Manufacturing method for energy storage devices

Abstract

To provide a power storage device including a high-quality laminate.SOLUTION: A buffer layer 24 is provided between a laminate 10 of a plurality of layers for power storage devices provided in a cylindrical die 21 and a punch 22 inserted into e.g., an opening 21a of the die 21. The laminate 10 in the die 21 is pressurized by the punch 22 via the buffer layer 24 while being heated. A powder 26 flowing along a surface shape of the heated and pressurized laminate 10 is used for the buffer layer 24. In the case of pressurization using the punch 22, the laminate 10 is pushed in an isotropic manner by the powder 26 of the buffer layer 24 flowing along the surface shape. Thus, provided is the high-quality laminate 10 in which breakage or fault of internal layers is suppressed. Further, provided is a high-quality power storage device using such a laminate 10.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a power storage device.

Background Art

[0002] Various power storage devices are known, such as a multilayer ceramic capacitor including a laminate of an electrode layer and a dielectric layer, and a solid-state battery including a laminate of an electrode layer and an electrolyte layer. For example, as a method for manufacturing a positive electrode-solid electrolyte composite for an all-solid-state power storage element, a laminate in which a plate-shaped positive electrode made of a ceramic sintered body containing a positive electrode active material and a plate-shaped solid electrolyte made of a ceramic sintered body having ion conductivity are laminated is heated and pressurized by a hot pressing method, and a technique for integrating the positive electrode and the solid electrolyte by a solid-phase reaction is known.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in hot pressing of a laminate of dissimilar layers such as an electrode layer and a dielectric layer, or an electrode layer and an electrolyte layer, for example, a laminate provided in a cylindrical die is pressed by a punch inserted from an opening of the die, and heating and pressurization are performed. In this case, if there are irregularities on the surface of the laminate facing the flat pressing surface of the punch, or if irregularities are formed on the surface of the laminate due to deformation accompanying heating, when pressurizing with the punch, starting from the irregularities on the surface of the laminate, there is a risk of occurrence of defects such as breakage of layers in the laminate and delamination due to fusion after breakage. Such defects can lead to a deterioration in the quality of the laminate and further a deterioration in the quality of the power storage device including the laminate.

[0005] In one aspect, the present invention aims to realize an energy storage device comprising a high-quality laminate. [Means for solving the problem]

[0006] In one embodiment, the process includes a first placement step of placing a first buffer layer between a laminate of multiple layers provided inside a cylindrical die and a first punch inserted into a first opening of the die, and a heating and pressurizing step of heating the laminate inside the die and pressurizing it with the first punch through the first buffer layer, wherein the first buffer layer flows along the surface shape of the laminate being heated and pressurized. Furthermore, it is non-reactive with the laminate. A method for manufacturing an energy storage device using powder is provided. [Effects of the Invention]

[0007] In one respect, it becomes possible to realize energy storage devices with high-quality laminates. [Brief explanation of the drawing]

[0008] [Figure 1] This diagram illustrates an example of hot pressing of a laminate. [Figure 2] This figure illustrates an example of hot pressing of a laminate according to an embodiment. [Figure 3] This figure illustrates an example of a hot pressing process for a laminate according to an embodiment. [Modes for carrying out the invention]

[0009] First, we will describe an example of hot pressing of a laminated structure. Figure 1 illustrates an example of hot pressing of a laminate. Figure 1(A) schematically shows a cross-sectional view of an example of a laminate being hot pressed. Figure 1(B) schematically shows a cross-sectional view of an example of the hot pressing process of a laminate.

[0010] For hot pressing, for example, a laminate 10 in which a plurality of layers (also referred to as a layer group) are laminated as shown in FIG. 1(A) is used. As an example, FIG. 1(A) shows a laminate 10 which is a battery element of a solid battery such as a lithium ion secondary battery.

[0011] The laminate 10 includes an electrolyte layer 13, a positive electrode layer 11, and a negative electrode layer 12 as a plurality of layers, and has a structure in which these layer groups are laminated in a predetermined order. The positive electrode layer 11 and the negative electrode layer 12 (one or both of these are also referred to as electrode layers) are laminated via the electrolyte layer 13, and the electrode layers (positive electrode layer 11 or negative electrode layer 12) of the uppermost layer and the lowermost layer are covered with the electrolyte layer 13. From the opposing side surfaces 10a and 10b of the laminate 10, a part 11a of the side surface of the positive electrode layer 11 and a part 12a of the side surface of the negative electrode layer 12 are exposed. The side surfaces of the positive electrode layer 11 and the negative electrode layer 12 excluding the parts 11a and 12a are covered with the electrolyte layer 13. The parts 11a of the side surface of the positive electrode layer 11 and the parts 12a of the side surface of the negative electrode layer 12 exposed from the electrolyte layer 13 are the sites where the positive and negative external electrodes (terminals) of the solid battery having this laminate 10 as a battery element are connected. Note that the number of layers of the laminate 10 is not limited to that shown in FIG. 1(A) and the like.

[0012] The electrolyte layer 13 of the laminate 10 contains a solid electrolyte, for example, an oxide solid electrolyte such as LAGP represented by the general formula Li 1+x Al x Ge 2-x (PO4)3 (0 < x ≦ 1) is used.

[0013] The positive electrode layer 11 of the laminate 10 contains a positive electrode active material and a solid electrolyte. For the positive electrode active material of the positive electrode layer 11, cobalt lithium pyrophosphate (Li2CoP2O7, hereinafter referred to as "LCPO") and the like are used. For the solid electrolyte of the positive electrode layer 11, LAGP and the like are used. The positive electrode layer 11 may contain a conductive aid such as a carbon material.

[0014] The negative electrode layer 12 of the laminate 10 contains a negative electrode active material and a solid electrolyte. Titanium oxide (TiO2) or niobium pentoxide (Nb2O5) are used as the negative electrode active material in the negative electrode layer 12. LAGP or the like are used as the solid electrolyte in the negative electrode layer 12. The negative electrode layer 12 may also contain conductive additives such as carbon materials.

[0015] Furthermore, the solid electrolyte contained in the positive electrode layer 11 is also called the "first solid electrolyte," the solid electrolyte contained in the negative electrode layer 12 is also called the "second solid electrolyte," and the solid electrolyte contained in the electrolyte layer 13 is also called the "third solid electrolyte."

[0016] When forming the laminate 10, a paste is prepared for the electrolyte layer 13 by mixing a solid electrolyte with an organic binder, plasticizer, dispersant, etc. A paste is prepared for the positive electrode layer 11 by mixing a positive electrode active material and a solid electrolyte with an organic binder, plasticizer, dispersant, etc. A paste is prepared for the negative electrode layer 12 by mixing a negative electrode active material and a solid electrolyte with an organic binder, plasticizer, dispersant, etc.

[0017] Pastes for these electrolyte layers 13, positive electrode layers 11, and negative electrode layers 12 are used. By the screen printing method or doctor blade method, green sheets corresponding to each of the layer groups included in the laminate 10 as shown in Fig. 1(A) are formed, and the formed green sheets are laminated so as to be in the order of the layer group as shown in Fig. 1(A). Alternatively, pastes for the electrolyte layer 13, positive electrode layer 11, and negative electrode layer 12 are used and are applied and laminated in order from the lower layer to the upper layer so as to be in the order of the layer group as shown in Fig. 1(A). During lamination, the positive electrode layer 11 and the negative electrode layer 12 face each other through the electrolyte layer 13, and lamination is performed such that a portion where the positive electrode layer 11 and the negative electrode layer 12 do not overlap with each other is formed. The structure laminated in this way is dried under predetermined conditions to remove relatively low-boiling organic components, and then, if necessary, is cut at a predetermined position, that is, at a position corresponding to the portion where the positive electrode layer 11 and the negative electrode layer 12 do not overlap with each other. By cutting, a structure is obtained in which a part 11a of the side surface of the positive electrode layer 11 and a part 12a of the side surface of the negative electrode layer 12 are exposed from the opposing side surfaces 10a and 10b, respectively. Then, heat treatment is performed on the structure under predetermined conditions, and degreasing is performed mainly to burn out and remove organic components such as binders. Thereby, a degreased laminate 10 in which the layer group as shown in Fig. 1(A) is laminated is formed.

[0018] In addition, a coating layer made of a material such as glass or ceramics may be formed on the portion that becomes the outer surface of the laminate 10 instead of the electrolyte layer 13 or further outside the electrolyte layer 13. In this case, a paste in which a material such as glass is mixed with a binder or the like is prepared, a structure is formed in which the portion that becomes the outer surface of the laminate 10 is laminated with the paste, and the structure is dried, cut if necessary, and further degreased.

[0019] The laminate 10 as shown in Fig. 1(A) is further heat-treated under predetermined conditions, and firing is performed mainly to sinter the solid electrolyte (when a coating layer is formed, the material such as glass thereof is further sintered).

[0020] Here, for example, when nothing is placed on the laminate 10 or when baking is performed with a lightweight plate placed thereon for warp suppression, since the laminate 10 has a structure containing different materials, voids and cracks are likely to occur inside the laminate 10 due to differences in shrinkage rate and shrinkage start temperature between different materials. When the layer group of the laminate 10 is thin, due to cracks or the like generated inside, there is also a risk of breakage of the electrolyte layer 13, the positive electrode layer 11, or the negative electrode layer 12, or a short circuit due to contact between the broken positive electrode layer 11 and the negative electrode layer 12.

[0021] In view of such points, it is considered to perform hot pressing on the laminate 10 as shown in FIG. 1(A) using the hot press device 20 as shown in FIG. 1(B). Here, an example of hot pressing of one laminate 10 using the hot press device 20 will be described.

[0022] The hot press device 20 shown in FIG. 1(B) includes a cylindrical die 21, a punch 22 inserted into one opening 21a of the die 21, and a punch 23 inserted into the other opening 21b (opposite to the opening 21a) of the die 21. As the cylindrical die 21, a cylindrical or rectangular cylindrical one, or one with a circular or polygonal planar shape of the opening 21a and the opening 21b can be used. As the punch 22 and the punch 23, a cylindrical or rectangular cylindrical one that can be inserted into the opening 21a and the opening 21b of the die 21 can be used. For the die 21, the punch 22, and the punch 23, for example, those made of graphite are used.

[0023] Incidentally, one opening 21a of the die 21 is also referred to as the "first opening", the punch 22 inserted into this opening 21a is also referred to as the "first punch", the other opening 21b of the die 21 is also referred to as the "second opening", and the punch 23 inserted into this opening 21b is also referred to as the "second punch".

[0024] Alternatively, one opening 21a of the die 21 is also referred to as the "second opening", the punch 22 inserted into this opening 21a is also referred to as the "second punch", the other opening 21b of the die 21 is also referred to as the "first opening", and the punch 23 inserted into this opening 21b is also referred to as the "first punch".

[0025] During the hot pressing of the laminate 10, for example, the degreased and unbaked laminate 10 (one example here) is placed on a punch 23 inserted into the lower opening 21b of the die 21, and a punch 22 is inserted into the upper opening 21a of the die 21. As a result, the laminate 10 is sandwiched between the punch 22 and punch 23 from above and below within the die 21. From this state, the punch 22 and punch 23 are guided by the die 21 and pressurized toward the laminate 10. Figure 1(B) schematically shows this pressurization process as pressurization 30.

[0026] When the laminate 10 is pressed by punches 22 and 23 in this manner, it is heated using a heating device (not shown), such as a heater placed outside the die 21, punches 22 and 23. Figure 1(B) schematically shows this heating process as heating 40. The heating is carried out under conditions that cause the degreased laminate 10 to be fired. This firing process mainly sinters the solid electrolyte (and, if a coating layer is formed, the glass or other material) contained in the degreased laminate 10.

[0027] According to the hot press method shown in Figure 1(B), by heating and pressurizing the laminate 10, it is expected that the thermal deformation of the laminate 10 during heating can be suppressed by the pressurization, while the solid electrolyte can be sintered by the heating.

[0028] However, the surfaces 10c and 10d of the degreased laminate 10, that is, the surfaces 10c and 10d facing the flat pressure surfaces 22a and 23a of the punches 22 and 23, respectively, may have irregularities formed due to the heat treatment for degreasing. If irregularities are formed on the surfaces 10c and 10d of the laminate 10, it may not be possible to form a high-quality laminate 10 using the hot press shown in Figure 1(B).

[0029] For example, during the heat treatment for degreasing, organic components such as binders may be removed from the inside of the laminate 10, or deformation may occur due to the heat and removal of organic components during the heat treatment, which may result in the formation of irregularities on the surface 10c of the laminate 10 after degreasing. The height of the irregularities formed on the surface 10c of the laminate 10 after degreasing (the difference in height between the bottom of the recess and the top of the convex) is, for example, about a few micrometers. Furthermore, irregularities may be formed not only on the surface layer 10c of the laminate 10 after degreasing (electrolyte layer 13 in this example), but also on the internal layers (positive electrode layer 11 and negative electrode layer 12 and the electrolyte layer 13 between them in this example).

[0030] The degreased laminate 10, with its surface 10c having irregularities, is set in a hot press device 20 as shown in Figure 1(B), and heated and pressurized. At this time, the flat pressurizing surface 22a of the punch 22 of the hot press device 20 faces the surface 10c of the laminate 10 on the punch 22 side. The surface 10c of the laminate 10 with irregularities is then pressed by the flat pressurizing surface 22a of the punch 22 (pressurization 30).

[0031] As the laminate 10 is pressed by the flat pressing surface 22a of the punch 22, the irregularities on the surface 10c are flattened while the layers are pressurized. However, in this case, the flat pressing surface 22a of the punch 22 first contacts the protrusions on the irregularities of the surface 10c of the laminate 10 and begins to press locally on those protrusions, gradually pressing down on the entire surface 10c. When pressed by the flat pressing surface 22a of the punch 22 in this way, the irregularities on the surface 10c of the laminate 10 can act as a crater, potentially causing fracture. Specifically, fractures can occur that sever one or more of the electrolyte layer 13, positive electrode layer 11, and negative electrode layer 12 contained in the laminate 10. Since the degreased laminate 10, from which organic components such as binders have been removed, is relatively brittle, such fractures are likely to occur even at relatively low pressures applied by the punch 22. Fracture may lead to a reduction in the area of ​​the positive or negative electrode layer within the laminate 10, an increase in resistance, and other problems.

[0032] Furthermore, if firing proceeds while fractures have occurred, the fractured layers may fuse together, potentially leading to tomography. If the layers included in the laminate 10 are relatively thin and the displacement in the stacking direction due to tomography is relatively large, there is a risk of contact between the layers, for example, contact between the fractured positive electrode layer 11 and the negative electrode layer 12, leading to a short circuit.

[0033] Thus, in the case of a laminate 10 in which irregularities are formed on the surface 10c after degreasing, hot pressing may cause fracture or tomographic fracture due to fusion after fracture in the layers within the laminate. Fracture or tomographic fracture of the laminate 10 can lead to a decrease in the quality of the laminate 10, and further to a decrease in the quality and performance of solid-state batteries using the laminate 10.

[0034] Here, we have used the surface 10c of the laminate 10 on the punch 22 side, which is pressed by one punch 22 in the hot press device 20, as an example. However, the same thing can happen to the surface 10d (Figure 1(B)) of the laminate 10 on the punch 23 side, which is pressed by the other punch 23. That is, after degreasing, irregularities can be formed on the surface 10d of the laminate 10, similar to surface 10c. When surface 10d is pressed by the flat pressure surface 23a of punch 23, the irregularities on surface 10d can act as a starting point, causing fractures and torpor formation similar to those described above. This can lead to a deterioration in the quality of the laminate 10 and the solid-state battery using it.

[0035] Furthermore, it is conceivable to increase the thickness of the layers of the laminate 10, for example, by increasing the thickness of the uppermost and lowermost electrolyte layers 13 (or coating layers using glass, etc.), in order to obtain a laminate 10 that suppresses the formation of irregularities on the surface 10c and surface 10d after degreasing, thereby suppressing fracture and tomography caused by irregularities. However, in this case, in order to make the laminate 10 the predetermined thickness, it is necessary to remove the contact surfaces with punches 22 and 23 after hot pressing to make them thinner, which is time-consuming. Alternatively, it is conceivable to sandwich a sheet material such as a carbon sheet between the laminate 10 and punches 22 and 23. However, in this case, relatively large irregularities or undulations of the sheet material will be reflected in the surface shape of the laminate 10, so it is necessary to remove the surface to flatten it, which is time-consuming. For this reason, using these methods is not advisable.

[0036] Furthermore, here we used the laminated body 10, which is a battery element of a solid-state battery, a type of energy storage device, as an example. In addition, regarding the laminated body, which is a capacitor element of a multilayer ceramic capacitor, a type of energy storage device, that is, the laminated body of an electrode layer (internal electrode layer) and a dielectric layer, when a laminated body is formed by laminating green sheets, etc., and then hot-pressed, surface irregularities may be formed due to the formation of the laminated body (heat treatment for degreasing, etc.), resulting in fracture or torticollation during hot pressing, and consequently, a deterioration in the quality of the laminated body and the multilayer ceramic capacitor may occur.

[0037] In view of the above points, a high-quality laminate and an energy storage device equipped with such a laminate are realized using the method shown below as an embodiment. [Embodiment] Figure 2 illustrates an example of hot pressing of a laminate according to an embodiment. Figure 2 schematically shows a cross-sectional view of an example of the hot pressing process for a laminate.

[0038] Here, we will use the hot pressing of a laminate 10 (Figure 1(A)), which is a battery element of a solid-state battery such as a lithium-ion secondary battery, as an example. Here, we will use the hot pressing of a single laminate 10 as an example.

[0039] The laminate 10 comprises multiple layers (also called a group of layers), including an electrolyte layer 13 containing a solid electrolyte, a positive electrode layer 11 containing a positive electrode active material and a solid electrolyte, and a negative electrode layer 12 containing a negative electrode active material and a solid electrolyte, and has a structure in which these group of layers are stacked in a predetermined order. The laminate 10 is stacked so that the positive electrode layer 11 and the negative electrode layer 12 face each other via the electrolyte layer 13, and has a structure in which the sides of the positive electrode layer 11 and the sides of the negative electrode layer 12, excluding some parts 11a and 12a, are covered by the electrolyte layer 13. The electrolyte layer 13, positive electrode layer 11, and negative electrode layer 12 are each made of the materials described above. Specifically, the electrolyte layer 13 is made of, for example, a solid electrolyte such as LAGP. The positive electrode layer 11 is made of, for example, a positive electrode active material such as LCPO, a solid electrolyte such as LAGP, and a conductive additive such as a carbon material. The negative electrode layer 12 may contain, for example, a negative electrode active material such as TiO2 or Nb2O5, a solid electrolyte such as LAGP, or a conductive additive such as a carbon material.

[0040] Furthermore, the solid electrolyte contained in the positive electrode layer 11 is also called the "first solid electrolyte," the solid electrolyte contained in the negative electrode layer 12 is also called the "second solid electrolyte," and the solid electrolyte contained in the electrolyte layer 13 is also called the "third solid electrolyte."

[0041] When forming the laminate 10, first, as described above, pastes for the electrolyte layer 13, positive electrode layer 11, and negative electrode layer 12 are prepared using organic binders, plasticizers, dispersants, etc., and a structure is formed by laminating these pastes in a predetermined order. Then, the formed structure is dried, cut if necessary, and degreased. For example, the structure is degreased by holding it at 500°C for 10 hours in an oxygen-containing atmosphere. This forms the degreased laminate 10 shown in Figure 2.

[0042] Furthermore, a coating layer made of glass, ceramics, or other materials may be formed on the outer surface of the laminate 10, either in place of the electrolyte layer 13 or on the outside of the electrolyte layer 13.

[0043] For hot pressing the degreased laminate 10, a hot press apparatus 20 as shown in Figure 2 is used, as described above. The hot press apparatus 20 has a cylindrical die 21, a punch 22 inserted into one opening 21a of the die 21, and a punch 23 inserted into the other opening 21b of the die 21 (opposite to opening 21a). The cylindrical die 21 can be cylindrical or rectangular, and the planar shapes of the openings 21a and 21b can be circular or polygonal. The punches 22 and 23 can be cylindrical or prismatic in shape that can be inserted into the openings 21a and 21b of the die 21. For example, the die 21, punches 22 and 23 can be made of graphite.

[0044] In this embodiment, when hot pressing the laminate 10, for example, as shown in Figure 2, a buffer layer 25 is placed on a punch 23 inserted into the lower opening 21b of the die 21. The degreased and unbaked laminate 10 (one example here) is placed on the buffer layer 25. Another buffer layer 24 is placed on the laminate 10. Then, a punch 22 is inserted into the upper opening 21a of the die 21. In this embodiment, the laminate 10 is positioned inside the die 21 so as to be sandwiched between the punch 22 and punch 23 from above and below, via the buffer layers 24 and 25, respectively. The thickness of each of the buffer layers 24 and 25 is set to, for example, a range of 0.5 mm to 1 mm.

[0045] Furthermore, one opening 21a of the die 21 is also called the "first opening," and the punch 22 inserted into this opening 21a is also called the "first punch." The other opening 21b of the die 21 is also called the "second opening," and the punch 23 inserted into this opening 21b is also called the "second punch." In this case, the buffer layer 24 placed between the laminate 10 and the punch 22 inside the die 21 is also called the "first buffer layer," and the buffer layer 25 placed between the laminate 10 and the punch 23 inside the die 21 is also called the "second buffer layer." In addition, in this case, the process of placing the buffer layer 24 between the laminate 10 and the punch 22 is also called the "first placement process," and the process of placing the buffer layer 25 between the laminate 10 and the punch 23 is also called the "second placement process."

[0046] Alternatively, one opening 21a of the die 21 may be called the "second opening," and the punch 22 inserted into this opening 21a may be called the "second punch," while the other opening 21b of the die 21 may be called the "first opening," and the punch 23 inserted into this opening 21b may be called the "first punch." In this case, the buffer layer 24 placed between the laminate 10 and the punch 22 within the die 21 may be called the "second buffer layer," and the buffer layer 25 placed between the laminate 10 and the punch 23 within the die 21 may be called the "first buffer layer." Furthermore, in this case, the process of placing the buffer layer 24 between the laminate 10 and the punch 22 may be called the "second placement process," and the process of placing the buffer layer 25 between the laminate 10 and the punch 23 may be called the "first placement process."

[0047] The buffer layers 24 and 25, which are placed between the laminate 10 and the punches 22 and 23 within the die 21, respectively, use powder 26 consisting of a collection of multiple particles 26a (also called a group of particles 26a), as shown in the enlarged view of a portion of the buffer layer 24 in Figure 2.

[0048] The particle group 26a of the powder 26 in the buffer layer 24 and buffer layer 25 uses physically and chemically stable particles 26a that are less prone to sintering with each other under the heating and pressurizing conditions during hot pressing, have good slipperiness between particles 26a, and have low reactivity (also called "unreactive") with the laminate 10 and punches 22 and 23. The powder 26, which is an aggregate of such particles 26a, exhibits fluidity when pressed by punches 22 and 23 in the die 21, as described later. For example, graphite particles or hexagonal boron nitride (h-BN) particles are used for the particle group 26a of the powder 26 in the buffer layer 24 and buffer layer 25. That is, for example, graphite powder or h-BN powder is used as powder 26. For example, particles with a particle size in the range of 0.1 μm to 10 μm are used for the particle group 26a.

[0049] Furthermore, the powder 26 in buffer layers 24 and 25 can be made of various materials, not limited to graphite powder or h-BN powder, as long as it possesses the above-mentioned properties and exhibits fluidity under the heating and pressurizing conditions during hot pressing.

[0050] Furthermore, the powder 26 of buffer layer 24 and buffer layer 25 may be an aggregate of particles 26a of one type of material, or an aggregate of particles 26a of multiple types of materials. The powder 26 of buffer layer 24 and buffer layer 25 does not necessarily have to be an aggregate of spherical particles 26a, but may be an aggregate of particles 26a of various shapes, or an aggregate of particles 26a of various shapes mixed together. The powder 26 of buffer layer 24 and buffer layer 25 does not necessarily have to be an aggregate of particles 26a of the same particle size, but may be an aggregate of particles 26a with a relatively narrow or broad constant particle size distribution.

[0051] As shown in Figure 2, the degreased laminate 10 is sandwiched between punches 22 and 23 from above and below, via buffer layers 24 and 25, respectively, within the die 21. From this state, punches 22 and 23 are guided by the die 21 and pressurized toward the laminate 10. Figure 2 schematically shows this pressurization process as pressurization 30. For example, the laminate 10 is pressurized at a pressure in the range of 10 MPa to 30 MPa.

[0052] When the laminate 10 is pressed by punches 22 and 23 in this manner, it is heated using a heating device (not shown), such as a heater. Figure 2 schematically shows this heating process as heating 40. The heating is carried out under conditions that would cause the degreased laminate 10 to sinter. For example, the laminate 10 is sintered under conditions of being held at 600°C for 2 hours in an atmosphere containing nitrogen or oxygen. Through this heating and sintering process, the solid electrolyte (and, if a coating layer is formed, the glass or other material) contained in the degreased laminate 10 is mainly sintered.

[0053] During heating and pressurization, the laminate 10 is pressed from above and below by punches 22 and 23 via buffer layers 24 and 25. At this time, the powder 26 (group of particles 26a) in the buffer layer 24, which is interposed between the surface 10c of the laminate 10 and the flat pressurizing surface 22a of the punch 22, flows along the surface shape of the laminate 10, i.e., the shape of surface 10c. Similarly, the powder 26 (group of particles 26a) in the buffer layer 25, which is interposed between the surface 10d of the laminate 10 and the flat pressurizing surface 23a of the punch 23, flows along the surface shape of the laminate 10, i.e., the shape of surface 10d. The laminate 10 is pressed from above and below by punches 22 and 23 via buffer layers 24 and 25, which use powder 26 exhibiting such fluidity, and is heated and pressurized.

[0054] Furthermore, the process of applying pressure to the laminate 10 inside the die 21 with the punch 22 via the buffer layer 24 while heating, or the process of applying pressure with the punch 23 via the buffer layer 25 while heating, or the process of applying pressure with the punch 22 and punch 23 via the buffer layer 24 and buffer layer 25 while heating, is also called the "heating and pressurizing process".

[0055] The heating and pressurizing of the laminate 10 will be further explained with reference to Figure 3. Figure 3 illustrates an example of a hot pressing process for a laminate according to an embodiment. Figure 3(A) schematically shows a cross-sectional view of a key part of an example of a hot pressing process for a laminate. Figure 3(B) schematically shows a cross-sectional view of a key part of an example of a laminate after the hot pressing process.

[0056] Figures 3(A) and 3(B) schematically show a portion of the laminate 10, a portion of the buffer layer 24, and a portion of the punch 22, which correspond to the Q1 portion shown in Figure 2 above. For example, as shown in Figure 3(A), if the surface 10c of the degreased laminate 10 is flat, when heating and pressurizing using the hot press device 20, the flat surface 10c of the laminate 10 is pressed (pressurized 30) by the flat pressing surface 22a of the punch 22 via the buffer layer 24. At this time, the powder 26 of the buffer layer 24 flows along the surface shape of the laminate 10, in the example of Figure 3(A), the shape of the flat surface 10c. The laminate 10 is pressed by the punch 22 via the buffer layer 24 through which the powder 26 flows along the shape of the flat surface 10c. After heating and pressurizing using the hot press device 20, i.e., after firing, a laminate 10 having a flat surface 10c is obtained, for example, as shown in Figure 3(B). Thus, after heating and pressurizing (firing) using the hot press device 20, the original surface shape that the laminate 10 had after degreasing and before firing, that is, the shape of the flat surface 10c in the example of Figures 3(A) and 3(B), can be reproduced.

[0057] Furthermore, the surface 10c of the degreased laminate 10 may have irregularities formed as a result of the heat treatment for degreasing. It should be noted that irregularities may be formed not only on the surface layer 10c of the degreased laminate 10 (in this example, the electrolyte layer 13), but also on the internal layers (in this example, the positive electrode layer 11, the negative electrode layer 12, and the electrolyte layer 13 between them). If irregularities exist on the surface 10c of the degreased laminate 10, during heating and pressurization using the hot press device 20, the surface 10c of the laminate 10 with these irregularities is pressed (pressurized 30) by the flat press surface 22a of the punch 22 via the buffer layer 24. At this time, the powder 26 of the buffer layer 24 flows along the surface shape of the laminate 10, that is, the shape of the surface 10c with irregularities. The laminate 10 is pressed by the punch 22 via the buffer layer 24 through which the powder 26 flows along the shape of the surface 10c with irregularities.

[0058] The space between the surface 10c of the uneven laminate 10 and the flat pressing surface 22a of the punch 22 is filled with the powder 26 of the buffer layer 24. The uneven surface 10c of the laminate 10 is pressed uniformly by the powder 26 of the buffer layer 24 that fills the space between it and the flat pressing surface 22a of the punch 22. As a result, localized pressure on the surface 10c of the uneven laminate 10 is suppressed, preventing fractures from occurring inside the laminate 10 with the unevenness of its surface 10c as the starting point, and preventing tormentoring due to fusion after fracture. After heating and pressurizing using the hot press device 20, i.e., after firing, for example, a laminate 10 is obtained that has an uneven surface 10c and has suppressed internal fractures and tormentoring. Thus, after heating and pressurizing (firing) using the hot press device 20, the original surface shape that the laminate 10 had after degreasing and before firing, that is, the shape of the uneven surface 10c, can be reproduced.

[0059] Furthermore, during heating and pressurizing using the hot press device 20, even if the laminate 10 initially has a flat surface 10c, it is possible that it may deform during the heating and pressurizing process due to differences in shrinkage rates and shrinkage initiation temperatures between dissimilar materials, resulting in a surface 10c with irregularities. In addition, even if the laminate 10 initially has an irregular surface 10c, it is possible that it may deform further during the heating and pressurizing process due to differences in shrinkage rates and shrinkage initiation temperatures between dissimilar materials, resulting in a change in the shape of the irregularities on the surface 10c.

[0060] Thus, even when the surface shape of the laminate 10 changes during the heating and pressurizing process, the method of placing the powder 26 of the buffer layer 24 between the laminate 10 and the punch 22 allows the powder 26 between them to flow along the changing surface shape of the laminate 10, following that surface shape when the laminate 10 is pressed by the punch 22. The laminate 10 is pressed by the punch 22 via the buffer layer 24, through which the powder 26 flows along the shape of the surface 10c that changes during the heating and pressurizing process. Therefore, the laminate 10 is fired (sintered) by heating and pressurizing, for example, with the shape of the surface 10c that has changed during that process. The laminate 10 is pressed uniformly by the powder 26 of the buffer layer 24, and localized pressure is suppressed. Therefore, fractures occurring inside the laminate 10 based on the irregularities of its surface 10c, and tomography occurring due to fusion after fracture, are suppressed. Even if the shape of the surface 10c changes during the heating and pressurizing process, for example, the laminate 10 can be fired (sintered) with the changed shape of the surface 10c, thereby suppressing internal fracture and stratification.

[0061] Furthermore, when the laminate 10 is heated and pressurized using the hot press device 20, the surface 10c is pressed with a predetermined pressure via the powder 26 of the buffer layer 24, thereby suppressing internal fracture and torticulture, while reducing the height of any irregularities that were present on the surface 10c from the beginning or that arose during the heating and pressurizing process. In other words, as the powder 26 of the buffer layer 24 flows to follow the irregularities that change during the heating and pressurizing process, the surface 10c is pressed, and the reduction of irregularities progresses. In this case, after heating and pressurizing using the hot press device 20, i.e., after firing, the laminate 10 will have a relatively flattened surface 10c with reduced irregularity height, and internal fracture and torticulture will be suppressed.

[0062] Alternatively, when the laminate 10 is heated and pressurized using the hot press device 20, the surface 10c is pressed with a predetermined pressure via the powder 26 of the buffer layer 24, thereby suppressing internal fracture and torticultural deformation, while any irregularities that were initially present on the surface 10c or that arose during the heating and pressurizing process can be eliminated. That is, as the surface 10c of the laminate 10 is pressed while the powder 26 of the buffer layer 24 flows to follow the irregularities that change during the heating and pressurizing process, the reduction of irregularities progresses, and the irregularities can be eliminated. In this case, after heating and pressurizing using the hot press device 20, i.e., after firing, a laminate 10 is obtained with a flattened surface 10c where the irregularities have disappeared, and internal fracture and torticultural deformation have been suppressed.

[0063] Thus, after heating and pressurizing the laminate 10 using the hot press device 20, a laminate 10 having a relatively flattened surface 10c with reduced irregularities, or a laminate 10 having a flattened surface 10c with no irregularities, may be obtained. When heating and pressurizing the laminate 10 using the hot press device 20, the hot press conditions, such as the pressure during pressurization, may be adjusted so that such a laminate 10 having a relatively flattened surface 10c, or a laminate 10 having a flattened surface 10c, is obtained.

[0064] In this example, we have used the surface 10c of the laminate 10 on the punch 22 side, which is pressed through the buffer layer 24 by one punch 22 in the hot press apparatus 20. However, the same applies to the surface 10d (Figure 2) of the laminate 10 on the punch 23 side, which is pressed through the buffer layer 25 by the other punch 23.

[0065] Next, we will explain the processing of the laminate 10 after hot pressing as described above. As shown in Figure 2 above, the degreased laminate 10 is positioned inside the die 21 so as to be sandwiched between punches 22 and 23 from above and below, via buffer layers 24 and 25, respectively. From this state, the degreased laminate 10 is heated and pressurized to sinter it. After sintering by heating and pressurizing, the laminate 10 is removed from the die 21 from which punches 22 and 23 have been withdrawn, and is taken outside the hot press device 20.

[0066] At this time, it is possible that particles 26a of the powder 26 of the buffer layer 24 and buffer layer 25 may adhere to and remain on the surface 10c and surface 10d of the fired laminate 10 after it has been removed from the hot press apparatus 20. In such cases, the fired laminate 10 that has been removed is ultrasonically cleaned using an ultrasonic cleaning apparatus. By using powder 26 of the non-reactive particle group 26a, which has low reactivity with the laminate 10, as the buffer layer 24 and buffer layer 25, the particles 26a of the powder 26 that have adhered to the surface 10c and surface 10d of the fired laminate 10 can be easily removed by ultrasonic cleaning. As a result, a fired laminate 10 is obtained in which the remaining particles 26a of the powder 26 on the surface 10c and surface 10d are suppressed.

[0067] A solid-state battery is manufactured using the laminated body 10 that has been fired as described above. For example, an external electrode is formed that connects to a part 11a of the positive electrode layer 11 exposed from the side surface 10a of the laminated body 10, and an external electrode is formed that connects to a part 12a of the negative electrode layer 12 exposed from the side surface 10b of the laminated body 10, thereby manufacturing a solid-state battery. For example, the external electrode is formed by applying silver (Ag) paste to the side surfaces 10a and 10b of the laminated body 10, respectively, and firing it. In addition to Ag paste, a conductive paste containing conductive particles such as various metal particles or carbon particles may be used for the external electrode. Furthermore, the external electrode may be formed by depositing various metals using sputtering or plating methods. After applying and firing a conductive paste containing Ag, etc., depositing various metals using sputtering or plating methods may be performed to form the external electrode.

[0068] A solid-state battery can be, for example, a lithium-ion secondary battery. In this case, during charging, lithium ions are conducted from within the positive electrode layer 11 to the negative electrode layer 12 via the electrolyte layer 13, and during discharging, lithium ions are conducted from within the negative electrode layer 12 to the positive electrode layer 11 via the electrolyte layer 13. In a solid-state battery that is a lithium-ion secondary battery, charging and discharging operations are realized by this lithium ion conduction.

[0069] According to the method described in this embodiment, a high-quality laminate 10 is realized in which defects such as internal fracture and stratification are suppressed, and a high-quality solid-state battery using such a laminate 10 is realized.

[0070] In this embodiment, the laminated body 10, which is a battery element of a solid-state battery, a type of energy storage device, was used as an example. In addition, the same method can be used for the laminated body, which is a capacitor element of a multilayer ceramic capacitor, another type of energy storage device, that is, a laminated body of an electrode layer (internal electrode layer) and a dielectric layer. Specifically, a method can be employed in which a hot press device 20 as described above is used, and buffer layers 24 and 25 are placed between the laminated capacitor element to be hot-pressed and the punches 22 and 23, respectively, and then heated and pressurized. This allows for the same effects as described for the laminated battery element 10. A high-quality laminated capacitor element can be realized, and a high-quality multilayer ceramic capacitor using such a laminate can be realized.

[0071] Furthermore, the method of using buffer layers 24 and 25 of a predetermined powder 26 during hot pressing using the hot pressing apparatus 20 described above is applicable not only to laminates in which relatively small irregularities are formed on the surface (such as the laminate 10 described above), but also to laminates in which relatively large steps are formed on the surface reflecting steps in the internal structure. Even in laminates in which such steps are formed on the surface, the powder 26 flows along the surface shape, and the surface is pressed uniformly. As a result, a high-quality laminate is realized that has steps on the surface reflecting the internal structure, and in which internal fractures are suppressed.

[0072] Furthermore, when performing hot pressing using the hot press apparatus 20 described above, it is not always necessary to place buffer layers 24 and 25 on the upper and lower surfaces of the laminate and apply pressure with punches 22 and 23. For example, if irregularities are formed on one of the upper and lower surfaces of the laminate but not on the other, the powder 26 can be placed as a buffer layer only on the surface where the irregularities are formed and applied pressure with punches 22 and 23.

[0073] Furthermore, when performing a hot press using the hot press apparatus 20 as described above, multiple laminates to be heated and pressurized may be placed on the lower buffer layer 25 located on the lower punch 23 inside the die 21. An upper buffer layer 24 is placed on these multiple laminates, and the upper punch 22 is placed on top of it, and heating and pressurization are performed. When multiple laminates are placed on the buffer layer 25 in this manner, in order to suppress lateral stretching and displacement of the laminates during pressurization (in the direction parallel to the pressurizing surface 23a of the punch 23), they can be arranged so that, for example, no gaps are created between adjacent laminates or between the end laminates and the inner wall surface of the die 21.

[0074] In addition, when multiple laminates are placed on the buffer layer 25, the multiple laminates can be arranged so that gaps are provided between adjacent laminates and between the end laminates and the inner wall surface of the die 21. Multiple laminates arranged in this manner, including the gaps, are covered by the upper buffer layer 24. The powder 26 of the upper buffer layer 24 enters the gaps between adjacent laminates and between the end laminates and the inner wall surface of the die 21, thereby restricting the deformation and displacement of the multiple laminates during pressurization, and suppressing elongation and displacement of the laminates in the lateral direction (in the direction parallel to the pressurizing surface 23a of the punch 23).

[0075] (Examples) A cross-sectional SEM (Scanning Electron Microscope) image of the laminate 10 after firing by hot pressing, obtained using the method described in this embodiment, was obtained. It was confirmed that by using the buffer layer 24 and buffer layer 25 as described above, the formation of voids in the electrolyte layer 13, positive electrode layer 11, and negative electrode layer 12 constituting the laminate 10 is suppressed, and fracture and tomographic formation due to fusion after fracture are suppressed, resulting in a high-quality laminate 10. It was confirmed that by hot pressing with appropriately adjusted pressure during pressurization, a high-quality laminate 10 with relatively flat surfaces 10c and 10d can be obtained.

[0076] (Comparative Example 1) Cross-sectional SEM images were obtained of a laminate 10 obtained by firing a degreased laminate without applying pressure, in the case of a conventional fired laminate 10 that does not employ hot pressing. In the conventional fired laminate 10, fracture and tomography of the electrolyte layer 13, positive electrode layer 11, and negative electrode layer 12 that constitute it are relatively suppressed, but a relatively large number of voids are formed inside. These voids formed inside the laminate 10 lead to an increase in electrical resistance and a decrease in lithium ion conduction efficiency in the laminate 10.

[0077] (Comparative Example 2) Cross-sectional SEM images were obtained of the laminate 10 after firing by hot pressing without using buffer layers 24 and 25. Numerous fractures occurred in the laminate 10 after firing by hot pressing without using buffer layers 24 and 25.

[0078] Furthermore, a cross-sectional SEM image of the laminate 10 after firing by hot pressing using a carbon sheet instead of buffer layers 24 and 25 was obtained. In the laminate 10 after firing by hot pressing using a carbon sheet, relatively large irregularities or undulations of the carbon sheet were reflected in the shape of the surface 10c and surface 10d of the laminate 10, and relatively large irregularities tended to form on the surface 10c and surface 10d. When such relatively large irregularities are formed, surface processing is required to make the surface shape of the laminate 10 flatter.

[0079] Furthermore, in the laminate 10 after firing by hot pressing without using buffer layers 24 and 25, tomography sometimes occurred in the electrolyte layer 13, positive electrode layer 11, and negative electrode layer 12 that constitute it. Tormography may lead to a reduction in the area of ​​the positive or negative electrode layer within the laminate 10, an increase in resistance, etc. If the displacement due to tomography becomes large, there is a concern that a short circuit may occur due to contact between the fractured positive electrode layer 11 and the negative electrode layer 12.

[0080] As described above, by using a method of firing by hot pressing with buffer layers 24 and 25 of a predetermined powder 26, it becomes possible to realize a high-quality laminate 10, etc. Furthermore, it becomes possible to realize a high-quality energy storage device such as a solid-state battery using such a laminate 10, etc. [Explanation of symbols]

[0081] 10 Laminate 10a, 10b side 10c, 10d surface 11 Positive electrode layer 11a, 12a part 12 Negative electrode layer 13 Electrolyte layer 20 Hot press machine 21 dice 21a, 21b opening 22, 23 punches 22a, 23a Pressure surface 24, 25 Buffer Layers 26 powder 26a particle 30 Pressurization 40 heating

Claims

1. A first arrangement step involves placing a first buffer layer between a laminate of multiple layers provided inside a cylindrical die and a first punch inserted into the first opening of the die. A heating and pressing step in which the laminate in the die is heated and pressed by the first punch through the first buffer layer, It has, A method for manufacturing an energy storage device, wherein the first buffer layer uses a powder that flows along the surface shape of the laminate, which is heated and pressurized, and is non-reactive with the laminate.

2. The process includes a second placement step of placing a second buffer layer between the laminate in the die and a second punch inserted into a second opening on the opposite side of the first opening of the die, The heating and pressurizing step includes a step of heating the laminate in the die and pressurizing it with the second punch through the second buffer layer, The method for manufacturing an energy storage device according to claim 1, wherein the second buffer layer uses the powder which flows along the surface shape of the laminate that is heated and pressurized and which is non-reactive with the laminate.

3. The method for manufacturing an energy storage device according to claim 1, wherein the powder is graphite powder.

4. The method for manufacturing an energy storage device according to claim 1, wherein the powder is hexagonal boron nitride powder.

5. The laminate provided in the die is A positive electrode layer comprising a positive electrode active material and a first solid electrolyte, A negative electrode layer comprising a negative electrode active material and a second solid electrolyte, An electrolyte layer comprising a third solid electrolyte is provided between the positive electrode layer and the negative electrode layer, A method for manufacturing an energy storage device according to any one of claims 1 to 4, including the method described above.

6. The laminate, before being placed inside the die, contains organic components. The method for manufacturing an energy storage device according to claim 5, wherein the laminate, which has been heat-treated to remove the organic components, is placed inside the die.

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