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

Abstract

To provide an all-solid-state battery and a manufacturing method thereof having a moisture-proof cover layer.SOLUTION: An all-solid-state battery includes an oxide-based solid electrolyte layer having ionic conductivity, a laminate in which electrode layers containing electrode active materials are alternately stacked, and a cover layer provided on at least one of the upper surface and the lower surface of the laminate in the stacking direction, and the cover layer includes a filler material that is insulating and has a plate-like shape.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] In recent years, the demand for secondary batteries has expanded rapidly, and lithium-ion secondary batteries using organic electrolytes have been put into practical use. However, due to concerns about electrolyte leakage, there is a growing expectation for safer oxide-based solid electrolytes, and the development of all-solid-state batteries using oxide-based solid electrolytes is actively progressing. Furthermore, to improve capacity density, it is desirable to stack multiple battery units. When stacking multiple units, a technology has been disclosed in which cover layers are provided above and below the stacking direction of the all-solid-state battery (see, for example, Patent Documents 1 and 2). Patent Document 3 describes a moisture-proof layer in contact with the stack to suppress the decrease in battery capacity due to the reaction between the active material contained in the electrode layer and moisture. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-82522 [Patent Document 2] Japanese Patent Publication No. 2020-149782 [Patent Document 3] International Publication No. 2018 / 181545 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, in Patent Document 3, a moisture-proof layer is provided after firing the laminate using methods such as spray coating or dip coating, and the moisture resistance of the laminate before the moisture-proof layer is formed is not guaranteed.

[0005] This invention has been made in view of the above problems, and aims to provide an all-solid-state battery equipped with a moisture-resistant cover layer and a method for manufacturing the same. [Means for solving the problem]

[0006] The all-solid-state battery according to the present invention comprises a laminate in which an oxide-based solid electrolyte layer having ion conductivity and an electrode layer containing an electrode active material are alternately stacked, and a cover layer provided on at least one of the upper and lower surfaces in the stacking direction of the laminate, wherein the cover layer contains a filler material that is insulating and has a plate-like shape.

[0007] In the above-described all-solid-state battery, the average thickness of the multiple filler materials may be 0.05 μm or more and 1 μm or less, the D50% diameter may be 1 μm or more and 50 μm or less, and the average aspect ratio may be 3 or more and 500 or less.

[0008] In the above-described all-solid-state battery, the filler material may be oriented in the in-plane direction of the cover layer.

[0009] In the above-mentioned all-solid-state battery, the conductivity of the filler material, including its electronic and ionic conductivity, is 10 -8 It is also acceptable if the S / cm is less than or equal to the stated value.

[0010] In the above-described all-solid-state battery, the filler material may be alumina or boron nitride.

[0011] In the above-described all-solid-state battery, the cover layer may contain a glass material having a lower sintering temperature than the filler material.

[0012] In the above-described all-solid-state battery, the cover layer may contain a glass material which is an oxide-based solid electrolyte having a NASICON-type crystal structure.

[0013] In the above-described all-solid-state battery, the cover layer may contain a glass material having a melting point of 500°C or higher and 700°C or lower.

[0014] In the all-solid-state battery described above, the cover layer contains a glass material, and in the cover layer, the filler material may have a volume ratio of 5 vol% or more and 60 vol% or less with respect to the glass material.

[0015] In the all-solid-state battery described above, the cover layer may contain a glass material having the same composition as the main component of the oxide-based solid electrolyte layer.

[0016] In the all-solid-state battery described above, the electrode layer contains an oxide-based solid electrolyte, and the cover layer may contain a glass material having the same composition as the oxide-based solid electrolyte contained in the electrode layer.

[0017] The method for manufacturing an all-solid-state battery according to the present invention includes a preparation step of preparing a ceramic laminate in which a cover sheet containing a filler material having insulating properties and a plate-like form is laminated on at least one of the upper surface and the lower surface in the lamination direction of a laminate in which a solid electrolyte green sheet containing oxide-based solid electrolyte powder having ion conductivity and an internal electrode pattern containing electrode active material powder are alternately laminated, and a firing step of firing the ceramic laminate.

Advantages of the Invention

[0018] According to the present invention, it is possible to provide an all-solid-state battery provided with a cover layer having moisture-proof properties and a method for manufacturing the same.

Brief Description of the Drawings

[0019] [Figure 1] It is a schematic cross-sectional view showing the basic structure of an all-solid-state battery. [Figure 2] It is a schematic cross-sectional view of a laminated all-solid-state battery. [Figure 3] It is a schematic cross-sectional view of another laminated all-solid-state battery. [Figure 4] (a) is a diagram schematically showing a cross-section of the cover layer, and (b) is an enlarged view of the filler material. [Figure 5] It is a diagram illustrating the flow of a method for manufacturing an all-solid-state battery. [Figure 6] (a) and (b) are diagrams illustrating the lamination process. [Modes for carrying out the invention]

[0020] The embodiments will be described below with reference to the drawings.

[0021] (Embodiment) Figure 1 is a schematic cross-sectional view showing the basic structure of an all-solid-state battery 100. As illustrated in Figure 1, the all-solid-state battery 100 has a structure in which a solid electrolyte layer 30 is sandwiched between a first internal electrode 10 (first electrode layer) and a second internal electrode 20 (second electrode layer). The first internal electrode 10 is formed on the first main surface of the solid electrolyte layer 30. The second internal electrode 20 is formed on the second main surface of the solid electrolyte layer 30. For example, the first internal electrode 10, the second internal electrode 20, and the solid electrolyte layer 30 are sintered bodies obtained by sintering powdered material.

[0022] When the all-solid-state battery 100 is used as a secondary battery, one of the first internal electrode 10 and the second internal electrode 20 is used as the positive electrode and the other as the negative electrode. In this embodiment, as an example, the first internal electrode 10 is used as the positive electrode layer and the second internal electrode 20 is used as the negative electrode layer.

[0023] The solid electrolyte layer 30 has a NASICON-type crystal structure and is mainly composed of an oxide-based solid electrolyte having ion conductivity. The solid electrolyte of the solid electrolyte layer 30 is, for example, an oxide-based solid electrolyte having lithium ion conductivity. The solid electrolyte is, for example, a phosphate-based solid electrolyte. The phosphate-based solid electrolyte having a NASICON-type crystal structure has high conductivity and the property of being stable in the atmosphere. The phosphate-based solid electrolyte is, for example, a phosphate containing lithium. The phosphate is not particularly limited, and examples include lithium titanium phosphate salts in combination with Ti (for example, LiTi2(PO4)3). Alternatively, Ti can be partially or entirely replaced with a tetravalent transition metal such as Ge, Sn, Hf, or Zr. Also, in order to increase the Li content, it may be partially replaced with a trivalent transition metal such as Al, Ga, In, Y, or La. More specifically, for example, Li 1+x Al x Ge 2-x (PO4)3, and Li 1+x Al x Zr 2-x (PO4)3, Li 1+x Al x Ti 2-x (PO4)3 and the like can be mentioned. For example, a Li-Al-Ge-PO4-based material to which the same transition metal as the transition metal contained in the phosphate having an olivine-type crystal structure contained in the first internal electrode 10 and the second internal electrode 20 is preferably added in advance. For example, when the first internal electrode 10 and the second internal electrode 20 contain a phosphate containing Co and Li, it is preferable that the Li-Al-Ge-PO4-based material to which Co is added in advance is contained in the solid electrolyte layer 30. In this case, an effect of suppressing the elution of the transition metal contained in the electrode active material into the electrolyte can be obtained. When the first internal electrode 10 and the second internal electrode 20 contain a phosphate containing a transition element other than Co and Li, it is preferable that the Li-Al-Ge-PO4-based material to which the transition metal is added in advance is contained in the solid electrolyte layer 30.

[0024] The first internal electrode 10, used as the positive electrode, contains a material having an olivine-type crystal structure as the electrode active material. It is preferable that the second internal electrode 20 also contains the same electrode active material. Examples of such electrode active materials include phosphates containing a transition metal and lithium. The olivine-type crystal structure is found in natural olivine and can be identified by X-ray diffraction.

[0025] Typical examples of electrode active materials with an olivine-type crystal structure include LiCoPO4 containing Co. Phosphates in which the transition metal Co is replaced in this chemical formula can also be used. Here, the ratio of Li and PO4 may vary depending on the valency. It is preferable to use Co, Mn, Fe, Ni, etc. as the transition metal.

[0026] Electrode active materials having an olivine-type crystal structure act as positive electrode active materials in the first internal electrode 10, which acts as the positive electrode. For example, if the electrode active material having an olivine-type crystal structure is contained only in the first internal electrode 10, then this electrode active material acts as the positive electrode active material. When the electrode active material having an olivine-type crystal structure is also contained in the second internal electrode 20, which acts as the negative electrode, although the mechanism of action is not fully understood, it is presumed that this is based on the formation of a partial solid solution state with the negative electrode active material, resulting in an increase in discharge capacity and an increase in the operating potential associated with discharge.

[0027] When both the first internal electrode 10 and the second internal electrode 20 contain electrode active materials having an olivine-type crystal structure, each electrode active material preferably contains a transition metal that may be the same or different from each other. "May be the same or different from each other" means that the electrode active materials contained in the first internal electrode 10 and the second internal electrode 20 may contain the same type of transition metal, or they may contain different types of transition metals. The first internal electrode 10 and the second internal electrode 20 may contain only one type of transition metal, or they may contain two or more types of transition metals. Preferably, the first internal electrode 10 and the second internal electrode 20 contain the same type of transition metal. More preferably, the electrode active materials contained in both electrodes have the same chemical composition. The inclusion of the same type of transition metal or the same composition of electrode active materials in the first internal electrode 10 and the second internal electrode 20 increases the similarity of the compositions of both internal electrode layers, which has the effect of allowing the all-solid-state battery 100 to withstand actual use without malfunction, depending on the application, even if the terminals are connected in reverse polarity.

[0028] The second internal electrode 20 contains a negative electrode active material. By containing the negative electrode active material in only one electrode, it becomes clear that the electrode in question acts as the negative electrode and the other electrode acts as the positive electrode. Alternatively, both electrodes may contain a known substance as the negative electrode active material. Regarding the negative electrode active material of the electrodes, prior art in secondary batteries can be appropriately referenced, and examples include compounds such as titanium oxide, lithium titanium composite oxide, lithium titanium composite phosphate, carbon, and lithium vanadium phosphate.

[0029] In the fabrication of the first internal electrode 10 and the second internal electrode 20, in addition to these electrode active materials, an ionic conductive solid electrolyte and a conductive material (conductive additive) are added. For these components, an internal electrode paste can be obtained by uniformly dispersing a binder and a plasticizer in water or an organic solvent. The conductive additive may include carbon materials. The conductive additive may also include metals. Examples of metals used as conductive additives include Pd, Ni, Cu, Fe, and alloys containing these. The solid electrolyte contained in the first internal electrode 10 and the second internal electrode 20 can be, for example, the same as the main component solid electrolyte of the solid electrolyte layer 30.

[0030] The thickness of the solid electrolyte layer 30 is, for example, 5 μm to 30 μm, 7 μm to 25 μm, or 10 μm to 20 μm. The thicknesses of the first internal electrode 10 and the second internal electrode 20 are, for example, 5 μm to 50 μm, 7 μm to 45 μm, or 10 μm to 40 μm. The thickness of each layer can be measured, for example, as the average value of the thickness of 10 different points in one layer.

[0031] Figure 2 is a schematic cross-sectional view of a stacked all-solid-state battery 100a, in which multiple battery units are stacked. The all-solid-state battery 100a comprises a stacked chip 60 having a substantially rectangular parallelepiped shape. In the stacked chip 60, a first external electrode 40a and a second external electrode 40b are provided so as to be in contact with two side surfaces, which are two of the four surfaces other than the top and bottom surfaces at the stacking direction ends. These two side surfaces may be adjacent to each other or may be two opposing sides. In this embodiment, the first external electrode 40a and the second external electrode 40b are provided so as to be in contact with two opposing side surfaces (hereinafter referred to as two end surfaces).

[0032] In the following description, components having the same composition range, thickness range, and particle size distribution range as the all-solid-state battery 100 will be given the same reference numerals, and detailed explanations will be omitted.

[0033] In the all-solid-state battery 100a, multiple first internal electrodes 10 and multiple second internal electrodes 20 are alternately stacked via a solid electrolyte layer 30. The edges of the multiple first internal electrodes 10 are exposed on the first end face of the stacked chip 60, but not on the second end face. The edges of the multiple second internal electrodes 20 are exposed on the second end face of the stacked chip 60, but not on the first end face. As a result, the first internal electrodes 10 and the second internal electrodes 20 are alternately conductive to the first external electrode 40a and the second external electrode 40b. The solid electrolyte layer 30 extends from the first external electrode 40a to the second external electrode 40b. Thus, the all-solid-state battery 100a has a structure in which multiple battery units are stacked.

[0034] A cover layer 50 is laminated on the upper surface of the laminate of the first internal electrode 10, the solid electrolyte layer 30, and the second internal electrode 20. The cover layer 50 is in contact with the uppermost internal electrode (either the first internal electrode 10 or the second internal electrode 20) and also in contact with a part of the solid electrolyte layer 30. Another cover layer 50 is laminated on the lower surface of the laminate. This cover layer 50 is in contact with the lowermost internal electrode (either the first internal electrode 10 or the second internal electrode 20) and also in contact with a part of the solid electrolyte layer 30. For example, the cover layer 50 is a sintered body obtained by sintering powder material.

[0035] The first internal electrode 10 and the second internal electrode 20 may be provided with a current collector layer. For example, as illustrated in Figure 3, a first current collector layer 11 may be provided within the first internal electrode 10. Also, a second current collector layer 21 may be provided within the second internal electrode 20. The first current collector layer 11 and the second current collector layer 21 are mainly composed of a conductive material. For example, metal, carbon, etc. can be used as the conductive material for the first current collector layer 11 and the second current collector layer 21. By connecting the first current collector layer 11 to the first external electrode 40a and the second current collector layer 21 to the second external electrode 40b, the current collection efficiency is improved.

[0036] In stacked solid-state batteries such as the solid-state battery 100a in Figures 2 and 3, it is necessary to provide moisture resistance to the stacked solid-state battery in order to suppress the decrease in battery capacity caused by the reaction between the electrode active material contained in the electrode layer and moisture. Therefore, the cover layer 50 according to this embodiment has a structure that provides moisture resistance.

[0037] Figure 4(a) is a schematic representation of a cross-section of the cover layer 50. In Figure 4(a), the hatches of the glass material 50a and the first internal electrode 10 are omitted. Also, the filler material 50b is depicted in black. As illustrated in Figure 4(a), the cover layer 50 includes a glass material 50a and an insulating filler material 50b. For example, each filler material 50b is randomly dispersed within the glass material 50a. The filler material 50b has a plate-like shape.

[0038] Since the filler material 50b has a plate-like shape rather than a roughly circular granular shape, each filler material 50b is oriented from the formation of the sheet before firing of the cover layer 50 through the firing process. As a result, the cover layer 50 can maintain its shape against shrinkage during firing of the first internal electrode 10, the second internal electrode 20, and the solid electrolyte layer 30. Consequently, the cover layer 50 itself becomes moisture-resistant. Orientation will also occur if rod-shaped filler material is used, but the plate-like shape is advantageous for shape retention. Furthermore, the plate-like shape is also advantageous in terms of preventing moisture intrusion because it can suppress moisture intrusion across a larger surface area.

[0039] Figure 4(b) is an enlarged view of the filler material 50b. As illustrated in Figure 4(b), in a cross-section along the lamination direction of each layer, the maximum length in the planar direction of the plate is defined as length L. The maximum thickness in the direction perpendicular to the maximum length is defined as thickness t. For example, an SEM image with a field of view of 5000x is obtained in a cross-section along the lamination direction of each layer. Each filler material 50b is extracted from this SEM image, and the length L and thickness t of each filler material 50b are measured. For example, the average thickness t of each filler material 50b is between 0.05 μm and 1 μm, the average length L (D50% diameter) is between 1 μm and 50 μm, and the average aspect ratio between length L and thickness t is between 3 and 500. In addition, the maximum width w of each filler material 50b can be measured by observing a cross-section at a different position and parallel to the said cross-section. The average maximum width w of each filler material 50b is between 1 μm and 50 μm.

[0040] It is preferable that each filler material 50b is oriented in the in-plane direction of the cover layer 50. This is because even if the first internal electrode 10, the second internal electrode 20, and the solid electrolyte layer 30 shrink during firing, the shape of the cover layer 50 in the in-plane direction can be maintained, and the moisture resistance of the cover layer 50 is improved. Here, each filler material 50b being oriented in the in-plane direction of the cover layer 50 means that when the angle between the direction of the particle size d of each filler material 50b and the in-plane direction of the cover layer 50 is measured in the above SEM image, the average value of the angle of each filler material 50b is between 0° and 45°. This angle includes both upward sloping to the right and upward sloping to the left with respect to the in-plane direction.

[0041] From the viewpoint of providing sufficient insulation to the cover layer 50, it is preferable that the filler material 50b has sufficient insulation properties. For example, the conductivity of each filler material 50b, including electronic conductivity and ionic conductivity, is 10 -8 Preferably, S / cm or less, 10 -12 It is more preferable that it be less than or equal to S / cm, -14It is even more preferable that the density is less than or equal to S / cm. For example, alumina, boron nitride, silica, magnesia, titania, etc. can be used as the filler material 50b.

[0042] Observation of glass material 50a using SEM images confirms that it is amorphous.

[0043] It is preferable that the glass material 50a has a lower sintering temperature than the filler material 50b. In this case, sintering of the cover layer 50 as a whole is promoted during firing, and the cover layer 50 after firing becomes highly dense. As a result, high adhesion can be obtained between the cover layer 50 and other layers. In addition, the higher sintering temperature of the filler material 50b suppresses the sintering of the filler material 50b during batch firing, maintaining the shape of the filler material 50b and enabling the shape of the cover layer 50 to be maintained.

[0044] From the viewpoint of improving the adhesion of the cover layer 50, it is preferable that the glass material 50a has a common structure with the oxide-based solid electrolyte that is the main component of the solid electrolyte layer 30, the oxide-based solid electrolyte contained in the first internal electrode 10, and the oxide-based solid electrolyte contained in the second internal electrode 20. For example, it is preferable that the glass material 50a has a NASICON-type crystal structure. It is also preferable that the glass material 50a has the same composition as the oxide-based solid electrolyte that is the main component of the solid electrolyte layer 30. Furthermore, it is preferable that the glass material 50a has the same composition as the solid electrolyte contained in the first internal electrode 10. Furthermore, it is preferable that the glass material 50a has the same composition as the solid electrolyte contained in the second internal electrode 20. As the glass material 50a, for example, Li-Al-Ge-PO4-based material (LAGP), Li-Al-Zr-PO4-based material, Li-Al-Ti-PO4-based material, etc. can be used. For example, the glass material 50a has a melting point of 500°C or higher and 700°C or lower.

[0045] If the proportion of filler material 50b in the cover layer 50 is small, the cover layer 50 may not achieve sufficient moisture resistance. Therefore, it is preferable to set a lower limit on the proportion of filler material 50b in the cover layer 50. For example, glass material 50a and Filler material 50b The volume ratio of the filler material 50b to the total volume is preferably 5 vol% or more, preferably 10 vol% or more, more preferably 20 vol% or more, and even more preferably 30 vol% or more. The volume ratio is determined by performing FIB processing on the cross section of the all-solid-state battery 100, then observing it with an SEM, and repeating the FIB processing and SEM observation to obtain a cross-sectional image of the entire cover layer 50 of the all-solid-state battery 100, and then processing these images to construct a three-dimensional structure. Since a clear contrast ratio is generated between the filler material 50b and the glass material 50a in the SEM image, the volume ratio of the filler material 50b can be calculated based on the brightness and darkness.

[0046] On the other hand, if the proportion of filler material 50b in the cover layer 50 is large, sufficient adhesion to the cover layer 50 may not be obtained. Therefore, it is preferable to set an upper limit on the proportion of filler material 50b in the cover layer 50. For example, glass material 50a and Filler material 50b The volume ratio of the filler material 50b to the total volume is preferably 70 vol% or less, more preferably 60 vol% or less, and even more preferably 50 vol% or less.

[0047] The thickness of the cover layer 50 is, for example, between 5 μm and 500 μm, between 10 μm and 400 μm, or between 15 μm and 300 μm. The thickness of the cover layer 50 can be measured, for example, as the average value of the thicknesses of 10 different points in one layer.

[0048] Next, we will explain the manufacturing method of the all-solid-state battery 100a illustrated in Figure 2. Figure 5 is a diagram illustrating the flow of the manufacturing method of the all-solid-state battery 100a.

[0049] (Process for preparing raw material powder for the solid electrolyte layer) First, a raw material powder for the solid electrolyte layer that constitutes the solid electrolyte layer 30 described above is prepared. For example, a raw material powder for an oxide-based solid electrolyte can be prepared by mixing raw materials, additives, etc., and using a solid-phase synthesis method. The obtained raw material powder can be adjusted to the desired average particle size by dry grinding. For example, the desired average particle size can be adjusted using a planetary ball mill with 5 mmφ ZrO2 balls.

[0050] (Process for preparing raw material powder for the cover layer) First, the raw material powders for the ceramics that make up the cover layer 50 are prepared. For example, raw materials and additives can be mixed and a solid-phase synthesis method can be used to prepare the raw material powders for the cover layer. The raw material powders include the raw material powders for the glass material 50a and the raw material powders for the filler material 50b.

[0051] (Process for preparing electrode layer paste) Next, internal electrode pastes for fabricating the first internal electrode 10 and the second internal electrode 20 described above are prepared individually. For example, an internal electrode paste can be obtained by uniformly dispersing a conductive additive, electrode active material, solid electrolyte material, sintering aid, binder, plasticizer, etc., in water or an organic solvent. The solid electrolyte paste described above may be used as the solid electrolyte material. Carbon materials may be used as the conductive additive. Metals may also be used as the conductive additive. Examples of metals used as conductive additives include Pd, Ni, Cu, Fe, and alloys containing these. Pd, Ni, Cu, Fe, alloys containing these, and various carbon materials may be used further.

[0052] The paste for internal electrodes contains, for example, one or more glass components such as Li-BO compounds, Li-Si-O compounds, Li-CO compounds, Li-SO compounds, and Li-PO compounds as sintering aids.

[0053] (Process for preparing paste for external electrodes) Next, an external electrode paste is prepared for the fabrication of the first external electrode 40a and the second external electrode 40b described above. For example, an external electrode paste can be obtained by uniformly dispersing a conductive material, glass frit, binder, plasticizer, etc., in water or an organic solvent.

[0054] (Solid electrolyte green sheet manufacturing process) A solid electrolyte slurry having a desired average particle size is obtained by uniformly dispersing raw material powder for the solid electrolyte layer in an aqueous solvent or organic solvent together with a binder, dispersant, plasticizer, etc., and then performing wet grinding. At this time, a bead mill, wet jet mill, various kneaders, high-pressure homogenizer, etc. can be used, and it is preferable to use a bead mill from the viewpoint that particle size distribution adjustment and dispersion can be performed simultaneously. A binder is added to the obtained solid electrolyte slurry to obtain a solid electrolyte paste. A solid electrolyte green sheet 51 can be produced by coating with the obtained solid electrolyte paste. The coating method is not particularly limited, and a slot die method, reverse coating method, gravure coating method, bar coating method, doctor blade method, etc. can be used. The particle size distribution after wet grinding can be measured, for example, using a laser diffraction measuring device using the laser diffraction scattering method.

[0055] (Lamination process) As illustrated in Figure 6(a), an internal electrode paste 52 is printed on one surface of a solid electrolyte green sheet 51. An inverse pattern 53 is printed on the areas of the solid electrolyte green sheet 51 where the internal electrode paste 52 is not printed. The same material as the solid electrolyte green sheet 51 can be used as the inverse pattern 53. Multiple printed solid electrolyte green sheets 51 are stacked alternately with a slight offset. As illustrated in Figure 6(b), a laminate is obtained by pressing a cover sheet 54 onto the top and bottom of the stacking direction. In this case, a laminate with a roughly rectangular parallelepiped shape is obtained such that the internal electrode paste 52 for the first internal electrode 10 is exposed on one end face and the internal electrode paste 52 for the second internal electrode 20 is exposed on the other end face. The cover sheet 54 can be formed by coating the raw material powder for the cover layer using the same method as in the solid electrolyte green sheet manufacturing process. The cover sheet 54 is formed to be thicker than the solid electrolyte green sheet 51. The coating can be made thicker during application, or by layering multiple coated sheets.

[0056] Next, the external electrode paste 55 is applied to each of the two end faces using a dipping method or the like, and then dried. This yields a molded body for forming the all-solid-state battery 100a.

[0057] (Firing process) Next, the obtained ceramic laminate is fired. The firing conditions are under an oxidizing or non-oxidizing atmosphere, and the maximum temperature is preferably 400°C to 1000°C, more preferably 500°C to 900°C, but there are no particular limitations. To sufficiently remove the binder before reaching the maximum temperature, a step may be included in which the laminate is held at a temperature lower than the maximum temperature in an oxidizing atmosphere. To reduce process costs, it is desirable to fire at the lowest possible temperature. After firing, a re-oxidation treatment may be performed. Through the above steps, an all-solid-state battery 100a is produced.

[0058] Furthermore, by sequentially layering the internal electrode paste, the current collector paste containing a conductive material, and the internal electrode paste, a current collector layer can be formed within the first internal electrode 10 and the second internal electrode 20.

[0059] According to the manufacturing method of this embodiment, since the filler material 50b has a plate-like shape rather than a roughly circular granular shape, each filler material 50b is oriented during firing of the cover layer 50. As a result, the cover layer 50 can maintain its shape against shrinkage during firing of the first internal electrode 10, the second internal electrode 20, and the solid electrolyte layer 30. Furthermore, the filler material 50b has insulating properties. Therefore, the cover layer 50 itself becomes moisture-resistant. [Examples]

[0060] (Example 1) Alumina with a plate-like form, an average thickness t of 0.5 μm, a D50% diameter of 10 μm, an average aspect ratio of 20, and a maximum width w of 50 μm was used as the filler material. Li-Al-Ge-PO glass was pulverized in a wet ball mill until the D50% diameter was 1.5 μm and used as the glass material. The filler material and glass material were mixed in a volume ratio of 30:70 and uniformly dispersed in water or an organic solvent along with a binder, dispersant, plasticizer, etc., to obtain a slurry. The obtained slurry was coated to produce a green sheet of the desired thickness. Cover sheets were placed on the top and bottom layers of a laminate of solid electrolyte sheets on which each electrode was printed, and pressed together to obtain a ceramic laminate. This ceramic laminate was degreased by heat treatment and fired.

[0061] No interlayer delamination due to heat treatment was observed in any of the layers. Observation of the cross-sectional SEM image after heat treatment revealed that plate-like alumina filler particles were dispersed in a state oriented in the in-plane direction of the cover layer, and LAGP sintered on the surface, functioning as an adhesive between the alumina fillers. In addition, the LAGP in the cover layer sintered with the LAGP in each electrode layer and solid electrolyte layer, improving the adhesion between the cover layer and the electrode layer, and between the cover layer and the solid electrolyte layer. Furthermore, by mixing a small amount of filler material (30 vol%) compared to the glass material, LAGP sintered frequently around the alumina fillers, forming a cover layer with high density.

[0062] (Example 2) Boron nitride with a plate-like form, an average thickness t of 0.5 μm, a D50% diameter of 7 μm, an average aspect ratio of 14, and a maximum width w of 50 μm was used as the filler material. Li-Al-Ge-PO glass was pulverized in a wet ball mill until the D50% diameter was 1.5 μm and used as the glass material. The filler material and glass material were mixed in a volume ratio of 30:70 and uniformly dispersed in water or an organic solvent along with a binder, dispersant, plasticizer, etc., to obtain a slurry. The obtained slurry was coated to produce a green sheet of the desired thickness. Cover sheets were placed on the top and bottom layers of a laminate of solid electrolyte sheets on which each electrode was printed, and pressed together to obtain a ceramic laminate. This ceramic laminate was degreased by heat treatment and fired.

[0063] No interlayer delamination due to heat treatment was observed in any of the layers. Observation of cross-sectional SEM images after heat treatment revealed that the plate-like boron nitride filler particles were dispersed in an in-plane orientation within the cover layer, and LAGP sintered on the surface, functioning as an adhesive between the boron nitride fillers. Furthermore, the LAGP in the cover layer sintered with the LAGP in each electrode layer and the solid electrolyte layer, improving the adhesion between the cover layer and the electrode layer, and between the cover layer and the solid electrolyte layer. In addition, by mixing a smaller amount of filler material (30 vol%) than the glass material, LAGP sintered frequently around the alumina filler, forming a highly dense cover layer.

[0064] (Example 3) Boron nitride with a plate-like form, an average thickness t of 0.5 μm, a D50% diameter of 10 μm, an average aspect ratio of 20, and a maximum width w of 50 μm was used as the filler material. Li-Al-Ge-PO glass was pulverized in a wet ball mill until the D50% diameter was 1.5 μm and used as the glass material. The filler material and glass material were mixed in a volume ratio of 70:30 and uniformly dispersed in water or an organic solvent along with a binder, dispersant, plasticizer, etc., to obtain a slurry. The obtained slurry was coated to produce a green sheet of the desired thickness. Cover sheets were placed on the top and bottom layers of a laminate of solid electrolyte sheets on which each electrode was printed, and pressed together to obtain a ceramic laminate. This ceramic laminate was degreased by heat treatment and fired.

[0065] No interlayer delamination due to heat treatment was observed in any of the layers. Observation of cross-sectional SEM images after heat treatment revealed that the plate-like boron nitride filler particles were dispersed in a state oriented in the in-plane direction of the cover layer, and LAGP sintered on the surface, functioning as an adhesive between the boron nitride fillers. In addition, the LAGP in the cover layer sintered with the LAGP in each electrode layer and the solid electrolyte layer, improving the adhesion between the cover layer and the electrode layer, and between the cover layer and the solid electrolyte layer.

[0066] (Comparative Example 1) Alumina with an irregular shape (not a plate shape) and a D50% diameter of 3 μm was used as the filler material. Li-Al-Ge-PO glass was pulverized in a wet ball mill until the D50% diameter was 1.5 μm and used as the glass material. The filler material and glass material were mixed in a volume ratio of 30:70 and uniformly dispersed in water or an organic solvent along with a binder, dispersant, plasticizer, etc., to obtain a slurry. The obtained slurry was coated to produce a green sheet of the desired thickness. Cover sheets were placed on the top and bottom layers of a laminate of solid electrolyte sheets, each with an electrode printed on it, and pressed together to obtain a ceramic laminate. This ceramic laminate was degreased by heat treatment and fired.

[0067] (Moisture resistance test) The moisture resistance of the cover layer was evaluated for Examples 1-3 and Comparative Example 1. Specifically, to evaluate the moisture resistance of the cover layer, a constant temperature chamber was set to 85°C and 85% humidity, and the all-solid-state battery was placed in the chamber for one week to conduct a moisture resistance test. As a result, if the shape did not change at all, it was judged that the moisture resistance was good ("○"). If it became difficult to maintain the shape, it was judged that the moisture resistance was poor ("×"). The results are shown in Table 1. [Table 1]

[0068] As shown in Table 1, Examples 1 to 3 were judged to have good moisture resistance ("○"). This is thought to be because the use of plate-shaped filler material caused each filler material to orient itself during the firing of the cover layer, thus maintaining the shape of the cover layer. On the other hand, Comparative Example 1 was judged to have poor moisture resistance ("×"). This is thought to be because the use of irregularly shaped filler material caused each filler material to not orient itself, resulting in the cover layer not being able to maintain its shape.

[0069] (Adhesion test) The adhesion of the cover layer was evaluated for Examples 1-3 and Comparative Example 1. Specifically, a peel resistance test was conducted to determine the adhesion of the cover layer. The peel resistance test was performed by attaching an adhesive tape to the cover layer and rapidly and forcefully peeling it off. As a result, if no residue remained on the tape, the adhesion was judged to be good ("○"). If a small amount of residue remained on the tape, the adhesion was judged to be moderately good ("△"). If most of the residue remained on the tape, the adhesion was judged to be poor ("×"). The results are shown in Table 1.

[0070] Examples 1 and 2 were judged to have good adhesion ("○"). This is thought to be because the cover layer contained a large amount of glass material. Example 3 was judged to have moderately good adhesion ("△"). This is thought to be because the amount of glass material in the cover layer was reduced.

[0071] Although embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention as described in the claims. [Explanation of symbols]

[0072] 10 1st internal electrode 20 Second internal electrode 30 Solid electrolyte layer 40a First external electrode 40b 2nd external electrode 50 Cover Layer 50a Glass material 50b Filler material 51 Solid Electrolyte Green Sheet 52 Paste for internal electrodes 53 Reverse Pattern 54 Cover Sheets 55 Paste for external electrodes 60-layer chip 100,100a all solid state battery

Claims

1. A laminate in which a solid electrolyte layer containing a NASICON-type solid electrolyte and an electrode layer containing a NASICON-type solid electrolyte and an electrode active material are alternately stacked, The laminate comprises a cover layer provided on at least one of the upper and lower surfaces in the stacking direction, which contains a NASICON-type solid electrolyte, The cover layer comprises an all-solid-state battery containing a filler material that is insulating and has a plate-like shape.

2. The all-solid-state battery according to claim 1, wherein the average thickness of the multiple filler materials is 0.05 μm or more and 1 μm or less, the D50% diameter is 1 μm or more and 50 μm or less, and the average aspect ratio is 3 or more and 500 or less.

3. The all-solid-state battery according to claim 1 or claim 2, wherein the filler material is oriented in the in-plane direction of the cover layer.

4. The conductivity of the filler material, including its electronic and ionic conductivity, is 10 －８ A solid-state battery according to claim 1 or claim 2, wherein the S / cm is less than or equal to S.

5. The all-solid-state battery according to claim 1 or claim 2, wherein the filler material is alumina or boron nitride.

6. The all-solid-state battery according to claim 1 or 2, wherein the NASICON-type solid electrolyte contained in the cover layer has a lower sintering temperature than the filler material.

7. The all-solid-state battery according to claim 1 or claim 2, wherein the NASICON-type solid electrolyte included in the cover layer is sintered with the NASICON-type solid electrolyte included in the solid electrolyte layer and the NASICON-type solid electrolyte included in the electrode layer.

8. The all-solid-state battery according to claim 1 or claim 2, wherein the NASICON-type solid electrolyte contained in the cover layer has a melting point of 500°C or higher and 700°C or lower.

9. The all-solid-state battery according to claim 1 or claim 2, wherein the cover layer has a volume ratio of 5 vol% or more and 60 vol% or less with respect to the NASICON-type solid electrolyte contained in the cover layer.

10. The all-solid-state battery according to claim 1 or 2, wherein the NASICON-type solid electrolyte contained in the cover layer has the same composition as the NASICON-type solid electrolyte contained in the solid electrolyte layer.

11. The all-solid-state battery according to claim 1 or claim 2, wherein the NASICON-type solid electrolyte contained in the cover layer has the same composition as the NASICON-type solid electrolyte contained in the electrode layer.

12. A preparation step of preparing a ceramic laminate in which a cover sheet containing NASICON-type solid electrolyte powder and an insulating, plate-shaped filler material is laminated on at least one of the upper and lower surfaces in the lamination direction of a laminate in which a solid electrolyte green sheet containing NASICON-type solid electrolyte powder and an internal electrode pattern containing NASICON-type solid electrolyte powder and electrode active material powder are alternately laminated, A method for manufacturing an all-solid-state battery, comprising a firing step of firing the ceramic laminate.

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