JP7748164B2 - All-solid-state battery and method for manufacturing the same - Google Patents

Description

The present invention relates to an all-solid-state battery and a manufacturing method thereof.

Demand for secondary batteries has expanded rapidly in recent years, and lithium-ion secondary batteries using organic electrolytes have been put to practical use. However, due to concerns about electrolyte leakage and other issues, expectations are growing 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 battery units, techniques have been disclosed for providing cover layers above and below the stacking direction of the all-solid-state battery (see, for example, Patent Documents 1 and 2).

Japanese Patent Application Laid-Open No. 2021-82522 Japanese Patent Application Laid-Open No. 2020-149782 International Publication No. 2018/181545

It is desirable for the cover layer to be composed of a material that does not interdiffuse with the solid electrolyte layer during firing, and therefore in Patent Documents 1 and 2, a material with the same composition as the solid electrolyte layer is used for the cover layer material. However, in stacked all-solid-state batteries, in addition to the cover layer and solid electrolyte layer, numerous layers made primarily of different materials, such as positive electrode layers, negative electrode layers, and reverse pattern layers, are stacked. If such stacked all-solid-state batteries are to be co-fired, there is a concern that delamination may occur due to differences in the shrinkage behavior of each layer.

In Patent Document 3, a moisture-proof layer is provided in contact with the laminate to prevent a decrease in battery capacity due to a reaction between the active material contained in the electrode layer and moisture. However, in Patent Document 3, the moisture-proof layer is provided using a method such as spray coating or dip coating after the laminate is fired, and the moisture-proof properties of the laminate before the moisture-proof layer is formed are not guaranteed.

The present invention was developed in consideration of the above-mentioned problems, and aims to provide an all-solid-state battery equipped with a moisture-proof cover layer that can suppress delamination during batch firing, and a method for manufacturing the same.

The all-solid-state battery according to the present invention comprises a laminated structure in which ion-conductive oxide-based solid electrolyte layers and electrode layers 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 laminated structure, the cover layer including an oxide-based solid electrolyte and an insulating filler material having a higher sintering temperature than the oxide-based solid electrolyte.

In the cover layer of the above-mentioned all-solid-state battery, the volume ratio of the filler material to the oxide-based solid electrolyte may be 10 vol% or more.

In the all-solid-state battery, the filler material may have an electrical conductivity including electronic conductivity and ionic conductivity of 10 ⁻⁸ S/cm or less.

In the all-solid-state battery, the filler material may be alumina or _SiO2 glass.

In the above-mentioned all-solid-state battery, the shape of the filler material may have an average cross-sectional circularity of 0.6 or more.

In the above-mentioned all-solid-state battery, the D50% particle size of the filler material may be 0.5 μm or more and 8 μm or less.

In the above-described all-solid-state battery, between the oxide-based solid electrolyte layer and the cover layer, the D0% particle size in the particle size distribution of the solid electrolyte of one layer may be between the D0% particle size and the D10% particle size in the particle size distribution of the solid electrolyte of the other layer, and the D100% particle size in the particle size distribution of the solid electrolyte of the one layer may be between the D90% particle size and the D100% particle size in the particle size distribution of the solid electrolyte of the other layer.

In the above-mentioned all-solid-state battery, the oxide-based solid electrolyte of the cover layer may be a solid electrolyte with a NASICON crystal structure.

In the above-mentioned all-solid-state battery, the main component of the solid electrolyte layer may be a solid electrolyte with a NASICON crystal structure.

In the above-described all-solid-state battery, the oxide-based solid electrolyte of the cover layer may have the same composition as the main component of the solid electrolyte layer.

In the above-mentioned all-solid-state battery, the oxide-based solid electrolyte of the cover layer may be a glass material.

In the above-mentioned all-solid-state battery, the electrode layer may contain an oxide-based solid electrolyte having ion conductivity.

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 an oxide-based solid electrolyte powder and an insulating filler material having a higher sintering temperature than the oxide-based solid electrolyte powder is laminated on at least one of the upper and lower surfaces in the stacking direction of a laminate in which solid electrolyte green sheets containing an oxide-based solid electrolyte powder with ion conductivity and internal electrode patterns containing electrode active material powder are alternately stacked; and a firing step of firing the ceramic laminate.

In the above-described method for manufacturing an all-solid-state battery, the sintering temperature of the oxide-based solid electrolyte powder in the cover sheet may be lower than the firing temperature in the firing step, and the sintering temperature of the filler material may be higher than the firing temperature in the firing step.

The present invention provides an all-solid-state battery equipped with a moisture-proof cover layer that can suppress relative delamination during co-firing, and a method for manufacturing the same.

FIG. 1 is a schematic cross-sectional view showing the basic structure of an all-solid-state battery. FIG. 1 is a schematic cross-sectional view of a stacked-type all-solid-state battery. FIG. 1 is a schematic cross-sectional view of another stacked-type all-solid-state battery. FIG. 2 is a schematic cross-sectional view of a cover layer. FIG. 1 is a diagram illustrating a flow of a method for manufacturing an all-solid-state battery. 1A and 1B are diagrams illustrating a lamination process.

The following describes the embodiment with reference to the drawings.

(Embodiment)
Fig. 1 is a schematic cross-sectional view showing the basic structure of an all-solid-state battery 100. As illustrated in Fig. 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 a first main surface of the solid electrolyte layer 30. The second internal electrode 20 is formed on a second main surface of the solid electrolyte layer 30.

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 a positive electrode, and the other is used as a negative electrode. In this embodiment, as an example, the first internal electrode 10 is used as a positive electrode layer, and the second internal electrode 20 is used as a negative electrode layer.

The solid electrolyte layer 30 has a NASICON-type crystal structure and is primarily 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. A phosphate-based solid electrolyte having a NASICON-type crystal structure has high conductivity and is stable in air. The phosphate-based solid electrolyte is, for example, a phosphate containing lithium. The phosphate is not particularly limited, but examples include lithium phosphate complexes with Ti (e.g., _LiTi2 ( _PO4 ) ₃ ). Alternatively, Ti can be partially or completely substituted with tetravalent transition metals such as Ge, Sn, Hf, and Zr. Furthermore, to increase the Li content, Ti can be partially substituted with trivalent transition metals such as Al, Ga, In, Y, and La. More specifically, examples include Li1 _{+ xAlxGe2 -x} (PO4) ₃ , Li1 _{+ xAlxZr2} -x( _PO4 ) ₃ , and Li1+ _{xAlxTi2 - x} ( _PO4 ) ₃ . For example, a Li _-Al- Ge- _PO4 -based material to which the same transition metal as that contained in the phosphate having an olivine crystal structure contained in the first internal electrode 10 and the second internal electrode ₂₀ has been added in advance is preferred. For example, when the first internal electrode 10 and the second internal electrode 20 contain a phosphate containing Co and Li, it is preferred that the solid electrolyte layer 30 contains a Li-Al-Ge- _PO4 -based material to which Co has been added in advance. 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 solid electrolyte layer 30 contains a Li-Al-Ge-PO ₄ based material to which the transition metal has been added in advance.

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

A typical example of an electrode active material having an olivine crystal structure is _LiCoPO4 , which contains Co. Phosphates in which the transition metal Co is substituted in this chemical formula can also be used. Here, the ratio of Li and _PO4 can vary depending on the valence. Note that it is preferable to use Co, Mn, Fe, Ni, etc. as the transition metal.

An electrode active material with an olivine crystal structure acts as a positive electrode active material in the first internal electrode 10, which acts as a positive electrode. For example, if only the first internal electrode 10 contains an electrode active material with an olivine crystal structure, that electrode active material acts as a positive electrode active material. If the second internal electrode 20 also contains an electrode active material with an olivine crystal structure, the second internal electrode 20, which acts as a negative electrode, exhibits the effects of increased discharge capacity and increased operating potential with discharge, which are presumed to be due to the formation of a partial solid solution with the negative electrode active material, although the mechanism of action is not fully understood.

When both the first internal electrode 10 and the second internal electrode 20 contain an electrode active material having an olivine crystal structure, the respective electrode active materials preferably contain transition metals that may be the same or different. "May be the same or different" 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 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 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. By containing the same type of transition metal or electrode active material of the same composition in the first internal electrode 10 and the second internal electrode 20, the similarity in the compositions of the two internal electrode layers is increased. This 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 attached in the wrong direction.

The second internal electrode 20 contains a negative electrode active material. By including a negative electrode active material in only one electrode, it becomes clear that the one electrode functions as a negative electrode and the other electrode functions as a positive electrode. It is also possible to include a material known as a negative electrode active material in both electrodes. For the negative electrode active material of the electrode, reference can be made to conventional secondary battery technology, and examples include compounds such as titanium oxide, lithium titanium composite oxide, lithium titanium composite phosphate, carbon, and lithium vanadium phosphate.

When producing the first internal electrode 10 and the second internal electrode 20, in addition to these electrode active materials, a solid electrolyte with ion conductivity 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 a carbon material or the like. The conductive additive may also include a metal. Metals that can be 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 the same as the main solid electrolyte of the solid electrolyte layer 30, for example.

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 thickness of the first internal electrode 10 and the second internal electrode 20 is, 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 thickness of 10 different points on one layer.

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

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 assigned the same reference numerals and detailed description will be omitted.

In the all-solid-state battery 100a, multiple first internal electrodes 10 and multiple second internal electrodes 20 are alternately stacked with solid electrolyte layers 30 interposed between them. The edges of the multiple first internal electrodes 10 are exposed at the first end face of the stacked chip 60 but not at the second end face. The edges of the multiple second internal electrodes 20 are exposed at the second end face of the stacked chip 60 but not at the first end face. As a result, the first internal electrodes 10 and second internal electrodes 20 are alternately electrically connected 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. In this way, the all-solid-state battery 100a has a structure in which multiple battery units are stacked.

A cover layer 50 is laminated on the upper surface of the laminated structure of the first internal electrode 10, solid electrolyte layer 30, and second internal electrode 20. The cover layer 50 contacts the uppermost internal electrode (either the first internal electrode 10 or the second internal electrode 20) and also contacts a portion of the solid electrolyte layer 30. A cover layer 50 is also laminated on the lower surface of the laminated structure. The cover layer 50 contacts the lowermost internal electrode (either the first internal electrode 10 or the second internal electrode 20) and also contacts a portion of the solid electrolyte layer 30.

The first internal electrode 10 and the second internal electrode 20 may each include a current collector layer. For example, as illustrated in FIG. 3, a first current collector layer 11 may be provided within the first internal electrode 10. Furthermore, 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 primarily composed of a conductive material. For example, metal, carbon, etc. may be used as the conductive material for the first current collector layer 11 and the second current collector layer 21. 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 improves current collection efficiency.

Stacked all-solid-state batteries such as the all-solid-state battery 100a in Figures 2 and 3 are made up of multiple stacked layers made primarily of different materials. Therefore, when attempting to collectively fire these layers, there is a risk of delamination occurring due to differences in the shrinkage behavior of each layer. Furthermore, to prevent a decrease in battery capacity caused by a reaction between the electrode active material contained in the electrode layer and moisture, it is necessary to provide moisture resistance to the stacked all-solid-state battery. Therefore, the cover layer 50 according to this embodiment has a moisture-proof configuration that can prevent delamination during collectively firing.

Figure 4 is a schematic diagram showing a cross section of the cover layer 50. As shown in Figure 4, the cover layer 50 contains an oxide-based solid electrolyte 50a and an insulating filler material 50b that has a higher sintering temperature than the solid electrolyte 50a. For example, particles of the solid electrolyte 50a and particles of the filler material 50b are randomly dispersed and arranged.

During the co-firing, the solid electrolyte 50a contained in the cover layer 50 is sintered along with the solid electrolyte layer 30 and the solid electrolyte contained in the electrode layer that the cover layer 50 is in contact with, thereby achieving high adhesion between the cover layer 50 and the solid electrolyte layer 30 and the electrode layer that the cover layer 50 is in contact with. This makes it possible to suppress delamination between the layers.

Furthermore, because the sintering temperature of the filler material 50b contained in the cover layer 50 is higher than that of the solid electrolyte 50a, the filler material 50b does not sinter or grow during co-firing, thereby maintaining the particle shape of the filler material 50b. This suppresses in-plane shrinkage of the cover layer 50 and suppresses or absorbs the stress or strain caused by differences in the shrinkage behavior of each layer, thereby controlling delamination.

Furthermore, since the filler material 50b in the cover layer 50 has insulating properties, the cover layer 50 provides moisture resistance.

For these reasons, the cover layer 50 according to this embodiment can suppress delamination during co-firing and also achieve moisture resistance.

For example, the filler material 50b may be alumina (Al ₂ O ₃ ), SiO ₂ glass, ZrO ₂ or the like.

If the particle size of the filler material 50b is too small, the filler particles may form agglomerates, which may cause voids when co-fired with the solid electrolyte 50a. Therefore, it is preferable to set a lower limit for the D50% particle size of the filler material 50b. For example, the D50% particle size of the filler material 50b is preferably 0.5 μm or more, more preferably 1.0 μm or more, and even more preferably 2.0 μm or more. The particle size of the filler material 50b can be measured in the powder stage using a particle size distribution measuring device that utilizes laser diffraction/scattering, and can be measured by image analysis of SEM images after firing.

If the particle size of the filler material 50b is too large, the filler particles will be larger than the thickness of one cover sheet layer, which may result in an unsmooth sheet. Therefore, it is preferable to set an upper limit on the D50% particle size of the filler material 50b. For example, the D50% particle size of the filler material 50b is preferably 8 μm or less, more preferably 6 μm or less, and even more preferably 4 μm or less.

From the perspective of achieving high adhesion between the cover layer 50 and the solid electrolyte layer 30 and electrode layer that the cover layer 50 is in contact with, it is preferable that the filler material 50b have an irregular shape. If the particles of the filler material 50b present on the surface that contacts the solid electrolyte layer 30 and electrode layer are spherical, they will come into point contact with the solid electrolyte layer 30 and electrode layer, whereas if the particles of the filler material 50b are irregular, they will come into surface contact with the solid electrolyte layer 30 and electrode layer more frequently, further improving adhesion. In this case, "irregular shape" means that the shape of the filler material 50b has an average cross-sectional circularity of 0.6 or more.

If the amount of filler material 50b in the cover layer 50 is small, sufficient moisture resistance may not be achieved. Therefore, it is preferable to set a lower limit on the amount of filler material 50b in the cover layer 50. For example, if the total volume of the solid electrolyte 50a and filler material 50b in the cover layer 50 is 100 vol%, the ratio of filler material 50b is preferably 10 vol% or more, more preferably 20 vol% or more, and even more preferably 30 vol% or more. Regarding the volume ratio, a cross-section of the all-solid-state battery 100 is subjected to FIB processing and then observed with an SEM. By repeating the FIB processing and SEM observation, a cross-sectional image of the entire cover layer 50 of the all-solid-state battery 100 is obtained, and this is then image-processed to construct a three-dimensional structure. Because the contrast ratio between the filler material 50b and the glass material is clearly evident in the SEM image, the volume ratio of the filler material 50b can be calculated based on light and dark.

On the other hand, if the amount of filler material 50b in the cover layer 50 is large, the amount of solid electrolyte 50a will be small, and sufficient adhesion may not be achieved. Therefore, it is preferable to set an upper limit on the amount of filler material 50b in the cover layer 50. For example, if the total volume of the solid electrolyte 50a and filler material 50b in the cover layer 50 is 100 vol%, the ratio of filler material 50b is preferably 80 vol% or less, more preferably 70 vol% or less, and even more preferably 65 vol% or less.

From the viewpoint of obtaining sufficient moisture resistance, the filler material 50b preferably has sufficient insulating properties. For example, the conductivity of the filler material 50b, including electronic conductivity and ionic conductivity, is preferably 10 ⁻⁸ S/cm or less, more preferably 10 ⁻¹² S/cm or less, and even more preferably 10 ⁻¹⁴ S/cm or less.

From the perspective of improving the adhesion of the cover layer 50, it is preferable that the solid electrolyte 50a have a structure common to 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 solid electrolyte 50a have a NASICON-type crystal structure. It is also preferable that the solid electrolyte 50a have the same composition as the oxide-based solid electrolyte that is the main component of the solid electrolyte layer 30. It is also preferable that the solid electrolyte 50a be a glass material.

Furthermore, by having the particle size distribution of the solid electrolyte 50a in the cover layer 50 and the particle size distribution of the oxide-based solid electrolyte in the solid electrolyte layer 30 be similar, the timing of softening of the solid electrolyte particles in each layer is synchronized during co-firing, facilitating sintering between the layers. Therefore, it is preferable that the solid electrolyte 50a in the cover layer 50 have a particle size distribution that is similar to that of the oxide-based solid electrolyte, the main component, in the solid electrolyte layer 30. For example, a similar particle size distribution is defined as a state in which the D0% particle size in the particle size distribution of the solid electrolyte in one layer falls between the D0% and D10% particle sizes in the particle size distribution of the solid electrolyte in the other layer, and the D100% particle size in the particle size distribution of the solid electrolyte in the other layer falls between the D90% and D100% particle sizes in the particle size distribution of the solid electrolyte in the other layer.

The thickness of the cover layer 50 is, for example, 5 μm or more and 100 μm or less, 10 μm or more and 85 μm or less, or 15 μm or more and 70 μm or less. The thickness of the cover layer 50 can be measured, for example, as the average thickness of 10 different points on one layer.

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.

(Process for producing raw material powder for solid electrolyte layer)
First, raw material powder for the solid electrolyte layer that constitutes the above-described solid electrolyte layer 30 is prepared. For example, raw materials, additives, etc. are mixed and a solid-phase synthesis method or the like is used to prepare raw material powder for an oxide-based solid electrolyte. The obtained raw material powder can be dry-pulverized to adjust the average particle size to a desired value. For example, the desired average particle size is adjusted using a planetary ball mill with 5 mm diameter _ZrO2 balls.

(Cover layer raw material powder preparation process)
First, a ceramic raw material powder for the cover layer 50 is prepared. For example, raw materials, additives, etc. are mixed and the raw material powder for the cover layer can be prepared using a solid-phase synthesis method or the like. The raw material powder includes raw material powder for the solid electrolyte 50a and raw material powder for the filler material 50b. The obtained raw material powder can be adjusted to a desired average particle size by dry milling. For example, the desired average particle size can be adjusted using a planetary ball mill with 5 mm diameter _ZrO2 balls.

(Electrode layer paste preparation process)
Next, internal electrode pastes for producing the first internal electrode 10 and the second internal electrode 20 are individually prepared. For example, the internal electrode pastes can be obtained by uniformly dispersing a conductive additive, an electrode active material, a solid electrolyte material, a sintering additive, a binder, a plasticizer, etc. in water or an organic solvent. The solid electrolyte paste described above may be used as the solid electrolyte material. A carbon material or the like may be used as the conductive additive. A metal may be used as the conductive additive. Examples of metals for the conductive additive include Pd, Ni, Cu, Fe, and alloys containing these. Pd, Ni, Cu, Fe, alloys containing these, and various carbon materials may also be used.

The sintering aid in the internal electrode paste contains one or more glass components, such as Li-B-O compounds, Li-Si-O compounds, Li-C-O compounds, Li-S-O compounds, and Li-P-O compounds.

(External electrode paste preparation process)
Next, an external electrode paste for producing the first external electrode 40 a and the second external electrode 40 b is prepared. For example, the external electrode paste can be obtained by uniformly dispersing a conductive material, glass frit, a binder, a plasticizer, etc. in water or an organic solvent.

(Solid electrolyte green sheet manufacturing process)
The raw material powder for the solid electrolyte layer is uniformly dispersed in an aqueous or organic solvent along with a binder, dispersant, plasticizer, etc., and then wet-pulverized to obtain a solid electrolyte slurry having a desired average particle size. A bead mill, wet jet mill, various kneaders, high-pressure homogenizer, etc. can be used for this process. A bead mill is preferred because it allows for simultaneous adjustment of particle size distribution and dispersion. A binder is added to the resulting solid electrolyte slurry to obtain a solid electrolyte paste. The resulting solid electrolyte paste can be coated to produce a solid electrolyte green sheet 51. The coating method is not particularly limited, and includes slot die coating, reverse coating, gravure coating, bar coating, doctor blade coating, etc. The particle size distribution after wet-pulverization can be measured, for example, using a laser diffraction measurement device employing a laser diffraction scattering method.

(Lamination process)
As illustrated in FIG. 6( a), an internal electrode paste 52 is printed on one side of a solid electrolyte green sheet 51. A reverse pattern 53 is printed on the areas of the solid electrolyte green sheet 51 where the internal electrode paste 52 is not printed. The reverse pattern 53 may be the same as the solid electrolyte green sheet 51. After printing, multiple solid electrolyte green sheets 51 are stacked with alternating offsets. As illustrated in FIG. 6( b), a laminate is obtained by pressing cover sheets 54 from above and below in the stacking direction. In this case, a laminate having a substantially rectangular parallelepiped shape is obtained, with the internal electrode paste 52 for the first internal electrode 10 exposed on one end surface and the internal electrode paste 52 for the second internal electrode 20 exposed on the other end surface. The cover sheet 54 can be formed by applying raw material powder for the cover layer using a method similar to that used in the solid electrolyte green sheet preparation process. The cover sheet 54 is formed thicker than the solid electrolyte green sheet 51. The thickness may be increased during coating, or by stacking multiple coated sheets.

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

(Firing process)
Next, the obtained ceramic laminate is fired. Firing conditions include, but are not limited to, an oxidizing atmosphere or a non-oxidizing atmosphere, with a maximum temperature of preferably 400°C to 1000°C, more preferably 500°C to 900°C. A step of maintaining the temperature in an oxidizing atmosphere at a temperature lower than the maximum temperature may be provided in order to sufficiently remove the binder before the maximum temperature is reached. Firing at as low a temperature as possible is desirable to reduce process costs. After firing, a reoxidation treatment may be performed. Through the above steps, an all-solid-state battery 100a is produced.

In addition, by sequentially stacking an internal electrode paste, a collector paste containing a conductive material, and an internal electrode paste, a collector layer can be formed within the first internal electrode 10 and the second internal electrode 20.

In the manufacturing method according to this embodiment, the solid electrolyte 50a contained in the cover layer 50 is sintered during the firing process, along with the solid electrolyte contained in the solid electrolyte layer 30 and electrode layer that the cover layer 50 is in contact with. This results in high adhesion between the cover layer 50 and the solid electrolyte layer 30 and electrode layer that it is in contact with. This makes it possible to suppress delamination between the layers.

In addition, because the sintering temperature of the filler material 50b contained in the cover layer 50 is higher than the sintering temperature of the solid electrolyte 50a, the filler material 50b does not sinter or grow during co-firing, maintaining the particle shape of the filler material 50b. This prevents in-plane shrinkage of the cover layer 50, suppressing deformation of the cover layer 50 and preventing delamination.

Furthermore, since the filler material 50b in the cover layer 50 has insulating properties, moisture resistance is achieved by the cover layer 50, which suppresses shape change.

The sintering temperature of the raw material powder of the solid electrolyte 50a is preferably lower than the firing temperature in the firing process, and the sintering temperature of the filler material 50b is preferably higher than the firing temperature in the firing process. In this case, sintering the solid electrolyte 50a improves the adhesion of the cover layer 50 and maintains the particle shape of the filler material 50b.

Example 1
Irregularly shaped alumina with a D50% particle size of 3 μm was used as the filler material. Li-Al-Ge-P-O-based glass (hereinafter referred to as LAGP-g), a solid electrolyte obtained by melt quenching, was ground to a D50% particle size of 1.5 μm using a wet ball mill. The filler material and solid electrolyte were mixed at 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 resulting slurry was applied to fabricate a cover sheet with the desired thickness. A ceramic laminate was obtained by placing cover sheets on the top and bottom layers of a stack of solid electrolyte green sheets with printed electrodes and pressing them together. This ceramic laminate was degreased and fired by heat treatment.

No delamination due to heat treatment was observed in any of the layers. Observation of cross-sectional SEM images after heat treatment revealed that LAGP-g had sintered on the surface of the irregularly shaped alumina filler particles, functioning as an adhesive between the alumina fillers. Furthermore, the LAGP-g in the cover layer had sintered with the LAGP-g in each electrode layer and solid electrolyte layer, improving adhesion between the cover layer and electrode layer, and between the cover layer and solid electrolyte layer.

Example 2
Irregularly shaped _SiO2 glass with a D50% particle size of 3 μm was used as the filler material. LAGP-g, a solid electrolyte obtained by melt quenching, was ground to a D50% particle size of 1.5 μm using a wet ball mill. The filler material and solid electrolyte were mixed at 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 resulting slurry was applied to fabricate a cover sheet of the desired thickness. Cover sheets were placed on the top and bottom layers of a stack of solid electrolyte green sheets with printed electrodes and pressed together to obtain a ceramic laminate. This ceramic laminate was degreased and fired by heat treatment.

No delamination due to heat treatment was observed in any of the layers. Observation of cross-sectional SEM images after heat treatment revealed that LAGP-g had sintered on the surface of the irregularly shaped _SiO2 glass filler particles, functioning as an adhesive between the _SiO2 glass fillers. Furthermore, LAGP-g in the cover layer had sintered with LAGP-g in each electrode layer and solid electrolyte layer, improving adhesion between the cover layer and electrode layer, and between the cover layer and solid electrolyte layer.

Example 3
Irregularly shaped alumina with a D50% particle size of 3 μm was used as the filler material. LAGP-g, a solid electrolyte obtained by melt quenching, was ground to a D50% particle size of 1.5 μm using a wet ball mill. The filler material and solid electrolyte were mixed at a volume ratio of 20:80 and uniformly dispersed in water or an organic solvent along with a binder, dispersant, plasticizer, etc. to obtain a slurry. The resulting slurry was applied to fabricate a cover sheet of the desired thickness. Cover sheets were placed on the top and bottom layers of a stack of solid electrolyte green sheets with printed electrodes and pressed together to obtain a ceramic laminate. This ceramic laminate was degreased and fired by heat treatment.

No delamination due to heat treatment was observed in any of the layers. Observation of cross-sectional SEM images after heat treatment revealed that LAGP-g had sintered on the surface of the irregularly shaped alumina filler particles, functioning as an adhesive between the alumina fillers. Furthermore, LAGP-g in the cover layer had sintered with LAGP-g in each electrode layer and solid electrolyte layer, improving adhesion between the cover layer and electrode layer, and between the cover layer and solid electrolyte layer.

Example 4
Spherical alumina with a D50% particle size of 3 μm was used as the filler material. LAGP-g, a solid electrolyte obtained by melt quenching, was ground to a D50% particle size of 1.5 μm using a wet ball mill. The filler material and solid electrolyte were mixed at 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 resulting slurry was applied to fabricate a cover sheet of the desired thickness. Cover sheets were placed on the top and bottom layers of a stack of solid electrolyte green sheets with printed electrodes and pressed together to obtain a ceramic laminate. This ceramic laminate was degreased and fired by heat treatment.

No delamination due to heat treatment was observed in any of the layers. Observation of cross-sectional SEM images after heat treatment revealed that LAGP-g had sintered on the surface of the irregularly shaped alumina filler particles, functioning as an adhesive between the alumina fillers. Furthermore, LAGP-g in the cover layer had sintered with LAGP-g in each electrode layer and solid electrolyte layer, improving adhesion between the cover layer and electrode layer, and between the cover layer and solid electrolyte layer.

Example 5
Irregularly shaped alumina with a D50% particle size of 3 μm was used as the filler material. LAGP-g, a solid electrolyte obtained by melt quenching, was ground to a D50% particle size of 1.5 μm using a wet ball mill. The filler material and solid electrolyte were mixed at 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 resulting slurry was applied to fabricate a cover sheet of the desired thickness. Cover sheets were placed on the top and bottom layers of a stack of solid electrolyte green sheets with printed electrodes and pressed together to obtain a ceramic laminate. This ceramic laminate was degreased and fired by heat treatment.

No delamination due to heat treatment was observed in any of the layers. Observation of cross-sectional SEM images after heat treatment revealed that LAGP-g had sintered on the surface of the irregularly shaped alumina filler particles, functioning as an adhesive between the alumina fillers. Furthermore, LAGP-g in the cover layer had sintered with LAGP-g in each electrode layer and solid electrolyte layer, improving adhesion between the cover layer and electrode layer, and between the cover layer and solid electrolyte layer.

Example 6
Irregularly shaped alumina with a D50% particle size of 3 μm was used as the filler material. LAGP-g, a solid electrolyte obtained by melt quenching, was ground to a D50% particle size of 1.5 μm using a wet ball mill. The filler material and solid electrolyte were mixed at a volume ratio of 10:90 and uniformly dispersed in water or an organic solvent along with a binder, dispersant, plasticizer, etc. to obtain a slurry. The resulting slurry was applied to fabricate a cover sheet of the desired thickness. A ceramic laminate was obtained by placing cover sheets on the top and bottom layers of a stack of solid electrolyte green sheets with printed electrodes and pressing them together. This ceramic laminate was degreased and fired by heat treatment.

No delamination due to heat treatment was observed in any of the layers. Observation of cross-sectional SEM images after heat treatment revealed that LAGP-g had sintered on the surface of the irregularly shaped alumina filler particles, functioning as an adhesive between the alumina fillers. Furthermore, LAGP-g in the cover layer had sintered with LAGP-g in each electrode layer and solid electrolyte layer, improving adhesion between the cover layer and electrode layer, and between the cover layer and solid electrolyte layer.

(Comparative Example 1)
LAGP-g, a solid electrolyte obtained by melt quenching, was pulverized in a wet ball mill to a D50% particle size of 1.5 μm and uniformly dispersed in water or an organic solvent together with a binder, dispersant, plasticizer, etc. to obtain a slurry. The resulting slurry was applied to produce a cover sheet of the desired thickness. In other words, no filler material was used. A ceramic laminate was obtained by placing cover sheets on the top and bottom layers of a stack of solid electrolyte green sheets on which each electrode had been printed and pressing them together. This ceramic laminate was then degreased and fired by heat treatment.

The LAGP-g in the cover layer sintered with the LAGP-g in each electrode layer and solid electrolyte layer, ensuring adhesion between the cover layer and electrode layer, and between the cover layer and solid electrolyte layer. However, because the cover layer did not contain filler material, it underwent significant in-plane shrinkage during heat treatment, making it difficult to maintain its shape.

(Comparative Example 2)
A slurry was obtained by uniformly dispersing irregularly shaped alumina with a D50% particle size of 3 μm in water or an organic solvent along with a binder, dispersant, plasticizer, etc. The resulting slurry was then coated to produce a cover sheet of the desired thickness. In other words, no solid electrolyte was used. A ceramic laminate was obtained by placing cover sheets on the top and bottom layers of a stack of solid electrolyte green sheets on which each electrode had been printed and then pressing them together. This ceramic laminate was then degreased and fired by heat treatment.

Because it does not contain glass material, the cover layer does not shrink even when heat treated, and adhesion to the electrode layers and solid electrolyte layer was not achieved.

(Adhesion test)
The adhesion of the cover layer was evaluated for Examples 1 to 4 and Comparative Examples 1 and 2. Specifically, a peel resistance test was conducted to evaluate the adhesion of the cover layer. The peel resistance test was conducted by attaching adhesive tape to the cover layer and then rapidly and forcefully peeling it off. As a result, if there was no adhesion on the tape, the adhesion was evaluated as good (◯). If there was a small amount of adhesion on the tape, the adhesion was evaluated as somewhat good (△). If most of the adhesion was on the tape, the adhesion was evaluated as poor (×). The results are shown in Table 1.

For Comparative Examples 1 and 2, the adhesion was judged to be poor (×). For Comparative Example 1, this is thought to be because the cover layer did not contain a filler material, making it unable to maintain its shape. For Comparative Example 2, this is thought to be because the cover layer did not contain a solid electrolyte, making it impossible to achieve good adhesion. In contrast, for Examples 1 to 4, the adhesion was judged to be good (◯) or somewhat good (△). This is thought to be because good adhesion was achieved by including both a solid electrolyte and a filler material in the cover layer. Note that the better adhesion in Examples 1 to 3 than in Example 4 is thought to be due to the use of an irregularly shaped filler material.

(Moisture-proof test)
The moisture resistance of the cover layer was evaluated for Examples 1 to 4 and Comparative Examples 1 and 2. Specifically, to evaluate the moisture resistance of the cover layer, a thermostatic chamber at 85°C was set to a humidity of 85%, and the all-solid-state battery was left standing in the thermostatic chamber for one week to perform a moisture resistance test. As a result, if there was no change in shape, the moisture resistance was evaluated as good (◯). If the shape was maintained but the cover surface was altered, the moisture resistance was evaluated as somewhat good (△). If it became difficult to maintain the shape, the moisture resistance was evaluated as poor (×).

For Comparative Examples 1 and 2, the moisture resistance was rated as poor (×). For Comparative Example 1, this is thought to be because the cover layer did not contain an insulating filler material. For Comparative Example 2, this is thought to be because the cover layer did not contain a solid electrolyte, preventing good adhesion. In contrast, for Examples 1 to 4, the moisture resistance was rated as good (◯) or somewhat good (△). This is thought to be because the cover layer, which provided good adhesion, contained an insulating filler material. The reason that Examples 1, 2, and 4 had better adhesion than Example 3 is thought to be because the volume ratio of the filler material to the solid electrolyte in the cover layer was 30 vol% or higher.

Although the 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 variations are possible within the scope of the gist of the present invention as set forth in the claims.

REFERENCE SIGNS LIST 10 First internal electrode 20 Second internal electrode 30 Solid electrolyte layer 40a First external electrode 40b Second external electrode 50 Cover layer 50a Solid electrolyte 50b Filler material 51 Solid electrolyte green sheet 52 Internal electrode paste 53 Reverse pattern 54 Cover sheet 55 External electrode paste 60 Laminated chip 100, 100a All-solid-state battery

Claims (14)

a laminated structure in which ion-conductive oxide-based solid electrolyte layers and electrode layers containing an electrode active material are alternately laminated;
a cover layer provided on at least one of an upper surface and a lower surface in a stacking direction of the laminated structure,
The cover layer is an all-solid-state battery including an oxide-based solid electrolyte and an insulating filler material having a higher sintering temperature than the oxide-based solid electrolyte. The all-solid-state battery described in claim 1, wherein the volume ratio of the filler material to the oxide-based solid electrolyte in the cover layer is 10 vol% or more. 3. The all-solid-state battery according to claim 1, wherein the filler material has an electrical conductivity including electronic conductivity and ionic conductivity of 10 ⁻⁸ S/cm or less. 4. The all-solid-state battery according to claim 1, wherein the filler material is alumina or _SiO2 glass. The all-solid-state battery described in any one of claims 1 to 4, characterized in that the shape of the filler material has an average cross-sectional circularity of 0.6 or more. The all-solid-state battery described in any one of claims 1 to 5, wherein the D50% particle size of the filler material is 0.5 μm or more and 8 μm or less. The all-solid-state battery described in any one of claims 1 to 6, characterized in that, between the oxide-based solid electrolyte layer and the cover layer, the D0% particle size in the particle size distribution of the solid electrolyte of one layer falls between the D0% particle size and the D10% particle size in the particle size distribution of the solid electrolyte of the other layer, and the D100% particle size in the particle size distribution of the solid electrolyte of the one layer falls between the D90% particle size and the D100% particle size in the particle size distribution of the solid electrolyte of the other layer. The all-solid-state battery described in any one of claims 1 to 7, wherein the oxide-based solid electrolyte of the cover layer is a solid electrolyte with a NASICON crystal structure. The all-solid-state battery described in any one of claims 1 to 8, wherein the main component of the solid electrolyte layer is a solid electrolyte with a NASICON crystal structure. The all-solid-state battery described in any one of claims 1 to 9, wherein the oxide-based solid electrolyte of the cover layer has the same composition as the main component of the solid electrolyte layer. The all-solid-state battery described in any one of claims 1 to 10, wherein the oxide-based solid electrolyte of the cover layer is a glass material. The all-solid-state battery described in any one of claims 1 to 11, wherein the electrode layer contains an oxide-based solid electrolyte having ion conductivity. a preparation step of preparing a ceramic laminate in which a cover sheet containing an oxide-based solid electrolyte powder and an insulating filler material having a higher sintering temperature than the oxide-based solid electrolyte powder is laminated on at least one of an upper surface and a lower surface in the lamination direction of a laminate in which solid electrolyte green sheets containing an oxide-based solid electrolyte powder having ion conductivity and internal electrode patterns containing an electrode active material powder are alternately laminated;
and a firing step of firing the ceramic laminate. the sintering temperature of the oxide-based solid electrolyte powder of the cover sheet is lower than the firing temperature in the firing step;
The method for manufacturing an all-solid-state battery according to claim 13 , wherein a sintering temperature of the filler material is higher than a firing temperature in the firing step.