Electrode, battery, and production method for electrode

Abstract

An electrode 100 according to the present disclosure includes an electrode active material 20, and a solid electrolyte 10 which is in contact with the electrode active material 20. The solid electrolyte 10 includes a first solid electrolyte 11 and a second solid electrolyte 12 having a composition which differs from the composition of the first solid electrolyte 11. The first solid electrolyte 11 includes a first oxide containing Li, B, Y, and O. The first oxide has a crystal structure belonging to a space group P 21 / c. The second solid electrolyte 12 includes a second oxide containing Li and O. The melting point of the second oxide is lower than the melting point of the first oxide.

Description

Electrode, battery, and method for manufacturing an electrode

[0001] This disclosure relates to electrodes, batteries, and methods for manufacturing electrodes.

[0002] Research and development of solid-state batteries are actively underway as a next-generation battery. One of the challenges of solid-state batteries is that the high resistance of the electrodes prevents the full utilization of the battery capacity. Therefore, there is a need to reduce the resistance of the electrodes. To reduce the resistance of the electrodes, it is important to form a good interface between the solid electrolyte and the electrode active material. For example, a sintered body of a solid electrolyte and an electrode active material easily forms a good interface between the solid electrolyte and the electrode active material, making it suitable for electrodes in solid-state batteries.

[0003] Patent Document 1 describes a positive electrode active material for an all-solid-state battery containing a lithium nickel-based composite oxide, comprising a positive electrode active material including a positive electrode containing the positive electrode, a negative electrode, and a solid electrolyte layer, comprising a positive electrode containing the positive electrode active material, a negative electrode, and a solid electrolyte layer, wherein the positive electrode active material comprises a plurality of primary particles aggregated to form secondary particles in which at least a portion of the primary particles are arranged radially, a first boron coating portion present on the surface of the secondary particles, and a second boron coating portion present on the surface of primary particles inside the secondary particles. Patent Document 1 states that the first boron coating portion and the second boron coating portion each contain boron oxide, lithium boron oxide, or a combination thereof.

[0004] Japanese Patent Publication No. 2023-16671

[0005] This disclosure provides an electrode in which crack formation is suppressed and a battery using the same.

[0006] This disclosure provides an electrode comprising: an electrode active material; and a solid electrolyte in contact with the electrode active material, wherein the solid electrolyte comprises a first solid electrolyte and a second solid electrolyte having a composition different from that of the first solid electrolyte, the first solid electrolyte comprises a first oxide containing Li, B, Y, and O, the first oxide has a crystalline structure belonging to space group P21 / c, and the second solid electrolyte comprises a second oxide containing Li and O, the melting point of the second oxide being lower than that of the first oxide.

[0007] According to this disclosure, it is possible to provide an electrode in which crack formation is suppressed and a battery using the same.

[0008] Figure 1 is a cross-sectional view showing the schematic configuration of the electrode in the first embodiment. Figure 2 is a process diagram showing the manufacturing method of the electrode in the first embodiment. Figure 3 is a cross-sectional view showing the schematic configuration of the battery in the second embodiment. Figure 4 is the powder X-ray diffraction pattern of the sintered body of Example 3. Figure 5 is a scanning electron microscope (SEM) image (5000x magnification) of the cross-section of the positive electrode molded body sample of Example 5 after the firing step. Figure 6 is an SEM image (5000x magnification) of the cross-section of the positive electrode molded body sample of Comparative Example 1 after the firing step.

[0009] (Knowledge forming the basis of this disclosure) Sintered bodies of materials containing a solid electrolyte and an electrode active material are used as electrodes for solid-state batteries. Sintered bodies are manufactured, for example, by simultaneously firing an electrode molded body, which is made by molding a material containing an electrode active material powder and a solid electrolyte powder, attached to a solid electrolyte molded body, which is made by molding a solid electrolyte layer material. The present inventors have obtained the following knowledge regarding electrodes that are sintered bodies. During the firing process of the molded body, cracks may occur in the sintered body due to differences in the thermal shrinkage rate of the electrode molded body and the thermal shrinkage rate of the solid electrolyte molded body. Also, during the charging and discharging process of electrodes made of sintered bodies, cracks may occur in the electrodes due to differences in the expansion and contraction rates of the solid electrolyte and the electrode active material. The occurrence of cracks in electrodes reduces the charge and discharge characteristics of the electrodes, and in some cases, makes it impossible to charge and discharge the electrodes. Patent Document 1 does not adequately consider the viewpoint of suppressing the occurrence of cracks in electrodes.

[0010] The inventors of this invention diligently studied the composition of solid electrolytes in order to realize an electrode that suppresses crack formation and has excellent charge-discharge characteristics, and arrived at the present invention.

[0011] Embodiments of this disclosure will be described below with reference to the drawings. This disclosure is not limited to the embodiments described below.

[0012] (First Embodiment) [Electrode] Figure 1 is a cross-sectional view showing the schematic configuration of the electrode 100 in the first embodiment. The electrode 100 includes an electrode active material 20 and a solid electrolyte 10. The solid electrolyte 10 is in contact with the electrode active material 20. A gap 50 may exist between the solid electrolyte 10 and the electrode active material 20. The electrode 100 is used, for example, as the positive or negative electrode of a solid-state battery.

[0013] The solid electrolyte 10 includes a first solid electrolyte 11 and a second solid electrolyte 12 having a different composition from that of the first solid electrolyte 11. The first solid electrolyte 11 includes a first oxide containing Li, B, Y, and O. The first oxide has a crystalline structure belonging to space group P21 / c. In electrode 100, the first oxide is in a crystalline phase. The second solid electrolyte 12 includes a second oxide containing Li and O. The melting point of the second oxide is lower than that of the first oxide. In electrode 100, the second oxide includes a crystalline phase, an amorphous phase, or a mixed phase of a crystalline phase and an amorphous phase. The second oxide may be an amorphous phase or a mixed phase of a crystalline phase and an amorphous phase. A second oxide having such a configuration is suitable for suppressing crack formation in electrode 100.

[0014] The electrode 100 may be a sintered body. As described above, the electrode 100, which is a sintered body, is manufactured, for example, by co-firing an electrode molded body, which is made by molding a material containing the powder of the electrode active material 20 and the powder of the solid electrolyte 10, with an electrolyte layer molded body, which is made by molding the material of the solid electrolyte layer.

[0015] In this specification, "sintering" refers to the phenomenon in which bonding occurs between particles when a molded body of powder material is heated, resulting in densification of the molded body accompanied by volume shrinkage. "Firing" refers to the heat treatment for sintering.

[0016] In the electrode 100 according to this embodiment, the solid electrolyte 10 includes a first solid electrolyte 11 and a second solid electrolyte 12 having a lower melting point than the first solid electrolyte 11. With this configuration, the second solid electrolyte 12 is likely to be present in the void 50 during the sintering process. The second solid electrolyte 12 may be present filling the void 50, or it may be present spreading to cover the inner circumference of the void 50. This promotes densification of the electrode molded body, reducing the difference between the thermal shrinkage rate of the electrode molded body and the thermal shrinkage rate of the solid electrolyte molded body. As a result, the generation of stress in different directions at the interface between the electrode molded body and the solid electrolyte molded body is mitigated, and the generation of cracks in the sintered body is suppressed. Furthermore, in the electrode 100 made of a sintered body, the generation of stress caused by the difference between the expansion and contraction rates of the first solid electrolyte 11 and the expansion and contraction rates of the electrode active material 20 is mitigated during the charge and discharge process. This is because the second solid electrolyte 12, which is softer than the first solid electrolyte 11, is present in a part of the void 50. As a result, the occurrence of cracks in the electrode 100 is suppressed. Thus, the electrode 100 is suitable for suppressing the occurrence of cracks.

[0017] The fact that the melting point of the second oxide contained in electrode 100 is lower than that of the first oxide can be confirmed, for example, by TG-DTA (thermogravimetric-differential thermal analysis). However, it is assumed that the melting point of the first oxide is known. First, about 10 mg is taken from electrode 100 to be used as a sample. It is desirable that the sample does not contain the electrode active material 20. Measurement is performed while the sample is heated, and a TG-DTA graph is obtained. The TG-DTA graph includes a TG (thermogravimetric) curve and a DTA (differential thermal analysis) curve. Since an endothermic reaction occurs at the melting point of each substance, it appears as an endothermic peak on the DTA curve. By using the tangent method for each endothermic peak, the melting point of each substance can be determined. By comparing the two melting points obtained in this way, it can be confirmed that the melting point of the second oxide is lower than that of the first oxide. The fact that the melting point of the second oxide contained in electrode 100 is lower than that of the first oxide can also be confirmed, for example, by DSC (Differential Scanning Calorimetry). The melting point of each substance appears as an endothermic peak on the DSC curve. The peak temperature of each endothermic peak corresponds to the melting point of each substance. By comparing the two melting points obtained in this way, it can be confirmed that the melting point of the second oxide is lower than that of the first oxide.

[0018] The melting point of the first oxide is, for example, in the range of 850°C to 950°C. The melting point of the second oxide is, for example, in the range of 500°C to less than 850°C.

[0019] As described above, the first solid electrolyte 11 contains a first oxide containing Li, B, Y, and O. The first oxide has a crystalline structure belonging to space group P21 / c. In electrode 100, the first oxide is in a crystalline phase.

[0020] The first oxide may have a composition represented by the following formula (1).

[0021] Li 6-α1-β1 Y 1-α1-β1 Zr α1 Ce β1 B3O9...Formula (1)

[0022] In the above formula (1), 0 ≦ α1 ≦ 0.4 and 0 ≦ β1 ≦ 0.025 are satisfied. The first oxide having the composition represented by the above formula (1) is suitable for improving the potential stability and sinterability of the electrode 100.

[0023] In the above formula (1), at least one selected from the group consisting of 0 < α1 ≦ 0.4 and 0 < β1 ≦ 0.025 may be satisfied. That is, the first oxide may further contain at least one element selected from the group consisting of Zr and Ce. An oxide having such a composition is suitable for improving the potential stability, ionic conductivity, and sinterability of the electrode 100. Such an oxide can be obtained by substituting (doping) at least one doping element selected from the group consisting of Zr and Ce for an oxide composed of Li, B, Y, and O. For example, a part of Li and a part of Y in the oxide composed of Li, B, Y, and O may be substituted with at least one doping element selected from the group consisting of Zr and Ce.

[0024] In the above formula (1), α1 = 0 and β1 = 0 may be satisfied. That is, the first oxide may have a composition represented by Li6YB3O9. In other words, the first oxide may consist of Li, B, Y, and O.

[0025] In the above formula (1), α1 = 0.1 and β1 = 0.025 may be satisfied. That is, the first oxide may have a composition represented by Li 5.875 Y 0.875 Zr 0.1 Ce 0.025 B3O9.

[0026] The first solid electrolyte 11 may contain the first oxide as a main component. "Main component" means the component contained the most in terms of mass ratio. The first solid electrolyte 11 may consist of the first oxide. In this case, except for inevitable impurities, the first solid electrolyte 11 does not contain elements other than the constituent elements of the first oxide.

[0027] The first solid electrolyte 11 is Li 5.875 Y 0.875 Zr 0.1 Ce0.025 It may be composed of a first oxide having a composition represented by B3O9.

[0028] The structure of the first oxide contained in the first solid electrolyte 11 can be evaluated, for example, by X-ray diffraction measurement. The ratio of the components contained in the first oxide can be evaluated, for example, by analyzing the results of X-ray diffraction measurement by the Rietveld method. When the second oxide contained in the second solid electrolyte 12 is a crystal phase, the structure of the second oxide and the ratio of the components contained in the second oxide can be evaluated, for example, by the same method as the first oxide. When the second oxide contained in the second solid electrolyte 12 is an amorphous phase or a mixed phase of a crystal phase and an amorphous phase, the structure of the second oxide can be evaluated, for example, by fluorescent X-ray analysis. The ratio of the components contained in the second oxide can be evaluated, for example, by analyzing the results of fluorescent X-ray analysis by the fundamental parameter method or the calibration curve method. The structure of the third oxide contained in the electrode active material 20 described later and the ratio of the components contained in the third oxide can be evaluated, for example, by the same method as the first oxide.

[0029] In the electrode 100, the first oxide as the first solid electrolyte 11 can exist, for example, in the state of particles having a median diameter of 0.05 μm or more and 50 μm or less.

[0030] In this specification, "median diameter" means the particle diameter when the cumulative volume in the volume-based particle size distribution is 50%. The volume-based particle size distribution is measured by a laser diffraction particle size distribution measuring device at the raw material stage, and at the electrode 100 stage, it is measured by image analysis of the cross section.

[0031] The median diameter of the particles of the first oxide, which serves as the first solid electrolyte 11, may be a value calculated from an electron microscope image of the cross-section of the electrode 100. Specifically, the cross-section of the electrode 100 is observed with a scanning electron microscope (SEM). The magnification is, for example, 3000x. Using image analysis software, the Ferret diameter of the particles of the first oxide present in two or more different observation fields is measured. The "Ferret diameter" is the length of the perpendicular line obtained when the particle is sandwiched between two parallel lines in a fixed direction, and is, for example, the Ferret diameter in the direction defined by the image analysis software (the horizontal direction of the image). The number of particles to be measured is, for example, 185 or more. That is, the width of the observation field is adjusted so that 185 or more particles are included in two or more different observation fields. Next, the volume of each particle is calculated by considering it as a sphere with the measured Ferret diameter. A particle size distribution is created by plotting the particle size (= Ferret diameter, in 0.1 μm increments) on the horizontal axis and the volume it occupies in the whole group of particles with that particle size on the vertical axis. The particle size at which the cumulative volume in this particle size distribution is 50% is considered to be the median diameter of the first oxide particles contained in electrode 100.

[0032] As described above, the second solid electrolyte 12 contains a second oxide containing Li and O. In this embodiment, the second oxide does not contain Y.

[0033] The second solid electrolyte 12 may contain a secondary oxide containing Li, M, and O. M is at least one selected from the group consisting of B, C, P, S, Bi, and Sb. The secondary oxide containing Li, M, and O is suitable for suppressing the occurrence of cracks in the electrode 100.

[0034] The second oxide may have a composition represented by the following formula (2).

[0035] Li α2 M β2 O γ2 ...Formula (2)

[0036] In the above formula (2), the conditions 0 < α² ≤ 3, 0 < β² ≤ 1, and 0 < γ² ≤ 4 are satisfied. The second oxide having the composition represented by the above formula (2) is suitable for suppressing the occurrence of cracks in the electrode 100.

[0037] In the above formula (2), M may be one selected from the group consisting of B, P, S, Bi, and Sb.

[0038] In the above formula (2), M may be B and C.

[0039] In the above formula (2), M is B, and the conditions α2=3, β2=1, and γ2=3 may be satisfied. That is, the second oxide may have a composition represented by Li3BO3.

[0040] In the above formula (2), M is P, and the conditions α2=3, β2=1, and γ2=4 may be satisfied. That is, the second oxide may have a composition represented by Li3PO4.

[0041] In the above formula (2), M is S, and the conditions α2=2, β2=1, and γ2=4 may be satisfied. That is, the second oxide may have a composition represented by Li2SO4.

[0042] In the above formula (2), M is Bi, and α2=1, β2=1, and γ2=2 may be satisfied. That is, the second oxide may have a composition represented by LiBiO2.

[0043] In the above formula (2), M is Sb, and α2=1, β2=1, and γ2=2 may be satisfied. That is, the second oxide may have a composition represented by LiSbO2.

[0044] In the above formula (2), M is B and C, and the conditions α2 = 2.2, β2 = 1, and γ2 = 3 may be satisfied. The second oxide is Li 2.2 B 0.2 C 0.8 It may have a composition represented by O3.

[0045] The second solid electrolyte 12 may contain a second oxide as its main component. The second solid electrolyte 12 may consist solely of the second oxide. In this case, the second solid electrolyte 12, excluding unavoidable impurities, does not contain any elements other than the constituent elements of the second oxide.

[0046] The second solid electrolyte 12 may consist of a second oxide having a composition represented by Li3BO3.

[0047] As described above, in electrode 100, the second oxide includes a crystalline phase, an amorphous phase, or a mixed phase of a crystalline phase and an amorphous phase. A second oxide having such a configuration is suitable for suppressing the occurrence of cracks in electrode 100.

[0048] As described above, the second oxide may be an amorphous phase or a mixed phase of a crystalline phase and an amorphous phase. For example, if the second oxide is an amorphous phase or a mixed phase of a crystalline phase and an amorphous phase, the occurrence of cracks in the electrode 100 is easily suppressed.

[0049] The second oxide is Li3BO3 and Li 2.2 C 0.8 B 0.2 The second oxide may contain at least one selected from the group consisting of O3. A second oxide having such a configuration is suitable for suppressing the occurrence of cracks in the electrode 100.

[0050] R1 is defined as the ratio of the mass of the first solid electrolyte 11 to the total mass of the electrode active material 20 and solid electrolyte 10 contained in the electrode 100. R2 is defined as the ratio of the mass of the second solid electrolyte 12 to the total mass of the electrode active material 20 and solid electrolyte 10 contained in the electrode 100. In this case, R1 may be greater than R2. That is, the electrode 100 may satisfy R1 > R2. With such a configuration, it is easy to realize an electrode 100 that has an excellent balance between suppression of crack occurrence and charge / discharge characteristics.

[0051] The ratio of R1 to R2 (R1 / R2) may be 4 or greater. Electrodes 100 that satisfy R1 / R2 ≥ 4 offer a better balance between crack suppression and charge / discharge characteristics.

[0052] R1 / R2 may be 5 or greater, 8 or greater, 10 or greater, or even 15 or greater.

[0053] The ratio of R1 to R2 (R1 / R2) may be less than 50. R1 / R2 may be 45 or less, 40 or less, 35 or less, 30 or less, 25 or less, or even 20 or less.

[0054] R1 and R2 can be determined, for example, using time-of-flight secondary ion mass spectrometry (TOF-SIMS) as follows. First, a cross-sectional image (magnification 1000x) of the cross-section of the electrode 100 is obtained by TOF-SIMS. The area of ​​the electrode active material 20, the area of ​​the first solid electrolyte 11, and the area of ​​the second solid electrolyte 12 are measured in the cross-sectional image. From the measured values, the ratio of the area of ​​the first solid electrolyte 11 to the total area of ​​the electrode active material 20 and solid electrolyte 10, and the ratio of the area of ​​the second solid electrolyte 12 to the total area of ​​the electrode active material 20 and solid electrolyte 10 are calculated. In this embodiment, the ratio of the area of ​​the first solid electrolyte 11 is considered to be the ratio of the volume of the first solid electrolyte 11 to the total volume of the electrode active material 20 and solid electrolyte 10. Similarly, the ratio of the area of ​​the second solid electrolyte 12 is considered to be the ratio of the volume of the second solid electrolyte 12 to the total volume of the electrode active material 20 and solid electrolyte 10. R1 can be determined by multiplying the volume ratio of the first solid electrolyte 11 by the density of the first solid electrolyte 11. R2 can be determined by multiplying the volume ratio of the second solid electrolyte 12 by the density of the second solid electrolyte 12.

[0055] The electrode active material 20 comprises a third oxide containing Li, Me, and O. Me may be at least one selected from the group consisting of Co, Ni, Mn, and Al.

[0056] In the electrode active material 20 having the above configuration, Li is sufficiently incorporated into the crystal structure of the tertiary oxide contained in the electrode active material 20, so diffusion of Li ions is unlikely to occur. Therefore, the tertiary oxide contained in the electrode active material 20 can be co-fired with the tertiary oxide contained in. Specifically, the electrode active material 20 does not react easily with the tertiary oxide, and the tertiary oxide 12 does not easily react with the electrode active material 20, so a reaction layer containing impurities is unlikely to form at the interface between the tertiary oxide 11, the tertiary oxide 12 and the electrode active material 20 in the sintered body. As a result, excellent ionic conductivity is achieved in the electrode 100.

[0057] A tertiary oxide is a material that has the ability to intercept and release metal ions such as lithium ions. As described above, a tertiary oxide contains Li, Me, and O. Me may be at least one selected from the group consisting of Co, Ni, Mn, and Al. Examples of tertiary oxides include LiCoO2, Li(Ni,Co,Mn)O2, and Li(Ni,Co,Al)O2. In other words, a tertiary oxide may consist of Li, Me, and O. In this disclosure, when an element in a formula is represented as "(Ni,Co,Mn)", this notation indicates at least one element selected from the group of elements in parentheses. That is, "(Ni,Co,Mn)" is synonymous with "at least one selected from the group consisting of Ni, Co, and Mn". The same applies to other elements.

[0058] The tertiary oxide may include at least one selected from the group consisting of LiCoO2, Li(Ni,Co,Mn)O2, and Li(Ni,Co,Al)O2. The tertiary oxide may be LiCoO2 or Li(Ni,Co,Mn)O2.

[0059] The tertiary oxide may further contain a doped element comprising at least one selected from the group consisting of Al, Mg, and Zr. The doped element may be included, for example, by substituting (doping) at least a portion of Ni, Co, and Mn in the tertiary oxide.

[0060] The electrode active material 20 may contain a tertiary oxide as its main component. The electrode active material 20 may consist solely of a tertiary oxide. In this case, the electrode active material 20, excluding unavoidable impurities, does not contain any elements other than the constituent elements of the tertiary oxide. The electrode 100 may contain particles of the tertiary oxide as the electrode active material 20.

[0061] In electrode 100, Li may be present in a first molar ratio of 1.2 to 3.3 relative to Me in electrode active material 20, and B may be present in a second molar ratio of 0.09 to 1.2 relative to Me in electrode active material 20. With such a configuration, the occurrence of cracks in electrode 100 is easily suppressed.

[0062] The first and second molar ratios can be determined, for example, by acid-decomposing a sample from which a portion of electrode 100 has been separated, followed by inductively coupled plasma emission spectroscopy (ICP-OES).

[0063] The first molar ratio may be in the range of 1.25 to 3.25, and the second molar ratio may be in the range of 0.1 to 1.1. With such a configuration, the occurrence of cracks in the electrode 100 is more easily suppressed.

[0064] In electrode 100, the tertiary oxide as the electrode active material 20 may exist in the form of particles having a median diameter of, for example, 0.05 μm to 7 μm. A tertiary oxide having such a configuration is suitable for suppressing the occurrence of cracks in electrode 100.

[0065] In electrode 100, the tertiary oxide as the electrode active material 20 may exist in the form of particles having a median diameter of 0.5 μm or more and 2 μm or less. A tertiary oxide having such a configuration is suitable because it suppresses the occurrence of cracks in electrode 100.

[0066] The median diameter of the third oxide particles as the electrode active material 20 can be determined by the same method as described for determining the median diameter of the first oxide particles as the first solid electrolyte 11.

[0067] The third oxide as the electrode active material 20 may be primary particles, or it may be secondary particles which are aggregates of multiple primary particles.

[0068] The electrode 100 may further include a conductive additive 30. The conductive additive 30 contributes to the formation of conductive paths in the electrode 100. By including the conductive additive 30, the resistance of the electrode 100 can be reduced.

[0069] Examples of conductive additives 30 include carbon materials such as graphite, carbon black, carbon fiber, and carbon nanotubes. Other known materials include metals such as gold, platinum, silver, palladium, aluminum, copper, nickel, stainless steel, and iron, conductive oxides such as ITO, or mixtures thereof. Graphite may be natural graphite or artificial graphite. Examples of carbon black include acetylene black and Ketjen black. Carbon materials may be crystalline or amorphous. Conductive additives 30 typically have particle shapes on the order of nanometers or micrometers. Particle shapes may include spherical, ellipsoidal, flaky, or fibrous.

[0070] The content of the electrode active material 20 in the electrode 100 is, for example, 20% by mass or more and 99% by mass or less. The content of the solid electrolyte 10 in the electrode 100 is, for example, 1% by mass or more and 80% by mass or less. The content of the conductive additive 30 in the electrode 100 is, for example, 0% by mass or more and 30% by mass or less.

[0071] The thickness of the electrode 100 is not particularly limited. For example, the electrode 100 may have a thickness of 4 μm to 200 μm. With such a configuration, it is easier to realize an electrode 100 that is less prone to crack formation.

[0072] The thickness of the electrode 100 can be determined, for example, by observing the cross-section of the electrode 100 with a scanning electron microscope (SEM) and performing image analysis on the obtained cross-sectional image. Specifically, the distance from the surface to the back surface of the electrode 100 is measured at multiple locations along the thickness direction of the electrode 100, and the average of these measured values ​​is considered to be the thickness of the electrode 100.

[0073] [Method for Manufacturing an Electrode] Figure 2 is a process diagram showing the method for manufacturing the electrode 100 in the first embodiment.

[0074] A method for manufacturing the electrode 100 includes, for example, steps ST1, ST2, and ST3. Step ST1 is a step of mixing the electrode active material 20 and the solid electrolyte 10 to obtain a mixed material. The solid electrolyte 10 includes a first solid electrolyte 11 and a second solid electrolyte 12 having a different composition from that of the first solid electrolyte 11. Step ST2 is a step of molding the mixed material to obtain an electrode molded body. Step ST3 is a step of firing the electrode molded body at a temperature of 500°C to 800°C. As described above, the first solid electrolyte 11 includes a first oxide containing Li, B, Y, and O. The first oxide has a crystalline structure belonging to space group P21 / c. The second solid electrolyte 12 includes a second oxide containing Li and O. The melting point of the second oxide is lower than that of the first oxide.

[0075] In this embodiment, step ST3 can be performed with the electrode molded body attached to the solid electrolyte molded body, which is formed from the material of the solid electrolyte layer. According to this manufacturing method, an electrode 100 in which crack occurrence is suppressed can be obtained. Specifically, in step ST3, the second solid electrolyte 12 is more likely to be present in the void 50, and the densification of the solid electrode molded body is promoted, so the difference between the thermal shrinkage rate of the electrode molded body and the thermal shrinkage rate of the solid electrolyte molded body is reduced. As a result, the generation of stress in different directions at the interface between the electrode molded body and the solid electrolyte molded body is mitigated, so the generation of cracks in the sintered body is suppressed. Furthermore, in the electrode 100 made of a sintered body, the generation of stress caused by the difference between the expansion and contraction rates of the first solid electrolyte 11 and the expansion and contraction rates of the electrode active material 20 is mitigated during the charge and discharge process. This is because the second solid electrolyte 12, which is softer than the first solid electrolyte 11, is present in a part of the void 50. As a result, the generation of cracks in the electrode 100 is suppressed.

[0076] According to this embodiment, in step ST3, the difference between the thermal shrinkage rate of the electrode molded body and the thermal shrinkage rate of the solid electrolyte molded body can be reduced. The thermal shrinkage rate of the solid electrolyte molded body in step ST3 is, for example, in the range of 20% to 35%. The thermal shrinkage rate of the electrode molded body in step ST3 is, for example, in the range of 10% to 20%. When the solid electrolyte 10 consists only of the first solid electrolyte 11, the thermal shrinkage rate of the electrode molded body in step ST3 is, for example, less than 10%. When the width of the molded body before step ST3 is defined as r1 and the width of the molded body after step ST3 is defined as r2, the thermal shrinkage rate of the molded body can be calculated from the formula {1 - (r2 / r1)} × 100. The molded body may be a disc-shaped pellet. In this case, the width of the molded body is the diameter of the pellet.

[0077] As described above, the second solid electrolyte 12 may contain a second oxide containing Li, M, and O. M is at least one selected from the group consisting of B, C, P, S, Bi, and Sb. The second oxide containing Li, M, and O is suitable for suppressing the occurrence of cracks in the electrode 100.

[0078] In step ST1, the mixed material may further contain a conductive additive 30. The conductive additive 30 may be a carbon material.

[0079] In step ST1, a mixture of materials containing electrode active material 20, first solid electrolyte 11, and second solid electrolyte 12 is mixed to prepare a slurry-like mixed material. In addition to the electrode active material 20, first solid electrolyte 11, and second solid electrolyte 12, the mixed material may also contain, for example, a conductive additive 30, a binder, and a solvent. Alternatively, the binder and solvent may be mixed beforehand to prepare a binder solution, and the mixed material may be prepared by mixing the electrode active material 20, first solid electrolyte 11, second solid electrolyte 12, and conductive additive 30 into the binder solution.

[0080] Thermoplastic resins such as polyvinyl butyral, polyvinylidene fluoride, cellulose, acrylic, urethane, and polyvinyl alcohol can be used as binders. Typical solvents include organic solvents such as anhydrous alcohol (e.g., anhydrous ethanol), toluene, butyl acetate, ethyl acetate, NMP, terpineol, isopropanol, n-butanol, terpineol, texanol, acetone, methyl ethyl ketone, and cyclohexane. The slurry may also contain a plasticizer. The type of plasticizer is not particularly limited, and phthalate esters such as dioctyl phthalate and diisononyl phthalate can be used. Furthermore, the slurry may contain a dispersant.

[0081] In step ST2, the mixed material is applied to a substrate to form a coating film. The substrate may be a resin substrate, a glass substrate, a ceramic substrate, or a metal substrate. After forming the coating film, the solvent is removed from the coating film. This yields an electrode molded body. To remove the solvent from the coating film, the coating film may be heated or allowed to air dry. If necessary, the coating film may be pressed or hot-pressed. An electrode molded body may also be produced by molding and drying the mixed material without using a substrate. Alternatively, after applying the mixed material to a substrate to form a coating film, the coating film may be pulverized, and the raw material powder obtained by pulverization may be pressed or hot-pressed to produce an electrode molded body.

[0082] The manufacturing method may further include, between step ST2 and step ST3, heating the electrode molded body at a temperature lower than the firing temperature (ambient temperature) to remove the binder (step ST4). In step ST4, the binder contained in the electrode molded body is decomposed and removed; that is, the binder is degreased. This prevents the binder contained in the electrode molded body from rapidly decomposing during firing in step ST3. However, the heating conditions in step ST4 are not particularly limited. Step ST4 is carried out, for example, at a heating temperature (ambient temperature) of 300°C or higher for a heating time of 0.1 to 48 hours. Step ST4 is carried out, for example, under air or an inert atmosphere. The inert atmosphere is, for example, a nitrogen gas atmosphere or a noble gas atmosphere. A small amount of oxygen may also be mixed into the inert atmosphere.

[0083] In step ST3, the electrode molded body is fired at a temperature of 500°C to 800°C. In this embodiment, by using the electrode active material 20, first solid electrolyte 11, and second solid electrolyte 12 having the above configuration, the oxide contained in the electrode active material 20, the first oxide contained in the first solid electrolyte 11, and the second oxide contained in the second solid electrolyte 12 can be co-fired at a relatively low temperature of 500°C to 800°C. Furthermore, the formation of a reaction layer at the interface between the first solid electrolyte 11 and the second solid electrolyte 12 and the electrode active material 20 can be suppressed.

[0084] The lower limit of the firing temperature (ambient temperature) in step ST3 may be 600°C. The upper limit of the firing temperature (ambient temperature) in step ST3 may be 750°C or 700°C. The firing temperature in step ST3 may be in the range of 500°C to 700°C. When the firing temperature in step ST3 is in the range of 500°C to 700°C, the formation of a reaction layer at the interface between the first solid electrolyte 11 and the second solid electrolyte 12 and the electrode active material 20 can be further suppressed.

[0085] Step ST3 is carried out, for example, under air or an inert atmosphere. The inert atmosphere is, for example, a nitrogen gas atmosphere or a noble gas atmosphere. A small amount of oxygen may also be mixed into the inert atmosphere. The firing time for step ST3 is, for example, 0.3 hours to 15 hours.

[0086] If the mixed material contains a carbon material as the conductive additive 30, it is desirable that step ST3 be carried out under an inert atmosphere. This is because if firing is performed under atmospheric conditions, the carbon material is likely to be released into the atmosphere. By performing firing under an inert atmosphere, the release of carbon material into the atmosphere can be suppressed.

[0087] (Second Embodiment) [Battery] Figure 3 is a cross-sectional view showing the schematic configuration of the battery 1000 in the second embodiment.

[0088] The battery 1000 comprises a positive electrode 101, a negative electrode 102, and an electrolyte layer 103. The electrolyte layer 103 is positioned between the positive electrode 101 and the negative electrode 102. The electrode 100 described in the first embodiment is used for either the positive electrode 101 or the negative electrode 102. By using the electrode 100 for either the positive electrode 101 or the negative electrode 102, the battery 1000 can be charged and discharged, and an excellent initial discharge capacity is achieved.

[0089] The electrode 100 described in the first embodiment may be used as a positive electrode 101 or as a negative electrode 102.

[0090] The positive electrode 101 includes a positive electrode active material. The positive electrode active material is a material that has the ability to intercept and release metal ions such as lithium ions. When electrode 100 is used as the positive electrode 101, the positive electrode active material corresponds to the electrode active material 20 described above.

[0091] The negative electrode 102 contains a negative electrode active material. The negative electrode active material is a material that has the ability to intercept and release metal ions such as lithium ions. When electrode 100 is used as the negative electrode 102, the negative electrode active material can be a metal material, a carbon material, an oxide, a nitride, a tin compound, a silicon compound, etc. The metal material may be a pure metal or an alloy. Examples of metal materials include lithium metal and lithium alloys. Examples of carbon materials include natural graphite, coke, carbon in the process of graphitization, carbon fibers, spheroidal carbon, artificial graphite, and amorphous carbon. From the viewpoint of capacity density, at least one selected from the group consisting of silicon (Si), tin (Sn), silicon compounds, and tin compounds can be suitably used as the negative electrode active material. In addition to the negative electrode active material, the negative electrode 102 may also contain a solid electrolyte, a conductive additive, etc.

[0092] The electrolyte layer 103 contains a solid electrolyte. The solid electrolyte is, for example, a sulfide solid electrolyte, a complex hydride solid electrolyte, a porous oxide solid electrolyte impregnated with an electrolyte solution, or an oxide solid electrolyte. The composition of the solid electrolyte contained in the electrolyte layer 103 may be the same as or different from the composition of the solid electrolyte contained in the negative electrode 102. The composition of the solid electrolyte contained in the electrolyte layer 103 may be the same as or different from the composition of the solid electrolyte contained in the positive electrode 101. The positive electrode 101, the electrolyte layer 103, and the negative electrode 102 may all contain solid electrolytes of the same composition.

[0093] In the battery 1000, the positive electrode 101, the negative electrode 102, and the electrolyte layer 103 may be sintered bodies. In this case, the positive electrode 101, the negative electrode 102, and the electrolyte layer 103 can be integrally formed by co-firing. Integrating the positive electrode 101, the negative electrode 102, and the electrolyte layer 103 by co-firing ensures reliable contact between the positive electrode 101, the negative electrode 102, and the electrolyte layer 103. As a result, the conductivity of lithium ions in the battery 1000 can be improved.

[0094] A sintered battery 1000 can be manufactured, for example, by firing a laminate of a positive electrode green sheet, an electrolyte layer green sheet, and a negative electrode green sheet. Each sheet is obtained by coating a slurry containing raw material powder onto a substrate and drying it.

[0095] (Other Embodiments) (Note) The above description of embodiments discloses the following technologies.

[0096] (Technical 1) An electrode comprising: an electrode active material; and a solid electrolyte in contact with the electrode active material, wherein the solid electrolyte includes a first solid electrolyte and a second solid electrolyte having a composition different from that of the first solid electrolyte, the first solid electrolyte includes a first oxide containing Li, B, Y, and O, the first oxide has a crystalline structure belonging to space group P21 / c, the second solid electrolyte includes a second oxide containing Li and O, and the melting point of the second oxide is lower than that of the first oxide.

[0097] The electrode in Technology 1 is suitable for suppressing the occurrence of cracks.

[0098] (Technology 2) The electrode according to Technology 1, wherein the second solid electrolyte comprises a second oxide containing Li, M, and O, and M is at least one selected from the group consisting of B, C, P, S, Bi, and Sb. The second oxide containing Li, M, and O is suitable for suppressing the occurrence of cracks in the electrode.

[0099] (Technology 3) The electrode according to Technology 1 or 2, wherein the second oxide includes a crystalline phase, an amorphous phase, or a mixed phase of a crystalline phase and an amorphous phase. The second oxide having such a configuration is suitable for suppressing the occurrence of cracks in the electrode.

[0100] (Technology 4) An electrode according to any one of Techniques 1 to 3, wherein the ratio of the mass of the first solid electrolyte to the total mass of the electrode active material and the solid electrolyte contained in the electrode is greater than the ratio of the mass of the second solid electrolyte to the total mass. With such a configuration, an electrode that balances crack suppression and charge / discharge characteristics is easily realized.

[0101] (Technical 5) The electrode according to Technical 4, wherein when the ratio of the mass of the first solid electrolyte to the total mass is defined as R1, and the ratio of the mass of the second solid electrolyte to the total mass is defined as R2, the ratio of R1 to R2 (R1 / R2) is 4 or more. Electrodes satisfying R1 / R2≧4 offer an excellent balance between suppression of crack occurrence and charge / discharge characteristics.

[0102] (Technical 6) The electrode according to any one of Technical 1 to 5, wherein the electrode active material comprises a tertiary oxide containing Li, Me, and O, and Me is at least one selected from the group consisting of Co, Ni, Mn, and Al. With such a configuration, excellent ionic conductivity is achieved in the electrode.

[0103] (Technical 7) The electrode according to Technical 6, wherein Li is present in a first molar ratio of 1.2 to 3.3 relative to Me in the electrode active material, and B is present in a second molar ratio of 0.09 to 1.2 relative to Me in the electrode active material. With such a configuration, the occurrence of cracks in the electrode is easily suppressed.

[0104] (Technical 8) The electrode active material is an electrode according to any one of Technical 1 to 5, having a median diameter of 0.5 μm or more and 2 μm or less. An electrode active material having such a configuration is suitable because it suppresses the occurrence of cracks in the electrode.

[0105] (Technical 9) An electrode according to any one of Technical 1 to 8, wherein the electrode is a sintered body. When the electrode is a sintered body, the effect of suppressing crack formation is easily achieved.

[0106] (Technology 10) An electrode according to any one of the technologies 1 to 9, further comprising a carbon material. With such a configuration, the resistance of the electrode can be reduced.

[0107] (Technical 11) A battery comprising: a positive electrode; a negative electrode; and an electrolyte layer disposed between the positive electrode and the negative electrode, wherein the positive electrode or the negative electrode includes an electrode as described in any one of Technical 1 to 10.

[0108] According to the battery of technology 11, it is possible to charge and discharge it, and excellent initial discharge capacity is achieved.

[0109] (Technical 12) The battery according to Technical 11, wherein the positive electrode, the negative electrode, and the electrolyte layer are sintered bodies. With this configuration, the conductivity of lithium ions in the battery can be improved.

[0110] (Technical 13) A method for manufacturing an electrode, comprising: mixing an electrode active material and a solid electrolyte to obtain a mixed material; and firing a molded body of the mixed material at a temperature of 500°C to 800°C, wherein the solid electrolyte comprises a first solid electrolyte and a second solid electrolyte having a composition different from that of the first solid electrolyte; the first solid electrolyte comprises a first oxide containing Li, B, Y, and O; the first oxide has a crystalline structure belonging to space group P21 / c; the second solid electrolyte comprises a second oxide containing Li and O; and the melting point of the second oxide is lower than that of the first oxide.

[0111] According to the electrode manufacturing method of Technology 13, an electrode in which crack formation is suppressed can be obtained.

[0112] (Technical 14) The method for manufacturing an electrode according to Technical 13, wherein the molded body is fired at a temperature of 500°C to 700°C. With this configuration, the formation of a reaction layer at the interface between the first solid electrolyte, the second solid electrolyte and the electrode active material can be further suppressed.

[0113] (Technical 15) The method for manufacturing an electrode according to Technical 13 or 14, wherein the mixed material further contains a carbon material, and the molded body is fired in an inert atmosphere. With such a configuration, the emission of the carbon material into the atmosphere can be suppressed.

[0114] (Technical 16) The method for manufacturing an electrode according to any one of Technical 13 to 15, wherein the mixed material further comprises a binder, and the manufacturing method further comprises heating the molded body at a temperature lower than the firing temperature to remove the binder. With such a configuration, it is possible to suppress the rapid decomposition of the binder contained in the molded body during subsequent firing.

[0115] Details of this disclosure will be explained below using examples and comparative examples.

[0116] [Mixed Materials] <<Example 1>> As the particles of the electrode active material (third oxide), LiCoO2 powder (manufactured by Toyoshima Seisakusho Co., Ltd., median diameter: 5 μm) was prepared. Hereinafter, LiCoO2 with a median diameter of 5 μm will be referred to as LCO-1. ​​As the particles of the first solid electrolyte (first oxide), Li6Y(BO3)3 doped with Zr and Ce was prepared. 5.875 Y 0.875 Zr 0.1 Ce 0.025 (BO3)3 (manufactured by Canon Optron, oxide solid electrolyte LYB-A) powder was prepared. Below, Li 5.875 Y 0.875 Zr 0.1 Ce 0.025 (BO3)3 is referred to as LYBO. LYBO had a crystal structure belonging to the space group P21 / c. The melting point of LYBO was 870°C. As particles of the second solid electrolyte (second oxide), powder of Li3BO3 (manufactured by Toyoshima Seisakusho Co., Ltd.) was prepared. Hereafter, Li3BO3 will be referred to as LBO. The melting point of LBO was 700°C.

[0117] LCO-1, LYBO, and LBO were mixed so that the mass ratio of LCO-1:LYBO:LBO was 50:49:1. The mixing was carried out using a mortar and pestle over a period of 15 minutes. This yielded the mixed material of Example 1.

[0118] <<Example 2>> LCO-1, LYBO, and LBO were mixed so that the mass ratio of LCO-1:LYBO:LBO was 50:47:3. The mixed material of Example 2 was obtained by the same method as in Example 1, except for this.

[0119] <<Example 3>> LCO-1, LYBO, and LBO were mixed so that the mass ratio of LCO-1:LYBO:LBO was 50:45:5. The mixed material of Example 3 was obtained by the same method as in Example 1, except for this step.

[0120] <<Example 4>> LCO-1, LYBO, and LBO were mixed so that the mass ratio of LCO-1:LYBO:LBO was 50:43:7. The mixed material of Example 4 was obtained by the same method as in Example 1, except for this.

[0121] <<Example 5>> LCO-1, LYBO, and LBO were mixed so that the mass ratio of LCO-1:LYBO:LBO was 50:40:10. The mixed material of Example 5 was obtained by the same method as in Example 1, except for this.

[0122] <<Comparative Example 1>> In Comparative Example 1, only LYBO, the first solid electrolyte from Example 1, was used as the solid electrolyte. LCO-1 and LYBO were mixed so that the mass ratio of LCO-1 to LYBO was 50:50. The mixed material of Comparative Example 1 was obtained by the same method as in Example 1, except for this difference.

[0123] <<Comparative Example 2>> In Comparative Example 2, only LBO, the second solid electrolyte from Example 1, was used as the solid electrolyte. LCO-1 and LBO were mixed so that the mass ratio of LCO-1 to LBO was 50:50. The mixed material of Comparative Example 2 was obtained by the same method as in Example 1, except for this difference.

[0124] <<Example 6>> As the electrode active material (third oxide) particles, LiCoO2 powder (manufactured by Toyoshima Seisakusho Co., Ltd., median diameter: 1 μm) was prepared. Hereinafter, LiCoO2 with a median diameter of 1 μm will be referred to as LCO-2. LCO-2, LYBO, and LBO were mixed so that the mass ratio of LCO-2:LYBO:LBO was 50:45:5. The mixed material of Example 6 was obtained by the same method as in Example 1, except for this step.

[0125] <<Example 7>> As particles of the second solid electrolyte (second oxide), Li3BO3 (manufactured by Toyoshima Seisakusho Co., Ltd.) was used as the base material. Raw materials containing a Li source, a B source, and a C source were mixed in a predetermined molar ratio, and the composition was adjusted so that a portion of the C component in the raw materials was replaced with a B component. After that, the Li obtained was subjected to heat treatment. 2.2 B 0.2 C 0.8 O3 was used. Below, Li 2.2 B 0.2 C 0.8O3 is referred to as LBCO. LCO-2, LYBO, and LBCO were mixed so that the mass ratio of LCO-2:LYBO:LBCO was 50:45:5. The mixed material of Example 7 was obtained by the same method as in Example 6, except for this.

[0126] Table 1 shows the median diameter of the electrode active material particles, the ratio of the mass of the electrode active material to the total mass of the electrode active material and solid electrolyte contained in the mixed material, the ratio of the mass of the first solid electrolyte, and the ratio of the mass of the second solid electrolyte. The ratios of the mass of the first solid electrolyte and the mass of the second solid electrolyte were considered as R1 and R2, respectively.

[0127]

[0128] [Calculation of Molar Ratios] The molar ratio of Li to Me and the molar ratio of B to Me in the electrode active material were calculated from the mass ratio of each material in the mixed material shown in Table 1. In this embodiment, Me was Co. The calculated molar ratios of Li and B were considered as the first and second molar ratios, respectively. The results are shown in Table 2.

[0129]

[0130] [Powder X-ray Diffraction Measurement] To investigate the crystal structure of the sintered body made from the mixed material, the following firing test was performed using the mixed material of Example 3. First, the mixed material was molded. Then, the molded body was fired at 650°C for 2 hours in a nitrogen atmosphere to obtain a sintered body. The sintered body was crushed to obtain a pulverized material.

[0131] Powder X-ray diffraction measurements were performed on the pulverized material of the sintered body. The measurement conditions for the powder X-ray diffraction measurements were as follows.

[0132] Device name: MiniFlex600 (manufactured by Rigaku Corporation) X-ray source: Cu-Kα Tube voltage: 15kV Tube current: 40mA Scan speed: 10deg / min Scan step: 0.01deg

[0133] Figure 4 shows the X-ray diffraction pattern of the sintered body of Example 3.

[0134] In the X-ray diffraction pattern of the sintered body of Example 3, a peak attributed to LBO, the second solid electrolyte, was observed. This suggests that the second solid electrolyte in the sintered body is not a completely amorphous phase, but rather a crystalline phase or a mixed phase of crystalline and amorphous phases. Furthermore, the X-ray diffraction pattern of the sintered body of Example 3 contained no peaks other than those attributed to LCO, the electrode active material, LYBO, the first solid electrolyte, and LBO, the second solid electrolyte. In other words, no new crystalline phase (secondary crystalline phase) was formed from the electrode active material, the first solid electrolyte, and the second solid electrolyte in the sintered body of Example 3. From these results, it can be inferred that when using the electrode active material, first solid electrolyte, and second solid electrolyte of Examples 1 to 5, a reaction layer containing impurities is unlikely to form at the interface between the solid electrolyte and the electrode active material in the sintered body.

[0135] [Preparation of Two-Layer Pellets] Two-layer pellets were prepared using the mixed materials of Examples 1 to 5, Comparative Examples 1 to 2, and Examples 6 to 7 by the following method. The two-layer pellet consisted of a positive electrode pellet and a solid electrolyte pellet.

[0136] (Preparation of Binder Solution) A predetermined amount of acrylic resin powder was placed in a 150 mL container as the binder. Super-dehydrated ethanol was added to the container so that the mass ratio of acrylic resin to ethanol was 30:70, and the mixture was stirred until the acrylic resin powder was completely dissolved. The stirring was performed using a mix rotor (AS ONE, VMRC-5) at 50°C, 100 rpm, and for 8 hours. In this way, a binder solution was obtained.

[0137] (Preparation of positive electrode slurry) The mixed materials in the mass ratios shown in Table 1 were placed in a 50 mL container and stirred using a rocking mill (Seiwa Giken Co., Ltd., RM-10) at 700 rpm for 1 hour. A positive electrode mixture was obtained in this manner. Subsequently, a binder solution was added to the container and stirred so that the mass ratio of positive electrode mixture to acrylic resin was 100:18. The stirring was performed using a rotational and revolving mixer (Shinki Co., Ltd., Rentaro) at 2000 rpm for 30 minutes. A positive electrode slurry was obtained in this manner.

[0138] (Preparation of Solid Electrolyte Slurry) The solid electrolyte powder was placed in a 50 mL container. Binder solution was added to the container and stirred so that the mass ratio of solid electrolyte powder to acrylic resin was 100:18. Stirring was performed using a rotational and revolving mixer (Shin-Kee Co., Ltd., Rentaro) at 2000 rpm for 30 minutes. A solid electrolyte slurry was obtained in this manner.

[0139] (Molded body for two-layer pellets) A positive electrode slurry was coated onto a PET film using a replicator, and the coated film was dried on a hot plate at a set temperature of 80°C. After confirming that ethanol had been sufficiently removed from the coated film, the dried film was peeled off the PET film and punched out with an 8 mm diameter hand punch. In this way, a disc-shaped punched film for positive electrode pellets was obtained.

[0140] The solid electrolyte slurry was processed in the same manner as the positive electrode slurry to obtain a disc-shaped die-cut film for solid electrolyte pellets with a diameter of 8 mm. The die-cut film for solid electrolyte pellets was crushed in a mortar for 15 minutes to obtain a raw material powder for solid electrolyte pellets.

[0141] Next, 80 mg of solid electrolyte pellet raw material powder was packed into an 8 mm diameter hand press and pressurized for 60 seconds. Then, 4 mg of positive electrode pellet punched film was packed into the press and pressurized by uniaxial pressing. In this way, a two-layer pellet molded body consisting of a positive electrode pellet molded body and a solid electrolyte pellet molded body was obtained. The pressurizing conditions were 100 MPa for 1 minute.

[0142] The molded body for the two-layer pellet was heated in an electric furnace to degrease the binder. The heating conditions in the degreasing step were 350°C (ambient temperature), under air, for 48 hours, with a gas flow of 50 mL / min and a heating rate of 100°C / hour. Next, the molded body for the two-layer pellet was fired in an electric furnace. The heating conditions in the firing step were 650°C (ambient temperature), under a nitrogen atmosphere, for 2 hours, with a gas flow of 50 mL / min and a heating rate of 100°C / hour. In this way, a two-layer pellet consisting of a positive electrode pellet and a solid electrolyte pellet was obtained.

[0143] [Evaluation of Thermal Shrinkage Rate of Cathode Molded Body] Using the mixed materials of Example 5 and Comparative Example 1, a disc-shaped die-cut film for cathode pellets with a diameter of 8 mm was obtained by the method described above. These were designated as the cathode molded body sample of Example 5 and the cathode molded body sample of Comparative Example 1, respectively. A disc-shaped die-cut film for solid electrolyte pellets with a diameter of 8 mm was obtained by the method described above. This was designated as the solid electrolyte molded body sample. A firing step was performed on both the cathode molded body sample and the solid electrolyte molded body sample under the heating conditions described above. The diameter of each of the cathode molded body sample and solid electrolyte molded body sample was measured after the firing step. When the diameter of the sample before the firing step was defined as r1 and the diameter of the sample after the firing step was defined as r2, the thermal shrinkage rate of the sample was calculated using the formula {1 - (r2 / r1)} × 100. The results are shown in Table 3.

[0144]

[0145] [Evaluation of Cross-Sections of Cathode Molded Bodies] Scanning electron microscope (SEM) images of cross-sections were obtained for the cathode molded body samples of Example 5 and Comparative Example 1 after the firing step. Figure 5 is an SEM image (5000x magnification) of the cross-section of the cathode molded body sample of Example 5 after the firing step. Figure 6 is an SEM image (5000x magnification) of the cross-section of the cathode molded body sample of Comparative Example 1 after the firing step. Note that the cathode molded body sample of Comparative Example 1 had many voids and was easily crumbled, so the cross-section was taken with the voids filled with resin. In Figure 6, the dark gray area corresponds to the resin.

[0146] As shown in Table 3, the thermal shrinkage rate of the solid electrolyte molded body sample was 22%. In contrast, the thermal shrinkage rate of the positive electrode molded body sample of Comparative Example 1 was 8%, showing a significant difference from the thermal shrinkage rate of the solid electrolyte molded body sample. The thermal shrinkage rate of the positive electrode molded body sample of Example 5 was 15%, and the difference from the thermal shrinkage rate of the solid electrolyte molded body sample was suppressed. As can be seen from the comparison between Figure 5 and Figure 6, the occurrence of cracks was suppressed in the positive electrode molded body sample of Example 5 after the firing step compared to the positive electrode molded body sample of Comparative Example 1 after the firing step. From these results, it can be inferred that when the mixed materials of Examples 1 to 5 are used, the generation of stress in different directions at the interface between the electrode molded body and the solid electrolyte molded body is mitigated, and the occurrence of cracks in the sintered body is suppressed.

[0147] [Evaluation of Charge / Discharge Characteristics of Positive Electrode Half Cells] Using the two-layer pellets of Examples 1 to 5, Comparative Examples 1 to 2, and Examples 6 to 7, charge / discharge tests of positive electrode half cells were performed using the following method.

[0148] First, a 290 nm thick Au thin film was formed on the positive electrode pellet side of the two-layer pellet by sputtering using a magnetron sputter coater (Sanyu Electronics, SC-701MC). The film was then dried in a vacuum dryer at 80°C for 12 hours. Next, a 300 μm thick Li metal foil was placed on the solid electrolyte pellet side of the two-layer pellet, with the solid polymer electrolyte film in between. In other words, the solid polymer electrolyte film was laminated so that the Au thin film, two-layer pellet, solid polymer electrolyte film, and Li metal foil were arranged in this order, thereby obtaining a laminate. A LiTFSI-PEO film was used as the solid polymer electrolyte film. The molar ratio of PEO to LiTFSI in the LiTFSI-PEO film was 18:1. The laminate was placed in a sealed two-electrode cell (Hosen Co., Ltd., HS flat cell) to obtain a positive electrode half-cell. To avoid pellet cracking, a spring constant of 1000 gf / mm was selected for the lamination direction of the laminate. The above cell assembly was performed in a glove box with a dew point of -80°C using cells (HS flat cells manufactured by Hosen Co., Ltd.).

[0149] Next, a charge-discharge test of the positive electrode half-cell was performed in constant current (CC) mode at 60°C, and the charge-discharge curve for the first cycle was obtained. The cell was charged with a constant current of 0.02C until the voltage reached 4.2V, and then rested for 3 hours after charging. Subsequently, it was discharged with a constant current of 0.02C until the voltage reached 3.0V, and then rested for 3 hours after discharge. An electrochemical evaluation device (Biologic, VSP-300) was used for charging and discharging. The results are shown in Table 4. In the positive electrode half-cell, the side into which Li is inserted corresponds to discharge, and the side from which Li is removed corresponds to charging. In Table 4, the charging capacity of the positive electrode half-cell obtained from the charge-discharge curve for the first cycle is labeled as "initial discharge capacity". In this disclosure, "C rate" refers to the multiplier of the current value based on the theoretical capacity (theoretical relative capacity) of the electrode active material. For example, a current value of 1C is the current value that charges and discharges the theoretical capacity in 1 hour.

[0150] Furthermore, the charge and discharge cycles were repeated under the same conditions, and the discharge capacity after the third cycle was measured. The discharge capacity retention rate after the third cycle was calculated by dividing the discharge capacity after the third cycle by the initial discharge capacity and multiplying by 100. The results are shown in Table 4.

[0151]

[0152] ≪Discussion≫ As shown in Table 4, the positive electrode half-cells of Examples 1 to 5 and Examples 6 to 7 showed improved initial discharge capacity and discharge capacity retention rate in the third cycle compared to the positive electrode half-cell of Comparative Example 1. This is thought to be because the occurrence of cracks in the positive electrode pellet molded body was suppressed during the firing process in the positive electrodes of Examples 1 to 5 and Examples 6 to 7. In addition, in the positive electrode half-cell of Comparative Example 2, which used only LBO, the second solid electrolyte of Example 1, the ionic conductivity of LBO is about an order of magnitude lower than that of LYBO, resulting in high cell resistance and making charging and discharging impossible.

[0153] Furthermore, in Examples 6 to 7, which used a positive electrode active material with a smaller median diameter (median diameter: 1 μm) than the positive electrode active material (median diameter: 5 μm) used in Examples 1 to 5, both the initial discharge capacity and the discharge capacity retention rate after 3 cycles were improved compared to the positive electrode half-cells of Examples 1 to 5. This result suggests that reducing the median diameter of the positive electrode active material can suppress crack formation in the electrode, thereby improving charge-discharge characteristics. For example, when the median diameter of the positive electrode active material is between 0.5 μm and 2 μm, crack formation is more easily suppressed, and it is thought that an electrode with even better charge-discharge characteristics can be realized.

[0154] The electrodes of this disclosure are suitable for use as electrodes in solid-state batteries.

Claims

1. An electrode comprising: an electrode active material; and a solid electrolyte in contact with the electrode active material, wherein the solid electrolyte comprises a first solid electrolyte and a second solid electrolyte having a composition different from that of the first solid electrolyte, the first solid electrolyte comprises a first oxide containing Li, B, Y, and O, the first oxide has a crystalline structure belonging to space group P21 / c, the second solid electrolyte comprises a second oxide containing Li and O, and the melting point of the second oxide is lower than that of the first oxide.

2. The electrode according to claim 1, wherein the second solid electrolyte comprises a second oxide containing Li, M, and O, and M is at least one selected from the group consisting of B, C, P, S, Bi, and Sb.

3. The electrode according to claim 1, wherein the second oxide comprises a crystalline phase, an amorphous phase, or a mixed phase of a crystalline phase and an amorphous phase.

4. The electrode according to claim 1, wherein the ratio of the mass of the first solid electrolyte to the total mass of the electrode active material and the solid electrolyte contained in the electrode is greater than the ratio of the mass of the second solid electrolyte to the total mass.

5. The electrode according to claim 4, wherein when the ratio of the mass of the first solid electrolyte to the total mass is defined as R1, and the ratio of the mass of the second solid electrolyte to the total mass is defined as R2, the ratio of R1 to R2 (R1 / R2) is 4 or more.

6. The electrode according to claim 1, wherein the electrode active material comprises a tertiary oxide containing Li, Me, and O, and Me is at least one selected from the group consisting of Co, Ni, Mn, and Al.

7. The electrode according to claim 6, wherein Li is present in a first molar ratio of 1.2 to 3.3 with respect to Me contained in the electrode active material, and B is present in a second molar ratio of 0.09 to 1.2 with respect to Me contained in the electrode active material.

8. The electrode according to claim 1, wherein the electrode active material has a median diameter of 0.5 μm or more and 2 μm or less.

9. The electrode according to claim 1, wherein the electrode is a sintered body.

10. The electrode according to claim 1, further comprising a carbon material.

11. A battery comprising: a positive electrode; a negative electrode; and an electrolyte layer disposed between the positive electrode and the negative electrode, wherein the positive electrode or the negative electrode includes the electrode described in any one of claims 1 to 10.

12. The battery according to claim 11, wherein the positive electrode, the negative electrode, and the electrolyte layer are sintered bodies.

13. A method for manufacturing an electrode, comprising: mixing an electrode active material and a solid electrolyte to obtain a mixed material; and firing a molded body of the mixed material at a temperature of 500°C to 800°C, wherein the solid electrolyte comprises a first solid electrolyte and a second solid electrolyte having a composition different from that of the first solid electrolyte; the first solid electrolyte comprises a first oxide containing Li, B, Y, and O; the first oxide has a crystalline structure belonging to space group P21 / c; the second solid electrolyte comprises a second oxide containing Li and O; and the melting point of the second oxide is lower than that of the first oxide.

14. The method for manufacturing an electrode according to claim 13, wherein the molded body is fired at a temperature of 500°C or more and 700°C or less.

15. The method for manufacturing an electrode according to claim 13, wherein the mixed material further contains a carbon material, and the molded body is fired in an inert atmosphere.

16. The method for manufacturing an electrode according to claim 13, wherein the mixed material further comprises a binder, and the manufacturing method further comprises heating the molded body at a temperature lower than the firing temperature to remove the binder.

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