Electrode composite, battery, and method for manufacturing same

Abstract

The present invention provides: an electrode composite which is a laminate of a positive electrode layer and a solid electrolyte layer, has good contact between electrode active material particles and solid electrolyte particles, is not susceptible to the occurrence of a short circuit, and can achieve good battery output power; a secondary battery which uses the electrode composite, has a high output power, and is capable of reducing the risk of a short circuit; and a method for manufacturing the same. Provided is an electrode composite which is applied to a secondary battery. The electrode composite includes a positive electrode active material layer and an electrolyte layer. The positive electrode active material layer has a first surface that is in contact with the electrolyte layer and a second surface that is located on the opposite side of the first surface while including a plurality of first active material particles and a plurality of second active material particles that have a higher average aspect ratio than the plurality of first active material particles. The position of the center of gravity of the plurality of second active material particles is located at the farther side from the first surface than the position of the center of gravity of the plurality of first active material particles.

Description

Electrode assembly, battery, and manufacturing method thereof

[0001] The present disclosure relates to an electrode assembly for a secondary battery, a battery, and a method for manufacturing the same.

[0002] Generally, secondary batteries are composed of electrodes (positive and negative electrodes) and an electrolyte, and charge and discharge occur through the movement of ions between the electrodes via the electrolyte. Such secondary batteries are used in a wide range of applications, from small devices such as mobile phones to large devices such as electric vehicles. Therefore, further improvement in the performance of secondary batteries is required.

[0003] In recent years, research and development of so-called all-solid-state batteries, which use inorganic solid electrolytes as electrolytes, has progressed. All-solid-state batteries are expected to improve the safety and increase the capacity and power output of secondary batteries by replacing conventional organic electrolyte solutions with solid electrolytes. However, in all-solid-state batteries, it is difficult to form a good interface between the electrode active material particles and the solid electrolyte particles. In secondary batteries using conventional electrolyte solutions, a good interface can be formed relatively easily because the electrolyte solution that permeates the electrode coats the electrode active material particles. Therefore, increasing the surface area by reducing the particle size of the electrode active material particles expands the contact interface, enabling higher power output (Patent Document 1).

[0004] However, in the case of all-solid-state batteries, contact between electrode active material particles and solid electrolyte particles occurs, limiting contact, making it difficult to form a good interface. The above-mentioned problem is particularly likely to occur in oxide-based all-solid-state batteries using oxide-based solid electrolytes. This is because they lack the plasticity of sulfide-based solid electrolytes, which further reduces contact between particles. For this reason, all-solid-state batteries, particularly oxide-based all-solid-state batteries, tend to have high battery resistance, making it difficult to achieve high output. To improve contact, known techniques include sintering using mechanical pressure and pulse current heating, and providing protrusions on the surface of electrode active material particles. Patent Document 2 discloses a manufacturing method for obtaining a well-operating all-solid-state battery by stacking a solid electrolyte layer and a positive electrode active material layer and then producing a laminate by spark plasma sintering (SPS) at 800°C for 5 minutes. Patent Document 3 discloses particulate lithium cobalt oxide (LCO) positive electrode active material particles having protrusions deposited in multiple directions on the outside of a shell portion of the particulate lithium cobalt oxide (LCO) positive electrode active material.

[0005] JP 2007-103040 A JP 2021-034205 A JP 2020-198301 A

[0006] A laminate, which is the basic structure of an all-solid-state battery, has a structure in which a solid electrolyte layer is sandwiched between a positive electrode layer and a negative electrode layer. The use of metallic lithium as the negative electrode has been considered, and a particularly challenging issue is the formation of a good interface by improving interparticle contact in the laminate of the positive electrode layer and the solid electrolyte layer. According to the inventors' research, when a laminate using a ternary positive electrode material (NMC) and a garnet-type solid electrolyte (LLZ), which are materials similar to those described in Patent Document 2, was fabricated by spark plasma sintering, the improvement in contact was limited and insufficient. Furthermore, the sintering temperature of 800°C is high in terms of energy conservation and side reactions (such as between the negative electrode active material and the solid electrolyte), leaving room for improvement. Patent Document 3 mentions the possibility of improving interparticle contact (increasing contact probability) by providing multiple protrusions on the outer shell of particulate lithium cobalt oxide (LCO), which is the positive electrode active material. However, the improvement in contact with the above structure is insufficient, and further improvement is required. Furthermore, the protrusions are thought to pose a risk of causing a short circuit when the solid electrolyte layer is thinned.

[0007] According to at least one aspect of the present disclosure, there are provided an electrode composite that is a laminate of a positive electrode layer and a solid electrolyte layer, which has good contact between electrode active material particles and solid electrolyte particles, is less likely to cause short circuits, and provides good battery output, and a battery including the electrode composite and a negative electrode layer. Specifically, there is provided a battery that achieves both improved contact between the electrode active material particles and the solid electrolyte particles and prevention of short circuits by reducing the particle size and unevenly distributing the positive electrode active material in the positive electrode layer. Furthermore, according to another aspect of the present disclosure, there are provided methods for manufacturing the electrode composite and the secondary battery.

[0008] According to at least one aspect of the present disclosure, there is provided an electrode composite applicable to a secondary battery, the electrode composite including a positive electrode active material layer and an electrolyte layer, the positive electrode active material layer having a first surface in contact with the electrolyte layer and a second surface located opposite the first surface, and including a plurality of first active material particles and a plurality of second active material particles exhibiting a higher average aspect ratio than the plurality of first active material particles, the centers of gravity of the plurality of second active material particles being located farther from the first surface than the centers of gravity of the plurality of first active material particles. Also according to at least one aspect of the present disclosure, there is provided a secondary battery including the above-mentioned electrode composite, a negative electrode, and a current collector.

[0009] According to at least one aspect of the present disclosure, there is provided a method for manufacturing an electrode composite applicable to a secondary battery, the method including: a lamination step of laminating a first material layer containing active material particles and a second material layer containing solid electrolyte particles to form a laminate; a pressure and current application step of applying a positive pressure and an AC voltage in a lamination direction of the laminate to form a composite; and a sintering step of sintering the composite in an oxygen-containing atmosphere to form an electrode composite.

[0010] According to at least one aspect of the present disclosure, there is also provided a method for manufacturing a secondary battery, the method including: manufacturing an electrode composite by the above-described manufacturing method; and stacking the electrode composite, a negative electrode, and a current collector.

[0011] According to the present disclosure, it is possible to provide an electrode composite that is a laminate of a positive electrode layer and a solid electrolyte layer that has good contact between electrode active material particles and solid electrolyte particles, is less likely to cause short circuits, and provides good battery output; a secondary battery that uses the electrode composite and has high output and can reduce the risk of short circuits; and a method for manufacturing the same.

[0012] FIG. 1A is an image diagram showing a method for manufacturing an electrode composite, and FIG. 1B is an image diagram showing a method for manufacturing an electrode precursor. FIG. 2A is a diagram schematically showing the configuration of a particle placement device 1, and FIG. 2B is a diagram schematically showing the configuration of a filling device. FIGS. 3A to 3D are schematic diagrams showing, in stages, the state of the filler being transported on the substrate and the vicinity of the surface of the substrate. FIG. 4A is a diagram schematically showing the configuration of a filling device when brush fibers are used as the carrier material, and FIG. 4B is a diagram schematically showing the configuration of a filling device when an elastic material is used. FIG. 5 is a diagram schematically showing the configuration of a transfer unit. FIG. 6 is a schematic diagram of a carrier material being transported on a substrate. FIG. 7A is a schematic diagram showing the state of particles before the settling process, FIG. 7B is a schematic diagram showing the state of particles after the settling process, and FIG. 7C is a schematic diagram explaining the settling device. FIG. 8A is a schematic diagram showing a filling device without a belt device, and FIG. 8B is a diagram schematically showing its operation. FIG. 9 is an enlarged view of the vicinity of the surface of the substrate during the filling process using the filling device. FIG. 10A is a schematic diagram of the second substrate after the first particles P1 have been transferred, FIG. 10B is a schematic diagram of the second substrate after the second particles P2 have been filled, FIG. 10C is a schematic diagram showing a cross section of the substrate and the particles arranged on the substrate, FIG. 10D is a schematic diagram of the second substrate before the settling step, and FIG. 10E is a schematic diagram of the second substrate after the settling step. FIG. 11A is a schematic diagram of the configuration of a positive electrode precursor molding device, and FIG. 11B is a schematic diagram of a cross section of a positive electrode precursor. FIG. 12A is a schematic diagram explaining the stacking in a die, and FIG. 12B is a schematic diagram showing the state in which pressure is applied from above and below in the stacking direction. FIG. 13 is a schematic diagram of the spark plasma sintering device used in the third step. FIG. 14A is a schematic diagram of a cross section in which a plurality of substrates having a particle layer for a negative electrode arranged on the laminate after the fourth step are stacked, and FIG. 14B is a schematic diagram of a cross section in which a negative electrode precursor is stacked on an electrode composite. Fig. 15A is an SEM image taken from above the positive electrode precursor prepared in the first step, and Fig. 15B is an SEM image of a cross section of the positive electrode precursor. Fig. 16A is an SEM image of a cross section of the positive electrode layer of the electrode composite, Fig. 16B is an EDX image of cobalt contained in the positive electrode active material particles, and Fig. 16C is an EDX image of ytterbium contained in the solid electrolyte particles. Fig. 17A shows the positive electrode active material particles (LiCoO ２) and FIG. 17B is a cross-sectional SEM image of the cathode active material particles in the laminate. FIG. 18A is a cross-sectional SEM image of the electrode composite after re-sintering in the fifth step, FIG. 18B is a diagram schematically showing the cross-sectional structure of FIG. 18A, FIG. 18C is a partial enlarged view of FIG. 18A, and FIG. 18D is a partial enlarged view of FIG. 18B. FIG. 19A is a cross-sectional SEM image of the electrode composite, FIG. 19B is an EDX image of Co contained in the cathode active material particles, FIG. 19C is an SEM image taken from above the compact, and FIG. 19D is a cross-sectional SEM image of the compact. FIG. 20 is a schematic diagram showing the inside of a die during spark plasma sintering. FIG. 21 is an example of a charge / discharge curve in charge / discharge measurement. FIG. 22 is an enlarged image of the cross-sectional SEM image of the laminate. Figure 23A is an example of an EDX image of cobalt atoms in a cross section of a laminate used to determine the particle morphology and uneven distribution in the examples, Figure 23B is an example of an image after dilation processing was performed on Figure 23A, and Figure 23C is an example of an image in which each particle is detected in the cross section of the laminate.

[0013] In the present disclosure, expressions such as "XX or more and YY or less" or "XX to YY" representing a numerical range mean a numerical range including the lower and upper limits, which are the endpoints, unless otherwise specified. When a numerical range is described in stages, the upper and lower limits of each numerical range can be combined arbitrarily. Furthermore, in the present disclosure, expressions such as "at least one selected from the group consisting of XX, YY, and ZZ" mean any of XX, YY, ZZ, a combination of XX and YY, a combination of XX and ZZ, a combination of YY and ZZ, or a combination of XX, YY, and ZZ.

[0014] As a result of the inventors' investigations, it was found that in order to increase the output of an oxide-based all-solid-state battery, it is important to increase the surface area of ​​the active material particles in the positive electrode and improve their contact with the solid electrolyte. Specifically, by reducing the particle size of the positive electrode active material in the positive electrode layer and unevenly distributing it, the contact interface with the solid electrolyte particles can be expanded and electronic conductivity within the positive electrode can be improved. Furthermore, by unevenly distributing the small-sized positive electrode active material particles, which are thought to be primarily responsible for electronic conductivity, on the current collector side, the risk of short-circuiting can be further reduced. In this disclosure, ionic conductivity and electronic conductivity are evaluated using an index known as the "rate characteristics" of a prototype battery for convenience.

[0015] The electrode composite includes a positive electrode active material layer and an electrolyte layer. The electrode composite may further include a current collector. The electrode composite is preferably a laminate in which the positive electrode active material layer and the electrolyte layer are laminated. The electrode composite may also be a laminate in which a current collector is further laminated. The electrolyte layer is preferably a solid electrolyte layer.

[0016] The positive electrode active material layer has a first surface in contact with the electrolyte layer and a second surface opposite the first surface. A current collector can be disposed on the second surface. The positive electrode active material layer also includes a plurality of first active material particles and a plurality of second active material particles having a higher average aspect ratio than the plurality of first active material particles. The positive electrode active material layer preferably further includes solid electrolyte particles.

[0017] The first active material particles preferably have a minor axis greater than 130 nm, more preferably greater than 250 nm, and even more preferably greater than 500 nm. The minor axis of the first active material particles is preferably, for example, 250 to 20,000 nm, and more preferably 500 to 10,000 nm.

[0018] The second active material particles preferably have a minor axis of 130 nm or less, more preferably 150 nm or less, and even more preferably 100 nm or less. The minor axis of the second active material particles is preferably, for example, 1 to 150 nm, and more preferably 5 to 100 nm.

[0019] The plurality of second active material particles have a higher average aspect ratio than the plurality of first active material particles. The average aspect ratio of the active material particles can be confirmed by the SEM observation method described below. The second active material particles preferably have an aspect ratio of the minor axis to the major axis of at least 2. That is, the ratio of the major axis to the minor axis (major axis / minor axis) is preferably 2.0 or more. The aspect ratio of the minor axis to the major axis of the second active material particles is more preferably 1.5 or more, and even more preferably 3.0 or more. The first active material particles preferably have an aspect ratio of the minor axis to the major axis of less than 2. That is, the ratio of the major axis to the minor axis (major axis / minor axis) is preferably less than 2.0.

[0020] The first active material particles preferably have a minor axis greater than 130 nm or an average aspect ratio smaller than 2. The second active material particles preferably have a minor axis of 130 nm or less and an aspect ratio of the minor axis to the major axis of 2 or more.

[0021] By having the second active material particles have a minor axis of 130 nm or less and an aspect ratio of the minor axis to the major axis of 2 times or more, the surface area of ​​the active material particles in the positive electrode layer can be increased, improving contact with the solid electrolyte particles. On the other hand, if only second active material particles are used, many small-sized second active material particles will be present on the electrolyte layer side of the electrode composite, making short circuits more likely to occur. By including first active material particles and second active material particles in the electrode composite, good contact between the electrode active material particles and the solid electrolyte particles and suppression of short circuits can be achieved, resulting in good battery output. For example, by performing re-sintering under specific conditions in the manufacturing method of the electrode composite described below, a positive electrode active material layer containing first active material particles and second active material particles can be obtained.

[0022] The active material particles are not particularly limited and known active material particles can be used. For example, a composite oxide containing lithium can be used. Specifically, for example, lithium cobalt oxide (LiCoO ２ ) and other Li-Co oxide active material particles, LiMO ２(M is an element selected from the group consisting of Ni, Mn, and Co), ４ Oxide-based active material particles, lithium vanadium compounds (Li ３ V ２ (P.O. ４ ) ３ , LiVOPO ４ ), olivine-type phosphate compounds (LiMPO ４ (M is one or more elements selected from the group consisting of Co, Ni, Mn, Fe, Mg, V, Nb, Ti, Al, and Zr). Also, a positive electrode active material that does not contain lithium may be used.

[0023] The active material particles may be commercially available products, or may be separately prepared materials. The active material particles preferably contain Li, Co, and O. That is, the first active material particles and the second active material particles preferably contain a positive electrode active material containing Li, Co, and O. The first active material particles and the second active material particles preferably contain at least one of lithium cobalt oxide and a compound in which part of the Li and Co in lithium cobalt oxide is substituted with at least one selected from the group consisting of Ni, Mn, Mg, Al, Fe, Si, C, and B. As the lithium cobalt oxide, for example, Cellseed C-5H (trade name, manufactured by Nippon Chemical Industry Co., Ltd.) can be used.

[0024] The centers of gravity of the second active material particles are located farther from the first surface than the centers of gravity of the first active material particles. Specifically, in cross-sectional observation of the positive electrode active material layer with a scanning electron microscope (SEM), the centers of gravity of the second active material particles are located closer to the second surface than the centers of gravity of the first active material particles, i.e., on the opposite side of the first surface in contact with the solid electrolyte layer.

[0025] In the present disclosure, the center of gravity of the active material particles refers to the average distance from the edge of the positive electrode active material layer on the second surface side to the active material particles. The center of gravity can be measured using a scanning electron microscope by the measurement method described below. For example, in the electrode composite manufacturing method described below, the center of gravity of each active material particle can be controlled by resintering under specific conditions. This method is preferable because it allows the center of gravity of each active material particle to be controlled during the positive electrode molding process without complex steps. Other control methods include, for example, a method in which a material containing first active material particles and a material containing second active material particles are prepared in advance, and the material containing the second active material particles is positioned farther from the first surface than the material containing the first active material particles to manufacture the electrode composite. The center of gravity of each active material particle in cross-sectional observation of the positive electrode active material layer using a scanning electron microscope (SEM) can be measured by the method described below.

[0026] The fact that the center of gravity positions of the first active material particles and the second active material particles satisfy the above relationship indicates that, in a cross-sectional observation of the positive electrode active material layer, the second active material particles having a small minor axis and a specific shape are unevenly distributed toward the second surface side relative to the first active material particles having a large minor axis. That is, the second active material particles contained in the positive electrode active material layer are preferably unevenly distributed toward the second surface side. Furthermore, the first active material particles contained in the positive electrode active material layer are preferably unevenly distributed toward the first surface side.

[0027] In the present disclosure, "active material particles being unevenly distributed on the second surface side (or the first surface side)" means that, in cross-sectional observation of the positive electrode active material layer by SEM, 60% or more of the observed active material particles are located in one-third of the region of the second surface side (or the first surface side). In other words, "plurality of second active material particles being unevenly distributed on the second surface side" means that, of all second active material particles identified in cross-sectional observation of the positive electrode active material layer by SEM, 60% or more of the particles are contained in one-third of the region of the second surface side of the positive electrode active material layer. A specific method for determining uneven distribution of active material particles will be described later.

[0028] By distributing the second active material particles having a small minor axis closer to the second surface than the first active material particles having a large minor axis, the contact interface with the solid electrolyte particles is widened, improving the contact between the electrolyte particles and the active material particles. Furthermore, since the second active material particles having a high aspect ratio between the minor axis and the major axis are prone to charge concentration, distributing the second active material particles closer to the second surface, i.e., the current collector side, facilitates the transfer of electrons from the current collector side. For these reasons, the electrode composite having the above configuration can improve the output of the secondary battery. The center of gravity of each active material particle in cross-sectional observation of the positive electrode active material layer using a scanning electron microscope (SEM) can be measured using the method described below.

[0029] The solid electrolyte particles are not particularly limited, and ion-conductive solids that are commonly used in all-solid-state batteries can be used. For example, Li-Yb oxide-based solid electrolyte particles, Li-B oxide-based solid electrolyte particles, Nasicon-type solid electrolyte particles (LiAlTi(PO ４ ) ３ , LiAlGe (PO ４ ) ３ etc.), Li-P-O solid electrolyte particles (Li ３ P.O. ４ , LiPON (Li ３ P.O. ４ Examples of such particles include particles in which some of the O in the above-mentioned formula (II) is replaced with N.

[0030] The solid electrolyte particles may be commercially available products or may be separately prepared as a material. As a commercially available product, for example, lithium borate (manufactured by Toshima Manufacturing Co., Ltd.) is preferably used. As a separately prepared product, for example, solid electrolyte particles in which the lithium and boron of lithium borate are partially substituted with carbon are preferably used. Furthermore, it is preferable to use Li-Yb oxide-based solid electrolyte particles. As the Li-Yb oxide-based solid electrolyte particles, for example, Li ５．９ Yb ０．８１ La ０．０９ Zr ０．１ (BO ３ ) ３etc. can be used. The solid electrolyte particles may be contained in both the positive electrode active material layer and the electrolyte layer. In this case, the solid electrolyte particles contained in the positive electrode active material layer and the electrolyte layer may be the same or different. It is more preferable that the solid electrolyte particles contained in the positive electrode active material layer and the electrolyte layer are the same.

[0031] The electrode composite preferably further includes a current collector. The current collector exchanges electrons with the positive electrode active material layer. The current collector is preferably stacked so as to be in contact with the second surface of the positive electrode active material layer. That is, the second surface is preferably the surface in contact with the current collector. As described above, the first surface of the positive electrode active material layer is the surface in contact with the electrolyte layer. The electrolyte layer and the first active material particles contained in the positive electrode active material layer are preferably in contact with each other via the first surface.

[0032] The first active material particles preferably have an inner surface within the particle. Here, the inner surface refers to the surface present inside the active material particle. When the first active material particles have an inner surface within the particle, the contact interface with the electrolyte is expanded, and the output characteristics of the battery can be improved. For example, by controlling the sintering atmosphere in the manufacturing process described below and reducing and decomposing the active material particles, first active material particles having an inner surface within the particle can be obtained. The fact that the active material particles have an inner surface within the particle can be confirmed by cross-sectional observation using a SEM described below.

[0033] The inner surface of the active material particle preferably forms pores within the active material particle that communicate with the outer surface of the active material particle. By forming pores on the inner surface, the active material particle can function as voids that mitigate volume fluctuations of the active material particle during charging and discharging. Furthermore, by connecting the inner surface to the outer surface of the active material particle, contact with the electrolyte is possible, and the contact interface can also be expanded. For example, by controlling the sintering atmosphere in the manufacturing process described below and reducing and decomposing the active material particles, active material particles having pores formed by the inner surface can be obtained. The fact that the inner surface of the active material particle forms pores can be confirmed by cross-sectional observation using a SEM described below.

[0034] The second active material particles preferably have a higher number density per unit volume than the first active material particles. That is, the second active material particles preferably have a smaller volume per particle than the first active material particles. The second active material particles have a smaller volume per particle and a higher number density than the first active material particles, which increases the surface area of ​​the active material particles and widens the contact interface with the electrolyte. As a result, the output characteristics of the battery can be improved. The volume of each active material particle can be confirmed by cross-sectional observation using a SEM, as described below.

[0035] The second active material particles preferably include flakes having a thickness smaller than the average particle size of the first active material particles and / or needle-shaped bodies having an axial diameter smaller than the average particle size of the first active material particles. In the present disclosure, "flak-shaped bodies" refers to particles having a flat shape with an aspect ratio of the minor axis to the major axis of at least 2. Also, "needle-shaped bodies" refers to particles having a needle-like shape with an aspect ratio of the minor axis to the major axis of at least 2.

[0036] The inclusion of the flaky and / or needle-shaped bodies in the second active material particles improves contact between the electrolyte particles and the active material particles, and the concentration of electric charge facilitates electron transfer, thereby improving the output characteristics of the battery. For example, by performing re-sintering under specific conditions in the method for producing an electrode composite described below, the second active material particles can be configured to include the flaky and / or needle-shaped bodies. The shape of the second active material particles can be confirmed by cross-sectional observation using a SEM described below.

[0037] The second active material particles are preferably present at a distance from the first active material particles. That is, the second active material particles and the first active material particles are preferably not in contact with each other within the positive electrode active material layer. The presence of the second active material particles at a distance from the first active material particles increases the surface area of ​​the active material particles, widening the contact interface with the electrolyte and improving the battery output characteristics. Furthermore, the second active material particles can be unevenly distributed near the current collector, facilitating electron transfer between the current collector and the second active material particles, improving electron diffusion within the positive electrode and improving the battery output characteristics. For example, by re-sintering the spark plasma sintered sample in the manufacturing process described below, a configuration can be achieved in which the second active material particles are present at a distance from the first active material particles. The position and state of the active material particles can be confirmed by cross-sectional observation using a SEM, as described below.

[0038] In terms of the dispersion of the positions in the thickness direction of the positive electrode active material layer, the first surface is preferably larger than the second surface. That is, in terms of the positions in the thickness direction of the positive electrode active material layer, the first surface is preferably more dispersed than the second surface. By adopting the above configuration, a good contact interface is formed between the active material particles and the solid electrolyte, and charge concentration is likely to occur, facilitating electron exchange, thereby improving the output characteristics of the battery. The dispersion state can be confirmed by cross-sectional observation using a SEM, as described below.

[0039] The first surface preferably has a portion overlapping with a plurality of first active material particles in the thickness direction of the electrode composite. Furthermore, the first surface preferably does not have a portion overlapping with a plurality of second active material particles in the thickness direction of the electrode composite 17. That is, the first surface preferably contacts the plurality of first active material particles with the electrolyte layer, and the first surface preferably does not contact the second active material particles. This configuration allows a good contact interface to be formed between the first active material particles and the electrolyte layer, and furthermore, by keeping the second active material particles P2, which are likely to cause a short circuit, away from the first surface PP, the risk of a short circuit can be reduced. The electrode composite may further include a negative electrode active material layer. The negative electrode active material layer is preferably laminated so as to contact the electrolyte layer of the electrode composite.

[0040] <Method for Manufacturing Electrode Composite> Hereinafter, with reference to the drawings, an example of a method for manufacturing an electrode composite, which is a laminate formed by stacking positive electrode active material layers and electrolyte layers, will be described. The method for manufacturing an electrode composite includes the following five steps (steps 1, 2, 3, 4, and 5): (1) step 1 (S101 in FIG. 1A ) of preparing a positive electrode precursor using a method for manufacturing a positive electrode precursor described below; (2) step 2 (S102 in FIG. 1A ) of stacking a positive electrode precursor and a solid electrolyte in a sintering mold (hereinafter referred to as a die) used for spark plasma sintering; (3) step 3 (S103 in FIG. 1A ) of performing spark plasma sintering; (4) step 4 (S104 in FIG. 1A ) of removing the sample from the die and performing post-treatment as necessary; and (5) step 5 (S105 in FIG. 1A ) of performing re-sintering to adjust the composition of the positive electrode active material.

[0041] (First Step) The first step is a step of preparing a positive electrode precursor. Here, the positive electrode precursor is a structure in which a resin substrate, on which positive electrode active material particles and solid electrolyte particles are arranged, is laminated on a substrate. The resin substrate is selected arbitrarily from one sheet to multiple sheets according to the desired battery capacity. The presence of the resin substrate inhibits the ionic conductivity and electronic conductivity of the structure. Therefore, the structure does not function as a positive electrode, and only functions as a positive electrode after the resin substrate is removed by heat treatment, which will be described later. For this reason, in the present disclosure, the structure is referred to as a positive electrode precursor. A method for producing a positive electrode precursor will be described in detail.

[0042] <Method for Producing Positive Electrode Precursor> An example of a method for producing a positive electrode precursor will be described below with reference to the drawings. The method for producing a positive electrode precursor includes the following five steps (step I, step II, step III, step IV, and step V). (I) Step I of arranging first particles P1 (cathode active material particles or solid electrolyte particles) on a resin substrate having a holding portion for holding particles (T101 in FIG. 1B ); (II) Step II of allowing the first particles P1 to settle on the holding portion (T102 in FIG. 1B ); (III) Step III of arranging second particles P2 (first solid electrolyte particles or cathode active material particles) in regions of the resin substrate where the first particles P1 are not arranged (T103 in FIG. 1B ); (IV) Step IV of allowing the first particles P1 and second particles P2 (cathode active material particles and solid electrolyte particles) to settle on the holding portion (T104 in FIG. 1B ); and (V) Step V of stacking the resin substrate on which the first and second particles are arranged on a substrate (T105 in FIG. 1B ).

[0043] (Step I and Step II) Step I and Step II are steps of arranging first particles on a resin substrate and allowing the first particles to settle in a holding portion on the resin substrate. The first particles are positive electrode active material particles or solid electrolyte particles. In Step I and Step II, particles are arranged on the resin substrate using a particle arrangement device 1. The particle arrangement device 1 will be described below.

[0044] 2A is a diagram schematically illustrating the configuration of the particle arrangement device 1. Hereinafter, a particle arrangement method will be described using the case where the above-described positive electrode active material particles are used as the first particles P1 as an example. As described above, the first particles P1 may be solid electrolyte particles.

[0045] The particle placement device 1 includes a first storage container 21a that stores and supplies a first substrate 11a, a first belt device 22a that transports the first substrate 11a, and a pattern forming device 23 that forms a concave-convex pattern on the first substrate 11a. The particle placement device 1 also includes a first filling device 24a that arranges first particles P1 in recesses of the concave-convex pattern formed on the first substrate 11a. The particle placement device 1 also includes a second storage container 21b that stores and supplies a second substrate 11b, and a second belt device 22b that transports the second substrate 11b. The second substrate 11b is a resin substrate equipped with a holding portion that holds the first particles P1.

[0046] The particle placement device 1 has a transfer section 25a in which rollers 223 respectively possessed by a first belt device 22a and a second belt device 22b face each other, and in the transfer section 25a, a first particle P1 is transferred from a first substrate 11a to a second substrate 11b.

[0047] Furthermore, the particle placement device 1 has a first settling device 24b that causes the first particles P1 to settle in the holding portion. Note that devices that are less relevant to explaining the effects of the present invention, such as a peeling and recovery device that peels and recovers the first base material 11a from the first belt device 22a after transfer and various cleaning devices, will not be shown in the drawings or described in detail.

[0048] In the particle arrangement device 1, the pattern forming device 23, the first filling device 24a, and the transfer unit 25a correspond to a first arrangement unit that arranges the first particles P1 in a pattern on the second substrate 11b, and the first settling device 24b corresponds to a first settling unit that settles the first particles P1 into the holder of the substrate 11b.

[0049] Below, the method of particle placement and sedimentation on the second substrate 11b by the particle placement device 1 will be explained along the flow of each process. First, the first substrate 11a is supplied from the first storage container 21a to the first belt device 22a by a supply means (not shown). When a UV-curable liquid is applied by a pattern formation device 23 (described later), it is preferable that at least the surface of the first substrate 11a is made of a material that is highly wettable by the UV-curable liquid. In addition, it is preferable that the surface of the first substrate 11a is smooth.

[0050] The first substrate 11a may be a sheet made of a resin such as polyester that has been subjected to a hydrophilic or lipophilic treatment in accordance with the ultraviolet-curable liquid (water-based or oil-based) to be used. The first substrate 11a may be a substrate that is individually cut out like cut paper, a continuous substrate wound into a roll like roll paper, or a continuous substrate that is alternately folded like continuous paper.

[0051] The first belt device 22a transports the supplied first substrate 11a to a pattern formation position of the pattern forming device 23. The first belt device 22a has drive rollers 221a and 222a, a pressure roller 223a, and a belt-like transport member 224a suspended between them. At this time, the pressure roller 223a is rotated by being driven.

[0052] The conveying member 224a is preferably made of a material selected from resin or metal, such as a polyimide resin belt. The drive rollers 221a and 222a are preferably made of metal, such as stainless steel rollers. The pressure roller 223a is preferably a soft roller having an elastic layer on its surface, such as a soft roller having a silicone rubber elastic layer on the surface of a stainless steel core.

[0053] 2A, the first belt device 22a is used as a conveying device for conveying the first base material 11a, but a roller device may be used instead of the belt device. The same applies to the second belt device 22b described later.

[0054] The pattern forming device 23 forms a fine concave-convex pattern on the first substrate 11a that has been transported to the pattern forming position. Methods for forming the concave-convex pattern include UV imprinting, thermal imprinting, UV inkjet printing, printing, and laser etching.

[0055] When the pattern forming device 23 forms a concave-convex pattern by a UV imprint method, the pattern forming device 23 has a coating means for coating an ultraviolet-curable liquid onto the first substrate 11a. The pattern forming device 23 also has an imprinting means for imprinting a mold having a concave-convex pattern formed on its surface onto the ultraviolet-curable liquid on the first substrate 11a, and a light source for irradiating the ultraviolet-curable liquid with ultraviolet rays. Typically, ultraviolet-curable liquid silicone rubber (PDMS) or resin is used as the ultraviolet-curable liquid, a film mold is used as the mold, and a UV lamp is used as the light source.

[0056] When the first filling device 24a uses the support material S1 carrying the first particles P1 to fill the recesses on the substrate 11a with the first particles P1, the opening diameter of the recesses in the concave-convex pattern on the first substrate 11a is preferably larger than the volume-based cumulative 50% particle size (median diameter) of the first particles P1. Furthermore, the opening diameter of the recesses is preferably smaller than the average size of the support material S1. Here, the opening diameter of the recesses in the concave-convex pattern is preferably the opening diameter in the short direction of the recesses, and more preferably the maximum opening diameter in the short direction of the recesses. By setting the opening diameter as described above, the first particles P1 can contact the bottom and side portions (typically the bottom surface) of the recesses in the concave-convex pattern. Meanwhile, the support material S1 cannot contact the bottom and side portions of the recesses. This allows the first particles P1 that contact the bottom and side portions of the recesses to be captured by the concave-convex pattern, while preventing the support material S1 from being captured by the concave-convex pattern. In other words, it is preferable that the first particles P1 can contact the bottoms and side surfaces of the recesses of the uneven pattern, and the first support material S1 cannot contact the bottoms and side surfaces of the recesses of the uneven pattern.

[0057] Although the pattern forming device 23 forms a concave-convex pattern on the first substrate 11a, a substrate with a concave-convex pattern pre-formed on its surface may be used as the first substrate 11a. Alternatively, the pattern forming device 23 may form a concave-convex pattern directly on the surface of the conveying member 224a of the first belt device 22a, or a conveying member having a concave-convex pattern on its surface may be used as the conveying member 224a. In this case, in consideration of durability, it is preferable to use a metal belt made of stainless steel, aluminum, or the like, and form the concave-convex pattern on the surface by a micromachining technique such as laser etching, wet etching, or dry etching.

[0058] The first base material 11a having the concave-convex pattern formed on its surface is transported by the first belt device 22a to the filling position of the first filling device 24a. Fig. 2B is a diagram showing a schematic configuration of the filling device. The configuration of the first filling device 24a will be described below.

[0059] The first filling device 24a has a filling container 242a that stores a filler 241a, a stirring screw member 243a that stirs and conveys the filler 241a, a recovery member 244a that recovers the filler, and a magnetic member 247a.

[0060] The filler 241a includes first particles P1 and a support material S1 that supports the first particles P1. The filler 241a is a mixture of multiple powders, including a powder composed of multiple first particles P1 and a powder composed of multiple support materials S1. The filler 241a contained in the filling container 242a is thoroughly mixed when stirred and transported by the stirring screw member 243a. As a result, the first particles P1 are supported on the surface of the support material S1. The forces acting between the particles when supported include electrostatic forces due to frictional charging and the like, as well as van der Waals forces and liquid bridging forces.

[0061] The support material S1 is a magnetic particle. The support material S1 is preferably a particle in which the surface of a resin particle in which ferrite core particles or a magnetic material is dispersed is coated with a resin composition. For example, a magnetic particle such as a standard carrier (Standard Carrier P02 manufactured by the Japan Imaging Society) can be used. The particle size and material of the support material S1 are appropriately selected according to the particle size and material of the first particles P1. This allows the first particles P1 to be stably supported. Furthermore, even if the first particles P1 are small in particle size and prone to agglomeration, the support material S1 also plays a role in loosening the agglomeration by stirring and transporting the particles with the support material S1. The particle size of the support material S1 can be appropriately adjusted by the size (area, width, depth) of the recess. For example, the cumulative 50% particle size (median diameter) based on volume is preferably 50 to 100 μm.

[0062] Recovery member 244a has roller 245a that can rotate in the direction of arrow d2 in the figure, and magnet 246a that is arranged inside roller 245a and fixed to filling container 242a. Magnetic member 247a is arranged opposite filling container 242a across transport member 224a, and has magnet 248a inside.

[0063] The magnet 246a has a plurality of N and S poles alternately arranged along the rotation direction of the recovery member 244a. The magnet 248a has a plurality of N and S poles alternately arranged along the transport direction of the transport member 224a. Furthermore, the magnet 246a has a magnetic pole of a different polarity (N1 pole in the embodiment shown in FIG. 2B ) at a position closest to and facing the most downstream magnetic pole of the magnet 248a (S1 pole in the embodiment shown in FIG. 2B ), and an N2 pole of the same polarity as the N1 pole is arranged at the most downstream position.

[0064] The magnet 246a and the magnet 248a may be composed of a plurality of magnets, and the type of magnet constituting the magnet 246a and the magnet 248a is not particularly limited. For example, a permanent magnet such as a rare earth magnet, a ferrite magnet, a neodymium magnet, or a samarium-cobalt magnet, or a plastic magnet, or a means for generating a magnetic field such as an electromagnet can be used. The magnet 248a may be configured to be movable in the transport direction of the first substrate 11a or in the opposite direction.

[0065] Note that a regulating member for regulating the filler 241 a on the first base material 11 a or a collecting member for re-collecting the filler 241 a that cannot be collected by the collecting member 244 a may be provided upstream or downstream of the collecting member 244 a in the transport direction of the transport member 224 a. The collecting member for re-collecting the filler 241 a may be a member similar to the collecting member 244 a, or may be a simple member such as a fixed magnet or a regulating member, or a collecting member that performs collection by air blowing.

[0066] Next, the process of filling the recesses on the first substrate 11a with the first particles P1 by the first filling device 24a will be described with reference to Fig. 2B and Figs. 3A to 3D. The first substrate 11a carried and transported by the first transport member 224a is transported to the loading position of the first filling device 24a by the first transport member 224a moving in the direction of the solid arrow d1 in Fig. 2B.

[0067] The filler 241a is transported by the stirring screw member 243a and supplied onto the first substrate 11a (dotted line a in FIG. 2B). At this time, a magnetic field is formed by the magnetic member 247a and the recovery member 244a, and the filler 241a containing the magnetic particle carrier material S1 forms multiple magnetic chains on the first substrate 11a due to the magnetic field. The filler 241a supplied onto the first substrate 11a is transported on the first substrate 11a while forming magnetic chains as the first substrate 11a moves (dotted line b in FIG. 2B).

[0068] Figures 3A-C are schematic diagrams of filler 241a being transported on the first substrate 11a. For illustrative purposes, filler 241a other than the filler forming a single magnetic strand is omitted from the illustration. As described above, the filler 241a on the first substrate 11a forms magnetic strands along the magnetic field lines of the generated magnetic field. As the first substrate 11a moves, the magnetic strands change shape as they are transported, as shown in Figures 3A, 3B, and 3C. Because a particularly strong magnetic force acts near the magnet 248a, the transport speed v2 of the filler 241a is smaller than the movement speed v1 of the first substrate 11a when the filler 241a moves away from the magnetic pole, and is larger when the filler 241a moves away from the magnetic pole. In other words, the filler 241a on the first substrate 11a has a non-zero relative speed with respect to the first substrate 11a.

[0069] FIG. 3D is an enlarged view of the vicinity of the surface of the first substrate 11a in FIGS. 3A-C. Although not shown in FIGS. 3A-C, as shown in FIG. 3D, a concave-convex pattern 111a is formed on the first substrate 11a. The filler 241a contacts this concave-convex pattern 111a and is transported together with the first substrate 11a at a non-zero relative speed with respect to the first substrate 11a while being subjected to a magnetic force (arrow Fm in the figure) in a direction perpendicular to the surface of the first substrate 11a. As a result, the first particles P1 supported on the support material S1 are transported while being rubbed against the concave-convex pattern 111a on the surface of the first substrate 11a.

[0070] At this time, the particle size of the first particles P1 is smaller than the opening diameter of the recesses of the uneven pattern 111a, and the particle size of the first support material S1 is larger than the opening diameter of the recesses, so the first particles P1 can contact the bottom surfaces (bottoms) and side surfaces of the recesses of the uneven pattern 111a, but the support material S1 cannot. In other words, only the first particles P1 in the filler 241a selectively contact the bottom surfaces and side surfaces of the recesses.

[0071] The first particles P1 that come into contact with the recesses are strongly restrained by the physical restraining force due to the structure of the concave-convex pattern 111a and by non-electrostatic adhesive forces such as electrostatic adhesive forces and adhesive forces with the structural materials that make up the first base material 11a and the concave-convex pattern 111a, and are detached from the support material S1. Note that, for the sake of explanation, in Fig. 3D, the first particles P1 are supported on the surface of the support material S1, but it is acceptable for particles P1 that are not supported on the support material S1 to exist during the agitation, supply, or transport of the filler 241a.

[0072] As shown in Fig. 2B, downstream of the magnetic member 247a, a recovery member 244a is disposed with a gap between it and the first transport member 224a. As the first base material 11a moves, the filler 241a is transported to the vicinity of the most downstream magnetic pole (pole S1) of the magnet 248a. Under the influence of the magnetic field formed by the magnet 246a, the filler 241a moves from the first base material 11a to the recovery member 244a and is recovered (dotted line c in Fig. 2B).

[0073] As described above, during the transport process (dotted lines a, b, and c in FIG. 2B ), the recesses of the concave-convex pattern 111 a on the surface of the first base material 11 a are in sufficient contact with the plurality of fillers 241 a. Therefore, after the fillers 241 a are collected by the collection member 244 a, the first particles P1 are selectively and densely arranged in the recesses of the concave-convex pattern 111 a.

[0074] 3A to 3D, the first particles P1 are all shown with the same particle size, but in reality there is a particle size distribution, and depending on the material, they may form agglomerated secondary particles. Furthermore, in most cases, the particles are not spherical as shown. Even in such cases, only particles that can contact the recesses of the uneven pattern 111a are selectively and densely packed, so coarse powder and secondary particles that may adversely affect the particle placement process are easily excluded.

[0075] In this way, the amount of the first particles P1 filled into the recesses of the concave-convex pattern 111a can be controlled by the size (area, width, depth) of the recesses and the particle size of the first particles P1. Specifically, the area of ​​the recesses is approximately the filling area, and the layer thickness of the filled first particles P1 is determined by the depth of the recesses.

[0076] For example, to obtain a thin layer (single layer) that accounts for 50% of the area of ​​the substrate, the area ratio of the recesses (the area ratio of the recesses to the entire concave-convex pattern) should be 50%, and the depth of the recesses should be equal to or less than the particle size of the first particles P1. In this case, the opening width of the recesses should be larger than the median diameter of the first particles P1 and smaller than the average size (here, the average particle size) of the support material S1.

[0077] Although the first particles P1 may have a wide particle size distribution (broad particle size distribution), the support material S1 preferably has a narrow particle size distribution, and is more preferably monodisperse. This makes it easier to prevent the support material S1 from contacting the bottom (or bottom surface) or side surface of the recess. If the support material S1 can contact the bottom or side surface of the recess, there is a risk that the support material S1 will also be restrained and filled into the recess.

[0078] Furthermore, the opening width of the recesses in the uneven pattern 111a is preferably smaller than four times the particle diameter of the first particles P1. By making the opening width smaller than four times the particle diameter of the first particles P1, the probability that the first particles P1 will contact two points, the bottom and side surfaces of the recesses in the uneven pattern 111a, can be increased. In this way, the first particles P1 that come into multi-point contact with the uneven pattern 111a are strongly constrained by the uneven pattern 111a, thereby increasing the efficiency of filling the uneven pattern 111a with the first particles P1. The same applies to the particle diameter of the second particles P2 (described later) and the size of the recesses in the uneven pattern formed by the first particles P1 on the second substrate. Furthermore, when brush fibers are used as the carrier material, the "average particle diameter of the carrier material" in the above description becomes the "average fiber diameter of the carrier material."

[0079] The filler 241a collected by the collecting member 244a is transported by the rotating collecting member, roller 244a (dotted line in FIG. 2B). The filler 241a transported by roller 244a falls into filling container 242a (dotted line in FIG. 2B) due to the magnetic field generated by two adjacent, repelling magnetic poles of the same polarity (N1, N2) and the influence of gravity. The filler 241a is then again stirred and transported by stirring screw member 243a, and this process is repeated thereafter.

[0080] The weight ratio of the first particles P1 to the support material S1 in the filler 241a in the filling container 242a is determined by an inductance sensor that measures magnetic permeability, a patch density sensor that measures and predicts the reflection density on a substrate, or the like, which are common in electrophotographic devices. At least one of the first particles P1 and the support material S1 is replenished by a replenishment means (not shown) as needed. This allows stable filling over a long period of time.

[0081] Although the filling device described here uses magnetic particles as a carrier material to form a magnetic brush, filling the recesses with the particulate material, the filling device method is not limited to this. Brush fibers can also be used as the carrier material. Alternatively, an elastic material, at least the surface of which is made of an elastic body, can also be used as the carrier material.

[0082] 4A is a diagram schematically illustrating the configuration of a filling device 24c when brush fibers are used as the carrier material. The filling device 24c has a roller 2410 with brush fibers on its surface. The roller 2410 is a so-called brush roller, with brush fibers planted on its surface. The brush fibers of the roller 2410 may be made of, for example, nylon, rayon, acrylic, vinylon, polyester, or vinyl chloride. The surface of the fiber may be subjected to a surface treatment in order to adjust the chargeability or rigidity.

[0083] The filling device 24c has a supply member that supplies the filler 241a to the roller 2410. The filler 241a contains a powder composed of a plurality of first particles P1 and is stored in a filling container 242a. In this example, the filler 241a does not contain the carrier material S1, which is magnetic particles. The filler 241a is stirred and transported by a stirring screw member 243a and supplied to a supply member 249.

[0084] The supply member 249 supplies the filler 241a to the roller 2410, and its configuration is not particularly limited. For example, the supply member 249 can be a roller whose surface is made of an elastic, porous foam material. Typically, an elastic sponge roller having a foamed skeleton structure and a relatively low-hardness polyurethane foam formed on a core metal can be used. Note that, in addition to urethane, various rubber materials such as nitrile rubber, silicone rubber, acrylic rubber, hydrin rubber, and ethylene propylene rubber can be used as the foam material.

[0085] The supplied filler 241a is filled into the foam material on the surface of the supply member 249 and is transported to a supply section that comes into contact with the roller 2410. In the supply section, the filler 241a filled into the foam material is charged by contact with the brush fibers of the roller 2410 and is carried by the brush fibers of the roller 2410. Furthermore, the supply member 249 may also have a function of stripping off and refreshing the filler 241a remaining on the roller 2410. The filler 241a supplied to the roller 2410 comes into contact with the first substrate 11a as the brush fibers move.

[0086] At this time, the first particles P1 in the filler 241a can contact the bottom and side surfaces of the recesses of the uneven pattern 111a on the surface of the first substrate 11a, but the brush fibers cannot. That is, the fiber diameter of the brush fibers is set to be larger than the opening width of the recesses of the uneven pattern 111a. The fiber diameter of the brush fibers can be measured by placing glass on the surface of the roller 2410 and taking an image of the brush fibers through the glass using an optical microscope. At this time, the fiber diameters of approximately 100 brush fibers are measured, the fiber diameter distribution is measured, and the average diameter is calculated.

[0087] The movement of the transport member 224a and the rotation of the roller 2410 cause the brush fibers of the roller 2410 to rub against the surface of the first substrate 11a, so that the first particles carried by the brush fibers are densely arranged in the recesses of the uneven pattern 111a on the surface of the first substrate 11a.

[0088] 4B is a diagram showing a schematic configuration of a filling device 24d when an elastic material is used as the carrier material. The filling device 24d has a similar configuration to the filling device 24c, but differs in that a roller 2411 having an elastic material is used instead of the roller 2410 having brush fibers. The roller 2411 is a roller having an elastic layer formed on its surface.

[0089] The elastic layer is formed of an elastic material such as a rubber material, such as silicone rubber, acrylic rubber, nitrile rubber, urethane rubber, or fluororubber. The surface shape of the elastic layer may be controlled by adding spherical resin particles or other fine particles. If the elastic layer has convex portions on its surface, the size of the convex portions of the elastic layer is set larger than the size of the concave portions of the concave-convex pattern 111a. The size of the convex portions of the elastic layer can be measured in the same manner as the fiber diameter of the brush fibers described above.

[0090] The movement of the transport member 224a and the rotation of the roller 2411 causes the elastic material on the surface of the roller 2411 to rub against the surface of the first base material 11a, thereby causing the first particles carried by the elastic material to be densely arranged in the recesses of the concave-convex pattern 111a on the surface of the first base material 11a.

[0091] By using brush fibers or elastic materials as the carrier material as shown in Figures 4A and 4B, it is not necessary to include magnetic particles in the filler. Furthermore, the configuration of the filling device can be simplified. On the other hand, when magnetic particles are used as the carrier material as shown in Figure 2B, there is greater freedom in the size and shape of the carrier material than when using brush fibers or elastic materials. Furthermore, magnetic particles allow for greater freedom in the movement of the carrier material on the substrate.

[0092] For these reasons, when magnetic particles are used as the support material, particles such as the first particles P1 can be more efficiently supplied onto the substrate, and recesses on the substrate can be more efficiently filled. Furthermore, when magnetic particles are used as the support material, even if the support material deteriorates during the process, the support material can be replenished or replaced without stopping the process.

[0093] The method of filling recesses with particles by rubbing a support material carrying the particles allows for a larger amount of dispersed particles to be supplied to the recesses, resulting in stable and dense filling, compared to filling methods using a restricting member such as a blade. This advantage becomes more pronounced as the particle size of the particles to be filled becomes smaller, since the particles tend to aggregate more easily. The particle size of the first particles P1 is preferably 0.01 to 50 μm, more preferably 0.05 to 20 μm, and even more preferably 0.1 to 10 μm.

[0094] The first substrate 11a, in which the recesses of the concave-convex pattern 111a have been filled with the first particles 1 by the first filling device 24a, is transported to the transfer unit 25a by the first belt device 22a. Here, as shown in FIG. 2A, the second belt device 22b, like the first belt device 22a, has drive rollers 221b and 222b, a pressure roller 223b, and a belt-like transport member 224b suspended therebetween. At this time, the pressure roller 223b is driven to rotate. In the transfer unit 25a, the pressure roller 223a of the first belt device 22a and the pressure roller 223b of the second belt device 22b face each other.

[0095] The second substrate 11b is supplied from the second storage container 21b to the second belt device 22b and transported in the direction of the arrow in FIG. 2A. The supplied second substrate 11b is transported in synchronization with the transport of the first substrate 11a to the transfer unit 25a. In the transfer unit 25a, the first particles P1 filled in the first substrate 11a are transferred to the second substrate 11b.

[0096] That is, the first substrate 11a can also be referred to as a transfer substrate for transferring the first particles P1 to the second substrate 11b. The concave-convex pattern formed on the surface of the first substrate 11a can also be referred to as a transfer concave-convex pattern. This transfer process will be described below with reference to FIG. 5.

[0097] 5 is a diagram showing a schematic configuration of the transfer unit 25a. The transfer unit 25a is composed of the pressure roller 223a and the conveying member 224a of the first belt device 22a, and the pressure roller 223b and the conveying member 224b of the second belt device 22b. As described above, the pressure rollers 223a and 223b rotate drivenly, and the two rollers are in contact with each other via the conveying members 224a and 224b. At least one of the pressure rollers 223a and 223b is a soft roller having an elastic layer on its surface, and a nip is formed where the two rollers contact each other.

[0098] The first substrate 11a and the second substrate 11b, which have been filled with the first particles P1 by the first filling device 24a, are transported at approximately the same speed by their respective transport members (224a and 224b) and enter a nip formed by contact between the pressure rollers 223a and 223b. In the nip, the first particles P1 on the first substrate 11a come into contact with the second substrate 11b and are transferred onto the second substrate 11b.

[0099] The second substrate 11b has a stronger adhesive force to the first particles P1 than the first substrate 11a has to the first particles P1. In other words, the adhesive force of the first particles P1 to the second substrate 11b is stronger than the adhesive force of the first particles P1 to the first substrate 11a. As a result, the first particles P1 on the first substrate 11a are transferred to the second substrate 11b at the nip portion.

[0100] The material of the second substrate 11b is not particularly limited, and a substrate of the same material as the first substrate 11a can be used. Note that, like the first substrate 11a, the second substrate 11b may be a substrate that is individually cut like cut paper, a continuous substrate that is wound into a roll like roll paper, or a continuous substrate that is alternately folded like continuous paper.

[0101] The second substrate 11b is preferably surface-treated to enhance adhesion so as to transfer the contacted first particles P1. For example, the second substrate 11b preferably has a holding portion coated with an adhesive on its surface. Furthermore, the back surface of the second substrate 11b (the surface to which the first particles P1 are not transferred) also preferably has a holding portion coated with the same adhesive as the front surface, and the surface is preferably covered with a protective film or the like. This prevents misalignment between the substrates when stacking multiple substrates 11b, and firmly fixes the positive electrode active material particles and solid electrolyte particles between the substrates by sandwiching them between the upper and lower surfaces (stacking direction). This suppresses particle movement during stacking, storage, transportation, heat treatment, and pressure application of the stack, allowing the desired electrode to be formed.

[0102] The adhesive is not particularly limited, and may be an acrylic adhesive, a rubber adhesive, a silicone adhesive, etc. Alternatively, it may be a thermoplastic resin or a photocurable resin whose adhesive strength changes in response to external disturbances such as heat or light.

[0103] The particle placement device 1 may have a coating means such as a dispenser or inkjet head that coats the surface of the second substrate 11b during transport. Alternatively, the substrate 11b pre-coated with the adhesive may be supplied from the second storage container 21b. In this case, it is preferable that the adhesive is covered with a release film and that a peeling means be provided to peel off the release film when the substrate is supplied. The type and amount of adhesive to be applied are adjusted as appropriate depending on the shape and material of the concave-convex pattern used, the particle size and material of the first particles P1 and the second particles P2 (described later), etc., but it is preferable that the adhesive has a greater adhesive strength than the concave-convex pattern 111a. Comparison of adhesive strength can be measured using a common method using a nanoindenter.

[0104] At the nip portion, the first particles P1 are restrained by the adhesive force generated between the first particles P1 and the second substrate 11b. When the conveying members 224a and 224b pass through the nip portion and are separated from each other, the first particles P1 on the first substrate 11a are transferred to the second substrate 11b.

[0105] The second substrate 11b onto which the first particles P1 have been transferred is transported by the transport member 224b to the settling position of the first settling device 24b. The first settling device 24b has the same configuration and function as the first filling device 24a (FIG. 2B). The difference is that the ratio of the first particles P1 to the carrier material S2 in the filler 241b is low. The carrier material S2 contained in the filler 241b also serves to collect excess particles P1" that are not in contact with the second substrate 11b. As the settling process progresses, the excess particles P1" are collected in the settling device 24b, so the filler 241b contains a low ratio of the first particles P1. By maintaining a low ratio of the first particles P1 to the support material S2 in the filler 241b, the settling of the first particles P1 and the recovery of excess particles P1" can be carried out over a long period of time. When the first settling device 24b is started up, it is preferable to use only the support material S2 as the filler 241b. This is because the purpose of the first settling device 24b is to cause the first particles P1 on the second substrate 11b to settle into the holder 13 by rubbing against the magnetic particles, which are the support material S2. The process of settling the first particles P1 will be explained using the figures.

[0106] The first settling device 24b has a configuration similar to that of the first filling device 24a (FIG. 2B), and contains a carrier material S2 containing a plurality of magnetic particles as filler 241a. The type and particle size of the carrier material S2 may be the same as or different from that of the carrier material S1. FIG. 6 is a schematic diagram of the carrier material S2 being transported on the second substrate 11b. For the sake of explanation, the figure shows one magnetic particle, but magnetic chains containing a plurality of magnetic particles may be formed.

[0107] First particles P1 are arranged on the holding portion 13 on the second substrate 11b. The holding portion 13 is exposed in the non-transfer portion on the second substrate 11b where the first particles P1 are not arranged, and recesses consisting of the first particles P1 are formed, so to speak. In this case, it is preferable that the opening diameter of the recesses of the concave-convex pattern formed on the second substrate 11b is smaller than the average size of the support material S2. This makes it possible to prevent the support material S2 from being arranged on the second substrate 11b.

[0108] The support material S2 comes into contact with the first particles P1 arranged on the holding portion 13 of the second substrate 11b, and is transported together with the second substrate 11b at a non-zero relative speed with respect to the second substrate 11b while receiving a magnetic force in a direction perpendicular to the surface of the second substrate 11b (the direction of arrow Fm in FIG. 6). As a result, the support material S2 is transported while being rubbed against the unevenness formed by the first particles P1 arranged on the holding portion 13 of the second substrate 11b. At this time, the first particles P1 arranged on the holding portion 13 of the second substrate 11b are subjected to a force in a direction that causes them to settle into the holding portion. When an adhesive is used as the holding portion, the settling of the particles causes the adhesive to be exposed to the surface through the gaps between the particles. Furthermore, the support material S2 can collect excess particles P1" that are not in contact with the second substrate 11b and rearrange (rotate and move) irregularly shaped particles that have a small contact area with the second substrate 11b, thereby forming a dense pattern of the first particles P1.

[0109] FIG. 7A is a schematic diagram of the second substrate 11b before the settling step, and FIG. 7B is a schematic diagram of the second substrate 11b after the settling step. Before the settling step (FIG. 7A), the first particles P1 are arranged in contact with the surface of the holder 13. In addition, excess particles P1" that are not in contact with the surface of the holder 13 are present on the first particles P1. After the settling step (FIG. 7B), the first particles P1 settle into the holder 13, the contact area between the particles and the holder increases, and the first particles P1 are tightly constrained. This allows the second particles P2, which will be described later, to be stably arranged.

[0110] Furthermore, excess particles P1" can be collected by rubbing with the support material S2 and placed in the portion of the holding unit 13 where the first particles P1 are not placed. As excess particles P1" are collected, the ratio of the first particles P1 to the support material S2 increases, but this ratio can be controlled by a method similar to that of the first filling device 24a described above. In other words, the ratio (weight ratio) of the first particles P1 to the support material S2 can be controlled by an inductance sensor that measures using magnetic permeability, which is common in electrophotographic devices, or a patch concentration sensor that measures and predicts the reflection density on a substrate, etc.

[0111] The support material S2 and the first particles P1 recovered from the first settling device 24b may be used as fillers to be replenished to the first filling device 24a. In this case, it is preferable that the support material S2 is made of the same magnetic particles as the support material S1. It is also more preferable that the ratio of the first particles P1 to the support material S2 in the filler 241b in the first settling device 24b is controlled to be lower than the ratio of the first particles P1 to the support material S1 in the filler 241a in the first filling device 24a.

[0112] The settling step of the first particles P1 is not limited to the first settling device 24b, but can also be performed using other devices. For example, FIG. 7C is a schematic diagram illustrating the settling device 25. The particle settling device 25 has pressure rollers 223c and 223d, and the pressure roller 223d rotates drivenly. At least one of the pressure rollers 223c and 223d is preferably a soft roller having an elastic layer on its surface. For example, a soft roller having an elastic layer of silicone rubber or fluororubber on the surface of a stainless steel core can be used. Furthermore, at least one of the pressure rollers 223c and 223d may have a built-in heater (not shown).

[0113] The substrate 11b having the first particles P1 arranged on its surface is transported by a belt device to a pressure section between the pressure rollers 223c and 223d. When pressed by the pressure rollers 223c and 223d, the first particles P1 arranged on the surface of the substrate 11b settle into the holder 13 of the substrate 11b. At this time, the heater described above may be used to facilitate settling of the first particles P1 into the holder 13 of the substrate 11b. Furthermore, a heat source may be provided upstream of the particle settling device 25 to heat the holder 13 of the substrate 11b.

[0114] Since the pressure roller 223c comes into contact with the first particles P1 arranged on the substrate, it is preferable to coat the surface with a material with good releasability, such as fluorine, to prevent particle adhesion. A cleaning mechanism for removing particles adhering to the pressure roller 223c may also be provided. It is more preferable to apply pressure to the first particles P1 arranged on the substrate 11b while they are covered with a protective material (not shown). In this case, the protective material used is preferably a material with good releasability, such as a fluorine sheet if it is a resin or nichrome foil if it is a metal. If a protective material is used, a removal mechanism (not shown) for removing the protective material is provided downstream of the particle settling device 25 and upstream of the third filling device 24.

[0115] The particle settling device 25 may be any other known pressurizing device. For example, an isostatic pressure pressurizing device (CIP / HIP), a uniaxial pressure pressurizing device, or even a weight or magnet may be used for pressure application. Furthermore, if the particles have a high specific gravity, the particles may be allowed to settle by their own weight. In this case, it is preferable to promote the settling of the particles by storing the substrate under heating, such as in an oven.

[0116] When storing a substrate on which particles are arranged under heating, the heating temperature and storage time are appropriately adjusted according to the physical properties (shape, particle size, specific gravity, adhesiveness, viscoelasticity, etc.) of the particles and the adhesive used in the retaining portion. If the heating temperature or storage time is insufficient, the particles will not settle sufficiently, and the adhesive as the retaining portion will not be easily exposed to the surface through the gaps between the particles. On the other hand, if the heating temperature or storage time is excessive, the particles will tend to move in the planar direction as they settle, significantly reducing the density of the arranged particles. It is preferable to maintain the densely arranged state of the first particles P1 and allow them to settle efficiently by adjusting the heating temperature from 20°C to 100°C using a heater or the like.

[0117] (Steps III and IV) Steps III and IV are steps of arranging second particles P2 (solid electrolyte particles) in portions of the holding portion on the resin substrate where the first particles P1 (cathode active material) are not arranged, and allowing the first particles and second particles to settle in the holding portion on the resin substrate. In steps III and IV, particles are arranged on the resin substrate using a particle arrangement device 2. The particle arrangement device 2 will be described below.

[0118] [Particle placement device 2] As the second filling device 24c, for example, a simple device that does not use a belt device can be used. Fig. 8A shows an example of the device. The second filling device 24c has a filling container 242c that contains a filler 241c, a stirring screw member 243c that stirs and conveys the filler 241c, a magnetic member 247c, a magnet 248c, and a regulating member 249c.

[0119] Filler 241c is contained in filling container 242c. Filler 241c has second particles P2 and a support material S3 that supports the second particles P2. The second particles P2 are solid electrolyte particles. Filler 241c is a mixture of multiple powders including a powder composed of multiple second particles P2 and a powder composed of multiple support materials S3. Support material S3 may be the same as or different from support materials S1 and S2. The support material S3 is selected appropriately depending on the particle size and material of second particles P2 and the opening width of the void portion described above.

[0120] FIG. 8B is a schematic diagram illustrating the operation of the filling device. The substrate 11b, on which the first particles P1 have been placed through the above-described steps I and II, is fixed to the filling device 24c by a substrate fixing member (not shown). The filler 241c, sufficiently stirred by the stirring screw member 243c, is supplied in an appropriate amount by the magnetic member 247c (arrow a in FIG. 8B) that has moved from its home position and the regulating member 249c. The supplied filler 241c is rubbed on the substrate 11b as the magnetic member 247c reciprocates (arrow b in FIG. 8B). After the desired number of rubs, the magnetic member 247c moves to a distant home position where the magnetic force acting on the filler 241c on the substrate is sufficiently weakened (arrow c in FIG. 8B). Excess filler 241c supplied to the substrate 11b falls downward due to gravity and is collected in a collection container (not shown). It is preferable to use air blowing or vibration at this time.

[0121] The method for rubbing the filler 241c on the substrate 11b is not limited to the above-described method. The rubbing may be performed by fixing the magnetic member 247c and reciprocating the substrate 11b, or by moving both the magnetic member 247c and the substrate 11b at a relative speed so that the filler 241c is rubbed on the substrate 11b.

[0122] 9 is an enlarged view of the vicinity of the surface of the second substrate 11b during the filling process using the second filling device 24c. After the above-described steps I and II, an uneven pattern is formed on the second substrate 11b, having protrusions formed by the placement of the first particles P1 and recesses where the first particles P1 are not placed. The holding portion 13 is exposed in the recesses on the second substrate 11b where the first particles P1 are not placed. In the filling process using the second filling device 24c, the second particles P2 are placed on the holding portion 13 on the surface of the second substrate 11b.

[0123] The filler 241c comes into contact with the concave-convex pattern on the second substrate 11b, and is transported together with the second substrate 11b at a non-zero relative speed with respect to the second substrate 11b while being subjected to a magnetic force (indicated by the arrow Fm in the figure) in a direction perpendicular to the surface of the second substrate 11b. As a result, the second particles P2 carried by the support material S3 are transported while being rubbed against the concave-convex pattern on the surface of the second substrate 11b.

[0124] At this time, the opening width of the recesses of the uneven pattern formed on the second substrate 11b is set to a size that allows the second particles P2 to contact the recesses but prevents the support material S3 from contacting them. That is, the opening diameter of the recesses of the uneven pattern on the second substrate 11b is preferably larger than the cumulative 50% particle size (median diameter) of the second particles P2 in the volume-based particle size distribution. Furthermore, the opening diameter of the recesses is preferably smaller than the average size of the support material S3. Here, the opening diameter of the recesses of the uneven pattern is preferably the opening diameter in the short direction of the recesses, and more preferably the maximum opening diameter in the short direction of the recesses. This allows only the second particles P2 in the filler 241c to selectively contact the recesses.

[0125] The second particles P2 that come into contact with the recesses are strongly restrained by the physical restraining force due to the structure of the concave-convex pattern, and by the electrostatic adhesion and adhesive force with the second substrate 11b and the structural material that constitutes the concave-convex pattern (here, the first particles P1), and are detached from the support material S3. Note that, for the sake of explanation, in Fig. 9, the second particles P2 are supported on the surface of the support material S3, but it is acceptable for particles P2 that are not supported on the support material S3 to exist during the agitation, supply, or transport of the filler 241c.

[0126] FIG. 10A is a schematic diagram of the second substrate 11b after the first particles P1 have been transferred by the transfer unit 25a, showing the second substrate 11b viewed from a direction perpendicular to the substrate surface. As shown in FIG. 10A, a line pattern is formed on the second substrate 11b, in which arrangement regions in which the first particles P1 are arranged in a line are aligned. The first particles P1 are densely arranged within this line-shaped region, and the first particles P1 are not arranged in other areas (white areas in FIG. 10A), exposing the surface of the second substrate 11b. The line-shaped region in which the first particles P1 are held is referred to as the first pattern portion. The line-shaped region in which the second particles P2 are held and located in the gaps between the first pattern portions is referred to as the second pattern portion.

[0127] FIG. 10B is a schematic diagram of the second substrate 11b after the second particles P2 have been filled by the second filling device 24c, viewed from a direction perpendicular to the substrate surface. As shown in FIG. 10B, the second particles P2 are densely arranged in the areas where the first particles P1 were not arranged. Furthermore, the first particles P1 and the second particles P2 are densely arranged at the boundary between the areas where the first particles P1 are arranged and the areas where the second particles P2 are arranged. FIG. 10C is a schematic cross-sectional view of the substrate and the particles arranged on the substrate at the dashed line position in FIG. 10B. The first particles P1 and the second particles P2 are arranged on the holding portion 13 of the second substrate 11b. Note that particles can also be filled in small gaps between the first particles P1 using a similar method. In this case, it is possible to fill the gaps between the first particles P1 using a filler containing particles with a particle size corresponding to the gaps between the first particles P1 using the same method as described above, thereby forming an even denser thin film.

[0128] In step IV, the settling step of the first particles P1 and the second particles P2 can be performed using the second filling device 24c. In this case, similar to the settling step of the first particles P1 in step II, the filler 241c is preferably the support material S2.

[0129] FIG. 10D is a schematic diagram of second substrate 11b before the precipitation step in step IV, and FIG. 10E is a schematic diagram of second substrate 11b after the precipitation step. Before the precipitation step ( FIG. 10D ), second particles P2 are arranged in contact with holder 13, and excess particles P2″ that are not in contact with holder 13 are present on second particles P2. After the precipitation step ( FIG. 10E ), first particles P1 and second particles P2 settle onto holder 13, increasing the contact area between the particles and the holder, and strongly constraining first particles P1 and second particles P2. This suppresses particle movement during storage and transport of substrate 11b and a positive electrode precursor formed by laminating substrate 11b on base 14, as described below. Furthermore, particle movement is suppressed during heat treatment and pressure application of the positive electrode precursor, as described below, allowing a desired electrode to be formed.

[0130] After step IV and before step V, which will be described later, third particles P3 may be further arranged on the second substrate 11b. The third particles P3 can be arranged using the particle arrangement device 1 or particle arrangement device 2 by using the holding portion 13 exposed between the particles after the settling step and the unevenness formed by the first particles P1 and the second particles P2. The third particles P3 may be the same as the second particles P2, or may be different solid electrolyte particles or active material particles. When using the same solid electrolyte particles as the second particles P2, it is preferable to use particles classified toward the smaller particle size side in the particle size distribution. Alternatively, the particle arrangement and settling steps may be repeated to arrange multiple particles, such as the third particles P3, fourth particles P4, and fifth particles P5, multiple times.

[0131] In the above description, the placement and sedimentation of the first particles P1 was performed using the particle placement device 1, and the placement and sedimentation of the second particles P2 was performed using the particle placement device 2. However, the particle placement device used in each step is not limited, and either particle placement device may be used. For example, the first particles P1 may be placed using the particle placement device 2. In this case, a separately prepared PDMS mold or a resin film mold may be fixed and used instead of the substrate 11b in FIG. 8A. The first particles P1 filled in the recesses of the mold may be transferred to the second substrate 11b using a transfer roller similar to that used in the particle placement device 1. Alternatively, the substrate 11b may be stacked on the mold, packaged in a vacuum packaging bag (Co-pack), and then pressed and transferred using an isostatic pressure device.

[0132] In the particle arrangement devices 1 and 2, the coverage of the resin substrate surface by the particles (particles P1, P2, ...) arranged on the substrate 11b is preferably 60% or more, more preferably 70% or more, and even more preferably 80% or more. In the present disclosure, the coverage of the resin substrate surface refers to the ratio (area %) of the area covered by the active material particles and solid electrolyte particles to the total area of ​​the resin substrate surface. The coverage of the substrate by the particle layer can be measured by photographing the area where the particle layer is formed using an optical microscope from the direction perpendicular to the substrate and calculating the area ratio of particles P1 and P2 within that area using image processing software.

[0133] (Step V) Step V is a step of laminating the resin substrate (second substrate 11b) on which the particles have been arranged in the above step onto a substrate 14. That is, this is a step of forming a positive electrode precursor, which is a laminate. The number of resin substrates laminated is determined according to the desired electrode capacity. Furthermore, it is preferable that the substrate 14 also serves as a current collector, and a known current collecting material can be used. As the substrate 14, a known current collecting material such as a precious metal such as gold foil, platinum foil, or silver foil, an Al foil, or a SUS foil can be used.

[0134] FIG. 11A is a schematic diagram illustrating the configuration of a positive electrode precursor molding apparatus. The positive electrode precursor molding apparatus includes a conveying device 31 that conveys a substrate 11b on which a particle layer (positive electrode active material layer) 12 containing first particles P1 and second particles P2 has been formed, and a stage 32 that can be moved quickly and easily in the vertical direction by an actuator (not shown). The conveying device 31 receives the substrate 11b on which the particle layer 12 has been formed using a particle placement device and conveys it to the stage 32. Examples of the conveying device 31 that can convey the substrate 11b include a belt conveyor, a roller, and a robot arm. When the conveying device 31 conveys the substrate 11b to the stage 32, the stage 32 moves in the vertical direction by the thickness of the substrate 11b and the particle layer 12. By repeating the conveying by the conveying device 31 and the movement of the stage 32, multiple substrates 11b on which particle layers 12 have been formed are stacked on a base 14, and a positive electrode precursor 15 is formed.

[0135] At this time, it is preferable that an adhesive is applied to the back surface of the substrate 11b on which the particle layer 12 is formed. This adhesive adheres the substrates 11b to each other, increasing the strength of the structure and preventing misalignment between the substrates even after step V. Furthermore, by sandwiching the particle layer 12 between the substrates 11b between the upper and lower adhesives, the particles are firmly held during the steps described below and during storage of the positive electrode precursor, preventing misalignment. The adhesive may be applied using a coating device (not shown) before lamination, or a pre-coated substrate may be used and the protective film coated on the coated surface may be peeled off before lamination.

[0136] It is preferable to have a static elimination step of eliminating static electricity from the substrate immediately before forming the positive electrode precursor 15. The particle layer 12 and substrate 11b formed using the particle arrangement device are easily charged, and electrostatic repulsion and attraction occur between the substrates 11b when stacked. Therefore, when stacking in step V, the substrates may be stacked in a misaligned state or may wrinkle, making it difficult to obtain the desired positive electrode precursor. In the static elimination step, static electricity is preferably eliminated contactlessly using an electrostatic elimination blower or the like.

[0137] Furthermore, after positive electrode precursor 15 is formed, it is preferable to have a degassing step in which the positive electrode precursor is degassed to remove air between the substrates. In the degassing step, degassing is preferably performed using a vacuum packaging machine, a vacuum oven, or the like. Furthermore, a pressurizing step may be performed before or after the degassing step. The pressurizing step is preferably performed using a common pressurizing means such as vacuum degassing, isostatic pressing, a hydraulic press, or a roller press. In particular, it is preferable to perform pressurizing by combining vacuum degassing and isostatic pressing.

[0138] FIG. 11B is a schematic cross-sectional view of a positive electrode precursor 15 produced by the above-described positive electrode precursor manufacturing method (Steps I to V). The positive electrode precursor is a structure including a substrate 14 and a substrate 11b on which a particle layer 12 is formed. More specifically, it is a structure in which a substrate 11b is laminated on a substrate 14, and a particle layer 12 containing positive electrode active material particles and solid electrolyte particles is disposed on the substrate 14. The positive electrode precursor can be laminated in one or more sheets, arbitrarily selected according to the desired battery capacity. That is, a single positive electrode precursor may be used, or multiple sheets may be laminated. Furthermore, as shown in FIG. 11B, the substrate 11b and the particle layer 12 may be repeatedly laminated in this order from the substrate 14 side, or the order may be reversed, with the particle layer 12 and the substrate 11b repeatedly laminated in this order from the substrate 14 side. Furthermore, the same layers may be repeatedly laminated, such as the substrate 11b, the particle layer 12, the particle layer 12, and the substrate 11b.

[0139] (Second Step) The second step (S101 in FIG. 1A) is a lamination step in which a first material layer containing active material particles that form the positive electrode active material layer and a second material layer containing solid electrolyte particles that form the electrolyte layer are laminated to form a laminate. The positive electrode precursor prepared in the first step can be used as the first material layer containing active material particles that form the positive electrode active material layer. In the second step, after the first step of preparing the positive electrode precursor, the positive electrode precursor prepared in the first step and the solid electrolyte that forms the electrolyte layer are laminated in a die used for spark plasma sintering. That is, the lamination step preferably includes a step of surrounding the laminate with a dielectric. Specific steps are described below.

[0140] 12A and 13B are schematic diagrams illustrating the lamination process within a die. As shown in FIG. 12B , the die 51 has a hollow cylindrical shape, allowing cylindrical punches 52 to be inserted from above and below in the lamination direction to apply pressure. As shown in FIG. 12A , the punch 52 is inserted into the die 51 from below in the lamination direction, a carbon sheet 53 is laminated on the punch 52, and the positive electrode precursor 15 prepared in the first step is laminated on the carbon sheet 53. The positive electrode precursor 15 is laminated so that the substrate 14 on the side not laminated with the base material 11b contacts the carbon sheet 53. That is, the above-described active material particles and solid electrolyte particles are disposed on the upper side (the side not contacting the carbon sheet 53) of the positive electrode precursor 15 laminated on the carbon sheet 53. The substrate 14 of the positive electrode precursor is pre-processed to a size that fits inside the cylinder.

[0141] An appropriate amount of solid electrolyte particles 54 is supplied from above the stacked positive electrode precursor 15 and pressed evenly to form a surface. The surface is preferably formed by inserting a punch 52 from above in the stacking direction. A carbon sheet 53 is stacked on the formed surface, and a punch 52 is inserted from above in the stacking direction ( FIG. 12B ). A release material may be inserted between the carbon sheet 53 and each layer of the stack containing the positive electrode precursor and the solid electrolyte. Examples of the release material include gold foil and platinum foil. The materials for the die and punch are not particularly limited, and commercially available graphite or cemented carbide materials can be used. The die and punch are preferably made of graphite, as this eliminates the need for atmospheric control in the third step described below.

[0142] A vibration step may be performed after the second step. By applying vibration using a commercially available vibrator (such as a small vibration unit manufactured by Sansho Industry Co., Ltd.), the solid electrolyte particles 54 in the die are packed more uniformly, enabling dense molding.

[0143] (Third Step) The third step (S103 in FIG. 1A) is a pressure and current application step in which a positive pressure and an AC voltage are applied to the laminate formed in the second step in the stacking direction to form a composite. The pressure and current application step preferably includes a step of heating the laminate. In the present disclosure, spark plasma sintering is performed as the pressure and current application step. Specific steps are described below. FIG. 13 is a schematic diagram of a spark plasma sintering apparatus 61 used in the third step. The spark plasma sintering apparatus 61 mainly includes an electrode 62, a DC pulse power supply 63 that supplies a pulse current, a pressure shaft 64 that applies current and pressure to the sample, a spacer 65, and a chamber 66. Furthermore, the pressure can be controlled in the direction of the arrow in the figure using a pressure mechanism and control unit (not shown). The pressure during pressure application is preferably 5 to 800 MPa. Furthermore, the temperature can be adjusted using a temperature sensor and control unit (not shown). The sintering temperature is preferably 200 to 1000°C.

[0144] The sample is arranged so that it is sandwiched between an upper spacer 65 and a lower spacer 65 in a stacked state within the die. The die is arranged so that the base 14 of the positive electrode precursor is on the upper side relative to the substrate 11b and the solid electrolyte. In other words, the upper side refers to the electrode side to which a positive voltage (current) is applied (the upper electrode 62 in FIG. 13). In other words, the die is arranged so that the surface of the solid electrolyte particles formed in the second step is located on the lower side in FIG. 13. Spark plasma sintering is performed on the sample. Spark plasma sintering is preferably performed in an air atmosphere. Other suitable gases include Ar, N ２ , Ar—H ２ The sintering may be carried out in an atmosphere. The sintering time is preferably 1 to 30 minutes. By carrying out sintering in the third step, an electrolyte layer having ion conductivity is formed.

[0145] (Step 4) The fourth step (S104 in FIG. 1A ) involves removing the composite from the die after spark plasma sintering and performing post-treatment. The sample is removed from the die, and the carbon sheet and release agent attached to both sides of the sample are removed using a knife or similar tool. Since the carbon sheet attached to the solid electrolyte side (the side opposite the substrate 14) must be removed reliably, the surface is further polished with an abrasive sheet or similar tool to remove the carbon sheet. During step 4, the substrate 14 may be released from the sample; in this case, the sample can be stacked on the positive electrode current collector so that the positive electrode surface is in contact with the positive electrode current collector during battery assembly, as described below.

[0146] (Fifth Step) The fifth step (S105 in FIG. 1A) is a sintering step in which the composite is sintered in an oxygen-containing atmosphere to form an electrode composite. Specifically, this is a step in which re-sintering is carried out to adjust the composition and shape of the positive electrode active material. Specific steps will be described below. In the spark plasma sintering in the third step (S103 in FIG. 1A), the positive electrode active material is easily reduced by the reducing gas generated when the resin substrate is removed and by the graphite die. In particular, a positive electrode active material containing Co, typically lithium cobalt oxide (LiCoO ２ ), LiCoO ２ The so-called ternary NMC, in which some of the Co is replaced with Ni or Mn, and lithium cobalt phosphate (LiCoPO ４ ) are easily reduced. Because the composition of the positive electrode active material changes due to reduction, re-sintering is carried out in the fifth step to oxidize the positive electrode active material and return it to its original composition.

[0147] In the spark plasma sintering in the third step, a reducing gas is generated when the resin substrate is removed, as described above. It is believed that the generated gas uniformly contacts the positive electrode active material particles, causing the positive electrode active material particles to be reduced and decomposed into cobalt oxide, cobalt, or the like, and that small particles that tend to be unevenly distributed are unevenly distributed toward the substrate 14. Furthermore, it is believed that re-sintering in the fifth step oxidizes the unevenly distributed small particles (cobalt oxide or cobalt) to produce second active material particles (lithium cobalt oxide).

[0148] The reason for this is speculated as follows. Figure 20 is a schematic diagram of the inside of the die during spark plasma sintering. Due to the temperature increase (up to 450°C) caused by spark plasma sintering, the substrate 11b is lost and reducing gas (CO) is generated. Furthermore, the surrounding graphite die reduces and decomposes the lithium cobalt oxide (P1) in the particle layer 12. Meanwhile, the solid electrolyte particles (P2) are sintered together with the solid electrolyte particles 54. The lithium cobalt oxide (P1) is converted to cobalt oxide or cobalt through reduction and decomposition, and exists primarily as primary particles with a porous structure. However, some of the particles are thought to be unevenly distributed on the substrate 14 (current collector) side in smaller sizes. While the reason for this uneven distribution is unclear, it is thought that the pulse current (voltage), temperature distribution, particle shape, particle weight, void distribution, and other factors may play a role. It is thought that the re-sintering in the fifth step oxidizes the small particles unevenly distributed on the substrate 14 side in the third step and generates second active material particles. That is, by performing the fifth step, it is possible to configure the positive electrode active material layer to contain second active material particles having a minor axis of 130 nm or less and an aspect ratio of the minor axis to the major axis of at least 2. The particle size and shape of the second active material particles can be controlled by conditions such as the sintering temperature and sintering time of re-sintering.

[0149] The resintering is preferably performed using a muffle furnace or a tubular furnace. The sintering temperature is preferably 400 to 800°C. The sintering time is preferably 0.1 to 10 hours. The sintering is preferably performed in an oxygen-containing atmosphere, such as the air or an oxygen atmosphere. By performing the resintering under the above conditions, it is possible to obtain a configuration in which second active material particles having a minor axis of 130 nm or less and an aspect ratio of the minor axis to the major axis of 2 or more are present in the positive electrode active material layer.

[0150] The above-described first step (S101 in FIG. 1A) to fifth step (S105 in FIG. 1A) can produce electrode composite 17 in which a positive electrode layer and an electrolyte layer are stacked. That is, electrode composite 17 is an electrode composite including a positive electrode active material layer and an electrolyte layer.

[0151] <Method for manufacturing secondary battery> A secondary battery can be manufactured using the above-described electrode composite (electrode composite 17). The secondary battery has an electrode composite, a negative electrode, and a current collector. The method for manufacturing the secondary battery is not particularly limited, and a plurality of methods can be used. The method for manufacturing the secondary battery preferably includes a step of manufacturing the electrode composite by the above-described method, and a step of stacking the manufactured electrode composite, negative electrode, and current collector. An example of the manufacturing method will be described below.

[0152] A negative electrode is formed on the surface of the electrode composite 17 facing the electrolyte layer (the surface opposite to the positive electrode surface). A typical negative electrode used in ordinary secondary batteries can be used. A metal foil or the like may be laminated on the electrode composite, or negative electrode active material particles may be disposed on the electrode composite to form a negative electrode active material layer. That is, an electrode composite having a negative electrode active material layer in contact with the electrolyte layer can also be used as the electrode composite. A secondary battery can include an electrode composite having a negative electrode active material layer in contact with the electrolyte layer, a first current collector in contact with the positive electrode active material layer, and a second current collector in contact with the negative electrode active material layer. A method for forming a negative electrode will be described below.

[0153] When a metal such as lithium metal or indium is used as the negative electrode, a metal foil may be laminated directly on the electrode composite 17, or a polymer electrolyte may be interposed therebetween as a buffer layer. Alternatively, a metal negative electrode may be formed on the electrode composite 17 by a vacuum process such as sputtering or vapor deposition.

[0154] When negative electrode active material particles such as graphite, silicon (Si), or lithium titanate (LTO) are used as the negative electrode, the negative electrode precursor can be manufactured using a method similar to the above-described method for manufacturing the positive electrode precursor. That is, a resin substrate for the negative electrode, on which at least negative electrode active material particles are disposed, is prepared, and the resin substrate is laminated on a substrate 14 to obtain the negative electrode precursor. The particle layer formed on the negative electrode precursor may be a particle layer containing negative electrode active material particles and solid electrolyte particles, or a particle layer containing only negative electrode active material particles. It may also be a particle layer containing multiple types of negative electrode active material particles. The negative electrode precursor is heat-treated to remove the resin substrate, thereby obtaining the negative electrode. The negative electrode can be laminated on an electrode composite, as in the case of using a metal foil.

[0155] Alternatively, a negative electrode may be formed by laminating a resin substrate having the above-described particle layer formed on the electrolyte layer side of the electrode composite 17 (the surface opposite to the positive electrode side) and then performing a heat treatment to remove the resin substrate. Laminating a resin substrate having a particle layer for the negative electrode formed thereon can be performed on the electrode composite 17 after the fifth step (S105 in FIG. 1A ), or may be performed on the electrode composite 17 after the fourth step (S104 in FIG. 1A ), or may be performed on the electrode composite 17 after the second step (S102 in FIG. 1A ).

[0156] FIG. 14A is a schematic cross-sectional view of a plurality of substrates 11b, on which anode particle layers 12 are arranged, stacked on an electrode composite 17 after the fourth step (S104 in FIG. 1A). FIG. 14B is a schematic cross-sectional view of anode precursor 16 stacked on electrode composite 17 after the second step (S102 in FIG. 1A). The anode precursor 16 is a structure in which a resin substrate and a substrate 14 are stacked in this order, facing the cathode precursor 15. The resin substrate may be a single sheet, or multiple sheets may be stacked. Furthermore, a bipolar laminate and a secondary battery can be manufactured by stacking cathode and anode substrates 11b on both sides of a substrate 14, which also serves as an electrode current collector, with solid electrolyte particles 54 interposed between them. When manufacturing a secondary battery using the above method, the heat treatment used to manufacture the electrode composite 17 can simultaneously form the anode, thereby reducing the heat treatment process. In addition to the above method, the anode may also be formed using conventional anode forming methods, such as a coating process.

[0157] The manufactured components can be stacked in the order of positive electrode current collector, positive electrode, electrolyte, negative electrode, and negative electrode current collector, and packaged in a laminate film to produce a laminated battery, or packaged in a coin case to produce a coin battery.

[0158] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples. In the following examples, unless otherwise specified, the number of parts is based on parts by mass.

[0159] The positive electrode active material particles and solid electrolyte particles used in the examples and comparative examples will be described. The positive electrode active material particles used were lithium cobalt oxide (LiCoO2: Cellseed C-5H) manufactured by Nippon Chemical Industry Co., Ltd. The solid electrolyte particles Li ５．９ Yb ０．８１ La ０．０９ Zr ０．１ (BO ３ ) ３ was synthesized by the method described in JP-A-2022-130301. ３ BO ３ (Toyoshima Manufacturing Co., Ltd.), H ３ BO ３ (Kishida Chemical), Yb ２ O ３ (manufactured by Kojundo Kagaku Kenkyusho), La ２ O ３ (Kishida Chemical), ZrO ２ (manufactured by Nippon Denko) was prepared as a raw material for the solid electrolyte. ５．９ Yb ０．８１ La ０．０９ Zr ０．１ (BO ３ ) ３ The materials were weighed out at a predetermined stoichiometric ratio so that the total weight of the positive electrode active material particles and the solid electrolyte particles were mixed in a mortar and pestle. The mixed powder was cold uniaxially molded using a Shimadzu hydraulic press SSP-10A and heat-treated in an air atmosphere. The heating temperature was 650°C and the holding time was 720 minutes. The obtained pre-fired body was pulverized using a mortar and pestle to synthesize a solid electrolyte powder. The synthesized solid electrolyte was treated in a planetary ball mill P-7 (manufactured by Fritsch Japan) using Φ5 mm zirconia beads at 370 rpm for 100 hours to obtain solid electrolyte particles. An electrode composite was produced using the above-mentioned positive electrode active material particles and solid electrolyte particles by the above-mentioned method. A more specific procedure is as follows.

[0160] (Step 1) A polyethylene terephthalate resin (PET) having a thickness of 2 μm was used as the substrate 11b. An acrylic adhesive was applied to both sides of the substrate 11b to a thickness of 1.5 μm to form the holding part 13. The positive electrode active material particles P1 and the solid electrolyte particles P2 were arranged on the holding part 13 and allowed to settle by the method described in Steps I to IV above.

[0161] A Pt foil was used as the substrate 14. Three substrates 11b, each having cathode active material particles P1 and solid electrolyte particles P2 held by a holder 13, were stacked on the substrate 14 by the method described in step V above, to obtain a cathode precursor. The cathode active material particles P1 and solid electrolyte particles P2 were firmly held in place from above and below between the stacked substrates 11b. The substrates 11b were also firmly stacked on the substrate 14 with high precision. A cathode precursor was prepared by the above steps.

[0162] 15A and 15B are SEM images of the positive electrode precursor prepared in the first step (S101 in FIG. 1A). FIG. 15A is an image taken from the upper side (the side where the particles are arranged) of the substrate 11b, and FIG. 15B is a cross-sectional image of the substrate 11b. On the substrate 11b, positive electrode active material particles P1 were arranged in a line shape, and solid electrolyte particles P2 were arranged so as to fill the spaces between them (FIG. 15A). Note that the layers were stacked so that the lines formed by the positive electrode active material particles P1 did not overlap between the stacked substrates 11b. This was done to prevent the electronic conduction of the positive electrode active material particles P1 and the ionic conduction of the solid electrolyte particles P2 from being cut off in the stacking direction.

[0163] The positive electrode active material particles P1 on the substrate 11b were located closer to the base 14 (downward in FIG. 15B ) than the solid electrolyte particles P2. This is because the positive electrode active material particles P1 were precipitated in the holder 13 in step II (T102 in FIG. 1B ) of the method for producing a positive electrode precursor. This is also because the positive electrode active material particles P1 used in the examples were heavier than the solid electrolyte particles P2.

[0164] (Second Step) In the second step (S102 in FIG. 1A ), a cylindrical graphite die (Φ10 mm) was used as the die 51, and a cylindrical graphite punch (Φ10 mm) was used as the punch 52. A carbon sheet 53, the positive electrode precursor 15 prepared in the first step, solid electrolyte particles 54 (200 mg), a release material (gold foil), and the carbon sheet 53 were stacked in the die by the method described above to form a laminate (S102 in FIG. 1A ). A commercially available carbon sheet with a thickness of 0.2 mm was used. The same solid electrolyte particles as those used in the first step were used. The solid electrolyte particles 54 are particles that form the electrolyte layer in the electrode composite.

[0165] (Third Step) A pressurizing and current-applying step was performed on the laminate. In this example, the pressurizing and current-applying step involved spark plasma sintering, which included a step of heating the laminate. The spark plasma sintering was performed in an air atmosphere (inside the chamber 66). The sintering temperature was 600°C, the sintering time (600°C maintenance time) was 5 minutes, and the pressure was 30 MPa.

[0166] (Step 4) After step 3, the composite (electrode composite 17 formed by laminating a positive electrode active material layer and an electrolyte layer) was removed from the die. FIG. 16 shows a cross-sectional SEM image and an EDX image of electrode composite 17 formed by laminating a positive electrode layer and an electrolyte layer, which was removed from the die in step 4 (S104 in FIG. 1A). FIG. 16A shows a cross-sectional SEM image of the positive electrode layer of electrode composite 17. FIG. 16B shows an EDX image of cobalt (Co) contained in the positive electrode active material particles of the positive electrode layer of electrode composite 17. FIG. 16C shows an EDX image of ytterbium (Yb) contained in the solid electrolyte particles of the positive electrode layer of electrode composite 17.

[0167] 16A to 16C, the substrate 11b was not observed in a sheet shape, and it was confirmed that the resin substrate had disappeared in step 3. In the positive electrode layer of electrode composite 17 after step 3, a particle group containing Co and a particle group containing Yb were arranged, and materials containing carbon, oxygen, etc. were present so as to fill the gaps between the particle groups.

[0168] FIG. 17A shows the positive electrode active material particles (LiCoO ２) is a cross-sectional SEM image of the cathode active material particles in the laminate after the third step, which were removed from the die. The cathode active material particles before spark plasma sintering (FIG. 17A) maintained the morphology of the raw material CellSeed C-5H both within the particles and on the particle surface. Meanwhile, the cathode active material particles after spark plasma sintering (FIG. 17B) had changed to a so-called porous structure in which voids existed within the particles. Furthermore, X-ray analysis of the cathode active material particles after spark plasma sintering revealed that the main composition had changed to cobalt oxide and cobalt. This is thought to be due to the reduction and decomposition of lithium cobalt oxide caused by the reducing gas (CO) generated when the base material 11b disappears during spark plasma sintering and the reduction caused by the graphite die.

[0169] (Step 5) The composite was re-sintered to form an electrode composite. Figure 18 is a cross-sectional SEM image of the electrode composite 17 re-sintered in step 5 (S105 in Figure 1A). Resintering was performed in a muffle furnace at a sintering temperature of 600°C, for a sintering time (600°C maintenance time) of 1 hour, and in air. From the bottom of the paper in Figures 18A and 18C, the solid electrolyte layer (SEL) and the positive electrode active material layer (AAML) are stacked in this order via the first surface PP. Figure 18C is a partial enlarged view of Figure 18A. Figures 18B and 18D each show a schematic diagram of the cross-sectional structure of Figures 18A and 18C. Similarly, Figure 18D corresponds to a partial enlarged view of Figure 18B.

[0170] As is clear from the cross-sectional SEM images of Figures 18A and 18C and the schematic diagrams of Figures 18B and 18D, the center of gravity BP (P2) of the plurality of second active material particles P2 was located farther from the first surface PP than the center of gravity BP (P1) of the plurality of first active material particles P1. In Figure 18B, region P1 indicates the region where the first active material particles are present, and region P2 indicates the region where the second active material particles are present. Region P1 was in contact with the solid electrolyte layer (SEL) via the first surface PP. In other words, the electrolyte layer and the first active material particles were in contact via the first surface.

[0171] Furthermore, the first surface PP was in contact with the P1 region at multiple locations in the layer thickness direction. That is, the first surface had portions overlapping with multiple first active material particles in the layer thickness direction. The substrate on top of the positive electrode layer was removed before photographing. The positive electrode active material particles after resintering were significantly different in shape from the particle image after spark plasma sintering ( FIG. 17B ), changing into particles P11 having a granular form and some voids, and particles P12 having a larger aspect ratio and smaller particle size than P11.

[0172] FIG. 19A is a cross-sectional SEM image of electrode composite 17, and FIG. 19B is an EDX image of Co contained in the positive electrode active material particles. Particle P12 was unevenly distributed along the surface direction of the substrate side (upper side of FIGS. 19A and 19B) compared to particle P11. Furthermore, as a result of X-ray analysis, both particles P11 and P12 were identified as oxides containing Li, Co, and O. Furthermore, EDX and EELS analysis using TEM confirmed that the substance present around P11 and P12 was an oxide of boron (B) containing lithium (Li) and carbon (C).

[0173] This is believed to be achieved by the following mechanism. Figures 19C and 19D show an SEM image (Figure 19C) taken from above (the side where the particles are located) of a compact produced by stacking the substrate 11b on a substrate and sintering it in a muffle furnace, and a cross-sectional SEM image (Figure 19D) of the compact. The positive electrode active material particles after resintering change from the morphology of the raw material lithium cobalt oxide particles to have a porous structure with voids within the particles and protrusions precipitated in multiple directions on the particle surfaces (Patent Document 3). Based on their shape and composition, particles P12 confirmed in Figures 18A to 18D and 26A are believed to be the above-mentioned protrusions. In other words, it is believed that the protrusions precipitated on the surfaces of the lithium cobalt oxide particles have become detached from the lithium cobalt oxide particles and are unevenly distributed.

[0174] The void distribution will be explained below. The particle layer 12 on the substrate 11b is characterized in that the P2 particles are located farther from the substrate 14 than the P1 particles due to the settling process. This is thought to create voids around the P1 particles, particularly on the substrate 14 side, making it easier for minute primary particles (cobalt oxide or cobalt) to be unevenly distributed on the substrate 14 (current collector) side. It is thought that by re-sintering after spark plasma sintering, the primary particles unevenly distributed on the current collector side are oxidized with the surrounding lithium carbonate and converted into lithium cobalt oxide in the shape of the protrusions.

[0175] An all-solid-state secondary battery was fabricated using the electrode assembly 17 obtained by the above-described method and evaluated. The fabrication method and evaluation method for the all-solid-state secondary battery will be described below.

[0176] <Method of Manufacturing All-Solid-State Secondary Battery> A positive electrode current collector (Al foil, thickness 20 μm), an electrode composite 17, a negative electrode material (indium foil, thickness 50 μm, manufactured by Nilaco), and a negative electrode current collector (Cu foil, thickness 20 μm) were laminated in this order, and a tab lead for an extraction electrode previously welded to the current collector was packaged in an aluminum laminate film so as to be located outside the laminate. In this example, the substrate 14 of the electrode composite 17 was peeled off, and the positive electrode current collector and the positive electrode surface of the electrode composite 17 were laminated so as to contact each other. If the substrate 14 is not peeled off, the positive electrode current collector and the substrate 14 can also be laminated so as to contact each other. Thereafter, the laminate was formed into a laminate cell shape using a vacuum packaging machine (manufactured by TOSPACK), and pressurized (196 MPa) for 1 minute using an isostatic pressure device (manufactured by Nikkiso) to produce an all-solid-state secondary battery including the electrode composite, the negative electrode, and the current collector.

[0177] <Evaluation Method of All-Solid-State Secondary Battery> The output characteristics and short-circuit evaluation of the all-solid-state secondary battery were performed and judged according to the following criteria. Details are explained below.

[0178] (Evaluation of Output Characteristics of All-Solid-State Secondary Battery) The mass M (g / cm) of the active material particles per unit area of ​​the substrate 11b on which the particle layer is formed ２ ) to calculate the total mass of the positive electrode active material particles (M × number of layers × positive electrode area cm ２) was calculated. The active material particle mass M per unit area was determined as follows. The weight of the first substrate 11a was measured after the first particles P1 were filled by the first filling device 24a in the particle arrangement device 1. Next, the weight of the first substrate 11a was measured after the above-mentioned first particles P1 were transferred to the second substrate 11b. The difference was calculated to determine the mass of the first particles P1 on the second substrate 11b. Then, the active material particle mass M per unit area was calculated by dividing the mass of the first particles P1 by the area of ​​the second substrate 11b (the area of ​​the uneven region).

[0179] Another calculation method is to use ICP emission spectroscopy. The active material particle mass per unit area M (g / cm) is calculated in advance by the above-mentioned method or the like. ２ Three levels of substrates 11b on which particle layers with clearly defined Co atoms are formed are prepared. These substrates are dissolved by microwave acid decomposition (ETHOS PRO), and the acid decomposition solution is diluted with ultrapure water. Then, ICP-AES measurement (CIROS CCD) is performed to quantify the Co element. The active material particle mass per unit area M (g / cm) relative to the obtained element concentration is calculated. ２ From the calibration curve, the active material particle mass M (g / cm) per unit area of ​​the resin substrate on which the particle layer to be measured is formed can be calculated. ２ ) can be obtained.

[0180] In the present disclosure, the current values ​​at current rates of 0.1 C, 0.2 C, 0.3 C, ... 0.8 C were determined from the total mass of the positive electrode active material particles, and charge / discharge measurements (constant current charge / constant current discharge) were performed in ascending order of current rate. The charge / discharge measurements were performed at room temperature using a charge / discharge device (manufactured by Biologic). Figure 21 shows an example of a measured charge / discharge curve. The vertical axis represents the battery cell voltage (V vs. Li / Li ＋ The horizontal axis represents the capacity (mAh / g) of the battery cell. The capacity of the battery cell is the capacity per mass of the positive electrode active material particles.

[0181] The actual capacity of the lithium cobalt oxide was 120 mAh / g, and the cutoff voltage (vs. Li) was 4.2 V (charge) / 2.6 V (discharge). The capacity retention rate was calculated when charge / discharge measurements were performed under the above conditions. The capacity retention rate is the ratio of the discharge capacity to the charge capacity (discharge capacity / charge capacity × 100 (%)). Charge / discharge measurements (three cycles) were performed starting from a low current rate (0.1 C). If the charge capacity was 120 mAh / g (during the charge time, the cutoff voltage was not exceeded) and the capacity retention rate (average value of three cycles) was 80% or higher, the next current rate was set and the charge / discharge measurements were repeated. If the charge capacity and capacity retention rate did not meet the above criteria, the charge / discharge measurements were terminated, and the maximum current rate that met the criteria was used as the battery output of the prototype battery and evaluated according to the following criteria. The evaluation results are shown in Table 1. A: Battery output is 0.5C or more B: Battery output is 0.3C or more and 0.4C or less C: Battery output is 0.2C or less

[0182] (Battery Short-Circuit Evaluation) Ten batteries with the same specifications were fabricated using the above-described all-solid-state secondary battery fabrication method. The actual capacity of the lithium cobalt oxide was 120 mAh / g, and charge / discharge measurements and resistance measurements were performed under the conditions of a cutoff voltage (vs. Li) of 4.2 V (charge) / 2.6 V (discharge). Cases where three or more batteries were short-circuited and charge / discharge measurements were impossible were evaluated as C, cases where one or more (two or less) batteries were short-circuited were evaluated as B, and cases where charge / discharge measurements were possible without short-circuiting in all batteries were evaluated as A. The evaluation results are shown in Table 1.

[0183] <Method for evaluating particle morphology and particle uneven distribution> After evaluation of the all-solid-state secondary battery, the particle morphology and particle uneven distribution of the positive electrode active material in the positive electrode were evaluated and judged according to the following criteria. Details are explained below.

[0184] After the evaluation, the all-solid-state secondary battery was disassembled, and the electrode composite 17 was removed. It is desirable to peel off the substrate, current collector, and negative electrode to leave only the laminate, in order to facilitate the cross-section processing described below. However, if peeling is not possible, the laminate including the non-peeled members may be subjected to the processing and evaluation described below. In the present disclosure, the all-solid-state secondary battery was disassembled after the evaluation, and the electrode composite 17 was removed with the indium foil still attached.

[0185] <Evaluation of particle morphology and uneven distribution> The method for evaluating particle morphology and uneven distribution will be described. The particle morphology and uneven distribution were evaluated by observing the cross section of the laminate using an SEM. The cross section of the electrode composite 17 was observed by processing the cross section with a broad ion beam (BIB) using Ar, and using a two-dimensional image of the cross section obtained with a scanning electron microscope (SEM). Hereinafter, the above-mentioned method for observing two-dimensional images will be referred to as BIB-SEM.

[0186] <BIB-SEM Imaging Method> Cross-sectional images of the electrode composite 17 were taken using a BIB-SEM. The BIB-SEM imaging conditions are described below. The electrode composite 17 removed from the all-solid-state secondary battery after evaluation described above was cut with a wire saw (DWS3400 / wire diameter 170 μm, diamond diameter 30 μm) to obtain a cut surface along the stacking direction. The cut surface was subjected to cross-sectional processing using a broad ion beam of Ar (SM-09010 Cross Section Polisher manufactured by JEOL). The cross-sectional processing conditions were a voltage of 6 kV and a current of 150 to 200 mA. A cross section in the stacking direction of the laminate was obtained as a BIB-SEM image, and cross-sectional observation was performed.

[0187] In this disclosure, cross-sectional images were taken using a BIB-SEM, but instead of a broad ion beam (BIB), a fine ion beam (FIB) with varying ion particle intensity and beam diameter can also be used. The cross-sectional area was photographed using an electron microscope (ULTRA55) under the following conditions: Observation conditions: Acceleration voltage 2 kV, Magnification: 20,000 times.

[0188] Next, elemental and compositional analysis of each particle of the laminate was performed using SEM-EDX (XFlash Detector 630M manufactured by Bruker Corporation), and the positive electrode active material particles were identified. A method for identifying positive electrode active material particles will be described. The laminate was analyzed using X-ray diffraction (XRD) or the like, and the materials constituting the electrode were identified. Thereafter, the specific elements contained in the positive electrode active material particles and the solid electrolyte particles were detected and identified using SEM-EDX using the method described above. In the present disclosure, Co was detected as the specific element contained in the positive electrode active material particles, and Yb was detected as the specific element contained in the solid electrolyte particles, and identified.

[0189] The materials constituting the laminate can be identified by electron energy loss spectroscopy (EELS) in a TEM, in addition to the X-ray diffraction described above. Furthermore, Raman spectroscopy and TOF-SIMS can also be used. The materials constituting the laminate may also be identified by a combination of the above analytical methods.

[0190] The morphology of the particles identified as positive electrode active material particles was evaluated using BIB-SEM images. Among the particles identified as positive electrode active material particles, particles P12, which had a minor axis of 130 nm or less and an aspect ratio (major axis / minor axis) of the minor axis to the major axis of 2:1 or more, and particles P11, which had a minor axis of more than 130 nm and an aspect ratio (major axis / minor axis) of the minor axis to the major axis of 2:1 or less, were determined using the following determination method. Particles P12 are particles exhibiting a higher average aspect ratio than particles P11. That is, particles P12 are second active material particles in the present disclosure, and particles P11 are first active material particles in the present disclosure.

[0191] When particles P12 and particles P11 coexisted within the laminate, the particle morphology was judged as ◯. When only particles P12 or particles P11 were present within the laminate, the particle morphology was judged as ×. Note that when the observed positive electrode active material particles contained active material particles having protrusions on the particle surface of the same morphology as particles P12, the particle morphology was judged as △. The results are shown in Table 1.

[0192] Furthermore, when the center of gravity of particle P12 was located farther from the electrolyte layer than the center of gravity of particle P11, in other words, closer to the current collector, the particle distribution was determined to be ◯ by the following determination method. The results are shown in Table 1.

[0193] Comparative Example 1 A secondary battery was fabricated by the same manufacturing method as in Example, except that the fifth step (S105 in FIG. 1A) was omitted in the manufacturing method of the laminate.

[0194] (Comparative Example 2) The positive electrode layer and the solid electrolyte layer were formed separately. The positive electrode layer was formed by sintering a positive electrode precursor produced under the same conditions as in the Example in a muffle furnace (600°C, sintering time 1 hour, in an air atmosphere). The solid electrolyte layer was formed by filling only solid electrolyte particles into a die using the same method as in the Example laminate production method, followed by spark plasma sintering and re-sintering. The positive electrode layer and the solid electrolyte layer were laminated, and a secondary battery was produced using the same production method as in the Example.

[0195] Comparative Example 3 A secondary battery was manufactured using the same manufacturing method as in Example 1, except that in the manufacturing method for the laminate, the material of the die and punch used in the second step was changed from graphite to cemented carbide, and the sintering step was changed from spark plasma sintering to sintering by hot pressing (manufactured by Sansho Industry Co., Ltd.) The sintering temperature of the hot pressing in the sintering step was 600°C, the sintering time was 1 hour, and the pressure was 30 MPa. No pressure was applied until the temperature rose from room temperature to 550°C, and the application of pressure began after the temperature reached 550°C.

[0196] For Comparative Examples 1 to 3, the particle morphology and uneven distribution, as well as the output power and occurrence of short circuits in the secondary battery were evaluated using the same methods as in Example 1. The results are shown in Table 1. For "particle morphology," a rating of ◯ was given when particles P12 and particles P11 coexisted within the laminate, an X was given when only particles P12 or particles P11 were present, and a △ was given when the observed positive electrode active material particles contained active material particles having protrusions on their particle surfaces of the same morphology as particles P12. For "particle uneven distribution," the positions of the centers of gravity of particles P12 and P11 were determined by the method described below, and a rating of ◯ was given when the position of the center of gravity of particle P12 was located farther from the electrolyte layer, in other words, near the current collector, and an X was given when the above conditions were not met.

[0197] The particle morphology and the method for determining uneven particle distribution will be described below. As an example, a detailed description will be given using FIG. 22 (400 × 600 pixels), which is an enlarged image of FIG. 19A (a cross-sectional SEM image of electrode composite 17 of the example). The position of the center of gravity of particle P12 being located farther from the electrolyte layer than the position of the center of gravity of particle P11 means that the position of the center of gravity of particle P12 is closer to the current collector. In other words, in FIG. 22, the position of the center of gravity of particle P12 is located above the position of the center of gravity of particle P11.

[0198] The particle morphology and uneven distribution in the positive electrode active material layer were determined using the following procedure: (1) Identify the region where the positive electrode active material particles exist. (2) Evaluate the morphology of the positive electrode active material particles in the region and determine whether they are particle P11 or particle P12. (3) Measure the center of gravity of particle P11 and the center of gravity of particle P12 and compare the center of gravity positions. In the following determination method, openCV was used for image processing, and analysis was performed using Python. Other analysis methods may be used as long as they can perform similar analysis.

[0199] (1) Identification of Regions Where Positive Electrode Active Material Particles Exist The regions where positive electrode active material particles exist were identified by performing elemental and compositional analysis of each particle in the cross section of the laminate using SEM-EDX (XFlash Detector 630M manufactured by Bruker Corporation), and the positions where elements specific to the active material particles existed were identified as the regions where positive electrode active material particles existed (positive electrode active material layers).

[0200] In the examples, the positive electrode active material particles are LiCoO ２ Since the SEM-EDX image was used, Co was detected by SEM-EDX to identify the active material particles. Specifically, the EDX image of Co atoms shown in FIG. 23A was binarized using a brightness threshold of 55, and dilation processing was performed with a kernel size of 3 × 3. The image after dilation processing is shown in FIG. 23B. In the image after dilation processing, the white areas are areas where Co is present, and these areas were identified as areas where positive electrode active material particles are present.

[0201] (2) Morphology Evaluation of Positive Electrode Active Material Particles The morphology of the positive electrode active material particles in the region was evaluated to determine whether they were particles P11 or P12. The determination of whether the particles were P11 or P12 was performed by detecting the particles in the region identified by the method in (1) through boundary detection and determining their shapes.

[0202] The cross-sectional SEM image of electrode composite 17 was converted to a grayscale and normalized to an overall average brightness of 150 and a standard deviation of ±30. An image with enhanced edges was obtained using a sharpening filter ("-3 / 7, -3 / 7, -3 / 7", "-3 / 7, 1+6×3 / 7, 3 / 7", "-3 / 7, -3 / 7, -3 / 7"), and then binarized using a brightness threshold of 170. From the obtained image, only the region where active material particles were present was cut out using the region identified in (1) above as a mask.

[0203] To remove noise, the cut-out image was subjected to opening processing with a kernel size of 2 × 2. Next, in order to perform the Watershed method for determining boundaries, parts that were definitely background, parts that were definitely foreground (here, active material particles), and parts that could not be determined were determined using the following method.

[0204] The image that underwent the above opening process was subjected to an expansion process of the white areas, and the black areas were determined to be definitely the background. Next, the distance between the foreground and background was calculated, and areas that were 10% or more away from the background were determined to be definitely the foreground. In addition, the boundary region between the foreground and background was defined, and each particle was detected by applying the Watershed method. An example of an image in which each particle was detected is shown in Figure 23C.

[0205] The outline of each detected particle was approximated by the smallest rectangle that surrounded it, and the minor axis and major axis of each particle were determined. Particles with a minor axis greater than 130 nm (7 pixels) or an aspect ratio of the minor axis to the major axis less than 2 were designated P11 (first active material particles). Particles with a minor axis less than 130 nm (7 pixels) and an aspect ratio of the minor axis to the major axis greater than 2 were designated P12 (second active material particles).

[0206] The aspect ratio of the minor axis to the major axis was calculated for all detected particles, and the average aspect ratios of the particles determined to be P11 and the average aspect ratios of the particles determined to be P12 were calculated, respectively, to obtain the average aspect ratio. For example, 39 particles P11 and 324 particles P12 were detected in Figure 23C. It was also confirmed that the average aspect ratio of the detected particles P12 was higher than the average aspect ratio of the detected particles P11.

[0207] Furthermore, among the particles determined to be active material particles by the above determination method, when active material particles having protrusions on the outermost surface were included, the particle morphology was determined to be "△". For active material particles having protrusions on the outermost surface, the length and aspect ratio of the protrusions were analyzed from the number of image pixels. In Comparative Example 2, analysis of 100 protrusions on three active material particles revealed an average length of 400 nm and an aspect ratio of 40. Similarly, analysis of 100 protrusions on three active material particles in Comparative Example 3 revealed an average length of 250 nm and an aspect ratio of 25.

[0208] (3) Comparison of Particle Centroid Positions The particle centroid positions were calculated by assuming that all particles had the same density and calculating the average of the coordinate positions of all pixels for each particle determined by the above-mentioned method. In the image in which each particle was detected by the above-mentioned method (2), the end of the region where the positive electrode active material particles existed, which was in contact with the current collector, was set to 0, and the direction toward the side in contact with the electrolyte layer was set to the Y-axis direction. The sum of the coordinates in the Y-axis direction of all pixels of a particle determined to be particle P11 was divided by the total number of pixels occupied by the particle determined to be particle P11 to calculate the centroid position of particle P11. The centroid position of particle P12 was also calculated in the same manner as particle P11.

[0209] 23C , where the thickness of the positive electrode active material layer AAML is 310 pixels, with the reference point (Y=351) on the first surface PP side and the reference point (Y=41) on the second surface SP side, the position of the center of gravity of particle P11 is Y=251, and the relative distance from the first surface PP is (351-225) / (351-41)=126 / 310, and the position of the center of gravity of particle P12 is Y=165, and the relative distance from the first surface PP is (351-165) / (351-41)=186 / 310. That is, the position of the center of gravity BP(P2) of the plurality of second active material particles P2 was located farther from the first surface PP than the position of the center of gravity BP(P1) of the plurality of first active material particles P1. In other words, the second active material particles P2 are unevenly distributed on the second surface SP side, and the first active material particles P1 are unevenly distributed on the first surface PP side.

[0210] In addition, the following analysis was also performed to confirm the region where each particle was distributed. Among the pixels determined to be regions where active material particles exist in FIG. 23C , the region from the upper limit to the lower limit of the coordinate in the Y-axis direction was defined as the distribution region in the active material layer thickness direction, and the location of each particle was determined. The particle distribution was determined by calculating the center of gravity of each particle, and the center of gravity position was determined as the particle position. The positions of the second active material particles were determined using the above-described method, and the degree of uneven distribution was confirmed. When 60% or more by number of all the observed second active material particles were contained in one-third of the region on the second surface side of the positive electrode active material layer, it was determined that the second active material particles were unevenly distributed on the second surface side.

[0211] In Figure 23C, of ​​the particles P12 (324 particles) detected by the above-mentioned method, the number of particles P12 present in the upper one-third of the image where the active material is present was 210. That is, 65% by number of the particles P12 were unevenly distributed in the upper one-third. In Figure 23C, the upper side of the image is the second surface that contacts the current collector. That is, in Figure 23C, 65% by number of the second active material particles were unevenly distributed on the second surface side.

[0212] Furthermore, based on the particle positions determined above, the degree of dispersion of the first and second active material particles was confirmed. The degree of dispersion of each active material particle was compared between a one-third region including the first surface side of the positive electrode active material layer and a one-third region including the second surface side based on histograms of the distance distribution between the centers of gravity of each particle.

[0213] Furthermore, in FIG. 23C , of the particles P11 (39 particles) detected by the above-described method, 24 particles P11 were located in the lower one-third of the region where the active material was present. That is, 62% by number of the particles P11 were unevenly distributed in the lower one-third. In FIG. 23C , the lower side of the image is the first surface that contacts the electrolyte layer. That is, in FIG. 23C , 62% by number of the first active material particles were unevenly distributed on the first surface side.

[0214] Furthermore, in Figure 23C, the average area per particle of particles P12 detected by the above-mentioned method was 43 pixels, and the average area per particle of particles P11 was 101 pixels. The volume per particle of the first active material particles was 43 x 43 / 7 = 264 cubic pixels, and the volume per particle of the second active material particles, since they are isotropic particles, was 101^(3 / 2) = 1015 cubic pixels. Since a sufficient observation area was secured in this example, it can be assumed that the particle area (number of pixels) on the SEM image and the actual particle volume are approximately proportional. It was found that the second active material particles P2 had a smaller volume per particle than the first active material particles P1.

[0215] The battery of this example contained positive electrode active material particles P12 (second active material particles) having a minor axis of 130 nm or less and an aspect ratio (major axis / minor axis) of 2 times or more, and other particles P11. Furthermore, particles P12 were unevenly distributed on the positive electrode current collector side (substrate side). These characteristics are thought to have improved battery output and suppressed battery short circuits.

[0216] The reason why the above-mentioned features improve battery output will be explained. It is generally known that increasing the contact area between the active material particles and the solid electrolyte particles in the electrode is important for improving battery output. The reason why the positive electrode active material particles have protrusions on their surfaces improves battery output (Patent Document 3) is thought to be because the surface area of ​​the active material particles increases, thereby increasing the contact area with the solid electrolyte particles. On the other hand, in this example, the protrusions formed on the surfaces of the positive electrode active material particles are further detached from the positive electrode active material particles. This is thought to further increase the surface area of ​​the positive electrode active material particles and improve battery output. It is preferable that at least a portion of the protrusions is detached from the surfaces of the positive electrode active material particles, and it is more preferable that all of the protrusions are detached.

[0217] Furthermore, positive electrode active material particles with relatively high electronic conductivity, such as lithium cobalt oxide used in the examples, can provide electronic conductivity without the aid of a conductive additive. The uneven distribution of small-diameter, large-aspect-ratio particles P12 (second active material particles) near the positive electrode current collector (substrate) is believed to improve electron transfer to the current collector. These effects are believed to improve the diffusibility of lithium ions and electrons within the positive electrode, thereby improving battery output.

[0218] On the other hand, particles P12 (second active material particles) with small particle diameters and large aspect ratios are prone to charge concentration and are likely to cause short circuits. In particular, when the positive electrode layer and solid electrolyte layer are molded together, if the solid electrolyte layer is thin (for example, 100 μm or less), the presence of particles P12 (second active material particles) on the electrolyte layer side is likely to cause short circuits. In this example, particles P12 (second active material particles), which could cause short circuits, are unevenly distributed on the positive electrode current collector (substrate) side, which is thought to make it less likely for battery short circuits to occur.

[0219] The present disclosure is not limited to the above-described embodiments, and various modifications and variations are possible without departing from the spirit and scope of the present invention. Therefore, the following claims are appended to clarify the scope of the present disclosure. This application claims priority based on Japanese Patent Application No. 2024-012253, filed January 30, 2024, the entire contents of which are incorporated herein by reference.

Claims

1. An electrode composite for use in a secondary battery, the electrode composite comprising a positive electrode active material layer and an electrolyte layer, the positive electrode active material layer having a first surface in contact with the electrolyte layer and a second surface located on the opposite side to the first surface, the electrode composite comprising a plurality of first active material particles and a plurality of second active material particles exhibiting a higher average aspect ratio than the plurality of first active material particles, the centers of gravity of the plurality of second active material particles being located farther from the first surface than the centers of gravity of the plurality of first active material particles.

2. The electrode composite according to claim 1, wherein the plurality of second active material particles are unevenly distributed on the second surface side.

3. The electrode composite according to claim 1 or 2, wherein the plurality of first active material particles are unevenly distributed on the side of the first surface.

4. The electrode composite according to any one of claims 1 to 3, wherein the first active material particles have a minor axis greater than 130 nm, and the second active material particles have a minor axis of 130 nm or less and an aspect ratio of the minor axis to the major axis of 2 or more.

5. The electrode composite according to any one of claims 1 to 4, wherein, in cross-sectional observation of the positive electrode active material layer by SEM, the center of gravity of the plurality of second active material particles is located farther from the first surface than the center of gravity of the plurality of first active material particles.

6. The electrode composite according to any one of claims 1 to 5, wherein the second surface includes a surface in contact with a current collector that exchanges electrons with the positive electrode active material layer.

7. The electrode composite of claim 6, further comprising a current collector in contact with said second surface.

8. The electrode composite according to any one of claims 1 to 7, wherein the first active material particles and the second active material particles include positive electrode active material particles containing Li, Co, and O.

9. The electrode composite according to any one of claims 1 to 8, wherein the first active material particles and the second active material particles contain at least one of lithium cobalt oxide and a compound in which some of the Li and Co in lithium cobalt oxide have been substituted with at least one element selected from the group consisting of Ni, Mn, Mg, Al, Fe, Si, C, and B.

10. The electrode composite according to any one of claims 1 to 9, wherein the first active material particles have an inner surface within the particle.

11. The electrode composite according to claim 10, wherein the inner surface constitutes the pores of the first active material particles.

12. The electrode composite according to any one of claims 1 to 11, wherein the second active material particles have a smaller volume per particle than the first active material particles.

13. The electrode composite according to any one of claims 1 to 12, wherein the first active material particles have protrusions on the particle surfaces.

14. An electrode composite according to any one of claims 1 to 13, wherein the second active material particles include flake-shaped bodies having a thickness smaller than the average particle size of the first active material particles and / or needle-shaped bodies having an axial diameter smaller than the average particle size of the first active material particles.

15. The electrode composite according to any one of claims 1 to 14, wherein the second active material particles are spaced apart from the first active material particles.

16. The electrode composite according to any one of claims 1 to 15, wherein the electrolyte layer and the first active material particles are in contact with each other via the first surface.

17. The electrode composite according to any one of claims 1 to 16, wherein the dispersion of the first active material particles is greater than the dispersion of the second active material particles in the thickness direction of the positive electrode active material layer.

18. An electrode composite according to any one of claims 1 to 17, wherein the first surface has a portion that overlaps with the plurality of first active material particles in the layer thickness direction.

19. The electrode composite according to any one of claims 1 to 18, further comprising a negative electrode active material layer in contact with the electrolyte layer.

20. A secondary battery comprising the electrode composite according to any one of claims 1 to 19, a negative electrode, and a current collector.

21. A secondary battery comprising the electrode composite according to claim 19, a first current collector in contact with the positive electrode active material layer, and a second current collector in contact with the negative electrode active material layer.

22. A method for manufacturing an electrode composite applicable to a secondary battery, comprising: a lamination step of laminating a first material layer containing active material particles and a second material layer containing solid electrolyte particles to form a laminate; a pressure and current application step of applying positive pressure and AC voltage in the lamination direction of the laminate to form a composite; and a sintering step of sintering the composite in an oxygen-containing atmosphere to form an electrode composite.

23. The method for producing an electrode composite according to claim 22, wherein the laminating step includes a step of surrounding the laminate with a dielectric.

24. The method for producing an electrode composite according to claim 22 or 23, wherein the pressurizing and current-passing step includes a step of heating the laminate.

25. A method for producing a secondary battery, comprising the steps of: producing an electrode composite by the production method according to any one of claims 22 to 24; and laminating the electrode composite, a negative electrode, and a current collector.

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