All-solid-state secondary batteries

Abstract

To provide an all-solid secondary battery having a good cycle characteristic.SOLUTION: An all-solid secondary battery 10 comprises: a positive electrode layer 1; a negative electrode layer 2; and a solid electrolyte layer 3 held between the positive electrode layer 1 and the negative electrode layer 2. The solid electrolyte layer 3 has: a first phase which includes a first solid electrolyte containing Li, Si, P and O, and having a γ-Li3 PO4 type crystal structure; and a second phase which includes a second solid electrolyte containing Li, Si, P and O, and having a composition different from that of the first solid electrolyte and having a Li4SiO4 type crystal structure. The all-solid secondary battery has: a first layered region 31 formed between the positive electrode layer 1 and the negative electrode layer 2 uninterruptedly, which includes the first phase and of which a volume percentage of the second phase is equal to or smaller than a volume percentage of the first phase; and a second layered region 32 including the second phase formed between the positive electrode layer 1 and the negative electrode layer 2 uninterruptedly, and disposed adjacent to the positive electrode layer 1 or the negative electrode layer 2, in which the volume percentage of the second phase is above a volume percentage of the first phase.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This invention relates to an all-solid-state secondary battery. [Background technology]

[0002] In recent years, advancements in electronics technology have been remarkable, leading to the miniaturization, weight reduction, thinning, and increased functionality of portable electronic devices. Consequently, there is a strong demand for smaller, lighter, thinner, and more reliable batteries, which power these devices. Therefore, all-solid-state rechargeable batteries, which use solid electrolytes, are attracting attention. Conventionally, sulfide-based and oxide-based solid electrolytes have been primarily used as solid electrolytes in all-solid-state rechargeable batteries.

[0003] Sulfide-based solid electrolytes have excellent plasticity, allowing for the formation of an interface between the solid electrolyte and the active material by compaction. However, sulfide-based solid electrolytes generate hydrogen sulfide when they react with water, posing a safety concern.

[0004] On the other hand, oxide-based solid electrolytes do not pose a risk of generating hydrogen sulfide through reaction with water and are therefore safe. However, in order to obtain high ionic conductivity in oxide-based solid electrolytes, densification is necessary, which requires sintering at high temperatures. However, in sintering to form a dense solid electrolyte layer, the oxide-based solid electrolyte and the active material may react, and a reaction layer with low ionic conductivity may be formed at the interface between the oxide-based solid electrolyte and the active material.

[0005] As an oxide-based solid electrolyte that is relatively stable with respect to the active material, LSPO(Li 3+x Si x P 1-x O4) is known (see Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Solid State Ionics 283(2015)109-114

Summary of the Invention

Problems to be Solved by the Invention

[0007] In conventional all-solid-state secondary batteries, there is a further requirement to improve the cycle characteristics. The present invention has been made in view of the above problems, and an object thereof is to provide an all-solid-state secondary battery having good cycle characteristics. [[ID=I3]]

Means for Solving the Problems

[0008] In order to solve the above problems, the following means are provided. An all-solid-state secondary battery according to one aspect of the present invention includes a positive electrode layer, a negative electrode layer, and a solid electrolyte layer sandwiched between the positive electrode layer and the negative electrode layer. The solid electrolyte layer includes a first phase including a first solid electrolyte containing Li, Si, P, and O and having a γ-Li3PO4 type crystal structure, and a second phase including a second solid electrolyte containing Li, Si, P, and O, having a composition different from that of the first solid electrolyte, and having a Li4SiO4 type crystal structure. The all-solid-state secondary battery has a first layered region continuously formed between the positive electrode layer and the negative electrode layer, and a second layered region including the second phase continuously formed between the positive electrode layer and the negative electrode layer, disposed adjacent to the positive electrode layer or the negative electrode layer, and having a volume ratio of the second phase exceeding that of the first phase.

Effects of the Invention

[0009] The all-solid-state secondary battery of the present invention includes a first phase containing a first solid electrolyte containing Li, Si, P, and O and having a γ-Li3PO4-type crystal structure, and Li, Si, P, and O, having a composition different from that of the first solid electrolyte, and a second phase containing a second solid electrolyte having a Li4SiO4-type crystal structure. It has a first layered region continuously formed between the positive electrode layer and the negative electrode layer, and a second phase continuously formed between the positive electrode layer and the negative electrode layer, which is disposed adjacent to the positive electrode layer or the negative electrode layer and has a volume ratio of the second phase exceeding that of the first phase. It has a solid electrolyte layer having a second layered region. Therefore, the all-solid-state secondary battery of the present invention has good cycle characteristics.

Brief Description of the Drawings

[0010] [Figure 1] It is a schematic cross-sectional view showing an all-solid-state secondary battery according to the first embodiment. [Figure 2] It is a schematic cross-sectional view showing an enlarged part of the all-solid-state secondary battery 10 shown in FIG. 1. [Figure 3] It is a schematic view for explaining a method of measuring the thickness of the second layered region, and is a schematic view showing a straight line L1 selected from 10 straight lines drawn in a secondary electron image of one field of view and its peripheral region.

Embodiments for Carrying Out the Invention

[0011] The present invention includes the following aspects. [1] It has a positive electrode layer, a negative electrode layer, and a solid electrolyte layer sandwiched between the positive electrode layer and the negative electrode layer. The solid electrolyte layer includes a first phase containing a first solid electrolyte containing Li, Si, P, and O and having a γ-Li3PO4-type crystal structure. It contains Li, Si, P, and O, has a composition different from that of the first solid electrolyte, and has a second phase containing a second solid electrolyte having a Li4SiO4-type crystal structure. It includes the first phase, the volume ratio of the second phase is not more than the volume ratio of the first phase, a first layered region continuously formed between the positive electrode layer and the negative electrode layer. An all-solid-state secondary battery comprising the second phase continuously formed between the positive electrode layer and the negative electrode layer, and a second layered region disposed adjacent to the positive electrode layer or the negative electrode layer, wherein the volume ratio of the second phase exceeds the volume ratio of the first phase.

[0012] [2] The all-solid-state secondary battery according to [1], wherein the second layered region has a volume ratio of 80 volume% or more of the second phase. [3] The all-solid-state secondary battery according to [1] or [2], wherein the ratio of the thickness of the second layered region to the thickness of the solid electrolyte layer is 0.1 or more and less than 0.5.

[0013] [4] The all-solid-state secondary battery according to any one of [1] to [3], wherein the second layered region is arranged adjacent to the negative electrode layer. [5] The all-solid-state secondary battery according to any one of [1] to [4], wherein the negative electrode layer comprises a negative electrode active material containing Ti.

[0014] The all-solid-state secondary battery of this embodiment will be described in detail below, with reference to the drawings as appropriate. The drawings used in the following description may be enlarged for convenience in order to clearly illustrate the features of the present invention. Therefore, the dimensional ratios of each component may differ from those of the actual components. The materials, dimensions, etc., exemplified in the following description are examples only, and the present invention is not limited to them. It can be implemented with appropriate modifications without changing the essence of the invention.

[0015] [All-solid-state secondary battery] Figure 1 is a schematic cross-sectional view of the all-solid-state secondary battery 10 of this embodiment. The all-solid-state secondary battery 10 has a laminate 4, a first external terminal 5, and a second external terminal 6. The first external terminal 5 and the second external terminal 6 are made of a conductive material. The first external terminal 5 and the second external terminal 6 are in contact with opposing surfaces of the laminate 4, respectively. The first external terminal 5 and the second external terminal 6 extend in a direction that intersects (is perpendicular to) the laminate surface of the laminate 4.

[0016] The laminate 4 has a positive electrode layer 1, a negative electrode layer 2, and a solid electrolyte layer 3 sandwiched between the positive electrode layer 1 and the negative electrode layer 2. The laminate 4 is a sintered body formed by laminating the positive electrode layer 1 and the negative electrode layer 2 with the solid electrolyte layer 3 in between and sintering them. The number of positive electrode layers 1 and negative electrode layers 2 included in the laminate 4 may be one layer each, or two or more layers each. As shown in Figure 1, the solid electrolyte layer 3 is present not only between the positive electrode layer 1 and the negative electrode layer 2, but also between the positive electrode layer 1 and the second external terminal 6, and between the negative electrode layer 2 and the first external terminal 5. Also, as shown in Figure 1, one end of the positive electrode layer 1 is connected to the first external terminal 5. One end of the negative electrode layer 2 is connected to the second external terminal 6.

[0017] The all-solid-state secondary battery 10 is charged or discharged by the exchange of ions between the positive electrode layer 1 and the negative electrode layer 2 via the solid electrolyte layer 3.

[0018] "Solid electrolyte layer" The solid electrolyte layer 3 can move ions in response to an externally applied electric field. The solid electrolyte forming the solid electrolyte layer 3 is a substance (e.g., particles) that can move ions in response to an externally applied electric field. The solid electrolyte layer 3 has a first phase containing a first solid electrolyte having a γ-Li3PO4 type crystal structure and containing Li, Si, P, and O, and having a different composition from the first solid electrolyte and containing a second solid electrolyte having a Li4SiO4 type crystal structure.

[0019] The solid electrolyte layer 3 may consist only of the first and second phases. The solid electrolyte layer 3 may also contain phases other than the first and second phases, to the extent that the effects of the present invention are not impaired. The phases other than the first and second phases may, for example, consist of a metal oxide having a different composition and crystal structure from the first and second phases.

[0020] The first solid electrolyte contained in the first phase is less reactive with the active material and has a stable γ-Li3PO4 type crystal structure, therefore Li 3+x Si x P 1-xIt is preferably O4 (0 < x < 0.6), and more preferably that x in the formula is 0.1 or more and less than 0.6. The first solid electrolyte may consist only of Li, Si, P, and O, and may contain at least one element selected from the group consisting of Ti, Co, Mn, and Ni as long as it can maintain a γ-Li3PO4 type crystal structure as required by the characteristics required for the all-solid-state secondary battery 10. Specifically, the first solid electrolyte is Li 3+x Si x P 1-x It may be a solid solution composed of O4 (0 < x < 0.6) and at least one element selected from the group consisting of Ti, Co, Mn, and Ni. The first solid electrolyte is, for example, Li 3+x Si x P 1-x It may be one in which a part of P in O4 (0 < x < 0.6) is substituted by at least one element selected from the group consisting of Ti, Co, Mn, and Ni.

[0021] In addition, the first phase may contain, in addition to the first solid electrolyte, components derived from, for example, a sintering aid, an active material material forming the positive electrode layer 1 and / or the negative electrode layer 2, etc., as long as the effects of the present invention are not impaired.

[0022] The second solid electrolyte contained in the second phase is difficult to react with the active material and has a stable Li4SiO4 type crystal structure. Therefore, Li 3+x Si x P 1-x It is preferably O4 (0.6 ≤ x ≤ 0.9), and more preferably that x in the formula is 0.7 or more and 0.8 or less. The second solid electrolyte may consist only of Li, Si, P, and O, and may contain at least one element selected from the group consisting of Ti, Co, Mn, and Ni as long as it can maintain a Li4SiO4 type crystal structure as required by the characteristics required for the all-solid-state secondary battery 10. Specifically, the second solid electrolyte is Li 3+x Si x P 1-xThe solid solution may consist of O4 (0.6 ≤ x ≤ 0.9) and at least one element selected from the group consisting of Ti, Co, Mn, and Ni. The second solid electrolyte may be, for example, Li 3+x Si x P 1-x In O4 (0.6 ≤ x ≤ 0.9), some of the P may be substituted with at least one element selected from the group consisting of Ti, Co, Mn, and Ni.

[0023] Furthermore, the second phase may contain not only the second solid electrolyte, but also components derived from, for example, a sintering aid, an active material that forms the positive electrode layer 1 and / or the negative electrode layer 2, to the extent that it does not impair the effects of the present invention.

[0024] If the laminate 4 is a sintered body, a sintering aid may be used as a material for the solid electrolyte layer 3 along with the first solid electrolyte and the second solid electrolyte for manufacturing reasons such as improving productivity and yield when forming the solid electrolyte layer 3. In this case, the solid electrolyte layer 3 may contain a sintering aid that remains without being removed during the firing process for manufacturing the laminate 4. Any sintering aid that has a sinterability-improving effect can be used, and known ones can be used. Specifically, examples of sintering aids include compounds containing lithium (Li), boron (B), zinc (Zn), bismuth (Bi), etc.

[0025] Figure 2 is a schematic cross-sectional view showing an enlarged portion of the all-solid-state secondary battery 10 shown in Figure 1. As shown in Figure 2, the solid electrolyte layer 3 is made up of a first layered region 31 and a second layered region 32 (layered region in the claims) stacked together. As shown in Figure 2, the first layered region 31 and the second layered region 32 are arranged continuously between the positive electrode layer 1 and the negative electrode layer 2, respectively. In the all-solid-state secondary battery 10 shown in Figure 2, the first layered region 31 is arranged adjacent to the positive electrode layer 1, and the second layered region 32 is arranged adjacent to the negative electrode layer 2. In this embodiment, since the second layered region 32 is arranged adjacent to the negative electrode layer 2, the all-solid-state secondary battery 10 has even better cycle characteristics.

[0026] In this embodiment, the first layered region 31 is arranged adjacent to the positive electrode layer 1 and the second layered region 32 is arranged adjacent to the negative electrode layer 2, but the solid electrolyte layer 3 may also be arranged such that the second layered region 32 is arranged adjacent to the positive electrode layer 1 and the first layered region 31 is arranged adjacent to the negative electrode layer 2.

[0027] In this embodiment, as shown in Figure 2, the first layered region 31 and the second layered region 32 are described as having only one layer each. However, the first layered region 31 and the second layered region 32 may each have multiple layers, as long as at least one layer of the second layered region 32 is arranged adjacent to the positive electrode layer 1 or the negative electrode layer 2. Therefore, in this embodiment, the number of layers in the first layered region 31 and the number of layers in the second layered region 32 are the same, or the number of layers in the second layered region 32 is one more than the number of layers in the first layered region 31. It is preferable that the first layered region 31 and the second layered region 32 each have only one layer, as this facilitates manufacturing.

[0028] The first layered region 31 includes the first phase. The first layered region 31 may or may not include the second phase. If the first layered region 31 includes the second phase, the volume ratio of the second phase contained in the first layered region 31 is less than or equal to the volume ratio of the first phase. Furthermore, the first layered region 31 does not include the second phase that is continuously formed between the positive electrode layer 1 and the negative electrode layer 2.

[0029] The second layered region 32 includes a second phase continuously formed between the positive electrode layer 1 and the negative electrode layer 2. The second layered region 32 may also include a first phase surrounded by the second phase. Alternatively, the second layered region 32 may include a first phase surrounded by the second phase and either the positive electrode layer 1 or the negative electrode layer 2 (the negative electrode layer 2 in the example shown in Figure 2). The second layered region 32 is one in which the volume ratio of the second phase exceeds the volume ratio of the first phase. Preferably, the volume ratio of the second phase in the second layered region 32 is 80 volume% or more, and more preferably 90 volume% or more. When the volume ratio of the second phase is 80 volume% or more, the second phase is more likely to be formed continuously between the positive electrode layer 1 and the negative electrode layer 2, and the all-solid-state secondary battery 10 has even better cycle characteristics. The volume ratio of the second phase included in the second layered region 32 may be 100 volume%.

[0030] The ratio of the thickness of the second layered region 32 to the thickness of the solid electrolyte layer 3 (thickness of the second layered region 32 / thickness of the solid electrolyte layer 3) is not particularly limited, but is preferably 0.1 or more and less than 0.5, and more preferably 0.1 or more and 0.2 or less. When the ratio of the thickness of the second layered region 32 to the thickness of the solid electrolyte layer 3 is 0.1 or more and less than 0.5, the all-solid-state secondary battery 10 has even better cycle characteristics. This is presumed to be because the second layered region 32, which is arranged adjacent to the positive electrode layer 1 or the negative electrode layer 2, has a significant effect in mitigating stress caused by the expansion and contraction of the positive electrode active material contained in the positive electrode layer 1 or the negative electrode active material contained in the negative electrode layer 2 (the negative electrode active material contained in the negative electrode layer 2 in the example shown in Figure 2).

[0031] "Positive electrode layer" As shown in Figure 1, the positive electrode layer 1 includes, for example, a positive electrode current collector 1A and a positive electrode active material layer 1B. The positive electrode active material layer 1B may be formed on both sides of the positive electrode current collector 1A, or on only one side, as shown in Figure 1.

[0032] (Positive electrode current collector) The positive electrode current collector 1A has excellent conductivity. The positive electrode current collector 1A is made of metals such as silver, palladium, gold, platinum, aluminum, copper, nickel, stainless steel, and iron, and their alloys. The positive electrode current collector 1A may also contain a positive electrode active material such as a lithium vanadium compound (LiV2O5, Li3V2(PO4)3, LiVOPO4).

[0033] (Cathode active material layer) The positive electrode active material layer 1B contains a positive electrode active material. The positive electrode active material layer 1B may also contain a conductive additive and a solid electrolyte.

[0034] (Cathode active material) The positive electrode active material is not particularly limited, as long as it is capable of reversibly releasing and intercalating lithium ions, and desorption and insertion of lithium ions. For example, positive electrode active materials used in known lithium-ion secondary batteries can be used.

[0035] The positive electrode active material is preferably one or more selected from, for example, transition metal oxides and transition metal composite oxides.

[0036] Examples of positive electrode active materials include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese spinel (LiMn2O4), and LiNi (General formula: LiNi x Co y Mn z M a A composite metal oxide represented by O2 (x+y+z+a=1, 0≦x≦1, 0≦y≦1, 0≦z≦1, 0≦a≦1, M represents one or more elements selected from Al, Mg, Nb, Ti, Cu, Zn, Cr), lithium titanate (Li4Ti5O 12 ), etc. may also be used.

[0037] A lithium-free positive electrode active material may be used as the positive electrode active material. A lithium-free positive electrode active material can be used by first placing a negative electrode active material doped with metallic lithium and / or lithium ions in the negative electrode layer 2, and then starting the all-solid-state secondary battery 10 from discharge. Examples of lithium-free positive electrode active materials include metal oxides (MnO2, V2O5, etc.).

[0038] (Conductive additive) The conductive additive is not particularly limited as long as it improves the electronic conductivity within the positive electrode active material layer 1B, and known conductive additives can be used. Examples of conductive additives include carbon-based materials such as graphite, carbon black, graphene, and carbon nanotubes; metals such as gold, platinum, silver, palladium, aluminum, copper, nickel, stainless steel, and iron; conductive oxides such as ITO (indium tin oxide); or mixtures thereof. The conductive additive may be in the form of a powder or fibers.

[0039] (solid electrolyte) The solid electrolyte contained in the positive electrode active material layer 1B improves the ionic conductivity within the positive electrode active material layer 1B. One or more known solid electrolytes can be used as the solid electrolyte. The same solid electrolyte as the first or second solid electrolyte used in the solid electrolyte layer 3 described above may also be used.

[0040] "Negative electrode layer" As shown in Figure 1, the negative electrode layer 2 includes, for example, a negative electrode current collector 2A and a negative electrode active material layer 2B. The negative electrode active material layer 2B may be formed on both sides of the negative electrode current collector 2A, or on only one side, as shown in Figure 1.

[0041] (Negative electrode current collector) The negative electrode current collector 2A is the same as the positive electrode current collector 1A. Preferably, the negative electrode current collector 2A contains an AgPd alloy. When the negative electrode current collector 2A contains an AgPd alloy, the all-solid-state secondary battery 10 has even better cycle characteristics. As the AgPd alloy, for example, one containing Ag and Pd in ​​a molar ratio of 8:2 (Ag:Pd) can be used.

[0042] (Negative electrode active material layer) The negative electrode active material layer 2B contains a negative electrode active material. The negative electrode active material layer 2B may also contain a conductive additive and a solid electrolyte.

[0043] (Negative electrode active material) The negative electrode active material is a compound capable of intercalating and releasing ions. The negative electrode active material is a compound exhibiting a lower potential than the positive electrode active material. The same material as the positive electrode active material can be used for the negative electrode active material. The negative electrode active material and positive electrode active material used in the all-solid-state secondary battery 10 are determined by considering the potentials of the negative electrode active material and the positive electrode active material.

[0044] In the all-solid-state secondary battery 10 of this embodiment, it is preferable that the negative electrode layer 2 contains a negative electrode active material containing Ti. This is because it results in an all-solid-state secondary battery 10 with good cycle characteristics. As the negative electrode active material containing Ti, known materials can be used, for example, lithium titanate (Li4Ti5O 12 ) and the like can be used as preferred.

[0045] (Conductive additive) The conductive additive improves the electronic conductivity of the negative electrode active material layer 2B. The conductive additive can be made from the same material as that used for the positive electrode active material layer 1B.

[0046] (solid electrolyte) The solid electrolyte contained in the negative electrode active material layer 2B improves ion conduction within the negative electrode active material layer 2B. One or more known solid electrolytes can be used as the solid electrolyte. The same solid electrolyte as the first or second solid electrolyte used in the solid electrolyte layer 3 described above may also be used.

[0047] In this embodiment of the all-solid-state secondary battery 10, as shown in Figure 1, the negative electrode layer 2 has a negative electrode current collector 2A and a negative electrode active material layer 2B as an example. However, the negative electrode layer may also serve as both a negative electrode current collector and a negative electrode active material layer. A negative electrode layer that serves as both a negative electrode current collector and a negative electrode active material layer exhibits a lower potential than the positive electrode active material.

[0048] The negative electrode layer, which serves as both the negative electrode current collector and the negative electrode active material layer, preferably contains a metal selected from the group consisting of silver (Ag), palladium (Pd), gold (Au), and platinum (Pt). This is because Ag, Pd, Au, and Pt do not melt and are not easily oxidized even when the sintering process for producing the laminate 4 is carried out in an atmospheric environment. The negative electrode layer, which serves as both the negative electrode current collector and the negative electrode active material layer, may be made of any of the above metals, or it may be made of an alloy containing any of the above metals.

[0049] The negative electrode layer, which serves as both the negative electrode current collector and the negative electrode active material layer, preferably contains an AgPd alloy. When the negative electrode layer, which serves as both the negative electrode current collector and the negative electrode active material layer, contains an AgPd alloy, a high-energy-density all-solid-state secondary battery is obtained. As the AgPd alloy, for example, one containing Ag and Pd in ​​a molar ratio of 8:2 (Ag:Pd) can be used.

[0050] [Manufacturing method for all-solid-state secondary batteries] Next, a method for manufacturing the all-solid-state secondary battery 10 of this embodiment will be described. First, the laminate 4 is manufactured. The laminate 4 can be manufactured, for example, using a co-firing method or a sequential firing method, and it is preferable to use the co-firing method. The co-firing method is a method of manufacturing the laminate 4 by firing all the materials that will form each layer at once after stacking them. The sequential firing method is a method of firing each layer as it is formed. The co-firing method allows the laminate 4 to be manufactured with fewer steps than the sequential firing method. In addition, the laminate 4 manufactured by the co-firing method is denser than the laminate 4 manufactured using the sequential firing method. The manufacturing method of the laminate 4 will be explained below, using the case of manufacturing the laminate 4 using the co-firing method as an example.

[0051] First, the materials of the positive electrode current collector 1A, positive electrode active material layer 1B, solid electrolyte layer 3, negative electrode active material layer 2B, and negative electrode current collector 2A that constitute the laminate 4 are made into pastes, and pastes corresponding to the materials of each layer are manufactured.

[0052] In this embodiment, a first paste that forms the first layered region 31 and a second paste that forms the second layered region 32 are manufactured as the paste for the solid electrolyte layer 3. The first paste is obtained, for example, by mixing particles made of a first solid electrolyte, particles made of a second solid electrolyte (optionally included), and a sintering aid in a predetermined volume ratio and forming a paste. The particles made of the first solid electrolyte and the particles made of the second solid electrolyte can be manufactured by known manufacturing methods according to their respective compositions. The second paste is obtained, for example, by mixing particles made of a second solid electrolyte with particles made of a first solid electrolyte and a sintering aid, which are optionally included, in a predetermined volume ratio and forming a paste.

[0053] The method for pasteuring each material used in the manufacture of the laminate 4 is not particularly limited, and for example, a method of mixing the powders of each material with a vehicle to obtain a paste can be used. Here, "vehicle" is a general term for the medium in the liquid phase. In this embodiment, the vehicle includes a solvent, a binder, and a plasticizer. For example, dihydroterpineol can be used as the solvent. For example, ethylcellulose can be used as the binder.

[0054] Next, a green sheet is prepared. The green sheet is obtained by applying a paste prepared for each material onto a substrate such as a PET (polyethylene terephthalate) film, drying it as needed, and then peeling off the substrate. The method of applying the paste is not particularly limited, and known methods such as screen printing, coating, transfer, and doctor blade can be used.

[0055] Next, the green sheets prepared for each material are stacked in the desired order and number of layers to create a laminated sheet. When laminating the green sheets, alignment and cutting are performed as necessary. For example, when creating a parallel or series-parallel battery, it is preferable to align the green sheets so that the end face of the positive electrode current collector 1A and the end face of the negative electrode current collector 2A do not coincide, and then stack the respective green sheets. The green sheet that forms the laminated sheet may consist of a pre-fabricated solid electrolyte layer unit, a positive electrode unit, and a negative electrode unit.

[0056] The procedure for manufacturing the positive electrode unit is as follows: First, a paste for the positive electrode active material layer 1B is printed onto a substrate such as a PET film by screen printing and dried to form the positive electrode active material layer 1B. Next, a paste for the positive electrode current collector 1A is printed onto the positive electrode active material 1B by screen printing and dried to form the positive electrode current collector 1A. Then, a paste for the positive electrode active material layer 1B is printed onto the positive electrode current collector 1A by screen printing and dried to form the positive electrode active material layer 1B. After that, the positive electrode unit is obtained by peeling off the PET film. The positive electrode unit is a green sheet in which the positive electrode active material layer 1B, the positive electrode current collector 1A, and the positive electrode active material layer 1B are laminated in this order.

[0057] Furthermore, a negative electrode unit is fabricated using a similar procedure. The negative electrode unit is a green sheet in which a solid electrolyte layer 3, a negative electrode active material layer 2B, a negative electrode current collector 2A, and a negative electrode active material layer 2B are laminated in this order. Alternatively, the solid electrolyte layer unit is prepared by applying a paste for the first layered region 31 onto a substrate such as a PET film using the doctor blade method, and drying it to form a sheet-like first layered region 31. Next, a paste for the second layered region 32 is applied onto the first layered region 31 using the doctor blade method, and drying it to form a sheet-like second layered region 32. The solid electrolyte layer unit may also be prepared by first forming the second layered region 32, and then forming the first layered region 31 on top of the second layered region 32. The solid electrolyte layer unit is a green sheet in which the first layered region 31 and the second layered region 32 are laminated.

[0058] Next, the fabricated positive electrode unit and negative electrode unit are stacked via a solid electrolyte layer unit. At this time, the second layered region 32 of the solid electrolyte layer unit is positioned to face the negative electrode unit during stacking. This results in a laminated sheet in which the positive electrode active material layer 1B, positive electrode current collector 1A, positive electrode active material layer 1B, first layered region 31, second layered region 32, negative electrode active material layer 2B, negative electrode current collector 2A, negative electrode active material layer 2B, second layered region 32, and first layered region 31 are stacked in this order. When stacking the positive electrode unit, solid electrolyte layer unit, and negative electrode unit, they are stacked alternately with a slight offset so that the positive electrode unit extends only to one end face of the laminated sheet and the negative electrode unit extends only to the opposite end face of the laminated sheet.

[0059] Next, the fabricated laminated sheets are pressed together to improve the adhesion of each layer and form a laminated substrate. Pressurization can be performed using, for example, a die press, hot water isostatic press (WIP), cold water isostatic press (CIP), or hydrostatic press. It is preferable to perform pressurization while heating. The heating temperature during pressurization can be, for example, 40 to 95°C. Next, the laminated substrate obtained after pressurization is cut using a dicing device to form laminated chips. Subsequently, the obtained laminated chips are subjected to a debindering and firing process. This yields a laminated body 4 made of sintered material.

[0060] The debinding and firing process can be carried out, for example, by placing the laminate on a ceramic base. The debinding and firing process can be, for example, a process of heating to 550°C to 1100°C in an air atmosphere. The heating time (firing time) can be, for example, 0.1 hours to 6 hours. The heating temperature and firing time in the debinding and firing process can be appropriately determined according to the composition of each layer constituting the laminate 4.

[0061] The sintered laminate 4 (sintered body) may be polished by barrel polishing in a cylindrical container with an abrasive such as alumina. This allows for chamfering of the corners of the laminate 4. The polishing of the laminate 4 may also be performed using sandblasting. Sandblasting is preferred because it can remove only specific parts of the surface of the laminate 4.

[0062] Next, a first external terminal 5 and a second external terminal 6 are formed on the opposing sides of the fabricated laminate 4, respectively. The first external terminal 5 and the second external terminal 6 can be formed using methods such as sputtering, dipping, screen printing, and spray coating, respectively. By following the above steps, an all-solid-state secondary battery 10 can be manufactured.

[0063] The all-solid-state secondary battery 10 of this embodiment has a solid electrolyte layer 3 comprising: a first phase containing a first solid electrolyte having a γ-Li3PO4 type crystal structure and a second phase containing a second solid electrolyte having a different composition from the first solid electrolyte and a Li4SiO4 type crystal structure, the first layer containing the first phase with the volume ratio of the second phase being less than or equal to the volume ratio of the first phase and continuously formed between the positive electrode layer 1 and the negative electrode layer 2, and a second layer containing the second phase being continuously formed between the positive electrode layer 1 and the negative electrode layer 2 and arranged adjacent to the positive electrode layer 1 or the negative electrode layer 2 (negative electrode layer 2 in the example shown in Figure 2) with the volume ratio of the second phase being greater than the volume ratio of the first phase.

[0064] The reason why the all-solid-state secondary battery 10 of this embodiment exhibits good cycle characteristics is not entirely clear, but it is presumed that this is because the second layered region 32, which sufficiently contains the second phase, is continuous between the positive electrode layer 1 and the negative electrode layer 2, and is positioned adjacent to either the positive electrode layer 1 or the negative electrode layer 2 (the negative electrode layer 2 in the example shown in Figure 2), resulting in good bonding and adhesion between the solid electrolyte layer 3 and the positive electrode layer 1 and / or the negative electrode layer 2 (only the negative electrode layer 2 in the example shown in Figure 2), which are positioned adjacent to the second layered region 32 of the solid electrolyte layer 3.

[0065] Although embodiments of the present invention have been described in detail above with reference to the drawings, the configurations and combinations thereof in each embodiment are merely examples, and additions, omissions, substitutions, and other modifications to the configurations are possible without departing from the spirit of the present invention. [Examples]

[0066] "Example 1" (First paste) Li as the first solid electrolyte 3+x Si x P 1-x Particles made of O4 (where x is 0.5 in the formula) and Li as the second solid electrolyte. 3+x Si x P 1-x Particles consisting of O4 (where x is 0.75) were mixed with ethylcellulose and dihydroterpineol in a volume ratio of 55:45 (first solid electrolyte:second solid electrolyte), and the mixture was wet-mixed in a ball mill to prepare the first paste of Example 1. The particles consisting of the first solid electrolyte and the particles consisting of the second solid electrolyte were produced by the method shown below.

[0067] (Production of particles consisting of the first solid electrolyte) Li2CO3, SiO2, and Li3PO4 were prepared as starting materials. Li2CO3, SiO2, and Li3PO4 were weighed out in a molar ratio of 2:1:1 and wet-mixed using a ball mill with water as the dispersion medium for 16 hours. The resulting mixture was calcined at 1200°C for 2 hours. 3.5 Si 0.5 P 0.5 Particles consisting of O4 were obtained. The obtained particles were subjected to X-ray diffraction measurements using CuKα rays with an X-ray diffractometer (X'pert PRO, PANlytical), and it was confirmed that they had a γ-Li3PO4 type crystal structure. Through the above steps, particles consisting of the first solid electrolyte of Example 1 were obtained.

[0068] (Production of particles consisting of a second solid electrolyte) Li2CO3, SiO2, and Li3PO4 were prepared as starting materials. Li2CO3, SiO2, and Li3PO4 were weighed out in a molar ratio of 6:3:1 and wet-mixed using a ball mill with water as the dispersion medium for 16 hours. The resulting mixture was calcined at 1200°C for 2 hours. 3.75 Si 0.75 P 0.25 Particles consisting of O4 were obtained. The obtained particles were subjected to X-ray diffraction measurements using CuKα rays with an X-ray diffractometer (X'pert PRO, PANlytical), and it was confirmed that they had a Li4SiO4 type crystal structure. Through the above steps, particles consisting of the second solid electrolyte of Example 1 were obtained.

[0069] (Second paste) The same Li as the first solid electrolyte used in the first paste. 3+x Si x P 1-x Particles consisting of O4 (where x is 0.5 in the formula) and the same Li as the second solid electrolyte used in the first paste. 3+x Si x P 1-x Particles consisting of O4 (where x is 0.75 in the formula) were mixed with ethylcellulose and dihydroterpineol in a volume ratio of 5:95 (first solid electrolyte:second solid electrolyte), and the mixture was wet-mixed in a ball mill to prepare the second paste of Example 1.

[0070] (Preparation of positive electrode current collector paste) A powder made from an AgPd alloy containing Ag and Pd in ​​a molar ratio of 8:2 (Ag:Pd) was added to ethyl cellulose and dihydroterpineol in a ball mill and wet-mixed to prepare the positive electrode current collector paste of Example 1. (Preparation of positive electrode active material layer paste) Lithium cobalt oxide (LiCoO2), ethyl cellulose, and dihydroterpineol were added to a ball mill and wet-mixed to prepare the positive electrode active material layer paste of Example 1.

[0071] (Preparation of negative electrode paste) Lithium titanate (Li4Ti5O 12The powder, ethyl cellulose, and dihydroterpineol were added to a ball mill and wet-mixed to prepare the first negative electrode paste of Example 1. Next, the powder made of an AgPd alloy containing Ag and Pd in ​​a molar ratio of 8:2 (Ag:Pd), ethyl cellulose, and dihydroterpineol were added to a ball mill and wet-mixed to prepare the second negative electrode paste of Example 1.

[0072] The ethylcellulose used in each of the above pastes is the binder. Dihydroterpineol is the solvent.

[0073] (Fabrication of the positive electrode unit) A positive electrode active material layer paste was applied to a substrate made of PET (polyethylene terephthalate) film to a thickness of 5 μm using screen printing, and dried at 80°C for 5 minutes. After drying, a positive electrode current collector paste was applied to the positive electrode active material layer paste to a thickness of 5 μm using screen printing, and dried at 80°C for 5 minutes. After drying, a positive electrode active material layer paste was applied to the positive electrode current collector paste to a thickness of 5 μm using screen printing, dried at 80°C for 5 minutes, and then peeled off from the substrate. This resulted in a positive electrode unit in which the positive electrode active material layer, the positive electrode current collector layer, and the positive electrode active material layer were laminated in this order.

[0074] (Fabrication of solid electrolyte layer unit) A first paste was applied to a substrate made of PET (polyethylene terephthalate) film to a thickness of 18 μm using screen printing, and dried at 80°C for 10 minutes. After drying, a second paste was applied to the first paste to a thickness of 2 μm using screen printing, dried at 80°C for 5 minutes, and then peeled off from the substrate. This resulted in a solid electrolyte layer unit in which a sheet made with the first paste and a sheet made with the second paste were laminated together.

[0075] (Fabrication of the negative electrode unit) A 5 μm thick layer of first negative electrode paste was applied to a substrate made of PET (polyethylene terephthalate) film using screen printing, and dried at 80°C for 5 minutes. After drying, a 5 μm thick layer of second negative electrode paste was applied to the first negative electrode paste using screen printing, and dried at 80°C for 5 minutes. After drying, a 5 μm thick layer of first negative electrode paste was applied to the second negative electrode paste using screen printing, dried at 80°C for 5 minutes, and then peeled off from the substrate. This resulted in a negative electrode unit in which a sheet made using the first negative electrode paste, a sheet made using the second negative electrode paste, and a sheet made using the first negative electrode paste were laminated together.

[0076] (Fabrication of all-solid-state secondary batteries) A laminated sheet forming a laminate 4 was obtained by alternately stacking 25 positive electrode units and 25 negative electrode layer units with a solid electrolyte layer unit in between. At this time, the sheet made using the second paste in the solid electrolyte layer unit within the laminated sheet was arranged to face the negative electrode unit. Furthermore, the laminated sheet was laminated so that the top and bottom surfaces were solid electrolyte layer units. In addition, the positive electrode units were stacked offset so that they extended only to one end face of the laminated sheet, and the negative electrode units extended only to the opposite end face of the laminated sheet.

[0077] Next, the fabricated laminated sheets were compressed together and cut using a dicing device to produce laminated chips. Subsequently, the laminated chips underwent a debinding and firing process to obtain the laminate of Example 1, which consists of a sintered body. In the debinding and firing process, the material was heated at 900°C for 1 hour in an air atmosphere. Next, a first external terminal and a second external terminal were formed on the opposing sides of the fabricated laminate using the Au sputtering method. Through the above process, the all-solid-state secondary battery 10 of Example 1 shown in Figure 1 was obtained.

[0078] Example 2 An all-solid-state secondary battery 10 of Example 2 was obtained in the same manner as in Example 1, except that the solid electrolyte layer unit was fabricated by the method described below. A first paste was applied to a substrate made of PET (polyethylene terephthalate) film to a thickness of 12 μm using screen printing, and dried at 80°C for 10 minutes. After drying, a second paste was applied to the first paste to a thickness of 8 μm using screen printing, dried at 80°C for 5 minutes, and then peeled off from the substrate. This yielded a solid electrolyte layer unit of Example 2, in which a sheet made using the first paste and a sheet made using the second paste were laminated together.

[0079] "Example 3" An all-solid-state secondary battery 10 of Example 3 was obtained in the same manner as in Example 1, except that the solid electrolyte layer unit was fabricated by the method described below. A first paste was applied to a substrate made of PET (polyethylene terephthalate) film to a thickness of 10 μm using screen printing, and dried at 80°C for 10 minutes. After drying, a second paste was applied to the first paste to a thickness of 10 μm using screen printing, dried at 80°C for 10 minutes, and then peeled off from the substrate. This yielded the solid electrolyte layer unit of Example 3, in which a sheet made using the first paste and a sheet made using the second paste were laminated together.

[0080] "Example 4" An all-solid-state secondary battery 10 of Example 4 was obtained in the same manner as in Example 1, except that the solid electrolyte layer unit was fabricated by the method described below. A first paste was applied to a substrate made of PET (polyethylene terephthalate) film to a thickness of 2 μm using screen printing, and dried at 80°C for 5 minutes. After drying, a second paste was applied to the first paste to a thickness of 18 μm using screen printing, dried at 80°C for 10 minutes, and then peeled off from the substrate. This yielded the solid electrolyte layer unit of Example 4, in which a sheet made using the first paste and a sheet made using the second paste were laminated together.

[0081] Example 5 An all-solid-state secondary battery 10 of Example 5 was obtained in the same manner as in Example 1, except that a second paste was prepared by the method shown below, and a solid electrolyte layer unit was prepared using this paste by the method shown below. The second paste of Example 5 was prepared in the same manner as in Example 1, except that the first solid electrolyte and the second solid electrolyte were mixed in a volume ratio of 3:7 (first solid electrolyte: second solid electrolyte).

[0082] A first paste was applied to a substrate made of PET (polyethylene terephthalate) film to a thickness of 16 μm using screen printing, and dried at 80°C for 10 minutes. After drying, the second paste of Example 5 was applied to the first paste to a thickness of 4 μm using screen printing, dried at 80°C for 5 minutes, and then peeled off from the substrate. This yielded a solid electrolyte layer unit of Example 5, in which a sheet made using the first paste and a sheet made using the second paste were laminated together.

[0083] "Example 6" An all-solid-state secondary battery 10 of Example 6 was obtained in the same manner as in Example 1, except that the sheet made using the second paste in the solid electrolyte layer unit within the laminated sheet was arranged to face the positive electrode unit.

[0084] Example 7 An all-solid-state secondary battery 10 of Example 7 was obtained in the same manner as in Example 1, except that a laminating sheet that would become the negative electrode layer, prepared by the method described below, was used instead of the negative electrode unit, and the solid electrolyte layer unit was prepared by the method described below.

[0085] (Preparation of negative electrode layer paste) A powder made from an AgPd alloy containing Ag and Pd in ​​a molar ratio of 8:2 (Ag:Pd) was added to ethyl cellulose and dihydroterpineol in a ball mill and wet-mixed to prepare the negative electrode layer paste of Example 7. (Preparation of laminated sheets to form the negative electrode layer) The negative electrode layer paste from Example 7 was applied to a substrate made of PET (polyethylene terephthalate) film to a thickness of 5 μm using screen printing, dried at 80°C for 5 minutes, and then peeled off from the substrate. This yielded a lamination sheet that would serve as the negative electrode layer.

[0086] A first paste was applied to a substrate made of PET (polyethylene terephthalate) film to a thickness of 16 μm using screen printing, and dried at 80°C for 10 minutes. After drying, a second paste was applied to the first paste to a thickness of 4 μm using screen printing, dried at 80°C for 5 minutes, and then peeled off from the substrate. This yielded the solid electrolyte layer unit of Example 7, in which a sheet made using the first paste and a sheet made using the second paste were laminated together.

[0087] "Comparative Example 1" A comparative example 1 all-solid-state secondary battery 10 was obtained in the same manner as in Example 1, except that a lamination sheet that would become the solid electrolyte layer, prepared by the method described below, was used instead of the solid electrolyte layer unit. The first paste and the second paste from Example 1 were mixed in a volume ratio of 1:1 to prepare the solid electrolyte layer paste of Comparative Example 1. Then, the paste of the solid electrolyte layer of Comparative Example 1 was applied to a substrate made of PET (polyethylene terephthalate) film to a thickness of 20 μm using screen printing, dried at 80°C for 10 minutes, and then peeled off from the substrate. This yielded a lamination sheet that would become the solid electrolyte layer of Comparative Example 1.

[0088] Table 1 shows the first and second solid electrolytes used as materials for the solid electrolyte layer and the configuration of the negative electrode layer for the all-solid-state secondary batteries 10 obtained in Examples 1 to 7 and Comparative Example 1.

[0089] [Table 1]

[0090] Furthermore, for the all-solid-state secondary batteries 10 of Examples 1 to 7 and Comparative Example 1, the presence or absence of the first layered region, the volume percentage of the second phase in the first layered region (volume %), the presence or absence of the second layered region, the volume percentage of the second phase in the second layered region (volume %), the location of the second layered region, the thickness ratio of the second layered region to the solid electrolyte layer (second layered region / solid electrolyte layer), and the capacity retention rate (capacity after 1000 cycles / initial capacity) were determined using the method described below.

[0091] First, the all-solid-state secondary battery 10 was cut in the center of the chip to expose the cross-section, and a clear cross-section was obtained using a cross-section polisher (CP). The all-solid-state secondary battery 10 was cut so as to divide the laminate between the first external terminal and the second external terminal, when viewed from the laminate surface, approximately in the center. The obtained cross-section was then observed at 5000x magnification using a scanning electron microscope (SEM) to obtain 10 fields of view of secondary electron images. The contrast of the 10 secondary electron images obtained allowed for the identification of the first and second phases in the positive electrode layer, negative electrode layer, and solid electrolyte layer, respectively. As a result, it was confirmed that the solid electrolyte layer consisted only of the first and second phases in all fields of view.

[0092] Next, for each field of view, the first and second phases, which were distinguished by the contrast of the secondary electron image, were extracted, and it was confirmed whether or not there was a second phase that was positioned adjacent to the positive or negative electrode layer and continuously formed between the positive and negative electrode layers. If the continuously formed second phase was present, the region consisting of the first phase surrounded by the second phase, the first phase surrounded by the positive or negative electrode layer adjacent to the continuously formed second phase, and the continuously formed second phase was considered to be a second layered region, and it was determined that a second layered region existed. Furthermore, for regions of the solid electrolyte layer in each field of view that are not the second layered region, we confirmed whether or not a first layered region containing the first phase and continuously formed between the positive electrode layer and the negative electrode layer exists.

[0093] Next, each secondary electron image was converted to a monochrome image and binarized. Then, the number of pixels in the portion corresponding to the second layered region within each field of view and the number of pixels in the portion corresponding to the second phase within the second layered region were measured and added together. Finally, the volume percentage (volume %) of the second phase within the second layered region was calculated using the formula shown below. Volume percentage of the second phase within the second layered region (volume %) = (Number of pixels of the second phase within the second layered region in the entire field of view / Number of pixels in the portion corresponding to the second layered region in the entire field of view) × 100

[0094] Furthermore, the number of pixels in the portion corresponding to the first layered region within each field of view and the number of pixels in the portion corresponding to the second phase within the first layered region were measured and added together. Next, the volume percentage (volume %) of the second phase within the first layered region was calculated using the formula shown below. Volume percentage of the second phase within the first layered region (volume %) = (Number of pixels of the second phase within the first layered region in the entire field of view / Number of pixels in the portion corresponding to the first layered region in the entire field of view) × 100

[0095] Next, ten straight lines were drawn across each of the ten secondary electron images of the above ten fields of view, in a direction perpendicular to the stacking plane of the stacked structure 4 (stacking direction). The ten straight lines were placed at equal intervals. The length of the portion of each straight line that overlapped the solid electrolyte layer was measured, the average value was calculated for each field of view, and then the average value of 10 fields of view was calculated to determine the thickness of the solid electrolyte layer.

[0096] Furthermore, for each of the 10 straight lines mentioned above, if there is a continuously formed second phase, the length from the positive or negative electrode layer adjacent to the continuously formed second phase until the first appearance of the first phase beyond the continuously formed second phase was measured. Note that the first phase surrounded by the second phase, and the first phase surrounded by the positive or negative electrode layer adjacent to the continuously formed second phase, were considered as part of the continuously formed second phase, and the length from the first appearance of the first phase beyond the second phase was measured accordingly.

[0097] Figure 3 is a schematic diagram illustrating the method for measuring the thickness of the second layered region. It shows one straight line L1 selected from the 10 straight lines drawn in one field of view of the 10 secondary electron images described above, and its surrounding region. In Figure 3, reference numeral 11 indicates the first phase, reference numeral 21 indicates the second phase, and reference numeral 22 indicates the second phase continuously formed between the positive electrode layer 1 and the negative electrode layer 2. Reference numeral L1 indicates one straight line selected from 10 straight lines drawn on a secondary electron image of one field of view. Reference numeral t2 in Figure 3 indicates the length on the straight line L1 from the perspective of the negative electrode layer 2 adjacent to the second phase 22, which is formed by continuously forming the second phase 21, until the first appearance of the first phase 11 beyond the continuously formed second phase 22.

[0098] The length from the first appearance of the first phase 11 beyond the continuously formed second phase 22, as measured in this manner, was measured by calculating the average value of the 10 straight lines for each field of view, and then the average value of the 10 fields of view was calculated to determine the thickness of the second layered region. Using the thickness of the solid electrolyte layer and the thickness of the second layered region obtained in this way, the thickness ratio (second layered region / solid electrolyte layer) was calculated.

[0099] As a result of measurements using the above method, it was confirmed that in all solid-state secondary batteries 10 of Examples 1 to 7, one first layered region was continuously formed between the positive electrode layer and the negative electrode layer within the solid electrolyte layer in all fields of view. Furthermore, it was confirmed that in all solid-state secondary batteries 10 of Examples 1 to 7, the volume percentage of the second phase within the first layered region was 50 volume% or less.

[0100] Furthermore, in the all-solid-state secondary batteries 10 of Examples 1 to 7, it was confirmed that in all fields of view, there is one second layered region in the solid electrolyte layer that includes a second phase continuously formed between the positive electrode layer and the negative electrode layer, is located adjacent to either the positive electrode layer or the negative electrode layer, and whose volume ratio exceeds that of the first phase. In other words, in the all-solid-state secondary batteries 10 of Examples 1 to 7, one first layered region and one second layered region were present in the solid electrolyte layer in all fields of view. On the other hand, in the all-solid-state secondary battery of Comparative Example 1, only the first layered region was present in the solid electrolyte layer in all fields of view, and the second layered region was absent.

[0101] Furthermore, in the all-solid-state secondary batteries 10 of Examples 1 to 5 and Example 7, it was confirmed that the second layered region was located adjacent to the negative electrode layer in all fields of view. In addition, in the all-solid-state secondary battery 10 of Example 6, it was confirmed that the second layered region was located adjacent to the positive electrode layer in all fields of view.

[0102] (Measurement of capacity retention rate (capacity after 1000 cycles / initial capacity)) Using an electrochemical testing apparatus (manufactured by Hokuto Denko Co., Ltd.), constant current charge-discharge tests (CC-CC) were performed on the all-solid-state secondary batteries 10 of Examples 1 to 7 and Comparative Example 1 using the method described below. The battery was charged using a constant current charge rate of 0.2C (the current value at which charging is completed in 10 hours when charging at 1mA at 25℃) until the battery voltage reached 4.0V (CC charging), and then discharged using a constant current discharge rate of 0.2C until the battery voltage reached 1.0V (CC discharge). The discharge capacity (μAh) after the completion of charging and discharging was detected, and the discharge capacity (initial capacity) Q1 of the first cycle was determined.

[0103] The all-solid-state secondary battery whose battery capacity Q1 was determined was then charged again using a constant current charge rate of 0.2C until the battery voltage reached 4.0V (CC charging), and then discharged using a constant current discharge rate of 0.1C until the battery voltage reached 1.0V (CC discharge). The above charge and discharge cycles were counted as one cycle, and 1000 charge and discharge cycles were performed. After that, the discharge capacity Q2 after 1000 charge and discharge cycles was determined.

[0104] From the discharge capacities Q1 and Q2 obtained in this manner, the capacity retention rate E after 1000 cycles was calculated using the following formula. The results are shown in Table 1. E(%) = (Q2 / Q1) × 100

[0105] Table 1 shows the presence or absence of a second layer region, the volume percentage of the second phase in the second layer region, the location of the second layer region, the thickness ratio of the second layer region to the solid electrolyte layer (second layer region / solid electrolyte layer), and the capacity retention rate (capacity after 1000 cycles / initial capacity) for all solid-state secondary batteries 10 in Examples 1 to 7 and Comparative Example 1.

[0106] As shown in Table 1, the all-solid-state secondary batteries 10 of Examples 1 to 7 exhibited higher capacity retention rates compared to the all-solid-state secondary battery of Comparative Example 1, which lacked a second layer-like region in the solid electrolyte layer. This is presumed to be because, in the all-solid-state secondary batteries 10 of Examples 1 to 5 and Example 7, the presence of a second layer-like region in the solid electrolyte layer improves the bonding and adhesion between the solid electrolyte layer and the negative electrode layer 2. Furthermore, in the all-solid-state secondary battery 10 of Example 6, the presence of a second layer-like region in the solid electrolyte layer improves the bonding and adhesion between the solid electrolyte layer and the positive electrode layer 1.

[0107] In particular, the all-solid-state secondary batteries 10 of Examples 1 to 3, in which the volume ratio of the second phase in the second layer region was 80 volume% or more, exhibited a higher capacity retention rate compared to the all-solid-state secondary battery 10 of Example 5, in which the volume ratio of the second phase in the second layer region was 70 volume%. Furthermore, the all-solid-state secondary batteries 10 of Examples 1 and 2, in which the ratio of the thickness of the second layered region to the thickness of the solid electrolyte layer was 0.1 or more and less than 0.5, exhibited a higher capacity retention rate compared to the all-solid-state secondary batteries 10 of Examples 3 and 4, in which the above-mentioned thickness ratio was 0.5 or more.

[0108] Furthermore, the all-solid-state secondary battery 10 of Example 1, in which the second layered region is located adjacent to the negative electrode layer, exhibited a higher capacity retention rate compared to the all-solid-state secondary battery 10 of Example 6, in which the second layered region is located adjacent to the positive electrode layer. Furthermore, the all-solid-state secondary batteries 10 of Examples 1 and 2, in which the negative electrode layer includes a negative electrode current collector made of an AgPd alloy and a negative electrode active material containing Ti, had the same volume ratio of the second phase in the second layered region as in Examples 1 and 2, and exhibited a higher capacity retention rate compared to the all-solid-state secondary battery 10 of Example 7, in which the negative electrode layer is made of an AgPd alloy that serves as both the negative electrode current collector and the negative electrode active material layer. [Explanation of symbols]

[0109] 1...Positive electrode layer, 1A...Positive electrode current collector, 1B...Positive electrode active material layer, 2...Negative electrode layer, 2A...Negative electrode current collector, 2B...Negative electrode active material layer, 3...Solid electrolyte layer, 4...Laminate, 5...First external terminal, 6...Second external terminal, 10...All-solid-state secondary battery, 31...First layered region, 32...Second layered region (layered region).

Claims

1. It has a positive electrode layer, a negative electrode layer, and a solid electrolyte layer sandwiched between the positive electrode layer and the negative electrode layer. The solid electrolyte layer contains Li, Si, P, and O, and γ-Li ３ PO ４ A first phase comprising a first solid electrolyte having a crystal structure of type, It contains Li, Si, P, and O, and has a different composition from the first solid electrolyte, Li ４ SiO ４ It has a second phase containing a second solid electrolyte having a crystal structure of the type, A first layered region is formed continuously between the positive electrode layer and the negative electrode layer, comprising the first phase, wherein the volume ratio of the second phase is less than or equal to the volume ratio of the first phase. An all-solid-state secondary battery comprising the second phase formed continuously between the positive electrode layer and the negative electrode layer, and a second layered region disposed adjacent to the positive electrode layer or the negative electrode layer, wherein the volume ratio of the second phase exceeds the volume ratio of the first phase.

2. The all-solid-state secondary battery according to claim 1, wherein the second layered region has a volume ratio of 80 volume% or more of the second phase.

3. The all-solid-state secondary battery according to claim 1 or claim 2, wherein the ratio of the average thickness of the second layered region to the average thickness of the solid electrolyte layer is 0.1 or more and less than 0.

5.

4. The all-solid-state secondary battery according to claim 1 or claim 2, wherein the second layered region is arranged adjacent to the negative electrode layer.

5. The all-solid-state secondary battery according to claim 1 or claim 2, wherein the negative electrode layer comprises a negative electrode active material containing Ti.

Images