Method for producing ion conducting structure

Abstract

This method for producing an ion conducting structure comprises a slurry preparation step (S21), a structure forming step (S22-S24, S28, S29) and a firing step (S27). The slurry preparation step is for preparing a slurry in which dispersed in a solvent are composite particles 120 each including a core phase (121) that comprises an oxide-based ion conductor and a shell phase (122) that comprises an amorphous-substance-containing ion conductor including an amorphous phase in at least a part thereof. The structure forming step is for using the slurry to mold a structure. The firing step is for firing the structure to produce an ion conducting structure. The oxide-based ion conductor has higher ion conductivity than the amorphous-substance-containing ion conductor. The amorphous-substance-containing ion conductor has a lower Young's modulus than the oxide-based ion conductor.

Description

Method for producing ion-conductive structure CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Patent Application No. 2023-186670, filed on October 31, 2023, the contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a method for producing an ion-conducting structure.

[0003] Patent Document 1 discloses that an electrode layer having an ordered porous structure is formed on a substrate made of a solid electrolyte layer.

[0004] Special Publication No. 2021-514101

[0005] When forming a structure using a slurry in which raw material particles are dispersed in a solvent, the raw material particles are coated with an organic substance to prevent them from reacting with the solvent. The organically coated raw material particles have an increased specific surface area and a reduced solid content in the slurry. As a result, when the slurry is sintered into a structure, the structure does not shrink completely, resulting in a lower density after sintering.

[0006] In view of the above, an object of the present disclosure is to improve the density of an ion conductive structure after sintering in a method for producing an ion conductive structure using a slurry containing raw material particles.

[0007] To achieve the above object, one aspect of the present disclosure includes a slurry preparation step, a structure forming step, and a firing step.

[0008] In the slurry preparation step, a slurry is prepared by dispersing composite particles including a core phase made of an oxide-based ion conductor and a shell phase made of an amorphous-containing ion conductor at least partially containing an amorphous phase in a solvent. In the structure forming step, a structure is formed using the slurry. In the firing step, the structure is fired to produce an ion-conductive structure. The oxide-based ion conductor has higher ionic conductivity than the amorphous-containing ion conductor. The amorphous-containing ion conductor has a smaller Young's modulus than the oxide-based ion conductor.

[0009] The amorphous-containing ionic conductor of the shell phase has a low melting point, a low Young's modulus, and is an amorphous material, which can improve the coverage of the core phase with the shell phase, thereby suppressing the reaction of the oxide-based ionic conductor of the composite particles with the solvent in the slurry.

[0010] Furthermore, the amorphous-containing ionic conductor contained in the shell phase can promote interparticle bonding during sintering, thereby increasing the density of the sintered structure and forming a dense structure.

[0011] 1 is a cross-sectional view showing the configuration of a secondary battery according to a first embodiment; FIG. 2 is a perspective view showing a specific example of an anode structure; FIG. 3 is a perspective view showing a specific example of an anode structure; FIG. 4 is a perspective view showing a specific example of an anode structure; FIG. 5 is a view showing an anode side particle; FIG. 6 is a view showing a specific example of a cathode active material and a coating layer; FIG. 7 is a view showing a specific example of a cathode active material and a coating layer; FIG. 8 is a view showing a specific example of a solid electrolyte composite; FIG. 9 is a view showing a crystal structure of a pyrochlore oxide; FIG. 10 is a view showing a manufacturing process of a pyrochlore oxide; FIG. 11 is an SEM image of a pyrochlore oxide and amorphous-containing LiF; FIG. 12 is an SEM image of a cathode active material and a coating layer; FIG. 13 is a flowchart showing a manufacturing method of an anode structure using a stereolithography 3D printer; FIG. 14 is a flowchart showing a manufacturing method of an anode structure using an extrusion 3D printer; FIG. 15 is an SEM image of an anode structure; FIG. 16 is a table showing examples and comparative examples of anode structures; FIG. 17 is a table showing examples and comparative examples of cathode active materials; FIG. 18 is a view showing an anode structure according to a second embodiment; FIG. 19 is a view showing an anode structure according to a third embodiment; FIG. 19 is a view showing an anode structure according to a fourth embodiment; FIG. 19 is a cross-sectional view showing the configuration of a secondary battery according to a fifth embodiment. FIG. 13 is a diagram showing a specific example of a solid electrolyte composite provided in a positive electrode of a fifth embodiment.

[0012] Hereinafter, several embodiments for carrying out the present disclosure will be described with reference to the drawings. In each embodiment, parts corresponding to matters described in the preceding embodiment will be assigned the same reference numerals, and duplicated explanations may be omitted. In each embodiment, when only a part of the configuration is described, other previously described embodiments may be applied to the other parts of the configuration. In addition to combinations of parts that are specifically specified as being combinable in each embodiment, it is also possible to partially combine embodiments even if not specified, as long as there is no particular problem with the combination.

[0013] First Embodiment Hereinafter, an embodiment in which the pyrochlore oxide of the present disclosure is applied to a solid electrolyte for a secondary battery will be described with reference to the drawings. A secondary battery 10 of this embodiment is a lithium ion battery in which lithium ions are conducted as conduction ions.

[0014] The secondary battery 10 of this embodiment is an all-solid-state battery that uses a solid electrolyte for the solid electrolyte layer 15, and is an anode-free battery in which, in the initial state, no negative electrode active material is provided in the negative electrode layer 12. The secondary battery 10 of this embodiment is a battery cell, and is used as a stack in which a plurality of secondary batteries 10 are connected together as needed.

[0015] As shown in Fig. 1, a secondary battery 10 includes, as its components, an anode current collector 11, an anode layer 12, a cathode current collector 13, a cathode layer 14, and a solid electrolyte layer 15. These components 11 to 15 are stacked in the cell thickness direction. In Fig. 1, the left-right direction is the cell thickness direction.

[0016] The solid electrolyte layer 15 is sandwiched between a pair of electrode layers 12, 14. The solid electrolyte layer 15 and the pair of electrode layers 12, 14 constitute an electrode structure 16. One of the pair of electrode layers 12, 14 is an anode layer 12, and the other is a cathode layer 14. The anode layer 12 is provided on one surface of the solid electrolyte layer 15, and the cathode layer 14 is provided on the other surface of the solid electrolyte layer 15.

[0017] The anode layer 12 and the solid electrolyte layer 15 are in contact with each other, and the cathode layer 14 and the solid electrolyte layer 15 are in contact with each other. The anode layer 12 and the cathode layer 14 are connected via the solid electrolyte layer 15. The secondary battery 10 is charged and discharged by the conduction of lithium ions between the anode layer 12 and the cathode layer 14 via the solid electrolyte layer 15.

[0018] A laminate including the anode layer 12, the cathode layer 14, and the solid electrolyte layer 15 is provided between the anode current collector 11 and the cathode current collector 13. The anode current collector 11 and the anode layer 12 are in contact. The cathode current collector 13 and the cathode layer 14 are in contact. The anode current collector 11 and the cathode current collector 13 are connected via the laminate.

[0019] Any material that can be used as a current collector for a lithium ion battery can be used for the negative electrode current collector 11 and the positive electrode current collector 13. In this embodiment, Cu is used as the negative electrode current collector 11, and Al is used as the positive electrode current collector 13.

[0020] The negative electrode layer 12 is a structure that constitutes the negative electrode, and receives lithium ions when the secondary battery 10 is charged and releases lithium ions when the secondary battery 10 is discharged. The negative electrode layer 12 is an ion-conductive structure that has ion conductivity.

[0021] The negative electrode layer 12 is configured as a porous body having numerous pores, and can be referred to as a porous layer. The secondary battery 10 of this embodiment is an anode-free battery, and in its initial state, no negative electrode active material is present in the negative electrode layer 12. The initial state refers to a state in which the components of the secondary battery 10 are assembled and the secondary battery 10 is not being charged. When the secondary battery 10 is charged, elements constituting conductive ions are precipitated in the negative electrode layer 12. Specifically, when the secondary battery 10 is charged, lithium ions released from the positive electrode active material are conducted from the positive electrode layer 14 to the negative electrode layer 12, and lithium metal is precipitated in the pores of the negative electrode layer 12. The lithium metal precipitated in the pores of the negative electrode layer 12 functions as the negative electrode active material. When the secondary battery 10 is charged and discharged, a precipitation / dissolution reaction of lithium metal as the negative electrode active material occurs in the pores of the negative electrode layer 12, accepting or releasing lithium ions.

[0022] The negative electrode layer 12 has a three-dimensional structure. The negative electrode layer 12 can have a regular porous structure in which pores are regularly formed, or an irregular porous structure in which pores are irregularly formed. Regular porous structures include structures in which a large number of pores of the same shape are formed and the pore diameter is uniform, and structures in which pores of different shapes and pore diameters are regularly arranged and the pore distribution is regular. Irregular porous structures include structures in which a large number of pores of different shapes are formed and the pore diameter is nonuniform, and structures in which the pore diameter is uniform but the pores are randomly arranged and the pore distribution is irregular.

[0023] In the ordered porous structure, the deposition / dissolution reaction of lithium metal occurs uniformly. Therefore, the ordered porous structure of the negative electrode layer 12 can minimize localized deposition of lithium metal, thereby reducing the possibility of short circuiting.

[0024] Forms A1 to A4 in Figures 2 and 3 show specific examples of the anode layer 12 having an ordered pore structure. Form A5 in Figure 4 shows a specific example of the anode layer 12 having an irregular pore structure. In Figures 2 to 4, the vertical direction in the figures corresponds to the cell thickness direction. Although not shown in Figures 2 to 4, a cathode current collector 11 is provided above the anode layer 12.

[0025] The regular porous structures of Forms A1 to A4 and the irregular porous structure of Form A5 can be manufactured using, for example, a 3D printer. The regular porous structures of Forms A1 to A4 are obtained by regularly molding a structure having a predetermined shape, resulting in a structure with regularly formed pores. The irregular porous structure of Form A5 is obtained by molding using a raw material containing a pore-forming agent, for example, and then removing the pore-forming agent by sintering, resulting in a structure with irregularly formed pores.

[0026] Here, the features of each of the ordered porous structures of Forms A1 to A4 will be described. Note that the ordered porous structure of the negative electrode layer 12 can adopt various forms and is not limited to Forms A1 to A4.

[0027] The anode layer 12 of form A1 has multiple columnar structures arranged in parallel. The anode layer 12 of form A1 is formed parallel to the cell thickness direction. The anode layer 12 of form A1 is formed linearly to connect the solid electrolyte layer 15 and the anode current collector 11, and the multiple columnar structures form an ion conduction path. Lithium ions are conducted inside the secondary battery 10 in the cell thickness direction. Therefore, the anode layer 12 of form A1 can improve ion conductivity. Furthermore, the anode layer 12 of form A1 can reduce the degree of curvature of the multiple columnar structures, thereby reducing ion conduction loss caused by the columnar structures bending and making the ion conduction path complex. As a result, ion conductivity can be improved, and the input / output performance of the secondary battery 10 can be improved.

[0028] The negative electrode layer 12 of form A2 has a three-dimensional lattice structure in which a plurality of columnar structures intersect to form a three-dimensional lattice structure. The negative electrode layer 12 of form A2 has structures formed not only in the direction parallel to the cell thickness direction but also in the direction perpendicular to the cell thickness direction, and can have improved strength compared to the negative electrode layer 12 of form A1.

[0029] The negative electrode layer 12 of form A3 has a parallel cross structure, in which multiple layers each consisting of multiple parallel-arranged columnar structures are stacked in the cell thickness direction. In adjacent layers of columnar structures, the multiple columnar structures are arranged orthogonally. The negative electrode layer 12 of form A3 has structures formed not only in the direction parallel to the cell thickness direction but also in the direction perpendicular to the cell thickness direction, thereby improving strength compared to the negative electrode layer 12 of form A1. Furthermore, the negative electrode layer 12 of form A3 can be formed by sequentially stacking layers each consisting of multiple parallel-arranged columnar structures, improving formability compared to the negative electrode layer 12 of form A2.

[0030] The negative electrode layer 12 of the configuration A4 has a planar lattice structure, in which a plurality of columnar structures intersect to form a two-dimensional lattice structure. The negative electrode layer 12 of the configuration A4 can also have improved strength compared to the negative electrode layer 12 of the configuration A1.

[0031] The negative electrode layer 12 preferably has a pore diameter in the range of 0.1 to 50 μm. The negative electrode layer 12 also preferably has a shaped width of the structure forming the pores in the range of 1 to 100 μm. The shaped width of the negative electrode layer 12 is the distance between adjacent pores.

[0032] 5, the negative electrode layer 12 mainly comprises a sintered body formed by sintering ion-conductive negative electrode composite particles 120. The negative electrode layer 12 may contain a conductive additive and a binder. The negative electrode layer 12 may further contain an electrolyte solution and a polymer.

[0033] The negative electrode composite particle 120 is a composite particle composed of a core phase 121 and a shell phase 122. The core phase 121 is formed in a particulate shape, and the shell phase 122 is formed so as to cover at least a portion of the core phase 121. The shell phase 122 may cover the entire surface of the core phase 121, or may cover only a portion of the core phase 121. The core phase 121 is an oxide-based ion conductor, and the shell phase 122 is an amorphous-containing ion conductor that contains an amorphous phase in at least a portion thereof.

[0034] The negative electrode layer 12 is produced by sintering a slurry in which negative electrode composite particles 120 are dispersed in a solvent. The oxide-based ion conductor of the core phase 121 reacts with the solvent in the slurry, and lithium ions, which are conductive ions, tend to elute from the oxide-based ion conductor.

[0035] The shell phase 122 of the negative electrode composite particle 120 is provided to suppress a reaction between the oxide-based ion conductor of the core phase 121 and the solvent in the slurry, thereby suppressing the elution of lithium ions from the oxide-based ion conductor. In order to suppress a reaction between the core phase 121 and the solvent in the slurry, it is desirable that the coverage of the core phase 121 with the shell phase 122 is high.

[0036] When an oxide-based ion conductor is organically coated, the specific surface area increases, the solid content in the slurry decreases, and the density of the sintered structure decreases. In contrast, the shell phase 122 of this embodiment promotes interparticle bonding during sintering, thereby increasing the density after sintering.

[0037] If the solid content in the slurry is too low, the density of the sintered negative electrode layer 12 will be low. On the other hand, if the solid content in the slurry is too high, there is a risk that the negative electrode composite particles 120 will not be slurried even when mixed with a solvent and stirred. Therefore, in order to reliably slurried the negative electrode composite particles 120 and increase the density of the sintered negative electrode layer 12, it is desirable to set the solid content in the slurry within the range of 30 to 60 vol %.

[0038] Furthermore, when the negative electrode layer 12 is manufactured using a stereolithography 3D printer that irradiates a slurry with a laser, it is desirable to include in the slurry a light absorbing material that has a lower light transmittance than the negative electrode composite particles 120. The light absorbing material is a material that has a higher absorbance than the negative electrode composite particles 120. For example, a conductive additive made of a carbon material can be used as the light absorbing material. By using a constituent material of the negative electrode layer 12, such as a conductive additive, as the light absorbing material, the constituent material of the negative electrode layer 12 can also function as a light absorbing material, eliminating the need to provide a separate light absorbing material.

[0039] The light-absorbing material in the slurry prevents scattering of the laser light when the slurry is irradiated with a laser by a 3D printer. This allows the stereolithography 3D printer to achieve the desired modeling width and perform modeling with high precision.

[0040] The constituent material of the core phase 121 and the constituent material of the shell phase 122 are ion-conductive substances with different chemical compositions. The constituent material of the core phase 121 has a higher ion conductivity than the constituent material of the shell phase 122. For this reason, in this embodiment, in order to increase the ion conductivity of the anode composite particle 120, the volume ratio of the core phase 121 in the anode composite particle 120 is set to be equal to or greater than the volume ratio of the shell phase 122.

[0041] The core phase 121 is an oxide-based ion conductor and an oxide-based solid electrolyte. For example, a pyrochlore-type oxide, a garnet-type oxide, or the like can be used as the core phase 121. For example, an example of a pyrochlore-type oxide is Li １．２５ La ０．５８ Nb ２ O ６ F (LLNOF), Li １．２５La ０．５８ Ta ２ O ６ As the garnet-type oxide, for example, Li ７ La ３ Zr ２ O １２ LLNOF and LLTOF have higher ionic conductivity, lower melting points, and lower Young's moduli than LLZ. Furthermore, LLNOF and LLTOF contain less lithium in their structures than LLZ, and therefore are less likely to react with the solvent in the slurry.

[0042] The constituent material of the shell phase 122 contains at least Li and F, for example, LiF, LiNb ６ O １５ An example of the shell phase 122 is LiF. In this embodiment, LiF is used as the shell phase 122.

[0043] The constituent material of the shell phase 122 has a lower melting point than the constituent material of the core phase 121. Therefore, by heating at a temperature equal to or higher than the melting point of the constituent material of the shell phase 122 and lower than the melting point of the constituent material of the core phase 121 during production of the negative electrode composite particles 120, the shell phase 122 melts, and the coverage of the core phase 121 by the shell phase 122 can be improved.

[0044] The constituent material of the shell phase 122 has a lower Young's modulus than the constituent material of the core phase 121. For example, Li １．２５ La ０．５８ Nb ２ O ６ The Young's modulus of F is about 100 GPa, and the Young's modulus of LiF in the crystalline phase is about 50 to 70 GPa. By using a material with a low Young's modulus for the shell phase 122, the contact area between the shell phase 122 and the core phase 121 can be increased, and the coverage of the core phase 121 by the shell phase 122 can be improved.

[0045] The material of the shell phase 122 is an amorphous-containing ion conductor that contains at least a portion of an amorphous phase. The material of the shell phase 122 may be entirely amorphous, or may contain a mixture of amorphous and crystalline phases. When the material of the shell phase 122 contains an amorphous phase and a crystalline phase, it is desirable that the volume ratio of the amorphous phase be equal to or greater than the volume ratio of the crystalline phase.

[0046] The amorphous phase has a lower Young's modulus than the crystalline phase. Therefore, a high volume ratio of the amorphous phase in the shell phase 122 can increase the contact area between the shell phase 122 and the core phase 121, thereby improving the coverage of the core phase 121 with the shell phase 122.

[0047] Furthermore, the amorphous phase has an irregular particle shape rather than a specific shape, which also increases the contact area between the shell phase 122 and the core phase 121, thereby increasing the coverage of the core phase 121 with the shell phase 122.

[0048] The positive electrode layer 14 releases lithium ions when the secondary battery 10 is charged and receives lithium ions when the secondary battery 10 is discharged. The positive electrode layer 14 includes positive electrode composite particles 140. The positive electrode layer 14 may include a conductive additive and a binder. The positive electrode layer 14 may include, in addition to the positive electrode composite particles 140, an electrolyte solution and a polymer.

[0049] 6 and 7 show specific examples of the positive electrode composite particle 140. Fig. 6 shows an embodiment in which the coating layer 142 has a first phase 142a and a second phase 142b, and Fig. 7 shows an embodiment in which the coating layer 142 has a first phase 142a, a second phase 142b, and a third phase 142c.

[0050] 6 and 7 , the positive electrode composite particle 140 is a ceramic composite particle containing a positive electrode active material 141 and a coating layer 142 that coats the positive electrode active material 141. The positive electrode active material 141 is a ceramic particle that undergoes an oxidation-reduction reaction, and releases or accepts lithium ions, which are conductive ions, through the oxidation-reduction reaction. The coating layer 142 has two or more phases.

[0051] As the positive electrode active material 141, for example, a layered rock salt type active material, an olivine type active material, a spinel type active material, or an acid halide type active material can be used. As the layered rock salt type active material, for example, LiNi ｘ Mn ｙ Co ｚ O ２ (NMC), LiNi ｘ Co ｙ Al ｚ O ２ (NCA) can be used. As an olivine-type active material, for example, LiFePO ４ (LFP), LiMn ｘ Fe １－ｘ P.O. ４ (LMFP), LiMnPO ４ (LMP), LiCoPO ４ (LCP), LiNiPO ４ (LNP) can be used. As the spinel type active material, for example, LiMn ２ O ４ (LMO), LiNi ０．５ Mn １．５ O ４ (LNMO) can be used. As the acid halide active material, for example, Li ２ MnO ３－ｘ F ｘ can be used.

[0052] The coating layer 142 covers at least a portion of the positive electrode active material 141. The coating layer 142 is provided to prevent the positive electrode active material 141 from coming into contact with and reacting with other materials, such as the solid electrolyte of the solid electrolyte layer 15. The coating layer 142 contains two or more phases made of different ion conductors. The coating layer 142 contains a first phase 142a made of an oxide-based ion conductor and a second phase 142b made of an amorphous-containing ion conductor that at least partially contains an amorphous phase.

[0053] The coating layer 142 may cover the entire surface of the positive electrode active material 141, or may cover only a portion of the positive electrode active material 141. To prevent the positive electrode active material 141 from coming into contact with and reacting with the solid electrolyte layer 15, etc., it is desirable that the coverage of the positive electrode active material 141 by the coating layer 142 be as high as possible. In this embodiment, the coverage of the positive electrode active material 141 by the coating layer 142 is set to 70% or more.

[0054] In the positive electrode layer 14, from the viewpoint of battery capacity, it is desirable that the volume ratio of the positive electrode active material 141 is as high as possible. On the other hand, if the volume ratio of the coating layer 142 is low, the coverage rate of the positive electrode active material 141 by the coating layer 142 decreases. In this embodiment, the volume ratio of the coating layer 142 to the positive electrode active material 141 is set within a range of 5 to 50%.

[0055] It is desirable that the thickness of the coating layer 142 be as thin as possible in order to increase the volume ratio of the positive electrode active material 141. On the other hand, if the thickness of the coating layer 142 is thin, the coverage of the positive electrode active material 141 by the coating layer 142 decreases. In this embodiment, the thickness of the coating layer 142 is set to a range of 1 to 100 nm.

[0056] The coating layer 142 has multiple phases including at least a first phase 142a and a second phase 142b. Forms B1 to B3 shown in Fig. 6 differ in the configuration of the first phase 142a and the second phase 142b in the coating layer 142. Note that the first phase 142a and the second phase 142b in the coating layer 142 are not limited to the configurations shown in Forms B1 to B3 in Fig. 6.

[0057] The constituent material of the first phase 142a and the constituent material of the second phase 142b are ion-conductive substances with different chemical compositions. The constituent material of the second phase 142b has a lower ionic conductivity than the constituent material of the first phase 142a. Therefore, in order to ensure the ionic conductivity of the coating layer 142, it is desirable to set the volume ratio of the first phase 142a in the coating layer 142 to be equal to or greater than the volume ratio of the second phase 142b.

[0058] The coating layer 142 of form B1 has a random structure in which the first phase 142a and the second phase 142b are randomly mixed. The first phase 142a of form B1 is in the form of particles, and the first phase 142a is surrounded by the second phase 142b.

[0059] The coating layer 142 of Form B2 has a core-shell structure in which the outer surface of a particulate first phase 142a that forms a core is coated with a second phase 142b that forms a shell. In Form B2, the particulate first phase 142a is individually coated with the second phase 142b to form core-shell particles.

[0060] The coating layer 142 of Form B3 has a laminated structure in which a first phase 142a and a second phase 142b are formed in layers. In Form B3, the outer surface of the positive electrode active material 141 is coated with the second phase 142b, and the outer surface of the second phase 142b is coated with the first phase 142a. In other words, in Form B3, the second phase 142b and the first phase 142a are laminated in this order on the outer surface of the positive electrode active material 141.

[0061] The positive electrode composite particles 140 can be formed by coating the positive electrode active material 141 with the coating layer 142 by mechanochemically mixing the raw materials while applying compressive and shearing forces, for example.

[0062] Form B1 can be produced by using as starting materials the positive electrode active material 141, the first phase 142a, and the second phase 142b, and mixing them while applying compressive and shear forces. Form B2 can be produced by using as starting materials the positive electrode active material 141 and core-shell particles in which the first phase 142a is coated with the second phase 142b, and mixing them while applying compressive and shear forces.

[0063] Form B3 can be produced by using positive electrode active material 141 and second phase 142b as starting materials, mixing them while applying compressive force and shear force to produce composite particles, and then mixing this composite particle with first phase 142a while applying compressive force and shear force.

[0064] When coating by mechanochemical coating, it is desirable that there is a significant difference in particle size between the coating particles that make up the coating layer 142 and the particles to be coated that make up the positive electrode active material 141. Specifically, it is desirable that the particle size of the coating particles be 1 / 10 or less of the particles to be coated.

[0065] Since the particles to be coated, that is, the positive electrode active material 141, generally range from 1 to 10 μm, the coating particles must be at most 1 μm or less. However, if 1 μm coating particles are used, the thickness of the coating layer 142 increases, leading to an increase in resistance. Therefore, in order to form a coating layer 142 of 100 nm or less, it is more desirable that the coating particles be 100 nm or less.

[0066] Alternatively, the positive electrode active material 141 can be coated with the coating layer 142 by a method such as a uniaxial ball mill or a planetary ball mill.

[0067] Furthermore, the coating layer 142 can also be coated on the positive electrode active material 141 by liquid phase coating or vapor phase coating.

[0068] In the liquid-phase coating, a precursor solution for the coating layer 142 is prepared, and the precursor solution for the reaction suppression layer is coated on the surface of the positive electrode active material 141, dried, and then heat-treated to form the reaction suppression layer. Coating the precursor onto the positive electrode active material 141 can be performed by any method that can coat the powder of the positive electrode active material 141 with a solution, and can be performed using, for example, a tumbling fluidized bed coating device.

[0069] For the vapor coating, for example, chemical vapor deposition (CVD), atomic layer deposition (ALD), sputtering, or the like can be used.

[0070] In any of Forms B1 to B3, the second phase 142b is interposed between the positive electrode active material 141 and the first phase 142a, and the second phase 142b increases the contact area between the positive electrode active material 141 and the coating layer 142.

[0071] The first phase 142a of the coating layer 142 can be made of the same material as the core phase 121 of the negative electrode composite particle 120. The second phase 142b of the coating layer 142 can be made of the same material as the shell phase 122 of the negative electrode composite particle 120.

[0072] The first phase 142a is an oxide-based ion conductor and an oxide-based solid electrolyte. For example, a pyrochlore-type oxide or a garnet-type oxide can be used as the first phase 142a. For example, an example of the pyrochlore-type oxide is Li １．２５ La ０．５８ Nb ２ O ６ F (LLNOF), Li １．２５ La ０．５８ Ta ２ O ６ As the garnet-type oxide, for example, Li ７ La ３ Zr ２ O １２ (LLZ) can be used.

[0073] The constituent material of the second phase 142b contains at least Li and F in the composition, for example, LiF, LiNb ６ O １５ An example of the second phase 142b is LiF. The material of the second phase 142b can have a low Young's modulus by containing at least Li and F in its composition. In this embodiment, LiF is used as the second phase 142b.

[0074] The constituent material of the second phase 142b has a lower melting point than the constituent material of the first phase 142a. Therefore, by heating the cathode composite particle 140 at a temperature equal to or higher than the melting point of the constituent material of the second phase 142b and lower than the melting point of the constituent material of the first phase 142a during production of the cathode composite particle 140, the second phase 142b melts, and the contact area between the first phase 142a and the second phase 142b can be increased.

[0075] The material of the second phase 142b has a lower Young's modulus than the material of the first phase 142a. By using a material with a lower Young's modulus for the second phase 142b, the contact area between the second phase 142b and the positive electrode active material 141 and the contact area between the second phase 142b and the first phase 142a can be increased. As a result, the coverage of the positive electrode active material 141 by the coating layer 142 can be improved.

[0076] The material of the second phase 142b is an amorphous-containing ion conductor that contains at least a partial amorphous phase. The material of the second phase 142b may be entirely amorphous, or may contain both amorphous and crystalline phases. When the material of the second phase 142b contains both amorphous and crystalline phases, it is desirable that the volume ratio of the amorphous phase be equal to or greater than the volume ratio of the crystalline phase.

[0077] The amorphous phase has a lower Young's modulus than the crystalline phase. Therefore, a high volume ratio of the amorphous phase in the second phase 142b can increase the contact area between the second phase 142b and the positive electrode active material 141 and the contact area between the second phase 142b and the first phase 142a. As a result, the coverage of the positive electrode active material 141 by the coating layer 142 can be improved.

[0078] Furthermore, the amorphous phase has an irregular particle shape rather than a specific shape. This also increases the contact area between the second phase 142b and the positive electrode active material 141 and the contact area between the second phase 142b and the first phase 142a. As a result, the coverage of the positive electrode active material 141 by the coating layer 142 can be increased.

[0079] As shown in Fig. 7, the coating layer 142 may include a third phase 142c having electronic conductivity in addition to a first phase 142a and a second phase 142b having ionic conductivity. Forms B1 to B3 shown in Fig. 7 differ in the configuration of the first phase 142a, the second phase 142b, and the third phase 142c in the coating layer 142. Note that the first phase 142a, the second phase 142b, and the third phase 142c in the coating layer 142 are not limited to the configurations shown in Forms B1 to B3 in Fig. 7.

[0080] The third phase 142c may be made of a carbon material such as carbon black. When the coating layer 142 includes the third phase 142c having electronic conductivity, the electronic conductivity of the positive electrode layer 14 can be improved and the amount of the conductive additive in the positive electrode layer 14 can be reduced.

[0081] 6 and 7 show an example in which the second phase 142b covers the entire outer surface of the first phase 142a in the coating layer 142, but the second phase 142b does not necessarily have to cover the entire outer surface of the first phase 142a.

[0082] 8 shows an example in which the second phase 142b coats a portion of the outer surface of the first phase 142a in the coating layer 142 included in the positive electrode composite particle 140 of form B2. In this way, in the coating layer 142, it is sufficient that the second phase 142b coats at least a portion of the outer surface of the first phase 142a.

[0083] The solid electrolyte layer 15 has ion conductivity and allows lithium ions to move between the anode layer 12 and the cathode layer 14. The solid electrolyte layer 15 includes a solid electrolyte composite 150. The solid electrolyte layer 15 may also include a binder. The solid electrolyte layer 15 may further include an electrolytic solution or a polymer. The solid electrolyte layer 15 has a higher density than the anode layer 12, which is a porous layer. For this reason, the solid electrolyte layer 15 can be called a dense layer.

[0084] 9 , the solid electrolyte composite 150 is a composite having multiple phases including at least a first phase 151 and a second phase 152. The first phase 151 is an oxide-based ion conductor and a solid electrolyte. The second phase 152 is an amorphous-containing ion conductor that contains at least an amorphous phase in a portion thereof. The second phase 152 is provided to increase the contact area between the solid electrolyte layer 15 and the electrode layers adjacent to the solid electrolyte layer 15, such as the anode layer 12 and the cathode layer 14, thereby reducing the interface resistance.

[0085] Forms C1 and C2 shown in FIG. 9 differ in the configuration of the first phase 151 and the second phase 152 of the solid electrolyte composite 150.

[0086] The solid electrolyte composite 150 of Form C1 has a random structure in which a first phase 151 and a second phase 152 are randomly mixed. The first phase 151 of Form C1 is in the form of particles, and the first phase 151 is surrounded by the second phase 152.

[0087] The solid electrolyte composite 150 of Form C2 has a core-shell structure in which a particulate first phase 151 serves as a core phase and a second phase 152 serves as a shell phase. In Form C2, the particulate first phases 151 are individually coated with the second phases 152. That is, the second phases 152 of Form C2 are not integrated, and the second phases 152 are separated for each first phase 151.

[0088] The first phase 151 of the solid electrolyte composite 150 can be made of the same material as the core phase 121 of the negative electrode composite particle 120. The second phase 152 of the solid electrolyte composite 150 can be made of the same material as the shell phase 122 of the negative electrode composite particle 120.

[0089] The first phase 151 is an oxide-based ion conductor and an oxide-based solid electrolyte. １．２５ La ０．５８ Nb ２ O ６ F (LLNOF), Li １．２５ La ０．５８ Ta ２ O ６ For example, a pyrochlore-type oxide such as (LLTOF) can be used.

[0090] The constituent material of the second phase 152 contains at least Li and F in its composition, and is, for example, LiF, LiNb ６ O １５ An example of the second phase 152 is F. In this embodiment, LiF is used as the second phase 152.

[0091] The constituent material of the second phase 152 is a material having a lower melting point than the constituent material of the first phase 151. Therefore, by heating the solid electrolyte composite 150 at a temperature equal to or higher than the melting point of the constituent material of the second phase 152 and lower than the melting point of the constituent material of the first phase 151 during production of the solid electrolyte composite 150, the second phase 152 melts, which increases the contact area between the first phase 151 and the second phase 152 and reduces the interface resistance.

[0092] The constituent material of the second phase 152 is a material having a lower Young's modulus than the constituent material of the first phase 151. By using a material with a low Young's modulus for the second phase 152, the contact area between the solid electrolyte layer 15 and the adjacent electrode layer can be increased, and the interface resistance can be reduced.

[0093] The constituent material of the second phase 152 is an amorphous-containing ion conductor that contains at least a partial amorphous phase. The constituent material of the second phase 152 may be entirely amorphous, or may contain both amorphous and crystalline phases. When the constituent material of the second phase 152 contains both amorphous and crystalline phases, it is desirable that the volume ratio of the amorphous phase be equal to or greater than the volume ratio of the crystalline phase.

[0094] Amorphous phase LiF has a lower Young's modulus than crystalline phase LiF. Therefore, by increasing the volume ratio of the amorphous phase in second phase 152, the contact area between solid electrolyte layer 15 and the adjacent electrode layer can be increased, and the interface resistance can be reduced.

[0095] Furthermore, the amorphous phase has an irregular particle shape rather than a specific shape, which also increases the contact area between the solid electrolyte layer 15 and the adjacent electrode layer, thereby reducing the interface resistance.

[0096] Here, the pyrochlore oxides used as the core phase 121 of the negative electrode composite particle 120, the first phase 142a of the coating layer 142 included in the positive electrode composite particle 140, and the first phase 151 of the solid electrolyte composite 150 will be described.

[0097] The pyrochlore oxide of this embodiment has the composition formula "Aa ２－α Ab （１＋α）／３ B ２ O ７－β X γ" In the above composition formula, O represents an oxygen atom, and Aa, Ab, B, and X represent any element or group. Aa, Ab, and B each represent a different type of cation, and O and X each represent a different type of anion. Aa is an alkali metal cation. Pyrochlore oxides contain multiple cations in their composition, including the alkali metal cation Aa and multiple cations Ab and B other than the alkali metal cation Aa. In other words, pyrochlore oxides contain multiple cations in their composition, including the alkali metal cation Aa.

[0098] As shown in FIG. 10, the pyrochlore oxide is ６ It has a crystal structure in which a three-dimensional network of octahedra consisting of BO is formed. ６ is a cation B in the center, with O at the vertex, and adjacent B ６ It shares a vertex with BO. ６ In the three-dimensional network, a hexagonal tunnel structure is formed in which cations A and anions X are arranged.

[0099] In the above composition formula, 0.6<α<2.0, 0<β≦1, and 0<γ≦1. A change in α changes the composition ratio of Aa and Ab, and a change in β and γ changes the composition ratio of O and X.

[0100] The cation Aa is an alkali metal cation. The alkali metal represented by Aa can be any of Li, Na, K, Rb, and Cs. Mg or H, other than alkali metals, may also be used as the cation Aa. In other words, the cation Aa contains at least one selected from Li, Na, K, Rb, Cs, Mg, and H. In this embodiment, Li is used as Aa. The composition ratio (2-α) of Aa is within the range of 0<(2-α)<1.4.

[0101] The cation Ab contains at least a lanthanoid. The lanthanoid represented by Ab can be at least one of La, Ce, Nd, and Sm. In this embodiment, La is used as Ab. The composition ratio (1+α) / 3 of Ab is within the range of 0.53<(1+α) / 3<1.

[0102] The basic structure of the cation Ab is a lanthanoid, and a portion of the lanthanoid constituting Ab may be substituted with an alkaline earth metal (Ca, Mg, Sr, etc.). The pyrochlore oxide of this embodiment has a pyrochlore structure in which α is 0.6<α<2.0 and β is 0<β≦1 in the composition formula. This is thought to result in defects in the crystal structure, improving ionic conductivity. In this embodiment, La is used as Ab.

[0103] In the pyrochlore oxide of this embodiment, the cation A in the general pyrochlore structure composition formula "A2B2O7" is a composite cation of lithium metal and lanthanoid, which is thought to contribute to the improvement of the ionic conductivity of the pyrochlore oxide.

[0104] The cation B is a metal cation different from Aa and Ab, and is a transition metal or a metal selected from Groups 13 to 15 elements. B forms an octahedron surrounded by six O atoms in the crystal. The transition metal represented by B can be a Group 4 transition metal or a Group 5 transition metal, and more specifically, at least one of Nb, Ta, Ti, Zr, Hf, and V can be used. The Group 13 element represented by B can be Al, Ga, or In, the Group 14 element can be Ge or Sn, and the Group 15 element can be Sb or Bi. In this embodiment, Nb or Ta is used as B.

[0105] The anion X is an anion that can substitute for the O atoms that constitute the pyrochlore structure. X has electronegativity and polarizability different from those of the O atoms. At least one of O, F, Cl, Br, I, S, OH, and P can be used as the anion represented by X. The composition ratio γ of X is in the range of 0<γ≦1, and at least a portion of the O atoms that constitute the pyrochlore structure are substituted with X. In this embodiment, F is used as X.

[0106] The pyrochlore oxide of this embodiment has a defect structure in which lattice defects are included in the crystal due to some of the O atoms constituting the pyrochlore structure being substituted with anions that have different electronegativity and polarizability from the O atoms. It is believed that the pyrochlore oxide of this embodiment has improved ionic conductivity due to the presence of the defect structure in the pyrochlore structure.

[0107] In the pyrochlore oxide of this embodiment, a defect structure is formed in which some of Aa and Ab are missing. The composition formula of a general pyrochlore structure is "A ２ B ２ O ７ ", and the composition ratio of cation A is 2. In contrast, in the pyrochlore oxide of this embodiment, the composition ratios of Aa and Ab are "2-α" and "(1+α) / 3," respectively, and since 0.6<α<2.0, the sum of the composition ratios of Aa and Ab is less than 2. In other words, in the crystal structure of the pyrochlore oxide of this embodiment, at least one of Aa and Ab is partially deficient. The composition ratio corresponding to the deficient portions of Aa and Ab is (2α-1) / 3.

[0108] In addition to the deviation in the composition ratio, a defect structure can also be formed by making the sum of the valences of the cations consisting of Aa, Ab, and B and the anions consisting of O and X in the above composition formula negative.

[0109] Furthermore, the pyrochlore oxide of this embodiment is a complex anion compound in which a plurality of anions such as O and X are contained in the pyrochlore structure, and BO ６ Since there is an anion represented by X in the coordinated octahedral structure, the alkali metal of Aa is BO６ Without relying on the coordination octahedron, BO ６ It is believed that this is why the pyrochlore-type oxide of this embodiment has high ionic conductivity when used in an electric field such as a battery.

[0110] Furthermore, since α, β, and γ in the composition formula affect lattice defects and ionic conductivity, it is desirable to use them within appropriate ranges. Large values ​​of α, β, and γ increase the defect concentration in the crystal lattice, but if they exceed a certain amount, the concentration of the alkali metal represented by Aa decreases, resulting in a decrease in ionic conductivity. Therefore, it is desirable to control α within the range of 0.6<α<2.0, β within the range of 0<β≦1, and γ within the range of 0<γ≦1.

[0111] In this embodiment, the pyrochlore oxide is “Li １．２５ La ０．５８ Nb ２ O ６ F (LLNOF)" or "Li １．２５ La ０．５８ Ta ２ O ６ The pyrochlore oxide used is represented by the formula (LLTOF) where Li is used as the cation Aa, La is used as the cation Ab, Nb or Ta is used as the cation B, and F is used as the anion X, with α=0.75, β=1, and γ=1.

[0112] The pyrochlore oxide of this embodiment has a composition of 1×10 －３ The pyrochlore-type oxide of this embodiment has an ionic conductivity significantly higher than that of other oxide-type solid electrolytes such as garnet-type oxides.

[0113] Next, a method for producing a pyrochlore oxide according to this embodiment will be described. In this embodiment, amorphous LiF is simultaneously formed when producing a pyrochlore oxide. For example, in the production process of a pyrochlore oxide, by adding LiF, a raw material for producing the pyrochlore oxide, in an amount greater than the required amount, amorphous LiF can be formed on the surface of the pyrochlore oxide.

[0114] 11 shows a method for producing a pyrochlore-type oxide according to this embodiment, which includes a first mixing step S10, a first firing step S11, a second mixing step S12, a molding step S13, and a second firing step S14, performed in this order.

[0115] First, a lanthanum source, a lithium source, and either a niobium source or a tantalum source are prepared as raw materials for the pyrochlore oxide, and a first mixing step S10 is performed in which these are mixed. As the lanthanum source, the lithium source, the niobium source, and the tantalum source, metal oxides, metal carbonates, etc. can be used. In this embodiment, La is used as the lanthanum source. ２ O ３ , Li as a lithium source ２ CO ３ , Nb as a niobium source ２ O ５ , Ta as a tantalum source ２ O ５ In the first mixing step, La ２ O ３ And Li ２ CO ３ and Nb ２ O ５ and Ta ２ O ５ Mix either of the above in a specified ratio.

[0116] Next, the mixture prepared in the first mixing step is fired in the first firing step S11. In the first firing step S11, two firing steps are performed. In the first step, the mixture is pre-fired in air at 500°C for 6 hours. Pre-fire removes moisture and other substances from the mixture, increasing its reactivity. Following pre-fire, the mixture is fired in air at 1200°C for 4 hours. This produces Li, a precursor of the target product. ０．５ La ０．５ Nb ２ O ６ Or Li ０．５ La ０．５ Ta ２ O ６ is obtained.

[0117] Next, a second mixing step S12 is performed in which a fluorine source is prepared as a raw material and mixed with the precursor. Metal fluorides can be used as the fluorine source. In this embodiment, LiF and LaF are used as the fluorine source. ３ LiF is a fluorine source and a lithium source, and LaF ３ is a fluorine source and a lanthanum source. In the second mixing step, LiF and LaF ３ and the precursor at a predetermined ratio. In this embodiment, LiF is added in an amount greater than the amount required to produce a pyrochlore-type oxide.

[0118] Next, the precursor, LiF, and LaF ３ The mixed powder is processed into a pellet shape and subjected to a molding step S13 in which the mixed powder is pressed at 100 MPa. ３ The mixture is formed into pellets.

[0119] Next, the precursor, LiF, and LaF ３ In the second firing step S14, the precursor, LiF, and LaF are fired in a nitrogen atmosphere. ３ The mixture is heated at 1000° C. for 6 hours for firing. In the second firing step S14, firing may be performed in a sealed state or in a state covered with a mother powder in order to prevent deviation in composition due to volatilization of the Li element and the F element.

[0120] By cooling the product of the second firing step, the composition formula "Li １．２５ La ０．５８ Nb ２ O ６ F" or "Li １．２５ La ０．５８ Ta ２ O ６ The resulting pyrochlore oxide is in the form of particles. The outer surface of the pyrochlore oxide is coated with LiF, and particles with a core-shell structure having a core phase of pyrochlore oxide and a shell phase of LiF can be obtained.

[0121] The amorphization of LiF can be promoted by controlling the cooling conditions after the second firing step. Specifically, the amorphization of LiF can be promoted by increasing the cooling rate of the product, and the volume fraction of amorphous material can be increased.

[0122] In the above manufacturing process, La ２ O ３ And Li ２ CO ３ and Nb ２ O ５ Or Nb ２ O ５ Any of the above, LiF, and LaF ３ By changing the mixing ratio of "Li ２－α La （１＋α）／３ Nb ２ O ７－β F γ " or "Li ２－α La （１＋α）／３ Ta ２ O ７－β F γ A pyrochlore-type solid electrolyte represented by La ２ O ３ And Li ２ CO ３ and Nb ２ O ５ Or Nb ２ O ５ Any of the above, LiF, and LaF ３ By changing the mixing ratio of the elements, it is possible to adjust α, β, and γ in the composition formula. Furthermore, part of the material sublimes during firing. Therefore, it is possible to adjust α, β, and γ by changing the firing conditions, furnace atmosphere, and furnace size in the first and second firing steps.

[0123] Figure 12 shows SEM images of LLNOF, a pyrochlore oxide, and amorphous-containing LiF. The upper part of Figure 12 shows a core-shell structure in which LLNOF is covered with amorphous-containing LiF, and the lower part shows a random structure in which LLNOF and amorphous-containing LiF are randomly mixed. The manufacturing method of this embodiment provides a composite of LLNOF and amorphous-containing LiF shown in Figure 12.

[0124] Fig. 13 is an SEM image of a positive electrode composite particle 140. In the example shown in Fig. 13, NMC is used as a positive electrode active material 141, and a coating layer 142 has a random structure in which LLNOF and amorphous-containing LiF are randomly mixed.

[0125] Next, a method for manufacturing the anode layer 12 using a 3D printer will be described. For example, a stereolithography method or an extrusion method can be used as a method for manufacturing the anode layer 12 using a 3D printer. When manufacturing the anode layer 12, a solid electrolyte layer 15 is used as a substrate, and the anode layer 12 is formed on the solid electrolyte layer 15. In the method for manufacturing the anode layer 12 described below, LLNOF is used as the oxide-based ion conductor, and amorphous-containing LiF is used as the amorphous-containing ion conductor.

[0126] The manufacturing method using stereolithography will be described with reference to Fig. 14. First, a powder preparation step S20 is performed to prepare anode composite particles 120, which are raw material powder for the anode layer 12. In the powder preparation step S20, particles with a core-shell structure made of LLNOF and amorphous-containing LiF were used as the anode composite particles 120. The average particle size of the anode composite particles 120 was 2 µm. The proportions of LLNOF and amorphous-containing LiF in the anode composite particles 120 were 90 vol% and 10 vol%.

[0127] Next, a slurry preparation step S21 is performed. In the slurry preparation step S21, the negative electrode composite particles 120 and the acrylic photocurable resin are mixed and stirred to prepare a slurry. The slurry is a suspension in which solid particles are dispersed in a solvent, and is a highly viscous fluid. The ratio of the negative electrode composite particles 120 to the acrylic photocurable resin in the slurry was 52 vol % and 48 vol %.

[0128] Next, a slurry application step S22 is performed. In the slurry application step S22, the slurry is applied in a layer using a 3D printer. In this embodiment, the thickness of the slurry is 10 μm. The slurry is applied onto the solid electrolyte layer 15. The application of the slurry can be performed in a pattern corresponding to the shape of the negative electrode layer 12 to be formed. The pores in the negative electrode layer 12 may be formed by the pattern of the structure, or may be formed using a pore-forming agent. When a pore-forming agent is used, the pore-forming agent may be mixed into the slurry.

[0129] Next, a laser irradiation step S23 is performed. In the laser irradiation step S23, ultraviolet light is irradiated onto the applied slurry to harden the photocurable resin. In this embodiment, the laser diameter of the laser irradiation is set to 10 μm. As a result, a layered structure is formed.

[0130] Next, in a determination step S24, it is determined whether or not a predetermined number of layers have been stacked. In this embodiment, the number of layers is four. The slurry application step S22 and the laser irradiation step S23 are repeated until the predetermined number of layers have been stacked. This results in a laminated structure in which layered structures are stacked. Steps S22 to S24 are structure molding steps in which the laminated structure is molded.

[0131] If it is determined in S24 that the lamination is complete, a cleaning step S25 is performed to remove portions of the laminated structure that have not been cured by laser irradiation. In the cleaning step S25, ultrasonic cleaning, immersion cleaning, cleaning using suction filtration, etc. in various solvents can be used. The solvent used in the cleaning step can be a photocurable resin similar to the photocurable resin used in the slurry, ethanol, etc.

[0132] After the cleaning step S25, a pressurizing step may be performed to pressurize the laminated structure. The pressurizing treatment can be performed using, for example, a cold isostatic press (CIP) or a warm isostatic press (WIP).

[0133] Next, a degreasing step S26 is performed to remove the photocurable resin that has been cured by laser irradiation from the laminated structure. The degreasing step S26 can be performed by baking the laminated structure at a temperature of, for example, about 600°C.

[0134] Next, a firing step S27 is performed. The firing step S27 can be performed by heating the laminated structure at a temperature of, for example, about 1000°C. This allows the negative electrode layer 12 to be produced. The amorphous-containing LiF contained in the negative electrode composite particles 120 can promote interparticle bonding during sintering, thereby increasing the density of the sintered negative electrode layer 12 and giving it a dense structure. In the firing step S27, firing may be performed in a sealed state or in a state covered with a mother powder in order to prevent composition deviation due to volatilization of the Li element and the F element.

[0135] By performing the above steps S20 to S27, the negative electrode layer 12 can be manufactured using a stereolithography 3D printer. The negative electrode layer 12 is formed on the solid electrolyte layer 15.

[0136] Next, the extrusion-based manufacturing method will be described with reference to Fig. 15. Here, differences from the stereolithography method of Fig. 14 will be described.

[0137] In the extrusion method shown in FIG. 15, in a slurry preparation step S21, negative electrode composite particles 120, a dispersant, and a binder are mixed and stirred to prepare a slurry.

[0138] Next, a tube extrusion step S28 is performed. In the tube extrusion step S28, the slurry is applied in a layer shape using a 3D printer. The slurry is applied onto the solid electrolyte layer 15. The application of the slurry is performed in a pattern corresponding to the shape of the negative electrode layer 12 to be formed.

[0139] Next, a drying step S29 is performed. In the drying step S29, the applied slurry is dried. As a result, a layer structure is formed. In the drying step S29, the applied slurry may be heated.

[0140] The tube extrusion step S28 and the drying step S29 are repeated until it is determined in S24 that the predetermined number of layers have been stacked, thereby obtaining a laminated structure in which layered structures are stacked. S28, S29, and S24 constitute the structure molding step for molding the laminated structure.

[0141] After the lamination is completed, a firing step S27 is performed, whereby the negative electrode layer 12 can be manufactured using an extrusion-type 3D printer.

[0142] Fig. 16 is an SEM image of the manufactured anode layer 12. The anode layer 12 shown in Fig. 16 is formed in a lattice shape. The two anode layers 12 shown in Fig. 16 have different pore sizes. In Fig. 16, the anode layer 12 shown on the left side has larger pores than the anode layer 12 shown on the right side.

[0143] Next, the residual Li ratio and post-sintering density of structures formed using a stereolithography 3D printer will be described using examples and comparative examples shown in Figure 17. Examples A1 to A4 and comparative examples A1 to A3 differ in the material of the core phase 121, the amorphous volume ratio of the shell phase 122, the presence or absence of the shell phase 122, and the presence or absence of an organic coating.

[0144] The residual Li ratio is the ratio of the amount of lithium contained in the raw material powder after slurried to the amount of lithium contained in the raw material powder before slurried. If the amount of lithium contained in the raw material powder before and after slurried is the same, the residual Li ratio will be 100%.

[0145] In Examples A1 to A4, raw material powder was used in which a core phase 121 of an oxide-based ion conductor was coated with a shell phase 122 of an amorphous-containing ion conductor. In Comparative Example A1, raw material powder was used in which a core phase 121 of an oxide-based ion conductor was coated with a shell phase 122 of an ion conductor that was 100% crystalline. In Comparative Example A2, raw material powder consisting of only an oxide-based ion conductor was used. In Comparative Example A3, raw material powder in which an oxide-based ion conductor was subjected to an organic coating was used.

[0146] In Example A1, LLNOF was used as the core phase 121, and 100% amorphous LiF was used as the shell phase 122. In Examples A2 to A4 and Comparative Examples A1 to A3, differences from Example A1 will be explained.

[0147] Example A2 uses 50% crystalline and 50% amorphous LiF as the shell phase 122. Example A3 uses LLTOF as the core phase 121. Example A4 uses LLZ as the core phase 121.

[0148] Comparative Example A1 uses 100% crystalline LiF as the shell phase 122. Comparative Example A2 uses LLZ as the core phase 121, and does not provide a shell phase 122. Comparative Example A3 uses LLZ as the core phase 121, does not provide a shell phase 122, and provides an organic coating.

[0149] In Examples A1 and A2 and Comparative Example A1, LLNOF was used as the core phase 121. In Example A1, the residual Li ratio was 100% and the density after sintering was 88%. In Example A2, the residual Li ratio was 99% and the density after sintering was 85%. In Comparative Example A1, the residual Li ratio was 95% and the density after sintering was 82%.

[0150] Examples A1 and A2, which used amorphous-containing LiF, had improved residual Li ratios and post-sintered densities compared to Comparative Example A1, which used 100% crystalline LiF. Because the amorphous phase has a lower Young's modulus and is amorphous than the crystalline phase, Examples A1 and A2, which used amorphous-containing LiF, are thought to have a higher coverage of the core phase 121 with the shell phase 122, thereby suppressing the elution of lithium ions from the core phase 121. Furthermore, because amorphous-containing LiF promotes interparticle bonding during sintering, Examples A1 and A2 are thought to have improved post-sintered densities. Example A1, which has a higher volume fraction of the amorphous phase than Example A2, has improved residual Li ratios and post-sintered densities compared to Example A2.

[0151] In Example A3, the residual Li ratio was 100% and the density after sintering was 87%. Even in Example A3 in which LLTOF was used as the core phase 121, high values ​​for the residual Li ratio and the density after sintering were obtained by using 100% amorphous LiF as the shell phase 122.

[0152] In Example A4, the residual Li ratio was 92% and the density after sintering was 80%. In Comparative Example A2, the residual Li ratio was 60%. In Comparative Example A2, coating was not possible and a sintered body could not be obtained. In Comparative Example A3, the residual Li ratio was 100% and the density after sintering was 72%.

[0153] Example A4 and Comparative Examples A2 and A3 use LLZ as the core phase 121. Comparative Example A2, which uses only LLZ, had a significantly reduced residual Li ratio, and furthermore, coating using a 3D printer was not possible. Comparative Example A3, in which an organic coating was applied to LLZ, had a high residual Li ratio, but the density after sintering was low due to the increased specific surface area caused by the organic coating. In contrast, Example A4, which has a shell phase 122 of amorphous LiF, had a significantly improved residual Li ratio compared to Comparative Example A2. Furthermore, although Example A4 had a lower residual Li ratio than Comparative Example A3, the density after sintering was improved. This is thought to be because the 100% amorphous LiF used as the shell phase 122 promoted interparticle bonding during sintering, improving the density after sintering.

[0154] Comparing Examples A1 and A2, which used pyrochlore-type oxides (LLNOF, LLTOF) as the core phase 121, with Example A4, which used a garnet-type oxide (LLZ) as the core phase 121, Examples A1 and A2 had a higher residual Li fraction and a higher density after sintering than Example A4. This is thought to be because pyrochlore-type oxides have a lower melting point and a lower Young's modulus than garnet-type oxides, resulting in a higher residual Li fraction and a higher density after sintering.

[0155] Next, the coverage and discharge characteristics of the positive electrode composite particles 140 will be described using an example and a comparative example shown in FIG. 18. Examples B1 to B8 and comparative examples B1 to B7 differ in the positive electrode active material 141 or the coating layer 142. The coverage in FIG. 18 is the coverage of the positive electrode active material 141 by the coating layer 142. The discharge characteristics in FIG. 18 are the dischargeable time until the secondary battery 10 reaches the lower limit voltage when discharged at 5 C. In FIG. 18, the coverage and discharge characteristics are shown as relative values ​​when the value of comparative example B1 is set to 100%.

[0156] In Example B1, NMC was used as the positive electrode active material 141, LLNOF was used as the first phase 142a of the coating layer 142, and 100% amorphous LiF was used as the second phase 142b, with the volume ratios of the first phase 142a and the second phase 142b being 90 vol% and 10 vol%. In Examples B2 to B8 and Comparative Examples B1 to B7, differences from Example B1 will be explained.

[0157] In Example B2, 50% crystalline and 50% amorphous LiF is used as the second phase 142b. In Example B3, the volume ratios of the first phase 142a and the second phase 142b are 70 vol% and 30 vol%, respectively. In Example B4, LLTOF is used as the first phase 142a.

[0158] In Example B5, LMFP is used as the positive electrode active material 141. In Example B6, a third phase 142c made of carbon is provided in the coating layer 142, and the volume ratios of the first phase 142a, the second phase 142b, and the third phase 142c are 89 vol%, 8 vol%, and 3 vol%, respectively. In Example B7, LLZ is used as the first phase 142a. In Example B8, the volume ratios of the first phase 142a and the second phase 142b are both 50 vol%.

[0159] Comparative Example B1 uses 100% crystalline LiF as the second phase 142b. Comparative Example B2 uses 100% crystalline LiF as the second phase 142b, and the volume ratios of the first phase 142a and the second phase 142b are both 50 vol%. Comparative Example B3 does not include the second phase 142b. Comparative Example B4 uses LLTOF as the first phase 142a, and does not include the second phase 142b.

[0160] Comparative Example B5 does not have the first phase 142a and uses 100% crystalline LiF as the second phase 142b. Comparative Example B6 uses LLZ as the first phase 142a and 100% crystalline LiF as the second phase 142b. Comparative Example B7 uses LiNbO3 as the first phase 142a and does not have the second phase 142b.

[0161] In Examples B1, B2, and B3 and Comparative Example B1, NMC was used for the positive electrode active material 141, and LLNOF was used for the first phase 142a of the coating layer 142. Examples B1, B2, and B3, which used amorphous-containing LiF as the second phase 142b, had improved coverage and discharge characteristics compared to Comparative Example B1, which used 100% crystalline LiF. Because the amorphous phase has a lower Young's modulus than the crystalline phase and is amorphous, Examples B1, B2, and B3, which used amorphous-containing LiF, had a higher coverage of the positive electrode active material 141 with the coating layer 142, which is thought to have suppressed the reaction between the positive electrode active material 141 and the solid electrolyte.

[0162] In Example B4, LLTOF is used as the first phase 142a, but amorphous LiF is used as the second phase 142b, thereby achieving a higher coverage and better discharge characteristics than Comparative Example B1.

[0163] In Example B5, LMFP is used as the positive electrode active material 141, but by providing a coating layer 142 made of LLNOF and 100% amorphous LiF, a higher coverage and better discharge characteristics than in Comparative Example B1 are obtained.

[0164] In Example B6, the discharge characteristics are improved compared to Example B1. In Example B6, the third phase 142c having electronic conductivity is provided in the coating layer 142, and it is believed that the presence of the third phase 142c improved the discharge characteristics.

[0165] In Example B7 and Comparative Example B6, NMC was used as the positive electrode active material 141, and LLZ was used as the first phase 142a of the coating layer 142. Example B7, which used 100% amorphous LiF as the second phase 142b, had improved coverage and discharge characteristics compared to Comparative Example B6, which used 100% crystalline LiF.

[0166] In Example B8 and Comparative Example B2, NMC was used for the positive electrode active material 141, LLNOF was used for the first phase 142a of the coating layer 142, and the volume ratios of the first phase 142a and the second phase 142b were both 50 vol %. Example B8, which used 100% amorphous LiF as the second phase 142b, had improved coverage and discharge characteristics compared to Comparative Example B2, which used 100% crystalline LiF.

[0167] Comparative Examples B3 and B4, which do not include the second phase 142b, have significantly lower coverage and discharge characteristics than Comparative Example B1. It is believed that the low coverage of Comparative Examples B3 and B4 causes the positive electrode active material 141 to react with other materials, such as the solid electrolyte, resulting in increased resistance and decreased discharge characteristics.

[0168] In Comparative Example B5, in which the coating layer 142 is made of 100% crystalline LiF, the coverage is higher than in Comparative Example B1, but the discharge characteristics are significantly reduced. It is believed that the low ionic conductivity of LiF increases the resistance of the coating layer 142, resulting in a reduction in the discharge characteristics.

[0169] Comparative Example B7, which used LiNbO3 as the coating layer 142, had a higher coverage than Comparative Example B1, but the discharge characteristics were significantly reduced. It is believed that the low ionic conductivity of LiNbO3 increased the resistance of the coating layer 142, resulting in a reduction in the discharge characteristics.

[0170] In the present embodiment described above, in the positive electrode composite particle 140 in which the positive electrode active material 141 is coated with the coating layer 142, the coating layer 142 includes a first phase 142a having high ionic conductivity and a second phase 142b including an amorphous phase. The second phase 142b including the amorphous phase has a low Young's modulus and is amorphous, which can improve the contact between the positive electrode active material 141 and the coating layer 142 and can increase the coverage of the positive electrode active material 141 by the coating layer 142. This can suppress the positive electrode active material 141 from reacting with other materials, while improving the ionic conductivity of the coating layer 142 by the first phase 142a having high ionic conductivity.

[0171] In this embodiment, the amorphous-containing ionic conductor of the second phase 142b contained in the coating layer 142 is a material having a lower melting point than the first phase 142a. This also improves the contact between the positive electrode active material 141 and the first phase 142a. This improves the coverage of the positive electrode active material 141 with the coating layer 142, thereby improving the ionic conductivity of the positive electrode layer 14 while suppressing reaction with other materials.

[0172] In this embodiment, a pyrochlore-type oxide is used as the first phase 142a of the coating layer 142. Since pyrochlore-type oxides have higher ionic conductivity than other oxide-type solid electrolytes, the ionic conductivity of the coating layer 142 can be improved.

[0173] Furthermore, pyrochlore oxides have high oxidation resistance, so by using a pyrochlore oxide for the coating layer 142, it is possible to achieve both low resistance and high charge / discharge stability.

[0174] In this embodiment, the volume ratio of the first phase 142a is equal to or greater than the volume ratio of the second phase 142b in the coating layer 142 of the positive electrode composite particle 140. In this way, by increasing the volume ratio of the first phase 142a, which has high ionic conductivity, the ionic conductivity of the coating layer 142 can be improved.

[0175] In this embodiment, a material containing at least Li and F in its composition is used as the second phase 142b of the coating layer 142. This can reduce the Young's modulus of the second phase 142b, thereby improving the contact between the positive electrode active material 141 and the first phase 142a.

[0176] In this embodiment, an ion conductor containing at least a portion of an amorphous phase is used as the second phase 142b of the coating layer 142, and the volume ratio of the amorphous phase in the second phase 142b is equal to or greater than the volume ratio of the crystalline phase, thereby reducing the Young's modulus of the second phase 142b and improving the contact between the positive electrode active material 141 and the first phase 142a.

[0177] In this embodiment, a third phase 142c having electronic conductivity can be provided in the coating layer 142. This can improve the electronic conductivity of the positive electrode layer 14 and reduce the amount of conductive additive in the positive electrode layer 14.

[0178] In this embodiment, a solid electrolyte composite 150 including a first phase 151 made of an oxide-based ion conductor and a second phase 152 made of an amorphous-containing ion conductor is used as the solid electrolyte layer 15. The amorphous-containing ion conductor of the second phase 152 has a lower Young's modulus than the first phase 151 and is an amorphous material, which can increase the contact area between the solid electrolyte layer 15 and the electrode layers adjacent to the solid electrolyte layer 15, such as the anode layer 12 and the cathode layer 14. This can reduce the interfacial resistance between the solid electrolyte layer 15 and the adjacent electrode layers, thereby improving ionic conductivity.

[0179] In this embodiment, a pyrochlore oxide is used as the first phase 151 of the solid electrolyte composite 150. A pyrochlore oxide has higher ionic conductivity than other oxide-type solid electrolytes, and the solid electrolyte composite 150 containing a pyrochlore oxide can improve the ionic conductivity of the solid electrolyte layer 15.

[0180] In this embodiment, a material containing at least Li and F in its composition is used as the second phase 152 of the solid electrolyte composite 150. This can reduce the Young's modulus of the second phase 152 and increase the contact area between the solid electrolyte layer 15 and the adjacent electrode layer. This can reduce the interfacial resistance between the solid electrolyte layer 15 and the adjacent electrode layer and improve ion conductivity.

[0181] In this embodiment, the anode layer 12 is produced using a slurry containing anode composite particles 120. The anode composite particles 120 include a core phase 121 made of an oxide-based ion conductor and a shell phase 122 made of an amorphous-containing ion conductor that at least partially contains an amorphous phase. The amorphous-containing ion conductor of the shell phase 122 has a lower Young's modulus than the core phase 121 and is an amorphous material, which can improve the coverage of the core phase 121 with the shell phase 122. This can prevent the oxide-based ion conductor of the anode composite particles 120 from reacting with the solvent in the slurry, and can prevent lithium ions, which are conductive ions, from eluting from the oxide-based ion conductor.

[0182] Furthermore, the amorphous-containing LiF contained in the shell phase 122 can promote interparticle bonding during sintering, thereby increasing the density of the sintered anode layer 12 and forming a dense structure, thereby suppressing short circuits caused by lithium metal precipitation inside the structure when lithium metal precipitates in the anode layer 12.

[0183] In this embodiment, a pyrochlore-type oxide is used as the core phase 121 of the anode composite particle 120. Pyrochlore-type oxides have higher ionic conductivity than other oxide-type solid electrolytes, and the inclusion of a pyrochlore-type oxide in the anode composite particle 120 can improve the ionic conductivity of the anode layer 12. Furthermore, lithium ions are less likely to elute from pyrochlore-type oxides than from other oxides such as garnet-type oxides. Therefore, by using a pyrochlore-type oxide as the oxide-based ionic conductor for the core phase 121, the elution of lithium ions can be effectively suppressed.

[0184] In this embodiment, a material containing at least Li and F in its composition is used for the shell phase 122 of the anode composite particle 120. This can reduce the Young's modulus of the shell phase 122 and improve the coverage of the core phase 121 with the shell phase 122. This can suppress the elution of lithium ions, which are conductive ions, from the oxide-based ion conductor of the anode composite particle 120.

[0185] In this embodiment, an ion conductor containing at least a portion of an amorphous phase is used as the shell phase 122 of the negative electrode composite particle 120, and the volume ratio of the amorphous phase is equal to or greater than the volume ratio of the crystalline phase in the shell phase 122. This can reduce the Young's modulus of the shell phase 122 and improve the coverage of the core phase 121 by the shell phase 122.

[0186] In this embodiment, the volume ratio of the core phase 121 in the anode composite particle 120 is set to be equal to or greater than the volume ratio of the shell phase 122. The constituent material of the shell phase 122 has higher ionic conductivity than the constituent material of the core phase 121. Therefore, by increasing the volume ratio of the core phase 121 in the anode composite particle 120, the ionic conductivity of the anode composite particle 120 can be increased.

[0187] In this embodiment, the negative electrode layer 12 is manufactured from the slurry using a 3D printer. This makes it possible to easily manufacture the negative electrode layer 12 having an ordered porous structure in which pores are regularly formed.

[0188] In this embodiment, the anode layer 12 is manufactured using a stereolithography 3D printer in which a photocurable resin is cured by laser irradiation. The photocurable resin easily reacts with an oxide-based ion conductor in a slurry. Therefore, by using anode composite particles 120 in which a core phase 121 made of an oxide-based ion conductor is coated with a shell phase 122 made of an amorphous-containing ion conductor, the oxide-based ion conductor of the core phase 121 and the photocurable resin can be prevented from reacting with each other, thereby preventing lithium ions, which are conductive ions, from eluting from the oxide-based ion conductor.

[0189] In this embodiment, the solid content of the slurry is set to a range of 30 to 60 vol %, which ensures that the negative electrode composite particles 120 are slurried and increases the density of the negative electrode layer 12 after sintering.

[0190] In this embodiment, a light absorbing material can be included in the slurry. By including a light absorbing material in the slurry, scattering of the laser light can be suppressed when the slurry is irradiated with a laser by a 3D printer. This allows the stereolithography 3D printer to achieve the desired modeling width and perform modeling with high precision.

[0191] Second Embodiment Next, a second embodiment of the present disclosure will be described. Only the differences from the first embodiment will be described below.

[0192] 19 , the anode layer 12 of the second embodiment has a pore distribution in which the porosity changes from the side closer to the solid electrolyte layer 15 to the side farther from the solid electrolyte layer 15, with the porosity increasing closer to the solid electrolyte layer 15. In the anode layer 12, the porosity is low on the side farther from the solid electrolyte layer 15 (i.e., the side closer to the anode current collector 11) and high on the side closer to the solid electrolyte layer 15.

[0193] 19 , the pore diameter of the anode layer 12 is smaller on the side farther from the solid electrolyte layer 15, and is larger on the side closer to the solid electrolyte layer 15. When the pore diameter of the anode layer 12 is uniform, the porosity on the side closer to the solid electrolyte layer 15 can be increased by making the number of pores on the side closer to the solid electrolyte layer 15 larger than the number of pores on the side farther from the solid electrolyte layer 15. FIG. 19 shows an example in which pores in the anode layer 12 are formed irregularly using a pore-forming agent.

[0194] In the anode layer 12, the conduction rate of electrons is faster than the conduction rate of lithium ions. Therefore, in the anode layer 12, lithium metal is preferentially deposited from pores closer to the solid electrolyte layer 15. When the pores of the anode layer 12 closer to the solid electrolyte layer 15 are filled with lithium metal, lithium metal deposition occurs competitively in the pores of the anode layer 12 farther from the solid electrolyte layer 15 and in the solid electrolyte layer 15. If lithium metal deposition occurs in the solid electrolyte layer 15, it may lead to a short circuit.

[0195] In contrast, by increasing the pore size on the side of the anode layer 12 closer to the solid electrolyte layer 15 and increasing the porosity, the pores on the side closer to the solid electrolyte layer 15 are less likely to be filled with lithium metal. This allows lithium metal to be deposited as uniformly as possible in all the pores from the side of the anode layer 12 closer to the solid electrolyte layer 15 to the side farther from the solid electrolyte layer 15.

[0196] Increasing the porosity of the anode layer 12 on the side closer to the solid electrolyte layer 15 may reduce the contact between the anode layer 12 and the solid electrolyte layer 15. In contrast, the solid electrolyte layer 15 of the second embodiment uses a solid electrolyte composite 150 containing the second phase 152 of amorphous-containing LiF, which can improve the contact between the anode layer 12 and the solid electrolyte layer 15. This makes it possible to prevent a reduction in the contact between the anode layer 12 and the solid electrolyte layer 15, even when the porosity of the anode layer 12 on the side closer to the solid electrolyte layer 15 is increased.

[0197] The pore distribution of the anode layer 12 may be such that the porosity increases from the side farther from the solid electrolyte layer 15 to the side closer to the solid electrolyte layer 15, and the porosity may change continuously or stepwise. In order to deposit lithium metal as uniformly as possible in the pores throughout the anode layer 12, a continuous change in porosity is desirable. On the other hand, when the anode layer 12 is manufactured using, for example, a 3D printer, multiple layers of material are stacked, and the porosity is fixed for each layer. For this reason, a configuration in which the porosity of the anode layer 12 changes stepwise has the advantage of being easier to manufacture.

[0198] Third Embodiment Next, a third embodiment of the present disclosure will be described. Only the differences from the above embodiments will be described below.

[0199] Fig. 20 shows a partially enlarged cross section of the anode layer 12 of the third embodiment. As shown in Fig. 20, an electron conduction layer 123 having electron conductivity is formed on the surface of the anode layer 12. The electron conduction layer 123 is provided on the inner surfaces of the pores of the anode layer 12. The electron conduction layer 123 can be formed by coating with a carbon material such as carbon black.

[0200] By providing the electron conductive layer 123 on the surface of the anode layer 12, the electron conductivity of the anode layer 12 can be improved and the deposition of lithium metal in the anode layer 12 can be promoted. In addition, by providing the electron conductive layer 123 on the surface of the anode layer 12, the amount of conductive additive in the anode layer 12 can be reduced.

[0201] Fourth Embodiment Next, a fourth embodiment of the present disclosure will be described. Only the differences from the above embodiments will be described below.

[0202] FIG. 21 shows a partially enlarged cross section of the anode layer 12 of the fourth embodiment. As shown in FIG. 21 , in the fourth embodiment, the anode layer 12 includes an ion-electron conductive phase 124. The ion-electron conductive phase 124 is composed of a material having ionic and electronic conductivity. The ion-electron conductive phase 124 can be obtained, for example, by imparting electronic conductivity to a pyrochlore oxide used as the core phase 121 of the anode composite particle 120. For example, by subjecting an ionically conductive pyrochlore oxide to a reduction treatment, the pyrochlore oxide can be imparted with electronic conductivity in addition to ionic conductivity. Metals that form alloys with Li, such as Ag, Au, Sn, and In, can also be used as the ion-electron conductive phase 124.

[0203] The inclusion of the ion-electron conductive phase 124 in the anode layer 12 can improve the ionic conductivity and electronic conductivity of the anode layer 12 and promote lithium metal deposition in the anode layer 12. Furthermore, the inclusion of the ion-electron conductive phase 124 in the anode layer 12 can reduce the amount of conductive additive in the anode layer 12.

[0204] Fifth Embodiment Next, a fifth embodiment of the present disclosure will be described. Only the differences from the above embodiments will be described below.

[0205] 22 , in the fifth embodiment, the positive electrode layer 14 includes a solid electrolyte composite 143. The solid electrolyte composite 143 of the positive electrode layer 14 may have a configuration similar to that of the solid electrolyte composite 150 of the solid electrolyte layer 15. Furthermore, the positive electrode layer 14 may include an electrolytic solution and a polymer.

[0206] 23 , the solid electrolyte composite 143 provided in the positive electrode layer 14 is a composite having multiple phases including at least a first phase 143 a and a second phase 143 b, and can also be referred to as a positive electrode composite. In the solid electrolyte composite 143 provided in the positive electrode layer 14, the first phase 143 a is an oxide-based ion conductor, and the second phase 143 b is an amorphous-containing ion conductor that at least partially contains an amorphous phase. The material constituting the second phase 143 b has a lower melting point and a lower Young's modulus than the material constituting the first phase 143 a.

[0207] The solid electrolyte composite 143 provided in the positive electrode layer 14 may have a random configuration in which first phases 143 a and second phases 143 b are randomly provided, as shown in Form D1 in FIG. 23 , or may have a core-shell structure in which the first phase 143 a is a core phase and the second phase 143 b is a shell phase, as shown in Form D2 in FIG. 23 .

[0208] The oxide-based ion conductor of the first phase 143a may be a pyrochlore-type oxide, such as LLNOF or LLTOF. The amorphous-containing ion conductor of the second phase 143b may be amorphous-containing LiF containing an amorphous phase. The volume ratio of the amorphous phase in the amorphous-containing LiF of the second phase 143b is preferably equal to or greater than the volume ratio of the crystalline phase.

[0209] In this way, by providing the positive electrode layer 14 with a solid electrolyte composite including the first phase 143 a made of an oxide-based ion conductor and the second phase 143 b made of an amorphous-containing ion conductor, the ionic conductivity of the positive electrode layer 14 can be improved.

[0210] Furthermore, the solid electrolyte composite provided in the positive electrode layer 14 contains the second phase 143b made of an amorphous-containing ion conductor, which can improve the contact between the positive electrode layer 14 and the solid electrolyte layer 15 and reduce the interface resistance.

[0211] The present disclosure is not limited to the above-described embodiments, and various modifications can be made as follows without departing from the spirit of the present disclosure. Furthermore, the means disclosed in the above-described embodiments may be combined as appropriate within the scope of feasibility.

[0212] For example, in the above embodiments, the present disclosure has been described as being applied to a lithium-ion battery in which the conductive ions are lithium ions, but the present disclosure may also be applied to secondary batteries in which the conductive ions are different. Specifically, the present disclosure may be applied to a potassium-ion battery in which potassium ions are conductive, a sodium-ion battery in which sodium ions are conductive, or the like.

[0213] Furthermore, in the above-described first embodiment, an example has been described in which the positive electrode composite particles 140 are combined with the solid electrolyte layer 15 made of an oxide-based solid electrolyte (a pyrochlore-type oxide or a garnet-type oxide). However, the positive electrode composite particles 140 may also be combined with the solid electrolyte layer 15 made of a sulfide-based solid electrolyte.

[0214] Furthermore, in the first embodiment, an example was described in which ceramic composite particles were applied to the positive electrode composite particles 140 and the positive electrode active material 141 was used as the ceramic particles that undergo an oxidation-reduction reaction, but materials other than the positive electrode active material 141 may also be used as the ceramic particles. For example, in a secondary battery including a negative electrode active material, the negative electrode active material may be used as the ceramic particles, and the negative electrode active material may be coated with a coating layer to form ceramic composite particles. In a solid oxide electrolysis cell (SOEC) including an electrode active material, the electrode active material may be used as the ceramic particles, and the electrode active material may be coated with a coating layer to form ceramic composite particles.

[0215] In addition, in each of the above embodiments, the secondary battery 10 has been described as an anode-free battery in which no negative electrode active material is initially provided. However, the negative electrode layer 12 may be configured to initially include a negative electrode active material. When the negative electrode layer 12 is configured to initially include a negative electrode active material, the negative electrode layer 12 does not need to be porous. The negative electrode active material may be an oxide-based negative electrode active material (e.g., Li ４ Ti ５ O １２ , TiO ２ (B) TiNb ２ O ７ When the negative electrode layer 12 is a porous body, the Li metal may be vapor-deposited on the surface of the porous body.

[0216] Furthermore, in the fifth embodiment, an example in which the positive electrode layer 14 is provided with a solid electrolyte composite has been described, but the negative electrode layer 12 may also be provided with a solid electrolyte composite.

[0217] Furthermore, in the above-described first embodiment, an example has been described in which the anode layer 12 is formed using a slurry containing composite particles composed of a core phase and a shell phase. However, a slurry containing composite particles may be used to form an ion-conductive structure other than the anode layer 12.

[0218] Furthermore, in each of the above embodiments, an example has been described in which the negative electrode layer 12 of the secondary battery 10 is produced by a wet process using a slurry in which particles are dispersed in a solvent, but this is not limiting, and the secondary battery 10 may also be produced by a dry process that does not use a solvent.

[0219] The secondary battery 10 described in each of the above embodiments may also be configured as a bipolar battery. A bipolar battery has a structure in which multiple battery cells are stacked and connected in series, and adjacent battery cells share a current collector. In other words, the current collector that contacts the positive electrode of one adjacent battery cell contacts the negative electrode of the other adjacent battery cell.

[0220] The features of the method for producing an ion-conductive structure disclosed in this specification are as follows: (Item 1) A method for producing an ion-conductive structure, comprising: a slurry preparation step (S21) of preparing a slurry in which composite particles (120) including a core phase (121) made of an oxide-based ion conductor and a shell phase (122) made of an amorphous-containing ion conductor at least partially containing an amorphous phase are dispersed in a solvent; a structure forming step (S22 to S24, S28, S29) of molding a structure using the slurry; and a firing step (S27) of firing the structure to produce an ion-conductive structure, wherein the oxide-based ion conductor has a higher ionic conductivity than the amorphous-containing ion conductor, and the amorphous-containing ion conductor has a smaller Young's modulus than the oxide-based ion conductor. (Item 2) A method for producing an ion-conductive structure according to Item 1, wherein the oxide-based ion conductor is a pyrochlore-type oxide. (Item 3) The pyrochlore-type oxide has a composition formula of Aa ２－α Ab （１＋α）／３ B ２ O ７－β X γItem 4: A method for producing an ion-conductive structure according to any one of items 1 to 3, wherein the amorphous-containing ionic conductor contains at least Li and F in its composition. Item 5: A method for producing an ion-conductive structure according to any one of items 1 to 4, wherein the amorphous-containing ionic conductor contains a crystalline phase and an amorphous phase, and the volume ratio of the amorphous phase is equal to or greater than the volume ratio of the crystalline phase. Item 6: A method for producing an ion-conductive structure according to any one of items 1 to 5, wherein the volume ratio of the core phase in the composite particle is equal to or greater than the volume ratio of the shell phase. (Item 7) A method for producing an ion-conductive structure according to any one of items 1 to 6, wherein the ion-conductive structure has an ordered porous structure in which pores are regularly formed. (Item 8) A method for producing an ion-conductive structure according to any one of items 1 to 7, wherein the molding step involves molding the structure using a 3D printer. (Item 9) A method for producing an ion-conductive structure according to item 8, wherein the slurry contains a photocurable resin, and the molding step includes a laser irradiation step (S23) of curing the photocurable resin by laser irradiation. (Item 10) A method for producing an ion-conductive structure according to any one of items 1 to 9, wherein the slurry contains a light absorbing material having a lower light transmittance than the composite particles. (Item 11) A method for producing an ion-conductive structure according to any one of items 1 to 10, wherein the solid component ratio of the slurry is within a range of 30 to 60 vol %.(Item 12) The ion conductive structure is an anode layer (12) of a secondary battery (10), the secondary battery including a solid electrolyte layer (15) in contact with the anode layer and a cathode layer (14) provided on the solid electrolyte layer opposite the anode layer, and the anode layer is formed on the solid electrolyte layer using the solid electrolyte layer as a substrate. (Item 13) The ion conductive structure according to item 12, wherein the anode layer does not initially contain an anode active material, and elements constituting conduction ions that conduct between the cathode layer and the anode layer can be precipitated in the anode layer. (Item 14) The oxide-based ion conductor contains at least one of a pyrochlore-type oxide and a garnet-type oxide, and the amorphous-containing ion conductor contains at least Li and F in its composition.

[0221] Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and modifications within the scope of equivalents. In addition, although various combinations and forms are shown in the present disclosure, other combinations and forms including only one element, more, or less than one element are also within the scope and spirit of the present disclosure.

Claims

1. a slurry preparation step (S21) of preparing a slurry in which composite particles (120) including a core phase (121) made of an oxide-based ion conductor and a shell phase (122) made of an amorphous-containing ion conductor at least partially containing an amorphous phase are dispersed in a solvent; a structure forming step (S22 to S24, S28, S29) of forming a structure using the slurry; A firing step (S27) of firing the structure to produce an ion conductive structure; Equipped with the oxide-based ionic conductor has a higher ionic conductivity than the amorphous-containing ionic conductor, the amorphous-containing ionic conductor has a smaller Young's modulus than the oxide-based ionic conductor, The oxide-based ion conductor contains conductive ions, and the shell phase suppresses a reaction between the oxide-based ion conductor and a solvent in the slurry, thereby suppressing elution of the conductive ions from the oxide-based ion conductor.

2. A method for producing an ion conductive structure as described in claim 1, wherein the oxide-based ion conductor is a pyrochlore-type oxide.

3. The composition formula of the pyrochlore oxide is Aa 2−α Ab (1+α) / 3 B 2 O 7−β X γ , 3. The method for producing an ion-conductive structure according to claim 2, wherein Aa is an alkali metal, Ab contains at least a lanthanoid, B is a cationic metal different from Aa and Ab, X is an anion that can be substituted for an O atom constituting said pyrochlore-type oxide, and in said composition formula, α is in the range of 0.6<α<2.0, β is in the range of 0<β≦1, and γ is in the range of 0<γ≦1, and the structure contains a defect structure.

4. A method for producing an ion-conductive structure as described in claim 1, wherein the amorphous-containing ion conductor contains at least Li and F in its composition.

5. A method for manufacturing an ion-conductive structure as described in claim 1, wherein the amorphous-containing ion conductor contains a crystalline phase and an amorphous phase, and the volume ratio of the amorphous phase is equal to or greater than the volume ratio of the crystalline phase.

6. A method for producing an ion-conductive structure as described in claim 1, wherein the volume ratio of the core phase in the composite particle is equal to or greater than the volume ratio of the shell phase.

7. A method for producing an ion-conductive structure as described in claim 1, wherein the ion-conductive structure has an ordered porous structure in which pores are regularly formed.

8. A method for manufacturing an ion-conductive structure as described in claim 1, wherein the molding process involves molding the structure using a 3D printer.

9. The slurry contains a photocurable resin, 9. The method for producing an ion-conductive structural member according to claim 8, wherein the molding step includes a laser irradiation step (S23) of curing the photocurable resin by laser irradiation.

10. A method for producing an ion conductive structure as described in claim 1, wherein the slurry contains a light absorbing material having a lower light transmittance than the composite particles.

11. A method for producing an ion-conductive structure as described in claim 1, wherein the solid content of the slurry is in the range of 30 to 60 vol %.

12. The ion conductive structure is a negative electrode layer (12) of a secondary battery (10), The secondary battery includes a solid electrolyte layer (15) in contact with the negative electrode layer, and a positive electrode layer (14) provided on the solid electrolyte layer on the opposite side of the negative electrode layer, The method for producing an ion-conductive structural member according to claim 1 , wherein the negative electrode layer is formed on the solid electrolyte layer, using the solid electrolyte layer as a substrate.

13. The negative electrode layer is initially free of negative electrode active material, 13. The method for producing an ionically conductive structural member according to claim 12, wherein an element constituting conduction ions that conduct between the positive electrode layer and the negative electrode layer can be deposited on the negative electrode layer.

14. The oxide-based ionic conductor contains at least one of a pyrochlore-type oxide and a garnet-type oxide, 2. The method for producing an ion-conductive structural member according to claim 1, wherein the amorphous-containing ion conductor contains at least Li and F in its composition.