All-solid-state batteries

Abstract

To provide an all-solid-state battery that maintains conductive paths with a simple structure and process, and can improve capacity degradation. [Solution] The all-solid-state battery comprises a solid electrolyte layer, a first electrode layer provided on a first main surface of the solid electrolyte layer, and a second electrode layer provided on a second main surface of the solid electrolyte layer, wherein a carbon material forms a mesh-like layer in a portion of the thickness of the first electrode layer.

Description

[Technical Field]

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

[0002] Stacked solid-state batteries are safe and easy-to-handle rechargeable batteries that eliminate concerns about ignition and leakage, and can be reflow soldered. They are being considered as a replacement for conventional lithium-ion batteries that use electrolytes, and are expected to be used in a wide range of fields. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2021 / 090774 [Patent Document 2] International Publication No. 2014 / 073470 [Patent Document 3] Special Publication No. 2020-507893 [Patent Document 4] Japanese Patent Publication No. 2006-164833 [Patent Document 5] Japanese Patent Publication No. 2012-252833 [Overview of the project] [Problems that the invention aims to solve]

[0004] In stacked solid-state batteries, expansion and contraction stress in the electrode layers during charging and discharging can cause cracks to form inside the electrodes, potentially disrupting the conductive path and leading to performance degradation. Therefore, various countermeasures are being considered (see, for example, Patent Documents 1-3).

[0005] Patent Document 1 proposes a structure in which an intermediate layer containing carbon material is provided between the electrode layer and the active material layer to strengthen the bond between the carbon material and the solid electrolyte, thereby making internal crack fracture less likely. However, this configuration results in a low capacity density per unit volume.

[0006] Patent Document 2 discloses increasing the electron conduction pathways to the positive electrode active material by bonding fibrous carbon to the positive electrode active material. However, this configuration requires a special manufacturing method to produce composite particles in which the positive electrode active material and fibrous carbon are fused, which increases manufacturing time and cost.

[0007] This invention has been made in view of the above problems, and aims to provide an all-solid-state battery that can maintain a conductive path with a simple structure and process and improve capacity degradation. [Means for solving the problem]

[0008] The all-solid-state battery according to the present invention comprises a solid electrolyte layer, a first electrode layer provided on a first main surface of the solid electrolyte layer, and a second electrode layer provided on a second main surface of the solid electrolyte layer, wherein a carbon material forms a mesh-like layer in a portion of the thickness of the first electrode layer.

[0009] In the above-described all-solid-state battery, the thickness of the carbon material layer may be 1 nm or more and 3 μm or less.

[0010] In the above-described all-solid-state battery, the thickness of the carbon material layer may be 0.001% or more and 10% or less relative to the thickness of the first electrode layer.

[0011] In the first electrode layer of the all-solid-state battery described above, the carbon material layers may be arranged in multiple layers spaced apart from each other.

[0012] In the above-described all-solid-state battery, when the first electrode layer is viewed in plan view, if a 100 μm × 100 μm square region in the carbon material layer is divided into 15 × 15 = 225 squares of the same size, the current collection area occupancy rate, which is (total number of squares on which the carbon material is arranged) / 225 × 100%, may be 50% or more.

[0013] In the above all-solid-state battery, in a cross-section including the stacking direction of the solid electrolyte layer, the first electrode layer, and the second electrode layer, the layer of the carbon material may have a wave shape.

[0014] In the above all-solid-state battery, the carbon material may be a carbon nanotube.

[0015] In the above all-solid-state battery, the carbon material may be fibrous.

[0016] In the above all-solid-state battery, the total length of the carbon material may be 5 μm or more.

Advantages of the Invention

[0017] According to the present invention, it is possible to provide an all-solid-state battery that can maintain a conductive path with a simple structure and process and improve capacity degradation.

Brief Description of the Drawings

[0018] [Figure 1] It is a schematic cross-sectional view showing the basic structure of an all-solid-state battery. [Figure 2] It is a schematic cross-sectional view for explaining the outline of the positive electrode layer and the negative electrode layer. [Figure 3] It is a partial cross-sectional perspective view of a stacked all-solid-state battery in which a plurality of battery units are stacked. [Figure 4] It is a cross-sectional view taken along line A-A' of FIG. 3. [Figure 5] It is a cross-sectional view taken along line B-B' of FIG. 3. [Figure 6] It is a diagram for explaining the conduction between the electrode active material and the external electrode by a conductive aid. [Figure 7] It is a schematic cross-sectional view for explaining the conductive aids included in the positive electrode layer and the negative electrode layer. [Figure 8] It is a diagram for explaining the conduction between the electrode active material and the external electrode by a conductive aid. [Figure 9]This is a schematic cross-sectional view illustrating the conductive additives present in the positive and negative electrode layers. [Figure 10] (a) is an XY plan view of the conductive additive layer, (b) is a diagram showing the result of dividing (a) into 15 × 15 = 225 squares of the same size, and (c) is a diagram showing the squares in which carbon material is placed, even if only partially. [Figure 11] (a) is an XY plan view of the conductive additive layer, (b) is a diagram showing the result of dividing (a) into 15 × 15 = 225 squares of the same size, and (c) is a diagram showing the squares in which carbon material is placed, even if only partially. [Figure 12] (a) is an XY plan view of the conductive additive layer, (b) is a diagram showing the result of dividing (a) into 15 × 15 = 225 squares of the same size, and (c) is a diagram showing the squares in which carbon material is placed, even if only partially. [Figure 13] (a) and (b) are perspective views illustrating the carbon material contained in the conductive additive layer, and (c) is a diagram illustrating the laminated cross-section of the positive electrode layer. [Figure 14] This is a schematic cross-sectional view illustrating the conductive additives present in the positive and negative electrode layers. [Figure 15] This diagram illustrates a flow chart of the manufacturing process for all-solid-state batteries. [Figure 16] (a) and (b) are diagrams illustrating the lamination process. [Figure 17] This diagram illustrates a method for forming an internal electrode pattern. [Figure 18] This is a diagram illustrating the lamination process. [Modes for carrying out the invention]

[0019] Before describing the embodiments, an overview of all-solid-state batteries will be provided.

[0020] FIG. 1 is a schematic cross-sectional view showing the basic structure of all-solid-state battery 100. As illustrated in FIG. 1, all-solid-state battery 100 has a structure in which solid electrolyte layer 30 is sandwiched by positive electrode layer 10 and negative electrode layer 20. For example, positive electrode layer 10 is formed on the first major surface of solid electrolyte layer 30, and negative electrode layer 20 is formed on the second major surface of solid electrolyte layer 30. Positive electrode layer 10, negative electrode layer 20, and solid electrolyte layer 30 are sintered bodies of powder materials.

[0021] Solid electrolyte layer 30 is mainly composed of a solid electrolyte having ion conductivity. The solid electrolyte of 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 having a NASICON structure. The phosphate-based solid electrolyte having a NASICON structure has high conductivity and the property of being stable in the atmosphere. The phosphate-based solid electrolyte is, for example, a phosphate containing lithium. The phosphate is not particularly limited, and examples thereof include a composite lithium phosphate salt with Ti (for example, LiTi2(PO4)3). Or, Ti can be partially or entirely replaced with a tetravalent transition metal such as Ge, Sn, Hf, Zr, etc. Also, in order to increase the Li content, it may be partially replaced with a trivalent transition metal such as Al, Ga, In, Y, La, etc. More specifically, for example, Li 1+x Al x Ge 2-x (PO4)3, or Li 1+x Al x Zr 2-x (PO4)3, Li 1+x Al x Ti 2-xExamples include (PO4)3. For example, a Li-Al-Ge-PO4 system material is preferred in which the same transition metal as the transition metal contained in the olivine-type crystal structure phosphate contained in the positive electrode layer 10 and the negative electrode layer 20 is pre-added. For example, if the positive electrode layer 10 and the negative electrode layer 20 contain a phosphate containing Co and Li, it is preferable that the solid electrolyte layer 30 contains a Li-Al-Ge-PO4 system material with Co pre-added. In this case, the effect of suppressing the elution of the transition metal contained in the electrode active material into the electrolyte can be obtained. If the positive electrode layer 10 and the negative electrode layer 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 system material with the transition metal pre-added.

[0022] Figure 2 is a schematic cross-sectional view illustrating the outline of the positive electrode layer 10 and the negative electrode layer 20. As illustrated in Figure 2, the positive electrode layer 10 has a structure in which the positive electrode active material 11, solid electrolyte 12, etc., are dispersed. The negative electrode layer 20 has a structure in which the negative electrode active material 21, solid electrolyte 22, etc., are dispersed. By having the positive electrode layer 10 comprise the positive electrode active material 11 and the negative electrode layer 20 comprise the negative electrode active material 21, the all-solid-state battery 100 can be used as a secondary battery. By having the positive electrode layer 10 comprise the solid electrolyte 12 and the negative electrode layer 20 comprise the solid electrolyte 22, ionic conductivity is obtained in the positive electrode layer 10 and the negative electrode layer 20.

[0023] The positive electrode active material 11 is, for example, an electrode active material having an olivine-type crystal structure. An electrode active material having an olivine-type crystal structure may also be contained in the negative electrode layer 20. Examples of such electrode active materials include phosphates containing a transition metal and lithium. The olivine-type crystal structure is the crystal structure found in natural olivine and can be identified by X-ray diffraction.

[0024] Typical examples of electrode active materials with an olivine-type crystal structure include LiCoPO4 containing Co and P. 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. As a positive electrode active material containing Co and P, LiCo2P3O 10 Li2CoP2O7, Li6Co5(P2O7)4, etc., can also be used.

[0025] For example, if the electrode active material having an olivine-type crystal structure is contained only in the positive electrode layer 10, then this electrode active material acts as the positive electrode active material. If the electrode active material having an olivine-type crystal structure is also contained in the negative electrode layer 20, 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.

[0026] When both the positive electrode layer 10 and the negative electrode layer 20 contain electrode active materials having an olivine-type crystal structure, each electrode active material preferably contains transition metals 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 positive electrode layer 10 and the negative electrode layer 20 may contain the same type of transition metal, or they may contain different types of transition metals. The positive electrode layer 10 and the negative electrode layer 20 may contain only one type of transition metal, or they may contain two or more types of transition metals. Preferably, the positive electrode layer 10 and the negative electrode layer 20 contain the same type of transition metal. More preferably, the electrode active materials contained in both electrodes have the same chemical composition. The similarity of the compositions of both internal electrode layers is increased by the inclusion of the same type of transition metal or the same composition of electrode active materials in the positive electrode layer 10 and the negative electrode layer 20. 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 connected in reverse (positive and negative).

[0027] The negative electrode layer 20 functions as a negative electrode layer by containing the negative electrode active material 21. By containing the negative electrode active material in only one electrode, it becomes clear that the electrode in question acts as a negative electrode and the other electrode acts as a positive electrode. However, 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.

[0028] Solid electrolytes 12 and 22 are not particularly limited as long as they are oxide-based solid electrolytes having ionic conductivity. Solid electrolytes 12 and 22 are, for example, oxide-based solid electrolytes having lithium ion conductivity. The solid electrolyte is, for example, a phosphate-based solid electrolyte having a NASICON structure. The phosphate-based solid electrolyte is, for example, a lithium-containing phosphate. The phosphate is not particularly limited, but examples include a lithium phosphate composite salt with Ti (e.g., LiTi2(PO4)3). Alternatively, Ti can be partially or completely substituted with a tetravalent transition metal such as Ge, Sn, Hf, or Zr. Furthermore, to increase the Li content, it may be partially substituted with a trivalent transition metal such as Al, Ga, In, Y, or La. More specifically, for example, Li 1+x Al x Ge 2-x (PO4)3 and Li 1+x Al x Zr 2-x (PO4)3, Li 1+x Al x Ti 2-x Examples include (PO4)3. Solid electrolytes 12 and 22 can be, for example, the same as the main component solid electrolyte of the solid electrolyte layer 30. Alternatively, if the electrode active material contains Co and P, it is preferable that solid electrolytes 12 and 22 contain Co. Although the detailed mechanism is unknown, it is because including Co during co-calcination tends to improve the oxidation resistance stability of the solid electrolyte, thereby making it easier to ensure cycle stability.

[0029] Figure 3 is a partial cross-sectional perspective view of a stacked all-solid-state battery 100a in which multiple battery units are stacked. Figure 4 is a cross-sectional view taken along line AA of Figure 3. Figure 5 is a cross-sectional view taken along line BB of Figure 3. The all-solid-state battery 100a includes a stacked chip 60 having a substantially rectangular parallelepiped shape. In the stacked chip 60, a positive electrode external electrode 40a is provided so as to be in contact with the first end face of the four faces other than the top and bottom faces at the stacking direction ends, and a negative electrode external electrode 40b is provided so as to be in contact with the second end face opposite the first end face.

[0030] In Figures 3 to 5, the X-axis direction is the direction in which the first and second end faces of the stacked chip 60 face each other, and the direction in which the positive external electrode 40a and the negative external electrode 40b face each other. The Y-axis direction is the width direction of the positive electrode layer 10 and the negative electrode layer 20, and the direction in which two of the four sides of the stacked chip 60 (excluding the two end faces) face each other. The Z-axis direction is the stacking direction, and the direction in which the top and bottom surfaces of the stacked chip 60 face each other. The X-axis direction, the Y-axis direction, and the Z-axis direction are mutually orthogonal.

[0031] In the following description, components having the same composition range and thickness range as the all-solid-state battery 100 are given the same reference numerals, and detailed explanations are omitted.

[0032] In the all-solid-state battery 100a, multiple positive electrode layers 10 and multiple negative electrode layers 20 are alternately stacked via a solid electrolyte layer 30. The X-axis edges of the multiple positive electrode layers 10 are drawn out to the first end face of the stacked chip 60, but not to the second end face. The X-axis edges of the multiple negative electrode layers 20 are drawn out to the second end face of the stacked chip 60, but not to the first end face. As a result, the positive electrode layers 10 and negative electrode layers 20 are alternately conductive to the positive electrode external electrode 40a and the negative electrode external electrode 40b. The solid electrolyte layer 30 extends from the positive electrode external electrode 40a to the negative electrode external electrode 40b. Thus, the all-solid-state battery 100a has a structure in which multiple battery units are stacked.

[0033] A cover layer 50 is laminated on the upper end surface of the laminated portion of the positive electrode layer 10, the solid electrolyte layer 30, and the negative electrode layer 20. This cover layer 50 is in contact with the uppermost internal electrode layer (either the positive electrode layer 10 or the negative electrode layer 20) and also in contact with a portion of the solid electrolyte layer 30. Another cover layer 50 is laminated on the lower end surface of the laminate. This cover layer 50 is in contact with the lowest internal electrode layer (either the positive electrode layer 10 or the negative electrode layer 20) and also in contact with a portion of the solid electrolyte layer 30. For example, the cover layer 50 is a sintered body obtained by sintering powder material.

[0034] As illustrated in Figure 4, the region where the positive electrode layer 10 connected to the positive external electrode 40a and the negative electrode layer 20 connected to the negative external electrode 40b face each other is the region that generates battery capacity. Therefore, this region is referred to as the battery capacity region 70. In other words, the battery capacity region 70 is the region where two adjacent internal electrode layers connected to different external electrodes face each other.

[0035] The region where two positive electrode layers 10 connected to the positive electrode external electrode 40a face each other without being connected to the negative electrode layer 20 connected to the negative electrode external electrode 40b is referred to as the first end margin 80a. Similarly, the region where two negative electrode layers 20 connected to the negative electrode external electrode 40b face each other without being connected to the positive electrode layer 10 connected to the positive electrode external electrode 40a is referred to as the second end margin 80b. In other words, the end margin is the region where internal electrode layers connected to the same external electrode face each other without being connected to internal electrode layers connected to different external electrodes. The first end margin 80a and the second end margin 80b are regions where no battery capacity is generated.

[0036] As illustrated in Figure 5, in the stacked chip 60, the region extending from the two sides of the stacked chip 60 to the positive electrode layer 10 and the negative electrode layer 20 is referred to as the side margin 90. That is, the side margin 90 is a region provided in the stacked body that covers the ends of the multiple positive electrode layers 10 and negative electrode layers 20 that extend to the two sides.

[0037] In addition to the configuration described in Figure 2, the positive and negative electrode layers of an all-solid-state battery contain a conductive additive from the standpoint of conductivity. The conductive additive ensures conductivity between the external electrode and the electrode active material. The conductivity between the external electrode and the electrode active material due to the conductive additive will be explained below with reference to schematic cross-sectional diagrams.

[0038] Figure 6 is a diagram illustrating the conductivity between the electrode active material and the external electrode due to the conductive additive. As illustrated in the upper panel of Figure 6, the conductive additive 113 in the positive electrode layer 110 ensures conductivity between the positive electrode active material 111 and the positive electrode external electrode 140a. The conductive additive 123 in the negative electrode layer 120 ensures conductivity between the negative electrode active material 121 and the negative electrode external electrode 140b. The solid electrolyte layer 130 facilitates the movement of lithium ions between the positive electrode layer 110 and the negative electrode layer 120.

[0039] In this configuration, repeated charging and discharging cycles and subsequent lithium ion movement can cause repeated expansion and contraction of the positive electrode layer 110 and the negative electrode layer 120, potentially leading to cracks in both layers. In this case, as illustrated in the lower panel of Figure 6, the positive electrode active material 111 in the positive electrode layer 110 may become isolated from its surroundings, potentially severing the conductive path with the positive electrode external electrode 140a. Similarly, the negative electrode active material 121 in the negative electrode layer 120 may become isolated from its surroundings, potentially severing the conductive path with the negative electrode external electrode 140b. As a result, the battery capacity may decrease. Therefore, it is conceivable to modify the structure of the electrode layers; however, this may increase the manufacturing time and cost of the electrode layers.

[0040] (Embodiment) In this embodiment, a configuration is described that can maintain the conductive path and improve capacitance degradation with a simple structure and process. The specific configuration is described below.

[0041] Figure 7 is a schematic cross-sectional view illustrating the conductive additives provided in the positive electrode layer 10 and the negative electrode layer 20. The positive electrode layer 10 includes a conductive additive layer 13. The conductive additive layer 13 does not consist solely of a dense layer of conductive additives, but rather the conductive additives have a mesh-like structure. Therefore, the positive electrode active material 11 and solid electrolyte 12 described in Figure 2 may also be arranged in the conductive additive layer 13. In this embodiment, the conductive additive layer 13 has a mesh-like structure in which multiple fibrous carbon materials spread out planarly to form a layer when viewed from the Z-axis direction. The mesh-like structure of carbon materials refers to a structure in which multiple carbon materials contact each other at some point to conduct electricity, forming a three-dimensional network, and other materials (electrode active material and solid electrolyte) can exist within this three-dimensional network.

[0042] Furthermore, the conductive additive layer 13 has a thickness that is only a portion of the thickness of the positive electrode layer 10. Therefore, the conductive additive layer 13 does not constitute the entire thickness of the positive electrode layer 10. For example, as will be described later for Figures 10(a) to 12(c), when viewed from the Z-axis direction, if a 100 μm × 100 μm square region is divided into 15 × 15 = 225 squares of the same size, the carbon area occupancy rate, which is (total number of squares containing carbon material in the component analysis image) / 225 × 100%, is 50% or more in the region that has thickness in the Z-axis direction and extends in the X-axis and Y-axis directions. In the positive electrode layer 10, the region that is not the conductive additive layer 13 is the region where the carbon area occupancy rate, which is (total number of squares containing carbon material in the component analysis image) / 225 × 100%, is less than 30% when a 100 μm × 100 μm square region is divided into 15 × 15 = 225 squares of the same size.

[0043] According to this embodiment, the carbon material is not dispersed throughout the entire positive electrode layer 10, but rather concentrated in a portion to form the conductive additive layer 13. As illustrated by the rightward and leftward arrows in the upper diagram of Figure 8, a high-density conductive path is formed. Furthermore, since the carbon material constituting the conductive additive layer 13 is fibrous, it can stretch flexibly in the length direction even when tensile stress is applied. As a result, even if cracks occur within the positive electrode layer 10, the conductivity between the carbon material and the positive electrode active material 11 is ensured. Therefore, capacity degradation can be improved. Moreover, because the fibrous carbon material is flexible, the strength of the positive electrode layer 10 is improved, and cracking of the positive electrode layer 10 can be suppressed. In addition, since it is only necessary to disperse the fibrous carbon material in layers within the positive electrode layer 10, the conductive path can be maintained with a simple structure and process.

[0044] Furthermore, since the positive electrode active material 11 and the solid electrolyte 12 can also be placed within the conductive additive layer 13, the movement of lithium ions in the thickness direction within the positive electrode layer 10 becomes easier, as illustrated in the lower panel of Figure 8. For example, if a metal foil or the like is placed as a current collector layer, the movement of lithium ions in the thickness direction within the electrode layer may be hindered.

[0045] For example, in the positive electrode layer 10, the thickness of the conductive additive layer 13 is preferably 1 nm or more and 3 μm or less, more preferably 10 nm or more and 1 μm or less, and even more preferably 100 nm or more and 500 nm or less. The thickness of the conductive additive layer can be measured by measuring the thickness at 10 different points and taking the average value.

[0046] For example, in the positive electrode layer 10, the thickness of the conductive additive layer 13 is preferably 0.001% to 10%, more preferably 0.01% to 1%, and even more preferably 0.1% to 0.5% relative to the thickness of the positive electrode layer 10.

[0047] The negative electrode layer 20 also includes a conductive additive layer 23 in which conductive additives are concentrated. For example, in the negative electrode layer 20, the thickness of the conductive additive layer 23 is preferably 1 nm or more and 3 μm or less, more preferably 10 nm or more and 1 μm or less, and even more preferably 100 nm or more and 500 nm or less.

[0048] For example, in the negative electrode layer 20, the thickness of the conductive additive layer 23 is preferably 0.001% to 10%, more preferably 0.01% to 1%, and even more preferably 0.1% to 0.5% relative to the thickness of the negative electrode layer 20.

[0049] Furthermore, in the example shown in Figure 7, the positive electrode layer 10 and the negative electrode layer 20 each had one conductive additive layer. However, as illustrated in Figure 9, the positive electrode layer 10 and the negative electrode layer 20 may each have multiple conductive additive layers spaced apart from each other. In this case, the conductivity between the electrode active material and the external electrode is further improved.

[0050] Next, the planar structure of the conductive additive layer 13 as viewed from the Z-axis direction will be described. Figure 10(a) is an XY plan view of the conductive additive layer 13. The region in Figure 10(a) is a square region of 100 μm × 100 μm. As illustrated in Figure 10(a), in the conductive additive layer 13, fibrous carbon material 14 is dispersed in the XY plane to form a mesh-like structure.

[0051] Figure 10(b) shows the result of dividing Figure 10(a) into 15 × 15 = 225 squares of the same size. Figure 10(c) shows an extracted diagram of squares in which carbon material 14 is placed, at least partially. In Figure 10(c), a mesh pattern is added to the squares in which carbon material 14 is placed. Similarly, in subsequent figures, a mesh pattern is added to the squares in which carbon material 14 is placed. The ratio of the number of squares in which carbon material 14 is placed out of 225 squares is defined as the current collection area occupancy rate. That is, current collection area occupancy rate = (total number of squares in which carbon material 14 is placed) / 225 × 100%. In the example of Figure 10(c), the current collection area occupancy rate is 54%.

[0052] Figure 11(a) is a plan view of the conductive additive layer 13 when the current collection area occupancy rate is high. Figure 11(b) is a diagram of Figure 11(a) divided into 15 × 15 = 225 squares. Figure 11(c) is a diagram showing squares in which carbon material 14 is placed, even if only partially. In the example of Figure 11(c), the current collection area occupancy rate is 99%.

[0053] The current collection area occupancy rate (%) is preferably 50% or more, more preferably 67% or more, and even more preferably 90% or more.

[0054] Furthermore, even with the same current collection area occupancy rate, it is preferable that the carbon material 14 is dispersed as continuously as possible. For example, Figure 12(a) is a plan view of a conductive additive layer 13 with the same current collection area occupancy rate as Figure 10(a). Figure 12(b) is a diagram showing Figure 12(a) divided into 15 × 15 = 225 squares. Figure 12(c) is a diagram showing extracted squares in which the carbon material 14 is placed, even if only partially. In the example of Figure 12(c), the current collection area occupancy rate is 54%, the same as in the case of Figure 10(c).

[0055] However, in the case of Figure 10(c), the carbon material 14 is more dispersed than in the case of Figure 12(c). Therefore, we identify the regions in which the squares on which the carbon material 14 is placed are continuous via any side. For example, in the example of Figure 10(c), three regions in which the squares with the mesh pattern are continuous are identified. The largest of these regions has 107 squares with the mesh pattern. The ratio of this number to the total number of squares is defined as the continuity rate. That is, continuity rate = (number of squares in the largest region in which the squares on which the carbon material 14 is placed are adjacent to each other) / 225 × 100%. In the example of Figure 10(c), the continuity rate is 48%. In the example of Figure 12(c), it is 18%. This continuity rate is preferably 30% or more, more preferably 50% or more, and even more preferably 90% or more.

[0056] Figure 13(a) is a perspective view illustrating the carbon material 14 contained in the conductive additive layers 13 and 23. As illustrated in Figure 13(a), the carbon material 14 has a fibrous shape and has a major axis and a minor axis. The aspect ratio (major axis:minor axis), which is the ratio of the major axis to the minor axis, is preferably 100:1 to 3000:1, more preferably 125:1 to 1000:1, and even more preferably 150:1 to 500:1.

[0057] To ensure a sufficient conductive distance, the total length of the carbon material 14 is preferably 1.5 μm or more, more preferably 2.5 μm or more, and even more preferably 5 μm or more.

[0058] Furthermore, the carbon material 14 does not need to extend in a straight line in the positive electrode layer 10 and the negative electrode layer 20; it may be curved, as illustrated in Figure 13(b). Also, when using carbon nanotubes, the hollow portion may be a void or filled with other materials.

[0059] Figure 13(c) illustrates a cross-sectional view of the stacked layers of the positive electrode layer 10. The stacked cross-section can be exposed by grinding or other methods to remove material from the all-solid-state batteries 100 and 100a. The stacked cross-section can also be observed using a scanning electron microscope (SEM). The average diameter of the carbon material 14 can be calculated by randomly observing 300 carbon material 14 samples, measuring the shortest portion, and taking the average value. The average diameter of the carbon material 14 in the negative electrode layer 20 can be measured using a similar procedure.

[0060] In the example shown in Figure 7, the positive electrode layer 10 and the negative electrode layer 20 were provided with a conductive additive layer parallel to the XY plane. However, as illustrated in Figure 14, the positive electrode layer 10 and the negative electrode layer 20 may have a wave shape in the XZ cross-section. This configuration allows for the formation of three-dimensional conductive paths in both the XY plane and the Z axis direction. Furthermore, it can absorb tensile stress in the Z axis direction, thereby enhancing the crack suppression effect. It should be noted that even such a wave-shaped conductive additive layer appears to spread planarly in a plan view relative to the electrode layer.

[0061] Next, a method for manufacturing the all-solid-state battery 100a having the configuration shown in Figure 7 will be described. Figure 15 is a diagram illustrating a flow chart of the manufacturing method for the all-solid-state battery 100a.

[0062] (Electrolyte raw material powder preparation process) First, a raw material powder for the solid electrolyte layer that constitutes the solid electrolyte layer 30 described above is prepared. For example, a raw material powder for an oxide-based solid electrolyte can be prepared by mixing raw materials, additives, etc., and using a solid-phase synthesis method. The obtained raw material powder can be adjusted to the desired average particle size by dry grinding. For example, the desired average particle size can be adjusted using a planetary ball mill with 5 mmφ ZrO2 balls.

[0063] (Process for preparing the cover raw material powder) First, the raw material powder for the ceramics that make up the cover layer 50 is prepared. For example, the raw material powder for the cover layer can be prepared by mixing raw materials and additives and using a solid-phase synthesis method. The obtained raw material powder can be adjusted to the desired average particle size by dry grinding. For example, the desired average particle size can be adjusted using a planetary ball mill with 5 mmφ ZrO2 balls.

[0064] (Process for preparing paste for internal electrodes) Next, the internal electrode pastes for fabricating the positive electrode layer 10 and the negative electrode layer 20 are prepared separately. For example, the electrode active material and solid electrolyte material are highly dispersed using a bead mill or the like to produce a ceramic paste consisting only of ceramic particles. The ceramic paste and binder can then be mixed to produce the internal electrode paste.

[0065] The paste for internal electrodes contains 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 a sintering aid.

[0066] (Process for preparing paste for external electrodes) Next, an external electrode paste is prepared for the fabrication of the positive 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.

[0067] (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.

[0068] (Lamination process) As illustrated in Figure 16(a), an internal electrode pattern 52 is formed on one surface of the solid electrolyte green sheet 51. In the areas on the solid electrolyte green sheet 51 where the internal electrode pattern 52 is not formed, an inverse pattern 53 is formed. The same material as the solid electrolyte green sheet 51 can be used as the inverse pattern 53. Then, as illustrated in Figure 16(b), multiple solid electrolyte green sheets 51 are stacked alternately with a slight offset.

[0069] Figure 17 illustrates a method for forming the internal electrode pattern 52. As illustrated in Figure 17, after applying the internal electrode paste 52a onto the solid electrolyte green sheet 51, the carbon material 14 is sprayed using a spray 80 containing a dispersion of carbon material 14 mixed with compressed air. Since the fibrous carbon material 14 is entangled, it is dispersed using an ultrasonic homogenizer or wet jet mill with an appropriate dispersant. After that, the internal electrode paste 52a is applied again. This allows the internal electrode pattern 52 to be formed. If the positive electrode layer 10 and the negative electrode layer 20 are provided with multiple conductive additive layers 13 and 23, the procedure in Figure 17 can be repeated.

[0070] Furthermore, when spraying with spray 80, it is preferable to observe the overlapping distribution of the carbon material 14 under a microscope and determine the number of sprays required so that the entire surface is connected with the carbon material 14 and lithium ions can pass through without the mesh becoming clogged. The spray density can also be adjusted by changing the carbon type and dilution concentration. The spraying state can be quantified and confirmed using spray film thickness, film resistance, etc.

[0071] Next, as illustrated in Figure 18, a laminate is obtained by pressing the cover sheet 54 from above and below in the stacking direction. In this case, a roughly rectangular parallelepiped green chip is obtained in the laminate such that the internal electrode pattern 52 for the positive electrode layer 10 is exposed on one end face and the internal electrode pattern 52 for the negative electrode layer 20 is exposed on the other end face. The cover sheet 54 can be formed by coating the raw material powder for the cover layer using the same method as in the solid electrolyte green sheet manufacturing process. The cover sheet 54 is formed to be thicker than the solid electrolyte green sheet 51. It may be made thicker during coating, or it may be made thicker by stacking multiple coated sheets.

[0072] (Firing process) Next, the laminated body is fired to obtain a laminated chip 60. The firing conditions are not particularly limited to an oxidizing atmosphere or a non-oxidizing atmosphere, with a maximum temperature preferably set to 400°C to 1000°C, more preferably 500°C to 900°C. A step may be included in which the body is held at a temperature lower than the maximum temperature in an oxidizing atmosphere in order to sufficiently remove the binder before reaching the maximum temperature. To reduce process costs, it is desirable to fire at the lowest possible temperature. After firing, a re-oxidation treatment may be performed.

[0073] (External electrode formation process) Subsequently, a paste for external electrodes is applied to two end faces of the laminated chip 60, formed, and cured to create a positive external electrode 40a and a negative external electrode 40b. Through these steps, an all-solid-state battery 100a is produced.

[0074] In the above embodiment, a conductive additive layer was provided on both the positive electrode layer 10 and the negative electrode layer 20. However, providing a conductive additive layer on at least one of them will yield effects such as improved capacitance degradation. [Examples]

[0075] (Examples 1-4 and Comparative Examples) A stacked all-solid-state battery was fabricated according to the manufacturing method described in Figures 15 to 17. In all of Examples 1 to 4, three conductive additive layers were formed on both the positive electrode layer and the negative electrode layer. In Examples 1 to 3, three conductive additive layers were formed parallel to the XY plane, as explained in Figure 9. In Example 4, three conductive additive layers were formed in a corrugated shape, as explained in Figure 14. In the comparative example, no conductive additive layers were formed.

[0076] As explained in Figure 17, after spraying the carbon material, the current collection area occupancy rate was 30% in Example 1, 50% in Example 2, 99% in Example 3, and 99% in Example 4. No change occurred in these current collection area occupancy rates after firing.

[0077] (0.2C cycle test) To confirm the resistance to expansion and contraction, the charge and discharge cycles were repeated 10 times at 0.2C, and the discharge capacity retention rate (the ratio of the capacity after 10 cycles to the initial capacity (%)) was measured. Measurements were performed on 5 samples for each of Examples 1-4 and the comparative example. Of the 5 samples, the number of samples with a discharge capacity retention rate of 80% or more was counted. Furthermore, after polishing, the cross-section along the lamination direction was observed, and the number of samples without internal cracks (fissures) was counted.

[0078] (2C cycle test) To confirm the resistance to expansion and contraction, the charge and discharge cycles were repeated 100 times at 2C, and the degradation of discharge capacity (ratio of capacity after 100 cycles to initial capacity (%)) was measured. Measurements were performed on 5 samples for each of Examples 1-4 and the comparative example. Of the 5 samples, the number of samples with a discharge capacity retention rate of 80% or more was counted. Furthermore, after polishing, the cross-section along the lamination direction was observed, and the number of samples without internal cracks (fissures) was counted.

[0079] (Maximum voltage continuous charging test) To confirm the resistance to expansion and contraction, continuous charging was performed at the maximum voltage, and the degradation of discharge capacity (ratio of capacity after continuous charging to initial capacity (%)) after 1000 hours was measured. Measurements were performed on five samples for each of Examples 1-4 and the comparative example. Of the five samples, the number of samples with a discharge capacity retention rate of 80% or more was counted. Furthermore, after polishing, the cross-section along the lamination direction was observed, and the number of samples without internal cracks (fissures) was counted.

[0080] The results are shown in Table 1. [Table 1]

[0081] In the comparative example, since there were a total of 7 samples without cracking, it can be seen that there were a total of 8 samples with cracking. Since there were a total of 8 samples with a discharge capacity retention rate of 80% or higher, it can be seen that there were a total of 7 samples with a discharge capacity retention rate below 80%. From these results, it is considered that in the comparative example, because a conductive additive layer of fibrous carbon material was not provided in the electrode layer, cracking occurred in the electrode layer, and the conductivity between the electrode active material and the external electrode decreased. In the comparative example, because there were a large number of samples with a discharge capacity retention rate below 80% and a large number of samples with cracking, it was judged as a failure ("×").

[0082] In contrast, in Example 1, the number of samples with cracks in the electrode layer decreased significantly, and the number of samples with a discharge capacity retention rate below 80% also decreased significantly. This is thought to be because the presence of a conductive additive layer of fibrous carbon material in the electrode layer suppressed cracking of the electrode layer and maintained conductivity between the electrode active material and the external electrode. In Example 1, the number of samples with a discharge capacity retention rate below 80% and the number of samples with cracks were small, so it was judged as a pass ("△").

[0083] In Example 2, compared to Example 1, the number of samples with cracks in the electrode layer was further reduced, and the number of samples with a discharge capacity maintenance rate below 80% was also further reduced. This is thought to be due to the increased current collection area occupancy rate. In Example 3, compared to Example 2, the number of samples with cracks in the electrode layer was reduced. This is thought to be due to the increased current collection area occupancy rate. In Example 4, cracking was suppressed even more than in Example 3. This is thought to be because the conductive additive layer was made wave-shaped, which allowed for the absorption of tensile stress in the thickness direction. In Example 2, the number of samples with a discharge capacity maintenance rate below 80% and the number of samples with cracks were lower than in Example 1, so it was judged as good ("〇"). In Example 3, the number of samples with cracks was lower than in Example 1, so it was judged as very good ("◎").

[0084] 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]

[0085] 10 Positive electrode layer 11 Cathode active material 12 Solid electrolyte 13 Conductive additive layer 20 Negative electrode layer 21 Negative electrode active material 22 Solid electrolyte 23 Conductive additive layer 30 Solid electrolyte layer 40a Positive external electrode 40b Negative external electrode 50 Cover Layers 51 Solid Electrolyte Green Sheet 52 Internal electrode pattern 53 Reverse Pattern 54 Cover Sheets 60 stacked chips 70 Side Margin 100,100a solid state battery

Claims

1. A solid electrolyte layer, A first electrode layer 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 of the solid electrolyte layer, An all-solid-state battery in which a carbon material forms a mesh-like layer in a portion of the thickness of the first electrode layer.

2. The all-solid-state battery according to claim 1, wherein the thickness of the carbon material layer is 1 nm or more and 3 μm or less.

3. The all-solid-state battery according to claim 1, wherein the thickness of the carbon material layer is 0.001% or more and 10% or less relative to the thickness of the first electrode layer.

4. The all-solid-state battery according to claim 1, wherein in the first electrode layer, multiple layers of the carbon material are provided spaced apart from each other.

5. The all-solid-state battery according to claim 1, wherein, when the first electrode layer is viewed in plan view, in the layer of carbon material, if a 100 μm × 100 μm square region is divided into 15 × 15 = 225 squares of the same size, the current collection area occupancy rate, which is (total number of squares on which the carbon material is arranged) / 225 × 100%, is 50% or more.

6. The all-solid-state battery according to claim 1, wherein in a cross-section including the stacking direction of the solid electrolyte layer, the first electrode layer, and the second electrode layer, the layer of carbon material has a wave shape.

7. The all-solid-state battery according to claim 1, wherein the carbon material is a carbon nanotube.

8. The all-solid-state battery according to claim 1, wherein the carbon material is fibrous.

9. The all-solid-state battery according to claim 1, wherein the total length of the carbon material is 5 μm or more.

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