and negative electrode active material powders.

[0079] The active material was confirmed to be lithium vanadium phosphate Li3V2(PO4)3 by X-ray diffraction (XRD) and inductively coupled plasma (ICP) emission spectroscopy. The X-ray diffraction pattern was identified using JCPDS Card 74-3236: Li3V2(PO4)3.

[0080] (Preparation of Positive Electrode Active Material Paste and Negative Electrode Active Material Paste) The positive electrode active material paste and the negative electrode active material paste were prepared by adding 15 parts of ethyl cellulose as a binder and 65 parts of dihydroterpineol as a solvent to 100 parts of the obtained positive electrode active material and negative electrode active material powders, and mixing and dispersing the mixture.

[0081] (Preparation of solid electrolyte paste) The solid electrolyte was prepared using the following procedure. Starting materials were Li2CO3 (lithium carbonate), TiO2 (titanium oxide), Al2O3 (aluminum oxide), and NH4H2PO4 (ammonium dihydrogen phosphate). Each material was weighed so that the molar ratio of Li, Al, Ti, and PO4 was 1.3:0.3:1.7:3.0 (=Li:Al:Ti:PO4). These materials were wet-mixed in a ball mill for 16 hours, then dehydrated and dried. The resulting powder was calcined in air at 800°C for 2 hours, and after calcination, wet-pulverized again in a ball mill for 16 hours. Finally, the solid electrolyte powder was dehydrated and dried.

[0082] The obtained solid electrolyte powder was analyzed using an XRD device and an ICP emission spectrometer, and it was found to be Li with a Nasicon-type crystal structure. 1.3 Al 0.3 Ti 1.7 It was confirmed that the compound was (PO4)3 (lithium aluminum titanium phosphate). The X-ray diffraction pattern was identified using JCPDS Card 35-0754: LiTi2(PO4)3.

[0083] 100 parts of this solid electrolyte powder was mixed with 100 parts of ethanol and 200 parts of toluene as solvents in a ball mill, followed by wet mixing in a ball mill. Then, 16 parts of a polyvinyl butyral binder and 4.8 parts of benzyl butyl phthalate were added and wet mixed in a ball mill to prepare a solid electrolyte paste.

[0084] (Production of solid electrolyte layer sheet) Two sheets of the outermost solid electrolyte layer were prepared by applying the solid electrolyte paste onto a PET film using a doctor blade sheet molding machine. The outermost solid electrolyte layer sheet was prepared to a thickness that would result in a thickness of 5 μm when formed into a laminate chip, as described below. Two sheets of the inner solid electrolyte layer that would result in a thickness of 6 μm when formed into a laminate chip, two sheets of the inner solid electrolyte layer that would result in a thickness of 7 μm, and one sheet of the inner solid electrolyte layer that would result in a thickness of 9 μm were also prepared using the same procedure. Furthermore, 24 sheets of the same-thickness solid electrolyte layer that would result in a thickness of 5 μm when formed into a laminate chip were also prepared using the same procedure.

[0085] (Preparation of Positive Electrode Current Collector Paste and Negative Electrode Current Collector Paste) To prepare the positive electrode current collector and the negative electrode current collector, Cu powder and the prepared positive electrode active material and negative electrode active material powder were mixed at a volume ratio of 80 / 20, and then 100 parts of the mixture, 10 parts of ethyl cellulose as a binder, and 50 parts of dihydroterpineol as a solvent were added, mixed, and dispersed to prepare a positive electrode current collector layer paste and a negative electrode current collector layer paste.

[0086] (Preparation of external electrode paste) A thermosetting external electrode paste was prepared by mixing and dispersing Cu powder, epoxy resin, and a solvent in a ball mill.

[0087] An all-solid-state secondary battery was fabricated by the following procedure using the outermost solid electrolyte layer sheet, the inner solid electrolyte layer sheet, the uniform-thickness solid electrolyte layer sheet, the positive electrode current collector paste, the negative electrode current collector paste, and the external electrode paste.

[0088] (Production of positive electrode unit) A 5 μm-thick cathode active material layer was printed on a portion of the main surface of the outermost solid electrolyte layer sheet using screen printing and dried at 80°C for 10 minutes. A 5 μm-thick cathode current collector layer was printed on this cathode active material layer using screen printing and dried at 80°C for 10 minutes. Furthermore, a 5 μm-thick cathode active material layer was printed on the cathode current collector layer using screen printing and dried at 80°C for 10 minutes, thereby forming a cathode layer in which the cathode current collector layer was sandwiched between the cathode active material layers on a portion of the main surface of the outermost solid electrolyte layer sheet. Next, a solid electrolyte layer (side margin layer) having approximately the same height as the cathode layer was printed on the main surface of the outermost solid electrolyte layer sheet where the cathode layer was not printed and dried at 80°C for 10 minutes. Next, the PET film was peeled off to produce a cathode unit in which the cathode layer and solid electrolyte layer were printed on the main surface of the outermost solid electrolyte layer. Similarly, a positive electrode unit was fabricated in which a positive electrode layer and a solid electrolyte layer were printed on the main surface of a solid electrolyte layer of the same thickness.

[0089] (Production of negative electrode unit) The negative electrode unit was fabricated in the same manner as the positive electrode unit.

[0090] (Fabrication of all-solid-state secondary batteries) The positive electrode unit and the negative electrode unit were stacked with one end of the positive electrode layer and one end of the negative electrode layer offset to form a laminate chip. The solid electrolyte layer located at the end of one side (lower side) was designated the "first solid electrolyte layer," and the positive electrode unit and the negative electrode unit were alternately stacked in this order, so that, counting the solid electrolyte layers in order in the stacking direction, 6 μm-thick inner solid electrolyte layers were arranged at the 14th and 18th layers, 7 μm-thick inner solid electrolyte layers were arranged at the 15th and 17th layers, 9 μm-thick inner solid electrolyte layers were arranged at the 16th layer, 5 μm-thick inner solid electrolyte layers were arranged at the 1st and 31st layers, and 5 μm-thick solid electrolyte layers were arranged at the 2nd to 13th layers and the 19th to 30th layers. This resulted in the production of a laminated substrate consisting of a total of 31 solid electrolyte layers, in the stacking direction: 1 outermost solid electrolyte layer / 12 equal-thickness solid electrolyte layers / 5 inner solid electrolyte layers / 12 equal-thickness solid electrolyte layers / 1 outermost solid electrolyte layer.

[0091] A plurality of sheets of the outermost solid electrolyte layer were laminated on the upper and lower surfaces of the laminated substrate to form outer layers each made of a solid electrolyte layer, with the thickness of the outer layers on the upper and lower surfaces being the same.

[0092] The laminated substrate was thermocompressed using a die press to enhance adhesion at the interfaces of the layers, and then cut to produce laminated chips. The laminated chips were then placed on a ceramic setter and held at 600°C for 2 hours in a nitrogen atmosphere to remove the binder. The laminated chips were then fired by holding them at 750°C for 2 hours in a nitrogen atmosphere, and then removed after natural cooling.

[0093] (External electrode formation process) A Cu external electrode paste was applied to the end faces of the fired laminated chip and held at 150°C for 30 minutes for thermal curing to form external electrodes, thereby producing an all-solid-state secondary battery according to Example 1.

[0094] (Solid electrolyte layer thickness evaluation) The thickness t of the outermost solid electrolyte layer of the all-solid-state secondary battery according to Example 1 a、 Thickness of the inner solid electrolyte layer tb (t b1、 t b2、 t b3、 t b2’、 t b3’ ), the thickness of the same-thickness solid electrolyte layer was calculated by image analysis after obtaining a cross-sectional photograph of the stacked layers of the all-solid-state secondary battery using a field emission scanning electron microscope (FE-SEM). The cross-sectional photograph of the stacked layers was obtained by continuously capturing images in the vertical direction at a magnification of 700x at the center of the all-solid-state secondary battery so that all stacked layers were captured. Furthermore, at the center of the cross-sectional photograph of the stacked layers, a line perpendicular to the positive electrode active material layer 1B or the negative electrode active material layer 2B located at the end in the stacking direction was drawn, and the length between the adjacent positive electrode active material layer 1B and the negative electrode active material layer 2B on that line was defined as the thickness of the solid electrolyte layer sandwiched between the adjacent positive electrode active material layer 1B and the negative electrode active material layer 2B. In this embodiment, the thickness of the solid electrolyte layer refers to the thickness of the solid electrolyte layer at the center in the width direction of the laminate 10. Here, the width direction of the laminate refers to the direction in which the laminate 10 is sandwiched between the positive electrode external electrode 60 and the negative electrode external electrode 70, which is the x direction in FIG. 3. As a result of measuring the thickness, the thicknesses of the 1st to 13th and 19th to 31st solid electrolyte layers were 5 μm, the thicknesses of the 14th and 18th solid electrolyte layers were 6 μm, the thicknesses of the 15th and 17th solid electrolyte layers were 7 μm, and the thickness of the 16th solid electrolyte layer was 9 μm. The thickness ratio of the outermost solid electrolyte layer to the thinnest of the inner solid electrolyte layers was 1.2 (6 μm / 5 μm), and the thickness ratios of the adjacent inner solid electrolyte layers were approximately 1.2 (7 μm / 6 μm) and approximately 1.3 (9 μm / 7 μm). Note that since the same-thickness solid electrolyte layers have the same thickness as the outermost solid electrolyte layer, the thickness ratio of the outermost solid electrolyte layer to the thinnest of the inner solid electrolyte layers is the same as the thickness ratio of the inner solid electrolyte layer to the same-thickness solid electrolyte layer adjacent to it.

[0095] (Comparative Example 1) The all-solid-state secondary battery according to Comparative Example 1 differs from Example 1 in that all 31 solid electrolyte layers have the same thickness of 5 μm. That is, the all-solid-state secondary battery according to Comparative Example 1 does not have an inner solid electrolyte layer.

[0096] (Comparative Example 2) The all-solid-state secondary battery according to Comparative Example 2 differs from Example 1 in that the first solid electrolyte layer has a thickness of 15 μm, and the other solid electrolyte layers have the same thickness of 5 μm. That is, the all-solid-state secondary battery according to Comparative Example 2 has a configuration in which, of the two outermost solid electrolyte layers, one solid electrolyte layer has a thickness of 5 μm, while the other solid electrolyte layer has a thickness of 15 μm.

[0097] Example 2 The all-solid-state secondary battery according to Example 2 differs from Example 1 in that the thickness of the inner solid electrolyte layer of the 14th and 18th layers is 8 μm, the thickness of the inner solid electrolyte layer of the 15th and 17th layers is 11 μm, and the thickness of the inner solid electrolyte layer of the 16th layer is 17 μm. In the all-solid-state secondary battery according to Example 2, the thickness ratio of the outermost solid electrolyte layer to the thinnest inner solid electrolyte layer among the inner solid electrolyte layers was 1.6 times (8 μm / 5 μm), and the thickness ratios of the adjacent inner solid electrolyte layers were approximately 1.4 times (11 μm / 8 μm) and approximately 1.5 times (17 μm / 11 μm), respectively.

[0098] Example 3 The all-solid-state secondary battery according to Example 3 differs from Example 1 in that the thicknesses of the five inner solid electrolyte layers are all the same.

[0099] Example 4 The all-solid-state secondary battery according to Example 4 differs from Example 1 in that the thickness of the inner solid electrolyte layer of the 14th and 18th layers is 11 μm, the thickness of the inner solid electrolyte layer of the 15th and 17th layers is 12 μm, and the thickness of the inner solid electrolyte layer of the 16th layer is 13 μm. In the all-solid-state secondary battery according to Example 4, the thickness ratio of the outermost solid electrolyte layer to the thinnest inner solid electrolyte layer among the inner solid electrolyte layers was 2.2 times (11 μm / 5 μm), and the thickness ratios of the adjacent inner solid electrolyte layers were approximately 1.1 times (12 μm / 11 μm) and approximately 1.1 times (13 μm / 12 μm), respectively.

[0100] Example 5 The all-solid-state secondary battery according to Example 5 differs from Example 1 in that the inner solid electrolyte layer has three layers, the 15th and 17th inner solid electrolyte layers have a thickness of 6 μm, and the 16th inner solid electrolyte layer has a thickness of 7 μm. In the all-solid-state secondary battery according to Example 5, the thickness ratio of the outermost solid electrolyte layer to the thinnest inner solid electrolyte layer among the inner solid electrolyte layers was 1.2 times (6 μm / 5 μm), and the thickness ratio of the adjacent inner solid electrolyte layers was approximately 1.2 times (7 μm / 6 μm).

[0101] Example 6 The all-solid-state secondary battery according to Example 6 differs from Example 1 in that the inner solid electrolyte layer has three layers, the 15th and 17th inner solid electrolyte layers have a thickness of 8 μm, and the 16th inner solid electrolyte layer has a thickness of 11 μm. In the all-solid-state secondary battery according to Example 6, the thickness ratio of the outermost solid electrolyte layer to the thinnest inner solid electrolyte layer among the inner solid electrolyte layers was 1.6 times (8 μm / 5 μm), and the thickness ratio of the adjacent inner solid electrolyte layer was approximately 1.4 times (11 μm / 8 μm).

[0102] Example 7 The all-solid-state secondary battery according to Example 7 differs from Example 1 in that the inner solid electrolyte layer has two layers, the 15th inner solid electrolyte layer has a thickness of 6 μm, and the 16th inner solid electrolyte layer has a thickness of 7 μm. In the all-solid-state secondary battery according to Example 7, the thickness ratio of the outermost solid electrolyte layer to the thinnest inner solid electrolyte layer among the inner solid electrolyte layers was 1.2 times (6 μm / 5 μm), and the thickness ratio of the adjacent inner solid electrolyte layers was approximately 1.2 times (7 μm / 6 μm).

[0103] Example 8 The all-solid-state secondary battery according to Example 8 differs from Example 1 in that the inner solid electrolyte layer has two layers, the 15th inner solid electrolyte layer has a thickness of 8 μm, and the 16th inner solid electrolyte layer has a thickness of 11 μm. In the all-solid-state secondary battery according to Example 8, the thickness ratio of the outermost solid electrolyte layer to the thinnest inner solid electrolyte layer among the inner solid electrolyte layers was 1.6 times (8 μm / 5 μm), and the thickness ratio of the adjacent inner solid electrolyte layer was approximately 1.4 times (11 μm / 8 μm).

[0104] Example 9 The all-solid-state secondary battery according to Example 9 differs from Example 1 in that the inner solid electrolyte layer is one layer, and the thickness of the 16th inner solid electrolyte layer is 15 μm. In the all solid state secondary battery according to Example 9, the ratio of the thickness of the outermost solid electrolyte layer to the thickness of the inner solid electrolyte layer was 3 times (15 μm / 5 μm).

[0105] Example 10 The all-solid-state secondary battery according to Example 10 differs from Example 1 in that the inner solid electrolyte layer is one layer, and the thickness of the 20th inner solid electrolyte layer is 15 μm. In the all solid state secondary battery according to Example 10, the ratio of the thickness of the outermost solid electrolyte layer to the thickness of the inner solid electrolyte layer was 3 times (15 μm / 5 μm).

[0106] (Battery evaluation) The all-solid-state secondary batteries produced in the present examples and comparative examples can be evaluated for the following battery characteristics.

[0107] [Charge / discharge cycle test] The negative and positive electrode external terminals of the all-solid-state secondary batteries fabricated in this example and comparative example were sandwiched between measurement probes, and charging and discharging were performed under the following charging and discharging conditions. Charge and discharge currents are expressed as C (C) rate notation. C rate is expressed as nC (μA) (n is a number) and refers to the current at which the nominal capacity (μAh) can be charged and discharged at 1 / n (h). For example, 1C is the charge and discharge current at which the nominal capacity can be charged in 1 h, and 2C is the charge and discharge current at which the nominal capacity can be charged in 0.5 h. For example, for a lithium-ion secondary battery with a nominal capacity of 100 μAh, the current at 0.1C is 10 μA (calculation formula: 100 μA × 0.1 = 10 μA). Similarly, the current at 0.2C is 20 μA, and the current at 1C is 100 μA.

[0108] In an environment of 25°C, the battery was charged at a constant current of 0.2 C rate (CC charging) until the battery voltage reached 1.6 V, and then discharged at a constant current of 0.2 C rate until the battery voltage reached 0 V (CC discharging). This cycle of charging and discharging was counted as one cycle, and after repeating this cycle up to 1000 times, the discharge capacity retention rate was evaluated as the charge-discharge cycle characteristic. The charge-discharge cycle characteristic in this embodiment was calculated using the following calculation formula (1). Discharge capacity retention rate after 1000 cycles (%) = (discharge capacity after 1000 cycles ÷ discharge capacity after 1 cycle) × 100 (1)

[0109] (result) Table 1 shows the results of the charge-discharge cycle test for the all-solid-state secondary batteries according to Examples 1 to 10 and Comparative Examples 1 and 2.

[0110] Based on Table 1, the all-solid-state secondary batteries according to Examples 1 to 6, which had three or more inner solid electrolyte layers in the central portion in the stacking direction, had cycle characteristics of 90% or more. Furthermore, among the all-solid-state secondary batteries according to Examples 1 to 6, the all-solid-state secondary batteries according to Examples 1 to 4 having five or more inner solid electrolyte layers had higher cycle characteristics than the all-solid-state secondary batteries having three or more inner solid electrolyte layers. Furthermore, comparing Example 1 and Example 2, both of which have the same five-layer inner solid electrolyte layer, Example 1, in which the thickness ratio of adjacent inner solid electrolyte layers was approximately 1.2 to approximately 1.3, had higher cycle characteristics than Example 2, in which the thickness ratio of adjacent inner solid electrolyte layers was approximately 1.4 to approximately 1.5. Comparing Example 5 and Example 6, both of which have the same three-layer inner solid electrolyte layer, Example 5, in which the thickness ratio of adjacent inner solid electrolyte layers was approximately 1.2, had higher cycle characteristics than Example 6, in which the thickness ratio of adjacent inner solid electrolyte layers was approximately 1.4. Comparing Example 7 and Example 8, both of which have the same two-layer inner solid electrolyte layer, Example 7, in which the thickness ratio of adjacent inner solid electrolyte layers was approximately 1.2, had higher cycle characteristics than Example 8, in which the thickness ratio of adjacent inner solid electrolyte layers was approximately 1.4. From these results, it can be said that when multiple inner solid electrolyte layers are provided, the thickness ratio of adjacent inner solid electrolyte layers is preferably 1.3 or less, and more preferably 1.2 or less. If the difference in thickness is too large, it is difficult to achieve uniform heat generation throughout the entire all-solid-state secondary battery, and therefore it is thought that a smoother change in thickness is preferable. Furthermore, comparing Example 1 and Example 4, both of which have the same five-layer inner solid electrolyte layer, Example 1, in which the thickness ratio of adjacent inner solid electrolyte layers was approximately 1.2 to approximately 1.3, had better cycle characteristics than Example 4, in which the thickness difference was approximately 1.1, which was smaller than Example 1. This result is thought to be due to the difference in the thickness ratio between the outermost solid electrolyte layer and the thinnest inner solid electrolyte layer among the inner solid electrolyte layers. That is, the ratio in Example 1 was 1.2, while in Example 4 it was 2.2. A thickness ratio of 1.2 to 2.2 is more preferable for the thickness ratio between the outermost solid electrolyte layer and the thinnest inner solid electrolyte layer among the inner solid electrolyte layers. Considering the comparison between Example 2 and Example 4, it is thought that the thickness ratio between the outermost solid electrolyte layer and the thinnest inner solid electrolyte layer among the inner solid electrolyte layers is preferably 1.6 or less, and more preferably 1.2 or less. Furthermore, comparing Example 9 and Example 10, which have the same single inner solid electrolyte layer and the same thickness, Example 9, in which the inner solid electrolyte layer is located in the center (16th layer) of the stacking direction of the stack, had higher cycle characteristics than Example 10, in which the inner solid electrolyte layer is located at a position (20th layer) shifted from the center of the stacking direction of the stack. This result shows that it is preferable to locate the inner solid electrolyte layer in the center of the stacking direction of the stack.

[0111] [Table 1]

[0112] Example 11 The all-solid-state secondary battery according to Example 11 has 29 inner solid electrolyte layers, the thickness of the second and 30th inner solid electrolyte layers being 6 μm, and the thickness of the inner solid electrolyte layers increasing by 1 μm from those layers inward (i.e., the thickness of the third and 29th inner solid electrolyte layers is 7 μm, the thickness of the fourth and 28th inner solid electrolyte layers is 8 μm, the thickness of the fifth and 27th inner solid electrolyte layers is 9 μm, the thickness of the sixth and 26th inner solid electrolyte layers is 10 μm, the thickness of the seventh and 25th inner solid electrolyte layers is 11 μm, the thickness of the eighth and 24th inner solid electrolyte layers is 12 μm, The thickness of the inner solid electrolyte layer of Example 1 is 12 μm, the thickness of the inner solid electrolyte layer of the 9th and 23rd layers is 13 μm, the thickness of the inner solid electrolyte layer of the 10th and 22nd layers is 14 μm, the thickness of the inner solid electrolyte layer of the 11th and 21st layers is 15 μm, the thickness of the inner solid electrolyte layer of the 12th and 20th layers is 16 μm, the thickness of the inner solid electrolyte layer of the 13th and 19th layers is 17 μm, the thickness of the inner solid electrolyte layer of the 14th and 18th layers is 18 μm, the thickness of the inner solid electrolyte layer of the 15th and 17th layers is 19 μm, and the thickness of the inner solid electrolyte layer of the 16th layer is 20 μm. In the all-solid-state secondary battery according to Example 11, the thickness ratio of the outermost solid electrolyte layer to the adjacent inner solid electrolyte layer was 1.2 times (6 μm / 5 μm), and the thickness ratios of the adjacent inner solid electrolyte layers were approximately 1.2 times (7 μm / 6 μm), approximately 1.1 times (8 μm / 7 μm), approximately 1.1 times (9 μm / 8 μm), approximately 1.1 times (10 μm / 9 μm), and approximately 1.1 times (11 μm / 10 μm), respectively. ), approximately 1.1 times (12 μm / 11 μm), approximately 1.1 times (13 μm / 12 μm), approximately 1.1 times (14 μm / 13 μm), approximately 1.1 times (15 μm / 14 μm), approximately 1.1 times (16 μm / 15 μm), approximately 1.1 times (17 μm / 16 μm), approximately 1.1 times (18 μm / 17 μm), approximately 1.1 times (19 μm / 18 μm), approximately 1.1 times (20 μm / 19 μm).

[0113] As a result of the charge-discharge cycle test, the 1000-cycle cycle characteristic was 96%. The thickness gradient of the inner solid electrolyte layer was also continuous, and the cycle characteristic was 96%, which was the best value. It was found that a continuous thickness gradient extending to the outermost solid electrolyte layer results in a more uniform temperature distribution and improved cycle characteristics.

[0114] Examples 12 to 20 The all-solid-state secondary batteries according to Examples 12 to 20 were fabricated in the same manner as in Example 1, except that the solid electrolyte material of any one or all of the outermost solid electrolyte layer, the inner solid electrolyte layer, and the uniform thickness solid electrolyte layer was changed to a material other than LATP, and the battery evaluation was performed in the same manner as in Example 1.

[0115] Example 12 The all-solid-state secondary battery according to Example 12 was fabricated in the same manner as in Example 1, except that the solid electrolyte material of the outermost solid electrolyte layer, the inner solid electrolyte layer, and the uniform thickness solid electrolyte layer was changed to LZP (LiZr2(PO4)3), and the battery was evaluated in the same manner as in Example 1. The LZP solid electrolyte was fabricated by the following synthesis method.

[0116] LZP was produced using Li2CO3 (lithium carbonate), ZrO2 (zirconium oxide), and NH4H2PO4 (ammonium dihydrogen phosphate) as starting materials, weighed out so that the molar ratio of Li, Zr, and PO4 was 1:2:3 (=Li:Zr:PO4), using the same synthesis method as in Example 1. XRD measurement and ICP analysis confirmed that the obtained solid electrolyte was LiZr2(PO4)3.

[0117] Example 13 In the all-solid-state secondary battery according to Example 13, the solid electrolyte material of the outermost solid electrolyte layer, the inner solid electrolyte layer, and the same-thickness solid electrolyte layer was LLZ (Li7La3Zr2O 12 ), an all-solid-state secondary battery was produced in the same manner as in Example 1, and the battery evaluation was carried out in the same manner as in Example 1. The LLZ solid electrolyte was produced by the following synthesis method.

[0118] LLZ was prepared using Li2CO3 (lithium carbonate), La2O3 (lanthanum oxide), and ZrO2 (zirconium oxide) as starting materials, weighed out so that the molar ratio of Li, La, and Zr was 7:3:2 (=Li:La:Zr), and synthesized in the same manner as in Example 1. The solid electrolyte obtained from XRD measurement and ICP analysis was Li7La3Zr2O 12 It was confirmed that this is the case.

[0119] Example 14 In the all-solid-state secondary battery according to Example 14, the solid electrolyte materials of the outermost solid electrolyte layer, the inner solid electrolyte layer, and the same-thickness solid electrolyte layer were LLTO (Li 0.3 La 0.55 Except for changing the electrolyte to TiO3, an all-solid-state secondary battery was fabricated in the same manner as in Example 1, and the battery was evaluated in the same manner as in Example 1. The solid electrolyte of LLTO was prepared by the following synthesis method.

[0120] LLTO was prepared using Li2CO3 (lithium carbonate), La2O3 (lanthanum oxide), and TiO2 (titanium oxide) as starting materials, weighed out so that the molar ratio of Li, La, and Ti was 0.3:0.55:1.0 (=Li:La:Ti), and synthesized in the same manner as in Example 1. The solid electrolyte obtained from XRD measurement and ICP analysis showed that the 0.3 La 0.55 It was confirmed to be TiO3.

[0121] Example 15 In the all-solid-state secondary battery according to Example 15, the solid electrolyte materials of the outermost solid electrolyte layer, the inner solid electrolyte layer, and the same-thickness solid electrolyte layer were LSPO (Li 3.5 Si 0.5 P 0.5 Except for changing the procedure of Example 1 to O4), an all-solid-state secondary battery was fabricated in the same manner as in Example 1, and the battery evaluation was performed in the same manner as in Example 1. The LSPO solid electrolyte was prepared by the following synthesis method.

[0122] LSPO was prepared by weighing out Li2CO3, SiO2, and commercially available Li3PO4 as starting materials in a molar ratio of 2:1:1, wet-mixing them in a ball mill using water as a dispersion medium for 16 hours, and then dehydrating and drying. The resulting powder was calcined in air at 950°C for 2 hours, wet-pulverized again in a ball mill for 16 hours, and finally dehydrating and drying to obtain a solid electrolyte powder. The results of XRD measurement and ICP analysis showed that the powder contained Li 3.5 Si 0.5 P 0.5 It was confirmed to be O4 (LSPO).

[0123] (Examples 16 to 20) In the all-solid-state secondary batteries according to Examples 16 to 20, the solid electrolyte material of the outermost solid electrolyte layer and the uniform thickness solid electrolyte layer was LATP, but the solid electrolyte material of the inner solid electrolyte layer was changed to a material other than LATP. All-solid-state secondary batteries were fabricated in the same manner as in Example 1, and battery evaluation was performed in the same manner as in Example 1.

[0124] Example 16 For the all-solid-state secondary battery according to Example 16, an all-solid-state secondary battery was produced in the same manner as in Example 1, except that the solid electrolyte material of the inner solid electrolyte layer was changed to LTP, and the battery evaluation was carried out in the same manner as in Example 1.

[0125] LTP was produced using Li2CO3 (lithium carbonate), TiO2 (titanium oxide), and NH4H2PO4 (ammonium dihydrogen phosphate) as starting materials, weighing each material so that the molar ratio of Li, Ti, and PO4 was 1.0:2.0:3.0 (=Li:Ti:PO4), using the same synthesis method as in Example 1. XRD measurement and ICP analysis confirmed that the resulting solid electrolyte was LiTi2(PO4)3.

[0126] Example 17 For the all-solid-state secondary battery according to Example 17, an all-solid-state secondary battery was produced in the same manner as in Example 1, except that the solid electrolyte material of the inner solid electrolyte layer was changed to LAGP, and the battery evaluation was carried out in the same manner as in Example 1.

[0127] LAGP was prepared by the same synthesis method as in Example 1, except that the starting material TiO2 was replaced with GeO2, and the molar ratio of Li, Al, Ge, and PO4 was weighed to be 1.3:0.3:1.7:3.0 (=Li:Al:Ge:PO4). The solid electrolyte obtained from XRD measurement and ICP analysis showed that the 1.3 Al 0.3 Ge 1.7 It was confirmed that the result was (PO4)3.

[0128] Example 18 For the all-solid-state secondary battery according to Example 18, an all-solid-state secondary battery was produced in the same manner as in Example 1, except that the solid electrolyte material of the inner solid electrolyte layer was changed to LYZP, and the battery evaluation was carried out in the same manner as in Example 1.

[0129] LYZP was prepared using Li2CO3 (lithium carbonate), Y(NO3)3 (yttrium nitrate), ZrO(NO3)2·2H2O (zirconium oxynitrate), and NH4H2PO4 (ammonium dihydrogen phosphate) as starting materials, weighed out so that the molar ratio of Li, Y, Zr, and PO4 was 1.1:0.1:1.9:3.0 (=Li:Y:Zr:PO4), and synthesized in the same manner as in Example 1. XRD measurement and ICP analysis showed that the solid electrolyte contained Li 1.3 Y 0.3 Zr 1.7 It was confirmed that the result was (PO4)3.

[0130] Example 19 For the all-solid-state secondary battery according to Example 19, an all-solid-state secondary battery was produced in the same manner as in Example 1, except that the solid electrolyte material of the inner solid electrolyte layer was changed to LLZ, and the battery evaluation was carried out in the same manner as in Example 1.

[0131] Example 20 For the all-solid-state secondary battery according to Example 20, an all-solid-state secondary battery was produced in the same manner as in Example 1, except that the solid electrolyte material of the inner solid electrolyte layer was changed to LATP+LGPT, and the battery evaluation was performed in the same manner as in Example 1.

[0132] (result) Table 2 shows the results of the charge-discharge cycle test for the all-solid-state secondary batteries according to Examples 12 to 20. For reference, Table 2 also shows the results for Example 1.

[0133] Based on Table 2, when the solid electrolyte materials of the outermost solid electrolyte layer, the inner solid electrolyte layer, and the uniform thickness solid electrolyte layer were all the same, Example 1, which used LATP, had the best cycle characteristics, and the other solid electrolyte materials (Examples 12 to 15) had comparable cycle characteristics. Furthermore, when the solid electrolyte material of the outermost solid electrolyte layer and the uniform thickness solid electrolyte layer was LATP and the solid electrolyte material of the inner solid electrolyte layer was different from LATP (Examples 16 to 20), the cycle characteristics were equivalent.

[0134] [Table 2]

[0135] Although the present invention has been described in detail above, the above-mentioned embodiments and examples are merely illustrative, and the invention disclosed herein includes various modifications and variations of the above-mentioned specific examples. [Explanation of symbols]

[0136] 1 Positive electrode layer 1A positive electrode current collector 1B Cathode active material layer 2. Negative electrode layer 2A negative electrode current collector 2B Negative electrode active material layer 3 Side margin layer 4 Outer layer 5 Solid electrolyte layer 5A, 15A, 25A outermost solid electrolyte layer 5B, 15B, 25B Inner solid electrolyte layer 15a, 25a Same thickness solid electrolyte layer 60 Positive external electrode 70 Negative external electrode 10 Laminate 100, 101, 200 All-solid-state secondary battery

Claims

1. An all-solid-state secondary battery having a laminate body including a plurality of positive electrode layers each including a positive electrode active material layer, a plurality of negative electrode layers each including a negative electrode active material layer, and a plurality of solid electrolyte layers each including a solid electrolyte, in which the positive electrode layers and the negative electrode layers are alternately laminated with the solid electrolyte layers interposed therebetween, The plurality of solid electrolyte layers are arranged on both ends of the stacking direction of the stack, and an outermost solid electrolyte layer (thickness t ａ ) and an inner solid electrolyte layer (thickness t ｂｎ (1≦n)>t ａ ) and The solid electrolyte has any one of a Nasicon type, a garnet type, a perovskite type, and a lysicone type crystal structure.

2. 2. The all-solid-state secondary battery according to claim 1, comprising a plurality of inner solid electrolyte layers thicker than the outermost solid electrolyte layer, wherein among the plurality of inner solid electrolyte layers, the inner solid electrolyte layer disposed closer to a center in the stacking direction has a greater thickness.

3. a plurality of inner solid electrolyte layers thicker than the outermost solid electrolyte layer, and a thickness of the n-th inner solid electrolyte layer counting from the inner solid electrolyte layer arranged at the center in the stacking direction among the plurality of inner solid electrolyte layers is t ｂｎ When t ｂ（ｎ＋１） <t ｂｎ <t ｂ（ｎ＋１） ×2 The all-solid-state secondary battery according to claim 1 or 2,

4. When the total number of the outermost solid electrolyte layers and the inner solid electrolyte layers is p and the number of the inner solid electrolyte layers is q, 3≦q≦p−2 The all-solid-state secondary battery according to any one of claims 1 to 3,

5. 5. The all-solid-state secondary battery according to claim 1, wherein the solid electrolyte has one of a Nasicon type, a garnet type, and a perovskite type crystal structure.

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