Positive electrode layer, manufacturing method of positive electrode layer and all-solid-state battery

Abstract

The purpose of this disclosure is to provide a positive electrode layer with low resistance. To achieve the above objective, this disclosure provides a positive electrode layer for an all-solid-state battery, comprising a positive electrode active material and a coated sulfide solid electrolyte, wherein the coated sulfide solid electrolyte has a sulfide solid electrolyte and a coating layer containing a metal sulfate covering the surface of the sulfide solid electrolyte, and in the S2p spectrum of the coated sulfide solid electrolyte measured by X-ray photoelectron spectroscopy (XPS), the ratio of the peak intensity P2 appearing near 167 eV to the peak intensity P1 appearing near 163 eV (P2 / P1) is 0.15 or more and less than 0.36.

Description

Technical Field

[0001] This disclosure relates to a positive electrode layer, a method for manufacturing the positive electrode layer, and an all-solid-state battery. Background Technology

[0002] All-solid-state batteries are batteries with a solid electrolyte layer between the positive and negative electrode layers. Compared with liquid batteries with electrolytes containing flammable organic solvents, they have the advantage of being easier to simplify safety devices.

[0003] It is known that a coating layer is formed on the surface of the active material to suppress the increase of interfacial resistance between the active material and other materials. For example, Japanese Patent Application Laid-Open No. 2010-080168 discloses an all-solid-state lithium secondary battery with a positive electrode layer containing a Li sulfate-coated oxide-based positive electrode active material and a sulfide-based solid electrolyte material. The Li sulfate-coated oxide-based positive electrode active material has a Li sulfate-containing coating formed on the surface of the oxide-based positive electrode active material.

[0004] Japanese Patent Application Publication No. 2021-86834 discloses a positive electrode active material for lithium secondary batteries, comprising a lithium metal oxide active material and a coating on the surface of the active material. The coating comprises a sulfur compound containing a sulfur compound selected from Li₂S, Li₂SO₄, and Li₂S₂. n O x (n is one or more of the following: 1 ≤ n ≤ 8) Summary of the Invention

[0005] From the viewpoint of high input / output efficiency in all-solid-state batteries, a positive electrode layer with low resistance is required. This disclosure was made in view of the above-mentioned problems, and its main objective is to provide a positive electrode layer with low resistance.

[0006] To address the aforementioned issues, this disclosure provides a positive electrode layer for an all-solid-state battery, comprising a positive electrode active material and a coated sulfide solid electrolyte. The coated sulfide solid electrolyte has a sulfide solid electrolyte and a coating layer containing metal sulfate covering the surface of the sulfide solid electrolyte. In the S2p spectrum of the coated sulfide solid electrolyte measured by X-ray photoelectron spectroscopy (XPS), the ratio (P2 / P1) of the peak intensity P2 appearing near 167 eV to the peak intensity P1 appearing near 163 eV is 0.15 or more and less than 0.36.

[0007] According to this disclosure, a positive electrode layer with low resistance is formed by including a specified coated sulfide solid electrolyte in the positive electrode layer.

[0008] In the above disclosure, the sulfide solid electrolyte preferably contains Li, P and S, the peak appearing near 163 eV is from the PS bond, and the peak appearing near 167 eV is from the SO bond.

[0009] In the above disclosure, the preferred metal sulfate is lithium sulfate.

[0010] In the above disclosure, it is preferable that the surface of the positive electrode active material is coated with a material of the general formula Li. x AO y (A is at least one selected from Nb, B, Al, Si, P, S, Ti, Zr, Mo, Ta, W, and x and y are positive numbers) represents a Li ion-conducting oxide.

[0011] In addition, this disclosure provides a method for manufacturing a positive electrode layer for an all-solid-state battery, comprising: a step of forming a coating layer containing metal sulfate on the surface of a sulfide solid electrolyte by heat-treating it in a dry gas at a temperature of 100°C or higher and less than 190°C for 5 minutes or more and 1 hour or less, thereby obtaining a coated sulfide solid electrolyte; and a step of forming the positive electrode layer by coating a slurry containing the coated sulfide solid electrolyte and a positive electrode active material and drying it.

[0012] According to this disclosure, a low-resistivity positive electrode layer can be manufactured by using a coated sulfide solid electrolyte obtained by heat-treating a sulfide solid electrolyte in a dry gas at a specified temperature and for a specified time.

[0013] In addition, this disclosure provides an all-solid-state battery comprising: a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer is the positive electrode layer described above.

[0014] According to this disclosure, by using the above-described positive electrode layer, a low-resistance all-solid-state battery is achieved.

[0015] In this disclosure, there is an effect of providing a positive electrode layer with low resistance. Attached Figure Description

[0016] Hereinafter, the features, advantages, and technical and industrial significance of exemplary embodiments of the present disclosure will be described with reference to the accompanying drawings, in which the same symbols denote the same elements.

[0017] Figure 1 This is a schematic cross-sectional view showing an example of a coated sulfide solid electrolyte of the present disclosure.

[0018] Figure 2 This is a flowchart illustrating an example of a method for manufacturing the positive electrode layer of this disclosure.

[0019] Figure 3 This is a schematic cross-sectional view showing an example of an all-solid-state battery of this disclosure.

[0020] Figure 4 The S2p spectrum is obtained by XPS measurement of the coated sulfide solid electrolytes prepared in Example 3 and Comparative Example 1. Detailed Implementation

[0021] The following provides a detailed description of the positive electrode layer, the method for manufacturing the positive electrode layer, and the all-solid-state battery disclosed herein.

[0022] A. Positive electrode layer

[0023] The following describes the details of the positive electrode layer of this disclosure. The positive electrode layer of this disclosure comprises a defined coated sulfide solid electrolyte and a positive electrode active material. Figure 1 This is a schematic cross-sectional view showing an example of the coated sulfide solid electrolyte of this disclosure. The coated sulfide solid electrolyte 11 of this disclosure has a sulfide solid electrolyte 11a and a coating layer 11b containing metal sulfate on the surface of the coated sulfide solid electrolyte 11a. Furthermore, in the S2p spectrum obtained by X-ray photoelectron spectroscopy (XPS) of the coated sulfide solid electrolyte 11, the ratio (P2 / P1) of the peak intensity P2 appearing near 167 eV to the peak intensity P1 appearing near 163 eV is 0.15 or more and less than 0.36. In addition, the positive electrode layer of this disclosure is used in all-solid-state batteries.

[0024] According to this disclosure, a low-resistance positive electrode layer is formed by comprising a specified coated sulfide solid electrolyte.

[0025] Previously, coated positive electrode active materials were known to form a coating layer containing lithium niobate (LiNbO3) on the surface of the positive electrode active material. This coating layer has the function of suppressing the formation of a high-resistivity layer at the interface between the positive electrode active material and the sulfide solid electrolyte, and reducing the interfacial resistance during lithium ion migration at the interface. On the other hand, when using this type of coated positive electrode active material, sulfur in the sulfide solid electrolyte reacts with oxygen in the lithium niobate, sometimes forming a resistive layer. For example, it is speculated that the following side reaction will occur.

[0026] LiNbO3+0.95Li3PS4→0.08Li5(NbS2)7+0.75Li3PO4+0.2Nb2PS 10 +0.59Li2S

[0027] (The change in heat function (ΔH) per mole of Li3PS4 = -160.9 kJ / mol)

[0028] Furthermore, Japanese Patent Application Publication No. 2010-080168 discloses a Li sulfate-coated oxide-based positive electrode active material having a Li sulfate-containing coating formed on its surface. When a Li sulfate-containing substance is formed on the surface of the positive electrode active material, as shown in the following reaction formula, the Li sulfate-containing substance reacts with the sulfide electrolyte, sometimes forming a resistive layer. For example, it is speculated that the side reaction shown in the following reaction formula may occur.

[0029] Li2SO4+0.89Li3PS4→0.89Li3PO4+0.44S8O+Li2S

[0030] (The change in heat function (ΔH) per mole of Li3PS4 = -166.3 kJ / mol)

[0031] In contrast, this disclosure uses a coated sulfide solid electrolyte whose surface is pre-coated with a coating layer containing metal sulfate. It is presumed that this coated sulfide solid electrolyte undergoes changes in surface energy due to the chemical bonding between the metal sulfate-containing coating layer and the sulfide solid electrolyte, thus suppressing the aforementioned side reactions between the Li-containing sulfate and the sulfide solid electrolyte. Furthermore, by coating the surface of the sulfide solid electrolyte with a metal sulfate-containing coating layer, the formation of a high-resistivity layer due to the reaction between the positive electrode active material and the sulfide solid electrolyte can be suppressed.

[0032] Furthermore, even when using a positive electrode active material with a coating layer containing lithium niobate (LiNbO3) on its surface, the metal sulfates in the coating layer of the coated sulfide solid electrolyte are unlikely to react with lithium niobate (there are no thermodynamically stable compounds). Therefore, the formation of a high-resistivity layer can be suppressed.

[0033] 1.Coated sulfide solid electrolyte

[0034] The coated sulfide solid electrolyte disclosed herein has a surface of sulfide solid electrolyte and coated sulfide solid electrolyte and contains a coating layer of metal sulfate.

[0035] In the S2p spectrum obtained by X-ray photoelectron spectroscopy (XPS) of a coated sulfide solid electrolyte, the ratio (P2 / P1) of the peak intensity P2 appearing near 167 eV to the peak intensity P1 appearing near 163 eV is 0.15 or more and less than 0.36. The aforementioned P2 / P1 can be 0.18 or more, or 0.20 or more. On the other hand, the aforementioned P2 / P1 can be 0.35 or less, or 0.30 or less.

[0036] The peaks appearing near 163 eV originate from PS bonds, for example, between 159 eV and 163 eV, while the peaks appearing near 167 eV originate from SO bonds, for example, between 165 eV and 175 eV. A larger P2 / P1 value indicates a lower proportion of PS bonds and a higher proportion of SO bonds on the surface of the coated sulfide solid electrolyte, indicating a more advanced coating layer formation.

[0037] According to this disclosure, if the P2 / P1 ratio is too small, the resistance to lithium-ion conduction cannot be reduced. This is presumably because the coating layer is not formed sufficiently, and the reaction between the sulfide solid electrolyte and the positive electrode active material fails to suppress the formation of a high-resistivity layer. Furthermore, even if the P2 / P1 ratio is too large, the battery resistance cannot be reduced. This is presumably because an excessive coating layer is formed, restricting the lithium-ion pathway.

[0038] (1) Covering layer

[0039] The coating layer of this disclosure is formed on the surface of a sulfide solid electrolyte and contains a metal sulfate. Examples of metal sulfates include alkali metals such as Li and Na. Li-containing metal sulfates are preferred, with Li₂SO₄ being particularly preferred due to its high Li conductivity. Furthermore, Li₂SO₄ is a sulfate containing only Li as a metal element, thus other metal elements do not react with the positive electrode active material or the sulfide solid electrolyte. Therefore, the formation of a resistive layer caused by such reactions is suppressed, reducing resistance to lithium-ion conduction.

[0040] Furthermore, the film thickness of the coating layer disclosed herein is not particularly limited; for example, it can be 1 nm or more, or 5 nm or more. On the other hand, it can be 20 nm or less, or 15 nm or less. This is because by making the coating layer thinner, the resistance to lithium-ion conduction can be further reduced. The film thickness of the coating layer can be analyzed using methods such as X-ray fluorescence analysis (XRF).

[0041] The coating disclosed herein coats at least a portion of the surface of a sulfide solid electrolyte. The coating may be formed on a portion of the surface of the sulfide solid electrolyte or on the entire surface. The coverage of the coating may be, for example, 50% or more, 70% or more, or 90% or more.

[0042] It is hypothesized that in the coated sulfide solid electrolyte of this disclosure, the higher the oxygen content on the surface, the more advanced the formation of the coating layer. The oxygen content (%) on the surface of the coated sulfide solid electrolyte is calculated using the elemental concentrations of each element obtained by XPS, by the following formula.

[0043] Oxygen content (%) = (O element concentration / concentration of elements other than O) × 100

[0044] The oxygen content (%) on the surface of the aforementioned coated sulfide solid electrolyte is, for example, 5% or more, 20% or more, or 40% or more.

[0045] For example, in the case of a coated sulfide solid electrolyte containing Li, P, S, Br and I, the percentage of oxygen on the surface of the coated sulfide solid electrolyte (%) is calculated using the elemental concentrations of each element (O, S, P, Li, Br and I) obtained from XPS by the following formula.

[0046] Oxygen content (%) = {O element concentration / (S + P + Li + Br + I element concentration)} × 100

[0047] (2) Sulfide solid electrolyte

[0048] The sulfide solid electrolyte of this disclosure typically contains sulfur (S) as the main anionic element. Preferably, the sulfide solid electrolyte of this disclosure contains Li, P, and S. The sulfide solid electrolyte of this disclosure may contain only Li, P, and S, or it may contain other elements. Examples of other elements include X (where X is a halogen). Examples of X include F, Cl, Br, and I. X may be one or more elements. Preferably, the sulfide solid electrolyte also contains at least one of Br and I.

[0049] Furthermore, the sulfide solid electrolyte of this disclosure preferably contains an ionic conductor comprising Li, P, and S. The ionic conductor preferably has an anionic structure of the original composition (PS4). 3- It is the main component of anions because of its high chemical stability. The proportion of the original anionic structure relative to all anionic structures in the ionic conductor is, for example, 70 mol% or more, 80 mol% or more, or 90 mol% or more. The proportion of the original anionic structure can be determined by, for example, Raman spectroscopy, NMR, or XPS.

[0050] In addition to the aforementioned ionic conductors, sulfide solid electrolytes may also contain lithium halides. Examples of lithium halides include LiF, LiCl, LiBr, and LiI, with LiCl, LiBr, and LiI being preferred. The proportion of LiX (X = F, I, Cl, Br) in the sulfide solid electrolyte is, for example, 5 mol% or more, and may be 15 mol% or more. On the other hand, the proportion of the aforementioned LiX is, for example, 30 mol% or less, and may be 25 mol% or less.

[0051] The sulfide solid electrolyte may have a composition represented by xLiI·yLiBr·z(αLi2S·(1-α)P2S5). Here, x + y + z = 100, 0 ≤ x < 100, 0 ≤ y < 100, 0 < z ≤ 100, 0.70 ≤ α ≤ 0.80. x may also be greater than 0. In this case, x may be 5 or more, or may be 10 or more. Additionally, x may be 50 or less, or may be 30 or less. Further, y may also be greater than 0. In this case, y may be 5 or more, or may be 10 or more. Additionally, y may be 50 or less, or may be 30 or less. z may be 50 or more, or may be 60 or more. α may be 0.72 or more, or may be 0.74 or more. On the other hand, α may be 0.78 or less, or may be 0.76 or less.

[0052] The sulfide solid electrolyte may be a glass-based sulfide solid electrolyte, a glass-ceramic sulfide solid electrolyte, or a crystalline sulfide solid electrolyte.

[0053] As the shape of the sulfide solid electrolyte, for example, a granular shape can be cited. The average particle diameter (D50) of the sulfide solid electrolyte is, for example, 0.1 μm or more, and may also be 1 μm or more. On the other hand, the average particle diameter (D50) of the sulfide solid electrolyte is, for example, 50 μm or less, and may also be 30 μm or less. The average particle diameter (D50) can be determined, for example, by observation with a scanning electron microscope (SEM). It is preferable that the number of samples is large, for example, 100 or more. Additionally, the sulfide solid electrolyte preferably has a high ionic conductivity. The ionic conductivity at 25°C is, for example, 1×10 -5 S / cm or more, and may be 1×10 -4 S / cm or more, and may also be 1×10 -3 S / cm or more.

[0054] (3) Coated sulfide solid electrolyte

[0055] The proportion of the coated sulfide solid electrolyte in the positive electrode layer is, for example, 5% by weight or more and 75% by weight or less, and may also be 10% by weight or more and 60% by weight or less. If the proportion of the coated sulfide solid electrolyte is small, it may not be possible to sufficiently form an ion conduction path. On the other hand, if the proportion of the coated sulfide solid electrolyte is large, the volume energy density may decrease.

[0056] The positive electrode layer of the present disclosure may contain only the coated sulfide solid electrolyte as the solid electrolyte, or may contain other solid electrolytes. The total proportion of the coated sulfide solid electrolyte relative to all the solid electrolytes contained in the positive electrode layer is, for example, 50% by weight or more, and may be 70% by weight or more, or may also be 90% by weight or more.

[0057] As for the method of manufacturing coated sulfide solid electrolyte, there is no particular limitation as long as the above-mentioned coated sulfide solid electrolyte can be obtained. For example, the method described in "B. Method for manufacturing positive electrode layer 1. Process for manufacturing coated sulfide solid electrolyte" can be cited later.

[0058] Alternatively, the coated sulfide solid electrolyte of this disclosure can also be manufactured by subjecting the aforementioned sulfide solid electrolyte to oxygen plasma treatment. In this case, the oxygen plasma conditions are adjusted so that the P2 / P1 ratio of the S2p energy spectrum of the coated sulfide solid electrolyte obtained by XPS falls within a specified range.

[0059] 2. Positive electrode active material

[0060] The positive electrode layer of this disclosure has a positive electrode active material. As an example of the positive electrode active material of this disclosure, an oxide active material can be mentioned. Oxide active materials are particularly prone to forming a high-resistivity layer between themselves and the sulfide solid electrolyte. Examples of oxide active materials include, for example, LiCoO2, LiMnO2, LiNiO2, LiVO2, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 and other layered active substances in rock salt, LiMn2O4, Li4Ti5O 12 Li(Ni) 0.5 Mn 1.5 Spinel-type active materials such as Li2O4, olivine-type active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4, orthorhombic manganese-type active materials such as Li2Ti3O7, and solid solution-type active materials containing Li2MnO3, etc.

[0061] Alternatively, the active oxide material can also be, for example, Li using the general formula Li x M y O z (M is a metallic element other than Li, x = 0.02 to 2.2, y = 1 to 2, z = 1.4 to 4) represents a substance. In the above general formula, M is preferably at least one selected from Co, Al, Mn, Ni, V, Fe and Si, and more preferably at least one selected from Co, Ni, Al and Mn.

[0062] The preferred active oxide materials are lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), and lithium nickel oxide.

[0063] Preferably, a coating containing an ion-conducting oxide is formed on the surface of the positive electrode active material disclosed herein. The Li ion-conducting oxide is not particularly limited; examples include those made of the general formula Li. x AO y(A is at least one selected from Nb, B, Al, Si, P, S, Ti, Zr, Mo, Ta, W, and x and y are positive numbers) represents Li ion-conducting oxides. Specifically, examples include LiNbO3, Li3BO3, LiBO2, LiAlO2, Li4SiO4, Li2SiO3, Li3PO4, Li2SO4, Li2TiO3, and Li4Ti5O. 12 Examples of suitable oxides include Li₂Ti₂O₅, Li₂ZrO₃, Li₂MoO₄, and Li₂WO₄. Additionally, Li ion-conducting oxides can also be composite compounds of Li ion-conducting oxides. LiNbO₃ is preferred.

[0064] The coating thickness is preferably in the range of 0.1 nm to 100 nm, and more preferably in the range of 1 nm to 20 nm. If the coating is too thick, the Li ion conductivity and electronic conductivity may decrease. Furthermore, methods for measuring the coating thickness include, for example, X-ray fluorescence analysis (XRF) and transmission electron microscopy (TEM).

[0065] Furthermore, it is preferable that the coating has a high coverage rate on the surface of the positive electrode active material, specifically, preferably 50% or more, more preferably 80% or more. Alternatively, the coating may cover the entire surface of the positive electrode active material. Moreover, methods for measuring the coating coverage rate include, for example, X-ray photoelectron spectroscopy (XPS). For instance, when a coating containing lithium niobate (LiNbO3) is formed on the surface of lithium nickel cobalt manganese oxide (NCM) used as the positive electrode active material, the molar number of Ni, Co, Mn, and Nb on the surface of the positive electrode active material can be determined by XPS, and the molar fraction of Nb relative to the total molar number of Ni, Co, Mn, and Nb can be calculated.

[0066] The proportion of the positive electrode active material in the positive electrode layer is, for example, 20% by weight or more, 30% by weight or more, or 40% by weight or more. On the other hand, the proportion of the positive electrode active material is, for example, 90% by weight or less, 85% by weight or less, or 80% by weight or less.

[0067] 3. Positive electrode layer

[0068] The positive electrode layer of this disclosure contains the aforementioned coated sulfide solid electrolyte and positive electrode active material. Additionally, if necessary, it may further contain at least one of a conductive material and a binder.

[0069] Examples of conductive materials include carbon materials, metal particles, and conductive polymers. Examples of carbon materials include granular carbon materials such as acetylene black (AB) and Ketjen black (KB), as well as fibrous carbon materials such as carbon fibers, carbon nanotubes (CNTs), and carbon nanofibers (CNFs). The proportion of the conductive material in the positive electrode layer is, for example, 0.1% by weight or more and 10% by weight or less, or 0.3% by weight or more and 10% by weight or less.

[0070] Examples of adhesives include rubber-based adhesives and fluoride-based adhesives. The content of the adhesive in the positive electrode layer is, for example, 0.1% by weight or more and 30% by weight or less, or 0.1% by weight or more and 15% by weight or less.

[0071] The thickness of the positive electrode layer is, for example, 0.1 μm or more and 1000 μm or less.

[0072] B. Manufacturing method of positive electrode layer

[0073] Figure 2 This is a flowchart illustrating an example of a method for manufacturing the positive electrode layer of this disclosure. Figure 2 In the manufacturing method shown, firstly, a coating layer containing metal sulfate is formed on the surface of the sulfide solid electrolyte by heat-treating it in a dry gas at a temperature of 100°C or higher and less than 190°C for 5 minutes to 1 hour, thereby obtaining a coated sulfide solid electrolyte (coated sulfide solid electrolyte manufacturing process). Next, a slurry containing the coated sulfide solid electrolyte and a positive electrode active material is applied and dried, thereby forming a positive electrode layer (positive electrode layer formation process).

[0074] According to this disclosure, a positive electrode layer for all-solid-state batteries with low resistance can be manufactured. The manufacturing method of the positive electrode layer of this disclosure will be described below, step by step.

[0075] 1. Manufacturing process of coated sulfide solid electrolyte

[0076] The sulfide solid electrolyte used in this process is the same as the sulfide solid electrolyte described in "A. Positive electrode layer 1. Coated sulfide solid electrolyte (2) Sulfide solid electrolyte" above, so the description is omitted here.

[0077] The dry gas is a low dew point gas with a dew point temperature below 0°C. The dew point temperature can be, for example, below -50°C or below -60°C. The oxygen concentration in the dry gas is, for example, below 20% by volume. Alternatively, the dry gas can be, for example, dry air.

[0078] Heat treatment in dry gas can be performed, for example, by using a heating plate or similar method in a dry gas glove box.

[0079] The heat treatment temperature in dry gas is typically above 100°C, but can be above 120°C or even above 130°C. If the heat treatment temperature is too low, the coating layer cannot be sufficiently formed, and the formation of a high-resistivity layer cannot be suppressed. On the other hand, the temperature is typically below 190°C, but can be below 180°C or even below 170°C. If the heat treatment temperature is too high, sometimes an excessive coating layer can form, restricting the lithium-ion pathway.

[0080] The heat treatment time in dry gas is usually more than 5 minutes and less than 1 hour.

[0081] Furthermore, the coated sulfide solid electrolyte produced by this process is identical to the content described in "A. Positive Electrode Layer 1. Coated Sulfide Solid Electrolyte" above, and therefore will not be described here. Moreover, according to this process, coated sulfide solid electrolytes with a coating layer containing lithium sulfate are typically produced.

[0082] 2. Positive electrode layer formation process

[0083] This process involves forming a positive electrode layer by coating a slurry containing a coated sulfide solid electrolyte and a positive electrode active material and then drying it. Depending on the requirements, the slurry may also contain binders, conductive materials, and solvents. Furthermore, the term "solvent" has a broader meaning, including dispersion media.

[0084] The aforementioned slurry is preferably applied to the current collector. There are no particular limitations on the application method of the slurry; any known application method can be used. Furthermore, the positive electrode layer produced through the above processes is the same as described in "A. Positive Electrode Layer" above, and therefore will not be described here.

[0085] C. All-solid-state batteries

[0086] Figure 3 This is a schematic cross-sectional view illustrating the all-solid-state battery of this disclosure. Figure 3 The all-solid-state battery 10 shown includes: a positive electrode layer 1, a negative electrode layer 2, a solid electrolyte layer 3 disposed between the positive electrode layer 1 and the negative electrode layer 2, a positive current collector 4 for collecting current in the positive electrode layer 1, and a negative current collector 5 for collecting current in the negative electrode layer 2. In this disclosure, the positive electrode layer 1 is the positive electrode layer described in "A. Positive Electrode Layer" above.

[0087] According to this disclosure, by using the above-described positive electrode layer, a low-resistance all-solid-state battery is achieved.

[0088] 1. Positive electrode layer

[0089] Regarding the positive electrode layer of this disclosure, the content is the same as that described in "A. Positive Electrode Layer" above, so it is omitted here.

[0090] 2. Negative electrode layer

[0091] The negative electrode layer disclosed herein is a layer containing at least a negative electrode active material. Additionally, the negative electrode active material layer may, as needed, contain at least one of a solid electrolyte, a conductive material, and a binder.

[0092] The negative electrode active material is not particularly limited; examples include metallic active materials, carbon active materials, and oxide active materials. Examples of metallic active materials include elemental metals and metal alloys. Examples of metallic active materials include Si, Sn, In, and Al. Metal alloys are preferably alloys containing the aforementioned metallic elements as main components.

[0093] On the other hand, examples of carbon-active materials include mesophase carbon microspheres (MCMB), highly oriented graphite (HOPG), hard carbon, and soft carbon. Additionally, examples of oxide-active materials include Li₄Ti₅O₂. 12 Lithium titanate, etc.

[0094] The proportion of the negative electrode active material in the negative electrode layer is, for example, 20% by weight or more, 30% by weight or more, or 40% by weight or more. On the other hand, the proportion of the negative electrode active material is, for example, 80% by weight or less, 70% by weight or less, or 60% by weight or less.

[0095] As a solid electrolyte, it is the same as the content described in "3. Solid Electrolyte Layer" below, so it is omitted here.

[0096] Regarding the conductive materials and adhesives, the content is the same as described in "A. Positive Electrode Layer" above, and therefore will not be described here. The thickness of the negative electrode layer is, for example, 0.1 μm or more and 1000 μm or less.

[0097] 3. Solid electrolyte layer

[0098] The solid electrolyte layer of this disclosure is disposed between the positive electrode layer and the negative electrode layer. The solid electrolyte layer contains at least a solid electrolyte and may further contain a binder.

[0099] The solid electrolyte can be a conventionally known solid electrolyte commonly used in all-solid-state lithium-ion batteries, such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, halides, etc., with sulfide solid electrolytes being preferred. As for sulfide solid electrolytes, the content described in "A. Positive Electrode Layer" above is the same, so it is omitted here.

[0100] Regarding the adhesive, the information is the same as described in "A. Positive Electrode Layer", so it is omitted here. The thickness of the solid electrolyte layer is, for example, 0.1 μm or more and 1000 μm or less.

[0101] 4. All-solid-state batteries

[0102] In this disclosure, "all-solid-state battery" refers to a battery having a solid electrolyte layer (at least a layer containing a solid electrolyte). Furthermore, the all-solid-state battery of this disclosure has at least one power generation element, and may also have two or more power generation elements, each having a positive electrode layer, a solid electrolyte layer, and a negative electrode layer. In the case of an all-solid-state battery with multiple power generation elements, they can be connected in parallel or in series. The power generation element typically has a positive current collector and a negative current collector. The positive current collector is, for example, disposed on the surface of the positive electrode layer opposite to the solid electrolyte layer. Examples of materials for the positive current collector include metals such as aluminum, SUS, and nickel. Examples of shapes for the positive current collector include foil and mesh. Additionally, a carbon coating may be formed on the surface of the positive electrode layer side of the positive current collector. On the other hand, the negative current collector is, for example, disposed on the surface of the negative electrode layer opposite to the solid electrolyte layer. Examples of materials for the negative current collector include metals such as copper, SUS, and nickel. Examples of shapes for the negative current collector include foil and mesh.

[0103] The all-solid-state battery of this disclosure can also include an outer casing for housing the aforementioned power generation element. Examples of such outer casings include laminated casings and shell-type casings. Furthermore, the all-solid-state battery of this disclosure can also include a constraint clamp that applies a thickness-direction constraint pressure to the aforementioned power generation element. Known clamps can be used as the constraint clamp. The constraint pressure can be, for example, 0.1 MPa or more and 50 MPa or less, or 1 MPa or more and 20 MPa or less. If the constraint pressure is low, a good ion conduction pathway and a good electron conduction pathway may not be formed. On the other hand, if the constraint pressure is high, the constraint clamp becomes larger, and the volumetric energy density may decrease.

[0104] The type of all-solid-state battery disclosed herein is not particularly limited, but lithium-ion secondary batteries are typical. The applications of all-solid-state batteries are not particularly limited; examples include power sources for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), gasoline vehicles, and diesel vehicles. They are particularly preferred for use as power sources for driving hybrid electric vehicles, plug-in hybrid electric vehicles, or electric vehicles. Furthermore, the all-solid-state battery disclosed herein can be used as a power source for mobile bodies other than vehicles (e.g., railways, ships, aircraft), and also as a power source for electronic devices such as information processing devices.

[0105] Furthermore, this disclosure is not limited to the embodiments described above. The embodiments described above are illustrative, and all technical solutions having a structure that is substantially the same as the technical concept described in the claims of this disclosure and performing the same effect are included within the technical scope of this disclosure.

[0106] [Example 1]

[0107] (Fabrication of the negative electrode structure)

[0108] Prepare the negative electrode active material (Si particles, average particle size 0.5 μm), sulfide solid electrolyte (10LiI·15LiBr·75(0.75Li2S·0.25P2S5) (mol%), average particle size 0.5 μm), conductive material (VGCF-H), and binder (SBR). Weigh them in a weight ratio of negative electrode active material: sulfide solid electrolyte: conductive material: binder = 47.0: 44.6: 7.0: 1.4 and mix them with a dispersion medium (diisobutyl ketone). Disperse the resulting mixture using an ultrasonic homogenizer (UH50, manufactured by SMT Co., Ltd.) to obtain a negative electrode slurry. Apply the obtained negative electrode slurry to the negative electrode current collector (Ni foil, thickness 22 μm) using a doctor blade coating method and dry at 100°C for 30 minutes. Then, the same coating is applied to the opposite side of the negative current collector, thus obtaining a two-sided negative electrode structure with a negative electrode layer and a negative current collector. The thickness of the negative electrode layer on one side is 60 μm.

[0109] (Preparation of coated sulfide solid electrolyte)

[0110] For 2 g of sulfide solid electrolyte (10LiI·15LiBr·75(0.75Li2S·0.25P2S5) (mol%), average particle size 0.5 μm), a heating treatment was performed at 100 °C for 5 minutes using a heating plate in dry air with a dew point of -70 °C and an oxygen volume concentration of 20%. This resulted in a lithium sulfate-containing coating layer forming on the surface of the sulfide solid electrolyte, yielding a coated sulfide solid electrolyte.

[0111] (Fabrication of components for the positive electrode)

[0112] The positive electrode active material (LiNi) prepared for coating with LiNbO3 using a rotary flow granulation coating device. 0.8 Co 0.15 Al 0.05 O2 (average particle size 10 μm), the above-obtained coated sulfide solid electrolyte, conductive material (VGCF-H), and binder (SBR) were weighed in a weight ratio of positive electrode active material: coated sulfide solid electrolyte: conductive material: binder = 83.3:14.4:2.1:0.2 and mixed with a dispersion medium (diisobutyl ketone). The resulting mixture was dispersed using an ultrasonic homogenizer (UH-50, manufactured by SMT Co., Ltd.) to obtain a positive electrode slurry. The obtained positive electrode slurry was coated onto an Al foil (15 μm thick) using a doctor blade coating method and dried at 100°C for 30 minutes. This yielded a positive electrode component having a positive electrode layer and an Al foil. The thickness of the positive electrode layer was 100 μm.

[0113] (Fabrication of components for solid electrolyte layers)

[0114] A sulfide solid electrolyte (10LiI·15LiBr·75(0.75Li2S·0.25P2S5) (mol%), average particle size 2.0 μm) and a binder (SBR) were weighed at a weight ratio of sulfide solid electrolyte: binder = 99.6:0.4. These were mixed with a dispersion medium (diisobutyl ketone). The resulting mixture was dispersed using an ultrasonic homogenizer (UH-50, manufactured by SMT Co., Ltd.) to obtain a slurry for a solid electrolyte layer. The obtained slurry for the solid electrolyte layer was applied to an Al foil (15 μm thick) using a doctor blade coating method and dried at 100°C for 30 minutes. This yielded a component for a solid electrolyte layer having an Al foil and a solid electrolyte layer. The thickness of the solid electrolyte layer was 30 μm.

[0115] (The fabrication of an all-solid-state battery)

[0116] The negative electrode structure and solid electrolyte layer are cut into 7.2cm × 7.2cm dimensions using a component. On the other hand, the positive electrode is cut into 7.0cm × 7.0cm dimensions using a component.

[0117] The solid electrolyte layer of the solid electrolyte layer component is brought into contact with the negative electrode layer on one surface of the negative electrode structure, and then brought into contact with the negative electrode layer on the other surface of the negative electrode structure. The resulting laminate is pressed using a rolling method with a linear pressure of 1.6 t / cm. Next, Al foil is peeled off from each solid electrolyte layer to expose the solid electrolyte layer. Then, the positive electrode layer of the positive electrode component is directly bonded to the exposed solid electrolyte layer. The resulting laminate is pressed using a rolling method with a linear pressure of 1.6 t / cm. Next, Al foil is peeled off from each positive electrode active material layer to expose the positive electrode active material layer, and then pressed using a rolling method with a linear pressure of 5 t / cm. Next, a positive electrode current collector (Al foil, 15 μm thick) is placed on each of the rolled positive electrode active material layers. Finally, current collector connectors are placed on the positive and negative electrode current collectors, and lamination is performed to seal the layers, thus obtaining an all-solid-state battery.

[0118] [Examples 2-4 and Comparative Example 4]

[0119] For 2 g of sulfide solid electrolyte (10LiI·15LiBr·75(0.75Li2S·0.25P2S5) (mol%), average particle size 0.5 μm), heating was performed using a heating plate in dry air at a dew point of -70°C and an oxygen volume concentration of 20%, under the conditions shown in Table 1. This yielded a coated sulfide solid electrolyte. A completely solid-state battery was fabricated in the same manner as in Example 1, except that the obtained coated sulfide solid electrolyte was used.

[0120] [Compare Example 1 and Compare Example 3]

[0121] For the sulfide solid electrolyte (10LiI·15LiBr·75(0.75Li2S·0.25P2S5) (mol%), average particle size 0.5 μm), coated sulfide solid electrolytes were obtained by loading them in dry air at room temperature for the times shown in Table 1.

[0122] Except for using the obtained coated sulfide solid electrolyte, an all-solid-state battery was fabricated in the same manner as in Example 1.

[0123] [Comparative Example 2]

[0124] The sulfide solid electrolyte (10LiI·15LiBr·75(0.75Li2S·0.25P2S5) (mol%), average particle size 0.5μm) was used directly without heat treatment in dry air. Otherwise, the all-solid-state battery was fabricated in the same manner as in Example 1.

[0125] (XPS measurement)

[0126] X-ray photoelectron spectroscopy (XPS) was performed on the coated sulfide solid electrolytes prepared in Examples 1-4 and Comparative Examples 1-4. The ratio (P2 / P1) of the peak intensity P2 appearing near 167 eV to the peak intensity P1 appearing near 163 eV in the S2p spectrum is shown in Table 1. Furthermore, the peak appearing near 163 eV originates from PS bonds, and the peak appearing near 167 eV originates from SO bonds. Additionally, Figure 4 The S2p spectrum is obtained by XPS measurement of the coated sulfide solid electrolytes prepared in Example 3 and Comparative Example 1.

[0127] Using the elemental concentrations of each element (O, S, P, Li, Br, and I) obtained from XPS, the oxygen content (%) on the surface of the coated sulfide solid electrolytes prepared in Examples 1-4 and Comparative Examples 1-4 was calculated using the following formula. The relative values ​​of oxygen content in Examples 1-4 and Comparative Examples 2-4 when the oxygen content of Comparative Example 1 is set to 1 are shown in Table 1.

[0128] Oxygen content (%) = O / (S+P+Li+Br+I)

[0129] (Charge / Discharge Test)

[0130] The all-solid-state batteries obtained in Examples 1 to 4 and Comparative Examples 1 to 4 were subjected to dimensional constraint at a constraint voltage of 5 MPa and constant current-constant voltage (CC-CV) charging at 0.0194 A until 4.05 V. Then, they were discharged at 0.0194 A until 3.0 V. Then, the all-solid-state batteries were charged again. This charging was taken as the initial charging. The resistance from the start of discharge (0 seconds) to 0.1 seconds was calculated based on the voltage drop after 0.1 seconds from the start of the initial discharge. The results are shown in the "Initial 0.1s Resistance" column of Table 1. Furthermore, the resistance from 0.1 seconds to 10 seconds was calculated based on the voltage drop after 0.1 seconds to 10 seconds. The results are shown in the "Initial 10s Resistance" column of Table 1. Furthermore, it is believed that the "Initial 0.1s Resistance" is related to the interfacial resistance between the positive electrode active material and the sulfide solid electrolyte. It is believed that the "initial 10s resistance" is related to the ion conduction resistance within the positive electrode layer.

[0131] (Evaluation of reaction resistance under high cycling conditions)

[0132] The all-solid-state batteries obtained in Examples 1-4 and Comparative Examples 1-4 were subjected to dimensional constraint at a constraint voltage of 5 MPa and then constant current-constant voltage (CC-CV) charging at 0.461 mA until 4.35 V. They were then discharged at 0.461 mA until 3.0 V. The all-solid-state batteries were then charged again. This initial charge was taken as the initial charge. Cycling was performed at 2C up to 100 cycles for evaluation.

[0133] The internal resistance was evaluated using the impedance method. Specifically, after the initial charge-discharge cycle, the system was adjusted to 40% SOC, and the orifice component of the impedance was calculated. The same internal resistance evaluation was then performed after 100 cycles. The resistance increase rate (in times) was calculated using the following formula. The results are shown in Table 1.

[0134] Resistance increase rate (times) = Internal resistance after 100 cycles ÷ Internal resistance after 1 cycle

[0135] Table 1

[0136]

[0137] The results in Table 1 confirm that the resistance of the all-solid-state batteries of Examples 1 to 4 is lower than that of the all-solid-state batteries of Comparative Examples 1 to 4.

Claims

1. A positive electrode layer for an all-solid-state battery, comprising a positive electrode active material and a coated sulfide solid electrolyte, wherein the coated sulfide solid electrolyte has a sulfide solid electrolyte and a coating layer that coats the surface of the sulfide solid electrolyte and contains a metal sulfate, The sulfide solid electrolyte has a composition represented by xLiI·yLiBr·z(αLi₂S·(1-α)P₂S₅), wherein, x + y + z = 100, 0 ≤ x < 100, 0 ≤ y < 100, 0 < z ≤ 100, 0.70 ≤ α ≤ 0.80, and the coated sulfide solid electrolyte is obtained by heat-treating the sulfide solid electrolyte at a temperature of 100°C or higher and 170°C or lower for 5 minutes or longer and 1 hour or shorter in a dry gas having a dew point temperature of 0°C or lower and an oxygen concentration of 20 vol% or lower, For the positive electrode layer, in the S2p energy spectrum measured for the coated sulfide solid electrolyte by X-ray photoelectron spectroscopy (XPS), the ratio P2 / P1 of the peak intensity P2 appearing around 167 eV to the peak intensity P1 appearing around 163 eV is 0.15 or higher and 0.29 or lower, The sulfide solid electrolyte comprises an ionic conductor containing Li, P, and S, wherein PS4 3- The proportion of all anionic structures is over 70 mol%. The peak appearing around 163 eV comes from the P-S bond, The peak appearing around 167 eV comes from the S-O bond, The metal sulfate is a lithium sulfate salt, The film thickness of the coating layer is 1 nm or more and 20 nm or less, The coating rate of the coating layer is 50% or more, The proportion of the coated sulfide solid electrolyte in the positive electrode layer is 5 wt% or more and 75 wt% or less, The total proportion of the coated sulfide solid electrolyte relative to all the solid electrolytes contained in the positive electrode layer is 50 wt% or more, The oxygen amount on the surface of the coated sulfide solid electrolyte is 5% or more, and the oxygen amount is calculated by the following formula, Oxygen amount = (O element concentration / Concentration of elements other than O element) × 100.

2. The positive electrode layer according to claim 1, The surface of the positive electrode active material is coated with a material of the general formula Li x AO y The Li ion-conducting oxide is represented, wherein, A is at least one selected from Nb, B, Al, Si, P, S, Ti, Zr, Mo, Ta, W, and x and y are positive numbers.

3. A method for manufacturing a positive electrode layer for an all-solid-state battery, which is a method for manufacturing the positive electrode layer according to claim 1 or 2, comprising: A step of forming a coating layer containing a metal sulfate on the surface of the sulfide solid electrolyte by heat-treating the sulfide solid electrolyte at a temperature of 100°C or higher and 170°C or lower for 5 minutes or longer and 1 hour or shorter in a dry gas having a dew point temperature of 0°C or lower and an oxygen concentration of 20 vol% or lower to obtain a coated sulfide solid electrolyte; and A step of forming the positive electrode layer by coating and drying a slurry containing the coated sulfide solid electrolyte and a positive electrode active material.

4. An all-solid-state battery, comprising: A positive electrode layer, A negative electrode layer, and A solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer is the positive electrode layer according to claim 1 or 2.

Images