All-solid-state battery and method for manufacturing the same
The all-solid-state battery's innovative void structure with specific circularity and porosity parameters addresses complexity and performance issues, ensuring stable ion conductivity and mechanical strength.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- TAIYO YUDEN KK
- Filing Date
- 2021-09-30
- Publication Date
- 2026-06-23
AI Technical Summary
Existing methods for forming voids in solid electrolyte layers of all-solid-state batteries are complex and do not adequately address performance degradation issues such as reduced ion conductivity and mechanical strength due to irregularly shaped voids.
The all-solid-state battery design incorporates a solid electrolyte layer with voids having a circularity of 0.4 or more, occupying 50% or more of the total area, and a porosity between 2% and 30%, with median pore sizes ranging from 0.01 μm to 5 μm, to effectively absorb volume changes and maintain conductivity and mechanical strength.
This design suppresses performance deterioration by reducing electric field concentration and maintaining ionic conductivity and mechanical strength, enhancing the battery's operational stability.
Smart Images
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Abstract
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 and other issues, there is a growing expectation for safer solid electrolytes, and the development of all-solid-state batteries using oxide-based solid electrolytes is actively underway (see, for example, Patent Documents 1-3). [Prior art documents] [Patent Documents]
[0003] [Patent Document 1] International Publication No. 2013 / 175993 [Patent Document 2] International Publication No. 2020 / 184476 [Patent Document 3] International Publication No. 2008 / 059987 [Overview of the Initiative] [Problems that the invention aims to solve]
[0004] Patent Document 1 discloses a method for improving cycle characteristics by introducing voids into a solid electrolyte layer to absorb volume changes. However, this requires forming multiple electrolyte layers with different porosities, making the process complicated. Patent Document 2 proposes a structure in which voids are introduced into the side margin layer. However, introducing voids into the side margin layer is considered insufficient to cope with internal stress. Patent Document 3 proposes a structure in which voids are introduced into a region close to the electrode layer within the solid electrolyte layer. However, this process is extremely complicated.
[0005] This invention has been made in view of the above problems, and aims to provide an all-solid-state battery and a method for manufacturing the same that can suppress the performance degradation of the solid electrolyte layer. [Means for solving the problem]
[0006] The all-solid-state battery according to the present invention comprises a solid electrolyte layer, a first electrode layer provided on the first main surface of the solid electrolyte layer and containing an electrode active material, and a second electrode layer provided on the second main surface of the solid electrolyte layer and containing an electrode active material, wherein the total area of each void having a circularity of 0.4 or more in the cross-section of the solid electrolyte layer is 50% or more of the total area of all voids.
[0007] In the cross-section of the solid electrolyte layer of the all-solid-state battery described above, the porosity may be 2% or more and less than 30%.
[0008] In the cross-section of the solid electrolyte layer of the all-solid-state battery described above, the median pore size of each void may be 0.01 μm or more and less than 5 μm.
[0009] In the above-described all-solid-state battery, the thickness of the solid electrolyte layer may be 3 μm or more and 30 μm or less.
[0010] The present invention relates to a method for manufacturing an all-solid-state battery, comprising the steps of: preparing a raw material powder by pulverizing a solid electrolyte material in the presence of an organic solvent to chemically bond organic groups with oxygen (O) interposed on the surface of the solid electrolyte material; preparing a laminate having a green sheet containing the raw material powder; a paste coating for a first electrode layer containing electrode active material formed on the first main surface of the green sheet; and a paste coating for a second electrode layer containing electrode active material formed on the second main surface of the green sheet; and firing the laminate, characterized in that the total area of each void having a circularity of 0.4 or more in the cross-section of the solid electrolyte layer obtained by firing the green sheet is 50% or more of the total area of all voids. [Effects of the Invention]
[0011] According to the present invention, it is possible to provide an all-solid-state battery capable of suppressing performance deterioration of a solid electrolyte layer and a method for manufacturing the same.
Brief Description of the Drawings
[0012] [Figure 1] It is a schematic cross-sectional view showing a basic structure of an all-solid-state battery. [Figure 2] (a) is a diagram illustrating a SEM image of a cross-section of a solid electrolyte layer in which irregularities are formed and voids are formed, and (b) is a diagram illustrating a SEM image of a cross-section of a solid electrolyte layer according to an embodiment. [Figure 3] It is a schematic cross-sectional view of an all-solid-state battery according to an embodiment. [Figure 4] It is a schematic cross-sectional view of another all-solid-state battery. [Figure 5] It is a diagram illustrating a flow of a method for manufacturing an all-solid-state battery. [Figure 6] (a) and (b) are diagrams illustrating a lamination process.
Modes for Carrying Out the Invention
[0013] Hereinafter, embodiments will be described with reference to the drawings.
[0014] (Embodiment) FIG. 1 is a schematic cross-sectional view showing a 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.
[0015] 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 the present embodiment, as an example, it is assumed that 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.
[0016] 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 is stable in the atmosphere. The phosphate-based solid electrolyte is, for example, a phosphate containing lithium. The phosphate is not particularly limited, and examples thereof include lithium phosphate composite salts with Ti (for example, LiTi2(PO4)3). Alternatively, Ti can be partially or completely substituted with tetravalent transition metals such as Ge, Sn, Hf, and Zr. Also, in order to increase the Li content, it may be partially substituted with trivalent transition metals such as Al, Ga, In, Y, and 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. 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 solid electrolyte layer 30 contains a Li-Al-Ge-PO4-based material to which Co is 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-PO4-based material to which the transition metal is added in advance.
[0017] 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.
[0018] 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] When the all-solid-state battery 100 is used as a battery and charged and discharged, volume changes occur in the first internal electrode 10 and the second internal electrode 20. To absorb this volume change, it is desirable that voids be formed in the solid electrolyte layer 30. However, the method for forming voids in the solid electrolyte layer 30 tends to be complex. Furthermore, it is desirable that the degradation of performance such as ion conductivity and mechanical strength can be suppressed when voids are formed in the solid electrolyte layer 30.
[0024] Figure 2(a) illustrates an SEM image of a cross-section of a solid electrolyte layer with irregular voids. The shaded areas represent voids. As illustrated in Figure 2(a), each void has an irregular shape. In region A, the voids are linear, bent, and curved, resulting in pointed portions. In such areas, electric field concentration is likely to occur, potentially leading to the formation of leak paths. In region B, the spacing between voids is reduced. Geometrically, in such regions, the conduction paths for lithium ions are narrowed. Therefore, ionic conductivity may decrease. Furthermore, reduced spacing between voids may reduce the mechanical strength of the solid electrolyte layer. For these reasons, the structure shown in Figure 2(a) may result in a deterioration of the performance of the solid electrolyte layer.
[0025] In contrast, the solid electrolyte layer 30 according to this embodiment has a structure that can suppress performance degradation. Figure 2(b) is a diagram illustrating an SEM image of a cross-section of the solid electrolyte layer 30. This cross-section is, for example, a cross-section along the stacking direction of the first internal electrode 10, the solid electrolyte layer 30, and the second internal electrode 20. As illustrated in Figure 2(b), a plurality of voids 31 are formed in the solid electrolyte layer 30.
[0026] In the cross-section of the solid electrolyte layer 30, at least one of these voids 31 has a circularity of 0.4 or greater. Having a circularity of 0.4 or greater in the voids 31 suppresses sharpness of the voids 31. This suppresses electric field concentration around the voids 31.
[0027] In this embodiment, the total area of each void 31 having a circularity of 0.4 or more in the cross-section of the solid electrolyte layer 30 is 50% or more of the total area of all voids. This structure increases the amount of voids with a circularity of 0.4 or more, and sufficiently reduces electric field concentration throughout the solid electrolyte layer 30. Circularity is calculated as 4π × (area) / (perimeter). 2 It can be expressed as follows.
[0028] Furthermore, as the circularity of the voids 31 decreases, the shape of the voids 31 deviates from a circle and becomes elongated, so the diameter (maximum length) of the voids 31 tends to increase. Therefore, if there are many voids with a circularity of less than 0.4, many places will occur where the spacing between voids is narrow. Conversely, as the circularity of the voids 31 approaches 1, they become closer to a circle, so the diameter (maximum length) of the voids 31 tends to decrease. Therefore, if the total area of each void 31 with a circularity of 0.4 or more is 50% or more of the total area of all voids, the number of places where the spacing between voids 31 is narrow is reduced. As a result, the decrease in ion conductivity and the decrease in mechanical strength of the solid electrolyte layer 30 can be suppressed.
[0029] Since it is preferable that many voids 31 with high circularity are formed, the total area of each void 31 having a circularity of 0.4 or higher is preferably 55% or more, and more preferably 60% or more, of the total area of all voids.
[0030] Furthermore, in order to make the shape of the void 31 closer to a perfect circle, it is preferable that the circularity is close to 1. Therefore, it is preferable that the total area of each void 31 having a circularity of 0.45 or more is 50% or more of the total area of all voids, and it is more preferable that the total area of each void 31 having a circularity of 0.5 or more is 50% or more of the total area of all voids.
[0031] The circularity of each void 31 can be measured, for example, by binarizing a 60 μm × 40 μm SEM image to extract the voids in the solid electrolyte layer 30 and measuring their area and perimeter.
[0032] In the solid electrolyte layer 30, if the diameter of each void 31 is small, there is a risk that the volume change cannot be sufficiently absorbed in each void 31. Therefore, it is preferable to set a lower limit on the median pore diameter of each void 31. For example, the median pore diameter of each void 31 is preferably 0.01 μm or more, more preferably 0.02 μm or more, and even more preferably 0.03 μm or more.
[0033] On the other hand, if the diameter of each void 31 is large, the mechanical strength may decrease around the void 31. Therefore, it is preferable to set an upper limit on the median diameter of each void 31. For example, the median diameter of each void 31 is preferably less than 5 μm, more preferably 4 μm or less, and even more preferably 3 μm or less.
[0034] The pore size of each void 31 can be measured, for example, by binarizing a 60 μm × 40 μm SEM image to extract the voids in the solid electrolyte layer 30, measuring the area, and calculating the equivalent diameter of a circle.
[0035] If the porosity (the ratio of the total area of each void 31) in the cross-section of the solid electrolyte layer 30 is small, the solid electrolyte layer 30 may not be able to sufficiently absorb the volume change. Therefore, in this embodiment, it is preferable to set a lower limit on the porosity. For example, in the cross-section of the solid electrolyte layer 30, the porosity is preferably 2% or more, more preferably 3% or more, and even more preferably 4% or more.
[0036] On the other hand, if the porosity is large, sufficient ionic conductivity and mechanical strength may not be obtained in the solid electrolyte layer 30, and the performance of the solid electrolyte layer 30 may deteriorate. Therefore, in this embodiment, it is preferable to set an upper limit on the porosity. For example, in the cross-section of the solid electrolyte layer 30, the porosity is preferably less than 30%, more preferably 25% or less, and even more preferably 20% or less.
[0037] The thickness of the solid electrolyte layer 30 is, for example, 3 μm to 30 μm, 5 μm to 25 μm, or 8 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, 10 μm to 40 μm, or 15 μm to 30 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.
[0038] Figure 3 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).
[0039] 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.
[0040] 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.
[0041] A cover layer 50 is laminated on the upper surface of the laminated structure of the first internal electrode 10, the solid electrolyte layer 30, and the second internal electrode 20 (in the example of Figure 3, the upper surface of the first internal electrode 10, which is the uppermost layer). A cover layer 50 is also laminated on the lower surface of the laminated structure (in the example of Figure 3, the lower surface of the first internal electrode 10, which is the lowest layer). The cover layer 50 is mainly composed of inorganic materials such as Al, Si, Zr, and Ti (e.g., Al2O3, SiO2, ZrO2, TiO2, etc.). The cover layer 50 may also mainly contain the main components of the solid electrolyte layer 30.
[0042] 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 4, 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.
[0043] 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.
[0044] (Process for preparing raw material powder for the solid electrolyte layer) First, raw material powders for the solid electrolyte layer that constitute the solid electrolyte layer 30 described above are prepared. For example, by mixing raw materials and additives and using a solid-phase synthesis method, a solid electrolyte material for an oxide-based solid electrolyte can be prepared. The obtained solid electrolyte material can be adjusted to a desired average particle size by grinding it in the presence of an organic solvent. For example, the desired average particle size can be adjusted using a planetary ball mill with 5 mmφ ZrO2 balls. By grinding in the presence of an organic solvent, organic groups with oxygen (O) interposed, such as ethoxy groups and propyl groups, are chemically bonded to the dangling bonds on the surface of the raw material powder. Organic groups with oxygen (O) interposed are, for example, alkoxy groups represented by RO bonds (where R is an alkyl group, etc.).
[0045] (Process for preparing raw material powder for the cover layer) First, the raw material powder for the ceramics constituting the cover layer 50 is prepared. For example, raw materials and additives can be mixed and a solid-phase synthesis method can be used to produce the raw material powder for the cover layer. 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. If the solid electrolyte layer 30 and the cover layer 50 have the same composition, the raw material powder for the solid electrolyte layer can be used as a substitute.
[0046] (Process for preparing paste for internal electrodes) Next, an internal electrode paste is prepared for the fabrication of the first internal electrode 10 and the second internal electrode 20 described above. 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. If the composition of the first internal electrode 10 and the second internal electrode 20 is different, each internal electrode paste may be prepared individually.
[0047] 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.
[0048] (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.
[0049] (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.
[0050] (Lamination process) As illustrated in Figure 6(a), an internal electrode paste 52 is printed on one surface of the solid electrolyte green sheet 51. The thickness of the internal electrode paste 52 is equal to or greater than the thickness of the 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 same reverse pattern 53 as that of the solid electrolyte green sheet 51 can be used. 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 is alternately exposed on two end faces of the laminate. The cover sheet 54 can be formed by coating it with 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. It may be made thicker during coating, or by stacking multiple coated sheets.
[0051] 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.
[0052] (Firing process) Next, the resulting 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.
[0053] 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.
[0054] In the manufacturing method according to this embodiment, organic groups with oxygen (O) interposed, such as ethoxy groups and propyl groups, are chemically bonded to the surface of the raw material powder for the solid electrolyte layer. Because the organic groups with oxygen (O) interposed are stably bonded, they tend to remain without desorbing even when the raw material powder begins to sinter and densify. In the firing process, the organic groups with oxygen (O) interposed desorb and gasify after the ambient temperature exceeds the sintering start temperature. In this case, because the solid electrolyte is densified around the organic groups with oxygen (O), the gas is not released to the outside and becomes spherical. This spherical gas portion forms a void 31.
[0055] For example, by adjusting the average particle size of the raw material powder for the solid electrolyte layer, the firing temperature of the firing process, and the firing time of the firing process, the total area of each void 31 with a circularity of 0.4 or more in the cross-section of the solid electrolyte layer 30 can be made to be 50% or more of the total area of the voids.
[0056] Furthermore, by adjusting the average particle size of the solid electrolyte material for the solid electrolyte layer, the firing temperature of the firing process, and the firing time of the firing process, the porosity in the cross-section of the solid electrolyte layer 30 can be set to 2% or more and less than 30%.
[0057] Furthermore, by adjusting the average particle size of the solid electrolyte material for the solid electrolyte layer, the firing temperature of the firing process, and the firing time of the firing process, the median pore size of each void 31 in the cross-section of the solid electrolyte layer 30 can be set to 0.01 μm or more and less than 5 μm. [Examples]
[0058] A solid-state battery was fabricated according to the following embodiment, and its characteristics were investigated.
[0059] (Example 1) Ethanol was used as the organic solvent. In the presence of this organic solvent, a solid electrolyte material having a Li-Al-Ge-PO system composition and an average particle size of 2 μm was pulverized using a bead mill. Ethoxy groups from the organic solvent were chemically bonded to the surface of the solid electrolyte material that was newly exposed by pulverization. Pellets were prepared using the solid electrolyte material to which the ethoxy groups had been chemically bonded, and they were calcined at 600°C.
[0060] (Example 2) Ethanol was used as the organic solvent. In the presence of this organic solvent, a solid electrolyte material having a Li-Al-Ge-PO system composition and an average particle size of 2 μm was pulverized using a bead mill. Ethoxy groups from the organic solvent were chemically bonded to the surface of the solid electrolyte material that was newly exposed by pulverization. The solid electrolyte material with the chemically bonded ethoxy groups was mixed with a binder to form a sheet. The sheets were laminated, the binder was removed by heat treatment, and then the sheets were fired at 600°C.
[0061] (Comparative Example 1) Ethanol was used as the organic solvent. In the presence of this organic solvent, a solid electrolyte material having a Li-Al-Ge-PO system composition and an average particle size of 2 μm was pulverized using a bead mill. Ethoxy groups from the organic solvent were chemically bonded to the surface of the solid electrolyte material that was newly exposed by pulverization. The solid electrolyte material with chemically bonded ethoxy groups, the solid electrolyte material without bonded ethoxy groups, and a binder were mixed and molded into a sheet. The sheets were laminated, the binder was removed by heat treatment, and then the sheets were fired at 600°C.
[0062] (Comparative Example 2) Ethanol was used as the organic solvent. In the presence of this organic solvent, a solid electrolyte material having a Li-Al-Ge-PO system composition and an average particle size of 2 μm was pulverized using a bead mill. Ethoxy groups from the organic solvent were chemically bonded to the surface of the solid electrolyte material that was newly exposed by pulverization. The solid electrolyte material with chemically bonded ethoxy groups was mixed with solid electrolyte material without ethoxy groups in a mortar, molded into pellets, and fired at 600°C.
[0063] For each sample in Examples 1 and 2 and Comparative Examples 1 and 2, cross-sections were imaged using a scanning electron microscope (SEM), and the circularity of each void was measured. The SEM imaging range was set to 60 μm × 40 μm. In the cross-section of each sample, the ratio of the total area of each void with a circularity of 0.4 or higher to the total area of all voids was calculated. This ratio was 61.3% for Example 1 and 62.6% for Example 2. Comparative Example 1 Then it was 21.5%, Comparative Example 2 The result was 38.4%. Next, the porosity (the ratio of the total area of voids in the cross-section) was measured for each sample. The porosity was 10.4% for Example 1, 11.86% for Example 2, 28.2% for Comparative Example 1, and 13.8% for Comparative Example 2. Next, the median pore size of each void was measured for each sample. The median pore size was 0.10 μm for Example 1, 0.33 μm for Example 2, 0.05 μm for Comparative Example 1, and 0.03 μm for Comparative Example 2.
[0064] Next, the ionic conductivity (S / cm) of the samples from Examples 1 and 2 and Comparative Examples 1 and 2 was measured by AC impedance measurement. The ionic conductivity (S / cm) for Example 1 was 7.85 × 10⁻⁶. -5 In Example 2, the values were 5.13 × 10⁻⁶. -5 In Comparative Example 1, the ratio was 1.06 × 10⁻⁶. -5 In Comparative Example 2, the result was 2.18 × 10⁻⁶. -5 These results show that the ionic conductivity is higher in Examples 1 and 2 compared to Comparative Examples 1 and 2. Furthermore, by performing the AC impedance measurement, the absolute value of the phase difference ( / deg) at 1 Hz was measured. The absolute value of the phase difference ( / deg) at 1 Hz was 57.2 in Example 1, 65.7 in Example 2, 55.0 in Comparative Example 1, and 55.4 in Comparative Example 2. These results show that the leakage characteristics are better in Examples 1 and 2 compared to Comparative Examples 1 and 2. These results show that the performance degradation of the solid electrolyte can be suppressed by making the ratio of the total area of each void with a circularity of 0.4 or more to the total area of all voids in the cross-section of the solid electrolyte layer 50% or more. In addition, for Examples 1 and 2, it was confirmed from the SEM images that a good solid-solid interface is formed within the solid electrolyte layer due to the gas pressure when voids are created. [Table 1]
[0065] 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]
[0066] 10 1st internal electrode 11. First current collector layer 20 Second internal electrode 21. Second current collector layer 30 Solid electrolyte layer 31 void 40a First external electrode 40b 2nd external electrode 50 Cover Layers 51 Solid Electrolyte Green Sheet 52 Paste for internal electrodes 53 Reverse Pattern 54 Cover Sheets 55 Paste for external electrodes 60 stacked chips 100,100a solid state battery
Claims
1. A solid electrolyte layer, A first electrode layer containing an electrode active material is provided on the first main surface of the solid electrolyte layer, The solid electrolyte layer comprises a second electrode layer provided on the second main surface and containing an electrode active material, An all-solid-state battery characterized in that, in the cross-section of the solid electrolyte layer, the total area of each void having a circularity of 0.4 or more is 50% or more and 62.6% or less of the total area of all voids, the porosity is 11.86% or less, and the median pore size of each void is 0.10 μm or more.
2. The all-solid-state battery according to claim 1, characterized in that the porosity in the cross-section of the solid electrolyte layer is 2% or more.
3. The all-solid-state battery according to claim 1 or 2, characterized in that the median value in the cross-section of the solid electrolyte layer is less than 5 μm.
4. The all-solid-state battery according to any one of claims 1 to 3, characterized in that the thickness of the solid electrolyte layer is 3 μm or more and 30 μm or less.
5. The main component of the solid electrolyte layer is Li １＋ｘ Al ｘ Ge ２－ｘ (PO ４ ) ３ A solid-state battery according to any one of claims 1 to 4, characterized in that it is the same as described above.
6. A process to produce a raw material powder by pulverizing a solid electrolyte material in the presence of an organic solvent, thereby chemically bonding organic groups with oxygen (O) interposed on the surface of the solid electrolyte material. A step of producing a laminate comprising: a green sheet containing the raw material powder; a paste coating for a first electrode layer containing electrode active material formed on the first main surface of the green sheet; and a paste coating for a second electrode layer containing electrode active material formed on the second main surface of the green sheet. The process includes firing the laminate, A method for manufacturing an all-solid-state battery, characterized in that, in the cross-section of the solid electrolyte layer obtained by firing the green sheet, the total area of each void having a circularity of 0.4 or more is 50% or more and 62.6% or less of the total area of all voids, the porosity is 11.86% or less, and the median value of the pore diameter of each void is 0.10 μm or more.