Electrode, battery, and production method for electrode

Abstract

An electrode 100 according to the present disclosure comprises an electrode active material 20 and a solid electrolyte 10 that is in contact with the electrode active material 20. The electrode active material 20 contains an oxide 21 containing lithium, titanium, and oxygen. In the oxide 21 contained in the electrode active material 20, the ratio of a substance amount M2 of lithium to a substance amount M1 of titanium (M2 / M1) is greater than 0.8. The solid electrolyte 10 contains an oxide containing lithium, boron, yttrium, and oxygen. The oxide contained in the solid electrolyte 10 includes a crystal structure belonging to a space group P21 / c.

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 an all-solid-state battery comprising a negative electrode having a negative electrode active material layer containing a negative electrode active material and a solid electrolyte, a positive electrode having a positive electrode active material layer, and a solid electrolyte layer. The negative electrode active material is TiO2 and Li4Ti5O 12 A titanium compound containing one or both of the following, and the solid electrolyte is Li 1+x Al x Ge 2-x It may be an LAGP compound represented by (PO4)3. The all-solid-state battery includes a sintered body obtained by firing a laminate containing a negative electrode active material layer, a solid electrolyte layer, and a positive electrode active material layer.

[0004] International Publication No. 2023 / 282146

[0005] This disclosure provides an electrode with excellent ion conductivity 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 electrode active material comprises an oxide containing lithium, titanium, and oxygen, and in the oxide contained in the electrode active material, the ratio of the amount of substance of lithium to the amount of substance of titanium is greater than 0.8; and the solid electrolyte comprises an oxide containing lithium, boron, yttrium, and oxygen, and the oxide contained in the solid electrolyte has a crystal structure belonging to space group P21 / c.

[0007] According to the present disclosure, an electrode excellent in ionic conductivity and a battery using the same can be provided.

[0008] FIG. 1 is a cross-sectional view showing a schematic configuration of an electrode in the first embodiment. FIG. 2 is a process diagram showing a method for manufacturing the electrode in the first embodiment. FIG. 3 is a cross-sectional view showing a schematic configuration of a battery in the second embodiment. FIG. 4A is a powder X-ray diffraction pattern of (a) a sintered body, (b) an electrode active material, and (c) a solid electrolyte in Example 1. FIG. 4B is a partially enlarged view of the powder X-ray diffraction patterns of (a) to (c) in FIG. 4A. FIG. 5 is a powder X-ray diffraction pattern of (a) a sintered body, (b) an electrode active material, and (c) a solid electrolyte in Comparative Example 1. FIG. 6 is a powder X-ray diffraction pattern of (a) a sintered body, (b) an electrode active material, and (c) a solid electrolyte in Comparative Example 2. FIG. 7 is a charge-discharge curve of the first cycle of the negative electrode half-cell in Example 1.

[0009] (Finding underlying the present disclosure) When producing a sintered body by firing a material containing a solid electrolyte and an electrode active material, the solid electrolyte and the electrode active material may react with each other, and a reaction layer containing impurities may be formed at the interface between the two. The reaction layer inhibits the movement of ions in the sintered body. When the sintered body with the formed reaction layer is used as an electrode, the charge-discharge characteristics of the electrode deteriorate. In Patent Document 1, sufficient consideration has not been given to the viewpoint of suppressing the formation of the reaction layer in the sintered body.

[0010] The present inventors have intensively studied the combination of a solid electrolyte and an electrode active material in order to suppress the formation of the reaction layer and realize an electrode having excellent ionic conductivity, and arrived at the present invention.

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments.

[0012] (First Embodiment) [Electrode] FIG. 1 is a cross-sectional view showing a schematic configuration of an 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.

[0013] The electrode active material 20 contains an oxide containing lithium, titanium, and oxygen. In the oxide contained in the electrode active material 20, the ratio (M2 / M1) of the amount of substance M2 of lithium to the amount of substance M1 of titanium is greater than 0.8. The solid electrolyte 10 contains an oxide containing lithium, boron, yttrium, and oxygen. The oxide contained in the solid electrolyte 10 has a crystal structure belonging to the space group P21 / c.

[0014] In the electrode active material 20 having the above structure, since lithium is sufficiently incorporated into the crystal structure of the oxide contained in the electrode active material 20, the diffusion of lithium ions is unlikely to occur. Therefore, the oxide contained in the electrode active material 20 can be co-fired with the oxide contained in the solid electrolyte 10 having the above structure. Specifically, the electrode active material 20 and the solid electrolyte 10 are unlikely to react during firing, and a reaction layer containing impurities is unlikely to be formed at the interface between the solid electrolyte 10 and the electrode active material 20 in the sintered body. As a result, since the crystal structure of the oxide contained in the electrode active material 20 and the crystal structure of the oxide contained in the solid electrolyte 10 are maintained, excellent ion conductivity is realized in the electrode 100.

[0015] The electrode 100 is manufactured, for example, by firing a molded body of a material containing the powder of the electrode active material 20 and the powder of the solid electrolyte 10. The electrode 100 can be a sintered body. As described above, when the electrode 100 is a sintered body, it is possible to form a good interface between the electrode active material 20 and the solid electrolyte 10. Further, although both the electrode active material 20 and the solid electrolyte 10 contain oxides, the ion conductivity of the electrode 100 can be increased. Furthermore, when the electrode 100 is a sintered body, it is possible to manufacture a solid battery by co-firing the electrode 100, a second electrode as a counter electrode, and an electrolyte layer.

[0016] The electrode 100 is used, for example, as the positive electrode or the negative electrode of a solid battery.

[0017] In this specification, "sintering" means a phenomenon in which when a molded body of a powder material is heated, a bond occurs between particles and the molded body is densified with volume shrinkage. "Firing" means a heat treatment for sintering.

[0018] The lower limit of the ratio (M2 / M1) in the electrode active material 20 may be 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, or even 1.5. The upper limit of the ratio (M2 / M1) is, for example, 2.5. The upper limit of the ratio (M2 / M1) may also be 2.4, 2.3, or even 2.2.

[0019] The ratio (M2 / M1) in the electrode active material 20 may be in the range of 1.5 to 2.5. Electrode active material 20 with a ratio (M2 / M1) in the range of 1.5 to 2.5 is less prone to lithium ion diffusion.

[0020] The ratio (M2 / M1) in the electrode active material 20 may be in the range of 1.8 to 2.2. Electrode active material 20 with a ratio (M2 / M1) in the range of 1.8 to 2.2 is even less prone to lithium ion diffusion.

[0021] The oxide contained in the electrode active material 20 is a material that has the ability to intercept and release metal ions such as lithium ions. As described above, the oxide contained in the electrode active material 20 contains lithium, titanium, and oxygen, and in the oxide, the ratio of the amount of substance of lithium M2 to the amount of substance of titanium M1 (M2 / M1) is greater than 0.8. Examples of oxides containing lithium, titanium, and oxygen include Li4TiO4, Li2TiO3, Li2Ti2O5, and Li4Ti5O 12 Examples include lithium titanates such as Li2Ti3O7 and LiTiO2. In other words, the oxide contained in the electrode active material 20 may consist of lithium, titanium, and oxygen. Among these, Li4TiO4, Li2TiO3, LiTiO2, and Li2Ti2O5 are suitable because their ratio (M2 / M1) is greater than 0.8.

[0022] The oxide contained in the electrode active material 20 may have a crystal structure belonging to the space group C2 / c. By using an oxide having a crystal structure belonging to the space group C2 / c, the effect of achieving excellent ionic conductivity in the electrode 100 is easily realized.

[0023] The structure of the oxide contained in the electrode active material 20 can be evaluated by X-ray diffraction measurement. The ratio of components contained in the oxide can be evaluated by analyzing the results of the X-ray diffraction measurement using the Rietveld method. The structure of the oxide contained in the solid electrolyte 10 and the ratio of components contained in the oxide can also be evaluated by the same method.

[0024] The oxide contained in the electrode active material 20 may include at least one selected from the group consisting of Li4TiO4, Li2TiO3, LiTiO2, and Li2Ti2O5. The oxide contained in the electrode active material 20 may also be Li2TiO3.

[0025] The electrode active material 20 may mainly consist of an oxide containing lithium, titanium, and oxygen. The electrode active material 20 may consist of an oxide containing lithium, titanium, and oxygen. In this case, the electrode active material 20 does not contain any elements other than the constituent elements of the oxide, except for unavoidable impurities. The electrode 100 may contain particles of an oxide containing lithium, titanium, and oxygen as the electrode active material 20. "Main component" means the component that is present in the largest amount by mass.

[0026] In electrode 100, the oxide as the electrode active material 20 may exist in the form of particles having a median diameter of, for example, 0.05 μm or more and 7 μm or less.

[0027] The median diameter of the oxide particles as the electrode active material 20 can 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, 3000 times. Using image analysis software, the Feret diameter of the oxide particles present in two different observation fields of view is measured. The "Feret diameter" is the length of the perpendicular line formed by sandwiching the particle with two parallel lines in a fixed direction. The number of particles to be measured is, for example, 185 or more. That is, the size of the observation field of view is adjusted so that 185 or more particles are included in two different observation fields of view. Next, the volume of each particle is calculated by regarding it as a sphere having the measured Feret diameter. A particle size distribution is created with the particle size (= Feret diameter, 0.1 μm intervals) on the horizontal axis and the volume occupied by the group of particles having that particle size on the vertical axis. The particle diameter when the cumulative volume in this particle size distribution is 50% is regarded as the median diameter of the oxide particles contained in the electrode 100.

[0028] In this specification, the "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 type particle size distribution measuring device at the raw material stage. At the stage of the electrode 100, it is measured by image analysis of the cross section.

[0029] As described above, the solid electrolyte 10 contains an oxide containing lithium, boron, yttrium and oxygen, and the oxide has a crystal structure belonging to the space group P21 / c. The oxide contained in the solid electrolyte 10 may have a composition represented by the following formula (1). The oxide having the composition represented by the following formula (1) is suitable for improving the potential stability and sinterability of the electrode 100.

[0030] Li 6-x-y Y 1-x-y Zr x Ce y B3O9 ··· Formula (1)

[0031] In the above formula (1), 0 ≤ x ≤ 0.4 and 0 ≤ y ≤ 0.025 are satisfied.

[0032] In the above formula (1), at least one selected from the group consisting of 0 < x ≤ 0.4 and 0 < y ≤ 0.025 may be satisfied. That is, the oxide contained in the solid electrolyte 10 may further contain at least one element selected from the group consisting of Zr and Ce. Oxides having such a composition are suitable for improving the potential stability and sinterability of the electrode 100. Oxides having such a composition can be obtained by doping an oxide consisting of lithium, boron, yttrium, and oxygen with at least one element selected from the group consisting of Zr and Ce. For example, a portion of the lithium and a portion of the yttrium in an oxide consisting of lithium, boron, yttrium, and oxygen may be substituted with at least one element selected from the group consisting of Zr and Ce.

[0033] In the above formula (1), x = 0 and y = 0 may be satisfied. That is, the oxide contained in the solid electrolyte 10 may have a composition represented by Li6YB3O9. That is, the oxide contained in the solid electrolyte 10 may consist of lithium, boron, yttrium, and oxygen.

[0034] In the above equation (1), x = 0.1 and y = 0.025 may also be satisfied. That is, the oxide contained in the solid electrolyte 10 is Li 5.875 Y 0.875 Zr 0.1 Ce 0.025 It may have a composition represented by B3O9.

[0035] The solid electrolyte 10 may mainly consist of an oxide containing lithium, boron, yttrium, and oxygen. In this case, the solid electrolyte 10 does not contain any elements other than the constituent elements of the oxide, except for unavoidable impurities.

[0036] The solid electrolyte 10 is Li 5.875 Y 0.875 Zr 0.1 Ce 0.025 It may consist of an oxide having a composition represented by B3O9.

[0037] In electrode 100, the oxide as the solid electrolyte 10 may exist in the form of particles having a median diameter of, for example, 0.05 μm or more and 50 μm or less.

[0038] The median diameter of the oxide particles as the solid electrolyte 10 can be determined by the same method as described for determining the median diameter of the oxide particles as the electrode active material 20.

[0039] In the powder X-ray diffraction pattern of the pulverized material of electrode 100 using Cu-Kα rays, the integrated intensity of the first peak, which is the maximum peak in the diffraction angle range 2θ of 17° to 19°, is I (17°-19°) The integral intensity I of the second peak, which is the largest peak in the diffraction angle range 2θ between 27.5° and 29°. (27.5°-29°) The sum of these is the integral intensity I of the third peak, which is the largest peak in the diffraction angle range 2θ between 33° and 35°. (33°-35°) The value obtained by dividing by (I (33°-35°) (I (27.5°-29°) +I (17°-19°) )) may be between 0 and 0.1. The integral intensity I of the third peak (33°-35°) This is thought to reflect the reaction layer containing newly generated impurities. (33°-35°) (I (27.5°-29°) +I (17°-19°) When the value is 0 or greater and 0.1 or less, the crystal structure of the oxide contained in the electrode active material 20 and the crystal structure of the oxide contained in the solid electrolyte 10 are maintained in the sintered body of the electrode 100, and the formation of a reaction layer is sufficiently suppressed. Therefore, excellent ionic conductivity is achieved in the electrode 100 equipped with the electrode active material 20 and the solid electrolyte 10.

[0040] I (33°-35°) (I (27.5°-29°) +I (17°-19°) The lower limit of ) may be 0.01, 0.02, 0.03, or even 0.04. (33°-35°) (I (27.5°-29°) +I (17°-19°) The upper limit of ) may be 0.09, 0.08, 0.07, or even 0.06.

[0041] Electrode 100 is 0.02 ≤ I (33°-35°) (I (27.5°-29°) +I(17°-19°) The condition ) ≤ 0.03 may also be satisfied.

[0042] The integrated intensity of powder X-ray diffraction peaks can be calculated, for example, using software included with the X-ray diffraction apparatus (e.g., PDXL, included with Rigaku's powder X-ray diffraction apparatus). In this case, the integrated intensity of powder X-ray diffraction peaks can be obtained, for example, from the height of each diffraction peak.

[0043] Generally, in powder X-ray diffraction patterns using Cu-Kα rays, for crystal structures belonging to space group P21 / c, the maximum peak in the diffraction angle range 2θ between 27.5° and 29° reflects the (11-2) plane.

[0044] Generally, in powder X-ray diffraction patterns using Cu-Kα rays, for crystal structures belonging to the space group C2 / c, the largest peak in the diffraction angle range 2θ between 17° and 19° reflects the (002) plane.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] [Method for Manufacturing an Electrode] Figure 2 is a process diagram showing the method for manufacturing the electrode 100 in the first embodiment.

[0049] 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. Step ST2 is a step of obtaining a molded body of the mixed material. Step ST3 is a step of firing the molded body of the mixed material at a temperature of 500°C to 800°C. The electrode active material 20 contains an oxide containing lithium, titanium, and oxygen, and in the oxide, the ratio of the amount of substance of lithium M2 to the amount of substance of titanium M1 (M2 / M1) is greater than 0.8. The solid electrolyte 10 contains an oxide containing lithium, boron, yttrium, and oxygen, and the oxide has a crystalline structure belonging to space group P21 / c.

[0050] According to this manufacturing method, the crystalline structure of the oxide contained in the electrode active material 20 and the crystalline structure of the oxide contained in the solid electrolyte 10 are maintained in the sintered body. Therefore, an electrode 100 can be obtained that can achieve excellent ionic conductivity.

[0051] In step ST1, the mixed material may further contain a conductive additive 30. The conductive additive 30 may be a carbon material.

[0052] In step ST1, a mixture of materials containing the electrode active material 20 and the solid electrolyte 10 is mixed to prepare a slurry-like mixed material. In addition to the electrode active material 20 and the solid electrolyte 10, 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, the solid electrolyte 10, and the conductive additive 30 into the binder solution.

[0053] 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.

[0054] 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 a molded body of the mixed material. 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. Alternatively, a molded body may be produced by molding and drying the mixed material without using a substrate. After applying the mixed material to a substrate to form a coating film, the coating film may be crushed, and the raw material powder obtained by crushing may be pressed or hot-pressed to produce a molded body.

[0055] The manufacturing method may further include, between step ST2 and step ST3, heating the molded body of the mixed material to remove the binder (step ST4). In step ST4, the binder contained in the molded body is decomposed and removed; that is, the binder is degreased. In step ST4, the molded body may be heated at a temperature (ambient temperature) lower than the firing temperature (ambient temperature) in step ST3. This prevents the binder contained in the molded body from rapidly decomposing due to the 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 hours 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.

[0056] In step ST3, the molded body is fired at a temperature of 500°C to 800°C. In this embodiment, by using the electrode active material 20 and solid electrolyte 10 having the above configuration, the oxide contained in the electrode active material 20 and the oxide contained in the solid electrolyte 10 can be co-fired at a relatively low temperature of 500°C to 800°C.

[0057] 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 solid electrolyte 10 and the electrode active material 20 can be further suppressed.

[0058] 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.

[0059] 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.

[0060] (Second Embodiment) [Battery] Figure 3 is a cross-sectional view showing the schematic configuration of the battery 1000 in the second embodiment.

[0061] 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.

[0062] The electrode 100 described in the first embodiment is suitable for use as a negative electrode 102.

[0063] The positive electrode 101 contains 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. Examples of positive electrode active materials include lithium-containing transition metal oxides and lithium-containing transition metal phosphates. Among these, lithium-containing transition metal oxides are suitable for the positive electrode 101. Examples of lithium-containing transition metal oxides include lithium cobaltate, lithium nickelate, lithium manganeseate, and lithium cobalt nickel manganese composite oxide. In addition to the positive electrode active material, the positive electrode 101 may also contain a solid electrolyte, a conductive additive, and the like.

[0064] 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 positive electrode 101. 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 positive electrode 101, the electrolyte layer 103, and the negative electrode 102 may all contain solid electrolytes of the same composition.

[0065] 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.

[0066] 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.

[0067] (Other Embodiments) (Note) The above description of embodiments discloses the following technologies.

[0068] (Technical 1) An electrode comprising: an electrode active material; and a solid electrolyte in contact with the electrode active material, wherein the electrode active material comprises an oxide containing lithium, titanium, and oxygen, and in the oxide contained in the electrode active material, the ratio of the amount of substance of lithium to the amount of substance of titanium is greater than 0.8; and the solid electrolyte contains an oxide containing lithium, boron, yttrium, and oxygen, and the oxide contained in the solid electrolyte has a crystal structure belonging to space group P21 / c.

[0069] According to the electrode of Technology 1, excellent ionic conductivity is achieved.

[0070] (Technology 2) The electrode according to Technology 1, wherein the ratio in the electrode active material is in the range of 1.5 to 2.5. Electrode active materials in which the ratio is in the range of 1.5 to 2.5 are less prone to lithium ion diffusion.

[0071] (Technology 3) The electrode according to Technology 1 or 2, wherein the ratio in the electrode active material is in the range of 1.8 or more and 2.2 or less. The electrode active material in which the ratio is in the range of 1.8 or more and 2.2 or less is even less prone to lithium ion diffusion.

[0072] (Technical 4) The electrode according to any one of Technical 1 to 3, wherein the oxide contained in the electrode active material has a crystal structure belonging to the space group C2 / c. With such a configuration, the effect of achieving excellent ionic conductivity in the electrode is easily realized.

[0073] (Technical 5) The oxide contained in the solid electrolyte has a composition represented by the following formula (1): Li 6-x-y Y 1-x-y Zr x Ce y B3O9 ... Formula (1) An electrode according to any one of the techniques 1 to 4, wherein the conditions 0 ≤ x ≤ 0.4 and 0 ≤ y ≤ 0.025 are satisfied in formula (1). Oxides having such a composition are suitable for improving the potential stability and sinterability of electrodes.

[0074] (Technical 6) The electrode according to Technical 5, wherein the conditions x = 0.1 and y = 0.025 are satisfied in formula (1). Oxides having such a composition are suitable for improving the potential stability and sinterability of electrodes.

[0075] (Technical 7) An electrode according to any one of Technical 1 to 6, wherein the electrode is a sintered body. Because the electrode is a sintered body, it is possible to form a good interface between the electrode active material and the solid electrolyte. Furthermore, it is possible to manufacture a solid battery by simultaneously firing the electrode, the second electrode as a counter electrode, and the electrolyte layer.

[0076] (Technical 8) In the powder X-ray diffraction pattern of the pulverized electrode using Cu-Kα rays, the integrated intensity of the first peak, which is the largest peak in the diffraction angle range 2θ of 17° to 19°, is I (17°-19°) The integral intensity I of the second peak, which is the largest peak in the diffraction angle range 2θ between 27.5° and 29°. (27.5°-29°) The sum of these is the integral intensity I of the third peak, which is the largest peak in the diffraction angle range 2θ between 33° and 35°. (33°-35°) The value obtained by dividing by (I (33°-35°) (I (27.5°-29°) +I (17°-19°) An electrode according to any one of the technical items 1 to 7, wherein the value of )) is 0 or more and 0.1 or less. (33°-35°) (I (27.5°-29°) +I (17°-19°) When the value is between 0 and 0.1, excellent ionic conductivity is achieved in an electrode equipped with an electrode active material and a solid electrolyte.

[0077] (Technical 9) An electrode according to any one of Technical 1 to 8, further comprising a carbon material. With such a configuration, the resistance of the electrode can be reduced.

[0078] (Technical 10) 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 claim 1.

[0079] According to the battery of technology 10, it is possible to charge and discharge it, and excellent initial discharge capacity is achieved.

[0080] (Technical 11) The battery according to Technical 10, wherein the positive electrode, the negative electrode, and the electrolyte layer are sintered bodies. With such a configuration, the conductivity of lithium ions in the battery can be improved.

[0081] (Technical 12) 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 electrode active material comprises an oxide containing lithium, titanium, and oxygen, the ratio of the amount of substance of lithium to the amount of substance of titanium in the oxide contained in the electrode active material is greater than 0.8, and the solid electrolyte comprises an oxide containing lithium, boron, yttrium, and oxygen, and the oxide contained in the solid electrolyte has a crystal structure belonging to space group P21 / c.

[0082] According to the electrode manufacturing method of Technology 12, an electrode can be obtained in which the crystal structure of the oxide contained in the electrode active material and the crystal structure of the oxide contained in the solid electrolyte are maintained in the sintered body, thereby achieving excellent ionic conductivity.

[0083] (Technical 13) The method for manufacturing an electrode according to Technical 12, wherein the molded body of the mixed material 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 solid electrolyte and the electrode active material can be further suppressed.

[0084] (Technical 14) The method for manufacturing an electrode according to Technical 12 or 13, wherein the mixed material further contains a carbon material, and in the firing process, a molded body of the mixed material is fired in an inert atmosphere. With such a configuration, the emission of carbon material into the atmosphere can be suppressed.

[0085] (Technical 15) A method for manufacturing an electrode according to any one of Technical 12 to 14, wherein the mixed material further comprises a binder, and between the mixing and firing, the method further comprises heating a molded body of the mixed material to remove the binder, wherein the heating is performed at a temperature lower than the firing temperature in the firing. With such a configuration, it is possible to suppress the rapid decomposition of the binder contained in the molded body during subsequent firing.

[0086] Details of this disclosure will be explained below using examples and comparative examples.

[0087] [Materials] <Example 1> As the electrode active material particles, Li2TiO3 (manufactured by High Purity Chemical Laboratory Co., Ltd.) powder was prepared. As the solid electrolyte particles, Li6Y(BO3)3 Zr and Ce doped Li 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.

[0088] Li2TiO3 had a crystal structure belonging to the space group C2 / c. LYBO had a crystal structure belonging to the space group P21 / c.

[0089] ≪Comparative Example 1≫ As the particle of the electrode active material, anatase-type TiO2 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) powder was prepared. As the particle of the solid electrolyte, the same LYBO powder as in Example 1 was prepared.

[0090] ≪Comparative Example 2≫ As particles with electrode active material, Li4Ti5O 12 Powder (manufactured by Toyoshima Seisakusho Co., Ltd.) was prepared. As solid electrolyte particles, the same LYBO powder as in Example 1 was prepared.

[0091] [Powder X-ray Diffraction Measurement] For Example 1, Comparative Examples 1 and 2, the following firing tests were performed to investigate the crystal structure of the sintered bodies made from the mixed material of electrode active material and solid electrolyte. First, a mixed material was obtained by mixing electrode active material powder and solid electrolyte powder in a 1:1 mass ratio using a mortar and pestle for 15 minutes. After molding the mixed material, the molded body was fired at 650°C for 2 hours under nitrogen conditions. The fired molded body was pulverized to obtain pulverized material.

[0092] Powder X-ray diffraction measurements were performed on the electrode active material, solid electrolyte, and sintered body. The measurement conditions for the powder X-ray diffraction measurements were as follows.

[0093] Device name: MiniFlex600 (manufactured by Rigaku Corporation) X-ray source: Cu-Kα Tube current: 15kV Tube voltage: 40mA Scan speed: 10deg / min Scan step: 0.01deg

[0094] Figure 4A shows the X-ray diffraction pattern of Example 1, where (a) is the X-ray diffraction pattern of the sintered body, (b) is the X-ray diffraction pattern of the electrode active material, and (c) is the X-ray diffraction pattern of the solid electrolyte. Figure 4B is a partially enlarged view of Figure 4A. Figure 5 shows the X-ray diffraction pattern of Comparative Example 1, where (a) is the X-ray diffraction pattern of the sintered body, (b) is the X-ray diffraction pattern of the electrode active material, and (c) is the X-ray diffraction pattern of the solid electrolyte. Figure 6 shows the X-ray diffraction pattern of Comparative Example 2, where (a) is the X-ray diffraction pattern of the sintered body, (b) is the X-ray diffraction pattern of the electrode active material, and (c) is the X-ray diffraction pattern of the solid electrolyte.

[0095] Based on the obtained X-ray diffraction patterns, the presence or absence of peaks other than those attributed to the electrode active material and solid electrolyte was investigated. As a result, the X-ray diffraction pattern (a) of the sintered body of Example 1 did not contain any peaks other than those attributed to the electrode active material and solid electrolyte. In other words, no new crystalline phase (secondary crystalline phase) was generated from the electrode active material and solid electrolyte in the sintered body of Example 1. From this result, it can be inferred that when the electrode active material and solid electrolyte of Example 1 are used, 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. On the other hand, the X-ray diffraction patterns (a) of the sintered bodies of Comparative Examples 1 and 2 contained peaks other than those attributed to the electrode active material and solid electrolyte. From this result, it can be inferred that when the electrode active material and solid electrolyte of Comparative Examples 1 and 2 are used, a reaction layer is formed at the interface between the solid electrolyte and the electrode active material in the sintered body.

[0096] From the X-ray diffraction patterns (a) of the sintered bodies of Example 1, Comparative Examples 1 and 2, the integrated intensity of the first peak I (17°-19°) , the integrated intensity of the second peak I (27.5°-29°) , and the integrated intensity of the third peak I (33°-35°) We calculated I. (33°-35°) (I (27.5°-29°) +I (17°-19°) The following was calculated. The results are shown in Tables 1 and 2.

[0097]

[0098]

[0099] As shown in Table 2, the sintered body of Example 1 is 0 ≤ I (33°-35°) (I (27.5°-29°) +I (17°-19°) The condition ) ≤ 0.1 was satisfied.

[0100] [Preparation of Two-Layer Pellets] Two-layer pellets were prepared using the electrode active materials and solid electrolytes of Example 1, Comparative Examples 1 and 2 by the following method. The two-layer pellet consisted of a negative electrode pellet and a solid electrolyte pellet.

[0101] (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.

[0102] (Preparation of negative electrode slurry) Electrode active material and solid electrolyte were prepared so that the mass ratio of electrode active material to solid electrolyte was 20:80. The electrode active material powder and solid electrolyte powder 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. In this way, a negative electrode mixture was obtained. Subsequently, a binder solution was added to the container and stirred so that the mass ratio of negative electrode mixture to acrylic resin was 100:18. Stirring was performed using a rotational-orbital mixer (Shinki Co., Ltd., Rentaro) at 2000 rpm for 30 minutes. In this way, a negative electrode slurry was obtained.

[0103] (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.

[0104] (Molded body for two-layer pellets) After coating a PET film with a negative electrode slurry using a replicator, 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 punched film for negative electrode pellets was obtained.

[0105] The solid electrolyte slurry was processed in the same manner as the negative electrode slurry to obtain punched membranes for solid electrolyte pellets. The punched membranes for solid electrolyte pellets were then crushed in a mortar for 15 minutes to obtain raw material powder for solid electrolyte pellets.

[0106] Next, 80 mg of raw material powder for solid electrolyte pellets was packed into an 8 mm diameter hand press and pressurized for 60 seconds. Then, 4 mg of punched membrane for negative electrode pellets was packed into the press and pressurized by uniaxial pressing. In this way, a two-layer pellet molded body consisting of a negative electrode pellet molded body and a solid electrolyte pellet molded body was obtained. The pressurizing conditions were 100 MPa and 1 minute.

[0107] The molded body for the two-layer pellets was heated in an electric furnace to degrease the binder. The heating conditions were 350°C (ambient temperature), under atmospheric pressure, for 48 hours, with a gas flow of 50 mL / min and a heating rate of 100°C / hour. Finally, the molded body for the two-layer pellets was fired in an electric furnace. The firing conditions 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, two-layer pellets were obtained.

[0108] [Evaluation of charge / discharge characteristics of negative electrode half-cells] Using the two-layer pellets of Example 1, Comparative Examples 1 and 2, charge / discharge tests of negative electrode half-cells were performed by the following method.

[0109] First, a 290 nm thick Au thin film was formed on the negative electrode pellet side of the two-layer pellet by sputtering, and 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 a 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, and a laminate was obtained. A LiTFSI-PEO film was used as the solid polymer electrolyte film. The molar ratio of PEO: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 negative electrode half-cell. To avoid pellet cracking, a spring constant of 1000 gf / mm was selected for the lamination direction of the laminate.

[0110] Next, a charge-discharge test of the negative electrode half-cell was performed in constant current (CC) mode at 60°C to obtain the charge-discharge curve for the first cycle. The cell was discharged at a constant current of 0.02C until the voltage reached 0.2V. The cell was then charged at a constant current of 0.02C until the voltage reached 3V. An electrochemical evaluation device (Biologic, VSP-300) was used for charging and discharging. Figure 7 shows the charge-discharge curve for the first cycle of the negative electrode half-cell in Example 1. In the negative electrode half-cell, the side into which Li is inserted corresponds to discharge (charging in a battery), and the side from which Li is removed corresponds to charging (discharging in a battery). In Table 3, the charging capacity of the negative electrode half-cell obtained from the charge-discharge curve for the first cycle is referred to as the "initial discharge capacity".

[0111]

[0112] ≪Discussion≫ In the negative electrode half-cell of Example 1, discharge was possible and excellent initial discharge capacity was achieved. This is thought to be because, in the negative electrode half-cell of Example 1, a reaction layer that inhibits ion movement was not formed at the interface between the solid electrolyte and the electrode active material. On the other hand, discharge was not possible in the negative electrode half-cells of Comparative Examples 1 and 2. This is thought to be because, in the negative electrode half-cells of Comparative Examples 1 and 2, ion movement was inhibited due to the formation of a reaction layer at the interface between the solid electrolyte and the electrode active material.

[0113] 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 electrode active material contains an oxide containing lithium, titanium, and oxygen, and in the oxide contained in the electrode active material, the ratio of the amount of substance of lithium to the amount of substance of titanium is greater than 0.8; and the solid electrolyte contains an oxide containing lithium, boron, yttrium, and oxygen, and the oxide contained in the solid electrolyte has a crystal structure belonging to space group P21 / c.

2. The electrode according to claim 1, wherein the ratio in the electrode active material is in the range of 1.5 or more and 2.5 or less.

3. The electrode according to claim 1, wherein the ratio in the electrode active material is in the range of 1.8 or more and 2.2 or less.

4. The electrode according to claim 1, wherein the oxide contained in the electrode active material has a crystal structure belonging to the space group C2 / c.

5. The oxide contained in the solid electrolyte has a composition represented by the following formula (1): Li 6-x-y Y 1-x-y Zr x Ce y B3O9 ... Equation (1) The electrode according to claim 1, wherein in equation (1), 0 ≤ x ≤ 0.4 and 0 ≤ y ≤ 0.025 are satisfied.

6. The electrode according to claim 5, wherein in formula (1), x = 0.1 and y = 0.025 are satisfied.

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

8. In the powder X-ray diffraction pattern of the pulverized electrode using Cu-Kα rays, the integrated intensity of the first peak, which is the largest peak in the diffraction angle range 2θ of 17° to 19°, is I (17°-19°) The integral intensity I of the second peak, which is the largest peak in the diffraction angle range 2θ between 27.5° and 29°. (27.5°-29°) The sum of these is the integral intensity I of the third peak, which is the largest peak in the diffraction angle range 2θ between 33° and 35°. (33°-35°) The electrode according to claim 1, wherein the value obtained by dividing by is 0 or more and 0.1 or less.

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

10. 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 claim 1.

11. The battery according to claim 10, wherein the positive electrode, the negative electrode, and the electrolyte layer are sintered bodies.

12. 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 electrode active material comprises an oxide containing lithium, titanium, and oxygen, the ratio of the amount of substance of lithium to the amount of substance of titanium in the oxide contained in the electrode active material is greater than 0.8, and the solid electrolyte comprises an oxide containing lithium, boron, yttrium, and oxygen, and the oxide contained in the solid electrolyte has a crystalline structure belonging to space group P21 / c.

13. The method for manufacturing an electrode according to claim 12, wherein, in the firing process, the molded body of the mixed material is fired at a temperature of 500°C or more and 700°C or less.

14. The method for manufacturing an electrode according to claim 12, wherein the mixed material further comprises a carbon material, and in the firing process, a molded body of the mixed material is fired in an inert atmosphere.

15. The method for manufacturing an electrode according to claim 12, wherein the mixed material further comprises a binder, and between the mixing and firing, the method further comprises heating a molded body of the mixed material to remove the binder, wherein the heating is performed at a temperature lower than the firing temperature in the firing.

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